U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007-5193

Prepared in cooperation with the New Jersey Department of Environmental Protection

Recovery of Ground-Water Levels From 1988 to 2003 and 

Analysis of Potential Water-Supply Management Options 

in Critical Area 1, East-Central New Jersey

Recovery of Ground-Water Levels From 

1988 to 2003 and Analysis of Potential 

Water-Supply Management Options in 

Critical Area 1, East-Central New Jersey

By Frederick J. Spitz, Martha K. Watt, and Vincent T. dePaul

In cooperation with the New Jersey Department of Environmental Protection

Scientific Investigations Report 2007–5193

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Spitz, F.J., Watt, M.K., and dePaul, V.T., 2008, Recovery of ground-water levels from 1988 to 2003 and analysis of 

potential water-supply management options in Critical Area 1, east-central New Jersey: U.S. Geological Survey Scientific Investigations Report 2007-5193, 40 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................4

Description of Study Area ...................................................................................................................4

Hydrogeology.........................................................................................................................................4

Previous Investigations........................................................................................................................5

Recovery Of Ground-Water Levels .............................................................................................................5

Ground-Water-Flow System................................................................................................................5

Changes in Withdrawals and Water Levels from 1988 to 2003 .....................................................6

Evaluation Of Water-Supply Management Options ...............................................................................11

Ground-Water-Flow Model ...............................................................................................................11

Buffer Analysis....................................................................................................................................12

Water-Supply Management Models ...............................................................................................14

Ground-Water Management Process....................................................................................14

Formulation .................................................................................................................................16

Input. ................................................................................................................................19

Output. ................................................................................................................................19

Base Applications......................................................................................................................19

Current (2003) Well Locations (Management Models MM01 and MM02)..............19

Regularly Spaced Well Locations (Management Model MM03)..............................24

Clean Slate (Management Model MM04) ....................................................................24

Reallocation to Small Volume Wenonah-Mount Laurel Aquifer and Englishtown 

Aquifer System Potable Users (Management Model MM05)......................27

Trade-Off Analysis .....................................................................................................................27

Maximum Allowable Drawdown in the Wenonah-Mount Laurel aquifer and 

Englishtown aquifer system (Management Models MM06 and MM07)....27

Minimum Allowable Head in the Wenonah-Mount Laurel aquifer and 

Englishtown aquifer system (Management Model MM08)..........................29

Maximum Allowable Drawdown at the 250-mg/L Isochlor in the Upper 

Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy 

Aquifers (Management Models MM09 and MM10)......................................29

Maximum Allowable Velocity at the 250-mg/L Isochlor in the Upper 

Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy 

Aquifers (Management Models MM11 and MM12)......................................29

Maximum Allowable Withdrawal Rates at Wells (Management Models 

MM13 and MM14)...............................................................................................32

Comparison of Water-Supply Management Models ...........................................................32

Limitations of the Analysis..........................................................................................................................35

Summary and Conclusions.........................................................................................................................36

References Cited..........................................................................................................................................37

Glossary.........................................................................................................................................................39
iv

Figures

1. Map showing location of Water Supply Critical Area 1, east-central New Jersey ..........3

2. Generalized hydrogeologic section through the New Jersey Coastal Plain......................5

3–6. Maps, sections, and graphs showing—

3. Wenonah-Mount Laurel aquifer (a) potentiometric surfaces along section 

A-A’, 1988-2003; (b) withdrawals in the depleted zone of Critical Area 1, 

1980-2003; and (c) water-level changes in Critical Area 1, 1988-2003, 

east-central New Jersey....................................................................................................7

4. Englishtown aquifer system (a) potentiometric surfaces along section 

A-A’, 1988-2003; (b) withdrawals in the depleted zone of Critical Area 1, 

1980-2003; and (c) water-level changes in Critical Area 1, 1988-2003, 

east-central New Jersey....................................................................................................8

5. Upper Potomac-Raritan-Magothy aquifer (a) potentiometric surfaces along 

section A-A’, 1988-2003; (b) withdrawals in the depleted zone of Critical Area 1, 

1980-2003; and (c) water-level changes in Critical Area 1, 1988-2003, 

east-central New Jersey....................................................................................................9

6. Middle Potomac-Raritan-Magothy aquifer (a) potentiometric surfaces along 

section A-A’, 1988-2003; (b) withdrawals in the depleted zone of Critical Area 1, 

1980-2003; and (c) water-level changes in Critical Area 1, 1988-2003, 

east-central New Jersey..................................................................................................10

7–13. Maps showing—

7. Transects and withdrawal points used in the buffer analysis for the (a) Upper 

and (b) Middle Potomac-Raritan-Magothy aquifers in Critical Area 1, 

east-central New Jersey..................................................................................................13

8. Aquifer subareas and management model constraints for the (a) WenonahMount Laurel aquifer, (b) Englishtown aquifer system, (c) Upper PotomacRaritan-Magothy aquifer, and (d) Middle Potomac-Raritan-Magothy aquifer 

in Critical Area 1, east-central New Jersey..................................................................15

9. Simulated potentiometric surface in the (a) Wenonah-Mount Laurel aquifer, 

(b) Englishtown aquifer system, (c) Upper Potomac-Raritan-Magothy aquifer, 

and (d) Middle Potomac-Raritan-Magothy aquifer for management model 

MM01 in Critical Area 1, east-central New Jersey .....................................................20

10. Simulated optimal withdrawals in the (a) Wenonah-Mount Laurel aquifer, 

(b) Englishtown aquifer system, (c) Upper Potomac-Raritan-Magothy aquifer, 

and (d) Middle Potomac-Raritan-Magothy aquifer for management model 

MM01 in Critical Area 1, east-central New Jersey .....................................................21

11. Simulated constraints in the (a) Wenonah-Mount Laurel aquifer, (b) Englishtown 

aquifer system, (c) Upper Potomac-Raritan-Magothy aquifer, and (d) Middle 

Potomac-Raritan-Magothy aquifer for management model MM01 in Critical Area 

1, east-central New Jersey..............................................................................................22

12. Current (2003) well locations and unmanaged withdrawals used in the (a) 

Wenonah-Mount Laurel aquifer, (b) Englishtown aquifer system, (c) Upper 

Potomac-Raritan-Magothy aquifer, and (d) Middle Potomac-RaritanMagothy aquifer for management model MM01 in Critical Area 1, 

east-central New Jersey..................................................................................................25
v

13. Regularly spaced well locations used in the (a) Wenonah-Mount Laurel aquifer, 

(b) Englishtown aquifer system, (c) Upper Potomac-Raritan-Magothy aquifer, 

and (d) Middle Potomac-Raritan-Magothy aquifer for management model 

MM03 in Critical Area 1, east-central New Jersey .....................................................26

14–19. Graphs showing—

14. (a) Trade-off curves and (b) source of water to wells for management 

models MM06 and MM07 with various maximum allowable drawdowns in 

the Wenonah-Mount Laurel aquifer and Englishtown aquifer system for 

current (2003) and regularly spaced well locations in Critical Area 1, 

east-central New Jersey..................................................................................................28

15. (a) Trade-off curve and (b) source of water to wells for management model 

MM08 with various minimum allowable head in the Wenonah-Mount Laurel 

aquifer and Englishtown aquifer system for regularly spaced well locations 

in Critical Area 1, east-central New Jersey..................................................................30

16. (a) Trade-off curves and (b) source of water to wells for management models 

MM09 and MM10 with various maximum allowable drawdowns at the 

250-milligram per liter isochlor in the Upper and Middle Potomac-RaritanMagothy aquifers for current (2003) and regularly spaced well locations 

in Critical Area 1, east-central New Jersey..................................................................31

17. (a) Trade-off curves and (b) source of water to wells for management models 

MM09 and MM10 with various maximum allowable velocities at the 

250-milligram per liter isochlor in the Upper and Middle Potomac-RaritanMagothy aquifers for current (2003) and regularly spaced well locations 

in Critical Area 1, east-central New Jersey..................................................................33

18. (a) Trade-off curves and (b) source of water to wells for management models 

MM13 and MM14 with various maximum withdrawal rates in the WenonahMount Laurel, Englishtown, and Upper and Middle Potomac-Raritan-Magothy 

aquifers for regularly spaced well locations and clean slate in Critical Area 1, 

east-central New Jersey..................................................................................................34

19. Summary of additional withdrawals computed by the management models 

for Critical Area 1, east-central New Jersey ................................................................35

Tables

1. Withdrawals from and model locations of production wells in the depleted zone 

of Critical Area 1, east-central New Jersey...........................................................................17

2. Summary of water-supply management models and results in Critical Area 1, 

east-central New Jersey...........................................................................................................23
vi

Conversion Factors and Datums

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

Flow rate

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

cubic foot per second (ft3/s) 0.646317 million gallons per day (Mgal/d)

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

million gallons per day (Mgal/d) 365.25 million gallons per year (Mgal/yr)

million gallons per day (Mgal/d) 0.0006944 gallons per minute (gal/min)

Specific capacity

gallon per minute per foot 

[(gal/min)/ft)]

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

Hydraulic conductivity

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

Hydraulic gradient

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

Transmissivity*

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

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

(NGVD 29).

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

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

*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.

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

25 °C).

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

or micrograms per liter (μg/L).
Recovery of Ground-Water Levels From 1988 to 2003 and 

Analysis of Potential Water-Supply Management Options 

in Critical Area 1, East-Central New Jersey

By Frederick J. Spitz, Martha K. Watt, and Vincent T. dePaul

Abstract

Water levels in four confined aquifers in the New Jersey 

Coastal Plain within Water Supply Critical Area 1 have 

recovered as a result of reductions in ground-water withdrawals initiated by the State in the late 1980s. The aquifers are 

the Wenonah-Mount Laurel, the Upper and Middle PotomacRaritan-Magothy, and Englishtown aquifer system. Because 

of increased water demand due to increased development in 

Monmouth, Ocean, and Middlesex Counties, five base and 

nine alternate management models were designed for the four 

aquifers to evaluate the effects resulting from potential reallocation of part of the Critical Area 1 reductions in withdrawals. 

The change in withdrawals and associated water-level changes 

in the aquifers for 1988-2003 are discussed. Generally, withdrawals decreased 25 to 30 Mgal/d (million gallons per day), 

and water levels increased 0 to 80 ft (feet).

The Regional Aquifer-System Analysis (RASA) groundwater-flow model of the New Jersey Coastal Plain developed 

by the U.S. Geological Survey was used to simulate groundwater flow and optimize withdrawals using the Ground-Water 

Management Process (GWM) for MODFLOW. Results of 

the model were used to evaluate the effects of several possible water-supply management options in order to provide 

the information to water managers. The optimization method, 

which provides a means to set constraints that support mandated hydrologic conditions, then determine the maximum 

withdrawals that meet the constraints, is a more cost-effective 

approach than simulating a range of withdrawals to determine 

the effects on the aquifer system. The optimization method is 

particularly beneficial for a regional-scale study of this kind 

because of the large number of wells to be evaluated. Before 

the model was run, a buffer analysis was done to define an 

area with no additional withdrawals that minimizes changes 

in simulated streamflow in aquifer outcrop areas and simulated movement of ground water toward the wells from areas 

of possible high chloride concentrations in the northern and 

southern parts of the Critical Area.

Five base water-supply management models were developed. Each management model has an objective function, 

decision variables, and constraints. Two of the five management models were test cases: clean slate option and reallocation from the Wenonah-Mount Laurel aquifer and Englishtown 

aquifer system to small volume wells for potable water use. 

Nine other models also were developed as part of a trade-off 

analysis between withdrawal amounts and constraint values. 

The 14 management models included current (2003) or regularly spaced well locations with variations on the constraints 

of ground-water head, drawdown, velocity at the 250-mg/L 

(milligram per liter) isochlor, and withdrawal rate.

Results of each management model were evaluated in 

terms of withdrawals, heads, saltwater intrusion, and source 

of water by aquifer. Each trade-off curve was defined by 

using six to nine separate management model runs. Results of 

the management models designed in this study indicate that 

a withdrawal reallocation of 5 to 20 Mgal/d within Critical 

Area 1 would increase the area of heads below -30 ft and the 

velocity at the 250-mg/L isochlor by up to 4 times that of the 

simulated 2003 results; the range of values are 0 to 521 square 

miles and 1 to 20 feet per year, respectively. The increase in 

area of heads below -30 ft was larger in the Middle PotomacRaritan-Magothy aquifer than in other aquifers because that 

area was negligible in 2003. The range of modeled withdrawals is closely tied to management-model design. Interpretation 

of management model results is provided as well as a discussion of limitations.

Introduction

Ground-water development in the New Jersey Coastal 

Plain has occurred primarily near large population centers, 

creating large regional cones of depression in several New 

Jersey Coastal Plain aquifers. In the northern Coastal Plain, 

water-level measurements in the Wenonah-Mount Laurel 

aquifer, Englishtown aquifer system, and the Upper and 

Middle Potomac-Raritan-Magothy aquifers in 1983 were as 

low as 196, 249, 59, and 91 ft below NGVD 29, respectively 

(Eckel and Walker, 1986). The continued decline of water 

levels in these confined aquifers posed the threat of serious 

adverse effects to the water supply in some areas, including 

the depletion of ground-water supplies, saltwater intrusion, 
2 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

and reduction of ground-water flow to streams (N.J. Department of Environmental Protection, 1996). In response to these 

water-resource threats, the N.J. Department of Environmental 

Protection (NJDEP) designated two water supply Critical 

Areas1 where excessive withdrawals create undue stress or 

long-term adverse effects on the water supply (Hoffman and 

Lieberman, 2000).

The criteria upon which the NJDEP designates a critical water-supply area include one or more of the following 

hydrologic conditions: (1) shortage of surface water due to 

diversions from surface- or ground-water sources that leaves 

insufficient surface water for permitted, certified, or registered diversions or for environmental protection purposes 

within a drainage area of at least 10 mi2; and (2) shortage 

of ground water due to diversions exceeding the long-term, 

safe, or dependable yield of an aquifer in an area of at least 

10 mi2 (New Jersey Administrative Code, 2005). The NJDEP 

may demonstrate such a shortage by a verified mathematical 

ground-water model, or if such a model is unavailable, by one 

or more of the following: (a) a progressive lowering of ground 

water to the extent that existing wells of 50 feet or more in 

depth are threatened by declining water levels or rendered 

inoperative and (b) a reduction of the average potentiometric 

surface in a confined aquifer such that the 30-foot contour 

below NGVD 29 is within 5 miles of saltwater or intersects 

the 250-mg/L isochlor.

On the basis of the low water levels measured in 1983 by 

the U.S. Geological Survey (USGS), the NJDEP determined 

that four aquifers, namely—Wenonah-Mount Laurel aquifer, 

Englishtown aquifer system, Upper Potomac-Raritan-Magothy 

aquifer, and Middle Potomac-Raritan-Magothy aquifer—were 

depleted in east-central New Jersey such that designation of an 

area of critical water supply concern was warranted. Specifically, it was determined that adverse conditions existed and 

that special measures were required to ensure the integrity 

and viability of the water supply. Therefore, in July 1985 and 

June 1990, by administrative order, the NJDEP designated 

Water Supply Critical Area 1 in Middlesex, Monmouth, and 

Ocean Counties (fig. 1). The boundary of the depleted zone of 

Critical Area 1 corresponds to the average 1983 potentiometric 

contour 30 feet below NGVD 29 for each affected aquifer, as 

published in Eckel and Walker (1986). The extent of Critical 

Area 1 is a “composite” that includes the largest surface extent 

of the depleted zones and threatened margins for all four 

aquifers. The threatened margin, consisting of a 3-mile wide 

area, surrounds the depleted zone of each aquifer (Hoffman 

and Lieberman, 2000).

In an effort to improve the management of ground-water 

resources in the confined aquifers within Critical Area 1, the 

NJDEP set out alternate water-supply plan procedures starting 

in 1986. Actual reductions in withdrawals were implemented 

starting in 1989. Within Critical Area 1, ground-water withdrawals from production wells in the depleted zone were 

reduced by 50 percent of 1983 rates in the Wenonah-Mount 

Laurel aquifer, Englishtown aquifer system, and Middle Potomac-Raritan-Magothy aquifer, and by 40 percent of 1983 rates 

in the Upper Potomac-Raritan-Magothy aquifer. Withdrawals 

in the threatened margin were limited at 1983 rates. Purveyors had the opportunity to interconnect with alternative water 

sources—shallower non-restricted aquifers, ground-water 

sources outside the Critical Area, other purveyors, or surfacewater supplies. New withdrawal allocations (with the exception of temporary construction dewatering and ground-water 

remediation activities) were prohibited by the New Jersey 

Water Supply Management Act (New Jersey Statutes Annotated, 1981). After designation of the Critical Area, withdrawal 

reductions resulted in water-level recovery in the affected 

aquifers from 1988 to 2003 and accompanying changes in the 

ground-water-flow system. Outside of the Critical Area, development of water supply is less regulated, and water quantity 

and quality concerns may occur. For example, the NJDEP has 

denied allocation requests when new or increased withdrawals outside of the Critical Area divert water from an affected 

aquifer and adversely affect the aquifers within the Critical 

Area (Fred Sickles, New Jersey Department of Environmental 

Protection, written commun., 2007).

