U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2005-5067

Prepared in cooperation with the City of Virginia Beach Department of Public Utilities

Simulated Changes in Water Levels Caused by Potential 

Changes in Pumping from Shallow Aquifers of Virginia 

Beach, Virginia
Simulated Changes in Water Levels 

Caused by Potential Changes in Pumping 

from Shallow Aquifers of Virginia Beach, 

Virginia

By Barry S. Smith

Prepared in cooperation with the

City of Virginia Beach Department of Public Utilities

Scientific Investigations Report 2005-5067

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.
iii

Contents

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

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

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

Study Area .......................................................................................... 3

Previous Studies .................................................................................... 3

Shallow Aquifer System ................................................................................. 5

Conceptual Hydrogeologic Framework ......................................................... 5

Changes in Ground-Water Levels ............................................................... 5

Simulation of Ground-Water Flow ..................................................................... 7

Model Layers ....................................................................................... 7

Refined Grid .......................................................................................... 7

Ground-Water Flow ................................................................................. 7

Simulated Changes in Water Levels .................................................................. 7

Cessation of Dewatering at Borrow Pits ......................................................... 12

Pumping to Irrigate a Golf Course ............................................................... 12

Pumping to Irrigate Lawns of a Hypothetical Neighborhood ................................. 16

Pumping to Irrigate the Golf Course and the Hypothetical

Neighborhood during a Summer Drought ...................................................... 17

Summary and Conclusions .............................................................................. 22

Acknowledgments ....................................................................................... 24

References Cited .......................................................................................... 24

Figures

1-2. Maps showing—

 1. Location of the Transition Area within the southern watersheds

 of Virginia Beach, Va. ..................................................................... 2

 2. Surficial geology of the Transition Area ................................................ 4

3. Schematic showing conceptual hydrogeologic framework of the

shallow aquifer system ..................................................................... 6

4. Graph showing water-level measurements from the spring of 2001

to the spring of 2004 from continuous recorders in the shallow

aquifer system ................................................................................. 8

 5-10. Maps showing—

 5. Simulated hydraulic conductivities of the calibrated model. ........................ 9

 6. Refined grid and boundaries of the ground-water flow model ..................... 10

 7. Simulated ground-water flow patterns ................................................ 11

 8. Simulated recoveries caused by cessation of dewatering at

 two borrow pits ........................................................................... 13

 9. Simulated recoveries in the sand aquifer of the Yorktown confining

 unit caused by cessation of dewatering at two borrow pits ........................ 14
iv

 10. Simulated drawdowns in the sand aquifer of the Yorktown confining

 unit caused by pumping 300,000 gallons per day at a golf course .................. 15

11. Graph showing drawdown 50 feet from a well pumping 10 gallons per

minute from the sand aquifer of the Yorktown confining unit ........................... 17

 12-16. Maps showing—

 12. Simulated drawdowns in the sand aquifer of the Yorktown

 confining unit (model layer 4) caused by pumping 150,000

 gallons per day at a hypothetical neighborhood .................................... 18

 13. Simulated drawdowns in the sand aquifer of the Yorktown

 confining unit caused by pumping 300,000 gallons per day

 at a hypothetical neighborhood ...................................................... 19

 14. Simulated drawdowns in the sand aquifer of the Yorktown

 confining unit (model layer 4) caused by pumping 300,000

 gallons per day at a golf course and 300,000 gallons per day

 at a hypothetical neighborhood ...................................................... 20

 15. Simulated drawdowns in the sand aquifer of the Yorktown

 confining unit caused by pumping 150,000 gallons per day at a

 golf course (maximum drawdown of 5 feet) and 150,000 gallons

 per day at a hypothetical neighborhood ............................................. 21

 16. Simulated ground-water flow patterns in the sand aquifer of

 the Yorktown confining unit (model layer 4) caused by pumping

 150,000 gallons per day at a golf course and 150,000 gallons

 per day at a hypothetical neighborhood ............................................. 23
v

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)

square foot (ft2) 0.09290 square meter (m2)

square inch (in2) 6.452 square centimeter (cm2)

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)

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

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

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

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

cubic foot per day (ft3/d) 0.02832 cubic meter per day (m3/d)

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)

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) 

Vertical coordinate information is referenced to the North American Vertical Datum of 1929 

(NGVD 29).

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

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

*Hydraulic conductivity: The standard unit for hydraulic conductivity is cubic foot per day per 

square foot of aquifer cross-sectional area (ft3/d)ft2. In this report, the mathematically reduced 

form, foot per day ft/d), is used for convenience.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Conversion Factors, Datum, Altitude, and HydraulicConductivity Units
Abstract

A steady-state ground-water flow model of the southern 

watersheds of Virginia Beach, Virginia, was refined and used 

to simulate changes in aquifer water levels caused by potential changes in pumping in the Transition Area of Virginia 

Beach, Va., a 20-square mile planning zone that runs through 

the middle of the city. Cessation of dewatering at borrow pits, 

pumping to irrigate a golf course, pumping to irrigate lawns of 

a hypothetical neighborhood, and pumping to irrigate both the 

golf course and lawns of the hypothetical neighborhood were 

simulated.

Simulated recoveries from cessation of dewatering of 

borrow pits were generally restricted to the immediate area of 

the pits. The simulated recoveries averaged about 20 feet (ft) 

near the center of the cells representing the active areas of the 

pits and 2 ft at the cells representing the extent of the pits.

At a golf course, 4 hypothetical wells pumping 300,000 

gallons per day (gal/d) from the Yorktown sand aquifer 

resulted in drawdowns averaging 10 ft in the pumping cells 

and 1 ft at a distance of 1.2 miles (mi) from the center of the 

pumping cells. The extent of the 1-ft drawdown was virtually 

the same as that simulated previously and reported in a permit 

application for the golf course.

Simulated pumping of 150,000 gal/d from 4 cells in the 

confined sand aquifer representing a 40-acre neighborhood 

resulted in drawdowns averaging 7 ft in the pumping cells and 

1 ft at a distance of 0.8 mi from the center of the cells. Simulated pumping of 300,000 gal/d from the same 4 cells resulted 

in drawdowns averaging 15 ft in the pumping cells and 1 ft at 

a distance of 1.4 mi from the center of the cells.

