COMPUTER-MODEL ANALYSIS OF THE USE OF 

DELAWARE RIVER WATER TO SUPPLEMENT 

WATER FROM THE POTOMAC-RARITANMAGOTHY AQUIFER SYSTEM IN SOUTHERN 

NEW JERSEY 

U.S. GEOLOGICAL SURVEY 

Water lteaourcea lnveatigation 80-31 

'rettarect In cooperation with the 

Delaware ltlver loaln Commlulon 
~--------------------~~------------------------~--------------------------~~~~~~~----------~--~ BIBLf~GR.APHIC D.AT.A '1. Report No. 80-31 12. 3. Recipient's Accession No. 

SHEET 

5. Report Date 

May 1980 

.4. Tide and Subtitle Computer-model analysis of the use of Delaware 

River water to supplement water from the PotomacRaritan-Magothy aquifer system in southern ~-----------------------------~ 6. 

New Jersey 

7. Author(s) Arlen w,. Harbaugh, James E. Luzier, 

Flavian Stellerine 

8. Performing Organization Rept. 

No.USGS/WRI 80-31 

9. Performing Organization Name and Address 

U.S. Geological Survey, Water Resources Division 

Room 436, Federal Building 

P.Q. Box 1238 

Trenton, N.J. 08607 

10, Project/Task/'\liork Unit No. 

11. Contract/Gram No. 

12, Sponsoring OrganizatiOn N~me and Address 

U.S. Geological Survey, Water Resources Division 

Room 436, Federal Building 

13. Type of Report & Period 

Covered 

Final 

P.O. Box 1238 14. 

Trenton, N.J. 08607 

15. Supplementary Notes Prepared in cooperation with the Delaware River Basin Commission. 

16. Abstracts A computer model of the Potomac-Raritan-Magothy aquifer system was used to 

simulate the effects of supplementing ground water with water from the Delaware River. 

Replacen1ent of ground water pumpage with surface water in a 150-square-mile area near 

Camden, N.J., was simulated. Artificial recharge of surface water was also simulated 

in the same area. A series of nine simulations was made. The simulations include the 

period 1974 to 2000. Two projections for water use were used. Also, in some of the 

model simulations a line of injection wells was simulated to prevent movement of saline 

water into pumping centers. 

17. Key Words and Document Analysis. 17a. Descriptors 

7'"Simulation analysis, *Conjunctive use, "''"Water supply, 

"'(Computer models, Forecasting, New Jersey, Ground water, 

Coastal Plain 

17b. Identifiers/Open-Ended Terms 

None 

17 c:. COSA Tl Fie Id lGro:..:p 

18. Availability Statemer:t 

No restriction on distribution 

FORM NTIS..35 !REV 10 73, E!\iXJRSED BY ANSI AND UNESCO. 

19. Security Class (This 

Report) 

-UNCLASSIFIED 

20. Security Class (This 

Page 

UNCLASSIFIED 

THIS FORM MAY BE REPRODUCED 

2l. No. of Pages 

47 

22. Price 

USCOMM·DC 826!-·~"74 
COMPUTER-MODEL ANALYSIS OF THE USE OF DELAWARE RIVER WATER 

TO SUPPLEMENT WATER FROM THE POTOMAC-RARITAN-MAGOTHY 

AQUIFER SYSTEM IN SOUTHERN NEW JERSEY 

By Arlen W. Harbaugh, James E. Luzier, and 

Flavian Stellerine 

U.S~ GEOLOGICAL SURVEY 

Water-Resources Investigations 80-31 

Prepared in cooperation with the 

Delaware River Basin Commission 

May 1980 
UNITED STATES OF 

Cecil Andrus, Secretary 

GEOLOGICAL SURVEY 

H. William Menard, Director 

For additional information write to: 

U.S. Geological Survey 

P.O. Box 1238 

Federal Bldg. 

Trenton, NJ 08607 

INTERIOR 
CONTENTS 

Page 

Abstract--------------------------------------------- 1 

Introduction----------------------------------------- 2 

Purpose and scope-------------------------------- 2 

Previous studies--------------------------------- 2 

Location and extent of study area---------------- 3 

Geohydrology----------------------------------------- 3 

Conjunctive use of Delaware River water and 

ground water--------------------------------------- 7 

Availability of surface water-------------------- 7 

Selection of area-------------------------------- 7 

Computer model simulations--------------------------- 8 

Group A simulations------------------------------ 11 

Group B simulations------------------------------ 17 

Group C simulatiDns------------------------------ 30 

Discussion of results-------------------------------- 37 

Effect of the head barrier----------------------- 37 

Effect of water-use growth rate------------------ 37 

Steady state conditions-------------------------- 38 

Stopping head declines--------------------------- 38 

Summary and conclusions------------------------------ 39 

References------------------------------------------- 40 

TABLES 

Table 1. Summary of model simulations--------------- 9 

2. Model flow rates at end of 1999 

for group A simulations------------------ 20 

3. Model flow rates at end of 1999 

for group B simulations------------------ 29 

4. Model flow rates at end of 1999 

for group C simulations------------------ 36 

iii 
ILLUSTRATIONS 

Page 

Figure 1 . Index map of southern New Jers 4 

2. Cross section of Potomac-Raritan-Magothy 

aquifer system--------------------------------- 5 

3- Contour map showing potentiometric heads at the 

start of the model simulations (1974)---------- 10 

4-6. Contour map showing potentiometric heads the 

end of 1999: 

4. Simulation A. No conjunctive-use scheme 

is applie 13 

5. Simulation AO with conjunctive-use 

s 14 

6. Simulation A90 with conjunctive-use 

scheme plus 90 percent recharge---------- 15 

7. Perspective view of potentiometric heads for 

simulations A, AO, and 16 

8-9. Hydrographs for group A simulations at: 

8. Site 1----------------------------------- 18 

9. Site 19 

10-12. Contour map showing potentiometric heads at 

the end of 1999 for: 

10. Simulation B. No conjunctive-use 

scheme is applie 22 

11. Simulation BO with conjunctive-use 

s 23 

12. Simulation B90 with conjunctive-use 

scheme plus 90 percent recharge---------- 24 

13. Perspective view of potentiometric heads in 

simulations B, BO, and 25 

14-16. Hydrographs for group B simulations at: 

14. Site 1----------------------------------- 26 

15. Site 2----------------------------------- 27 

16 .. Site 28 

17-19. Contour map showing potentiometric heads at the 

end of 1999 for: 

17. Simulation C. No conjunctive-use 

scheme is applie 31 

18. Simulation CO with conjunctive-use 

s 32 

19. Simulation C90 with conjunctive-use 

scheme plus 90 percent recharge---------- 33 

20-21. Hydrographs for group C simulations at: 

20. Site 1----------------------------------- 34 

21. Site 35 

iv 
CONVERSION FACTORS 

To obtain SI 1 units 

et (ft) Os3048 meters (m) 

cubic feet cubic meters 

per second ( 3 /s) per second (m 3 /s) 

miles (m) 1.609 kilometers (km 

square miles (mi 2 ) 2.590 square kilometers (km 2 ) 

National Geodetic Vertical Datum of 1929 (NGVD of 1929). 

