U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with Warren County, Virginia

Preliminary Assessment of the Hydrogeology 

and Groundwater Availability in the Metamorphic 

and Siliciclastic Fractured-Rock Aquifer Systems 

of Warren County, Virginia

Scientific Investigations Report 2010–5190
Cover.  Hogback Mountain in Shenandoah National Park. View looking near Boyds Mill to the southwest. 

(Photograph by David L. Nelms, U.S. Geological Survey, July 2009.)
Preliminary Assessment of the Hydrogeology 

and Groundwater Availability in the Metamorphic 

and Siliciclastic Fractured-Rock Aquifer Systems 

of Warren County, Virginia 

By David L. Nelms and Roger M. Moberg, Jr.

Prepared in cooperation with Warren County, Virginia

Scientific Investigations Report 2010–5190

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Nelms, D.L., and Moberg, R.M., Jr., 2010, Preliminary assessment of the hydrogeology and groundwater availability 

in the metamorphic and siliciclastic fractured-rock aquifer systems of Warren County, Virginia: U.S. Geological Survey 

Scientific Investigations Report 2010–5190, 74 p. 

(available online at http://pubs.usgs.gov/sir/2010/5190/)

ISBN 978 1 4113 3017 7
iii

Acknowledgments

The authors gratefully acknowledge the many individuals, establishments, and authorities in Warren County that permitted access to individual wells and springs. The authors also 

thank the property owners that granted access to their property for collection of water-level data 

and stream- and spring-discharge data. Special thanks is given to Douglas P. Stanley, County 

Administrator of Warren County, for his efforts with project logistics and support. 

The authors also acknowledge U.S. Geological Survey employees, Melinda Chapman and 

Mark Kozar, for their contributions to this report.

v

Contents

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

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

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

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

Description of the Study Area ............................................................................................................2

Conceptual Model of Groundwater Flow.................................................................................2

Climate...........................................................................................................................................5

Well- and Spring-Numbering System................................................................................................6

Previous Investigations........................................................................................................................7

Hydrogeology..................................................................................................................................................7

Geology...................................................................................................................................................7

Hydrogeologic Units....................................................................................................................8

Metamorphic Rock Unit of the Blue Ridge Physiographic Province .........................9

Orthopyroxene Granodiorite Gneiss.......................................................................9

Orthopyroxene Quartz Diorite Gneiss...................................................................10

Megacrystic Orthopyroxene Syenogranite-Monzogranite Gneiss .................10

Old Rag Granite ........................................................................................................10

Orthopyroxene Monzogranite-Quartz Monzodiorite..........................................10

Swift Run Formation ................................................................................................10

Metadiabase Dikes..................................................................................................10

Catoctin Formation ..................................................................................................10

Weverton Formation of the Chilhowee Group.....................................................10

Harpers Formation of the Chilhowee Group........................................................11

Antietam Formation of the Chilhowee Group......................................................11

Siliciclastic Rock Unit of the Great Valley Section of the Valley and Ridge 

Physiographic Province .....................................................................................11

Martinsburg Formation ...........................................................................................11

Massanutten Sandstone ........................................................................................11

Carbonate Rock Unit of the Great Valley Section of the Valley and Ridge 

Physiographic Province .....................................................................................11

Structural Geology.....................................................................................................................11

Bedding-Plane Partings, Joints, Cleavage, and Foliations........................................12

Folds ................................................................................................................................12

Faults ................................................................................................................................13

Surficial Geology........................................................................................................................14

Hydrology .............................................................................................................................................14

Hydrogeologic Characteristics................................................................................................14

Well Depths........................................................................................................................14

Depth to Bedrock..............................................................................................................17

Water-Bearing Zones.......................................................................................................18

Well Yields..........................................................................................................................21

Aquifer Properties ............................................................................................................25

Water Levels......................................................................................................................25

Streamflow and Spring Discharge.................................................................................30
vi

Relation of Geology to Groundwater Flow.............................................................................33

Relation Between Groundwater and Surface Water...........................................................34

Apparent Age of Groundwater................................................................................................35

Revised Conceptual Model of Groundwater Flow ...............................................................40

Groundwater Availability ............................................................................................................................43

Effective Recharge .............................................................................................................................43

Water Budgets for Gaged Basins ....................................................................................................48

Water Budgets for Ungaged Basins................................................................................................50

Drought Effects....................................................................................................................................54

Summary........................................................................................................................................................56

References Cited..........................................................................................................................................57

Appendixes ...................................................................................................................................................63

Figures

1. Map showing generalized geologic province map of Warren County, Virginia, 

and location of study area...........................................................................................................3

2. Generalized hydrogeologic section across Warren County, Virginia..................................4

3. Graph showing average monthly precipitation for National Weather Service 

climatological stations 445851 Mt. Weather in Loudoun County, Virginia, at an 

elevation of 1,720 ft above NGVD 29 and 443229 Front Royal in Warren County, 

Virginia, at an elevation of 930 ft above NGVD 29 ...................................................................5

4. Map showing average annual total precipitation for Warren County, Virginia, 

based on parameter-elevation regressions on independent slopes model (PRISM) .......6

5. Map showing generalized hydrogeologic units of Warren County, Virginia ......................8

6. Graphic representation of joint types and bedding in folded rocks...................................12

7. Photograph showing fold in the Middle Ordovician Edinburg Formation in roadcut 

on State Route 679 at intersection with State Route 677 near streamflow-gaging 

station 01631000 South Fork Shenandoah River near Front Royal, Virginia......................13

8. Boxplots showing summary statistics of well-construction and hydrologic 

characteristics of the rock types in Warren County, Virginia .............................................16

9–15. Maps showing—

9. Depth to bedrock in Warren County, Virginia ...............................................................17

10. Depth to top of upper reported water-bearing zones in Warren County, Virginia..19

11. Depth to top of lower reported water-bearing zones in Warren County, Virginia..20

12. Reported well yields in Warren County, Virginia..........................................................21

13. Density of wells with reported well yields less than 5 gallons per minute in 

Warren County, Virginia....................................................................................................23

14. Density of wells with reported well yields greater than 50 gallons per minute 

in Warren County, Virginia................................................................................................24

15. Locations of streamflow-gaging stations, springs, and wells in the long-term 

water monitoring network for Warren County, Virginia ..............................................27

16. Graphs showing relation between water levels in wells 45V 4 and 45V 3 in Warren 

County, Virginia, and in well 46W175 in Clarke County, Virginia, and quarterly 

standardized precipitation index and daily snowfall at National Weather Service 

climatological station 443229 Front Royal, Virginia...............................................................28
vii

17. Aerial photographs showing land use in 2002 and 2007 for the area surrounding 

wells 45V 3 and 45V 4 in Warren County, Virginia .................................................................29

18. Photograph showing landscape modification around well 45V 4 

in Warren County, Virginia.........................................................................................................30

19–22. Hydrographs showing—

19. Relation between water levels in well 45V 3 in Warren County, Virginia, 

and combined effects of barometric pressure and Earth tides, and of 

teleseismic earthquakes ..................................................................................................31

20. Daily mean discharge at streamflow-gaging stations 01630700 Gooney Run 

at Route 622 near Glen Echo, Virginia, 01636242 Crooked Run below Route 340 

at Riverton, Virginia, and 0163626650 Manassas Run at Route 645 near Front 

Royal, Virginia.....................................................................................................................32

21. Quarterly discharges from springs 45VS 1 and 46VS 17 

in Warren County, Virginia................................................................................................33

22. Relation between evapotranspiration and unit value discharge at streamflowgaging stations 01630700 Gooney Run at Route 622 near Glen Echo, Virginia, 

01636242 Crooked Run below Route 340 at Riverton, Virginia, and 0163626650 

Manassas Run at Route 645 near Front Royal, Virginia ..............................................35

23. Aerial photograph and pseudosection showing multifrequency electromagnetic 

survey along the South Fork Shenandoah River near Front Royal, Virginia .....................36

24. Map showing apparent age and percentage of young water fraction for sampling 

sites in Warren County, Virginia...............................................................................................37

25. Graph showing atmospheric mixing ratios of chlorofluorocarbon-11, chlorofluorocarbon-12, chlorofluorocarbon-113, and sulfur hexafluoride for North American air 

and estimated monthly concentration of tritium in precipitation for Virginia...................38

26. Generalized conceptual hydrogeologic longitudinal section of the flow system 

in the Blue Ridge Physiographic Province in Warren County, Virginia .............................41

27. Generalized conceptual hydrogeologic sections along strike and cross-strike 

in the siliciclastic fractured-rock flow system (Martinsburg Formation) in 

Warren County, Virginia.............................................................................................................42

28. Graphs showing relation between annual precipitation at National Weather Service 

climatological station 443229 Front Royal, Virginia, and effective recharge at 

streamflow-gaging stations 01630700 Gooney Run at Route 622 near Glen Echo, 

Virginia, 01636242 Crooked Run below Route 340 at Riverton, Virginia, and 

0163626650 Manassas Run at Route 645 near Front Royal, Virginia ..................................47

29. Map showing drainage basins and parcel acreage in Warren County, Virginia.............51

30. Graph showing relation between estimated domestic water usage at buildout 

and varying percentages of annual effective recharge estimated from the linear 

regression method of Yager and others (2008) for ungaged basins in 

Warren County, Virginia.............................................................................................................54

31. Graphs showing relation between annual rates of precipitation at National 

Weather Service climatological station 443229 Front Royal, Virginia, mean 

streamflow and mean base flow at streamflow-gaging stations 01630700 Gooney 

Run at Route 622 near Glen Echo, Virginia, 01636242 Crooked Run below Route 340 

at Riverton, Virginia, and 0163626650 Manassas Run at Route 645 near 

Front Royal, Virginia ...................................................................................................................55
viii

Tables

1. Well-construction characteristics for the rock types and hydrogeologic units 

in Warren County, Virginia.........................................................................................................15

2. Transmissivity values estimated from specific capacity tests of supply wells 

by rock type in Warren County, Virginia..................................................................................25

3. Apparent ages and uncertainties from chlorofluorocarbons, sulfur hexafluoride, 

and tritium/helium-3 dating methods and percentage of young fraction in water 

samples from wells and springs in Warren County, Virginia, 2003–2005 ..........................39

4. Summary of annual water budget components for the Gooney Run, Crooked Run, 

and Manassas Run Basins in Warren County, Virginia, 2001–2007 ...................................44

5. Annual and seasonal estimates of riparian evapotranspiration based on periods 

of streamflow diurnal cycling at gages 01630700 Gooney Run at Route 622 near 

Glen Echo, Virginia, and 0163626650 Manassas Run at Route 645 near Front Royal, 

Virginia, from calendar years 2003 to 2008.............................................................................45

6. Linear regression equations relating effective recharge to annual precipitation 

at gages 01630700, Gooney Run at Route 622 near Glen Echo, Virginia, 01636242, 

Crooked Run below Route 340 at Riverton, Virginia, and 0163626650, Manassas 

Run at Route 645 near Front Royal, Virginia, 2001–2007.......................................................46

7. Physical and geologic characteristics, estimated effective recharge rates, and 

estimated water use at buildout of ungaged basins in Warren County, Virginia.............52

Appendixes

1. Discharge and water-quality field properties from springs in Warren County, 

Virginia, 2003–2008. ....................................................................................................................64

2. Summary of average dissolved gas compositions (nitrogen, argon, oxygen, carbon 

dioxide, methane, and neon), recharge temperatures, and quantities of excess air 

in water samples from wells and springs in Warren County, Virginia, 2003–2005...........66

3. Concentrations of chlorofluorocarbons and sulfur hexafluoride in North American 

air, 1940–2006...............................................................................................................................67

4. Summary of average chlorofluorocarbon concentrations and calculated 

atmospheric partial pressures in water samples from wells and springs in 

Warren County, Virginia, 2003–2005.........................................................................................68

5. Summary of average chlorofluorocarbon-based model piston-flow apparent 

recharge dates, ages, and uncertainties in water samples from wells and springs 

in Warren County, Virginia, 2003–2005 ....................................................................................69

6. Summary of average chlorofluorocarbon-based model ratio apparent recharge 

dates, ages, and uncertainties in water samples from wells and springs in Warren 

County, Virginia, 2003–2005 .......................................................................................................70

7. Summary of average sulfur hexafluoride data in water samples from wells and 

springs in Warren County, Virginia, 2003–2005......................................................................71

8. Summary of tritium, dissolved helium, and dissolved neon data in water samples 

from wells and springs in Warren County, Virginia, 2003–2005 ..........................................72

9. Summary of apparent tritium/helium-3 ages in water samples from wells and 

springs in Warren County, Virginia, 2003–2005......................................................................73

10. Summary of oxygen (d18O ) and hydrogen (d2H) isotopic data in water samples 

from wells and springs in Warren County, Virginia, 2003–2005 ..........................................74
ix

Conversion Factors and Datum

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

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

Flow rate

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second per square

mile [(ft3/s)/mi2]

 0.01093 cubic meter per second per square

 kilometer [(m3/s)/km2]

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

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

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

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

Specific capacity

gallon per minute per foot 

[(gal/min)/ft)]

 0.2070 liter per second per meter [(L/s)/m]

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Transmissivity

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

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Volume

liter (L) 3.785 gallon (gal)

cubic centimeter (cm3) 0.06102 cubic inch (in3) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32

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 1983 (NAD 83).

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

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 25 °C).

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

Acronyms and Abbreviations:

τ	 	 Apparent tritium/helium-3 age 3

H/3He Tritium/helium-3 3

Hetrit Tritiogenic tritium

Ar Argon

bls Below land surface

BFI Base-flow index

CFCs Chlorofluorocarbons (Freon)

DEM Digital elevation model

ER Effective recharge (mean base flow or groundwater discharge)

ET Evapotranspiration

FO DTS Fiber-optic distributed temperature sensing system

GIS Geographic information system

GPS Global positioning system

GWSI Ground-Water Site Inventory database 

N2 Nitrogen

Ne Neon

NWS National Weather Service

P Precipitation

PRISM Parameter-elevation regressions on independent slopes model

RET Riparian evapotranspiration

RO Mean surface-runoff 

DS Change in groundwater storage

SF6 Sulfur hexafluoride

USGS U.S. Geological Survey

VDEQ Virginia Department of Environmental Quality

WU Water usage (withdrawals)
Abstract

Expanding development and the prolonged drought from 

1999 to 2002 drew attention to the quantity and sustainability 

of the groundwater resources in Warren County, Virginia. 

The groundwater flow systems of the county are complex and 

are controlled by the extremely folded and faulted geology 

that underlies the county. A study was conducted between 

May 2002 and October 2008 by the U.S. Geological Survey, 

in cooperation with Warren County, Virginia, to describe the 

hydrogeology of the metamorphic and siliciclastic fracturedrock aquifers and groundwater availability in the county 

and to establish a long-term water monitoring network. The 

study area encompasses approximately 170 square miles and 

includes the metamorphic rocks of the Blue Ridge Physiographic Province and siliciclastic rocks of the Great Valley 

section of the Valley and Ridge Physiographic Province.

Well depths tend to be shallowest in the siliciclastic rock 

unit (predominantly in the Martinsburg Formation) where 

75 percent of the wells are less than 200 feet deep. Median 

depths to bedrock are generally less than 40 feet across the 

county and vary in response to the presence of surficial 

deposits, faults, siliciclastic rock type, and topographic setting. 

Water-bearing zones are generally within 200 feet of land 

surface; median depths, however, are slightly deeper for the 

hydrogeologic units of the Blue Ridge Province than for those 

of the Great Valley section of the county. Median well yields 

for the different rock units generally range from 10 to 20 gallons per minute. High-yielding wells tend to cluster along 

faults, along the eastern contact of the Martinsburg Formation, 

and within potential lineament zones. Specific capacity is 

relatively low and ranges from 0.003 to 1.43 gallons per 

minute per foot with median values from 0.12 to 0.24 gallon 

per minute per foot. Transmissivity values derived from 

specific capacity data range over four orders of magnitude 

from 0.6 to 380 feet squared per day.

Estimates of effective groundwater recharge from 

2001 to 2007 ranged from 2.4 to 29.4 inches per year in the 

Gooney Run, Manassas Run, and Crooked Run Basins, with 

averages of 15.3, 14.2, and 5.3 inches per year, respectively. 

Base flow accounted for between 57 and 86 percent of mean 

streamflow in the Gooney Run and Manassas Run Basins 

and averaged about 70 percent in these Blue Ridge Province 

basins. In the siliciclastic rock-dominated Crooked Run Basin 

of the Great Valley, base flow accounted for between 33 and 

65 percent of mean streamflow and averaged about 54 percent. 

The high base-flow index values (percentage of streamflow 

from base flow) in these basins indicate that groundwater is 

the dominant source of streamflow during wet and drought 

conditions. About 50 percent of the precipitation that fell on 

the Blue Ridge basins from 2001 to 2007 was removed by 

evapotranspiration, and between 33 and 36 percent of the 

precipitation reached the water table as effective recharge. 

Nearly 76 percent of the precipitation was removed by 

evapotranspiration in the Crooked Run Basin, and effective 

recharge averaged about 12 percent of precipitation between 

2001 and 2007. Average values of runoff in all three basins 

were less than 15 percent of precipitation.

Groundwater flow systems in the county are extremely 

vulnerable to current climatic conditions. Successive years of 

below-average effective recharge cause declines in water 

levels, spring discharges, and streamflows. However, these 

systems can recover quickly because effective recharge 

increases with increasing precipitation. Lack of precipitation, 

especially snow, during the critical recharge period 

(January–April) can have an effect on the amount of recharge 

to the groundwater system and eventual stream base flow. 

Estimated values of annual mean base flow have approached 

and have been below the average regression-derived recharge 

rates during a period classified as having above-average 

precipitation. This relation is indicative of groundwater 

systems with limited storage that are highly responsive to 

current meteorological conditions. Slight changes in annual 

amounts of precipitation or timing of the precipitation can 

affect groundwater recharge. The report of well failures during 

this investigation may be related to the close relation between 

recharge and precipitation.

Preliminary Assessment of the Hydrogeology 

and Groundwater Availability in the Metamorphic 

and Siliciclastic Fractured-Rock Aquifer Systems 

of Warren County, Virginia

By David L. Nelms and Roger M. Moberg, Jr.
2 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Introduction

The metamorphic and siliciclastic fractured-rock aquifer 

systems of the Blue Ridge Physiographic Province (Blue 

Ridge) and of the Great Valley section of the Valley and Ridge 

Physiographic Province (Valley and Ridge), respectively, are 

present over an extensive region of the Northern Shenandoah 

Valley and are increasingly being relied upon to supply water 

to local communities. This is an area with an expanding 

economy and a growing population, and, to meet future water 

needs, these aquifer systems are likely to be developed to 

supplement current withdrawals from the carbonate aquifer 

system and surface-water bodies in the region. A study was 

conducted between May 2002 and October 2008 by the 

U.S. Geological Survey (USGS), in cooperation with Warren 

County, VA, to describe the hydrogeology and groundwater 

availability of the metamorphic and siliciclastic fractured-rock 

aquifers in the county and to establish a long-term water 

monitoring network. An improved understanding of this 

complex aquifer system is required to effectively develop 

and manage it as a sustainable water supply. Hydrogeologic 

information provided by a detailed aquifer evaluation and 

description will provide useful information to better address 

questions about (1) the quantity of water available for use, 

(2) the effects of increased pumpage on groundwater levels 

and instream flows, and (3) the quality of the groundwater 

supply and its vulnerability to current and potential future 

sources of contamination.

Previous groundwater studies in Warren County generally 

have focused on proposed local development or hazardous 

waste sites. These studies were conducted without the benefit 

of knowledge gained from long-term data networks or from 

a systematic evaluation of the groundwater resources in the 

areas underlain by the metamorphic and siliciclastic rocks 

in the county. Future land-use and water-supply planning 

activities in the county should benefit from these data and 

knowledge gained during the course of this study.

Purpose and Scope

This report describes the hydrogeology and groundwater 

availability of the metamorphic and siliciclastic fractured-rock 

aquifer systems in Warren County, VA, and provides hydrogeologic information that can be used to guide the development and management of these important water resources. The 

area in this report encompasses the non-carbonate formations 

in Warren County, VA, consisting of the Blue Ridge rocks in 

the eastern half of the county and primarily of the Martinsburg 

Formation outcrop belt in the western half of the county. 

Water budgets that include effective groundwater recharge are 

presented for the Gooney Run, Crooked Run, and Manassas 

Run Basins for 2003–2007. In addition, water budgets are 

presented for ungaged basins for estimated water usage at 

buildout. This report also includes data on groundwater levels, 

spring discharges, and streamflows collected as part of a 

long-term water-resources monitoring network and data on 

apparent groundwater ages.

Description of the Study Area

Warren County is within the Blue Ridge and Valley and 

Ridge Physiographic Provinces of Virginia (Fenneman, 1938, 

p. 691), at the northern end of the Shenandoah Valley, about 

75 miles (mi) west of Washington, D.C. (fig. 1). Clarke and 

Frederick Counties are to the north, Shenandoah County is 

to the west, and Fauquier and Rappahannock Counties are to 

the east. Warren County, including the independent town of 

Front Royal, encompasses about 217 square miles (mi2). In 

2000, Warren County had a population of 31,584 (U.S. Census 

Bureau, 2003). Altitudes range from 3,474 feet (ft) above 

National Geodetic Vertical Datum of 1929 (NGVD 29) on 

Hogback Mountain in the southeastern part of the county to 

about 410 ft above NGVD 29 where the Shenandoah River 

flows out of the county. The study area encompasses about 

170 mi2 and includes both the Blue Ridge and the Valley and 

Ridge Physiographic Provinces, the latter commonly referred 

to as the Great Valley section (fig. 1). The Great Valley 

section of the central Appalachian Valley and Ridge Province 

extends nearly 1,000 mi from southern New York to central 

Alabama (Yager and others, 2008). The area of investigation 

includes (1) the metamorphic rocks that underlie the Blue 

Ridge Physiographic Province in the eastern part of Warren 

County, which are the oldest bedrock units in the study area; 

and (2) the siliciclastic rocks (sandstone, siltstone, and shale) 

that underlie the western edge of the Great Valley section, 

which are the youngest bedrock units in the study area (fig. 1). 

The Blue Ridge is a mountainous terrain with steep slopes and 

well-developed drainage networks. In the siliciclastic areas, 

the terrain can be gently rolling or steep along the slopes 

and ridge of Massanutten Mountain. These areas are highly 

dissected with well-developed trellis drainage networks that 

align along the predominant fractures that are parallel and 

perpendicular to the strike of the bedding (Yager and others, 

2008). In the central part of the county, the Great Valley 

section is predominantly underlain by soluble carbonate rocks 

that form karst features (such as sinkholes, caves, estavelles, 

swallet holes, and sinking streams) resulting from dissolution 

of these rocks.

Conceptual Model of Groundwater Flow

The groundwater flow systems in the Blue Ridge and in 

the Great Valley section of the Valley and Ridge Physiographic 

Province are complex and often are controlled by the underlying geology of the respective provinces. The hydrogeologic 

section shown in figure 2 represents a conceptual idea of 

groundwater movement through both of these flow systems 

and the karst flow systems of central Warren County. In both 

areas, the rocks are highly deformed by folding, faulting, and 
Introduction 3

Figure 1. Generalized geologic province map of Warren County, Virginia, and location of study area.

Massanutten

Figure 1. Generalized geologic province map of Warren County, Virginia and location of study area.

A

A’

EXPLANATION

Geologic province boundary—As 

 defined by the top of the Antietam

 Formation

Boundary between carbonate and

 siliciclastic rock types in the Great 

 Valley

Federal lands boundary

Line of section

National Weather Service (NWS)

 climatological station and 

 identification number

A A’

NWS

443229

George Washington NF

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Study area

LOCATION OF PHYSIOGRAPHIC PROVINCES, NATIONAL WEATHER SERVICE

STATION, AND STUDY AREA IN VIRGINIA

Washington, D.C. Shenandoah

Valley

Piedmont

Valley

and

Ridge

Coastal Plain

BLUE RIDGE

Appalachian

Plateau

NWS

445851

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

Elevation from U.S. Geological Survey National 

Elevation Dataset digital elevation model, 2001, 

30-meter resolution

7820'

7810'

38

50'

39

0 2 4 KILOMETERS

0 2 4 MILES

NWS

443229

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas Run

Passage Creek

Shenandoah

Geology from Rader and Conley (1995), Rader and 

Gathright (2001), Rader and others (2001, 2003), 

Virginia Division of Mineral Resources (2003), and 

Southworth and others (2009).

Shenandoah

River

Skyline

Drive

George Washington NF

Shenandoah

NP

Horseshoe

Bend

The Point

Massanutten

Mountain

Bentonville

Limeton

Buckton

Riverside

Rockland

Front Royal

55

81

635

611

612

626

522

637

627 522

340 639

661

658

624

638

603

643

638

66

647

604

607

673

619

678

660

615

605

649

622

631

613

634

340

637

55

Siliciclastic Valley

Carbonate

Ridge

Metamorphic

Blue

Great
4 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 2. Generalized hydrogeologic section across Warren County, Virginia. Modified from Rader and Conley (1995). Line of section 

A

–

A’ shown in figure 1.

0.5 0 1.0 2.0 MILES

0.5 0 1.0 2.0 KILOMETERS

Discharge to major

streams and springs

Discharge to mountain

streams and springs

Dissolution-enlarged

opening

Flow in bedrock is typically

parallel to strike

Flow in bedrock follows

irregular fracture networks

Diffuse recharge

through residuum

Concentrated recharge

through sinkholes

and losing streams

? ?

VERTICAL EXAGGERATION 3.1X

3,5003,0002,5002,0001,5001,000

500

0

–500

–1,000

A

ALTITUDE, IN FEET ABOVE OR BELOW NGVD 29

3,5003,0002,5002,0001,5001,0005000–500–1,000

A’

ALTITUDE, IN FEET ABOVE OR BELOW NGVD 29 Front Royal Fault

Massanutten

Mountain

South Fork

Shenandoah River

Flint Run

Round Mountain

Mount

Marshall

Greasy Run

Great Valley Section of the

Valley and Ridge Physiographic Province Blue Ridge Physiographic Province

General Direction of Groundwater Flow Local RegionalRechargeWater-filled fracture or conduitContactFault

—Arrow indicates direction of relative motion

Figure 2. Generalized hydrogeologic section across Warren County, Virginia. Modified from Rader and Conley (1995). Line of section A–A’ shown in figure 1.

Carbonate rocksSandstoneShale

Valley and Ridge Physiographic Province 

Great Valley Section

QuartziteMetavolcanic and MetaigneousRegolith

Blue Ridge Physiographic Province

EXPLANATION
Introduction 5

weathering processes. In order to depict the depth range of 

most wells, the steepness of the geologic structures is overexaggerated in figure 2. Groundwater flow generally follows 

the topography (for example, from higher elevation to lower 

elevation), but actual flow paths often are controlled by the 

underlying geologic structure.

Climate

Climatic data for the region were obtained from National 

Weather Service (NWS) climatological station 445851 

Mt. Weather, which is located to the east in Loudoun County 

at an elevation of 1,720 ft above NGVD 29, and from NWS 

climatological station 443229 Front Royal, which is located in 

Warren County at an elevation of 930 ft above NGVD 29. The 

periods of record for these two stations are 103 and 12 years 

for temperature data and 104 and 12 years for precipitation 

data, respectively (National Oceanic and Atmospheric 

Administration, 2006). The normal values are based on the 

NWS’s current normal climatological period from 1971 to 

2000 for the Mt. Weather station, whereas the normal values 

for the Front Royal station are based on the period of record 

from 1996 to 2007. The mean annual air temperature at the 

Mt. Weather station is 10.6 degrees Celsius (°C) with the 

coldest month being January (–1.8 °C) and the warmest being 

July (22.3 °C). The colder periods of the year are between 

November and April, and the warmer periods are between 

May and October. The mean annual air temperature at the 

Front Royal station is 12.6 °C with the coldest month being 

January (1.6 °C) and the warmest being July (23.8 °C). The 

colder periods of the year are between November and April, 

and the warmer periods are between May and October.

Average annual precipitation at the Mt. Weather station is 

43.3 inches (in.). During an average year, precipitation would 

be highest in May (4.5 in.) and lowest in February (2.5 in.). 

The average annual precipitation of 41.8 in. at the Front 

Royal station is about 2 in. lower than annual precipitation 

at the Mt. Weather station. In an average year, monthly totals 

are highest in September (6.3 in.) and lowest in December 

(2.0 in.) at the Front Royal station. Although precipitation 

is relatively evenly distributed throughout an average year, 

average monthly precipitation tends to be lower for December 

through February than for March through September (fig. 3).

A grid of average annual precipitation interpolated from 

parameter-elevation regressions on independent slopes model 

(PRISM) for Warren County, VA, is shown in figure 4 and 

was extracted from the National PRISM data (PRISM Climate 

Group, Oregon State University, http://www.prismclimate.

org, created May 12, 2009). The normal values are based on 

the NWS’s current normal climatological period from 1971 

to 2000. PRISM is an analytical model that generates gridded 

estimates of annual precipitation from point data at NWS 

climatological stations and a digital elevation model (DEM) 

(Di Luzio and others, 2008). The PRISM grid estimates that 

average annual precipitation ranges from 38.5 to 59.6 in. 

across Warren County. The higher values illustrate the 

orographic effect on precipitation of the elevated areas of 

the Blue Ridge in the eastern part of the county. The lowest 

values also illustrate orographic effects caused by mountain 

ranges to the west in Shenandoah County and West Virginia 

Figure 3. Average monthly precipitation for National Weather Service climatological stations (A) 445851 

Mt. Weather in Loudoun County, Virginia, at an elevation of 1,720 feet above National Geodetic Vertical 

Datum of 1929 (NGVD 29) and (B) 443229 Front Royal in Warren County, Virginia, at an elevation of 930 ft 

above NGVD 29. The normal values for station 445851 are based on the National Weather Service's current 

normal climatological period from 1971 to 2000. The normal values for station 443229 are based on the 

period 1996 to 2007.

0

2

4

6

8

Average

0

2

4

6

8

Average

MONTH

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

AVERAGE MONTHLY PRECIPITATION, IN INCHES

Figure 3. Average monthly precipitation for National Weather Service climatological stations (A) 445851 Mt. Weather 

located in Loudoun County, Virginia, at an elevation of 1,720 ft above NGVD 29 and (B) 443229 Front Royal located in 

Warren County, Virginia, at an elevation of 930 ft above NGVD 29. The normal values for station 445851 are based on 

the National Weather Service’s current normal climatological period from 1971 to 2000. The normal values for station 

443229 are based on the period 1996 to 2007.

A

B
6 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 4. Average annual total precipitation for Warren County, Virginia, based on parameter-elevation regressions on independent 

slopes model (PRISM). The normal values are based on the National Weather Service's current normal climatological period from 

1971 to 2000. Data from PRISM Climate Group, Oregon State University, http://www.prismclimate.org, created May 12, 2009.

to the west-northwest and Massanutten Mountain along the 

western boundary of the study area. The lowest average annual 

precipitation is present in the northern parts of the county in 

the Great Valley. This area is the northern extent of the rain 

shadow centered on Harrisonburg, VA, which is caused by the 

mountain ranges to the west (Nuckels and others, 1991).

Well- and Spring-Numbering System

A unique USGS identifier was assigned to each well 

and spring for this study, for the purpose of storing wellconstruction and site information in the Groundwater Site 

Inventory database, which is part of the National Water 

Massanutten

Mountain

EXPLANATION

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and

 siliciclastic rock types in the Great 

 Valley

Federal lands boundary

Figure 4. Average annual precipitation across Warren County, Virginia, based on parameter-elevation regressions on independent 

slopes model (PRISM). The normal values are based on the National Weather Service’s current normal climatological period from 1971 

to 2000. Data from PRISM Climate Group, Oregon State University, http://www.prismclimate.org, created 12 May 2009.

Skyline

Drive

George Washington NF

Shenandoah

NP

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Riverside

Buckton

Front Royal

522

522

340

66

340

George Washington NF

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

Elevation from U.S. Geological Survey National 

Elevation Dataset digital elevation model, 2001, 

30-meter resolution

Average annual total precipitation—In 

 inches

59.6

38.5

39.3

39.5

39.8

40.2

40.7

41.5

42.7

45.2

53.1

7820'

7810'

38

50'

39

0 2 4 KILOMETERS

0 2 4 MILES

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas Run

Passage Creek

Shenandoah

Shenandoah

River

81

55

55

Siliciclastic Carbonate

Ridge

Metamorphic

Blue

Great

Valley
Hydrogeology 7

Information System maintained by the USGS. These USGS 

identifiers are based on the Virginia coordinate grid number of 

the USGS standard series 7.5-minute topographic quadrangle 

in which the well is located, and the chronological order in 

which the well was entered. For example, the USGS number 

45V 3 corresponds to the third well entered by the USGS in 

the area covered by the Front Royal quadrangle, which has a 

Virginia coordinate grid number of 45V. Springs are numbered 

in a similar manner with the addition of "S" after the Virginia 

coordinate grid number of the USGS standard series 7.5-

minute topographic quadrangle.

Previous Investigations

Cady (1936) conducted the first comprehensive study 

of the groundwater resources of the Shenandoah Valley, 

which included Warren County. Cady noted that well depths 

were relatively shallow across the county and mostly ranged 

in depth between 50 and 150 ft, which is probably related 

to cable-tool drilling capabilities available at that time. He 

also noted the presence of an “8-foot cavity in the limestone 

having been encountered at 460 feet” in a well, 1.25 mi south 

of Front Royal that, according to the driller, had a yield that 

was “unlimited.” Of particular interest to the current study, 

Cady (1936) surprisingly noted that rocks in the Blue Ridge 

are a “fairly good source of ground water.” Hack (1965) 

provided a detailed explanation of the geomorphology of the 

Shenandoah Valley of Virginia and West Virginia. A regional 

investigation from Maine to Virginia by Cederstrom (1972) 

suggested that wells constructed for high capacity use are the 

best indicators of the potential of the rocks to yield water. 

Trainer and Watkins (1975) conducted a geohydrologic 

reconnaissance of the upper Potomac River Basin that focused 

on the hydrologic characteristics of the rocks, base flow and 

low flow of streams, water management, and chemical quality 

of groundwater. Rader and others (1996) compiled the geology 

of the Lord Fairfax Planning District at a scale of 1:100,000. 

