Scientific Investigations Report 2007–5250

Ground-Water Resources Program

Scientific Investigations Report 2007–5250

Private Domestic-Well Characteristics and the

Distribution of Domestic Withdrawals among

Aquifers in the Virginia Coastal Plain

Private Domestic-Well Characteristics and the

Distribution of Domestic Withdrawals among

Aquifers in the Virginia Coastal Plain

Ground-Water Resources Program

Scientific Investigations Report 2007–5250
Cover. Aerial photograph of rural residences self supplied with ground water from private domestic wells in eastern 

Hanover County, Virginia, November 1, 2002 (photograph taken by Jason P. Pope, U.S. Geological Survey).
Private Domestic-Well Characteristics and the 

Distribution of Domestic Withdrawals among 

Aquifers in the Virginia Coastal Plain

By Jason P. Pope, E. Randolph McFarland, and R. Brent Banks

Ground-Water Resources Program

Scientific Investigations Report 2007–5250

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Suggested citation:

Pope, J.P., McFarland, E.R., and Banks, R.B., 2008, Private domestic-well characteristics and the distribution of 

domestic withdrawals among aquifers in the Virginia Coastal Plain: U.S. Geological Survey Scientific Investigations 

Report 2007–5250, 47 p. (available online at http://pubs.water.usgs.gov/sir2007-5250)
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................5

Description of Study Area ...................................................................................................................6

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

Aquifers and Confining Units in the Virginia Coastal Plain.....................................................................8

Surficial Aquifer..................................................................................................................................11

Yorktown Confining Zone...................................................................................................................11

Yorktown-Eastover Aquifer ...............................................................................................................11

Saint Marys Aquifer............................................................................................................................11

Piney Point Aquifer.............................................................................................................................11

Aquia Aquifer.......................................................................................................................................12

Peedee Aquifer....................................................................................................................................12

Virginia Beach Aquifer.......................................................................................................................12

Potomac Confining Zone ...................................................................................................................12

Potomac Aquifer.................................................................................................................................12

Private Domestic-Well Characteristics....................................................................................................13

Selection of Localities for Sampling of Domestic-Well Records................................................15

Sampling of Private Domestic-Well Records.................................................................................15

General Characteristics of Private Domestic Wells .....................................................................19

Characteristics of Incidentally Sampled Private Irrigation Wells ..............................................19

Spatial Variability in Domestic-Well Characteristics....................................................................21

Estimated Elevations of Domestic-Well Screens ..........................................................................21

Assumptions and Limitations Related to Estimating Domestic-Well Characteristics.............29

Distribution of Domestic Wells and Withdrawals among Aquifers.....................................................29

Analyses of Hydrogeologic-Unit Elevations by Locality...............................................................29

Assignment of Domestic Wells and Withdrawals to Aquifers ....................................................30

Assumptions and Limitations Related to Assigning Domestic Wells 

and Withdrawals to Aquifers ..............................................................................................40

Spatial Distribution of Self-Supplied Domestic Withdrawals for a Ground-Water Model 

of the Virginia Eastern Shore........................................................................................................41

Summary and Conclusions.........................................................................................................................45

Acknowledgments.......................................................................................................................................46

References Cited..........................................................................................................................................46

Figures

1. Map showing locations of counties and independent cities, the Chesapeake Bay 

impact crater, and other important geographic and physiographic features 

of the Virginia Coastal Plain........................................................................................................2

2. Pie chart showing estimated ground-water withdrawals by category of use 

in the Virginia Coastal Plain in 2000...........................................................................................3

3. Map showing populations and percentages of populations in Virginia Coastal 

Plain localities served by self-supplied ground water in 2000..............................................4
iv

4. Generalized hydrogeologic section and directions of ground-water flow 

in the Virginia Coastal Plain ........................................................................................................9

5. Stratigraphic correlations of hydrogeologic units of the Virginia Coastal Plain..............10

6. Conceptual diagram demonstrating the relations among well depth, well head 

and screen elevations, land-surface elevation, and hydrogeologic unit elevations ......13

7. Flow chart of steps in the process of analyzing private domestic-well data, 

the apportionment of private domestic wells among aquifers, and the spatial 

distribution of self-supplied domestic withdrawals by aquifer in the Virginia 

Coastal Plain................................................................................................................................14

8. Histogram of depths to bottom of screen for private domestic wells in 

the Virginia Coastal Plain ..........................................................................................................19

9. Map showing median depths to bottom of screen by locality for private 

domestic wells in the Virginia Coastal Plain ..........................................................................22

10. Histograms of estimated domestic well-screen elevations for Virginia Coastal 

Plain localities .............................................................................................................................24

11–12. Maps showing:

 11. Population data by census block group in 2000, estimated public 

 water-supply areas, and road features in the Virginia Eastern Shore 

 ground-water model domain ...................................................................................43

 12. Estimated self-supplied domestic withdrawals of ground water 

 in the Virginia Eastern Shore in 2000, by ground-water model grid cell ..........44

Tables

1. Area, population, and water-supply characteristics of Virginia Coastal Plain 

localities, based on 2000 population and water-use data....................................................16

2. Estimated ground-water withdrawals in Virginia Coastal Plain localities in 2000...........17

3. Statistics for depth, in feet, to bottom of well screen for sample of private 

domestic wells in Virginia Coastal Plain localities................................................................20

4. Statistics for estimated elevation, in feet, of middle of well screen for a sample 

of private domestic wells in Virginia Coastal Plain localities..............................................23

5. Median elevations, in feet, of top of hydrogeologic units in Virginia Coastal 

Plain localities .............................................................................................................................31

6. Minimum elevations, in feet, of top of hydrogeologic units in Virginia Coastal 

Plain localities .............................................................................................................................32

7. Maximum elevations, in feet, of top of hydrogeologic units in Virginia Coastal 

Plain localities .............................................................................................................................33

8. Mean elevations, in feet, of top of hydrogeologic units in Virginia Coastal 

Plain localities .............................................................................................................................34

9. Proportions of Virginia Coastal Plain localities occupied by each 

hydrogeologic unit......................................................................................................................35

10. Number of sampled domestic wells assigned to each aquifer in the Virgnia 

Coastal Plain localities for which data were collected........................................................37

11. Estimated proportions of sampled domestic wells assigned to each aquifer 

in the Virginia Coastal Plain localities for which data were collected..............................38

12. Estimated self-supplied domestic withdrawals in 2000 by aquifer in Virginia 

Coastal Plain localities for which data were collected........................................................39
v

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L)

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

)

Flow rate

gallon per day (gal/d) 0.003785 cubic meter per day (m3

/d)

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

/s)

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

(NGVD 1929).

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

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

Abbreviations Used in this Report:

DEM digital elevation model

ESRI Environmental Systems Research Institute, Inc.

GIS geographic information system

HRPDC Hampton Roads Planning District Commission

NED National Elevation Dataset

RASA Regional Aquifer-System Analysis

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

UWWCR Uniform Water Well Completion Reports

VDEQ Virginia Department of Environmental Quality
vi

Terms Used in this Report

Domestic water use — as defined by the USGS National Water-Use Information Program, water 

used for all indoor household purposes, such as drinking, preparing food, bathing, clothes and 

dish washing, and toilet flushing, and for outdoor purposes, such as lawn and garden watering.

Independent city — an incorporated place that is a primary division of a State and not legally 

part of any county. The U.S. Census Bureau considers independent cities as county-equivalent 

entities for most purposes, and independent cities are included with counties as primary 

subdivisions of a State. Independent cities are designated only in Virginia and in three other 

States in the United States.

Irrigation water use — as defined by the USGS National Water-Use Information Program, 

water that is applied by an irrigation system to assist in the growing of crops and pastures or 

to maintain vegetation on recreational lands, such as parks and golf courses. In some areas of 

the Virginia Coastal Plain, private irrigation wells commonly are used to irrigate the lawns of 

individual residences. 

Public-supply water use — as defined by the USGS National Water-Use Information Program, 

water withdrawn by public and private water suppliers that furnish water to at least 25 people 

or have a minimum of 15 connections. Water is publicly supplied for a variety of uses, including 

domestic, commercial, industrial, thermoelectric power, and public water use. 

Private domestic well — a well supplying water to an individual residence for domestic use.

Private irrigation well — a well supplying water to an individual residence exclusively for 

outdoor purposes, such as lawn and garden watering.

Self-supplied withdrawal — water withdrawn directly from the source by a user rather than 

being obtained from a public supply. In Virginia, almost all known self-supplied withdrawals are 

from ground-water sources.
Abstract

A comprehensive analysis of private domestic wells 

and self-supplied domestic ground-water withdrawals in the 

Coastal Plain Physiographic Province of Virginia indicates that 

the magnitudes of these withdrawals and their effects on local 

and regional ground-water flow are larger and more important 

than previous reports have stated. Self-supplied ground-water 

withdrawals for domestic use in the Virginia Coastal Plain 

are estimated to be approximately 40 million gallons per day, 

or about 28 percent of all ground-water withdrawals in the 

area. Contrary to widely held assumptions, only 22 percent of 

domestic wells in the Virginia Coastal Plain are completed in 

the shallow, unconfined surficial aquifer to which the water is 

returned directly by home septic systems. Fifty-three percent 

of the wells are completed in six deeper confined aquifers, and 

the remaining 25 percent are completed in the Potomac aquifer 

and confining zone, the deepest units in the confined system. 

Assuming an equal rate of withdrawal per well, 78 percent 

of domestic ground-water withdrawal, or about 30 million 

gallons per day, is removed from the regional confined 

ground-water system.

Domestic ground-water withdrawal from an estimated 

200,000 private wells supplies more than 15 percent of the 

population of the area and provides almost the entire source of 

water in some rural counties. The geographic distribution of 

these withdrawals is dependent on the self-supplied population 

and is highly variable. Domestic-well characteristics vary 

spatially as well, primarily because of geographic differences 

in depths to particular aquifers, but also because of welldrilling practices that are influenced by geographic, regulatory, 

and socioeconomic factors.

Domestic ground-water withdrawals in the Virginia 

Coastal Plain were characterized as part of a larger study to 

analyze the regional ground-water flow system. Characterizing 

the withdrawals required differentiation of the withdrawals 

among the aquifers in the area in addition to determination 

of the geographic distribution of the withdrawals. Because 

of a lack of comprehensive data on private-well construction 

and distribution, a sample of private domestic-well records 

was used to estimate well characteristics and approximate 

the proportion of wells and withdrawals associated with 

each aquifer. Construction data on 2,846 private domestic 

wells were collected from 29 counties and independent cities 

(localities) having appreciable self-supplied populations and 

representing private domestic withdrawals of about 31 million 

gallons per day. Within each locality, geographically stratified 

random sampling of well records by tax plat characterized 

details of well construction for the population of domestic 

wells. Because neither specific location data nor aquifer 

elevations were available for individual wells, the primary 

aquifer in which each well is completed was estimated by 

cross-referencing the screen elevation estimated from the well 

record with a generalized configuration of hydrogeologic 

units underlying the locality in which the well is located. For 

each locality, summarizing the results of this process allowed 

the determination of the proportion of wells and withdrawals 

associated with each aquifer.

Additional evaluation of spatial data was used to apply 

the domestic withdrawal rates developed for each aquifer in 

each locality to a detailed ground-water study of the portion of 

the Virginia Coastal Plain east of the Chesapeake Bay, which 

is known as the Eastern Shore Peninsula. Because domestic 

withdrawal estimates are based on the self-supplied population, the geographic distribution of withdrawals within each 

of the Eastern Shore counties was estimated by using population data from the 2000 U.S. Census at the resolution 

of census block groups and further refining the distribution 

based on road density. The allocation of withdrawals among 

aquifers was then determined by cross-referencing the spatial 

distribution of withdrawals with the previously determined 

proportion of wells and withdrawals associated with each 

aquifer in each county. This procedure resulted in a detailed 

spatial distribution of domestic withdrawals for the Eastern 

Shore Peninsula and provides an example of how the 

domestic-well data and withdrawal estimates could be applied 

to other ground-water investigations.

Private Domestic-Well Characteristics and the 

Distribution of Domestic Withdrawals among 

Aquifers in the Virginia Coastal Plain

By Jason P. Pope, E. Randolph McFarland, and R. Brent Banks
2 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Introduction

Ground water is a vital and heavily used resource in 

the Virginia Coastal Plain Physiographic Province (fig. 1) 

for water supply to a large and growing regional population. 

Approximately 3.29 million people live in the Coastal Plain 

of Virginia, which is about 46 percent of Virginia’s total 

population of 7.08 million, based on analysis of 2000 census 

block group data (U.S. Census Bureau, 2001, 2003a). The 

rate of ground-water withdrawal in this area has increased 

almost continuously since the beginning of the 20th century, 

from less than 10 million gallons per day (Mgal/d) to almost 

140 Mgal/d, and the most substantial increase has occurred in 

the last half century.

Figure 1. Locations of counties and independent cities, the Chesapeake Bay impact crater, and other important 

geographic and physiographic features of the Virginia Coastal Plain.

0

0

25 50 MILES

25 50 KILOMETERS

39 ̊

38 ̊

37 ̊

78 ̊ 77 ̊ 76 ̊

PRINCE

WILLIAM

STAFFORD

CAROLINE

SPOTSYLVANIA

KING GEORGE

Fredericksburg

FAIRFAX

KING AND QUEEN

KING WILLIAM

MIDDLESEX

LANCASTER

RICHMOND

NORTHUMBERLAND

ESSEX

WESTMORELAND

HANOVER

HENRICO NEW KENT Richmond MATHEWS

GLOUCESTER

ACCOMACK

NORTHAMPTON

DINWIDDIE

SUSSEX

SURRY

ISLE OF WIGHT

CHARLES CITY

CHESTERFIELD

SOUTHAMPTON

Chesapeake

Virginia

Beach Emporia

GREENSVILLE

Suffolk

Franklin

PRINCE

GEORGE

Petersburg

Hopewell

Colonial

Heights

Norfolk

Portsmouth

Poquoson

Hampton Newport News

YORK

Williamsburg

JAMES

CITY

NORTH CAROLINA

MARYLAND

Delaware Fall Line

ATLANTIC OCEAN

CHESAPEAKE BAY

IMPACT CRATER

CHESAPEAKE BAY

Figure 1. Locations of counties and independent cities, the Chesapeake Bay impact crater, and other important

geographic and physiographic features of the Virginia Coastal Plain.

River

James

River

Coastal plain localities in which

 well data were collected

Coastal plain localities in which

 well data were not collected

EXPLANATION

ARLINGTON Washington, D.C.

Alexandria

VIRGINIA

NORTH CAROLINA

DELAWARE

MARYLAND

PENNSYLVANIA

VIRGINIA COASTAL PLAIN

CHESAPEAKE BAY

ATLANTIC OCEAN

Potomac River

River

Rappahannock

York

Eastern Shore

of Virginia
Introduction 3

In 2000, ground water was withdrawn from the Northern 

Atlantic Coastal Plain aquifer system in Virginia at an 

estimated rate of 137.4 Mgal/d (fig. 2) based on an analysis 

of the most recent data (U.S. Geological Survey, 2002). This 

sum includes withdrawals from portions of counties and 

independent cities (see “Terms Used in this Report”) only 

partially in the Coastal Plain Physiographic Province and 

accounts for nearly 44 percent of the estimated total groundwater withdrawal of 313.5 Mgal/d for all of Virginia. Of the 

137.4 Mgal/d in withdrawals, 62.6 Mgal/d (46 percent) were 

used for industrial and commercial purposes, 38.5 Mgal/d 

(28 percent) were self supplied for domestic purposes, 

32.3 Mgal/d (24 percent) were used for public supply, and 

2.5 Mgal/d (2 percent) were used for agricultural irrigation. 

The remaining 1.5 Mgal/d were used for other purposes 

(fig. 2; U.S. Geological Survey, 2002). 

Continued, long-term withdrawals for industrial, 

commercial, public-supply, domestic, and irrigation uses 

have caused ground-water levels to decline by as much as 

200 feet (ft) near large pumping centers, resulting in growing 

concern among water users and resource managers about 

local and regional ground-water supplies. Large declines in 

water levels have altered ground-water flow gradients from 

a previous seaward direction to a landward direction (Harsh 

and Laczniak, 1990), which creates the potential for saltwater 

intrusion. Projected increases in withdrawals could result in 

further water-level declines and limit continued use of the 

ground-water resources of the Virginia Coastal Plain. 

Concern about this limited resource has resulted in 

regulation and management of ground-water withdrawals by 

the Virginia Department of Environmental Quality (VDEQ). 

In order to maintain and provide a scientific basis for sound 

ground-water management decisions, the VDEQ and other 

State and local agencies participate in cooperative programs 

with the U.S. Geological Survey (USGS) to develop and 

enhance the scientific understanding of Virginia Coastal Plain 

hydrogeology. In recent years, concern about limitations of 

ground-water resources, hydrogeologic effects of the recently 

discovered Chesapeake Bay impact crater (fig. 1) and the 

saline water associated with its sediments, and current and 

proposed withdrawals of saline ground water for public water 

supplies have all led to comprehensive and ongoing investigations of the aquifer system.

The VDEQ regulates large withdrawals in heavy-use 

areas of the Coastal Plain, which are designated Ground Water 

Management Areas (Virginia Department of Environmental 

Quality, 2006a). These areas include southeastern Virginia 

and the two Eastern Shore counties of 

Accomack and Northampton. In the Ground 

Water Management Areas, withdrawals 

greater than 300,000 gallons per month 

must be approved by the Virginia Groundwater Withdrawal Permit Program, which 

requires the evaluation of the potential 

effects of new withdrawals on the groundwater system. Elsewhere in the Coastal 

Plain and in Virginia, the VDEQ requires 

non-agricultural withdrawals of greater than 

10,000 gal per day (gal/d) to be recorded 

and reported annually (Virginia Department 

of Environmental Quality, 2006b). 

As part of the regulatory program of 

the VDEQ, total withdrawals of almost 

100 Mgal/d for commercial, industrial, 

public-supply, and some agricultural use for 

the year 2000 were directly measured and 

reported from site-specific data. Detailed 

location, elevation, and construction data 

for over 1,100 wells in these categories are 

maintained by the VDEQ. Borehole logs 

for these wells generally were analyzed by 

professional geologists and hydrologists; 

therefore, good data on aquifer sources 

usually are available for these reported 

withdrawals. For wells with no aquifer data available, accurate 

well-location and screen-elevation data allow the aquifers to 

be inferred from available spatial data on hydrogeologic unit 

elevations. Thus, reasonably complete information is available for wells associated with major reported withdrawals, 

which enables a better understanding of the effects of these 

withdrawals on the ground-water flow system.

In contrast to the large, regulated and reported groundwater withdrawals that compose about 72 percent of the 

Industrial/Commercial

62.6 million gallons per day

45.6 percent 

Domestic (self-supplied)

38.5 million gallons per day

28 percent 

Public supply

32.3 million gallons per day

23.5 percent

Irrigation

2.5 million gallons per day

1.8 percent 

Other

1.5 million gallons per day

1.1 percent 

Figure 2. Estimated ground-water withdrawals by category of use in the Virginia 

Coastal Plain in 2000 (derived from U.S. Geological Survey, 2002).
4 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

estimated withdrawals in the Virginia Coastal Plain, little is 

known about domestic supplies to individual homes from 

private wells, which compose the remaining 28 percent. 

Little information is readily available on the locations or rates 

of these withdrawals, and even less is known about which 

aquifers are the sources of the water. Self-supplied domestic 

withdrawals in Virginia have been estimated almost entirely 

from population data because these withdrawals are not 

measured or reported, as is the case in many states (Hutson 

and others, 2004). In 2000, about 22 percent of the Virginia 

Coastal Plain population, or approximately 723,500 people, 

relied on ground water for household use; over 71 percent 

of these users, or approximately 514,400 people, were self 

supplied. This population of self-supplied domestic users is 

spatially variable, as shown in figure 3.

Figure 3. Populations and percentages of populations in Virginia Coastal Plain localities served by self-supplied 

ground water in 2000 (locations shown in fig. 1).

Figure 3. Populations and proportions of populations in Virginia Coastal Plain localities served by self-supplied

ground water in 2000 (locations shown in fig. 1).

0

1–25

26–50

51–75

76–100

PERCENTAGE OF LOCALITY POPULATION 

SERVED BY SELF-SUPPLIED GROUND WATER

Numbers on map indicate

self-supplied population

Washington, D.C.

19,321

8,542

16,209

0

5,089

13,989

41,380

0

0

35,211

0

0 0

1,410

500

8,390

60

0

12,538

6,126

14,247

8,081

0

24,870

6,290

9,431

17,711

25,112 9,187

0 31,368

12,064

0

44,918

8,667

7,532

6,809 5,579 7,539

5,479

0

6,367

7,089

13,331

3,101

3,643

16,280

28,664 12,748

9,517

0

0

25 50 MILES

25 50 KILOMETERS

ATLANTIC OCEAN

CHESAPEAKE BAY

39 ̊

38 ̊

37 ̊

78 ̊ 77 ̊ 76 ̊

NORTH CAROLINA

MARYLAND

Fall Line

DELAWARE

EXPLANATION
Introduction 5

Population estimates indicate that domestic wells may 

number nearly 200,000 in the Virginia Coastal Plain and 

withdrawals from these wells make up a large component of 

ground-water use, but recorded data on these wells are not 

readily available. Virginia laws have required reporting of well 

locations and construction details as part of household water 

well construction regulations since 1992. However, records 

for domestic wells installed prior to 1992 are less common, 

records for wells installed prior to 1982 are extremely rare, 

and no records were found for wells installed earlier than 

1977. Well permit applications and completion reports are 

managed by local health departments, and these documents 

are often available only in paper files. Detailed location and 

construction data submitted on domestic-well forms may 

be incomplete, and the identification of source aquifers 

for domestic wells is not required. The approach of using 

population data to estimate domestic withdrawals is adequate 

for estimating rates of water use by geographic area, but it is 

inadequate for detailed ground-water resource studies because 

it fails to identify the source aquifers.

For a study of the complex, multiaquifer system underlying the Virginia Coastal Plain, withdrawal rates alone are of 

limited use without accompanying information regarding the 

aquifers supplying the water. Considerable spatial variation 

among water-supply aquifers can occur, and the hydrogeologic 

effects of withdrawals from shallow wells screened in the 

water-table aquifer may be different from withdrawals from 

deep wells screened in the lowermost confined aquifer. 

Nonetheless, the approach used with regulated wells to assign 

measured withdrawals to specific aquifers is not possible 

for domestic wells. Because domestic withdrawals are not 

measured and domestic-well locations and construction details 

typically are not readily available, a complete accounting of 

all domestic wells and withdrawals would require a substantial 

investment of time and resources. 

The process of apportioning estimated, self-supplied 

domestic ground-water withdrawals in Virginia to specific 

wells or aquifers generally has not been attempted because 

domestic wells and withdrawals were thought to be insignificant in the context of a regional ground-water flow system and 

because domestic-well data are difficult to obtain, incomplete, 

or of poor quality. Consequently, while some previous 

assessments of ground water in the Virginia Coastal Plain have 

acknowledged the large magnitude of self-supplied domestic 

withdrawals, the effects of these withdrawals on regional 

ground-water conditions has been given little emphasis. 

