-SIM 

IN 

Tl N 

U.S. GEOLO'GICAL SURVEY - 'I 

ND 

MA 

s 

Water-Resources Investigations 80-11 

Prepared in cooperation with the New Jersey 

Department of Environmental Protection, Division 

of Water Resources 

N 

-M G 

E J 

Raritan BaY 
50272 ·t Ol 

REPORT DOCUMENTATION l:_REPORT NO. 3. Recipient's Accession No. 

PAGE 

Title and Subtitle -S projection of 5. Report Date 

in the Potomac-Raritan-Magothy aquifer system, Coastal Plain, 

New Jersey 6. 

June 1980 

. Luzier 

9. Performing Organization Name and Address 

Geological Survey 

Resources Division 

East State Street 

, New Jersey 08607 

Sponsoring Organization Name and Address 

Resources Division 

Sui::>pl<em~entary Notes 

8. Performing Organization Rept. No. 

USGS/WRI/NTIS/80-11 

10. Project/Task/Work Unit No. 

Contract(C) or Grant(G) No. 

Type of Report & Period Covered 

Final 

14. 

in cooperation with the New Jersey Department of Environmental Protection, 

of Water Resources 

-modeT was used fo-sTmuTafe ffie- response of the 

system to pumping stresses during the 18-year period, 1956-73. 

model was used to compute projected potentiometric heads and trends to the year 

Three sets of conditions were simulated: (1) no increase in extrac-

(2) continued growth in ground-water extractions at the rate of 3 percent 

; and (3) continued growth in ground-water extractions at the rate of 3 percent 

, 1n tion with the activation of a freshwater head barrier in the freshwater transition zone. 

Under the first set of conditions, further head reduction would cease over very 

within two years. Under the second set of conditions, the broad cone of 

ion would broaden and Heads would range from 60 to 160 feet below NGVD 

th declines after 1973 90 feet in some areas. The resultant 

would accelerate the movement of salty water toward 

centers. If a freshwater head barrier were constructed across a 5-mile 

in Gloucester, Camden, and Counties, the total rates of ection 

would range from about 56 cubic feet per second in year 1984 to about 95 cubic 

per second in year 2000. Barrier rates would be to about 20 

of the water 

Document Analysis a. Descriptors 

models, "''simulation analyses, , 

water, hydrologic properties, 

Identifiers/Open-Ended Terms 

Potomac Raritan Formation, Magothy Formation, New Jersey, 

Coastal Plain 

COSATI Field/Group 

Availability Statement 19. Security Class (This Report) 

Unclassified 

21. No. of Pages 

80 

No triction on distribution 1------------------------1--------------

20. Security Class (This Page} 

Unclassified 

See Instructions on Reverse 

22. Price 

OPTIONAL fORM 272 (4-77) 

(Formerly NT!$-35) 

Department of Commerce 
N J 

J 

By J . Luzier 

U.S. GE L ICAL SURVEY 

Water-Resources Investigations 80-11 

Prepared in cooperat n with the New Jersey 

Department of vironmental teet ion, Division 

of Water Resources 

May 1980 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

H. W. Menard, Director 

r additional information write to: 

U.S ological Survey 

436 deral Building 

P.O. Box 1238 

enton, New Jersey 08607 
CONTENTS 

Ab s t r act . . . . . . .. . . .. . . .. .. . . .. .. . - .. . . . . .. .. .. .. . . • . . . . 

Introduction .................................................. . Purpose and scope .. o • • • • • • • • • • • • • • • • • • • • • • • • •. • • • • • • • • • •• 

P r e v i o u s s t u d i e s . . . . . . . . . . . . . . . o • • • • o • • • • • • • • • ···: • • • • • • • • • .. • • 

Acknowledgments ........ o ... o .. o ........ o o o o............ . o. 0 • .. •• 

Contour maps used in report .......................... . 

The Potomac-Raritan-Magothy aqui r system .....................•.•.. 

General description ........................................... . Salty ground water ........................................ . . 

Digital model ...................................................... . Computer program and mathematical description .........•........ 

Grid size and boundaries ....................................... . Hydro log i c par am e t e r s .................•........................ 

Transmissivity ........................................... . Storage coefficient ....................................... . Confining layer.......................................... . Recharge from overlying aquifers and precipitation .•.......... 

Ground-water extractions, 1956-73 ............................. . Parameter adjustment and acceptance of the model ................... . Matching of well hydrographs and 1973 potentiometric surface .. . Comparison of steady-state solution to prepumping conditions 

(1900±) ...................................................... . Sensitivity of parameter adjustment ........................... . Model application in water management •.............................. 

Projected changes in potentiometric surface, 1974-2000, 

on the basis of 1973 well distribution ..................•.... 

Extractions held at zero growth rate .............•........ 

Ex tractions increasing at 1. 7 percent per year ............ . Extractions increasing at 3.0 percent per year .......... . Estimating amount of artificial recharge. required to 

delay or prevent migration of salty ground water ...........•. 

Ground-water velocities near fresh to salty water transition zone .. . Model-estimated ground-water budgets ............................... . Suggestions for further study ...................................... . 

Summar y and con c l us ions . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References .......................................................... . 

Figure 1. 

2. 

3. 

4. 

5. 

6. 

ILLUSTRATIONS 

Map showing location of the study area ............... . Map showing altitude of the top of the PotomacRaritan-Magothy aquifer system ........................ . Map showing altitude of the bottom of the PotomacRaritan-Magothy aquifer system ....................... . Cross section showing approximate distribution of 

chloride in the aquifer system ..............•.......... 

Summarized flow chart of the computer program and the 

digital model ........................................•. 

