A Surficial Hydrogeologic Framework for the 

Mid-Atlantic Coastal Plain 

By Scott W. Ator, Judith M. Denver, David E. Krantz, Wayne L. Newell, 

and Sarah K. Martucci 

Professional Paper 1680 
U.S. DEPARTMENT OF THE INTERIOR 

GALE A. NORTON, Secretary 

U.S. GEOLOGICAL SURVEY 

P. Patrick Leahy, Acting Director 

Any use of trade. product, or firm names in this report is for 

identification purposes only and does not constitute endorsement 

by the U.S. Government. 

Reston, Virginia 2005 

Library of Congress Cataloging-in-Publications Data 

A surficial hydrogeologic framework for the Mid-Atlantic coastal plain I by Scott W. Ator 

... [et al.]. 

p. em.- (Professional paper; 1680) 

Includes bibliographic references. 

ISBN 0-607-95745-1 

1. Hydrogeology-Middle Atlantic States (U.S.) 2. Hydrogeology-Atlantic Coast (U.S.) 

I. Ator, Scott W. II. U.S. Geological Survey professional paper; 1680. 

GB1016.6S87 2005 

551.49'0975-dc22 

For sale by U.S. Geological Survey, 

Branch of Information Services 

Box 25286, Federal Center 

Denver, CO 80225 

2005047878 
Foreword 

The U.S. Geological Survey (USGS) is committed to serve the Nation with accurate and timely scientific information that helps enhance and protect the overall quality of life. and facilitates effective 

management of water, biologicaL energy, and mineral resources. Information on the quality of the 

Nation's water resources is of critical interest to the USGS because it is so integrally linked to the 

long-term availability of water that is clean and safe for drinking and recreation and that is suitable 

for industry. irrigation, and habitat for fish and wildlife. Escalating population growth and increasing 

demands for the multiple water uses make water availability. now measured in terms of quantity and 

quality, even more critical to the long-term sustainability of our communities and ecosystems. 

The USGS implemented the National Water-Quality Assessment (NAWQA) Program to support 

nationaL regionaL and local information needs and decisions related to water-quality management 

and policy. Shaped by and coordinated with ongoing efforts of other FederaL State, and local agencies, the NA WQA Program is designed to answer: What is the condition of our Nation's streams and 

ground water? How are the conditions changing over time? How do natural features and human 

activities affect the quality of streams and ground water. and where are those effects most pronounced? By combining information on water chemistry, physical characteristics. stream habitat, and 

aquatic life. the NAWQA Program aims to provide science-based insights for current and emerging 

water issues. NA WQA results can contribute to informed decisions that result in practical and effective water-resource management and strategies that protect and restore water quality. 

Since 1991. the NA WQA Program has implemented interdisciplinary assessments in more than 50 of 

the Nation's most important river basins and aquifers. referred to as Study Units. Collectively, these 

Study Units account for more than 60 percent of the overall water use and population served by public water supply, and are representative of the Nation's major hydrologic landscapes, priority ecological resources. and agricultural, urban, and natural sources of contamination. 

Each assessment is guided by a nationally consistent study design and methods of sampling and analysis. The assessments thereby build local knowledge about water-quality issues and trends in a particular stream or aquifer while providing an understanding of how and why water quality varies 

regionally and nationally. The consistent. multi-scale approach helps to determine if certain types of 

water-quality issues are isolated or pervasive, and allows direct comparisons of how human activities 

and natural processes affect water quality and ecological health in the Nation's diverse geographic 

and environmental settings. Comprehensive assessments on pesticides, nutrients, volatile organic 

compounds. trace metals, and aquatic ecology are developed at the national scale through comparative analysis of the Study-Unit findings. 

The USGS places high value on the communication and dissemination of credible. timely. and relevant science so that the most recent and available knowledge about water resources can be applied in 

management and policy decisions. We hope this NAWQA publication will provide you the needed 

insights and information to meet your needs, and thereby foster increased awareness and involvement 

in the protection and restoration of our Nation's waters. 

The NA WQA Program recognizes that a national assessment by a single program cannot address all 

water-resource issues of interest. External coordination at all levels is critical for a fully integrated 

understanding of watersheds and for cost-effective management, regulation, and conservation of our 

Nation's water resources. The Program, therefore, depends extensively on the advice. cooperation, 

and information from other FederaL State. interstate. TribaL and local agencies, non-government 

organizations, industry. academia, and other stakeholder groups. The assistance and suggestions of 

all are greatly appreciated. 

Robert M. Hirsch 

Associate Director for Water 

CONTENTS 

Foreword ................................................................................................................................................................................ III 

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

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

Purpose of a hydrogeologic framework....................................................................................................................... 2 

Limitations of previous data for regional investigations .. .. .. .. .. .... .. .. .. .. .. .. .. .. .. .. .. .... .. .. .. .. .... .. .. .. .... .. .. .. .. .... .. .. .. .... .. .. .. .. . 4 

The Mid-Atlantic Coastal Plain................................................................................................................................... 5 

Acknowledgements ...................................................................................................................................................... 6 

Development of the regional surficial hydrogeologic framework .. .. .. .......... ............ ............ ............ ............ ........ ........ ...... ... 7 

Delineation of regional physiography ............ ......... ..... ...... . . . . .......... ....... ..... . ............ ............ ... ..... . ............. ....... .... . .... 7 

Delineation of regional geology ... . . ............ ............ ....... .... . . . ............ ....... ... . . . .......... .............. ......... ............. ....... .... . .... 8 

Delineation of hydrogeologic subregions .................................................................................................................... 10 

The regional surficial hydrogeologic framework ................................................................................................................... lO 

Subregion 1: Coastal Lowlands ................................................................................................................................... 10 

Subregion 2: Middle Coastal Plain- Mixed Sediment Texture .................................................................................. 13 

Subregion 3: Middle Coastal Plain - Fine Sediments ................................................................................................. 13 

Subregion 4: Middle Coastal Plain- Sands with Overlying Gravels .......................................................................... 14 

Subregion 5: Inner Coastal Plain- Upland Sands and Gravels ................................................................................... 16 

Subregion 6: Inner Coastal Plain- Dissected Outcrop Belt.. ...................................................................................... 17 

Subregion 7: Alluvial and Estuarine Valleys ............................................................................................................... 19 

Evaluation of the regional framework at the local scale ........................................................................................................ 19 

Subregion 1: Coastal Lowlands ................................................................................................................................... 22 

Subregion 2: Middle Coastal Plain- Mixed Sediment Texture .................................................................................. 23 

Subregion 3: Middle Coastal Plain- Fine Sediments ................................................................................................. 23 

Subregion 4: Middle Coastal Plain- Sands with Overlying Gravels .......................................................................... 24 

Subregion 5: Inner Coastal Plain- Upland Sands and Gravels ................................................................................... 25 

Subregion 6: Inner Coastal Plain - Dissected Outcrop Belt.. ...................................................................................... 26 

Subregion 7: Alluvial and Estuarine Valleys ............................................................................................................... 26 

Framework application .......................................................................................................................................................... 27 

Intended uses ............................................................................................................................................................... 27 

Limitations ................................................................................................................................................................... 27 

Summary ................................................................................................................................................................................ 28 

References., ............................................................................................................................................................................. 29 

Appendix 1: Technical notes ................................................................................................................................................. 36 

by Sarah K. Martucci 

Geology coverages ....................................................................................................................................................... 36 

Physiography coverage ................................................................................................................................................ 36 

Hydrogeologic framework coverage ............................................................................................................................ 36 

Reference ..................................................................................................................................................................... 36 

Appendix 2: Geologic setting of the Mid-Atlantic Coastal Plain .......................................................................................... 38 

by David E. Krant::: 

Physiography ............................................................................................................................................................... 38 

Structure ....................................................................................................................................................................... 39 

Geologic history .......................................................................................................................................................... 40 

The Piedmont - Coastal Plain transition (The Fall Zone) .......................................................................................... .42 

Weathering of surficial units ........................................................................................................................................ 42 

References ................................................................................................................................................................... 42 

Contents V 
PLATES (in pocket at end of report) 

Plates 1--4. Maps showing: 

1. Physiography of the Mid-Atlantic Coastal Plain 

2. Surficial and subcropping geology of the Mid-Atlantic Coastal Plain 

3. Predominant texture of surficial geologic units in the Mid-Atlantic Coastal Plain 

4. Hydrogeologic subregions of the Mid-Atlantic Coastal Plain 

FIGURES 

I. Map showing the Mid-Atlantic Coastal Plain ..................................................................................................................... 3 

2. Generalized geologic section through eastern Virginia showing the eastward-thickening sedimentary wedge 

typical of the Mid-Atlantic Coastal Plain ................................................................................................................. 6 

Figures 3-8. Generalized hydrogeologic section showing idealized flow through: 

3. Subregion 1, the Coastal Lowlands, on the Delmarva Peninsula in Virginia .......................................................... 12 

4. Subregion 3, the Middle Coastal Plain- Fine Sediments, along the James River in southern Virginia ................. 14 

5. Subregion 4, the Middle Coastal Plain- Sands with Overlying Gravels, on the Delmarva Peninsula ................... 15 

6. Subregion 5, the Inner Coastal Plain- Upland Sands and Gravels, in southern Maryland .................................... 16 

7. Subregion 6, the Inner Coastal Plain- Dissected Outcrop Belt, in southern Maryland and northern Virginia ...... 18 

8. Subregion 7, the Alluvial and Estuarine Valleys, near Washington, D.C ................................................................ 20 

9. Map showing the location of selected local-scale studies within the Mid-Atlantic Coastal Plain .................................... 21 

TABLES 

1. Comparison of physiographic subprovinces developed for New Jersey to those in the remainder of 

the Mid-Atlantic Coastal Plain north of the Potomac River ..................................................................................... 8 

2. Hydrogeologic subregions within the Mid-Atlantic Coastal Plain ................................................................................... 11 

CONVERSION FACTORS AND ABBREVIATIONS 

Multiply 

meter (m) 

kilometer (km) 

square kilometer (km2 ) 

centimeter per year (em/year) 

By 

3.281 

0.621 

0.368 

0.3937 

To obtain 

foot 

mile 

square mile 

inch per year 

Sea level: In this report, ''sea level" refers to the National Geodetic Vertical Datum of 1929-a geodetic datum d:-rived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929. 

VI Contents 
A Surficial Hydrogeologic Framework for the Mid-Atlantic 

Coastal Plain 

by Scott W. Ator, Judith M. Denver, David E. Krantz, Wayne L. Newell, and Sarah 1<. 

Martucci 

ABSTRACT 

A surficial hydrogeologic framework was 

developed for the Mid-Atlantic Coastal Plain, 

from New Jersey through North Carolina. The 

framework includes seven distinct hydrogeologic 

subregions within which the primary natural physical factors affecting the flow and chemistry of 

shallow ground water and small streams are relatively consistent. Within most subregions, the 

transport of chemicals from the land surface to 

ground water and streams can be described by a 

fairly uniform set of natural processes; some subregions include mixed hydrogeologic settings that 

are indistinguishable at the regional scale. The 

hydrogeologic framework and accompanying 

physiographic and geologic delineations are presented in digital and printed format. 

The seven hydrogeologic subregions that 

constitute the framework were delineated prin1arily on the basis of physiography and the predominant texture (typical grain size) of surficial and 

(where surficial sediments are particularly thin) 

subcropping sediments. Physiography for the 

Mid-Atlantic Coastal Plain was constructed by 

standardizing and extrapolating previously published interpretations for the Coastal Plain of 

South Carolina and New Jersey, based on sin1ilar 

work in the other States. Surficial and subcropping 

geology were similarly compiled from previous 

publications by resolving inconsistencies in 

nomenclature, interpretation, and scale, and interpolating across unmapped areas. A bulk sediment 

texture was determined for each mapped geologic 

unit on the basis of published descriptions. 

Fundamental differences among the seven 

hydrogeologic subregions are described on the 

basis of hypotheses about surficial and shallow 

subsurface hydrology and water chemistry in each, 

as well as variable land use, soils, and topography. 

On the regional scale, the Coastal Lowlands (Subregion 1), the Middle Coastal Plain- Fine Sediments (Subregion 3 ), the Middle Coastal Plain -

Sands with Overlying Gravels (Subregion 4 ), and 

the Inner Coastal Plain- Upland Sands anc1 Gravels (Subregion 5) are relatively homogeneo•1s in 

terms of hydrogeology, although an examiration 

of results from small-scale studies within tl'~ 

Coastal Plain demonstrates that even these areas 

are quite variable, locally. Moderate topographic 

relief and primarily permeable surficial sediments 

promote good drainage of the land surface in Subregion 4, for example, but drainage is comnonly 

poor in the Coastal Lowlands (Subregion 1) due to 

flat topography and low elevations. Agriculture is 

cotnmon in both subregions, although artificial 

drainage is typically required to support cultivation in Subregion 1. Important physiographic differences are evident among the remaining three 

subregions, although sediment textures witl'in the 

Middle Coastal Plain - Mixed Sediment Texture 

(Subregion 2), the Inner Coastal Plain- Dissected 

Outcrop Belt (Subregion 6), and the Alluvial and 

Estuarine Valleys (Subregion 7) are variable even 

at the regional scale. 

Abst1·act 
INTRODUCTION 

Many features of the modem landscape are 

related to the underlying geology. Interrelated geologic and hydrologic processes directly or indirectly 

affect the spatial patterns seen in ecological communities, water quality and availability, soils, and land use. 

Defining and illustrating the spatial variability of 

hydrogeologic processes is fundamental to many environmental studies. 

A regional surficial hydrogeologic framework 

was developed for the Mid-Atlantic Coastal Plain of 

New Jersey, Pennsylvania, Delaware, Maryland, Virginia, North Carolina, and the District of Columbia 

(fig. 1 ). Seven distinct hydrogeologic subregions with 

relatively consistent physical properties for the surficial aquifer or other shallow sediments were defined. 

Within most framework subregions, the occurrence, 

fate, and transport of chemicals in the shallow groundwater system and stream base flow can be described 

and predicted on the basis of a fairly uniform set of natural conditions. The seven subregions represent areas 

of similar geology (primarily unconsolidated siliciclastic sediments) along a continuum of sediment textures 

(grain sizes) and physiography. The framework is 

designed to help explain spatial variability in regional 

water quality and provide a template for synthesizing 

water-quality data. The hydrogeologic framework 

could also be useful for explaining the spatial distribution of other landscape variables or in the design of 

regional environmental studies. Combined with other 

spatial data (such as soils or topography), the framework illustrates the basic physical setting in the MidAtlantic Coastal Plain. 

The framework represents a summary of the 

variable hydrogeology in the Mid-Atlantic Coastal 

Plain on a regional scale; generalized descriptions of 

the environmental setting of different subregions 

become less applicable for progressively smaller areas. 

This limitation is a result of the generalizations, interpolations, and similar approaches used in the subregion 

delineations, as well as real variability in physiography 

and geology in the Coastal Plain. A review of results 

and data from local investigations within the study area 

can be useful for defining and describing this heterogeneity. 

The surficial hydrogeologic framework presented and discussed in this report was developed primarily from physiographic, stratigraphic, and 

sediment -texture data compiled in a digital format. 

These data are also presented. The hydrozeologic 

framework, with the physiographic and g~ologic coverages, is intended to extend hydrogeologic understanding from recent mapping and other hvestigations 

in a consistent manner over a multi-state region. 

The purpose, development, intended uses, and 

limitations of the hydrogeologic framework are 

described in this report. Hypotheses about surficial and 

shallow subsurface hydrology and water chemistry are 

described and contrasted among the seve'l hydrogeologic subregions defined by the framework. Other spatial landscape variables (such as soils and land use) are 

used to illustrate and explain differences among and 

within the Coastal Plain subregions defin~d in the 

framework. Hypotheses that relate the physical properties of the framework subregions to water quality are 

compared with results from local investigations to 

demonstrate the applicability and limitations of the 

framework at different spatial scales. Nutrient data 

were used in many of these evaluations b~cause they 

are widely available and are sensitive to oxic or reducing conditions and therefore a more general indicator 

of geochemistry. Technical notes about tl'~ available 

digital versions of the framework, physiography, and 

geology are included in Appendix 1. A discussion of 

the regional physiography and geology 0'1 which the 

framework is based is presented in Appendix 2. 

Purpose of a Hydrogeologic Framewr ... k 

A regionally consistent hydrogeologic framework describes key components of the physical setting 

for environmental studies. The texture anrl chemical 

composition of surficial and near-surface geologic 

materials affect the moven1ent of water, '"hich in tum 

affects the formation of soils and topographic features, 

land-use patterns, and the structure of ecological communities. Soils are related to the physical and chemical 

properties of the sediments or rocks frorr which they 

formed and the drainage characteristics of the area. 

