Cover. Generalized block diagram showing hydrogeology of the Atlantic Coastal Plain, North and South Carolina.
Groundwater Availability in the Atlantic 

Coastal Plain of North and South Carolina

Edited by Bruce G. Campbell and Alissa L. Coes

Chapter A

Groundwater Availability in the Atlantic Coastal Plain of 

North and South Carolina

By Bruce G. Campbell, Jason M. Fine, Matthew D. Petkewich, Alissa L. Coes, and Silvia Terziotti

Chapter B

Hydrogeologic Framework of the Atlantic Coastal Plain, 

North and South Carolina

By Joseph A. Gellici and Jeff C. Lautier

Chapter C

Simulation of Groundwater Flow in the Atlantic Coastal Plain, 

North and South Carolina and Parts of Eastern Georgia and 

Southern Virginia, Predevelopment to 2004

By Alissa L. Coes, Bruce G. Campbell, Matthew D. Petkewich, and Jason M. Fine

Groundwater Resources Program 

Professional Paper 1773

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Campbell, B.G., and Coes, A.L., eds., 2010, Groundwater availability in the Atlantic Coastal Plain of North and South 

Carolina: U.S. Geological Survey Professional Paper 1773, 241 p., 7 pls.

Library of Congress Cataloging-in-Publication Data

Groundwater availability in the Atlantic coastal plain of North and South Carolina / edited by Bruce G. Campbell and 

Alissa L. Coes.

 p. cm. -- (Professional paper ; 1773)

 Includes bibliographical references.

 ISBN 978-1-4113-2765-8

 1. Groundwater--North Carolina. 2. Groundwater--South Carolina. 3. Coastal plains--North Carolina. 4. Coastal 

plains--South Carolina. I. Campbell, Bruce G. II. Coes, Alissa L. III. Series: Professional paper (Geological Survey 

(U.S.)) ; 1773. 

 TD223.1.N8.G76 2010

 553.7’909756--dc22

 2010011268

ISBN 978-1-4113-2765-8 
iii

Foreword

An adequate supply of groundwater is essential for the Nation’s health and economic well 

being. Increased use of groundwater resources and the effects of drought have led to concerns 

about the future availability of groundwater to meet domestic, agricultural, industrial, and environmental needs. The resulting effects of competition for groundwater from human and environmental uses need to be better understood to respond to the following basic questions that are 

being asked about the Nation’s ability to meet current and future demands for groundwater. Do 

we have enough groundwater to meet the needs of the Nation? Where are these groundwater 

resources? Is groundwater available where it is needed? To help answer these questions, the 

U.S. Geological Survey’s (USGS) Groundwater Resources Program is conducting large-scale 

multidisciplinary regional studies of groundwater availability, such as this study of the Atlantic 

Coastal Plain aquifer system in North and South Carolina.

Regional groundwater availability studies quantify current groundwater resources, evaluate how 

those resources have changed through time, and provide tools that decision makers can use 

to forecast system responses to future development and climate variability and change. These 

quantitative studies are, by design, large in scope, can include multiple aquifers, and address 

critical groundwater issues. The USGS has previously identified the Nation’s principal aquifers, 

and they will be used as a framework to classify and study regional groundwater systems.

The groundwater availability studies being conducted for each regional groundwater flow system emphasize the use of long-term groundwater monitoring data, in conjunction with groundwater models, to improve understanding of the flow systems and assess the status and trends 

in groundwater resources in the context of a changing water budget for the aquifer system. The 

results of these individual groundwater availability studies will be used collectively as building 

blocks towards a national assessment of groundwater availability. In addition, these studies will 

provide the foundational information and modeling tools needed to help State and local resource 

managers make water availability decisions based on the latest comprehensive quantitative 

assessment given their regional water-management constraints and goals. 

Matthew C. Larsen, Associate Director for Water

U.S. Geological Survey
iv

Acknowledgments

This study was funded by the U.S. Geological Survey (USGS) Groundwater Resources Program. Jeffrey Lautier and Nathaniel Wilson of the North Carolina Division of Water Resources 

(NCDWR) and Joseph Gellici of the South Carolina Department of Natural Resources (SCDNR) 

provided assistance with the hydrogeologic framework of the model. Robert Devlin of the South 

Carolina Department of Health and Environmental Control provided groundwater use data for the 

South Carolina Atlantic Coastal Plain. Nathaniel Wilson of the NCDWR provided groundwater 

use data for the North Carolina Atlantic Coastal Plain.

Funding for the coring work in South Carolina was provided through the USGS National Geologic 

Cooperative Mapping Program. David C. Prowell (retired) of the USGS initiated the study, coordinated the drilling activities, described the cores, and determined allostratigraphic and geologic 

contacts. Jean M. Self-Trail (USGS) described and assigned ages to Cretaceous calcareous 

nannofossils. Raymond A. Christopher (Clemson University, retired) described and assigned ages 

to Cretaceous palynomorphs. Laurel M. Bybell (USGS) described and assigned ages to Tertiary 

calcareous nannofossils. Norman O. Frederiksen (USGS) and Lucy E. Edwards (USGS) described 

and assigned ages to Tertiary palynomorphs. Karen E. Agerton (SCDNR) assisted in the collection and description of the cores and in the particle-size analyses. Andrew Wachob (SCDNR) 

obtained the geophysical logs. Eugene Cobbs, II, Eugene Cobbs, III, and Donald Queen (all of the 

USGS) drilled the cores and constructed some of the monitor wells used in the study.
v

Executive Summary

The Atlantic Coastal Plain aquifers and confining units of North and South Carolina are composed 

of crystalline carbonate rocks, sand, clay, silt, and gravel and contain large volumes of highquality groundwater. The aquifers have a long history of use dating back to the earliest days of 

European settlement in the late 1600s. Although extensive areas of some of the aquifers have or 

currently (2009) are areas of groundwater level declines from large-scale, concentrated pumping 

centers, large areas of the Atlantic Coastal Plain contain substantial quantities of high-quality 

groundwater that currently (2009) are unused. 

Groundwater use from the Atlantic Coastal Plain aquifers in North Carolina and South Carolina 

has increased during the past 60 years as the population has increased along with demands for 

municipal, industrial, and agricultural water needs. While North Carolina and South Carolina work 

to increase development of water supplies in response to the rapid growth in these coastal populations, both States recognize that they are facing a number of unanswered questions regarding 

availability of groundwater supplies and the best methods to manage these important supplies.

An in-depth assessment of groundwater availability of the Atlantic Coastal Plain aquifers of North 

and South Carolina has been completed by the U.S. Geological Survey Groundwater Resources 

Program. This assessment includes (1) a determination of the present status of the Atlantic 

Coastal Plain groundwater resources; (2) an explanation for how these resources have changed 

over time; and (3) development of tools to assess the system’s response to stresses from potential 

future climate variability. Results from numerous previous investigations of the Atlantic Coastal 

Plain by Federal and State agencies have been incorporated into this effort.

The primary products of this effort are (1) comprehensive hydrologic datasets such as groundwater levels, groundwater use, and aquifer properties; (2) a revised hydrogeologic framework; 

(3) simulated water budgets of the overall study area along with several subareas; and (4) construction and calibration of a numerical modeling tool that is used to forecast the potential effects 

of climate change on groundwater levels.

Hydrogeologic Framework

Interpretations of the hydrogeologic frameworks of the North and South Carolina Coastal Plain 

have evolved separately during the past 100 years but are combined in this report. Hydrostratigraphic correlations of the Atlantic Coastal Plain sediments at the North Carolina–South Carolina 

border are presented. Data from 309 boreholes located in North and South Carolina, eastern 

Georgia, and southern Virginia were used to define the hydrogeologic framework of the Atlantic 

Coastal Plain aquifers and confining units in the study area. The study area encompasses several 

formal aquifer systems contained within the sediments of the Atlantic Coastal Plain. Aquifers and 

confining units located in North Carolina and Virginia are part of the Northern Atlantic Coastal 

Plain aquifer system. In South Carolina, aquifers and confining units in the Atlantic Coastal Plain 

sediments are part of either the Southeastern Coastal Plain aquifer system or the Floridan aquifer 

system. Because the study area crosses the boundaries of these formal aquifer systems, no new 

formal regional aquifer system will be designated, and the units under study will be referred to as 

the North and South Carolina Atlantic Coastal Plain aquifers and confining units. 
vi

The hydrogeologic framework of the North Carolina Atlantic Coastal Plain aquifers and confining 

units consists of nine aquifers separated by eight confining units. From top to bottom, the aquifers 

are the surficial aquifer, Yorktown aquifer, Castle Hayne aquifer, Beaufort aquifer, Peedee aquifer, 

Black Creek aquifer, Upper Cape Fear aquifer, Lower Cape Fear aquifer, and Early Cretaceous aquifer. The uppermost aquifer (the surficial aquifer in most places) is a water-table aquifer, and the 

bottom of the system is underlain by various types of crystalline bedrock. Sedimentary deposits 

forming the aquifers are of Holocene to Cretaceous age and are composed mostly of sand, with 

lesser amounts of gravel and limestone. The confining units between the aquifers are composed 

primarily of clay and silt. Total thickness of the aquifers and confining units ranges from 0 feet 

along the Fall Line to more than 10,000 feet at Cape Hatteras, North Carolina. The most prominent 

structural feature of the study area is the Cape Fear Arch, the axis of which trends in a southeast 

direction. The hydrostratigraphy was primarily determined from correlations of geophysical logs 

and drill cutting descriptions from 149 wells distributed across the North Carolina Coastal Plain. 

Aquifers were defined using these logs and cuttings, as well as water-level and water-quality data 

and evidence of the continuity of pumping effects. Structure contour and thickness maps delineate 

the aquifers and confining units. Hydrogeologic sections depict the correlation of these aquifers 

throughout the North Carolina Coastal Plain.

The hydrogeologic framework of the South Carolina Coastal Plain consists of 15 hydrostratigraphic 

units (eight aquifers and seven intervening confining units) that are delineated from records of 

38 core holes and 68 water wells. Isopach and structure-contour maps, together with hydrogeologic 

cross sections, depict the thickness, altitude, and geographic extent of each of the aquifers and 

confining units in the South Carolina Coastal Plain. The aquifers and confining units are composed 

of sedimentary materials, such as gravel, sand, silt, clay, and limestone, and range from Late Cretaceous to Tertiary in age. Thickness of the materials ranges from 0 feet at the Fall Line to approximately 4,000 feet in southernmost South Carolina. Biostratigraphic and allostratigraphic data and 

borehole geophysical logs were used to identify and correlate aquifers and confining units from 

well to well. Aquifers and confining units are characterized in terms of their lithology, hydrologic 

properties, and geophysical-log signature. A new hydrostratigraphic nomenclature, first introduced 

at the Savannah River Site in western South Carolina, is extended across the entire South Carolina 

Coastal Plain. The aquifers are, in descending order, the surficial aquifer, Upper Floridan aquifer, 

Middle Floridan aquifer, Gordon aquifer, Crouch Branch aquifer, McQueen Branch aquifer, Charleston aquifer, and Gramling aquifer. Each aquifer, except for the unconfined surficial aquifer, has an 

associated confining unit of the same name located stratigraphically above the aquifer. 

Hydrostratigraphic correlations of the Atlantic Coastal Plain aquifers and confining units at the 

North Carolina–South Carolina border were made to resolve differences between data used to 

delineate the hydrogeologic framework within the two States. Detailed hydrostratigraphic cross 

sections at two locations—between Marietta, North Carolina, and Little Peedee State Park, South 

Carolina, and between Calabash, North Carolina, and Myrtle Beach, South Carolina—indicate that 

the downdip area correlates well but the updip area is more complex. 

Hydrologic System Modeling

A three-dimensional finite-difference numerical code (MODFLOW-2000) was used to simulate 

groundwater flow within the aquifers and confining units of the Coastal Plain of North and South 

Carolina and parts of Georgia and Virginia. A new groundwater flow model of this area was 

deemed necessary because previous groundwater models had hydrogeologic inconsistencies at 

the North Carolina–South Carolina border, and a large amount of new hydraulic, geologic, waterlevel, and water-use data was available for analysis.
vii

The approximately 70,500-square-mile study area was represented in the model by a grid of 

130 rows and 275 columns made up of 4-square-mile cells. The hydrogeologic system of alternating layers of permeable sand or crystalline carbonate rocks separated by confining units of silt, 

clay, or low-permeability crystalline carbonate rocks was represented by 16 deformed grid model 

layers. Model layer 1 was designated as a specified-head boundary in areas where the surficial 

aquifer is underlain by confining units, and recharge was defined by variable-head cells in areas 

where the aquifers crop out. The no-flow lower model boundary at the bottom of model layer 16 

simulates the top of bedrock. The northwestern and southeastern no-flow boundaries of all layers 

were located at a geologic boundary and the saltwater transition zone, respectively; the northeastern and southwestern boundaries were simulated as specified-head boundaries and were located 

along large rivers.

The flow simulation began with a steady-state stress period representing predevelopment flow 

conditions prior to 1900; transient stress periods represent subsequent pumping and variable 

recharge through 2004. The model was calibrated to conditions representing the three flow systems of pre-1900, 1980, and 2004. The model was calibrated with a type of parameter estimation 

using pilot points and regularized inversion. 

Future uses of the numerical flow model could include optimization techniques to assist in the 

management of local or subregional groundwater problems such as substantial water-level 

declines at concentrated pumping centers. The potential effects of new wells on existing groundwater users could be simulated and evaluated. The model could be converted to a variable-density 

type to simulate saltwater encroachment problems. The local grid refinement package available 

for MODFLOW-2000 could be used to assist with either of these uses.

Water Budget Analysis

The groundwater budgets for the Atlantic Coastal Plain aquifers and confining units of North and 

South Carolina have changed over time as a result of withdrawals superimposed on the original, 

natural flow system and from natural variability in the climate, which results in variable recharge 

rates. Simulation results indicate that high rates of withdrawals produce outflows from storage 

within the aquifers and confining units and decreases in baseflows to rivers in the inner Coastal 

Plain. High rates of precipitation cause increases in storage rates within the aquifer system and 

higher baseflows to the rivers. Overall, the 2004 rates of groundwater withdrawals changed the 

flow system in subregional areas, but the flow system in large parts of the area’s aquifers and 

confining units remains relatively unchanged from predevelopment. Concentrated withdrawals 

combined with poor aquifer properties, however, have produced large groundwater level declines 

in some areas.

The calibrated groundwater flow model of the Atlantic Coastal Plain aquifers and confining units of 

North and South Carolina (presented in Chapter C of this report) was used to calculate an overall 

budget and several local groundwater budgets for the study area. The largest component of the 

predevelopment and 2004 water budgets is vertical interlayer flow. The next largest budget component is the volume of water that flows into and out of the specified-head boundaries. The total 

inflow through all specified-head boundaries is approximately equal to the outflow and is approximately 3,700 and 3,600 million gallons per day (Mgal/d) for the predevelopment and 2004 model 

budgets, respectively. Two other sources of water for the model are (1) a specified recharge rate 

of about 1,230 Mgal/d for predevelopment and 2004 and (2) inflow from rivers at 13.5 Mgal/d for 

predevelopment and 16.4 Mgal/d for 2004. Water is removed from the model area by discharge to 

rivers at rates of 1,051 Mgal/d for predevelopment and 964 Mgal/d for 2004. Discharge of water 
viii

through pumping wells is another large component of groundwater flow for the model and accounts 

for 482 Mgal/d in the 2004 water budget. Additionally, during the time simulated by the model 

(1900–2004), water enters and is released from storage. For the 2004 water budget, rates of flow 

into and out of storage are 43 and 56 Mgal/d, respectively. 

A detailed, simulated groundwater flow budget is presented for the North Carolina Central Coastal 

Plain Capacity Use Area, a 15-county area in which groundwater levels have been declining since 

before 1960 in the Black Creek and Upper Cape Fear aquifers. The budget analysis for this area 

revealed that most predevelopment groundwater flow is concentrated in the upper aquifers of 

Tertiary age. Predevelopment groundwater flow occurs primarily into and out of the surficial aquifer, 

which is simulated as a specified-head boundary. These rates of flow are 98.2 Mgal/d into the 

specified head boundary and 85.4 Mgal/d out of the boundary. Predevelopment groundwater flows 

within the aquifers and confining units of Cretaceous age are characterized as sluggish because of 

low water-level gradients. In 2004, the largest water budget component for the area is specifiedhead flow into and out of the surficial aquifer at 199 and 55.6 Mgal/d, respectively. Vertical flow is 

highest in the upper layers and decreases with depth for both predevelopment and 2004 conditions. 

The decrease from predevelopment to 2004 is not as pronounced as in the predevelopment budget. 

Additional downward flow of water replaces water that is removed from the aquifers by pumping. Water is removed from storage from the Black Creek, Upper Cape Fear, and Lower Cape Fear 

aquifers at rates of 3.52, 2.85, and 1.73 Mgal/d, respectively, as a result of pumping from these 

aquifers. Lateral groundwater flow into this area increased from predevelopment rates for some 

of the model layers and most significantly to 5.52 Mgal/d through the Upper Cape Fear aquifer 

because of pumping. 

Simulated groundwater flow budgets for predevelopment conditions in the Sumter, South Carolina 

area, indicate that recharge and specified-head inflow rates were 8.01 and 4.03 Mgal/d, respectively. Lateral flow within the model layers was less than 1 Mgal/d for each layer, except within 

the Crouch Branch aquifer (2.81 Mgal/d) and McQueen Branch aquifer (2.21 Mgal/d). The simulated 2004 groundwater budget for the Sumter area includes pumping from the Crouch Branch and 

McQueen Branch aquifers at rates of 1.20 and 8.53 Mgal/d, respectively. Recharge to the surficial 

aquifer (8.01 Mgal/d), specified-head flow into the surficial aquifer (5.13 Mgal/d), and lateral flow 

into the Crouch Branch and McQueen Branch aquifers at rates of 2.88 and 7.65 Mgal/d, respectively, are the major sources of water to the Sumter area. Changes in storage are insignificant in 

the Sumter area in 2004. 

For the Aiken, South Carolina area, recharge is by far the greatest source of groundwater at a rate 

of 33.6 Mgal/d. Water flows into the surficial aquifer through rivers and lateral groundwater flow at 

rates of 1.47 and 2.67 Mgal/d, respectively. Lateral flow also occurs in the Upper Floridan confining unit and the Crouch Branch aquifer at rates of 1.68 and 1.39 Mgal/d, respectively. Discharge of 

groundwater from the surficial aquifer to rivers is the most substantial loss of water in the Aiken 

area at 16.2 Mgal/d. Water also flows out of the Aiken area through lateral flow within the surficial 

aquifer, Upper Floridan confining unit, Upper Floridan aquifer, Middle Floridan aquifer, Gordon 

confining unit, Crouch Branch aquifer, and McQueen Branch aquifer at rates that vary between 

1.33 and 8.50 Mgal/d, with the highest rate occurring in the surficial aquifer. Pumping during 2004 

in the Aiken area caused an increase in the downward flow of water within all of the aquifers 

present in the area. Most of the groundwater withdrawals in the Aiken area are from pumping the 

Crouch Branch and McQueen Branch aquifers at rates of 1.27 and 5.41 Mgal/d, respectively. With 

the exception of a decrease in discharge to rivers in the surficial aquifer of 6.1 Mgal/d for the 2004 

water budget, all other budget terms are similar to those of predevelopment. Changes in storage 

are insignificant in the Aiken area.
ix

Contents

Foreword ........................................................................................................................................................iii

Acknowledgments........................................................................................................................................iv

Executive Summary.......................................................................................................................................v

Chapter A

Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

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

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

Methods of Investigation.....................................................................................................................5

Data Compilation..........................................................................................................................6

Numerical Model .........................................................................................................................6

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

Study Area.......................................................................................................................................................7

Physiography and Climate...................................................................................................................7

Capacity Use Areas..............................................................................................................................7

Geologic History and Setting .......................................................................................................................7

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

Hydrologic System.........................................................................................................................................8

Surface Water.......................................................................................................................................8

Groundwater..........................................................................................................................................8

Development of the Hydrologic System ....................................................................................................9

Groundwater Development History ...................................................................................................9

Water Use ............................................................................................................................................10

Development and Changes to the Hydrologic Budget ..........................................................................10

Simulated Groundwater Budget Analysis ......................................................................................10

Regional Groundwater Budget.........................................................................................................10

North Carolina Central Coastal Plain Capacity Use Area Groundwater Budget ............16

Sumter, South Carolina, Groundwater Budget......................................................................19

Aiken, South Carolina, Groundwater Budget........................................................................19

Effects of Potential Future Climate Variability on Groundwater Levels.....................................24

Groundwater Level Monitoring Network Analysis in North and South Carolina..............................25

Summary and Conclusions.........................................................................................................................42

References ...................................................................................................................................................44
x

Chapter B

Hydrogeologic Framework of the Atlantic Coastal Plain, North and South Carolina

Introduction...................................................................................................................................................49

Previous Investigations......................................................................................................................53

Nomenclature and Classification of Hydrostratigraphic Units ...................................................53

Methods of Investigation...................................................................................................................55

North Carolina Methods of Investigation .......................................................................................55

South Carolina Methods of Investigation .......................................................................................56

Hydrogeologic Cross Sections .........................................................................................................57

Pre-Cretaceous Basement Rocks and Structural Geology of the Coastal Plain ..............................61

North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy .....................................................61

Surficial Aquifer..................................................................................................................................64

Yorktown Confining Unit and Aquifer...............................................................................................67

Castle Hayne Confining Unit and Aquifer .......................................................................................72

Beaufort Confining Unit and Aquifer ...............................................................................................77

Peedee Confining Unit and Aquifer .................................................................................................82

Black Creek Confining Unit and Aquifer .........................................................................................87

Upper Cape Fear Confining Unit and Aquifer.................................................................................92

Lower Cape Fear Confining Unit and Aquifer.................................................................................97

Lower Cretaceous Confining Unit and Aquifer............................................................................102

South Carolina Coastal Plain Allostratigraphy and Biostratigraphy .................................................105

Late Cretaceous Formations...........................................................................................................105

Beech Hill Formation...............................................................................................................105

Clubhouse Formation ..............................................................................................................105

Cape Fear Formation ...............................................................................................................105

Collins Creek Formation..........................................................................................................106

Pleasant Creek Formation ......................................................................................................106

Shepherd Grove Formation ....................................................................................................106

Caddin Formation.....................................................................................................................106

Cane Acre Formation ..............................................................................................................107

Coachman Formation ..............................................................................................................107

Bladen Formation.....................................................................................................................107

Donoho Creek Formation........................................................................................................107

Peedee Formation....................................................................................................................108

Sawdust Landing Formation ..................................................................................................108

Tertiary Formations...........................................................................................................................108

Rhems Formation .....................................................................................................................109

Lang Syne Formation...............................................................................................................109

Williamsburg Formation..........................................................................................................109

Fishburne Formation................................................................................................................110

Congaree Formation................................................................................................................110

Warley Hill Formation..............................................................................................................110

Santee Formation.....................................................................................................................110

Harleyville Formation...............................................................................................................111

Dry Branch Formation.............................................................................................................111

Tobacco Road Sand Formation..............................................................................................111
xi

Ashley Formation .....................................................................................................................111

Hawthorn Group.......................................................................................................................112

Upland Unit................................................................................................................................112

Undifferentiated Quaternary Units........................................................................................112

South Carolina Coastal Plain Hydrostratigraphy..................................................................................112

Surficial Aquifer................................................................................................................................116

Age and Stratigraphic Correlation........................................................................................116

Lithology and Texture..............................................................................................................116

Hydrologic Properties .............................................................................................................116

Geophysical-Log Signature....................................................................................................117

Floridan Aquifer System...................................................................................................................117

Upper Floridan Confining Unit................................................................................................118

Age and Stratigraphic Correlation...............................................................................118

Lithology and Texture.....................................................................................................118

Hydrologic Properties ....................................................................................................118

Geophysical-Log Signature...........................................................................................119

Upper Floridan Aquifer............................................................................................................119

Age and Stratigraphic Correlation...............................................................................119

Lithology and Texture.....................................................................................................119

Hydrologic Properties ....................................................................................................120

Geophysical-Log Signature...........................................................................................120

Middle Floridan Confining Unit ..............................................................................................120

Age and Stratigraphic Correlation...............................................................................120

Lithology and Texture.....................................................................................................120

Hydrologic Properties ....................................................................................................120

Geophysical-Log Signature...........................................................................................121

Middle Floridan Aquifer .........................................................................................................121

Age and Stratigraphic Correlation...............................................................................121

Lithology and Texture.....................................................................................................121

Hydrologic Properties ....................................................................................................122

Geophysical-Log Signature...........................................................................................122

Gordon Confining Unit .......................................................................................................... 122

Age and Stratigraphic Correlation...............................................................................122

Lithology and Texture.....................................................................................................122

Hydrologic Properties ....................................................................................................122

Geophysical-Log Signature...........................................................................................122

Gordon Aquifer.........................................................................................................................123

Age and Stratigraphic Correlation...............................................................................123

Lithology and Texture.....................................................................................................123

Hydrologic Properties ....................................................................................................123

Geophysical-Log Signature...........................................................................................123

Meyers Branch Confining System/Crouch Branch Confining Unit ..........................................124

Age and Stratigraphic Correlation........................................................................................124

Lithology and Texture..............................................................................................................124

Hydrologic Properties .............................................................................................................124

Geophysical-Log Signature....................................................................................................124
xii

Dublin Aquifer System/Crouch Branch Aquifer...........................................................................124

Age and Stratigraphic Correlation........................................................................................125

Lithology and Texture..............................................................................................................125

Hydrologic Properties .............................................................................................................126

Geophysical-Log Signature....................................................................................................126

Allendale Confining System/McQueen Branch Confining Unit.................................................126

Age and Stratigraphic Correlation........................................................................................126

Lithology and Texture..............................................................................................................127

Hydrologic Properties .............................................................................................................127

Geophysical-Log Signature....................................................................................................127

Midville Aquifer System...................................................................................................................127

McQueen Branch Aquifer......................................................................................................128

Age and Stratigraphic Correlation...............................................................................128

Lithology and Texture.....................................................................................................128

Hydrologic Properties ....................................................................................................128

Geophysical-Log Signature...........................................................................................128

Charleston Confining Unit.......................................................................................................128

Age and Stratigraphic Correlation...............................................................................129

Lithology and Texture.....................................................................................................129

Hydrologic Properties ....................................................................................................129

Geophysical-Log Signature...........................................................................................129

Charleston Aquifer...................................................................................................................129

Age and Stratigraphic Correlation...............................................................................129

Lithology and Texture.....................................................................................................129

Hydrologic Properties ....................................................................................................130

Geophysical-Log Signature...........................................................................................130

Appleton Confining System/Gramling Confining Unit .................................................................130

Age and Stratigraphic Correlation........................................................................................130

Lithology and Texture..............................................................................................................130

Hydrologic Properties .............................................................................................................130

Geophysical-Log Signature....................................................................................................131

Ridgeland Aquifer System/Gramling Aquifer...............................................................................131

Age and Stratigraphic Correlation........................................................................................131

Lithology and Texture..............................................................................................................131

Hydrologic Properties .............................................................................................................131

Geophysical-Log Signature....................................................................................................132

Discussion .........................................................................................................................................132

Correlation of Hydrostratigraphic Units Across the North Carolina–

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

Summary......................................................................................................................................................136

References .................................................................................................................................................139

Appendix B1. Aquifer and confining unit top surface altitudes interpreted from 

borehole geophysical logs, cores, and other data in the Coastal Plain of 

North Carolina, South Carolina, eastern Georgia, and southern Virginia...................147

Appendix B2. Core description of ORG-393 (#68, section I–I′, Plate 7 )......................................156
xiii

Chapter C

Simulation of Groundwater Flow in the Atlantic Coastal Plain, North and South Carolina 

and Parts of Georgia and Virginia, Predevelopment to 2004

Introduction.................................................................................................................................................163

Model Development ..................................................................................................................................163

Simulation of Groundwater Flow.............................................................................................................163

Spatial Discretization .......................................................................................................................166

Temporal Discretization...................................................................................................................166

Boundary Conditions........................................................................................................................169

Recharge...................................................................................................................................169

Groundwater Use.....................................................................................................................169

Hydraulic Properties Used in Model Calibration.........................................................................179

Observations Used in Model Calibration ......................................................................................179

Groundwater Levels ................................................................................................................180

River Baseflow .........................................................................................................................180

Model Calibration..............................................................................................................................180

Model Fit—Groundwater Levels...........................................................................................196

Model Fit—Stream Baseflow ................................................................................................215

Simulated Regional Water Budget........................................................................................215

Sensitivity Testing and Analysis ............................................................................................236

Model Limitations..............................................................................................................................238

Future Opportunities for Improvements.................................................................................................239

References .................................................................................................................................................240

Plates

[In pocket]

1. Northwest to southeast hydrogeologic cross section A–A′ through 

the South Carolina Coastal Plain

2. Northwest to southeast hydrogeologic cross section B–B′ and west to east 

hydrogeologic cross section C–C′ through the South Carolina Coastal Plain

3. Northwest to southeast hydrogeologic cross section D–D′ and west to east 

hydrogeologic cross section E–E′ through the North Carolina Coastal Plain

4. West to east hydrogeoloic cross section F–F′ through the North Carolina 

Coastal Plain

5. Southwest to northeast hydrogeologic cross section G–G′ through the 

North Carolina Coastal Plain

6. Southwest to northeast hydrogeologic cross section D′–H through the 

North Carolina Coastal Plain

7. Southwest to northeast hydrogeologic cross sections I–I′ and A′–C′ through 

the South Carolina Coastal Plain
xiv

Figures

Chapter A

A1–A4. Maps showing—

 A1. The Atlantic Coastal Plain along the Atlantic Coast of North and South

Carolina and parts of northern Florida, Georgia, Virginia, and Maryland ...........2

 A2. Locations of selected groundwater level monitoring sites and hydrographs 

showing the effects of the 1998–2002 drought in North and South Carolina......3

 A3. Capacity Use Areas in North and South Carolina ...................................................4

 A4. Locations of areas of detailed groundwater budgets, 

North and South Carolina ..........................................................................................11

A5–A7. Schematic diagrams showing—

 A5. Simulated water budget in the Atlantic Coastal Plain aquifer system of 

North and South Carolina for predevelopment and 2004 .....................................12

 A6. Simulated predevelopment groundwater budget for the 

Atlantic Coastal Plain of North and South Carolina..............................................13

 A7. Simulated 2004 groundwater budget for the Atlantic Coastal Plain 

of North and South Carolina......................................................................................14

A8. Graph showing simulated water budget per stress period from predevelopment 

to 2004 in the Atlantic Coastal Plain of North and South Carolina .................................15

A9–A14. Schematic diagrams showing—

 A9. Simulated groundwater flow budget for predevelopment conditions 

in the North Carolina Central Coastal Plain Capacity Use Area .........................17

 A10. Simulated groundwater flow budget for 2004 conditions in the 

North Carolina Central Coastal Plain Capacity Use Area ....................................18

 A11. Simulated groundwater flow budget for predevelopment 

conditions in the Sumter, South Carolina, area .....................................................20

 A12. Simulated groundwater flow budget for 2004 conditions 

in the Sumter, South Carolina, area .........................................................................21

 A13. Simulated groundwater flow budget for predevelopment 

conditions in the Aiken, South Carolina, area........................................................22

 A14. Simulated groundwater flow budget for 2004 conditions 

in the Aiken, South Carolina, area............................................................................23

A15. Graphs showing simulated net recharge rates for decadal stress periods 

from 2010 to 2100 used in the climate variability scenarios for the Atlantic 

Coastal Plain groundwater flow model for North and South Carolina ..........................25

A16. Map showing locations of wells used in the climate variability scenarios in 

the Atlantic Coastal Plain of North Carolina, South Carolina, and Georgia..................26

A17–A22. Graphs showing simulated and observed groundwater levels

for observation wells in the—

 A17. Upper Floridan aquifer, 1900–2100, in the Atlantic Coastal Plain 

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

 A18. Castle Hayne/Pungo River/Middle Floridan aquifer, 1900–2100, 

in the Atlantic Coastal Plain of North and South Carolina...................................28

 A19. Beaufort/Gordon aquifer, 1900–2100, in the Atlantic Coastal Plain 

of North and South Carolina......................................................................................29

 A20. Peedee/Crouch Branch aquifer, 1900–2100, in the Atlantic Coastal 

Plain of North and South Carolina............................................................................30
xv

 A21. Black Creek/McQueen Branch aquifer, 1900–2100, in the 

Atlantic Coastal Plain of North Carolina and Georgia ..........................................31

 A22. Upper Cape Fear/Charleston aquifers, 1900–2100, in the 

Atlantic Coastal Plain of North and South Carolina..............................................32

A23–A29. Maps showing prediction standard error of the groundwater level 

monitoring network in the—

 A23. Yorktown/Upper Floridan aquifers in the Atlantic Coastal Plain 

of North and South Carolina......................................................................................34

 A24. Castle Hayne/Pungo River/Middle Floridan aquifers in the 

Atlantic Coastal Plain of North and South Carolina..............................................35

 A25. Beaufort/Gordon aquifers in the Atlantic Coastal Plain of 

North and South Carolina ..........................................................................................36

 A26. Peedee/Crouch Branch aquifer in the Atlantic Coastal Plain of 

North and South Carolina ..........................................................................................37

 A27. Black Creek/McQueen Branch aquifer in the Atlantic Coastal 

Plain of North and South Carolina............................................................................38

 A28. Upper Cape Fear/Charleston aquifer in the Atlantic Coastal Plain 

of North and South Carolina......................................................................................39

 A29. Lower Cape Fear/Gramling aquifer in the Atlantic Coastal Plain 

of North and South Carolina......................................................................................40

Chapter B

B1–B3. Maps showing—

 B1. Location of the study area, major geological features, and 

the Atlantic Coastal Plain of North and South Carolina .......................................50

 B2. Location of observation wells and boreholes in the Atlantic Coastal 

Plain of North and South Carolina and parts of Virginia and Georgia ...............51

 B3. Altitude of the top of the crystalline basement rocks underlying 

the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007 ..........................................................................62

B4. Stratigraphic correlations of hydrogeologic units of the 

North and South Carolina Coastal Plain .............................................................................63

B5–B36. Maps showing—

 B5. Areal extent and altitude of the top of the surficial aquifer (layer 1) 

in the Atlantic Coastal Plain of North and South Carolina 

Coastal Plain and parts of Virginia and Georgia, 2007..........................................65

 B6. Thickness of the surficial aquifer in the Atlantic Coastal Plain of 

North and South Carolina (layer 1) and parts of Virginia and Georgia, 2007 ....66

 B7. Areal extents and the top altitudes of the Yorktown confining unit 

(North Carolina) and Upper Floridan confining unit (South Carolina) 

(layer 2), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................68

 B8. Thickness of the Yorktown confining unit (North Carolina) and 

Upper Floridan confining unit (South Carolina) (layer 2) in the 

Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007 ..........................................................................69

 B9. Areal extents and the top altitudes of the Yorktown aquifer 

(North Carolina) and Upper Floridan aquifer (South Carolina) 

(layer 3), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................70
xvi

 B10. Thickness of the Yorktown aquifer (North Carolina) and Upper Floridan 

aquifer (South Carolina) (layer 3) in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 ...............................71

 B11. Areal extents and the top altitudes of the Castle Hayne confining unit 

(North Carolina) and the Middle Floridan confining unit (South Carolina) 

(layer 5), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................73

 B12. Thickness of the Castle Hayne confining unit (North Carolina) and 

the Middle Floridan confining unit (South Carolina) (layer 4) in the 

Atlantic Coastal Plain of North Carolina and South Carolina and 

parts of Virginia and Georgia, 2007 ..........................................................................74

 B13. Thickness of the Castle Hayne aquifer (North Carolina) and the 

Middle Floridan aquifer (South Carolina) (layer 5) in the Atlantic 

Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia, 2007........................................................................................................75

 B14. Areal extents and top altitudes of the Castle Hayne aquifer 

(North Carolina) and the Middle Floridan aquifer (South Carolina) 

(layer 5) in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................76

 B15. Areal extents and the top altitudes of the Beaufort confining unit 

(North Carolina) and the Gordon confining unit (South Carolina) 

(layer 6), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................78

 B16. Thickness of the Beaufort confining unit (North Carolina) and the Gordon 

confining unit (South Carolina) (layer 6), in the Atlantic Coastal Plain of 

North and South Carolina and parts of Virginia and Georgia, 2007....................79

 B17. Areal extents and the top altitudes of the Beaufort aquifer 

(North Carolina) and the Gordon aquifer (South Carolina) (layer 7), 

in the Atlantic Coastal Plain of North and South Carolina and parts 

of Virginia and Georgia, 2007 ....................................................................................80

 B18. Thickness of the Beaufort aquifer (North Carolina) and the Gordon 

aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of 

North and South Carolina and parts of Virginia and Georgia, 2007....................81

 B19. Areal extents and the top altitudes of the Peedee confining unit 

(North Carolina) and the Crouch Branch confining unit (South Carolina) 

(layer 8), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................83

 B20. Thickness of the Peedee confining unit (North Carolina) and the 

Crouch Branch confining unit (South Carolina) (layer 8), in the 

Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007 ..........................................................................84

 B21. Areal extents and the top altitudes of the Peedee aquifer (North Carolina) 

and the Crouch Branch aquifer (South Carolina) (layer 9), in the 

Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.........................................................................................85

 B22. Thickness of the Peedee aquifer (North Carolina) and the Crouch Branch 

aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 ...............................86
xvii

 B23. Areal extents and the top altitudes of the Black Creek confining unit 

(North Carolina) and the McQueen Branch confining unit (South Carolina) 

(layer 10), in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007 ..........................................................................88

 B24. Thickness of the Black Creek confining unit (North Carolina) and the 

McQueen Branch confining unit (South Carolina) (layer 10), in the 

Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.........................................................................................89

 B25. Areal extents and the top altitudes of the Black Creek aquifer 

(North Carolina) and the McQueen Branch aquifer (South Carolina) 

(layer 11), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................90

 B26. Thickness of the Black Creek aquifer (North Carolina) and the 

McQueen Branch aquifer (South Carolina) (layer 11), in the 

Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007 ..........................................................................91

 B27. Areal extents and the top altitudes of the Upper Cape Fear 

confining unit (North Carolina) and the Charleston confining 

unit (South Carolina) (layer 12), in the Atlantic Coastal Plain 

of North and South Carolina and parts of Virginia and Georgia, 2007 ...............93

 B28. Thickness of the Upper Cape Fear confining unit (North Carolina) 

and the Charleston confining unit (South Carolina) (layer 12), 

in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................94

 B29. Areal extents and the top altitudes of the Upper Cape Fear aquifer 

(North Carolina) and the Charleston aquifer (South Carolina) (layer 13), 

in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.........................................................................................95

 B30. Thickness of the Upper Cape Fear aquifer (North Carolina) and the 

Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal 

Plain of North and South Carolina and parts of Virginia and Georgia, 2007 .....96

 B31. Areal extents and the top altitudes of the Lower Cape Fear confining 

unit (North Carolina) and the Gramling confining unit (South Carolina) 

(layer 14), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ..................................................................98

 B32. Thickness of the Lower Cape Fear confining unit (North Carolina) and 

the Gramling confining unit (South Carolina) (layer 14), in the 

Atlantic Coastal Plain of North and South Carolina and parts 

of Virginia and Georgia, 2007 ....................................................................................99

 B33. Areal extents and the top altitudes of the Lower Cape Fear aquifer 

(North Carolina) and Gramling aquifer (South Carolina) (layer 15), 

in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007 ........................................................................100

 B34. Thickness of the Lower Cape Fear aquifer (North Carolina) and 

Gramling aquifer (South Carolina) (layer 15), in the Atlantic Coastal 

Plain of North and South Carolina and parts of Virginia and Georgia, 2007 ...101

 B35. Areal extents and the top altitudes of the Lower Cretaceous confining 

unit and Lower Cretaceous aquifer in North Carolina (layer 16), in the 

Atlantic Coastal Plain of North Carolina and part of Virginia, 2007 ..................103
xviii

 B36. Thickness of the Lower Cretaceous confining unit and Lower 

Cretaceous aquifer in North Carolina (layer 16), in the Atlantic 

Coastal Plain of North Carolina and part of Virginia, 2007 .................................104

B37. Generalized hydrogeologic framework of the South Carolina 

Coastal Plain along strike and dip......................................................................................113

B38. Hydrostratigraphy at the Savannah River Site as defined by Aadland 

and others (1995) compared to the hydrostratigraphy of the 

South Carolina Coastal Plain downdip of the Savannah River 

Site, as defined in this study ...............................................................................................114

B39. Current hydrostratigraphic correlations of the South Carolina 

Coastal Plain compared to past correlations...................................................................115

B40–B41. Hydrostratigraphic correlation cross sections from—

 B40. DIL-121, Little Peedee State Park, Dillion County, SC, to

BB 45M, Marietta, Robeson County, NC ...............................................................133

 B41. HOR-973-1165, Myrtle Beach, Horry County, SC, to

HOR-388/HH 39J, Calabash, Brunswick County, NC ...........................................134

B42. Graphs showing continuous groundwater altitudes from the Marietta, 

North Carolina, monitoring station, Robeson County, North Carolina, and 

Calabash, North Carolina, monitoring station, Brunswick County, North Carolina...135

Chapter C

C1–C2. Maps showing—

 C1. Location of the Atlantic Coastal Plain in North and South Carolina 

and parts of Virginia and Georgia ..........................................................................164

 C2. Locations of natural characteristics within distinct areas of the 

Atlantic Coastal Plain Physiographic Province, with a focus on 

the study area in North and South Carolina, southeastern Virginia, 

and eastern Georgia.................................................................................................165

C3. Generalized cross section of the aquifers and confining units of the 

Atlantic Coastal Plain of North and South Carolina, 2007..............................................166

C4. Maps showing Atlantic Coastal Plain groundwater model grid showing 

boundary conditions in layer 1, which represents the surficial aquifer......................168

C5–C7. Graphs showing—

 C5. Continuous precipitation data from precipitation stations in the 

Atlantic Coastal Plain of North and South Carolina and parts 

of Virginia and Georgia ............................................................................................170

 C6. Simulated recharge by model stress period for hydrogeologic 

units in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia ..........................................................................171

 C7. Groundwater use by model layer for wells in in the Atlantic Coastal 

Plain of North and South Carolina and parts of Virginia and Georgia .............171

C8. Maps showing locations of water-use wells and 2004 withdrawal 

amounts from the—

 C8A. Yorktown aquifer (North Carolina) and the Upper Floridan aquifer 

(South Carolina) (layer 3), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia .......................................172

 C8B. Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer 

(South Carolina) (layer 5), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................173
xix

 C8C. Beaufort aquifer (North Carolina) and the Gordon aquifer (South Carolina) 

(layer 7), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ................................................................174

 C8D. Peedee aquifer (North Carolina) and Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................175

 C8E. Black Creek aquifer (North Carolina) and McQueen Branch aquifer 

(South Carolina) (layer 11), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................176

 C8F. Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer 

(South Carolina) (layer 13), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................177

 C8G. Lower Cape Fear aquifer (North Carolina) and the Gramling aquifer 

(South Carolina) (layer 15) , in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................178

C9. Maps showing locations of water-level wells completed in the—

 C9A. Yorktown aquifer (North Carolina) and Upper Floridan aquifer 

(South Carolina) (layer 3) in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................181

 C9B. Castle Hayne aquifer (North Carolina) and Middle Floridan aquifer 

(South Carolina) (layer 5), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................182

 C9C. Beaufort aquifer (North Carolina) and the Gordon aquifer 

(South Carolina) (layer 7), in the Atlantic Coastal Plain of 

North and South Carolina and parts of Virginia and Georgia, 2007..................183

 C9D. Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................184

 C9E. Black Creek aquifer (North Carolina) and the McQueen Branch aquifer 

(South Carolina) (layer 11), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................185

 C9F. Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer 

(South Carolina) (layer 13), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................186

 C9G. Lower Cape Fear aquifer (North Carolina) and the Gramling aquifer 

(South Carolina) (layer 15), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................187

C10. Maps showing calibrated horizontal hydraulic conductivities for the— 

 C10A. Yorktown aquifer (North Carolina) and the Upper Floridan aquifer 

(South Carolina) (layer 3), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................189

 C10B. Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer 

(South Carolina) (layer 5), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................190

 C10C. Beaufort aquifer (North Carolina) and the Gordon aquifer 

(South Carolina) (layer 7), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................191

 C10D. Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................192
xx

 C10E. Black Creek aquifer (North Carolina) and the McQueen Branch aquifer 

(South Carolina) (layer 11), in the Atlantic Coastal Plain of 

North and South Carolina and parts of Virginia and Georgia, 2007..................193

 C10F. Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer 

(South Carolina) (layer 13), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................194

 C10G. Lower Cape Fear aquifer (North Carolina) and the Gramling aquifer 

(South Carolina) (layer 15), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................195

C11. Graph showing observed and simulated water levels for predevelopment 

calibration, in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia..............................................................................................197

C12. Graph showing water-level residuals and simulated water levels for 

predevelopment calibration in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia...................................................197

C13. Maps showing simulated water levels and water-level residuals for 

steady-state calibration for the—

 C13A. Yorktown aquifer (North Carolina) and the Upper Floridan aquifer 

(South Carolina) (layer 3), in the Atlantic Coastal Plain of North

and South Carolina and parts of Virginia and Georgia, 2007 .............................198

 C13B. Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer 

(South Carolina) (layer 5), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................199

 C13C. Beaufort aquifer (North Carolina) and the Gordon aquifer 

(South Carolina), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia...............................................200

 C13D. Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................201

 C13E. Black Creek aquifer (North Carolina) and the McQueen Branch aquifer 

(South Carolina) (layer 11), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................202

 C13F. Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer 

(South Carolina) (layer 13), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................203

 C13G. Lower Cape Fear aquifer (North Carolina) and the Gramling aquifer 

(South Carolina) (layer 15), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................204

 C13H. Lower Cretaceous confining unit and Lower Cretaceous aquifer 

(North Carolina) (layer 16), in the Atlantic Coastal Plain of 

North Carolina and parts of Virginia, 2007 ............................................................205

C14. Graph showing observed and simulated water levels for 1980 calibration 

in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia.............................................................................................................206

C15. Graph showing water-level residuals and simulated water levels for 1980 

calibration in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia ...................................................................................206
xxi

C16. Maps showing simulated water levels and water-level residuals for 

1980 calibration for the—

 C16A. Yorktown aquifer (North Carolina) and the Upper Floridan aquifer 

(South Carolina) (layer 3), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................207

 C16B. Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer 

(South Carolina) (layer 5), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................208

 C16C. Beaufort aquifer (North Carolina) and the Gordon aquifer 

(South Carolina) (layer 7), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................209

 C16D. Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Georgia, 2007....................................................210

 C16E. Black Creek aquifer (North Carolina) and the McQueen Branch aquifer 

(South Carolina) (layer 11), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................211

 C16F. Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer 

(South Carolina) (layer 13), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................212

 C16G. Lower Cape Fear aquifer (North Carolina) and the Gramling aquifer 

(South Carolina) (layer 15), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................213

 C16H. Lower Cretaceous confining unit and the Lower Cretaceous aquifer in 

North Carolina (layer 16), in the Atlantic Coastal Plain of North Carolina 

and parts of Virginia, 2007 .......................................................................................214

C17. Graph showing observed and simulated water levels for 2004 calibration 

in the Atlantic Coastal Plain of North and South Carolina and parts of

Virginia and Georgia.............................................................................................................216

C18. Graph showing water-level residuals and simulated water levels for 2004 

calibration in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia..............................................................................................216

C19. Maps showing simulated water levels and water-level residuals for 

2004 calibration for the—

 C19A. Yorktown aquifer (North Carolina) and the Upper Floridan aquifer 

(South Carolina) (layer 3), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................217

 C19B. Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer 

(South Carolina) (layer 5), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................218

 C19C. Beaufort aquifer (North Carolina) and the Gordon aquifer (South Carolina)

(layer 7), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007 ................................................................219

 C19D. Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Georgia, 2007....................................................220

 C19E. Black Creek aquifer (North Carolina) and the McQueen Branch aquifer 

(South Carolina) (layer 11), in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia, 2007.....................................221
xxii

 C19F. Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer 

(South Carolina) (layer 13), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................222

 C19G. Lower Cape Fear aquifer (North Carolina) and the Gramling aquifer 

(South Carolina) (layer 15), in the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007 .............................223

 C19H. Lower Cretaceous confining unit and the Lower Cretaceous aquifer 

(North Carolina) (layer 16), in the Atlantic Coastal Plain of 

North Carolina and parts of Virginia, 2007 ............................................................224

C20. Map showing locations of wells in the Atlantic Coastal Plain of 

North and South Carolina and southeastern Georgia with 

continuous observed groundwater levels, 2007..............................................................225

C21. Hydrographs of simulated and observed water levels for the—

 C21A. Yorktown aquifer (North Carolina) and Upper Floridan aquifer 

(South Carolina).........................................................................................................226

 C21B. Castle Hayne aquifer (North Carolina) and Middle Floridan aquifer 

(South Carolina).........................................................................................................227

 C21C. Beaufort aquifer (North Carolina) and Gordon aquifer (South Carolina).........228

 C21D. Peedee aquifer in North Carolina...........................................................................229

 C21E. Crouch Branch aquifer in South Carolina.............................................................230

 C21F. Black Creek aquifer in North Carolina...................................................................231

 C21G. McQueen Branch aquifer in South Carolina........................................................232

 C21H. Upper Cape Fear aquifer in North Carolina..........................................................233

 C21I. Charleston aquifer in South Carolina.....................................................................234

 C21J. Lower Cape Fear aquifer in North Carolina..........................................................235

C22. Graph showing simulated groundwater budget per model stress period from 

predevelopment to 2004 in the Atlantic Coastal Plain aquifers of North and 

South Carolina and parts of Virginia and Georgia...........................................................236

C23. Graphs showing relative composite sensitivities for aquifer parameters 

and aquifer–parameter pilot points ...................................................................................237
xxiii

Tables

Chapter A

A1. Statistics for analysis of effects of climate variability on groundwater levels 

in the Atlantic Coastal Plain of North and South Carolina...............................................33

A2. Prediction standard-error statistics for the analysis of the groundwater 

level monitoring networks in the Atlantic Coastal Plain of North Carolina, 

South Carolina, and parts of eastern Georgia and southern Virginia............................41

Chapter B

B1. Model layers and Atlantic Coastal Plain hydrogeologic units for southern Virginia, 

North Carolina, South Carolina, and eastern Georgia......................................................54

B2. Wells used in cross sections on Plates 1–7.......................................................................58

Chapter C

C1. Model layers in relation to Atlantic Coastal Plain hydrogeologic units 

in North Carolina, South Carolina, eastern Georgia, and southern Virginia...............167

C2. Median and maximum model-layer thicknesses in the Atlantic Coastal Plain 

model simulating groundwater flow, predevelopment to 2004, in North and 

South Carolina and parts of Virginia and Georgia...........................................................167

C3. Descriptions of precipitation stations in part of the Atlantic Coastal Plain 

in South Carolina and Georgia............................................................................................170

C4. Ranges of reported aquifer transmissivity, and calculated and simulated 

hydraulic conductivities for the aquifers in the Atlantic Coastal Plain 

of North and South Carolina and parts of Virginia and Georgia...................................179

C5. Streamflow and baseflow data used in model calibration and calibrated 

streambed conductance for selected sites in South Carolina and Georgia...............188

C6. Calibrated hydraulic conductivity values, and calibrated values of specific yield, 

specific storage, and vertical anisotropy in the model layers representing 

the aquifers and confining units in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia...........................................................196

C7. Statistics for model calibration based on predevelopment conditions for 

aquifers in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia..............................................................................................197

C8. Statistics for model calibration based on 1980 conditions for aquifers

 in the Atlantic Coastal Plain of North and South Carolina and parts 

of Virginia and Georgia ........................................................................................................206

C9. Statistics for model calibration based on 2004 conditions for aquifers 

in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia.............................................................................................................216

C10. Observed and simulated mean annual baseflows for selected streamgages 

in the Atlantic Coastal Plain of South Carolina and parts of Georgia..........................235
xxiv

Conversion Factors

Inch/pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.58998 square kilometer (km2)

Flow rate

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

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

cubic foot per day (ft3/d) 0.67944 cubic meter per day (m3/d)

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

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

Hydraulic conductivity

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

Transmissivity*

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

Riverbed conductance

foot squared per day per foot [(ft2/d)/ft] 0.09290 meter squared per day per meter [(m2/d)/m]

Hydraulic gradient

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

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

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

°F=(1.8×°C)+32

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

°C=(°F–32)/1.8

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

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

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

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

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

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

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

micrograms per liter (μg/L).
xxv

Acronyms and Abbreviations

ACP Atlantic Coastal Plain

CCPCUA Central Coastal Plain Capacity Use Area

CUA Capacity Use Area

DEM Digital Elevation Model

DWR Division of Water Resources

ENSO El Niño/Southern Oscillation

FL Florida

GA Georgia

GCM Global Climate Model

GIS Geographic Information System

GPS Global Positioning System

Ma Mega annum (million years)

MAGICC Model for the Assessment of Greenhouse Gas Induced Climate Change

MODFLOW-2000 Modular Flow Model

NC North Carolina

NCCPCUA North Carolina Central Coastal Plain Capacity Use Area

NED National Elevation Dataset

NWIS National Water Information System

Ohm-m Ohm-meters

Φ The logarithmic transformation of the ratio of a grain diameter in 

 millimeters to a standard grain diameter of 1 millimeter

R2 Coefficient of determination of a linear regression

RASA Regional Aquifer-System Analysis

SC South Carolina

SCDHEC South Carolina Department of Health and Environmental Control

SCDNR South Carolina Department of Natural Resources

SCENGEN Scene Generator

SP Spontaneous Potential

SRS Savannah River Site

TDEM Time Domain Electromagnetic

USGS U.S. Geological Survey

VA Virginia

Introduction

Groundwater withdrawals from Atlantic Coastal Plain 

(ACP) aquifers in North Carolina (NC) and South Carolina 

(SC) have increased during the past 30 years in response to 

demands for water by a rapidly increasing population. The 

combined populations of counties in the NC and SC ACP 

totaled nearly 6 million people, with 3.2 million located 

in NC and 2.5 million in SC (Campbell, 1997; Perry and 

Mackun, 2001). These respective populations composed about 

40 percent of the total NC population and about 60 percent 

of the total SC population. In NC, the population increased 

21.4 percent from 1990 to 2000 (Perry and Mackun, 2001) 

and is projected to increase another 13.7 percent by the year 

2015 (Campbell, 1997). The population in SC increased 

15.1 percent from 1990 to 2000 and is projected to increase an 

additional 13.2 percent by 2015. While NC and SC endeavor 

to meet water-supply needs in response to rapid coastal population growth, both States recognize that better information is 

needed regarding groundwater supplies. 

Historically, groundwater use from the ACP aquifers 

in North and South Carolina dates to at least 1670 when 

European settlers arrived in what is now Charleston, SC, and 

constructed shallow, hand-dug wells (Lynch and others, 1882; 

fig. A1). With time and increasing population, Charleston 

began to have water-quality problems with the surficial aquifer, so other sources of water supply were sought, especially 

deeper, confined aquifers. Developing these deeper aquifers 

for adequate groundwater supplies led to declining water 

levels in the study area, which in some cases, date back to the 

latter part of the 19th century. 

The recent drought (1998–2002) in the Eastern United 

States highlighted the problem of declining groundwater 

levels. During the drought, surficial aquifer groundwater 

levels in the ACP and Piedmont of the Carolinas declined to 

some of the lowest levels on record (Gellici and others, 2004; 

Weaver, 2005). While drought conditions do not affect the 

deeper, confined aquifers to the same extent as the shallow 

aquifers, additional water was pumped from the deep aquifers during the drought to supply increased water demands 

in the area resulting from the lack of precipitation. During 

the 1998–2002 drought, ACP groundwater levels declined an 

average of 8.7 feet (ft) in SC, and record-low groundwater 

levels were recorded at many of the groundwater monitoring 

stations (Gellici and others, 2004; fig. A2). In NC, record-low 

groundwater levels were observed during water year 20021 in 

100 of 137 wells monitored in the State (Weaver, 2005). 

North and South Carolina water-resource regulatory 

agencies recognize the need for cooperation in addressing critical groundwater issues. The States further recognize the need 

for current groundwater management tools, such as an updated 

groundwater flow model for the ACP region. Currently (2009), 

neither NC nor SC has an up-to-date groundwater flow model 

of the ACP. However, since the completion of the U.S. Geological Survey (USGS) Regional Aquifer System Analysis 

(RASA) models in both States in the 1980s, an abundance of 

groundwater use, water-level, and hydrogeologic framework 

data have been collected. 

One approach taken by NC and SC for dealing with water 

demands in critical areas is to manage groundwater resources 

on a smaller scale (subregional) by way of establishing Capacity Use Areas in which groundwater withdrawals are individually permitted and groundwater levels are regularly monitored 

(fig. A3). However, there remains a need to examine all the 

competing demands across the ACP to better understand the 

cumulative effects on the regional groundwater resources now 

and in the future. The situation in the ACP is not unlike what 

is occurring in areas across the United States that use other 

major aquifers (Reilly and others, 2008). Groundwater systems 

under stress from population increases and climatic variability 

accentuate the need for an updated status on the availability of 

groundwater resources throughout the United States. An assessment of the current status of the groundwater flow in principal 

aquifers, such as the ACP aquifers and confining units, could 

be invaluable for assessing groundwater availability.

The USGS Groundwater Resources Program is using the 

quantitative work previously conducted by the RASA Program 

and other water-related investigations conducted by local, 

State, and other Federal agencies to provide updated quantitative assessments of groundwater availability in areas of critical 

importance. The focus of this study is to define a consistent 

hydrogeologic framework spanning the two States within the 

ACP aquifers and confining units and to improve the fundamental knowledge of groundwater availability in the ACP 

aquifers of North and South Carolina, including water fluxes, 

storage, and water use by a variety of human activities. 

Chapter A. Groundwater Availability in the Atlantic 

Coastal Plain of North and South Carolina

By Bruce G. Campbell, Jason M. Fine, Matthew D. Petkewich, Alissa L. Coes, and Silvia Terziotti 

1

 Water year is the period October 1 through September 30 and is identified 

by the year in which the period ends. For example, water year 2002 began on 

October 1, 2001, and ended on September 30, 2002.
2 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A1. The Atlantic Coastal Plain along the Atlantic Coast of North and South Carolina and parts of northern Florida, Georgia, 

Virginia, and Maryland.

Cape Fear

Arch

Gulf

Trough

Albemarle

Embayment

Albemarle

Sound

Pamlico

Sound

Southeast Georgia

Embayment

Atlantic

Ocean

Hilton

Head

Charleston

Savannah

Myrtle

Wilmington

Greenville

Virginia

Beach

Edenton

Beach

Florence

Fall

Line

CHARLES

BRADFORD

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

West

Virginia

Kentucky

Tennessee

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Blue Ridge/Ridge and Valley

Piedmont

Sand Hills

Inner Coastal Plain

Outer Coastal Plain

EXPLANATION

PHYSIOGRAPHIC PROVINCES

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

York R.

James

River

Chowan

River

Roanoke

River

Tar

River

Neuse

River

River

Cape

Fear

River

River

Peedee

River Santee

River

Black

Lumber

R.

Catawba

Wateree

River

River

Broad

Saluda

Savannah

Edisto

Ogeechee

Altamaha

Salkehatchie

Coosawhatchie

Congaree

River

R.

River

River

River

R.

R.

R.

Figure A1. The Atlantic Coastal Plain along the Atlantic Coast of North and South Carolina and 

 parts of northern Florida, Georgia, Virginia, and Maryland.
Introduction 3

Figure A2. Locations of selected groundwater level monitoring sites and hydrographs showing the effects of the 1998–2002 drought 

in North and South Carolina.

North Carolina

32°

33°

34°

35°

36°

37°

77° 76° 75° 83° 82° 81° 80° 79° 78°

38°

31°

Georgia 

Florida

South 

Carolina 

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Well and number CHN-101

HAM-83

CHN-101

NC-194

BR-079

NC–194

Figure A2. Locations of selected groundwater level monitoring sites and hydrographs showing the effects of the 

 1998-2002 drought in North and South Carolina. 

406

404

402

400

398

DEPTH TO WATER, IN FEET

BELOW LAND SURFACE

1993 1994 1995 1996

NC–194 Black Creek aquifer

BR–079

HAM–83 CHN–101

24

22

20

18

16

14

DEPTH TO WATER, IN FEET

BELOW LAND SURFACE

BR–079 Castle Hayne aquifer

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007

30

32

34

36

38

40

42

44

46

DEPTH TO WATER, IN FEET

BELOW LAND SURFACE

1977 1979 1981 1983

HAM–83 Upper Floridan aquifer 12

13

14

15

16

17

18

19

20

DEPTH TO WATER, IN FEET

BELOW LAND SURFACE

CHN–101 Gordon aquifer

1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006

Atlantic

Ocean
4 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A3. Capacity Use Areas in North and South Carolina.

EXPLANATION

CAPACITY USE AREAS

0 50 100 MILES

0 50 100 KILOMETERS

Central Coastal Plain Capacity Use Area

Peedee Capacity Use Area

Waccamaw Capacity Use Area

Trident Capacity Use Area

Low Country Capacity Use Area

Capacity Use Area number 1

Figure A3. Capacity Use Areas in North and South Carolina.

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Virginia

North Carolina

Tennessee

South Carolina

Georgia

32°

33°

34°

35°

36°

77° 76° 75° 83° 82° 81° 80° 79° 78°

Atlantic

Ocean

Purpose and Scope

The purpose of this report is to describe the status and 

trends of groundwater availability on a regional scale within 

the ACP aquifers and confining units underlying NC, SC, 

and parts of eastern Georgia (GA) and southern Virginia 

(VA). Study results presented here build on previous, related 

investigations that have involved the ACP aquifers and confining units and have included numerical modeling. This report 

is organized into three chapters accompanied by a series of 

plates that detail the hydrostratigraphy of the aquifers and 

confining units.This chapter, Chapter A, summarizes background information on the groundwater resources of the study 

area and focuses on providing an analysis and assessment of 

groundwater availability in the ACP aquifers of North and 

South Carolina. Included are descriptions of the effects of 

development on the flow system (hydrologic budget analysis), 

groundwater sustainability and management, and an evaluation of the adequacy of monitoring networks to assess effects 

of groundwater use and climate variations at a regional scale. 

The results of a numerical modeling tool are used to develop 

an understanding of how groundwater conditions can be 

affected by a variety of natural (climatic) and anthropogenic 

developments now (2009) and in the future. Chapter B brings 

together the current available geologic, lithologic, and hydrologic properties, as well as geophysical information to define 

a regional hydrogeologic framework for the ACP aquifers 

and confining units system of NC and SC. Also included in 

Chapter B is a presentation of hydrostratigraphic correlations 

of the ACP aquifers and confining units at the NC–SC border 

using detailed cross sections. The framework described in 

Chapter B was used to develop the numerical modeling tool. 

Chapter C documents the development of a three-dimensional 

finite-difference numerical model of the regional groundwater 

flow within the ACP aquifers and confining units. The numerical model is used to evaluate the groundwater availability 

described in Chapter A. Previous groundwater modeling 

efforts of the study area were not comprehensive, and the area 

simulated was restricted to either the NC or SC Coastal Plain. 

The current groundwater modeling effort fully simulates the 

aquifers and confining units in three dimensions as opposed to 

previous efforts that did not fully simulate the confining units 

within the flow system. 
Introduction 5

Specific objectives of the NC and SC ACP regional 

groundwater availability analysis are to (1) develop a better 

understanding of the three-dimensional nature of the hydrogeologic framework including the confining units of the ACP 

of NC and SC and resolve differences between disparate forms 

of information regarding delineation of the hydrogeologic 

framework within the two States; (2) determine groundwater 

flow directions and use enhanced groundwater budget analysis 

techniques to estimate the water budget components (recharge, 

discharge, change in storage) for the aquifers and confining 

units; (3) quantify the groundwater resources of the study area 

to enable the forecasting (assessment of groundwater sustainability) of the response (effects on groundwater levels) to 

potential future climate variations at scales relevant to making 

water-management decisions; and (4) conduct a geospatial 

analysis of the groundwater level monitoring networks in the 

ACP aquifers in North and South Carolina.

Groundwater flow models are commonly used analytical 

tools for quantifying groundwater flow and budgets. Modeling 

results also can be used to evaluate future stresses given likely 

management scenarios and the design of monitoring networks 

that address specific long-term questions. In this case, study 

objectives were met by developing a numerical groundwater 

flow model of the aquifers and confining units that make up 

the flow system using the USGS modular finite-difference 

groundwater flow model, MODFLOW-2000 (Harbaugh and 

others, 2000). The ACP groundwater flow model of NC and 

SC represents transient three-dimensional groundwater flow 

from 1900 to 2004 and includes several enhancements over 

previous modeling efforts owing to additional data availability, 

improved MODFLOW capabilities, and improved computer 

technology. Tasks undertaken to construct the groundwater 

flow model and evaluate groundwater availability include: 

1. Compilation of geologic and hydrologic data collected 

since publication of previous models discussed in the 

“Previous Investigations” section;

2. Construction of model input and calibration datasets 

based on the data compilation.

3. Calibration of the groundwater flow model and evaluation 

of model fit;

4. Evaluation of model results including hydraulic head, 

water budget, and changes in head and water budget 

through time;

5. Predictive simulations and evaluation of hypothetical 

future groundwater conditions given selected climatic 

scenarios; and

6. Evaluation of current and historic groundwater level 

monitoring networks.

The first task is accomplished through data and interpretations developed from a series of core holes drilled in the SC 

Coastal Plain over the past decade along with slightly revised 

interpretations of the hydrostratigraphy of the NC Coastal 

Plain from geophysical log interpretations and analysis of 

continuous groundwater levels. Also, detailed hydrostratigraphic cross sections have been developed at the NC–SC 

border to connect the hydrostratigraphies. The second task is 

achieved through the use of historical data such as groundwater levels, aquifer properties, and water-use data. These 

data were compiled and converted to groundwater flow model 

input and utilized for model calibration. The third task was 

achieved by use of both manual and automated model calibration and parameter estimation techniques until a satisfactory 

fit was achieved between simulated and observed groundwater levels and stream baseflow estimates. Model calibration 

was completed for predevelopment, 1980, and 2004 conditions. The fourth task was achieved with the presentation of 

groundwater flow simulation results including potentiometric 

surface maps of the aquifer for the calibration periods, detailed 

analysis of the overall groundwater budget over time along 

with areas of local groundwater budgets. Changes in groundwater levels and water budgets over time are extracted from 

the model and presented for the three calibration periods along 

with various periods of record of groundwater levels available 

from selected long-term observation wells. The fifth task was 

achieved through the use of a climatic model that was used 

to simulate possible precipitation variability to the year 2100. 

These predicted precipitation rates were then converted to 

groundwater model input, and the model was used to predict 

possible groundwater levels at selected sites. The sixth task 

was achieved with the use of geostatistical techniques to 

evaluate the adequacy of the groundwater level monitoring 

network in the study area. 

Methods of Investigation

Knowledge of groundwater resources and how they are 

assessed has changed substantially since the last groundwater 

modeling efforts were undertaken for the ACP aquifers and 

confining units of NC and SC. The groundwater flow simulation and visualization tools are much improved over ones used 

in past efforts. Much new data are available from parts of 

the study area that were not monitored in the past along with 

extended records from sites that have been monitored for long 

periods of time. A current assessment of groundwater availability of the ACP aquifers of NC and SC would include basic 

information on the hydrostratigraphic framework, aquifer and 

confining unit boundaries, potentiometric surfaces of the units, 

aquifer and confining unit hydraulic properties, and quantification of human-induced changes to the flow system and water 

budgets related to groundwater pumping. 

This assessment of groundwater availability of the ACP 

aquifers of NC and SC consisted of the collection, integration, 

and use of both new and existing data along with the construction and calibration of a groundwater flow model. The model 

is the primary tool used in the assessment of groundwater 

availability of the study area. The results, conclusions, and 

limitations discussed in this report are based on the analyses 

of these data along with the interpretation of results from the 

groundwater flow model.
6 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Data Compilation

Major types of data used in the study include (1) groundwater levels, both synoptic and continuous types; (2) groundwater use data, consisting of both estimated and recorded 

groundwater pumping rates, locations, and aquifer assignments; (3) hydrostratigraphic data such as aquifer and confining unit extents, along with top and bottom altitudes; and 

(4) estimates of stream baseflows derived from the analysis of 

streamflow records at selected sites.

The regional hydrogeologic framework of the ACP was 

constructed by examining strata outcrops, core and drill cuttings samples, micro and macro fossils, and geophysical logs 

obtained from numerous boreholes. These data were integrated 

into detailed descriptions of the lithology, thickness, geometry, 

and relative permeability of the ACP sediments at 309 borehole 

locations within the study area. The top and bottom altitudes of 

the ACP aquifers and confining units from the 309 boreholes 

were extrapolated over the study area to the known extents of 

the units. This hydrostratigraphy is described in detail in Chapter B of this report. Historical groundwater level, groundwater 

use, and stream flows, were compiled from 1900 to 2004 and 

used in the model construction and calibration process. 

Numerical Model

A finite-difference numerical modeling technique 

(MODFLOW-2000, Harbaugh and others, 2000) was used to 

simulate groundwater flow in the ACP aquifers and confining 

units over a 104-year period from 1900 to 2004. This model is 

described in detail in Chapter C of this report. The methods of 

investigation used in the modeling effort included conceptual 

model evaluation and revision, data compilation, model construction and calibration, and sensitivity analysis. The existing 

conceptual models were evaluated to determine the appropriateness of boundary conditions, model layering, and methods 

of approximating field conditions. Hydraulic, water-use, and 

water-level data for 1900 to 2004 were compiled from various 

State agencies and other USGS investigations for inclusion 

in the model. These data also included synoptic groundwater 

altitude and groundwater baseflow measurements made in 

the fall of 2004. The model was calibrated by approximating 

steady-state, predevelopment groundwater conditions for year 

1900 and simulating transient conditions through 2004. The 

sensitivity of the calibrated model to the modeled parameters 

was evaluated to determine the relative importance of the 

parameters to simulated results.

The updated version of the USGS three-dimensional 

finite-difference modular flow model (MODFLOW-2000; 

Harbaugh and others, 2000) provided a more robust method 

for simulating field conditions than the numerical codes used 

in the NC and SC RASA models. Revision of the flow model 

included active simulation of the ACP aquifers and confining 

units in the study area and incorporation of hydraulic properties, water-level and water-use data, and groundwater baseflow 

data acquired since the previous studies.

These modeling techniques produced groundwater altitudes and flow directions that were compared to both synoptic 

and continuous field measurements of groundwater altitudes 

and evaluated with statistical methods. Global climate models 

(GCMs) were employed to predict future variations in precipitation rates that were then converted into variations in net recharge 

rates and input into the groundwater model. Geographic 

information system (GIS) techniques were used to analyze the 

groundwater level monitoring networks in North and South 

Carolina to quantify the extents of the coverage distributions.

Previous Investigations

Although many recent investigations related to ACP 

geology and groundwater have taken place in North and South 

Carolina, only investigations of regional extent will be cited 

here. One of the first regional studies of groundwater resources 

in the study area was by Darton (1896), who described existing artesian wells and the prospects for additional artesian 

wells. A comprehensive study of the geology and groundwater 

resources of the NC ACP was conducted by Clark and others 

(1913). Winner and Coble (1996) described the hydrogeologic framework of the NC ACP. Lautier (1998, 2002, 2006) 

describes parts of the hydrogeology of the NC ACP. The Winner and Coble report contains an extensive listing of previous 

hydrologic and geologic investigations of the NC ACP. Giese 

and others (1997) described the simulation of groundwater 

flow in the NC ACP using a finite-difference groundwater flow 

model. Eimers and others (1990) presented a model that simulated groundwater flow in the Cretaceous aquifers of NC. 

Numerous local and subregional hydrologic and geologic 

investigations of the SC ACP have been conducted. The first 

comprehensive study of the geology of the SC ACP was by 

Cooke (1936). Colquhoun and others (1983) described the 

surface and subsurface stratigraphy, structure, and aquifers of 

the SC ACP. Aucott (1996) produced a comprehensive report 

on the hydrology of the SC ACP. The Aucott report contains 

an extensive listing of previous hydrologic and geologic investigations of the SC ACP. Campbell and van Heeswijk (1996) 

described the simulation of groundwater flow within the 

Cretaceous aquifers of the SC ACP. A recent addition to the 

stratigraphic delineation of the Atlantic and Gulf Coastal Plain 

is the identification of Supergroups of Coastal Plain sediments 

by Weems and others (2004). A surficial geologic map of the 

ACP was compiled by Newell and others (2002).

Several important regional-scale groundwater modeling 

investigations of the ACP have taken place in both NC and 

SC. The NC RASA model was one of the first developed in 

the National RASA Program (Giese and others, 1997). The 

computer model used the Trescott (1975) code as modified by 

Leahy (1982), and was calibrated to 1980 groundwater conditions. The NC RASA model was updated by Eimers and others 

(1990). The SC RASA model was developed by Aucott (1988, 

1996), calibrated to predevelopment and 1982 conditions, and 

later recalibrated by Campbell and van Heeswijk (1996) using 

data collected in 1989.
Geologic History and Setting 7

Study Area

The ACP area extends from eastern Georgia through 

South and North Carolina and into southern Virginia (fig. A1). 

The study area extends from the Fall Line to areas both on and 

offshore that contain fresh groundwater. Vertically, the study 

includes all of the ACP aquifers and confining units. 

The ACP aquifers underlie an area of approximately 

25,000 square miles (mi2) in NC and 22,500 mi2 in SC. The 

study area extends into eastern GA and encompasses approximately 5,000 mi2

 there, along with approximately 3,000 mi2

in southern VA; additionally, the study area includes approximately 15,000 mi2

 offshore. This entire study area lies approximately between latitude 31° and 37° 30′ N and longitude 76° 

and 30′ and 83° W (fig. A1). 

Physiography and Climate

The ACP of North and South Carolina is characterized 

by rolling hills and deeply incised river valleys in the inner 

Coastal Plain and gently rolling to flat topography in the outer 

Coastal Plain, which generally slopes toward the Atlantic 

Ocean (fig. A1). Major river valleys, such as the Savannah, 

Congaree, Wateree, Pee Dee, Cape Fear, Neuse, Tar, and 

Roanoke Rivers dominate the inner Coastal Plain topography. 

These river valleys within the inner Coastal Plain typically 

contain extensive wetlands and are flanked by broad, relatively 

flat uplands in the interstream areas. The inner Coastal Plain is 

characterized by relatively high land-surface altitudes, which 

range from about 50 ft to more than 700 ft above the National 

Geodetic Vertical Datum of 1929 (NGVD 29) at the Fall Line. 

The Sand Hills region is characterized by long gentle slopes, 

rounded summits cut by stream valleys, and well-defined 

flood plains along rivers. Dense networks of tributaries that 

extend across the entire study area contribute runoff to the 

major rivers. 

The outer Coastal Plain is characterized by low landsurface altitudes, which range from 0 to about 50 ft and 

average 20 ft above NGVD 29 throughout most of the area. 

The outer Coastal Plain is characterized as a low, broad plain 

with numerous coastal terraces. Parts of the area are swampy, 

and large streams and their tributaries are affected by oceanic 

tides. Two major estuaries are on the NC coast within the outer 

Coastal Plain—Albemarle and Pamlico Sounds (fig. A1).

The climate in the SC and NC ACP is temperate and is 

characterized by hot, humid summers and moderate winters. 

Annual precipitation rates for the study area in SC are about 

50 to 52 inches (in.) (South Carolina State Climatology Office, 

2007), and rates in NC are 40 to 55 in. (State Climate Office of 

North Carolina, 2007). The precipitation is relatively uniformly distributed and is seasonal in nature with wet winters, 

springs, and summers and with dry autumns. Streamflow is 

greatest during the winter months and decreases during spring 

and summer when evapotranspiration rates are highest. 

Capacity Use Areas

As a way of managing declining groundwater levels, both 

NC and SC began establishing Capacity Use Areas (CUA) in 

which groundwater withdrawals are permitted and groundwater levels are monitored. CUA1 (fig. A3) was established 

in 1967 in NC because of groundwater level declines related 

to phosphate mine de-watering in the Castle Hayne aquifer 

(North Carolina Division of Water Resources, 2005). In 2002, 

the NC Central Coastal Plain CUA (CCPCUA) was established to regulate withdrawals from the Black Creek and 

Upper Cape Fear aquifers. Under the 2002 CCPCUA regulations, several counties and municipalities were required to 

reduce withdrawals by 25 percent by 2008 and by 75 percent 

by 2018. Overall groundwater level declines are estimated to 

be as much as 200 ft near pumping centers in the CCPCUA. 

In 1979, the first CUA in SC was established as the Waccamaw CUA, to monitor 200-ft drawdowns from predevelopment levels in the Black Creek aquifer (fig. A3). In 1981, the 

Low Country area was designated as a CUA because of saltwater encroachment in the Upper Floridan aquifer. More recently, 

in 2002, the Trident area was designated as a CUA because of 

225-ft drawdowns in one of the sand aquifers of Late Cretaceous age underlying the area. The five-county Peedee area 

of SC was designated as a CUA in 2003 because of declining 

groundwater levels in several of the Cretaceous sand aquifers.

Geologic History and Setting

The ACP sediments that underlie the study area consist 

of unconsolidated sand, silts, and clays along with crystalline 

carbonate units of Late Cretaceous, Tertiary, and Quaternary 

age that unconformably overlie consolidated crystalline bedrock of Paleozoic and Triassic age. These sediments are part 

of the Atlantic Continental margin that extends over most of 

the length of the eastern United States (Gohn, 1988). The ACP 

sediments are bordered to the west by the Piedmont rocks of 

Precambrian and Paleozoic age at the Fall Line (fig. A1). The 

study area has a long and complex tectonic history related to 

the opening and continued extension of the Atlantic Ocean. 

The geologic history of ACP sediments begins with the 

continental fragmentation and rifting in the early Mesozoic, 

continuing with continental drifting, and progressing to the 

opening of the modern Atlantic Ocean in the late Mesozoic 

and Cenozoic Eras (Gohn, 1988). 

The ACP sediments are part of the geologic evidence of 

the rifting and post-rifting of the Atlantic Continental margin. Major post-rift basins within the study area include the 

Albemarle embayment in southern VA and northern NC and 

the Southeast Georgia embayment in coastal GA (fig. A1). 

Between these basins is an area of relatively higher altitude 

called the Cape Fear Arch. Sediments on the Cape Fear Arch 

are thinner and less complete stratigraphically than the thicker 

sections of sediments in the basins (Gohn, 1988). 
8 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Hydrogeology

Extensive areas of the ACP sediments in North and 

South Carolina are composed of permeable gravels, sands, 

and crystalline carbonate sediments that have substantial 

water-transmission capacity. This water-transmission capacity 

coupled with high precipitation rates in the study area result in 

large quantities of high-quality groundwater available in many 

parts of the North and South Carolina ACP. These groundwater resources are used for various purposes, including 

municipal, irrigation, and industrial supplies. 

A long and complex history of sediment deposition has 

created a framework of aquifers and low-permeability confining units. These sediments overlie crystalline rocks of Paleozoic age and generally thicken and dip toward the Atlantic 

Ocean from the Fall Line. The axis of the Cape Fear Arch is 

located a few miles northeast and approximately parallel to 

the NC–SC State boundary (fig. A1) and produces a second 

dip component that causes the ACP sediments to thicken to the 

southwest and northeast of the arch axis (Gohn, 1988). 

The aquifers and confining units of Tertiary age are found 

only in the southwestern and northeastern parts of the study 

area. These units do not extend across the Cape Fear Arch. The 

units of Cretaceous age extend across the Cape Fear Arch, but 

most do not underlie the entire study area. 

Properties of the ACP aquifers and confining units, such 

as horizontal and vertical hydraulic conductivities and specific 

storage, are not well known across the study area. More information is available on the upper units compared to the deeper 

units, which contain fewer wells. Many hydraulic values are 

available that are derived from various types of aquifer or laboratory tests; however, these values are distributed randomly, 

and large parts of the study area have essentially no available 

data. The available hydraulic property data are described in 

detail by unit in Chapter B of this report. In parts of the study 

area without hydraulic data, parameter estimation techniques 

described in Chapter C of this report were used to estimate 

horizontal hydraulic conductivities, anisotropies, and specific 

storage values. 

Hydrologic System

In the NC and SC Atlantic Coastal Plain, the unconfined 

surficial aquifer is recharged by water from precipitation; then 

groundwater is lost by seepage to streams and evapotranspiration. A small amount of water in the surficial aquifer percolates through confining units to recharge underlying aquifers. 

Additional recharge to deeper underlying aquifers occurs 

where the confined aquifers crop out along the Fall Line in the 

inner Coastal Plain and Sand Hills Physiographic Provinces. 

In this region, streams typically gain water from the aquifers. Water is lost from the deep aquifers by upward leakage 

through confining units and by pumping.

Surface Water

The major rivers in the NC and SC ACP are, from north 

to south, the James, Chowan, Roanoke, Tar, Neuse, Cape 

Fear, Lumber, Pee Dee, Black, Santee, Edisto, Salkehatchie, 

Savannah, Ogeechee, and Altamaha Rivers (fig. A1). Most of 

these major rivers originate in the Piedmont Physiographic 

Province, flow through the inner and outer Coastal Plain 

Physiographic Provinces and discharge to the Atlantic Ocean. 

Smaller rivers originate near the inner margin of the ACP sediments. All of the major rivers except the Edisto are regulated, 

and most of the smaller rivers are unregulated. 

Where the major rivers cross the Fall Line and pass from 

the crystalline rock of the Piedmont to the unconsolidated ACP 

sediments, the rivers incise into the ACP sediments below 

the surfical aquifer, and most of the reaches are gaining. In 

general, streams in the southern part of the inner Coastal Plain 

are well connected to the groundwater system and are gaining. 

Streams in the northern part of the inner Coastal Plain are on 

an escarpment and are more poorly connected to the groundwater system than streams located in the southern part. 

Groundwater

The hydrogeologic units of the NC and SC Coastal Plain 

have been described in the following publications: Aucott 

(1996), Winner and Coble (1996), Lautier (1998, 2002, 2006), 

and Harrelson and Fine (2006). The aquifers consist of layers 

of permeable sand or carbonate rocks separated by confining units of silt, clay, or low-permeability carbonate rocks. 

The hydrogeologic units in the NC Coastal Plain differ from 

those in the SC Coastal Plain in number, nomenclature, age, 

and lithology. As part of this investigation, the hydrogeologic 

units at the NC–SC border were correlated (Chapter B), and 

this correlation was used as the framework for defining the 

hydrogeologic units/model layers used in the modeling results. 