In response to the changes in the ground-water-flow 

system and demands for additional water supply, the NJDEP 

is reevaluating allocations within the Critical Area and the 

effects of possible changes in allocations on the ground-water 

resources. During 2005-06, the USGS, in cooperation with the 

NJDEP, used an existing regional ground-water-flow model 

and a formal optimization technique to evaluate effects of 

several water-supply management options to provide needed 

information on additional withdrawals to water managers. 

These techniques were selected over standard trial and error 

withdrawal scenarios for cost and time efficiencies and applicability to the specific concerns in Critical Area 1. Such an 

approach is particularly beneficial for a regional-scale study of 

this kind because of the large number of wells to be evaluated.

A buffer analysis was conducted prior to the optimization 

to define an area of no additional withdrawals that minimizes 

changes in simulated streamflow in aquifer outcrop areas and 

simulated movement of ground water from areas that may 

have high chloride values in the northern and southern parts of 

the Critical Area. The revised USGS Regional Aquifer-System 

Analysis (RASA) flow model of the New Jersey Coastal 

Plain (Voronin, 2004) was used with the new Ground-Water 

Management Process (GWM) for MODFLOW (Ahlfeld and 

others, 2005) to analyze the ground-water-flow system. Model 

runs that incorporate proposed changes in allocations and 

recent changes in development outside the Critical Area were 

used to quantify the effects of such changes.

This approach used in this study is applicable to other 

studies of the Atlantic Coastal Plain because of similar 

hydrogeology and water-resource concerns (for example, 

water-level declines and saltwater intrusion). The approach 

also is applicable to optimization studies that use redefined 

constraints. The development of an upper bound on the gradient constraint in this study is applicable to optimization studies 

of contaminant movement where setting a lower bound is not 

an option. 1

Words in bold are defined in the glossary at the end of the report.
Introduction 3

Figure 1. Location of Water Supply Critical Area 1, east-central New Jersey.

OCEAN

SUSSEX

ATLANTIC

BURLINGTON

MORRIS

SALEM

WARREN

MONMOUTH

CUMBERLAND

HUNTERDON

BERGEN

CAPE MAY

MIDDLESEX SOMERSET

MERCER

CAMDEN GLOUCESTER

PASSAIC

ESSEX

UNION

HUDSON

COASTAL PLAIN

PIEDMONT

HIGHLANDS

VALLEY AND RIDGE

75° 73°30'

40°30'

39°

CONNECTICUT NEW YORK

PENNSYLVANIA

Base from U.S. Geological Survey digital data, 1:100,000

Universal Transverse Mercator Projection, Zone 18, NAD83

EXPLANATION

Rows

Columns

NEW JERSEY

Critical Area 1—From New Jersey

Department of Environmental Protection

(unpublished). Boundary is approximate

and should not be used for regulatory

compliance purposes

Regional Aquifer-System Analysis

model boundary (Martin, 1998)

Threatened

margin

Depleted

zone

DELAWARE RIVER

Sandy

Hook

DELAWARE

MARYLAND 0 25 50 MILES

0 25 50 KILOMETERS

AT L A N T I C O C E A N

Smart Growth Areas—From New Jersey

Department of Community Affairs (2006)

Manasquan

Reservoir

RARITAN BAY

FALL LINE
4 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

Purpose and Scope

The purpose of this report is to present the results of an 

analysis of the effects of an increase in water allocations that 

were reduced with the implementation of Critical Area 1 in 

east-central New Jersey. This report describes the hydrogeology of the study area and the recovery of the ground-water 

levels in the Wenonah-Mount Laurel aquifer, Englishtown 

aquifer system, Upper Potomac-Raritan-Magothy aquifer, and 

Middle Potomac-Raritan-Magothy aquifer from 1988 to 2003. 

The model and software used to simulate the additional watersupply allocation also are described.

In this report (1) the effects of proposed changes in withdrawals within the Critical Area are quantified; (2) the hydrologic constraints modeled within the Critical Area are defined; 

and (3) the optimal amount and distribution of additional 

withdrawals that result from the simulation, subject to the 

constraints, are presented. This report documents the formulation of 14 management models that demonstrate the effects of 

withdrawal locations and volumes on head, drawdown, location of the 250-mg/L isochlor, and withdrawal rate. Landward 

movement of the 250-mg/L isochlor is used to define saltwater 

intrusion.

Description of Study Area

Critical Area 1 is located in the northern Coastal Plain 

and includes parts of Middlesex, Monmouth, and Ocean Counties (fig. 1). The total area is approximately 906 mi2

. According to data from the U.S. Census Bureau, Middlesex, Monmouth, and Ocean Counties are the third, fourth, and seventh 

most populated counties in the State, respectively (New Jersey 

Department of Labor and Workforce Development, accessed 

February 19, 2006). According to data collected in 2000, these 

three counties accounted for 89 Mgal/d, or 22 percent, of the 

total ground water withdrawn in the State from production 

wells (Hutson and others, 2004).

The boundaries for the two areas comprising Critical Area 1, the inner depleted zone and the outer threatened 

margin, are shown in figure 1. The threatened margin is a 

3-mile-wide area surrounding the depleted zone, except along 

the northern edge where the threatened margin is not indicated 

(the depleted zone abuts the Fall Line). These areas are further refined as aquifer subareas. (See section “Water-Supply 

Management Models”) Regulation of withdrawals in Critical 

Area 1 was implemented using the boundaries for individual 

aquifers, not the composite boundary (Hoffman and Lieberman, 2000, p. 25).

Hydrogeology

The New Jersey Coastal Plain is a seaward-dipping 

wedge of unconsolidated sediments that range in age from 

Cretaceous to Holocene (Zapecza, 1989, table 2). These sediments consist mainly of clay, silt, sand, and gravel and are 

divided into different hydrogeologic units. In Critical Area 1, 

the total thickness of the sediments increases from about 150 

ft at the outcrops in Middlesex County to about 1,800 ft near 

the barrier islands in Ocean County. The sediments crop out 

at land surface in northeast-southwest trending bands (strike) 

and dip to the southeast at 10 to 60 ft/mi (fig. 2). Hydrogeologic 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 

(fig. 2). A detailed discussion of the hydrogeology of the New 

Jersey Coastal Plain is found in Zapecza (1989).

The regulated aquifers in Critical Area 1, in order of 

increasing depth, are the Wenonah-Mount Laurel aquifer, 

Englishtown aquifer system, Upper Potomac-Raritan-Magothy 

aquifer, and Middle Potomac-Raritan-Magothy aquifer. The 

Wenonah-Mount Laurel aquifer consists of the coarse-grained 

part of the Wenonah Formation and the Mount Laurel Sand; 

it is 60 to 80 ft thick in Monmouth and Ocean Counties 

(Zapecza, 1989). The aquifer is used most heavily in southeast 

Monmouth and northeast Ocean Counties because of its uniform thickness and good water quality (Jablonski, 1968). The 

Wenonah-Mount Laurel aquifer is in good hydraulic connection with the underlying Englishtown aquifer system because 

of the leaky confining unit that separates them (Zapecza, 1989, 

p. B14).

The Englishtown aquifer system is composed of fineto medium-grained sand of the Englishtown formation and 

ranges in thickness from 40 ft near the outcrop in Monmouth 

County to greater than 140 ft near the barrier islands in Monmouth County. The Englishtown aquifer system is underlain 

by the Merchantville-Woodbury confining unit, which is 

the most extensive confining unit in the Coastal Plain. In 

Monmouth County this confining unit reaches thicknesses 

of greater than 100 ft and forms an effective impediment to 

flow between the Englishtown aquifer system and the Upper 

Potomac-Raritan-Magothy aquifer below.

The Potomac-Raritan-Magothy aquifer system contains the most productive aquifers in the Coastal Plain and 

is divided into three aquifers—the upper, middle, and lower. 

The Upper Potomac-Raritan-Magothy aquifer is the most 

extensive hydrogeologic unit of the three. In the northeastern 

Coastal Plain, the Upper Potomac-Raritan-Magothy aquifer 

corresponds to the Old Bridge Sand Member of the Magothy 

Formation. In Monmouth and Ocean Counties, the Upper 

Potomac-Raritan-Magothy aquifer is greater than 200 ft thick 

and consists mainly of permeable coarse-grained sediments 

with thin localized clay beds. In the northeastern Coastal 

Plain, the Middle Potomac-Raritan-Magothy aquifer corresponds to the Farrington Sand Member of the Raritan Formation. The thickness of the Middle Potomac-Raritan-Magothy 

aquifer is less than 50 ft near the outcrop area to more than 

150 ft near the junction of Mercer, Middlesex, and Monmouth 

Counties. Although the top of the Middle Potomac-RaritanMagothy aquifer can be traced into northern Ocean County, it 

is not possible to separate it from underlying sediments. The 
Recovery Of Ground-Water Levels 5

Lower Potomac-Raritan-Magothy aquifer is not present in the 

northeastern Coastal Plain.

Previous Investigations

Various regional studies describe the hydrogeologic 

framework of, and ground-water flow in, the New Jersey 

Coastal Plain. Zapecza (1989) describes the hydrogeologic 

framework. Synoptic water-level studies have been done for 

each of the major confined aquifers every 5 years since 1978 

by the USGS. For each synoptic study, water levels were 

measured during the fall and represented annual average conditions. The most recent published work is the 1998 synoptic 

study by Lacombe and Rosman (2001) that comprises a series 

of maps showing water levels in the aquifers. Water levels 

from the 2003 synoptic study are on file at the USGS office 

in West Trenton, N.J. (V.T. dePaul, U.S. Geological Survey, 

written commun., 2007). The maps show the areas of decline 

(1978 to 1988) and recovery (1988 to 2003) of water levels 

in the aquifers underlying Critical Area 1. In addition, Martin 

(1998) and Voronin (2004) describe simulated ground-water 

flow in the New Jersey Coastal Plain (discussed farther on).

County-wide water-resource studies for Middlesex, Monmouth, and Ocean Counties were done by Barksdale and others (1943), Jablonski (1968), and Anderson and Appel (1969), 

respectively. Barlow and Dickerman (2001) and Granato and 

Barlow (2005) describe simulations related to water-supply 

management; these two studies were conducted in areas outside of New Jersey.

Recovery Of Ground-Water Levels

The ground-water flow system, changes in ground-water 

withdrawals, and changes in water levels in the study area 

during 1988-2003 are described in this section. Within Critical 

Area 1, withdrawal reductions initiated in 1985 and 1990 have 

resulted in increased water levels and other changes in the 

ground-water-flow system.

Ground-Water-Flow System

A detailed discussion of ground-water flow in the New 

Jersey Coastal Plain is found in Martin (1998). Flow in New 

Jersey Coastal Plain aquifers is affected by the hydraulic properties of the saturated sediments, the amount of recharge, and 

the locations of recharge and discharge.

Prior to water-supply development, water flowed through 

the aquifers from recharge areas to discharge areas. The 

aquifers were recharged by precipitation that fell on aquifer 

outcrop areas. Infiltration that reached the shallow groundwater system discharged to a local stream or pond. Infiltration also may have traveled vertically into deeper underlying 

hydrogeologic units and eventually discharged to larger rivers 

AQUIFER—Number refers to

model layer (table 1)

CONFINING UNIT—Number 

refers to model layer

Not to scale

EXPLANATION LOWER POTOMAC-RARITAN-MAGOTHY AQUIFER (A10)

MIDDLE POTOMAC-RARITAN-MAGOTHY AQUIFER (A9)

UPPER POTOMAC-RARITAN-MAGOTHY AQUIFER (A8)

CONFINING UNIT BETWEEN THE LOWER AND MIDDLE POTOMAC-RARITAN-MAGOTHY AQUIFERS (C9)

CONFINING UNIT BETWEEN THE MIDDLE AND UPPER POTOMAC-RARITAN-MAGOTHY AQUIFERS (C8)

MERCHANTVILLE-WOODBURY CONFINING UNIT (C7)

ENGLISHTOWN AQUIFER SYSTEM (A7)

FALL LINE

HOLLY BEACH WATERBEARING ZONE (A1)

ESTUARINE CLAY

CONFINING UNIT (C1)

CONFINING UNIT OVERLYING THE

RIO GRANDE WATER-BEARING ZONE (C2)

VINCENTOWN AQUIFER (A5)

NAVESINK-HORNERSTOWN CONFINING UNIT (C5)

BASAL KIRKWOOD CONFINING UNIT (C3) 

PINEY POINT AQUIFER (A4)

VINCENTOWN-MANASQUAN CONFINING UNIT (C4) 

WENONAH-MOUNT LAUREL AQUIFER (A6)

UPPER KIRKWOOD-COHANSEY AQUIFER (A2)

NORTHWEST SOUTHEAST

ATLANTIC

OCEAN

BEDROCK

MARSHALLTOWN WENONAH CONFINING UNIT (C6)

LOWER KIRKWOOD-COHANSEY AND

CONFINED KIRKWOOOD AQUIFER (A3)

Figure 2. Generalized hydrogeologic section through the New Jersey Coastal Plain.
6 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

or Raritan Bay. In Critical Area 1, predevelopment flow paths 

indicate ground water flowed from areas of high ground-water 

levels in Middlesex County and Monmouth County toward 

topographic low points—Raritan Bay and the Atlantic Ocean 

(Schaefer and Walker, 1981).

After water-supply development, the location and the 

amount of ground-water withdrawals controlled ground-waterflow paths. Withdrawals lowered ground-water levels creating 

cones of depression, redistributed recharge and discharge areas 

by reversing flow direction, reduced ground-water discharge 

to streams and induced ground-water recharge from streams, 

and changed flow between aquifers. In the Upper PotomacRaritan-Magothy aquifer in northern Monmouth County, 

increased withdrawals lowered ground-water levels to below 

NGVD 29. As a result, the ground-water-flow direction has 

reversed, converting previous discharge areas into recharge 

areas. In areas where the Upper Potomac-Raritan-Magothy 

aquifer is in good hydraulic connection with Raritan Bay, 

seawater is now able to recharge the aquifer (Pucci and others, 

1994).

Changes in Withdrawals and Water Levels from 

1988 to 2003

 Since the early 1900s withdrawals in the northern New 

Jersey Coastal Plain have increased steadily. By the late 

1950s, ground-water withdrawals created regional cones of 

depression in both the Upper Potomac-Raritan-Magothy and 

Middle Potomac-Raritan-Magothy aquifers along the coastline of Raritan Bay and near the Raritan River, respectively 

(Farlekas, 1979). In the 1970s and 1980s withdrawals leveled 

off, but water levels continued to decline. Total withdrawals 

in the depleted zone of Critical Area 1 for the four aquifers of 

interest equaled 76.7 Mgal/d in 1983.

During 1983-88, total withdrawals in Critical Area 1 

increased by only 2 percent; however, water levels continued 

to decline as much as 52 ft and 34 ft in the Wenonah-Mount 

Laurel aquifer and Englishtown aquifer system, respectively 

(Rosman and others, 1995). Water levels declined 2 to 3 ft 

in the Upper Potomac-Raritan-Magothy aquifer in Middlesex and Monmouth Counties, 14 ft on average in the Middle 

Potomac-Raritan-Magothy aquifer in Monmouth County, and 

as much as 20 ft in Ocean County. Cones of depression within 

the Upper Potomac-Raritan-Magothy and Middle PotomacRaritan-Magothy aquifers broadened and deepened. In 1988, 

the lowest observed water levels were 200 ft, 220 ft, 40 ft, and 

100 ft below NGVD 29 in the Wenonah-Mount Laurel aquifer, 

Englishtown aquifer system, Upper Potomac-Raritan-Magothy aquifer, and Middle Potomac-Raritan-Magothy aquifer, 

respectively.

During 1988-93, withdrawal reductions in Critical Area 1 

initiated by NJDEP went into effect. The total reduction in 

withdrawals in the depleted zone of Critical Area 1 was about 

34 Mgal/d. Compliance by individual purveyors depended 

on when they could obtain an alternative water source. For 

example, the Manasquan Reservoir, a regional surface-water 

alternative source, was not available until July 1990 (Jan 

Gheen, N.J. Department of Environmental Protection, oral 

commun., 2006). The first year that most of the purveyors 

were in compliance with Critical Area 1 regulations was 1991.

