DEC 291978

Summary Appraisals of the

Nation's Ground-Water 

Resources South 

Atlantic-Gulf Region
SUMMARY APPRAISALS OF THE 

NATIONS GROUND-WATER RESOURCESSOUTH ATLANTIC-GULF REGION
SOURIS-RED-RAINY 

NDAK TMINN

ARKANSAS-WHITE-RED 

H

SOUTH ATLANTIC-GULF

Geographic Index to the Series, U.S. Geological Survey Professional Paper 813, Summary Appraisals of the Nations Ground-Water R

Boundaries shown are those established by the United States Water-Resources Council for Water-Resources Regions in the United 
Summary Appraisals of the 

Nation's Ground-Water 

Resources South 

Atlantic-Gulf Region

By D. J. CEDERSTROM, E. H. BOSWELL, and G. R. TARVER 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 813-0

A summary of the occurrence and quality 

of ground water and its present and 

potential significance in the regional 

water supply

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1979
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Cataloging in Publication Data

Cederstrom, Dagfin John, 1908-

Summary appraisals of the Nation's ground water resources-South 

Atlantic-gulf region.

(Geological Survey professional paper 813-0)

Bibliography: p. 033-035.

Supt. of Docs, no.: I 19. 16P813-0

1. Water, Underground-Gulf States. 2. Water, Underground-Southern States.

I. Boswell, Ernest H., 1919- joint author. II. Tarver, George R., joint author.

III. United States. Geological Survey. IV. Title. V. Series: United States.

Geological Survey. Professional paper 813-0. 

GB1018.C4 553' . 79'0976 78-23386

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 024-001-03137-0
CONTENTS

Page

mjoui Abstract di*i> ------- ---- - - - __ ____ O1 v/A

Introduction - 1

Geographic setting 2

Geologic framework 2

Structure - 2

____ ___-_ 2

__________ 7

. - 10

.__________.. 10

_.._..__......__. 11

 12

 14

 . 14

Geology 

Ground-water supplies - 

Present and projected ground-water use 

Ground-water quality 

Ground water in the Coastal Plain province -

Cretaceous aquifers -

Lower Tertiary aquifers -

Tertiary limestone aquifer -

Lower Tertiary aquifers other than the

Tertiary limestone aquifer - 

Upper Tertiary aquifers - 

Quaternary aquifers 

Ground water in the Piedmont province - 

Ground water in the Valley and Ridge province and 

Cumberland Plateau section 

Ground water in the Blue Ridge province-

- 17

. ig

 20

.____ 21

.-. 21

.____ 22

Saline-water resources 22

Page

Development and management of ground-water resources 022 

Objectives 22

Natural recharge 23 

Development of unconfined sandy aquifers - 23 

Development of confined sandy aquifers 23 

Development of the Tertiary limestone aquifer - - 24 

Development of aquifers in the Appalachian Mountains

and the Piedmont 26

Other management procedures 26

Multiple sources of fresh ground water - ~ 26

Use and management of saline water 26

Artificial recharge of ground water 27

Recharge using effluent from treated sewage 29

Freshwater storage in saline aquifers 29

Low-flow augmentation of streams 29

Ground water for pumped storage 30

Conjunctive use of ground water and surface water 30

Ground-water problems 30

Data needs 32

Summary and conclusions - - 32

Selected references 33

ILLUSTRATIONS

Page

FRONTISPIECE. Ground-water regions of the United States.

FIGURE 1. Map showing location, drainage, and principal physiographic subdivisions, South Atlantic-Gulf Region 03

2. Map showing average annual rainfall in the South Atlantic-Gulf Region - - 4

3. Map showing location of major structural features and depth below sea level of basement rock in the Coastal Plain province - 5

4. Geologic map of the South Atlantic-Gulf Region - - - - 6

5. Map showing types of aquifers in the South Atlantic-Gulf Region 9

6. Map showing configuration of the top and areal extent of the Tuscaloosa Group - - - 13

7. Map showing configuration of the top and areal extent of the Tertiary limestone aquifer 15

8. Map showing depth to the base of potable water in the Tertiary limestone aquifer 17

9. Map showing the altitude of the base of freshwater in Alabama and Mississippi 19

10. Map showing large springs in Georgia 25

TABLES

Page

TABLE 1. Generalized correlation of Coastal Plain stratigraphic units and aquifers - ----- - 08

2. Maximum reported yields of wells in Upper Cretaceous aquifers, Mississippi to North Carolina 14

3. Recharge rates to the Tertiary limestone aquifer based on estimates of flow through the aquifer 24

4. Recharge rates to the Tertiary limestone aquifer based on spring discharge - 25
VI CONTENTS

CONVERSION FACTORS

[The following factors may be used to convert the U.S. customary units published herein to the International System of Units (SI)]

Multiply U.S. customary units

Inches (in.) 

Feet (ft) 

Miles (mi)

Square miles (mi2)

Cubic feet per second (ft3/s) 

Gallons per minute (gal/min)

Million gallons per day (Mgal/d)

Cubic feet per second per square mile [(ft3/s)/mi2]

Gallons per day per square mile [(gal/d)/mi2]

Cubic feet (ft3)

Feet per mile (ft/mi)

Feet per day (ft/d)

Feet squared per day (ft2/d)

By 

Length

25.4

.3048

1.609

Area 

2.590

Flow

28.32

.02832

To obtain SI units

Millimeters (mm) 

Meters (m) 

Kilometers (km)

Square kilometers (km2)

Liters per second (L/s)

Cubic meters per second (m3/s)

.06309 Liters per second (L/s) 

6.309x 10" 5 Cubic meters per second (m3/s)

3,785

.0109

.00146

Volume 

0.02832

Gradient

18.9

.189

Cubic meters per day (m3/d)

Cubic meters per second per square kilometer

[(m3/s)/ km2] 

Cubic meters per day per square kilometer

[(m3/d)/km2]

Cubic meters (m3)

Centimeters per kilometer (cm/km) 

Meters per kilometer (m/km)

Hydraulic conductivity

0.3048 Meters per day (m/d)

Transmissivity

0.0929 Meters squared per day (m2/d)

The conversion from temperature in degrees Farenheit (°F) to temperature in degrees (Celsius (°C) is expressed by: °C= (5/9) (°F-32).
SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER 

RESOURCES SOUTH ATLANTIC-GULF REGION

By D. J. CEDERSTROM, E. H. BOSWELL, and G. R. TARVER

ABSTRACT

Precipitation in the 270,000-square-mile South Atlantic-Gulf Region ranges from 44 to 80 inches, and the average runoff is about 15 

inches. The ground-water discharge that forms the base flow of 

streams is conservatively estimated to be about 78,000 million gallons 

per day the equivalent of about 6 inches of precipitation. On this 

basis, the regional sustained ground-water supply is about 286,000 

gallons per day per square mile. Projected water use through 2020 

indicates that about 10 percent of the supply will meet the region's 

requirement for ground water.

Enormous quantities of ground water are available in the South 

Atlantic-Gulf States in the extensive aquifers that underlie the Coastal 

Plain province. Large supplies of ground water can be developed also 

in places in the Cumberland Plateau and the Valley and Ridge provinces. In the Piedmont and Blue Ridge provinces ground water is 

available only in modest quantities.

The principal Coastal Plain aquifers consist largely of deltaic sand 

and gravel deposits of Cretaceous to Quaternary age; however, a notable exception is the highly permeable Tertiary limestone aquifer, 

which underlies parts of four States. Ground water in the Blue Ridge 

and the Valley and Ridge provinces is available from openings along 

fissures and joints in consolidated rocks and from the unconsolidated 

sand and gravel in the residuum and alluvium that overlie the bedrock. In parts of these areas faulting and folding has created favorable 

conditions for the development of moderate supplies of ground water. 

In the Piedmont province modest quantities of water are available 

from joints and fractures. Solution cavities in massive limestone units 

in some areas underlying the Cumberland Plateau section yield very 

large quantities of ground water.

Most of the major Coastal Plain aquifers are recharged where they 

are exposed and water moves downdip to the south. The general direction of ground-water movement in the Coastal Plain aquifers is seaward. There is, however, movement of water vertically and laterally 

that affects pressure and quality in every aquifer.

Ground water of good chemical and physical quality is available generally except in a small area in western Alabama and eastern Mississippi and in some small coastal areas. Freshwater extends to depths 

of slightly more than 3,000 feet in some areas. In many areas, water 

can be produced that does not require any treatment for general use. 

The more common objectionable constituents or properties are excessive iron, fluoride, hardness, color, and acidity. Contamination or 

pollution of ground water is not a major regional problem, but it is 

significant in local areas. Many of these local problems of contamination were the result of earlier improper disposal of oil-field and industrial waste. Saltwater intrusion either direcdy from the sea or from 

estuaries has been reported in every State in the region, and the potential for the proliferation of this problem is very large.

The relationship of ground water and surface water is significant 

at many places in the region where large ground-water withdrawals

affect swamps, lakes, and the flow of streams and springs. There is a 

potential in some areas for using ground water during dry periods for 

low-flow augmentation of stream supplies. In other areas it is feasible 

to recharge ground-water reservoirs artificially by means of injection 

wells, pits, and water spreading.

Although large water-level declines caused by withdrawals have occurred locally, water-level changes have been small or modest when 

considered on a regional basis owing to the abundant rainfall and favorable recharge conditions.

The saline-water resources of the region are known to be extremely 

large. In some areas where the availability of freshwater is limited, 

saline ground water is available for desalinization to supplement freshwater supplies. Also, the saline aquifers are potential storage sites for 

injected freshwater.

Ground-water problems generally are not severe. Critical situations 

are restricted to areas where large quantities of ground water are 

being withdrawn or where aquifers are contaminated by oil-field or 

industrial waste. Large withdrawals in coastal areas have caused some 

saltwater intrusion. In other localities, highly mineralized water may 

have migrated along fault zones to freshwater aquifers. Many of the 

present problems can be resolved or ameliorated by redistributing 

withdrawals or developing alternative water sources.

INTRODUCTION

This report describing the ground-water resources of 

the South Atlantic-Gulf Region is one of a series of regional ground-water appraisals that summarize data in 

many published reports and unpublished data in the files 

of Federal, State, and other agencies. The report discusses the enormous quantities of ground water that can 

be obtained by conventional development methods in 

many areas in the region and suggests that, by conjunctive use of surface water and ground water, larger volumes of water can be made available.

About three-fourths of the region is in the Atlantic and 

Eastern Gulf Coastal Plains where the geologic units 

that make up the aquifers are limestone or unconsolidated sand and gravel. The remainder of the region is 

underlain by the older consolidated rocks of the Appalachian Highlands which contain ground water in fractures and solution cavities.

Freshwater at some localities is known to occur at 

depths greater than 3,000 feet. There are only a few 

areas of very limited extent where freshwater is not

01
O2 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

available in usable quantities. Water-quality problems 

are those usually amenable to simple treatment.

The largely undeveloped ground-water resources in 

the region will be one of the controlling factors in future 

economic development. Industrial expansion and intensive agricultural development will place increasing demands on water. It is, therefore, essential that sound 

appraisals of the water resources be available to planners 

and managers to meet the need for additional demands 

for water.

GEOGRAPHIC SETTING

The South Atlantic-Gulf Region, which comprises an 

area of about 270,000 square miles in the southeastern 

part of the United States, is drained by streams flowing 

to the Atlantic Ocean and the Gulf of Mexico between 

the James River drainage in Virginia and the lower Mississippi River drainage. It includes all of Alabama, Florida, Georgia, North Carolina, South Carolina, and parts 

of Mississippi and Virginia (fig. 1). The region includes 

parts of the Appalachian Highlands and the Coastal 

Plain two of the eight major physiographic divisions of 

the United States (Fenneman, 1938).

The Coastal Plain province occupies about 70 percent 

of the region, the Piedmont province about 25 percent, 

and the Blue Ridge province, Valley and Ridge province, 

and Cumberland Plateau section together constitute 

about 5 percent. The Coastal Plain is separated from the 

rest of the region by the Fall Line, the irregular topographic boundary between the coastal deposits and the 

older rocks of the Appalachian Highlands.

Precipitation extremes in the South Atlantic-Gulf Region range from about 44 inches in parts of the Coastal 

Plain to 80 inches in small areas in the mountains of 

North Carolina and South Carolina (fig. 2). Thunderstorms are particularly common in Florida, occurring 70 

days or more a year. As much as 5 inches of rain in 24 

hours along the Gulf Coast and as much as 3% inches in 

24 hours on the Coastal Plain along the Atlantic and inland from the Gulf is not uncommon. Such storms frequently result in floods of short duration.

Average runoff in the region is 15 inches per year 

(Murray and Reeves, 1977, p. 19). Runoff ranges from 

about 10 inches per year along the Atlantic Coast up to 

30 inches along the panhandle of Florida and the Alabama-Mississippi coast, where thick permeable sands in 

the coastal areas absorb much of the heavy rainfall. Runoff is about 15 inches in the more inland areas where the 

annual rainfall is 45 to 50 inches. In the mountainous 

areas, runoff is about half the total precipitation. The 

difference of about 35 inches between average runoff and 

the average rainfall over the Coastal Plain and Piedmont

provinces is lost by evaporation and transpiration.

The flow of streams varies with precipitation and is 

generally highest in February and March and lowest in 

October, except in central and southern Florida where 

flows are highest in October and low in late fall and in 

May.

Average annual air temperature ranges from about 

60°F (16°C) in southern Virginia to 70°F (21°C) in the 

northern Gulf Coast, and to 77°F (25°C) in southern 

Florida.

v, 

GEOLOGIC FRAMEWORK

STRUCTURE

The Piedmont province is made up of ancient sedimentary rocks that have been intruded by igneous rocks and 

subjected to repeated stress. Throughout the area rocks 

have been fractured, faulted, and folded. The Triassic 

basins within the Piedmont province are infaulted blocks 

of younger sedimentary rocks.

The Coastal Plain has been subjected to repeated 

somewhat gentle differential movements. There are now 

a series of highs and intervening sags in the basement 

rock surface and overlying sediments along the entire 

coastline (fig. 3). Irregularities in the basement surface 

may be due to movement in pre-Cretaceous times; however, persistent movement in places has affected the 

younger sediments.

The northernmost major structural high in the South 

Atlantic-Gulf Region is the Cape Fear Arch (fig. 3). To 

the south a definite sag in the basement is known as the 

Southeast Georgia Embayment. Crossing the neck of 

Florida the basement rises again across the Ocala Uplift 

and then falls away in the Southwest Georgia Embayment. The Chattahoochee Anticline, more or less parallel 

to the river of the same name, passes to the west of the 

Southwest Georgia Embayment.

The major structures have created irregularities in the 

outcrop pattern, the most marked being the pattern over 

the Cape Fear Arch.