The long-term annual precipitation rate for the Coastal 

Plain of SC is about 48 inches per year (in/yr; Badr and others, 

2004). In NC, the long-term average is about 50 in/yr (Giese 

and others, 1997). Much of this total precipitation is lost 

to evapotranspiration (in SC, 34 in., and in NC, 33 in.) and 

streamflow (in SC, 13 in., and in NC, 16 in.). About 1 in. is 

estimated to recharge the deeper aquifers in both SC and NC 

and eventually discharges to the Atlantic Ocean. 

Recharge to the surficial aquifer of the ACP occurs in 

most interstream areas. Recharge to the deeper ACP aquifers, 

however, occurs predominantly where underlying confined 

aquifers crop out near the Fall Line. Published estimates of 

recharge rates to the surficial aquifer range from 3 to 47 in/yr 

(Aucott, 1996; Giese and others, 1997; Mew and others, 2002; 

Coes and others, 2007). The wide range of published recharge 

rates can be attributed to the various methods used to calculate the rates and the scales (local to regional) that the methods employ (Coes and others, 2007). Recharge rates used in 

regional groundwater modeling studies tend to be in the lower 
Development of the Hydrologic System 9

range of 3 to 5 in/yr. In areas where confining units restrict 

the vertical movement of groundwater between the surficial 

aquifer and the underlying aquifers, recharge rates through the 

confining units are estimated to be lower, ranging from 0.5 to 

1.4 in/yr (Winner, 1976; Winner and Simmons, 1977; Aucott, 

1996; Giese and others, 1997; Heath and Spruill, 2003).

Discharge from the predevelopment ACP aquifers 

occurred by seepage into streams and lakes; evapotranspiration from soil zones; and upward leakage through confining 

units to stream valleys, estuaries, and the Atlantic Ocean 

(Aucott, 1996; Winner and Coble, 1996). Recharge to and 

discharges from the aquifer were equal under predevelopment conditions with no changes in storage. The majority of 

groundwater discharged from shallow aquifers, other than the 

amount lost to evapotranspiration, provided the baseflow of 

perennial streams. Discharge from deeper aquifers was primarily upward leakage through confining units.

Development of the Hydrologic System 

Predevelopment groundwater flow through the ACP 

aquifers and confining units of NC and SC was generally from 

recharge areas to discharge areas and perpendicular to the 

coast, except for the deeper, confined aquifers in SC, which 

had a predevelopment flow direction parallel to the coast 

toward the northeast (Aucott, 1996; Giese and others, 1997). 

Predevelopment groundwater flow through confining units 

generally is considered to be vertically downward in recharge 

areas in the inner Coastal Plain and vertically upward in discharge areas in the outer Coastal Plain (Aucott, 1996; Campbell and van Heeswijk, 1996; Winner and Coble, 1996). In the 

inner Coastal Plain, the groundwater in the shallow aquifers 

generally has short flow paths from recharge areas to discharge 

areas along streams. In the outer Coastal Plain, where the aquifers are not hydraulically connected to the streams, groundwater flow paths are longer, and hydraulic gradients are not as 

steep as those in the inner Coastal Plain.

Discharge components from the postdevelopment ACP 

aquifers and confining units are the same as the predevelopment, plus additional discharge from groundwater pumping 

along with changes in storage. Pumping generally increased 

from 1900 to 2004. The total pumpage in 2004 is approximately 479 million gallons per day (Mgal/d) in the study 

area and, in some cases, has resulted in large alterations to 

the natural groundwater flow system. The most substantial 

withdrawals are for municipal and industrial supply in the cities of Aiken, Andrews, Florence, Mount Pleasant, and Sumter 

in SC and the Counties of Beaufort, Craven, Duplin, New 

Hanover, Onslow, Robeson, and Sampson in NC (fig. B1). 

These groundwater withdrawals, in some cases, have resulted 

in substantial drawdowns and widespread cones of depression.

Groundwater Development History

The ACP aquifers of NC and SC have a long history of 

development dating back to at least the original settlements 

by the Spanish and British settlers in the 1500s and 1600s. 

Shallow wells were hand dug into the surficial aquifer that 

provided fresh water for early residents. Deeper, drilled wells 

that were able to exploit confined aquifers were constructed at 

Charleston, SC, and Edenton, NC, in the mid-1800s (fig. A1). 

Few records of groundwater use for the study area exist prior 

to about 1980, so much of the data available are estimated 

from well construction dates and historic population figures 

for cities and towns. Reconstructions of historical pumpage 

from the SC and NC ACP aquifers are presented in Aucott 

(1996) and in Giese and others (1997), respectively. Since 

about 1980, more complete records of withdrawals are available, and these records have been incorporated into this study.

Beginning about 1940, groundwater withdrawals began 

to have an effect on the potentiometric surfaces of the ACP 

confined aquifers of NC and SC (Aucott, 1996; Giese and others, 1997). Groundwater withdrawal estimates indicate rapid 

increases in the volumes of groundwater withdrawn from the 

ACP aquifers through the early 1980s when the increase in the 

rates of withdrawals began to moderate. 

Groundwater withdrawals in SC in 1982 are described by 

Aucott (1996), and groundwater withdrawals in NC in 1980 

are described by Giese and others (1997). In SC, the largest 

withdrawals for municipal and industrial uses are from the 

Sumter, Florence, Myrtle Beach, and the Savannah River sites 

(fig. B1). These withdrawals created substantial declines in the 

potentiometric surfaces of the pumped aquifers, especially in 

the Florence and Myrtle Beach, SC, areas. In NC, the 1980 

potentiometric surfaces of the ACP confined aquifers indicated 

lower water levels in the northern part of the ACP due primarily to heavy, concentrated pumpage from the Lower Cape Fear 

aquifer in southern VA. There were also large declines in the 

potentiometric surface of the Lower Cape Fear, Upper Cape 

Fear, and Black Creek aquifers in the central part of the NC 

Coastal Plain area. Large-scale declines in the potentiometric 

surface of the Castle Hayne aquifer are associated with mine 

dewatering in the central eastern part of the NC ACP.

In 2004, in the study area, the potentiometric surfaces of 

the ACP aquifers were mapped in detail from a set of synoptic water-level measurements from all of the aquifers. In SC, 

Hockensmith (2008a, b, 2009) presents the synoptic measurements in the form of potentiometric maps. The most prominent 

feature within the Tertiary aquifers is the large water-level 

decline associated with pumping at Savannah, GA (fig. A1). 

Less severe declines occur in the Charleston, SC, area. Much 

of the updip area of the Tertiary aquifers is unaffected by 

pumping and is, therefore, close to predevelopment conditions. In the Cretaceous aquifers, a deep cone of depression 

is centered on the Andrews area in the southern Georgetown 

County area in eastern SC (fig. B1) along with a smaller scale 

depression near Sumter, SC. Other pumping centers that have 

developed noticeable cones of depression are centered on the 

Charleston and Florence, SC, areas (fig. A1).
10 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

During 2004, in the NC ACP aquifers, potentiometric 

declines occurred in the eastern NC ACP due to the mine 

dewatering described above, in the Cretaceous aquifers of 

the central NC Coastal Plain area, and along the VA–NC 

border. Additional areas of groundwater level declines were 

the southern NC Coastal Plain near the SC border within the 

Cretaceous aquifers. 

Water Use

Groundwater use data for the study area were obtained 

from various State agencies charged with collecting the 

information from well owners. In SC, the South Carolina 

Department of Health and Environmental Control (SCDHEC) 

collects groundwater use data from users who withdraw more 

than 3 million gallons in any month (SCDHEC, 2009). The 

SCDHEC groundwater use database was accessed, aquifer 

assignments were made for all wells with sufficient data (well 

location, depth, and screened interval), and the groundwater 

use data were assigned to the model stress periods. In NC, 

non-agricultural users are required to report groundwater use 

of more than 0.1 Mgal/d, and agricultural users are required 

to report more than 1.0 Mgal/d (North Carolina Division 

of Water Resources, 2009). These data were compiled and 

assigned to the model stress periods. 

Groundwater use data for areas in southern Virginia 

were provided by the USGS Virginia Water Science Center (Jason Pope, U.S. Geological Survey, written commun., 

2006). Groundwater use data for eastern GA were provided 

by the USGS Georgia Water Science Center (Dorothy Payne, 

U.S. Geological Survey, written commun., 2006). These data 

provided for VA and GA were part of ongoing groundwater 

modeling studies being conducted in the ACP aquifers. 

Development and Changes to the 

Hydrologic Budget

Groundwater availability in the ACP of North and South 

Carolina generally is good, in that supply exceeds demand in 

most areas. However, concentrated pumping combined with 

relatively poor aquifer properties in some areas has produced 

groundwater level declines, some of which are subregional in 

scale. In much larger parts of the study area where groundwater is plentiful, aquifer properties are good, and there is little 

or no groundwater use. Also, many of these areas in the ACP 

are underlain by several aquifers, all containing high-quality, 

potable groundwater (Lee, 1993; Knobel and others, 1998). 

This section of the report discusses uses of the groundwater model (presented in Chapter C of this report) to present 

general and detailed groundwater flow budgets for the overall 

study area and three sub-areas—NC Central Coastal Plain 

Capacity Use Area (CCPCUA), Sumter, SC, and Aiken, SC. 

Climate variability, which affects precipitation and net recharge 

in the model, has been projected to the year 2100, and the 

effects on simulated groundwater levels have been analyzed. 

Simulated Groundwater Budget Analysis

The ACP aquifers of North and South Carolina contain 

local, intermediate, and regional groundwater flow regimes 

as described by Toth (1963). The inner Coastal Plain (fig. A1) 

is an area of local and intermediate flow systems in which 

the recharged water moves relatively quickly to discharge 

areas, primarily streams and rivers. A small percentage of the 

recharged water moves vertically into deep aquifers of the 

regional flow system. Groundwater flow in the outer Coastal 

Plain moves locally through the surficial system, but predominantly moves regionally through the deep, confined aquifers 

and confining units. As aquifers are developed and large 

volumes of water are produced from the system through wells, 

substantial volumes of groundwater can be diverted from the 

local and intermediate flow systems into the regional flow 

system (Johnston, 1997). Reduced baseflow to surface-water 

bodies and reductions in the volume of water stored in the 

aquifers are the primary changes to the regional groundwater 

budget as a result of the withdrawals.

The groundwater budgets presented are derived from 

the calibrated, regional groundwater flow model described 

in Chapter C of this report. The model simulates groundwater flow over an area of approximately 144,000 mi2

 with a 

constant finite-difference cell size of 4 mi2. Using a regional 

model of this size with a relatively coarse model grid imparts 

assumptions and limitations into the derived groundwater 

budgets. With a 4-mi2 grid size, the local and intermediate 

flow systems in the inner Coastal Plain cannot be simulated 

with a high degree of accuracy. This grid size also limits the 

accuracy of the simulation of surface-water features, such as 

streams and rivers. The model employs a specified-head layer 

to simulate the surficial aquifer in the outer Coastal Plain; 

however, the model does provide a reasonable simulation of 

the regional groundwater flow system in the deep, confined 

aquifers of this area. 

The calibrated groundwater flow model is used to calculate groundwater budgets for the study area and for three 

sub-areas. These three sub-areas include the 15-county area of 

the NCCPCUA, and the Sumter and Aiken, SC, areas (fig. A4). 

These sub-areas were selected for detailed analysis because 

they have long histories of groundwater use, and detailed 

records of groundwater use and water-level data are available. 

Amounts of groundwater use are also some of the highest 

in the study area; this analysis could help water managers in 

these areas understand the resource to a better degree.

Regional Groundwater Budget

In the simulated predevelopment groundwater flow budget, recharge from precipitation and a small amount of leakage 

from rivers are balanced by discharge to rivers and outflow 

to lateral boundaries (fig. A5). Because the aquifers were 

developed and pumping rates increased in the model, the 2004 

simulated groundwater budget is different. Recharge is still the 
Development and Changes to the Hydrologic Budget 11

Figure A4. Locations of areas of detailed groundwater budgets, North and South Carolina.

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census, 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Virginia

North Carolina

Tennessee

South Carolina

Georgia

Central Coastal Plain

capacity use

water budget area

Sumter County

water budget area 

Aiken County

water budget area 

Figure A4. Locations of areas of detailed groundwater budgets, North and South Carolina.

32°

33°

34°

35°

36°

77° 76° 75° 83° 82° 81° 80° 79° 78°

Atlantic

Ocean

primary source of water to the aquifers, but additional sources 

and a small volume of leakage from the rivers are present. In 

2004, simulated withdrawals from the system by wells create 

an inflow of water to the aquifers and confining units from 

storage and lateral boundaries. These simulated withdrawals 

also result in reduced groundwater discharge to rivers. 

Simulated groundwater flow budgets for the area are 

presented in several ways. The first is an overall view of the 

simulated major water-budget components in the study area 

for predevelopment and 2004 (fig. A5). Next are water budgets 

that quantify the inflow and outflow of water to and from the 

groundwater flow system for each hydrologic component and 

model layer for predevelopment and 2004 (figs. A6 and A7, 

respectively). Also included is a simulated water budget for 

stress periods from predevelopment to 2004 (fig. A8). The 

water-budget components include inflow from recharge, 

inflow and outflow through specified-head boundaries and rivers, inflow to and outflow from storage, and outflow by wells. 

Flow rates are depicted in the figures and discussed later in 

this chapter in the “Development and Changes to the Hydrologic Budget” section. 

The largest component of the predevelopment and 2004 

water budgets is vertical interlayer flow (figs. A6 and A7). 

Vertical interlayer flow is the volume of groundwater that 

moves from one layer within the aquifers and confining units to 

adjacent layers under a hydraulic gradient. This gradient can be 

natural, related to recharge, or manmade (related to withdrawals). The next largest budget components are the inflows and 

outflows through the specified-head boundaries. Flow from or 

to the specified-head boundaries is derived from the vertical 

and horizontal hydraulic gradient at the boundary. The total 

inflow through all specified-head boundaries is approximately 

equal to outflow through specified-head boundaries and is 

approximately 3,700 and 3,600 Mgal/d for the predevelopment 

and 2004 model water budgets, respectively. During the model 

simulation of predevelopment conditions, about 70 percent of 

the groundwater enters the study area through specified-head 

boundaries in the surficial aquifer (layer 1), Black Creek/

McQueen Branch aquifer (layer 11), Lower Cape Fear/

Gramling aquifer (layer 15), and Lower Cretaceous aquifer 

(layer 16); 74 percent flows out of the study area through 

specified-head boundaries in the surficial aquifer (layer 1), 
12 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A5. Simulated water budget in the Atlantic Coastal Plain aquifer system of North and South Carolina 

for A, predevelopment and B, 2004. [Mgal/d, million gallons per day]

A

B

Recharge from

precipitation

1,230 Mgal/d 

Leakage from

rivers

13 Mgal/d 

Recharge from

precipitation

1,230 Mgal/d 

Change in

storage

–14 Mgal/d 

Leakage from

rivers

16 Mgal/d 

Net leakage and

lateral flow

193 Mgal/d 

Discharge to

rivers

1,050 Mgal/d 

Discharge to

rivers

963 Mgal/d 

Withdrawals

477 Mgal/d 

Figure A5. Simulated water budget in the Atlantic Coastal Plain aquifer system of North 

 and South Carolina for (A) predevelopment and (B) 2004. [ Mgal/d, million

 gallons per day] 

 

Net leakage and

lateral flow

180 Mgal/d 
Development and Changes to the Hydrologic Budget 13

Figure A6. Simulated 

predevelopment groundwater 

budget for the Atlantic 

Coastal Plain of North and 

South Carolina.

Figure A6. Simulated predevelopment groundwater budget for the Atlantic Coastal Plain

 of North and South Carolina.

Recharge inflow

Specified-head inflow

River inflow

1,230.76

807.89

13.51

Specified-head inflow 5.73

Specified-head inflow 35.20

Specified-head inflow

Specified-head outflow

Specified-head outflow

2.65 Specified-head outflow

<1.00

34.03

<1.00

Specified-head inflow 36.06

Specified-head inflow <1.00

Specified-head inflow

Specified-head outflow

Specified-head outflow

12.81 Specified-head outflow

12.41

<1.00

34.20

Specified-head inflow <1.00

Specified-head inflow 4.40

Specified-head inflow

Specified-head outflow

Specified-head outflow

<1.00 Specified-head outflow

<1.00

7.63

<1.00

Specified-head inflow 515.00

Specified-head inflow <1.00

Specified-head inflow

Specified-head outflow

Specified-head outflow

4.46 Specified-head outflow

26.50

<1.00

1,853.00

Specified-head inflow <1.00

Specified-head inflow 1,535.00

Specified-head inflow

Specified-head outflow

Specified-head outflow

352.00 Specified-head outflow

<1.00

500.86

22.13

Specified-head outflow

River outflow

1,015.17

1,051.45

surficial aquifer

Layer 1

Yorktown/Upper Floridan

confining unit

Layer 2

Yorktown/Upper Floridan

aquifer

Layer 3

1,072

1,086

949

958

Castle Hayne/Pungo River/

Middle Floridan confining unit

Layer 4

Castle Hayne/Pungo River/

Middle Floridan aquifer

Layer 5

592

600

559

564

Beaufort/Gordon

confining unit

Layer 6

Beaufort/Gordon

aquifer

Layer 7

439

420

411

392

Peedee/Crouch Branch

confining unit

Layer 8

Peedee/Crouch Branch

aquifer

Layer 9

333

336

316

319

66

72

Black Creek/McQueen Branch

confining unit

Layer 10

Black Creek/McQueen Branch

aquifer

Layer 11

65

71.5

518

35

Upper Cape Fear/Charleston

confining unit

Layer 12

Upper Cape Fear/Charleston

aquifer

Layer 13

Lower Cape Fear/Gramling

confining unit

Layer 14

Lower Cape Fear/Gramling

aquifer

Layer 15

518

34

508

1,874

Lower Cretaceous

aquifer

Layer 16

506

1,871

21.0

350

Inflows

Inflows

Outflows

Flow direction, all

 flows are in million

 gallons per day Outflows

Aquifer name

Layer 

EXPLANATION

Confining unit name

Layer 

Interlayer

Inflow

Interlayer

Outflow

Interlayer

Outflow Interlayer

Inflow
14 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A7. Simulated 2004 

groundwater budget for the 

Atlantic Coastal Plain of 

North and South Carolina.

Figure A7. Simulated 2004 groundwater budget for the Atlantic Coastal Plain

 of North and South Carolina.

Net storage

Recharge inflow

Specified-head inflow

River inflow

–17.20

1,230.76

1,032.83

16.36

Net storage

Specified-head inflow

–2.00

4.00

Net storage

Specified-head inflow

–1.00

22.85

Net storage

Specified-head inflow

<1.00

1.41

Net storage

Specified-head inflow

–0.53

14.80

Net storage

Specified-head inflow

–1.00

<1.00

Net storage

Specified-head inflow

–0.91

13.63

Net storage

Specified-head inflow

–1.00

<1.00

Net storage

Specified-head inflow

–6.05

6.00

Net storage

Specified-head inflow

1.00

<1.00

Net storage

Specified-head inflow

–5.00

657.00

Net storage

Specified-head inflow

3.00

<1.00

Net storage

Specified-head inflow

5.06

407.00

Net storage

Specified-head inflow

2.72

<1.00

Net storage

Specified-head inflow

8.69

435.00

Net storage

Specified-head inflow

<1.00

478.00

Specified-head outflow

River outflow

Pumping wells

844.79

963.51

1.40

<1.00 Pumping wells

<1.00 Specified-head outflow

119.49 Pumping wells

28.11 Specified-head outflow

<1.00 Specified-head outflow

106.79 Pumping wells

11.86 Specified-head outflow

<1.00 Specified-head outflow

29.81 Pumping wells

33.00 Specified-head outflow

<1.00 Specified-head outflow

36.82 Pumping wells

2.34 Specified-head outflow

Recharge outflow

Specified-head outflow 1.04

84.00 Pumping wells

23.00 Specified-head outflow

<1.00 Specified-head outflow

41.20 Pumping wells

862.00 Specified-head outflow

<1.00 Specified-head outflow

60.90 Pumping wells

934.00 Specified-head outflow

<1.00 Pumping wells

Specified-head outflow

Total pumping 482 million

 gallons per day

125.00

surficial aquifer

Layer 1

Yorktown/Upper Floridan

confining unit

Layer 2

Yorktown/Upper Floridan

aquifer

Layer 3

1,219

1,339

885

825

762

Castle Hayne/Pungo River/

Middle Floridan confining unit

Layer 4

Castle Hayne/Pungo River/

Middle Floridan aquifer

Layer 5

793

494

583

461

Beaufort/Gordon

confining unit

Layer 6

Beaufort/Gordon

aquifer

Layer 7

556

356

457

328

Peedee/Crouch Branch

confining unit

Layer 8

Peedee/Crouch Branch

aquifer

Layer 9

316

280

441

264

177

39

Black Creek/McQueen Branch

confining unit

Layer 10

Black Creek/McQueen Branch

aquifer

Layer 11

176

38

704

21

Upper Cape Fear/Charleston

confining unit

Layer 12

Upper Cape Fear/Charleston

aquifer

Layer 13

Lower Cape Fear/Gramling

confining unit

Layer 14

Lower Cape Fear/Gramling

aquifer

Layer 15

705

20

888

Lower Cretaceous

aquifer

Layer 16

1,082

884

159

511

Inflows

Inflows

Outflows

Flow direction, all

 flows are in million

 gallons per day Outflows

Aquifer name

Layer 

EXPLANATION

Confining unit name

Layer 

Interlayer

Inflow

Interlayer

Outflow

Interlayer

Outflow Interlayer

Inflow
Development and Changes to the Hydrologic Budget 15

5,000

4,000

3,000

2,000

1,000

0

–1,000

–2,000

–3,000

–4,000

–5,000

FLOW, IN MILLION GALLONS PER DAY

BEGINNING DATE AND STRESS PERIOD NUMBER

Figure C22. Simulated groundwater budget per model stress period from predevelopment to 2004 in the Atlantic Coastal Plain

 aquifers of North and South Carolina and parts of Virginia and Georgia.

1900 1909 1919 1929 1939 1949 1959 1969 1979 1981 1983 1985 1987 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Recharge in

Rivers in

Specified-head in

Storage in

Storage out

Specified-head out

Rivers out

Wells out

EXPLANATION

Figure A8. Simulated water budget per stress period from predevelopment to 2004 in the Atlantic Coastal Plain of North and 

South Carolina.

Upper Cape Fear/Charleston aquifer (layer 13), and the Lower 

Cape Fear/Gramling aquifer (layer 15; fig. A6). In the simulated 2004 water budget, 45 percent of the groundwater enters 

the study area through specified-head boundaries in the surficial aquifer (layer 1), Black Creek/McQueen Branch aquifer 

(layer 11), Upper Cape Fear/Charleston aquifer (layer 13), 

Lower Cape Fear/Gramling aquifer (layer 15), and Lower Cretaceous aquifer (layer 16); 61 percent of the groundwater flows 

out of the study area through specified-head boundaries in the 

surficial aquifer (layer 1), Upper Cape Fear/Charleston aquifer 

(layer 13), and Lower Cape Fear/Gramling aquifer (layer 15; 

fig. A7). Two other sources of water to the groundwater budget 

are recharge, which is 1,231 Mgal/d for predevelopment and 

2004, and inflow through rivers at 13.5 Mgal/d for predevelopment and 16.4 Mgal/d for 2004. Water is removed from the 

simulated water budget through discharge to rivers at rates of 

1,051 Mgal/d for predevelopment and 964 Mgal/d for 2004 

(figs. A6 and A7, respectively). Discharge of water through 

wells is another component of flow in the model and accounts 

for 482 Mgal/d for the 2004 water budget (fig. A7). Additionally, as groundwater is pumped over time, water flows into and 

out of storage in the simulated model. Storage is defined as the

volume of water an aquifer releases or takes in per unit surface 

area of the aquifer per unit change in head (Theis, 1938). For 

the 2004 water budget, rates of flow into and out of storage are

43 and 56 Mgal/d, respectively (fig. A8). In figure A7, net storage changes are depicted for each layer. Net storage changes 

are negative for flow out of storage (fig. A7, layers 1, 2, 3, 5, 6, 

7, 8, 9, and 11); net storage changes are positive for flow into 

storage (fig. A7, layers 10, 12, 13, 14, and 15). Storage changes 

are less than 1.0 Mgal/d for layers 4 and 16.

Changes in the water-budget components over time can be 

evaluated by reviewing figure A8, in which net changes in flow 

are depicted across specified-head boundaries by stress period. 

Prior to about 1983, there was a net flow of water out of the 

simulated flow regime through specified-head boundaries. After 

about 1983, there was a net flow of water into the simulated 

water budget through specified-head boundaries. The change 

in the net flow through specified-head boundaries roughly 

corresponds to an increase in total simulated water use (groundwater withdrawals), indicating that the withdrawals may intercept water that would have discharged to streams and wetlands. 

The next largest components of the water budget are 

recharge from precipitation and discharge to rivers. Simulated 
16 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

groundwater discharge to rivers decreased over time from 

1,051 Mgal/d for predevelopment to 964 Mgal/d for 2004. 

For all stress periods, the simulated recharge varies over time 

based on the reported annual precipitation from gaging stations 

in the inner Coastal Plain. In general, groundwater flows into 

the simulated area from storage at rates between about 2 and 

455 Mgal/d for all stress periods except the steady-state predevelopment stress period when there is no contribution from storage. At the modeled regional scale, the net flow of groundwater 

into or out of the simulated flow regime from storage is tied to 

the variability in the recharge rate. During periods of relatively 

high recharge (above 1,500 Mgal/d), a net loss of water occurs 

as water flows out of the simulated flow regime into storage (for

example, stress period 16, fig. A8). During periods of relatively 

low recharge (less than 1,500 Mgal/d), a net increase occurs 

in the volume of water flowing into the simulated flow regime 

from storage (for example, stress periods 24–26, fig. A8). 

In summary, the groundwater budgets for the ACP aquifers and confining units have changed over time as a result of 

withdrawals superimposed on the original natural flow system 

and from natural variability in the climate, which results in 

variable recharge rates. High rates of withdrawals produce 

outflows from storage within the system and decreases in 

baseflows to the inner Coastal Plain rivers. High rates of precipitation cause increases in storage rates within the aquifers 

and confining units and higher baseflows to the rivers. Overall, 

the 2004 rates of groundwater withdrawals have not changed 

groundwater flow within the aquifers and confining units to 

any substantial degree; however, concentrated withdrawals 

combined with poor aquifer properties have produced large 

groundwater level declines in some areas. 

North Carolina Central Coastal Plain Capacity 

Use Area Groundwater Budget

Detailed groundwater flow budgets for three sub-areas 

of the study area are presented. These sub-areas were selected 

on the basis of relatively high groundwater withdrawals and 

availability of detailed water-use data. The effects of the 

withdrawals on groundwater levels and water budgets vary 

subtantially for the three areas. The NC CCPCUA has had 

major changes in the groundwater budget as a result of concentrated withdrawals over the past 30 years. The Aiken and 

Sumter, SC, areas have had less change to the groundwater 

flow systems because the aquifers tend to have relatively high 

horizontal hydraulic conductivities and transmissivities. 

The CCPCUA is a 15-county area in the central part of 

the North Carolina ACP where the population was approximately 912,000 in 2000 (Perry and Mackun, 2001; fig. A4). 

Approximately 40 Mgal/d of groundwater was used in the 

CCPCUA in 2004 by public potable supply systems operated by cities and counties. Water for many residents in the 

area is self-supplied by domestic wells. Pumpage data from 

these domestic wells are unavailable (State of North Carolina, 

2004). Groundwater use in the CCPCUA is regulated by NC 

(State of North Carolina, 2001). Groundwater levels have been 

declining since at least 1960 in the Black Creek and Upper 

Cape Fear aquifers in the vicinity of the CCPCUA as a result 

of concentrated withdrawals. 

Simulated predevelopment groundwater flow in the CCPCUA occurs predominantly in the surficial, Yorktown, and 

Castle Hayne/Pungo River aquifers and their related confining 

units (layers 1–5; fig. A9). Specified-head inflow and outflow 

of this area occurs primarily in the surficial aquifer (layer 1) at 

rates of 98.20 Mgal/d and 85.40 Mgal/d, respectively. Vertical flow is highest in the upper layers. Downward rates vary 

from 1.28 to 97.3 Mgal/d, and upward rates vary from 1.04 

to 84.00 Mgal/d. The vertical component of flow decreases 

substantially below the Castle Hayne/Pungo River aquifer 

(layer 5). Lateral flow into the CCPCUA occurs in the Yorktown aquifer (layer 3) and Upper Cape Fear aquifers (layer 13) 

at rates of 1.64 and 1.86 Mgal/d, respectively. Lateral flow 

out of the CCPCUA occurs in the Yorktown (layer 3), Castle 

Hayne/Pungo River (layer 5), Peedee (layer 9), and Upper 

Cape Fear aquifers (layer 13) at rates of 9.06, 5.12, 2.77, and 

1.08 Mgal/d, respectively.

The simulated 2004 water budget for the CCPCUA 

includes pumping from the Yorktown aquifer (layer 3), Castle 

Hayne/Pungo River aquifer (layer 5), Peedee aquifer (layer 9), 

Black Creek aquifer (layer 11), and Upper Cape Fear aquifer 

(layer 13) at rates of 1.39, 97.54, 4.09, 27.8, and 20.98 Mgal/d, 

respectively (fig. A10). Specified-head inflow and outflow 

affecting the surficial aquifer (layer 1) were 199.32 and 

55.64 Mgal/d, respectively. As in the predevelopment budget, 

vertical flow is highest in the upper layers and decreases with 

depth; however, the decrease is not as sharp as in the predevelopment budget. Additional downward flow from the specified 

heads in the surficial aquifer (layer 1) replaces water that is 

removed from the aquifers by pumping. Upward flow in the 

CCPCUA is substantially less than downward flow (fig. A10). 

Water is removed from storage in the Black Creek (layer 11), 

Upper Cape Fear (layer 13), and Lower Cape Fear aquifers 

(layer 15) at rates of 3.52, 2.85, and 1.73 Mgal/d, respectively, 

as a result of pumping from these aquifers. Simulated lateral 

flow into the CCPCUA increased from predevelopment rates 

for some of the model layers but mostly for the Upper Cape 

Fear aquifer (2004 rate of 5.52 Mgal/d) because of pumping. 

Lateral flow out of the CCPCUA for the 2004 water budget 

generally decreased from the predevelopment rates (figs. A9

and A10). 

As of 2004, large volumes of groundwater being pumped 

in the CCPCUA had affected groundwater levels and flow 

regimes (State of North Carolina, 2004) in the aquifers and 

confining units underlying the area. As the simulated groundwater flow budget analysis indicates, groundwater continues to 

be removed from storage in many of the hydrogeologic units, 

and groundwater level declines continue to occur. Until these 

reductions in groundwater storage are lowered or stopped, 

groundwater availability will continue to decline in this area. 
Development and Changes to the Hydrologic Budget 17

Figure A9. Simulated 

groundwater flow budget for 

predevelopment conditions 

in the North Carolina Central 

Coastal Plain Capacity 

Use Area.

Figure A9. Simulated groundwater flow budget for predevelopment conditions in the North Carolina

 Central Coastal Plain capacity use area.

Specified-head inflow 98.20 85.40 Specified-head outflow

<1.00 Intralayer outflow

9.06 Intralayer outflow

<1.00 Intralayer outflow

5.12 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

2.77 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

1.08 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

Intralayer inflow <1.00

Intralayer inflow 1.64

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow 1.86

Intralayer inflow <1.00

Intralayer inflow <1.00

surficial aquifer

Layer 1

Yorktown

confining unit

Layer 2

Yorktown

aquifer

Layer 3

97.3

84.0

94.0

79.2

Castle Hayne/Pungo River

confining unit

Layer 4

Castle Hayne/Pungo River

aquifer

Layer 5

31.5

24.7

31.7

24.6

Beaufort

confining unit

Layer 6

Beaufort

aquifer

Layer 7

13.0

10.4

13.0

10.4

Peedee

confining unit

Layer 8

Peedee

aquifer

Layer 9

8.59

6.13

8.43

5.95

3.45

3.38

Black Creek confining unit

Layer 10

Black Creek aquifer

Layer 11

3.41

3.36

2.12

2.67

Upper Cape Fear

confining unit

Layer 12

Upper Cape Fear

aquifer

Layer 13

Lower Cape Fear

confining unit

Layer 14

Lower Cape Fear

aquifer

Layer 15

2.11

2.64

1.28

1.04

1.30

1.05

Inflows

Inflows

Outflows

Flow direction, all

 flows are in million

 gallons per day Outflows

Aquifer name

Layer 

EXPLANATION

Confining unit name

Layer 

Interlayer

Inflow

Interlayer

Outflow

Interlayer

Outflow Interlayer

Inflow
18 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A10. Simulated 

groundwater flow budget for 

2004 conditions in the North 

Carolina Central Coastal 

Plain Capacity Use Area.

Figure A10. Simulated groundwater flow budget for 2004 conditions in the North Carolina

Specified-head inflow 199.32 55.64 Specified-head outflow

<1.00 Intralayer outflow

1.39 Pumping wells

7.84 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

Pumping wells

97.54

2.53 Intralayer outflow

<1.00 Intralayer outflow

Pumping wells

<1.00

<1.00 Intralayer outflow

<1.00 Intralayer outflow

4.09 Pumping wells

1.65 Intralayer outflow

<1.00 Intralayer outflow

Pumping wells

27.81

1.00 Intralayer outflow

<1.00 Intralayer outflow

Pumping wells

20.98

<1.00 Intralayer outflow

Pumping wells

<1.00 Intralayer outflow

<1.00

<1.00 Intralayer outflow

Intralayer inflow <1.00

Intralayer inflow 1.77

Intralayer inflow <1.00

Intralayer inflow 2.01

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

<1.00

Intralayer inflow <1.00

<1.00

Intralayer inflow <1.00

3.52

Intralayer inflow 1.38

<1.00

Intralayer inflow <1.00

<2.85

Intralayer inflow 5.52

0.51

Intralayer inflow <1.00

1.73

Intralayer inflow <1.00

surficial aquifer

Layer 1

Yorktown

confining unit

Layer 2

Yorktown

aquifer

Layer 3

197

54.5

194

50.0

Castle Hayne/Pungo River

confining unit

Layer 4

Castle Hayne/Pungo River

aquifer

Layer 5

148

11.5

148

11.7

Beaufort

confining unit

Layer 6

Beaufort

aquifer

Layer 7

148

11.7

44.5

6.09

Peedee

confining unit

Layer 8

Peedee

aquifer

Layer 9

44.8

6.06

40.6

1.91

33.4

1.82

Black Creek confining unit

Layer 10

Black Creek aquifer

Layer 11

34.0

<1.00

13.6

3.06

Upper Cape Fear

confining unit

Layer 12

Upper Cape Fear

aquifer

Layer 13

Lower Cape Fear

confining unit

Layer 14

Lower Cape Fear

aquifer

Layer 15

Not present

Layer 16

13.9

2.97

3.58

6.24

3.95

6.00

Inflows

Inflows

Outflows

Flow direction, all

 flows are in million

 gallons per day Outflows

Aquifer name

Layer 

EXPLANATION

Confining unit name

Layer 

Interlayer

Inflow

Interlayer

Outflow

Interlayer

Outflow Interlayer

Inflow
Development and Changes to the Hydrologic Budget 19

Sumter, South Carolina, Groundwater Budget

Sumter, SC, is a city of approximately 45,000 people 

and is located in Sumter County in the central part of the SC 

ACP (fig. A4). The city depends solely on groundwater from 

19 wells open to the Crouch Branch and McQueen Branch 

aquifers for potable water. Reported groundwater use in 

2004 for Sumter County was about 18 Mgal/d (Childress and 

Bristol, 2005). Sumter County is not located in a capacity-use 

regulated area, and no major groundwater level declines are 

known to have occurred in the area.

The primary sources of groundwater in the Sumter area 

(fig. A4), for the simulated predevelopment water budget are 

recharge, specified-head boundaries, and lateral flow for all 

simulated aquifer and confining unit layers (fig. A11). Predevelopment recharge and specified-head inflow rates were 8.01 and 

4.03 Mgal/d, respectively. Lateral flow was less than 1 Mgal/d 

for each model layer, except the Crouch Branch (layer 9) and 

the McQueen Branch aquifers (layer 11) for which lateral flow 

was 2.81 and 2.21 Mgal/d, respectively. Groundwater flow out 

of the Sumter area occurred through specified-head outflow for 

the surficial aquifer (layer 1; 5.67 Mgal/d) and through lateral 

flow within the surficial aquifer (layer 1; 1.57 Mgal/d), Crouch 

Branch aquifer (layer 9; 7.42 Mgal/d), and the McQueen 

Branch aquifer (layer 11; 2.27 Mgal/d). Intralayer flow generally decreases with depth from the surficial aquifer to the 

Crouch Branch aquifer. Below the Crouch Branch aquifer 

(layer 9), intralayer flow rates are less than 1 Mgal/d. Downward flow generally is twice as much as upward flow in the 

Sumter area (fig. A11). 

The simulated 2004 water budget for the Sumter area 

includes pumping from the Crouch Branch and McQueen 

Branch aquifers (layers 9 and 11, respectively) at rates of 

1.20 and 8.53 Mgal/d, respectively (fig. A12). The major 

sources of groundwater in the Sumter area are recharge and 

specified-head inflow to the surfical aquifer (layer 1) at rates 

of 8.01 Mgal/d and 5.13 Mgal/d, respectively, and lateral flow 

from outside of the Sumter water-budget area into the Crouch 

Branch and McQueen Branch aquifers (layers 9 and 11) at 

rates of 2.88 and 7.65 Mgal/d, respectively. Other than through 

pumping, groundwater flows from the Sumter area by discharge to specified-head boundaries in the surficial aquifer 

(layer 1, 3.44 Mgal/d), along with intralayer outflow from the 

surficial aquifer (1.56 Mgal/d), the Crouch Branch aquifer 

(layer 9, 6.93 Mgal/d), and the McQueen Branch aquifer 

(layer 11, 1.36 Mgal/d). As in the simulated predevelopment 

budget, vertical flow decreases with depth; however, in the 

2004 water budget, reported flow is substantially greater in 

the McQueen Branch confining unit and aquifer (layers 10 

and 11) because of pumping from the McQueen Branch 

aquifer. Downward flow is as much as six times greater than 

upward flow in the Sumter area (fig. A12). Changes in storage 

are insignificant in the Sumter area for the 2004 stress period. 

Simulated lateral flow into the McQueen Branch aquifer 

(layer 11, 7.65 Mgal/d) in the 2004 water budget tripled from 

the simulated predevelopment rate of 2.21 Mgal/d (fig. A11) 

as a result of increased pumping from this aquifer. Lateral 

groundwater flow from the Sumter area did not change greatly 

from the simulated predevelopment rates except for the 

McQueen Branch aquifer (layer 11) from which lateral flow 

decreased by half (fig. A12). The simulated 2004 water budget 

indicates little effect on groundwater availability from withdrawals by the city of Sumter as noted by the small changes in 

storage in the aquifers that are pumped.

Aiken, South Carolina, Groundwater Budget

Aiken is a city of about 25,000 people located in Aiken 

County in western SC (fig. A4). The city of Aiken uses mostly 

groundwater from the Crouch Branch and McQueen Branch 

aquifers as a drinking-water supply source. Aiken County 

is not located in a capacity-use regulated area, and no major 

groundwater level declines are known to have occurred in 

the area.

The primary components of the groundwater budget 

in the Aiken area during simulated predevelopment groundwater flow conditions were recharge, rivers, and vertical 

flow through all of the model layers (fig. A13). Recharge is 

the largest source of groundwater at a rate of 33.60 Mgal/d. 

Water flows into the surficial aquifer (layer 1) from rivers 

(1.47 Mgal/d) and by lateral groundwater flow (2.67 Mgal/d). 

Lateral inflow also occurs through the Upper Floridan confining unit (layer 2) and Crouch Branch aquifer (layer 9) at 

rates of 1.68 and 1.39 Mgal/d, respectively. Discharge of 

groundwater from the surficial aquifer (layer 1) to rivers is the 

most substantial loss of groundwater from the Aiken area at 

16.2 Mgal/d in the simulated predevelopment water budget. 

Groundwater also flows from the Aiken area by lateral flow 

through the surficial aquifer, the Upper Floridan confining 

unit and aquifer (layers 2 and 3), the Middle Floridan aquifer (layer 5), the Gordon confining unit (layer 6), the Crouch 

Branch aquifer (layer 9), and the McQueen Branch aquifer 

(layer 11) at rates that vary between 1.33 and 8.50 Mgal/d, 

with the highest lateral-flow rate occurring in the surficial 

aquifer. Downward vertical flow occurs throughout the 

groundwater system in the Aiken area, whereas upward vertical flow occurs in layers 1–10. Downward predevelopment 

water flow is considerably greater than upward predevelopment flow throughout the Aiken area.

Pumping rates during 2004 in the Aiken area increased 

downward groundwater flow through all of the aquifer and 

confining units compared to predevelopment flow rates 

(fig. A14). During 2004, withdrawals in the Aiken area from 

the Crouch Branch and McQueen Branch aquifers (layers 9 

and 11) are at rates of 1.27 and 5.41 Mgal/d, respectively. 

With the exception of a decrease in discharge to rivers from 

the surficial aquifer (layer 1) of 6.1 Mgal/d, all other 2004 

budget terms are similar to those of predevelopment (figs. A13

and A14). The simulated 2004 water budget indicates little 

effect on groundwater availability from withdrawals by the 

city of Aiken as noted in the small changes in storage within 

the pumped aquifers.
20 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A11. Simulated 

groundwater flow budget 

for predevelopment 

conditions in the Sumter, 

South Carolina, area.

Figure A11. Simulated groundwater flow budget for predevelopment conditions in the Sumter,

Recharge inflow

Specified-head inflow

8.01

4.03 5.67 Specified-head outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

1.57 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

7.42 Intralayer outflow

<1.00 Intralayer outflow

2.27 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow 2.81

Intralayer inflow <1.00

Intralayer inflow 2.21

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

surficial aquifer

Layer 1

8.77

3.21

8.38

2.95

8.12

2.79

7.83

2.62

7.55

2.47

7.25

2.32

6.95

2.18

6.91

2.17

0.213

0.09

0.213

0.09

0.065

9E-07

Not present

Layer 16

Not present

Layer 15

0.065

9E-07

7.7E-06

9E-07

Inflows

Inflows

Outflows

Flow direction, all

 flows are in million

 gallons per day Outflows

Aquifer name

Layer 

EXPLANATION

Confining unit name

Layer 

Interlayer

Inflow

Interlayer

Outflow

Interlayer

Outflow Interlayer

Inflow

Upper Floridan

confining unit

Layer 2

Upper Floridan

aquifer

Layer 3

Middle Floridan

confining unit

Layer 4

Middle Floridan

aquifer

Layer 5

Gordon

confining unit

Layer 6

Gordon

aquifer

Layer 7

Crouch Branch

confining unit

Layer 8

Crouch Branch

aquifer

Layer 9

McQueen Branch 

confining unit

Layer 10

McQueen Branch aquifer

Layer 11

Charleston

confining unit

Layer 12

Charleston

aquifer

Layer 13

Gramling

confining unit

Layer 14
Development and Changes to the Hydrologic Budget 21

Figure A12. Simulated 

groundwater flow budget for 

2004 conditions in the Sumter, 

South Carolina, area.

Figure A12. Simulated groundwater flow budget for 2004 conditions in the Sumter,

Net storage

Recharge inflow

Specified-head inflow

<1.00

8.01

5.13 3.44 Specified-head outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

0.00 Pumping wells

1.20 Pumping wells

8.53 Pumping wells

1.56 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

6.93 Intralayer outflow

<1.00 Intralayer outflow

1.36 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

2.88

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

7.65

<1.00

surficial aquifer

Layer 1

Upper Floridan

confining unit

Layer 2

Upper Floridan

aquifer

Layer 3

10.2

1.71

9.85

1.47

Middle Floridan

confining unit

Layer 4

Middle Floridan

aquifer

Layer 5

9.61

1.35

9.37

1.22

Gordon

confining unit

Layer 6

Gordon

aquifer

Layer 7

9.12

1.11

8.87

1.00

Crouch Branch

confining unit

Layer 8

Crouch Branch

aquifer

Layer 9

8.63

<1.00

8.58

<1.00

2.38

<1.00

McQueen Branch 

confining unit

Layer 10

McQueen Branch aquifer

Layer 11

2.37

<1.00

<1.00

<1.00

Charleston

confining unit

Layer 12

Charleston

aquifer

Layer 13

Gramling

confining unit

Layer 14

Not present

Layer 16

Not present

Layer 15

<1.00

<1.00

<1.00

<1.00

Inflows

Inflows

Outflows

Flow direction, all

 flows are in million

 gallons per day Outflows

Aquifer name

Layer 

EXPLANATION

Confining unit name

Layer 

Interlayer

Inflow

Interlayer

Outflow

Interlayer

Outflow Interlayer

Inflow
22 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A13. Simulated 

groundwater flow budget for 

predevelopment conditions in 

the Aiken, South Carolina, area.

Figure A13. Simulated groundwater flow budget for predevelopment conditions in the Aiken,

River inflow

Specified-head inflow

1.47

2.67

River outflow

Intralayer outflow

16.2

8.50

4.72 Intralayer outflow

1.37 Intralayer outflow

<1.00 Intralayer outflow

2.21 Intralayer outflow

1.33 Intralayer outflow

<1.00 Intralayer outflow

<1.00 Intralayer outflow

4.70 Intralayer outflow

<1.00 Intralayer outflow

2.39 Intralayer outflow

Intralayer inflow 1.68

Recharge inflow 33.60

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow <1.00

Intralayer inflow 1.39

Intralayer inflow <1.00

Intralayer inflow <1.00

surficial aquifer

Layer 1

Upper Floridan

confining unit

Layer 2

Upper Floridan

aquifer

Layer 3

21.3

8.99

13.7

4.43

Middle Floridan

confining unit

Layer 4

Middle Floridan

aquifer

Layer 5

11.3

2.69

10.3

2.28

Gordon

confining unit

Layer 6

Gordon

aquifer

Layer 7

8.06

1.71

6.83

1.88

Crouch Branch

confining unit

Layer 8

Crouch Branch

aquifer

Layer 9

5.92

1.18

5.96

1.16

1.73

0.24

McQueen Branch 

confining unit

Layer 10

McQueen Branch aquifer

Layer 11

1.72

0.24

Not present

Layer 16

Not present

Layer 15

Not present

Layer 16

Not present

Layer 15

Not present

Layer 15

Inflows

Inflows

Outflows

Flow direction, all

 flows are in million

 gallons per day Outflows

Aquifer name

Layer 

EXPLANATION

Confining unit name

Layer 

Interlayer

Inflow

Interlayer

Outflow

Interlayer

Outflow Interlayer

Inflow
Development and Changes to the Hydrologic Budget 23

Figure A14. Simulated 

groundwater flow budget for 

2004 conditions in the Aiken, 

South Carolina, area.

Figure A14. Simulated groundwater flow budget for 2004 conditions in the Aiken,

River inflow

Intralayer inflow

Net Storage

1.47

2.27

<1.00

Net storage

Recharge inflow

<1.00

33.6

River outflow

Intralayer outflow

10.1

8.52

Intralayer outflow

Pumping wells

4.24

<1.00

1.57 Intralayer outflow

Intralayer outflow

Pumping wells

1.39

<1.00

Intralayer outflow

Pumping wells

<1.00

1.27

Intralayer outflow

Pumping wells

<1.00

5.41

<1.00 Intralayer outflow

2.00 Intralayer outflow

<1.00 Intralayer outflow

6.06 Intralayer outflow

1.38 Intralayer outflow

Intralayer inflow

Net storage

1.45

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow

Net storage

<1.79

<1.00

Intralayer inflow

Net storage

<1.00

<1.00

Intralayer inflow 1.57

surficial aquifer

Layer 1

Upper Floridan

confining unit

Layer 2

Upper Floridan

aquifer

Layer 3

23.8

5.09

17.8

2.18

Middle Floridan

confining unit

Layer 4

Middle Floridan

aquifer

Layer 5

16.0

1.11

15.3

0.88

Gordon

confining unit

Layer 6

Gordon

aquifer

Layer 7

13.6

0.66

12.4

0.73

Crouch Branch

confining unit

Layer 8

Crouch Branch

aquifer

Layer 9

11.4

0.32

11.5

0.32

5.48

0.01

McQueen Branch 

confining unit

Layer 10

McQueen Branch aquifer

Layer 11

5.46

0.01

Not present

Layer 16

Not present

Layer 15

Not present

Layer 14

Not present

Layer 13

Not present

Layer 12

Inflows

Inflows

Outflows

Flow direction, all

 flows are in million

 gallons per day Outflows

Aquifer name

Layer 

EXPLANATION

Confining unit name

Layer 

Interlayer

Inflow

Interlayer

Outflow

Interlayer

Outflow Interlayer

Inflow
24 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Effects of Potential Future Climate Variability on 

Groundwater Levels

Groundwater levels and flows in the North and South 

Carolina ACP are dependent on climate and climatic variations, which must be considered for effective management of 

the groundwater resources. Climate tends to vary temporally 

and spatially in the study area based on various phenomena, 

including the El Niño–Southern Oscillation (ENSO), seasonal 

changes, and tropical events. Many groundwater management 

techniques rely on averages of long-term climatic conditions 

and underestimate the importance of variations from these 

averages (Alley, 2001).

In the Southeastern United States, North and South 

Carolina have some of the warmest climates in the United 

States; however, during the past 100 years, cooling periods 

have occurred that have given the Southeastern United States 

an overall cooling trend of 1 to 2 degrees Celsius (°C) (Burkett 

and others, 2001). Annual precipitation rates in the Southeastern 

States, which are among the highest in the United States, have 

increased by 20 to 30 percent during the past 100 years (Burkett 

and others, 2001). Much of the increase in annual precipitation 

rates can be attributed to an increase in rainfall intensity. 

At least some of the variability in climate, especially 

temperature and precipitation rates, in the Southeastern United 

States is attributed to the effects of the ENSO phenomenon 

(Boyles and others, 2004). The ENSO phenomenon occurs 

as an oscillation between cold (El Niño) and warm (La Niña) 

water temperatures at the surface of the tropical Pacific Ocean. 

The ENSO cycle typically is 3–7 years. El Niño is the cooler 

phase of the ENSO phenomenon and results in cooler and 

wetter winters and drier summers for the Southeast; La Niña, 

the warmer phase, typically results in drier winters and wetter 

summers and can result in more tropical storms. 

The sensitivity of groundwater resources to climate 

variability and change has been explored in several areas of 

the United States at various scales. Stockton and Boggess 

(1979) examined the potential geohydrologic implications of 

climate change on the groundwater resources of the United 

States. Vaccaro (1991) analyzed the sensitivity of groundwater 

recharge to climate variability in an area of the Columbia 

Plateau in Washington. Historical, synthetic, and projected 

climate variations, including variations resulting from global 

warming, were used in the analysis of recharge rates for the 

Ellensburg basin in the Columbia Plateau. Closer to the ACP 

study area, Ayers and others (1994) presented a sensitivity 

analysis of the potential effects of climate change on water 

resources in the Delaware River basin. More recently, Hanson and Dettinger (2005) evaluated the responses of both 

ground- and surface water in the Santa Clara–Calleguas basin 

in California to simulated climate variations. In the Hanson 

and Dettinger study (2005), Global Climate Models (GCMs) 

were used to predict future precipitation rates for the study 

area, which then were used to estimate groundwater and 

surface-water inflows and outflows in a regional groundwater 

flow model of the area. That study demonstrated that predicted 

climate variations from GCMs can be linked to groundwater flow models to produce realistic local-scale groundwater 

responses.

The calibrated groundwater flow model described in 

Chapter C of this report is used to simulate groundwater level 

changes as a result of possible variations in precipitation rates 

from 2010 to 2100. An ensemble of GCMs was used to predict 

the precipitation variability. The GCM is contained in an overall 

model developed by the National Center for Atmospheric 

Research (Wigley, 2003) termed the Model for the Assessment of Greenhouse Gas Induced Climate Change (MAGICC). 

MAGICC is coupled to a graphical interface named Scene Generator (SCENGEN), which can be used to visualize and extract 

results. The MAGICC model was run with two atmospheric 

emissions scenarios—a “reference” scenario, which assumes 

no changes are made by the global community to the 2000 

atmospheric emissions, and a “policy” scenario, which assumes 

changes will be made that will lower the levels of greenhouse 

gases emitted. For instance, in 2100, the “policy” scenario 

assumes that the level of carbon dioxide atmospheric concentrations is reduced from about 700 to about 600 parts per million.

The MAGICC/SCENGEN model predicts the rate of 

change in precipitation or temperature for a user-selected area, 

which can be as large as the entire planet. An area within the 

MAGICC/SCENGEN model that encompasses the Southeastern United States was selected, and the rate of change in precipitation for this area was predicted on a decadal scale from 

2010 to 2100. Reference and policy model runs were completed, and the results of the mean, maximum, and minimum 

precipitation-rate changes were recorded. These predicted 

precipitation-rate changes, in percent, were used to specify 

future recharge rates over decadal stress periods from 2010 to 

2100 in the groundwater flow model (fig. A15). 

Predicted groundwater level altitudes at selected 

observation-well sites were plotted for the Yorktown/Upper 

Floridan aquifers (layer 3), Castle Hayne/Pungo River/Middle 

Floridan aquifers (layer 5), Beaufort/Gordon aquifers (layer 7), 

Peedee/Crouch Branch aquifer (layer 9), Black Creek/

McQueen Branch aquifer (layer 11), and Upper Cape Fear/

Charleston aquifer (layer 13, figs. A6, A16–A22; table A1). The 

groundwater model was run in transient mode without pumpage to evaluate the difference in groundwater level altitudes 

attributable to simulated future variations in the recharge rates. 

Varying the recharge rates changes groundwater levels from 3 

to 45 ft in the higher altitude areas of the southern portion of 

the model area where recharge is applied. The same recharge 

variations produce less than 0.2 ft of change in groundwater 

levels in the northern portion of the model area, downdip and 

away from the area of specified recharge. 

Simulated groundwater levels for the climate-prediction 

scenarios were calculated for two observation wells that are 

in the Upper Floridan aquifer (layer 3) in South Carolina—

HAM-83 and BFT-429 (figs. A16 and A17). The simulated and 

observed groundwater levels match closely at well BFT-429 

but less closely at well HAM-83. The reference and policy 

scenarios for well HAM-83 produce similar groundwater 
Groundwater Level Monitoring Network Analysis in North and South Carolina 25

levels by 2100. At well BFT-429, the reference and policy 

scenarios produce essentially the same simulated groundwater 

levels by 2100 (table A1).

Simulated groundwater levels for the climate-prediction 

scenarios were calculated for two observation wells in 

the Castle Hayne/Pungo River/Middle Floridan aquifers 

(layer 5)—COL-92 and ON-227, in South and North Carolina, 

respectively (figs. A16 and A18). The simulated and observed 

groundwater levels match closely at well ON-227 but less 

closely at well COL-92. The reference and policy scenarios 

for wells COL-92 and ON-227 produce essentially the same 

simulated groundwater levels by 2100 (table A1). 

Simulated groundwater levels for the climate-prediction 

scenarios were calculated for two observation wells in the 

Beaufort/Gordon aquifers (layer 7)—CHN-101 and ON-265, in 

South and North Carolina, respectively (figs. A16 and A19). The 

simulated and observed groundwater levels at these sites match 

closely at well ON-265 but less closely at well CHN-101. The 

reference and policy scenarios for these wells produce essentially the same groundwater levels by 2100 (table A1). 

Simulated groundwater levels for the climate-prediction 

scenarios were calculated for two observation wells in the 

Peedee/Crouch Branch aquifer (layer 9)—AL-7 and S 22J9, 

in South and North Carolina, respectively (figs. A16 and A20). 

The simulated and observed groundwater levels at these sites 

match closely at well S 22J9 but less closely at well AL-7. The 

policy scenario for well AL-7 produces a minimum groundwater 

level about 0.6 ft higher than the reference scenario in 2100. For 

well S 22J6, the reference and policy scenarios produce essentially the same groundwater levels by 2100 (table A1).

Simulated groundwater levels for the 

climate-prediction scenarios were calculated 

for two observation wells in the Black Creek 

and McQueen Branch aquifer (layer 11)—

30AA04 and T 29G4, in Georgia and North 

Carolina, respectively (figs. A16 and A21). 

The simulated and observed groundwater 

levels at these sites match closely at well 

T 29G4 but less closely at well 30 AA04. 

The policy scenario for well 30 AA04 produces a minimum groundwater level 1.73 ft 

lower than the reference scenario. For well 

T 29G4, the reference and policy scenarios 

produce essentially the same groundwater 

levels by 2100 (table A1).

Simulated groundwater levels for the 

climate-prediction scenarios were calculated 

for two observation wells in the Upper Cape 

Fear/Charleston aquifer (layer 13)—FLO128 and M 30L3, in South and North Carolina, respectively (figs. A16 and A22). The 

simulated and observed groundwater levels 

at these sites are presented, and the results 

match closely at both wells. The reference 

and policy scenarios for these wells produce 

essentially the same groundwater levels by 

2100 (table A1).

These simulations of the potential effects of future climate variability indicate that groundwater resources in some 

places in the study area are susceptible to substantial fluctuations in groundwater levels. The more susceptible areas are in 

the inner Coastal Plain, and the less susceptible areas are in the 

outer Coastal Plain (fig. A1). Simulation results indicate that 

groundwater availability should not be substantially affected 

by potential future climate variations related to changes in precipitation rates in the outer Coastal Plain. Simulation results, 

however, do indicate that these potential precipitation variations could have an effect on groundwater availability in the 

inner Coastal Plain, especially if the precipitation rates tend to 

be lower than the reference scenario.

Groundwater Level Monitoring 

Network Analysis in North and 

South Carolina

Knowledge of current and historical groundwater levels is 

a key component of the assessment of groundwater availability in the North and South Carolina ACP. Without groundwater 

level data, it would be difficult to evaluate changes over time 

and, therefore, groundwater availability. Groundwater level 

data have been collected in the study area since about 1840, 

but networks of wells for collecting groundwater level data 

systematically were not established in the North and South 

Carolina ACP aquifers until 1931 in NC (Burchard, 1936) and 

Figure A15. Simulated net recharge rates for decadal stress periods from 2010 

to 2100 used in the climate variability scenarios for the Atlantic Coastal Plain 

groundwater flow model for North and South Carolina.

Figure A15. Simulated net recharge rates for decadal stress periods

 from 2010 to 2100 used in the climate variability scenarios for the

 Atlantic Coastal Plain groundwater flow model for North and

 South Carolina.

0.0009

0.0007

0.0008

0.0006

0.0005

0.0004

0.0003

0.0002

0.0009

0.0007

0.0008

0.0006

0.0005

0.0004

0.0003

0.0002

RECHARGE RA

TES, FOOT PER DAY

Reference Scenario Recharge Rates

Mean

Minimum

Maximum

Mean

Minimum

Maximum

YEAR

2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

Policy Scenario Recharge Rates
26 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A16. Locations of wells used in the climate variability scenarios in the Atlantic Coastal Plain of North Carolina, 

South Carolina, and Georgia.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Groundwater well screened in layer 3

Groundwater well screened in layer 5

Groundwater well screened in layer 7

Groundwater well screened in layer 9

Groundwater well screened in layer 11

Groundwater well screened in layer 13

EXPLANATION

AL-7

M 30L3

T 29G4 S 22J9

30AA04

ON-265

ON-227

HAM-83 COL-92

FLO-128

CHN-101

BFT-429

Figure A16. Locations of wells used in the climate variability scenarios in the Atlantic Coastal Plain of North Carolina, 

 South Carolina, and Georgia.

Atlantic

Ocean
Development and Changes to the Hydrologic Budget 27

Figure A17. Simulated and observed groundwater levels for observation wells in the Upper Floridan aquifer, 1900–2100, in the 

Atlantic Coastal Plain of South Carolina.

Figure A17. Simulated and observed groundwater levels for observation wells in the Upper Floridan aquifer, 

 1900-2100, in the Atlantic Coastal Plain of South Carolina.

22.95

22.90

22.85

22.80

22.75

22.70

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD 29

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

12.40

12.20

12.00

11.80

11.60

11.40

11.20

Policy minimum

Policy mean

Policy maximum

Policy minimum

Policy mean

Policy maximum

HAM–83 Policy BFT–429 Policy

25

20

15

10

5

0

1900 1910 1920 1930 1940

YEARS YEARS

1950 1960 1970 1980 1990 2000 2010 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

15

10

5

0

–5

–10

–15

Simulated

Observed

Simulated

Observed

HAM–83 Simulated and observed water levels BFT–429 Simulated and observed water levels

22.95

22.90

22.85

22.80

22.75

22.70

2100

12.40

12.20

12.00

11.80

11.60

11.40

11.20

HAM–83 Reference BFT–429 Reference

Reference minimum

Reference mean

Reference maximum

Reference minimum

Reference mean

Reference maximum

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100
28 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A18. Simulated and observed groundwater levels for observation wells in the Castle Hayne/Pungo River/Middle Floridan 

aquifer, 1900–2100, in the Atlantic Coastal Plain of North and South Carolina.

Figure A18. Simulated and observed groundwater levels for observation wells in the Castle Hayne/Pungo River/

 Middle Floridan aquifer, 1900-2100, in the Atlantic Coastal Plain of North and South Carolina.

9.40

9.38

9.36

9.34

9.32

9.30

9.28

9.26

9.24

9.22

9.20

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD 29

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

Policy minimum

Policy mean

Policy maximum

Policy minimum

Policy mean

Policy maximum

COL–92 Policy ON–227 Policy

10

8

6

4

2

0

–2

1900 1910 1920 1930 1940

YEARS YEARS

1950 1960 1970 1980 1990 2000 2010 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

37

35

33

31

29

27

25

Simulated

Observed

Simulated

Observed

COL–92 Simulated and observed water levels ON–227 Simulated and observed water levels

9.40

9.38

9.36

9.34

9.32

9.30

9.28

9.26

9.24

9.22

9.20

34.2776

34.2774

34.2772

34.2770

34.2768

34.2766

34.2764

34.2776

34.2774

34.2772

34.2770

34.2768

34.2766

34.2764

COL–92 Reference ON–227 Reference

Reference minimum

Reference mean

Reference maximum

Reference minimum

Reference mean

Reference maximum

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100
Development and Changes to the Hydrologic Budget 29

Figure A19. Simulated and observed groundwater levels for observation wells in the Beaufort/Gordon aquifer, 1900–2100, in the 

Atlantic Coastal Plain of North and South Carolina.

Figure A19. Simulated and observed groundwater levels for observation wells in the Beaufort/Gordon aquifer, 

 1900-2100, in the Atlantic Coastal Plain of North and South Carolina. 

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD 29

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

CHN–101 Policy ON–265 Policy

14

12

10

8

6

4

2

1900 1910 1920 1930 1940

YEARS YEARS

1950 1960 1970 1980 1990 2000 2010 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

16

14

12

10

8

6

4

2

CHN–101 Simulated and observed water levels ON–265 Simulated and observed water levels

13.108

13.106

13.104

13.102

13.100

13.098

13.096

13.094

13.092

13.090

13.108

13.106

13.104

13.102

13.100

13.098

13.096

13.094

13.092

13.090

14.9635

14.9630

14.9625

14.9620

14.9615

14.9610

14.9605

14.9635

14.9630

14.9625

14.9620

14.9615

14.9610

14.9605

CHN–101 Reference ON–265 Reference

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

Policy minimum

Policy mean

Policy maximum

Policy minimum

Policy mean

Policy maximum

Simulated

Observed

Simulated

Observed

Reference minimum

Reference mean

Reference maximum

Reference minimum

Reference mean

Reference maximum
30 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A20. Simulated and observed groundwater levels for observation wells in the Peedee/Crouch Branch aquifer, 

1900–2100, in the Atlantic Coastal Plain of North and South Carolina.

Figure A20. Simulated and observed groundwater levels for observation wells in the Peedee/Crouch Branch

 aquifer, 1900-2100, in the Atlantic Coastal Plain of North and South Carolina. 

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD 29

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

AL–7 Policy S 22J9 Policy

200

180

160

140

120

100

80

60

40

1900 1910 1920 1930 1940

YEARS YEARS

1950 1960 1970 1980 1990 2000 2010 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

30

25

20

15

10

5

0

AL–7 Simulated and observed water levels S 22J9 Simulated and observed water levels

168

166

164

162

160

158

156

154

152

150

168

166

164

162

160

158

156

154

152

150

24.67

24.66

24.65

24.64

24.63

24.62

24.61

24.60

24.59

24.58

24.67

24.66

24.65

24.64

24.63

24.62

24.61

24.60

24.59

24.58

AL–7 Reference S 22J9 Reference

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

Policy minimum

Policy mean

Policy maximum

Policy minimum

Policy mean

Policy maximum

Simulated

Observed

Simulated

Observed

Reference minimum

Reference mean

Reference maximum

Reference minimum

Reference mean

Reference maximum
Development and Changes to the Hydrologic Budget 31

Figure A21. Simulated and observed groundwater levels for observation wells in the Black Creek/McQueen Branch aquifer, 

1900–2100, in the Atlantic Coastal Plain of North Carolina and Georgia.

Figure A21. Simulated and observed groundwater levels for observation wells in the Black Creek/McQueen 

 Branch aquifer, 1900-2100, in the Atlantic Coastal Plain of North Carolina and Georgia.

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD 29

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

30AA04 Policy T 29G4 Policy

240

220

200

180

160

140

120

100

1900 1910 1920 1930 1940

YEARS YEARS

1950 1960 1970 1980 1990 2000 2010 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

90

80

70

60

50

40

30

20

10

0

30AA04 Simulated and observed water levels T 29G4 Simulated and observed water levels

270

260

250

240

230

220

210

270

260

250

240

230

220

210

81.08

81.06

81.04

81.02

81.00

80.98

80.96

80.94

80.92

81.08

81.06

81.04

81.02

81.00

80.98

80.96

80.94

80.92

30AA04 Reference T 29G4 Reference

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

Policy minimum

Policy mean

Policy maximum

Policy minimum

Policy mean

Policy maximum

Simulated

Observed

Simulated

Observed

Reference minimum

Reference mean

Reference maximum

Reference minimum

Reference mean

Reference maximum
32 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A22. Simulated and observed groundwater levels for observation wells in the Upper Cape Fear/Charleston aquifers, 

1900–2100, in the Atlantic Coastal Plain of North and South Carolina.

Figure A22. Simulated and observed groundwater levels for observation wells in the Upper Cape Fear/Charleston

 aquifers, 1900-2100, in the Atlantic Coastal Plain of North and South Carolina. 

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD 29

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

FLO–128 Policy M 30L3 Policy

100

80

60

40

20

0

–20

–40

–60

1900 1910 1920 1930 1940

YEARS YEARS

1950 1960 1970 1980 1990 2000 2010 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

90

80

70

60

50

40

30

20

10

FLO–128 Simulated and observed water levels M 30L3 Simulated and observed water levels

91.00

90.50

90.00

89.50

89.00

88.50

88.00

87.50

87.00

86.50

91.00

90.50

90.00

89.50

89.00

88.50

88.00

87.50

87.00

84.60

84.55

84.50

84.45

84.40

84.35

84.30

84.60

84.55

84.50

84.45

84.40

84.35

84.30

FLO–128 Reference M 30L3 Reference

1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

Policy minimum

Policy mean

Policy maximum

Policy minimum

Policy mean

Policy maximum

Simulated

Observed

Simulated

Observed

Reference minimum

Reference mean

Reference maximum

Reference minimum

Reference mean

Reference maximum
Groundwater Level Monitoring Network Analysis in North and South Carolina 33

1940 in SC (Warren, 1944). A compilation of groundwater 

level measurements for the NC ACP (Stephenson and Johnson, 

1912) included many individual groundwater level measurements from various ACP aquifers. 

Groundwater level compilations for North and South 

Carolina that include recent (2005–2006) and earlier groundwater levels can be found in Waters (2003), Webb (2006), 

Agerton and others (2007), and DePaul and others (2008). 

Substantial resources have been and continue to be expended 

in both States to monitor groundwater levels, but no quantitative effort has been made to assess the efficacy of the respective groundwater level network coverage.

Several studies have been conducted to evaluate groundwater level networks (Swain and Sonenshein, 1994; Olea and 

Davis, 1999; Prinos, 2005). Swain and Sonenshein (1994) 

used “confidence polygons” to define the monitoring area for 

each observation well in Broward County, Florida. The boundaries of these polygons were determined by the endpoints of 

radial lines from each well oriented toward other neighboring 

wells. The lengths of these lines were statistically estimated 

distances to the points at which groundwater levels can be 

predicted within specified criteria. The water-level data were 

analyzed for temporal variations, and the results of the spatial 

and temporal analysis were combined into a single coefficient 

that was used to evaluate the network and for future management decisions. Prinos (2005) took a similar approach using 

the Miami–Dade County, Florida, groundwater level network. 

While this type of analysis is appropriate at a county scale, it 

is not useful at a regional scale. Olea and Davis (1999) used 

a geostatistical approach to analyze the High Plains aquifer 

groundwater level observation network in western Kansas. In 

their study, the kriging standard deviation of the well locations 

was used as a measure of reliability in spatial estimation. The 

larger kriging standard deviations of the well locations were 

considered to be less reliable estimates, while the smaller 

kriging standard deviations were considered to be more 

reliable estimates. 

The groundwater level monitoring network of the North 

and South Carolina ACP was characterized in a method similar 

to that of Olea and Davis (1999). Continuous groundwater 

level well-location maps were generated for each aquifer 

using data from 609 current and historical wells: 174 wells 

completed in the Yorktown/Upper Floridan aquifers (layer 3, 

fig. A23), 87 wells completed in the Castle Hayne/Pungo 

River/Middle Floridan aquifers (layer 5, fig. A24), 73 wells 

completed in the Beaufort/Gordon aquifers (layer 7, fig. A25), 

97 wells completed in the Peedee/Crouch Branch aquifer 

(layer 9, fig. A26), 95 wells completed in the Black Creek/

McQueen Branch aquifer (layer 11, fig. A27), 52 wells completed in the Upper Cape Fear/Charleston aquifer (layer 13, 

fig. A28), and 31 wells completed in the Lower Cape Fear/

Gramling aquifer (layer 15, fig. A29). Groundwater level 

data for NC were obtained from the North Carolina Division 

of Water Resources (2007), and groundwater level data for 

Table A1.SC were obtained from Waters (2003). Groundwater level 

Statistics for analysis of effects of climate variability on groundwater levels in the Atlantic Coastal Plain of North and South Carolina.

[Water levels are in feet above NGVD 29]

Well 

number

Model 

layer Aquifer 

Reference—2010 Reference—2100 Policy—2010 Policy—2100

Minimum

 water 

level

Mean 

water 

level

Maximum

 water 

level

Minimum 

water 

level

Mean 

water 

level

Maximum 

water 

level

Minimum 

water 

level

Mean 

water 

level

Maximum 

water 

level

Minimum 

water 

level

Mean 

water 

level

Maximum 

water 

level

BFT-429 3 Upper Floridan 12.30 12.30 12.30 11.24 11.32 11.58 12.30 12.30 12.30 11.25 11.31 11.58HAM-83 3 Upper Floridan 22.94 22.94 22.94 22.72 22.76 22.90 22.94 22.94 22.94 22.73 22.76 22.90COL-92 5 Middle Floridan 9.38 9.38 9.38 9.22 9.25 9.37 9.38 9.38 9.38 9.23 9.26 9.37ON-227 5 Castle Hayne 34.28 34.28 34.28 34.28 34.28 34.28 34.28 34.28 34.28 34.28 34.28 34.28ON-265 7 Beaufort 14.96 14.96 14.96 14.96 14.96 14.96 14.96 14.96 14.96 14.96 14.96 14.96CHN-101 7 Gordon 13.10 13.10 13.10 13.09 13.09 13.11 13.10 13.10 13.10 13.09 13.09 13.11AL- 7 9 Lynches 157.56 157.56 157.56 152.38 155.76 166.62 157.56 157.56 157.56 152.93 155.73 166.62S 22J9 9 Peedee 24.66 24.66 24.66 24.66 24.66 24.66 24.59 24.59 24.59 24.59 24.59 24.59T 29G4 11 Black Creek 81.07 81.07 81.07 81.07 81.07 81.07 80.93 80.95 81.01 80.94 80.95 81.0130AA04 11 McQueen Branch 231.85 231.85 231.85 218.11 229.11 265.42 231.85 231.85 231.85 219.84 228.85 265.42FLO- 128 13 Charleston 87.92 87.92 87.92 87.04 87.80 90.35 87.92 87.92 87.92 87.16 87.79 90.35M 30L3 13 Upper Cape Fear 84.55 84.55 84.55 84.34 84.34 84.36 84.55 84.55 84.55 84.34 84.34 84.36
34 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A23. Prediction standard error of the groundwater level monitoring network in the Yorktown/Upper Floridan aquifers in the 

Atlantic Coastal Plain of North and South Carolina.

EXPLANATION

Standard error prediction, in feet

1

2

3

4

Extent of Yorktown/Upper

 Floridan aquifers

Well locations

Figure A23. Prediction standard error of the groundwater level monitoring network in the Yorktown/Upper Floridan 

aquifers in the Atlantic Coastal Plain of North and South Carolina.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

Yorktown

aquifer

Upper Floridan

aquifer
Groundwater Level Monitoring Network Analysis in North and South Carolina 35

Figure A24. Prediction standard error of the groundwater level monitoring network in the Castle Hayne/Pungo River/Middle 

Floridan aquifers in the Atlantic Coastal Plain of North and South Carolina.

EXPLANATION

Standard error prediction, in feet

1

2

3

4

Extent of Castle Hayne/Pungo

 River and Middle Floridan

 aquifers

Well locations

Figure A24. Prediction standard error of the groundwater level monitoring network in the Castle Hayne/Pungo River

 /Middle Floridan aquifers in the Atlantic Coastal Plain of North and South Carolina.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

Castle Hayne/Pungo

River aquifer

Middle Floridan

aquifer
36 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A25. Prediction standard error of the groundwater level monitoring network in the Beaufort/Gordon aquifers in the Atlantic 

Coastal Plain of North and South Carolina.

EXPLANATION

Standard error prediction, in feet

1

2

3

4

5

Extent of Beaufort/Gordon aquifers

Well locations

CHARLES

BRADFORD

Fall

Line

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Figure A25. Prediction standard error of the groundwater level monitoring network in the Beaufort/Gordon aquifers in

 the Atlantic Coastal Plain of North and South Carolina.

Atlantic

Ocean

Beaufort

aquifer

Gordon

aquifer

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean
Groundwater Level Monitoring Network Analysis in North and South Carolina 37

Figure A26. Prediction standard error of the groundwater level monitoring network in the Peedee/Crouch Branch aquifer in the 

Atlantic Coastal Plain of North and South Carolina.

EXPLANATION

Standard error prediction, in feet

3

4

5

Extent of Peedee/Crouch Branch aquifer

Well locations

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

Peedee/Crouch Branch

aquifer

Figure A26. Prediction standard error of the groundwater level monitoring network in the Peedee/Crouch Branch aquifer 

 in the Atlantic Coastal Plain of North and South Carolina.
38 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A27. Prediction standard error of the groundwater level monitoring network in the Black Creek/McQueen Branch aquifer in 

the Atlantic Coastal Plain of North and South Carolina.

EXPLANATION

Standard error prediction, in feet

4

5

6

Extent of Black Creek/McQueen

 Branch aquifer

Well locations

Figure A27. Prediction standard error of the groundwater level monitoring network in the Black Creek/McQueen

 Branch aquifer in the Atlantic Coastal Plain of North and South Carolina.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

Black Creek/McQueen Branch

aquifer
Groundwater Level Monitoring Network Analysis in North and South Carolina 39

Figure A28. Prediction standard error of the groundwater level monitoring network in the Upper Cape Fear/Charleston aquifer in the 

Atlantic Coastal Plain of North and South Carolina.

EXPLANATION

Standard error prediction, in feet

Extent of Upper Cape Fear/Charleston

 aquifer

Well locations

4

3

5

6

7

CHARLES

BRADFORD

Fall

Line

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Upper Cape Fear/Charleston

aquifer

Figure A28. Prediction standard error of the groundwater level monitoring network in the Upper Cape Fear/Charleston

 aquifer in the Atlantic Coastal Plain of North and South Carolina.
40 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure A29. Prediction standard error of the groundwater level monitoring network in the Lower Cape Fear/Gramling aquifer in the 

Atlantic Coastal Plain of North and South Carolina.

EXPLANATION

Standard error prediction, in feet

4

3

5

Extent of Lower Cape Fear/Gramling

 aquifer

Well locations

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

Lower Cape Fear/Gramling

aquifer

Figure A29. Prediction standard error of the groundwater level monitoring network in the Lower Cape Fear/Gramling 

 aquifer in the Atlantic Coastal Plain of North and South Carolina.
Groundwater Level Monitoring Network Analysis in North and South Carolina 41

prediction maps were created by using ordinary kriging with 

first-order trend removal (figs. A23–A29).

Prediction standard-error maps were produced from the 

predicted water-level surface maps to quantify the uncertainty 

of prediction across the aquifer extent (figs. A23–A29). The 

prediction standard-error maps show the spatial distribution 

of the range of error for the predicted surface (in this case, 

potentiometric surface) within each mapped contour interval. 

Note that the prediction standard-error maps tend to have high 

errors when they are generated from data with wide ranges of 

water-level altitudes and (or) data with clustered distributions 

of wells and (or) large areas void of wells.

The prediction standard-error maps, which show the 

relative accuracy and completeness of the water-level network, 

can be used to help identify areas with high uncertainties 

associated with water-level predictions (figs. A23–A29). The 

yellow areas shown on the maps have the smallest errors, and 

the networks in these areas represent the system well; the gray 

areas have the largest errors, and the networks in these areas 

do not represent the system well.

Overall, the predicted mean standard errors are lower 

in the shallow aquifers of the North and South Carolina 

ACP than in the deep aquifers. The predicted mean standard error for water levels was lowest for the Yorktown/

Upper Floridan aquifers (layer 3, fig. A23) and the SC part 

of the Castle Hayne/Pungo River/Middle Floridan aquifers 

(layer 5, fig. A24) (mean standard error between 10 and 18 ft 

for layer 3, table A2). The predicted mean standard error for 

water levels was higher in the NC part of the Castle Hayne/

Pungo River/Middle Floridan aquifers (layer 5, fig. A24) and 

the Beaufort/Gordon aquifers (layer 7, fig. A25), and in the NC 

part of the Peedee/Crouch Branch aquifer (layer 9, fig. A26) 

(mean standard error between 29 and 35 ft, table A2). The predicted mean standard error for water levels was highest in the 

Black Creek/McQueen Branch aquifer (layer 11, fig. A27) and 

the Upper Cape Fear/Charleston aquifer (layer 13, fig. A28) 

(mean standard errors of 48 and 55 ft, respectively, table A2). 

The predicted mean standard error for the Lower Cape Fear/

Gramling aquifer (layer 15, fig. A29) is 31.07 ft, substantially 

less than those for the Black Creek/McQueen Branch aquifer 

(layer 11) and Upper Cape Fear/Charleston aquifer (layer 13, 

table A2). The difference in the predicted mean standard error 

is most likely because the range of water-level altitudes in the 

Lower Cape Fear/Gramling aquifer is less than the range of 

water-level altitudes in the Black Creek/McQueen Branch and 

Upper Cape Fear/Charleston aquifers. Water-level altitudes in 

the Lower Cape Fear/Gramling aquifer, therefore, have less 

uncertainty associated with them. 

The groundwater level network in NC has a more 

comprehensive coverage than the groundwater level network 

in SC, especially in the deep aquifers—the Black Creek/

McQueen Branch, Upper Cape Fear/Charleston, and Lower 

Cape Fear/Gramling aquifers. The predicted mean standard 

error for water levels in these deeper aquifer layers, therefore, 

generally is lower in NC than in SC. The groundwater level 

network has been a priority of the State of NC for decades; 

efforts have been made to acquire property, install observation 

wells, and collect either continuous or intermittent groundwater levels. By contrast, only a few sites in the western 

part of the SC ACP contain multiple wells for monitoring 

groundwater levels in all of the aquifers present at these 

locations. Most of the other groundwater level observation 

wells are single wells, some of which were installed for other 

purposes, such as water supply, and may be screened across 

several aquifers.

Overall, the groundwater level monitoring networks 

in North and South Carolina provide better coverage in the 

shallower aquifers—the Yorktown/Upper Floridan; Castle 

Hayne/Pungo River/Middle Floridan; Beaufort/Gordon; and 

Peedee/Crouch Branch aquifers—than in the deeper aquifers. 

Table A2. Prediction standard-error statistics for the analysis of the groundwater level 

monitoring networks in the Atlantic Coastal Plain of North Carolina, South Carolina, and 

parts of eastern Georgia and southern Virginia.

[mi2, square mile; ft, feet]

Model 

layer

Area,

in mi2

Minimum, 

in ft

Maximum, 

in ft

Range, 

in ft

Mean, 

in ft

Standard 

deviation, 

in ft

L3 East 20,982 0.40 15.94 15.55 10.06 2.83

L3 West 20,812 0.45 31.41 30.96 18.38 7.25

L5 East 25,219 13.64 46.93 33.29 35.20 5.58

L5 West 16,891 8.66 14.75 6.09 12.69 1.10

L7 East 15,160 2.20 37.53 35.33 30.51 5.51

L7 West 25,245 19.14 41.57 22.43 29.42 6.47

L9 49,916 22.94 43.17 20.23 31.59 5.09

L11 51,079 36.67 59.35 22.68 48.51 3.95

L13 41,889 22.47 80.71 58.24 55.35 12.78

L15 32,024 20.36 46.36 26.00 31.07 6.05
42 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Predicted groundwater levels in the shallower aquifers generally were accurate to within plus or minus 0 to 40 ft, while 

predicted groundwater levels in the Black Creek/McQueen 

Branch and Upper Cape Fear/Charleston aquifers generally 

were accurate to within plus or minus 30 to 80 ft. In addition, 

the groundwater level monitoring network in NC is more accurate for regional groundwater level coverage than the network 

in SC for the deeper aquifers—Black Creek/McQueen Branch; 

Upper Cape Fear/Charleston; and Lower Cape Fear/Gramling aquifers—because of the more comprehensive coverage. 

Regional potentiometric maps derived from the groundwater 

level data networks in North and South Carolina need to be 

used with the understanding of the strengths and weaknesses 

of the network. Continuous groundwater level networks are a 

key factor in determining trends in groundwater availability in 

the study area. 

Summary and Conclusions

The ACP aquifers and confining units are valuable 

natural resources that provide large quantities of high-quality 

groundwater for domestic and municipal supply, irrigation, 

and industrial uses. This chapter provides a regional analysis 

of groundwater availability for the area that will be useful for 

water-resource planning and management on a regional scale. 

