Simulation of proposed increases in 

ground-water withdrawals from the 

Atlantic City 800-foot sand, New Jersey 

Coastal Plain

By Daryll A. Pope

Prepared in cooperation with the New Jersey Department of Environmental Protection

Scientific Investigations Report 2006-5114

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia: 2006

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iii

Contents

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

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

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

Study Area and Hydrogeologic Setting.............................................................................................3

Simulation of ground-water flow ................................................................................................................4

Approach................................................................................................................................................4

Ground-water withdrawal data..........................................................................................................6

Simulation of potentiometric surfaces, drawdowns, and flow budgets......................................6

RASA model..................................................................................................................................6

CPOPT model................................................................................................................................6

CMAC model...............................................................................................................................10

Limitations of the models...................................................................................................................10

Simulated effects of ground-water withdrawals ...................................................................................13

Full-allocation conditions ..................................................................................................................13

Scenarios .............................................................................................................................................13

Scenario 1 ...................................................................................................................................13

Scenario 2 ...................................................................................................................................14

Scenario 3 ...................................................................................................................................14

Scenario 4 ...................................................................................................................................14

Scenario 5 ...................................................................................................................................15

Scenario 6 ...................................................................................................................................15

Scenario 7 ...................................................................................................................................15

Effects of increased withdrawals on ground-water flow...................................................15

Summary and Conclusions.........................................................................................................................16

References Cited..........................................................................................................................................17

Figures

1. Map showing location of the study area, New Jersey Coastal Plain..................................2

2. Diagrammatic hydrogeologic section A-A’ through the New Jersey Coastal Plain .........4

3-5. Maps showing—

3. Estimated potentiometric surfaces for the Atlantic City 800-foot sand,

New Jersey, using the RASA model.................................................................................7

4. Simulated drawdown from simulated 1998 conditions to full-allocation 

conditions and incremental drawdown from the previous scenario for 

scenarios 1 through 7, Atlantic City 800-foot sand, New Jersey.................................8

5. Estimated potentiometric surfaces resulting from full-allocation conditions 

and drawdown from full-allocation levels in successive scenarios 1 through 

7 that each include the drawdown from previous scenarios, Atlantic City

800-foot sand, New Jersey ................................................................................................9
iv

6. Graphs showing flow budgets for the confined freshwater part of the Atlantic 

City 800-foot sand, New Jersey, under full-allocation conditions and scenarios 

1 through 7: (a) flow from sources, (b) change from previous scenario, 

(c) increase from full-allocation...............................................................................................10

7. Conceptual cross section showing flow-budget area and flow terms for the

Atlantic City 800-foot sand, New Jersey.................................................................................11

8. Map showing simulated potentiometric surfaces and pathlines from the

250-milligram-per-liter isochlor using the Cape May Atlantic City 800-foot sand

model, Atlantic City 800-foot sand, New Jersey....................................................................12

Tables

1. Description of model scenarios for the Atlantic City 800-foot sand and the 

deep part of the Kirkwood-Cohansey aquifer system, New Jersey. ...................................5

2. Travel times of particles from the 250-milligram-per-liter isochlor to production 

wells, Atlantic City 800-foot sand, New Jersey. ....................................................................13
Conversion Factors and Datums

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

cubic foot (ft3) 7.4805 gallon (gal) 

Flow rate

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

million gallons per year (Mgal/yr) 15.99 cubic meter per second (m3/s)

Hydraulic conductivity

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

Transmissivity*

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

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

(NGVD 1929).

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

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

*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.
vi
Simulation of proposed increases in ground-water 

withdrawals from the Atlantic City 800-foot sand, 

New Jersey Coastal Plain

By Daryll A. Pope

Abstract

The confined Atlantic City 800-foot sand and the 

unconfined Kirkwood-Cohansey aquifer system (surficial 

aquifer) are major sources of water for southeastern New 

Jersey. Because of recent concerns about streamflow depletion 

resulting from ground-water withdrawals and the potential 

ecological effects on stream habitat in the area, the focus on 

future withdrawals has been shifted away from the surficial 

aquifer to the confined Atlantic City 800-foot sand until the 

effects of increased withdrawals from the surficial aquifer can 

be investigated. A study was conducted to evaluate the effects 

of seven proposed increases in ground-water withdrawals from 

the Atlantic City 800-foot sand and the Kirkwood-Cohansey 

aquifer system on the Atlantic City 800-foot sand. The proposed withdrawals are increases above the 2004 allocated rates 

(full allocation). The effects of full-allocation ground-water 

withdrawals and the cumulative effect of withdrawals for each 

of seven proposed increases in withdrawals were simulated 

using three previously published ground-water flow models: the New Jersey Coastal Plain Regional Aquifer System 

Analysis model, the Coastal Plain Optimization model, and a 

model of the Atlantic City 800-foot sand in Atlantic County, 

New Jersey. These models were used to simulate changes in 

water levels, the source supplying the increased ground-water 

flow, and the effects on saltwater movement towards production wells in Cape May County as a result of the proposed 

increased withdrawals at proposed or existing wells.

The results of the simulations represent the effects of the 

proposed increase from full-allocation withdrawals to an additional 1,825 Mgal/yr (million gallons per year) from the Atlantic City 800-foot sand and an additional 1,045 Mgal/yr from 

the deep part of the Kirkwood-Cohansey aquifer system near 

the updip limit of the Atlantic City 800-foot sand. Most of the 

simulated decline in water levels in Atlantic County occurred 

as the result of the proposed increased withdrawals simulated 

for the New Jersey American Water Company wells. Simulated declines in water levels in Cape May were caused mainly 

by the simulated increased withdrawals for the Cape May City 

Desalination Plant wells. The additional water to supply the 

proposed increases in the scenarios was primarily horizontal 

flow from the unconfined updip part of the Kirkwood-Cohansey aquifer system, which accounted for 63 percent of the 

inflow, and flow from the overlying Kirkwood-Cohansey 

aquifer system into the Atlantic City 800-foot sand, which 

supplied 27 percent of the additional water. Because the withdrawals were made from the confined aquifer and the deeper 

part of the unconfined aquifer, the effect on streamflow was 

substantially less than would have occurred had the withdrawals been made directly from the shallower parts of the unconfined aquifer. The travel times from the 250-mg/L isochlor to 

production wells in Stone Harbor were longer as a result of all 

the additional withdrawals. For some scenarios, withdrawals 

in Atlantic County caused the saltwater to move slightly faster 

towards the production wells. These effects were offset by the 

increase in travel time caused by the potential increased withdrawals simulated for the Cape May City desalination wells, 

which either diverted water towards the desalination wells or 

increased the travel time towards production wells.

Introduction

The confined Atlantic City 800-foot sand and the overlying unconfined Kirkwood-Cohansey aquifer system are major 

sources of water for southeastern New Jersey (fig. 1). Water 

levels in the Atlantic City 800-foot sand near Atlantic City 

were as low as 100 ft below NGVD of 1929 in 1998 and have 

been slowly declining. There are concerns about the longterm sustainability of the Atlantic City 800-foot sand and the 

ability to supply projected future ground-water withdrawals. 

In addition, recent concerns about streamflow depletion due 

to ground-water withdrawals from the unconfined KirkwoodCohansey aquifer system and potential ecologic effects on 

stream habitat in the area, including part of the Pinelands 

National Reserve, have shifted focus on future withdrawals 

away from the surficial aquifer to the confined Atlantic City 

800-foot sand until the effects of increased withdrawals from 

the surficial aquifer can be studied. In 2004, a large number of 

requests for increased withdrawals (in excess of the previously 
0 10 20 MILES

0 10 20 KILOMETERS

40

30'

39

30'

40

39

76 75 30' 75 74

Maryland

Pennsylvania

Delaware

New York

74 30'

Ocean

County

Burlington

County

Atlantic

County

Cumberland

County

Delaware Bay

Atlantic City

Atlantic Ocean

Hamilton Township Barrier Islands proposed well

New Jersey

American

proposed wells

Cape May

County

Base from U.S. Geological Survey Digital data, 1:2,000,000

Universal Transverse Mercator Projection, Zone 18, NAD 83 EXPLANATION

OUTCROP OF THE KIRKWOOD FORMATION

FLOW BUDGET AREA--Extent of budget area for

the freshwater part of the Atlantic City

800-foot sand

ESTIMATED LOCATION OF THE

250-MILLIGRAM-PER-LITER CHLORIDE

ISOCHLOR

UPDIP LIMIT OF THE CONFINING UNIT

OVERLYING THE ATLANTIC CITY

800-FOOT SAND

LIMIT OF THE NEW JERSEY RASA MODEL

LIMIT OF THE CAPE MAY ATLANTIC CITY

800-FOOT SAND MODEL

LINE OF HYDROLOGIC SECTION--

Shown in figure 2

A A’

Stafford Township

proposed wells

Cape May City

proposed

well

Barnegat Township

proposed well

Little Egg Harbor

proposed well

Atlantic City MUA

proposed well

Stone Harbor

New Jersey

A’

A

Figure 1. Location of the study area, New Jersey Coastal Plain.

