U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 02–4105

Preliminary Hydrogeologic Assessment and 

Study Plan for a Regional Ground-Water 

Resource Investigation of the Blue Ridge and 

Piedmont Provinces of North Carolina

Prepared in cooperation with

The Groundwater Section of the North Carolina Department of Environment 

and Natural Resources, Division of Water Quality

By Charles C. Daniel, III, and Paul R. Dahlen

Raleigh, North Carolina

2002
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

CHARLES G. GROAT, Director

For additional information write to: Copies of this report can be purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

3916 Sunset Ridge Road Box 25286, Federal Center

Raleigh, NC 27607 Denver, CO 80225

dc_nc@usgs.gov 1-888-ASK-USGS

Information about U.S. Geological Survey programs in North Carolina can be obtained on the Internet at 

http://nc.water.usgs.gov

The use of firm, trade, and brand names in this report is for identification purposes only and 

does not constitute endorsement by the U.S. Geological Survey.
PREFACE

Preface III

This report provides background 

information on two related topics—(1) the 

existing knowledge regarding the hydrogeologic 

framework of the complex heterogeneous 

fractured rock aquifer system that underlies the 

Blue Ridge and Piedmont of western North 

Carolina and (2) an outline of plans for a longterm study of ground-water conditions to advance 

current understanding of the resource in this 

region. Among the issues to be addressed are 

ambient ground-water quality on a regional scale, 

the potential for ground-water contamination, 

infiltration and recharge rates, the role of geologic 

structure in ground-water movement, time of 

travel between recharge and discharge areas, 

design of monitoring networks, implications for 

remediation, and policy development for groundwater management. The purpose of this report is 

to integrate information from basic research, field 

and laboratory experiments, and knowledge 

gained from hydrogeologic case studies in 

fractured-rock terranes to establish the basis for a 

long-term, multiyear study of ground water in the 

region. The report also provides information for 

nonspecialists about the potential of this fracturedrock terrane as a water source, and about regional 

ground-water-quality issues. The concept and 

design of a type-area site-selection process, its use 

in selecting sites for detailed studies of the 

ground-water resource, and characteristics of sites 

selected for the first phase of the study also are 

described.

The Blue Ridge and Piedmont 

physiographic provinces of western North 

Carolina cover 30,544 square miles in 65 counties. 

In 2000 the population of the region was 

approximately 6.11 million people. Of the total 

population, an estimated 1.97 million people, or 

32.3 percent (based on the 1990 census), relied on 

ground water for a variety of uses, including 

commercial, industrial, and most importantly, 

potable supplies. Population in the region has 

grown substantially during the past 6 decades—in 

some counties the rate of growth has been greater 

than 1 percent per year. Ground-water use and the 

number of ground-water users has tended to 

parallel this growth in population.

In a region generally considered to have 

abundant water resources, summertime water 

rationing, water-quality degradation, and other 

problems have focused attention on the fact that 

there are limitations to the quantity and quality of 

available surface water. Consequently, ground 

water, which has been used principally for 

domestic supplies, is under consideration as a 

source for large public supplies or as a means to 

supplement available surface-water resources.

Ground water in the Blue Ridge and 

Piedmont Provinces traditionally has not been 

considered as a source for large supplies because 

of readily available and seemingly limitless 

surface-water supplies and the perception that 

ground water in the Blue Ridge and Piedmont 

Provinces occurs in a complex, generally 

heterogeneous geologic environment. Some 

reluctance to use ground water for large supplies is 

derived from the reputation of aquifers in these 

provinces for producing low yields to wells. Even 

with an increased understanding of the occurrence 

and movement of ground water in these fracturedrock terranes and with new skills and tools to aid 

in development and management of this resource, 

other issues fuel a continuing reluctance to explore 

the potential of these fractured-rock terranes as a 

public water source.

Concern about contaminated ground water 

is one such issue. As the population has grown, so 

has the number of real and potential sources of 

ground-water contamination. The same complex 

heterogeneous environment that thwarts groundwater development also hampers removal and 

remediation of contaminated water and aquifer 

materials. Concern about radon and other 

naturally occurring radionuclides in crystalline 

rock aquifers is another example.

Plans for the study described in this report 

were first developed in Raleigh, North Carolina, in 

1999 as a result of a series of informal meetings 

between ground-water professionals from the 

Water Resources Discipline of the U.S. Geological 

Survey and the Groundwater Section of the North 

Carolina Division of Water Quality. The purpose 

of these meetings was to present information 
IV Preface

considered to be the state of knowledge about ground water 

in the Blue Ridge and Piedmont Provinces. It also was a 

goal of these meetings to identify what was not known and 

to speculate about emerging issues. An outline for these 

discussions was provided by the document, “Ground-Water 

Resources Evaluation Program,” written by the Groundwater Section staff in Raleigh. It became apparent during 

the course of these discussions that the participants believed 

that there were a sufficient number of issues to warrant an 

interdisciplinary investigation of ground water on a regional 

scale.

In planning the study, participants recognized that a 

number of issues regarding ground water in the Blue Ridge 

and Piedmont Provinces of North Carolina needed to be 

addressed, and that a study of this magnitude would require 

a willingness to dedicate resources and people to an effort 

that could span a decade or more. Study issues tended to fall 

into three general categories dealing with quality, quantity, 

and availability. Specifically, how much water is available? 

How can it be developed? What is its quality? What types of 

contamination have occurred and how is it being assessed 

and remediated? What are the safeguards to protect the 

resource and preserve it for future use? What are the longterm goals for management and utilization?

As with any resource, questions such as these can 

only be answered by a better understanding of the physical 

processes involved. If past research serves as an indicator of 

the future, not only will some questions be answered, but 

new questions will emerge, and new research and policy 

issues will be identified. We hope that this report will help 

scientists, managers, and the lay reader better understand 

the hydrogeologic system under investigation, the need for 

the study currently in progress, and initial steps taken to 

identify field sites for detailed research.

Charles C. Daniel, III

Paul R. Dahlen
Contents V

CONTENTS

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

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

Purpose and scope ....................................................................................................................................................... 3

Acknowledgments....................................................................................................................................................... 4

Description of the study area....................................................................................................................................... 4

Physiography..................................................................................................................................................... 4

Precipitation ...................................................................................................................................................... 6

Runoff................................................................................................................................................................ 6

Population growth and water use ...................................................................................................................... 6

Previous investigations................................................................................................................................................ 7

Hydrogeologic setting ........................................................................................................................................................... 9

Crystalline rock ........................................................................................................................................................... 9

Sedimentary rock ........................................................................................................................................................ 10

Hydrogeologic units .................................................................................................................................................... 10

Hydrogeologic belts .................................................................................................................................................... 15

Hydrologic conditions in the study area................................................................................................................................ 17

Ground-water source and occurrence.......................................................................................................................... 20

Ground-water recharge................................................................................................................................................ 21

Ground-water storage.................................................................................................................................................. 23

Ground-water flow system .......................................................................................................................................... 25

Transition zone between saprolite and bedrock .......................................................................................................... 26

Hydrogeologic terranes ......................................................................................................................................................... 29

Massive or foliated crystalline rocks mantled by thick regolith.................................................................................. 32

Massive or foliated crystalline rocks mantled by thin regolith ................................................................................... 33

Sedimentary rocks in the early Mesozoic basins ........................................................................................................ 33

Ground-water quality ............................................................................................................................................................ 34

State ground-water issues and problems ............................................................................................................................... 38

Available ground-water data ....................................................................................................................................... 41

Asheville Region ............................................................................................................................................... 41

Mooresville Region........................................................................................................................................... 42

Winston-Salem Region...................................................................................................................................... 42

Raleigh Region.................................................................................................................................................. 42

Central Office.................................................................................................................................................... 42

Ground-water data deficiencies................................................................................................................................... 43

Study design .......................................................................................................................................................................... 43

Objectives.................................................................................................................................................................... 44

Approach ..................................................................................................................................................................... 45

Site-selection criteria................................................................................................................................................... 46

Required criteria for all sites ............................................................................................................................. 46

Optional criteria for selected sites..................................................................................................................... 47

Site-characterization procedures ................................................................................................................................. 47

Standard procedures for all study sites.............................................................................................................. 47

Specialized techniques for selected study sites................................................................................................. 47

Active and potential type-area study sites................................................................................................................... 48

Sites having crystalline rock mantled by thick regolith .................................................................................... 48

Sites having crystalline rock mantled by thin regolith ...................................................................................... 50

Organization and Federal-State interaction................................................................................................................. 51

Proposed products ....................................................................................................................................................... 52

Selected references................................................................................................................................................................ 52
VI Contents

FIGURES

1. Map showing locations of the Blue Ridge and Piedmont Provinces of North Carolina 

and the 65 counties in the study area ....................................................................................................................... 5

2. Graph showing growth in population and number of people supplied by ground water in the Blue Ridge 

and Piedmont Provinces of North Carolina, 1940–2000......................................................................................... 7

3–5. Maps showing:

3. Study areas of previous reconnaissance ground-water investigations that are sources 

of well data for the Ground-Water Resource Evaluation Program in the North Carolina 

Blue Ridge and Piedmont................................................................................................................................. 8

4. Exposed early Mesozoic basins in eastern North America .............................................................................. 11

5. Hydrogeologic units within the Blue Ridge and Piedmont Provinces of North Carolina................................ 14

6. Graph showing average yield of wells of average construction in the hydrogeologic units of the 

Blue Ridge and Piedmont Provinces of North Carolina .......................................................................................... 15

7. Map showing geologic belts and some major structural features within the Blue Ridge and Piedmont 

Provinces of North Carolina..................................................................................................................................... 16

8. Diagram showing principal components of the ground-water system in the Blue Ridge and Piedmont 

Provinces of North Carolina..................................................................................................................................... 18

9. Diagram showing the reservoir-pipeline conceptual model of the Blue Ridge-Piedmont ground-water 

system and the relative volume of ground-water storage within the system............................................................ 19

10. Map showing locations of gaging stations and drainage basins in the Blue Ridge and Piedmont of 

North Carolina for which estimates of ground-water recharge were determined by the technique 

of hydrograph separation ......................................................................................................................................... 22

11. Graphs showing relation of porosity and specific yield to total ground-water storage 

and available water in the regolith ........................................................................................................................... 25

12–15. Diagrams showing:

12. A conceptual view of the North Carolina Blue Ridge and Piedmont ground-water flow system 

showing the unsaturated zone (lifted up), the water-table surface, the saturated zone, and directions 

of ground-water flow ........................................................................................................................................ 26

13. Conceptual variations of transition zone thickness and texture that develop 

on different parent rock types........................................................................................................................... 27

14. An idealized weathering profile through the regolith, and relative permeability............................................. 28

15. The transition zone between bedrock and saprolite functioning as a primary transmitter 

of contaminated ground water to a stream........................................................................................................ 29

16. Graph showing relation of average well yield to the average saturated thickness of regolith 

for hydrogeologic units in the Blue Ridge and Piedmont Provinces of North Carolina.......................................... 32

17. Maps showing geographic variation of median concentrations of (A) total dissolved solids, and 

(B) nitrite plus nitrate in ground water, by county, in North Carolina..................................................................... 37

18. Map showing locations of active and potential study sites in the Asheville, Mooresville, Winston-Salem, 

and Raleigh Regions of the North Carolina Department of Environment and Natural Resources.......................... 40

TABLES

1. Classification and lithologic description of hydrogeologic units in the Blue Ridge and Piedmont Provinces 

of North Carolina ..................................................................................................................................................... 12

2. Relative percentages of hydrogeologic units in the Blue Ridge and Piedmont Provinces of North Carolina ......... 13

3. Geologic belts of the Blue Ridge, Piedmont, and Coastal Plain Provinces of North Carolina................................ 17

4. Water budgets of selected streams in the Blue Ridge and Piedmont Provinces of North Carolina ......................... 21

5. Properties of regolith at three well locations in the Piedmont northwest of Greensboro, North Carolina............... 24

6. General hydrologic characteristics of the hydrogeologic terranes of the Blue Ridge and Piedmont Provinces 

within the Appalachian Valleys-Piedmont Regional Aquifer-System Analysis (APRASA) study area ................. 31

7. Selected statistics for selected properties and constituents of ground water in the Blue Ridge and Piedmont 

Provinces, Appalachian Valleys-Piedmont Regional Aquifer-System Analysis (APRASA) study area................. 36
Contents VII

CONVERSION FACTORS, VERTICAL DATUM, TEMPERATURE, AND DEFINITIONS

Multiply By To obtain

Length

inch (in.) 2.54 centimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

square foot (ft2) 0.0929 square meter

acre 0.4047 hectare

square mile (mi2) 2.590 square kilometer

Volume

gallon (gal) 3.785 liter

million gallons (Mgal) 3,785 cubic meter

cubic foot (ft3) 0.02832 cubic meter

Flow

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

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

Radioactivity

picocurie per liter (pCi/L) 3.785 becquerel per liter

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD 

of 1929)—a geodetic datum derived from a general adjustment of the first-order level nets of the 

United States and Canada, formerly called Sea Level Datum of 1929.

Temperature: Temperature conversions between degrees Celsius (°C) and degrees Fahrenheit (°F) 

can be made by using the following equations:

°F = (1.8 x °C) + 32

°C = 5/9 (°F – 32)

Definitions:

μg/L microgram per liter

mg/L milligram per liter

+/- plus or minus

Cover photographs: Research activities at the North Carolina State University Lake Wheeler Field Research Laboratory, 

Raleigh, North Carolina (taken by Charles C. Daniel, III).
Abstract 1

Preliminary Hydrogeologic Assessment and Study 

Plan for a Regional Ground-Water Resource 

Investigation of the Blue Ridge and Piedmont 

Provinces of North Carolina

By Charles C. Daniel, III,1 and Paul R. Dahlen2

ABSTRACT

Prolonged drought, allocation of surface-water 

flow, and increased demands on ground-water supplies 

resulting from population growth are focuses for the 

need to evaluate ground-water resources in the Blue 

Ridge and Piedmont Provinces of North Carolina. 

Urbanization and certain aspects of agricultural 

production also have caused increased concerns about 

protecting the quality of ground water in this region.

More than 75 percent of the State's population 

resides in the Blue Ridge and Piedmont Provinces in an 

area that covers 30,544 square miles and 65 counties. 

Between 1940 and 2000, the population in the 

Piedmont and Blue Ridge Provinces increased from 

2.66 to 6.11 million; most of this increase occurred in 

the Piedmont. Of the total population, an estimated 

1.97 million people, or 32.3 percent (based on the 1990 

census), relied on ground water for a variety of uses, 

including commercial, industrial, and most 

importantly, potable supplies.

Ground water in the Blue Ridge and Piedmont 

traditionally has not been considered as a source for 

large supplies, primarily because of readily available 

and seemingly limitless surface-water supplies, and the 

perception that ground water in the Blue Ridge and 

Piedmont Provinces occurs in a complex, generally 

heterogeneous geologic environment. Some reluctance 

to use ground water for large supplies derives from the 

reputation of aquifers in these provinces for producing 

low yields to wells, and the few high-yield wells that 

are drilled seem to be scattered in areas distant from 

where they are needed. Because the aquifers in these 

provinces are shallow, they also are susceptible to 

contamination by activities on the land surface.

In response to these issues, the North Carolina 

Legislature supported the creation of a Resource 

Evaluation Program to ensure the long-term 

availability, sustainability, and quality of ground water 

in the State. As part of the Resource Evaluation 

Program, the North Carolina Division of Water Quality, 

Groundwater Section, in cooperation with the U.S. 

Geological Survey, initiated a multiyear study of 

ground water in the Blue Ridge and Piedmont 

Provinces. The study began in 1999.

Most of the study area is underlain by a 

complex, two-part, regolith-fractured crystalline rock 

aquifer system. Thickness of the regolith throughout 

the study area is highly variable and ranges from 0 to 

more than 150 feet. The regolith consists of an 

unconsolidated or semiconsolidated mixture of clay 

and fragmental material ranging in grain size from silt 

to boulders. Because porosities range from 35 to 

55 percent, the regolith provides the bulk of the water 

storage within the Blue Ridge and Piedmont 

ground-water system. At the base of the regolith is the 

transition zone where saprolite grades into 

unweathered bedrock. The transition zone has been 

identified as a potential conduit for rapid ground-water 

flow. If this is the case, the transition zone also may 

serve as a conduit for rapid movement of contaminants 

to nearby wells or to streams with channels that cut into 

1U.S. Geological Survey, Raleigh, North Carolina. 2

North Carolina Department of Environment and Natural Resources, 

Division of Water Quality, Groundwater Section.
2 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

or through the transition zone. How rapidly a 

contaminant moves through the system largely may be 

a function of the characteristics of the transition zone. 

The transition zone is one of several topics identified 

during the literature review and data synthesis, for 

which there is a deficiency in data and understanding of 

the processes involved in the movement of ground 

water to surface water.

Because the Blue Ridge and Piedmont study 

area is so large, and the hydrogeology diverse, it is not 

feasible to study all of the area in detail. A more 

feasible approach is to select areas that are most 

representative of the land use, geology, and hydrology 

to obtain an understanding of the hydrologic processes 

in the selected areas, and transfer the knowledge from 

these local "type areas" to similar regional 

hydrogeologic areas.

For the purpose of this study, the term "type 

area" applies to a 10- to 100-square mile area within a 

hydrogeologic terrane where information is sufficient 

to develop and test a concept of ground-water flow by 

using analytical or numerical methods that can be 

validated by field measurements. Ideally, these type 

areas are selected to be representative of the flow 

system that is present wherever a particular 

hydrogeologic terrane is present.

This report consists of two basic parts. The first 

part describes the results of a comprehensive review 

and synthesis of information and literature that 

provides the basic background for the study. This 

includes current (2002) knowledge regarding general 

geology and the hydrogeologic framework of the 

fractured-rock aquifer system that underlies the Blue 

Ridge and Piedmont Provinces. In spite of the quantity 

of information identified during the literature review 

and the amount of past work that has been documented, 

there are still research needs to be met.

The second part of the report describes State 

ground-water issues and problems, available data, and 

data deficiencies. It also describes the design and 

implementation of efforts to characterize ground-water 

quality and to quantify factors that influence the 

movement and availability of ground water in the 

hydrogeologic terranes characterized by (1) massive or 

foliated crystalline rocks overlain by thick regolith and 

(2) massive or foliated crystalline rocks overlain by 

thin regolith.

As of September 2001, seven sites had been 

identified as potential study sites to be used to 

characterize the hydrogeology and water quality of 

type areas considered representative of the larger 

terranes. Detailed geologic mapping, core drilling, well 

installation, and surface and borehole geophysical 

surveys are in progress at four of the sites.

INTRODUCTION

Historically, ground-water investigations in the 

Blue Ridge and Piedmont Provinces of North Carolina 

have received less emphasis than investigations of the 

more productive Coastal Plain aquifers. Coastal Plain 

aquifers supply water to most of that region's population, 

and these aquifers have received well-justified scientific 

attention. In contrast, the aquifers of the Blue Ridge and 

Piedmont serve only a small percentage of the municipal 

population because abundant rainfall and relief provide 

adequate surface-water resources. However, the small 

communities and rural population of the Blue Ridge and 

Piedmont Provinces are dependent upon ground-water 

supplies. Droughts, allocation of surface-water flow, 

contamination incidents, and increased demands on 

ground-water supplies have focused the need to evaluate 

ground-water resources in the Blue Ridge and Piedmont 

Provinces. 

North Carolina has abundant water resources; 

however, ground-water characteristics in the regolithbedrock aquifer system of the State are complex and 

poorly understood. More than 75 percent of the State's 

population resides in the Blue Ridge and Piedmont 

Provinces (North Carolina Department of Commerce, 

1999), and the ground-water resources of this area of the 

State are important for supporting this large population.

The study area for ground-water investigations in 

the Blue Ridge and Piedmont Provinces of North Carolina 

is in the Appalachian Highlands of the eastern United 

States. The study area covers 30,544 square miles in 

western North Carolina. The geologic framework and 

hydrology of the study area are diverse and complex. 

Metamorphic and igneous rocks underlie most of the Blue 

Ridge and Piedmont, and regolith overlies these rock 

types. During 1990, 32.3 percent of the approximately 

4.94 million people living within the 65 counties of the 

study area relied on ground water for potable supplies. 

Most of this water was supplied by wells at single-family 

homes. Ground water pumped from aquifers in the 

Piedmont supplied about 30 percent of the population 

within that province. However, ground water in the Blue 

Ridge Province supplied nearly 51.1 percent of the 

population. Well yields in sedimentary basins (principally 

the Deep River Triassic basin) in the Piedmont Province 

are among the lowest in the State.
Purpose and Scope 3

The contribution to surface water by ground water 

from shallow aquifers commonly is overlooked, but it is 

an important component in watershed hydrology (Winter 

and others, 1998). About 46 percent of the annual 

discharge of Blue Ridge and Piedmont streams in the 

eastern United States originates as ground water 

(Rutledge and Mesko, 1996). The ground water carries 

not only naturally occurring dissolved constituents to the 

surface water but, in contaminated areas, also has the 

potential to carry contaminants to surface waters. Thus, 

understanding the ground-water system in the Blue Ridge 

and Piedmont Provinces is important not only to small 

communities and rural populations who depend on 

ground water for potable drinking water, but also to 

municipalities because of the potential for contaminated 

ground water to contaminate surface-water supplies.

