Regional Aquifer-System Analysis

Summary of the Hydrogeology of the Valley and Ridge, 

Blue Ridge, and Piedmont Physiographic Provinces in the 

Eastern United States

Professional Paper 1422-A

U.S. Department of the Interior

U.S. Geological Survey
Summary of the Hydrogeology of the Valley 

and Ridge, Blue Ridge, and Piedmont 

Physiographic Provinces in the Eastern 

United States

By Lindsay A. Swain, Thomas O. Mesko, and Este F. Hollyday

U.S. Department of the Interior

U.S. Geological Survey

Regional Aquifer-System Analysis—

Appalachian Valley and Piedmont

Professional Paper 1422-A
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

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Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report.

ISBN 0-607-98077-X

Suggested citation: 

Swain, L.A., Mesko, T.O., and Hollyday, E.F., 2004, Summary of the hydrogeology of the Valley and Ridge, Blue Ridge, 

and Piedmont Physiographic Provinces in the Eastern United States: U.S. Geological Survey Professional Paper 1422-A, 

23 p.

Library of Congress Cataloging-in-Publication Data

Swain, Lindsay A.

Summary of the hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont physiographic provinces in the 

eastern United States / by Lindsay A. Swain, Thomas O. Mesko, and Este F. Hollyday.

p. cm. -- (Professional paper ; 1422) (Regional aquifer-system analysis--Appalachian Valley and Piedmont ; A)

Includes bibliographical references.

ISBN 0-607-98077-X (pbk.)

1. Aquifers--Appalachian Region. 2. Aqufers--Piedmont (U.S. : Region) I. Mesko, Thomas O. II. Hollyday, E. F. 

III. Title. IV. Series. V. Series: U.S. Geological Survey professional paper ; 1422. 

GB1199.3.A6S93 2004

551.49’0974--dc22

2004053336
 iii

Foreword

The Regional Aquifer-System Analysis Program

The RASA Program represents a systematic effort to study a number of the Nation’s most important aquifer systems, which, in aggregate, underlie much of the country and which represent an 

important component of the Nation’s total water supply. In general, the boundaries of these studies are identified by the hydrologic extent of each system and, accordingly, transcend the political 

subdivisions to which investigations have often arbitrarily been limited in the past. The broad 

objective for each study is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will 

contribute to the effective management of the system. The use of computer simulation is an important element of the RASA studies to develop an understanding of the natural, undisturbed hydrologic system and the changes brought about in it by human activities and to provide a means of 

predicting the regional effects of future pumping or other stresses.

The final interpretive results of the RASA Program are presented in a series of U.S. Geological 

Survey Professional Papers that describe the geology, hydrology, and geochemistry of each 

regional aquifer system. Each study within the RASA Program is assigned a single Professional 

Paper number beginning with Professional Paper 1400.

Charles G. Groat

Director

 v

Contents

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

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

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

Background, Major Objectives, and Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Purpose and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Summary of Previous Investigations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Hydrogeologic Terranes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Hydraulic Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Storage Coefficient and Specific Yield. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Transmissivity from Specific Capacity of Wells. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Transmissivity from Streamflow Recession. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Ground-Water Recharge and Discharge, and Hydrologic Budgets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Ground-Water Flow in Selected Basins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Water Geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Ground-Water Development and Potential for Future Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

References Cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figures

1. Map showing the Appalachian Valley and Piedmont Regional Aquifer-System Analysis 

study area and physiographic provinces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

2. Generalized block diagram of the principal hydrogeologic components of regolith and 

bedrock in the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces . . . . . . . . . . . . . . .5

3. Map showing hydrogeologic terranes of the Valley and Ridge, Blue Ridge, 

and Piedmont Physiographic Provinces in the Eastern United States. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

4. Boxplots showing variation of transmissivity values estimated from well records 

and streamflow records in the three physiographic provinces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

5. Map showing the distribution of streamflow-gaging stations in the study area that 

were used in recession and base-flow analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

6. Graph showing the relation between mean recharge and an estimator of mean 

recharge that is a linear function of precipitation and relief for the 

Blue Ridge and Piedmont Physiographic Provinces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

7. Map of the Appalachian Valley and Piedmont Regional Aquifer-System Analysis study area

and location of three type-area studies where ground-water flow was modeled. . . . . . . . . . . . . . . . . . 14

8. Boxplots showing distribution of dissolved-solids concentrations in ground water, 

spring water, and surface water in the three physiographic provinces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

9. Trilinear diagram showing reaction paths for evolution of chemical composition 

of ground water in the Appalachian Valley and Piedmont Regional 

Aquifer-System Analysis study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

10. Map showing estimated withdrawals at pumping centers, by county, in the 

Appalachian Valley and Piedmont aquifer system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

11. Map showing areas where future development of municipal and industrial 

ground-water supplies from the Appalachian Valley and Piedmont aquifer 

system has good potential. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
vi 

Tables

1. Hydrogeologic conditions that control the transmissivity of the hydrogeologic 

terranes in various provinces and locations in the Appalachian Valley and 

Piedmont Regional Aquifer-System Analysis study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2. Statistical distribution of ground-water recharge and discharge, in inches per year, 

for basins in the Appalachian Valley and Piedmont Regional Aquifer-System 

Analysis study area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3. Comparison of selected characteristics of the three type areas and ground-water flow 

models in the Appalachian Valley and Piedmont Regional Aquifer-System 

Analysis study area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4. Typical proportions of major ions in ground water in the Appalachian Valley and 

Piedmont Regional Aquifer-System Analysis study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Conversion Factors and Horizontal Datum

Water-Quality Unit

milligram per liter (mg/L)

Horizontal coordinate information is referenced to the North American Datum of 1983.

Multiply By To obtain

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2)

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

billion gallons per day (Bgal/d) 3.785 billion liters per day (BL/d)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

gallon per minute per foot [(gal/min)/ft)] 0.2070 liter per second per meter [(L/s)/m]

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d)
Summary of the Hydrogeology of the Valley and Ridge, 

Blue Ridge, and Piedmont Physiographic Provinces in the 

Eastern United States

By Lindsay A. Swain, Thomas O. Mesko, and Este F. Hollyday

Abstract

The Appalachian Valley and Piedmont Regional AquiferSystem Analysis study (1988-1993) analyzed rock types in the 

142,000-square-mile study area, identified hydrogeologic terranes, determined transmissivity distributions, determined the 

contribution of ground water to streamflow, modeled groundwater flow, described water quality, and identified areas suitable for the potential development of municipal and industrial 

ground-water supplies. Ground-water use in the Valley and 

Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces exceeds 1.7 billion gallons per day.

Thirty-three rock types in the study area were analyzed, 

and the rock types with similar water-yielding characteristics 

were combined and mapped as 10 hydrogeologic terranes. 

Based on well records, the interquartile ranges of estimated 

transmissivities are between 180 to 17,000 feet squared per day 

(ft2

/d) for five hydrologic terranes in the Valley and Ridge; 

between 9 to 350 ft2/d for two terranes in the Blue Ridge; and 

between 9 to 1,400 ft2/d for three terranes in the Piedmont Physiographic Province. Based on streamflow records, the interquartile ranges of estimated transmissivities for all three physiographic provinces are between 290 and 2,900 ft2

/d. The mean 

ground-water contribution to streams from 157 drainage basins 

ranges from 32 to 94 percent of mean streamflow with a median 

of 67 percent. In three small areas in two of the physiographic 

provinces, more than 54 percent of ground-water flow was 

modeled as shallow and local. Although ground-water chemical 

composition in the three physiographic provinces is distinctly 

different, the water generally is not highly mineralized, with a 

median dissolved-solids concentration of 164 milligrams per 

liter, and is mostly calcium, magnesium, and bicarbonate. 

Based on aquifer properties and current pumpage, areas favorable for the development of municipal and industrial groundwater supplies are underlain by alluvium of glacial origin near 

the northeastern part of the study area, by clay-free carbonate 

rocks primarily in the Valley and Ridge Physiographic Province, and by siliciclastic rocks in the three northernmost Mesozoic basins.