GEOLOGY

The South Atlantic-Gulf Region may be divided into 

two broad components: (1) the Coastal Plain province, 

about 196,000 square miles, made up of soft unconsolidated sand, gravel, and clay and consolidated or semiconsolidated limestone and (2) the remainder (Piedmont 

province, Blue Ridge province, Valley and Ridge province, and Cumberland Plateau section), about 74,000 

square miles, consisting for the most part of hard consolidated rocks indurated and metamorphosed sedimentary rocks and crystalline igneous rocks.
SOUTH ATLANTIC-GULF REGION O3

35°

90° 85° 80°

FIGURE L Map showing location, major drainage, and principal physiographic subdivisions of the South Atlantic-Gulf Region.
O4 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

Line of equal 

precipitation, 

interval 4 inches

I I I I I I 

100 200 300 400 500 600 KILOMETERS

FIGURE 2-. Average annual precipitation in the South Atlantic-Gulf Region.
SOUTH ATLANTIC-GULF REGION 05

Basement rock contour 

Shows altitude of basement rock 

surface. Dashed where approximately located. Contour interval 500 and WOO feet. Datum 

is mean sea level

90° 85° 80"

FIGURE 3. Major structural features and depth below sea level of basement in the Coastal Plain province.
06 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

FIGURE 4r-Geologic map of the South Atlantic-Gulf Region.
SOUTH ATLANTIC-GULF REGION 07

The Coastal Plain province is underlain by unconsolidated clay, sand, and gravel and consolidated or semiconsolidated limestone. The deposits, which range in age 

from Cretaceous to Holocene, form a hugh arc extending 

from southern Virginia through the Carolinas, Georgia, 

Alabama, and into eastern Mississippi (fig. 4). From a 

thin edge at the Fall line, most of the deposits thicken 

seaward; a southward projection forms the peninsula of 

Florida.

In most places, the Coastal Plain beds have a gentle 

dip seaward. Each formation was generally overlapped 

by the next younger formation and their eroded edges 

are now exposed in a succession of older (inland) to 

younger (seaward) arcuate belts. The surface exposures 

of some formations are irregular. For instance, in northern North Carolina the inner edges of older strata were 

beveled by the advancing seas, and younger formations 

extend to the Fall Line.

The Coastal Plain formations are rarely uniform laterally (along the strike) or downdip. Nearshore sandy

EXPLANATION

SEDIMENTARY ROCKS

QUATERNARY 

HOLOCENE AND PLEISTOCENE

UPPER TERTIARY 

PLIOCENE AND MIOCENE

LOWER TERTIARY

OLIGOCENE, EOCENE, AND 

PALEOCENE

CRETACEOUS

JURASSIC AND TRIASSIC

UPPER PALEOZOIC

PERMIAN, PENNSYLVANIAN,

AND MISSISSIPPIAN

LOWER PALEOZOIC 

ORDOVICIAN AND CAMBRIAN

YOUNGER PRECAMBRIAN

In southeastern United States 

includes metamorphosed Paleozoic

OLDER PRECAMBRIAN 

Metamorphic and igneous rocks

INTRUSIVE ROCKS 

PALEOZOIC

Chiefly granitic 

rocks

FIGURE 4. Continued.

deltaic continental sediments thicken downdip and grade 

into deeper water silty or limy marine deposits. Laterally, sediments may also change in proportions of sand 

and clay, or may become limy.

Sandy terrace deposits were superimposed upon the 

older formations throughout the Atlantic and Gulf 

Coastal regions during the Pleistocene Epoch.

Table 1 shows the stratigraphic units and aquifers of 

Cretaceous to Quaternary age that underlie the Coastal 

Plain province.

The Blue Ridge province is underlain by igneous and 

metamorphic rocks of older age which have been subjected to repeated stress.

The provinces outside the Coastal Plain are underlain 

by consolidated sedimentary rocks. In the Valley and 

Ridge province, these rocks have been greatly folded and 

faulted. In the adjacent Cumberland Plateau section the 

rocks have been subjected to less folding and faulting.

GROUND-WATER SUPPLIES

Most of the South Atlantic-Gulf Region is underlain by 

aquifers that are generally capable of yielding to wells 

50 gal/min or more of water containing less than 1,000 

milligrams per liter (mg/L) of dissolved solids (fig. 5 and 

table 1). Lower yields are characteristic of aquifers in 

the consolidated rocks that underlie the Blue Ridge, Valley and Ridge, and Piedmont provinces. In the Piedmont, Blue Ridge, Valley and Ridge provinces, and the 

Cumberland Plateau section, wells may intersect openings that result from structural deformation and solution, and yields range from substantial to meager.

The most prolific sources of ground water in the South 

Atlantic-Gulf Region are the highly permeable clastic 

and limestone aquifers in the Coastal Plain province. In 

small areas in western Alabama, eastern Mississippi, 

southeastern North Carolina, and northeastern South 

Carolina, these aquifers contain only saline water.

The aquifers occurring within each physiographic 

province in the South Atlantic-Gulf Region generally are 

not separate units operating independently; rather, each 

is a part of a complex system. Because of this interrelation, it is generally irrelevant to estimate quantities of 

water that are available from the individual aquifers. It 

is more meaningful to estimate the quantity available 

from the entire system.

Because the base flow of streams is supported almost 

entirely by ground-water outflow, the quantity of ground 

water available can be estimated by separating the total 

amount of streamflow from a region into its component 

parts overland flow and base flow. The base-flow component is the approximate yield of the ground-water reservoirs under the existing hydrologic conditions.
08 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

§ O
SOUTH ATLANTIC-GULF REGION O9

90° 85° 80° 75°

rv;

I1

x

v-<

KENTUCKY

_----^

EXPLANATION

Patterned areas are underlain by aquifers.. 

generally capable of yielding to individual wells 50 gpm or. more of water 

containing less than 1000 mg/L of 

dissolved solids (includes areas where 

more highly mineralized water is 

actually used)

Unconsolidated and semiconsolidated aquifers

Consolidated-rock aquifers

Both unconsolidated and 

consolidated-rock aquifers

n

Not known to be underlain 

by aquifers that will generally 

yield as much as 50 gpm to - 

wells

100 200 300 MILES

T~ 

100 200

~T 

300 KILOMETERS

35°

30°

25°

FIGURE 5. Types of aquifers in the South Atlantic-Gulf Region.

Many investigators of the water resources in areas 

within the Mid-Atlantic Region have estimated the percentage of streamflow that is base flow, or ground-water 

discharge. In the Coastal Plain, base flow ranges from 

about 40 to 95 percent of the total streamflow; a conservative average would be about 55 percent. In that 

part of the region underlain by consolidated rocks, base 

flow ranges from about 25 to 90 percent of the streamflow, a conservative average being about 40 percent.

Wilson and Iseri (1967) show that the total annual 

streamflow from the South Atlantic-Gulf Region averages about 303,000 ft3/s or 196,000 Mgal/d, 60 percent 

of which flows into the Gulf of Mexico. However, the 

proportion of this streamflow that originates in the

Coastal Plain as opposed to the remainder of the region 

was not determined. Using only 40 percent (the conservation average percent of streamflow that is baseflow in 

the consolidated rocks part of the region) and applying 

this figure to the entire streamflow from the region, the 

average total yield of ground water from the South Atlantic-Gulf Region under present hydrologic conditions 

is at least 78,000 Mgal/d or about 286,000 (gal/d)/mi2 

 the equivalent of about 6 inches of annual recharge. It 

is impractical and, in fact, environmentally undesirable 

to intercept all of this water before it is discharged into 

streams; however, the amount indicates the order of 

magnitude of ground water available as a potential 

resource.
O10 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

There is also in storage in the ground-water reservoirs 

of the region about 600,000 billion cubic feet of water 

having a dissolved-solids concentration of less than 

3,000 mg/L (M. I. Kaufman, oral commun., 1977). This 

volume of water is sufficient to cover the entire region 

to a depth of about 80 feet; however, much of this water 

cannot be withdrawn economically using present techniques. Moreover, the environmental effects of removing 

excessive amounts of ground water from storage may not 

be acceptable.

The hydrologic properties of an aquifer provide a 

means of measuring or predicting the aquifer's watersupply potential. In this regional appraisal of groundwater resources, data are not available covering the regional variation in physical properties and hydrologic 

characteristics, and instead ranges or averages for hydraulic properties are used. Terms used to describe hydraulic characteristics in this study include the following:

Transmissivity. The rate at which water is transmitted through a unit width of an aquifer under 

a unit hydraulic gradient. Depends on the hydraulic conductivity and thickness of the aquifer. 

Expressed in units of square feet per day (ft2/d).

Hydraulic conductivity. The volume of water that 

will move in unit time under a unit hydraulic gradient through a unit area measured at right angles to the direction of flow. Expressed in units 

of feet per day (ft/d).

Storage coefficient. The volume of water that an 

aquifer releases from or takes into storage per 

unit surface area of the aquifer per unit change 

in head dimensionless.

The values of transmissivity and hydraulic conductivity as defined above expressed in square feet per day and 

feet per day may be converted to units of transmissibility 

(gallons per day per foot) and permeability (gallons per 

day per square foot) by multiplying by 7.48. Explanations of the derivation and application of values for hydrologic properties are given by Lohman (1972).

PRESENT AND PROJECTED 

GROUND-WATER USE

The withdrawal of fresh and saline water for all uses 

from all sources in the South Atlantic-Gulf Region in 

1975 was reported to be 43,000 Mgal/d. Surface water 

accounted for 38,000 Mgal/d or about 88 percent of the 

total, and ground water accounted for 12 percent. Consumptive use was 3,700 Mgal/d (Murray and Reeves, 

1977, table 17).

Ground-water withdrawals in the region for all purposes in 1975 totaled about 5,500 Mgal/d (Murray and

Reeves, 1977). The largest withdrawal, 1,953 Mgal/d, 

was for self-supplied industrial use. Public water supplies accounted for 1,500 Mgal/d, and rural and livestock, 660 Mgal/d. About 53 Mgal/d or 1 percent of the 

total was saline ground water used by self-supplied industries. Included in the total is 1,500,000 acre-ft of 

water withdrawn for irrigation (about 1,340 Mgal/d on 

an annual basis).

Ground water supplies about 48 percent of all water 

used for public supplies and 42 percent of all irrigation 

water in the region. The total of ground-water withdrawal is only about 7 percent of the estimated 78,000 

Mgal/d available from the region.

Projections for future water needs made by the Water 

Resources Council (1968, table 1-2) are shown in the following table:

Projected water requirements, South Atlantic-Gulf Region

[Million gallons daily. From U.S. Water Resources Council, 1968] 

Withdrawals, surface and ground water Consumptive use

1980

53,180

2000

87,440 130,190

1980

3,395

2000

5,655 8,265

Assuming that ground water continues to supply 14 

percent of all water withdrawn in the region, projected 

ground-water use would be as shown in the following 

table:

Projected ground-water requirements based on the 1970 rate

[Million gallons daily] 

Projected ivithdrawals Projected consumptive use

1980

7,445

WOO

12,242

2020

18,227

1980

475

2000

792

2020

1,157

If one-fourth, or about 19,000 Mgal/d, of the estimated available ground-water supply can be withdrawn 

without serious environmental effects, the projected regional ground- water needs through 2020 can be met.

Large-capacity wells can be constructed in perhaps 40 

percent of the region (fig. 5); hence, most of the groundwater development in the region will probably be in the 

most favorable area.

GROUND-WATER QUALITY

In the South Atlantic-Gulf Region good-quality ground 

water is generally taken for granted. In most of the region enough water of good quality is available for current 

requirements; however, simple treatment for excessive 

iron, corrosiveness, and hardness is common.

In this report the following classification is used for 

water hardness in terms of the amount of calcium carbonate (or its equivalent) that it contains:
SOUTH ATLANTIC-GULF REGION Oil

[Values in milligrams per liter]

0_60 - __________ .__ Soft.

61-120 - Moderately hard.

More than 180 Very hard.

In the sandy coastal plain formations there is normally 

a progressive increase in the mineral content of ground 

water downdip. Along the outcrop of the aquifers the 

water is low in mineral content but may be somewhat 

corrosive, and water from many wells is high in iron.

The high chloride concentrations in water in some Upper Cretaceous aquifers appear to be related to the 

permeability of the sediments. In places, saltwater has 

been replaced by freshwater that has moved farther 

downdip in high permeable sediments than in the shallower but less permeable sediments. The movement of 

water is slower in less permeable sediments.

Freshwater contains less than 1,000 mg/L of dissolved solids; however, some water supplies use water 

that has a dissolved-solids concentration higher than 

1,000 mg/L, and some water containing up to 2,000 mg/ 

L is suitable for irrigating some crops. In this report saline water is classified as follows according to the dissolved-solids concentration:

Description Dissolved solids mg/L)

Fresh- ... Less than 1,000.

Slightly saline -1,000 to 3,000.

Moderately saline -3,000 to 10,000.

Very saline 10,000 to 35,000.

Brine ~ - More than 35,000.

The younger Tertiary aquifers contain freshwater that 

extends to or even beyond the coast in most areas (Hathaway and others, 1976). In much of the coastal area the 

Tertiary limestone aquifer is protected from seawater 

intrusion by a cover of Miocene clays and marls of low 

permeability. However, deep saline water has migrated 

into the freshwater zone in a few places in response to 

sharp lowering of pressure.

The Pleistocene and Holocene unconsolidated sediments commonly yield slightly acidic water that is low 

in dissolved solids.

Colored ground water occurs in a few places in Florida 

where turbid stream waters can move into the aquifers. 

In Mississippi, some Eocene aquifers yield colored water 

in their downdip extensions.

Outside the Coastal Plain, water is generally limited 

in quantity but of good quality. As the depth of groundwater occurrence commonly does not exceed a few 

hundred feet and the aquifers have long been free of seawater, the high salinity that is common in the deep zones 

of the Coastal Plain aquifers is not a problem. The aquifer materials with the exception of the carbonate rocks 

are relatively insoluble, and therefore the dissolved-solids concentration in the ground water is low.

In moving downdip, the slightly acidic water becomes 

neutralized, iron content decreases, and the hardness of 

water increases. Because of ion exchange at greater 

depth, the water becomes a soft sodium bicarbonate type 

(Cederstrom, 1957, p. 36). Still farther downdip the 

water becomes saline owing to the presence of seawater 

with which the formations were once saturated.

A similar progression is seen in water in some limestone aquifers. In those aquifers water may be initially 

harder than that in sandy formations, but hardness does 

not everywhere become excessive downdip owing to 

base-exchange action. Stringfield (1966) notes that although raw water for public supplies in Florida ranges 

up to 1,000 mg/L of hardness, only 9 percent of those 

supplies has a hardness greater than above 250 mg/L. 