   Simulation of proposed increases in withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain
permitted allocation) from the Atlantic City 800-foot sand 

were received and are under consideration by the New Jersey 

Department of Environmental Protection (NJDEP). Water 

managers want to be able to evaluate the cumulative and incremental effects of these proposed increases on the Atlantic City 

800-foot sand. Therefore, the U.S. Geological Survey (USGS), 

in cooperation with the NJDEP, conducted a study to simulate 

the effects of these proposed increases in withdrawals from 

this aquifer.

Threats to the sustainable water supply in the Atlantic City 800-foot sand include saltwater intrusion from the 

Atlantic Ocean, saltwater intrusion from Delaware Bay, 

and potential effects of withdrawals from the Atlantic City 

800-foot sand on the overlying Kirkwood-Cohansey aquifer 

system. Saltwater intrusion is possible in Cape May where the 

250-mg/L isochlor is located onshore (fig. 1) and the Atlantic 

City 800-foot sand crops out beneath Delaware Bay. Although 

the 250-mg/L isochlor is at least 5 miles offshore of Atlantic 

City (fig. 1) and is considered a long-term threat to water 

quality, increased withdrawals from the Atlantic City 800-foot 

sand might increase the rate of saltwater intrusion in Atlantic 

County from offshore areas. Withdrawals from the Atlantic 

City 800-foot sand could contribute to streamflow depletion in 

the Kirkwood-Cohansey aquifer system.

The USGS used three published ground-water flow 

models of the New Jersey Coastal Plain to simulate the effects 

of withdrawals from the Atlantic City 800-foot sand. The 

New Jersey Coastal Plain Regional Aquifer System Analysis (RASA) model (Voronin, 2003) was used to evaluate the 

decline in water levels that could result from the proposed 

increased withdrawals. The RASA model also was used to 

produce flow budgets for the freshwater part of the aquifer 

to determine the source of water for each of the proposed 

increases in withdrawals. The model of the Atlantic City 

800-foot sand in Cape May County (CMAC) (Voronin and 

others, 1996) was used to determine the effects of the various 

proposed increases in withdrawals on the rate and direction 

of water movement from the current location of the 250-mg/L 

isochlor. The New Jersey Coastal Plain Optimization model 

(CPOPT) (Pope and Gordon, 1999) was used to provide 

boundary conditions to the smaller-scale CMAC model. The 

CPOPT model simulates the location of an idealized sharp 

interface between freshwater and saltwater in the Coastal Plain 

aquifers. Because the interface is closer to the shore south and 

east of Cape May, the CPOPT model provides more realistic 

boundary flows than the RASA model.

Purpose and Scope

This report describes simulations in which increased 

withdrawals were made from the Atlantic City 800-foot sand 

and the unconfined Kirkwood-Cohansey aquifer system to 

determine the effects on the Atlantic City 800-foot sand. Fullallocation conditions were simulated to determine conditions 

that would occur if all wells in the Atlantic City 800-foot sand 

were pumped at the permitted allocation rate (2004). Output 

from the full-allocation simulation serves as a baseline for 

comparison with the output from the seven alternate withdrawal scenarios. The seven scenarios are described along 

with the incremental and cumulative effects of the increased 

withdrawals on the water levels in the Atlantic City 800-foot 

sand and on sources of water to wells. The report describes the 

models used to simulate the withdrawal scenarios and provides details on the proposed increases in withdrawals. Output 

from the simulations—water levels, drawdowns, flow budgets, 

and travel times of particles from saltwater areas to wells—are 

presented in figures and tables.

Study Area and Hydrogeologic Setting

The study area includes Atlantic and Cape May Counties, 

and parts of Ocean and Burlington Counties and is defined 

by the limits of the Atlantic City 800-foot sand in the Coastal 

Plain of New Jersey (fig. 1). The study area can be defined as 

the freshwater part of the Atlantic City 800-foot sand from the 

updip limit of the confining unit overlying the Atlantic City 

800-foot sand to the 250-mg/L isochlor (fig. 1).

The hydrogeologic framework used in this report is that 

developed for the USGS New Jersey Coastal Plain RASA 

Project (Zapecza, 1989). The New Jersey Coastal Plain is 

a seaward-dipping wedge of unconsolidated sediments that 

range in age from Cretaceous to Holocene. These sediments 

consist mainly of clay, silt, sand, and gravel. Units that are 

mostly sand and gravel are permeable and are considered 

aquifers, and those that are mostly silt and clay are relatively 

impermeable and are considered confining units. The aquifers 

of interest in this report are the Piney Point aquifer, the Atlantic City 800-foot sand, and the Kirkwood-Cohansey aquifer 

system (fig. 2). The Kirkwood-Cohansey aquifer system is an 

unconfined aquifer composed of sediments of the Cohansey 

and Kirkwood Formations except where overlain by Quaternary sediments in Cape May County. In updip areas, the Kirkwood Formation constitutes the deeper part of the aquifer system. In downdip areas, the Kirkwood Formation is confined 

and is referred to as the Atlantic City 800-foot sand. Major 

confining units are the composite confining unit which separates the Atlantic City 800-foot sand and the underlying Piney 

Point aquifer and the confining unit overlying the Atlantic City 

800-foot sand. The outcrop of the Kirkwood-Cohansey aquifer 

system and the updip limit of the confining unit overlying the 

Atlantic City 800-foot sand are shown in figure 1. Further 

information on the hydrogeology of the Kirkwood-Cohansey 

aquifer system and the Atlantic City 800-foot sand is available 

in McAuley and others (2001) and Sugarman (2001).

The potentiometric surface of the Atlantic City 800-foot 

sand ranges in altitude from 15 ft above NGVD of 1929 near 

the updip edge of the overlying confining unit to greater than 

100 ft below NGVD of 1929 within the cone of depression 

centered near Atlantic City in 1998 (Lacombe and Rosman, 

2001, sheet 3). The aquifer is recharged by vertical flow 

Introduction   
from the overlying Kirkwood-Cohansey aquifer system. This 

recharge occurs throughout the extent of the aquifer, but is 

much more significant near the updip limit of the confining 

unit overlying the Atlantic City 800-foot sand where the two 

aquifers are in direct contact and where the overlying confining unit is thinner and more permeable. The aquifer also 

is recharged by lateral flow from the Kirkwood-Cohansey 

aquifer system in areas near the updip limit of the overlying 

confining unit.

Simulation of ground-water flow

Approach

The effects of full-allocation ground-water withdrawals (the maximum allowed by the NJDEP permit) and the 

cumulative effects of withdrawals for each of seven proposed 

increases in withdrawals from the Atlantic City 800-foot sand 

were simulated. The scenarios are listed in table 1 in the order 

in which they were simulated, along with the current allocation, the proposed increase in withdrawals for each scenario 

and details about the withdrawal rates for the wells. All 

scenario simulations were based on full-allocation withdrawals from the Atlantic City 800-foot sand. The full-allocation 

conditions serve as a baseline for scenarios 1 through 7. The 

simulation of additional withdrawals for each scenario was 

cumulative; each scenario included the increase described for 

that scenario as well as the increases for all previous scenarios. 

The simulations were done using three different ground-water 

flow models, the revised New Jersey Coastal Plain Regional 

Aquifer Systems Analysis model (RASA) (Voronin, 2003), 

the Coastal Plain Optimization model (CPOPT) (Pope and 

Gordon, 1999), and a model of the Atlantic City 800-foot sand 

in Atlantic County (CMAC) (Voronin and others, 1996). The 

order of the scenarios was set by NJDEP to reflect the order in 

which they would be considering the proposed permit modifications.