In the most recent comprehensive report on the Virginia 

Coastal Plain ground-water flow system, Harsh and Laczniak 

(1990) noted that complete records on domestic use were not 

available but concluded that domestic use represents only a 

small percentage of total ground-water use from the confined 

flow system. The reasoning behind this conclusion was that 

most ground water withdrawn for self-supplied domestic use 

is pumped from the unconfined aquifer and returned to the 

aquifer through septic-tank discharge. The large proportion 

of ground-water withdrawals supplied by domestic wells, 

however, indicated that a more thorough investigation of the 

withdrawals and wells was needed. Furthermore, State and 

local ground-water professionals questioned the assumption 

that the unconfined aquifer is the water source for most 

domestic self-supply wells. Experts have cited numerous 

examples of domestic wells tapping confined aquifers and 

have noted that many new and replacement wells have screens 

installed in the confined aquifer system to provide a more 

dependable source of high-quality water than can be provided 

by shallow wells in the unconfined aquifer.

The relatively large withdrawals of self-supplied 

domestic ground water in this region, along with evidence 

that an appreciable proportion of private domestic wells are 

screened in the confined aquifers, motivated a comprehensive 

study of private domestic wells and self-supplied ground-water 

withdrawals in the Virginia Coastal Plain. The most immediate 

need for this information was to address a substantial, longstanding gap in the ground-water withdrawal data 

being applied to the Virginia Coastal Plain and Virginia 

Eastern Shore regional ground-water models currently 

under development. 

Purpose and Scope

This report documents the results of an investigation 

completed between 2002 and 2005 to collect data pertaining 

to private, domestic water-supply wells in the Virginia Coastal 

Plain from a statistical sampling of well-construction records 

dating from 1977 through 2002. The methods developed for 

selecting and sampling the records, estimating and analyzing 

elevation data to assign wells to aquifers, and estimating 

withdrawals by aquifer are discussed along with the results. 

The methods were developed and the data were collected and 

analyzed to enhance understanding of the geographic variability in the characteristics of domestic wells and the aquifers 

used for domestic water supply.

Data were compiled and are summarized in this report 

from 2,846 records of domestic water-supply wells in the 29 

counties and independent cities (called localities hereafter) in 

the Virginia Coastal Plain that have appreciable populations 

self supplied with ground water. Statistics on reported well and 

screen depths and estimated screen elevations are presented 

for each locality, and spatial variations in well-screen depths 

and elevations are described and explained. Other ancillary 

data from the sampling of private domestic-well records also 

are summarized. Data collected incidentally for 91 private 

irrigation wells from 8 counties are not included with the 

domestic-well information but are presented separately.

Methods for combining well data and spatial data on 

aquifer configurations to estimate the proportion of private 

domestic wells in each locality intersecting each Coastal 

Plain aquifer are discussed. These estimated proportions were 

evaluated along with water-use data to estimate aggregate rates 

of ground-water withdrawal from each aquifer from private 

domestic wells in each locality.
6 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

An example application from the Virginia Eastern Shore 

Peninsula is presented to demonstrate how the domestic 

withdrawal rates estimated by aquifer for each county or city 

were spatially distributed within a geographic area based on 

population and road density. The analysis presented here 

was done to support the development of a ground-water 

model of the Eastern Shore Peninsula; these methods and 

techniques could be used to address similar questions in 

similar settings elsewhere.

This report focuses on the localities within the Virginia 

Coastal Plain study area with appreciable populations self supplied with ground water from domestic wells. This excludes 

almost entirely urban localities, such as the independent Cities 

of Hampton and Norfolk, but includes other large independent 

cities with some rural areas, such as Virginia Beach and 

Chesapeake. The shaded localities in figure 1 are localities for 

which well data were collected.

Description of Study Area

The Coastal Plain Physiographic Province, henceforth 

called the Coastal Plain, occupies the entire eastern part of 

Virginia, a total area of approximately 13,000 square miles 

(mi2) between approximately west longitude 77 degrees 

30 minutes and the Atlantic Ocean (fig. 1). The Maryland and 

North Carolina borders bound the area to the north and south, 

respectively. 

The Coastal Plain is defined geologically by the underlying mostly unconsolidated sediments of fluvial-deltaic and 

marine origin that thin to the west near the Fall Line (fig. 1), 

where the Coastal Plain sediments meet the crystalline rock 

of the Piedmont Physiographic Province. Fifty Virginia 

counties and independent cities lie entirely or partially 

within the Coastal Plain, which encompasses a land area of 

approximately 8,755 mi2, or approximately 22 percent of the 

total Virginia land area.

The Virginia Coastal Plain population is concentrated in 

large urban areas, including the northern Virginia metropolitan 

area near Washington, D.C.; the Cities of Fredericksburg, 

Richmond, and Petersburg along the western boundary of 

the Coastal Plain; and the southeastern Virginia Cities of 

Chesapeake, Hampton, Norfolk, Portsmouth, and Virginia 

Beach near the mouth of the Chesapeake Bay (fig. 1; 

U.S. Census Bureau, 2003b). The remainder of the Virginia 

Coastal Plain is relatively sparsely populated, ranging from 

small towns to outlying rural areas composed of forested and 

agricultural lands.

The climate in this region is temperate, and annual mean 

precipitation is approximately 43 inches (National Climatic 

Data Center, 2005). The topography of the Virginia Coastal 

Plain is characterized by rolling terrain with deeply incised 

stream valleys in the northwestern section and gently rolling 

to level terrain with broad stream valleys in the eastern and 

southern sections. Land-surface elevations decline seaward, 

ranging from over 300 ft in the western Coastal Plain to sea 

level relative to National Geodetic Vertical Datum of 1929 

(NGVD 1929) at the Atlantic coast. 

Several major rivers drain eastward into Chesapeake Bay, 

and most become brackish as they enter estuarine areas east 

of the Fall Line. Consequently, rivers throughout most of the 

Virginia Coastal Plain are not used for water supply. The rivers 

and bay, however, subdivide the Virginia Coastal Plain into 

several regions. The area south of the Potomac River and north 

of the Rappahannock River is known as the Northern Neck 

Peninsula; the area between the Rappahannock and the York 

River is known as the Middle Peninsula; the area between 

the York and James Rivers is known as the York-James 

Peninsula; and the area south of the James River is referred to 

as southeastern Virginia. The area east of Chesapeake Bay is 

known as the Eastern Shore Peninsula. Additionally, the area 

of transition along the Fall Line between the Coastal Plain 

and the Piedmont Physiographic Provinces is known as the 

Fall Zone.

Previous Investigations

Numerous reports of previous investigations provide 

information useful to understanding the history of private 

domestic wells and historical self-supplied ground-water 

withdrawals in the Virginia Coastal Plain. While none of these 

reports has domestic wells and withdrawals as the primary 

focus, all mention domestic-well characteristics as part of the 

general discussion of wells and water resources. Comprehensive and thorough surveys of the literature on Virginia Coastal 

Plain geology and hydrogeology are provided in several 

major publications on those topics, particularly Meng and 

Harsh (1988), Harsh and Laczniak (1990), and more recently, 

McFarland and Bruce (2006). 

Sanford (1913) provided some of the earliest comprehensive information on ground-water resources in Virginia. 

His report describes the geology and hydrogeology of the 

Coastal Plain in great detail as it was understood at that 

time. Sanford’s report is particularly useful as background 

information on private domestic wells because it also includes 

a county-by-county overview of “water bearing beds” and 

characteristics of local wells, including some domestic wells. 

Sanford’s discussion of wells, domestic and otherwise, is not 

a formal survey, however, so it is difficult to make definitive 

conclusions about domestic-well characteristics across the 

study area. Nonetheless, some trends are apparent even from 

his brief discussion. At the time of Sanford’s report (1913), 

most domestic supply wells apparently were shallow, dug 

wells, particularly in areas near the Fall Line where other 

aquifers are not available at depth. Drilled wells apparently 

were less common for domestic purposes, though not rare. 

Numerous deep, drilled domestic wells were reported in many 

areas of the Coastal Plain, particularly where the aquifer 

system is thicker. In fact, drilled domestic wells up to 700 ft 

deep were noted by Sanford (1913), but it is unclear from his 
Introduction 7

work what proportion of domestic wells were in each depth or 

construction category. 

A few decades later, Cederstrom produced a series of 

reports covering the counties of southeastern Virginia (1945), 

the York-James Peninsula (1957), and the Middle Peninsula 

(1969) that provide information on characteristics of wells 

used for domestic supply at the time. In general, these reports 

describe the domestic-well distribution much as Sanford 

(1913) did. Although shallow, dug wells were clearly the most 

common source of self-supplied domestic water, deeper drilled 

wells were sometime used, and their distribution depended 

mostly on local hydrogeologic conditions. 

More recent investigations by the Commonwealth of 

Virginia provide the most comprehensive data on domestic 

wells and withdrawals in the Virginia Coastal Plain available 

to date. Ground-water investigations in the Eastern Shore 

Peninsula (Sinnott and Tibbitts, 1968), the York-James Peninsula (Virginia State Water Control Board, 1973), southeastern 

Virginia (Virginia State Water Control Board, 1974), the 

Middle Peninsula (Siudyla and others, 1977), and the Northern 

Neck Peninsula (Newton and Siudyla, 1979) address domestic 

water supply and include detailed information on selected 

individual private domestic wells. In addition to discussing 

the most commonly used aquifers for domestic supply, these 

reports include lists of domestic-well construction data with 

locations retrieved from well-completion records, and some of 

these records include information on the aquifers in which the 

wells were completed. 

The report on the Eastern Shore Peninsula (Sinnott and 

Tibbitts, 1968) indicates that many homes obtained water 

from dug or driven wells in the surficial aquifer, but deeper 

aquifers were used occasionally for domestic purposes. The 

Middle Peninsula report (Siudyla and others, 1977) also notes 

the importance of the unconfined aquifer for domestic supply 

but mentions the use of deeper aquifers by “many moderate 

to light water users,” including domestic users in Essex, 

King William, and King and Queen Counties. Interestingly, 

the report by Siudyla and others (1977) notes the prevalent 

use of the surficial and Yorktown-Eastover aquifers on the 

eastern part of the peninsula, where brackish water is found in 

the deeper aquifers. This brackish water is now known to be 

associated with the Chesapeake Bay impact crater.

The report by Newton and Siudyla (1979) on the 

ground-water resources of the Northern Neck Peninsula 

provides the most recent published information on domestic 

wells in Virginia. The report notes that the surficial aquifer 

is a “significant source of domestic ground water,” but also 

indicates the frequent use of other deeper aquifers for domestic supply. Most notably, several of the domestic wells listed 

in the report by Newton and Siudyla (1979) for Lancaster 

County apparently were completed in the Potomac aquifer. As 

a group, the reports that mention domestic wells document the 

continued importance of the surficial aquifer in most localities 

but also discuss the use of several confined aquifers, depending on local conditions. 

The USGS has been involved in the study of Virginia 

Coastal Plain hydrogeology since the beginning of the 20th

century, but the most current knowledge of this system is 

summarized in two reports completed as part of the USGS 

Regional Aquifer-System Analysis (RASA) program in the 

1980s. A comprehensive description of the hydrogeologic 

system was developed by Meng and Harsh (1988), and a 

related computer model of ground-water flow was developed 

by Harsh and Laczniak (1990). Subsequently, a report by 

Richardson (1994) described the hydrogeology and groundwater flow system of the Eastern Shore Peninsula of Virginia 

in greater detail than the previous reports and included the 

development of a computer model to simulate ground-water 

flow and saltwater intrusion in the Eastern Shore. The 

descriptions of the Virginia Coastal Plain and Eastern Shore 

hydrogeology and the two computer models have been 

updated since their initial creation and adopted by the VDEQ 

as resource-management tools for evaluating the potential 

effects of current and proposed withdrawals (McFarland, 

1998). Neither modeling study, however, included domestic 

withdrawals because domestic use was assumed to represent 

only a small portion of water not returned to the flow system, 

and it was thought that there could be no practical way of 

collecting domestic withdrawal data by aquifer.

Several developments in more recent years have 

advanced the understanding of the geology and hydrology of 

the Virginia Coastal Plain in general and the Eastern Shore 

in particular. The most important of these is the discovery 

of a large meteor-impact crater beneath the Chesapeake Bay 

(fig. 1), which substantially revised the previous understanding of the ground-water system (Powars and Bruce, 1999; 

Powars, 2000). In addition to a variety of improvements in 

the understanding of certain geologic relations, improved 

understanding of ground-water flow and geochemistry in the 

system was made possible by the accumulation of additional 

hydrologic data (McFarland, 1998). Substantial amounts of 

withdrawal and water-level data have been collected, which 

has improved the understanding of the relations between wells 

and aquifers. Also, recent advances in computer modeling and 

data-processing technologies and practices have improved 

simulation capabilities and revealed inadequacies in the 

previous models (McFarland, 1998).

Consequently, the USGS began a project in 2000, in 

cooperation with the VDEQ and the Hampton Roads Planning 

District Commission (HRPDC), to develop a new, comprehensive understanding of the hydrogeology of the Virginia Coastal 

Plain. The goals of the project are to incorporate the most current information about the geology, hydrology, and hydrologic 

conditions of the region and provide information and tools 

to meet the needs of future ground-water resource managers. 

A large and fundamental component of the project was the 

production of a revised and refined description of the Virginia 

Coastal Plain aquifer system that provides enhanced detail 

and incorporates new understandings of geologic relations 

(McFarland and Bruce, 2006). The work by McFarland and 

Bruce (2006) represents the most comprehensive and current 
8 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

understanding of the configuration (framework) of aquifers 

and confining units in the Virginia Coastal Plain. It is being 

used to support the development of a revised USGS computer 

model of the ground-water flow system that reflects current 

hydrogeologic concepts and conditions and can be used for 

predicting future ground-water conditions (Heywood, 2003). 

Concurrently, a computer model of the Eastern Shore of 

Virginia is being developed by the USGS to more accurately 

simulate ground-water flow and saltwater intrusion than has 

been possible with the Richardson (1994) model. 

An important motivation for revising and updating the 

two ground-water models, in addition to incorporating new 

geologic information and better modeling technology, is the 

need for better ground-water withdrawal data in the study area. 

Most of the work on withdrawal data has focused on improving the completeness and accuracy of recorded information 

on large, regulated wells and the reported withdrawals, and 

on ensuring that the screens of these wells are correctly 

related to the newly configured aquifers and confining units, 

as described by McFarland and Bruce (2006). Another 

quite different but equally important improvement in the 

withdrawal data is the recent understanding that a large part 

of the ground-water withdrawal total for the Virginia Coastal 

Plain is composed of unregulated and unreported self-supplied 

withdrawals by domestic users from private wells. 

Aquifers and Confining Units in the 

Virginia Coastal Plain

The Virginia Coastal Plain aquifer system is a subdivision 

of the more extensive Northern Atlantic Coastal Plain aquifer 

system. The geology of this region consists of a seawardthickening wedge of eastward-dipping strata of unconsolidated 

to partly consolidated sediments of Cretaceous, Tertiary, 

and Quaternary age that overlie a basement of consolidated 

bedrock (McFarland and Bruce, 2006). The sediments of 

the Coastal Plain were deposited by seaward progradation 

of fluvial plains and deltas along the continental margin, 

followed by a series of marine transgressions and regressions 

(McFarland and Bruce, 2006). This depositional environment 

resulted in a thick, eastward-dipping sequence of nonmarine 

strata mostly of Cretaceous age covered by a much thinner 

sequence of marine strata of Tertiary age, which is covered by 

a very thin layer of terrace and flood-plain deposits mostly of 

Quaternary age (Meng and Harsh, 1988). The entire wedge 

of sediments ranges from a thin edge near the Fall Line to 

a thickness of more than 6,000 ft near the coast (Meng and 

Harsh, 1988).

The sediments of the Coastal Plain in Virginia were 

altered during the Tertiary period by the impact of a comet 

or meteorite near the current mouth of the Chesapeake Bay 

(Powars and Bruce, 1999). The crater left by this impact 

disrupted the entire sequence of sediments present at the time 

and was quickly filled by a complex variety of impact-related 

sediments that were buried by millions of years of subsequent 

deposition (McFarland and Bruce, 2006). The buried impact 

crater now extends more than 50 miles (mi) across part of the 

southeastern Virginia Coastal Plain (fig. 1). 

The thick sequence of Coastal Plain sediments forms 

a complex, multilayered system of permeable aquifers and 

relatively less-permeable confining units (Meng and Harsh, 

1988; fig. 4). Ground water in this system originates primarily 

from precipitation that infiltrates to the water-table aquifer 

and then either flows laterally to discharge in nearby streams 

or downward to recharge deeper confined aquifers (Harsh and 

Laczniak, 1990). Ground-water flow is mostly lateral through 

the confined aquifers from recharge areas in the west to 

discharge areas near the Atlantic coast and major rivers, except 

in areas around major municipal and industrial withdrawal 

centers (McFarland and Bruce, 2006).

The entire sequence of Virginia Coastal Plain aquifers 

and confining units, as described by McFarland and Bruce 

(2006), is presented in figure 5 in relation to the corresponding 

geologic units and time periods. This complex aquifer system 

has 19 interrelated and overlapping hydrogeologic units in 

the sequence of sediments overlying the bedrock basement, 

including units associated with the Chesapeake Bay impact 

crater. McFarland and Bruce (2006) is the primary source of 

the information on hydrogeology used and described herein, 

including elevations of the hydrogeologic units. Consequently, 

reference is made to McFarland and Bruce (2006) for greater 

detail on the characteristics and extent of all the hydrogeologic 

units described in condensed form in this report.

Of the hydrogeologic units described by McFarland and 

Bruce (2006), 10 are considered to be important water-supply 

sources for private domestic wells in the Virginia Coastal 

Plain. These units, from top (land surface) to bottom (basement), include the following: surficial aquifer, Yorktown 

confining zone, Yorktown-Eastover aquifer, Saint Marys 

aquifer, Piney Point aquifer, Aquia aquifer, Peedee aquifer, 

Virginia Beach aquifer, Potomac confining zone, and Potomac 

aquifer (fig. 5). 

Notably, the Yorktown and Potomac confining zones are 

included here as aquifers because they may be indistinguishable from adjacent aquifers at a local scale and may yield 

water to wells completed in them. Additionally, screens for 

industrial or municipal wells, when compared by elevation to 

defined hydrogeologic unit elevations, have been known to 

intersect these units. While this situation may seem unusual 

using the traditional concept of aquifers and confining units, 

it is entirely consistent with the descriptions for these units 

outlined by McFarland and Bruce (2006).
Aquifers and Confining Units in the Virginia Coastal Plain 9 Figure 4. Generalized hydrogeologic section and directions of ground-water flow in the Virginia Coastal Plain (from McFarland and Bruce, 2006).

0 

VERTICAL SCALE GREATLY EXAGGERATED 

500 

0 

-500 

-1,000 

-1,500 

FEET 

WEST EAST 

AQUIA 

AQUIFER 

YORKTOWN-EASTOVER AQUIFER 

SUFFOLK SCARP SURFICIAL AQUIFER 

EXPLANATION 

AQUIFER 

CONFINING UNIT OR ZONE 

SAPROLITE 

BEDROCK 

DIRECTION OF GROUND-WATER FLOW 

FRACTURES 

YORKTOWN CONFINING ZONE 

NANJEMOY-MARLBORO CONFINING UNIT 

POTOMAC CONFINING ZONE 

POTOMAC CONFINING ZONE 

PIEDMONT 

PHYSIOGRAPHIC 

PROVINCE COASTAL PLAIN PHYSIOGRAPHIC PROVINCE 

Chesapeake Bay 

POTOMAC AQUIFER 

CALVERT CONFINING UNIT 

PINEY POINT AQUIFER 

10 0 20 MILES 

20 KILOMETERS 10 0 

FALL ZONE 

Figure 4. Generalized hydrogeologic section and directions of ground-water flow in the Virginia Coastal Plain (from McFarland and Bruce, 2006).

ELEVATION, IN FEET ABOVE AND BELOW NGVD 29

ELEVATION, IN FEET ABOVE AND BELOW NGVD 29

SALTWATER INTERFACE 

EXMORE MATRIX CONFINING UNIT 

CHICKAHOMINY CONFINING UNIT 

EXMORE CLAST CONFINING UNIT 

CHESAPEAKE BAY IMPACT CRATER 

500 

-500 

-1,000 

-1,500 

FEET
10 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Figure 5. Stratigraphic correlations of hydrogeologic units of the Virginia Coastal Plain (modified 

from McFarland and Bruce, 2006). Vertical arrows indicate major hydrologic associations that cross 

stratigraphic boundaries; minor overlaps of hydrogeologic units among adjacent geologic formations are 

not depicted.

GEOLOGIC FORMATION

Powars and Bruce, 1999;

Powars, 2000

HYDROGEOLOGIC UNIT

McFarland and Bruce, 2006 ERA/EON PERIOD EPOCH

Quaternary

Holocene undifferentiated

Pleistocene surficial aquifer

Bacons Castle Yorktown

confining zone late Chowan River Pliocene

Yorktown Yorktown confining zone

early Yorktown-Eastover

aquifer Eastover

late Saint Marys

confining unit 

Saint Marys Miocene Saint Marys aquifer

middle Calvert confining unit

Calvert

Cenozoic

Tertiary

early Piney Point

aquifer Oligocene late Old Church

early Delmarva Beds

Chickahominy Chickahominy confining unit

late

Exmore

tsunami-breccia

Exmore matrix confining unit

Exmore clast confining unit

Eocene megablock beds Potomac confining zone

Potomac aquifer

middle Piney Point Piney Point

aquifer Nanjemoy early

Marlboro

Clay

Nanjemoy-Marlboro

confining unit

late Aquia Paleocene Aquia aquifer

early Brightseat

Peedee

clayey silty sand confining zone

organic-rich clay

glauconite quartz sand Peedee

Late red beds aquifer

Virginia Beach confining zone

glauconitic sand Virginia Beach aquifer

upper Cenomanian

beds

Upper Cenomanian

Me confining unit sozoic

Cretaceous

Potomac confining zone

Early Potomac Potomac aquifer

Jurassic

Triassic Undifferentiated Basement Paleozoic

Proterozoic

Figure 5. Stratigraphic correlations of hydrogeologic units of the Virginia Coastal Plain (modified from

McFarland and Bruce, 2006). Vertical arrows indicate major hydrologic associations that cross

stratigraphic boundaries; minor overlaps of hydrogeologic units among adjacent geologic formations

are not depicted.
Aquifers and Confining Units in the Virginia Coastal Plain 11

Surficial Aquifer

The surficial aquifer is a heterogeneous aquifer of sand 

and gravel covering the entire Virginia Coastal Plain (fig. 4). 

The top of the aquifer is at land surface, and its thickness 

ranges from several tens of feet in upland areas to a few tens 

of feet or less to the east. Most of the surficial aquifer is 

underlain by various confining units or zones. Near the Fall 

Line or along major rivers, however, the surficial aquifer 

directly overlies and may be connected to deeper aquifers. 