Map showing finite difference grid and boundaries used 

in the digital model .................................. . 

iii 

1 

2 

2 

4 

4 

4 

5 

5 

1 0 

1 3 

1 3 

1 9 

21 

21 

23 

25 

28 

32 

33 

39 

45 

45 

49 

49 

51 

51 

57 

57 

62 

62 

66 

68 

70 

3 

6 

7 

¢11 

14 

16 
ILLUSTRATIONS~-Continued 

Page 

7. Map showing distribution of transmissivity used in the 

model for the Potomac-Raritan-Magothy aquifer system. 24 

8. Map showing thickness of the Merch8ntville FormationWoodbury Clay confining layer .................. ,··~·· 26 

9 Map showing distribution of vertical hydraulic 

conductivity of the Merchantville Formation-Woodbury 

Clay confining layer used in the model............... 29 

10. Map showing the composite potentiometric surface of 

the Englishtown and Wenonah-Mount Laurel 

aquifers, 1959............... .. . . . . . . . . . . . . . . . . . . . . . . 30 

11. Perspective view of the composite potentiometric 

surface (1959) over the confining layer and the 

computed steady-state (1900±) potentiometric surface 

of the Potomac-Raritan-Magothy aquifer system........ 31 

12. Perspective view of the distribution of ground-water 

extractions from the Potomac-Raritan-Magothy 

aquifer in 1956, 1965, and 1973 system............... 35 

13. Map showing potentiometric surface of the PotomacRaritan-Magothy aquifer system, 1956 .. ~··8··········· 36 

14. Map showing potentiometric surface of the PotomacRaritan-Magothy aquifer system, 

November-December 1973 ............................. o o 37 

15 Perspective view of the potentiometric surfaces 

of the Potomac-Raritan-Magothy aquifer system 

observed in 1956 and 1973, respectively.............. 38 

16 Map showing potentiometric surface of the PotomacRaritan-MagotHy aquifer system, December 1973, 

computed by model.................................... 40 

17. Observed and computed hydrographs of wells parallel to 

or located within the outcrop area along the 

northwestern side of the cone of depression.......... 41 

18. Observed and computed hydrographs of wells located in 

the northwestern part of the cone of depression...... 42 

19. Observed and computed hydrographs of wells located in 

the southern part of the cone of depression.......... 43 

20. Map showing comparison of model-produced steady-state 

(1900±) potentiometric surface of the PotomacRaritan-Magothy aquifer system and that of Barksdale 

and others (1958, fig. 19)........................... 46 

21. Map showing the theoretical flow pattern and location 

of the interface between freshwater and salty water 

in the Potomac-Raritan-Magothy aquifer system 

before any pumping of ground water................... 47 

22. Graph showing effect of model-wide changes in 

parameters at observation well 9................ ..... 48 

23. Graph showing actual and projected ground-water 

extractions from the Potomac-Raritan-Magothy aquifer 

system, 1956-2000..................................... 50 

24. Observed and projected hydrograph trends of wells 1, 

2, 3, 4, and 5........................................ 52 

iv 
Table 

USTRATIONS--Continued 

Page 

25. Observed and projected hydrograph trends of wells 6, 

7 ' and 8 ......... e • • • • • • • • • • • • • • • • • • • ••••••••• s • • • • • 53 

26. Observed and projected hydrograph trends of wells 9 

and 10 ....................•.•...................... $. 54 

27. Map showing potentiometric surface of the PotomacRaritan-Magothy aquifer system at year 2000 

computed by model with annual extraction growth 

rate of 1. 7 percent................................... 55 

28. Perspective potentiometric surfaces of the PotomacRaritan-Magothy aquifer system observed in 1973 

and projected to year 2000 using annual extraction 

growth rates of 1.7 and 3.0 pe~cent............. ... .. 56 

29. Map showing potentiometric surface of the PotomacRaritan-Magothy aquifer system computed by model 

with annual extraction growth rate of 3.0 percent. 58 

30. Map showing potentiometric surface of the PotomacRaritan-Magothy aquifer system in year 2000 

computed by model with freshwater head barrier 

activated in 1984 and maintained at an altitude 

of 10 feet........................................... 59 

31. Perspective potentiometric surfaces of the PotomacRaritan-Magothy aquifer system computed by model 

at various time periods after activation of 

freshwater head barrier in 1984...................... 61 

32. Computed ground-water budget rates in the fine-grid 

1 • 

2. 

3. 

4. 

5. 

6. 

area, 1900± to the year 2000. .. ...................... 65 

TABLES 

Vertical variation in heads and chlorides at 

Ragov in well (well 13)................................. 9 

Time step sequencing used in the digital model, 

1956-2000 ...................... ~.................... . . 18 

Laboratory determined vertical hydraulic conductivities 

of the Merchantville Formation and Woodbury Clay 

determined from cores................................. 27 

Annual extraction rates, 1956-73. ....................... 34 

Estimated average ground-water velocities near the 

leading edge of the transition zone................... 63 

Computed ground-water budget net flux rates in cubic 

feet per second within the fine-grid area for various 

runs of the model...................................... 64 

v 
FACTORS FOR CONVERTING INCH-POUND UNITS TO 

INTERNATIONAL S EM UNITS (SI) 

Inch-pound units of measure have been used in this report 

may be converted to SI (International System of Units, a modernized 

ic system of measurement) by use of the following table: 

und units 

are feet ( 2 ) 

c feet per second 

ft 3 s) 

lens (gal) 

lens per minute (gal/min) 

hes (in) 

d- rce per square inch 

(lb in 2 ) 

B 

0.3048 

000929 

0.02832 

3 .. 7854 

0.06309 

2.54 

6.895 

vi 

To obtain SI units 

meters ( m) 

square meters ( 

cubic meters per second 

(m 3 /s) 

liters (L) 

liters per second (L/ s) 

centimeters (em) 

kilopascals 

(kPa) 
ABSTRACT 

The Potomac-Raritan-Magothy aquifer system of Cretaceou 

age, which is the principal source of water to the major 

population and industrial centers in the Coastal Plain of New 

Jersey, has undergone continuous and wid pread reduction in 

head. The reduced head, already below sea level throughout 

most of the aquifer system, in conjunction with encroachment 

of salty water toward centers of pumping, threatens the 

continued use of the aquifer as a source of freshwater in th 

area. 

A single layer, two-dimensional finite difference 

digital model was used to simulate the response of the 

aquifer system to pumping stresses during the 18-year period 

1956-73. Model simulations were based on close agreement 

between (1) observed and calculated heads and head trends for 

10 observation wells during the period, 1956-73; and (2) the 

computed nonpumping steady-state potentiometric surface and a 

potentiometric surface based on early water-level 

observations (1900±). In addition, the hydrologic budget 

estimated by the model appears to be reasonable for the 

transient (1956-73) and the steady-state (1900±) solutions 

The model was used to compute projected potentiometric 

heads and trends to the year 2000. Three sets of conditions, 

all using the 1973 distribution'of pumping centers, were 

simulated. The conditions are: 

(1) no increase in ground-water extractions; 

(2) continued growth in ground-water extractions at 

the rate of 1.7 and 3 percent annually and; 

(3) continued growth in ground-water extractions at the 

rate of 3 percent annually, in conjunction with the 

activitation of a freshwater head barrier in the 

fresh-salty water transition zone. 