The RASA model was used to simulate the effects of the 

increased withdrawals throughout the Atlantic City 800-foot 

sand. The Atlantic City 800-foot sand in the RASA model is 

the confined part of the lower Kirkwood-Cohansey aquifer 

system and confined Kirkwood aquifer model layer. The scale 

of the model is fine enough to simulate existing and additional proposed wells adequately. The output from the RASA 

model is displayed by presenting potentiometric surfaces 

and drawdown from the scenarios and flow budgets for the 

freshwater part of the Atlantic City 800-foot sand. The original 

calibration of the RASA model, including a description of the 

model boundary conditions, is documented in Martin (1998). 

Revisions to the model and a recalibration to 1998 conditions 

are described in Voronin (2003).

The CPOPT model was used to provide boundary conditions to the CMAC model of the Atlantic City 800-foot sand 

in Cape May. The CPOPT model also was used to simulate the 

freshwater/saltwater interface (50 percent of seawater concentration) and, therefore, provide adequate boundary flows 

to the CMAC submodel. The grid size of the CPOPT model, 

however, was too coarse to use for simulations of existing and 

proposed withdrawals throughout the Atlantic City 800-foot 

sand. The simulation of the sharp interface and calibration 

Confined part of Cohansey the Sand

Rio Grande water-bearing zone

Lower aquifer

Middle aquifer

Upper aquifer

Englishtown aquifer system

Vincentown aquifer

Wenonah-Mount Laurel aquifer

Piney Point aquifer

Atlantic City 800-foot sand

Kirkwood-Cohansey

aquifer system

Confining unit

EXPLANATION

NOT TO SCALE

Bedrock

Holly Beach

water-bearing zone Fall

Line

A A'

Potomac-RaritanMagothy

aquifer system

DELAWARE

RIVER ATLANTIC

OCEAN

Location of section shown in inset map on figure 1

Figure 2. Diagrammatic hydrogeologic section A-A’ through the New Jersey Coastal Plain. (Modified from Zapecza and others, 1987)

 Simulation of proposed increases in withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain
Table 1. Description of model scenarios for the Atlantic City 800-foot sand and the deep part of the Kirkwood-Cohansey aquifer system, New Jersey.

[Total withdrawals for scenarios 1 through 7 are cumulative; each scenario includes proposed increases from all previous scenarios. NJDEP, New Jersey Department of Environmental Protection; Mgal/yr, million gallons per year; cfs, cubic feet per second; MUA, Municipal Utility Authority; confined, withdrawals were made from Atlantic City 800-foot sand; unconfined, withdrawals were made from the deep part of the unconfined Kirkwood-Cohansey aquifer system; NA, not available.]

Scenario 

identifier Description

NJDEP water 

allocation 

permit number Characteristics

Existing 

allocation rate 

(2005)

(Mgal/yr)

Proposed 

increased 

rate 

(Mgal/yr)

Total rate 

for permit 

(Mgal/yr)

Part of model 

unit in which 

new withdrawals occur

FA Full allocation in 

Atlantic City 800-foot sand

NA Full allocation based on 1998 water-use for all wells in the 

Atlantic City 800-foot sand. All other aquifers pumping at 1998 rates.

NA NA NA NA

S1 Hamilton Township 5034 New well 10 added for proposed increase. Two existing 

wells pumping at full-allocation rate.

768 429 1,197 Confined

S2 New Jersey American 

Water Company

5206X Increase of 625 Mgal/yr at four existing wells. New well 21 

in Cohansey aquifer pumping at 430 Mgal/yr. 

925 625 1,550 Confined

S3 Barnegat Township 5301 New well 6 in deep part of Kirkwood-Cohansey aquifer 

system.

0 289 289 Unconfined

S4 Cape May City 5210 New well 7 for desalinization. Total of 900 Mgal/yr split 

evenly between existing well 6 and new well 7.

415 485 900 Confined

S5 Atlantic City MUA 5306 New well 27. Total of 900 Mgal/yr, split evenly between 

existing wells 14 and 25 and new well 27.

730 170 900 Confined

S6 Little Egg Harbor 

Township

5037 New well 11 added for proposed increase. Three existing 

wells pumping at full-allocation rate.

577 116 693 Confined

S7 Stafford Township 5038 Three new wells (8, 9, and 10) pumping equal amounts 

from the deep part of Kirkwood-Cohansey aquifer system updip from confining unit limit. Existing wells pumping at full allocation from the Atlantic City 800-ft sand.

653 756 1,409 Unconfined 

Simulation of ground-water flow   
of the CPOPT model are documented in Pope and Gordon 

(1999).

The CMAC model is a fine-scale model of the Atlantic 

City 800-foot sand nested within the regional CPOPT model. 

The CMAC model was used to represent the ground-water 

flow in the Atlantic City 800-foot sand in Cape May County at 

a scale that is appropriate for particle-tracking analysis. Pathlines and travel times of particles placed along the 250-mg/L 

isochlor in the Atlantic City 800-foot sand were tracked 

towards discharge locations at production wells in Stone Harbor (fig. 1). The proposed increase in withdrawals for Cape 

May City (scenario 4) is for desalination, and simulated withdrawals were made from the seawater side of the 250-mg/L 

isochlor. The CMAC model was used to evaluate the effects of 

the increased withdrawals for desalination on the movement of 

the 250-mg/L isochlor in the Atlantic City 800-foot sand. The 

hydrogeology of the Atlantic City 800-foot sand in the Cape 

May area and the design and calibration of the CMAC model 

are documented in Voronin and others (1996).

Ground-water withdrawal data

In the full-allocation simulation, withdrawals from the 

Atlantic City 800-foot sand were set at full-allocation rates as 

of 2004, and withdrawal rates in all other Coastal Plain aquifers were set at reported 1998 rates. The distribution of fullallocation withdrawals among a group of wells corresponding 

to a single NJDEP permit was determined using the percentage 

of the reported 1998 withdrawals that was produced by each 

of the individual wells. That is, a well that is pumping at 50 

percent of the 1998 withdrawals for a permit was estimated to 

pump 50 percent of the full-allocation withdrawals. In cases 

where only monthly allocation numbers were available for the 

Atlantic City 800-foot sand, annual allocations were estimated 

by multiplying the monthly allocation by 12.

Simulation of potentiometric surfaces, 

drawdowns, and flow budgets

RASA model

The estimated potentiometric surfaces using the RASA 

model for the Atlantic City 800-foot sand under full allocation 

and those generated for each scenario are shown in figure 3. 

The estimated potentiometric surface is calculated by subtracting the difference between the 1998 calibrated potentiometric 

surface and the potentiometric surface measured in 1998 from 

the simulated potentiometric surface for each scenario. The 

estimated potentiometric surfaces show the overall effect of 

the proposed increase in withdrawals on the regional resource. 

For each scenario, the locations of the existing and proposed 

wells associated with the allocation permit for which the 

increase is requested are shown in red. All other wells active 

during the simulation are shown in blue. The simulated incremental drawdowns resulting from each scenario are shown in 

figure 4. The full-allocation simulated drawdown map shows 

the drawdown from simulated 1998 conditions to full allocation. The simulated drawdowns for successive scenarios 1 

through 7, each of which includes drawdown from the previous scenario, are shown in figure 4. The cumulative simulated 

drawdown from full allocation for each scenario and the estimated potentiometric surface under full allocation simulated 

using the RASA model is shown in figure 5.