The surficial aquifer is moderately used across the entire 

Virginia Coastal Plain, providing water primarily to users 

of relatively small volumes. This aquifer was the source of 

0.4 Mgal/d of reported, regulated withdrawals in 2002, which 

was less than 1 percent of the reported total for the Virginia 

Coastal Plain (Quinlan, 2004). However, the surficial aquifer 

is the source of many unregulated and unreported domestic 

and agricultural withdrawals. Because it is shallow and 

easily accessible, the surficial aquifer historically has been 

an important water supply, but drought and decreasing water 

quality in recent years have caused users in some locations 

to abandon wells in the surficial aquifer in search of more 

dependable water supplies in deeper aquifers.

Yorktown Confining Zone

Designation as a confining zone addresses the variable 

configuration of this unit, which separates the underlying 

Yorktown-Eastover aquifer from the overlying surficial aquifer 

(figs. 4, 5). Both of these adjacent aquifers are extremely 

heterogeneous, and the confining zone between them exhibits 

characteristics of both units. Discontinuities in composition 

and texture across small distances mean that this zone functions as a confining unit only at the local level, despite its 

regional extent, and leakage may be enhanced in other areas 

where fine-grained interbeds do not exist. In practice, then, the 

surficial aquifer and the Yorktown-Eastover aquifer are closely 

related by the Yorktown confining zone between them, and 

these three units together form an array of hydraulic connections that link the unconfined and confined ground-water flow 

system. Thus, while no withdrawals have been reported for the 

Yorktown confining zone, its function as an aquifer in places 

is consistent with the definition of the unit by McFarland and 

Bruce (2006).

Yorktown-Eastover Aquifer

The Yorktown-Eastover aquifer is a heterogeneous and 

widely used aquifer that extends across most of the Virginia 

Coastal Plain except for several of the northwestern counties 

(fig. 4). The aquifer, composed of sand with some interbedded 

silt, is overlain across most of its extent by the Yorktown 

confining zone. However, in locally incised areas along rivers 

where it outcrops on steep slopes, it usually is covered by 

sediments of the surficial aquifer. The Yorktown-Eastover 

aquifer is hydraulically continuous on a regional scale but 

can exhibit local discontinuities as the result of interbedded 

fine-grained sediments. 

The Yorktown-Eastover aquifer is a major source of 

both public and private water supplies, second only to the 

Potomac aquifer as a ground-water supply resource. It is an 

important source of water in the eastern part of the Virginia 

Coastal Plain, particularly on the Eastern Shore. In 2002, the 

Yorktown-Eastover aquifer supplied almost 6 Mgal/d in regulated, reported ground water across its extent, almost 6 percent 

of the total ground-water withdrawals for the Virginia Coastal 

Plain (Quinlan, 2004). Because it is generally a shallow and 

accessible aquifer with high-quality water, it is also commonly 

used for private domestic water supplies.

Saint Marys Aquifer

The Saint Marys aquifer is a homogeneous, little-used 

aquifer of limited regional extent composed of marine sands 

and shells. It consists of two separate areas—a northern 

part that covers most of the Eastern Shore and a southern 

part mostly in the City of Suffolk. The Saint Marys aquifer 

directly overlies the Calvert confining unit (fig. 5). It ranges 

in thickness from 150 ft to 200 ft in the northern part and is 

approximately 50 ft thick in the southern part. 

The Saint Marys aquifer is a very limited water-supply 

resource only in its southern part, where it is considered a 

marginal water-production zone. No regulated withdrawals 

from the Saint Marys aquifer have been reported to the VDEQ, 

but the aquifer could provide limited water supplies. The 

northern part contains brackish water.

Piney Point Aquifer

The Piney Point aquifer is an extensive, homogenous, 

sandy aquifer that extends across most of the Virginia Coastal 

Plain, except in the southern part near the Fall Line, dipping 

eastward across its entire extent. Because it is composed of 

formations which both predate and post-date the Chesapeake 

Bay impact crater, the Piney Point aquifer extends across 

the crater (fig. 4). The aquifer is as much as 150 ft thick at 

its deepest section across the lower parts of Northern Neck 

Peninsula. 

The Piney Point aquifer is a moderately used groundwater resource that supplies water to small municipalities in 

the middle sections of the Northern Neck Peninsula, Middle 

Peninsula, and York-James Peninsula. The Piney Point aquifer 

is not considered a productive aquifer south of the James 

River. In 2002, this aquifer produced a total of approximately 

5.1 Mgal/d of regulated, reported ground water, less than 

5 percent of the total reported ground-water withdrawals from 

the Virginia Coastal Plain aquifer system (Quinlan, 2004).
12 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Aquia Aquifer

The Aquia aquifer is a homogeneous aquifer that is 

composed of medium to coarse sands and extends across 

all of the Virginia Coastal Plain except in the areas of the 

Chesapeake Bay impact crater, the Virginia Eastern Shore, and 

the southeastern zone near the Fall Line (fig. 4). Across most 

of its extent, the Aquia aquifer is no more than 50 ft thick.

The Aquia aquifer is a relatively minor water-supply 

resource, perhaps because of its composition or because it 

is relatively thin in some areas. The Aquia aquifer is used to 

supply public water to a few small towns and is tapped by 

a few private domestic wells, mostly in the northern part of 

the study area. In 2002, the Aquia aquifer was the source of 

approximately 0.2 Mgal/d in reported, regulated ground-water 

withdrawals, less than 1 percent of the reported ground-water 

use in the Virginia Coastal Plain (Quinlan, 2004).

Peedee Aquifer

The Peedee aquifer is a relatively heterogeneous 

aquifer composed of discontinuous fine-grained sediments 

interbedded with coarse-grained sediments. The extent of the 

Peedee aquifer is limited to the southern parts of the Cities 

of Chesapeake and Virginia Beach, and it is never more than 

several tens of feet thick. The Peedee aquifer overlies the 

Virginia Beach confining zone (fig. 5).

The Peedee aquifer is identified as a localized hydrogeologic unit that may provide a ground-water flow path 

across the southeastern part of the study area. It may represent 

the northern edge of the Peedee aquifer in North Carolina but 

appears to be a localized and unused water-supply resource in 

Virginia.

Virginia Beach Aquifer

The Virginia Beach aquifer is a relatively homogenous 

aquifer consisting of coarse-grained sands. It extends across 

most of Virginia Beach and westward across Chesapeake 

and Suffolk and into the southeastern corner of Southampton 

County where it attains thicknesses up to 70 ft. The Virginia 

Beach aquifer is a hydraulically continuous unit throughout 

its relatively limited extent and provides public water supplies 

to small towns and light commercial and industrial facilities, 

mostly in the City of Suffolk. Reported withdrawals from the 

Virginia Beach aquifer totaled less than 0.1 Mgal/d in 2002, 

less than 1 percent of the total ground-water withdrawals in 

the Virginia Coastal Plain (Quinlan, 2004).

Potomac Confining Zone

The Potomac confining zone overlies the Potomac 

aquifer across nearly its entire extent (fig. 5) and extends 

across the entire Virginia Coastal Plain except where it has 

been disrupted by the Chesapeake Bay impact crater (fig. 4). 

This unit is characterized by discontinuous clay interbeds and 

is designated as a confining zone to account for its variable 

configuration in the transition from the Potomac aquifer below 

to the overlying hydrogeologic units. The Potomac confining 

zone was defined and mapped for the first time by McFarland 

and Bruce (2006), so no withdrawals have been reported 

historically for this unit. Analyses of municipal and industrial 

withdrawal data have revealed, however, that some wells may 

be screened in the Potomac confining zone, and the possibility 

of production wells in this zone is consistent with the description of this unit by McFarland and Bruce (2006).

Potomac Aquifer

The Potomac aquifer is a highly heterogeneous aquifer 

that immediately overlies the bedrock basement and occupies 

the lowermost position in the hydrogeologic system (figs. 4, 

5). The Potomac aquifer is the thickest aquifer in the Virginia 

Coastal Plain aquifer system and ranges in thickness from 

a thin edge near the Fall Line to several thousand feet at the 

coast. This sand and gravel aquifer is hydraulically continuous 

on a regional scale but contains local discontinuities as a result 

of many fine-grained clay interbeds. The aquifer extends 

across the entire Virginia Coastal Plain except for the interior 

of the Chesapeake Bay impact crater and is overlain across 

most of its extent by the Potomac confining zone, except for 

incised areas along major river channels and near the Fall 

Line. In these areas, the Potomac aquifer may crop out but is 

usually covered by sediments of the surficial aquifer, possibly 

providing direct hydraulic connections between the confined 

and unconfined systems.

The Potomac aquifer is the largest and most heavily 

used source of ground water in the Virginia Coastal Plain, 

supplying regulated withdrawals of more than 95 Mgal/d 

in 2002, about 89 percent of the reported annual total of 

107 Mgal/d (Quinlan, 2004). The Potomac aquifer is an 

important water-supply source across most of its extent, except 

where it thins out near the Fall Line or where development is 

limited by brackish zones associated with the Chesapeake Bay 

impact crater and the Atlantic Ocean. Most withdrawals from 

the Potomac aquifer are regulated industrial and municipal 

withdrawals, including two large historical withdrawals for 

paper pulp mills located at Franklin and at West Point (in 

eastern King William County). In areas where brackish ground 

water underlies large populations, desalinization facilities have 

been developed to allow increased use of water resources from 

the Potomac aquifer. Increased development of the Potomac 

aquifer is expected as demand for water continues to grow in 

metropolitan areas of the southeastern Virginia Coastal Plain, 

but decreasing water levels in wells in recent decades have 

caused increased concerns about additional withdrawals from 

this aquifer in areas where it is heavily used.
Private Domestic-Well Characteristics 13

Private Domestic-Well Characteristics

Domestic-well records were collected for this study 

in localities with appreciable populations self supplied 

with ground water. Within each selected locality, private 

domestic-well records were collected with a random-sampling 

technique, usually spatially stratified. Construction characteristics of private domestic wells determined from the sampled 

records in a locality were used to estimate the construction 

characteristics for the entire population of domestic wells in 

that locality. Of primary interest were the depths or elevations 

of the well screens or other information useful for designating 

the aquifers in which the wells were completed.

The parameter of most interest for this study is the 

depth of the well or, more specifically, the depth to the well 

screen. Well-screen elevations are more useful than depths 

for comparing wells spatially, but the calculation of screen 

elevations is dependent on well-head elevations, which usually 

were not available in collected well records. Consequently, 

well-screen elevations were estimated from well-screen depths 

by using aggregated median land-surface elevation values 

computed from a digital elevation model for each locality. 

Several assumptions were required to estimate 

well-screen elevations from the limited available data, but 

the estimated screen elevations provide the basis of the 

comparison among well characteristics by locality. To clarify 

the relations and approximations invoked in this study, a 

conceptual example comparing measured, site-specific well 

data to estimated well data, as used in this study, is given in 

figure 6. The steps involved in data collection and analysis 

for this and subsequent sections of this report are outlined 

in a flow chart in figure 7. The flow chart demonstrates the 

relations between the study components and summarizes the 

methods, techniques, and products discussed in this report.

Unconfined

aquifer

Confined

aquifer

Confined

aquifer

Figure 6. Conceptual diagram demonstrating the relations among well depth, well head and screen elevations,

land-surface elevation, and hydrogeologic unit elevations for examples in which (A) domestic well and aquifer

elevations are measured, and (B) domestic well and aquifer elevations are estimated.

Confining

unit

Confining unit

(A)

Well

Unconfined

aquifer

Confining

unit

Confined

aquifer

Confined

aquifer

Confining unit

Maximum 

surface

elevation

(B)

Minimum 

surface

elevation

Median

surface

elevation

Well depth known

Well location known exactly (latitude

 and longitude)

Unit elevations measured at well

Well and screen elevations measured

Aquifer intersection known

Well depth known

Well location known approximately (by locality)

Unit elevations estimated from aggregated locality data

Well elevation, land-surface elevation estimated

Screen elevation calculated from well depth and

 estimated well elevation data

Aquifer intersection estimated

Maximum

unit top

elevation Minimum

unit top

elevation

Median

unit top

elevation

Well

Well

screen Well

screen

Figure 6. Conceptual diagram demonstrating the relations among well depth, well head and screen elevations, landsurface elevation, and hydrogeologic unit elevations for examples in which (A) domestic-well and aquifer elevations are 

measured, and (B) domestic-well and aquifer elevations are estimated.
14 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Figure 7. Flow chart of steps in the process of analyzing private domestic-well data, the apportionment of private domestic 

wells among aquifers, and the spatial distribution of self-supplied domestic withdrawals by aquifer in the Virginia Coastal 

Plain.

Sampled well

screen depths

for each locality 

Well screen 

elevations for

each locality

Compare wellscreen elevations

to aquifer elevations

for each locality

Proportion of 

wells by aquifer

for each locality

Aggregate of

land-surface 

and unit 

elevations

by locality

Aquifer 

association for

each domestic

well

Summarize

aquifer 

determinations

for each locality

Rasters of 

hydrogeologic

unit elevations

Spatial

analysis of

unit elevations

Subtract well

depth from 

median locality

elevation

McFarland and Bruce (2006)

Population

for each

locality

Self-supplied

population for

each locality

Self-supplied

domestic 

withdrawal by

aquifer for each

locality

Subtract 

publicly supplied 

population

Apply per-capita

use coefficient 

Self-supplied

domestic 

withdrawal 

for each locality

USGS Water-Use Information Progam

2000 Census Data

Population by

census block

group

Self-supplied

population by

census block

group

Self-supplied

population by

ground-water

model cell area

Self-supplied

withdrawal by

model cell for

each aquifer

Figure 7. Flow chart of steps in the process of analyzing private domestic well data, the apportionment of private domestic

wells among aquifers, and the spatial distribution of self-supplied domestic withdrawals by aquifer in the Virginia

Coastal Plain.

Hydrogeologic Information Well Data and Analysis Distribution of Ground-Water Withdrawals

Road-density

analysis

Apply per-capita

use coefficient and 

multiply withdrawal

by aquifer proportion Multiply withdrawal

by aquifer proportion 

Subtract 

publicly supplied 

population
Private Domestic-Well Characteristics 15

Selection of Localities for Sampling of 

Domestic-Well Records

Virginia Coastal Plain localities were selected for 

inclusion in the study of private domestic wells based on their 

self-supplied populations in 2000 (U.S. Geological Survey, 

2002; Hutson and others, 2004). Selected localities were those 

with appreciable self-supplied domestic populations within the 

boundaries of the Coastal Plain. Predominantly urban localities in which most or all of the population is publicly supplied 

were excluded, as were localities in which most of the land 

area or population is located outside of the Coastal Plain.

Spatial analyses were used to calculate populations and 

areas of localities only partially within the Coastal Plain. 

Using geographic information system (GIS) software, locality 

boundary polygons were compared to spatial information on 

surficial geology defining the extent of Coastal Plain sediments. The source of the spatial geologic data was a geologic 

map of the Virginia Coastal Plain by Mixon and others (1989), 

from which a generalized Fall Line corresponding to the western limit of contiguous Coastal Plain sediments was digitized. 

Spatial data on population used for this study were taken from 

2000 census block group data (U.S. Census Bureau, 2001), 

the highest level of spatial resolution available. The proportion 

of each Virginia locality situated within the Coastal Plain was 

calculated on the basis of both area and population. From the 

population proportion, the 2000 water-use estimates were used 

to calculate estimated ground-water use in the Coastal Plain 

localities, presumably withdrawn from wells in Coastal Plain 

sediments.

Of the 50 Virginia localities entirely or partially located 

within the Coastal Plain, 29 localities were selected for 

sampling of private domestic-well records (tables 1, 2; fig. 1). 

All Virginia Coastal Plain localities are given in figure 1 and 

tables 1 and 2, along with area, population, and ground-water 

use data; and the localities selected for sampling are shaded. 

The process of selecting or rejecting localities only 

partly occupying the Coastal Plain required the interpretation 

of limited available geographic data. Neither the detailed 

geologic analysis nor the detailed population analysis by 

census block group had been examined at the time of the 

sampling design, so some localities that might otherwise 

have been included based on the stated selection criteria and 

the information in table 1 were excluded from this study. For 

example, Chesterfield, Dinwiddie, and Spotsylvania Counties 

all have only small portions of their land areas within the 

Coastal Plain (fig. 1), but their self-supplied populations may 

be large enough to merit their inclusion. However, the county 

populations within the Coastal Plain also appear to be located 

in publicly supplied areas; this is a level of spatial resolution 

that is not captured in table 1. Stafford County could have 

been included based on its relatively large Coastal Plain area, 

but it was excluded based on its small self-supplied population. Localities in the northern panhandle of the Coastal Plain 

were not included because supporting data on hydrogeologicunit elevations were not available in that area, which includes 

Arlington, Fairfax, and Prince William counties and the City 

of Alexandria. 

For the aforementioned reasons, the sampling of domestic 

wells may have excluded the wells of close to 100,000 people 

who rely on self-supplied ground water, mostly in the northern 

Coastal Plain of Virginia. The other Virginia Coastal Plain 

localities that were excluded from sampling are those with 

populations supplied predominantly or entirely with municipal 

water (tables 1, 2).

The 29 localities selected for sampling include approximately 412,000 people who are self supplied with ground 

water from private domestic wells. USGS methods used 

here for estimating self-supplied domestic withdrawals are 

based almost entirely on per-capita water-use estimates rather 

than information on available numbers of domestic wells or 

measured withdrawals from such wells. In fact, the population served by domestic supply is entirely calculated as the 

difference between the census population of a locality and the 

publicly supplied population total for that same locality from 

U.S. Environmental Protection Agency (USEPA) community 

water-supply records. The self-supplied population for each 

locality then was multiplied by the per-capita domestic wateruse coefficient (75 gal/d for Virginia), to obtain the estimated 

self-supplied domestic withdrawal rate (Hutson and others, 

2004). Furthermore, it is possible to estimate the number 

of private domestic wells for a given locality based on the 

average household size in the locality, the total self-supplied 

domestic population, and the public-supply population. This 

estimate was calculated for each locality and is included in 

table 1.

Sampling of Private Domestic-Well Records

In Virginia, most available records for private domestic 

wells are collected and maintained by the local health department for each locality. These are paper records stored in file 

cabinets in health department offices, and the data typically are 

not available in electronic form. Consequently, the sampling 

approach involved manually collecting well data from the 

files of local health departments. Regional VDEQ offices and 

local well-drilling companies also were considered as sources 

of data for this study, but data-collection efforts ultimately 

focused on the records from local health departments based 

on consultation with State and local experts who believe 

these records are the best source of current, locality-level 

information on domestic wells. Local health departments were 

contacted in localities selected for domestic-well sampling, 

and all granted access to available domestic-well data.

Since 1992, Virginia regulations require drillers of private 

domestic wells to complete Uniform Water Well Completion 

Reports (UWWCRs) and file them with the health department 

in the locality where a well is drilled (Virginia Department of 

Health, 2005). These completion reports contain information 

on the general location, construction details, and installation 

date of each well.
16 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Table 1. Area, population, and water-supply characteristics of Virginia Coastal Plain localities, based on 2000 population and water-use 

data.

[Shading indicates locality in which well data were collected for this study. —, not applicable]

Locality

(fig. 1)

Coastal 

Plain 

area, in 

square 

miles

Area 

proportion 

within

 Coastal Plain

Population

proportion 

within 

Coastal 

Plain

Total

populationa

Coastal 

Plain 

population

Selfsupplied

proportionb

Self-supplied 

Coastal Plain 

population

Census 

household 

sizeb

Estimated 

number of 

domestic 

wells

Accomack County 466 1.000 1.000 38,998 38,998 0.495 19,321 2.45 7,895

Alexandria, City of 17 0.982 1.000 128,283 128,283 0.127 16,280 2.04 7,972

Arlington County 15 0.562 0.857 189,453 162,377 0.022 3,643 2.15 1,698

Caroline County 504 0.937 1.000 22,121 22,121 0.603 13,331 2.69 4,963

Charles City County 200 1.000 1.000 6,926 6,926 0.885 6,126 2.59 2,362

Chesapeake, City of 351 1.000 1.000 199,184 199,184 0.177 35,211 2.79 12,617

Chesterfield County 122 0.280 0.413 259,903 107,345 0.112 12,064 2.73 4,425

Colonial Heights, City of 6 0.908 1.000 16,897 16,897 0.030 500 2.37 211

Dinwiddie County 127 0.250 0.694 24,533 17,020 0.737 12,538 2.58 4,852

Emporia, City of 2 0.913 1.000 5,665 5,665 0.011 60 2.43 25

Essex County 269 1.000 1.000 9,989 9,989 0.682 6,809 2.46 2,768

Fairfax County 88 0.224 0.280 973,393 272,488 0.047 12,748 2.74 4,660

Franklin, City of 4 1.000 1.000 8,346 8,346 0.000 0 2.39 0

Fredricksburg, City of 6 0.963 1.000 19,279 19,279 0.000 0 2.09 0

Gloucester County 220 1.000 1.000 34,780 34,780 0.715 24,870 2.62 9,478

Greensville County 173 0.582 1.000 11,560 11,560 0.726 8,390 2.51 3,337

Hampton, City of 54 1.000 1.000 146,437 146,437 0.000 0 2.49 0

Hanover County 246 0.513 0.897 86,320 77,472 0.324 25,112 2.71 9,282

Henrico County 173 0.724 0.560 262,300 146,873 0.214 31,368 2.39 13,121

Hopewell, City of 9 1.000 1.000 22,354 22,354 0.000 0 2.43 0

Isle of Wight County 323 1.000 1.000 29,728 29,728 0.471 13,989 2.61 5,359

James City County 153 1.000 1.000 48,102 48,102 0.368 17,711 2.47 7,183

King and Queen County 333 1.000 1.000 6,630 6,630 0.949 6,290 2.48 2,536

King George County 187 1.000 1.000 16,803 16,803 0.185 3,101 2.70 1,148

King William County 285 1.000 1.000 13,146 13,146 0.699 9,187 2.69 3,412

Lancaster County 124 1.000 1.000 11,567 11,567 0.474 5,479 2.23 2,460

Mathews County 86 1.000 1.000 9,207 9,207 0.941 8,667 2.32 3,729

Middlesex County 139 1.000 1.000 9,932 9,932 0.758 7,532 2.27 3,311

New Kent County 224 1.000 1.000 13,462 13,462 0.701 9,431 2.65 3,555

Newport News, City of 56 1.000 1.000 180,150 180,150 0.000 0 2.50 0

Norfolk, City of 57 1.000 1.000 234,403 234,403 0.000 0 2.45 0

Northampton County 211 1.000 1.000 13,093 13,093 0.652 8,542 2.39 3,572

Northumberland County 188 1.000 1.000 12,259 12,259 0.615 7,539 2.24 3,367

Petersburg, City of 27 0.947 1.000 33,740 33,740 0.000 0 2.38 0

Poquoson, City of 19 1.000 1.000 11,566 11,566 0.000 0 2.75 0

Portsmouth, City of 33 1.000 1.000 100,565 100,565 0.000 0 2.51 0

Prince George County 281 1.000 1.000 34,749 34,749 0.410 14,247 2.76 5,154

Prince William County 54 0.156 0.413 280,813 116,014 0.247 28,664 2.94 9,736

Richmond County 195 1.000 1.000 8,809 8,809 0.633 5,579 2.40 2,322

Richmond, City of 47 0.709 0.915 197,790 181,059 0.000 0 2.21 0

Southampton County 607 1.000 1.000 17,482 17,482 0.462 8,081 2.53 3,188

Spotsylvania County 81 0.193 0.841 90,395 76,038 0.084 6,367 2.87 2,219

Stafford County 136 0.494 0.711 92,446 65,760 0.145 9,517 3.01 3,159

Suffolk, City of 408 1.000 1.000 63,677 63,677 0.255 16,209 2.69 6,019

Surry County 263 1.000 1.000 6,829 6,829 0.745 5,089 2.61 1,952

Sussex County 508 0.987 1.000 12,504 12,504 0.113 1,410 2.41 584

Virginia Beach, City of 303 1.000 1.000 425,257 425,257 0.097 41,380 2.70 15,306

Westmoreland County 247 1.000 1.000 16,718 16,718 0.424 7,089 2.43 2,921

Williamsburg, City of 5 1.000 1.000 11,998 11,998 0.000 0 2.07 0

York County 125 1.000 1.000 56,297 56,297 0.798 44,918 2.78 16,137

Total 8,755 — — 4,526,838 3,291,938 0.156 514,390 2.59 197,994

a U.S. Census Bureau, 2003a.

b U.S. Geological Survey, 2002.
Private Domestic-Well Characteristics 17

Table 2. Estimated ground-water withdrawals in Virginia Coastal Plain localities in 2000.