Potentiometric surfaces in each of the four aquifers along 

cross section A-A’ through the New Jersey Coastal Plain at 

5-year intervals from 1988 to 2003 are shown in figures 3 to 

6. Ground-water withdrawals in the depleted zone from 1980 

to 2003 and the total change in water levels from 1988 to 2003 

also are shown. The cross section is the same as that used 

in the prior synoptic studies of water levels in the confined 

aquifers of the New Jersey and Delaware Coastal Plain (V.T. 

dePaul, U.S. Geological Survey, written commun., 2007). The 

cross section does not necessarily pass through the deepest 

parts of the cones of depression; therefore, some of the lowest 

water levels are not shown on the figures.

A cross section depicting water-level altitudes in the 

Wenonah-Mount Laurel aquifer is shown in figure 3a. Withdrawals in the Wenonah-Mount Laurel aquifer were small, 

about 2 Mgal/d in 1988, and less than 0.5 Mgal/d by 1991 

(fig. 3b). Withdrawals after 1991 remained relatively stable 

through 2003. Water levels in the Wenonah-Mount Laurel 

aquifer recovered more than 50 ft during 1988-93 (Lacombe 

and Rosman, 1997). The cone of depression along the coastline in southern Monmouth and northern Ocean Counties 

decreased in extent. Water levels continued to rise in the cone 

of depression by as much as 50 ft during 1993-98 (Lacombe 

and Rosman, 2001), then remained fairly stable during 

1998-2003. The total 15-year change in water levels in the 

Wenonah-Mount Laurel aquifer is shown in figure 3c. Water 

levels recovered by more than 80 ft in a 72 mi2 area along the 

coast in southern Monmouth and northern Ocean Counties. 

Water levels recovered over 10 ft in more than 50 percent of 

Critical Area 1.

A cross section depicting water-level altitudes in the 

Englishtown aquifer system is shown in figure 4a. Withdrawals in the Englishtown aquifer system totaled about 9 Mgal/d 

in 1988 and declined to about 6 Mgal/d by 1991 (fig. 4b). 

After 1991, withdrawals remained fairly stable through 2003. 

Water levels in the Englishtown aquifer system rose more than 

50 ft, and the cone of depression decreased in extent during 

1988-93. Water levels continued to rise in the cone of depression, up to 50 ft during 1993-98, then remained fairly stable 

during 1998-2003. The total 15-year change in water levels in 

the Englishtown aquifer system is shown in figure 4c. Water 

levels recovered by more than 80 ft in a 110 mi2 area along 

the coast in southern Monmouth and northern Ocean Counties. Water levels rose by more than 10 ft in over 76 percent of 

Critical Area 1. The water-level recovery in the Englishtown 

aquifer system is similar to that in the Wenonah-Mount Laurel 

aquifer because the two aquifers are in good hydraulic connection, but the recovery was greater in the Englishtown aquifer 

system because most of the withdrawals that affected the two 

aquifers were made from this aquifer. The Englishtown aquidfer system and Wenonah-Mount Laurel aquifer also have low 
Recovery Of Ground-Water Levels 7

A A'

WITHDRAWALS, IN MILLION

GALLONS PER DAY

YEAR

DISTANCE, IN MILES

ALTITUDE, IN FEET RELATIVE TO NGVD 29

200150100

50

0

-50

-100-150-200-250

543210

1980 1985 1990 1995 2000 2003

0 5 10 15 20 25 30 35 40

POTENTIOMETRIC SURFACE

VERTICAL SCALE GREATLY EXAGGERATED

2003 simulated (steady state)2003 observed1998 observed1993 observed1988 observed

S. Brunswick Twp.

Fall line

Critical Area 1 boundary

Outcrop

Freehold

Howell Twp.

Manasquan River

Pt. Pleasant

Atlantic Ocean

Land surface

L T A T N A O CI A E C N

NEW YORK

NEW JERSEY

0 10 MILES

0 10 KILOMETERS

A

A'

EXPLANATION

Decline, in feet

Greater than 8060 - 8040 - 6020 - 4010 - 20

10 - 2020 - 4040 - 80Greater than 80No substantial change

Recovery, in feet

Aquifer outcrop 

74° 74°30'

40°30'

40°

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

Critical Area 1—From NewJersey Department of Environmental Protection(unpublished). Boundary is approximate and should not be used for regulatorycompliance purposes

Depleted zone

Threatened margin

(a)

(b)

(c)

Figure 3. Wenonah-Mount Laurel aquifer (a) potentiometric surfaces along section A-A’, 1988-2003; (b) withdrawals in the depleted zone of Critical Area 1, 1980-2003; and (c) water-level changes in Critical Area 1, 1988-2003, east-central New Jersey. (Potentiometric surfaces from Rosman and others (1995), Lacombe and Rosman, (1997), Lacombe and Rosman, (2001) and V.T. dePaul (U.S. Geological Survey, written commun., 2007))
8 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management OptionsYEAR 1980 1985 1990 1995 2000 2003 POTENTIOMETRIC SURFACE 2003 simulated (steady state) 2003 observed 1998 observed 1993 observed 1988 observed

A

ALTITUDE, IN FEET RELATIVE TO NGVD 29

200150100

50

0

-50

-100-150-200-250

DISTANCE, IN MILES

0 5 10 15 20 25 30 35

A'

40

S. Brunswick Twp.

Fall line

Critical Area 1 boundary Outcrop

Freehold

Howell Twp.

Manasquan River

Pt. Pleasant

Atlantic Ocean

Land surface

WITHDRAWALS, IN MILLION

GALLONS PER DAY

1210

86420

VERTICAL SCALE GREATLY EXAGGERATED

L T A T N A O CI A E C N

NEW YORK

NEW JERSEY

0 10 MILES

0 10 KILOMETERS

A

A'

74° 74°30'

40°30'

40°

EXPLANATION

Decline, in feet

Greater than 8060 - 8040 - 6020 - 4010 - 20

10 - 2020 - 4040 - 80Greater than 80No substantial change

Recovery, in feet

Aquifer outcrop 

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

Critical Area 1—From NewJersey Department of Environmental Protection(unpublished). Boundary is approximate and should not be used for regulatorycompliance purposes

Depleted zone

Threatened margin

(a)

(b)

(c)

Figure 4. Englishtown aquifer system (a) potentiometric surfaces along section A-A’, 1988-2003; (b) withdrawals in the depleted zone of Critical Area 1, 1980-2003; and (c) water-level changes in Critical Area 1, 1988-2003, east-central New Jersey. (Potentiometric surfaces from Rosman and others (1995), Lacombe and Rosman, (1997), Lacombe and Rosman, (2001) and V.T. dePaul (U.S. Geological Survey, written commun., 2007))
Recovery Of Ground-Water Levels 9

A A'

WITHDRAWALS, IN MILLION

GALLONS PER DAY

5040302010

0

YEAR

1980 1985 1990 1995 2000 2003

DISTANCE, IN MILES

0 5 10 15 20 25 30 35 40

ALTITUDE, IN FEET RELATIVE TO NGVD 29

200175150125100

755025

0

-25-50-75

POTENTIOMETRIC SURFACE

2003 simulated(steady state)2003 observed1998 observed1993 observed1988 observed

S. Brunswick Twp.

Fall line

Critical Area 1 boundary

Outcrop

Freehold

Howell Twp.

Manasquan River

Pt. Pleasant

Atlantic Ocean

Land surface

VERTICAL SCALE GREATLY EXAGGERATED

L T A T N A O CI A E C N

NEW YORK

NEW JERSEY

0 10 MILES

0 10 KILOMETERS

A

A'

74° 74°30'

40°30'

40°

EXPLANATION

Decline, in feet

Greater than 8060 - 8040 - 6020 - 4010 - 20

10 - 2020 - 4040 - 80Greater than 80No substantial change

Recovery, in feet

Aquifer outcrop 

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

Critical Area 1—From NewJersey Department of Environmental Protection(unpublished). Boundary is approximate and should not be used for regulatorycompliance purposes

Depleted zone

Threatened margin

(a)

(b)

(c)

Figure 5. Upper Potomac-Raritan-Magothy aquifer (a) potentiometric surfaces along section A-A’, 1988-2003; (b) withdrawals in the depleted zone of Critical Area 1, 1980-2003; and (c) water-level changes in Critical Area 1, 1988-2003, east-central New Jersey. (Potentiometric surfaces from Rosman and others (1995), Lacombe and Rosman, (1997), Lacombe and Rosman, (2001) and V.T. dePaul (U.S. Geological Survey, written commun., 2007))
10 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

WITHDRAWALS, IN MILLION

GALLONS PER DAY

353025201510

50

YEAR

1980 1985 1990 1995 2000 2003

POTENTIOMETRIC SURFACE

2003 simulated(steady state)2003 observed1998 observed1993 observed1988 observed

DISTANCE, IN MILES

0 5 10 15 20 25 30 35 40

A A'

ALTITUDE, IN FEET RELATIVE TO NGVD 29

200175150125100

755025

0

-25-50-75

S. Brunswick Twp.

Fall line

Critical Area 1 boundary

Outcrop

Freehold

Howell Twp.

Manasquan River

Pt. Pleasant

Atlantic Ocean

Land surface

VERTICAL SCALE GREATLY EXAGGERATED

L T A T N A O CI A E C N

NEW YORK

NEW JERSEY

0 10 MILES

0 10 KILOMETERS

A

A'

74° 74°30'

40°30'

40°

EXPLANATION

Decline, in feet

Greater than 8060 - 8040 - 6020 - 4010 - 20

10 - 2020 - 4040 - 80Greater than 80No substantial change

Recovery, in feet

Aquifer outcrop 

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

Critical Area 1—From NewJersey Department of Environmental Protection(unpublished). Boundary is approximate and should not be used for regulatorycompliance purposes

Depleted zone

Threatened margin

(a)

(b)

(c)

Figure 6. Middle Potomac-Raritan-Magothy aquifer (a) potentiometric surfaces along section A-A’, 1988-2003; (b) withdrawals in the depleted zone of Critical Area 1, 1980-2003; and (c) water-level changes in Critical Area 1, 1988-2003, east-central New Jersey. (Potentiometric surfaces from Rosman and others (1995), Lacombe and Rosman, (1997), Lacombe and Rosman, (2001) and V.T. dePaul (U.S. Geological Survey, written commun., 2007))
Evaluation Of Water-Supply Management Options 11

transmissivity (Martin, 1998, figs. 56-59), which contributes 

to a slower recovery of water levels, compared to recovery in 

the Upper Potomac-Raritan-Magothy and Middle PotomacRaritan-Magothy aquifers.

A cross section depicting water-level altitudes in the 

Upper Potomac-Raritan-Magothy aquifer is shown in figure 5a. Withdrawals from this aquifer were relatively stable 

at about 40 Mgal/d during 1981-87, then decreased during 

1988-96 (fig. 5b). Withdrawals increased slightly during 

1997-2002, then decreased in 2003. Water levels rose about 

25 ft during 1988-93. Water levels dropped by about 10 ft 

during 1993-98, and then remained stable until 2003. The 

total 15-year change in water levels in the Upper PotomacRaritan-Magothy aquifer is shown in figure 5c. The recovery 

was 10 to 20 ft, and as much as 40 ft in most of Monmouth 

County. Water levels declined 10 to 40 ft in a 48 mi2 area in 

northern Ocean County within the composite boundary for 

Critical Area 1 but outside the boundary for the depleted zone 

of the Upper Potomac-Raritan-Magothy aquifer. No withdrawals from the Upper Potomac-Raritan-Magothy aquifer were 

reported for this area in the late 1980s, but withdrawals have 

been reported more recently. In 2003, seven wells within this 

area withdrew 702 million gallons.

A cross section depicting water-level altitudes in the 

Middle Potomac-Raritan-Magothy aquifer is shown in figure 

6a. Withdrawals decreased by more than half during 1988-93. 

In 1988 withdrawals were about 30 Mgal/d, but by 1993 had 

decreased to about 11 Mgal/d. Then withdrawals remained 

stable until 1998, and increased slightly during 1998-2003 

(fig. 6b). Water levels, which rose about 20 ft over a large 

part of the Critical Area during 1988-93, rose by about 15 ft 

in the eastern part of the Critical Area and remained stable 

elsewhere during 1993-98. Water levels remained stable during 1998-2003. The total 15-year change in water levels in the 

Middle Potomac-Raritan-Magothy aquifer is shown in figure 

6c. Water levels recovered 80 ft or more in areas near Raritan 

Bay. Recoveries of 20 to 40 ft occurred in a 114 mi2 area along 

the Monmouth and Ocean County border, but most of the 

recovery was 10 to 40 ft.

Evaluation Of Water-Supply 

Management Options

The Wenonah-Mount Laurel aquifer, Englishtown aquifer 

system, Upper Potomac-Raritan-Magothy aquifer, and Middle 

Potomac-Raritan-Magothy aquifer are hydraulically connected 

both horizontally and vertically to aquifers and confining 

units beyond the extent of Critical Area 1. Thus, to examine 

the effect of withdrawals on these specific aquifers, the larger 

hydrologic system and associated stresses must be simulated. 

Accordingly, a regional ground-water-flow model was used in 

this study that involves the entire New Jersey Coastal Plain.

The existing ground-water-flow model of the New Jersey 

Coastal Plain was used to simulate flow in and around Critical Area 1. Results from the RASA model have been used to 

understand the regional flow system and the source of water to 

wells in the major aquifers of the Coastal Plain. The input data 

for the RASA model were formatted for use with MODFLOW 

(Harbaugh and McDonald, 1996), a modular finite-difference 

ground-water-flow model. The original version of this model 

was constructed and calibrated as part of the USGS RASA 

program (Martin, 1998). The model was revised by Voronin 

(2004) to improve simulation capabilities. For a detailed 

discussion of the model design, calibration, and boundaries of 

the original and revised RASA models, refer to Martin (1998) 

and Voronin (2004). The RASA model has been shown to be 

an effective tool for simulating ground-water flow in the New 

Jersey Coastal Plain based on its wide use and the reasonable estimates it provides of the source of water to wells (for 

example, Gordon, 2007). The extent of the RASA model is 

shown in figure 1.

The current study combines optimization along with the 

ground-water flow modeling to determine optimal withdrawals 

at the optimal locations. This approach includes setting hydrologic constraints and evaluating the resulting model-calculated 

withdrawals, whereas the traditional model scenarios involve 

setting withdrawals and evaluating the resulting model-calculated hydrologic conditions. The water-supply management 

models used in the current study were developed using the 

Ground-Water Management Process (GWM) for MODFLOW 

(Ahlfeld and others, 2005). Several water-supply management 

options were simulated to evaluate the effects of proposed 

changes in the withdrawal allocations within Critical Area 1. 

These options included using current well locations, regularly 

distributed well locations, and variations of these such as 

clean slate and reallocation. A buffer analysis is described 

below that was done to limit the number and type of the 

constraints used in the optimization. Comparisons of results of 

all the simulations are provided in the following sections, and 

limitations of the water-supply management modeling also are 

discussed.

Ground-Water-Flow Model

For this study, the revised version of the RASA model 

(Voronin, 2004) was used to evaluate the effects of pumping 

optimal withdrawal amounts at optimal locations on mandated 

hydrologic conditions within Critical Area 1. This revised 

model simulates flow in the hydrogeologic units that comprise 

the New Jersey Coastal Plain and includes (1) a rediscretization of the RASA model parameters with a finer grid cell size, 

(2) updated boundary fluxes, (3) a spatially variable recharge 

rate that is based on recharge rates determined as part of recent 

studies of the surficial aquifers in the Coastal Plain, and (4) 

updated ground-water withdrawal data from 1981-98.

The grid in the revised model consists of 135 rows and 

245 columns with a cell size of 0.25 mi2 over most of Critical 

Area 1, 0.31 mi2 elsewhere in the Coastal Plain, and up to 3.16 

mi2 in offshore areas. The ratio of the number of new cells to 
12 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

the original number of cells is 25 to 1 in onshore areas. One 

benefit of rediscretization is that it allows modeled withdrawals to be located more accurately. (Withdrawals are simulated 

as a net sink that occurs throughout the model cell closest to 

each well location.) Revisions to stress periods in the RASA 

model were made to incorporate updated withdrawal data 

in the revised model. The Coastal Plain hydrogeologic units 

were discretized into 10 aquifers and 9 intervening confining 

units as in the RASA model. All of the units were modeled as 

confined with a constant saturated thickness. Certain aquifers, 

such as the Wenonah-Mount Laurel aquifer and Englishtown 

aquifer system, are not continuous throughout the Coastal 

Plain. The limit of these aquifers in the southeast is modeled 

as a no-flow boundary. In the case of the Englishtown aquifer 

system, its absence resulted in vertical hydraulic connection 

between confining units.