Overall, the ACP of North and South Carolina can be 

divided into the inner and outer Coastal Plain areas, which 

have different types of groundwater flow systems. Surfacewater features, such as rivers and streams, control the 

groundwater flow patterns in the inner Coastal Plain. In this 

area, groundwater discharge from the aquifers provides large 

quantities of baseflow to the rivers and streams. Groundwater 

flow in the inner Coastal Plain typically is characterized by 

relatively steep gradients and short flow paths. Groundwater 

flow in the outer Coastal Plain typically is sluggish, with long, 

regional to subregional flow paths. Hydraulic conductivities in 

the outer Coastal Plain generally are good and result in most 

areas being able to produce large volumes of high-quality 

groundwater. Many areas of the outer Coastal Plain are underlain by several productive aquifers, which provide groundwater users with choices in production rates and water quality. 

Overall, groundwater availability in the ACP aquifers 

and confining units of North and South Carolina is good in 

that supply generally exceeds demand. However, problems 

can occur locally when concentrated groundwater withdrawals 

lower groundwater levels to an extent that supply in specific 

locations is threatened.

A regionalized hydrologic simulation tool (a calibrated 

groundwater flow model) developed for this study (presented 

in Chapter C of this report) was used to assess groundwater 

availability with detailed groundwater budgets and also used 

to evaluate potential groundwater level responses to potential 

future climate variability. The regional model is able to assess 

how the system responds to the cumulative effects of human 

and environmental stresses at the aquifer-wide scale. For more 

detailed intermediate- and local-scale groundwater availability questions, the regional model provides a framework from 

which smaller-scaled issues can be examined. 

The analysis of regional-scale groundwater budgets 

indicated that the largest component of the predevelopment 

and 2004 water budgets is vertical interlayer flow. The next 

largest budget component is the volume of water that flows 

into and out of the simulated specified-head boundaries. The 

total inflow through all specified-head boundaries is approximately equal to the outflow and is approximately 3,700 and 

3,600 Mgal/d for the predevelopment and 2004 model budgets, respectively. Two other sources of water include a specified recharge rate of about 1,230 Mgal/d for predevelopment 

and 2004, and inflow from rivers at 13.5 Mgal/d for predevelopment and 16.4 Mgal/d for 2004. Water is removed from the 

model area by discharge to rivers at rates of 1,051 Mgal/d for 

predevelopment and 964 Mgal/d for 2004. Discharge of water 

through pumping wells is another component of flow for the 

model and accounts for 482 Mgal/d in the 2004 water budget. 

Additionally, during the time simulated by the model (1900–

2004), water enters and is released from storage. For the 2004 

water budget, rates of flow into and out of storage are 43 and 

56 Mgal/d, respectively.

In addition to the regional-scale groundwater flow 

budget, the budgets of three sub-areas of the study area were 

analyzed in detail. The North Carolina Central Coastal Plain 

Capacity Use Area is a 15-county area in which groundwater levels have been declining since before 1960 in the 

Black Creek and Upper Cape Fear aquifers as a result of 

large-scale withdrawals. 

In the Sumter, South Carolina, area, a large wellfield 

has withdrawn municipal drinking water from the Cretaceous 

aquifers underlying the town for more than 50 years. These 

withdrawals have only slightly modified the predevelopment groundwater flow system of the area with no substantial 

changes in groundwater storage. The aquifers underlying the 

Sumter area have relatively good groundwater transmission 

properties, and the area is adjacent to the inner Coastal Plain 

where direct recharge is available. 

The Aiken, South Carolina, area, has received most of its 

potable water needs from the Cretaceous aquifers underlying 

the city. These withdrawals have produced a greater overall 

downward flow gradient in the system compared to predevelopment conditions and have decreased streamflow to a 

small extent.

The calibrated groundwater flow model (described in 

Chapter C of this report) was used to simulate potential 

effects on groundwater levels resulting from possible temporal 

variations in precipitation rates from 2010 to 2100. Temporal variations in precipitation rates from 2010 to 2100 were 

determined using an ensemble of global climate models. The 

predicted precipitation variability was converted to a specified 

net recharge rate for the groundwater flow model. Varying the 

recharge rates produces changes in groundwater levels in the 

higher altitudes of the model area where recharge is applied. 
Summary and Conclusions 43

The recharge variations produce little changes in groundwater 

levels in the model areas downdip and away from the area of 

active recharge. 

The groundwater level monitoring networks of the 

North and South Carolina ACP were evaluated by kriging the 

standard deviation of the network well locations as a measure 

of reliability in spatial estimation. The larger kriging standard 

deviations of the well locations were considered the less reliable estimates, while the smaller kriging standard deviations 

of the well locations are considered the more reliable estimates. Continuous groundwater level well location maps were 

generated for each aquifer using data from 609 current and 

historic wells. The predicted mean standard error was lower in 

the shallower aquifers of the North and South Carolina ACP 

than in the deeper aquifers. The groundwater level network 

in North Carolina has a more comprehensive coverage than 

the groundwater level network in South Carolina, especially 

in the deep aquifers—Black Creek/McQueen Branch, the 

Upper Cape Fear/Charleston, and Lower Cape Fear/Gramling 

aquifers. The predicted mean standard error for water levels 

in these deep aquifers, therefore, generally is lower in North 

Carolina than in South Carolina.

Many future challenges will face water-resource managers in the ACP of NC and SC with only a few primary ones 

discussed here. Demands for potable water from a rapidly 

growing population, especially in the coastal areas, are of primary concern. Also of concern are the potential effects on the 

ecosystem, especially on fragile wetlands and other habitats, 

from projected increasing groundwater withdrawals over the 

coming years. Lateral saltwater encroachment is occurring in 

at least one place within the study area—the northeastern end 

of Hilton Head Island, SC, in the Upper Floridan aquifer. 

In order to quantify groundwater availability and to effectively evaluate the sustainability of the groundwater system, 

it is important to continually update the conceptual hydrologic model and maintain and enhance current tools used to 

understand the system response to a multitude of stresses. An 

iterative process that enables monitoring, analysis of basic data, 

and then implementation of selected management practices on 

a continual basis can provide insights to assist decision makers 

now and in the future. Awareness and integration of newly 

available geologic and hydrologic information, improvements 

to the existing groundwater monitoring networks, and technical 

advancements and capabilities associated with the simulation 

tools are examples of enhancements that could be made over 

time to assist water managers with decision making processes. 

Examples of current (2009) activities that enhance the 

understanding of the regional hydrologic system include 

the following: 

1. The South Carolina Water Plan (Badr and others, 2004) 

contains a detailed plan for a comprehensive groundwater 

quality and level monitoring network. Implementation 

of this plan would provide basic data for future hydrologic simulations. 

2. The North Carolina Water Supply Plan (North Carolina 

Division of Water Resources, 2001) contains recommendations for management of the groundwater level declines 

in the North Carolina Central Coastal Plain Capacity Use 

Area. These recommendations could be implemented to 

improve the sustainability of the aquifers. Recent revisions to the plan call for approaches to analyze the cumulative effects of projected groundwater withdrawals. The 

plan calls for using hydrologic models as the primary tool 

to make these analyses. 

3. The South Carolina Department of Health and Environmental Control has expanded the number of Capacity Use 

Areas within the South Carolina Coastal Plain to four. 

This program could be expanded to all of the SC Coastal 

Plain counties to better manage the groundwater resources 

of these areas.
44 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

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the central Coastal Plain, North Carolina: U.S. Geological 

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101 p.

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systems of the United States for predevelopment and development conditions: U.S. Geological Survey Professional 

Paper 1425, 34 p.

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Geochemistry of the northern Atlantic Coastal Plain aquifer 

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57 p.

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Water Resources, 33 p.

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system: U.S. Geological Survey Professional Paper 1404–I, 

106 p. + 24 pls.

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Creeping Swamp watershed, North Carolina, with reference 

to potential effects of stream channelization: U.S. Geological Survey Water-Resources Investigations Report 77–26, 

54 p.

Introduction

This chapter focuses on the hydrogeologic framework 

of the aquifers and confining units composing the Atlantic Coastal Plain (ACP) of North Carolina (NC) and South 

Carolina (SC). This is an area of approximately 47,500 square 

miles (mi2), extending from the Fall Line to the present-day 

coastline, and from southern Virginia (VA) to eastern Georgia 

(GA) (fig. B1). The study area encompasses several formal 

aquifer systems contained within the sediments of the ACP. 

Aquifers and confining units located in the ACP of North 

Carolina and Virginia are part of the Northern ACP aquifer 

system (Trapp and Meisler, 1992). In South Carolina, aquifers 

and confining units in the ACP sediments are part of either the 

Southeastern Coastal Plain aquifer system (Miller, 1992) or 

the Floridan aquifer system (Miller, 1986). As the study area 

crosses the boundaries of these formal aquifer systems, no new 

regional-scale formal aquifer systems are designated, and the 

units under study will be referred to as the North and South 

Carolina ACP aquifers and confining units. 

Included within this chapter is (1) a description of the 

hydrogeologic framework of the ACP aquifers and confining 

units of North and South Carolina in terms of its geometry 

(thickness, dip, and lateral extent), lithology and texture, 

hydrologic properties, and geophysical-log response; (2) an 

explanation of the connection of the newly defined SC hydrostratigraphic units, allostratigraphic formations, and biostratigraphic zones to the hydrostratigraphic units defined by Aucott 

and others (1987), Colquhoun and others (1983), and Miller 

and Renken (1988); (3) an extension of the SC hydrostratigraphic nomenclature and hierarchical classification scheme 

that was introduced at the U.S. Department of Energy Savannah River Site (SRS) (Aadland and others, 1995) to other 

regions of the SC ACP; and (4) a correlation of hydrostratigraphic units across the NC–SC border. Moreover, a generalized description of the NC framework is described along with 

a more detailed description of the SC framework. Because the 

SC framework presented in this report is new, more detail is 

being supplied for SC than for the NC framework discussion.

Hydrostratigraphic correlations in North and South 

Carolina have historically been based on different types of 

data. In NC, over the past 40 years, the State has installed an 

extensive network of groundwater monitoring wells and has 

collected a database of continuous and synoptic groundwater 

level data (Robertson, 2007). The network contains 548 wells 

at 181 stations, most of which are in the ACP. These sites have 

wells screened in all of the major ACP aquifers present at the 

sites. These groundwater data have allowed for the delineation 

of aquifer boundaries by providing the means to determine 

where substantial differences in hydraulic head occur or by 

allowing a comparision of long-term groundwater level variations at various screen depths. South Carolina has no comparable long-term network of well clusters except in a small area 

of the western SC ACP (Agerton and others, 2007). However, 

the subsurface stratigraphic framework of SC is better understood than that of NC owing to an extensive coring program 

conducted by the U.S. Department of Energy and the South 

Carolina Water Resources Commission from 1984 to 1995 

(Aadland and others, 1995), and to an extensive U.S. Geological Survey (USGS) coring program conducted from 1995 

to 2000. Without a comprehensive network of groundwater 

observation wells, SC has relied on stratigraphic correlation 

to define the aquifers and confining units of the Coastal Plain. 

None of the previous studies of the NC–SC ACP area have 

attempted to establish the correlation of hydrogeologic units 

across the NC–SC State line.

Separate interpretations of the hydrogeologic frameworks 

for the North and South Carolina ACP have evolved during the 

past 100 years (Sloan, 1908; Clark and others, 1912). More 

recently, the NC regional hydrogeology has been described in 

several publications by Winner and Coble (1996) and Lautier (1998a, b, 2002, 2006). Winner and Coble (1996) used 

data that were available before 1989. Trapp and Horn (1997) 

included the NC ACP hydrogeology in a groundwater atlas. 

Lautier (1998a, b, 2002, 2006) sought to provide more detailed 

hydrogeologic framework interpretations covering three different multi-county areas, and used data collected before and after 

1989. These recent efforts have included many NC monitoring network station observation wells (fig. B2) that have been 

installed since 1989 and corehole information from the USGS 

Coastal Carolina Project (U.S. Geological Survey, 2007). 

However, the entire NC Coastal Plain was not covered by 

these reports (Lautier, 1998a, b, 2002, 2006). 

Chapter B. Hydrogeologic Framework of the Atlantic 

Coastal Plain, North and South Carolina

By Joseph A. Gellici1 and Jeff C. Lautier2

1

 South Carolina Department of Natural Resources, Land, Water and 

Conservation Division, Hydrology Section, Columbia, SC.

2

 North Carolina Department of Environment and Natural Resources, 

Division of Water Resources, Raleigh, NC.
50 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B1. Location of the study area, major geological features, and the Atlantic Coastal Plain of North and South Carolina.

Norfolk

Arch

Unnamed

Arch

Cape Fear

Arch

Gulf

Trough

Albemarle

Embayment

Albemarle

Sound

Southeast Georgia

Embayment

Atlantic

Ocean

Horry

Aiken

Wake

Burke

Pitt Hyde

Berkeley

Bladen

Pender

Nash

Robeson

Sampson

Duplin

Colleton

Onslow

Columbus

Laurens

Bertie

Orangeburg

Jasper

Sumter

Kershaw

Long

Florence

Johnston

Emanuel

Bulloch

Hoke

Moore

Cumberland

Richland

Jones

Screven

Brunswick

Bryan

Harnett

Lexington

Sussex

Hampton

Craven

Clarendon

Martin Dare

Gates

Barnwell

Washington

Dillon

Lenoir

Bibb

Beaufort

Wilson

Wayne

Greene

Suffolk

Dinwiddie

Edgecombe

Halifax

Bamberg

Hertford

Williamsburg

Chesterfield

Toombs

Marlboro

Charleston

Tattnall

Carteret

Twiggs

Dorchester

Darlington

Lee

Tyrrell Washing- ton

Southampton

Effingham

McIntosh

Northampton

Wilkinson Jenkins

Pamlico

Allendale

Johnson

Scotland

Evans

Candler

Chesapeake

Chowan

Greensville

Treutlen

Isle of

Wight

Currituck

Camden

Perquimans

Pasquotank

Virginia

Beach

Glascock

New

Hanover

CHARLES

BRADFORD

Prince

George

Lee

Surry

Chesterfield

Marion

Georgetown

Calhoun

Beaufort

Jefferson

Richmond

Houston

Baldwin

Montgomery

Chatham

Liberty

Richmond

Hilton

Head

Mount

Pleasant

Orangeburg

Cope Holly

Hill

Mount Holly

Kiawah Island

Fripp

Island

Tybee Island

Edisto

Beach

Wadmalaw

Island

Midville

Dublin

Appleton

Eutaw

Springs Saint

Stephens

Ridgeland

Myrtle

Beach

Columbia Florence

Fort Motte

Rhems

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Blue Ridge/Ridge and Valley

Piedmont

Sand Hills

Inner Coastal Plain

Outer Coastal Plain

U.S. Department of Energy Savannah

 River Site

EXPLANATION

PHYSIOGRAPHIC PROVINCES

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Figure B1. Location of the study area, major geological features, and the Atlantic Coastal Plain of

 North and South Carolina.
Introduction 51

Figure B2. Location of observation wells and boreholes in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia (see Appendix B1 for more well information).

Fall

Line

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

Observation well

Continuous borehole

Figure B2. Location map of hydrostratigraphic boreholes in the Atlantic Coastal Plain of North and South Carolina

 and parts of Virginia and Georgia, 2007 (see Appendix 1 for more well information).

61

71

77

93

104

103

110

78

59

58 57

56

70

60

53 82

49 48

38

30

37

43

46

39

47

45 44

33

36

31

35

32

50 51

55

67

68

66

69

76

92 91 87

88

103

109 102

89

90 101

282

276

273

272

271

270

269

268

190

189

188

187

186

185

42

105

182 183

115

181

180

179

178

177

176

128 120

26

175

174

122

173

172

171

170

169 170

167

165

166

164

163

162

161 160

159

158

155

154

153

152

151 150

149

148

309

308

307

306

305

304

303

302

301

300

399

297

296

295

294

293

292

291

290

288

287

286

283 278

277

251

252 251

250

143

107

12

111

73

22

130

116

118

86

126

133 129

146

10

249 248

247

246

28

9

267

245

244 243

266

265

34

264

101

263

75

241

240

239 235

112

63

13

7 133

134

2

120

233

232

230

229

262

261

227

226

224

20

24 23

223

141

222

221

231 220

62

219

218

260

217 216

259

258

257

256

255

254

210

208

140 142

109

6

124

19

3

21

15

27

4

18

201

200

198

197 196

194 193

126

275 276

16

11

279

284

285 280

281 289

5

25

64

65 54

121 99

127

74

117

123

106

136

145 8

146 147 192 132

14 199

215

214

205

209 203 207

206 204 195

225

202

184

242

236

234 237

228

158

238

157

191

212

213211

139

135

138

137 1

97

79

94

85

96 95

83

81

84

52

80

72

114

17

40

41

See inset

for

well locations

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean
52 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

The two most commonly used statewide hydrogeologicframework studies of the SC ACP are those of Colquhoun 

and others (1983) and Aucott and others (1987). The report 

by Colquhoun and others is, at its core, a delineation of the 

lithostratigraphic formations of the ACP. Aquifers were superimposed onto their lithostratigraphic cross sections and were 

named after prominent geologic formations composing the 

system; however, no structure contour or thickness maps of 

the aquifers and confining units were provided. Consequently, 

Colquhoun and others (1983) has been used primarily in 

geological studies rather than in hydrological studies. Aucott 

and others (1987), on the other hand, emphasizes hydrostratigraphic units and provides structure contour and thickness 

maps of the aquifers; therefore, that report has been used 

primarily in hydrological studies such as Campbell and van 

Heeswijk (1996). Both reports have been used and cited extensively (Logan and Euler, 1989; Newcome, 1989; Rodriguez 

and others, 1994; Castro and others, 1995; Hockensmith and 

Waters, 1997, 1998; Hockensmith, 2001).

The work described in this report is a cooperative effort 

among the NC Division of Water Resources, the SC Department of Natural Resources, and the USGS to describe the 

current (2007) state of knowledge of the hydrostratigraphy 

and groundwater conditions of the NC and SC ACP. Another 

major objective of the study is the attempt to link the NC and 

SC hydrostratigraphic units across the State border. Chapter C

of this report describes a calibrated groundwater flow model 

of the NC and SC ACP aquifers and confining units that was 

constructed from the hydrostratigraphic framework described 

in this chapter. Uses of the model to simulate detailed groundwater flow budgets and potential future recharge variations 

from climate change are described in Chapter A. 

The NC hydrostratigraphic framework is based on previous publications by Lautier (1998a, b, 2002, 2006) and Winner 

and Coble (1996). However, major revisions were made to 

the Aucott and others (1987) SC hydrogeologic framework. 

These revisions were primarily based on recent data collected during the drilling of 38 continuous coreholes within 

the SC ACP (fig. B2) along with geophysical logs and drill 

cutting descriptions from 68 water wells. Revisions to the SC 

hydrostratigraphic framework also are based on work done by 

Aadland and others (1995) at the SRS in western SC (fig. B1). 

This work introduced the concept of hydrostratigraphic units 

as provinces, systems, units, and zones to the SC ACP. 

Since Aucott and others (1987) was published, much 

additional groundwater and stratigraphic data have become 

available for the SC ACP, mainly from coreholes, well-cluster 

sites, and water wells. A series of coreholes and well clusters were drilled at the SRS in Aiken and Barnwell Counties 

(fig. B1) during the mid- to late-1980s (Bledsoe, 1984, 1987, 

1988; Bledsoe and others, 1990). Coreholes and well clusters 

also were drilled just outside the borders of the SRS in Aiken, 

Barnwell, and Allendale Counties during the late 1980s and 

early 1990s (Logan, 1987; Kuntz and Griffin, 1988; Gellici 

and others, 1995). Sidewall cores were collected from a 

2,900-ft test hole (JAS-426) in Jasper County (Self-Trail and 

Bybell, 1997) and from a 3,833-ft test hole in Beaufort County 

(Temples and Englehardt, 1997). Five cores were drilled in 

Sumter County to characterize a landfill in the county (Prowell, 1993; Vroblesky, 1994). A core was drilled for an aquifer 

storage-and-recovery study in Horry County (Castro and 

others, 1995). Two coreholes were drilled in Darlington and 

Florence Counties that were used for developing a groundwater flow model (Falls, 1994; Rodriguez and others, 1994). 

Two coreholes were drilled in Aiken County for a watersupply study (Krambis, 2000; Harrelson and others, 2002; 

Gellici, 2007b), and two were drilled in Charleston County for 

an aquifer storage-and-recovery study (Campbell and others, 1997; Petkewich and others, 2004). A 1,000-ft corehole 

was drilled in Charleston County for a stratigraphic study 

(Bybell and others, 1998). Other deep cores were drilled as 

part of the Coastal Carolina Project, which was a collaboration 

between the South Carolina Department of Natural Resources 

(SCDNR) and the USGS, including two coreholes in Orangeburg County (Gellici, 2007a), two in Richland County, and 

a single core in each of the following counties: Berkeley, 

Charleston, Chesterfield, Colleton, Darlington, Dillon, Horry, 

Lee, Lexington, and Sumter (fig. B2).

Also of importance are original cores used by Aucott 

and others (1987) that have since been re-sampled for paleontological analyses and stratigraphically revised. These 

re-sampled cores include the revised Cretaceous stratigraphy 

of the USGS-Clubhouse Crossroads #1 (DOR-0052) core 

in Dorchester County (Gohn, 1992), the revised Cretaceous 

stratigraphy of the USGS-St. George No. 1 (DOR-211) core 

in Dorchester County (Self-Trail and Gohn, 1996), the revised 

Tertiary stratigraphy of the USGS-Pregnall No. 1 (DOR-208) 

core in Dorchester County (Edwards and others, 1997), and 

additional samples and revisions of the USGS-Brittons Neck 

(MN-0078) core in Marion County (D.C. Prowell, U.S. Geological Survey, written commun., 2002). 

Hydrogeologic frameworks of the ACP in VA and GA 

were used in the study, primarily for selection of appropriate 

groundwater flow model boundaries for the model presented in 

Chapter C of this report. Inclusion of these boundaries requires 

that areas of southern VA and eastern GA be included in this 

study. In VA, the hydrogeologic frameworks of Meng and Harsh 

(1988) and McFarland and Bruce (2006) were correlated with 

the hydrogeologic framework of the NC Coastal Plain. In GA, 

the hydrogeologic frameworks of Brooks and others (1985), 

Clark and others (1985), and Faye and Mayer (1997) were used 

to extend the new SC hydrostratigraphy into the study area.
Introduction 53

Previous Investigations

Of the numerous published reports involving the mapping 

and characterization of the NC Coastal Plain hydrogeologic 

framework, only studies of regional importance are mentioned 

here. Stephenson and Johnson (1912) conducted the first 

comprehensive survey of the groundwater resources of the NC 

Coastal Plain. LeGrand (1964) presented a broad review of the 

hydrogeology of the Gulf and ACP, and outlined a hydrogeologic classification based on concepts of groundwater recharge 

and discharge conditions. Brown and others (1972) divided the 

ACP sediments from New York to NC into 17 chronostratigraphic units and mapped lithofacies and intrinsic permeability 

based on interpretations of geophysical logs and well cuttings. 

Nelson (1964) presented a multi-county study of the Swanquarter area of the NC Coastal Plain, which mapped the major 

aquifers and confining units and defined the contemporaneous 

potentiometric surfaces. Narkunas (1980) presented a multicounty groundwater study and hydrogeologic framework of 

the central part of the NC Coastal Plain that used data from 

NC monitoring network wells installed up to that time. Winner and Lyke (1989) presented a hydrogeologic framework 

study of the Cretaceous aquifers of the central part of the NC 

Coastal Plain. Winner and Coble (1996) provided a hydrogeologic framework study of the entire NC Coastal Plain, using 

data that were available up to 1989. Lautier (1998a, b, 2002, 

2006) provided a hydrogeologic framework and assessment 

of the groundwater resources and conditions in three areas of 

the NC Coastal Plain. The following recent studies, although 

more localized, are important in delineating the hydrostratigraphy of the NC Coastal Plain: (1) Self-Trail and others (2004a) 

provide descriptions of the physical stratigraphy and geophysical logs from a corehole in Bladen County, NC (figs. B1, B2); 

(2) Weems and others (2007) provide descriptions of the 

physical stratigraphy and geophysical logs from a corehole in 

Bertie County, NC.

Geologic and hydrologic investigations of the SC ACP 

date back to at least 1843 when Ruffin (1843) published an 

agricultural survey of the State that included geological interpretations. Sloan (1907a, b) summarized the geology and mineral resources of SC. Darton (1896) investigated the artesian 

wells of North and South Carolina. Cooke (1936) published 

a geologic map and geological descriptions of the SC ACP. 

A report has been written about the groundwater resources of 

every County in the SC ACP including Orangeburg County 

(Siple, 1975); Georgetown and Horry Counties (Zack, 1977); 

Clarendon and Williamsburg Counties (Johnson, 1978); 

Beaufort, Colleton, Hampton, and Jasper Counties (Hayes, 

1979); Sumter and Florence Counties (Park, 1980); Charleston, Berkeley, and Dorchester Counties (Park, 1985); Aiken, 

Allendale, Bamberg, and Barnwell Counties (Logan and Euler, 

1989); Calhoun County (Greaney, 1993); Darlington, Dillon, 

Florence, Marion, and Marlboro Counties (Rodriguez and 

others, 1994); Kershaw County (Newcome, 2002); Richland 

County (Newcome, 2003); Lee County (Newcome, 2004a); 

Chesterfield County (Newcome, 2004b); Lexington County 

(Agerton and Baker, 2006); Hampton County (Newcome and 

Gellici, 2006); and Clarendon County (Newcome, 2006). Siple 

(1957) and Newcome (1989) provide overviews of the groundwater resources of the entire SC ACP (fig. B1).

Statewide potentiometric maps of the SC ACP aquifers 

are provided in the following reports: Aucott and Speiran 

(1985), Gawne (1990, 1994), Stringfield and Campbell (1993), 

Hockensmith and Waters (1997, 1998), and Hockensmith 

(2001, 2003a, b, 2008a, b, 2009). Aquifer-test results for the 

SC ACP are mainly found in Aucott and Newcome (1986), 

Newcome (1993, 2005), and Aadland and others (1995). 

The following reports are considered to contain important stratigraphic information for the SC ACP: Siple (1967), 

Colquhoun and others (1983), Prowell and others (1985), 

Owens and Sohl (1989), Nystrom and others (1991), Sohl 

and Owens (1991), Gohn (1992), Gohn and Campbell (1992), 

Fallaw and Price (1995), Self-Trail and Gohn (1996), Edwards 

and others (1997), Falls and others (1997), Bybell and others (1998), Christopher and others (1999), Prowell and others 

(2000a), Christopher and Prowell (2002), Prowell and others 

(2003), and Self-Trail and others (2004). The following reports 

contain important hydrostratigraphic information for the SC 

ACP: Siple (1967), Colquhoun and others (1983), Aucott and 

others (1987), Miller and Renken (1988), Bledsoe and others 

(1990), Aadland and others (1995), and Falls and others (1997).

Nomenclature and Classification of 

Hydrostratigraphic Units

Hydrostratigraphic nomenclature and the classification 

of hydrostratigraphic units as provinces, systems, units, and

zones is adopted from Aadland and others (1995) and conforms 

to guidelines established by the USGS (Laney and Davidson, 

1986) and the SC Hydrostratigraphic Subcommittee (Burt, 

1987a, b). Topping the classification hierarchy (level 1) are 

hydrogeologic provinces, which define major regional rock or 

sediment packages that behave as a single unified hydrologic 

unit. The two hydrogeologic provinces in SC are the Southeastern Coastal Plain hydrogeologic province and the Piedmont 

hydrogeologic province (Aadland and others, 1995). Ranked 

at level 2 are aquifer and confining systems. Aquifer systems 

are composed of one or more aquifers that transmit water on a 

regional scale. Confining systems are composed of one or more 

confining units that impede regional groundwater flow. 

The building blocks of the classification system are 

aquifer units and confining units (level 3). As defined by the 

SC Hydrostratigraphic Subcommittee, an aquifer is a mappable 

(greater than 400 mi2) body of rock or sediments that is sufficiently permeable to conduct groundwater and yield significant 

quantities of water to wells and springs (Bates and Jackson, 

1980). A confining unit is a mappable (greater than 400 mi2) 

body of rock or sediments of significantly lower hydraulic 

conductivity than an adjacent aquifer, and is an impediment to 

groundwater flow into or out of an aquifer (Lohman, 1972). 
54 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Aquifers and confining units are formally named for a 

geographic or cultural feature that is located near a designated 

type-well locality where the system or unit is representative 

and well defined. In this report, confining units carry the name 

of the underlying aquifer. 

In areas where a confining unit pinches out and two 

aquifers coalesce, a new name has been given to the aquifer. In 

areas where a confining system thins and no longer regionally 

separates the overlying and underlying aquifers, a single aquifer system is defined and named by combining the names of 

the two coalescing aquifer systems (Aadland and others, 1995). 

Where aquifer systems have combined, the individual aquifer 

and confining units can and commonly do extend into and form 

part of the combined system (Aadland and others, 1995).

Aquifers and confining units can be informally subdivided into zones (level 4) that are characterized by properties 

substantially different from the rest of the unit, such as hydraulic 

conductivity, water chemistry, lithology, or color. Names of 

aquifer and confining zones are informal and describe the unique

property that differentiates the zone from the rest of the unit.

The aquifers and confining units of NC and SC are part of 

a much larger series of hydrogeologic units within the ACP. The 

correlations of ACP hydrostratigraphic units in the neighboring 

States of VA and GA are presented in table B1. Correlations 

with the Tertiary and Cretaceous aquifers are shown along with 

the corresponding groundwater flow model layers that are used 

in Chapter C of this report. The hydrostratigraphy of the VA 

Coastal Plain is derived from work by McFarland and Bruce 

(2006) and includes eight aquifers with their corresponding 

confining units. In eastern GA, the hydrostratigraphy of Clarke 

and others (1985) and Brooks and others (1985) includes five 

aquifers, along with their intervening confining units. 

Table B1. Model layers and Atlantic Coastal Plain hydrogeologic units for southern Virginia, North Carolina, South Carolina, and 

eastern Georgia.

Southern Virginia 1 North Carolina 2 Model 

layer South Carolina 3 Eastern Georgia 4, 5

Surficial aquifer Surficial aquifer 1 Surficial aquifer Surficial aquifer

Yorktown confining zone Yorktown confining unit 2 Upper Floridan 

confining unit

Upper Floridan–Jacksonian 

confining unit

Yorktown–Eastover aquifer Yorktown aquifer 3 Upper Floridan aquifer Upper Floridan–Jacksonian 

aquifer Saint Marys confining unit Castle Hayne–Pungo River 

confining unit

4 Middle Floridan 

confining unit

Saint Marys aquifer Castle Hayne–Pungo River aquifer 5 Middle Floridan aquifer

Calvert confining unit

Piney Point aquifer

Nanjemoy–Marlboro 

confining unit

Beaufort confining unit 6 Gordon confining unit Gordon confining unit

Aquia aquifer Beaufort aquifer 7 Gordon aquifer Gordon aquifer

Peedee confining zone Peedee confining unit 8 Crouch Branch 

confining unit

Dublin confining unit

Peedee aquifer Peedee aquifer 9 Crouch Branch aquifer Dublin aquifer

Virginia Beach confining zone Black Creek confining unit 10 McQueen Branch 

confining unit

Midville confining unit

Virginia Beach aquifer Black Creek aquifer 11 McQueen Branch aquifer Midville aquifer

Potomac confining zone Upper Cape Fear confining unit 12 Charleston confining unit Unnamed confining unit

Potomac aquifer Upper Cape Fear aquifer 13 Charleston aquifer

Lower Cape Fear confining unit 14 Gramling confining unit

Lower Cape Fear aquifer 15 Gramling aquifer

Lower Cretaceous confining unit 16 Not Present

Lower Cretaceous aquifer

Basement Basement Basement Basement

1

 McFarland and Bruce, 2006. 

2

 Winner and Coble, 1996.

3 Chapter C, this volume.

4

 Clarke and others, 1985.

5

 Brooks and others, 1985.
Introduction 55

Methods of Investigation

Because of the depth of most of the sediments and the 

extensive surficial land cover, the majority of ACP sediments of North and South Carolina were not directly examined. Therefore, most of the interpretations of the deeper 

stratigraphy and hydrostratigraphy of the ACP come from 

data collected at boreholes of various kinds. The most valuable wells for hydrogeologic mapping purposes are properly 

constructed groundwater monitoring wells, which provide 

values of hydraulic head that are truly representative of the 

aquifer. Used in conjunction with borehole geophysical logs, 

well-to-well correlations were made in order to determine 

the three-dimensional hydrogeologic framework. Detailed 

stratigraphic data from coreholes and drill cuttings were collected to assist with correlations, although the primary concern 

was the continuity of hydraulically connected permeable and 

less permeable strata through the Coastal Plain. Quaternary 

through Cretaceous sedimentary sections were separated 

into component hydrogeologic units, mapped, and described 

across the study area using groundwater levels, borehole 

geophysical logs, paleontologic data, borehole lithologic 

logs, chloride concentrations, aquifer-test data, and surface 

resistivity measurements.

In previous framework studies in the NC and SC ACP, 

investigators had to rely mainly on geophysical logs, auger 

holes, and drill cuttings from water wells and from a few 

coreholes to delineate hydrogeologic units and to correlate 

them across the Coastal Plain. Cores were generally unavailable because of the costs associated with obtaining cores. With 

the advent of wireline coring, the costs and time requirements 

of coring have been reduced, and the number of coreholes in 

the study area has increased considerably (Shuter and Teasdale, 1989). Cores were visually examined, and samples from 

known depths were dated and analyzed. Coreholes drilled 

continuously to bedrock allow for an entire stratigraphic 

sequence of the ACP to be studied directly and related to other 

cores, drill cuttings, and outcrops. Cores were used to interpret 

geophysical logs, thereby improving hydrostratigraphic delineation and correlation with water wells that have geophysical 

logs but have not been cored. 

Methods used to analyze the geologic, hydrogeologic, 

and geophysical data in NC and SC were combined to produce 

cross sections that correlate the ACP aquifers and confining 

units across the NC–SC border at two locations. One of these 

locations is in the inner Coastal Plain, and one is in the outer 

Coastal Plain.

North Carolina Methods of Investigation

In NC, data from 149 wells, primarily groundwater monitoring wells drilled by the State of North Carolina, were used 

to build the hydrogeologic framework (fig. B2, Appendix B1). 

Geophysical logs obtained from these wells include, in most 

cases, the 16- and 64-inch short- and long-normal resistivity, spontaneous-potential, gamma-radiation, and single-point 

resistance. Continuous groundwater level data have been 

collected at many of these sites, and these data were used for 

regional correlations.

Borehole geophysical logs, including spontaneous potential, gamma ray, single-point resistance, and resistivity logs 

from boreholes in the study area were interpreted and correlated in order to identify and map hydrogeologic units. The 

spontaneous potential (SP) log is a recording over depth of the 

difference between the potential of a movable electrode in the 

borehole and the fixed potential of a surface electrode (Keys, 

1990). The SP is the resulting effect of several electromotive 

forces, including clay potential, liquid junction potential, and 

electrokinetic potential. The right-hand boundary of the curve 

generally indicates impermeable formations such as clay. The 

left-hand boundary generally indicates formations of higher 

permeability such as those made up of sand or porous limestone. The SP log was used in this study to determine permeable bed boundaries and to estimate thickness and percentage 

of permeable materials. In addition, the SP log permitted 

correlation of beds from well to well, in conjunction with 

gamma-ray, resistivity, and lithologic logs. Natural gammaray logs measure the natural gamma radiation emitted by a 

geologic formation (Keys, 1990). High natural gamma curve 

values are typically indicative of high amounts of clay and 

phosphate minerals in the area of study, whereas lower curve 

values are indicative of the presence of limestone and sand in 

the geologic section. Gamma-ray curves in many cases were 

valuable for correlation, by virtue of having produced distinctive signatures across zones of phosphate mineralization. 

Single-point resistance logs measure the electrical resistance, 

in ohms, between an electrode in a well and an electrode at 

the land surface, or between two electrodes in a well. The 

measurement does not take into account the length or crosssectional area of the current travel path, and thus cannot be 

used for quantitative interpretation (Keys, 1990). However, 

the single-point resistance curve was used for interpreting 

lithology and for thin bed detection. Normal-resistivity logs 

measure formation resistivity, which takes into account the 

length and cross-sectional area of the current travel path. Thus, 

short- and long-normal measurements take into account the 

intrinsic properties of the material and were used for quantitative interpretation of formation fluids. The long-normal curve 

provides a reading beyond the flushed zone of the borehole 

where formation fluids are generally undisturbed by drilling 

fluid (Keys, 1990). 

Resistivity curves were used in combination with SP and 

gamma ray curves to help distinguish between freshwater- and 

saltwater-bearing strata, and between permeable and nonpermeable strata. This combination of log types was used 

to identify and correlate aquifer and confining unit tops and 

bases, and to calculate the percentage of permeable material 

and the net thickness, in feet, of permeable material in each 

aquifer. Differences in chloride concentrations across confining units and similarities in chloride concentrations within the 

same aquifer were taken into account in order to accurately 

subdivide the hydrogeologic section.
56 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Lithologic logs were used in combination with borehole 

geophysical logs to define vertical and lateral stratigraphic 

variations in the subsurface. Four coreholes were constructed 

in the NC Coastal Plain by the USGS between 2001 and 2005. 

These included the Fort Fisher corehole in New Hanover 

County, the Elizabethtown corehole in Bladen County, the 

Cove City corehole in Craven County, and the Hope Plantation 

corehole in Bertie County. Formation tops from lithostratigraphic logs and USGS coreholes were used in accordance 

with well log correlations to determine the relation between 

stratigraphic and hydrogeologic units. 

The drawdown effects and lateral transmission of 

drawdown effects observed from regional pumping and from 

aquifer tests were used to identify the lateral continuity of an 

aquifer. Aquifer-test data were used to determine transmissivity, specific capacity, horizontal hydraulic conductivity, 

storativity, and specific storage of aquifers and confining beds.

South Carolina Methods of Investigation

In SC, data from 38 coreholes and 68 water wells were 

used to build the hydrogeologic framework (fig. B2, Appendix 1). Some of the cores were drilled specifically for this 

study, whereas others were drilled for previous investigations 

dating back to 1975 (Gohn, 1992). Cores were described 

in terms of their lithology, grain size, sorting, induration, 

mineralogy, fossils, structures, and color. Geophysical logs 

obtained from each corehole and water well included, in 

most cases, the 16- and 64-inch short- and long-normal 

resistivity, spontaneous-potential, gamma-radiation, and 

single-point resistance.

Several types of paleontology samples were collected 

from the SC ACP cores and were microscopically analyzed for 

palynomorphs (pollen and spores from terrestrial plants and 

cysts of dinoflagellates) and calcareous nannofossils (remains 

of golden-brown, single-celled algae that live only in the 

oceans) in order to determine the age of the sediments (SelfTrail and Gohn, 1996; Self-Trail and Bybell, 1997; and Christopher and others, 1999). Approximately 700 paleontological 

age dates were collected in this manner during the course of 

the study. These analyses were essential in delineating the 

allostratigraphic units and, subsequently, in correlating the 

aquifers and confining units across the SC ACP. Samples that 

contained age-diagnostic fossil assemblages were assigned a 

fossil zonation. Fossil zonations for calcareous nannofossils 

are from Perch-Nielson (1985a, b), and zonations for pollen are from Christopher and others (1999) for the Turonian 

through Santonian Stages, from Christopher and Prowell 

(2002) for the Maastrichtian Stage, and from D.C. Prowell 

and R.A. Christopher (U.S. Geological Survey and Clemson 

University (retired), respectively, written commun., 2002) for 

the Campanian Stage.

Allostratigraphic formations, which are unconformitybounded formations, were determined using core, fossil, and 

borehole geophysical data (Gellici, 2007a, b). Unconformities were identified in the cores by noting distinct changes in 

lithology and texture, rooting structures, hardpans, erosional 

surfaces, irregular contacts, burrowing, and transgressive lag 

deposits. Lag deposits in updip regions of the SC ACP typically consist of beds of poorly sorted quartz sand and gravel; 

downdip, they typically consist of beds of glauconite, phosphate, quartz sand and pebbles, and phosphatized bone, teeth, 

and shell fragments. Fossil data were examined to determine if 

assemblages changed vertically across lag deposits, signifying 

paleontological evidence of an unconformity. Radiation spikes 

on the gamma-ray log were used as further evidence of unconformities, especially in downdip sections consisting of marine 

deposits. Final determinations were made on allostratigraphic 

formation boundaries by using a combination of these data 

(core, fossil, and geophysical) and by correlation with nearby 

cores and outcrops that had biostratigraphic control.

Sedimentary layers were differentiated on the basis of 

relative permeability, primarily by visual inspections of the 

cores and by interpretations of geophysical logs. Particle-size 

analyses (available for about half of the cores and usually only 

from sandy intervals) and permeameter tests (available for 

about a quarter of the cores and in small numbers) also were 

used to help differentiate layers. Adjacent permeable layers 

were combined as potential aquifers and adjacent impermeable 

layers as potential confining units. 

Borehole geophysical data were combined with groundwater level data (where available), and were used to delineate 

the major hydrostratigraphic units in specific coreholes in SC. 

A lack of groundwater level head differences across potential 

confining beds would indicate vertical hydraulic continuity 

and, therefore, the absence of a confining unit and a single 

aquifer. The presence of groundwater level differences across 

potential confining beds would indicate hydraulic separation 

and, therefore, the occurrence of a confining unit and two 

separate aquifers. With a few exceptions, hydrostatic head 

data obtained from well-cluster sites were available only in the 

west-central region of the SC ACP. This region was, therefore, 

the starting point for aquifer delineation and for correlation of 

hydrostratigraphic units across the rest of the Coastal Plain. 

After delineation of aquifers and confining units, the 

hydrostratigraphic units were identified and correlated by 

using the allostratigraphic and biostratigraphic data collected 

from the project and with borehole geophysical logs. Several 

of the cores used by Aadland and others (1995) in their development of the west-central SC framework were age-dated, 

providing the ages of formations composing the aquifers and 

confining units defined in west-central SC. For example, the 

Crouch Branch confining unit consists mainly of strata of early 

Paleocene age. Clay beds of early Paleocene age in other cores 

were mapped as a continuation of the Crouch Branch confining unit. The same process was used for the aquifers. 

Lateral hydraulic continuity of the aquifers and confining 

units was never directly measured and can only be assumed. 

Breaches in the confining unit caused by structural features 

such as faulting, or by changes in lithology caused by changing depositional settings, can exist between wells. Generally, 

aquifers and confining units in SC were more difficult to 
Introduction 57

delineate and map on the eastern side of the SC ACP. Confining units are not as well defined as they are on the western 

side. This is probably due to the different depositional settings 

of the SC ACP whereby deltaic environments predominated on 

the western side and continental shelf environments predominated on the eastern side. 

All available data from each corehole or water well used 

in the study were analyzed to select the top and bottom altitudes of each hydrostratigraphic unit present at that location. 

Selected wells were used to develop detailed cross sections, 

which are described in detail below. The top and bottom 

altitudes, along with the unit’s geographic extent, were used 

to create structure contour and thickness maps of each aquifer 

and confining unit. 

Hydrogeologic Cross Sections

A series of cross sections was constructed within the 

study area (two regional strike sections, five regional dip 

sections, Plates 1–7, table B2) in order to illustrate the lateral 

distribution and thickness of the each hydrogeologic unit. 

Lines representing the altitude of land surface were superimposed on each cross section to indicate potential recharge–

discharge relations. Land surface altitude data were obtained 

from a USGS digital elevation model by plotting the lines of 

section on the model surface. The vertical scale on the sections is 1 inch (in.) to 200 ft, and the horizontal scale is 1 in. 

to 10 miles (mi) in SC. In NC, the vertical scale is 1 in. to 

178 ft vertically, and 1 in. is equal to 17,700 ft horizontally. 

The different scales were used to allow the cross sections to be 

presented in the maximum size feasible to fit on the plates. All 

latitude and longitude coordinates of well locations are referenced to the North American Datum of 1983 (NAD 83). The 

depths of the SC coreholes and water wells that did not reach 

the underlying consolidated basement rocks were projected 

to the basement contact, and the top altitudes of the contacts 

were estimated.

Section A–A′ (Plate 1; table B2), a dip section located in 

southwestern SC, illustrates the correlation of hydrogeologic 

units among coreholes AIK-817 (Logan, 1987), ALL-348 

(Kuntz and others, 1989), JAS-426 (Self-Trail and Bybell, 

1997), and BFT-2055 (Temples and Englehardt, 1997). Total 

depths are 561, 1,734, 2,900, and 3,833 ft, respectively. 

Sidewall cores were obtained from JAS-426 and BFT-2055 to 

basement; the other two boreholes were continuously cored 

to basement. 

Section B–B′ (Plate 2; table B2), a dip section located 

in the central part of the SC ACP, illustrates the correlation of 

hydrogeologic units among coreholes RIC-585 (unpublished), 

RIC-543 (unpublished), SUM-296 (Prowell, 1993; Vroblesky, 

1994), BRK-644 (unpublished), and CHN-820 (Self-Trail 

and others, 2004b). Total depths are 469, 557, 725, 1,826, and 

1,536 ft, respectively. RIC-585, RIC-543, and BRK-644 were 

continuously cored to basement. SUM-296 and CHN-820 

were continuously cored but did not reach basement.

Section C–C′ (Plate 2; table B2), a dip section located in 

northeastern SC, illustrates the correlation of hydrogeologic 

units among coreholes CTF-81 (unpublished), DAR-228 (Falls, 

1994; Rodriguez and others, 1994), and FLO-268 (Curley, 

1990), water well FLO-317, and coreholes MRN-78 (Reid 

and others, 1986) and HOR-973/1165 (Castro and others, 1995). 

Total depths are 245, 447, 716, 464, 1,230, and 1,427 ft, respectively. All of the coreholes were continuously cored to basement; 

however, the water well, FLO-317, did not reach basement.

Section D–D′ (Plate 3; table B2), located just inside NC 

and parallel to the NC–SC border, shows the dip-oriented 

correlations of hydrogeologic units among wells SC-A-3-83 

(W 51A), Carver School (W 50G), Town of Laurinburg 

(X 49D), Division of Water Resources (DWR) Rowland 

(Z 47R), DWR Marietta (BB 45M), DWR Clarendon 

(DD 42N), Town of Tabor City (EE 42B), and DWR Calabash 

(HH 39J). Total depths are 104, 105, 349, 548, 552, 879, 330, 

and 1,335 ft, respectively. Only the DWR Rowland (Z 47R) 

and DWR Clarendon (DD 42N) sites are drilled to basement.

Section E–E′ (Plate 3; table B2), located in the central 

part of the NC Coastal Plain, shows the dip-oriented correlations of hydrogeologic units among wells Town of Farmville 

(M 27M), Town of Farmville (M 26Q), Bell Arthur (M 26U), 

Bell Arthur (N 25G), Town of Winterville (N 24P2), DWR 

Conley Station (N 23P), DWR Blackjack Station (N 22Y), 

DWR Chocowinity Station (N 21M), DWR Bath Station 

(O 17I), DWR Winsteadville Station (O 15N), DWR Sladesville Station (O 13F), DWR Swanquarter (P 11E), and DWR 

Hydeland Station (O 10W). Total depths are 396, 496, 497, 

408, 400, 802, 210, 456, 702, 710, 472, 302, and 1,503 ft, 

respectively. Only the Town of Farmville (M 26Q) hole is 

drilled to basement.

Section F–F′ (Plate 4; table B2), located in the northern 

part of the NC Coastal Plain, shows the dip-oriented correlation of hydrogeologic units among wells DWR Cremo Station 

(G 19B), USGS Valhalla (G 15F), DWR Three Mile Desert 

Station (E 13M), USGS PA-T2-62 (F 10Q), DWR Big Flatty 

Station (G 9C), and Rapp Oil Kellogg No. 1 (G 6L). Total 

depths are 1,192, 528, 1210, 704, 731, and 5,140 ft, respectively. The only bore hole that is drilled to basement is DWR 

Cremo Station (G 19B). 

Section G–G′ (Plate 5; table B2), oriented southwestnortheast within the central part of the NC Coastal Plain, illustrates the strike-oriented correlation of hydrogeologic units 

among wells DWR Marietta Station (BB 45M), DWR Boardman Station (AA 43Q), DWR Bladenboro Station (Z 41M), 

DWR Elizabethtown Station (Y 39M), DWR White Lake 

Prison Station (Y 38B), DWR White Lake Farm Well No. 5 

(Y 37E), DWR Black Lake (X 36P), DWR Six Runs Station 

(V 35T), Town of Warsaw (T 32Y), Carolina Turkeys (S 31A), 

North Lenoir Water Corporation (P 28W), Environment and 

Natural Resources (ENR) Maury Research Station (O 27J), 

DWR West Research Campus (M 25F2), DWR Gold Point 

Station (J 22P), DWR Cremo Station (G 19B), and DWR 

Gates County Prison (C 16Q). Total depths are 552, 497, 575, 

501, 497, 258, 440, 433, 360, 320, 408, 568, 574, 644, 1,192, 

and 1,080 ft, respectively. The boreholes that are drilled to 
58 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Table B2. Wells used in cross sections on Plates 1–7.—Continued 

[GR, Gamma Ray; SPR, Single Point Resistance; SN, Short Normal; LN, Long Normal; SP, Spontaneous Potential]

Crosssection well 

number on 

Plates 1–7

Cross 

section

Plate 

number Local name of well

NC quadrangle 

number/

SC county 

number

Station identification

Well 

depth, 

in feet

Geophysical logs 

used on Plate

North Carolina

1 D–D′ 3 SC-A-3-83 W 51A 344958079351501 104 GR

2 D–D′ 3 Carver School W 50G 344844079324201 105 GR

3 D–D′ 3 Town of Laurinburg X 49D 344418079284701 349 GR, SPR

4 D–D′ 3 DWR Rowland Z 47R 343156079174701 548 SP, GR, SPR

5 D–D′, G–G′ 3, 5 DWR Marietta BB 45M 342224079073901 552 SP, GR, SPR

6 D–D′ 3 DWR Clarendon DD 42N 341200078530001 879 SP, GR, SPR

7 D–D′ 3 Town of Tabor City EE 42B 340914078521601 330 SP, GR, SPR

8 D–D′, D′–H 3, 6 DWR Calabash HH 39J 335334078352101 1,335 SP, GR, SPR

9 E–E′ 3 Town of Farmville M 27M 353529077344701 396 SP, SPR

10 E–E′ 3 Town of Farmville M 26Q 353518077353901 496 SP, GR, SPR

11 E–E′ 3 Bell Arthur M 26U 353542077305902 497 SP, SPR

12 E–E′ 3 Bell Arthur N 25G 353352077281203 408 SP, SPR

13 E–E′ 3 Town of Winterville N 24P2 353132077240401 400 SP, SPR

14 E–E′ 3 DWR Conley Station N 23P 353146077193402 802 SP, GR, SPR

15 E–E′ 3 DWR Blackjack Station N 22Y 353043077146001 210 SP, GR, SPR

16 E–E′ 3 DWR Chocowinity Station N 21M 353038077060101 456 SP, SPR

17 E–E′ 3 DWR Bath Station O 17I 352832076470101 702 SP, GR, SPR

18 E–E′ 3 DWR Winsteadville Station O 15N 352749076380903 710 SP, GR, SPR

19 E–E′, D′–H 3, 6 DWR Sladesville Station O 13F 352854076290901 472 SP, GR, SPR

20 E–E′ 3 DWR Swanquarter P 11E 352440076194501 302 SP, SPR

21 E–E′ 3 DWR Hydeland Station O 10W 352527076123103 1,503 SP, GR, SPR

22 F–F′, G–G′ 4, 5 DWR Cremo Station G 19B 360900076560002 1,192 SP, GR, SPR

23 F–F′ 4 USGS Valhalla G 15F 360828076391801 528 SP, GR, SPR

24 F–F′ 4 DWR Three Mile Desert Station E 13M 361744076274401 1,210 SP, GR, SPR, SN, LN

25 F–F′ 4 USGS PA-T2-62 F 10Q 361130076140001 704 SP, SPR

26 F–F′, D′–H 4, 6 DWR Big Flatty Creek Station G 9C 360859076075801 731 SP, GR, SPR

27 F–F′ 4 Rapp Oil Kellog No. 1 G 6L 360702075511001 5,140 SP, SN

28 G–G′ 5 DWR Boardman Station AA 43Q 342620078581801 497 SP, GR, SPR

29 G–G′ 5 DWR Bladenboro Station Z 41M 343027078451901 575 SP, GR, SPR

30 G–G′ 5 DWR Elizabethtown Station Y 39M 343739078364601 501 SP, GR, SPR

31 G–G′ 5 DWR White Lake Prison Station Y 38B 343917078311207 497 SP, GR, SPR

32 G–G′ 5 DWR White Lake Farm Well 

No. 5

Y 37E 343950078295001 258 SP, GR, SPR

33 G–G′ 5 DWR Black Lake X 36P 344122078245001 440 SP, GR, SPR

34 G–G′ 5 DWR Six Runs Station V 35T 345113078154504 433 SP, GR, SPR

35 G–G′ 5 Town of Warsaw T 32Y 350040078053401 360 GR, SPR

36 G–G′ 5 Carolina Turkeys S 31A 350914077555601 320 SP, GR, SPR

37 G–G′ 5 North Lenoir Water Corporation P 28W 352115077332301 408 SP, GR, SPR
Introduction 59

Table B2. Wells used in cross sections on Plates 1–7.—Continued 

[GR, Gamma Ray; SPR, Single Point Resistance; SN, Short Normal; LN, Long Normal; SP, Spontaneous Potential]

Crosssection well 

number on 

Plates 1–7

Cross 

section

Plate 

number Local name of well

NC quadrangle 

number/

SC county 

number

Station identification

Well 

depth, 

in feet

Geophysical logs 

used on Plate

North Carolina—Continued

38 G–G′ 5 ENR Maury Research Station O 27J 352840077355508 568 SP, GR, SPR

39 G–G′ 5 DWR West Research Campus M 25F2 353641077241402 574 SP, GR, SPR

40 G–G′ 5 DWR Gold Point Station J 22P 355124077145306 644 SP, GR, SPR, SN

41 G–G′ 5 DWR Gates County Prision C 16Q 362604076434401 1,080 SP, GR, SPR, SN

42 D′–H 6 Brunswick County Hospital FF 35W 340029078173001 263 SP, GR, SPR

43 D′–H 6 Brunswick Tech FF 34N 340224078134501 212 SP, SPR

44 D′–H 6 DWR Bolivia Station FF 33D 340416078084201 300 SP, GR, SPR

45 D′–H 6 Colonial Trask 3 EE 31H 340825077573801 1,254 SP, GR, SPR

46 D′–H 6 Coastal States Foy CC 29L 341700077465001 1,304 GR

47 D′–H 6 DWR Topsail Beach Station BB 28J 342357077404201 1,348 SP, GR, SPR

48 D′–H 6 DWR Deppe Station V 23X 345013077181301 1,001 SP, GR, SPR

49 D′–H 6 DWR Godley Station Q 16G 351856076434103 1,012 SP, GR, SPR, SN

50 D′–H 6 DWR Grassy Point Station O 15U 352542076353201 391 SP, SPR

51 D′–H 6 DWR New Lake Station M 12L 353720076211801 1,011 SP, GR, SPR

52 D′–H 6 DWR Newlands Station J 11V 355050076160705 1,449 SP, GR, SPR

South Carolina

53 A–A′ 1 New Ellenton (DNR/SRS 

corehole)

AIK-817 332616081462001 561 SP, GR, SPR, LN

54 A–A′, I–I′ 1, 7 Appleton ALL-348 330130081230401 1,734 SP, GR, SPR, LN

55 A–A′ 1 Gillisonville JAS-426 323704080594508 2,900 SP, GR, SPR, LN

56 A–A′, A′–C′ 1, 2 Hilton Head BFT-2055 321128080421500 3,833 SP, GR, SPR, LN

57 B–B′ 2 Horrell Hill RIC-585 335656080502709 469 SP, GR, SPR, LN

58 B–B′ 2 Eastover RIC-543 335229080421009 557 SP, GR, SPR, LN

59 B–B′, I–I′ 2, 7 Manchester SUM-296 334238080315600 725 SP, GR, SPR, LN

60 B–B′ 2 Saint Stephen BRK-644 332415079560209 1,826 SP, GR, SPR, LN

61 B–B′, A′–C′ 2, 7 Santee Coastal Reserve CHN-820 330921079215009 1,536 SP, GR, SPR, LN

62 C–C′ 2 Cheraw State Park CTF-81 343835079544209 245 SP, GR, SN, LN

63 C–C′ 2 Lake Darpo DAR-228 342731079524809 447 SP, GR, SPR, LN

64 C–C′ 2 Florence FLO-268 341013079472109 716 SP, GR, SN, LN

65 C–C′ 2 Pamplico FLO-317 335940079360509 464 SP, GR, SPR, LN

66 C–C′ 2 Brittons Neck MRN-78 335143079195008 1,230 SP, GR, SPR, LN

67 C–C′, A′–C′ 2, 7 Myrtle Beach HOR-973/1165 334321078541208 1,427 SP, GR, SPR, LN

68 I–I′ 7 Clark Middle School ORG-393 333029080515409 1,138 SP, GR, SPR, LN

69 I–I′ 7 Lake City FLO-274 335120079460200 1,090 SP, GR, SPR, LN

70 I–I′ 7 Little Peedee State Park DIL-121 341943079170209 647 SP, GR, SPR, LN

71 A′–C′ 7 Edisto Island COL-364 323013080174609 977 SP, GR, SPR, LN

72 A′–C′ 7 Sullivans Island CHN-635 324552079495809 2,540 SP, GR, SPR, LN
60 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

basement are: DWR White Lake Prison Station (Y 38B), 

DWR Bladenboro Station (Z 41M), ENR Maury Research Station (O 27J), and DWR Cremo Station (G 19B).

Section D′–H (Plate 6; table B2), oriented southwestnortheast in the outer Coastal Plain of NC, illustrates the 

strike-oriented correlation of hydrogeologic units among 

wells DWR Calabash Station (HH 39J), Brunswick County 

Hospital (FF 35W), Brunswick Tech (FF 34N), DWR Bolivia 

Station (FF 33D), Colonial Trask 3 (EE31H), Coastal States 

Foy (CC 29L), DWR Topsail Beach Station (BB 28J), DWR 

Deppe Station (V 23X), DWR Godley Station (Q 16G), DWR 

Grassy Point Station (O 15U), DWR Sladesville Station 

(O 13F), DWR New Lake Station (M 12L), DWR Newlands 

Station (J 11V), and DWR Big Flatty Creek Station (G 9C). 

Total depths are 1,335, 263, 212, 300, 1,254, 1,304, 1,348, 

1,001, 1,012, 391, 472, 1,011, 1,449, and 731 ft, respectively. 

The bore holes that are drilled to basement are Colonial 

Trask 3 (EE31H) and DWR Topsail Beach Station (BB 28J).

Section I–I′ (Plate 7; table B2), oriented southwestnortheast in the inner Coastal Plain of SC, illustrates the 

strike-oriented correlation of hydrogeologic units among coreholes ALL-348 (Kuntz and others, 1989), ORG-393 (Gellici, 

2007a), SUM-296 (Prowell, 1993; Vroblesky, 1994), FLO-274 

(Falls, 1994; Rodriguez and others, 1994), and DIL-121 

(unpublished). Total depths are 1,734, 1,138, 725, 1,090, and 

647 ft, respectively. All of the coreholes were continuously 

cored to basement with the exception of SUM-296.

Section A′–C′ (Plate 7; table B2), oriented southwestnortheast in the outer Coastal Plain of SC, illustrates the 

strike-oriented correlation of hydrogeologic units among coreholes BFT-2055 (Temples and Englehardt, 1997) and COL364, water well CHN-635, and coreholes CHN-820 (Self-Trail 

and others, 2004) and HOR-973/1165 (Castro and others, 

1995). Total depths are 3,833, 977, 2,540, 1,536, and 1,427 ft, 

respectively. Sidewall cores to basement were obtained from 

BFT-2055. COL-364 and CHN-820 were continuously cored, 

but did not reach basement. HOR-973/1165 was continuously cored to basement, and water well CHN-635 did not 

reach basement.

The NC cross sections show three geophysical log traces: 

gamma, spontaneous potential, and single-point resistance. A 

generalized lithologic log shows the position and thickness of 

sand units, units of mostly clay and silt, and basement rocks. 

Plots of groundwater levels over time are presented on the 

NC plates for selected wells. The position of the saltwaterfreshwater transition zone in NC also is indicated by the 

presence of groundwater containing 250 milligrams per liter 

(mg/L) of chloride. Results of laboratory analyses of chloride 

concentrations in groundwater samples collected at discrete 

depths in selected wells are presented along with the date of 

sample collection. 

Eight columns of information are provided on Plates 1, 2,

and 7 for each corehole for the SC sections. Beginning at the 

left, column 1 shows geologic formations, which are allostratigraphic units. Most formation contacts were determined 

using core data, geophysical logs, and paleontological data 

(D.C. Prowell, U.S. Geological Survey, written commun., 

2002). Column 2 shows the estimated calcareous nannofossil zones based on diagnostic fossil assemblages (Column 3) 

recovered from core samples, contacts identified in cores, 

and geophysical-log response. New formation names may be 

needed where a single formation contains several calcareous 

nannofossil zones. For example, the Williamsburg Formation 

contains NP 6, NP 8, and NP 9 fossil zones, each of which 

probably represents an unconformity. The formation may need 

to be raised to group rank and defined by three new formations. The same applies to the Santee Formation; however, 

introducing and formalizing new geologic names was beyond 

the scope of this study. 

Column 3 shows the paleontological age determination 

at specific depths. Sample depth and pollen and calcareous 

nannofossil zonations are shown on this column. Depths 

are in feet below land surface. Formation boundaries determined from intervals that have age-diagnostic fossils are 

more reliable than intervals that did not yield age-diagnostic 

fossils or that were barren of fossils. Formations in intervals 

that were barren of fossils were picked on the basis of core 

data, geophysical logs, and by dip and strike projections with 

other coreholes that have biostratigraphic control, or with 

outcrop data. 

Column 4 is an overlay of the spontaneous-potential 

log in units of millivolts and the natural gamma-radiation 

log with units in counts per second. Column 5 is altitude, in 

feet, relative to the National Geodetic Vertical Datum of 1929 

(NGVD 29). Column 6 is depth, in feet, below land surface. 

Column 7 is a lithologic log of the cores. At the water wells, 

lithology was estimated from drill cuttings and geophysical 

logs because no cores were available from these wells. An 

explanation of the lithology symbols is provided on each Plate. 

Column 8 is an overlay of the single-point resistance log (units 

are electrical resistance, in ohms) and the 64-in., long-normal 

resistivity log (units are electrical resistivity, in ohm-meters). 

Where the coreholes did not reach basement rock, depth to 

basement was estimated from the map of Prowell and others (2000a). No single-point resistance log was available for 

several of the coreholes, so the 16-in. short-normal electric log 

was used in its place. 

Data collected from the coreholes and water wells presented on the cross sections were used to construct the hydrostratigraphic correlations from hole to hole across the ACP 

of NC and SC. Correlations at the NC–SC border were made 

using the available data at two locations—updip and downdip. 
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 61

Pre-Cretaceous Basement Rocks and 

Structural Geology of the Coastal Plain

The basement complex in SC consists of Paleozoic 

metamorphic and igneous rocks and consolidated to semiconsolidated Triassic sedimentary rocks (Aadland and others, 

1995). Origins of these rocks are different, but their hydraulic 

properties are similar. The rocks are generally massive, dense, 

and practically impermeable, except where fracture openings 

are encountered. Few water wells tap the basement complex 

in the ACP of NC and SC except in updip regions near the Fall 

Line where groundwater in ACP sediments is limited.

The following is a general description of basement rocks 

underlying the ACP and is based on cores used in this report: 

“...a narrow early Mesozoic basin crosses the upper third of 

the Coastal Plain from Barnwell County to Dillon County 

and another large basin underlies the southernmost part of the 

Coastal Plain. Both of these basins are characterized by continental redbeds locally overlain by flood basalts. Of the remaining basement-rock types, slates and phyllites characterize the 

northern Coastal Plain areas and high-grade gneisses characterize the western and eastern Coastal Plain areas. Locally, 

intrusive granites were encountered in the western part of the 

Coastal Plain” (D.C. Prowell, U.S. Geological Survey, written 

commun., 2000). 

The most prominent structural feature is the Cape Fear 

Arch (fig. B1), which has had a major effect on the distribution and thickness of sediments in the NC and SC ACP. The 

arch is a southeastward plunging anticline that intersects the 

NC coastline near Cape Fear. Along the axis of the arch, from 

the Fall Line to the coast, basement rocks dip 13 feet per mile 

(ft/mi) (Maher, 1971). The arch is asymmetrical in cross section, with the northeast limb steeper than the southwest limb. 

Tertiary sediments are absent along the crest and generally 

absent along the flanks of the arch. Some Late Cretaceous 

sediments are also missing from the crest of the arch. Owens 

and Gohn (1985) postulated that the arch was a depocenter 

during the early part of the Late Cretaceous, which is supported in this study by the increasing thickness of the Cape 

Fear Formation toward the arch.

Locations of Cretaceous and Cenozoic faults in the 

southeastern ACP were compiled by Prowell (1983). Most 

of the faults are northeast-trending, reactivated, high-angle 

reverse faults that are associated with early Mesozoic rift 

basins (Snipes and others, 1993). The most studied fault in 

the SC ACP is the Pen Branch Fault, located near the center 

of the SRS (Snipes and others, 1993). The Pen Branch is the 

northern boundary fault of the Dunbarton Basin, a Triassic 

rift basin that underlies the southeastern half of SRS. Offsets 

are about 100 ft at the base of the Late Cretaceous section 

and decrease to about 30 ft at the top of the Late Eocene Dry 

Branch Formation. These offsets are large enough to breach 

confining units, especially in updip regions where confining 

units are thin. 

The slopes of basement rocks differ across the Coastal 

Plain, largely due to the effects of the Cape Fear Arch. 

Basement rocks dip to the southeast about 35 ft/mi on the 

western side of the SC ACP from Aiken County (AIK-817) 

to Hilton Head Island (BFT-2055) (Plate 1). On the eastern 

side, from Chesterfield County (CTF-81) to Myrtle Beach 

(HOR-973/1165), basement rocks dip 15 ft/mi. From Myrtle 

Beach to Hilton Head Island (along the coast), basement rocks 

have a slope of 17 ft/mi. In SC, the top of the crystalline basement rock ranges in altitude from 300 ft near the Fall Line 

to –4,000 ft in southernmost SC (fig. B3; Appendix B1). The 

thickness of the crystalline basement rocks is unknown.

Basement rocks at the Orangeburg corehole (ORG-393) 

are redbeds that consist of mudstone, pebbly mudstone, 

sandstone, and conglomeritic sandstone of probable Triassic 

age (Appendix B2). The rocks are poorly sorted and dense 

from compaction and iron cementation. Pebbles consist of 

quartz, feldspar, and a variety of metamorphic rock fragments. 

The unit is massive to crudely bedded. Primary intergranular 

porosity is low; however, common slickensided surfaces indicate the occurrence of secondary-fracture porosity that could 

increase flow through the rocks. 

North Carolina Coastal Plain 

Stratigraphy and Hydrostratigraphy

Stratigraphic units of the NC Coastal Plain are both 

marine and non-marine in origin and range in age from early 

Cretaceous to Quaternary (Sohl and Owens, 1991). Figure B4 presents the stratigraphy and hydrogeologic units of 

the North and South Carolina Coastal Plain. For NC, recent 

geological and hydrogeological reports, including data from 

147 wells drilled primarily by the State of NC, were used to 

develop the hydrogeological framework. No new stratigraphic 

interpretations of the NC Coastal Plain are presented in this 

report; therefore, the geologic units shown on the stratigraphic 

correlation chart (fig. B4) will not be described, and the reader 

is referred to the following references for details: Brown and 

others (1972), Gohn (1988), and Lautier (1998a, b, 2002, 

2006). Many of these NC Coastal Plain units extend into 

southern Virginia (McFarland and Bruce, 2006).

The hydrostratigraphic interpretation of the NC Coastal 

Plain has evolved from early work by Stephenson (1907, 

1923) to the more recent work of Winner and Coble (1996) 

and Lautier (1998a, b, 2002, 2006). The aquifers and confining units are discussed in descending order. Although the NC 

Tertiary units are in similar positions stratigraphically to units 

in SC, they are not continuous or hydraulically connected 

between the two States because there is a structural high along 

the NC–SC border and the younger (Tertiary) units have been 

eroded away there (see sections A–C′, Plate 7; D′–H, Plate 6; 

and I–I′, Plate 7).
62 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B3. Altitude of the top of the crystalline basement rocks underlying the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007.

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

Extent of aquifer

Altitude contour in feet above

 or below NGVD 29. Contour

 interval is variable

Hydrostratigraphic borehole

–100

–500

–1,000

–2,000

–2,000

–1,000

–500

100

300

200

200

300

0

0

0

0

–3,000

–4,000

–5,000

–500

–1,000

–2,000

–3,000

–4,000

Atlantic

Ocean

Figure B3. Altitude of the top of the crystalline basement rocks underlying the Atlantic Coastal Plain of North 

and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean
Pre-Cretaceous Basement Rocks and Structural Geology of the Coastal Plain 63

Figure B4. Stratigraphic correlations of hydrogeologic units of the North and South Carolina Coastal Plain. (aq., aquifer; cu, confining unit)

64 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B4. Stratigraphic correlations of hydrogeologic units of the North and South Carolina Coastal Plain. (aq., aquifer; cu, confining unit) 

PeriodTERTIARY CRETACEOUS (part)

Quaternary

Epoch Pliocene Oligocene Paleocene Late Early Late Early Miocene Late Late Middle Early Early Eocene Late Late Middle Early EarlyAge

zone

Model

Layer

South Carolina

Formation

South Carolina

Inner Coastal Plain (west) Outer Coastal Plain (west) Outer Coastal Plain (east) Formation Aquifers and CU

North Carolina

Quaternary undifferentiated

Formations absent in eastern SC owing to uplift of the Cape Fear Arch

Ebenezer

Coosawhatchie

Upland unit/Marks Head

Parachucla

Tiger Leap

Ashley absent

Drayton absent

Harleyville absent

Caddin absent

Shepherd absent

Pleasant Creek absent

Collins Creek absent

Ashley

Drayton/Suwannee

Tobacco Road Sand

Updip Upper Floridan aq.

Updip Middle Floridan aq. Middle Floridan aquifer

Gordon confining unit

Gordon aquifer

Gordon aquifer

McQueen Branch aquifer

generally absent in area

McQueen Branch 

confining unit

McQueen Branch 

confining unit

McQueen Branch CU

Charleston

aquifer

Charleston

aquifer

Gramling aquifer Gramling aquifer

Gramling confining unit Gramling confining unit Gramling confining unit

Dry Branch (updip)

Parkers Ferry/Ocala (downdip)

Harleyville

Santee

Warley Hill Warley Hill absent

Congaree Congaree absent

Fourmile/Fishburne

Williamsburg

Lang Syne

Rhems

Piacenzian

Zanclean

Messinian

Tortonian

Serravallian

Langhian

Burdigalian

Aquitanian

Chattian

Rupelian

Priabonian

Bartonian

Lutetian

Ypresian

Thanetian

Selandian

Danian

Campanian

Santonian

Coniacian

Turonian

Cenomanian

Triassic

Paleozoic Basement

Maastrichtian

NN 16

NN 13–15

NN 12

NN 11

NN 10

NN 7–9

NN 6

NN 5

NN 4

NN 2–3

NN 1

NP 25

NP 24

NP 22–23

NP 21

NP 19-20

NP 18

NP 17

NP 16

NP 15

NP 14

NP 13

NP 12

NP 11

NP 10

NP 9

NP 8

NP 7

NP 6

NP 5

NP 4

NP 3

NP 2

NP 1

CC26

CC25

CC 24

CC 23

CC22

CC21

CC20

CC19

CC 18

CC 17

CC 16

CC 15

CC 14

CC 13

CC 12

CC 11

CC 10

CC 9

A

B

Su

c

b

a

a/b

Hc

Mt

Sawdust Landing

Upper Peedee/Steel Creek

Middle Peedee/Steel Creek

Lower Peedee/Steel Creek

Middle Donoho Creek

Lower Donoho Creek

Upper Donoho Creek

Bladen

Coachman

Cane Acre

Caddin

Shepherd Grove

Pleasant Creek

Collins Creek

Cape Fear

Clubhouse

Beech Hill

Hawthorn Group

surficial aquifer

Black Creek Grp.

Sawdust Landing absent Sawdust Landing absent

upper Donoho Cr. absent

Pleasant Creek absent

upper Donoho Cr. absent

Crouch Br. aq.

Crouch Br. aq.

McQueen Br. aquifer

Not present in South Carolina

??

Upper Floridan 

confining unit

Upper Floridan aquifer

(Parkers Ferry/Ocala)

Middle Floridan

confining unit

Gordon confining unit

surficial aquifer surficial aquifer Undifferentiated

Yorktown

Pungo River

Belgrade

Riverbend

Castle Hayne

Beaufort

Peedee

Black Creek

Middendorf

Cape Fear

Lower

Cretaceous

Lower

Cretaceous

aquifer

Lower

Cape Fear

aquifer

Upper

Cape Fear

aquifer

Black Creek

aquifer

Peedee

aquifer

Beaufort

aquifer

Castle

Hayne

aquifer

Yorktown

aquifer

Lower Cape Fear CU

Upper Cape Fear CU

Black Creek CU

Castle Hayne CU

Beaufort CU

Peedee

confining unit

Rockpoint

Member

Surficial 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Yorktown confining unit

Paleontology

Tiger Leap absent

Crouch Branch 

confining unit

Crouch Branch 

aquifer

Crouch Branch 

confining unit

Charleston 

confining unit

McQueen Branch 

aquifer

Charleston 

confining unit

Crouch Branch 

confining unit

C

D

V

V/

IV

IV

Cu

Cm

Cl

b

a
64 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Surficial Aquifer

The surficial aquifer (model layer 1, Chapter C) is the 

uppermost aquifer in the system of aquifers and confining 

units that compose the hydrogeologic framework of the NC 

Coastal Plain (fig. B4, Appendix B1). The surficial aquifer 

is unconfined; thus the water table fluctuates in response to 

changes in groundwater storage. The surficial aquifer is the 

first aquifer to receive recharge, storing water as it moves 

laterally to rivers, lakes, and other discharge areas, and downward in smaller quantities to deeper, confined aquifers. The 

surficial aquifer is uniformly present across the NC Coastal 

Plain, except where it is fully incised by rivers or streams. 

The top is equivalent to land surface, which generally slopes 

toward the coast and ranges in altitude from about 0 to 600 ft 

(fig. B5, Appendix B1). The thickness of the surficial aquifer 

in NC ranges from less than 10 ft in the central, northern, and 

southern parts of the NC Coastal Plain to more than 100 ft 

in parts of the Sand Hills and coastal areas (figs. B1, B6; 

Appendix B1).

The surficial aquifer is primarily composed of permeable sediments of Quaternary age, but it also contains older 

sediments in some areas because of the varying stratigraphic 

position of the first underlying confining layer. Included are 

the overlying soils, which vary in infiltration capacity across 

the region, thus affecting the rates at which recharge occurs. In 

terms of lithology, the surficial aquifer is generally composed 

of layers of sand and shell beds that vary highly in hydraulic 

conductivity due to variations in clay content and degree of 

cementation. In the outer Coastal Plain of NC (fig. B1), shallow sediments were deposited in a marginal marine environment (Brown and others, 1972), consisting of fine-grained 

sand, silt, clay, shell material, peat, and combinations thereof. 

Within the inner Coastal Plain of NC (fig. B1), shallow 

sediments become increasingly fluvial in character, become 

coarser and more poorly sorted, and consist of sand, sandy 

clay, clay, and scattered gravel units. 
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 65

Figure B5. Areal extent and altitude of the top of the surficial aquifer (layer 1) in the Atlantic Coastal Plain of North and South 

Carolina Coastal Plain and parts of Virginia and Georgia, 2007.

Atlantic

Ocean

100

EXPLANATION

200

Extent of aquifer

Structure contour—Approximate altitude

 of top of the surficial aquifer. Datum is

 NGVD 29. Contour interval is variable

Hydrostratigraphic borehole

Figure B5. Areal extent and altitude of the top of the surficial aquifer (layer 1) in the Atlantic Coastal Plain of 

North and South Carolina Coastal Plain and parts of Virginia and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

50

100

100

200

300

400

500

50

100

200

300

400

400

300

400 400

300

50

300

400 500

600

500

500

200

100

50

100

200

Fall

Line
66 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B6. Thickness of the surficial aquifer in the Atlantic Coastal Plain of North and South Carolina (layer 1) and parts of Virginia 

and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

50

10

10

10

10

10

10

100

100

100

50

50

50

50

50

10

10

10

10

10

100 100

100

10

100

50

50

10

10

10

50

50

50

50

50

100

50

10

10

50 50

50

50

50

50

50

50

5

50

10

100

100

Atlantic

Ocean

EXPLANATION

100

Extent of aquifer

Line of equal thickness in feet.

 Contour interval is variable

Hydrostratigraphic borehole

Figure B6. Thickness of the surficial aquifer in the Atlantic Coastal Plain of North and South Carolina (layer 1) and 

parts of Virginia and Georgia, 2007. 

Fall

Line
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 67

Yorktown Confining Unit and Aquifer

The Yorktown confining unit (model layer 2, Chapter C) 

consists of a series of clay and silt beds that do not compose a 

single unit because they vary greatly in stratigraphic position. 

The top of the Yorktown confining unit ranges in altitude from 

less than –100 ft to over 100 ft (fig. B7, Appendix B1). The 

confining unit thickness ranges from less than 10 to more than 

50 ft in the NC Coastal Plain (fig. B8). Where Yorktown aquifer sands are present and the confining unit pinches out, these 

sands are included in the surficial (or unconfined) aquifer.

The Yorktown aquifer (model layer 3, Chapter C) is present only in the northern half of the NC Coastal Plain and is 

bounded to the west by the Fall Line (fig. B1). The aquifer is 

made up primarily of the Yorktown Formation of Pliocene age, 

but also contains part of the Miocene Pungo River Formation 

in the NC East Central Coastal Plain. It contains Quaternaryage sands in areas where the confining unit is in a higher 

stratigraphic position. The lithology of the aquifer consists of 

lenticular quartz sands that are fine to medium grained, shelly 

and clayey, and interbedded with blue to gray colored clay. Layers of shell material and gray colored shell marls are typically 

present. The unit generally contains numerous phosphatic zones. 

The aquifer is shallow enough in the western part of the NC 

Coastal Plain to be incised by streams and rivers, allowing direct 

discharge to surface water. The Yorktown aquifer is recharged 

by water moving downward from the overlying surficial aquifer.

Although outliers of the Yorktown Formation are present 

in Robeson, Bladen, Columbus, and Duplin Counties (fig. B1), 

they are not separated from the surficial aquifer by a recognizable confining unit. These outliers, are therefore not considered to be a distinct aquifer in these areas. The Yorktown 

aquifer is thus absent over the entire southern part of the NC 

Coastal Plain. 

The Yorktown aquifer ranges in observed altitudes from 

–100 ft near the NC coast to 100 ft along the Fall line in NC 

(fig. B9). The aquifer thickens eastward from where it directly 

overlies basement rock at the Fall Line to a maximum of more 

than 300 ft in easternmost NC (fig. B10). Beds which compose 

the Yorktown confining unit and aquifer are equivalent in 

terms of their stratigraphic relation to Miocene, Pliocene, and 

younger formations in SC that are not grouped into a separate 

aquifer, and are considered to be part of the surficial aquifer. 

Therefore, there is no counterpart to the Yorktown confining 

unit and aquifer in SC. 

Reported transmissivities by Lautier (1998a) for the 

Yorktown aquifer in the northeastern NC Coastal Plain ranged 

from 1 to 2,350 feet squared per day (ft2/d), and horizontal 

hydraulic conductivities were in the range of 0.2 to 98 feet 

per day (ft/d), based on five aquifer tests. Winner and Coble 

(1996) used geophysical and lithologic data from 52 wells 

to estimate an average horizontal hydraulic conductivity of 

22 ft/d.
68 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B7. Areal extents and the top altitudes of the Yorktown confining unit (North Carolina) and Upper Floridan confining unit 

(South Carolina) (layer 2), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

Extent of confining unit. Dashed where

 approximately located.

Structure contour—Approximate altitude of top of

 Yorktown (NC) and Upper Floridan (SC) confining

 units. Datum is NGVD 29. Contour interval is

 50 feet. Dashed where approximately located

Hydrostratigraphic borehole

Atlantic

Ocean

Figure B7. Areal extents and the top altitudes of the Yorktown confining unit (North Carolina) and Upper Floridan 

confining unit (South Carolina) (layer 2), in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.

50

0

50

50

–50

–100

100

100

200

100

50

0

–50

Fall

Line

Upper Floridan

confining unit

Yorktown

confining unit
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 69

Figure B8. Thickness of the Yorktown confining unit (North Carolina) and Upper Floridan confining unit (South Carolina) (layer 2) in 

the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

Fall

Line

 

EXPLANATION

200

Extent of confining unit. Dashed where

 approximately located.

Line of equal thickness, in feet. Contour

 interval is variable

Hydrostratigraphic borehole

50

50

10

10

10

10

10

10

10

10

300

200

100

10

10

10

50

Figure B8. Thickness of the Yorktown confining unit (North Carolina) and Upper Floridan confining unit (South Carolina)

 (layer 2) in the Atlantic Coastal Plain of North and South Carolina (layer 2) and parts of Virginia and Georgia, 2007.

Upper Floridan

confining unit

Yorktown

confining unit
70 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B9. Areal extents and the top altitudes of the Yorktown aquifer (North Carolina) and Upper Floridan aquifer (South Carolina) 

(layer 3), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where

 approximately located

Structure contour—Approximate altitude

 of top of Yorktown (NC) and Upper Floridan (SC)

 aquifers. Datum is NGVD 29. Contour interval is

 variable. Dashed where approximately located

Hydrostratigraphic borehole

Fall

Line

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

 

EXPLANATION

200

100

100 150

50

–50

–100

0

0

–200

–200

–50 –100

0

50

100

150

150

200

200

250

250

–300

Figure B9. Areal extents and the top altitudes of the Yorktown aquifer (North Carolina) and Upper Floridan 

aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia, 2007.