[Shading indicates locality in which well data were collected for this study. Data for localities partially within the Coastal Plain are calculated from the proportion of 

the locality population within the Coastal Plain. Mgal/d; million gallons per day; —, not applicable]

Locality

(fig. 1)

Coastal 

Plain 

proportion 

Selfsupplied

proportiona

Locality ground-water withdrawal (Mgal/d)a Coastal Plain ground-water withdrawal (Mgal/d)

Public 

supply Domestic Industrial/commercial Irrigation Total Public supply Domestic Industrial/commercial Irrigation Total

Accomack County 1.000 0.495 0.82 1.42 3.01 1.01 6.26 0.82 1.42 3.01 1.01 6.26

Alexandria, City of 1.000 0.127 0.00 1.22 0.01 0.00 1.23 0.00 1.22 0.01 0.00 1.23

Arlington County 0.857 0.022 0.00 0.32 0.00 0.04 0.36 0.00 0.27 0.00 0.03 0.31

Caroline County 1.000 0.603 0.33 1.00 0.00 0.01 1.34 0.33 1.00 0.00 0.01 1.34

Charles City County 1.000 0.885 0.04 0.46 0.00 0.07 0.57 0.04 0.46 0.00 0.07 0.57

Chesapeake, City of 1.000 0.177 4.53 2.64 0.05 0.00 7.22 4.53 2.64 0.05 0.00 7.22

Chesterfield County 0.413 0.112 0.00 2.22 0.34 0.01 2.57 0.00 0.92 0.14 0.00 1.06

Colonial Heights, City of 1.000 0.030 0.00 0.04 0.00 0.00 0.04 0.00 0.04 0.00 0.00 0.04

Dinwiddie County 0.694 0.737 0.00 1.36 0.00 0.06 1.42 0.00 0.94 0.00 0.04 0.99

Emporia, City of 1.000 0.011 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Essex County 1.000 0.682 0.41 0.51 0.00 0.00 0.92 0.41 0.51 0.00 0.00 0.92

Fairfax County 0.280 0.047 0.20 3.48 0.04 0.11 3.83 0.06 0.97 0.01 0.03 1.07

Franklin, City of 1.000 0.000 1.11 0.00 0.00 0.00 1.11 1.11 0.00 0.00 0.00 1.11

Fredricksburg, City of 1.000 0.000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Gloucester County 1.000 0.715 0.00 1.87 0.00 0.01 1.88 0.00 1.87 0.00 0.01 1.88

Greensville County 1.000 0.726 0.00 0.63 0.00 0.03 0.66 0.00 0.63 0.00 0.03 0.66

Hampton, City of 1.000 0.000 0.00 0.00 0.00 0.03 0.03 0.00 0.00 0.00 0.03 0.03

Hanover County 0.897 0.324 1.22 2.10 0.00 0.03 3.35 1.09 1.88 0.00 0.03 3.01

Henrico County 0.560 0.214 0.16 4.20 0.00 0.08 4.44 0.09 2.35 0.00 0.04 2.49

Hopewell, City of 1.000 0.000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Isle of Wight County 1.000 0.471 1.44 1.05 33.72 0.00 36.21 1.44 1.05 33.72 0.00 36.21

James City County 1.000 0.368 9.63 1.33 0.01 0.00 10.97 9.63 1.33 0.01 0.00 10.97

King and Queen County 1.000 0.949 0.01 0.47 0.00 0.00 0.48 0.01 0.47 0.00 0.00 0.48

King George County 1.000 0.185 0.79 0.23 0.06 0.00 1.08 0.79 0.23 0.06 0.00 1.08

King William County 1.000 0.699 0.53 0.69 19.47 0.01 20.70 0.53 0.69 19.47 0.01 20.70

Lancaster County 1.000 0.474 0.41 0.41 0.00 0.00 0.82 0.41 0.41 0.00 0.00 0.82

Mathews County 1.000 0.941 0.00 0.65 0.00 0.01 0.66 0.00 0.65 0.00 0.01 0.66

Middlesex County 1.000 0.758 0.15 0.56 0.00 0.00 0.71 0.15 0.56 0.00 0.00 0.71

New Kent County 1.000 0.701 0.17 0.71 0.00 0.01 0.89 0.17 0.71 0.00 0.01 0.89

Newport News, City of 1.000 0.000 2.35 0.00 0.00 0.00 2.35 2.35 0.00 0.00 0.00 2.35

Norfolk, City of 1.000 0.000 0.00 0.00 0.22 0.03 0.25 0.00 0.00 0.22 0.03 0.25

Northampton County 1.000 0.652 0.26 0.64 0.05 0.57 1.52 0.26 0.64 0.05 0.57 1.52

Northumberland County 1.000 0.615 0.16 0.57 0.02 0.00 0.75 0.16 0.57 0.02 0.00 0.75

Petersburg, City of 1.000 0.000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Poquoson, City of 1.000 0.000 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Portsmouth, City of 1.000 0.000 0.00 0.00 0.42 0.04 1.60 0.00 0.00 0.42 0.04 1.60

Prince George County 1.000 0.410 0.17 1.02 0.00 0.00 1.19 0.17 1.02 0.00 0.00 1.19

Prince William County 0.413 0.247 0.64 5.20 0.10 0.04 5.98 0.26 2.15 0.04 0.02 2.47

Richmond County 1.000 0.633 0.02 0.42 0.00 0.01 0.45 0.02 0.42 0.00 0.01 0.45

Richmond, City of 0.915 0.000 0.00 0.00 0.02 0.06 0.08 0.00 0.00 0.02 0.05 0.07

Southampton County 1.000 0.462 0.50 0.61 5.03 0.00 6.14 0.50 0.61 5.03 0.00 6.14

Spotsylvania County 0.841 0.084 0.00 0.57 0.01 0.00 0.58 0.00 0.48 0.01 0.00 0.49

Stafford County 0.711 0.145 0.00 1.00 0.01 0.01 1.02 0.00 0.71 0.01 0.01 0.73

Suffolk, City of 1.000 0.255 5.39 1.22 0.06 0.00 6.67 5.39 1.22 0.06 0.00 6.67

Surry County 1.000 0.745 0.13 0.38 0.00 0.18 1.00 0.13 0.38 0.00 0.18 1.00

Sussex County 1.000 0.113 0.51 0.11 0.17 0.01 0.80 0.51 0.11 0.17 0.01 0.80

Virginia Beach, City of 1.000 0.097 0.00 3.10 0.01 0.12 3.23 0.00 3.10 0.01 0.12 3.23

Westmoreland County 1.000 0.424 0.91 0.53 0.02 0.04 1.50 0.91 0.53 0.02 0.04 1.50

Williamsburg, City of 1.000 0.000 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.01 0.01

York County 1.000 0.798 0.07 3.37 0.00 0.00 3.44 0.07 3.37 0.00 0.00 3.44

Total — 0.156 33.06 48.31 62.85 2.64 148.31 32.34 38.54 62.56 2.46 137.36

a U.S. Geological Survey, 2002.
18 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Prior to this 1992 regulation, the Virginia State Water 

Control Board (now part of the VDEQ) collected information 

on new domestic wells, which was recorded on Virginia 

Water Well Completion Reports (Form GW–2) submitted 

to the appropriate regional office of the State Water Control 

Board. Some of these forms are still on file in regional 

VDEQ offices, but many are now located in the files of local 

health departments. These GW–2 forms require much more 

detailed information than the UWWCR and were intended 

to be completed by professional staff of the Virginia State 

Water Control Board or VDEQ. However, VDEQ and local 

health department officials indicated that these completion 

reports typically were submitted for only a small portion of 

the domestic wells drilled (T.S. Bruce, Virginia Department of 

Environmental Quality, oral commun., 2002). Even after the 

UWWCR form was introduced in 1992, the GW–2 form often 

was used in place of the UWWCR, but this practice appears 

to have declined with time. Of the 2,846 records collected for 

the period 1977 through 2002, 1,518 were GW–2 forms, and 

1,328 were UWWCR forms. 

Regardless of the form used to report domestic-well data, 

this survey revealed that the form rarely was filled out completely or accurately. Lithologic logs on these forms for private 

domestic wells are extremely generalized or non-existent, 

and information was almost never included about aquifers 

that were intersected. Requested location data on the GW–2 

form includes latitude and longitude, but these coordinates 

rarely were supplied by the well driller or homeowner. The 

postal address of the property is requested on both forms, 

but a complete postal address rarely was given. Instead, 

local driving directions often were given, which is useful for 

locating an individual property but of little use for locating 

wells with any automated address system. Potentially useful 

location data generally included on the well form is the county 

tax-map identification number, which indicates the location 

of the property in the county tax-plat book. However, most of 

the locality tax maps are available only in paper form, not as 

spatially referenced digital maps useful in a GIS. Digitizing 

and georeferencing all county tax maps was not within the 

scope of project resources. Furthermore, several localities 

updated their tax-map systems at least once between 1977 and 

2002, the period of record covered by this study, and it was 

often difficult to discern which tax-map system was used for a 

given well permit.

Following initial examination of the well forms, a 

database was created to record the useful information common 

for most of the domestic wells. Database fields included 

locality name, location of well or property, tax-map identification number, health department identification number, type 

of well record (UWWCR or GW–2), well-completion date, 

drilling method (usually auguring or boring for shallow wells, 

and mud-rotary drilling for deeper wells), hole diameter, 

hole depth, depth to the top of the well screen, depth to the 

bottom of the well screen, well type (domestic supply well, 

or domestic irrigation well), and miscellaneous notes. Data 

were not available on measured withdrawals from any of the 

domestic wells.

The goal of the data-collection phase of this study was 

the acquisition of a representative sample of domestic-well 

characteristics for each locality. Consequently, the sampling 

scheme initially was designed to select well records randomly 

from the domestic-well files located in each health department 

office. In most counties, however, it was quickly discovered 

that domestic-well records typically are filed in groups by 

tax-map number; therefore, tax-map grouping was used to 

spatially stratify the random sampling approach and assure 

that wells were geographically distributed across the locality. 

Thus, approximately the same number of well records was 

collected for each tax-map group in a particular locality. 

The total number of well records collected for each locality was influenced by the amount of time needed to collect and 

record the well data from health department files and by the 

number of records needed to acquire a representative sample 

of the population. The goal of this approach was to obtain 

for each county the percentage of domestic wells intersecting each of the Coastal Plain aquifers from a sampling of 

well-completion reports. Mathematically, well depth could be 

considered a continuous random variable, but well depth can 

be used to determine the aquifer in which the well is screened. 

Consequently, the problem can be simplified by sorting the 

well depths into discrete categories representing the aquifers 

used for domestic water supply and creating a categorical 

variable. The proportion of the population of wells in each of 

these aquifers then can be estimated from the proportion of the 

sampled well records. 

The number of records sampled in each locality had to 

be large enough to generate statistically significant results. 

In other words, the sample size had to be large enough so 

that the sample proportion of wells in each aquifer was an 

accurate estimator of the population proportion. Going a step 

further, a confidence interval for the estimation was developed 

for a given error bound on the population proportion. For 

an error bound of 0.05 on the population proportion with a 

90-percent level of confidence, a sample size of 271 well 

records was required. This turned out to be an unrealistic 

sample size based on time constraints for the project, which 

allowed only one day for sampling in each locality. It quickly 

became apparent during the study that a sample of 100 well 

records for each locality was a reasonable goal. The required 

sample size becomes smaller with a lower confidence level 

and higher error bound on the proportion of wells in each 

aquifer. Actually, by changing the error bound to 0.10, a more 

realistic sample size of 68 was obtained, which was well 

within the time constraints of the study. Stated another way, if 

100 records were sampled for a given locality, the error bound 

typically would be between 0.05 and 0.10, with a 90-percent 

confidence level. These error criteria were judged to be acceptable for this study.

In practice, data collection from the files of each health 

department involved randomly selecting each well record 

file from a tax-map group, manually recording the data into 
Private Domestic-Well Characteristics 19

the database, then returning the well record to its place in the 

file cabinet along with a temporary flag to prevent multiple 

sampling of the same record. In a few localities, the use of 

other organizational schemes required quick adjustments to the 

sampling method in an attempt to gather samples with an even 

geographic distribution across the locality. In Charles City 

County and City of Virginia Beach, records were arranged by 

year of well installation. In King and Queen County, records 

were arranged alphabetically by owner. Records were arranged 

by road or address in City of Chesapeake, Henrico County, 

Prince George County, and Surry County (for records since 

2001 only).

General Characteristics of Private 

Domestic Wells

In all, 2,846 records of private domestic wells were 

collected from spatially stratified random samples of well 

records in 29 localities in the Virginia Coastal Plain. The 

deepest (865 ft) of the sampled wells is located in Lancaster 

County on the Northern Neck Peninsula. The shallowest well 

(14 ft) is located in King William County. The mean depth to 

the bottom of a well screen is 202.2 ft, and the median depth 

is 141.5 ft, which indicates the depth distribution is skewed 

toward greater depths. The most common value, or mode, is 

40 ft. The sample standard deviation is 173.5 ft. A histogram 

of all well depths is presented in figure 8, along with summary 

statistics for the depths to the bottoms of the well screens.

Installation dates for sampled wells ranged from 1977 to 

2002, the year of the sampling effort. In most localities, well 

records became more numerous in later years, particularly 

after 1992 when new well regulations took effect. It was 

not possible to discern definitive trends in well installation 

frequency from sampled records, because they are obscured by 

obvious trends in data collection and organization.

Of the wells for which records were sampled, 2,017 

(70.9 percent) were drilled using the mud-rotary method. Well 

diameters ranged from 1.25 inches (in.) to 6.25 in., and 4 in. 

was the most common value. Drilled wells ranged from 22 ft 

to 865 ft in depth, with a median value of 245 ft and a mean 

value of 267.4 ft. Recorded screen intervals for rotary-drilled 

wells ranged from 2 to 156 ft, with 10 ft being the most 

common interval and 15 ft being the median. Of the total 

wells for which data were collected, 800 were bored wells 

(28.1 percent). Bored wells ranged in depth from 14 ft to 93 ft, 

with a median depth of 43 ft and a mean of 44.5 ft. Of the 

bored wells, 517 (64.6 percent) had a diameter of 30 in., and 

271 (33.8 percent) had a diameter of 24 in.

The remaining wells that were not mud-rotary drilled 

or bored were constructed using a variety of methods. Seven 

sampled wells in the City of Suffolk were jetted. Five wells 

in a variety of locations were constructed with the cable-tool 

method, and the deepest of these was 235 ft. Two sampled 

wells were dug, one was augured by hand, and two in 

Northampton County were driven by hand. Records indicated 

that 11 wells in Greensville County were constructed in 

bedrock by the air-rotary method; the deepest of these was 

305 ft. One well record in New Kent County had no construction method specified.

Well-screen depths substantially influence the hydrogeologic effects of domestic wells; thus, screen depth was 

the parameter investigated in the most detail for this study. 

Statistics for depth to bottom of well screen are presented by 

locality in table 3. Because the distribution of screen depths in 

most localities is often skewed, or otherwise far from normal, 

the median screen depth is thought to be the most representative statistic for each locality. These summary statistics alone 

provide an incomplete perspective of the varied distribution 

of well depths in each locality; however, they provide a 

condensed overview for comparing well characteristics among 

localities. The spatial variations in well depths are discussed in 

more detail below.

Characteristics of Incidentally Sampled Private 

Irrigation Wells

In the process of randomly sampling records for private 

domestic wells, records for 91 private irrigation wells (usually 

used for watering lawns and gardens) were obtained for the 

following localities: Accomack County, City of Chesapeake, 

James City County, Northampton County, City of Poquoson, 

City of Suffolk, City of Virginia Beach, and York County. 

Although these irrigation well records were found among the 

records for domestic wells, some localities maintain separate 

files for private irrigation wells. These wells are classified by 

VDEQ as Class IV wells, and applications for Class IV wells 

are subject to an expedited permitting process with fewer 

Figure 8. Histogram of depths to bottom of screen for private 

domestic wells in the Virginia Coastal Plain.

NUMBER = 2,846

MEDIAN = 141.5 FEET

MINIMUM = 14 FEET

MAXIMUM = 865 FEET

MEAN = 202.2 FEET

STANDARD DEVIATION = 173.5 FEET

900

0

100

200

800

700

600

500

300

400

DEPTH TO BOTTOM OF WELL SCREEN, IN FEET

0 100 200 300 400 500 600 700

FREQUENCY (NUMBER OF WELLS)

DESCRIPTIVE STATISTICS
20 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Table 3. Statistics for depth, in feet, to bottom of well screen for a sample of private domestic wells in 

Virginia Coastal Plain localities.

[Values in feet are relative to National Geodetic Vertical Datum of 1929]

Locality

(fig. 1)

Number

sampled Median Mean Maximum Minimum Standard deviation Variance Mode

Accomack County 96 190.0 193.3 290 100 50.1 2506.2 160

Caroline County 122 51.0 114.2 606 21 125.3 15712.3 42

Charles City County 81 45.0 115.0 450 25 111.9 12528.9 42

Chesapeake, City of 103 70.0 79.0 600 25 58.8 3463.1 80

Essex County 95 248.0 221.6 534 26 163.6 26761.9 42

Gloucester County 96 90.0 113.4 584 25 104.7 10954.2 90

Greensville County 54 38.3 76.4 305 16 79.9 6391.4 28

Hanover County 110 220.0 210.4 450 20 155.8 24261.5 45

Henrico County 90 47.0 115.1 355 27 108.8 11827.7 36

Isle of Wight County 123 380.0 303.1 500 26 164.9 27205.4 440

James City County 72 255.0 261.9 540 40 94.1 8855.4 230

King and Queen County 109 250.0 225.7 595 22 153.2 23458.8 300

King George County 101 352.0 357.6 820 30 200.5 40186.1 320

King William County 107 166.0 182.1 541 14 146.8 21548.7 45

Lancaster County 97 445.0 412.3 865 24 253.9 64453.3 622

Mathews County 106 110.0 106.1 168 30 21.7 470.5 120

Middlesex County 102 102.5 198.7 696 21 177.7 31594.6 120

New Kent County 98 225.0 229.2 560 28 121.5 14759.7 200

Northampton County 115 160.0 159.7 300 16 58.8 3454.2 160

Northumberland County 110 454.0 476.0 809 20 235.4 55421.6 400

Prince George County 102 55.8 92.4 370 27 74.6 5563.3 49

Richmond County 93 305.0 272.6 590 30 130.5 17031.3 290

Southampton County 123 202.0 194.5 387 22 106.9 11431.0 30

Suffolk, City of 101 440.0 328.5 693 24 220.2 48488.9 30

Surry County 107 54.0 159.0 432 21 147.9 21861.7 300

Sussex County 86 45.5 71.5 362 18 64.3 4137.5 34

Virginia Beach, City of 96 73.0 80.3 212 25 39.8 1582.9 40

Westmoreland County 113 232.0 229.8 648 27 163.8 26829.5 42

York County 38 120.0 159.8 445 45 103.1 10625.5 120

All records 2,846 141.5 202.2 865 14 173.5 30094.8 40

regulatory requirements. The occurrence of these wells seems 

to vary widely depending on the locality, but health department and VDEQ professionals indicated that irrigation wells 

are quite common in many suburban areas and are sometimes 

referred to as “sprinkler wells.” Unlike private domestic wells, 

private irrigation wells often are found in areas served by 

public water supplies. 

Private irrigation wells are of keen interest among many 

ground-water and water-use professionals in the Virginia 

Coastal Plain. The spatial distribution and construction 

characteristics of these wells are not well documented and 

very little is known about water use for private household 

irrigation purposes. The well reports are filed separately in 

some localities, and no specific effort was made during this 

investigation to evaluate the occurrence of irrigation wells or 

the magnitude of withdrawals for private household irrigation, 

which was beyond the scope of this report. Therefore, the 

characteristics of these wells are not included in the analyses 

of private domestic wells. Instead, the characteristics of the 

sampled domestic irrigation wells are presented separately. 

The irrigation wells for which records were collected 

were mostly small-diameter drilled wells, ranging in depth 
Private Domestic-Well Characteristics 21

from 26 ft to 590 ft and in diameter from 1.25 in. to 4.5 in. 

The median well depth was 116 ft, the mean depth was 

121.2 ft, and the most common depth was 140 ft. Screens 

ranged from 2 ft to 100 ft in length. Many (41 percent) of the 

sampled wells were specifically classified as being located in 

subdivisions. Most private irrigation wells clearly intersected 

either the surficial aquifer or the Yorktown-Eastover aquifer, 

but seven private irrigation wells in James City County had 

depths that likely would place them in either the Aquia or 

Potomac aquifers.

Spatial Variability in Domestic-Well 

Characteristics

Well construction is spatially variable across the Virginia 

Coastal Plain because of local conditions and needs, but it 

is most strongly associated with well depth and available 

aquifers. Shallow, bored wells, for example, are more common 

in the southwestern part of the Virginia Coastal Plain near the 

Fall Line where water is available from the surficial aquifer 

and local bedrock is relatively shallow. Drilled wells are more 

common in other areas where water from deeper aquifers is 

available.

Spatial variations in well characteristics, particularly 

well depth, are more apparent when the data are examined by 

locality. Median depths of private domestic wells are shown by 

locality in figure 9, and a few general trends are immediately 

apparent. Some variation in well depths by locality appears to 

be the result of a variety of socioeconomic factors, but these 

correlations are not definitive. For example, there may be 

a correlation between median home value and median well 

depth, which is not particularly surprising because deeper 

wells are more costly to construct. Similarly, median family 

income also appears to be somewhat correlated with well 

depth by locality.

