Prepared in cooperation with the Virginia Department of Environmental Quality

Hydrogeologic Framework and Hydrologic Conditions 

of the Piney Point Aquifer in Virginia

PIEDMONT 

COASTAL PLAIN 

APPALACHIAN

PLATEAUS BLUE RIDGE

Fall zone

VALLEY AND RIDGE

Scientific Investigations Report 2017–5041

U.S. Department of the Interior

U.S. Geological Survey
Cover. Geologists of the U.S. Geological Survey (USGS) and Virginia Department of Environmental Quality (VA DEQ) processing a sediment 

core from the Banbury Cross corehole, USGS borehole 57G128, York County, Virginia. The core is from 1 of 366 boreholes that intersect the 

Piney Point aquifer in Virginia. Extents, compositions, configurations, and geologic relations of six geologic units that compose the Piney Point 

aquifer were determined from geologists’ logs of sediment core and cuttings, borehole geophysical logs, and drillers’ logs. Investigation of 

the Piney Point aquifer was jointly undertaken by USGS and the VA DEQ under the USGS Cooperative Studies Program. Photograph by T. Scott 

Bruce, Virginia Department of Environmental Quality.
Hydrogeologic Framework and Hydrologic 

Conditions of the Piney Point Aquifer 

in Virginia

By E. Randolph McFarland

Prepared in cooperation with the Virginia Department of Environmental Quality

Scientific Investigations Report 2017–5041

U.S. Department of the Interior

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

RYAN K. ZINKE, Secretary

U.S. Geological Survey

William H. Werkheiser, Acting Director

U.S. Geological Survey, Reston, Virginia: 2017

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

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For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

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

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

Suggested citation:

McFarland, E.R., 2017, Hydrogeologic framework and hydrologic conditions of the Piney Point aquifer in Virginia: U.S. 

Geological Survey Scientific Investigations Report 2017–5041, 63 p., 2 pl., and CD-ROM, https://doi.org/10.3133/

sir20175041.

ISSN 2328-031X (print)

ISSN 2328-0328 (online)

ISBN 978-1-4113-4148-7
iii

Acknowledgments

This study was supported by the Virginia Department of Environmental Quality (VA DEQ). Special 

thanks for program planning go to Scott W. Kudlas and T. Scott Bruce of the VA DEQ. C. Richard 

Berquist of the Virginia Division of Geology and Mineral Resources generously provided geologic logs of boreholes in the southwestern part of the study area, and John T. Haynes of James 

Madison University generously provided petrographic analyses of limestone of the Piney Point 

Formation. Thanks also are extended to the many drillers and owners of water-supply wells, 

who provided well data from across the Virginia Coastal Plain. The scientific integrity of this 

report was aided greatly by reviews from Mark D. Kozar and Jason P. Pope of the U.S. Geological Survey (USGS). The editorial and graphical quality of the report was aided greatly by Ruth 

Larkins and Denis Sun of the USGS.

This project has been funded in part by the U.S. Environmental Protection Agency (EPA) under 

assistance agreement BG—98392505—1 to the VA DEQ. The contents of this document do not 

necessarily reflect the views and policies of the EPA, nor does the EPA endorse trade names or 

recommend the use of commercial products mentioned in this document.
iv

Contents

Acknowledgments........................................................................................................................................iii

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

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

Purpose and Scope ..............................................................................................................................2

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

Geologic Setting...........................................................................................................................6

Groundwater Conditions.............................................................................................................6

Methods of Investigation.....................................................................................................................7

Hydrogeologic Framework of the Piney Point Aquifer in Virginia .........................................................8

Previous Studies ...................................................................................................................................8

Geologic Units .......................................................................................................................................8

Nanjemoy Formation Potapaco Member.................................................................................9

Nanjemoy Formation Woodstock Member..............................................................................9

Piney Point Formation ...............................................................................................................15

Composition of Limestone ...............................................................................................15

Extent of Limestone ..........................................................................................................19

Gosport Formation Equivalent Sediments .............................................................................20

Oligocene-Age Sediments .......................................................................................................20

Old Church Formation ...............................................................................................................23

Calvert Formation, Newport News Unit and Basal Plum Point Member..........................23

Fine-Grained Calvert Formation Plum Point Member..........................................................25

Structural Configuration ....................................................................................................................25

Faults............................................................................................................................................27

Impact-Crater Resurge Channel .............................................................................................28

Hydrologic Conditions of the Piney Point Aquifer in Virginia ...............................................................29

Groundwater Withdrawals................................................................................................................29

Temporal Trends.........................................................................................................................29

Spatial Distribution of Reported Withdrawals ......................................................................30

Groundwater Levels ...........................................................................................................................32

Regional Water-Level Trends...................................................................................................32

Water-Level Cone of Depression ............................................................................................32

Water-Level Interactions on the York-James Peninsula.....................................................35

Seasonal Water Demand.................................................................................................35

Water-Table Recharge.....................................................................................................38

Cyclic Pumping..................................................................................................................38

Hydraulic Properties...........................................................................................................................38

Historical Aquifer Tests.............................................................................................................40

Well Specific Capacity..............................................................................................................43

Aquifer-Component Test...........................................................................................................43

Groundwater Research Station......................................................................................43

Pumping and Water-Level Measurement.....................................................................44

Antecedent Water-Level Depth Trend...........................................................................47

Water-Level Drawdown and Recovery.........................................................................48
v

Conceptual Two-Layer Aquifer Model ..........................................................................48

Geologic-Unit Transmissivities and Hydraulic Conductivities...................................51

Assumptions and Limitations..........................................................................................52

Water Quality.......................................................................................................................................53

Major Ions...................................................................................................................................53

Solution Channeling ..................................................................................................................53

Iron ...............................................................................................................................................53

Chloride........................................................................................................................................54

Resource-Management Considerations.........................................................................................56

Aquifer Characterization ..........................................................................................................56

Regulatory Implications............................................................................................................56

Summary and Conclusions.........................................................................................................................57

References Cited..........................................................................................................................................59

Appendix 1. Borehole Geologic-Unit Top-Surface Altitudes, Piney Point Aquifer, Virginia.........63

Appendix 2 Aquifer-Component Test Data, Piney Point Aquifer, Virginia.......................................63

Plates

1. Location of Boreholes an Extent of Productive Limestone in the Piney Point 

Aquifer in Virginia ..........................................................................................................in pocket

2. Hydrogeologic Sections A–A’, B–B’, and C–C’ of the Piney Point Aquifer 

in Virginia ........................................................................................................................in pocket

Figures

1. Map showing locations of boreholes, lines of hydrogeologic section, and extent 

of the Piney Point aquifer and productive limestone in Virginia...........................................3

2. Generalized hydrogeologic section and direction of predevelopment groundwater 

flow in the Coastal Plain in Virginia ...........................................................................................4

3. Simplified stratigraphic relations among hydrogeologic units of the Virginia Coastal 

Plain and geologic units that compose the Piney Point aquifer...........................................5

4. Representative sediment lithologies and resistivity log from the Banbury Cross 

corehole, York County, Virginia.................................................................................................11

5. Representative sediment lithologies and resistivity log from the Surprise Hill 

corehole, Northumberland County, Virginia...........................................................................13

6. Map showing altitude and configuration of the top surface of the Nanjemoy 

Formation Potapaco Member across the Northern Neck, upper Middle Peninsula, 

and upper York-James Peninsula in Virginia .........................................................................14

7. Map showing altitude and configuration of the top surface of the Nanjemoy 

Formation Woodstock Member across the Northern Neck, upper Middle 

Peninsula, and upper York-James Peninsula in Virginia .....................................................16
vi

8. Map showing altitude and configuration of the top surface of the Piney Point 

Formation across the Northern Neck, upper Middle Peninsula, and upper 

York-James Peninsula in Virginia.............................................................................................17

9. Photographs showing representative examples of limestone of the Piney Point 

Formation in Virginia. A, Contrasting cementation among slabbed samples from 

Haynesville borehole 57M 7, Richmond County, Virginia. B, Photograph from 

video log of open-hole “barefoot” borehole 55H 30, New Kent County, Virginia.............18

10. Map showing altitude and configuration of the top surface of sediments 

equivalent to the Gosport Formation across the Northern Neck, upper Middle 

Peninsula, and upper York-James Peninsula in Virginia .....................................................21

11. Map showing altitude and configuration of the top surface of Oligocene-age 

sediments across the Northern Neck, upper Middle Peninsula, and upper 

York-James Peninsula in Virginia.............................................................................................22

12. Map showing altitude and configuration of the top surface of the Old Church 

Formation across the Northern Neck, upper Middle Peninsula, and upper 

York-James Peninsula in Virginia.............................................................................................24

13. Map showing altitude and configuration of the top surface of the Calvert Formation, 

Newport News unit and basal Plum Point Member across the Northern Neck, 

upper Middle Peninsula, and upper York-James Peninsula in Virginia ............................26

14. Graphs showing reported and estimated domestic groundwater withdrawals 

during 1900–2009 from A, all aquifers in the Virginia Coastal Plain and B, the 

Piney Point aquifer .....................................................................................................................30

15. Maps showing locations and rates of reported groundwater withdrawals from 

the Piney Point aquifer, in Virginia, during A, 2004 and B, 2009 ..........................................31

16. Graphs showing A, yearly mean water levels in selected observation wells in the 

Piney Point aquifer, in Virginia, during 1906–2015 and B, map showing locations 

of selected observation wells in the Piney Point aquifer.....................................................33

17. Maps showing estimated water levels in the Piney Point aquifer during A, 

September 2008, B, May 2009, and C, August 2009, and D, production- and 

observation-well locations........................................................................................................34

18. Graphs showing water levels in continuously measured observation wells A, 

57G129 and 57G130 in York County, B, 55H 27 in New Kent County, and C, 58F 53 in 

the City of Newport News, Virginia, during March–September 2015, D, total daily 

rainfall downloaded from Weather Underground weather station KVAWILLI12 

on September 23, 2015, and E, locations of observation wells, selected production 

wells, weather station, and faults............................................................................................36

19. Graphs showing hydrodynamic intractions in northern York County, Viginia, 

during March 6–8, 2015: A, water levels in observation wells 57G129 and 57G130, 

B, vertical hydraulic gradient between observation wells 57G129 and 57G130, C, 

groundwater-withdrawal rates for production well 57G 55, and D, groundwaterwithdrawal rates for production well 57G134 ........................................................................39

20. Maps showing A, locations of historical aquifer tests and estimates of transmissivity 

of the Piney Point aquifer in Virginia and Maryland, and B, locations and specific 

capacities of wells in the Piney Point aquifer........................................................................42

21. Diagram showing litho-stratigraphy and well construction at the groundwater 

research station in York County, Virginia................................................................................45
vii

22. Graphs showing A, data collected prior to and during an aquifer test at the groundwater research center in York County, Virginia, for observation-well water levels and 

antecedent water-level trends, B, barometric pressure downloaded on September 23, 

2015, from Weather Underground weather stations KVAWILL119, KVAWILL120, and 

KVAQILL121, and C, tidal stage of James River at the U.S. Geological Survey gaging 

station 02042222 in Charles City County, Virginia, during March 15–19, 2015...................46

23. Graphs showing aquifer test water-level A, drawdowns and B, recoveries in 

observation well 57G129 at the groundwater research station in York County, 

Virginia, March 17–19, 2015 ......................................................................................................49

24. Conceptual model of the flow response of a two-layer confined aquifer to an aquifer 

test during A, the early part of the test, and B, the late part of the test............................50

25. Map showing distribution of iron and chloride in water in the Piney Point 

aquifer, Virginia ...........................................................................................................................55

Tables

1. Groundwater-withdrawal rates from all aquifers in the Atlantic Coastal Plain 

in Virginia during 2002 and 2009, and from the Piney Point aquifer during 2004 

and 2009........................................................................................................................................29

2. Estimates of transmissivity and storativity of the Piney Point aquifer in Virginia 

and an adjacent part of Maryland, using aquifer tests, 1972–2011....................................41

3. Summary of well specific capacities in the Piney Point aquifer in Virginia and 

an adjacent part of Maryland ...................................................................................................43

4. Estimates of the transmissivities and hydraulic conductivities of geologic units 

composing the Piney Point aquifer, using aquifer testing at the groundwater 

research station in York County, Virginia, March 2015.........................................................51
viii

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

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) 

Flow rate

inch per year (in/yr) 2.54 centimeter per year (cm/yr)

foot per year (ft/yr) 0.3048 meter per year (m/yr)

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

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

Aquifer hydraulic properties

foot per minute (ft/min) 0.3048 meter per minute (m/min)

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d)

gallon per minute per foot (gal/min/ft) 0.20699 liter per second per meter (L/s/m)

Datum

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

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

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

Supplemental Information

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L).
Hydrogeologic Framework and Hydrologic Conditions of 

the Piney Point Aquifer in Virginia

By E. Randolph McFarland

Abstract

The Piney Point aquifer in Virginia is newly described 

and delineated as being composed of six geologic units, in a 

study conducted by the U.S. Geological Survey in cooperation with the Virginia Department of Environmental Quality 

(VA DEQ). The eastward-dipping geologic units include, in 

stratigraphically ascending order, the

• sand of the Nanjemoy Formation Woodstock Member,

• interbedded limestone and sand of the Piney Point 

Formation,

• silty and clayey sand of the Gosport Formation equivalent sediments,

• silty sand of the Oligocene-age sediments,

• silty fine-grained sand of the Old Church Formation, 

and

• silty sand of the Calvert Formation, Newport News unit 

and basal Plum Point Member.

Identification of geologic units is based on typical sediment lithologies of geologic formations. Fine-grained sediments that compose confining units positioned immediately 

above and below the Piney Point aquifer are also described.

The Piney Point aquifer is one of several confined aquifers within the Virginia Coastal Plain and includes a highly 

porous and solution-channeled indurated limestone within 

the Piney Point Formation from which withdrawals are made. 

The limestone is relatively continuous laterally across central 

parts of the Northern Neck, Middle Peninsula, and YorkJames Peninsula. Other geologic units are of variable extent. 

The configurations of most of the geologic units are further 

affected by newly identified faults that are aligned radially 

from the Chesapeake Bay impact crater and create constrictions or barriers to groundwater flow. Some geologic units are 

also truncated beneath the lower Rappahannock River by a 

resurge channel associated with the impact crater.

Groundwater withdrawals from the Piney Point aquifer increased from approximately 1 million gallons per day 

(Mgal/d) during 1900 to 7.35 Mgal/d during 2004. As a result, 

a water-level cone of depression in James City and northern 

York Counties was estimated to be as low as 70 feet (ft) below 

the National Geodetic Vertical Datum of 1929 (NGVD 29) by 

2005. Withdrawals decreased to 5.01 Mgal/d by 2009 as withdrawals were shifted toward other sources, and by 2015 water 

levels had recovered to approximately 50 ft below NGVD 29.

The mean estimated transmissivity of the Piney Point 

aquifer in York and James City Counties is 16,300 feet squared 

per day (ft2/d), but farther north it is only 925 ft2/d. The mean 

well specific capacity in York and James City Counties is 

11.4 gallons per minute per foot (gal/min/ft). Farther north in 

Virginia, mean specific capacity is only 2.26 gal/min/ft, and 

in Maryland it is 0.99 gal/min/ft. The northward decrease in 

specific capacity probably reflects the northward decrease in 

transmissivity, which results from poor development of the 

solution-channeled limestone.

An aquifer test in northern York County induced vertical 

leakage to the solution-channeled limestone from overlying 

silty sand and a change in response of the aquifer to pumping 

from a single layer to two layers. Transmissivity of the limestone of approximately 19,800 ft2

/d was distinguished from the 

silty sand of approximately 2,500 ft2/d.

Most of the water in the Piney Point aquifer is slightly 

alkaline with moderate concentrations primarily of sodium 

and bicarbonate that are slightly undersaturated with respect to 

calcite. Iron concentrations are generally less than 0.3 milligrams per liter (mg/L). Mixing of freshwater with seawater 

has elevated chloride concentrations to the southeast to as 

much as 7,120 mg/L.

Information on the Piney Point aquifer can benefit waterresource management in siting production wells, predicting likely well yield, and anticipating water-level response 

to withdrawals. Models that vertically discretize individual 

geologic units can potentially be used to evaluate groundwater 

flow in greater detail by representing lateral flow and vertical 

leakage among the geologic units.

Because groundwater withdrawals are made primarily 

from the limestone and sand of the Piney Point Formation, the 

VA DEQ has considered regarding the limestone and sand singly as a regulated aquifer apart from the other geologic units. 

Under current policy in Virginia, if only the limestone and 

sand were regarded as a regulated aquifer, a greater amount 

of drawdown would be allowed than is allowed for the Piney 

Point aquifer consisting of six geologic units. Some production wells intercept multiple geologic units, and the units can 

undergo water-level decline and vertical leakage induced by 

pumping from the limestone and sand. Whether the other 

geologic units are to be regarded as regulated aquifers is an 

additional consideration for the VA DEQ.
2 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Introduction

The Atlantic Coastal Plain Physiographic Province 

(Coastal Plain) stretches from Cape Cod, Massachusetts southward to the Gulf of Mexico and offshore to the Continental 

Shelf. In the eastern part of Virginia, the Coastal Plain occupies an area of approximately 13,000 square miles (mi2

, fig. 1). 

Groundwater in the Virginia Coastal Plain is a heavily used 

resource. The rate of groundwater withdrawal is estimated to 

have been close to zero during the late 1800s but increased 

continuously during the 20th century. Since 2000, withdrawal 

rates for Coastal Plain aquifers in Virginia have been maintained at approximately 130 million gallons per day (Mgal/d) 

(Masterson and others, 2016). As a result, groundwater levels 

have declined by as much as 200 feet (ft) near major withdrawal centers, and flow gradients have been altered from a 

previously seaward direction to a landward direction, creating 

the potential for saltwater intrusion. Continued withdrawal is 

expected to further water-level declines and intrusion potential, and thereby limit continued use of the resource.

In order to manage the groundwater resource, the Virginia 

Department of Environmental Quality (VA DEQ) regulates 

groundwater withdrawals. Withdrawals within the Virginia 

Coastal Plain of 300,000 gallons or more during any month 

must be approved under the VA DEQ Groundwater Withdrawal Permitting Program. Groundwater users are required 

to submit withdrawal-related information needed to evaluate 

the potential effects of the withdrawals on the aquifer system. In order to provide a valid context within which to make 

resource-management decisions, the VA DEQ has also maintained a sound scientific understanding of Virginia Coastal 

Plain geology and hydrology through a cooperative program 

of hydrogeologic investigation with the U.S. Geological Survey (USGS). Advancements made by recent studies include 

discovery of the Chesapeake Bay impact crater (Powars 

and Bruce, 1999), revision of the hydrogeologic framework 

(McFarland and Bruce, 2006), digital model simulation of 

groundwater flow (Heywood and Pope, 2009), characterization 

of groundwater chemical quality (McFarland, 2010), detailed 

analysis of the Potomac aquifer (McFarland, 2013), and development of a strategy to monitor the movement of saltwater 

(McFarland, 2015).

In addition to the management efforts, improved information on the Piney Point aquifer is needed to effectively plan for 

a sustainable water supply. The Piney Point aquifer supplies 

urban and suburban areas from large municipal wells that produce as much as 400 gallons per minute (gal/min). Widespread 

rural areas are supplied by smaller commercial and domestic 

wells that produce 10–50 gal/min. The productive part of the 

aquifer, however, is limited to a solution-channeled limestone 

in which most water-supply wells are completed. Moreover, 

large withdrawals from the productive limestone are geographically concentrated within a relatively small area centered on 

James City County. A resulting water-level cone of depression 

has been estimated at times to be deeper than 80 ft below sea 

level (Heywood and Pope, 2009). Water demands from the 

Piney Point aquifer are expected to expand as a result of ongoing development along the Interstate 64 corridor (plate 1).

The Piney Point aquifer is one of several confined aquifers of intermediate thickness and depth within the Virginia 

Coastal Plain (fig. 2). The Piney Point aquifer occupies much 

of the Coastal Plain in Virginia and adjacent parts of Maryland and North Carolina (fig. 1). The aquifer is a composite, 

however, of several geologic units that have different lateral 

extents (fig. 3). Although the geologic units are stratigraphically and lithologically distinct, they have not been individually described and delineated in a hydrologic context. Of 

greatest importance, the extent, continuity, and other hydrologic aspects of the productive limestone are poorly known. 

Moreover, withdrawals, water levels, hydraulic properties, 

and flow interaction of the Piney Point aquifer have not been 

comprehensively documented.

To address the information needs, a study of the Piney 

Point aquifer was undertaken by the USGS in cooperation 

with the VA DEQ. Aquifer sediments were described, and 

other hydrologic aspects were characterized, by different study 

components completed during 2009, 2013, and 2015.

Purpose and Scope

The Piney Point aquifer is characterized to address information needs for water-resource management in the Virginia 

Coastal Plain. The focus is geographically constrained to the 

area surrounding the productive limestone (fig. 1), designated 

here as the study area, in which withdrawals from the Piney 

Point aquifer are made. Although the Piney Point aquifer 

subcrops along major river valleys that cross its westernmost margin, within the designated study area, the aquifer is 

entirely confined.

A hydrogeologic framework of the Piney Point aquifer is 

presented. Extents, compositions, configurations, and geologic 

relations of six geologic units that compose the Piney Point 

aquifer are described and are illustrated by photographs of 

sediment lithologies, structural-contour maps, and hydrogeologic sections. Structural features of the Piney Point aquifer 

are also described.

Hydrologic conditions of the Piney Point aquifer are 

described. Groundwater withdrawals in the Virginia Coastal 

Plain during 1900–2009 are summarized to distinguish among 

large regulated withdrawals and small unregulated withdrawals from the Piney Point aquifer and other aquifers. Spatial and 

temporal water-level trends in the Piney Point aquifer are summarized regionally for 1906–2015, within the cone of depression centered on James City County for 2008–09, and on the 

York-James Peninsula for March–September 2015. Aquifertest estimates of transmissivity and storativity of the Piney 

Point aquifer are presented and are summarized and compared 

to well specific capacities to determine spatial trends. Results 

of an aquifer test conducted by the VA DEQ in York County 

also are presented and analyzed to determine transmissivi-
Introduction 3

SUSSEX COUNTY

CAROLINE

COUNTY

HANOVER

COUNTY

City of Suffolk

SURRY COUNTY

ESSEX

COUNTY

SOUTHAMPTON

CHESTERFIELD

COUNTY

SPOTSYLVANIA

COUNTY

HENRICO

COUNTY

City of

Chesapeake

KING AND QUEEN

COUNTY

YORK

COUNTY

ISLE OF WIGHT

COUNTY

GREENSVILLE

NEW KENT

COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE GEORGE

COUNTY

GLOUCESTER

COUNTY

WESTMORELAND

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

JAMES CITY

COUNTY

MIDDLESEX

COUNTY

LANCASTER

COUNTY

City of

Norfolk

NORTHUMBERLAND

COUNTY

MATHEWS

COUNTY

City of

Richmond

City of

Hampton

City of Newport News

City of

Petersburg City of

Poquoson

City of

Portsmouth

City of

Hopewell

Franklin

City of Colonial Heights

City of

Williamsburg

City of

Fredericksburg

EMPORIA

NORTH CAROLINA

VIRGINIA

MARYLAND

West Point

City of

Virginia Beach

DINWIDDIE

COUNTY

NORTHAMPTON

COUNTY

F A L L Z O N E

Chesapeake Bay

impact crater

A

A'

B

B'

C

C'

A

A'

B

B'

C

C'

LIMIT OF PINEY POINT AQUIFE

R

N

O R T H E R N

N E C K

M I D D L E

P E N I N S U L A

Y

O

R

K - J

A

M

E S

P E N I N S U L A

S O U T H E A S T E R N

V I R G I N I A

V I R G I N I A E A S T E R N

S

H

O

R E

A

TLANTIC

OCEAN

Po t o mac River

Rappahannock River

York River

James River

C H E

S

A

P

E

A

K

E

B

A

Y

77° 76°

38°

37°

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500,000

Extent of study area

EXPLANATION

Extent of productive limestone

Line of hydrogeologic section

Borehole intersecting limestone

Borehole not intersecting limestone

A A'

0 8 16 MILES

0 8 16 KILOMETERS

PIEDMONT COASTAL PLAIN 

APPALACHIAN 

BLUE RIDGE

Fall zone

PLATEAUS

Physiographic provinces in Virginia

VALLEY AND RIDGE

Extent of

study area

Figure 1. Locations of boreholes, lines of hydrogeologic section, and extent of the Piney Point aquifer and 

productive limestone in Virginia. (Hydrogeologic sections are shown on plate 2.)
4 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

0

VERTICAL SCALE GREATLY EXAGGERATED

5000-500-1,000-1,500

WEST EAST

AQUIA

AQUIFER

YORKTOWN-EASTOVER AQUIFER

SUFFOLK SCARP SURFICIAL AQUIFER

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

Altitude, in feet relative to the National Geodetic Vertical Datum of 1929

Altitude, in feet relative to the National Geodetic Vertical Datum of 1929 EXMORE MATRIX CONFINING UNIT

CHICKAHOMINY CONFINING UNIT

EXMORECLASTCONFININGUNIT

CHESAPEAKE BAY IMPACT CRATER

500

-500

-1,000-1,500

EXPLANATION

AquiferConfining unit or zoneSaproliteBedrockFracturesDirection of groundwater flow

S a l t w a t e r - t r a n s i t oi n e n o z

Figure 2. Generalized hydrogeologic section and direction of predevelopment groundwater flow in the Coastal Plain in Virginia. (From McFarland and Bruce, 2006) The Saint Marys, Peedee, and Virginia Beach aquifers are of limited extent and are not shown.
Introduction 

5

Hydrogeologic units

(From McFarland and Bruce, 2006) Geologic units in this report

Surficial aquifer

Yorktown confining zone

Yorktown-Eastover aquifer

Saint Marys confining unit

Saint Marys aquifer

Calvert confining unit

Calvert Formation, Calvert Beach Member

Calvert Formation, fine-grained Plum Point Member

Piney Point aquifer

Calvert Formation, basal Plum Point Member

Calvert Formation, Newport News unit

Old Church Formation

Not present within 

Chesapeake Bay 

impact crater

Oligocene-age sediments Present only in eastern Northern 

Neck and Middlesex County

Present 

only within 

Chesapeake 

Bay impact 

crater

Chickahominy confining unit Gosport Formation equivalent sediments

Exmore Matrix confining unit Piney Point Formation Laterally continuous limestone present only north of James River

Exmore Clast confining unit Nanjemoy Formation, Woodstock Member

Nanjemoy-Marlboro confining unit

Nanjemoy Formation, Potapaco Member

Marlboro clay

Aquia aquifer

Present 

only in 

southeastern 

Virginia

Peedee confining zone

Peedee aquifer

Virginia Beach confining zone

Virginia Beach aquifer

Upper Cenomanian confining unit

Potomac confining zone

Potomac aquifer

Basement bedrock

Figure 3. Simplified stratigraphic relations among hydrogeologic units of the Virginia Coastal Plain (adapted from McFarland and Bruce, 2006) and geologic units that compose the Piney Point aquifer. Associations among some hydrogeologic units and geologic units that cross stratigraphic boundaries are not shown.
6 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

ties and hydraulic conductivities among, and flow interaction 

between, geologic units that compose the Piney Point aquifer.

The relevance of the above information to water-resource 

management is discussed. Applications of data and concepts 

to aid characterization of the aquifer are described. Additionally, implications for regulation of the Piney Point aquifer 

are examined.