The size and shape of valleys and upland~ are controlled by geology and the movement of water, which 

is the primary erosive agent in humid ten1perate areas 

such as the eastern United States. The spatial distribution of geologic and water resources also helps determine patterns of land use by humans and other 

organisms. In the Mid-Atlantic Coastal Plain, for 

example, broad, flat, well-drained areas ere typically 

2 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
PHYSIOGRAPHIC PROVINCES 

25 ~~~=== National 

Base modified 

Atlas of 

from 

the 

U

United 

.S. Geological 

States, 1970, 

Survey, =~==--_j 1:7,500,000, Albers equal-area projection 

Modified from Feneman, 1938; 

Feneman and Johnson, 1946 

Figure 1. The Mid-Atlantic Coastal Plain. 

Base map from U.S. Geological Survey 0 

digital data; 1:100,000; Lambert conic 

conformal projection; North American I I Datum of 1983 25 

25 50 

I I 

I I 

50 75 

I 

75 

I 

"0 100 MILES"' 

I 

100 KILOMETERS 

Introduction 3 
used for agriculture; more poorly drained lowlands 

commonly remain forested wetlands, unless ditched or 

otherwise artificially drained for cultivation. 

The physical properties of near-surface geologic 

materials are particularly important in water-quality 

studies because they directly affect the flow and quality 

of streams and ground water. The permeability of surficial deposits affects ground-water recharge and the 

formation of stream-drainage networks. Dense stream 

networks tend to form in areas where impermeable 

deposits limit infiltration and surface runoff is generated during precipitation. This runoff may enhance soil 

erosion and the transport of surficial contaminants such 

as fertilizers, pesticides, and volatile organic compounds (VOCs) directly to streams, estuaries, and the 

ocean. In contrast, stream networks are typically more 

dispersed in areas of thick permeable surficial sediments, and a greater percentage of precipitation percolates through the unsaturated zone to recharge the 

water table. Because water is an effective solvent, natural water quality is related to the chemical composition of the rocks and sediments through which it flows 

(Freeze and Cherry, 1979; Hem, 1985). Ground-water 

chemistry is also largely determined by the length of 

ground-water flowpaths and the extent to which overlying strata allow for contact with oxygen in the atmosphere. For example, nitrate is stable and may travel 

long distances in well-oxygenated ground water 

(Freeze and Cherry, 1979), but may be lost to denitrification where impermeable overlying deposits (confining layers) produce reducing conditions in the aquifer. 

The surficial hydrogeologic framework for the 

Mid-Atlantic Coastal Plain was developed as a tool for 

understanding regional water quality and directing 

future regional water-quality assessments. As part of 

the National Water-Quality Assessment (NAWQA) 

program (Gilliom and others, 1995), the U.S. Geological Survey (USGS) has been collecting water-quality 

data in different areas of the Coastal Plain since the late 

1980s. Data from these and other studies are periodically compiled and analyzed for regional or national 

assessments of water quality and to direct future 

NAWQA sampling efforts. The hydrogeologic framework provides a template for analyzing existing waterquality data and for planning environmental sampling 

in the Mid-Atlantic Coastal Plain. The hydrogeologic 

variability described by the framework can be compared to previous data or results from NAWQA and 

other regional programs to identify any significant gaps 

in the current understanding of Coastal Plain water 

quality and to help guide future sampling in the region. 

Limitations of Previous Data for Regional 

Investigations 

Previously available spatial geologic and hydrologic data for the Mid-Atlantic region often were of 

limited use for regional water-quality studies due to 

insufficient detail, incomplete coverage, or inconsistencies among sources. In regional or national classifications, the Coastal Plain is sometimes considered to 

be generally homogeneous compared to other geologic 

regions or physiographic provinces (Ator and Ferrari, 

1997). This characterization is due in part to the lack of 

a regionally consistent database of geologic and hydrologic properties for the Coastal Plain. Regional spatial 

data sets typically lack the resolution necessary for indepth analyses and can be used only to relate water 

quality to broadly defined rock types. For example, 

digital geologic data are available for the entire United 

States at a scale of 1 :2,500,000 (King and Beikman, 

1974; Schruben and others, 1994). At this scale, 

locally heterogeneous areas like the Coastal Plain are 

necessarily combined into a few comprehensive mapping units. An analysis of ground-water quality in the 

Mid-Atlantic region using this approach showed nitrate 

concentrations were particularly variable in the Coastal 

Plain (Ator and Ferrari, 1997). 

Regions of similar surficial hydrogeologic properties have been previously delineated for selected 

parts of the Mid-Atlantic Coastal Plain. Available local 

geologic mapping at the level of individual formations 

is commonly used in these studies, although scales, 

methods, and nomenclature may vary among the different maps that are usually required to cover relatively 

large areas. "Hydrogeomorphic regions" have been 

defined for the Delmarva Peninsula on the basis of surficial geology, geomorphology, soils, and physiography 

to help explain spatial variability in shallow groundwater quality (Hamilton and others, 1989). A similar 

approach has been used to evaluate base-flow nitrate 

concentrations in non-tidal streams of the entire Chesapeake Bay Watershed; 11 distinct regions were delineated for this study, including three within the Coastal 

Plain (Bachman and others, 1998). Similar hydrogeologic areas within the Coastal Plain of Virginia have 

been delineated on the basis of geology and soil drainage, the two most significant variables in an empirical 

4 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
model constructed to predict ground-water discharge 

(Richardson, 1994 ). Geologic data from multiple publications have been compiled to support water-quality 

investigations within the Potomac River Basin (Gerhart 

and Brakebill, 1996) and the Albemarle-Pamlico 

Drainages (McMahon and Lloyd, 1995). 

Previous conceptual frameworks of the hydrogeology of the entire Mid-Atlantic Coastal Plain have 

focused mainly on the confined aquifer system. In studies of the entire aquifer system, Coastal Plain surficial 

deposits (commonly including post-Miocene sediments) are often combined into comprehensive "surficial" aquifers (Brown and others, i972; Trapp, 1992). 

This convention is useful when considering the entire 

extent and depth of Coastal Plain aquifers, but often 

excludes important textural and geochemical variability among surficial deposits. 

The Mid-Atlantic Coastal Plain 

The Coastal Plain Physiographic Province is a 

broad, relatively low relief terrace along the Atlantic 

Ocean and Gulf of Mexico margins of the United States 

(Fenneman, 1938; Fenneman and Johnson, 1946) 

(Appendix 2, this report). The Mid-Atlantic Coastal 

Plain includes areas of the Coastal Plain Physiographic 

Province in New Jersey, Pennsylvania, Delaware, 

Maryland, Virginia, North Carolina, and the District of 

Columbia (fig. 1). The 114,000-km2 (square kilometer) 

area is bordered by the Fall Zone to the west and the 

Atlantic Ocean to the east, and ranges in width from 

about 24 km (kilometers) in northern New Jersey to 

240 km in central North Carolina. The Mid-Atlantic 

Coastal Plain is gently inclined from altitudes of 80 to 

100 m (meters) at the Fall Zone down to sea level, and 

the land surface varies from nearly fiat to deeply 

incised, with as much as 100 m of local relief. Most 

areas are less than 55 m above sea level. The maximum 

altitude for the Coastal Plain in the Mid-Atlantic 

Region exceeds 175m along the Fall Zone in southcentral North Carolina. The Coastal Plain is cut by the 

valleys of major rivers and their tributaries that are currently flooded as estuaries, such as Chesapeake Bay, 

Delaware Bay, and Albemarle Sound. Slopes are typically steepest near the Fall Zone and along incised valleys of major streams (Verdin, 1997). 

The climate on the Mid-Atlantic Coastal Plain is 

humid and temperate to subtropical. Annual precipitation varies spatially, but is estimated at 120 em/year 

(centimeters per year) for the entire study area. Most of 

this precipitation (about 51 percent) evaporates or is 

transpired by plants; the remainder recharges ground 

water or runs off directly to streams, depending on the 

permeability and saturation of the land surface (Leahy 

and Martin, 1993). 

The Coastal Plain is underlain by a heterogeneous wedge of unconsolidated and semi-consolidated 

sediments that overlies a crystalline basement that dips 

steeply toward the Atlantic Ocean (fig. 2, Appendix 2). 

Most of the sediments are siliciclastic, and are derived 

from the erosion of the hard rocks of the Piedmont and 

the Blue Ridge and Appalachian Mountains; however, 

a band of Eocene and Oligocene carbonate rocks (limestone) crops out in south-central North Carolina. In the 

Mid-Atlantic Region of the United States, the wedge of 

Coastal Plain sediments thickens from a few meters at 

the Fall Zone to more than 3,000 m beneath Cape Hatteras, North Carolina (Owens and Gohn, 1985; Gohn, 

1988; Winner and Coble, 1996). Depositional environments range from fluvial to marine, resulting from the 

many marine transgressions and regressions across the 

Coastal Plain since the Cretaceous Period (Appendix 

2). Surficial units are nearly fiat-lying in most areas, 

and are generally Miocene or younger in age. 

Coastal Plain geologic units form a vertical 

series of alternating aquifers and leaky confining units. 

Unconsolidated units contain various amounts of 

gravel, sand, silt, and clay, depending on their depositional environments (Trapp, 1992). Although most 

units yield at least some usable water, permeable gravel 

and sand deposits and carbonate rocks are generally the 

most productive aquifers. Most ground water is 

recharged to an unconfined surficial aquifer and discharges to a nearby surface-water body. A small percentage (approximately 3 percent) of ground water 

from the surficial aquifer recharges confined aquifers 

and follows long regional fiowpaths with accordingly 

long travel times to discharge to larger rivers, estuaries, 

or the ocean (Leahy and Martin, 1993). Ground water 

that is not withdrawn for consumption will ultimately 

discharge to streams as base flow or to other surfacewater bodies. Base flow accounts for about 40 to 95 

percent of streamflow in the Mid-Atlantic Coastal Plain 

(Sinnott and Cushing, 1978; Leahy and Martin, 1993). 

In general, the surficial aquifer in the Mid-Atlantic Coastal Plain includes the upper approximately 30 

m of the Coastal Plain sedimentary sequence; however, 

this thickness varies considerably depending upon the 

Introduction 5 
WEST EAST 

METERS ::... METERS "' 300 CQ 

300 Q) 

<::: 

~ 

Quaternary sedime 

Sea level Sea level 

-l 

L1J 

> L1J 

-l 

<( 

L1J -300 - 300 (I) 

5: 

0 

-l 

L1J 

co 

a: 

0 -600 -600 L1J 

> 0 

co 

<( 

(I) 

a: 

L1J -900 - 900 IL1J 

:2 

~ 

w' 

0 

:::> -1,200 -1,200 I5 

<( 

-1,500 - 1,500 

-1,800 -1,800 

- 2,100 Vertical scale greatly exaggerated - 2,100 

Figure 2. Generalized geologic section through eastern Virginia showing the eastward-thickening sedimentary wedge typical 

of the Mid-Atlantic Coastal Plain (modified from Meng and Harsh, 1988). 

thickness, bedding, and lithology of the sediments 

(Trapp, 1992). For example, on the Delmarva Peninsula near the Delaware-Maryland border, a thick 

sequence of lagoonal silt-clay is an effective confining 

unit within a few meters of the land surface (Shedlock 

and others, 1999). In contrast, in southern New Jersey, 

the combined sands of the Kirkwood and Cohansey 

Formations overlain by the coarse gravelly sands of the 

Bridgeton Formation (Newell and others, 1995, 2000; 

Owens and others, 1999) creates a hydraulically connected surficial aquifer that approaches 150 m in thickness (Zapecza, 1989). 

Acknowledgments 

The hydrogeologic framework was developed 

through a joint effort of the NAWQA program and the 

Geologic Discipline of the USGS. Thoughtful comments on the framework and/or the manuscript for this 

paper were provided by Harry Hansen of the Mary land 

Geological Survey; Kelvin Ramsey of the Delaware 

Geological Survey; and Marian Berndt, William Cunningham, George Harlow, Andrew LaMotte, David 

Powars, Seymour Subitzky, Kelly Warner, and Otto 

Zapecza of the USGS. 

6 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
DEVELOPMENT OF THE REGIONAL SURFICIAL 

HYDROGEOLOGIC FRAMEWORK 

The Mid-Atlantic Coastal Plain is subdivided 

into seven hydrogeologic subregions, primarily on the 

basis of physiography and the predominant texture of 

near-surface sediments. These are primary natural 

physical factors that affect the flow and quality of 

ground water in the surficial aquifer and the base flow 

of small streams. Physiography and sediment texture 

are related to the overall geologic history and setting in 

the Coastal Plain, which are summarized in Appendix 

2. The initial step in creating the framework was to 

compile physiographic and geologic data from published and unpublished sources. This step was facilitated by the various geologic mapping and similar 

investigations that have occurred in the region in recent 

decades (see below). Relatively contiguous hydrogeologic regions were delineated on the basis of the combination of physiography and surficial sediment texture 

(Appendix 1). 

Delineation of Regional Physiography 

Physiography for the Mid-Atlantic Coastal Plain 

(plate 1) was constructed by standardizing and extrapolating previous physiographic interpretations for areas 

within and adjacent to the region. Prominent regional 

scarps and similar topographic features define the three 

major divisions (Inner, Middle, and Outer Coastal 

Plain) and the Alluvial and Estuarine Valleys; the further delineations of subprovinces within these divisions are defined by more subtle topographic or 

geomorphic differences. Physiography for North Carolina and Virginia was largely extrapolated from earlier 

work in South Carolina. Physiographic subprovinces in 

Maryland and Delaware were delineated by extrapolation from earlier work in New Jersey. Delineation of 

regional physiography was guided by the work of 

Colquhoun and others ( 1991 ), who produced a comprehensive regional view of physiography in their map of 

the Quaternary history of the Atlantic Coastal Plain 

from New Jersey through Georgia. 

The physiography of the Virginia and North 

Carolina Coastal Plain was based largely on the physiography developed by Colquhoun ( 1969, 197 4) for the 

Coastal Plain of South Carolina. The broad platform of 

the Coastal Plain can be divided into three physiographic subprovinces with similar land-surface characteristics (Appendix 2). Colquhoun (1969, 1974) 

defined the Upper, Middle, and Lower Coastal Plain in 

South Carolina; these designations were extended 

northward to the Potomac River as the Inner, Middle, 

and Outer Coastal Plain (respectively) with the aid of 

various local studies (Oaks and Coch, 1973; DuBar and 

others, 1974; Daniels and Gamble, 1974; Johnson and 

Peebles, 1986; Cleaves and others, 1987; Mixon and 

others, 1989; Owens, 1989). A fourth physiographic 

subprovince includes the alluvial and estuarine valleys 

of the major rivers that cut across the Coastal Plain, 

which were delineated largely on the basis of topography. The Inner Coastal Plain was further subdivided 

into the Inner Coastal Plain - Dissected Outcrop Belt, 

the outcrop area of the deeply weathered, oldest 

Coastal Plain sediments, and the Inner Coastal Plain -

Upland Sands and Gravels, including the discontinuous 

coarse fluvial sediments that cap hilltops along the 

inner margin of the Coastal Plain. 

The Suffolk Scarp (plate 1, Appendix 2) marks 

the landward extent of the Outer Coastal Plain in this 

interpretation. Spruill and others (1998) applied this 

physiographic division to North Carolina and southern 

Virginia. This boundary coincides with a major hydrologic difference on either side of the scarp; the hydrologic change across the Surry Scarp (Colquoun and 

others, 1991) is generally less pronounced. In the Outer 

Coastal Plain east of the Suffolk Scarp, the land surface 

is exceptionally fiat (Verdin, 1997) and poorly drained, 

and the creeks are almost entirely tidal. Because of the 

low slope of the land surface, the water table is generally close to the land surface and has a very low gradient. This area contains abundant depressional wetlands 

(pocosins and Carolina Bays) that are wet seasonally or 

perennially, whereas in the Middle Coastal Plain (west 

of the Suffolk Scarp), many of these depressions have 

been drained by headward cutting of streams. In addition, the stream drainage network in the Outer Coastal 

Plain is poorly developed because the land surface is 

generally younger than approximately 120,000 years 

(Wehmiller and others, 1988). In contrast, the land surface of the Middle Coastal Plain is 200,000 to approximately 3 million years old, and the stream drainage 

network has been entrenched and extended during 

numerous glacial low stands of sea level (Mixon and 

others, 1989). 

The physiographic classification of the Coastal 

Plain by Colquhoun (1969, 1974) is not easily applicable north of the Potomac River (Appendix 2). Much of 

the Coastal Plain in Mary land, the northern and central 

Development of the Regional Surficial Hydrogeologic Framework 7 
Delmarva Peninsula, and New Jersey has been located 

at a higher elevation than the Coastal Plain to the south 

since the late Pliocene Epoch (Colquhoun and others, 

1991), and deposition of Pleistocene marginal-marine 

units has been minimal outside of the broad valleys of 

Chesapeake and Delaware Bays. Consequently, much 

of the land surface of the northern Coastal Plain has 

been exposed longer than that of the Middle and Outer 

Coastal Plain to the south. Also, the Coastal Plain north 

of the Potomac River has been subjected to a different 

set of weathering processes, including cryoturbation 

and other periglacial soil processes (Newell and others, 

2000). 