Flow budgets for the freshwater part of the aquifer under 

full allocation and in each of the seven scenarios are shown in 

figure 6. The flows from various sources to the freshwater part 

of the Atlantic City 800-foot sand [in cubic ft per second (cfs)] 

for full allocation conditions and for each scenario are shown 

in figure 6a. The incremental change in flow from the previous 

scenario for each source for each scenario is shown in figure 

6b. The change in flow, for each source, from the full-allocation condition is shown in figure 6c. The area for which the 

flow budgets are calculated and a conceptual cross section 

showing the flow-budget terms are shown in figure 7. In areas 

updip from the updip limit of the confining unit overlying the 

Atlantic City 800-foot sand (fig. 1), the Kirkwood-Cohansey 

aquifer system was simulated in the RASA model using two 

model layers. The deeper of these two layers represents the 

Kirkwood-Cohansey aquifer system in areas updip from the 

limit of the overlying confining unit and the Atlantic City 800-

foot sand in areas downdip of the limit line. The shallower of 

the two layers represents the unconfined Kirkwood-Cohansey 

aquifer system. The flow term “From overlying unconfined 

Kirkwood-Cohansey aquifer system” refers to flow from the 

unconfined Kirkwood-Cohansey aquifer system (which overlies the Atlantic City 800-foot sand) vertically downward into 

the Atlantic City 800-foot sand. The flow term “From unconfined aquifer updip” refers to flow within the model layer representing the Atlantic City 800-foot sand in areas where it is 

unconfined and the Kirkwood part of the Kirkwood-Cohansey 

aquifer system. The updip limit line of confining unit overlying the Atlantic City 800-foot sand is shown in blue on figures 

1, 3, 4, and 5. The flow term “From underlying Piney Point 

aquifer” represents vertical flow from the underlying Piney 

Point aquifer to the Atlantic City 800-foot sand. The flow term 

“From 250-mg/L saltwater zone” represents flow from the 

zone within the Atlantic City 800-foot sand where the chloride 

concentration in the water is assumed to be greater than 250 

mg/L. This zone corresponds to the area east and south of the 

250-mg/L isochlor shown in black on figures 1, 3, 4, and 5. 

The flow term “From Delaware Bay” represents flow from 

the area in Delaware Bay where the Atlantic City 800-foot 

sand may be unconfined beneath the bay and, therefore, is in 

contact with saltwater.

CPOPT model

The potentiometric surfaces simulated by the CPOPT 

model are similar to those simulated by the RASA model, but 

because of the larger model grid size of the CPOPT model, the 

cones of depression simulated by the CPOPT model are not as 

   Simulation of proposed increases in withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain
Ocean

Burlington

Cumberland

Cape May

7415’

7430’

3945’

7445’

3930’75

7515’

3915’

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

7415’

7430’

3945’

7445’

3930’75

7515’

3915’

Atlantic

Ocean

Burlington

Cumberland

Cape May

Atlantic

Ocean

Burlington

Cumberland

Cape May

Atlantic

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

-20

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-30

-30

-40 -40 -40

-140

-30

-30

-30

-30

-140

10 20 MILES

0 10 20 KILOMETERS

0

UPDIP LIMIT OF CONFINING UNIT OVERLYINGTHE ATLANTIC CITY 800-FOOT SAND

ESTIMATED LOCATION OF 250-MILLIGRAM-PER LITERISOCHLOR

ESTIMATED POTENTIOMETRIC SURFACE IN THE ATLANTICCITY-880 FOOT SAND--Estimated potentiometric surface is simulated potentiometric surface minus the difference between the calibrated 1998 simulated potentiometric surface and the observed 1998 water levels. Contour interval is variable. Datum is NGVD of 1929

PRODUCTION WELLS--Location of production wells in theAtlantic City 800-foot sand 

EXPLANATION

PRODUCTION WELLS ASSOCIATED WITH SCENARIO--Location of production wells in the Atlantic City 800-foot sand that were associated with each scenario. Withdrawals were not necessarilyincreased at all wells (see table 1)

Full-Allocation heads Scenario 1 Scenario 2 Scenario 3 Scenario 4

Scenario 5 Scenario 6 Scenario 7

-20

Figure 3. Estimated potentiometric surfaces for the Atlantic City 800-foot sand, New Jersey, using the RASA model.

Simulation of ground-water flow   
Ocean

Burlington

Cumberland

Cape May

7415’

7430’

3945’

7445’

3930’75

7515’

3915’

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

7415’

7430’

3945’

7445’

3930’75

7515’

3915’

Atlantic

Ocean

Burlington

Cumberland

Cape May

Atlantic

Ocean

Burlington

Cumberland

Cape May

Atlantic

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN ATLANTIC OCEAN ATLANTIC OCEAN 35

5

10

15

20

25

1

5

10

1

10

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10

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15

1

10 20 MILES

0 10 20 KILOMETERS

0

UPDIP LIMIT OF CONFINING UNIT OVERLYINGTHE ATLANTIC CITY 800-FOOT SAND

ESTIMATED LOCATION OF 250-MILLIGRAM-PER LITERISOCHLOR

SIMULATED DRAWDOWN IN ATLANTIC CITY800-FOOT SAND, IN FEET--Shows drawdownfrom previous scenario resulting from the simulatedincrease in withdrawals. Contour interval is variable

PRODUCTION WELLS--Location of production wells in theAtlantic City 800-foot sand 

EXPLANATION

PRODUCTION WELLS ASSOCIATED WITH SCENARIO--Location of production wells in the Atlantic City 800-foot sand that were associated with each scenario. Withdrawals were not necessarilyincreased at all wells (see table 1)

Drawdown to full-allocation Scenario 1 Scenario 2 Scenario 3 Scenario 4

Scenario 5 Scenario 6 Scenario 7

5

Figure 4. Simulated drawdown from simulated 1998 conditions to full-allocation conditions and incremental drawdown from the previous scenario for scenarios 1 through 7, Atlantic City 800-foot sand, New Jersey.

   Simulation of proposed increases in withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain
Ocean

Burlington

Cumberland

Cape May

7415’

7430’

3945’

7445’

3930’75

7515’

3915’

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

74 39 45’ 73 45 39 30’ 

Atlantic

Ocean

Burlington

Cumberland

Cape May

7415’

7430’

3945’

7445’

3930’75

7515’

3915’

Atlantic

Ocean

Burlington

Cumberland

Cape May

Atlantic

Ocean

Burlington

Cumberland

Cape May

Atlantic

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

NEW

JERSEY

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

ATLANTIC

OCEAN

-20

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1

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10 20 MILES

0 10 20 KILOMETERS

0

UPDIP LIMIT OF CONFINING UNIT OVERLYINGTHE ATLANTIC CITY 800-FOOT SAND

ESTIMATED LOCATION OF 250-MILLIGRAM-PER LITERISOCHLOR

ESTIMATED POTENTIOMETRIC SURFACE IN THE ATLANTICCITY-880 FOOT SAND UNDER FULL ALLOCATION--Estimated potentiometric surface is simulated potentiometricsurface minus the difference between the calibrated 1998simulated potentiometric surface and the observed 1998 waterlevels. Contour interval is 20 feet. Datum is NGVD of 1929

SIMULATED DRAWDOWN IN ATLANTIC CITY 800-FOOT SAND, IN FEET--Shows drawdown from full-allocation conditions resulting from the simulated increase in withdrawals. Contour interval is variable

PRODUCTION WELLS--Location of production wells in theAtlantic City 800-foot sand 

EXPLANATION

PRODUCTION WELLS ASSOCIATED WITH SCENARIO--Location of production wells in the Atlantic City 800-foot sand that were associated with each scenario. Withdrawals were not necessarilyincreased at all wells (see table 1)

Full-Allocation heads Scenario 1 Scenario 2 Scenario 3 Scenario 4

Scenario 5 Scenario 6 Scenario 7

Figure 5. Estimated potentiometric surfaces resulting from full-allocation conditions and drawdown from full-allocation levels in successive scenarios 1 through 7 that each include the drawdown from previous scenarios, Atlantic City 800-foot sand, New Jersey.

Simulation of ground-water flow 
deep or as wide as those simulated by the RASA model. In the 

Cape May area, the simulated potentiometric surfaces from the 

CPOPT model are similar to those from the RASA model. The 

location of the saltwater interface in the Atlantic City 800-foot 

sand under full-allocation conditions or in any of the increased 

withdrawal scenarios does not change substantially from the 

position simulated in 1988 (Pope and Gordon, 1999). Boundary conditions for the CMAC model were obtained laterally 

along the limits of the CMAC model and vertically from the 

overlying and underlying aquifers.