Bicarbonate, however, may increase above 300 mg/L.

Low bicarbonate concentrations may be related to 

rapid recharge through sinkholes and solution openings 

by water having a low carbon dioxide concentration, 

whereas high bicarbonate concentrations may be expected where recharge water is high in carbon dioxide 

as a result of percolation through soil that is rich in organic matter (Trainer and Heath, 1976).

Although the quality of ground water in the Coastal 

Plain is generally good, contamination problems exist or 

may develop in certain areas. In most places ground 

water does not receive the amount of contamination that 

streams do. Surface contaminants tend to be degraded, 

diluted, and filtered before reaching the aquifer. Water 

moving miles downdip through sandy aquifers is almost 

everywhere free of organic contamination.

Ground water can be degraded, however. Heavy application of fertilizers, a concentration of septic tanks, 

sanitary landfills, or feed lots are sources of organic contaminants that may pollute both ground water and 

streams.

In some industrial areas, heavy metals or nondegradable contaminants may be present in waste water entering the ground-water reservoir. These are not filtered 

out by movement through sandy beds.

Limestone terranes that are not protected by a thick 

sandy or silty soil cover are particularly susceptible to . 

contamination from the surface. Although such water 

may be diluted, no filtering action occurs, and contaminants may persist for miles.

GROUND WATER IN THE 

COASTAL PLAIN PROVINCE

Except in the Florida Peninsula, the Coastal Plain 

strata are generally present as a series of overlapping 

beds that dip gently seaward. The exposed inland outcrop areas absorb rainfall that moves downgradient, ordinarily seaward. Water accumulates in interfluve areas
O12 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

and moves slowly to the streams in response to gravity. 

In such areas, water occurs under unconfined (water-table) conditions.

Downdip the water is confined within the aquifer by 

permeable overlying material, such as clay, and is under 

pressure from the water filling the aquifer back to the 

outcrop area. Water will rise in wells drilled in such an 

aquifer, and the water occurs under confined (artesian) 

conditions.

This simple explanation suits the confined systems as 

a whole and is applicable without notable qualifications 

throughout the Coastal Plain. In much of the Florida 

Peninsula and in some smaller areas, recharge is local 

rather than at "inland" exposures of the formations.

A part of the potential recharge water in the outcrop 

area of the formations is rejected and becomes part of 

the sreamflows. Part of the water entering these strata, 

however, moves downdip into the confined parts of the 

aquifers. Some of the recharge that is not discharged as 

base flow to streams in the outcrop area leaks upward 

through confining beds downgradient from the outcrop 

area (Siple, 1967b).

Numerous aquifers are present in the Coastal Plain 

province of the South Atlantic-Gulf Region. They vary 

in areal distribution and extent, and some differ in name 

from one State to another even though they are lateral 

equivalents (table 1). Perhaps the most prolific aquifer 

is the Tertiary limestone aquifer which crops out or is 

near the surface in Florida, southern Alabama, central 

Georgia, and southeastern South Carolina and is made 

up of Paleocene to Miocene limy formations that function 

as one aquifer. The sand aquifers in the Tuscaloosa 

Group and correlative units of Cretaceous age crop out 

generally along the Fall Line and extend seaward beneath the younger formations from North Carolina to 

Mississippi. In the Western part of the region the thick 

permeable sand beds of the Miocene Series form an extensive aquifer system.

CRETACEOUS AQUIFERS

The Cretaceous deposits of the region have an outcrop 

area of about 40,000 mi2 from Mississippi to Virginia 

(fig. 4) and extend seaward under a cover of younger sediments. Although the downdip limit of freshwater (water 

containing less than 1,000 mg/L dissolved solids) in the 

Cretaceous aquifers is not known in parts of the region, 

the areal extent of freshwater in these aquifers probably 

exceeds 70,000 square miles.

Except in North Carolina and Virginia, the Lower 

Cretaceous sedimentary rocks (including the aquifers) 

are overlapped in the subsurface and do not crop out. 

These rocks contain salty water in the region except in 

North Carolina and Virginia and in a limited area in Mississippi (where the quality of water is inferred from geophysical logs). At Franklin, Isle of Wright County, Va., 

industrial and municipal pumpage from Lower Cretaceous deposits has caused water-level declines over a 

1,300 square-mile area that extends into North Carolina 

(Brown and Cosner, 1974). Yields of individual wells are 

as high as 2,500 gal/min in Virginia, and the aquifer is 

a source of large ground-water supplies in North 

Carolina.

Upper Cretaceous formations crop out along the inner 

edge of the Coastal Plain from Mississippi to North Carolina. The Tuscaloosa aquifers, which extend over 500 

miles from Mississippi to North Carolina, form one of the 

more extensive ground-water reservoirs in the region 

(fig. 6). In Mississippi and southwestern Alabama the 

Tuscaloosa Group consists of the Coker and Gordo Formations. In Georgia, units within the Tuscaloosa are not 

differentiated. The correlative units of the Tuscaloosa in 

North and South Carolina are the Cape Fear 

Formation and, in the updip areas, the overlying Middendorf Formation. Yields of 1,000 gal/min from the 

Tuscaloosa aquifers are common, and, where the full 

thickness is developed, yields of 3,000 gal/min may be 

possible.

In Mississippi and northwestern Alabama, the McShan 

and Eutaw Formations overlie the Tuscaloosa Group. 

Sand beds in these formations are fair aquifers in some 

areas.

Above the Eutaw Formation, except in east-central 

Mississippi, are sand beds in the Selma Group. In northern Mississippi, these beds are in the Coffee Sand and 

the Ripley Formation. In eastern Alabama and western 

Georgia, the Selma includes in ascending order the Blufftown Formation, Ripley Formation, including the Cusseta Sand Member, and Providence Sand. These units 

are only fair aquifers near their outcrop, but downdip in 

Alabama high yields are available from combinations of 

these strata. In eastern Georgia, South Carolina, and 

North Carolina, the aquifers correlative with Selma sequences are the Black Creek and Peedee Formations.

The yields from wells in the Cretaceous aquifers will 

vary from place to place in each aquifer and from aquifer 

to aquifer. Table 2 shows the maximum reported yield 

from each aquifer in several counties in each State. 

These values do not imply that such yields can be obtained everywhere in the aquifer or that such yields are 

the maximum possible yields.

The highest average transmissivities for Cretaceous 

aquifers are those for the Tuscaloosa Group (Formation). 

The Coker Formation is an extremely productive aquifer 

in eastern Mississippi where the highest transmissivity, 

80,200 ft2/d, was reported for a well 1,857 feet deep in 

Noxubee County, Miss. (Newcome, 1971, p. 36). Results
SOUTH ATLANTIC-GULF REGION O13

Structure contour 

Shows altitude of top of 

Tuscaloosa Group (Formation) 

and correlative rocks. Dashed 

where approximately located. 

Contour interval 500 and 1000 

feet. Datum is mean sea level

25°

85' 80"

FIGURE 6. Outcrop area, depth below sea level to the top, and downdip limit of freshwater in the Tuscaloosa Group (Formation) and

correlative rocks.
O14 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

TABLE 2. Maximum reported yields of wells in Upper Cretaceous 

aquifers, Mississippi to North Carolina

State and county

Alabama:

Autauqa 

BarbourBullock- - - 

DaleGreene 

Houston 

MontgomeryTuscaloosa 

Georgia:

Bibb - 

Houston - 

Macon - 

Peach 

Screven----- 

Sumpter ~ 

Terrell

Mississippi:

Chickasaw 

Clay--------

Lee - 

LowndesMonroe 

Noxubee 

Oktibbeha - 

North Carolina: 

Bertie 

Bladen - -

Colombus - 

Craven 

Duplin - 

Greene 

Hertford 

Hoke 

JohnstonLenoir

Martin 

Onslow 

Fender 

Pitt 

Robeson 

Sampson 

Wayne 

South Carolina:

Beaufort . 

Colleton 

Hampton 

Horry 

Sumter 

Williamsburg 

Yield 

(gal/min)

Drawdown 

(ft)

Aquifer

500

350

515

11,400

11,000

11,000

460

700

1,000

200

640

600

500

500

1,850

1,230

656

870

800

1,000

600

900

770

600

2,300

1,600

1,200

1,000

550

650

700

500

2,000

700

750

550

1,000

900

300

1,300

1,000

700

500

600

380

1,100

800

775

800-1,000 

650 

720

3,300

100

1,200

500

1,200

1,690

1,100

212

32

40 

 

70 

23 

flow

flow

57

42

57

71

90

122

67

52(?)

80

40

122

flow 

flow 

flow

120

Coker.

Blufftown-Providence Sand.

Gordo.

Ripley.

Coker.

Gordo.

McShan.

Providence Sand.

Coker.

Gordo.

Gordo.

McShan.

Coker.

Blufftown-Providence Sand.

Do.

Do.

Do.

Providence Sand-Clayton. 

Blufftown-Providence Sand. 

Providence Sand-Clayton.

Eutaw-McShan.

Gordo.

Eutaw-McShan.

Gordo.

Coker.

Gordo.

Coker.

Gordo.

Tuscaloosa (?). 

Black Creek. 

Peedee.

Do.

Tuscaloosa(?)-Black Creek. 

Black Creek-Peedee. 

Black Creek. 

Tuscaloosa(?).

Do.

Do.

Do.

Black Creek.

Tuscaloosa(?)-Black Creek. 

Black Creek-Peedee. 

Black Creek-Peedee(?). 

Black Creek. 

Peedee. 

Tuscaloosa(?). 

Black Creek(?). 

Lower Cretaceous. 

Tuscaloosa(?)-Black Creek. 

Tuscaloosa(?).

Do. 

Black Creek.

Do.

Upper Cretaceous

(Tuscaloosa?).

Lower Black Creek-Tuscaloosa. 

Black Creek(?)-Tuscaloosa. 

Upper CretaceousPeedee-Black CreeW?). 

Black Creek. 

Upper Cretaceous

(Tuscaloosa?). 

Peedee-Black Creek.

'Estimated.

of about 30 tests in Cretaceous aquifers in Mississippi 

indicate an average transmissivity of 1,200 ft2/d for the 

Eutaw and McShan Formations and 6,500 ft2/d for the 

Gordo Formation (Newcome, 1971). Similar conditions 

can be expected in adjoining parts of Alabama. Siple 

(1960, p. 165) reported a transmissivity of 26,700 ft2/d 

for a well developed in his "Tuscaloosa Formation" (Cape 

Fear Formation) in South Carolina, a value accepted by 

Callahan (1964, p. 10) for use in evaluating the Tuscaloosa aquifer in Georgia and adjoining states.

In northeastern North Carolina transmissivities in 

Cretaceous aquifers range from 190 to 27,000 ft2/d 

(Lindskov, 1972, table 4). A reasonable value for the average transmissivity is 10,000 ft2/d. In the opinion of 

R. C. Heath (written commun., 1977), most of the water 

withdrawn from the Cretaceous aquifers in North Carolina is derived from compression of the aquifer, expansion of the water, and drainage of the confining beds. In 

northeastern South Carolina, the hydraulic conductivity 

averages about 30 ft/d (A. L. Zack, oral commun., 1977).

Water in and near the outcrops and in the updip parts 

of the Cretaceous aquifers is generally low in dissolved 

solids, high in iron, and slightly acid (corrosive). Although much higher concentrations of iron have been reported in places in Mississippi and Alabama, 2 or 3 mg/ 

L is common in most areas. Downdip the water becomes 

neutral or slightly alkaline, and the iron content decreases sharply.

Water from some wells in North Carolina is hard, presumably because recharge is by seepage down through 

overlying limy Miocene sediments. Samples high in bicarbonate and low in hardness from deeper wells in the 

same area have presumably traveled for some distance 

downdip from their point of origin. In South Carolina, 

water from tjie Black Creek aquifer is characterized by 

low iron and high fluoride.

At varying distances downdip and at depth, water in 

the Cretaceous aquifers is highly mineralized owing to 

the fact that the sediments were once saturated with saline waters.

LOWER TERTIARY AQUIFERS

TERTIARY LIMESTONE AQUIFER

The Tertiary limestone aquifer, the most extensive 

and widely used aquifer in the South Atlantic-Gulf Region, underlies an area of about 90,000 square miles 

which includes Florida (where it is referred to as the 

Floridan aquifer), southern and coastal Georgia, and adjacent parts of Alabama and South Carolina (fig. 7). Local names for this aquifer are given in table 1. The aquifer is the source of some of the largest ground-water 

supplies in the United States (Stringfield, 1966, p. 1). It 

has been commonly referred to as the "principal artesian 

aquifer," although in many areas it is an unconfined aquifer. The aquifer includes parts of several geologic units 

(table 1) that are principally Tertiary limestone but contain intercalated beds and lenses of dolomite, sand, silt, 

marl, and clay in which porosity and permeability differ 

greatly from place to place. The aquifer thickness increases in a seaward direction from about 50 feet in its
SOUTH ATLANTIC-GULF REGION O15

87° 86°

32°

 H ALABAMAEXPLANATION

Sinkholes breaching Hawthorn ForITiatlOTl or vniinoror A^I/I/>AV^/\ ^nnn»:4-M,.......«,^j uitoi,iiiiig iiawuiiurii rormation or younger Miocene deposits

txsxsxszszxxxi

Aquifer at or near the land surface

Structure contours

Drawn on top of aquifer; dashed

where approximate. Ticks indicate

depression. Contour interval 100

feet; datum is mean sea level

FIGURE 1-. Distribution and structure contour map of the top of the Tertiary limestone aquifer. (From Stringfield, 1966, fig. 23).
O16 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

updip areas in Georgia to more than 2,500 feet in parts 

of Florida (Klein, 1971).

Most of the massive limestone of Tertiary age has been 

removed by erosion from the Cap Fear Arch. Nevertheless, the Tertiary limestone of North Carolina is considered a hydrologic equivalent of this aquifer.

The several limestone units constituting the aquifer 

(table 1) are principally of marine origin and generally 

grade into or interfinger with clastic deposits toward the 

continental landmass to the north from which the elastics 

were derived. These peripheral clastic facies are not considered part of the aquifer. The aquifer is near the surface and in hydraulic continuity with the unconfined shallow aquifers over an extensive area where overlying 

rocks of lesser permeability are perforated by innumerable sinkholes, particularly around the Ocala Uplift (fig. 

3). Elsewhere the impermeable clays of the Hawthorn 

Formation overlie the aquifer; however, this formation 

is breached in a few places, as near Parris Island and 

Brickyard Point, Beaufort County, South Carolina.

Ground-water development is extensive, including 

withdrawal of hundreds of millions of gallons per day to 

meet the water-supply needs of numerous major cities, 

such as Savannah, Jacksonville, and St. Petersburg; the 

phosphate, pulp, paper, and allied chemical and other industries; and for citrus and other crop irrigation. 