Ground water in the Blue Ridge and Piedmont 

Provinces has been investigated in previous studies 

(Mundorff, 1948; LeGrand, 1967; Cederstrom, 1972, for 

example); however, the focus of these studies often was 

on ground-water quantity in the deeper bedrock aquifers. 

Relatively few studies have focused on shallow 

ground-water resources in the regolith, the ground-water 

contribution to streams (Rutledge and Mesko, 1996), or 

ground-water quality (Briel, 1997). Because of the 

relative lack of focus on shallow ground-water conditions 

in the Blue Ridge and Piedmont, there is a scarcity of 

information on shallow ground-water quality, movement, 

and storage.

The North Carolina Department of Environment 

and Natural Resources (NCDENR), Division of Water 

Quality, Groundwater Section (hereafter referred to as the 

Groundwater Section), has a mission to "promote the 

stewardship of North Carolina's ground-water resources 

for the protection of human health and the environment" 

(North Carolina Division of Water Quality, Groundwater 

Section, 1999). In order to fulfill this mission, the 

Groundwater Section needs to better understand the 

hydrogeology of the State's aquifers and the quality of 

water in these aquifers. Critical to this endeavor is 

understanding the movement of subsurface contaminants 

and(or) the movement of contaminants spilled at the land 

surface to supply wells or to surface-water bodies. The 

Groundwater Section has the goal of systematically 

developing hydrogeologic knowledge, widely distributing 

hydrogeologic data and interpretations, and providing the 

public with useful and meaningful information about 

North Carolina's near-surface aquifers (North Carolina 

Division of Water Quality, Groundwater Section, 1999).

As part of this mission, the Groundwater Section 

implemented a Resource Evaluation Program to evaluate 

ground-water resources across the State, with a focus on 

water quality. Given the natural division of the State into 

two major ground-water systems—with porous 

sedimentary aquifers beneath the Coastal Plain in the east 

and fractured crystalline bedrock beneath the Blue Ridge 

and Piedmont in the west—it was logical to evaluate 

these areas separately. A major effort is underway to 

review past ground-water studies in the Blue Ridge and 

Piedmont, develop plans for a long-term evaluation of 

ground-water resources in these provinces, and begin 

identifying and selecting study sites for research that will 

fill gaps in current knowledge. The study, which began in 

1999, is being conducted cooperatively by the U.S. 

Geological Survey (USGS) and the Groundwater Section. 

The title of this cooperative study is “Ground-Water 

Resource Evaluation Program in the North Carolina Blue 

Ridge and Piedmont.”

 Principal objectives of the study are to (1) define 

the hydrogeologic framework of the Blue Ridge and 

Piedmont; (2) identify and characterize the hydrologic 

processes active in each province; (3) investigate the 

functioning of representative ground-water flow systems 

in the regolith-fractured rock aquifer systems by means of 

applied research, analytical methods, and computer 

simulation; (4) refine the present understanding of 

recharge and discharge processes and their role in 

determining ground- and surface-water quality; 

(5) estimate regional water budgets, including rates of 

natural discharge and recharge, changes in aquifer 

storage, and withdrawals; (6) determine the importance 

and interrelation of surface- and ground-water flow 

systems and their effects on water quality and potential 

for development; and (7) develop a comprehensive 

ground-water database for the region. This report is the 

first major information product resulting from the study 

and provides the hydrogeologic and organizational 

background for meeting the long-term objectives of the 

study. Results of this study, when combined with other 

studies in the Blue Ridge and Piedmont Provinces of 

North Carolina and the eastern United States, will help in 

the management of the Nation’s water resources by 

defining the quality and quantity of these resources.

Purpose and Scope

The purpose of this report is to synthesize existing 

information about ground-water resources in the Blue 

Ridge and Piedmont Provinces of western North Carolina 

and to describe plans for quantifying the ground-water 

quality, hydrologic processes, and aquifer characteristics 

in these two physiographic provinces. The report has two 

basic parts.
4 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

The first part of the report describes the general 

geology and hydrogeology of the Blue Ridge and 

Piedmont study area. This includes current knowledge 

regarding the hydrogeologic framework of the complex 

heterogeneous fractured-rock aquifer system that 

underlies these physiographic provinces. Hydrogeologic 

terranes and conceptual flow systems within the study 

area are defined and described. A table of generalized 

hydrologic characteristics for each hydrogeologic terrane 

is provided for comparison of hydrogeologic terranes 

throughout the study area. Included in this discussion is 

background material describing certain fundamentals of 

ground-water hydrology to help the lay reader better 

understand the hydrologic characteristics of the aquifer 

system. 

The second part of the report describes State 

ground-water issues and problems, available data and data 

deficiencies, and outlines the design of a long-term 

regional study of ground-water resources in a study area 

that covers 30,544 square miles and 65 counties in 

western North Carolina. Information from basic research, 

field and laboratory experiments, and knowledge gained 

from hydrogeologic case studies in fractured-rock 

terranes is used to establish the basis for a long-term, 

multiyear study of ground water in the region. The report 

describes the organization, and approaches for 

accomplishing the objectives of this regional groundwater study, which began in 1999, and is being conducted 

cooperatively by the USGS and the Groundwater Section. 

In addition, the report describes the criteria used to select 

sites for in-depth studies, site characterization procedures 

to be employed, and the characteristics of sites selected 

for the first phase of the study. Because field work began 

at several sites while this report was in preparation, short 

summaries of ongoing work at these sites are included. 

Information products, including databases, that are 

expected to be generated during the study also are 

described in the second part of the report.

Acknowledgments

The authors wish to acknowledge the significant 

contribution of USGS hydrologist, William L. 

Cunningham, for his assistance with an early version of 

this report. We thank him for his time and effort. The 

technical reviews of the report manuscript provided by 

Rick E. Bolich, Donald J. Geddes, Tina P. Parsons, and 

Matt J. Heller of the Groundwater Section and Melinda J. 

Chapman, Anthony J. Tesoriero, the late Andrew G. 

Warne, and Lester J. Williams of the USGS also are 

appreciated. Rick E. Bolich, Donald J. Geddes, Tina P. 

Parsons, and Matt J. Heller also are recognized for their 

efforts in identifying and obtaining access to potential 

study sites and for providing information about available 

data in the Groundwater Section regional offices.

Description of the Study Area

North Carolina lies within three physiographic 

provinces of the southeastern United States (fig. 1): the 

Blue Ridge, the Piedmont, and the Coastal Plain 

(Fenneman, 1938). The Blue Ridge and Piedmont 

physiographic provinces encompass about 96,000 square 

miles (mi2) and extend for about 1,000 miles (mi) from 

near New York City to near Montgomery, Alabama. The 

Piedmont Province is less than 40 mi wide in New Jersey, 

but is about 150 mi wide in North Carolina. The Blue 

Ridge Province extends southwestward from a very 

narrow section in southern Pennsylvania to northern 

Georgia; the province reaches its widest point in eastern 

Tennessee and western North Carolina, where it is nearly 

100 mi wide. In North Carolina, the Blue Ridge and 

Piedmont Provinces encompass about 55 percent of the 

State, all or part of 65 counties, and cover 30,544 mi2

.

Physiography

In western North Carolina, the Blue Ridge 

Province contains the greatest mountain masses, highest 

altitudes, and the most rugged topography in eastern 

North America. The province is marked by steep, forestcovered slopes that are cut by numerous small stream 

valleys. More than 40 mountain peaks are greater than 

6,000 feet (ft) in altitude, and another 82 peaks range 

between 5,000 and 6,000 ft in altitude (Conrad and others, 

1975). The province is bounded on the west by the Ridge 

and Valley Province in Tennessee. On the east, the 

boundary between the Blue Ridge and the Piedmont is 

marked by the escarpment of the Blue Ridge front—a 

prominent topographic feature thought to be associated, 

in part, with faulting. The Blue Ridge front rises more 

than 1,700 ft above the Piedmont surface at the North 

Carolina-Virginia border and reaches a maximum relief of 

nearly 2,500 ft in central North Carolina.

The topography of the Piedmont Province consists 

of low, well-rounded hills and long, northeast-trending 

valleys and ridges. The surfaces of many ridge tops and 

interstream divides are relatively flat and are thought to be 

remnants of an ancient erosional surface of low relief. 

More recent erosion and downcutting by streams has 

dissected the Piedmont surface and created local 

topographic relief of 100 to 200 ft between interstream 

divides and stream bottoms. The Piedmont surface is 

300 to 600 ft in altitude along the eastern border with the 
Description of the Study Area 5

Figure 1. Locations of the Blue Ridge and Piedmont Provinces of North Carolina and the 65 counties in the study area.
6 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

Coastal Plain Province, and rises gradually to the west to 

about 1,500 ft in altitude at the foot of the Blue Ridge 

front.

Scattered across the undulating Piedmont surface 

are remnants of once higher mountains that, because of 

their resistance to erosion, stand as much as 500 to 

1,600 ft above the local land surface. Some form 

prominent lines of hills. Others are isolated hills and 

mountains called monadnocks. Although more common 

in the western Piedmont, these elevated features are found 

throughout the province.

The Piedmont Province is bounded on the east by 

the Fall Line (fig. 1), which delineates the boundary 

between the hard, weathering-resistant crystalline rocks 

of the Piedmont and the less resistant sedimentary rocks 

of the Coastal Plain Province. At the Fall Line, the swift 

flowing streams of the Piedmont enter the Coastal Plain 

over a zone of rapids and low falls.

The Coastal Plain has little relief in contrast to the 

adjoining Piedmont. The Coastal Plain is marked by lowgradient streams flowing in broad valleys. The Coastal 

Plain is mostly composed of sand and clay units that 

thicken seaward from a feather edge at the Fall Line 

(fig. 1). Along the western edge of the Coastal Plain, the 

sediments are underlain at shallow depth by crystalline 

Piedmont rocks.

Precipitation

Precipitation within the study area ranges from a 

minimum of about 30 inches per year (in/yr) in the central 

Piedmont to a maximum in excess of 80 in/yr in 

southwestern North Carolina. Average (1951–80) 

precipitation in most areas is 40 to 50 in/yr (U.S. 

Geological Survey, 1986, p. 52). The area of maximum 

precipitation occurs in the Blue Ridge Province in 

northeastern Georgia, eastern Tennessee, and 

southwestern North Carolina as a result of orographic 

effects of the mountain ridges (Kopec and Clay, 1975).

Runoff

Average annual runoff (1951–80) ranges from a 

minimum of less than 10 inches (in.) to a maximum of 

about 50 in. The average runoff is 10 to 20 in/yr in most 

areas (U.S. Geological Survey, 1986, p. 52; Gebert and 

others, 1987). Runoff generally is higher in areas of the 

western Piedmont and Blue Ridge Provinces compared to 

the rest of the study area because of higher precipitation, 

steep hillslopes and streambed gradients, shorter growing 

seasons, lower temperatures, and lower evapotranspiration. During periods of low flow (usually September and 

October), most of the sustained nonregulated streamflow 

is from ground-water discharge.

Population Growth and Water Use

Population and industrial growth in the Blue Ridge 

and Piedmont Provinces of North Carolina have resulted 

in increased demands on water resources. Between 1940 

and 2000, population in the Piedmont and Blue Ridge 

increased from 2.66 to 6.11 million; most of this increase 

occurred in the Piedmont (fig. 2). The number of people 

supplied by ground water between 1960 and 1980 also 

increased, although the percentage of the total population 

supplied by ground water remained fairly constant at 

47 to 48 percent. Between 1980 and 1990, however, there 

was a 15.6 percent decrease in the population supplied by 

ground water. This decrease is attributed almost entirely 

to the high rate of population growth in four Piedmont 

counties (Forsyth, Guilford, Mecklenburg, and Wake; 

fig. 1) containing large urban areas (Winston-Salem, 

Greensboro, Charlotte, and Raleigh, respectively) that are 

supplied primarily by surface-water-based municipal 

supplies. Subtracting the populations of these four 

counties from the calculation results in a population of 

about 43 percent supplied by ground water in 1990. This 

percentage is closer to the previous 20-year trend. The 

decrease in the percentage of population supplied by 

ground water is important because of the implied increase 

in surface-water usage. Data for the number of people 

supplied by ground water in 2000 are not yet available; 

once the data are available, however, it will be possible to 

determine whether the decline in ground-water users in 

1990 was a short-term fluctuation or the beginning of a 

long-term trend. If this new trend continues, surfacewater resources may not be adequate to meet increased 

demands, and alternative water sources will be needed.

Currently (2002), most ground-water use is for 

domestic supplies. Dependence on ground-water supplies 

is not evenly divided between the two provinces. In 1990, 

about 30 percent of the population living within the 

Piedmont relied on ground water for potable supplies. In 

the Blue Ridge, ground water supplied 51.1 percent of the 

population (U.S. Bureau of the Census, 1992). Municipal 

and industrial water supplies in the two provinces are 

derived almost exclusively from surface-water sources. 

The potential for future development of surface water 

becomes limited, however, as the most suitable sites for 

reservoirs become inhabited or are used for other 

purposes, as land purchase and development costs 

increase, and as environmental concerns regarding 

surface-water impoundments cause delays in approval of 

necessary permits. In order to meet the increased demand 

for water, ground-water resources may need to be 
Previous Investigations 7

developed in the future to a much greater extent than in 

the past.

Previous Investigations

Between 1946 and 1971, reconnaissance 

ground-water-resource investigations were completed for 

14 areas that encompassed all 65 counties in the Blue 

Ridge and Piedmont Provinces of North Carolina (fig. 3). 

The results of these studies are contained in the published 

reports cited in figure 3. Included in the reports are maps 

that show well locations in each county and tables of well 

records that provide details of well construction, yield, 

use, topographic setting, water-bearing formations, and 

miscellaneous notes. Data were compiled from these 

reports for drilled wells completed in bedrock and 

statistically analyzed by Daniel (1989) to determine 

relations between well yield and construction, 

topographic setting, hydrogeologic units, lithotectonic 

belts, and other characteristics. A hydrogeologic unit map 

of the Blue Ridge and Piedmont Provinces of North 

Carolina also was compiled by Daniel and Payne (1990) 

as part of this work.

The hydrogeology of the Blue Ridge and Piedmont 

Provinces of the eastern and southeastern United States is 

described by LeGrand (1967), Heath (1984), and Swain 

and others (1991). A book dealing with various groundwater-related topics ranging from availability to quality in 

the Piedmont of the eastern United States was compiled 

by Daniel and others (1992). The hydrology of the Valley 

and Ridge, Blue Ridge, and Piedmont Provinces, 

extending from Pennsylvania to Alabama, was studied as 

part of the USGS’s Regional Aquifer-System Analysis 

(RASA) Program; this study, known as the Appalachian 

Valleys-Piedmont RASA, resulted in the production of 

numerous reports that are listed in a bibliography 

compiled by Sun and others (1997). The hydrologic 

characteristics of shallow aquifer systems in the Valley 

and Ridge, Blue Ridge, and Piedmont were investigated 

by Rutledge and Mesko (1996).

The hydrogeologic framework of the Piedmont of 

North Carolina was described by Harned (1989) as part of 

a reconnaissance study of ground-water quality. Details of 

the hydrogeologic framework, particularly the nature of 

Figure 2. Growth in population and number of people supplied by ground water in the Blue Ridge 

and Piedmont Provinces of North Carolina, 1940 – 2000 (modified from Daniel, 1992a). Population data 

compiled from U.S. Bureau of the Census (1952, 1963, 1973, 1982, 1992) and U.S. Census Bureau 

(2001). Population supplied by ground water compiled from MacKichan and Kammerer (1961), North 

Carolina Division of State Budget and Management (1979, 1984), and U.S. Bureau of the Census 

(1992).
8 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont Figure 3. Study areas of previous reconnaissance ground-water investigations that are sources of well data for the Ground-Water Resource Evaluation Program in the North Carolina Blue Ridge and Piedmont.
Hydrogeologic Setting 9

the transition zone between bedrock and regolith, were 

refined by Harned and Daniel (1992). Ground-water 

recharge rates for selected sites in the Blue Ridge and 

Piedmont of North Carolina have been estimated by 

Daniel and Sharpless (1983), Harned and Daniel (1987), 

and Daniel (1990a, b). Detailed studies of ground-water 

recharge in the central Piedmont have been made by 

Daniel (1996), Mew and others (1996), and Daniel and 

Harned (1998). The distribution of fracture permeability 

with depth in fractured bedrock beneath different 

topographic settings in the Piedmont of North Carolina 

has been statistically characterized by Daniel (1992b) and 

Daniel and others (1997). The nature of the relation 

between well yield and topographic setting has been 

further investigated by McKelvey (1994), Ali (1998), and 

Daniel and Ali (1999); these authors found a relation 

between well yields and subdivisions of topographic 

settings based on drainage patterns and the implied 

presence or absence of bedrock fracturing.

HYDROGEOLOGIC SETTING

The geology of the Blue Ridge and Piedmont 

Provinces is complex; the hydrogeology of these 

physiographic provinces is equally complex. All major 

classes of rocks—metamorphic, igneous, and 

sedimentary—are present, although metamorphic rocks 

are the most abundant. The metamorphic and igneous 

rocks range in composition from felsic to ultramafic and 

in age from Precambrian in the Blue Ridge to Triassic and 

Jurassic in the Piedmont. Three or more periods of 

igneous intrusion (Fullagar, 1971) have resulted in the 

emplacement of plutonic bodies that range in size from 

batholiths down to dikes, sills, and veins. Most intrusions 

have been metamorphosed, deformed, and fractured, but 

some are massive and have little or no foliation. The 

degree of metamorphism of the rocks varies from low 

rank to high rank. Many have been folded and refolded 

during multiple metamorphic and orogenic events. Within 

the crystalline rocks of the Piedmont are down-faulted 

basins (grabens) filled with sedimentary rocks of Triassic 

age.

The rocks are broken and displaced by numerous 

faults and zones of shearing, some of which are many 

miles in length. Rock fractures without displacement, 

called joints, are ubiquitous. The joints commonly cluster 

in groups oriented generally in one or more preferred 

directions. All rocks have been subjected to uplift, 

weathering, and erosion, which have resulted in the 

widening of fractures and the formation of new openings, 

such as stress-relief fractures. These breaks in the 

otherwise solid rock are the conduits through which 

ground water flows in the bedrock.

Bedding and planes of metamorphic foliation 

generally are folded and tilted and can have almost any 

attitude and orientation. Fractures, bedding, and foliation 

create heterogeneities in the rocks and result in permeability that typically is greatest parallel to bedding, 

foliation, and zones of fracture concentration; permeability typically is least at right angles to the plane of these 

features.

Bedrock may be exposed at land surface on steep 

slopes, rugged hilltops, or in stream valleys, but nearly 

everywhere else it is overlain by unconsolidated material 

that may reach depths greater than 100 ft. Collectively this 

unconsolidated material, which is composed of saprolite, 

alluvium, and soil, is referred to as regolith. Saprolite is 

clay-rich, residual material derived from the in-place 

weathering of bedrock. When the bedrock weathers to 

form saprolite, the relict structures generally are retained, 

and the directional properties of permeability also are 

retained. In many valleys, the saprolite has been removed 

by erosion and the bedrock is exposed or thinly covered 

by alluvial deposits. Soil is present nearly everywhere as 

a thin mantle covering both the saprolite and alluvium. 

The water-storing and transmitting characteristics of 

bedrock and regolith, and the hydrologic relation between 

them, is a major factor in the water-supply potential of the 

ground-water system in the Blue Ridge and Piedmont 

Provinces.

Crystalline Rock

Metamorphic and igneous crystalline rocks 

underlie most of the Blue Ridge and Piedmont. 

Metamorphic and igneous rocks in these provinces range 

in composition from felsic to ultramafic and range in age 

from Middle Proterozoic for granitic rocks in the Blue 

Ridge (Tilton and others, 1960) to Triassic-Jurassic for 

the unmetamorphosed dikes and sills of mafic 

composition that intrude older Piedmont rocks (Weigand 

and Ragland, 1970; Ragland and others, 1983). Rocks that 

crop out in the Piedmont underlie parts of the Atlantic 

Coastal Plain at depth.

Bedding and foliation within metamorphic bedrock 

usually are folded and tilted, can exhibit variable 

orientations, and commonly intersect one another in 

systematic geometric patterns. Bedrock generally is 

weathered to saprolite; however, relict structures and 

directional properties controlling permeability or 

hydraulic conductivity are retained in places. Although 

most rocks in the area have been metamorphosed and 

have strong directional fabrics, igneous intrusives 
10 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

emplaced after the last metamorphic event in the late 

Paleozoic tend to be less foliated and less fractured. Most 

of the rocks were subjected to uplift during the Cenozoic 

Era and subsequent weathering and erosion, which 

opened or widened existing fractures and created new 

ones by stress relief. Fault zones of different types, scales, 

and orientations are common; some are characterized by 

an extensive and intricate network of fractures.

Ground-water flow within metamorphosed 

carbonate rocks of the Blue Ridge and Piedmont 

Provinces can be substantial. Most of the reported areas of 

high well yields, however, are outside of North Carolina 

(Causey, 1965; McGreevy and Sloto, 1976, 1977). 

