U.S. Department of the Interior

U.S. Geological Survey

Data Series 996

Version 1.1, December 2020

Water Availability and Use Science Program

Digital Elevations and Extents of Regional Hydrogeologic Units

in the Northern Atlantic Coastal Plain Aquifer System

From Long Island, New York, to North Carolina

New York

New Jersey

Virginia

Delaware

Maryland
Cover photographs (top to bottom). The shore of Long Island Sound at Rock Point, 

East Marion, New York. Glacial deposits shown are a remnant of the Roanoke Point moraine 

(Christopher Schubert, USGS, 2003).

USGS hydrologist measuring the radioactivity at the base of the Bridgeton Formation, at the 

contact with the underlying Cohansey sand, New Jersey (Otto Zapecza, USGS, 1991).

Ditched stream through soybean fields in Kent County, Delaware (Mark Nardi, USGS, 2010).

Cross section at Calvert Cliffs on the shore of the Chesapeake Bay in Calvert County, Maryland, 

showing Coastal Plain geologic layers and seeps of groundwater along contacts (David Butts, 

Maryland Department of Natural Resources, 2015).

USGS wire-line coring rig used to obtain continuous core of sediment and basement bedrock 

from within the Chesapeake Bay impact crater, Bayside, Mathews County, Virginia. The lower 

Chesapeake Bay and adjacent tidal marsh are in the background (E. Randolph McFarland, 

USGS, 2001).
Water Availability and Use Science Program

Data Series 996

Version 1.1, December 2020

U.S. Department of the Interior

U.S. Geological Survey

Digital Elevations and Extents of Regional 

Hydrogeologic Units in the Northern Atlantic 

Coastal Plain Aquifer System From 

Long Island, New York, to North Carolina

By Jason P. Pope, David C. Andreasen, E. Randolph McFarland, and 

Martha K. Watt
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia:

First release: 2016

Revised: December 2020 (ver. 1.1)

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Pope, J.P., Andreasen, D.C., McFarland, E.R., and Watt, M.K., 2016, Digital elevations and extents of regional hydrogeologic units in the Northern Atlantic Coastal Plain aquifer system from Long Island, New York, to North Carolina

(ver. 1.1, December 2020): U.S. Geological Survey Data Series 996, 28 p., https://doi.org/10.3133/ds996. 

ISSN 2327-638X (online)
iii

Contents

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

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

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

Location and Physical Setting ............................................................................................................5

Methods Used ................................................................................................................................................5

Sources of Data.....................................................................................................................................5

Delineation of Regional Hydrogeologic Units ..................................................................................6

GIS Formats for Digital Datasets........................................................................................................8

Regional Hydrogeologic Unit Elevations and Extents..............................................................................8

Bedrock Basement...............................................................................................................................8

Potomac-Patuxent Aquifer..................................................................................................................8

Potomac-Patuxent Confining Unit....................................................................................................10

Potomac-Patapsco Aquifer...............................................................................................................11

Potomac Confining Unit ....................................................................................................................12

Magothy Aquifer ................................................................................................................................12

Magothy Confining Unit .....................................................................................................................14

Matawan Aquifer................................................................................................................................15

Matawan Confining Unit ...................................................................................................................16

Monmouth-Mount Laurel Aquifer....................................................................................................17

Monmouth-Mount Laurel Confining Unit .......................................................................................18

Aquia Aquifer.......................................................................................................................................19

Nanjemoy-Marlboro Confining Unit.................................................................................................20

Piney Point Aquifer.............................................................................................................................21

Calvert Confining Unit ........................................................................................................................22

Lower Chesapeake Aquifer...............................................................................................................23

Lower Chesapeake Confining Unit...................................................................................................24

Upper Chesapeake Aquifer...............................................................................................................25

Upper Chesapeake Confining Unit...................................................................................................26

Surficial Aquifer..................................................................................................................................27

Limitations and Recommended Use of Data ...........................................................................................27

Acknowledgments.......................................................................................................................................27

File Organization...........................................................................................................................................27

References Cited..........................................................................................................................................27
iv

Figures

1. Map showing location and extent of the Northern Atlantic Coastal Plain

study area, showing elevation and bathymetry.......................................................................2

2. Correlation chart showing regional hydrogeologic units and corresponding

state-level hydrogeologic units for the Northern Atlantic Coastal Plain

aquifer system...............................................................................................................................4

3–20. Maps showing location and extent of the—

3. Potomac-Patuxent regional aquifer.................................................................................9

4. Potomac-Patuxent regional confining unit ...................................................................10

5. Potomac-Patapsco regional aquifer..............................................................................11

6. Potomac regional confining unit.....................................................................................12

7. Magothy regional aquifer.................................................................................................13

8. Magothy regional confining unit.....................................................................................14

9. Matawan regional aquifer................................................................................................15

10. Matawan regional confining unit....................................................................................16

11. Monmouth-Mount Laurel regional aquifer....................................................................17

12. Monmouth-Mount Laurel regional confining unit........................................................18

13. Aquia regional aquifer......................................................................................................19

14. Nanjemoy-Marlboro regional confining unit.................................................................20

15. Piney Point regional aquifer.............................................................................................21

16. Calvert regional confining unit ........................................................................................22

17. Lower Chesapeake regional aquifer..............................................................................23

18. Lower Chesapeake regional confining unit...................................................................24

19. Upper Chesapeake regional aquifer...............................................................................25

20. Upper Chesapeake regional confining unit...................................................................26

Tables

1. Primary sources of information for hydrogeologic units in States within

the Northern Atlantic Coastal Plain...........................................................................................5

2. Names of digital data files for elevations and extents of regional hydrogeologic

units of the Northern Atlantic Coastal Plain aquifer system.................................................7
v

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 259.0 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

gallon (gal) 3.785 cubic decimeter (dm3

) 

million gallons (Mgal) 3,785 cubic meter (m3

)

Flow rate

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

/s)

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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

Supplemental Information

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

Unit name descriptors such as “lower” and “upper” are shown without capital letters for 

internal consistency in this report, except for Lower Cretaceous, which corresponds to a 

formal geologic unit name. This format may differ from the source references.
vi

Abbreviations

DEM digital elevation model

DOD U.S. Department of Defense

EPA U.S. Environmental Protection Agency

GIS geographic information system

NACP Northern Atlantic Coastal Plain

NED National Elevation Dataset

NGDC National Geophysical Data Center

NOAA National Oceanic and Atmospheric Administration

ppm parts per million

TIN triangular irregular network

USGS U.S. Geological Survey
Digital Elevations and Extents of Regional Hydrogeologic Units

in the Northern Atlantic Coastal Plain Aquifer System 

From Long Island, New York, to North Carolina

By Jason P. Pope,1 David C. Andreasen,2 E. Randolph McFarland,1 and Martha K. Watt1

1

U.S. Geological Survey.

2

Maryland Geological Survey.

Abstract

Digital geospatial datasets of the extents and top 

elevations of the regional hydrogeologic units of the 

Northern Atlantic Coastal Plain aquifer system from 

Long Island, New York, to northeastern North Carolina were 

developed to provide an updated hydrogeologic framework 

to support analysis of groundwater resources. The 19 regional 

hydrogeologic units were delineated by elevation grids and 

extent polygons for 20 layers: the land and bathymetric 

surface at the top of the unconfined surficial aquifer, the 

upper surfaces of 9 confined aquifers and 9 confining units, 

and the bedrock surface that defines the base of all Northern 

Atlantic Coastal Plain sediments. The delineation of the 

regional hydrogeologic units relied on the interpretive work 

from source reports for New York, New Jersey, Delaware 

and Maryland, Virginia, and North Carolina rather than 

from re-analysis of fundamental hydrogeologic data. This 

model of regional hydrogeologic unit geometries represents 

interpolation, extrapolation, and generalization of the earlier 

interpretive work. Regional units were constructed from 

available digital data layers from the source studies in order 

to extend units consistently across political boundaries and 

approximate units in offshore areas.

Though many of the Northern Atlantic Coastal Plain 

hydrogeologic units may extend eastward as far as the edge 

of the Atlantic Continental Shelf, the modeled boundaries of 

all regional hydrogeologic units in this study were clipped to 

an area approximately defined by the furthest offshore extent 

of fresh to brackish water in any part of the aquifer system, as 

indicated by chloride concentrations of 10,000 milligrams per 

liter. Elevations and extents of units that do not exist onshore 

in Long Island, New York, were not included north of New 

Jersey. Hydrogeologic units in North Carolina were included 

primarily to provide continuity across the Virginia-North 

Carolina State boundary, which was important for defining 

the southern edge of the Northern Atlantic Coastal Plain 

study area.