Simulated pumping of 150,000 gal/d at the golf course 

and another 150,000 gal/d in the hypothetical neighborhood 

resulted in drawdowns that averaged 5 ft around the cells representing the golf course wells spaced 1,300 ft apart and 7 ft 

around the contiguous cells representing the 40-acre neighborhood. A drawdown of 1 ft encompassed most of the eastern 

half of the Transition Area.

Introduction

Virginia Beach encompasses more than 300 mi2 of coastal 

lowlands and wetlands in southeastern Virginia (fig. 1). The 

northern half of Virginia Beach is suburban and urban. The 

city had approximately 425,000 residents in the 2000 census. 

The southern half is rural with approximately 5,100 residents 

(Johnson, 1999). More than 3 million tourists also visited the 

city in 2003 (Virginia Beach Department of Economic Development, 2003).

The population of Virginia Beach is increasing, estimated 

at 432,000 in 2003 (Virginia Beach Department of Economic 

Development, 2003), but the city has a limited supply of 

freshwater. Most of the city’s drinking water comes from 

Lake Gaston, which is more than 100 mi to the west. Privately 

owned wells also provide a limited amount of freshwater from 

shallow depths, generally less than 150 ft (Johnson, 1999). 

The shallow wells provide water for residents and small to 

moderately sized businesses, including golf courses and farms. 

Supplies of local ground water are limited, however, because 

of low to moderate aquifer permeability and high concentrations of iron, manganese, chloride, and (or) sulfide ions in 

some areas. At depths greater than approximately 150 ft, 

the water is generally too saline to drink. The Lake Gaston 

pipeline supplies water for the northern urban and suburban 

boroughs of Virginia Beach, up to 45 million gallons per day 

(Mgal/d); but the southern rural boroughs rely on local ground 

water. The residents of the southern boroughs of the city pump 

about 380,000 gallons of ground water per day assuming that 

each resident uses 75 gal/d (Johnson, 1999).

The city of Virginia Beach has an interest in preserving 

the limited supply of water in the shallow aquifers for drinking water, irrigation, lawn watering, heat pumps, and potentially for desalination. In 1979, city leaders drew a “Green 

Line” between the northern and southern boroughs of Virginia 

Beach. The Green Line marks the northern boundary of a buffer zone called the Transition Area (Johnson, 1999). The area 

was zoned for parks, recreation, and limited residential growth 

to buffer the rural boroughs of the south from the expanding 

suburbs of the north.

Simulated Changes in Water Levels Caused by Potential 

Changes in Pumping from Shallow Aquifers of Virginia 

Beach, Virginia

By Barry S. Smith
2 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

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Figure 1. Location of the Transition Area within the southern watersheds of Virginia Beach, Va.
Introduction 3

Open land available for new construction, however, is 

limited in the northern half of Virginia Beach and restricted 

in the southern half, and the Transition Area has become an 

area for new construction. Open-pit mines and golf courses 

also operate in the Transition Area, so that declines in groundwater levels are a concern in and around the Transition Area.

Proposed land-use changes in the Transition Area are 

scrutinized by the Virginia Beach Planning Commission, the 

City Council, and citizen groups trying to balance the services 

required by an expanding population with the desire to preserve the remaining rural and natural settings that attract new 

businesses and citizens to the city. For most of the Transition 

Area, water is supplied by the city through pipelines, but wells 

also supply some freshwater and surface mines also pump 

water.

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

the Virginia Beach Department of Public Utilities, began a 

study of the shallow-aquifer system in Virginia Beach in 1996. 

The purpose of the Virginia Beach shallow aquifer study was 

to better understand the distribution of fresh ground water, its 

susceptibility to contamination, and its sustainability as a longterm water supply. Results from the cooperative study can be 

found in several reports (Johnson, 1999; Smith and Harlow, 

2002; Smith, 2003).

Purpose and Scope

Ground-water flow in the Transition Area of Virginia 

Beach was the focus of the present phase of the Virginia 

Beach study. The purpose of this report is to present the results 

of simulated ground-water flow and changes in water levels 

caused by potential changes in pumping from the shallow 

aquifers of the Transition Area. Four potential changes in 

pumping were simulated: (1) cessation of dewatering at two 

borrow pits, (2) pumping to irrigate a golf course, (3) pumping to irrigate lawns in a hypothetical neighborhood, and (4) 

pumping to irrigate both a golf course and a neighborhood of 

lawns during a summer drought.

Ground-water flow in the Transition Area was simulated 

using a computer model of the southern watersheds constructed during a previous phase of the Virginia Beach shallow-aquifer study (Smith, 2003). The original model grid was 

refined in the zone representing the eastern half of the Transition Area. Refinement of the grid did not change the calibration statistics from those of the original ground-water flow 

model, and the refined model was used for the simulations.

Study Area

The Transition Area encompasses approximately 20 

mi2 within the city of Virginia Beach (fig. 1). Farm fields 

and pasture lands, wooded areas and wetlands, residential 

neighborhoods, small businesses and commercial properties, 

golf courses and ponds, surface mines, drainage ditches, tidal 

streams, and the city government complex are located in the 

Transition Area. The Transition Area is in two watersheds–the 

North Landing River and the Back Bay watersheds (fig. 1). 

West Neck Creek and the wetlands adjacent to the creek 

divide the Transition Area east and west (fig. 2). The western 

Transition Area is underlain by the Lynnhaven Member of the 

Pleistocene (glacial-aged) Tabb Formation and is a generally 

low, poorly drained flatland. The eastern Transition Area is 

underlain by the Lynnhaven Member and the Poquoson Member of the Tabb Formation; a sand ridge called Pungo Ridge 

marks the contact of the members. West Neck Creek is tidal 

and the average water level in the creek is about 1 ft above sea 

level in the study area.

Previous Studies

Ground-water availability and quality in the Transition 

Area were investigated as part of a comprehensive search for 

a fresh ground-water supply for the city of Virginia Beach by 

Betz-Converse-Murdoch, Inc., Potomac Group (1981, p. IV7). The composition and capacity of the water-bearing zones 

vary significantly from one site to another, according to the 

report. A tenfold decrease in the permeability of water-bearing zones within a horizontal distance of several hundred feet 

is common, precluding the development of large, productive 

well fields over much of the city. The potential for intrusion 

of saltwater also limits the amount of freshwater that can be 

withdrawn from wells.