Rader and Gathright (2001) and Rader and others (2001, 2003) 

compiled the geology of the northern Virginia area, including 

Warren County, at a 1:100,000 scale. Doctor and others (2008) 

provided details of the bedrock structural controls on the 

occurrence of sinkholes and springs in the northern Great Valley karst and also suggested that deep karst development may 

have been caused by rising fluids under hypogenic (confined) 

conditions in the geologic past. Yager and others (2008) 

developed a finite-element model for the Shenandoah Valley 

of Virginia and West Virginia that simulated groundwater 

flow in the folded, fractured sedimentary rocks by specifying 

variable directions of the hydraulic conductivity tensor in 

order to match changes in the strike and dip of bedrock across 

the valley.

Several investigations specifically dealt with the geology 

and hydrology of Warren County. DeKay (1972) described the 

development of groundwater supplies in Shenandoah National 

Park. The geology of the Front Royal, Strasburg, Linden, and 

Flint Hill quadrangles were mapped at a scale of 1:24,000 by 

Rader and Biggs (1975, 1976) and Lukert and Nuckols (1976) 

and included sections on hydrogeology by R.H. DeKay. 

Orndorff and others (1999) mapped the geology of the Middletown quadrangle at a scale of 1:24,000. Rader and Webb 

(1979) divided the county into 11 units in terms of factors 

affecting land modification, such as soils, drainage characteristics, erodibility, stability, ease of excavation, and potential 

use and limitations. Morgan and others (2003) mapped the 

Pleistocene and Holocene colluvial fans and terraces in parts 

of the Blue Ridge in the county. As part of the revision of the 

geology of Shenandoah National Park, Southworth and others 

(2009) mapped the geology of parts of Warren County. The 

U.S. Department of Agriculture conducted the soil survey 

of the county (Holmes and others, 1984). Allingham (1987) 

describes the results of a groundwater study conducted for 

Warren County. Several groundwater age-dating studies have 

sites in and adjacent to the county and indicate that apparent 

ages are less than 60 years (Plummer and others, 2001; Nelms 

and others, 2003). Orndorff (2006) studied the karst landscape 

in the Rockland area of the county in order to evaluate 

potential hazards and develop best-management practices to 

minimize effects of land-use activities on the karst system 

and biota.

Hydrogeology

The Blue Ridge and the western part of the Great Valley 

section of the Valley and Ridge in Warren County, VA, are 

characterized by metamorphic and siliciclastic fractured-rock 

aquifer systems, respectively. Mesoproterozoic to Lower Cambrian metamorphic rocks underlie the Blue Ridge in eastern 

Warren County. Siliciclastic rocks of the Upper Ordovician 

Martinsburg Formation and Silurian Massanutten Sandstone 

underlie the western part of the county. The bedrock in both 

of these areas is variably fractured, folded, and faulted (Yager 

and others, 2008), and the regolith material consists of a 

mantle of residuum (weathered bedrock), alluvium (stream 

deposits), and colluvium (gravity deposits). The underlying 

geology is a strong control on the occurrence and flow of 

groundwater, and water generally moves under fracture or 

diffuse-flow conditions. Lower Cambrian to Upper Ordovician 

limestone and dolostone underlie the central part of Warren 

County, in which karst aquifers that exhibit both conduit- and 

diffuse-flow conditions are developed.

Geology

The geology of Warren County is the major control on the 

occurrence and movement of groundwater. About 300 million 

years ago, the late Paleozoic Alleghanian orogeny folded and 

faulted all of the rocks that underlie the county. The terrain 

that has developed is a direct reflection of the underlying 

lithology and geologic structure. The mountainous terrain of 
8 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

the Blue Ridge formed in response to the resistant nature of 

the underlying metamorphic rocks (Hack, 1965). Generally, 

the Great Valley section is a gently to moderately rolling 

terrain with low relief, except on the slopes of Massanutten 

Mountain and areas underlain by the low permeability shale 

and siltstone of the Martinsburg Formation, which exhibit 

highly dissected drainage patterns. 

Hydrogeologic Units

The Blue Ridge and the western part of the Great Valley 

section of Warren County can be subdivided into hydrogeologic units based on the mapped geologic formations (fig. 5). 

In general, these hydrogeologic units are grouped on the basis 

of gross lithology or rock type: Metamorphic—metavolcanic, 

metaigneous, and metasedimentary rocks; and Siliciclastic—

sandstone, siltstone, and shale.

Figure 5. Generalized hydrogeologic units of Warren County, Virginia.

Massanutten

Mountain

Geology from Rader and Conley (1995), Rader and Gathright 

(2001), Rader and others (2001, 2003), Virginia Division of 

Mineral Resources (2003), and Southworth and others (2009).

Figure 5. Generalized hydrogeologic units of Warren County, Virginia.

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

Elevation from U.S. Geological Survey National 

Elevation Dataset digital elevation model, 2001, 

30-meter resolution

7820'

7810'

38

50'

39

0 2 4 KILOMETERS

0 2 4 MILES

Skyline

Drive

George Washington NF

Shenandoah

NP

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Riverside

Buckton

Front Royal

522

66

Front

Happy Creek Fault

Royal Fault

Om

Om

Om

Zcm

Zcm

Zcm

Zcm

Yor

Ob

Ob

Ob

Ob

Ob

Ob

Ce

Ce

Ce

Cch

Cch

Cwa

Cwa

Yom

OCc

OCc

Zcm

Oeln

Yos

Yod

Yor

Yom

Os

Os

Yoq

Cca

Cca

Cwa

Yom

Yod

Cca

OCc

Sm

Ccw

Ct

Cca

Cca

Cch

Cca

Sm

Oeln

Sm

Os

Os

Os

Ccw

Zsr

Zsr

Zsr

Zcp

Zsr

Zcp

Zcp

Zcp

Zcp

Zcp

Zsr

Zcp

Zsr

Zsr

Zmd

Zcp Zmd

Zmd

Zmd

Zmd

Zmd

Zmd

Oeln

Oeln

Oeln

Oeln

Yom

Yom

Yor Zcm

Zcm

Zcm

Zcm

Zcm

Om

Om

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas Run

Passage Creek

Shenandoah

Shenandoah

River

81

522

340

340

55

55
Hydrogeology 9

Figure 5. Generalized hydrogeologic units of Warren County, Virginia.—Continued

The hydrogeologic characteristics vary among these units and 

between the major rock type groupings. The carbonate rock 

unit in the Great Valley section of the central part of Warren 

County is an additional group, but it is not described in detail 

in this report. Descriptions of the individual hydrogeologic 

units are provided below. The map symbol indicated in the 

following text identifies the respective hydrogeologic unit in 

figure 5.

Metamorphic Rock Unit of the Blue Ridge 

Physiographic Province

The classification of hydrogeologic units as metamorphic 

is based on the grouping established in Yager and others 

(2008). These units represent the oldest rocks in Warren 

County and are on the eastern side of the Shenandoah Valley 

in the Blue Ridge. The metamorphic rock unit consists 

of Mesoproterozoic Old Rag Granite and the unnamed 

monzodiorite and gneissic units; Neoproterozoic metaclastic 

rocks of the Swift Run Formation; metadiabase dikes, metabasalt, and metavolcanic phyllite of the Neoproterozoic Catoctin 

Formation; and the metasedimentary rocks of the Lower 

Cambrian Weverton, Harpers, and Antietam Formations of the 

Chilhowee Group (fig. 5).

Orthopyroxene Granodiorite Gneiss

The Mesoproterozoic orthopyroxene granodiorite gneiss 

(Yod) consists of dark-gray, medium- to coarse-grained, 

amphibole-bearing orthopyroxene granodiorite gneiss that 

is compositionally layered and strongly foliated. Alternating 

centimeter-scale layers of quartz and feldspars with dark layers of pyroxene and amphibole define the compositional layers 

and strong foliation. This unit is composed of alkali feldspar 

(microcline or orthoclase), plagioclase, quartz, amphibole, and 

orthopyroxene (Southworth and others, 2009).

EXPLANATION

HYDROGEOLOGIC UNITS

Stonehenge Limestone

Martinsburg Formation

Edinburg Formation, Lincolnshire and

 New Market Limestones

Beekmantown Group

Conococheague Limestone

Elbrook Formation

Waynesboro Formation

Massanutten Sandstone

SYSTEM

(age)

Cwa

Ce

OCc

Os

Ob

Oeln

Ct Tomstown Dolomite 

Cca Antietam Formation

Cch Harpers Formation

Weverton Formation

Catoctin Formation

Metavolcanic phyllite

Metabasalt

Swift Run Formation

Orthopyroxene monzogranite-quartz monzodiorite

Old Rag Granite

Megacrystic orthopyroxene syenogranite-monzogranite gneiss

Orthopyroxene quartz diorite gneiss

Orthopyroxene granodiorite gneiss

Zcp

Zcm

Zsr

Zmd Metadiabase dikes

Ccw

Yom

Yor

Yoq

Yod

Yos

Om

Sm Carbonate

Metamorphic

Siliciclastic

ROCK UNIT

FAULTS

Thrust—Sawteeth on upper plate. 

 Dashed where inferred

Strike-slip—Showing strike and direction of 

 relative motion. Dashed where inferred

Normal—Bar on downthrown side. Dashed 

 where inferred

Unclassified fault—Movement unknown. 

 Dashed where inferred

FOLDS

Syncline

Overturned syncline

Federal lands boundary

Anticline

Overturned anticline

Figure 5. Generalized hydrogeologic units of Warren County, Virginia.—Continued

CONTACT

Chilhowee Group

Mesoproterozoic

Upper Neoproterozoic

Middle

Lower

Lower

Middle

Upper

Silurian

Ordovician Cambrian
10 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Orthopyroxene Quartz Diorite Gneiss

The Mesoproterozoic orthopyroxene quartz diorite gneiss 

(Yoq) consists of greenish-gray to black, medium-grained, 

compositionally layered, strongly foliated orthopyroxene 

quartz-diorite gneiss. This gneiss is orthopyroxene-, biotite-, 

and garnet-bearing and is present as a xenolith within 

the Old Rag Granite. Alternating domains of quartz and 

feldspar and of garnet, biotite, and orthopyroxene define the 

compositional layering. The gneiss is composed of orthoclase, 

plagioclase, quartz, orthopyroxene, and biotite (Southworth 

and others, 2009).

Megacrystic Orthopyroxene Syenogranite-Monzogranite Gneiss

The Mesoproterozoic megacrystic orthopyroxene 

syenogranite-monzogranite gneiss (Yos) consists of dark-gray 

to dark-greenish-gray, very coarse grained, megacrystic 

orthopyroxene syenogranite-monzogranite gneiss that is 

strongly foliated. This gneiss is orthopyroxene-, amphibole-, 

and clinopyroxene-bearing with subhedral to euhedral, 

monocrystalline alkali-feldspar megacrysts. Alternating 

quartzofeldspathic layers and domains of orthopyroxene 

and amphibole define the compositional layering, and the 

strong foliation parallels this layering. The gneiss is primarily 

composed of alkali-feldspar microperthite (microcline), 

plagioclase, and quartz, but also contains orthopyroxene, 

amphibole, and clinopyroxene. The gneiss weathers to form 

light-gray, spheroidal boulders (Southworth and others, 2009).

Old Rag Granite

The Mesoproterozoic Old Rag Granite (Yor) consists of 

white to light-gray, medium- to coarse-grained, inequigranular, 

garnetiferous leucogranite and garnetiferous syenogranite that 

is nonfoliated to weakly foliated and massive. The granite is 

biotite- and orthopyroxene-bearing and contains gray and blue 

quartz grains. The granite is primarily composed of orthoclase, 

plagioclase, quartz, garnet, and biotite. Dikes of mediumgrained, equigranular alkali-feldspar granite, syenogranite, and 

pegmatite have intruded the Old Rag Granite (Southworth and 

others, 2009).

Orthopyroxene Monzogranite-Quartz Monzodiorite

The Mesoproterozoic orthopyroxene monzogranitequartz monzodiorite (Yom) consists of dark-green to black, 

medium- to coarse-grained, inequigranular, orthopyroxene 

monzogranite and quartz monzodiorite that are massive and 

nonfoliated. The rocks are orthopyroxene-, amphibole-, and 

clinopyroxene-bearing. The unit is composed of alkali-feldspar 

microperthite (microcline), plagioclase, quartz, orthopyroxene, 

amphibole, and clinopyroxene. Planar alignment of ferromagnesian minerals defines the weak foliation (Southworth and 

others, 2009). 

Swift Run Formation

The Neoproterozoic Swift Run Formation (Zsr) consists 

of three rock types: a pink to gray, sandy and pebbly metagraywacke and meta-arkose that is dark greenish brown; a 

tuffaceous phyllite that is silver gray and purple; and thin beds 

of metabasalt. The thickness of the Swift Run is from 0 to 

150 ft (Rader and Conley, 1995).

Metadiabase Dikes

The Neoproterozoic metadiabase dikes (Zmd) consist 

of dark-greenish-gray, fine- to medium-grained metadiabase 

that is massive to schistose in texture. The metadiabase is 

predominantly composed of chlorite, albite, epidote, and 

actinolite. This unit is similar in composition to the metabasalt 

of the Catoctin Formation and has been interpreted as feeder 

dikes for these volcanic flows (Southworth and others, 2009).

Catoctin Formation

In Warren County, the Neoproterozoic Catoctin Formation is divided into two units: metabasalt and metavolcanic 

phyllite (fig. 5). The metabasalt (Zcm) consists of dark-green, 

amygdaloidal metabasalt (greenstone) and chlorite schist 

interlayered with thin, discontinuous, finely laminated phyllitic 

metasiltstone and thin metasandstone and dark, variegated, 

vesicular tuffaceous phyllite and mud-lump (rip-up) breccias 

(Reed, 1955). The metabasalt is massive (very thick bedded) 

to schistose, aphanitic (fine grained) with well-developed 

cleavage and columnar jointing. Near the top and bottom 

of some metabasalt beds are albite, quartz, calcite, epidote, 

chlorite, and jasper amygdules (Rader and Conley, 1995). 

The metabasalt is interpreted as a series of basaltic flows, 

which tend to form prominent ledges. Epidosite locally 

is present as light green, blocky masses in the metabasalt 

breccia (Southworth and others, 2002, 2009). Badger and 

Sinha (1988) determined a rubidium-strontium (Rb/Sr) age of 

570 ± 36 million years (Ma) for the metabasalt of the Catoctin 

Formation in Virginia. 

The metavolcanic phyllite (Zcp) is dark grayish blue 

to dusky red phyllite and slate that is mottled to lustrous 

and contains white to green, elongated vesicles and smeared 

sericite and chlorite blebs. This unit has been interpreted 

as vesicular flows, volcanic tuffs, pumice, and volcanic ash 

deposits (Southworth and others, 2009). The overall thickness 

of the Catoctin is from 2,000 to 2,500 ft (Rader and 

Conley, 1995).

Weverton Formation of the Chilhowee Group

The Lower Cambrian Weverton Formation (Ccw) of the 

Chilhowee Group consists of a 150-ft basal quartz-cemented 

conglomerate. The basal conglomerate has subangular to 

rounded quartz and shale clasts within a matrix of sand-size 
Hydrogeology 11

quartz and lithic grains. The middle part of the Weverton 

consists of a light-gray, conglomeratic quartzite with greenishgray sandy phyllite and micaceous sandstone interbeds. The 

upper 150 ft of the Weverton consists of quartz-pebble conglomerate and micaceous sandstone. Brezinski (1992) named 

and mapped these three units of the Weverton as the Buzzard 

Knob, Maryland Heights, and Owens Creek Members north of 

Warren County, but these units have not been delineated in the 

study area and are not shown in figure 5. The thickness of the 

Weverton is about 500 ft (Rader and Conley, 1995).

Harpers Formation of the Chilhowee Group

The Lower Cambrian Harpers Formation (Cch) of the 

Chilhowee Group consists of phyllite and sandy phyllite with 

interbedded gray to olive-gray lithic sandstone in the lower 

900 ft. The upper 1,100 ft of the Harpers consist of sandstone 

and quartzite that are gray, fine to medium grained, and, in 

parts, ferruginous. The thickness of the Harpers is 2,000 ft 

(Rader and Conley, 1995).

Antietam Formation of the Chilhowee Group

The Lower Cambrian Antietam Formation (Cca) of the 

Chilhowee Group consists of very light gray quartzite interbedded with greenish-gray, sandy metasiltstone in the lower 

part. Skolithos tubes are numerous in the quartzite beds. The 

Antietam Formation becomes coarser grained higher in the 

formation from a bioturbated, very light gray, medium-bedded, 

well-sorted, fine- to medium-grained sandstone to a mediumgray, calcareous, crossbedded, coarse-grained sandstone 

(Southworth and others, 2002). The thickness of the Antietam 

is from 440 to 600 ft (Rader and Conley, 1995).

Siliciclastic Rock Unit of the Great Valley Section of the 

Valley and Ridge Physiographic Province

The siliciclastic rock unit is composed of clastic sedimentary rocks that primarily consist of silica-bearing minerals, 

such as quartz. In Warren County, the siliciclastic rocks are 

present in the western part of the Great Valley section and are 

the youngest rocks in the county. This unit consists of shale, 

sandstone, and siltstone of the Middle and Upper Ordovician 

Martinsburg Formation and sandstone, quartzite, conglomerate, and sandy shale of the Silurian Massanutten Sandstone 

(fig. 5).

Martinsburg Formation

The Middle and Upper Ordovician Martinsburg Formation (Om) consists of more than 3,000 ft of silty shale that 

is an olive-green to dark-gray siltstone and sandstone that 

is medium to coarse grained and locally contains pebbles. 

The Martinsburg in the Massanutten synclinorium along the 

western part of Warren County is the deepest water deposit 

for the Cambrian and Ordovician rocks of the Shenandoah 

Valley. The Stickley Run Member forms the basal unit of 

the Martinsburg Formation and may be as much as 900 ft 

thick (Epstein and others, 1995). The Stickley Run Member 

consists of gray to medium-dark-gray calcareous shale and 

medium-gray to grayish-black, olive-gray, grayish-orange 

limestone. The limestone is very thin bedded, platy, very fine 

grained, laminated, and argillaceous (clay rich). The upper 

100 to 200 ft of the Martinsburg consists of sandstone that 

is brown, medium to coarse grained, and fossiliferous in the 

lower portion. The overall thickness of the Martinsburg ranges 

from 3,500 ft (Rader and Conley, 1995) to as much as 5,000 ft 

thick (Orndorff and others, 1999).

Massanutten Sandstone

The Silurian Massanutten Sandstone (Sm) consists of 

sandstone and quartzite that is white to medium gray and fine 

to coarse grained. Lenses of quartz-pebble conglomerate and 

thin, black sandy shale layers are present within the sandstone 

and quartzite and contain plant fossils (Pratt and others, 1978). 

The Massanutten Sandstone forms the ridgeline of Massanutten Mountain in the western part of Warren County. The 

thickness of the Massanutten is approximately 900 ft (Rader 

and Conley, 1995).

Carbonate Rock Unit of the Great Valley Section of the 

Valley and Ridge Physiographic Province

The carbonate rock unit consists of dolostone, shale, 

limestone, and sandstone of the Lower Cambrian Tomstown 

Dolomite and Waynesboro Formation; dolostone, dolomitic 

limestone, shale, and calcareous siltstone of the Middle and 

Upper Cambrian Elbrook Formation; laminated limestone, 

dolomitic limestone, dolostone, and calcareous sandstone of 

the Upper Cambrian and Lower Ordovician Conococheague 

Limestone including the Big Spring Station Member; 

dolostone, limestone, and chert of the Lower Ordovician 

Stonehenge Limestone (including Stoufferstown Member) and 

the Lower and Middle Ordovician Rockdale Run Formation 

of the Beekmantown Group; and limestone and shale of the 

Middle Ordovician Edinburg Formation, Lincolnshire and 

New Market Limestones (fig. 5). The combined thickness of 

the carbonate rock unit is approximately 10,000 ft (Rader and 

Conley, 1995).

Structural Geology

Warren County is located on the west limb of the Blue 

Ridge–South Mountain anticlinorium, which is also the 

eastern limb of the first-order Massanutten synclinorium. 

The Massanutten synclinorium is a complexly folded 

synclinorium with numerous tight, upright, second- and 

third-order disharmonic folds (anticlines and synclines) that 

verge up the limbs of the higher-order synclinorium. The 

Massanutten synclinorium contains about a 3-mi-thick section 

of siliciclastic and carbonate rocks. The eastern limb of the 

synclinorium is characterized by rocks with near vertical dips 
12 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

to the northwest or locally overturned beds dipping steeply to 

the southeast (Southworth and others, 2002; Yager and others, 

2008). The rocks in Frederick County are on the western limb 

of the Massanutten synclinorium and dip gently southeast 

(Harlow and others, 2005; Yager and others, 2008).

The Mesoproterozoic to Lower Cambrian rocks of the 

Blue Ridge have been folded and thrust faulted over the 

younger rocks of the Great Valley and form the northwest 

flank of the Blue Ridge–South Mountain anticlinorium, which 

plunges gently northeastward (Gathright and Nystrom, 1974) 

and extends from southern Pennsylvania to central Virginia 

(Cloos, 1951). These rocks were folded and transported 

by faulting from the east a distance of more than 100 mi 

during the tectonic activity of the Alleghanian orogeny about 

300 million years ago (Southworth and others, 2007). The 

Mesoproterozoic rocks of the Blue Ridge have undergone 

amphibolite- to granulite-facies metamorphism, and the 

younger rocks of the Blue Ridge have undergone lower 

greenschist-facies metamorphism. Most of the carbonate rocks 

of the Great Valley were not buried deep enough to become 

metamorphosed (Southworth and others, 2002, 2009).

The structural deformation in both the Valley and Ridge 

and Blue Ridge has created weaknesses in the competent 

bedrock that are of hydrologic significance because these 

features enhance weathering and create pathways for groundwater movement. Furthermore, bedding, joints, and foliations 

in the bedrock are preserved as relicts in the mantle of regolith 

material, which facilitates movement of water from the surface 

into the groundwater systems of the county (Harlow and 

others, 2005).

Bedding-Plane Partings, Joints, Cleavage, and Foliations

Groundwater moves through fractures in the bedrock that 

result from various processes. Groundwater movement and 

storage occurs in the secondary permeability of these partings. 

Bedding-plane partings (fig. 6) are separations between 

different beds in sedimentary rocks. Partings can develop 

along foliations in the metamorphic rocks of the Blue 

Ridge. The tectonic forces of the Alleghanian orogeny 

resulted in the formation of at least four types of joints 

(fractures) and their associated orientations in the rocks: 

dip, oblique, strike, and tension (fig. 6). Extension in the 

least principal stress direction causes dip joints to form 

perpendicular to fold axes. Conjugate sets of oblique 

joints form as the rocks are sheared. Strike joints form 

parallel to fold axes, whereas tension joints form along 

fold hinges (Harlow and others, 2005). Joint types vary 

with rock type. Brittle deformation is characteristic of 

the carbonate, sandstone, metavolcanic, and granitic 

rocks; ductile deformation is characteristic of the finer 

grained rocks such as the shale of the Martinsburg 

Formation and phyllite in the Blue Ridge. Joints also 

form along cleavage in rocks of the Great Valley and 

Blue Ridge. Axial planar cleavage is most evident in the 

shale of the Martinsburg Formation (Harlow and others, 

2005), and flow along cleavage planes may be more prevalent 

than along bedding, especially in the Martinsburg Formation 

(C.S. Southworth, U.S. Geological Survey, written commun., 

2009). Partings between the numerous metabasalt flows of the 

Catoctin Formation can be horizontal to moderately southeast 

dipping and form bedrock terraces and benches (Southworth 

and others, 2009). Columnar jointing also is present in the 

Catoctin Formation because of shrinkage during cooling of the 

basalt to form hexagonal joints, but it is relatively uncommon 

in the county (Lukert and Nuckols, 1976).

Dips of bedding-plane partings, cleavage, various joint 

types, and foliations (in the metamorphic rocks of the Blue 

Ridge) are highly variable, range from horizontal to vertical, 

and can be overturned. However, steeply dipping beds are 

prevalent in the county because of location on the highly 

deformed eastern limb of the Massanutten synclinorium. Dip 

directions generally are to the northwest or southeast (Southworth and others, 2002; Yager and others, 2008). Although the 

strike of the rocks in Warren County is variable, the general 

strike is N. 30° E. (Yager and others, 2008). Foliations in the 

metamorphic Mesoproterozoic rocks of the Blue Ridge follow 

the northwest strike of the belts (Southworth and others, 

2009). Groundwater flows through partings developed along 

the dominant foliations, which are predominantly cleavage, 

rather than through primary bedding in the Blue Ridge (Yager 

and others, 2008).

Folds

Folds in Warren County are the result of at least two 

tectonic events from the east, which caused the limbs of the 

synclines and west limbs of anticlines to be oversteepened and 

locally overturned (Rader and Biggs, 1975). Deformation has 

the character of many subsidiary folds developed on the limbs 

of the major folds. Folds of various types formed in the Blue 

Ridge–South Mountain anticlinorium and the Massanutten 

synclinorium, which are broad, northeast-trending first-order 

Figure 6. Joint types and bedding in folded rocks. Modified from 

Earth Science Australia (2004); Harlow and others (2005).

Dip joint

Strike joint

Oblique joints

(conjugate

shear joints)

Tension joints

Maximum principal

stress direction

Bedding

Figure 6. Graphic representation of joint types and bedding in folded 

rocks (modified from Earth Science Australia, 2004; Harlow and others, 

2005).

Bedding plane
Hydrogeology 13

fold complexes (Southworth and others, 2009). These lowerorder folds have axes that follow the strike of the rocks to the 

northeast and plunge to the north-northeast generally at low 

angles (Rader and Biggs, 1975). Orndorff and others (1999) 

noted an apparent disharmony in fold wavelength in response 

to rheological differences of the rock units. Folds in the Martinsburg Formation have shorter wavelengths than the folds 

in the Cambrian and Lower Ordovician carbonate rocks, with 

intermediate wavelengths in Middle Ordovician limestone. 

As an example, a small anticline in the Middle Ordovician 

Edinburg Formation near streamflow-gaging station 01631000 

South Fork Shenandoah River near Front Royal, VA, is shown 

in figure 7. The sinuous appearance of some of the hydrogeologic units in figure 5 is the result of folding.

Faults

Faults mapped in Warren County are thrust, normal, 

transverse, or cross-strike faults. Thrust faults strike northnortheast parallel to the structural grain with variable dips generally to the southeast, whereas local back thrusts dip steeply 

to the northwest (Rader and Biggs, 1975; Yager and other, 

2008). Gathright (1976) noted that bedrock exposures of these 

faults are rare and usually covered by unconsolidated deposits 

or a thick mantle of saprolite (weathered rock), but bedrock 

along the fault trace is intensely fractured as evidenced by 

brecciated and mylonitized rocks. The intense fracturing along 

these faults allows for preferential ground-water flow, but 

mylonitized zones may be sealed and inhibit flow and storage 

of groundwater. Some of the faults, especially along the 

boundary between the Great Valley section and Blue Ridge, 

have been folded and faulted as evidenced by the sinuous and 

offset fault traces in figure 5 (Southworth and others, 2007). 

The Front Royal fault (fig. 5) is a shallow-dipping thrust 

fault that is part of the frontal Blue Ridge thrust fault system 

(Southworth and others, 2009). The Front Royal fault in 

places trends obliquely across the structural grain (Southworth 

and others, 2009) and is an overthrust salient of the Blue 

Ridge–South Mountain anticlinorium (Rader and Biggs, 1975) 

in which rocks of the Blue Ridge overlie the younger rocks of 

the Great Valley section in the county.

The high-angle normal faults, which are transverse or 

cross-strike faults, generally strike north-northwest across the 

structural grain, but some of these faults parallel the structural 

grain in the Blue Ridge (fig. 5). These high-angle faults (60° to 

75°) often truncate and offset folded rocks and thrust faults in 

the county and correspond with topographic lineaments (Bailey and others, 2006; Southworth and others, 2009). McCoy 

and others (2005a, b) and Kozar and others (2007) noted the 

effects that cross-strike faults have on hydraulic properties, 

well yields, and flow in the counties of West Virginia in the 

Shenandoah Valley.

Figure 7. Fold in the Middle Ordovician Edinburg Formation in roadcut on State Route 679 

at intersection with State Route 677 near streamflow-gaging station 01631000 South Fork 

Shenandoah River near Front Royal, Virginia. Note groundwater seepage along bedding-plane 

partings (arrow). Photograph by Michael Strader, U.S. Geological Survey, March 2005.

Figure 7. Fold in the Middle Ordovician Edinburg Formation in roadcut on State Route 679 at intersection with State 

Route 677 near streamflow gaging station 01631000 South Fork Shenandoah River near Front Royal, Virginia. Note 

groundwater seepage along bedding-plane partings (arrow). Photograph taken by Michael Strader, U.S. Geological 

Survey, March 2005.

Bedding

Fold

axis

Bedding

Fold

axis
14 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Surficial Geology

Deposits of unconsolidated surficial materials cover most 

of the area in Warren County and are noticeably absent where 

bedrock crops out. These deposits are the result of various 

processes, such as running water, chemical weathering, gravity, extreme rainfall events, and freeze-thaw cycles. Residuum 

and saprolite, which are the result of weathering of the parent 

bedrock, vary in thickness in response to factors, such as rock 

type, fracture density, and topographic setting. Hack (1965) 

states that residuum and saprolite in the Blue Ridge can range 

from stony clay loam of the relatively resistant rocks of the 

Catoctin Formation to a coarse-grained sandy saprolite with 

core stones in areas underlain by the granitic rocks. Areas 

underlain by the siliciclastic rocks of the Martinsburg Formation and the carbonate rocks of Middle Ordovician age and 

the upper parts of the Beekmantown Group tend to have a thin 

mantle of residual material, whereas the older carbonate units 

can have a thick mantle of residuum of siliceous residues with 

core stones of sandstone and chert (Hack, 1965). Southworth 

and others (2009) related the type of surficial deposit to 

topographic setting: (1) colluvium is present in the highlands, 

(2) debris-fan deposits are generally in coves and hollows of 

slopes, (3) alluvial fans are located on the lower slopes and 

valleys on the west side of the Blue Ridge, and (4) fluvial 

terrace deposits of sandstone cobbles are located along major 

rivers in the Shenandoah Valley. Groundwater movement in 

areas of the Blue Ridge where coarse material is present along 

the stream valleys can be rapid as interflow or subsurface 

stormflow (Wright, 1990). A thick apron of alluvial or colluvial deposits and areas with a thick mantle of coarse-grained 

residuum and saprolite could potentially allow for significant 

groundwater storage.

Hydrology

Warren County is characterized by metamorphic and 

siliciclastic fractured-rock aquifer systems as well as karst 

systems in the central part of the county that have developed 

in the folded and fractured rocks. Diffuse-flow conditions are 

characteristic of the fractured-rock aquifer systems in areas 

underlain by the metamorphic and siliciclastic rocks. Conduitand diffuse-flow conditions are present in the karst aquifer 

systems (Wright, 1990). Porous media flow is present in the 

mantle of regolith material as well as preferential groundwater 

flow along relict structures in the regolith. The fractured-rock 

and karst aquifers generally are considered unconfined, and 

topography is the driving force behind groundwater movement; however, confined aquifers may be present locally 

(Harlow and others, 2005). The source of groundwater 

recharge is precipitation that falls in the county. Recharge 

occurs by percolation of water through the regolith mantle and 

along partings in the rock and by direct inflow into sinkholes 

and from sinking streams. Groundwater eventually discharges 

to streams often in the form of springs.

Hydrogeologic Characteristics

Each of the rock units has distinctive hydrogeologic 

characteristics that were evaluated by analyzing the records 

recorded by local well drillers. More than 350 well records 

from files maintained by the Virginia Departments of 

Environmental Quality (VDEQ) and Health, Virginia Division of Geology and Mineral Resources, Warren County, 

and USGS were analyzed. The results of this analysis are 

presented in tabular form (table 1) and in graphical form 

as boxplots (fig. 8), and they are described in detail below. 

The blue-shaded areas in figure 8 represent the 95-percent 

confidence intervals. In most cases, the respective confidence 

intervals for the rock units overlap, which indicates that wells 

drilled in the three rock units are not significantly different 

statistically. This is expected because nearly all of the wells in 

the analysis were drilled for domestic use (Cederstrom, 1972), 

where lower yields and shallower depths are acceptable for 

typical household use compared to municipal supply wells 

that generally need a much greater water supply. Maps shown 

in the following sections were derived from well-construction 

data by using an inverse distance-weighted method in ArcGIS®

ArcMap® version 9.3 that used a power of 2, variable search 

radius of 12 points around each point to create a contour grid 

of the respective hydrogeologic characteristic.

During this investigation, a long-term water-monitoring 

network was initiated for the county. Water levels were 

measured continuously in well 45V 3; discharge and field 

water-quality properties were measured quarterly at springs 

45VS 1 and 46VS 17 (appendix 1). Descriptions of seasonal 

and spatial changes in water levels and discharges are 

provided below. Streamflow and field water-quality properties 

were measured at gaging stations 01630700 Gooney Run at 

Route 622 near Glen Echo, VA, 01636242 Crooked Run below 

Route 340 at Riverton, VA, and 0163626650 Manassas Run 

at Route 645 near Front Royal, VA. Description of streamflow 

characteristics from these gages are discussed in the section on 

groundwater availability.