A previous physiographic classification for New 

Jersey was extended southward and applied to the 

Coastal Plain of Delaware and Maryland. Newell and 

others (1995, 2000) defined five physiographic subprovinces for the New Jersey Coastal Plain: the Interior 

Plateau, Central Upland, Southern Upland, Interior 

Lowlands, and Coastal Lowlands. These subprovinces 

were modified slightly or renamed for consistency with 

the remainder of the study area (table 1; plate 1). The 

Interior Plateau of New Jersey is equivalent to the Inner 

Coastal Plain - Dissected Outcrop Belt in this interpretation; this subprovince also includes the subcrop areas 

of the Lower Cretaceous units in Delaware, Maryland, 

northern Virginia, and southern North Carolina. The 

Southern Uplands in New Jersey are equivalent to the 

Inner Coastal Plain- Upland Sands and Gravels, 

including the areas of Central Delmarva and southern 

Maryland covered by similar coarse, upland deposits. 

The Coastal Lowlands (New Jersey) are equivalent to 

the Outer Coastal Plain in this physiographic interpretation, with the exception of an upper terrace, which is 

included in the Middle Coastal Plain. Within the Middle Coastal Plain, the Central Upland of New Jersey 

(Newell and others, 1995, 2000) and a similar area of 

southern Maryland between the Patuxent River and 

Chesapeake Bay were further delineated as the Middle 

Coastal Plain- Dissected Uplands. These areas are 

more incised than the remainder of the Middle Coastal 

Plain (hereafter referred to as the Middle Coastal Plain 

- Terraces) (McCartan, 1990; McCartan and others, 

1995; Newell and others, 1995, 2000), although 

extremely permeable sands underlie the area in New 

Jersey (Zapecza, 1989), while the area in Maryland 

contains relatively impermeable silts (Glaser, 1976). 

Delineation of Regional Geology 

Surficial and subcropping geology for the MidAtlantic Coastal Plain (plate 2) were compiled and 

interpreted from available published (Maryland Geological Survey, 1933; Owens, 1967; Cleaves and others, 1968; Owens and Denny, 1978; Owens and Denny, 

1979; Mixon, 1985; North Carolina Geological Survey, 

1985; Owens and Denny, 1986; Mixon and others, 

1989; Ramsey and Schenck, 1990; Oertel and Foyle, 

1995; New Jersey Department of Environmental Protection, 1996; Winner and Coble, 1996) and unpubTable 1. Comparison of physiographic subprovinces developed for New Jersey to those in the remainder of the 

Mid-Atlantic Coastal Plain north of the Potomac River 

Physiographic subprovince within the Coastal Plain 

New Jersey 1 North of the Potomac River for this report 

Interior Plateau Inner Coastal Plain- Dissected Outcrop Belt 

Central Upland Middle Coastal Plain- Dissected Uplands 

Southern Upland Inner Coastal Plain -Upland Sands and Gravels 

Interior Lowlands Alluvial and Estuarine Valleys (in part) 

Coastal Lowlands (upper terrace) Middle Coastal Plain - Terraces 

Coastal Lowlands (remainder) Outer Coastal Plain 

1 From Newell and others (1995). 

8 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
lished sources. Surficial geology was extracted from 

mapping for a wider area of the Atlantic Coastal Plain, 

from Long Island, New York through Georgia (W.L. 

Newell, U.S. Geological Survey, co-author of this 

paper). Formation contacts were interpolated across 

unmapped areas and inconsistencies in nomenclature, 

interpretation, and scale were resolved to the extent 

possible. The greatest available detail from each original map was typically preserved when resolving differences among sources, regardless of the detail in 

adjacent areas. For this reason, the edges of some original sources remain obvious on plate 2. On the Delmarva Peninsula, for example, the individual units of 

the Chesapeake Group are delineated in Delaware 

(Ramsey and Schenck, 1990) but not in Maryland. The 

regional correlation of stratigraphic units is based 

largely on those of Jordan and Smith (1983) and the 

USGS Regional Aquifer-System Analysis Program 

(Meng and Harsh, 1988; Zapecza, 1989; Vroblesky and 

Fleck, 1991; Trapp, 1992; Winner and Coble, 1996). 

Predominant sediment texture for each geologic 

unit (plate 3) was derived from the descriptions of the 

sediments in original publications (see plate 2, Appendix 2) and the stratigraphy in key locations, such as the 

Oak Grove corehole (Virginia Division of Mineral 

Resources, 1980) and the Haynesville corehole 

(Mixon, 1989) in Virginia. The predominant sediment 

texture reflects the dominant overall texture of each 

geologic unit at the regional scale and may not accurately reflect local conditions in all areas. Many important small-scale facies changes among and within 

mapped units were omitted. The Cape May Formation, 

for example, is primarily sandy (as shown on plates 2 

and 3), although it contains an estuarine clay up to 38 

m thick that serves as a local confining unit (Gill, 

1962). Additionally, the boundaries between adjacent 

units as mapped do not necessarily represent abrupt 

textural changes; lateral changes in sediment texture 

may be gradational. The Omar Formation on the southem Delmarva Peninsula is predominantly sandy in the 

east, but becomes gradually more fine-grained towards 

the Chesapeake Bay. 

Mapped geologic units are grouped largely into 

three textural classes: sands and gravels, mixed sediments, and silts and clays (plate 3). Sands and gravels 

are coarse-grained, typically very permeable deposits 

indicative of relatively high-energy depositional areas 

such as beaches, high-gradient streams, or dunes. The 

medium and coarse quartz sands and gravels of the 

Columbia Formation1 on the Delmarva Peninsula were 

deposited as bedload from a braided river system (Jordan, 1964; Hansen, 1971, Groot and Jordan, 1999); fine 

sands of the Choptank Formation were deposited in a 

marine inner-shelf setting (Cleaves and others, 1968; 

Glaser, 1971; Vroblesky and Fleck, 1991). Finergrained, less permeable silts and clays are generally 

deposited in more sluggish environments such as estuaries, swamps, marshes, or the deeper continental 

shelf. The Bacons Castle Formation contains clayey silt 

and silty fine sand deposited in a shallow bay or estuary 

(Meng and Harsh, 1988; Ramsey, 1988; Mixon and 

others, 1989). Geologic units with neither coarse nor 

fine bulk texture are labeled as "mixed sediments." 

These units represent transitional environments (such 

as fluvial deltas) or contain lateral or vertical facies 

changes indistinguishable at the regional scale. The 

Windsor Formation contains a fining-upward sequence 

including sand with gravel, silt, and clay (Oaks and 

Coch, 1973; Mixon and others, 1989). 

In addition to the three major textural classes, the 

geologic maps also include other lithologies that are 

less common to the Coastal Plain. Because of the 

geochemical importance of organic deposits (Drever, 

1997), peat is included in the lithologic description of 

modem swamps and marshes. The subcrop map (plate 

2) includes the only consolidated rocks in the study 

area. The River Bend and Castle Hayne Formations in 

North Carolina form an extremely productive aquifer 

typically comprising alternating beds of marine limestone, sandy limestone, and sand (Winner and Coble, 

1996). Selected subcropping older rocks of the Piedmont Province are shown along the Fall Zone on plate 

2, where they are unconformably overlain by unconsolidated Coastal Plain sediments. 

The geology presented in plate 2 represents the 

lithostratigraphy of the Mid-Atlantic Coastal Plain, 

while the accompanying map of predominant sediment 

texture (plate 3) approximates hydrostratigraphy. 

Lithostratigraphic units are defined on the basis of sediment size, sorting, internal structure, age, mineralogy, 

boundary surfaces (such as unconformities), or other 

properties deemed significant by the original investigators. Conversely, hydrostratigraphic units are delin1 The term "Columbia Formation" is used herein for consistency with current usage of the Delaware Geological Survey (see, 

for example, Ramsey and Schenck, 1990, and Groot and Jordan, 

1999). These and equivalent deposits are also known as the 

"Columbia Group" (Jordan and Smith, 1983). 

Development of the Regional Surficial Hydrogeologic Framework 9 
eated primarily on the basis of texture or related 

hydrologic properties such as permeability or hydraulic 

conductivity; adjacent lithostratigraphic formations 

with similar hydrologic properties are generally 

included in the same hydrostratigraphic unit. The 

delineation of geologic units in publications compiled 

for this study varied; in many areas, only lithostratigraphy or hydrostratigraphy was available. These differences were resolved as much as possible in delineating 

the regional geology, although some inconsistencies 

remain in plate 2 (such as the difference in mapping 

resolution among different states). These inconsistencies likely have a minimal effect on the regional hydrologic framework, which is based largely on the maps of 

predominant sediment texture and physiography. 

Delineation of Hydrogeologic Subregions 

Hydrogeologic subregions within the MidAtlantic Coastal Plain (plate 4) were defined from a 

combination of the physiography (plate 1) and the predominant texture of surficial geologic units (plate 3). 

Some of the hydrogeologic subregions correspond 

directly to the physiographic subprovinces; others were 

generalized within subprovinces based on sediment 

texture (table 2). 

Physiographic subprovinces (plate 1) with relatively consistent surficial sediment texture were translated directly to hydrogeologic subregions, including 

the Outer Coastal Plain (as the Coastal Lowlands, Subregion 1) and the Alluvial and Estuarine Valleys (Subregion 7). The Inner Coastal Plain- Dissected Outcrop 

Belt physiographic subprovince corresponds to the 

hydrogeologic subregion of the same name (Subregion 

6), with the addition of a part of the northern Delmarva 

Peninsula. The upland sands and gravels overlying the 

lower Tertiary and Cretaceous formations of the Inner 

Coastal Plain are particularly thin in this area, so the 

top of the subcropping Vincentown Formation (Owens, 

1967) was used as the southern edge of Subregion 6 in 

this area. This boundary marks the southeastern (downdip) limit of near-surface (subcropping) Lower-Tertiary and Cretaceous formations on the Delmarva Peninsula (plate 2). 

The remaining hydrogeologic framework subregions within the Coastal Plain were defined on the 

basis of predominant surficial sediment texture (plate 

3). The Middle Coastal Plain was subdivided into Subregions 2, 3, and 4 with predominantly mixed, fine, and 

coarse surficial sediments, respectively. The Middle 

Coastal Plain- Dissected Uplands in New Jersey and 

Maryland were included with Subregions 4 and 3, 

respectively, because of similar geomorphology and 

sediment textures. These deposits include the sandy 

and extremely permeable Kirkwood and Cohansey 

Formations in New Jersey and the silty, generally 

impermeable Calvert Formation in Maryland (plate 2). 

For similar reasons, the relatively contiguous broad 

uplands within the Inner Coastal Plain - Upland Sands 

and Gravels on the Delmarva Peninsula and in southern 

New Jersey were included in Subregion4, as well. The 

largely discontinuous upland sand and gravel deposits 

near the Fall Zone within the Inner Coastal Plain 

became Subregion 5. 

THE REGIONAL SURFICIAL HYDROGEOLOGIC 

FRAMEWORK 

The hydrogeologic framework (plate 4) represents a summary of the surficial and near-surface 

hydrogeology of the Mid-Atlantic Coastal Plain on a 

regional scale. The seven hydrogeologic subregions 

are described in terms of variable physiography (plate 

1) and geology (plates 2 and 3 ), the two variables used 

to define the framework. Soils (Schwarz and Alexander, 1995), topography (Verdin, 1997), land use 

(from the early 1990s; Vogelmann and others, 1998), 

and hypotheses about the hydrology and chemistry of 

small streams and shallow ground water (table 2) are 

also compared and contrasted among hydrogeologic 

subregions; these environmental conditions are related 

to the underlying hydrogeologic setting. 

Subregion 1: Coastal Lowlands 

The Coastal Lowlands form the low-relief platform of the Outer Coastal Plain, including the margins 

of the Atlantic Ocean and major estuaries. The land 

surface is flat and low-lying, with altitudes generally 

less than 8 m (fig. 3). The surficial sediments were 

deposited in estuarine and near-shore marine environments during the Holocene and late Pleistocene 

Epochs, and are primarily fine-grained, except for linear ridges of sand associated with ancient shorelines. 

The Coastal Lowlands are extremely poorly 

drained because of their flat topography and low elevation. There are numerous tidal wetlands and pocosins. 

10 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
Table 2. Hydrogeologic subregions within the Mid-Atlantic Coastal Plain 

[km2, square kilometers] 

Land use, early 1990s1 (percent) 

Barren Summary of hypothesized hydrology 

Hydrogeologic subregion Area (km2) Physiographic extent Agriculture Urban Forest land Wetland and water quality 

1 Coastal Lowlands 22,000 Outer Coastal Plain 27 6 20 46 Poor drainage due to low elevation and little 

relief. Shallow water table and abundant 

wetlands; streams sluggish or tidal. Ground 

water and small streams poorly oxidized. 

2 Middle Coastal Plain - 21,000 Middle Coastal Plain - 27 3 48 2 21 Drainage and oxidation varies with geology. 

Mixed Sediment Texture Terraces Moderate topographic relief. 

3 Middle Coastal Plain - 8,000 Middle Coastal Plain - 25 4 60 2 9 Fine sediments and moderate relief promote 

Fine Sediments Terraces and Maryland part runoff and limit infiltration. Essentially no 

of Middle Coastal Plain - unconfined aquifer; most ground water 

Dissected Uplands confined and poorly oxidized. 

4 Middle Coastal Plain - 26,000 Middle Coastal Plain - 39 7 38 15 Coarse sediments promote infiltration and 

Sands with Overlying Gravels Terraces, New Jersey part of oxidation in surficial ground water. Runoff 

Middle Coastal Plain - possible in areas of steep slope. 

Dissected Uplands, and Inner 

Coastal Plain- Upland Sands 

and Gravels on Delmarva 

Peninsula and in southern New 

-f Jersey ::r 

C1l 

:c 

C1l 5 Inner Coastal Plain - 6,000 Inner Coastal Plain- Upland 23 10 59 2 6 Coarse sediments promote oxidation in CQ 

c;· Upland Sands and Gravels2 Sands and Gravels, except on shallow ground water and infiltration, through :I 

!. Delmarva Peninsula and in runoff is great due to large topographic relief. CJ) southern New Jersey Streams typically incised through to older 5. geologic units; this may be reflected in stream (;' 

!: chemistry. 

::::1: 

< c.. 6 Inner Coastal Plain - 11,000 Inner Coastal Plain - Dissected 28 16 46 3 7 Large relief promotes runoff, particularly in 

0 Dissected Outcrop Belt CQ 3 Outcrop Belt areas of fine sediment. Drainage and oxidation C1l 

0 of ground water varies with geology. 

0 

CQ 

(;' 7 Alluvial and Estuarine Valleys 19,000 Alluvial and Estuarine Valleys 22 5 39 32 Poor drainage common due to flat topography 

::t' and fine surficial sediments. Wetlands are t» 

3 common. These are often ground-water C1l 

~ discharge areas. 

~ ;II;' 1

Vogelmann and others (1998). Percentages are rounded to the nearest whole number and may not sum to 100. 2Previously called Middle Coastal Plain- Deeply Dissected Sands with Overlying Gravels (Ator and others, 2000). 3Previously called Inner Coastal Plain (Ator and others, 2000). 
WEST EAST 

METERS METERS 

5 5 

Wetland Wetland Saltwater marsh 

_, 

L.U 

> L.U 

_, Sea level Sea level 

<t 

L.U 

(/) 

5 

0 

_, 

L.U 

C) -5 - 5 / c:c: 

0 Leaky confining unit L.U / > 

0 

C) 

<t 

(/) 

____-/' c:c: -10 - 10 L.U 

IL.U J ~ 

z Confining unit 

L.UCl 

~ 

I- - 15 -15 

~ <t 

- 20 Vertical scale x 20 

EXPLANATION 

~~; ~-=~ -:~ Wetland or marsh 

Brackish water 

- Generalized groundwater flow 

--- - - Water table 

Figure 3. Generalized hydrogeologic section showing idealized flow through Subregion 1, the Coastal Lowlands, on the 

Delmarva Peninsula in Virginia (modified from Speiran, 1996). 

Natural streams are low gradient (if not tidal) and the 

water table is typically very shallow (fig. 3). Natural 

areas are mostly swamps or marshes; "blackwater" 

streams are common. Soil types reflect chronic poor 

drainage and poor oxidation, and soils of swamps and 

marshes contain abundant organic matter. 

Water quality in natural areas of the Coastal 

Lowlands is controlled by the topography and geology. 