Faust and others (1981, table 2, p. 16) of Geotrans, Inc., 

determined hydraulic properties of aquifers and confining 

units in the shallow aquifer system from four aquifer tests 

conducted in and near the Transition Area by Converse Ward 

Davis Dixon, Inc. (1981) in conjunction with Betz-ConverseMurdoch, Inc., Potomac Group (1981) for the city of Virginia 

Beach. They simulated observed drawdowns from the aquifer 

tests using a ground-water flow and solute-transport model.

The availability and quality of ground water in the 

shallow aquifers were investigated as part of the Virginia 

Department of Environmental Quality permit applications to 

withdraw ground water for two golf courses in the Transition Area. Ground-water flow models were used in each of 

those investigations, one for the Tournament Players Club of 

Virginia Beach and the other for the Heron Ridge Golf course 

(Malcolm Pirnie, Inc., 1997a and 1997b).

As part of the continuing study of the shallow aquifer 

system that began in 1996, the USGS has collected continuous 

cores and geophysical logs from test holes in the shallow aquifers and has revised the conceptual hydrogeologic framework 

of the system to depths of approximately 200 ft (Smith and 

Harlow, 2002). A water-level and water-quality monitoring 

network has been established in the city and continuous waterlevel measurements are being collected for several wells. The 

USGS also simulated ground-water flow and the distribution 

of saline water, as indicated by chloride concentrations, in the 

shallow aquifers of the southern watersheds of Virginia Beach 

(Smith, 2003).
4 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

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Figure 2. Surficial geology of the Transition Area of Virginia Beach, Va.
Shallow Aquifer System 5

Shallow Aquifer System

The Columbia aquifer, the Yorktown confining unit, and 

the Yorktown-Eastover aquifer comprise the hydrogeologic 

units of the shallow aquifer system of Virginia Beach (fig. 3). 

The shallow system is separated from deeper units by the 

continuous St. Marys confining unit, defined predominantly by 

muddy, very fine sand, sandy clay, and silt deposits of marine 

origin (Powars, 2000, p. 37). Reflecting the local topography, 

ground water in the shallow aquifer system flows from the 

higher areas such as sand ridges and poorly drained upland 

flats to lower areas such as marshes, streams, tidal inlets, and 

bays where the aquifers of the shallow system discharge.

Conceptual Hydrogeologic Framework

The Columbia aquifer is defined as the predominantly 

sandy surficial deposits above the Yorktown confining unit. 

The Yorktown confining unit is composed of a series of very 

fine sandy to silty clay units of various colors at or near the 

top of the Yorktown Formation. The Yorktown confining unit 

varies in thickness and in composition, but on a regional scale 

is a leaky confining unit. The Yorktown-Eastover aquifer is 

defined as the predominantly sandy deposits of the Yorktown 

Formation and the upper part of the Eastover Formation above 

the confining clays of the St. Marys Formation (Meng and 

Harsh, 1988, p. C50-C51).

The Columbia and Yorktown-Eastover aquifers are 

poorly confined throughout most of the southern watersheds 

of Virginia Beach, including the Transition Area (fig. 3). In 

the humid climate of Virginia Beach, the periodic recharge of 

freshwater through the shallow aquifer system occurs often 

enough to create a steady-state balance (dynamic equilibrium) whereby freshwater flows continually down and away 

from the center of the higher ground and the sand ridges to 

discharge into and mix with saline water in the tidal rivers, 

bays, salt marshes, and the Atlantic Ocean (Smith, 2003, p. 

30). Fresh ground water from the Columbia aquifer also leaks 

down through the Yorktown confining unit into the upper 

half of the Yorktown-Eastover aquifer and flows within the 

Yorktown-Eastover above saline water in the lower half of the 

aquifer.

Ground-water recharge is minimal in much of the Transition Area because the soils are not permeable, particularly 

in the western half of the area, and the proportion of uplands 

(recharge areas) to tidal wetlands (discharge areas) is relatively small. Ground-water recharge rates are probably higher 

beneath the sand ridges of the Transition Area, particularly in 

the eastern half of the area beneath Pungo Ridge. Net recharge 

in the calibrated ground-water flow model of the southern 

watersheds varies from 0 to 4 in/yr, depending on the land-surface elevation and depth to the water table. Sensitivity analyses, however, indicated that the maximum recharge rate could 

be as high as 5 in/yr (Smith, 2003, fig. 22, p. 43).

Withdrawal of ground water in the study area is a small 

fraction of the ground-water budget. Total domestic groundwater use was estimated at 380,000 gal/d for the 5,100 

residents of the southern boroughs of Virginia Beach compared to an estimated ground-water budget of 7.0 Mgal/d for 

the southern watersheds (Smith, 2003, p. 44). Open-pit mines 

also pump water from the Columbia aquifer, but most of that 

water is returned adjacent to the pits. Pumping to irrigate 

golf courses and lawns results in a net loss of water from the 

shallow system, but those uses are sporadic and have not been 

documented for the study area.

Changes in Ground-Water Levels

In the study area, water levels in the shallow aquifers 

normally are highest in late winter or early spring when trees 

and other plants are dormant, the sun is low in the sky, and 

evapotranspiration is at a minimum. Ground-water recharge 

generally requires adequate precipitation, dormant vegetation, 

and wet soils to allow infiltration of water, and subsequent percolation of water to the water table.

Ground-water levels usually begin to decline after the 

opening of leaves in March and April, when rates of evapotranspiration increase. Water levels normally continue to 

decline through the summer to seasonal lows in the late summer and early fall when evapotranspiration is high and soil 

moisture can become depleted. The resulting dry soil typically 

retains much of the precipitation that falls during these periods, thereby limiting recharge to the water-table aquifer.

 Water levels in wells of the shallow aquifers respond to 

changes in rates of evapotranspiration and recharge; however, 

the response time depends on antecedent conditions such as 

moisture in the unsaturated zone, the depth of the water table 

below land surface, the depth of the open interval of the well, 

and the permeability of the sediments above the open interval.