Introduction

The aquifers of the Valley and Ridge, Blue Ridge, and 

Piedmont Physiographic Provinces are a major source of 

drinking-water supplies in the United States. The aquifers 

underlie the District of Columbia and parts of 11 States—New 

Jersey, Delaware, Pennsylvania, Maryland, Virginia, West Virginia, Tennessee, North Carolina, South Carolina, Georgia, and 

Alabama—a total area of about 142,000 mi2 (fig. 1). For the 

purposes of this report, the small area in the New England Physiographic Province that is within the study area in New Jersey 

and Pennsylvania was treated as part of the Piedmont Physiographic Province. The analysis of aquifers in that part of the 

Valley and Ridge, New England, and Piedmont Provinces that 

lie within New York State and the New England States is 

described in publications of the Northeastern Glacial Valleys 

Regional Aquifer-System Analysis.

An average annual rainfall of 43 inches provides an average of about 13 inches of recharge to the aquifers of the unglaciated part of the three physiographic provinces. In 1990, the 

aquifers provided water supplies for about 38 million people in 

rural households and municipal or county water systems in the 

area. The larger ground-water supply systems are within Bergen, Morris, Essex, and Union Counties, New Jersey; and Blair, 

Lehigh, and Montgomery Counties, Pennsylvania. In 1985, 

about 1.7 Bgal/d were withdrawn from the aquifers for all uses 

in the study area. Although pumping stresses have produced 

local cones of depression, almost 90 percent of the study area 

has no significant ground-water-level decline. However, 

despite the enormous amounts of untapped water available from 

the aquifers, sufficient quantities of ground water are not always 

available to meet local municipal or industrial needs.

During 1988-93, the U.S. Geological Survey (USGS) conducted a Regional Aquifer-System Analysis (RASA) of the 

aquifers of the Valley and Ridge, Blue Ridge, and Piedmont 

Physiographic Provinces, which included the review and synthesis of many previous studies and hydrologic data, the acquisition of additional well records, and the extensive use of 

hydrograph recession analysis and statistical methods to organize and summarize hydraulic and water-quality data. The 
2 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

Appalachian Valley and Piedmont Regional Aquifer-System 

Analysis (APRASA), summarized in this report, is one of about 

two dozen USGS RASA programs that provide quantitative 

appraisals of the major ground-water systems of the United 

States.

Background, Major Objectives, and Approach

The aquifer systems of the three physiographic provinces 

consist of hundreds of aquifers composed of metamorphic, 

igneous, and sedimentary rock units. Although the groundwater reservoirs in these units typically lack regional continuity, 

the rock units may be considered to form a complex regional 

aquifer system that is characterized primarily by local groundwater flow. Ground-water development has not been extensive. 

Large withdrawals have been concentrated in a few areas—primarily in the more densely populated northeastern part of the 

study area. In this area, rapid industrial growth and urban 

expansion have caused all sources of freshwater to be used at or 

near maximum capacity. Future growth and expansion is 

expected to cause the same problems in urban areas in the 

southern and western parts of the study area. Hydrologic processes of recharge, discharge, storage, ground-water flow, and 

stream-aquifer relations within the three physiographic provinces are poorly understood. This lack of hydrologic understanding is due primarily to the diverse and complex nature of 

the hydrologic system. The APRASA study advances understanding of the system and provides a basis for more efficient 

use and management of the ground-water resources in the three 

physiographic provinces.

Specifically, the objectives of the APRASA study were: 

(1) to provide a description of the hydrologic framework; (2) to 

identify the major processes that affect ground-water quantity 

and quality; (3) to quantify the components of ground-water 

flow in local “type areas;” (4) to provide regional estimates of 

the ground-water budget; (5) to determine the relation between 
Introduction 3

surface-water and ground-water flow systems; (6) to provide a 

description of ground-water quality; and (7) to develop a database to aid in planning, development, and management of the 

ground-water resources in the three physiographic provinces. 

The hydrogeologic framework was described in terms of hydrogeologic terranes based on the relation between the hydraulic 

properties of the rocks and the lithology, structure, topography, 

or other relevant features. The type areas, where ground-water 

flow was simulated with digital models, were selected to be representative of the different hydrogeologic terranes and typical 

combinations of terranes. Within the type areas, emphasis was 

placed on factors controlling recharge and discharge and on 

response to ground-water development.

To meet the project objectives, efforts concentrated on the 

assembly and analysis of the vast amount of data primarily in 

the National Water Information System (NWIS) database of the 

USGS including the data for well records, streamflow daily values, water quality, and water use. Prior to the study, much information existed on the geologic framework, and aquifer hydraulic characteristics had been measured in several places. 

However, the greatest amount of hydrogeologic data and a few 

ground-water flow models were clustered in the northeast and 

at widely scattered waste-disposal sites throughout the study 

area. Data are scarce in many areas where large untapped 

ground-water supplies exist. A data-collection effort was undertaken to fill data gaps in well records southwest of Pennsylvania 

and Maryland.

Well records in the Ground-Water Site Inventory (GWSI) 

database of the USGS for Pennsylvania were analyzed statistically to determine factors related to the water-yielding potential 

of the rocks in order to classify hydrogeologic terranes (Knopman, 1990; Knopman and Hollyday, 1993). A computerassisted analysis of streamflow recession was developed to 

determine recession characteristics, basin diffusivity, and 

ground-water recharge and discharge (Rutledge, 1998). A 

computer-assisted method was developed for compiling, 

analyzing, and plotting large quantities of water-quality data on 

trilinear diagrams (Briel, 1993). A geographic information system database of well records and mapped geologic units was 

developed to assist in the classification of hydrogeologic terranes and the analysis of ground-water recharge and discharge 

(Mesko, 1993).

Purpose and Scope

The APRASA was conducted to describe various aspects 

of the geology, hydrology, and geochemistry of the aquifers of 

the Valley and Ridge, Blue Ridge, and Piedmont Physiographic 

Provinces. This report summarizes important aspects of the 

hydrogeologic framework, hydraulic properties of the hydrogeologic terranes, typical flow systems, and geochemistry, 

which are discussed in detail in USGS Professional Papers 

1422-B through 1422-D (Rutledge and Mesko, 1996; Hollyday 

and Hileman, 1996; and Briel, 1997) and USGS Hydrologic 

Investigations Atlas HA-732-B (Mesko and others, 1999). 

Emphasis in those four reports is placed on classification and 

description of hydrogeologic terranes, surface-water and 

ground-water relations, and ground-water geochemistry. 

Descriptions of local ground-water flow systems are contained 

in the following three reports: USGS Water-Resources Investigations Reports 94-4090 (Chichester, 1996) and 94-4147 

(Lewis-Brown and Jacobson, 1995), and USGS Water-Supply 

Paper 2341-C (Daniel and others, 1997).

Professional Paper 1422-B (Rutledge and Mesko, 1996) 

presents an analysis of streamflow hydrograph recession and 

base flow in 157 drainage basins in, or partially in, the 

APRASA study area. The analysis of streamflow recession provides estimates of master recession curves, recession indexes, 

and transmissivity of the rocks. The recession index is related to 

basin relief, precipitation, basin latitude, the yield of wells in the 

basin, and low-flow variables. The base flow analysis provides 

estimates of ground-water recharge and discharge, and the 

remaining components of the water budget of each basin. 

Ground-water recharge and base-flow index also are related to 

basin relief, precipitation, the well yields in the basin, and lowflow variables.

Professional Paper 1422-C (Hollyday and Hileman, 1996) 

presents an analysis of geology and records of wells in the Valley and Ridge Physiographic Province, which resulted in a classification and map of hydrogeologic terranes. Specific capacity 

and median value of reported drawdowns were used to estimate 

statistical parameters of potential municipal and industrial well 

yields in the five hydrogeologic terranes.