The relatively young sediments are poorly weathered. 

Natural shallow ground water is likely well-buffered 

with relatively high pH (near neutral) and conductance; 

however, ground water could be quite acidic in predominantly quartz sediments with weathering organic matter. Major-ion chemistry reflects the available soluble 

minerals. Because of the chronic poor drainage and 

abundant organic matter in the many swamps and 

marshes, poorly-oxygenated ground water is anticipated, except in rare sandy areas. Iron is likely reduced 

and highly mobile in ground water under these conditions and may precipitate in streams. Only the most soluble pesticides applied in such areas are likely to 

infiltrate to ground water through the fine-grained, 

organic-rich soils and sediments. Most of the nitrogen 

that reaches the ground water would occur in reduced 

forms (such as ammonium) or escape as nitrogen gas 

following denitrification. Nitrate is expected only in the 

rare sandy areas. 

Parts of the Coastal Lowlands are artificially 

drained for agriculture, particularly in North Carolina 

and in southeastern Delaware and Maryland. Drainage 

ditches and channelized streams can affect local water 

quality by facilitating runoff from agricultural fields 

(Evans and others, 1989). Applied pesticides, fertilizers, and livestock manure can bypass the natural 

ground-water system and run off quickly to receiving 

water bodies, increasing the likelihood of eutrophica12 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
tion and bacterial contamination. Streams in such areas 

may carry greater loads of nutrients and pesticides than 

would be expected under natural drainage conditions. 

Land use and land cover in the Coastal Lowlands 

reflect the chronic poor drainage. Nearly half (46 percent) of the area is wetlands; another 21 percent is forested or barren (table 2). Only 27 percent of the Coastal 

Low lands is used for agriculture and 6 percent is urban, 

mostly in the Norfolk-Virginia Beach area of Virginia 

and in resort areas along the Atlantic Ocean. 

Subregion 2: Middle Coastal Plain - Mixed 

Sediment Texture 

Subregion 2 includes the broad platform of the 

Middle Coastal Plain just inland of the Coastal Lowlands across most of the Coastal Plain south of Delaware Bay. Surficial sediments were deposited during 

Pleistocene sea-level highstands. Physiographic 

boundaries within this area are typically scarps (such as 

the Suffolk Scarp) or other time-indicator elevation 

breaks that were also formed during Pleistocene transgressions. The land surface is moderately dissected by 

streams, and local relief generally ranges from 5 to 10 

m. The surficial sediments of the Middle Coastal Plain 

were deposited in near-shore marine and estuarine 

environments. Sediment texture varies laterally and 

vertically with changes in depositional systems from 

littoral marine to estuarine and deltaic environments. 

Sediment grain sizes are mixed, and range from coarse 

sands associated with shorelines to clays and silts 

deposited in back-barrier lagoons and estuaries. 

Variable hydrologic and water-quality conditions are expected in Subregion 2, reflecting the variable geology. In well-drained sandy areas, the water 

table is expected to be relatively deep. If the sediments 

are extensively weathered and well-drained, natural 

ground water is probably very dilute and slightly 

acidic. Nitrate or pesticides would have a strong potential to infiltrate to the well-oxygenated shallow ground 

water if applied in such areas. Conversely, poorer 

drainage is anticipated in areas of Subregion 2 with 

finer surficial sediments. As in the Coastal Lowlands 

(Subregion 1 ), abundant organic matter and anoxic 

ground water are expected in such areas. Pesticides are 

less likely to infiltrate to ground water and nitrogen 

species in ground water would be mostly reduced (such 

as in ammonium or organic forms). Iron in ground 

water of such areas is expected to be mobile and may 

precipitate when discharged to streams. Artificial 

ditching is used for agriculture in some poorly drained 

parts of Subregion 2 (such as southeastern Delaware 

and Maryland), with similar hydrologic effects as in the 

Coastal Lowlands. 

The distribution of land uses in Subregion 2 is 

similar to the overall distribution for the Mid-Atlantic 

Coastal Plain (table 2). About two-thirds of the subregion is forested (48 percent) or wetlands (21 percent). 

Another 27 percent is used for agriculture, probably in 

areas with relatively good drainage or artificial ditching. Only 3 percent of Subregion 2 is urbanized. 

Subregion 3: Middle Coastal Plain -Fine 

Sediments 

Subregion 3 is the dissected inner part of the 

Middle Coastal Plain with predominantly fine-grained 

sediments at the land surface (fig. 4 ). The local relief 

ranges from 15 to 45 m. This subregion is associated 

with Pliocene estuarine deposits of the Bacons Castle 

Formation in Virginia and northern North Carolina, and 

fine-grained Miocene and Pliocene marine sediments 

of the Chesapeake Group (primarily the Calvert Formation) in southern Maryland. 

Subregion 3 represents a fairly unique physical 

and geochemical setting in the Coastal Plain. With relatively impermeable sediments (mostly silt) near the 

surface, Subregion 3 probably lacks an extensive surficial aquifer; most usable ground water is likely confined (fig. 4). The marine and estuarine silts of 

Subregion 3 are so impermeable that weathering is 

minimal and chemically reduced compounds probably 

occur in these sediments at shallow depths. As a result, 

natural ground water is expected to be poorly oxygenated and could contain considerable concentrations of 

dissolved minerals. Fine-textured surficial sediments 

and moderate relief would promote overland runoff 

and limit infiltration. For this reason, fairly low concentrations of pesticides and nutrient compounds are anticipated in ground water, but concentrations could be 

elevated in streams during high flows in areas where 

they are applied. 

Development in Subregion 3 is fairly limited 

(table 2). Sixty percent of the area is forested; another 

11 percent is wetlands or barren. Less than 30 percent 

of Subregion 3 has been developed for agricultural (25 

percent) or urban ( 4 percent) use. 

The Regional Surficial Hydrogeologic Framework 13 
--' 

UJ 

~ --' 

~ Cl) 

NORTHWEST 

METERS 

60 -

Relatively impermeable surface sediments 

SOUTHEAST 

METERS 

' 60 

5 

0 

--' UJ 

co 

a: 

0 

UJ 

> 

0 

co 

<! 

Cl) 

a: 

promote surface runoff rather than infiltration to Undifferentiated surficial deposits 

ground water Most ground water is confined -\ 

30 L- / ·s Bacons Castle Forma ~ an~ Yorktown Formation (fine member) ~ _ .------""-,___--,t- 30 - - ?-" l. - ~ 7:-- -~----- ·-

UJ 

1-

LJ.J 

-------"" -- Stream ///___ ! \,, .// / 

Sea _ '-...__ ~ " } \ Eastover Formation./nd sand aco~s Castle F~rmation ~ _ Sea 

:2 

z 

LJ.J0 

::::> 

tlevel 1---_____ ___ _: ____ -;..,.....,'-~..---:o-----;--.--.--c-....,~:-:-c-:-;::-=~~----------t level 

St Marys Formation and clay facies of Eastover Formation 

Calvert Formation 

5 Lower Tertiary formations, undivided 30-L--------------------------------~__: ____ __: ______________________________ -L _30 <! Vertical scale x 20 

EXPLANATION 

Predominantly sand-Relatively high permeability 

Silty clay and fine sand-Relatively low permeability 

---- Generalized flow 

----- Water table 

Figure 4. Generalized hydrogeologic section showing idealized flow through Subregion 3, the Middle Coastal Plain - Fine 

Sediments, along the James River in southern Virginia (modified from Meng and Harsh, 1988). 

Subregion 4: Middle Coastal Plain - Sands with 

Overlying Gravels 

Subregion 4 is defined by the superposition of 

upper-delta-plain sands and gravels that overlie marine 

inner-shelf sands on the Middle Coastal Plain. This 

stratigraphic setting occurs in New Jersey, the Delmarva Peninsula, southern Maryland, and central and 

southern North Carolina. The underlying sediments are 

typically Miocene and Pliocene units of the Chesapeake Group, such as the Choptank Formation in southern Maryland, the Yorktown Formation in North 

Carolina, and the Cohansey Formation in New Jersey. 

The original broad, flat upland surface has not been 

completely dissected by developing stream networks. 

Local relief is generally less than 30m, but the land surface is more deeply incised near the major rivers that 

cut across the Middle Coastal Plain. 

Good drainage is anticipated in Subregion 4 due 

to the moderate topographic relief and underlying 

sands and gravels (fig. 5). Coarse surficial sediments 

promote infiltration of water and oxidation in the surficial aquifer, which is more than 100 m thick in parts of 

New Jersey. Limited overland runoff is anticipated, but 

may be significant in some developed or unusually 

steep areas. Stream channels are expected to be generally sandy, but may contain considerable amounts of 

organic matter. Because sediments in this subregion are 

composed primarily of relatively insoluble quartz, natural water quality probably reflects the chemistry of 

precipitation. Streams and ground water in natural 

areas may be fairly dilute with relatively low conductance and pH. 

Streams and ground water in Subregion 4 are 

expected to be particularly vulnerable to anthropogenic 

effects. The coarse permeable sediments of the area 

generally provide little protection to ground water from 

chemical applications at or near the land surface. 

Nitrate is the dominant anticipated nitrogen species in 

areas of fertilizer or manure application and may travel 

a considerable distance from its source in the well-oxygenated ground water. Nitrate concentrations also 

could be quite high in streams, but may be lower due to 

biological uptake or denitrification in streambed 

organic matter. Applied pesticides also may move fairly 

easily into and through the aquifers of this subregion, 

although pesticide mobility may be limited by organic 

matter in streambeds or the soil. 

Land use and land cover in Subregion 4 reflect 

the excellent drainage. Nearly 40 percent of the subre14 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
... 

U1 

....J 

w 

> 

UJ 

....J WEST <( 

~ METERS 

5 30 0 

....J 

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co 

c:: Sea level 0 

UJ 

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co 

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-30 

- 60 

-90 

Vertical scale x 20 

Shallow ground water is typically 

well oxygenated along entire flowpath to stream 

EXPLANATION 

Aquifer sediments-Relatively high permeability 

Confining layer-Relatively low permeability 

- Generalized flow 

----- Water table 

EAST 

--

METERS 

30 

- 30 

- 60 

- 90 

Figure 5. Generalized hydrogeologic section showing idealized flow through Subregion 4, the Middle Coastal Plain- Sands with Overlying Gravels, on the Delmarva 

peninsula (modified from Bachman and Wilson, 1 984) . 
gion is used for agriculture (table 2); no other subregion is more than 28 percent agricultural. Another 38 

percent of Subregion 4 is forested and 15 percent is 

wetland (mostly along streams). Seven percent of Subregion 4 is urban; much of the urbanization is in New 

Jersey near Philadelphia and New York City. 

Subregion 5: Inner Coastal Plain- Upland Sands 

and Gravels 

Subregion 5 includes parts of the innermost 

Coastal Plain near the Fall Zone, which are overlain by 

a sheet of fluvial sands and gravels and are generally 

deeply dissected. Local relief ranges from 30 to 45 m. 

The upland gravels range in age from Miocene to 

Pliocene and overlie nearshore marine sands or saprolite of crystalline rocks (fig. 6). Surficial units are commonly completely incised and frequently there is no 

hydrologic connectivity between upland deposits on 

adjacent hills (fig. 6). 

_J 

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NORTHWEST 

METERS 

60 

45 

30 

Ground water is typically 

well-oxygenated in upland 

sand and gravel 

' ' \ 

This subregion also includes the sand and gravel 

caps on adjacent Piedmont hills, which are erosional 

remnants of a previously wider area of Coastal Plain 

sediments that overlay the outer margin of the Piedmont. Because the sands and gravels are very permeable, they are difficult to erode; rainwater percolates 

through the sands rather than eroding them. In many 

areas, the surrounding saprolite of the Piedmont is 

eroding faster than the gravel caps, which further 

enhances the local relief. 

The hydrology of Subregion 5 is similar to that 

of Subregion 4. Surficial sediments are extremely permeable and promote rapid infiltration to well-oxygenated ground water, although surface runoff could be 

considerable in areas with steep slopes. Unlike conditions in Subregion 4, however, these sediments are laterally discontinuous and relatively thin (fig. 6). Ground 

water within the fluvial sands and gravels might travel 

only relatively short distances before encountering 

much older underlying geologic units, with very differSOUTHEAST 

METERS 

60 

Ground-water chemistry may change 

with flow to stream through 

less permeable sediment 

45 

30 

15~--------------------------------------------------------J_15 

Vertical scale x 20 

EXPLANATION 

Coarse, fluvial upland sand and gravel-High permeability (Brandywine Formation) 

- Marine silty sand-Intermediate to high permeability (Choptank Formation) 

Marine silt and clay-Low permeability (Calvert Formation) 

- Generalized flow 

- - -- Water table 

Figure 6. Generalized hydrogeologic section showing idealized flow through Subregion 5, the Inner Coastal Plain- Upland 

Sands and Gravels, in southern Maryland (modified from Krantz and Powars, 2000). 

16 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
ent geochemical environments. The chemistry of 

stream water can be affected by any transformations 

that occur as the ground water passes through these 

older units. 

Ground-water quality within the upland gravels 

of Subregion 5 is expected to reflect local land uses, 

although the chemistry of even small streams may 

reflect geochemical alterations in older underlying geologic units. Fairly dilute and slightly acidic natural 

ground-water quality is anticipated within the upland 

sands and gravels. The predominantly quartz sediments 

are deeply weathered and would provide few soluble 

minerals to alter the chemistry of infiltrating precipitation. As in Subregion 4, ground water within the upland 

gravels of Subregion 5 is particularly vulnerable to 

contamination from surficial sources. Nitrate is likely 

the dominant nitrogen species in the well-oxygenated 

ground water of the upland gravels, but may be lost to 

denitrification if the water flows through older sediments with reducing conditions on the way to streams. 

Pesticides are likely transported relatively easily to 

ground water in the upland gravels. Pesticides in 

streams may be mostly attributable to surface runoff; 

much of the ground-water discharge to streams will be 

from older, possibly confined aquifers. Streams also 

may contain iron mobilized in the reducing conditions 

of confined aquifers. 

Much like adjacent Subregion 3, Subregion 5 is 

dominantly forested (59 percent) and about 25 percent 

agricultural (table 2). Subregion 5 is also one of the 

most urbanized subregions (10 percent). Most of the 

urban land is near Richmond, Virginia, or the small part 

of Subregion 5 in Pennsylvania. Sand and gravel pits 

are common in parts of Subregion 5. 

Subregion 6: Inner Coastal Plain- Dissected 

Outcrop Belt 

Subregion 6 is the outcrop and subcrop belt of 

lower Tertiary and Cretaceous formations along the 

Fall Zone (fig. 7). Locally, these older units may be 

covered with upper Tertiary or Quaternary sands and 

gravels, particularly in the northern Delmarva Peninsula (fig. 7). Tertiary and Cretaceous units have generally been exposed at or near the land surface for 

millions of years, and are typically deeply weathered. 

Some units are leached and oxidized to depths of tens 

of meters. The permeability and geochemistry of units 

in Subregion 6 are widely variable due to original differences in sediment texture in complex depositional 

environments and post -depositional alteration of the 

sediments (leaching and weathering). For example, 

quartz sand is dominant in fluvial formations, and glauconite is common in marine units. These lithologic 

contrasts affect aquifer recharge and water-quality 

characteristics. The landscape is deeply dissected with 

75 to 90 m of relief, and streams typically cut into the 

subcropping units. 

Variable hydrologic characteristics are expected 

in Subregion 6, reflecting the variable permeability and 

lithology of underlying geologic units. In areas with 

permeable sand or gravel units at the land surface, infiltration is more likely than surface runoff, and well-oxygenated ground water is likely in a shallow surficial 

aquifer. These areas also provide most of the recharge 

to the lower Tertiary and Cretaceous formations as they 

become major regional confined aquifers toward the 

east and south (Leahy and Martin, 1993). Conversely, 

in areas with surficial silts or clays, most precipitation 

probably runs off across the land surface. Most of the 

ground water in these areas is likely confined and under 

reducing conditions. Although infiltration rates vary, 

runoff could be an important transport mechanism for 

nutrients, pesticides, or other surficial contaminants to 

streams in areas of the subregion with steep slopes, 

regardless of sediment texture. 

In North Carolina, Subregion 6 includes the 

Sand Hills (fig. 1), with flat-topped or rounded hills 

that range from 150 to 200 m in elevation and up to 100 

m of local relief. The hills are capped by loose eolian 

and fluvial sand overlying a fluvial-deltaic deposit of 

intercalated clay and clay-silt lenses with layers of 

hematite-cemented sandstone of the Middendorf Formation (Lyke, 1992). Both units are completely incised 

by stream valleys, which restrict the movement of 

water to deeper, confined parts of these units. Despite 

the relatively steep slopes in some areas, infiltration 

and recharge rates to these sandy areas are particularly 

high and some wells yield more than 100 gallons of 

water per minute (Robison and Mann, 1977). 