Water levels have been measured in numerous wells open 

to the shallow aquifers in Virginia Beach (Smith, 2003, table 

5, p. 22). The shallow aquifers respond readily to changes in 

rates of evapotranspiration and ground-water recharge, processes which are generally controlled by natural factors, but 

also can be affected by human activities. Most well records in 

the study area indicate seasonal and periodic changes in water 

levels, but the average water levels in those wells generally 

have remained steady over the long term. A few wells in the 

southern watersheds, however, show long-term declines in 

water levels (Smith, 2003, fig. 9, p. 23).

Precipitation and ground-water levels have been unusual 

in recent years in the study area and throughout Virginia. Four 

years of drought ended in 2003, which was one of the wettest years ever recorded in Virginia. The drought had reached 

severe, extreme, or exceptional conditions in August 2002 in 

Virginia Beach and in virtually all of Virginia. The severity of 

the drought in Virginia was reduced slightly by above-average 

rainfall in September 2002. From October through December 

2002, precipitation was above average for most of the State, 
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Figure 3. Conceptual hydrogeologic framework of the shallow aquifer system in Virginia Beach, Va. (Modified from Johnson, 1999.)
Simulation of Ground-Water Flow 7

ending the drought in Virginia. Average or above-average precipitation was recorded in almost every month for the remainder of the 2003 water year, culminating with Hurricane Isabel 

in mid-September 2003 (White and others, 2004, p. 2).

As indicated by three continuous records from wells 

in the study area, water levels in the shallow aquifer system 

were affected by the drought, but recovered quickly when 

the drought ended in September 2002 (fig. 4). Water levels 

in the continuous-record wells dropped to record lows in the 

summers of 2001 and 2002 but rose quickly at the end of the 

drought, as did most wells in the shallow aquifer system. In 

the autumn of 2002, water levels rose abruptly in response 

to an exceptionally wet period, and by the middle of 2003, 

water levels were above average. One of the wells (61C 44) 

shows water levels below the NGVD of 1929 over much of 

the recorded period, which probably indicates the effects of 

nearby ground-water pumping.

Simulation of Ground-Water Flow

A calibrated computer model of the southern watersheds 

of Virginia Beach was used to simulate ground-water flow patterns in the Transition Area for this investigation (Smith, 2003, 

p. 30). The finite-difference model of the watersheds assumes 

that ground-water flow is laminar (not turbulent). The aquifers 

are assumed to be homogeneous (uniform in composition) 

and isotropic (aquifer properties do not change with flow 

direction) within each representative elemental volume (cell). 

Horizontal hydraulic conductivity of each hydrogeologic unit 

was assumed to be greater than vertical because the sediments 

of the southern watersheds generally were deposited in stratified layers (Jacob, 1963, p. 274). Temperature and density 

gradients were assumed to be uniform in the shallow aquifer 

system.

Model Layers

Model layers and hydraulic properties are the same as 

those documented previously (Smith, 2003, p. 33). The three 

conceptual units of the shallow aquifer system are assigned 

to seven model layers to represent the most common local 

configuration of shallow aquifers and confining units of the 

southern watersheds. The Columbia aquifer is divided into two 

layers of equal thickness, one upper (layer 1) and one lower 

(layer 2). The Yorktown confining unit is divided into three 

layers of equal thickness to approximate two confining units 

(layers 3 and 5) and an aquifer in between (layer 4), which 

represents the simplest configuration of the local hydrogeology throughout much of the southern watersheds of Virginia 

Beach. The Yorktown-Eastover aquifer is divided into two 

layers of equal thickness, one upper (layer 6) and one lower 

(layer 7).

Each model layer in the study area is assigned a uniform 

hydraulic conductivity except the uppermost, layer 1, representing the top half of the Columbia aquifer (fig. 5). Layer 1 

is assigned three separate zones of hydraulic conductivity representing wetland, upland, or Poquoson. The transmissivities 

within each layer of the model vary with the unit thickness.

The model layers are designated Type 3 convertible, 

meaning that the transmissivity is calculated from saturated thickness and hydraulic conductivity (McDonald and 

Harbaugh, 1988, p. 5-38). Inter-block (cell) conductance is 

calculated by harmonic means and all cells are non-wettable 

(Harbaugh and others, 2000, p. 57).

Refined Grid

To better define simulated hydrogeologic boundaries and 

ground-water flow patterns in the Transition Area, the grid of 

the previous model was refined. Cell nodes representing the 

Transition Area east of West Neck Creek were reduced from 

1,312 ft per side in the previous model to 656 ft per side in 

the refined model (fig. 6). Constant-head and drain cells were 

deleted where necessary in the refined model to conform to the 

new configuration. The change in cell size caused no change 

in the calibration statistics between the two models; Root 

Mean Square Error was 1.99 ft and no other changes were 

made to the model (Smith, 2003, p. 37).

Ground-Water Flow

The refined model was used to simulate ground-water 

flow in the Transition Area, which is divided east and west 

by West Neck Creek and the wetlands adjacent to the creek. 

Simulated ground-water flow patterns in the shallow aquifer 

system reflect the local topography as would be expected. 

Simulated water levels in the aquifers are generally higher 

beneath sand ridges and poorly drained upland flats and lower 

beneath marshes, streams, tidal inlets, and bays where the 

aquifers of the shallow system discharge.

Ground water flows into the western half of the Transition Area from higher ground to the northwest as indicated by 

simulated vectors and water-level contours (fig. 7). From the 

northwest, ground water flows toward the southeast beneath 

poorly drained upland flats fanning outward to discharge to the 

wetlands along West Neck Creek and along the North Landing 

River. Ground water flows into the eastern half of the Transition Area from higher ground to the north, flows toward the 

south beneath upland flats and sand ridges, and fans outward 

to discharge to the wetlands adjacent to West Neck Creek, and 

to the tidal inlets and wetlands of the Back Bay and the Atlantic Ocean beyond the Transition Area.

Simulated Changes in Water Levels

The refined model was used to simulate ground-water 

flow and changes in water levels caused by potential changes 
8 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

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Figure 4. Water-level measurements from the spring of 2001 to the spring of 2004 from 

continuous recorders in the shallow aquifer system in Virginia Beach, Va. (See figure 1 for 

well locations.)
Simulated Changes in Water Levels 9

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Figure 5. Simulated hydraulic conductivities of the calibrated model in the study area.
10 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

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Figure 6. Refined grid and boundaries of the ground-water flow model of the southern watersheds of Virginia Beach, Va.
Simulated Changes in Water Levels 11

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Figure 7. Simulated ground-water flow patterns in the shallow aquifer system (model layer 4) in and around the Transition Area of Virginia Beach, Va.
12 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

in pumping from the shallow aquifers of the Transition Area. 