A datum plane derived from a general adjustment of the first order level 

nets of both the United States and Canada, formerly called ''mean sea 

level." The datum was derived from the average sea level over a period 

of many years at 26 tide stations along the Atlantic, Gulf of Mexico, 

and Pacific Coasts. 

1 International System (metric) of units. 

v 
COMPUTER-MODEL ANALYSIS OF THE USE OF DELAWARE RIVER WATER 

TO SUPPLEMENT WATER FROM THE POTOMAC-RARITAN-MAGOTHY 

AQUIFER SYSTEM IN SOUTHERN NEW JERSEY 

By 

Arlen W. Harbaugh, James E. Luzier, and Flavian Stellerine 

ABSTRACT 

A computer model of the Potomac-Raritan-Magothy aquifer 

system was used to simulate the effects of supplementing 

ground water with water from the Delaware River. Replacement 

of ground water pumpage with surface water in a 150-squaremile area near Camden, N.J., was simulated. Artificial 

recharge of surface water was also simulated in the same 

area. A series of nine simulations ~as made. The 

simulations include the period 1974 to 2000. Two projections 

for water use were used. Also, in some of the model 

simulations a line of injection wells was simulated to 

prevent movement of saline water into pumping centers. 

The simulations indicate that heads will be as much as 

100 feet higher in the year 2000 near the 150-square-mile 

area than that if only ground water would be used without 

supplement of surface water. In the model simulations, 

heads recover upon application of surface water, but start 

declining again within 2 years. The rate of head decline 

after surface-water application is slower than before the 

application. 
INTRODUCTION 

Pumpage from the Potomac-Raritan-Magothy aqui r system in 

southern New Jersey has increased significantly since 1900, nearly 

doubling during 1956-73. Pumping has caused head (water-level) 

declines over a large part of the aquifer system, and the 

possibility exists that the declines are causing water of poor 

quality to move toward pumping centers. Potential sources of 

water of poor quality include: saline water from the Delaware 

River estuary, contaminated water from certain reaches of the 

Delaware River, water from overlying aquifers, and saline water 

already within the aquifer. To reduce pumping stress on the 

aquifer system, the use of Delaware River water has been proposed. 

Water would be withdrawn from the river in the vicinity of 

Trenton, NoJ., where its quality is considered good. Minimal 

treatment would, thus, be required. The river water could be used 

for public supply to supplement the ground water and to recharge 

the aquifer. 

Pur se and Sco e 

This report presents the results of a study in which a 

computer model of the Potomac-Raritan-Magothy aquifer system was 

used to simulate the effect of using Delaware River water to 

supplement the aquifer water. 

Results of model simulations are presented in head-contour . maps, hydrographs, and flow-rate tables. Velocity of ground-water 

flow is also shown. 

Previous Studies 

Studies of coastal-plain geology and ground-water resources 

that include the Potomac-Raritan-Magothy aquifer syste~ have been 

made in New Jersey, Pennsylvania, Delaware, and New York since 

about 1900. Most of the studies were restricted to a specific 

area, such as a county; collectively, the studies served as the 

basis for regional quantitative appraisals. County studies 

include those of Anderson and Appel (1969), Barksdale and others (19~3), Hardt and Hilton (1969), Jablonski (1968), Sundstrom and 

ckett (1971), Rosenau and others (1969), Rush (1968), Vecchioli 

and Palmer (1962), and Farlekas and ~thers (1976). Regional 

praisals include those of Parker and others (1964), Gill and 

rlekas (1976), Barksdale and others (1958), and Luzier (1980). 

The digital model was developed by Luzier (1980) for use in 

edicting head distribution resulting om extracting or 

njecting freshwater. The theory of the model, its calibration, 

and some water-level predictions are described in d ail by Luzier 

(1980). cause the model is a simplified representation of the 

r ional aquifer system, results of simulations are only 

approximations. Many loc hydrologic details are not included. 

2 
Location 

The study area lies within the Coastal Plain physic aphic 

province (Fenneman, 1938) and i~ almost entirely within New Jersey 

(fig. 1). It is a low lying, gently rolling plain that ranges 1n 

altitude from sea level to about 390 ft. The province is border 

on the west by the Fall Line, which separates the rolling hills of 

the Piedmont from the flat lowland of the Coastal Plain. The Fall 

Line lies along the west edge of the Potomac-Raritan-Magothy 

aquifer system, which extends slightly into eastern Pennsylvania. 

The study area is bordered on the north by Raritan Bay, on the 

south by Delaware Bay, and on the east by the Atlantic Ocean. A 

subarea of special study, referred to as area I (fig. 1'), includes 

about 150 mi 2 and incorporates parts of Burlington, Camden, and 

Gloucester Counties. Although the model includes the Potomac- . Raritan-Magothy aquifer system in the entire Coastal Plain of New 

Jersey, model accuracy decreases north of Burlington and Ocean 

Counties. Results of simulations are, therefore, not shown in 

this area. 

GEOHYDROLOGY 

The Potomac group, along with the Raritan and Magothy 

Formations, consists of a regionally extensive wedge-shaped 

aqui r system of interbedded sand, silt, a clay. The aqui r 

system underlies the entire Coastal Plain of New Jersey and parts 

of adjacent states and extends approximately 100 mi offshore to 

the continental slope. The aquifer system is exposed in a narrow 

outcrop belt along the Fall Line and the Delaware River. Between 

the outcrop near Camden and the coastline near Atlantic City, the 

top of the aquifer system dips to the southeast at about 40 ft/mi; 

whereas, the top of the bedrock dips to the southeast at about 90 

ft/mi. At Atlantic City, the top and bottom of the wedge-shaped 

aquifer system lie at about 2,500 ft and 5,000 ft, respectively, 

below National Geodetic Vertical Datum of 1929. Sediments of 

approximately equivalent age (Early to Late Cretaceous) thicken 

seaward to more than 13,000 ft near the axis of the Baltimore 

Canyon trough about 60 mi off the New Jersey coast (Schlee and 

others, 1976, p. 927-940). Figure 2 is a cross section of the 

aquifer system. 

The Potomac group, chiefly of Early Cretaceous age, is the 

oldest and thickest part of the aqui r system. This unit~ in New 

Jersey, is a sequence of sand, silt, and silty clay. The Raritan 

rmation, of Late Cretaceous age, consists of sand and clay and 

overlies the Potomac group. The Magothy Formation, which consists 

chie y of coarse beach sand and associated marine and lagoonal 

clay and silt, unconformably overlies the Raritan Formation and is 

of Late Cretaceous age. The Magothy Formation thins southward 

along coastal New Jersey. In contrast, the Raritan thins only 

slightly. The underlying Potomac group nearly triples in 

thickness southward. For a more detailed discussion of coastalplain stratigraphy, the reader is re red to Perry and others 

3 
EXPlANATION 

Line of 250-mi!!igrams-per-!iter chloride 

concentration in the bottom of the Potomac· 

Raritan-Magothy aquifer system. South and 

east of this line, chloride concentrations 

increase. · 

A---------------------A 

I 

I 

I 

CROSS-SECTION 

PENNS VI. VANIA 

DELAWARE 

BAY 

CUMBERLAND 

COUNTY 

BURliNGTON 

COUNTY 

ATLANTIC 

COUNTY 

/ / 

/ 

/ / 

/" 

OCEAN 

COUNTY 

MONMOUTH 

COUNTY 

,./11.:__ I ----....... ,_'-'1.-........r./1 __ I 

I 

I 

) ~ CAPE MAY 

i'l COUNTY 

ATlANTIC OCEAN 

0 !i 10 1!i 

1 ...... L..f'Ti'-f-'rtl-....-'-1 r---,-l-1---,.___,..ll MilES I ill I I I I I KilOMETERS 

5 0 !i 1G Hi 20 

figure m~p of southern New Jersey.,showing line of 250-milligrams-per-liter chloride 

concentrationl. cross section A • A'. and area 1. 1 

4 
w 

a: 

<( 

·NORTH ~a: 

A ...Jw 

w~ NGVD . o a: 

of 1929 

-500' 

-1000' 

-1500' 

-2000' L 

-2500' 

-3000" 

-3500' 

-------------

LINE OF 250 

mg/1 CHLORIDE -

CONCENTRATION 

~ 

Figure 2 .. --Cross section of Potomac-Raritan-Magothy aquifer system 

(Modified from Luzier, 1980,fig. 4) .. 