Throughout the area, the aquifer yields water to tens of 

thousands of domestic, industrial, and irrigation wells, 

but most of the large industrial supplies are developed 

in coastal areas.

The wide range in hydraulic characteristics in the Tertiary limestone aquifer reported by Stringfield (1966, p. 

101-109) is representative of an aquifer composed of 

sediments that range from interbedded sand and clay to 

cavernous limestone. The reported transmissivities 

range from 3,700 to 134,000 ft2/d, hydraulic conductivities from 35 to 334 ft/d, and storage coefficients from 

0.00019 to 0.021. These values do not indicate the true 

potential; for example, Callahan (1964, table 4) estimated 

transmissivity values in Georgia as high as 268,000 

ft2/d for his determinations of ground-water flow through 

the aquifer.

. Large springs having yields ranging up to hundreds 

of millions of gallons per day from the Tertiary limestone 

aquifer are numerous in Florida and Georgia. Silver 

Springs and Rainbow Springs in central Florida are the 

largest, their combined flow averaging about 1,000 

Mgal/d (Rosenau and Faulkner, 1974). Well yields of 

2,000 gal/min are common. Locally, yields up to 11,000 

'gal/mm are known, and a natural flow of 20,000 gal/min 

is reported for a well in central Florida (Pascale, 1975). 

The base flow of streams is well sustained as a result of 

ground-water discharge through springs.

Under natural conditions, the aquifer contains potable 

water as defined by Klein (1971) to depths of more than 

2,000 feet in parts of the area (fig. 8). The extent and 

thickness of the freshwater body is dependent upon the 

rainfall and the geologic and hydrologic properties of the 

rocks.

Since the last emergence of the land from the sea, the 

aquifer has been flushed of seawater in most areas. In 

southern Florida and in places along the eastern seaboard where the potentiometric head is low, the aquifer 

has not been completely flushed, and the water is saline. 

Increases in salinity with depth are commonly abrupt immediately below an impermeable stratum underlying a 

freshwater zone.

In the Georgia and South Carolina coastal plains, 

water at depth inland is fresh through the full thickness 

of the aquifer. At Savannah, Ga., the section is about 

600 feet thick, but 70 percent of the water produced in 

that area comes from two upper zones that have a combined thickness of about 100 feet (McCollum and 

Counts, 1964). Saline water occurs in the lower part of 

the aquifer at Hilton Head Island, S. C., and the entire 

aquifer is saline in most of Beaufort County, S. C. (L. 

R. Hayes, oral commun., 1977). At Brunswick, Ga., the 

500- to 1,000-foot zone is fresh; saline water is present 

from 1,000 to 1,400 feet and low chloride water occurs 

from 1,400 to 1,700 feet (R. L. Wait, 1965, p. 67).

The freshwater in the aquifer is generally hard. In the 

recharge area, the water may contain less than 20 mg/ 

L hardness as calcium and magnesium bicarbonate, but 

almost everywhere downdip the hardness is generally in 

excess of 100 mg/L.

At centers of heavy pumping, lowered head tends to 

induce upward flow of deeper, possibly saline, water. 

Many wells have been drilled through several zones of 

the aquifer, thereby providing direct flow paths for 

deeper more highly mineralized water to migrate upward (or laterally) and contaminate the freshwater reservoir. Upward movement may occur in a short time and 

is, therefore, the greater hazard.

In southwestern Florida, the mineral content of 

ground water along the Peace River is high. Kaufman 

and Dion (1967) suggested that here deep ground water 

rises "along a linear zone (fault?) of greater vertical 

permeability." In eastern Florida, "upward leakage of 

highly mineralized water from deep artesian zones" is in 

part "along fault zones" (Klein, 1971).

Saline water is moving laterally from points of vertical 

leakage into well fields at Brunswick, Ga. (Wait and 

Gregg, 1967). At Jacksonville, Fla., saline water has 

migrated into the lowermost zone of the Tertiary limestone aquifer, thus eliminating it as a source of potable 

water.
SOUTH ATLANTIC-GULF REGION O17

Contamination by seawater is possible in coastal 

areas where the overlying confining bed is breached. 

Seawater is presently migrating toward the Savannah 

wells from the Hilton Head Island, S.C., area (Counts 

and Donsky, 1963, p. 72); however, under existing hydraulic conditions, salt water will require many years to 

reach the center of heaving pumping.

 I i 1 i 

LOWER TERTIARY AQUIFERS OTHER THAN THE 

TERTIARY LIMESTONE AQUIFER

The Paleocene, Eocene, and Oligocene sediments that 

make up the lower Tertiary aquifers (exclusive of the 

Tertiary limestone aquifer) in the region have an outcrop 

area of 45,000 square miles from Mississippi to Virginia 

(fig. 4). They dip seaward under a cover of younger sedEXPLANATION

Contour showing depth to base of potable 

water in the Tertiary limestone aquifer. 

Contour interval 250 feet. Dashed where 

inferred. Datum is land surface

Area where water in the Tertiary limestone 

aquifer contains more than 250 mg/L 

of chloride or more than 500 mg/L of 

dissolved solids

50 MILES

50 KILOMETERS

30°

85° 80°

FIGURE 87 Depth to the base of potable water in the Tertiary limestone aquifer (Floridan aquifer) in Florida.
O18 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

iments. Although the individual lower Tertiary aquifers 

are not as extensive areally as the Cretaceous aquifers, 

they are major sources of ground water where they occur 

in the region (table 1).

The lower Tertiary aquifers include limestone beds 

that grade laterally into the Tertiary limestone aquifer 

(table 1). These strata have poor hydraulic connection 

with one another, and development of maximum supplies 

in any one place would require either several wells ending in different aquifers or a well screened at various 

levels.

Without exception, water in the lower Tertiary aquifers is fresh in the area of outcrop and for a few tens of 

miles downdip, beyond which the water is saline. Maximum development at present is ordinarily confined to 

whatever productive stratum lies nearest the surface. 

Additional supplies are available at greater depths in 

many places, but in other places the deeper beds yield 

only saline water.

The lower Tertiary aquifers in Mississippi, Alabama, 

and western Georgia (table 1) are highly productive. 

Yields ranging up to 2,000 gal/min to individual wells 

are common. A well field in Tertiary limestone yielded 

as much as 15 Mgal/d at Ft. Gaines, Ga. (Callahan, 1964, 

p. 19). Well yields of 2,000 gal/min or more could be 

reasonably expected from efficiently constructed wells at 

many places in the Pascagoula River basin in Mississippi 

(Newcome, 1967b, p. 1). Deeper parts of some of the 

Tertiary aquifers in Mississippi, in areas where freshwater extends to depths of 3,000 feet (fig. 9), remain 

virtually untapped and are potential sources of future 

water supplies.

The Castle Hayne Limestone, separated from the Tertiary limestone aquifer by erosion across the Cape Fear 

Arch, is the principal source of water supplies in the 

coastal plain area of North Carolina. Withdrawals of 

water from the Castle Hayne in Beaufort County, N. C., 

for mining exceeded 60 Mgal/d in 1974 (North Carolina 

Department of Natural Resources, 1974).

The lower Tertiary aquifers exhibit a very wide range 

in hydraulic properties. The estimated average transmissivity for the Castle Hayne Limestone in North Carolina is about 25,000 ft2/d (R. C. Heath, written commun., 1977), and the range for the lower Tertiary 

aquifers in South Carolina is from 350 to 13,400 ft2/d 

(C. A. Spiers, oral commun., 1977). Callahan (1964, p. 

19) reported that transmissivities ranged from 940 to 

20,000 ft2/d in Georgia.

A compilation of about 110 aquifer tests made in lower 

Tertiary aquifers in Mississippi (Newcome, 1971) shows 

a range in hydraulic conductivity from near 1 to about 

240 ft/d. Corresponding values for transmissivity in an 

aquifer 100 feet thick would be as much as 24,000 ft2/

d. The average transmissivity for a 100-foot aquifer 

would be about 6,400 ft2/d. Values for lower Tertiary 

aquifers in Alabama are estimated to be about the same.

UPPER TERTIARY AQUIFERS

Miocene and Pliocene sediments make up the upper 

Tertiary aquifers in the South Atlantic-Gulf Region. 

These sediments crop out over an area of about 70,000 

square miles from Mississippi to Virginia (fig. 4).

Miocene beds are widely distributed in the region and 

extend from Mississippi to Virginia, although absent 

over the Cape Fear Arch. From Georgia to central South 

Carolina, Miocene limestones are significant parts of the 

upper Tertiary limestone aquifer.

In the Florida panhandle, Alabama, and Mississippi, 

the Miocene beds dip toward the south and southwest 

and thicken rapidly. The total Miocene section is as much 

as 5,000 feet thick in southwestern Mississippi, but only 

the higher beds contain freshwater. The depth to base 

of freshwater in the area (fig. 9) ranges from 500 feet 

near the northern limit of those formations to as much 

as 3,000 feet near the coast and near the mouth of Pearl 

River in Mississippi.

Units of Pliocene age overlie the Miocene deposits and 

are part of the freshwater hydrologic system of the Gulf 

Coastal area. The Citronelle Formation of Pliocene age 

is the source of water for many domestic and public-supply wells, but most large yield wells have been drilled 

into the underlying Miocene aquifers where water is under higher artesian pressure.

Practially all domestic and municipal water supplies 

and most industrial supplies along the Gulf Coast in 

western Florida, Alabama, and Mississippi are obtained 

from Miocene to Pliocene aquifers. Well yields commonly 

exceed 1,000 gal/min. At Pensacola, in western Florida, 

municipal wells yield 1,500 to 2,000 gal/min, and pumpage exceeded 17 Mgal/d in 1970. In the Pascagoula 

River basin in Mississippi, with careful programs of exploration and development, individual well yields of 

2,000 gal/min could become commonplace, and yields of 

5,000 gal/min are not unreasonable to expect in some 

places (Newcome, 1967b, p. 35).

The upper Tertiary aquifers are characterized by high 

hydraulic conductivity and transmissivity values. Lindskov (1972, table 4) reported transmissivity values ranging from 44 to 2,710 ft2/d for aquifers in the Yorktown 

Formation in North Carolina. Callahan (1964, p. 47) refers to transmissivities ranging from 4,540 to 66,800 ft2/ 

d in northwestern Florida and southern Alabama and indicates that conditions are similar in the Atlantic Coastal 

area of Georgia in the Pliocene to Holocene aquifers 

(Callahan, 1964, p. 50). In southern Mississippi the upper Tertiary aquifers, mostly of Miocene age, are among
SOUTH ATLANTIC-GULF REGION O19

the most productive in the State. Newcome (1971) summarized about 130 aquifer tests that indicated hydraulic 

conductivities ranging from 5 to 334 ft/d. The average 

hydraulic conductivity for all tests was 94 ft/d. Assuming 

that the average aquifer is 100 feet thick, the average

transmissivity would be 9,400 ft2/d. The largest transmissivity value for the Miocene aquifer system in Mississippi was 84,000 ft2/d at a site in Harrison County 

(Newcome, 1971, p. 25). 

There appears to be little contamination of deep aqui-

 1000 

Contour showing altitude of base of 

freshwater. Contour interval 500 

feet. Datum is mean sea level. 

Dashed where approximate

0

1

0 100

100

1

1

200

200

1

300 MILES

1

1 1 

300 KILOMETERS

EXPLANATION

Line of abrupt change 

in base of freshwater

Area where saline water 

occurs above freshwater

Area where freshwater occurs 

only in surficial deposits

FIGURE 9. Altitude of the base of freshwater in Alabama and Mississippi.
O20 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

fers by seawater, but contamination of the shallower 

aquifers that are hydraulically connected to estuarine 

streams probably occurs in a few places (Newcome, 

1967b, p. 29).

QUATERNARY AQUIFERS

Pleistocene and Holocene sediments make up the Quaternary aquifers in the South Atlantic-Gulf Region. The 

sediments crop out over an area of about 40,000 square 

miles, primarily in the coastal area from Mississippi to 

Virginia (fig. 4).

In the western Florida panhandle, the upper Tertiary 

and Quaternary units (Miocene to Holocene) constitute 

a large unconfined (water table) aquifer. The sand and 

gravel deposits are thickest to the south and west and 

thin to the north and east. Wells 200 to 400 feet deep, 

capable of producing 1,000 to 2,000 gal/min, are common. The quality of the water is excellent except for the 

erratic occurrence of excessive iron. The aquifer is susceptible to saltwater encroachment near estuaries.

During the drought of 1954 to 1956, the minimum discharge or ground-water outflow at 10 of 15 gaging stations in the Florida panhandle was 0.308 (Mgal/d)/mi2 

(Pride and Crooks, 1962, table 2, p. 34-35), equal to 

about 6.5 inches of precipitation. Thus, in the 6,500 

square mile panhandle area, a minimum of about 2,000 

Mgal/d would be available for development if the environmental effects of the withdrawals were acceptable.

Deposits of Miocene to Holocene age also make up an 

important freshwater aquifer in southwestern Florida. 

The aquifer is about 130 ft thick in western Collier 

County, but thins eastward and wedges out toward Dade 

and Broward Counties. Most of the wells near the Gulf 

are generally less than 100 feet deep, and the municipal 

water-supply wells are properly spaced and discharged 

at low rates to prevent saltwater encroachment (McCoy, 

1962). Wells inland yield up to 1,300 gal/min. The quality 

of the water is good except for a high iron content.

The highly productive Biscayne aquifer, predominantly highly permeable limestone of Quaternary age, is 

the most important source of freshwater for populous 

southeastern Florida, including the Miami area (Parker 

and others, 1955). The aquifer underlies about 3,000 

square miles of Dade, Broward, and parts of Palm Beach 

Counties. It is as much as 400 feet thick along the shoreline, but is more commonly less than 200 feet thick and 

thins to a featheredge 40 miles to the west. It is estimated that about two-thirds of the 60 inches annual rainfall infiltrates the zone of saturation in Dade County 

(Parker and others, 1955, p. 221).

Well yields commonly exceed 2,000 gal/min (Pascale, 

1975). An estimated 120 billion gallons of water was 

pumped from a 600 mi2 area in the coastal ridge in 1965, 

of which 22 billion gallons was consumptive use. Although copious supplies are available, one of the factors 

limiting withdrawals is the susceptibility of the aquifer 

to saltwater encroachment from the ocean and from tidal 

canals.

Prior to the 1930's, little attention was paid to the detrimental effects of the tidal canals; however, water management practices initiated in 1945 have effectively stabilized the saltwater instrusion. These are (1) the 

importation of freshwater through canals to maintain 

higher water levels, (2) the construction of salinity-barrier dams in tidal canals to prevent the intrusion of salty 

water and furnish additional water to infiltrate into the 

aquifer, and (3) the shifting of pumping to new well fields 

to the west.