Four potential changes in pumping were simulated: (1) cessation of dewatering at borrow pits, (2) pumping to irrigate a 

golf course, (3) pumping to irrigate lawns in a hypothetical 

neighborhood, and (4) pumping to irrigate both a golf course 

and a neighborhood of lawns during a summer drought.

Steady state was assumed for all of the simulations. 

A new steady state is reached when the temporary changes 

in water levels related to aquifer storage cease and a new, 

unchanging (steady) water level results. The new steady state 

represents the maximum change after all available storage is 

depleted and thus is a worst case for each simulation. 

Cessation of Dewatering at Borrow Pits

In Virginia Beach, surface mines that remove earth 

materials are called borrow pits. Some pits extend below the 

water table where ground water and precipitation can collect 

in pools. Most operators pump the excess water out of the pit 

(dewater) to reach sand and gravel deposits; others use floating 

barges to mine the deposits beneath the water table (wet mining). Three borrow pits operate in proximity to each other near 

West Neck Creek in the eastern Transition Area (fig. 8), one of 

which is a wet mine. Water removed from a pit can be pumped 

into a drain to run off the site or, in order to reduce the effects 

of pumping, returned to a dug channel surrounding the pit.

The ground-water flow model was used to simulate the 

potential recovery (rise in water levels) from cessation of 

dewatering operations. Constant heads were applied near the 

bottom of layer 1 in the model to represent the center nodes of 

the two mines that dewater near West Neck Creek. The constant heads were placed near the permitted operating depths of 

the mines. The model was run to steady state with, and then 

without, the constant heads, and the differences (recoveries 

in water levels) were contoured. The amount of ground water 

diverted by the pits, 0.6 Mgal/d in the simulation, is 8 percent 

of the estimated amount of ground water, approximately 7 

Mgal/d, flowing through the shallow aquifers of the southern 

watersheds of Virginia Beach (Smith, 2003, p. 44).

The simulated recoveries in the water table were generally restricted to the immediate area of the pits (fig. 8). The 

recoveries averaged about 20 ft near the center of the cells 

representing the active areas of the pits and 2 ft at the outer 

edges of the cells representing the extent of the pits. Simulated 

recoveries of 1 ft encompassed all three pits and reached 1 

mi toward the west and northwest indicating that changes in 

water levels could potentially extend to the wetlands adjacent 

to West Neck.

The pits could also have a small effect on water levels 

in the confined sand aquifer of the Yorktown Formation. 

Simulated recoveries of 3 ft encompassed the immediate area 

beneath the pits in the confined sand aquifer, layer 4 in the 

model, and recoveries of 1 ft extended 2 mi beyond the pits 

(fig. 9). One reason that the confined sand aquifer would be 

affected by pumping over a larger area than the water-table 

aquifer is that the confined sand aquifer (as simulated in the 

model) is separated from possible sources of surface water by 

continuous silt and clay units.

The simulations represent a reasonable approximation of 

the water-level recoveries in and around the pits following cessation of pumping. The amount of water that must be removed 

from the pits at any one time varies considerably with daily 

weather conditions, seasons, and changing mining operations. 

But those short-term variations and the resulting changes in 

ground-water levels average out over time. When the mines 

close and the pumping ends, ground-water levels will readily 

adjust to a new steady state; however, the new ground-water 

levels will reflect a changed topography and hydrogeology.

The topographic relief in and around the pits is more 

intricate and variations in ground-water levels are more 

complex than represented by the 7 layers of the model and the 

model cells which are 656 ft by 656 ft square in and around 

the pits. The geometry of the model is, however, refined within 

the constraints of practical topographic and hydrogeologic 

information and represents a concise and reasonable approximation of the ground-water flow system.

Pumping to Irrigate a Golf Course

Ground water is pumped from the confined sand aquifers 

and used to irrigate golf courses in Virginia Beach. One course 

located adjacent to West Neck Creek in the eastern part of 

the Transition Area uses water removed from nearby open-pit 

mines to supplement irrigation. If the mines stopped pumping 

water, that golf course would probably supplement irrigation 

with water from wells.

Ground-water pumping to irrigate golf courses would be 

expected to peak during dry summer months when evapotranspiration is at maximum. Applications for permits to withdraw 

ground water indicate a maximum rate of 300,000 gal/d could 

be pumped from a well field in the Transition Area (Malcolm 

Pirnie, 1997b, Permit Part 14, p. 1-7).

The ground-water flow model was used to simulate 

steady-state drawdowns from a hypothetical well field pumping from the confined sand aquifer (layer 4 of the model). 

Steady-state drawdowns represent the maximum possible 

drawdowns that would be caused by pumping all of the wells 

continuously until the declines in water levels ceased to 

expand or deepen—a worst-case simulation. Simulated steadystate pumping of 300,000 gal/d from 4 cells representing 4 

wells (75,000 gallons per well) that are 1,300 ft apart would 

result in aquifer drawdowns averaging 10 ft at the pumping 

cells and 1 ft at a distance of 1.2 mi from the center of the 

pumping cells (fig. 10). The extent of the 1-ft drawdown is 

virtually the same as that reported by Malcolm Pirnie (1997b, 

App. C) for a hypothetical well field of approximately the 

same location and configuration. The simulation also indicated 

that pumping 300,000 gal/d in layer 4 could cause drawdowns 

of 0.5 ft in the wetlands between the golf course and West 

Neck Creek (layer 1).
Simulated Changes in Water Levels 13

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Figure 8. Simulated recoveries caused by cessation of dewatering at two borrow pits in the Transition Area of

Virginia Beach, Va.
14 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

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Figure 9. Simulated recoveries in the sand aquifer of the Yorktown confining unit (model layer 4) caused by cessation of 

dewatering at two borrow pits in the Transition Area of Virginia Beach, Va.
Simulated Changes in Water Levels 15

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Figure 10. Simulated drawdowns in the sand aquifer of the Yorktown confining unit (model layer 4) caused by pumping 

300,000 gallons per day at a golf course in the Transition Area of Virginia Beach, Va.
16 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

Pumping to Irrigate Lawns of a Hypothetical 

Neighborhood

Thousands of residential lawns in Virginia Beach are 

watered from wells pumping the shallow aquifers. During a 

dry summer and fall in 1985, many residential irrigation wells 

failed on the Great Neck and Little Neck peninsulas. Virtually 

all of the wells that went dry during that drought used suction-lift, shallow pumps that fail below a depth of 33 to 34 feet 

(Leahy, 1986, App. A, p. 3). New wells were driven deeper 

and non-suction, eductor pumps were installed to alleviate the 

problem. The effect from numerous residential wells pumping 

simultaneously from the confined shallow aquifers to irrigate 

lawns, however, is still unknown and a concern in Virginia 

Beach.