Water quality in the Inner Coastal Plain - Dissected Outcrop Belt is also expected to vary with geology. Natural ground water in sandy areas is likely 

dilute and acidic (as in Subregions 4 and 5); iron may 

be common, particularly in glauconitic units. Although 

concentrations are expected to vary with land use, 

nitrate would dominate nitrogen speciation in ground 

water of sandy areas, but could be lost to denitrification 

The Regional Surficial Hydrogeologic Framework 17 
... 

co 

WEST 

METERS 

w 

> 90 

o_. 60 tOw 

<(> 

CI)W 

a:-' 

W<( 30 1-w 

WCI) Sea level ~$: 

Zo --' 

ujw -30 ooo 

~a: -60 t::o 

~ <( -90 Vertical scale x 20 

Water may infiltrate readily 

and ground water may be welloxygenated in permeable deposits 

Ground-water quality varies with variable EAST 

geology. Impermeable deposits and steep METERS 

slopes may pro surface runoff 90 

60 

Potomac 30 

River 

"-,.. 

_..,.Q~ :=:::::::::==~~iii~~;~~~ 1 Sea level 

- 30 

-60 Potomac Group ......_ 

-- --------------------------------------------------------------

--- ~-90 

EXPLANATION 

Aquifers-Relatively permeable 

.. Primarily clay and silt-Relatively impermeable 

- Generalized flow 

----- Water table 

Figure 7. Generalized hydrogeologic section showing idealized flow through Subregion 6, the Inner Coastal Plain- Dissected Outcrop Belt, in southern Maryland 

and northern Virginia (modified from Otton, 1955). 
as aquifers become confined. Pesticide transport to 

ground water in these areas may be mitigated by loamy 

soils. Water quality in confined aquifers will likely be 

less affected by local land use, as in Subregion 3, and 

more affected by land use in upgradient recharge areas. 

The Inner Coastal Plain - Dissected Outcrop 

Belt is the most urbanized of the seven hydrogeologic 

subregions; 16 percent of the area has been developed 

for residential, commercial, or industrial purposes 

(table 2). This relatively large percentage of urbanization is due to the position of the subregion along the 

Fall Zone, where most major Mid-Atlantic cities (such 

as Baltimore, New York, Philadelphia, Richmond, and 

Washington) are located. Much (28 percent) of the 

remainder of the subregion is agricultural, although, as 

in most subregions, more than half of the Inner Coastal 

Plain - Dissected Outcrop Belt remains forested ( 46 

percent) or wetlands (7 percent). 

Subregion 7: Alluvial and Estuarine Valleys 

Subregion 7, the Alluvial and Estuarine Valleys, 

includes the incised valleys of the major rivers that cut 

across the Coastal Plain, commonly southeastward, 

perpendicular to the regional strike. The sediments that 

fill the valleys range in age from Pliocene to Holocene, 

although most are middle Pleistocene or younger. The 

deeper parts of the valleys are filled by coarse-grained 

alluvial sediments; the upper section of the infill 

sequence is typically composed of fine-grained, 

organic-rich sediments deposited in alluvial floodplain or estuarine environments (fig. 8). Sediment in 

the larger rivers generally contains a rich suite of minerals transported from the Piedmont and the Blue 

Ridge and Appalachian Mountains. 

The surficial hydrology of the Alluvial and Estuarine Valleys is controlled by the relatively impermeable uppermost sediments and flat topography. The 

minor relief and shallow slopes within the valleys promote infiltration instead of surface runoff, in spite of 

the fine-grained surficial sediments. Wetlands are common. The abundance of organic matter and fine-grained 

silt and clay in the surficial deposits can lead to reducing conditions in shallow ground water, although welloxygenated ground water is expected within sandy 

surficial sediments. Ground-water flowpaths in subregion 7 are probably relatively short, particularly in the 

narrower valleys to the north (fig. 8). 

Given the variable hydrologic conditions and 

land use, water quality in the Alluvial and Estuarine 

Valleys is most likely variable, but largely reflects the 

generally poor drainage and reducing conditions. Infiltrating precipitation is expected to be well buffered by 

the available soluble minerals in the relatively young, 

poorly drained sediments. Natural ground water in 

such areas could have relatively high conductance and 

pH (near neutral), but ground water in relatively insoluble quartz sediments would more likely be acidic. In 

flat areas with fine-grained surficial sediments, ammonia and organic nitrogen are the dominant expected 

nitrogen species. Pesticide mobility is likely limited in 

such areas by the fine-grained sediment, low gradient, 

and abundant organic matter. In areas with sandy, more 

permeable sediments, nitrate or pesticides may be 

readily transported to ground water. Overland transport 

of nutrients, pesticides, and other potential surficial 

contaminants is limited in the valleys by the flat topography. 

Nearly one third (32 percent) of the Alluvial and 

Estuarine Valleys is wetlands, reflecting the chronic 

poor drainage (table 2). Another 39 percent of the subregion is forested, while only 22 percent is used for 

agricultural purposes and 5 percent is urban. 

EVALUATION OF THE REGIONAL FRAMEWORK 

AT THE LOCAL SCALE 

Numerous local-scale water-quality and hydrologic studies have been conducted recently throughout 

the Mid-Atlantic Coastal Plain (fig. 9). Results of these 

local studies were examined within the context of the 

hypotheses presented in the previous section about predominant processes controlling regional chemical 

transport and transformations in each subregion. 

Although the regional framework is not intended for 

application at the local scale, comparisons to localscale hydrogeology in different areas. demonstrate the 

range of hydrogeologic conditions in some subregions. 

An understanding of this hydrogeologic variability will 

help to determine the limitations on water-quality or 

hydrologic hypotheses at different scales in the context 

of the regional framework. 

Variable redox conditions and permeability 

caused by differences in geomorphology and depositional environments are the major natural processes 

affecting the transport and transformation of chemicals 

in ground water and surface water throughout the 

Evaluation of the Regional Framework at the Local Scale 19 
-' 

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cr: 

0 

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0 

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cr: 

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UJ0 

::::> 

I-

~ ~ 

WEST 

METERS 

15 

Sea level 

- 15 

- 30 

--45 

' ' ' 

~ 

Sand 

and 

gravel 

Ve rti cal scale x 20 

Alluvial and Estuarine Valleys (Su bregion 7) 

Potomac River 

'-....... 

s;• '""'"'"' 1 

Potomac Group 

EXPLANATION 

---+ Generalized groundwater flow 

----- Water table 

Sand and gravel 

EAST 

METERS 

15 

Sea level 

- 15 

- 30 

--45 

Figure 8. Generalized hydrogeologic section showing idealized flow through Subregion 7, the Alluvial and Estuarine Valleys. 

near Washington, D.C. (modified from Owens. 1967). 

20 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
0 

n 

"' .,. 

2. 

L_--~~~ ~~~~--L-------~----------_j~ Base map from U.S. Geological Survey digital data; i~ 

1:100,000; Lambert conic conformal projection; 

North American Datum of 1983 

EXPLANATION 

Hydrogeologic subregions 

c::::::::J Subregion 1-Coastal Lowlands 

IIIIIIIMIIIII 

® 

© 

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® 

® 

@ 

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CD 

Q) 

® 

© 

® 

® 

@ 

® 

@ 

:t®.:~:~ 

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® 

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Subregion 2-Middle Coastal Plain- Mixed 

Sediment Texture 

Subregion 3-Middle Coastal Plain- Fine 

Sediments 

Subregions 4-Middle Coastal PlainSands with Overlying Gravels 

Subregion 5-lnner Coastal Plain- Upland 

Sands and Gravels 

Subregion 6--lnner Coastal Plain -

Dissected Outcrop Belt 

Subregion 7-AIIuvial and Estuarine Valleys 

Local study sites 

25 

Spruill and others, 1997, 1998 

Richardson and Brockman, 1992 

Speiran, 1996 

Speiran, 1996; Hamilton and others, 1993 

Werkheiser, 1990 

Johnson, 1999 

Evans and others, 1989 

Evans and others, 1989 

Evans and others, 1989 

Evans and others, 1989 

Denver, 1986; Denver, 1993; Hamilton and 

others, 1993; Koterba and others, 1993 

Hamilton and others, 1993 

Correll and others, 1992 

Gilliam and others, 1996 

Gilliam and others, 1996 

Hamilton and others, 1993; Bohlke and 

Denver, 1995 

Denver, 1993 

Stackelberg and others, 1997; Kauffman and 

others, 2001 

Wilson and Fleck, 1990 

Bachman and Ferrari, 1995 

Vowinkel and Battaglin, in press 

Harlow and Bell, 1996 

Froelich and others, 1978 

McFarland, 1995 

McFarland, 1997 

Brown, 1958 

50 75 100 MILES 

0 25 50 75 100 KILOMETERS 

Figure 9. The location of selected local-scale studies within the Mid-Atlantic Coastal Plain. 

Evaluation of the Regional Framework at the Local Scale 21 
Coastal Plain. Although one chemical environment 

may dominate, each subregion exhibits a range of 

redox conditions. Where variability in the physical setting is lowest (as in Subregions 1, 3, 4, and 5), variability in the redox conditions is likewise hypothesized to 

be low, and differences in water chemistry may be 

closely related to differences in land use or chemical 

applications. Where the physical setting is more variable (as in Subregions 2, 6, and 7), a greater variability 

is expected in the chemical environments that develop. 

Subregion 1: Coastal Lowlands 

Local studies indicate that ground-water quality 

in the Coastal Lowlands (Subregion 1) is predominantly influenced by reducing conditions in poorly 

drained shallow aquifer sediments. Ground water is 

well-oxygenated, however, in isolated areas of Subregion 1 with well-drained sandy soils and aquifer sediments, such as in beach-ridge or dune deposits. 

In North Carolina, ground-water quality in agricultural areas of Subregion 1 is related to soil drainage 

and organic content. In 1994 and 1995, nitrate concentrations in ground water of the surficial aquifer in these 

areas with poorly drained soils (fig. 9, site A) had a 

median concentration of only 0.05 mg/L 2 (milligrams 

per liter) (Spruill and others, 1997). Low concentrations of nitrate were attributed to reducing conditions 

in shallow ground water that develop because of the 

poor soil drainage and the high organic content of surficial sediments. Concentrations of ammonia and 

organic carbon in these samples were relatively high, 

compared to other nearby parts of the Coastal Plain. 

Where soils are moderately well-drained, the median 

nitrate concentration was slightly higher (0.2 mg/L); 

water from one well had a concentration of nitrate 

greater than 7 mg/L. Overall, nitrate concentrations in 

ground water were inversely correlated with the 

organic content of the water; water with more than 2 to 

3 mg/L of dissolved organic carbon generally had less 

than 2 mg/L of nitrate. Atrazine was detectable in some 

shallow wells, although rarely at concentrations 

exceeding 0.1 !lg/L (micrograms per liter) (Ator and 

Ferrari, 1997). 

Similar ground-water quality is also attributed to 

soil drainage and organic content in other areas of Sub2 Contrations of nitrogen species cited in this report are in 

equivalent concentrations of elemental nitrogen. 

region 1. In York County, Virginia (fig. 9, site B) in 

1990, nitrate concentrations in ground water from 21 

wells were as high as 16 mg/L, although the median 

was less than 0.1 mg/L. While reducing conditions 

prevailed in the surficial aquifer, nitrate was stable in 

some well-drained sandy zones (Richardson and 

Brockman, 1992). In an agricultural field at Leatherberry Creek in Accomack County, Virginia (fig. 9, site 

C) in 1993, nitrate was not detectable and dissolved 

oxygen was less than 1 mg/L in ground water 

recharged through fine-grained sediments with high 

organic content. In ground water from sandy sediments with low organic content, however, nitrate concentrations ranged from 9.9 mg/L to 14 mg/L, and 

dissolved oxygen was greater than 4 mg/L (Speiran, 

1996). Subregion 1 near Townsend, Virginia (fig. 9, site 

D) contains forests and salt marshes underlain by 

mixed coarse and fine sediments with abundant organic 

matter; ground water contains little dissolved oxygen. 

Speiran ( 1996) found that nitrate concentrations in 

ground water flowing through this area from an adjacent agricultural field decreased with increasing distance from the field due to denitrification. In Somerset 

County, Maryland (fig. 9, site E), dissolved iron 

(present under reducing conditions) was the most common water-quality problem reported in the surficial 

aquifer; nitrate contamination has been reported in 

small areas of well-drained soils (Werkheiser, 1990). 

Iron and sulfur are also widespread in the ground water 

of Virginia Beach, Virginia (fig. 9, site F) (Johnson, 

1999). 

Tile drains and ditches that intercept the water 

table have been installed to promote soil drainage for 

agriculture throughout Subregion 1. In North Carolina, 

they are considered significant sources of nitrate delivery to streams as they oxidize the surface layer of the 

soils and promote localized nitrification (Evans and 

others, 1989). Nitrate is lost to denitrification at depth 

in the surficial aquifer beneath artificial drainage systems at four water-management research sites (fig. 9, 

sites G, H, I and J), although it is present in the ditches 

that drain the top of the soil layer (Evans and others, 

1989). In Subregion 1 within the Albemarle-Pamlico 

Drainages in 1994 and 1995 (fig. 9, site A), nitrate was 

barely detectable in ground water discharging to 

streams, and concentrations were slightly higher in the 

streams themselves (Spruill and others, 1998). 

22 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
Subregion 2: Middle Coastal Plain- Mixed 

Sediment Texture 

The variable depositional environments and sediment textures in Subregion 2 are reflected in the variability of local water quality. Aquifer and stream 

conditions in the coarse-grained areas of this subregion 

resemble conditions in parts of Subregion 4. Where 

finer-grained sediments predominate, however, conditions are similar to those in Subregion 1. 

The variable hydrogeology of Subregion 2 is 

particularly evident on the Delmarva Peninsula 

(Hamilton and others, 1993). Near Fairmount, Delaware (fig. 9, site K), Subregion 2 is underlain by a thick 

sequence (more than 27 m) of predominantly sandy 

sediments. Ground water is well-oxygenated throughout the surficial aquifer and the chemical composition 

of the water reflects the predominance of agriculture in 

aquifer recharge areas. Nitrate (at concentrations as 

high as 41 mg/L) and other chemicals associated with 

fertilizer, manure, and lime applications are present 

throughout the flow system, including at the base of the 

aquifer, and in a small local stream system (Denver, 

1986). Pesticides commonly used on com and soybean 

crops were also detected in ground water at low concentrations during the late 1980s (Denver, 1993). Pesticides were most common in shallow parts of the 

system associated with agriculture and were less common at depth (Koterba and others, 1993). 

Near Townsend, Virginia (fig. 9, site D), the surficial aquifer of Subregion 2 ranges from about 7 to 14 

m thick, and includes permeable sand and gravel with 

some shells. As in Fairmount, land use is predominantly agricultural and ground water is well-oxygenated. Nitrate concentrations in ground-water samples 

collected during the late 1980s and early 1990s were as 

high as 34 mg/L (Hamilton and others, 1993; Speiran, 

1996). 

Near Willards, Maryland (fig. 9, site L), Subregion 2 is very similar to Subregion 1. The area is mostly 

flat and poorly drained with woodlands and swamps. 

Agriculture is common, although most of the fields are 

artificially drained. All of the natural streams in this 

area and the Pocomoke River have been artificially 

channelized. Surficial sediments in this area of Subregion 2 include a relatively thin (about 3- to 9-m thick) 

sandy layer with high organic content underlain by 

clay, silt, peat, and sand that form a discontinuous confining layer over more sand. Sand dunes with residential and agricultural land use occur on the surface in 

some areas. In the early 1990s, chemical conditions in 

ground water of the surficial sandy aquifer ranged from 

well-oxygenated (with nitrate concentrations as high as 

9.8 mg/L) to reducing (with undetectable nitrate) 

(Hamilton and others, 1993). Small-scale changes in 

redox conditions were evident in water from some 

shallow wells where both nitrate (indicating oxygenated conditions) and dissolved iron (indicating reducing conditions) were detected. Concentrations of 

nitrate in surface water from the area varied seasonally 

from about 5 mg/L to undetectable. The highest concentrations occurred in the winter and spring (when 

drainage from ditch systems is greatest) and the lowest 

occurred in the summer (when the water table is lower 

and ditch systems are dry or stagnant). 

Subregion 3: Middle Coastal Plain- Fine 

Sediments 

Subregion 3 has no continuous unconfined aquifer; fine-grained estuarine and marine sediments dominate the surficial deposits in most areas. Most ground 

water used in this region is withdrawn from confined 

aquifers, although some shallow unconfined wells may 

be used for domestic supply (Meng and Harsh, 1988). 

Elevated concentrations of nitrate have been measured 

in a few shallow wells near agricultural areas of Subregion 3 within the Patuxent River watershed (McFarland, 1995). 