~ 

SOUTH 

A' 

--

NGVD 

.of 1929 ~ 

-500' 

-1000' 

-1500' 

-2000' 

-2500' ' 

...;.;,3000' 

-3500' 

V1 
(1975) and Petters (1976). Brown, Miller, and Swain (1972) and 

Schlee and others (1976) contain a detailed discussion of the 

structural and stratigraphic framework. 

The Potomac-Raritan-Magothy aquifer system is overlain by a 

confining layer consisting of the Merchantville Formation and the 

Woodbury Clay. The Woodbury Clay is the least permeable confining 

layer in the Coastal Plain of New Jersey (Barksdale and others, 

1958, p. 136). These units effectively separate the PotomacRaritan-Magothy aquifer system and overlying aquifers, such as the 

Englishtown Formation and the Wenonah Formation-Mount Laurel Sand. 

The Potomac group and the Raritan and Magothy Formations seem 

to function as a hydrologic un Barksdale and others (1958, p. 

91) believe that the major aquifers within this system are 

hydraulically connected. Long-term records of observation wells 

indicate that much of the aquifer system in New Jersey responds 

uniformly to pumping stress (Luzier, 1980). Most notably, 

potentiometric heads in most of the confined part of the aquifer 

system have been declining at 1.5 to 2.5 ft/yr in recent years 

(1966-76) (Luzier, 1980). The aquifer system is the most heavily 

pumped in New Jersey, yielding 224 ft 3 /s in 1973 in Salem, 

Gloucester, Camden, and Burlington Counties. Individual wells 

yield more than 4.5 ft 3 /s. 

A large part of the Potomac-Raritan-Magothy aquifer system contains salty water, but the division between salty and fresh 

water is not distinct. Chloride concentration ranges from less 

than 10 mg/L to 27,000 mg/L (Luzier, 1980)~ Its concentration 

changes gradually laterally and with depth. A line of 0 mg/L 

chloride concentration (estimated) at the bottom of the aquifer 

system (Gill and Farlekas, 1976) is shown in figure 1. Chloride 

concentration increases downdip from this line. The line of 250 

mg/L chloride concentration at the top of the aquifer system is 

farther downdip (fig. 2). 

6 
CONJUNCTIVE USE OF DELAWARE RIVER WATER 

AND GROUND WATER 

The use of Delaware River water to s~pplem~nt ground-water 

supplies is one method of slowing the rate of potentiometric head 

decline in the Potomac-Raritan-Magothy aquifer system due to 

pumping. The Delaware River Basin Commission (DRBC) developed the 

idea of using river water for supply at high flow and ground water 

at low flow. This management method is termed, in this report, 

conjunctive use of Delaware River water and ground water or, more 

simply, conjunctive use. This report contains the results of 

computer simulations of the conjunctive use. 

Availability of Surface Water 

Use of Delaware River water at high flows min1m1zes effects 

of river withdrawals on downstream locations. Seasonally, flow of 

the Delaware River varys widely. For example, in 1976, maximum 

daily flow at Trenton, N.J., was 99,600 ft 3 /s, and minimum flow 

was 3,280 ft 3 /s (U.S. Geological Survey, 1977). DRBC is 

considering enforcing a policy requiring a minimum flow of 3,000 

ft 3 /s at Trenton (DRBC 1975). This minimum flow was used for the 

purposes of this reporte If, for example, 3,200 ft 3 /s is flowing 

at Trenton, then 200 ft 3 /s could be withdrawn for conjunctive use. 

The assumption is also made that water for conjunctive use would 

be withdrawn in the vicinity of Trenton. 

Withdrawals of 200 and 600 ft 3 /s were assumed to be the 

minimum and maximum for conjunctive use. Accordingly, Geological 

Survey records of streamflow for water years 1913-76 were analyzed 

to find when streamflow at Trenton was less than 3,200 and 3,600 

ft /s~ Daily flows were tabulated by months to find the average 

number of days per month that streamflow was less than 3,200 and 

3,600 ft 3 /s. If streamflow was less than a given rate for more 

than 3 days in a month, flow was considered inadequate for 

withdrawal during the whole month. Flow was less than 3,200 ft 3 /s 

during more than 3 days each month from July through November. 

During the other 7 months, flow was more than 3600 ft 3 /s during 

all but 3 or less days of each month. Thus, as much as 600 ft 3 /s 

is considered available for conjunctive use 7 months a year. 

To compare the long-term average with extreme low flow, the 

drought of 1962-66 was examined. Each year was analyzed 

separately to find the number of days in each month that flow was 

less than 3,200 ft 3 /s. Three of the years, 1963-65, had flows 

less than 3,200 ft 3 /s during more than 3 days during each of 6 

months rather than the average of 5 montbs. 

Selection of Area 

Although no direct cost estimates were made, it would be most 

feasible to apply conjunctive use to areas near Trenton where 

water demand is large, as Trenton would be the point of 

withdrawal. The area in which conjunctive-use schemes were 

7 
s lated is about 150 mi 2 , which is indicated as area I in this 

report. (See fig. 1.) Forty percent of the total water withdrawn 

om the Potomac-Raritan-Ma aqui r system in New sey is 

used this area. 

COM R MODEL SI~ULATIONS 

A computer model of the Potomac-Raritan-Magothy ifer 

stem (Luzier, 1980) was used to simulate ground-water response 

to conjunctive use of water om the Delaware River ground 

wa The model simulations are projections from 1974 through 1999~ The computer simulations were divided into three groups. 

The simulations in each group share a common set of assumptions 

about aqui conditions. The first simulation in each group 

shows response of the aquifer to the assumptions alone. The 

second and third simulations show response to conjunctive use. 

The effect of conjunctive use can be obtained by comparing 

simulations incorporating conjunctive use with the corresponding 

base simulation. 

A summary of the model simulations and a brief description of 

conditions in each is given in table 1. nReplacement of pump e" 

in this table and throughout this report indicates that water from 

the Delaware River is simulated to supply the projected water use 

in area I for 7 months of each year from 1984 through 1999. At 

all other times, the simulated supply for water use is ground 

water .. 

nNinety percent recharge" indicates that artificial recharge 

was simulated in area I r 7 months of each year from 1984 

through 1999 at 90 percent of the projected water-use rate for 

area I. Recharge was simulated at the locations of wells existing 

in 1973, and the recharge distribution was the same as the 

istribut n of projected water use. None of the simulations 

consider recharge separately om replacement of pumpage because 

of the h h cost of re More detailed discussion of each 

of simulations follows this section. 