Despite possible socioeconomic factors, most of 

the variation in well depth appears to be related to local 

hydrogeologic conditions. In general, median well depths tend 

to increase to the east, as the aquifer system becomes thicker 

and more transmissive and a larger number of aquifers are 

available for water supply. This trend is disrupted in localities 

near the Chesapeake Bay or Atlantic coast, where deeper 

aquifers contain brackish water. The effect of the buried 

Chesapeake Bay impact crater, which contains brackish water, 

can be observed in the relatively shallow well depths of York, 

Gloucester, Mathews, and Middlesex Counties. In contrast, 

the much greater median well depths in Northumberland and 

Lancaster Counties result from the availability of the very 

productive, high-quality Potomac aquifer. In the southeastern 

Virginia localities of the cites of Virginia Beach and Chesapeake, shallow well depths are the result of brackish water at 

deeper intervals. For the Eastern Shore counties of Accomack 

and Northampton, very shallow wells in the unconfined 

surficial aquifer are uncommon because of reported agricultural contamination and because the first confined aquifer, 

the Yorktown-Eastover, is a good source of water at moderate 

depths. However, salty water occupies the aquifers underlying 

the Yorktown-Eastover aquifer across the Eastern Shore, 

effectively prohibiting deeper domestic wells.

Estimated Elevations of Domestic-Well Screens

It is most appropriate to compare wells spatially based on 

screen elevations rather than depths, because land-surface and 

well-head elevations vary appreciably by locality across the 

study area. In the Virginia Coastal Plain, land-surface elevations decline from highest values in localities near the Fall 

Line to lowest values in southeastern localities, and aquifer 

elevations dip similarly from west to east. Unfortunately, 

useful well-location information typically is not available for 

private domestic wells. Furthermore, well-head elevations 

needed for calculating screen elevations from screen depths 

typically were not reported on private well records, and the 

principal technique for estimating the elevation from a map 

or digital elevation model (DEM) depends on appropriate 

well-location information. Short of a tremendous effort to 

locate each individual well manually on a map or digitize taxplot maps to provide approximate locations, the best location 

attribute immediately available for a well record is the locality, 

which somewhat constrains the well-head elevation depending 

on the variability of land-surface elevation within the locality. 

Consequently, the best practical elevation data for the well is 

the median land-surface elevation for the locality. While this 

approach produces only a rough approximation of well-screen 

elevations, it allows more direct comparison between wells 

across localities than well depth alone. All subsequent 

analyses are based on the use of estimated well-screen elevations, which were also used to evaluate the aquifers intersected 

by each well. Estimated values for the elevations of the middle 

of the well screens are summarized statistically by locality in 

table 4, which also includes the median land-surface elevation 

for each locality.

Histograms of the elevations of the middle of well 

screens are arranged in alphabetical order by locality in 

figures 10A–E. The multimodal distributions seen in many 

of these histograms reveal groups of well-screen elevations 

that appear to correspond to various aquifers intersected by 

the wells. This is why the distribution of screen elevations 

becomes larger and more complex toward the east as the aquifer system becomes thicker and a larger number of aquifers are 

present. For example, the distribution of well-screen elevations 

in Northumberland County (fig. 10D) has three or more peaks, 

while the distribution in Greensville County (fig. 10B) appears 

to have only one peak. It is apparent from subsequent analyses 

that these peaks in the domestic-well histograms correspond 

at least approximately to the aquifers used for domestic water 

supply in each locality.
22 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Figure 9. Median depths to bottom of screen by locality for private domestic wells in the Virginia Coastal Plain 

(locality names are shown in fig. 1).

38–73

74–120

121–202

203–305

306–454

MEDIAN DEPTH TO BOTTOM

OF SCREEN, IN FEET

0

0

25 50 MILES

25 50 KILOMETERS

39 ̊

38 ̊

37 ̊

78 ̊ 77 ̊ 76 ̊

Fall Line

EXPLANATION

NORTH CAROLINA

MARYLAND

DELAWARE

ATLANTIC OCEAN

CHESAPEAKE BAY

352

445

220 166

103

250

454 305

232

248

51

56

45

47

54

225

255

120

90 110

160

190

73

440

380

38

46

202

70

Figure 9. Median depths to bottom of screen by locality for private domestic wells in the Virginia Coastal Plain

(locality names are shown in fig. 1).

Washington, D.C.
Private Domestic-Well Characteristics 23

Table 4. Statistics for estimated elevation, in feet, of middle of well screen for a sample of private domestic wells in 

Virginia Coastal Plain localities.

[Values in feet are relative to National Geodetic Vertical Datum of 1929]

Locality

(fig. 1)

Median 

elevation 

(ft)

Number

sampled Median Mean Maximum Minimum Standard deviation Variance Mode

Accomack County 8 96 -174.5 -178.5 -87 -277 49.2 2420.5 -205

Caroline County 178 122 127.0 66.8 157 -413 120.2 14454.6 136

Charles City County 61 81 16.0 -50.1 36 -374 106.6 11365.5 19

Chesapeake, City of 14 103 -51.0 -60.0 -9 -581 58.4 3413.9 -51

Essex County 114 95 -119.0 -100.5 88 -413 159.3 25385.2 72

Gloucester County 48 96 -31.0 -54.7 26 -529 104.7 10953.5 -27

Greensville County 83 54 44.8 22.1 67 -140 52.3 2730.3 55

Hanover County 156 110 -54.0 -44.8 136 -279 147.7 21814.0 111

Henrico County 139 90 92.0 29.4 112 -196 101.5 10306.5 103

Isle of Wight County 61 123 -314.0 -237.4 38 -434 163.7 26800.4 -374

James City County 61 72 -185.3 -192.8 21 -469 93.1 8662.0 -164

King and Queen County 117 109 -119.0 -99.7 95 -471 148.9 22169.5 -138

King George County 82 101 -260.5 -269.6 52 -728 198.4 39366.2 52

King William County 97 107 -61.0 -78.1 83 -437 140.8 19829.9 52

Lancaster County 60 97 -375.0 -345.3 36 -795 250.9 62953.8 36

Mathews County 9 106 -87.5 -85.7 -19 -144 20.5 421.7 -101

Middlesex County 64 102 -27.5 -127.1 43 -622 177.3 31437.0 9

New Kent County 81 98 -139.0 -140.6 53 -469 118.1 13937.8 -97

Northampton County 12 115 -77.0 -75.4 64 -215 58.3 3401.6 -77

Northumberland County 63 110 -381.5 -404.6 43 -739 233.5 54529.4 -272

Prince George County 108 102 52.3 18.6 81 -252 70.8 5011.8 59

Richmond County 103 93 -192.0 -162.5 73 -480 127.3 16204.2 -180

Southampton County 69 123 -125.5 -121.4 49 -313 105.4 11111.7 39

Suffolk, City of 45 101 -381.5 -278.8 23 -643 219.1 48013.4 15

Surry County 89 107 35.0 -67.0 68 -338 145.2 21095.6 -206

Sussex County 100 86 54.5 30.4 82 -260 61.7 3803.6 66

Virginia Beach, City of 6 96 -61.3 -69.4 -17 -196 39.2 1537.2 -59

Westmoreland County 69 113 -156.0 -156.1 42 -574 161.0 25932.9 27

York County 34 38 -71.0 -112.9 -1 -401 105.0 11032.4 -71
24 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Figure 10 Figure 10A. A. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities.

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ELEVATION OF MIDDLE OF WELL SCREEN, IN FEET RELATIVE TO NGVD 29

0 5 10 15 20 0 5 10 15 20 25 30 35 40 45 50 55 60 65

0 5 10 15 20 25 30 35 40 45 0 5 10 15 20 25 30 35

0 5 10 15 20 25 30 0 5 10 15 20 25 30 35 40 45 50

Accomack County Caroline County

Charles City County City of Chesapeake 

Essex County Gloucester County

FREQUENCY (NUMBER OF WELLS) FREQUENCY (NUMBER OF WELLS)
Private Domestic-Well Characteristics 25

Figure 10B. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities.

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Greensville County Hanover County

Henrico County Isle of Wight County

James City County King and Queen County

Figure 10B. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities.

0 5 10 15 20 0 5 10 15 20 25 30 35 40

0 5 10 15 20 25 30 0 5 10 15 20 35

0 5 10 15 20 0 5 10 15 20

FREQUENCY (NUMBER OF WELLS) FREQUENCY (NUMBER OF WELLS)

ELEVATION OF MIDDLE OF WELL SCREEN, IN FEET RELATIVE TO NGVD 29
26 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Figure 10C. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities.

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King George County King William County

Lancaster County Mathews County

Middlesex County New Kent County

Figure 10C. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities.

FREQUENCY (NUMBER OF WELLS) FREQUENCY (NUMBER OF WELLS)

0 5 10 15 0 5 10 15 20 25 30 35

0 5 10 15 0 5 10 15 20 25 30 35 40 45 50 55 60

0 5 10 15 20 25 0 5 10 15

ELEVATION OF MIDDLE OF WELL SCREEN, IN FEET RELATIVE TO NGVD 29
Private Domestic-Well Characteristics 27

Figure 10 Figure 10D. D. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities.

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Northampton County Northumberland County

Prince George County Richmond County

Southampton County City of Suffolk

FREQUENCY (NUMBER OF WELLS) FREQUENCY (NUMBER OF WELLS)

0 5 10 15 20 25 30 35 0 5 10 15

0 5 10 15 20 25 30 35 40 45 50 55 0 5 10 15

0 5 10 15 20 0 5 10 15 20 25 30

ELEVATION OF MIDDLE OF WELL SCREEN, IN FEET RELATIVE TO NGVD 29
28 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Figure 10 Figure 10E. E. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities. Histograms of estimated domestic well-screen elevations for Virginia Coastal Plain localities.

200

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0 5 10 15 20

Surry County Sussex County

City of Virginia Beach Westmoreland County

York County

FREQUENCY (NUMBER OF WELLS)

ELEVATION OF MIDDLE OF WELL SCREEN, IN FEET RELATIVE TO NGVD 29
Distribution of Domestic Wells and Withdrawals among Aquifers 29

Assumptions and Limitations Related to 

Estimating Domestic-Well Characteristics

The approach of estimating well characteristics from a 

stratified random sample and estimating self-supplied water 

use from population data was chosen because it was the only 

practical way to answer the necessary questions given the 

limitations in both data and resources. The use of population 

data and coefficients to estimate self-supplied domestic 

withdrawals commonly is applied in the USGS National 

Water Use Program and has been used without exception in all 

States and territories in the compilation of the 2000 water-use 

data (Kenney, 2004). Even with unlimited resources, it would 

be impossible to complete a census of all private domestic 

wells because records simply do not exist for many of the 

wells that have been drilled. In general terms, the stratified 

random sampling approach used for estimating well data and 

the coefficient-based approach of indirectly estimating water 

use from population data are associated with advantages and 

limitations that are well documented in the water-use literature 

(National Research Council Water Science and Technology 

Board, 2002).

Aside from the incomplete nature of the sampled records, 

one of the primary questions in any sampling effort is whether 

the sample is representative of the population. Neglecting 

formal statistical treatment of variability in the data, there are a 

number of uncontrollable factors that could affect the validity 

of the sampled well data. While great effort was expended 

to obtain a good, spatially stratified random sample of the 

well records available, some evidence indicates that the well 

records on file in a locality may not be truly representative of 

the wells extant in the locality. 

For example, the estimated total number of records on 

file in many localities is much smaller than the total number 

of wells estimated from the population in the locality, which 

indicates that records do not exist for many wells. Furthermore, the lack of data prior to the late 1970s casts doubt on 

the completeness of the analyses. Clearly, many wells were 

installed in the Coastal Plain prior to the late 1970s, but no 

data are available on the characteristics of these earlier wells, 

which may still be in use. With these limitations in mind, 

the sample taken for this study may overestimate the depth 

of the well distribution for many localities. Several health 

department officials indicated a trend toward installing deeper, 

drilled wells for new homes and as replacements for shallow 

wells that fail during drought conditions. Unfortunately, the 

lack of earlier data makes this trend impossible to quantify. 

Nonetheless, this limitation should be considered with the 

sample results. 

It would be more accurate to describe this study as a 

sample of the population of wells drilled since 1977 rather 

than as a sample of the population of all Virginia Coastal 

Plain wells. However, the well records sampled do not show 

a noticeable change in well-depth characteristics with time 

over the sampling period 1977 to 2002 other than perhaps 

a small increase in depths during the first few years that data 

were available.

Distribution of Domestic Wells and 

Withdrawals among Aquifers

The distribution of domestic wells and withdrawals 

among the aquifers of the Virginia Coastal Plain was based on 

the evaluation of the construction characteristics of sampled 

wells (described in the previous section of this report) and 

aggregated information on land-surface and hydrogeologicunit elevations from the localities of interest. Neither 

aquifer-unit elevations nor aquifer designations were available 

for individual wells, so digital hydrogeologic-unit elevations 

developed for the McFarland and Bruce (2006) study were 

used to create a generalization of aquifer and confining-unit 

elevations for each locality. Estimated well-screen elevations 

were then compared to median aquifer elevations in each 

locality to estimate the primary aquifer in which each well was 

completed. A simple diagram of the spatial relations involved 

in this analysis is provided in figure 6, which illustrates well 

depth, well-head and well-screen elevations, land-surface 

elevation, and aquifer and confining-unit elevations for an 

example well location. The analysis involved in determining 

the aquifer for a well from measured screen and aquifer data 

(fig. 6A) is compared with the analysis in which the wellscreen and aquifer elevations are estimated, as in this report 

(fig. 6B). The process is conceptually simple, but a number of 

assumptions are required to produce the necessary estimates.

From the determination of the aquifer for each well, 

the proportion of private domestic wells completed in each 

aquifer was calculated for each locality, and the proportions 

from all localities were summed for the entire Virginia 

Coastal Plain. For each locality, the estimated proportions of 

wells in each aquifer were used along with estimated rates 

of private domestic ground-water withdrawals derived from 

USGS water-use data (U.S. Geological Survey, 2002; Hutson 

and others, 2004) to compute rates of withdrawal from each 

aquifer. The steps involved in data collection, estimation, and 

analysis are outlined in a flow chart in figure 7. This chart 

illustrates the process of analyzing private domestic-well 

data, apportioning private domestic wells and withdrawals 

among aquifers, and distributing self-supplied domestic 

withdrawals spatially. 

Analyses of Hydrogeologic-Unit Elevations 

by Locality

Data on land-surface and hydrogeologic-unit top 

elevations for each locality were derived from DEMs for the 

Virginia Coastal Plain produced from the work of McFarland 

and Bruce (2006). Using a GIS, McFarland and Bruce (2006)

developed maps of the structural contours (top elevations) and 
30 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

extents of each of 19 aquifers and confining units and bedrock 

basement. The structural contours were used to develop raster 

representations of unit-top elevations in feet relative to NGVD 

1929 at a horizontal resolution of 264 ft (1/20 mile). 

The DEM used for the land-surface elevation and the top 

elevation of the surficial aquifer was derived from the National 

Elevation Dataset (NED; U.S. Geological Survey, 2004). The 

standard 30-meter (98.4 ft) NED raster data were resampled 

to the same 264-ft horizontal resolution as the rasters of the 

top elevations of aquifers and confining units, and the units of 

elevation were rounded and converted to integers to match the 

other unit-elevation rasters.

Statistical analyses of each of the 20 raster data sets were 

completed with a GIS. The GIS also was used to aggregate 

unit-top elevations by locality. Using Environmental Systems 

Research Institute, Inc. (ESRI), ArcGIS software, the “Zonal 

Statistics as Table” tool was implemented to summarize each 

of the raster grids by using polygons of the locality boundaries 

as the spatial zones for the computation. For localities situated 

in both the Piedmont and Coastal Plain, the Fall Line was 

used with the boundary polygons to create new polygons for 

only the Coastal Plain portion of the localities. Calculated 

aggregate statistics included the median, minimum, maximum, 

and mean values.

Data on the elevations of aquifers and confining units 

were not available for several northwestern Coastal Plain 

localities that were not included in the McFarland and Bruce 

(2006) study of the regional hydrogeology. These localities 

include the City of Alexandria, and Arlington, Fairfax, and 

Prince William Counties. Hydrogeologic-unit elevations were 

also not available for the City of Emporia in the southwestern 

part of the Virginia Coastal Plain because it is just outside of 

the McFarland and Bruce (2006) study area. As a result, these 

localities were not included in this study.

Of particular concern in the analyses were aquifers and 

confining units that do not extend across entire localities. 

Many of the hydrogeologic units pinch out as the wedge of 

Coastal Plain sediments thins to the west, and other units associated with the impact crater are limited in extent by the very 

nature of the impact event and subsequent geologic processes. 

The use of summary top-elevation values for an entire locality 

for aquifers and confining units that occupy only a small part 

of the locality was found to produce unsatisfactory results for 

the aggregate median unit elevations, specifically by creating 

negative unit thicknesses. To address this problem, units 

were considered to be present in a locality for the aggregate 

hydrogeology if they extended across more than 50 percent of 

the area; otherwise, they were considered to be absent. 

The statistical analyses of DEMs for land-surface 

elevations and hydrogeologic-unit top elevations resulted in 

aggregate elevation values for each of these units for each 

locality. Aggregated values of elevations for each of these 

units are presented in tables 5–9. The most useful and appropriate aggregate elevation values for the hydrogeologic units 

are the median top elevations, presented in table 5, but other 

statistical values are presented to provide a measure of the 

variability of each of the unit surfaces within the boundaries of 

each locality. The minimum hydrogeologic-unit top elevations 

for each locality are presented in table 6, the maximum unit 

top elevations are presented in table 7, and the mean unit top 

elevations are presented in table 8. The proportions of each 

locality occupied by each hydrogeologic unit are presented in 

table 9 to more completely depict the known extent of each 

unit, including those considered to be absent in certain localities for the aggregated hydrogeology. Much more detailed 

information on the spatial variability of Virginia Coastal Plain 

hydrogeology is documented by McFarland and Bruce (2006). 

Clearly, the aggregated approach used here is a simplification 

but one that was necessary for this analysis.

Assignment of Domestic Wells and Withdrawals 

to Aquifers

With estimated well-screen elevations and a generalization of hydrogeologic-unit top elevations available for each 

locality of interest, it was possible to relate wells to hydrogeologic units on an aggregate basis simply by cross-referencing 

the estimated well-screen elevations with the estimated, 

aggregate hydrogeologic-unit elevations for each locality. 

This approach does not consider the component of variation 

in well-screen elevations due to the variable land-surface 

elevation within each locality, and it does not incorporate the 

sometimes substantial range of variation in the elevation of 

hydrogeologic units within a single locality. Nonetheless, the 

approach was valid for this region primarily because the land 

surface and the various hydrogeologic units are relatively flat 

and dip gently in approximately the same direction, which is 

to the east. Partly because of this configuration, the difference 

between the elevations of aquifers in which private domestic 

wells are completed generally is larger than either the variability in the land-surface elevation within a locality or the 

variability in the top elevation for each of the aquifer units. 

This set of conditions in many cases allows for considerable 

uncertainty with respect to a well-screen elevation without 

changing the estimate of the aquifer the well is thought 

to intersect.

 In practice, each of the wells in a locality was assigned 

to an aquifer by comparing the estimated screen top and 

bottom elevations to the calculated median values for the 

hydrogeologic units present in the locality. This sometimes 

resulted in the initial assignment of a well to more than one 

hydrogeologic unit; in these cases, the assigned unit was the 

one intersected by the larger portion of the well screen. In 

some cases, the comparison of well-screen elevations resulted 

in the assignment of a well to a confining unit only; in these 

cases, the vertically closest aquifer unit was assigned as the 

most likely unit intersected by the well screen. In most cases, 

however, only one aquifer designation was apparent, and it 

was a reasonable aquifer selection.
Distribution of Domestic Wells and Withdrawals among Aquifers 31

Table 5. Median elevations, in feet, of top of hydrogeologic units in Virginia Coastal Plain localities.[SURF, surficial aquifer; YTCZ, Yorktown confining zone; YEAQ, Yorktown-Eastover aquifer; SMCU, Saint Marys confining unit; SMAQ, Saint Marys aquifer; CACU, Calvert confining unit; PPAQ, Piney Point aquifer; CHCU, Chickahominy confining unit; XMCU, Exmore matrix confining unit; XCCU, Exmore clast confining unit; NMCU, NanjemoyMarlboro confining unit; AQAQ, Aquia aquifer; PDCU, Peedee confining unit; PDAQ, Peedee aquifer; VBCZ, Virginia Beach confining zone; VBAQ, Virginia Beach aquifer; UCCU, Upper Cenomanian confining unit; POCZ, Potomac confining zone; POAQ, Potomac aquifer; BSMT, basement; –, unit is not present over less than 50 percent of the locality area. Shading indicates locality in which well data were collected]

Locality (fig. 1)a SURF YTCZ YEAQ SMCU SMAQ CACU PPAQ CHCU XMCU XCCU NMCU AQAQ PDCU PDAQ VBCZ VBAQ UCCU POCZ POAQ BSMT

Accomack County 8 -70 -97 -357 -526 -713 -890 -999 – – – – – – – – – -1,199 -1,322 -4,984

Caroline County 178 – – – – 94 – – – – 74 24 – – – – – -24 -96 -376

Charles City County 61 – – 10 – 16 -26 – – – -61 -112 – – – – – -141 -158 -658

Chesapeake, City of 14 -15 -27 -124 – -427 -440 – – – -457 -473 -554 -630 -601 -616 -619 -766 -776 -2,466

Chesterfield County 133 – – – – – – – – – – – – – – – – – – 33

Colonial Heights, City of 62 – – – – – – – – – – – – – – – – – – 10

Dinwiddie County 149 – – – – – – – – – – – – – – – – – – 38

Essex County 114 – – 86 – 12 -41 – – – -89 -182 – – – – – -299 -318 -1,523

Franklin, City of 29 11 -3 -35 – – -50 – – – -59 -77 – – – – -108 -191 -215 -822

Fredricksburg, City of 93 – – – – – – – – – – – – – – – – 41 -49 -142

Gloucester County 48 32 5 -104 – -223 -288 -371 -578 – – – – – – – – -587 -607 -1,776

Greensville County 83 – – – – – – – – – – – – – – – – – – -16

Hampton, City of 8 -22 -37 -165 – -408 -456 -600 -792 -871 – – – – – – – -1,407 -1,423 -2,061

Hanover County 156 – – 100 – 69 – – – – 43 -26 – – – – – -45 -70 -187

Henrico County 139 – – 100 – 76 – – – – 47 – – – – – – 1 -11 -179

Hopewell, City of 44 – – – – – – – – – 25 – – – – – – 6 0 -227

Isle of Wight County 61 36 -9 -54 – – -138 – – – -156 -193 – – – – – -245 -264 -1,127

James City County 61 53 13 -24 – -98 -105 – – – -165 -226 – – – – – -259 -282 -1,224

King and Queen County 117 – – 12 – -39 -80 – – – -159 -225 – – – – – -283 -355 -1,361

King George County 82 – – – – 78 – – – – 14 -59 – – – – – -132 -189 -1,244

King William County 97 – – 60 – 24 -22 – – – -47 -111 – – – – – -181 -216 -1,005

Lancaster County 60 0 -26 -49 – -155 -259 – – – -355 -491 – – – – – -517 -529 -2,263