Introduction

The U.S. Geological Survey (USGS) Northern Atlantic 

Coastal Plain (NACP) aquifer system groundwater availability 

study is part of a national assessment of groundwater availability 

conducted through the USGS Groundwater Resources Program. A 

major goal of these studies is to provide updated information about

the current status of groundwater resources in principal aquifers 

and to develop tools and datasets to assist State, county, municipal, 

and water-management agencies with making long-term 

groundwater-management decisions (Reilly and others, 2008).

Although the NACP (fig. 1) aquifer system is one of the 

smallest by area of the 66 principal aquifer systems in the 

Nation recognized by the U.S. Geological Survey (Miller, 2000), 

it ranks 13th overall in terms of total groundwater withdrawals 

(Reilly and others, 2008). Despite abundant precipitation (about 

45 inches per year [in/yr]), the supply of fresh surface water in 

this region is limited because many of the coastal surface waters 

are brackish estuaries. As a result, many communities in the 

NACP rely heavily on groundwater to meet their water demand. 

These groundwater resources, however, can be limited by the 

amount of available drawdown, drought, saltwater intrusion, 

and agricultural and industrial contamination.

Increases in population and changes in land use during 

the past 100 years have resulted in diverse, increased demands 

for freshwater throughout the NACP. Substantial groundwater 

withdrawals had begun in the northern part of the study area 

by the late 1800s. By 1900, about 100 million gallons per day 

(Mgal/d) of water was pumped from the NACP aquifer system 

(Masterson and others, 2016b). Groundwater serves as a vital 

source of drinking water for the approximately 20 million 

people who live in the region and accounts for about 

40 percent of the drinking water supply (Kenny and others, 

2009). Total groundwater withdrawal in 2005 was estimated 

to be about 1,500 Mgal/d in the study area and included 

withdrawals for industrial and commercial use, irrigation, 

self-supplied domestic, and many other purposes in addition 

to municipal water supply (Masterson and others, 2013). 
2 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Figure 1. Location and extent of the Northern Atlantic Coastal Plain study area, showing elevation and bathymetry.

James River

Potom

R

ac

iver

masterson_nacp_fig 01_v3

Long Island

Trenton

New York City

Philadelphia

Dover Baltimore

Annapolis

Richmond

Greenville

Cape

May

Virginia

Beach

78° 75° 72°

DC

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34°30' N and 41°30' N

Central meridian 75°30' W 

North American Datum of 1983

Chesapeake Bay

Delaware Bay

Long Island Sound

Susquehanna

MA

RI

CONNECTICUT

NEW YORK

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

ERAWALED

NORTH CAROLINA

Pamlico Sound

Albemarle

Sound

ATLANTIC OCEAN

Continental Shelf margin

River

DELMARVA

PENINSULA

0 50 100 MILES

0 50 100 KILOMETERS

Study area

Raritan Bay

Fall Zone James River

Potomac River

EXPLANATION

Elevation, in feet above or

 below NAVD 88 

High : 0

Low : –7,105

Bathymetry—Data from National

 Oceanic and Atmospheric

 Administration (undated) and

 Amante and Eakins (2009)

Topography—Data from

 U.S. Geological Survey

 (undated) 

High : 563

Low : 1

Modeled extent of unit elevations

Northern Atlantic Coastal Plain

 study area

Chesapeake Bay impact crater

41°

38°

35°
Introduction 3

The effects of these large withdrawals include extensive 

declines in water levels and resulting changes in the aquifers of 

the NACP, many of which extend across State lines and create 

the potential for a variety of interstate and regional groundwater-management issues. A groundwater availability study 

of the NACP was conducted primarily to address the regional 

challenges in analyzing and understanding groundwater 

resources. As part of the study, the hydrogeology and hydrologic conditions of the NACP aquifer system are discussed 

in detail by Masterson and others (2013). The analyses of 

groundwater flow and availability in the NACP aquifer 

system are detailed in Masterson and others (2016a) and were 

based on a regional groundwater model of the aquifer system 

documented in Masterson and others (2016b).

A fundamental component of understanding groundwater 

flow in this region is the detailed delineation of the various 

aquifers and confining units that make up this complex system. 

At the regional level, this delineation involves correlation of 

hydrogeologic units described and mapped at the state level, 

as well as some generalization of these units to fit the scale 

of the regional hydrogeologic model. In a comprehensive 

study of the NACP aquifer system as part of the USGS 

Regional Aquifer-System Analysis (RASA) program, the 

regional hydrogeologic framework was described in detail 

by Trapp (1992). The report by Trapp (1992) also outlines 

about a century of previous investigations contributing to 

understanding the hydrogeology of the NACP aquifer system. 

Information on the geometry of the aquifer system, however, 

is available only on paper maps, not in digital form. In addition, approximately two decades of subsequent investigations 

have contributed substantially to the cumulative knowledge 

about the NACP aquifer system. 

The various revisions to the delineation of the NACP 

regional aquifer system are described in detail in Masterson 

and others (2013) and include much more data than previously 

published on unit geometries and a substantially improved 

understanding of unit correlations across State boundaries. 

Various recent state-level studies by the USGS and cooperating agencies have redefined several of the aquifers and 

confining units in the system. Among other details, the 

understanding of spatial differences within the Potomac 

aquifer system from north to south has been considerably 

enhanced (Andreasen and others, 2013; McFarland, 2013). 

Also, substantial recent work has described the geometry 

and characteristics of the Chesapeake Bay impact crater 

buried within the Coastal Plain of Virginia, which has had 

a tremendous effect on the aquifer system and groundwater 

flow in that area (McFarland and Bruce, 2006). In addition 

to incorporating the results of many additional studies, the 

revisions to the NACP regional aquifer system include updates 

to regional names for aquifers and confining units that are 

more consistent with local names in the NACP focus area of 

New York, New Jersey, Delaware, Maryland, and Virginia. 

Also, important advancements in computer mapping technology during the two decades since the last NACP framework 

report have resulted in the ability to better map, visualize, and 

understand the aquifer system in three dimensions. State-level 

datasets delineating hydrogeologic unit geometries have been 

published in several state-level studies, but the current data 

series report and accompanying data release include the first 

comprehensive digital dataset describing the geometry of the 

entire NACP aquifer system.

Purpose and Scope

This report describes spatially referenced digital datasets 

delineating the regional hydrogeologic units of the NACP 

aquifer system, which are provided in a related data release 

(Pope and others, 2016). The 19 regional hydrogeologic 

units are delineated by elevation grids and extent polygons 

for 20 layers: the land and bathymetric surface at the top 

of the unconfined surficial aquifer, the upper surfaces of 

9 confined aquifers and 9 interlayered confining units, and 

the bedrock surface defining the base of all NACP sediments. 

Polygons defining the extents of the regional hydrogeologic 

units are also described and included. Except for the layer 

defining the land surface and bathymetric elevations, each 

of the regional hydrogeologic unit top elevation layers 

corresponds to the base of one or more other units, so that unit 

thicknesses may be determined by comparison of the various 

overlapping surfaces, depending on the units present at any 

particular location.

The regional hydrogeologic units presented here and 

available in the data release are described in detail in a 

report on the hydrogeology and hydrologic conditions of the 

NACP aquifer system (Masterson and others, 2013), which 

introduces and supports a recent comprehensive analysis of 

groundwater availability in this aquifer system (Masterson and 

others, 2016a). That NACP groundwater availability study 

relied on analyses from a regional NACP groundwater flow 

model (Masterson and others, 2016b), for which the regional 

hydrogeologic units presented in the current report are a 

fundamental component.

This report, along with the NACP hydrologic conditions 

report by Masterson and others (2013), updates the NACP 

regional framework information provided by Trapp (1992), 

incorporating more than two decades of additional work 

in various parts of the study area. The report synthesizes 

information from state-level investigations in New York 

(Smolensky and others, 1989), New Jersey (Zapecza, 

1989; Voronin, 2003), Maryland and Delaware (Andreasen 

and others, 2013), Virginia (McFarland and Bruce, 2006; 

McFarland, 2013), and North Carolina (Gellici and Lautier, 

2010) and is dependent on these investigations for definition 

and interpretation of hydrogeologic units. The associations 

between the state-level units and the regional hydrogeologic 

units included in this report are shown in figure 2.

The construction of the regional hydrogeologic unit 

elevations and extents adhered as closely as possible to the 

referenced state-level data, combining units vertically where 

necessary and appropriate for regional representation and 

joining units and unit extents smoothly across boundaries. 
4 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

The goal was to produce consistent regional hydrogeologic 

units to support regional analyses and groundwater modeling. 

Individual state-level datasets and publications should remain 

the preferred sources of data for studies at more detailed scales.