The model boundaries in the revised model are the same 

as those used in the original model. The northwestern limit 

of the Coastal Plain is the Fall Line, which is modeled as 

a no-flow boundary. Flows at the northeast and southwest 

limits are computed from simulated flows from larger areal 

models (Leahy and Martin, 1993; Pope and Gordon, 1999). 

Flows in the Upper Potomac-Raritan-Magothy and Middle 

Potomac-Raritan-Magothy aquifers at the southwest boundary between Delaware and New Jersey were estimated on the 

basis of water-level declines to account for the large increases 

in withdrawals in Delaware during 1988-98 that were not 

included in the larger areal models. The southeastern boundary 

in the Upper Potomac-Raritan-Magothy and Middle PotomacRaritan-Magothy aquifers is a no-flow boundary, representing 

the downdip limit of freshwater.

Most of the Coastal Plain hydrogeologic units have 

outcrop areas that receive recharge from precipitation and are 

in direct contact with streams. The upper boundary in model 

cells that contain stream reaches is a head-dependent flow 

boundary. For the revised model, streams were modeled using 

the River and Drain packages of MODFLOW. The upper 

boundary in remaining onshore areas is a specified recharge. 

A spatially variable recharge rate was applied to these cells. 

The rate is equal to long-term precipitation minus long-term 

evapotranspiration and surface-water runoff. The upper boundary in offshore areas is a constant equivalent freshwater head. 

The lower boundary is crystalline bedrock and was modeled as 

a no-flow boundary.

Subsequent minor changes have been made to the 

revised model. The vertical conductance of the VincentownManasquan confining unit was modified to improve the representation of the geohydrologic framework. Also, the model 

was updated from 1998 to 2003 to include the most recent 

withdrawal data, and flow in the hydrogeologic units was 

simulated using a newer version of MODFLOW (Harbaugh 

and others, 2000). No additional calibration or sensitivity 

analysis was done.

To simplify the modeling process, a steady-state RASA 

model was used. In this case, steady-state conditions are those 

that occur when there is no further change in simulated heads 

with time as a result of applied stresses, such as withdrawals 

for 2003. In the cones of depression in Critical Area 1, heads 

simulated by a steady-state RASA model using withdrawal 

conditions for 2003 were higher than heads simulated by 

the transient RASA model using 2003 data. (Heads from the 

steady-state RASA model are higher than observed water 

levels for 2003 shown in figures 3-6.) The difference between 

simulated steady-state heads and observed water levels is 

approximately 30 ft in the Wenonah-Mount Laurel aquifer 

and Englishtown aquifer system. The difference between the 

steady-state and transient models is due to aquifer storage 

effects; the difference between the steady-state model and 

observed data is due to coarse model grid size. Given that 

a simulation period of more than 40 years was necessary to 

reach steady-state conditions in these aquifers in the New 

Jersey Coastal Plain after applying a withdrawal stress (A.D. 

Gordon, U.S. Geological Survey, written commun., 2006), the 

steady-state RASA model may overestimate heads for transient periods of shorter duration.

Buffer Analysis

To minimize the effects of managed withdrawals on 

simulated streamflow in aquifer outcrop areas and minimize 

increases in simulated landward ground-water flow in areas 

near the 250-mg/L isochlor in Raritan Bay, a buffer area was 

defined in the northern part of the Critical Area for the Upper 

Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy aquifers. A buffer area was determined to be unnecessary 

for the Wenonah-Mount Laurel aquifer and Englishtown aquifer system because withdrawals from these aquifers are not as 

great as those from the Upper Potomac-Raritan-Magothy and 

Middle Potomac-Raritan-Magothy aquifers, and streamflow 

depletion and saltwater intrusion are less of a concern in these 

aquifers. In the northern part of the Critical Area, it was determined, on the basis of the most recent (2003) chloride data, 

that there is no measurable saltwater intrusion in the WenonahMount Laurel aquifer and Englishtown aquifer system. A 

single well in the Englishtown aquifer system at Sandy Hook 

was found to have elevated chloride concentrations (15,100 

mg/L), however.

To determine the width of the buffer area for the Upper 

Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy aquifers, 11 transects were developed—6 perpendicular 

to the coastline of Raritan Bay and 5 perpendicular to each 

aquifer’s outcrop area (fig. 7). An origin point (0 miles) was 

designated near the coastline of Raritan Bay and at the downdip extent of each aquifer’s outcrop area. For each steady-state 

simulation with 1998 withdrawal conditions, locations of additional withdrawals of 1 Mgal/d from the Upper Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy aquifers 

were placed along each transect at 1, 6, or 11 miles from the 

origin point. The total additional withdrawals in each of these 

simulations was 22.3 Mgal/d in Critical Area 1 based on data 

supplied by NJDEP (Jan Gheen, N.J. Department of Environ-
Evaluation Of Water-Supply Management Options 13

74°30' 74°

40°30'

40°15'

0 5 MILES

0 5 KILOMETERS

MONMOUTH

MIDDLESEX

SOMERSET

MERCER

MONMOUTH

MIDDLESEX

SOMERSET

MERCER

74°30' 74°

40°30'

40°15'

(a)

(b)

EXPLANATION

Transect type

Withdrawal point and distance from

origin point, in miles

Coast Outcrop

Coast Outcrop

0

1

6

11

1

0

1

6

11

1

Aquifer outcrop area

Five-mile buffer line

Base from U.S. Geological Survey digital data, 1:24,000

Universal Transverse Mercator Projection, Zone 18, NAD83

Critical Area 1—From New Jersey 

Department of Environmental 

Protection (unpublished). Boundary 

is approximate and should not be 

used for regulatory compliance 

purposes

Threatened margin

Depleted zone

Figure 7. Transects and withdrawal points used in the buffer analysis for the (a) Upper and (b) Middle Potomac-Raritan-Magothy 

aquifers in Critical Area 1, east-central New Jersey.
14 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

mental Protection, written commun., 2004). To reduce well 

interference, simulations of withdrawals along the outcrop 

transects and along the coastal transects were run separately. 

Head and drawdown along each transect, and horizontal and 

vertical flow at the origin points, were evaluated for changes 

from the base 1998 steady-state simulation. Results indicated 

that the largest change in horizontal flow occurred between 1 

and 6 miles from the origin point for all transects.

A water-budget analysis was done using the computer 

program Zonebudget (Harbaugh, 1990) to evaluate changes 

in vertical flow to streams and horizontal flow in the outcrop areas in more detail. Results indicated that the percent 

change in vertical flow to streams in the outcrop area was 

most affected by withdrawals located at 1 mile from the origin 

point. Decreases in streamflow in the Upper Potomac-RaritanMagothy aquifer were more than twice that in the Middle 

Potomac-Raritan-Magothy aquifer at this distance. This may 

have occurred because (1) more streams are located in the 

outcrop area of the Upper Potomac-Raritan-Magothy aquifer 

than in the outcrop area of the Middle Potomac-Raritan-Magothy aquifer, (2) the Upper Potomac-Raritan-Magothy aquifer 

is thinner in its updip area and is affected more by losses in 

horizontal flow due to withdrawals than the Middle PotomacRaritan-Magothy aquifer, and (3) the Upper Potomac-RaritanMagothy aquifer is subject to increased vertical flow to the 

Middle Potomac-Raritan-Magothy aquifer due to withdrawals 

in the Middle Potomac-Raritan-Magothy aquifer.

Because the largest change in heads and flow occurred 

from 1 to 6 miles from the origin point and the largest change 

in flow to streams in the outcrop area occurred at 1 mile 

from the origin point, a 5-mile-wide buffer area was defined 

from the downdip boundary of the Upper Potomac-RaritanMagothy and Middle Potomac-Raritan-Magothy outcrop areas 

and from the coast of Raritan Bay (fig. 7). No withdrawals 

were managed in this buffer area, so the presence of the buffer 

further limited the area of managed withdrawals.

Water-Supply Management Models

The optimization of withdrawals in Critical Area 1 using 

the GWM process (Ahlfeld and others, 2005) for MODFLOW 

is described in this section. The area of managed withdrawals 

does not include the entire area within the Critical Area boundary (fig. 1), but rather subareas of the four aquifers within the 

boundary (fig. 8). For example, the area of managed withdrawals for the Wenonah-Mount Laurel aquifer and Englishtown aquifer system extends from mid-Ocean County north 

to their respective outcrop areas. A brief discussion of GWM 

(Ahlfeld and others, 2005) also is provided in this section. The 

formulation, solution, and applications of the water-supply 

management model are presented along with a comparison of 

results.

Ground-Water Management Process

Each management formulation of GWM consists of a set 

of decision variables, an objective function, a set of constraints, and a solution process. Each of these components is 

discussed in further detail below. GWM supports several types 

of decision variables; however, only flow-rate decision variables, which are managed withdrawal rates at well sites, were 

used in this study. Flow-rate decision variables can extend 

over one or more specified model cells and be active during 

one or more model stress periods (only one stress period is 

used for steady-state simulations).

GWM supports a single objective function, which is to 

minimize or maximize the weighted sum of decision variables. 

In this study, the objective function was to maximize withdrawals at the well sites. The objective function is an equation 

designed to identify the best possible management solution 

among many possible solutions.

GWM supports several types of constraints; however, 

only two types were used in this study—upper and lower 

bounds on the flow-rate decision variables and hydraulic-head 

based constraints, including head, drawdown, and velocity. 

Constraints represent limits imposed on the values of the decision variables. Typically, only a subset of constraints controls 

the optimal solution. Binding constraints restrict the value 

of the objective function because they prevent decision variables from taking on values that further improve the objective function and, therefore, bind the solution. Conversely, 

nonbinding constraints do not affect the optimal values of the 

decision variables and could be removed from the management formulation without changing the solution.

A response-matrix technique is used in GWM to solve 

several types of management formulations. This study 

involves only linear formulations. The solution process is used 

to determine the decision-variable values, such as withdrawal 

rates, that optimize the objective function while satisfying 

the constraints, thus resulting in the greatest allocation of 

withdrawals. The Response Matrix Solution (RMS) Package of GWM uses the Ground-Water Flow (GWF) Process of 

MODFLOW to compute the change in head at each constraint 

location that results from a perturbation of a flow-rate decision 

variable. Then, these changes are used to compute response 

coefficients (response functions) between the simulated wells 

and computed heads. The resulting matrix of response coefficients then is combined with other components of the linear 

management formulation, such as decision variables, to form 

a complete linear formulation, which is then solved by use of 

the simplex algorithm, which is part of the RMS Package.

GWM first calls the GWF Process for the base-condition run. The status of each constraint is determined at this 

point as either satisfied, not met, or near-binding. Next, the 

management formulation is converted into a form that can 

be solved using linear-programming techniques (that is, the 

simplex algorithm), the response matrix is generated by the 

required GWF Process runs, the linear program is solved by 

the simplex algorithm, and an optimal solution, if possible, 
Evaluation Of Water-Supply Management Options 15 OCEAN BURLINGTON MONMOUTH

MIDDLESEX

MERCER

SOMERSET

UNION

OCEAN

BURLINGTON

MONMOUTH

MIDDLESEX

MERCER

SOMERSET

UNION

OCEAN

BURLINGTON

MONMOUTH

MIDDLESEX

MERCER

SOMERSET

UNION

OCEAN

BURLINGTON

MONMOUTH

MIDDLESEX

MERCER

SOMERSET

UNION

(d) (c)

(a) (b)

EXPLANATION

Boundary of subarea ofmanaged withdrawals

Initial constraints

Aquifer outcrop area20 ft drawdown-30 ft head5 ft drawdown

74°30' 74°

40°30'

74°30' 74°

40°30'

40°

74°30' 74°

40°30'

40°40°

74°30' 74°

40°30'

40°

0 10 20 30 MILES0 10 20 30 KILOMETERS

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

Figure 8. Aquifer subareas and management model constraints for the (a) Wenonah-Mount Laurel aquifer, (b) Englishtown aquifer system, (c) Upper PotomacRaritan-Magothy aquifer, and (d) Middle Potomac-Raritan-Magothy aquifer in Critical Area 1, east-central New Jersey.
16 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

is obtained. At this point, the value of the objective function, 

the optimal values of withdrawal for each of the flow-rate 

decision variables, and the binding constraints are determined. 

The last step in a successful GWM run is a final run of the 

GWF Process using the optimal flow rates determined by the 

simplex algorithm. This run should indicate that all constraints 

are either satisfied or near-binding.

Formulation

The goal of the optimization is to maximize additional 

withdrawals (greater than 2003 withdrawals), given reasonable hydrologic constraints, in the four aquifers of concern in 

Critical Area 1. Comparison between 2003 withdrawals and 

(full) base allocation depends on which limits are used. Base 

allocation has annual and monthly limits. Using annual limits, 

2003 withdrawals from most wells are comparable to base 

allocation (table 1). Although this difference in withdrawals 

can be quantified, the effect on resulting optimal withdrawals 

cannot be known without making additional model runs.

What constitutes a reasonable hydrologic constraint is 

somewhat uncertain, and therefore, an evaluation was done to 

determine how different constraint values affect the optimal 

withdrawals (that is, a tradeoff analysis). The constraints were 

selected in coordination with NJDEP. An implied constraint 

was that resulting effects (for example, low water levels) 

would not be as unfavorable as the effects during the time of 

pre-reduction withdrawal allocations.

The statement of the water-supply management problem 

that is solved by use of GWM is formulated as

maximize

QwnTQwn � ,

N

n=1

(1)

subject to

0 ≤ Qwn ≤ Qwn ,

u (2)

hi,j,k,t ≤ hi,j,k,t , l (3)

ddi,j,k,t ≤ ddi,j,k,t , and (or) u (4)

(hi,j,k,t)1 - (hi,j,k,t)2

∆x

≥ (gradi,j,k,t)1,2 , (5)

where

N	 is the total number of flow-rate decision

variables;

n represents both the location of the nth well 

site and the stress period (or periods) 

during which the well operates;

Qwn is the managed withdrawal rate at a well site;

TQwn is the total duration of withdrawal at well site 

n;

Qwn

u

	 is the specified upper bound on the managed

withdrawal rate at a well site;

hi,j,k,t is the model-calculated head in cell i,j,k at the 

end of stress period t;

hi,j,k,t

l 	 is the specified lower bound on head at

location i,j,k at the end of stress period t;

ddi,j,k,t is the model-calculated drawdown in cell i,j,k 

at the end of stress period t;

ddi,j,k,t

u 	 is the specified upper bound on drawdown at

location i,j,k at the end of stress period t;

(hi,j,k,t)1 is the model-calculated (higher) head in cell 

i,j,k at the first location at the end of stress

period t;

(hi,j,k,t)2 is the model-calculated (lower) head in cell 

i,j,k at the second location at the end of 

stress period t;

∆x is the distance between two well locations; 

and

(gradi,j,k,t)1,2	 is the specified lower bound on gradient

between well locations 1 and 2 (discussed 

in more detail below).

The total number of flow-rate decision variables used 

in this study depends on the management option tested. Four 

types of initial constraints were used in the water-supply management models (also see fig. 8):

Constraint 

number Description

1 Maximum allowable withdrawal rate

2 Maximum allowable drawdown of 20 ft throughout 

the Wenonah-Mount Laurel aquifer and Englishtown aquifer system

3 Minimum allowable head of -30 ft along the northern buffer in the Upper Potomac-Raritan-Magothy 

and Middle Potomac-Raritan-Magothy aquifers

4 Maximum allowable drawdown of 5 ft along 

the downdip 250-mg/L isochlor in the Upper 

Potomac-Raritan-Magothy and Middle PotomacRaritan-Magothy aquifers

Constraint 1 was set equal to 500 gal/min (0.72 Mgal/d) 

for management models involving regularly spaced well 

locations. This value represents a typical specific capacity for 

a large well and can represent multiple wells in a model cell. 