Mathews County 9 -21 -35 -150 – -291 -440 -542 -762 -832 – – – – – – – -1236 -1278 -2,303

Middlesex County 64 31 2 -28 – -116 -188 – – – -258 -377 – – – – – -438 -450 -1,819

New Kent County 81 – – 1 – -12 -29 – – – -93 -149 – – – – – -181 -210 -936

Newport News, City of 25 -17 -56 -137 – -247 -294 -346 -544 – – – – – – – – -430 -474 -1,707

Norfolk, City of 10 -48 -84 -193 – -499 -545 -679 -820 – – – – – – – – -765 -786 -2,368

Northampton County 12 -60 -90 -258 – -589 -958 -1,088 -1267 -1316 – – – – – – – – – -3,938

Northumberland County 63 25 -3 -23 – -137 -264 – – – -368 -508 – – – – – -549 -569 -2,561

Petersburg, City of 140 – 111 – – – – – – – – – – – – – – 59 24 6

Poquoson, City of 4 -21 -46 -138 – -391 -460 -620 -835 -965 – – – – – – – -1,526 -1,542 -2,133

Portsmouth, City of 10 -23 -42 -155 – -380 -397 – – – -419 -441 – – – – -466 -583 -599 -2,098

Prince George County 108 108 83 – – – – – – – 26 – – – – – – 13 -19 -242

Richmond County 103 – – 17 – -34 -142 – – – -221 -314 – – – – – -420 -464 -1,962

Richmond, City of 177 – – – – – – – – – – – – – – – – – – 68

Southampton County 69 68 25 0 – – – – – – -30 -40 – – – – – -43 -72 -521

Spotsylvania County 211 – – – – – – – – – – – – – – – – 37 -29 -108

Stafford County 141 – – – – – – – – – – 85 – – – – – 24 -11 -283

Suffolk, City of 45 20 -12 -69 -163 -202 -196 – – – -222 -250 – – – – -307 -410 -430 -1,541

Surry County 89 75 50 2 – – -84 – – – -85 -132 – – – – – -182 -218 -874

Sussex County 100 85 58 – – – – – – – – – – – – – – 16 -10 -261

Virginia Beach, City of 6 -34 -58 -197 – -648 -715 – – – -754 -768 -843 -885 -912 -924 -962 -1,094 -1,130 -3,460

Westmoreland County 69 – – 50 – -7 -98 – – – -150 -286 – – – – – -369 -418 -2,039

Williamsburg, City of 70 68 39 -19 – -143 -157 – – – -199 -271 – – – – – -302 -309 -1,361

York County 34 14 -8 -124 – -244 -299 -413 -601 – – – – – – – – -527 -562 -1,735 aLocalities are those included in a previous study of the hydrogeologic framework by McFarland and Bruce (2006).
32 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain Table 6. Minimum elevations, in feet, of top of hydrogeologic units in Virginia Coastal Plain localities. [SURF, surficial aquifer; YTCZ, Yorktown confining zone; YEAQ, Yorktown-Eastover aquifer; SMCU, Saint Marys confining unit; SMAQ, Saint Marys aquifer; CACU, Calvert confining unit; PPAQ, Piney Point aquifer; CHCU, Chickahominy confining unit; XMCU, Exmore matrix confining unit; XCCU, Exmore clast confining unit; NMCU, Nanjemoy- Marlboro confining unit; AQAQ, Aquia aquifer; PDCU, Peedee confining unit; PDAQ, Peedee aquifer; VBCZ, Virginia Beach confining zone; VBAQ, Virginia Beach aquifer; UCCU, Upper Cenomanian confining unit; POCZ, Potomac confining zone; POAQ, Potomac aquifer; BSMT, basement; –, unit is not present over less than 50 percent of the locality area. Shading indicates locality in which well data were collected] Locality (fig. 1)a SURF YTCZ YEAQ SMCU SMAQ CACU PPAQ CHCU XMCU XCCU NMCU AQAQ PDCU PDAQ VBCZ VBAQ UCCU POCZ POAQ BSMT Accomack County 0 -197 -199 -516 -741 -833 -1,002 -1,099 – – – – – – – – – -1,542 -1,560 -7,566 Caroline County 0 – – – – 18 – – – – -39 -128 – – – – – -232 -243 -1,289 Charles City County 0 – – -74 – -73 -76 – – – -124 -177 – – – – – -214 -228 -1,043 Chesapeake, City of 0 -58 -74 -186 – -626 -663 – – – -688 -709 -755 -799 -895 -908 -934 -1,082 -1,119 -3,597 Chesterfield County 0 – – – – – – – – – – – – – – – – – – -370 Colonial Heights, City of 1 – – – – – – – – – – – – – – – – – – -75 Dinwiddie County 49 – – – – – – – – – – – – – – – – – – -45 Essex County 0 – – -25 – -81 -158 – – – -246 -345 – – – – – -421 -440 -1,833 Franklin, City of 1 -2 -24 -45 – – -57 – – – -68 -83 – – – – -149 -217 -249 -849 Fredricksburg, City of 2 – – – – – – – – – – – – – – – – -23 -74 -211 Gloucester County 0 -38 -63 -147 – -295 -412 -538 -828 – – – – – – – – -1,435 -1,462 -2,127 Greensville County 22 – – – – – – – – – – – – – – – – – – -270 Hampton, City of 0 -65 -99 -204 – -475 -585 -826 -1,029 -1,106 – – – – – – – -1,705 -1,717 -2,324 Hanover County 1 – – 50 – -14 – – – – -43 -107 – – – – – -165 -182 -922 Henrico County 0 – – -24 – 24 – – – – -49 – – – – – – -108 -130 -611 Hopewell, City of 0 – – – – – – – – – -7 – – – – – – -23 -32 -273 Isle of Wight County 0 -48 -100 -178 – – -307 – – – -341 -394 – – – – – -498 -525 -1,720 James City County 0 -25 -48 -113 – -210 -250 – – – -291 -345 – – – – – -415 -428 -1,615 King and Queen County 0 – – -57 – -147 -182 – – – -245 -357 – – – – – -418 -454 -1,656 King George County 0 – – – – -27 – – – – -57 -168 – – – – – -300 -319 -1,664 King William County 0 – – -60 – -81 -96 – – – -171 -265 – – – – – -292 -366 -1,338 Lancaster County 0 -37 -95 -145 – -226 -429 – – – -450 -556 – – – – – -597 -623 -2,604 Mathews County 0 -75 -101 -173 – -351 -586 -789 -979 -1,162 – – – – – – – -1,798 -1,815 -2,552 Middlesex County 0 -49 -83 -147 – -252 -439 – – – -381 -486 – – – – – -723 -749 -2,485 New Kent County 0 – – -56 – -107 -122 – – – -191 -269 – – – – – -305 -360 -1,347 Newport News, City of 0 -74 -99 -183 – -407 -426 -512 -681 – – – – – – – – -949 -1,012 -1,989 Norfolk, City of 0 -73 -104 -224 – -622 -693 -785 -985 – – – – – – – – -1,306 -1,356 -2,637 Northampton County 0 -193 -199 -457 – -757 -1,020 -1,099 -1,299 -1,349 – – – – – – – – – -5,999 Northumberland County 0 -35 -68 -105 – -197 -379 – – – -451 -593 – – – – – -620 -702 -3,005 Petersburg, City of 1 – 4 – – – – – – – – – – – – – – 1 -4 -115 Poquoson, City of 0 -46 -90 -173 – -447 -556 -785 -985 -1,101 – – – – – – – -1,700 -1,713 -2,296 Portsmouth, City of 0 -32 -86 -188 – -454 -479 – – – -502 -520 – – – – -545 -702 -721 -2,342 Prince George County 0 56 -17 – – – – – – – -108 – – – – – – -152 -185 -759 Richmond County 0 – – -28 – -129 -234 – – – -343 -460 – – – – – -494 -545 -2,335 Richmond, City of 1 – – – – – – – – – – – – – – – – – – -96 Southampton County 0 -21 -35 -46 – – – – – – -98 -146 – – – – – -257 -287 -945 Spotsylvania County 0 – – – – – – – – – – – – – – – – -26 -69 -438 Stafford County 0 – – – – – – – – – – -24 – – – – – -34 -55 -732 Suffolk, City of 0 -33 -94 -199 -264 -345 -365 – – – -384 -395 – – – – -472 -640 -685 -2,180 Surry County 0 -4 -34 -62 – – -188 – – – -224 -298 – – – – – -319 -348 -1,417 Sussex County 1 51 -10 – – – – – – – – – – – – – – -171 -208 -913 Virginia Beach, City of 0 -124 -163 -261 – -713 -837 – – – -989 -1,006 -1,081 -1,126 -1,278 -1,296 -1,348 -1,358 -1,440 -4,669 Westmoreland County 0 – – -40 – -65 -195 – – – -278 -414 – – – – – -490 -564 -2,600 Williamsburg, City of 1 22 -20 -34 – -157 -181 – – – -219 -294 – – – – – -327 -340 -1,424

York County 0 -63 -128 -209 – -622 -684 -749 -949 – – – – – – – – -1,437 -1,454 -2,551 aLocalities are those included in a previous study of the hydrogeologic framework by McFarland and Bruce (2006).
Distribution of Domestic Wells and Withdrawals among Aquifers 33

Table 7. Maximum elevations, in feet, of top of hydrogeologic units in Virginia Coastal Plain localities.[SURF, surficial aquifer; YTCZ, Yorktown confining zone; YEAQ, Yorktown-Eastover aquifer; SMCU, Saint Marys confining unit; SMAQ, Saint Marys aquifer; CACU, Calvert confining unit; PPAQ, Piney Point aquifer; CHCU, Chickahominy confining unit; XMCU, Exmore matrix confining unit; XCCU, Exmore clast confining unit; NMCU, Nanjemoy-Marlboro confining unit; AQAQ, Aquia aquifer; PDCU, Peedee confining unit; PDAQ, Peedee aquifer; VBCZ, Virginia Beach confining zone; VBAQ, Virginia Beach aquifer; UCCU, Upper Cenomanian confining unit; POCZ, Potomac confining zone; POAQ, Potomac aquifer; BSMT, basement; –, unit is not present over less than 50 percent of the locality area. Shading indicates locality in which well data were collected]

Locality (fig. 1a SURF YTCZ YEAQ SMCU SMAQ CACU PPAQ CHCU XMCU XCCU NMCU AQAQ PDCU PDAQ VBCZ VBAQ UCCU POCZ POAQ BSMT

Accomack County 64 -24 -49 -151 -243 -370 -540 -728 – – – – – – – – – -779 -909 -3,526Caroline County 315 – – – – 156 – – – – 129 90 – – – – – 42 16 197Charles City County 176 – – 90 – 74 35 – – – 30 -22 – – – – – -11 -19 -271Chesapeake, City of 41 3 -5 -99 – -279 -284 – – – -297 -335 -354 -361 -365 -366 -368 -480 -496 -1,835Chesterfield County 303 – – – – – – – – – – – – – – – – – – 160Colonial Heights, City of 149 – – – – – – – – – – – – – – – – – – 29Dinwiddie County 231 – – – – – – – – – – – – – – – – – – 139Essex County 250 – – 130 – 92 79 – – – 30 -57 – – – – – -151 -198 -1,099Franklin, City of 88 53 3 -22 – – -44 – – – -52 -62 – – – – -94 -161 -199 -783Fredricksburg, City of 253 – – – – – – – – – – – – – – – – 50 -34 -87Gloucester County 159 50 39 -24 – -103 -138 -283 -448 – – – – – – – – -319 -356 -1,374Greensville County 178 – – – – – – – – – – – – – – – – - - 50Hampton, City of 36 2 0 -123 – -327 -369 -420 -578 -640 – – – – – – – -633 -683 -1,859Hanover County 300 – – 135 – 92 – – – – 86 51 – – – – – 26 7 151Henrico County 321 – – 157 – 110 – – – – 90 – – – – – – 99 89 188Hopewell, City of 104 – – – – – – – – – 53 – – – – – – 18 0 -158Isle of Wight County 114 65 44 -8 – – -52 – – – -63 -76 – – – – – -154 -174 -824James City County 157 83 75 32 – -53 -59 – – – -108 -163 – – – – – -194 -207 -941King and Queen County 273 – – 130 – 65 37 – – – 31 -65 – – – – – -165 -202 -865King George County 232 – – – – 150 – – – – 92 75 – – – – – -5 -27 -523King William County 271 – – 125 – 73 34 – – – 64 -7 – – – – – -26 -69 -249Lancaster County 164 30 0 -21 – -90 -178 – – – -282 -387 – – – – – -443 -463 -1,960Mathews County 67 39 19 -124 – -245 -364 -410 -564 -578 – – – – – – – -671 -693 -2,038Middlesex County 152 50 25 1 – -69 -125 – – – -201 -290 – – – – – -369 -407 -1,562New Kent County 182 – – 104 – 61 47 – – – 38 -33 – – – – – -73 -98 -484Newport News, City of 86 38 25 -88 – -186 -211 -268 -345 – – – – – – – – -326 -338 -1,494Norfolk, City of 34 -10 -25 -135 – -413 -424 -546 -618 – – – – – – – – -626 -647 -2,125Northampton County 42 0 -69 -208 – -326 -860 -953 -1092 -1150 – – – – – – – – – -2,999Northumberland County 183 46 12 36 – -52 -168 – – – -239 -357 – – – – – -465 -523 -2,221Petersburg, City of 193 – 117 – – – – – – – – – – – – – – 93 52 78Poquoson, City of 24 -11 -15 -124 – -328 -396 -524 -709 -823 – – – – – – – -1,165 -1,250 -1,992Portsmouth, City of 32 0 -9 -124 – -337 -347 – – – -348 -380 – – – – -393 -492 -497 -1,905Prince George County 172 136 117 – – – – – – – 133 – – – – – – 101 100 9Richmond County 212 – – 101 – 43 -23 – – – -72 -180 – – – – – -313 -338 -1,662Richmond, City of 304 – – – – – – – – – – – – – – – – – – 180Southampton County 137 110 64 26 – – – – – – 26 12 – – – – – 50 16 21Spotsylvania County 322 – – – – – – – – – – – – – – – – 50 -5 75Stafford County 398 – – – – – – – – – – 118 – – – – – 71 58 74Suffolk, City of 100 62 29 -5 -72 -85 -48 – – – -54 -65 – – – – -149 -224 -260 -862Surry County 175 103 73 47 – – -47 – – – 22 12 – – – – – 4 -54 -393Sussex County 231 116 107 – – – – – – – – – – – – – – 75 53 44Virginia Beach, City of 80 -20 -35 -138 – -509 -510 – – – -549 -591 -673 -731 -599 -606 -627 -749 -758 -2,507Westmoreland County 212 – – 112 – 79 45 – – – 4 -134 – – – – – -243 -291 -1,431Williamsburg, City of 106 75 64 -16 – -120 -137 – – – -175 -249 – – – – – -282 -286 -1,294York County 123 77 59 -15 – -113 -125 -280 -363 – – – – – – – – -277 -299 -1,301 aLocalities are those included in a previous study of the hydrogeologic framework by McFarland and Bruce (2006).
34 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain Table 8. Mean elevations, in feet, of top of hydrogeologic units in Virginia Coastal Plain localities. [SURF, surficial aquifer; YTCZ, Yorktown confining zone; YEAQ, Yorktown-Eastover aquifer; SMCU, Saint Marys confining unit; SMAQ, Saint Marys aquifer; CACU, Calvert confining unit; PPAQ, Piney Point aquifer; CHCU, Chickahominy confining unit; XMCU, Exmore matrix confining unit; XCCU, Exmore clast confining unit; NMCU, Nanjemoy-Marlboro confining unit; AQAQ, Aquia aquifer; PDCU, Peedee confining unit; PDAQ, Peedee aquifer; VBCZ, Virginia Beach confining zone; VBAQ, Virginia Beach aquifer; UCCU, Upper Cenomanian confining unit; POCZ, Potomac confining zone; POAQ, Potomac aquifer; BSMT, basement; –, unit is not present over less than 50 percent of the locality area. Shading indicates locality in which well data were collected] Locality (fig. 1)a SURF YTCZ YEAQ SMCU SMAQ CACU PPAQ CHCU XMCU XCCU NMCU AQAQ PDCU PDAQ VBCZ VBAQ UCCU POCZ POAQ BSMT Accomack County 15 -71 -99 -349 -528 -706 -893 -993 – – – – – – – – – -1,210 -1,324 -5,165 Caroline County 164 – – – – 98 – – – – 70 16 – – – – – -41 -92 -440 Charles City County 64 – – 13 – 8 -23 – – – -56 -108 – – – – – -139 -158 -670 Chesapeake, City of 13 -19 -34 -133 – -433 -443 – – – -462 -487 -550 -616 -602 -619 -631 -783 -798 -2,533 Chesterfield County 125 – – – – – – – – – – – – – – – – – – -13 Colonial Heights, City of 61 – – – – – – – – – – – – – – – – – – 3 Dinwiddie County 145 – – – – – – – – – – – – – – – – – – 44 Essex County 99 – – 72 – 14 -40 – – – -91 -186 – – – – – -292 -315 -1,513 Franklin, City of 39 18 -4 -35 – – -50 – – – -59 -76 – – – – -114 -189 -217 -821 Fredricksburg, City of 114 – – – – – – – – – – – – – – – – 38 -50 -144 Gloucester County 48 22 0 -97 – -214 -280 -380 -610 – – – – – – – – -625 -656 -1,774 Greensville County 89 – – – – – – – – – – – – – – – – – – -39 Hampton, City of 9 -24 -44 -162 – -407 -464 -617 -801 -874 – – – – – – – -1,282 -1,317 -2,074 Hanover County 144 – – 98 – 66 – – – – 35 -33 – – – – – -51 -70 -201 Henrico County 127 – – 100 – 76 – – – – 41 – – – – – – -5 -17 -185 Hopewell, City of 43 – – – – – – – – – 31 – – – – – – 6 -7 -224 Isle of Wight County 55 31 -13 -67 – – -146 – – – -163 -205 – – – – – -253 -272 -1,157 James City County 58 50 17 -33 – -103 -115 – – – -169 -230 – – – – – -265 -286 -1,235 King and Queen County 109 – – 18 – -33 -72 – – – -133 -216 – – – – – -284 -326 -1,345 King George County 87 – – – – 71 – – – – 20 -51 – – – – – -135 -186 -1,202 King William County 96 – – 53 – 17 -26 – – – -55 -124 – – – – – -173 -221 -907 Lancaster County 57 2 -30 -53 – -153 -266 – – – -358 -488 – – – – – -516 -531 -2,260 Mathews County 10 -22 -43 -152 – -292 -448 -555 -755 -837 – – – – – – – -1,235 -1,267 -2,294 Middlesex County 61 23 -4 -52 – -139 -227 – – – -267 -378 – – – – – -467 -484 -1,873 New Kent County 76 – – 15 – -11 -30 – – – -88 -149 – – – – – -186 -210 -939 Newport News, City of 24 -23 -54 -140 – -261 -305 -357 -533 – – – – – – – – -483 -514 -1,718 Norfolk, City of 9 -43 -79 -189 – -502 -546 -685 -821 – – – – – – – – -867 -894 -2,368 Northampton County 15 -62 -99 -282 – -577 -957 -1,070 -1,258 -1,303 – – – – – – – – – -4,322 Northumberland County 58 18 -12 -26 – -131 -268 – – – -361 -495 – – – – – -538 -577 -2,572 Petersburg, City of 125 – 108 – – – – – – – – – – – – – – 60 25 1 Poquoson, City of 5 -23 -46 -139 – -391 -460 -623 -827 -957 – – – – – – – -1,505 -1,528 -2,126 Portsmouth, City of 9 -20 -45 -152 – -383 -400 – – – -424 -439 – – – – -463 -583 -601 -2,113 Prince George County 96 107 82 – – – – – – – 24 – – – – – – -10 -33 -274 Richmond County 90 – – 23 – -34 -135 – – – -209 -311 – – – – – -407 -449 -1,976 Richmond, City of 159 – – – – – – – – – – – – – – – – – – 64 Southampton County 65 60 25 -2 – – – – – – -32 -45 – – – – – -65 -92 -529 Spotsylvania County 186 – – – – – – – – – – – – – – – – 35 -30 -128 Stafford County 143 – – – – – – – – – – 77 – – – – – 24 -3 -273 Suffolk, City of 44 17 -17 -80 -163 -208 -194 – – – -215 -243 – – – – -303 -409 -435 -1,499 Surry County 83 71 41 3 – – -92 – – – -88 -135 – – – – – -181 -211 -879 Sussex County 98 87 58 – – – – – – – – – – – – – – 1 -24 -294 Virginia Beach, City of 7 -41 -69 -198 – -646 -709 – – – -756 -776 -853 -900 -917 -931 -972 -1,078 -1,110 -3,467 Westmoreland County 75 – – 46 – -7 -88 – – – -138 -269 – – – – – -376 -422 -2,007 Williamsburg, City of 66 66 35 -19 – -142 -157 – – – -199 -272 – – – – – -304 -311 -1,361

York County 37 13 -8 -104 – -233 -284 -415 -596 – – – – – – – – -578 -613 -1,699

aLocalities are those included in a previous study of the hydrogeologic framework by McFarland and Bruce (2006).
Distribution of Domestic Wells and Withdrawals among Aquifers 35

Table 9. Proportions of Virginia Coastal Plain localities occupied by each hydrogeologic unit. [SURF, surficial aquifer; YTCZ, Yorktown confining zone; YEAQ, Yorktown-Eastover aquifer; SMCU, Saint Marys confining unit; SMAQ, Saint Marys aquifer; CACU,Calvert confining unit; PPAQ, Piney Point aquifer; CHCU, Chickahominy confining unit; XMCU, Exmore matrix confining unit; XCCU, Exmore clast confining unit; NMCU,Nanjemoy-Marlboro confining unit; AQAQ, Aquia aquifer; PDCU, Peedee confining unit; PDAQ, Peedee aquifer; VBCZ, Virginia Beach confining zone; VBAQ, Virginia Beach aquifer; UCCU, Upper Cenomanian confining unit; POCZ, Potomac confining zone; POAQ, Potomac aquifer; BSMT, basement; –, unit is not present over less than 50 percent of the locality area. Shading indicates locality in which well data were collected]