Well Depths

Reported well depths in Warren County (table 1; fig. 8) 

range from 46 to 1,345 feet below land surface (ft bls). The 

deepest well depth inventoried during this study was a 1,345-ft 

industrial well completed in the Martinsburg Formation 

that yielded 120 gallons per minute (gal/min) with 200 ft of 

drawdown. The shallowest ranges of well depths are generally 

from large-diameter, hand-dug or bored wells. Well depths 

tend to be shallowest in the siliciclastic rock unit (predominantly in the Martinsburg Formation) where 75 percent of 

the wells are less than 200 ft deep. In the metamorphic rocks 

of the Blue Ridge, more than 75 percent of the wells are less 

than 400 ft deep. More than 75 percent of the wells are less 

than 550 ft deep in the carbonate rocks. The distribution of 

well depths is slightly different than was determined for more 

than 1,800 wells in Clarke County (Nelms and Moberg, 2010), 
Hydrogeology 15

Table 1. Well-construction characteristics for the rock types and hydrogeologic units in Warren County, Virginia.[nd, not determined; n, number of sites. Hydrogeologic units: Yoq, Orthopyroxene quartz diorite gneiss; Yos, Megacrystic orthopyroxene syenogranite-monzogranite gneiss; Yor, Old Rag Granite; Yom, Orthopyroxene monzogranite-quartz monzodiorite; Zcm, Catoctin Formation metabasalts; Om, Martinsburg Formation; Ccw, Weverton Formation; Cch, Harpers Formation; Cca, Antietam Formation; Cwa, Waynesboro Formation; Ce, Elbrook Limestone; OCc, Concocheague Limestone; Os, Stonehenge Limestone; Ob, Beekmantown Group undivided; Oeln, Edinburg Formation, Lincolnshire, and New Market Limestones; Om, Martinsburg Formation]

Statistic

Rock type

Metamorphic Silici- clastic Carbonate

Hydrogeologic unit

Yoq Yos Yor Yom Zcm Ccw Cch Cca All Om Cwa Ce OCc Os Ob Oeln All

Well depth, in feet below land surface

Minimum 93 175 55 82 65 165 185 145 55 46 125 200 170 439 65 120 65

Mean nd nd 190 297 314 235 305 317 292 196 318 339 391 nd 316 268 335

Median nd nd 165 253 254 235 283 260 250 150 243 313 293 nd 310 230 300

Maximum nd nd 520 600 900 305 560 505 900 1345 705 680 720 nd 700 580 720

n 1 1 18 10 68 2 18 12 130 132 10 28 16 1 35 8 98

Well yield, in gallons per minute

Minimum 35 6 3 0.5 0.2 10 0.5 1 0.2 1 0 1 0.75 50 2 2 0

Mean nd nd 21.9 12.1 13.6 11 17.25 26.2 16.1 25 25.1 18 36.37 nd 27.2 57 27.6

Median nd nd 20 12 12 11 10 16 12 17.5 10 10 15 nd 17.5 13 12

Maximum nd nd 50 30 50 12 75 80 80 130 10 70 10 nd 10 200 20

n 1 1 18 10 68 2 18 12 130 132 10 28 16 1 35 8 98

Depth to bedrock, in feet below land surface

Minimum 3 nd 30 25 3 35 8 15 3 8 25 8 12 34 8 nd 8

Mean nd nd 59.5 53.3 36 35 56.3 48.1 43.9 36.7 62.5 29.8 28 nd 41.6 nd 39

Median nd nd 64 35 28 35 35 40 35 24 32.5 25 22 nd 35 nd 33

Maximum nd nd 80 88 108 35 370 140 370 100 134 90 50 nd 105 nd 134

n 1 1 18 10 68 2 18 12 130 132 10 28 16 1 35 8 98

Upper water-bearing zone reported, in feet below land surface

Minimum nd nd 52 160 61 280 95 70 52 40 85 93 202 426 55 140 55

Mean nd nd 91 284 213 280 219 240 220 151 251 267 446 nd 223 140 266

Median nd nd 91 258 181 280 200 232 200 130 158 270 491 nd 178 140 199

Maximum nd nd 130 460 600 280 420 420 600 455 560 585 600 nd 620 140 620

n 1 1 18 10 68 2 18 12 130 132 10 28 16 1 35 8 98

Lower water-bearing zone reported, in feet below land surface

Minimum nd nd 52 270 85 280 175 130 52 40 110 159 245 434 55 140 55

Mean nd nd 91 346 252 280 279 277 264 158 258 293 457 nd 252 140 288

Median nd nd 91 328 220 280 260 243 250 140 168 270 491 nd 225 140 248

Maximum nd nd 130 460 625 280 530 480 625 455 560 585 600 nd 620 140 620

n 1 1 18 10 68 2 18 12 130 132 10 28 16 1 35 8 98
16 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 8. Summary statistics of well-construction and hydrologic characteristics of the rock types in Warren County, Virginia.

which borders Warren County on the north. In Clarke County, 

median well depths were (1) deeper in the metamorphic 

rocks of the Blue Ridge, which is a reflection of the elevated 

setting and relatively low hydraulic conductivity of these 

hydrogeologic units, and (2) shallower in the carbonate rocks 

in response to the occurrence of dissolution-enlarged openings 

and relatively low relief. The abundance of relatively shallow 

wells may contribute to the frequent occurrence of well 

failures reported in Warren County during drought and 

wet conditions.

DEPTH TO BEDROCK,

IN FEET BELOW LAND SURFACE

DEPTH TO TOP OF UPPER

REPORTED WATER-BEARING ZONE,

IN FEET BELOW LAND SURFACE

DEPTH TO TOP OF LOWER

REPORTED WATER-BEARING ZONE,

IN FEET BELOW LAND SURFACE

WELL DEPTH, IN FEET BELOW LAND SURFACE WELL YIELD, IN GALLONS PER MINUTE

1,400

1,200

1,000

800

600

400

200

0

800

600

400

200

0

400

300

200

100

0

800

600

400

200

0

0.1

1.0

10

100

1,000

Carbonate Metamorphic

ROCK TYPE

Siliciclastic

Carbonate Metamorphic

ROCK TYPE

Siliciclastic

Figure 8. Summary statistics of well-construction and hydrologic characteristics of the rock units in Warren County, Virginia.

84 118 122

68 111 90

44 84 47

43 66 39

43 66 39

EXPLANATION

Upper outlier

75th percentile

Number of values

Whiskers are 1.5 x 

 interquartile range

Median

25th percentile

Lower outlier

Blue shading indicates 

 95% confidence interval

84

Carbonate

Metamorphic

Siliciclastic

ROCK TYPE
Hydrogeology 17

Depth to Bedrock

Median reported depths to bedrock from driller’s logs are 

generally less than 40 ft bls across the county (table 1; fig. 8). 

More than 75 percent of the wells reported depths to bedrock 

of less than 80 ft bls. The deepest depth to bedrock (370 ft) 

inventoried was for a well located 0.5 mi south of the Shenandoah River near Morgan Ford where Rader and Conley (1995) 

mapped terrace deposits overlying the Harpers Formation and 

the Happy Creek fault. Generally, depths to bedrock tend to be 

(1) relatively deep (greater than 50 ft bls) in the eastern part 

of the county, in areas where alluvial and colluvial deposits 

are extensive, and along faults; and (2) relatively shallow 

(less than 50 ft bls) in the interfluve areas, along the eastern 

slopes of Massanutten Mountain, and in areas underlain by the 

Martinsburg Formation (fig. 9). The rocks in the eastern part 

of the county are older and more highly deformed than those 

to the west; these factors, in conjunction with the presence of 

alluvial and colluvial deposits from the mountainous areas, 

could contribute to the formation of a thick residuum and 

consequently result in deeper depths to bedrock. The areas of 

deeper depths to bedrock in figure 9 coincide with the areas 

where alluvium and colluvium along the North Fork, South 

Fork, and Shenandoah Rivers are present along the base of 

Figure 9. Depth to bedrock in Warren County, Virginia.

Massanutten

EXPLANATION

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and 

 siliciclastic rock types in the 

 Great Valley

Federal lands boundary

Well—Depth to bedrock reported on

 well-completion forms

Fault and fold symbology is shown in figure 5.

George Washington NF

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

Elevation from U.S. Geological Survey National 

Elevation Dataset digital elevation model, 2001, 

30-meter resolution

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas

Run

Passage Creek

Shenandoah

Shenandoah

River

Front

Happy Creek Fault

Royal Fault

Skyline

Drive

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Buckton

Riverside

Front Royal

55

81

522

522

340

66

649

340

55

Carbonate Siliciclastic

Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

1–25

26–50

51–75

76–100

101–150

151–300

No data

Depth to bedrock, in feet
18 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

mountains and where smaller streams mantle the bedrock 

(Hack, 1965; Rader and Biggs, 1975, 1976; Lukert and 

Nuckols, 1976; Rader and Conley, 1995). Preferential movement of groundwater along faults, especially where the acidic 

rocks of the Blue Ridge are juxtaposed with carbonate rocks, 

could facilitate deep weathering profiles. The shallow bedrock 

depths in the interfluve areas may indicate that the rocks have 

low permeability, which can limit the development of deep 

weathering profiles. Hack (1965) states that the Martinsburg 

Formation generally lacks residuum. Much of the county has 

some mantle over the bedrock, but groundwater storage in this 

regolith is believed to be minimal (Harlow and others, 2005); 

however, the areas with a thick sequence of regolith overlying 

the bedrock, especially the carbonate areas, may have considerable groundwater storage potential. 

Water-Bearing Zones

The depth to water-bearing zones on State wellcompletion reports, when recorded, provides insight into 

where groundwater is present at depth, which is an important 

characteristic in fractured-rock settings (table 1; fig. 8). A well 

can encounter single or multiple water-bearing zones. Often, 

only the major water-bearing zones are recorded, whereas 

the smaller quantities of water are usually missing from the 

reports. If a single water-bearing zone was recorded, then the 

depths of the upper and lower zones were considered to be 

equivalent. Median values for the depth of the upper waterbearing zones indicate that water generally is encountered 

between 130 and 400 ft bls throughout the county (fig. 8). 

Occasionally, the upper water-bearing zone is not encountered 

until depths greater than 400 ft bls (fig. 8). The reported 

water-bearing zones for wells completed in the siliciclastic 

rocks of the Martinsburg Formation are shallower than those 

in the carbonate and metamorphic rocks. Nelms and Moberg 

(2010) stated that, in general, median depths of the upper 

water-bearing zones in Clarke County are slightly deeper for 

the hydrogeologic units of the Blue Ridge, where relief is 

greater and hydraulic conductivity is generally lower, than 

those of the units in the Great Valley section of the county. To 

some degree, the same is true for Warren County, but sparse 

reporting of water-bearing zones did not allow for an equivalent evaluation. A similar, yet deeper, distribution of depth to 

the top of the lower water-bearing zones is evident in Warren 

County (table 1; fig. 8). 

Spatial distribution of the depths to water-bearing zones 

across the county provides insight into the topographic and 

geologic controls on the occurrence of groundwater. The 

depth to the top of the upper water-bearing zone is mapped 

in figure 10. In general, the upper water-bearing zone is 

encountered in the first 200 ft bls. Depths generally are greater 

than 200 ft bls along faults and fold axes in Rockland and 

Bentonville and in elevated areas of the Blue Ridge in the 

northeastern and southeastern parts of the county (fig. 10). 

The deeper water zones along faults and fold axes could be the 

result of high permeability and ability to transmit water along 

these features. The deeper depths in the elevated areas may be 

because drilling had to continue past shallower depths in order 

to meet usage requirements.

A similar spatial pattern exists for the depth to the top 

of the lower water-bearing zone (fig. 11), but a larger area 

of the county encounters the lower bearing zones at depths 

greater than 200 ft bls. Cady (1936) and Hack (1965) suggest 

that water-bearing zones in carbonate rocks may be present to 

depths as great as 2,000 ft bls. Recent drilling in the carbonate 

rock unit in Frederick County encountered more than 

100 gal/min from a single water zone at 1,339 ft bls, possibly 

associated with the Apple Pie Ridge fault (G.E. Harlow, Jr., 

U.S. Geological Survey, written commun., 2005). Wright 

(1990) reported that a well located on a ridgetop in the 

metamorphic rocks of the Blue Ridge in Clarke County 

encountered freshwater at about 5,000 ft bls. As stated earlier, 

the deepest well inventoried for this study in Warren County 

was 1,345 ft deep, was in the siliciclastic rocks (table 1), 

and yielded 120 gal/min. All of these examples indicate 

the possibility of encountering water-bearing zones at 

substantial depths.

The statistical and spatial distribution of water-bearing 

zones is consistent with the conceptual idea that the groundwater flow systems are topographically driven and controlled 

by geologic structure. The relatively shallow nature of the 

water-bearing zones and well depths may contribute to the 

frequent occurrence of well failures observed during this 

study. In addition, the aquifer systems in the county have 

been determined to be susceptible to contamination from 

near-surface sources (Nelms and others, 2003). The 

susceptibility to both droughts and contamination should 

be considered during future water-resources management 

activities in the county.
Hydrogeology 19

Figure 10. Depth to top of upper reported water-bearing zones in Warren County, Virginia.

Massanutten

EXPLANATION

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and

 siliciclastic rock types in the 

 Great Valley

Federal lands boundary

Well—Depth to water-bearing zones

 reported on well-completion forms

Fault and fold symbology is shown in figure 5.

Figure 10. Depth to top of upper reported water-bearing zones in Warren County, Virginia.

George Washington NF

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

Elevation from U.S. Geological Survey National 

Elevation Dataset digital elevation model, 2001, 

30-meter resolution

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

Front

Happy Creek Fault

Royal Fault

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas

Run

Passage Creek

Shenandoah

Shenandoah

River

Skyline

Drive

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Buckton

Riverside

Front Royal

55

81

522

522

340

66

340

55

Carbonate Siliciclastic

Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

30–150

151–200

201–250

251–300

301–350

351–400

401–450

451–500

501–1,000

No data

Depth to top of upper reported 

water-bearing zones, in feet below 

land surface
20 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 11. Depth to top of lower reported water-bearing zones in Warren County, Virginia.

Massanutten

EXPLANATION

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and 

 siliciclastic rock types in the 

 Great Valley

Federal lands boundary

Well—Depth to water-bearing zones 

 reported on well-completion forms

Fault and fold symbology is shown in figure 5.

Figure 11. Depth to top of lower reported water-bearing zones in Warren County, Virginia.

George Washington NF

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

Elevation from U.S. Geological Survey National 

Elevation Dataset digital elevation model, 2001, 

30-meter resolution

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

Front

Happy Creek Fault

Royal Fault

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas

Run

Passage Creek

Shenandoah

Shenandoah

River

Skyline

Drive

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Buckton

Riverside

Front Royal

55

81

522

522

340

66

340

55

Carbonate Siliciclastic

Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

30–150

151–200

201–250

251–300

301–350

351–400

401–450

451–500

501–1,000

No data

Depth to top of lower reported 

water-bearing zones, in feet below 

land surface
Hydrogeology 21

Massanutten

EXPLANATION

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and

 siliciclastic rock types in the

 Great Valley

Federal lands boundary

Fault and fold symbology is shown in figure 5.

Potential lineament zone—

 Number indicates trend

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

Front

Happy Creek Fault

Royal Fault

N. 10 W

N. 55 W

N. 10 W

Carbonate

Siliciclastic

Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

Reported well yield, in 

gallons per minute

0.00–10.00

10.01–20.00

20.01–40.00

40.01–80.00

80.01–200

Well Yields

Reported well yields in Warren County range from 0 to 

200 gal/min (table 1; fig. 8). The median well yields for the 

different rock units generally range from 10 to 20 gal/min, 

which is typical for domestic wells in fractured-rock and 

karst aquifer systems. Dry holes are common, and filing of 

completion reports is not required. Most of the well-yield data 

are derived from short-duration, airlift tests conducted after 

total depth of the wells had been reached. Results from the 

Tukey’s multiple comparison test, which is a nonparametric 

analysis of variance test performed on rank-transformed data 

to determine which group or groups are significantly different, 

indicate that the hydrogeologic units are not significantly 

different (p-values > 0.05). This lack of statistical difference 

is to be expected because a majority of the wells are for 

domestic use (Cederstrom, 1972), and maximum yields 

for the rock units may not have been obtained. Generally, 

the higher yields are in wells finished in the carbonate and 

siliciclastic (predominantly the Martinsburg Formation) rock 

units (fig. 12). Productivity of the carbonate aquifers is well 

known, but the high yields in the Martinsburg Formation 

Figure 12. Reported well yields in Warren County, Virginia.
22 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

contradict the normal premise that the Martinsburg is a 

low-yielding unit (Cady, 1936, 1938; Trainer and Watkins, 

1975; Hinkle and Sterrett, 1976, 1977, 1978; Wright, 1990; 

Yager and others, 2008). A majority of the high-yielding wells 

in the Martinsburg is present along the eastern margin of this 

formation. The extent of the Martinsburg Formation depicted 

in figure 5 includes the Stickley Run Member, which is a 

carbonate rock. Therefore, the high-yielding wells may obtain 

water from carbonate rocks rather than from the siliciclastic 

rocks of the Martinsburg Formation. In Berkeley County, WV, 

Shultz and others (1995) determined that the Martinsburg 

had higher median well yields than those from the carbonate 

rocks. Nelms and Moberg (2010) identified a similar pattern 

in the Martinsburg and stated that a majority of these wells 

were located within Landsat lineament zones, near or along 

mapped faults, within isolated fault slices, or near the eastern 

contact of the Martinsburg with the older carbonate units 

where well depths could penetrate the basal Stickley Run 

Member. Another possible explanation is that the shale in the 

Martinsburg Formation is typically highly fractured, much 

more so than the carbonates; therefore, the secondary permeability may be greater (M.D. Kozar, U.S. Geological Survey, 

written commun., 2010). Furthermore, Shultz and others 

(1995) and Kozar and Weary (2009) showed that proximity to 

faults affects well yields for all rock types in the Great Valley 

of the northern Shenandoah Valley region.

In the Blue Ridge, well yields tend be slightly greater 

in the valleys and hillsides than on ridgetops. This pattern 

typically is seen in fractured-rock settings, and the prevailing 

theory is that fractures may be more concentrated in valley 

settings than along ridgetops (Powell and Abe, 1985).

Alignment of high-yielding wells can suggest control by 

an underlying geologic structure. Wells with reported yields 

greater than 40 gal/min align along the straight segment of the 

Shenandoah River just east of Horseshoe Bend. Extension of 

this alignment across the carbonate rock units connects two 

wells having similar high yields near the eastern contact of 

the Martinsburg Formation. The trend (N. 55° W., fig. 12) of 

the alignment nearly parallels the trend of Landsat lineament 

zones identified in Clarke County by Hubbard (1990) and 

of the small transverse fault southeast of Happy Creek fault 

(fig. 12). The alignment of high-yielding wells across many 

hydrogeologic units coincident with the straight stream 

segment at a trend similar to lineament zones to the north 

suggests the presence of structural weakness usually associated with lineaments, cross-strike faults, or both. Interestingly, 

a subtle alignment of high-yielding wells with a trend of 

N. 55° W. just south of the small transverse fault mentioned 

above may suggest structural offset or width of the lineament 

zone. McCoy and others (2005a, b) and Kozar and others 

(2007) noted the importance that cross-strike faults have on 

hydraulic properties, well yields, and flow in Berkeley and 

Jefferson Counties, WV. In the Gooney Run watershed, wells 

with yields between 20 and 40 gal/min align with a trend of 

N. 10° W. (fig. 12) that extends to a cluster of high-yielding 

wells located just north of the first major bend in the South 

Fork Shenandoah River downstream from Front Royal. This 

trend is similar to that of a lineament zone in Clarke County 

that nearly crosses the entire county (Hubbard, 1990). Future 

mapping could identify structural features that might be 

conducive for locating high-yield wells in the county.

A density analysis using ArcGIS® ArcMap® version 9.3 

was conducted to further identify areas where well yields tend 

to cluster either as low (less than 5 gal/min) or high (greater 

than 50 gal/min) yields. Many of the areas with the highest 

density of low-yielding wells are present in the center of fault 

blocks, and wells depths are not deep enough to penetrate the 

bounding faults (fig. 13). High-yielding wells in the county 

generally tend to cluster along faults, along potential lineament zones, in areas underlain by carbonate rocks, along the 

major rivers, and along the eastern extent of the Martinsburg 

Formation (fig. 14). A comparison of density clusters (figs. 13, 

14) indicates that some areas contain a dense concentration 

of both low- and high-yielding wells. This is one example of 

the degree of complexity inherent with fractured-rock and 

karst aquifer systems, which has been identified in other areas 

within the northern Shenandoah Valley region (McCoy and 

others, 2005a, b; Nelms and Moberg, 2010). The clusters of 

both low- and high-yielding wells near Horseshoe Bend on the 

Shenandoah River and near Bentonville in the south illustrate 

this complexity. Interpretations of the well-yield density 

analysis are affected by data distribution across the study area. 

The statistical and spatial analyses described previously 

are not a rigorous evaluation of the yielding capacity of the 

hydrogeologic units in the county. As stated earlier, wells in 

the dataset were drilled for domestic purposes and have been 

sited in accordance with local ordinances and not to maximize 

well yield. In addition, most of the drilled wells are 6 in. in 

diameter, which can be a limiting factor in well production. 

Also, more than 75 percent of the wells have depths less than 

400 ft. Cady (1936) observed that the average yield of wells 

drilled deeper than 300 ft in the carbonate rocks is three times 

as great as those drilled shallower than 300 ft. The relation 

between well yield and depth for the metamorphic rocks has 

not been thoroughly investigated. Cressler and others (1983), 

Daniel (1989), Swain (1993), Hansen and Simcox (1994), and 

Loiselle and Evans (1995) indicated that yields may increase 

with depth of exploration in crystalline rocks.
Hydrogeology 23

Figure 13. Density of wells with reported well yields less than 5 gallons per minute in Warren County, Virginia.

Massanutten

EXPLANATION

Fault and fold symbology is shown in figure 5.

Well—Reported well yield less than

 5 gallons per minute

Figure 13. Density of wells with reported well yields less than 5 gallons per minute in Warren County, Virginia.

Geologic province boundary—As defined

 by the top of the Antietam Formation

Boundary between carbonate and

 siliciclastic rock types in the

 Great Valley

Federal lands boundary

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas

Run

Passage Creek

Shenandoah

Shenandoah

River

Front

Happy Creek Fault

Royal Fault

Skyline

Drive

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Buckton

Riverside

Front Royal

55

81

522

522

340

638

66

340

55

Carbonate

Siliciclastic

Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

0–1.0

1.1–2.0

2.1–3.0

3.1–4.0

4.1–5.0

Density of wells with reported well yields 

 less than 5 gallons per minute—Number 

 of wells per square mile
24 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 14. Density of wells with reported well yields greater than 50 gallons per minute in Warren County, Virginia.

Figure 14. Density of wells with reported well yields greater than 50 gallons per minute in Warren County, Virginia.

Massanutten

EXPLANATION

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and 

 siliciclastic rock types in the Great 

 Valley

Federal lands boundary

Fault and fold symbology is shown in figure 5.

Well—Reported well yield greater than

 50 gallons per minute

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas

Run

Passage Creek

Shenandoah

Shenandoah

River

Front

Happy Creek Fault

Royal Fault

Skyline

Drive

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Buckton

Riverside

Front Royal

55

81

522

522

340

66

340

55

Carbonate

Siliciclastic

Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

0–0.5

0.6–1.0

1.1–1.5

1.6–2.0

2.1–2.5

Density of wells with reported well yields 

greater than 50 gallons per minute—Number 

of wells per square mile
Hydrogeology 25

Aquifer Properties

Sufficient data to calculate specific capacity (Q/s), which 

is the ratio of well yield to water-level drawdown in a pumped 

well, were available for 50 wells located in Warren County. 

Specific capacity from short duration pumping tests (less than 

2 hours) in the three rock types is relatively low and ranges 

from 0.003 to 1.43 gallons per minute per foot [(gal/min)/ft] 

with median values from 0.12 to 0.24 (gal/min)/ft (table 2). 

Although median values for the rock units differ slightly, the 

distribution is similar to the findings from the analysis of well 

yields presented in the previous section where well yield was 

generally higher in the siliciclastic unit (Martinsburg Formation) and carbonate unit than in the metamorphic unit. Values 

of transmissivity (T) were estimated using the following 

equations (Driscoll, 1986) for these specific capacity data:

T = 1,500(Q/s), for unconfined aquifers, and

T = 2,000(Q/s), for confined aquifers,

where T is transmissivity in gallons per day per foot, Q is 

well yield in gallons per minute, and s is water-level drawdown in feet. Equations 1 and 2 were used to provide estimates for both unconfined and confined conditions present in 

the county. Transmissivity values derived from the specific 

capacity data range over four orders of magnitude from 0.6 to 

380 feet squared per day (ft2/d; table 2). The median values 

of transmissivity for the different rock units are of the same 

order of magnitude, but the overall range and median values 

of transmissivity for the metamorphic rock unit are lower 

than the overall ranges and median values for the other rock 

units. Median values of transmissivity for the metamorphic, 

siliciclastic, and carbonate rock units under unconfined conditions are 24, 49, and 40 ft2

/d, respectively, and under confined 

conditions are 32, 65, and 54 ft2/d, respectively. Yager and 

others (2008) also estimated transmissivity values for the 

Shenandoah Valley from specific capacity data; median values 

of transmissivity for the metamorphic, siliciclastic, and carbonate rock units were 54, 108, and 269 ft2

/d, respectively. In 

the future, accurate and consistent reporting of well yield, test 

duration, and static and production water levels could facilitate more detailed evaluations of the yielding potentials and 

aquifer properties of the different rock units.

Water Levels

Fluctuations in water levels can result from natural 

and anthropogenic factors. The primary natural factors are 

precipitation, groundwater evapotranspiration, and discharge 

from the aquifer system to springs and streams (Harlow and 

others, 2005). Other natural factors are barometric, earth tide, 

and earthquake effects. Pumpage withdrawals for water-supply 

demands as well as surface and subsurface injection are the 

primary anthropogenic activities that cause groundwater-level 

fluctuations. In general, recharge of precipitation to the aquifer 

Table 2. Transmissivity values estimated from specific capacity tests of supply wells by rock 

type in Warren County, Virginia.

[n, number of sites; (gal/min)/ft, gallon per minute per foot of drawdown; ft2/d, foot squared per day]

Rock type n Minimum Median Maximum

Specific capacity, in (gal/min)/ft

Metamorphic 14 0.007 0.12 0.41

Siliciclastic 29 0.003 0.24 1.00

Carbonate 7 0.03 0.20 1.43

Transmissivitya (unconfined conditions), in ft2/d

Metamorphic 14 1.4 24 83

Siliciclastic 29 0.6 49 200

Carbonate 7 5.7 40 290

Transmissivitya (confined conditions), in ft2/d

Metamorphic 14 1.8 32 110

Siliciclastic 29 0.8 65 270

Carbonate 7 7.6 54 380

a

 Estimates of transmissivity are based on equations from Driscoll (1986):

 T = 1,500(Q/s) for unconfined aquifers

 T = 2,000(Q/s) for confined aquifers 

 where T is transmissivity in gallons per day per foot, Q is discharge in gallons per minute, and s is draw-

 down in the pumped well in feet.

(1)

(2)
26 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

system causes water levels to rise. Over time, such as seasonally, these levels slowly decline as water discharges to springs 

and streams in the area and as evapotranspiration limits 

groundwater recharge. Harlow and others (2005) describe the 

amount of seasonal water-level fluctuation as being variable 

and controlled by (1) contributing area of recharge, (2) topographic relief, (3) position in the flow system, (4) amount 

of evapotranspiration (ET), (5) aquifer permeability, and 

(6) groundwater discharge to springs and streams. Seasonal 

water-level fluctuations tend to be greater in the elevated 

recharge areas and in areas underlain by low permeability 

rocks; however, water levels in discharge areas near streams 

and springs and in areas underlain by permeable rocks tend to 

fluctuate less.

The establishment of a long-term water-level network 

in Warren County began during this investigation to quantify 

seasonal groundwater-level fluctuations. A pressure transducer 

was temporarily installed in well 45V 4 to monitor continuous 

water levels at 15-minute intervals as the area around this well 

was modified from agricultural to a mixed land use (fig. 15). 

Well 45V 4 was a 610-ft-deep, 6-in.-diameter observation well 

with 55 ft of casing and a water-bearing zone at 140 ft bls. 

This well is located in an elevated area within the siliciclastic 

rock unit near the boundary with the carbonate rock unit, 

penetrates 230 ft of shale, and terminates in the Stickley Run 

Member of the Martinsburg Formation. Continuous water 

levels were recorded between May 2004 and November 2005 

(fig. 16). During this period, water levels fluctuated approximately 6 ft and tended to respond to precipitation events, 

especially in the summer months when water levels would 

sharply rise. This sharp rise may be a loading response caused 

by water-saturated sediments exerting pressure on water in the 

unsaturated zone, causing the water table in the aquifer to be 

at pressures greater than atmospheric. Because the wellbore is 

vented to atmospheric pressure, the water in the well quickly 

rises, yet the volume of groundwater recharge may be small. 

In January 2005, the water levels declined about 4 ft in 6 days 

(fig. 16). This decrease in water levels coincided with construction activities (figs. 17, 18). The overall short-term effect 

of extensive local earth removal and modification activities 

and construction of several nearby ponds was minimal, 

however, and water levels quickly began to recover. A similar, 

yet smaller, decline in water levels occurred at the beginning 

of February 2005 and is likely related to construction activities similar to those that occurred in January 2005. Within 

1 month, the water levels had recovered, and the remainder 

of the water-level record closely mirrored regional conditions 

observed in well 46W175 located in Clarke County, which 

has the longest period of record in the northern Shenandoah 

Valley of Virginia (Nelms and Moberg, 2010). Well 45V 4 was 

abandoned in November 2005.

Water levels were measured quarterly in well 45V 3 from 

May 2004 until November 2005 when a pressure transducer 

was installed to monitor continuous water levels at 15-minute 

intervals and to provide information on seasonal water-level 

fluctuations for areas underlain by the Martinsburg Formation 

(fig. 16). Well 45V 3 is a 435-ft-deep, 10-in.-diameter 

production well with 58 ft of casing and a water-bearing 

zone at 140 ft bls. This well is located approximately 1,100 ft 

southwest of well 45V 4 (fig. 15) in an elevated area within 

the siliciclastic rock unit near the boundary with the carbonate 

rock unit. The original intent of this well was to supply a 

mixed-use land development, which is now on a public 

surface-water supply where irrigation water is provided by the 

constructed ponds mentioned earlier. Water levels recorded 

in well 45V 3 (fig. 16) indicate that water levels are generally 

responsive to current meteorological conditions. Intense thunderstorms, tropical storms, or hurricanes cause sudden, but 

temporary, water-level rises during the summer and autumn, 

similar to observations for well 45V 4. A sharp decline in 

water levels occurred between January and April 2005, and 

the magnitude of this change was nearly five times the change 

observed in well 45V 4 for that same period. The overall 

trend in water levels in well 45V 3 has been increasing since 

November 2005, which is the opposite of water-level trends 

observed in long-term wells 46W175 (fig. 16) and 46W179 

in Clarke County (Nelms and Moberg, 2010). Explanation 

of these opposing trends is perplexing and may be the result 

of differences in recharge mechanisms, storage potential, or 

land-use activity. Well 45V 3 is the only well in the northern 

Shenandoah Valley of Virginia in which water levels in the 

Martinsburg Formation are continuously monitored. Wells 

46W175 and 46W179 monitor water levels in carbonate 

bedrock and residuum, respectively. Differences in recharge 

mechanisms and storage between carbonate and siliciclastic 

rock units seem reasonable considering the relatively low 

permeability and potentially large storage potential in the 

highly fractured shale of the Martinsburg Formation. In other 

words, infiltration into the siliciclastic units may occur more 

slowly than infiltration into carbonate rock units. 

The degree of alteration of the landscape is evident 

from aerial photographs acquired in 2002 and 2007 as part 

of the Commonwealth of Virginia’s Base Mapping Program 

(fig. 17). The significant tree removal (decreased transpiration), recontouring of the landscape (decreased or rerouted 

runoff), and irrigation water use could collectively contribute 

to enhance recharge to the aquifer system, which would result 

in higher local water levels. Another possibility is that water 

levels in well 45V 3 are still recovering from the substantial 

decrease observed in January 2005. Well 45V 3 is located 

in the higher elevations of the development area, and land 

surface is about 40 ft higher than at well 45V 4. A majority of 

the landscape modification occurred at the lower elevations, 

and figure 18 shows an example of the degree of downcutting. 

The topography slopes, and groundwater probably flows away 

from well 45V 3; this may have been enhanced by blasting 

and re-contouring in the lower areas. The water levels in well 

45V 3 may have not had sufficient time to equilibrate to the 

modified landscape. Continued monitoring in this well, and 

additional water-level measurements in wells completed in 

the Martinsburg Formation, could assist in assessing local and 

regional water-level trends.
Hydrogeology 27

Figure 15. Streamflow-gaging stations, springs, and wells in the long-term water monitoring network for Warren County, Virginia.

Crooked Run

Lake

Frederick

Manassas Run

Massanutten

Figure 15. Location of streamflow gaging stations, springs, and wells in the long-term water monitoring network for Warren 

County, Virginia.

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

Skyline

Drive

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Buckton

Riverside

Front Royal

55

81

635

611

612

626

522

637

627

522

340

639

661

658

624

638

603

643

638

66

647

604

607

673

619

678

660

615

605

649

622

631

613

634

340

637

55

Gooney Run

Front

Happy

Creek

Fault

Royal Fault

R

R 45V 4

45V 3

0163626650

46VS 17

Drainage basin for primary 

 streamflow-gaging station

01635500

01634000

01630700

45VS 1

01631000

01630700

Carbonate

Siliciclastic Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

EXPLANATION

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and

 siliciclastic rock types in the Great 

 Valley

Federal lands boundary

Fault and fold symbology is shown in figure 5.

R Real-time well

Continuous spring discharge

 and water-quality site

Sites are labeled with U.S. Geological 

 Survey identification numbers

Real-time streamflow-gaging 

 and water-quality station
28 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 16. Relation between water levels in wells (A) 45V 4 and (B) 45V 3 in Warren County, Virginia, and 

in (C) well 46W175 in Clarke County, Virginia, and (D) quarterly standardized precipitation index and (E) daily 

snowfall at National Weather Service climatological station 443229 Front Royal, Virginia.

2003 2004 2005 2006 2007 2008 2009

5

10

15

20

CALENDAR YEAR

DAILY SNOWFALL,

IN INCHES

Figure 16. Relation between water levels in wells (A) 45V 4 and (B) 45V 3 in Warren County, Virginia, and in (C) well 

46W175 in Clarke County, Virginia, and (D) quarterly standardized precipitation index and (E) daily snowfall at 

National Weather Service climatological station 443229 Front Royal, Virginia.

0

25

D

E

510

515

520

525

530

WATER-LEVEL ALTITUDE, IN FEET ABOVE NGVD 29

Quarterly Daily

Daily

555

560

565

570

575

505

535

550

580

535

540

545

550

555

560

565

A 45V 4

B 45V 3

C 46W175

Daily

Site construction begins

Site construction begins

–3

–2

–1

0

1

2

3

QUARTERLY STANDARDIZED

PRECIPITATION INDEX 

Extremely wet

Extremely dry
Hydrogeology 29

Figure 17. Land use in (A) 2002 and (B) 2007 for the area surrounding wells 45V 3 

and 45V 4 in Warren County, Virginia.

!

!