Hydrologic Investigations Atlas HA-732-B (Mesko and 

others, 1999) presents an analysis of geology and records of 

wells in the Blue Ridge and Piedmont Physiographic Provinces, 

which resulted in a classification and map of hydrogeologic terranes. Reported yields of nondomestic wells were used to estimate statistical parameters of nondomestic well yields in the 

two hydrogeologic terranes of the Blue Ridge and the three 

hydrogeologic terranes of the Piedmont Physiographic Provinces.

Professional Paper 1422-D (Briel, 1997) presents an analysis of the major-ion chemistry of water withdrawn from wells, 

issuing from springs, and from streams in the study area. Comparisons were made by physiographic province and water 

source. The principal chemical processes that operate in the 

ground-water flow system are explained using trilinear 

diagrams.

Summary of Previous Investigations

Hundreds of reports describing the hydrology, geology, 

and water chemistry of parts of the Appalachian Valley and 

Piedmont aquifer systems have been published. Many of these 

reports were used in making the observations described in the 

RASA series. A few of the reports provided major contributions 

to the knowledge of the aquifer system and are noted here.

Fuller (1905) related the importance of secondary openings to the storage and movement of ground water, particularly 
4 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

in joints in the crystalline-rock aquifers of the Blue Ridge and 

Piedmont, in open channels and caverns in the carbonate rocks 

of the Valley and Ridge, and at greater depth in the fractures and 

joints in the siliciclastic rocks in the Mesozoic basins of the 

Piedmont. McGuinness (1963) stated that the rocks of the Piedmont are among the Nation’s most reliable aquifers for small 

yields needed for domestic supply; large yields are not common. McGuiness (1963) concluded that the carbonate rocks of 

the Valley and Ridge are erratic in the yield of water to wells. 

For the Piedmont, LeGrand (1967) succinctly summarized 

ground-water occurrence, flow, water quality, well siting, well 

hydraulics, and aquifer response to pumping. Parizek and others 

(1971) combined several papers and articles dealing with 

ground-water occurrence, flow, and geochemistry in carbonate 

rocks of the Valley and Ridge in central Pennsylvania. In a 

study of well yields in the northern quarter of the APRASA 

study area, Cederstrom (1972) stressed the desirability of relying on the hydrologic analysis of municipal and industrial well 

records, which he believed represented an effort to develop a 

maximum supply of water. Trainer and Watkins (1975) developed the concept of combining rock types and soil thicknesses 

into geohydrologic terranes for the Upper Potomac River Basin. 

Cressler and others (1983) stated that large well yields are available in the Piedmont near Atlanta, Ga., but only in areas where 

the rocks have localized increases in permeability, which are 

associated with selected stratigraphic or structural features.

The National Water Summary for 1984 (U.S. Geological 

Survey, 1985) provided a uniform discussion, with selected key 

references, of water use, principal aquifers, and ground-water 

development and management in each of the 11 states in the 

APRASA study area. The state geologic maps of each of the 11 

states provided a wealth of stratigraphic and structural information. Patchen and others (1985a, b) provided a concise summary 

of the stratigraphy of the Valley and Ridge Physiographic Province, which allowed correlation of aquifers among states. 

Daniel (1989) discussed the importance of well diameter, well 

depth, topography, and the transition zone between regolith and 

bedrock on large well yields. Swain and others (1991) discussed 

the geology, hydrology, water use, and water problems in the 

APRASA study area and presented the planned objectives of 

and methods for the APRASA study. Daniel and others (1993) 

edited the proceedings from the first conference on ground 

water in the Piedmont. The proceedings contains more than 60 

papers covering a vast variety of topics that deal with quantity 

and quality of ground water in the Piedmont.

Finally, the greatest source of information on the aquifer 

systems is contained in the hundreds of reports published by the 

11 states and in USGS Open-File Reports and Water-Resources 

Investigations Reports series. Many of these studies were conducted by the USGS in cooperation with various State, county, 

and municipal governments. These reports and supporting computer files provide the basic hydrologic data, as well as interpretations of the local hydrology, without which, this regional 

study could not have been successfully completed.

Hydrogeologic Terranes

Hydrogeologic terranes, rather than aquifers and confining 

units, were identified because of the complexity of the geology 

in the APRASA study area. For the purpose of this study, a 

hydrogeologic terrane is defined as a regionally mappable area 

characterized by similar water-yielding properties in a grouping 

of selected rock types. The term “terrane” was used because the 

original intent was to include climatic, geomorphic, and pedologic variables, in addition to bedrock lithology, in the analysis. Five hydrogeologic terranes were identified in the Valley 

and Ridge, three in the Piedmont, and two in the Blue Ridge 

Physiographic Provinces.

The Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces are underlain by metamorphic, igneous, and 

sedimentary rocks; gneiss, schist, granite, and siliciclastic sedimentary rock underlie almost two-thirds of the study area. Following faulting and folding, as well as one or more periods of 

metamorphism and igneous intrusion of the rocks in most of the 

study area, the entire area was uplifted during the Cenozoic Era. 

Subsequent weathering and erosion enlarged existing fractures 

in the bedrock and may have created new fractures by stress 

relief.

The water-storage and transmissive characteristics of the 

bedrock and regolith, and the hydraulic connection between the 

bedrock and regolith determine the water-supply potential of 

the hydrogeologic terranes (fig. 2). Because of the relatively 

high porosity of the regolith, most recharge is stored in this unit 

and is released slowly to underlying bedrock fractures. Because 

fractures and dissolution openings in the bedrock are conduits 

for ground-water flow, well yields are greatest where wells 

intersect fractures or dissolution openings that are large, numerous, or both. Under natural (pre-pumping) conditions, most 

ground-water flow is within 200 feet below land surface. However, an analysis of well records in seven areas of the Piedmont 

Physiographic Province indicated that four of these seven areas 

have average well yields that are substantially greater for wells 

completed between 400 and 600 feet below land surface compared with wells completed between 100 and 200 feet below 

land surface (Mesko and others, 1999).

Hydrogeologic terranes were classified within each of the 

three physiographic provinces by relating rock type, as 

described in State geologic maps, to records of either specific 

capacity or well yields in the GWSI database. State geologic 

maps were scanned, edited, and annotated to produce coverages 

of the mapped occurrence of each geologic unit in the study 

area. Geologic units with the same rock type were merged to 

create a coverage of more than 50 rock types. Records of 62,345 

wells in the APRASA part of the three physiographic provinces 

were retrieved from the GWSI database for each State. Values 

of either specific capacity (Valley and Ridge) or yield (Blue 

Ridge and Piedmont) were retrieved from each well record, 

grouped by province and rock type, and analyzed to derive statistical characteristics of specific capacity or yield for 33 rock 

types for which these data were sufficiently numerous for 
Hydraulic Properties 5

statistical analysis. For each physiographic province, the rock 

types were then ranked in order of increasing specific capacity 

or yield and grouped into two or more hydrogeologic terranes 

according to selected ranges in median specific capacity (Valley and Ridge) or median yield (Blue Ridge and Piedmont).

For the Valley and Ridge, potential well yields were estimated by multiplying the values of specific capacity by the 

medians of reported drawdowns for municipal and industrial 

wells. Included in these estimates were all records of municipal 

and industrial wells with casing diameter equal to, or greater 

than, 7 inches that were located in valleys. The interquartile 

ranges in estimated potential yields of these most-productive 

wells in the five hydrogeologic terranes of the Valley and Ridge 

were 70 to 280 gal/min for siliciclastic rock, 65 to 850 gal/min 

for argillaceous carbonate rock, 80 to 720 gal/min for limestone, 210 to 1,400 gal/min for dolomite, and 170 to 

580 gal/min for alluvium (Hollyday and Hileman, 1996). For 

the Blue Ridge, the interquartile ranges in reported yields of 

nondomestic wells in the two hydrogeologic terranes were 8 to 

32 gal/min for gneiss-granite, and 10 to 61 gal/min for schistsandstone (Mesko and others, 1999). For the Piedmont, the 

interquartile ranges in reported yields of nondomestic wells in 

the three hydrogeologic terranes were 5 

to 20 gal/min for phyllite-gabbro, 10 to 

60 gal/min for gneiss-schist, and 35 to 

220 gal/min for shale-sandstone.