Under the first set of conditions, further head 

reduction would cease over very large regions within two 

years. Under the second set of conditions involving a 3 

percent growth rate similar to that experienced during the 

simulation period, the broad cone of depression already 

encompassing most of the New Jersey Coastal Plain would 

broaden and deepen. Heads would range from 60 to 160 feet 

below National Geodetic Vertical Datum of 1929. The 

reduction of head after 1973 would approach 90 feet in some 

areas. The resultant steeper hydraulic gradients would 

accelerate the rate of movement of salty ground water toward 

the pumping centers. A freshwater head barrier could be 

established in the transition zone to prevent migration of 

salty ground water across a 35-mile stretch in Gloucester, 

Camden, and Burlington Counties. A line of injection wells 
would be required, with total rates of injection to the head 

rrier ranging from about 56 cubic feet per second in 1984 

o about 95 cubic feet per second in 2000. Barrier recharge 

rates would be equivalent to about 20 percent of the ground 

water pumped in the fine-grid area in any particular year for 

percent increase in extractions. 

INTRODUCTION 

Pur se and Sco e 

Ground-water extractions from the Potomac-Raritan-Magothy 

quifer system in the New Jersey Coastal Plain haVe almost doubled 

n he last 18 years, 1956-73, causing a continuous and widespread 

decline in water levels. Growth of industry and population along 

t e Delaware River and Raritan Bay since 1900 was responsible for 

he initial deilland for ground water. However, in recent years, 

much of the additional ground-water demand has been shifting 

gradually away from these areas toward the more lightly populated 

eas of the coastal plain. This shift has generally moved 

add tional pumping centers away from the outcrop of the aquifer 

stem, resulting in placement of many pumping centers in 

imity to a large body of salty ground water that presently 

o cupies the aquifer system throughout much of the southern half 

f he coastal plain. 

The more recently developed pumping centers tap downdip parts 

he aqui r system remote from important recharge areas along 

e Delaware River ana adjacent outcrop. Consequently, the wells 

strongly artesian and, when they are pumped, widespread 

sure reductions occur throughout much of. the aquifer system. 

oad cones of depression with potentiometric heads well below sea 

evel have already encompassed most of the aquifer system, 

n luding that portion containing the salty ground water. 

ease of head in the aquifer system slowly causes updip 

m g ation of the salty ground wat~r; thus, the fresh ground water 

threatened with contamination. Similarly, induced recharge 

om the salty (250 to 3,000· mg/L chloride), lower reach of the 

Delaware River southwest of Philadelphia and Camden is moving 

downd p in response to aquifer heads that are decreased below sea 

el. All of these factors are critical to the future 

ab lity and development of ground water in the region. 

The U S Geological Survey, in cooperation with the Division 

Water Resources of the New Jersey Department of Environmental 

o ection, is conducting a program of geohydrologic studies of 

qu er systems in the New Jersey Coastal Plain. These studies 

ze digital computer simulations. The area of this study lies 

m inly within the Coastal Plain of New Jersey but extends slightly 

o the nearby states (fig. 1). The study was started in 1972. 

976 the U. S. Army Corps of Engineers furnished additional 

nancial support for the investigation because of their interest 

n using the model to explore several water-management 

a teroatives. 

2 
40° oo' 40°00' 

EXPLANATION 

D 

AREA OF REPORT 

0 20 40 KILOMETER 

1.--Location of the study area. 

3 
The digital model constructed for this study is designed for 

use in predicting head distribution within the aquifer system 

(primarily in Burlington, Camden, Gloucester and Salem Counties) 

in response to pumping or injecting freshwater. Future pumping 

sites and pumping rates may be specified, with or without a 

redistribution or discontinuance of any of those wells already in 

existence. The sites and rates may be varied with time. Examples 

are illustrated in the report. 

Previous Studies 

Numerous studies of coastal-plain geology and ground-water 

resources have been made in New Jersey, and the adjacent states of 

Pennsylvania, Delaware, and New York since about 1900. Most of 

the reports were restricted to a limited area, such as a county~ 

County studies included those of Anderson and Appel (1969), 

Barksdale and others (1943), Hardt and Hilton (1969), Jablonski 

(1968), Sundstrom and Pickett (1971), Rosenau and others (1969), 

Rush (1968), Vecchioli and Palmer (1962), and Farlekas and others 

(1976). Regional appraisals include those of Parker and others 

( 1 964), Gill and Farlekas ( 1976), Nem ickas ( 1976), and Barksdale 

and others (1958). The latter study by Barksdale and others 

includes the most complete and perceptive study of the PotomacRaritan-Magothy aquifer system published to date, and has been 

widely referenced during this study. 

Acknowled nts 

This study was greatly facilitated by the cooperation of many 

well owners who made their wells available for measurement in 

November and December 1973. All well owners generously provided 

reeords or estimates of ground-water extraction when requested. 

e assistance provided by well drilling firms in allowing access 

to newly completed wells for geophysical logging and furnishing of 

well records is greatly appreciated. 

Prof. George F. Pinder, Roger Pa-g-e, and William G. Price of 

Princeton University provided assistance in setting up the 

plotting program used to produce the three-dimensional perspective 

views and contour maps presented in this report. 

Contour Ma s Used in Re rt 

All contour maps presented in the report have been produced 

from data input files used in the simulation model, or from data 

output files such as head maps, generated by the model. In 

preparing data input files, hand drawn contour maps are 

interpolated to obtain values for the variable sized elements 

throughout the model. These values were then coded, keypunched, 

and placed in magnetic storage. The values were then linearly 

reinterpolated by a computer program to an equal size grid (1 mi 2 ) 

and machine contoured or drawn in perspective using the PURVUE 

plotting program written by Price (1976). The interpolation 

4 
procedures, particularly in large elements of the model grid 

outside the principal area of interest (the fine-grid area), ma 

lead to some loss of detail in comparison to the original maps 

Therefore, contour maps credited to other workers should be 

considered as modified versions of the orig al. 