F ure 3 shows potentiometric heads at the 

simul ons (1974). These heads are the result o 

calibrat n simulation made by Luzier (1980). 

actual pumping rates om 1956-73 were used. The 

water b get showing flow to discharge areas and 

areas. Bud values for 1974 are shown below. 

inning of all 

the model 

is simulation, 

model computes a 

om recharge 

8 
Table 1 • -Summary of model simulations 

Model Water-use *Head 

simulation rate barrier 

Group A 

A 3 percent No 

growth. 

AO 3 percent No 

growth. 

A90 3 percent No 

growth. 

Group B 

B 3 percent Yes 

growth .. 

BO 3 percent Yes 

growth. 

B90 3 percent Yes 

growth. 

Group C 

c 1 and 2 No 

percent growth .. 

co 1 and 2 No 

percent growth. 

C90 1 and 2 No 

percent growth .. 

* Artificial recharge to maintain a constant 

head 1 0 feet above NGVD of 1929, beginning 

in 1984. 

Conjunctive-use scheme 

None. 

Replacement of pumpage. 

Replacement of pumpage 

plus 90 percent 

recharge. 

None. 

Replacement of pumpage. 

Replacement of pumpage. 

plus 90 percent 

recharge. 

None. 

Replacement of pumpage. 

Replacement of pumpage 

plus 90 percent 

recharge. 

9 
EXPLANATION 

LINE OF EQUAL POTENTIOMETRIC HEAD· 

Datum is NGVO of 1929. Negative sign 

md•cates head is below sea level 

Contour interval 20 feet. 

0 !i ,10 15 

l...l..i' 'L,-\'rl-'...ti-.....---A-1 .,.---,t.l--r---'1 MILES jilll I I I I KILOMETERS 

5 0 5 Hl 15 20 

Figure 3.--Potentiometric heads at the start of the model simulations, 197 4 

(from 1980) .. 

10 
Mass balance term 

Pumping- - - - - - - - - - - - - - - - -

Net induced recharge from Delaware River 

(consists of net induced recharge from 

constant head boundary along and 

near Delaware River) 

Leakage from overlying aquifers- -

Cubic feet per 

second 

336 

95 

99 

Recharge from precipitation on outcrop area- 96 

Release from aquifer storage - - - - - - - -

Other sources - - - - - - - - - - - - - - - (consists of net induced recharge from 

constant head boundary other than along and 

near Delaware River. See Luzier [1980] for 

description and location of constant head 

boundary) 

1 

39 

In devising the conjunctive-use schemes used in this report, 

proximity to the Delaware River at Trenton, demand for water, and 

availability of water in the Delaware River were considered. 

Other factors would have to be evaluated before management schemes 

could be implemented. For example, before water from the Delaware 

could be substituted for ground water or used for artificial 

recharge, the chemical quality and treatment of the water would 

have to be studied. Also, current research on artificial recharge 

of aquifers would need to be investigated. 

Initial trial simulations used monthly values for pumping and 

artificial recharge, so that the monthly effects of conjunctive 

use could be simulated. Trial simulations were then made using 

average annual rates for pumping and artificial recharge. 

Although the annual method could not simulate the monthly effects 

of conjunctive use, both methods resulted in essentially the same 

average annual water levels. Therefore, all subsequent 

simulations used average annual rates. For example, if recharge 

at rate, Q, is specified for 1 months of the year, then recharge 

of (7/12)Q was applied for the entire year. 

Grou A Simulations 

Annual water-use rates for group A simulations were projected 

through the use of a 3 percent annual growth, which according to 

Luzier (1980) is the highest expected growth rate. The yearly 

water-use rate was determined by multiplying the previous year's 

value by 1.03. The water-use rate for 1974 was determined by 

multiplying actual 1973 pumping rates by 1.03. Thus, spatial 

11 
distribution of projected water use during 1974 to 2000 is assumed 

to be the same as in 1973. Outside of area I, the projected 

water-use rate is supplied by ground water. Inside area I, the 

sources which supply the water-use rate are varied in each 

simulation as listed below. 

Simulation A: No conjunctive use--entire water 

use comes from pumpage 

Simulation AO: replacement of pumpage by surface 

water for 7 months annually 

Simulation A90: replacement of pumpage by surface 

water for 7 months annually plus 

recharge at 90 percent of the 

projected water-use rate 

Results from group A simulations are shown by potentiometric 

head contour maps (figs. 4-6). The effects of conjunctive use in 

simulations AO and A90 may be seen by comparing with simulation A. 

Comparing figures 4 and 5 indicates that heads in the center of 

the large cone of depression near area I are up to 60 ft higher in 

the year 2000 as a result of conjunctive use. The effects of 

recharge are shown in figure 6. The center of the cone of 

depression in simulations AO and A90 is shifted to the south. The 

shift is a result of reduction of net ground-water withdrawal in 

area I; whereas, south of area I there is no reduction. Far om 

area I, the effects of conjunctive use are small (figs. 4 and 6). 

Heads in group A simulations at the end of 1999 are also shown in 

perspective (fig. 7). 

Figures 4-6 show average ground-water speed contours as well 

as potentiometric head contours. The speed contours were 

constructed from velocity values, which were calculated by Darcy's 

Law. Velocity cannot be contoured because velocity indicates both 

direction and magnitude of flow; therefore, only the magnitude of 

velocity (speed) was contoured~ Direction of flow may be 

determined by the direction of the potentiometric gradient. 

Direct n of flow is toward decreasing heads and perpend ar to 

head contours. It was assumed when calculating the velocities 

that the aqui r contains only fresh water and that effective 

porosity is 25 percent. Also, it was assumed that one-third of 

the aqui r thickness consists of sand and that water moves only 

through the sand. Luzier (1980) found that 20 to 50 percent of 

aquifer thickness is sand. Because of these assum ions and the 

regional approximations used in making the model, the speed 

contours are generali and are regional in nature. The speed 

contours may be used to estimate the rate of movement of 

contaminants in the aquifer if it is assumed that contaminants 

move with (at the same speed as) the water without consideration 

12 
EXPlANATION 

LINE OF EQUAL POTENTrOMETRIC HEADDatum is NGVO of 1929. Negative sign indicates 

head is below sea level. 

e 1 Hydrograph site 

figure 4.~-Heads at tile end of 1999 

SdlltiiUI. 

J 

5 0 5 10 15 

l-1 J...,' ~,-~• '.-.J.'-ril-....-..~..1 .....-----.-J-1--r_,i MILES Jill! I I f KILOMETERS 

!i 0 10 Hi 20 

r simulation A without coniunctive-use 

13 
EXPLANATION 

LINE OF EQUAL POTENTIOMETRIC HEAO--

'<O Datum is NGVD of 1929. Negative sign indicates 

"-.._ head is below sea level. 

Figure 

Contour interval 20 feet. 

LINE OF EQUAL GROUND-WATER SPEEDContour values 30 and 300 feet per year. 