The extents of all regional hydrogeologic units were 

clipped to an area approximately defined by the furthest 

offshore extent (in any unit) of the 10,000 milligram per liter 

(mg/L) chloride concentration contour (Charles, 2016). This 

delineation was chosen because it is approximately the halfway point between the chloride concentration in freshwater 

and modern sea water. Relatively little data on hydrogeologic 

unit elevations are available in offshore or saline areas of 

the aquifer system, and several of the source reports for this 

regional study defined a limited offshore extent. Extending 

the regional hydrogeologic units as presented here involves 

some extrapolation of unit elevations from source reports. 

However, some brackish parts of the aquifer system adjacent 

to the Chesapeake Bay impact crater in Virginia are important 

for groundwater supply and have been the subject of intensive 

recent investigation (McFarland and Bruce, 2006); therefore, 

inclusion of these brackish areas in the regional extent was 

important. Furthermore, the entire area around the impact 

crater was included in the selected extent even though most 

of the groundwater in the crater-fill units is very saline, 

because the identification of the impact-crater units represents 

a substantial addition to the knowledge of local and regional 

hydrogeology (McFarland and Bruce, 2006), and these units 

are known to substantially influence regional groundwater flow 

(Heywood and Pope, 2009). Units on Long Island that are not 

reported to exist onshore are not included north of Raritan Bay 

in the regional dataset because information on offshore extents 

and elevations are extremely sparse in that area. 

The study area for this investigation includes only the 

northeastern part of North Carolina because the focus of this 

analysis is the NACP hydrogeologic system from Long Island 

to the Virginia-North Carolina border. The hydrogeology 

and hydrogeologic conditions in the Coastal Plain of 

North Carolina and South Carolina were separately described 

NACP New York

(Long Island) New Jersey Delaware Maryland Virginia North Carolina

surficial upper glacial Holly Beach, 

unconfined upper Kirkwood-Cohansey surficial

upper Chesapeake Holly Beach upper Chesapeake Yorktown Yorktown

upper Chesapeake confined upper Kirkwood-Cohansey Pocomoke, 

Manokin

Pocomoke, 

Ocean City, 

Manokin

Yorktown-Eastover Yorktown

lower Chesapeake Saint Marys Pungo River

lower Chesapeake lower Kirkwood-Cohansey,

confined Kirkwood

Milford, 

Frederica, 

Federalsburg, 

Cheswold

Choptank, 

Calvert Saint Marys Pungo River

Calvert basal Kirkwood Calvert Castle Hayne

Piney Point Piney Point Castle Hayne

Nanjemoy-Marlboro Vincentown-Manasquan Nanjemoy-Marlboro* Beaufort

Aquia Vincentown Rancocas Aquia* Beaufort

Monmouth-Mount Laurel Navesink-Hornerstown Severn Peedee

Monmouth-Mount Laurel Wenonah-Mount Laurel Mount Laurel Monmouth Peedee

Matawan Marshalltown-Wenonah Matawan Virginia Beach Black Creek

Matawan Englishtown Matawan Virginia Beach Black Creek

Magothy Merchantville-Woodbury Matawan-Magothy Cape Fear

Magothy Magothy upper Potomac-Raritan-Magothy Magothy Magothy upper Cape Fear, 

lower Cape Fear

Potomac Raritan Magothy-Patapsco Potomac,*

upper Cenomanian upper Cenomanian 

Potomac-Patapsco Lloyd middle Potomac-Raritan-Magothy upper Patapsco,

lower Patapsco Potomac* Lower Cretaceous

Potomac-Patuxent Arundel Clay

Potomac-Patuxent lower Potomac-Raritan-Magothy Patuxent, 

Waste Gate

Patuxent, 

Waste Gate

bedrock basement

absent

unnamed

unnamed

unnamed

absent absent

absent

absent

masterson_nacp_fig 05_new

Figure 2. Regional hydrogeologic units and corresponding state-level hydrogeologic units for the Northern Atlantic Coastal Plain 

(NACP) aquifer system. Unit names for New York are from Smolensky and others (1989); for New Jersey, from the U.S. Geological 

Survey New Jersey Water Science Center (unpub. data, 2011); for Virginia, from McFarland and Bruce (2006); and for North Carolina, 

from Gellici and Lautier (2010). Units for Delaware and Maryland are from Andreasen and others (2013), but the units in Delaware 

were not the primary focus of that report. Regional units are from Masterson and others (2013) and this report. Units shaded in gray 

are confining units; units that are unshaded are aquifer units. Aquifers and associated confining units indicated with an asterisk 

are truncated in part of Virginia by sediments related to the Chesapeake Bay impact crater. Hydrogeologic units shown in bold 

italic font are those in southern Maryland that extend across the State border into northern Virginia. Unit name descriptors such as 

“lower” and “upper” are shown without capital letters for internal consistency in this report, except for Lower Cretaceous, which 

corresponds to a formal geologic unit name. This format may differ from the source references.
Methods Used 5

in a previous groundwater availability study by Campbell and 

Coes (2010). Regional hydrogeologic units in North Carolina 

are included only to provide continuity across the VirginiaNorth Carolina State boundary, which was important for 

defining the southern edge of the NACP study area.

Location and Physical Setting

The part of the NACP that was included in this investigation occupies a land area of more than 30,000 square miles 

and a total area of about 50,000 square miles along the eastern 

seaboard of the United States from Long Island, New York, 

southward to the northeastern part of North Carolina (fig. 1). 

A seaward-dipping wedge of mostly unconsolidated stratified 

sediments composed of clay, silt, sand, and gravel underlies 

this area, ranging in age from Early Cretaceous to Holocene. 

This sedimentary wedge forms a complex groundwater system 

in which layers of sand and gravel function predominantly as 

aquifers, and layers of silt and clay function as confining units. 

The western limit of the NACP is the Fall Zone, the transition 

between older consolidated bedrock near land surface and the 

unconsolidated sedimentary deposits of the NACP. From the 

Fall Zone, the bedrock dips beneath the sedimentary wedge 

to constitute the basement that underlies the entire study area 

(McFarland and Bruce, 2006).

The NACP sedimentary wedge is aligned approximately 

parallel to the Fall Zone and dips and thickens to the east 

and south from a thin edge in the Fall Zone. Sediments 

in the NACP are typically thousands of feet thick along 

the coast, with a maximum thickness of about 10,000 feet 

(ft) near the edge of the Continental Shelf. Coastal Plain 

sediments are continuous along the entire Continental 

Shelf, from Newfoundland in the north to Honduras in 

the south, but are entirely submerged north of Cape Cod, 

Massachusetts (Trapp, 1992). The eastern end of Long Island 

is considered the northern limit of the continuous exposure of 

Coastal Plain sediments. 

The complex and variable topography of the NACP—

reflecting rising and falling sea levels, erosion and deposition 

by major rivers, and several episodes of glaciation on Long 

Island—is described in detail in Masterson and others (2013). 

Land-surface elevations are relatively low, ranging from a 

few hundred feet above the North American Vertical Datum 

of 1988 (NAVD 88) in the Fall Zone to approximately zero 

along the coastline. Ocean depth generally is less than a few 

hundred feet across most of the offshore parts of the study 

area, though it increases to thousands of feet at the edge of the 

Continental Shelf.

Methods Used

Definitions and dimensions of regional hydrogeologic 

units described in this report were constructed from the most 

current, available data from state-level reports. These data 

vary in their composition, but all included (at a minimum) 

hydrogeologic unit elevations in the form of contour lines and 

defined unit extents delineated by polygon boundaries. These 

datasets were the fundamental building blocks of the regional 

hydrogeologic units described in this report. The development of hydrogeologic unit elevations for the various source 

reports typically involved the construction of unit elevation 

contours from point data (commonly well logs) interpreted 

by hydrologists and geologists. However, log data were not 

used for the delineation of the regional hydrogeologic units 

described in this report, of which construction relied almost 

entirely on the hydrogeologic unit layer contours described in 

the source reports. 

Sources of Data

The regional hydrogeologic units presented here primarily 

were derived from the most recently published spatial data 

available for States and subregions within the NACP (table 1). 

These publications outline the history of the development of 

hydrogeologic interpretations in the individual areas.

Digital hydrogeologic data for Long Island, New York, 

were obtained from the USGS New York Water Science 

Center as digitized versions of files described in the report by 

Smolensky and others (1989). The data used for the current 

study consisted of elevation contours and extents for the 

primary regional hydrogeologic units present on Long Island, 

which do not include a series of units located between the 

surficial aquifer and the Magothy aquifer elsewhere in the 

study area (fig. 2). The report by Smolensky and others (1989) 

mentions the reported presence of these additional Coastal Plain 

units offshore of Long Island, but includes no spatial information regarding the exact location or geometry of these units.