THE POTOMAC-RARITAN-MAGOTHY AQUIFER S EM 

General Descri tion 

The Potomac Group, along with the overlying Raritan and 

Magotny Formations, make up the regionally extensive PotomacRaritan-Magothy aquifer system. The aquifer system consists of 

wedge-shaped interbedded sand, silt, and clay and underlies the 

entire Coastal Plain of New Jersey and parts of adjacent states 

and extends seaward probably at least 100 mi to the continental 

slope. The aquifer system is exposed in a narrow outcrop along 

the ll Line and the Delaware River. Between the outcrop area 

near Camden and the coastline near Atlantic City, the top surface 

(fig. 2) of the aquifer system dips at about 40 ft/mi; whereas, 

the bedrock surface at the bottom of the aquifer system (fig. 3) 

dips at about 90 ft/mi. At Atlantic City, the top and bottom of 

the wedge-shaped aquifer system lie at about a depth of 2,500 ft 

and 5,000 ft, respectively, below NGVD of 1929. According to data 

presented by Schlee and others (1976, p. 927-940), 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. 

The aqui r is overlain by the Merchantville-Woodbury 

confining layer consisting of the Merchantville Formation and the 

Woodbury Clay. The Woodbury Clay retains a tough, dense character 

wnerever encountered and is probably the least permeable confining 

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

1958, p. 136). These units form an effective but leaky separation 

between the studied aquifer and overlying aquifers such as the 

Englishtown aquifer and the Wenonah-Mount Laurel aquifer. 

According to Perry and others (1975, p. 1529-1535), the 

oldest and thickest part of the aquifer system is in the Lower 

Cretaceous part of the Potomac Group. This unit, in New Jersey, 

is a nonmarine deltaic sequence of sand, silt, and silty clay. 

Marine sand associated with the deltaic sequence may be present 

seaward under the Outer Continental Shelf. 

On the basis of glauconite and various fossils, the overlying 

sand and clay of the Raritan Formation of Late Cretaceous age are 

considered chiefly of marine origin along coastal New Jersey 

except in the Raritan Bay area where they may be chiefly nonmarine 

(Perry and others, 1975, p. 1535). In the Delaware Valley area, 

the Raritan is chiefly nonmarine. 

5 
MILES 

KILOMETERS 

EXPLANATION 

~~-~!~!!~!!S_f_r:Y-~!:._o~uJ:!.~~: ~ne;c~~~~;~~;Y F;l.ay 

: •• :. Aq'utte;·a.yste'm::: • Potomac Group and 

•• ·.:; :·:-~~~~r·?~ • •• :: .:·. :. ~~~~=~ d Magothy 

I i i't j li If 1•1 j j t 1"1 .. ( j ·, j ·, 

Bedrock 

L o c; a I Ion and n u ~b e r of o b s e r vat 1 on 

well referred to in text. 

-·400-

Line shows altitude of the top of the 

aquifer ayatem. Contour interval 200 

feet. Datum Ia NGVD 0 F 1 9 2 9. 

Line of Section, figure 4. 

-- -- -- 250 mg/L 

Chlor'lde conco·ntratlon near 

bottom of IIClUifer system In 

mllllgrama per liter. 

TRANSITION ZONE 

~250mg/\.--

ChI or i d 11 c o·n c e rrt ration· near 

I top flf aqltllfer ayatem lf1 

I * ~~milligrams per !Iter. 

#lt L.~ v ,::.-~$'I 

""' ,f:P .J? I 

I 

I 

I 

CAPE MAY 

COUNTY 

---- .QE~~RE BAY 

----.... ............... 

z 

~ u 

0 

u 

;::: 

z 

:5 

< 

---

/ 

Figure 2. --Altitude of the top of the Potomac-Rari tan-Magothy aquifer sys tern 

(modified from unpublished map by H, E. Gill, U.S. Geological 

Survey, personal communication, 1974, and from Gill and Far1ekas, 

1976). 
"'-/ '* I $t 

~I 

:"' ( \ 

\ 

\ 

\ 

\ 

\ 

\ 

I 

,. .. ) '(' 

I 

I 

\ 

) 

" &.... 

S MILES 

0,_._~~.,.---<12 KILOMETERS 

OC AN OUN Y 

EXPLANATION 

Line shows altitude of the bottom of 

the AQuifer System (bedrock surface); 

Ct'ntour interval 400 feet. Datum is 

"GVD of 1929. 

Location and number of observation 

well referred to in text. 

:z 

~ u 

0 

u 

;:::: 

z 

:5 

1-

< 

/ 

Figure 3.--Altitude of the bottom of the Potomac-Raritan-Magothy aquifer system 

(modified from Gill and Farlekas, 1976). 7 
The Magothy Formation, which consists chiefly of coarse beach 

d and associated marine and lagoonal clay and silt, 

rmably overlies the Raritan Formation and is of Late 

ceous age. This rmation thins southward along coastal New 

whereas, the Raritan shows little thinning and the 

ing Potomac Group nearly triples in thickness southward. 

detailed discussion of coastal-plain stratigraphy the 

eferred to Perry and others, 1975, and Petters, 1976. 

is also referred to Brown and others (1972) and Schlee 

(1976) for a detailed discussion of the structural and 

ic framework 

The tomac Group and the Raritan and Magothy Formations 

ap a to nction together as a hydrologic system. Barksdale and 

hers (1958, p. 91) bel eve that the major aquifers within this 

em are h raulically connected with each other at some 

i not locall . Individual aquifers and intervening 

s appear to ack continuity. However, the aquifers are 

what more continuous than the clay beds. Long-term records at 

ster observation wells and records at individual observation 

we ls, some of which are quite remote from pumping centers, 

emonstrate that much of the aquifer system in New Jersey responds 

rmly to pumping stress. Most notably, potentiometric heads 

ughout most of the confined portion of the aquifer system have 

declining at rates of about 1.5 to 2.5 ft/yr in recent years 

66-76) 

ll 6 near Medford (fig. 3) is one of a cluster of three · each screened at different levels near the top, middle, and 

( 30, 670 and 1,043 ft below mean sea level, respectively) 

e stud ed h rologic unit. Despite numerous intervening clay 

between each screened interval, rates of head decline have 

nearly identical in each int.erval for the period of record. 

addition the average head difference is only about 3 ft. The 

deeper zones have nearly identical heads, which are about 3 ft 

gher than that in the upper zone. Similarly, wells 9 and 10 

Tree and New Brooklyn Park locations) are at sites where each 

two wells screened at intervals vertically separated by 400 

well 9) and 550 ft (well 10). Rates of head decline are quite 

ar in all zones, although head differences between the upper 

d deeper zones are about 7 to 10 ft at the Elm Tree site, and 

ut 12 to 17 ft at the New Brooklyn Park site. At each site, 

eepest zone has the head of highest altitude. Such head 

rences with depth are to be expected in the aquifer system 

probably are a result of pumping stress. 