Upper Floridan

aquifer

Yorktown

aquifer
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 71

Figure B10. Thickness of the Yorktown aquifer (North Carolina) and Upper Floridan aquifer (South Carolina) (layer 3) in the Atlantic 

Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where

 approximately located

Structure contour—Approximate altitude

 of top of Yorktown (NC) and Upper Floridan (SC)

 aquifers. Datum is NGVD 29. Contour interval is

 variable. Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

 

EXPLANATION

200

100

10

10

10

50

50

50

10

10

300

200

200

100

100

100

10

100

100

100

100

10

10

10

10

Figure B10. Thickness of the Yorktown aquifer (North Carolina) and Upper Floridan aquifer (South Carolina) (layer 3) in the 

Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Upper Floridan

aquifer

Yorktown

aquifer

Fall

Line
72 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Castle Hayne Confining Unit and Aquifer

The Castle Hayne confining unit (model layer 4, Chapter C) consists of clay and silt beds that vary in stratigraphic 

position between the upper part of the Castle Hayne Formation 

and younger units of variable age that overlie this formation across the NC Coastal Plain (fig. B4). The Castle Hayne 

confining unit is absent at a number of wells in the central and 

southern NC Coastal Plain, leaving the Castle Hayne aquifer 

in direct hydraulic connection with the shallower Yorktown or 

surficial aquifers. In many areas where the Castle Hayne aquifer is close to the surface, the Castle Hayne confining unit is 

thin or absent, and water-level differences are slight between 

the surficial and Castle Hayne aquifers. The top of the Castle 

Hayne confining unit ranges in altitude from –600 to over 

61 ft (fig. B11, Appendix B1), and the thickness ranges from 

less than 1 to more than 300 ft in Currituck County (fig. B12). 

The Middle Floridan confining unit and aquifer in SC are 

equivalent to the Castle Hayne confining unit and aquifer in 

NC. However, the units are not continuous or hydraulically 

connected between the two States.

The Castle Hayne aquifer (model layer 5, Chapter C) is 

the most productive aquifer in the NC Coastal Plain. Transmissivity exceeds 35,000 ft2

/d, and the aquifer can yield up to 

1,000 gallons per minute (gal/min) where it is best developed 

in the east-central part of the NC Coastal Plain. The aquifer is 

made up primarily of the Castle Hayne Formation of Eocene 

age, but also includes the Oligocene Belgrade and Riverbend 

Formations, where present above the Castle Hayne Formation (fig. B4). In areas where the underlying Beaufort confining unit is missing or deeper in the stratigraphic section, the 

aquifer may also include part or all of the Beaufort Formation of Paleocene age. The Castle Hayne aquifer contains the 

uppermost part of the Peedee Formation in localized areas 

where the Beaufort Formation is missing. In the northeastern 

NC Coastal Plain, the aquifer commonly contains sands of 

the Pungo River Formation in its upper part. The equivalent 

units to the Castle Hayne aquifer in SC are the Upper and 

Middle Floridan aquifers, although these are not contiguous or 

hydraulically connected. 

In terms of lithology, the Castle Hayne aquifer in the central and southern NC Coastal Plain may be generally described 

as a sandy, molluscan-mold limestone (Spring Garden 

Member) and a bryozoan-echinoid skeletal limestone (Comfort Member). The aquifer lithology grades downward into a 

calcareous, fine-grained sandstone. Where the Belgrade and 

River Bend Formations make up the upper part of the aquifer 

in Pender, Onslow, Jones, and Cartaret Counties (fig. B1), 

lithologies include oyster shells in a tan to orange sand matrix, 

fossiliferous, clayey sand, calcarenite, and sandy, molluscanmold limestone. In the northeastern Coastal Plain, the aquifer 

is thin and composed primarily of sandy, glauconitic biomicrite, interbedded with pale green dolomite. The usefulness of 

the Castle Hayne aquifer as a water source greatly diminishes 

in the counties north of the Albemarle Sound (fig. B1) due to a 

reduction in transmissivity and hydraulic conductivity. 

The Castle Hayne aquifer thickens from west to east, to a 

maximum of 530 ft, and becomes more deeply buried toward 

the east (fig. B13; Plates 3, 4, and 5). The top of the Castle 

Hayne aquifer ranges in observed altitudes of –759 ft in the 

easternmost parts of the NC Outer Banks to 61 ft in Lenoir 

County (fig. B14, Appendix B1).

The Castle Hayne aquifer is recharged by water that 

leaks through its confining layer from the shallower Yorktown 

and surficial aquifers. In the outcrop area of the Castle Hayne 

Formation in northern Craven, eastern Jones, Onslow, Pender, 

New Hanover, and Brunswick Counties (fig. B1), the aquifer is 

overlain only by a thin veneer of sediments of post-Yorktown 

age, which allows for greater recharge rates, especially where 

substantial clay layers are absent in the shallow subsurface. 

Hydrograph data from groundwater monitoring sites (Plates 3,

4, and 5) indicate that where the Castle Hayne aquifer is 

present in the shallow subsurface, nearly identical seasonal 

water-level fluctuations occur in the surficial and Castle Hayne 

aquifers, indicating a similar rate of recharge to both aquifers. 
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 73

Figure B11. Areal extents and the top altitudes of the Castle Hayne confining unit (North Carolina) and the Middle Floridan confining 

unit (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining units. Dashed where

 approximately located

Structure contour—Approximate altitude of

 top of Castle Hayne (NC) and Middle Floridan (SC)

 confining units. Datum is NGVD 29. Contour

 interval is variable. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

EXPLANATION

200

0

0

–50

–100

50

50

–300

–200

–400

–600

–500

–400

–300

–200

–100

–50

50

50 0

200

150

–600

–50

–100

Middle Floridan

confining unit

Castle Hayne

confining unit

Figure B11. Areal extents and the top altitudes of the Castle Hayne confining unit (North Carolina) and the 

Middle Floridan confining unit (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007.
74 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B12. Thickness of the Castle Hayne confining unit (North Carolina) and the Middle Floridan confining unit (South Carolina) 

(layer 4) in the Atlantic Coastal Plain of North Carolina and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Extent of confining units. Dashed where

 approximately located

Line of equal thickness, in feet. Contour

 interval is variable. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

EXPLANATION

200

10

200

100

50

10

300

10

50

50

100

100200

300

100

10 10

50

Middle Floridan

confining unit

Castle Hayne

confining unit

Figure B12. Thickness of the Castle Hayne confining unit (North Carolina) and the Middle Floridan confining unit (South Carolina)

(layer 4) in the Atlantic Coastal Plain of North Carolina and South Carolina and parts of Virginia and Georgia, 2007.
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 75

Figure B13. Thickness of the Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer (South Carolina) (layer 5) in the 

Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Extent of confining units. Dashed where

 approximately located

Structure contour—Approximate altitude of

 top of Castle Hayne (NC) and Middle Floridan (SC)

 confining units. Datum is NGVD 29. Contour

 interval is variable. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

200

0

–200

0

–800

–600

–600

–400

50

0

–200

200

200

–600

–400

EXPLANATION

200

Middle Floridan

aquifer

Castle Hayne

aquifer

Figure B13. Areal extents and top altitudes of the Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer (South

Carolina) (layer 5) in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007. 
76 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B14. Areal extents and top altitudes of the Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer (South 

Carolina) (layer 5) in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007. 

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifers. Dashed where

 approximately located

Line of equal thickness in feet. Contour

 interval is variable. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

10

50

50

0

50

50

10

10

50

100

EXPLANATION

200

10

10

10

10

50

100

200 300

300

10

10

Middle Floridan

aquifer

Castle Hayne

aquifer

Figure B14. Thickness of the Castle Hayne aquifer (North Carolina) and the Middle Floridan aquifer (South Carolina) (layer 5)

 in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 77

Beaufort Confining Unit and Aquifer

The Beaufort confining unit (model layer 6, Chapter C) 

is composed of clays and silts in the upper part of the Beaufort 

Formation and the lower part of the Castle Hayne Formation 

(fig. B4). West of the updip limit of the Castle Hayne Formation, the confining unit can include clay and silt beds in the 

lower part of the Yorktown Formation, or where the Yorktown 

is missing clay and silt beds of Quaternary age. The top altitude of the Beaufort confining unit ranges from 0 ft parallel to 

the Fall Line to as deep as –1,127 ft in the northeastern part of 

the NC Coastal Plain (fig. B15, Appendix B1). The thickness of 

the Beaufort confining unit ranges from zero, in areas where it 

is eroded or pinches out, to a maximum of about 50 ft, where 

it is best developed in northeastern NC (fig. B16). The Gordon 

confining unit and aquifer in SC are equivalent to the Beaufort 

confining unit and aquifer in NC; however, the units are not 

continuous or hydraulically connected between the two States.

The Beaufort aquifer (model layer 7, Chapter C) extends 

through the eastern section of the northern half of the NC 

Coastal Plain. The aquifer is made up primarily of glauconitic, fossiliferous, and some clayey sands and intermittent 

thin limestone beds of the Paleocene Beaufort Formation. 

The aquifer also may include sandy limestone and sands of 

the lowermost Castle Hayne Formation (fig. B4). At some 

locations, the Beaufort aquifer includes sands and clays of 

the uppermost part of the Peedee Formation. Geophysical 

logs and water-level data indicate that the Beaufort aquifer is 

hydraulically connected to the Castle Hayne aquifer in many 

areas of the eastern NC Coastal Plain because of discontinuous confining beds. In these areas, the Beaufort is part of the 

Castle Hayne aquifer (Plate 6). Lloyd (1968) reported an average transmissivity of 1,600 ft2

/d in Chowan County, based on 

an average of 22 aquifer-test calculations. Winner and Coble 

(1996) reported an average horizontal hydraulic conductivity 

of 35 ft/d. 

The top of the Beaufort aquifer ranges in observed altitude from over –1,000 ft in northeastern NC to –5 ft in Jones 

County (fig. B17, Appendix B1). The maximum observed 

thickness of the aquifer is about 300 ft in northeastern NC 

(fig. B18). 
78 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B15. Areal extents and the top altitudes of the Beaufort confining unit (North Carolina) and the Gordon confining unit 

(South Carolina) (layer 6), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifers. Dashed where

 approximately located

Structure contour—Approximate altitude of

 Beaufort (NC) and Gordon (NC) confining units.

 Datum is NGVD 29. Contour interval is variable.

 Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

50

100 0

–200

–400

–400

–600

–800

–1,000

–800

–600

–400

–200

0

50

50

50

100

200

Beaufort

confining unit

Gordon

confining unit

Figure 15. Areal extents and the top altitudes of the Beaufort confining unit (North Carolina) and the Gordon 

confining unit (South Carolina) (layer 6), in the Atlantic Coastal Plain of North and South Carolina and parts of

Virginia and Georgia, 2007.

Atlantic

Ocean
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 79

Figure B16. Thickness of the Beaufort confining unit (North Carolina) and the Gordon confining unit (South Carolina) (layer 6), in 

the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining units. Dashed where

 approximately located

Line of equal thickness, in feet. Contour

 interval is variable. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

50

10

10

10

10

10

50

50

–300 –200

0

50

50

50

50

10

50

100

100

10

50

Gordon

confining unit

Beaufort

confining unit

Figure B16. Thickness of the Beaufort confining unit (North Carolina) and the Gordon confining unit (South Carolina) 

(layer 6), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.
80 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B17. Areal extents and the top altitudes of the Beaufort aquifer (North Carolina) and the Gordon aquifer (South Carolina) 

(layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining units. Dashed where

 approximately located

Structure contour—Approximate altitude of

 top of Beaufort (NC) and Gordon (SC) aquifers.

 Datum is NGVD 29. Contour interval is variable.

 Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

0

–1,200

–1,000

–800

–600

–400

–200

100

200300 400

0

–200

–400

–600

–800

–1,000

Gordon

aquifer

Beaufort

aquifer

Figure B17. Areal extents and the top altitudes of the Beaufort aquifer (North Carolina) and the Gordon aquifer 

(South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and 

Georgia, 2007.
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 81

Figure B18. Thickness of the Beaufort aquifer (North Carolina) and the Gordon aquifer (South Carolina) (layer 7), in the Atlantic 

Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

10

50

50

100

Extent of aquifers. Dashed where

 approximately located

Line of equal thickness, in feet. Contour

 interval is variable. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

10

100

200

300

200

200

300

200

100

200

50

50

10 10

50

10

50

10

10

50

100

100

300

EXPLANATION

200

Gordon

aquifer

Beaufort

aquifer

50

Figure B18. Thickness of the Beaufort aquifer (North Carolina) and the Gordon aquifer (South Carolina) (layer 7), 

in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007
82 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Peedee Confining Unit and Aquifer

The Peedee confining unit (model layer 8, Chapter C) 

comprises beds of clay and silt with varying amounts of sand, 

and is positioned stratigraphically near the contact of the 

Paleocene Beaufort and Late Cretaceous Peedee Formations 

in the eastern NC Coastal Plain (fig. B4). West of the updip 

limit of the Beaufort Formation, the Peedee confining unit 

is composed of the uppermost Peedee or in the lower part 

of the Yorktown Formations, or in beds of early Quaternary 

age (where the Yorktown is absent). The top of the Peedee 

confining unit varies from about 0 ft in the southeastern part 

of the NC Coastal Plain to more than –1,324 ft in the eastern 

NC Coastal Plain (fig. B19, Appendix B1). The thickness of 

the Peedee confining unit varies between 0 ft, where it pinches 

out, to a maximum observed value of about 50 ft in Craven 

County (fig. B20). In areas where the Peedee aquifer is directly 

overlain by the surficial aquifer, the Peedee aquifer acts as 

a semi-confined aquifer, and water levels are affected by 

seasonal recharge variations. In SC, the Peedee confining unit 

and aquifer are equivalent to the Crouch Branch confining unit 

and aquifer. 

The Peedee aquifer (model layer 9, Chapter C) is present over most of the eastern NC Coastal Plain except for the 

northeastern counties. The aquifer pinches out to the north, 

just north of Warsaw, NC (well 35, Plate 5). 

The Peedee aquifer is composed mainly of the Late 

Cretaceous Peedee Formation, but also may include part of 

the Late Cretaceous Black Creek Formation, and the lower 

part of the Beaufort Formation, where present (fig. B4). Updip 

from the western limit of the Beaufort Formation, the Peedee 

aquifer also may include sediments of Quaternary age. In 

areas where the Peedee Formation is directly overlain by the 

Yorktown Formation, sands in the upper part of the Yorktown 

Formation can be included in the Peedee aquifer. Due to the 

number of formations included, the lithology of the aquifer 

is variable. In general terms, the lithology is characterized as 

greenish gray to light brown, silty to clayey, fine- to very finegrained quartz sand with trace quantities of glauconite, phosphorite, oyster shells, and pyrite. In southeastern Brunswick 

and north central New Hanover Counties (fig. B1), the Rocky 

Point Member makes up the uppermost part of the Peedee Formation, consisting of gray, sandy, moldic limestone, grading 

downward to calcareous sandstone. In some areas, the updip 

limit of the Peedee aquifer extends a few miles further to the 

west than the limit of the Peedee Formation, as delineated on 

the NC geologic map (Brown and others, 1985) because the 

Peedee aquifer contains older and younger beds below and 

above the Peedee Formation.

Various investigators have reported transmissivity values 

for the Peedee aquifer, including Lautier (2002), who calculated a range of 240 to 1,170 ft2

/d for the central part of 

the NC Coastal Plain. In the southern part of the NC Coastal 

Plain, Lautier (2006) reported a range of 40 to 340 ft2/d for the 

Peedee aquifer. Harden and others (2003) estimated transmissivity values in Brunswick County between 3,000 and 

6,000 ft2/d. 

The top altitudes of the Peedee aquifer range from 86 ft 

in Lenoir County to about –1,355 in Dare County (fig. B21, 

Appendix B1). The maximum thickness of the Peedee aquifer 

is about 300 ft in Brunswick County (fig. B22). 

The Peedee aquifer primarily receives recharge by vertical leakage from overlying aquifers. Recharge also occurs in 

interstream areas where heads are lower in the Peedee aquifer 

than in shallower aquifers. Where the head is higher in the 

Peedee than in overlying aquifers, discharge occurs to streams 

and rivers. The rate of recharge is directly proportional to the 

vertical hydraulic conductivity and head difference across 

the confining bed, and inversely proportional to the thickness 

of the confining bed. Regional differences in these factors, 

as well as variations in the transmissivity of the aquifer, can 

cause recharge rates to vary across the study region. 
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 83

Figure B19. Areal extents and the top altitudes of the Peedee confining unit (North Carolina) and the Crouch Branch confining unit 

(South Carolina) (layer 8), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Structure contour—Approximate altitude of

top of Peedee/Crouch Branch confining unit.

 Datum is NGVD 29. Contour interval is variable.

 Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

0

0

–200

–400

–600

–800

200

0

–200

–400

–600

–800

–1,000

–1,200

–1,400 –1,600

Peedee/Crouch Branch

confining unit

Figure B19. Areal extents and the top altitudes of the Peedee confining unit (North Carolina) and the Crouch Branch 

confining unit (South Carolina) (layer 8), in the Atlantic Coastal Plain of North and South Carolina and parts of

Virginia and Georgia, 2007.
84 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B20. Thickness of the Peedee confining unit (North Carolina) and the Crouch Branch confining unit (South Carolina) (layer 8), 

in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Line of equal thickness, in feet. Contour interval

 is variable. Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

EXPLANATION

200

10

50

50

10

200

200

300

10

100

50

300

10

Peedee/Crouch Branch

confining unit

Figure B20. Thickness of the Peedee confining unit (North Carolina) and the Crouch Branch confining unit (South Carolina) 

(layer 8), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 85

Figure B21. Areal extents and the top altitudes of the Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where

 approximately located

Structure contour—Approximate altitude

 of Peedee/Crouch Branch aquifer. Datum is

 NGVD 29. Contour interval is 200 feet. Dashed

 where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

EXPLANATION

200

0

0

50

400

200

200

200

0

–200

–400

–800

–600

–400

200

–600

–800

–1,000

–1,200

–1,400

–1,600

–1,800

Peedee/Crouch Branch

aquifer

Figure 21. Areal extents and the top altitudes of the Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia, 2007.

Fall

Line
86 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B22. Thickness of the Peedee aquifer (North Carolina) and the Crouch Branch aquifer (South Carolina) (layer 9), in the 

Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where

 approximately located

Line of equal thickness, in feet. Contour interval

 is variable. Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

10

10

10

50

100

100

10

50

200

100

500

50

300

400

500

400

300

100

200

400

Peedee/Crouch Branch

aquifer

Figure B22. Thickness of the Peedee aquifer (North Carolina) and the Crouch Branch aquifer (South Carolina) (layer 9), 

in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 87

Black Creek Confining Unit and Aquifer

The Black Creek confining unit (model layer 10, Chapter C) separates the Peedee aquifer from the Black Creek 

aquifer. Over most of the eastern NC Coastal Plain, the Black 

Creek confining unit is a thick, massive section of clay and silt 

with variable amounts of sand. This unit is primarily within 

the Black Creek Formation, but also contains lower clay and 

silt beds of the Peedee Formation (fig. B4). In the western NC 

Coastal Plain, the Black Creek confining unit may also include 

the lower part of the Yorktown Formation. Where the Yorktown is absent, the Black Creek confining unit includes clay 

and silt beds in the lower part of the Quaternary formations. 

The confining unit has been incised in major stream valleys 

in many parts of the western Coastal Plain and is well developed only in the interfluvial areas. The top of the Black Creek 

confining unit ranges in altitude from a high of over 200 ft to a 

low of –1,511 ft (fig. B23, Appendix B1). Over the entirety of 

the NC Coastal Plain, the Black Creek confining unit ranges 

in thickness from less than 10 ft along the updip limit to more 

than 200 ft in southeastern NC (fig. B24). The Black Creek 

confining unit and aquifer are equivalent to the McQueen 

Branch confining unit and aquifer in SC. The units are hydraulically connected between NC and SC.

The Black Creek aquifer (model layer 11, Chapter C) 

is made up primarily of the Late Cretaceous Black Creek 

Formation, but also includes permeable beds from older and 

younger formations in the NC Coastal Plain; in localized 

areas, it includes sands in the lower part of the Peedee Formation (fig. B4). In some places in northern Wayne and Greene, 

western Pitt, and Martin Counties, the Black Creek aquifer 

includes sands or shell beds in the lower part of the Yorktown 

Formation. Where the Yorktown and Peedee aquifers are 

absent in the southern part of the Coastal Plain, sands in the 

lower part of the Quaternary units make up part of the Black 

Creek aquifer. In the southwestern Coastal Plain, the Late 

Cretaceous Middendorf Formation interfingers with the Black 

Creek aquifer and appears to be connected hydraulically. Due 

to variations in the stratigraphic position of the Upper Cape 

Fear confining unit, the top of which defines the base of the 

Black Creek aquifer, sands in the Cape Fear Formation are 

included in the Black Creek aquifer over localized areas. 

The Black Creek aquifer is made up of alternating beds 

of sand and clay. The sands are generally gray to olive gray in 

color, fine to medium grained, poorly sorted, and contain variable amounts of glauconite, phosphorite, shell fragments, and 

lignite, and traces of mica, pyrite, and marcasite. The lignite is 

of primary origin from organic material deposited along with 

the inorganic part of the sediments. Clays are generally gray to 

black and organic-rich. Individual sands appear to be laterally 

discontinuous based on electric log correlation (Plates 3, 4, 5,

and 6). However, it is evident that sands in the aquifer are well 

connected hydraulically over long distances, due to the widespread lateral transmission of drawdown effects from concentrated pumping centers in the central part of the NC Coastal 

Plain. The Black Creek aquifer is heavily used in the central 

and southern Coastal Plains due to its high-quality water and 

negligible treatment costs. Due to overuse of the Black Creek 

aquifer in the central part of the NC Coastal Plain, the State of 

NC has implemented mandatory withdrawal reduction rules in 

conjunction with capacity-use law in order to manage drawdown effects (North Carolina Division of Water Resources, 

2001). Reduction rules were applied in this part of the NC 

Coastal Plain to the Upper and Lower Cape Fear aquifers as 

well. Reported transmissivities of the Black Creek aquifer 

range from 290 to 1,700 ft2/d from an analysis of 15 aquifer 

tests (Lautier, 2002, 2006). 

The Black Creek aquifer pinches out along the Fall Line 

at the updip limit of the sediments. The approximate updip 

limit extends eastward through Wayne, Wilson, Edgecombe, 

and Martin Counties (fig. B1) to the NC coast, south of Albemarle Sound. The Black Creek Formation is present to the 

north of Albemarle Sound, but consists primarily of clay and 

is therefore mapped as part of the Upper Cape Fear confining 

unit. The altitude of the top of the Black Creek aquifer ranges 

from 317 ft above NGVD 29 in Richmond County to –1,612 ft 

in Dare County (fig. B25, Appendix B1). The Black Creek 

aquifer reaches a minimum thickness of less than 10 ft along 

the updip limit and a maximum thickness of 442 ft in Onslow 

County (fig. B26). The Black Creek aquifer is poorly defined 

in counties further east of Craven County. 
88 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B23. Areal extents and the top altitudes of the Black Creek confining unit (North Carolina) and the McQueen Branch confining 

unit (South Carolina) (layer 10), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Structure contour—Approximate altitude of top of

 Black Creek/McQueen Branch confining unit.

 Contour interval is 200 feet. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

200

–200

–400

–600

200

200

200

200

400

0

–800

–200

–400

–600

–800

–1,000

–1,200

–1,400

–1,600

0

Black Creek/

McQueen Branch

confining unit

Figure B23. Areal extents and the top altitudes of the Black Creek confining unit (North Carolina) and the McQueen

Branch confining unit (South Carolina) (layer 10), in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007.

Fall

Line
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 89

Figure B24. Thickness of the Black Creek confining unit (North Carolina) and the McQueen Branch confining unit (South Carolina) 

(layer 10), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Line of equal thickness, in feet. Contour

 interval is variable. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

10

200

100

100

50

100

10

100

200

200

50

10

10

50

Black Creek/

McQueen Branch

confining unit

Figure B24. Thickness of the Black Creek confining unit (North Carolina) and the McQueen Branch confining unit 

(South Carolina) (layer 10), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.
90 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B25. Areal extents and the top altitudes of the Black Creek aquifer (North Carolina) and the McQueen Branch aquifer 

(South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Structure contour—Approximate altitude of top of

 Black Creek/McQueen Branch aquifer. Datum is

 NGVD 29. Contour interval is 200 feet. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

200

–200

–200

–400

–600–800

200

200

200

200

0

–1,000

–1,200

–800

–600

–1,000

–400

–600

–800 –1,000

–1,200

–1,400

–1,600

2,000

–2,200

–2,400

–1,800

Black Creek/

McQueen Branch

aquifer

Figure B25. Areal extents and the top altitudes of the Black Creek aquifer (North Carolina) and the McQueen 

Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007.

Fall

Line
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 91

Figure B26. Thickness of the Black Creek aquifer (North Carolina) and the McQueen Branch aquifer (South Carolina) (layer 11), 

in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where

 approximately located

Line of equal thickness, in feet. Contour interval

 is variable. Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

EXPLANATION

200

10

10

10 50

10

300

100

10

50

100

10 200

200

100

50 300

300

100

50

10

200

300

200

50

10

Black Creek/McQueen

Branch aquifer

Figure B26. Thickness of the Black Creek aquifer (North Carolina) and the McQueen Branch aquifer (South Carolina) 

(layer 11), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007

Fall

Line
92 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Upper Cape Fear Confining Unit and Aquifer

The Upper Cape Fear confining unit (model layer 12, 

Chapter C) consists of beds of clay and silt and variable but 

lesser amounts of sand that are in the upper part of the Cape 

Fear Formation and the lower part of the Black Creek Formation in some places (fig. B4). Where the Yorktown Formation 

directly overlies the Cape Fear Formation in the northern 

Coastal Plain, beds of low permeability in the lower part of 

the Yorktown Formation make up part of the Upper Cape Fear 

confining unit in some areas. In places where the Cape Fear 

Formation is directly overlain by sediments of Quaternary age, 

clays and silts in the lower part of the Quaternary are considered to be part of the confining unit. The altitude of the top of 

the Upper Cape Fear confining unit ranges from 200 ft along 

the updip limit to about –1,200 ft in southeastern NC (fig. B27, 

Appendix B1). The thickness of the Cape Fear confining unit 

ranges from about 50 ft over most of the NC Coastal Plain to 

about 100 ft along the NC–SC border (fig. B28). In SC, the 

Upper Cape Fear confining unit and aquifer are correlative and 

hydraulically connected to the Charleston confining unit and 

aquifer in SC.

The Upper Cape Fear aquifer (model layer 13, Chapter C) is made up primarily of the upper part of the Cape Fear 

Formation of Upper Cretaceous age. In some places, the Cape 

Fear aquifer can also include the Middendorf Formation or 

lowermost sands of the Black Creek Formation (fig. B4). The 

Black Creek aquifer is present over most of the NC Coastal 

Plain, pinching out either at the Fall Line or a few miles to 

the east of the Fall Line. Over the majority of the NC Coastal 

Plain, the lithology of the aquifer consists of alternating 

layers of clay and gray to red, poorly sorted, fine- to coarsegrained sand. Conglomerates and gravel beds are also common and increase the permeability of the aquifer. Also present 

throughout are accessory iron oxide minerals such as pyrite, 

marcasite, and siderite. Sediments of the Cape Fear Formation 

are interpreted to be nonmarine in origin, and were deposited 

in a fluvial-deltaic environment. In the easternmost counties 

of the NC Coastal Plain, thin limestone beds are present in the 

Cape Fear Formation, indicating the juxtaposition of marine 

and nonmarine sediments downdip. Although individual sand 

beds in the Cape Fear aquifer appear to be laterally discontinuous based on electric logs, drawdown effects are easily transmitted laterally through the aquifer over widespread areas. 

 Large cones of depression have formed around pumping 

centers in the central part of the NC Coastal Plain, in Bladen 

County and surrounding counties in the southern NC Coastal 

Plain, and in the northeastern NC Coastal Plain due to largevolume pumping from the southern Virginia area. Reported 

transmissivities in the Upper Cape Fear aquifer range from 

25 to 440 ft2/d in the central NC Coastal Plain (Lautier, 2002) 

based on analyses of three aquifer tests. In the northeastern 

NC Coastal Plain, transmissivity from one aquifer test produced a result of 920 ft2

/d (Lautier, 1998a). 

The top of the Upper Cape Fear aquifer ranges in 

observed altitudes from about –1,400 ft in Dare County to 

over 200 ft in Moore County, near the Fall Line (fig. B29,

Appendix B1). The Upper Cape Fear aquifer ranges in thickness from less than 10 ft along the updip limit of the aquifer to 

665 ft in northeastern NC (fig. B30).

In NC, both the Upper and Lower Cape Fear aquifers 

are composed of sediments that are considered to be Upper 

Cretaceous in age, although inadequate data exist to determine 

with much confidence where the top of the Early Cretaceous is 

present. In SC, the equivalent to the Upper Cape Fear aquifer 

is the Charleston aquifer and confining unit. The Charleston 

and Upper Cape Fear aquifers are connected hydraulically as 

evidenced by water-level declines in Columbus and Robeson 

Counties, NC, due to pumping from the Charleston aquifer 

in SC. 
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 93

Figure B27. Areal extents and the top altitudes of the Upper Cape Fear confining unit (North Carolina) and the Charleston confining 

unit (South Carolina) (layer 12), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Structure contour—Approximate altitude of the top of

 the Upper Cape Fear/Charleston confining unit.

 Datum is NGVD 29. Contour interval is 200 feet.

 Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

–1,200 –1,000

–1,000

–800

–800

0

–600

–400

–1,200

–200

–1,400 400

–600

–600

–800

–1,000

–1,200

–1,400

–1,600

–1,800

–2,000

–2,200

–2,400

–2,600

Upper Cape Fear /

Charleston confining 

unit

Figure B27. Areal extents and the top altitudes of the Upper Cape Fear confining unit (North Carolina) and the 

Charleston confining unit (South Carolina) (layer 12), in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia, 2007.

Fall

Line
94 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B28. Thickness of the Upper Cape Fear confining unit (North Carolina) and the Charleston confining unit (South Carolina) 

(layer 12), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Line of equal thickness, in feet. Contour interval

 is variable. Dashed where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

10

10

10 50

50

50

100

50

10

10

100

100

200

100

300

400

50

50

10

50

50

Upper Cape Fear/Charleston

confining unit

Figure B28. Thickness of the Upper Cape Fear confining unit (North Carolina) and the Charleston confining unit

 (South Carolina) (layer 12), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 95

Figure B29. Areal extents and the top altitudes of the Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer 

(South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where

 approximately located

Structure contour—Approximate altitude of the top of

 the Upper Cape Fear/Charleston aquifer. Datum is

 NGVD 29. Contour interval is 200 feet. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

–200

–800

–1,200 –1,000

–400

–600

–800

–400

–400

–600

–800

–1,000

–1,200

–1,400

–1,600

–1,800

–2,000

–2,200

–2,400

–200

200

0

–1,200

–1,000

–1,400

–1,400

 

Figure B29. Areal extents and the top altitudes of the Upper Cape Fear aquifer (North Carolina) and the 

Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007.

Upper Cape Fear/ 

Charleston

aquifer
96 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B30. Thickness of the Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer (South Carolina) (layer 13), in the 

Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007 

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where

 approximately located

Line of equal thickness, in feet.

 Contour interval is variable. Dashed

 where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

10

10

50

50

50

50

10

10

10

100

200

200

200

300

300

400

400

500

100

100

200

200

300

50

100

50

50

300

Upper Cape Fear/ 

Charleston

aquifer

Figure 30. Thickness of the Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer (South Carolina) (layer 13), 

in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007 
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 97

Lower Cape Fear Confining Unit and Aquifer

The Lower Cape Fear confining unit (model layer 14, 

Chapter C) separates the upper and lower parts of the Cape 

Fear Formation into two distinct aquifers. Substantial differences in hydraulic head are measured in observation wells 

screened in the Upper and Lower Cape Fear aquifers across 

the NC Coastal Plain. This confining unit consists of regionally correlative clay and silt beds in the approximate middle 

of the Cape Fear Formation (fig. B4). The top altitude of the 

Lower Cape Fear confining unit varies from about –200 ft 

in the updip limit to about –1,200 ft in the downdip limit 

(fig. B31, Appendix B1). The thickness of the Lower Cape Fear 

confining unit is about 50 ft across most of the NC Coastal 

Plain, and about 100 ft near the NC–VA border (fig. B32,

Appendix B1). At the NC–SC border, the Lower Cape Fear 

confining unit and aquifer are correlative and hydraulically 

connected to the Gramling confining unit and aquifer in SC.

The Lower Cape Fear aquifer (model layer 15, Chapter C) primarily comprises the lower part of the Cape Fear 

Formation of Upper Cretaceous age (fig. B4) and may also 

include sediments of early Cretaceous age. The Lower Cape 

Fear aquifer consists of alternating beds of nonmarine sand, 

gravel, and clay of similar color and character as the Upper 

Cape Fear aquifer. The basal portion of the Lower Cape 

Fear aquifer contains reworked materials from the underlying Paleozoic basement crystalline rocks in areas where the 

Lower Cretaceous aquifer is missing. This unit is overlain 

by the Upper Cape Fear aquifer throughout the study area, 

and is present mostly in the eastern half of the NC Coastal 

Plain. However, the updip limit is close to the Fall Line in the 

northernmost counties. The Lower Cape Fear aquifer pinches 

out at the basement surface, and does not crop out or subcrop 

elsewhere in the Coastal Plain. The aquifer is underlain by the 

Lower Cretaceous aquifer in the northeastern part of the NC 

Coastal Plain; elsewhere, the Lower Cape Fear is the deepest 

aquifer in the region. In the northwestern NC Coastal Plain, 

the aquifer is overlain only by the Upper Cape Fear, Yorktown, 

and surficial aquifers, and recharge rates in this area may be 

higher than in other areas. 

The updip limit of the Lower Cape Fear aquifer is along a 

line starting from southern Robeson County, through Bladen, 

Sampson, Duplin, Lenoir, Greene, Wilson, Edgecombe, 

Halifax, and Northampton Counties (fig. B1). The top of the 

Lower Cape Fear aquifer ranges from an altitude of about 

–200 ft along the updip limit to about –1,200 ft along the 

downdip limit (fig. B33, Appendix B1). The thickness of the 

Lower Cape Fear aquifer ranges from about 10 ft in places 

along the updip limit to as much as 500 ft at the downdip limit 

(fig. B34). The Lower Cape Fear aquifer probably achieves 

greater thickness in the Albemarle Embayment; however, 

the base of the aquifer is poorly defined by existing data in 

that area. 
98 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B31. Areal extents and the top altitudes of the Lower Cape Fear confining unit (North Carolina) and the Gramling confining unit 

(South Carolina) (layer 14), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Structure contour—Approximate altitude of the top of

 the Lower Cape Fear/Gramling confining unit. Datum is

 NGVD 29. Contour interval is 200 feet. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

EXPLANATION

200

–800

–200

–400

–600

–200

–400

–200

–200

–400

–600

–600

–400

–200

–200

0

–800

–1,000

–1,200

–1,400

–1,600

–1,800

–2,000

–2,200 –2,400

–2,600

–2,800

0

–800

–1,000

–1,000

–1,000

 

–800

Lower Cape Fear/

Gramling

confining unit

Figure B31. Areal extents and the top altitudes of the Lower Cape Fear confining unit (North Carolina) and the 

Gramling confining unit (South Carolina) (layer 14), in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007.

Fall

Line
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 99

Figure B32. Thickness of the Lower Cape Fear confining unit (North Carolina) and the Gramling confining unit (South Carolina) 

(layer 14), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of confining unit. Dashed where

 approximately located

Line of equal thickness, in feet.

 Contour interval is variable. Dashed

 where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

EXPLANATION

200

50

50

50

50

50

50

100

100

300

300

200

200

200

200

100

100

50

50

100

100 200

300

500

400

100

300

50

Lower Cape Fear/ 

Gramling

confining unit

Figure B32. Thickness of the Lower Cape Fear confining unit (North Carolina) and the Gramling confining unit 

(South Carolina) (layer 14), in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.
100 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B33. Areal extents and the top altitudes of the Lower Cape Fear aquifer (North Carolina) and Gramling aquifer (South Carolina) 

(layer 15), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where approximately located

Structure contour—Approximate altitude of the top of

 the Lower Cape Fear/Gramling aquifer. Datum is

 NGVD 29. Contour interval is 200 feet. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

EXPLANATION

200

0

–200

–400

–800

–800

–600

–200

–800

–600

–600

–800

–200

–400

–1,000

–1,000

–1,000

–1,200

–1,400

–1,600

–1,800

–2,000

–2,200

–2,400 –2,400

–2,200

–2,600

–2,800

–3,000

–1,000

–1,200

–1,000

–400

–600

–800

–1,000

Lower Cape Fear/ 

Gramling

aquifer

Figure B33. Areal extents and the top altitudes of the Lower Cape Fear aquifer (North Carolina) and Gramling 

aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia, 2007.

Fall

Line
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 101

Figure B34. Thickness of the Lower Cape Fear aquifer (North Carolina) and Gramling aquifer (South Carolina) (layer 15), in the Atlantic 

Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

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Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where

 approximately located

Line of equal thickness, in feet.

 Contour interval is variable. Dashed

 where approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

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83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

EXPLANATION

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Lower Cape Fear/

Gramling aquifer

Figure B34. Thickness of the Lower Cape Fear aquifer (North Carolina) and Gramling aquifer (South Carolina) (layer 15), 

in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007
102 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Lower Cretaceous Confining Unit and Aquifer

The Lower Cretaceous aquifer (model layer 16, Chapter C) was first defined in NC by Winner and Coble (1996) 

to classify permeable sediments of Early Cretaceous age 

beneath the Lower Cape Fear aquifer in the Albemarle 

Embayment and extending south into Cartaret County, NC. 

In this area, beds thicken greatly eastward so that they make 

up approximately one-third to one-half of the total thickness of NC Coastal Plain sediments along the northern NC 

coastline. Based on available information, it is unclear where 

the boundary is between the Lower Cape Fear and Lower 

Cretaceous aquifers. It is also not possible to determine the 

position and extent of an intervening confining unit between 

the Lower Cape Fear and Lower Cretaceous aquifers. The 

Lower Cape Fear aquifer may include a substantial thickness of sediments of Early Cretaceous age. Because of a 

lack of water-level information, it is also uncertain whether 

the Lower Cretaceous aquifer constitutes a single aquifer, or 

could be divided by confining units into more than one aquifer. The Lower Cretaceous aquifer contains saltwater over 

most of its extent in the NC Coastal Plain, except in its updip

fringes, as defined by Winner and Coble (1996). 

The freshwater portion of the Lower Cretaceous aquifer 

varies in altitude from –200 ft to –1,200 ft (fig. B35, Appendix B1), and its thickness ranges from about 50 ft to as much 

as 800 ft in NC (fig. B36). There is no SC equivalent to the 

Lower Cretaceous aquifer. The underlying basement rocks 

and structural elements are discussed in a previous section of 

this report.
North Carolina Coastal Plain Stratigraphy and Hydrostratigraphy 103

Figure B35. Areal extents and the top altitudes of the Lower Cretaceous confining unit and Lower Cretaceous aquifer in North Carolina 

(layer 16), in the Atlantic Coastal Plain of North Carolina and part of Virginia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

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Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. Dashed where approximately located

Structure contour—Approximate altitude of the top of

 the Lower Cretaceous aquifer. Datum is NGVD 29.

 Contour interval is 200 feet. Dashed where

 approximately located

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

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83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

EXPLANATION

200

–200

–400

–600

–800

–1,000

–1,200

Lower Cretaceous

aquifer

Figure B35. Areal extents and the top altitudes of the Lower Cretaceous confining unit and Lower Cretaceous 

aquifer in North Carolina (layer 16), in the Atlantic Coastal Plain of North Carolina and part of Virginia, 2007.

Fall

Line
104 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B36. Thickness of the Lower Cretaceous confining unit and Lower Cretaceous aquifer in North Carolina (layer 16), in the 

Atlantic Coastal Plain of North Carolina and part of Virginia, 2007.

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

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AL

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Mexico Gulf of Mexico

Atlantic

Ocean

Extent of aquifer. 

Line of equal thickness, in feet.

 Contour interval is variable

Hydrostratigraphic borehole

Virginia

North Carolina

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Maryland

32°

33°

34°

35°

36°

37°

38°

31°

83° 82° 81° 80° 79° 78° 77° 76° 75°

Atlantic

Ocean

Fall

Line

EXPLANATION

200

500

400

300

200

100

100

100 50

50

800

1,200 Lower Cretaceous

confining unit and

aquifer

Figure B36. Thickness of the Lower Cretaceous confining unit and Lower Cretaceous aquifer in North Carolina 

(layer 16), in the Atlantic Coastal Plain of North Carolina and part of Virginia, 2007.
South Carolina Coastal Plain Allostratigraphy and Biostratigraphy 105

South Carolina Coastal Plain 

Allostratigraphy and Biostratigraphy

Correlation of hydrostratigraphic units across the SC 

ACP was made possible in large part by the biostratigraphic 

and allostratigraphic frameworks developed during the 

past 10 years as part of the USGS Coastal Carolina project 

(U.S. Geological Survey, 2007). Although hydrostratigraphic 

boundaries do not directly coincide with biostratigraphic or 

allostratigraphic boundaries, strong relations exist that are 

useful in correlating hydrostratigraphic units from well to 

well over long distances. The following is a summary of the 

allostratigraphic formations and biostratigraphic zones, from 

oldest to youngest, that were used in the development of the 

new hydrogeologic framework for the SC ACP. Although not a 

comprehensive description, this summary provides an overview of the allostratigraphic formations, their age and fossil 

zonations, and their distributions across the SC ACP (fig. B4; 

Plates 1, 2, and 7).

Late Cretaceous Formations

The Cretaceous section of the SC ACP consists of late 

Cretaceous Cenomanian to Maastrichtian sediments that 

were deposited between 98 and 65 million years ago. These 

sediments reach a maximum thickness of about 2,200 ft in 

Beaufort County. Thirteen formations of Cretaceous age were 

identified in the cores, several of which may warrant being 

raised to group rank and divided into additional formations. 

Formations constituting the lower part of the section 

generally alternate between oxidized, red to brown, coarsegrained clastic sediments deposited in fluvial-deltaic environments (Beech Hill and Cape Fear Formations), and gray to 

black, fine-grained clastic sediments deposited in marginalmarine environments (Clubhouse, Collins Creek, and Pleasant Creek Formations; fig. B4) (Gohn, 1992; Self-Trail and 

others, 2004b). Formations constituting the middle part of the 

Cretaceous section are dominated by gray to black, laminated, 

fine- to coarse-grained clastic sediments that were deposited 

in deltaic and shallow marine environments (Shepherd Grove, 

Caddin, Cane Acre, Coachman, Bladen, and Donoho Creek 

Formations). Formations constituting the upper part generally 

consist of light-colored, calcareous and clastic sediments that 

were deposited in deltaic to deep marine environments (Sawdust Landing and Peedee/Steel Creek Formations). 

Formation tops were determined from the cores used 

in this study and are expressed in feet relative to NGVD 29. 

The lithic character of most formations changes geographically across the SC ACP in response to changing depositional 

environments. As such, the lithologic descriptions provided 

are generalized and may not be an accurate description of the 

various formations in all areas of the SC ACP.

Beech Hill Formation

The Beech Hill Formation is the basal formation of the 

SC ACP and was defined at corehole DOR-37 (Gohn and 

others, 1977 and Gohn, 1992) in southern Dorchester County 

where it was provisionally assigned a Cenomanian age (corresponding to calcareous nannofossil zone CC 9; Gohn, 1992). 

At its type section, the Beech Hill Formation consists of 

yellow, green, and brown to red, noncalcareous clayey sand 

and clay. Beds typically are indurated but in some places are 

unconsolidated. In the Berkeley County corehole (BRK-644), 

permeable unconsolidated clayey sand layers are interbedded with hard, nodular clay beds. The Beech Hill Formation 

is present only in the outer SC ACP from Horry to Beaufort 

Counties and as far inland as northern Dorchester County 

where it constitutes the lower 25 ft of corehole in northern 

Dorchester County (DOR-211). The altitude at the top of the 

formation ranges from –1,164 ft in Berkeley County (BRK644) to –1,317 ft at Myrtle Beach (HOR-973/1165), and from 

–2,530 ft in Jasper County (JAS-426) to –3,350 ft at Hilton 

Head Island (BFT-2055) (Plate 7). The Beech Hill Formation 

reaches a maximum thickness of 470 ft thick at Hilton Head 

Island (BFT-2055) (Plate 1).

Clubhouse Formation

The Clubhouse Formation was defined at the corehole 

DOR-37 in southern Dorchester County (Gohn, 1992) and was 

assigned a late Cenomanian(?) and early Turonian age (calcareous nannofossil zones CC 10–11). At its type section, the 

Clubhouse Formation consists of gray and grayish-green laminated silty sand and silty clay and is slightly calcareous. Thin 

sand beds of the formation at Hilton Head Island are screened 

in a supply well for the town. The formation is present only 

in the outer Coastal Plain from Myrtle Beach to Hilton Head 

Island and as far inland as northern Jasper County (Plates 1

and 7). The Clubhouse Formation overlies the Beech Hill 

Formation. The altitude of the top of the Clubhouse Formation ranges from –1,264 ft at Myrtle Beach (HOR-973/1165) 

to –2,830 ft at Hilton Head Island (BFT-2055). The formation 

reaches a maximum thickness of 520 ft at Hilton Head Island 

(BFT-2055) (Plate 1).

Cape Fear Formation

The Cape Fear Formation was named by Stephenson 

(1907) for crops out along the Cape Fear River in NC (fig. A1). 

A late Turonian to early Coniacian age was assigned to the 

formation (calcareous nannofossil zones CC 12–13) (Gohn, 

1992; Christopher and others, 1999). Sediments of the formation are highly oxidized and generally noncalcareous, making 

them difficult to date. The Cape Fear Formation consists of 

fining-upward beds (5 to 30 ft thick) of poorly sorted clay, 

sand, and gravel. Beds are commonly weakly cemented with 
106 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

silica, which reduces porosity and permeability. Common 

colors include gray, green, yellow, orange, and red. Feldspar 

is widespread and is partially weathered to kaolinite. The 

formation is present throughout the Coastal Plain, except in 

the northern parts of Aiken and Lexington Counties. The Cape 

Fear Formation overlies pre-Cretaceous bedrock in the inner 

Coastal Plain and primarily the Clubhouse and Beech Hill 

Formations in the outer Coastal Plain. Altitudes range from 

+155 ft in Chesterfield County (CTF-81) to –954 ft at Myrtle 

Beach (HOR-973/1165), and from –369 ft in Aiken County 

(AIK-817) to –2,758 ft at Hilton Head Island (BFT-2055) 

(Plates 1, 2 and 7). The formation reaches a maximum thickness of 615 ft in northern Dorchester County (DOR-211).

Collins Creek Formation

The Collins Creek Formation was defined at the 

CHN-820 corehole (Plates 2 and 7) in northeastern Charleston County (Self-Trail and others, 2004) and was assigned a 

middle to late Coniacian age (calcareous nannofossil zones 

CC 14–15). At its type section, the Collins Creek Formation 

consists predominantly of olive-gray, poorly sorted, fine to 

coarse organic-rich sand. Beds of sandy clay, clayey sand, and 

cemented zones of sand and shell fragments also are present 

(Self-Trail and others, 2004). The formation is slightly calcareous in the lower half and noncalcareous in the upper half. 

Sand beds of the Collins Creek Formation form part of a deep 

aquifer in coastal counties. The formation is absent in the inner 

Coastal Plain. A line drawn from northern Allendale County 

to northern Horry County approximates the updip limit of the 

formation (fig. B1). The Collins Creek Formation overlies the 

Cape Fear Formation throughout its extent. The altitude of the 

top of the formation ranges from –700 ft in Marion County 

(MRN-78) to –1,412 ft in Charleston County (CHN-820), and 

from –1,154 ft in Allendale County (ALL-348) to –2,510 ft 

at Hilton Head Island (BFT-2055) (Plate 7). The formation 

reaches a maximum thickness of 248 ft at Hilton Head Island 

(BFT-2055) (Plate 1).

Pleasant Creek Formation

The Pleasant Creek Formation was defined at the 

CHN-820 corehole (Plates 2 and 7) in northeastern Charleston County (Self-Trail and others, 2004b) and was assigned a 

Santonian age (calcareous nannofossil zone CC 16). At its type 

section, the lower part of the formation consists of olive-gray, 

poorly sorted, fine to coarse glauconitic sand with scattered 

0.5- to 1.5-ft-thick silica-cemented sand and shell zones. Most 

of the formation (more than 200 ft at the type section) consists 

of dark greenish-gray, dry and tight sandy clay that breaks 

with a conchoidal fracture. The formation locally contains 

beds consisting of up to 30-percent shell fragments and beds 

of sand and shell up to 3 ft thick that are cemented with 

calcium carbonate (Self-Trail and others, 2004b). The Pleasant Creek Formation has been found only in downdip cores. 

The formation overlies the Collins Creek Formation except 

at the Myrtle Beach corehole (HOR-973/1165) where the 

Pleasant Creek Formation overlies the Cape Fear Formation. 

The altitude of the top of the formation ranges from –568 ft in 

Marion County (MRN-78) to –1,703 ft in southern Dorchester 

County (DOR-37). The formation is absent at the south end 

of the SC ACP in Jasper County (JAS-426; Plate 1) and at 

Hilton Head Island (BFT-2055). The Pleasant Creek Formation reaches a maximum thickness of 259 ft at Myrtle Beach 

(HOR-973/1165) (Plate 7).

Shepherd Grove Formation

The Shepherd Grove Formation was defined at corehole 

DOR-37 in southern Dorchester County (Gohn, 1992) and was 

assigned a late Santonian to early Campanian age (calcareous 

nannofossil zone CC 17). At its type section, the Shepherd 

Grove Formation is generally a fine-grained unit that consists 

of gray to olive-gray calcareous, silty clay, clayey silt, and 

clayey fine sand. Shell fragments are common. On the western 

side of the SC ACP, the formation extends inland only to about 

northern Jasper County. The formation reaches farther inland 

on the eastern side of the Coastal Plain, extending updip to 

about northern Florence County where it is present as a clayey 

sand unit at the FLO-268 corehole (Plate 2). The Shepherd 

Grove Formation overlies the Cape Fear Formation in the 

east-central parts of the Coastal Plain, the Pleasant Creek 

Formation in most of the outer SC ACP cores (Plate 7), and 

the Collins Creek Formation in Beaufort and Jasper Counties (Plate 1). The altitude of the top of the formation ranges 

from –201 ft in Dillon County (DIL‐121) to –547 ft at Myrtle 

Beach (HOR-973/1165), and from –1,932 ft in Jasper County 

(JAS-426) to –2,466 ft at Hilton Head Island (BFT-2055) 

(Plates 1, 2, and 7). The formation reaches a maximum thickness of 183 ft in northern Charleston County (CHN-820).

Caddin Formation

The Caddin Formation was defined at corehole DOR-37 

in southern Dorchester County (Gohn, 1992) and was 

assigned an early Campanian age (calcareous nannofossil 

zones CC 17–18). At its type section, the Caddin Formation 

consists of light olive-gray to greenish-gray, clayey, calcareous, fine-grained glauconitic sand. Glauconite locally constitutes up to 20 percent of the formation. In northern Berkeley 

County (BRK-644), the formation consists of a dark-greenish 

gray to greenish-black glauconitic sandy marl. A line drawn 

from northern Jasper County to northern Horry County 

approximates the updip limit of the formation (fig. B1). The 

Caddin Formation overlies the Shepherd Grove Formation. The altitude of the top of the formation ranges from 

–380 ft in Marion County (MRN-78) to –463 ft at Myrtle 

Beach (HOR-973/1165), and from –1,875 ft in Jasper County 

(JAS-426) to –2,329 ft at Hilton Head Island (BFT-2055) 

(Plates 1 and 2). The Caddin Formation reaches a maximum 

thickness of 137 ft at Hilton Head (BFT-2055). 
South Carolina Coastal Plain Allostratigraphy and Biostratigraphy 107

Cane Acre Formation

The Cane Acre Formation is the lowermost formation of 

the Black Creek Group. The formation was defined at corehole 

DOR-37 in southern Dorchester County (Gohn, 1992) and 

was assigned a middle Campanian age (calcareous nannofossil zone CC 19). At its type section, the formation consists of 

light-gray to light-olive-gray calcareous fine-grained sandy 

clay, calcareous silty clay, and calcareous fine- to mediumgrained clayey sand. Updip, at the ORG-393 corehole in 

Orangeburg (and elsewhere updip) the formation consists of 

light-gray medium- to coarse-grained sand and clayey sand 

and forms part of an aquifer (Plate 7; Appendix B2). The Cane 

Acre Formation is present over most of the SC ACP except in 

extreme updip areas along the Fall Line and in the northeastern part of the SC ACP in Chesterfield and Marlboro Counties. 

The formation overlies the Cape Fear Formation in the inner 

Coastal Plain (Plate 2), the Shepherd Grove Formation in 

the east-central part of the SC ACP (Plate 2), and the Caddin 

Formation in the outer Coastal Plain (Plate 2). The altitude of 

the top of the formation ranges from –188 ft in Dillon County 

(DIL-121) to –394 ft at Myrtle Beach (HOR-973/1165), and 

from +233 ft in Aiken County (AIK-2448) to –2,222 ft at 

Hilton Head Island (BFT-2055). The Cane Acre Formation 

reaches a maximum thickness of 210 ft at the southern part of 

the SRS in Barnwell County (BRN-335) (fig. B1).

Coachman Formation

The Coachman Formation is part of the Black Creek 

Group. The formation was defined at corehole DOR-37 in 

southern Dorchester County (Gohn, 1992) where it was 

assigned a middle and late Campanian age. Data collected for 

this study indicate that the age of the Coachman Formation 

is middle Campanian (calcareous nannofossil zone CC 20) 

(D.C. Prowell, U.S. Geological Survey, written commun., 

2005). At its type section, the formation consists of gray and 

gray-green, calcareous, silty clay, clayey silt, and fine sand. An 

unconformity, identified in downdip cores and from paleontological evidence, suggests that the Coachman Formation can 

be divided into two formations in the eastern and southeastern 

parts of the SC ACP (D.C. Prowell, U.S. Geological Survey, 

written commun., 2005). This unconformity is identified 

on the cross sections with a dashed line. Because a formal 

division of the formation is beyond the scope of this report, 

the units were combined and named Coachman. The Coachman Formation is present over most of the SC ACP except 

in extreme updip areas along the Fall Line. The Coachman 

Formation overlies the Cane Acre Formation everywhere 

except in Darlington County (DAR-228) where it overlies 

Cape Fear sediments (Plate 2). Altitudes range from +120 ft 

in Darlington County (DAR-228) to –282 ft at Myrtle Beach 

(HOR-973/1165), and from –562 ft in Barnwell County 

(BRN-335) to –2,130 ft at Hilton Head Island (BFT-2055). 

The formation has a maximum thickness of 181 ft in northern 

Dorchester County (DOR-211).

Bladen Formation

The Bladen Formation is the second youngest formation of the Black Creek Group. The Bladen Formation was 

named by Owens (1989) for exposures along the Cape 

Fear River in NC. The formation was described at corehole DOR-37 in southern Dorchester County (Gohn, 1992), 

where it was assigned a late Campanian age. Paleontological data collected for this study indicate that the age of the 

formation is late middle Campanian (calcareous nannofossil 

zone CC 21) (D.C. Prowell, U.S. Geological Survey, written commun., 2005). At the DOR-37 corehole in southern 

Dorchester County, the formation consists of olive-gray to 

gray, calcareous, silty clay, clayey silt, and fine sand. Sand 

content increases toward the upper part of the formation. Thin 

cemented beds are common, and mollusks (especially oysters) 

are locally common. The Bladen Formation is present over 

most of the Coastal Plain, except in far updip areas near the 

Fall Line. The formation thickens considerably from west 

to east, and overlies the Coachman Formation everywhere 

except in some updip areas in the northwest (for example, 

AIK-817) where the formation overlies Cane Acre sediments. 

The altitude of the top of the Bladen Formation ranges from 

+193 ft in Chesterfield County (CTF-81) to –260 ft at Myrtle 

Beach (HOR-973/1165), and from +246 ft in Aiken County 

(AIK-2249) to –1,940 ft at Hilton Head Island (BFT-2055, 

Plates 1, 2, and 7). The formation has a maximum thickness of 

224 ft in southern Dorchester County (DOR-37).

Donoho Creek Formation

The Donoho Creek Formation is the uppermost formation of the Black Creek Group. The formation was named by 

Owens (1989) for exposures along the Cape Fear River in 

NC. The Donoho Creek Formation was described at corehole 

DOR-37 in southern Dorchester County (Gohn, 1992), where 

it was assigned an early Maastrichtian age. Recent paleontological data, however, indicate that the age of the formation 

is late Campanian (calcareous nannofossil zones CC 22–23) 

(Self-Trail and others, 2002; D.C. Prowell, U.S. Geological 

Survey, written commun., 2005). At DOR‐37, the undivided 

Donoho Creek Formation is described as consisting of olivegray to gray calcareous, clayey silt and fine sand, and calcareous silty clay. A basal, megafossiliferous clayey sand is 10 ft 

thick. The Donoho Creek Formation is present throughout the 

Coastal Plain, except in the northeastern counties of Kershaw, 

Chesterfield, Marlboro, and Darlington. The formation overlies the Bladen Formation everywhere except in the northern 

parts of Aiken and Lexington Counties, where it probably 

forms the basal Cretaceous Formation. The altitude of the 

top of the Donoho Creek Formation ranges from +401 ft in 

Aiken County (AIK-2448) to –1,856 ft at Hilton Head Island 

(BFT-2055), and from +129 ft in Lee County (LEE-75) to 

–229 ft at Myrtle Beach (HOR-973/1165). The formation 

reaches a maximum thickness of 292 ft in Allendale County 

(ALL-348) (Plates 1, 2, and 7).
108 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Paleontological evidence and physical evidence of unconformities in coreholes indicate that the Donoho Creek Formation can be subdivided. A biostratigraphic subdivision of the 

formation has been proposed, but has not been formalized 

(D.C. Prowell, U.S. Geological Survey, oral commun., 2002). 

For the purposes of this report, the Donoho Creek Formation is divided into three informal units—the lower, middle, 

and upper Donoho Creek units corresponding to calcareous 

nannofossil subzones CC 22a/b, CC 22c, and zone CC 23, 

respectively (Plates 1, 2, and 7). 

Peedee Formation

The “Peedee beds” were first described by Ruffin (1843), 

and the Peedee Formation was formally named by Stephenson (1923) who designated an exposure on the Great Pee Dee 

River at Burches Ferry in Florence County as the type locality. 

The formation was described at corehole DOR-37 in southern 

Dorchester County (Gohn, 1992), where it was assigned a 

Maastrichtian age (calcareous nannofossil zones CC 25–26). 

At the DOR-37 corehole, the formation consists of a basal 

gray to olive-gray calcareous, clayey sand unit that grades 

upward into similarly colored calcareous, silty clay. The undivided Peedee is present across most of the SC ACP except in 

the eastern and northeastern parts, where uplift along the Cape 

Fear Arch caused erosion. The Peedee Formation overlies the 

Donoho Creek Formation everywhere. The altitude of the top 

of the Peedee Formation ranges from +176 ft in Lee County 

(LEE-75) to –5 ft at Myrtle Beach (HOR-973/1165), and from 

+348 ft in Aiken County (AIK-2449) to –1,672 ft at Hilton 

Head Island (BFT-2055). The formation reaches a maximum 

thickness of 233 ft in northern Dorchester County (DOR-211). 

At its type locality in Florence County, the Peedee 

Formation consists of dark-green to gray, fossiliferous, 

glauconitic clayey sand and silt. In west-central SC, a fluvial, 

coarse-grained, age-equivalent unit of the Peedee Formation 

was named the Steel Creek Formation (Fallaw and Price, 

1995) because of substantial differences in Peedee Formation 

lithology at its type locality compared to that observed at the 

SRS (fig. B1). At the SRS, the Peedee Formation consists of 

light-colored fine- to coarse-grained quartz sand and oxidized 

kaolinitic clay (Fallaw and Price, 1995), and constitutes a 

productive aquifer. 

Christopher and Prowell (2002) recognized unconformities in the Peedee section in cores drilled throughout the 

Coastal Plain, and proposed a subdivision of the formation 

into three unconformity-bounded palynological zones. These 

zones were informally called the lower, middle, and upper 

Peedee units where Peedee-type lithologies were observed, 

and the lower, middle, and upper Steel Creek units where Steel 

Creek–type lithologies were observed (calcareous nannofossil 

zones CC 25a, CC 25b, and CC 26a, respectively). This same 

informal subdivision and terminology is used in this report 

(Plates 1, 2, and 7).

Sawdust Landing Formation

The Sawdust Landing Formation was named for exposures at Sawdust Landing on the Santee River in Calhoun 

County, SC (Muthig and Colquhoun, 1988). Until recently, 

fossils were unavailable from the formation, and most geologists considered it to be of early Paleocene age (Colquhoun 

and Muthig, 1991; Nystrom and others, 1991; Aadland and 

others, 1995; Fallaw and Price, 1995). Frederiksen and others 

(2000), however, recovered a late Cretaceous palynomorph 

from the Sawdust Landing Formation at a depth of 320.7 ft, in 

one of the Orangeburg County coreholes, ORG-393 (Appendix B2). The pollen assemblage contained the palynomorph 

Rugubivesiculities, which placed the Sawdust Landing Formation in the late Cretaceous (Frederiksen and others, 2000), 

corresponding to calcareous nannofossil subzone CC 26b. The 

Sawdust Landing Formation is now considered Maastrichtian 

in age and is thought to represent the uppermost Cretaceous 

Formation in the SC ACP (Christopher and Prowell, 2002).

At the ORG-393 corehole, the Sawdust Landing Formation consists of poorly sorted, fine to very coarse sand in a 5 

to 20 percent dense clay matrix (Appendix B2). Feldspar is 

common, and sparse quartz gravel and lignite clasts are locally 

present. The formation is present only in the central and westcentral parts of the Coastal Plain, and is absent downdip and 

on the eastern side of the Coastal Plain. The altitude of the 

top of the Sawdust Landing Formation ranges from +320 ft 

in Richland County (RIC-585) to –420 ft in Allendale County 

(ALL-348). The formation has a maximum thickness of 49 ft 

in Sumter County (SUM-296).

Tertiary Formations

The Tertiary section of the SC ACP consists of early 

Paleocene to Miocene (65 to 5 million years (Ma)) sediments 

that reach a maximum thickness of about 1,600 ft at Hilton 

Head Island in Beaufort County (Plate 1). Thirteen formations 

and the undifferentiated Hawthorn Group were identified in 

the cores. Several of the formations may warrant being raised 

to group rank and further divided into additional formations. 

Formations constituting the Paleocene section (Rhems, 

Lang Syne, and Williamsburg) generally consist of gray to 

black carbonaceous clay interbedded with light-colored quartz 

sand. Early Paleocene sediments are particularly fine grained 

across most of the SC ACP, whereas late Paleocene sediments 

are coarser and become increasingly fossiliferous downdip. 

These sediments were probably deposited in back-barrier, 

estuarine, and marginal-marine environments. Formations constituting the early and middle Eocene section (Fishburne, Congaree, and Warley Hill) consist of light-gray and green glauconitic quartz sand and kaolinitic clayey sand. The Fishburne 

and Warley Hill Formations become increasingly fossiliferous 

downdip, whereas sediments of the Congaree Formation are 

generally absent downdip. These sediments were probably 

deposited in deltaic and open-marine environments. The upper 
South Carolina Coastal Plain Allostratigraphy and Biostratigraphy 109

middle Eocene section (Santee Formation) is dominated by 

light-green and gray marl and cream-colored limestone, with 

the limestone deposited in an open-marine environment. The 

formation grades updip into calcareous and noncalcareous 

quartz sand. Formations constituting the late Eocene section 

(Harleyville, Dry Branch, and Tobacco Road Sand) generally consist of yellow, brown, purple, and red quartz sand and 

clayey sand in updip regions, and yellowish-gray, gray, and 

cream-colored limestone in downdip regions. The Dry Branch 

Formation grades to mixed carbonate/clastic sediments in the 

west-central part of the SC ACP and to pure carbonate sediments near the present-day coast, where it is called the Parkers 

Ferry Formation. The Harleyville Formation typically consists 

of clayey fine-grained limestone and calcareous clay in downdip regions. These formations were probably deposited in 

shallow to open-marine environments. The Oligocene section 

comprises the Tiger Leap, Drayton, and Ashley Formations, 

which consist of yellowish-gray, calcareous, silty and sandy 

clay. These sediments were probably deposited in open-marine 

environments. The Miocene section consists of the informal 

Upland unit. The Upland unit consists of yellow, brown, 

purple, and red poorly sorted clayey sand and gravel in updip 

regions. The Hawthorn Group, which consists of a phosphatic 

limestone, clayey sand, and clay, is thought to be the downdip 

age-equivalent unit of the Upland unit.

Rhems Formation

The type locality of the Rhems Formation is at Perkins 

Bluff on the Black River, about 5 mi from the town of Rhems 

in Williamsburg County, SC, where it was first described by 

Sloan (1908). The Rhems Formation was later abandoned 

by Cooke (1936) and then reinstated by Van Nieuwenhuise 

and Colquhoun (1982). The formation was assigned an early 

Paleocene age (calcareous nannofossil zones NP 1–3). At its 

type section, the Rhems Formation consists of light-gray to 

black shale interlaminated with thin seams of fine-grained 

sand and mica. At the Orangeburg County corehole ORG-393, 

the formation consists of thin layers of grayish-black silty, 

carbonaceous clay laminated with very thin layers of greenishgray and light-gray well-sorted, very fine quartz sand (Plate 7;

Appendix B2). Other unconformities in the early Paleocene 

are evident from cores and fossils, and the formation may be 

divided in the future. The Rhems is present in the western, 

central, and southern parts of the Coastal Plain, but absent in 

counties along the NC border and in counties that border the 

Fall Line. The Rhems Formation overlies the Sawdust Landing 

Formation in the west-central and central parts of the Coastal 

Plain, and the Peedee Formation in coastal counties. The 

altitude of the top of the Rhems Formation ranges from +297 ft 

in Lexington County (LEX-844) to –1,560 ft at Hilton Head 

Island (BFT-2055; Plate 7). The formation reaches a maximum 

thickness of +159 ft in southern Dorchester County (DOR-37) 

and in Berkeley County (BRK-644).

Lang Syne Formation

The type locality of the Lang Syne Formation is at 

Tombs Field Gully on Lang Syne Plantation, near Fort Motte 

in Calhoun County, SC (Sloan, 1908). A reference section 

in Calhoun County (Muthig and Colquhoun, 1988) was 

described as consisting of red and yellow (where weathered) 

or white, gray, and black (where freshly exposed) interbedded sand, silt, and clay and thin beds of silicified shell debris. 

Opaline claystone is the most characteristic lithology. The 

formation was assigned an early to late Paleocene age (Fallaw 

and Price, 1992) and corresponds to calcareous nannofossil 

zones NP 4–5. At the Sumter County corehole SUM-296, the 

Lang Syne Formation consists of brown and gray low-density, 

opaline claystone (fuller’s earth). The formation overlies the 

Rhems Formation. Several unconformities are noted in the formation (D.C. Prowell, U.S. Geological Survey, written commun., 2005), but for the purposes of this report, these units are 

combined and are called Lang Syne. The top of the undivided 

Lang Syne Formation has altitudes that range from +337 ft 

in Lexington County (LEX-844) to –1,475 ft at Hilton Head 

Island (BFT-2055). The Lang Syne Formation reaches a maximum thickness of 297 ft in Charleston County (CHN-800).

Williamsburg Formation

The Williamsburg Formation was named for exposures 

in Williamsburg and Berkeley Counties, SC (Sloan, 1908). 

The name was abandoned by Cooke (1936) and reinstated by 

Van Nieuwenhuise and Colquhoun (1982) who assigned a late 

Paleocene age (calcareous nannofossil zones NP 5–9). At its 

type section, the Williamsburg Formation consists of sandy 

shale, fuller’s earth, fossiliferous clayey sand (Lower Bridge 

Member), and fossiliferous clayey sand and mollusk-rich, bioclastic limestones (Chicora Member) (Van Nieuwenhuise and 

Colquhoun, 1982; Edwards and others, 1997). At the Allendale 

County corehole ALL-348, the Williamsburg Formation consists of gray to black interbedded clay and coarse quartz sand 

overlying shelly clay and calcareous clay (Plates 1 and 7). 

In west-central SC, at the SRS, age-equivalent sediments are 

called the Snapp Formation (Aadland and others, 1995; Fallaw 

and Price, 1995). Several unconformities were observed in the 

coreholes drilled for this study (D.C. Prowell, U.S. Geological Survey, written commun., 2005). The unconformities are 

noted on the cross sections, but are combined and called Williamsburg. The undivided Williamsburg Formation is present 

in the west-central and southern parts of the SC ACP from 

Barnwell County to Orangeburg County and in all counties to 

the southeast. The formation is absent on the eastern side of 

the SC ACP and in counties that border the Fall Line. The Williamsburg Formation overlies the Lang Syne Formation. The 

altitude of the top of the Williamsburg Formation ranges from 

+117 ft in Barnwell County (BRN-335) to –1,285 ft at Hilton 

Head Island (BFT-2055). The formation reaches a maximum 

thickness of 207 ft in Jasper County (JAS-426).
110 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Fishburne Formation

The Fishburne Formation was defined at corehole 

DOR‐37 in southern Dorchester County (Gohn and others, 1983), and was assigned an early Eocene age (Ypresian, 

calcareous nannofossil zones NP 10–11). At its type section, 

the formation consists of greenish-gray to pale-olive finely 

crystalline, nodular, glauconitic, clayey microfossil-mollusk 

limestone. The formation is present mainly in coastal areas of 

Beaufort, Colleton, Dorchester, Jasper, and southern Charleston Counties. At the Allendale (ALL-348) and Berkeley 

(BRK-644) County coreholes, late Paleocene to early Eocene 

sediments were dated and assigned an NP 10 zone (Plates 1

and 2). These sediments are included with the Fishburne Formation but may constitute a separate formation (D.C. Prowell, 

U.S. Geological Survey, written commun., 2005). Palynological assemblages indicate that some sand beds that overlie the 

Williamsburg Formation in west-central SC are equivalent 

in age with the Fishburne Formation and were subsequently 

named the Fourmile Formation at the SRS (Aadland and 

others, 1995; Fallaw and Price, 1995). Where present, the 

Fishburne overlies the Williamsburg Formation. The altitude 

of the top of the Fishburne Formation ranges from –392 ft at 

the type section in Dorchester County (DOR-37) to –1,219 ft 

at Hilton Head Island (BFT-2055). The formation reaches a 

maximum thickness of 120 ft in southern Colleton County at 

Edisto Beach (COL-364).

Congaree Formation

The type locality of the Congaree Formation is in 

Calhoun County, SC. Sloan (1908) described the “Congaree 

Phase” as shale and sand of early and middle Eocene age. 

The Congaree Formation has been assigned a probable early 

Eocene to early middle Eocene age (calcareous nannofossil 

zones NP 12–14) (Fallaw and Price, 1995). In Aiken County, 

at the AIK-817 corehole, the formation consists of pale yellow 

and gray moderately to poorly sorted, medium to coarse quartz 

sand with little to no interstitial clay. The term Huber Formation refers to an updip age-equivalent facies of the Congaree 

Formation that is characterized by commercial kaolin beds 

capping the formation and cross-bedded coarse sand with 

kaolin balls (Nystrom and others, 1991). Several unconformities in the section were observed in coreholes and in outcrops 

in Aiken County. The Congaree Formation was informally 

subdivided into three units corresponding to zones NP 12, 

13, and 14 (D.C. Prowell, U.S. Geological Survey, written 

commun., 2005). The separate NP zones are shown on the 

cross sections (Plates 1, 2, and 7) where core and fossil data 

indicate their presence, but they are combined here and called 

the Congaree Formation. The undivided Congaree Formation is present in the western part of the SC ACP from Aiken 

County south to Allendale County and east to Orangeburg 

County. Downdip, widespread erosion by the overlying Santee 

Formation has left only scattered remnants of the formation 

(Plates 1 and 7). The Congaree Formation directly overlies 

crystalline bedrock at the Fall Line and overlies Cretaceous 

and Paleocene sediments elsewhere. The altitude of the top 

of the Congaree Formation ranges from +460 ft in northern 

Aiken County (AIK-2448) to –264 ft at the Allendale corehole 

(ALL-348). The formation reaches a maximum thickness of 

106 ft in central Aiken County (AIK-817; Plate 1).

Warley Hill Formation

The type locality of the Warley Hill Formation is in 

eastern Calhoun County, SC (Sloan, 1907a, b) and is assigned 

a middle Eocene age (calcareous nannofossil zone NP 15) 

(Fallaw and Price, 1995). The formation consists of green or 

yellowish-green glauconitic quartz sand and silt with moderate 

interstitial clay (Nystrom and others, 1991). At the Orangeburg County corehole ORG-393, the formation consists of 

olive-gray glauconitic sandy clay and marl consisting of 

fine- to very coarse-grained quartz sand in a 60- to 70-percent 

clay matrix that is cemented with calcium carbonate (Appendix B2). A second unconformity in the NP 15 zone is recognized in cores drilled for this study (D.C. Prowell, U.S. Geological Survey, written commun., 2005). Because the Warley 

Hill Formation has not been formally subdivided, both units 

are noted on the cross sections but are combined in this report 

and called the Warley Hill Formation. The Formation is present in the central and west-central parts of the SC ACP from 

Barnwell and Allendale Counties east to Calhoun County. The 

Warley Hill Formation overlies the Congaree Formation. The 

altitude of the top of the Warley Hill Formation ranges from 

+76 ft in Orangeburg County (ORG-393) to –209 ft in Allendale County (ALL-348). The formation reaches a maximum 

thickness of 54 ft in Allendale County (ALL-348).

Santee Formation

The Santee Formation was named after the Santee River 

for exposures at Eutaw Springs in Orangeburg County, about 

4 mi east-northeast of Eutawville, SC (Sloan, 1908). The 

formation was assigned a middle to early late Eocene age by 

Cooke and MacNeil (1952) and a late middle Eocene age at 

the SRS (Fallaw and Price, 1995). Edwards and others (1997) 

dated the Santee section at corehole DOR-208 in Dorchester 

County as late middle Eocene (calcareous nannofossil zones 

NP 16–18). Updip, the formation consists of yellow, tan, and 

white calcareous and noncalcareous quartz sand and clay (Tinker Creek Formation of Fallaw and Price, 1995). The formation becomes calcareous downdip in central Barnwell County, 

where it consists largely of light-green and gray clayey 

calcilutite and calcareous silt and clay (marl), with the carbonate content generally greater than 75 percent (Blue Bluff marl 

unit of Huddlestun and Hetrick, 1986). Farther downdip, in the 

Allendale County corehole ALL-348, the Santee Formation 

consists of a lower sandy limestone and calcareous sand unit, a 

middle Blue Bluff marl unit, and an upper unit that consists of 

permeable, cream-colored, bioclastic shelly limestone dominated by bryozoans and pelecypods. The formation grades to 

pure carbonates between Allendale County and the SC coast. 
South Carolina Coastal Plain Allostratigraphy and Biostratigraphy 111

Several geologic units in the study area have been dated 

as NP 16, including the Blue Bluff marl unit (Fallaw and 

Price, 1995), the Moultrie Member described by Edwards 

and others (1997) at the DOR-208 corehole in Dorchester 

County, and the type section of the Santee Formation (Ralph 

Willoughby, South Carolina Geological Survey, oral commun., 2007). During the course of the study, several unconformities were noted in the upper middle Eocene section that 

may warrant a subdivision of the Santee Formation into four 

units (D.C. Prowell, U.S. Geological Survey, written commun., 2005). These are noted on the cross sections (Plates 1,

2, and 7), but the entire late middle Eocene section is referred 

to as the Santee Formation in this report, including the updip 

clastic facies.

The undivided Santee Formation is present in the western and southern parts of the SC ACP, from southern Aiken 

County south to Beaufort County and northeast to Charleston 

County. The formation is absent in the eastern half of the SC 

ACP and in updip counties. The Santee Formation overlies the 

Warley Hill and Congaree Formations in updip counties and 

the Fishburne Formation and Paleocene sediments in downdip 

counties. The altitude of the top of the Santee Formation ranges 

from +237 ft in southern Aiken County (AIK-892) to –498 ft at 

Hilton Head Island (BFT-2055). The formation reaches a maximum thickness of 721 ft at Hilton Head Island (BFT-2055).

Harleyville Formation

The Harleyville Formation has its type locality in northern Dorchester County, SC. The formation was originally 

described by Ward and others (1979) and raised to formation 

status by Weems and Lemon (1984). Generally, the formation consists of clayey fine-grained limestone and calcareous 

clay (Ward and others, 1979). The Harleyville Formation 

was dated as early late Eocene at the corehole DOR-208 in 

Dorchester County (calcareous nannofossil zone NP 18) where 

it was described as a yellowish-gray fossiliferous limestone 

(packstone) with abundant pelecypods (Edwards and others, 

1997). The formation is present only in the southern part of 

the SC ACP from Hampton County, east to Dorchester County, 

and in all counties to the southeast. The altitude of the top 

of the Harleyville Formation ranges from –8 ft in northern 

Dorchester County (DOR-37) to –360 ft at Hilton Head Island 

(BFT-2005). The formation reaches a maximum thickness of 

138 ft at Hilton Head Island (BFT-2055). 

Dry Branch Formation

The Dry Branch and Parkers Ferry Formations are considered age-equivalent units in this report. The Dry Branch 

has its type locality in Richmond County, GA (Huddleston 

and Hetrick, 1979, 1986; see Nystrom and others, 1991, for 

a historic overview of the formation) and has been dated as 

late Eocene (calcareous nannofossil zone NP 19–20; Fallaw 

and Price, 1995). Updip, in northern Barnwell County, SC 

(BRN-358), the formation is noncalcareous and consists of 

yellow, tan, and orange moderately sorted fine to coarse quartz 

sand interbedded with tan clay. Farther downdip, in Allendale County (ALL-348), the formation transitions to a mixed 

clastic/carbonate unit and consists of moderately sorted, fine to 

medium calcareous sand and sandy calcarenite. A 20-ft thick 

moldic limestone is present near the top of the formation. The 

formation grades into pure carbonates at the coast, where it is 

called the Parkers Ferry Formation or, further south, the Ocala 

Limestone. In this report, the name Parkers Ferry Formation 

is used in reference to the formation south of the Orangeburg 

Scarp (fig. B1). The Dry Branch/Parkers Ferry Formation is 

present in the western part of the Coastal Plain, from Aiken 

County to Beaufort County and east to Charleston County. It 

overlies the Santee and Congaree Formations. The altitude of 

the top of the formation ranges from +478 ft in northern Aiken 

County (AIK-2448) to –170 ft at Hilton Head Island (BFT2055). The Dry Branch Formation reaches a maximum thickness of 215 ft in southern Colleton County at Edisto Beach 

(COL-364).

Tobacco Road Sand Formation

The Tobacco Road Sand Formation has its type locality 

in Richmond County, GA (Huddleston and Hetrick, 1978). 

In SC, the formation consists of red, brown, tan, purple, 

and orange medium- to very coarse-grained quartz sand and 

quartz granules with minor to moderate interstitial clay (Nystrom and others, 1991). The Tobacco Road Sand was assigned 

a late Eocene age by Huddlestun and Hetrick (1986), corresponding to calcareous nannofossil zone NP 19–20. Few fossils have been found in the formation, and its age is uncertain. 

Recent evidence from GA indicates that the Tobacco Road 

Sand Formation is Oligocene in age and may be an updip 

facies of the Tiger Leap Formation (D.C. Prowell, U.S. Geological Survey, written commun., 2007). In this report, the 

Tobacco Road Sand Formation is considered late Eocene. The 

Tobacco Road Sand is present on the western side of the SC 

ACP from Aiken County south to Allendale County and possibly east to Orangeburg County. The formation overlies the 

Dry Branch Formation. The altitude of the top of the Tobacco 

Road Sand Formation ranges from +473 ft in Aiken County 

(AIK-2449) to +184 ft in Allendale County (ALL-348). The 

formation reaches a maximum thickness of 60 ft in Allendale 

County (ALL-348).

Ashley Formation

The name Ashley was applied to beds in marl pits along 

the Ashley River in Dorchester County, SC (fig. B1). Later 

the unit was called the Ashley member of the Cooper Formation (Ward and others, 1979) and raised to formation status 

by Weems and Lemon (1984). The Ashley Formation was 

assigned a late Oligocene age in the DOR-37 core in Dorchester 

County (Hazel and others, 1977), corresponding to calcareous 
112 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

nannofossil zone NP 24. At corehole DOR-208 in Dorchester 

County, the Ashley Formation consists of a homogenous section 

of yellowish-gray fine-grained clayey calcarenite (Edwards 

and others, 1997). Small amounts of fine-grained glauconite 

and phosphate sand are present throughout the formation. The 

formation is present only in the southern part of the SC ACP 

from Beaufort County to Charleston County and inland as far as 

northern Dorchester County. The Ashley Formation overlies the 

Harleyville, Dry Branch, and Santee Formations. The altitude of 

the top of the Ashley Formation ranges from +48 ft in Dorchester County (DOR-211) to –88 ft at Hilton Head Island (BFT2055). The formation reaches a maximum thickness of 141 ft in 

southern Dorchester County (DOR-37). 

Hawthorn Group

The Hawthorn Formation consists mainly of phosphatic 

limestone (Dall and Harris, 1892; Matson and Clapp, 1909). 

The formation was raised to group status in Georgia by Huddlestun (1988) and was later revised by Weems and Edwards 

(2001), who included five formations in the group. According 

to Weems and Edwards (2001), the group consists of the late 

Oligocene Tiger Leap Formation, most likely corresponding to 

calcareous nannofossil zone NP 25, and the Miocene Parachucla, Marks Head, Coosawhatchie, and Ebenezer Formations, 

most likely corresponding to calcareous nannofossil zones 

NN 1–12. The Hawthorn Group is present in the southern part 

of the SC ACP, where it overlies the Parkers Ferry Formation 

and possibly the Ashley Formation. The altitude of the top 

of the Hawthorn Group ranges from +19 ft in Jasper County 

(JAS-426) to –53 ft at Hilton Head Island (BFT-2055). The 

Hawthorn Group reaches a maximum thickness of 101 ft in 

Jasper County (JAS-426).