45V 4

45V 3

78 78 11' 11'30"

78 78 11' 11'30"

3859'30"

3859'

3859'30"

3859'

0 0.2 0.4 MILE

0 0.2 0.4 KILOMETER

45V 4

45V 3

!

!

Figure 17. Land use in (A) 2002 and (B) 2007 for the area around wells 45V 3 and 

45V 4 in Warren County, Virginia.

Virginia Base Mapping Program (2007)

Scale 1 in.:200 ft

Virginia Base Mapping Program (2002)

Scales 1 in.:200 ft and 1 in.:400 ft

B

A

340

340
30 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Although well 45V 3 yielded 130 gal/min, storage is 

probably somewhat limited as evidenced by the demonstrated 

effects of barometric pressure and earth tides, as well as 

earthquake effects in the water-level data. The combined 

effects of barometric pressure and earth tides (diurnal cycles) 

are indicated by fluctuations of less than 0.1 ft change in 

water levels shown in figure 19. Because of cyclic heating of 

atmospheric water vapor and ozone, daily barometric lows 

generally occur in the early morning and early afternoon, and 

highs occur in the late morning and late afternoon (Chapman 

and Lindzen, 1970; Merritt, 2004). In addition, barometric 

pressure changes in response to passage of storms can affect 

groundwater levels (Merritt, 2004). The gravitational forces of 

the Sun and Moon acting upon the rotating Earth cause solid 

earth tides, like ocean tides. Earth tides cause the underlying 

rock matrix to expand and contract, which causes the pressure 

of the water to rise and fall in the aquifer (Merritt, 2004). The 

earth tide cycle (high and low tides) contributes to the diurnal 

water-level fluctuations shown in figure 19 with a maximum 

about every 12 hours. The maximum earth tide ranges occur 

when the Sun and Moon are aligned at new- and full-Moon 

phases, and a minimum occurs at first- and third-quarter 

phases of the Moon. Because groundwater-level fluctuations 

from both earth tides and barometric fluctuations normally 

are less than 0.1 ft in magnitude, the effects can be considered 

negligible in the water-level record, as most recharge events 

generally are of a greater magnitude. 

Water-level oscillations in response to the sudden arrival 

of teleseismic wave trains also have been observed in well 

45V 3. Similar to earth tides, yet more rapid, these seismic 

wave trains cause the rock matrix to expand and contract, 

which causes oscillatory pore pressure changes (Cooper and 

others, 1965; Liu and others, 1989). Water, which is incompressible, flows into and out of the well in response to the pore 

pressure changes. Water levels in well 45V 3 responded to 

the magnitude 8.4 earthquake that occurred on September 12, 

2007, in Southern Sumatra, Indonesia, about 10,000 mi away 

(fig. 19). Water-level oscillations of 0.1 ft were recorded in 

well 45V 3 about 45 minutes after the earthquake occurred 

and lasted for nearly 90 minutes. Generally, magnitude 7.0 or 

greater earthquakes located thousands of miles away can cause 

a slight response in water levels monitored in well 45V 3; 

local and even regional earthquakes of lower magnitude, 

however, have no effect on water levels in this well. 

Streamflow and Spring Discharge

The quantity of water discharging from the aquifer 

systems in the county can be characterized by streamflow and 

spring discharge. A large part of streamflow is groundwater 

discharge (base flow). Springs oftentimes are the origination 

of flows at the headwaters for many of the streams in the 

county. Dry stream segments during drought conditions 

usually are the result of cessation of flow at an upstream 

spring. A long-term network to monitor streamflow and 

spring discharge was established during this investigation. 

Three streamflow-gaging stations were established: 01630700 

(Gooney Run at Route 622 near Glen Echo), 01636242 

(Crooked Run below Route 340 at Riverton), and 0163626650 

(Manassas Run at Route 645 near Front Royal) (fig. 15). In 

the mid-Atlantic region of the United States, 1 cubic foot per 

second (ft3/s) of flow generally requires 1 mi2 of drainage area 

Figure 18. Landscape modification around well 45V 4 in Warren County, Virginia. Photograph 

taken by Roger M. Moberg, Jr., U.S. Geological Survey, November 3, 2005. Figure 18. Landscape modification around well 45V 4 located in Warren County, Virginia. 

Photograph taken by Roger M. Moberg, Jr., U.S. Geological Survey, on November 3, 2005.
Hydrogeology 31

(Poff, 1999). Mean streamflows for the period of record (2002 

through 2008) at streamflow gages 01630700, 01636242, 

and 0163626650 were 34.8, 24.9, and 18.0 ft3/s, respectively 

(fig. 20). Abundant deposits of alluvium and colluvium overlie 

the metamorphic rock unit in the Gooney Run and Manassas 

Run Basins. The ratios of mean streamflow to drainage area in 

these two basins are 1.6 and 1.7 ft3/s of flow per square mile of 

drainage area, respectively; these ratios probably are the result 

of above-average rainfall during the period of record and are 

not representative of average hydrologic conditions. Streamflow at gage 01636242 is regulated by Lake Frederick and 

has a ratio of mean streamflow to drainage area of about half 

of what is normal for the mid-Atlantic region. This low ratio 

may be related to reduced releases from Lake Frederick after 

the drought between 1999 and 2002. Results of hydrograph 

separation for these gaging stations are discussed later in 

this report.

Pressure transducers were installed at two springs—

45VS 1 (Weddle) and 46VS 17 (High Knob)—to measure 

stage, and estimates of continuous spring discharge were 

made by correlating periodic discharge measurements with 

the recorded stage (fig. 15). Physical limitations at these sites 

prevented the development of stage-discharge ratings; the 

quarterly discharge measurements (fig. 21), however, can 

provide insight into the range of flows and possible size of the 

drainage areas that contribute flow to these springs. Spring 

45VS 1 is located in the Rockland area of the county, which 

is underlain by the carbonate rock unit. Quarterly discharge 

measurements between August 2003 and October 2008 

(appendix 1) ranged from 0.001 to 1.76 ft3/s with an average 

of 0.42 ft3/s (fig. 21), which indicates that the drainage area on 

average is approximately less than 0.5 mi2. Results of dyetracing tests in the area by Orndorff (2006) indicated relatively 

short flow paths for springs larger than spring 45VS 1. For 

carbonate springs, Jones (1987) stated that flow to springs is 

not controlled by surface-water divides but probably follows 

the geologic structure. The seasonality of flow is evident in the 

hydrographs (fig. 21). Flow generally increases in the winter 

and early spring when evapotranspiration is at a minimum, and 

flow decreases from late spring to late autumn. The overall 

decreasing trend during the period of record is similar to the 

trend observed in carbonate springs and wells in neighboring 

Clarke County and is indicative of an aquifer system that over 

time drains to a base level controlled by springs and streams in 

the area (Nelms and Moberg, 2010).

Spring 46VS 17 is located in the Blue Ridge on the 

northwest slope of High Knob Mountain. The spring is 

developed where the slope breaks at the contact between 

bedrock of the Catoctin Formation and the overlying deposit 

of alluvium and colluvium. Quarterly discharge measurements between August 2003 and October 2008 (appendix 1) 

ranged from dry to 0.22 ft3/s, with an average of 0.07 ft3/s 

Figure 19. Relation between water levels in well 45V 3 in Warren County, Virginia, and combined effects 

of barometric pressure and Earth tides, and of teleseismic earthquakes.

Magnitude 8.4 - Southern Sumatra, Indonesia

September 12, 2007, 11:10:26 UTC

SEPT. 11, 2007 SEPT. 12, 2007

LOCAL TIME

EASTERN DAYLIGHT SAVING

06:00 12:00

102.5

102.6

102.7

102.8

102.9

103.0

45V 3 Water level

Interval: 5 min.

Period of seismic wave arrivals

Earthquake event

Figure 19. Relation between water levels in well 45V 3 located in Warren County, Virginia, and 

combined effects of barometric pressure and earth tides, and of teleseismic earthquakes. 

WATER LEVEL, IN FEET BELOW LAND SURFACE

Water-level oscillation

Barometric pressure and

earth tide effects

Barometric pressure and

earth tide effects
32 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 20. Daily mean discharge at streamflow-gaging stations (A) 01630700 Gooney Run at Route 622 near Glen Echo, Virginia, 

(B) 01636242 Crooked Run below Route 340 at Riverton, Virginia, and (C) 0163626650 Manassas Run at Route 645 near Front Royal, 

Virginia. Red dashed line indicates average of daily mean streamflows at each gaging station for the respective period of record. DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

Figure 20. Daily mean discharge at streamflow gaging stations (A) 01630700 Gooney 

Run at Route 622 near Glen Echo, Virginia, (B) 01636242 Crooked Run below Route 340 

at Riverton, Virginia, and (C) 0163626650 Manassas Run at Route 645 near Front Royal, 

Virginia. Red dashed line indicates average streamflow at each gaging station for the 

respective period of record.

0.1

1

10

100

1,000

10,000

0.1

1

10

100

1,000

10,000

0.1

1

10

100

1,000

10,000

2002 2003 2004 2005 2006 2007 2008 2009

CALENDAR YEAR

A. USGS 01630700 Gooney Run at Route 622 near Glen Echo, VA

B. USGS 01636242 Crooked Run below Route 340 at Riverton, VA

C. USGS 0163626650 Manassas Run at Route 645 near Front Royal, VA
Hydrogeology 33

(fig. 21), which indicates that the drainage area on average 

is approximately less than 0.1 mi2. This estimate of drainage 

area is similar to the drainage area above the spring delineated 

using the topographic divides (0.12 mi2). Nelms and Moberg 

(2010) state that delineation of a spring’s drainage area based 

on surface-water divides in the Blue Ridge generally provides 

sufficient area to supply the mean discharge and probably 

represents the major contributing area to the spring. The 

seasonality of discharge is not readily identifiable in spring 

46VS 17 and is more responsive to current meteorological 

conditions (fig. 21). Nelms and Moberg (2010) identified a 

similar lack of seasonality in Blue Ridge springs and attributed 

it to relatively low discharge rates, probable small drainage 

areas, and the susceptibility of these aquifer systems to current 

meteorological conditions.

As discussed earlier, values of mean discharge 

can be used to estimate drainage area. In the Blue 

Ridge, delineation of the drainage area of a spring 

based on surface-water divides often provides 

sufficient area to supply the mean discharge and 

probably represents the contributing area to the 

spring. In the Great Valley, mean discharge often 

only provides a guide for the size of the area 

needed. Wright (1990) stated that these estimates 

of discharge per unit area may not represent an 

easily definable or discrete area surrounding a 

spring and may or may not be coincident with 

surface-water divides.

Relation of Geology to 

Groundwater Flow

In the Blue Ridge, relict structures in the 

regolith material can transmit water from elevated 

areas to nearby streams in the form of interflow 

and shallow groundwater flow where the water 

table is above the top of bedrock. The unconsolidated surficial materials in the riparian areas of 

the Blue Ridge can function as local flow systems 

above the fractured-rock aquifers. Groundwater 

flow in the bedrock of the Blue Ridge is likely 

controlled by the orientation of the foliations and 

joints, but the dominant flow direction is difficult 

to ascertain. Southworth (1990) suggested that 

water recharged on the western slopes of the 

mountains of the Blue Ridge flows down the dip 

of the rock units and eventually discharges to 

springs and in valleys on the eastern sides of the 

mountains. The well-developed dendritic drainage 

networks in the Blue Ridge are probably a reflection of the irregular and highly variable fracture 

network developed in the underlying metamorphic 

bedrock, faults, and the weathering characteristics 

of these rocks. The abundance of alluvial and colluvial 

deposits along these streams facilitates rapid transmission of 

interflow or subsurface stormflow (Wright, 1990).

In the Great Valley section, the preferred direction of 

groundwater flow is probably along strike of bedding planes 

and cleavage in the sedimentary rock units; therefore, the 

dominant direction of groundwater flow is generally from 

elevated areas to the northeast or southwest along the strike 

of the rocks. Groundwater flow along the other joint types 

is topographically driven along the strike of the respective 

feature. In the siliciclastic rocks of the Great Valley section 

of the county, regional flow may be limited by the highly 

dissected terrain, and local flow systems may dominate. 

Drainage networks in the Great Valley section of the county 

often follow cross joints in the rock (Hack and Young, 1959). 

Many of the streams and creeks flow normal to strike; however, many of the low-order tributaries parallel the strike of the 

Figure 21. Quarterly discharges from springs 45VS 1 and 46VS 17 in Warren 

County, Virginia.

Dry

46VS 17

High Knob Spring

(Metamorphic)

2003 2004 2005 2006 2007 2008

CALENDAR YEAR

0.00

0.05

0.10

0.15

0.20

0.25

Dry

45VS 1

Weddle Spring

(Carbonate)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

QUARTERLY DISCHARGE, IN CUBIC FEET PER SECOND

Figure 21. Quarterly discharges from springs 45VS 1 and 46VS 17 in Warren County, 

Virginia.
34 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

rocks especially in the northwestern part of the county. Stream 

density (length of streams per drainage area) is generally low 

for areas underlain by the permeable carbonate rocks and 

higher for the less permeable rock types such as those in the 

Blue Ridge.

Orndorff and Harlow (2002) and Harlow and others 

(2005) noted that springs in the Shenandoah Valley are 

structurally controlled and usually are present where fault 

planes intersect the surface. Numerous springs in Warren 

County are present along faults and within lineament zones 

in both the Great Valley and Blue Ridge; however, many 

springs also are present along fold axes where joints verge. 

Travertine deposits commonly are present at and downstream 

from springs in the Great Valley and are formed by waters that 

are supersaturated with respect to calcium carbonate (Orndorff 

and Harlow, 2002).

Relation Between Groundwater and 

Surface Water

Groundwater is a major component of streamflow, 

usually in the form of direct discharge from springs at the 

headwaters of streams and directly through streambeds 

or streambanks. In the Blue Ridge, rapid transmission of 

interflow, subsurface stormflow, spring discharge, and, to 

some degree, direct groundwater discharge from the bedrock 

sustain streamflow. Generally, streamflow is limited by current 

meteorological conditions such that periods of flow cessation 

frequently occur in the elevated areas of the Blue Ridge and 

Massanutten Mountain during extended dry periods, especially 

in the late summer and early autumn. The overburden (regolith 

material) overlying the bedrock in the Blue Ridge plays a 

more important role than it does in the Great Valley section. 

Wright (1990) emphasized the importance of subsurface 

stormflow in the overburden that can rapidly transmit water 

to springs and streams in the Blue Ridge. The porous nature 

of the regolith material in the stream valleys is conducive for 

infiltration, movement, and temporary storage of subsurface 

water. Although this water is considered to be groundwater, 

in reality, the subsurface stormflow and, to some degree, 

interflow are probably more representative of water moving 

quickly through the overburden and not of the bedrock as 

evidenced by the seasonality of flow conditions and rapid 

response to extreme precipitation events.

Diurnal streamflow cycles frequently observed between 

April and October at gaging stations 01630700 (Gooney Run) 

and 0163626650 (Manassas Run) illustrate the connection 

between groundwater in the coarse surficial deposits of the 

riparian areas and streamflow. Infiltration in losing reaches 

and riparian evapotranspiration can cause diurnal flow cycles 

(Constantz and others, 1994; Lundquist and Cayan, 2002; 

Czikowsky and Fitzjarrald, 2004). Streamflow at gaging 

stations 01630700 (Gooney Run) and 0163626650 (Manassas 

Run) sharply decreases about 3 hours after sunrise and then 

gradually increases about 4 hours after sunset during the growing season (fig. 22). This asymmetrical diurnal streamflow signal is characteristic of evapotranspiration effects (Czikowsky 

and Fitzjarrald, 2004). In addition, Czikowsky and Fitzjarrald 

(2004) state that these diurnal signals are not in response to 

thermal expansion of the water or in response to losing reaches 

where large diurnal temperature ranges affect the viscosity of 

the water, which can alter the hydraulic conductivity of the 

streambed (Constantz and others, 1994). As the period of the 

streamflow recession increases, the amplitude of the diurnal 

signal tends to decrease. Changes in evapotranspiration rates 

as the growing season progresses contribute to variations in 

the amplitude effects (Czikowsky and Fitzjarrald, 2004). The 

steep slope of the stream profile and permeable nature of the 

coarse surficial deposits suggest rapid drainage of groundwater 

to the stream, which would increase the distance between 

the root zone and the water table. At extreme low-flow 

conditions (below 1 ft3/s), the diurnal streamflow signal is not 

evident. Diurnal streamflow signals are seldom observed at 

gaging station 01636242 (Crooked Run) because most of the 

stream is incised into the bedrock and groundwater levels are 

likely deeper; potential evapotranspiration effects, therefore, 

are minimal.

In the Great Valley section of the county, groundwater 

is the dominant source of streamflow during wet and drought 

conditions, and most of the streams and creeks begin as 

springs (Nelms and Moberg, 2010). Point discharge from 

springs can occur as the start of flows of streams and creeks, 

along banks, and as discrete discharge through streambeds 

in the Great Valley. For the most part, streams, creeks, and 

rivers simply function as aqueducts. In the carbonate terrains, 

surface-water flow often is a source of recharge to the groundwater system by inflow through sinkholes, swallet or swallow 

holes, streambeds (sinking or losing streams), and estavelles 

(Nelms and Moberg, 2010). Field reconnaissance of spring 

locations throughout the county was conducted during this 

investigation. Identification of subaqueous spring discharge in 

streams and creeks, especially along the major rivers, however, is difficult. Lane and others (2008) identified subaqueous 

spring discharge to the Shenandoah River in Clarke County by 

a thermal anomaly detected by using a fiber-optic distributed 

temperature sensing system. In Warren County, zones of 

increased conductive water at and below the streambed 

were identified during a multifrequency electromagnetic 

survey along the 2-mi reach downstream from gaging station 

01631000 (South Fork Shenandoah River at Front Royal) in 

the siliciclastic rock unit (fig. 23). These zones may represent 

discrete areas of concentrated fractures where groundwater is 

either discharging to the river or flowing beneath the river as 

underflow. Managers of the water resources and those working 

to detect potential contaminant sources within the county 

should note that a large part of streamflow at different flow 

regimes comes directly from groundwater discharge.
Hydrogeology 35

Apparent Age of Groundwater

Groundwater apparent ages were estimated by a multiple 

tracer approach whereby the environmental tracers—chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6

), and tritium/

helium-3 (3H/3He)—are used to date young waters (less than 

60 years). Two springs located in the Great Valley section 

and 12 springs and a public-supply well in the Blue Ridge 

of Warren County were sampled during the summer months 

of 2003–2005 (fig. 24). Timing of the sampling coincided 

with the period of the year when seasonal spring flows and 

groundwater levels are low; therefore, estimates of apparent 

groundwater ages should represent a higher percentage of the 

older groundwater ages in the flow systems. Analytical data 

are presented in appendixes 2–10. A detailed explanation of 

the sampling and analytical methods is provided in Nelms and 

Harlow (2003). 

Groundwater dating with CFCs (Busenberg and Plummer, 1992) is based on Henry’s law of solubility, which is a 

function of the temperature during recharge and salinity of the 

groundwater. Concentrations of dissolved nitrogen (N2) and 

argon (Ar) were used to estimate recharge temperatures and 

Figure 22. Relation between evapotranspiration and unit value discharge 

at streamflow-gaging stations 01630700 Gooney Run at Route 622 near Glen 

Echo, Virginia, 01636242 Crooked Run below Route 340 at Riverton, Virginia, and 

0163626650 Manassas Run at Route 645 near Front Royal, Virginia. Unit value 

discharges have been smoothed with a ±1-hour average function.

12 13 14 15 16 17 18 19 20

0

5

10

15

20

25

30

JUNE 2005

Figure 22. Relation between evapotranspiration and unit value discharge at 

streamflow gaging stations 01630700 Gooney Run at Route 622 near Glen Echo, 

Virginia, 01636242 Crooked Run below Route 340 at Riverton, Virginia, and 

0163626650 Manassas Run at Route 645 near Front Royal, Virginia. Unit value 

discharges have been smoothed with a ±1-hour average function.

JULY 2003

DISCHARGE, IN CUBIC FEET PER SECOND

12 13 14 15 16 17 18 19 20

0

10

20

30

40

Gage 01630700

Gage 0163626650

Gage 01636242

Gage 01630700

Daylight hours

Gage 0163626650

Daylight hours
36 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 23. Multifrequency electromagnetic survey along the South Fork Shenandoah River near Front Royal, Virginia.

40

30

20

10

0

10

20

30

40

50

60

70

DEPTH BELOW RIVER

SURFACE, IN FEET

1,000 2,000 3,000 4,000 5,000 6,000 7,000

DISTANCE, IN FEET

CONDUCTIVITY, IN 

MILLISIEMENS PER METER

Virginia Base Mapping Program (2007)

Scale 1 in.:200 ft

7813’30”

38

56’30”

38

55’30”

38

55’

38

56’

78

12’30” 78 78 12’ 13’

Om

Oeln

Ob

Ob

EXPLANATION

Figure 23. Multi-frequency electromagnetic survey along the South Fork Shenandoah River near Front 

 Royal, Virginia.

Om

Oeln

Ob

0 0.2 0.4 MILE

0 0.2 0.4 KILOMETER

Contact

Bedding—Identified from aerial

 photography

Electrical transmission lines

Multifrequency electromagnetic

 survey trace

Streamflow-gaging station 01631000

 South Fork Shenandoah River at

 Front Royal, Virginia

Martinsburg Formation

Edinburg Formation, Lincolnshire,

 and New Market Limestones

Beekmantown Group

Formation (from Rader and Conley, 1995)
Hydrogeology 37

Figure 24. Apparent age and percentage of young water fraction for sampling sites in Warren County, Virginia. Apparent age 

data for Shenandoah National Park sites from Plummer and others (2000) and for Virginia Aquifer Susceptibility site from Nelms 

and others (2003).

Massanutten

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and 

 siliciclastic rock types in the Great 

 Valley

Federal lands boundary

SHENANDOAH

PAGE

FREDERICK CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

McKay Spring

(8.0, NP)

Gravel Spring NE

Dickeys Ridge Spring

Indian Run Shelter Spring

(0.3-1.4, NP)

(2.8, NP)

45VS 3

45VS 1

45VS 2

46VS 13

Shenandoah National Park Spring

Shenandoah National Park Well

Virginia Aquifer Susceptibility Well

EXPLANATION

Age dating sampling site—Source 

 project, site number, and name denoted

Warren County Spring

Warren County Well

Figure 24. Apparent age and percentage of young water fraction for sampling sites in Warren County, Virginia. Apparent

age data for Shenandoah National Park sites from Plummer and others (2000) and for Virginia Aquifer Susceptibility site

from Nelms and others (2003).

Apparent age and percentage of young 

 water fraction, in years. NP indicates not 

 possible

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas

Run

Passage Creek

Shenandoah

Shenandoah

River

Skyline

Drive

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Buckton

Riverside

Front Royal

55

81

522

522

340

66

649

55

340

Carbonate

Siliciclastic Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

46VS 8

Rock Spring

(4.0-8.6, 98.2%)

45VS 2

McKay Spring

(8.0, NP)

45US 3

Clegg Spring

(6.1, NP)

45VS 1

Weddle Spring

(0.6 to 2.3, NP)

46VS 6

McAfee Spring

(0.0-3.6, NP)

44US 2

Paulisch Spring

(0.1 to 2.6, NP)

Gravel Spring NE

Hogback Spring #5

45US 5

Chester Gap Spring

(1.0, NP)

46VS 1

High Knob Spring #6

(0.1, NP)

45VS 4

Zoo Spring at Gate 4

(2.7, 92.4%)

Dickeys Ridge Spring

Indian Run Shelter Spring

46V 1

High Knob Salt Lick Well 1

(4.0 to 4.6, NP)

46VS 2

Andrews Spring along Rt 55

(10.0-16.1, 80.4-99.5%)

44U 3

Shenandoah River State Park #2

(19.8, 15.6%)

46VS 13

Freezeland spring box 3 - West

(4.2, NP)

Browntown Valley

Overlook Spring

45VS 3

Zoo Spring across

522 in mule field

(1.2, NP)

46VS 12

Freezeland spring at

telephone pole

(10.6 to 14.6, 97.0%)

45U 3

Dickeys Ridge Well

(8.0-9.7, 47-55%)

(0.7-4.3, NP)

(0.3-1.4, NP)

(2.8, NP)

(0.6-4.8, NP)

(0.2-3.8, NP)

Zoo Turtle Spring

(0.6, NP)

45US 6

(2.7, 92.4%)
38 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

excess air in groundwater (Heaton, 1981; Heaton and Vogel, 

1981; Heaton and others, 1983; Busenberg and others, 1993), 

and salinity corrections are not necessary for waters as dilute 

as those from the springs sampled in Clarke County (Plummer 

and Busenberg, 2000). The apparent CFC age of the water 

sample was determined by comparing the calculated partial 

pressures of CFCs in solubility equilibrium with the sample 

to the historical atmospheric CFC concentrations in North 

American air (fig. 25). 

The SF6 dating method (Busenberg and Plummer, 2000) 

is similar to the CFC dating method (fig. 25). Unlike CFCs, 

SF6 in groundwater can be derived from anthropogenic and 

terrigenic sources, and it is generally not affected by sorption 

and biodegradation processes. SF6 can be affected by excess 

air in groundwater, which is attributed to air entrainment 

during recharge (Heaton and Vogel, 1981).

Tritium (3H) is the radioactive isotope of hydrogen with a 

half-life of 12.43 years (International Atomic Energy Agency, 

1981) and has been used as an indicator of groundwater 

recharge since 1952 (Clark and Fritz, 1997). Production of 3H 

in the atmosphere naturally occurs by cosmic ray spallation, 

but the principal source since about 1952 has been the atmospheric testing of thermonuclear weapons (fig. 25). Because 

3

H levels in water are not unique to a specific year, the 3H 

method was used primarily to confirm the presence of young 

water. The 3H/3He method is based on the radioactive decay of 3

H to 3He such that the helium isotope mass balance is used to 

determine the amount of tritiogenic 3He (3Hetrit) derived from 

3

H (Schlosser and others, 1988, 1989). If the 3Hetrit is confined 

in the aquifer, apparent 3H/3He ages of the water samples (t) 

can be calculated from the following formula (Schlosser and 

others, 1988, 1989):

(3)

where T1/2 is the half-life of tritium. Neon (Ne) concentrations 

are used to correct 3Hetrit for samples that contain terrigenic 

helium from crustal and mantle sources such as 

crystalline rocks.

Determination of final apparent age estimates was 

based on the comparison of the estimates from the different 

tracers and whether the sample indicates piston flow or binary 

mixtures (table 3). The final apparent age estimates range from 

less than 0.1 to 16.1 years. About 73 percent of the samples 

contained some fraction of waters with apparent ages that 

were less than 5 years. Because of contamination (in terms 

of age determinations) of the CFCs and year of recharge, the 

percentage of the young fraction in binary mixtures could 

not be determined for all samples. For the samples in which 

determination of the young fraction was possible, the young 

fraction ranged from approximately 80 to 99.5 percent. 

These high percentages indicate that a majority of the water 

discharging is close to being piston flow, which would have a 

young fraction of 100 percent.

Figure 25. Atmospheric mixing ratios of chlorofluorocarbon-11 (CFC-11), 

chlorofluorocarbon-12 (CFC-12), chlorofluorocarbon-113 (CFC-113), and sulfur 

hexafluoride (SF6) for North American air and estimated monthly concentration of 

tritium in precipitation for Virginia. Tritium data derived from estimation technique of 

Michel (1989) and are not corrected for radioactive decay. Modified from Plummer 

and Busenberg (2000).

[ ]

3

1/2 3 / ln 2 1 ,

Hetrit T

H



      = × +    

SF6 x 100

Bomb peak

3H

1940 1950 1960 1970 1980 1990 2000

0

100

200

300

400

500

600

700

0

200

400

600

800

1,000

1,400

1,200

YEAR

CONCENTRATION IN AIR, IN PARTS PER TRILLION (VOLUME) 

TRITIUM CONCENTRATION IN PRECIPITATION,

 IN TRITIUM UNITS

Figure 25. Atmospheric mixing ratios of chlorofluorocarbon-11 (CFC-11), chlorofluorocarbon-12 (CFC-12), 

chlorofluorocarbon-113 (CFC-113), and sulfur hexafluoride (SF6) for North American air and estimated monthly

concentration of tritium (

3

H) in precipitation for Virginia. Tritium data derived from estimation technique of Michel

(1989) and are not corrected for radioactive decay. Modified from Plummer and Busenberg (2000).

CFC-11

CFC-12

CFC-113
Hydrogeology 39

Table 3. Apparent ages and uncertainties from chlorofluorocarbons, sulfur hexafluoride, and tritium/helium-3 dating methods and percentage of young fraction in water samples from wells and springs in Warren County, Virginia, 2003–2005.[CFC-11, (trichlorofluoromethane, CFC13); CFC-12, (dichlorodifluoromethane, CF Cl 2 2); CFC-113, (trichlorotrifluoroethane, C2F Cl 3 3); SF6, sulfur hexafluoride; 3H/3He, tritium/helium-3; 

NP, not possible; C, contaminated. Final apparent ages and percentages are shaded. Numbers in parentheses indicate possible recharge years before and after atmospheric peak concentration. See figure 24 for location of wells and springs]

USGS

local no. Date

Apparent age and uncertainty. in years Percentage of young fraction Piston flow

CFC-11/

CFC-12

CFC-113/

CFC-12

CFC-113/

CFC-11 SF6 3H/3He CFC-11

(1)

CFC-11

(2)

CFC-12

(1)

CFC-12

(2)

CFC-113

(1)

CFC-113

(2)

CFC-11/

CFC-12

CFC-113/

CFC-12

CFC-113/

CFC-11

44US 2 08/18/2004 18.1 ± 0.7 NP C C 14.1 ± 0.4 NP NP NP NP 2.6 0.1 ± 0.3 NP NP NP45US 3 08/18/2004 22.1 ± 0.7 NP C C 15.1 ± 0.7 NP NP NP NP 2.6 6.1 ± 0.4 NP NP NP45US 5 08/18/2004 C C C C Mod. C NP NP NP 9.6 1.0 ± 0.2 NP NP NP45US 6 08/08/2005 C C C C 10.1 ± 2.8 10.1 ± 4.2 NP NP NP 20.1 0.6 ± 0.4 NP NP NP45VS 1 08/14/2003 18.1 NP 12.6 ± 3.2 NP 13.6 ± 0.4 NP NP NP NP 0.6 2.3 ± 0.2 NP NP NP45VS 2 08/21/2003 13.1 ± 1.8 5.1 ± 4.6 12.1 ± 1.4 NP C C NP NP NP C 8.0 ± 0.6 NP NP NP45VS 3 08/09/2005 11.1 ± 3.9 11.6 ± 5.7 Mod. C 11.6 ± 3.2 8.1 ± 6.7 NP NP NP 19.1 1.2 ± 0.2 NP NP NP45VS 4 08/09/2005 18.6 ± 0.4 NP 13.6 ± 1.4 NP 15.1 ± 0.7 NP NP NP 10.1 20.6 2.7 ± 0.3 NP NP 92.446V 1 08/14/2003 C C 18.1 ± 0.7 NP 15.1 ± 0.4 NP NP NP NP 4.6 4.0 ± 0.2 NP NP NP46VS 1 08/14/2003 16.6 ± 1.1 NP 13.1 ± 1.1 NP 8.1 ± 3.2 8.1 ± 6.7 NP NP NP 0.1 –0.1 ± 0.2 NP NP NP46VS 2 08/18/2004 19.6 ± 0.7 NP 16.6 ± 0.7 NP 16.6 ± 0.4 NP NP 16.1 ± 0.4 13.1 13.1 NP NP 99.5 80.446VS 6 08/23/2004 C C C C C C NP NP NP 3.6 0.0 ± 0.3 NP NP NP46VS 8 08/23/2004 14.1 ± 1.8 6.1 ± 4.6 3.6 ± 6.0 3.6 12.6 ± 1.1 3.6 NP NP 9.6 ± 0.7 8.6 4.0 ± 0.4 NP NP 98.246VS 12 08/10/2005 17.1 ± 0.7 2.1 Mod. C 15.6 ± 0.4 NP NP NP 14.6 20.1 10.6 ± 0.6 NP NP 97.046VS 13 08/10/2005 C C C C 14.6 ± 1.1 0.6 NP NP NP 18.6 4.2 ± 0.4 NP NP NP
40 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Generally, the youngest apparent ages and binary 

mixtures are present at springs and wells in the upper reaches 

of the watersheds, whereas the older ages are present in the 

lower reaches (fig. 24). Nelms and Moberg (2010) sampled 

springs in Clarke County between 2003 and 2005 and noted 

that apparent ages were older and the percentage of the young 

water fraction decreased during this period, which indicates a 

relation with hydrologic conditions. Extremely wet conditions 

existed in 2003 and became progressively drier between 2004 

and 2005. This distribution and temporal changes of apparent 

ages and mixing fractions is consistent with an aquifer system 

that is topographically driven with local flow systems containing young waters that are superimposed on a subregional 

to regional flow system with older waters. Therefore, under 

different hydrologic conditions, temporal changes in waterquality trends and dye-tracer studies would be expected 

to occur.

Plummer and others (2001) determined that apparent 3

H/3He ages for spring water in Shenandoah National Park 

located in the Blue Ridge predominantly ranged from 0 to 

3 years (fig. 24). Large precipitation events caused specific 

conductance and temperature to increase in these springs 

within a few hours of the event and then to decrease to values 

less than pre-storm base-flow values. Plummer and others 

(2001) also determined that mobile atmospheric constituents 

have flushing rates through groundwater to streams that 

average less than 3 years at base-flow conditions. These 

findings illustrate the close relation between spring flow and 

precipitation in the Blue Ridge. Additionally, the movement of 

contaminants from the surface to outlets such as springs and 

streams can be very rapid in the Blue Ridge. 

Water discharging from springs in Warren County is 

generally younger than water from wells. The apparent ages 

for the well samples, however, are still young enough to be 

considered susceptible to contamination (Nelms and others, 

2003) and to droughts. Well 46V 1, which is located near the 

top of High Knob and about 1,000 ft from spring 46VS 1 

(fig. 24), has water with apparent ages that range from 

4.0 to 4.6 years; however, the apparent age of groundwater 

from spring 46VS 1 is 0.1 year. Well 45U 3 is located along 

Dickeys Ridge in Shenandoah National Park and has apparent 

ages that range from 8.0 to 9.7 years (Plummer and others, 

2001). The CFC and 3H/3He data indicate that between 47 and 

55 percent of young water mixes with old (pre-CFC) waters 

(Plummer and others, 2001). The water-bearing zones reported 

for well 45U 3 were 600 and 625 ft bls in the metabasalt of the 

Catoctin Formation (DeKay, 1972). Nelms and others (2003) 

estimated an apparent age of 19.8 years and a binary mixture 

of 15.6 percent young water with pre-CFC water for well 

44U 3 located along the South Fork Shenandoah River west 

of Limeton.