The widespre extent of head reduction in the aquifer system 

lustrated by water-level data given in table 1 observed at 

Ragovin well (well 13, fig. 3). Five intervals in this 

don oil test well were jet perforated, screened, and pump 

s ed in 1974. Although the well is located about 22 mi downdip 

the nearest pumping wells (at Clayton) and at least 29 mi 

the nearest large pumping center in Camden County, the rate 

ad decline for the period of 1974-77 was about 1.6 ft/yr in 

8 
Table Ver ical 

Altitude of top 

of 10 foot 

perforated and 

screened interval 

-1998* 

-2495 

ar ation in 

(we 

Al ti e of 

uncorrected 

head 

-32.0 

-51 . 7 

ad 

3, f g 

nd 

2 

Al 

h r 

itude 

reshwater 

head 

(correc ed 

-15 1 

-23.5 

c 

0 

-3017 -62.7 -8 18 000 

-3195 -7 3 0 7 -9 9 22 

-3318 -78.4 3 6 0 

-3465** 59 3 1 0 2 2 '0 

* Top of screen in existing observation wel (s nee 1 4) 

** Top of screen in original observation well; during ent e 

period of record, 1962-74, no measurable amount of pressu e 

reduction occurred although well appeared (from tests) to 

be open to a thick basal sand. 

*** Heads corrected for density temperature and pressure 

at time of measurement. 

9 

n 
upper part of the aquifer system (-1,998-ft zone, table 1). 

e rate r the same period at the New Brooklyn Park well (well 

fig. 2), 21 mi updip from well 13 and about 6 mi from any 

ing wells, was about 3.0 ft/yr. These data and similar data 

om other remote observation wells such as the Butler Place well 

ll 8, fig. 2) and the Island Beach well, located at the coast 

ea rnegat Light (fig. 2) indicate that significant head 

decline is occurring throughout the aquifer system in coastal New 

ersey, and probably for considerable distances offshore. 

It should be noted that the basal sand unit at the Ragovin 

servation well appears to be completely isolated from the rest f~the aquifer system. Intervening zones (-2,495 ft and below, 

table 1) were backfilled after testing and rates of head change 

re not known. 

Salt Ground Water 

A large part of the aquifer system in the southern Coastal 

ain of New Jersey contains salty ground water with chloride 

concentrations ranging from less than 250 to as high as 27,000 

The concentration of chloride increases with depth as well 

wards the ocean. 

A generalized cross section of the aquifer system (line A-A', . 2) from the Delaware River southward across the transition 

z o n e to the Rag o v in we ll ( we ll 1 3 , fig . 2 ) i s shown i n fig u r e 4 . 

Figure 4 was constructed on the basis of chloride data observed in 

wells 6, 10, and 13 and the chloride concentration observed at 

tman, Glassboro, and Clayton (about 30, 50, and 120 mg/L 

chloride, respectively); together with the assumption that 

increases of chloride concentration with depth are similar to 

those reported by Rosenau and others (1969, p. 31) for the Salem 

C t area. Their report states that the chloride concentrations 

are 44, 700, 879, 1, 760, and 2, 05'7 mg/L for depths of 263, 350, 

50, 709, and 714ft below land surface. There is no sharp 

n erface between fresh ground water and salty ground water. For 

actical purposes a transition zone (or diffusion zone) is 

defined At one boundary of the transition zone the chloride 

oncentration of the ground water increases with depth and reaches 

50 mg/L at the bottom of the aquifer system. At the other 

ndary of the transition zone the chloride concentration of the 

ound water reaches 250 mg/L at the top of the aquifer system 

• 4 ) • 

Results of hundreds of water analyses throughout the coastal 

ain suggest that background chloride concentration in the 

aquifer probably ranges from about 2 to 5 mg/L. Farlekas and 

thers (1976, p. 137) report average chloride concentrations of 

lls in the confined parts of the aquifer in Camden County 

(excluding the New Brooklyn Park well) to be 4.1 mg/L, and Rush 

(1968, p. 36) reports that most wells in Burlington County have 

chloride concentrations of less than 5 mg/L. Chloride 

concentrations in excess of 6 to 8 mg/L are probably a result of 

10 
........ 

........ 

NORTH 

A wa: 

0 WELL6 

Well screen location. Number is 

chloride concentration in mg/l 

_ 0 0 _.. Line of equal chloride concentration 

- e in mg/L; highly generalized 

WELL 10 WEll13" 

Miles 

Kilometers 

Vertical exaggeration : x 26 

4 --Cross section distribution of chloride in the Potomac 

fer system ( of section shown on 2) 

-500' 

- 1000' 

- 1500' 

-20008 

- 2500' 

-3000: 
induced from a source exterior to the aqui r system, such 

a contamination source in the outcrop or salty reaches of the 

aware River (Delaware Memorial Bridge to Philadelphia), or the 

ge body· of salty ground water within the aquifer system. r 

am le the chloride concentrations of 16 and 21 mg/L at the site 

we 6 (fig. 4) are obably related to the large body of 

y ground water. The same conclusion is held r well 9 

en s tes 6 and 10, in which the chloride concentration was 

ted to be 19 mg (1963) at an altitude of about 1,083 ft 

ow NGVD of 1929. (A. Co Schultes and Sons, Inc., personal 

ommunication, Dec. 28, 1976). On the basis of all available 

rmation, a broad transition zone has been delineated which is 

able to the aquifer system as a whole. The chloride 

s ibut on shown in figure 4 should be consider as a 

eralized first approximation because additional control points 

uld eveal isochlorides that are more complex in extent and in 

pumping wells in the southern part of the New Jersey 

Plain have been s tdown due to encroachment of the salty 

ound water although a substantial amount of ground water with a 

loride concentration of less than 250 mg/L is being pumped near 

nd within the transition zone. Most of the aquifer system within 

nd south of the transition zone is encompassed by large cones of 

epression with heads reduced well below sea level. Consequently, 

alty ground water derived in part from the salty reaches of the 

aware River below Philadelphia is moving, however slowly, into 

major pumping centers within and near the transition zone. 