During the growing season, one inch of water once a 

week is recommended for most lawns to maintain a healthy 

deep root system. A typical irrigated suburban lawn consumes 

10,000 gallons of water in excess of rainwater each year in the 

United States (Vickers, 2001, p. 140). That water is usually 

consumed on hot summer days when water demand is high but 

rainfall has not been adequate. If lawns were watered every 

other week because of inadequate rainfall during a typical 

12-week summer, then 10,000 gallons would generally be consumed in 6 applications, which is equal to about 1,700 gallons 

per application.

A similar approximation can be reached from another 

perspective. A suburban lot might have about 3,000 ft2 to 

water. If one inch (0.083 ft) of water is applied, then about 

249 ft3 or 1,870 gallons of water would be pumped during each 

application.

A well pumping 10 gal/min could withdraw 1,870 gallons 

in 187 minutes, about 3.1 hours. To estimate the water-level 

decline (drawdown) from pumping 10 gal/min, the Theis 

(1935) non-equilibrium equation was used in a spreadsheet 

documented by Halford and Kuniansky (2002, p. 16). The 

spreadsheet is currently (2005) available on-line at http://

water.usgs.gov/pubs/of/ofr02197/spreadsheets. A hydraulic 

conductivity of 50 ft/day was assumed for the confined sand 

aquifer (Smith, 2003, p. 35, fig. 17) and a storage coefficient 

of 0.0005–equal to an aquifer thickness of 10 ft times the 

average specific storage of 5 x 10-5/ft. The average specific 

storage is from four aquifer tests in the southern watersheds of 

Virginia Beach (Faust and others, 1981, p. 12, table 2).

Drawdown would be about 1.5 ft at a property line 50 

ft from a well pumping 1,870 gallons for 3.1 hours (fig. 11). 

Drawdown is rapid at the beginning of pumping but slows with 

time as compression of the aquifer matrix diminishes. About 

70 percent of the total drawdown would have occurred after 

3.1 hours. If pumping continued after 3.1 hours, drawdown 

would reach 2 ft (95 percent of the total drawdown) at the 

property line after 18 hours. A new steady state (virtually no 

more water from storage and no appreciable changes in water 

levels) would be approached at about 2.1 ft after 24 hours.

Nearby residents, however, might pump water at the same 

time, which could also lower water levels at the property line. 

If an adjacent neighbor with a similar-sized lot pumped ground 

water at the same rate and at the same time, drawdown at the 

property line after 3.1 hours would double to about 3 ft. A 

short time after the pumping stopped, water levels at the property line would start rising at the same rates as they declined 

and would be nearly recovered in another 3.1 hours. Other 

pumps in the neighborhood, however, could also contribute to 

drawdowns in the aquifer. These additional drawdowns would 

accumulate and dissipate in proportion to their distances from 

each other and rates of pumping.

A neighborhood covering 40 acres with about 80 homes 

(0.5 acre lots) could have 80 wells pumping at 1,870 gal/min 

or approximately 150,000 gallons of water per application. 

Every resident would not pump at the same time, however, and 

the total pumping would probably be spread out over a day’s 

time. The ground-water flow model of the southern watersheds 

was used to simulate steady-state pumping of 150,000 gal/d 

from the confined sand aquifer (layer 4 in the model).

Model cells representing the hydrologic units in the 

Transition Area east of West Neck Creek are 656 ft by 656 ft 

or 10 acres each, so that 40 acres is represented by 4 contiguous cells. Pumping 37,500 gal/d from each of the 4 cells in the 

confined sand aquifer near the east end of the Transition Area 

would cause drawdowns averaging 7 ft in the pumping cells 

and 1 ft at a distance of 0.8 mi from the center of the cells 

(fig. 12). Typically, wells pump water from an average depth 

of about 70 ft in the study area, so a maximum drawdown 

of 7 ft represents just 10 percent of the depth to the confined 

aquifer. Any such changes in water levels, however, would be 

temporary because the wells would be pumping only when 

needed, usually during the daylight hours of the growing season. The simulation also indicated that pumping 150,000 gal/d 

in layer 4 would result in negligible drawdowns in the water 

table (layer 1).

More water would be pumped to irrigate larger lawns. If 

the size of each lawn was 6,000 ft2, twice as much water, or 

300,000 gallons, might be pumped. More water also would be 

pumped if little or no rain fell on the 0.5-acre-per-lot neighborhood during the summer because residents might water every 

week instead of every other week. Pumping 300,000 gal/d 

from 4 contiguous cells in the confined sand aquifer would 

result in drawdowns averaging 15 ft in the pumping cells and 1 

ft at a distance of 1.4 mi from the center of the cells (fig. 13). 

A maximum drawdown of 15 ft represents about 20 percent of 

the available drawdown to the top of the aquifer. Such a drawdown would only be expected near the center of the neighborhood at the end of a summer day when all of the wells are 

pumping. The simulation also indicated that pumping 300,000 

gal/d in layer 4 at the hypothetical site could cause a drawdown of 0.5 ft at the edge of the wetlands adjacent to West 

Neck Creek (layer 1).

Water levels in the confined aquifer probably range from 

about 3 to 6 ft above the NGVD of 1929 in and around the 

Transition Area (fig. 7). A 15-ft drawdown could possibly 

lower water levels in the aquifer below sea level at some loca-
Simulated Changes in Water Levels 17

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tions, but only while all of the wells were pumping and only 

for short periods of time.