CMAC model

The simulated potentiometric surfaces and particle pathlines from the 250-mg/L isochlor in the Atlantic City 800-foot 

sand for full-allocation conditions and the seven scenarios 

produced by the CMAC model are shown in figure 8. The 

location of the 250-mg/L isochlor and withdrawals for each 

scenario (shown as proportional circles) also are shown. Only 

in scenario 4, which has additional withdrawals for Cape May 

City, are the additional withdrawals located within the limits 

of the CMAC model. All other scenarios show the effects of 

withdrawals outside Cape May County (outside the limits of 

the CMAC model) on the movement of freshwater near the 

250-mg/L isochlor in the Atlantic City 800-foot sand in Cape 

May County (fig. 1). Travel times from particle starting locations to discharge points for all scenarios are shown in table 2. 

The particle identifier numbers shown in table 2 are the same 

as those shown on fig. 8.

Limitations of the models

All models are an approximation of the actual groundwater-flow system and are based on simplified representations of complex heterogeneous systems. Assumptions such 

as isotropy and vertical homogeneity within each layer are 

examples of simplified representations that can be a source of 

simulation errors. In addition, each of the three models used 

in this report were designed to answer specific questions and, 

therefore, have unique limitations. The RASA model was 

designed primarily to simulate freshwater flow in the confined 

part of the ground-water system of the New Jersey Coastal 

Plain on a regional scale. Simulation of flow to streams in the 

unconfined Kirkwood-Cohansey aquifer system is included in 

the RASA model as a boundary condition for deeper confined 

aquifers. Therefore, the simulated effects of scenario withdrawals on streamflow in streams overlying the KirkwoodCohansey aquifer system are limited. However, the simulation 

of the interaction between the Kirkwood-Cohansey aquifer 

system and the confined Atlantic City 800-foot sand is appropriate because the RASA model was designed to represent the 

confined aquifers. The CPOPT model has the same types of 

limitations as the RASA model but because the CPOPT model 

is more coarsely discretized, the limitations are greater. The 

CPOPT model, however, simulates the freshwater gradients 

(a) Flow from sources

10

15

20

25

30

FA S1 S2 S3 S4 S5 S6 S7

SCENARIO

FLOW, IN CUBIC FEET PER

SECOND

(b) Change from previous scenario

-1.00

-0.50

0.00

0.50

1.00

1.50

S1 S2 S3 S4 S5 S6 S7

SCENARIO

FLOW, IN CUBIC FEET PER SECOND 

(c) Increase from Full Allocation

-0.50

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

S1 S2 S3 S4 S5 S6 S7

SCENARIO

FLOW, IN CUBIC FEET PER SECOND 

From overlying unconfined

Kirkwood-Cohansey

aquifer system 

From unconfined part of 

aquifer, updip 

From underlying Piney Point 

aquifer

From 250-milligram-per liter

saltwater zone

From Delaware Bay

0

5

-1.50

-1.00

EXPLANATION

Figure 6. Flow budgets for the confined freshwater part of the 

Atlantic City 800-foot sand, New Jersey, under full-allocation 

conditions and scenarios 1 through 7: (a) flow from sources, (b) 

change from previous scenario, (c) increase from full-allocation. 

(mg/L, milligram per liter; FA, Full Allocation, S1, indicates scenario 

number).

10 Simulation of proposed increases in withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain
Ocean

Burlington

Cumberland

Cape May

7415’

7430’

3945’

7445’

3930’75

7515’

3915’

74 39 45’ 73 45 39 30’ 

Atlantic

NEW

JERSEY ATLANTIC

OCEAN

10 20 MILES

0 10 20 KILOMETERS

0

UPDIP LIMIT OF CONFINING UNIT OVERLYINGTHE ATLANTIC CITY 800-FOOT SAND

ESTIMATED LOCATION OF 250-MILLIGRAM-PER LITERISOCHLOR

UPDIP LIMIT OF CONFINING UNIT OVERLYING THEATLANTIC CITY 800-FOOT SAND IN DELAWARE BAY

FLOW--From 250-milligram-per liter saltwater zone

EXPLANATION

BUDGET AREA--Extent of budget area for thefreshwater part of the Atlantic City 800-foot sand

FLOW--From unconfined part of aquifer, updip

FLOW--From Delaware Bay

Delaware

Bay

Model layer representingCohansey aquifer

Model layer representingKirkwood Formation andAtlantic city 800-foot sand

Kirkwood-Cohanseyaquifer system

Kirkwood-Cohanseyaquifer system

Atlantic City800-foot sand

From underlyingPiney Point aquifer

From overlyingunconfined KirkwoodCohansey aquifer system

Well

Well

Pond

From 250-mg/Lsaltwater zone

Saltwater

Budget Area 

Atlantic Ocean

From unconfinedpart of aquifer, updip

Confining unit underlying Atlantic City 800-foot sand

West East

Figure 7. Conceptual cross section showing flow-budget area and flow terms for the Atlantic City 800-foot sand, New Jersey.

Simulation of ground-water flow 11
39

22’30”

7445’

7452’30”

3915’75

3907’30”

7507’30”

74 30’ 39 15’ 74 22’30” 39 22’30” 74 37’30” 

3922’30”

7445’

7452’30”

3915’75

3907’30”

7507’30”

74 30’ 39 15’ 74 22’30” 39 22’30” 74 37’30” 74 30’ 39 15’ 74 22’30” 39 22’30” 74 37’30” 74 30’ 39 15’ 74 22’30” 39 22’30” 74 37’30” 74 30’ 39 15’ 74 22’30” 39 22’30” 74 37’30” 

1 2 3 4 56 7

8

1 2 3 4 56 7

8

1 2 3 4 567

8

1 2 3 4 56 7

8

1 2 3

4 5 67

8

1 2 3

4 5 6

7

8

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4 5 6 7

8

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4 5 67

8

10 20 MILES

0 10 20 KILOMETERS

0

ESTIMATED LOCATION OF 250-MILLIGRAM-PER LITERISOCHLOR

SIMULATED POTENTIOMETRIC CONTOUR--Shows thealtitude at which water levels would have stood in tightly case wells. Contour interval is 10 feet. Datum is NGVD of 1929

FLOW PATH OF WATER PARTICLE DETERMINED BYPARTICLE-TRACKING ANALYSIS OF SIMULATIONRESULTS--Number is particle identifier

EXPLANATION

Full-Allocation heads Scenario 1 Scenario 2 Scenario 3 Scenario 4

Scenario 5 Scenario 6 Scenario 7

5

1

GROUND-WATER WITHDRAWALS--In million gallons per year

Less than 51

51 - 105.99

106 - 189.99

190 - 297.99

298 - 483.98

Figure 8. Simulated potentiometric surfaces and pathlines from the 250-milligram-per-liter isochlor using the Cape May Atlantic City 800-foot sand model, Atlantic City 800-foot sand, New Jersey.

12 Simulation of proposed increases in withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain
near the saltwater-freshwater interface and is, therefore, more 

appropriate than the RASA model is for providing boundary 

conditions to the CMAC model near the interface in Cape May 

County. The CMAC model was designed with finer grid spacing than the RASA model and includes a thin clay layer within 

the Atlantic City 800-foot sand. This model was designed 

to estimate particle travel-times from the existing 250-mg/L 

isochlor to production wells. This travel time, however, is an 

estimate of the advective movement of the ground water near 

the interface and not of the actual interface itself, which was 

not simulated.

Because the increased withdrawals simulated in this 

report are from the confined aquifers or from deep within the 

unconfined aquifer, no attempt was made to quantify the effect 

on streamflow in individual streams in the outcrop area of the 

Kirkwood-Cohansey aquifer system. The simulation of these 

proposed increases is appropriate given the purposes for which 

the models were constructed and will not violate the assumptions associated with the boundary conditions of the original 

models.

Simulated effects of ground-water 

withdrawals

Simulation results for the full-allocation simulation and 

the seven scenarios representing proposed increases in groundwater withdrawals and the effects on water levels, drawdown 

in water levels, and travel times from the 250 mg/L isochlor to 

production wells are discussed in the following sections.

Full-allocation conditions

Under full-allocation conditions, the estimated potentiometric surface in the Atlantic City 800-foot sand developed 

a cone of depression centered on the barrier islands with 

minimum water levels of almost 120 ft below NGVD of 1929 

(fig. 3). Results from the RASA model show that the increase 

of withdrawals from 1998 rates to full-allocation rates caused 

water levels to decline by 15 to 30 ft from simulated 1998 

water levels on the barrier island and in onshore areas in 

Atlantic County. Declines of 15 to 25 ft from simulated 1998 

water levels occurred in southern Cape May County. Declines 

of greater than 35 to 40 ft from simulated 1998 water levels 

occurred at the center of a local cone in Ocean County. Under 

full-allocation conditions, the wells at Stone Harbor will not 

be affected by the 250-mg/L chloride water for at least 720 

years (table 2, fig. 8).