12 
DIGITAL MODEL 

Use of a digital model to study an aquifer is based on the 

premise that if past head changes within the aquif~r can be 

simulated by the model, then so can those of the ture~ He 

changes are determined by measuring water els in wells$ Th 

historical period chosen for simulating past head chang s was 

1956-73 A starting (1956) head distribution in the aquifer 

system was input into the model, along with the head distribut n 

over the confining layer, annual ground-water extraction rates 

(1956 through 1973), hydraulic properties of the aquifer system 

and confining layer, and sources of recharge from rivers and 

precipitation. The model calculated heads spatially on the ba e 

of input data during the 18-year simulation period. Computed head 

distributions were used to compare the measured head distribu 

Various parameters and/or boundary conditions were then modi 

and adjusted within tolerable limits until a good match or be 

fit was achieved between the observed and the calculated head 

changes. The model, which is an abstraction of the physical 

system, is then considered to have reached an acceptable leve of 

performance to justify its use as a management tool. 

Co uter Pro am and Mathematical Descri tion 

The two-dimensional ground-water flow equation in a confine 

aquifer, if the x and y coordinates are alined with the principal 

components of the transmissivity tensor, can be approximately 

written as, 

;:;. 

X ll 

where 

h ::: 

T ::: 

s ::: 

Q ::: 

R ::: 

K ::: 

m ::: 

H ::: 

x,y 

1:::. X' 1:::. y 

t ::: 

0 h Q 

+ 

K R 

+ + -- !::,. X • y m !::. x.t::,.y 

head, in feet; 

transmissivity, in cubic feet per second per foot; 

storage coefficient (dimensionless); 

rate of ground-water extraction or injection, in 

cubic feet per second; 

recharge, in cubic feet per second; 

vertical hydraulic conductivity of the confining layer, 

in feet per second; 

thickness of the confining layer, in feet; 

head in a sub- or superjacent aquifer, or in a stream 

over the confining layer, in feet; 

::: rectangular coordinates, in et; 

::: space increments, in feet; 

time, in seconds. 

Equation 1 is approximately solved by using a finitedifference method described by Pinder and Bredehoeft (1968, p. 

1073-1075), Pinder (1970), and Trescott and others (1976) Figure 

5 is a flow chart of the computer program and the digital model. 

The finite-difference method approximates the surface of the 

13 
NO 

NO 

YES 

ADJUST TRANSMISSIVITIES 

AND STORAGE COEFFICIENT 

LIMIT LEAKAGE 

COMPUTE HEADS IMPLICITLY ALONG ROWS 

COMPUTE HEADS IMPLICITLY ALONG COLUMNS 

NUMBER OF ITERATIONS? 

COMPUTE 

MASS BALANCE 

STOP 

YES 

COMPUTE 

MASS BALANCE 

COMPLETED 

TEMPORALLY? 

YES 

NO 

5e--Flow chart of the computer program and the digital model. 

14 
aquifer system by a mesh of elements (fig. 6). At the center o 

each element is a node where data are either given or compu 

An iterative, alternating-direction implicit method was used 

to solve simultaneously equations which describe the head at each 

node. Equation 1 is time dependent and time~in the numerical 

model used is advanced in increments which are one and one-half 

times the previous time step. At each time step, an iterative 

process is carried out to achieve a head solution; head 

distributions computed in successive iterations are compar r 

each node, when the difference between the head computed in one 

iteration and that computed in the succeeding iteration is less 

than an assumed limit, error of closure, the solution for that 

time step is achieved. A pumping period is considered either as 

one time step or many time steps during a simulation, and each 

time step ends with a complete head distribution calculated by the 

model. 

Table 2 shows how computations are advanced through time with 

the typical number of iterations required during each time step 

In selecting the time sequence and closure criterion, trial runs 

were made initially, using more than twice as many time steps as 

shown and with closure tolerances ranging from 0.01 to 1 ft. The 

comparison of closure criteria of 0.5 and 0.05 ft, shown in table 

2, resulted in nearly a doubling of iterations, and thus 

computation time. Calculated head differences after 18 years 

differed by only 0.07 to 0 2 ft for the two closure criteria. 

Therefore, 0.5 ft has been used in all runs with little sacrifice 

in accuracy and a great savings in computer time. 

The model used in this investigation was developed from the 

model in Pinder (1970); however, several changes in the 

computational method were made: 

1. Transient leakage through confining layers is not 

included in the model. Only steady leakage defined 

as K/m(H-h) (equation l) is used. 

2. The method of simulating constant head boundaries was 

changed. Pinder (1970) used a high leakage coefficient at 

nodes where a constant head was specified in order to force 

aquifer heads to be almost equal to the constant head in t 

confining unit. The program was changed so that the solution 

routine. skips head calculation at constant head nodes. 

3. Conversion from water table conditions to artesian 

conditions and vice versa was added to the model. The 

method is similar to, but not as rigorous as, that used by 

Trescott (1976, p. 10-11). At the start of a pumping period 

transmissivity is computed as saturated thickness of the $ 

aquifer times hydraulic conductivity. Specific yield is us 

for storage coefficient if aquifer head is below the aqui r 

top at the start of the pumping period. Otherwise, a 

confined storage coefficient is used. The effect of testing 

15 
Location diagram 

boundaries used 

in tal model 

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

Constant head boundary 

0 

I 

0 

........ 

"' ' '\ 

\ 

CUMBERlAND COUNTY f 

I I I ! : I I I 

CAPE MAY 

COUNTY 

! I 

I 

illllllllllllllllllllllllllllllllllllllllllllll 

5 90 80 75 

Figure 6 --Finite difference and 

16 
/ 

I 

OCEAN COUNTY 

I 

EXPLANATION 

Merchantville Fm. 5 

and Woodbury Clay 

Potomac Group and 

Raritan and Magothy 

Formations 

MilES 

0 4 8 12 KilOMETERS 

I 

1

1111111111111111111111111111111 I 

20 10 5 

boundaries used in the digital model. 