Nutrient concentrations in streams of Subregion 

3 in Mary land indicate that nitrate is not transported to 

streams in base flow, possibly due to denitrification 

prior to ground-water discharge. Synoptic surveys of 

nutrient concentrations in small tributaries of the 

Patuxent River during base flow were conducted in 

1994 and 1995 (Preston, 1996). Although sampled 

streams drain watersheds comprising up to 70-percent 

agriculture, the median nitrate concentrations in stream 

water never exceeded 0.5 mg/L, and concentrations 

were greater than 2.0 mg/L in only 2 percent of the 

samples. The fine-grained surficial sediments of this 

area of Subregion 3 have a high potential for denitrification (Krantz and Powars, 2000). 

In the Rhode River watershed in Anne Arundel 

County, Maryland (fig. 9, site M), Subregion 3 is 

underlain by approximately 4 m or less of permeable 

sediments overlying a shallow confining layer. The 

confining layer forces ground water from upland agriEvaluation of the Regional Framework at the Local Scale 23 
cultural areas to flow through an anoxic zone beneath a 

riparian forest prior to discharging to the river. Nitrate 

concentrations in ground water decrease from as high 

as 10.5 mg/L to below 1 mg/L as water flows beneath 

the forest, likely due to denitrification (Correll and others, 1992). 

Subregion 4: Middle Coastal Plain- Sands with 

Overlying Gravels 

The surficial aquifer in Subregion 4 is very thick 

and permeable; ground water and streams of Subregion 

4 are particularly vulnerable to contamination from 

chemicals applied to the land surface. Nitrate contamination, for example, has been documented throughout 

the subregion (Bachman, 1984; Denver 1986; Andres, 

1991; Stackelberg and others, 1997; Spruill and others, 

1998; Clawges and others, 1999). Although relatively 

high concentrations of contaminants are typical in shallow ground water in areas of application, concentrations in stream base flow are more variable and 

generally lower. Base flow represents a mixture of 

ground water from the entire watershed, including any 

areas with little or no chemical application. Also, 

ground water from longer flowpaths is often relatively 

old and reflects historical application rates. Once discharged to the stream, water can undergo a variety of 

chemical changes, including denitrification, biologic 

nutrient uptake, sorption or desorption of charged ions, 

or degradation of organic compounds. 

In areas of Subregion 4 in North Carolina (fig. 9, 

sites Nand 0), excess nitrogen was detected in ground 

water beneath well-drained soils even when farmers 

applied recommended amounts of nitrogen (Gilliam 

and others, 1996). The surficial aquifer ranges from 3 

to 10 m thick beneath these sites. The mean concentration of nitrate in some wells was greater than 10 mg/L; 

the concentration at one well near animal-waste application was 190 mg/L. Nitrate concentrations decreased 

with depth in the surficial aquifer at both sites, although 

nitrate was present at the base of the surficial aquifer. 

Concentrations of nitrate in the streams adjacent to 

these sites ranged from 3 to 12 mg/L, although these 

samples may reflect contributions from overland runoff 

as well as base flow. 

Some hydrogeologic variability is evident within 

Subregion 4 on the Delmarva Peninsula. Across the 

Peninsula, the spatial distribution of nitrate in Subregion 4 in areas of thick, sandy surficial sediments is 

related to land use, drainage patterns, and soil (Shedlock and others, 1999). Areas with well-drained soils 

and incised streams (the Well-Drained Upland of 

Hamilton and others, 1993) typically had the highest 

median concentrations of nitrate in ground water, 

despite relatively long ground-water flowpaths. These 

areas also had the greatest concentration of agriculture, 

however. Areas where forests and forested wetlands 

were interspersed with agricultural fields and poorly 

incised streams (the Poorly Drained Upland) had lower 

median nitrate concentrations. The spatial distribution 

of nitrate in stream base flow was similar, although 

median surface-water concentrations were lower than 

median ground-water concentrations in both areas. 

Near Locust Grove, Maryland (fig. 9, site P) (in 

the Well Drained Upland), variable ground-water quality is primarily related to variable chemical application 

rates rather than chemical changes within the aquifer. 

The surficial aquifer of Subregion 4 in this area ranges 

from about 7 to 22 m thick; land use is more than 95 

percent agricultural (Hamilton and others, 1993). 

Ground water in the surficial aquifer system is aerobic 

throughout much of the flow system, although some 

evidence of denitrification was found near the base of 

the aquifer at the contact with the deeper confining bed. 

In the early 1990s, concentrations of nitrate in ground 

water ranged from 1.3 to 15 mg/L, and decreased with 

depth and age of water in the flow system. Differences 

in ground-water nitrate concentrations throughout 

most of the aquifer system were related to changes in 

fertilizer application rates over time, and not denitrification (Bohlke and Denver, 1995). Nitrate concentrations during base flow in Chesterville Branch, a local 

stream, were between 9 and 10 mg/L during this 

period. Chemical and isotopic data indicate that 

ground-water discharges relatively unaltered to Chesterville Branch through sandy streambed sediments, 

bypassing any potential chemical changes in the riparian zone. 

Near Vandyke, Delaware (fig. 9, site Q) (in the 

Poorly Drained Upland), local reducing conditions and 

denitrification occur near a wetland within Subregion 

4. This area is mostly agricultural with a wooded 

depressional wetland containing a seasonal pond (Denver, 1993). The surficial aquifer ranges from 10 to 14 

m thick. Topography is hummocky and the water table 

ranges from above land surface near the depressional 

wetland during a period of high water table to 2 m 

below the depression during a dry period. The water 

24 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
table ranged from 1 to 3 m below land surface beneath 

local topographic highs. Surficial sediments are generally sandy except near the depression where they are 

finer-grained and organic-rich. Ground-water flowpaths are short and localized and vary temporally, particularly around the depressional wetland. During wet 

periods, when the pond contains water, slow infiltration 

through pond sediments recharges the surficial aquifer 

and forn1s a mound on the water table. During dry periods, the water table is below the pond depression and 

relatively fiat. From 1988 through 1990, concentrations of nitrate were as high as 9 n1g/L beneath topographic highs, and ranged from less than 0.1 to 5 mg/L 

near the depression. Seasonal water-quality analyses 

were similar in upland wells and varied near the 

depression where reducing conditions affected water 

chemistry during periods of high water table and pondwater infiltration. 

Subregion 4 in New Jersey is underlain by highly 

permeable sands and gravels that range in thickness 

frmn less than 15m in the northwest to more than 150 

m in the southeast (Zapecza, 1989 ). The water table is 

generally shallow and ranges from 0 to 14 m below 

land surface. In the Glassboro area (fig. 9. site R), concentrations of nitrate in shallow ground water in 1996 

were highest in san1ples from agricultural areas 

(median, 13 mg/L ), reflecting intensive agriculture and 

well-drained, well-aerated soils. Concentrations were 

lower in new and older urban areas (n1edians, 2.6 and 

3.5 mg/L, respectively) and consistently below 1 n1g/L 

in undeveloped (forested) areas. Pesticides were found 

in both urban and agricultural areas in samples from 7 5 

to 80 percent of the wells, generally at levels below 

applicable Federal drinking-water standards. VOCs 

were most common in water from urban areas. With 

tin1e, contaminants in the surficial aquifer may tnove 

deeper into the system and into surface water (Stackelberg and others, 1997 ). Ground-water flow modeling of 

the Glassboro region indicates that water recharged at 

a ground-water divide in the thicker parts of this system 

may be in the flow system for over 200 years before 

discharging to local strean1s (Kauffman and others, 

2001 ). In thinner parts of the system, base flow 

includes ground water that recharged less than 10 years 

ago. Modeling estimated that nitrate concentrations in 

streatns were reduced about 40 percent below groundwater discharge concentrations, probably because of 

denitrification in streambed sediments or in-stream loss 

(Kauffn1an and others, 2001, Stackelberg and others, 

2001). Szabo and others (1994) found that concentrations of nitrate and pesticides decreased with depth in 

the Kirkwood-Cohansey aquifer system, but that these 

chemicals have not yet penetrated to deep parts of the 

system. 

In undeveloped areas of Subregion 4, water quality is very similar to that of precipitation. A large part 

of Subregion 4 in New Jersey is covered by pine forests 

and swamps. Surface-water chemistry in these areas is 

very similar to that of precipitation, as surficial sediments are predmninantly quartz sand and precipitation 

is the major source of dissolved constituents in ground 

and surface water (Fusillo and others, 1980). Groundand surface-water chemistry are similar, although 

ground water has higher pH. bicarbonate, and dissolved iron concentrations, especially in swamoy 

areas. Oxidation of iron as it discharges to sur~ace 

water and drainage from organic-rich swan1py areas 

around streams results in a decreased pH in surface 

water to a median value of 4.5. 

Subregion 5: Inner Coastal Plain- Upland Sands 

and Gravels 

Limited information available for Subregion 5 

indicates that the permeable sands and gravels of this 

subregion yield usable quantities of well-oxygenated 

water. Hand-dug domestic wells have been installed in 

the upland sands and gravels (mapped as the Brandywine Formation) of the Maryland part of this subregion 

with sufficient saturated thickness (Otton, 195:). 

Recent mapping of zones of denitrification potential 

indicate that surficial geologic conditions and soils 

would promote nitrification in ground water in these 

upland deposits (Krantz and Powars, 2000). 

Near Waldorf, Maryland (fig. 9, siteS), ~nbregion 5 contains mostly sand and gravel overlying the 

silt and clay of the Calvert Formation. In four l~')reholes, these include up to 12 n1 of medium to c':larse, 

orange or tan feldspar-bearing sands and (commonly 

iron-stained) gravel. At one site. these sediments are 

overlain by 3m of silt and fine sand. These sediments 

form a surficial aquifer with a saturated thickness of 3 

to 14 n1. One ground-water sample frmn this aquifer in 

1961 was "soft" (hardness= 59 mg/L)3 with 430 J..Lg/L 

of iron~ another was "hard" (hardness= 150 mg/L), 

3 Hardness values are expressed as equivalent concentrations 

of calcium carbonate. 

Evaluation of the Regional Framework at the Local Scc-'e 25 
with 490 J..tg/L of iron and 110 mg/L of sulfate (Wilson 

and Fleck, 1990). 

Subregion 6: Inner Coastal Plain- Dissected 

Outcrop Belt 

The variable geology of Subregion 6 is reflected 

in its variable ground-water and stream chemistry. In 

many areas. the surficial deposits of this subregion are 

dominated by deeply weathered permeable sands and 

gravels, and ground-water quality largely reflects overlying land use. In some areas, however, reducing conditions occur in less permeable sediments. In North 

Carolina. for example, variable nitrate and iron concentrations in water indicate variable redox conditions 

(North Carolina Department of Natural Resources and 

Community Development. 1979). 

The Morgan Creek watershed, near Locust 

Grove. Maryland (fig. 9, site P), provides an example of 

ground- and surface-water chemistry in a part of Subregion 6 where the stream valley is completely incised 

through the surficial aquifer into a deeper confining 

unit (Bohlke and Denver. 1995 ). This watershed is 

adjacent to Chesterville Branch (fig. 9, site P) and 

shares the same agricultural land use and sandy aquifer 

conditions. However, the confining bed beneath the 

unconfined surficial aquifer is at a much shallower 

depth beneath Morgan Creek than Chesterville Branch. 

Nitrate concentrations are elevated in shallow ground 

water, but much of the nitrate is lost to denitrification 

prior to discharge into Morgan Creek. Chemical and 

isotopic evidence indicate that much of the denitrification occurs where ground-water flowpaths pass 

through an anoxic zone at the top of the confining bed 

near the discharge area into Morgan Creek. Nitrate 

concentrations range from 2 to 3 mg/L in Morgan 

Creek, and from 9 to 10 mg/L in Chesterville Branch. 

In the Upper Cretaceous Englishtown-Mt. Laurel and Tertiary Rancocas aquifer systems in southern 

New Castle County, Delaware (fig. 9, site T), water 

chemistry in Subregion 6 is affected by different redox 

environments in unconfined and confined parts of the 

systems. Water samples from wells in unconfined parts 

of each system had nitrate concentrations above 0.4 

mg/L (an estimated threshold for natural nitrate concentrations in the area; Han1ilton and others, 199 3) and 

as high as 15 mg/L (Bachman and Ferrari, 1995). In 

confined parts of these aquifer systems, nitrate was 

undetectable (less than 0.02 mg/L) and concentrations 

of dissolved iron, an indicator of reducing conditions, 

were generally greater than 300 J..tg/L. Nitrate and iron 

concentrations were generally inversely correlated. 

In the Potomac-Raritan-Magothy aquifer system 

in Subregion 6 along the Fall Zone in New Jersey (fig. 

9. site U), the vulnerability of the aquifer to nitrate and 

pesticide contamination is similarly greater in outcrop 

areas relative to confined parts of the aquifers. Vowinkel and Battaglin (in press) found that the median 

nitrate concentration in ground water of unconfined 

outcrop areas was 0.3 mg/L; the median concentration 

in confined areas was less than 0.1 mg/L. Pesticides 

were also detectable (at low concentrations) in outcrop 

areas. 

Subregion 7: Alluvial and Estuarine Vr'lleys 

Depositional environments in the alluvial and 

estuarine sediments associated with rna jo"" rivers in the 

Coastal Plain (Subregion 7) are highly variable: ground 

water may exhibit reducing conditions as~ociated with 

organic matter and fine-grained sediments, or oxidizing conditions associated with sandy surficial sediments. The scale of these depositional environments 

varies with the scale of the river valley, gP.nerally 

decreasing from south to north. Because much of Subregion 7 is along brackish and saline water bodies, saltwater intrusion into aquifer sediments is dso possible. 

Local-scale data from along the Potomac, Patuxent, 

Pocomoke, James, and Cape Fear Rivers (fig. 1) denlonstrate some of the variability in geology and water 

quality in Subregion 7. 

The alluvial deposits along the Potomac River 

range from coarse to fine and commonly contain 

organic matter. At Dahlgren, Virginia (fig. 9, site V) 

these sediments are predominantly sandy with local 

silt, clay, gravel, and organic matter. They range from 

2 to 10 m thick and contain a water-table aquifer (Harlow and Bell, 1996). The geochemical ervironment in 

these sediments varies from well-oxygenated to reducing, with iron and manganese concentrati<Jns inversely 

correlated with dissolved oxygen. Some ground-water 

samples contained elevated sodium and chloride concentrations, likely from road salt applications, and 

(possibly) from brackish-water intrusion in a narrow 

zone along the river. Upstream, near Wasl'ington, D.C., 

(fig. 9, site W), valley sediments include thick fluvial 

sand and gravel at the base, grading upward to silt, clay, 

and organic matter (Froelich and others, 1978). Current 

26 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
deposition in the estuarine Potomac River in this area 

and downstream includes an organic-rich gray and 

black clay or silty clay ( Callendar and others, 1984; 

Hiortdahl, 1997). 

Local-scale ground-water flow and water quality 

were studied in relation to nutrient transport in Subregion 7 along the Patuxent River in an area with predominantly sandy surficial sediments (fig. 9, site X) 

(McFarland, 1995 ). This unconfined flow systen1 is 

predominantly oxygenated, with nitrate concentrations 

generally ranging fron1 6 to 10 mg/L, although denitrification may occur in ground water beneath a forested 

lowland adjacent to the Patuxent River. 

In the Pocomoke River Valley near Willards, 

Maryland (fig. 9, site L), sediments are comprised of 

fine-grained alluvium and under reducing conditions. 

Alluvium includes sand, peat, clay, and gravel (Owens 

and Denny, 1979). Ground water in the alluvium of 

Green Run, a tributary to the Pocomoke River, contained iron concentrations as high as 61,000 J..Lg/L in 

1990 (Hamilton and others, 1993). 

Valleys in the southern part of the study area contain a similar mix of sedin1ents. The James River Valley 

near the Fall Zone (fig. 9, site Y) is underlain by "very 

poorly sorted sand, gravel, cobbles, and boulders with 

noncohesive silt and clay" (McFarland, 1997). Lithologic logs are available from two wells near the Cape 

Fear River in Sampson County, North Carolina (fig. 9, 

site Z). At one well, the upper 6 m of sediment includes 

a tight, red clay with about 20 percent fine to very fine 

angular quartz sand. This is underlain by another 6 m 

of tan medium to coarse sand. At the other well location, the upper clay layer is missing and the surficial 

deposits include 7 m of rust -colored medium and 

coarse sand (Brown, 1958). 

FRAMEWORK APPLICATION 

Several characteristics of the surficial hydrogeologic framework presented in this report n1ake it more 

or less useful for various purposes. Although limitations in scale and resolution are inherent, the framework can be a valuable tool for sumn1arizing regional 

hydrogeologic conditions for the purpose of analyzing 

data, designing sampling networks, or general environmental investigations. Conclusions drawn from examination of the framework at the local scale, however, can 

be misleading or incorrect, and should be used with 

caution. 