Metamorphosed carbonate rocks in North Carolina are 

limited almost exclusively to the Murphy and Blue Ridge 

belts in the Blue Ridge physiographic province. The most 

prominent occurrence in the Murphy belt is the Murphy 

Marble; in the Blue Ridge belt, the most extensive 

exposures of carbonate rock are found in the vicinity of 

the Grandfather Mountain window where the Shady 

Dolomite is exposed beneath the Linville Falls fault 

(Bryant and Reed, 1970). Linville Caverns, which were 

formed by dissolution of the Shady Dolomite, lie in the 

southwestern part of the window. According to Daniel 

(1989), the rocks of the Murphy belt were the source of 

the highest average well yield (25.5 gallons per minute 

[gal/min]) of the 14 belts that were evaluated. In contrast, 

the lowest average well yields were from noncarbonate 

crystalline rocks in the Smith River allochthon and 

noncarbonate sedimentary rocks in the Triassic basins; 

both belts provide an average yield of about 11.5 gal/min. 

The high yields in the Murphy belt may be a result of 

several factors, including the presence of solution 

openings in the carbonate rocks and high recharge rates 

associated with abundant precipitation in southwestern 

North Carolina. Large bodies of metamorphosed 

carbonate rocks are not found in the North Carolina 

Piedmont, although some small carbonate (marble) 

bodies have been mapped in the Inner Piedmont and 

Kings Mountain belts (Goldsmith and others, 1988).

Sedimentary Rock

Several sedimentary basins within the Piedmont 

Province of North Carolina contain rocks of early 

Mesozoic age (fig. 4). These basins are part of a series of 

elongated, down-faulted basins that crop out in a 

discontinuous belt almost 1,500 mi long extending from 

northeastern Nova Scotia to South Carolina. The 

Mesozoic basins in North Carolina are the Deep River, 

Danville, and Davie County basins (fig. 4). The largest 

basin in North Carolina is the Deep River basin, which is 

bordered on its eastern margin by the Jonesboro fault. 

Based on physiography, structure, and lithology, the Deep 

River basin is divisible into three subbasins, the Durham, 

Sanford and Wadesboro, which are named for the largest 

city in each subbasin (Reinemund, 1955). The total 

thickness of Triassic sedimentary rocks in the Deep River 

basin ranges from 7,000 to 10,000 ft. 

These basins were formed in Triassic and Jurassic 

times during the incipient rifting of the continents that 

formed the Atlantic Ocean. Concurrently, they filled with 

thick sequences of continental sediment eroded from 

surrounding crystalline highlands. These rift-basin 

sedimentary rocks primarily consist of interbedded red 

shale, sandstone, and siltstone. Locally, conglomerate and 

lacustrine black mudstone are common, and coal is 

present in the Richmond, Va., Danville, and Deep River 

basins of North Carolina (fig. 4). Interbedded basaltic lava 

flows have been identified in some basins (Froelich and 

Olsen, 1985).

Most geologic formations within the early 

Mesozoic basins strike northeast and dip from 5 to 40 

degrees toward the main border fault; dips are commonly 

toward the northwest or southeast. These Mesozoic 

deposits lie unconformably on Precambrian and 

Paleozoic crystalline rocks. Intrusive dikes and sills 

predominantly composed of diabase are common in and 

adjacent to the early Mesozoic basins (Ragland, 1991).

Hydrogeologic Units

Within the Blue Ridge and Piedmont of North 

Carolina are hundreds of rock units that have been defined 

and named by various conventions in keeping with 

classical geologic nomenclature. The geologic 

nomenclature, however, does little to reflect the waterbearing potential of the different units. To overcome this 

shortcoming and to reduce the number of rock units to the 

minimum necessary to reflect the differences in waterbearing potential, a classification scheme based on origin, 

composition, and texture was devised (table 1). The 

classification of hydrogeologic units shown in table 1 

reflects not only the primary porosity of rocks but also the 

potential of the rocks for developing secondary porosity 

in the form of fractures and solution openings. 

Composition and texture also reflect, in part, the rate and 

depth of weathering of these rock units and the waterbearing properties of the resulting regolith.

The origin of the hydrogeologic units in table 1 is 

indicated by the rock class (igneous, metamorphic, or 

sedimentary) or subclass (metaigneous, metavolcanic, or 

metasedimentary). The composition of the igneous, 

metaigneous, and metavolcanic rocks is designated as 
Sedimentary Rock 11

Figure 4. Exposed early Mesozoic basins in eastern North America (from Smoot and Robinson, 1988, fig. 1).
12 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

Table 1. Classification and lithologic description of hydrogeologic units in the Blue Ridge and Piedmont Provinces 

of North Carolina

[From Daniel, 1989]

Symbol Hydrogeologic unit Lithologic description

IGNEOUS INTRUSIVE ROCKS

IFI Igneous, felsic intrusive Light-colored, mostly granitic rocks, fine- to coarse-grained, some porphyritic, usually 

massive, locally foliated; includes granite, granodiorite, quartz diorite, quartz 

monzonite, alaskites.

III Igneous, intermediate intrusive Gray to greenish-gray, medium- to coarse-grained, massive rocks of dioritic 

composition; includes assemblages of closely associated diorite and gabbro where 

they are too closely associated to be mapped separately.

IMI Igneous, mafic intrusive Dark greenish-gray to black, medium- to coarse-grained intrusive bodies; primarily 

gabbroic in composition, includes closely associated gabbro and diorite where they are 

too closely associated to be mapped separately, ultramafic rocks, diabase, dunite.

METAMORPHIC ROCKS

Metaigneous Rocks (Intrusive)

MIF Metaigneous, felsic Light-colored, massive to foliated metamorphosed bodies of varying assemblages of 

felsic intrusive rock types; local shearing and jointing are common.

MII Metaigneous, intermediate Gray to greenish-gray, medium- to coarse-grained, massive to foliated, well-jointed, 

metamorphosed bodies of dioritic composition.

MIM Metaigneous, mafic Massive to schistose greenstone, amphibolite, metagabbro and metadiabase, may be 

strongly sheared and recrystallized; metamorphosed ultramafic bodies are often 

strongly foliated, altered to serpentine, talc, chlorite-tremolite schist and gneiss.

Metavolcanic Rocks (Extrusive-Eruptive)

MVF Metavolcanic, felsic Chiefly dense, fine-grained, light-colored to greenish-gray felsic tuffs and felsic crystal 

tuffs, includes interbedded felsic flows. Felsic lithic tuffs, tuff breccias, and some 

epiclastic rocks; recrystallized fine-grained groundmass contains feldspar, sericite, 

chlorite, and quartz. Often with well-developed cleavage, may be locally sheared; 

phyllitic zones are common throughout the Carolina slate belt.

MVI Metavolcanic, intermediate Gray to dark grayish-green tuffs and crystal tuffs generally of andesitic composition; 

most with well-developed cleavage; also includes interbedded lithic tuffs and flows of 

probable andesitic and basaltic composition and minor felsic volcanic rocks.

MVM Metavolcanic, mafic Grayish-green to dark-green, fine- to medium-grained andesitic to basaltic tuffs, crystal 

tuffs, crystal-lithic tuffs, tuff breccias and flows; pyroclastic varieties may contain 

lithic fragments; commonly exhibits prominent cleavage; alteration minerals include 

chlorite, epidote, calcite, and tremolite-actinolite.

MVE Metavolcanic, epiclastic Primarily coarse sediments including interbedded graywackes and arkoses and minor 

conglomerates, interbedded argillites and felsic volcanic rocks; much of the sequence 

is probably subaqueous in origin and most of the rocks were derived from volcanic 

terranes.

MVU Metavolcanic, undifferentiated Volcanic rocks of all origins (extrusive and eruptive) and compositions (felsic to mafic) 

interbedded in such a complex assemblage that mapping of individual units is not 

practical.

Metasedimentary Rocks

ARG Argillite Fine-grained, thinly laminated rock having prominent bedding plane and axial plane 

cleavage; locally includes beds of mudstone, shale, thinly laminated silt-stone, 

conglomerate, and felsic volcanic rock.

GNF Gneiss, felsic Mainly granitic gneiss; light-colored to gray, fine- to coarse-grained rocks, usually with 

distinct layering and foliation, often interlayered with mafic gneisses and schists.

GNM Gneiss, mafic Mainly biotite hornblende gneiss; fine- to coarse-grained, dark gray to green to black 

rock, commonly with distinct layering and foliation, often interlayered with biotite and 

hornblende gneisses and schists, and amphibolite layers at some places.

MBL Marble Fine- to medium-grained, recrystallized limestone and dolostone; found primarily in the 

Murphy belt.

PHL Phyllite Light-gray to greenish-gray to white, fine-grained rock having well-developed cleavage; 

composed primarily of sericite but may contain chlorite; phyllitic zones are common 

throughout the Carolina slate belt and probably represent zones of shearing, although 

displacement of units is usually not recognizable.
Hydrogeologic Units 13

QTZ Quartzite Metasandstone, often feldspathic to highly feldspathic, thin- to thick-bedded with graded 

bedding at some places, includes meta-arkose and metaconglomerate; often 

interbedded with mica schist, phyllite, and slate.

SCH Schist Schistose rocks containing primarily the micas muscovite or biotite or both, occasional 

sericite and chlorite schists; locally interlayered with hornblende gneiss and schist, 

commonly with distinct layering and foliation.

SLT Slate Fine-grained metamorphic rock formed from such rocks as shale and volcanic ash, 

possesses the property to part along planes independent of the original bedding (slaty 

cleavage).

MISCELLANEOUS

TRI Triassic sedimentary rocks Mainly red beds, composed of shale, sandstone, arkose, and conglomerate (fanglomerate 

near basin margins).

CPL Coastal Plain basement Undifferentiated crystalline basement rocks of igneous and metamorphic origin overlain 

unconformably by sedimentary sands, gravels, clays, and marine deposits.

Table 1. Classification and lithologic description of hydrogeologic units in the Blue Ridge and Piedmont Provinces 

of North Carolina (Continued)

[From Daniel, 1989]

Symbol Hydrogeologic unit Lithologic description

felsic, intermediate, or mafic except for the addition in the 

metavolcanic group of epiclastic rocks and 

compositionally undifferentiated rocks. These two groups 

were added to the metavolcanic group because they 

represent significant areas of metavolcanic rocks with 

distinct characteristics. The epiclastic rocks are the result 

of volcaniclastic deposits being reworked by sedimentary 

processes that included sufficient admixture of terrigenous 

sediment during deposition to make the rocks texturally 

distinct. The areas mapped as compositionally 

undifferentiated rocks contain complex and small-scale 

stratigraphic changes that make differentiation of separate 

units impractical. Composition also is shown in the 

metasedimentary units of gneiss, marble, and quartzite. 

The other metasediments are designated primarily on the 

basis of texture (grain size, degree of metamorphism, and 

development of foliation).

Two miscellaneous classifications account for the 

sedimentary rocks within the Triassic basins and the 

undifferentiated crystalline basement rocks east of the Fall 

Line that are overlain unconformably by sediments of 

Cretaceous age and younger.

By using the classification scheme in table 1 and the 

most recent geologic maps available, Daniel and Payne 

(1990) compiled a hydrogeologic unit map for the Blue 

Ridge and Piedmont Provinces in North Carolina (fig. 5). 

The percentage of the study area underlain by each 

hydrogeologic unit is given in table 2. Well-location maps 

were superimposed on the hydrogeologic unit map, and 

the units corresponding to the well locations were coded 

and entered into a computerized data file for analysis to 

determine the well yields in each unit (Daniel, 1989). The 

relation between well yield and hydrogeologic unit 

identified by Daniel (1989) is shown in figure 6. 

Additional analyses were made by Daniel (1989) to 

determine the relation between well yield, and other well 

characteristics, and topographic setting. These data also 

have been used to determine the average saturated 

thickness of regolith associated with each hydrogeologic 

Table 2. Relative percentages of hydrogeologic 

units in the Blue Ridge and Piedmont Provinces of 

North Carolina

Hydrogeologic unita

a

 Hydrogeologic units are named and described in 

table 1.

Percent

GNF 22

GNM 18

MIF 9.9

QTZ 7.3

ARG 6.4

MVF 6.3

IFI 5.4

SCH 5.2

TRI 5.1

MII 3.1

MVU 3.0

MIM 1.9

MVE 1.9

PHL 1.7

SLT 0.8

IMI 0.7

MVM 0.6

MVI 0.5

III 0.1

MBL 0.1
14 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont Figure 5. Hydrogeologic units within the Blue Ridge and Piedmont Provinces of North Carolina (from Daniel and Payne, 1990).
Hydrogeologic Belts 15

unit and the relation between well yield and the saturated 

thickness of regolith. The saturated thickness of regolith 

associated with a well is a computed characteristic 

described in Daniel (1989, p. A15).

Hydrogeologic Belts

The Blue Ridge and Piedmont Provinces are 

divided into a number of northeast-trending geologic belts 

(fig. 7) that provide a convenient and rational means of 

grouping the hydrogeologic units. Within a belt, rocks are 

to some degree similar with respect to general 

appearance, metamorphic rank, structural history, and 

relative abundance of igneous, metaigneous, 

metasedimentary, and metavolcanic rocks (Butler and 

Ragland, 1969). These northeast-trending belts tend to 

have distinct hydrogeologic properties (Daniel, 1989). 

Areally, the most significant are the Blue Ridge, Inner 

Piedmont, Charlotte, Carolina slate, and Raleigh belts. 

Two geologic belts important to this study have been 

added to the generally recognized belts. These are the 

Triassic basins and the Coastal Plain directly east of the 

Fall Line, where crystalline rocks are exposed along 

valleys and underlie sediments in interstream areas at 

shallow depth. A brief summary of the belts and the 

hydrogeologic units that constitute the belts is given in 

table 3. 

Figure 6. Average yield of wells of average construction in the hydrogeologic units of the Blue Ridge and Piedmont 

Provinces of North Carolina (modified from Daniel, 1989).
16 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont Figure 7. Geologic belts and some major structural features within the Blue Ridge and Piedmont Provinces of North Carolina (from Brown and Parker, 1985).
Hydrologic Conditions in the Study Area 17

HYDROLOGIC CONDITIONS IN THE STUDY AREA

Metamorphic and igneous crystalline rocks 

underlie most of the Blue Ridge and Piedmont Provinces. 

Because the underlying crystalline rocks are similar in 

character, these provinces are often grouped as one unit 

for hydrologic studies. The two provinces, however, have 

discernible differences in hydrology, largely because of 

differences in topographic relief, regolith thickness, and 

climate. Within the Piedmont crystalline rocks, extending 

from Nova Scotia to South Carolina (fig. 4), are large rift 

basins that have been filled with sedimentary deposits of 

Mesozoic age (Smoot and Robinson, 1988). The 

sedimentary rocks of the Mesozoic basins are distinct 

from the metamorphic and igneous crystalline rocks of 

the Blue Ridge and Piedmont and, therefore, comprise a 

separate hydrogeologic terrane.

The Blue Ridge-Piedmont ground-water system is 

composed of four elements (fig. 8). These components are 

(1) the unsaturated zone in the regolith, which generally 

contains the organic layers of the surface soil; (2) the 

saturated zone in the regolith; (3) the lower saturated 

regolith, which contains the transition zone between 

saprolite and bedrock; and (4) the fractured crystalline 

bedrock system.

The surficial or uppermost layer is composed of 

saprolite, alluvium, and soil, collectively referred to as 

regolith (Daniel and Sharpless, 1983). The thickness of 

Table 3. Geologic belts of the Blue Ridge, Piedmont, and Coastal Plain Provinces of North Carolina

[From Daniel, 1989; hydrogeologic units are described in table 1]

Belt Letter 

designation Boundaries Dominant 

hydrogeologic units

Murphy belt MU Surrounded by metasedimentary rocks of Blue Ridge 

belt.

SCH, SLT, MBL

Blue Ridge belt BR Sedimentary rocks of Valley and Ridge on northwest 

and Brevard fault zone on southeast.

GNF, GNM, SCH, QTZ, PHL

Chauga belt

(includes Brevard fault zone)

CA Blue Ridge belt on northwest, Inner Piedmont on 

southeast.

GNF, GNM

Inner Piedmont belt IP Chauga and Blue Ridge belts on northwest, Kings 

Mountain and Charlotte belts on southeast.

GNM, MIF

Smith River allochthon SR Blue Ridge belt on northeast and Sauratown 

Mountains anticlinorium on southeast.

GNF

Sauratown Mountains

anticlinorium

SA Smith River allochthon on northwest, Inner Piedmont 

belt on southwest, and Dan River Triassic basin 

and Milton belt on southeast.

GNM, GNF, QTZ

Kings Mountain belt KM Inner Piedmont belt on northwest and Charlotte belt 

on southeast.

SCH, MIF, GNF

Charlotte belt CH Kings Mountain and Inner Piedmont belts on 

northwest, Milton belt on north, Gold Hill shear 

zone and Carolina slate belt on southwest.

MII, MIF, MIM, IFI, MVU

Milton belt MI Igneous and metaigneous rocks of Charlotte belt on 

south, Carolina slate belt on southeast, Dan River 

Triassic basin and Sauratown Mountains 

anticlinorium on northwest.

GNM, GNF

Gold Hill shear zone GH Metavolcanic and metaigneous rocks of Charlotte 

belt on northwest and metavolcanic rocks of 

Carolina slate belt on southeast.

PHL

Carolina slate belt CS Gold Hill, Charlotte, and Milton belts on northwest, 

Coastal Plain on southeast.

ARG, MVE, MVU in southwestern half of belt — MVF, 

ARG, MVU, MIF, MII in 

northeastern half of belt

Raleigh belt RA Bordered by Carolina slate belt rocks on east and 

west, Coastal Plain sediments on the south.

MIF, GNF, SCH

Triassic basins TR Several bodies of sedimentary rock downfaulted into 

the metamorphic crystalline rocks of the Piedmont.

TRI

Coastal Plain CP Western margin of Coastal Plain Province. CPL
18 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

the regolith throughout the study area is highly variable 

and ranges from 0 to more than 150 ft. The regolith 

consists of an unconsolidated or semiconsolidated 

mixture of clay and fragmental material ranging in grain 

size from silt to boulders. With porosities that range from 

35 to 55 percent, the regolith provides the bulk of the 

water storage within the Blue Ridge and Piedmont 

ground-water system (Heath, 1980).

Saprolite is the clay-rich, residual material derived 

from in-place weathering of bedrock. Saprolite 

commonly is highly leached and differs substantially in 

texture and mineral composition from the unweathered 

crystalline parent rock in which principal secondary 

openings are along fractures. Saprolite is granular 

material having principal secondary openings between 

mineral grains and rock fragments. Because saprolite is 

the product of in-place weathering of the parent bedrock, 

some of the textural features of the bedrock, including 

fractures, are retained. Saprolite usually is the dominant 

component of the regolith, in that alluvial deposits are 

restricted to locations of active and former stream 

channels and river beds; soil generally is restricted to a 

thin mantle on top of both the saprolite and alluvial 

deposits (fig. 8).

In the transition zone, unconsolidated material 

grades into bedrock. The transition zone consists of 

partially weathered bedrock and lesser amounts of 

saprolite. Particles range in size from silts and clays to 

large boulders of unweathered bedrock. The thickness 

and texture of the transition zone depend primarily on the 

texture and composition of the parent rock. The best 

defined transition zones usually are those associated with 

highly foliated metamorphic parent rock, whereas those 

of massive igneous rocks are poorly defined, with 

saprolite present between masses of unweathered rock 

(Harned and Daniel, 1992).

Stewart (1962) and Stewart and others (1964) 

tested saprolite cores collected in the vicinity of the 

Figure 8. Principal components of the ground-water system in the Blue Ridge and Piedmont 

Provinces of North Carolina (from Harned and Daniel, 1992).
Hydrologic Conditions in the Study Area 19

Georgia Nuclear Laboratory (in the Piedmont of 

northeastern Georgia) for several properties, including 

porosity, specific yield, and permeability. These data 

indicate that porosity, although variable, changes only 

slightly with depth through the saprolite profile; once the 

transition zone is reached, porosity begins to decrease 

sharply. The highest permeability values were found in 

the soil near land surface and within the transition zone.

Specific yield is the ratio of the volume of water a 

saturated rock (or other Earth material) will yield by 

gravity, to the total volume of rock. The distinction 

between porosity and specific yield is important; porosity 

indicates the total volume of pore space in the rock, 

whereas specific yield refers to the volume of water that 

will drain from the saturated rock. The two values are not 

equal because some water is retained within openings by 

surface tension and as a film on rock surfaces. The ratio of 

the volume of water retained to the total volume of rock is 

the specific retention. 

Porosity and ground-water storage are the major 

differences in the water-bearing characteristics of the 

regolith and bedrock (fig. 9). The regolith can store water 

in pore spaces between rock particles. Crystalline 

bedrock, on the other hand, does not have any significant 

intergranular porosity; thus, water is stored in narrow 

planar openings formed along fractures. Joints, faults, and 

stress-relief fractures are among the most common 

secondary openings in crystalline bedrock. Joints and 

faults typically are the product of tectonic activity; stress 

relief fractures form as erosion removes overburden and 

the underlying rock expands. The porosity of regolith 

decreases with depth in the transition zone as the degree 

of weathering decreases (Stewart, 1962; Stewart and 

others, 1964). Porosity in fractured bedrock ranges from 

1 to 10 percent (Freeze and Cherry, 1979, table 2.4), but 

porosities of 10 percent are atypical. Porosity values of 

1 to 3 percent are more typical in the North Carolina 

Piedmont (Daniel and Sharpless, 1983).