Table 1. Primary sources of information for hydrogeologic units in States within the 

Northern Atlantic Coastal Plain.

Geographic area Source of data 

New York (Long Island) Smolensky and others, 1989

New Jersey Zapecza, 1989; U.S. Geological Survey, unpub. data, 2011

Maryland-Delaware Andreasen and others, 2013

Virginia McFarland and Bruce, 2006; McFarland, 2013

North Carolina Gellici and Lautier, 2010; McFarland, 2013
6 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

For New Jersey, digital data on the New Jersey 

hydrogeologic framework were obtained from the USGS 

New Jersey Water Science Center (unpub. data, 2011). These 

data include updates to Voronin (2003) and to the New Jersey 

hydrogeologic framework described by Zapecza (1989). The 

digital data obtained from New Jersey included unit elevation 

contours and extents, as well as unit elevation rasters.

Digital data for Maryland and Delaware and adjacent 

areas of Virginia were obtained from the Maryland Coastal 

Plain Aquifer Information System (MCPAIS), which was 

developed cooperatively by the Maryland Geological Survey 

and the USGS Maryland-Delaware-District of Columbia 

Water Science Center. The MCPAIS, documented in a report 

by Andreasen and others (2013), is a geographic-informationsystem tool that includes hydrogeologic unit elevation 

contours and rasters, as well as polygon unit extents and a 

variety of other related hydrogeologic data. Hydrogeologic 

unit elevations for Delaware and northern Virginia were 

included in the MCPAIS for continuity with Maryland, but 

were not the focus of the MCPAIS (Andreasen and others, 

2013). The MCPAIS hydrogeologic data were used for 

Delaware because the scale of the data was more appropriate 

for regional analysis than local-scale information otherwise 

available for Delaware. 

Data for Virginia and adjacent areas of Maryland and 

North Carolina were obtained from a recent publication by 

McFarland and Bruce (2006) on the hydrogeologic framework 

of the Virginia Coastal Plain. Available digital data include 

extents, elevation contours, and elevation rasters, along 

with a variety of other hydrogeologic information. Several 

of the Virginia hydrogeologic units described in the current 

report extend into northeastern North Carolina. A subsequent 

investigation, specifically focused on the extent and characteristics of the Potomac aquifer in Virginia, also was useful 

in the correlation of hydrogeologic units across the VirginiaNorth Carolina border (McFarland, 2013). Information 

from Andreasen and others (2013) was used to supplement 

hydrogeologic information in northern Virginia because that 

report includes the most recent analysis of hydrogeologic units 

along the Maryland-Virginia border.

Hydrogeologic data obtained for the northeastern corner 

of the North Carolina Coastal Plain are documented by 

Gellici and Lautier (2010) as part of the recent groundwater 

availability study for the Atlantic Coastal Plain of North and 

South Carolina (Campbell and Coes, 2010). The report by 

McFarland (2013) incorporates information from more recent 

publications to revise and update the understanding of some of 

the correlations between Virginia and North Carolina Coastal 

Plain hydrogeologic units, and the unit delineations in the 

current report reflect that revised understanding.

Delineation of Regional Hydrogeologic Units

The correlation of hydrogeologic units across State 

boundaries was based on previous regional studies, such as 

Trapp (1992), as well as the cooperative work of individual 

authors of the source data, which includes studies across State 

boundaries. The regional units for the current report aggregate 

the units described in the various source reports with the 

correlation of equivalent units across State boundaries, the 

combination of multiple local units into more generalized 

regional units, the interpolation of individual units across 

State boundaries, and the extrapolation of individual units into 

offshore areas not included in source datasets.

Elevation contours and unit extent polygons were 

assembled and adjusted for each of the regional hydrogeologic 

units listed in figure 2, except for the elevation dataset 

describing the land and bathymetric surface. A uniform 

regional dataset of basement surface elevation contours was 

assembled from state-level source data to define the bottom 

of the NACP aquifer system. 

Elevations for the land and bathymetric surface—which 

define the top of the surficial aquifer—were obtained from 

a digital elevation model (DEM) assembled at a horizontal 

resolution of 100 ft and a vertical resolution of 1 ft for the 

entire study area. Land-surface elevation data for the project 

DEM were obtained from the USGS National Elevation 

Dataset (NED) at 30-meter (1 arc second) resolution 

(U.S. Geological Survey, n.d.), and bathymetric elevation data 

were assembled from two sources: the National Oceanic and 

Atmospheric Administration (NOAA) 90-meter (3 arc second) 

U.S. Coastal Relief model (National Oceanic and Atmospheric 

Administration, n.d.) and the NOAA ETOPO1 1 arc minute 

global relief model (Amante and Eakins, 2009). The higherresolution terrestrial NED was used as the basis for the 

topographic and bathymetric model, and NED elevations 

were rounded systematically to the nearest integer, in feet. 

Elevations greater than zero were defined as terrestrial areas, 

and all NED elevations between zero and 1 ft were rounded 

up to a value of 1. Areas with NED values of zero or less were 

defined as submerged areas, and the two bathymetric datasets 

were used to fill in the defined submerged areas with elevations at or below NAVD 88. The resulting combined DEM, 

with a horizontal resolution of 100 ft, became the baseline for 

the initial analyses of all other hydrogeologic unit elevations. 

This regional 100-ft topographic and bathymetric DEM is 

provided with the data release for this report (Pope and others, 

2016), with the file name nacp_dem100ft (table 2). 

For each of the remaining hydrogeologic units and 

the basement surface, combined elevation contours were 

converted to triangular irregular networks (TINs) as a simple 

linear interpolation of the contours, and the TINs were 

then converted to rasters at the desired resolution of 100 ft, 

with raster cells coincident with the project topographic 

and bathymetric DEM. A series of comparisons between 

the hydrogeologic unit elevation rasters were conducted to 

eliminate vertical conflicts (intersections) between elevations 

in different hydrogeologic unit layers and produce an internally consistent elevation model of all the hydrogeologic units 

in the NACP aquifer system. Extent polygons of individual 

hydrogeologic units were used to constrain the horizontal 

extents of the unit rasters to their defined areas, and systematic 
Methods Used 7

comparisons between unit elevations were used to make final 

adjustments to individual unit elevations. The project DEM 

described previously was used as the ultimate upper boundary 

of all unit elevations because data for elevations at the surface 

of the earth generally are more accurate than for any of the 

subsurface units defined primarily by relatively sparse welllog and outcrop data. 

The model of hydrogeologic unit dimensions created 

by this process (at 100-ft horizontal resolution) was then 

sampled into a regional MODFLOW groundwater model 

(with 1-mile horizontal resolution) as a part of a project to 

further investigate and understand groundwater flow and 

availability in the study area (Masterson and others, 2016a, 

2016b). During the subsequent process of simulation and 

analysis of groundwater flow, adjustments and corrections to 

the regional hydrogeologic unit extents and elevations were 

made in some parts of the study area to correct previous errors 

and represent the best understanding of flow-system geometry. 

In order to represent the incorporated changes and to reflect 

the most appropriate resolution of the final three-dimensional 

model of hydrogeologic unit elevations, the unit elevations 

from the groundwater model were exported to uniform rasters 

at a resolution of 2,640 ft (0.5 mile). Systematic comparisons 

between regional hydrogeologic unit elevations at this scale 

produced the final regional hydrogeologic units published in 

this report. The final resolution characterizes the generalized 

regional nature of this model of hydrogeologic units and is 

sufficient to preserve the resolution of the source interpretive 

reports. Elevation values in the final rasters are interpolated to 

decimal feet from the integer values of the higher-resolution 

working files.

As components of a model of hydrogeologic unit 

elevations, the published digital unit elevations and extents 

(Pope and others, 2016) adhere to some basic guidelines used 

in the construction of the unit layers. The tops of all units have 

been assigned elevations across their entire regional extents, 

as defined from the extents in the various state-level source 

reports. However, the unit elevations in many of the source 

reports were not always referenced against land-surface or 

bathymetric elevations at the resolution of the best available 

topographic and bathymetric data. This means that contoured 

unit top elevations may be truncated by topographic and 

bathymetric elevations or, in some instances, by the elevations 

of other hydrogeologic units. This is common for units that 

crop out or subcrop in the Fall Zone, where land-surface 

elevations are highly variable. It is also common for many 

units in areas where river channels deeply incise the NACP 

and where land-surface elevations vary substantially across 

the river valleys. 

Where topographic or bathymetric surface elevations 

conflicted with modeled elevations of hydrogeologic units, 

the topographic and bathymetric elevations were used, and the 

Table 2. Names of digital data files for elevations and extents of regional hydrogeologic units of the Northern Atlantic Coastal Plain 

(NACP) aquifer system available in Pope and others (2016).