Upland Unit

The Upland unit is an informal term for deposits that are 

present at higher altitudes in the west-central SC ACP (Fallaw 

and Price, 1992). The unit consists of red, purple, gray, orange, 

yellow, and tan poorly sorted, clayey, fine to very coarse sand 

and gravel. Colquhoun (1992) assigned the “upland” to the 

Oligocene and/or Miocene. Fallaw and Price (1995) assigned 

the unit to the Miocene, and Nystrom and others (1991) 

suggested a middle Miocene age (possibly corresponding to 

calcareous nannofossil zones NN 2–3). The unit is probably 

age-equivalent to one or more of the Miocene formations of 

the Hawthorn Group. The Upland unit is present in the western 

SC ACP from Aiken County to Allendale County and east to 

Lexington and Orangeburg Counties. The Upland unit overlies 

the Tobacco Road Sand, with the altitude of the top ranging 

from +494 ft in northern Aiken County (AIK-2448) to +282 ft 

in Allendale County (ALL-348). The unit reaches a maximum 

thickness of 98 ft in Allendale County (ALL-348). 

Undifferentiated Quaternary Units

Undifferentiated sediments are present toward the top of 

most coreholes south of the Orangeburg Scarp. These sediments are mapped as “undifferentiated Quaternary units.” 

At the Orangeburg corehole ORG-393, the upper 22 ft of 

sediments consist of yellowish-brown and reddish-orange 

poorly sorted, very fine to very coarse, clayey sand and gravel. 

Accessory minerals include opaque heavy minerals, mica, and 

feldspar. Undifferentiated Quaternary units overlie Cretaceous 

sediments in the east and Tertiary sediments in the west. The 

altitude of the top of the Quaternary ranges from +253 ft in 

Orangeburg County (ORG-393) to +8 ft in Charleston County 

(CHN-802). The sediments reach a maximum thickness of 

74 ft in Charleston County (CHN-800).

South Carolina Coastal Plain 

Hydrostratigraphy

The Southeastern Coastal Plain hydrogeologic province 

(fig. B1) in SC encompasses an area of about 22,500 mi2 

(Aucott, 1996). About 95 percent of South Carolina’s groundwater resources are in the province (Newcome, 1989). The 

Southeastern Coastal Plain consists of a sequence of Mesozoic 

and Cenozoic sedimentary units that are composed of unconsolidated to semiconsolidated layers of sand, clay, limestone, 

and marl. The province thickens from the Fall Line to the 

coast, where it reaches a maximum thickness of about 4,000 ft 

at the southernmost part of the State. Hydrostratigraphic units 

are described in descending order in terms of their geometry, 

age and stratigraphic correlation, lithology and texture, hydrologic properties, and geophysical-log signature. A generalized 

dip and strike section illustrates the hydrostratigraphic units 

delineated for this report (fig. B37). 

In this study, seven hydrostratigraphic systems of the 

Southeastern Coastal Plain hydrogeologic province are delineated in SC—four aquifer systems and three confining systems 

(fig. B4). Six of these systems correlate with those mapped at 

SRS (Aadland and others, 1995) (fig. B38). A new basal system, defined herein as the Ridgeland aquifer system (fig. B38), 

is not present at SRS and is found only in the outer Coastal 

Plain. A comparison chart relates the hydrostratigraphic 

units defined in this study to those delineated and defined by 

Colquhoun and others (1983), Miller (1986), Aucott and others 

(1987), and Miller and Renken (1988) (fig. B39).

 In ascending order, the aquifer systems are the Ridgeland, Midville, Dublin, and Floridan. The Ridgeland is the 

lowermost system of the Coastal Plain (figs. B4 and B38). It 

consists of a single aquifer informally named the Gramling. 

Additional aquifers may occur in the Ridgeland, but few wells 

fully penetrate the system, and hydrologic data are sparse. The 

Midville aquifer system consists of the newly defined Charleston aquifer and Charleston confining unit and the previously 

defined McQueen Branch aquifer (Aadland and others, 1995). 

The Charleston aquifer and confining unit occur only in the 
South Carolina Coastal Plain Allostratigraphy and Biostratigraphy 113

Figure B37. Generalized hydrogeologic framework of the South Carolina Coastal Plain along strike and dip.

Coastline

Beaufort Co.

Fall Line 

Aiken Co.

Middle Floridan, Upper Floridan, and

 surficial aquifers projected updip

 in this report

Generalized hydrogeologic framework of South Carolina along dip.

Generalized hydrogeologic framework of South Carolina along strike.

Pre-Cretaceous basement

McQueen Branch aquifer

McQueen Branch aquifer

McQueen Branch confining unit

Charleston aquifer

Gramling confining unit

Gramling aquifer

Charleston confining unit

Crouch Branch aquifer

not drawn to scale

not drawn to scale

EXPLANATION

Location of sections A–A’ and B–B’ in

in South Caroilna 

surficial aquifer

Figure B37. Generalized hydrogeologic framework of the South Carolina Coastal Plain along strike and dip.

(Northwest)

(Southeast)

A A’

Jasper Co.

(Southwest)

B

A

B

Dillon Co.

(Northeast)

B’

A

A’ B

B’

Crouch Branch confining unit

Gordon aquifer

Gordon confining unit

Middle Floridan aquifer

Upper Floridan aquifer

Upper Three Runs aquifer Steed Pond aquifer

surficial aquifer

Middle Floridan conf. unit

Upper Floridan

confining unit

SOUTHEASTERN COASTAL PLAIN HYDROGEOLOGIC PROVINCE 

SOUTHEASTERN COASTAL PLAIN HYDROGEOLOGIC PROVINCE 

Upper Floridan confining unit

Middle Floridan confining unit

Gordon confining unit

Crouch Branch confining unit

McQueen Branch confining unit

Charleston confining unit

Gramling confining unit

Gramling aquifer

Pre-Cretaceous basement

Charleston aquifer

McQueen Branch aquifer

Crouch Branch aquifer

Gordon aquifer

Middle Floridan aquifer

Upper Floridan aquifer

Uplift of

Cape Fear

Arch

confining zone
114 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

middle and lower parts of the Coastal Plain and are not present 

at SRS. The McQueen Branch, which was defined at SRS, 

occurs over most of the Coastal Plain. The Dublin aquifer 

system contains a single aquifer—Crouch Branch—that was 

defined at SRS. It occurs over most of the Coastal Plain. East 

of the Congaree/Santee River basins, the Dublin contains several thick and continuous clay units that may divide the system 

into several aquifers (fig. B37). 

The Floridan aquifer system occurs in the western part of 

the Coastal Plain, from the Fall Line to the coast. In the central 

and southern parts of SRS, the Floridan consists of the Gordon 

and Upper Three Runs aquifers separated by the Gordon confining unit (Aadland and others, 1995) (fig. B38). In northern 

SRS, the Gordon and Upper Three Runs aquifers coalesce 

to form the Steed Pond aquifer (Aadland and others, 1995) 

(fig. B37). Downdip from SRS, the Gordon aquifer and confining unit persist, but the Upper Three Runs aquifer splits into 

the Middle and Upper Floridan aquifers, which are separated 

by the Middle and Upper Floridan confining units, and the 

surficial aquifer. To accommodate the flow model described 

in Chapter C and to maintain the lateral continuity of the 

modeled layers, the Gordon, Middle and Upper Floridan, and 

surficial aquifers are all extended into updip regions where the 

Upper Three Runs and Steed Pond aquifers would normally 

occur (fig. B37). This was done by stratigraphic correlation. 

In ascending order, the confining systems are the Appleton, Allendale, and Meyers Branch, all defined at the SRS 

(Aadland and others, 1995). Each system consists of a single 

confining unit: the Gramling, McQueen Branch, and Crouch 

Branch (figs. B4 and B38). Several aquifers and confining 

units contain zones that have unique hydrogeologic properties. 

Many of the hydrostratigraphic units described herein 

are present at one of the Orangeburg coreholes (ORG-393; 

fig. B2). This core, therefore, is used as a reference section 

in this report. A detailed description of the core is provided 

in Appendix B2. Although not a part of the groundwater flow 

model presented in Chapter C, a short description of the part 

of the Pre-Cretaceous basement buried beneath the SC ACP is 

provided in this report.

Figure B38. Hydrostratigraphy at the Savannah River Site as defined by Aadland and others (1995) compared to the 

hydrostratigraphy of the South Carolina Coastal Plain downdip of the Savannah River Site, as defined in this study.

Upper Three Runs

aquifer 

Gordon

aquifer 

Crouch Branch

confining unit

McQueen Branch

confining unit

unnamed

confining unit

McQueen Branch

aquifer

McQueen Branch aquifer

Charleston aquifer

Crouch Branch

aquifer

Crouch Branch

confining unit

McQueen Branch

confining unit

Crouch Branch

aquifer

Gramling

confining unit

Gramling

aquifer

Steed Pond aquifer

FLORIDAN - MIDVILLE AQUIFER SYSTEM

Gordon confining unit

FLORIDAN

AQUIFER

SYSTEM

MEYERS

BRANCH

CONFINING

SYSTEM

ALLENDALE

CONFINING

SYSTEM

APPLETON

CONFINING

SYSTEM

DUBLIN

AQUIFER

SYSTEM

MIDVILLE

AQUIFER

SYSTEM

MEYERS

BRANCH

CONFINING

SYSTEM

ALLENDALE

CONFINING

SYSTEM

APPLETON

CONFINING

SYSTEM

DUBLIN

AQUIFER

SYSTEM

MIDVILLE

AQUIFER

SYSTEM

RIDGELAND

AQUIFER

SYSTEM

FLORIDAN

AQUIFER

SYSTEM

Gordon aquifer

Middle Floridan aquifer

Upper Floridan aquifer

Surficial aquifer

Middle Floridan confining unit

Charleston confining unit

Upper Floridan confining unit

Gordon confining unit

Savannah River Site (SRS) Downdip from Savannah River Site

(Aadland and others, 1995)

(This report)

Figure B38. Hydrostratigraphy at the Savannah River Site as defined by Aadland and others

 (1995) compared to the hydrostratigraphy of the South Carolina Coastal Plain downdip 

 of the Savannah River Site, as defined in this study.
South Carolina Coastal Plain Hydrostratigraphy 115

Figure B39. Current hydrostratigraphic correlations of the South Carolina Coastal Plain compared to past correlations.

This report 

surficial aquifer

(layer 1)

Upper Floridan

confining unit

(layer 2)

FLORIDAN AQUIFER SYSTEM

MEYERS

BRANCH

CONFINING

SYSTEM

ALLENDALE

CONFINING

SYSTEM

DUBLIN

AQUIFER

SYSTEM

APPLETON

CONFINING

SYSTEM

RIDGELAND

AQUIFER

SYSTEM

MIDVILLE AQUIFER

SYSTEM

Upper Floridan

aquifer

(layer 3) Floridan

aquifer system

 Black Creek

aquifer 

 Middendorf

aquifer 

 Cape Fear

aquifer 

 Middendorf

aquifer

system 

 Peedee and

Black Creek

aquifer systems 

 Upper Floridan

aquifer

 Chattahoochee

River

confining unit

 Chattahoochee

River

aquifer

 (Pearl River

aquifer updip)

 Pearl River

aquifer

 (Tertiary sand

aquifer updip) (Tertiary sand

aquifer system

updip)

 Tertiary 

Limestone

Aquifer System

 Black Mingo

Aquifer System

 Tertiary sand

aquifer

Middle Floridan

confining unit

(layer 4)

Gordon

confining unit

(layer 6)

Crouch Branch

confining unit

(layer 8)

McQueen Branch

confining unit

(layer 10)

Charleston

confining unit

(layer 12)

Gramling

confining unit

(layer 14)

Black Warrior River

confining unit

Black Warrior River

aquifer

Charleston

aquifer

(layer 13)

Gramling

aquifer

(layer 15)

McQueen Branch

aquifer

(layer 11)

Crouch Branch

aquifer

(layer 9)

Gordon

aquifer

(layer 7)

Middle Floridan

aquifer

(layer 5)

Upper confining unit

middle confining unit/

Lower Floridan

aquifer

unnamed

confining unit

unnamed

confining beds

unnamed

confining beds

unnamed

confining unit

unnamed

confining unit

unnamed

confining unit

unnamed

confining beds

unnamed

confining beds

surficial aquifer surficial aquifer unnamed 

Aucott and others

(1987)

Miller (1986)

Miller and Renken

(1988)

Colquhoun

and others

(1983)

Figure B39 Current hydrostratigraphic correlations of the South Carolina 

 Coastal Plain compared to past correlations.
116 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Surficial Aquifer

The surficial aquifer (model layer 1, Chapter C) is the 

water-table aquifer and consists mainly of terrace sediments 

that were deposited during transgressions and regressions 

of the sea since post-Miocene time. The surficial aquifer is 

present over most of the middle and outer parts of the SC 

ACP, ranges in altitude from about +600 ft in Aiken County 

to 0 ft along the coast, and reaches a maximum thickness of 

about 50 ft (figs. B5 and B6; Plates 1, 2, and 7; Appendix B1). 

Quaternary sediments are generally absent in coreholes in the 

west-central and updip parts of the SC ACP, and in this area, 

the surficial aquifer is of late Eocene through Miocene age. 

The surficial aquifers in NC and SC are equivalent and are 

hydraulically connected. 

Age and Stratigraphic Correlation

In most of SC, the surficial aquifer consists of strata of 

Quaternary age that probably correlate with Quaternary deposits described below the Orangeburg Scarp (Colquhoun, 1969), 

and with the surficial aquifer of Aucott and others (1987). Of 

the 38 coreholes used in SC, 18 penetrated undifferentiated 

Quaternary sediments. No dates, however, were obtained from 

core samples. 

In the southern and central parts of the SRS, the watertable aquifer is called the Upper Three Runs aquifer, and in the 

northern part of the SRS, it is called the Steed Pond aquifer 

(fig. B37). The Upper Three Runs aquifer consists of the 

clastic phase of the Santee Formation, Dry Branch Formation, Tobacco Road Sand, and Upland unit. In this report, 

the clastic Santee is mapped as the updip extension of the 

Middle Floridan aquifer (figs. B4 and B37), the Dry Branch is 

mapped as the updip extension of the Upper Floridan aquifer, 

and the Tobacco Road Sand and Upland unit are combined 

and mapped as the updip extension of the surficial aquifer. As 

such, the surficial aquifer at the SRS and surrounding areas 

consists of late Eocene(?) (Tobacco Road Sand) and early 

Miocene deposits (Upland unit).

Lithology and Texture

The surficial aquifer is lithologically heterogeneous but 

generally consists of quartz gravel and sand, silt, clay, and 

shelly sand. The surficial aquifer in Beaufort, Jasper, and 

Colleton Counties was described by Hayes (1979) as follows: 

“Pleistocene deposits consist of brown, gray, and green clays 

interbedded with white to buff, subangular to angular, quartz 

sand. Shell beds composed of oyster shells embedded in a 

matrix of dark-green to gray clay are common along the coast. 

The Pliocene and Holocene deposits are not well known.” 

Dale and Park (1999), in a study of the shallow aquifer at Hilton Head Island, described the Holocene deposits as clay, silty 

clay, and sand. They determined that the Pleistocene Wando 

Formation consists of three units: a sand unit, a silt and silty 

sand unit with shells, and a clay and silty clay unit with shells. 

Park (1985) described surficial sediments in Charleston, Berkeley, and Dorchester Counties that were deposited 

as four Pleistocene formations: “The Wicomico generally is 

composed of fine sand, but it can contain some clay, coarse 

sand, and gravel locally.” The Talbot Formation “generally 

consists of very fine gray to red or pink thin-bedded sand and 

clay.” Cooke (1936, p. 151) described the Pamlico Formation 

at Johns Island as “...containing 5 ft of green glauconitic claysand, underlain by 3 ft of sand, in turn underlain by 2 ft of 

Pleistocene shell. The thickest sequence of Pamlico deposits 

occurs in the coastal section of Charleston County where 40 to 

60 ft of sand, clay, and shell overlie the Cooper Formation.” 

The Penholoway Formation (as described by Cooke, 1936, 

p. 147–148) consists of “dark grey pebbly sand...passing 

upward into fine black carbonaceous sand,” overlain by 15 ft 

of “fine white crossbedded sand, weathering yellow (beach of 

river deposit).”

Pelletier (1985) described shallow deposits in Georgetown and Horry Counties and the southern part of Marion 

County as “undifferentiated near-surface clay, sand, limestone, 

and shell of Tertiary and Quaternary age.” At the SRS, the 

aquifer consists of variably colored, moderately to poorly 

sorted, fine- to coarse-grained sand, pebbly sand, and minor 

clay beds of the Tobacco Road Sand, and poorly sorted, clayey 

sand, pebbly sand, and conglomerate of the Upland unit (Aadland and others, 1995). At the Orangeburg corehole ORG-393, 

the aquifer consists of moderately to poorly sorted, fine to very 

coarse clayey sand of Quaternary and possibly Oligocene age 

(Appendix B2).

Hydrologic Properties

Transmissivity values calculated for five aquifer tests at 

Hilton Head Island range from 80 to 1,200 ft2/d and average 

about 500 ft2/d (Dale and Park, 1999). Horizontal hydraulic 

conductivity values calculated for these tests range from 4 to 

65 ft/d and average 27 ft/d. Horizontal hydraulic conductivity values derived from minipermeameter tests of 231 core 

samples average 8 ft/d for the aquifer (Tobacco Road Sand) 

at the SRS (Aadland and others, 1995). At Wadmalaw Island, 

near Charleston, SC, transmissivity values calculated from two 

aquifer tests of the surficial aquifer are 190 and 270 ft2/d, and 

hydraulic conductivity values are 20 ft/d (Hockensmith, 1997).

At the SRS, the surficial aquifer is generally connected 

with the underlying clastic phases of the Upper and Middle 

Floridan aquifers. In some areas of the SRS, however, confining beds located near the base of the Upper Floridan (Dry 

Branch Formation) impede the vertical movement of water 

and often support a hydraulic-head difference between the 

surficial aquifer and the underlying clastic phase of the Middle 

Floridan aquifer (Aadland and others, 1995). Farther downdip, in Beaufort, Colleton, Hampton, and Jasper Counties, 

the Upper Floridan confining unit supports a hydraulic-head 

difference between the surficial aquifer and the Upper Floridan 

aquifer (Dale and Park, 1999). 
South Carolina Coastal Plain Hydrostratigraphy 117

Geophysical-Log Signature

During the construction of deep wells, the surficial

aquifer typically is cased off to prevent caving; consequently, 

electric logs of these sediments generally are unavailable. 

Natural gamma counts vary depending on the lithology of the 

unit. At the SRS, the Tobacco Road Sand and the Upland unit 

have high interstitial clay and record elevated gamma counts. 

In areas where the Upper Floridan confining unit is present, 

the surficial aquifer is easily identified from the underlying 

confining unit by relatively low natural gamma counts (see 

Hayes, 1979).

Floridan Aquifer System

The Floridan aquifer system overlies the Meyers Branch 

confining system, and is correlated with the Pearl River 

aquifer of Miller and Renken (1988) in updip regions and 

with the Floridan aquifer of Miller (1986) in downdip regions 

(fig. B39). In the western part of the SC coastal area, the Floridan aquifer system is commonly referred to as the principal 

artesian aquifer (Hayes, 1979); it consists of platform carbonates and is a highly productive aquifer system. Inland, the 

system transitions from pure carbonates to mixed carbonate/

clastic deposits and, farther updip, to purely clastic deposits. 

The updip clastic equivalents are hydraulically connected to 

the downdip carbonate rocks and are thus considered part of 

the Floridan aquifer system. The system extends from the Fall 

Line to the coast and from the Savannah River to about the 

center of the SC ACP (fig. B1). In this study, the aquifer system consists of the Gordon, informally named Middle Floridan, and Upper Floridan aquifers, and the Gordon, informally 

named Middle Floridan, and Upper Floridan confining units 

(figs. B37 and B38).

At the SRS, Aadland and others (1995) divided the 

Floridan aquifer system into two aquifers, the Upper Three 

Runs and Gordon aquifers, which are separated by the Gordon 

confining unit (figs. B37 and B38). The Upper Three Runs 

aquifer consists of Eocene and Miocene sediments that include 

the clastic facies of the Santee Formation (called the Tinker 

Creek Formation at SRS; Fallaw and Price, 1995), Dry Branch 

Formation, Tobacco Road Sand, and Upland unit (fig. B4). 

Clay beds are thin, and, for the most part, these four formations are hydraulically connected at the SRS and were grouped 

as a single aquifer (Upper Three Runs) by Aadland and others 

(1995). The Gordon aquifer at the SRS (Aadland and others, 1995) consists of late Paleocene to early middle Eocene 

sediments that include the Williamsburg Formation (called 

the Snapp Formation at the SRS; Fallaw and Price, 1995), 

Fishburne Formation (called the Fourmile Formation at the 

SRS; Fallaw and Price, 1995), and the Congaree Formation 

(fig. B4). These three formations are hydraulically connected 

at the SRS and were grouped as a single aquifer (Gordon) by 

Aadland and others (1995) (fig. B4). The Gordon confining 

unit, which supports a head difference up to 40 ft at the SRS, 

consists of the middle Eocene Warley Hill Formation and the 

lower part of the Santee Formation (the Blue Bluff marl unit 

of Huddlestun and Hetrick, 1986). In the northern part of the 

SRS, the Gordon confining unit thins and no longer separates 

the Upper Three Runs and Gordon aquifers. The Upper Three 

Runs and Gordon aquifers coalesce and form the Steed Pond 

aquifer of Aadland and others (1995) (fig. B37). 

Downdip from the SRS, in the vicinity of the Allendale 

County corehole (ALL-348), the Upper Three Runs aquifer 

splits into three aquifers (fig. B37)—the surficial aquifer and 

the Upper and Middle Floridan aquifers. The surficial aquifer 

consists mainly of Miocene and Quaternary sediments, the 

Upper Floridan aquifer consists of Oligocene and late Eocene 

carbonate sediments of the upper part of the Parkers Ferry 

Formation, and the Middle Floridan aquifer consists of middle 

Eocene carbonate sediments of the upper part of the Santee 

Formation (fig. B4). In order to maintain the lateral continuity 

of the groundwater flow model layers that are presented in 

Chapter C of this report, these three aquifers were extended 

updip into parts of the inner Coastal Plain. The surficial aquifer is extended updip by correlation of the Tobacco Road Sand 

and Upland unit, the Upper Floridan aquifer is extended updip 

by correlation of clastic age-equivalent sediments of the Parkers Ferry Formation (Dry Branch Formation), and the Middle 

Floridan aquifer is extended updip by correlation of clastic 

age-equivalent sediments of the Santee Formation (Tinker 

Creek Formation) (fig. B4). Although the clastic phases of the 

surficial, Upper Floridan, and Middle Floridan aquifers are 

hydraulically connected at the SRS, they are not combined as 

a single aquifer but instead are mapped as separate units from 

the Fall Line to the coast by stratigraphic correlation of the 

formations composing the aquifers. The Gordon aquifer also is 

mapped as a separate unit from the Fall Line to the coast. The 

Gordon aquifer persists to the coast, but generally contains 

only early Eocene (Fishburne Formation) and late Paleocene 

sediments (Williamsburg Formation) in downdip areas. For 

the most part, the Congaree Formation has been eroded by the 

overlying Santee Formation, and only thin (less than 20 ft) 

remnants of the formation remain in a few of the downdip 

coreholes. In contrast, the Santee section thickens substantially from about 175 ft at the Allendale corehole (ALL-348) 

to about 400 ft at the Jasper County corehole (JAS-426) 

(Plate 1). At JAS-426, Santee sediments overlie Williamsburg 

sediments, and the Congaree Formation is absent (Plate 1). 

The Williamsburg Formation forms the Gordon aquifer here 

and, together with the Fishburne Formation, forms most of the 

Gordon aquifer in downdip regions of the Coastal Plain. 

The Floridan aquifer system of this report is correlated 

with the Tertiary sand aquifer and the Floridan aquifer system 

of Aucott and others (1987) (fig. B39). The Tertiary sand aquifer consists of an upper and a lower part. The upper part is the 

updip clastic equivalent of the Floridan aquifer system (Aucott 

and others, 1987). The upper part extends from about the Fall 

Line to the carbonate/clastic interface in Barnwell, Orangeburg, and Clarendon Counties (see fig. 2 in Aucott and others, 

1987) where it then becomes the Floridan aquifer system. The 
118 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

upper part includes early to late Eocene sediments that consist 

of sand and clay of the Congaree Formation; marl, sand, and 

clay of the McBean Formation (an updip mixed carbonate/

clastic facies of the Santee Formation); and sand and clay 

of the Barnwell Group (Dry Branch Formation and Tobacco 

Road Sand). The upper part correlates, to some extent, with 

the Upper Three Runs aquifer at the SRS (Aadland and others, 

1995), which consists of middle to late Eocene and Miocene 

sediments that include the Santee and Dry Branch Formations, 

Tobacco Road Sand, and Upland unit. The Upper Three Runs 

aquifer, however, does not include the Congaree Formation, 

which forms part of the underlying Gordon aquifer. 

The lower part of the Tertiary Sand aquifer of Aucott 

and others (1987) (fig. B39) extends south from its outcrop 

in the north-central part of the SC ACP to the SC coast. The 

lower part includes Paleocene to early Eocene sediments 

that consist of sand, clay, and limestone of the Black Mingo 

Group (see the report sections on the Williamsburg and 

Fishburne Formations). The lower part of the Tertiary Sand 

aquifer correlates, to some extent, with the Gordon aquifer at 

the SRS (Aadland and others, 1995), which consists of late 

Paleocene to early middle Eocene sediments and includes the 

Williamsburg Formation, the Fishburne Formation, and the 

Congaree Formation. 

Sediments penetrated in reference well P-27 at the SRS 

are characteristic of the updip clastic phase of the Floridan 

aquifer system (Aadland and others, 1995). At well P-27, the 

system is 216 ft thick and consists of clay, sandy clay, and 

sand of the Snapp Formation (late Paleocene) and Fourmile 

Formation (early Eocene), all of the Orangeburg Group 

(middle Eocene) and Barnwell Group (late Eocene) sediments, 

and the overlying Upland unit (Miocene). The Floridan aquifer 

system includes all sediments from the top of the Meyers 

Branch confining system to the surficial aquifer. No reference 

well is known for the downdip Floridan aquifer system. 

Miller (1986) considered late Paleocene strata to be 

part of the Floridan aquifer system in areas of Georgia and 

Florida. In South Carolina, however, Miller terminated the 

base of the Floridan aquifer system either in rocks of early 

Eocene age or in rocks of middle Eocene age (Miller, 1986). 

Aadland and others (1995) included the Gordon aquifer in 

the Floridan aquifer system in west-central SC. The Gordon 

aquifer includes not only early and middle Eocene strata, but 

it also includes late Paleocene strata. To maintain consistency 

with the mapping of Aadland and others, the Floridan aquifer 

system in this report also includes the Gordon aquifer.

Upper Floridan Confining Unit

The Upper Floridan confining unit (model layer 2, Chapter C) overlies the Upper Floridan aquifer. The confining unit 

extends from the southernmost SC coast to southern Allendale 

County and from the Savannah River to western Colleton 

County (figs. B1, B37; Plates 1, 2, and 7). The confining unit 

is absent from central Allendale County to the Fall Line, 

where the underlying Upper Floridan aquifer is essentially 

unconfined. The confining unit generally thickens from east to 

west in Beaufort and Jasper Counties and along the Ridgeland 

trough (see fig. 7 of Hughes and others, 1989), reaching a 

maximum thickness in SC of about 120 ft in the southern part 

of Beaufort County. In southeastern Georgia, the Upper Floridan confining unit is more than 300 ft thick (Appendix B1). 

The confining unit thins to 10–20 ft over the Beaufort arch in 

Beaufort County (Hayes, 1979; Waddell, 1989) (fig. B1). From 

Jasper County (JAS-426) to Hilton Head Island (BFT-2055), 

the confining unit dips about 2 ft/mi to the south-southeast 

(fig. B8; Plate 1). 

Age and Stratigraphic Correlation

The confining unit consists mainly of Miocene formations of the Hawthorn Group, which include the Parachucla, 

Marks Head, Coosawhatchie, and Ebenezer Formations 

(Weems and Edwards, 2001) (fig. B4). Sediments of the late 

Oligocene Tiger Leap Formation may compose lower parts 

of the confining unit. The confining unit is correlated with the 

“upper confining unit” of Ransom and others (2006), Falls and 

others (2005), and Miller (1986). 

Lithology and Texture

The lithology of the Upper Floridan confining unit is heterogeneous, generally consisting of phosphatic, clayey sand, 

sandy clay, sandy dolomitic limestone, and highly phosphatic 

dolomitic sandy and clayey limestone (Hayes, 1979). Duncan 

(1972) describes it as “olive green silt and sand interbedded 

with thin discontinuous lenses of marl and limestone.” North 

and south of the Beaufort arch, the confining unit consists 

of an upper phosphatic clay unit, a middle sandy dolomitic 

limestone, and a lower silty clay unit (Waddell, 1989). At the 

Jasper County corehole (JAS-426), the unit is about 100 ft 

thick and consists of olive-gray and greenish-gray phosphatic 

sandy clay, clayey sand, and calcareous clayey sand. In a 

corehole at Tybee Island, GA, the confining unit consists 

of calcareous sand (Ebenezer Formation), phosphatic sand 

(Coosawhatchie Formation), and calcareous phosphatic sand 

(Marks Head Formation) (Foyle and others, 2001; Weems and 

Edwards, 2001). A hard phosphatic limestone is present in 

some places at the base of the confining unit, and is referred to 

as “cap rock.” Colquhoun (1972) stated that the cap rock consists of “dense, hard, cherty limestone which is occasionally 

phosphatic.” Parts of the confining unit, particularly in Jasper 

County, are permeable enough to be used for local domestic 

supplies (Hayes, 1979). 

Hydrologic Properties

Hydrographs (Dale and Park, 1999), water-level data 

(Siple, 1960), and isotopic data from the Beaufort County area 

(Burt, 1989) all indicate that the Upper Floridan confining unit 

is a leaky confining unit. Water from the overlying surficial 

aquifer seeps downward through the Upper Floridan confining 

unit and into the underlying Upper Floridan aquifer. Vertical 
South Carolina Coastal Plain Hydrostratigraphy 119

hydraulic conductivities of 2.3 × 10–4 and 2.5 × 10–4 ft/d were 

measured for samples collected from the Upper Floridan confining unit at several offshore sites (Falls and others, 2005). 

An average vertical hydraulic conductivity of 5.4 × 10–4 ft/d 

was reported for 11 samples of the Marks Head Formation that 

were collected from beneath the Savannah River near Tybee 

Island (U.S. Army Corps of Engineers, 1998; Falls and others, 

2005; fig. B1).

Geophysical-Log Signature

Phosphate is common in the Upper Floridan confining unit, 

resulting in high counts on the natural gamma-ray log. Zones 

of concentrated phosphate are present as natural gamma spikes, 

which are commonly found at formation contacts (lag beds) 

(see fig. 4 in Falls and others, 2005). In southern Jasper County, 

several natural gamma spikes are commonly present and mark 

formation contacts. The confining unit normally is cased off 

before drilling into the underlying limestone, so few electric logs 

are available through the unit. Where available, resistivity is 

generally lower in the confining unit than in the Upper Floridan

aquifer. Electric logs are useful in identifying permeable zones 

in the Upper Floridan confining unit, which are commonly 

obscured on the natural gamma-ray log by phosphate. 

Upper Floridan Aquifer

The Upper Floridan aquifer (model layer 3, Chapter C) 

extends from the southern SC coast to Aiken County. The 

aquifer overlies the Middle Floridan confining unit in downdip areas and the Middle Floridan aquifer in updip areas. The 

Upper Floridan aquifer is overlain by the Upper Floridan 

confining unit downdip and the surficial aquifer updip (fig. B4; 

Plates 1, 2, and 7). The carbonate phase of the aquifer is 

present from the SC coast to central Allendale County, and 

from the Coosawhatchie and Salkehatchie Rivers in Beaufort, 

Jasper, and Hampton Counties, west to the Savannah River 

(fig. A1). The aquifer thins in northwestern Colleton and southern Allendale Counties, where it transitions to the updip clastic 

phase. The clastic phase of the Upper Floridan aquifer persists 

inland to Aiken County, where it pinches out about 15 mi 

south of the Fall Line. Hydraulic continuity of the clastic and 

carbonate phases of the aquifer is thought to occur, so the two 

phases are considered a single aquifer (fig. B9). 

Allendale County is an area that is transitional between 

the clastic and carbonate phases of the aquifer. A 20-ft 

sandy limestone toward the top of the late Eocene section at 

ALL-348 probably represents the updip limit of the carbonate 

phase of the Upper Floridan aquifer. The ALL-348 corehole is 

located above the Orangeburg Scarp, and erosion of the limestone has likely occurred south of the scarp in the southern 

part of the County, reemerging in northern Hampton County. 

In northern Allendale (ALL-357) and southern Barnwell 

Counties (BRN-335) the late Eocene Dry Branch Formation 

forms the clastic phase of the aquifer and consists predominantly of sand and interbedded sand and clay. 

The carbonate phase of the Upper Floridan aquifer 

thickens from Colleton County toward the southwest in the 

direction of the Savannah River, reaching a maximum thickness of about 200 ft in southern Beaufort County (fig. B10, 

Appendix B1). The aquifer thins from southern Beaufort 

County towards Edisto Beach in southern Colleton County. At 

Edisto Beach, a thick (200+ ft) late Eocene sequence of marl 

and calcareous sand exists at corehole COL-364, but permeable limestone beds are absent. The updip clastic phase of the 

aquifer thickens from the Fall Line to Barnwell County, where 

it reaches a maximum thickness of about 130 ft (fig. B10, 

Appendix B1). 

The Upper Floridan aquifer dips to the south-southeast 

about 5 ft/mi (fig. B9; Plate 1). Dips are shallow in the southern part of the SC ACP. From Jasper County (JAS-426) to 

Hilton Head Island (BFT-2055), the aquifer dips only about 

1 ft/mi to the south-southeast. Shallow dips are the result of a 

post-Eocene localized structural event that warped the surface 

of the aquifer in these areas (Hughes and others, 1989), forming the Ridgeland trough in southern Jasper County (Heron 

and Johnson, 1966) and the Beaufort arch in Beaufort County 

(Siple, 1960). In southern Jasper County, for example, the 

Upper Floridan aquifer dips more steeply than it does in 

northern Beaufort County. In northern Beaufort County, the 

dip of the aquifer flattens out before reversing toward the 

north-northwest (landward). The aquifer then dips back to 

the southeast in southern Beaufort County. The structural 

event had the effect of “buckling” the aquifer across Beaufort 

County, forming a southwest- to northeast-trending arch from 

Port Royal Island to the southern part of Beaufort County, and 

forming a trough in the southern part of Jasper County (see 

fig. 5 of Hughes and others, 1989; see fig. 5 of Spigner and 

Ransom, 1979). The arch extends offshore from Hilton Head 

Island (Falls and others, 2005).

Age and Stratigraphic Correlation

The carbonate phase of the Upper Floridan aquifer consists of the upper sections of the Parkers Ferry Formation (late 

Eocene; also known as the Ocala Limestone) (fig. B4; Plates 1,

2, and 7). The aquifer may also include Oligocene sediments, 

which are thought to thin north of the Savannah River and 

pinch out to the north-northwest of Hilton Head Island (Foyle 

and others, 2001). The updip clastic phase of the Upper Floridan aquifer consists mainly of the Dry Branch Formation (late 

Eocene). The aquifer is correlated with the upper parts of the 

Upper Floridan aquifer of Miller (1986), with the upper parts 

of the Floridan aquifer system of Aucott and others (1987), 

with “Zone 1” and “Zone 2” of McCollum and Counts (1964), 

with the “upper hydrogeologic unit” of Spigner and Ransom 

(1979), and with the “upper permeable zone” of Hayes (1979).

Lithology and Texture

The carbonate phase of the Upper Floridan aquifer consists of white to light-gray indurated and fossiliferous limestone (Hayes, 1979). Allochems consist largely of bryozoans 
120 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

and pelecypods. The clastic phase consists of yellow, tan, and 

orange moderately sorted fine to coarse quartz sand interbedded with tan clay. In Allendale County (ALL-348), the aquifer 

is a mix of clastic and carbonate sediments and consists of 

moderately sorted fine to medium calcareous sand, sandy 

calcarenite, and local sandy limestone.

Hydrologic Properties

Transmissivity values of the carbonate phase of the Upper 

Floridan aquifer range from less than 500 ft2/d at Port Royal 

Island to about 70,000 ft2/d at Hilton Head Island (Hughes and 

others, 1989). Variations in transmissivity mainly reflect differences in aquifer thickness across the area. Transmissivity values 

generally increase to the southwest towards Georgia, where the 

aquifer is thickest. Hydraulic conductivity values range from 

350 to 500 ft/d, except on northern Port Royal Island, where 

they range from 50 to 150 ft/d (Hughes and others, 1989). 

Transmissivity decreases substantially updip where the aquifer 

consists of quartz sand and clay. Few hydraulic data, however, 

are available in these areas. An aquifer test at the SRS indicated 

a transmissivity of 420 ft2/d and a hydraulic conductivity of 

13 ft/d for the aquifer (D’Appolonia, Inc., 1981).

Geophysical-Log Signature

The gamma ray is the most useful log for delineating the 

aquifer in downdip areas. Limestone composing the aquifer 

emits little radiation, and gamma counts are some of the lowest in SC. The lowest natural gamma counts were found in late 

Eocene limestone, and slightly higher counts occur in Oligocene limestone. Electric logs are strongly affected by groundwater salinity and can be useful in identifying the interface 

between fresh and brackish water in the aquifer.

Middle Floridan Confining Unit

The informally named Middle Floridan confining unit 

(model layer 4, Chapter C) overlies the Middle Floridan 

aquifer and is overlain by the Upper Floridan aquifer (fig. B37; 

Plates 1, 2, and 7). In areas where the Middle Floridan aquifer 

is absent, the Middle Floridan confining unit directly overlies 

the Gordon confining unit. In areas where the Upper Floridan aquifer is absent, the confining unit underlies the Upper 

Floridan confining unit or the surficial aquifer (Plates 1, 2,

and 7). The Middle Floridan confining unit is present only in 

the western and central parts of the SC ACP owing to uplift 

of the Cape Fear Arch (fig. B1) in the east. The confining unit 

reaches a maximum thickness of more than 300 ft in Beaufort 

County and dips to the south about 4 ft/mi (figs. B11 and B12; 

Plate 1; Appendix B1). The Middle Floridan confining unit in 

SC is roughly equivalent in stratigraphic position to the Castle 

Hayne confining unit in NC; however, the units are not continuous or hydraulically connected between the two States.

Age and Stratigraphic Correlation

The Middle Floridan confining unit consists of the 

Harleyville Formation (early late Eocene) and the lower parts 

of the Parkers Ferry Formation (late Eocene; also known as 

the Ocala Limestone) (fig. B4; Plates 1, 2, and 7). In parts 

of Dorchester and Charleston Counties, the confining unit 

may also include the Ashley Formation (late Oligocene). The 

Middle Floridan confining unit is probably correlated with 

the lower to middle sections of the Upper Floridan aquifer 

of Miller (1986), with lower sections of the Floridan aquifer 

system of Aucott and others (1987), with the “semiconfining 

units” of Gawne and Park (1992), and with the “middle zone 

of low permeability” of Hayes (1979). The “middle confining 

unit” that separates the Upper and Lower Floridan aquifers 

is “...generally found in the middle part of rocks of middle 

Eocene age” (Miller, 1986). The Middle Floridan confining 

unit of this report is younger and is present in the lower part of 

rocks of late Eocene age.

Lithology and Texture

Downdip, at Hilton Head Island, the Middle Floridan 

confining unit consists of fine calcarenites and calcilutites 

containing minor amounts of quartz sand and clay (Gawne and 

Park, 1992). Most of the confining unit is poorly consolidated 

and interbedded with thin layers of hard limestone. A sidewall 

core (382 ft) from the Hilton Head Island corehole (BFT-2055) 

consists of calcite (64 percent), quartz (14 percent), dolomite 

(14 percent), illite/smectite (5 percent), kaolinite (3 percent), 

and traces of feldspar (Core Laboratories, 1992). A laser 

particle-size analysis of the sample indicates that the core contains 10 percent fine sand, 18 percent very fine sand, 40 percent silt, and 32 percent clay.

Updip, at the Allendale County corehole (ALL-348), the 

confining unit consists of a relatively homogenous section of 

friable, moderately sorted, fine-grained calcareous quartz sand 

and, infrequently, calcareous quartz sand in a lime mud matrix. 

Allochems include pelecypods, bryozoans, and foraminifera. 

On the basis of visual estimations, the percentage of clastic 

and carbonate clasts is about equal. This mixed clastic/carbonate section grades upward to moldic sandy limestone (Upper 

Floridan aquifer). 

Hydrologic Properties

Static water-level differences among six well pairs in the 

Upper and Middle Floridan aquifers at Hilton Head Island did 

not exceed 0.7 ft (Gawne and Park, 1992). Water levels were 

slightly higher in the Upper Floridan aquifer at four of the six 

sites. During low-discharge, short-duration aquifer tests of 

the Middle Floridan aquifer, water levels in adjacent Upper 

Floridan aquifer wells did not lower substantially, confirming 

that “...the two aquifers are separated by a unit of low permeability” (Gawne and Park, 1992). 

Water levels in an Upper Floridan aquifer observation 

well did not lower appreciably during a 96-hour aquifer test 
South Carolina Coastal Plain Hydrostratigraphy 121

of the Middle Floridan well at Hilton Head Island (Groundwater Management Associates, Inc., 2006). During this test, 

the Middle Floridan aquifer well was pumped at a rate of 

1,000 gal/min and had a drawdown of 70.3 ft after 96 hours. 

The Upper Floridan aquifer observation well, located 105 ft 

from the pumping well, had a drawdown of 0.5 ft. Nearby 

production wells in the Upper Floridan aquifer may have 

contributed to the 0.5-ft drawdown in the observation well. In 

addition, no appreciable water-level declines were observed in 

an Upper Floridan aquifer observation well during a 65-hour 

aquifer test of the underlying Middle Floridan aquifer at the 

Allendale County corehole (pumping 63 gal/min) (Karimjee 

and Hodges, 1996). 

Horizontal hydraulic conductivity, measured from a sidewall core at Hilton Head Island (BFT-2055) is 4.1 × 10–2 ft/d 

(Temples and Englehardt, 1997). Updip, at the Allendale 

County corehole (ALL-348), the confining unit supports a 

static hydraulic-head difference of about 40 ft. 

Geophysical-Log Signature

In general, natural gamma radiation levels in the Middle 

Floridan confining unit are slightly elevated on the natural 

gamma-ray log relative to the adjacent Upper and Middle 

Floridan aquifers, and resistivity values are slightly lower. 

Zones of low radiation and high resistivity, however, occur in 

the Middle Floridan confining unit and may indicate permeable zones (Plate 1). Negative potentials on the SP log also are 

associated with permeable zones in the confining unit. 

Middle Floridan Aquifer 

The informally named Middle Floridan aquifer (model 

layer 5, Chapter C) overlies the Gordon confining unit and is 

overlain by the Middle Floridan confining unit where present 

in downdip areas (fig. B37; Plates 1, 2, and 7). The Middle 

Floridan aquifer is present only in the western and central 

parts of the SC ACP owing to uplift of the Cape Fear Arch 

(fig. B1) in the east. The Middle Floridan aquifer reaches a 

maximum thickness of about 100 ft in Jasper County and 

dips to the south about 7 ft/mi (figs. B13 and B14; Plate 1). 

The Middle Floridian aquifer in SC is roughly equivalent in 

stratigraphic position to the Castle Hayne aquifer in NC; however, the units are not continuous or hydraulically connected 

between the two States.

The Middle Floridan aquifer was informally named by 

Gawne and Park (1992) at Hilton Head Island, where it is now 

widely used for irrigation and drinking water. The aquifer is 

generally thin (less than 100 ft), and its lateral continuity is not 

well understood. In the west-central part of the Coastal Plain, 

the aquifer is known to be present in Allendale (ALL-348) and 

Bamberg (BAM-68) Counties, where it is used as a source of 

drinking water for small towns. Updip from these sites, however, from northern Allendale County (ALL-357) to central 

Barnwell County (BRN-349) and east to central Orangeburg 

County (ORG-393), the permeable limestone section of the 

Middle Floridan aquifer is at its updip limits, and the aquifer is only about 10 to 20 ft thick. In these areas, the Santee 

Formation is still relatively thick (100 ft), but most of the 

formation consists of marl (Blue Bluff marl unit) and forms 

the underlying Gordon confining unit (fig. B4). Only the upper 

part of the Santee Formation contains permeable limestone 

beds. In northern Barnwell County (BRN-358) and farther 

east in northern Orangeburg County (ORG-256), no limestone 

is present in the entire SC ACP sequence. At these coreholes, 

the Santee Formation consists of quartz sand and clay (called 

the Tinker Creek Formation in northern SRS and the McBean 

Formation elsewhere). The Middle Floridan aquifer continues 

updip in a clastic phase and pinches out about 20 mi south of 

the Fall Line.

South of the SRS, geophysical logs show some permeability in the Santee section at the Jasper County corehole 

(JAS-426); however, the Gulf Trough, a low-permeability 

feature of Tertiary age in the outer Georgia Coastal Plain, 

may extend into SC in this area and may reduce permeability 

of the Middle Floridan aquifer (Patterson and Herrick, 1971) 

(fig. B1). Well yields and hydraulic properties of the Middle 

Floridan aquifer are unknown in Jasper County. Farther south, 

in Beaufort County, local variations in permeability may limit 

the use of the aquifer in certain areas. At Hilton Head Island 

(BFT-2055), however, the aquifer is highly permeable (see 

discussion below). Northeast of Hilton Head, at Edisto Beach 

(COL-364), permeability is low, and the town uses a deeper 

local aquifer zone in the Eocene strata.

Age and Stratigraphic Correlation

The Middle Floridan aquifer consists of the upper part of 

the Santee Formation (late middle Eocene) (fig. B4; Plates 1,

2, and 7). The aquifer is correlated with the “middle Floridan 

aquifer” of Gawne and Park (1992) and, to some extent, with 

the lower part of the Upper Floridan aquifer of Miller (1986), 

with sections of the Floridan aquifer system of Aucott and others (1987), with “Zone 4” and (or) “Zone 3” of McCollum and 

Counts (1964), and possibly with the “lower permeable zone” 

of Spigner and Ransom (1979).

Lithology and Texture

Downdip, at Hilton Head Island, the Middle Floridan 

aquifer consists of hard moldic limestone that is interbedded with poorly consolidated shelly limestone in a lime mud 

matrix (Gawne and Park, 1992). Allochems are mainly shell 

fragments of gastropods, bivalves, and bryozoans. Updip, at 

the Allendale County corehole (ALL-348), the aquifer consists 

of hard moldic limestone and shelly limestone in a lime mud 

matrix. The Middle Floridan aquifer contains minor amounts 

(less than 10 percent) of fine-grained quartz sand and terrigenous mud. Glauconite composes up to 3 percent of the 

unit. Pelecypod and bryozoan shell fragments are common. 

Wells completed in the Middle Floridan aquifer in Allendale 

County are commonly gravel-packed and screened to filter out 

the sand. 
122 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

At the Bamberg County corehole (BAM-68), the Middle 

Floridan aquifer consists of a hard moldic limestone that 

grades downward to moderately hard permeable and shelly 

calcarenite in a lime mud matrix. Allochems consist mainly 

of pelecypod shell fragments with minor bryozoans. Minor 

quartz sand (less than 10 percent) is present. Calcarenite beds 

grade downward to shelly calcilutite and sandy marl to form 

the underlying Gordon confining unit.

Hydrologic Properties

Transmissivity values from six Middle Floridan aquifer 

tests at Hilton Head Island range from 2,300 to 26,700 ft2/d 

and average 10,500 ft2/d (Gawne and Park, 1992). The wide 

range of values is attributed mainly to differences in aquifer 

thickness and to local variations in hydraulic conductivity. 

Horizontal hydraulic conductivity values, calculated from four 

of the tests, range from 220 to 290 ft/d and average 260 ft/d. 

Transmissivity and hydraulic conductivity generally 

decrease updip in Allendale County. Four aquifer tests in the 

county have values that range from 3,300 to 6,300 ft2/d and 

average 4,400 ft2/d (Newcome, 2005). Horizontal hydraulic 

conductivity values range from 55 to 105 ft/d and average 

about 75 ft/d (Gellici and others, 1995).

Geophysical-Log Signature

Resistivity of the Middle Floridan aquifer is moderately 

high [100 Ohm-meters (ohm-m)] in updip areas and decreases 

slightly in SC coastal counties (Plate 1). The aquifer is often 

difficult to identify on geophysical logs in downdip areas where

it is marked by slight increases in resistivity together with 

decreases in natural gamma counts and negative potentials. 

Subtle decreases in gamma counts often indicate “clean” limestone intervals and corresponding increases in permeability.

Gordon Confining Unit

The Gordon confining unit (model layer 6, Chapter C) 

overlies the Gordon aquifer and is overlain by the Middle 

Floridan aquifer (fig. B37; Plates 1, 2, and 7). The confining 

unit is present only in the western and central parts of the SC 

ACP. In the eastern SC ACP, formations that compose the 

Gordon confining unit are absent due to uplift of the Cape 

Fear Arch (Plate 7). The confining unit reaches a maximum 

thickness greater than 300 ft in Beaufort County and dips to 

the south about 8 ft/mi (figs. B15 and B16; Plates 1 and 2; 

Appendix B1). The Gordon confining unit in SC is roughly 

equivalent in stratigraphic position to the Beaufort confining 

unit in NC; however, the units are not continuous or hydraulically connected between the two States.

Age and Stratigraphic Correlation

The Gordon confining unit consists of the Warley Hill 

Formation (middle middle Eocene) and the lower part of the 

Santee Formation (late middle Eocene) (fig. B4; Plates 1, 2,

and 7). The Gordon confining unit correlates with the Gordon 

confining unit of Aadland and others (1995) and is part of the 

Pearl River aquifer of Miller and Renken (1988). The confining unit also correlates with the Tertiary sand aquifer of Aucott 

and others (1987), and possibly with the “middle confining 

unit” of Miller (1986) (fig. B39).

Lithology and Texture

In the central part of the SRS, the Gordon confining unit 

consists of fine-grained glauconitic clayey sand and clay of 

the Warley Hill Formation. The confining unit is generally thin 

(less than 20 ft) but supports static head difference of more 

than 40 ft at the SRS. In the southern part of the SRS, the confining unit consists of the Warley Hill interval and the overlying Blue Bluff marl unit of the Santee Limestone (Plate 1). 

The Blue Bluff unit consists of laminated clayey calcilutite, 

calcarenite, and calcareous silt and clay with indurated limestone nodules and lenses. Glauconite content can be as great 

as 30 percent. Thin-section analyses indicate that the dominant 

allochems are foraminifers, echinoderms, pelecypods, bryozoans, and broken skeletal debris (Aadland and others, 1995). 

The Blue Bluff lithology is known to extend as far east as 

the Orangeburg corehole (ORG-393) (Gellici, 2007a). At the 

ORG-393 corehole, the confining unit is a gray and olivecolored marl, which consists of very fine and fine quartz sand 

(40 percent), clay (30 percent), and shell fragments in a calcareous matrix (Appendix B2). Megafossils include bivalves, 

gastropods, and bryozoans.

Hydrologic Properties

Permeameter tests of three calcareous clay samples from 

the “C-well” series of coreholes in Barnwell and Allendale 

Counties indicate that vertical hydraulic conductivity values of the Gordon confining unit range from 1.2 × 10–4 to 

2.0 × 10–4 ft/d, and average 1.5 × 10–4 ft/d (Aadland and others, 1995). The confining unit supports a head difference of 

about 40 ft at the Allendale corehole (ALL-348) and 50 ft at 

the Orangeburg corehole (ORG-393). The Gordon confining 

unit thickens downdip to about 300 ft at the Jasper County 

corehole (JAS-426) where it may contain permeable limestone 

as indicated by geophysical logs (Plate 1).

Geophysical-Log Signature

Resistivity is generally low in the Gordon confining unit 

owing to the fine-grained character of the unit. Long-normal 

resistivity averages only 13 ohm-m at the Orangeburg corehole (ORG-393) (Plate 7). In downdip areas, slight increases 

in resistance on the single-point log, along with negative 

deflections on the spontaneous-potential log and low gamma 

counts, suggest permeability in the confining unit (see corehole BFT-2055, Plate 1). Gamma spikes from high concentrations of glauconite and phosphate commonly are present at the 

base of the Gordon confining unit and can be used as a marker 

for the Santee/Warley Hill contact.
South Carolina Coastal Plain Hydrostratigraphy 123

Gordon Aquifer

The Gordon aquifer (model layer 7, Chapter C) is the 

lowermost aquifer of the Floridan aquifer system. The Gordon 

aquifer overlies the Crouch Branch confining unit and is 

overlain by the Gordon confining unit (fig. B37; Plates 1, 2,

and 7). The aquifer is present in the western and central parts 

of the SC ACP. In the eastern SC ACP, formations that compose the Gordon aquifer are absent due to uplift of the Cape 

Fear Arch. The aquifer reaches a maximum thickness of more 

than 300 ft in Beaufort County and dips to the south about 

14 ft/mi (figs. B17 and B18; Plate 1; Appendix B1). The Gordon confining unit in SC is roughly equivalent in stratigraphic 

position to the Beaufort confining unit in NC; however, the 

units are not continuous or hydraulically connected between 

the two States.

Age and Stratigraphic Correlation

The Gordon aquifer consists of several formations that 

are hydraulically connected. Updip, the aquifer consists mainly 

of the Congaree (early Eocene and early middle Eocene) and 

Williamsburg Formations (late Paleocene) (fig. B4; Plates 1,

2, and 7). In some updip wells, the Gordon aquifer can also 

include beds of the Fishburne Formation (early Eocene; called 

the Fourmile Formation in updip areas), beds of the Warley 

Hill Formation (middle middle Eocene), and beds of the lower 

part of the Santee Formation (late middle Eocene). South of 

Allendale County, the Congaree Formation is eroded, and 

the Gordon aquifer consists of the Williamsburg Formation 

and (where present) the Fishburne Formation (fig. B4). In the 

northern part of the SRS and updip from the SRS, confining beds of the overlying Gordon confining unit thin, and the 

Gordon and Upper Three Runs aquifers coalesce to form the 

Steed Pond aquifer (fig. B38) (Aadland and others, 1995). In 

this report, the Steed Pond aquifer is not modeled. Instead, the 

Gordon aquifer is extended to updip areas by correlation with 

the Congaree Formation.

The Gordon aquifer is correlated with the Gordon aquifer 

of Aadland and others (1995), with the lower part of the Pearl 

River aquifer of Miller and Renken (1988), with the lower part 

of the Tertiary sand aquifer system of Colquhoun and others 

(1983), and with the lower part of the Tertiary sand aquifer of 

Aucott and others (1987) (fig. B39).

Lithology and Texture

In updip regions, in and around the SRS, the Gordon 

aquifer is characterized by unconsolidated, poorly to moderately sorted fine- to coarse-grained sand and clayey sand with 

local gravel (Plates 1, 2, and 7). The sand fraction consists 

of quartz with sparse lignite, muscovite, glauconite, feldspar, 

and monazite. Particle-size analyses of 661 samples of the 

aquifer from the SRS and surrounding areas indicate 2 percent 

gravel, 95 percent sand, and 3 percent mud (Aadland and 

others, 1995). Nearly 70 percent of the samples contain less 

than 2 percent mud. Grain size averages 1.6 Φ (lower medium 

sand). Phi (Φ) is defined as the logarithmic transformation 

of the ratio of a grain diameter in millimeters to a standard 

grain diameter of 1 millimeter (Friedman and Sanders, 1978). 

Most of the samples were either moderately sorted (about 

37 percent) or poorly sorted (about 30 percent). Downdip, in 

southern Barnwell and Allendale Counties, quartz sand grades 

into glauconitic, quartz-rich, fossiliferous grainstone, packstone, and wackestone (Aadland and others, 1995). Dominant 

allochems include foraminifers, pelecypods, and minor other 

mollusks, echinoderms, and bryozoans. Glauconite can be as 

high as 60 percent. Farther downdip, at the DOR-208 corehole 

in Dorchester County, the Congaree Formation is eroded, and 

the Gordon aquifer consists mainly of the Williamsburg Formation (Chicora Member), which consists of moldic quartzbearing pelecypod limestone, calcareous laminated silty clay, 

and well-sorted silt and fine sand (Edwards and others, 1997). 

At the Orangeburg corehole ORG-393, the aquifer consists 

of gray and greenish-gray moderately sorted, fine- to coarsegrained clayey sand and interbedded sand and carbonaceous 

clay (Appendix B2).

Hydrologic Properties

Generally, the Gordon aquifer is not as productive as the 

Crouch Branch or McQueen Branch aquifers. Transmissivity 

values calculated from 15 aquifer tests in the central part of 

the SRS average about 2,000 ft2/d (Gellici and others, 1995). 

In central Barnwell County, the Gordon aquifer transmissivity 

averages about 4,900 ft2/d owing to increases in aquifer thickness. Hydraulic conductivity values range from 24 to 41 ft/d 

and average 35 ft/d. Storage coefficients average 3.3 × 10–4. 

South of the SRS, at the Allendale corehole (ALL-348), sieve 

analyses indicate that hydraulic conductivity decreases owing 

to a downdip increase in the percentage of mud, a decrease in 

grain size, and poorer sorting (Robertson and Thayer, 1990). 

Two aquifer tests of the Gordon aquifer in southern Charleston 

County produced transmissivity values of 750 and 900 ft2/d. 

Geophysical-Log Signature

Resistivity decreases downdip due to increases in groundwater specific conductance and clay content of the Gordon 

aquifer. In northern Barnwell County, long-normal resistivity ranges from 200 to 300 ohm-m; in southern Barnwell 

County, from 100 to 150 ohm-m; and in Allendale County, 

from 40 to 80 ohm-m. Resistivity of the Gordon aquifer is 

consistently lower than that of the Cretaceous aquifers, possibly reflecting water chemistry differences (see corehole 

ORG-393 on Plate 7). Gamma radiation in the updip sections 

of the Congaree Formation is distinctly low and can be used, 

to some degree, to identify the Congaree interval (see corehole ORG-393 on Plate 7). Radiation increases downdip and 

is especially high in glauconite-rich beds of the aquifer. In 

downdip areas, negative deflections on the SP log, in conjunction with small increases in resistance on the single-point log, 

indicate permeability in the aquifer. This type of geophysical 

log response is particularly evident at the Hilton Head Island 
124 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

corehole (BFT-2055), in the interval from 1,230 to 1,480 ft 

(Plate 1). Strong negative SP signals and increases in resistance suggest permeability in this interval. No wells, however, 

have been completed in the Gordon aquifer in the Hilton Head 

area, and yields are unknown.

Meyers Branch Confining System/

Crouch Branch Confining Unit

The Meyers Branch confining system was defined by 

Aadland and others (1995) at type well P-24 at the SRS in 

Barnwell County, where it was named for Meyers Branch. The 

confining system hydraulically separates the Dublin and Floridan aquifer systems and is present in the western and southern 

parts of the SC ACP. The Meyers Branch confining system 

is correlated with the Chattahoochee River confining unit of 

Miller and Renken (1988) (fig. B39). At P-24, the system is 

134 ft thick and consists of clay and silty clay of the Peedee/

Steel Creek Formation (Maastrichtian) and interbedded clay 

and clayey sand of the Sawdust Landing (Maastrichtian), 

Lang Syne (early Paleocene), and Snapp Formations (late 

Paleocene). The Meyers Branch confining system consists of a 

single confining unit—the Crouch Branch. 

The Crouch Branch confining unit (model layer 8, 

Chapter C) overlies the Crouch Branch aquifer and underlies 

the Gordon aquifer in the western and southern parts of the 

SC ACP (fig. B37; Plates 1, 2, and 7). The Crouch Branch 

confining unit is generally absent in the eastern part of the SC 

ACP owing to uplift of the Cape Fear Arch (fig. B1). Updip, 

in Aiken and Lexington Counties, clay beds composing the 

confining unit thin and are locally absent. In these areas, the 

Crouch Branch aquifer coalesces with the overlying Gordon 

aquifer. The Crouch Branch confining unit reaches a maximum thickness of more than 300 ft in Colleton and Charleston 

Counties, dipping to the south-southeast about 16 ft/mi in the 

western part of the Coastal Plain, and 8 ft/mi in the eastern 

part (figs. B19 and B20; Plates 1, 2, and 7; Appendix B1). The 

Crouch Branch confining unit in SC is roughly equivalent in 

stratigraphic position to the Peedee confining unit in NC. The 

units are continuous and hydraulically connected between the 

two States.

Age and Stratigraphic Correlation

The Crouch Branch confining unit consists primarily 

of the Rhems (early Paleocene) and Lang Syne (early late 

Paleocene) Formations (fig. B4; Plates 1, 2, and 7). In some 

areas, the Sawdust Landing Formation (latest Maastrichtian), 

the upper Peedee/Steel Creek units (late Maastrichtian), and 

the lower parts of the Williamsburg Formation (late Paleocene) are included in the confining unit. The Crouch Branch 

confining unit is correlated with the Crouch Branch confining 

unit mapped in west-central SC by Aadland and others (1995). 

The confining unit is also correlated with “confining beds” that 

separate the Black Creek and Tertiary Limestone/Tertiary Sand 

aquifer systems of Colquhoun and others (1983) and with the 

unnamed confining unit that separates the Black Creek and 

Tertiary sand aquifers of Aucott and others (1987) (fig. B39).

Lithology and Texture

At the Orangeburg corehole (ORG-393), the Crouch 

Branch confining unit consists of carbonaceous silty-clay that 

is thinly laminated with well-sorted very fine to fine quartz 

sand and silt (Rhems Formation; Appendix B2). Sand laminations are several tenths of an inch thick. Very fine grained mica 

and lignite are common in the sand laminations. Downdip, at 

the Berkeley corehole (BRK-644), the Crouch Branch confining unit (Rhems Formation) consists of 50 to 70 percent very 

fine to fine-grained well-sorted quartz sand in a calcareous 

clay matrix with minor mica and traces of glauconite and lignite. Indurated layers (less than 1 ft thick) of shelly limestone 

are present at various places throughout the unit. At the Sumter corehole (SUM-296) the unit correlates with the Lang Syne 

Formation, which consists mainly of semiconsolidated opaline 

claystone (Vroblesky, 1994). Secondary opaline silicification 

characterizes much of the Crouch Branch confining unit and 

is commonly concentrated to the degree that the formation 

breaks with a conchoidal fracture. 

Hydrologic Properties

Permeameter tests of 18 clay and sandy clay samples 

from the Crouch Branch confining unit at the SRS indicate 

vertical hydraulic conductivity values ranging from 3.4 × 10–6

to 1.7 × 10–2 ft/d and averaging 1.3 × 10–4 ft/d (Aadland 

and others, 1995). Horizontal hydraulic conductivity values 

from 13 clay and sandy clay samples range from 3.7 × 10–5

to 3.2 × 10–1 ft/d and average 4.9 × 10–4 ft/d (Aadland and 

others, 1995). The confining unit supports a head difference of 

about 13 ft at the Allendale corehole (ALL-348) and 24 ft at 

the Orangeburg corehole (ORG-393). 

Geophysical-Log Signature

Resistivity is low and gamma radiation relatively high 

owing to the high clay content of the Crouch Branch confining unit. Long-normal resistivity averages 18 ohm-m at the 

Orangeburg corehole (ORG-393). Anomalously high resistivity of opaline claystones that form the confining unit may be 

due to unsaturated conditions at the site or to induration from 

silica cement. 

Dublin Aquifer System/Crouch Branch Aquifer

The Dublin aquifer system overlies the Allendale 

confining system and underlies the Meyers Branch confining system. The Dublin aquifer system is present across most 

of the Coastal Plain, although it coalesces with the Midville 

and Floridan systems updip and in the eastern part of the SC 

ACP (Aadland and others, 1995). The Dublin aquifer system 
South Carolina Coastal Plain Hydrostratigraphy 125

is correlated with the upper part of the Chattahoochee River 

aquifer of Miller and Renken (1988) (fig. B39). Clarke and 

others (1985) defined the system at type well 21U4, near the 

town of Dublin, GA. In SC, sediments at reference well P-22 

at the SRS in Barnwell County are characteristic of the aquifer 

system (Aadland and others, 1995). At this well, the Dublin 

aquifer system is 213 ft thick and consists of unconsolidated 

well-sorted sand and lignitic, micaceous, clayey sand of the 

Black Creek Group (Campanian), and moderately sorted 

medium to coarse sand and interbedded sand and clay of the 

Peedee/Steel Creek Formation (Maastrichtian). The system 

consists of a single aquifer—the Crouch Branch aquifer. Several confining beds in the eastern part of the SC ACP may warrant splitting the Dublin aquifer system into several aquifers. 

The Crouch Branch aquifer (model layer 9, Chapter C) 

overlies the McQueen Branch confining unit and is overlain 

by the Crouch Branch confining unit (fig. B37; Plates 1, 2,

and 7). The Crouch Branch aquifer is present over most of 

the SC ACP but is absent or thins considerably in the northeastern part of SC in Chesterfield, Darlington, Dillon, and 

Marlboro Counties (figs. B21 and B22). In the southern part 

of the Coastal Plain, the aquifer is fine grained. Production 

wells in Beaufort and Charleston Counties usually bypass 

the Crouch Branch aquifer and are completed in the deeper 

Charleston and Gramling aquifers. Sandy clay and calcareous 

clay beds divide the Crouch Branch aquifer in the eastern half 

of the Coastal Plain. The aquifer reaches a maximum thickness 

of more than 500 ft in Berkeley and Williamsburg Counties 

(fig. B22) and in southern SC, but much of the aquifer in these 

counties consists of low-permeability, fine-grained sediments. 

The Crouch Branch aquifer dips to the south-southeast about 

18 ft/mi in the western part of the SC ACP and 2 ft/mi in the 

eastern part (fig. B21; Plates 1, 2, and 7; Appendix B1). The 

shallow dip in the east is the result of erosion or nondeposition 

of the upper parts of the aquifer owing to uplift along the Cape 

Fear Arch. The Crouch Branch aquifer in SC is equivalent in 

stratigraphic position to the Peedee aquifer in NC (fig. B4). 

The units are continuous and hydraulically connected between 

the two States.

Age and Stratigraphic Correlation

In the western part of the SC ACP, the aquifer consists of 

the upper part of the upper Donoho Creek unit (late Campanian), the Peedee/Steel Creek Formation (Maastrichtian) and, in 

some places, the Sawdust Landing Formation (late Maastrichtian) (fig. B4; Plates 1, 2, and 7). In some areas, the Sawdust 

Landing Formation and the upper Peedee/Steel Creek unit 

consist of dense sandy clay and clayey sand, and are included 

in the overlying Crouch Branch confining unit. In the eastern 

and southern parts of the Coastal Plain, the Sawdust Landing Formation and the upper Donoho Creek unit (calcareous 

nannofossil zone CC 23) are absent. Also in the east, parts of 

the Bladen Formation are permeable and are included in the 

Crouch Branch aquifer (see report section “Allendale Confining System/McQueen Branch Confining Unit”) (fig. B4). 

Confining zones consisting of laminated sand and clay 

and beds of sandy marl are present in the eastern part of the 

inner and outer SC ACP (Plates 2 and 7) where they locally 

divide the Crouch Branch aquifer into three aquifer zones. The 

lower aquifer zone consists mainly of the Bladen Formation; 

the middle zone consists of the Donoho Creek Formation; and 

the upper zone consists of the Peedee Formation.

The Crouch Branch aquifer is correlated with the Crouch 

Branch aquifer mapped in west-central SC by Aadland and others (1995). The aquifer also is correlated with the Black Creek 

aquifer system of Colquhoun and others (1983) and with the 

Black Creek aquifer of Aucott and others (1987) (fig. B39).

Lithology and Texture

In the west-central part of the Coastal Plain, from the 

SRS to Orangeburg, the Crouch Branch aquifer is characterized by unconsolidated, poorly sorted, fine- to coarse-grained 

sand and clayey sand in a kaolinite matrix and by interbedded 

fine sand and carbonaceous clay (Plates 1, 2, and 7). Sediments are finer grained and more glauconitic and calcareous 

in the southern and eastern parts of the SC ACP than elsewhere. In Berkeley County (BRK-644), the aquifer consists of 

glauconitic and calcareous fine-grained clayey sand and limey 

clay (Peedee Formation), laminated clay and fine- to mediumgrained sand with scattered shells (Donoho Creek Formation), 

and glauconitic and calcareous fine- to medium-grained clayey 

sand (Bladen Formation).

At the Orangeburg corehole (ORG-393), the lower part of 

the Crouch Branch aquifer (upper Donoho Creek unit) consists 

predominantly of quartz sand laminated with carbonaceous 

clay (Appendix B2). Mean grain size of five particle-size 

analyses ranges from 3.7 to 1.3 Φ (very fine to medium sand) 

and averages 2.8 Φ (fine sand). Most of the samples are very 

fine or fine grained, and most are poorly sorted. Sand averages 

83 percent and mud 17 percent. The middle part of the Crouch 

Branch aquifer (Peedee/Steel Creek Formation) consists of 

unconsolidated, slightly clayey, fine- to very coarse-grained 

quartz sand (Appendix B2). Mean grain size of 12 particle-size 

analyses ranges from 2.9 to 0.2 Φ (fine to coarse grained) and 

averages 1.4 Φ (medium grained). Most of the samples are 

poorly sorted. Gravel averages 2 percent, sand 88 percent, and 

mud 10 percent. The upper part of the Crouch Branch aquifer 

(Sawdust Landing Formation) consists of fine- to very coarsegrained quartz sand in a kaolinite clay matrix (Appendix B2). 

The matrix constitutes up to 35 percent of the aquifer and is 

dense in places. Mean grain size of three particle-size analyses 

ranges from 2.2 to 0.4 Φ (fine to coarse grained) and averages 1.4 Φ (medium grained). All of the samples are poorly 

sorted. Gravel averages 4 percent, sand 78 percent, and mud 

18 percent.

Particle-size analyses of 305 samples from the Crouch 

Branch aquifer in the SRS area indicate 3 percent gravel, 

86 percent sand, and 11 percent mud (Aadland and others, 

1995). Grain size of the samples averages 1.4 Φ (medium 

grained), and most (about 70 percent) are poorly sorted. 
126 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Hydrologic Properties

The Crouch Branch is a highly productive aquifer, especially in the west-central and updip parts of the Coastal Plain, 

where it is thick and consists of unconsolidated medium- to 

coarse-grained sand. The Crouch Branch aquifer is, however, 

generally less permeable and transmissive than the underlying 

McQueen Branch aquifer.

Transmissivity calculated from a 7-day aquifer test at 

Cope (fig. B1) in western Orangeburg County is 11,000 ft2/d 

(Newcome, 2005). This transmissivity is essentially the same 

as that calculated for the aquifer in west-central SC in and 

around the SRS (Aadland and others, 1995). A storage coefficient of 2.6 × 10–4 is calculated from the test, and the hydraulic 

conductivity is estimated at 85 ft/d. Downdip, at Holly Hill 

(fig. B1) in the southeast corner of Orangeburg County, transmissivity is only 2,100 ft2

/d (Newcome, 2005), and hydraulic 

conductivity is 21 ft/d. The lower values reflect changing 

depositional environments from coarse-grained lithofacies 

in the northern part of the County to fine-grained lithofacies 

in the southeastern part of the County. Farther to the east, 

21 aquifer tests of the Crouch Branch aquifer produce transmissivity values that range from about 1,000 to 6,200 ft2

/d and 

average 2,400 ft2/d (median of 1,700 ft2/d). These tests were in 

Dillon, Florence, Marion, and Marlboro Counties (Rodriguez 

and others, 1994).

Geophysical-Log Signature

Resistivity signatures of the Crouch Branch aquifer on 

the long-normal log are similar to those of the McQueen 

Branch aquifer [see coreholes AIK-817 (Plate 1), ALL-348 

(Plate 1), and ORG-393 (Plate 7)]. They are highest in the 

west and in updip areas where the aquifer consists of coarsegrained sediments and where groundwater is freshest. Downdip, mineralization of the Crouch Branch aquifer groundwater 

increases and resistivity decreases. To the east, Crouch Branch 

aquifer sediments are finer grained, clay content increases, and 

resistivity correspondingly decreases. The Sawdust Landing Formation typically has a lower resistivity than other 

formations that compose the Crouch Branch aquifer, primarily because of its high clay content. Some intervals of the 

Sawdust Landing consist of very poorly sorted quartz grains 

completely embedded in a dense kaolinite matrix. 

In the western SC ACP, low radiation levels are a characteristic feature of the upper Donoho Creek unit of the Crouch 

Branch aquifer. Peedee/Steel Creek lithologies generally have 

higher radiation levels and typically contain gamma spikes. 

Gamma spikes are not always associated with lag beds in the 

Peedee/Steel Creek interval; some may be associated with 

concentrations of monazite or with coarse-grained sediments 

that are more likely to contain greater amounts of gammaemitting feldspar. 

Allendale Confining System/

McQueen Branch Confining Unit

The Allendale confining system hydraulically separates 

the Midville and Dublin aquifer systems (fig. B38). The confining system is present across most of the Coastal Plain, but 

thins greatly in updip and eastern parts of the SC ACP (Aadland and others, 1995) where the Midville and Dublin systems 

coalesce. Miller and Renken (1988) treated the Midville and 

Dublin as a single system (their Chattahoochee River aquifer), and so the Allendale confining system has no correlative 

unit in their framework (fig. B39). Aadland and others (1995) 

defined the system at type well ALL-348 near the town of 

Appleton in Allendale County, SC, where it is 162 ft thick and 

consists mainly of clay, silty clay, and calcareous silt and clay 

of the Black Creek Group (Campanian). The Allendale confining system contains a single confining unit—the McQueen 

Branch confining unit.

The McQueen Branch confining unit (model layer 10, 

Chapter C) overlies the McQueen Branch aquifer and underlies 

the Crouch Branch aquifer over most of the SC ACP (fig. B37; 

Plates 1, 2, and 7). In counties along the Fall Line, clay beds 

composing the confining unit thin and are locally absent. In 

these areas, the McQueen Branch and Crouch Branch aquifers coalesce. The confining unit reaches a maximum thickness of about 240 ft in southern Beaufort County, dipping to 

the south-southeast about 18 ft/mi in the western part of the 

Coastal Plain, and 8 ft/mi in the eastern part (figs. B23 and 

B24; Plates 1, 2, and 7; Appendix B1). The McQueen Branch 

confining unit in SC is equivalent in stratigraphic position to 

the Black Creek confining unit in NC. The units are continuous 

and hydraulically connected between the two States.

Age and Stratigraphic Correlation

In the western and central parts of the SC ACP, the 

McQueen Branch confining unit consists of all or parts of 

three formations that, in ascending order, are the upper part of 

the Coachman (middle Campanian), the Bladen (late middle 

Campanian), and the Donoho Creek (late Campanian) (fig. B4; 

Plates 1, 2, and 7). Typically, the lower and middle units of the 

Donoho Creek Formation (subzones CC 22a/b and CC 22c) 

and the lower half of the upper Donoho Creek unit (calcareous nannofossil zone CC 23) form part of the confining unit. 

A fine- to medium-grained sand facies in the upper half of the 

upper Donoho Creek unit forms part of the overlying Crouch 

Branch aquifer in the west-central area of the State. 

The McQueen Branch confining unit is correlated with 

the McQueen Branch confining unit mapped in west-central 

SC by Aadland and others (1995). The confining unit also is 

correlated with the “confining beds” between the Middendorf 

and Black Creek aquifer systems of Colquhoun and others 

(1983) and with the unnamed confining unit between the Middendorf and Black Creek aquifers of Aucott and others (1987) 

in updip regions (fig. B39).
South Carolina Coastal Plain Hydrostratigraphy 127

Lithology and Texture

At the Orangeburg corehole (ORG-393), the confining 

unit consists of laminated sand and silty clay in a carbonaceous 

clay matrix (Coachman Formation); shelly calcareous clay 

(Bladen Formation); sandy marl, calcareous clay, and carbonaceous clay (lower and middle Donoho Creek units); and silty 

clay with fine-grained sand (lower part of upper Donoho Creek 

unit) (Appendix B2). Results of a detailed petrographic study of 

a sample from the middle Donoho Creek unit (1,028 ft) in the 

Allendale corehole (ALL-348) indicate that the sample contains fine quartz and clay minerals with minor to trace amounts 

of muscovite, collophane, heavy minerals, organic debris, 

pyrite, and skeletal fragments, including foraminifers, pelecypods, and bryozoans (Aadland and others, 1995). 

In the eastern part of the SC ACP the thickness and permeability of the Bladen Formation increase. At the SRS, for 

example, the formation is 40 to 50 ft thick and consists of lowpermeability, fine-grained calcareous silt and clay. In Florence 

County, the formation thickens to more than 100 ft and consists 

of permeable glauconitic sand and interbedded sand and clay. 

The permeable sand beds of the formation are considered part 

of the overlying Crouch Branch aquifer. As a result, the thickness of the confining unit decreases and that of the Crouch 

Branch aquifer increases (fig. B22 and Plate 7). The thick 

McQueen Branch confining unit that effectively separates the 

McQueen Branch and Crouch Branch aquifers from the SRS to 

Orangeburg is essentially split by permeable sand beds of the 

Bladen Formation. These sand beds may well constitute a separate aquifer; however, no hydraulic-head data are available, and 

the sand is included in the overlying Crouch Branch aquifer. 

Clay beds of the upper Coachman and lower Bladen Formations form the McQueen Branch confining unit in the east. 

At Florence (fig. B1), the McQueen Branch confining unit 

is anomalously thick (130 ft) (Plate 7) and effectively separates 

the Crouch Branch and McQueen Branch aquifers. The confining unit thins in all directions away from Florence. In areas 

from northern Charleston County to Horry County and inland to 

Berkeley County, the confining unit can be difficult to delineate 

and map owing to the absence of substantial clay beds in the 

Coachman and Bladen Formations. The section in the Berkeley 

County corehole (BRK-644, Plate 2) consists of fine-grained 

glauconitic sand and interbedded calcareous sand and clay. 

Hydrologic Properties

Permeameter tests of nine clay and sandy clay samples 

from the McQueen Branch confining unit at the SRS (fig. B1) 

indicate vertical hydraulic conductivity values that range 

from 6.8 × 10–5 to 2.1 × 10–2 ft/d and average 3.8 × 10–4 ft/d 

(Bledsoe and others, 1990). Horizontal hydraulic conductivity values from five clay and sandy clay samples range from 

4.7 × 10–5 ft/d to 4.1 × 10–3 ft/d and average 3.5 × 10–4 ft/d. 

During a 7-day aquifer test (pumped at a rate of 2,200 gal/min) 

of the McQueen Branch aquifer at Cope, in Orangeburg 

County, water-level declines in the overlying Crouch Branch 

aquifer were negligible, indicating good separation in the area. 

The confining unit supports a static head difference of about 

40 ft in Allendale County (ALL-348). Potentiometric maps of 

the McQueen Branch and Crouch Branch aquifers in Florence County (1992) show a head difference of 180 ft at the 

center of a cone of depression in the McQueen Branch aquifer 

(Rodriguez and others, 1994).

Geophysical-Log Signature

Low resistivity values on the long-normal electric log 

and high radiation values on the gamma-ray log typically 

are recorded throughout the McQueen Branch confining unit 

owing to its high clay content (Plate 1). At the Orangeburg 

corehole (ORG-393), the resistivity averages only 5 ohm-m 

through the confining unit. Gamma-ray spikes commonly 

mark lag beds in the confining unit. At Orangeburg (fig. B1), 

a spike at 557 ft marks a lag bed at the base of the upper 

Donoho Creek unit (Plate 7) that consists of coarse-grained 

calcareous sand with phosphate, clay clasts, bivalve fragments, 

shark teeth, and rare pieces of bone. Hard, calcite-cemented 

beds in the Bladen Formation are commonly marked by spikes 

on the single-point resistance log. 

Midville Aquifer System

The Midville aquifer system overlies the Appleton 

confining system and underlies the Allendale confining 

system (fig. B38). The aquifer system is present over most of 

the Coastal Plain, although it coalesces with the Dublin and 

Floridan systems in updip regions (Aadland and others, 1995). 

The system is correlated with the lower part of the Chattahoochee River aquifer of Miller and Renken (1988) (fig. B39). 

Clarke and others (1985) defined the system at type well 

28X1, near the town of Midville, GA (fig. B1). In SC, sediments at reference-well P-24 at the SRS in Barnwell County 

are characteristic of the aquifer system (Aadland and others, 

1995). At this well, the Midville is 271 ft thick and consists of 

unconsolidated medium to very coarse sand of the Middendorf 

Formation (Late Cretaceous) and fine-grained clayey sand of 

the lower part of the Black Creek Group (Campanian). At the 

SRS, the system consists of a single aquifer—the McQueen 

Branch aquifer (fig. B38) (Aadland and others, 1995). In the 

downdip region of the Coastal Plain, this study has defined 

a system consisting of the McQueen Branch aquifer and 

the informally named “Charleston aquifer” and “Charleston 

confining unit” (fig. B4). The Charleston and McQueen Branch 

aquifers are hydraulically connected in the middle part of the 

Coastal Plain, but in the lower part, the Charleston underlies 

the McQueen Branch and is separated from it by thick clay 

beds that form the Charleston confining unit (Plates 1, 2,

and 7). The Charleston aquifer and confining unit are named 

after Charleston County where the aquifer is a major source of 

drinking water. 
128 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

McQueen Branch Aquifer

The McQueen Branch aquifer (model layer 11, Chapter C) overlies the Gramling confining unit in the inner Coastal 

Plain and the Charleston confining unit in the outer Coastal 

Plain, and is overlain throughout much of the SC ACP by the 

McQueen Branch confining unit (fig. B38; Plates 1, 2, and 7). 

The aquifer is present over most of the Coastal Plain, but is fine 

grained in Beaufort, Colleton, and Jasper Counties and may not 

yield sufficient water in those counties to be considered a productive aquifer. The McQueen Branch aquifer reaches a maximum thickness of about 350 ft in Barnwell County (fig. B26). 

The aquifer dips to the south-southeast about 25 ft/mi in the 

western part of the SC ACP and 8 ft/mi in the eastern part 

(fig. B25; Plates 1 and 2; Appendix B1). The McQueen Branch 

aquifer in SC is equivalent in stratigraphic position to the 

Black Creek aquifer in NC (fig. B4). The units are continuous 

and hydraulically connected between the two States.

Age and Stratigraphic Correlation

In updip regions of the SC ACP, the McQueen Branch 

aquifer consists of all or parts of three formations that, in 

ascending order, are the upper part of the Cape Fear (late 

Turonian to Coniacian), the Cane Acre (middle Campanian), and 

the lower part of the Coachman (middle Campanian) (fig. B4; 

Plates 1, 2, and 7). In updip areas, the aquifer primarily consists 

of the Cane Acre Formation. In the eastern part of the Coastal 

Plain, the aquifer can also include strata of the upper part of the 

Shepherd Grove Formation (late Santonian to early Campanian) 

and the Caddin Formation (early Campanian) (Plate 2).