As a general rule, the abundance of fractures and 

size of fracture openings in the crystalline bedrock 

decreases with depth. At depths below 750 ft, the pressure 

of the overlying material, or lithostatic pressure, holds 

fractures closed, and the porosity can be less than 

1 percent (Daniel, 1989, 1992). Because of its higher 

porosity, the regolith functions as a reservoir that slowly 

feeds water downward into fractures in the bedrock 

(fig. 9). These fractures form an intricate interconnected 

network of pipelines that transmit water to springs, 

wetlands, streams, and wells.

Figure 9. The reservoir-pipeline conceptual model of the Blue Ridge-Piedmont ground-water system and the relative volume 

of ground-water storage within the system (modified from Heath, 1984).
20 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

Small supplies of water that are adequate for 

domestic needs can be obtained from the regolith through 

large-diameter bored or dug wells. Most wells, however, 

especially where moderate supplies of water are needed, 

are relatively small in diameter and are cased through the 

regolith and finished with open holes, often of substantial 

depth, drilled into the bedrock. Being deeper, bedrock 

wells generally have much higher yields than regolith 

wells because they have a much larger available 

drawdown.

Because fractures in the bedrock decrease in size 

and abundance with depth, contamination of these 

aquifers is difficult to remediate, especially if the 

contaminant is heavier than water. The situation is even 

more acute if the contaminant has low solubility in water. 

Contaminants that settle or move into deeper parts of 

fractured-rock aquifers tend to become trapped as fracture 

widths become narrower and ground-water velocities 

diminish. The surface tension of dense, insoluble 

contaminants may be sufficient to hold the contaminants 

in place in narrow fractures (Pankow and Cherry, 1996; 

Wolfe and others, 1997).

Ground-Water Source and Occurrence

The continuous movement of water in the 

environment is referred to as the hydrologic cycle 

(Meinzer, 1942; Chow, 1964), and quantification of the 

various components of the hydrologic cycle is referred to 

as a water budget. The water budget of an area can be 

expressed by the following general form of a mass 

balance equation:

Inflow = Outflow Change in storage. ± (1)

This simple expression can be expanded by including 

the various components of the hydrologic cycle that fall 

into the categories of inflow, outflow, and change in 

storage. The relation between these components is 

shown diagrammatically as follows:

Under natural conditions, at the watershed scale, 

precipitation represents 100 percent of the input to 

surface-water and ground-water supplies. Part of the 

precipitation is returned to the atmosphere by evaporation 

from soil, wet surfaces, and surface-water bodies and by 

transpiration by vegetation. These return paths to the 

atmosphere are collectively referred to as evapotranspiration.

Streamflow has two components: (1) surface 

runoff, which consists of overland flow from areas that 

cannot absorb precipitation as fast as it falls, and 

precipitation that falls directly onto bodies of water; and 

(2) ground-water discharge into the stream channel, also 

called base flow. Storage also has two components: 

(1) water stored in the ground and (2) water stored in 

surface-water bodies. The change in ground-water storage 

is the difference between ground-water recharge (from 

infiltration) and ground-water discharge (as base flow). 

The change in surface-water storage is the difference 

between inflow to and outflow from stream channels, 

lakes, and other surface-water bodies.

 When these components of the water budget are 

analyzed on a monthly basis in the North Carolina Blue 

Ridge and Piedmont, a pattern, or seasonality, is apparent. 

The highest ground-water recharge occurs in the cooler, 

nongrowing season during the months of January through 

March, and the lowest ground-water recharge occurs at 

the height of the growing season during the months of 

June through September (Daniel and Sharpless, 1983, 

fig. 7). Seasonality in ground-water recharge is caused 

primarily by seasonal variations in the rate of 

evapotranspiration. Seasonal patterns in precipitation 

have less effect on recharge. In fact, long-term records 

indicate that precipitation in North Carolina is rather 

evenly distributed during the year, and the wettest months 

are commonly June and July, near the low point of 

seasonal ground-water recharge.

Components of the water budget that are important 

to this regional study include (1) the volume of water that 

is stored in the ground and (2) rates of recharge to and 

discharge from the ground-water system, which result in 

changes in ground-water storage. When rates of groundwater recharge exceed rates of discharge, the amount of 

Inflow = Outflow + Change in storage

Precipitation = Evapotranspiration + Streamflow + Ground water + Surface water

Rain + Snow Evaporation + Transpiration Overland 

runoff +

Base

flow

Groundwater 

recharge 

(from 

infiltration)

–

Groundwater 

discharge 

(as base 

flow)

Inflow to 

stream 

channels 

and lakes

–

Outflow 

from 

stream 

channels 

and lakes
Ground-Water Recharge 21

ground water in storage increases and the water table 

rises. When rates of ground-water discharge (including 

withdrawals from wells) exceed rates of recharge, as 

usually occurs during droughts, the amount of ground 

water in storage decreases and the water table declines. 

When changes in ground-water storage are small, 

ground-water recharge is roughly equal to ground-water 

discharge. To account for seasonal variations in the water 

budget resulting from variations in precipitation, 

evaporation, and transpiration, it is useful to express 

components of the water budget on a yearly basis because 

annual variations tend to be small. Over longer periods, 

perhaps a decade or more, net changes in the water budget 

tend to be near zero. This assumes that ground water is not 

used to such an extent that long-term declines in the water 

table have occurred.

Ground-Water Recharge

Estimates of ground-water recharge rates in the 

Blue Ridge and Piedmont were made by analyzing longterm streamflow data from 11 selected gaging stations 

using an analytical technique for determining the groundwater component of total streamflow, which is known as 

hydrograph separation (Rorabaugh, 1964; Pettyjohn and 

Henning, 1979; Sloto, 1991; Rutledge, 1993; Rutledge 

and Daniel, 1994). The Blue Ridge-Piedmont drainage 

basins for which recharge characteristics were determined 

are shown in figure 10. Statistical summaries of average 

annual streamflow, overland runoff, ground-water 

discharge, and ground-water discharge as a percentage of 

average annual streamflow are presented in table 4. By 

assuming no long-term changes in ground-water storage, 

the ground-water component of streamflow (base flow) is 

considered to be equal to ground-water recharge.

Estimates of recharge on a regional scale are based 

on assumptions of uniform conditions in the underlying 

aquifers and in the drainage basins with respect to factors 

such as soils, topography, land use, and land cover, all of 

which affect infiltration. Because conditions in drainage 

basins rarely are uniform throughout the entire basin, the 

estimates may not precisely quantify recharge in all areas.

Assuming that ground-water discharge is equal to 

ground-water recharge, the average ground-water 

recharge in the 11 selected Blue Ridge-Piedmont drainage 

basins ranges from 3.3 in/yr (24 percent of average annual 

streamflow) in the Rocky River basin to 18.2 in/yr 

(73 percent of average annual streamflow) in the French 

Broad River basin (table 4). The average annual recharge 

for the 11 basins is 8.6 in/yr, or 47 percent of average 

annual streamflow.

Correlations between recharge rates and 

hydrogeologic units (and derived regolith) are not 

immediately apparent. None of the basins that were 

studied are sufficiently small enough to characterize 

recharge rates according to individual hydrogeologic 

units. All 11 basins contain multiple hydrogeologic units 

in varying proportions. Recharge rates also depend on 

other factors that vary from basin to basin. An important 

factor is the infiltration capacity of the soil, which 

depends not only on soil properties derived from 

weathering of the bedrock, but on land use and land cover. 

When land use and land cover are considered 

Table 4. Water budgets of selected streams in the Blue Ridge and Piedmont Provinces of North Carolina

[Modified from Harned and Daniel, 1987; locations of gaging stations are shown in figure 10]

Map 

number 

(fig. 10)

Stream name

Average annual 

streamflow 

(inches)

Overland runoff 

(inches)

Ground-water 

discharge 

(inches)

Ground-water discharge 

as percentage of average 

annual streamflow 

(percent)

 1 French Broad River 25.1 6.9 18.2 73

 2 Second Broad River 19.2 6.8 12.4 65

 3 Jacob Fork 26.4 13.9 12.5 47

 4 Sugar Creek 23.8 16.2 7.6 32

 5 Rocky River 13.2 9.9 3.3 24

 6 Yadkin River 17.7 8.1 9.6 54

 7 Reedy Fork 15.4 6.1 9.3 60

 8 East Fork Deep River 15.1 8.9 6.2 41

 9 Big Alamance Creek 13.4 7.1 6.3 47

10 Haw River 12.5 8.7 3.8 31

11 Neuse River 13.8 7.9 5.9 43

Average 17.8 9.1 8.6 47
22 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont Figure 10. Locations of gaging stations and drainage basins in the Blue Ridge and Piedmont of North Carolina for which estimates of ground-water recharge were determined by the technique of hydrograph separation.
Ground-Water Storage 23

independently of other factors, recharge rates and 

infiltration capacities are highest in forested areas and 

lowest in urban areas. Recharge rates and infiltration 

capacities typically are intermediate in agricultural areas 

(Chow, 1964). Topography also is important because 

runoff rates are low on gentle slopes, allowing more time 

for infiltration. The cooler temperatures and shorter 

growing season observed at higher altitudes may explain 

the high ground-water recharge rate found in the French 

Broad River basin, which lies entirely within the Blue 

Ridge Province.

Recharge varies from month to month and year to 

year, depending on amounts and seasonal distribution of 

precipitation, evaporation, transpiration, land use, and 

other factors. Another important aspect of recharge and 

discharge involves timing. Recharge occurs during and 

immediately following periods of precipitation and, thus, 

is intermittent. Discharge, on the other hand, is a 

continuous process as long as ground-water levels are 

above levels at which discharge occurs. Between periods 

of recharge, however, ground-water levels decline, and 

discharge declines. Most recharge of the ground-water 

system occurs during late fall, winter, and early spring 

when plants are dormant and evaporation rates are low.

Estimates of ground-water recharge, whether 

determined by hydrograph separation or some other 

technique, are often needed to construct ground-water 

flow models and to calculate mass transport, time of 

travel, or other measures of advective ground-water 

movement. Some of the recharge estimates shown in 

table 4 are for large basins (fig. 10); these estimates may 

not be appropriate for site-specific studies because local 

hydrogeologic conditions and land use at a specific site 

may not be typical of an entire basin. For site-specific 

studies, local recharge estimates may have to be 

determined for small basins or subbasins similar to the 

estimates determined by Daniel (1996) for 12 basins and 

subbasins in Orange County and by Daniel and Harned 

(1998) for 15 basins and subbasins in Guilford County. If 

greater refinement of recharge estimates is needed for 

small areas within a basin or subbasin, apportionment of 

the watershed estimate based on local land use, slope, and 

soil type may be appropriate (Mew and others, 1996). 

Ground-Water Storage

Nearly all ground-water storage in the Blue Ridge 

and Piedmont ground-water system is in the regolith. The 

quantity stored in the bedrock is small by comparison. 

Ground-water levels decline during the summer and early 

fall when atmospheric conditions enhance evaporation 

and plants transpire substantial quantities of water, and 

rise during the winter and early spring when plants are 

dormant.

The depth to the water table in the Blue Ridge and 

Piedmont Provinces varies from place to place and from 

time to time depending on the topography, climate, and 

properties of the water-bearing materials. Although 

climate and the water-bearing properties of different 

bedrock lithologies and regoliths can vary greatly on a 

regional basis, locally they can be quite similar. 

Therefore, topography probably has the greatest influence 

on the depth to the water table in a specific area (Daniel 

and others, 1997).

In stream valleys and areas adjacent to ponds and 

lakes, the water table may be at or very near land surface. 

On slopes, upland flats, and broad interstream divides of 

the Blue Ridge and Piedmont Provinces, the water table 

generally ranges from a few feet to a few tens of feet 

beneath the surface. On hills and rugged ridge lines, 

however, the water table can be at considerably greater 

depths. In effect, the water table typically is a subdued 

replica of the land surface. The depth to the water table 

and the relation of the water table to the saturated 

thickness of regolith reflect the timing of recharge, the 

amount of water in storage, and the movement of ground 

water to discharge areas.

Although higher rates of ground-water recharge 

typically occur during the months of January through 

March (Daniel and Sharpless, 1983), the water table 

usually does not reach its greatest height in the eastern 

and central Piedmont until May or June. The 2- to 

3-month lag between the time of maximum ground-water 

recharge and the time of highest water table is attributed 

to the time required for recharge to move through the 

unsaturated zone to the water table. A similar lag was 

reported by Daniel and others (1997) for 36 wells tapping 

regolith and bedrock in the southwestern Piedmont of 

North Carolina, where peak recharge usually occurs 

during the months of February through April, but groundwater levels commonly are highest in July or August. The 

fact that peak recharge and ground-water levels lag about 

a month behind the eastern Piedmont is attributed to the 

higher elevation, cooler climate, and later start to the 

growing season in the southwestern Piedmont. In the Blue 

Ridge, the higher elevations result in even shorter growing 

seasons and lower temperatures than in the Piedmont. 

Seasonal changes in ground-water levels in the Blue 

Ridge reflect these climatic conditions with a longer 

period of seasonal high water table and shorter period of 

seasonal low water table when compared to the Piedmont.

The amount of ground water in storage can be 

estimated from the saturated thickness of regolith. 

Because regolith is unconsolidated and subject to collapse 
24 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

into open boreholes, well casing typically is installed 

through the regolith to the top of unweathered bedrock 

during the well-drilling process. Therefore, the depth of 

surface casing in a drilled well is a good approximation of 

regolith thickness in the Blue Ridge and Piedmont 

(Daniel and Sharpless, 1983; Snipes and others, 1983). 

The remainder of the borehole is completed as a selfsupporting open hole drilled into the bedrock. By 

subtracting the depth to water from the depth of casing, an 

estimate of the saturated thickness of regolith is obtained. 

If the water level in the well is below the bottom of the 

casing, the saturated thickness of regolith is assumed to be 

zero.

Surface casing is usually set no more than 1 or 2 ft 

into fresh bedrock, just below the interface between the 

bedrock and the overlying regolith. Wells drilled in North 

Carolina since the passage of the North Carolina Well 

Construction Act of 1967 (Heath and Coffield, 1970), 

however, are required to have a minimum of 20 ft of 

casing regardless of the depth to bedrock. More recent 

revisions to the regulations require 35 ft of casing in wells 

tapping the argillites of the slate belt. Many of the records 

used by Daniel (1989) to estimate regolith thickness were 

for wells drilled prior to 1967. Records of casing depths 

as shallow as 1 ft in wells on bare-rock exposures were 

included in the data compilation. These data better reflect 

the natural range of depths to bedrock and, thus, provide 

for a more accurate approximation of regolith thickness.

A statistical summary of data on depth of well 

casing, depth to water, and estimated saturated thickness 

of regolith for wells in different topographic settings in 

the Piedmont is presented in Daniel (1989, table 5). The 

average depth of well casing for all wells in this data 

summary is 52.0 ft. The average depth to water is greatest 

beneath hills and ridges and least beneath valleys and 

draws. Consequently, the saturated thickness of regolith is 

least beneath hills and ridges (average 20.4 ft) and 

greatest beneath valleys and draws (average 33.6 ft). The 

saturated thickness of regolith beneath slopes (average 

24.6 ft) is intermediate to these extremes. The average 

saturated thickness of regolith for all wells in the data 

summary is 24.0 ft.

The quantity of ground water available from 

storage at a specific site can be estimated from the 

following general relation:

available ground water in storage

= saturated thickness of regolith

× specific yield.

(2)

In the absence of site-specific data, values of specific 

yield can be derived from the relation developed for 

northeastern Georgia (fig. 11A). Sufficient similarities 

exist between the Piedmont of northeastern Georgia 

and the Piedmont of North Carolina that this 

information can be used with reasonable limits of 

confidence. The depth of weathering, lithology of the 

underlying bedrock, and geologic structures are similar 

in both areas. Furthermore, Daniel and Sharpless 

(1983) report that dewatering of saprolite during a 

pumping test in a similar hydrogeologic setting 

(fractured mafic gneiss and schist) in Guilford County 

could be explained by a specific yield of 0.20.

Based on average thicknesses of saturated regolith 

presented by Daniel (1989, table 5) and the relations 

shown in figure 11B, the average quantity of available 

ground water in storage in the Piedmont is calculated to 

be 0.55 million gallons per acre (Mgal/acre) beneath hills 

and ridges, 0.77 Mgal/acre beneath slopes, and 

1.22 Mgal/acre beneath valleys and draws. Overall, the 

average quantity of ground water available in the 

Piedmont is calculated to be 0.73 Mgal/acre.

Table 5. Properties of regolith at three well locations in the Piedmont northwest of 

Greensboro, North Carolina

[From Harned and Daniel, 1992; well locations and construction characteristics are given in Daniel 

and Sharpless, 1983; NA, not applicable]

Well pair numbers

Total 

regolith 

thickness 

(feet)

Soil and 

saprolite 

thickness 

(feet)

Transition 

zone 

thickness 

(feet)

Regolith 

saturated 

thickness on 

March 3, 1989 

(feet)

Topography

Gu-383, AH-13 45.9 35.8 10.1 29.6 side of draw

Gu-385, AH-4 65.7 48.1 17.6 48.1 side of draw

Gu-386, AH-1 46.2 27.9 18.3 28.3 side of draw

Average 52.6 37.3 15.3 35.3 NA
Ground-Water Flow System 25

Ground-water storage in the Blue Ridge is similar 

to ground-water storage in the Piedmont. The least 

amount of available water is stored beneath hills and 

ridges, and the greatest amount is stored beneath valleys 

and draws. The average quantity of available ground 

water in the Blue Ridge of North Carolina is calculated to 

be 0.97 Mgal/acre.

Where a discrete transition zone is present between 

the saprolite and the underlying unweathered bedrock 

(Harned and Daniel, 1992), the relations between porosity 

and depth and specific yield and depth are nonlinear. 

Consequently, equation 2 becomes nonlinear, and a plot 

of this relation is nonlinear, as shown in figure 11B. The 

quantity of water available from storage in the regolith 

can be estimated from figure 11B. Although groundwater levels fluctuate seasonally, in the absence of being 

over pumped, few wells in the Blue Ridge or Piedmont go 

dry, suggesting that seasonal fluctuations of the water 

table occur primarily within the saprolite. As shown in 

figure 11B, water available from storage in the saprolite 

follows a more or less linear part of the relation with a 

specific yield of about 0.20 (fig. 11A). Therefore, the 

contribution to base flow from water in storage in the 

saprolite can be estimated by the linear equation:

water from storage 0.20 change in water table. = × (3)

Based on this equation and a 4- to 12-ft natural annual 

variation in the water table (Daniel, 1996; Daniel and 

others, 1997; Daniel and Harned, 1998), the quantity of 

water in storage is estimated to increase or decrease by 

0.31–0.89 Mgal/acre in 1 year.

Ground-Water Flow System

The ground-water flow system serves two 

hydraulic functions: (1) it transmits water from recharge 

areas to discharge areas and (2) it stores water to the 

extent of its porosity. Thus, the ground-water system 

serves as both a conduit and a reservoir. In most 

hydrogeologic settings, ground-water systems are more 

effective as reservoirs than as conduits.

Water from precipitation enters the ground-water 

system in recharge areas, which generally include all the 

Figure 11. Relation of porosity and specific yield to total ground-water storage and available water in the regolith (from Daniel and 

others, 1997, fig. 27). A. Variation of porosity and specific yield with depth in the regolith (modified from Stewart, 1962); B. Total 

ground water in storage below the water table and water available by gravity drainage.
26 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

land surfaces higher than the adjacent stream valleys. A 

conceptual view of the ground-water flow system for a 

typical area in the North Carolina Blue Ridge or Piedmont 

is shown in figure 12. After infiltration, water slowly 

moves downward through the unsaturated zone. Water 

moves vertically and laterally through the saturated zone, 

discharging as seepage springs on steep slopes and as 

bank and channel seepage into streams, lakes, or swamps 

where the saturated zone is near land surface. Some 

ground water is returned to the atmosphere by 

evapotranspiration (soil moisture evaporation and plant 

transpiration). In the regolith, ground-water movement 

primarily is through intergranular flow, although relict 

rock fabric and structure can influence ground-water 

movement. In bedrock, ground-water flow is through 

fractures, and the flow paths from recharge areas to 

discharge areas commonly are more circuitous than those 

in the regolith.