17 
f--' 

co 

Table 2.--Time step sequencing used in the digital model, 1956-2000 

Days since Elapsed time 

Year Time step Length of start of since start 

number time step pumping of pumping 

(days) period (days) 

1956 (1st) 1 7.42 7.42 7.42 

2 1 1 . 1 2 18.54 18.54 

3 16.68 35.22 35.22 

4 25.03 60.25 60.25 

5 37.54 97.79 97.79 

6 56.31 154.10 154.10 

7 84.46 238.56 238.56 

8 126.69 365.25 365.25 

195'7 (2nd) 9 44.95 44.95 410.20 

1 0 67.43 112.38 477.63 

1 1 101.15 213.53 578.78 

12 151.72 365.25 730.50 

1958 (3rd) 1 6 1,095.75 

1973 (18th) 76 6,574.50 

(End of 

simulation [1957 sequence repeated 

period) for all succeeding years] 

2000 (44th) 180 or 1 92* 16,071.00 

(End of 

projections) 

* During one projection described later, in which a freshwater injection barrier was 

emplaced in 1984, the number of time steps was increased that year from 4 to 16 

Typical number of 

iterations required 

to calculate new head 

within closure of 

0.5 ft 0. 05 ft ----

1 1 17 

6 1 1 j~ 1 1 

J~ 8 

5 8 

lf 6 

5 5 

!t 5 

1 1 17 

3 1 0 

4 10 

lt 9 6~) 117 

to prevent any possibility of inducing error because of the sudden change in stress. 
for water tabl artesian conversion at the start of a 

period rather than every iteration as Trescott 978 

considered small for the co itions s at in this 

Heads throughout the aquifer system are generally decl n 

at a slow rate of 3 ft/yr or less. I much eater rate 

head change are simulat , then significant errors could 

occur .. 

Output modifications to this model include automaticall 

scaled page size hydrographs and a map of head dif ence bet 

observed and computed surfaces for any given year. In additi 

ground-water budget computations, normally computed only 

entire model, have been modified to give a complete analysis 

the principal area of interest, the fine-grid area 

Grid Size and Boundaries 

The grid size consists of a fine grid of 2,800 elements i 

the Burlington, Camden, Gloucester, and Salem County areas 

surrounded by a coarse, variable sized grid of 1,600 elements 

(fig. 6). Within the fine-grid area, element sizes range om 

0.25 mi 2 with side dimensions of 2,640 ft, to 1 mi 2 with side 

dimensions of 5,280 ft. About 1,100 mi 2 of land and water 

surfaces are covered by the fine grid, which is 54 mi long and 0 

mi wide; whereas, many thousands of square miles are cover b 

the coarse grid. 

The small element sizes in the fine grid were chosen to 

define pumping centers, the outcrop belt, and the Delaware and 

Schuylkill Rivers. Outside the fine-grid area, the definitio 

capability progressively decreases as the element sizes become 

quite large or very long and narrow (fig. 6). Grid expansion 

outside the fine-grid area allows incorporation of the rest o 

aquifer system, including pumping centers, without a prohibitive 

increase in computer cost. However, simulation and predictive 

capability become progressively more generalized with distanc 

from the boundaries of the fine grid because of the coarseness o 

data definition. 

The Potomac-Raritan-Magothy aquifer system is extensive and 

the boundaries distant from the outcrop area are uncertain 

Therefore, the coarse grid has been extended seaward to includ 

the continental slope about 100 mi off the New Jersey coast. I 

has also been extended to the northeast about 100 mi from Rari an 

Bay and to the southwest about 40 mi from Delaware Bay (fig 6) 

These last two "side" boundaries are treated in the model as 

infinite sources of water (constant heads) This approximat o 

clearly an arbitrary truncation of the aquifer system, but at uch 

a great distance from the area of interest, the error resulting 

from fixing heads along the boundaries due to pumping stresse n 

the fine-grid area are assumed to be negligible. The seaward 

boundary, which is roughly parallel to the continental slope, i 

treated as an impermeable or no-flow boundary. According to 

Sheridan and Knebel (1976, p. 1112-1117), high resolution se sm 

19 
es near the continental slope show evidence of h h angle 

rillal faults om near surface to depths of 3.7 to 4.0 mi. In 

er beds thought to be of Early Cretaceous age, 295 ft of 

tical ement has been detected. According to Sheridan and 

ebel (1976, p. 1113) " e position and strike of these faults 

n ide with and parallel the East Coast magnetic anomaly 

e p eted as the fundamental seaward basement boundary of the 

timore Canyon trough " The large vertical movement associated 

h the fault zone probably provides evidence for termination of 

able beds and; the efo e the continental slope is treated as 

flow boundary. 

urth major boundar for which a great deal of hydrologic 

eologic evidence s available, lies roughly parallel to the 

crop of the aquife system and extends to the Fall Line 

a ent to the New Jerse Coastal Plain. This boundary was 

ated as having two d stinctly different hydrologic 

aract istics, dep ng on the occurrence of extensive clays in 

the shallow part of the aquifer system. In most of the outcrop 

south of Trenton the Potomac-Raritan-Magothy aquifer system 

trenched by the southwestwardly flowing Delaware River. This 

a of the aqui r system was modeled as being constant head. 

on evidence which included water quality, temperature and 

gradients, Barksdale and others (1958, p. 101-128) recognized 

nduced echarge om the Delaware River accounted for a 

antial po ion of the total water withdrawn from the aqui r 

he vicinity of the river course. Furthermo~e, the potential 

nduced recharge was estimated to be 4 to 10 million gallons 

y al d) per mile of aquifer along the river. The 

f the iver bottom was considered the most important 

or in con rol ing induced recharge. Only a few feet of clay 

ilt wo ld greatly reduce the amount of water that could 

rate the aquifer In a study of the effects of a proposed 

n argement and deepen1ng of a ship channel (Philadelphia to 

) from a de h of 25 ft to a depth of 45 ft, the consulting 

s of Powell and Leggette and Brashears (1954, Appendix A2-1), 

uded on the bases of boring and pumping tests that: 

Deposits of highly permeable sand and gravel are in 

onta t with the iver in the central channel) while finer 

ained mater al is normally present in the shallows between 

the excavated channel and the river banks. 