The McQueen Branch aquifer is correlated with the 

McQueen Branch aquifer mapped in west-central SC by Aadland and others (1995) (fig. B38), with the Middendorf aquifer of 

Aucott and others (1987) in updip regions, and with the Middendorf aquifer system of Colquhoun and others (1983) (fig. B39).

Lithology and Texture

The McQueen Branch aquifer is characterized by unconsolidated, poorly sorted, fine- to coarse-grained sand and 

clayey sand with local gravel (Plates 1, 2, and 7). The sand 

fraction consists of quartz with sparse carbonaceous material, 

mica, feldspar, and monazite. The amount of interstitial clay of 

39 sand samples from the P-well series at the SRS ranges from 

5 to 30 percent. Most of the clay matrix consists of kaolinite 

with minor to trace amounts of illite and smectite (Strom and 

Kaback, 1992). Gravel, feldspar, and interstitial clay are more 

abundant in the lower section of the aquifer (Cape Fear Formation). Clay and sandy clay beds as thick as 20 ft are present, especially towards the top of the aquifer in updip areas. 

Particle-size analyses of 285 samples of the aquifer from the 

SRS and surrounding areas indicate 4 percent gravel, 86 percent sand, and 10 percent mud (Aadland and others, 1995). 

Grain size of the samples averages 1.3 Φ (medium sand) and 

most, about 75 percent, are poorly sorted. (See Appendix B2

for a detailed lithologic description of the McQueen Branch 

aquifer at the Orangeburg corehole.)

McQueen Branch aquifer sediments are fine grained, glauconitic, and slightly calcareous in the southern and eastern parts 

of the Coastal Plain. The Cane Acre Formation, which consists 

of medium-grained quartz sand in Allendale County, transitions 

to marl downdip in Jasper County (Plate 1). Permeable sediments of the aquifer generally are absent downdip in Jasper and 

Beaufort Counties and in the east in Colleton County. As such, 

the McQueen Branch aquifer is pinched out in these areas. 

Hydrologic Properties

The McQueen Branch aquifer is one of the most productive aquifers in the Coastal Plain of SC, especially in the 

west-central and updip parts of the SC ACP where it is thick 

and consists of unconsolidated coarse-grained sand. Generally, 

the aquifer thins to the east and south where it is less permeable. Results from a 7-day aquifer test made at Cope (fig. B1) 

in western Orangeburg County indicate a transmissivity of 

27,000 ft2/d (Newcome, 2005). Horizontal hydraulic conductivity is 140 ft/d, and the storage coefficient is 2.7 × 10–4. 

Transmissivity values of eight aquifer tests in the central part 

of the SRS (southern Aiken County) range from 14,000 to 

50,000 ft2/d and average about 29,000 ft2/d (Aadland and others, 1995). To the east, results from 27 aquifer tests indicate 

that transmissivity values range from 300 to 9,100 ft2/d and 

average 3,800 ft2/d (median of 2,500 ft2/d). These tests are 

from Darlington, Dillon, Florence, Marion, and Marlboro 

Counties (Rodriguez and others, 1994). At the coast, in 

Charleston County, where the aquifer is rarely used, transmissivity from a single test is 630 ft2

/d. 

Geophysical-Log Signature

Resistivity values from the McQueen Branch aquifer 

interval on the long-normal log strongly reflect the dissolvedsolids concentrations of groundwater and clay content. In updip 

areas, resistivity values typically exceed 1,000 ohm-m; in the 

central part of the SC ACP, they typically exceed 100 ohm-m; 

and along the coast, values rarely exceed 10 ohm-m (Plates 1,

2, and 7). The upper part of the aquifer commonly contains 

sandy clay and clayey sand beds that are marked by decreases 

in resistivity (see ORG-393 on Plate 7). Natural gamma radiation levels are relatively high in the lower part of the McQueen 

Branch aquifer, which consists of the Cape Fear Formation, 

and relatively low in the Cane Acre section. Gamma spikes are 

noted in the aquifer and are associated with concentrations of 

heavy minerals, mica, feldspar, and monazite.

Charleston Confining Unit

The informally named Charleston confining unit (model 

layer 12, Chapter C) was identified in this study. The confining unit overlies the Charleston aquifer and underlies the 

McQueen Branch aquifer in the middle and lower parts of the 

SC ACP (fig. B37; Plates 1, 2, and 7). Formations composing 

the unit are absent updip, and the confining unit pinches out 

(fig. B37). In these updip areas, the Charleston and McQueen 
South Carolina Coastal Plain Hydrostratigraphy 129

Branch aquifers coalesce and are connected (fig. B37 and 

Plate 1). The confining unit reaches a maximum thickness of 

about 450 ft in Charleston County, dipping to the south-southeast about 18 ft/mi in the western part of the Coastal Plain, 

and 8 ft/mi in the eastern part (figs. B27 and B28; Plates 1, 2,

and 7; Appendix B1). The Charleston confining unit in SC is 

equivalent in stratigraphic position to the Upper Cape Fear 

confining unit in NC. The units are continuous and hydraulically connected between the two States.

Age and Stratigraphic Correlation

The Charleston confining unit consists primarily of the 

Late Cretaceous Shepherd Grove (late Santonian to early 

Campanian) and Caddin (early Campanian) Formations 

(fig. B4; Plates 1, 2, and 7). On the eastern side of the SC 

ACP, the Caddin Formation is permeable, and the Charleston 

confining unit consists of the upper part of the Pleasant Creek 

Formation (Santonian) and the Shepherd Grove Formation 

(fig. B4). Generally, the confining unit is correlated with the 

unnamed confining unit that overlies the Middendorf aquifer 

of Aucott and others (1987) in downdip regions (fig. B39).

Lithology and Texture

The Shepherd Grove Formation forms most of the 

Charleston confining unit and consists of noncalcareous to 

slightly calcareous clay, silty clay, clayey silt, and clayey fine 

sand. The formation typically is laminated with very fine to 

fine-grained quartz sand. Sparse lignite, pyrite, and mica are 

present, and shell fragments are common in downdip cores. 

The Caddin Formation at the Berkeley corehole (BRK-644, 

Plate 2) consists of indurated calcareous sandy clay with 

sparse shell fragments, lignite, and mica. The matrix has a 

slight conchoidal fracture and is described as “hard and dry.” 

The sand fraction is very fine to fine grained and commonly 

contains glauconite. Tight, calcite-cemented sand beds (less 

than 2 ft) are present in some places throughout the formation. 

In northern Charleston County, the Pleasant Creek Formation (CHN-820) consists of dark greenish-gray, dry and tight 

sandy clay that breaks with a conchoidal fracture. Locally, the 

formation contains beds consisting of up to 30 percent shell 

fragments, and beds of sand and shell up to 3 ft thick that are 

cemented with calcium carbonate. 

Hydrologic Properties

No hydrologic data are available for the Charleston confining unit. On the basis of its lithology, it is expected that the 

unit is an effective confining unit. Core samples that appeared 

to be dry were recovered from the Charleston confining unit 

interval at CHN-820, implying that little water is moving 

through the unit.

Geophysical-Log Signature

Resistivity values on the long-normal electric log are 

generally less than 10 ohm-m, reflecting the high clay content 

in the Charleston confining unit. Resistivity remains very low, 

even in those cores described as being “dry.” Hard, cemented 

zones are noted on the single-point electric log as highresistance spikes. Natural gamma radiation is consistently high 

and generally flat throughout the confining unit, reflecting the 

high clay content (Plate 2). No radiation spikes are observed 

in the unit. The SP trace is flat and essentially rides the shale 

baseline, indicating low permeability. 

Charleston Aquifer

The informally named Charleston aquifer (model 

layer 13, Chapter C) was defined in this study; it overlies the 

Gramling confining unit and underlies the Charleston confining unit in the middle and outer parts of the SC ACP (fig. B37; 

Plates 1, 2, and 7). In the southernmost counties, sediments 

composing the aquifer are fine grained and may not yield 

sufficient water to wells. At Hilton Head Island (fig. B1), for 

example, production wells bypass the Charleston interval and 

are screened in the deeper Gramling aquifer. In the central 

part of the Coastal Plain, the aquifer thins and coalesces with 

the overlying McQueen Branch aquifer (fig. B37; Plate 1). 

Farther updip, at the SRS (fig. B1), formations that compose 

the Charleston are absent. The aquifer reaches a maximum 

thickness of more than 300 ft in Jasper County (fig. B30). The 

Charleston aquifer dips to the south-southeast about 20 ft/mi 

in the western part of the SC ACP and 15 ft/mi in the eastern 

part (fig. B29; Plates 1 and 2; Appendix B1). The Charleston 

aquifer in SC is equivalent in stratigraphic position to the 

Upper Cape Fear aquifer in NC. The units are continuous and 

hydraulically connected between the two States.

Age and Stratigraphic Correlation

The Charleston aquifer consists primarily of the Late 

Cretaceous Collins Creek Formation (middle to late Coniacian). In places, the aquifer also contains the upper part of the 

Cape Fear Formation (late Turonian to Coniacian) and, in the 

eastern part of the Coastal Plain, the Pleasant Creek Formation 

(Santonian) (fig. B4; Plates 1, 2, and 7). In general, the aquifer 

is correlated with the Middendorf aquifer of Aucott and others 

(1987) in downdip regions and with the Middendorf aquifer 

system of Colquhoun and others (1983) (fig. B39). 

Lithology and Texture

The Charleston aquifer consists of unconsolidated sand, 

clayey sand, and clay. The sand fraction consists of poorly 

sorted, fine- to very coarse-grained quartz with up to 10 percent mica, sparse glauconite, pyrite nodules, and lignite. Shell 

fragments are common in some beds. Calcite-cemented beds 

of sand and shells, up to 2 ft thick, are present in the aquifer. 

Lignitic sand beds, a characteristic lithology of the aquifer, are 

common in the upper part of the aquifer. 
130 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Hydrologic Properties

Charleston aquifer transmissivity values calculated from 

aquifer tests at Mount Holly and Saint Stephens in Berkeley 

County are 3,100 and 4,100 ft2/d, respectively (Newcome, 

2005; fig. B1). The well at Mount Holly has a storage coefficient of 2 × 10–4. Transmissivity values from six tests at Mount 

Pleasant in Charleston County range from 1,500 to 2,400 ft2/d 

and average 1,800 ft2/d (Newcome, 2005).

Geophysical-Log Signature

Within the Charleston aquifer, resistivity values on the 

long-normal log are 30 to 40 ohm-m inland (in northern Berkeley County at corehole BRK-644), and generally less than 

20 ohm-m in coastal counties (Plates 1, 2, and 7). These differences reflect greater mineralization of groundwater in coastal 

counties [greater than 1,000 milligrams per liter (mg/L) of total 

dissolved solids in Charleston County and about 350 mg/L of 

total dissolved solids at Saint Stephen in Berkeley County]. 

In Charleston County, a group of three sand beds separated by 

clay beds forms the Charleston aquifer and is noted on electric 

logs as alternating zones of high and low resistivity (Gohn and 

Campbell, 1992) (see CHN-635 on Plate 7). 

Appleton Confining System/

Gramling Confining Unit

The Appleton is the lowermost confining system of the 

SC ACP. Aadland and others (1995) defined the system at type 

well ALL-348 near the town of Appleton (fig. B1) in Allendale 

County, SC, where it is 237 ft thick and consists of saprolite, 

which is derived from igneous rock, and interbedded sand, 

clayey sand, and clay of the Late Cretaceous Cape Fear Formation. In updip areas, the confining system hydraulically separates SC ACP sediments from underlying basement rocks; in 

downdip areas, the system separates the Ridgeland and Midville aquifer systems. The Appleton confining system underlies 

the entire Coastal Plain, although the unit thins considerably 

to the northwest (Aiken County) where it consists only of 

saprolite. The system is correlated with the Black Warrior 

River confining unit of Miller and Renken (1988) (fig. B39). 

The system contains a single confining unit, informally called 

the “Gramling confining unit,” after Gramling Creek, just east 

of Orangeburg, SC (fig. B1) (Gellici, 2007a).

The Gramling confining unit (model layer 14, Chapter C) 

is the lowermost confining unit in the Coastal Plain. The 

confining unit overlies basement crystalline rocks in the inner 

and middle parts of the SC ACP and the Gramling aquifer in 

the lower part. The unit is overlain by the Charleston aquifer across most of the SC ACP (fig. B37; Plates 1, 2, and 7), 

reaching a maximum thickness of over 300 ft in Florence 

County (fig. B32; Plate 7; Appendix B1). The confining unit 

dips to the south-southeast about 24 ft/mi in the western part 

of the Coastal Plain, and 10 ft/mi in the eastern part (fig. B31; 

Plates 1 and 2; Appendix B1).

Age and Stratigraphic Correlation

The Gramling confining unit consists of saprolite and 

the Late Cretaceous Cape Fear Formation (late Turonian to 

Coniacian) (fig. B4; Plates 1, 2, and 7). The confining unit is 

correlated with the “unnamed” basal confining unit of Aadland 

and others (1995) (fig. 38) and with the lowermost unnamed 

confining unit that overlies the Cape Fear aquifer of Aucott 

and others (1987) (fig. B39). The Gramling confining unit is 

mapped as “crystalline rocks of the Piedmont” in the updip 

area of the SC ACP and as the Middendorf aquifer system by 

Colquhoun and others (1983).

Lithology and Texture

The Gramling confining unit is characterized by unconsolidated to semiconsolidated beds of clay, clayey sand, sand, 

and gravel. The sand fraction consists of poorly sorted, fine- to 

very coarse-grained quartz with minor feldspar and sparse 

mica, lignite, and monazite. Friable coarse-grained feldspar 

grains that are partially weathered to kaolinite are common 

throughout the confining unit. Much of the Gramling confining 

unit is consolidated in varying degree by silica cement. Beds 

were deposited in a series of fining-upward sequences (5 to 

30 ft thick). Interstitial clay can be high due to weathering of 

feldspar to kaolinite, but some sand beds lack clay and silica 

cement and are unconsolidated and permeable. A sidewall core 

(2,300 ft) from the Jasper County corehole (JAS-426, Plate 1) 

contains quartz (42 percent), illite/smectite/mica (23 percent), 

potassium feldspar (18 percent), kaolinite (12 percent), albite 

(3 percent), and plagioclase (2 percent) (Core Laboratories, 

1997). (See Appendix B2 for a detailed lithologic description 

of the Gramling confining unit at the Orangeburg corehole, 

ORG-393.)

Hydrologic Properties

Permeability is generally low, and is controlled principally by post-depositional processes within the Gramling 

confining unit. Primary intergranular porosity is low owing 

to poor sorting and interstitial clay. Porosity and permeability are further reduced by alteration of feldspar to authigenic 

clay, by silica cementation, and by compaction. Silty-clay 

samples from the Allendale corehole (ALL-348) have vertical hydraulic conductivity values that range from 3.8 × 10–3 to 

1.6 × 10–2 ft/d and average 1.1 × 10–2 ft/d (Core Laboratories, 

1992; Gellici and others, 1995).

Beds of permeable unconsolidated sand and gravel are 

present in the Gramling confining unit where little or no porefilling cement or clay is present (Plates 1, 2, and 7). The beds 

typically are thin (<20 ft), are of limited lateral extent, and 

are probably poorly connected with other permeable beds. An 

aquifer test of a well that is reported to be completed in the 

confining unit indicates a transmissivity of 1,200 ft2/d (Rodriguez and others, 1994).
South Carolina Coastal Plain Hydrostratigraphy 131

In downdip areas, where the Gramling confining unit 

overlies the Gramling aquifer, delineating the boundary 

between the confining unit and underlying aquifer can be difficult (see Plate 7). Lithologies of the two units are similar, and 

the contact is indefinite. Some degree of hydraulic connection 

can be expected across the confining unit.

Geophysical-Log Signature

Low resistivity values on the long-normal electric log 

are a characteristic feature of the Gramling confining unit 

(Plates 1, 2, and 7). Even beds of loose sand and little clay 

have values that rarely exceed 20 ohm-m. This response is 

probably caused by mineralized formation water, which is 

the result of long residence times or of dissolution of labile 

framework grains. Interstitial clay in the confining unit also 

causes low resistivity values. Permeable sand beds in the 

confining units are identified as slight deflections to the left on 

the spontaneous-potential log together with slight increases in 

resistance on the single-point electric log. 

Ridgeland Aquifer System/Gramling Aquifer

The Ridgeland aquifer system was defined in this study 

based on the unique hydrogeologic properties of sediments 

penetrated at corehole JAS-426, in Jasper County, SC (fig. B1). 

The aquifer system is named after the town of Ridgeland, SC, 

located about 10 mi west of the corehole. The aquifer system 

overlies crystalline basement rocks and underlies the Appleton 

confining system. Ridgeland is the lowermost aquifer system 

of the SC ACP (fig. B38). A line drawn from northern Jasper 

County to northern Horry County approximates the updip limit 

of the aquifer system. North of this line, the system pinches 

out against crystalline basement rocks. The system thickens 

to more than 1,000 ft at Hilton Head Island (BFT-2055), and 

thins towards the northeast to about 300 ft at Myrtle Beach 

(HOR-973/1165) (fig. 34). The Ridgeland aquifer system 

correlates generally with the Black Warrior River aquifer of 

Miller and Renken (1988) and with the Cape Fear aquifer of 

Aucott and others (1987) (fig. B39). 

The type section of the Ridgeland aquifer system is from 

2,397 to 2,796 ft (399 ft) in the JAS-426 corehole in Jasper 

County, SC (Plate 1), and includes the Late Cretaceous Beech 

Hill and Clubhouse Formations and the lower part of the 

Cape Fear Formation (fig. B4). The Ridgeland aquifer system 

consists of interbedded silty clay, sandy silty clay, and silty 

clayey sand, with minor gravel and feldspar. Median grain 

size of 22 sidewall core samples ranges from 6 to 2 Φ (silt to 

medium-grained sand) and averages 3.25 Φ (very fine-grained 

sand) (Core Laboratories, 1997). Gravel, sand, silt, and clay 

average 1, 50, 42, and 7 percent, respectively. Empiricallyderived hydraulic conductivity of these same samples ranges 

from less than 0.5 to 2 ft/d and averages about 1 ft/d (Core 

Laboratories, 1997). 

Interbedded sand and clay characterize the Ridgeland 

aquifer system. Thick sand units are generally absent. As a 

result, delineating the boundaries of specific aquifers and 

confining units can be difficult. In addition, few wells fully 

penetrate the system, and hydrologic data are sparse. As such, 

the vertical and lateral hydraulic continuity of the system are 

unknown. More than one aquifer may be present. For the purposes of this report, however, the entire system is informally 

referred to as the “Gramling aquifer,” named after the overlying confining unit. 

The Gramling aquifer (model layer 15, Chapter C) 

constitutes the entire Ridgeland aquifer system, and is present 

primarily in the southern part of the SC ACP (fig. B33). The 

aquifer overlies basement rocks and underlies the Gramling 

confining unit (fig. B37; Plates 1–5). The Gramling aquifer 

reaches a maximum thickness of more than 1,000 ft in Beaufort County, dipping to the south about 19 ft/mi in the western part of the Coastal Plain, and 14 ft/mi in the eastern part 

(figs. B33 and B34; Plates 1 and 3; Appendix B1).

Age and Stratigraphic Correlation

The Gramling aquifer is present at the base of the SC 

ACP sequence and includes the Late Cretaceous Beech Hill 

(Cenomanian) and Clubhouse Formations (late Cenomanian(?) to early Turonian) and the lower part of the Cape Fear 

Formation (late Turonian to Coniacian) (fig. B4; Plates 1–5). 

The aquifer is generally correlated with the Cape Fear aquifer 

of Aucott and others (1987) and with the Middendorf aquifer 

system of Colquhoun and others (1983) (fig. B39). 

Lithology and Texture

The Gramling aquifer is characterized by unconsolidated 

to semiconsolidated interbedded and laminated sand, clayey 

sand, silt, and clay. The sand fraction consists mainly of quartz 

but can contain moderate amounts of feldspar, particularly in 

the Beech Hill and Cape Fear Formations. Minor to sparse 

mica and lignite are present. Calcareous sediments are common in the Clubhouse Formation. Grain size is predominantly 

fine with minor coarse sand and gravel. Coarser sand is more 

common in the Beech Hill and Cape Fear Formations. Silicacemented beds in the Cape Fear Formation are common and 

reduce permeability of the aquifer. A sidewall core (2,440 ft) 

from the Jasper County corehole (JAS-426, Plate 1) within the 

Gramling aquifer contains quartz (61 percent), potassium feldspar (15 percent), illite/smectite/mica (12 percent), kaolinite 

(10 percent), and albite (2 percent) (Core Laboratories, 1997).

Hydrologic Properties

Few hydrologic data are available for the Gramling 

aquifer. Currently (2008), the Gramling aquifer is used only 

at Hilton Head and Fripp Islands in Beaufort County and may 

be partially screened in a supply well at Kiawah Island in 

Charleston County (fig. B1). Gramling aquifer transmissivity, 
132 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

calculated from an aquifer test of the well at Fripp Island, is 

200 ft2/d (Newcome, 2005). In a supply well at Hilton Head 

Island (BFT-2055), 18 well screens were emplaced through 

the interval from 2,782 to 3,840 ft. The screens range in length 

from 8 to 18 ft and tap thin sand beds that compose the Gramling aquifer. Transmissivity calculated from an aquifer test of 

BFT-2055 is 1,200 ft2/d (Newcome, 2005).

Geophysical-Log Signature

Low resistivity on the long-normal electric log 

(<20 ohm-m) and high radiation on the gamma-ray log characterize the Gramling aquifer. Spontaneous-potential (SP) logs 

are flat and smooth where clayey sediments predominate, and 

they have slight negative deflections adjacent to thin, permeable sand beds (Plate 7). Water in the aquifer is slightly brackish, causing the low resistivity and negative SP response. A 

fine-grained lithology and high interstitial-clay content cause 

elevated radiation levels on the gamma-ray log. Gamma-ray 

spikes are noted in the aquifer in some wells, indicating lag 

beds of glauconite and phosphate, concentrations of heavy 

minerals, or radioactive minerals such as monazite.

Discussion 

Several important differences exist between the framework developed in this study and that of Aucott and others 

(1987) (fig. B39). These differences include the following: 

1. The Middendorf aquifer mapped in updip regions by 

Aucott is comparable to the McQueen Branch aquifer 

mapped in updip areas of this report. Fossil data, however, 

indicate that strata traditionally mapped as the Middendorf aquifer in downdip areas (Santonian) are older than 

strata mapped as the Middendorf aquifer in updip areas 

(Campanian). In this report, the older strata are mapped as 

the Charleston aquifer, and the younger strata are mapped 

as the McQueen Branch aquifer.

2. The Tertiary sand aquifer of Aucott is divided into the 

Gordon, Middle Floridan, and Upper Floridan aquifers 

and confining units for this report.

3. The Floridan aquifer system of Aucott is divided into the 

Middle and Upper Floridan aquifers and associated confining units for this report.

4. The Floridan aquifer system is extended down-section to 

include late Paleocene strata of the Gordon aquifer and 

laterally to include clastic sediments in updip regions for 

this report.

5. Confining units are named after the aquifer that they confine for this report.

Most of the McQueen Branch aquifer consists of the 

Cane Acre Formation (middle Campanian), which was previously mapped as the Middendorf Formation (Colquhoun 

and others, 1983; Fallaw and Price, 1995). Hazel and others 

(1977) originally assigned an early late Austinian age to the 

Middendorf, indicating a Santonian or early Campanian age. 

Gohn (1992), citing several supporting paleontological studies 

(Christopher, 1982; Valentine, 1984; Sohl and Owens, 1991), 

assigned strata of Santonian age to the Middendorf Formation at the USGS-Clubhouse Crossroads #1 corehole. Recent 

studies of cores and outcrops (Prowell and others, 2003) and 

paleontological data collected from the ORG-393 corehole 

and other updip coreholes indicate that much of these updip 

strata that were mapped as the Middendorf Formation are not 

Santonian but, instead, are Campanian (calcareous nannofossil 

zone CC 18–19). In this report, therefore, the name Cane Acre 

Formation is used in place of the Middendorf Formation.

The hydrogeologic framework developed for this study 

relies heavily on paleontological data to make delineations and 

correlations of the hydrostratigraphic units. Hydraulic-head 

data, available from well-cluster sites or from wireline formation tests, would be useful to verify vertical hydraulic continuity of the aquifers and to determine if head differences exist 

across confining units. Currently, these data are lacking in the 

eastern Coastal Plain, where cluster sites are scarce and hydrostratigraphic units are not well defined owing to the lithologic 

complexity of the SC ACP in these areas. Generally, statichead differences between adjacent aquifers in SC are small. 

Aquifers, therefore, are not clearly distinguished by groundwater levels that are obtained from wells spaced several miles 

apart. Well-cluster sites would help to resolve the relatively 

small static-head differences observed between aquifers.

Parts of the inner Coastal Plain are deeply incised by 

streams, which can break the lateral hydraulic continuity of 

aquifers. Groundwater in these areas discharges along the 

flanks of valley walls and into surrounding streams, creating 

hydraulically isolated “islands” of groundwater. As such, the 

lateral continuity of aquifers in these updip areas is obscure. 

Water levels measured for the same aquifer but on different 

ridges may have no relation to one other because the aquifer 

is not hydraulically connected across the valley. Although 

aquifers in this report were mapped well into the inner Coastal 

Plain, the hydraulic continuity of the aquifers in this region 

is uncertain.

Correlation of Hydrostratigraphic Units 

Across the North Carolina–

South Carolina Border

In order to determine the continuity of hydrostratigraphic 

units across the border between NC and SC, two cross sections 

were constructed from southwest to northeast along approximate structural strike using four wells. Figure B40 includes 

data from USGS corehole DIL-121 and the NC DWR Marietta 

(BB 45M) monitoring station. Figure B41 includes data from 

a cored well from Myrtle Beach, SC (HOR-973-1165), and the 

NC DWR Calabash (HOR-388/HH 39J) monitoring station. 
South Carolina Coastal Plain Hydrostratigraphy 133Figure B40. Hydrostratigraphic correlation cross section from DIL-121, Little 

Peedee State Park, Dillion County, SC, to BB 45M, Marietta, Robeson County, NC.

Crouch Branch confining unit/SC Peedee confining unit/NC

Crouch Branch aquifer/SC

Peedee aquifer/NC

McQueen Branch aquifer/SC

Black Creek aquifer/NC

Charleston aquifer/SC

Upper Cape Fear aquifer/NC

1

2

3

4

5

Figure B40. Hydrostratigraphic correlation cross section from DIL-121, Little Peedee State Park, Dillion County, SC, to 

BB 45M

Marietta

Robeson County

NC

Altitude

Altitude

WELL NUMBERNAMEDEPTH (FT)ALTITUDE (FT)

: DIL–121: Little Peedee State Park: 646.8: 90.0

WELL NUMBERNAMEDEPTH (FT)ALTITUDE (FT)

: BB–45M: Marietta: 600.0: 94.0

McQueen Branch confining unit/SC Black Creek confining unit/NC

Charleston confining unit/SC Upper Cape Fear confining unit/NC

Gramling confining unit/SC Lower Cape Fear confining unit/NC

Well screen

Water level Aquifer

Well screen

Water level Aquifer

surficial

Crouch

Branch

McQueen

Branch

CU

McQueen

Branch

Gramling

confining

unit

Chareleston CU

Charleston

surficial

Peedee

CU

Peedee

Black Creek

CU

Black

Creek

Upper

Cape

Fear

CU

Upper

Cape

Fear

Basement

Bedrock
134 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure B41. Hydrostratigraphic correlation cross section from HOR-973-1165, Myrtle 

Beach, Horry County, SC, to HOR-388/HH 39J, Calabash, Brunswick County, NC.

Crouch Branch confining unit/SC

Peedee confining unit/NC

1

13.4

3.8

42.7

105.5

3

4

5

6

Figure B41. Hydrostratigraphic correlation cross section from HOR-973-1165, Myrtle 

BeachHorry CountySCto HOR388/HH 39JCalabashBrunswick CountyNC

WELL NUMBER

NAME

DEPTH (FT)

ALTITUDE (FT)

: HOR–973–1165

: Myrtle Beach

: 1,427.00

: 23.00Altitude (Ft)

Well screen

Water level

Depth (Ft)

Resistance

(Ohms) Long normal

(Ohms-M)

Short normal

(Ohms-M)

Aquifer

surficial

Crouch

Branch

Well screen

Water level Aquifer

surficial

Peedee

CU

Black Cr.

CU

Upper

Cape

Fear CU

Lower

Cape

Fear CU

Lower

Cape

Fear

Basement

Upper

Cape

Fear 

Black Cr.

Peedee

McQueen

Br. CU

Charleston

CU

Gramling

CU

Gramling

Bedrock Charleston

McQueen

Branch

100

–100

–200

–300

–400

–500

–600

–700

–800

–900

–1,000

–1,100

–1,200

–1,300

200

300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,400

1,427

0

0

100

200

300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,350

–100

–200

–300

–400

–500

–600

–700

–800

–900

–1,000

–1,100

–1,200

0

0

0 0

–20–40–601050

Gamma ray

(CPS)

SP

(MVOL)

0200

–115–65

100

Gamma ray

(CPS)

SP

(MVOL)

01

70150

120

Altitude (Ft)

Depth (Ft)

Long normal

(Ohms-M)

Short normal

(Ohms-M) –20 –10 1030507090 140

Gramling aquifer/SC

Lower Cape Fear aquifer/NC

McQueen Branch aquifer/SC

Black Creek aquifer/NC

Charleston aquifer/SC

Upper Cape Fear aquifer/NC

McQueen Branch confining unit/SC

Black Creek confining unit/NC

Charleston confining unit/SC

Upper Cape Fear confining unit/NC

Gramling confining unit/SC Lower Cape Fear confining unit/NC

WELL NUMBER

NAME

DEPTH (FT)

ALTITUDE (FT)

: HOR–300 HH 39J

: Calabash

: 1,350.00

: 48.00

Crouch Branch

aquifer/SC

Peedee

aquifer/NC
Correlation of Hydrostratigraphic Units Across the North Carolina–South Carolina Border 135

Correlations across the NC–SC border were limited by 

disparate strengths and weaknesses among the data available 

in each State. The NC Division of Water Resources maintains 

an extensive network of groundwater monitoring stations in 

the NC Coastal Plain; well nests screened in each of the major 

aquifers make it possible to delineate aquifer boundaries by 

determining where substantial differences in hydraulic head 

occur, or by the comparison of long-term water-level variations at various screen depths. South Carolina does not have 

the advantage of a network of nested groundwater level observation well stations. The subsurface stratigraphic framework 

of NC is not as clearly understood as in SC, where the USGS 

Coastal Carolina project has been completed and regional 

interpretations have been made. The mapping of hydrogeologic units in SC, then must rely almost exclusively on 

stratigraphic correlation from a corehole network rather than a 

monitoring station network. 

The hydrostratigraphic correlations of the ACP sediments at the 

NC–SC border determined by this 

study are illustrated in figures B40

and B41. At the updip location 

(fig. B40), between Marietta, NC, 

and Little Peedee State Park, the 

surficial aquifer is present at both 

locations. Underlying the surficial 

aquifer is the Peedee/Crouch Branch 

aquifer in SC and the Peedee/Crouch 

Branch confining unit in NC. The 

Peedee/Crouch Branch confining 

unit is not present in SC. The Black 

Creek/McQueen Branch confining 

unit along with the Black Creek/

McQueen Branch aquifer are present 

in both locations. The Upper Cape 

Fear/Charleston aquifer and confining unit are present at both locations, 

but the correlations are questionable 

due to the relative thinness of the 

units in SC. The Upper Cape Fear 

aquifer is the lowermost unit present 

at the Marietta location, whereas the 

Gramling confining unit is the lowermost ACP unit present in SC.

At the downdip location 

(fig. B41) along the NC–SC coast, 

the ACP hydrostratigraphy is correlated between Myrtle Beach, SC, and 

Calabash, NC. The surficial aquifer 

is present at both locations and is 

underlain by the Crouch Branch 

aquifer in SC and the Peedee confining unit in NC. The Crouch Branch 

confining unit is not present at the 

Myrtle Beach location. The Peedee 

aquifer underlies the Crouch Branch 

Figure B42. Continuous groundwater altitudes from the A, Marietta, North Carolina, 

monitoring station, Robeson County, North Carolina, and B, Calabash, North Carolina, 

monitoring station, Brunswick County, North Carolina.

A

B

100

80

60

40

20

0

–20

120

100

80

60

40

20

0

–20

–40

–60

1970 1975 1980 1985 1990 1995 2000 2005 2010

1970 1975 1980 1985 1990 1995 2000 2005 2010

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD 29

Surficial aquifer

Peedee aquifer

Black Creek aquifer 194 feet

Black Creek aquifer 363 feet

Black Creek aquifer 516 feet

Upper Cape Fear aquifer

Surficial aquifer

Peedee aquifer

Black Creek aquifer 516 feet

Black Creek aquifer 660 feet

Upper Cape Fear aquifer 516 feet

Lower Cape Fear aquifer

Figure B42. Continuous groundwater altitudes from the (A) Marietta, North Carolina, monitoring

 station, Robeson County, North Carolina, and (B) Calabash, North Carolina monitoring station,

 Brunswick County.

confining unit at Calabash. The Black Creek/McQueen Branch 

aquifer and confining unit underlie the Peedee aquifer at both 

locations. Below these units are the Upper Cape Fear/Charleston aquifer and confining unit. The lowermost units present are 

the Lower Cape Fear/Gramling aquifer and confining unit. 

Continuous groundwater levels collected at the Marietta 

and Calabash, NC, stations have been collected since the early 

1970s (fig. B42; Plates 5, 6, and 7). At the Marietta station, 

groundwater levels are collected within the four aquifers that 

underlie the site: the surficial aquifer, the Peedee aquifer, the 

Black Creek aquifer (three locations within the aquifer), and 

the Upper Cape Fear aquifer. Overall groundwater levels at 

the Marietta station have been declining over the period of 

record most likely because of withdrawals from the City of 

Florence, SC (fig. B1). The overall vertical groundwater gradient at the Marietta station is downward, indicating an area of 
136 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

groundwater recharge. Groundwater levels within the 516-ft 

level of the Black Creek aquifer have declined the most at the 

Marietta station in response to withdrawals from the Black 

Creek/McQueen Branch aquifers in Dillon, Florence, and 

Marlboro Counties in SC and in Robeson and Bladen Counties 

in NC (fig. B1). No comparable continuous groundwater levels 

were collected from the DIL-121 site in SC.

At the Calabash, NC, station, groundwater levels are 

collected within the five aquifers that underlie the site: the surficial, Peedee, Black Creek (two locations within the aquifer), 

Upper Cape Fear, and Lower Cape Fear aquifers. Groundwater 

levels in the Peedee and Black Creek aquifers at the Calabash 

station declined from the early 1970s until the early 1990s 

in response to withdrawals in Horry County, SC, and Brunswick County, NC. In about 1992, Myrtle Beach, SC (fig. B1) 

switched from a groundwater source to a surface-water source 

for raw potable water. From the early 1990s until the present 

(2008), groundwater levels in the Peedee and Black Creek 

aquifers have stabilized. The overall vertical groundwater 

gradient at the Calabash station is upward, indicating an area 

of groundwater discharge. No comparable continuous groundwater levels were collected from the HOR-973/1165 site in SC.

Overall, at the coastal site, hydrostratigraphic units 

correlate well in the coastal area along the NC–SC State line 

because most of the units are present (fig. B41). Correlations 

further updip, between Dillon County, SC, and Robeson 

County, NC, are more problematic, and will need further work.

Summary

The North Carolina (NC) and South Carolina (SC) segment of the Atlantic Coastal Plain (ACP) consists of approximately 45,000 square miles and extends from the Fall Line 

to offshore under the present-day Atlantic Ocean. The hydrogeologic frameworks of the North and South Carolina Coastal 

Plain have evolved separately over the past 100 years, but 

are both described in this report. The hydrostratigraphic units 

present at the NC–SC border are correlated.

The hydrogeologic framework of the NC Coastal Plain 

aquifers and confining units consists of nine aquifers separated 

by eight confining units. From top to bottom, the aquifers are 

the surficial aquifer, Yorktown aquifer, Castle Hayne aquifer, 

Beaufort aquifer, Peedee aquifer, Black Creek aquifer, Upper 

Cape Fear aquifer, Lower Cape Fear aquifer, and Lower Cretaceous aquifer. The uppermost aquifer, the surficial aquifer in 

most places, is a water-table aquifer; the bottom of the system 

is underlain by various types of crystalline bedrock. The 

sedimentary deposits forming the aquifers are of Holocene to 

Cretaceous age and are composed mostly of sand, with lesser 

amounts of gravel and limestone. The confining units between 

the aquifers are composed primarily of clay and silt. The total 

thickness of the aquifers and confining units ranges from zero, 

along the Fall Line, to more than 5,000 feet (ft) in easternmost 

NC. Prominent structural features are the increasing easterly 

dip of the sediments along with the Cape Fear Arch, the axis 

of which trends in a southeast direction. The hydrostratigraphy 

was primarily determined from correlations of geophysical 

logs and drill cutting descriptions from 145 wells distributed 

across the NC Coastal Plain. Aquifers and confining units were 

defined by using the geophysical logs and drill cuttings, as 

well as water-level and water-quality data and evidence of the 

continuity of pumping effects. Structure contour and thickness 

maps delineate the aquifers and confining units. Hydrogeologic sections depict the correlation of these aquifers throughout the NC Coastal Plain.

The thickness of the surficial aquifer in NC ranges from 

less than 10 ft in the central, northern, and southern parts of 

the NC Coastal Plain to more than 100 ft in parts of the Sandhills and coastal areas. The surficial aquifer is primarily composed of permeable sediments of Quaternary age, but it also 

contains older sediments in various places due to the varying 

stratigraphic position of the first confining layer. Included are 

the overlying soils, which vary in infiltration capacity across 

the region, thus affecting the rates at which recharge occurs. 

The Yorktown aquifer is present only in the northern half 

of the NC Coastal Plain and is bounded to the west by the Fall 

Line. Although outliers of the Yorktown Formation are present 

in Robeson, Bladen, Columbus, and Duplin Counties, they 

are not separated from the surficial aquifer by a recognizable 

confining unit, and therefore are not considered to be a distinct 

aquifer in these areas. The Yorktown aquifer is absent over the 

entire southern part of the Coastal Plain. The Yorktown aquifer 

ranges in observed altitudes from –100 ft in Dare County to 

100 ft in Greene County. The aquifer thickens eastward from 

where it directly overlies basement rock at the Fall Line to a 

maximum of 300 ft in easternmost NC. Reported transmissivities for the Yorktown aquifer in the northeastern NC Coastal 

Plain ranged from 1.0 to 2,350 square feet per day (ft2/d), and 

horizontal hydraulic conductivities ranged from 0.2 to 98 feet 

per day (ft/d), based on five aquifer tests. The Yorktown 

confining unit can be described as a series of clay and silt 

beds that do not compose a single unit because the beds vary 

substantially in stratigraphic position. The top of the Yorktown 

confining unit ranges in altitude from less than –100 ft to over 

100 ft. The thickness of the confining unit ranges from less 

than 10 to more than 50 ft in the NC Coastal Plain.

The Castle Hayne aquifer typically is a sandy, molluscanmold limestone and a bryozoan-echinoid skeletal limestone 

and is the highest yielding aquifer in the NC Coastal Plain. 

Aquifer transmissivity exceeds 35,000 ft2/d, and aquifer yields 

can be up to 1,000 gallons per minute (gal/min). The Castle 

Hayne aquifer is roughly equivalent to the Middle Floridan 

aquifer in SC, although the two are not contiguous or hydraulically connected. The Castle Hayne aquifer thickens from west 

to east, to a maximum of 530 ft, and becomes more deeply 

buried toward the east. The top of the Castle Hayne aquifer 

ranges in observed altitudes from over –600 ft in the easternmost parts of NC to 65 ft in Lenoir County. The Castle Hayne 

aquifer is recharged by water that leaks through its confining 

layer from the overlying Yorktown and surficial aquifers. The 
Summary 137

Castle Hayne confining unit consists of clay and silt beds that 

vary in stratigraphic position between the upper part of the 

Castle Hayne Formation and younger units of variable age, 

which overlie this formation across the Coastal Plain. The 

top of the Castle Hayne confining unit ranges in altitude from 

–600 to over 75 ft, while the thickness ranges from less than 

1 to more than 200 ft on the Currituck County outer banks. 

The Beaufort aquifer extends through the eastern section of the northern half of the NC Coastal Plain and is made 

up primarily of glauconitic, fossiliferous, clayey sands and 

intermittent thin limestone beds of the Paleocene Beaufort 

Formation. An average transmissivity of 1,600 ft2/d in Chowan 

County, based on the average of 22 aquifer-test calculations, 

is reported. The top of the Beaufort aquifer ranges in observed 

altitude from over –1,300 ft in the Outer Banks to 27 ft in 

Lenoir County. The maximum observed thickness of the 

aquifer is 132 ft in Dare County. In SC there is no Beaufort 

aquifer equivalent because the Beaufort Formation is primarily 

composed of clay or silt and is considered to be a part of the 

Crouch Branch confining unit. The Beaufort confining unit is 

composed of clays and silts in the upper part of the Beaufort 

Formation and the lower part of the Castle Hayne Formation. 

The top altitudes of the Beaufort confining unit range from 

27 ft in Lenoir County to as much as –1,000 ft in the northeastern part of the NC Coastal Plain. The thickness of the 

Beaufort confining unit ranges between zero, in areas where 

it is eroded or pinches out, to a maximum of about 300 ft in 

northeastern NC. 

The Peedee aquifer is present over most of the eastern 

NC Coastal Plain except for the northeastern counties. The 

Peedee aquifer is composed principally of the Late Cretaceous 

Peedee Formation. Reported transmissivity values for the 

Peedee aquifer range from 240 to 1,170 ft2/d for the central 

part of the NC Coastal Plain. In the southern part of the NC 

Coastal Plain, the values are reported to range from 40 to 

340 ft2/d for the Peedee aquifer. The maximum thickness of 

the Peedee aquifer is 300 ft in Brunswick County. The top 

ranges in altitude between 88 ft in Lenoir County to –800 ft in 

Carteret County. In SC, the Peedee aquifer is equivalent to the 

Crouch Branch aquifer. Sediments of equivalent age are also 

referred to as the Peedee aquifer in Virginia.

The Peedee confining unit is composed of beds of clay 

and silt with varying amounts of sand that are positioned 

stratigraphically near the contact of the Paleocene Beaufort 

and Late Cretaceous Peedee Formations in the eastern NC 

Coastal Plain. The thickness of the Peedee confining unit varies between 0 ft to a maximum of 121 ft in Craven County. 

The top of the Peedee confining unit varies from about 0 ft in 

the southeastern part of the NC Coastal Plain to over –800 ft 

in the eastern Coastal Plain. 

The Black Creek aquifer is made up primarily of the 

Late Cretaceous Black Creek Formation, but also includes 

permeable beds from older and younger formations in the 

NC Coastal Plain and, in localized areas, sands in the lower 

part of the Peedee Formation. Reported transmissivities 

from 15 aquifer tests in the Black Creek aquifer range from 

290 to 1,700 ft2/d. The Black Creek aquifer pinches out along 

the Fall Line at the updip limit of the sediments. The Black 

Creek aquifer reaches a minimum thickness of less than 10 ft 

along the updip limit and a maximum thickness of 442 ft in 

Onslow County. The altitude of the top of the Black Creek 

aquifer ranges from 317 ft in Richmond County to –1,207 ft in 

Craven County. The Black Creek aquifer is equivalent to the 

McQueen Branch aquifer and confining unit in SC. The Black 

Creek confining unit separates the Peedee aquifer from the 

Black Creek aquifer. The Black Creek confining unit ranges 

in thickness from less than 10 ft along the updip limit to more 

than 400 ft in southeastern NC. The top of the Black Creek 

confining unit ranges in altitude from a low of –800 ft to a 

high of over 200 ft.

The Upper Cape Fear aquifer is made up primarily of 

the upper part of the Cape Fear Formation of Late Cretaceous 

age. Reported transmissivities from three aquifer tests in the 

Upper Cape Fear aquifer range from 25 to 920 ft2/d in the NC 

Central Coastal Plain. The top of the Upper Cape Fear aquifer 

ranges in observed altitudes from –1,400 ft in Dare County to 

200 ft in Moore County, near the Fall Line. The Upper Cape 

Fear aquifer ranges in thickness from 665 ft in northeastern 

NC to less than 10 ft along the updip limit of the aquifer. 

The Charleston and Upper Cape Fear aquifers are connected 

hydraulically as evidenced by water-level declines in Columbus and Robeson Counties, NC, that are due to pumping from 

the Charleston aquifer in SC. The Upper Cape Fear confining unit consists of beds of clay, silt, and variable but lesser 

amounts of sand that are in the upper part of the Cape Fear 

Formation and in the lower part of the Black Creek Formation 

in some places. The altitude of the top of the Upper Cape Fear 

confining unit ranges from –200 ft along the updip limit to 

about –1,200 ft in southeastern NC. The thickness of the Cape 

Fear confining unit ranges from about 50 ft over most of the 

NC Coastal Plain to about 500 ft in southern Virginia. 

The Lower Cape Fear aquifer is composed primarily of 

the lower part of the Cape Fear Formation of Upper Cretaceous age. The top of the Lower Cape Fear aquifer ranges 

from about –200 ft along the updip limit to about –1,200 ft 

along the downdip limit. The thickness of the Lower Cape 

Fear aquifer ranges from about 10 ft in places along the updip 

limit to as much as 500 ft in the downdip limit. In SC, the 

Lower Cape Fear aquifer is correlated to the Gramling aquifer. 

The Lower Cape Fear confining unit separates the upper 

and lower parts of the Cape Fear Formation into two distinct 

aquifers. The top altitude of the Lower Cape Fear confining unit varies from about –200 ft in the updip limit to about 

–1,200 ft in the downdip limit. The thickness of the Lower 

Cape Fear confining unit is about 50 ft over most of the NC 

Coastal Plain and about 100 ft thick near the North Carolina–

Virginia border.

The Lower Cretaceous aquifer consists of permeable 

sediments of Lower Cretaceous age beneath the Lower Cape 

Fear aquifer in the Albemarle Embayment and extending south 

into Cartaret County, NC. The freshwater part of the Lower 

Cretaceous aquifer varies in altitude from –200 ft to –1,200 ft. 
138 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

The freshwater part of the thickness of the Lower Cretaceous 

aquifer ranges from about 50 ft to as much as 800 ft in NC.

Fifteen hydrostratigraphic units were delineated in SC 

using core, fossil, borehole geophysical, and hydraulic-head 

data, and a new hydrostratigraphic nomenclature is applied. 

There are eight Tertiary/Quaternary units. The surficial aquifer 

blankets a variety of units from the Upper Floridan aquifer 

in the southern part of SC to the Crouch Branch aquifer in 

the eastern part of SC. The surficial aquifer described here 

is comparable to the surficial aquifer of Aucott and others 

(1987). The surficial aquifer is mainly Quaternary (undifferentiated), consists of sand, clayey sand, and shell beds, and is 

present throughout the SC ACP. The Upper Floridan confining unit overlies the Upper Floridan aquifer in downdip areas 

and has no comparable unit in the framework of Aucott and 

others (1987). The Upper Floridan confining unit is Miocene 

(Hawthorn Group), consists of phosphatic sandy clay and 

sandy limestone, and is present in the southern regions of the 

Coastal Plain. The Upper Floridan aquifer overlies the Middle 

Floridan confining unit and is comparable to the upper parts 

of the Floridan aquifer system of Aucott and others (1987). 

The Upper Floridan aquifer is late Eocene and possibly early 

Oligocene (includes Dry Branch/Parkers Ferry and Drayton(?) Formations), consists of limestone (downdip) and 

sand (updip), and is present in the western half of the Coastal 

Plain. The Middle Floridan confining unit overlies the Middle 

Floridan aquifer and has no comparable unit in the framework 

of Aucott and others (1987). The Middle Floridan confining 

unit is late Eocene (Harleyville and Dry Branch/Parkers Ferry 

Formations), consists of fine-grained calcarenites and calcilutites, and is present in the western half of the Coastal Plain. 

The Middle Floridan aquifer overlies the Gordon confining 

unit and is comparable to the lower parts of the Floridan aquifer system of Aucott and others (1987). The Middle Floridan 

aquifer is late middle Eocene (Santee Formation), consists of 

limestone (downdip) and sand (updip), and is present only in 

the western half of the Coastal Plain. The Gordon confining 

unit overlies the Gordon aquifer and has no comparable unit 

in the framework of Aucott and others (1987). The Gordon 

confining unit is middle Eocene (Santee and Warley Hill 

Formations), consists of marl, glauconitic clayey sand, and 

sandy clay, and is present in the western half of the Coastal 

Plain. The Gordon aquifer overlies the Crouch Branch confining unit and is comparable to the lower part of the Tertiary 

sand aquifer of Aucott and others (1987). The Gordon aquifer 

is predominantly late Paleocene through early middle Eocene 

(Williamsburg, Fishburne, and Congaree Formations), consists 

of sand, clayey sand, and limestone, and is present throughout 

the western half of the Coastal Plain. The Crouch Branch confining unit is early Paleocene and early late Paleocene (Rhems 

and Lang Syne Formations), consists of carbonaceous clay, 

fine sand, and opaline claystone, and is present mainly west 

of the Congaree/Santee Rivers. The Crouch Branch confining 

unit overlies the Crouch Branch aquifer and is comparable to 

the confining unit that separates the Black Creek and Tertiary 

sand aquifers of Aucott and others (1987). 

There are seven Cretaceous units. The Crouch Branch 

aquifer overlies the McQueen Branch confining unit and is 

comparable to the Black Creek aquifer of Aucott and others (1987). The Crouch Branch aquifer is late Campanian 

through Maastrichtian (Donoho Creek, Peedee/Steel Creek, 

and Sawdust Landing Formations), consists of sand and clayey 

sand, and is present throughout the SC ACP except in the 

north-northeast regions. The McQueen Branch confining unit 

overlies the McQueen Branch aquifer and is comparable to the 

confining unit that separates the Middendorf and Black Creek 

aquifers of Aucott and others (1987). The McQueen Branch 

confining unit is middle to late Campanian (Coachman, 

Bladen, and Donoho Creek Formations), consists of carbonaceous clay and fine sand, and is present throughout the SC 

ACP except near the Fall Line. The McQueen Branch aquifer 

overlies the Gramling confining unit in the inner Coastal Plain 

and the Charleston confining unit in the outer Coastal Plain. 

The McQueen Branch aquifer is comparable to the Middendorf aquifer of Aucott and others (1987). The McQueen 

Branch aquifer is Turonian through middle Campanian (Cape 

Fear, Cane Acre, and Coachman Formations), consists of sand 

and clayey sand, and is present throughout most of the Coastal 

Plain. The Charleston confining unit is comparable to the 

confining unit separating the downdip Middendorf and Black 

Creek aquifers of Aucott and others (1987). The Charleston 

confining unit is Santonian through early Campanian (Pleasant 

Creek, Shepherd Grove, and Caddin Formations), consists of 

calcareous sandy clay and clayey sand, and is present in the 

lower half of the Coastal Plain. The Charleston aquifer, which 

was mapped as the Middendorf aquifer by Aucott and others 

(1987), overlies the Gramling confining unit. The Charleston 

aquifer is Coniacian through Santonian (Cape Fear, Collins 

Creek, and Pleasant Creek Formations), consists of lignitic 

sand and clayey sand, and is present in the lower half of 

the Coastal Plain. The Gramling confining unit overlies the 

Gramling aquifer and is comparable to the confining unit that 

separates the Cape Fear and Middendorf aquifers of Aucott 

and others (1987). The Gramling confining unit is Turonian 

through Coniacian (Cape Fear Formation), consists of silicacemented gravel, sand, and clay, and is present throughout the 

Coastal Plain. The basal Gramling aquifer is comparable to the 

Cape Fear aquifer of Aucott and others (1987). The Gramling 

aquifer is Cenomanian through Coniacian (Beech Hill, Clubhouse, and Cape Fear Formations), consists of gravel, sand, 

and clay, and is present in the lower half of the Coastal Plain.

Several important differences exist between the current 

hydrogeologic framework in SC and previous frameworks. 

The Middendorf aquifer mapped in updip regions by Aucott is 

comparable to the McQueen Branch aquifer mapped in updip 

areas of this report. Fossil data, however, indicate that strata 

mapped as the Middendorf aquifer in downdip areas (Santonian) are older than strata mapped as the Middendorf aquifer 

in updip areas (Campanian). In this report, the older strata are 

mapped as the Charleston aquifer, and the younger strata are 

mapped as the McQueen Branch aquifer. The Tertiary sand 

aquifer of Aucott is divided into the Gordon, Middle Floridan, 
References 139

and Upper Floridan aquifers and confining units. The Floridan 

aquifer system of Aucott is divided into the Middle and Upper 

Floridan aquifers and associated confining units. The Floridan 

aquifer system is extended down-section to include late Paleocene strata of the Gordon aquifer and laterally to include clastic sediments in updip regions for this report. Confining units 

are named after the aquifer that they confine for this report.

In order to determine the continuity of hydrogeologic 

units across the border between NC and SC, two hydrogeologic cross sections were constructed from south to north 

along approximate structural strike, using four wells. The 

sections indicate that most of the late Cretaceous aquifers and 

confining units correlate across the border. The exceptions are 

the Peedee and Gramling confining units. 

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Appendix B1 147

Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued[Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present]

Borehole 

location 

on 

figure B3

Borehole 

number

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Top surface altitude, in feet

Land 

surface/ 

top of 

surficial 

aquifer

Yorktown/

Upper 

Floridan 

confining 

unit

Yorktown/ 

Upper 

Floridan 

aquifer

Castle 

Hayne/

Pungo 

River/ 

Middle 

Floridan 

confining 

unit

Castle 

Hayne/ 

Pungo 

River/ 

Middle 

Floridan 

aquifer

Beaufort/ 

Gordon 

confining 

unit

Beaufort/

Gordon 

aquifer

Peedee/

Crouch 

Branch 

confining 

unit

Peedee/ 

Crouch 

Branch 

aquifer

Black 

Creek/ 

McQueen 

Branch 

confining 

unit

Black 

Creek/ 

McQueen 

Branch 

aquifer

Upper 

Cape 

Fear/ 

Charleston 

confining 

unit

Upper 

Cape 

Fear/ 

Charleston 

aquifer

Lower 

Cape 

Fear/

Gramling 

confining 

unit

Lower 

Cape 

Fear/ 

Gramling 

aquifer

Lower 

Cretaceous 

aquifer

Basement 

rock

North Carolina

1 AA 26X 34.660000 –77.478889 10 — — — — — — –221 –246 –533 –607 –1006 –1092 –1202 –1267 — –14452 AA 27W 34.433333 –77.563889 37 — — — — — — –172 –195 –488 –546 –955 –1035 –1135 –1206 — –13633 AA 35N 34.455982 –78.307832 28 — — — — — — –6 –14 –150 –233 –366 –407 –517 –577 — –6424 AA 43Q 34.438889 –78.971667 80 — — — — — — 48 31 –12 –28 –180 –309 — — — –4165 B 20U 36.507222 –77.005834 69 — — — — 9 –9 — — — — –38 –85 –275 –339 –606 –7526 BB 28J 34.399976 –77.678170 60 — — 2 –17 — — –110 –142 –447 –505 –862 –1000 –1088 –1154 — –12887 BB 28N 34.675000 –77.708333 34 — — — — — — –114 –142 –440 –480 –814 –869 –1076 –1137 — –12138 BB 45M 34.373333 –79.127222 94 — — — — — — — — 34 –11 –266 –368 — — — –4559 C 14T 36.436111 –76.501389 25 –58 –108 –217 –277 –326 –346 — — — — –427 –449 –755 –770 –1221 –2088

10 C 22Q 36.434167 –77.227500 105 66 50 — — — — — — — — –1 –15 –27 –82 — –415

11 D 10A 36.411111 –76.175000 8 –64 –106 –410 –547 –624 –646 — — — — –817 –862 –1104 –1327 –1612 –2814

12 D 12V 36.333333 –76.366667 15 –58 –93 –320 –375 –449 –475 — — — — –524 –577 –1209 –1271 –1450 –260513 D 18M 36.380000 –76.890833 38 — — — — –50 –62 — — — — –114 –170 –270 –302 — –90214 DD 37L 34.208333 –78.441667 48 — — — — — — –8 –30 –222 –266 –448 –476 –597 –714 — –88415 DD 42N 34.210698 –78.896111 108 — — — — — — 15 6 –187 –204 –333 –432 –542 –586 — –77116 E 7J 36.305834 –75.929723 5 –80 –150 –615 –759 –948 –1000 — — — — –1423 –1469 –1763 –1910 –2203 –451617 E 25J 34.210278 –78.896667 37 — — — — — — — — — — 16 –3 –49 –67 — –18218 EE 36K 34.128756 –78.338547 61 — — — — — — 10 3 –307 –373 –592 –618 –754 –834 — –105419 EE 39O 34.125932 –78.663792 60 — — — — — — –5 –20 –272 –290 –433 –506 –647 –742 — –90120 G 6L 36.117222 –75.852778 10 –79 –116 –520 –560 –1060 –1160 — — — — –1310 –1500 –2165 –2325 –2700 –505521 G 19B 36.164722 –76.937778 65 37 1 — — –55 –71 — — — — –109 –145 –363 –451 –991 –103322 G 24O 36.126667 –77.411667 93 65 53 — — — — — — — — 17 11 –89 –150 — –24523 GG 31J 33.973611 –77.919444 9 — — –95 –113 — — –171 –219 –461 –539 –835 –905 –1045 –1125 — –151524 GG 31P 33.944444 –77.997778 25 — — –27 –43 — — –65 –89 –451 –616 –800 –867 –988 –1094 — –152525 H 24Q 36.030000 –77.397222 90 79 50 — — — — — — — — –5 –19 –158 –255 — –30626 HH 39J 33.892777 –78.589421 — — — — — — — — 47 –354 –420 –643 –700 –805 –875 — –128627 HH 39K 36.301111 –77.436667 50 — — — — — — –12 –50 –349 –416 –638 –694 –802 –868 — –128228 I 13X 35.916795 –76.469963 11 –25 –53 –261 –292 –417 –496 — — — — –594 –767 –990 –1008 –1750 –210029 J 7T 35.863889 –75.925000 3 –143 –189 –532 –617 –1127 –1207 –1324 –1355 –1511 –1612 –1709 –1852 –2548 –2682 –2900 –511930 J 22P 35.482494 –77.597095 75 61 47 — — — — — — 5 –47 –165 –193 –437 –461 — –56931 J 26H 35.892778 –77.538333 50 — — — — — — — — — — 21 10 — — — –29932 J 28J 35.895277 –77.678888 88 — — — — — — — — — — — — — — — –8533 J 28S 35.854167 –77.687500 98 — — — — — — — — — — 86 34 –24 –84 — –12634 K 17A 35.823880 –76.758325 33 –20 –44 –115 –123 –211 –238 — — –322 –395 –500 –632 –900 –950 — –155035 K 26M 35.790983 –77.547998 33 — — — — — — — — — — –23 –29 –195 — — –290
148 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued [Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present] Borehole location on figure B3 Borehole number Latitude (decimal degrees) Longitude (decimal degrees) Top surface altitude, in feet Land surface/ top of surficial aquifer York- town/ Upper Floridan confining unit York- town/ Upper Floridan aquifer Castle Hayne/ Pungo River/ Middle Floridan confining unit Castle Hayne/ Pungo River/ Middle Floridan aquifer Beau- fort/ Gordon confin- ing unit Beau- fort/ Gordon aquifer Peedee/ Crouch Branch confining unit Peedee/ Crouch Branch aquifer Black Creek/ McQueen Branch confining unit Black Creek/ McQueen Branch aquifer Upper Cape Fear/ Charles- ton confining unit Upper Cape Fear/ Charles- ton aquifer Lower Cape Fear/ Gramling confin- ing unit Lower Cape Fear/ Gramling aquifer Lower Creta- ceous aquifer Base- ment rock North Carolina—Continued 36 K 27N 35.790000 –77.639444 104 70 44

—

—

—

—

—

—

—

— 37 –2 –66 –152

— –200

37 K 28V 35.756389 –77.689444 95

—

—

—

—

—

—

—

—

—

— 1 –9 –35 –71

— –197

38 K 30T 35.771388 –77.838055 120

—

—

—

—

—

—

—

—

—

— 74 60

—

—

— 1

39 L 24B 35.749580 –77.364980 55 37 28

—

—

—

— 15 5 –3 –29 –199 –217 –435 –483

— –635

40 L 25P 35.856521 –77.248202 13 3 –7

—

—

—

—

—

— –38 –47 –88 –122 –344 –412

— –442

41 L 28F 35.731111 –77.740278 121 99 82

—

—

—

—

—

—

—

— 78 41

—

—

— –124

42 M 17X 35.637500 –76.854167 40

—

—

— –63 –222 –245 –348 –367 –453 –570 –647 –692 –1173 –1243

— –1550

43 M 24L 35.626957 –77.359692 20

—

—

—

—

—

— –10 –26 –50 –84 –252 –267 –475 –520

— –636

44 M 26Q 35.607778 –77.596111 80 72 50

—

—

—

—

—

— 27 16 –96 –156 –393 –400

— –423

45 M 29P 35.605555 –77.821388 90

—

—

—

—

—

—

—

—

—

— 56 –7

—

—

— –58

46 M 29Q 35.601388 –77.810833 85 77 71

—

—

—

—

—

—

—

— 49 –21

—

—

— –65

47 M 29R 35.600278 –77.815833 75 69 63

—

—

—

—

—

— 57 49 37 27

—

—

— –87

48 M 30L 35.631433 –77.852263 103 73 63

—

—

—

—

—

—

—

— 41 36

—

—

— –45

49 M 31I 35.640278 –77.937222 122 103 97

—

—

—

—

—

—

—

— 81 72

—

—

— 64

50 N 21M 35.536399 –77.119290 33

—

— 10 –1 –76 –87 –180 –209 –286 –328 –520 –550 –825 –850

— –1400

51 N 23P 35.529964 –77.326652 70 64 55

—

—

—

— 2 –44 –131 –216 –372 –404 –601 –610

— –860

52 N 31I 35.311944 –78.032500 135

—

—

—

—

—

—

—

— 100 91 37 17

—

—

— –66

53 N 31M 35.541666 –77.971666 145

—

—

—

—

—

—

—

—

—

—

—

—

—

—

— 73

54 O 17I 35.473171 –76.782610 8 –2 –16 –103 –119

—

—

—

— –620 –650 –690 –720 –1070 –1100

— –2000

55 O 23L 35.463640 –77.275232 42 32 24 4 1 —

— –94 –112 –212 –262

—

— –634 –728

— –1036

56 O 27J 35.477778 –77.599722 77 69 47

—

—

—

—

—

— 15 –7 –123 –199 –339

—

— –449

57 O 27J 35.475000 –77.591666 78 62 35

—

—

—

—

—

— 10 –16 –122 –202 –337 –396

— –467

58 O 28K 35.455055 –77.668767

—

—

—

—

—

—

—

—

—

—

— –89 –153 –269 –297

—

—

59 O 28K 35.455055 –77.668767 37

—

—

—

—

—

—

—

— 24 15 –48 –114 –260 –280

— –350

60 O 30J 35.469778 –77.849778 97

—

—

—

—

—

—

—

— 70 65 –4 –23

—

—

— –115

61 O 30Q 35.438889 –77.898611 128

—

—

—

—

—

—

—

—

—

— 22 –12

—

—

— –96

62 O 41L 35.464444 –78.778611 290

—

—

—

—

—

—

—

— 278 264

—

—

—

—

— 209

63 P 17I 35.386451 –76.783141 9 –26 –34 –42 –75

—

—

—

— –611 –678 –780 –800 –1130 –1150

— –2100

64 P 18V 35.343707 –76.861047 36 6 –14 –50 –108

—

—

—

— –560 –640 –780 –800 –1130 –1150

— –2050

65 P 19M 35.373479 –76.951008 27 23 3 –39 –45

—

—

—

— –443 –540 –700 –720 –1070 –1100

— –1500

66 P 22J 35.381484 –77.087762 41

—

— 9 –15

—

— –219 –237 –411 –519 –610 –630 –990 –1010

— –1350

67 P 22J 35.387222 –77.173333 48 33 26 –4 –20 –98 –116 –126 –140 –307 –390 –734 –762 –875 –925

— –1210

68 P 22U 35.332429 –77.172490 26

—

— 3 –40

—

— –168 –192 –362 –482 –580 –600 –875 –930

— –1260

69 P 26U 35.336736 –77.511829 72

—

—

—

—

—

— 60 44 –125 –172 –342 –363 –608 –648

— –760

70 P 27A 35.416111 –77.592222 78

—

—

—

—

—

—

—

— 14 –24 –150 –192 –342

—

— –362
Appendix B1 149

Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued[Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present]

Borehole 

location 

on 

figure B3

Borehole 

number

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Top surface altitude, in feet

Land 

surface/ 

top of 

surficial 

aquifer

Yorktown/

Upper 

Floridan 

confining 

unit

Yorktown/ 

Upper 

Floridan 

aquifer

Castle 

Hayne/

Pungo 

River/ 

Middle 

Floridan 

confining 

unit

Castle 

Hayne/ 

Pungo 

River/ 

Middle 

Floridan 

aquifer

Beaufort/ 

Gordon 

confining 

unit

Beaufort/

Gordon 

aquifer

Peedee/

Crouch 

Branch 

confining 

unit

Peedee/ 

Crouch 

Branch 

aquifer

Black 

Creek/ 

McQueen 

Branch 

confining 

unit

Black 

Creek/ 

McQueen 

Branch 

aquifer

Upper 

Cape 

Fear/ 

Charleston 

confining 

unit

Upper 

Cape 

Fear/ 

Charleston 

aquifer

Lower 

Cape 

Fear/

Gramling 

confining 

unit

Lower 

Cape 

Fear/ 

Gramling 

aquifer

Lower 

Cretaceous 

aquifer

Basement 

rock

North Carolina—Continued

71 P 31M 35.375556 –77.957222 118 — — — — — — — — — — 78 56 — — — –5272 P 31Y 35.335556 –77.985556 66 — — — — — — — — — — 50 33 — — — –8473 P 35U 35.343056 –78.256944 125 — — — — — — — — 117 108 86 70 — — — 1074 P 38O 35.374444 –78.567500 210 — — — — — — — — 190 160 124 109 — — — 6275 P 41O 35.382222 –78.828333 239 — — — — — — — — 229 220 — — — — — 18376 Q 25D 35.327137 –77.478071 65 — — — — — — 11 –15 –135 –185 –341 –381 –559 –595 — –73577 Q 27R 35.269344 –77.618238 44 — — — — — — 36 9 –57 –138 –330 –380 — — — –58678 Q 30H 35.551111 –77.934722 130 — — — — — — — — — — 97 54 — — — –4279 Q 30I 35.301111 –77.866389 105 — — — — — — — — 93 72 –50 –108 — — — –24480 Q 31D 35.322222 –77.970000 63 — — — — — — — — 60 53 –22 — — — — –10581 Q 32D 35.319444 –78.061944 164 — — — — — — — — 150 128 93 57 — — — –4082 Q 32I 35.553333 –77.935555 133 — — — — — — — — — — 123 116 — — — 5583 Q 32M 35.329444 –78.060555 138 — — — — — — — — 128 121 44 31 — — — –3784 Q 32O 35.299166 –78.038611 175 — — — — — — — — — — 75 51 — — — –8885 Q 32W 35.261667 –78.034167 185 — — — — — — — — 157 151 31 11 — — — –7786 Q 36U 35.250833 –78.348056 180 — — — — — — — — 130 108 10 –1 — — — –11987 R 21O 35.210833 –77.156667 23 — — — — — — –241 –273 –433 –473 –770 –790 –980 –1000 — –141088 R 23U 35.175833 –77.250556 47 — — 22 12 — — –223 –323 –395 –740 –760 10000 –900 –930 — –130089 R 23W 35.177222 –77.297778 34 — — — — –137 –158 –203 –272 –385 –420 –718 –734 –860 –890 — –120090 R 23X 35.172305 –77.311178 46 — — 29 6 –97 –104 –174 –210 –368 –434 –716 –732 –844 –882 — –119091 R 24N 35.206666 –77.390000 60 — — 56 46 –44 –50 –97 –160 –306 –344 –612 –626 –790 –810 — –99392 R 25J 35.221944 –77.425833 55 — — — — –27 –44 –69 –136 –263 –297 –539 –571 –677 –795 — –92593 R 27A 35.238611 –77.595000 43 — — — — — — 23 –13 –83 –177 –333 –379 –593 –623 — –69794 R 29T 35.196160 –77.752000 110 — — — — — — 68 60 –6 –54 –262 –288 — — — –49095 R 31C 35.244508 –77.963034 150 — — — — — — — — 127 100 13 –6 — — — –17096 R 32E 35.241944 –78.068055 120 — — — — — — — — — — 66 52 — — — –9197 R 32O 35.205556 –78.075000 160 — — — — — — — — 141 135 44 16 — — — –16898 R 39P 35.191667 –78.654167 143 — — — — — — — — 95 86 29 9 — — — –6099 R 45N 34.810394 –77.487225 325 — — — — — — — — — — 251 226 — — — 143

100 R 49M 35.205278 –79.464167 505 — — — — — — — — — — 349 295 — — — 281101 S 21I 35.137500 –77.105556 27 — — — — –199 –223 — — –633 –701 –893 –905 –1135 –1150 — –1600102 S 21Y 35.095556 –77.152222 21 — — — — –294 –307 –339 –355 –558 –660 –900 –920 –1140 –1160 — –1590103 S 22J 35.137475 –77.171389 28 — — 10 1 — — –319 –346 –502 –594 –830 –860 –1050 –1072 — –1490104 S 26I 35.139489 –77.530205 55 — — 45 39 7 –5 –65 –91 –230 –275 –439 –483 –683 –701 — –875105 S 39T 35.104444 –78.589722 170 — — — — — — — — 103 74 41 –5 –110 –145 — –180
150 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued [Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present] Borehole location on figure B3 Borehole number Latitude (decimal degrees) Longitude (decimal degrees) Top surface altitude, in feet Land surface/ top of surficial aquifer York- town/ Upper Floridan confining unit York- town/ Upper Floridan aquifer Castle Hayne/ Pungo River/ Middle Floridan confining unit Castle Hayne/ Pungo River/ Middle Floridan aquifer Beau- fort/ Gordon confin- ing unit Beau- fort/ Gordon aquifer Peedee/ Crouch Branch confining unit Peedee/ Crouch Branch aquifer Black Creek/ McQueen Branch confining unit Black Creek/ McQueen Branch aquifer Upper Cape Fear/ Charles- ton confining unit Upper Cape Fear/ Charles- ton aquifer Lower Cape Fear/ Gramling confin- ing unit Lower Cape Fear/ Gramling aquifer Lower Creta- ceous aquifer Base- ment rock North Carolina—Continued 106 S 41W 35.090556 –78.788056 125

—

—

—

—

—

—

—

— 96 90 49 9 —

—

— –75

107 S 42O 35.119167 –78.911667 240

—

—

—

—

—

—

—

—

—

— 113 74

—

—

— –28

108 S 48H 35.144722 –79.371667 475

—

—

—

—

—

—

—

—

—

— 299 229

—

—

— 206

109 T 22A 35.082778 –77.180278 34

—

— –20 –38 –289 –302 –334 –342 –529 –644 –872 –922 –1110 –1150

— –1550

110 T 29G 35.056327 –77.807143 127

—

—

—

—

—

— 45 35 –79 –113 –301 –323 –270 –290

— –550

111 T 48T 35.033333 –79.348889 350

—

—

—

—

—

—

—

—

—

— 198 144

—

—

— 102

112 U 18Q 34.933879 –76.890064 26 –21 –34 –74 –84 –489 –516 –674 –747 –1017 –1064 –1350 –1400 –1770 –1800

— –2800

113 U 26J 34.969429 –77.503222 71

—

— 61 47 –11 –25 –123 –153 –289 –323 –685 –715 –850 –890

— –1080

114 U 34B 34.988899 –78.189350 145

—

—

—

—

—

—

—

— 99 71 –58 –93 –190 –208

— –310

115 U 35D 34.975278 –78.306111 155

—

—

—

—

—

—

—

— 104 81 –67 –112 –191 –204

— –297

116 U 38T 34.944167 –78.507778 134

—

—

—

—

—

—

—

— 95 59 –30 –86 –166 –176

— –219

117 U 41A 34.987500 –78.754167 130

—

—

—

—

—

—

—

— 88 70 11 –20

—

—

— –103

118 U 46O 34.975278 –79.236667 253

—

—

—

—

—

—

—

— 231 218 126 51

—

—

— –4

119 U 53M 34.960556 –79.791111 340

—

—

—

—

—

—

—

— 332 317

—

—

—

—

— 225

120 V 19W 34.848611 –76.962500 41 16 1 –187 –245

—

— –759 –796 –915 –1207 –1429 –1519 –1874 –1924

— –2365

121 V 23X 34.837042 –77.303278 45

—

—

—

— –195 –221 –421 –458 –641 –761 –1025 –1100 –960 –1010

— –1540

122 V 24G 34.900000 –77.395833 52

—

—

—

— –168 –186 –298 –328 –448 –598 –888 –928 –1028 –1068

— –1318

123 V 42U 34.843611 –78.838333 147

—

—

—

—

—

—

—

— 125 113 –86 –119

—

—

— –237

124 V 45U 34.843151 –79.087593 185

—

—

—

—

—

—

—

— 173 160 55 –103

—

—

— –167

125 V 52I 34.891667 –79.686111 325

—

—

—

—

—

—

—

— 303 283 147

—

—

—

— 117

126 W 22V 34.757222 –77.193333 37 1 –11 –116 –167

—

— –584 –634 –755 –983 –1220 –1261 –1410 –1446

— –1769

127 W 25F 34.604530 –78.241805 26

—

—

—

—

—

— –198 –258 –392 –433 –748 –794 –994 –1020

— –1210

128 W 29D 34.824016 –77.812048 45

—

—

— 9 –1

— –95 –125 –213 –245 –544 –579

—

—

— –743

129 W 36N 34.786111 –78.396944 125

—

—

—

—

—

— 72 56 31 13 –119 –150 –231 –259

— –279

130 W 43L 34.801561 –78.973485 151

—

—

—

—

—

—

—

— 138 126 –51 –127

—

—

— –209

131 W 48V 34.766389 –79.366389 208

—

—

—

—

—

—

—

— 152 124 –29 –101

—

—

— –156

132 W 51V 34.759722 –79.610556 250

—

—

—

—

—

—

—

— 186 177 68 16

—

—

— 5

133 X 24S 34.692198 –77.351180 20

—

— –82 –98

—

— –400 –440 –676 –838 –1063 –1174 –1270 –1306

— –1550

134 X 26R 34.427778 –77.619444 50

—

—

—

— –145 –163 –200 –215 –385 –445 –876 –930 –1040 –1070

— –1223

135 X 26U 34.700000 –77.533333 57

—

— –33 –71

—

— –357 –409 –473 –531 –973 –1003 –1219 –1241

— –1351

136 X 45J 34.726944 –79.092778 166

—

—

—

—

—

—

—

— 154 132 –32 –184

—

—

— –296

137 X 26S 34.672222 –77.505556 38

—

— 30 8 —

— –122 –142 –462 –552 –880 –942 –996 –1046

— –1212

138 Y 25D 34.697222 –77.537500 65

—

— –35 –73

—

— –329 –387 –459 –511 –947 –993 –1204 –1226

— –1330

139 Y 25Q 34.611365 –77.482799 66

—

— –14 –86

—

— –404 –456 –548 –674 –988 –1044 –1280 –1300

— –1400

140 Y 30S 34.604749 –77.856070 14

—

—

—

—

—

— –24 –46 –298 –342 –673 –744

—

—

— –902
Appendix B1 151

Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued[Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present]

Borehole 

location 

on 

figure B3

Borehole 

number

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Top surface altitude, in feet

Land 

surface/ 

top of 

surficial 

aquifer

Yorktown/

Upper 

Floridan 

confining 

unit

Yorktown/ 

Upper 

Floridan 

aquifer

Castle 

Hayne/

Pungo 

River/ 

Middle 

Floridan 

confining 

unit

Castle 

Hayne/ 

Pungo 

River/ 

Middle 

Floridan 

aquifer

Beaufort/ 

Gordon 

confining 

unit

Beaufort/

Gordon 

aquifer

Peedee/

Crouch 

Branch 

confining 

unit

Peedee/ 

Crouch 

Branch 

aquifer

Black 

Creek/ 

McQueen 

Branch 

confining 

unit

Black 

Creek/ 

McQueen 

Branch 

aquifer

Upper 

Cape 

Fear/ 

Charleston 

confining 

unit

Upper 

Cape 

Fear/ 

Charleston 

aquifer

Lower 

Cape 

Fear/

Gramling 

confining 

unit

Lower 

Cape 

Fear/ 

Gramling 

aquifer

Lower 

Cretaceous 

aquifer

Basement 

rock

North Carolina—Continued

141 Y 34P 35.215833 –79.146111 34 — — — — — — 1 –30 –107 –123 –255 –294 –451 –474 — –544142 Y 38B 34.655278 –78.522500 65 — — — — — — — — –38 –49 –168 –203 –318 –365 — –425143 Y 39G 34.632500 –78.620833 130 — — — — — — 100 86 10 1 –135 –177 –311 –330 — –384144 Y 42F 34.644444 –78.916667 140 — — — — — — — — 114 67 –185 –242 — — — –327145 Z 41M 34.507500 –78.755278 116 — — — — — — 68 50 –14 –33 –151 –196 –367 –408 — –459146 Z 45V 34.501111 –79.109444 108 — — — — — — — — 40 –10 –258 –438 — — — –504147 Z 47R 34.532009 –79.296151 145 — — — — — — — — 61 33 –170 –288 — — — –357

South Carolina

148 AIK–0817 33.437778 –81.770278 418 — 374 — — — 346 240 231 23 12 — — — — — –120149 AIK–0826 33.542500 –81.485833 296 295 294 — — — 266 241 220 –0 –21 — — — — — –210150 AIK–0892 33.337500 –81.708611 354 — 264 — 236 — 207 — 74 –175 –199 — — –370 — — –396151 AIK–0902 33.353611 –81.808889 — — — — — — 231 139 68 –86 –119 — — — — — –317152 AIK–2448 33.624444 –81.849722 489 — 477 — — — 459 — 400 — — — — — — — 367153 AIK–2449 33.539444 –81.855000 493 — 464 — — — 429 — 347 239 232 — — — — — 180154 ALL–0348 33.025000 –81.384722 281 123 111 26 –39 –122 –165 –353 –464 –841 –881 — –1155 –1208 — — –1441155 ALL–0357 33.113333 –81.506111 242 — 170 72 57 15 –71 –200 –280 –665 –696 — — –978 — — –1154156 BAM–0068 33.055833 –81.098333 109 108 107 46 –26 –115 –177 –343 –443 –843 –893 –1123 –1193 –1243 –1493 — –1593157 BAM–0076 33.242500 –81.182500 214 — 154 — 24 — –16 –176 –236 –626 –686 — — –986 — — –1136158 BAM–0083 33.288333 –81.043056 151 150 149 — 79 49 –40 –91 –173 –591 –649 — — –951 — — –1136159 BFT–2055 32.191111 –80.704167 9 –56 –111 –231 –541 –591 –1221 –1476 –1673 –2036 — –2223 — –2661 –2761 — –3821160 BFT–2067 32.325556 –80.823611 19 –46 –98 –181 –424 –487 –1031 –1251 –1431 –1861 — –2031 –2281 –2531 –2681 — –3481161 BFT–2092 32.313611 –80.488889 9 –66 –98 –138 –461 –546 –936 –1291 –1541 –1841 — –2071 –2391 –2521 –2571 — –3591162 BRK–0430 33.078056 –79.999444 17 — — 8 — –133 –178 –283 –523 –983 –1063 –1223 –1513 –1643 –1818 — –2233163 BRK–0437 33.366944 –80.117222 81 — — — — — 54 –34 –199 –739 –779 –879 –1029 –1194 –1469 — –1719164 BRK–0644 33.404167 –79.933889 74 — — — — — 51 –108 –202 –689 –710 –842 –1010 –1208 –1475 — –1707165 BRN–0240 33.438889 –81.239167 206 205 204 — 164 — 122 63 14 –228 –241 — — –576 — — –647166 BRK–2689 33.291111 –79.686944 34 — — — — — 8 –153 –296 –749 –816 –1016 –1216 –1396 –1616 — –1916167 BRN–0295 33.126944 –81.229167 194 — 174 68 24 –26 –88 –266 –356 –696 –776 — — –1136 — — –1286168 BRN–0303 33.245833 –81.616111 294 — 190 — 134 — 95 –56 –126 — –316 — — –633 — — –776169 BRN–0335 33.146667 –81.607500 206 — 156 — 62 44 –26 –157 –266 –541 –583 — — –815 — — –994170 BRN–0349 33.178611 –81.314444 208 — 184 — 54 28 –33 –218 –297 –627 –710 — — –1015 — — –1118171 BRN–0358 33.321389 –81.407222 264 — 203 — 144 102 92 –16 –64 –346 –378 — — –676 — — –770172 BRN–0386 33.242778 –81.403333 — — 180 — 110 61 20 –89 –145 –495 –550 — — –870 — — –1000
152 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued [Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present] Borehole location on figure B3 Borehole number Latitude (decimal degrees) Longitude (decimal degrees) Top surface altitude, in feet Land surface/ top of surficial aquifer York- town/ Upper Floridan confining unit York- town/ Upper Floridan aquifer Castle Hayne/ Pungo River/ Middle Floridan confining unit Castle Hayne/ Pungo River/ Middle Floridan aquifer Beau- fort/ Gordon confin- ing unit Beau- fort/ Gordon aquifer Peedee/ Crouch Branch confining unit Peedee/ Crouch Branch aquifer Black Creek/ McQueen Branch confining unit Black Creek/ McQueen Branch aquifer Upper Cape Fear/ Charles- ton confining unit Upper Cape Fear/ Charles- ton aquifer Lower Cape Fear/ Gramling confin- ing unit Lower Cape Fear/ Gramling aquifer Lower Creta- ceous aquifer Base- ment rock South Carolina—Continued 173 BRN–0921 33.402778 –81.414444 349