Scenarios

Simulation results for the seven scenarios representing 

proposed increases in ground-water withdrawals are discussed 

in the following sections.

Scenario 1

Scenario 1 represents a proposed increase of 429 Mgal/yr 

for the Hamilton Township Municipal Utility Authority 

(MUA) wells. All of the additional withdrawals were simulated at one proposed well location (well 10) in the Atlantic 

City 800-foot sand (table 1). Withdrawals from all existing 

wells were simulated at full-allocation rates. The Hamilton 

Township wells are located near the updip limit of the aquifer 

in Atlantic County. Simulated drawdowns of 10 ft to greater 

than 25 ft below the full-allocation potentiometric surface 

occurred in the vicinity of the well field (fig. 4) as a result of 

the increased withdrawals simulated using the RASA model. 

The flow budget from the RASA model (fig. 6a) shows that 

the additional water is supplied primarily by horizontal flow 

from the unconfined updip part of the Kirkwood-Cohansey 

aquifer system. This increase could affect streamflow near the 

updip limit of the aquifer; however, the effect would probably be distributed over a larger area than would be affected if 

Table 2. Travel times of particles from the 250-milligram-per-liter isochlor to production wells, Atlantic City 800-foot sand, New Jersey.

[Labels S1 through S7 refers to scenario 1 through scenario 7]

Particle 

identifier

Travel time, in years

Full allocation S1 S2 S3 S4 S5 S6 S7

1 1,700 1,600 1,500 1,500 2,100 2,100 2,100 2,100

2 1,800 1,700 1,600 1,600 1,000 1,000 1,000 1,000

3 1,800 1,800 1,700 1,700 760 760 760 760

4 1,500 1,500 1,400 1,400 1,100 1,100 1,100 1,100

5 1,100 1,100 1,000 1,000 7,000 8,100 8,100 8,100

6 870 860 830 830 1,300 1,300 1,300 1,300

7 730 720 710 710 920 910 910 910

8 720 720 730 730 750 740 740 740

Simulated effects of ground-water withdrawals 13
withdrawals were made directly from the unconfined Kirkwood-Cohansey aquifer system.

Travel times for some of the particles tracked using the 

CMAC model from the 250-mg/L isochlor to production wells 

in Cape May County are slightly shorter than those in fullallocation conditions. The shortest travel time (particle 8) was 

still 720 years (table 2; fig. 8).

Scenario 2

Scenario 2 represents a proposed increase of 

1,055 Mgal/yr for the New Jersey American Water Company 

(NJAWC) with 625 Mgal/yr of the total equally simulated at 

four wells in the Atlantic City 800-foot sand. The remaining 

430 Mgal/yr is simulated at a proposed well location (well 21) 

in the unconfined Kirkwood-Cohansey aquifer system (table 

1). These withdrawals caused simulated drawdown of 5 to 

15 ft from scenario 1 over much of the extent of the Atlantic 

City 800-foot sand in Atlantic County (fig. 4). The simulated 

cone of depression near Atlantic City deepened as much as 25 

ft (fig. 3) using the RASA model. The flow budget produced 

from the RASA model (fig. 6a) shows that most of the additional water for scenario 2 is provided by horizontal flow from 

the unconfined updip part of the Kirkwood-Cohansey aquifer 

system. Most of the remaining water to supply the increased 

withdrawals is flow from the overlying Kirkwood-Cohansey 

aquifer system and from the saltwater part of the Atlantic City 

800-foot sand.

The simulated increase in flow from the saltwater part 

of the aquifer gives warning of potential saltwater flow from 

the east. However, because the 250-mg/L isochlor is still more 

than 5 miles offshore from Atlantic City, the simulated problem is not immediate. Travel times from the 250-mg/L isochlor in Cape May County using the CMAC model decreased 

slightly from those in scenario 1, with the shortest travel time 

being 710 years (table 2).

The effect of the additional 430 Mgal/yr withdrawals 

from the unconfined Kirkwood-Cohansey aquifer system cannot be adequately evaluated using the RASA model because 

that model was designed to simulate the confined aquifers in 

the New Jersey Coastal Plain. The effect of these withdrawals 

on streamflow and the water table near the well field can be 

evaluated using other methods.

Scenario 3

Scenario 3 represents a proposed increase of 289 Mgal/yr 

for the Barnegat Township MUA (table 1). Because the 

proposed well is updip from the area where the confining unit 

overlying the Atlantic City 800-foot sand pinches out (fig. 4), 

the withdrawals are assumed to come from the deep unconfined updip part of the Kirkwood-Cohansey aquifer system. 

In areas updip from the limit of the Atlantic City 800-foot 

sand, the Kirkwood-Cohansey aquifer system was modeled 

using two layers. The proposed well was modeled in the lower 

of these two layers. The drawdown and flow budget for the 

Atlantic City 800-foot sand generated using the RASA model 

for this scenario were essentially unchanged from the previous 

scenario (fig. 6a, b, and c). Because the simulated withdrawals 

are from the unconfined updip part of the Kirkwood-Cohansey 

aquifer, they affect simulated water levels in the overlying 

Kirkwood-Cohansey aquifer system and simulated flow to and 

from streams. The coarse grid size of the RASA model, however, is not appropriate to quantify these changes on a local 

scale. Travel times from the 250-mg/L isochlor to production 

wells in Cape May County (table 2; fig. 8) generated using the 

CMAC model were unchanged by the increased withdrawals 

from this proposed well in southern Ocean County from those 

shown in scenario 2.

Scenario 4

Scenario 4 represents a proposed increase of 485 Mgal/yr 

in withdrawals for the Cape May City desalination wells 

located near the tip of the Cape May Peninsula. The total withdrawals for desalination are 900 Mgal/yr to be taken equally 

from two wells (existing well 6 and proposed well 7) (table 1). 

Using the RASA model, the increase causes additional drawdown from the previous scenario of 10 to 30 ft in the onshore 

part the Atlantic City 800-ft sand in Cape May County where 

the 250-mg/L isochlor is present (fig. 4).

Because the flow budget area in the RASA model was 

defined for the Atlantic City 800-foot sand as the freshwater 

part of the aquifer, the Cape May withdrawals do not occur 

inside the flow budget area. Therefore, the changes to the 

flow-budget graphs resulting from this increase (fig. 6b) are 

different from those of other scenarios in that the increased 

demand causes flow to change direction toward the saltwater 

zone. The negative value of the flow term “From 250-mg/L 

saltwater zone” indicates that water flows out of the flowbudget area toward the saltwater zone to provide the additional 

water for this scenario. Small increases in flow from above, 

from updip, and from the bay into the flow budget area also 

provide the additional water.

The simulated travel times and pathlines of the particles 

from the 250-mg/L isochlor to production wells in Cape May 

County generated using the CMAC model are shown in table 

2 and figure 8. In this scenario, the wells at Stone Harbor are 

not affected by the 250-mg/L chloride water for 750 years. 

The travel times for particle numbers 2, 3, and 4 are significantly shorter than under full-allocation conditions because 

these particles now move towards the Cape May City desalination wells rather than towards Stone Harbor. Travel times 

for particle numbers 1, 5, 6, and 7 are longer in this scenario 

than under full-allocation conditions because of changing flow 

patterns that occur from the addition of the desalination wells. 

Travel time for particle 8 (the particle with the shortest travel 

time under full-allocation conditions) to the Stone Harbor 

wells is basically unaffected (travel time increases slightly to 

750 years) by the increase in withdrawals for desalination.

14  Simulation of proposed increases in withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain
Increased flow into the flow-budget area is from updip 

areas, the overlying aquifers, and from Delaware Bay (fig. 

6b). Flow from the Delaware Bay is of concern because of the 

potential for higher concentrations of chloride. The location of 

the outcrop of the Atlantic City 800-foot sand under the Delaware Bay is not clearly known and is estimated to be farther 

west than particle 1 shown on figure 8. The travel time for this 

particle to the Cape May desalination wells is simulated to be 

2,100 years.