[Files for each unit include elevation rasters in GRID format, elevation data in ASCII (.txt) format, and unit extents in polygon shapefile (.shp) format]

Layer Hydrogeologic unit Elevation raster file Elevation ASCII file Extent polygon file

1 Surficial aquifer nacp_aq01surf nacp_aq01surf.txt nacp_hyd_unit_bound.shp

2 Upper Chesapeake confining unit nacp_cu01 nacp_cu01.txt nacp_cu01_ext.shp

3 Upper Chesapeake aquifer nacp_aq02upch nacp_aq02upch.txt nacp_aq02upch_ext.shp

4 Lower Chesapeake confining unit nacp_cu02 nacp_cu02.txt nacp_cu02_ext.shp

5 Lower Chesapeake aquifer nacp_aq03loch nacp_aq03loch.txt nacp_aq03loch_ext.shp

6 Calvert confining unit nacp_cu03 nacp_cu03.txt nacp_cu03_ext.shp

7 Piney Point aquifer nacp_aq04pipt nacp_aq04pipt.txt nacp_aq04pipt_ext.shp

8 Nanjemoy-Marlboro confining unit nacp_cu04 nacp_cu04.txt nacp_cu04_ext.shp

9 Aquia aquifer nacp_aq05aq nacp_aq05aq.txt nacp_aq05aq_ext.shp

10 Monmouth-Mount Laurel confining unit nacp_cu05 nacp_cu05.txt nacp_cu05_ext.shp

11 Monmouth-Mount Laurel aquifer nacp_aq06moml nacp_aq06moml.txt nacp_aq06moml_ext.shp

12 Matawan confining unit nacp_cu06 nacp_cu06.txt nacp_cu06_ext.shp

13 Matawan aquifer nacp_aq07mtwn nacp_aq07mtwn.txt nacp_aq07mtwn_ext.shp

14 Magothy confining unit nacp_cu07 nacp_cu07.txt nacp_cu07_ext.shp

15 Magothy aquifer nacp_aq08mgty nacp_aq08mgty.txt nacp_aq08mgty_ext.shp

16 Potomac confining unit nacp_cu08 nacp_cu08.txt nacp_cu08_ext.shp

17 Potomac-Patapsco aquifer nacp_aq09popt nacp_aq09popt.txt nacp_aq09popt_ext.shp

18 Potomac-Patuxent confining unit nacp_cu09 nacp_cu09.txt nacp_cu09_ext.shp

19 Potomac-Patuxent aquifer nacp_aq10_popx nacp_aq10_popx.txt nacp_aq10popx_ext.shp

20 Basement nacp_cu10bsmt nacp_cu10bsmt.txt nacp_hyd_unit_bound.shp

NA Topography and bathymetry (100 feet) nacp_dem100ft nacp_dem100ft.txt nacp_area_bnd_fmwk.shp
8 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

topographic or bathymetric elevations were assigned to the 

intersected units in the regional framework. This resulted in 

several hydrogeologic units with areas of zero thickness and 

top elevations equal to topographic or bathymetric elevations; 

in some instances, several consecutive units were affected. The 

result may be hydrogeologic units that are highly variable or 

intermittently absent (thickness of zero) within their defined 

extents. Although this circumstance may seem to be the result 

of data artifacts, it actually provides a reasonable model of 

the affected hydrogeologic units, some of which have been 

observed to be widely sculpted by erosion, creating windows or 

channels to deeper units that have not been altered or truncated 

entirely (McFarland and Bruce, 2006). Regardless, even at a 

relatively coarse resolution, representation of the complexity 

of the interlayered NACP aquifer system is challenging, 

particularly when interpolating thin units across large areas. 

GIS Formats for Digital Datasets

 Geographic information system (GIS) software 

(ArcGIS 10.1 from Environmental Systems Research Institute) 

was used to construct the digital raster surfaces representing 

the top elevations of the regional hydrogeologic units, 

as well as the polygons of unit extents. The 20 elevation 

rasters—the tops of each of the 19 units and the regional 

basement—have a common horizontal resolution of 2,640 ft 

(0.5 mile) and are aligned to the same base raster, though the 

rasters may define units that have different spatial extents. 

Land surface, bathymetric, and unit elevation values are in 

integer feet, relative to the NAVD 88. Raster files are provided 

in both ESRI GRID format and in an American Standard Code 

for Information Interchange (ASCII) format that can be read 

by a wide variety of GIS systems. Polygon features delineating 

the extents of the various hydrogeologic units are provided in 

shapefile (.shp) format.

The higher resolution (100 ft) DEM of the topographic 

and bathymetric surface described in the Methods section of 

this report is also included with the digital data (table 2). This 

raster dataset, with elevations to the nearest integer foot, is 

not used to define the regional hydrogeologic units described 

in this report but is provided for use in other possible 

applications in the NACP at greater detail than the NACP 

regional hydrogeology.

All geospatial datasets use a custom Albers Equal-Area 

Conical projected coordinate system with a central meridian of 

–75.5 degrees and standard parallels of 34.5 and 41.5 degrees.

The horizontal datum is the North American Datum of 1983

(NAD 83).

Regional Hydrogeologic Unit 

Elevations and Extents

The delineation of regional hydrogeologic units requires 

recognition of unit equivalents across state boundaries. 

Furthermore, the use of the regional framework data requires 

an understanding of the relations between the regional 

hydrogeologic units and those in individual States. The NACP 

regional hydrogeologic units are described by Masterson and 

others (2013); brief discussions in the current report primarily 

provide details regarding the relations between the regional 

and State units in the construction of the digital data. The unit 

relations are outlined in the chart in figure 2.

Bedrock Basement

The bedrock basement defines the bottom of the entire 

NACP aquifer system, and the approximate intersection of the 

basement surface with the land surface defines the western 

edge of the NACP in the Fall Zone where Coastal Plain 

sediments approach a thickness of zero (fig. 1). The basement 

itself is not a hydrogeologic unit but instead serves as a 

relatively impermeable lower boundary for the aquifer system 

and is included here for this reason. The bedrock basement is 

readily distinguished from the various sediments across the 

extent of the NACP, but data delineating the basement surface 

are highly variable and generally sparse. Few wells penetrate 

to basement in the eastern part of the study area, and the lack 

of offshore data required substantial extrapolation of elevation 

contours beyond the coastline. Nevertheless, the various data 

sources used for the definition of the regional surface showed 

general agreement regarding the slope and elevation of the 

basement surface with areas of higher definition where more 

supporting data were available.

Potomac-Patuxent Aquifer

The Potomac-Patuxent regional aquifer is the lowermost 

hydrogeologic unit in the NACP aquifer system, and it directly 

overlies the regional basement in a large part of the study area 

(fig. 3). The regional aquifer includes the lower PotomacRaritan-Magothy aquifer system in New Jersey, and the 

Patuxent and Waste Gate aquifers in Delaware, Maryland, and 

northern Virginia (fig. 2). Its presence in the northern part of 

the Virginia Coastal Plain is indicated by Andreasen and others 

(2013). In Delaware, Maryland, and northern Virginia, this 

regional aquifer combines two aquifers that have been locally 
Regional Hydrogeologic Unit Elevations and Extents 9

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EXPLANATION

Modeled extent of Potomac-Patuxent aquifer

Modeled extent of unit elevations

ds_Pope_nacp_fig 03

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

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ATLANTIC OCEAN

41°

38°

35°

Figure 3. Location and extent of the Potomac-Patuxent regional aquifer.

differentiated and may have somewhat different hydrologic 

conditions: the overlying Patuxent aquifer and the deeper 

Waste Gate aquifer (Andreasen and others, 2013). 

The Potomac-Patuxent aquifer is absent beneath Long 

Island, New York, and most of the Coastal Plain of Virginia 

and North Carolina within the study area (fig. 3). In these 

areas, stratigraphically similar sediments do not exist, have not 

been differentiated from shallower units, or are not separated 

from the overlying Potomac-Patapsco aquifer by a regional 

confining unit. In these areas, the Potomac-Patapsco aquifer is 

the lowermost unit in the NACP aquifer system. 

The Potomac-Patuxent regional aquifer is bounded 

by an overlying confining unit over much of its extent, but 

the aquifer crops out or subcrops in the Fall Zone, where 

it approaches land surface, and it may be hydrologically 

continuous with sediments of the surfical aquifer.
10 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Potomac-Patuxent Confining Unit

The Potomac-Patuxent regional confining unit (fig. 4) 

overlies the Potomac-Patuxent aquifer and separates the 

aquifer from the Potomac-Patapsco aquifer above. The 

regional confining unit includes the unnamed confining unit 

overlying the lower Potomac-Raritan-Magothy aquifer in 

New Jersey and the Arundel Clay confining unit in Delaware, 

Maryland and northern Virginia (fig. 2). The PotomacPatuxent confining unit is composed of hard clays and silts 

within the fluvial-deltaic Potomac and Raritan Formations 

in New Jersey, Delaware, Maryland, and northern Virginia 

(Trapp, 1992). Its presence in the northern part of the Virginia 

Coastal Plain is indicated by Andreasen and others (2013).