North of Palm Beach County, a shallow sand aquifer 

extends along most of the coastal area. In Duval County, 

more than 40,000 wells produce 10 to 25 Mgal/d (Fairchild, 1972) from a shallow aquifer system consisting of 

Miocene to Holocene deposits.

The coastal aquifers in the Quaternary deposits (fig. 

4) generally yield only small supplies to wells. They are 

relatively low in permeability, and the storage capacity 

at any one place usually is small; however, these aquifers 

absorb rainfall readily, and in many areas they are a perennial source of small water supplies and recharge to 

streams and underlying aquifers.

Where Quaternary aquifers are extensive in humid 

areas, both storage and recharge potential are favorable. 

At Elizabeth City, N. C., for instance, 14 shallow wells 

yield a total of 450 gal/min more than half the city supply (R. C. Heath, oral commun. Nov. 30, 1972). The 

greater cost in such developments may be the cost of 

land and pipelines rather than that of the wells. Along 

some of the larger rivers in the region, alluvium as much 

as 75 feet thick may yield up to 1,000 gal/min. Sustained 

yields of this magnitude should not be expected except 

where wells are properly spaced and recharge conditions 

are favorable.

Data on hydraulic characteristics of the Quaternary 

deposits are limited because few aquifer tests have been 

made. Large wells in Quaternary aquifers are not common because of limited available drawdown, and in many 

localities, the water requires treatment for most uses. 

A noteworthy exception is the Biscayne aquifer, the major source of water supplies in southeastern Florida. Parker and others (1955, p. 2) reported that the Biscayne is 

among the most permeable aquifers investigated by the 

Geological Survey. Transmissivities for the aquifer 

range from 400,000 to 2,670,000 ft2/d, and the average is 670,000 ft2/d. The average storage coefficient is 

0.20. A reasonable value for transmissivity of Quaternary deposits in North Carolina is about 750 ft2/d (R. C. 

Heath, written commun., 1977). Transmissivity values 

for Quaternary aquifers in South Carolina range from
SOUTH ATLANTIC-GULF REGION 021

850 to 2,000 ft2/d (C. A. Spiers, oral commun., 1977), 

and Callahan (1964, p. 50) estimated that values could 

be as large as 66,800 ft2/d in the Pliocene to Holocene 

section in Georgia.

The chief value of the Quaternary deposits in the hydrologic system is their function of absorbing and storing 

large volumes of precipitation for gradual release to underlying aquifers and to streams.

GROUND WATER IN THE PIEDMONT 

PROVINCE

In describing the occurrence of ground water in the 

Piedmont and Blue Ridge provinces, LeGrand (1967, p. 

8) states

The water table, representing the top of the reservoir, generally lies 

in the clay, or disintegrated rock materials. In the lower part of the 

reservoir, water occurs in interconnecting fractures in bedrock; the 

fractures diminish in number and size with increasing depth. Water 

enters the fractures by seeping through the overlying clay, and drilled 

wells draw water from these fractures. The source of this water is precipitation in the general area of a well and not in some remote place.

Minor valleys generally mark zones of fracture and, in 

places, fault zones, and yields are significantly higher 

there than elsewhere (Baker, 1957). The majority of 

wells in the Piedmont, however, are located for convenience on high ground, commonly under the community 

water tank. These wells nearly always are low yielding; 

consequently, the Piedmont is considered an area where 

well yields are low (fig. 5).

LeGrand (1967, p. 9) stated that 90 percent of all 

ground water in the area occurs in the first 100 feet below the water table and that generally two wells 200 feet 

deep each will yield more water than one well 400 feet 

deep. Yields of up to 500 gal/min have been reported 

from wells in crystalline rocks (Johnson and others, 

1968), but many deep wells yield less than 75 gal/min.

The source of recharge in the Piedmont is the precipitation that saturates the saprolite (weathered rock) that 

overlies unweathered rock. Where the saprolite cover is 

thick or sandy, wells will have the better yields. A well 

in crystalline rocks ordinarily draws water from a limited 

area in the general vicinity of the well, and fissure zones 

supplying water to the well are commonly limited in extent. Wells must be widely spaced in order to avoid mutual interference, and successive wells located along the 

same rock lineament will create more mutual interference than if successive wells are located at right angles 

to the "grain" of a rock mass. Wells near a stream may 

have significantly higher yields than wells distant from 

such a source of recharge.

The 7-day, 2-year low flow in Pickens County, S.C., 

ranges from 0.3 to 0.7 (Mgal/d)/mi2 (Johnson and others, 

1968). This measurement of ground-water discharge to 

the stream, at the time of low hydraulic gradients, indicates that the average annual recharge is at least 6.3 

to 17.5 inches.

An example of ground-water development in the Piedmont province is at Tega Cay, S. C., where 22 wells averaging 580 feet in depth were drilled to provide water 

for a resort (McCall, 1972). The well sites were located 

on the basis of a careful evaluation of geology and hydrology. Yields ranged from less than 10 gal/min to 370 

gal/min and averaged 109 gal/min. From this group, 14 

wells yielding an average of 160 gal/min were selected 

as supply wells. Most of the water is obtained from below 

a depth of 450 feet. This well field is on a peninsula jutting into Lake Wylie, a possible source of recharge that 

may have been a factor in the high yields obtained even 

though the path to the wells was circuitous and the 

source of recharge somewhat distant. Tests for coliform 

bacteria in the well waters were negative, suggesting 

that if the lake is a source of much of the recharge, slow 

filtration through the fine-grained saprolite has been 

highly effective in removing the bacteria. However, in 

areas where the saprolite cover is thin, filtration of surface-water seepage would not be very effective.

GROUND WATER IN THE

VALLEY AND RIDGE PROVINCE

AND CUMBERLAND PLATEAU SECTION

A small part of the study area lies within the folded 

Appalachians, largely that area in Alabama and Georgia 

drained by the headwaters of the Coosa River. The underlying rocks are Paleozoic limestone, dolomite, sandstone, and shale, mostly overlain by a mantle of residual 

material. In the Valley and Ridge province (fig. 1), the 

rocks are not only crumpled by compressive stresses but 

are broken into several huge segments, some of which 

have slid over the more stable masses. Lesser displacements occur along high-angle faults. The Paleozoic rocks 

of the Cumberland Plateau section, adjacent to the Valley and Ridge province on the northwest, are gently 

warped.

Synclines (downwarps of rock strata) may be thought 

of as favorable locations for ground-water development 

in the sense that water funnels into troughs, but circulation is poor due to the compression of fractures in deep 

synclinal troughs and the water may be of inferior quality. Anticlines (upwarps), on the other hand, tend to 

crack the rock into open fractures along their crests during folding and are favorable recharge areas.

In this area of large-scale deformation, the more brittle rocks were shattered and sheared; subsequently, dissolution by percolating water enlarged the fractures in 

limestone and dolomite (the carbonate rocks). Fractures 

in sandstone, unless calcareous, are not enlarged by later 

solution. True (noncalcareous) shales, initially poor aqui-
O22 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

fers, scarcely improve in water-bearing character as a 

result of deformation and later dissolution.

The hydrology of shattered consolidated rocks is 

greatly different from that of the unconsolidated sandy 

formations. In shattered limestone, water can move 

nearly as fast as through a pipe, and in both fractured 

limestone and sandstone filtering action is lacking. The 

cone of depression around a well in a highly fractured 

rock mass enlarges quickly, and water may move rapidly 

to a well from long distances. Stored water in the carbonate rocks may be that filling an open cavern, an interconnected series of smaller openings, or in the unconsolidated materials overlying the limestone that is 

hydraulically connected to water in the caverns. Although the rate of recharge in a carbonate rock terrane 

overlain by a clay mantle may be low, water can flow 

rapidly to a well from a large surrounding area and high 

yields with small drawdowns are possible.

In Talladega County, Ala., the Cambrian dolomites 

are highly productive (Causey, 1965). One well yields 

1,100 gal/min with 27 feet of drawdown and has been 

pumped at 1,600 gal/min. A well in Precambrian(?) marble yields 900 gal/min with 72 feet of drawdown.

Cressler (1970) notes that in northwestern Georgia, 

1,000 gal/min should be available in many places from 

properly located wells. Near Huntsville, Ala., just north 

of this report area in the Cumberland Plateau section, 

a recently completed well 160 feet deep yielded 2,900 

gal/min with 20 feet of drawdown (W. J. Powell, oral 

commun., March 1, 1972).

In Calhoun County, Ala., a 95-foot well in Cambrian 

dolomite yielded 257 gal/min with only 1.6 ft of drawdown; whereas, a 550-foot well yielded about as much 

with 15 feet of drawdown (Warman and Causey, 1962). 

It is entirely possible that drilling to 400 or 500 feet in 

strongly deformed areas may intersect a low-or high-angle fault from which large quantities of water may be 

obtained; therefore, it seems likely that deep drilling is 

desirable where maximum production is sought. Drilling 

in the most convenient locations relative to points of use 

can easily result in failure; whereas, sites a mile or a few 

miles distant that are selected on the basis of structural 

control may provide ample water at very low cost.

It is probable that the ground-water potential of the 

Valley and Ridge province is generally underrated, although many examples are known of failures to develop 

productive wells.

GROUND WATER IN THE 

BLUE RIDGE PROVINCE

In the rugged Blue Ridge province weathered rock 

cover (residuum) is commonly thin or absent except in 

valleys. Ground water generally occurs in residuum or 

alluvium and in fractures in the underlying igneous and

metamorphic rocks. Small water supplies are available 

from the springs that drain the fracture systems and residuum. Well yields depend on the number and degree 

of interconnection of fractures penetrated by the well but 

commonly are only a few gallons per minute. Where all 

the available water is stored in fractures, the yield diminishes as stored water is pumped and the water level 

declines. LeGrand (1967) determined that wells are more 

productive and have a more stable yield where there is 

a thick mantle of residuum and that most interconnected 

fractures occur no deeper than 150 feet below the surface. Few wells produce significant quantities of water 

from depths greater than 300 feet.

Ground water in the province is generally of good quality. The dissolved-solids concentration is very low, and 

the principal quality problems are excessive iron and acidity (low pH). Aquifers in rock fractures are subject to 

contamination, however, in areas where the residuum is 

too thin to be an effective filter.

SALINE-WATER RESOURCES

Vast quantities of saline water are available in the 

South Atlantic-Gulf Region. This saline-water resource 

is mostly in aquifers in the unconsolidated rocks that underlie the Coastal Plain above the Paloezoic "basement" 

rocks to depths that approach 20,000 feet in southern 

Florida and southwestern Mississippi. All permeable deposits below the deepest freshwater (fig. 9) are 

saturated with saline water, some of which has a much 

higher dissolved-solids concentration than seawater.

Some of the dissolved minerals are of economic value; 

however, the most likely reason for immediate development will be utilization of slightly saline and moderately saline water. Some water containing up to about 

2,000 mg/L of dissolved solids can be used for irrigation. 

Slightly saline water can be blended with freshwater to 

augment ground-water supplies for public and industrial 

uses. Desalting operations for public water supplies and 

other uses are more economical where the raw water has 

a low concentration of dissolved solids.

Saline aquifers offer reservoir space for injection'and 

temporary storage of freshwater. The Norfolk, Va., injection project demonstrated that only 15 percent of the 

injected water was not potable upon recovery (Brown 

and Silvey, 1977, p. 51). Injection and storage could be 

used to provide a supplemental source of water to meet 

peak demands or as an emergency source.

DEVELOPMENT AND MANAGEMENT OF 

GROUND-WATER RESOURCES

OBJECTIVES

The manager has the responsibility of examining the 

alternatives for developing sources of supply; that is, a
SOUTH ATLANTIC-GULF REGION O23

ground-water supply based on conventional development 

and management procedures as against supplies based 

on unconventional technologies. The planner is necessarily responsive to public expression regarding acceptable 

types of development and to the economic and social aims 

and interests of the particular States concerned. One of 

the major considerations confronting both manager and 

planner is the effect of ground-water development on the 

environment, particularly if a drastic lowering of water 

levels or large reduction in streamflow is involved. 

Where these constraints take precedence, dollar costs 

will be of minor significance in reaching final decisions.

In dealing with total available supply, ground water 

is not an entity separate from surface water. Much of the 

ground water that is not lost by evapotranspiration becomes the base flow of streams. Capture by wells of 

ground water moving toward a stream or induced infiltration of streamflow is highly desirable in many places 

but does not increase the total water supply. The increase in the ground-water supply is balanced by decrease in streamflow.

Where there is salvage of evapotranspiration loss, that 

salvage is an addition to the total water supply available 

for man's use; however, the effects on the environment 

must be considered. Reuse of water, the use of treated 

sewage effluent, or the use of poor-quality water for cooling or other purposes will conserve the total available 

supply. Use of ground water that would otherwise discharge into saline estuaries is ah addition to the total 

supply in most situations.

The above mentioned management techniques are intended to show that the total available supply can be increased by utilizing aquifer storage during the low 

streamflow months and making up the resultant underground reservoir deficiency by capture of streamflow 

during the high-flow period.

Although the value of conventional approaches to 

many problems is granted (wider spacing of wells, for 

instance), emphasis here is placed on procedures that are 

not generally in use in the region but which have been 

demonstrated to be effective in other areas. Objections 

to any of the suggested management procedures may be 

based on costs; however, alternate sources would also be 

expensive.

NATURAL RECHARGE

The overland and ground-water runoff in the southeastern Coastal Plain is about one-third the total rainfall, 

roughly 15 inches, and the remainder is assigned to evapotranspiration loss and ground-water recharge (Pierce, 

1966). Estimates of ground-water recharge have ranged 

from 1 to 11 inches (Callahan, 1964). Recharge of 6 inches 

would amount to about 0.29 (Mgal/d)/mi2 .

Some extreme exceptions to this generalization are

highly permeable localities in areas underlain by the 

sandy Cretaceous formations. Callahan (1964, p. 12) 

states that in places the Cretaceous sand aquifers may 

discharge to streams the equivalent of 40 inches per 

year. Thomson and others (1956) showed that in one 

place the 7-day, 2-year flow (1937-55) of streams fed by 

Cretaceous aquifers was about 1.04 (Mgal/d)/mi2 

equivalent to about 22 inches of recharge.

DEVELOPMENT OF UNCONFINED SANDY AQUIFERS

Unconfined aquifers are similar to surface reservoirs 

in that water pumped from storage can be replenished 

by natural or artifical recharge. Recharge may be seasonal precipitation or it may be from another natural 

source (streams, lakes, or leakage from deeper aquifers). 

Overdraft, within limits, during dry periods leaves storage space for the surplus water available for recharge 

during wet periods a condition that can be planned. 