Hydrogeologic terranes were 

mapped (fig. 3) by assigning rock types 

to the appropriate hydrogeologic terrane based on specific capacity (Valley 

and Ridge) or yield (Blue Ridge and 

Piedmont). The dolomite hydrogeologic terrane in the Valley and Ridge 

Physiographic Province has the largest 

median potential well yield and is predominantly dolomite with limestone in 

widely distributed valleys of Alabama, 

Georgia, and Tennessee, and in valleys 

primarily along the southeastern margin of the Valley and Ridge in Maryland, New Jersey, Pennsylvania, Virginia, and West Virginia (fig. 3). The 

shale-sandstone hydrogeologic terrane 

in the Piedmont Physiographic Province has the largest median well yield 

of any hydrogeologic terrane in either 

the Blue Ridge or Piedmont Physiographic Provinces and is predominantly shale, sandstone, and siltstone in 

the Mesozoic basins in Maryland, New 

Jersey, Pennsylvania, and Virginia.

Hydrogeologic terranes with 

intermediate values of transmissivity 

may act as either an aquifer or a confining unit to an adjacent hydrogeologic 

terrane depending upon their relative 

transmissivities. Geologic structure is complex within the study 

area, and faults and folds, as much as stratigraphic position, 

may determine which hydrogeologic terranes are aquifers or 

confining units within a local structural setting (fig. 3).

Hydraulic Properties

The hydraulic properties of the terranes of the study area 

were estimated from well and streamflow data compiled from 

various sources and published reports describing the hydrogeologic characteristics of geologic units within the terranes. The 

sources of well data included site inventories by project staff, 

published reports, unpublished USGS well data, and data from 

the GWSI database in NWIS. The source of mean-daily streamflow data was the USGS data in NWIS.

Storage Coefficient and Specific Yield

A storage coefficient of 0.0005 was used for estimating the 

transmissivity of the hydrogeologic terranes from the specific 
6 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces
Hydraulic Properties 7

capacity of wells (Theis and others, 1963). This value is about 

an order of magnitude lower than the median value of storage 

coefficient reported by Trainer and Watkins (1975, table 2, 

p. 18) from aquifer tests in the carbonate and siliciclastic rocks 

of the Valley and Ridge, the Blue Ridge, and the Piedmont 

Physiographic Provinces in the Potomac River Basin. The value 

is within the mid-range of values of storage coefficient reported 

by Lewis-Brown and Jacobsen (1995, table 3, p. 19) for siliciclastic sedimentary rocks in the Newark Basin of New Jersey. 

The value is less than an order of magnitude higher than the 

storage coefficient selected by Daniel and others (1997, p. C58) 

for estimating the transmissivity of fractured gneiss and schist 

in the Piedmont of North Carolina.

The storage coefficient of granular material, including 

regolith, under water-table conditions is equal to the specific 

yield. A range in specific yield from 0.01 to 0.08 (Rutledge and 

Mesko, 1996, p. B15) was used for estimating the transmissivity of the rocks in the three physiographic provinces from 

stream-basin diffusivity methods (Rorabaugh and Simons, 

1966). This range corresponds to the 25th and 75th percentiles 

in a distribution of 21 values of specific yield taken from published reports (Rutledge and Mesko, 1996, table 5, p. B18). 

Transmissivity from Specific Capacity of Wells

Values of specific capacity were converted to estimates of 

transmissivity (fig. 4) by using the method described by Theis 

and others (1963). Percentile values of specific capacity of 

municipal and industrial wells in the Valley and Ridge Physiographic Province (Hollyday and Hileman, 1996, fig. 12, p. C21) 

and nondomestic wells in the Blue Ridge and Piedmont Physiographic Provinces (Mesko and others, 1999, fig. 5) were 

selected from boxplots of the distribution of specific-capacity 

values of wells in the 10 hydrogeologic terranes. The nondomestic wells recorded in GWSI for the study area are primarily 

used for municipal, industrial, and commercial water supply. 

The inclusion of water uses other than municipal and industrial 

in the nondomestic category would tend to lower the values of 

transmissivity compared to values derived from municipal and 

industrial data alone.
8 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces
Hydraulic Properties 9

The equation given by Theis and others (1963, eq. 6, 

p. 337) computes a value of T′, which must be used in a diagram 

(Theis and others, 1963, fig. 99, p. 334) to estimate transmissivity from specific capacity. Because it is difficult to select values 

of transmissivity from this diagram for specific capacity values 

less than 1.0, the original equation given by Theis and others 

(1963, eq. 1, p. 332) was modified for contemporary units and 

programmed into a spreadsheet to iteratively calculate transmissivity. The modified equation is: 

 , (1)

where

T is transmissivity, in feet squared per day;

Q is discharge of the well, in gallons per minute;

s is drawdown in the pumping well, in feet;

Q/s is specific capacity, in gallons per minute per foot;

ln is the natural logarithm;

r is the radius of the pumped well, in feet;

S is the storage coefficient, in feet per foot; and

t is the time since pumping started, in days.

The following average values for well radius and duration 

of pumping were determined from data for municipal and 

industrial wells in the GWSI database; radius of 0.33 ft (8-inch 

diameter well) and time of 0.33 day (8 hours of pumping). A 

storage coefficient of 0.0005 was estimated from values in the 

literature as described heretofore. These three fixed values were 

used in all calculations of transmissivity from specific capacity. 

Using the spreadsheet, a final value of transmissivity was calculated by iteration from an initial estimate until final and initial 

transmissivity values differed by less than 0.01 percent. This 

convergence typically occurred within three to five manual iterations.

Considering all 10 of the hydrogeologic terranes, 80 percent (10th to 90th percentile) of the values for estimated transmissivity range from 2.6 to 84,000 ft2/d (fig. 4). For any 1 of the 

10 hydrogeologic terranes, the interquartile range (25th to 

75th percentile) is typically slightly greater than one order of 

magnitude; the siliciclastic-rock and alluvium hydrogeologic 

terranes have the smallest ranges—slightly greater than onehalf order of magnitude. Well records were analyzed separately 

for each of the three physiographic provinces. Consequently, 

pairs of terranes where each is selected from a different province may have estimated transmissivity distributions with considerable overlap. As examples, siliciclastic rock (Valley and 

Ridge) and shale-sandstone (Piedmont), gneiss-granite (Blue 

Ridge) and phyllite-gabbro (Piedmont), and schist-sandstone 

(Blue Ridge) and gneiss-schist (Piedmont) are three pairs of 

hydrogeologic terranes from different physiographic provinces 

that are not likely to have significant differences in their estimated transmissivities. In contrast, the rock types in the three 

hydrogeologic terranes of the Piedmont could be regrouped into 

five new terranes and still have significant differences among 

their median values of estimated transmissivity because of the 

large sample of wells in the Piedmont. However, the large overlap among the five distributions of estimated transmissivity for 

these five new terranes probably would not indicate a usable 

difference among the five terranes for water-supply purposes; 

fewer terranes (three) would be more useful.

The transmissivity varies greatly among the hydrogeologic 

terranes in part because of differences in the character of the 

water-yielding openings within each terrane. These openings 

include (1) intergranular openings in sand and gravel of glacial 

origin; (2) conduits and caverns dissolved in carbonate rocks; 

(3) networks of many small dissolution openings along joints, 

bedding planes, or fractures, that when acting together, provide 

a uniform distribution of permeability of large to moderate 

magnitude; and (4) networks of many openings along joints, 

bedding planes, or fractures that are partly plugged with clay 

residuum and, that when acting together, provide a uniform distribution of permeability of moderate to low magnitude. In 

those terranes that are characterized by openings of type 1, 3, 

and 4, laminar flow predominates; however, in terranes with 

conduits and caverns, turbulent flow may occur.