Locality (fig. 1)a SURF YTCZ YEAQ SMCU SMAQ CACU PPAQ CHCU XMCU XCCU NMCU AQAQ PDCU PDAQ VBCZ VBAQ UCCU POCZ POAQ BSMT

Accomack County 1.00 0.95 1.00 1.00 1.00 1.00 0.92 0.90 0.16 0.14 0.10 0.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Caroline County 1.00 0.00 0.00 0.48 0.00 0.73 0.12 0.00 0.00 0.00 0.87 0.88 0.00 0.00 0.00 0.00 0.00 0.87 0.87 1.00Charles City County 1.00 0.13 0.18 0.89 0.00 0.58 0.78 0.00 0.00 0.00 0.99 0.94 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Chesapeake, City of 1.00 0.98 1.00 1.00 0.00 1.00 1.00 0.00 0.00 0.00 1.00 1.00 0.51 0.51 0.93 0.93 1.00 1.00 1.00 1.00Chesterfield County 1.00 0.00 0.00 0.15 0.00 0.00 0.00 0.00 0.00 0.00 0.20 0.00 0.00 0.00 0.00 0.00 0.00 0.21 0.26 1.00Colonial Heights, City of 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.15 0.24 1.00Dinwiddie County 1.00 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.42 0.46 1.00Essex County 1.00 0.00 0.00 0.76 0.00 0.94 0.98 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Franklin, City of 1.00 0.80 0.99 1.00 0.00 0.00 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.02 0.02 1.00 1.00 1.00 1.00Fredricksburg, City of 1.00 0.00 0.00 0.00 0.00 0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.92 0.92 1.00Gloucester County 1.00 0.77 1.00 1.00 0.00 1.00 1.00 0.59 0.53 0.47 0.41 0.41 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Greensville County 1.00 0.24 0.25 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.22 0.22 1.00Hampton, City of 1.00 0.82 1.00 1.00 0.00 1.00 1.00 1.00 1.00 0.97 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Hanover County 1.00 0.00 0.00 0.50 0.00 0.57 0.15 0.00 0.00 0.00 0.61 0.60 0.00 0.00 0.00 0.00 0.00 0.67 0.67 1.00Henrico County 1.00 0.00 0.00 0.51 0.00 0.56 0.15 0.00 0.00 0.00 0.60 0.46 0.00 0.00 0.00 0.00 0.00 0.74 0.77 1.00Hopewell, City of 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.73 0.00 0.00 0.00 0.00 0.00 0.00 0.80 1.00 1.00Isle of Wight County 1.00 0.86 1.00 1.00 0.17 0.33 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.01 0.01 0.31 1.00 1.00 1.00James City County 1.00 0.67 0.98 1.00 0.00 1.00 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00King and Queen County 1.00 0.31 0.34 0.97 0.00 1.00 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00King George County 1.00 0.00 0.00 0.00 0.00 0.73 0.27 0.00 0.00 0.00 0.96 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00King William County 1.00 0.06 0.10 0.87 0.00 0.95 0.79 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Lancaster County 1.00 0.99 1.00 1.00 0.00 1.00 1.00 0.07 0.01 0.00 0.93 0.93 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Mathews County 1.00 0.81 1.00 1.00 0.00 1.00 1.00 1.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Middlesex County 1.00 0.75 0.91 1.00 0.00 1.00 1.00 0.25 0.18 0.18 0.75 0.75 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00New Kent County 1.00 0.21 0.29 0.89 0.00 0.97 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Newport News, City of 1.00 0.89 1.00 1.00 0.00 1.00 1.00 0.82 0.51 0.15 0.18 0.18 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Norfolk, City of 1.00 1.00 1.00 1.00 0.00 1.00 1.00 0.65 0.60 0.14 0.35 0.35 0.00 0.00 0.01 0.01 0.35 1.00 1.00 1.00Northampton County 1.00 0.94 1.00 1.00 0.50 1.00 1.00 1.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.46 0.46 1.00Northumberland County 1.00 0.52 0.66 1.00 0.00 1.00 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Petersburg, City of 1.00 0.47 0.56 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.30 0.00 0.00 0.00 0.00 0.00 0.00 0.63 0.63 1.00Poquoson, City of 1.00 0.78 1.00 1.00 0.00 1.00 1.00 1.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Portsmouth, City of 1.00 0.90 1.00 1.00 0.00 1.00 1.00 0.01 0.00 0.00 0.99 0.99 0.00 0.00 0.06 0.06 0.98 1.00 1.00 1.00Prince George County 1.00 0.59 0.70 0.41 0.00 0.00 0.00 0.00 0.00 0.00 0.90 0.44 0.00 0.00 0.00 0.00 0.00 0.99 1.00 1.00Richmond County 1.00 0.05 0.05 0.85 0.00 1.00 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Richmond, City of 1.00 0.00 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.08 0.09 1.00Southampton County 1.00 0.69 0.89 0.73 0.00 0.00 0.21 0.00 0.00 0.00 0.73 0.73 0.00 0.00 0.18 0.18 0.19 0.99 0.99 1.00Spotsylvania County 1.00 0.00 0.00 0.00 0.00 0.33 0.00 0.00 0.00 0.00 0.35 0.35 0.00 0.00 0.00 0.00 0.00 0.76 0.76 1.00Stafford County 1.00 0.00 0.00 0.00 0.00 0.21 0.00 0.00 0.00 0.00 0.43 0.56 0.00 0.00 0.00 0.00 0.00 0.73 0.76 1.00Suffolk, City of 1.00 0.91 1.00 1.00 0.53 0.84 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.50 0.50 1.00 1.00 1.00 1.00Surry County 1.00 0.85 0.96 1.00 0.00 0.02 0.70 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Sussex County 1.00 0.84 0.91 0.38 0.00 0.00 0.04 0.00 0.00 0.00 0.47 0.40 0.00 0.00 0.00 0.00 0.00 0.97 0.97 1.00Virginia Beach, City of 1.00 1.00 1.00 1.00 0.00 1.00 1.00 0.12 0.11 0.04 0.88 0.88 0.55 0.55 0.86 0.86 0.88 1.00 1.00 1.00Westmoreland County 1.00 0.00 0.00 0.76 0.00 0.92 0.99 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00Williamsburg, City of 1.00 0.78 0.99 1.00 0.00 1.00 1.00 0.00 0.00 0.00 1.00 1.00 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00York County 1.00 0.73 1.00 1.00 0.00 1.00 1.00 0.64 0.62 0.33 0.36 0.36 0.00 0.00 0.00 0.00 0.00 1.00 1.00 1.00

aLocalities are those included in a previous study of the hydrogeologic framework by McFarland and Bruce (2006).
36 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Once the aquifer designations were assigned for each of 

the wells, these designations were summarized by locality. The 

number of wells assigned to each aquifer within each locality 

is listed in table 10, along with the number and proportion of 

wells assigned to each aquifer for the entire Virginia Coastal 

Plain. The proportion of wells assigned to each aquifer within 

each locality is listed in table 11, along with the proportions 

for the entire Virginia Coastal Plain. 

Nine different Coastal Plain aquifers and confining units 

were intersected by wells in this analysis: the Potomac aquifer 

(POAQ), the Potomac Confining Zone (POCZ), the Virginia 

Beach aquifer (VBAQ), the Aquia aquifer (AQAQ), the Piney 

Point aquifer (PPAQ), the Saint Marys aquifer (SMAQ), the 

Yorktown-Eastover aquifer (YEAQ), the Yorktown confining 

zone (YTCZ), and the surficial aquifer (SURF). In addition, 

some wells in localities near the Fall Line intersect the bedrock basement immediately beneath Coastal Plain sediments. 

These wells were included because they intersect fractured 

bedrock directly beneath the Potomac aquifer sediments 

and may effectively withdraw water from the Coastal Plain 

aquifer system.

By using a published per-capita withdrawal coefficient 

of 75 gal/d for private domestic users in Virginia (Hutson and 

others, 2004), the mean daily self-supplied domestic withdrawal rate was calculated for each of the aquifers for each 

locality. The results of these calculations are listed in table 12, 

and the withdrawal totals for each locality correspond to the 

withdrawal totals for the “domestic” column in table 2.

In aggregate, the results for all the localities for which 

data were collected (tables 10, 11) reveal that 21.7 percent of 

the domestic wells and withdrawals in the Virginia Coastal 

Plain are associated with the unconfined surficial aquifer, 

32.9 percent are associated either with the Yorktown-Eastover 

aquifer or the Yorktown confining zone, 8.3 percent are associated with the Piney Point aquifer, 11.3 percent are associated 

with the Aquia aquifer, and 25.1 percent are associated 

either with the Potomac aquifer or the Potomac confining 

zone. Three wells intersect the Saint Marys aquifer, and five 

wells intersect the Virginia Beach aquifer, which results in a 

very small portion of withdrawals associated with these two 

aquifers (tables 10, 11, 12). In addition, 14 wells in localities 

near the Fall Line intersect the bedrock, which indicates that 

bedrock wells are a small source of water in areas where the 

Coastal Plain aquifer system is very thin (tables 10, 11, 12). 

These results question the previously held assumption 

by some water-resources experts that private domestic 

withdrawals are unimportant to regional ground-water flow 

because they are taken from the unconfined aquifer and 

quickly replaced by return flow through home septic systems. 

This new information about domestic wells indicates that 

withdrawals from several confined aquifers of the Virginia 

Coastal Plain actually make up 78 percent of the estimated 

self-supplied domestic total. This represents about 24 Mgal/d 

for the localities sampled, or about 30 Mgal/d for all Virginia 

Coastal Plain localities. This is water that is effectively 

removed permanently from the confined system, though it may 

recharge the surficial aquifer through septic-tank discharge or 

flow into streams and rivers. The magnitude of these estimated 

withdrawals from the confined aquifers indicates that selfsupplied domestic withdrawals of ground-water may have a 

much more important role in the regional ground-water flow 

system than previously believed.

Ongoing ground-water modeling investigations in this 

region may provide additional information about the relative 

influence of these withdrawals. In fact, ground-water model 

simulations indicate that domestic withdrawals have a less 

pronounced effect on the hydrogeologic system than large, 

centralized municipal and industrial withdrawals of similar 

magnitude, because the domestic withdrawals are more 

evenly distributed in time and space. The more numerous and 

spatially distributed domestic wells individually pump less 

water, so the relatively diffuse withdrawals from these wells 

do not appear to cause well-defined cones of depression in 

the Coastal Plain aquifers, and they have not lowered regional 

ground-water levels or altered ground-water flow rates as 

substantially as the larger industrial and municipal withdrawals (C.E. Heywood, U.S. Geological Survey, written 

commun., 2007).

Considerable local variation is apparent in the association of wells and withdrawals to aquifers. Consequently, the 

results from assigning wells to aquifers by locality can best 

be considered in terms of groups of spatially related localities. 

Because of the spatial correlation of hydrogeologic conditions, 

it is not surprising to find that adjacent localities yield similar 

results in this type of analysis. Some of this correlation can 

be visually noted in the similar appearance of the well-screen 

elevation histograms (figs. 10A–E) and more analytically from 

similar proportions in table 11.

For example, results were similar for Lancaster and 

Northumberland Counties in adjacent locations on the end 

of the Northern Neck Peninsula. In Northumberland County, 

41.8 percent of the withdrawals were determined to be from 

the Potomac aquifer, while the percentage of wells in this 

aquifer in Lancaster County was 38.1. The proportions for the 

Aquia aquifer and the Piney Point aquifer also were similar, 

with some differences between the proportions in the shallower system, which actually could be the result of increased 

error where the units are closer together. The results in the 

Northern Neck counties of Richmond and Westmoreland 

also are similar, probably because of similar hydrogeologic 

conditions in these two adjacent localities. The similarities 

and differences between these two counties and Lancaster and 

Northumberland to the east also are notable. 

Moving south to the Middle Peninsula of Virginia, the 

similarities between well proportions by aquifer are notable 

for Essex and Middlesex Counties. The largest difference in 

the well-screen distribution is the generally shallower characteristic of the distribution in Essex County, which is up-dip of 

Middlesex County; thus, the available aquifers are located at 

higher elevations. The distribution among aquifers in Essex 
Distribution of Domestic Wells and Withdrawals among Aquifers 37

Table 10. Number of sampled domestic wells assigned to each aquifer in the Virginia Coastal Plain localities for 

which data were collected.

[SURF, surficial aquifer; YTCZ, Yorktown confining zone; YEAQ, Yorktown-Eastover aquifer; SMAQ, Saint Marys aquifer; PPAQ, 

Piney Point aquifer; AQAQ, Aquia aquifer; VBAQ, Virginia Beach aquifer; POCZ, Potomac confining zone; POAQ, Potomac aquifer; 

BSMT, basement]

Locality

(fig. 1)

Sample

number SURF YTCZ YEAQ SMAQ PPAQ AQAQ VBAQ POCZ POAQ BSMT

Accomack County 96 0 0 96 0 0 0 0 0 0 0

Caroline County 122 92 0 0 0 0 4 0 7 18 1

Charles City County 81 53 0 0 0 2 10 0 1 15 0

Chesapeake, City of 103 7 10 85 0 0 1 0 0 0 0

Essex County 95 37 0 0 0 10 32 0 3 13 0

Gloucester County 96 0 7 83 0 6 0 0 0 0 0

Greensville County 51 41 0 0 0 0 0 0 0 0 13

Hanover County 110 47 0 0 0 0 8 0 4 51 0

Henrico County 90 59 0 0 0 0 1 0 0 30 0

Isle of Wight County 123 7 23 2 0 1 9 0 2 79 0

James City County 72 0 1 7 0 20 34 0 0 10 0

King and Queen County 109 33 4 0 0 33 28 0 1 10 0

King George County 101 13 0 0 0 0 13 0 5 70 0

King William County 107 48 0 0 0 3 25 0 2 29 0

Lancaster County 97 20 3 2 0 23 12 0 0 37 0

Mathews County 106 2 1 103 0 0 0 0 0 0 0

Middlesex County 102 8 21 38 0 13 11 0 0 11 0

New Kent County 98 15 0 0 0 19 41 0 1 22 0

Northampton County 115 14 0 101 0 0 0 0 0 0 0

Northumberland County 110 6 10 1 0 37 8 0 2 46 0

Prince George County 102 0 1 71 0 0 0 0 8 22 0

Richmond County 93 18 0 0 0 45 29 0 0 1 0

Southampton County 123 24 1 4 0 0 3 0 11 80 0

Suffolk, City of 101 9 22 3 3 0 2 5 24 33 0

Surry County 107 0 28 37 0 0 5 0 8 29 0

Sussex County 86 0 38 30 0 0 0 0 1 17 0

Virginia Beach, City of 96 23 14 59 0 0 0 0 0 0 0

Westmoreland County 113 42 0 0 0 15 45 0 2 9 0

York County 38 0 0 28 0 10 0 0 0 0 0

Total number of wells 2,846 618 184 750 3 237 321 5 82 632 14
38 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Table 11. Estimated proportions of sampled domestic wells assigned to each aquifer in the Virginia Coastal 

Plain localities for which data were collected.

[SURF, surficial aquifer; YTCZ, Yorktown confining zone; YEAQ, Yorktown-Eastover aquifer; SMAQ, Saint Marys aquifer; PPAQ, 

Piney Point aquifer; AQAQ, Aquia aquifer; VBAQ, Virginia Beach aquifer; POCZ, Potomac confining zone; POAQ, Potomac aquifer; BSMT, basement. Sum of proportions for some localities may not equal 1.000 because of rounding]

Locality

(fig. 1)

Sample

number SURF YTCZ YEAQ SMAQ PPAQ AQAQ VBAQ POCZ POAQ BSMT

Accomack County 96 0.000 0.000 1.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Caroline County 122 0.754 0.000 0.000 0.000 0.000 0.033 0.000 0.057 0.148 0.008

Charles City County 81 0.654 0.000 0.000 0.000 0.025 0.123 0.000 0.012 0.185 0.000

Chesapeake, City of 103 0.068 0.097 0.825 0.000 0.000 0.010 0.000 0.000 0.000 0.000

Essex County 95 0.389 0.000 0.000 0.000 0.105 0.337 0.000 0.032 0.137 0.000

Gloucester County 96 0.000 0.073 0.865 0.000 0.063 0.000 0.000 0.000 0.000 0.000

Greensville County 51 0.759 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.241

Hanover County 110 0.427 0.000 0.000 0.000 0.000 0.073 0.000 0.036 0.464 0.000

Henrico County 90 0.656 0.000 0.000 0.000 0.000 0.011 0.000 0.000 0.333 0.000

Isle of Wight County 123 0.057 0.187 0.016 0.000 0.008 0.073 0.000 0.016 0.642 0.000

James City County 72 0.000 0.014 0.097 0.000 0.278 0.472 0.000 0.000 0.139 0.000

King and Queen County 109 0.303 0.037 0.000 0.000 0.303 0.257 0.000 0.009 0.092 0.000

King George County 101 0.129 0.000 0.000 0.000 0.000 0.129 0.000 0.050 0.693 0.000

King William County 107 0.449 0.000 0.000 0.000 0.028 0.234 0.000 0.019 0.271 0.000

Lancaster County 97 0.206 0.031 0.021 0.000 0.237 0.124 0.000 0.000 0.381 0.000

Mathews County 106 0.019 0.009 0.972 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Middlesex County 102 0.078 0.206 0.373 0.000 0.127 0.108 0.000 0.000 0.108 0.000

New Kent County 98 0.153 0.000 0.000 0.000 0.194 0.418 0.000 0.010 0.224 0.000

Northampton County 115 0.122 0.000 0.878 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Northumberland County 110 0.055 0.091 0.009 0.000 0.336 0.073 0.000 0.018 0.418 0.000

Prince George County 102 0.000 0.010 0.696 0.000 0.000 0.000 0.000 0.078 0.216 0.000

Richmond County 93 0.194 0.000 0.000 0.000 0.484 0.312 0.000 0.000 0.011 0.000

Southampton County 123 0.195 0.008 0.033 0.000 0.000 0.024 0.000 0.089 0.650 0.000

Suffolk, City of 101 0.089 0.218 0.030 0.030 0.000 0.020 0.050 0.238 0.327 0.000

Surry County 107 0.000 0.262 0.346 0.000 0.000 0.047 0.000 0.075 0.271 0.000

Sussex County 86 0.000 0.442 0.349 0.000 0.000 0.000 0.000 0.012 0.198 0.000

Virginia Beach, City of 96 0.240 0.146 0.615 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Westmoreland County 113 0.372 0.000 0.000 0.000 0.133 0.398 0.000 0.018 0.080 0.000

York County 38 0.000 0.000 0.737 0.000 0.263 0.000 0.000 0.000 0.000 0.000

All localities 0.217 0.065 0.264 0.001 0.083 0.113 0.002 0.029 0.222 0.005
Distribution of Domestic Wells and Withdrawals among Aquifers 39

Table 12. Estimated self-supplied domestic withdrawals in 2000 by aquifer in Virginia Coastal Plain localities for 

which data were collected.

[SURF, surficial aquifer; YTCZ, Yorktown confining zone; YEAQ, Yorktown-Eastover aquifer; SMAQ, Saint Marys aquifer; PPAQ, 

Piney Point aquifer; AQAQ, Aquia aquifer; VBAQ, Virginia Beach aquifer; POCZ, Potomac confining zone; POAQ, Potomac aquifer; 

BSMT, basement; Mgal/d, million gallons per day. Units of estimated withdrawal values are million gallons per day]

Locality

(fig. 1) SURF YTCZ YEAQ SMAQ PPAQ AQAQ VBAQ POCZ POAQ BSMT Total (Mgal/d)

Accomack County 0.00 0.00 1.42 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.42

Caroline County 0.75 0.00 0.00 0.00 0.00 0.03 0.00 0.06 0.15 0.01 1.00

Charles City County 0.30 0.00 0.00 0.00 0.01 0.06 0.00 0.01 0.09 0.00 0.46

Chesapeake, City of 0.18 0.26 2.18 0.00 0.00 0.03 0.00 0.00 0.00 0.00 2.64

Essex County 0.20 0.00 0.00 0.00 0.05 0.17 0.00 0.02 0.07 0.00 0.51

Gloucester County 0.00 0.14 1.62 0.00 0.12 0.00 0.00 0.00 0.00 0.00 1.87

Greensville County 0.48 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.15 0.63

Hanover County 0.81 0.00 0.00 0.00 0.00 0.14 0.00 0.07 0.87 0.00 1.88

Henrico County 1.54 0.00 0.00 0.00 0.00 0.03 0.00 0.00 0.78 0.00 2.35

Isle of Wight County 0.06 0.20 0.02 0.00 0.01 0.08 0.00 0.02 0.67 0.00 1.05

James City County 0.00 0.02 0.13 0.00 0.37 0.63 0.00 0.00 0.18 0.00 1.33

King and Queen County 0.14 0.02 0.00 0.00 0.14 0.12 0.00 0.00 0.04 0.00 0.47

King George County 0.03 0.00 0.00 0.00 0.00 0.03 0.00 0.01 0.16 0.00 0.23

King William County 0.31 0.00 0.00 0.00 0.02 0.16 0.00 0.01 0.19 0.00 0.69

Lancaster County 0.08 0.01 0.01 0.00 0.10 0.05 0.00 0.00 0.16 0.00 0.41

Mathews County 0.01 0.01 0.63 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.65

Middlesex County 0.04 0.12 0.21 0.00 0.07 0.06 0.00 0.00 0.06 0.00 0.56

New Kent County 0.11 0.00 0.00 0.00 0.14 0.30 0.00 0.01 0.16 0.00 0.71

Northampton County 0.08 0.00 0.56 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.64

Northumberland County 0.03 0.05 0.01 0.00 0.19 0.04 0.00 0.01 0.24 0.00 0.57

Prince George County 0.00 0.01 0.71 0.00 0.00 0.00 0.00 0.08 0.22 0.00 1.02

Richmond County 0.08 0.00 0.00 0.00 0.20 0.13 0.00 0.00 0.00 0.00 0.42

Southampton County 0.12 0.00 0.02 0.00 0.00 0.01 0.00 0.05 0.40 0.00 0.61

Suffolk, City of 0.11 0.27 0.04 0.04 0.00 0.02 0.06 0.29 0.40 0.00 1.22

Surry County 0.00 0.10 0.13 0.00 0.00 0.02 0.00 0.03 0.10 0.00 0.38

Sussex County 0.00 0.05 0.04 0.00 0.00 0.00 0.00 0.00 0.02 0.00 0.11

Virginia Beach, City of 0.74 0.45 1.91 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.10

Westmoreland County 0.20 0.00 0.00 0.00 0.07 0.21 0.00 0.01 0.04 0.00 0.53

York County 0.00 0.00 2.48 0.00 0.89 0.00 0.00 0.00 0.00 0.00 3.37

Total 6.41 1.69 12.10 0.04 2.38 2.32 0.06 0.67 5.01 0.16 30.84
40 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

County is also very similar to that in King and Queen County, 

which lies directly to the south and almost along the strike of 

the hydrogeologic units.

In the similar well distributions in Gloucester and 

Mathews Counties, the lack of deep withdrawals is a result 

of the presence of the buried Chesapeake Bay impact crater, 

which is now known to be the source of brackish ground-water 

found at depth (McFarland and Bruce, 2005). The small 

numbers of deeper wells in Gloucester probably are located in 

the western part of the county and outside of the saline zone.

Farther south on the York-James Peninsula, the differences between the well distributions by aquifer in York and 

James City Counties may be the result of their somewhat 

different hydrogeologic settings despite their close proximity, 

because York County partly overlies the buried impact crater. 

New Kent, King and Queen, and King William Counties all 

have somewhat similar well distributions that are likely the 

result of their close proximity to each other. The causes of 

apparent small differences in the well distributions are unclear. 