Constraint 1 was set equal to the specific capacity of the well 

minus it’s current (2003) withdrawals for management models 
Evaluation Of Water-Supply Management Options 17

Table 1. Withdrawals from and model locations of production wells in the depleted zone of Critical Area 1, east-central New Jersey.—Continued[NJDEP, New Jersey Department of Environmental Protection; USGS, U.S. Geological Survey; BWA, Bureau of Water Allocation; MM05, management model 05; ft, foot; Mgal/d, million gallons per day; WD, Water Department; WC, Water Company; WU, Water Utililty; MUA, Municipal Utilities Authority; NJ, New Jersey; Co, Company; ---, not available or not applicable; model locations in bold contain more than one well]

Well owner Local well name

Well depth 

(ft)

Depth to top of 

open interval 

(ft)

Depth to 

bottom of open 

interval (ft)

NJDEP USGS

BWA permit 

number

Well permit 

number

1Allocation 

(Mgal/d)

Local well 

number2

Model location 4Withdrawal (Mgal/d)

Layer3 Row Column 2003 5MM05

Atlantic Highlands Borough WD Atlantic Highlands PW 6 251 198 248 5325 29-25383 0.54 250714 7 36 232 0.194 ---Avon By The Sea Borough WD Avon PW 1 504 424 504 5132 49-00017 0.16 250014 6 59 213 --- 0.035

PW 2 501 419 501 do. 49-00018 --- 250011 6 59 213 --- 0.035

Belmar Borough WD 2 Elec(10) 581 --- --- 5138 49-00023 0.48 250018 7 60 211 --- 0.014

Belmar 3 Elec(12) 594 563 594 do. 29-00045 --- 250016 7 60 211 --- 0.0144 Elec(11) 679 601 671 do. 49-00024 --- 250026 7 61 213 --- 0.0147 Sub 648 --- --- do. 49-00022 --- 250015 7 60 211 --- 0.014PW 13 605 555 605 do. 29-06956 --- 250023 7 60 211 0.225 0.014PW 14 550 --- --- do. 29-10462 --- 250497 7 60 211 --- 0.014

Brick Township MUA Forg Pond 9-73 1,779 1,441 1,779 5172 29-06841 1.88 290045 9 63 193 0.191 ---

Fp 10 1,832 1,607.25 1,827 do. 29-07791 --- 290046 8 63 193 0.221 ---Fp 11 1,800 1,565 1,800 do. 29-08356 --- 290595 8 64 193 0.722 ---PW 12 1,860 1,700 1,860 do. 29-12006 --- 290779 8 63 193 0.835 ---

Brielle Borough WD Brielle PW 2 750 690 750 5279 29-00069 0.23 250030 7 64 203 0.139 0.041

Brielle PW 3 820 770 820 do. 29-05292 --- 250028 7 64 201 0.105 0.041

Englishtown Borough WD Englishtown PW 2 384 363 384 5191 28-05400 0.25 250056 8 25 196 0.181 ---Farmingdale Borough WD Farmingdale PW 3 460 420 460 5126 29-04386 0.16 250063 7 48 202 --- 0.041

PW 4 470 410 470 do. 29-06088 --- 250064 7 48 202 --- 0.041

Freehold Borough WD PW 3 567 468 567 5059 29-04419 1.07 250099 8 32 200 0.220 ---

PW 6 943 835 943 do. 29-11217 --- 250503 9 31 200 0.190 ---PW 7 884 771 884 do. 29-13480 --- 250561 9 32 200 0.300 ---WaterWorks Rd 8 229 136 224 do. 29-25736 --- 250730 7 32 200 0.358 ---

Freehold Township WD PW 3 212 150 212 5009 29-05302 1.87 250105 7 31 200 0.299 ---

10 Jackson Mill Rd 697 633 691 do. 29-14513 --- 250722 8 39 195 0.182 ---Jackson Mills T Plant 11 1,002 918 997 do. 29-24426 --- 250725 9 39 195 0.422 ---Koenig Lane T Plant 13 680 584 673 do. 29-24703 --- 250726 8 37 198 0.118 ---Edwards Dr Plant 12 211 149 206 do. 29-24425 --- 250727 7 31 200 0.152 ---PW 14 993 927 988 do. 29-33928 --- 250774 8 38 195 1.110 ---PW 15 983 918 978 do. 29-33929 --- 250775 8 38 195 0.320 ---

Gordons Corner WC Gordons PW 5 670 580 670 5185X 29-06353 2.20 250230 9 24 203 0.279 ---

PW 6 712 592 708 do. 29-07402 --- 250231 9 24 203 0.387 ---Gordons PW 7 594 524 594 do. 29-05790 --- 250244 8 30 206 0.162 ---PW 4 810 741 810 do. 29-05548 --- 250249 9 27 202 0.175 ---PW 10 800 740 800 do. 29-10864 --- 250452 9 27 202 0.456 ---PW 11 576 479 576 do. 29-12877 --- 250564 8 29 206 0.187 ---

Jackson Township MUA PW 1 557 511 557 5075 29-03574 0.72 290229 7 50 188 --- 0.041

PW 3 559 513 559 do. 29-03797 --- 290228 7 48 175 --- 0.041Jackson PW 8 1,462 1,276 1,462 do. 29-08936 --- 290576 9 48 185 0.669 ---PW 9 1,430 1,276 1,430 do. 29-08937 --- 290575 9 48 185 0.331 ---

Lakehurst Borough WD Lakehurst Boro Tw14/PW15 1,029 937 1,024 5262 29-42955 0.33 291380 8 56 172 0.396 ---Lakewood Township MUA Lakewood PW 1 817 752 817 5079 29-05721 0.66 290430 7 63 185 --- 0.027

PW 2 762 680 762 do. 29-04116 --- 290431 7 63 188 --- 0.027Lakewood PW 3 741 673 741 do. 29-05110 --- 290433 7 62 187 --- 0.027Lakewood PW 7 1,625 1,410 1,620 do. 29-09259 --- 290588 9 59 190 0.444 ---

Lavallette Borough WD PW 3 1,808 1,120 1,180 5136 33-00001 0.06 290452 7 77 188 --- 0.065Manchester Township WU Manchester PW 10 1,189 1,013 1,184 5043 29-23401 1.68 291040 8 61 178 0.212 ---

PW 12 1,146 997 1,141 do. 29-23400 --- 291041 8 61 178 0.699 ---11 Util Easement 1,146 991.33 1,141 do. 29-25969 --- 291101 8 61 178 0.318 ---
18 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options Table 1. Withdrawals from and model locations of production wells in the depleted zone of Critical Area 1, east-central New Jersey.—Continued [NJDEP, New Jersey Department of Environmental Protection; USGS, U.S. Geological Survey; BWA, Bureau of Water Allocation; MM05, management model 05; ft, foot; Mgal/d, million gallons per day; WD, Water Department; WC, Water Company; WU, Water Utililty; MUA, Municipal Utilities Authority; NJ, New Jersey; Co, Company; ---, not available or not applicable; model locations in bold contain more than one well] Well owner Local well name Well depth (ft) Depth to top of open interval (ft) Depth to bottom of open interval (ft) NJDEP USGS BWA permit number Well permit number

1Allocation 

(Mgal/d)

Local well 

number2

Model location 4Withdrawal (Mgal/d)

Layer3 Row Column 2003 5MM05

Marlboro Township MUA 1-Prod 716 647 716 5055 29-06360 0.77 250269 9 26 210 0.500 ---

4A-Prod 720 638.5 720 do. 29-12777 --- 250543 9 26 210 0.412 ---3-Prod 710 624.2 710 do. 29-11251 --- 250549 9 25 211 0.235 ---

NJ American WC 1 Gondola Rsvr 1,154 999 1,149 5018X 29-15170 2.13 250721 8 55 208 0.246 ---

Swimming R Res Tp 2 655 575 655 do. 29-21611 --- 250729 8 40 218 0.116 ---Jumping Br 6 1,080 1,000 1,075 do. 29-11335 --- 250501 8 55 211 0.811 ---

NJ American WC Bay Head 5 834 750 834 5062X 49-00002 0.46 290005 7 70 200 --- 0.041

Bay Head 6 818 778 818 do. 29-00087 --- 290006 7 70 200 0.131 0.041Monterey 16 1,496 1,375 1,495 do. 33-01159 --- 290070 8 76 191 0.487 ---

NJ American WC 1-1975/Yellow Brk Well 860 --- --- 5078X 29-07784 2.48 250493 8 46 201 0.243 ---

Aldrich PW 2 440 354 440 do. 29-03105 --- 250168 6 48 195 0.214 0.027Aldrich Wc 3/Htmua 396 336 396 do. 29-04381 --- 250166 6 47 194 --- 0.027Aldrich Wc 4/Htmua 4 550 363 550 do. 29-05346 --- 250165 7 50 193 0.375 0.027Lakewood PW 6 582 520 582 do. 29-03324 --- 290450 7 53 189 0.330 0.021Lakewood PW 7 757 697 757 do. 29-04304 --- 290434 7 59 185 0.275 0.021Lakewood PW 8 758 600 758 do. 29-04834 --- 290438 7 56 186 0.221 0.021Lakewood PW 9 698 569 698 do. 29-05496 --- 290449 7 56 191 0.275 0.021Lakewood PW 10 1,607 1,357 1,602 do. 29-06549 --- 290440 9 56 187 0.820 ---

Parkway WC Parkway 1 A 649 594 644 5184 29-16728 0.06 250710 7 59 195 --- 0.062Point Pleasant Borough WD Pt Pleasant PW 3 798 748 798 5150 49-00075 1.13 290532 7 67 200 0.159 0.082

Pt Pleasant PW 5 1,342 1,256 1,342 do. 29-03345 --- 290531 8 67 199 0.868 ---

Sea Girt Borough WD Sea Girt PW 5 710 660 710 5237 29-04102 0.01 250374 7 64 206 --- 0.011Seaside Heights Borough WD Seaside Heights Wd-7 1,590 1,389 1,580 5093 33-37776 0.67 291365 8 79 186 0.633 ---Spring Lake Borough PW 1 711 631 711 5089 49-00014 0.27 250383 7 63 208 --- 0.021

PW 2 707 640 700 do. 49-00015 --- 250384 7 63 208 --- 0.021Spring Lake PW 3 705 640 705 do. 49-00016 --- 250385 7 63 209 --- 0.021PW 4 670 600 670 do. 29-04721 --- 250386 7 61 210 0.138 0.021

Spring Lake Heights Borough Spring Lake Hgts PW 2 711 660 711 5266 29-00398 0.30 250389 7 61 207 0.108 0.041

PW 3 680 630 680 do. 29-05075 --- 250388 7 62 207 --- 0.041PW 1 600 570 600 do. 29-00180 --- 250387 6 61 207 --- 0.035Spring Lake Hgts PW 4 564 485 561 do. 29-07506 --- 250391 6 62 209 --- 0.035

United Water NJ PW 42 1,342 1,198 1,337 5000X 33-32509 1.72 291221 8 67 181 0.227 ---

Toms River PW 30 1,875 1,754 1,715 do. 33-10224 --- 290626 9 70 177 1.447 ---

Wall Township WD Allenwood 1 740 688.58 740.42 5149 29-02869 0.80 250428 7 60 204 0.146 0.021

Allenwood 2 710 658 710 do. 29-02870 --- 250427 7 60 203 0.196 0.021Imperial 2 662 627 657 do. 49-00032 --- 250442 7 57 209 --- 0.021Rt 34 649 549 649 do. 29-05289 --- 250441 7 55 205 0.194 0.021Imperial 1 465 435 465 do. 29-02871 --- 250443 6 57 209 --- 0.021Rosehill 2A 456 421 451 do. 29-17963 --- 250698 6 56 209 --- 0.021Imperial 3 455 425 455 do. 29-09107 --- 250465 6 57 209 --- 0.021West Belmar 575 440 575 do. 29-02868 --- 250440 6 60 210 --- 0.021

1Current base allocation in depleted zone and threatened margin for all wells associated on BWA permit (Jan Gheen, NJDEP, written. commun., 2004).2Number of wells associated with BWA is based on Regional Aquifer-System Analysis model data (Voronin, 2004).3Layer 6 is the Wenonah-Mount Laurel aquifer, 7 is the Englishtown aquifer system, 8 is the Upper or Undifferentiated Potomac-Raritan-Magothy aquifer, and 9 is the Middle Potomac-Raritan-Magothy 

aquifer.

4Values for 2003 are actual unmanaged withdrawals; values for MM05 are the maximum managed withdrawals allowed for the well (FVMAX).5Only wells in the Wenonah-Mount Laurel aquifer and Englishtown aquifer system were simulated.
Evaluation Of Water-Supply Management Options 19

involving current well locations. In this case, the goal was to 

determine the additional withdrawal possible.

Constraint 2 represents a maximum allowable drawdown in the Wenonah-Mount Laurel aquifer and Englishtown 

aquifer system. If no constraint was applied to these aquifers, 

substantial drawdown would occur in order to compensate 

for constraints 3 and 4 applied to the Upper Potomac-RaritanMagothy and Middle Potomac-Raritan-Magothy aquifers.

Constraint 3 represents a minimum allowable head at a 

5-mile distance from outcrop areas susceptible to streamflow 

depletion and coastal areas susceptible to saltwater intrusion 

in the Upper Potomac-Raritan-Magothy and Middle PotomacRaritan-Magothy aquifers. The buffer area minimizes, but 

does not eliminate, the effect of withdrawals on head changes 

and saltwater intrusion in the northern part of the Critical 

Area.

Constraint 4 represents a maximum allowable drawdown 

at the downdip 250-mg/L isochlor in the Upper PotomacRaritan-Magothy and Middle Potomac-Raritan-Magothy 

aquifers. As mentioned previously, landward movement 

of the 250-mg/L isochlor is used to define saltwater intrusion. (Isochlor locations in this report are more continuous 

than shown.) The constraint is not based on a buffer analysis 

because saltwater intrusion is a regional feature in the southern 

part of the Critical Area, whereas saltwater intrusion is a localized feature in the northern part. Also, in the northern part, it is 

not known whether increased chloride concentrations are due 

primarily to ground-water flow or leakage from Raritan Bay. 

Few wells are screened in the Wenonah-Mount Laurel aquifer 

and Englishtown aquifer system in the southern part of the 

Critical Area. Measured chloride concentrations are very low 

(less than 25 mg/L), given the limited number of wells. The 

limited amount of data on chloride concentrations precludes 

delineation of isochlor locations in these aquifers. Future 

monitoring wells might be useful in these aquifers in this area.

Input

Each GWM run includes a set of files that are added to a 

standard MODFLOW run. These include a GWM file (analogous to a MODFLOW name file), an objective function file 

(OBJFNC), a decision variables file (DECVAR), constraint 

files (VARCON and HEDCON), and a solution and outputcontrol parameters file (SOLN). Details on these files are 

described in Ahlfeld and others (2005).

The goal for most of the GWM runs was to determine the 

additional withdrawals that could be obtained beyond unmanaged withdrawals included in the MODFLOW WEL Package. If more than one well was simulated within a model cell, 

the withdrawals were combined into a single well to satisfy 

the GWM requirement of only one well per cell.

Output

Output from GWM that was evaluated for this study 

includes simulated heads, optimal withdrawal values and well 

locations, and constraint values and locations. Geographic 

Information System and Fortran postprocessing plotting software were developed by D.A. Pope and M.M. Chepiga (U.S. 

Geological Survey, written commun., 2006). This software 

may be useful in future studies involving GWM. Examples 

of output for the first management model tested are shown 

in figures 9-11. The output types shown in figures 9-11 were 

produced and analyzed for each management model, but are 

not included in this report. Simulated heads are shown in 

figure 9; optimal withdrawal rates, locations of withdrawals, 

and whether certain withdrawals are binding constraints, in 

figure 10; and constraints, locations, and whether certain constraints are binding (based on distance to right-hand side), 

in figure 11.

Base Applications

A summary of the 14 management models is presented in 

table 2. The management models are designated by a two-letter prefix “MM” followed by a sequence number and (or) letter. Five base management models were run (MM01-MM05). 

Nine other management models (MM06-MM14) were run 

as part of a trade-off analysis between withdrawal amounts 

and constraint values. The management models are evaluated 

in terms of additional withdrawals, simulated area of heads 

below -30 ft NGVD in Critical Area 1, maximum saltwater 

intrusion velocity (ground-water velocity at the 250-mg/L 

isochlor), and number of binding constraints.

Statements about the -30 ft potentiometric contours are 

with respect to 2003 heads. The 1983 -30 ft contour, which 

defines the Critical Area boundary, has decreased in extent 

over time as a result of reductions in withdrawals. Thus, 

no change in the Critical Area boundary would need to be 

considered until the -30 ft contour extends beyond the 1983 

-30 ft contour.

Maximum saltwater intrusion velocity was determined 

by solving equation 7 (shown farther on) for velocity along 

the 250-mg/L isochlor and recording the largest value. This 

value is an estimate because MODFLOW is a constant-density 

flow model and not a variable-density flow model, such as 

SEAWAT (Langevin and others, 2003), that would simulate 

freshwater/saltwater interactions more accurately. Estimates of 

travel time of saltwater to wells would require use of particle 

tracking software in many locations and for many model runs.