The confining unit ranges in thickness from a thin western 

edge in the Fall Zone to more than 1,000 ft along the Atlantic 

coast in Delaware and pinches out south of the Potomac River 

in Virginia (Andreasen and others, 2013; McFarland, 2013). 

Regionally, this confining unit separates the underlying PotomacPatuxent aquifer from the Potomac-Patapsco aquifer above. 

Figure 4. Location and extent of the Potomac-Patuxent regional confining unit.

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ds_Pope_nacp_fig 04

ATLANTIC OCEAN

EXPLANATION

Modeled extent of Potomac-Patuxent 

confining unit

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°
Regional Hydrogeologic Unit Elevations and Extents 11

Potomac-Patapsco Aquifer

The Potomac-Patapsco regional aquifer (fig. 5) includes 

the Lloyd aquifer in New York (Long Island), the Middle 

Potomac-Raritan-Magothy aquifer in New Jersey, the upper 

and lower Patapsco aquifers in Delaware and Maryland, the 

undifferentiated Potomac aquifer in Virginia, and the Lower 

Cretaceous aquifer in North Carolina (fig. 2). In Maryland and 

Delaware, the Potomac-Patapsco aquifer combines two local 

aquifers—the upper Patapsco and lower Patapsco—separated 

by an intervening confining unit (Andreasen and others, 2013). 

In most of the Coastal Plain of Virginia (where the 

Potomac-Patuxent aquifer is absent) and North Carolina, 

the Potomac-Patapsco regional aquifer is composed of the 

single, heterogeneous Potomac aquifer (McFarland and 

Bruce, 2006; McFarland, 2013). In these locations, and in 

Long Island, N.Y., the Potomac-Patapsco aquifer is bounded 

below by the bedrock basement. The aquifer is bounded by 

an overlying confining unit over much of its extent, but the 

aquifer crops out or subcrops in the Fall Zone, where its top 

elevation approaches land surface and it may be hydrologically continuous with sediments of the unconfined surficial 

aquifer. Beneath the Eastern Shore of Virginia and the Chesapeake Bay, the Potomac-Patapsco aquifer is absent where it 

has been replaced by sediments of low permeability related to 

the Chesapeake Bay impact crater (fig. 5). 

Figure 5. Location and extent of the Potomac-Patapsco regional aquifer.

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Modeled extent of Potomac-Patapsco aquifer 

Potomac-Patapsco aquifer replaced by low-permeability 

sediments filling the Chesapeake Bay impact crater

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

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35°
12 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Potomac Confining Unit 

The Potomac-Patapsco aquifer is overlain over much 

of its extent by the regionally identified but locally highly 

variable Potomac regional confining unit (fig. 6). This unit 

is referred to as the Raritan confining unit in New York, the 

unnamed confining unit overlying the Middle PotomacRaritan-Magothy aquifer in New Jersey, the MagothyPatapsco confining unit in Delaware and Maryland, the 

Potomac confining zone in northern and central Virginia, 

and the upper Cenomanian confining unit in southeastern 

Virginia and northeastern North Carolina (fig. 2). Beneath the 

Eastern Shore of Virginia and the Chesapeake Bay, this unit is 

absent where it has been replaced by sediments of low permeability related to the Chesapeake Bay impact crater (fig. 6). 

Magothy Aquifer 

The Magothy regional aquifer is composed of two 

geographically separate northern and southern sections 

(fig. 7). The northern section is composed of the Magothy 

aquifer in New York, Delaware, and Maryland; and the 

upper Potomac-Raritan-Magothy aquifer in New Jersey 

(fig. 2). The Magothy aquifer is confined over much of its 

extent, but it crops out or subcrops in the Fall Zone where 

its top elevation approaches land surface and it may be 

hydrologically continuous with sediments of the unconfined 

surfical aquifer. On Long Island, sediments of the overlying 

Matawan and Monmouth Groups, as well as the local 

Jameco Gravel of Pleistocene age, are included in this 

regional aquifer (Smolensky and others, 1989).

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Modeled extent of Potomac confining unit 

Potomac confining unit replaced by low-permeability 

sediments filling the Chesapeake Bay impact crater

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 6. Location and extent of the Potomac regional confining unit.
Regional Hydrogeologic Unit Elevations and Extents 13

The Magothy aquifer on Long Island is in direct connection with the overlying unconfined upper glacial aquifer 

(regionally, the surficial aquifer) over most of its extent, 

and the water table is known to be present in the Magothy 

aquifer in some locations (Smolensky and others, 1989). The 

boundary between the surficial upper glacial aquifer and the 

Magothy aquifer on Long Island only is an unconformity that 

reflects the modification of the top of the Magothy aquifer by 

glacial activity in this area (Smolensky and others, 1989). The 

southern boundary of this section of the regional Magothy 

aquifer is north of the Potomac River in Maryland. 

The separate southern section of the Magothy aquifer 

is composed of the upper and lower Cape Fear aquifers in 

northeastern North Carolina. The sediments of these aquifers 

are of similar age and composition to the northern section 

of the Magothy aquifer, but these units are entirely separate. 

The Cape Fear aquifers are identified in North Carolina 

but not in Virginia, and their relation with the aquifers of 

southern Virginia is uncertain (McFarland and Bruce, 2006; 

McFarland, 2013). Consequently, the modeled extent of 

the southern section of the Magothy regional aquifer in this 

report is coincident with the border between Virginia and 

North Carolina. The known extent of this unit is not well 

constrained, and its correlation with other units is not well 

understood, but this unit may represent a subdivision of the 

Virginia Beach aquifer in Virginia.

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Modeled extent of Magothy aquifer

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 7. Location and extent of the Magothy regional aquifer.
14 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Magothy Confining Unit

Like the Magothy aquifer, the Magothy regional confining 

unit is composed of two geographically separate northern and 

southern sections (fig. 8). In the northern section, the Magothy 

confining unit overlies the Magothy regional aquifer over most 

of its extent, except on Long Island where the surficial aquifer 

directly overlies the Magothy aquifer, and except where it 

outcrops or subcrops in the Fall Zone. The regional confining 

unit includes the Merchantville-Woodbury confining unit in New 

Jersey and the Matawan-Magothy confining unit in Delaware 

and Maryland (Andreasen and others, 2013). On Long Island, 

the Magothy aquifer is confined over a limited extent along the 

southern shore by the local Gardiners Clay (Smolensky and others, 

1989), but the Gardiners Clay is not included in the regional 

confining unit because of uncertainty regarding continuity with 

the rest of the regional unit. The Gardiners Clay also has a much 

different composition than the regional confining unit and includes 

sediments of much different ages (Smolensky and others, 1989). 

The southern section of the Magothy regional confining 

unit has an approximate and modeled extent coincident with 

the border between Virginia and North Carolina. This section 

is composed of the Cape Fear confining unit identified in 

North Carolina but not in Virginia. Regionally, this confining 

unit delineates a subdivision of the Virginia Beach aquifer 

in Virginia into the Black Creek and Cape Fear aquifers in 

northern North Carolina, reflecting different interpretations of 

the unit configuration in the two locations. However, the extent 

of this possible division is not well constrained, so it is represented here with an extent following the State-line boundary.

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Modeled extent of Magothy confining unit

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

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35°

Figure 8. Location and extent of the Magothy regional confining unit.
Regional Hydrogeologic Unit Elevations and Extents 15

Matawan Aquifer

The Matawan regional aquifer includes a northern section in 

New Jersey, Delaware, and Maryland and a laterally discontinuous 

southern section in southeastern Virginia and northeastern North 

Carolina (fig. 9). The northern section of the Matawan regional 

aquifer includes the Englishtown aquifer in New Jersey and 

Delaware and the Matawan aquifer in Maryland (fig. 2). On 

Long Island, the regional Matawan aquifer is absent, though 

equivalent sediments of the Matawan Group are included with 

the regional Magothy aquifer (Smolensky and others, 1989). The 

southern limit of this section of the Matawan aquifer is north of the 

Maryland-Virginia State line and east of the Chesapeake Bay.