Description of the Study Area

Eastern Virginia is encompassed by the Atlantic Coastal 

Plain Physiographic Province (Coastal Plain) (fig. 1). Primary urban centers include the cities of Fredericksburg and 

Richmond along the western margin, and several cities and 

counties to the east and south. The remainder of the Virginia 

Coastal Plain is mostly rural and fairly evenly divided between 

cropland and forest. Land-surface altitudes range from more 

than 300 ft above sea level across some western uplands to 

sea level along the Atlantic coast. Rolling terrain and deeply 

incised stream valleys are present to the northwest, and gently 

rolling-to-level terrain, broad stream valleys, and extensive 

wetlands are present to the east and south. Primary rivers 

include the Potomac, Rappahannock, York, and James Rivers 

(fig. 1), which receive flow from dense and extensive networks 

of tributaries that extend across their entire drainage basins. 

These rivers collectively drain to the east and southeast into 

the Chesapeake Bay and become estuarine upon entering the 

Virginia Coastal Plain. Distinct landmasses defined by the 

estuarine rivers include, from north to south, the Northern 

Neck, Middle Peninsula, York-James Peninsula, and Southeastern Virginia (fig. 1). Chesapeake Bay separates these parts 

of the Virginia Coastal Plain to the west from the Virginia 

Eastern Shore to the east.

Geologic Setting

The Coastal Plain is underlain by a seaward-thickening 

wedge of regionally extensive, generally eastward-dipping 

strata of unconsolidated to partly consolidated sediments of 

Cretaceous, Paleogene, Neogene, and Quaternary age that 

unconformably overlie a basement of consolidated bedrock 

(fig. 2). The sediment wedge extends from Cape Cod, Massachusetts, southward to the Gulf of Mexico and offshore to 

the Continental Shelf. Sediment thickness in Virginia ranges 

from 0 ft at its western margin to more than 6,000 ft along 

the Atlantic coast. The sediments were deposited by seaward 

progradation of fluvial plains and deltas along the North 

American continental margin, followed by a series of transgressions and regressions by the Atlantic Ocean in response to 

changes in sea level. Fluvial strata primarily of Cretaceous age 

are overlain by marine strata of Paleogene and Neogene age, 

which are overlain in turn by terrace and flood-plain deposits 

primarily of Quaternary age.

Coastal Plain sediments in Virginia near the mouth of 

the present-day Chesapeake Bay were affected during the 

Eocene Epoch by the impact of an asteroid or comet (Powars 

and Bruce, 1999). The buried Chesapeake Bay impact crater 

is greater than 50 miles (mi) in diameter and extends across a 

large part of the southeastern Virginia Coastal Plain (fig. 1). 

The crater formed within the preexisting sediments and contains unique impact-related materials as deep as basement bedrock. Subsequent deposition has buried crater-fill sediments 

approximately 1,000 ft below the present-day land surface.

The Piedmont Physiographic Province (Piedmont) lies to 

the west of the Coastal Plain (figs. 1 and 2) and is underlain 

by igneous and metamorphic bedrock of late Proterozoic and 

early Paleozoic age, along with fault-bounded structural basins 

containing sedimentary and igneous bedrock of Triassic and 

Jurassic age. The transitional part of the Coastal Plain adjacent 

to the Piedmont is designated as the Fall Zone, a belt several 

miles wide through which streams have eroded Coastal Plain 

sediments to expose Piedmont bedrock in the valley floors 

(Mixon and others, 1989). From the Fall Zone, the Piedmont 

bedrock slopes eastward beneath the sediment wedge to constitute the basement that underlies the Coastal Plain.

Groundwater Conditions

Virginia Coastal Plain sediments form a series of hydrogeologic units (fig. 3) (McFarland and Bruce, 2006). Permeable sediments, through which most groundwater flows, are 

designated as aquifers, and less permeable sediments that 

restrict flow are designated as confining units or zones. None 

of the hydrogeologic units span the entire Virginia Coastal 

Plain. A complex history of sediment deposition has produced 

numerous lateral variations in sediment composition. Consequently, the positions of hydrogeologic-unit margins are divergent, and their aerial distribution has a complex overlapping 

configuration. In particular, major discontinuities are present 

along the margin of the Chesapeake Bay impact crater (fig. 2).

Groundwater in the Virginia Coastal Plain is present in 

pores between the sediment grains. Precipitation that infiltrates 

the land surface and percolates to the water table either flows 

relatively short distances and discharges to nearby streams or 

leaks downward to recharge deeper confined aquifers (fig. 2). 

Flow through the confined aquifers is primarily lateral in the 

down-dip direction to the east and toward major withdrawal 

centers and discharge areas along large rivers and the Atlantic 

coast. Dense saline water at the transition zone between freshwater and saltwater causes the confined groundwater to discharge by upward leakage across intervening confining units 

and zones. In addition, stagnant saltwater within sediments 

filling the Chesapeake Bay impact crater has been theorized 

to cause a lateral divergence of flow to either side of the crater 

(McFarland, 2010).

Groundwater withdrawal in the Virginia Coastal Plain 

increased continuously during the past century and totaled 

approximately 130 Mgal/d for the past decade (Masterson and 

others, 2016). An estimated 200,000 small and unregulated 

withdrawals widely span the Virginia Coastal Plain to supply 

primarily individual domestic use (Pope and others, 2008) and 
Introduction 7

probably result in localized water-level declines. Most large 

withdrawals are regulated by the VA DEQ. Regional waterlevel cones of depression as deep as 150 ft below sea level 

are centered on the largest individual withdrawals that supply 

industrial facilities at the cities of Franklin and West Point 

(fig. 1), where all but the deepest part of the aquifer system 

contains freshwater. As a result, the hydraulic gradient across 

the Virginia Coastal Plain has been regionally redirected 

landward and approximately doubled from pre-pumping conditions. Farther east and closer to saltwater, many additional 

large withdrawals supply public drinking water and diverse 

other uses and have an additive effect that contributes to the 

landward hydraulic gradient. Current (2017) region-wide 

rates of water-level decline vary between approximately 1 and 

2 feet per year. In addition, removal of withdrawn water from 

aquifer storage has resulted in sediment compaction and widespread land subsidence (Eggleston and Pope, 2013).

Methods of Investigation

Extents, compositions, configurations, and geologic 

relations of the six geologic units that compose the Piney 

Point aquifer in Virginia were determined. Data were compiled from records on file at the USGS Virginia Water Science 

Center that contain drillers’, geologists’, and geophysical logs 

of 366 boreholes within and in proximity to the productive 

limestone part of the Piney Point aquifer. Geophysical logs of 

165 boreholes were interpreted to distinguish geologic relations and determine extents and altitudes among geologic units 

that compose the Piney Point aquifer. Stratigraphic correlation 

of the geologic units among boreholes was supported by construction of three hydrogeologic sections. The sections were 

oriented to intercept 29 boreholes with the highest quality 

data, including descriptions of sediment core or drill cuttings. 

The geologic units were further delineated by construction 

of seven structural-contour maps that represent the altitudes 

and configurations of their top surfaces, along with that of the 

Nanjemoy Formation Potapaco Member, which forms the base 

of the Piney Point aquifer. Alignments of faults that intercept 

the geologic units and a resurge channel associated with the 

Chesapeake Bay impact crater that truncate some geologic 

units were interpreted from stratigraphic correlation and 

structure-contour mapping.

Petrographic analyses of the productive limestone part 

of the Piney Point aquifer were provided by John T. Haynes 

of James Madison University, Department of Geology and 

Environmental Science. Sediment descriptions from drillers’ 

logs and from geologists’ logs of drill cuttings and sediment 

cores were examined to determine the presence or absence of 

the productive limestone within each borehole and to estimate 

the lateral extent of the productive limestone.

Annual rates of groundwater withdrawals in the Virginia 

Coastal Plain during 1900–2009 were obtained from a groundwater model of the North Atlantic Coastal Plain recently 

developed by USGS (Masterson and others, 2016). Data 

were summarized to distinguish between withdrawals from 

the Piney Point aquifer and those from other aquifers. Large 

industrial, municipal, and commercial withdrawals that are 

regulated by the VA DEQ were distinguished from estimates 

of unregulated domestic withdrawals.

Water-level measurements for the Piney Point aquifer 

were obtained from two sources. Firstly, the USGS National 

Water Information System (NWIS) provided region-wide 

long-term discrete water levels measured during 1906–2015 

in 19 wells and continuously measured water levels during 

March–September 2015 in 4 wells located on the York-James 

Peninsula. Second, continuously measured water levels during 

2008–09 in 10 production wells within the cone of depression 

(Heywood and Pope, 2009) centered on James City County 

were obtained from the James City Service Authority (JCSA). 

Seasonal high and low static water levels were estimated from 

these data by graphical analysis. Water-level measurements 

from both sources were summarized to determine spatial and 

temporal trends. For comparison to water levels on the YorkJames Peninsula, continuously measured rates of withdrawal 

from two production wells during March 6–8, 2015, were 

obtained from the City of Newport News Waterworks. Daily 

rainfall during March 1, 2015–September 23, 2015, was 

downloaded on September 23, 2015, from the Weather Underground Web site for weather station KVAWILLI12.

Hydraulic properties of the Piney Point aquifer were 

estimated from 14 aquifer tests conducted during 1972–2011 

in Virginia and an adjacent part of Maryland. Estimates of 

aquifer transmissivity and storativity were compiled from time 

series water-level measurements and allied aquifer-test data 

on file at the USGS Virginia Water Science Center, and from 

other published sources. Transmissivity values were summarized to determine spatial trends. For comparison, specific 

capacities were compiled from the USGS NWIS records for 

53 wells completed in the Piney Point aquifer in Virginia and 

from a published source (Drummond, 1984) of 123 wells 

in Maryland.

Transmissivities and hydraulic conductivities among, 

and flow interaction between, geologic units that compose 

the Piney Point aquifer were determined by using an aquifer 

test conducted by the VA DEQ in York County during March 

17–19, 2015. Water levels were measured at 1-second intervals during test antecedent, drawdown, and recovery periods. 

Drawdown and recovery data were adjusted for antecedent 

water-level trends using (1) continuously measured tide stages 

compiled from the USGS NWIS of the estuarine James River 

at USGS gaging station 02042222 in Charles City County and 

(2) continuously measured barometric pressure downloaded 

on September 23, 2015, from the Weather Underground Web 

sites for weather stations KVAWILLI19, KVAWILLI20, and 

KVAWILLI21. Early test response of the productive limestone 

was distinguished from late test response of the combined 

geologic units on the basis of a two-layer aquifer conceptual 

model and using the graphical aquifer-test analysis method of 

Cooper and Jacob (1946).
8 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Hydrogeologic Framework of the Piney 

Point Aquifer in Virginia

The Piney Point aquifer spans much of the Coastal Plain 

in Virginia and adjacent parts of Maryland and North Carolina (fig. 1). Although the Piney Point aquifer subcrops along 

major river valleys that cross its westernmost margin, the 

aquifer is entirely confined within the designated study area 

that surrounds the productive limestone from which withdrawals from the aquifer are made (see section “Introduction”). The 

study area spans the Northern Neck, Middle Peninsula, and 

York-James Peninsula in Virginia and part of Maryland near 

the Potomac River (fig. 1; plate 1).

The Piney Point aquifer is one of several aquifers of 

intermediate thickness and depth (fig. 2). It generally consists 

of marine, medium- to coarse-grained, variably fossiliferous 

and calcified quartz, glauconite, and phosphate sand. These 

sediments were deposited across the Atlantic Continental Shelf 

between approximately 11 and 49 million years ago during 

parts of the Eocene, Oligocene, and Miocene Epochs (McFarland and Bruce, 2006). 

The Piney Point aquifer is positioned above silty and 

clayey fine- to medium-grained glauconite and quartz sand and 

clay of the Nanjemoy-Marlboro confining unit across most 

of its extent except within the Chesapeake Bay impact crater, 

where it is above the clay of the Chickahominy confining unit 

(fig. 2). It is positioned below the silty fine-grained quartz sand 

of the Calvert confining unit across most of its extent, except 

to the southwest where it is below the clay and clayey finegrained quartz sand of the Saint Marys confining unit.

Previous Studies

For more than a century, the Piney Point aquifer has been 

designated with increasing specificity. Early hydrologic studies of the Virginia Coastal Plain generally described an aquifer 

consisting of sediments of the Pamunkey and (or) Chesapeake 

Groups or their equivalents, of which individual geologic 

formations that compose the Piney Point aquifer are only parts 

(Darton, 1896; Sanford, 1913; Cederstrom, 1939, 1945, 1946, 

1968; Geraghty and Miller, Consulting Ground-Water Geologists, 1967; Virginia State Water Control Board, 1973; Siudyla 

and others, 1977, 1981; Ellison and Masiello, 1979; Newton 

and Siudyla, 1979; Wigglesworth and others, 1984). Subsequently, several closely timed studies designated the Chickahominy-Piney Point aquifer to include sediments of the Piney 

Point Formation and associated formations (Hamilton and Larson, 1988; Laczniak and Meng, 1988; Meng and Harsh, 1988; 

Harsh and Laczniak, 1990). Similar designation was made for 

equivalent sediments in adjacent states during approximately 

the same period, including the Piney Point aquifer in Maryland 

(Vroblesky and Fleck, 1991) and the Castle Hayne aquifer in 

North Carolina (Winner and Coble, 1996).

Designation by previous studies of the ChickahominyPiney Point aquifer in Virginia was based on sediments that 

are lithologically similar to those of the Piney Point Formation, are thought to be of late Eocene age, and were geologically designated at the time as the Chickahominy Formation. 

Following the discovery of the Chesapeake Bay impact crater, 

sediments of late Eocene age in the Virginia Coastal Plain 

were reclassified (Powars and Bruce, 1999; Powars, 2000). 

The Chickahominy Formation currently (2017) is geologically 

recognized as a clay associated with the impact crater and has 

been hydrologically designated as the Chickahominy confining unit (fig. 3 left side) (McFarland and Bruce, 2006). Hence, 

inclusion of the Chickahominy Formation as part of the Piney 

Point aquifer has been superseded.

Some previous studies included sediments as part of 

the Chickahominy-Piney Point aquifer generally south of the 

James River that are now recognized as composing several 

geologic formations ranging in age from Late Cretaceous 

through late Miocene (Powars, 2000). Accordingly, these 

sediments have been re-designated as composing several other 

hydrogeologic units and are no longer considered part of the 

Piney Point aquifer (McFarland and Bruce, 2006).

Because of their vertical proximity, sediments of several 

individual geologic formations were considered by previous 

studies to be closely connected hydraulically and thereby 

were designated as a single Piney Point aquifer (Hamilton and 

Larson, 1988; Laczniak and Meng, 1988; Meng and Harsh, 

1988; Harsh and Laczniak, 1990; McFarland and Bruce, 2006; 

McFarland, 2010). The sediments were assumed to function 

as a continuous medium through which water moves essentially uninterrupted at local and regional scales. Groundwater 

withdrawal, however, is primarily from a productive solutionchanneled limestone and interbedded sand that compose the 

Piney Point Formation.

Geologic Units

Lithologies and other aspects are individually described 

for the six geologic units that compose the Piney Point aquifer. 

Descriptions are geographically constrained to the designated 

study area surrounding the productive limestone from which 

withdrawals from the Piney Point aquifer are made. Finegrained sediments of confining units that immediately overlie 

and underlie the aquifer are also described.

The geologic units are presented in stratigraphically 

ascending order. Descriptions include sediment geologic 

relations; texture; mineralogic composition; color based on 

the Munsell soil color classification system (Munsell Color, 

1998); borehole resistivity-log signature; and geologic-unit 

extents, top-surface altitudes, and configurations.

The geologic units are based on interpretation undertaken 

during 2013 of drillers’, geologists’, and geophysical logs of 

366 boreholes located within the study area (fig. 1; plate 1); 

logs are on file at the USGS Virginia and West Virginia Water 

Science Center. Geologic relations among, and altitudes of, the 

geologic units were determined from geophysical logs of 165 

of the boreholes and digitally tabulated (Appendix 1; McFarland, 2017). Hydrogeologic sections illustrate the stratigraphic 
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 9

correlation of the geologic units among 29 borehole resistivity 

logs (plate 2).

Altitudes were not tabulated for all geologic units at 

every borehole (Appendix 1; McFarland, 2017). Many boreholes lack geophysical logs and were generally used only to 

determine the presence of limestone of the Piney Point Formation on the basis of drillers’ logs (see section “Piney Point 

Formation”). Typically in these instances, only the top-surface 

altitude of the Piney Point Formation is tabulated if the limestone is present. Additionally, among boreholes having geophysical logs, not all are deep enough to intercept all geologic 

units. The quality of parts of some geophysical logs precludes 

the interpretation of some geologic-unit altitudes. Two of the 

geologic units are present only at a relatively small number of 

boreholes in the northeastern part of the study area.

A series of structural-contour maps delineate top-surface 

altitudes and configurations of the geologic units, along with 

the underlying fine-grained sediments that form the base of 

the Piney Point aquifer. Top surfaces are contoured only to 

the extent of boreholes used in this study. Most geologic units 

span westward beyond the boreholes and are approximated 

by the generalized western limit of the Piney Point aquifer 

(McFarland and Bruce, 2006). Two of the geologic units are 

constrained to the far northeast and are represented by separate 

western limits. At eastward locations, most of the geologic 

units were either excavated by, or have not been preserved 

within, the Chesapeake Bay impact crater. Borehole data along 

the impact crater, however, are not adequate to delineate these 

margins, which are likely highly complex.

The geologic units are designated here in a hydrologic 

context and are based primarily on litho-stratigraphic correlation. By contrast, formally recognized geologic formations 

represent specific intervals of time. Although geologic formations can exhibit a single typical lithology, sediment composition within a formation commonly varies as a result of changing depositional environments or in proximity to formation 

contacts where burrowing or other forms of sediment reworking have occurred. Interpretation of borehole geophysical logs 

cannot solely provide a reliable basis to determine formation 

contacts but can discern differences in sediment lithology. 

Moreover, differences in sediment lithology that affect their 

hydraulic properties are of primary importance for characterizing groundwater systems.

Accordingly, the geologic units are designated primarily 

on the basis of distinct sediment lithologies that are generally typical of their corresponding geologic formations and 

have assigned their names. Stratigraphic contacts among the 

geologic units, however, are not everywhere identical to those 

among the formally recognized geologic formations. Where 

known or suspected, differences from recognized formations 

are noted among individual descriptions of the geologic units.

Nanjemoy Formation Potapaco Member

Within the study area, fine-grained sediments of the Potapaco Member of the Nanjemoy Formation underlie and form 

the base of the Piney Point aquifer. The Nanjemoy Formation 

Potapaco Member along with the deeper Marlboro Clay are 

together hydrologically designated as the Nanjemoy-Marlboro 

confining unit (fig. 3, left side) (McFarland and Bruce, 2006). 

Most of the Piney Point aquifer outside the study area is also 

underlain by the Nanjemoy-Marlboro confining unit, which 

is as thick as several tens of feet or more at depths as much as 

several hundred feet (fig. 2). The Nanjemoy-Marlboro confining unit functions hydraulically as a continuous medium that 

regionally impedes horizontal flow but allows relatively slow, 

vertical groundwater movement as leakage between overlying 

and underlying aquifers.

The Nanjemoy Formation Potapaco Member is composed 

of early Eocene-age, marine, silty and clayey, fine- to mediumgrained glauconite and quartz sand (figs. 4 and 5). Sediment 

core and drill cuttings exhibit colors varying among greenish black (10G 2.5/1; Munsell Color, 1998), very dark gray 

(5Y 3/1), dark olive gray (5Y 3/2), greenish gray (10Y 5/1), 

and dark greenish gray (5GY 3/1 and 10GY 4/1). Borehole 

resistivity logs generally exhibit a relatively flat signature 

typical of fine-grained sediments with some variation resulting from differences in silt and (or) clay content (figs. 4 and 5, 

plate 2).

The top surface of the Nanjemoy Formation Potapaco 

Member, and therefore the base of the Piney Point aquifer, 

dips eastward (fig. 6; plate 2, sections A-A' and B-B'). The 

top-surface altitude within the study area ranges from 22 ft at 

borehole 53K 21 in New Kent County to -516 ft at borehole 

60L 21 in Northumberland County. The configuration of the 

top surface is further affected by faults (see section “Faults”).

Exclusive of the Chesapeake Bay impact crater, sediments of the Nanjemoy Formation Potapaco Member span the 

entire study area and beyond. Top-surface altitude contours, 

however, are drawn for this study only as far as the extent 

of boreholes located within the study area. The Nanjemoy 

Formation Potapaco Member is absent in several boreholes in 

Gloucester and Middlesex Counties in proximity to the impact 

crater (fig. 6) and is truncated in the same area by a resurge 

channel associated with the impact crater (plate 2, section 

B-B') (see section “Impact-Crater Resurge Channel”). The 

Nanjemoy Formation Potapaco Member originally spanned 

at least part of the area of the impact crater but was excavated 

during the impact event (Powars and Bruce, 1999). Disrupted 

clasts of the Nanjemoy Formation Potapaco Member are common throughout sediments that now fill the impact crater.

Nanjemoy Formation Woodstock Member

Within the study area, coarse-grained sediments of 

the Woodstock Member of the Nanjemoy Formation form 

the lowermost part of the Piney Point aquifer (fig. 3, right 

side). The Nanjemoy Formation Woodstock Member is 

composed of early Eocene-age, marine, variably shelly and 

pebbly, medium- to coarse-grained quartz and glauconite 

sand (figs. 4 and 5). Sediment core and drill cuttings exhibit 

colors varying among greenish gray (10Y 5/1), light greenish 
10 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia -135 -140 -145 -150 -155 -160 -165

-170-175-180

Depth, in feet relative to National Geodetic Vertical Datum of 1929

-152 

-148 

-139 

-176 -182 

-179 

Calvert Formation fine-grained Plum Point Member Calvert Formation, Newport News unit and basal Plum Point Member Old Church Formation 

Borehole

interval

Resistivity

curve 

Lithologic

contact and

altitude

Sediment

core position

and altitude 

Increasingresistivity

Silty, fine- to medium-grainedquartz, glauconite,and phosphate sand 

Silty, shelly and pebbly, medium- to coarse-grained quartz and phosphate sand

Silty and clayey, microfossiliferous,fine-grainedquartz sand 
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 11

-175-180-185-190-195-200-205-210-215

Depth, in feet re

-176 -182 -197 -204 

-179 

-185 -191 -195 -198 -211 

Old Church Formation Piney Point Formation Nanjemoy Formation Woodstock Member Nanjemoy Formation Potapaco Member

Off scale Off scale 

Silty and clayey, fine- to medium-grained glauconite sand and quartz 

Pebbly, medium- to coarse-grained quartz and glauconite sand

Moldic calcite-cemented, shelly and pebbly,medium- to coarse-grained quartz and glauconite sand 

y, 

g

quartz, glauconite,and phosphate sand 

Figure 4. Representative sediment lithologies and resistivity log from the Banbury Cross corehole (USGS well number 57G128), York County, Virginia. Sediment-core sections and samples are shown at approximate actual size. Altitudes are in feet relative to National Geodetic Vertical Datum of 1929. Corehole location shown on plate 1. Photos of sediment core by T. Scott Bruce, Virginia Department of Environmental Quality, and of Piney Point limestone samples by David Powars, U.S. Geological Survey.
12 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia -300 -310 -320 -330 -340 -350 -360 -370

-380-390-400

Depth, in feet relative to National Geodetic Vertical Datum of 1929 Oligocene- age sediments

-349 

-346 

-342 

-336 

-328 

-318 

-375 

-403 

-361 

-384 

Calvert Formation, Newport News unit and basal Plum Point Member 

Calvert Formation fine-grained Plum Point Member Old Church Formation Gosport Formation equivalent sediments 

Silty, fine- to medium-grained quartz, glauconite, and phosphate sand 

Silty, shelly, medium- to coarse-grained quartz sand 

Silty and clayey, microfossiliferous, fine-grained quartz sand 

Silty and clayey, microfossiliferous,fine-grained quartz and glauconite sand 

Silty, shelly, medium- to coarse-grained quartz, glauconite, and phosphate sand 

Borehole

interval

Resistivity

curve 

Lithologic

contact and

altitude

Sediment

core position

and altitude 

Increasingresistivity
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 13

-390-400-410-420-430-440-450-460-470-480

Depth, in feet re

-403 

-432 -466 

-418 

-424 

-435 

-474 

Formation equivalent sediments Piney Point Formation Nanjemoy Formation Woodstock Member Nanjemoy Formation Potapaco Member Silty and clayey, fine- to 

medium-grained glauconite and quartz sand 

Shelly, medium- to coarse-grained quartz and glauconite sand

Massive calcite-cemented, shelly and pebbly, medium- to coarse-grained quartz and glauconite sand 

Pebbly, medium- to coarse-grained quartz and glauconite sand 

microfossiliferous,fine-grained quartz and glauconite sand 

Figure 5. Representative sediment lithologies and resistivity log from the Surprise Hill corehole (USGS well number 60L 22), Northumberland County, Virginia. Sediment-core sections are shown at approximate actual size. Corehole location shown on plate 1. Correlation to other boreholes shown on plate 2, section A-A’. Altitudes are in feet relative to National Geodetic Vertical Datum of 1929. All photos by T. Scott Bruce, Virginia Department of Environmental Quality.
14 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Rappahannock River

Pamunkey River Mattaponi River

Chickahominy River

James River

York River

P O T O M A C R I V E R

Rappahannock River

C

H

E

S

A

P

E

A

K

E

B

A

Y

James River

CAROLINE

COUNTY

HANOVER

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Poquoson

City of

Hopewell

City of

Williamsburg

NORTHUMBERLAND COUNTY

City of

Newport News

HENRICO

COUNTY

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

Chesapeake

Bay impact

crater

Resurge

channel

N

O

R T H

E R N

N E C K

M I D

D

L

E

P

E

N

I

N S U L A

Y

O

R

K - J

A M E S

P E N I N S U L A

A

A'

B

B'

C

C'

A

A'

B

B'

C

C'

D

D

D

D

D

U

U

D

U

U

U

U

U

U

U

D

D

U

LIMIT

OF PINEY POINT A

Q

UIFER

77°15' 77° 76°45' 76°30' 76°15'

38°15'

38°

37°45'

37°30'

37°15'

MARYLAND

VIRGINIA

PIEDMONT COASTAL PLAIN 

APPALACHIAN 

BLUE RIDGE

Fall zone

PLATEAUS

Physiographic provinces in Virginia

VALLEY AND RIDGE

Extent of

study area

-50

-150

-100

-200

-250

0

-300

-350

-400

-450

-500

-300

-350

-400

-353

5

22

11

-6

10

21

-73

-79

-77

-75

-89

-81

-87

-38

-26

-82

-91

-68

-48 -87 -46

-42

-21

-22

-27

-13

-42

-38

-34

-30

-12 -19

-20

-24

-204

-153

-423

-463

-462

-466

-516

-454

-401

-389

-352

-387

-379

-434

-435

-258

-249

-322

-315 -330

-290

-291 -320

-252

-346 -341

-180

-200

-194

-218

-240

-242

-244

-217

-248

-266

-259

-252

-234

-251

-253

-213

-250

-222

-278

-230

-292

-223

-211 -212

-156

-111

-172 -191

-197

-147

-148

-202

-163

-214

-173

-185

-167

-187

-148

-170

-168 -139

-166

-131

-197

-190

-188

-187

-184

-198

-131

-184

-174

-115

-123

-164

-110

-155

-124

-109

-112

-169.8

-172.5

-180.5

-296

-358

-287

-174

-175

-187

-188

-192

-193

-146.8

-387

-396

-401

-500 -501

-140

-188

-132

-219

-202

-194

-241

-273

-185

-132.4

-164.2

-189

-289

-291

0 8 16 MILES

0 8 16 KILOMETERS

EXPLANATION

Line of hydrologic section

Line of equal altitude—Interval is 

50 feet. Datum is NGVD 1929

Fault and up (U) and down (D) 

blocks

Borehole location

Number is altitude of top surface, 

in feet. Datum is NGVD 1929

Unit is absent

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500 000

A A'

-50

-22

D

U

Figure 6. Altitude and configuration of the top surface of the Nanjemoy Formation Potapaco Member across the 

Northern Neck, upper Middle Peninsula, and upper York-James Peninsula in Virginia.
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 15

gray (10GY 7/1), light brownish gray (10YR 6/2), and light 

olive (10Y 5/4). Borehole resistivity logs generally exhibit 

an upward increasing signature that indicates a coarseningupward texture (figs. 4 and 5; plate 2). Some sediments 

included here possibly are overlying sand of the lowermost 

part of the Piney Point Formation that is not interbedded with 

limestone (see section “Piney Point Formation”) and is contiguous with the Nanjemoy Formation Woodstock Member.