During the period of high recharge, the intercepted 

ground-water outflow to the stream, although much 

greater in volume, is insignificant in relation to the total 

flow of moderate sized or large streams. The amount of 

intercepted ground-water flow to streams during lowflow periods is small because the normal ground-water 

contribution to the stream at that time is small. Planning 

the development of unconfined aquifers can involve many 

combinations of numbers and locations of wells and. well 

fields relative to streams or other sources of recharge. 

Additional flexibility is provided by various methods of 

artifical recharge.

In widely separated well fields the recharge that falls 

upon a well field in an unconfined aquifer is not the only 

water available to those wells. Water flows to the pumping wells from all directions; thus the wells draw in water 

replenished by recharge over many square miles.

Removing water from storage in unconfined aquifers 

lowers the water level, thereby reducing the losses to 

evapotranspiration.

DEVELOPMENT OF CONFINED SANDY AQUIFERS

Only part of the recharge water in the outcrop area is 

removed by evapotranspiration, discharged as streamflow, or intercepted by withdrawals. Some moves downdip into the confined part of the aquifer.

Applying Darcy's Law and assuming a transmissivity 

of 27,000 ft2/d and an average hydraulic gradient of 2.5 

ft/mi, 0.5 Mgal/d will move downdip in a typical aquifer 

across each mile of the section. Increasing the hydraulic 

gradient in the confined aquifer (by establishing a cone 

of depression or by raising the head in the recharge area) 

would increase the downdip flow proportionately. Further application of Darcy's Law indicates that a 5-mile 

width of aquifer would transmit 10 Mgal/d if the hydraulic gradient were increased to 10 ft/mi.
O24 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

The transmissivity of the aquifer establishes the first 

constraint on ground-water development. Acceptable 

pumping lifts in deepening cones of depression establishes the second constraint. Larger volumes of water 

would be made available by increasing the drawdown 

and the eventual extent of the cone of depression. Leakage from aquifers above and below might occur, providing additional water to that which moves laterally and 

diminishing the supply in the other aquifers. A temporary bonus is water released from storage as a result of 

lowering the pressure during the water-level decline. 

Artificial recharge in either the unconfined or confined 

zones of the aquifer will increase the available water supply. Where enough data are available, and through the 

use of analog and digital modeling, the optimum combination of recharge, hydraulic gradient, and pumping lift 

can be planned and problems can be minimized.

Certain effects on the environment, such as the potential for land subsidence, should be considered when large 

withdrawals from confined aquifers are planned.

DEVELOPMENT OF THE TERTIARY LIMESTONE AQUIFER

Callahan (1964, p. 26) points out that in the Valdosta, 

Ga., area the base flow of streams was relatively low in 

the fall of 1954, 0.014 to 0.054 ft3/s/mi2 or 0.009 to 

0.035 (Mgal/d)/mi2 , but that much of the infiltrating rainfall of 1.25 ft3/s/mi2 (0.81 (Mgal/d)/mi2) may have moved 

downdip in the principal artesian aquifer rather than 

emerging as base flows of streams. According to H. B. 

Counts (oral commun., Feb. 18,1977), in November 1972 

the total flow of the Withlacoochee River, an estimated 

12 Mgal/d, drained into two sinkholes and much more 

could have been accepted.

Estimates of rates of recharge to the Tertiary limestone aquifer have been made by determining outflow 

through the aquifer (table 3) according to various published values or estimates of transmissivity and hydraulic gradients. These are given below for the several 

large areas.

In the Alachua-Bradford-Clay-Union County, Fla., 

area the recharge computation of 0.08 (Mgal/d)/mi2 (table 3) is based on a transmissivity value derived from 

development of the upper 200 feet of the aquifer (Clark 

and others, 1964) in an area where the aquifer is about 

1,000 feet thick.

In the Green Swamp (Florida) recharge area the outflow is limited by the cross-sectional area through which 

water must flow (Pride and others, 1966). Hence, although the transmissivity is higher in the western basin, 

the cross-sectional area through which discharge takes 

place is smaller, and the apparent recharge is smaller.

It was estimated that in Hillsborough County, Fla., in 

the late 1950's about 100 Mgal/d entered the county

TABLE 3. Recharge rates to the Tertiary limestone aquifer 

based on estimates of flow through the aquifer

Area 

(mi2)

Aquifer

flow 

(Mgal/d)

Recharge rate 

per square mile

(ft3/s) (Mgal/d)

Equivalent 

precipitation 

(in/yr)

Florida:

Alachua-Bradford ClayUnion Counties above 

the 75-ft contour.

525

Orange County 950

Polk County:

Alfia and Peace 640 

Rivers 

Kissimmee River 415 

Green Swamp area 870

Western basin 160 

'Eastern basin 208

Hillsborough County:

Local 1,040

Inflow - - 566

45

210

163

151

114.8

121.8

166.2

22.1

67.4

450

100

0.132

.34

.395

.536

.204

.217

.214

.501

.67 

.274

0.085

.22

.255

.364

.132

.140

.191

.138

.324

.432

.177

4.62

5.36

7.65 

2.7 min. 

2.9 avg. 

4.0 max.

2.9 

6.8

9.1 

3.72

from the north and east through the aquifer, but there 

was additional local recharge of about 0.43 (Mgal/d/mi2 , 

equivalent to 9.1 inches of precipitation per year (Menke 

and others, 1961, p. 15). Results of other determinations 

are given in the table.

Although only 0.2 to 0.5 Mgal/d of water per square 

mile of recharge area moves downdip at present, potential production from the artesian beds in the aquifer is 

much greater. When gradients are increased, the flow is 

increased proportionally, and additional ground water 

that is now discharged to streams or springs would be 

captured. For instance, there are large springs northwest of where the Miocene deposits overlap older strata 

(fig. 10). These springs may represent potential recharge to the Tertiary limestone aquifer that cannot pass 

southeastward under the Miocene cover and through 

fault zones under existing hydraulic gradients.

Some or much recharge through the top of the aquifer 

will also be available if gradients are increased, and in 

some areas water from deeper sources may rise along 

faults. In some instances additional water would be available through capture of evapotranspiration loss and from 

inflow from streams originating outside the area.

Florida's two largest springs, Silver Springs and Rainbow Springs, each have a ground-water drainage area of 

about 625 square miles underlain by a thin or broken clay 

cover. The average combined flow for the two springs 

was almost 1,000 Mgal/d in 1968 (Faulkner, 1970). Discharge ranged from 0.5 to 1.3 (Mgal/d)/mi2 (table 4). An 

annual recharge rate of 10.6 to 28 inches of rainfall is 

thus indicated. Additional water was probably lost by 

evapotranspiration from the water table.

Freshwater is discharged through springs from the 

Tertiary limestone aquifer in more than one-half 

(30,000 square miles) of the Florida land area. Estimated flow of springs cataloged by Callahan (1964) and
SOUTH ATLANTIC-GULF REGION 025

EXPLANATION

Tertiary limestone

Approximate area of 

Miocene overlap

y D

Inferred fault

U.upthrown side; D,

downthrown side

87°

FIGURE 10. Location of large springs in Georgia and northern 

Florida. (Modified from Ca'llahan, 1964, figs. 5 and 7.)

Stringfield (1966) probably represents less than half the 

total discharge of all springs. With all cataloged springs 

considered at maximum flow, recharge is estimated to be 

about 0.32 (Mgal/d)/mi2 or about 7 inches of rainfall.

The minimum flow of cataloged springs (half the total) 

is equal to 82 percent of the 3,000 Mgal/d of ground 

water pumped in all of Florida during 1970 (Murray and 

Reeves, 1977).

Spring discharge, like base-flow measurements, does 

not take into account water "lost" by underground flow 

downdip or by evapotranspiration. Hence, the value of 

0.32 (Mgal/d)/mi2 noted above is only an indication of the 

volumes available.

Recharge to the Tertiary limestone aquifer may occur 

through the Miocene cover at a very low rate. The rate 

is dependent on the thickness, the hydraulic conductivity 

of the overlying stratum, and the gradients involved. 

For instance, a highly conservative estimate of recharge 

through the thick Miocene cover in the Okefenokee 

Swamp area is about 0.035 (Mgal/d)/mi2 under maximum 

development (Callahan, 1964, p. 27). An extremely large 

volume of water is in storage in the Tertiary limestone 

aquifer in Florida and Georgia. Seventy thousand square 

miles of Florida and Georgia are underlain by waterbearing strata with thicknesses ranging from several 

hundred feet to a maximum of about 2,000 feet (fig. 8). 

In northwestern Florida a part of the aquifer thickness 

shown includes aquifers below the Tertiary limestone

TABLE 4. Recharge rates to the Tertiary limestone aquifer based on 

spring discharge

Area 

(mi2)

Total

flow

(Mgal/d)

Flow 

per square mile

(ft3/s) (Mgal/d)

Precipitation 

(in./yr)

Florida Springs area - 30,000

Silver Springs 625

Rainbow Springs- 625

Northwestern Peninsular 

Florida above the 30-40-ft 

contours 1,950

North Central-Peninsular 

Florida above the 50-60-ft

South Central Lake District 

above the 70-ft contour - 6,000

2,456

9,824

348

531

833

315

468

684

95

181

544

0.127 

.5

.862

1.314

2.06

.780

1.16

1.67

.0754

.0743

.139

0.082

.328

.557

.849

1.333

.504

.748

1.094

-.0487

.048 

.09

1.72 min. 

6.88 max.

11.7 min. 

17.8 avg. 

28 max.

10.6 min. 

15.7 avg. 

22.9 max.

1.0

1.0 

1.9

aquifer. In the other States the volume of water stored 

in the Tertiary limestone aquifer is much less but is significant. Withdrawing much of this water in storage cannot be considered today in view of undesirable environmental effects that would occur.

Recharge to the Tertiary limestone aquifer would increase if water levels were lowered. About 70 percent 

of the 48 to more than 55 inches of rainfall in the area is 

lost by evapotranspiration. Where the area is riddled 

with sinkholes (fig. 7), it must be assumed that a high 

percentage of the rainfall will enter the ground and that 

much of it will be available to wells, either in the area 

of recharge or downdip in the confined part of the 

aquifer.

The volume of water that would move downdip 

through the upper 500 feet of a mile-wide section of the 

aquifer assuming a transmissivity of 60,000 ft2/d and a 

hydraulic gradient of 2 ft/mi is estimated to be 0.9 Mgal/ 

d.

If gradients were increased to 4 ft/mi and if 1,000 feet 

of the aquifer were penetrated, 3.6 Mgal/d would flow 

through each linear mile of the aquifer (taken along the 

strike). In any one well field of limited areal extent, however, water will be drawn into that center of discharge 

laterally and from downdip, and "leakage" will take place 

through the roof and the floor. On the basis of calculations of maximum recharge as derived from the flow of 

springs (table 4), maintaining a discharge of 3.6 Mgal/d 

might require as little as 3 square miles of recharge area. 

With lowering of the water table and capture of some 

evapotranspiration loss, the recharge area required 

would be even smaller.

Maximum production of water supplies from wells will 

necessarily take into account the tendency to induce a 

lateral flow of saline water into the well field from the 

sea. Also, in certain areas there is a tendency for sinkholes to occur as a result of lowering water levels. In any
026 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

event, monitor wells and mathematical models of the 

aquifer would be beneficial in understanding the behavior of the hydrologic system where maximum stress is 

approached.

The Tertiary limestone aquifer is exceedingly complex 

and differs greatly in its physical makeup from place to 

place. The generalizations given here can only bring out 

several of the pertinent factors that must be considered.

DEVELOPMENT OF AQUIFERS IN THE 

APPALACHIAN MOUNTAINS AND THE PIEDMONT

Success in developing ground-water supplies in the 

part of the region outside the Coastal Plain can be enhanced by applying scientific principles and modern techniques. Although many unsuccessful or low-yielding 

water wells are known, the ground-water potential of the 

upland area has probably been underrated. Numerous 

reports of high-yielding wells in this part of the region 

indicate that well-site selection based on various geologic 

and hydrologic criteria and exploratory techniques can 

result in very productive wells.

It is now know that remote-sensing techniques can 

identify the lines of structural deformation with which 

many highly productive wells are associated. Remote 

sensing may be useful in identifying soil or vegetation 

types that may be useful in locating ground water. Geophysical techniques may help in identifying and delineating solution openings in carbonate rocks.

Ground reconnaissance by trained personnel will improve the chances for locating satisfactory well sites. In 

a study of the occurrence of ground water in the Piedmont and Blue Ridge provinces, LeGrand (1967) found 

that topography and soil thickness are good indices for 

siting high-yielding wells. The most favorable locations 

are in valleys or draws that have a thick cover of alluvium, residuum, or weathered rock.

Except in cavernous carbonate-rock aquifers, the volume of ground water that is available is directly related 

to (1) the number, size, and depth of fracture openings 

and (2) the thickness and permeability of the soil cover. 

The soil cover, where present, is the source of recharge 

to the underlying fractures and also serves as a storage 

reservoir when saturated. Experience has shown that in 

many areas most interconnecting fractures occur within 

150 feet of the land surface, and drilling deeper than 

about 300 feet is generally not justified (LeGrand, 1967, 

p. 5).

OTHER MANAGEMENT PROCEDURES

Management procedures other than those already discussed may be employed where the supply of potable 

ground water appears to be limited. Briefly they fall under these major headings: (1) use of multiple sources of 

water, (2) use of saline water for special purposes, (3) 

artificial recharge, and (4) conjunctive use of ground 

water and surface water.

MULTIPLE SOURCES OF FRESH GROUND WATER

Where fairly thick sand terraces border large losing 

streams, an inexpensive source of ground water can be 

developed (Paulson and others, 1962). Assuming that the 

river terrace is rather wide, maximum advantage might 

be taken of such a shallow aquifer by pumping naturally 

filtered river water from wells near the river during periods of high flow and by pumping from wells as far back 

from the river as practicable in the low-flow period.

In a situation where a supply from a confined aquifer 

is declining, wells in the terrace deposits might be relied 

upon to a maximum extent in the higher rainfall months 

during which time the deep aquifer would be drawn upon 

less. In the following rather brief low-flow river period, 

the confined aquifer might then supply much or all of the 

water needed.

Where wells in confined aquifers yield a reliable supply 

of highly mineralized water, river terrace water might 

be used for blending, and furthermore at times of maximum availability, excess freshwater from the shallow 

aquifer might be used to recharge the confined aquifer.

In most places where higher or inland terrace deposits 

are present, it is questionable whether those deposits 

would yield supplies large enough to function economically in a combination system; however, there is a possibility that higher inland terrace deposits may be as 

thick as 150 feet in some areas. The use of shallow well 

water as a source of municipal supply at Elizabeth City, 

N. C., has been noted above. In Norfolk, Va., as much 

as 60 gal/min has been developed from wells in terrace 

sands (Cederstrom, 1945).