Hydrograph site 

0 5 HI 15 

._I ._,.,, ''r'l',...,..'.t!-.-'-1 .--~1___,.__,1 MilES 11111 I I I KilOMETERS 

!i 0 10 15 20 

Heads at the end of 1999 for simulation AO with conjurective-1.ue 

scheme. 

14 
EXPlANATION 

UNE OF EQUAL POTENTIOMETRIC 

Datum is i\IGVO of 1929 Negative sign indicates 

head is below sea level. 

Contour interval 20 feet. 

LINE OF EQUAL GROUND-WATER 

'-.. Contour values 30 and 300 feet per vear. 

~ 1 Hydrograph site 

II Hl Hi 21'1 

figure 6.--Heads at the end of 1999 for simulation A90 with conjunctive-use scheme 

plus 90 perceswt recllar;e15 
filllte 1 .. -I' en• ettiv e vieW pouotiatlleuit \II 11-. 11-0. and A90 attlleeo4 of 1999. 
of dispersion. The speed contours also show the effects of 

conjunctive use. For example, figures 4 and 5 show that 

simulation AO (fig. 5) has little effect on speed contours, except 

in the vicinity of area I, where both the 30 ft/yr and 300 ft/yr 

contours are moved a few miles west. 

Results of group A simulations are also presented in 

hydrographs at selected sites. The site locations are shown in 

figures 4, 5, and 6, and the hydrographs are shown in figures 8 

and 9. The hydrographs show an increase in head as a result of 

conjunctive use starting in 1984. 

Flows for group A simulations at the end of 1999 are given in 

table 2. One of the primary reasons for considering conjunctive 

use is the concern over the amount of recharge induced into the 

Potomac-Raritan-Magothy aquifer system from the Delaware River& 

Table 2 shows the effectiveness of conjunctive use in decreasing 

inflow from the Delaware. For example, in simulation AO, an 

average withdrawal of 168 ft 3 /s from the river near Trenton for 

conjunctive use will reduce net induced recharge by 127 ft 3 /s, as 

compared with simulation A. Reduction of net induced recharge 

from the river is about 75 percent of the surface-water withdrawal 

for simulations AO and A90. 

To evaluate the cost of implementing the conjunctive-use 

schemes, one must know the projected water-use rate, the 

withdrawal rate from the river, the pumping rate, and the 

artificial recharge rate within area I. These rates may be 

calculated from the 1973 pumping rate in area I, which is 133 

ft 3 /s. 

For example, consider group A simulations in 1984, the first 

year of conjunctive use$ If water-use rate, U, is the 1973 rate 

compounded at 3 percent annually for 11 years, then: 

U = 133 x 1.03 11 = 184 ft 3 /s 

Consider simulation A90 for 1984, in particular. The pumping rate 

is 0 for 7 months of the year and U for 5 months. This is an 

average rate of 5/12(U) or 77 ft 3 /s* The recharge rate is 90 

percent of U or 166 ft 3 /s for 7 months and 0 for 5 months, an 

average yearly rate of 97 ft 3 /s. The withdrawal rate from the 

river is the pumpage replacement rate plus the artificial recharge 

rate. This is 0 for 5 months and U + 90 percent of U or 350 ft 3 /s 

r 7 months. These calculations may be made at any time in 

oups A, B, and C simulations. 

Gr 

For group B simulations, annual water use was projected, as 

for group A, by applying a 3 percent annual growth in pumping to 

wells existing in 1973. A head barrier makes group B simulations 

different from group A9 

17 
18.0 r--- r--

-72.0 

A 

--90.0 __L_, ___ , _ __...._ ____ ____. 

N 

"' en 

- e.g 

,..... 

m 

- 0 

00 

m 

'I""" 

Q") 

~ 

'!""' 

00 

00 

m 

'I""" 

N 

m 

m 

'I""" 

Figure 8.--Hydrographs for group A simulations at site 1. 

e.g 

en 

m 

'I""" 

0 

0 

0 

N 

~ 

0 

0 

N 
0.00 

-18.0 

-36.0 

0. 

N 

-~.0 l SIMULATIOJ 

A90 

0. 

1.1.. 

0 

~ -72.0 ...... :::;) 

w ..... 

-( 

c 

Z.....a 

-..c: 

.. u c_ -90.0 

-( ..... ,siMULATION w«X: :z:W AO 

> ~u oc 

...... -108 w 

~ 

0 

-126 

-144 

r SIMULATION 

A 

-162 

N (J:) 0 ~ 00 N (.0 0 ~ 

" " 00 00 0') 0') 0 0 

m 0') en Cl) Cl m m 0 0 ,_ .... N N ,_ \""' ... ..... .... 

9.--Hydrographs for group A simulations at site 2. 

19 
Table --Model flow rates at end of 1999 for group A simulations 

(cubic feet per second) 

Leakage Recharge from Release 

Withdrawal Net induced from precipitation from 

tvbdel Artificial from recharge from overlying on outcrop aquifer (~her 

Pumping recharge Delaware River 1 Delaware River 2 aquifers area storage sources 3 

A 

AO 

725 

557 152 

168 

320 

the Delaware River is not 

a par~t of the model, but it is a result of the 

the simulations .. 

2 Consists of net induced recharge from constant 

head boundary along and near Delaware Rivero 

3 Consists of net J.uv.uv~ recharge from constant 

than along and near Delaware 

(1980) for description and 

head boundary 

See 

constant head 

300 

64 

169 

134 

95 

96 

96 

96 

1 

10 

8 142 

N 

0 
The head barrier consists of 19 simulated wells with heads 

maintained at 10 ft above National Geodetic Vertical Datum of 1929 

beginning in 1984. These simulated wells (fig. 10) are along the 

saltwater-freshwater transition zone (Luzier, 1980). This barrier 

was considered by Luzier (1980) as a means of preventing further 

northwestward movement of salt water. It is assumed for the 

simulations that the 10 ft head is maintained by injection of 

fresh water supplied from a source external to the 

Potomac-Raritan-Magothy aquifer system. Identification of a 

source need not be specified for modeling purposes. Besides 

preventing the movement of salt water, the barrier provides 

recharge to the Potomac-Raritan-Magothy aquifer. Specific group B 

simulations are listed below. 

Simulation B: no conjunctive use--entire water use 

comes from pumpage 

Simulation BO: replacement of pumpage by surface 

water for 7 months annually 

Simulation B90: replacement of pumpage by surface 

water for 7 months annually plus 

recharge at 90 percent of the projected 

water-use rate 

Potentiometric contour maps from group B simulations are 

shown in figures 10-12. Comparison of simulation BO with 

simulation Bat the end of 1999 (figs. 10 and 11) shows that the 

conjunctive-use scheme without recharge results in heads that are 

about 60 ft higher at the center of the cone of depression near 

area IG Figure 13 shows perspective views of heads in group B 

simulations at the end of 1999. The ridge caused by the barrier 

wells is prominent in these views. 

The effect of the head barrier is also apparent in the group 

B simulation hydrographs (figs. 14-16). See figures 10-12 for 

hydrograph locations. In the hydrographs, simulation B, which has 

no conjunctive use, shows a rise in head beginning in 1984. This 

rise is a result of the head barrier. The effect of the barrier 

is greatest close to the barrier. The hydrograph at site 3 which 

is close to the barrier, shows a large effect from the barrier 

(simulation B) and only a slight additional effect from 

co unctive use (simulations BO and B90). (See fig. 16.) 