For the hydrogeologic terranes in which laminar flow predominates, the methods developed for aquifer-test analysis for 

porous media are applicable. For the hydrogeologic terranes in 

which turbulent flow may occur, these aquifer-test methods 

only generally indicate how an equivalent porous media might 

respond to stress. The response curves of aquifer tests outside of 

cavernous areas generally match the classic non-leaky type 

curves, especially for short tests, and the leaky or delayed-yield 

type curves for longer tests. Water-level response in cavernous 

areas can be unusually small, almost instantaneous, and approximately the same at the pumped well and at a considerable distance from the pumped well. In areas in which ground-water 

flow is predominantly in conduits, caverns, joints, bedding 

planes, and fractures, cones of depression are typically asymmetric.

When all 10 hydrogeologic terranes are considered 

together, the range in estimated transmissivity is more than 

4 orders of magnitude (fig. 4) as a result of the wide variation in 

hydrogeologic conditions. The conditions that most affect 

transmissivity are the type of water-yielding openings (intergranular, conduit, or fracture), the rock composition, and the 

degree of dissolution. In unconsolidated deposits, high transmissivities usually are associated with clean, coarse-grained 

materials such as glacial outwash within the alluvium hydrogeologic terrane. In consolidated rocks, high transmissivities 

usually are associated with soluble rocks in areas in which vigorous ground-water flow has enhanced development and widening of dissolution openings. The variations in transmissivities 

for the geographic areas underlain by the terranes are produced 

by a combination of hydrologic and geologic conditions 

(table 1). The ranges in estimated transmissivities given in 

table 1 are a generalization of the interquartile ranges shown for 

each hydrogeologic terrane in figure 4. An exception is the 

western-toe, whose range was taken from a source document 

(see table 1, footnote b).

In general, the largest values of transmissivity (greater 

than 7,000 ft2/d for the 75th percentile in table 1) occur in the 

alluvium hydrogeologic terrane near the northeastern end of the 

T 15.32Q

s

--- – 0.577 r

2

S′

4Tt -------- ⎝ ⎠ ⎛ ⎞ – ln ⎝ ⎠ ⎛ ⎞ =
10 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

Table 1. Hydrogeologic conditions that control the transmissivity of the hydrogeologic terranes in various provinces and locations in the 

Appalachian Valley and Piedmont Regional Aquifer-System Analysis study area.

[Range in estimated transmissivity is approximately between the 25th percentile and the 75th percentile of a distribution of estimated transmissivities (fig. 4, with 

the exception of western-toe); ft2

/d, foot squared per day]

Terranea

a

With the exception of the western-toe, see figs. 3 and 4 for mapped distribution of hydrogeologic terrane, description, and estimated transmissivity. For 

western-toe subdivision of the dolomite terrane (Elkton aquifer) see Hollyday and Hileman, 1996, figs. 7 and 8, and p. C13-C16 for distribution and description.

Locality Water-yielding 

opening Rock composition Degree of 

dissolution

Generalized, 

interquartile range in 

estimated 

transmissivity, in ft2

/d

Alluvium Glacial margin in 

Pennsylvania and 

New Jersey

Intergranular Siliciclastic, some 

carbonate

Not a factor 5,000 - 17,000

Western-toe 

subdivision of 

the dolomite 

terrane (Elkton aquifer)

Southeastern margin of 

the Valley and Ridge

Conduits and 

caverns

Dolomite Well developed 900 - 17,000b

b

Based on an interquartile range in specific capacity of 3.3 to 55 (gal/min)/ft (Hollyday and Hileman, 1996, fig. 13, p. C23).

Dolomite Valley and Ridge; 

carbonate-rock valleys 

in the Blue Ridge and 

the Piedmont

Conduits and dissolution networksDolomite, limestone, 

marble

Moderate to 

well developed

2,000 - 13,000

Limestone Valley and Ridge; 

carbonate-rock valleys 

in the Blue Ridge and 

Piedmont

Dissolution networks and conduitsLimestone, marble Moderate to 

well developed

700 - 7,000

Argillaceous 

carbonate 

rock

Valley and Ridge Minor dissolution 

networks

Argillaceous limestone and dolomite; 

carbonate-rich 

shale

Poor to 

moderately 

developed

300 - 6,000

Siliciclastic 

rock; shalesandstone

Valley and Ridge; 

Piedmont

Fracture networks; 

minor intergranular

Sandstone, siltstone, 

noncalcareous 

shale

Not a factor 130 - 1,300

Schistsandstone; 

gneiss-schist

Blue Ridge; Piedmont Fracture networks Sandstone, schist, 

gneiss, etc.

Not a factor 20 - 400

Gneiss-granite; 

phyllitegabbro

Blue Ridge; Piedmont Fracture networks Granite, gneiss, 

phyllite, gabbro, 

etc.

Not a factor 9 - 130
Ground-Water Recharge and Discharge, and Hydrologic Budgets 11

Valley and Ridge (fig. 3), in the western-toe subdivision of the 

dolomite terrane (Hollyday and Hileman, 1996, p. C13-C16) 

along the southeastern margin of the Valley and Ridge, in the 

dolomite hydrogeologic terrane throughout the Valley and 

Ridge, and within carbonate-rock valleys in the Blue Ridge and 

Piedmont Physiographic Provinces (Mesko and others, 1999, 

fig. 1). The alluvium hydrogeologic terrane is adjacent to the 

glacial margin. It is derived from outwash sand and gravel, and 

has large, well-connected intergranular pore spaces. The 

western-toe subdivision of the dolomite hydrogeologic terrane 

(renamed the Elkton aquifer in Hollyday and others, 1997) is in 

an area of high relief at the toe of the slope of the northwestern 

edge of the Blue Ridge Mountains. The western-toe subdivision 

(Elkton Aquifer) is dolomite overlain by saturated thick residuum, colluvium, and alluvium, and contains numerous caverns 

and conduits. The dolomite terrane throughout much of the Valley and Ridge has moderate relief resulting from a resistant, 

protective cap of residual chert. The terrane is predominantly 

dolomite and limestone, and contains conduits and dissolution 

networks. The carbonate-rock valleys are in four areas of low to 

moderate relief in the Piedmont and in two areas of high relief 

in the Blue Ridge. In the Blue Ridge, these valleys are typically 

adjacent to highlands underlain by quartzite. The erosion of the 

quartzite results in a colluvial and alluvial apron covering the 

limestone, dolomite, and marble in the valley, a hydrologic setting very similar to the Elkton aquifer.

The smallest values of transmissivity (less than 

1,300 ft2

/d) occur in the hydrogeologic terranes of dense, consolidated rock that lack significant amounts of soluble, carbonate minerals throughout the three physiographic provinces. 

These terranes (siliciclastic rock, shale-sandstone, schistsandstone, gneiss-schist, gneiss-granite, and phyllite-gabbro) 

occupy almost all of the Blue Ridge and Piedmont Physiographic Provinces and much of the northern half of the Valley 

and Ridge Province (fig. 3). The terranes include siliciclastic 

sedimentary, metamorphic, and igneous rocks with fracture networks that may be plugged, more or less, with fine-grained, 

insoluble residue.

Transmissivity from Streamflow Recession

Streamflow recession index values (Rutledge and Mesko, 

1996) were transformed to estimates of transmissivity (fig. 4) 

using the method described by Rorabaugh and Simons (1966, 

p. 12). Percentile values of recession index for basins in each of 

the three physiographic provinces were picked from boxplots of 

the distribution of recession-index values (Rutledge and Mesko, 

1996, fig. 7, p. B11).

The equation given by Rorabaugh and Simons (1966, 

p. 12) may be rearranged to the following form to estimate 

transmissivity from recession index (Rutledge and Mesko, 

1996, p. B15):

 , (2)

where

T is transmissivity, in feet squared per day;

Sy is the apparent specific yield of the zone of watertable fluctuation, in feet per foot;

a is the average distance from the stream to the 

hydrologic divide, in feet; and

K is the recession index, in days per log cycle of decline

in discharge.