Revised Conceptual Model of Groundwater Flow

In the Blue Ridge, elevated topography provides the 

driving force for groundwater flow, and the water table is 

generally a subdued reflection of the land surface (fig. 26). 

The high density of streams in the Blue Ridge is probably the 

result of the underlying low permeability rocks. The porous 

nature of the overlying regolith material (overburden) and the 

sharp contrast in permeability with the underlying bedrock 

coupled with numerous streams and steep terrain are probably 

more conducive for the development of local flow systems. 

Wright (1990) and Nelms and Moberg (2010) stated that 

subsurface stormflow through the porous overburden moves 

rapidly to streams and springs in the Blue Ridge because 

of the steep terrain. Although the terrain is steep, overland 

flow is probably a minor component of runoff compared to 

subsurface stormflow (Whipkey, 1965). When siting potential 

sources of contamination in the future, the importance of 

subsurface stormflow in the Blue Ridge should be taken into 

consideration, especially in areas near stream valleys filled 

with alluvial and colluvial deposits. Groundwater flow in 

the bedrock is controlled primarily by the irregular fracture 

network and steep terrain (Wright, 1990). Local flow systems 

may be controlled by stress relief or other brittle fracturing; 

however, bedding-plane partings in the metasedimentary 

rocks, partings between basalt flows in the Catoctin Formation, and foliations in the metamorphic rocks may facilitate 

more of a subregional- to regional-type flow. Southworth 

(1990) proposed that water recharged on the western slopes of 

the mountains of the Blue Ridge flows downdip along bedding 

planes and eventually discharges to springs and in valleys on 

the eastern sides of the mountains. 

Conceptualization of the groundwater flow system in the 

siliciclastic rocks on the western edge of the county, predominantly underlain by the Martinsburg Formation, is more 

similar to the groundwater flow system of the Blue Ridge than 

to that in the carbonate rocks of the Great Valley. Although 

the Martinsburg terrain is less steep and lower in altitude than 

the terrain of the Blue Ridge, local flow systems probably 

are dominant in response to the high density of streams that 

have formed the trellis (structurally controlled) drainage 

network. However, subsurface stormflow is probably a minor 

factor because of the lack of regolith material overlying the 

Martinsburg Formation (Hack, 1965) and less steep terrain. 

Groundwater moves along cleavage, bedding-plane partings, 

and longitudinal and cross-strike joints in a stair-step pattern 

(fig. 27). The interfluve to stream areas may act as local flow 

cells, where groundwater flowing along paths parallel to the 

dip direction of the bedding is younger than groundwater flowing opposite the dip direction (Burton and others, 2002). Hack 

and Young (1959) stated that many of the streams and creeks 

flow along the cross-strike joints. Evapotranspiration and, to 

a lesser extent, surface runoff may be greater than in the other 

areas of the county because of the low permeability of the 

rock and the absence of regolith material. Springs seldom 

form in areas underlain by the Martinsburg, and seeps are 

much more common.
Hydrogeology 41

Figure 26. Generalized conceptual hydrogeologic longitudinal section of the flow system in the Blue Ridge 

Physiographic Province in Warren County, Virginia. Modified from Nelms and Moberg (2010).

600

800

1,000

1,200

1,400

600

800

1,000

1,200

1,400

0 500 1,000 1,500

DISTANCE, IN FEET

2,000 2,500 3,000 3,500

SOUTH

FEET

NORTH

FEET

Figure 26. Generalized conceptual hydrogeologic longitudinal section of 

the flow system in the Blue Ridge Physiographic Province in Warren 

County, Virginia. Modified from Nelms and Moberg (2010).

Water table

Bedding-plane partings and joints

EXPLANATION

Regional flow

Subsurface stormflow

Regional flow along 

bedding-plane partings

Longitudinal flow along 

streams in alluvium and 

colluvium

Local flow 

Catoctin Formation

Weverton Formation

Saprolite

Regolith material Alluvium and colluvium

or overburden

HYDROGEOLOGIC UNIT FLOW TYPE

Hydrogeologic unit

contact

Intermittent

spring

Alluvium, colluvium, and

debris-fan deposits

Perennial

Land surface spring
42 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 27. Generalized conceptual hydrogeologic sections along strike and cross-strike in the siliciclastic fracturedrock flow system (Martinsburg Formation) in Warren County, Virginia.

0 2,000 4,000 6,000 8,000

540

560

580

600

620

640

660

680

700

540

560

580

600

620

640

660

680

700

2,000

0

4,000

SOUTH

FEET

NORTH

FEET

DISTANCE, IN FEET

DISTANCE, IN FEET

Regional flow along cross-strike plane

Local flow (Fast) along cross-strike plane

Figure 27. Generalized conceptual hydrogeologic sections along strike and cross-strike in the 

siliciclastic fractured-rock flow system (Martinsburg Formation) in Warren County, Virginia. 

Local flow (Slow) along cross-strike plane

Regional flow along strike

Local flow along strike

Unsaturated zone Unsaturated zone

STRIKE-PARALLEL PLANE CROSS-STRIKE PLANE

Water table

Bedding and cleavage

EXPLANATION

μ

0 2,000 4,000 FEET

0 500 1,000 METERS

550

500

600

650

700

750

ALTITUDE, IN FEET ABOVE 

NGVD 29

EXPLANATION

West Run

Dry Run

Molly Camel Run

?

?

?

Cross-strike plane

Intermittent 

stream

Tension 

joints

Dip joints

Strike-parallel plane

Cross-strike parallel

Strike-parallel

Molly Camel Run

Dry Run

Land surface
Groundwater Availability 43

Groundwater Availability

The prolonged drought between 1999 and 2002 caused 

concern about current and future demands on the county’s 

groundwater resources. In order to address these concerns, 

various components related to groundwater availability were 

determined during this investigation. Effective recharge rates 

to the groundwater system were estimated by a hydrograph 

separation technique that separates streamflow into base-flow 

(groundwater discharge) and surface-runoff components. 

Annual water budgets for the years 2001 through 2007 were 

developed for the basins gaged during this investigation. 

These water budgets include precipitation, mean annual 

streamflow and mean annual base-flow data, ET, changes in 

groundwater storage (from water-level data), estimates of 

specific yield, and water withdrawal data. For the 15 ungaged 

basins in the county, effective recharge was calculated using 

regression equations developed by Yager and others (2008) for 

the Shenandoah Valley area and was compared to projected 

water-supply demands.

Effective Recharge

Effective recharge (ER) is the part of precipitation that 

percolates to the water table and recharges the groundwater 

system but does not represent the total recharge to a basin. 

Total recharge has two components: (1) effective recharge and 

(2) riparian evapotranspiration (RET). RET is the quantity of 

water consumed by evaporation and transpiration by plants 

in riparian zones. Rutledge and Mesko (1996) reported that 

estimated values of RET ranged from 1 to 2 inches per year 

(in/yr) in the Appalachian Valley and Ridge from Alabama 

to New Jersey. Recharge occurs throughout a basin, but rates 

generally lessen toward discharge areas. Sinkholes in the 

Great Valley section and alluvium and colluvium in stream 

valleys of the Blue Ridge, however, can allow for substantial 

and rapid recharge. The amount of recharge depends on many 

factors, including antecedent soil-moisture conditions, the 

timing, duration, and intensity of precipitation, depth to the 

water table, and soil and bedrock characteristics (Harlow and 

others, 2005).

PART, a streamflow partitioning program (Rutledge, 

1993), is a hydrograph separation technique that separates 

streamflow into its base-flow (groundwater discharge) and 

surface-runoff components. Effective recharge is equivalent 

to mean base flow (by means of unit conversion) because 

groundwater discharge over a long period approximately 

equals groundwater recharge (Richardson, 1982). Nelms and 

others (1997) estimated a median effective recharge of 

11.1 in/yr in 46 basins and 8.4 in/yr in 73 basins in the northern Blue Ridge and Valley and Ridge Physiographic Provinces 

of Virginia, respectively. PART was applied to two unregulated 

streams [stations 01630700 (Gooney Run) and 0163626650 

(Manassas Run)] and one regulated stream [station 01636242 

(Crooked Run)] (table 4). A major assumption of PART is 

that the surface-water drainage basin and the recharge area 

coincide. Harlow and others (2005) noted that the validity of 

this assumption is uncertain. The unconsolidated deposits in 

the stream valleys of the Blue Ridge may have a larger effect 

on streamflow characteristics than the remaining areas of a 

basin do. Groundwater flow beneath surface-water divides in 

karst areas is well documented by dye-tracer studies (Jones, 

1987; Orndorff, 2006). Regardless, the PART method provides 

a conservative estimate of effective recharge.

Streamflow-gaging station 01630700, Gooney Run at 

Route 622 near Glen Echo, VA, is in the southeastern corner 

of the county, has a drainage area of 20.5 mi2, and has been 

in operation since May 2002 (fig. 15). The entire drainage 

area above this station is underlain by metamorphic bedrock, 

primarily the Mesoproterozoic granitic rocks, and debris-fan 

deposits and colluvium overlie the bedrock in about 33 percent 

of the basin. Very poorly sorted boulders and cobbles in a 

fine-grained matrix of sand, silt, and clay characterize the 

debris-fan deposits, and the colluvium consists of clastsupported cobbles and boulders (Southworth and others, 

2009). The presence of these deposits over such a large area 

of the basin contributes to the strong diurnal streamflow signal 

(fig. 22) caused by RET frequently observed during base-flow 

conditions. To estimate annual effective recharge rates during 

the peak of the drought before the gage was installed, a linear 

regression equation was developed between effective recharge 

rates for gaging station 01630700 and those for streamflowgaging station 01635500, Passage Creek above Route 55 near 

Buckton, VA (fig. 15), between 2003 and 2007. Estimates 

of effective groundwater recharge between 2001 and 2007 

at the Gooney Run gage ranged from 10.0 to 28.1 in/yr with 

an average of 15.3 in/yr (table 4). Base flow accounted for 

between 64 and 86 percent of mean streamflow and averaged 

71 percent between 2001 and 2007. These percentages are 

referred to as base-flow index (BFI). Nelms and others (1997) 

correlated partial-record streamflow data at gaging station 

01630700 with continuous streamflow data and estimated an 

annual effective recharge rate of 16.5 in/yr.

Streamflow-gaging station 0163626650, Manassas Run 

at Route 645 near Front Royal, VA, is in the northeastern part 

of the county, has a drainage area of 11.2 mi2, and has been 

in operation since May 2002 (fig. 15). The station is approximately 1,000 ft downstream from the Happy Creek fault. 

Metamorphic rocks of the Neoproterozoic Catoctin Formation 

and the Lower Cambrian Chilhowee Group underlie nearly 

the entire drainage area (99.3 percent) above this station. 

Carbonate rocks of the Lower Cambrian Waynesboro Formation underlie the small part of the basin downstream from 

the Happy Creek fault. Unconsolidated surficial deposits 

overlie the bedrock in about 11 percent of the basin and are 

concentrated along the stream valleys. The concentration of 

relatively coarse-grained surficial deposits along the stream 

valleys facilitates RET effects on streamflow, which are similar 

to the RET effects at gaging station 01630700 (Gooney Run) 

(fig. 22). To estimate annual effective recharge rates during 

the peak of the drought before the gage was installed, a linear 
44 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Table 4. Summary of annual water budget components for the Gooney Run, Crooked Run, and Manassas Run Basins in Warren County, Virginia, 2001–2007.[DA, drainage area; mi2, square miles; in/yr, inches per year; 

P, precipitation at National Weather Service station 443229 Front Royal SE located in Warren County, VA; ET, evapotranspiration; SF, mean 

streamflow; RO, runoff; ER, effective recharge estimated from streamflow partitioning program PART (Rutledge, 1993); ΔS, change in groundwater storage; WU, water usage; BFI, base-flow index. Percentages of annual precipitation are shown in parentheses. Blue-shaded rows indicate years with above-average precipitation, and unshaded rows indicate years with below-average precipitation]

Station no. 

(fig. 15) Station DA (mi2

)

Calendar

year a

Inflowb

(in/yr)

Outflowb

(in/yr) Percent of normal ER WU percent of ER BFI P c ET SF d RO d ER d DS e WU f

01630700 Gooney Run at Route 622 near Glen 

Echo, Virginia

20.5 2001 36.7 19.2 17.6 6.3 11.3 –0.2 0.1 67 0.7 64.1

2002 43.4 25.8 17.9 6.5 11.4 –0.4 0.1 67 0.7 63.52003 59.2 19.7 38.4 10.3 28.1 1.0 0.1 166 0.3 73.12004 45.1 21.9 23.3 6.6 16.6 –0.1 0.1 99 0.5 71.52005 39.6 19.4 19.9 5.4 14.6 0.2 0.1 86 0.6 73.12006 43.2 21.1 22.0 6.9 15.0 0.0 0.1 89 0.6 68.42007 31.6 19.8 11.7 1.7 10.0 0.0 0.1 59 0.8 85.6

Average 42.7 21.0

(49.2)

21.5

(50.4)

6.3

(14.8)

15.3

(35.8)

0.1

(0.2)

0.1

(0.2)

0.5 70.9

01636242 Crooked Run below Route 340 at 

Riverton, Virginia

46.9 2001 36.7 29.7 7.0 4.7 2.4 –0.2 0.2 37 8.1 33.7

2002 43.4 36.4 7.2 4.8 2.4 –0.4 0.2 37 7.9 33.42003 59.2 34.2 22.7 7.9 14.8 2.1 0.2 230 1.3 65.32004 45.1 34.2 11.0 4.8 6.2 –0.3 0.2 96 3.1 56.32005 39.6 32.3 7.7 3.4 4.3 –0.5 0.2 66 4.5 55.62006 43.2 34.8 7.8 4.1 3.7 0.5 0.2 58 5.1 47.82007 31.6 25.1 6.1 2.9 3.3 0.2 0.2 51 5.9 53.3

Average 42.7 32.4

(75.9)

9.9

(23.2)

4.6

(10.8)

5.3

(12.4)

0.2

(0.5)

0.2

(0.5)

3.6 53.5

0163626650 Manassas Run at Route 645 near 

Front Royal, Virginia

11.2 2001 36.7 20.2 16.4 6.9 9.5 –0.2 0.3 59 2.9 57.9

2002 43.4 26.9 16.6 7.1 9.6 –0.4 0.3 60 2.8 57.42003 59.2 20.6 37.4 8.0 29.4 1.0 0.3 183 0.9 78.72004 45.1 23.2 21.7 6.9 14.8 –0.1 0.3 92 1.8 68.02005 39.6 16.1 23.1 6.2 16.9 0.2 0.3 105 1.6 73.02006 43.2 26.2 16.7 5.7 11.1 0.0 0.3 69 2.5 66.12007 31.6 20.8 10.5 2.3 8.2 0.0 0.3 51 3.3 77.7

Average 42.7 22.0

(51.5)

20.3

(47.5)

6.2

(14.5)

14.2

(33.3)

0.1

(0.2)

0.3

(0.7)

1.9 70.0

a For the years 2001–2002 at streamflow gages 01630700 and 0163626650 and for the years 2001–2004 at streamflow gage 01636242, estimates are based on linear regression with streamflow-gaging 

station 01635500 Passage Creek above Route 55 near Buckton, VA.

b Water-budget equation is 

P = ET + RO + ER + 

DS + WU. Estimates of SF and ER were determined from PART, which is a streamflow partitioning program (Rutledge, 1993). RO is estimated as the difference between SF and ER. The terms 

P, RO, DS, WU, and ER are known, measured, or estimated; therefore, solution of the water-budget equation provides an estimation of ET.

c Normal annual precipitation of 39.7 inches at National Weather Service station 443229 Front Royal is based on the period of record from 1996 to 2007.d To convert inches per year to cubic feet per second, divide value by 13.5837 and then multiply by drainage area (in square miles).e DS is based on the highest water levels recorded for the respective calendar year subtracted from the highest value for the previous year. For the calendar years 2001–2004, 

DS was calculated using 

water-level data from well 46W175 in Clarke County, VA. For calendar years 2005–2007, 

DS was calculated using water levels measured at well 45V.

f Source is 2000 U.S. Census population data (U.S. Census Bureau, 2003). Individual water use is estimated to be 75 gallons per day.
Groundwater Availability 45

regression equation was developed between effective recharge 

rates for gaging station 0163626650 and those for streamflowgaging station 01635500 (Passage Creek). Estimates of 

effective groundwater recharge between 2001 and 2007 at 

the Manassas Run gage ranged from 8.2 to 29.4 in/yr with 

an average of 14.2 in/yr (table 4). Base flow accounted for 

between 57 and 79 percent of mean streamflow and averaged 

70 percent between 2001 and 2007. The high BFI values at 

gaging stations 01630700 (Gooney Run) and 0163626650 

(Manassas Run) indicate that groundwater is the dominant 

source of streamflow during wet and drought conditions.

The diurnal streamflow signals observed at gaging 

stations 01630700 (Gooney Run) and 0163626650 (Manassas 

Run) illustrate the combined effect that evapotranspiration 

processes and the presence of shallow unconsolidated surficial 

deposits in the stream valleys can have on streamflow in the 

Blue Ridge, particularly during the warmer months of the 

spring and summer seasons. A majority of the area in both 

basins is forested, especially along the riparian areas where 

these surficial deposits are present in and near the streams. 

Analysis of the diurnal streamflow signal, similar to the 

method developed by Czikowsky and Fitzjarrald (2004), 

provides estimates of RET. Periods of streamflow cyclicity 

between April and October were identified, and the differences 

between maximum daily streamflows for consecutive days 

were calculated to determine the amount of RET. Statistical 

analysis of these daily changes in streamflow provides 

estimates of RET for 2003–2008 (table 5). Average values for 

the annual means probably are biased high by inclusion of 

streamflows where diurnal signals may have included effects 

of recent precipitation events and not only responses to RET.

However, the average values for annual medians (1.6 and 

2.5 in.) are similar to values of RET estimated by Rutledge and 

Mesko (1996). A seasonal trend is evident where RET values 

tend to be high between April and June and progressively 

lessen as the growing season progresses (table 5). Because 

deforestation and construction of riparian buffer strips are 

likely to impact streamflow in these and in other Blue Ridge 

basins, monitoring might be advisable. 

Streamflow-gaging station 01636242 Crooked Run 

below Route 340 at Riverton, VA, is in the northern part of 

the county, has a drainage area of 46.9 mi2, and has been 

in operation since October 2004 (fig. 15). A majority of the 

drainage basin for this gage is located in neighboring counties 

to the north. The station is approximately 450 ft downstream 

from the contact between the siliciclastic rocks of the Middle 

and Upper Ordovician Martinsburg Formation and the Middle 

Ordovician carbonate rocks. The station is slightly less than 

1 mi from the confluence with the Shenandoah River. Part 

of the flow in Crooked Run is regulated by Lake Frederick, 

which is located in Frederick County; however, only about 

7 percent of the drainage area of Crooked Run is upstream 

Table 5. Annual and seasonal estimates of riparian evapotranspiration based on periods of streamflow diurnal cycling at 

gages 01630700 Gooney Run at Route 622 near Glen Echo, Virginia, and 0163626650 Manassas Run at Route 645 near Front 

Royal, Virginia, from calendar years 2003 to 2008.

[Estimates of riparian evapotranspiration are in inches per year. DA, drainage area; mi2, square miles]

Station no.

(fig. 15) Station DA(mi2)

Annual riparian evapotranspirationa Seasonal riparian evapotranspirationa

Year Mean Median Seasonb Mean Median

01630700 Gooney Run at Route 622 

near Glen Echo, Virginia

20.5 2003 9.5 4.3 1 10.0 2.0

2004 7.0 1.4 2 4.1 0.5

2005 8.9 0.7 3 0.2 0.1

2006 18.5 1.3

2007 3.4 1.0

2008 4.8 0.9

Average 8.7 1.6

0163626650 Manassas Run at Route 

645 near Front 

Royal, Virginia

11.2 2003 9.0 4.8 1 8.7 2.4

2004 12.8 4.7 2 3.7 1.0

2005 5.8 2.4 3 0.3 0.3

2006 6.0 1.2

2007 3.3 0.7

2008 7.6 1.2

Average 7.4 2.5

a

 Periods of streamflow cyclicity between April and October were identified, and the differences between maximum daily streamflows for consecutive days were calculated to determine the amount of riparian evapotranspiration.

b

 Seasons are grouped by the following months, and seasonal estimates of riparian evapotranspiration are from the period 2003–2008: 1–April, 

May, and June; 2–July, August, and September; and 3–October, November, and December.
46 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

from the spillway for Lake Frederick. Siliciclastic rocks of 

the Martinsburg Formation underlie about 74 percent of the 

drainage area above this station, and carbonate rocks underlie 

the remainder. Quaternary alluvium is present mainly along 

Crooked Run and is absent along the tributaries (Rader and 

Conley, 1995). For the most part, the streambeds for Crooked 

Run and its tributaries are in bedrock. The tributaries align 

with the cross-strike joints; however, Crooked Run generally 

follows the contact between the siliciclastic and carbonate 

rocks (fig. 15). In order to estimate annual effective recharge 

rates during the peak of the drought (2002) prior to gage 

installation, a linear regression equation was developed 

between effective recharge rates for gage 01636242 and those 

for streamflow-gaging station 01635500 between 2005 and 

2007. Estimates of effective groundwater recharge between 

2001 and 2007 range from 2.4 to 14.8 in/yr with an average 

at the Crooked Run gage of 5.3 in/yr (table 4). Base flow 

accounted for between 33 and 65 percent of mean streamflow 

and averaged 54 percent between 2001 and 2007. Although 

this stream is regulated, the average effective recharge is 

similar to the value of 4.9 in/yr estimated by Nelms and 

others (1997) for gaging station 01615000 Opequon Creek 

near Berryville, VA, which monitors a similar distribution of 

rock types. The average BFI (54 percent) is much lower than 

the averages for Gooney Run and Manassas Run and may be 

reflective of the low permeability of the Martinsburg Formation and (or) an artifact of regulation.

Analysis of data collected from Warren County’s longterm water monitoring network and of effective recharge 

rates indicates a positive correlation with current climatic 

conditions. Comparison of annual recharge rates at streamflow 

gages 01630700, 0163626650, and 01636242 to annual precipitation illustrates the relation between these two hydrologic 

factors (fig. 28). Annual effective recharge ranges from 22 to 

50 percent of annual precipitation for the gages in the Blue 

Ridge and averages from 33 to 36 percent (table 4). Annual 

effective recharge ranges from 6 to 25 percent of annual 

precipitation with an average of 12 percent for gage 01636242 

in the siliciclastic rocks of the Valley and Ridge. The timing 

and type of precipitation are critical in determining the amount 

of water that will actually recharge the groundwater system. 

The prime period for groundwater recharge is between January 

and April of each year when plants are dormant, evapotranspiration is at a minimum, and average monthly precipitation 

is low. For example, in the years 2002 and 2006, precipitation 

and snowfall for the winter quarters were below average, and 

effective recharge rates deviate from the apparent correlation. 

Generally, water levels, spring discharges, and streamflows 

normally are at the yearly high by April of each year and 

progressively decline to their lowest in the early autumn. 

Intense rainfall associated with hurricanes, tropical storms, 

or thunderstorms can cause levels and flows to increase short 

term. However, it is uncertain whether actual recharge occurs 

during these storms or if the responses observed in observation 

wells are a function of saturated sediments in the unsaturated 

zone exerting pressure on the gases in the unsaturated zone, 

which, in turn, causes the water table to be at pressures greater 

than atmospheric pressures (Freeze and Cherry, 1979).

The relation between estimated effective recharge and 

annual precipitation was investigated by linear regression 

analysis. The equations developed for streamflow gages 

01630700, 01636242, and 0163626650 are given in table 6. 

These equations should not be considered predictive because 

of the short period of record of these gages and the inclusion 

of estimated recharge rates by regression with another gage. 

The steep slopes of the regressions for gages 01630700 

and 0163626650 (0.66P and 0.75P, respectively) indicate 

that effective recharge is closely related to precipitation. 

Variability, however, is less at gage 01630700 than at gage 

0163626650 (fig. 28). The difference in variability between 

these gages may be in response to such factors as the amount 

and type of unconsolidated surficial material, amount and 

spatial distribution of precipitation, size of drainage basin, 

and shape and orientation of the drainage basin. The drainage 

area above gage 01630700 has (1) nearly 3 times the amount 

of unconsolidated surficial material, (2) higher mean annual 

precipitation and greater range of precipitation amounts, 

and (3) a drainage area that is about 2 times larger than the 

drainage area above gage 0163626650. The amphitheatershaped, north-facing orientation of the drainage area for gage 

01630700 (fig. 15) is uniquely different from the east-west 

aligned drainage area for gage 0163626650. All of these 

factors contribute to the variability between these basins; 

however, both of these basins are influenced by the abundance 

Table 6. Linear regression equations relating effective recharge to annual precipitation at gages 01630700, 

Gooney Run at Route 622 near Glen Echo, Virginia, 01636242, Crooked Run below Route 340 at Riverton, Virginia, 

and 0163626650, Manassas Run at Route 645 near Front Royal, Virginia, 2001–2007.

[DA, drainage area; mi2, square miles; in/yr, inches per year; R2, coefficient of determination; ER, effective recharge; P, precipitation. 

Shading indicates dominant rock type: Green, metamorphic rocks in the Blue Ridge Physiographic Province; Brown, siliciclastic 

rocks of the Valley and Ridge Physiographic Province]

Station no.

(fig. 15) Gage DA(mi2)

Equation

(in/yr) R2

01630700 Gooney Run at Route 622 near Glen Echo, Virginia 20.5 ER = 0.66P – 12.98 0.87

01636242 Crooked Run below Route 340 at Riverton, Virginia 46.9 ER = 0.45P – 13.78 0.77

0163626650 Manassas Run at Route 645 near Front Royal, Virginia 11.2 ER = 0.75P – 17.80 0.76
Groundwater Availability 47

Figure 28. Relation between annual precipitation at National Weather Service climatological station 443229 Front Royal, Virginia, and 

effective recharge at streamflow-gaging stations 01630700 Gooney Run at Route 622 near Glen Echo, Virginia, 01636242 Crooked Run 

below Route 340 at Riverton, Virginia, and 0163626650 Manassas Run at Route 645 near Front Royal, Virginia. For the years 2001–2002 at 

streamflow-gaging stations 01630700 and 0163626650 and for the years 2001–2004 at streamflow-gaging station 01636242, estimates are 

based on linear regression with streamflow-gaging station 01635500 Passage Creek above Route 55 near Buckton, Virginia. Effective 

recharge rates for remaining years are estimated with the streamflow partitioning software package PART (Rutledge, 1993).

ANNUAL PRECIPITATION, IN INCHES

10%

20%

30%

40%

50%

60%

70%

90%

80%

100%

0

5

10

15

20

25

30

35

40

45

MEAN ANNUAL EFFECTIVE RECHARGE, IN INCHES

25 30 35 40 45 50 55 60 65

2007

2001

2005

2004

2006

2002

2003

BELOW-AVERAGE PRECIPITATION ABOVE-AVERAGE PRECIPITATION

10%

20%

30%

40%

50%

60%

70%

90%

80%

100%

0

5

10

15

20

25

30

35

40

45

MEAN ANNUAL EFFECTIVE RECHARGE, IN INCHES

25 30 35 40 45 50 55 60 65

2007

2001 2005

2004

2006

2002

2003

BELOW-AVERAGE PRECIPITATION ABOVE-AVERAGE PRECIPITATION

Figure 28. Relation between annual precipitation at National Weather Service climatological station 443229 Front Royal, 

Virginia, and effective recharge at streamflow gaging stations 01630700 Gooney Run at Route 622 near Glen Echo, Virginia, 

01636242 Crooked Run below Route 340 at Riverton, Virginia, and 0163626650 Manassas Run at Route 645 near Front Royal, 

Virginia. For the years 2001-2002 at streamflow gaging stations 01630700 and 0163626650 and for the years 2001-2004 at 

streamflow gaging station 01636242, estimates are based on linear regression with streamflow gaging station 01635500 

Passage Creek above Route 55 near Buckton, Virginia. Effective recharge rates for remaining years are estimated with the 

streamflow partitioning software package PART (Rutledge, 1993).

EXPLANATION

01630700 Gooney Run at Route 622 near Glen Echo, VA

01636242 Crooked Run below Route 340 at Riverton, VA

0163626650 Manassas Run at Route 645 near Front Royal, VA

2001 Calendar year

STREAMFLOW-GAGING STATION Average effective recharge and 

 95-percent confidence interval

10% Percentage of annual precipitation

Metamorphic basins

Siliciclastic basin
48 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

of unconsolidated surficial material overlying the bedrock 

(33 percent at gage 01630700 compared to 11 percent at gage 

0163626650). The drastic difference in permeability between 

these deposits and the bedrock combined with correlation of 

recharge rates and precipitation, diurnal streamflow signals 

in response to RET, and factors listed above suggest that the 

unconsolidated surficial material in the riparian area functions 

as a local flow system above the fractured-rock aquifers. In 

the strict sense, the assumptions of PART are not violated, but 

estimated effective recharge rates may be more reflective of 

these local riparian flow systems and not of the fractured-rock 

aquifers. Development of these local flow systems for water 

supply is generally not feasible because the unconsolidated 

deposits are thin, of limited extent, and highly susceptible to 

current climatic conditions and surface contaminants. The 

fractured-rock aquifers are the principal source for current 

and future water supplies; the average recharge rates for 

gages 01630700 and 0163626650, therefore, should be used 

with caution and may not accurately represent recharge to the 

bedrock aquifers in the Blue Ridge.

The slope of the linear regression for gage 01636242 suggests that a positive relation exists between estimated effective 

recharge and annual precipitation (table 6). The low slope of 

the regression (0.45P) indicates that other factors, such as 

permeability, evapotranspiration, and runoff, may affect the 

relation between groundwater recharge and precipitation. The 

siliciclastic part of the Martinsburg Formation generally is 

considered to be relatively impermeable with a thin mantle 

of residuum (Cady, 1936, 1938; Hack, 1965; Trainer and 

Watkins, 1975; Hinkle and Sterrett, 1976, 1977, 1978; Wright, 

1990; Yager and others, 2008). The dense stream network in 

this basin and average ratio of mean streamflow to drainage 

area (1.37 cubic feet per second per square mile [(ft3/s)/mi2]) 

is characteristic of low permeability terrains. The relatively 

high average value for ET (table 4) suggests that downward 

percolation of precipitation is slow, and evapotranspiration 

at or near land surface consumes the infiltrating water. The 

combination of the aforementioned factors and the lack of 

unconsolidated surficial deposits in the drainage area above 

gage 01636242 suggests that the estimated effective recharge 

rates reflect recharge to the fractured-rock aquifers in siliciclastic terrains.

Nelms and others (1997) estimated effective recharge 

rates for other gages in and around the county using hydrograph separation methods (PART). An effective recharge rate 

of 6.2 in/yr for 1933–1983 was estimated at gaging station 

01635500 Passage Creek above Route 55 near Buckton, 

VA, which drains the siliciclastic rock unit. Gaging station 

01636270 Borden Marsh Run at Route 624 near Boyce, VA, 

which is predominantly underlain by the carbonate rock unit, 

had an estimated effective recharge rate of 12.8 in/yr. Effective 

recharge rates for the North Fork and South Fork Shenandoah 

River (stations 01633000 and 01631000, respectively) were 

estimated to be 6.3 and 8.8 in/yr, respectively. Harlow and 

others (2005) estimated an effective recharge rate of 7.7 in/yr 

for 1938–2002 at gaging station 01634500 Cedar Creek near 

Winchester, VA, with the entire drainage area above this station underlain by siliciclastic bedrock. The period studied by 

Harlow and others (2005) was at the height of the 1999–2002 

drought. Effective recharge estimated for 2001–2002 ranged 

from 3.2 to 6.2 in/yr for siliciclastic and carbonate basins. 

Nelms and Moberg (2010) estimated average effective 

recharge rates of approximately 12 in/yr for two carbonate 

basins in Clarke County for 2001–2007.

The knowledge that groundwater is a major component 

of streamflow in the county should be noted when evaluating 

water-resources issues. The values for BFI, which is base flow 

as a percentage of mean streamflow, indicate that groundwater 

composes about 70 and 54 percent of mean streamflow in the 

metamorphic and siliciclastic terrains, respectively (table 4). 

Harlow and others (2005) and Nelms and Moberg (2010) 

determined that groundwater is an even greater component of 

streamflow in carbonate terrains with values of BFI between 

80 and 90 percent. Both of these investigations state that 

springs are commonly the start of flows for streams in the 

carbonate terrains, and spring discharges, especially during 

drought conditions, often are a large part of the streamflow. 

Water Budgets for Gaged Basins

Water budgets represent an estimate of the amount of 

water entering and leaving a basin plus or minus changes in 

storage during a specified time period (Harlow and others, 

2005). Precipitation is the dominant inflow to a basin; outflows 

are streamflow, ET, and groundwater and surface-water 

withdrawals. All of the water-budget components are in terms 

of mean annual values. The water-budget equation can take 

many forms (Healy and others, 2007), but a simplified 

version that is most relevant in water-supply planning can 

be written as:

P = ET + RO + DS + WU + ER, (4)

where

P is precipitation, in inches per year;

ET is evapotranspiration, in inches per year;

RO is mean runoff, in inches per year;

	 DS is change in groundwater storage, in inches 

per year;

WU is water usage (withdrawals), in inches per 

year; and

ER is effective recharge (mean base flow or 

groundwater discharge), in inches per year.

This form of the water-budget equation assumes that groundwater and surface-water divides are coincident and does not 

take into account underflow that may enter or leave a basin. 

Underflow in a basin in Pennsylvania that is underlain by 

carbonate rock has been estimated to be 2.4 in/yr (Senior and 

others, 1997).
Groundwater Availability 49

The terms P, RO, DS, WU, and ER are either known, 

measured, or estimated; solution of the water-budget equation, 

therefore, provides an estimation of ET. Harlow and others 

(2005) noted that the term ET also includes deviations from 

the assumptions of the equation, such as underflow between 

basins, other losses, and errors in the other terms. Average 

annual water budgets for calendar years 2001 and 2007 were 

prepared for Gooney Run, Manassas Run, and Crooked Run 

Basins (table 4) using methods discussed in this report.