Transition Zone Between Saprolite and Bedrock

In the transition zone, unconsolidated saprolite 

grades into bedrock. The transition zone consists of 

partially weathered bedrock and lesser amounts of 

saprolite, with particles ranging in size from clays to large 

boulders of unweathered bedrock (fig. 8). The thickness 

and texture of this zone depend largely on the texture and 

composition of the parent rock. Well-defined transition 

zones usually are associated with highly foliated 

metamorphic parent rock, whereas transition zones 

associated with massive igneous rocks commonly are 

poorly defined, having saprolite present between masses 

of unweathered rock. A diagram showing how the 

transition zone can vary because of different rock type is 

presented in figure 13. The incipient planes of weakness 

produced by mineral alignment in the foliated rocks 

facilitates separation at the onset of weathering, resulting 

Figure 12. Conceptual view of the North Carolina Blue Ridge and Piedmont ground-water flow system showing the unsaturated zone 

(lifted up), the water-table surface, the saturated zone, and directions of ground-water flow (from Daniel, 1990b).
Transition Zone Between Saprolite and Bedrock 27

Figure 13. Conceptual variations of transition zone thickness and texture that develop on 

different parent rock types (from Harned and Daniel, 1992). A. A distinct transition zone on highly 

foliated schists, gneisses, and slates; B. An indistinct transition zone on massive bedrock.
28 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

in numerous rock fragments. More massive rocks do not 

possess these closely spaced planes of weakness, so 

weathering tends to progress along more widely spaced 

fractures, resulting in a less distinct transition zone.

In the North Carolina Piedmont, 90 percent of the 

records for cased bedrock wells indicate that the 

combined thicknesses of the regolith and transition zones 

is 97 ft or less (Daniel, 1989). Data for three pairs of wells 

drilled at a test site in Guilford County, North Carolina 

(table 5), indicate that the average transition zone in that 

area is about 15 ft thick. Transition zones identified in 

Georgia (Stewart, 1962) and Maryland (Nutter and Otton, 

1969) were described as being more permeable than the 

upper regolith, and even slightly more permeable than the 

soil zone (fig. 14). This observation is substantiated by 

reports from well drillers of so-called "first water," 

"sand," and "boulders" at the base of the regolith (Nutter 

and Otton, 1969).

The high permeability of the transition zone 

probably is the result of incomplete weathering in the 

lower regolith. Chemical alteration of the bedrock has 

progressed to a stage of mineral expansion and extensive 

fracture development in the crystalline rock, yet it has not 

progressed so far that formation of clays and other 

weathering by-products has been sufficient to clog the 

fractures. An idealized weathering profile shown in 

figure 14 (Nutter and Otton, 1969) illustrates that as the 

degree of weathering increases, clay fractions also 

increase, which results in decreased permeability in the 

saprolite as compared to the transition zone.

The presence of a zone of high permeability on top 

of the bedrock may create a zone of increased groundwater flow in the ground-water system. For example, well 

drillers may find water at a relatively shallow depth, yet 

complete a dry hole after setting casing through the 

regolith and transition zone and into the unweathered 

bedrock. In this case, although ground water probably is 

present and moving within the transition zone, the dry 

hole indicates a poor hydraulic connection between the 

regolith reservoir, the bedrock fracture system, and the 

well.

Figure 14. An idealized weathering profile through the regolith, and relative 

permeability (modified from Nutter and Otton, 1969).
Hydrogeologic Terranes 29

The transition zone also may serve as a conduit for 

rapid movement of contaminants to nearby wells, or to 

streams with channels that are cut into or through the 

transition zone. How rapidly a contaminant moves 

through the system may largely be a function of the 

characteristics of the transition zone. If the ground water 

is contaminated, a well-developed transition zone will 

serve as a conduit of rapid movement for the 

contaminated water. The transition zone in figure 15 

serves as a conduit for landfill leachate that eventually 

discharges to a local stream, which has incised into the 

transition zone. Because the distance from the point 

where water enters the terrestrial part of the hydrologic 

cycle in the Piedmont to where water discharges to a 

stream commonly is less than half a mile, contaminants 

entering the ground-water system and moving through the 

transition zone can rapidly become dispersed to surfacewater bodies.

Figure 15 also illustrates how the thickness of the 

transition zone (table 5) can be determined. The depth of 

the bored well, completed to auger refusal, indicates the 

thickness of soil and saprolite. The depth to unweathered 

rock, as approximated by the casing depth in the drilled 

well, gives the total regolith thickness. By subtracting 

casing depth in the bored well from casing depth in the 

drilled well, an estimate of the thickness of the transition 

zone is obtained.

HYDROGEOLOGIC TERRANES

Understanding the hydrogeology of the Blue Ridge 

and Piedmont study area is complicated by the fact that 

the geology is complex and the porosity and permeability 

in the bedrock is almost exclusively secondary. As a 

result, the permeability is extremely variable, and not 

easily defined for a particular geologic formation or even 

a particular rock type. Consequently, the distinction 

between aquifers and confining units, which is the usual 

approach for describing the hydrogeologic framework of 

an area, is obscured. A more useful approach is to divide 

the study area into hydrogeologic terranes based upon 

factors related to the occurrence and distribution of 

secondary porosity and permeability.

For the purpose of this discussion, a hydrogeologic 

terrane is defined primarily by a combination of rock type, 

regolith conditions, and topographic setting, all of which 

are relatively homogeneous with respect to (1) the wateryielding potential of the earth materials, as indicated by 

the specific capacity of wells or base flow of streams; (2) 

ground-water storage; and (3) ground-water quality. 

Figure 15. The transition zone between bedrock and saprolite functioning as a primary transmitter of 

contaminated ground water to a stream (from Harned and Daniel, 1992).
30 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

Currently, it appears that terranes are most easily 

distinguished primarily on the basis of rock type and 

secondarily by consideration of rock texture, regolith 

thickness and texture, rock structure, topographic setting, 

and nongeologic factors, some of which are not well 

understood. In general, water-yielding characteristics of 

the various hydrogeologic terranes within the Blue Ridge 

and Piedmont Provinces (table 6) are highly dependent on 

the saturated thickness of the regolith and transition zone. 

Therefore, variability in the thickness and texture of the 

regolith, which can store a substantial amount of ground 

water, is perhaps the most important of the secondary 

factors.

The USGS identified four hydrogeologic terranes in 

the Blue Ridge and Piedmont Provinces as part of the 

Appalachian Valleys-Piedmont Regional Aquifer-System 

Analysis (APRASA) study (Swain and others, 1991). The 

four terranes include (1) massive or foliated crystalline 

rocks mantled by thick regolith, (2) massive or 

foliated crystalline rocks mantled by thin regolith, 

(3) metamorphosed carbonate rocks, and (4) sedimentary 

rocks of the Mesozoic basins (table 6). These hydrogeologic terranes are thought to be associated with local or 

intermediate flow systems as described by Toth (1963).

The ground-water hydrology of the study area is 

best described in terms of conceptual flow systems. For 

the purpose of this study, a conceptual flow system is, in 

most cases, the three-dimensional flow net that is 

perceived to exist within a hydrogeologic terrane. In 

accordance with work by Toth (1963), local and 

intermediate systems of ground-water flow have been 

identified in the study area. Local flow systems mainly 

occur at depths shallower than 800 ft in the Blue Ridge and 

Piedmont Provinces; they commonly occur between 

adjacent drainage basin divides that range from a few 

thousand feet to a few miles apart. Analyses to date 

suggest that local flow systems represent greater than 

95 percent of total ground-water flow (Daniel, 1989; 

Daniel and others, 1997). Conversely, the intermediate 

flow systems likely range in depth from 800 to 5,000 ft 

and traverse adjacent drainage basin divides in places. The 

intermediate flow systems probably represent less than 

5 percent of the total ground-water flow. The 

hydrogeologic terranes discussed in this report are more 

closely associated with local flow systems than with 

intermediate flow systems. Deep, confined flow systems 

(Hobba and others, 1979, figs. 12, 13) are thought to be 

absent in these terranes, but if present, the quantity of 

ground water in circulation likely would be insignificant 

relative to the shallower, more localized, systems.

Because the sedimentary rocks of the Mesozoic 

basins are distinct from the metamorphic and igneous 

crystalline rocks of the Piedmont and Blue Ridge, the 

hydrogeology of the Blue Ridge and Piedmont Provinces 

has been divided into two distinct geologic settings based 

on differences in lithology—(1) crystalline-rock terranes, 

which make up 86 percent of the total Piedmont area and 

all of the Blue Ridge area, and (2) sedimentary-rock 

terranes of the early Mesozoic basins, which make up 

14 percent of the Piedmont.

Although metamorphosed carbonate rocks, as 

discussed in a previous section, can contain substantial 

quantities of ground water, metamorphosed carbonate 

rocks in North Carolina are limited almost exclusively to 

the Murphy and Blue Ridge belts in the Blue Ridge 

Province. No large bodies of metamorphosed carbonate 

rock are present in the North Carolina Piedmont. Because 

of their limited areal extent and relatively low well yields 

in North Carolina, the metamorphosed carbonate rocks are 

grouped with other crystalline rocks for the purpose of 

describing hydrogeologic terranes in this report. The 

hydrogeologic terranes important to this study are 

described in the following sections.

Core samples from the North Carolina State University Upper 

Piedmont Agricultural Research Station, Rockingham County, North Carolina (photo taken by D.J. Geddes, Groundwater Section, Division of Water Quality, North Carolina Department of 

Environment and Natural Resources).
Table 6. General hydrologic characteristics of the hydrogeologic terranes of the Blue Ridge and Piedmont Provinces within the Appalachian Valleys-Piedmont Regional Aquifer-System 

Analysis (APRASA) study area

[Modified from Swain and others, 1991; <, less than or equal to]

Hyrogeologic 

terrane

Hydrologic characteristics

Topographic 

relief Recharge Discharge Type of porosity or permeability Type of flow Depth of flow, in feet Confined or unconfined Regolith storage Well yield

Massive or foliated 

crystalline rocks, thick regolith

Low to high Precipitation on 

topographic highs

To streams Intergranular in 

regolith, fracture

Diffuse, 

fracture

Shallow to 

intermediate, 

< 800

Mostly 

unconfined

Large Proportional to 

regolith thickness.

Massive or foliated 

crystalline rocks, thin regolith

Low to high Precipitation on 

topographic highs

To streams Fracture Fracture Shallow 

(mostly) to intermediate, 

< 500

Unconfined Small Low.

Metamorphosed 

carbonate rocks

Low to 

moderate

Precipitation on 

topographic highs

To streams Dissolution 

openings, some fractures

Conduit, 

fracture

Shallow Unconfined Small to 

moderate

Variable, some 

very high.

Mesozoic sedimentary 

basins

Low to 

moderate

Precipitation on 

topographic highs

To streams Intergranular, 

some fractures

Diffuse, 

fracture

Shallow 

(mostly) to intermediate, 

< 800

Mostly 

unconfined

Small Variable, 

decreasing from north to south.

Hydrogeologic Terranes 31
32 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

Massive or Foliated Crystalline Rocks Mantled 

by Thick Regolith

Although most wells in the Blue Ridge and 

Piedmont Provinces are open to fractured crystalline 

rocks, storage characteristics of the overlying regolith 

probably control the long-term quantity of water 

(sustained yield) available to wells (fig. 16). The 

thickness of regolith overlying crystalline rocks is highly 

variable and ranges from 0 to more than 150 ft. As defined 

for this study, "thick regolith" is regolith that is greater 

than 50 ft thick. The water-yielding capacity of the rocks 

in this hydrogeologic terrane is dependent upon not only 

the saturated thickness of regolith but also the density, 

width, spacing, and interconnectivity of the fractures in 

the crystalline rocks.

The hydrogeologic units producing the lowest well 

yields also tend to be the units with the least saturated 

thicknesses of regolith (compare figs. 6 and 16); most of 

these units belong to the category of metavolcanic rocks 

and the Triassic sedimentary rocks (TRI) in the 

miscellaneous category (table 1). The units producing 

intermediate well yields and having intermediate values 

of saturated thickness of regolith belong, in general, to the 

igneous and metaigneous rock categories. The units with 

the highest well yields and greatest saturated thicknesses 

of regolith belong to the category of metasedimentary 

rocks and the Coastal Plain basement rocks (CPL) in the 

Figure 16. Relation of average well yield to the average saturated thickness of regolith for hydrogeologic units in the 

Blue Ridge and Piedmont Provinces of North Carolina.
Sedimentary Rocks in the Early Mesozoic Basins 33

miscellaneous category (table 1). For wells that tap the 

Coastal Plain basement rocks east of the Fall Line, 

Coastal Plain sediments function as a layer of regolith and 

store water that recharges fractures in the underlying 

bedrock. Wells in the CPL unit have some of the highest 

yields and greatest saturated thicknesses of regolith. 

Although there are exceptions and some overlap in 

categories of hydrogeologic units, a general pattern is 

apparent in figure 16 that indicates the saturated thickness 

of regolith (and by implication, the total thickness of 

regolith) and well yield correlate with hydrogeologic 

units that are classified according to their water-bearing 

potential and susceptibility to weathering, as discussed in 

the “Hydrogeologic Units” section.

Foliated crystalline rocks generally are anisotropic 

in terms of physical properties, such as orientation of 

fractures and primary permeability. Fractures typically 

are at high angles to bedding and foliation. In the eastern 

and southeastern United States, compressive forces that 

formed the Appalachian Mountains were oriented 

generally northwest to southeast. Bedding and 

compositional layering (including schistosity and 

gneissic banding) tend to be oriented northeast to 

southwest, and fractures tend to be oriented northwest to 

southeast, although local variation does occur. Schistose 

rocks contain minerals, such as mica and chlorite, that 

have laminated-type cleavage planes and are able to 

withstand extreme folding and deformation without 

creating any major secondary permeability. As a result, 

wells completed in foliated, schistose rocks generally 

yield only small amounts of water. 

This hydrogeologic terrane has the highest average 

water-yielding capability for the Blue Ridge and 

Piedmont. Based on data from 1,421 bedrock wells 

located throughout the 65-county study area, the average 

thickness of regolith in this terrane is 82.0 ft and the 

average yield is 20.2 gal/min.

This terrane is most commonly identified with 

areas that have broad interstream divides and gentle relief. 

In these areas, stream channels typically are not deeply 

incised and have not eroded through the underlying 

regolith into bedrock. The rate of weathering at the 

regolith-bedrock boundary apparently exceeds, or at least 

keeps pace with, the rate of erosion at the land surface. 

The thickest regolith tends to occur beneath the 

interstream uplands and in areas overlying fracture zones 

that have facilitated deep weathering.

Massive or Foliated Crystalline Rocks Mantled 

by Thin Regolith

Massive crystalline rocks that are fractured can be 

locally important sources of ground water; however, 

storage generally is small within the fractures. In areas of 

North Carolina, porosities of 1 to 3 percent are common 

for the fractured rocks (Daniel and Sharpless, 1983). 

Yields of wells open to massive, unmantled, fractured 

rocks must be sustained by an extensive fracture network 

connected to a surface-water body or nearby area with 

saturated regolith; otherwise, well yields will be small.

As defined for this study, "thin regolith" is regolith 

that is 50 ft or less in thickness. Based on data from 

1,723 bedrock wells located throughout the 65-county 

study area, the average thickness of regolith in this terrane 

is 30.1 ft—values fall within a range of 1–50 ft, and the 

average yield is 15.2 gal/min. 

This terrane is identified most commonly with 

areas that have sharp-crested ridges, mountains, and steep 

hillsides. In these areas of rugged relief, stream channels 

typically are deeply incised and have eroded through the 

underlying regolith into bedrock. Beneath the ridges, 

mountains, and steep hillsides, the rate of weathering at 

the regolith-bedrock boundary apparently cannot keep 

pace with the rate of erosion at the land surface. As a 

result, regolith tends to be thin or absent, and bedrock 

outcrops can be found at land surface.

Sedimentary Rocks in the Early Mesozoic Basins

Ground water in sedimentary rocks within the early 

Mesozoic basins of the eastern United States (fig. 4) is 

stored and transmitted primarily through a complex 

network of joints, fractures, faults, and bedding planes. To 

a lesser extent, water moves through interstitial pore 

spaces and locally enlarged solution channels. 

Unfractured Mesozoic sedimentary rock typically has a 

negligible capacity to store and transmit water. Finegrained rocks—siltstones, claystones, shales—often 

predominate, and the primary porosity that originally 

existed in the rocks has commonly been reduced by 

compaction and cementation. Additionally, permeability 

generally decreases with increasing depth below land 

surface. Well yields tend to decrease substantially from 

north to south along this band of sedimentary basins; in 

fact, yields of wells tapping the rocks of the Durham, 

Sanford, and Wadesboro subbasins in North Carolina and 

South Carolina (fig. 4) are among the lowest in the 

Piedmont.

Some preferential alignment is typical of 

secondary openings in consolidated-rock aquifers of the 
34 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

early Mesozoic basins; thus, the aquifers are anisotropic 

to some degree. In wells open to the Brunswick Group in 

the Newark basin (basin 15, fig. 4), drawdown was noted 

in an observation well 2,400 ft from a pumped well in a 

direction parallel to the strike of the formation beds, 

whereas no drawdown was evident in observation wells 

600 ft from a pumped well in a direction perpendicular to 

the strike (Herpers and Barksdale, 1951). Similar 

observations of the anisotropy of the Brunswick Group 

have been documented by Vecchioli and others (1962) 

and Vecchioli (1965).

Preferential flow along strike probably is caused by 

variable degrees of fracturing in dipping beds. In a highly 

fractured bed, horizontal flow in the direction of strike 

may not be impeded by structural boundaries, but 

horizontal flow in the direction of dip may be bounded by 

adjacent, relatively unfractured beds and by the closure of 

fractures at depth.

The Mesozoic basins (fig. 4) contain beds or rock 

units that are significant aquifers locally, particularly in 

the northern Piedmont (Pennsylvania and New Jersey). 

The most productive water-yielding zones in the 

sedimentary rocks are in fractured red shale, sandstone, 

and conglomerate. Fractured-shale and sandstone 

aquifers yield as much as 1,500 gal/min in the basins in 

northern Virginia, Pennsylvania, and New Jersey 

(Carswell and Rooney, 1976; Nemickas, 1976). Black 

mudstones, basaltic rocks, diabase dikes and sills, and 

thermally metamorphosed rocks in the sedimentary 

basins commonly produce lower yields. These 

hydrogeologic units are tapped primarily for domestic 

supplies, and well yields generally are less than 5 gal/min, 

although there are notable exceptions for wells tapping 

some of the thicker, more highly fractured diabase dikes. 

In North Carolina, it is not uncommon when locating well 

sites in the Durham, Sanford, and Wadesboro subbasins 

(fig. 4) to conduct field mapping or magnetometer surveys 

in an effort to locate diabase dikes. In these southern 

basins, wells drilled into dikes commonly have higher 

yields than wells drilled into the surrounding fine-grained 

sedimentary rocks.

More than 10 percent of the ground water pumped 

within the northern Piedmont during 1985 was from the 

Newark basin (basin 15, fig. 4; Swain and others, 1991). 

The highest yielding wells are large-diameter (10 in. or 

more), relatively deep (200 to 600 ft deep) wells used for 

public supply and industry. Yields of 500 gal/min are 

common from these wells. Lowest yielding wells are 

small-diameter (6 in. or less) domestic wells, which 

generally are less than 250 ft deep. Yields of 10 to 20 gal/

min are common from these wells.

In contrast to the Mesozoic basins in the northern 

Piedmont, the Mesozoic basins in North Carolina produce 

only small supplies of water. With an average well yield 

of 11.6 gal/min (Daniel, 1989), the TRI hydrogeologic 

unit (table 1; fig. 6) has the lowest average yield of any 

hydrogeologic unit in the Blue Ridge or Piedmont of 

North Carolina. It is worth pointing out that among the 

Mesozoic basins in North Carolina, the Deep River basin 

(composed of subbasins 1, 2, and 3 in figure 4) has the 

lowest average yield, and the Danville basin (basin 5 in 

figure 4) has the highest. The sedimentary rocks in the 

Deep River basin are dominated by claystones, siltstones, 

and other fine-grained sedimentary rocks that produce 

low yields to wells. Sandstones are limited in thickness 

and extent. The Danville basin, however, contains 

sandstone units that locally produce higher yields to wells 

than the metamorphic rocks outside the basin.

GROUND-WATER QUALITY

Ground-water quality in the crystalline-rock 

terranes of the Blue Ridge and Piedmont Provinces 

generally is suitable for drinking and most other purposes. 

Mineral composition of the regolith and bedrock strongly 

affects ground-water quality. Water from most 

light-colored, felsic metamorphic and igneous rocks is 

soft (hardness less than 60 milligrams per liter [mg/L], as 

CaCO3), slightly acidic (pH less than 7.0), and contains 

low concentrations of dissolved solids (Powell and Abe, 

1985). Water moving through these silica-rich rocks 

remains relatively low in dissolved solids because of the 

chemically resistant nature of the silicate minerals. Water 

from the dark-colored, mafic metamorphic and igneous 

rocks generally is hard and somewhat alkaline (pH greater 

than 7.0) and contains moderate concentrations of 

dissolved solids as a result of the solubility of calciumand magnesium-bearing minerals in these rocks. 

Corrosion of pipes and plumbing fixtures and relatively 

high concentrations of iron and manganese are the most 

common water-quality problems.

Water from wells in the sedimentary rocks in the 

Mesozoic basins generally is hard (hardness greater than 

120 mg/L, as CaCO3) to very hard (hardness greater than 

180 mg/L, as CaCO3), somewhat alkaline, and contains 

moderate concentrations of dissolved solids. High 

concentrations of sulfate (greater than 250 mg/L) are a 

common problem with water from deep wells and directly 

correspond to high concentrations of dissolved solids. As 

in crystalline rocks, ground water in sedimentary rocks 

locally contains elevated concentrations of iron and 

manganese. Concentrations of dissolved solids and 
Ground-Water Quality 35

sulfate tend to increase with well depth (Swain and others, 

1991).