Although estimates of transmissivity could be made for 

specific basins, the intent was to give estimates of the range in 

transmissivities in each of the physiographic provinces in the 

APRASA study area. For this estimate, the 25th and 75th percentile values of recession indexes for each province as provided by Rutledge and Mesko (1996, fig. 7, p. B11) were used. 

A range in a of 1,000 to 2,000 ft and a range in Sy of 0.01 to 0.08 

were obtained by reviewing the literature (Rutledge and Mesko, 

1996, p. B15). These ranges were used in equation 2 in order to 

estimate log-normal distributions of transmissivity for the three 

physiographic provinces (fig. 4).

The distributions of transmissivities estimated from 

streamflow records generally lie within the midrange of distributions estimated from well records when all distributions are 

considered together (fig. 4). This similarity suggests that the 

two sets of distributions may be related to the same physical 

controls. The variation in the distributions estimated from 

streamflow records, however, is much less than the variation in 

distributions estimated from the well records. This difference 

may be due to the fact that streamflow is the integrated discharge from several rock types or terranes and is derived primarily from regolith and rock at shallow depths. Integrated discharge and release from shallow depths would tend to reduce 

the variation in estimated transmissivities. Creating subsets of 

the recession-index data by basins underlain by rocks with predominantly small well yields and basins underlain by rocks with 

large well yields resulted in greatly increased variation in the 

distributions of recession index (and, presumably, estimated 

transmissivity) for the Valley and Ridge and the Piedmont 

Physiographic Provinces (Rutledge and Mesko, 1996, figs. 13 

and 14, p. B16 and B17).

Ground-Water Recharge and Discharge, 

and Hydrologic Budgets

Mean rates of ground-water recharge and discharge were 

estimated by an analysis of the base flow of streams (Rutledge 

and Mesko, 1996, p. B19-B28) (fig. 5). Ground-water recharge 

and discharge are important components of the hydrologic budget of any basin. The analytical methods were applied over 10- 

or 30-year periods of continuous record, so that the effects of 

changes in ground-water storage could be considered negligible. The mean ground-water discharge (base flow), therefore, 

may be considered to be equal to effective recharge. The mean 

T ground-water recharge should exceed the mean effective 

0.933Sya

2

K = ------------------------
12 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

recharge by an amount equal to the riparian evapotranspiration—losses to the atmosphere from the stream channel and 

adjacent, shallow ground water.

Two computerized methods were used in base-flow analysis—recession-curve displacement, which estimates groundwater recharge; and base-flow record estimation (adapted from 

methods called streamflow partitioning), which estimates 

ground-water discharge. The documentation of the computerized methods, including detailed discussion of the mathematical 

development of the methods, instructions for execution of the 

programs, and comparisons between results of the programs 

and those of the corresponding manual methods were reported 

by Rutledge (1998).

Ground-water recharge and discharge (effective recharge) 

were determined by independent methods. Yet the sense and 

magnitude of the difference between recharge and discharge 

(table 2) is to be expected if a small amount of evapotranspiration were occuring from the ground-water reservoir. Riparianzone evapotranspiration ranges between 0.4 and 3.8 in/yr (Rutledge and Mesko, 1996, p. B21), and mean riparian-zone evapotranspiration (the difference between mean recharge and mean 

discharge) is usually between 1 and 2 in/yr (table 2).

The median of the mean ground-water discharge (table 2) 

may be used to calculate a rough estimate of total ground-water 

discharge in the study area. If the 157 basins are assumed to be 

representative of the entire study area, then a median groundwater discharge of 12 in/yr (table 2) indicates that as much as 

90 Bgal/d of ground water may be available for use in the 

142,000 mi2 study area.

A comparison of precipitation and recharge for the study 

area shows a considerable amount of scatter (Rutledge and 

Mesko, 1996, fig. 19); however, the best-fit linear equation has 

an approximate unit gradient of 0.86 and an X-intercept of 

about 28 in/yr. The intercept may depend on total evapotranspiration and may represent a threshold that must be exceeded by 

precipitation before recharge is significant. The relation 

between precipitation and recharge for each physiographic 

province is positive (Rutledge and Mesko, 1996, fig. 20). The 
Ground-Water Flow in Selected Basins 13

relation between basin relief and recharge tends to be negative 

for the Valley and Ridge Physiographic Province; however, the 

relation is positive for the Blue Ridge and Piedmont Physiographic Provinces (Rutledge and Mesko, 1996, fig. 21). For 

these two physiographic provinces, a reasonably good estimator 

of recharge can be derived from precipitation and basin relief 

(fig. 6).

The base-flow index is calculated as the ratio of mean 

ground-water discharge (base flow) to mean streamflow. 

This index is ideal for basin comparisons when the various 

basins have differing periods of streamflow record or when 

the available period of record is short. The base-flow index 

of 157 basins in the APRASA study area ranges from 32 to 

94 percent, and the 25th, 50th, and 75th percentiles are 59, 

67, and 75 percent, respectively. The base-flow index is 

exceptionally large in the Blue Ridge Physiographic Province for the 28 basins south of Roanoke, Va., as compared 

with the index for 16 basins in the northern part of the province. This anomaly is accompanied by a significant 

increase in precipitation and a very slight decrease in 

evapotranspiration south of Roanoke.

Simple water-budget equations were combined with 

the results of the base-flow analysis to obtain hydrologic 

budgets of basins in the study area. Except for the Blue 

Ridge Physiographic Province south of Roanoke, Va., the 

median values for components of the budgets of the study 

area (sample size, 72) are precipitation, 43 in/yr; evapotranspiration, 26 in/yr; streamflow, 16 in/yr; ground-water 

recharge, 12 in/yr; ground-water discharge, 11 in/yr; and 

storm runoff, 6 in/yr. For the southern part of the Blue 

Ridge Physiographic Province (sample size, 17), the 

median values are precipitation, 58 in/yr; evapotranspiration, 25 in/yr; streamflow, 38 in/yr; ground-water recharge, 

33 in/yr; ground-water discharge, 29 in/yr; and storm runoff, 8 in/yr. The map location, physical characteristics, 

streamflow recession characteristics, components of hydrologic budgets, and base-flow index for each basin are listed 

in Rutledge and Mesko (1996, tables 1, 2, 3, and 4).

Ground-Water Flow in Selected Basins

The fundamental approach to quantifying groundwater flow in the APRASA was similar to that of other 

RASA studies (Sun, 1986) in that available geologic and 

hydrologic data were compiled and used to describe the 

regional aquifer systems. In the APRASA study, however, 

the lack of regional continuity of the ground-water reservoirs and the diverse nature of the aquifers devalued the 

development of a regional ground-water flow model for the 

entire study area. A more logical approach was to select 

“type areas” that were considered representative of conditions in those settings and hydrogeologic terranes that are 

most important to water supply. For this approach, a flow 

system was conceptualized for each hydrogeologic terrane 

or combination of terranes, and ground-water flow in 

selected type areas was analyzed and simulated by using 

ground-water flow models. These models were used primarily to improve the understanding of ground-water flow related 

to various hydrogeologic components and streams. At the time 

of the study, pumping stresses were so small or localized in the 

type areas that it would have been very difficult to calibrate a 

transient-flow model with any regional significance. Techniques used to quantify recharge, discharge, storage, and flow 

Table 2. Statistical distribution of ground-water recharge and discharge, in inches per year, for basins in the Appalachian Valley and 

Piedmont Regional Aquifer-System Analysis study area.

Distribution

1981 to 1990

(number of samples, 157)

1961 to 1990

(number of samples, 89)

Mean 

recharge

Mean 

discharge

Mean 

recharge

Mean 

discharge

Maximum 46 42 50 46

75th percentile 18 16 19 17

Median 13 12 13 12

25th percentile 10 9 10 9

Minimum 5 4 6 5
14 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

within the type areas may be transferable to other areas with 

similar hydrologic settings and hydrogeologic terranes.