Flows for group B simulations are shown in table 3. Inflow 

om the head barrier is included in this table As more surface 

water is used for conjunctive-use and recharge schemes, less 

inflow from the barrier wells is required to maintain heads at 10 

ft~ 

21 
til 1 

EXPLANATION 

LINE OF EQUAL POTENTIOMETRIC HEADDatum IS NGVO ol 1929 Negative sign indicates 

head is bel ow sea level. 

Contour 1n1erval 20 feet 

LINE OF EQUAL GROUND-WATEfl SPEED--

Contour values 30 and 300 fetH per year. 

HEAD BARHIER WELL-Head IS 

at 10 teet, mean sea level, at these locations 

starting in 1984 

Hydrograph Site 

10 15 

I I I I I I I I MilES 

........._,jr'TI'rl ,..,, 1+-..,.--....._,.1 --rl-'----rl ---' Kll OME TE RS 

ll 10 '15 20 

Figure HL--Heads at the end of 1999 for simulation B without conjunctive--use 

scheme .. 

22 
l \"-I \"'"\ 

,~\ (/,/ 

EXPLANATION ~--~--\ \---~r/ Ll•dt OF EQUAL POTENTIOMETRIC HEAD- \..,_, 

Datum IS NGVD of 1929 Negat1ve sign mdicates ''--<, 

head IS below sea level. ~ 

Contour mterval 20 feet. 

' 'Jq LINE OF EQUAL GROUND-WATER SPEED-

' Contour values 30 and 300 feet per year. 

\ 

HEAD BARRIER WELL-Head is maintained 

0 at 10 feet, mean sea level, at these locations 

starting in 1984. 

e 1 Hydrograph site 

5 HI 15 

L..J..,JYr+r+---.-___j_l ..--~I___...___JI MILES I I I KILOMETERS 

10 1!i 20 

Figure 11.--Heads at the end of 1999 for simulation BO with conjunctive-use 

SC~Ie·JDe. 

/ \" 

23 
0 

EXPLANATION 

LINE OF EQUAl POTENTIOMETRIC HEADDatum is NGVD of 1929. Negative sign indicates 

head is below sea level. 

Contour interval 20 feet. 

LINE OF EQUAL GROUND-WATER SPEEDContour values 30 and 300 feet per year. 

HEAD BARRIER WELL-Head is maintained 

at 10 feet, mean sea level, at these locations 

starting in 1984. 

Hyd;og;aph siie 

,-

{ .. 

{ 

\ 

I 

I 

I 

/(' "' '-..,.........._~- .... '\.,..--1"./1 --1 

{ 

I 

I 

) 

0 !i 10 15 

~.._! !..f' 'TI'rf'rtl-.,........._1 ,-...,.-'-1 _,.-...J! Ml LES I 11 I I I I I KILOMETERS 

5 0 10 15 20 

Figure 12.*-Heads at the end of 1999 for simulation 890 with conjunctive-use scheme 

phu 90 percent recharge. 

24 
f \ 

1111 1 

e \3 _ .. I' 

0 

r 

5 

ll" c t i ~ e v i e11'1 of p o te 11 ti o m e H i t b e a t1 s I o r s i m u I at i o 

B. BO. B91l at til• end of 1999· 

'2.5 
36.0 ~---,---~----,----.-----,-------,--------y------. 

18.0 

SIMULATION 

~~ I I B90 

w 

u.. 0.00 

z 

...J 

< 

u 

:::r::t- ~ 

uw -18.0 

di> 

I r 

t-u --..__ 

w_ -----------SIMULATION ~!;; 

0 

80 

&-

~ !': -36.0 

&-

0 

c.. 

-54.0 

-72.0 L_ ___ _L ____ L_ ____ ..L_ ___ ___.l'-----..,.4.----

N 

m "" ..... 

(.0 

m "" ...... 

0 

eo 

m 

..... 

~:::r 

co 

m 

..... 

00 

00 

0') 

..... 

N 

m 

m 

OF"' 

Figure 14 .. --Hydrographs for group B simulations at site 1.. 

~SIMULATION B 

w 

m 

m 

..... 

0 

0 

0 

N 

'l1.t 

0 

0 

N 

N 

(}'\ 
l:j 

.... 

aq 

s:::: 

~ 

.... 

OJ 

. 

I 

~ '< c.. 

6 

aq 

'1 

.§ 

P" 

OJ 

S' 

'1 

~ 0 

.§ 

to 

OJ 

.... 

a 

s:::: 

...... 

~ .... 

0 

::s 

OJ 

~ 

OJ 

.... 

..... 

(\) 

p 

POTENTIOMETRIC HEAD, IN FEET 

NATIONAl GEODETIC VERTICAl DATUM OF 1929 

I I I 6, w .... o .... :g j:j ~ o-, coo. 0 !XI 

0 0 0 0 0 0 

1972 ;_------~--~---.--------,-------.--------.------~ 

1976 

1980 

1984 

1988 

1992 

1996 

2000 (I) ~ · :5:: :5:: s: 

c c me tc~ tcr cor Ol> ol> 

...; ...; ...; 

0 0 0 

2004 2 2 2 

27 
1972 

1976 

l,:j 

..... aq 

J: 

...., 

CD 1980 .... 

Cl) 

. 

I 

I 

~ 0.. 

11 

~ 1984 ., 

.§ 

P" 

Ill 

S' 

...., 

~ 0 1988 .§ 

b:l 

Ill 

.... 

~ ..... 

~ .... 

0 1992 

::s 

Ill 

~ 

Ill 

::;: 

CD 

Cl:) 

. 1996 

I 

...... 

N 

0 

POTENTIOMETRIC HEAD, IN FEET 

NATIONAL GEODETIC VERTICAl DATUM OF 1929 

I I 

i! w ... 0 en co 0 0 b b 0 

I 

.... 

CIO 

b 

28 
Table 3.--Model flow rates at end of 1999 for group B simulations 

feet per second) 

Leakage Recharge from Inflow Release 

Withdrawal Net induced from precipitation from fran 

Model Ar·tificial from recharge fran overlying on outcrop head aquifer Other 

simulation Pumping recharge Delaware River 1 Delaware River 2 aquifers area barrier storage sources 3 

B 725 -- --

BO 557 -- 168 

B90 557 152 320 

1 Withdrawal from the Delaware River is not 

a part of the model, but it is a result of the 

assumptions used in the simulations. 

2 Consists of net induced recharge from constant 

head boundary along and near Delaware River$ 

3 Consists of net induced recharge from constant 

head boundary other than along and near Delaware 

River. See Luzier (1980) for description and 

location of constant head boundary~ 

248 147 96 93 7 138 

134 115 96 73 6 136 

35 79 96 56 6 135 

N 

\0
Grou C Simulations 

For group C simulations, projected water-use outside of area 

I is calculated through the use of a 2 percent annual water-use 

growth for wells existing in 1973. In area I, however, 1 percent 

annual growth is applied. The 2 percent and 1 percent values were 

generalized from estimates of water use for Camden, Burlington, 

and Gloucester Counties up to year 2030 provided by the U.S. Army 

Corps of Engineers (written commun., 1978). 

Group C simulations are listed below. There is no head 

barrier. 