The top surface of the Nanjemoy Formation Woodstock 

Member dips eastward (fig. 7; plate 2, sections A-A' and 

B-B'). Top-surface altitude within the study area ranges from 

48 ft at borehole 53K 21 in New Kent County to -493 ft at 

borehole 60L 21 in Northumberland County. The thickness 

of the Nanjemoy Formation Woodstock Member ranges from 

0 to more than 30 ft but in most boreholes is between 10 and 

20 ft (plate 2). The configuration of the Nanjemoy Formation 

Woodstock Member is further affected by faults (see section “Faults”).

Exclusive of the Chesapeake Bay impact crater, sediments of the Nanjemoy Formation Woodstock Member span 

most of the study area. The Nanjemoy Formation Woodstock 

Member is absent in several boreholes in Gloucester and 

Middlesex Counties in proximity to the impact crater (fig. 7) 

and is truncated in the same area by a resurge channel associated with the impact crater (plate 2, section B-B') (see section 

“Impact-Crater Resurge Channel”). The Nanjemoy Formation 

Woodstock Member originally spanned at least part of the area 

of the impact crater but was excavated during the impact event 

(Powars and Bruce, 1999).

The Nanjemoy Formation Woodstock Member is also 

absent in borehole 54G 10 in Charles City County (fig. 7) 

where it pinches out southeastward (plate 2, section B-B'). At 

borehole 54G 10, the Piney Point aquifer is composed of only 

the Calvert Formation, Newport News unit and basal Plum 

Point Member. The Nanjemoy Formation Woodstock Member is also absent in several boreholes to the north in eastern 

Westmoreland County and Maryland, and to the south in Surry 

County. Continuity of the Nanjemoy Formation Woodstock 

Member to the north and south of the study area is uncertain.

Piney Point Formation

Within the study area, coarse-grained sediments of the 

Piney Point Formation form the next to lowest part of the 

Piney Point aquifer (fig. 3, right side), from which most 

groundwater from the aquifer is withdrawn. The Piney Point 

Formation is composed of middle Eocene-age, marine, variably shelly, pebbly, and calcite-cemented, medium- to coarsegrained quartz and glauconite sand (figs. 4 and 5). Sediment 

core and drill cuttings exhibit colors ranging from greenish 

gray (10Y 5/1) and light bluish gray (5B 7/1 and 10B 7/1) 

to yellow (2.5Y 7/6) and olive yellow (2.5Y 6/6). Borehole 

resistivity logs exhibit an elevated signature typical of coarsegrained sediments with some variation resulting from differences in sand texture and (or) degree of cementation (figs. 4 

and 5; plate 2). Resistivity on some logs extends off the scale.

The top surface of the Piney Point Formation dips 

eastward (fig. 8; plate 2, sections A-A' and B-B'). Top-surface 

altitude within the study area ranges from 53 ft at borehole 

53H 13 in Henrico County to -479 ft at borehole 60L 21 in 

Northumberland County. Thickness of the Piney Point Formation ranges from 0 to nearly 50 ft, but in most boreholes 

is between 20 and 40 ft (plate 2). The configuration of the 

Piney Point Formation is further affected by faults (see section “Faults”).

Exclusive of the Chesapeake Bay impact crater, sediments of the Piney Point Formation span most of the study 

area. The Piney Point Formation is absent in several boreholes 

in Gloucester and Middlesex Counties in proximity to the 

impact crater (fig. 8) and is truncated in the same area by a 

resurge channel associated with the impact crater (plate 2, section B-B') (see section “Impact-Crater Resurge Channel”). The 

Piney Point Formation originally spanned at least part of the 

area of the impact crater but was excavated during the impact 

event (Powars and Bruce, 1999). Disrupted clasts of the Piney 

Point Formation, including limestone, are common throughout 

sediments that now fill the impact crater.

The Piney Point Formation is also absent in several 

boreholes in northwestern Westmoreland and Essex Counties 

(fig. 8) where it pinches out westward (plate 2, section A-A'). 

Here the Piney Point aquifer is composed of only the Calvert 

Formation, Newport News unit and basal Plum Point Member, 

and the Nanjemoy Formation Woodstock Member. The Piney 

Point Formation also is absent in borehole 54G 10 in Charles 

City County where it pinches out southeastward (plate 2, 

section B-B'). At borehole 54G 10, the Piney Point aquifer is 

composed of only the Calvert Formation, Newport News unit 

and basal Plum Point Member.

Composition of Limestone

Unique to the Piney Point Formation, calcite cementation that is well developed forms substantial intervals of 

indurated limestone. Cementation also can be present in other 

geologic units but is generally isolated in single beds, commonly referred to as “ledges.” Limestone in the Piney Point 

Formation exhibits either a highly porous solution-channeled 

moldic structure (fig. 4, fig. 9A, left side) or a low-porosity 

massive structure (fig. 5, fig. 9A, right side). Production wells 

completed in moldic limestone yield as much as 400 gal/min; 

massive limestone probably accounts for other wells having considerably lower yields. The limestone is commonly 

interbedded with uncemented sand (fig. 9B). Where limestone 

intervals are sufficiently thick and structurally competent, 

some production wells have been completed below their casings as open boreholes in the limestone, commonly referred to 

as “barefoot” wells. By contrast, where cementation has not 

developed, limestone is absent from the Piney Point Formation, which consists entirely of uncemented sand in which 

wells must be screened. Some uncemented sand of the lowermost part of the Piney Point Formation that is not interbedded 

with limestone possibly is included in the underlying Nanje-
16 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Rappahannock River

Pamunkey River Mattaponi River

Chickahominy River

James River

York River

P O T O M A C R I V E R

Rappahannock River

C

H

E

S

A

P

E

A

K

E

B

A

Y

James River

CAROLINE

COUNTY

HANOVER

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Poquoson

City of

Hopewell

City of

Williamsburg

NORTHUMBERLAND COUNTY

City of

Newport News

HENRICO

COUNTY

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

Chesapeake

Bay impact

crater

Resurge

channel

N

O

R T H

E R N

N E C K

M I D

D

L

E

P

E

N

I

N S U L A

Y

O

R

K - J

A M E S

P E N I N S U L A

A

A'

B

B'

C

C'

A

A'

B

B'

C

C'

D

D

D

D

D

U

U

D

U

U

U

U

U

U

U

D

D

U

LIMIT

OF PINEY POINT A

Q

UIFER

77°15' 77° 76°45' 76°30' 76°15'

38°15'

38°

37°45'

37°30'

37°15'

MARYLAND

VIRGINIA

PIEDMONT COASTAL PLAIN 

APPALACHIAN 

BLUE RIDGE

Fall zone

PLATEAUS

Physiographic provinces in Virginia

VALLEY AND RIDGE

Extent of

study area

1

9

4

3

-2

-7

48

-4

21

19

24 -1

-1 31

-7

-93

-54

-58

-61

-51

-79

-95

-19

-12

-96

-65

-65

-42

-14

-62 -14

-18

-404

-429

-426

-432

-441

-370

-361

-319

-367

-363

-410

-414

-242 -274

-224

-286

-319

-278

-274

-243 -337

-331

-204

-223

-225

-228

-204

-230

-248

-241

-192

-207

-224

-195

-267

-273

-143

-142 -160

-179

-131

-132

-178

-198

-167

-173

-136

-157

-154

-124

-156

-155

-120

-119

-172

-172

-130

-155 -175 -158

-103

-116

-104

-101

-152.2

-169.5

-20

-275

-170

-169

-171

-174

-132.8

-300

-493

-383

-379

-169

-165

-118.4

-168

-145

-151

-337

-326

-300

-303

-239

-197

-190

-193

-261

-267

-247

-220

-246

-244

-159

-171

-174

-135

-476 -471

-157

-159

-161

-175

-157.8

-206

-390

0

-50

-250

-150

-200

-100

-300

-350

-400

-450

50

-350

0 8 16 MILES

0 8 16 KILOMETERS

EXPLANATION

Line of hydrologic section

Line of equal altitude—Interval is 

50 feet. Datum is NGVD 1929

Fault and up (U) and down (D) 

blocks

Borehole location

Number is altitude of top surface, 

in feet. Datum is NGVD 1929

Unit is absent

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500 000

A A'

-50

-42

D

U

Figure 7. Altitude and configuration of the top surface of the Nanjemoy Formation Woodstock Member across the 

Northern Neck, upper Middle Peninsula, and upper York-James Peninsula in Virginia.
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 17

Rappahannock River

Pamunkey River Mattaponi River

Chickahominy River

James River

York River

P O T O M A C R I V E R

Rappahannock River

C

H

E

S

A

P

E

A

K

E

B

A

Y

James River

CAROLINE

COUNTY

HANOVER

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Poquoson

City of

Hopewell

City of

Williamsburg

NORTHUMBERLAND COUNTY

City of

Newport News

HENRICO

COUNTY

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

Chesapeake

Bay impact

crater

Resurge

channel

N

O

R T H

E R N

N E C K

M I D

D

L

E

P

E

N

I

N S U L A

Y

O

R

K - J

A M E S

P E N I N S U L A

A

A'

B

B'

C

C'

A

A'

B

B'

C

C'

D

D

D

D

D

U

U

D

U

U

U

U

U

U

U

D

D

U

LIMIT

OF PINEY POINT A

Q

UIFER

77°15' 77° 76°45' 76°30' 76°15'

38°15'

38°

37°45'

37°30'

37°15'

MARYLAND

VIRGINIA

PIEDMONT COASTAL PLAIN 

APPALACHIAN 

BLUE RIDGE

Fall zone

PLATEAUS

Physiographic provinces in Virginia

VALLEY AND RIDGE

Extent of

study area

-150

-100

-200

0

-50

-250

-300

-350

-400

-450

50

3

4

5

6

22

16

22

43

30

35 27

22 53 22

17

-98

-99

-59

-78

-96

-71

-99 -89

-78

-71

-46

-41

-14

-43

-182

-123

-373

-401

-399

-403

-428

-350

-330

-330

-388

-209

-235

-193

-240

-281

-250

-249

-208

-156

-185

-186

-196

-189

-176

-219

-219

-216

-182

-192

-219

-211

-161

-165

-216

-249

-250

-219

-203

-254

-222

-198

-205 -213

-123

-125 -131

-153

-111

-114

-154

-141

-120

-132

-119

-143

-133

-132

-132

-131

-103

-101

-115

-138

-122

-139

-133

-105

-121

-90.4

-112.2

-104.8

-126.5

19

-253

-190

-239

-121

-127

-144

-148

-145

-146

-144

-140

-151

-147

-98.8

-108.5

-172

-180

-166

-262

-360

-354

-369

-390

-279

-286

-245

-273

-335

-479

-459

-455

-301

-319

-317

-149.5 -210

-150

-180

-206

-148

-192

0 8 16 MILES

0 8 16 KILOMETERS

EXPLANATION

Extent of productive limestone

Line of hydrologic section

Line of equal altitude—Interval is 

50 feet. Datum is NGVD 1929

Fault and up (U) and down (D) 

blocks

Borehole location

Number is altitude of top surface, 

in feet. Datum is NGVD 1929

Unit is absent

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500 000

A A'

-50

-46

D

U

Figure 8. Altitude and configuration of the top surface of the Piney Point Formation across the Northern Neck, upper 

Middle Peninsula, and upper York-James Peninsula in Virginia.
18 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

A

B

Moldic cementation Massive cementation

Altitude: -195 feet Altitude: -198 feet Altitude: -196 feet

Figure 9. Representative examples of 

limestone of the Piney Point Formation 

in Virginia. A, Contrasting cementation 

among slabbed samples from Haynesville 

borehole 57M 7, Richmond County, Virginia 

(from Mixon and others, 1989). Examples 

are shown at approximately actual size. B, 

Photograph from video log of open-hole 

“barefoot” borehole 55H 30, New Kent 

County, Virginia. View is downward from 

altitude -92 feet relative to the National 

Geodetic Vertical Datum of 1929. Depth 

below land surface is shown on the photo. 

Borehole diameter is approximately 4 

inches. Drilled limestone ledges alternate 

with beds of unconsolidated sand to form 

a counterclockwise corkscrew pattern 

along the borehole wall. Video logging 

performed by the Virginia Department of 

Environmental Quality. Borehole locations 

are shown on plate 1.

moy Formation Woodstock Member (see section “Nanjemoy 

Formation Woodstock Member”). Conversely, some overlying sand of the lowermost part of the Old Church Formation 

possibly is included in the Piney Point Formation (see section 

“Old Church Formation”).

Petrographic analyses of limestone of the Piney Point 

Formation were performed by John Haynes at James Madison 

University, Department of Geology and Environmental Science. Thin sections were fabricated of limestone samples collected at altitudes from -185 ft to -192 ft in the Banbury Cross 

corehole (USGS well number 57G128; plate 1; Appendix 1; 

McFarland, 2017) from which a continuous sediment core was 

obtained by the VA DEQ during 2014. Examination of hand 

specimens and thin sections produced the following description of the limestone (J.T. Haynes, James Madison University, 

written commun., 2016):

Textures of hand samples are medium to very 

coarse grained, with many shell fragments reaching or exceeding 1 inch (in.) in the long dimension. 

Thin sections exhibit impure limestones including 

bioclastic grainstones and packstones, with very 

minor areas of patchy wackestones. Non-carbonate 

framework grains and cements are variable but compose less than 50 percent of the sample. Framework 

grains consist of various aluminosilicate and phosphate minerals subordinate to abundant calcareous 

bioclasts.
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 19

Principal framework grains are pelecypod fragments 

(70 to 75 percent of the framework grain population), monocrystalline quartz (5 to 10 percent), glauconite and collophane (5 to 10 percent), ostacode 

fragments (1 to 3 percent), polycrystalline quartz 

including some that are extensively fractured (1 to 

3 percent), and bioclastic debris including bryozoans, calcareous algae, echinoderms, gastropods, and 

forams (1 to 3 percent). A few large bioclasts are 

broken in one or more places, probably as a result 

of reworking by currents subsequent to death of the 

organism and disarticulation. Some small bioclasts 

are also fragmental, but unbroken and nearly whole 

forams, gastropods, and bryozoans are present as 

well. Quartz, glauconite, and collophane grains are 

subangular to rounded, indicating moderate to extensive transport and reworking in the marine environment. Packing of quartz, glauconite, and collophane 

grains is minimal, and many grains appear to be 

matrix supported rather than grain supported. Minimal compaction possibly was followed by relatively 

early cementation.

Ferroan and non-ferroan calcite and dolomite were 

differentiated in thin section by staining using the 

standard procedure of Dickson (1965). Most framework grains are cemented by equant to sub-equant 

sparry non-ferroan calcite or by isopachous non-ferroan calcite. Equant to sub-equant sparry calcite has 

also partly to completely replaced the original shell 

structure of much of the pelecypod bioclastic debris. 

The matrix consists of micrite and a few patchy 

areas with a small percentage of aluminosilicate 

clay minerals (based on the brown color of these 

regions). This matrix of mixed carbonate and likely 

sparse aluminosilicate minerals acts as a cement. 

Other secondary cement minerals include pyrite as 

cubes and framboids that partly to nearly completely 

replace some glauconite grains. Pyrite is abundant 

to numerous as small matrix-supported grains in 

micrite, and as variably sized grains in some large 

biomoldic pores that developed as pelecypod fragments were dissolved or destroyed.

Porosity is predominantly biomoldic and relatively 

abundant. Most large pores are partly to completely 

dissolved or destroyed pelecypod fragments. Some 

biomoldic pores are rimmed with crusts of isopachous non-ferroan calcite. Some of the distinctive 

reticulate pores of the original stereomic microstructure in a few echinoderm fragments have been 

filled by glauconite. Many glauconite grains also 

exhibit sparse to abundant grain moldic porosity. Minor fracture porosity is also present. A few 

collophane grains have complex internal structure, 

including fractures that have been reduced—and 

in some grains completely filled—by glauconite. A 

few glauconite grains likewise have fractures that 

are now reduced by collophane. In some collophane 

grains, the fracture pattern gives the appearance of a 

micro-septarian nodule despite the small sand size of 

the grains.

Extent of Limestone

The presence of limestone within the Piney Point Formation largely determines the productivity of wells in the Piney 

Point aquifer. The lateral extent of the limestone, however, 

has been only approximately known on the basis of anecdotal 

experience and not delineated systematically. Moreover, the 

limestone is not distinguishable from uncemented sand based 

solely on borehole geophysical logs.

To address the above, the lateral extent of limestone 

in the Piney Point Formation was estimated on the basis of 

sediment descriptions. Drillers’ logs, and geologists’ logs of 

drill cuttings and sediment core, were examined to determine 

the presence or absence of limestone across corresponding 

intervals within each borehole within the study area (fig. 1; 

plate 1). An area was then delineated to represent where the 

limestone is relatively continuous laterally. A belt approximately 10 mi wide spans northwestern Northumberland 

County and southeastern Richmond and Essex Counties, and 

broadens to nearly 30 mi southward across King and Queen 

County, Middlesex County, eastern King William and New 

Kent Counties, and western Gloucester County. Farther southward, laterally continuous limestone narrows to approximately 

10 mi across James City County, northernmost York County, 

and the City of Williamsburg. Laterally continuous limestone 

does not extend south of the James River.

From the main area of laterally continuous limestone, a 

second narrow belt approximately 5 mi wide extends to the 

northwest across parts of Westmoreland, Richmond, Essex, 

and King and Queen Counties (fig. 1; plate 1). Delineation of 

this additional area, however, is based on only five boreholes 

that indicate the presence of limestone. Lateral continuity is 

less certain than for the main area.

The Piney Point Formation within the delineated areas 

consists mostly of limestone interbedded with uncemented 

sand (fig. 9B). Sediment descriptions from most boreholes 

within the delineated areas indicate the presence of limestone, but a minority of boreholes indicate that it is absent 

where cementation has not developed. Conversely, outside the 

delineated areas the Piney Point Formation consists mostly 

of uncemented sand. Most boreholes outside the delineated 

areas indicate that the limestone is absent, but a minority of 

boreholes indicate it is present at relatively isolated locations 

where cementation has developed. In addition, the number 

and density of boreholes varies and is generally smaller to the 

north. Given greater borehole coverage, continuous limestone 

would possibly have been delineated differently.

Within the delineated areas of laterally continuous limestone, the maximum altitude of the Piney Point Formation is 

approximately -40 ft (fig. 8). Hence, the limestone is entirely 
20 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

in the subsurface and does not crop out. The Piney Point 

Formation in Virginia is stratigraphically correlative to the 

Castle Hayne Formation in North Carolina (Winner and Coble, 

1996). Limestone of the Castle Hayne Formation is extensively developed but is not laterally continuous with that of 

the Piney Point Formation in Virginia. Deposition of carbonate 

sediments either did not take place or was not preserved across 

the intervening Norfolk arch.

Limestone of the Castle Hayne Formation in North Carolina was deposited in a tropical marine environment (Baum, 

1980). Limestone of the Piney Point Formation in Virginia 

also was probably deposited in similarly warm conditions. By 

contrast, farther north in Maryland the Piney Point Formation is described as a glauconitic sand (Andreasen and others, 

2013). Limestone that dominates the productive part of the 

Piney Point aquifer in Virginia possibly is poorly developed 

across much of Maryland. Cold ocean temperatures north of 

Virginia during the Eocene Epoch possibly precluded deposition of carbonate sediments.

Gosport Formation Equivalent Sediments

Fine-grained sediments that are equivalent in age to the 

Gosport Formation form an intermediate part of the Piney 

Point aquifer (fig. 3, right side). On the basis of microfossil 

analysis (L.E. Edwards, U.S. Geological Survey, written commun., 2007), the presence of sediments of late middle Eocene 

age that are equivalent to the Gosport Formation in Georgia 

was determined in the Surprise Hill core (borehole 60L 22) in 

Northumberland County (plate 1). The Surprise Hill core is the 

first known presence of sediments of this age in the Virginia 

Coastal Plain outside of the Chesapeake Bay impact crater.

Gosport Formation equivalent sediments are composed 

of middle Eocene-age, marine, silty and clayey, variably 

microfossiliferous and pebbly, fine- to medium-grained quartz 

and glauconite sand (fig. 5). The Surprise Hill core exhibits a 

fairly uniform color of dark greenish gray (10Y 4/1). Borehole 

resistivity logs exhibit a uniformly flat signature typical of 

fine-grained sediments but with a distinctive broad U-shaped 

profile (fig. 5; plate 2).

The top surface of the Gosport Formation equivalent 

sediments dips eastward (fig. 10; plate 2, sections A-A' and 

B-B'). The top-surface altitude within the study area ranges 

from -274 ft at borehole 58L 7 in Lancaster County to -431 ft 

at well 60L 21 in Northumberland County. Thickness of the 

Gosport Formation equivalent sediments ranges from 0 to 

approximately 50 ft, but in most boreholes is approximately 

30 ft (plate 2).

Gosport Formation equivalent sediments span only the 

most northeastern part of the study area on the eastern Northern Neck and in Middlesex County (fig. 10). The distinctive 

U-shaped profile exhibited by the resistivity log from the 

Surprise Hill corehole (borehole 60L 22) was correlated to 

resistivity logs from 21 other boreholes to infer the presence 

of Gosport Formation equivalent sediments. This signature 

does not appear on resistivity logs from boreholes located to 

the west where Gosport Formation equivalent sediments pinch 

out (plate 2, sections A-A' and B-B').

Gosport Formation equivalent sediments are also absent 

in several boreholes to the south in Gloucester and Middlesex 

Counties in proximity to the Chesapeake Bay impact crater 

(fig. 10) and are truncated by a resurge channel associated with 

the impact crater (plate 2, section B-B') (see section “ImpactCrater Resurge Channel”). Gosport Formation equivalent sediments possibly originally spanned at least part of the area of 

the impact crater but were excavated during the impact event.

Where Gosport Formation equivalent sediments are 

present, the Piney Point aquifer differs from elsewhere. Total 

thickness of the Piney Point aquifer is substantially increased 

(plate 2, sections A-A' and B-B'). Moreover, the fine-grained 

sediments create a large vertical separation between coarsergrained underlying and overlying sediments that compose 

other parts of the aquifer. The Piney Point aquifer is thereby 

effectively divided vertically into distinct upper and lower 

aquifers. Conversely, where Gosport Formation equivalent 

sediments are absent across most of the study area, coarsegrained sediments that compose different parts of the Piney 

Point aquifer are in closer vertical proximity or direct contact.

Oligocene-Age Sediments

Coarse-grained sediments of Oligocene age form an 

intermediate part of the Piney Point aquifer (fig. 3, right side). 

On the basis of microfossil analysis (L.E. Edwards, U.S. Geological Survey, written commun., 2007), the presence of sediments of Oligocene age was determined in the Surprise Hill 

core (borehole 60L 22) in Northumberland County (plate 1). 

Oligocene-age sediments are composed of marine, silty, shelly, 

medium- to coarse-grained quartz, glauconite, and phosphate 

sand (fig. 5). The Surprise Hill sediment core and drill cuttings 

from borehole 59K 36 in Lancaster County (plate 1) exhibit 

colors ranging from greenish gray (5GY 5/1) to dark olive 

gray (5Y 3/2) and black (5Y 2.5/1 and 5Y 2.5/2). Borehole 

resistivity logs exhibit an elevated signature typical of coarsegrained sediments with some variation resulting from differences in sand texture and silt content. Some overlying sand 

of the lowermost part of the Old Church Formation possibly 

is included with the Oligocene-age sediments (see section 

“Old Church Formation”). Conversely, some Oligocene-age 

sediments possibly are included with the overlying Calvert 

Formation, Newport News unit and basal Plum Point Member 

(see section “Calvert Formation, Newport News unit and basal 

Plum Point Member”).

The top surface of the Oligocene-age sediments dips 

eastward (fig. 11; plate 2, sections A-A' and B-B'). The topsurface altitude within the study area ranges from -266 ft at 

borehole 58L 7 in Lancaster County to -421 ft at well 60L 21 

in Northumberland County. The thickness of the Oligoceneage sediments ranges from 0 to more than 20 ft, but in most 

boreholes, it is approximately 10 ft (plate 2).

Oligocene-age sediments span only the most northeastern 

part of the study area on the eastern Northern Neck and in 
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 21

Rappahannock River

Pamunkey River Mattaponi River

Chickahominy River

James River

York River

P O T O M A C R I V E R

Rappahannock River

C

H

E

S

A

P

E

A

K

E

B

A

Y

James River

CAROLINE

COUNTY

HANOVER

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Poquoson

City of

Hopewell

City of

Williamsburg

NORTHUMBERLAND COUNTY

City of

Newport News

HENRICO

COUNTY

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

Chesapeake

Bay impact

crater

Resurge

channel

N

O

R T H

E R N

N E C K

M I D

D

L

E

P

E

N

I

N S U L A

Y

O

R

K - J

A M E S

P E N I N S U L A

A

A'

B

B'

C

C'

A

A'

B

B'

C

C'

D

D

D

D

D

U

U

D

U

U

U

U

U

U

U

D

D

U

LIMIT

OF PINEY POINT A

Q

UIFER

77°15' 77° 76°45' 76°30' 76°15'

38°15'

38°

37°45'

37°30'

37°15'

MARYLAND

VIRGINIA

PIEDMONT COASTAL PLAIN 

APPALACHIAN 

BLUE RIDGE

Fall zone

PLATEAUS

Physiographic provinces in Virginia

VALLEY AND RIDGE

Extent of

study area

LIMIT OF GOSPORT FOR MATION EQU IVALENT SEDI M ENTS

-288

-344

-371

-368

-375

-431

-385

-318

-303

-323

-320

-364

-356

-338

-274

-314

-281

-338

-346

-410

-409

-300

-350

-400

-300

0 8 16 MILES

0 8 16 KILOMETERS

EXPLANATION

Line of hydrologic section

Line of equal altitude—Interval is 

50 feet. Datum is NGVD 1929

Fault and up (U) and down (D) 

blocks

Borehole location

Number is altitude of top surface, 

in feet. Datum is NGVD 1929

Unit is absent

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500 000

A A'

-300

-274

D

U

Figure 10. Altitude and configuration of the top surface of sediments equivalent to the Gosport Formation across the 

Northern Neck, upper Middle Peninsula, and upper York-James Peninsula in Virginia.
22 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Rappahannock River

Pamunkey River Mattaponi River

Chickahominy River

James River

York River

P O T O M A C R I V E R

Rappahannock River

C

H

E

S

A

P

E

A

K

E

B

A

Y

James River

CAROLINE

COUNTY

HANOVER

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Poquoson

City of

Hopewell

City of

Williamsburg

NORTHUMBERLAND COUNTY

City of

Newport News

HENRICO

COUNTY

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

Chesapeake

Bay impact

crater

Resurge

channel

N

O

R T H

E R N

N E C K

M I D

D

L

E

P

E

N

I

N S U L A

Y

O

R

K - J

A M E S

P E N I N S U L A

A

A'

B

B'

C

C'

A

A'

B

B'

C

C'

D

D

D

D

D

U

U

D

U

U

U

U

U

U

U

D

D

U

LIMIT

OF PINEY POINT A

Q

UIFER

77°15' 77° 76°45' 76°30' 76°15'

38°15'

38°

37°45'

37°30'

37°15'

MARYLAND

VIRGINIA

PIEDMONT COASTAL PLAIN 

APPALACHIAN 

BLUE RIDGE

Fall zone

PLATEAUS

Physiographic provinces in Virginia

VALLEY AND RIDGE

Extent of

study area

LIMIT OF OLIGOCENE-AGE SEDIMENTS

-335

-346

-345

-349

-421

-376

-300

-288

-311

-309

-359

-348 -323

-333

-332

-266

-269

-273

-402

-282

-324

-335

-330

-403

-300

-350

-400

-250

0 8 16 MILES

0 8 16 KILOMETERS

EXPLANATION

Line of hydrologic section

Line of equal altitude—Interval is 

50 feet. Datum is NGVD 1929

Fault and up (U) and down (D) 

blocks

Borehole location

Number is altitude of top surface, 

in feet. Datum is NGVD 1929

Unit is absent

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500 000

A A'

-300

-266

D

U

Figure 11. Altitude and configuration of the top surface of Oligocene-age sediments across the Northern Neck, upper 

Middle Peninsula, and upper York-James Peninsula in Virginia.
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 23

Middlesex County (fig. 11). The corresponding interval on the 

resistivity log from the Surprise Hill corehole was correlated 

to resistivity logs from 23 other boreholes to infer the presence of Oligocene-age sediments. These intervals generally 

coincide with those of underlying Gosport Formation equivalent sediments, which have the same extent. The intervals do 

not correlate with resistivity logs from boreholes located to the 

west where Oligocene-age sediments pinch out (plate 2, sections A-A' and B-B').