In the southern part of the study area, sediments of 

similar age and composition to the northern section of the 

Matawan aquifer form a local unit known as the Virginia 

Beach aquifer in southeastern Virginia that may be the thin 

northern edge of the Black Creek aquifer of North Carolina 

(McFarland and Bruce, 2006). The Virginia Beach and Black 

Creek aquifers are entirely separate from the units making up 

the Matawan aquifer of Maryland, Delaware, and New Jersey, 

but approximately equivalent in stratigraphic position.

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ds_Pope_nacp_fig 09

ATLANTIC OCEAN

Modeled extent of Matawan aquifer

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 9. Location and extent of the Matawan regional aquifer.
16 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Matawan Confining Unit 

The Matawan regional confining unit, like the Matawan 

aquifer it overlies, consists of two discontinuous sections in 

the northern and southern parts of the study area (fig. 10). In 

the northern section, the Monmouth-Mount Laurel aquifer 

is separated from the Matawan aquifer below by a regional 

confining unit that includes the Marshalltown-Wenonah 

confining unit in New Jersey and the Matawan confining unit 

in Delaware and Maryland (fig. 2). 

In the southern section in Virginia and Maryland, the 

regional confining unit separates the overlying Peedee 

aquifer from underlying units. This part of the Matawan 

confining unit includes the Virginia Beach confining 

zone in Virginia and the Black Creek confining unit in 

North Carolina.

78° 75° 72°

41°

38°

35°

ATLANTIC OCEAN

Modeled extent of Matawan confining unit

Modeled extent of unit elevations

EXPLANATION

VIRGINIA

VIRGINIA

WEST

PENNSYLVANIA

NORTH CAROLINA

MARYLAND

NEW

JERSEY

RI

MA

NEW YORK CONNECTICUT

DELAWARE

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

Figure 10. Location and extent of the Matawan regional confining unit.
Regional Hydrogeologic Unit Elevations and Extents 17

Monmouth-Mount Laurel Aquifer

The Monmouth-Mount Laurel regional aquifer includes 

a northern section in New Jersey, Delaware, and Maryland 

and a laterally discontinuous southern section in southeastern 

Virginia and northeastern North Carolina (fig. 11). The northern 

section of the Monmouth-Mount Laurel regional aquifer 

includes the Wenonah-Mount Laurel aquifer in New Jersey, the 

Mount Laurel aquifer in Delaware, and the Monmouth aquifer in 

Maryland (fig. 2). On Long Island, laterally equivalent sediments 

are included and grouped with the regional Magothy aquifer.

In the southern part of the study area, sediments of 

similar age form a unit known locally as the Peedee aquifer, 

which is not continuous with the northern section of the 

Monmouth-Mount Laurel aquifer but is considered part of 

the same regional aquifer. The extent of the Peedee aquifer is 

poorly constrained in southern Virginia because of sparse data 

(McFarland and Bruce, 2006).

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ds_Pope_nacp_fig 11

ATLANTIC OCEAN

Modeled extent of MonmouthMount Laurel aquifer

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 11. Location and extent of the Monmouth-Mount Laurel regional aquifer.
18 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Monmouth-Mount Laurel Confining Unit 

The Monmouth-Mount Laurel regional confining 

unit, like the Monmouth-Mount Laurel aquifer, consists of 

two discontinuous sections in the northern and southern 

parts of the study area (fig. 12). The northern section of 

the Monmouth-Mount Laurel regional aquifer is separated 

from the Aquia aquifer above by the regional confining unit 

that includes the Navesink-Hornerstown confining unit in 

New Jersey and the Severn confining unit in Delaware and 

Maryland (fig. 2). The thickness of the Monmouth-Mount 

Laurel confining unit is generally less than 100 ft.

The southern section of the regional confining unit 

includes the Peedee confining zone in Virginia and the 

Peedee confining unit in North Carolina. The designation 

of the unit as a confining zone in Virginia reflects the 

variable configuration and composition of the sediments 

above the Peedee aquifer and the transition to the overlying 

Aquia aquifer (McFarland and Bruce, 2006). The thickness 

of this section may be as great as several tens of feet in 

Virginia and up to 50 ft in North Carolina (McFarland and 

Bruce, 2006; Gellici and Lautier, 2010).

VIRGINIA

NORTH CAROLINA

NEW

JERSEY

RI

MA

NEW YORK CONNECTICUT

DELAWARE

78° 75° 72°

41°

38°

35°

ATLANTIC OCEAN

VIRGINIA

WEST

PENNSYLVANIA

MARYLAND

Modeled extent of Monmouth-Mount Laurel

confining unit

Modeled extent of unit elevations

EXPLANATION

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

0 50 100 KILOMETERS

Figure 12. Location and extent of the Monmouth-Mount Laurel regional confining unit.
Regional Hydrogeologic Unit Elevations and Extents 19

Aquia Aquifer

The Aquia regional aquifer (fig. 13) includes the Vincentown aquifer in New Jersey, the Rancocas aquifer in Delaware, 

the Aquia aquifer in Maryland and Virginia, and the Beaufort 

aquifer in North Carolina (fig. 2). The Aquia aquifer is not 

present on Long Island, but it may exist offshore south and east 

of Long Island. In the vicinity of the Chesapeake Bay impact 

crater in Virginia, the Aquia aquifer has been replaced by units 

related to the impact crater (McFarland and Bruce, 2006). 

Otherwise, the aquifer pinches out along its eastern boundary 

and has a very narrow extent in New Jersey. It is confined over 

most of its extent, but it crops out or subcrops in a narrow band 

in the Fall Zone where its top elevation approaches land surface.

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ds_Pope_nacp_fig 13

ATLANTIC OCEAN

Modeled extent of Aquia aquifer

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 13. Location and extent of the Aquia regional aquifer.
20 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Nanjemoy-Marlboro Confining Unit

Over most of its extent, the Aquia aquifer is overlain by the 

Nanjemoy-Marlboro regional confining unit, which separates 

the aquifer from the Piney Point regional aquifer above (fig. 14). 

This regional confining unit includes the Vincentown-Manasquan 

confining unit in New Jersey; the Nanjemoy-Marlboro Clay 

confining unit in Delaware, Maryland, and Virginia; and the 

Beaufort confining unit in North Carolina (fig. 2).

In the vicinity of the Chesapeake Bay impact crater, the 

Nanjemoy-Marlboro regional confining unit includes sediments

related to the impact crater. The impact disrupted or removed 

older and deeper sedimentary units that were present at the 

time of the impact, and the resulting crater was filled by 

impact-related sediments. The hydrogeologic units related to the 

impact crater and described in detail by McFarland and Bruce 

(2006) include the Exmore matrix and Exmore clast confining 

units, composed of crater-fill material deposited during and 

immediately after the impact, and the Chickahominy confining 

unit, composed of sediments which were later deposited in 

a depression above the impact-related sediments and extend 

well beyond the immediate area of the impact. Together, the 

Exmore confining units reach a maximum thickness of more 

than 4,500 ft. The confining units fill the area within the 

impact crater, either directly overlying the basement in the 

crater center or overlying the Potomac-Patapsco confining 

unit and aquifer around the crater margin where those units 

were not removed by the impact. For the purposes of regional 

hydrogeology, these units are all quite impermeable and have 

been grouped together in the same confining unit. 

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ATLANTIC OCEAN

Modeled extent of NanjemoyMarlboro confining unit

EXPLANATION

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

Outline of Chesapeake Bay 

impact crater

Modeled extent of unit elevations

41°

38°

35°

Figure 14. Location and extent of the Nanjemoy-Marlboro regional confining unit.
Regional Hydrogeologic Unit Elevations and Extents 21

Piney Point Aquifer

The Piney Point regional aquifer (fig. 15) includes the 

Piney Point aquifer in New Jersey, Delaware, Maryland, and 

Virginia, as well as the Castle Hayne aquifer in North Carolina 

(fig. 2). The Piney Point aquifer has not been identified 

onshore north of New Jersey (Smolensky and others, 1989). 

The aquifer is confined over its extent. It is thickest in the west 

and thinnest in the east, where it pinches out just offshore of 

the Atlantic Coast.

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ds_Pope_nacp_fig 15

ATLANTIC OCEAN

Modeled extent of Piney Point aquifer

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 15. Location and extent of the Piney Point regional aquifer.
22 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Calvert Confining Unit

The Calvert regional confining unit (fig. 16) separates 

the Piney Point regional aquifer from the lower Chesapeake 

regional aquifer above and includes the basal Kirkwood 

confining unit in New Jersey, the Calvert confining unit in 

Delaware, Maryland, and Virginia, and the Castle Hayne 

confining unit in North Carolina (fig. 2). As with the aquifers

it separates, this confining unit is absent in Long Island 

(fig. 16).