Simulation C: no conjunctive use--entire water use 

comes from pumpage 

Simulation CO: replacement of pumpage by surface 

water for 7 months annually 

Simulation ego: replacement of pumpage by surface 

water for 7 months annually plus 

recharge at 90 percent of the projected 

water-use rate 

Results from group C simulations are shown in potentiom ric 

contour maps (figs. 17-19) and in hydrographs (figs. 20-21). 

Conjunctive use without recharge results in a head difference of 

more than 30 ft. between simulations C and CO at the end of 1999, 

(figs_ 17 and 19). The flows for group C simulations are shown in 

table 4. Again, conjunctive use is effect e in reducing the 

stress on the Potomac-Raritan-Magothy aquifer systemo 

30 
I 

EXPLANATION I ---_! 

' LINE OF EQUAL POTENTIOMETRIC HEAD-

'<0 Datum is NGVO of 1929 Negative sign indicates 

'- head is below sea level. 

' Contour interval 20 feet. 

'J. LINE OF EQUAL GROUND-WATER SPEED-

'0' Contour values 30 and 300 fP.et per year. 

" 1 e Hydrograph site 

F i g u r e 17. --H e a d s a t t h e e n d o f 1 9 9 9. f o r s i m u I a t i o n C w i t h o u t c o n j u n c t i v e - u s e -

scheme. 

31 
• 1 

\ __ .... I 

EXPLANATION 

LINE Or t:QUAL POTENTIOMETRIC HEADDatum is NGVD of 1929. Negative sign indicates 

head is beiow sea level. 

Contour interval 20 feet. 

LINE OF EQUAL GROUi~O-WATER SPEEDContour values 30 and 300 feet per year . 

Hydrograph site 

5 0 !i 11:1 15 

~.....1 ''-T'Yt'-+'rtl-.-'-1 ,.-.,-~-1 __,___,1 MILES 

jiHI I ' I KilOMETERS 

5 (I 10 15 20 

figure 18.--Heads at the end of 1999 for simulation CO with coniunctive-use 

scheme. 

32 
• 1 

EXPLANATION 

LINE OF EQUAL POTENTIOMETRIC HEADDatum is NGVD of 1929 

head is below sea level. 

Contour interval 20 feet. 

Negative sign indicates 

LINE OF EQUAL GROUNDWATER SPEEDContour values 30 and 300 feet per year . 

Hydrograph site 

0 5 10 15 

w..,.• '1.,-1'~'-rtl--.--.~-1 ,.---.-LI---.____JI MILES jill I I I I KILOMETERS 

5 0 HI 15 20 

F i g u r e 1 9 .• - H e a d s at t h e · e n d o f 1 9 9 9 f o r s i m u I a t i o n 1 C 9 0 

scheme phu 90 percent recharge. 

with conjunctive-use 

33 
1972 

1976 

1980 

I 

U'l 

.+l> 

0 

-

1984 ~ 

1988 

1992 

1996 

2000 

2004 

POTENTIOMETRIC HEAD, IN FEET 

NATIONAL GEODETIC VERTICAL DATUM OF 1929 

en 

:s: 

c 

.r- ("'))> 

-1 

0 

2 

I 

w 

!"l 

0 

41 

..... 

00 

0 

~ 

:s: 

c 

nr 

Ol> 

-1 

0 

2 

0 

0 

0 

I 

I 

5!! 

s: 

nC "'r 

0~ 

0 

2 

.... 

CX) 

0 

I 

1 I 

I 

f-rj 

..... crq 

~ 

'"1 

(l) 

t,:) 

0 

. I 

I 

q 

0. 

., 

0 

crq 

'"1 

.§ 

P' 

(/) 

b' 

., 

IQ. 

'"1 

0 

,§ 

0 

(/) 

,... 

a 

~ 

~ ..... 

0 

\::l 

(/) 

~ 

(/) 

..... 

rl-

(!) 

..... 

. 
-18.0r-------~--------,---------.--------.---------.--------~------~--------~ 

0. 

N 

0. --36.0 u... I I -----....,siMULATION 0 ...... C90 w~ 

~:l .... z< 

-o 

........ -54.0 

a< 

<u 

w- :ct- I ~--- ~ , ~SIMULATION 

uw co 

-> a&: :u ~ -72.0 

~:u 

Oo 

t=O 

zw 

wC) 

.... o ..... A.< -90.0 

z I ~SIMULATION 0 c .... 

<( 

z 

-108 

N CD 0 ~ ClO N CD 0 ~~ 

"""" """ ClO ClO en 0') 0 

en 0') 0') en 0') 0') 0') 0 i~ - - - - - - - N 

Figure 21,~--Hydrographs for .group C simulations at site 2 .. 

w 

V1 
w 

0\ 

Table 4.--Model flow rates at end of 1999 for group C simulations 

(cubic feet per second) 

Leakage Recharge from Release 

Withdrawal Net induced from precipitation from 

tvbdel Artificial 

recharge 

from recharge fran overlying on outcrop aquifer Other 

simulation Pumping Delaware River 1 Delaware River 2 aquifers area storage sources 3 

c 

co 

5 

411 

411 

101 

192 

from the Delaware River is not 

a part of the model, but it is a result of the 

assumptions used in the simulations. 

2 Consists of net induced recharge from constant 

head boundary along and near Delaware River. 

3 Consists of net induced recharge from constant 

head boundary other than along and near Delaware 

River. See Luzier (1980) for description and 

location of constant head 

176 

10.2 

38 83 

96 

96 

96 

6 

5 

5 

104 

101 

99 
DISCUSSION OF RESULTS 

Effect of the Head Barrier 

The effect of the simulated head barrier may be seen by 

comparing the results of group B simulations with those of group 

A. At and near the barrier, group B heads (figs. 10-12) are 

higher than group A (figs. 4-6), and the cone of depression near 

area I is much smaller and shallower in group B. The higher heads 

in group B are the result of water injected into the aquifer at 

the barrier (table 3). This additional water causes less water to 

infiltrate from the river in group B simulations than in group A 

(tables 2 and 3). 

The head barrier is included to prevent the northward 

movement of saline water toward pumping centers. By comparing ~ne 

direction of head gradient, which is the direction of ground-water 

flow, for groups A and B, one can see the effect of the barrier. 

In group A, the direction of flow near the barrier is generally 

from the south toward the center of the cone of depression. In 

group B, however, the direction of flow is different on each side 

of the barrier. North of the barrier, simulated flow is toward 

the center of the cone of depression. This flow consists of fresh 

water from the barrier wells. South of the barrier, direction of 

flow is reversed. Thus, saline water on the south does not pass 

the barrier. 

The effectiveness of the head barrier is dependent upon 

maintaining a continuous line of head at 10 feet or more. 

Although 19 wells were used to simulate the head barrier, it would 

probably be desirable to use more wells in a real situation. The 

10 foot heads maintained in the simulated wells are average 

values. Heads at each injection site would be much higher than 

this average value. The greater the spacing is between wells, the 

higher the heads must be at each well in order to prevent heads 

between wells from dropping below 10 feet. 