Certain constraints may be very close to binding, but as 

a result of GWM precision, are not identified as such. Recent 

conditions (2003) also are included in the table for comparison. Only substantial changes between management models 

listed in table 2 are noted in the text. Each management model 

is discussed in more detail below.

Current (2003) Well Locations (Management Models 

MM01 and MM02)

Reductions in allocations and development of alternative 

withdrawal plans were required of all purveyors in Critical 

Area 1; this involved several hundred wells in aquifer sub-
20 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNIONOCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION

0

30

60

-30

90

60

30

60

60

-30

0

30

60

-60

90

60

0

0

30

0

30

60

-30

90

30

-30

0

30

60

90

120

-60

60

90

120

Aquifer outcrop areaArea of heads below -30 feet

Boundary of subarea ofmanaged withdrawals

SIMULATED POTENTIOMETRICCONTOUR--Shows altitude of headsabove NGVD 1929. Interval is 30 feetBoundary of buffer area250-milligram per liter isochlor--FromLacombe and Rosman (2001) for MiddlePotomac-Raritan-Magothy aquifer

30

-30

-30

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

(d) (c)

(a) (b)

EXPLANATION

74°30' 74°

40°30'

74°30' 74°

40°30'

40°

74°30' 74°

40°30'

40°40°

74°30' 74°

40°30'

40°

0 10 20 30 MILES0 10 20 30 KILOMETERS

Figure 9. Simulated potentiometric surface in the (a) Wenonah-Mount Laurel aquifer, (b) Englishtown aquifer system, (c) Upper Potomac-Raritan-Magothy aquifer, and (d) Middle Potomac-Raritan-Magothy aquifer for management model MM01 in Critical Area 1, east-central New Jersey.
Evaluation Of Water-Supply Management Options 21 OCEAN BURLINGTON MONMOUTH

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0.0000.001 - 0.3990.400 - 0.7990.800 - 1.199

Greater than 1.200

Binding constraint

Optimal withdrawals—In milliongallons per day

Boundary of subarea ofmanaged withdrawalsBoundary of buffer area250-milligram per liter isochlor—FromLacombe and Rosman (2001) for MiddlePotomac-Raritan-Magothy aquifer

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

(d) (c)

(a) (b)

EXPLANATION

74°30' 74°

40°30'

74°30' 74°

40°30'

40°

74°30' 74°

40°30'

40°40°

74°30' 74°

40°30'

40°

0 10 20 30 MILES0 10 20 30 KILOMETERS

Aquifer outcrop area

Figure 10. Simulated optimal withdrawals in the (a) Wenonah-Mount Laurel aquifer, (b) Englishtown aquifer system, (c) Upper Potomac-Raritan-Magothy aquifer, and (d) Middle Potomac-Raritan-Magothy aquifer for management model MM01 in Critical Area 1, east-central New Jersey.
22 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNIONOCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION Distance to right-hand side—Shows how far away optimal solution is from specified constraint value, in feet 0.000 - 3.999 4.000 - 7.999 8.000 - 11.999 12.000 - 15.999 Greater than 16.000 Binding constraint Aquifer outcrop area Boundary of subarea of managed withdrawals

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

(d) (c)

(a) (b)

EXPLANATION

74°30' 74°

40°30'

74°30' 74°

40°30'

40°

74°30' 74°

40°30'

40°40°

74°30' 74°

40°30'

40°

0 10 20 30 MILES0 10 20 30 KILOMETERS

Figure 11. Simulated constraints in the (a) Wenonah-Mount Laurel aquifer, (b) Englishtown aquifer system, (c) Upper Potomac-Raritan-Magothy aquifer, and (d) Middle Potomac-Raritan-Magothy aquifer for management model MM01 in Critical Area 1, east-central New Jersey.
Evaluation Of Water-Supply Management Options 23

Table 2. Summary of water-supply management models and results in Critical Area 1, east-central New Jersey.[MLRW, Wenonah-Mount Laurel aquifer; EGLS, Englishtown aquifer system; UPRM, Upper Potomac-Raritan-Magothy aquifer; MPRM, Middle Potomac-Raritan-Magothy aquifer; PRM, Upper and Middle Potomac-Raritan-Magothy aquifers; mi2, square miles; CR, current; RS, regularly spaced; dd, drawdown; hd, head; vel, velocity; hd03-20, simulated head 2003 minus 20; ft; foot; ft/yr, foot per year; gal/min, gallons per minute; Mgal/d, million gallons per day; mg/L, milligrams per liter; ---, not applicable]

Management model

Well 

design

Constraints1 Withdrawals (Mgal/d)

2Area of heads below -30 ft 

in Critical Area 1 (mi2)

Maximum velocity of 250-mg/L 

isochlor (ft/yr) Number of binding constraints3

Designation Description FVMAX (gal/min) MLRW, EGLS PRM north PRM south Unmanaged Additional MLRW EGLS UPRM MPRM UPRM MPRM Areal Lateral MLRW, EGLS PRM

--- Current (2003) conditions4 --- --- --- --- --- 23.7 --- 64 118 143 0 3.3 11.5 --- --- --- ---

MM01 Current (2003) well locations CR Cs dd=20 hd=-30 dd=5 23.7 7.0 137 175 242 3 4.5 11.5 14 1 10 5MM02 Within Smart Growth Areas CR Cs dd=20 hd=-30 dd=5 23.7 7.0 137 175 241 3 4.7 11.5 13 1 9 5MM03 Regularly distributed well locations RS 500 dd=20 hd=-30 dd=5 23.7 9.7 160 192 238 3 4.5 11.3 22 1 19 4MM04 Clean slate5 RS 500 hd03-20 hd=-30 hd03-20 --- (23.7+11.9) 155 194 204 2 6.5 7.8 60 0 29 31MM05a Reallocation to small volume wells6 CR Cs hd=-30 23.7 0.2 71 124 144 0 3.3 11.5 7 0 7 0MM05b dd=20 hd=-30 23.7 0.9 123 161 156 0 3.5 11.3 36 0 36 0MM05c dd=20 hd=-30 dd=5 23.7 0.9 123 161 156 0 3.5 11.3 36 0 36 0MM06 Vary dd in MLRW, EGLS CR Cs dd=5 hd=-30 dd=5 23.7 5.8 86 134 237 3 4.3 11.6 13 1 9 5

dd=50 23.7 7.6 209 231 246 3 4.5 11.5 13 2 10 5

MM07 Vary dd in MLRW, EGLS RS 500 dd=5 hd=-30 dd=5 23.7 5.7 87 135 235 3 4.5 11.5 15 2 15 2

dd=50 23.7 12.6 255 269 242 3 4.5 11.3 17 2 4 15

MM08 Vary hd in MLRW, EGLS RS 500 hd=-110 hd=-30 dd=5 23.7 12.3 254 260 239 3 4.7 11.3 19 1 17 3

hd=-10 23.7 0.7 65 119 144 0 3.3 11.5 2 0 2 0

MM09 Vary dd at 250-mg/L isochlor in PRM CR Cs dd=20 hd=-30 dd=1 23.7 2.6 95 140 161 0 3.5 11.5 5 2 4 3

dd=20 23.7 17.4 175 211 510 486 11.1 11.5 20 2 9 13

MM10 Vary dd at 250-mg/L isochlor in PRM RS 500 dd=20 hd=-30 dd=1 23.7 4.9 86 135 162 0 3.5 11.5 7 1 7 1

dd=20 23.7 17.3 200 232 471 462 13.6 10.9 31 4 18 17

MM11 Vary vel at 250-mg/L isochlor in PRM CR Cs dd=20 hd=-30 vel=9.8 23.7 8.5 174 206 403 185 9.8 9.9 12 2 6 8

vel=20 23.7 19.3 175 211 507 499 14.7 19.9 15 2 5 12

MM12 Vary vel at 250-mg/L isochlor in PRM RS 500 dd=20 hd=-30 vel=9.4 23.7 11.6 191 218 390 280 9.4 9.5 23 2 14 11

vel=20 23.7 19.7 186 221 481 500 13.0 18.1 31 2 12 21

MM13 Vary FVMAX RS 250 dd=20 hd=-30 dd=5 23.7 8.1 161 193 252 3 4.7 11.3 26 1 19 8

2,500 23.7 10.6 148 184 227 2 4.3 11.5 11 2 11 2

MM14 Vary FVMAX for clean slate5 RS 250 hd03-20 hd=-30 hd03-20 --- (23.7-2.8) 157 172 0 0 0.4 3.0 63 0 32 31

2,500 --- (23.7+32.0) 2 8 521 499 14.3 1.3 24 3 14 13

1 Maximum withdrawal allowed for well (FVMAX) for current well design equals specific capacity (Cs) minus unmanaged withdrawal.2 Area of depleted zone in Critical Area 1 is approximately 740 mi2.3 Areal constraints are within aquifer subarea, lateral constraints are along subarea boundary.4 Includes no managed withdrawals.5 Removal of wells extending beyond aquifer subareas to include all of Critical Area 1.6 Variations a and b (or c) involve a different number of wells.
24 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

areas. In this study, the number of managed withdrawals had 

to be reduced in order to make optimization runs feasible. 

Accordingly, only production wells with 2003 withdrawals 

greater than 0.1 Mgal/d were used. Production wells account 

for the largest withdrawals in Critical Area 1. Withdrawal 

locations of these wells are indicative of future withdrawal 

locations. Small wells grouped on one allocation permit having an aggregate withdrawal greater than 0.1 Mgal/d or withdrawals for other uses were not included. Other withdrawals 

that were not specifically managed were included as unmanaged withdrawals (23.7 Mgal/d) in the simulations. If those 

withdrawals were managed, minor changes would be expected 

in the overall additional withdrawals and well locations.

Almost 90 percent of all withdrawals were accounted 

for in aquifer subareas using the above criteria. Nine of the 

59 wells (not identified in table 1) were located in duplicate 

model cells reducing the total number of wells with managed 

withdrawals to 50. Well locations for managed withdrawals 

(MM01) in the Wenonah-Mount Laurel aquifer, Englishtown 

aquifer system, Upper Potomac-Raritan-Magothy aquifer, 

and Middle Potomac-Raritan-Magothy aquifer are shown in 

figure 12. Management model MM02 is a variation of MM01 

and includes only wells in Smart Growth Areas (New Jersey 

Department of Community Affairs, accessed January 27, 

2006). Smart Growth Areas are shown in figure 1. The MM02 

configuration contained six fewer wells than MM01, but the 

results for the two management models were virtually identical. The four types of initial constraints described on page 16 

were used in MM01 and MM02.

Model results for each of the four aquifers are shown in 

figures 9-11. Results are listed in table 2. An additional 7.0 

Mgal/d of withdrawals was obtained using MM01. In this 

management model, the largest withdrawals were from the 

Upper Potomac-Raritan-Magothy aquifer (3.9 Mgal/d); the 

smallest withdrawals were from the Wenonah-Mount Laurel 

aquifer (0.2 Mgal/d). Data on the simulated area of heads 

below -30 ft, maximum saltwater intrusion velocity, and number of binding constraints are listed in the table. The combined 

simulated area of heads below -30 ft in the four aquifers is less 

than double the area in 2003 (table 2).

Regularly Spaced Well Locations (Management Model 

MM03)

For this management model, unmanaged withdrawals 

were located at current production wells. Managed withdrawals were located at regularly spaced intervals in the subareas 

of the Wenonah-Mount Laurel aquifer, Englishtown aquifer 

system, Upper Potomac-Raritan-Magothy aquifer, and Middle 

Potomac-Raritan-Magothy aquifer (fig. 13). The purpose of 

this configuration was to evaluate how much in additional 

withdrawals could be obtained given a regular distribution of 

wells. The additional withdrawals are derived only from managed withdrawals. Regularly spaced wells were used in order 

to demonstrate how the locations of managed wells affect the 

optimal solution. The resulting distribution may not represent 

all realistic sites, but it does represent general areas of water 

availability.

The number of wells used likely has an effect on the 

optimal solution, perhaps not on the total amount withdrawn 

by all wells, but on the amount of withdrawals at individual 

wells. Also, if too few wells are used, the allowable maximum 

withdrawal rates may be reached, and the maximum overall 

withdrawal may not be obtained. Sixty-five wells were used, 

allocated among the four aquifers of concern. The wells also 

were offset vertically to maximize withdrawal potential. The 

four types of initial constraints described on page 16 were 

used in MM03.

As expected, regularly spaced well locations result in 

greater additional withdrawals than current well locations 

(table 2). An additional 9.7 Mgal/d was obtained with MM03. 

The largest withdrawals are from the Englishtown aquifer system (3.9 Mgal/d); the smallest withdrawals are from the Upper 

Potomac-Raritan-Magothy aquifer (1.2 Mgal/d). Data on the 

simulated area of heads below -30 ft, maximum saltwater 

intrusion velocity, and number of binding constraints are listed 

in table 2. For MM03, the combined simulated area of heads 

below -30 ft in the four aquifers almost doubled compared to 

2003 conditions (table 2).

Clean Slate (Management Model MM04)

This management model is designed to represent the 

development of water supply in Critical Area 1 assuming that 

withdrawals had been made only at regularly spaced well locations from the outset. For MM04, there were no unmanaged 

withdrawals in the entire Critical Area, including the threatened margin, in all four aquifers of concern. All withdrawals 

were managed at regularly spaced well locations inside the 

aquifer subareas. Management model MM04 used initial constraints 1 and 3 described on page 16, but used modifications 

of initial constraints 2 and 4. The maximum areal drawdown in 

the Wenonah-Mount Laurel aquifer and Englishtown aquifer 

system, and the maximum drawdown at the 250-mg/L isochlor 

in the Upper Potomac-Raritan-Magothy and Middle PotomacRaritan-Magothy aquifers were changed to head constraints of 

20 ft below simulated 2003 heads.

Management model MM04 yields the most additional 

withdrawals (11.9 Mgal/d) of the five base management 

models (MM01-MM05). The largest withdrawals are from 

the Middle Potomac-Raritan-Magothy aquifer; the smallest 

withdrawals are from the Wenonah-Mount Laurel aquifer; 

actual values are not listed due to the absence of unmanaged 

withdrawals. The distribution of withdrawals was spread 

throughout the aquifer subareas. Data on the simulated area of 

heads below -30 ft, maximum saltwater intrusion velocity, and 

number of binding constraints are listed in table 2. For MM04, 

the combined simulated area of heads below -30 ft in the four 

aquifers less than doubled compared to 2003 conditions.
Evaluation Of Water-Supply Management Options 25 OCEAN BURLINGTON MONMOUTH

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Well and unmanaged withdrawals--In million gallons per day

Small-volume well

Boundary of buffer area250-milligram per liter isochlor--FromLacombe and Rosman (2001) for MiddlePotomac-Raritan-Magothy aquifer

0.000 - 0.3990.400 - 0.7990.800 - 1.1991.200 - 1.599

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

(d) (c)

(a) (b)

EXPLANATION

Aquifer outcrop areaBoundary of subarea ofmanaged withdrawals

74°30' 74°

40°30'

74°30' 74°

40°30'

40°

74°30' 74°

40°30'

40°40°

74°30' 74°

40°30'

40°

0 10 20 30 MILES0 10 20 30 KILOMETERS

Figure 12. Current (2003) well locations and unmanaged withdrawals used in the (a) Wenonah-Mount Laurel aquifer, (b) Englishtown aquifer system, (c) Upper PotomacRaritan-Magothy aquifer, and (d) Middle Potomac-Raritan-Magothy aquifer for management model MM01 in Critical Area 1, east-central New Jersey.
26 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNIONOCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION OCEAN BURLINGTON MONMOUTH MIDDLESEX MERCER SOMERSET UNION Boundary of buffer area 250-milligram per liter isochlor--From Lacombe and Rosman (2001) for Middle Potomac-Raritan-Magothy aquifer Well (d) (c) (a) (b) EXPLANATION Aquifer outcrop area Boundary of subarea of managed withdrawals 74°30' 74° 40°30' 74°30' 74° 40°30' 40° 74°30' 74° 40°30' 40° 40° 74°30' 74° 40°30' 40°

0 10 20 30 MILES0 10 20 30 KILOMETERS

Base from U.S. Geological Survey digital data, 1:24,000Universal Transverse Mercator Projection, Zone 18, NAD83

Figure 13. Regularly spaced well locations used in the (a) Wenonah-Mount Laurel aquifer, (b) Englishtown aquifer system, (c) Upper Potomac-Raritan-Magothy aquifer, and (d) Middle Potomac-Raritan-Magothy aquifer for management model MM03 in Critical Area 1, east-central New Jersey.
Evaluation Of Water-Supply Management Options 27

Reallocation to Small Volume Wenonah-Mount Laurel 

Aquifer and Englishtown Aquifer System Potable Users 

(Management Model MM05)

Management model MM05 is designed to represent 

managed withdrawals of up to 30 Mgal/yr for potable use 

at current well locations from the Wenonah-Mount Laurel aquifer and Englishtown aquifer system in the depleted 

zone. Locations of the small volume wells (Jan Gheen, New 

Jersey Department of Environmental Protection, written 

commun., 2006) are shown in figure 12 and listed in table 1. 