USE AND MANAGEMENT OF SALINE WATER

In most places freshwater occurs in near-surface formations, whereas at greater depths the water is saline. 

Use of saline water after desalinization may relieve the 

draft on a freshwater aquifer.

In most aquifers, particularly those that are confined, 

pressure head increases with depth; therefore, where 

the shallow freshwater stratum is drawn upon heavily, 

the poor-quality water at greater depth may migrate 

upward. Where the beds underlying the freshwater aquifer are silts, lenticular clays, or massive rocks riddled 

with solution channels or broken by faults, contamination 

may become a real concern. Utilization of the deeper 

water for special purposes, therefore, would tend to reduce the head in the lower aquifer and minimize that concern as well as add to the total supply.
SOUTH ATLANTIC-GULF REGION O27

One problem of using deep poor-quality water is that 

hydraulic connection may be established in the borehole 

between the deep and shallow aquifers. Saline-water 

wells should, therefore, be grouted through the freshwater strata.

In special cases where contamination of the upper stratum has taken place, pressure-relief wells may be drilled 

to diminish head in the deeper stratum. This technique 

was attempted in Brunswick, Ga., to minimize the upward movement of saline water in the Tertiary limestone 

aquifer. However, sufficient reduction of pressure head 

to completely halt the upward flow of saltwater could not 

be effected owing to the high transmissivity of the saltwater aquifer (Harlan Counts, oral commun., Nov. 30, 

1972).

In many downdip localities in Alabama, Mississippi, 

and the Carolinas, the deeper Cretaceous aquifers yield 

water that is fresh, whereas the overlying formations are 

saline. In such places the water developer farmer, municipality, or industrialist must bear the cost of a well 

1,000 feet or more in depth or use shallower water of 

inferior quality. Additionally, an obvious disadvantage 

is the danger of contamination of freshwater aquifer by 

movement of saline water from above as heavy pumping 

from the deeper aquifer continues. To guard against degradation of water in the deeper aquifer, water users 

should be encouraged to use the more cheaply developed 

inferior shallow water to the fullest extent possible in 

order to maintain a low-pressure head in the formation.

In some areas where relatively shallow water is of inferior quality and freshwater is available only at considerable depth, nearly all users initially will develop the 

shallower source of inferior water. In these areas, taking 

advantage of normal pressure differentials (where 

deeper aquifers have higher heads), connector wells 

which would allow freshwater to move upward to dilute 

the saline water aquifer might be desirable.

In an ideal situation a connector well would be centrally located with reference to several heavily pumped 

shallower wells or to a local supply consisting of many 

private wells. With maintenance of lower head in the 

upper formation through heavy withdrawals for air conditioning or other purposes not requiring the highest 

quality water, normal upward flow of freshwater 

through the connector well would be accelerated, and in 

time all wells in the general area might benefit from an 

improvement in the quality of water. Owing to normal 

head differences, even during periods of no pumping, 

flow would continue upward and outward into the shallower stratum, although the flow would be less than 

when pumps are operating.

Where the deep aquifers contain saline water and 

there is surplus water under higher pressure in shallow 

aquifers, the system could be reversed, thereby storing

freshwater in a saline-water reservoir.

In most confined aquifers there is a downdip transition 

from freshwater to saline water. Planners may consider 

measures to forestall lateral or updip movement of saline 

water into centers of freshwater withdrawal. An example is the situation at Montgomery, Ala., where water 

from both the Eutaw and Gordo Formations is of good 

quality (Knowles and others, 1963). West of Montgomery, the chloride content of water in the Eutaw Formation increases rapidly. Flowing wells tapping the Eutaw Formation west of Montgomery along the Alabama 

River lower the head of water in the Eutaw Formation 

and bleed off highly saline water, thereby affording a 

measure of long-term protection to the Montgomery supply. The flowing wells discharge highly saline water 

(1,150, 1,330, and 1,600 mg/L chloride).

Where a well field is threatened by lateral intrusion of 

poor-quality water, including the intrusion of seawater, 

artificial recharge by injection wells, connector wells, or 

a combination of water spreading and connector wells, 

might be employed to create freshwater barriers between the well field and the source of contamination.

ARTIFICIAL RECHARGE OF GROUND WATER

Ground-water discharge accounts for a large part of 

streamflow; hence, development of ground-water supplies may not add greatly to the total available supply of 

water. Additional water can be made available to the 

system, however, by reducing losses due to evapotranspiration, by recycling of water, and by interception of 

high-flow components of streamflow. Interception of high 

streamflow in the past has been almost entirely accomplished by the construction of surface reservoirs. However, in recent years in California the recharging of underground reservoirs with water pumped from distant 

streams is widely practiced. The practice is less common 

in the mid-western States and unusual in the eastern 

States.

Methods range from collecting storm runoff in pits to 

constructing canals and pipelines that bring water to the 

recharge basins or injection wells. Difficulties attend 

these efforts in places, depending on type of water used, 

hydraulic characteristics, climatological conditions, and 

the methodology employed. Nevertheless, the practicality of artificial recharge is well established, and we may 

expect that, generally, technology will provide satisfactory answers to most problems.

In the arid West, ground-water levels generally occur 

well below the level of ephemeral streams, and there is 

storage space for whatever recharge water can be made 

available. In the humid Southeast, however, groundwater levels generally are fairly close to the surface. 

Addition of water to the unconfined aquifers will be lim-
O28 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

ited by space requirements and may only promote more 

rapid lateral migration of that water to the streams.

Storage space can be provided by pumping during the 

dry periods, which are times of maximum demand and 

low streamflow. Water levels will decline, and space will 

then be provided for receiving and storing the excess 

water that becomes available during wet periods.

The most likely sites in the region for artificial recharge are those places where large cones of depression 

or significant water-level declines have been caused by 

ground-water withdrawals.

The techniques of water spreading by flooding, or by 

ditches, furrows, and pits, are outlined generally by 

Muckel and Schiff (1955). The effectiveness of recharge 

by spreading water on the surface, as opposed to pits or 

injection wells, depends upon the soil type, the type of 

cover material, and of course, the permeability of the 

formation beneath the soil cover. Bare soils tend to need 

treatment, but soil covered with undisturbed vegetation 

is highly receptive to infiltration. Intermittent flooding 

and drying and chemical treatment of the soil are beneficial in some areas.

Losing streams are uncommon in the East except in 

limestone terrain. Where streams lose water naturally 

or as a result of pumping from connected aquifers, small 

low-head dams would facilitate infiltration.

From Mississippi to southern North Carolina the 

sandy sediments store a tremendous volume of water. 

The amount of water that will drain from a sandy column 

upon lowering of the water table (specific yield) ranges 

from 15 to 20 percent in medium- to coarse-grained sediments. Assuming a value of 20 percent, a square mile 

of unconfined sandy reservoir in which the water level 

could be lowered 10 feet would have a capacity of 418 

million gallons equal to 24 inches of water or a pumping 

rate of 1.14 Mgal/d for 12 months. In this situation, assuming an annual recharge rate of 6 inches, there is an 

annual recharge deficit of 18 inches of water or 0.86 

Mgal/d that can be provided by artificial recharge during 

a high rainfall season.

The thick weathered rock mantle (saprolite) that lies 

above consolidated rocks in the southern Piedmont has 

a high storage capacity (Stewart, 1962), but depending 

on the clay content, vertical drainage may be slow. Repeated flooding of the saprolite surface may be highly 

effective and preferable to trying to increase storage by 

injection wells that penetrate fresh rock at some depth. 

Flooding might be accomplished by constructing distributaries from large streams and rivers that would divert 

part of the high flows. In some instances, abandoned 

quarries in the Piedmont may lose water through fissures in the walls and floor and thus function as large 

recharge pits.

Where confined aquifers are intensively developed, 

the potentiometric surface may be greatly depressed. An 

eventual natural limitation on ground-water development in some areas may be forestalled by employing artificial recharge. Recharge by injection of water through 

wells built for the purpose is an alternate method to 

spreading water. Injection through wells is the only 

method for immediately recharging confined aquifers. 

The method is especially attractive if accomplished by 

gravity rather than under pressure, thereby conserving 

energy. The injection-well method of storing water or 

recharging aquifers is feasible where surplus water that 

is chemically and physically suitable for the operation is 

available. The characteristics of the available water must 

be such that clogging of the well screen and the aquifer 

are minimal.

Where rivers are bordered by sandy terrace deposits 

or other thin shallow aquifers, gravity recharge connector wells might be constructed to conduct naturally filtered water to deep confined aquifers in which the head 

is depressed. The operation might be restricted to periods when river stage rises above some predetermined 

point. Such recharge wells would be particularly suited 

to areas underlain by the highly permeable limestone 

aquifers.

This method might be considered for parts of Florida 

and along the Atlantic coast into South Carolina. Heavy 

draft is imposed upon the limestone aquifer in those 

areas, and additional draft may be expected in the future. Hence, maintaining a relatively high head upgradient from major well fields might do much to forestall 

potential saltwater intrusion and in any event would help 

minimize pumping costs.

Cool water is necessary in the development of water 

supplies for some industrial uses. In Hopewell, Va., cold 

surface water has been recharged during the winter 

months through wells that are ordinarily pumped to supply a chemical plant. Cold water stored temporarily in 

the ground and pumped out during the hot summer season is particularly advantageous in processing operations 

(Cederstrom, 1945).

Injection wells ending in sandy sediments might need 

to introduce water under pressure in order to achieve a 

significant (economically practical) rate of acceptance. 

High efficiencies might be achieved if the injection and 

formation waters are compatible and if the water injected is free of gases and particulate matter. However, 

chemical or biochemical actions that form slimes may occur, which would reduce the efficiency. Where hard 

waters are injected into aquifers, carbonate precipitates 

would be likely to form unless the waters were pretreated. Turbidity would also have to be reduced to insignificant amounts. Where the aquifer to be injected is
SOUTH ATLANTIC-GULF REGION 029

a cavernous or highly shattered limestone or dolomite, 

as in the Appalachian Highlands and in some Coastal 

Plain formations, there may be little or no difficulty with 

clogging. In all instances, treatment to remove pollutants would be desirable.

RECHARGE USING EFFLUENT FROM TREATED SEWAGE

About 1,300 sewage-disposal systems in the United 

States in 1967 disposed of 19.8 billion gallons of treated 

sewage effluent by land-disposal methods (Wilson and 

Beckett, 1968). About two-thirds of these systems were 

used specifically for waste-water treatment as such, and 

one-third for crop benefits gained.

This practice may be considered as a method of continuous artificial recharge. The controlled spreading or 

spraying of treated sewage effluent on a soil surface allows oxidation and plant and biochemical action to take 

place, which upgrades the character of that water. After 

percolation down to the unconfined aquifer, the purified 

effluent may move into the confined aquifers or laterally 

to springs and streams. The aquifers are recharged or 

streamflow is augmented, presumably without deleterious ecological and health effects.

Disposal of effluent proceeds more slowly than other 

methods of recharge, allowing ample time for purification by plants and soils. Ground-water recharge should 

take place, however, even when only light applications 

of effluent are available, because the soil is kept near the 

saturation point and summer rains will tend to percolate 

through to the water table instead of being retained to 

satisfy soil-moisture requirements.

The sandy beds in the outcrop areas of the post-Paleozoic aquifers seem ideal for land disposal of effluent 

from treated sewage. The climate is favorable for functioning of digestion lagoons all year, the permeability of 

the surficial materials is high, the sands are thick, and 

in many places the water level is low enough to favor the 

process. Tremendous areas covered by the coastal sandy 

terrace formations likewise offer ideal sites for land disposal of effluent.

In some instances, as a result of the land disposal of 

treated sewage effluent, the quality of stream water 

might be upgraded to the extent that less treatment 

would be required by some of the downstream consumers. More water would be available for downstream 

consumers or, conversely, less water from upstream 

would have to be provided to maintain flow at a standard 

required for dilution of contaminants.

Land disposal of treated sewage effluent in relatively 

impermeable terrain may be feasible even though the 

geologic setting is quite different from that in the sandy 

areas. Here the objective would be to provide water for 

dry-weather irrigation and augmentation of flow of small

streams.

Briefly, on the presumption that there are no adverse 

environmental effects, the process of land disposal of 

treated sewage offers a constant source of water for 

ground-water recharge or low-flow augmentation of 

streams, provides a solution to the problem of finding 

space for disposal of solid sewage waste, eliminates gross 

pollution of surface streams, and may upgrade the quality of soil in disposal areas.

FRESHWATER STORAGE IN SALINE AQUIFERS

Artificial recharge offers some significant advantages 

in those parts of the Coastal Plain where sandy confined 

strata are now saturated with saline water, as in northeastern North Carolina. Freshwater can be injected 

through wells and stored in the saline-water confined 

beds and pumped back for later use. The feasibility of 

storage under such conditions has been demonstrated 

(Cederstrom, 1957, p. 45-52), and further work to determine quantitative and other factors involved is now 

underway (Brown and Silvey, 1977; Kimbler and others, 

1973).

Some coastal areas where there is a short but fairly 

high summer demand may find this method of increasing 

their supply advantageous as an alternative to piping in 

freshwater from inland wells or surface reservoirs. The 

large volume of water available from shallow wells in a 

high-rainfall winter season may suffice for recharge operations to the confined saline-water beds.

LOW-FLOW AUGMENTATION OF STREAMS

Low-flow augmentation is a technique for increasing 

the volume of streamflow by releasing stored water from 

reservoirs or by discharging water from wells into 

streams or reservoirs. This method is commonly practiced to increase streamflow during dry periods, thereby 

increasing the water supply for downstream users. It is 

also a technique for improving the capacity of the 

stream to accept and dilute wastes or to provide a better 

recreational environment.

Within the belt of Upper Cretaceous formations in 

Mississippi and Alabama, the chalk beds of the Selma 

Group are an extreme example of low-permeability formations. Streams originating within the chalk belt or impermeable clay belts are intermittent, flowing during 

and shortly after heavy rains. In dry weather the stream 

bed becomes dry, and in wet weather surface runoff is 

almost the equivalent of rainfall (Pierce, 1966). Chalk 

and clay offer a minimum of storage and thus increase 

the effect of floods. Streams originating in these areas 

cannot be sources of water supply during the dry seasons 

without storage.
030 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

Where justified by economic, environmental, or general esthetic considerations, this situation could be ameliorated by development of the aquifers underlying the 

streams. Widely spaced wells might be located along the 

streams and discharge directly into the streams or into 

minor tributaries. Examples of aquifers that might be 

used in this way are the Eutaw Formation and the Tuscaloosa Group.

Ground water from some aquifers would make a particularly desirable dilutant for highly contaminated 

streams; also, because ground water is somewhat oxygenated it would act positively in reducing biochemicaloxygen demands.