Oligocene-age sediments are absent in several boreholes 

to the south in Gloucester and Middlesex Counties in proximity to the Chesapeake Bay impact crater (fig. 11). These 

sediments were deposited more recently than the impact event, 

however, so could not have been excavated during the impact 

event. If Oligocene-age sediments originally spanned part of 

the area of the impact crater, they possibly were not preserved. 

Alternatively, some part of Oligocene-age sediments that do 

span the area of the impact crater possibly is included here 

with the Calvert Formation, Newport News unit and basal 

Plum Point Member (see section “Calvert Formation, Newport News unit and basal Plum Point Member”). In addition, 

unlike underlying Gosport Formation equivalent sediments 

and deeper geologic units, Oligocene-age sediments are not 

truncated by a resurge channel associated with the impact 

crater (plate 2, section B-B') (see section “Impact-Crater 

Resurge Channel”).

Old Church Formation

Within the study area, fine-grained sediments of the Old 

Church Formation form the next to highest part of the Piney 

Point aquifer (fig. 3, right side). The Old Church Formation is 

composed of late Oligocene-age, marine, silty, variably shelly 

and pebbly, fine-to-medium grained quartz, glauconite, and 

phosphate sand (figs. 4 and 5). Sediment core and drill cuttings 

exhibit a fairly uniform color of dark olive gray (5Y 3/2) to 

black (5Y 2.5/2). Borehole resistivity logs exhibit a uniformly 

flat signature typical of fine-grained sediments (figs. 4 and 

5; plate 2). Some coarser-grained sand of the lowermost part 

of the Old Church Formation possibly is included with the 

underlying Oligocene-age sediments (see section “OligoceneAge Sediments”). Conversely, other coarser-grained sand of 

the uppermost part of the Old Church Formation possibly is 

included with the overlying Calvert Formation, Newport News 

unit and basal Plum Point Member (see section “Calvert Formation, Newport News unit and basal Plum Point Member”).

The top surface of the Old Church Formation dips eastward (fig. 12; plate 2, sections A-A' and B-B'). The top-surface 

altitude within the study area ranges from 50 ft at borehole 

53J 23 in Hanover County to -405 ft at borehole 60L 21 in 

Northumberland County. The thickness of the Old Church Formation ranges from 0 to nearly 20 ft, but in most boreholes is 

less than 10 ft (plate 2). The configuration of the Old Church 

Formation is further affected by faults (see section “Faults”).

Exclusive of the Chesapeake Bay impact crater, sediments of the Old Church Formation span most of the study 

area. Across most of the Piney Point aquifer, the fine-grained 

sediments create a relatively thin vertical separation between 

coarser-grained underlying and overlying sediments that compose other parts of the aquifer.

Fine-grained sediments of the Old Church Formation 

are absent in several boreholes in Gloucester and Middlesex 

Counties in proximity to the Chesapeake Bay impact crater 

(fig. 12). The Old Church Formation was deposited more 

recently than the impact event, however, so could not have 

been excavated during the impact event. If fine-grained sediments of the Old Church Formation originally spanned part of 

the area of the impact crater they were not preserved. Conversely, some coarser-grained sand of the Old Church Formation that does span the area of the impact crater possibly is 

included with the overlying Calvert Formation, Newport News 

unit and basal Plum Point Member (see section “Calvert Formation, Newport News unit and basal Plum Point Member”). 

In addition, like the underlying Oligocene-age sediments and 

unlike deeper geologic units, fine-grained sediments of the 

Old Church Formation are not truncated by a resurge channel 

associated with the impact crater (plate 2, section B-B') (see 

section “Impact-Crater Resurge Channel”).

The Old Church Formation is also absent in several 

boreholes in northwestern Westmoreland and Essex Counties 

(fig. 12) where it pinches out westward (plate 2, section A-A'). 

Here the Piney Point aquifer is composed of only the Calvert 

Formation, Newport News unit and basal Plum Point Member, 

and the Nanjemoy Formation Woodstock Member. Likewise, 

the Old Church Formation is absent in several boreholes in 

western New Kent and Charles City Counties (fig. 12) where 

it pinches out southeastward (plate 2, section B-B'). Here the 

Piney Point aquifer is composed of only the Calvert Formation, Newport News unit and basal Plum Point Member.

Calvert Formation, Newport News Unit and Basal 

Plum Point Member

Coarse-grained sediments of the Calvert Formation 

Newport News unit and basal part of the Plum Point Member 

form the uppermost part of the Piney Point aquifer (fig. 3, 

right side). The early Miocene-age Newport News unit of the 

Calvert Formation is stratigraphically distinct from and lower 

than the middle Miocene-age Plum Point Member (Powars and Bruce, 1999). In a hydrologic context, however, the 

Newport News unit within the study area exhibits a similar 

lithology and is contiguous with directly overlying sediments 

of the basal part of the Plum Point Member. Accordingly, both 

parts of the Calvert Formation are designated here as a single 

geologic unit composing the uppermost part of the Piney Point 

aquifer. Some Oligocene-age sediments (see section “Oligocene-Age Sediments”) and (or) coarser-grained sand of the 

Old Church Formation (see section “Old Church Formation”) 

in proximity to the Chesapeake Bay impact crater possibly are 

included. The remainder of the Plum Point Member overlying 

its basal part consists of fine-grained sediments that are not 
24 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Rappahannock River

Pamunkey River Mattaponi River

Chickahominy River

James River

York River

P O T O M A C R I V E R

Rappahannock River

C

H

E

S

A

P

E

A

K

E

B

A

Y

James River

CAROLINE

COUNTY

HANOVER

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Poquoson

City of

Hopewell

City of

Williamsburg

NORTHUMBERLAND COUNTY

City of

Newport News

HENRICO

COUNTY

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

Chesapeake

Bay impact

crater

Resurge

channel

N

O

R T H

E R N

N E C K

M I D

D

L

E

P

E

N

I

N S U L A

Y

O

R

K - J

A M E S

P E N I N S U L A

A

A'

B

B'

C

C'

A

A'

B

B'

C

C'

D

D

D

D

D

U

U

D

U

U

U

U

U

U

U

D

D

U

LIMIT

OF PINEY POINT A

Q

UIFER

77°15' 77° 76°45' 76°30' 76°15'

38°15'

38°

37°45'

37°30'

37°15'

MARYLAND

VIRGINIA

PIEDMONT COASTAL PLAIN 

APPALACHIAN 

BLUE RIDGE

Fall zone

PLATEAUS

Physiographic provinces in Virginia

VALLEY AND RIDGE

Extent of

study area

-100

-150

-50

-200

0

50

-250

-250

-300

-350

-400

8

-8

10

29

25

21 10

10

28

50

36

-91

-94

-96

-95

-45

-74

-82

-94

-69

-94 -75

-73

-59

-31

-35

-171

-118

-329

-340

-339

-342

-366

-288

-281 -265

-303

-301

-355

-325

-321

-204 -228

-187

-235

-241

-229 -250

-222

-194 -266

-267

-144 -170

-180

-183

-191

-186

-158

-199

-212

-205

-197

-169

-187

-205

-160

-212

-242

-217

-193

-217

-200

-204

-113

-117 -125

-147

-106

-111

-151

-157

-127

-113

-137

-128

-123

-128

-127

-141

-135

-111

-131

-118

-131

-124

-95.8

-85.4

-121.5

-225

-274

-189

-139

-142

-138

-135

-143

-89.8

-165

-219

-259

-269

-405

-395

-398

-112

-113

-115

-135

-100.5

-102.2

-111

-143.5

-154

-215 -200

-145

-232

-244

-243

-145

-143

-314

-343

-331

-317

-325

-176

-178

-195

-187

0 8 16 MILES

0 8 16 KILOMETERS

EXPLANATION

Line of hydrologic section

Line of equal altitude—Interval is 

50 feet. Datum is NGVD 1929

Fault and up (U) and down (D) 

blocks

Borehole location

Number is altitude of top surface, 

in feet. Datum is NGVD 1929

Unit is absent

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500 000

A A'

-300

-265

D

U

Figure 12. Altitude and configuration of the top surface of the Old Church Formation across the Northern Neck, upper 

Middle Peninsula, and upper York-James Peninsula in Virginia.
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 25

part of the Piney Point aquifer, but instead partly compose the 

Calvert confining unit (see section “Calvert Formation FineGrained Plum Point Member”).

The Calvert Formation, Newport News unit and basal 

Plum Point Member are composed of early and middle Miocene-age, marine, silty, variably shelly and pebbly, mediumto coarse-grained quartz and phosphate sand (figs. 4 and 5). 

Sediment core and drill cuttings exhibit colors ranging from 

greenish gray (5GY 5/1 and 10Y 5/1) and dark greenish gray 

(10Y 3/2) to olive (5Y 5/3, 5Y 4/3, and 5Y 4/4), olive brown 

(2.5Y 4/3), olive gray (5Y 4/2), dark olive gray (5Y 3/2), very 

dark grayish brown (2.5Y 3/2), and black 5Y 2.5/2. Borehole 

resistivity logs exhibit an elevated signature typical of coarsegrained sediments with some variation resulting from differences in sand texture and silt content.

The top surface of the Calvert Formation, Newport News 

unit and basal Plum Point Member dips eastward (fig. 13; 

plate 2, sections A-A' and B-B'). The top-surface altitude 

within the study area ranges from 60 ft at borehole 53J 23 in 

Hanover County to -405 ft at borehole 59J 11 in Middlesex 

County. The thickness of the Calvert Formation, Newport 

News unit and basal Plum Point Member ranges from less 

than 20 ft to more than 40 ft, but in most boreholes is approximately 20 ft (plate 2). The configuration of the Calvert Formation, Newport News unit and basal Plum Point Member is 

further affected by faults (see section “Faults”).

The Calvert Formation, Newport News unit and basal 

Plum Point Member uniquely spans the entire study area and 

beyond (fig. 13). The top-surface altitude contours, however, 

are drawn for this study only as far as the extent of boreholes 

located within the study area. Where other geologic units 

that compose the Piney Point aquifer are present, the Calvert 

Formation, Newport News unit and basal Plum Point Member 

forms the uppermost part of the aquifer. In several boreholes 

in northwestern Westmoreland and Essex Counties, however, the Piney Point aquifer is composed of only the Calvert 

Formation, Newport News unit and basal Plum Point Member, 

along with the Nanjemoy Formation Woodstock Member, 

because other geologic units have pinched out (plate 2, section A-A'). Likewise, in several boreholes in western New 

Kent and Charles City Counties, the Piney Point aquifer is 

entirely composed of the Calvert Formation, Newport News 

unit and basal Plum Point Member (fig. 13) where all other 

geologic units have pinched out (plate 2, section B-B').

More broadly the Calvert Formation, Newport News unit 

and basal Plum Point Member entirely composes much of the 

Piney Point aquifer outside of the study area, including across 

the Chesapeake Bay impact crater (figs. 1 and 2). The Calvert 

Formation, Newport News unit and basal Plum Point Member 

was deposited more recently than the impact event so was 

not excavated during the impact event. Also like the underlying Old Church Formation and Oligocene-age sediments, and 

unlike deeper geologic units, the Calvert Formation, Newport 

News unit and basal Plum Point Member is not truncated by a 

resurge channel associated with the impact crater (plate 2, section B-B') (see section “Impact-Crater Resurge Channel”).

Fine-Grained Calvert Formation Plum Point 

Member

Within the study area, fine-grained sediments of the Plum 

Point Member of the Calvert Formation overlie the Piney 

Point aquifer. These sediments are distinct from the coarsergrained basal part of the Plum Point Member that along with 

the Newport News unit forms the uppermost part of the Piney 

Point aquifer. The fine-grained Plum Point Member and the 

overlying Calvert Beach Member of the Calvert Formation 

are together hydrologically designated as the Calvert confining unit (fig. 3, left side) (McFarland and Bruce, 2006). Most 

of the Piney Point aquifer outside of the study area is also 

overlain by the Calvert confining unit, which is as thick as a 

few hundred feet at depths of as much as several hundred feet 

(fig. 2). The Calvert confining unit functions hydraulically as 

a continuous medium that regionally impedes horizontal flow 

but allows relatively slow, vertical groundwater movement as 

leakage between overlying and underlying aquifers.

The Calvert Formation fine-grained Plum Point Member 

is composed of middle Miocene-age, marine, silty and clayey, 

microfossiliferous, fine-grained quartz sand (figs. 4 and 5). 

Shells are generally scattered, but foraminifera and diatoms 

are commonly abundant. Pervasive jointing, small-scale fractures, and a crumbly structure possibly enhance vertical leakage relative to other confining-unit sediments. Sediment core 

and drill cuttings exhibit colors, including mostly dark olive 

gray (5Y 3/2) and olive gray (5Y 4/2 and 5/2) but also dark 

gray (5Y 4/1), gray (5Y 5/1), dark grayish brown (2.5Y 4/2), 

grayish brown (2.5Y 5/2) and dark greenish gray (5GY 4/1). 

Borehole resistivity logs generally exhibit a relatively flat signature typical of fine-grained sediments (figs. 4 and 5; plate 2) 

with some moderate and generally isolated peaks resulting 

from interbedded shells.

Sediments of the fine-grained Calvert Formation Plum 

Point Member span the entire study area and beyond. Together 

with the Calvert Beach Member, the configuration of the 

Calvert confining unit has been previously mapped across the 

entire Virginia Coastal Plain (McFarland and Bruce, 2006) and 

is not duplicated here.

Structural Configuration

All geologic units that compose the Piney Point aquifer dip to the east (see section “Geologic Units”). Only the 

Calvert Formation, Newport News unit and basal Plum Point 

Member that forms the uppermost part of the Piney Point 

aquifer spans the entire study area. In proximity to the Chesapeake Bay impact crater, underlying geologic units were either 

excavated during the impact event or have not been preserved. 

In addition, the Nanjemoy Formation Woodstock Member, 

Piney Point Formation, and Old Church Formation pinch out 

to the northwest in Westmoreland and Essex Counties (plate 2, 

section A-A') and (or) to the southwest in New Kent and 

Charles City Counties (plate 2 section B-B'). Gosport Forma-
26 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Rappahannock River

Pamunkey River Mattaponi River

Chickahominy River

James River

York River

P O T O M A C R I V E R

Rappahannock River

C

H

E

S

A

P

E

A

K

E

B

A

Y

James River

CAROLINE

COUNTY

HANOVER

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Poquoson

City of

Hopewell

City of

Williamsburg

NORTHUMBERLAND COUNTY

City of

Newport News

HENRICO

COUNTY

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

Chesapeake

Bay impact

crater

Resurge

channel

N

O

R T H

E R N

N E C K

M I D

D

L

E

P

E

N

I

N S U L A

Y

O

R

K - J

A M E S

P E N I N S U L A

A

A'

B

B'

C

C'

A

A'

B

B'

C

C'

D

D

D

D

D

U

U

D

U

U

U

U

U

U

U

D

D

U

LIMIT

OF PINEY POINT A

Q

UIFER

77°15' 77° 76°45' 76°30' 76°15'

38°15'

38°

37°45'

37°30'

37°15'

MARYLAND

VIRGINIA

2

10

25

26

41

33

28 20

22

36

60

43

45 48

39

40

43

-96

-61

-86

-82

-87

-92

-98

-72

-95

-92

-67

-91

-89

-72 -71

-72

-87

-88

-39

-46

-47

-39

-31

-47

-64

-78

-93

-51

-73 -59

-58

-55

-63

-13

-40

-14

-23

-17

-148

-102

-296

-323

-322

-328

-375

-339

-263

-259

-243

-273

-270

-314

-281 -303

-296

-405

-303

-186 -209

-175

-216

-218

-194 -228

-198

-196

-172

-218

-229

-297

-296

-315

-122 -154

-150

-156

-164

-168

-166

-136

-160

-182

-179

-168

-138

-163

-190

-178

-129

-136

-142

-185 -177

-167

-103

-123

-130

-130

-115

-109

-100

-77.8

-80.5

-91.5

-200

-227

-108

-110

-108

-107

-66.4

-70.8

-111.5

-360

-357

-109

-186

-159

-170

-383

-218

-227

-281

-286

-295

-77

-83

-87

-78.2

-83

-104

-102

-107

-94

-107

-148

-109

-119

-193

-248

-307.64

-207 -214

-219

-217

-192

-165

-175

0

-50

-100

-100

-150

-200

-250

-250

-300

-350

50

-400

-200

PIEDMONT COASTAL PLAIN 

APPALACHIAN 

BLUE RIDGE

Fall zone

PLATEAUS

Physiographic provinces in Virginia

VALLEY AND RIDGE

Extent of

study area

0 8 16 MILES

0 8 16 KILOMETERS

EXPLANATION

Line of hydrologic section

Line of equal altitude—Interval is 

50 feet. Datum is NGVD 1929

Fault and up (U) and down (D) 

blocks

Borehole location—Number is 

altitude of top surface, in feet. 

Datum is NGVD 1929

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500 000

A A'

-300

-265

D

U

Figure 13. Altitude and configuration of the top surface of the Calvert Formation, Newport News unit and basal Plum 

Point Member across the Northern Neck, upper Middle Peninsula, and upper York-James Peninsula in Virginia.
Hydrogeologic Framework of the Piney Point Aquifer in Virginia 27

tion equivalent sediments and Oligocene-age sediments are 

limited to the northeast on the Northern Neck and in Middlesex County, and pinch out to the west. The configurations of 

most of the geologic units are further affected by faults and by 

a resurge channel associated with the impact crater.

Faults

Altitudes of most of the geologic units within the study 

area are offset by a series of faults (figs. 6–8, 12, and 13; 

plate 2). Faults have not been recognized, however, across 

the limited area spanned by the Gosport Formation equivalent 

sediments and the Oligocene-age sediments (figs. 10 and 11).

Alignments of high-angle to vertical faults that intercept 

the geologic units were interpreted from borehole geophysical 

logs and associated stratigraphic correlation and structure-contour mapping. The faults are inferred to account for localized 

vertical displacements of geologic-unit top surfaces of 30 ft or 

more among closely spaced boreholes. These displacements 

contrast sharply with the broadly uniform configurations of 

the geologic-unit top surfaces exhibited regionally. Potentially 

many more faults are present but have not been recognized 

because of sparse borehole data and inadequate spatial control.

Within the study area, three relatively long faults that 

extend into the Chesapeake Bay impact crater were previously 

delineated (McFarland and Bruce, 2006). Two of the previously delineated faults are in Gloucester County and form 

a closely spaced parallel pair (figs. 6–8, 12, and 13). These 

faults vertically displace sediments that compose the Potomac 

aquifer by more than 500 ft and have been theorized to form 

a deep narrow graben associated with the impact crater. The 

Piney Point aquifer here is composed solely of the Calvert 

Formation, Newport News unit and basal Plum Point Member 

because all other geologic units were either excavated during the impact event or have not been preserved (see section 

“Geologic Units”). The top surface of the Calvert Formation, 

Newport News unit and basal Plum Point Member is vertically 

offset across these faults by more than 50 ft (fig. 13).

The other previously delineated fault was originally 

mapped from southern York County westward across the city 

of Newport News and beneath the James River (McFarland 

and Bruce, 2006). On the basis of interpretation of additional 

borehole geophysical logs for this study, this fault extends 

farther west across northeastern Surry County (figs. 6–8, 12, 

and 13) and is closely associated with two newly delineated faults.

For this study, seven relatively short faults were newly 

delineated across the York-James Peninsula and southward 

beneath the James River and across northeastern Surry County 

(figs. 6–8, 12, and 13; plate 2). The newly delineated faults 

form sets that define distinct structures and appear to be 

related to some geomorphic features. The two northernmost 

faults in King William and New Kent Counties form a graben 

aligned with the Pamunkey River upstream from the town 

of West Point. Large river meanders developed within, and 

appear to be constrained by, the graben. Outside the southeastern end of the graben is also an abrupt southward turn in the 

Mattaponi River, resulting in its confluence with the Pamunkey River and forming the York River at West Point within the 

southeastern end of the graben.

Farther south in New Kent and James City Counties, a 

complex horst-like structure is aligned with the downstream 

part of the Chickahominy River and extends southeastward 

into northwestern York County (figs. 6–8 and 10–13). This 

structure is bounded on the northeast by two fault segments 

that together form a scissor fault, and on the southwest by 

another fault downthrown to the southwest. Similar to the 

West Point graben, this structure coincides with meanders of 

the Chickahominy River, along with its abrupt southward turn 

toward the confluence with the James River. Farthest south 

across northeastern Surry County, two newly delineated faults, 

along with extension of the previously delineated fault, define 

another horst flanked to the south by a narrow graben. This 

structure coincides with a large meander and peninsula of the 

James River. 

These fault-bounded structures possibly control alignment of river meanders and confluences. The three previously 

delineated faults extend upward from the Potomac aquifer and 

are theorized to be rooted in basement bedrock (McFarland 

and Bruce, 2006). Faults that were newly delineated for this 

study possibly are also rooted in bedrock. In addition, the 

combined array of faults is aligned radially from the Chesapeake Bay impact crater and possibly reflects an outer disruption zone that has been theorized to make up part of a broad 

regional impact structure (Powars and Bruce, 1999; Powars, 

2000). The extent and configuration of such a disruption zone 

is not known in detail, but possibly consists of a radial network of horsts and grabens. Because of sparse borehole data, 

the structures delineated for this study probably only partially 

represent the disruption zone, which potentially is considerably larger and more complex. If movement along disruptionzone faults has persisted from the impact event to the present, 

the faults likely extend to land surface and possibly have 

influenced topography and drainage.

The faults probably have hydraulic effects on the Piney 

Point aquifer. Sediment intergranular structure possibly is 

disrupted by movement to result in locally poor sorting, 

compaction, and a decrease in hydraulic conductivity along 

fault planes. Additionally, within the indurated limestone of 

the Piney Point Formation, faulting may have created discrete 

fractures that are either open and enhance groundwater flow 

or lined with fault gouge to impede flow. Faults also create 

local-scale irregularities in the lateral continuity of the limestone. The Piney Point Formation is partially to completely 

dislocated vertically along faults (plate 2, sections B-B' and 

C-C'). Lateral flow constrictions or barriers result where the 

limestone abuts, and is truncated by, adjacent geologic units. 

Such constrictions or barriers have been observed to affect 

groundwater flow as no-flow boundaries (see section “AquiferComponent Test”).
28 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Impact-Crater Resurge Channel

A resurge channel associated with the Chesapeake Bay 

impact crater is interpreted, on the basis of borehole geophysical logs and associated stratigraphic correlation and 

structure-contour mapping, to underlie the lower Rappahannock River. Some of the geologic units that compose the Piney 

Point aquifer are truncated by the resurge channel (see section 

“Geologic Units”).

In borehole 59K 36 in Lancaster County (plate 1), only 

the Calvert Formation, Newport News unit and basal Plum 

Point Member, Old Church Formation, and Oligocene-age 

sediments that form the upper to intermediate parts of the 

Piney Point aquifer are present (figs. 11–13; plate 2, section 

B-B'). These sediments are underlain by clay of the Chickahominy confining unit and poorly sorted sediments of the 

Exmore matrix confining unit, determined on the basis of drill 

cuttings and a geophysical log generated by the VA DEQ. 

Lower parts of the Piney Point aquifer, including the Gosport 

Formation equivalent sediments, Piney Point Formation, and 

the Nanjemoy Formation Woodstock Member, are absent in 

borehole 59K 36 along with the Nanjemoy Formation Potapaco Member that underlies and forms the base of the aquifer 

(figs. 6–8, and 10; plate 2, section B-B'). Similarly, on the 

basis of interpretation of geophysical logs of boreholes 59J 5 

and 59J 13 in Middlesex County (plate 1), only the upper to 

intermediate parts of the Piney Point aquifer are present, and 

the lower parts are replaced by the Chickahominy confining 

unit. By contrast, geophysical logs of other nearby boreholes 

in Gloucester and Middlesex Counties indicate that most or 

all of the geologic units that compose the Piney Point aquifer 

are present, and that the Chickahominy and Exmore matrix 

confining units are absent.

Sediments of the Exmore matrix and Chickahominy confining units fill the Chesapeake Bay impact crater (fig. 2; fig. 3, 

left side) and have been previously described in detail (McFarland and Bruce, 2006). The impact initially created a powerful outward surge of water and disrupted sediment during 

excavation of the 50-mi-wide crater cavity (Powars and Bruce, 

1999). Subsequently, the surrounding region was subjected to 

a violent inward resurge of water and excavated sediment that 

partly filled the crater cavity with the Exmore matrix confining 

unit. Remnants of the resurge are theorized to still be present 

outside the crater cavity across an outer disruption zone (see 

section “Faults”). Clay of the Chickahominy confining unit 

was then slowly deposited within the remaining unfilled part 

of the crater cavity during subsequent millennia.

Sediments of the Exmore matrix and Chickahominy 

confining units intercepted by boreholes 59K 36, 59J 5, and 

59J 13 are outside the crater cavity but possibly fill a resurge 

channel associated with the impact crater. The nearby northwestern boundary of the crater cavity exhibits an outward 

protrusion (plate 1) that coincides with a complex network 

of horsts and grabens collectively termed the Rappahannock Canyon (Poag and others, 2004). Compression ridges 

in basement bedrock and numerous faults within the Exmore 

matrix and Chickahominy confining units and older sediments 

were interpreted from seismic surveys near the mouth of the 

present-day Rappahannock River. The Rappahannock Canyon 

possibly focused the resurge of water and disrupted sediment 

into the crater cavity and was subsequently covered by clay of 

the Chickahominy confining unit.

Accordingly, for this study, a resurge channel was interpreted to extend from the crater cavity upstream beneath the 

present-day Rappahannock River (figs. 6–8, and 10; plate 2, 

section B-B'). Sediments of the Exmore matrix and Chickahominy confining units are preserved within the resurge channel outside the crater cavity. Conversely, the Gosport Formation equivalent sediments, Piney Point Formation, Nanjemoy 

Formation Woodstock Member, and Nanjemoy Formation 

Potapaco Member originally present outside the crater cavity 

were scoured away by resurge along the channel. These sediments remain preserved, however, at relatively short distances 

outside the channel.