Intended Uses 

The surficial hydrogeologic framework represents a regional sumn1ary of variable physical properties (physiography and surficial sediment textu~e) that 

affect the flow and chemistry of streams and sb allow 

ground water in the Mid-Atlantic Coastal Plain. Within 

each subregion, a fairly unifom1 set of natural conditions affects the occurrence, fate, and transport of 

chemicals from the land surface through the shallow 

ground-water system to streams. The framework is 

intended for use for any purpose for which sue, a 

regional summary of environmental conditions might 

be necessary or helpful. In regional environmental 

investigations, the framework can be useful for 

explaining the spatial distribution of different land 

uses, soil types, topographic features, mineral deposits, 

wetlands, freshwater availability, or ground-water 

quality. The distribution of hydrogeologic features 

described by the framework might also be conf1dered 

in the design of future environmental studies. The 

fran1ework could be useful as a predictive tool for preliminary environmental assessment, as well, although 

additional information would be needed to define the 

hydrogeology of local areas. 

Limitations 

The greatest limitations on the use of the framework are those of scale and resolution. The fran1ework 

is intended for use as a tool for regional hydrogeologic 

assessments; the uncertainty in the hydrogeolo:sic 

interpretations increases quickly as the framework is 

applied to sn1aller and smaller areas. The sever subregions defined by the framework represent areas of similar geology (primarily unconsolidated siliciclastic 

sediments) along a continuun1 of hydrogeologis characteristics (sediment textures and physiography). 

Although real differences are hypothesized to exist 

among these subregions on an aggregate basis, the 

local hydrogeologic variability within each subregion 

is such that the framework provides only general guidelines about the physical setting in small areas. Examination of the results of local hydrogeologic anc1 waterquality investigations in the Mid-Atlantic Coastal Plain 

demonstrate that even within the subregions pn~dicted 

Framework Application 27 
to be the most homogeneous, conditions are variable at 

the local scale. Subregion L for example. contains 

some well-drained areas with oxygenated ground water 

(Spruill and others, 1997), and smne areas of Subregion 4 are poorly drained with reducing conditions 

(Denver, 1993). 

The regional scale and resolution of the hydrogeologic framework are artifacts of the methods used in 

its development as well as real local-scale hydrogeologic differences among areas of the Mid-Atlantic 

Coastal Plain. Though mostly unconsolidated, sediments of the Coastal Plain are very diverse with respect 

to texture, which is very important to permeability and 

other hydrogeologic properties. A complex sequence 

of sediments ren1ains as a result of the drastic sea-level 

fluctuations and the consequent multiple marine transgressions across the Coastal Plain since the Early Cretaceous, particularly in the Pleistocene and Holocene 

Epochs (Appendix 2). Son1e fmmations grade laterally 

or vertically through a continuum of sediment sizes 

from gravel to clay. These variable deposits are combined by necessity into a set of comprehensive mapping units in geologic investigations, particularly those 

published at the state or regional scale. In creating the 

framework, a predominant sediment texture was 

defined for each of these variable comprehensive units 

(plates 2 and 3); the units were then further combined 

in delineating the seven hydrogeologic subregions 

(plate 4 ). 

The widely scattered distribution of data from 

field investigations also affects the accuracy of hydrogeologic delineations in son1e areas. Although the 

framework is not intended for use at the local scale, 

exan1ination of data and results fron1local-scale studies provides smne insight into the real hydrogeologic 

variability within each delineated subregion of the 

Coastal Plain. The lack of available local information 

for some areas (including much of Subregions 3 and 5, 

for example) affects the certainty of the hydrogeologic 

hypotheses described in this repm1. 

Some inherent limitations also should be considered when using the physiographic data (plate 1) and 

geologic data (plates 2 and 3 ). Although these n1aps 

represent a step toward regional uniformity, some 

inconsistencies among mapped areas remain to be 

resolved. The variable scale and resolution of original 

data sources remain evident in some areas, particularly 

for subcropping units on the Deln1arva Peninsula (plate 

2). Original sources also may differ in non1enclature 

and geologic interpretations; some geolog~sts consider 

different controls (such as biostratigraphy, depositional 

setting, or sediment size) when mapping lithostratigraphic units. Given the variability in seal~ and interpretations in published geologic data acros" the Coastal 

Plain (particularly for the surficial formati0ns), future 

regional compilations of this type will undoubtedly 

benefit from further investigations into the distribution 

and physical properties of near-surface Coastal Plain 

deposits and the processes responsible for their formation. 

SUMMARY 

A regional surficial hydrogeologic framework 

was developed for the Mid-Atlantic Coastal Plain, from 

New Jersey through North Carolina. A regionally consistent summary of the hydrogeology is a useful foundation for environmental investigations at tnany scales. 

The properties of near-surface geologic n1aterials are 

particularly fundamental to water-quality studies 

because they directly affect the flow and quality of 

strean1s and ground water. Previously available spatial 

geologic and hydrologic data for large areas are often 

of limited use for regional investigations d·1e to insufficient detail, incomplete coverage, or inconsistencies 

among sources. The hydrogeologic framework for the 

Mid-Atlantic Coastal Plain includes seven distinct 

hydrogeologic subregions within which the primary 

physical properties affecting the flow and chemistry of 

shallow ground water and small streams are relatively 

consistent, or rather, consistently heterogeneous. 

Within most subregions, the moven1ent of chemicals 

from the land surface to shallow ground water and 

strean1s can be described by a fairly uniform set of natural processes; some subregions include n1ixed hydrogeologic settings indistinguishable at the regional 

scale. The seven subregions represent arers of similar 

geology (mainly unconsolidated siliciclastic sediments) along a continuum of physiography and sediment textures. 

The seven hydrogeologic subregions that comprise the framework were delineated prin1arily on the 

basis of physiography and the predominart texture of 

near-surface sediments, the primary natural factors that 

affect the flow and quality of shallow ground water and 

small streams. Physiography was constructed by 

extrapolating and standardizing previously published 

physiographic interpretations for the Coastal Plain of 

28 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
South Carolina and New Jersey. Surficial and subcropping geology for the Mid-Atlantic Coastal Plain were 

similarly defined through a con1pilation of previously 

published data: contacts and correlations between formations were interpolated across unmapped areas, and 

inconsistencies in nomenclature, interpretation, and 

scale were resolved to the extent possible. A predominant sediment texture for each mapped geologic unit 

was derived from published descriptions of the sediments and stratigraphy at selected locations. Relatively 

contiguous hydrogeologic subregions were delineated 

on the basis of the con1binations of physiography and 

surficial geology: subcropping geology was used in a 

few cases where the surficial sedin1ents are particularly 

thin. 

Fundamental differences among the seven 

hydrogeologic subregions are defined in terms of variable soils, land-use distributions, topography. and 

hypotheses about the dominant hydrologic processes in 

the area. The Coastal Lowlands (Subregion 1) are 

extren1ely flat. low-lying, and poorly drained: wetlands 

are comtnon. Streams are mostly sluggish or tidaL and 

ground water is typically poorly oxygenated. Agriculture is common in Subregion 1. although most fields 

are artificially drained. With relatively impermeable 

surficial sediments, the Middle Coastal Plain - Fine 

Sedin1ents (Subregion 3) lacks an extensive surficial 

aquifer; n1ost usable ground water is confined and 

moderate relief promotes runoff of precipitation 

directly to strean1s. Subregion 3 is mostly forested. In 

the Middle Coastal Plain- Sands with Overlying Gravels (Subregion 4) and the Inner Coastal Plain- Upland 

Sands and Gravels (Subregion 5). extremely petmeable 

surficial sediments promote infiltration to well-oxygenated ground water, and water quality commonly 

reflects surficial land uses. The surficial aquifer of Subregion 4 is generally very thick: in Subregion 5. however, it is typically completely incised by streams. The 

Middle Coastal Plain- Mixed Sediment Texture (Subregion 2). the Inner Coastal Plain- Dissected Outcrop 

Belt (Subregion 6), and the Alluvial and Estuarine Valleys (Subregion 7) contain mixed hydrogeologic settings indistinguishable at the regional scale. Each 

represents a unique topography and physiography 

important to the flow and chemistry of streams and 

shallow ground water. 

Although the seven subregions that constitute the 

fran1ework represent distinct hydrogeologic settings on 

a regional scale. geologic variability within the Coastal 

Plain lin1its the usefulness of the framework at local 

scales. A review of the results of local investigations 

demonstrates that even the subregions hypothefized to 

be most homogeneous (such as Subregions 1 and 4) can 

be quite variable locally. On the local scale, the seven 

subregions defined by the framework must be interpreted along the continuum of natural settings tr at exist 

within the Mid-Atlantic Coastal Plain. 

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34 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
APPENDIX 1 

Technical Notes 
APPENDIX 1 -TECHNICAL NOTES 

by Sarah K. Martucci 

Four digital geographic data sets (coverages) 

were developed for the Mid-Atlantic Coastal Plain 

using Environmental Systems Research Institute 

(ESRI) Arc/Info Geographic Information System (GIS) 

software (version 7.2.1) on Microsoft Windows NT 4.0. 

All data are presented in the Albers Equal-Area Conic 

projection with a central meridian of 96 degrees in the 

NorthAn1erican Datum (NAD) of 1983 (Snyder, 1987). 

These data are not intended for use at scales greater 

than approximately 1: 1 ,000,000. The coverages are distributed for general use in Arc/Info export files and Spatial Data Transfer Standard (SDTS) format; metadata 

for each coverage are also presented in digital format. 

Geology Coverages 

Available published and unpublished data (see 

metadata and Delineation of Regional Geology, above) 

were appended to generate the surficial and subcropping geology coverages. Some of these data were previously available in digital format others were 

digitized from printed maps. All original data were projected to a common datum and clipped to the study 

area, as necessary. 

Attribute items (variables) included in the surficial and subcropping geology coverages are: formation, 

name, and lith. Formation is an abbreviation of the 

geologic formation name (noted in the item, name) and 

age. For example, formation "Tc" is the Tertiary-aged 

Calvert Formation. The item, Lith, describes the predominant sediment texture of each unit, as shown for 

the surficial geology on plate 3. 

The surficial geology coverage and its metadata 

are available from http://md.water.usgs.gov/publications/prop-1680/surfgeol.html. The subcropping geology coverage and its metadata are available from http:/ 

/md. water. usgs.gov /publications/prop-1680/subcrops.html. 

Physiography Coverage 

The surficial geology coverage was generalized 

to generate the physiography coverage. The arcs (geologic contacts) from the surficial geology that correspond to physiographic boundaries (mostly scarps) 

were selected and copied to a new coverage. This coverage was then built with polygon topology and attributed. Six physiographic subprovinces aF~ delineated in 

the physiographic coverage, in the item, prov. 

The physiographic coverage and accompanying 

metadata may be obtained from http:// 

md. water.usgs.gov /publications/prop-1680/phys.html. 

Hydrogeologic Framework CoveragE 

The physiography and geology coverages were 

combined and generalized to develop th~ hydrogeologic framework coverage. The surficial geology coverage was dissolved on lith and intersected with the 

physiography coverage. The resulting coverage was 

plotted at a scale of 1:1,000,000 and the s~ven relatively 

contiguous subregions were outlined by hand on the 

basis of physiography and predominant sediment texture. The arcs corresponding to these sul~;egion boundaries were copied from the intersected c 'Jverage to a 

new coverage; a few boundaries were al~o copied from 

the subcropping geology coverage or digitized on 

screen. Polygon topology was built and attributes were 

added to this new coverage to generate the hydrogeologic framework coverage. The hydroge'"llogic framework coverage includes seven distinct subregions 

identified by the items, fcode (an integer from 1 to 7) 

and name (table 2). 

The complete metadata and this dataset may be 

obtained from http:/ /md. water. usgs.gov /publications/ 

prop-1680/framework.html. 

Reference 

Snyder. J.P., 1987, Map projections -a working manual: U.S. 

Geological Survey Professional Paper 1395, 383 p. 

36 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
APPENDIX 2 

Geologic Setting of the Mid-Atlantic Coastal Plain 
APPENDIX 2- GEOLOGIC SETTING OF THE MID-ATLANTIC COASTAL PLAIN 

by David E. Krantz 

On a regional scale, the geometry and character 

of the shallow aquifer system in the Mid-Atlantic 

Coastal Plain is controlled by large-scale structural and 

depositional systems, and geologic processes operating 

over millions of years. The surficial aquifer, as the 

uppermost part of the hydrostratigraphic system, has 

variable but predictable properties inherited from this 

geologic setting and modified by local processes that 

shaped the land surface and chemically altered the surficial sediments. 

Physiography 

Each of the physiographic subprovinces (plate 1) 

has a characteristic geomorphology that is related to its 

geologic history. This geomorphic variability is critical 

to the development of stream networks, ground-water 

resources, and other hydrologic properties that control 

the shape and use of the land. 

The Inner Coastal Plain (plate 1) includes the 

greatest topographic relief in the study area. The Dissected Outcrop Belt includes some of the oldest landscapes in the Mid-Atlantic Coastal Plain. From the 

Washington, D.C. area to the north, this includes the 

deeply weathered Potomac Group (plate 2) and equivalent deposits along the Fall Zone. In North Carolina, 

this includes the area west and northwest (landward) of 

the Orangeburg Scarp (plate 1 ), and east of the Fall 

Zone across the crest of the Cape Fear arch (plate 2). 

The Inner Coastal Plain has a deeply incised drainage 

network, and is underlain primarily by Lower Tertiary 

and Cretaceous sediments. The land surface has been 

exposed for at least 5 million years, is deeply weathered, and has been extensively modified by colluviation 

(Newell and others, 1980). 

The Lower Cretaceous units of the Inner Coastal 

Plain are overlain locally by remnants of a broad veneer 

of upper Tertiary coarse sediments (the Upland Sands 

and Gravels). In many areas, these deposits are largely 

discontinuous and confined to isolated hilltops (Mixon 

and others, 1989). In New Jersey and the Delmarva 

Peninsula, however, this subprovince includes broad 

plains that slope gently to the southeast and are capped 

by deeply weathered fluvial coarse sands and gravels 

(the Bridgeton and ColumbiaFormationr, respectively) 

(Zapecza, 1989; Vroblesky and Fleck, 1991, Newell 

and others, 2000). The rolling upland is dissected by 

underfit streams in wide valleys; the moiern streams 

are much smaller than the alluvial valleys, which suggests that the drainage systems previously carried much 

more sediment eroded from the land surface (Newell 

and others, 2000). 

The Middle Coastal Plain - Terrac:es is a broad, 

seaward-sloping plain bounded to the ncihwest (landward) by the Orangeburg, Coates, and Broad Rock 

Scarps, and by the Suffolk Scarp to the routheast (seaward) (plate 1). Several less prominent scarps such as 

the Surry Scarp divide the Middle Coastal Plain into a 

series of stair-step terraces with progressively lower 

elevations moving seaward (Oaks and Coch, 1973, 

Colquhoun and others, 1991). The deposits of this subprovince include fluvial sediments that correlate with 

estuarine and shallow marine sequences seaward; these 

deposits are Pliocene and Early to Middle Pleistocene 

in age, and were produced by repeated s~a-level transgression and regression cycles (sea-level rises and falls, 

respectively). The land surface has been exposed longer 

than that of the Outer Coastal Plain, and has undergone 

moderate erosion and moderately deep weathering. 

Some original coastal landforms (such as barrier-island 

complexes) are preserved and recognizable in the 

younger sections of the Middle Coastal Plain- Terraces, particularly in North Carolina (Cclquhoun and 

others, 1991 ). 

The Middle Coastal Plain- Dissected Uplands 

(plate 1) are similar to the rest of the Middle Coastal 

Plain, with slightly greater stream incisiC''l. In New Jersey, this includes a highly dissected area of low hills 

and broad alluvial valleys. The land surface is largely 

covered by coarse colluvial sands and gravels. In Maryland, the geomorphology of this subprovince is similar, 

however, the area is underlain by the relatively impermeable silt and clay of the Calvert Form::ttion (McCartan and others, 1995). 

The Outer Coastal Plain (plate 1) encompasses 

the lowland areas generally within 16 to 24 km (kilometers) of the modern coastline, including the modern 

barrier islands and lagoons along the Atlantic Ocean 

38 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
and the extensive tidal marshes along the coastal bays. 

This subprovince also includes the estuarine terraces 

that parallel the lower reaches of the major rivers crossing the Coastal Plain. Its boundaries in North Carolina 

and Virginia are the Suffolk Scarp on the landward side 

and the modem Atlantic coastline. The Outer Coastal 

Plain is very flat with low relief, and has an immature 

(poorly developed) stream-drainage network. Much of 

the land surface is inherited from coastal landforms 

created during Late Pleistocene highstands of sea level, 

such as barrier island complexes and estuarine embayments (Colquhoun and others, 1991). 