Annual precipitation data (P, table 4), which include 

rainfall and snowfall, were obtained from the NWS climatological station 443229 Front Royal located in Warren County. 

Annual precipitation between 2001 and 2007 ranged from 31.6 

to 59.2 in. with an average value of 42.7, which is 3 in. more 

than the average value for the station for the period of record 

from 1996 to 2007. Therefore, the dominant inflow component 

(P) of the calculated water budgets probably represents an 

average annual precipitation value for above-normal conditions (table 4). Calendar years 2001, 2005, and 2007 are the 

only years for which estimates are provided for below-average 

precipitation conditions.

The estimation of ET is one of the shortcomings of any 

water-budget calculation. For the water budgets determined 

for the Gooney Run, Manassas Run, and Crooked Run Basins, 

ET is estimated by solution of equation 4 and also includes 

underflow, other losses, and errors (Harlow and others, 2005). 

However, the declines in water levels, spring discharges, and 

streamflows during the spring and summer months indicate 

that ET is probably the dominant outflow component for any 

water budget in the area. About 50 percent of the precipitation that fell on the Gooney Run and Manassas Run Basins 

between 2001 and 2007 was removed by ET; a much larger 

percentage (76 percent) of precipitation was removed by 

ET in the Crooked Run Basin (table 4). Harlow and others 

(2005) determined that ET was between 74 to 90 percent of 

the precipitation between 2001 and 2002 at the height of the 

last major drought in the region. ET for a period of average 

precipitation in two carbonate drainage basins in Clarke 

County was about 65 percent of precipitation (Nelms and 

Moberg, 2010).

The RO (surface or mean runoff) term is estimated by 

subtracting effective recharge (ER, table 4) (base flow) from 

mean streamflow (SF). The steep terrain of the Blue Ridge 

province is conducive for runoff, yet in the Gooney Run 

and Manassas Run Basins, RO was only about 15 percent 

of the precipitation for a period of above-average precipitation. Whipkey (1965) stated that overland flow is a lesser 

component of runoff than subsurface stormflow. The relatively 

high permeability of the unconsolidated surficial material 

could allow runoff to be intercepted by these deposits prior to 

the stream. The gently sloping to flat terrain in the Crooked 

Run Basin is not conducive to runoff; only 11 percent of the 

precipitation is runoff. Harlow and others (2005) determined 

that RO for predominantly carbonate drainage basins was 

well below 10 percent of the precipitation in 2001–2002 at 

the height of the last major drought in the region. Even during 

a period of average precipitation, RO in carbonate basins in 

Clarke County was less than 4 percent of precipitation (Nelms 

and Moberg, 2010). The high permeability of the carbonate 

rocks and low relief are not conducive for runoff.

Changes in groundwater storage (DS) are normally 

negligible in water-budget calculations in fractured-rock 

and karst terrains. Values for DS were included in the water 

budgets in table 4. For the calendar years 2001–2004, changes 

in groundwater storage were calculated using water-level data 

from well 46W175 located in Clarke County, VA. Changes 

in storage for the remaining years were calculated by using 

water levels measured at well 45V 3. In order to calculate DS, 

the water-level changes were multiplied by 0.01, which is the 

estimated specific yield of the zone of water-level fluctuation 

(Harlow and others, 2005). Although water-level fluctuations 

can be large in the county, changes in groundwater storage on 

average are very small (table 4).

The amount of water withdrawn from a basin is the 

component of greatest interest in any water budget. In all three 

basins, domestic withdrawal of groundwater is the primary 

use of water and was considered to be consumptive. In order 

to calculate total water usage (WU), shapefiles of the basin 

boundaries were intersected with population data (U.S. Census 

Bureau, 2003); the respective basin population estimates were 

multiplied by 75 gallons per day (gal/d), which is the per 

person water-use estimate for Virginia (Hutson and others, 

2004). The total daily domestic water usage for each basin 

was then converted to a yearly estimate and normalized across 

each respective basin (table 4). WU in Gooney Run, Manassas 

Run, and Crooked Run Basins is estimated to be 0.1, 0.3, 

and 0.2 in/yr, respectively, which is equal to 0.08, 0.14, and 

0.43 million gallons per day (Mgal/d), respectively. The total 

daily domestic water usage appears to be substantial; but in 

terms of the overall water budget, WU on average is only a 

small percentage (table 4). The assumption, however, that WU

is consumptive is not completely valid because the predominant method of sewage disposal in the county is by onsite 

septic wastewater-treatment systems. Landers and Ankcorn 

(2008) documented increases in base flow for watersheds with 

a high density of septic systems (greater than 200 systems per 

square mile) in metropolitan Atlanta, GA, in response to septic 

outflow of municipal surface-water supplies. Keyworth (2009) 

estimated that 85 percent of the wastewater discharged to 

septic systems is returned to the groundwater system.

For water-supply planning in fractured-rock and karst terrains, the most useful water-budget component is ER (effective 

recharge). Groundwater storage in the type of aquifer systems 

in Warren County is minimal; therefore, the amount of water 

that recharges the groundwater system each year is critical. 

For the period 2001–2007, about 34 percent of the precipitation that fell in the Gooney Run and Manassas Run Basins 

reached the water table as recharge (table 4). As stated earlier, 

a majority of this recharge is to the local riparian flow systems 

and not to the bedrock. During the same period, only 12 percent of the precipitation in the Crooked Run Basin was ER. 

Analysis of data collected by the long-term water monitoring 
50 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

network indicates that these systems are extremely vulnerable 

to current climatic conditions. Successive years of belowaverage ER cause declines in water levels, spring discharges, 

and streamflows; however, these systems can recover quickly 

as ER increases. As is shown in figure 28, ER tends to increase 

as precipitation increases, but lack of precipitation, especially 

snow, during the critical recharge periods (January–April) 

can have a substantial effect on the amount of ER. Evaluation 

of the effect that future development will have on the water 

resources often assumes an ER rate of 50 percent of normal. 

This assumption may be reasonable in the Crooked Run Basin, 

but may not adequately assess future effects in the Blue Ridge 

basins. An even lower percentage estimate could help plan 

for droughts in the future that may be more severe than the 

drought between 1999 and 2002. Future water-supply planning 

efforts should also include consideration of the percentage of 

water withdrawals in relation to ER. Future development could 

cause reductions in groundwater recharge (resulting from 

increases in impervious area), increased water consumption, or 

the transfer of water to other basins, and concomitant reductions in mean streamflow would be expected in these systems 

where groundwater is such a major component of streamflow.

Water Budgets for Ungaged Basins

Warren County was divided into 15 basins (fig. 29) based 

on the delineation of watershed boundaries digitized by the 

Virginia Department of Conservation and Recreation (Karl 

Huber, Virginia Department of Conservation and Recreation, 

written commun., 2006). In order to estimate ER rates for each 

of these ungaged basins (table 7), a linear regression model 

developed by Yager and others (2008), which is based on the 

percentage of the basin underlain by respective rock types, 

was used. The equation uses ER rates estimated by Nelms and 

others (1997) for 20 basins in the Shenandoah Valley and is

Rech = 5.5 + 4.3Carb + 3.6Meta + 10.1West, (5)

where the percentage of basin underlain by the respective rock 

unit [carbonate (Carb), metamorphic (Meta), and western-toe 

carbonate (West) are the explanatory variables]. The percentage of siliciclastic rocks is included implicitly (5.5), and the 

resultant ER rates are in inches per year. The results from this 

method (table 7) indicate an ER rate of 9.7 in/yr for the basins 

predominantly underlain by carbonate rocks, ER rates of 8.2 

to 9.3 in/yr in the Blue Ridge areas, and ER rates of 5.5 to 

6.9 in/yr for basins predominantly underlain by the siliciclastic rock unit. The range in regression-derived recharge 

rates for the siliciclastic basins is very similar to the average 

value (5.3 in/yr) estimated from hydrograph separation for 

the drainage area above the Crooked Run streamflow gage 

01636242 (table 4). Regression-derived ER rates for the basins 

predominantly underlain by the metamorphic rock unit of the 

Blue Ridge are about 40 percent less than those determined 

using hydrograph separation methods for the drainage areas 

for gages 01630700 and 0163626650 (15.3 in/yr and 14.2 in/yr, 

respectively). Yager and others (2008) primarily focused on the 

fractured-rock and karst aquifers of the Shenandoah Valley 

and used regression-derived recharge rates in model design, 

calibration, and sensitivity. Therefore, the regression-derived 

ER rates represent a more robust estimate of ER rates for the 

parts of the groundwater flow system used for water supply 

than the rates estimated from hydrograph separation, which 

may be influenced by local riparian flow systems in the unconsolidated surficial deposits.

Concerns about future demands on the groundwater 

resources can be addressed by evaluating certain components 

of water budgets in these ungaged basins. Warren County is 

densely parceled with more than 20,000 individual parcels 

with an average size of 5.4 acres, but about 10,300 of these 

parcels are less than 1 acre (fig. 29). An analysis was conducted to estimate total domestic water use at future buildout 

of these parcels. Single-family dwellings at buildout were 

assumed for each parcel in a basin with 2.48 people per household using 75 gal/d per person. The water-use totals shown 

in table 7 range from 0.04 to 1.38 in/yr, which is equivalent 

to 0.001 to 1.03 Mgal/d. Total domestic withdrawals in the 

county are estimated to be 3.8 Mgal/d at future buildout. 

Current evaluations of proposed developments by the county 

are based on the relation between demand and 50 percent of 

average ER rates. The regression-derived ER rates in table 7 

are considered to be average values, and various percentages 

of these rates are shown in figure 30 in relation to expected 

water use at buildout.

Water use at buildout is a small percentage of the average 

ER rates estimated for each ungaged basin and does not 

exceed the management threshold of 50 percent of average ER

rate for the respective basins (fig. 30). Consideration of lower 

percentages of average rates of ER, which would be characteristic of drought conditions, indicate that water use at buildout 

could be a substantial portion of recharge, and, in some basins, 

this use could exceed groundwater recharge. Successive years 

of below-average rainfall and snowfall, especially during the 

prime groundwater recharge months between January and 

April, would have a cumulative effect on recharge. The county 

has documented well failures during drought and wet conditions. These failures could have resulted from several factors 

including precipitation amounts and timing, shallow well 

depths, recharge rates less than the basinwide average value 

used for water-resources management, and well interference 

issues, among others. As stated earlier, groundwater is a dominant part of mean streamflow, and its effects on surface water 

should be considered in any water-resources management 

evaluation. Long-term monitoring data are necessary in the 

evaluation process to document changes in streamflows and 

groundwater levels as development progresses. In addition, 

Bredehoeft (2002) suggests that use of groundwater models 

are a better means of assessing sustainable development than 

those based solely on recharge, and accurate groundwater 

simulations rely upon long-term hydrologic data.
Groundwater Availability 51

Figure 29. Drainage basins and parcel acreage in Warren County, Virginia.

Massanutten

SHENANDOAH

PAGE

FREDERICK

CLARKE

FAUQUIER

RAPPAHANNOCK

Base from Warren County 1:2,400 scale Digital Line 

Graph Virginia State Plane North, FIPS 4501 projection

North American Datum 1983

 Central Meridian 7830’W

7820’

7810’

38

50’

39

0 2 4 KILOMETERS

0 2 4 MILES

Shenandoah

River

Gooney

Run

Run

Crooked 

Shenandoah

River

Fork North

South Fork 

Manassas

Run

Passage Creek

Shenandoah

Shenandoah

River

Skyline

Drive

Horseshoe

Bend

The Point

Bentonville

Limeton

Rockland

Buckton

Riverside

Front Royal

55

81

522

522

340

66

340

55

Carbonate

Siliciclastic

Ridge

Metamorphic

Blue

Great

Valley

George Washington NF

Shenandoah

NP

Mountain

Passage Creek

Cedar Creek

Tumbling Run

Cabin Run

Hazard Mill

Crooked Run

Willow

Brook Borden

Marsh

Run

Gooney Run

Happy Creek

Manassas

Run

Brown Hollow

Run

Dry Run

Rock Spring

Branch

North Fork 

Shenandoah 

River

0–0.5

0.6–1.0

1.1–5.0

5.1–10

10.1–100

>100

EXPLANATION

Parcel size, in acres

Geologic province boundary—As 

 defined by the top of the Antietam 

 Formation

Boundary between carbonate and 

 siliciclastic rock types in the Great 

 Valley

Federal lands boundary

Basin name—Coloration based on 

 dominant rock unit

Carbonate

Metamorphic

Siliciclastic

Basin boundary

Gooney Run

Willow Brook

Cabin Run

Figure 29. Drainage basins and parcel acreage in Warren County, Virginia.
52 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia Table 7. Physical and geologic characteristics, estimated effective recharge rates, and estimated water use at buildout of ungaged basins in Warren County, Virginia. [NGVD 29, National Geodetic Vertical Datum of 1929; Min, minimum; Max, maximum; np, not present. Shading indicates dominant rock type: Green, metamorphic rocks in the Blue Ridge Physio- graphic Province; Brown, siliciclastic rocks of the Valley and Ridge Physiographic Province; Yellow, carbonate rocks of the Valley and Ridge Physiographic Province] Basin Area (square miles) Altitude (feet above NGVD 29) Slope (degrees) Area (square miles) Stream density (miles per square mile) Rock type Number Name Min Mean Max Relief Min Mean Max Carbonate Metamorphic Siliciclastic PS45-BR Brown Hollow Run 25.6 487 915 3,443 2,956 0 10.7 53.5 2.36 0.75 0.9 0.71 PS45-VR Hazard Mill 16.3 490 875 2,263 1,773 0 12.6 56.8 3.53 0.09 np 3.44 PS46-BR Gooney Run 27.3 488 1,503 3,470 2,982 0 13.9 59.6 2.24 0.02 2.22 np PS47-BR Dry Run 10.4 454 829 2,418 1,964 0 10 45.6 2.08 0.79 1.05 0.24 PS47-VR Cabin Run 18.3 454 691 2,007 1,553 0 8.5 58.3 3.33 0.13 np 3.2 PS48-BR Happy Creek 22.1 458 1,160 2,564 2,106 0 11 46.0 2 0.48 1.51 np PS70-VR Tumbling Run 0.2 486 788 2,063 1,577 0 15.8 49.2 1.34 np np 1.34 PS75-VR Cedar Creek 1.7 486 607 714 228 0 6.8 33.6 3.53 0.34 np 3.19 PS77-VR Passage Creek 4.1 470 704 2,387 1,917 0 8.7 59.6 3.56 np np 3.56 PS78-VR North Fork Shenandoah River 16.4 456 653 2,368 1,911 0 9.3 54.2 3.53 0.05 np 3.48 PS79-VR Crooked Run 17.0 453 605 741 288 0 6.3 53.3 2.69 0.62 np 2.07 PS80-BR Manassas Run 23.5 423 939 2,388 1,965 0 10 55.2 2.11 0.78 1.33 np PS80-VR Willow Brook 11.0 425 577 691 265 0 4.4 54.9 1.57 1.57 np np PS81-BR Rock Spring Branch 15.8 408 1,002 2,206 1,798 0 11.4 42.9 2.09 0.12 1.97 np PS81-VR Borden Marsh Run 8.5 408 555 668 261 0 5.1 36.4 2.31 2 0.32 np
Groundwater Availability 53

Table 7. Physical and geologic characteristics, estimated effective recharge rates, and estimated water use at buildout of ungaged basins in Warren County, Virginia.—Continued[NGVD 29, National Geodetic Vertical Datum of 1929; Min, minimum; Max, maximum; np, not present. Shading indicates dominant rock type: Green, metamorphic rocks in the Blue Ridge Physiographic Province; Brown, siliciclastic rocks of the Valley and Ridge Physiographic Province; Yellow, carbonate rocks of the Valley and Ridge Physiographic Province]

Basin Annual precipitation (inches per year) Rock unit (percent of area) WU build- out a

(inches per 

year)c

ER b

(inches 

per 

year)c Number Name Min Mean Max Range Carbonate Metamorphic Siliciclastic

PS45-BR Brown Hollow Run 39.9 41.2 45.4 5.6 19.4 53 27.6 0.14 8.2PS45-VR Hazard Mill 39.8 40.4 41.4 1.7 2.5 0 97.5 0.23 5.6PS46-BR Gooney Run 40 46.4 59.6 19.6 0.5 99.5 0 0.10 9.0PS47-BR Dry Run 39.4 40.4 43.1 3.7 34.7 50 15.2 0.23 8.7PS47-VR Cabin Run 39.4 39.8 40.9 1.5 4.3 0 95.7 0.41 5.7PS48-BR Happy Creek 39.4 42.2 52 12.6 21.7 78.3 0 0.22 9.2PS70-VR Tumbling Run 39.2 39.7 40.2 1 0 0 100 0.07 5.5PS75-VR Cedar Creek 38.5 38.6 38.7 0.2 3.6 0 96.4 0.14 5.6PS77-VR Passage Creek 39.3 39.6 40.7 1.4 0 0 100 0.28 5.5PS78-VR N.F. Shenandoah River 38.7 39.2 40.6 2 1.3 0 98.7 0.25 5.5PS79-VR Crooked Run 39.2 39.3 39.4 0.2 32.5 0 67.5 0.24 6.9PS80-BR Manassas Run 39.3 40.9 45.2 5.9 32.8 67.2 0 0.89 9.3PS80-VR Willow Brook 39.2 39.3 39.5 0.3 100 0 0 0.18 9.7PS81-BR Rock Spring Branch 39.7 41.2 43.9 4.2 6.8 93.2 0 1.38 9.1PS81-VR Borden Marsh Run 39.3 39.5 39.9 0.6 95.3 4.8 0 0.04 9.7

a WU estimate assumes one household per parcel at buildout. Number of people per household is 2.48, and daily water use is 75 gallons per day per person.b Effective recharge (Rch) estimated by the following linear regression equation developed by Yager and others (2008) for the Shenandoah Valley, VA and WV:

 Rch = 5.5 + 4.3Carb + 3.6Meta + 10.1West, where the percentage of basin underlain by the respective rock unit is carbonate (Carb), metamorphic (Meta), and western-toe carbonate (West). The percentage of siliciclastics 

is included implicitly (5.5). Equation-derived effective recharge rates are in inches per year. 

c To convert inches per year to cubic feet per second, divide value by 13.5837 and then multiply by drainage area (in square miles). To convert cubic feet per second to million 

gallons per day, multiply value by 6.46.
54 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Figure 30. Relation between estimated domestic water usage at buildout and varying 

percentages of annual effective recharge estimated from the linear regression method of 

Yager and others (2008) for ungaged basins in Warren County, Virginia. Domestic usage is 

based on 2.48 individuals per parcel multiplied by 75 gallons per day per person normalized 

over the drainage basin area.

Drought Effects

Prior to the prolonged drought between 1999 and 2002, 

documentation of drought effects was constrained by the 

paucity of continuous data and limited knowledge of the 

fractured-rock and karst aquifer systems in the northern 

Shenandoah Valley. More than 20 wells went dry or had insufficient yield during this drought in Warren County. In addition, 

anecdotal evidence suggests that cessation of flow in streams 

and springs also was common. Complete evaluation of the 

drought effects of the 1999 to 2002 period is not feasible in the 

county because data were limited to gages on the larger stream 

basins, and no data on groundwater levels existed. Nelms and 

Moberg (2010) documented drought effects on groundwater 

levels for a long-term observation well in Clarke County 

that was finished in the carbonate rock unit. In addition, 

comparison of aerial photographs acquired prior to and during 

the drought in Clarke County assisted with the evaluation 

of drought effects on surface-water resources (Nelms and 

Moberg, 2010). Similar evaluation in Warren County was not 

feasible because resolution of the aerial photography during 

the drought was not sufficient for identification of surfacewater effects for a large part of the county.

Streamflow data collected during this investigation may 

provide some insight into possible effects of droughts in the 

future. Mean streamflow (SF, table 4) and base flow (ER, 

table 4) closely follow annual precipitation (fig. 31). Recovery 

from the drought between 1999 and 2002 was facilitated by 

well-above-average precipitation for about seven successive 

quarters in calendar years 2002 and 2003. Of particular note 

was total snowfall in the first quarter of 2003, which was 

about three times the normal snowfall recorded at NWS 

climatological station 443229 Front Royal. After 2003, the 

general precipitation trend has been downward, and flows 

generally have followed this trend. In 2005, precipitation was 

below average during the prime groundwater recharge period, 

0

2

4

6

8

10

12

UNGAGED BASIN

ANNUAL RATE, IN INCHES PER YEAR

100%

50%

30%

10%

Domestic water 

use at buildout

Figure 30. Relation between estimated domestic water usage at buildout and varying percentages 

of annual effective recharge estimated from the linear regression method of Yager and others 

(2008) for ungaged basins in Warren County, Virginia. Domestic usage based on 2.48 individuals 

per parcel multiplied by 75 gallons per day per person normalized over the drainage basin area. 

Domestic water 

use at buildout

Brown Hollow Run

Hazard Mill

Gooney Run

Dry Run

Cabin Run

Happy Creek

Tumbling Run

Cedar Creek

Passage Creek

N.F. Shenandoah River

Crooked Run

Manassas Run

Willow Brook

Rock Spring Branch

Borden Marsh Run
Groundwater Availability 55

Figure 31. Relation between annual rates of precipitation at National Weather Service climatological station 443229 

Front Royal, Virginia, mean streamflow and mean base flow at streamflow-gaging stations 01630700 Gooney Run 

at Route 622 near Glen Echo, Virginia, 01636242 Crooked Run below Route 340 at Riverton, Virginia, and 0163626650 

Manassas Run at Route 645 near Front Royal, Virginia. For the years 2001–2002 at streamflow-gaging stations 01630700 

and 0163626650 and for the years 2001–2004 at streamflow-gaging station 01636242, estimates are based on linear 

regression with streamflow-gaging station 01635500 Passage Creek above Route 55 near Buckton, Virginia. Mean 

streamflow and mean base-flow rates for the remaining years were estimated with the streamflow partitioning 

software package PART (Rutledge, 1993).

41.8

41.8

41.8

15.3

9.1

0

10

20

30

40

50

60

70

5.3

6.6

0

10

20

30

40

50

60

70

CALENDAR YEAR

14.2

9.1

2001 2002 2003 2004 2005 2006 2007

0

10

20

30

40

50

60

70

ANNUAL RATE, IN INCHES PER YEAR

Precipitation

Mean base flow

Mean streamflow

Precipitation

Mean base flow

Mean streamflow

Precipitation

Mean base flow

Mean streamflow

A. USGS 01630700 Gooney Run at Route 622 near Glen Echo, Virginia

B. USGS 01636242 Crooked Run below Route 340 at Riverton, Virginia

C. USGS 0163626650 Manassas Run at Route 645 near Front Royal, Virginia

Figure 31. Relation between annual rates of precipitation at National 

Weather Service climatological station 443229 Front Royal, Virginia, mean 

streamflow and mean base flow at streamflow gaging stations (A) 

01630700 Gooney Run at Route 622 near Glen Echo, Virginia, (B) 01636242 

Crooked Run below Route 340 at Riverton, Virginia, and (C) 0163626650 

Manassas Run at Route 645 near Front Royal, Virginia. For the years 

2001-2002 at streamflow gaging stations 01630700 and 0163626650 and 

for the years 2001-2004 at streamflow gaging station 01636242, estimates 

are based on linear regression with streamflow gaging station 01635500 

Passage Creek above Route 55 near Buckton, Virginia. Mean streamflow 

and mean base-flow rates for the remaining years were estimated with the 

streamflow partitioning software package PART (Rutledge1993)

EXPLANATION

Average effective recharge from hydrograph

 separation (2001–07)

Average effective recharge from linear 

 regression developed by Yager and 

 others (2008)

Value estimated from linear regression

 with streamflow-gaging station 01635500

Precipitation normal (1996–2007) for National 

 Weather Service climatological station 

 443229 Front Royal, Virginia
56 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

and flows declined at gages 01630700 and 01636242, but 

increased at gage 0163626650 (fig. 31). For 2006, the direct 

opposite was observed; flows increased at gages 01630700 and 

01636242 with increased precipitation, but decreased at gage 

0163626650. This discontinuity could result from an uneven 

areal distribution of precipitation across the county.

Although flows for the drought years 2001 and 2002 were 

estimated by linear regression from streamflow gage 01635500 

Passage Creek above Route 55 near Buckton, VA, flows equal 

to and less than the regressed values have been measured at 

gages 01630700, 01636242, and 0163626650. Therefore, the 

values from linear regression with flows from gage 01635500 

seem to be reasonable estimates during drought conditions 

and may actually overestimate flow. It should be noted that 

estimated values of mean base flow have approached the 

average ER estimated by the regression equation from Yager 

and others (2008). In the case of gage 01636242, however, the 

average ER is below the average ER estimated by the regression equation, which is indicative of groundwater systems 

with limited storage that are highly responsive to current 

meteorological conditions. Overall, precipitation during the 

period of this investigation is classified as average or above 

average, yet slight changes in annual amounts of precipitation 

or timing of the precipitation can affect groundwater recharge. 

The report of well failures during this investigation may be 

related to the close relation between recharge and precipitation. Kozar and others (2007) and Kozar and Weary (2009) 

demonstrate the utility of groundwater flow models in assessing changes in recharge with respect to groundwater levels and 

diminished streamflow and spring discharge.

Summary

Expanding development and the prolonged drought from 

1999 to 2002 focused attention on the quantity and sustainability of the groundwater resources in Warren County, VA. The 

groundwater flow systems are complex, and flow paths tend 

to be controlled by the extremely folded and faulted geology 

that underlies the county. A study was conducted between 

May 2002 and October 2008 by the USGS, in cooperation 

with Warren County, VA, to describe the hydrogeology and 

groundwater availability of the metamorphic and siliciclastic 

fractured-rock aquifers in the county and to establish a longterm water monitoring network. The study area encompasses 

approximately 170 square miles of the county and includes the 

metamorphic rocks of the Blue Ridge Physiographic Province 

and siliciclastic rocks of the Great Valley section of the Valley 

and Ridge Physiographic Province.

The fractured-rock aquifer systems in the study area are 

characterized by diffuse-flow conditions. Well depths tend to 

be shallowest in the siliciclastic rock unit (predominantly in 

the Martinsburg Formation) where 75 percent of the wells are 

less than 200 ft deep. In the metamorphic rocks of the Blue 

Ridge, more than 75 percent of the wells are less than 400 ft 

deep. Median depths to bedrock are generally less than 40 ft. 

Depths to bedrock generally tend to be (1) relatively deep 

[greater than 50 ft below land surface (bls)] in the eastern part 

of the county, in areas where alluvial and colluvial deposits 

are extensive, and along faults; and (2) relatively shallow 

(less than 50 ft bls) in the interfluve areas, on the eastern 

slopes of Massanutten Mountain, and in areas underlain by the 

Martinsburg Formation.

The upper water-bearing zone generally is encountered 

in the first 200 ft bls but can be at deeper depths along faults, 

fold axes, and in elevated areas. Occasionally, the upper 

water-bearing zone is not encountered until depths of more 

than 400 ft bls. Median well yields for the different rock units 

generally range from 10 to 20 gal/min. High-yielding wells 

tend to cluster along faults, along the eastern contact of the 

Martinsburg Formation, and within potential lineament zones. 

A comparison of density clusters indicates that some areas 

contain a dense concentration of low- and high-yielding wells, 

which illustrates the degree of complexity inherent within 

karst and fractured-rock aquifer systems. Specific capacity is 

relatively low and ranges from 0.003 to 1.43 (gal/min)/ft with 

median values from 0.12 to 0.24 (gal/min)/ft. Transmissivity 

values derived from specific capacity data range over 4 orders 

of magnitude from 0.6 to 382 ft2/d.

Groundwater levels generally are responsive to current 

meteorological conditions. Intense thunderstorms, tropical 

storms, or hurricanes cause sudden, temporary water-level 

rises during the summer and autumn. The prime groundwater 

recharge period is between January and April. Diurnal 

groundwater-level fluctuations in response to the combined 

effects of barometric pressure and earth tides, as well as 

oscillations caused by teleseismic wave trains from distant 

earthquakes of magnitude 7.0 or greater, have been observed 

in well 45V 3. Spring discharge in the carbonate areas tends to 

vary seasonally, whereas springs in the Blue Ridge are more 

responsive to current meteorological conditions and tend to 

have relatively low discharges.

Estimates of apparent groundwater age range from 

0.1 to 16.1 years. About 73 percent of the samples contained 

some fraction of waters with apparent ages that were less 

than 5 years. The percentage of the young fraction in binary 

mixtures ranged from approximately 80 to 99.5 percent. These 

high percentages indicate that a majority of the water discharging from the springs is young and is close to being piston flow. 

Water discharging from springs in Warren County is generally 

younger than water from wells. The young apparent ages and 

binary mixtures are generally characteristic of sites in the 

upper reaches of the watersheds; the older ages are usually 

characteristic of sites in the lower reaches. This distribution 

and temporal changes of apparent ages and mixing fractions 

is consistent with an aquifer system that is topographically 

driven and has local flow systems containing young waters 

that are superimposed on a subregional to regional flow 

system with older waters. Therefore, under different hydrologic conditions, temporal changes in water-quality trends and 

dye-tracer studies would be expected to occur.
References Cited 57

Estimates of effective groundwater recharge from 

hydrograph separation analyses from 2001 to 2007 range from 

8.2 to 29.4 in/yr with average values of 14.2 and 15.3 in/yr 

for two streamflow gages in the Blue Ridge Physiographic 

Province. Estimates of effective groundwater recharge range 

from 2.4 to 14.8 in/yr with an average of 5.3 in/yr for a gage 

in a basin that predominantly drains a siliciclastic rock unit in 

the Great Valley section of the Valley and Ridge Physiographic 

Province. A positive correlation between effective recharge 

rates and current climatic conditions is evident. Analysis of 

diurnal streamflow signals in the Blue Ridge gages indicates 

median riparian evapotranspiration rates of 1.6 and 2.5 in/yr. 

The regression-derived recharge rate for the siliciclastic basin 

in the Great Valley is similar to the average value estimated 

from hydrograph separation, but rates for the basins predominantly underlain by the metamorphic rock unit of the Blue 

Ridge are about 40 percent less than the rates for basins in the 

Great Valley. Effective recharge rates derived from hydrograph 

separation in the Blue Ridge may be reflective of local riparian 

flow systems in the unconsolidated surficial deposits, and 

recharge to the fractured-rock aquifers may be overestimated. 

Base flow accounted for about 70 percent of mean streamflow 

in the Blue Ridge and 54 percent for siliciclastic rock terrain 

in the Great Valley. The high base-flow index values (percentage of streamflow from base flow) indicate that groundwater 

is the dominant source of streamflow during wet and 

drought conditions.

In the Blue Ridge basins, about 50 percent of annual 

precipitation is removed by evapotranspiration, and approximately 34 percent of the precipitation reaches the water table 

as effective recharge. In the siliciclastic areas of the Great 

Valley, evapotranspiration removes about 76 percent of annual 

precipitation, and only 12 percent reaches the water table as 

effective recharge. The amount of runoff in the Blue Ridge is 

about 14 percent of the amount of annual precipitation and is 

about 11 percent in the siliciclastic areas. 

Current and projected water-use estimates are a small 

component of the overall water budgets in these basins and do 

not exceed the management threshold of 50 percent of average 

recharge rate for the respective basins. However, consideration 

of lower percentages of average rates of recharge, which 

would be indicative of drought conditions, indicate that water 

use at buildout could be a substantial percentage of recharge; 

in some basins, this amount of water use has been estimated to 

exceed groundwater recharge.

Groundwater flow systems in the county are extremely 

vulnerable to current meteorological conditions. Successive 

years of below-average effective recharge cause declines in 

water levels, spring discharges, and streamflows. However, 

these systems can recover quickly as effective recharge 

increases with increasing precipitation. Lack of precipitation, 

especially snow, during the critical recharge period (January–

April) can have a substantial effect on the amount of recharge 

to the groundwater system and eventually on stream base flow. 

Estimated values of annual mean base flow have approached 

and have been below the average regression-derived recharge 

rates during a period classified as above-average precipitation. 

This relation is indicative of groundwater systems with limited 

storage that are highly responsive to current meteorological 

conditions. Slight changes in annual amounts of precipitation 

or timing of the precipitation can affect groundwater recharge.

References Cited

Allingham, J.W., 1987, Ground water study for Warren 

County, Virginia: BCM Potomac, Inc.

Badger, R.L., and Sinha, A.K., 1988, Age and Sr isotopic 

signature of the Catoctin volcanic province—Implication for subcrustal mantle evolution: Geology, v. 16, no. 8, 

p. 692–695. 

Bailey, C.M., Hasty, B.A., and Kayser, Colleen, 2006, 

Transverse faults in the Virginia Blue Ridge—A legacy of 

Mesozoic tectonics [abs.]: Geological Society of America 

Abstracts with Programs, v. 38, no. 3, p. 67.

Bayer, R., Schlosser, Peter, Bönisch, G., Rupp, H., Zaucker, F., 

and Zimmek, G., 1989, Performance and blank components 

of a mass spectrometric system for routine measurement of 

helium isotopes and tritium by the 3He ingrowth method: 

Sitzungsberichte der Heidelberger Akademie der Wissenschaften, Mathematisch-naturwissenschaftliche Klasse, 

Jahrgang 1989, 5. Abhandlung, Springer-Verlag, 42 p.

Bredehoeft, J.D., 2002, The water budget myth revisited—

Why hydrogeologists model: Ground Water, v. 40, no. 4, 

p. 340–345.

Brezinski, D.K., 1992, Lithostratigraphy of the western Blue 

Ridge cover rocks in Maryland: Maryland Geological Survey, Report of Investigations No. 55, 69 p., scale 1:62,500.

Burton, W.C., Plummer, L.N., Busenberg, Eurybiades, Lindsey, B.D., and Gburek, W.J., 2002, Influence of fracture 

anisotropy on ground water ages and chemistry, Valley and 

Ridge Province, Pennsylvania: Ground Water, v. 40, no. 3, 

p. 242–257.

Busenberg, Eurybiades, and Plummer, L.N., 1992, Use of 

chlorofluorocarbons (CCl3F and CCl2F2) as hydrologic tracers and age-dating tools—The alluvium and terrace system 

of central Oklahoma: Water Resources Research, v. 28, 

no. 9, p. 2257–2283.