The extent and configuration of the resurge channel 

cannot be known in detail without additional information 

from boreholes and (or) seismic surveys. Channel width is 

constrained by nearby boreholes in which the Chickahominy 

and Exmore matrix confining units are absent, but the width is 

only approximated for this study as being the same as the present-day Rappahannock River. The channel extends upstream 

at least as far as borehole 59K 36 and possibly farther. Depth 

of the resurge channel also is unknown, although horsts and 

grabens making up the Rappahannock Canyon are interpreted 

as being seated in basement bedrock (Poag and others, 2004). 

Relatedly, the boundaries and internal structure of the resurge 

channel likely consists of complex arrays of faults but are 

unknown. Whether the alignment of the present-day Rappahannock River may have been influenced by the resurge channel is also unknown.
Hydrologic Conditions of the Piney Point Aquifer in Virginia 29

Hydrologic Conditions of the Piney 

Point Aquifer in Virginia

Spatial and temporal trends in withdrawal from the Piney 

Point aquifer are summarized. Regional water-level trends, a 

cone of depression, and interactions among water levels on 

the York-James peninsula are also described. Transmissivity, storativity, and horizontal hydraulic conductivity of the 

Piney Point aquifer are estimated using a series of aquifer 

tests. The hydrochemical composition of the Piney Point 

aquifer is summarized and analyzed to examine limestone 

solution channeling and distributions of the concentrations of 

iron and chloride. Lastly, considerations are offered regarding various aspects of managing the Piney Point aquifer as a 

water resource.

Groundwater Withdrawals

Withdrawals from the Piney Point aquifer were summarized for this study during 2015. Groundwater-withdrawal data 

for all aquifers within the entire Virginia Coastal Plain for the 

period 1900–2009 were obtained from a study by the USGS 

of the North Atlantic Coastal Plain (Masterson and others, 

2016), which encompasses Atlantic coast states from New 

York southward into North Carolina. Groundwater-withdrawal 

data are composed of separately determined rates of regulated 

reported withdrawals and unregulated unreported withdrawals.

Groundwater users in Virginia withdrawing 300,000 gallons or more during any month are required by law to report 

withdrawal rates to the VA DEQ (Code of Virginia, Title 62.1, 

Chapter 25). Reported withdrawals summarized here for 

1980–2009 consist of yearly mean daily rates for industrial, 

municipal, and commercial uses. For the period prior to 1980, 

reported withdrawals are based on rates previously compiled 

for a Regional Aquifer System Analysis (RASA) study of 

the Virginia Coastal Plain conducted by the USGS (Harsh 

and Laczniak, 1990). Withdrawal rates for recent periods are 

considered more accurate than those for earlier periods. In 

addition, an unknown number of withdrawals are suspected of 

being subject to regulatory requirements but are not reported.

Groundwater users in Virginia withdrawing less than 

300,000 gallons during any month are not required to report 

withdrawal rates. Unregulated withdrawals are generally for 

individual domestic use. Domestic withdrawals summarized 

for this study were broadly estimated on a decadal basis from 

U.S. Census population data and USGS water-use reports 

(Masterson and others, 2016). The distribution of withdrawals 

among individual aquifers within the Virginia Coastal Plain 

was determined using a previously documented method (Pope 

and others, 2008). Similar to reported withdrawals, the rates 

of domestic withdrawals are most uncertain for early periods. More specifically, early domestic withdrawals likely are 

underestimated because a greater proportion of the population 

relied on individual water sources during the 20th century.

Temporal Trends

During 1900–2009, withdrawals increased from all 

aquifers in the Virginia Coastal Plain and from the Piney 

Point aquifer individually. The total of withdrawals from all 

aquifers (fig. 14A) was approximately 20 Mgal/d during 1900; 

withdrawals were mostly from domestic wells. Total withdrawals peaked during 2002 at 146 Mgal/d, then decreased 

to 133 Mgal/d in 2009 (table 1) as a result of a reduction in 

reported withdrawals from 107 Mgal/d to 94.2 Mgal/d.

For the Piney Point aquifer (fig. 14B), approximately 

1 Mgal/d was withdrawn during 1900; withdrawals were 

almost entirely from domestic wells. Withdrawals from the 

Piney Point aquifer peaked during 2004 at 7.35 Mgal/d, most 

of which was reported (table 1). Withdrawals then decreased 

to 5.01 Mgal/d in 2009 as a result of a reduction in reported 

withdrawals from 4.97 Mgal/d to 2.63 Mgal/d; the 2009 

reported withdrawal value is similar to that of the domestic 

withdrawals, 2.38 Mgal/d.

In addition to reported and domestic withdrawal, relatively small rates of withdrawal for agricultural irrigation during 1980–2009 were broadly estimated for the USGS North 

Atlantic Coastal Plain study (Masterson and others, 2016) 

on the basis of remote-sensing data and a soil water-balance 

model. Approximately 14 Mgal/d for agricultural irrigation 

was estimated for all aquifers in the Virginia Coastal Plain, 

and only 0.3 Mgal/d was estimated for the Piney Point aquifer. 

Actual irrigation withdrawals from the Piney Point aquifer, 

however, are likely to be even less. Estimation of the distribution of agricultural irrigation withdrawals among individual 

Table 1. Groundwater-withdrawal rates from all aquifers in the 

Atlantic Coastal Plain in Virginia during 2002 and 2009, and from 

the Piney Point aquifer during 2004 and 2009.

Withdrawal type

Withdrawals

(million gallons per 

day)

All aquifers

2002 2009

Total 146 133

Domestic 38.5 38.5

Reported 107 94.2

Piney Point aquifer

2004 2009

Total 7.35 5.01

Domestic 2.38 2.38

Reported 4.97 2.63

York-James Peninsula 3.09 1.16

West Point 1.77 1.34

Northern Neck and Middle Peninsula 0.11 0.13
30 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

190019101920193019401950

19601970

1980

1990

20002010

0

1

2

3

4

5

6

7

8

Withdrawals, in millions of gallons per day

Withdrawals, in millions of

gallons per day

Piney Point aquifer—Estimated domestic withdrawals

Piney Point aquifer—Reported withdrawals

Piney Point aquifer—

Estimated domestic 

withdrawals

Piney Point aquifer—

Reported withdrawals

Other aquifers—

Estimated domestic 

withdrawals

Other aquifers—

Reported withdrawals

0

50

100

150

1900

19101920

1930194019501960

19701980199020002010

A. All aquifers

B. Piney Point aquifer

Figure 14. Reported and estimated domestic groundwater withdrawals during 1900–2009 from A, all aquifers in the 

Virginia Coastal Plain and B, the Piney Point aquifer.

aquifers was based on the distribution of reported withdrawals 

among the aquifers. As a result, withdrawals for agricultural 

irrigation from the surficial aquifer are probably underestimated because there are few reported withdrawals in the surficial aquifer. Likewise, withdrawals for agricultural irrigation 

from the Piney Point aquifer and other confined aquifers are 

probably overestimated because most reported withdrawals 

are for these aquifers.

Spatial Distribution of Reported Withdrawals

Additional information on individual withdrawal locations is unique to reported withdrawals. Accordingly, locations 

and rates of reported withdrawals from the Piney Point aquifer 

were differentiated among (1) the York-James Peninsula, (2) 

the town of West Point, and (3) the Northern Neck and Middle 

Peninsula (fig. 15; table 1). Withdrawal locations and rates are 

further distinguished between the peak year 2004 (fig. 15A, 

table 1 center column) and the most recent year of data 2009 

(fig. 15B, table 1 right column).

The largest reported withdrawals from the Piney Point 

aquifer are geographically concentrated on the York-James 

Peninsula and are mostly for municipal use to supply a large 

public drinking-water system. As a result, the York-James 

Peninsula has developed a water-level cone of depression in 

the Piney Point aquifer estimated at times to be deeper than 

80 ft below sea level (Heywood and Pope, 2009) (see section 

“Groundwater Levels”). Between 2004 and 2009, however, 

locations of withdrawals from the Piney Point aquifer on 

the York-James Peninsula became fewer (fig. 15), and the 

withdrawal rate decreased from 3.09 Mgal/d to 1.16 Mgal/d 

(table 1). During this period, reported municipal withdrawals 
Hydrologic Conditions of the Piney Point Aquifer in Virginia 31

MARYLAND

VIRGINIA

MARYLAND

VIRGINIA

sehC epa eka aB mi y ap t c r c a et r

sehC epa eka aB mi y ap t c r c a et r

James River

York River

P O T O M A C

R I V E R

Rappahannock River EPAS E HC EKA YAB

James River

York River

P O T O M A C

R I V E R

Rappahannock River EPAS E HC EKA YAB

N O R T H

E

R

N

N

E

C

K

M I D D L E

P E N I N

S

U

L

A

Y O R K - J

A

M

E

S

P

E

N I N

S

U L A

N O R T H

E

R

N

N

E

C

K

M I D D L E

P E N I N

S

U

L

A

Y O R K - J

A

M

E

S

P

E

N I N

S

U L A

CAROLINE

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE

GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Williamsburg

NORTHUMBERLAND

COUNTY

City of

Newport News

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

CAROLINE

COUNTY

SURRY COUNTY

ESSEX

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE

GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER COUNTY

MATHEWS

COUNTY

City of

Williamsburg

NORTHUMBERLAND

COUNTY

City of

Newport News

JAMES CITY

COUNTY

WESTMORELAND

COUNTY

WEST POINT

L MI IT OF PINEY POINT AQUIFER

L MI IT OF PINEY POINT AQUIFER

76°30' 76°45' 77°

38°

37°45'37°30'37°15'

76°30' 76°45' 77°

38°

37°45'37°30'37°15'

Area of detail

VIRGINIA

Base fromU.S. Geological Survey, 1973State of Virginia, 1:500 000

0 6 12 MILES0 6 12 KILOMETERS

EXPLANATION

Extent of productive 

limestone

Groundwater 

withdrawal, in gallons per minute

Less than 55 to 50Greater than 50 to 500Greater than 500

A. 2004 B. 2009

Figure 15. Locations and rates of reported groundwater withdrawals from the Piney Point aquifer, in Virginia, during 

A, 2004 and 

B, 2009.
32 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

shifted from the Piney Point aquifer to withdrawals and 

treatment of deeper brackish groundwater from the Potomac 

aquifer.

In addition to the York-James Peninsula, reported withdrawals at the town of West Point for mostly industrial use 

also decreased between 2004 and 2009 from 1.77 Mgal/d to 

1.34 Mgal/d (table 1). Other withdrawal data compiled for a 

separate study (McFarland, 2015) indicate further decreases 

by 2013 on the York-James Peninsula to 0.99 Mgal/d and at 

West Point to 0.76 Mgal/d. By contrast, the number of withdrawal locations on the Northern Neck and Middle Peninsula 

increased slightly between 2004 and 2009 (fig. 15) as the 

withdrawal rate increased from 0.11 Mgal/d to 0.13 Mgal/d 

(table 1). This increase is mostly due to increasing demands 

for municipal use that supplies small but expanding community drinking-water systems.

In summary, both reported and domestic withdrawals 

from the Piney Point aquifer increased from 1900 to 2004, but 

by 2009, reported withdrawals had decreased (fig. 14, table 1). 

A geographic shift in reported withdrawals, however, along 

with anticipated future increases in domestic withdrawals, 

indicates that the spatial distribution of withdrawals from the 

Piney Point aquifer is gradually broadening.

Groundwater Levels

Withdrawals from the Piney Point aquifer have resulted 

in water-level declines (see sections “Introduction” and 

“Groundwater Withdrawal”). Accordingly, trends in water levels in the Piney Point aquifer were analyzed at various spatial 

and temporal scales within the study area. Although the Piney 

Point aquifer subcrops along major river valleys that cross its 

westernmost margin, the aquifer is entirely confined within the 

designated study area surrounding the productive limestone in 

which withdrawals from the aquifer are made.

Regional Water-Level Trends

Long term trends in water levels in the Piney Point aquifer were evaluated during 2015. Historical water-level measurements in the Piney Point aquifer were compiled from the 

USGS NWIS database for Virginia. A previously documented 

method (McFarland, 2010) used well-construction data and 

the regional hydrogeologic framework (McFarland and Bruce, 

2006) to identify 19 observation wells (1) that are open to 

Piney Point aquifer and (2) from which two or more water 

levels were measured 1 year or more apart. Yearly mean water 

levels calculated from individual water-level measurements in 

each well span the period from 1906 to 2015 (fig. 16).

Most of the observation wells are located in James City 

County (fig. 16B) where the largest withdrawal from the Piney 

Point aquifer is made, mostly for municipal use to supply a 

large public drinking-water system (see section “Groundwater 

Withdrawal”). Most of the water levels in these wells were 

measured during 1960–1995 (fig. 16A). Water levels continuously declined during this period from close to or above sea 

level to as deep as nearly -60 ft. Water levels in well 56H 29 

measured after 1995 declined further until 2005, followed 

by partial recovery of approximately 14 ft by 2015. Water 

levels recovered as municipal withdrawals were shifted from 

the Piney Point aquifer to deeper brackish groundwater from 

the Potomac aquifer, which was then treated (see section 

“Groundwater Withdrawal”).

Only five of the observation wells are located outside of 

the area of large withdrawals in James City County (fig. 16B). 

Water levels in these wells remained close to or above sea 

level, including levels in three of the wells measured as 

recently as 2015 (fig. 16A). Hence, water levels in the Piney 

Point aquifer generally declined less outside of James City 

County than inside.

Water-Level Cone of Depression

A model simulation of the entire Virginia Coastal Plain 

aquifer system (Heywood and Pope, 2009) estimated that 

withdrawal from the Piney Point aquifer had by 2003 resulted 

in a water-level cone of depression as low as -80 ft in James 

City and northern York Counties. The distribution of actual 

water levels, however, was not determined accurately enough 

to evaluate this simulation result. Water levels had been 

measured at an inadequate number of locations and with varying frequency.

Accordingly, an analysis was undertaken during 2009 

to more accurately delineate the cone of depression in the 

Piney Point aquifer in James City and northern York Counties. 

Because of the paucity of observation-well data, water-level 

measurements from 10 active production wells in James City 

County (fig. 17D) were obtained from the James City Service 

Authority (JCSA) for the period from September 1, 2008, to 

August 31, 2009. All of the production wells are open to the 

part of the Piney Point aquifer composed of limestone in the 

Piney Point Formation (see section “Piney Point Formation”). 

The water levels were measured as part of JCSA’s Supervisory Control and Data Acquisition (SCADA) system used to 

operate water production and distribution. Water levels in all 

of these active production wells exhibited short-term fluctuations of multiple tens of feet resulting from pump cycling. The 

wells were not pumped continuously and, upon cessation of 

pumping, water levels rapidly recovered to a stable baseline. 

Graphical analysis identified approximate seasonal low static 

water levels in each production well during September 2008 

(fig. 17A) and August 2009 (fig. 17C), and a seasonal high 

static water level during May 2009 (fig. 17B).

The approximate seasonal static water levels in production wells were augmented with water levels in the only 

two nearby observations wells that were measured during 

the period (fig. 17D). Observation well 56H 29 is in James 

City County and is open to the limestone in the Piney Point 

Formation. Observation well 58F 53 is to the southeast in the 

City of Newport News approximately 8 mi beyond the extent 

of the limestone; well 58F 53 is open to the part of the Piney 
Hydrologic Conditions of the Piney Point Aquifer in Virginia 33

57G 54

58J 1

57G 58

57G 22

57G 50

56H 16

56H 15

56G 3

57H 9

56G 7

56G 38

57G 61

56H 9

56H 29

55H 27

57M 4

55H 19

55J 20

57F 10

-10-15-20-25-30-35-40-45-50-55-60

-5

50

25201510

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Altitude, in feet relative to National Geodetic Vertical Datum of 1929

MARYLAND

VIRGINIA

pasehC kae B e ya mi pact cra et r

James River

York River

POTOMAC RIVER

Rappahannock River EPASEHC EKA YAB JAMES CITY COUNTY

L MI IT OF PINEY POINT AQUIFER

76°30' 77°

38°

37°30'

Area of detail

VIRGINIA

0 6 12 MILES0 6 12 KILOMETERS

EXPLANATION

Extent of productive limestoneObservation well and number 58J 1

Base fromU.S. Geological Survey, 1973, State of Virginia, 1:500 000

58J 1

57M 4

57H 9

57G 61 57G 58

57G 50

57F 10

56H 29

56H 15

56G 38

56G 3

55J 20

55H 27

55H 19

57G 54

57G 22

56H 16

56H 9

56G 7

B

A

Figure 16.

A, Yearly mean water levels in selected observation wells in the Piney Point aquifer, in Virginia, during 1906–2015 and 

B, locations of selected observation wells 

in the Piney Point aquifer.
34 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

JAMES CITY

COUNTY

YORK

COUNTY

GLOUCESTER

COUNTY

NEW KENT

COUNTY

SURRY COUNTY

CHARLES

CITY

COUNTY

KING AND

QUEEN

COUNTY

City of

Williamsburg

City of

Newport News

JAMES CITY

COUNTY

YORK

COUNTY

GLOUCESTER

COUNTY

NEW KENT

COUNTY

SURRY COUNTY

CHARLES

CITY

COUNTY

KING AND

QUEEN

COUNTY

City of

Williamsburg

City of

Newport News

JAMES CITY

COUNTY

YORK

COUNTY

GLOUCESTER

COUNTY

NEW KENT

COUNTY

SURRY COUNTY

CHARLES

CITY

COUNTY

KING AND

QUEEN

COUNTY

City of

Williamsburg

City of

Newport News

JAMES CITY

COUNTY

YORK

COUNTY

GLOUCESTER

COUNTY

NEW KENT

COUNTY

SURRY COUNTY

CHARLES

CITY

COUNTY

KING AND

QUEEN

COUNTY

City of

Williamsburg

City of

Newport News

56H 50

56H 49

57H 31 56H 35

56G 69

56G 60

56G 64 56G 16

56G 52

57G100

56H 29

58F 53

76°55' 76°50' 76°45' 76°40' 76°35'

37°

25'

37°

20'

37°

15'

76°55' 76°50' 76°45' 76°40' 76°35'

37°

25'

37°

20'

37°

15'

76°55' 76°50' 76°45' 76°40' 76°35'

37°

25'

37°

20'

37°

15'

76°55' 76°50' 76°45' 76°40' 76°35'

37°

25'

37°

20'

37°

15'

A. SEPTEMBER 2008

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500 000

Yo r k

R i v e r

J a m e s R i v e r

B. MAY 2009

Yo r k

R i v e r

J a m e s R i v e r

C. AUGUST 2009

Yo r k

R i v e r

J a m e s R i v e r

D. WELL LOCATIONS AND IDENTIFIERS

Yo r k

R i v e r

J a m e s R i v e r

0 4 8 MILES

0 4 8 KILOMETERS

EXPLANATION

Extent of productive limestone

Water-level contour, in feet relative 

to National Geodetic Vertical 

Datum of 1929. Interval is 10 feet

Production well and water level, 

in feet relative to National 

Geodetic Vertical Datum of 1929

Observation well and water level, 

in feet relative to National 

Geodetic Vertical Datum of 1929

-30

-45

-24

-40

-30

-50

-20

-20

-30

-30

-40

-50

-20

-30

-20

-50

-40

-30

-20

-60

-20

-30

-40

-60

-28

-39 -59

-32 -56

-32

-55

-52

-58

-45

-26

-33 -53

-26

-48

-26

-52 -44

-49

-43

-20

-14

-27

-43

-63

-36 -60

-34

-58 -57

-61

-61

-25

-14

-24

-15

Area of detail

VIRGINIA

Figure 17. Estimated water levels in the Piney Point aquifer during A, September 2008, B, May 2009, and C, August 2009, and D, 

production- and observation-well locations.
Hydrologic Conditions of the Piney Point Aquifer in Virginia 35

Point aquifer composed of silty sand in the Calvert Formation, 

Newport News unit and basal Plum Point Member (see section “Calvert Formation, Newport News unit and basal Plum 

Point Member”).

Contour maps constructed from the approximate seasonal 

static water levels confirm the presence of a cone of depression in the Piney Point aquifer in James City and northern 

York Counties during 2008–09 (fig. 17A–C). The cone of 

depression had an oblong bi-lobate shape that was oriented 

with its long axis from northeastern James City County 

southward to the western part of the City of Williamsburg. 

Production well 57H 31 consistently had the lowest water 

levels. The lowest approximate seasonal static water level was 

-63 ft during September 2008. Likewise, the cone of depression was lowest at that time, based on water levels in the other 

wells. The water level in well 57H 31 recovered by 10 ft to 

-53 ft by May 2009 when the cone of depression also partly 

recovered. The water level in well 57H 31 then declined by 

6 ft to -59 ft by August 2009 as the cone of depression also 

declined. Fluctuation in the cone of depression resulted from 

a seasonal demand that usually occurs for the public drinkingwater system. The lowest part of, and the largest fluctuations 

in, the cone of depression during 2008–09 were at its center. 

By contrast, water levels on the higher flanks of the cone of 

depression to the northwest and southeast were relatively 

stable within a range of only 1 or 2 ft.

Water levels were measured in observation well 56H 29 

from 1985 through 2015 (fig. 16A). The yearly mean water 

level in well 56H 29 declined steadily to its lowest point of 

approximately -30 ft during 2003–05, which is 5 ft to 10 ft 

lower than its approximate seasonal static water levels during 2008–09 (fig. 17A–C). On the basis of relations between 

water levels in observation well 56H 29 and in the production 

wells during 2008–09, the center of the cone of depression in 

2003–05 was possibly as low as -70 ft. The yearly mean water 

level in well 56H 29 recovered to approximately -16 ft by 

2015 (fig. 16A). The center of the cone of depression probably 

also recovered by 2015 to approximately -50 ft. Water levels 

have recovered since 2005 because municipal withdrawals 

were shifted from the Piney Point aquifer to deeper brackish 

groundwater from the Potomac aquifer, which was then treated 

(see section “Groundwater Withdrawal”).

Water-Level Interactions on the York-James 

Peninsula

Interactions among water levels in the Piney Point aquifer 

on the York-James Peninsula during March–September 2015 

were examined. Continuous water-level measurements were 

compiled from the USGS NWIS database for Virginia for 

observation wells cooperatively maintained by USGS and the 

VA DEQ in northern York County, southern New Kent County, 

and northern City of Newport News (fig. 18).

Observation wells include collocated wells 57G129 and 

57G130 in northern York County (fig. 18E) that were constructed by the VA DEQ in early 2015 as part of a groundwater 

research station (see section “Aquifer-Component Test”). 

The research station is within the area of large groundwater 

withdrawals and the associated water-level cone of depression in James City and northern York Counties (see section 

“Water-Level Cone of Depression”). Well 57G129 is open to 

the part of the Piney Point aquifer composed of limestone in 

the Piney Point Formation (see section “Piney Point Formation”). Well 57G130 is open to the overlying part of the Piney 

Point aquifer composed of silty sand of the Calvert Formation, 

Newport News unit and basal Plum Point Member (see section “Calvert Formation, Newport News Unit and Basal Plum 

Point Member”). Continuous water-level measurement in both 

wells began on March 3, 2015 (fig. 18A).

Water levels at the groundwater research station were 

augmented with water levels in the only two nearby observations wells that were continuously measured during the period 

(figs. 18B and C). Both of these observation wells are outside 

the area of large groundwater withdrawals and the associated 

cone of depression (fig. 18E). Well 55H 27 is in southern New 

Kent County approximately 15 mi west of the research station 

and is open to the limestone in the Piney Point Formation. 

Well 58F 53 is sited beyond the extent of the limestone in the 

northern part of the City of Newport News approximately 

13 mi southeast of the research station and is open to silty sand 

in the Calvert Formation, Newport News unit and basal Plum 

Point Member.

Seasonal Water Demand

Water levels in observation wells 57G129 and 57G130 at 

the groundwater research station were affected during much 

of March 2015 by aquifer testing, which is discussed later in 

this report (see section “Aquifer-Component Test”). Throughout most of March–September 2015, water levels in the two 

wells remained within several hundredths of a foot of each 

other and fluctuated daily by several tenths of feet (fig. 18A). 

Both wells also exhibited a seasonal trend during the period 

not affected by aquifer testing. Water levels recovered from 

approximately -44 ft in early March to -42 ft by May, then 

declined to approximately -46.5 ft by September for a total 

decline of approximately 4.5 ft. Partial water-level recoveries 

of approximately 1 ft, however, also took place at four times 

during the period.

Water levels in observation wells 55H 27 and 58F 53 

during March–September 2015 (fig. 18B and C) differed in 

several respects from those in wells 57G129 and 57G130 at 

the groundwater research station. Water levels in well 55H 27 

were approximately 41 ft higher, and in well 58F 53 approximately 27 ft higher, than at the research station. Daily waterlevel fluctuations in well 55H 27 were only approximately 

0.1 ft and were timed differently from water levels at the 

research station. Water levels in well 58F 53 fluctuated even 

less, by only a few hundredths of a foot over periods as long 

as a day or more. Water levels in wells 55H 27 and 58F 53 

exhibited a seasonal trend that roughly coincided with the 
36 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

-2.5

-3

-3.5

-4

-4.5

-41

-42

-43

-44

-45

-46

-47

3

2

1

0

-16.3

-16.4

-16.5

-16.6

-16.7

-16.8

-16.9

-17

-17.1

-17.2

-17.4

-17.3

Total daily rainfall, in inches

Water level, in feet relative to

National Geodetic Vertical

Datum of 1929

Water level, in feet relative to

National Geodetic Vertical

Datum of 1929

Water level, in feet relative to

National Geodetic Vertical

Datum of 1929

March 2015 April 2015 May 2015 June 2015 July 2015 August 2015 September 2015

Pre-test recovery

Seasonal trend

Recovery 

test

Tank

filling

Flow meter 

testing Drawdown test

A. York County wells 57G129 and 57G130

B. New Kent County well 55H 27

C. City of Newport News well 58F 53

D. Weather station KVAWILLI12

57G129

57G130

Figure 18. Water levels in continuously measured observation wells A, 57G129 and 57G130 in York County, B, 55H 27 in New Kent 

County, and C, 58F 53 in the City of Newport News, Virginia, during March–September 2015, D, total daily rainfall downloaded from 

Weather Underground weather station KVAWILLI12 on September 23, 2015, and E, locations of observation wells, selected production 

wells, weather station, and faults.
Hydrologic Conditions of the Piney Point Aquifer in Virginia 37

LIMIT OF PINEY POINT AQUIFER

57G134

57G 55

58F 53

57G130

57G129

55H 27

KVAWILLI12 

JAMES CITY

COUNTY

YORK COUNTY

CHARLES CITY

COUNTY

SURRY COUNTY

GLOUCESTER

COUNTY

NEW KENT

COUNTY

PRINCE

GEORGE

COUNTY

City of

Williamsburg

City of

Newport News

KING AND QUEEN

COUNTY

J a m e s

R i v e r

Y o

r k

R i v

e

r

Y O R K - J A M E S

P E N I N S U L A

M I D

D

L

E

P

E

N I N S U L A

D

U

D

U

D

U

D

U

D

U

U

D

U

77° 76°55' 76°50' 76°45' 76°40' 76°35'

37°25'

37°20'

37°15'

0 4 8 MILES

0 4 8 KILOMETERS

Base from U.S. Geological Survey, 1973

State of Virginia, 1:500 000

E. Weather station KVAWILLI12

EXPLANATION

D

U

Extent of productive limestone

Fault and up (U) and down (D) blocks

Observation well and number

Production well and number

Weather station and number

57G134

55H 27

KVAWILLI12 Area of detail

VIRGINIA

Figure 18. Water levels in continuously measured observation wells A, 57G129 and 57G130 in York County, B, 55H 27 in New Kent 

County, and C, 58F 53 in the City of Newport News, Virginia, during March–September 2015, D, total daily rainfall downloaded from 

Weather Underground weather station KVAWILLI12 on September 23, 2015, and E, locations of observation wells, selected production 

wells, weather station, and faults.—Continued
38 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

research station but with a smaller overall decline of approximately 1 ft to 1.5 ft. Partial water-level recoveries in wells 

55H 27 and 58F 53 took place 3 or 4 times during the period 

of overall decline, which is similar to the timing of recoveries 

and declines at the research station, but only of a few tenths of 

a foot.