— 279

— 204 169 159

— 37

— –201

—

— –501

—

— –551

174 CAL–0129 33.731667 –80.879722 327

—

—

— 304

— 265 207 157 –99 –125

—

— –333

—

— –403

175 CAL–0131 33.659167 –80.663889 236

—

—

—

— 216 188 163 111 –314 –374

—

— –564

—

— –784

176 CHN–0182 33.200556 –79.435556 9 —

—

—

—

— –27 –107 –337 –796 –831 –1041 –1331 –1491 –1691

— –2141

177 CHN–0635 32.764444 –79.832778 6 —

— –66

— –281 –324 –409 –684 –944 –1124 –1364 –1804 –2018 –2254

— –2794

178 CHN–0800 32.782500 –79.945000 9 —

— –65

— –304 –346 –420 –735 –1038 –1221 –1376 –1841 –2041 –2291

— –2841

179 CHN–0802 32.940833 –79.657500 7 —

— –36

—

— –167 –263 –558 –843 –993 –1223 –1623 –1803 –2043

— –2593

180 CHN–0814 32.602778 –80.143611 4 —

— –96

— –321 –566 –656 –1021 –1296

— –1531 –1978 –2216 –2476

— –3046

181 CHN–0820 33.155833 –79.363889 9 —

—

—

—

— –33 –112 –358 –776 –826 –1019 –1377 –1530 –1691

— –2241

182 CLA–0056 33.634167 –80.360000 139

—

—

—

—

— 118 97 45 –426 –456 –601 –649 –741

—

— –1001

183 CLA–0064 33.694167 –80.213611 124

—

—

—

—

—

— 104 74 –341 –391 –544 –598 –676

—

— –1001

184 COL–0053 32.983889 –80.455833 49

—

— –9 –104 –149 –221 –436 –636 –1076 –1151 –1251 –1481 –1611 –1851

— –2201

185 COL–0241 33.015000 –80.928889 79 69 11 –21 –109 –201 –291 –440 –541 –941 –991 –1166 –1336 –1421 –1671

— –1888

186 COL–0336 32.723611 –80.621111 24 –24

— –56

— –216 –436 –556 –786 –1246 –1336 –1406 –1696 –1926 –2176

— –2576

187 COL–0348 32.883333 –80.580833 21 6 — –29 –141 –209 –269 –466 –639 –1129 –1189 –1269 –1489 –1699 –1944

— –2267

188 COL–0349 33.065278 –80.623889 74 48 20 2 –57 –126 –181 –358 –516 –946 –1006 –1126 –1316 –1416 –1656

— –1926

189 COL–0364 32.503611 –80.296111 9 –41

— –71

— –359 –661 –827 –1181 –1511

— –1741 –2141 –2341 –2461

— –3191

190 COL–0374 32.558889 –80.454722 4 –46

— –106

— –276 –526 –661 –976 –1346

— –1546 –1956 –2196 –2396

— –2946

191 COL–0382 32.783889 –80.859167 24 14 –11 –48 –191 –256 –458 –666 –806 –1356 –1416 –1466 –1696 –1976 –2146

— –2476

192 CTF–0081 34.643056 –79.911667 192

—

—

—

—

—

—

— 183

— 154

—

— –1

—

— –27

193 CTF–0082 34.537222 –79.908056 204

—

—

—

—

—

—

— 189

— 154

—

— –56

—

— –141

194 CTF–0088 34.447778 –80.216944 404

—

—

—

—

—

—

— 394 209 202

—

— 64

—

— –29

195 DAR–0090 34.268611 –79.807500 132

—

—

—

—

—

—

— 126 –43 –116

—

— –303

—

— –510

196 DAR–0226 34.367778 –80.189167 338 337 336 335 334 333 332 331 329 130 116

—

— –21

—

— –151

197 DAR–0228 34.458611 –79.880000 179 178 177 176 175 174 173 172 171

— 119

—

— –97

—

— –268

198 DIL–0114 34.451944 –79.405556 142

—

—

—

—

—

—

— 124 4 –20

—

— –228

—

— –405

199 DIL–0121 34.328611 –79.283889 94

—

—

—

—

—

—

— 71 –43 –91 –223 –237 –282 –534

— –534

200 DOR–0037 32.888056 –80.359167 17

—

— –3

— –215 –350 –528 –779 –1243 –1327 –1403 –1733 –1844 –2043

— –2445

201 DOR–0052 32.959444 –80.202222 29

—

— 19

— –192 –321 –541 –633 –1131 –1196 –1291 –1611 –1731 –1911

— –2341

202 DOR–0211 33.156944 –80.521667 77

—

— 47 –14 –53 –123 –326 –445 –883 –953 –1114 –1243 –1324 –1623

— –1885

203 FLO–0264 34.101944 –79.734167 105

—

—

—

—

—

—

— 67 –213 –255

—

— –405

—

— –675

204 FLO–0268 34.170278 –79.789167 112

—

—

—

—

—

—

— 103 –77 –237

—

— –329

—

— –579

205 FLO–0274 33.855556 –79.767222 74

—

—

—

—

—

—

— 44 –328 –359 –516 –596 –654

—

— –1003

206 FLO–0275 34.158333 –79.794722 119

—

—

—

—

—

—

— 96 –96 –221

—

— –381

—

— –621

207 FLO–0286 34.117778 –79.767222 115

—

—

—

—

—

—

— 77 –117 –233

—

— –385

—

— –635
Appendix B1 153

Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued[Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present]

Borehole 

location 

on 

figure B3

Borehole 

number

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Top surface altitude, in feet

Land 

surface/ 

top of 

surficial 

aquifer

Yorktown/

Upper 

Floridan 

confining 

unit

Yorktown/ 

Upper 

Floridan 

aquifer

Castle 

Hayne/

Pungo 

River/ 

Middle 

Floridan 

confining 

unit

Castle 

Hayne/ 

Pungo 

River/ 

Middle 

Floridan 

aquifer

Beaufort/ 

Gordon 

confining 

unit

Beaufort/

Gordon 

aquifer

Peedee/

Crouch 

Branch 

confining 

unit

Peedee/ 

Crouch 

Branch 

aquifer

Black 

Creek/ 

McQueen 

Branch 

confining 

unit

Black 

Creek/ 

McQueen 

Branch 

aquifer

Upper 

Cape 

Fear/ 

Charleston 

confining 

unit

Upper 

Cape 

Fear/ 

Charleston 

aquifer

Lower 

Cape 

Fear/

Gramling 

confining 

unit

Lower 

Cape 

Fear/ 

Gramling 

aquifer

Lower 

Cretaceous 

aquifer

Basement 

rock

South Carolina—Continued

208 FLO–0310 34.243333 –79.791667 129 — — — — — — — 117 –61 –151 — — –321 — — –531209 FLO–0313 34.033333 –79.662222 107 — — — — — — — 80 –283 –333 — — –493 — — –793210 FLO–0317 33.994444 –79.601389 86 — — — — — — — 56 –278 –349 –489 –534 –594 — — –914

211 GEO–0088 33.251667 –79.270833 4 — — — — — –16 –46 –301 –701 –746 –966 –1096 –1348 –1536 — –2046

212 GEO–0090 33.443889 –79.519722 25 — — — — — 10 –10 –145 –605 –655 –845 –1025 –1195 –1375 — –1675213 GEO–0185 33.356944 –79.381944 19 — — — — — –21 –111 –221 –686 –731 –921 –1131 –1301 –1481 — –1831214 GEO–0234 33.561944 –79.012222 4 — — — — — — –46 –96 –516 –541 –746 –876 –1076 –1246 — –1596215 GEO–0249 33.661944 –79.246667 41 — — — — — — 12 –64 –469 –501 –715 –879 –1019 –1159 — –1459216 GEO–0277 33.518889 –79.330556 18 — — — — — — –10 –94 –580 –627 –802 –982 –1132 –1272 — –1582217 GEO–0298 33.461111 –79.103056 10 — — — — — — –50 –147 –560 –605 –820 –970 –1190 –1350 — –1740218 HAM–0092 32.746944 –81.236111 111 25 –1 –44 — –189 –561 –681 –789 –1259 –1349 –1469 –1539 –1739 –1939 — –2189219 HAM–0191 32.873056 –81.117500 111 81 41 –39 –124 –166 –485 –614 –689 –1159 –1239 –1389 –1489 –1639 –1839 — –2059220 HOR–0287 33.853056 –79.071667 26 — — — — — — — 13 –324 –344 –524 –642 –774 –904 — –1154221 HOR–0998 34.020000 –79.223333 79 — — — — — — — 39 –251 –296 –421 –521 –621 –821 — –951222 HOR–1165 33.723333 –78.903889 22 — — — — — — — –6 –410 –457 –609 –694 –871 –1055 — –1352223 JAS–0426 32.618333 –80.995833 63 15 –83 –159 –227 –322 –627 –843 –940 –1547 — –1707 –1877 –2225 –2334 — –2733224 LEE–0019 34.063889 –80.064722 139 — — — — — — — 102 –180 –241 — — –416 — — –609225 LEE–0072 34.102778 –80.163889 174 — — — — — — — 143 –110 –136 — — –341 — — –496226 LEE–0075 34.202500 –80.174444 198 — — — — — — — 175 –12 –26 — — –229 — — –339227 LEX–0154 33.877778 –81.166667 347 346 346 344 343 342 341 340 339 — 219 — — 59 — — 51228 LEX–0844 33.745556 –81.107778 372 371 370 369 368 367 366 336 292 — 61 — — –162 — — –174229 MLB–0182 34.668889 –79.730556 189 188 187 186 185 184 183 182 181 180 179 — — –11 — — –71230 MLB–0183 34.638055 –79.593611 207 206 205 204 203 202 201 200 199 149 99 — — –36 — — –163231 MRN–0078 33.861944 –79.330556 29 — — — — — — — –6 –326 –341 –521 –636 –751 –951 — –1129232 MRN–0089 34.195278 –79.240833 79 — — — — — — — 62 –179 –236 –336 — –421 — — –701233 MRN–0125 34.151389 –79.378611 79 — — — — — — — 44 –159 –238 –371 –406 –446 — — –721234 ORG–0108 33.348611 –80.679722 141 — — — 121 31 –94 –139 –189 –609 –659 –809 –909 –979 –1159 — –1259235 ORG–0256 33.615278 –81.007500 284 — — — 259 214 202 142 72 –146 –176 — — –446 — — –516236 ORG–0262 33.526389 –80.571389 164 — — — 129 114 60 14 –31 –456 –501 –646 –706 –793 — — –1031237 ORG–0368 33.461111 –80.842500 192 — — — 163 122 –1 –58 –108 –458 –528 — — –793 — — –1008238 ORG–0380 33.368611 –81.028889 176 — 166 — 136 96 –29 –74 –124 –484 –536 — — –824 — — –1001239 ORG–0393 33.508056 –80.865000 252 — — — 203 161 58 –21 –46 –386 –441 — — –725 — — –864240 ORG–0429 33.279167 –80.428056 74 — — — 58 29 –26 –176 –311 –851 –896 –986 –1110 –1206 –1476 — –1726241 ORG–0461 33.247222 –80.819444 114 — — 64 15 –66 –166 –226 –306 –696 –776 –926 –1036 –1066 –1276 — –1366242 RIC–0062 33.830556 –80.630556 146 145 144 143 142 141 140 139 64 –209 –229 — — –441 — — –511
154 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued [Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present] Borehole location on figure B3 Borehole number Latitude (decimal degrees) Longitude (decimal degrees) Top surface altitude, in feet Land surface/ top of surficial aquifer York- town/ Upper Floridan confining unit York- town/ Upper Floridan aquifer Castle Hayne/ Pungo River/ Middle Floridan confining unit Castle Hayne/ Pungo River/ Middle Floridan aquifer Beau- fort/ Gordon confin- ing unit Beau- fort/ Gordon aquifer Peedee/ Crouch Branch confining unit Peedee/ Crouch Branch aquifer Black Creek/ McQueen Branch confining unit Black Creek/ McQueen Branch aquifer Upper Cape Fear/ Charles- ton confining unit Upper Cape Fear/ Charles- ton aquifer Lower Cape Fear/ Gramling confin- ing unit Lower Cape Fear/ Gramling aquifer Lower Creta- ceous aquifer Base- ment rock South Carolina—Continued 243 RIC–0543 33.874722 –80.702778 188 188 186 186 184 184 182 181 163 –104 –128

—

— –323

—

— –369

244 RIC–0585 33.948889 –80.840833 329

—

—

—

—

—

—

— 319 42 9 —

— –110

—

— –136

245 RIC–0613 34.111944 –80.884722 424 422 421 420 419 417 417 415 414 278 256

—

— 188

—

— 179

246 SUM–0296 33.710556 –80.532222 170

—

—

—

—

—

— 144 87 –355 –391

—

— –600

—

— –810

247 SUM–0328 34.033611 –80.456667 375 374 373 372 371 370 369 307 261 –6 –33

—

— –216

—

— –321

248 SUM–0340 33.990278 –80.358889 142 141 140 139 138 137 136 135 134 –122 –130

—

— –366

—

— –462

249 SUM–0347 33.841389 –80.264722 145

—

—

—

—

—

—

— 102 –315 –365

—

— –548

—

— –745

250 WIL–0176 33.731111 –79.462222 39

—

—

—

—

—

—

— –11 –461 –496 –661 –796 –881 –1111

— –1321

251 WIL–0208 33.583611 –79.870833 74

—

—

—

—

—

— 63 –31 –556 –594 –826 –941 –1066 –1276

— –1456

252 WIL–0211 33.681667 –79.557222 49

—

—

—

—

—

—

— 14 –521 –561 –756 –853 –946 –1201

— –1401

253 WIL–0213 33.772778 –79.448056 51

—

—

—

—

—

—

— 26 –399 –414 –569 –739 –844 –1049

— –1249

Eastern Georgia

254 24V001 32.702500 –82.717222 355

— 255 180 100 20 –70 –180 –220 –685 –730

—

— –1050

—

— –1450

255 24X005 32.955000 –82.638888 374

— 244

— 174 104 69 –101 –126

— –326

—

— –521

—

— –721

256 25T002 32.386944 –82.542778 350 300 100 –50 –170 –350 –400 –580 –790 –1341 –1481 –1800 –1850 –1961 –2021

— –2681

257 28X001 32.875555 –82.220833 268 208 148 98 43 –22 –62

— –261 –582 –601

—

— –961

—

— –1231

258 GA-LI-OT-1 31.691944 –81.348333 25 –25 –375 –625 –725 –875

— –1725 –2125 –2675

— –2975

— –3295 –3455

— –4239

259 34U001 32.585000 –81.427222 129 79 –21 –131 –231 –331 –521 –676 –811 –1321 –1351 –1651 –1821 –2101 –2291

— –2545

260 32Y019 33.064722 –81.720833 249

— 145 56 39 5 –76 –232 –283 –601 –635

—

— –941

—

— –1126

261 30Z017 33.230000 –81.878889 244

— 197

— 162

— 88 –3 –50 –246 –256

—

— –508

—

— –608

262 33X048 32.890278 –81.595278 109 89 75 –91 –119 –223 –256 –461 –540 –941 –983

— –1231 –1303

—

— –1591

263 33R045 32.131944 –81.611660 84 –27 –243 –393 –516 –637 –966 –1191 –1416 –2066

— –2216 –2366 –2666 –2766

— –3416

264 34S011 32.295277 –81.396666 79 –7 –198 –321 –446 –542 –871 –1121 –1321 –1971

— –2121 –2271 –2571 –2721

— –3251

265 Pooler Well 32.116944 –81.221944 19 –81 –281 –481 –581 –731 –1381 –1561 –1721 –2131

— –2381

— –2661 –2861

— –3781

266 Renken well 32.170277 –82.332500 219 169 –81 –281 –431 –631 –781 –1091 –1241 –1931 –2141 –2381 –2431 –2601 –2711

— –3444

267 35P109 31.911944 –81.316389 9 –91 –320 –551 –626 –795

— –1641 –1991 –2341

— –2591

— –2891 –3091

— –3941

Southern Virginia

268 50F 1 37.165278 –77.510000 189

—

—

—

—

—

—

—

—

—

—

—

—

—

—

— 134

269 51B 3 36.685830 –77.385280 123 110 56

—

—

—

—

—

—

—

—

— 22

—

— 10 –130

270 51D 1 36.943330 –77.399170 75

— 65

—

—

—

—

—

—

—

—

—

—

—

— 21 –33

271 51F 7 37.169720 –77.396110 170 140 110

—

—

—

—

—

—

—

—

— 88

—

— 52 6

272 51G 1 37.279167 –77.410000 56

—

—

—

—

—

—

—

—

—

—

—

—

—

—

— 6

273 51G 3 37.345560 –77.377780 180

—

— 83

— 33

—

—

—

—

—

— 12

—

— 2 –155

274 52E 2 37.083610 –77.362220 140

—

—

—

— 130

—

—

—

—

—

—

—

—

— 95 –250

275 52F 1 37.221111 –77.290000 131

—

—

—

—

—

—

—

—

—

—

—

—

—

—

— –39
Appendix B1 155

Appendix B1. Aquifer and confining unit top surface altitudes interpreted from borehole geophysical logs, cores, and other data in the Coastal Plain of North Carolina, South Carolina, eastern Georgia, and southern Virginia.—Continued[Borehole locations are on figure B3; borehole numbers in bold are coreholes; —, not present]

Borehole 

location 

on 

figure B3

Borehole 

number

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Top surface altitude, in feet

Land 

surface/ 

top of 

surficial 

aquifer

Yorktown/

Upper 

Floridan 

confining 

unit

Yorktown/ 

Upper 

Floridan 

aquifer

Castle 

Hayne/

Pungo 

River/ 

Middle 

Floridan 

confining 

unit

Castle 

Hayne/ 

Pungo 

River/ 

Middle 

Floridan 

aquifer

Beaufort/ 

Gordon 

confining 

unit

Beaufort/

Gordon 

aquifer

Peedee/

Crouch 

Branch 

confining 

unit

Peedee/ 

Crouch 

Branch 

aquifer

Black 

Creek/ 

McQueen 

Branch 

confining 

unit

Black 

Creek/ 

McQueen 

Branch 

aquifer

Upper 

Cape 

Fear/ 

Charleston 

confining 

unit

Upper 

Cape 

Fear/ 

Charleston 

aquifer

Lower 

Cape 

Fear/

Gramling 

confining 

unit

Lower 

Cape 

Fear/ 

Gramling 

aquifer

Lower 

Cretaceous 

aquifer

Basement 

rock

Southern Virginia—Continued

276 52F 7 37.192500 –77.351110 142 — 112 — — — — — — — — — 68 — — 22 –110277 53A 6 36.516670 –77.240560 120 59 34 — — — — — — — — — 6 — — –64 –400278 53A 4 36.584720 –77.204170 39 26 18 1 — — — — — — — — — –34 — –74 –411279 53C 1 36.772780 –77.174440 105 — 45 15 — — –20 — — — — — –49 — — –57 –500280 53D 3 36.978610 –77.150560 100 85 66 30 — 16 3 — — — — — –6 — — –20 –444281 53D 4 36.925000 –77.177780 90 — 52 20 — — 2 — — — — — –5 — — –38 –426282 53G 15 37.334170 –77.190000 17 — — — — –20 –36 — — — — — –91 — — –133 –300283 54A 3 36.589170 –77.110000 100 — 26 6 — — –2 — — — — –12 –20 –31 — –48 –500284 54C 2 36.819720 –77.066940 115 85 39 –7 — –25 –32 — — — — — –38 — — –59 –750285 54D 1 36.979170 –77.005830 110 78 58 –5 — –31 –50 — — — — — –98 — — –112 –620286 54G 10 37.332220 –77.097780 35 — — 15 –23 –49 –95 — — — — — –135 — — –142 –565287 55B 59 36.646111 –76.894444 20 — — — –70 –78 –88 — — — — –112 –116 –168 — –284 –1000288 55C 12 36.768056 –76.888333 15 — — — –69 –83 –109 — — — — — — –121 — –210 –1000289 55D 5 36.904167 –76.888889 90 69 32 9 –69 –79 –125 — — — — — –142 — — –158 –1000290 55E 1 37.045833 –76.935000 108 80 46 –2 –66 –73 –95 — — — — — –149 — — –202 –1250291 55F 20 37.222500 –76.951667 90 70 55 –24 –58 –80 –113 — — — — — –178 — — –205 –800292 56A 10 SOW 36.562500 –76.783889 45 — — –93 –104 –120 –136 — — — — –152 –229 –250 — –407 –1000293 56F 42 37.142222 –76.840833 110 75 60 14 –82 –123 –202 — — — — — –241 — — –256 –1000294 57B 2 36.704444 –76.687778 73 — –19 –41 –147 –201 –232 — — — — — — –252 — –384 –1000295 57C 32 36.806297 –76.743878 81 33 –45 –66 –135 –155 –203 — — — — — — –226 — –277 –1000296 57D 20 36.875556 –76.682222 50 40 –59 –100 –141 –203 –239 — — — — — –260 — — –290 –1250297 57E 10 SOW 37.043333 –76.716389 85 — 14 –37 –152 –175 –215 — — — — — –261 — — –268 –1250298 57F 4 VEP 37.165556 –76.699167 36 — — –29 –159 –194 –265 — — — — — –290 — — –339 –1300299 58A 2 SOW 36.568889 –76.583333 56 38 24 –103 –217 –249 –273 — — — — –286 –414 –440 — –576 –1874300 58A 76 SOW 36.615278 –76.555556 33 15 7 –133 –253 –275 –292 — — — — –305 –389 –417 — –580 –1750301 58B 12 36.734167 –76.553056 20 — — –92 –248 –274 –323 — — — — — — –335 — –461 –1750302 58C 7 36.810556 –76.619167 40 — –47 –86 –180 –236 –291 — — — — — — –310 — –356 –1500303 58D 6 36.994167 –76.558333 22 — –45 –121 –191 –269 –322 — — — — — –346 — — –361 –1500304 59C 13 36.871667 –76.463056 16 –1 –42 –194 –330 –344 –360 — — — — — — –383 — –492 –1750305 60B 20 36.690833 –76.342778 16 –24 –34 –150 –421 –435 –458 — — — — –476 –505 –569 — –734 –2250306 60C 7 36.854167 –76.321389 10 — — –127 –430 –448 –453 — — — — — — –472 — –649 –2250307 61A 12 36.598144 –76.208575 13 3 –28 –119 –531 –549 –587 –603 –696 — — –783 –791 –840 — –1012 –2750308 61B 11 36.707500 –76.129722 15 –59 –73 –177 –612 –638 –651 –673 –740 — — –776 –793 –848 — –1053 –2750309 63C 1 36.866667 –75.980833 20 –26 –36 –106 –837 –862 –866 — — — — –888 –897 –932 — –1096 –3000
156 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Appendix B2. Core description of ORG-393 (#68, section I–I′, Plate 7 ). 

Core was described by David C. Prowell of the U.S. Geological Survey. Depths are reported in feet below land surface.

See Plate 7 for a graphic lithology column. Colors are from the Rock-Color Chart, which uses the Munsell color system. 

Charts are distributed by the Geological Society of America, P.O. Box 9140, Boulder, CO 80301.

ORG-393 Depth (ft)

Surficial Aquifer

(Unnamed Quaternary unit)

Clayey sand, moderate yellowish brown (10-YR-5/4) (Schoeneberger and others, 2002) and moderate reddish 

brown (10R4/6) to moderate reddish orange (10-R-6/6), fine to very coarse quartz sand in a 20 to 40 percent clay 

matrix, poorly sorted; trace gravel (up to 20 mm); trace feldspar; local iron staining; poorly bedded with some 

evidence of cross beds (15 to 20 degrees) in clay- and silt-rich beds; poorly consolidated .................................................. 0–21.6

(Unnamed Oligocene unit)

Clayey sand, dark yellowish orange (10-YR-6/8), very fine to medium quartz sand and beds of fine to very 

coarse quartz sand in a 5 to 25 percent clay matrix, moderately to poorly sorted; 2 to 3 percent mica; trace 

feldspar; mottled texture; crudely bedded in fining-upwards sequence; poorly consolidated .......................................... 21.6–40.5

Silty clay, dark gray (N-3) with common dark yellowish orange staining (10-YR-6/6), very fine to fine quartz sand 

and silt in a 50 to 70 percent clay matrix, well sorted; 1 to 2 percent mica; trace pyrite as concretions and trace 

lignite/carbon clasts; thinly laminated beds; poorly consolidated .................................................................................... 40.5–49.4

Middle Floridan Aquifer

(Santee Formation, clastic phase)

Clayey sand, dark yellowish orange (10-YR-6/6), fine to coarse quartz sand near top of interval and very fine to 

fine sand near base, 5 to 25 percent clay matrix, moderately to well sorted; 1 to 2 percent mica; local blebs of 

carbon/manganese; local very thin clay stringers; crudely bedded with hint of cross bedding; poorly consolidated ...... 49.4–65.0

(Santee Formation, carbonate phase)

Marl, pale olive (10-Y-6/2), very fine to fine quartz sand and clay in a calcium carbonate matrix, well sorted; 

1 to 2 percent glauconite and phosphate(?); sparse silicified shells .................................................................................. 65.0–66.3

Limestone, yellowish gray (5-Y-7/2); impure limestone with 5 to 10 percent quartz sand, 5 to 10 percent shell 

fragments, and 5 percent clay, poorly to moderately sorted; sparse mollusk(?) shells extend across core diameter; 

local iron oxidation; weakly indurated except for local 0.5 ft beds of purer calcium carbonate ...................................... 66.3–76.0

Marl, greenish gray (5-G-6/1) and yellowish gray (5-Y-7/2), very fine to fine quartz sand and silt (10 to 20 percent) 

in a calcareous clay matrix (80 to 90 percent); 1 to 2 percent mica; sparse phosphate and shell fragments; 

trace glauconite; well-bedded ............................................................................................................................................ 76.0–82.5

Limestone, yellowish gray (5-Y-8/1) to white (N-9), impure limestone with 5 to 10 percent quartz sand and 

20 to 30 percent shell fragments, poorly sorted; local calcium carbonate cemented beds (0.3 to 0.5 ft), otherwise 

sediment is broken into coarse granules; shells consist of mollusks, pelecypods, bryozoans, and unidentified 

microfossils; fragmented texture ....................................................................................................................................... 82.5–91.5

Gordon Confining Unit

(Santee Formation, carbonate phase)

Marl, grayish olive green (5-GY-3/2), light olive gray (5-Y-5/2) and greenish gray (5GY-6/1), very fine to fine 

quartz sand (40 percent), clay (35 percent), and shell fragments (20 percent) in a calcareous matrix; megafossils 

are bivalves, gastropods, and bryozoans; sparse bone fragments and shark teeth; trace lignite, glauconite, and phosphate; 

phosphate especially abundant from 146 to 153 ft; large brown bivalves common from 153 to 158 ft; generally moderately 

to well-cemented with calcium carbonate; local hard layers (0.3 to 0.4 ft) of calcium carbonate; common burrows; 

well-bedded with thin laminations in clayey zones ........................................................................................................ 91.5–158.0
Appendix B2 157

Phosphatic marl, marl as described above but with a significant increase in phosphate and glauconite; phosphate 

and glauconite increase with depth composing 50 to 60 percent of the core towards the base of the interval ............ 158.0–177.4

(Warley Hill Formation)

Marl, olive gray (5-Y-3/2), fine to very coarse quartz sand and silt in a 60 to 70 percent clay matrix; 

weak reaction with hydrochloric acid; 5 to 30 percent glauconite; common very fine carbonaceous matter; 

sparse shell fragments; well laminated; well compacted .............................................................................................. 177.4–186.5

Clayey sand, olive gray (5-Y-3/2), fine to very coarse quartz sand in a 20 to 30 percent clay matrix, poorly sorted; 

5 to 10 percent glauconite; sparse gravel (3 to 4 mm); trace blue quartz and carbonaceous matter; massive ............. 186.5–189.5

(Congaree Formation)

Silty clay, grayish green (10-GY-5/2), very fine to fine quartz sand and silt in a 60 percent clay matrix, well sorted; 

2 to 4 percent mica; 1 to 2 percent glauconite; well laminated ..................................................................................... 189.5–194.3

Gordon Aquifer

(Congaree Formation)

Clayey sand, olive gray (5-Y-3/2), fine to coarse quartz sand in a 10 to 20 percent clay matrix, moderately sorted; 

sparse gravel (2 to 3 mm); trace glauconite; weak reaction with hydrochloric acid; massive ..................................... 194.3–208.0

Laminated sand and clay, dark greenish gray (5-GY-4/1) to light olive gray (5-Y-5/2), fine to very coarse quartz sand 

and gravel in a 5 percent clay matrix, poorly sorted; trace garnet, blue quartz, monazite and rutilated quartz; trace lignite 

and carbonaceous clay; thinly laminated cross-bedded clay and fine sand beds; loose to moderately compact .......... 208.0–212.5

Interbedded sand and clay, same as described above but thickly bedded ..................................................................... 212.5–228.0

Laminated sand and clay, same as described above but thinly bedded ......................................................................... 228.0–229.8

Clayey sand, light olive gray (5-Y-5/2), fine to very coarse quartz sand and gravel in 5 percent clay matrix (grain size 

coarsens with depth), poorly sorted; trace garnet, blue quartz, monazite, rutilated quartz, and glauconite; common 

lignite/carbonaceous clay; thinly laminated cross-bedded clay and fine sand beds; loose to moderately compact ..... 229.8–272.7

Crouch Branch Confining Unit

(Rhems Formation)

Laminated sand and clay, grayish black (N-2), very carbonaceous clay with 10 percent silt, locally interbedded 

with 1 to 4 mm thick, fine to very fine quartz sand, well sorted; common lignite and mica; low-angle cross beds 

locally coated with fine lignite; local pyritized roots/tubes and pyrite-cemented sand clasts; well laminated ............ 272.7–298.2

Crouch Branch Aquifer

(Sawdust Landing Formation)

Clayey sand, light blue (5-B-7/6) to greenish gray (5-G-6/1), fine to very coarse quartz sand in a 10 to 20 percent 

dense clay matrix, poorly sorted; 1 to 2 percent mica; trace feldspar, rutilated quartz, garnet, and monazite; 

common granular pyrite; very dense and massive ........................................................................................................ 298.2–308.0

Clayey sand, same as described above except occurring as fining-upwards sequences of very coarse to 

fine sand and lacking the dense clay matrix .................................................................................................................. 308.0–323.3

(upper Steel Creek unit)

Sandy clay, light gray (N-8), fine to coarse quartz sand (20 to 50 percent) in a dense clay matrix (50 to 80 percent); 

2 to 4 percent mica; trace rutilated quartz; slightly carbonaceous; evidence of carbonized roots and 

desiccation cracks; dense and indurated ....................................................................................................................... 323.3–330.0

Clayey sand, very light gray (N-8) with grayish orange (10-YR-7/4) staining, similar to that described above 

except with 70 to 80 percent sand in a stiff clay matrix, very poorly sorted; 5 to 7 percent mica; local gravel 

(up to 3 mm); grain size coarsens with depth; dense and indurated ............................................................................. 330.0–348.0
158 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Sand, very light gray (N-8), fine to coarse quartz sand in a 0 to 5 percent clay matrix, poorly sorted; 

grain size coarsens with depth; 2 to 4 percent mica and locally very micaceous with some grains up to 3 mm; 

lower 7 feet of interval contains common gravel (up to 5 mm) and white clay balls (up to 8 mm); 

trace monazite and lignite; low-angle cross beds in thin layers; poorly consolidated .................................................. 348.0–365.2

Interbedded sand and clay, similar to that described above except with alternating beds of sand and 

carbonaceous clay; sand beds are light gray (N-7) and are 0.2 to 5 feet thick, and clay beds are medium 

dark gray (N-4) and are 0.1 to 0.5 feet thick; the interval is predominately sand; poorly consolidated ....................... 365.2–398.0

(middle Steel Creek unit)

Interbedded sand and clay, similar to that described above except that sand beds are thinner (0.2 to 3 feet thick) 

and carbonaceous clay seams are increasingly present in the sand beds; lignite and pyrite also increase in 

this interval; poorly consolidated .......................................................................................................................................398.0–423.0

Clayey sand, light olive gray (5-Y-6/1), fine to very coarse quartz sand in a 5 to 10 percent clay matrix, 

poorly sorted; trace pyrite and lignite clasts; trace gravel; poorly consolidated ........................................................... 423.0–433.5

Sand, olive gray (5-Y-4/1), fine to medium quartz sand in a 5 to 10 percent clay matrix, moderately to well sorted; 

local gravel (up to 2 mm); trace lignite and pyritized lignite; possible burrows; massive; poorly consolidated ......... 433.5–444.7

Clayey sand, dark gray (N-3), very fine to fine quartz sand with many 20 mm flattened clay clasts; 5 percent mica; 

very unique; possible lag bed ........................................................................................................................................ 444.7–446.0

(lower Peedee unit)

Laminated sand and clay, sand layers are grayish green (5 GY-6/1) and clay layers are dark gray (N-3), 

very fine to fine quartz sand laminated with thin (2 to 10 mm) beds of micaceous carbonaceous clay 

(up to 20 percent); 5 to 8 percent mica; trace lignite; well laminated .......................................................................... 446.0–449.5

Sand, light gray (N-7), fine to very coarse quartz sand in a 0 to 5 percent clay matrix, poorly sorted; 

1 to 3 percent mica; trace lignite and pyritized lignite; trace rutilated quartz; massive texture ................................... 449.5–455.0

Laminated sand and clay, light olive gray (5-Y-6/1), very fine to fine quartz sand laminated with micaceous 

and carbonaceous clay, well sorted; 4 to 5 percent mica; trace glauconite and pyrite; sparse lignite fragments 

(up to 15 mm); well laminated with 3 to 8 mm clay layers separated by 20 to 50 mm sand layers ............................. 455.0–457.5

Glauconitic sand, light olive gray (5-Y-6/1), fine to very coarse quartz sand in a 0 to 5 percent clay matrix, poorly 

sorted; 1 to 3 percent mica; trace glauconite; local lignitic fragments (up to 3 mm) and pyritized lignite; 

possible in-situ weathered feldspars and/or white clay blebs; massive texture; poorly consolidated .......................... 457.5–468.0

(upper Donoho Creek unit)

Interbedded sand and clay, sand layers are light olive gray (5-Y-6/1) and clay layers are dark gray (N-3), very 

fine to fine quartz sand laminated with thin layers of carbonaceous clay, well sorted; some sand beds consist of 

fine to very coarse sand; 5 to 8percent mica; trace pyrite; well laminated with 3 to 5 mm clay layers and 

10 to 30 mm sand layers ............................................................................................................................................... 468.0–513.8

McQueen Branch Confining Unit

(upper Donoho Creek unit)

Silty clay, dark greenish gray (5-GY-4/1), very fine to fine quartz sand and silt in a 30 to 40 percent clay matrix, 

well sorted; 2 to 5 percent mica; trace glauconite, pyrite, lignite, and phosphate; common burrows; 

locally numerous bivalve molds/casts; well laminated ................................................................................................. 513.8–553.3

Lag bed, light olive gray (5-Y-5/2), calcareous sand lag bed, fine to coarse quartz sand in a 10 to 30 percent clay 

matrix, poorly sorted; weakly cemented with calcium carbonate; 1 to 2 percent mica; 1 percent granular phosphate 

(up to 6 mm); 1 percent very coarse sand; sparse carbonaceous clay clasts (up to 30 mm); common bivalve 

fragments; sparse shark teeth and bone fragments; massive texture; well indurated ................................................... 553.3–557.2

(middle Donoho Creek unit)

Marl, olive gray (5-Y-3/2) to olive black (5-Y-2/1), plastic carbonaceous clay to marl with 5 percent silt, well sorted; 

2 to 4 percent mica; weak reaction with hydrochloric acid; common bivalve shells (some preserved in mother-of-pearl); 

unidentified fossil fragments; very fossiliferous in lower part of interval; well laminated; well compacted ............... 557.2–568.0
Appendix B2 159

Sandy marl, olive gray (5-Y-3/2), very fine to fine quartz sand and silt in a 20 to 30 percent calcareous 

clay matrix, well sorted; 4 to 5 percent mica; trace glauconite/chlorite; common bivalve fragments and 

complete shells; evidence of local heavy bioturbation, otherwise, alternating 10–20 mm beds of calcareous 

sand and calcareous silty clay below 572.5 feet ........................................................................................................... 568.0–587.5

Marl, sand beds are dark grayish green (5-GY-4/1) and clayey marl beds are dark gray (N-3), very fine to fine 

calcareous sand interbedded with beds of clayey marl, well sorted; individual beds are 0.5 to 2.0 feet thick; 

2 to 4 percent mica; 1 percent glauconite; abundant megafossil shells (mostly bivalves); sand beds are 

massive and bioturbated; clayey marl beds are well laminated .................................................................................... 587.5–599.2

Lag bed, olive gray (5-Y-4/1), calcareous lag bed, fine to coarse quartz sand in a 10 to 30 percent clay matrix cemented 

with calcium carbonate, poorly sorted; 2 to 3 percent mica; 1 percent phosphate grains (up to 7 mm); trace 

glauconite; cemented sand clasts (up to 20 mm); common shell fragments (mostly bivalves); chaotic texture, 

especially in lower 4 feet .....................................................................................................................................................599.2–606.0

(Bladen Formation)

Sand, olive gray (5-Y-3/2), fine to medium quartz sand, well to moderately sorted; 2 to 4 percent mica; trace 

glauconite and rutilated quartz; extremely lignitic from 610 to 611 feet; local thin carbonaceous clayey 

layers (1 to 2 mm); well bedded with low-angle cross beds ......................................................................................... 606.0–611.0

Marl, olive gray (5-Y-3/2), very fine to fine quartz sand (10 percent) in a sticky calcareous clay/marl, well sorted; 

5 to 10 percent mica; 5 percent pyritized leaves/wood; common bivalve shells and shell fragments; possible 

bone fragments; increasing calcium carbonate cementation with depth; poorly laminated with shell fragments; 

well indurated towards bottom of interval .................................................................................................................... 611.0–623.0

Shelly limestone, light olive gray (5-Y-5/2), bivalve-rich bed cemented with calcium carbonate, well indurated ...... 623.0–625.4

Marl, olive gray (5-Y-3/2), very fine to fine quartz sand (10 percent) in a sticky calcareous clay/marl, well sorted; 

5 to 10 percent mica; 5 percent pyritized leaves/wood; common bivalve shells and shell fragments; possible 

bone fragments; poorly laminated with shell fragments; well indurated ...................................................................... 625.4–632.5

Shelly limestone, olive gray (5-Y-4/1), bivalve-rich bed cemented with calcium carbonate, well indurated............... 632.5–639.1

Marl, same as marl described above ............................................................................................................................. 639.1–642.0

Shelly limestone, same as shelly limestone described above ....................................................................................... 642.0–645.8

Marl, same as marl described above ............................................................................................................................. 645.8–651.0

Shelly limestone, same as shelly limestone described above ....................................................................................... 651.0–659.2

Marl, same as marl described above ............................................................................................................................. 659.2–669.8

(Coachman Formation)

Laminated sand and clay, light gray (N-7) to dark gray (N-3), very fine to fine sand in a 10 to 15 percent carbonaceous 

clay matrix, well sorted; 3 to 4 percent mica; trace glauconite/chlorite; trace very fine lignite; numerous lignite 

fragments (up to 60 mm) replaced by pyrite; abundant pyritized wood; no calcareous sediments or fossils 

(as seen in overlying section of core); thinly laminated with carbonaceous clay ......................................................... 669.8–692.9

McQueen Branch Aquifer

(Coachman Formation)

Clayey sand, very light gray (N-8) to light gray (N-7), fine to very coarse quartz sand in a 10 to 15 percent 

clay matrix, poorly sorted; 2 to 3 percent mica; trace monazite and rutilated quartz; local lignite fragments 

(up to 70 mm) that are partially replaced by pyrite; 1 percent gravel (up to 8 mm) in thin (0.3 to 0.5 ft) beds; 

evidence of cross beds; poorly consolidated ................................................................................................................. 692.9–711.2

(Cane Acre Formation)

Sandy clay, medium light gray (N-6), fine to coarse quartz sand (10 to 20 percent) in a dense waxy clay 

(70 to 80 percent); 2 to 4 percent mica; 1 percent lignite fragments (up to 50 mm); well bedded ............................... 711.2–716.0
160 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Clayey sand, medium gray (N-5), fine to very coarse quartz sand in a 5 to 10 percent clay matrix, moderately 

to poorly sorted; 5 percent very fine lignite; 2 percent mica; 1 percent gravel (up to 4 mm); 1 percent 

pyritized wood; large (up to 40 mm) lignite fragments; low-angle cross beds ............................................................. 716.0–724.2

Clay, light gray (N-7) to light olive gray (5-Y-6/1) with pale red (5-R-6/2) staining, dense, waxy clay containing 

5 to 10 percent fine to very coarse quartz sand; 2 to 5 percent mica; trace rutilated quartz and monazite; 

evidence of backfilled roots/mud cracks; evidence of slickensides and desiccation cracks ......................................... 724.2–741.0

Clayey sand, light gray (N-7) to medium gray (N-5) and olive gray (5-Y-4/1), fine to very coarse quartz sand in 

2 to 25percent clay matrix, poorly sorted; 1 to 2 percent gravel; 2 percent mica; 1 percent rutilated quartz and 

monazite; trace feldspar and lignite; massive to well bedded; poorly consolidated near top of interval but dense 

and well indurated below 748 feet ................................................................................................................................ 741.0–764.7

Sandy clay, olive gray (5-Y-4/1), very fine to fine quartz sand (20 percent) in a dense clay matrix (80 percent), 

well sorted; 2 to 3 percent mica; crudely bedded with evidence of roots/fractures; common carbonaceous matter .... 764.7–774.2

Sand, light olive gray (5-Y-6/1), fine to very coarse quartz sand in a 1 to 5 percent clay matrix, poorly sorted; 

1 percent gravel; 1 percent rutilated quartz; trace lignite; local thin (30 mm) carbonaceous clay layers; 

massive, poorly consolidated ........................................................................................................................................ 774.2–808.0

Sandy clay, brownish black (5-YR-2/1), fine to coarse quartz sand (20 percent) in a clay matrix (70 percent), 

poorly sorted; 8 percent lignite fragments (up to 20 mm); 2 percent mica; weak bedding; compact .......................... 808.0–809.5

Sand, sand is light olive gray (5-Y-6/1) to medium gray (N-5) and clay is grayish black (N-2), fine to very coarse 

quartz sand in a 5-percent clay matrix, poorly sorted; trace rutilated quartz and monazite; local lignite fragments 

(up to 20 mm); thick (0.5 ft) carbonaceous clay beds; hint of cross bedding; poorly consolidated ............................. 809.5–851.3

Silty clay, dark gray (N-3), very fine to fine quartz sand and silt (15 percent) in carbonaceous clay matrix 

(85 percent), well sorted; sand occurs in thin (1 to 3 mm) layers; 3 to 4 percent mica; 2 to 3 percent lignite; 

1 percent pyritized wood and granular pyrite; well laminated with slightly inclined bedding; compact ..................... 851.3–859.5

Sand, light olive gray (5-Y-6/1) to medium gray (N-5), fine to very coarse quartz sand in a 5 percent clay matrix, 

poorly sorted; 1 to 2 percent mica; trace rutilated and yellow quartz; abundant lignite and pyritized lignite 

from 865 to 867 feet; lignite fragments up to 50 mm; weakly bedded ......................................................................... 859.5–894.5

(Cape Fear Formation)

Sandy clay, very light gray (N-8), medium to very coarse quartz sand (20 to 30 percent) in a dense clay matrix 

(65 to 70 percent), poorly sorted; trace gravel (up to 2 mm); 1 to 2 percent mica; trace rutilated quartz and 

feldspar; evidence of backfilled roots/fractures; very compact .................................................................................... 894.5–900.0

Sand, olive gray (5-Y-4/1), fine to very coarse quartz sand in a 5 to 15 percent clay matrix, poorly sorted; 

trace rutilated quartz and lignite; trace gravel (up to 3 mm); moderately to poorly consolidated ................................ 900.0–908.0

Sandy gravel, olive gray (5-Y-4/1), same as described above but with 10 to 15 percent gravel (up to 5 mm) ............ 908.0–910.0

Sand, light olive gray (5-Y-6/1), fine to very coarse quartz sand in a 5 percent clay matrix, poorly sorted; 

1 percent mica; trace rutilated quartz and lignite; sparse gravel; massive texture with only faint signs of 

cross bedding; sand gets coarser with depth; poorly consolidated ............................................................................... 910.0–922.0

Clayey sand, light olive gray (5-Y-6/1), fine to very coarse quartz sand in a 5 to 10 percent clay matrix, poorly 

sorted; 2 to 4 percent mica; trace feldspar, rutilated quartz, and lignite; local pyritized nodules (up to 15 mm); 

grain size increases with depth; very dense and indurated ........................................................................................... 922.0–933.0

Sandy gravel, light olive gray (5-Y-6/1), same as described above except with 10 to 15 percent gravel 

(up to 15 mm) and an increase in feldspar (2 percent) ................................................................................................. 933.0–936.2

Clayey sand, light olive gray (5-Y-6/1) to olive gray (5-Y-4/1), fine to very coarse quartz sand in a dense clay matrix, 

poorly sorted; interval is a clayey sand grading downwards to sand and gravel (fining-upwards sequence); 

2 to 3 percent mica; 2 percent gravel (10 mm quartz and 6 mm feldspar) in basal 0.5 feet; 1 percent feldspar; 

trace rutilated quartz; very poorly bedded; very dense and indurated .......................................................................... 936.2–939.5

Sandy gravel, very light gray (N-8) to medium gray (N-5), same as describe above except basal gravel 

is 6 mm quartz and 3 mm feldspar ................................................................................................................................ 939.5–943.2
Appendix B2 161

Clayey sand, very light gray (N-8), fine to very coarse quartz sand in a dense clay matrix, poorly sorted; 

interval is a clayey sand grading downwards to very coarse sand and gravel (fining-upwards sequence); 

evidence of rooting or filled fractures at top of interval; 2 to 3 percent mica; 2 percent gravel; 

1 percent feldspar; trace rutilated quartz; very poorly bedded; dense and indurated ................................................... 943.2–955.8

Sandy gravel, light olive gray (5-Y-6/1) with local dark yellowish orange (10-YR-6/6) iron staining, fine to very coarse 

quartz sand in a 5 to 10 percent clay matrix, poorly sorted; 5 to 10 percent gravel (quartz grains up to 15 mm and 

feldspar grains up to 14 mm); 2 to 5 percent mica; 1 percent feldspar; massive texture; dense and well indurated .... 955.8–968.5

Clayey sand, light olive gray (5-Y-6/1), fine to medium quartz sand, moderately sorted; 2 to 4 percent mica; 

1 percent feldspar; trace rutilated quartz; massive texture; dense and well indurated.................................................. 968.5–970.5

Sandy gravel, medium light gray (N-6), fine to very coarse quartz sand and gravel, poorly sorted; gravel 

10 to 15 percent; 2 to 4 percent mica; 1 percent feldspar; trace rutilated quartz; faint evidence of cross bedding; 

dense and well indurated ......................................................................................................................................................970.5–977.0

Gramling Confining Unit

(Cape Fear Formation)

Sandy gravel, greenish gray (5-GY-6/1), fine to coarse quartz sand and gravel in a 5 to 10 percent clay matrix, 

moderately sorted; 3 to 4 percent mica; 1 percent feldspar (up to 8 mm); trace rutilated quartz; well indurated 

by silica(?) cement .......................................................................................................................................................... 977.0–998.5

Silty clay, greenish gray (5-GY-6/1) with moderate red (5-R-5/4) and dark yellowish orange (10-YR-6/6) staining, 

silt (10 percent) in a crumbly, dry clay matrix, well sorted; 4 to 10 percent mica; extensive iron staining; 

well laminated; slickensided fractures; root structures; dense and compact .............................................................. 998.5–1000.0

Clayey sand, olive gray (5-Y-4/1), fine to very coarse quartz sand in a 5 to 10 percent clay matrix, poorly sorted; 

5 to 10 percent mica (local 0.1 ft beds are 40 to 50 percent mica); 1 percent gravel (up to 12 mm); 

1 percent feldspar; well indurated and dense ............................................................................................................ 1000.0–1003.0

Sandy clay, grayish green (10-GY-5/2) with dark yellowish orange (10-YR-6/6) staining, fine to medium 

quartz sand in a 5 to 10 percent clay matrix, moderately sorted; grading downwards to fine to very coarse sand 

and gravel; 5 to 10 percent mica (local 0.1 ft beds are 40 to 50 percent mica); gravel up to 12 mm (quartz) 

and 4 mm (feldspar); local iron staining; massive and well indurated ..................................................................... 1003.0–1006.0

Sandy gravel, olive gray (5-Y-4/1), fine to very coarse quartz sand in a 5 to 10 percent clay matrix, poorly sorted; 

1 percent gravel (up to 12 mm); 5 to 10 percent mica (local thin beds contain 20 to 25 percent very coarse mica); 

trace rutilated and yellow quartz; massive texture; well indurated ........................................................................... 1006.0–1011.5

Sandy clay, brownish black (5-YR-2/1) to brownish gray (5-YR-4/1), fine to medium quartz sand (40 percent) 

in a waxy, carbonaceous clay matrix (60 percent), moderately sorted; 4 to 6 percent mica; 1 percent feldspar; 

trace rutilated quartz; evidence of clay-filled roots/fractures; well laminated .......................................................... 1011.5–1013.5

Sandy gravel, medium gray (N-5) to olive gray (5-Y-4/1) with moderate yellowish brown (10-YR-5/4) staining, 

fine to very coarse quartz sand and gravel, poorly sorted; 1 percent feldspar; trace rutilated quartz; gravel up to 

15 mm as rutilated quartz, 8 mm as smoky quartz, and 5 mm as feldspar; local iron staining; crude bedding ........ 1013.5–1023.4

Sandy clay, grayish green (10-GY-5/2), fine to medium quartz sand (35 percent) in a clay matrix (60 percent), 

well sorted; 1 to 2 percent mica; 1 percent feldspar; trace rutilated quartz; well laminated .................................... 1023.4–1025.0

Sandy gravel, grayish green (10-GY-5/2), fine to very coarse quartz sand and gravel in a clay matrix 5 to 15 percent 

clay matrix, poorly sorted; gravel up to 25 mm as quartz and 6 mm as feldspar; 1 to 2 percent mica; 

1 percent feldspar; trace rutilated quartz; massive to crudely bedded ...................................................................... 1025.0–1031.8

Clayey sand, light olive gray (5-Y-6/1), fine to very coarse quartz sand in a 5 to 10 percent clay matrix, 

poorly sorted; 5 to 10 percent mica (up to 8 mm); 1 percent gravel (up to 7 mm as rutilated quartz and 

up to 25 mm as smoky quartz); massive to poorly bedded; indurated ...................................................................... 1031.8–1034.0

Sandy gravel, light olive gray (5-Y-6/1) to grayish green (10-GY-5/2), fine to very coarse quartz sand and gravel, 

poorly sorted; 10 percent gravel (up to 30 mm as smoky quartz, 19 mm as rutilated quartz, 16 mm as white quartz, 

and 3 mm as feldspar); sparse slate-belt foliated quartz/rock pebbles; 1 to 2 percent mica; 1 percent feldspar; common 

clay clasts in lower 5 feet; trace garnet and lignite (up to 30 mm); weakly bedded; compact/cemented ................. 1034.0–1055.5
162 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Clayey sand, greenish gray (5-G-5/2), fine to coarse quartz sand in a clay matrix, poorly sorted; 2 to 3 percent 

mica; trace blue quartz, rutilated quartz, garnet, and feldspar; massive; semi-consolidated to well indurated ........ 1055.5–1058.0

Sandy gravel, greenish gray (5-G-5/2), fine to very coarse quartz sand and gravel, poorly sorted; gravel up to 8 mm 

as smoky quartz, 10 mm as slate belt quartz/rock pebbles, and 3 mm as feldspar; 2 to 3 percent mica; trace blue 

quartz, rutilated quartz, garnet, and feldspar; massive; semi-consolidated to well indurated .................................. 1058.0–1064.7

Clayey sand, grayish green (10-GY-5/2), fine to coarse quartz sand in a 25 to 30 percent clay matrix, 

poorly sorted; 3 to 4 percent mica; 1 percent feldspar; well indurated ..................................................................... 1064.7–1067.0

Sandy gravel, grayish green (10-GY-5/2), fine to very coarse quartz sand and gravel, poorly sorted; gravel up 

to 30 mm as smoky quartz, 20 mm as rutilated quartz, and 6 mm as feldspar; 3 to 4 percent mica; 1 percent 

feldspar; massive texture; well indurated ................................................................................................................. 1067.0–1073.0

Sandy clay, light olive gray (5-Y-6/1) with local dark yellowish orange (10-YR-6/6) iron staining, fine to 

medium quartz sand in a 10 to 20 percent clay matrix, well sorted; 2 to 3 percent mica; 1 percent feldspar; 

trace garnet; faint bedding disrupted by backfilled burrows/roots; bedding appears undulatory and 

local iron staining is present; well indurated ............................................................................................................ 1073.0–1074.9

Sandy gravel, grayish green (5-G-5/2) with local dark yellowish orange (10-YR-6/6) iron staining, fine to very 

coarse quartz sand and gravel, poorly sorted; gravel up to 7 mm as smoky quartz and 5 mm as feldspar; 

2 to 3 percent mica; 1 percent feldspar; trace garnet; massive texture; well indurated ............................................ 1074.9–1078.0

Sandy clay, light olive gray (5-Y-6/1) with local dark yellowish orange (10-YR-6/6) iron staining, fine to 

medium quartz sand in a 10 to 20 percent clay matrix, well sorted; faint bedding disrupted by 

backfilled burrow/roots; well indurated .................................................................................................................... 1078.0–1080.5

Sandy gravel, grayish green (5-G-5/2), fine to very coarse quartz sand and gravel, poorly sorted; 

common feldspar; local metamorphic rock fragments and clay clasts; mottled; massive to crudely 

bedded; poorly consolidated to indurated .................................................................................................................... 1080.5-1116.5

Piedmont Hydrogeologic Province

(Redbeds)

Sandstone, moderate reddish brown (10-R-4/6) mottled with light greenish gray (5-G-8/1), mudstone to 

pebbly mudstone to conglomeratic sandstone, very poorly sorted; highly fractured; slickensided surfaces; 

pebbles are quartz, feldspar, and a variety of metamorphic rock fragments; conglomeratic in lower 6 feet; 

massive to crudely bedded; indurated ........................................................................................................................1116.5–1138.0
Introduction

A three-dimensional, groundwater flow model of the 

Atlantic Coastal Plain (ACP) aquifers and confining units was 

developed, calibrated and is documented in this chapter. The 

hydrologic system of the Coastal Plain of North Carolina (NC) 

and South Carolina (SC) and parts of Georgia (GA) and Virginia (VA) was evaluated in order to update and combine two 

existing groundwater models that simulate groundwater flow 

and water use in the aquifers of the study area. Revision of the 

models was deemed necessary because additional hydraulic, 

geologic, water-level, and water-use data are available for use 

in model calibration, and hydrogeologic inconsistencies at the 

NC–SC border have been reconciled since the development of 

the previous models. 

The new model simulates groundwater flow at regional 

and intermediate spatial scales superimposed on a transient 

time scale from 1900 to 2004. Documented herein are the 

(1) development of a transient, three-dimensional groundwater 

flow model; (2) model calibration process and results; and 

(3) model limitations and future challenges. The modeling 

tool developed as part of this study can be used to evaluate 

groundwater availability within the study area by examining 

the effects of both human and climatic temporal changes on 

the groundwater budget components. An additional benefit of 

the transient, calibrated, three-dimensional numerical model 

is the ability to use the model to forecast system response to 

these same effects, thus providing insights into the longer-term 

sustainability of the system.

Model Development

The groundwater flow model of the ACP aquifers and 

confining units was constructed in several phases (fig. C1). 

The first phase required the preparation of a revised and 

updated hydrostratigraphic framework that combined separate frameworks from NC and SC. This effort is documented 

in Chapter B of this report. The study area has a relatively 

complex geologic structure that is dominated by arches and 

embayments and required the use of numerous hydrostratigraphic data (figs. C2, C3; table C1). The study area was subdivided into model cells of 4 square miles (mi2

) with 16 layers, 

and the simulation time from 1900 to 2004 was discretized 

into 29 stress periods. After the initial model was constructed, 

it was calibrated primarily by using automated parameter 

estimation techniques (Doherty, 2005). The following sections 

describe the model, the calibration process, and the simulation 

results in detail.

Simulation of Groundwater Flow

The USGS groundwater flow model, MODFLOW-2000 

(Harbaugh and others, 2000), was used to simulate the 

groundwater flow within the NC and SC Coastal Plain. The 

MODFLOW-2000 model simulates single-density groundwater flow in three dimensions by using a block-centered, 

finite-difference method. Groundwater sources and sinks were 

represented using the RIV package for rivers (McDonald and 

Harbaugh, 1983), the WEL package for wells (McDonald and 

Harbaugh, 1983), the RCH package for recharge (McDonald 

and Harbaugh, 1983), and the CHD package for specified 

heads (McDonald and Harbaugh, 1988). Groundwater flow 

was represented by using the LPF package, and the flow equations were solved by using the GMG package (Harbaugh and 

others, 2000). The NC–SC Coastal Plain model was calibrated 

using PEST (Doherty, 2005) from predevelopment to recent 

(2004) conditions using automated-parameter estimation of 

aquifer and confining unit hydraulic conductivity, specific 

storage, and anisotropy. Recharge and riverbed conductance 

were calibrated only during the initial steady-state stress 

period. The model was calibrated to reported groundwater 

levels and stream baseflows. Sensitivity analysis was performed on the parameters of hydraulic conductivity, specific 

storage, and anisotropy and the boundary conditions of 

recharge and head-dependent boundaries.

Chapter C. Simulation of Groundwater Flow in the 

Atlantic Coastal Plain, North and South Carolina and 

Parts of Georgia and Virginia, Predevelopment to 2004

By Alissa L. Coes, Bruce G. Campbell, Matthew D. Petkewich, and Jason M. Fine
164 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C1. Location of the Atlantic Coastal Plain in North and South Carolina and parts of Virginia and Georgia.

Albemarle

Sound

Pamlico

Sound

Atlantic

Ocean

Fall

Line

Study area. Dashed where

 approximately located

EXPLANATION

Horry

Aiken

Wake

Burke

Pitt Hyde

Berkeley

Bladen

Pender

Nash

Robeson

Sampson

Duplin

Colleton

Onslow

Columbus

Laurens

Bertie

Orangeburg

Jasper

Sumter

Kershaw

Long

Florence

Johnston

Emanuel

Bulloch

Hoke

Moore

Cumberland

Richland

Jones

Screven

Brunswick

Bryan

Harnett

Lexington

Sussex

Hampton

Craven

Clarendon

Martin Dare

Gates

Barnwell

Washington

Dillon

Lenoir

Beaufort

Wilson

Wayne Greene

Suffolk

Dinwiddie

Edgecombe

Halifax

Bamberg

Hertford

Williamsburg

Chesterfield

Toombs

Marlboro

Charleston

Tattnall

Carteret

Dorchester

Darlington

Lee

Tyrrell Washing- ton

Southampton

Effingham

McIntosh

Northampton

Jenkins Wilkinson

Pamlico

Allendale

Johnson

Scotland

Evans

Candler

Chesapeake

Chowan

Greensville

Treutlen

Isle of

Wight

Currituck

Camden

Perquimans

Pasquotank

Virginia

Beach

Glascock

New

Hanover

CHARLES

BRADFORD

Prince

George

Lee

Surry

Chesterfield

Marion

Georgetown

Calhoun

Beaufort

Jefferson

Richmond

Baldwin

Montgomery

Chatham

Liberty

Richmond

CHARLES

BRADFORD

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

West

Virginia

Kentucky

Tennessee

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

York R.

James

River

Chowan

Roanoke

River

River

Tar

River

Neuse

River

River

Cape

Fear

River

River

Peedee

River Santee

River

Black

Lumber

R.

Catawba

Wateree

River

River

Broad

Saluda

Savannah

Edisto

Ogeechee

Altamaha

Salkehatchie

Coosawhatchie

Congaree

River

R.

River

River

River

R.

R.

R.

Figure C1. The Atlantic Coastal Plain along the Atlantic Coast of North and South Carolina and 

 parts of northern Florida, Georgia, Virginia, and Maryland.
Simulation of Groundwater Flow 165

Figure C2. Locations of natural characteristics within distinct areas of the Atlantic Coastal Plain Physiographic Province, with a focus 

on the study area in North and South Carolina, southeastern Virginia, and eastern Georgia.

Norfolk

Arch

Unnamed

Arch

Cape Fear

Arch

Gulf

Trough

Albemarle

Embayment

Albemarle

Sound

Southeast Georgia

Embayment

CHARLES

BRADFORD

Hilton

Head

Mount

Pleasant

Charleston

Savannah

Andrews

Myrtle

Wilmington

Cherry

Point

Aiken Beach

Columbia

Florence

Sumter

Fall

Line

Goldsboro

Greenville

Virginia Beach

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Blue Ridge/Ridge and Valley

Piedmont

Sand Hills

Inner Coastal Plain

Outer Coastal Plain

Study area. Dashed where

 approximately located

Streamgage and index number (see table C5)

Raingage and index number (see table C3)

EXPLANATION

PHYSIOGRAPHIC PROVINCES

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Figure C2. Locations of natural characteristics within distinct areas of the Atlantic Coastal Plain Physiographic

 Province, with a focus on the study area in North and South Carolina, southeastern Virginia, and eastern

 Georgia.

5

1

4

6

6

2

1

3

5

9

2

8

10

3

4

7

1

2
166 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Spatial Discretization

The model boundary encompasses 143,000 mi2, of 

which about 56 percent is actively simulated. The regular grid 

consists of 130 rows and 275 columns of 4-mi2 cells; a maximum of 20,106 cells are active per model layer (fig. C4). The 

longest axis is oriented 43 degrees north of east.

The tops and extents of all aquifers and confining units, 

except for the surficial aquifer, were determined by using 

hydrostratigraphic data from 309 boreholes (figs. B2, B5–B36; 

Harrelson and Fine, 2006). The top of the surficial aquifer 

was created by using the mean altitude of the 30-meter (m) 

National Elevation Dataset (NED; U.S. Geological Survey, 

1999) within each model cell. The land-surface altitude at 

each borehole also was determined from 30-m NEDs. The 

hydrologic-unit tops were interpolated between the boreholes 

and extrapolated to the unit extents and offshore where data do 

not exist. Each hydrologic unit was defined as a single model 

layer, producing 16 layers (table C1). Each model layer was 

defined to have a nominal thickness of at least 2 feet (ft). In 

areas where aquifers or confining units are in reality absent, 

the cells in that nominal thickness were assigned the same 

hydraulic properties as the underlying hydrologic unit. Most 

model layers, therefore, actually contain the majority of a 

single hydrologic unit plus thin layers of overlying hydrologic 

units. Model layers had maximum thicknesses that ranged 

from 116 to 5,004 ft (table C2).

Temporal Discretization

The model simulates groundwater flow from predevelopment (before 1900) to 2004 using 29 stress periods. The 

first stress period represents conditions before 1900 using the 

steady-state approximation. Pumping for each of the following stress periods was as follows: eight 10-year stress periods 

representing 1900–1979; five 2-year stress periods representing 1980–1989; and fifteen 1-year stress periods representing 

1990–2004. Two time steps were used in each stress period.

Bedrock

Aquifer

Confining unit

Regional groundwater flow

Surface-water flow

Groundwater flow due to well

EXPLANATION

Figure C3. Generalized cross section of the aquifers and 

confining units of the Atlantic Coastal Plain of North and 

South Carolina, 2007.
Simulation of Groundwater Flow 167

Table C1. Model layers in relation to Atlantic Coastal Plain hydrogeologic units in North Carolina, South Carolina, eastern Georgia, and 

southern Virginia.

[N/A , not applicable]

Model 

layer Virginia1 North Carolina2 South Carolina3 Georgia4

1 Surficial Surficial Surficial Surficial

2 Yorktown confining unit Yorktown confining unit Upper Floridan confining unit Upper Three Runs aquifer

3 Yorktown aquifer Yorktown aquifer Upper Floridan aquifer

4 Saint Marys confining unit Pungo River confining unit Middle Floridan confining unit

Pungo River aquifer

Castle Hayne confining unit

5 Saint Marys aquifer Castle Hayne aquifer Middle Floridan aquifer

Calvert confining unit

Piney Point aquifer

6 Nanjemoy–Marlboro 

confining unit

Beaufort confining unit Gordon confining unit Gordon confining unit 

7 Aquia aquifer Beaufort aquifer Gordon aquifer Gordon aquifer 

Millers Pond confining unit

Millers Pond aquifer

8 Peedee confining unit Peedee confining unit Crouch Branch confining unit Upper Dublin confining unit

9 Peedee aquifer Peedee aquifer Crouch Branch aquifer Upper Dublin aquifer

Lower Dublin confining unit

Lower Dublin aquifer

10 N/A Black Creek confining unit McQueen Branch confining unit Upper Midville confining unit

11 N/A Black Creek aquifer McQueen Branch aquifer Upper Midville aquifer

Lower Midville confining unit

Lower Midville aquifer

12 Virginia Beach confining unit Upper Cape Fear confining unit Charleston confining unit N/A

13 Virginia Beach aquifer Upper Cape Fear aquifer Charleston aquifer N/A

14 Potomac confining unit Lower Cape Fear confining unit Gramling confining unit Basal confining unit

15 N/A Lower Cape Fear aquifer Gramling aquifer N/A

16 N/A Lower Cretaceous confining unit N/A N/A

Lower Cretaceous aquifer

1

 McFarland and Bruce, 2006.

2

 Winner and Coble, 1996.

3 Chapter B, this report.

4

 Cherry, 2006.

Table C2. Median and maximum model-layer thicknesses in the Atlantic 

Coastal Plain model simulating groundwater flow, predevelopment to 2004, 

in North and South Carolina and parts of Virginia and Georgia.

Model layer Median thickness, in feet Maximum thickness, in feet

1 35 213

2 9 255

3 10 311

4 14 726

5 18 257

6 15 116

7 35 353

8 43 364

9 309 690

10 49 249

11 130 432

12 88 463

13 142 624

14 130 815

15 281 1,058

16 2,736 5,004
168 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C4. Atlantic Coastal Plain groundwater model grid showing boundary conditions in layer 1, which represents the 

surficial aquifer.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Recharge cells

Specified-head cells (top layer only)

River cells

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Figure C4. Atlantic Coastal Plain groundwater model grid showing boundary conditions in layer 1, which represents the

surficial aquifer.
Simulation of Groundwater Flow 169

Boundary Conditions

Most of model layer 1 is a specified-head boundary in 

areas where the surficial aquifer is underlain by confining units 

(fig. C4). For regional models, the shallow water-table surface 

is often used as a source/sink boundary condition because the 

model grid scale precludes simulation of the water-table aquifer. This approach is appropriate when the water-table surface 

is relatively stationary. Because water-table surface maps are 

not readily available, the altitude of the water table used in 

model cells is estimated by a two-step process. First, a regression equation is developed using existing land and water-table 

altitudes from wells in the area. This equation is then used to 

predict the water-table surface for each model cell using mean 

land-surface altitudes available from Digital Elevation Models 

(DEM) (Kuniansky and others, 2009). For this study, 81 wells 

in NC with water-level measurements collected from 1942 to 

1980 were used to develop a regression for estimation of the 

water table prior to groundwater development. Error in the 

data used for the regression results from data collected at different times and the inability to use long-term average water 

levels during predevelopment. However, the temporal error 

is probably less than 7 ft for any given measurement based 

on the variations in water levels of the long-term monitoring 

wells. Additionally, these data are historical, and the locations 

of many of the wells were obtained by hand plotting the well 

on a 1:24,000-scale topographic map. The error in the landsurface altitude of these wells is generally considered to be 

less than 5 ft (half of the contour interval of the topographic 

map). The best-fit linear regression was achieved by estimating the water-table altitude from the land-surface altitude, with 

a coefficient of determination (R2) of 0.996, indicating that 

the linear regression explains 99.6 percent of the variation in 

water-table altitude. The linear regression equation is: 

WTalt = 0.9365(Lalt) – 2.403, (1)

where WTalt is the predicted water-table altitude and Lalt is the 

land-surface altitude at the well (units are in feet). All altitudes are referenced to the National Geodetic Vertical Datum 

of 1929 (NGVD 29). The root mean square error (standard 

error of the estimate) is 7.4 ft. Attempts to develop regressions for estimation of the water-table depth using depth to 

water from land-surface altitudes or log transforms of these 

data were abandoned after obtaining R2 values of 0.5 and less, 

which indicated a poor relation. Land-surface altitudes of the 

81 wells ranged from 3 to 600 ft NGVD 29. The majority of 

the data points represent land-surface altitudes less than 210 ft, 

with only five values greater than 210 ft. The regression equation is best used for estimating the water-table altitude over 

the lower ACP where land-surface altitude is less than 300 ft 

and greater than 3 ft. Additionally, once the mean land-surface 

altitude for a cell was less than 2.44 ft, the water-table altitude 

was set to 0 ft rather than using the regression equation, so that 

no water-table altitudes were set to negative values.

In an area of the inner Coastal Plain (fig. A1), model 

layer 1 contains active model cells, and recharge was defined 

for layer 1 in this area where the hydrogeologic units crop out 

near the Fall Line (fig. C2). The bottom altitude of model layer 

16 was set at the top of bedrock and was simulated as a noflow boundary. The depth to the top of bedrock was based on 

lithologic data from boreholes (Harrelson and Fine, 2006).

The northwest (updip) boundaries of all layers were 

simulated as no-flow boundaries and are located along the Fall 

Line (fig. C4). The southeast (downdip) termini of all model 

layers also were simulated with no-flow boundaries. These 

no-flow boundaries are located near the approximate location 

of the freshwater-saltwater divide. The onshore divide was 

defined where the chloride concentration of the groundwater 

reached 10,000 milligrams per liter (mg/L; Lee and others, 

1986; Aucott, 1996; Giese and others, 1997; Lautier, 1998, 

2001, 2006). The location of the offshore divide was not 

known and was defined to be at such a distance from the coast 

line as to not introduce boundary effects. The northeast and 

southwest boundaries were simulated as specified-head boundaries in layer 1 at the James River in Virginia to the northeast 

and the Altamaha River in Georgia to the southwest (fig. C1), 

and along groundwater flow paths in layers 2 through 16.

Recharge

Recharge was specified in the area east of where the 

hydrogeologic units crop out along the Fall Line (fig. C4) 

and where the land-surface altitudes are the highest in the 

study area. Recharge was considered spatially uniform across 

the area where recharge was applied. The recharge rate has 

a high degree of uncertainty associated with it; recharge 

was, therefore, adjusted during calibration within acceptable 

bounds during the initial steady-state stress period, producing 

a steady-state calibrated value of 0.0004 foot per day (ft/d) 

or 1.75 inches per year (in/yr). In the transient stress periods, 

recharge was varied temporally based on historical precipitation data from six stations in the inner Coastal Plain (table C3; 

figs. C2, C5). The percentage difference between the precipitation for each time step and the calibrated steady-state recharge 

value of 0.0004 ft/d was used to determine whether recharge 

during the time step should increase or decrease and by how 

much. Recharge was varied from a minimum of 0.000249 ft/d 

(1.09 in/yr) in time step 26 (2001) to a maximum of 

0.000541 ft/d (2.37 in/yr) in time step 23 (1998, fig. C6).

Groundwater Use

Water-use data from 1900 to 2004 for 3,957 wells as 

reported by State regulatory agencies (N.C. Wilson, North 

Carolina Department of Water Resources, oral commun., 

2005; South Carolina Department of Health and Environmental Control, written commun., 2007) and in previous model 

investigations (Aucott, 1988, 1996; Giese and others, 1997), 
170 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Table C3. Descriptions of precipitation stations in part of the Atlantic Coastal Plain in South Carolina and Georgia.

[NOAA, National Oceanic and Atmospheric Administration; ft NAVD 88, in feet relative to North American Vertical Datum of 1988]

NOAA station 

number

Station 

location

Map index 

number 

(see fig. C2 )

Altitude, 

in ft 

NAVD 88

Period 

of record

Annual mean 

precipitation, 

in inches

Annual maximum 

precipitation, 

in inches

Annual minimum 

precipitation, 

in inches

095882 Millen, GA 1 195 1882–2004 46.21 74.67 28.92

380074 Aiken, SC 2 400 1854–2004 47.11 71.36 22.38

380764 Blackville, SC 3 324 1884–2004 47.32 75.1 27.85

381310 Camden, SC 4 140 1849–2004 47.27 83.41 27.16

381588 Cheraw, SC 5 140 1882–2004 47.30 67.93 29.72

381944 Columbia, SC 6 242 1872–2004 43.92 74.49 27.11

Figure C5. Continuous precipitation data from precipitation stations in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia.

were used in this investigation (figs. C7, C8A–G). Only 

withdrawals greater than 3 million gallons per month were 

included in the model because smaller withdrawals are not 

required to be reported to the State agencies and, therefore, 

generally are unknown. Pumpage from domestic wells is not 

reported to the State agencies and was not included in the 

withdrawal volumes. Pumpage from domestic wells in the 

NC–SC Coastal Plain, however, is primarily from the surficial 

aquifer and is not applicable because layer 1 mostly has a 

specified head as the upper boundary. In some cases, pumpage 

for multiple wells was reported by agencies as a single rate; in 

these instances, the reported rate was subdivided over several 

wells. Most well records did not have an aquifer designated 

as the specific one from which pumping occurred. For all 

wells, the pumpage was attributed to the model layer or layers 

within which the tops and bottoms of the screened intervals 

were located. Wells screened in more than one layer had the 

pumpage divided equally between the multiple aquifer layers. 

Overall, recent water-use data are considered to be more accurate than historical water-use data.

Prior to 1900, no major pumping occurred from the 

NC–SC ACP aquifers. Withdrawals from the deep, confined 

aquifers began in 1879 in Charleston, SC, but the volumes 

were relatively small. Increased groundwater withdrawals 

from the ACP aquifers began in the 1940s from the Yorktown 

and Upper Floridan aquifers (model layer 3, table C1). Withdrawals from all of the aquifers generally have increased from 

1900 to 2004.

Map index number

(See fig. C2)

1

2

3

4

5

6

90

80

70

60

50

40

30

20

0.0006

0.0005

0.0004

0.0003

0.0002

0.0001

0

1900

Figure C5. Continuous precipitation data from precipitation stations in the Atlantic Coastal Plain of

 North and South Carolina and parts of Virginia and Georgia.

1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

PRECIPITATION, IN INCHES PER YEAR

RECHARGE, IN FEET PER DAY

–1900) 1

–1909) 2

–1919) 3

–1929) 4

–1939) 5

–1949) 6

–1959) 7

–1969) 8

–1979) 9

1981) 10

1983) 11

1985) 12

1987) 13

1989) 14

1990) 15

1991) 16

1992) 17

1993) 18

1994) 19

1995) 20

1996) 21

1997) 22

1998) 23

1999) 24

2000) 25

2001) 26

2002) 27

2003) 28

2004) 29
Simulation of Groundwater Flow 171

Figure C6. Simulated recharge by model stress period for hydrogeologic units in the Atlantic Coastal Plain of 

North and South Carolina and parts of Virginia and Georgia.

Figure C7. Groundwater use by model layer for wells in in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia. 

0.0006

0.0005

0.0004

0.0003

0.0002

0.0001

0

1900

Figure C5. Continuous precipitation data from precipitation stations in the Atlantic Coastal Plain of

 North and South Carolina and parts of Virginia and Georgia.

Figure C6. Simulated recharge by model stress period for hydrogeologic units in the Atlantic Coastal Plain

 of North and South Carolina and parts of Virginia and Georgia.

1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

RECHARGE, IN FEET PER DAY

(pre–1900) 1

(1900–1909) 2

(1910–1919) 3

(1920–1929) 4

(1930–1939) 5

(1940–1949) 6

(1950–1959) 7

(1960–1969) 8

(1970–1979) 9

(1980–1981) 10

(1982–1983) 11

(1984–1985) 12

(1986–1987) 13

(1988–1989) 14

(1990) 15

(1991) 16

(1992) 17

(1993) 18

(1994) 19

(1995) 20

(1996) 21

(1997) 22

(1998) 23

(1999) 24

(2000) 25

(2001) 26

(2002) 27

(2003) 28

(2004) 29

STRESS PERIOD (YEAR)

600

500

400

300

200

100

0

Figure C7. Groundwater use by model layer in the Atlantic Coastal Plain of North and South Carolina and parts

 of Virginia and Georgia.

WATER USE, IN MILLION GALLONS PER DAY

pre–1900 

1900–1909

1910–1919

1920–1929

1930–1939

1940–1949

1950–1959

1960--1969 

1970–1979

1980–1981

1982–1983

1984–1985

1986–1987

1988–1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Layer 3

Layer 5

Layer 7

Layer 9

Layer 11

Layer 13

Layer 15
172 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C8A. Locations of water-use wells and 2004 withdrawal amounts from the Yorktown aquifer (North Carolina) and the Upper 

Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Yorktown aquifer (NC) and

 Upper Floridan aquifer (SC). Dashed

 where approximately located.

Water-use well, in million

 gallons per day

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Less than 0.1

0.1 to 0.49

0.5 to 0.99

1.0 to 1.99

Greater than 2.0

Yorktown 

aquifer

Upper Floridan

aquifer

Figure C8A. Locations of water-use wells and 2004 withdrawal amounts from the Yorktown aquifer (North Carolina)

 and the Upper Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia.
Simulation of Groundwater Flow 173

Figure C8B. Locations of water-use wells and 2004 withdrawal amounts from the Castle Hayne aquifer (North Carolina) and the Middle 

Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Castle Hayne aquifer (NC) and

 Middle Floridan aquifer (SC). Dashed

 where approximately located.

Water-use well, in million

 gallons per day

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Less than 0.1

0.1 to 0.49

0.5 to 0.99

Castle Hayne 

aquifer

Middle Floridan

aquifer

Figure C8B. Locations of water-use wells and 2004 withdrawal amounts from the Castle Hayne aquifer (North Carolina)

 and the Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.
174 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C8C. Locations of water-use wells and 2004 withdrawal amounts from the Beaufort aquifer (North Carolina) and the Gordon 

aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Beaufort aquifer (NC) and

 Gordon aquifer (SC). Dashed

 where approximately located.

Water-use well, in million

 gallons per day

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Less than 0.1

Beaufort 

aquifer

Gordon

aquifer

Figure C8C. Locations of water-use wells and 2004 withdrawal amounts from the Beaufort aquifer (North Carolina)

 and the Gordon aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.
Simulation of Groundwater Flow 175

Figure C8D. Locations of water-use wells and 2004 withdrawal amounts from the Peedee aquifer (North Carolina) and Crouch Branch 

aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Less than 0.1

0.1 to 0.49

0.5 to 0.99

1.0 to 1.99

Peedee/Crouch

Branch

aquifer

Figure C8D. Locations of water-use wells and 2004 withdrawal amounts from the Peedee aquifer (North Carolina)

 and Crouch Branch aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Extent of Peedee aquifer (NC) and

 Crouch Branch aquifer (SC).

 Dashed where approximately located.

Water-use well, in million

 gallons per day
176 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C8E. Locations of water-use wells and 2004 withdrawal amounts from the Black Creek aquifer (North Carolina) and McQueen 

Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Black Creek aquifer (NC) and

 McQueen Branch aquifer (SC).

 Dashed where approximately located.

Water-use well, in million

 gallons per day

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Less than 0.1

0.1 to 0.4999

0.5 to 0.9999

1.0 to 1.9999

Greater than 2.0

Black Creek/McQueen

Branch aquifer

Figure C8E . Locations of water-use wells and 2004 withdrawal amounts from the Black Creek aquifer (North Carolina)

 and McQueen Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.
Simulation of Groundwater Flow 177

Figure C8F. Locations of water-use wells and 2004 withdrawal amounts from the Upper Cape Fear aquifer (North Carolina) and the 

Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Upper Cape Fear aquifer (NC)

 and Charleston aquifer (SC).

 Dashed where approximately located.

Water-use well, in million

 gallons per day

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Less than 0.1

0.1 to 0.49

1.0 to 1.99

Upper Cape Fear/

Charleston

aquifer

Figure C8F. Locations of water-use wells and 2004 withdrawal amounts from the Upper Cape Fear aquifer (North Carolina)

 and the Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.
178 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C8G. Locations of water-use wells and 2004 withdrawal amounts from the Lower Cape Fear aquifer (North Carolina) and 

the Gramling aquifer (South Carolina) (layer 15) , in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and 

Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Lower Cape Fear aquifer (NC)

 and Gramling aquifer (SC).

 Dashed where approximately located.

Water-use well, in million

 gallons per day

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Less than 0.1

0.1 to 0.49

1.0 to 1.99

Lower Cape Fear/

Gramling

aquifer

Figure C8G. Locations of water-use wells and 2004 withdrawal amounts from the Lower Cape Fear aquifer

 (North Carolina) and the Gramling aquifer (South Carolina) (layer 15) , in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.
Simulation of Groundwater Flow 179

Hydraulic Properties Used in Model Calibration

Initial horizontal hydraulic conductivity values for all 

aquifers were derived from published transmissivity data 

(table C4; Aucott and Newcome, 1986; Newcome, 1993, 

2000; Harrelson and Fine, 2006; Dorothy Payne, U.S. Geological Survey, written commun., December 2006; Michael Peck, 

U.S. Geological Survey, written commun., December 2006). 

Horizontal hydraulic conductivities for all aquifers, except the 

surficial aquifer, were adjusted during model calibration. Horizontal hydraulic conductivities were calculated by dividing the 

published transmissivity value at a well by either the thickness 

of the aquifer, if known, or the total length of the well screen 

if aquifer thickness was not known. Calculated hydraulic 

conductivities were not used if the resultant value was not 

representative of the typical hydraulic conductivity range 

for the type of aquifer being simulated. Horizontal hydraulic 

conductivity of the aquifer units is the best defined property 

in the model, and aquifer-test results used in this model are 

estimated to have an uncertainty factor of approximately one 

order of magnitude (Eve Kuniansky, U.S. Geological Survey, 

oral commun., December 2006). In general, more aquifer-test 

data are available for the shallow aquifers; therefore, they are 

better characterized than the deeper aquifers.

Specific storage values for the confined aquifers initially 

were derived from published storage coefficient data (Aucott 

and Newcome, 1986; Newcome, 1993, 2000) and adjusted 

during model calibration. Specific storage values were calculated in a similar manner to the hydraulic conductivity values 

using the reported storage coefficient and aquifer thickness, or 

screen length if thickness was unknown. Calculated specific 

storage values were not used if the resultant value was not 

representative of the typical storativity range for the type of 

aquifer being simulated. Uncertainty associated with the values of specific storage comes from several sources, including 

the aquifer test data-collection techniques, the data-analysis 

methodology, and the aquifer thickness at the aquifer test 

wells. Fetter (1988) indicates that values of specific storage are 

generally very small, 0.0001 ft–1 or less. 