The depth of effective circulation of water in the 

early Mesozoic basins is not known, but depth to the base 

of potable water appears to be between 1,000 and 2,000 ft 

in the northern basins (Wood and Wood, 1982) and 

shallower southward in Virginia and North Carolina. Few 

chemical data are available for water from deep aquifers. 

Most water samples have been taken from discharge 

points at the tops of wells and represent mixtures of water 

from all contributing aquifers. Water type (Piper, 1944) is 

variable with depth. Although calcium-magnesiumsodium-bicarbonate type water is common at shallow 

depths, a calcium-magnesium-sodium-sulfate type or 

calcium-sulfate type is found at moderate depths, and a 

sodium-chloride type is found in deep aquifers (Swain 

and others, 1991; Briel, 1997).

In the early Mesozoic basins, concentrations of the 

major cations and anions in potable water differ 

regionally (Wood and Wood, 1982). The calciummagnesium-bicarbonate-sulfate facies dominates in 

basins north of Culpeper, Va., except in Maryland, where 

the calcium-bicarbonate facies dominates. In North 

Carolina, sulfate generally is absent, and water mostly is 

a sodium-calcium-magnesium-bicarbonate type and 

rarely is a calcium-chloride type. Sodium-chloride type 

waters apparently dominate at depth in all basins in 

eastern North America. Regional differences in water 

chemistry may reflect regional differences in aquifer 

composition and ground-water residence times.

Ambient inorganic ground-water quality for the 

APRASA study area was evaluated by Briel (1997). 

Selected statistics computed from chemical analyses of 

18,008 ground-water samples (excluding spring-water 

samples) are presented in table 7. These data were 

compiled from 10,564 ground-water-quality sites in 

11 eastern States (New Jersey, Pennsylvania, Delaware, 

Maryland, Virginia, West Virginia, Tennessee, North 

Carolina, South Carolina, Georgia, and Alabama). Briel’s 

(1997) database included 4,173 analyses from 2,682 wells 

in North Carolina, or 25.4 percent of the ground-water 

sites and 23.2 percent of the ground-water analyses 

identified in the APRASA study area.

The range in ground-water quality throughout the 

Blue Ridge and Piedmont is apparent in the data. As an 

example, the range in specific conductance (table 7) 

between the 5th and 95th percentile is more than twice the 

mean and nearly four times the median (50th percentile) 

value. This indicates that regional data from an inorganic 

water-quality investigation cannot be applied with 

confidence to estimate water quality at any one individual 

site in North Carolina.

Although political subdivisions generally are of 

little hydrologic significance, water-resources 

investigations commonly are delimited by county 

boundaries; thus, counties provide a usable grid for 

describing geographic variations in water quality (Briel, 

1997). The geographic variation identified by county for 

total dissolved solids and nitrite plus nitrate (fig. 17) are 

examples based on Briel’s (1997) data. Similar maps can 

be generated for the remaining constituents shown in table 

7.

Since Briel (1997) compiled his database, 

additional ground-water-quality data have become 

available in North Carolina as a result of two recent 

studies. Cunningham and Daniel (2001) reported 

chemical analyses from 51 wells in Orange County. 

Analytes consisted of common cations and anions, metals 

and trace elements, nutrients, organic compounds, and 

radon. Samples also were screened for the presence of 

fuel compounds and pesticides by using immunoassay 

techniques. Dissolved oxygen, pH, temperature, specific 

conductance, and alkalinity were measured in the field. A 

similar sampling and analysis of water from 70 wells was 

conducted in Guilford County during 1996–97 (Ragland 

and others, 1997). A detailed description of dissolved 

radon measurements and the distribution of radon 

activities in Guilford County were reported by Spruill and 

others (1997). In Guilford and Orange Counties, median 

radon activities in ground-water samples are highest in 

felsic rocks and lowest in mafic rocks (Spruill and others, 

1997; Cunningham and Daniel, 2001). Radon activities in 

ground water from some hydrogeologic units are as much 

as 20 times higher than the criterion level of 

300 picocuries per liter (pCi/L) proposed by the U.S. 

Environmental Protection Agency (1999).

Another large and potentially informative database 

was compiled by the U.S. Department of Energy for the 

National Uranium Resource Evaluation (NURE) 

program. Samples were collected and analyzed during 

1975–79. By the end of the NURE program, groundwater sampling of the entire State was completed at a 

reconnaissance scale. The NURE database contains 

analyses for 5,778 ground-water sampling sites in North 

Carolina, along with latitude-longitude coordinates of the 

sampling sites. Using these coordinates, the data can be 

subdivided by county or physiographic province for 

further analyses similar to those performed by Briel 

(1997). The NURE ground-water samples were analyzed 

by neutron activation analyses for uranium, bromine, 

chlorine, fluorine, manganese, sodium, aluminum, 

vanadium, and dysprosium. The data are presented in a 

hydrogeochemical atlas compiled by Reid (1993).
Table 7. Selected statistics for selected properties and constituents of ground water in the Blue Ridge and Piedmont Provinces, Appalachian Valleys-Piedmont Regional AquiferSystem Analysis (APRASA) study area

[From Briel (1997; table 5); μS/cm, microsiemens per centimeter; °C, degrees Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; N, nitrogen; P, phosphorus; μg/L, micrograms per liter]

Property or constituent and unit

Blue Ridge Piedmont

Number of 

analyses Mean

Percentile values calculated 

from the data Number of analyses Mean Percentile values calculated from the data 5th 50th 95th 5th 50th 95th

Specific conductance, μS/cm at 25 °C 454 154 29 103 440 10,150 387 41 280 976Dissolved solids, residue on evaporation at 

180 °C, mg/L 393 94 23 73 220 5,551 227 37 159 554

pH, standard units 416 6.6 5.6 6.6 7.9 8,821 6.7 5.2 6.7 8.0Water temperature, °C 327 13.4 9.7 13.0 18.5 6,991 14.5 10.7 14.0 19.9Dissolved oxygen, mg/L 14 5.8 .9 6.2 8.2 2,274 4.4 .2 4.1 9.8Calcium, mg/L 442 14 1.2 8.3 42 5,098 38 2.2 25 100Magnesium, mg/L 477 3.8 .4 2.5 12 6,344 14 .7 6.6 36Sodium, mg/L 441 7.1 1.4 5 17 5,888 27 2 9.5 62Potassium, mg/L 411 3.3 .3 1.2 3.8 5,681 2.5 .4 1.4 6.1Bicarbonate, mg/L 349 43 6 32 121 4,589 89 6 60 247Alkalinity, mg/L as CaCO3 322 45 7 32 137 7,634 87 5 57 240Carbonate hardness, mg/L as CaCO3 479 48 6 29 124 8,268 120 8 65 357Sulfate, mg/L 471 7.7 .3 5 25 6,872 35 .8 13 110Chloride, mg/L 558 6.4 .7 2.1 29 8,739 25 1.1 7 88Fluoride, mg/L 290 .19 .1 .1 .4 3,543 .22 .1 .1 .5Dissolved silica, mg/L 443 18 5.8 16 35 5,838 19 5 17 37Nitrite plus nitrate, total, mg/L as N 236 1.1 .01 .2 4.7 2,366 4.9 .05 .99 20Ammonia, total, mg/L as N 106 .03 .01 .05 .05 1,096 1.4 .01 .05 .57Phosphorus, dissolved, mg/L as P 15 .05 .02 .03 .14 1,880 .32 .01 .03 .24Phosphorus, total, mg /L as P 134 .06 .01 .05 .16 2,115 .20 .01 .05 .45Iron, dissolved, μg/L 150 228 4 31 1,079 3,478 855 4 50 3,201Iron, total, μg/L 284 443 12 100 1,637 3,109 3,805 17 200 12,000Manganese, dissolved, μg/L 59 62 1 17 400 2,869 429 2 38 1,400Manganese, total, μg/L 168 254 .15 50 256 2,175 1,000 .10 50 3,958

36 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont
Ground-Water Quality 37 Figure 17. Geographic variation of median concentrations of (

A) total dissolved solids and (

B) nitrite plus nitrate in 

ground water, by county, in North Carolina (modified from Briel, 1997).
38 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

Limited data are available for organic compounds 

and microbiological pathogens in ground water. Wade and 

others (1997) investigated pesticide concentrations in 152 

wells statewide, with about two-thirds of these wells 

located in the Coastal Plain. Numerous site-specific, and 

often contaminant-specific, investigations have been 

completed under various regulatory programs across the 

State. This information has not been compiled for a 

number of reasons. Total coliform bacteria measurements 

are collected routinely from public water-supply wells. 

However, there is increased concern regarding groundwater transport of viruses, particularly in situations where 

ground-water supplies are “under the influence of surface 

water.” As stated in North Carolina regulations, a supply 

under the influence of surface water is a supply source 

less than 50 ft from a surface-water body. A recent USGSsponsored investigation (G. Patterson, U.S. Geological 

Survey, written commun., June 1999) determined a 

correlation between stomach ulcers and Helicobacter 

pylori in well water. Microbiological contaminants are an 

emerging issue for both ground-water and surface-water 

supplies.

The extensive ground-water-quality data available 

from Reid (1993), Briel (1997), Spruill and others (1997), 

and Cunningham and Daniel (2001) can be compiled and 

analyzed on a county-by-county basis. As the Blue Ridge 

and Piedmont ground-water study proceeds, the waterquality database will expand as samples are collected and 

analyzed at the type-area study sites. The work by Briel 

(1997) provides examples upon which analyses of 

ground-water-quality data from North Carolina can be 

modeled.

STATE GROUND-WATER ISSUES AND PROBLEMS

The diversity of ground-water flow conditions in 

the Blue Ridge and Piedmont Provinces accounts for the 

complexity and variety of ground-water issues and 

problems that exist within the study area. Management of 

ground-water supplies can be difficult because the most 

permeable parts of the regolith-bedrock aquifer system 

typically are shallow and unconfined and, therefore, 

vulnerable to contamination from numerous human 

activities at land surface. In addition, the aquifers 

commonly are hydraulically connected to streams and 

lakes, and contamination of the aquifers in the interstream 

areas may eventually lead to contamination of surfacewater bodies.

Problems related to ground-water development and 

protection within the Blue Ridge and Piedmont fall into 

two general categories—(1) ground-water availability 

and (2) ground-water quality. Well yields are highly 

variable, even from wells tapping the same hydrogeologic 

units. Increasing population growth, industrial 

development, and recent droughts have increased the 

demand for additional water supplies in the study area. 

Increased ground-water pumpage has caused declines in 

water levels in places, decreases in well yields, and 

interference between cones of depression associated with 

closely spaced pumping wells. Pumping of wells can 

induce infiltration from streams or reduce ground-water 

discharge to streams, thus reducing streamflow by an 

unacceptable amount (Wood and others, 1972).

The sustainable yield of aquifers in the Blue 

Ridge and Piedmont Provinces can be difficult to 

determine. Although the porosity of the regolith can be 

sufficient to store large quantities of water, it is difficult 

to determine whether the water in storage is available to 

supply bedrock wells during periods of limited recharge 

such as droughts. Data are not readily available to 

estimate aquifer boundaries and storage coefficients; 

both types of information are needed to determine the 

volume of water in storage. (See figure 11 and the 

related discussion in the section, “Ground-Water 

Storage.”) Recharge areas are not easily defined, which 

can contribute to the difficulty of protecting bedrock 

supply wells from contamination.

Water-quality problems result from natural 

geochemical processes as well as human activities. The 

mineral composition of rocks can be reflected in the 

chemical composition of ground water as weathering and 

dissolution release soluble components. Objection-able 

concentrations of iron and manganese often occur in 

water from wells completed in mafic igneous and 

metaigneous rocks. Hydrogen sulfide often is present in 

water from slates, shales, and other rocks containing 

disseminated sulfide minerals. Hardness may reach 

objectionable levels in water from rocks containing 

carbonates or other calcium-magnesium-bearing 

minerals. Other water-quality problems related to natural 

geochemical processes result from the duration of waterrock contact, seasonal variations in recharge (and 

accompanying changes in the water table), and the 

presence of trace metals, radon, radium, and uranium in 

the rocks and soils.

Nearly all substances are soluble to some extent in 

water. The density of a liquid also affects its underground 

movement. Substances less dense than water tend to 

accumulate at the top of the saturated zone; like 

petroleum, if a substance is relatively immiscible, it will 

tend to spread in all directions as a thin layer. Substances 

denser than water, such as brines and some chlorinated 

solvents, tend to move downward through the saturated 

zone to areas where their movement becomes restricted 

due to a decrease in the size and number of interconnected 

openings in the regolith or underlying bedrock.
State Ground-Water Issues and Problems 39

Of all the natural constituents in ground water, 

radionuclides potentially pose the greatest threat to 

human health in the Blue Ridge and Piedmont Provinces. 

Since 1984, indoor radon gas has gained national 

attention as a major cause of lung cancer in the United 

States (U.S. Environmental Protection Agency, 1992; 

National Cancer Institute, 1997). High concentrations of 

radium and uranium in drinking water are known to be 

carcinogenic (Gabler and others, 1988; U.S. 

Environmental Protection Agency, 1994). The crystalline 

rocks of the Piedmont consist, in part, of granite, granitic 

gneiss, and other felsic rocks that contain small to 

moderate amounts of uranium, which, through the 

process of radioactive decay, is a source of radon gas. The 

amounts of uranium are sufficient for radon to emanate 

from the regolith and the part of the underlying fractured 

rock above the water table (LeGrand, 1987). One of the 

pathways for radon gas migration into households is 

through ground water and aeration of the water at faucets 

and showerheads. In addition to radon, high 

concentrations of dissolved radium and uranium nuclides 

have been detected in a few locations in ground-water 

supplies tapping crystalline and sedimentary rocks of the 

Piedmont (Zapecza and Szabo, 1988). Recent studies 

have identified high radon activities in ground water in 

Guilford and Orange Counties in the central and eastern 

Piedmont of North Carolina (Spruill and others, 1997; 

Cunningham and Daniel, 2001).

Many ground-water-quality problems are the result 

of human activities, including the disposal of wastes onto 

the land surface, into shallow excavations and septic 

tanks, or through deep wells, mines, or sinkholes in areas 

underlain by limestone (karst topography). Ground-water 

quality also can be degraded by the use of fertilizers and 

other agricultural chemicals; leaks in sewers, storage 

tanks, and pipelines; and wastes in animal feedlots. The 

magnitude of a water-quality problem depends on the size 

of the area affected and the amount and concentration of 

the constituent involved, as well as its solubility and 

density. Affected areas can range in size from point 

sources, such as septic tanks, to large urban areas having 

leaky sewer systems and numerous municipal and 

industrial waste-disposal sites.

Potential water-quality problems related to human 

activity include:

• discharge from septic tanks;

• petroleum products leaking from storage tanks;

• improper handling and(or) transport of industrial chemicals;

• improperly constructed water-supply wells;

• agricultural activities (application of pesticides 

and fertilizers, feedlot and barnyard wastes, 

and leakage from fuel-storage tanks);

• highway de-icing salts; and

• infiltration of contaminated surface water from 

lakes and streams as a result of nearby pumping from wells.

This list does not include all water-quality problems 

that can result from human activity, but it is 

representative of some of the most important problems 

that have been identified in the Blue Ridge and 

Piedmont Provinces of North Carolina.

The NCDENR Division of Water Quality (DWQ) 

Groundwater Section is divided into seven geographic 

regions within the State (fig. 18). Because of their 

location in the Blue Ridge and Piedmont, four of these 

regions are involved in this study—the Asheville, 

Mooresville, Winston-Salem, and Raleigh Regions. 

Although there are ground-water-related issues and 

problems that are common to all regions, some issues and 

problems are more important in individual regions than in 

others. A few of these issues are described below.

Ground-water concerns in the Asheville Region are 

many and varied. This region has large land areas 

previously used for agricultural purposes, such as 

orchards and Christmas tree farms, that rapidly are being 

developed for residential use. Issues regarding past 

pesticide use and its effect on shallow soils and ground 

water are a growing concern in these areas. Additional 

concerns include source identification, fate, and transport 

of chlorinated solvents detected in water-supply wells 

tapping fractured bedrock aquifers, particularly in areas 

that are heavily dependent on ground water. Water-quality 

issues, such as radon, trace metals, and acidity, are 

naturally occurring and are associated with specific rock 

formations and lithologies in the region.

On average, more than 64 percent of the population 

in the 19-county Asheville Region is dependent on ground 

water as the sole source of drinking water; in 8 of these 

counties, 75 percent of the population relies on ground 

water as the only source of potable water. Growthoriented issues, such as water availability, sustained 

growth, and water quality, will continue to be concerns in 

the Asheville Region as North Carolina continues to 

develop.

Citizens in the Mooresville Region increasingly 

inquire about ground-water quality, particularly around 

the lakes (for example, Lake Norman), which are 

attracting residential development. Other concerns for 

this region include fate and transport of chlorinated 

solvents in the bedrock and the effects of poor well 
40 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont Figure 18. Locations of active and potential study sites in the Asheville, Mooresville, Winston-Salem, and Raleigh Regions of the North Carolina Department of Environment and Natural Resources.
Available Ground-Water Data 41

construction. Ground-water availability also is a concern 

because of recent droughts.

In the Winston-Salem Region, chlorinated 

solvents, petroleum, and nutrients are the predominant 

ground-water contaminants. Past and present agricultural 

activities also contribute to ground-water contamination 

in this region. Other issues in the region include proper 

well construction and abandonment and possible 

contamination from nondischarge facilities.

Chlorinated solvents and nutrients are the most 

common ground-water contaminants in the Raleigh 

Region. Agricultural products, such as ethylene 

dibromide, Lasso, and other pesticides, have been 

detected in water from wells. Like the Mooresville 

Region, growth-oriented issues are at the forefront of 

citizens’ concerns. This includes not only the quality, but 

also the quantity and availability of ground water.

Available Ground-Water Data

Groundwater Section regional staff in Asheville, 

Mooresville, Winston-Salem, and Raleigh primarily are 

responsible for reviewing applications for nondischarge 

permits (nondischarge wastewater disposal systems do 

not discharge wastewater to surface waters; rather, the 

discharge is applied either onto the land surface or into the 

subsurface) and National Pollutant Discharge Elimination 

System (NPDES) permits. Groundwater Section staff also 

are responsible for monitoring ground-water 

contamination incidents from sources other than 

underground storage tanks (USTs). Regional offices store 

paper files for each ground-water contamination incident, 

including comprehensive site assessments and corrective 

action plans, soil and water sample data, well records, and 

ground-water-level data. Incident locations and other site 

information are stored in digital databases at each 

regional office, as well as in a compiled database at the 

central office in Raleigh. The databases are available for 

downloading from the Internet, and an interactive 

Internet-based ground-water incident database is being 

tested.

The NCDENR Division of Waste Management 

(DWM) is responsible for regulating the State’s UST 

program, which includes responding to reports of leaking 

USTs. Much of the same data collected for non-UST 

ground-water incidents also is collected by the DWM for 

UST incidents.

The NCDENR Division of Environmental Health 

(DEH) regional staff monitor public water supplies in 

North Carolina. Water-quality and well-construction data 

are available for all public water-supply wells; some data 

are in digital format, and some are paper documents. 

Well drillers are required to submit Groundwater 

Section GW-1 forms that contain boring logs, information 

on well construction, well yield, depth to ground water, 

and hand-drawn maps of well locations. These forms are 

required for all wells drilled in the State. Paper copies of 

these forms are filed in the NCDENR regional offices and 

the Central Office in Raleigh. The Central Office staff 

scan and store these forms as digital images; however, the 

regional offices still rely on paper documents.

Another responsibility of the regional 

Groundwater Section staff is to monitor compliance of 

nondischarge permits. Results of ground-water sampling, 

when required by these permits, are forwarded by the 

permittees to the NCDENR regional offices and the 

Central Office in Raleigh. Central Office staff have 

entered much of these data into digital databases that can 

be queried, but regional staff continue to rely on paper 

documents. In cases where ground-water sampling and 

analysis are required, the sampling interval typically is 

three times per year, and targeted analytes vary depending 

on the type of facility being permitted. In addition to the 

data described above, each region also has unique data 

sets and ground-water issues as noted below. 

Asheville Region

Considerable data are available regarding groundwater quality, availability, and hydrogeologic conditions 

in the Asheville Region. More than 100,000 individual 

water wells are on record for the region. Water-level data 

have been collected from 70 monitoring wells in the 

region since 1965. In addition, ambient water quality was 

measured and recorded in 25 to 40 wells from 1974 to 

1987. Geophysical logs and pumping test data also are 

available for many of these wells and for some privately 

owned wells. The Asheville Region has digitally plotted 

more than 2,000 public water-supply, monitoring, and 

observation wells and more than 1,600 UST sites where 

spills or leaks have occurred. The ground-water incident 

sites have been mapped by converting digital site-location 

databases into geographic information system (GIS) 

compatible files. Ground-water resources in the region 

also are described in reports by LeGrand and Mundorff 

(1952), Marsh and Laney (1966), Sumsion and Laney 

(1967), Dodson and Laney (1968), and Trapp (1970). 