The maximum simulated withdrawal rate for these wells was 

30 Mgal/yr or the pre-Critical Area allocation, whichever is 

smaller (Jan Gheen, written commun., 2006). Three variations 

of management model MM05 (a, b, and c) were designed with 

different constraints.

For MM05a, only small volume wells in areas with 

observed water levels above -50 ft below NGVD 29 were 

managed. A head constraint value of -50 ft below NGVD 29 

was used for these wells. The value of head at each location 

was modified using the following equation to account for the 

difference (residual) between simulated heads and observed 

2003 water levels.

wlobs - residual = hsim , (6)

where

wlobs is the observed water level at a location,

hsim is the simulated head at a location, and

residual is the difference between the observed water 

level and simulated head (both positive and 

negative values).

The right-hand side of equation 3 was replaced by equation 6. Only initial constraints 1 and 3 described on page 16 

were applied. For MM05b, withdrawals at all small volume 

wells were managed, and initial constraint 2 was included. 

Management model MM05c is similar to MM05b, except that 

initial constraint 4 also was included to see whether a different 

result was obtained.

Results for the three MM05 simulations are listed in 

table 2. A maximum additional withdrawal of 0.9 Mgal/d was 

simulated in these runs. The largest withdrawals were evenly 

distributed in the Englishtown aquifer system (0.6 Mgal/d) for 

MM05b or MM05c. The amount of additional withdrawals 

simulated equals the maximum reallocation for the WenonahMount Laurel aquifer and Englishtown aquifer system. Thus, 

the increase of 0.9 Mgal/d can be accommodated if the initial 

constraints are acceptable. Data on the simulated area of 

heads below -30 ft, maximum saltwater intrusion velocity, 

and number of binding constraints are listed in table 2. For 

this management model, there were no substantial changes in 

results compared to 2003 conditions.

Trade-Off Analysis

A trade-off analysis was done to evaluate the quantities of 

additional withdrawals obtained by varying the constraint values (Ahlfeld and Mulligan, 2000). A trade-off analysis is useful because it provides water managers with (1) an understanding of how hydrologic constraints affect withdrawal patterns 

and (2) a range of outcomes based on alternative definitions of 

hydrologic constraints because constraints are often difficult to 

define. Determination of each point on a trade-off curve or bar 

in a chart requires the development and execution of a separate 

management model run. Six to nine management model runs 

were constructed to define each trade-off curve. Using more 

management model runs could better define the trade-off 

curve and associated results. Approximately 60 managementmodel runs were made. Some trade-off curves were used to 

test comparable constraints (for example, drawdown compared 

to head) to see if results were different.

Maximum Allowable Drawdown in the WenonahMount Laurel aquifer and Englishtown aquifer system 

(Management Models MM06 and MM07)

For this trade-off analysis, all initial constraints described 

on page 16 were held constant except for constraint 2, the 

maximum allowable drawdown in the Wenonah-Mount Laurel 

aquifer and Englishtown aquifer system, which was varied 

from 5 to 50 ft. Both current (MM06) and regularly spaced 

well locations (MM07) were tested.

The resulting trade-off curves and source of water to 

wells are shown in figures 14a and 14b. A maximum additional withdrawal of up to 12.6 Mgal/d was derived over 

this range for regularly spaced well locations; a maximum 

additional withdrawal of about 7.6 Mgal/d was derived for 

current well locations. The difference in additional withdrawals was small over the range for current well locations. Most 

of the source water was from the Englishtown aquifer system 

for regularly spaced well locations and the Upper PotomacRaritan-Magothy aquifer for current well locations. The 

distribution of withdrawals was concentrated in updip areas 

for regularly spaced well locations; the distribution for current 

well locations was similar and was dictated by those wells.

Data on the simulated area of heads below -30 ft, maximum saltwater intrusion velocity, and number of binding 

constraints for MM06 and MM07 are listed in table 2 only for 

the simulations at the endpoints on each curve. For both well 

configurations and maximum allowable drawdown constraint 

of 50 ft, the combined simulated area of heads below -30 ft 

in the four aquifers more than doubled compared to 2003 

conditions.
28 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY

ALLOWABLE DRAWDOWN, IN FEET

ALLOWABLE DRAWDOWN, IN FEET

5 10 20 25 30 50

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

35

30

25

20

15

10

5

0

35

30

25

20

15

10

5

0

Regularly spaced well location

Current well location

(a)

(b)

C R C

R C

R

C

R

C

R

C

R

Wenonah-Mount Laurel aquifer

Englishtown aquifer system

Upper Potomac-Raritan-Magothy aquifer

Middle Potomac-Raritan-Magothy aquifer

Current well location

Regularly spaced well location

C

R

Figure 14. (a) Trade-off curves and (b) source of water to wells for management models MM06 and MM07 with various maximum 

allowable drawdowns in the Wenonah-Mount Laurel aquifer and Englishtown aquifer system for current (2003) and regularly spaced 

well locations in Critical Area 1, east-central New Jersey.
Evaluation Of Water-Supply Management Options 29

Minimum Allowable Head in the Wenonah-Mount Laurel 

aquifer and Englishtown aquifer system (Management 

Model MM08)

For this trade-off analysis, all initial constraints described 

on page 16 were held constant except for constraint 2, the 

minimum allowable head (comparable to maximum allowable 

drawdown) in the Wenonah-Mount Laurel aquifer and Englishtown aquifer system, which was varied from -10 to -110 ft. 

Only withdrawals at regularly spaced well locations (MM08) 

were simulated because results for the previous trade-off curve 

were relatively flat for the current well locations.

Design of this management model is complicated by 

(1) wells located in areas with water levels lower than the 

particular head constraint and (2) the difference (residual) 

between the observed water levels and simulated 2003 heads. 

To address the first issue, only wells in areas with water levels 

greater than the constraint value were included in the simulation, similar to MM05a. To address the second issue, equation 

6 was applied as before.

The resulting trade-off curve and source of water to wells 

are shown in figures 15a and 15b. The trade-off curve is not 

smooth for several reasons: the removal of a well from the 

model depends on its position relative to an observed contour 

line and the accuracy of that line. Some simulations were 

infeasible, resulting in the removal of some wells in order 

to obtain an optimal solution. These complexities affect the 

results obtained using this management model. A maximum 

additional withdrawal of up to 12.3 Mgal/d was derived with 

the minimum allowable head constraint ranging from -10 to 

-110 ft below NGVD 29. The greatest change in benefit was 

associated with minimum allowable heads between -30 and 

-60 ft below NGVD 29. The largest source of water was the 

Englishtown aquifer system in most cases. The distribution of 

withdrawals was concentrated in updip areas.

Data on the simulated area of heads below -30 ft, maximum saltwater intrusion velocity, and number of binding 

constraints for MM08 are listed in table 2. Results are listed 

only for the simulation represented by the endpoints on the 

curve. For the minimum allowable head constraint of -110 ft, 

the combined simulated area of heads below -30 ft in the four 

aquifers more than doubled compared to 2003 conditions. 

For the maximum allowable head constraint of -10 ft, the 

total number of binding constraints decreased by 90 percent 

compared to that for MM03.

Maximum Allowable Drawdown at the 250-mg/L Isochlor 

in the Upper Potomac-Raritan-Magothy and Middle 

Potomac-Raritan-Magothy Aquifers (Management 

Models MM09 and MM10)

For this trade-off analysis, all initial constraints described 

on page 16 were held constant except for constraint 4, the 

maximum allowable drawdown of 5 ft along the 250-mg/L 

isochlor in Ocean County in the Upper Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy aquifers, which 

was varied from 1 to 20 ft. Simulations were run for current 

(MM09) and regularly spaced well locations (MM10).

The resulting trade-off curves and source of water to 

wells are shown in figures 16a and 16b. A maximum additional withdrawal of up to 17.4 Mgal/d was derived over this 

range for both well configurations. The higher additional 

withdrawals simulated using regularly spaced well locations 

diminishes with increasing drawdown (fig. 16a). Most of the 

source water was from the Upper Potomac-Raritan-Magothy 

aquifer with current (2003) well locations and the Englishtown 

aquifer system and Upper Potomac-Raritan-Magothy aquifer 

with regularly spaced well locations. The distribution of managed withdrawals was concentrated in updip areas for regularly spaced and current well configurations.

Data on the simulated area of heads below -30 ft, 

maximum saltwater intrusion velocity, and number of binding constraints for MM09 and MM10 are listed in table 2. 

Results are listed only for the simulations represented by the 

endpoints on each curve. For the largest drawdown constraint 

of 20 ft for both well configurations, the combined simulated 

area of heads below -30 ft in the four aquifers increased by 

more than 4 times compared to 2003 conditions. For regularly 

spaced well locations and the largest drawdown constraint, 

the combined maximum saltwater intrusion velocity increased 

by more than 50 percent in the Potomac-Raritan-Magothy 

aquifers. For both well configurations and the smallest drawdown constraint of 1 ft, the total number of binding constraints 

decreased by 50 percent compared to their respective baseline 

management model. For both well configurations and the 

largest drawdown constraint, the total number of binding constraints increased by 50 percent compared to their respective 

baseline management model.

Maximum Allowable Velocity at the 250-mg/L Isochlor 

in the Upper Potomac-Raritan-Magothy and Middle 

Potomac-Raritan-Magothy Aquifers (Management 

Models MM11 and MM12)

For this trade-off analysis, all initial constraints described 

on page 16 were held constant except for constraint 4, the 

maximum allowable velocity (comparable to maximum allowable drawdown) along the 250-mg/L isochlor in Ocean County 

in the Upper Potomac-Raritan-Magothy and Middle PotomacRaritan-Magothy aquifers, which was varied from approximately 9 to 20 ft/yr. Simulations were run for current (MM11) 

and regularly spaced well locations (MM12).

The maximum velocity constraint was implemented in 

GWM by defining an equivalent gradient-type constraint. 

A total of 37 node pairs along the 250-mg/L isochlor in the 

Upper Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy were used for computing the equivalent gradient 

constraints. Gradients across the 250-mg/L isochlor between 
30 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

ALLOWABLE HEAD, IN FEET

ALLOWABLE HEAD, IN FEET

-110 -90 -80 -70 -60 -50 -40 -30 -10

-115 -105 -95 -85 -75 -65 -55 -45 -35 -25 -15 -5

Regularly spaced well location

ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY

35

30

25

20

15

10

5

0

35

30

25

20

15

10

5

0

Wenonah-Mount Laurel aquifer

Englishtown aquifer system

Upper Potomac-Raritan-Magothy aquifer

Middle Potomac-Raritan-Magothy aquifer

R Regularly spaced well location

(a)

(b)

R

R R R

R

R

R

R

R

Figure 15. (a) Trade-off curve and (b) source of water to wells for management model MM08 with various minimum allowable head in 

the Wenonah-Mount Laurel aquifer and Englishtown aquifer system for regularly spaced well locations in Critical Area 1, east-central 

New Jersey.
Evaluation Of Water-Supply Management Options 31

(a)

(b)

ALLOWABLE DRAWDOWN AT THE 250-MILLIGRAM PER LITER ISOCHLOR, IN FEET

ALLOWABLE DRAWDOWN AT THE 250-MILLIGRAM PER LITER ISOCHLOR, IN FEET

ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY

Regularly spaced well location

Current well location

35

30

25

20

15

10

5

0

35

30

25

20

15

10

5

0

0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0

1.0 2.5 5.0 7.5 10.0 20.0

Wenonah-Mount Laurel aquifer

Englishtown aquifer system

Upper Potomac-Raritan-Magothy aquifer

Middle Potomac-Raritan-Magothy aquifer

Current well location

Regularly spaced well location

C

R

C

R C

R C

R C

R C

R

C R

Figure 16. (a) Trade-off curves and (b) source of water to wells for management models MM09 and MM10 with various maximum 

allowable drawdowns at the 250-milligram per liter isochlor in the Upper and Middle Potomac-Raritan-Magothy aquifers for current 

(2003) and regularly spaced well locations in Critical Area 1, east-central New Jersey.
32 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

two model locations can be related to velocity using the following equation:

(gradi,j,k,t)1,2 ≤

ne * vmax

K , (7)

where

(gradi,j,k,t)1,2	 is the specified lower bound on gradient

between model locations 1 and 2 

(discussed above),

vmax is the maximum velocity,

ne is the effective porosity (assumed to be 0.15), 

and

K is the hydraulic conductivity.

The value for effective porosity is based on Spayd and 

Johnson (2003, p. 16). The implementation of the constraint 

requires replacing equation 5 with an equation that defines 

an upper bound of the gradient. GWM only defines a lower 

bound of the gradient. Accordingly, equation 5 is modified as

≥ - ne * vmax

K . (hi,j,k,t)2 - (hi,j,k,t)1

∆x

(8)

The resulting trade-off curves and bar graphs of source 

of water to wells are shown in figures 17a and 17b. The left 

side of figure 17a contains a region in which solutions to 

the management model are infeasible; that is, one or more 

constraints cannot be met by any combination of withdrawals. 

This infeasibility occurs because there is already a background 

velocity that is greater than the value selected for the upper 

bound of the velocity constraint, which is related by the value 

chosen for ne. To obtain an optimal solution requires simulating a greater maximum velocity for the constraint value.

The greatest change in additional withdrawals was 

derived over a narrow range of velocities between 9 and 

12 ft/yr. In this range, a large change in withdrawals results 

from a small change in saltwater velocity. A maximum additional withdrawal of up to 20 Mgal/d was derived for both 

well configurations. Withdrawals level off on the right side of 

figure 17a because other constraints restrict the optimal solution. Regularly spaced locations may yield lower values for 

additional withdrawals at lower velocities because more wells 

are located close to 250-mg/L isochlor. Most of the source 

water was from the Upper Potomac-Raritan-Magothy aquifer 

for current (2003) well locations and from the Upper PotomacRaritan-Magothy and Middle Potomac-Raritan-Magothy 

aquifers for regularly spaced well locations. The distribution 

of withdrawals was somewhat random for both well configurations.

Data on the simulated area of heads below -30 ft, maximum saltwater intrusion velocity, and number of binding 

constraints for MM11 and MM12 are listed in table 2. Results 

are listed only for the simulations represented by the endpoints 

on each curve. For both well configurations and endpoints, 

the combined simulated area of heads below -30 ft in the four 

aquifers increased 3 to 4 times compared to 2003 conditions, 

potentially worsening initial constraint 3. For both well configurations and the largest velocities, the combined maximum 

saltwater intrusion velocity doubled in the Potomac-RaritanMagothy aquifers.

Maximum Allowable Withdrawal Rates at Wells 

(Management Models MM13 and MM14)

For this trade-off analysis, all initial constraints described 

on page 16 were held constant except for constraint 1, the 

maximum withdrawal rate at each well, which was varied 

from 250 to 2,500 gal/min (0.36 to 3.6 Mgal/d). This constraint was varied for regularly spaced well locations (MM13) 

and for the clean-slate option described above (MM14).

The resulting trade-off curves and source of water to 

wells are shown in figures 18a and 18b. A maximum additional withdrawal of up to 32 Mgal/d was obtained over 

this range with the clean-slate option; about 11 Mgal/d was 

obtained with regularly spaced locations. Negative additional 

withdrawals, or less than the unmanaged withdrawals, were 

derived using the minimum withdrawal rates. The variation 

in additional withdrawals was less than 3 Mgal/d over the 

range for regularly spaced well locations, which indicates that 

one of the constraints may be restricting the optimal solution 

substantially. Most of the source water was from the Upper 

Potomac-Raritan-Magothy aquifer for the clean-slate option 

and the Englishtown aquifer system for regularly spaced well 

locations. The distribution of withdrawals was concentrated in 

the north and west for the clean-slate option and in updip areas 

for regularly spaced well locations.

Data on the simulated area of heads below -30 ft, 

maximum saltwater intrusion velocity, and number of binding constraints for MM13 and MM14 are listed in table 2. 