In downdip locations deep wells yielding mineralized 

water might be constructed where such water is considered acceptable for augmenting the flow of streams with 

a low discharge. If the discharge of the receiving stream 

is low, addition of high-chloride water may not be tolerable, but in a stream with a higher discharge the increase in chloride concentration may be acceptable. Although esthetics would be served, the extent to which 

the ecosystem (if aquatic life is present) would be affected by dilution of a highly contaminated stream with 

saline ground water would have to be considered.

Areas that have desirable locations for users requiring 

moderate volumes of water for cooling purposes might 

benefit from low-flow augmentation. A rise of streamwater temperature might be acceptable in areas where 

the streams would otherwise be dry during low-rainfall 

seasons and where aquatic life is absent. Another effect 

of augmenting low flow with ground water that might be 

desirable is the dilution of small polluted flows.

Ground water may also be used in conjunction with 

surface-water reservoirs intended for low-flow augmentation. Depending on the geological setting and environmental considerations, ground water may be available to 

augment impounded surface water.

One advantage of the use of supplemental wells is that. 

their yield is not dependent upon rainfall in any particular year; thus even a relatively small amount of water 

pumped over a period of many months may furnish a 

very desirable increment to a surface-water supply. Furthermore, where wells are used for brief periods of time, 

ground-water withdrawals may be at rates greater than 

the aquifer can support continuously. Thus a well field 

might be pumped at two or three times the sustained 

yield of the aquifer if there is ample recharge during intervening periods of no pumping.

GROUND WATER FOR PUMPED STORAGE

In some areas there are extensive aquifers that are 

readily recharged. Transfer of water from these aquifers

to pumped-storage reservoir sites might help alleviate 

peak power shortages if the combination of aquifers and 

storage sites can be found. In localities where power is 

generated, the power excess generated in off-peak hours 

could be used for pumped storage of water. In watershort areas diversion of streamflow for storage may not 

be desirable where that flow is needed for dilution or 

where the flow is allocated to downstream users.

In the Piedmont, pumped storage of ground water is 

generally not practicable. In the Valley and Ridge Province, pumped storage might be practicable if high-yield 

wells can be constructed tapping major fractures of fault 

zones.

CONJUNCTIVE USE OF GROUND WATER AND 

SURFACE WATER

Conjunctive use is the technique for integrating withdrawals of surface water and ground water in order to 

provide maximum utilization of these resources. In many 

areas an economical and satisfactory water supply might 

be developed by taking advantage of both ground- and 

surface-water sources where neither source is sufficient 

to supply the total demand at all times.

With both sources developed, surface reservoirs may 

be drawn upon heavily in the high rainfall season. In the 

dry season, a ground-water reservoir not subject to 

short-term vagaries of precipitation might provide all or 

nearly all the supply and preclude possible expensive 

additions to the surface-supply system. Most aquifers 

may be overpumped for a period of weeks or a few 

months, discharging much more water than if they were 

in continuous use and at the same time providing more 

storage space for recharge.

Recharging aquifers by injecting excess water available from surface sources may be an economical operation where a water- treatment plant is already in operation for treatment of the surface water and if the cost 

of the treatment and well maintenance are not 

prohibitive.

Where surface supplies carry a heavy waste load, the 

cost of treatment of that water may be excessively high 

at times of low flow. At such times maximum reliance 

may be placed upon a well supply, granting the presence 

of suitable aquifers. Conversely, surface water of good 

quality may be mixed with poor-quality ground water to 

increase the total supply.

GROUND-WATER PROBLEMS

One of the most critical ground-water problems in the 

South Atlantic-Gulf Region is the regional lowering of 

potentiometric surfaces and the development of extensive cones of depression in areas where large ground-
SOUTH ATLANTIC-GULF REGION O31

water withdrawals have been made. In some areas of 

northeastern Mississippi withdrawals of water from the 

Eutaw Formation are exceeding the volume of water 

that the aquifer can transmit. At Mobile, Ala., and in 

some areas in Florida, concentrated withdrawals have 

caused intrusion of seawater. Contamination of the Tertiary limestone aquifer by saline water at Brunswick, 

Ga., is attributed to incomplete flushing of connate saline 

water (Gregg and Zimmerman, 1974, p. 36). In other 

areas, the lowered heads in cones of depression have induced the upward migration of saline water from underlying aquifers a potential threat where confining beds 

are leaky or where there is faulting.

Notable ground-water declines have occurred outside 

the region in the Franklin, Va., area, where water levels 

have declined about 185 feet since 1937-39 (Brown and 

Cosner, 1974) and the cone of depression extends into 

northern North Carolina. At Brunswick, Ga., pumpage 

of over 100 Mgal/d has induced upward migration of saline water (Krause and Gregg, 1972). In central Florida 

large industrial and agricultural withdrawals have lowered water levels in confined aquifers more than 50 feet 

since 1934 (Kaufman, 1967). In North Carolina dewatering for open-pit mining has lowered the potentiometric 

surface below sea level in an area of about 800 square 

miles (Peek, 1969, p. 12).

There is potential for saltwater encroachment along 

much of the Atlantic Coast and in some areas on the Gulf 

Coast where shallow aquifers are hydraulically connected to the sea or to estuaries. Withdrawals can cause 

lateral movement of saline water, and natural factors 

such as inundation by hurricane flooding can change the 

position of the freshwater-saltwater interface in estuaries.

Head differentials permit the movement of water 

through boreholes or damaged casing from one aquifer 

to another. Generally, the direction of movement is upward, and where the deeper confined aquifers contain 

water of undesirable quality, the shallower aquifers become contaminated. Deep water wells and oil-test wells 

are the common potential sources of this type of 

contamination.

Lowered water levels result in correspondingly lower 

pumping levels. Obviously, there is a direct cost relation 

between total pumping head and energy consumption. 

Excessive pumping lift can be attributed either to inefficient well construction or to water-level declines. Many 

water wells in the region have excessive pumping lifts 

due to poor well design or improper completion and development methods.

Land subsidence is a potential threat where large volumes of ground water are pumped from aquifers in uncompacted sediments. The areas in the South AtlanticGulf Region that have the highest subsidence potential

are Late Eocene and Quaternary deposits near the coastline where the effects would be most noticeable. Subsidence of as much as 4 inches was reported at Savannah, 

Ga. (Davis and others, 1963). More spectacular are sinkhole collapses related to ground-water withdrawals. Examples of this activity, some of which were catastrophic, 

have been reported by Newton and Hyde (1971, p. 1) and 

Kaufman (1967, p. 30). Sinkholes are restricted to those 

areas underlain by carbonate rocks.

Mining at some places causes problems of groundwater quantity and quality. Most public attention today 

is directed toward strip and pit mining. These operations 

may result in actual destruction of parts of shallow aquifers, and water-soluble mining products and byproducts 

can contaminate ground-water supplies. The need for 

low-grade coal and lignite to help meet energy requirements will intensify the problem caused by mining.

Landfills, considered an economical method for disposing of solid wastes for many years, commonly have been 

operated without consideration of the character and 

movement of leachate and without regard for the potential effect on water supplies. Improperly located or managed landfills can be expected to be a major source of 

ground-water contamination.

The technology of deep-well injection is now quite advanced but not without problems. Most of the injection 

operations are for waste disposal, and some wastes are 

highly toxic. The U.S. Geological Survey and other agencies and industries are conducting research to evaluate 

techniques and potential effects of injection. Current 

studies in the region, involving the Geological Survey, 

include ascertaining the feasibility of storing materials, 

liquids, and gases in artificial cavities in salt domes and 

in the extensive impermeable clay and chalk strata. The 

protection of ground-water resources is a primary consideration in planning injection for disposal or storage.

Problems with natural ground-water quality in the region are generally the result of excessive concentrations 

of iron, chloride, hydrogen sulfide, fluoride, or color. 

Acidic (low pH) and .hard waters are common. Some of 

these objectional constituents and properties are amenable to simple water treatment; however, the cost of 

treatment for excessive color, chloride, or fluoride may 

be prohibitive.

The unequal distribution of the ground-water resources in the South Atlantic-Gulf Region is a significant 

factor in future economic development. Generally, the 

largest undeveloped ground-water supplies are in the 

Coastal Plain. Generally, the available supply increases 

as aquifers thicken and become more numerous seaward. 

Because water-resources development engenders water 

problems, most of the major problems in the future can 

be expected in coastal areas.
O32 SUMMARY APPRAISALS OF THE NATION'S GROUND-WATER RESOURCES

DATA NEEDS

This description of the round-water resources of the 

South Atlantic-Gulf Region is based on data and interpretations resulting from geologic and water-resources 

studies. The volume of data available and the complexity 

of evaluating, planning, and managing water-resources 

development dictate the use of computer analysis and 

modeling for optimum utilization of these resources. A 

basic need is for additional data in areas where coverage 

is sparse and for studies that will point out areas where 

water problems may be-anticipated.

An immediate need is for management of the groundwater system in areas that have problems related to concentrated withdrawals. Digital and electric-analog 

models are useful tools for approximating solutions to 

hydrologic and related problems. Almost as urgent is the 

need for modeling entire aquifers or aquifer systems. 

Models are capable of simulating effects of past, present, 

and projected ground-water withdrawals basic needs 

in planning and managing water-resources development; 

however, model projections should be used with caution.

More data are needed about the magnitude of and the 

potential for saltwater encroachment in the Coastal Plain 

aquifers. Modeling can be an effective tool in studies related to this problem.

Artificial recharge, subsurface storage of liquids and 

gases, and subsurface disposal of wastes employ similar 

methodologies. Studies are needed to develop more satisfactory methods of operation and management in these 

fields. Many more data are needed on the properties of 

potential reservoir materials below the freshwater zone 

and on- the alternation, diffusion, and dispersion of injected substances.

Research is underway to ascertain the offshore extent 

of freshwater aquifers along the Atlantic coast. There is 

a need to intensify these studies and to expand the work 

to the Gulf Coast. The importance of these potential 

sources of water in the development of the coastal areas 

cannot be overemphasized.

Saline water as an economic resource has received little attention. Highly mineralized water and brines may 

contain minerals of economic value.

Further studies of land subsidence and sinkhole collapse, particularly with reference to prediction and prevention of catastrophic occurrences, are needed.

Use of reclaimed water will become more significant 

in total development of the resource. Studies are needed 

to find methods of reclaiming economic products from 

waste water. Also, the increasing cost of energy suggests the need for methods of recovering heat from cooling water.

Surface water and ground water are closely related in 

the highly permeable formations in the Coastal Plain.

Special studies are needed to evaluate and predict the 

effects of changes in either regimen.

SUMMARY AND CONCLUSIONS

The rapid population increase and industrial growth 

now underway in the South Atlantic-Gulf Region will 

accelerate as the energy situation becomes more critical. 

The reason is that economic development will favor areas 

in the Nation that have moderate climate, access to ample energy, abundant labor, and adequate water 

supplies.

With planning and management, the ground-water 

supply in the South Atlantic-Gulf Region is adequate to 

meet needs through 2020 if one-forth of the estimated 

ground-water yield of 78,000 Mgal/d in the region can 

be withdrawn. In 1970, 4,500 Mgal/d, about 14 percent 

of all water pumped in the region, was obtained from 

ground-water sources. If the same use ratio for ground 

water and surface water continues, projections indicate 

that about 12,200 Mgal/d would be needed in 2000 and 

about 18,200 Mgal/d in 2020. The projections indicate 

that consumptive use will account for only about 6 percent of the total, so most of the water will be available 

for reuse.

Although virtually the entire region is underlain by 

aquifers that will yield more than 50 gal/min to wells, 

the most prolific sources of ground water are (1) the Tertiary limestone aquifer, (2) the Miocene, Pliocene, and 

Quaternary sand and gravel aquifers that are more or 

less interconnected, and (3) the Tuscaloosa sand and 

gravel aquifers. The Tertiary limestone aquifer and the 

Miocene-through-Quaternary aquifers are the most prolific sources of water owing to extremely high transmissivities and favorable conditions for direct recharge from 

precipitation and streams. The Tuscaloosa aquifers, although capable of large yields, have a more limited potential owing to the relatively small recharge areas and 

the generally restricted interconnection with other 

aquifers.

Rapid advances in computer science and in mathematical and electronic modeling will provide useful tools for 

planners and managers; however, these tools will be only 

as accurate as the data on which their output is based. 

The collection, assimilation, and analysis of dependable 

ground-water data are prerequisites for successful planning and management.

Management of the major and minor aquifers will require establishing the optimum sustained yield of the 

aquifers. The optimum sustained yield of the aquifer is 

the condition whereby the maximum long-term withdrawal is accomplished with a minimum of undesirable 

effects. Undesirable effects include excessive diversion
SOUTH ATLANTIC-GULF REGION O33

of streamflow either by capture of ground-water discharge to streams or by increasing ground-water recharge from streams; water-level declines that result in 

uneconomical pumping lifts or land subsidence; and intrusion of poor-quality water from the sea, estuaries, 

surface sources, other aquifers, or other parts of the 

same aquifer.

Conjunctive use of surface and ground water and the 

optimum sustained development of aquifers, or any controlled development of water resources, are administered by water-management agencies. The most efficient 

utilization of the resource may require transferring 

water from one management area (for example, a basin) 

to another, suggesting the need for coordination among 

agencies.

Among the first problems confronting water managers 

will be the redistribution of withdrawals to minimize or 

terminate saltwater encroachment, reduce the extent of 

extremely deep cones of depression, and control pollution. Extraordinary coordination of water-management 

agencies may be required in the instances where cones 

of depression extend over hundreds of square miles.

Efficient use of ground water by the primary users is 

a means of conserving water resources by reducing the 

draft on the aquifer. One of the major considerations in 

water-deficient areas is the reuse of the waste water. 

Some waste water requires minimal treatment for many 

uses, and there are some uses for waste water containing 

a large load of suspended and dissolved materials. Beneficial use for water discharged from heat-exchange applications is highly probably.

Widespread artificial recharge of aquifers with surplus 

surface water and treated waste water (or in special instances, untreated waste water) is a inevitable, and high 

priority should be given to developing and applying this 

technique. Artificial recharge by wells is especially attrative if accomplished by gravity rather than under 

pressure, thereby conserving energy. Artificial recharge 

by spreading can be environmentally acceptable.

Less than 10 percent of the region's mean annual runoff (197,000 Mgal/d), if used for artificial recharge, could 

meet the entire projected requirement for ground water 

without significantly affecting streamflow. Systematic 

recharge of major aquifers during wet seasons would offset the effects of the removal of large quantities of 

ground water from storage, limiting the spread of cones 

of depression and avoiding undesirable effects such as 

large pumping lifts and saltwater intrusion.

One of the basic considerations in developing groundwater sources is the effect on the low flow of streams and 

on vegetation. These environmental considerations are 

among the constraints that should be considered in the 

optimum development of aquifers.

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