Charles City County would be expected to be similar 

to New Kent because of their close proximity and almost 

identical hydrogeologic setting, but the Charles City well 

distribution is characterized by much shallower well depths. A 

review of the well records reveals that all of the shallow wells 

in Charles City County are bored wells, although almost every 

record sampled in New Kent County is for a drilled well; this 

may indicate that the differences are related to the preferences 

of the local well driller(s), but perhaps other local conditions 

have influenced the distribution. 

Moving south again, the similarities between the well 

distributions in Surry and Isle of Wight Counties are very 

likely the result of their similar hydrogeologic setting. The 

difference between these two counties is that Isle of Wight 

is located farther south and east, where the Potomac aquifer 

becomes thicker and more productive. Therefore, Isle of 

Wight has a much higher proportion of wells in the Potomac 

aquifer. Isle of Wight County is very similar in its distribution 

of withdrawals by aquifer to the City of Suffolk immediately 

to its south, especially if the Potomac aquifer and Potomac 

confining zone are considered together. The only difference 

is caused by the local presence of the deeper Virginia Beach 

aquifer in Suffolk. The wells and withdrawals in Caroline, 

Henrico, and Hanover Counties all appear to be split between 

the unconfined surficial aquifer and the Potomac aquifer, and 

the Fall Line is close enough that intervening units are thin or 

nonexistent.

Greensville, Prince George, Sussex, and Southampton 

Counties in the southwestern section of the Virginia Coastal 

Plain can be grouped together based on their similar well and 

aquifer distributions. These counties have wells completed 

primarily in the shallow surficial aquifer, the Yorktown units, 

or the Potomac aquifer. The well distribution in Southampton 

differs somewhat from the others, possibly because its more 

eastern location makes the thicker Potomac aquifer more 

attractive to well drillers.

On the Eastern Shore, it was not surprising to find 

similar distributions of wells and aquifers in Accomack 

and Northampton Counties. The only real difference is that 

Northampton County has a few wells in the unconfined system 

in addition to the Yorktown-Eastover aquifer that is the only 

confined aquifer containing freshwater on the peninsula. In 

recent years, the installation of domestic wells in the surficial 

aquifer has been uncommon on the Eastern Shore because of 

concerns about both agricultural contamination and the effects 

of drought.

This discussion has focused primarily on hydrogeologic 

factors that have influenced well depth and aquifer distribution 

for domestic wells and withdrawals, but many other factors 

likely influence the distributions. Local well characteristics 

also appear to be correlated with variations in family income 

and household value, available local well drillers and their 

preferences, and a variety of water-quality issues that are 

beyond the scope of this report.

Assumptions and Limitations Related to 

Assigning Domestic Wells and Withdrawals 

to Aquifers

The overarching assumption for this analysis was that 

variability in land-surface and aquifer elevations within a 

locality are smaller than the vertical difference between 

aquifer units intersected by private domestic wells. If this were 

completely true, a frequency analysis of collected well depths 

(or elevations) for each locality would have a multimodal 

distribution with the number of groupings equal to the number 

of aquifers and with distinct divisions between the aquifer 

groups. Examination of the histograms in figure 10 reveals 

that this is not usually the case. The cumulative uncertainty 

associated with the estimation techniques used in the analysis 

of the available data is large enough to cause overlap among 

the well groupings and complicate the determination of 

the aquifer associated with each well. This problem could 

largely be resolved with the addition of accurate well-location 

data or accurate well-elevation data or both. Even with the 

limited available data, however, the approximate validity of 

the assumptions allows a reasonable determination of well 

proportions by aquifer for most localities.

The assumptions are most valid and the analyses are more 

robust for localities in which aquifer units typically intersected 

by domestic wells are thicker and farther apart and variations 

in land-surface elevation are small. Thus, the relative validity 

of the assumptions for each locality can be used to evaluate 

the confidence in assigning wells to aquifers. Because of the 

approximation used to assign the well-screen elevation from 

the median elevation for a particular locality, that estimation 

is more valid where the locality elevation is less variable. 

Furthermore, the process of comparing screen elevations to 

hydrogeologic-unit elevations is more valid where the units are 

less variable and the vertical distance between them is greater. 

In the Virginia Coastal plain, these ideal conditions generally 
Spatial Distribution of Self-Supplied Domestic Withdrawals for a Ground-Water Model of the Virginia Eastern Shore 41

are more likely to be present in the eastern localities than in 

other areas.

In the eastern localities, such as Northumberland County, 

the groupings of well-screen elevations correspond nicely to 

aquifer elevations. In Northumberland County, the median 

land-surface elevation is 63 ft (table 5), the range of surface 

elevations is 183 ft between the smallest and largest values 

(tables 6, 7), the mean is 58 ft (table 8), and the standard 

deviation is 41 ft. This means that most elevations in the 

county are between 20 ft and 100 ft. The difference between 

the median elevations of the aquifers of interest is well over 

100 ft in most cases. Furthermore, the range of elevations 

across the county for a given aquifer, such as the Potomac, 

is relatively small. Consequently, regardless of the actual 

land-surface elevation, a deep well drilled into the Potomac 

aquifer usually will be classified into the Potomac aquifer in 

this analysis. 

In Hanover County, however, the variability in the 

land-surface elevation is much larger, with a range of 299 ft 

between the smallest and largest values (tables 6, 7), although 

the range of well elevations is smaller. Nonetheless, the vertical separation between the two units used for water supply, the 

surficial and Potomac aquifers, is large enough to distinguish 

the wells in each unit. 

The analyses are less robust in some of the central 

Coastal Plain localities, such as King and Queen County, 

where a number of aquifers are used for water supply, but 

the vertical separation between the unit tops is small and the 

land-surface elevation is quite variable. Clearly, a much larger 

level of uncertainty is associated with the assignment of wells 

to aquifers in King and Queen County than in Northumberland 

County, for example. One consideration in the assignment of 

wells and withdrawals to closely spaced aquifers in localities 

like King and Queen County is that errors and uncertainties in 

the closely spaced assignments may balance out.

One way in which localities can be compared is by using 

maximum and minimum elevation values to identify the total 

possible variation in land surface or aquifer-unit elevation 

within each locality. This can be readily done with tables 6 

and 7, but this approach overstates the variation because 

the maximum and minimum values are sensitive to outliers. 

Perhaps a better evaluation of the assumptions might make 

use of the frequency distribution of land-surface and aquifer 

elevations for individual localities. The mean or median value 

for each surface could be examined along with an error bound 

based on the variability of each surface. This approach was 

not taken for this report, but it may be useful in more detailed 

evaluations of domestic wells within some localities.

Despite the inherent limitations, this analysis provides 

at least a reasonable approximation of the aquifers used for 

private domestic supply in each locality and for the entire 

study area, which is useful for a variety of ground-water 

investigations. With the implementation of the domestic 

water-use coefficient, this analysis also provides a method for 

estimating self-supplied domestic ground-water withdrawals 

by aquifer, which previously has not been possible.

Spatial Distribution of Self-Supplied 

Domestic Withdrawals for a GroundWater Model of the Virginia 

Eastern Shore

The spatial distribution of self-supplied domestic 

ground-water withdrawals on the Virginia Eastern Shore 

Peninsula was characterized in support of a separate effort to 

analyze the local ground-water flow system at a greater spatial 

resolution than could be supported by the previously described 

locality-level analyses. For an ongoing ground-water study of 

the mostly rural and agricultural Eastern Shore Peninsula of 

Virginia and a small part of Maryland, self-supplied domestic 

withdrawals are thought to be important. Therefore, these 

withdrawal estimates were needed for inclusion in a groundwater model under development for that peninsula. The well 

and withdrawal data for Accomack and Northampton Counties 

from this report initially were used, but it became apparent 

that applying the self-supplied withdrawals evenly across the 

entire county areas would produce unsatisfactory results. On 

the sparsely populated Eastern Shore Peninsula, much of the 

land area is marsh, forest, or agricultural fields, and human 

populations are unevenly distributed. A scheme was needed 

to spatially distribute domestic withdrawals in a way that 

would more closely simulate the population distribution and 

result in a more accurate representation of domestic wells and 

withdrawals in the ground-water model.

The methods described in this report for evaluating the 

proportion of private domestic wells in each aquifer and for 

calculating self-supplied withdrawals by aquifer provide 

data necessary for considering the hydrogeologic effects of 

domestic withdrawals. Because they rely on aggregation, by 

locality, of sampled well characteristics and the self-supplied 

population, these estimates are limited to the locality level. 

For many purposes, such as the Eastern Shore ground-water 

investigation, locality-level analysis is inadequate because 

it fails to capture variations in withdrawal distributions at 

smaller scales that are important in answering more localized 

questions. The example presented here demonstrates that better spatial resolution can be estimated or simulated even where 

water-use data are available only at the locality level. The 

steps involved in this analysis and their relation to the methods 

and results from other sections of this report are outlined in the 

flow chart in figure 7.

A ground-water model of the Virginia Eastern Shore 

Peninsula was initiated to produce an updated tool for evaluating the effects of ground-water withdrawals on the hydrogeologic system. Of particular interest was the problem of 

potential saltwater intrusion from the Atlantic Ocean and the 

Chesapeake Bay into the freshwater aquifers that provide the 

primary water supply for the peninsula. In order to improve on 

the spatial resolution of the previous Virginia Eastern Shore 

ground-water model (Richardson, 1994), a smaller model cell 
42 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

size of 1,000 ft was used with improved and updated groundwater modeling software.

The Virginia Eastern Shore ground-water model domain 

encompasses an area of just under 3,000 mi2, of which about 

980 mi2 is land. All of Accomack and Northampton Counties 

in Virginia (totaling 674.2 mi2) are included, along with parts 

of Somerset and Worcester Counties in Maryland (306.2 mi2). 

The total population of the simulated area was estimated at 

73,267 from 2000 census block group data, (U.S. Census 

Bureau, 2001), and almost 50,000 people (68 percent) are 

estimated to be self supplied with water from domestic wells, 

based on data from the USGS Water-Use Information Program 

(U.S. Geological Survey, 2002).

The model by Richardson (1994) did not simulate the 

effects of self-supplied domestic withdrawals, but water-use 

estimates indicate that these withdrawals may be important, 

especially considering that the withdrawals are mostly from 

the confined Yorktown-Eastover aquifer. Total withdrawals 

of ground-water in the Virginia Eastern Shore counties 

are estimated at over 7 Mgal/d in 2000, and self-supplied 

domestic withdrawals of approximately 2.74 Mgal/d make up 

about 29 percent of the total. With portions of Somerset and 

Worcester Counties in Maryland included within the boundary 

of the model, total estimated self-supplied domestic withdrawals for this area were estimated to be 3.74 Mgal/d. This total 

includes 2.00 Mgal/d for Accomack County, 0.74 Mgal/d for 

Northampton County, 0.71 Mgal/d for Somerset County, and 

0.30 Mgal/d for Worcester County.

 In order to estimate the distribution of domestic 

withdrawals, it was first necessary to estimate the spatial 

distribution of the self-supplied population for each county 

in a more realistic way using a GIS. The 2000 U.S. Census 

was very helpful in this respect, providing population and 

spatial data at the level of the census block group (U.S. Census 

Bureau, 2001), which is an improvement in resolution beyond 

the county level (fig. 11). The total population for each census 

block group, however, includes both the self-supplied and 

publicly supplied populations.

To eliminate the population in each census block group 

supplied with municipal drinking water, the public-supply 

areas were estimated by using city boundaries with additional 

adjustments based on limited local knowledge (fig. 11). 

Within these public-supply areas, point data on the publicly 

supplied population, available from the U.S. Environmental 

Protection Agency (2006), were used to subtract the publicly 

supplied population from the total population of the census 

block groups. This difference is the self-supplied domestic 

population for each census block group, which is zero for 

some census block groups in public-supply areas. 

Even with the self-supplied domestic population defined 

by census block group, better spatial resolution was needed. 

Application of domestic withdrawals evenly across entire census block groups would have resulted in simulated domestic 

withdrawals in unpopulated areas, including marshes, forests, 

and agricultural fields. As a result, high-resolution spatial data 

on road locations were used to further constrain the population 

distribution.

To identify road locations, GIS data that included all 

roads were used, including even small unpaved roads that were 

found to be important to the validity of this analysis (fig. 11). 

From these highly detailed road data, a road-density analysis 

was completed using GIS software, and the road-density calculation was used to distribute the population of each census 

block group among the ground-water model cells that are not 

located in public-supply areas. This resulted in a substantially 

more detailed distribution of the self-supplied population than 

is shown in figure 11. 

The self-supplied domestic water-use coefficient of 

75 gal/d for Virginia was applied to the estimated distribution 

of the self-supplied population to approximate the distribution 

of self-supplied withdrawals for the Eastern Shore Peninsula 

(fig. 12). Self-supplied domestic withdrawals for the model 

domain totaled 3.74 Mgal/d. While this distribution is an 

approximation, it is a more detailed and realistic depiction of 

domestic withdrawals than is available from any other source.

Sampled domestic-well data were then used to apply the 

estimated self-supplied withdrawals to individual aquifers. On 

the Eastern Shore Peninsula, the unconfined surficial aquifer 

overlies the Yorktown-Eastover aquifer, which was subdivided 

for the purposes of more localized analysis into the upper, 

middle, and lower Yorktown-Eastover aquifers (Richardson, 

1994). This subdivision is not necessarily supported by more 

recent analyses of the hydrogeology, but it was used because 

the Richardson study (1994) is the most current in-depth 

study of the hydrogeology of the Eastern Shore Peninsula 

of Virginia. Aquifers below the Yorktown-Eastover 

aquifers contain saline water and are not penetrated by 

any production wells. 

Estimated well-screen elevations were compared to 

estimated aquifer elevations, as described earlier in this 

report, and sampled private domestic wells were assigned 

aquifer designations so that the spatially distributed estimated 

withdrawals could be applied to individual aquifers. Analyses 

of sampled well records in Accomack County revealed that 

no wells intersected the surficial aquifer, so all wells were 

assigned to the three aquifers of the subdivided YorktownEastover aquifer. Of the sampled wells, 42 percent intersect 

the upper Yorktown-Eastover aquifer, 40 percent intersect the 

middle Yorktown-Eastover aquifer, and 18 percent intersect 

the lower Yorktown-Eastover aquifer. Similar analyses of well 

records in Northampton County indicated that 12 percent of 

the sampled wells intersect the surficial aquifer, 45 percent 

intersect the upper Yorktown-Eastover aquifer, 36 percent 

intersect the middle Yorktown-Eastover aquifer, and 7 percent 

intersect the lower Yorktown-Eastover aquifer. For the 

purposes of this study, the two Maryland counties were 

assumed to have similar well distributions as those in adjacent 

Accomack County. 

Not surprisingly, the distribution of wells by aquifer is 

quite similar between Northampton and Accomack Counties. 

However, Northampton County appears to have a smaller 
Spatial Distribution of Self-Supplied Domestic Withdrawals for a Ground-Water Model of the Virginia Eastern Shore 43

Figure 11. Population data by census block group in 2000 (derived from U.S. Census Bureau, 2001; U.S. Census Bureau, 

2003a), estimated public water-supply areas, and road features in the Virginia Eastern Shore ground-water model domain.

38 ̊

37 ̊

76 ̊ 75 ̊

MARYLAND

VIRGINIA

0

0

5 10 15 20 MILES

5 10 15 20 KILOMETERS

0–103

104–336

337–501

502–789

790–993

994–1,127

1,128–1,509

1,510–2,231

2,232–3,382

3,383–5,577

Approximate shoreline

Roads

NUMBER OF PEOPLE

EXPLANATION Boundary for domain of ground-water model

Estimated public-supply area

ATLANTIC OCEAN

CHESAPEAKE BAY

Northampton

County

Accomack

County

Somerset

County

Worcester

County
44 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

Figure 12. Estimated self-supplied domestic withdrawals of ground water in the Virginia Eastern Shore in 2000, by groundwater model grid cell.

38 ̊

37 ̊

76 ̊ 75 ̊

Figure 13. Estimated self-supplied domestic withdrawals of ground-water in the Virginia Eastern Shore in 2000, by ground-water

model grid cell.

MARYLAND

VIRGINIA

0

0

5 10 15 20 MILES

5 10 15 20 KILOMETERS

58–2,800

2,900–5,200

5,300–7,900

8,000–11,000

12,000–14,000

15,000–18,000

19,000–23,000

24,000–29,000

30,000–42,000

43,000–71,000

ESTIMATED WITHDRAWAL, IN GALLONS

PER DAY PER SQUARE MILE

EXPLANATION Boundary for domain of ground-water model

ATLANTIC OCEAN

CHESAPEAKE BAY
Summary and Conclusions 45

proportion of wells in the lower part of the Yorktown-Eastover 

aquifer and a larger proportion of wells in the surficial aquifer. 

This may be the result of less fresh ground water available at 

depth on the southern part of the peninsula. 

The estimated proportion of wells intersecting each 

aquifer in each county was used to estimate withdrawals from 

each of the aquifers for the Eastern Shore ground-water model. 

Total withdrawals of 3.74 Mgal/d in 2000 were composed 

of 0.09 Mgal/d from the surficial aquifer, 1.59 Mgal/d from 

the upper Yorktown-Eastover aquifer, 1.47 Mgal/d from the 

middle Yorktown-Eastover aquifer, and 0.59 Mgal/d from the 

lower Yorktown-Eastover aquifer. These withdrawals were 

spatially distributed in the model grid using the census block 

group and road density analyses described previously.

The example of the application of self-supplied groundwater withdrawals to the Eastern Shore ground-water model 

demonstrates how these well data, sampled by county, can be 

applied at greater resolution using other spatial data, such as 

population and road distributions. In this example, the well 

data were not spatially resolved beyond the county level. 

However, more localized studies using well data for smaller 

areas, such as individual tax plats, could provide even more 

detailed information on variations in water use by aquifer 

within a county. In a study in which wells could be located 

exactly, these analyses would be even more powerful.

Summary and Conclusions

Self-supplied domestic withdrawals of ground water, 

estimated to be approximately 38.5 Mgal/d for the year 

2000, are a substantial portion (about 28 percent) of total 

ground-water withdrawals in the Coastal Plain of Virginia. 

Little research previously has been done to comprehensively 

describe the nature and distribution of these withdrawals. 

Over 500,000 people, composing 15 percent of the total 

population of the Virginia Coastal Plain, depend on selfsupplied domestic withdrawals of ground water. In some rural 

localities of eastern Virginia, these withdrawals provide almost 

all of the available water supply. Estimates based on population analyses indicate that about 200,000 private domestic 

wells currently may be in use in the Virginia Coastal Plain. 

Despite the importance of this resource, little has been known 

previously about the locations of private domestic wells or the 

aquifers from which domestic withdrawals are taken.

Previously published ground-water models of the Virginia 

Coastal Plain have not accounted for domestic withdrawals, 

because the withdrawals are difficult to measure and because 

of the assumption that the hydrogeologic effects of these 

withdrawals are insignificant. Mounting evidence indicates, 

however, that an understanding of the magnitude and distribution of these withdrawals may be critical to understanding 

ground-water flow in the Coastal Plain of Virginia.

This study included a comprehensive assessment of 

construction characteristics for private domestic wells based 

on a survey of 2,846 wells in 29 Virginia Coastal Plain localities known to have appreciable self-supplied populations. The 

results of this assessment indicate that the depth distribution 

of these wells may be more varied than previously believed. 

Domestic-well depths range from 14 to 865 ft below land 

surface in the records sampled, with a median of 141.5 ft and a 

mean of 202.2 ft.

A technique presented here for estimating domestic-well 

screen elevations in the absence of definitive elevation or 

location data allows these wells to be referenced to a newly 

revised configuration of the Virginia Coastal Plain hydrogeology and, thereby, assigned to aquifers. This estimation 

technique reveals that only 22 percent of the domestic wells 

in the Virginia Coastal Plain are completed in the unconfined 

surficial aquifer. On the other hand, the 78 percent of wells 

completed in the confined aquifers includes 33 percent in 

the Yorktown-Eastover aquifer or Yorktown confining zone, 

8 percent in the Piney Point aquifer, 11 percent in the Aquia 

aquifer, and 25 percent in the Potomac aquifer and confining 

zone. A few remaining wells, about 1 percent, were found to 

intersect the Saint Marys aquifer, the Virginia Beach aquifer, 

or crystalline bedrock beneath Coastal Plain sediments near 

the Fall Line. These results directly contradict the previous 

assumption by some water-resources experts that domestic 

withdrawals are unimportant to regional ground-water 

flow because they are taken from the unconfined aquifer 

and quickly replaced by return flow through home septic 

systems. Based on this new information about domestic wells, 

withdrawals from the confined aquifers of the Virginia Coastal 

Plain actually make up 78 percent of the domestic total, or 

about 30 Mgal/d. Almost 10 Mgal/d of domestic withdrawals 

are from the Potomac aquifer across the Coastal Plain. 

The relatively large rate of total self-supplied domestic 

ground-water withdrawals from the confined aquifer system 

indicates the importance of considering domestic withdrawals 

in any complete analysis of Virginia Coastal Plain groundwater resources, because these deep domestic withdrawals 

represent an essentially permanent removal of water from the 

regional flow system. The total rate of domestic ground-water 

withdrawals is similar to that of the large, centralized municipal and industrial withdrawals, though results of ground-water 

flow modeling indicate that the effects of these withdrawals 

may be quite different. Ongoing ground-water modeling 

studies that incorporate the results of this investigation may 

reveal more about the effect of domestic withdrawals on the 

regional ground-water flow system. Furthermore, substantial 

local variations in the distribution of domestic withdrawals 

by aquifer indicate that a thorough investigation of domestic 

wells and withdrawals is needed in any comprehensive, local, 

water-resources assessment. 

An example of the incorporation of self-supplied 

domestic withdrawals to the Eastern Shore ground-water 

model demonstrates the application of the data and analyses 

presented here and introduces a GIS technique for distributing 

domestic withdrawals spatially based on geographic data. The 

importance of considering domestic withdrawals as part of the 
46 Private Domestic-Well Characteristics and Distribution of Domestic Withdrawals in the Virginia Coastal Plain

regional ground-water flow system may be revealed further by 

the results of ongoing modeling efforts for the Eastern Shore 

Peninsula and for the Virginia Coastal Plain as a whole, but 

the techniques for distributing estimated withdrawals spatially 

also could be useful in many other applications related to 

water-resource assessment and management.

Acknowledgments

This study was supported primarily by the USGS 

Office of Ground Water (OGW) through the Ground-Water 

Resources Program (GWRP). The authors gratefully acknowledge Paul Barlow of the OGW for his program and technical 

support during the study. 

T. Scott Bruce of the Virginia Department of Environmental Quality was especially helpful in providing background 

information on private domestic wells in the Virginia Coastal 

Plain, and thanks are extended to him for sharing his time and 

ideas.

The authors also wish to acknowledge the personnel of 

the Virginia Department of Health (VDH) for their support of 

this study and particularly for providing general background 

information on private domestic wells. Access to county 

well records was provided by the staff of the various local 

health departments in each of the localities studied. Local 

health department staff also frequently provided support 

in the sampling process and additional information about 

well characteristics in their individual localities. Thanks are 

extended to all local health department personnel for their time 

and cooperation in providing access to well records.

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