Results are listed only for the simulations represented by the 

endpoints on each curve. For the maximum withdrawal rate 

constraint and the regularly spaced well locations (MM13), 

the combined simulated area of heads below -30 ft in the four 

aquifers less than doubled compared to 2003 conditions. For 

the 2,500 gal/min withdrawal rate constraint and the cleanslate option (MM14), the simulated area of heads below -30 ft 

tripled in the four aquifers compared to 2003 conditions. For 

the 250 gal/min maximum withdrawal rate constraint and the 

clean-slate option, the maximum saltwater intrusion velocity 

was reduced substantially in the PRM aquifers compared to 

2003 conditions. For the 2,500 gal/min maximum withdrawal 

rate constraint and the clean-slate option, the total number of 

binding constraints decreased by 50 percent compared to that 

for MM04.

Comparison of Water-Supply Management 

Models

General conclusions reached by comparing the watersupply management models are (1) the largest volume of 

additional withdrawals were obtained for the clean slate 

option (MM14), and the smallest volume were obtained by 
Evaluation Of Water-Supply Management Options 33

ALLOWABLE VELOCITY AT THE 250-MILLIGRAM PER LITER ISOCHLOR, IN FEET PER YEAR

ALLOWABLE VELOCITY AT THE 250-MILLIGRAM PER LITER ISOCHLOR, IN FEET PER YEAR

ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY

9.8, 9.4 9.9, 9.5 10.3, 10 11.5 15 20

Approximate region of

infeasible solution

0 3 6 9 12 15 18 21

35

30

25

20

15

10

5

0

35

30

25

20

15

10

5

0

Regularly spaced well location

Current well location

C

R

(a)

(b) Wenonah-Mount Laurel aquifer

Englishtown aquifer system

Upper Potomac-Raritan-Magothy aquifer

Middle Potomac-Raritan-Magothy aquifer

Current well location

Regularly spaced well location

C

R

C

R C

R

C R C R C R

Figure 17. (a) Trade-off curves and (b) source of water to wells for management models MM09 and MM10 with various maximum 

allowable velocities at the 250-milligram per liter isochlor in the Upper and Middle Potomac-Raritan-Magothy aquifers for current (2003) 

and regularly spaced well locations in Critical Area 1, east-central New Jersey.
34 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

ALLOWABLE MAXIMUM WITHDRAWAL RATE, IN GALLONS PER MINUTE

ALLOWABLE MAXIMUM WITHDRAWAL RATE, IN GALLONS PER MINUTE

ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY

0 500 1,000 1,500 2,000 2,500

35

30

25

20

15

10

5

0

-5

59

54

49

44

39

34

29

24

19

35

30

25

20

15

10

5

0

-5

Regularly spaced well location

Clean slate

250 500 750 1,000 1,750 2,500

TOTAL WITHDRAWALS FOR CLEAN SLATE,

IN MILLION GALLONS PER DAY

(a)

(b) Wenonah-Mount Laurel aquifer

Englishtown aquifer system

Upper Potomac-Raritan-Magothy aquifer

Middle Potomac-Raritan-Magothy aquifer

Regularly spaced well location

Clean slate

R

S

R

S

R

S

R

S

R

S

R

S

R

S

Figure 18. (a) Trade-off curves and (b) source of water to wells for management models MM13 and MM14 with various maximum 

withdrawal rates in the Wenonah-Mount Laurel, Englishtown, and Upper and Middle Potomac-Raritan-Magothy aquifers for regularly 

spaced well locations and clean slate in Critical Area 1, east-central New Jersey.
Limitations of the Analysis 35

reallocation to small volume users (MM05); (2) additional 

withdrawals were greater when regularly spaced well locations 

were used than when current (2003) well locations were used; 

(3) managed withdrawals occurred in aquifer updip areas, 

except for MM11 and MM12, where managed withdrawals 

occurred throughout aquifer subareas; (4) the constraint to 

which the value of the objective function is most sensitive 

(based on shadow prices) appears to be the maximum allowable velocity at the southern 250-mg/L isochlor in the Upper 

Potomac-Raritan-Magothy and Middle Potomac-RaritanMagothy aquifers; (5) the Upper Potomac-Raritan-Magothy 

and Middle Potomac-Raritan-Magothy aquifers provide more 

water to the wells than the Englishtown aquifer system and 

Wenonah-Mount Laurel aquifer; (6) the Upper Potomac-Raritan-Magothy and Middle Potomac-Raritan-Magothy aquifers 

show the most variability in the source water to wells; and (7) 

increasing the maximum allowable velocity constraint at the 

250-mg/L isochlor or increasing the maximum withdrawal rate 

(clean-slate option) constraint yields the most withdrawals for 

the management models documented in this report.

Additional withdrawals that result when each management model is run are shown in figure 19. Simulations of 

the management models developed in this study resulted in 

available managed withdrawals that ranged from about 5 to 20 

Mgal/d. This withdrawal range is dependent on the management model design. For example, additional withdrawals 

could be obtained if maximum allowable constraints were 

increased or minimum allowable constraints were decreased. 

In designing the various management models, the best choice 

or acceptable thresholds of constraints are not known. The 

management models developed in this study are estimates of 

an optimal design. Thus, the feasibility of additional withdrawals depends on the threshold for accepting adverse effects 

and the response of the aquifer system based on the trade-off 

curves and bar charts, as well as the time horizon. Greater 

additional withdrawals may be obtained by combining or 

changing selected constraints; however, adverse effects may 

result. The use of competing constraints also affects results. 

Accordingly, additional management models may need to 

be evaluated. In addition, measures such as field monitoring 

(for example, for saltwater intrusion) would provide data that 

would improve management model design.

Limitations of the Analysis

The validity of results of this study should be evaluated 

in terms of associated limitations and assumptions. Data error 

may include interpreted potentiometric surfaces, observed 

250-mg/L isochlor locations, and withdrawal inaccuracies. 

The last example may be a source of error in the amount and 

location of managed withdrawals. Withdrawal data used in this 

study comes from values reported to the NJDEP by purvey1 2 3 4 5 6 7 8 9 10 11 12 13 14

MANAGEMENT MODEL NUMBER

Current well location

Regularly spaced well location

Clean slate

35

30

25

20

15

10

5

0

ADDITIONAL WITHDRAWALS, IN MILLION GALLONS PER DAY

-5

Figure 19. Summary of additional withdrawals computed by the management models for Critical Area 1, east-central New Jersey.
36 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

ors. (These data have been checked by USGS personnel and 

are maintained by the USGS West Trenton, N.J., office as an 

unpublished database.) These data represent the best information available, although the associated accuracy is not always 

known.

Limitations and assumptions of MODFLOW and GWM 

are relevant in the evaluation of management model results. 

This information is discussed in the reports that document 

the model codes. Limitations and assumptions of the RASA 

model and associated input data are discussed in the reports 

documenting that model by Martin (1998) and Voronin (2004). 

For example, there are differences between simulated heads 

and observed water levels due to model calibration. The model 

was not designed to detail changes in streamflow because of 

the large grid size, limited recharge input data, and type of 

stream boundary condition used. Despite these caveats, the 

RASA model has proven to be a good predictor when used in 

other hydrologic studies, particularly at a regional scale.

Limitations and assumptions of this study, in addition to 

those listed previously, include the use of different constraints 

or values of constraints that may lead to different results. Also, 

certain optimization designs may be too complex or impractical to simulate with the RASA model. Thus, optimization 

results are limited to the selected approach; effects on base 

flow, water quality, or other concerns cannot be evaluated. 

Steady-state conditions assume there is no further change in 

simulated heads with time as a result of withdrawal stresses 

for each of the model runs. These conditions represent the 

maximum effect of hydrologic stress; thus, estimates of 

optimized withdrawals are conservative. Ground-water velocity at the 250-mg/L isochlor is computed on the basis of a 

constant-density flow model, as opposed to a variable-density 

flow model, and uses an assumed value for effective porosity. 

However, density effects at the 250-mg/L isochlor location are 

minimal.

Summary and Conclusions

Ground-water levels in Water Supply Critical Area 1 in 

east-central New Jersey have recovered since the late 1980s as 

a result of reductions in ground-water withdrawals. Reductions 

in withdrawals were initiated by the New Jersey Department 

of Environmental Protection (NJDEP) in the depleted zones 

of the Wenonah-Mount Laurel aquifer, Englishtown aquifer 

system, Upper and Middle Potomac-Raritan-Magothy aquifers, and no additional withdrawals were allowed within the 

threatened margins. The intent of the reductions was to allow 

ground-water levels to recover to acceptable levels, but recent 

increased water demand as a result of development in Middlesex, Monmouth, and Ocean Counties has prompted the NJDEP 

to reevaluate the reductions for potential reallocations.

During 1988-2003, the most substantial changes in 

water levels were in the Wenonah-Mount Laurel aquifer and 

Englishtown aquifer system, where water levels recovered 

more than 80 ft along the coast in southern Monmouth and 

northern Ocean Counties. The recovery was greater than 40 ft 

over a large part of the Critical Area in these two aquifers. The 

amount of recovery in the Upper Potomac-Raritan-Magothy 

aquifer was the smallest—less than 40 ft. The largest withdrawals over the period were made from the Upper PotomacRaritan-Magothy aquifer, but water levels were not as low in 

this aquifer in 1988 as in the other three aquifers. The recovery 

in the Upper Potomac-Raritan-Magothy aquifer was 10 to 

20 ft over a large part of Monmouth County, but declines of 

10 to 40 ft were observed in a 48 mi2 area of northern Ocean 

County. Water levels in the Middle Potomac-Raritan-Magothy 

aquifer recovered 80 ft or more in areas along Raritan Bay, but 

most of the recovery was from 10 to 40 ft. A large area of 20- 

to 40-ft recovery occurred along the border of Monmouth and 

Ocean Counties.

To provide a technical basis to water-resource managers for the reallocations, the USGS used an existing regional 

ground-water-flow model along with optimization techniques 

to determine optimal withdrawals at selected locations within 

the Critical Area. Unlike previous simulation studies involving 

design of withdrawal scenarios and evaluation of effects, this 

study set the hydrologic constraints and then determined the 

optimal withdrawals. Such an approach is particularly beneficial for a regional-scale study of this kind because of the large 

number of wells to be simulated. A buffer analysis was done 

to define an area for no additional withdrawals to minimize 

changes in simulated streamflow in aquifer outcrop areas and 

simulated movement of ground water toward wells from areas 

of possible high chloride concentrations in the northern and 

southern parts of Critical Area 1. Five base water-supply management models were developed. Each management model 

has an objective function, decision variables, and constraints. 

Nine additional management models also were developed as 

part of a trade-off analysis between withdrawal amounts and 

constraint values. The 14 management models were used to 

simulate withdrawals at current (2003) and regularly spaced 

well locations with variations on ground-water head, drawdown, velocity at the 250-mg/L isochlor, and withdrawal rate 

constraints.

Results of each management model were analyzed in 

terms of withdrawals, heads, saltwater intrusion, and source 

water by aquifer. The results of approximately 60 management-model runs are documented in this report. The conclusions reached by comparing the results of the water-supply 

management models are (1) the largest volume of additional 

withdrawals was obtained using the clean-slate option 

(assumes withdrawals were optimized from the start of watersupply development); (2) greater withdrawals were derived 

using regularly spaced well locations than using current (2003) 

well locations; (3) managed withdrawals typically occurred in 

aquifer updip areas; (4) the most limiting constraint appears to 

be the maximum allowable velocity at the southern 250-mg/L 

isochlor; (5) the deeper aquifers provided more water to the 

wells than the shallower aquifers; (6) the deeper aquifers had 
References Cited 37

the most variability in the source of water to wells; and (7) 

increasing the maximum allowable velocity at the 250-mg/L 

isochlor or increasing the maximum withdrawal rate (cleanslate option) constraints yielded the most withdrawals for the 

management models. On the basis of the management models 

designed in this study, and caveats provided, the amount of 

available withdrawals within Critical Area 1 generally ranges 

from 5 to 20 Mgal/d.

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Glossary 39

Glossary

A

Aquifer Subarea the boundary of Critical 

Area 1 is a composite of the surface expression of each of four aquifers. Accordingly, the 

total area for managed withdrawals will differ 

for each aquifer. An aquifer subarea is the 

area relevant to a specific aquifer.

B

Base Allocation a purveyor’s portion of the 

safe or dependable yield of the affected water 

resource within the Critical Area.

Binding Constraints constraints that restrict 

the value of the objective function, or bind 

the solution of the management problem, by 

preventing decision variables from taking on 

values that further improve the objective 

function.

Buffer Area protective area designed to 

minimize the effects of managed groundwater withdrawals on simulated streamflow in 

aquifer outcrop areas and simulated saltwater 

intrusion in areas with ground-water chloride 

concentrations greater than 250 mg/L.

C

Clean Slate if withdrawals could have been 

optimized from the start of water-supply 

development in the Critical Area.

Constraints impose restrictions on the 

values that can be taken by the decision 

variables.

Critical Area a region where excessive 

water use or diversion causes undue stress, or 

wherein conditions pose a significant threat 

to the long-term integrity of a water-supply 

source, including a diminution of surface 

water due to excess ground-water withdrawal.

D

Decision Variables the decisions that are 

to be determined by the management model, 

such as the managed withdrawal rates at a 

set of wells. The values determined by the 

Ground-Water Management (GWM) Process 

for these decisions define the solution of the 

problem.

Depleted Zone an area within the Critical 

Area where ground-water levels in selected 

aquifers have declined so substantially that 

the water resource is of concern.

Distance to Right-Hand Side the value of 

the right-hand side of the constraint, in ft. It 

indicates how far away the optimal solution is 

from the specified constraint value.

F

Fall Line topographic boundary between 

physiographic provinces; the western margin 

of the Coastal Plain and the eastern margin of 

the Piedmont.

I

Isochlor contour line of equal chloride 

concentration.

M

Management Options alternative approaches 

for addressing a particular water-supply issue.

Managed Withdrawals are those from wells 

where the withdrawal rate is unknown at the 

start of the MODFLOW run and is determined 

as part of the GWM process.

Maximum Saltwater Intrusion Velocity the 

maximum steady-state rate of landward 

ground-water movement at the 250-mg/L 

isochlor computed using simulated gradients 

and aquifer properties.

N

Near-Binding Constraints those constraints 

in the final output from the Ground-Water 

Flow (GWF) Process (Ahlfeld and others, 

2005, p. 52) that were binding constraints in 

the linear program output. The difference can 

result from nonlinear responses in the GWF 

Process and precision limitations in the computation of heads.
40 Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options

O

Objective Function a measure of the performance of the management-decision process. 

The objective function is used to identify the 

best solution among many possible solutions 

and is stated in terms of one or more of the 

decision variables. The function may be maximized or minimized.

Optimization the methodology of making a 

decision as effective as possible; specifically, 

the mathematical procedures (for example, 

finding the maximum of a function) involved.

Optimal Solution one that satisfies all the 

constraints and gives the best possible value 

of the objective function.

R

Reallocation an increased apportionment of 

withdrawals, in this case, following reductions in Critical Area 1.

Regularly spaced well locations placement 

of equally spaced modeled wells that potentially maximizes (optimizes) withdrawals 

while keeping the number of wells manageable from a modeling standpoint.

S

Shadow price the resulting increase 

in benefit from relaxing each constraint. 

When the right-hand-side value of a binding 

constraint increases by a unit amount, the 

objective function will change by an amount 

determined by the shadow price. This implies 

that the optimal solution is quite sensitive to 

constraints that have large shadow prices.

Smart Growth Areas areas of well-planned, 

well-managed growth that adds new homes 

and creates new jobs, while preserving open 

space, farmland, and environmental resources.

T

Threatened Margin borders the depleted 

zone of a water supply Critical Area and 

located where the decline of ground-water 

levels in selected aquifers may accelerate 

saltwater intrusion.

Trade-Off Analysis an evaluation done to 

determine how various constraint values 

affect the optimal solution of the water-supply 

management problem.

U

Unmanaged Withdrawals specified “fixed” 

withdrawals that are simulated by the model 

and are not modified as part of the optimization solution (that is, managed withdrawals), 

but contribute to the total stress on the modeled ground-water-flow system.
For additional information, write to:

Director

U.S. Geological Survey

New Jersey Water Science Center

810 Bear Tavern Road, Suite 206

West Trenton, NJ 08628

or visit our Web site at:

http://nj.usgs.gov/

Document prepared by the West Trenton Publishing Service Center
Spitz and others—Recovery of Ground-Water Levels and Analysis of Potential Water-Supply Management Options—Scientific Investigations Report 2007-5193

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