The Alluvial and Estuarine Valleys of major rivers cross the Coastal Plain, generally toward the southeast (plate 1 ). These are typically broad, flat 

bottomlands and terraces parallel to the modem river 

channels; the area is poorly drained and perennially 

wet from ground-water discharge. Scarps along the 

river valleys were created when the valleys were 

flooded to form estuaries during the Pleistocene, and 

are connected to contemporary coastal scarps. The valleys in North Carolina are typically broader with 

greater volumes of alluvial fill than are valleys to the 

north that drain to the Chesapeake and Delaware Bays. 

The northern river valleys are more deeply incised, and 

the rivers transport a significantly lower suspendedsediment load than the southern rivers. The James 

River and the major rivers to the north are tidal and 

estuarine to the Fall Zone, whereas the rivers in North 

Carolina are fluvial (nontidal) half way across the Middle Coastal Plain (Fenneman, 1938). Weathering and 

erosion are dominated by physical processes to the 

north and chemical processes to the south. These 

changes in alluvial valley fill and weathering correspond to the transition from a humid temperate to a 

humid subtropical climate in southern Virginia and 

northern North Carolina (Soller and Mills, 1991 ). 

Structure 

The distribution of geologic units (plate 2) and 

hydrogeologic subregions (plate 4) in the Mid-Atlantic 

Coastal Plain reflects two large-scale geologic structures. The orientation and thickness of the entire 

Coastal Plain sedimentary sequence is controlled by 

the undulating surface of basement rocks upon which it 

rests. A crater in the lower Chesapeake Bay (plate 2) 

resulted from an itnpact that radically altered the entire 

geologic section and distribution of fresh ground water 

in eastern Virginia. 

Independent of the monoclinal seaward dip of 

the entire Mid-Atlantic Coastal Plain sequence, the distribution and thickness of the sedimentary units are 

controlled on the spatial scale of tens to hundreis of 

kilometers by a series of positive- and negative-relief 

structures (Owens and Gohn, 1985; Ward and others, 

1991; Trapp, 1992; Winner and Coble, 1996) Crlate 2, 

this report). From north to south, the depositional 

basins are the Raritan Embayment in northern New Jersey, the Salisbury Embayment in Maryland, Delaware, 

and Virginia, and the Albemarle Embayment in northeastern North Carolina. These basins are separc:ted by 

the South New Jersey Arch, the Norfolk Arch, c:T\d the 

Cape Fear Arch, which is the most prominent of the 

arches. The Neuse Arch is a smaller-scale feature on 

the northern flank of the Cape Fear Arch. These positive structures are believed to be associated with largescale tectonic features in the crystalline baseme'lt, and 

may have offsets of 300m (meters) relative to tl'~ adjacent basin. Differential vertical movement of t]'~Se 

structures throughout the Cretaceous and Cenozoic has 

created alternating sequences of thicker and thinner 

Coastal Plain strata along the regional strike, which is 

generally south-southwest to north-northeast, roughly 

parallel to the Atlantic coastline (Owens and Gohn, 

1985; Ward and others, 1991; Trapp, 1992; Winner and 

Coble, 1996). 

These regional structures mostly affect tte 

geometry of the deeper, confined aquifers, but th~y also 

influence the character of the surficial aquifer. For 

example, across the crest of the Cape Fear Arch, conlpacted and partially indurated (cemented) Cretr~eous 

sediments that were previously deeply buried lia. 

directly beneath a thin cover of Pliocene and Pla.istocene shallow-marine sediments that are comn1only 

less than 10m thick. The geometry of the surfisial 

aquifer is vastly different in the Albemarle Eml'ayment, where the combined thickness of the Pliocene 

and Pleistocene sequence approaches 180 m under the 

Outer Coastal Plain (Winner and Coble, 1996). 

Another effect of the Cape Fear Arch is the fonnation 

of a band of Lower Tertiary limestone and marls in the 

shallow subsurface along the flank of the arch in southeastern North Carolina, bounded approximately by the 

Northeast Cape Fear River to the west and the p.~mlico 

River to the north (plate 2). This area is one of the few 

APPENDIX 2 - Geologic Setting of the Mid-Atlantic Coastal Pia~,., 39 
places on the Mid-Atlantic Coastal Plain where a 

highly permeable carbonate sequence occurs. 

A different type of structure has a significant 

local effect in eastern Virginia. A recently discovered 

impact crater underlies the southern section of the 

Chesapeake Bay (Poag, 1996; Powars and Bruce, 

1999; Powars, 2000) (plate 2). The 90-km-wide crater 

was produced by the collision of a comet or meteorite 

35 million years ago in the late Eocene. The center of 

the crater lies beneath the town of Cape Charles, near 

the southern tip of the Delmarva Peninsula. The impact 

in the shallow ocean disrupted the entire 2-km-thick 

sequence of Coastal Plain sediments and fractured the 

crystalline rock of the basement. Subsidence occurred 

within and around the crater after the impact, and possibly as recently as the Holocene. The deep depression 

of the crater has controlled the deposition of marine 

and estuarine sediments, and the course of the major 

rivers running across the Coastal Plain. The extensively fractured debris inside the crater was flooded 

with seawater immediately after the impact, and these 

brines are retained today in the deeper aquifers; however, ground water in the surficial and upper confined 

aquifers is fresh (Poag, 1996; Powars and Bruce, 1999; 

Powars, 2000). 

Geologic History 

Throughout the Mid-Atlantic Coastal Plain, the 

distribution and type of sediments (and their hydrologic properties) have a similar pattern related to the 

regional geologic history. Major episodes of deposition have been controlled by long-term trends in global 

sea leveL regional tectonics, and climate. The entire 

continental margin has undergone a gradual subsidence 

since the rifting in the Jurassic that produced the Atlantic Ocean Basin. The Coastal Plain, however, has experienced a net uplift and tilting, with greater uplift of the 

landward edge and a hinge zone near the modern coastline (Owens and Gohn, 1985; Poag, 1985; Ward and 

Strickland, 1985 ). Three major episodes of sediment 

deposition were each dominated by a particular en vironment. These are the fluvial and deltaic deposition 

during the Early Cretaceous and early part of the Late 

Cretaceous, marine-shelf deposition from the Late Cretaceous to the Pliocene, and high-frequency, highamplitude sea-level fluctuations associated with glacial-interglacial cycles from the late Pliocene through 

the Quaternary. 

Early Cretaceous deposition on the Mid-Atlantic 

Coastal Plain was dominated by fluvial and deltaic systems that derived large volumes of clastic material 

from the erosion of the highlands (the Piedmont, Blue 

Ridge, and Appalachian Provinces). Thefe fluvial-deltaic sequences change to prodelta and shdlow-shelf 

facies downdip. Sands from the upper delta plain and 

river channels, and silt -clays of the lower delta plain 

were deposited in thick sequences all along the Atlantic 

margin; for example, the Potomac Group in Maryland 

thickens from 200 m beneath the Middle Coastal Plain 

to more than 1,000 m near the coast (Vrol:llesky and 

Fleck, 1991). This fluvial-deltaic depositional system 

is represented by the Potomac Group fron1 New Jersey 

through Virginia (Hansen, 1968; Jordan, 1983; Owens 

and others, 1999) and the Cape Fear and Middendorf 

Formations in North Carolina (Owens, 1989; Sohl and 

Owens, 1991) (plate 2, this report). These sediments 

overlie Paleozoic and Proterozoic crystalline basement 

rocks or Mesozoic rift-basin rocks, such as those of the 

Newark Supergroup in New Jersey. 

By the early part of the Late Cretace'"lus, regional 

subsidence of the continental margin and associated 

relative sea-level rise resulted in a transiti0n to a marginal-marine depositional system. These sequences 

are dominated by silts of the lower delta plain and 

prodelta, and silty sands deposited on the inner shelf. 

The Raritan Formation in northern New Jersey, the 

upper part of the Potomac Group from certral New Jersey through Virginia, and the Black Creet Group in 

North Carolina represent this transitional phase 

(Owens and Gohn, 1985; Gohn, 1988). Fully marine 

conditions prevailed through much of the latter part of 

the Late Cretaceous, represented by the ~1agothy and 

younger Cretaceous formations in New Jersey through 

Virginia, and the Peedee Formation in southern North 

Carolina (plate 2). 

During the Paleocene and Eocene, the entire 

Atlantic Margin was repeatedly flooded by extensive 

marine incursions that probably lapped well onto the 

Piedmont. Deep-water (middle- to outer-shelf) sediments are preserved beneath the modern Middle and 

Inner Coastal Plain. In many areas, however, these sediments were subsequently beveled or rem'Jved by erosion during late Tertiary transgressions (Trapp, 1992). 

The lower Tertiary is represented by the F ancocas 

Group in New Jersey and the Pamunkey Group in 

Maryland and Virginia (Ward, 1985). These units are 

typically dominated by glauconitic fine sands depos40 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 
ited in a poorly oxygenated shelf environment. Some 

units contain shallower water deposits, including nearshore well-sorted sands, and interbedded silts and 

muddy sands fron1 deltas. The Early Tertiary shelf 

south of central North Carolina was dominated by carbonates and marls (mixed carbonate and siliciclastic 

sedin1ents). The Eocene and Oligocene units in southem North Carolina are the Castle Hayne, River Bend, 

and Belgrade Formations (Ward and others, 1978) 

(plate 2, this report). 

A prolonged period of regression in the late Oligocene was followed by a significant global rise in sea 

level beginning in the early Miocene and continuing in 

cycles through most of the middle and late Miocene. 

Several large regional transgressive pulses deposited 

the marine sediments of the Kirkwood and Cohansey 

Formations in New Jersey (Newell and others, 1995, 

2000), the Chesapeake Group in Delaware, Maryland, 

and Virginia (Cleaves and others, 1968; Mixon and others, 1989), and the Pungo River Formation in the Albemarle Embayment of North Carolina (North Carolina 

Geological Survey, 1985 ). The marine sediments of 

these formations are typically shallow-shelf silty sands, 

commonly with abundant carbonate shells, and silts or 

silty fine sands deposited in partially protected coastal 

embayments or in deeper shelf settings. Coastal deposits, such as barrier-island sands, are generally not preserved in the Miocene sequences in Maryland and 

Virginia. In New Jersey, however, the Cohansey Formation and updip parts of the Kirkwood Formation 

have cotnplexly interbedded sediments fron1 fluvialdeltaic, coastal, and inner-shelf depositional environments. Several of the component members of the 

Miocene sequences are thick marine silts that act as 

confining layers; for example, in southern Maryland, 

the Calvert Formation is predominantly a tight clay that 

may be 60 m thick beneath parts of the Middle Coastal 

Plain (Otton, 1955) (plates 2 and 3, this report). 

The most extensive marine flooding of the MidAtlantic Coastal Plain in the last 5 million years 

occurred in the early Pliocene Epoch. This regional 

transgressive event deposited the marine sediments of 

the Yorktown Formation in Virginia and the Albemarle 

Embayn1ent of North Carolina and the correlative Duplin Formation across the crest of the Cape Fear Arch in 

southern North Carolina (Ward and Blackwelder, 

1980). During this time. however. the Coastal Plain in 

Maryland, the central Delmarva Peninsula, and New 

Jersey was elevated, possibly by tectonic uplift, and 

lower Pliocene marine sediments were not derosited 

(or were not preserved) in these areas. Upper F,iocene 

fluvial-deltaic, marine-deltaic, and estuarine tc shallow-marine deposits are represented by the Beaverdam 

Formation on the Delmarva Peninsula (Owens and 

Denny, 1979), the Bacons Castle and Chowan River 

Formations in Virginia and northern North Carolina 

(Mixon and others, 1989), and the Bear Bluff Fom1ation in southern North Carolina (Owens, 1989). The 

Windsor Formation that extends from Virginia into 

North Carolina (Oaks and Coch, 1973) and the Waccamaw Formation in southern North Carolina (D~1Bar 

and others, 1974; Owens, 1989) straddle the boundary 

between late Pliocene and early Pleistocene (plate 2). 

Several periods of deposition of coarse fluvial 

material onto the Coastal Plain were interspersed 

among the marine flooding events of the last 10 million 

years; these include the Bridgeton Formation (upper 

Miocene) in southern New Jersey, the Brandywine (or 

Upland) Gravels (Upper Miocene/Lower Plioc~ne) in 

southern Maryland, and the Columbia Formathn 

(upper Pliocene /lower Pleistocene) in Delaware (plate 

2). Although the Mid-Atlantic Coastal Plain was not 

glaciated, some of these large fluvial deposits were 

probably derived from the outwash of continertal glaciers transported down the major rivers and de~osited 

as extensive sheets of sands and gravels (Owens and 

Denny, 1979; Owens and Minard, 1979; Newell and 

others, 1995, 2000). 

A general lowering of sea level and high -amplitude glacial-interglacial cycles started in the late 

Pliocene and continued through the Quaternary (essentially the last 2.5 million years). Most of the tnodem 

land surface of the Coastal Plain was created and modified at this tin1e. During sea-levellowstands associated with glacial events, fluvial erosion was enhanced, 

and rivers and stream-drainage networks were incised 

(cut down). Colluviation, or the down slope transport 

of sediments, was active. In New Jersey and the central 

Delmarva Peninsula, cryoturbation- the defonnation 

of near-surface sediments by the formation of ke structures, such as ice wedges and permafrost- tum~d over 

the surficial sediments and restructured the land surface (Owens and Minard, 1979; Newell and others, 

2000). Periods of aridity allowed inland dunes and 

dune fields to fonn where sandy soils were not held in 

place by vegetation (Owens and Minard, 1979; Trapp, 

1992) 

APPENDIX 2 - Geologic Setting of the Mid-Atlantic Coastal PIC~in 41 
During the initial phase of each sea-level rise, 

river base levels rose and alluvial sediments aggraded 

to partly fill the incised valleys. As the transgression 

progressed, the valleys flooded to form estuaries; the 

ocean shoreline moved landward and shoreface erosion 

planed off and redistributed the sediments of the previously exposed Coastal Plain. At the peak of each highstand, the landward advance of the ocean shoreline was 

halted, the barrier islands prograded seaward to form 

wide sand ridges, and the inner shelf aggraded. The 

estuaries filled with organic-rich muds, with local 

deposits of muddy sands in shallow water, and 

expanded by lateral erosion of the banks to form the 

river-parallel scarp and terrace sets. If the river systems 

draining the Piedmont and the Blue Ridge and Appalachian Mountains transported sufficient sediment, fluvial deltas prograded into the heads of the estuaries. 

Delta progradation occurred repeatedly during the 

Pliocene and Pleistocene in North Carolina, forming a 

series of deltas that are preserved in topographic relief 

on the Middle Coastal Plain; examples include the 

Pliocene Roanoke Delta immediately south of the Virginia-North Carolina border, and the upper Pliocene I 

lower Pleistocene Tar River Delta, which is the large 

wedge-shaped feature in central North Carolina that is 

bisected by the modem Tar River. 

The Piedmont-Coastal Plain Transition (The Fall 

Zone) 

The transition between the Coastal Plain and 

Piedmont Provinces along the Fall Zone is characterized by relatively old, deeply weathered sediments. 

Precipitation typically infiltrates and flows quickly 

along short ground-water flowpaths to local streams in 

this area of highly permeable sands and gravels and 

considerable relief (McFarland, 1997). Isolated coarse 

sands and gravels cap the interfluves (hills that are erosional remnants between stream drainage systems) just 

west of the Fall Zone along much of the Mid-Atlantic 

Coastal Plain (Pazzaglia, 1993). The oldest of these 

remnant gravels are estimated to be middle Miocene 

and Pliocene in age (Mixon and others, 1989); any 

older deposits appear to have been completely removed 

by erosion. 

Weathering of Surficial Units 

The character of the surficial aquife~ is related to 

the original lithology and post -deposition weathering 

of its composite sediments. The leaching and alteration 

of surficial sediments to form less-reactiv~ hydrated 

and oxidized minerals is critical to the geochemical and 

hydrologic characteristics of the aquifer. Regional 

trends in the depth and extent of weatherirg are related 

to modem climate, paleoclitnate (particularly clin1atic 

extremes such as cryoturbation during pe:--iglacial conditions and the formation of inland dunes during 

extreme aridity), and the age and length of exposure of 

the sediments. Surficial sediments are generally more 

deeply weathered in the southern part of the MidAtlantic Coastal Plain and in areas with greater relief. 

The modem climatic transition in northern North Carolina from humid temperate (to the north) to humid subtropical coincides with an increase in weathering. In 

the Southeast, streams typically carry gre"'ter loads of 

suspended sediments and soil profiles are generally 

deeper than in units of equivalent age farther north 

(Owens and others, 1983). 

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44 A Surficial Hydrogeologic Framework for the Mid-Atlantic Coastal Plain 

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