The USGS has digital records of 752 water-supply 

wells (as of February 1, 2002) in the Ground-Water Site 

Inventory (GWSI) database for this region. Well data also 

are kept on file in the USGS District Office in Raleigh. 

The USGS maintains seven continuous-record 

observation wells in the region, as well as a number of 

continuous-record streamgaging stations.
42 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

The North Carolina Geologic Survey has mapped 

parts of this region at 1:12,000 scale. The geology also has 

been mapped by the USGS at a scale of 1:250,000 

(Hadley and Nelson, 1971; Rankin and others, 1972; 

Goldsmith and others, 1988).

Mooresville Region

Every well sampled for chemical analysis in the 

Mooresville Region has been located and marked on 

USGS 7.5-minute topographic quadrangles. Most of the 

sampling events and analytical results also have been 

recorded in a digital database and stored at the regional 

office.

Geology in the region has been mapped at 

1:250,000 scale by the USGS (Goldsmith and others, 

1988), and two publications available in the regional 

office describe lithology and ground-water chemistry in 

Iredell County (Peace, 1965; Groves, 1978). Groundwater resources in the region also are described in reports 

by LeGrand and Mundorff (1952), LeGrand (1954), and 

Floyd (1965).

The USGS has digital records of 2,055 watersupply wells (as of February 1, 2002) in the GWSI 

database for this region. Well data also are kept on file in 

the USGS District Office in Raleigh. The USGS 

maintains two continuous-record observation wells in the 

region.

Mecklenburg County, which lies in the southcentral part of the Mooresville Region, has developed an 

ambient well network from which water-level 

measurements and water-quality data have been collected 

for 28 wells. This information is available from the 

Mecklenburg County Department of Environmental 

Protection (Henry M. Sutton, Mecklenburg County 

Department of Environmental Protection, oral commun., 

2000).

Winston-Salem Region

Winston-Salem Region staff of the Groundwater 

Section monitored a water-level network composed of 

23 unused supply wells from 1974 to 1991, some of 

which were instrumented with continuous-paper 

hydrograph recorders. Some of these hydrographs are 

stored in the region. Water-quality data also were 

collected into the late 1980’s from a separate network of 

30 wells. The USGS maintains two long-term observation 

wells equipped with continuous water-level recorders in 

the region. The USGS has digital records of 2,194 watersupply wells (as of February 1, 2002) in the GWSI 

database for this region. Additional well records and well 

data are kept on file in the USGS District Office in 

Raleigh.

Geology in this region is described in several maps 

at different scales. The western part of the region is 

covered by two maps at a scale of 1:250,000 (Rankin and 

others, 1972; Espenshade and others, 1975). Geology in 

the eastern half of the region is mapped at a scale of 

1:125,000 (Carpenter, 1982). The southern part of the 

region in Davidson and Randolph Counties has been 

mapped at scales ranging from 1:48,000 to 1:62,500 

(Stromquist and others, 1971; Stromquist and Sundelius, 

1975; Seiders, 1981). Numerous publications are 

available that describe the geology and ground-water 

resources of the region, including reports by Mundorff 

(1948), LeGrand (1954), Bain (1966), Sumsion and 

Laney (1967), Peace and Link (1971), and Daniel and 

Sharpless (1983).

Raleigh Region

In addition to the typical data stored by all regional 

offices, the Raleigh Region has several continuous-paper 

hydrographs from selected wells. The USGS also has an 

observation well at Chapel Hill with water-level records 

covering the period from 1938 to present.

The USGS has digital records of 2,834 watersupply wells (as of February 1, 2002) in the GWSI 

database for this region. Well data also are kept on file in 

the USGS District Office in Raleigh. Note that wells in the 

eastern counties of the Raleigh Region that lie along the 

Fall Line (fig. 1) often tap bedrock beneath Coastal Plain 

sediment.

Geology in the region is described in several 

1:250,000-scale maps (Wilson, 1979; Wilson and Spence, 

1979; McDaniel, 1980; Wilson, 1981; Wilson and others, 

1981). Ground-water resources in the region are also 

described in reports by Mundorff (1946), Pusey (1960), 

Schipf (1961), Bain (1966), and May and Thomas (1968).

Central Office

As described above, most documents stored in the 

Groundwater Section regional offices also are stored in 

the Central Office files, and some have been digitized. In 

addition to the regulatory data, the Central Office also has 

initiated ground-water studies in the State and is a 

repository for data generated during these studies. One 

such study (North Carolina Division of Water Quality, 

Groundwater Section, 1997; Pippin and Heller, 1998) was 

performed in the Kings Mountain belt, which lies within 

the Mooresville Region, where water levels were 

recorded periodically from 28 wells, and an aquifer test 

was conducted. Data from this study are stored digitally.
Study Design 43

The Central Office staff also conducted studies to 

measure the effects of pesticides and intensive livestock 

operations (ILOs) on the State’s ground-water resources 

from 1995 to 1999; some of these sites were located in the 

Piedmont and Blue Ridge (Wade and others, 1997; North 

Carolina Division of Water Quality, Groundwater 

Section, 1998). Water-level and sampling analyses data 

have been recorded in digital spreadsheets since the 

study’s inception. Boring logs and other site information 

associated with this study are filed as paper documents.

A comprehensive digital spreadsheet has been 

compiled for over 900 wells that were used for ambient 

monitoring throughout the State. Digital water-level and 

water-quality data are available for a subset of these wells. 

Locations of these wells have been plotted using GIS 

software.

Ground-Water Data Deficiencies

Ground-water level, ground-water quality, and 

lithologic data have been and continue to be collected 

from selected sites in the Blue Ridge and Piedmont 

Provinces. Thousands of well-completion reports have 

been submitted by drillers to State and county agencies. 

Much of the information that has been gathered in the 

past, however, is not stored in a form that is readily 

available for analysis and interpretation. These data need 

to be reviewed, and data that can be used for this study 

need to be entered into computerized databases.

A regional characterization of land use, groundwater quality, recharge/discharge relations, soils and 

hydrogeologic characterization, and ground-water flow is 

needed in order to appropriately manage the resource. 

However, detailed, site-specific information also is 

needed to understand and manage local problems and 

solutions.

Ambient ground-water-quality monitoring is 

inadequate in the Blue Ridge and Piedmont, and there is 

no statewide program to address this deficiency. Currently 

(2002), there are only 12 long-term ground-water 

monitoring wells throughout the entire Blue Ridge and 

Piedmont region in the USGS-NCDENR Division of 

Water Resources cooperative ground-water-level network 

(Howe and Breton, 2001). The existing network is not 

sufficient to address ground-water resource concerns in 

the region. A program is needed to monitor ambient water 

quality so that trends can be evaluated. Both water-level 

and water-quality aspects of an ambient ground-water 

program are needed to manage and protect the resource.

The concept of a transition zone between regolith 

and bedrock, and possible variations due to rock texture, 

needs to be investigated. Research is needed to 

characterize the transition zone and define its role in the 

ground-water flow system. Physical controls on flow and 

transport within this zone also need to be identified and 

evaluated. If transition zones are identified and 

determined to be a significant component of the groundwater flow system, then the conceptual flow systems 

discussed previously may need to be subset based on the 

texture of the crystalline bedrock and the type of 

transition zone that is likely to occur—distinct or 

indistinct. The crystalline bedrock mantled by thick 

regolith conceptual system would become two conceptual 

systems: (1) highly foliated bedrock mantled by thick 

regolith and (2) massive bedrock mantled by thick 

regolith. Similarly, the crystalline bedrock mantled by 

thin regolith conceptual system would become two 

conceptual systems: (1) highly foliated bedrock mantled 

by thin regolith and (2) massive bedrock mantled by thin 

regolith.

Site characterization at the local and regional scale 

often is inadequate because recharge rates and travel 

times are virtually unknown, as are ground water/surface 

water interactions in these terranes. Further work is 

needed to develop methods of surface and(or) subsurface 

fracture delineation. Geochemical tracers and isotopic 

studies may be useful tools for flowpath studies and 

fracture delineation; certainly they would provide insight 

into the inter-connectivity of fracture networks.

STUDY DESIGN

This program is designed as an ongoing long-term 

collaborative investigation to improve the level of 

understanding of the ground-water system in the Blue 

Ridge and Piedmont of North Carolina. The program will 

be organized as a joint investigation using the resources of 

both the USGS and the NCDENR Division of Water 

Quality Groundwater Section. In particular, 

hydrogeologists from the Groundwater Section Central 

Office and four Regional Offices (Asheville, Mooresville, 

Winston-Salem, and Raleigh) will participate (fig. 18). 

Drilling equipment and crews will be provided by the 

Groundwater Section's Kinston Office.

In order to develop a long-term plan for 

characterization and eventual utilization of ground-water 

resources in the Blue Ridge and Piedmont of North 

Carolina, a summary and analysis of existing data and 

interpretive studies are needed. The evaluation of known 

hydrogeologic information, data, and interpretive needs 

presented in this report serves as a basis to develop studies 

that investigate ground-water quality, flow, transport, and 

contribution to streamflow throughout the Blue Ridge and 

Piedmont.
44 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

It is not feasible to obtain site-specific information 

for all areas in the Blue Ridge and Piedmont. A more 

feasible approach is to select areas of the Blue Ridge and 

Piedmont that are most representative of a particular 

area's land use, geology, and hydrology to obtain an 

understanding of the hydrologic processes in these areas, 

and transfer the information from these local “type areas” 

to similar regional hydrogeologic areas. Ideally, the type 

areas that are chosen will be representative of larger areas 

of the two provinces and will allow the hydrogeologic 

characteristics of the terranes to be studied and described 

in detail.

For the purpose of this study, the term "type area” 

applies to a 10- to 100-mi2 area within a hydrogeologic 

terrane where information is sufficient to develop and test 

a concept of ground-water flow by using analytical or 

numerical methods that can be validated by field 

measurements. Ideally, selected type areas will be 

representative of the flow system that is present wherever 

the particular hydrogeologic terrane is present.

In order to study and better understand the 

hydrogeology and water quality of ground water in the 

Blue Ridge and Piedmont, type areas will be identified 

during the first phase of the study in the hydrogeologic 

terranes characterized by (1) massive or foliated 

crystalline rocks overlain by thick regolith and 

(2) massive or foliated crystalline rocks overlain by thin 

regolith. Type areas may be identified in the areas 

underlain by sedimentary rocks of Mesozoic age (fig. 4) 

during a later phase of the study.

The type-area studies will be designed to address 

the issues and problems described previously. Much of 

the information needed to address these issues will be 

generated by this study. Within each NCDENR region, 

however, available data will be evaluated for inclusion in 

databases generated by the type-area studies. Identified 

data deficiencies will be addressed as needed. 

As planning and site selection proceed for the typearea studies, specific ground-water issues and data 

deficiencies can be selectively studied depending on the 

priorities identified during the selection process. These 

issues tend to fall into two general categories: 

(1) hydrogeology of regolith-fractured rock aquifer 

systems and (2) ground-water quality.

The movement and fate of specific chemicals and 

classes of chemicals in ground water also are critical 

issues in the Blue Ridge and Piedmont. If an appropriate 

site is identified, site-specific research will focus on 

water-quality issues related to microbial contamination, 

as well as the role of microbes in natural bioremediation 

of contaminant plumes. Migration of solvents and volatile 

organic compounds associated with petroleum-product 

UST releases are important concerns. Because of large 

livestock populations in this region, the presence of 

nutrients, especially nitrate and other nitrogen 

compounds, are of concern. As discussed above, radon 

and other radionuclides are common constituents in 

granite and granitic gneisses (felsic rocks), and can occur 

in ground water at concentrations that represent a health 

hazard. Felsic rocks are found throughout the Blue Ridge 

and Piedmont. Type areas underlain by felsic rocks will 

provide an opportunity to study the movement of radon 

and other radionuclides in ground water.

The type-area studies will collect ground-waterlevel, ground-water-quality, and hydrogeologic data for 

the purpose of gaining a better understanding of the 

movement and geochemistry of ground water within the 

hydrogeologic terranes that occur in these provinces. In 

order to accomplish the objectives of the study, a primary 

goal of the cooperative USGS-Groundwater Section study 

will be to develop standard procedures for the collection 

and digital storage of data that are generated. At this time, 

few standardized procedures are available to guide 

storage and accessibility of the data needed for this 

research. These data must be collected according to 

standard scientific guidelines, and the data and analyses 

based on these data must be readily available in digital 

form to the scientific and regulatory community, as well 

as to the general public. As part of this project, guidelines 

will be developed for the collection and storage of data. 

Once the data are readily available, they can be used in a 

broad range of research that addresses ground-waterrelated issues.

The planned work for this ground-water study has 

a wide-ranging scope, including basic data collection, 

routine interpretive work, and applied research. Work will 

be done jointly by the USGS and the Groundwater 

Section. The objectives of the study, the approach to be 

used to meet these objectives, and the selection of 

potential study sites are discussed in greater detail in the 

following sections.

Objectives

Objectives for the State’s Groundwater Section 

Resource Evaluation Program are described in “A 

Resource Evaluation Program for Ground Water in North 

Carolina” (North Carolina Division of Water Quality, 

Groundwater Section, 1999). This document was 

prepared by the Resource Evaluation Work Group of the 

Department of Environment and Natural Resources, 

Division of Water Quality, Groundwater Section, in 

October 1999. The cooperative study by the USGS and 

the Groundwater Section that is described in this report is 
Approach 45

referred to generally as the “Blue Ridge and Piedmont 

Ground-Water Project” and is a major component of the 

Groundwater Section's Resource Evaluation Program.

Based on the type-area concept, sites are being 

selected within the hydrogeologic terranes of the Blue 

Ridge and Piedmont Provinces so that ground-water 

conditions throughout the region can be evaluated based 

on data collection and analyses conducted at type-area 

study sites. Research to be conducted at each site will be 

designed to meet a consistent set of objectives. The 

objectives listed below have been compiled from the 

Resource Evaluation Program document (North Carolina 

Division of Water Quality, Groundwater Section, 1999), 

the U.S. Geological Survey “Proposal for Ground-Water 

Investigations in the Piedmont and Mountain Region of 

North Carolina” (W.L. Cunningham, U.S. Geological 

Survey, written commun., 1999), and discussions among 

key participants in the study. The objectives of the 

cooperative study are as follows:

1. Define hydrogeologic terranes and flow systems 

within the Blue Ridge and Piedmont Provinces;

2. Describe ground-water quality within each 

hydrogeologic terrane;

3. Determine vulnerabilities of ground water to 

contamination in each hydrogeologic terrane;

4. Determine the susceptibility of ground water to 

over use in each hydrogeologic terrane;

5. Quantify the components of ground-water flow 

systems in representative areas (type areas) within 

the hydrogeologic terranes; 

6. Assess the response of hydrogeologic systems to 

ground-water development;

7. Determine the effects of lithology, structure, 

topography and other relevant geologic or 

geomorphic features on ground-water quality, 

quantity, and flow;

8. Determine the relation between surface- and 

ground-water flow systems and their effects on the 

quality and availability of ground water;

9. Determine the potential effects of various types of 

land use and surface applications of chemicals, 

sludges, and other residues on ground-water 

quality;

10.Identify the hydrologic factors controlling groundwater recharge and discharge;

11.Provide regional estimates of the ground-water 

budget, including withdrawals, natural discharge, 

recharge, and aquifer storage;

12.Provide ongoing training and mentoring to 

Groundwater Section staff in order to upgrade the 

hydrogeologic skills needed to carry out the State's 

ground-water protection program;

13.Develop a digital database to aid in planning, 

developing, and managing ground-water resources 

in the Piedmont and Blue Ridge physiographic 

provinces; and

14.Provide outreach and education to the citizens of 

North Carolina.

A variety of approaches may be used to meet these 

objectives. Some may be used at all study sites; some may 

be used selectively at sites where unique approaches are 

needed or where unique opportunities for research and 

site characterization are unavailable at other sites. Some 

approaches planned for this study are discussed in the 

following section. 

Approach

The first year of the investigation was used 

primarily to evaluate the state of the science in the Blue 

Ridge and Piedmont Provinces of North Carolina. Project 

staff compiled and evaluated existing hydrologic data 

from the Blue Ridge and Piedmont, identified deficiencies 

in information and(or) data, identified potential type areas 

for future intensive study, and generated a plan of study 

for subsequent years of the study. Sources of data 

evaluated during the first year included the USGS, 

universities, county governments, well drillers, and 

NCDENR Divisions of Water Quality, Health, and Water 

Resources. Hydrologic data pertaining to soils, water 

quality, hydrogeology, surface water, ground water, 

precipitation, and the unsaturated zone were identified 

and cataloged for potential future use. By the end of the 

first year, drilling, geologic mapping, and other data 

collection had been initiated at several sites. By design, 

the scope of work will increase in subsequent years.

Because details of the investigation in future years 

will be determined during the first year of study, which is 

in progress, this discussion provides only a general 

overview of the work to be accomplished over the next 

9 years. As the study proceeds, data from the type-area 

studies, from applied research, and from the sources 

mentioned above will be verified and entered into the 

appropriate USGS National Water Information System 

(NWIS) database. Available GIS data will be identified 

and compiled. A library of interpretive information from 

North Carolina and applicable studies from other 

Appalachian States will be compiled. Areas of the Blue 

Ridge and Piedmont Provinces that are not well 

represented based on the data evaluation will be 

identified.

Following the first year, the work will focus on
46 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

• Filling in data and interpretive deficiencies 

identified during the first year;

• Characterizing individual type areas within the 

Blue Ridge and Piedmont;

• Installing type-area study sites for the longterm collection of ambient ground-water 

quality and quantity data;

• Conducting applied research within these complex hydrogeologic environments using

a. Unsaturated-zone techniques,

b.Geophysical techniques,

c. Geochemical techniques,

d. Flowpath analysis,

e. Ground-water flow modeling, and

f. Comprehensive watershed analysis techniques;

• Transferring type-area results to similar hydrogeologic areas;

• Providing outreach and education related to the 

ongoing work; and

• Providing ongoing training and mentoring to 

Groundwater Section staff in order to 

upgrade the hydrogeologic skills needed to 

carry out the State’s ground-water protection 

program.

To provide uniformity and consistency of research 

and data collection, a consistent approach will be used at 

each type-area study site (D.J. Geddes, M.J. Heller, 

R.E. Bolich, and K.M. Sarver, written commun., 2000). 

At individual sites, customized approaches based on 

unique geochemistry and hydrogeology may be necessary 

or a valuable addition to meet study goals. 

An example of common approaches to be used at 

each site might be

• Surface geophysics,

• Borehole geophysics,

• Geomorphology,

• Structural geology,

• Determination of regolith thickness,

• Well design, and

• Inorganic ground-water geochemistry.

Site-specific approaches might involve studies of

• Transport through the unsaturated zone,

• Soil chemistry,

• Isotope geochemistry,

• Organic chemistry,

• Age dating,

• Microbial contamination,

• Evaluation of interflow, and

• Analysis of quantity and quality of base flow in 

streams.

Additional details regarding site-selection criteria 

and approaches to be used to characterize the type areas 

are given in the following sections. Based on the siteselection criteria and the goals of this study, project staff 

have begun to identify study sites in type areas. Some of 

these sites are described in the section, “Active and 

Potential Type-Area Study Sites.”

Site-Selection Criteria

As part of the site-selection process to identify 

representative type areas for study, certain selection 

criteria are required to be met at all sites. Additional 

criteria may be considered at selected sites that will 

advance the goals of the study to better understand the 

geochemistry and behavior of ground-water flow systems 

in the major hydrogeologic terranes of the North Carolina 

Blue Ridge and Piedmont. The required and optional 

site-selection criteria are listed below.

Required Criteria for All Sites

The following criteria must be met when selecting 

any study site for inclusion in this project.

1. Study sites chosen for ground-water research must 

be representative of a hydrogeologic terrane within 

the Blue Ridge and Piedmont Provinces. The areas 

underlain by metamorphosed carbonate rocks in 

North Carolina are small and insignificant in terms 

of human population and, therefore, will not be 

considered separately from other crystalline rocks 

in this study. The areas underlain by sedimentary 

rocks in the Mesozoic basins are distinct from the 

areas underlain by crystalline rocks and represent 

only 5.1 percent (table 2) of the hydrogeologic 

units found in the Blue Ridge and Piedmont; 

furthermore, the sedimentary rocks in the Deep 

River basin (fig. 4) have the lowest well yields of 

all Mesozoic basins. For these reasons, the 

sedimentary rocks will not be evaluated during the 

first round of site selection. However, the largest of 

the Mesozoic basins in North Carolina, the Deep 

River basin (fig. 4), underlies major population 

centers and supplies ground water to a large and 

growing rural population in the eastern Piedmont. 

For this reason, there is interest in identifying a 

type area in the Deep River basin during a later 

phase of the study. During the initial phase of site 

selection, a selected site must fall within one of 

two terranes defined below:
Site-Characterization Procedures 47

a. Massive or foliated crystalline rock mantled by thick regolith, or

b. Massive or foliated crystalline rock mantled by thin regolith.

Varying hydrogeology (including yields to wells) 

and(or) geochemistry within these two terranes 

may require defining sub terranes.