The simulations represent a worst case because all of the 

wells in the neighborhood are presumed to be pumping until a 

new steady state is reached. Actual drawdowns would be less 

than those simulated because water levels would decline and 

then recover around each well as the pump turned on and off. 

The extent and depth of the actual drawdowns around each 

well depend on the distance between the wells, the depth of 

the well openings, the pumping rate and efficiency of each 

well, and the hydraulic properties of the aquifer and confining 

units, which tend to differ from one location to another.

Pumping to Irrigate the Golf Course and the 

Hypothetical Neighborhood during a Summer 

Drought

Irrigation of golf courses and neighborhood lawns would 

peak during dry summer months when evapotranspiration is at 

maximum. The possible effect of pumping water from the confined sand aquifer to irrigate the golf course and the hypothetical neighborhood during a typical summer dry spell (drought) 

was simulated with the ground-water flow model. Steady-state 

pumping of 300,000 gal/d from 4 cells representing 4 wells 

1,300 ft apart at the golf course and 300,000 gal/d from 4 

contiguous cells representing the hypothetical neighborhood 

resulted in drawdowns averaging 10 ft across the cells of the 

well field and 15 ft in the cells representing the neighborhood 

(fig. 14). A drawdown of 1 ft or more encompassed the entire 

eastern half of the Transition Area and beyond. The simulation 

also indicated that pumping 300,000 gal/d at each site in layer 

4 could cause drawdowns of 1.0 ft in the wetlands between the 

golf course and West Neck Creek (layer 1).

The drought would also cause a reduction or cessation in 

ground-water recharge to the water table that, depending on 

the length of the drought, could also contribute to water-level 

declines in the confined aquifer. A 25-percent reduction in the 

rate of recharge to the calibrated model resulted in a 1- to 2-ft 

decline in the water table in the Transition area.

Steady-state drawdowns represent a worst case because 

all of the wells are presumed to be pumping until the declines 

in water levels ceased. Actual drawdowns would be less than 

that because most of the residential wells would be turned off 

before a new steady state was reached.

A more realistic simulation could assume that the wells 

at the golf course and in the neighborhood would pump for 

about half a day, equal to pumping 150,000 gal/d at each site. 

Simulated steady-state pumping of 150,000 gal/d from each 

site resulted in drawdowns averaging 5 ft around the cells 

representing the golf course wells and 7 ft around the cells 

representing the residential wells (fig. 15). A drawdown of 1 ft 

encompassed most of the eastern half of the Transition Area. 

The simulation also indicated that pumping 150,000 gal/d at 

each site in layer 4 could cause drawdowns of 0.5 ft at the 

edge of the wetlands adjacent to West Neck Creek (layer 1).

Significant drawdowns in water levels of the confined 

sand aquifer would cause temporary changes in the directions 

and velocities of ground-water flow. Pumping 150,000 gallons 

of water from each of the two sites would cause ground water 

to flow toward the center of the well field at the golf course 

and the center of the hypothetical neighborhood for as long 

as the wells were pumping, as indicated by simulated flow 

vectors and contoured water levels in the confined aquifer 

Figure 11. Drawdown 50 feet from a well pumping 10 gallons per minute from the sand aquifer of the Yorktown confining unit, 

according to the Theis (1935) non-equilibrium equation.
18 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

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Figure 12. Simulated drawdowns in the sand aquifer of the Yorktown confining unit (model layer 4) caused by pumping 

150,000 gallons per day at a hypothetical neighborhood in the Transition Area of Virginia Beach, Va.
Simulated Changes in Water Levels 19

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Figure 13. Simulated drawdowns in the sand aquifer of the Yorktown confining unit (model layer 4) caused by pumping 

300,000 gallons per day at a hypothetical neighborhood in the Transition Area of Virginia Beach, Va.
20 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

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Figure 14. Simulated drawdowns in the sand aquifer of the Yorktown confining unit (model layer 4) caused by pumping 

300,000 gallons per day at a golf course (maximum drawdown of 10 feet) and 300,000 gallons per day at a hypothetical

neighborhood (maximum drawdown of 15 feet) in the Transition Area of Virginia Beach, Va.
Simulated Changes in Water Levels 21

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Figure 15. Simulated drawdowns in the sand aquifer of the Yorktown confining unit (model layer 4) caused by pumping 

150,000 gallons per day at a golf course (maximum drawdown of 5 feet) and 150,000 gallons per day at a hypothetical

neighborhood (maximum drawdown of 7 feet) in the Transition Area of Virginia Beach, Va.
22 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

(fig. 16). The ground-water velocities would be slow in general except near the centers of the pumping cells where larger 

vectors indicate that the velocities would be faster. When 

the wells are turned off, the water levels would recover and 

normal directions and velocities of ground-water flow would 

return.

Water pumped from the confined aquifers to irrigate 

lawns and golf courses would be consumed by vegetation and 

transpired to the atmosphere. Otherwise, the diverted ground 

water would have eventually discharged to the nearby ditches, 

wetlands, ponds, tidal streams, or bays resulting in a net loss 

to the surface-water bodies. 

Irrigation pumping in the Transition Area is in response 

to temporary daily, seasonal, and annual weather conditions 

and is not continuous. In response to the pumping, any nearby 

saline water would move temporarily a short distance toward 

the wells. After the pumps were turned off and as water levels 

recovered, that saline water would move a short distance away 

from the wells. The ground water removed for irrigation for 

the worst-case simulations, 0.6 Mgal/d, is 8 percent of the estimated 7 Mgal/d that flows through the shallow aquifer system 

of the southern watersheds (Smith, 2003, p. 44).

Summary and Conclusions

Water-level changes caused by pumping water from the 

shallow aquifers of the Transition Area, a 20-mi2 buffer zone 

that bisects Virginia Beach, were simulated. The simulations included cessation of dewatering at borrow pits, pumping to irrigate a golf course, pumping to irrigate lawns of a 

hypothetical neighborhood, and pumping to irrigate the golf 

course and the lawns of a hypothetical neighborhood during a 

summer drought. These pumping changes were simulated with 

a ground-water flow model that was documented in earlier 

stages of this investigation of the Virginia Beach shallow aquifer system; the model grid was refined for this stage of

the study.