Busenberg, Eurybiades, and Plummer, L.N., 2000, Dating 

young ground water with sulfur hexafluoride—Natural 

and anthropogenic sources of sulfur hexafluoride: Water 

Resources Research, v. 36, p. 3011–3030.
58 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Busenberg, Eurybiades, Weeks, E.P., Plummer, L.N., and 

Bartholomay, R.C., 1993, Age dating ground water by use 

of chlorofluorocarbons (CCl3F and CCl2F2) and distribution of chlorofluorocarbons in the unsaturated zone, Snake 

River Plain aquifer, Idaho National Engineering Laboratory, 

Idaho: U.S. Geological Survey Water-Resources Investigations Report 93–4054, 47 p.

Cady, R.C., 1936, Ground-water resources of the Shenandoah Valley, Virginia: Virginia Geological Survey, Bulletin 45,137 p.

Cady, R.C., 1938, Ground-water resources of northern Virginia: Virginia Geological Survey, Bulletin 50, 200 p.

Cederstrom, D.J., 1972, Evaluation of yields of wells in consolidated rocks, Virginia to Maine: U.S. Geological Survey 

Water-Supply Paper 2021, 38 p.

Chapman, Sydney, and Lindzen, R.S., 1970, Atmospheric 

tides, thermal and gravitational: Dordrecht, Holland, 

D. Reidel Publishing Co., 200 p.

Clark, I.D., and Fritz, Peter, 1997, Environmental isotopes in 

hydrogeology: New York, Lewis Publishers, 328 p.

Clarke, W.B., Jenkins, W.J., and Top, Z., 1976, Determination of tritium by mass spectrometric measurement of 3

He: 

International Journal of Applied Radiation and Isotopes, 

v. 27, p. 515–522.

Cloos, Ernst, 1951, Structural geology of Washington County, 

in The physical features of Washington County: Baltimore, Maryland Department of Geology, Mines, and Water 

Resources, p. 124–163. 

Constantz, Jim, Thomas, C.L., and Zellweger, Gary, 1994, 

Influence of diurnal variations in stream temperature on 

streamflow loss and groundwater recharge: Water Resources 

Research, v. 30, p. 3253–3264.

Cooper, H.H., Jr., Bredehoeft, J.D., Papadopulos, I.S., and 

Bennett, R.R., 1965, The response of well-aquifer systems 

to seismic waves: Journal of Geophysical Research, v. 70, 

p. 3915–3926.

Coplen, T.B., 1988, Normalization of oxygen and hydrogen 

isotope data: Chemical Geology, v. 72, no. 4, p. 293–297.

Coplen, T.B., 1996, New guidelines for reporting stable hydrogen, carbon, and oxygen isotope-ratio data: Geochimica 

Cosmochimica Acta, v. 60, p. 3359–3360.

Cressler, C.W., Thurmond, C.J., and Hester, W.G., 1983, 

Ground water in the greater Atlanta region: Georgia Department of Natural Resources Environmental Protection 

Division, Georgia Geologic Survey Information Circular 63, 

144 p.

Czikowsky, M.J., and Fitzjarrald, D.R., 2004, Evidence of 

seasonal changes in evapotranspiration in eastern U.S. 

hydrological records: Journal of Hydrometeorology, v. 5, 

p. 974–988.

Daniel, C.C., III, 1989, Statistical analysis relating well yield 

to construction practices and siting of wells in the Piedmont 

and Blue Ridge Provinces of North Carolina: U.S. Geological Survey Water-Supply Paper 2341–A, p. 27.

DeKay, R.H., 1972, Development of ground-water supplies in 

Shenandoah National Park, Virginia: Virginia Division of 

Mineral Resources Report 10, 158 p.

Di Luzio, Mauro, Johnson, G.L., Daly, Christopher, Eischeid, 

J.K., and Arnold, J.G., 2008, Constructing retrospective 

gridded daily precipitation and temperature datasets for the 

conterminous United States: Journal of Applied Meteorology and Climatology, v. 47, no. 2, p. 475–497.

Doctor, D.H., Weary, D.J., Orndorff, R.C., Harlow, G.E., Jr., 

Kozar, M.D., and Nelms, D.L., 2008, Bedrock structural 

controls on the occurrence of sinkholes and springs in the 

northern Great Valley karst, Virginia and West Virginia, in

Yuhr, L.B., Alexander, E.C., Jr., and Beck, B.F., eds., Proceedings of the 11th Multidisciplinary Conference on Sinkholes and Engineering and Environmental Impacts of Karst, 

September 23–26, 2008, Tallahassee, Florida, p. 12–22.

Driscoll, F.G., 1986, Groundwater and wells (2d ed.): St. Paul, 

Minnesota, Johnson Filtration Systems, Inc., 1089 p.

Earth Science Australia, 2004, Joint patterns in folds, accessed 

April 12, 2004, at http://earthsci.org/struct/fault/joint3.gif.

Ekwurzel, B., Schlosser, Peter, Smethie, W., Jr., Plummer, 

L.N., Busenberg, Eurybiades, Michel, R.L., Weppernig, R., 

and Stute, Martin, 1994, Dating of shallow groundwater—

Comparison of the transient tracers 3H/3He, chlorofluorocarbons and 85Kr: Water Resources Research, v. 30, no. 6, 

p. 1693–1708.

Epstein, J.B., Orndorff, R.C., and Rader, E.K., 1995, Middle 

Ordovician Stickley Run Member (new name) of the Martinsburg Formation, Shenandoah Valley, northern Virginia, 

in Stratigraphic Notes, 1994—Three short papers propose 

changes in stratigraphic nomenclature in Virginia, Kentucky, and Alaska: U.S. Geological Survey Bulletin 2135, 

p. 1–13. 

Fenneman, N.M., 1938, Physiography of Eastern United 

States: New York, McGraw-Hill, 534 p.

Freeze, R.A., and Cherry, J.A., 1979, Groundwater: New Jersey, Prentice-Hall, 604 p.

Gathright, T.M., II, 1976, Geology of the Shenandoah National 

Park, Virginia: Virginia Division of Mineral Resources Bulletin 86, 93 p.
References Cited 59

Gathright, T.M., Jr., and Nystrom, P.G., Jr., 1974, Geology 

of the Ashby Gap quadrangle, Virginia: Virginia Division of Mineral Resources Report of Investigations 36, 

scale 1:24,000, 55 p. 

Hack, J.T., 1965, Geomorphology of the Shenandoah Valley, 

Virginia, and West Virginia, and origin of the residual ore 

deposits: U.S. Geological Survey Professional Paper 484, 

84 p.

Hack, J.T., and Young, R.S., 1959, Entrenched meanders 

of the North Fork of the Shenandoah River, Virginia: 

U.S. Geological Survey Professional Paper 354–A, p. 1–10.

Hansen, B.P., and Simcox, A.C., 1994, Yields of bedrock wells 

in Massachusetts: U.S. Geological Survey Water-Resources 

Investigations Report 93–4115, 43 p. 

Harlow, G.E., Jr., Orndorff, R.C., Nelms, D.L., Weary, D.J., 

and Moberg, R.M., 2005, Hydrogeology and ground-water 

availability in the carbonate aquifer system of Frederick 

County, Virginia: U.S. Geological Survey Scientific Investigations Report 2005–5161, 30 p.

Healy, R.W., Winter, T.C., LaBaugh, J.W., and Franke, O.L., 

2007, Water budgets—Foundations for effective waterresources and environmental management: U.S. Geological 

Survey Circular 1308, 90 p.

Heaton, T.H.E., 1981, Dissolved gases—Some applications 

to ground-water research: Transactions of the Geological 

Society of South Africa, v. 84, p. 91–97.

Heaton, T.H.E., Talma A.S., and Vogel J.C., 1983, Origin and 

history of nitrate in confined groundwater in the Western 

Kalahari: Journal of Hydrology, v. 62, p. 243–262.

Heaton, T.H.E., and Vogel, J.C., 1981, Excess air in groundwater: Journal of Hydrology, v. 50, p. 201–216.

Hinkle, K.R., and Sterrett, R.M., 1976, Rockingham County 

groundwater, present conditions and prospects: Virginia 

State Water Control Board Planning Bulletin 300, 88 p.

Hinkle, K.R., and Sterrett, R.M., 1977, Shenandoah County 

groundwater, present conditions and prospects: Virginia 

State Water Control Board Planning Bulletin 306, 67 p.

Hinkle, K.R., and Sterrett, R.M., 1978, Augusta County 

groundwater, present conditions and prospects: Virginia 

State Water Control Board Planning Bulletin 310, 119 p.

Holmes, R., Wagner, D., and Racey, D., 1984, Soil survey of 

Warren County, Virginia: U.S. Department of Agriculture, 

Soil Conservation Service, 159 p.

Hubbard, D.A., Jr., 1990, Geologic map of Clarke County, 

Virginia and map of selected hydrogeologic components 

for Clarke County, Virginia: Virginia Division of Mineral 

Resources Publication 102, scale 1:50,000.

Hutson, S.S., Barber, N.L., Kenny, J.F., Linsey, K.S., Lumia, 

D.S., and Maupin, M.A., 2004, Estimated use of water in 

the United States in 2000: U.S. Geological Survey Circular 1268, 46 p.

International Atomic Energy Agency (IAEA), 1981, Statistical treatment of environmental isotope data in precipitation: 

Vienna, IAEA, Technical Report Series No. 206.

Jones, W.K., 1987, Overview of groundwater resources of 

Clarke County, Virginia, with emphasis on the carbonate 

aquifers west of the Shenandoah River, in Clarke County 

Groundwater Protection Plan, Lord Fairfax Planning District Commission, p. 7.1–7.22.

Keyworth, A.J., 2009, A quantitative assessment of water 

inputs and outputs to a small watershed in northwestern 

Wake County—Evaluating the effects of human use on 

groundwater resources: Master’s thesis, North Carolina 

State University, Department of Marine, Earth, and Atmospheric Sciences, 81 p., accessed August 2009 at http://

www.lib.ncsu.edu/theses/available/etd-11132008-153043/

unrestricted/etd.pdf.

Kozar, M.D., Paybins, K.S., Weary, D.J., and Pierce, H.A., 

2007, Hydrogeologic setting and ground-water flow in the 

Leetown area, West Virginia: U.S. Geological Survey Scientific Investigations Report 2007–5066, 70 p.

Kozar, M.D., and Weary, D.J., 2009, Hydrogeology and 

ground-water flow in the Opequon Creek watershed area, 

Virginia and West Virginia: U.S. Geological Survey Scientific Investigations Report 2009–5153, 61 p.

Landers, M.N., and Ankcorn, P.D., 2008, Methods to evaluate influence of onsite septic wastewater-treatment systems 

on base flow in selected watersheds in Gwinnett County, 

Georgia, October 2007: U.S. Geological Survey Scientific 

Investigations Report 2008–5220, 12 p. (Also available at 

http://pubs.usgs.gov/sir/2008/5220/.)

Lane, J.W., Jr., Day-Lewis, F.D., Johnson, C.D., Dawson, 

C.B., Nelms, D.L., Eddy-Miller, C.A., Wheeler, J.D., 

Harvey, C.F., and Karam, Hanan, 2008, Fiber-optic distributed temperature sensing—A new tool for assessment and 

monitoring of hydrologic processes, in Symposium on the 

Application of Geophysics to Engineering and Environmental Problems (SAGEEP), April 6–10, 2008, Philadelphia, 

PA, Proceedings: Denver, CO, Environmental and Engineering Geophysical Society, 9 p.

Liu, L.-B., Roeloffs, Evelyn, and Zheng, X.-Y., 1989, Seismically induced water level fluctuations in the Wali well, 

Beijing, China: Journal of Geophysical Research, v. 94, 

no. B7, p. 9453–9462. 

Loiselle, Marc, and Evans, David, 1995, Fracture density distributions and well yields in Coastal Maine: Ground Water, 

v. 33, no. 2, p. 190–196.
60 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Ludin, Andrea, Weppernig, Ralf, Bönisch, Gerhard, and 

Schlosser, Peter, 1998, Mass spectrometric measurement 

of helium isotopes and tritium in water samples: LamontDoherty Earth Observatory, Columbia University, Palisades, 

New York, Technical Report 98.6.

Lukert, M.L., III, and Nuckols, E.B., II, 1976, Geology of the 

Linden and Flint Hill quadrangles, Virginia with a section on Hydrogeology, by R.H. DeKay: Virginia Division 

of Mineral Resources Report of Investigations 44, scale 

1:24,000, 83 p.

Lundquist, J.D., and Cayan, D.R., 2002, Seasonal and spatial patterns in diurnal cycles in streamflow in the western 

United States: Journal of Hydrometeorology, v. 3, p. 591–

603.

McCoy, K.J., Podwysocki, M.H., Crider, E.A., and Weary, 

D.J., 2005a, Fracture trace map and single-well aquifer test 

results in a carbonate aquifer in Berkeley County, West 

Virginia: U.S. Geological Survey Open-File Report 2005–

1040, 1 pl.

McCoy, K.J., Podwysocki, M.H., Crider, E.A., and Weary, 

D.J., 2005b, Fracture trace map and single-well aquifer 

test results in a carbonate aquifer in Jefferson County, West 

Virginia: U.S. Geological Survey Open-File Report 2005–

1407, 1 pl.

Merritt, M.L., 2004, Estimating hydraulic properties of the 

Floridan aquifer system by analysis of earth-tide, oceantide, and barometric effects, Collier and Hendry Counties, 

Florida: U.S. Geological Survey Water-Resources Investigations Report 03–4267, 70 p.

Michel, R.M., 1989, Tritium deposition in the Continental 

United States, 1953–1983: U.S. Geological Survey WaterResources Investigations Report 89–4072, 46 p.

Morgan, B.A., Eaton, L.S., and Wieczorek, G.F., 2003, 

Pleistocene and Holocene colluvial fans and terraces in the 

Blue Ridge region of Shenandoah National Park, Virginia: 

U.S. Geological Survey Open-File Report 03–420, 25 p., 

1 pl., scale 1:100,000.

National Oceanic and Atmospheric Administration, 2006, 

Climatological data annual summary—Virginia: Asheville, 

NC, National Climatic Data Center, v. 116, no. 13, 24 p.

Nelms, D.L., and Harlow, G.E., Jr., 2003, Aquifer susceptibility in Virginia—Data on chemical and isotopic composition, 

recharge temperature, and apparent age of water from wells 

and springs, 1998–2000: U. S. Geological Survey Open-File 

Report 03–246, 101 p.

Nelms, D.L., Harlow, G.E., Jr., and Hayes, D.C., 1997, Baseflow characteristics of streams in the Valley and Ridge, the 

Blue Ridge, and the Piedmont Physiographic Provinces of 

Virginia: U.S. Geological Survey Water-Supply Paper 2457, 

48 p.

Nelms, D.L., Harlow, G.E., Jr., Plummer, L.N., and Busenberg, Eurybiades, 2003, Aquifer susceptibility in Virginia, 

1998–2000: U. S. Geological Survey Water-Resources 

Investigations Report 03–4278, 58 p.

Nelms, D.L., and Moberg, R.M., Jr., 2010, Hydrogeology and groundwater availability in Clarke County, Virginia: U.S. Geological Survey Scientific Investigations 

Report 2010–5112, 119 p.

Nuckels, E.H., Prugh, B.J., Jr., Michaels, P.J., and Jones, D.R., 

1991, National water summary 1988–89—Hydrologic 

events and floods and droughts: U.S. Geological Survey 

Water-Supply Paper 2375, p. 543–550. 

Orndorff, R.C., Epstein, J.B., and McDowell, R.C., 1999, 

Geologic map of the Middletown quadrangle, Frederick, 

Shenandoah, and Warren Counties, Virginia: U.S. Geological Survey Geologic Quadrangle Map GQ–1803, 

scale 1:24,000.

Orndorff, R.C., and Harlow, G.E., Jr., 2002, Field trip guide—

Hydrogeologic framework of the Northern Shenandoah 

Valley carbonate aquifer system, in Kuniansky, E.L., ed., 

U.S. Geological Survey Karst Interest Group Proceedings, Shepherdstown, West Virginia, August 20–22, 2002: 

U.S. Geological Survey Water-Resources Investigations 

Report 02–4174, p. 81–89.

Orndorff, Wil, 2006, Cedarville Enterprise Zone karst study, 

Final report: Virginia Department of Conservation and Recreation, Natural Heritage Program, 43 p.

Plummer, L.N., and Busenberg, Eurybiades, 2000, Chlorofluorocarbons, in Cook, P.G., and Herczeg, Andrew, eds., 

Environmental tracers in subsurface hydrology: Boston, 

Kluwer Academic Publishers, p. 441–478.

Plummer, L.N., Busenberg, Eurybiades, Böhlke, J.K., Carmody, R.W., Casile, G.C., Coplen, T.B., Doughten, M.W., 

Hannon, J.E., Kirkland, Wandee, Michel, R.L., Nelms, 

D.L., Norton, B.C., Plummer, K.E., Qi, Haiping, Revesz, 

Kinga, Schlosser, Peter, Spitzer, Shane, Wayland, J.E., and 

Widman, P.K., 2000, Chemical and isotopic composition of 

water from springs, wells, and streams in parts of Shenandoah National Park, Virginia, and vicinity, 1995–1999: 

U.S. Geological Survey Open-File Report 00–373, 70 p.

Plummer, L.N., Busenberg, E., Böhlke, J.K., Nelms, D.L., 

Michel, R.L., and Schlosser, P., 2001, Groundwater residence times in Shenandoah National Park, Blue Ridge 

Mountains, Virginia, U.S.A.—A multi-tracer approach: 

Chemical Geology, v. 179, p. 93–111. 
References Cited 61

Poff, Judy, ed., 1999, A homeowner’s guide to the development, maintenance, and protection of springs as a drinking 

water source: Virginia Water Resources Research Center 

Educational Report, 83 p.

Powell, J.D., and Abe, J.M., 1985, Availability and quality of ground water in the Piedmont province of Virginia: 

U.S. Geological Survey Water-Resources Investigations 

Report 85–4235, 32 p.

Pratt, L.M., Phillips, T.L., and Dennison, J.M., 1978, Evidence 

of non-vascular land plants from the Early Silurian (Llandoverian) of Virginia, U.S.A.: Review of Paleobotony and 

Palynology, v. 25, p. 121–149.

Rader, E.K., and Biggs, T.H., 1975, Geology of the Front 

Royal quadrangle, Virginia, with a section on Hydrogeology, by R.H. DeKay: Virginia Division of Mineral 

Resources Report of Investigations 40, scale 1:24,000, 91 p.

Rader, E.K., and Biggs, T.H., 1976, Geology of the Strasburg 

and Toms Brook quadrangles, Virginia, with a section on

Hydrogeology by R.H. DeKay: Virginia Division of Mineral 

Resources Report of Investigations 45, scale 1:24,000, 

104 p.

Rader, E.K., and Conley, J.F., 1995, Geologic map of Warren 

County, Virginia: Virginia Division of Mineral Resources 

Publication 138, scale 1:50,000.

Rader, E.K., and Gathright, T.M., II, 2001, Geologic map 

of the Front Royal 30 × 60-minute quadrangle—Portions 

of Clarke, Page, Rockingham, Shenandoah, and Warren 

Counties, Virginia: Virginia Division of Mineral Resources 

Publication 162, scale 1:100,000.

Rader, E.K., McDowell, R.C., Gathright, T.M., II, and Orndorff, R.C., 1996, Geologic map of Clarke, Frederick, Page, 

Shenandoah, and Warren Counties—Lord Fairfax Planning 

District: Virginia Division of Mineral Resources Publication 143, scale 1:100,000.

Rader, E.K., McDowell, R.C., Gathright, T.M., II, and Orndorff, R.C., 2001, Geologic map of the Virginia portion of 

the Winchester 30 × 60-minute quadrangle: Virginia Division of Mineral Resources Publication 161, scale 1:100,000.

Rader, E.K., McDowell, R.C., Gathright, T.M., II, and Orndorff, R.C., 2003, Raster images of the geologic map of the 

Virginia portion of the Winchester 30 × 60-minute quadrangle: Virginia Division of Mineral Resources Publication 171, Part A, scale 1:100,000.

Rader, E.K., and Webb, H.W., 1979, Geologic factors affecting 

land modification in Warren County, Virginia: Virginia Division of Mineral Resources Publication 15, scale 1:50,000.

Reed, J.C., Jr., 1955, Catoctin Formation near Luray, Virginia: Geological Society of America Bulletin, v. 66, no. 7, 

p. 871–896.

Richardson, C.A., 1982, Ground water in the Piedmont 

Upland of Central Maryland: U.S. Geological Survey 

Water-Supply Paper 2077, 42 p.

Rutledge, A.T., 1993, Computer programs for describing the 

recession of ground-water discharge and for estimating 

mean ground-water recharge and discharge from streamflow 

records: U.S. Geological Survey Water-Resources Investigations Report 93–4121, 45 p.

Rutledge, A.T., and Mesko, T.O., 1996, Estimated hydrologic 

characteristics of shallow aquifer systems in the Valley 

and Ridge, the Blue Ridge, and the Piedmont Physiographic Provinces based on analysis of streamflow recession and base flow: U.S. Geological Survey Professional 

Paper 1422–B, 58 p.

Schlosser, Peter, Stute, M., Dorr, H., Sonntag, C., and Munnich, K.O., 1988, Tritium/3

He dating of shallow groundwater: Earth and Planetary Science Letters, v. 89, p. 353–362.

Schlosser, Peter, Stute, M., Dorr, H., Sonntag, C., and Munnich, K.O., 1989, Tritiogenic 3

He in shallow groundwater: 

Earth and Planetary Science Letters, v. 94, p. 245–256.

Senior, L.A., Sloto, R.A., and Reif, A.G., 1997, Hydrogeology 

and water quality of the West Valley Creek Basin, Chester 

County, Pennsylvania: U.S. Geological Survey WaterResources Investigations Report 94–4137, 160 p.

Shultz, R.A., Hobba, W.A., Jr., and Kozar, M.D., 1995, 

Geohydrology, ground-water availability, and ground-water 

quality of Berkeley County, West Virginia, with emphasis 

on the carbonate-rock area: U.S. Geological Survey WaterResources Investigations Report 93–4073, 88 p. 

Southworth, C.S., 1990, Hydrogeologic setting of springs on 

Short Hill Mountain, Loudoun County, Virginia: U.S. Geological Survey Miscellaneous Field Studies Map 2112, 

scale 1:24,000.

Southworth, Scott, Aleinikoff, J.N., Bailey, C.M., Burton, 

W.C., Crider, E.A., Hackley, P.C., Smoot, J.P., and Tollo, 

R.P., 2009, Geologic map of the Shenandoah National Park 

region, Virginia: U.S. Geological Survey Open-File Report 

2009–1153, 96 p., 1 pl., scale 1:100,000. (Also available at 

http://pubs.usgs.gov/of/2009/1153/.)

Southworth, Scott, Brezinski, D.K., Drake, A.A., Jr., Burton, 

W.C., Orndorff, R.C., and Froelich, A.J., 2002, Digital 

geologic map and database of the Frederick 30′ × 60′ quadrangle, Maryland, Virginia, and West Virginia, Version 1.0: 

U.S. Geological Survey Open-File Report 02–437, 79 p., 

2 pls., scale 1:100,000.
62 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Southworth, Scott, Brezinski, D.K., Drake, A.A., Jr., Burton, 

W.C., Orndorff, R.C., Froelich, A.J., Reddy, J.E., Denenny, 

Danielle, and Daniels, D.L., 2007, Geologic map of the 

Frederick 30′ × 60′ quadrangle, Maryland, Virginia, and 

West Virginia: Pamphlet to accompany U.S. Geological 

Survey Scientific Investigations Map 2889, 42 p.

Sugisaki, R., Takeda, H., Kawabe, I., and Miyazaki, H., 1982, 

Simplified gas chromatographic analysis of H2, He, Ne, Ar, 

N2, and CH4 in subsurface gases for seismo-geochemical 

studies: Chemical Geology, v. 36, p. 217–226.

Swain, L.A., 1993, Hydrogeological characteristics of the 

bedrock aquifers in the Appalachian Valley and Ridge, 

Piedmont, and Blue Ridge Physiographic Provinces of the 

Eastern and Southeastern United States [abs.]: American 

Association of Petroleum Geologists Bulletin, v. 77/78, 

p. 1476.

Thatcher, L.L., Janzer, V.J., and Edwards, K.W., 1977, Methods for determination of radioactive substances in water and 

fluvial sediments: U.S. Geological Survey Techniques of 

Water-Resources Investigations, chap. A5, p. 79–81.

Trainer, F.W., and Watkins, F.A., Jr., 1975, Geohydrologic reconnaissance of the Upper Potomac River Basin: 

U.S. Geological Survey Water-Supply Paper 2035, 68 p.

U.S. Census Bureau, 2003, Census 2000 data for the State 

of Virginia: Department of Commerce, Census Bureau, 

accessed July 2008 at http://www.census.gov/census2000/

states/va.html. 

Virginia Division of Mineral Resources, 2003, Digital geospatial data for the geologic map of the Virginia portion of the 

Winchester 30 × 60-minute quadrangle: Virginia Division of 

Mineral Resources Publication 171, Part B, scale 1:100,000.

Whipkey, R.Z., 1965, Subsurface stormflow from forested 

slopes: Bulletin of the International Association of Scientific 

Hydrology, v. 10, no. 2, p. 74–85.

Wright, W.G., 1990, Ground-water hydrology and quality in 

the Valley and Ridge and Blue Ridge Physiographic Provinces of Clarke County, Virginia: U.S. Geological Survey 

Water-Resources Investigations Report 90–4134, 61 p.

Yager, R.M., Southworth, Scott, and Voss, C.I., 2008, Simulation of ground-water flow in the Shenandoah Valley, 

Virginia and West Virginia, using variable-direction 

anisotropy in hydraulic conductivity to represent bedrock 

structure: U.S. Geological Survey Scientific Investigations 

Report 2008–5002, 54 p.
Appendixes

1. Discharge and water-quality field properties from springs in Warren County, Virginia, 2003–2008 .....................................64

2. Summary of average dissolved gas compositions (nitrogen, argon, oxygen, carbon dioxide, methane, and neon), 

recharge temperatures, and quantities of excess air in water samples from wells and springs in Warren County, 

Virginia, 2003–2005 ..............................................................................................................................................................................66

3. Concentrations of chlorofluorocarbons and sulfur hexafluoride in North American air, 1940–2006 ....................................67

4. Summary of average chlorofluorocarbon concentrations and calculated atmospheric partial pressures 

in water samples from wells and springs in Warren County, Virginia, 2003–2005....................................................................68

5. Summary of average chlorofluorocarbon-based model piston-flow apparent recharge dates, ages, 

and uncertainties in water samples from wells and springs in Warren County, Virginia, 2003–2005 ...................................69

6. Summary of average chlorofluorocarbon-based model ratio apparent recharge dates, ages, and uncertainties 

in water samples from wells and springs in Warren County, Virginia, 2003–2005....................................................................70

7. Summary of average sulfur hexafluoride data in water samples from wells and springs in Warren County, 

Virginia, 2003–2005 ..............................................................................................................................................................................71

8. Summary of tritium, dissolved helium, and dissolved neon data in water samples from wells and springs 

in Warren County, Virginia, 2003–2005 .............................................................................................................................................72

9. Summary of apparent tritium/helium-3 ages in water samples from wells and springs in Warren County, 

Virginia, 2003–2005 ..............................................................................................................................................................................73

10. Summary of oxygen (d18O ) and hydrogen (d2H) isotopic data in water samples from wells and springs 

in Warren County, Virginia, 2003–2005 .............................................................................................................................................74
64 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Appendix 1. Discharge and water-quality field properties from springs in Warren County, Virginia, 2003–2008.

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; gal/min, gallons per minute; Gage ht., gage height; ft, feet; Temp., water temperature; °C, degrees 

Celsius; Sp. cond., specific conductance at 25 oC; mS/cm, microsiemens per centimeter; O2, dissolved oxygen; mg/L, milligrams per liter; pH in standard units; 

nd, not determined. Discharge measurement method: P, pygmy velocity meter; ADV, acoustic Doppler velocimeter; V, volumetric; F, flume. See figures 15 and 

24 for location of springs]

USGS

local no. Name Date Time

Discharge Gage

ht. (ft)

Temp

(°C)

Sp. 

cond

(μS/cm)

02

(mg/L) pH ft3

/s gal/min Method

44US 2 PAULISCH SPRING 08/18/2004 1100 nd nd nd nd 16.8 88 4.1 6.0

45US 3 CLEGG SPRING 08/18/2004 1220 nd nd nd nd 13.5 82 3.8 6.0

45US 5 CHESTER GAP SPRING 08/18/2004 1515 nd nd nd nd 11.4 187 7.9 5.8

45US 6 ZOO TURTLE SPRING 08/08/2005 1440 nd nd nd nd 14.9 211 8.0 6.2

45VS 1 WEDDLE SPRING 08/14/2003 1030 0.281 126 P nd 13.7 450 4.3 6.8

12/23/2003 1445 nd nd nd 3.84 12.4 476 7.1 7.5

02/25/2004 1223 1.010 453 P 3.60 10.9 471 6.3 7.2

04/30/2004 1440 1.760 790 P 3.70 11.7 475 4.8 7.0

06/09/2004 1200 1.090 489 P 3.52 12.8 481 4.3 7.3

07/26/2004 1042 1.130 507 P 3.17 13.6 498 5.2 6.9

11/05/2004 1543 0.333 149 P 2.97 13.8 503 5.9 7.0

01/20/2005 1340 0.463 208 P 3.00 12.3 516 6.9 7.2

04/29/2005 0945 0.429 192 P 3.20 11.8 508 7.1 7.2

07/05/2005 1328 0.309 139 P 2.96 13.2 491 13.8 6.9

11/03/2005 1730 0.108 48.5 ADV 2.89 13.2 514 6.9 7.0

01/20/2006 1150 0.245 110 ADV 2.86 11.7 493 7.4 6.8

04/28/2006 1135 0.229 103 P 2.90 12.5 510 4.7 7.0

07/28/2006 0905 0.147 66 ADV 2.94 13.3 503 6.6 7.0

11/02/2006 1052 0.089 39.9 ADV 2.96 13.3 508 4.7 7.0

01/29/2007 1435 0.224 100 ADV 3.17 12.3 503 6.4 7.3

05/02/2007 1455 0.368 165 ADV 3.34 12.1 503 6.7 7.1

08/01/2007 1540 0.151 68 ADV 2.96 13.2 461 5.5 7.1

12/04/2007 1155 0.001 0.4 ADV 2.75 12.2 497 7.5 7.3

03/05/2008 1356 0.151 68 ADV 2.78 12.1 482 5.4 7.1

04/21/2008 1424 0.280 126 ADV 3.01 12.1 514 7.6 7.2

07/28/2008 1631 0.274 123 ADV 3.14 13.2 521 6.0 7.1

10/28/2008 1230 0.118 53 ADV 2.98 13.2 516 5.7 7.2

45VS 2 MCKAY SPRING 08/21/2003 1140 nd nd nd nd 13.3 560 5.0 6.3

45VS 3 ZOO MULE FIELD 08/09/2005 1215 nd nd nd nd 12.0 103 6.7 6.0

45VS 4 ZOO GATE 4 SPRING 08/09/2005 1430 nd nd nd nd 12.5 50 7.1 6.0

46V 1 HIGH KNOB WELL 1 08/14/2003 1700 nd nd nd nd 11.2 120 11.0 7.1

46VS 1 HIGH KNOB SPRING 6 08/14/2003 1440 nd nd nd nd 10.4 60 10.0 5.6

46VS 2 ANDREWS SPRING 08/18/2004 1715 nd nd nd nd 12.1 95 4.8 6.4

46VS 6 MCAFEE SPRING 08/23/2004 1630 nd nd nd nd 16.3 227 6.2 6.2

46VS 8 ROCK SPRING 08/23/2004 1300 nd nd nd nd 10.0 55 8.4 6.2

46VS 12 FREEZELAND SPRING 

BOX 3-WEST

08/10/2005 1615 nd nd nd nd 12.0 99 9.6 6.6
Appendixes 65

Appendix 1. Discharge and water-quality field properties from springs in Warren County, Virginia, 2003–2008.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; gal/min, gallons per minute; Gage ht., gage height; ft, feet; Temp., water temperature; °C, degrees 

Celsius; Sp. cond., specific conductance at 25 oC; mS/cm, microsiemens per centimeter; O2, dissolved oxygen; mg/L, milligrams per liter; pH in standard units; 

nd, not determined. Discharge measurement method: P, pygmy velocity meter; ADV, acoustic Doppler velocimeter; V, volumetric; F, flume. See figures 15 and 

24 for location of springs]

USGS

local no. Name Date Time

Discharge Gage

ht. (ft)

Temp

(°C)

Sp. 

cond

(μS/cm)

02

(mg/L) pH ft3

/s gal/min Method

46VS 17 HIGH KNOB SPRING 08/14/2003 1322 0.014 6.3 V nd nd nd nd nd

12/22/2003 1600 0.199 89.3 V nd nd nd nd nd

02/25/2004 1500 0.108 48.5 V nd nd nd nd nd

04/30/2004 1040 0.191 85.7 V nd nd nd nd nd

06/09/2004 1524 0.090 40.4 V nd nd nd nd nd

07/26/2004 1330 0.024 10.8 V nd nd nd nd nd

11/05/2004 1145 0.073 32.8 V nd nd nd nd nd

01/20/2005 1500 0.215 96.5 V nd 7.5 nd nd nd

04/29/2005 1045 0.130 58.3 V nd 10.0 nd nd nd

06/20/2005 1600 0.083 37.3 V nd 13.0 nd nd nd

07/05/2005 1157 0.052 23.3 V nd 15.5 nd nd nd

11/04/2005 1359 0.013 5.8 V nd nd nd nd nd

01/20/2006 1323 0.131 58.8 V nd 7.0 nd nd nd

05/04/2006 1000 0.058 26.0 V nd nd nd nd nd

07/28/2006 1040 0.040 18.0 V nd 16.0 nd nd nd

11/02/2006 0920 0.050 22.4 F nd nd nd nd nd

01/29/2007 1235 0.077 34.6 V nd nd nd nd nd

05/02/2007 1130 0.149 66.9 V nd nd nd nd nd

08/01/2007 1200 0.007 3.1 V nd nd nd nd nd

12/04/2007 1400 0.000 0.0 V nd nd nd nd nd

03/05/2008 1230 0.032 14.4 V nd nd nd nd nd

04/19/2008 1050 0.000 0.0 V nd nd nd nd nd

07/28/2008 1335 0.0156 7.0 V 2.95 15.9 132 9.2 7.6

10/28/2008 1530 0.008 3.5 V 2.92 10.2 128 10.2 7.8
66 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia Appendix 2. Summary of average dissolved gas compositions (nitrogen, argon, oxygen, carbon dioxide, methane, and neon), recharge temperatures, and quantities of excess air in water samples from wells and springs in Warren County, Virginia, 2003–2005. [USGS, U.S. Geological Survey; Rech. elev., recharge elevation is land surface in feet above National Geodetic Vertical Datum of 1929; n, number of samples averaged; N2, nitrogen; Ar, argon; O2, oxygen; CO2, carbon dioxide; CH4, methane; mg/L, milligrams per liter; rech. temp., recharge temperature; °C, degrees Celsius; ex. air, excess air; ccSTP/L, cubic centimeters at standard temperature and pressure per liter; ccSTP/g, cubic centimeters at standard temperature and pressure per gram. See figure 24 for location of wells and springs] USGS local no. Date Rech. elev. (ft) USGS dissolved gasesa USGSb Lamont-Dohertyc,d

n N2 (mg/L) Ar (mg/L) Field

O2

(mg/l)

Lab

O2

(mg/L)

CO2

(mg/L)

CH4

(mg/L)

N2-Ar

rech.

temp.