The three published type-area studies (fig. 7) and the 

hydrogeologic settings (conceptual flow systems) that they represent are Cumberland Valley, Pa., (Chichester, 1996) with 

folded crystalline carbonate rocks mantled by thick and thin 

regolith; Indian Creek, N.C., (Daniel and others, 1997) with 

massive and foliated crystalline silicic rocks mantled by thick 

regolith; and Stony Brook, N.J., (Lewis-Brown and Jacobsen, 

1995) with Mesozoic sedimentary and igneous rocks mantled 

by very thin regolith. The Cumberland Valley type area is 

mostly within the Valley and Ridge Physiographic Province. 

The Indian Creek and Stony Brook type areas are within the 

Piedmont Physiographic Province. No type area was selected in 

the Blue Ridge Physiographic Province because of the lack of 

available data to construct or calibrate a model. However, the 

hydrogeologic setting in most of the Blue Ridge Physiographic 

Province is similar to the Indian Creek type area, provided that 

the greater relief—typical of the Blue Ridge—is taken into 

account. Small areas of the Blue Ridge that are underlain by carbonate rocks have a hydrogeologic setting similar to the Cumberland Valley type area.

The type areas and each associated model are similar in 

several ways. The average annual precipitation for all three sites 

is between 40 and 48 inches. The ground-water flow model 

selected for simulation in each type area was a modular, threedimensional, finite-difference, ground-water flow model 

(MODFLOW) documented by McDonald and Harbaugh 

(1988). In both the conceptual and digital models, flow through 

fractured and dissolved rock was simulated as flow through an 

equivalent porous medium. All three models were designed to 

simulate steady-state conditions. All model grids had equal 

spacing and were set parallel to bedding or foliation. Permeability was not considered isotropic and typically was least in the 

direction perpendicular to bedding or foliation. The water table 

was considered as the top of the model and impermeable rock 
Water Geochemistry 15

as the bottom of the model. Vertical changes in transmissivity 

were incorporated into the models, with the simulated transmissivity decreasing rapidly with depth below the water table and 

decreasing rapidly downdip in the case of gently dipping beds 

(Stony Brook type area). Results indicate that the volume of lateral ground-water flow decreases significantly in layers deeper 

than the first one to three layers below the water table. For all 

three type-area models, more than 54 percent of the groundwater flow occurs in the top one to three layers. 

The three type areas and the models have several differences (table 3). The Cumberland Valley, Pa., type area contains 

four of the five hydrogeologic terranes of the Valley and 

Ridge Physiographic Province and has the largest 

stream basin area. The Stony Brook and Indian Creek 

type areas contain the most transmissive hydrogeologic 

terranes in the Piedmont, but within much smaller 

stream basins. The Cumberland Valley, Pa., type area 

has much thicker regolith in some areas, greater depth to 

water, greater recharge, greater bedrock transmissivity, 

and larger ground-water withdrawals than the other two 

type areas. The Cumberland Valley, Pa., type-area 

model had an intermediate number of layers and the 

least anisotropy. Results indicate that the Cumberland 

Valley, Pa., type area had significantly more interbasin 

flow compared to the Stony Brook, N.J., type area—the 

only other type area with more than a single stream 

drainage basin. The larger interbasin flow appears to be 

related to the karst carbonate rocks that underlie the two 

basins within the Cumberland Valley, Pa., type area. 

Although specific values of model parameters are 

unlikely to be transferable to other areas, the methods 

and results of ground-water flow simulation used for the 

type area could guide further investigations to quantify 

ground-water conditions and flow in similar hydrogeologic settings and terranes.

Water Geochemistry

The chemistry of the water in rocks (including alluvium), springs, and streams in the three physiographic 

provinces was determined by assembling and interpreting 196,852 analyses of water from 15,263 sites stored 

primarily in the water-quality database in NWIS. The 

geographic distribution of water-quality sites in the 

study area is highly uneven (Briel, 1997, figs. 1, 2, 

and 3). For ground-water and surface-water sites, the 

majority of data are for the Piedmont Physiographic 

Province with emphasis on sites in Maryland, New Jersey, and Pennsylvania. For springs, most of the data are 

for the Valley and Ridge Physiographic Province with 

emphasis on sites in Maryland and Pennsylvania. For all 

three types of sites, the least amount of data is for the 

Blue Ridge Physiographic Province.

In the study area as a whole, typical ground water 

is not highly mineralized: the median dissolved-solids 

concentration is 164 mg/L. Typical ground water also is nearly 

neutral (median pH is 6.9) and is classified as moderately hard 

(median hardness is 82 mg/L as CaCO3). The chemical quality 

of ground water in each physiographic province, however, differs substantially.

Ground water in the Valley and Ridge Physiographic 

Province has the largest median dissolved-solids concentration 

(226 mg/L, fig. 8), is slightly basic (median pH is 7.3), and is 

classified as hard (median hardness is 149 mg/L as CaCO3). 

Ground water in this province also has high alkalinity and large 

concentrations of calcium, magnesium, sulfate, bicarbonate, 
16 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

Table 3. Comparison of selected characteristics of the three type areas and ground-water flow models in the Appalachian Valley and 

Piedmont Regional Aquifer-System Analysis study area.

[---, not available or not determined]

Type areas

Characteristics Cumberland Valley, Pa. Indian Creek, N.C. Stony Brook, N.J.

Setting

Physiographic province Mostly Valley and Ridge Piedmont Piedmont

Physiographic region Mostly Great Valley Inner Piedmont Newark Basin

Hydrogeologic setting 

(Conceptual flow system)

Folded crystalline carbonate 

rocks mantled by thick and 

thin regolith

Massive and foliated crystalline 

silicic rocks mantled by thick 

regolith

Mesozoic sedimentary and 

igneous rocks mantled by 

very thin regolith

Hydrogeologic terranes Dolomite, limestone, argillaceous carbonate, and siliciclastic rocksGneiss-schist Shale-sandstone, gneiss-schist

Rock types Limestone, dolomite, shale, 

diabase

Hornblende gneiss, granite Siltstone, shale, sandstone, 

diabase

Stream basins Conodoguinet and Yellow 

Breeches Creeks

Indian Creek Stony and Beden Brooks and 

Jacobs Creek

Basin area, in square miles 686 69 89

Regolith thickness, in feet 0 to 450 63 less than 10

Average or range in depth to 

water table, in feet

41 26 10 to 35

Recharge, in inches 12 to 15 10.4 8.6

Estimated storativity, regolith 0.05 0.01 to 0.20 0.01 to 0.10

Estimated storativity, bedrock Less than 0.02 0.0002 0.0001 to 0.001

Estimated transmissivity of 

regolith, in feet squared per 

day

140 to 1,000 180 to 3,600 ---

Estimated transmissivity of 

bedrock, in feet squared per 

day

1,000 to 40,000 92 to 330 200 to 3,200

Estimated streambed hydraulic conductivity, in feet per 

day

0.15 to 5.0 --- 0.025 to 0.38

Ground-water withdrawals, in 

million gallons per day

About 6 0.96 1.1

Base-flow distribution Losing upper stream reaches, 

gaining middle and lower 

reaches

Uniform across study area Too little data to estimate distribution

Model

Model area, in square miles 350 146 89

Grid spacing, in feet 1,320 500 500
Water Geochemistry 17

Number of active cells per 

layer

5,579 17,400 9,919

Anisotropy, row to column 1.33:1 Varies with topography 2:1, layer 1; 10:1, layer 2

Number of layers 5 11 2

Layer representation and 

thickness, in feet

Top 3 layers, regolith, bedrock, 

or both, 240, total; bottom 

2 layers, bedrock, 410, total

Top layer, saprolite, 20 to 30; second layer, saprolite-bedrock transition, 25; lower 9 layers, 

bedrock, 800, total

Top layer, soil and weathered 

rock, 75 to 208; bottom 

layer, bedrock, 292 to 425

Lateral changes in transmissivity occur withEach geologic unit Three topographic settings Faults or geologic unit by parts 

of study area

Boundaries Primarily head-dependent flux, 

specified flux, and no flow

Primarily specified flux at boundary and interior streamsPrimarily no-flow, and headdependent flux and specified 

flux at interior streams

Recharge distributed by Percent of distributed meanannual precipitationUniform over study area Base-flow estimates and geologic unit

Results

Lateral flow in top layer --- 55 percent of recharge 94 percent of recharge

Travel time in top layer, in 

years

8 to more than 10 10 to 20 ---

Interbasin flow 11.5 percent of one of two basin 

budgets

--- Less than 1 percent of any one 

of three basin budgets

Strong points of flow analysis Detailed head data; distributed 

base-flow data; analysis of 

interbasin flow in karst by 

particle tracking; consideration of effects of diabase dike

Distributed base-flow data; discretization of transmissivity by 

topography; use of water-quality 

data to verify concept of flow

Discretization of transmissivity of dipping beds; consideration of the hydrologic 

effects of a normal fault

Table 3. Comparison of selected characteristics of the three type areas and ground-water flow models in the Appalachian Valley and 

Piedmont Regional Aquifer-System Analysis study area.