2. Research stations must be easily accessible during 

both the installation phase and for on-going 

monitoring and research. Ideally, a site will not 

change ownership or land use during the period of 

research. Staff should be able to access the site 

during normal business hours.

3. Previous land use should be known.

4. Research at the site must yield data that will aid 

Groundwater Section staff in providing technical 

information requested by the citizens of North 

Carolina.

5. Educational outreach must be provided.

Optional Criteria for Selected Sites

In addition to meeting the required criteria for all 

sites, additional criteria may be considered for site 

selection.

1. Previous hydrogeologic investigations have been 

conducted at the site that can be built upon.

2. The site is being used for land application of 

sludge, pesticides, or other potential ground-water 

contaminants.

3. The site has a documented history of 

contamination.

Site-Characterization Procedures

A standardized approach will be used to 

characterize all of the study sites. In addition, specialized 

techniques may be used to describe unique features of a 

given site. A manual of standard procedures, including 

well-construction procedures, has been written by a 

workgroup selected from project staff and will be 

followed during all phases of work at the sites.

Standard Procedures for All Study Sites

The hydrogeologic characteristics of each study 

site, including topography, regolith thickness and 

composition, transition-zone thickness, type of bedrock 

(including mineralogy and texture), and geologic 

structure will be determined. The current and historic land 

use of a site will be documented.

Sites for boreholes will be selected based on 

topography, location relative to streams and lakes, and 

local geology. Continuous rock core will be collected at 

each borehole site using wire-line technology. These 

cores will be described and stored in continuous sections 

starting from the surface to a depth to be determined on 

site by the supervising hydrogeologist. The thickness and 

depth of the soil, saprolite, and transition zones will be 

determined from the coring. Coring also will allow 

scientists to study lithologic and structural characteristics 

including foliation and fracturing. 

Following completion of coring, clusters of 

observation wells will be constructed at each borehole 

site. Wells in a cluster will be installed to depths based on 

hydrogeologic information determined from the coring. 

Where coring is not necessary or practical, borehole 

geophysical techniques will be used to determine 

subsurface lithology and structure, as well as depth and 

orientation of fractures.

A minimum of three wells will be installed in each 

well cluster. The three wells will be screened at different 

depths to monitor ground-water levels and quality in the 

saprolite, transition zone, and bedrock. Where it is 

necessary to determine water-table elevations or locations 

of ground-water divides for accurate placement of 

observation wells, a series of 1-in.-diameter wells will be 

installed in a grid using a truck-mounted Geoprobe rig 

where possible. Each well will be surveyed to accurately 

determine the location and elevation of measuring points 

for water-level measurements. At sites where benchmarks 

are available, elevations will be converted to altitude and 

referenced to the National Geodetic Vertical Datum of 

1929. 

Specialized Techniques for Selected Study Sites

At selected study sites, specialized investigative 

techniques may be used in addition to the standard 

procedures. These techniques include aquifer tests to 

determine aquifer hydraulic properties, packer testing and 

sampling of fractures, age dating of ground water, soil 

chemistry analysis, flowpath analysis, and tracer studies. 

At sites where age dating, flow-path studies, or groundwater-quality sampling will be performed, wells to be 

used for aquifer tests or other studies requiring pumping 

will be at a sufficient distance so that cones of depression 

(Heath, 1989, p. 30) will not interfere with areas requiring 

ambient conditions.
48 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

Active and Potential Type-Area Study Sites

Using the two categories of hydrogeologic terranes 

described as (1) crystalline rock mantled by thick regolith 

and (2) crystalline rock mantled by thin regolith, some 

potential study sites are listed and briefly described 

below. The selection criteria described previously make 

no distinction between sites underlain by massive or 

foliated bedrock. However, it is important to recognize 

that the presence or absence of bedrock foliation, 

particularly if the rock is highly foliated, may influence 

the character of the transition zone. As the study proceeds 

and as data become available about the hydraulic 

characteristics of the transition zone, a subdivision of 

these crystalline rock categories into two additional 

categories—massive and weakly foliated, and highly 

foliated—may be necessary. Objectives for each site are 

included in each site description, along with other 

relevant information.

Preparation of this report has occurred at the same 

time that initial site selections were completed and test 

drilling and other activities, such as surface geophysical 

surveys, water-quality sampling, and installation of 

monitoring equipment, were taking place. Consequently, 

a brief statement of progress at sites that have already 

been selected is included, where appropriate, at the end of 

each site description.

Sites Having Crystalline Rock Mantled 

by Thick Regolith

Site: Langtree Peninsula at Lake Norman

Location: The site is located in the NCDENR 

Mooresville Region, Iredell County, N.C. (site 4, 

fig. 18).

Characteristics: Thick regolith overlies massive, weakly 

foliated crystalline bedrock of the Charlotte belt. The 

site is a recreational area located on a peninsula 

extending into Lake Norman. The property is owned by 

Davidson College.

Available information includes:

1. Subsurface information from existing well records 

and well tags.

2. Water-sample analyses from selected wells for 

volatile organic compounds (VOCs), nutrients, 

pesticides, herbicides, and bacteria.

3. Conceptual water budget developed by using data 

from the USGS streamgaging station at Norwood 

Creek, a similar basin, and the USGS rainfall 

gaging station at Norman Shores.

4. Changes in land use from 1960 to 1996.

5. A detailed regional geologic map (Goldsmith and 

others, 1988).

6. Topographic map—Lake Norman North, N.C., 

1:24,000-scale, USGS, 7.5-minute series 

topographic quadrangle.

Objectives for the site:

1. Characterize a typical Charlotte belt 

hydrogeologic setting.

2. Study the interaction between ground water on a 

peninsula and surface water in a manmade 

reservoir (Lake Norman) under natural and 

pumping conditions.

3. Provide the opportunity for students from nearby 

universities and colleges to observe site 

characterization and drilling activities, and to 

develop projects for senior theses.

Potential partners: Davidson College, The University of 

North Carolina at Charlotte

Selection criteria met: This site meets all five of the 

required criteria for site selection. Additionally, this 

site meets optional criteria 1.

Status: This site has been selected, and extensive work 

was done at the site during late 2000 and early 2001. 

Work completed as of September 2001 includes:

1. Continuous rock coring at seven sites.

2. Installation of 30 wells, including six clusters of 

three wells tapping saprolite, the transition zone, 

and bedrock.

3. Installation of water-level recorders and satellite 

telemetry on one cluster of three wells located on 

the drainage divide.

4. All well sites have been surveyed and referenced to 

a common datum so that water levels can be 

compared and the water table beneath part of the 

site can be mapped.

Site: Indian Creek Basin

Location: The site is located in the NCDENR 

Mooresville Region, Catawba, Gaston, and Lincoln 

Counties, N.C. (site 3, fig. 18).

Characteristics: Thick regolith overlies highly foliated 

and massive crystalline bedrock of the Inner Piedmont 

belt; foliated bedrock predominates. The primary study 
Active and Potential Type-Area Study Sites 49

area covers 69 mi2. Land use primarily is rural 

agricultural; forested land is the second most abundant.

Available information includes:

1. Hydrogeologic conditions, aquifer properties, and 

recharge rates were characterized to develop a 

digital ground-water flow model of the area 

(Daniel and others, 1997).

2. Geochemistry of ground and surface water has 

been characterized (Daniel and others, 1997).

3. A detailed regional geologic map (Goldsmith and 

others, 1988).

4. Topographic maps—Banoak, Cherryville, and 

Lincolnton West, N.C., 1:24,000-scale, USGS 

7.5-minute series topographic quadrangles.

Objectives for the site:

1. Refine the existing ground-water flow model to 

simulate flow beneath narrow valley bottoms and 

transient conditions, including aquifer response to 

ground-water withdrawals.

2. Apply new surface and subsurface technology, 

including surface geophysics, borehole 

geophysics, and well packers, to further 

characterize the bedrock aquifer.

Potential partners: None

Selection criteria met: This site meets four of the five 

required criteria; there currently is no educational 

outreach component. This criterion would have to be 

fulfilled. This site meets optional criteria 1.

Status: This site was not selected for the first phase of 

work.

Site: North Carolina State University Mountain

Horticultural Crops Research Station

Location: The site is located in the NCDENR Asheville 

Region, Henderson County, N.C. (site 2, fig. 18).

Characteristics: Thick (?) regolith overlies fractured 

bedrock of the Blue Ridge belt. Most of the site is used 

for orchards. The research station has been in operation 

since about 1950 and covers 273 acres. The French 

Broad River flows through the site.

Available information includes:

1. Records of chemical applications and changes in 

land use may be available because this is an 

agricultural research site.

2. A regional geologic map (Hadley and Nelson, 

1971).

3. Topographic map—Skyland, N.C., 1:24,000-

scale, USGS 7.5-minute series topographic 

quadrangle.

Objectives for the site:

1. Study the fate and transport of agricultural 

chemicals used for horticulture in ground water.

2. Study the interaction between ground-water flow 

and flow in a large river (French Broad River).

Potential partners: North Carolina State University 

(NCSU)

Selection criteria met: This site meets the five required 

criteria, and optional criteria 2. Results of studies and 

data will be made available to faculty and students at 

NCSU. 

Status: The site has been selected. Work completed as of 

September 2001 includes:

1. Reconnaissance of the site and well-site selection.

2. Obtained permission for the drilling of wells.

Site: National Training Center for Land-Based 

Technology and Watershed Protection

Location: The site is located in the NCDENR Raleigh 

Region, Wake County, N.C. (site 7, fig. 18).

Characteristics: Thick regolith overlies highly foliated 

bedrock of the Raleigh belt. The training center 

occupies over 30 acres at the NCSU Lake Wheeler 

Field Research Laboratory. Several water-supply wells 

currently are on the site.

Available information includes: 

1. A detailed geologic map by Heller (1996) and a 

regional geologic map by Wilson and others 

(1981).

2. Topographic map—Lake Wheeler, N.C., 

1:24,000-scale, USGS 7.5-minute series 

topographic quadrangle.

Objectives for the site:

1. Use the site primarily as a training site for 

Groundwater Section staff.

2. Provide educational outreach to the legislative and 

educational community. Outreach is a primary goal 

for this site.

Potential partners: NCSU College of Agriculture and 

Life Sciences

Selection criteria met: This site meets all five of the 

required criteria for site selection and optional 

criteria 1.
50 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

Status: This site has been selected and extensive work 

was done at the site during late spring and summer 

2001. Work completed as of September 2001 includes:

1. Completion of bedrock coring at three sites.

2. Installation of 10 wells in three clusters.

3. Installation of a bedrock production well and two 

observation wells for use in training methods of 

conducting aquifer tests and aquifer-test analysis 

on bedrock wells.

4. Running of borehole geophysical logs.

5. Collection of water-quality samples from one 

cluster of three wells.

6. Completion of a surface geophysical survey 

(square array resistivity) at one site to determine 

bedrock-fracture orientation.

Sites Having Crystalline Rock Mantled 

by Thin Regolith

Site: Bent Creek Demonstration Forest

Location: The site is located in the NCDENR Asheville 

Region, Buncombe County, N.C. (site 1, fig. 18).

Characteristics: Thin regolith overlies highly foliated 

fractured bedrock of the Blue Ridge belt. The 

demonstration forest occupies about 6,000 acres of the 

Bent Creek watershed and lies adjacent to Pisgah 

National Forest. The watershed occupies a breached 

anticline with the sulfide-rich Ashe Formation exposed 

at lower elevations along Bent Creek. Water in Bent 

Creek has low pH and reduced fish populations.

Available information includes: 

1. A detailed North Carolina Geological Survey 

(NCGS) bedrock geologic map (scale 1:12,000) 

that includes:

• rock-unit contacts and explanations,

• structural symbols,

• cross sections,

• index metamorphic minerals map,

• scintillation readings map,

• stream-sediment heavy minerals, and

• whole-rock geochemical analyses.

2. Mineral resources summary.

3. Traverse map including station locations.

4. Drainage basin map of heavy mineral occurrences, 

with the minerals indicated.

5. Petrographic thin sections and section 

descriptions.

6. Topographic maps—Asheville, Dunsmore 

Mountain, Enka, and Skyland, N.C., 1:24,000-

scale, USGS 7.5-minute series topographic 

quadrangles.

Objectives for the site:

1. Determine ground-water recharge rates in a 

pristine mountain environment.

2. Age date ground water.

3. Determine time of travel from recharge to 

discharge in Bent Creek.

4. Study the relation between ground-water quality 

and surface-water quality in Bent Creek.

5. Study the effects of ground-water quality on fauna 

in Bent Creek.

6. Study climatic effects on ground-water resources 

in the watershed.

Potential partners: N.C. Geological Survey; U.S. 

Department of Agriculture Forest Service.

Selection criteria met: Access to large areas of the site is 

limited; all other necessary criteria have been met.

Status: This site has been selected and work was started 

at the site during the summer of 2001. Work completed 

as of September 2001 includes:

1. Sites for eight well clusters were selected along 

Boyd Branch, clearances were obtained, and 

bedrock core drilling was begun. As of September 

2001, core drilling has been completed at six sites.

2. A site was selected for construction of a gaging 

station on Bent Creek. Permission has been 

obtained for construction of the gage, and 

fabrication of the gage is in progress.

Site: Morrow Mountain State Park

Location: The site is located in the NCDENR 

Mooresville Region, Stanly County, N.C. (site 5, 

fig. 18).

Characteristics: Thin regolith overlies highly foliated 

crystalline bedrock (metavolcanic slate and tuff) of the 

Carolina Slate belt.

Available information includes:

1. Several reports describing the geology of the 

Morrow Mountain area. The geology is described 

in a report on the Albemarle quadrangle by Conley 

(1962) and included in a regional geologic map by 

Goldsmith and others (1988). More recent 

1:24,000-scale mapping of the northern half of the 
Organization and Federal-State Interaction 51

Morrow Mountain 7.5-minute quadrangle, which 

includes the park, also is available (Ingram, 1999).

2. Topographic maps—Badin and Morrow 

Mountain, N.C., 1:24,000-scale, USGS 

7.5-minute series topographic quadrangles.

Objectives for the site:

1. Characterize a typical Carolina Slate belt 

hydrogeologic setting.

2. Provide educational outreach to the citizens of 

North Carolina by providing a display of the work 

being done at the research station in the park.

Potential partners: North Carolina Department of Parks 

and Recreation

Selection criteria met: This site meets all five of the 

required criteria for site selection. Additionally, this 

site meets optional criteria 1.

Status: This site was not selected for the first phase of 

work.

Site: North Carolina State University Upper Piedmont 

Agricultural Research Station

Location: The site is located in the NCDENR 

Winston-Salem Region, Rockingham County, N.C. 

(site 6, fig. 18).

Characteristics: Thin and thick regolith overlie foliated 

and fractured bedrock of the Milton belt. The research 

station contains about 670 acres where an ecological 

trail is being built. The site also hosts a 4-H camp. The 

research station is used for livestock and agricultural 

and horticultural (orchard) research.

Available information includes:

1. Agricultural chemical application data.

2. Crop records and changes in land use.

3. Climatological data from three weather stations.

4. Detailed regional geologic map (Carpenter, 1982).

5. Topographic maps—Reidsville and Southeast 

Eden, N.C., 1:24,000-scale, USGS 7.5-minute 

series topographic quadrangles.

Objectives for the site:

1. Characterize a typical Milton belt (fig. 7) 

hydrogeologic setting.

2. Determine effects of agricultural land uses on 

ground-water quality. Part of the research station is 

dedicated to livestock research; investigate the 

possible introduction and movement of nutrients in 

ground water in this area. Others parts of the 

research station are used for crop and orchard 

research; these areas can be studied for the 

occurrence of pesticides and other chemicals.

3. Study movement of nutrients and other chemicals 

in the unsaturated and saturated zone.

4. Study effects of ground water on surface-water 

quality in two bordering streams.

5. Study anisotropic ground-water flow. The 

structural attitude of bedrock (moderate dip of 

30–35 degrees southwest) beneath the research 

station provides an opportunity to study groundwater movement in the dip direction to the 

southwest, and oblique to compositional layering 

and foliation in a northeasterly direction.

6. Provide educational outreach to 4-H camp students 

and visitors to the research station’s ecological 

walking trail using visual displays.

Potential partners: North Carolina State University

Selection criteria met: This site meets all five of the 

required criteria for site selection. Additionally, this 

site meets optional criteria 2.

Status: This site has been selected, and work was started 

at the site during the late spring and summer of 2001. 

Work completed as of September 2001 includes:

1. Detailed geologic mapping of the watershed 

surrounding the site was begun by USGS 

geologists and Groundwater Section 

hydrogeologists.

2. A northwest-southeast-trending traverse extending 

from Carroll Creek to the north to Wolf Island 

Creek to the south has been proposed, and 

permission for construction of well clusters along 

the traverse was obtained.

3. Nine sites for clusters have been identified, and 

bedrock core drilling has been completed at four 

sites along the southeastern half of the traverse.

Organization and Federal-State Interaction

The Blue Ridge and Piedmont ground-water study 

is a major component of the Groundwater Section’s 

statewide Resource Evaluation Program and is designed 

as an ongoing, long-term collaborative investigation to be 

conducted jointly by the Groundwater Section and the 

USGS. Project direction will come from a central staff in 

Raleigh, North Carolina. This staff will consist of coproject leaders and staff from the Groundwater Section 

Central Office and the USGS, including hydrologists and 

hydrogeologists specializing in some combination of 

database administration, geology, geochemistry, groundand surface-water interactions, fractured-rock hydrology, 

and numerical flow simulation. 
52 Preliminary Hydrogeologic Assessment and Study Plan for a Regional Ground-Water Resource Investigation of the Blue Ridge and Piedmont

The study area is divided into four regions based on 

the NCDENR Regions headquartered in Asheville, 

Mooresville, Winston-Salem, and Raleigh (fig. 18). One 

Groundwater Section hydrogeologist will be designated 

as the Regional Project Manager for each region. These 

four Regional Project Managers will be responsible for 

defining the hydrogeologic framework and factors 

affecting flow in hydrogeologic terranes at study sites 

within their regions. They will collect and compile data, 

enter the data into computer files, and provide Central 

Office staff with descriptions of the hydrogeologic 

terranes. Further, they will formulate concepts of flow 

within these terranes and the criteria for selecting type 

areas for testing these concepts of flow. 

The Regional Project Managers will propose 

suitable type areas and conduct quantitative studies of 

ground-water flow, quality, and mass transport in the type 

areas selected and funded by the project. The Regional 

Project Manager will be responsible for all aspects of the 

site work, which will be conducted in cooperation with 

USGS personnel according to a site plan approved by the 

project staff. Proposed deviations from the site plan will 

be discussed among project staff until a course of action 

has been decided. If a course of action cannot be agreed 

upon, staff will meet to discuss options, and the co-project 

leaders will determine the suitable option.

Once type areas are selected and research has 

begun, the USGS North Carolina District of the USGS 

will pursue additional resources within the USGS, in 

particular the BRASS (Bedrock Regional Aquifer 

Systematics Study) Program of the Geologic Discipline 

and the Toxic Substances Hydrology Program of the 

Water Resources Discipline. Participation by staff from 

these programs would enhance the planned work with 

additional skills in detailed geologic mapping, surface 

and borehole geophysics, isotope chemistry, and other 

specialties.

During the spring of 2001, staff from the BRASS 

Program were invited to participate in work at the NCSU 

Upper Piedmont Agricultural Research Station in 

Rockingham County (site 6, fig. 18) by conducting 

detailed geologic mapping of the watershed surrounding 

the Research Station. BRASS staff also were asked to 

prepare geologic maps of the headwaters of the Cullasaja 

River in Macon County (fig. 1), which is being considered 

as a study site for comparison with the Bent Creek 

watershed (site 1, fig. 18). BRASS personnel are currently 

preparing geologic maps for these two areas.

Proposed Products

Interpretive reports will be published as collaborative efforts between the Groundwater Section and the 

USGS on various aspects of research at each identified 

type area. It is anticipated that publications will be prepared for State publication series, USGS publication 

series, and as articles and abstracts for professional 

journals and society meetings. Authorship will 

acknowledge significant contributions by staff from 

both agencies. Long-term data-collection results will 

be published on a regular schedule in the USGS annual 

data report for the North Carolina District.

Data collected during this study also will be 

stored in the USGS National Water Information System 

database and in a database to be designed and administered by the Groundwater Section. These data will be 

available to the general public through the USGS and 

Groundwater Section Internet sites. Some of these data 

will be available in real time. Digital data-collection 

platforms and satellite transmitters will be installed at 

each study site; at a minimum, one data-collection platform will be installed on one well cluster at each study 

site to provide continuous information on hydraulic 

heads in the regolith, transition zone, and bedrock parts 

of the ground-water system. As one example, a well 

cluster on the Langtree Peninsula at Lake Norman site 

has been instrumented (summer of 2001) and data are 

available on the Internet at http://water.usgs.gov/nc/

nwis/current/?type=gw (accessed April 22, 2002). The 

published reports and GIS coverages produced as part 

of this study also will be made available on the Internet.

The ultimate product is an increased understanding of the quantity, quality, and distribution of available 

ground water in the Blue Ridge and Piedmont that can 

be used by municipal, county, and State planners in 

developing sustainable and reliable water resources. 

The emphasis of this ongoing study is long-term protection of water quality in North Carolina.

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