The seasonal water-level trend during March–September 

2015 indicates a continuation of the fluctuation in the cone 

of depression observed during 2008–09 that resulted from 

seasonal demand that usually occurs for the public drinkingwater system (see section “Water-Level Cone of Depression”). 

Relatively low water levels, and large water-level daily fluctuations and seasonal declines, in observation wells 57G129 

and 57G130 at the groundwater research station (fig. 18A) 

reflect the locations of the wells toward the center of the cone 

of depression. Conversely, water levels in wells 55H 27 and 

58F 53 sited outside of the cone of depression were higher and 

relatively stable (fig. 18B and C).

Water-Table Recharge

Water levels in all four observation wells partially 

recovered at approximately the same times during the period 

of overall decline (fig. 18A–C). The water-level recoveries 

coincided with local rainfall events in early June, late June 

into early July, early August, and early September. Groundwater levels were augmented with daily rainfall totals during 

March–September 2015 (fig. 18D) that were downloaded on 

September 23, 2015, from the Web site wunderground.com for 

weather station KVAWILLI12 located approximately 0.5 mi 

north of the groundwater research station (fig. 18E)

The Piney Point aquifer receives direct recharge only 

under unconfined conditions across its westernmost margin 

where it subcrops along major river valleys. The nearest 

subcrop area has been mapped between approximately 3 mi 

to 30 mi west of the observation wells (McFarland and Bruce, 

2006). Conversely, the Piney Point aquifer is confined at the 

observation wells, where the altitude of the top surface is 

-59 ft at well 55H 27, -145 ft at wells 57G129 and 57G130, 

and -269 ft at well 58F 53.

On the basis of confinement of the Piney Point aquifer 

at the observation wells, partial water-level recoveries in the 

observation wells during the period of overall decline did not 

result from direct recharge to the Piney Point aquifer during 

the rainfall events. Instead, water levels in the Piney Point 

aquifer rose in response to an increase in hydrostatic pressure 

produced by recharge at the water table, which is positioned 

in the surficial aquifer within a few tens of feet or less from 

land surface.

Cyclic Pumping

Other than the period that was affected by aquifer testing 

(see section “Aquifer-Component Test”), water levels in observation wells 57G129 and 57G130 at the groundwater research 

station fluctuated regularly during March–September 2015 

generally three times daily by several tenths of feet (fig. 19A). 

The water levels were affected by pumping from two nearby 

municipal-supply production wells, including well 57G 55 

sited approximately 0.6 mi to the south and well 57G134 

approximately 1.3 mi to the southwest (fig. 18E). Continuously measured withdrawal rates obtained from the City of 

Newport News Waterworks (R.E. Harris, City of Newport 

News, written commun., 2015) indicate that pumping was 

cycled at roughly 4-hour intervals at rates of approximately 

200 gal/min in well 57G 55 and 550 gal/min in well 57G134 

(fig. 19C and D). Alternating periods of water-level decline 

and recovery in the observation wells coincided closely with 

pumping of the production wells.

Vertical hydraulic gradients between observation wells 

57G129 and 57G130 were calculated assuming that the water 

levels represent hydraulic head at the middle of each of the 

well open intervals. Water-level fluctuations in well 57G129 

were approximately twice as large as those in well 57G130 

and preceded those in well 57G130 by 1–2 hours (fig. 19A). 

Water levels in 57G129 declined below those in 57G130 during decline and rose above them during recovery. As a result, 

the vertical hydraulic gradient between the two wells regularly 

reversed direction between downward (positive values) during pumping and upward (negative values) during recovery 

(fig. 19B). This relation was maintained throughout March–

September 2015 other than when conditions were affected by 

aquifer testing.

Production wells 57G 55 and 57G134 are typical of 

municipal water-supply system wells in that they are operated on a regularly cycled multi-hour basis rather than 

continuously. Thus, throughout the area of large groundwater 

withdrawals from the Piney Point aquifer in James City and 

northern York Counties, vertical hydraulic gradients probably reverse frequently between limestone of the Piney Point 

Formation and overlying silty sand of the Calvert Formation, 

Newport News unit and basal Plum Point Member. Alternating 

periods of pumping among numerous production wells thereby 

create the potential for a zone of vertical leakage and mixing 

of water between the two geologic units. As a result, desirable 

sodium-bicarbonate water in the limestone can be mixed with 

undesirable water from the silty sand containing elevated concentrations of iron and hydrogen sulfide (see section “Iron”).

Hydraulic Properties

Aquifer tests conducted in the Piney Point aquifer 

between 1972 and 2011 provide estimates of aquifer transmissivity and storativity. Transmissivity and storativity values, 

along with measurements of specific capacities for wells 

open to the Piney Point aquifer, indicate a northward downward trend in transmissivity that probably results from poor 

development of solution-channeled limestone of the Piney 

Point Formation.

A specialized aquifer test conducted in York County 

during 2015 indicated that the transmissivity and horizontal 

hydraulic conductivity of interbedded limestone and sand of 

the Piney Point Formation are nearly an order of magnitude 
Hydrologic Conditions of the Piney Point Aquifer in Virginia 39

Withdrawals, in gallons

per minute

Withdrawals, in gallons

per minute Vertical hydraulic gradient

Water level, in feet relative to

National Geodetic Vertical

Datum of 1929

600

500

400

300

200

100

0

225

200

175

150

125

100

75

50

25

0

0.01

0.005

-0.005

0

-0.01

-43.8

-43.9

-44

-44.1

-44.2

-44.3

March 6, 2015 March 7, 2015 March 8, 2015

A. Observation wells 57G129 and 57G130

B. Vertical hydraulic gradient between 57G129 and 57G130

C. Withdrawal rate for 57G 55

D. Withdrawal rate for 57G134

57G129

57G130

Figure 19. Hydrodynamic intractions in northern York County, Viginia, during March 6–8, 2015: A, water levels 

in observation wells 57G129 and 57G130, B, vertical hydraulic gradient between observation wells 57G129 and 

57G130 (positive values are downward, and negative values are upward), C, groundwater-withdrawal rates for 

production well 57G 55, and D, groundwater-withdrawal rates for production well 57G134. (Well locations shown 

in figure 17.)
40 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

greater than that of overlying silty sand of the Calvert Formation, Newport News unit and basal Plum Point Member. In 

addition, pumping of the limestone and sand induces vertical 

leakage and water-level decline in the silty sand.

Historical Aquifer Tests

Results are summarized below for 14 aquifer tests conducted in the Piney Point aquifer in the Virginia Coastal Plain 

and an adjacent part of Maryland between 1972 and 2011. 

Estimates of aquifer transmissivity and storativity and allied 

information (table 2) were compiled during 2015. Information 

on the aquifer tests was obtained from three sources.

One source of information on aquifer tests in the Piney 

Point aquifer is groundwater-site data on file at the USGS 

Virginia Water Science Center. Records of wells open to the 

Piney Point aquifer contain time-series water-level data collected by drillers during five aquifer tests conducted between 

1972 and 2011 (table 2). Four of the aquifer tests were conducted at wells in proximity to large groundwater withdrawals 

in York and James City Counties (fig. 20A). The location of 

the fifth aquifer test was conducted to the north in Northumberland County. Only a production well was used in four of 

the aquifer tests. The fifth test included a production well and 

two observation wells. For the five aquifer tests, pumping was 

conducted for either 24 hours or 48 hours at constant rates 

ranging from 50 gal/min to 350 gal/min.

The transmissivity of the Piney Point aquifer was 

estimated using the method of Cooper and Jacob (1946) 

with USGS groundwater-site records from three aquifer tests 

containing measurements of water-level drawdown, recovery, 

and residual drawdown in production wells and observation 

wells. Estimates of transmissivity from another aquifer test 

were based only on drawdown in a production well. For the 

remaining aquifer test, only recovery and residual drawdown 

in a production well were used. Storativity of the Piney Point 

aquifer was estimated only from the aquifer test that included 

observation-well water levels during drawdown and recovery. 

Complete documentation of these aquifer-test analyses are on 

file at the USGS Virginia Water Science Center.

Another source of information on aquifer tests in the 

Piney Point aquifer is a series of four reports obtained from the 

VA DEQ and published by Russnow-Kane and Associates to 

document water-supply development of the Piney Point aquifer (Russnow-Kane and Associates, 1996a–c, 2010). Three of 

these aquifer tests were conducted during 1996 and the fourth 

during 2009 (table 2). All of the aquifer tests (1) were at wells 

sited in the area of large groundwater withdrawals in York and 

James City Counties (fig. 20A), (2) included one production 

well and one observation well, and (3) conducted pumping 

for 48 hours at constant rates ranging from 365 gal/min to 

543 gal/min. The transmissivity of the Piney Point aquifer was 

estimated using all of the aquifer tests with measurements of 

water-level drawdown and recovery in production wells and 

observation wells, and the method of Cooper and Jacob (Cooper and Jacob, 1946). Measurements from three of the aquifer 

tests also included residual drawdown in a production well. 

Storativity of the Piney Point aquifer was estimated using only 

one aquifer test with water-level drawdown and recovery in an 

observation well.

The third source of information on aquifer tests in the 

Piney Point aquifer is records published by the Maryland 

Geological Survey (Andreasen and others, 2012). Five aquifer 

tests at wells open to the Piney Point aquifer in the Maryland Coastal Plain (fig. 20A) were conducted between 1991 

and 1998 (table 2). Each of the aquifer tests included only 

a production well and no observation wells. Pumping was 

conducted for 11–24 hours at constant rates of 44 gal/min to 

77 gal/min. The transmissivity of the Piney Point aquifer was 

estimated using the method of Cooper and Jacob (1946). Only 

water-level drawdowns were used from two aquifer tests, and 

only recoveries were used for another two aquifer tests. For 

the remaining aquifer test, both drawdown and recovery were 

used. Because none of the aquifer tests included observation 

wells, storativity of the Piney Point aquifer was not estimated.

In total, information on 14 aquifer tests was obtained 

from three sources. Wells used for nine of the aquifer tests 

were in proximity to large groundwater withdrawals in York 

and James City Counties (fig. 20A). These aquifer tests also 

produced the largest estimates of the transmissivity for the 

Piney Point aquifer, with a mean of 16,300 feet squared per 

day (ft2/d). Estimates of transmissivity from these aquifer tests 

also vary over a large range from 840 ft2/d to 30,907 ft2/d. 

Three of these aquifer tests produced estimates of storativity 

ranging from 8.90x10-6 to 1.98x10-5.

The five remaining aquifer tests were conducted at locations farther north, including four in Maryland and one in 

northwestern Northumberland County, Va. (fig. 20A). These 

aquifer tests produced most of the small estimates of the transmissivity for the Piney Point aquifer, with a mean of 925 ft2

/d. 

These estimates of transmissivity also vary over a narrower 

range than those for locations farther south, from 260 ft2/d to 

1,900 ft2/d. None of these aquifer tests produced estimates 

of storativity.

Generally large estimates of the transmissivity of the 

Piney Point aquifer in the area of large groundwater withdrawal in York and James City Counties contrast with smaller 

estimates in northwestern Northumberland County and Maryland. Transmissivity possibly decreases northward through 

Virginia into Maryland. The thickness of the Piney Point Formation from which most withdrawals are made, however, is 

relatively constant from south to north (plate 2, section C-C'). 

Alternatively, solution-channeled limestone of the Piney Point 

Formation that dominates the productive part of the Piney 

Point aquifer to the south possibly is poorly developed to the 

north (see section “Extent of Limestone”). Southward and 

northward locations of the aquifer tests, however, are widely 

separated. No estimates of transmissivity are available for the 

intervening area that is more than 40 mi wide.
Hydrologic Conditions of the Piney Point Aquifer in Virginia 41

Table 2. Estimates of transmissivity and storativity of the Piney Point aquifer in Virginia and an adjacent part of Maryland, 

using aquifer tests, 1972–2011.

[nd, no data]

Well 

number

Test 

year Well type

Flow rate 

(gallons 

per 

minute)

Duration 

(hours)

Distance 

(feet)

Transmissivity 

drawdown 

(feet squared 

per day)

Transmissivity 

recovery 

(feet squared 

per day)

Transmissivity 

residual 

(feet squared 

per day)

Storativity 

drawdown

Storativity 

recovery

Groundwater-site data on file at the U.S. Geological Survey Virginia Water Science Center

56G 6 1972 Production 132 24 0 nd 2,200 7,800 nd nd

57G 29 1973 Production 316 24 0 3,800 10,000 9,100 nd nd

57G 55 2011 Production 350 48 0 19,000 18,000 18,000 nd nd

57G132 2011 Observation 0 0 71 16,000 20,000 20,000 8.6E-05 4.4E-05

57G133 2011 Observation 0 0 1,140 24,000 27,000 26,000 2.5E-05 2.3E-05

57G131 1986 Production 50 48 0 840 nd nd nd nd

58M 4 1983 Production 130 48 0 1,900 800 820 nd nd

Published reports provided by the Virginia Department of Environmental Quality

56G 691 1996 Production 395 48 0 13,027 17,424 15,151 nd nd

56G 291 1996 Observation 0 0 32.5 13,275 13,939 nd nd nd

56G 722 1996 Production 393 48 0 10,668 15,410 15,410 nd nd

56G 152 1996 Observation 0 0 36.4 17,555 15,410 nd nd nd

56G 803 2009 Production 543 48 0 25,213 29,480 nd nd nd

56G 793 2009 Observation 0 0 57 29,480 30,907 nd 1.98E-05 8.90E-06

57G1004 1996 Production 365 48 0 13,703 16,305 15,334 nd nd

57G 264 1996 Observation 0 0 30.5 12,152 12,152 nd nd nd

Maryland Geological Survey Open-File Report 12-02-20

SM Cd 35 1991 Production 44 24 0 nd 260 nd nd nd

SM Ee 54 1992 Production 77 11 0 nd 860 nd nd nd

SM Ef 95 1998 Production 62 24 0 690 710 nd nd nd

SM Eg 36 1997 Production 70 23 0 970 nd nd nd nd

SM Eg 37 1997 Production 70 23 0 1340 nd nd nd nd

1

Russnow-Kane and Associates, 1996c, Report on the hydrogeologic framework and well construction activities at the Norge production well site, 

Chickahominy-Piney Point aquifer well lot W-24, 15 p.

2

Russnow-Kane and Associates, 1996b, Report on the hydrogeologic framework and well construction activities at the Kristiansand production well site, 

Chickahominy-Piney Point aquifer well lot W-38, 15 p.

3

Russnow-Kane and Associates, 2010, Report on the hydrogeologic framework and well construction activities at the Summerplace production well site, 

Chickahominy-Piney Point aquifer well lot W-44-1, 13 p.

4

Russnow-Kane and Associates, 1996a, Report on the hydrogeologic framework and well construction activities at the Canterbury production well site, 

Chickahominy-Piney Point aquifer well lot W-22, 15 p.
42 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

SURRY

COUNTY

ESSEX

COUNTY

CAROLINE

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT

COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE

GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING

GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER

COUNTY

MATHEWS

COUNTY

City of

Williamsburg

VIRGINIA

MARYLAND

WEST POINT

WESTMORELAND

COUNTY

NORTHUMBERLAND

COUNTY

City of

Newport News

JAMES CITY

COUNTY

SURRY

COUNTY

ESSEX

COUNTY

CAROLINE

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT

COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE

GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING

GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER

COUNTY

MATHEWS

COUNTY

City of

Williamsburg

VIRGINIA

MARYLAND

WEST POINT

WESTMORELAND

COUNTY

NORTHUMBERLAND

COUNTY

City of

Newport News

JAMES CITY

COUNTY

Chesapeake Bay

impact crater

Chesapeake Bay

impact crater

Chesapeake Bay

impact crater

MI L O TI YE NI P F A T NI OP UQ FI RE

Pot om ac River

Rappahannock River

York River

James River

CHESAPEAKE BAY

Pot om ac River

Rappahannock River

York River

James River

CHESAPEAKE BAY

76°30’ 77°

38°37°30’

Base fromU.S. Geological Survey, 1973State of Virginia, 1:500,000

76°30’ 77°

38°37°30’

Base fromU.S. Geological Survey, 1973State of Virginia, 1:500,000

EXPLANATION

0 8 16 MILES0 8 16 KILOMETERS

A. ESTIMATED TRANSMISSIVITY B. SPECIFIC CAPACITY

Extent of productive limestoneLimit of Piney Point aquiferEstimated transmissivity, 

in feet squared per day

<1,0001,000—5,000>5,000–10,000>10,000–15,000>15,000–20,000>20,000

Specific capacity, in gallons 

per minute per foot

<11–5>5–10>10–50>50

Area of detail

VIRGINIA

58M 4

56G 79

57G 26

57G 29

56G 72

5 G6 6

56G 80

57G100

56G 69 56G 29 56G 15

57G 55

57G132

57G133

57G131

SM Cd 35

SM Ee 54

SM Ef 95

SM Eg 37SM Eg 36

Figure 20.

A, locations of historical aquifer tests and estimates of transmissivity of the Piney Point aquifer in Virginia and Maryland, and 

B, locations and specific 

capacities of wells in the Piney Point aquifer. Well data are presented for 

A in table 2 and are summarized for 

B in table 3.
Hydrologic Conditions of the Piney Point Aquifer in Virginia 43

Well Specific Capacity

In order to further investigate a possible regional trend in 

the transmissivity of the Piney Point aquifer, measurements of 

the specific capacities of 176 wells were compiled (fig. 20B). 

Specific capacity is calculated as the pumping rate of a well 

divided by its total water-level drawdown. Specific capacity 

is partly affected by aquifer transmissivity but also by well 

efficiency. The efficiency of a well is the product of (1) the 

well diameter and length of screened interval, which jointly 

determine the surface area of the well screen, (2) the degree of 

well development, and (3) the age and condition of the well, 

which can be compromised over time by sediment clogging, 

chemical corrosion, and loss of structural integrity.

Measurements of well specific capacities were obtained 

from two sources—the USGS NWIS database and the Maryland Geological Survey (table 3). The USGS NWIS database 

contains specific capacities for 53 wells open to the Piney 

Point aquifer, which were identified using a previously documented method (McFarland, 2010) with well-construction data 

and the regional hydrogeologic framework (McFarland and 

Bruce, 2006). Records published by the Maryland Geological 

Survey (Drummond, 1984) contain specific capacities for 123 

wells specified as open to the Piney Point aquifer.

Well specific capacities have been measured at a greater 

number of locations (fig. 20B) than those at which aquifer 

tests have been conducted (fig. 20A). Specific capacity was 

measured in 35 wells in the area of large groundwater withdrawals in York and James City Counties. Another 18 wells 

were measured farther north in Virginia at locations that span 

five counties in which no aquifer tests were conducted. Measurements of well specific capacity in Maryland have a high 

spatial density.

The largest specific capacities were measured in wells 

located in the area of large groundwater withdrawals in York 

and James City Counties (fig. 20B). These wells have a mean 

specific capacity of 11.4 gallons per minute per foot (gal/

min/ft) and a range of 0.19–72 gal/min/ft (table 3). Specific 

capacities measured in wells located farther north in Virginia 

have a smaller mean of 2.26 gal/min/ft and a smaller range 

of 0.12–7.57 gal/min/ft. Some of these wells have markedly 

small specific capacities at locations within only a few miles 

of the area of large groundwater withdrawals. The large number of wells located in Maryland have the smallest specific 

capacities, with a mean of 0.99 gal/min/ft and a small range of 

0.2–4 gal/min/ft.

Specific capacities of wells open to the Piney Point 

aquifer apparently decrease northward. This trend is probably 

unrelated to well efficiency. Among wells located in Virginia, 

specific capacity is not correlated with well-screen surface 

area (correlation coefficient 0.04). In addition, the mean screen 

surface area of 40.6 ft2 among wells located in the area of 

large withdrawals is actually slightly less than the mean screen 

surface area 49.1 ft2 for wells located farther north in Virginia. 

Well development, age, and condition which also affect well 

efficiency, are likely random and without a spatial trend.

Rather than well efficiency, the northward decrease in 

specific capacity more likely reflects a northward decrease in 

aquifer transmissivity resulting from poor development of the 

solution-channeled limestone of the Piney Point Formation 

(see section “Historical Aquifer Tests”). On the basis of markedly small specific capacities within only a few miles of the 

area of large groundwater withdrawals in York and James City 

Counties, transmissivity of the Piney Point aquifer possibly 

decreases abruptly northward.

Aquifer-Component Test

A specialized aquifer test was conducted by the VADEQ 

during March 2015 to determine hydraulic properties of, 

and flow interaction between, geologic units that compose 

the Piney Point aquifer. This aquifer test was conducted at a 

groundwater research station constructed by the VADEQ in 

northern York County.

Groundwater Research Station

The groundwater research station is located at observation wells 57G129 and 57G130 (fig. 18). This location is on 

the York-James Peninsula and is bounded by the York River 

Table 3. Summary of well specific capacities in the Piney Point aquifer in Virginia and an adjacent part of Maryland.

[gal/min/foot, gallons per minute per foot]

Area Number 

of wells Data source

Well specific capacity 

(gal/min/foot)

Mean Minimum Maximum

York and James City 

Counties 35 U.S. Geological Survey National Water Information System 11.4 0.19 72

North of York and 

James City Counties 18 U.S. Geological Survey National Water Information System 2.26 0.12 7.57

Maryland 123 Maryland Geological Survey Basic Data Report 14 0.99 0.2 4
44 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

approximately 3 mi to the northeast and the James River 10 mi 

to the southwest (fig. 1). 

Litho-stratigraphy at the groundwater research station is 

based on the Banbury Cross corehole (USGS well 57G128; 

plate 1; Appendix 1; McFarland, 2017) from which a continuous sediment core was obtained by the VA DEQ during 2014. 

The sediment core intersected all geologic units that compose the Piney Point aquifer (figs. 4 and 21), except Gosport 

Formation equivalent sediments and Oligocene-age sediments, 

which pinch out approximately 20 mi to the northeast (see section “Hydrogeologic Framework”). 

Land-surface altitude is approximately 80 ft and the 

bottom of the corehole is -265 ft (fig. 21). The Piney Point 

aquifer ranges in altitude from -148 ft to -204 ft and is entirely 

confined. Interbedded limestone and sand of the Piney Point 

Formation is present between -182 ft and -197 ft. The Piney 

Point aquifer is underlain by at least 61 ft of fine-grained sediment that composes the Nanjemoy-Marlboro confining unit. 

The Piney Point aquifer is overlain by 145 ft of fine-grained 

sediment that composes the Calvert confining unit and overlying Saint Marys confining unit. The relatively shallow surficial 

aquifer, Yorktown confining zone, and Yorktown-Eastover 

aquifer collectively range in altitude from 80 ft to -3 ft.

Preexisting production well 57G131 is sited at the 

groundwater research station and is cased with 4-inch (in.) 

-diameter steel into the top of interbedded limestone and sand 

of the Piney Point Formation (fig. 21). Only the uppermost 

50 ft of the casing is grouted. Below the casing, the well 

consists of an 8-in. diameter open borehole in the limestone 

and sand, commonly referred to as a “barefoot” well (see section “Piney Point Formation”). The open interval is mostly in 

interbedded limestone and sand of the Piney Point Formation, 

but it is also in the underlying sand of the Nanjemoy Formation Woodstock Member. A single-well aquifer drawdown test 

of well 57G131 was conducted in 1986 (see section “Historical Aquifer Tests”).

Production well 57G131 was augmented by observation 

wells 57G129 and 57G130 (figs. 18E and 21) constructed by 

the VA DEQ during early 2015. Observation wells 57G129 

and 57G130 are positioned 33 ft and 26 ft, respectively, from 

production well 56G131. Both observation wells are cased 

with 4.5-in.-diameter, fully grouted polyvinyl chloride (PVC), 

below which are gravel-packed 4-in.-diameter PVC screens 

with 0.020-in. slots.

Observation-well open intervals are positioned to 

distinguish between geologic units that compose the Piney 

Point aquifer. The open intervals are shown (fig. 21) as the 

9-in.-diameter gravel-packed intervals, which extend above 

and below the ends of the well screens. Well 57G129 is open 

entirely within interbedded limestone and sand of the Piney 

Point Formation. Well 57G130 is open mostly to the silty sand 

of the Calvert Formation, Newport News unit and basal Plum 

Point Member but also to part of the overlying sandy clay, silt 

of the Calvert Formation fine-grained Plum Point Member.

Pumping and Water-Level Measurement

Production well 57G131 was not active during 2015, 

except when pumped during the aquifer test. Continuous 

(2-min interval) measurements of water levels in observation wells 57G129 and 57G130 that are stored in the USGS 

NWIS database began on March 3, 2015 (fig. 18A). The 

research station is sited within the area of large groundwater 

withdrawals and an associated water-level cone of depression in James City and northern York Counties (see section 

“Water-Level Cone of Depression”). As a result, water levels 

in both observation wells were affected during early March 

and April–September 2015 by cyclical pumping of two nearby 

active municipal-supply production wells (see section “WaterLevel Interactions on the York-James Peninsula”). Production 

well 57G 55 is approximately 0.6 mi to the south, and production well 57G134 is approximately 1.3 mi to the southwest 

(fig. 18E).

Arrangements were made so that water levels at the 

groundwater research station would not be affected by the 

municipal-supply production wells during aquifer testing. 

Following initial background water-level measurements during early March, pumping of production wells 57G 55 and 

57G134 was discontinued on March 10 to allow observationwell water levels to recover prior to the aquifer test (fig. 18A). 

Recovery was partially interrupted twice. Maintenance of the 

water-supply system required resumption of pumping of production wells 57G 55 and 57G134 briefly during March 13–14 

for filling of water-storage tanks. A second interruption on 

March 16 resulted from the pumping of production well 

57G131 at the groundwater research station for a series of 

short tests of a flow meter installed for the aquifer test.

In addition to water levels measured and stored in the 

USGS NWIS database, the VADEQ measured water levels at 

1-second intervals in both observation wells prior to and during the aquifer test (fig. 22A) (Appendix 2; McFarland, 2017). 

These high temporal resolution measurements exhibited a 

sinusoidal periodicity during pre-test recovery of observation 

well 57G129 that was superimposed on the rising water level. 

A similar but more muted trend was exhibited by observation 

well 57G130.