Simulated cessation of dewatering two open-pit mines in 

the Transition Area resulted in recoveries in the shallow aquifer system that were generally restricted to the immediate area 

of the pits. The recoveries averaged about 20 ft near the center 

of the cells representing the active areas of the pits and 2 ft at 

the cells representing the edges of the pits.

The effect of pumping water from the confined sand 

aquifer to irrigate a golf course was also simulated. Simulated 

steady-state pumping of 300,000 gal/d from 4 cells (75,000 

gallons per cell) that are 1,300 ft apart would result in aquifer 

drawdowns averaging 10 ft in the pumping cells and 1 ft at a 

distance of 1.2 mi from the center of the pumping cells. The 

simulation also indicated that pumping 300,000 gal/d in layer 

4 could cause drawdowns of 0.5 ft in the wetlands between 

the golf course and West Neck Creek (layer 1). Steady-state 

drawdowns represent a worst case because all of the wells 

are presumed to be pumping until the declines in water levels 

cease. Actual drawdowns would be less.

The ground-water flow model also was used to simulate 

pumping for irrigating lawns of a hypothetical neighborhood. 

A 40-acre neighborhood of 80 homes (0.5-acre lots) might 

consume 150,000 gallons of water per application. Simulated 

pumping of 150,000 gal/d from 4 model cells would cause 

drawdowns averaging 7 ft in the pumping cells and 1 ft at a 

distance of 0.8 mi from the center of the cells. The simulation 

also indicated that pumping 150,000 gal/d in layer 4 would 

result in negligible drawdowns in the water table (layer 1).

If the simulated pumping was twice as much (300,000 

gal/d), then drawdowns would average about 15 ft in the cells 

representing the neighborhood, and 1 ft at a distance of 1.4 mi 

from the center of the cells. The simulation also indicated that 

pumping 300,000 gal/d in layer 4 at the hypothetical site could 

cause a drawdown of 0.5 ft at the edge of the wetlands adjacent to West Neck Creek (layer 1). Actual drawdowns around 

each home would be less than those simulated because water 

levels would decline and then recover around each well as the 

pumps turned on and off. The extent and depth of the actual 

drawdown around each well depend on the distance between 

the wells, the depth of the well openings, the pumping rate and 

efficiency of each well, and the local hydraulic properties of 

the aquifer and confining units, which tend to differ from one 

location to another.

Pumping from the confined sand aquifer to irrigate the 

golf course and the lawns of the hypothetical neighborhood 

during a summer drought also was simulated. Steady-state 

pumping of 300,000 gal/d at the golf course and 300,000 gal/d 

at the 40-acre neighborhood of homes resulted in drawdowns 

averaging 10 ft across the cells of the well field and 15 ft in the 

cells representing the hypothetical neighborhood. A drawdown 

of 1 ft or more encompassed the entire eastern half of the 

Transition Area. The simulation also indicated that pumping 

300,000 gal/d at each site in layer 4 could cause drawdowns of 

1.0 ft in the wetlands between the golf course and West Neck 

Creek (layer 1).

Steady-state drawdowns represent a worst case because 

all of the wells are presumed to be pumping until the declines 

in water levels ceased. Actual drawdowns would be less 

because most of the residential wells would be turned off 

before a new steady state was reached.

A more realistic simulation could assume that the wells at 

the golf course and in the neighborhood would pump for about 

half a day, equal to pumping 150,000 gal/d at each site. Simulated steady-state pumping of 150,000 gal/d from each site 

resulted in drawdowns averaging 5 ft in the cells representing 

the well field of the golf course and 7 ft around the contiguous cells representing the residents’ wells. A drawdown of 1 ft 

encompassed most of the eastern half of the Transition Area. 

The simulation also indicated that pumping 150,000 gal/d at 

each site in layer 4 could cause drawdowns of 0.5 ft at the 

edge of the wetlands adjacent to West Neck Creek (layer 1).

Irrigation pumping in the Transition Area is in response 

to temporary daily and seasonal moisture conditions and is not 
Summary and Conclusions 23

Figure 16. Simulated ground-water flow patterns in the sand aquifer of the Yorktown confining unit (model layer 4) caused by pumping 

150,000 gallons per day at a golf course (adjacent to West Neck Creek) and 150,000 gallons per day at a hypothetical neighborhood in 

the Transition Area of Virginia Beach, Va.

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24 Simulated Changes in Water Levels Caused by Potential Changes in Pumping

continuous. Drawdowns in water levels of the confined sand 

aquifer would cause temporary changes in the directions and 

velocities of ground-water flow. The ground-water velocities 

would be slow in general except near the centers of the pumping wells where the velocities would be faster. When the wells 

were turned off, the water levels would recover and normal 

directions and velocities of ground-water flow would return. In 

response to the pumping, any nearby saline water would move 

temporarily a short distance toward the wells. After the pumps 

were turned off and as water levels recovered, that saline water 

would move a short distance away from the wells.

As with any numerical models of natural phenomena, 

the ground-water flow simulations presented here are only 

approximations of complex systems. Daily, seasonal, and 

annual weather conditions will affect the amount of water 

that is removed from the borrow pits or pumped to irrigate 

golf courses or neighborhood lawns at any instant in time. 

But those short-term fluctuations and the resulting changes in 

ground-water levels average out over time. The topographic 

relief in and around the transition area also is more intricate 

and the variations in ground-water levels are more complex than represented by the ground-water flow model. The 

geometry of the calibrated model is, however, refined within 

the constraints of practical topographic and hydrogeologic 

information and represents a concise and reasonable approximation of the ground-water flow system in the study area. 

The simulations thus represent reasonable approximations of 

changes in water levels and ground-water flow patterns that 

could result from potential changes in ground-water pumping 

in the study area based on the available data and the principles 

of ground-water hydraulics.

Acknowledgments

The author thanks Thomas M. Leahy, III, and Rebecca L. 

Mitchell of the Virginia Beach Department of Public Utilities, 

Water Resources Division, and the citizens of Virginia Beach 

for their cooperation and support of the shallow ground-water 

study.

The author also recognizes USGS employees Roger 

Moberg, Karl Dydak, Rick Ahlin, and Russ Lotspiech for collecting information used in the report. Thanks also to Martha 

Erwin, the editor, Brent Banks and Ted Samsel, the illustrators, and USGS colleagues’ Dennis Risser and Jack Eggleston, 

the report reviewers.

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