Scenario 5

Scenario 5 represents a proposed increase of 170 Mgal/yr 

for the Atlantic City MUA (table 1). Withdrawals are at equal 

rates from a proposed well (well 27) and two existing wells 

(14 and 25). Drawdown from the previous scenario generated by the RASA model ranges from 0 to more than 5 ft 

over almost all of the Atlantic City 800-foot sand in Atlantic 

County (fig. 4). The flow budget from the RASA model (fig. 

6) shows that most of the additional water for this scenario 

comes from the unconfined updip part of the KirkwoodCohansey aquifer system and from the overlying KirkwoodCohansey aquifer system.

Travel times from the 250-mg/L isochlor to production 

wells in Cape May County (table 2; fig. 8) simulated using 

the CMAC model were not greatly affected by the increased 

withdrawals from central Atlantic County.

Scenario 6

Scenario 6 represents a proposed increase of 116 Mgal/yr 

for the Little Egg Harbor Township MUA wells (table 1). All 

of the additional water is withdrawn at the location of proposed new well 11. Simulated drawdown in the RASA model 

is limited to the immediate vicinity of the well field where 

more than 15 ft of drawdown from the previous scenario 

occurs locally (fig. 4). Because the withdrawals are near the 

updip limit of the aquifer, most of the additional water for this 

scenario comes from the unconfined updip part of the Kirkwood-Cohansey aquifer system (fig. 6).

Travel times from the 250-mg/L isochlor to production 

wells in Cape May County (table 2; fig. 8) generated using the 

CMAC model were unchanged from scenario 5.

Scenario 7

Scenario 7 represents a proposed increase of 756 Mgal/yr 

for the Stafford Township MUA wells (table 1). All of the 

additional water is withdrawn from three proposed wells (8, 

9, and 10). These new wells are located updip from the line 

where the Atlantic City 800-foot sand becomes confined, and 

withdrawals are simulated from the lower model layer representing the deep part of the unconfined Kirkwood-Cohansey 

aquifer system. Because of the location of the increased withdrawals, very little additional drawdown from what was simulated in scenario 6 occurred in the Atlantic City 800-foot sand 

using the RASA model (fig. 4). Drawdown was limited to the 

immediate vicinity of the well field. The three proposed wells 

are outside the flow-budget area for the Atlantic City 800-foot 

sand and, therefore, do not substantially affect the flow budget 

of the confined Atlantic City 800-foot sand determined using 

the RASA model (fig. 6a, b, and c). The area was modeled 

as unconfined; therefore, additional withdrawals could affect 

streamflow associated with this aquifer. The effects of these 

withdrawals on streamflow associated with, and water levels 

in, the overlying Kirkwood-Cohansey aquifer system could 

not be evaluated using the RASA model.

Travel times from the 250-mg/L isochlor to production 

wells in Cape May County (table 2; fig. 8) generated using the 

CMAC model were unchanged from scenario 6.

Effects of increased withdrawals on groundwater flow

The model generated water levels that result from 

incremental increases from full-allocation withdrawals to an 

additional 1,825 Mgal/yr of withdrawals from the Atlantic 

City 800-foot sand (scenarios 1, 2, 4, 5, and 6) and 1,045 

Mgal/yr from the deep part of the Kirkwood-Cohansey aquifer 

system near the updip limit of the Atlantic City 800-foot sand 

(scenarios 3 and 7). These increases resulted in a decrease in 

water levels at the cone of depression near Atlantic City from 

almost 120 ft below NGVD of 1929 to almost 140 ft below 

NGVD of 1929 (fig. 3). Most of this decline occurred as the 

result of the increased withdrawals simulated in scenario 2. 

Simulated water levels in Cape May County declined from 

altitudes ranging from -20 to -100 ft to altitudes ranging from 

-20 to -120 ft (fig. 3). These declines in water levels in Cape 

May County were caused mainly by the increased withdrawals 

simulated in scenario 4 (fig. 4).

Simulated drawdowns from full-allocation levels (fig. 

5) were greatest in Atlantic County and southern Cape May 

County. The drawdown in Atlantic County was greater than 

25 ft near the Hamilton Township wells (S1) and greater than 

10 ft over much of the extent of the Atlantic City 800-foot 

sand in the rest of Atlantic County. These drawdowns were 

primarily the result of the increased withdrawals by the Hamilton Township (S1) and NJAWC (S2) wells. Smaller effects 

resulted from the increased withdrawals by the Atlantic City 

MUA (S5). The drawdown from full-allocation conditions in 

Cape May of from 5 ft to more than 25 ft was the result of the 

increased withdrawals by the Cape May City wells (S4).

The additional water to supply the increased withdrawals in scenarios 1 through 7 came primarily from horizontal 

flow from the deep unconfined updip part of the KirkwoodCohansey aquifer system, which accounted for 63 percent 

of the inflow. Flow from the overlying Kirkwood-Cohansey 

aquifer system into the Atlantic City 800-foot sand supplied 

27 percent of the additional water. Flow from the Delaware 

Bay (10 percent) and from the underlying Piney Point aquiSimulated effects of ground-water withdrawals 15
fer (6 percent) accounted for the remaining inflows. Outflow 

was represented by an increase in flow towards the 250-mg/L 

isochlor as a result of the withdrawals of salty water in Cape 

May City (accounted for 6 percent decrease in total flow). The 

combined inflow from the Kirkwood-Cohansey aquifer system 

supplied 90 percent of the new withdrawals. Because the withdrawals were made from the confined part of the aquifer, the 

effect on streamflow was not as great as it would have been 

had the withdrawals come directly from the unconfined part of 

the Kirkwood-Cohansey aquifer system. The effect of withdrawals from the confined part of the aquifer would probably 

be distributed over a larger area in the unconfined part because 

of the intervening confining unit and would likely have less 

effect on streamflow in the individual streams nearest the 

proposed withdrawals.

The travel times of particles from the 250-mg/L isochlor 

to production wells in Stone Harbor were longer than those for 

full-allocation conditions as a result of the additional withdrawals for scenarios 1 through 7 (fig. 8). Withdrawals for 

scenarios 1, 2, 5, and 6 caused the saltwater to move slightly 

faster towards the production wells than did withdrawals in 

the other scenarios. These effects were small compared to the 

effects on travel time caused by the increased withdrawals in 

scenario 4 by the Cape May City desalination wells, which 

either diverted water towards the production wells or increased 

the travel time towards the Stone Harbor production wells.

Summary and Conclusions

There are concerns about the long-term sustainability of 

the Atlantic City 800-foot sand in southeastern New Jersey and 

its ability to supply water for projected future growth. Recent 

(2004) concerns about streamflow depletion have caused 

water-resource managers to consider a shift away from use 

of the unconfined Kirkwood-Cohansey aquifer system to the 

confined Atlantic City 800-foot sand. Threats to the sustainable water supply in the Atlantic City 800-foot sand include 

saltwater intrusion from the Atlantic Ocean and Delaware Bay 

and potential effects of withdrawals from the Atlantic City 

800-foot sand on the overlying Kirkwood-Cohansey aquifer 

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

with the New Jersey Department of Environmental Protection 

(NJDEP), conducted a study that included seven scenarios 

simulating proposed increases in withdrawals from the Atlantic City 800-foot sand that are under review by the NJDEP.

Full-allocation ground-water withdrawals and the cumulative withdrawals for each of seven scenarios with proposed 

increases in withdrawals were simulated. Maps of simulated 

potentiometric surfaces, drawdowns, and pathlines from the 

250-mg/L isochlor to production wells were produced along 

with flow budgets and travel times from saltwater zones 

(defined as areas where the chloride concentration is assumed 

to be above 250-mg/L). All scenarios were based on full-allocation withdrawals for the Atlantic City 800-foot sand. The 

simulation of additional withdrawals for each scenario was 

cumulative; each scenario included the increase described for 

that scenario as well as for all previous scenarios. The simulations were done using three different ground-water-flow models, which included the New Jersey Coastal Plain Regional 

Aquifer System Analysis (RASA) model, the Coastal Plain 

Optimization model (CPOPT), and a model of the Atlantic 

City 800-foot sand in Atlantic County (CMAC). The increased 

withdrawals simulated in this study were made from the Atlantic City 800-foot sand or from deep within the unconfined 

Kirkwood-Cohansey aquifer system, and no attempt was made 

to quantify the effect of the increased withdrawals on streamflow in individual streams.