Effect of Water-Use Growth Rate 

The effect of water-use growth rates may be seen by comparing 

group A simulations with group C. In 1999, the total projected 

water use in the Potomac-Raritan-Magothy aquifer is 725 ft 3 /s for 

group A simulations and 512 ft 3 /s for group C. This large 

difference results in higher heads in group C simulations. The 

head near the center of the cone of depression is 160 ft below sea 

level for simulation A (fig. 4) and 100 ft below sea level for 

simulation C (fig. 17). This head difference, caused by the 

different growth percentages, suggests that a firm estimate of 

water use is required before conjunctive use can be evaluated. No 

attempt has been made in this study to evaluate the validity of 

the two growth schemes used. 

37 
e hydrographs (figs. 8-9, 14-16, and 20-21) show sharp 

ncrease in head after ap ication df conjunctive use in 1984. 

kes 2 years or less for the heads to reach their maximum level 

before starting the downward trend again. The rapid re 

reflection of the low stor e coefficient of the aqui r tern 

If changes in stresses (pumping and artificial recharge) sto 

at any time during the model simulations, heads would approac 

steady-state conditions within 2 years3 Steady-state lev s would 

be ween the heads existing at the time that changes in stresses 

stopped and the heads that would have occurred 2 years later, 

assuming that changes in stresses did not stop. In the 

simulations, heads decrease slowly in response to the annual 

water-use increase except during 1984-85 in the conjunctive-use 

simulations. If changes in stresses stopped during slow head 

change, the steady state levels would be approximately e same as 

the water levels when the stresses became constant. 

Sto Head Declines 

Heads continue to decrease in the s ations after 2 years 

of conjunctive use because of the continued growth of pumping. 

Pumping outside of area I is growing at the assumed growth rate 

since no conjunctive use is appliede Inside area I, during the 

first year of conjunctive use, pumping decreases to 5/12 of the 

water-use rate. But in subsequent years, pumping increases ain 

inside of area I because the pumping during the 5 months of no 

conjunctive use is increasing at the assumed growth rate. 

Although growth in pumping rate is smaller than without 

conjunctive use, there is still growth. 

There are two methods of stopping head declines. One would 

be to hold the pumping rate constant with no artificial re~harge, 

and the other would be to balance pumpage with artificial 

recharge. If a constant pumping rate were maintained, then heads 

would approach steady state rapidly. Any increase in demand for 

water would have to be from a source outside the Potomac-RaritanMagothy aquifer system. 

Although it would be possible to stop head declines by 

balancing pump e and artificial recharge, the model simulations 

show t it would be difficult to stop declines ever ere by 

recharging in area I. is is because recharge is most ef ctive 

at the location of recharge, and the effect decreases rap ly away 

om the rechar e site. A comparison of simulations A (fig. 4) 

and A90 ( g shows that the effect of conjunctive use in 

simulat n A90 is greater in area I than r om area I~ 

most e ctive method of artificial recharge, then, would 

i ect water at every pumping location; however, this wo 

economically impractical. The recharge sc es s at in this 

st y were ap i within area I, a small but highly p areae 

ami ation o the r a r s ation A90 at sites 1 a 2 

38 
(figs. 8 and 9) shows that pumpage and recharge are close to being 

at equilibrium (no head decline or rise) at site 1, but not at 

site 2. Theoretically, enough water could be recharged in area I 

alone to offset or· even reverse declines in all areas. However, 

the amount of recharge required would result in a tremendous 

buildup of water levels within area I, causing much of the 

recharge to discharge into the Delaware River. The amount of 

recharge needed would be much greater than the total PotomacRaritan-Magothy aquifer system pumpage. It would be impractical 

to attempt to recharge this quantity of water. 

SUMMARY AND CONCLUSIONS 

Model results show that conjunctive use of Delaware River 

water and ground water could be an effective method of slowing declin~ of the potentiometric head in the Potomac-Raritan-Magothy 

aquifer system. In the simulations, heads rise when conjunctiveuse is first applied, but decline again within 2 years. Continued 

growth of water use causes the resumption of declines. Declines 

after conjunctive use begins are slower. Depending on the amount 

of water used and the conjunctive-use scheme applied, heads at 

year 2000 could be at or above present levels over a large area of 

the aquifer. 

39 
R ERENCES 

Anderson, H. R*, and App , C. A., 1969, Geology and ground-water 

resources of Ocean County, New Jersey: New Jersey Department of Conservation and anomie Development Special Report 

29, 93 p. 

r k s d a l e , H . C . , G r e e nm an , D . W ., Lang , S .. M .., Hi l ton , G .. S .. , and 

Outlaw, D. E., 1958, Ground-water resources of the tri-state 

r ion adjacent to the lower Delaware River: w rsey 

Department of Conservation and Economic Development Special 

Report 13, 190 p .. 

Barksdale, H. C .. , Johnson, M. E .. , Schaefer, E. J .. , Baker, R~ C., 

and DeBuchananne, G. D., 1943, The ground-water supplies of 

Middlesex County, New Jersey: New Jersey State Water Policy 

Commission Special Report 8, 154 p. 

Brown, P .. M .., Miller, J .. A., and Swain, F. M .., 1972, Structural 

and stratigraphic framework, and spatial distribution of 

permeability of the Atlantic Coastal Plain, North Carolina to 

New York: U .. S. Geological Survey Professional Paper 796, 

57 p. 

Delaware River Basin Commission, 1975, Water management of the 

Delaware River Basin: Staff report, 249 p. 

Farlekas, G. M., Nemickas, Bronius, and Gill, H. E., 1976, Geology 

and ground-water resources of Camden County, New Jersey: 

U. S. Geological Survey Water-Resources Investigations 76-76, 

146 p. 

nneman, N. M., 1938, Physiography of eastern United States: 

New York, McGraw-Hill Book Co.t 691 Pe 

Gill, H. E., and Farlekas, G. M., 1976, Geohydrologic maps of the 

Potomac-Raritan-Magothy aquifer system in the New Jersey 

Coastal Plain: U. S. Geological Survey Hydrologic Investigations Atlas HA-557$ 

Hardt, W. F .. , and Hilton, G .. S., 1969, Water resources and geology 

of Gloucester County, New Jersey: New Jersey Department of 

Conservation and Economic Development Special Report 30, 

130 p" 

Jablonski, L. A., 1968, Ground-water resources of Monmouth County, 

New Jersey: New Jersey Department of Conservation and 

Economic Development Special Report 23, 117 p., figs. 

Luzier, J .. E., 1980, Digita simulation and projection of head 

changes in the Potomac-Raritan-Magothy aquifer system, 

Coastal Plain, New Jersey: U. S. Geological Survey 

Water-Resources 

Investigations 80-11, 112 p. 

40 
REFERENCES, Continued 

Parker, G. G., Hely, A. G., Keighton, W. B., Olmsted, F. H., and 

others, 1964, Water resources of the Delaware River basin: 

U.S. Geological Survey Professional Paper 381, 200 p. 

Perry, W. J .. , Jr., Minard, J. P., Weed, E. G. A., Robbins, E. I., 

and Rhodehamel, E. C., 1975, Stratigraphy of Atlantic Coastal 

Margin of United States North of Cape Hatteras-Brief Survey: 

American Association of Petroleum Geologists Bulletin, v. 59, 

p. 1529-1548. 

Petters, S. W., 1976, Upper Cretaceous Subsurface Stratigraphy of 

Atlantic Coastal Plain of New Jersey: American Association 

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