Observation-well water-level measurements by the 

VADEQ continued during a 24-hour aquifer drawdown test 

begun on March 17 (fig. 22A). Production well 57G131 was 

pumped at a constant rate of 61 gal/min but was not continuously measured for water levels because of constrained access 

to the interior of the well. Water levels in observation well 

57G129 declined approximately from 124.35 ft below land 

surface to 125.10 ft below land surface. Water levels in observation well 57G130 declined more slowly and slightly less, 

approximately from 124.40 ft below land surface to 125.05 ft 

below land surface. As pumping continued, water levels in 

both wells began to stabilize and exhibit a sinusoidal periodicity similar to that during the pre-test recovery period.
Hydrologic Conditions of the Piney Point Aquifer in Virginia 45

Hydrogeologic units

(McFarland and Bruce, 2006)

100500-50-100-150-200-250-300

100

50

0

-50

-100-150-200-250-300

Altitude, in feet relative to National Geodetic Vertical Datum of 1929

Altitude, in feet relative to National Geodetic Vertical Datum of 1929

Surficial aquifer

Geologic units

(This study)

Lithology

Yorktown confining zoneYorktown-Eastover aquiferSaint Marys confining unitCalvert confining unitPiney Point aquiferNanjemoy-Marlboro confining unit

Calvert Formation, fine-grained 

Plum Point Member

Calvert Formation, Newport News unit 

and basal Plum Point Member

Old Church Formation

Piney Point Formation

Nanjemoy Formation Woodstock Member

Nanjemoy Formation Potapaco Member

Marlboro clay

Medium-grained sand

Sandy clay, silt

Shells and sand

Fine-grained sand

Clay, silt

Sandy clay, silt

Silty sand

Fine-grained sand

Limestone and sand

Coarse-grained sand

Clay, silt

Clay

Not to scale

(80)(55)(38)(-3)(-69)(-126)

(-148)

(-176)(-182)(-197)(-204)(-247)(-265)

(-185)

(-203)

(-134)

(-168)

(-186)

(-197)

Production

well

57G131

Observation

well

57G130

Observation

well

57G129

26 feet

33 feet

Grout

Open interval

4 inches

8 inches

4.5 inches

9 inches

4.5 inches

9 inches

Figure 21. Litho-stratigraphy and well construction at the groundwater research station in York County, Virginia. Colors of geologic units that compose the Piney Point aquifer correspond to plate 2. All fine-grained sediments are colored white. Other aquifers are colored gray. Open intervals of observation wells 57G129 and 57G130 are based on their gravel-packed intervals. The open interval of production well 57G131 is an open borehole.
46 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

2

1.5

1

0.5

0

-0.5

-1

-1.5

March 15 March 16 March 17 March 18 March 19

Tidal stage, in feet relative to the National

Geodetic Vertical Datum of 1929

Barometric pressure,

in inches of mercury Water level, in feet below land surface

30.4

-124

-125

-125.1

-125.2

-125.3

-124.1

-124.2

-124.3

-124.4

-124.5

-124.6

-124.7

-124.8

-124.9

30.3

30.2

30.1

30

29.9

29.8

29.7

29.6

Beginning of aquiferdrawdown testBeginning of aquiferrecovery testEnd of aquiferrecovery test

Observation

well 57G129

Observation

well 57G130

Logarithmic 

antecedent trend

Multiparametric 

antecedent trend

A

B

C

Figure 22. A, Data collected prior to and during an aquifer test at the groundwater research center in York County, 

Virginia, for observation-well water levels and antecedent water-level trends, B, barometric pressure downloaded on 

September 23, 2015, from Weather Underground weather stations KVAWILL119, KVAWILL120, and KVAQILL121, and C, 

tidal stage of James River at the U.S. Geological Survey gaging station 02042222 in Charles City County, Virginia, during 

March 15–19, 2015.
Hydrologic Conditions of the Piney Point Aquifer in Virginia 47

Pumping of production well 57G131 was discontinued 

after 24 hours to begin an aquifer recovery test (fig. 22A). 

Water levels in both observation wells rose in a manner similar to their decline during the drawdown test. After another 

24 hours, the recovery test was discontinued when municipalsupply production wells 57G 55 and 57G134 were reactivated.

Following the aquifer drawdown and recovery tests, 

water levels in both observation wells were affected by 

cyclical pumping of the municipal-supply production wells 

in a manner similar to that during early March (fig. 18A). 

Water levels remained higher, however, than those prior to 

the pre-test recovery period. Water levels in wells 57G129 

and 57G130 and other observation wells in the Piney Point 

aquifer exhibit a seasonal trend that results from a seasonal 

demand that occurred for the public drinking-water system 

(see section “Seasonal Water Demand”). This seasonal trend 

was interrupted in observation wells 57G129 and 57G130 by 

the pre-test recovery imposed at the groundwater research 

station. Following the aquifer test, water levels at the research 

station apparently did not readjust to the seasonal trend until 

early April.

Antecedent Water-Level Depth Trend

Analysis of the aquifer test required calculation of waterlevel drawdowns and recoveries from the measured waterlevel depths below land surface. If water levels prior to the 

aquifer test had been stable, drawdowns and recoveries could 

be calculated simply as the difference between water-level 

depths during the test and the water-level depth at the beginning of the test. Water levels were rising during the pre-test 

period, however, and exhibited a superimposed sinusoidal 

periodicity (see section “Pumping and Water-Level Measurement”). Water levels would have continued this antecedent 

trend had the aquifer test not been conducted. Consequently, 

drawdowns and recoveries from the aquifer test are the differences between water-level depths during the test and waterlevel depths at corresponding times that would have continued 

the antecedent trend.

In order to calculate water-level drawdowns and recoveries, an estimate was made of the antecedent water-level depth 

trend in observation well 57G129 during the aquifer test. The 

water-level depth trend during the pre-test period was first 

approximated on the basis of measured water-level depths, 

then was extrapolated during the aquifer test. Because water 

levels were affected by filling of water-storage tanks during 

March 13–14, pre-test water-level depths were used from 

March 15 to the beginning of the aquifer test on March 17 

(fig. 22A). Brief water-level fluctuations resulting from tests 

of a flow meter during March 16 also were omitted from the 

measured water-level depths.

A method of successive approximation was used to determine the pre-test water-level depth trend in observation well 

57G129. Initially, measured pre-test water-level depths were 

fitted by a logarithmic regression equation having the formula 

y = 0.507ln(x) – 130.79 (1)

where 

y is the approximate water-level depth, in ft, 

and 

x is time, in seconds.

This equation strongly correlates water-level depths 

measured during the pre-test recovery period (r2 = 0.95). It 

generally approximates the rising water levels but does not 

account for the superimposed sinusoidal periodicity (fig. 22A). 

Extrapolation of the logarithmic trend during the aquifer test 

also estimates water levels that are approximately 0.1 ft higher 

than those measured by the end of the aquifer test.

Accuracy of the logarithmic estimate of the antecedent water-level depth trend in observation well 57G129 was 

improved by accounting for the effects of barometric pressure and tides. Water levels in wells that are open to confined 

aquifers are in hydrostatic equilibrium with the overlying 

atmosphere. Changes in atmospheric pressure thereby produce inverse changes in water levels. In addition, loading 

and unloading of the earth’s surface by tidal surface water 

can produce direct changes in well water levels. Accordingly, 

continuously measured barometric pressure was downloaded 

on September 23, 2015, from the wunderground.com websites for weather stations KVAWILLI19, KVAWILLI20, and 

KVAWILLI21 (fig. 22B; Appendix 2; McFarland, 2017). 

Barometric pressure was initially close to 30 in. on March 15, 

declined to nearly 29.6 in. on March 17, then rose to nearly 

30.4 in. by March 19. Continuously measured tide stages also 

were compiled from the USGS NWIS database for the estuarine James River at USGS gaging station 02042222 in Charles 

City County (fig. 22C; Appendix 2; McFarland, 2017). Tide 

stage fluctuated regularly by approximately 2.5 ft.

In order to improve the accuracy of the antecedent waterlevel depth trend estimate, residual values calculated as the 

difference between measured and logarithmically approximated water-level depths were approximated using variations 

in barometric pressure and the equation 

y = -0.150(x) + 4.4925 (2)

where 

y is the approximate residual value, in ft, and 

x is barometric pressure, in inches. 

In turn, a second set of residual values calculated as 

the difference between barometrically and logarithmically 

approximated residual values was approximated using variations in tide stage with the equation 

y = 0.0159(x) + 0.0003 (3)

where 

y is the approximate residual value, in ft, and 

x is the tide stage, in ft, lagged by 5.5 hours 

from corresponding water-level 

measurements.
48 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Logarithmically approximated water-level depths were 

summed with barometrically and tide-stage approximated 

residuals to produce a multiparametric estimate of the antecedent water-level depth trend in observation well 57G129 

(fig. 22A; Appendix 2; McFarland, 2017). This estimate 

generally approximates rising water levels during the pre-test 

recovery period. In addition, the superimposed sinusoidal periodicity is generally accounted for probably as an effect of tides 

(fig. 22C). Extrapolation of the multiparametric trend during 

the aquifer test also estimates water levels that are within the 

measured range near the end of the aquifer test and lower than 

that estimated by the logarithmic trend alone. Water levels 

during the aquifer test were probably lowered progressively by 

the increase in barometric pressure (fig. 22B).

Water-Level Drawdown and Recovery

Water-level drawdowns and recoveries in observation 

well 57G129 imposed by the aquifer test were calculated as 

the difference between measured water-level depths below 

land surface and multiparametric estimates of antecedent 

water-level depths at corresponding times during the test 

(fig. 23; Appendix 2; McFarland, 2017). An approximate loglinear trend with respect to time is apparent during both the 

drawdown and recovery tests, except for the first 10 seconds, 

which were affected by release from well-bore storage and 

are omitted.

The rate of water-level change in observation well 

57G129 during the aquifer test is reflected by the slopes of 

the drawdown and recovery trends. Both trends changed slope 

twice to divide each test into three periods (fig. 23). Log-linear 

regression lines were fitted to drawdowns and recoveries for 

each of the three periods. The decrease in slope of the drawdown and recovery trends between period 1 and period 2 is 

probably the result of the change in aquifer response from a 

single layer to two layers (see section “Conceptual Two-Layer 

Aquifer Model”). 

The slope of the drawdown trend increased between 

period 2 and period 3 (fig. 23A). The slope of the recovery 

trend initially decreased during period 3 but then increased 

during most of period 3 (fig. 23B). Increased slopes of the 

drawdown and recovery tests during period 3 reflect a faster 

rate of water-level change and a reduction in the source of 

water to the pumped well. Similar increases were observed 

during previously conducted aquifer tests (see section “Historical Aquifer Tests”) at (1) production well 57G131 prior to 

construction of the groundwater research station, (2) production well 57G 55 sited approximately 0.6 mi to the south of 

the research station (fig. 18E), and (3) production well 57G100 

sited approximately 7 mi to the south (fig. 20A).

The increase in the slope of the drawdown and recovery 

trends between period 2 and period 3 is probably the result 

of interception of a fault-associated no-flow boundary. A 

high-angle to vertical fault near the groundwater research 

station (fig. 18E) was interpreted from stratigraphic correlation and structure-contour mapping (see section “Hydrogeologic Framework”). Vertical displacement across this fault is 

estimated to be as much as 50 ft, which is more than twice the 

thickness of the limestone and sand of the Piney Point Formation. Faults that intersect the Piney Point aquifer are generally 

recognized to produce various hydraulic effects (see section 

“Faults”). Lateral continuity of the limestone and sand is likely 

interrupted along the fault near the groundwater research station, which creates a vertically dislocated flow barrier where 

the Piney Point Formation is truncated by adjacent geologic 

units. Potentially many more faults are present but have not 

been recognized because of sparse borehole data and inadequate spatial control.

Conceptual Two-Layer Aquifer Model

The slopes of the drawdown and recovery trends in 

observation well 57G129 decreased between period 1 and 

period 2 probably because of a change in the response of the 

Piney Point aquifer from a single layer to two layers. Flow 

and water-level response of a two-layer confined aquifer to 

pumping has been theorized (Javandel and Witherspoon, 1983; 

Kruseman and de Ridder, 2000). Early response of the aquifer 

differs from late response. Initially upon pumping, flow and 

water-level decline take place only in the aquifer layer being 

pumped (fig. 24A). During this period drawdown is a function 

of the transmissivity solely of the pumped layer (T1). Assuming that other conditions are met (see section “Assumptions 

and Limitations”), drawdown will exhibit a log-linear trend 

with respect to time.

With continued pumping, vertical leakage and waterlevel decline are induced at a later time in the unpumped layer 

(fig. 24B). The unpumped layer thereby provides an additional source of water to the pumped well. Drawdown is now 

a function of the sum of the transmissivities of both layers 

(T1+2). Assuming that other conditions are met, drawdown will 

continue to exhibit a log-linear trend but have a lower slope 

than during the earlier period, which reflects the slower rate of 

drawdown. Water-level response during recovery is the inverse 

of that during drawdown.

On the basis of the conceptual two-layer aquifer model, 

transmissivities of the layers can be distinguished. Initial 

drawdown and recovery can be analyzed to estimate the transmissivity of the pumped aquifer layer (T1

; fig. 24A). Likewise, 

late drawdown and recovery can be analyzed to estimate the 

sum of the transmissivities of both layers (T1+2; fig. 24B). From 

these estimates, the transmissivity of the unpumped layer can 

be estimated as

T2 = T1+2 – T1 . (4)

In order to estimate the transmissivity of both aquifer 

layers, the early period must be distinguished from the late 

period. At the groundwater research station, interbedded 

limestone and sand of the Piney Point Formation generally 
Hydrologic Conditions of the Piney Point Aquifer in Virginia 49

0.097 feet

0.108 feet

0.096 feet

0.109 feet

Period 1 Period 2 Period 3 Period 1 Period 2 Period 3 Period 1 Period 2 Period 3 Period 1 Period 2 Period 3

(200 seconds)

(4,500 seconds)

(150 seconds)

(5,000 seconds)

0.85

0.8

0.75

0.7

0.65

0.6

0.55

0.5

0.45

0.4

0.35

0.3

0.25

10 100 1,000 10,000 100,000

Time, in seconds

Drawdown, in feet

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

10 100 1,000 10,000 100,000

Time, in seconds

Recovery, in feet

A. Drawdowns B. Recoveries

Figure 23. Aquifer test water-level A, drawdowns and B, recoveries in observation well 57G129 at the groundwater research station in York County, Virginia, March 17–19, 2015.
50 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia Pumped and unpumped layer Pre-pumping water level Confining unit Unpumped aquifer layer Pumped aquifer layer Confining unit Pumped layer Pumping water level Pumped layer Pumping water level Production well Observation wells A. Early in test Well water level Direction of flow Open interval

T1

Pumped and unpumped layerPre-pumping water levelConfining unitUnpumped aquifer layerPumped aquifer layerConfining unit

Unpumped layerPumping water level

Production well Observation wells

B. Late in test

Well water level

Direction of flow

Open interval

T1+2

Figure 24. Conceptual model of the flow response of a two-layer confined aquifer to an aquifer test during 

A, the early part of the test, and 

B, the 

late part of the test. T1 equals the transmissivity of the pumped aquifer layer. T1+2 equals the sum of the transmissivities of the pumped and unpumped aquifer layers. (Based on Javandel and Witherspoon, 1983, and Kruseman and de Ridder, 2000)
Hydrologic Conditions of the Piney Point Aquifer in Virginia 51

represent the pumped layer. Observation well 57G129 is open 

to the limestone and sand (fig. 21) and exhibited drawdown 

and recovery trends that decreased in slope at 200 seconds and 

150 seconds, respectively (fig. 23).

In addition, water levels measured in observation well 

57G130 during the aquifer test can provide a second independent estimate of the timing between the early and late periods. Well 57G130 is open mostly to silty sand of the Calvert 

Formation, Newport News unit and basal Plum Point Member, 

which was not pumped during the aquifer test. Water-level 

decline in well 57G130 reflects vertical leakage from the silty 

sand that was induced by pumping of the underlying limestone 

and sand. Water levels in well 57G130 lagged behind those in 

well 57G129 (fig. 22A). Exact timing of the onset of decline 

in well 57G130 is obscured by random water-level fluctuations of as much as several hundredths of a foot between 

successive 1-second interval measurements. The trend of a 

60-second moving average calculated from the water levels, 

however, indicates that the onset of decline is between 100 

and 300 seconds. Hence, the similar timing of decreases in 

slope of the drawdown and recovery trends in well 57G129 at 

200 seconds and 150 seconds probably represents the change 

in the response of the Piney Point aquifer from a single layer 

to two layers.

Geologic-Unit Transmissivities and Hydraulic 

Conductivities

Transmissivities and horizontal hydraulic conductivities 

of geologic units that compose the Piney Point aquifer were 

estimated on basis of the conceptual two-layer aquifer model 

and changes in slope of the drawdown and recovery trends in 

observation well 57G129. Estimates were made from the first 

4,500 seconds (75 min.) of the drawdown test and from the 

first 5,000 seconds (83.33 min.) of the recovery test (periods 1 

and 2; fig. 23). Later drawdowns and recoveries (period 3) 

probably were increased by interception of a fault-associated 

no-flow boundary (see section “Water-Level Drawdown and 

Recovery”) and were not used.

Transmissivities were estimated (table 4) using the 

graphical method of Cooper and Jacob (1946). The change in 

water level, in ft per log cycle of time, was approximated from 

a log-linear regression line fitted to each of the test periods 

(fig. 23). From the drawdowns and recoveries during period 1, 

transmissivities were calculated for interbedded limestone and 

sand of the Piney Point Formation in which pumping took 

place. From period 2, the sums of the transmissivities were 

calculated for the limestone and sand and the overlying silty 

sand of the Calvert Formation, Newport News unit and basal 

Plum Point Member, which was not pumped. Differences 

between these values were then calculated as transmissivities 

of the silty sand.

Horizontal hydraulic conductivities of interbedded 

limestone and sand of the Piney Point Formation, and of silty 

sand of the Calvert Formation, Newport News unit and basal 

Plum Point Member also were calculated (table 4) from the 

transmissivity estimates and the thicknesses of the geologic 

units (fig. 21). Unlike transmissivity, hydraulic conductivity 

accounts for the different thicknesses of the geologic units and 

thereby gives a more direct comparison between the sediment textures.

Table 4. Estimates of the transmissivities and hydraulic conductivities of geologic units composing the Piney Point aquifer, using 

aquifer testing at the groundwater research station in York County, Virginia, March 2015. 

[na, not applicable]

Geologic unit Test 

period

Drawdown test Recovery test

Change in 

water level 

per log cycle 

of time

(foot)

Transmissivity

(feet squared 

per day)

Horizontal 

hydraulic 

conductivity

(feet per 

minute)

Change in 

water level 

per log cycle 

of time 

(foot)

Transmissivity

(feet squared 

per day)

Horizontal 

hydraulic 

conductivity

(foot per 

minute)

Limestone and sand of the Piney 

Point Formation 1 0.108 19,900 0.92 0.109 19,800 0.91

Combined limestone and sand 

of the Piney Point Formation 

and silty sand of the Calvert 

Formation, Newport News unit 

and basal Plum Point Member

2 0.097 22,300 na 0.096 22,400 na

Silty sand of the Calvert 

Formation, Newport News unit 

and basal Plum Point Member

na na 2,400 0.06 na 2,600 0.07
52 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Transmissivities and horizontal hydraulic conductivities estimated from drawdowns differed only slightly from 

those estimated from recoveries (table 4). Transmissivity of 

interbedded limestone and sand of the Piney Point Formation 

was estimated from drawdowns to be 19,900 ft2/d and from 

recoveries to be 19,800 ft2/d. Horizontal hydraulic conductivity of the limestone and sand was calculated from drawdowns 

to be 0.92 feet per minute (ft/min) and from recoveries to be 

0.91 ft/min. By contrast, transmissivity of silty sand of the 

Calvert Formation, Newport News unit and basal Plum Point 

Member was estimated from drawdowns to be only 2,400 ft2/d 

and from recoveries to be 2,600 ft2/d, nearly an order of magnitude less than the limestone and sand. Horizontal hydraulic conductivity of the silty sand was more than an order of 

magnitude less, calculated from drawdowns to be 0.06 ft/min 

and from recoveries to be 0.07 ft/min. These contrasts are consistent with the different sediment textures of these geologic 

units (see section “Geologic Units”).

For comparison, a single-well aquifer drawdown test was 

conducted for production well 57G131 upon its completion 

in 1986 but 29 years prior to construction of the collocated 

groundwater research station (see section “Historical Aquifer Tests”). The earlier aquifer test resulted in an estimated 

a transmissivity of 840 ft2/d (table 2), which is considerably 

less than that estimated for this study. The earlier test used a 

pumping rate of 50 gal/min, which is only marginally different from the 61 gal/min used here. During the intervening 

29 years, however, prolonged pumping of water for production 

possibly substantially developed well 57G131 following the 

early aquifer test. In addition, the median estimate of transmissivity from aquifer tests of other parts of the Piney Point 

aquifer within Virginia is 15,410 ft2/d, which is similar to the 

estimates obtained for this study.

For further comparison, published estimates of the 

horizontal hydraulic conductivity of the Piney Point aquifer 

range across two orders of magnitude from 0.001 ft/min to 

0.49 ft/min (Hamilton and Larson, 1988). These estimates 

were indirectly derived, however, either from well specificcapacity tests or from groundwater-model calibration, which 

integrated all geologic units that compose the Piney Point 

aquifer. Hence, the published horizontal hydraulic conductivity estimates bracket those obtained for this study for silty 

sand of the Calvert Formation, Newport News unit and basal 

Plum Point Member but are exceeded by those for limestone 

and interbedded sand of the Piney Point Formation.

Assumptions and Limitations

Validity of the graphical aquifer-test analysis method of 

Cooper and Jacob (1946) requires the assumptions that (1) 

the aquifer has infinite areal extent; (2) the aquifer is homogeneous, isotropic and of uniform thickness; (3) the production 

well fully penetrates the aquifer; (4) flow to the production 

well is horizontal; (5) the aquifer is confined; (6) flow is 

unsteady; (7) water is released instantaneously from storage; 

(8) the diameter of the production well is small; and (9) time is 

large or the distance from the production well to the observation well is small. Conditions of the aquifer test generally meet 

these assumptions. Although a fault-associated no-flow boundary infers that the Piney Point aquifer is not of infinite areal 

extent (see section “Water-Level Drawdown and Recovery”), 

drawdowns and recoveries that were probably affected by 

this boundary during test period 3 were not used in estimating 

transmissivity. Likewise, drawdowns and recoveries during 

the first 10 seconds that were affected by release from wellbore storage were not used. Drawdowns and recoveries during 

periods 1 and 2 occurred after release from well-bore storage 

and before interception of the no-flow boundary, and provide 

generally valid estimates of transmissivity.

On the basis of the conceptual two-layer aquifer model, 

interbedded limestone and sand of the Piney Point Formation 

generally represent the pumped layer. Production well 57G131 

penetrates most of the limestone and sand but also part of 

the underlying sand of the Nanjemoy Formation Woodstock 

Member (fig. 21). This sand has a similar texture to sand that 

is interbedded with limestone of the Piney Point Formation. 

Hence, the two geologic units probably function hydraulically 

as a continuous medium through which water moves essentially uninterrupted.

Validity of the conceptual two-layer aquifer model 

requires the assumption that the aquifer layers are in direct 

contact (fig. 24). As applied here, interbedded limestone and 

sand of the Piney Point Formation generally represent the 

pumped layer, and overlying silty sand of the Calvert Formation, Newport News unit and basal Plum Point Member 

represents the unpumped layer. At the groundwater research 

station, however, these geologic units are vertically separated 

by a relatively thin interval of fine-grained sand of the Old 

Church Formation (fig. 21). The fine-grained sand is probably 

relatively restrictive of flow and possibly impeded the onset 

and magnitude of vertical leakage from the silty sand to the 

limestone and sand during the aquifer test. Although this effect 

is probably negligible, transmissivity and horizontal hydraulic 

conductivity of the silty sand could be underestimated.

Lastly, observation well 57G130 is open mostly to 

silty sand of the Calvert Formation, Newport News unit and 

basal Plum Point Member but also to part of the overlying 

sandy clay, silt of the fine-grained Calvert Formation Plum 

Point Member. Water-level decline in well 57G130 probably 

primarily reflects vertical leakage from the silty sand that was 

induced by pumping of underlying interbedded limestone and 

sand of the Piney Point Formation. Considering contrasts in 

sediment texture, any additional water leaked from the sandy 

clay, silt is likely to be negligible.
Hydrologic Conditions of the Piney Point Aquifer in Virginia 53

Water Quality

The chemical composition of water in the entire Piney 

Point aquifer in the Virginia Coastal Plain has been previously 

described (McFarland, 2010). Previously compiled hydrochemical data for the designated study area surrounding the 

productive limestone of the Piney Point aquifer are selectively 

summarized here (see section “Introduction”). New interpretations are also presented to elucidate aspects that are particular 

to the Piney Point aquifer.

Hydrochemical data on the Piney Point aquifer within 

the study area have a median pH value that is slightly alkaline, 

8.0, and a median dissolved solids value (reported as filtered 

residue) that is moderate, 226 milligrams per liter (mg/L) 

(McFarland, 2010). Analyses of chemical tracers indicate the 

ages of water in the Piney Point aquifer range from 20,000 

years to 37,000 years (Nelms and others, 2003). Water in most 

of the Piney Point aquifer generally is considered desirable 

for most uses. Some limitations can potentially result from 

elevated concentrations of iron and sulfide, or chloride.

Major Ions

The hydrochemical composition of most of the Piney 

Point aquifer is consistently dominated by sodium cations with 

a median concentration of 41.5 mg/L and bicarbonate anions 

with a median concentration of 135 mg/L (McFarland, 2010). 

Other major cations include calcium (median concentration 

15.0 mg/L), magnesium (median concentration 2.7 mg/L) 

and potassium (median concentration 7.9 mg/L). Other major 

anions include carbonate (median concentration 13.0 mg/L), 

sulfate (median concentration 6.9 mg/L), and chloride (median 

concentration 4.2 mg/L).

Water in the Piney Point aquifer originated as precipitation that infiltrated the land surface and underwent processes 

that controlled its chemical composition as it flowed through 

the subsurface. The water first came in contact with soil 

organic matter to form carbonic acid, which then dissolved 

minerals making up subsurface sediments. The chemical 

composition of shallow groundwater in the Virginia Coastal 

Plain is thereby typically dominated by calcium cations and 

bicarbonate anions (McFarland, 2010). With further lateral 

flow and downward leakage, however, deeper water has undergone cation exchange with clay minerals and glauconite that 

removed calcium from solution by adsorption and released 

sodium into solution (Foster, 1950). Additional dissolution of 

minerals has taken place in the subsurface, particularly within 

the Piney Point aquifer where calcite composes the limestone 

of the Piney Point Formation. Cation exchange has also continued, however, to adsorb calcium and release sodium.

Solution Channeling

The limestone of the Piney Point Formation exhibits 

well developed solution channeling that is largely attributed 

for the productivity of the Piney Point aquifer (see section 

“Piney Point Formation”). Throughout earth history, limestone and other carbonate sedimentary rocks have generally 

been deposited in warm shallow ocean basins. Deposition and 

subsequent diagenesis of limestone involve complex processes 

that are beyond the scope of this report. Some insight into the 

formation of solution channels in limestone of the Piney Point 

Formation, however, can be gained by examination of the 

chemical composition of water now present in the limestone.

Dissolution of calcite that composes the limestone produces calcium cations and bicarbonate anions. On the basis of 

theromodynamic equilibria (Freeze and Cherry, 1979), however, water tends to dissolve a particular mineral only until the 

concentrations of the ions being produced reach the point of 

saturation, at which dissolution will cease. Likewise, solutions 

having higher concentrations are said to be supersaturated and 

tend to precipitate the mineral. The degree of saturation with 

respect to a particular mineral can be assessed by the saturation index (SI), which is calculated from the concentrations 

of the associated ions and related mineral-solubility data. 

Concentrations below saturation produce SI values less than 

zero, at saturation produce a value of zero, and above saturation produce values greater than zero.

Accordingly, SI values with respect to calcite were 

calculated using the computer program WATEQ4F (Ball and 

Nordstrom, 1991) and compiled hydrochemical data for 34 

water samples collected from 21 wells open to the Piney Point 

aquifer within or in proximity to the limestone (McFarland, 

2010). Median SI values range from -9.1 to 0.9, with an overall median of -0.6. In addition, median values for 14 of the 

wells are between -1.9 and zero. Thus, most of the samples are 

slightly undersaturated with respect to calcite.