(°C)

N2-Ar

ex. air

(ccSTP/L)

n

Neon

x 10–8

(ccSTP/g)

n

Neon

x 10–8

(ccSTP/g)

Neon

ex. air

(ccSTP/L)

44US 2 08/18/2004 1305 2 15.4 0.6 4.1 0.8 68.3 0.0000 18.2 0.7 1 24.8 1 18.95 0.5845US 3 08/18/2004 829 2 17.1 0.6 3.8 2.2 40.2 0.0000 13.7 0.8 1 23.5 1 21.57 1.4645US 5 08/18/2004 1889 2 17.6 0.6 7.9 4.7 68.0 0.0000 13.9 2.0 1 25.9 1 20.30 1.1845US 6 08/08/2005 1067 2 17.1 0.6 8.0 5.5 71.0 0.0000 12.1 0.4 1 25.0 1 19.66 0.3445VS 1 08/14/2003 550 2 20.3 0.7 4.3 1.8 40.7 0.0004 12.2 3.4 2 36.5 1 24.89 3.0345VS 2 08/21/2003 500 2 23.9 0.8 5.0 0.8 45.0 0.0000 11.7 6.8 2 41.7 1 35.72 9.0445VS 3 08/09/2005 972 2 18.2 0.7 6.7 3.7 61.7 0.0000 11.9 1.3 1 28.2 1 20.71 0.8745VS 4 08/09/2005 875 2 18.1 0.6 7.1 5.6 31.9 0.0000 12.8 1.5 1 30.4 1 20.43 0.7746V 1 08/14/2003 1790 2 20.3 0.7 11.0 7.1 3.4 0.0000 7.9 2.5 1 29.8 1 32.35 7.1846VS 1 08/14/2003 1790 2 17.5 0.7 10.0 6.9 31.9 0.0000 9.7 0.4 1 25.0 1 19.83 0.4846VS 2 08/18/2004 803 2 18.5 0.7 4.8 2.6 41.4 0.0010 11.9 1.6 1 25.0 1 16.08 –1.7446VS 6 08/23/2004 893 2 15.9 0.6 6.2 0.3 77.6 0.0000 15.9 0.3 1 21.1 1 19.04 0.2946VS 8 08/23/2004 1761 2 17.5 0.7 8.4 4.8 34.5 0.0000 10.1 0.5 1 23.1 1 19.37 0.2646VS 12 08/10/2005 1693 2 18.6 0.7 9.6 6.1 13.1 0.0000 11.0 1.9 1 26.2 1 22.40 1.9946VS 13 08/10/2005 1669 2 17.8 0.6 8.5 5.6 52.5 0.0000 11.2 1.1 1 21.5 1 20.01 0.69

a Water samples for the determination of the dissolved gases (N2, Ar, O2, CO2, and CH4) in the U.S. Geological Survey Dissolved Gas Laboratory, Reston, VA, were analyzed using gas chromatography procedures (see http://water.usgs.gov/lab/cfc/, accessed January 6, 2010).b Water samples for the determination of neon in the U.S. Geological Survey Chlorofluorocarbon Laboratory in Reston, VA, were analyzed using gas chromatography procedure with a thermal 

conductivity detector, which is similar to the procedure described by Sugisaki and others (1982) (see http://water.usgs.gov/lab/cfc/, accessed January 6, 2010).

c Water samples for the determination of neon in the Noble Gas Laboratory at Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY, were analyzed by mass-spectrometric 

procedures outlined in Ekwurzel and others (1994) and Ludin and others (1998).

d Neon excess-air quantities are based on neon concentrations as determined by mass-spectrometric procedures.
Appendixes 67

Appendix 3. Concentrations of chlorofluorocarbons and sulfur hexafluoride in North American air, 1940–2006.

[CFC-11, (trichlorofluoromethane, CFC13); CFC-12, (dichlorodifluoromethane, CF2Cl2); CFC-113, (trichlorotrifluoroethane, C2F3Cl3); SF6, sulfur hexafluoride; 

Mod., modern; Cont., contaminated. Concentrations in parts per trillion by volume (pptv). Data from Plummer and others (2000) and E. Busenberg, U.S. Geological Survey, written commun., 2005]

Year CFC-11 CFC-12 CFC-113 SF6 Year CFC-11 CFC-12 CFC-113 SF6 Year CFC-11 CFC-12 CFC-113 SF6

1940.0 0.000 0.000 0.000 0.000 1965.0 26.251 67.916 2.848 0.120 1990.0 265.758 493.523 74.512 2.340

1940.5 0.000 0.396 0.000 0.000 1965.5 28.586 72.530 3.064 0.130 1990.5 266.861 497.131 76.633 2.440

1941.0 0.000 0.478 0.000 0.000 1966.0 31.199 77.643 3.280 0.140 1991.0 269.216 503.382 78.755 2.540

1941.5 0.000 0.559 0.000 0.000 1966.5 33.802 82.755 3.526 0.150 1991.5 270.100 508.779 80.287 2.650

1942.0 0.000 0.661 0.000 0.000 1967.0 36.743 88.518 3.771 0.160 1992.0 271.521 517.703 81.514 2.750

1942.5 0.000 0.762 0.000 0.000 1967.5 39.694 94.281 4.056 0.180 1992.5 272.217 520.468 82.300 2.860

1943.0 0.000 0.884 0.000 0.000 1968.0 43.033 100.735 4.331 0.190 1993.0 272.346 522.958 82.693 2.970

1943.5 0.000 1.006 0.000 0.000 1968.5 46.371 107.179 4.655 0.200 1993.5 272.445 526.007 82.987 3.090

1944.0 0.000 1.179 0.000 0.000 1969.0 50.246 114.355 4.979 0.210 1994.0 272.793 528.162 83.184 3.200

1944.5 0.000 1.342 0.000 0.000 1969.5 54.121 121.521 5.352 0.220 1994.5 272.187 533.305 83.528 3.320

1945.0 0.048 1.555 0.000 0.000 1970.0 58.513 129.347 5.726 0.230 1995.0 272.033 534.687 83.557 3.440

1945.5 0.055 1.769 0.000 0.000 1970.5 62.895 137.163 6.148 0.250 1995.5 271.327 534.789 83.650 3.570

1946.0 0.069 2.155 0.000 0.000 1971.0 67.674 145.508 6.570 0.260 1996.0 271.024 535.744 83.550 3.690

1946.5 0.081 2.531 0.000 0.000 1971.5 72.463 153.852 7.051 0.270 1996.5 269.514 537.406 83.500 3.820

1947.0 0.109 3.110 0.000 0.000 1972.0 77.839 162.919 7.543 0.280 1997.0 269.037 539.317 83.400 3.950

1947.5 0.139 3.700 0.000 0.000 1972.5 83.214 171.995 8.102 0.300 1997.5 268.009 540.882 83.300 4.080

1948.0 0.199 4.371 0.000 0.000 1973.0 89.354 182.027 8.652 0.320 1998.0 267.263 542.117 83.150 4.220

1948.5 0.248 5.041 0.000 0.000 1973.5 95.495 192.059 9.291 0.340 1998.5 266.310 543.728 83.000 4.320

1949.0 0.338 5.763 0.000 0.000 1974.0 102.202 202.884 9.929 0.360 1999.0 265.619 544.003 82.800 4.430

1949.5 0.427 6.485 0.000 0.000 1974.5 108.908 213.698 10.666 0.390 1999.5 264.188 544.587 82.600 4.540

1950.0 0.556 7.277 0.000 0.000 1975.0 114.572 224.025 11.392 0.420 2000.0 263.841 545.055 82.300 4.650

1950.5 0.676 8.070 0.000 0.000 1975.5 122.104 234.341 12.227 0.450 2000.5 263.234 546.269 82.100 4.770

1951.0 0.854 8.934 0.000 0.000 1976.0 128.920 244.190 13.072 0.480 2001.0 261.843 546.515 81.700 4.890

1951.5 1.023 9.798 0.000 0.000 1976.5 135.130 254.039 14.024 0.520 2001.5 260.795 546.102 81.300 5.010

1952.0 1.282 10.693 0.000 0.000 1977.0 142.085 263.268 14.987 0.550 2002.0 260.120 545.299 81.000 5.140

1952.5 1.530 11.597 0.000 0.054 1977.5 146.705 272.497 16.087 0.590 2002.5 258.569 544.724 80.600 5.270

1953.0 1.878 12.593 0.000 0.054 1978.0 149.964 282.407 17.187 0.630 2003.0 258.137 543.306 80.250 5.400

1953.5 2.216 13.599 0.491 0.054 1978.5 156.502 292.855 18.444 0.680 2003.5 256.051 542.758 79.900 5.530

1954.0 2.643 14.738 0.530 0.055 1979.0 159.801 298.090 19.701 0.730 2004.0 255.057 542.148 79.550 5.670

1954.5 3.060 15.876 0.579 0.055 1979.5 162.642 301.190 21.145 0.770 2004.5 253.467 541.233 79.100 5.780

1955.0 3.577 17.147 0.629 0.055 1980.0 168.584 311.212 22.588 0.830 2005.0 252.374 540.318 78.750 5.890

1955.5 4.094 18.417 0.687 0.056 1980.5 172.807 317.422 24.150 0.880 2005.5 250.983 539.698 78.400 6.000

1956.0 4.739 19.901 0.746 0.056 1981.0 175.996 322.737 25.721 0.940 2006.0 249.592 538.692 78.100 6.110

1956.5 5.375 21.385 0.805 0.057 1981.5 179.732 333.796 27.342 0.990

1957.0 6.091 23.062 0.874 0.058 1982.0 183.846 343.604 28.962 1.050 Mod. 284.000 550.000 87.000 6.200

1957.5 6.806 24.749 0.943 0.059 1982.5 188.347 352.721 30.759 1.120 Cont. 294.000 570.000 92.000 6.300

1958.0 7.462 26.498 1.021 0.060 1983.0 193.295 361.594 32.547 1.180

1958.5 8.108 28.256 1.110 0.061 1983.5 198.015 372.236 34.796 1.250

1959.0 8.764 30.218 1.188 0.062 1984.0 201.939 378.589 37.035 1.320

1959.5 9.419 32.179 1.287 0.064 1984.5 206.023 386.232 39.696 1.390

1960.0 10.294 34.517 1.385 0.066 1985.0 211.229 395.380 42.348 1.470

1960.5 11.168 36.855 1.493 0.069 1985.5 217.261 403.257 45.177 1.540

1961.0 12.291 39.477 1.601 0.072 1986.0 222.984 414.620 48.015 1.620

1961.5 13.424 42.089 1.728 0.076 1986.5 227.912 423.463 51.128 1.700

1962.0 14.854 45.098 1.856 0.079 1987.0 233.466 433.586 54.241 1.790

1962.5 16.275 48.096 1.994 0.084 1987.5 241.047 449.310 57.738 1.870

1963.0 18.024 51.613 2.141 0.088 1988.0 248.648 459.474 61.224 1.960

1963.5 19.763 55.130 2.308 0.095 1988.5 253.964 469.089 64.868 2.050

1964.0 21.839 59.226 2.475 0.100 1989.0 257.442 476.671 68.521 2.150

1964.5 23.906 63.312 2.661 0.110 1989.5 261.983 484.030 71.517 2.240
68 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Appendix 4. Summary of average chlorofluorocarbon concentrations and calculated atmospheric partial pressures in 

water samples from wells and springs in Warren County, Virginia, 2003–2005.

[USGS, U.S. Geological Survey; pg/kg, picograms per kilogram; CFC-11, trichlorofluoromethane (CFC13); CFC-12, dichlorodifluoromethane 

(CF2Cl2); CFC-113, trichlorotrifluoroethane (C2F3Cl3); N2-Ar Rech. temp., nitrogen-argon recharge temperature; °C, degrees Celsius; Rech. elev., 

recharge elevation in feet above National Geodetic Vertical Datum of 1929; pptv, parts per trillion by volume. See figure 24 for location of wells 

and springs] 

USGS

local no. Date

Average concentration in water

(pg/kg)a

N2-Ar

Rech.

temp.

(°C)

Rech.

elev.

(ft)

Average calculated atmospheric 

partial pressure

(pptv)

CFC-11 CFC-12 CFC-113 CFC-11 CFC-12 CFC-113

44US 2 08/18/2004 411.6 256.3 57.6 18.1 1,305 228.4 592.4 78.7

45US 3 08/18/2004 440.6 374.9 68.3 13.7 829 192.9 699.3 72.1

45US 5 08/18/2004 1,328.6 414.6 81.8 13.9 1,889 609.3 801.6 89.7

45US 6 08/08/2005 4,027.5 329.3 89.3 12.0 1,066 1,628.3 574.4 86.4

45VS 1 08/14/2003 1,673.3 320.2 81.6 12.2 550 664.3 537.2 76.4

45VS 2 08/21/2003 695.0 322.2 117.5 11.7 500 267.0 513.3 104.3

45VS 3 08/09/2005 687.5 331.2 87.7 11.9 972 274.8 567.7 83.4

45VS 4 08/09/2005 576.7 291.7 77.5 12.8 875 240.9 519.2 77.3

46V 1 08/14/2003 949.1 284.0 89.5 7.9 1,790 312.5 408.5 68.4

46VS 1 08/14/2003 642.6 314.4 97.2 9.7 1,790 235.0 503.1 84.1

46VS 2 08/18/2004 542.1 273.7 68.3 11.9 803 215.3 465.8 64.5

46VS 6 08/23/2004 561.7 302.7 154.0 15.9 893 276.0 628.5 184.9

46VS 8 08/23/2004 713.8 336.8 92.7 10.1 1,760 266.9 549.2 82.1

46VS 12 08/10/2005 658.1 333.2 82.8 11.0 1,693 257.1 559.3 76.4

46VS 13 08/10/2005 1,982.5 11,713.8 84.0 11.2 1,669 783.7 19,978.7 78.9

a

 Water samples for the determination of chlorofluorocarbons in the U.S. Geological Survey Chlorfluorocarbon Laboratory, Reston, VA, were 

analyzed using purge and trap gas chromatography with an electron-capture detector (Busenberg and Plummer, 1992; see http://water.usgs.gov/

lab/cfc/, accessed January 6, 2010).
Appendixes 69

Appendix 5. Summary of average chlorofluorocarbon-based model piston-flow apparent recharge dates, ages, and uncertainties in water samples from wells and springs in Warren County, Virginia, 2003–2005.[USGS, U.S. Geological Survey; CFC-11, trichlorofluoromethane (CFC13); CFC-12, dichlorodifluoromethane (CF Cl 2 2); CFC-113, trichlorotrifluoroethane (C2F Cl 3 3); NP, not possible; C, contaminated (sample concentration higher than that of water in equilibrium with modern North American air); Mod., modern. Apparent age uncertainties are based on changes in age resulting from 

uncertainty in nitrogen-argon (N2-Ar) recharge temperature of ±1 degree Celsius. Dates and ages are based on the North American air data in appendix 3. Numbers in parentheses indicate possible recharge years before and after atmospheric peak concentration. See figure 24 for location of wells and springs]

USGS

local no. Date

Model piston-flow

average apparent recharge datea

Model piston-flow

average apparent age and uncertainty a

(years)

CFC-11

(1)

CFC-11

(2)

CFC-12

(1)

CFC-12

(2)

CFC-113

(1)

CFC-113

(2)

CFC-11

(1)

CFC-11

(2)

CFC-12

(1)

CFC-12

(2)

CFC-113

(1)

CFC-113

(2)

44US 2 08/18/2004 1986.5 NP C C 1990.5 2005.5 18.1 ± 0.7 NP C C 14.1 ± 0.4 NP45US 3 08/18/2004 1982.5 NP C C 1989.5 NP 22.1 ± 0.7 NP C C 15.1 ± 0.7 NP45US 5 08/18/2004 C C C C Mod. Mod. C C C C Mod. C45US 6 08/08/2005 C C C C 1995.5 1995.5 C C C C 10.1 ± 2.8 10.1 ± 4.245VS 1 08/14/2003 1985.5 NP 1991.0 NP 1990.0 NP 18.1 NP 12.6 ± 3.2 NP 13.6 ± 0.4 NP45VS 2 08/21/2003 1990.5 1998.5 1991.5 NP C C 13.1 ± 1.8 5.1 ± 4.6 12.1 ± 1.4 NP C C45VS 3 08/09/2005 1994.5 1994.0 Mod. Mod. 1994.0 1997.5 11.1 ± 3.9 11.6 ± 5.7 Mod. C 11.6 ± 3.2 8.1 ± 6.745VS 4 08/09/2005 1987.0 NP 1992.0 NP 1990.5 NP 18.6 ± 0.4 NP 13.6 ± 1.4 NP 15.1 ± 0.7 NP46V 1 08/14/2003 C C 1985.5 NP 1988.5 NP C C 18.1 ± 0.7 NP 15.1 ± 0.4 NP46VS 1 08/14/2003 1987.0 NP 1990.5 NP 1995.5 1995.5 16.6 ± 1.1 NP 13.1 ± 1.1 NP 8.1 ± 3.2 8.1 ± 6.746VS 2 08/18/2004 1985.0 NP 1988.0 NP 1988.0 NP 19.6 ± 0.7 NP 16.6 ± 0.7 NP 16.6 ± 0.4 NP46VS 6 08/23/2004 C C C C C C C C C C C C46VS 8 08/23/2004 1990.5 1998.5 2001.0 2001.0 1992.0 2001.0 14.1 ± 1.8 6.1 ± 4.6 3.6 ± 6.0 3.6 12.6 ± 1.1 3.646VS 12 08/10/2005 1988.5 2003.5 Mod. Mod. 1990.0 NP 17.1 ± 0.7 2.1 Mod. C 15.6 ± 0.4 NP46VS 13 08/10/2005 C C C C 1991.0 2005.0 C C C C 14.6 ± 1.1 0.6

a Apparent chlorofluorocarbon recharge dates and ages were calculated using the chlorofluorocarbon program, version 3.0, revised February 2004 (Microsoft Excel®) by E. Busenberg and 

L.N. Plummer of the U.S. Geological Survey.
70 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Appendix 6. Summary of average chlorofluorocarbon-based model ratio apparent recharge 

dates, ages, and uncertainties in water samples from wells and springs in Warren County, 

Virginia, 2003–2005.

[USGS, U.S. Geological Survey; CFC-11, trichlorofluoromethane (CFC13); CFC-12, dichlorodifluoromethane 

(CF2Cl2); CFC-113, trichlorotrifluoroethane (C2F3Cl3); NP, not possible. Apparent age uncertainties are based on 

changes in age resulting from uncertainty in nitrogen-argon (N2Ar) recharge temperature of ±1 degree Celsius. 

Dates and ages are based on the North American air data in appendix 3. See figure 24 for location of wells and 

springs]

USGS

local no. Date

Model ratio

average apparent agea Percentage of young fraction

CFC-11/

CFC-12

CFC-113/

CFC-12

CFC-113/

CFC-11

CFC-11/

CFC-12

CFC-113/

CFC-12

CFC-113/

CFC-11

44US 2 08/18/2004 NP NP NP NP NP NP

45US 3 08/18/2004 NP NP NP NP NP NP

45US 5 08/18/2004 NP NP NP NP NP NP

45US 6 08/08/2005 NP NP NP NP NP NP

45VS 1 08/14/2003 NP NP NP NP NP NP

45VS 2 08/21/2003 NP NP NP NP NP NP

45VS 3 08/09/2005 NP NP NP NP NP NP

45VS 4 08/09/2005 NP NP 10.1 NP NP 92.4

46V 1 08/14/2003 NP NP NP NP NP NP

46VS 1 08/14/2003 NP NP NP NP NP NP

46VS 2 08/18/2004 NP 16.1 ± 0.4 13.1 NP 99.5 80.4

46VS 6 08/23/2004 NP NP NP NP NP NP

46VS 8 08/23/2004 NP NP 9.6 ± 0.7 NP NP 98.2

46VS 12 08/10/2005 NP NP 14.6 NP NP 97.0

46VS 13 08/10/2005 NP NP NP NP NP NP

a

 Apparent chlorofluorocarbon recharge dates and ages were calculated using the chlorofluorocarbon program 

version 3.0 revised February 2004 (Microsoft Excel®) by E. Busenberg and L.N. Plummer of the U.S. Geological Survey.
Appendixes 71

Appendix 7. Summary of average sulfur hexafluoride data in water samples from wells and springs in Warren County, Virginia, 2003–2005.[USGS, U.S. Geological Survey; n, number of samples averaged; SF6, sulfur hexafluoride; fmol/L, femtomoles per liter; °C, degrees Celsius; pptv, parts per trillion by volume; cc/L, cubic centimeters per liter; Meas. st. dev., standard deviation of measured values; Rtemp, recharge temperature; nd, not determined; C, contaminated (sample SF6 concentration greater than that of water in equilibrium with modern air). Apparent age uncertainties are based on standard deviation of measured ages, changes in recharge temperature (±1 °C) and excess air (±1 cc/L). Apparent recharge dates and ages are based on the North American air data in appendix 3. See figure 24 for location of wells and springs]

USGS

local no. Date n

SF6

concentration

in water

(fmol/L)a

Recharge

temperature

(°C)

SF6

partial

pressure

(pptv)

Excess

air

(cc/L)

Model SF6

partial

pressure

remove

excess air

(pptv)

Model SF6

apparent

recharge

date

(years)b

Model SF6

apparent 

age

(years)b

Model SF6apparent age uncertainity

Meas.

st. dev.

(years)

Rtemp

±1 °C

(years)

Excess air

±1 cc/L

(years)

44US 2 08/18/2004 2 1.429 18.1 5.73 0.7 5.14 2002.0 2.6 1.1 1.1 nd45US 3 08/18/2004 2 1.726 13.7 5.76 0.8 5.19 2002.0 2.6 1.8 1.1 3.545US 5 08/18/2004 2 1.268 13.9 4.44 2.0 3.45 1995.0 9.6 0.0 0.4 2.145US 6 08/08/2005 1 1.772 12.1 3.04 0.4 1.58 1985.5 20.1 nd 0.7 0.745VS 1 08/14/2003 2 2.481 12.2 7.71 3.4 5.41 2003.0 0.6 0.7 1.1 2.545VS 2 08/21/2003 2 4.428 11.7 13.49 6.8 7.30 C C nd nd nd45VS 3 08/09/2005 2 1.895 11.9 3.39 1.3 1.74 1986.5 19.1 0.0 0.4 0.745VS 4 08/09/2005 2 1.696 12.8 3.05 1.5 1.50 1985.0 20.6 0.0 0.4 0.746V 1 08/14/2003 2 2.115 7.9 5.76 2.5 4.50 1999.0 4.6 0.4 0.7 2.546VS 1 08/14/2003 2 1.982 9.7 5.82 0.4 5.58 2003.5 0.1 0.4 1.1 nd46VS 2 08/18/2004 2 1.029 11.9 3.19 1.6 2.66 1991.5 13.1 1.1 0.4 1.846VS 6 08/23/2004 2 1.450 15.9 5.28 0.4 4.98 2001.0 3.6 1.8 1.1 3.946VS 8 08/23/2004 2 1.369 10.1 4.09 0.6 3.81 1996.0 8.6 0.0 1.1 2.546VS 12 08/10/2005 2 1.583 11.0 2.99 1.9 1.55 1985.5 20.1 0.4 0.4 0.746VS 13 08/10/2005 2 1.910 11.2 3.47 1.1 1.82 1987.0 18.6 0.7 0.4 0.7

a Water samples for the determination of SF6 in the U.S. Geological Survey Chlorofluorocarbon Laboratory, Reston, VA, were analyzed using purge and trap gas chromatographic procedures 

(Busenberg and Plummer, 2000).

bApparent SF6 recharge dates and ages were calculated using the SF6 program revised February 2003 (Microsoft Excel®) by E. Busenberg of the U.S. Geological Survey.
72 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Appendix 8. Summary of tritium, dissolved helium, and dissolved neon data in water samples from wells and 

springs in Warren County, Virginia, 2003–2005.

[USGS, U.S. Geological Survey; 3H, tritium; TU, tritium unit (1 TU = 1 atom of 3H in 1018 atoms of hydrogen (H); 2σ, 2 standard 

deviations; ccSTP/g, cubic centimeters at standard temperature and pressure per gram; USGS, USGS Low-Level 3H Laboratory in 

Menlo Park, CA; LDEO, Noble Gas Laboratory at Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY; He, 

helium; Ne, neon; Δ4He (%), percentage of helium-4 (4He) greater than solubility equilibrium concentration; d3He = [(Rsample/Rair) – 1] × 

100; R is the ratio 3He/4He; Rair = 1.384 × 10-6; ΔNe (%), percentage of Ne greater than solubility equilibrium concentration; Terr. He 

(%), percentage of terrigenic helium; nd, not determined. See figure 24 for location of wells and springs]

USGS

local 

no.

Date 3

H

(TU)

3

H

error

2σ

(TU)

3

H

Laba

4

He x 10–8 

(ccSTP/g) D4

He

(%) c

d3He

(%) c

Ne x 10–8

(ccSTP/g) c

DNe

(%) c

Terr.

He

USGSb (%) LDEOc

44US 2 08/18/2004 6.6 0.5 USGS 6.100 4.496 4.76 –1.38 18.951 5.89 nd

45US 3 08/18/2004 6.3 0.4 USGS 6.420 5.251 18.33 7.35 21.574 14.06 nd

45US 5 08/18/2004 6.9 0.5 USGS 6.110 4.597 7.78 0.04 20.300 11.78 nd

45US 6 08/08/2005 6.4 0.5 USGS 6.088 4.660 5.24 –0.78 19.655 3.28 nd

45VS 1 08/14/2003 7.5 0.4 USGS 9.400 6.035 33.81 1.82 24.886 28.49 nd

45VS 2 08/21/2003 8.5 0.5 USGS 16.300 16.857 272.31 –40.16 35.720 83.25 45.4

45VS 3 08/09/2005 8.4 0.6 USGS 6.560 4.893 10.04 0.55 20.708 8.28 nd

45VS 4 08/09/2005 7.3 0.6 USGS 7.054 4.795 7.87 2.83 20.431 7.38 nd

46V 1 08/14/2003 9.4 0.3 USGS 6.600 8.074 83.83 4.28 32.350 67.74 nd

46VS 1 08/14/2003 7.5 0.5 USGS 6.200 4.622 6.12 –1.75 19.828 4.66 nd

46VS 2 08/18/2004 8.5 0.6 USGS 7.070 4.003 –10.53 15.52 16.078 –16.44 11.0

46VS 6 08/23/2004 6.3 0.4 USGS 6.530 4.456 1.47 –1.60 19.039 2.83 nd

46VS 8 08/23/2004 5.0 0.4 USGS 5.780 4.522 3.89 3.26 19.366 2.50 nd

46VS 12 08/10/2005 8.1 0.6 USGS 7.062 5.458 25.56 20.11 22.396 19.23 nd

46VS 13 08/10/2005 6.8 0.6 USGS 6.401 4.677 7.60 5.26 20.010 6.65 nd

a

 Water samples for the determination of tritium (3H) in the U.S. Geological Survey Low-Level 3H Laboratory, Menlo Park, CA, 

were enriched electrolytically and analyzed by liquid scintillation counting following procedures modified from Thatcher and others 

(1977). Water samples for the determination of 3H in the Noble Gas Laboratory at Lamont-Doherty Earth Observatory of Columbia 

University, Palisades, NY, were analyzed by the helium-3 ingrowth method (Clarke and others, 1976; Bayer and others, 1989).

b

 Water samples for the determination of helium-4 (4He) in the U.S. Geological Survey Chlorofluorocarbon Laboratory in Reston, 

VA, were analyzed using gas chromatography procedure with a thermal conductivity detector, which is similar to the procedure 

described by Sugisaki and others (1982) (see http://water.usgs.gov/lab/cfc/, accessed January 6, 2010). 

c

 Water samples for the determination of helium-3 (d3He), helium–4 (4He), and neon (Ne) in the Noble Gas Laboratory at LamontDoherty Earth Observatory of Columbia University, Palisades, NY, were analyzed by mass-spectrometric procedures outlined in 

Ekwurzel and others (1994) and Ludin and others (1998).
Appendixes 73

Appendix 9. Summary of apparent tritium/helium-3 ages in water samples from wells and 

springs in Warren County, Virginia, 2003–2005.

[USGS, U.S. Geological Survey; Uncorr., apparent age not corrected for terrigenic helium; Uncorr. err., one 

standard deviation age error of uncorrected apparent age; Corr., apparent age corrected for terrigenic helium; 

Corr. err., one standard deviation age error of apparent age corrected for terrigenic helium; Terr. He, terrigenic 

helium; N, no, terrigenic helium correction not needed; Y, yes, terrigenic helium correction needed; nd, not determined. All apparent age calculations based on recharge temperatures determined for the respective samples. See 

figure 24 for location of wells and springs]

USGS

local 

no.

Date

Tritium/Helium-3 (3H/3He) apparent age

Uncorr.

(years)

Uncorr err.

(years)

Corr.

(years)

Corr err.

(years)

Terr. He

(Y/N)

Final

(years)

Final error

(years)

44US 2 08/18/2004 0.1 0.3 –1.4 0.9 N 0.1 0.3

45US 3 08/18/2004 6.1 0.4 6.7 0.5 N 6.1 0.4

45US 5 08/18/2004 1.0 0.2 –3.3 0.7 N 1.0 0.2

45US 6 08/08/2005 0.6 0.4 1.3 0.2 N 0.6 0.4

45VS 1 08/14/2003 2.3 0.2 1.6 0.5 N 2.3 0.2

45VS 2 08/21/2003 nd nd 8.0 0.6 Y 8.0 0.6

45VS 3 08/09/2005 1.2 0.2 1.1 0.2 N 1.2 0.2

45VS 4 08/09/2005 2.7 0.3 2.0 0.3 N 2.7 0.3

46V 1 08/14/2003 4.0 0.2 3.3 0.3 N 4.0 0.2

46VS 1 08/14/2003 –0.1 0.2 0.1 0.3 N –0.1 0.2

46VS 2 08/18/2004 6.8 0.4 10.0 30.3 Y 10.0 30.3

46VS 6 08/23/2004 0.0 0.3 –1.4 0.9 N 0.0 0.3

46VS 8 08/23/2004 4.0 0.4 4.5 0.5 N 4.0 0.4

46VS 12 08/10/2005 10.6 0.6 11.0 0.6 N 10.6 0.6

46VS 13 08/10/2005 4.2 0.4 3.8 0.4 N 4.2 0.4
74 Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia

Appendix 10. Summary of oxygen (δ18O) and hydrogen (δ2H) 

isotopic data in water samples from wells and springs in Warren 

County, Virginia, 2003–2005.

[USGS, U.S. Geological Survey; per mil, parts per thousand; δ = [(Rsample/

Rstandard) – 1] × 1,000, where R is an isotope ratio. The 2σ precision of oxygenand hydrogen-isotope results is 0.2 and 1.5 per mil, respectively; d, deuterium 

excess. See figure 24 for location of wells and springs]

USGS

local no. Date

d18O

(per mil) a

d2H

(per mil) a

d

(per mil) b

44US 2 08/18/2004 –8.26 –51.7 14.4

45US 3 08/18/2004 –8.15 –50.8 14.4

45US 5 08/18/2004 –8.07 –47.9 16.7

45US 6 08/08/2005 –8.02 –49.0 15.2

45VS 1 08/14/2003 –8.03 –50.6 13.6

45VS 2 08/21/2003 –7.67 –48.8 12.6

45VS 3 08/09/2005 –8.11 –49.5 15.4

45VS 4 08/09/2005 –7.89 –48.4 14.7

46V 1 08/14/2003 –8.56 –51.8 16.7

46VS 1 08/14/2003 –8.54 –52.2 16.1

46VS 2 08/18/2004 –8.11 –49.7 15.2

46VS 6 08/23/2004 –8.28 –49.8 16.4

46VS 8 08/23/2004 –8.48 –51.0 16.8

46VS 12 08/10/2005 –8.34 –50.6 16.1

46VS 13 08/10/2005 –8.22 –50.2 15.6

a

 δ18O and δ2H were determined on water samples at the U.S. Geological 

Survey Stable Isotope Laboratory, Reston, VA. The stable isotope results are 

reported in per mil relative to VSMOW (Vienna Standard Mean Ocean Water; 

Coplen, 1996) and normalized (Coplen, 1988) on scales such that the oxygen 

and hydrogen isotopic values of SLAP (Standard Light Antarctic Precipitation) are –55.5 and –428 per mil, respectively.

b

 Deuterium excess is defined as d = d2H – 8d18O by Clark and Fritz (1997).
Prepared by:

USGS Enterprise Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

For additional information regarding this publication, contact:

David L. Nelms, Groundwater Specialist

USGS Virginia Water Science Center

1730 East Parham Road

Richmond, VA 23228

phone: 1-804-261-2600

email: dlnelms@usgs.gov

Or visit the USGS Virginia Water Science Center Web site at:

http://va.water.usgs.gov/
Nelms and Moberg—Hydrogeology and Groundwater Availability in Fractured-Rock Aquifer Systems of Warren County, Virginia—Scientific Investigations Report 2010–5190

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