No hydraulic property data were available for horizontal 

hydraulic conductivity of the confining units, specific storage 

of the confining units, specific yield of the surficial aquifer, 

and vertical anisotropy (defined as the ratio of horizontal 

hydraulic conductivity to vertical hydraulic conductivity) of 

the aquifers or confining units. Therefore, these inputs were 

calibrated during the simulation process. The initial values for 

these properties were set within the range of reasonable values 

for the aquifers and confining units. Fetter (1988) indicates 

that clay units typically will have a hydraulic conductivity 

ranging between 0.000003 and 0.003 ft/d. 

Observations Used in Model Calibration

Groundwater level and river baseflow observations were 

compiled for use in the model calibration and are available 

in the USGS National Water Information System (NWIS) 

database (U.S. Geological Survey, 2005). Groundwater levels 

from prior to 1980 were used to develop the predevelopment 

steady-state hydraulic-head observations, and groundwater 

levels from 1980 and 2004 were used to develop the transient hydraulic-head observations. Historical river baseflow 

data from streamgages were used to develop groundwater 

discharge observations.

Table C4. Ranges of reported aquifer transmissivity, and calculated and simulated hydraulic conductivities for the aquifers in the 

Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia.

[ft2/d, feet squared per day; ft/d, feet per day; —, data not available]

Aquifer Model 

layer

Reported transmissivity1, in ft2/d Horizontal hydraulic conductivity, in ft/d

Minimum Maximum Mean

Calculated Simulated

Minimum Maximum Minimum Maximum

Surficial and Upper Three Runs 1 20 15,000 1,300 11.8 — 216 216

Yorktown and Upper Floridan 3 2.0 530,000 20,000 4.00 1,340 2.0 1,150

Pungo River, Castle Hayne, and 

Middle Floridan

5 190 530,000 18,000 1.00 169 2.0 262

Beaufort and Gordon 7 10 21,000 3,200 2.10 1,340 0.8 169

Peedee and Crouch Branch 9 49 27,000 2,400 3.00 223 0.8 177

Black Creek and McQueen Branch 11 49 34,000 2,800 2.00 303 0.8 175

Upper Cape Fear and Charleston 13 130 31,000 5,300 1.00 102 0.5 129

Lower Cape Fear and Gramling 15 10 6,000 1,600 1.00 45.8 1.4 64.0

1

 Aucott and Newcome, 1986; Newcome, 1993; Newcome, 2000; Dorothy Payne and Michael Peck, U.S. Geological Survey, written commun., 2006; 

Harrelson and Fine, 2006.

Note: The calculated and simulated hydraulic conductivities were derived from a subset of the reported transmissivities; therefore, the minimum and 

maximum hydraulic conductivity values may not correlate to the minimum and maximum reported transmissivities for each layer. 
180 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Groundwater Levels

Observed groundwater level data for the NC and SC 

Coastal Plain were used for calibration of the flow model 

(fig. C9A–G). Minimal water-level data were available for the 

predevelopment period prior to 1900; therefore, water-level 

data collected prior to 1980 were used to develop hydraulichead observations for the steady-state calibration. Previous investigators considered groundwater pumping to have 

minimally affected pre-1980 regional water levels in the ACP 

(Aucott and Speiran, 1985). Predevelopment, steady-state 

head observations were derived at 1,073 wells. Head observations were obtained from 453 wells for the 1980 calibration 

and 738 wells for the 2004 calibration. Overall, the hydraulichead observations in each layer cover the known extent of 

each unit and generally are distributed evenly, with the exceptions of the southern portion of NC in the Beaufort/Gordon 

aquifers (layer 7, fig. C9C), the southern portion of SC in the 

Black Creek/McQueen Branch aquifer (layer 11, fig. C9E), 

and most of the Lower Cape Fear/Gramling aquifer (layer 15, 

fig. C9G). No head data were available for the Lower Cretaceous aquifer (layer 16). Continuous groundwater level observations over multiple years from individual wells were used to 

depict changes in groundwater levels over time.

The largest source of error associated with the groundwater level data is the location of the well and land-surface 

altitude at the well site. The locations for most of the wells 

(70 percent) that were used for calibration purposes were 

interpolated from topographic maps and therefore may have 

substantial error. Approximately 14 percent of the well site 

locations were determined by global positioning system equipment. It was unknown how 10 percent of the locations of the 

well sites were determined, and the remainder of the well locations were determined by using other means such as surveying 

techniques. To normalize all of the water-level observations, 

all of the well locations were used in an interpolation process 

using USGS DEMs to determine the land-surface altitude. 

The vertical accuracy of the DEM used was 49.21 ft (15 m) or 

less (M.A. Lowery, U.S. Geological Survey, written commun., 

2008) and was generally derived from USGS topographic 

maps with 10- or 20-ft contour intervals. Therefore, because 

of the uncertainty associated with the source of most of the 

land-surface data for the wells, the largest contour interval 

in the mapped study area, or 20 ft, was selected as one of the 

water-level calibration targets. That is, one of the primary 

goals of the calibration process was to match the observed 

groundwater levels within plus or minus 20 ft. Also, another 

calibration target was employed that uses the standard deviation of the water-level residuals (the observed subtracted from 

the calculated value) divided by the range in data (Kuniansky 

and others, 2004). This value is dimensionless and ideally 

should be less than 1.0. This statistic takes into account the 

range of water-level data. A good fit to the observed water 

levels would be approximately 0.1 (dimensionless), which was 

also a calibration target.

River Baseflow

River baseflows calculated for 10 USGS streamgaging 

sites on 8 rivers in the inner Coastal Plain and Sand Hills were 

used as observations of groundwater discharge for model 

calibration (fig. C2; table C5). Daily streamflow data from 

selected sites were used with the USGS computer program 

PART (Rutledge, 1998) to estimate the groundwater discharge 

component of the overall streamflow. The program PART 

uses linear interpolation to estimate groundwater discharge 

during periods of surface-water runoff based on antecedent 

streamflow recession. Streamgaging sites in the Sand Hills 

and southern part of the inner ACP were exclusively used in 

the baseflow analysis because streams in this area are well 

connected to the aquifers that are present. Streamgaging sites 

in the northern part of the inner Coastal Plain were not used in 

the baseflow analysis because streams in this area are not well 

connected to the underlying confined aquifers.

The accuracy of the daily streamflow records depends 

primarily on (1) the stability of the stage-streamflow relations 

or, if the control is unstable, the frequency of streamflow measurements; and (2) the accuracy of the observations of stage, 

measurements of streamflow, and interpretation of records 

(Cooney and others, 2003). A rating of the daily streamflow 

data is determined and is included in the USGS records for 

each station. These ratings are “excellent,” which means that 

95 percent of the daily streamflow data are within 5 percent 

of the true streamflow; “good” ratings are within 10 percent; 

“fair” ratings are within 15 percent; and “poor” ratings categorize daily streamflow data that have less than “fair” accuracy. 

Data from streamgages selected for inclusion in the model 

calibration are all from relatively small basins (generally less 

than 200 mi2) in the inner Coastal Plain. These inner Coastal 

Plain streams have unstable sandbeds that tend to shift over 

time or from high-flow events and, therefore, result in “poor” 

ratings. Thus, it is assumed that all of the streamflow data used 

in the model calibration are rated “poor,” and the accuracy 

of the groundwater discharge data is essentially unknown. A 

calibration target of 15 percent of observed streamflow was set 

for the discharge data. 

Streambed conductance was calibrated during the initial 

steady-state stress period. The mean streambed conductance 

values ranged from a low of 1.9 square feet per day per foot 

[(ft2/d)/ft] to a high of 80 (ft2/d)/ft (table C5).

Model Calibration

The NC–SC Coastal Plain model was calibrated to 

groundwater level and stream baseflow conditions from 

1900 to 2004 using 29 stress periods. The first stress period 

represents conditions before 1900 and assumes steady-state 

conditions (no pumping from the ACP aquifers). The first 

eight transient stress periods are each a decade in length and 

represent the time period from 1900 to 1980 when the accuracy in terms of location and volume of the withdrawal data 
Simulation of Groundwater Flow 181

Figure C9A. Location of water-level wells completed in the Yorktown aquifer (North Carolina) and Upper Floridan aquifer (South 

Carolina) (layer 3) in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

West

Virginia

ky

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Yorktown aquifer (NC)

 and Upper Floridan aquifer (SC).

 Dashed where approximately

 located.

Well

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Yorktown

aquifer

Upper Floridan

aquifer

Figure C9A. Location of water-level wells completed in the Yorktown aquifer (North Carolina) and Upper

Floridian aquifer (South Carolina) (layer 3) in the Atlantic Coastal Plain of North and South Carolina and

parts of Virginia and Georgia, 2007.

Atlantic

Ocean
182 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C9B. Locations of water-level wells completed in the Castle Hayne aquifer (North Carolina) and Middle Floridan aquifer 

(South Carolina) (layer 5), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

West

Virginia

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Castle Hayne aquifer (NC)

 and Middle Floridan aquifer (SC).

 Dashed where approximately

 located.

Well

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Castle Hayne

aquifer

Middle Floridan

aquifer

Figure C9B. Locations of water-level wells completed in the Castle Hayne aquifer (North Carolina) and

Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and

South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 183

Figure C9C. Locations of water-level wells completed in the Beaufort aquifer (North Carolina) and the Gordon aquifer (South Carolina) 

(layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

West

Virginia

ky

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Beaufort aquifer (NC)

 and Gordon aquifer (SC).

 Dashed where approximately

 located.

Well

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Beaufort

aquifer

Gordon

aquifer

Figure C9C. Locations of water-level wells completed in the Beaufort aquifer (North Carolina) and the Gordon

aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of

Virginia and Georgia, 2007.

Atlantic

Ocean
184 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C9D. Locations of water-level wells completed in the Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

West

Virginia

Kentucky

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Peedee aquifer (NC)

 and Crouch Branch aquifer (SC).

 Dashed where approximately

 located.

Well

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Peedee/

Crouch Branch

aquifer

Figure C9D. Locations of water-level wells completed in the Peedee aquifer (North Carolina) and the Crouch Branch 

aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and

Georgia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 185

Figure C9E. Locations of water-level wells completed in the Black Creek aquifer (North Carolina) and the McQueen Branch aquifer 

(South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

West

Virginia

Kentucky

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico

Atlantic

Ocean

Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Black Creek aquifer (NC)

 and McQueen Branch aquifer (SC).

 Dashed where approximately

 located.

Well

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Black Creek/

McQueen Branch

aquifer

 Figure C9E. Locations of water-level wells completed in the Black Creek aquifer (North Carolina) and the McQueen

 Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and parts of

 Virginia and Georgia, 2007.
186 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C9F. Locations of water-level wells completed in the Upper Cape Fear aquifer (North Carolina) and the Charleston aquifer 

(South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Upper Cape Fear aquifer (NC)

 and Charleston aquifer (SC).

 Dashed where approximately

 located.

Well

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Upper Cape Fear/

Charleston

aquifer

Figure C9F. Locations of water-level wells completed in the Upper Cape Fear aquifer (North Carolina) and the

Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and parts

of Virginia and Georgia, 2007.
Simulation of Groundwater Flow 187

Figure C9G. Locations of water-level wells completed in the Lower Cape Fear aquifer (North Carolina) and the Gramling aquifer 

(South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

Extent of Lower Cape Fear aquifer (NC)

 and Gramling aquifer (SC).

 Dashed where approximately

 located.

Well

EXPLANATION

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Lower Cape Fear/

Gramling

aquifer

Figure C9G. Locations of water-level wells completed in the Lower Cape Fear aquifer (North Carolina) and

the Gramling aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and parts of

Virginia and Georgia, 2007.
188 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

is least well known. The next five transient stress periods are 

each 2 years in length and represent the time period from 1980 

to 1990 when more accurate groundwater withdrawal data 

were available. The final 15 transient stress periods are each 

1 year in length and represent the period from 1990 to 2004, a 

period when relatively accurate water-use data were available 

for all of the ACP aquifers. The model was calibrated to conditions during predevelopment, 1980, and 2004.

The model was calibrated with an automated parameterestimation approach using the computer program PEST 

(Doherty, 2005), and the model used regularized inversion 

and pilot points (de Marsily and others, 1984; LaVenue and 

Pickens, 1992; Doherty, 2003; Hunt and others, 2007). Using 

this method, hydraulic conductivity values were estimated at 

pilot points distributed throughout the model; the estimated 

values then were interpolated to each active model grid cell 

(fig. C10A–G). The pilot points were spatially distributed 

to match well locations where hydraulic conductivity data 

were available; in areas where no hydraulic conductivity 

data were available, the pilot points were distributed in an 

approximate regularly spaced distribution. The estimation 

of hydraulic conductivities at the pilot points was conducted 

so that the weighted sum-of-squares differences between 

model-generated water-level values and stream baseflows and 

between field water-level measurements and stream baseflows 

were minimized.

The use of pilot points for parameterization resulted in 

many more parameters than would have resulted by using 

zones of uniform parameter values. Regularized inversion was 

used through PEST to numerically stabilize the overparameterized inverse problem (Doherty, 2003). In addition, by using 

regularization in the parameter-estimation process, a large 

number of parameters could be estimated, allowing for locations where heterogeneity likely exists to be identified through 

the calibration process (Doherty, 2003).

Parameters selected for estimation during model calibration were hydraulic conductivity, specific storage, and 

anisotropy of the aquifers and confining units. Riverbed 

conductance and recharge were estimated for steady-state 

conditions. Published horizontal hydraulic conductivity values 

from the NC and SC Coastal Plain aquifers were used as initial 

values for the hydraulic conductivity pilot points (Aucott 

and Newcome, 1986; Newcome, 1993, 2000; Harrelson and 

Fine, 2006; Dorothy Payne, U.S. Geological Survey, written 

commun., December 2006; Michael Peck, U.S. Geological 

Survey, written commun., December 2006). These values 

Table C5. Streamflow and baseflow data used in model calibration and calibrated streambed conductance for selected sites 

in South Carolina and Georgia.

[USGS, U.S. Geological Survey; mi2, square mile; ft3/s, cubic feet per second; in/yr, inches per year; (ft2/d)/ft, square feet per day per foot; SRS, Savannah River Site]

USGS 

station 

number

Station name

Map index 

number 

(See 

fig. C2 )

Drainage 

area, 

in mi2

Period of 

record, 

in years

Mean 

streamflow 

Mean 

baseflow Baseflow 

index, in 

percent of 

total flow

Calibrated streambed 

conductance [(ft2/d)/ft]

ft3/s in/yr ft3/s in/yr Mean Maximum

Minimum

02130900 Black Creek near McBee, 

SC

1 108 1960–2002 152 19.2 122 15.3 80 2.0 2.0 2.0

02196689 Little Horse Creek near 

Graniteville, SC

2 26.6 1990–1998 34.2 17.5 29.9 15.3 87 16 40 4

02197310 Upper Three Runs above 

Road C (SRS), SC

3 176 1975–1997 212 16.4 179 13.8 85 1.9 1.9 1.9

02197315 Upper Three Runs at 

Road A (SRS), SC

4 203 1980–2001 231 15.4 196 13.1 85 1.9 1.9 1.9

02173351 Bull Swamp Creek near 

Swansea, SC

5 34.4 2002–2002 6.47 2.6 5.26 2.08 81 33 40 30

02169570 Gills Creek near Columbia, SC6 59.6 1967–2002 74.4 17.0 47.4 10.8 64 40 40 40

02135300 Scape Ore Swamp near 

Bishopville, SC

7 96.0 1969–2002 98.0 13.9 74.7 10.6 76 2.0 2.0 2.0

02172500 South Edisto near Montmorenci, SC8 198 1941–1965 244 16.7 196 13.5 80 58 58 58

02197600 Brushy Creek near 

Wrens, GA

9 28.0 1959–1993 27.0 13.0 19.0 9.00 70 80 80 80

02197300 Upper Three Runs near 

Ellenton, SC

10 87.0 1967–2001 103 16.2 95.4 14.9 92 1.9 1.9 1.9
Simulation of Groundwater Flow 189

Figure C10A. Calibrated horizontal hydraulic conductivities for the Yorktown aquifer (North Carolina) and the Upper Floridan aquifer 

(South Carolina) (layer 3), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

00 4

75

800

00 4

50

200

002

001

001

1,000

100

00 6

10

800

10

5

01

01 05

57

100 05

57

5

01

50

10

400

00 4

50

57

75

5 5

50

100

10

50

57

5

5

50

Extent of Yorktown aquifer (NC) and

 Upper Floridan aquifer (SC). Dashed

 where approximately located

Horizontal hydraulic conductivity, in

 feet per day. Contour interval is

 variable

Well with known horizontal hydraulic

 conductivity value

Pilot point

EXPLANATION

Figure C10A. Calibrated horizontal hydraulic conductivities for the Yorktown aquifer (North Carolina) and

 the Upper Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Yorktown

aquifer

Upper Floridan

aquifer

Atlantic

Ocean
190 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C10B. Calibrated horizontal hydraulic conductivities for the Castle Hayne aquifer (North Carolina) and the Middle Floridan 

aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Castle Hayne aquifer (NC) and

 Middle Floridan aquifer (SC). Dashed

 where approximately located.

Horizontal hydraulic conductivity, in

 feet per day. Contour interval is

 variable

Well with known horizontal hydraulic

 conductivity value

Pilot point

EXPLANATION

200

50

5

100

5

50

01

01

10

5

75

100

5

50

50

75

75

100

50

50

57

Castle Hayne

aquifer

Middle Floridan

aquifer

Figure C10B. Calibrated horizontal hydraulic conductivities for the Castle Hayne aquifer (North Carolina) and

 the Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean
Simulation of Groundwater Flow 191

Figure C10C. Calibrated horizontal hydraulic conductivities for the Beaufort aquifer (North Carolina) and the Gordon aquifer 

(South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

50

Extent of Beaufort aquifer (NC) and

 Gordon aquifer (SC). Dashed

 where approximately located.

Horizontal hydraulic conductivity, in

 feet per day. Contour interval is

 variable

Well with known horizontal hydraulic

 conductivity value

Pilot point

EXPLANATION

Beaufort

aquifer

Gordon

aquifer

75

05

100 125

75

150

5

5

5

100

01

10

10

50

10

5

05

75

05

Figure C10C. Calibrated horizontal hydraulic conductivities for the Beaufort aquifer (North Carolina) and

 the Gordon aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and

 parts of Virginia and Georgia, 2007.
192 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C10D. Calibrated horizontal hydraulic conductivities for the Peedee aquifer (North Carolina) and the Crouch Branch aquifer 

(South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Peedee aquifer (NC) and

 Crouch Branch aquifer (SC). Dashed

 where approximately located.

Horizontal hydraulic conductivity, in

 feet per day. Contour interval is

 variable

Well with known horizontal hydraulic

 conductivity value

Pilot point

EXPLANATION

Peedee/

Crouch Branch

aquifer

50

50

10

10

01

5

5

5

50

5

5

5

50

100

75

125

150

Figure C10D. Calibrated horizontal hydraulic conductivities for the Peedee aquifer (North Carolina) and the Crouch

 Branch aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of

Virginia and Georgia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 193

Figure C10E. Calibrated horizontal hydraulic conductivities for the Black Creek aquifer (North Carolina) and the McQueen Branch 

aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Black Creek aquifer (NC) and

 McQueen Branch aquifer (SC). Dashed

 where approximately located.

Horizontal hydraulic conductivity, in

 feet per day. Contour interval is

 variable

Well with known horizontal hydraulic

 conductivity value

Pilot point

EXPLANATION

Black Creek/

McQueen Branch

aquifer

001

100

001

57

75

75

75

75

05

50

50

50

50

05

50

10

01

10

01

10

5

5

5

5

5

5

5

10

10

100

75

Figure C10E. Calibrated horizontal hydraulic conductivities for the Black Creek aquifer (North Carolina) and

 the McQueen Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
194 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C10F. Calibrated horizontal hydraulic conductivities for the Upper Cape Fear aquifer (North Carolina) and the Charleston 

aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Upper Cape Fear aquifer (NC) and

 Charleston aquifer (SC). Dashed

 where approximately located.

Horizontal hydraulic conductivity, in

 feet per day. Contour interval is

 variable

Well with known horizontal hydraulic

 conductivity value

Pilot point

EXPLANATION

Upper Cape Fear/

Charleston

aquifer

100

75

75

75

50

50

50

50

10 5

10

01

10

5

5

5

5

5

50

05

Figure C10F. Calibrated horizontal hydraulic conductivities for the Upper Cape Fear aquifer (North Carolina) and

 the Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and

 parts of Virginia and Georgia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 195

Figure C10G. Calibrated horizontal hydraulic conductivities for the Lower Cape Fear aquifer (North Carolina) and the Gramling 

aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

West

Virginia

ky

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

10

Extent of Lower Cape Fear aquifer (NC) and

 Gramling aquifer (SC). Dashed

 where approximately located.

Horizontal hydraulic conductivity, in

 feet per day. Contour interval is

 variable

Well with known horizontal hydraulic

 conductivity value

Pilot point

EXPLANATION

Lower Cape Fear/

Gramling

aquifer

50

10

10

10

5

5

50

05

50

Figure C10G. Calibrated horizontal hydraulic conductivities for the Lower Cape Fear aquifer (North Carolina) and

 the Gramling aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and

 parts of Virginia and Georgia, 2007.
196 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

were allowed to vary within reasonable limits during model 

calibration to obtain the best fit to the observation data. Few 

measurements of hydraulic conductivity were available for 

the confining units within the NC and SC ACP. The hydraulic 

conductivity within confining unit layers 4, 6, 8, 10, 12, and 

14 (table C1) was assumed to be spatially uniform. A reasonable value was assigned as the hydraulic conductivity of each 

confining unit layer; the values were allowed to vary within 

reasonable limits during model calibration.

Calibrated hydraulic conductivity values for the aquifers 

ranged from 0.5 to 1,150 ft/d; the highest mean value occurred 

in layer 3, and the lowest occurred in layer 9 (table C6; 

figs. C10A and D). Calibrated hydraulic conductivity values 

for the confining units ranged from 2.18E–05 ft/d in layer 10 

to 9.10E–02 ft/d in layer 2. Calibrated specific storage values 

were 1.50E–06 ft–1 for all confined aquifers and confining 

units except for layer 1, which had a calibrated specific yield 

of 0.1 ft–1. Calibrated vertical anisotropies for the aquifers 

ranged from 1.0 to 3.0 and from 1.3 to 3.0 for the confining 

units (table C6).

Model Fit—Groundwater Levels

Predevelopment groundwater flow was simulated by 

assuming steady-state conditions. The calibration included a 

total of 1,070 water-level measurements from 1900 to 1979—

276 in layer 3; 132 in layer 5; 99 in layer 7; 231 in layer 9; 

233 in layer 11; 86 in layer 13; and 13 in layer 15. The residuals, computed as the measured groundwater levels minus the 

simulated water levels, are normally distributed for layers 3, 

5, 7, 9, 11, and 13 and slightly skewed to the positive side for 

layer 15, which had only 13 observations (table C7; figs. C11,

C12). Calculated residuals range from –58 to 85 ft with mean 

residuals of 4.0, –2.6, –2.0, –2.7, –4.0, –1.2, and 14 ft for layers 3, 5, 7, 9, 11, 13, and 15, respectively (fig. C13). The root 

mean square error of the residuals for the layers ranged from 

10 to 27 ft. The percentage of simulated residuals within the 

20-ft calibration target varied between 52 and 87 percent for 

layers 3, 5, 7, 9, 11, and 13; the percentage of simulated values 

within the 20-ft calibration target was 8 percent for layer 15. 

Residuals for the predevelopment water levels from all of the 

layers combined produced an overall R2 of 0.96, and the percentage of predevelopment simulated water levels within the 

20-ft calibration target for all layers combined was 64 percent.

Another method for evaluating the fit of calibration is to 

divide the standard deviation of model residuals by the overall 

range of water-level observations for a particular layer. A ratio 

of less than 0.1 indicates that residuals are generally less than 

10 percent of the altitude range of the observations (Kuniansky and others, 2004). The fit of calibration for predevelopment conditions ranged from 0.04 to 0.09 for layers 3, 5, 7, 9, 

11, and 13; the fit of calibration was 0.16 for layer 15, most 

likely because the residuals were not normally distributed and 

because of the low number of observations available for this 

aquifer (table C7). The fit of calibration for the predevelopment water levels from all of the layers combined was 0.05. 

Groundwater conditions for 1980 were simulated assuming transient conditions. The calibration included a total of 

451 water-level measurements from 1980—163 in layer 3; 

52 in layer 5; 44 in layer 7; 99 in layer 9; 48 in layer 11; 35 in 

layer 13; and 10 in layer 15. The 1980 water-level residuals 

are distributed normally for layers 3, 5, 7, 9, 11, and 13 and 

slightly skewed to the positive side for layer 15 (table C8; 

figs. C14, C15). Calculated residuals range from –62 to 57 ft 

with mean residuals of 3.6, –1.0, –8.8, –10, 1.1, 6.3, and 4.8 ft 

for layers 3, 5, 7, 9, 11, 13, and 15, respectively (fig. C16). 

The percentage of simulated values within the 20-ft calibration 

Table C6. Calibrated hydraulic conductivity values, and calibrated values of specific yield, specific storage, and vertical anisotropy in the 

model layers representing the aquifers and confining units in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia. 

[ft/d, feet per day; ft, feet; —, no data; note: single horizontal hydraulic conductivity values were used for layers 1, 4, 6, 8, 10, 12, 14, and 16]

Layer 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Hydraulic 

property Statistic

Horizontal 

hydraulic 

conductivity (ft/d)

Minimum 216 9.90E–6 2.0 1.73E–3 2.0 2.13E–4 0.8 1.93E–4 0.8 2.18E–5 0.8 7.95E–5 0.5 2.81E–4 1.4 25.0

Maximum

9.10E–2 1,150 262 169 177 175 129 64.0

Mean 2.29E–2 176 46.1 26.3 18.3 22.9 22.4 26.3

Standard 

deviation

3.90E–2 253 49.5 32.8 26.4 35.1 28.5 18.3

Specific 

yield 

(ft–1)

Calibrated

0.1 — — — — — — — — — — — — — — —

Specific 

storage 

(ft–1)

Calibrated

— 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6 1.50E–6

Vertical 

anisotropy

Calibrated 1.8 3.0 2.3 3.0 1.9 1.3 3.0 3.0 1.1 1.6 1.3 3.0 1.5 2.4 1.0 3.0
Simulation of Groundwater Flow 197

Table C7. Statistics for model calibration based on predevelopment conditions for aquifers in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia.

[ft, feet]

Layer 3 Layer 5 Layer 7 Layer 9 Layer 11 Layer 13 Layer 15 Model

Number of observations 276 132 99 231 233 86 13 1,070

Range of observations (ft) 389 236 324 359 351 266 152 389

Minimum residual (ft) –50 –36 –33 –49 –54 –58 –35 –58

Maximum residual (ft) 85 30 31 51 48 69 43 85

Mean residual (ft) 4.0 –2.6 –2.0 –2.7 –4.0 –1.2 14 –0.9

Standard deviation of residuals (ft) 19 10 14 16 21 23 24 18

Root mean square error of residuals (ft) 19 10 14 16 21 23 27 18

Percentage of values within 20-foot error criteria 63 87 70 68 52 52 8.0 64

Calibration fit1 0.05 0.04 0.04 0.04 0.06 0.09 0.16 0.05

1

Calibration fit, standard deviation of residuals divided by the range of observations (Kuniansky and others, 2004).

Figure C11. Observed and simulated water 

levels for predevelopment calibration, in the 

Atlantic Coastal Plain of North and South 

Carolina and parts of Virginia and Georgia.

Figure C12. Water-level residuals and simulated 

water levels for predevelopment calibration in the 

Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia.

WATER-LEVEL RESIDUALS, IN FEET

NUMBER OF MEASUREMENTS

Figure C11. Observed and simulated water levels for predevelopment

 calibration, in the Atlantic Coastal Plain of North and South Carolina and

 parts of Virginia and Georgia.

Layer 3

Layer 5

Layer 7

Layer 9

Layer 11

Layer 13

Layer 15

350

300

250

200

150

100

50

0

–70 –50 –30 –20 10 30 50 70 90

450

400

350

300

250

200

150

100

50

0

SIMULATED WATER LEVEL, IN FEET ABOVE NGVD 29

100

80

60

40

20

0

–20

–40

–60

–80

100

RESIDUALS

0 50 100 150 200

OBSERVED WATER LEVEL, IN FEET

250 300 350 400 450

WATER-LEVEL RESIDUALS, IN FEET

NUMBER OF MEASUREMENTS

Figure C11. Observed and simulated water levels for predevelopment

 calibration, in the Atlantic Coastal Plain of North and South Carolina and

 parts of Virginia and Georgia.

Layer 3

Layer 5

Layer 7

Layer 9

Layer 11

Layer 13

Layer 15

350

300

250

200

150

100

50

0

–70 –50 –30 –20 10 30 50 70 90

450

400

350

300

250

200

150

100

50

0

SIMULATED WATER LEVEL, IN FEET ABOVE NGVD 29

100

80

60

40

20

0

–20

–40

–60

–80

–100

RESIDUALS

0 50 100 150 200

OBSERVED WATER LEVEL, IN FEET

250 300 350 400 450

Figure C12. Water-level residuals and simulated water levels for

 predevelopment calibration, in the Atlantic Coastal Plain of North and

South Carolina and parts of Virginia and Georgia

0 50 100 150 200

SIMULATED WATER LEVEL, IN FEET

250 300 350 400 450
198 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C13A. Simulated water levels and water-level residuals for steady-state calibration for the Yorktown aquifer (North Carolina) 

and the Upper Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

10

Extent of Yorktown aquifer (NC) and

 Upper Floridan aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Upper Floridan

aquifer

Yorktown

aquifer

350 003

00 3

052

052

002

051

001

001

001

05 05

05

52

0

0

400

100

150

150

200

200

250

250

52

400

350

350

200

150

Figure C13A. Simulated water levels and water-level residuals for steady-state calibration for the Yorktown aquifer

 (North Carolina) and the Upper Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 199

Figure C13B. Simulated water levels and water-level residuals for steady-state calibration for the Castle Hayne aquifer (North 

Carolina) and the Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

10

Extent of Castle Hayne aquifer (NC) and

 Middle Floridan aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION Middle Floridan

aquifer

Castle Hayne

aquifer

052

052

002

200

051

051

001

001

100

100

05

05

52

25

25

52

0

0

0

05

100

100

Figure C13B. Simulated water levels and water-level residuals for steady-state calibration for the Castle Hayne aquifer

 (North Carolina) and the Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
200 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C13C. Simulated water levels and water-level residuals for steady-state calibration for the Beaufort aquifer (North Carolina) 

and the Gordon aquifer (South Carolina), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and Georgia.

CHARLES

BRADFORD

Fall

Line

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

10

Extent of Beaufort aquifer (NC) and

 Gordon aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Gordon

aquifer

Beaufort

aquifer

350 003

00 3

300

052

052

002

002

051

150

001

100

05

50

05

52

25

52

52

0

0

001

350

350

52

0

Figure C13C. Simulated water levels and water-level residuals for steady-state calibration for the Beaufort aquifer

 (North Carolina) and the Gordon aquifer (South Carolina), in the Atlantic Coastal Plain of North and South Carolina

 and parts of Virginia and Georgia.

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean
Simulation of Groundwater Flow 201

Figure C13D. Simulated water levels and water-level residuals for steady-state calibration for the Peedee aquifer (North Carolina) 

and the Crouch Branch aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Peedee aquifer (NC) and

 Crouch Branch aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable.

 Hachures indicates depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Peedee/

Crouch Branch

aquifer

500

150

200

004

300 003

003

300

052

052

002

051

001

001

100

100

05

50

05

52

52

25

0

200

150

052

400

400

300 150

150

100

600

400

500

600 500

Figure C13D. Simulated water levels and water-level residuals for steady-state calibration for the Peedee aquifer

 (North Carolina) and the Crouch Branch aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
202 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C13E. Simulated water levels and water-level residuals for steady-state calibration for the Black Creek aquifer (North 

Carolina) and the McQueen Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Black Creek aquifer (NC) and

 McQueen Branch aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

Figure C13E. Simulated water levels and water-level residuals for steady-state calibration for the Black Creek aquifer

 (North Carolina) and the McQueen Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

EXPLANATION

Black Creek/

McQueen Branch

aquifer

400

00 4

00 3

300

003

300

052

052

052

002

002

200

50 1

150

150

001

05

25

52

52

400

500

500

200

250

250

300 Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean
Simulation of Groundwater Flow 203

Figure C13F. Simulated water levels and water-level residuals for steady-state calibration for the Upper Cape Fear aquifer (North 

Carolina) and the Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Upper Cape Fear aquifer (NC) and

 Charleston aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Upper Cape Fear/

Charleston

aquifer

052

002

002

051

051

051

001

100

05

05

150

50

25

300

Figure C13F. Simulated water levels and water-level residuals for steady-state calibration for the Upper Cape Fear

 aquifer (North Carolina) and the Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
204 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C13G. Simulated water levels and water-level residuals for steady-state calibration for the Lower Cape Fear aquifer (North 

Carolina) and the Gramling aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Lower Cape Fear aquifer (NC) and

 Gramling aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Lower Cape Fear/

Gramling

aquifer

002

051

001

100

05

05

05

52

250

Figure C13G. Simulated water levels and water-level residuals for steady-state calibration for the Lower Cape Fear

 aquifer (North Carolina) and the Gramling aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 205

Figure C13H. Simulated water levels and water-level residuals for steady-state calibration for the Lower Cretaceous confining unit 

and Lower Cretaceous aquifer (North Carolina) (layer 16), in the Atlantic Coastal Plain of North Carolina and parts of Virginia, 2007.

CHARLES

BRADFORD

Fall

Line

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

30

Extent of Lower Cretaceous confining unit

 and Lower Cretaceous aquifer (NC)

Water-level contour in feet above NGVD 29.

 Contour interval is variable

EXPLANATION

Lower Cretaceous

confining unit and

Lower Cretaceous

aquifer

20

04

03

Figure C13H. Simulated water levels and water-level residuals for steady-state calibration for the Lower Cretaceous

 confining unit and Lower Cretaceous aquifer (North Carolina) (layer 16), in the Atlantic Coastal Plain of North

 Carolina and parts of Virginia, 2007.

Atlantic

Ocean

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean
206    Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Table C8.  Statistics for model calibration based on 1980 conditions for aquifers in the Atlantic Coastal Plain of North and

South Carolina and parts of Virginia and Georgia.

[ft, feet]

Layer 3 Layer 5 Layer 7 Layer 9 Layer 11 Layer 13 Layer 15 Model

Number of observations 163 52 44 99 48 35 10 451

Range of observations (ft) 392 205 325 343 438 233 80 438

Minimum residual (ft) –25 –29 –28 –53 –49 –62 –34 –62

Maximum residual (ft) 39 25 19 24 57 50 38 57

Mean residual (ft) 3.6 –1 –8.8 –10 1.1 6.3 4.8 –1.0

Standard deviation of residuals (ft) 11 10 12 17 20 24 26 17

Root mean square error of residuals (ft) 12 11 15 20 20 24 25 17

Percentage of values within 20-foot error criteria 74 84 72 63 54 45 30 70

Calibration fit1 0.03 0.05 0.04 0.05 0.05 0.10 0.32 0.04

1

Calibration fit, standard deviation of residuals divided by the range of observations (Kuniansky and others, 2004).

Figure C14.  Observed and simulated water

levels for 1980 calibration in the Atlantic

Coastal Plain of North and South Carolina and

parts of Virginia and Georgia.

Figure C15.  Water-level residuals and

simulated water levels for 1980 calibration in

the Atlantic Coastal Plain of North and South

Carolina and parts of Virginia and Georgia.

WATER-LEVEL RESIDUALS, IN FEET

NUMBER OF MEASUREMENTS

Figure C14. Observed and simulated water levels for 1980 calibration, in

 the Atlantic Coastal Plain of North and South Carolina and parts of

 Virginia and Georgia.

160

140

120

100

80

60

40

20

0

–60 –40 –20 0 20 40 60

400

350

300

250

200

150

100

50

0

–50

–100

–150

–200

SIMULATED WATER LEVEL, IN FEET ABOVE NGVD 29

80

0

–80

RESIDUALS

–200 –100 0 100 200

OBSERVED WATER LEVEL, IN FEET

300 400

–200 –100 0

SIMULATED WATER LEVELIN FEET

100 200 300 400

Layer 3

Layer 5

Layer 7

Layer 9

Layer 11

Layer 13

Layer 15

WATER-LEVEL RESIDUALS, IN FEET

NUMBER OF MEASUREMENTS

Figure C14. Observed and simulated water levels for 1980 calibration, in

 the Atlantic Coastal Plain of North and South Carolina and parts of

 Virginia and Georgia.

160

140

120

100

80

60

40

20

0

–60 –40 –20 0 20 40 60

400

350

300

250

200

150

100

50

0

–50

–100

–150

–200

SIMULATED WATER LEVEL, IN FEET ABOVE NGVD 29

80

0

–80

RESIDUALS

–200 –100 0 100 200

OBSERVED WATER LEVEL, IN FEET

300 400

Figure C15. Water-level residuals and simulated water levels for 1980

 calibration, in the Atlantic Coastal Plain of North and South Carolina 

and parts of Virginia and Georgia.

–200 –100 0

SIMULATED WATER LEVEL, IN FEET

100 200 300 400

Layer 3

Layer 5

Layer 7

Layer 9

Layer 11

Layer 13

Layer 15
Simulation of Groundwater Flow 207

Figure C16A. Simulated water levels and water-level residuals for 1980 calibration for the Yorktown aquifer (North Carolina) and the 

Upper Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and 

Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Yorktown aquifer (NC) and

 Upper Floridan aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachures indicate depression

 WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Upper Floridan

aquifer

Yorktown

aquifer

003 052

052

051

100

001

001

100

05

05

05

52

52

52

0

0

002

00 3

400

400

–100

–50

150

150

200

200

Figure C16A. Simulated water levels and water-level residuals for 1980 calibration for the Yorktown aquifer (North Carolina)

 and the Upper Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
208 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C16B. Simulated water levels and water-level residuals for 1980 calibration for the Castle Hayne aquifer (North Carolina) 

and the Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Middle Floridan

aquifer

Castle Hayne

aquifer

50

Extent of Castle Hayne aquifer (NC) and

 Middle Floridan aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

50

50

05

52

52

0

0

25 0

50

100

100

50

052

50 2

50 2

002

00 2

051

50 1

001

00 1

05

52

0

Figure C16B. Simulated water levels and water-level residuals for 1980 calibration for the Castle Hayne aquifer 

 (North Carolina) and the Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 209

Figure C16C. Simulated water levels and water-level residuals for 1980 calibration for the Beaufort aquifer (North Carolina) and 

the Gordon aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and 

Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

10

Extent of Beaufort aquifer (NC) and

 Gordon aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Gordon

aquifer

Beaufort

aquifer

100

05 52

52

0

0

50

300

300

052

250

002

002

051

051

001

05

52

25

0

100

Figure C16C. Simulated water levels and water-level residuals for 1980 calibration for the Beaufort aquifer (North Carolina) 

 and the Gordon aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of

Virginia and Georgia, 2007.

Atlantic

Ocean
210 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C16D. Simulated water levels and water-level residuals for 1980 calibration for the Peedee aquifer (North Carolina) and the 

Crouch Branch aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

10

Extent of Peedee aquifer (NC) and

 Crouch Branch aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable.

 Hachures indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Peedee/

Crouch Branch

aquifer

100

100

250 200

600

600

500

300

004

00 3

00 3

300

052

50 2

052

002

002

001

001

05

05

52

52

0

0

150

150

400

500

400

051

150

100

Figure C16D. Simulated water levels and water-level residuals for 1980 calibration for the Peedee aquifer (North Carolina) 

 and the Crouch Branch aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and 

 parts of Georgia, 2007.
Simulation of Groundwater Flow 211

Figure C16E. Simulated water levels and water-level residuals for 1980 calibration for the Black Creek aquifer (North Carolina) and 

the McQueen Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

50

Extent of Black Creek aquifer (NC) and

 McQueen Branch aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachures indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Black Creek/

McQueen Branch

aquifer

400

00 3

00 3

300

300

003

052

50 2

052

002

002

002

200

051

150

051

001

001

100

–50

05

25

52

52

0

0

25

–50

–50 –100

–150

300

400

500

50

50

–150

250

003

250

200

100

0

Figure C16E. Simulated water levels and water-level residuals for 1980 calibration for the Black Creek aquifer (North Carolina) 

 and the McQueen Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l
212 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C16F. Simulated water levels and water-level residuals for 1980 calibration for the Upper Cape Fear aquifer (North Carolina) 

and the Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

50

Extent of Upper Cape Fear aquifer (NC) and

 Charleston aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachured to indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Upper Cape Fear/

Charleston

aquifer

052

002

002

051

50 1

150

150

001

00 1

05

05

05

50

300

52

25

52

52

25

–25

25

Figure C16F. Simulated water levels and water-level residuals for 1980 calibration for the Upper Cape Fear aquifer 

 (North Carolina) and the Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and 

 South Carolina and parts of Virginia and Georgia, 2007.
Simulation of Groundwater Flow 213

Figure C16G. Simulated water levels and water-level residuals for 1980 calibration for the Lower Cape Fear aquifer (North 

Carolina) and the Gramling aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

50

Extent of Lower Cape Fear aquifer (NC) and

 Gramling aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above NGVD 29.

 Contour interval is variable

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Lower Cape Fear/

Gramling

aquifer

002

051

001

00 1

05

50

52

50

05

Figure C16G. Simulated water levels and water-level residuals for 1980 calibration for the Lower Cape Fear aquifer 

 (North Carolina) and the Gramling aquifer aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and 

 South Carolina and parts of Virginia and Georgia, 2007.
214 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C16H. Simulated water levels for 1980 calibration for the Lower Cretaceous confining unit and the Lower Cretaceous aquifer 

in North Carolina (layer 16), in the Atlantic Coastal Plain of North Carolina and parts of Virginia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

MO

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

25

Extent of Lower Cretaceous confining unit

 and Lower Cretaceous aquifer (NC)

Water-level contour in feet above NGVD 29.

 Contour interval is variable

EXPLANATION

Lower Cretaceous

confining unit and

Lower Cretaceous

aquifer

52

Figure C16H. Simulated water levels for 1980 calibration for the Lower Cretaceous confining unit and the Lower

 Cretaceous aquifer in North Carolina (layer 16), in the Atlantic Coastal Plain of North Carolina and parts

 of Virginia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 215

target varied between 30 and 84 percent, and the root mean 

square error for the layers ranged from 11 to 25 ft. Residuals for the 1980 water levels from all of the layers combined 

produce an overall R2 of 0.95, and the percentage of 1980 

simulated water levels within the 20-ft calibration target for all 

layers combined was 70 percent. The fit of calibration for the 

1980 water-level data ranged from 0.03 to 0.10 for layers 3, 

5, 7, 9, 11, and 13; the fit of calibration was 0.32 for layer 15, 

most likely because the residuals were not distributed normally and because of the low number of observations available for this layer. The fit of calibration for the 1980 water 

levels from all layers combined was 0.04.

Groundwater conditions for 2004 were simulated assuming transient conditions. The calibration included a total of 

767 water-level measurements—139 in layer 3; 125 in layer 5; 

80 in layer 7; 162 in layer 9; 130 in layer 11; 94 in layer 13; 

and 37 in layer 15. The 2004 water-level residuals are distributed normally for all layers (table C9; figs. C17, C18). Calculated residuals range from –112 to 139 ft with mean residuals 

of 0.9, 0.8, –16, –7.1, 16, –5.0, and –5.5 ft for layers 3, 5, 7, 

9, 11, 13, and 15, respectively (fig. C19). The percentage of 

simulated values within the 20-ft calibration target varied 

between 27 and 82 percent, and the root mean square error 

for the layers ranged from 10 to 42 ft. Residuals for the 2004 

water levels from the layers combined produce an overall R2

of 0.89, and the percentage of 2004 simulated water levels 

within the 20-ft calibration target for all layers combined was 

55 percent. The fit of calibration for the 2004 water-level data 

ranged from 0.03 to 0.14. The fit of calibration for the 2004 

water levels from all layers combined was 0.05. 

Overall, simulated water-level trends followed observed 

continuous groundwater levels (figs. C20, C21). The model 

does not accurately represent observed groundwater levels in 

areas where heads have been obviously affected by pumping, 

but water-use data are not available, such as in well SU-50 in 

layer 9 (fig. C21E), where pumping was not reported prior to 

1983. Similarly, the model somewhat underestimates drawdown from pumping in some areas of layers 13 and 15 in NC, 

such as in wells O30J3 (fig. C21H) and G19B4 (fig. C21J), 

where water-use data are also missing. 

Model Fit—Stream Baseflow

Calculated and simulated mean annual baseflows were 

compared at 10 streamgaging locations in the inner Coastal 

Plain of NC and SC (fig. C2; table C10). Mean baseflows 

were underestimated at 9 of the 10 locations. In general, the 

smaller streams with lower baseflows had better fits than the 

larger streams with higher baseflows. Bull Swamp Creek near 

Swansea, SC, is the smallest stream and had the best fit, and 

Little Horse Creek near Graniteville, SC, had the poorest fit. 

Only three of the streams had a percentage of simulated annual 

baseflows within the 15-percent calibration criteria—Bull 

Swamp Creek near Swansea, SC, had 50 percent of simulated 

annual baseflows within the calibration criteria; Gills Creek 

at Columbia, SC, had 13 percent; and Scape Ore Swamp near 

Bishopville, SC, had 11 percent.

The low simulated mean annual baseflows relative to the 

calculated mean annual baseflows are a result of the scale of 

the model. The stream widths that the model simulated are all 

less than 100 ft during baseflow conditions (U.S. Geological 

Survey, 2005). An entire 2-mi by 2-mi model cell, however, 

is defined as a stream cell if any part of the stream is located 

within the cell boundaries. This scale issue produces an overall 

underestimation of baseflows by the model.

Simulated Regional Water Budget

Simulated water budget components for the model 

include inflow from recharge, inflow and outflow through 

specified-head boundaries and rivers, outflow to wells, and 

net changes in storage (fig. C22). The primary source of water 

to the model is inflow from specified-head boundaries, with 

the inflow ranging from a total of 2,570 to 3,310 million gallons per day (Mgal/d). The majority of this inflow is through 

the upper specified-head boundary in layer 1 and the lateral 

specified-head boundaries in layers 11, 13, 15, and 16. Inflow 

from recharge ranges from 766 to 1,660 Mgal/d; river inflow 

ranges from 12.3 to 20.0 Mgal/d. A minimum of 1.78 Mgal/d 

is released from storage in stress period 4 (1920–29), and a 

maximum of 456 Mgal/d is released from storage in stress 

period 24 (1999).

The primary water loss is through specified-head boundaries, which lose 2,620 to 3,510 Mgal/d. The majority of this 

loss is through the upper specified-head boundary in layer 1 

and the lateral specified-head boundaries in layers 13 and 15. 

Rivers discharge 879 to 1,110 Mgal/d of water from layer 1 

over all stress periods, and well withdrawals range from a 

minimum of 5 Mgal/d [in stress period 2 (1900–09)] to a maximum of 563 Mgal/d [in stress period 27 (2002)]. A minimum 

of 0 Mgal/d [in stress period 7 (1950–59)] and a maximum of 

286 Mgal/d [in stress period 16 (1991)] of water is added to 

storage over all stress periods. 

There are 16 specified-head cells in layer 1 that have 

anomalously high or low water budgets due to uneven altitude 

changes from the DEM averaging process described earlier. 

These cells are all located along the inner and outer Coastal 

Plain boundary (fig. C2) in southern Barnwell County, SC 

(fig. C1). Adjacent cells have a high or low water budget 

related to the specified head simulated in the surficial aquifer 

and tend to cancel each other so the overall water budget is 

unaffected. This problem is described in detail in Kuniansky 

and Danskin (2003). The model simulates historical groundwater levels reasonably well in the aquifers below this area 

(figs. C13C, C13D, C13E, C16C, C16D, C16E, C19C, C19D,

and C19E). The mean of the flow from layer 1 to layer 2 of 

all of the specified-head cells for predevelopment is –54 cubic 

feet per day (ft3/d). The mean of the flow from layer 1 to 

layer 2 of all of the specified-head cells for 2004 is 1,641 ft3/d. 

This difference indicates that the specified-head cells in layer 1 

are a small sink during predevelopment but change to a small 

source of water by 2004.
216 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C17. Observed and simulated water levels 

for 2004 calibration in the Atlantic Coastal Plain 

of North and South Carolina and parts of Virginia 

and Georgia.

Figure C18. Water-level residuals and simulated 

water levels for 2004 calibration in the Atlantic 

Coastal Plain of North and South Carolina and 

parts of Virginia and Georgia.

WATER-LEVEL RESIDUALS, IN FEET

NUMBER OF MEASUREMENTS

Figure C17. Observed and simulated water levels for 2004 calibration, in

 the Atlantic Coastal Plain of North and South Carolina and parts of

 Virginia and Georgia.

300

250

200

150

100

50

0

–160 –120 –80 –40 0 40 80 120

500

400

300

200

100

0

–100

–200

SIMULATED WATER LEVEL, IN FEET ABOVE NGVD 29

200

0

–200

RESIDUALS

–200 –100 0 100 200

OBSERVED WATER LEVEL, IN FEET

300 400 500

–200 –100 0

SIMULATED WATER LEVELIN FEET

100 200 300 400 500

Layer 3

Layer 5

Layer 7

Layer 9

Layer 11

Layer 13

Layer 15

WATER-LEVEL RESIDUALS, IN FEET

NUMBER OF MEASUREMENTS

Figure C17. Observed and simulated water levels for 2004 calibration, in

 the Atlantic Coastal Plain of North and South Carolina and parts of

 Virginia and Georgia.

300

250

200

150

100

50

0

–160 –120 –80 –40 0 40 80 120

500

400

300

200

100

0

–100

–200

SIMULATED WATER LEVEL, IN FEET ABOVE NGVD 29

200

0

–200

RESIDUALS

–200 –100 0 100 200

OBSERVED WATER LEVEL, IN FEET

300 400 500

Figure C18. Water-level residuals and simulated water levels for 2004

 calibration, in the Atlantic Coastal Plain of North and South Carolina 

 and parts of Virginia and Georgia.

–200 –100 0

SIMULATED WATER LEVEL, IN FEET

100 200 300 400 500

Layer 3

Layer 5

Layer 7

Layer 9

Layer 11

Layer 13

Layer 15

Table C9. Statistics for model calibration based on 2004 conditions for aquifers in the Atlantic Coastal Plain of North and 

South Carolina and parts of Virginia and Georgia.

[ft, feet]

Layer 3 Layer 5 Layer 7 Layer 9 Layer 11 Layer 13 Layer 15 Model

Number of observations 139 125 80 162 130 94 37 767

Range of observations (ft) 184 336 327 549 595 436 231 595

Minimum residual (ft) –40 –28 –68 –94 –112 –112 –62 –112

Maximum residual (ft) 72 28 39 45 139 139 66 139

Mean residual (ft) 0.9 0.8 –16 –7.1 16 –5.0 –5.5

Standard deviation of residuals (ft) 18 10 19 24 39 40 31 28

Root mean square error of residuals (ft) 18 10 25 25 42 37 31 28

Percentage of values within 20-foot error criteria 78 82 50 56 34 28 27 55

Calibration fit1 0.10 0.03 0.06 0.04 0.07 0.09 0.14 0.05

1

Calibration fit, standard deviation of residuals divided by the range of observations (Kuniansky and others, 2004).
Simulation of Groundwater Flow 217

Figure C19A. Simulated water levels and water-level residuals for 2004 calibration for the Yorktown aquifer (North Carolina) and the 

Upper Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and 

Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

50

Extent of Yorktown aquifer (NC) and

 Upper Floridan aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachured indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Upper Floridan

aquifer

Yorktown

aquifer

003

300

003

052

052

002

051

001

100

05

52

0

–50

–25

400

400

300

150

001

100

05

05

52

25

0

0

0

0

–50

–50

–25

200

150

002

0

Figure C19A. Simulated water levels and water-level residuals for 2004 calibration for the Yorktown aquifer

 (North Carolina) and the Upper Floridan aquifer (South Carolina) (layer 3), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.

Atlantic

Ocean
218 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C19B. Simulated water levels and water-level residuals for 2004 calibration for the Castle Hayne aquifer (North Carolina) and 

the Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and 

Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

Middle Floridan

aquifer

Castle Hayne

aquifer

50

Extent of Castle Hayne aquifer (NC) and

 Middle Floridan aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachures indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

001

25

25

0

0

0

0

0

0

0

–25

–100

–25

–50

100

05

52

50

250

50 2

50 2

200

200

150

150 001

100

05

52

0

–25

Figure C19B. Simulated water levels and water-level residuals for 2004 calibration for the Castle Hayne aquifer 

 (North Carolina) and the Middle Floridan aquifer (South Carolina) (layer 5), in the Atlantic Coastal Plain of North and 

 South Carolina and parts of Virginia and Georgia, 2007.
Simulation of Groundwater Flow 219

Figure C19C. Simulated water levels and water-level residuals for 2004 calibration for the Beaufort aquifer (North Carolina) and 

the Gordon aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and 

Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

10

Extent of Beaufort aquifer (NC) and

 Gordon aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachures indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Gordon

aquifer

Beaufort

aquifer

001

05

52

25

0

–50

–25

–25

0

0

0

0

0

–50

52

00 3

300

052

052

002

200

051

051

150

001

05

52

25

0

300

25

100 25 100

00 1

Figure C19C. Simulated water levels and water-level residuals for 2004 calibration for the Beaufort aquifer (North Carolina) 

 and the Gordon aquifer (South Carolina) (layer 7), in the Atlantic Coastal Plain of North and South Carolina and parts of

Virginia and Georgia, 2007.
220 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C19D. Simulated water levels and water-level residuals for 2004 calibration for the Peedee aquifer (North Carolina) and the 

Crouch Branch aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and parts of Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

10

Extent of Peedee aquifer (NC) and

 Crouch Branch aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachures indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Peedee/

Crouch Branch

aquifer

004

300

003

00 3

003

052

052

052

002

002

051

051

150

001

001

100

05

05

50

0 52

25

25

0

150

300

400

400

500

600

400

400

600 500

051

200

250

0

100

100

–50

0

–25

Figure C19D. Simulated water levels and water-level residuals for 2004 calibration for the Peedee aquifer (North Carolina) 

 and the Crouch Branch aquifer (South Carolina) (layer 9), in the Atlantic Coastal Plain of North and South Carolina and 

parts of Georgia, 2007.
Simulation of Groundwater Flow 221

Figure C19E. Simulated water levels and water-level residuals for 2004 calibration for the Black Creek aquifer (North Carolina) 

and the McQueen Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and South Carolina and parts of 

Virginia and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

50

Extent of Black Creek aquifer (NC) and

 McQueen Branch aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachures indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Black Creek/

McQueen Branch

aquifer

00 4

300

00 3

300

003

003

052

052

052

002

002

002

051

051

051

001

001

05

05

50

52

0

25

0

–150

50

400

400

500

500

250

-150

–50

25 0

50

200

002

052

250

00 3

0

–100

–50

–25

–25

–25 –25

–25

–100

Figure C19E. Simulated water levels and water-level residuals for 2004 calibration for the Black Creek aquifer

 (North Carolina) and the McQueen Branch aquifer (South Carolina) (layer 11), in the Atlantic Coastal Plain of North and

 South Carolina and parts of Virginia and Georgia, 2007.
222 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C19F. Simulated water levels and water-level residuals for 2004 calibration for the Upper Cape Fear aquifer (North Carolina) 

and the Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia 

and Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

50

Extent of Upper Cape Fear aquifer (NC) and

 Charleston aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachures indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Upper Cape Fear/

Charleston

aquifer

052

002

002

051

051

001

001

05

05

52

25

52

52

25

0

0

0

0

–50

0 –25

52-

–50

–25

–150

–50

0

150

–25

0

05

300

–50

–100

–150

Figure C19F. Simulated water levels and water-level residualsfor 2004 calibration for the Upper Cape Fear aquifer (North 

 Carolina) and the Charleston aquifer (South Carolina) (layer 13), in the Atlantic Coastal Plain of North and South Carolina 

 and parts of Virginia and Georgia, 2007.
Simulation of Groundwater Flow 223

Figure C19G. Simulated water levels and water-level residuals for 2004 calibration for the Lower Cape Fear aquifer (North Carolina) 

and the Gramling aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and parts of Virginia and 

Georgia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Atlantic

Ocean

50

Extent of Lower Cape Fear aquifer (NC) and

 Gramling aquifer (SC). Dashed

 where approximately located.

Water-level contour in feet above or below

 NGVD 29. Contour interval is variable.

 Hachures indicate depression

WATER-LEVEL RESIDUALS—Represents

 difference between simulated and

 observed water levels, in feet

Less than –20

–20 to 0

0 to 20

Greater than 20

EXPLANATION

Lower Cape Fear/

Gramling

aquifer

002

051

001

001

05

50

52

25

0

25 0

0

52

0

25

–25

–25

–25

–25

–25

–50

–100 –100

–50

Figure C19G. Simulated water levels and water-level residuals for 2004 calibration for the Lower Cape Fear aquifer (North 

 Carolina) and the Gramling aquifer (South Carolina) (layer 15), in the Atlantic Coastal Plain of North and South Carolina and 

 parts of Virginia and Georgia, 2007.
224 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C19H. Simulated water levels for 2004 calibration for the Lower Cretaceous confining unit and the Lower Cretaceous 

aquifer (North Carolina) (layer 16), in the Atlantic Coastal Plain of North Carolina and parts of Virginia, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

25

Extent of Lower Cretaceous confining unit

 and Lower Cretaceous aquifer (NC)

Water-level contour in feet above NGVD 29.

 Contour interval is variable. Hachures

 indicate depression

EXPLANATION

Lower Cretaceous

confining unit and

Lower Cretaceous

aquifer

25

0

–100

–50 –25

Figure C19H. Simulated water levels for 2004 calibration for the Lower Cretaceous confining unit and the

 Lower Cretaceous aquifer (North Carolina) (layer 16), in the Atlantic Coastal Plain of North

 Carolina and parts of Virginia, 2007.

Atlantic

Ocean
Simulation of Groundwater Flow 225

Figure C20. Locations of wells in the Atlantic Coastal Plain of North and South Carolina and southeastern Georgia with continuous 

observed groundwater levels, 2007.

CHARLES

BRADFORD

Fall

Line

LOCATION OF THE ATLANTIC AND GULF COASTAL PLAIN

WV

OH

KY VA

TN NC

GA

FL

SC

NJ

NY

DE

MD

PA

AL

MS

LA TX

OK AR

M0

KS IL IN

Mexico Gulf of Mexico

Atlantic

Ocean

Virginia

North Carolina

Maryland

32°

33°

34°

35°

36°

37°

83° 82° 81° 80° 79° 78° 77° 76° 75°

38°

31°

Georgia

Florida

South

Carolina

0 50 100 MILES

0 50 100 KILOMETERS

Base from digital files of:

U.S. Department of Commerce, Bureau of Census,

 1990 Precensus TIGER/Line Files-Political boundaries, 1991

U.S. Environmental Protection Agency, River File 3

U.S. Geological Survey, 1:100,000 scale 

Groundwater well screened in layer 3

Groundwater well screened in layer 5

Groundwater well screened in layer 7

Groundwater well screened in layer 9

Groundwater well screened in layer 11

Groundwater well screened in layer 13

Groundwater well screened in layer 15

EXPLANATION

BW-353

G 19B4

S 22J9

RIC-40

ON-256

CHN-14

36Q008

FLO-128

CHN-101

BFT-304

O 30J3

BFT-429

SU-50

HO-433

HH 39J3

R 17P1

ON-265

V 35T6 V 32V1

Figure C20. Locations of wells in the Atlantic Coastal Plain of North and South Carolina and southeastern Georgia

with continuous observed groundwater levels, 2007.

Atlantic

Ocean
226 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C21A. Hydrographs of simulated and observed water levels for the A, Yorktown aquifer (North Carolina) 

and B, Upper Floridan aquifer (South Carolina) (see fig. C20 for well locations).

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

60

40

20

0

–20

–40

–60

–80

–100

–120

–140

Figure C21A. Hydrographs of simulated and observed water levels for the Yorktown aquifer (North Carolina)

 A and Upper Floridan aquifer (South Carolina) B (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

A

Well 36Q008

Well BFT–429

15

10

5

0

–5

–10

–15

B
Simulation of Groundwater Flow 227

Figure C21B. Hydrographs of simulated and observed water levels for A, the Castle Hayne aquifer (North Carolina) 

and B, Middle Floridan aquifer (South Carolina) (see fig. C20 for well locations).

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

10

8

6

4

2

0

–2

–4

Figure C21B. Hydrographs of simulated and observed water levels for the Castle Hayne aquifer (North Carolina)

 A and Middle Floridan aquifer (South Carolina) B (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

A

Well R 17P1

Well BFT 304

20

15

10

5

0

–5

–10

–15

–20

–25

B
228 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C21C. Hydrographs of simulated and observed water levels for the A, Beaufort aquifer (North Carolina) 

and B, Gordon aquifer (South Carolina) (see fig. C20 for well locations).

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

16

14

12

10

8

6

4

2

0

Figure C21C. Hydrographs of simulated and observed water levels for the Beaufort aquifer (North Carolina)

 A and the Gordon aquifer (South Carolina) B (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

A

Well ON 265

Well CHN 101

14

12

10

8

6

4

2

B
Simulation of Groundwater Flow 229

Figure C21D. Hydrographs of simulated and observed water levels for the Peedee aquifer in North Carolina 

(see fig. C20 for well locations).

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

30

25

20

15

10

5

0

Figure C21D. Hydrographs of simulated and observed water levels for the Peedee aquifer in North Carolina

 (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

Well S 22J9

Well V 32V1

75

74

73

72

71

70

69

68

67

66

65
230 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C21E. Hydrographs of simulated and observed water levels for the Crouch Branch aquifer in 

South Carolina (see fig. C20 for well locations).

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

140

135

130

125

120

115

110

Figure C21E. Hydrographs of simulated and observed water levels for the Crouch Branch aquifer in

 South Carolina (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

Well SU 50

Well BW 353

210

205

200

195

190

185

180

175

170

165

160
Simulation of Groundwater Flow 231

Figure C21F. Hydrographs of simulated and observed water levels for the Black Creek aquifer in North Carolina 

(see fig. C20 for well locations).

50

40

30

20

10

0

–10

–20

Figure C21F. Hydrographs of simulated and observed water levels for the Black Creek aquifer in

 North Carolina (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

Well HH 39J3

Well ON 256

40

30

20

10

0

–10

–20

–30

–40

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed
232 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C21G. Hydrographs of simulated and observed water levels for the McQueen Branch aquifer in 

South Carolina (see fig. C20 for well locations).

330

325

320

315

310

305

300

295

290

Figure C21G. Hydrographs of simulated and observed water levels for the McQueen Branch aquifer in

 South Carolina (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

Well RIC 40

Well HO 433

50

0

--50

--100

--150

--200

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed
Simulation of Groundwater Flow 233

Figure C21H. Hydrographs of simulated and observed water levels for the Upper Cape Fear aquifer in 

North Carolina (see fig. C20 for well locations).

Figure C21H. Hydrographs of simulated and observed water levels for the Upper Cape Fear aquifer in

 North Carolina (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

Well V 35T6

Well O 30J3

100

75

50

25

0

–25

–50

100

90

80

70

60

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed
234 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Figure C21I. Hydrographs of simulated and observed water levels for the Charleston aquifer in South Carolina 

(see fig. C20 for well locations).

Figure C21I. Hydrographs of simulated and observed water levels for the Charleston aquifer in

 South Carolina (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

Well CHN 14

Well FLO 128

100

75

50

25

0

–25

–50

120

80

40

0

–40

–80

–120

Simulated

Observed

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed
Simulation of Groundwater Flow 235

Figure C21J. Hydrographs of simulated and observed water levels for the Lower Cape Fear aquifer in 

North Carolina (see fig. C20 for well locations).

Figure C21J. Hydrographs of simulated and observed water levels for the Lower Cape Fear aquifer in

 North Carolina (see fig. C22 for well locations). 

WATER LEVEL, IN FEET ABOVE OR BELOW NGVD 29

Well G 19B4

40

20

0

–20

–40

–60

–80

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Simulated

Observed

Table C10. Observed and simulated mean annual baseflows for selected streamgages in the Atlantic Coastal Plain of South Carolina 

and parts of Georgia.

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; ft3/d, cubic feet per day; SRS, Savannah River Site]

USGS 

station 

number

Station name

Map index 

number 

(See 

fig. C2)

Mean 

calculated 

annual 

baseflow, 

in ft3/s

Mean 

simulated 

annual 

baseflow, 

in ft3/s

Percentage of 

simulated 

annual baseflows 

within the 

15-percent 

error criteria

Mean 

observed 

annual 

baseflow, 

in ft3/d

Mean 

simulated 

annual 

baseflow, 

in ft3/d

02173351 Bull Swamp Creek near Swansea, SC 5 5.26 5.75 50 454,464 496,546

02169570 Gills Creek at Columbia, SC 6 47.4 29.7 13 4,096,225 2,562,899

02135300 Scape Ore Swamp near Bishopville, SC 7 74.7 41.9 11 6,453,856 3,622,829

02130900 Black Creek near McBee, SC 1 121 18.6 0 10,456,940 1,603,179

02197600 Brushy Creek near Wrens, GA 9 14.0 2.16 0 1,209,600 186,666

02196689 Little Horse Creek near Graniteville, SC 2 30.5 0.801 0 2,633,035 69,205

02197300 Upper Three Runs near New Ellenton, SC 10 95.4 7.08 0 8,242,208 611,828

02197310 Upper Three Runs above Road C (SRS), SC 3 95.4 8.17 0 8,242,208 705,796

02197315 Upper Three Runs at Road A (SRS), SC 4 41.9 4.14 0 3,622,666 358,110

02172500 South Fork Edisto near Montmorenci, SC 8 197 21.6 0 16,997,084 1,868,484
236 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

Sensitivity Testing and Analysis

The sensitivity of the calibrated model to the model 

inputs was evaluated to determine the relative importance 

of model parameters and boundary conditions on simulated 

groundwater levels and flows. Variations in parameters to 

which the calibrated model is most sensitive will result in 

larger differences in simulated groundwater levels than differences produced by variations in parameters to which the 

model is less sensitive. Sensitive parameters, therefore, are 

more likely to be accurately estimated during model calibration than less sensitive parameters. The sensitivity of the NC–

SC Coastal Plain model to the calibrated aquifer parameters of 

horizontal hydraulic conductivity, vertical anisotropy, specific 

storage, and specific yield was evaluated with composite sensitivity analysis. The sensitivity of the model to the specified 

head and recharge boundary conditions, streambed conductance, and well withdrawals was evaluated using the perturbation method.

Relative composite sensitivities were calculated for 432 

aquifer parameters used in model calibration (fig. C23). The 

parameters include 391 horizontal hydraulic conductivity 

values associated with pilot points in the aquifers and one 

confining unit, 8 horizontal hydraulic conductivity values in 

the confining units and one aquifer, 16 specific storage values, 

1 specific yield value, and 16 vertical anisotropy values. 

Relative composite sensitivities are a measure of composite 

changes in model outputs that are caused by small changes in 

the value of a modeled parameter (Doherty, 2005). For a given 

model parameter, a larger value of the associated relative 

composite sensitivity indicates more sensitivity of simulated 

conditions to the given parameter. 

The model is relatively more sensitive to the horizontal 

hydraulic conductivity of the confining units in layers 10, 12, 

and 14 and of the aquifer in layer 1 and to the specific storage 

of the aquifers and confining units in layers 11, 12, 13, 14, 

and 15. The model is relatively less sensitive to the horizontal 

hydraulic conductivity of the confining units in layers 4 and 6 

and of the aquifer in layer 16, to the specific storage of the 

confining unit in layer 10 and the aquifer in layer 16, and to 

the vertical anisotropy of the confining units in layers 2, 10, 

12, and 14. The model has relatively little sensitivity to the 

remaining hydraulic parameters. The model has a low sensitivity to the horizontal hydraulic conductivity pilot points for the 

aquifer in layers 3, 5, 7, 9, 11, 13, and 15 and for the confining 

unit in layer 2 relative to other hydraulic parameters.

Figure C22. Simulated groundwater budget per model stress period from predevelopment to 2004 in the Atlantic Coastal Plain 

aquifers of North and South Carolina and parts of Virginia and Georgia.

5,000

4,000

3,000

2,000

1,000

0

–1,000

–2,000

–3,000

–4,000

–5,000

FLOW, IN MILLION GALLONS PER DAY

BEGINNING DATE AND STRESS PERIOD NUMBER

Figure C22. Simulated groundwater budget per model stress period from predevelopment to 2004 in the Atlantic Coastal Plain

 aquifers of North and South Carolina and parts of Virginia and Georgia.

1900 1909 1919 1929 1939 1949 1959 1969 1979 1981 1983 1985 1987 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Recharge in

Rivers in

Specified-head in

Storage in

Storage out

Specified-head out

Rivers out

Wells out

EXPLANATION
Simulation of Groundwater Flow 237

The perturbation method was used to examine model 

sensitivity to the lateral specified heads on the northeast and 

southwest boundaries, the specified-head boundary defined 

for the top of layer 1, and the recharge boundary defined for 

layer 1. The perturbation method also was used to examine 

model sensitivity to streambed conductance and changes in 

groundwater withdrawals. Model sensitivity to these boundary conditions was examined by simulating a change in one 

boundary at a time and comparing the sum-of-squares error 

of the new simulation with that of the calibrated simulation.

To evaluate model sensitivity to the specified heads 

defined at the northeast and southwest boundaries for layers 2 through 16, 15 simulations were conducted where the 

northeast and southwest boundaries for layers 2 through 

16 were converted individually to no-flow boundaries. The 

sum-of-squares error of all 15 simulations was greater than 

Figure C23. Relative composite sensitivities for A, aquifer parameters and B, aquifer–parameter 

pilot points. Figure C23. Relative composite sensitivities for (A) aquifer parameters and (B) aquifer–

 parameter pilot points.

the sum-of-squares error of the calibrated model. The smallest increase in error was 1.0 percent for the conversion of 

boundaries for layer 11 to no flow; the largest increase in error 

was 1.1 percent for the conversion of boundaries for layer 15 

to no flow. 

To evaluate the sensitivity of the upper boundary 

of layer 1, four simulations were conducted in which the 

specified-head boundary was increased by 1 ft and decreased 

by 1 ft and in which the recharge rate was increased by 

10 percent and decreased by 10 percent. Increasing the upper 

specified-head boundary by 1 ft increased the sum-of-squares 

error by 2.5 percent; decreasing the specified-head boundary 

by 1 ft decreased the sum-of-squares error by 2.3 percent. Considering that the specified heads of the upper boundary were set

equal to the mean altitude in each 4-mi2

 cell, the sensitivity of 

the specified-head boundary is relatively small. Increasing the 

AQUIFER PARAMETER

RELATIVE COMPOSITE SENSITIVITY

0.1400

0.1200

0.1000

0.0800

0.0600

0.0400

0.0200

0.0000

0.0400

0.0300

0.0200

0.0100

0.0000

HKL10

HKL2 HKL3 HKL5 HKL7 HKL9 HKL11 HKL13 HKL15

SSL13

SSL15

SSL11

HKL12

HKL14

SSL14

HKL1

HKL8

SSL12

HKL16

HKL6

HKL4

V Ani L12

V Ani L14

V Ani L2

V Ani L10

V Ani L16

V Ani L7

V Ani L13

V Ani L3

V Ani L5

V Ani L15

V Ani L11

V Ani L1

V Ani L9

SSL10

SSL16

SSL9

SSL6

SSL3

SSL8

SSL7

SSL4

SSL5

SSL2

V Ani L8

SYL1

V Ani L4

V Ani L6

B

A

HK, horizontal conductivity

L, layer

SS, specific storage

V ani, vertical anisotropy

HK, horizontal conductivity

L, layer

SS, specific storage

V ani, vertical anisotropy
238 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

recharge rate by 10 percent decreased the sum-of-squares error 

by only 0.2 percent; decreasing the recharge rate by 10 percent 

increased the sum-of-squares error by only 0.6 percent, indicating little sensitivity of the model to the recharge rate. 

To evaluate the sensitivity of the model to streambed 

conductance, two simulations were conducted in which 

conductance values were decreased by half and increased by 

100 percent. Neither decreasing nor increasing the streambed 

conductance values changed the sum-of-squares error of the 

model. The model is not sensitive to streambed conductance, 

and the calibrated values may not be accurate estimates of true 

streambed conductance values.

To evaluate the sensitivity of the model to changes in 

groundwater withdrawals, three simulations were conducted 

in which pumping was decreased by 10 percent and increased 

by 10 and 20 percent. Decreasing pumping by 10 percent 

increased the sum-of-squares error by 30.2 percent; increasing 

pumpage by 10 percent decreased the sum-of-squares error 

by 20.4 percent. Increasing pumpage by 20 percent decreased 

the sum-of-squares error by 31.0 percent; increasing pumpage further did not further decrease the sum-of-squares error. 

The decrease in model error with the increase in groundwater 

withdrawals corresponds to the known underrepresentation of 

pumping in the model. Withdrawals less than 3 million gallons 

per month are not required to be reported to the State agencies 

and are, therefore, unknown.

Model Limitations

Numerical models are based on limited data and are 

simplifications of actual groundwater flow systems. The 

simplifications incorporated into the development of a groundwater model can limit the ability of the model to predict actual 

hydraulic conditions over time. Accuracy and prediction 

capabilities of this model are affected by the finite-difference 

discretization, boundary conditions, hydraulic properties, and 

observations used in the model calibration.

 The model was spatially discretized into a grid of 4-mi2

cells and was temporally discretized into 1 steady-state stress 

period and 28 transient stress periods. The relatively large size 

of the grid cells is adequate to represent regional groundwater 

flow conditions but limits the ability of the model to accurately 

simulate local flow conditions, such as discharge to wells or 

rivers. The 28 transient stress periods range in length from 

10 years (in the earlier periods of the model) to 1 year (in the 

more recent time periods of the model). The variable-length 

stress periods are appropriate for the accuracy of the water-use 

data and temporally sparse observations but cannot represent 

seasonal variation within the groundwater flow system.

Boundary choices can affect model uncertainty, run 

times, and stability. The lateral boundaries defined for the 

model are artificial and are not true boundaries of the natural hydrologic system. The northeastern and southwestern 

specified-head boundaries in the upper layer of the model 

were placed at two major rivers that act as natural hydraulic 

boundaries only for the directly incised upper hydrogeologic 

units. The northeastern and southwestern lateral specified-head 

boundaries in layers 2 through 16 were placed along groundwater flow paths. The model is not sensitive to the lateral 

specified-head boundaries; model error did not substantially 

change with the conversion of these boundaries from specified 

head to no flow. The northwestern no-flow boundary of the 

model was placed along the Fall Line, and the southeastern 

no-flow boundary of the model was placed at the freshwater/

saltwater divide, both of which can be considered natural 

hydraulic boundaries in the groundwater system. The locations 

of the freshwater/saltwater divides of the various aquifers are 

only approximately known and can be expected to change 

over time in response to transient pumping stresses. Care 

should be taken, however, when interpreting simulated water 

levels near all model boundaries.

The upper boundary of layer 1 has two zones: (1) in the 

outer Coastal Plain, the upper boundary of layer 1 is set as 

specified heads equal to the values calculated by equation 1; 

and (2) in an area along the Fall Line where confined hydrogeologic units crop out, net recharge was applied. Increasing 

and decreasing the specified heads in layer 1 did not substantially change model error. The recharge rate specified in the 

model is uncertain and was calibrated within reasonable limits 

during the steady-state stress period. The calibrated recharge 

rate was varied temporally during the transient stress periods 

based on historical precipitation data from six stations located 

in the inner Coastal Plain. These six stations represent a small 

fraction of the large area covered in the model where recharge 

is simulated, and precipitation data at these stations were collected over a 104-year period; therefore, the precipitation data 

most likely are subject to a degree of uncertainty. Increasing 

and decreasing the recharge rate by 10 percent, however, did 

not substantially change model error.

Groundwater withdrawals simulated in the model underrepresent actual historical water use because pumping rates 

less than 3 million gallons per month are not required to be 

reported to the State agencies and, therefore, are unknown. 

In addition, approximately 10 percent of the total volume 

of reported water use in SC was not simulated in the model 

because either the pumped aquifer was unknown or the 

well location was unknown. The calibrated model was very 

sensitive to groundwater withdrawals; model error improved 

by 31 percent when the amount of simulated groundwater 

withdrawals was increased by 20 percent. The sensitivity of 

the model to withdrawals and the known underrepresentation 

of pumping emphasize the importance and need for improved 

monitoring of groundwater use in both NC and SC. 

Hydraulic properties of horizontal hydraulic conductivity, 

vertical anisotropy, specific storage, and specific yield were all 

calibrated to some degree during the simulation process. Initial 

values of hydraulic conductivity and specific storage for the 

aquifer were derived from published transmissivity and storage coefficient data and are the best-defined hydraulic properties in the model. In some cases, however, aquifer thicknesses 

at the wells had to be assumed from screen length. The model 

was most sensitive to the hydraulic conductivity of the aquifer 
Future Opportunities for Improvements 239

in layer 1 and of the confining units in layers 10, 12, and 14, 

and to the specific storage of the aquifers and confining units 

in layers 11, 12, 13, 14, and 15. The model was less sensitive 

to hydraulic conductivity, vertical anisotropy, specific storage, 

and specific yield in other layers; these calibrated values may 

be less accurate than the values that are more sensitive. All of 

the calibrated hydraulic-property distributions are large-scale 

approximations of measured and estimated values.

The hydraulic heads used as steady-state and transient 

calibration targets have uncertainty associated with the accuracy of the land-surface altitudes of each well; the calibration target was to match simulated and observed water levels 

within 20 ft. In addition, the clustering of head data in one area 

and the lack of head data in other areas can lead to areas being 

overemphasized or underemphasized during model calibration, respectively. Care was taken during this study to limit 

the clustering of head data, but the lack of head data in some 

areas is a limitation that cannot be corrected. Finally, because 

of minimal predevelopment water-level data, hydraulic-head 

observations used in the steady-state calibration were derived 

from water levels collected prior to 1980. Major groundwater pumping began in the NC–SC Coastal Plain in the 

1940s; some of the groundwater levels used to develop the 

steady-state hydraulic-head observations may not reflect true 

steady-state conditions.

Stream baseflows simulated by the model do not accurately represent calculated baseflows. A scale issue occurs 

between the 2-mi by 2-mi model cells and the stream widths 

that the model simulates, which are less than 100 ft during 

baseflow conditions. Because of this scale issue, the model 

is not capable of accurately simulating baseflow for most 

streams. In addition, the model is insensitive to streambed 

conductance, and the calibrated values may not be accurate 

representations of true conductances.

Future Opportunities for Improvements

As with all numerical models of complex natural systems, there are many ways that the model can be improved. 

Moreover, taking advantage of opportunities to increase 

knowledge of the quantity and movement of groundwater 

in the aquifers and confining units also would benefit the 

short- and long-term use of the newly developed forecasting 

tool. The limitations discussed below also can be viewed as 

opportunities for further enhancement of the hydrogeologic 

framework, along with integration of any newly available 

hydrologic information. Future enhancements to the simulation codes could lead to opportunities to improve the numerical model. The cumulative effect of these enhancements could 

be to improve understanding of how groundwater flow within 

the aquifer and confining units occurs, thus enabling a better 

approximation of groundwater flow through the use of more 

realistic numerical models. 

The first recognized limitation is that the revised hydrostratigraphy presented in this report and used in the model is 

based on limited data. Additional continuous coreholes distributed throughout the study area could provide supplemental 

information regarding lithologic descriptions, paleontologic 

ages, and aquifer and confining unit hydrologic properties that 

could be used to update the hydrostratigraphic interpretations, 

resulting in more accurate top and bottom altitudes. Many of 

the more deeply buried units have few, if any, available aquifertest results. Additional test wells drilled into these more deeply 

buried units could provide opportunities for additional aquifer 

tests to be conducted to determine properties such as horizontal 

and vertical hydraulic conductivities and storage coefficients. 

As better simulation tools become available, the spatial discretization of the study area could be reduced, allowing for the 

more accurate simulation of groundwater–surface-water interactions. Refining the discretizaton of the study area could allow 

the surficial aquifer to be simulated as an active layer rather than 

as a specified-head boundary. Groundwater–surface-water interactions could be better quantified through detailed field studies

and the classification of streambed sediments. Streamgages are 

sparse in the inner Coastal Plain of the study area; additional 

streamgages on small tributaries could provide additional baseflow data and additional model calibration points. 

Recharge was applied to the water table without simulating the flow processes in the unsaturated zone. The unsaturated 

zone is known to vary from a few inches to as much as 200 ft 

in the study area. Transient storage in the unsaturated zone 

is not simulated in the model and most likely represents a 

substantial volume of groundwater in the inner Coastal Plain of 

the study area. A MODFLOW package, UZF1 (Niswonger and 

others, 2006), could be used to simulate this unsaturated flow.

The model does not simulate variable-density groundwater flow, which is an important element of groundwater flow 

in the coastal part of the study area. Future versions of the 

model could use the SEAWAT package (Langevin and others, 

2007). The addition of a variable-density flow capability to 

the model would allow for the simulation of regional saltwater 

encroachment processes and the potential effects of climate 

change related to sea-level changes. 

The water-use data included in the model are known to 

contain errors and omissions. Data prior to about 1980 are 

generally estimated from population figures. Current data 

are not always complete, and many wells cannot be accurately placed in the model as a result of missing construction 

information. A more complete and accurate water-use database would reduce the uncertainty associated with transient 

model simulations. Use of the Multinode-Well Package for 

MODFLOW (Halford and Hanson, 2002) could result in more 

accurate simulation of groundwater-use data for wells that are 

open to more than one aquifer. 

As new climate models are developed, updated versions of the groundwater model could be coupled directly to 

climate models to deliver efficient and less uncertain results. 

Coupling the model to optimization techniques such as the 

GWM package (Ahlfeld and others, 2005) also could provide 

a powerful management tool for groundwater users and State 

regulatory agencies. 
240 Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina

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24 pls.
Prepared by:

USGS Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

For additional information regarding this publication, contact:

Bruce G. Campbell, Groundwater Specialist

USGS South Carolina Water Science Center

Stephenson Center, Suite 129

720 Gracern Road

Columbia, SC 29210

email: bcampbel@usgs.gov

Or visit the USGS South Carolina Water Science Center Web site at:

http://sc.water.usgs.gov/

Groundwater Availability in the Atlantic

Coastal Plain of North and South Carolina

Campbell and Coes—Groundwater Availability in the Atlantic Coastal Plain of North and South Carolina—Professional Paper 1773

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