The increase in withdrawals from actual use in 1998 to 

full-allocation rates caused water levels to decline by 15 to 

30 ft from simulated 1998 water levels on the barrier islands 

and in onshore areas in Atlantic County. Declines of 15 to 25 

ft also occurred in southern Cape May County. Large declines 

of more than 35 ft occurred over localized areas in Ocean 

County. Under full-allocation conditions, the simulations 

showed that wells at Stone Harbor would not be affected by 

salty water for at least 720 years.

The proposed increase in withdrawals for Hamilton 

Township wells (scenario 1) resulted in simulated drawdown 

in the vicinity of the well field of 10 ft to greater than 25 ft 

below full-allocation potentiometric surfaces. Most of the 

additional water was supplied by horizontal flow from the 

unconfined updip part of the Kirkwood-Cohansey aquifer 

system. Travel times from the 250-mg/L isochlor to production 

wells in Cape May County were only slightly affected.

The proposed increase in withdrawals for the New Jersey 

American Water Company (NJAWC) wells (scenario 2) from 

the Atlantic City 800-foot sand caused simulated drawdown 

from scenario 1 of 5 to 15 ft over much of the extent of the 

Atlantic City 800-foot sand in Atlantic County and deepened 

the cone of depression near Atlantic City. Most of the additional water for scenario 2 was provided by horizontal flow 

from the unconfined updip part of the Kirkwood-Cohansey 

aquifer system. Travel times from the 250-mg/L isochlor in 

Cape May County decreased slightly. The effect of the additional 430 Mgal/yr withdrawals by NJAWC wells (scenario 

2) from the Kirkwood-Cohansey aquifer system cannot be 

adequately evaluated using the RASA model. The effect of 

these withdrawals on streamflow and the water table near the 

well field could not be determined.

In the scenario for Barnegat Township wells (scenario 

3), the proposed increase in withdrawals at a proposed well 

near the updip limit of the Atlantic City 800-foot sand was 

simulated. These withdrawals are assumed to be from the deep 

unconfined updip part of the Kirkwood-Cohansey aquifer system. The drawdown and flow budget for the Atlantic City 800-

foot sand for this scenario were essentially unchanged from 

the previous scenario because the withdrawals were made 

from the unconfined updip part of the Kirkwood-Cohansey 

aquifer system.

16 Simulation of proposed increases in withdrawals from the Atlantic City 800-foot sand, New Jersey Coastal Plain
Scenario 4 represents the proposed increase in withdrawals for the Cape May City Water Department wells for use 

in desalination. This increase caused additional simulated 

drawdowns of 10 to greater than 30 ft from the previous 

scenario in the onshore part of Cape May County where the 

250 mg/L isochlor is present. Most of the water to meet this 

increased demand came from a decrease in flow from the 250-

mg/L chloride zone. In this scenario, the wells at Stone Harbor 

would not be affected by the 250-mg/L chloride water for at 

least 750 years. Travel times for three particles from the 250-

mg/L isochlor were significantly shorter than in full-allocation 

conditions, but these particles now moved towards the Cape 

May City desalination wells rather than towards Stone Harbor 

wells. The simulated increase would not cause the 250-mg/L 

chloride water at particle 8 to reach the Stone Harbor wells 

any faster. Travel times for some particles were longer in this 

scenario than under full-allocation conditions.

Scenario 5 represents the proposed increase in withdrawals for the Atlantic City MUA wells. Simulated drawdown 

ranges from 0 to greater than 5 ft over much of the extent of 

the Atlantic City 800-foot sand in Atlantic County. Most of 

the additional water for this scenario flowed horizontally from 

the unconfined updip part of the Kirkwood-Cohansey aquifer 

system and from the overlying Kirkwood-Cohansey aquifer 

system. Travel times from the 250-mg/L isochlor to production 

wells in Cape May County were not greatly affected by these 

increased withdrawals from central Atlantic County.

Increased withdrawals for the Little Egg Harbor Township MUA wells (scenario 6) resulted in simulated drawdown 

only in the immediate vicinity of the well field. Because the 

withdrawals are near the updip limit of the aquifer, most of the 

additional water for this scenario came from the unconfined 

updip part of the Kirkwood-Cohansey aquifer system. Travel 

times from the 250-mg/L isochlor to production wells in Cape 

May County were not affected by these withdrawals.

The proposed increase in withdrawals for Stafford Township MUA wells (scenario 7) caused very little drawdown 

from the previous scenario and did not substantially affect the 

flow budget of the confined Atlantic City 800-foot sand. Simulated drawdown was limited to the immediate vicinity of the 

well field. Because the area was modeled as unconfined, there 

could be effects on streamflow resulting from these withdrawals; however, the effects of these withdrawals on streamflow 

and water levels in the Kirkwood-Cohansey aquifer system 

could not be evaluated using the RASA model. Travel times 

from the 250-mg/L isochlor to production wells in Cape May 

County were not affected by these withdrawals.

As a result of the increased withdrawals, simulated water 

levels in the vicinity of Atlantic City decreased from almost 

120 ft below NGVD of 1929 to almost 140 ft below NGVD of 

1929. The additional withdrawals in scenario 2 caused most 

of this decline. The additional water to meet the increased 

withdrawals in scenarios 1 through 7 was primarily supplied 

by horizontal flow from the unconfined updip part of the 

Kirkwood-Cohansey aquifer system, which accounted for 63 

percent of the inflow. In general, the travel times from the 

250-mg/L isochlor to production wells in Stone Harbor would 

be longer as a result of all the additional withdrawals for scenarios 1 through 7. The major change in simulated travel times 

was caused by withdrawals from Cape May City desalination 

wells, which either diverted water from the 250-mg/L isochlor 

towards the production wells or increased the travel time 

towards production wells.

References Cited

Lacombe and Rosman, 2001, Water levels in, extent of freshwater in, and water withdrawals from ten confined aquifers, New Jersey and Delaware Coastal Plain, 1998: U.S. 

Geological Survey Water-Resources Investigations Report 

00-4143, 10 plates.

Martin, Mary, 1998, Ground-water flow in the New Jersey 

Coastal Plain: U.S. Geological Survey Professional Paper 

1404-H, 146 p.

McAuley, S.D., Barringer, J.L., Paulachok, G.N., Clark, J.S., 

and Zapecza, O.L., 2001, Ground-water flow and quality 

in the Atlantic City 800-foot sand, New Jersey: New Jersey 

Geological Survey Report GSR 41, 86 p.

Pope, D.A., and Gordon, A.D., 1999, Simulation of groundwater flow and movement of the freshwater-saltwater 

interface in the New Jersey Coastal Plain: U.S. Geological 

Survey Water-Resources Investigations Report 98-4216, 

159 p.

Sugarman, P.J., 2001, Hydrostratigraphy of the Kirkwood and 

Cohansey Formations of Miocene age in Atlantic County 

and vicinity, New Jersey: New Jersey Geological Survey 

Report GSR 40, 26 p.

Voronin, L.M., Spitz, F.J., and McAuley, S.D., 1996, Evaluation of saltwater intrusion and travel time in the Atlantic 

City 800-foot sand, Cape May County, New Jersey, 1992, 

by use of a coupled-model approach and flow-path analysis: 

U.S. Geological Survey Water-Resources Investigations 

Report 95-4280, 38 p.

Voronin, L.M., 2003, Documentation of revisions to the 

Regional Aquifer System Analysis model of the New Jersey 

Coastal Plain: U.S. Geological Survey Water-Resources 

Investigations Report WRIR 03-4268, 49 p.

Zapecza, O.S., Voronin, L.M., and Martin, Mary, 1987, 

Ground-water withdrawal and water-level data used to 

simulate regional flow in the major Coastal Plain aquifers 

of New Jersey: U.S. Geological Survey Water-Resources 

Investigations Report 87-4038, 120 p., 10 pl.

Zapecza, O.S., 1989, Hydrogeologic framework of the New 

Jersey Coastal Plain: U.S. Geological Survey Professional 

Paper 1404-B, 47 p., 24 pl.

References Cited 17