[---, not available or not determined]

Type areas

Characteristics Cumberland Valley, Pa. Indian Creek, N.C. Stony Brook, N.J.

Table 3. Comparison of selected characteristics of the three type areas and ground-water flow models in the Appalachian Valley and 

Piedmont Regional Aquifer-System Analysis study area.—Continued
18 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

nitrate, and dissolved iron. Ground water in the Piedmont Physiographic Province, by contrast, has a smaller median 

dissolved-solids concentration (159 mg/L, fig. 8), is slightly 

acidic (median pH is 6.7), and is classified as moderately hard 

(median hardness is 65 mg/L as CaCO3). Ground water in this 

province has large concentrations of sodium, potassium, chloride, silica, ammonia, phosphorus, total iron, and manganese. 

Ground water in the Blue Ridge Physiographic Province has the 

smallest median dissolved-solids concentration (73 mg/L, 

fig. 8), is slightly acidic (median pH is 6.6), and is classified as 

soft (median hardness is 29 mg/L as CaCO3). Chemical quality 

of spring water in the study area is similar to that of water from 

wells, but more dilute (median dissolved-solids concentration is 

136 mg/L). Chemical quality of surface water in the study area 

is similar to that of ground water, but like spring water, is more 

dilute. Median concentrations of dissolved solids in surface 

water (107 mg/L) indicates that surface water typically contains 

about 35 percent less dissolved solids than ground water and 

21 percent less dissolved solids than spring water.

Typically, the order of abundance of major cations in 

ground water in all three provinces is calcium>magnesium>sodium; and for major anions, the order is bicarbonate>sulfate or chloride (table 4). For most water in the study 

area, the major dissolved ions are calcium, magnesium, and 

bicarbonate, which are produced by the dissolution of calcite 

and dolomite in the rocks. In parts of the Valley and Ridge 

Physiographic Province in Pennsylvania, the rocks contain significant amounts of either pyrite or gypsum, and sulfate 

becomes the dominant anion at higher ionic concentrations. 

Chloride typically is the third most abundant anion in water in 

the study area (the interquartile range in concentrations in 

ground water is 2.8 to 17 mg/L). The concentration of chloride 

and the variation in concentration in ground water is greatest in 

the Piedmont Physiographic Province. The geographic pattern, 

by county, of median chloride concentration in ground water 

(Briel, 1997, fig. 35) is similar to that for sodium (Briel, 1997, 

fig. 25). In addition, the geographic pattern of median chloride 

concentrations greater than 4.1 mg/L (Briel, 1997, fig. 35) is 

similar to the pattern of dense population distribution (greater 

than 100,000 per county; Swain and others, 1991, fig. 4), particularly in New Jersey, southeastern Pennsylvania, and the 

Atlanta, Georgia area. 

As part of the study of water chemistry in the APRASA 

study area, specific changes in the relative proportions of all 

major ions within the total concentration of solutes in water 

analyses are related to seven geochemical processes. These processes take specific reaction paths in a trilinear diagram (fig. 9). 

The most common reaction path (fig. 9, path 3) shows an evolutionary change in chemical composition of water that results 

from downgradient flow in recharge areas to deeper areas of 

more confined flow. Along this path, dissolved-solids concentration increases slightly, and chemical composition changes 

from a calcium-bicarbonate water to a mixed water containing 

calcium, magnesium, bicarbonate, and calcium sulfate. The 

dominant processes along this path involve the dissolution of 

dolomite and gypsum, and dedolomitization. Magnesium and 

sulfate concentrations increase, whereas calcium and bicarbonate concentrations remain constant. In the Blue Ridge and Piedmont Physiographic Provinces, secondary processes that affect 

water chemistry are represented by path 6 and path 2 (fig. 9). 

Along path 6, chemical composition changes as a result of the 

replacement of calcium and magnesium in the ground water by 

sodium ions loosely bound to clay minerals. Along path 2, 

chemical composition changes as a result of conservative mixing of freshwater with a sodium-chloride-sulfate water in areas 

of less vigorous ground-water circulation within the aquifer.

Ground-Water Development and Potential 

for Future Development

During development of the study area in the early 19th 

century, homes were located near streams and springs for transportation as well as water supply. Larger springs were developed for municipal supplies, and treatment plants eventually 

were constructed along streams to treat surface water. As population moved away from streams, shallow dug wells became a 

widespread source of household supply. Beginning in 1824 in 

New Brunswick, New Jersey (Carlston, 1943, p. 123), drilled 

wells began replacing dug wells as the main source of household supplies. Ground water withdrawn in 1985 for all uses in 

the study area was estimated in this study to be 1.7 Bgal/d. This 

represents only about 2 percent of the 90 Bgal/d estimated to be 

available from ground-water discharge. 

Approximately 82 percent of the 1.7 Bgal/d is withdrawn 

from widely dispersed locations throughout the study area. 

Only 18 percent of the ground water used is withdrawn at 

pumping centers within a few counties (fig. 10). For the most 

part, unusual water-level declines in response to pumping in 

these centers have corresponded primarily with times of 

drought, and water levels have recovered during times of normal precipitation. As a consequence, much of the study area, 

including these pumping centers, could be developed for additional municipal and industrial ground-water supplies. Because 

ground-water flow paths in the study area are relatively shallow 

Table 4. Typical proportions of major ions in ground water in the 

Appalachian Valley and Piedmont Regional Aquifer-System 

Analysis study area.

[Ca, calcium; Mg, magnesium; Na, sodium; HCO3, bicarbonate; SO4, sulfate; 

Cl, chloride]

Physiographic 

province

Cation proportions

Ca:Mg:Na

Anion proportions

HCO3:SO4:Cl

Valley and Ridge 70:20:10 85:08:07

Blue Ridge 50:25:25 80:04:16

Piedmont 50:30:20 80:08:12
Ground-Water Development and Potential for Future Development 19
20 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

APRASA study area

boundary
Ground-Water Development and Potential for Future Development 21

and short, however, ground-water interactions with surface 

water in regard to both water quantity and water quality are 

important constraints to consider in planning additional development.

Areas favorable for development of municipal and industrial ground-water supplies (fig. 11) may be summarized into 

four categories: (1) valley bottoms underlain by alluvium of 

glacial origin in New Jersey and Pennsylvania; (2) the Elkton 

aquifer along the southeastern edge of the Valley and Ridge 

Physiographic Province; (3) valley bottoms and rolling uplands 

underlain by relatively clay-free dolomite, limestone, and marble bedrock in all three physiographic provinces; and (4) the 

three (Mesko and others, 1999, fig. 1) northernmost Mesozoic 

basins in the study area. These areas were selected for their 

potential ability to provide municipal and industrial water supplies compared to other parts of the study area. Additionally, the 

northernmost Mesozoic basins were selected because of a large 

population with a rapidly growing need for water.
22 Summary of the Hydrogeology of the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces

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Physiographic Provinces in the Eastern United States

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