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ds_Pope_nacp_fig 16

ATLANTIC OCEAN

Modeled extent of Calvert confining unit

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 16. Location and extent of the Calvert regional confining unit.
Regional Hydrogeologic Unit Elevations and Extents 23

Lower Chesapeake Aquifer

The lower Chesapeake regional aquifer is composed of 

two discontinuous northern and southern sections (fig. 17). It 

includes the lower Kirkwood-Cohansey and confined Kirkwood aquifer system in New Jersey, the Milford, Frederica, 

Federalsburg, and Cheswold local aquifers in Delaware, 

the Choptank and Calvert local aquifers in Maryland, the 

Saint Marys aquifer in Virginia, and the Pungo River aquifer 

in North Carolina (fig. 2). The lower Chesapeake aquifer 

is absent on Long Island (Smolensky and others, 1989). In 

Maryland, this aquifer is limited to the Delmarva Peninsula 

and a small section west of the Chesapeake Bay (Andreasen 

and others, 2013). In Virginia, it is mostly absent west of 

the Chesapeake Bay except for a small portion south of the 

James River (McFarland and Bruce, 2006).

The lower Chesapeake aquifer is confined over most 

of its extent, but it includes updip, unconfined sections 

in New Jersey, Delaware, and Maryland where overlying 

confining units are absent and the aquifer likely is in direct 

hydraulic connection with the unconfined surficial aquifer 

(Andreasen and others, 2013).

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ds_Pope_nacp_fig 17

ATLANTIC OCEAN

Modeled extent of lower Chesapeake aquifer

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 17. Location and extent of the lower Chesapeake regional aquifer.
24 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Lower Chesapeake Confining Unit

The lower Chesapeake regional confining unit (fig. 18), 

separating the lower Chesapeake aquifer below from the 

upper Chesapeake aquifer above, includes an unnamed 

confining unit in New Jersey, the Saint Marys confining unit 

in Delaware, Maryland, and Virginia, and the Pungo River 

confining unit in North Carolina (fig. 2). The extent of the 

lower Chesapeake confining unit is shown in figure 18.

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ds_Pope_nacp_fig18

ATLANTIC OCEAN

Modeled extent of lower Chesapeake

confining unit

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 18. Location and extent of the lower Chesapeake regional confining unit.
Regional Hydrogeologic Unit Elevations and Extents 25

Upper Chesapeake Aquifer

The upper Chesapeake regional aquifer (fig. 19) includes 

the confined part of the upper Kirkwood-Cohansey aquifer 

in New Jersey; the Pocomoke and Manokin aquifers in 

Delaware; the Pocomoke, Ocean City, and Manokin aquifers 

in Maryland; the Yorktown-Eastover aquifer in Virginia; and 

the Yorktown aquifer in North Carolina (fig. 2). The upper 

Chesapeake aquifer is absent on Long Island (Smolensky and 

others, 1989).

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ds_Pope_nacp_fig19

ATLANTIC OCEAN

Modeled extent of upper Chesapeake aquifer

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 19. Location and extent of the upper Chesapeake regional aquifer.
26 Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System

Upper Chesapeake Confining Unit

The upper Chesapeake regional confining unit (fig. 20) 

overlies the upper Chesapeake aquifer over much of its 

extent and underlies the unconfined surficial aquifer. The 

regional confining unit includes the Holly Beach confining 

unit in New Jersey (only on the Cape May peninsula), the 

upper Chesapeake confining unit in Delaware and Maryland, 

the Yorktown confining zone in Virginia, and the Yorktown 

confining unit in North Carolina (fig. 2). The extent of the 

upper Chesapeake confining unit is shown in figure 20.

MA RI

NEW YORK CONNECTICUT

NEW

JERSEY

PENNSYLVANIA

VIRGINIA

WEST

MARYLAND

VIRGINIA

NORTH CAROLINA

DELAWARE

78° 75° 72°

ds_Pope_nacp_fig20

ATLANTIC OCEAN

Modeled extent of upper Chesapeake

confining unit

EXPLANATION

Modeled extent of unit elevations

Base from U.S. Geological Survey 1:2,000,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 34° 30' N and 41° 30' N

Central meridian 75° 30' W 

North American Datum of 1983

0 50 100 MILES

500 100 KILOMETERS

41°

38°

35°

Figure 20. Location and extent of the upper Chesapeake regional confining unit.
References Cited 27

Surficial Aquifer

The surficial aquifer is the uppermost aquifer in the 

NACP aquifer system, with its top defined as the land or 

bathymetric surface. The surficial aquifer is unconfined, 

mostly shallow, and exists throughout the NACP (fig. 1). Its 

thickness and characteristics are highly variable depending 

on local topography and depositional and erosional history. 

Across the NACP, the surficial aquifer is composed largely of 

permeable surficial sediments of Pleistocene to Holocene age, 

but may also include hydrologically continuous, permeable, 

older, underlying sediments where those sediments have 

not been differentiated from other units. In New Jersey, the 

regional surficial aquifer presented in this report includes 

the unconfined part of the undifferentiated upper KirkwoodCohansey aquifer and overlying local units that are hydraulically connected. The local, relatively shallow Holly Beach 

aquifer near Cape May, New Jersey, is also included in the 

regional surficial aquifer, where the underlying KirkwoodCohansey aquifer is confined. On Long Island, the surficial 

aquifer primarily is composed of thick glacial deposits and 

is referred to as the upper glacial aquifer. Across much of its 

extent on Long Island, the unconfined upper glacial aquifer is 

hydraulically continuous with the underlying Magothy aquifer 

(Smolensky and others, 1989). As a result, the bottom of the 

surficial upper glacial aquifer corresponds to the top of the 

Magothy aquifer on Long Island. 

The western extent of the surficial aquifer (and of the 

NACP) is defined by the extent of continuous Coastal Plain 

sediments in the Fall Zone, derived from a variety of surficial 

geologic maps of the study area and delineated by the extent 

polygon for the surficial aquifer, which also encompasses the 

extents of all other hydrogeologic units described in this report 

(fig. 1; table 1).

Limitations and Recommended 

Use of Data

The focus of this hydrogeologic framework is regional, 

and the regional correlation of the various hydrogeologic 

units involved considerable interpolation and extrapolation 

of unit elevations in areas where data were limited or absent. 

Conflicts between unit elevations among overlapping statelevel investigations were resolved by approximating unit 

elevations in the overlapping areas. In addition, the delineation 

of regional hydrogeologic units in some instances required 

aggregation of two or more local hydrogeologic units. Because 

of these necessary approximations, the most appropriate use 

of these data is for large-scale, regional-level analyses, as 

discussed in Masterson and others (2013) and Masterson and 

others (2016a). The use of state-level datasets that provided 

the fundamental data for this study (see Sources of Data) is 

suggested for more detailed work. These source publications 

also provide additional information on the spatial variability 

of data incorporated into the interpretations of hydrogeologic 

units described in this report.

Acknowledgments

The authors would like to thank Jennifer Krstolic of 

the USGS Virginia-West Virginia Water Science Center for 

assembling the high-resolution (100 ft) DEM of the land and 

bathymetric surface (fig. 1; table 2) which was also used to 

define the top of the surficial aquifer (layer 1) in the regional 

analysis of hydrogeologic units.

File Organization

File names provided in table 2 relate the documented 

digital geospatial files provided in the related data release 

(Pope and others, 2016) to the unit names given in this report.

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Andreasen, D.C., Staley, A.W., and Achmad, Grufron, 2013, 

Maryland Coastal Plain aquifer information system—

Hydrogeologic framework: Maryland Department of 

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availability in the Atlantic Coastal Plain of North and 

South Carolina: U.S. Geological Survey Professional 

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http://pubs.usgs.gov/pp/1773/.

Charles, E.G., 2016, Regional chloride distribution in the 

Northern Atlantic Coastal Plain aquifer system from 

Long Island, New York, to North Carolina: U.S. Geological 

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groundwater flow in the Coastal Plain aquifer system of 

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Finkelstein, J.S., and McCoy, K.J., 2013, Hydrogeology 

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Manuscript approved May 5, 2016

Prepared by the USGS Science Publishing Network

Edited by Kay P. Naugle

Layout by Caryl J. Wipperfurth

Reston Publishing Service Center

Illustrations by James E. Banton

Lafayette Publishing Service Center

For more information concerning this report, 

please contact:

Water Availability and Use Science Program

U.S. Geological Survey

150 National Center

12201 Sunrise Valley Drive

Reston, VA 20192 

https://www.usgs.gov/water-resources/

water-availability-and-use-science-program
Pope and others—Digital Elevations and Extents of Regional Hydrogeologic Units in the Northern Atlantic Coastal Plain Aquifer System—Data Series 996

ISSN 2327-638X (online)

, ver. 1.1

https://doi.org/10.3133/ds996