Given the prevalence of solution channels in the limestone, dissolution of calcite has clearly been an active hydrochemical process in the Piney Point aquifer. Incongruously, 

concentrations of calcium cations and bicarbonate anions 

have generally not fully reached saturation with respect to 

calcite. As calcium ions are produced, however, they are likely 

removed from solution by adsorption and replaced by sodium 

(Foster, 1950). Cation exchange is facilitated by clay minerals and especially glauconite, which is a dominant lithologic 

component of the limestone. The solution is thereby maintained below saturation with respect to calcite and is capable 

of continuing to dissolve calcite and form solution channels to 

a pronounced degree.

Iron

Withdrawals from the Piney Point aquifer are primarily made from the limestone of the Piney Point Formation, 

rather than other geologic units, in part, because of its greater 

production capacity but also because of its more desirable 

hydrochemical quality. Silty sand of the Calvert Formation, 

Newport News unit and basal Plum Point Member, however, 

is the most widespread geologic unit composing the aquifer 

(see section “Calvert Formation, Newport News unit and basal 

Plum Point Member”). The silty sand overlies the limestone 
54 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

throughout the study area. Beyond the extent of the limestone, 

silty sand entirely composes much of the Piney Point aquifer 

outside the study area. In contrast to the limestone, the hydrochemical composition of the silty sand is known anecdotally 

to have elevated concentrations of iron and hydrogen sulfide, 

which are generally considered undesirable for water supplies. 

Iron produces staining, clogging, and corrosion of plumbing, 

and hydrogen sulfide has a strong unpleasant odor.

Concentrations of hydrogen sulfide in water in the Piney 

Point aquifer have not been widely determined, but concentrations of iron were compiled for 104 water samples collected from 52 wells located within the study area and open 

to the Piney Point aquifer (fig. 25) (McFarland, 2010). Of 

the 104 samples, 83 that were collected from 44 wells exhibited iron concentrations below the secondary drinking-water 

standard (U.S. Environmental Protection Agency, 1990) of 

0.3 mg/L (fig. 25, blue symbols). These wells are located 

within or in proximity to limestone of the Piney Point Formation. By contrast, the largest iron concentrations ranging from 

2.4 mg/L to 3.0 mg/L were in samples collected from two 

wells located beyond the extent of the limestone (white symbols), in northwestern Westmoreland County and in southernmost Gloucester County. These wells are at least partly open 

to silty sand of the Calvert Formation, Newport News unit and 

basal Plum Point Member, based on comparison of compiled 

sample-interval altitudes to top-surface altitude contour maps 

of geologic units and aquifers (see section “Hydrogeologic 

Framework”) (McFarland and Bruce, 2006).

Another 16 water samples from 8 widely spaced wells 

had iron concentrations from greater than 0.3 mg/L to 

1.0 mg/L (fig. 25, yellow symbols), and one sample from one 

well sited near the town of West Point had a concentration 

of 1.3 mg/L (fig. 25, red symbol). On the basis of compiled 

sample-interval altitudes, 4 of the 8 wells are probably partly 

open to the silty sand of the Calvert Formation, Newport News 

unit and basal Plum Point Member. The other 4 wells appear 

to be open entirely to the limestone of the Piney Point Formation, but only the well near West Point is recorded as having 

been grouted to the top of the screen. Construction information 

for the other wells is insufficient to determine whether any 

sample water may have partly originated from other geologic 

units, such as through well gravel packs that are longer than 

their screened intervals. Alternatively, withdrawals from wells 

open only to the limestone can potentially induce vertical leakage and mixing with water from the overlying silty sand (see 

sections “Cyclic Pumping” and “Aquifer-Component Test”).

In summary, concentrations of iron are generally low 

throughout most of the Piney Point aquifer; most exceptions 

are likely attributable to water in the silty sand of the Calvert 

Formation, Newport News unit and basal Plum Point Member. 

Dissolved iron along with hydrogen sulfide probably originate primarily from dissolution of pyrite, which is a widespread secondary mineral in the silty sand but is also known 

to be present in the limestone of the Piney Point Formation. 

Therefore, some elevated iron concentrations originating from 

within the limestone cannot be entirely ruled out.

Chloride

Toward the southeastern part of the study area, the 

concentration of chloride in water in the Piney Point aquifer 

increases, and chloride becomes the dominant anion. Elevated 

chloride concentrations result from mixing of freshwater to the 

west with saltwater contained in the aquifer to the east.

Chloride-concentration contours for the Piney Point aquifer were mapped from a detailed delineation of the saltwatertransition zone in the eastern part of the Virginia Coastal Plain 

(McFarland, 2010). Chloride in water in the part of the aquifer 

southeast of the 250-mg/L chloride-concentration contour 

(fig. 25) exceeds the secondary maximum contaminant level 

(SMCL) of 250 mg/L (U.S. Environmental Protection Agency, 

1990). Likewise, the salinity of water in the part of the aquifer 

southeast of the 1,000-mg/L chloride-concentration contour 

is in the brackish range, and the water requires treatment 

to be suitable for most uses. Hydrochemical data include 

chloride concentrations in the Piney Point aquifer as great as 

7,120 mg/L (McFarland, 2010). Beyond the study area to the 

east, the chloride concentration in the Piney Point aquifer can 

potentially reach that of seawater, 19,000 mg/L.

Freshwater occupying the landward parts of coastal 

aquifers is typically separated from saltwater occupying the 

seaward parts. A landward sloping, diffusive density boundary 

is aligned parallel to the coast where mixing of freshwater and 

saltwater takes place in the aquifers. In the Virginia Coastal 

Plain, however, the saltwater-transition zone three-dimensionally exhibits a broad dome-shaped configuration centered on 

the Chesapeake Bay impact crater. The saltwater-transition 

zone thereby protrudes approximately 30 mi landward from a 

normal coast-parallel alignment (McFarland, 2010). Chlorideconcentration contours for the Piney Point aquifer (fig. 25) 

are similar to those for other aquifers that align closely with 

the margin of the impact crater. Most of the saltwater probably originated as seawater but is theorized to have remained 

immobilized for multiple millions of years within low-permeability sediments that fill the impact crater.

Groundwater withdrawals can potentially cause movement of saltwater from the transition zone toward pumped 

wells. Withdrawals from the Piney Point aquifer have lowered 

water levels below sea level (see section “Groundwater Levels”) and consequently have produced a landward hydraulic 

gradient that creates the potential for lateral saltwater intrusion. Although withdrawals in the Virginia Coastal Plain have 

increased continuously, the position of the saltwater-transition 

zone is known to be laterally stationary across regionally 

appreciable distances since it was first mapped more than 

100 years ago (Sanford, 1913). In addition, the age of freshwater currently in the Piney Point aquifer has been estimated 

to be 20,000 years to 37,000 years (Nelms and others, 2003). 

Thus, withdrawn water has not been displaced across regional 

distances, and region-wide lateral movement of saltwater 

could possibly take centuries.

Despite the lack of lateral movement of groundwater, 

changes in groundwater chloride concentration have been 
Hydrologic Conditions of the Piney Point Aquifer in Virginia 55

SURRY

COUNTY

ESSEX

COUNTY

CAROLINE

COUNTY

KING AND QUEEN

COUNTY

YORK

COUNTY

NEW KENT

COUNTY

KING WILLIAM

COUNTY

RICHMOND

COUNTY

PRINCE

GEORGE

COUNTY

GLOUCESTER

COUNTY

CHARLES CITY

COUNTY

KING

GEORGE

COUNTY

MIDDLESEX

COUNTY

LANCASTER

COUNTY

MATHEWS

COUNTY

City of

Williamsburg

VIRGINIA

MARYLAND

West Point

WESTMORELAND

COUNTY

NORTHUMBERLAND

COUNTY

City of

Newport News

JAMES

CITY

COUNTY

Chesapeake Bay

impact crater

Pot om ac River

Rappahannock River

York River

James River

CHESAPEA

KE

BA

Y

77° 76°30’

38°

37°

30’

Base fromU.S. Geological Survey, 1973

State of Virginia, 1:500,000

EXPLANATION

0 8 16 MILES

0 8 16 KILOMETERS

Extent of productive limestone

Limit of Piney Point aquifer

Line of equal chloride concentration—

Contour interval is 750 milligrams 

per liter

Concentration of iron in groundwater, 

in milligrams per liter

Less than 0.3

0.3—1.0

1.3

2.4—3.0

250

Area of detail

VIRGINIA

250

1,000

Figure 25. Distribution of iron and chloride in water in the Piney Point aquifer, Virginia.

observed in individual wells. Yearly rates of change in wells 

in some aquifers have been greater than 1,000 mg/L (McFarland, 2010) and have led to exceedances of the 250-mg/L 

SMCL. These changes have been attributed to localized 

upconing of the saltwater-transition zone directly beneath 

pumped wells. A vertical density adjustment takes place when 

a pumping-induced decline in freshwater head causes underlying saltwater to rise. Chloride concentrations in the Piney 

Point aquifer, however, have been relatively stable compared 

to those of other aquifers. Yearly rates of change were less 

than 20 mg/L in 21 of 23 wells in the Piney Point aquifer, 

which led to no exceedances of the 250-mg/L SMCL (McFarland, 2010). Although parts of the Piney Point aquifer contain 

saltwater, the area surrounding the productive limestone, from 

which withdrawals are made from the aquifer, is apparently 

located far enough inland to have so far precluded substantial 

increases in chloride concentration resulting from upconing as 

of 2015.
56 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

Resource-Management Considerations

Information on the Piney Point aquifer presented here 

can be used to support water-resource management efforts in 

the Virginia Coastal Plain. Applications of data and interpretive findings can aid in the characterization of the aquifer and 

provide a context for regulation of groundwater withdrawals.

Aquifer Characterization

Water-supply planning and development can be aided 

by information on the diverse lithologies and other aspects of 

the six geologic units that compose the Piney Point aquifer. 

Recognition of the individual geologic units could be critical 

for the success of well-field-scale water-supply development 

projects in the Piney Point aquifer. Sediment descriptions (see 

section “Geologic Units”), borehole-interval data (Appendix 1; McFarland, 2017), structural-contour maps (figs. 6–8 

and 10–13), and hydrogeologic sections (plate 2) can be used 

in the design and siting of production wells. Specifically, 

construction of high yielding wells can be facilitated by sitespecific estimation of geologic-unit depths and thicknesses, 

and targeting of the productive solution-channeled limestone 

that composes the Piney Point Formation.

More broadly, the potential for groundwater development among planning areas can be assessed on the basis of 

the mapped extent of continuous limestone (fig. 8; plate 1) 

and on apparent trends in aquifer transmissivity (see section 

“Hydraulic Properties”). Using this information, developmentproject designs can identify optimal production-well locations, 

estimate completion depths to optimize drilling operations and 

associated costs, and predict likely yields.

In addition to specific information that supports watersupply planning and development, a broadened perspective on 

the Piney Point aquifer provides accurate conceptualization 

of its hydrologic function that is fundamental to its effective management as a water resource. Patterns of water-level 

response to past withdrawals (see section “Water Levels”) 

can probably be anticipated from future withdrawals. Relations between lateral groundwater flow within geologic units 

and vertical leakage between them (see section “Conceptual 

2-Layer Aquifer Model”) can provide the basis for more 

detailed analysis of flow. Specifically regarding groundwater 

modeling, the Piney Point aquifer could be vertically discretized with greater resolution to represent the individual 

geologic units. Of particular interest in this regard is the northeastern part of the Piney Point aquifer that includes relatively 

thick and fine-grained Gosport equivalent sediments, which 

likely add a substantially low-permeability interval to the 

aquifer (plate 2, sections A-A' and B-B'). In addition to better 

representing the entire Virginia Coastal Plain aquifer system, 

incorporating this enhanced detail could be particularly important to analyses of smaller parts of the Piney Point aquifer at 

the sub-regional to county scale.

Regulatory Implications

Although the geologic units that compose the Piney Point 

aquifer have been designated collectively as a single aquifer, 

groundwater withdrawals are made primarily from the productive solution-channeled limestone and interbedded sand that 

compose the Piney Point Formation. Thus, the VADEQ has 

considered whether the limestone and sand should be singly 

regarded as the water-supply resource and regulated as an 

aquifer apart from the other geologic units from which withdrawals are generally not made.

The VA DEQ currently (2017) limits water-level drawdowns resulting from individual withdrawals to no more than 

80 percent of the vertical distance from the pre-development 

water level to the top surface of the aquifer from which the 

withdrawals are made. As the Piney Point aquifer is currently 

designated, the drawdown limit is relative to the top surface of 

silty sand of the Calvert Formation, Newport News unit and 

basal Plum Point Member. Limestone and interbedded sand of 

the Piney Point Formation are positioned at a lower altitude, 

which if regarded singly as the regulated aquifer, would allow 

a greater amount of drawdown than was allowed in 2017 and 

previously.

Some factors could complicate a decision by the VADEQ 

to regard the limestone and interbedded sand singly as the 

regulated aquifer. Some production wells have screened 

intervals that intercept not only the limestone and sand but 

also other geologic units, most commonly the overlying silty 

sand of the Calvert Formation, Newport News unit and basal 

Plum Point Member. In addition, the VA DEQ regards the well 

gravel pack to represent the entire open interval of the well, 

which typically extends above and below the well screen and 

can intercept geologic units other than the limestone and sand.

In addition to well construction, groundwater-flow interactions between the geologic units pertain to how the VA DEQ 

could regard the Piney Point aquifer in a regulatory context. 

Pumping induces lateral flow mostly in the limestone and 

sand of the Piney Point Formation, but pumping also lowers 

water levels and induces downward leakage in overlying silty 

sand of the Calvert Formation, Newport News unit and basal 

Plum Point Member (see section “Aquifer-Component Test”). 

Pumping among numerous production wells may also create the potential for a zone of mixing of water of contrasting 

chemical quality between the two geologic units (see section 

“Iron”).

In summary, multiple geologic units that compose the 

Piney Point aquifer as currently (2017) designated can potentially be intercepted by production wells and can undergo 

water-level decline and vertical leakage caused by pumping in 

the limestone and interbedded sand of the Piney Point Formation. Thus, for the VA DEQ to regard the regulated aquifer 

singly as the limestone and sand creates the additional consideration of whether the other geologic units are to be regarded 

as regulated aquifers.
Summary and Conclusions 57

Summary and Conclusions

A study of the Piney Point aquifer in Virginia was 

conducted by the U.S. Geological Survey in cooperation with 

the Virginia Department of Environmental Quality to provide 

information needed to effectively plan for a sustainable water 

supply. The Piney Point aquifer is one of several confined 

aquifers that occupy much of the Virginia Coastal Plain. The 

Piney Point aquifer is a composite of six separate geologic 

units with different lateral extents. The study was geographically constrained to the area surrounding one of the geologic 

units, a solution-channeled limestone from which most of the 

water from the Piney Point aquifer is produced, and within 

which the aquifer is entirely confined.

A hydrogeologic framework describes the extents, 

compositions, configurations, and geologic relations of the 

six geologic units that compose the Piney Point aquifer and 

the fine-grained sediments of confining units that immediately overlie and underlie the aquifer. Drillers’, geologists’, 

and geophysical logs of 366 boreholes located within, and in 

proximity to, the productive limestone part of the Piney Point 

aquifer were interpreted. Hydrogeologic sections represent 

stratigraphic correlation of the geologic units, and structuralcontour maps represent the altitudes and configurations of 

their top surfaces.

Geologic units that compose the Piney Point aquifer are 

in stratigraphically ascending order, the

• sand of the Nanjemoy Formation Woodstock Member,

• interbedded limestone and sand of the Piney Point 

Formation,

• silty and clayey sand of the Gosport Formation equivalent sediments,

• silty sand of the Oligocene-age sediments,

• silty fine-grained sand of the Old Church Formation, 

and

• silty sand of the Calvert Formation, Newport News unit 

and basal Plum Point Member.

The geologic units are underlain by silty and clayey sand of 

the Nanjemoy Formation Potapaco Member and overlain by 

silty clayey sand of the Calvert Formation fine-grained Plum 

Point Member, which form parts of confining units above 

and below the Piney Point aquifer. The geologic units are 

designated in a hydrologic context and named on the basis of 

sediment lithologies that are typical of corresponding geologic formations. Because of differing stratigraphic contacts, 

however, the geologic units are not everywhere identical to 

formally recognized geologic formations.

Water-supply wells in the Piney Point aquifer yield 

as much as 400 gallons per minute from highly porous and 

solution-channeled indurated limestone within the Piney Point 

Formation. The limestone is relatively continuous laterally 

across northwestern Northumberland County and southeastern 

Richmond and Essex Counties; and southward across King 

and Queen County, Middlesex County, eastern King William 

and New Kent Counties, and western Gloucester County. The 

limestone extends farthest south in James City County, northernmost York County, and the City of Williamsburg. Lateral 

continuity is less certain across other parts of Westmoreland, 

Richmond, Essex, and King and Queen Counties.

All geologic units that compose the Piney Point aquifer 

dip to the east. Only the Calvert Formation, Newport News 

unit and basal Plum Point Member spans the entire study area. 

Underlying geologic units in proximity to the Chesapeake Bay 

impact crater were either excavated during the impact event or 

have not been preserved. The Nanjemoy Formation Woodstock Member, Piney Point Formation, and Old Church Formation also pinch out to the northwest and southwest. Gosport 

Formation equivalent sediments and Oligocene-age sediments 

are of limited extent to the northeast and pinch out to the west.

The configurations of most of the geologic units that 

compose the Piney Point aquifer are further affected by an 

array of faults aligned radially from the Chesapeake Bay 

impact crater. A complex series of horsts and grabens possibly 

reflects an outer disruption zone that makes up part of a broad 

regional impact structure. The faults appear further related to 

some geomorphic features and to have influenced present-day 

topography and drainage. Faults also create irregularities in 

the lateral continuity of the geologic units. Interbedded limestone and sand of the Piney Point Formation are dislocated 

vertically along faults to abut adjacent geologic units and create lateral flow constrictions or barriers.

Some of the geologic units that compose the Piney Point 

aquifer are truncated beneath the lower Rappahannock River 

by a remnant resurge channel associated with the Chesapeake 

Bay impact crater. Post-impact resurge of water and excavated 

sediment across an outer disruption zone outside the crater 

cavity was focused along the channel into the crater cavity. 

Geologic units originally present outside the crater cavity were 

scoured away along the channel but remain preserved at short 

distances outside the channel.

Annual rates of groundwater withdrawal in the Virginia Coastal Plain during 1900–2009 were obtained from a 

published groundwater study of the North Atlantic Coastal 

Plain. Groundwater withdrawals from the Piney Point aquifer increased from approximately 1 million gallons per day 

(Mgal/d) during 1900 for mostly unregulated domestic use to 

7.35 Mgal/d during 2004 for mostly regulated uses. Withdrawals then decreased to 5.01 Mgal/d by 2009 as a result 

of a reduction in regulated uses. Large withdrawals that are 

geographically concentrated on the York-James Peninsula and 

supply public drinking water became fewer between 2004 

and 2009, and withdrawals decreased from 3.09 Mgal/d to 

1.16 Mgal/d. Withdrawals were shifted from the Piney Point 

aquifer to withdrawals and treatment of deeper brackish 

groundwater from the Potomac aquifer. Withdrawals from the 

Piney Point aquifer at the town of West Point for mostly industrial use also decreased during 2004–09 from 1.77 Mgal/d to 

1.34 Mgal/d. By contrast, withdrawals on the Northern Neck 
58 Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia

and Middle Peninsula became more numerous and increased 

from 0.11 Mgal/d to 0.13 Mgal/d, mostly for expanding community drinking-water systems. This geographic shift indicates 

that withdrawals from the Piney Point aquifer are gradually 

broadening.

Water levels in the Piney Point aquifer from discrete measurements made during 1906–2015 in 19 observation wells, 

continuous measurements during 2008–09 in 10 production 

wells, and continuous measurements during March–September 2015 in 4 wells were evaluated. Yearly mean water levels 

in observation wells in James City County during 1960–95 

declined from close to or above sea level to as deep as nearly 

-60 feet (ft). Water levels in one of the observation wells 

continued to decline until 2005, then partially recovered by 

approximately 14 ft by 2015. Water levels in other observation 

wells located outside James City County remained close to or 

above sea level.

A water-level cone of depression in the Piney Point aquifer in James City and northern York Counties was indicated by 

approximately seasonal static water levels in production wells 

during 2008–09. Fluctuation in the cone of depression resulted 

from a seasonal demand imposed on the public drinking-water 

system. At the center of the cone of depression, the seasonal 

static water level of -63 ft during September 2008 recovered 

to -53 ft by May 2009, and then declined to -59 ft by August 

2009. Water levels on the higher flanks of the cone of depression to the northwest and southeast were relatively stable 

within 1 or 2 ft.

On the basis of relations among water levels in observation wells and production wells, the center of the cone 

of depression in 2003–05 was possibly as low as -70 ft but 

probably recovered by 2015 to approximately -50 ft. Water 

levels recovered as withdrawals shifted away from the Piney 

Point aquifer. Continued seasonal fluctuation in the cone of 

depression during 2015 was indicated by water-level recovery 

in observation wells from early March to May, followed by 

decline through September. Also during decline, local rainfall events recharged the water table in the surficial aquifer, 

thereby increasing hydrostatic pressure and producing partial 

water-level recoveries in the underlying Piney Point aquifer.

Multi-hour water-level fluctuations of several tenths of 

a foot in observation wells open to the Piney Point aquifer 

in northern York County coincided with cyclical pumping of 

nearby production wells during 2015. The vertical hydraulic 

gradient between the limestone of the Piney Point Formation 

and overlying silty sand of the Calvert Formation, Newport 

News unit and basal Plum Point Member regularly reversed 

direction from downward during pumping to upward during 

recovery. Alternating periods of pumping among numerous 

production wells in the Piney Point aquifer in James City and 

northern York Counties widely create the potential for a zone 

of vertical leakage and mixing between the two geologic units.

Hydraulic properties of the Piney Point aquifer were 

estimated from 14 aquifer tests conducted during 1972–2011 

in Virginia and an adjacent part of Maryland. Estimated 

transmissivities in York and James City Counties range from 

840 feet squared per day (ft2/d) to 30,907 ft2/d with a mean of 

16,300 ft2/d. Smaller estimates of transmissivity farther north 

range from 260 ft2/d to 1,900 ft2/d with a mean of 925 ft2/d. 

Estimates of storativity from three aquifer tests range from 

8.90x10-6 to 1.98x10-5. For comparison, specific capacities were compiled of 53 wells in Virginia and 123 wells 

in Maryland. Well specific capacities in York and James 

City Counties range from 0.19 gallons per minute per foot 

(gal/min/ft) to 72.5 gal/min/ft, with a mean of 11.4 gal/min/ft. 

Smaller specific capacities farther north in Virginia range 

from 0.12 gal/min/ft to 7.57 gal/min/ft with a mean of 

2.26 gal/min/ft. The smallest specific capacities are for wells 

in Maryland, ranging from 0.2 gal/min/ft to 4 gal/min/ft, with 

a mean of 0.99 gal/min/ft. The northward decrease in specific 

capacity is probably unrelated to well efficiency but rather 

reflects the northward decrease in transmissivity resulting 

from poor development of the solution-channeled limestone.

Another aquifer test conducted in northern York County 

during March 17–19, 2015, was used to determine hydraulic 

properties of, and flow interaction between, geologic units that 

compose the Piney Point aquifer. Water-level depths below 

land surface measured prior to and during the aquifer test were 

used to estimate antecedent water-level depths and calculate 

water-level drawdowns and recoveries. Pumping of limestone 

and interbedded sand of the Piney Point Formation induced 

time-lagged water-level decline and vertical leakage in the 

overlying silty sand of the Calvert Formation, Newport News 

unit and basal Plum Point Member. Early decreases in slope 

of water-level drawdown and recovery log-linear trends with 

respect to time probably represent a change in the response of 

the Piney Point aquifer from a single layer to two layers. On 

this basis, transmissivity of the limestone and sand was estimated to be 19,800 ft2

/d to 19,900 ft2/d, and of the overlying 

silty sand to be 2,400 ft2/d to 2,600 ft2/d. Horizontal hydraulic conductivity of the limestone and sand was calculated to 

be 0.91 feet per minute (ft/min) to 0.92 ft/min, and of the 

silty sand to be 0.06 ft/min to 0.07 ft/min. Later increases in 

drawdown and recovery trend slopes are probably the result of 

interception of a fault-associated no-flow boundary.

Published hydrochemical data indicate that most of the 

water in the Piney Point aquifer is slightly alkaline, contains 

moderate concentrations of dissolved solids dominated by 

sodium cations and bicarbonate anions, and is from 20,000 

years old to 37,000 years old. The water is generally slightly 

undersaturated with respect to calcite. Calcite dissolution coupled with cation exchange by glauconite and clay minerals has 

produced well developed solution channeling in the limestone 

of the Piney Point Formation, to which the productivity of the 

Piney Point aquifer is largely attributed. The concentration of 

iron in water in the Piney Point aquifer is generally below the 

secondary drinking-water standard of 0.3 milligrams per liter 

(mg/L). Larger iron concentrations of as much as 3.0 mg/L are 

largely attributable to dissolution of pyrite by water in silty 

sand of the Calvert Formation, Newport News unit and basal 

Plum Point Member. Chloride concentrations to the southeast 

are as great as 7,120 mg/L and result from mixing of freshwa-
References Cited 59

ter with seawater from low-permeability sediments that fill the 

Chesapeake Bay impact crater. Changes in chloride concentration in wells result primarily from localized upconing of 

saltwater rather than region-wide lateral movement. Chloride 

concentrations have been more stable in the Piney Point aquifer than in some other aquifers, possibly because withdrawals 

from the aquifer are generally made relatively far inland.

The Piney Point aquifer was characterized to address 

information needs for water-resource management in the Virginia Coastal Plain. Recognition of individual geologic units 

that compose the Piney Point aquifer can be critical for successful design and siting of production wells in the productive 

solution-channeled limestone. The potential for groundwater 

development among planning areas also can be assessed to 

optimize production-well locations and drilling operations, 

and to predict likely yields. Accurate conceptualization of the 

hydrologic function of the Piney Point aquifer is provided by 

patterns of water-level response to withdrawals and by relations between lateral groundwater flow and vertical leakage 

among the geologic units. Flow can potentially be evaluated 

in greater detail by models that vertically discretize individual 

geologic units.

For the VA DEQ to singly regard the limestone and 

interbedded sand of the Piney Point Formation as a regulated 

aquifer, a greater amount of drawdown would be allowed than 

currently (2017) with the Piney Point aquifer considered to 

consist of six geologic units. Some production wells, however, intercept multiple geologic units. In addition, although 

pumping induces lateral flow mostly in the limestone and 

sand, water levels are lowered and vertical leakage is induced 

in other geologic units. Water of contrasting chemical quality 

can also mix from multiple geologic units. Whether the other 

geologic units are to be regarded as regulated aquifers is an 

additional consideration for the VA DEQ.

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Heading 1 63

Appendix 1. Borehole Geologic-Unit Top-Surface Altitudes, 

Piney Point Aquifer, Virginia

Available on CD-ROM in pocket or online at https://doi.org/10.3133/sir20175041.

Appendix 2 Aquifer-Component Test Data, Piney Point Aquifer, 

Virginia

Available on CD-ROM in pocket or online at https://doi.org/10.3133/sir20175041.

Publishing support provided by the 

U.S. Geological Survey Science Publishing Network, 

West Trenton Publishing Service Center 

For more information concerning the research in this report, contact:

Virginia Water Science Center

U.S. Geological Survey

1730 East Parham Road

Richmond, Virginia 23228

http://va.water.usgs.gov/
McFarland—Hydrogeologic Framework and Hydrologic Conditions of the Piney Point Aquifer in Virginia—Scientific Investigations Report 2017–5041

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