2) e major portion of induced recharge to nearby well 

ields in w Jersey probably occurs along the excavated 

hannel bottom. 

3 In most major well fields near the river in Camden and 

Bur ton Counties, uced recharge would account for 50 

o 80 percent of eduction a er clanged pumping. 

20 
(4) The proposed channel enlargement and deepening to 45 

would increase the effective area of infiltration by 30 

percent and expose more of the highly permeable stratifie 

zones of the aquifer. 

The ship channel has since been enlarged and is now 

maintained to a depth of about 45ft. 

Barksdale and others (1958, p. 115-116) indicated that with 

one reach of the Delaware River between Camden and Philadelphia, 

induced recharge probably cannot occur to much extent A thick 

clay bed extends within the Raritan Formation beneath the river 

effectively isolating the lower beds. A similar condition exist 

near the southwestern edge of the fine grid near the Delaware 

Memorial Bridge. Much of the aquifer system cropping out there is 

composed of thick clay beds which isolate the lower beds from the 

Delaware River. Clay beds in this reach of the river, and 

reach in Philadelphia, are simulated as part of the 

Merchantville-Woodbury confining layer. 

H 

Transmissivity 

Estimates of sand percentages of the aquifer thickness and 

estimates of permeability on the basis of specific capacity per 

foot of screen length, gallons per minute per foot squared 

[(gal/min)/ft 2 ] were incorporated into the computer program. 

According to Farlekas and others (1976, p. 39), specific 

capacities per foot o~ well screen observed in 95 wells, 12 inche 

in diameter or larger, in Camden County ranged from 0.12 to 2.29 

They found that wells in the outcrop area had the highest average 

specific capacities per foot of well screen [0.95 (gal/min)/ft 2 

for 60 wells]. For the remaining 35 wells located downdip from 

the outcrop the average specific capacity per foot of well screen 

was 0.52. The higher specific capacities in the outcrop area were 

attributed to better hydraulic properties and to the proximity of 

recharge, particularly the Delaware River. Geophysical logs 

clearly show that the thickest sand beds in the aquifer system 

generally occur in a belt along the outcrop, with a rapid thinning 

of sand beds and multiple interfingerings with clay and silt beds 

downdip towards the coast. Using the data presented by Farlekas 

and others (1976) and the sand percentages of the thickness of the 

aquifer system estimated from geophysical logs, the initial 

transmissivity distribution was generated on the bases of the 

following assumptions: 

(1) Fifty percent of the thickness in the outcrop 

is sand, with a specific capacity per foot of sand 

of 1.0 (gal/min)/ft 2 • 

21 
(2) In the area underlying the outcrop of the Merchantville 

rmation-Woodbury Clay (fig. 6), about 2 to 3 mi in 

width, sand percentage is 40 percent with a specific 

capacity per foot of sand also equal to 1.0 

(gal/min)/ft 2 • 

(3) om the outcrop area to 10 mi downdip (to row 14, 

fig. 6), sand was estimated to be 35 percent of the 

total thickness with a specific capacity per ot of 

sand of 0.6 (gal/min)/ft 2 • 

4) From row 13 to row 8 (fige 6), a distance of another 10 

mi, sand was estimated to be 25 percent of the total 

thickness, with a specific capacity per foot of sand of 

0.4 (gal/min)/ft 2 • 

(5) om row 7 to the seaward edge of the model, row 2 

(fig. 6), a distance of about 137 mi, sand was estimated 

to be 20 percent of the total thickness with a specific 

capacity per foot of sand of 0.2 (gal/min)/ft 2 • 

Transmissivity was calculated by an equation presented by 

Lohman (1972, p. 52). The equation is given by, 

wh e, 

s 

w 

4 KL 

2.30 log 10 (2.25 KLt/r 2S) w 

Q = well discharge 

s = drawdown in discharging well 

w 

K = hydraulic conductivity of sand near 

s = storage coefficient 

rw = well radius 

L = screen length 

t = time 

well screen 

reason for r lacing T in the equation by KL is that the 

ar ier work by Farlekas and others (1976) could be directly 

( 2) 

orporated into the computer calculation. The replacement is 

d only if the screened interval (L) is equal to the thickness 

the saturated sand ttat ef eatively contributes to flow to the 

l Howe v e r , most 1 at ~ e d i am e t e r well s in the s t u d y a r e a meet 

s criterion; therefor,' 1 the replacement is tolerable. 

arr ing equation (2) a ~ letting b represent the aquifer 

thickness times percentage of sand, the transmissivity of the 

aquifer (T = Kb) is give l by, 

22 
T = .. 183(b) og ( 3) 

1 0 

e value of the log term in the above equation is estimated to 

range om about 6 to 7 for typical large diameter wells (12-inch 

screen with 12-inch gravel pack) having 8-haur aquifer tests. A 

value of 6 was arbitrarily assigned for the log term to determine 

initial transmissivity distribution. 

The vicinity of well 4 (fig. 2) was used as an example to 

show the computation of transmissivity. Figures 2 and 3 indicate 

that the total thickness of the aquifer system near well 4 is 

about 200 ft. The location of well 4 is in the outcrop area; 

therefore, b = 100 ft (50 percent of 200 ft). The specific 

capacity per foot of screen (Q/swL) is assumed to be 1.0 

(gal/min) I ft 2 , then, 

T = 

0. 1 

= 21,100 ft 2 /day 

Figure 7 is the final transmissivity distribution used in the 

model. It should be noted that transmissivity in the vicinity of 

well 4 is 23,000 ft 2 /day instead of 21,100 ft 2 /day. The 

difference reflects adjustments made during the simulation runs. 

In general, adjustments in transmissivity were less than 20 

percent in and within 6 mi of the outcrop belt. Further downdip 

the transmissivity distribution generated by the described 

approach was reduced by 20 to 60 percent. These reductions were 

made during simulation runs together with other adjustments, such 

as leakage through the confining layer. 

Transmissivity adjustments affected the slope of the computed 

hydrograph trends. Vertical departure from the observed trends in 

confined portions of the aquifer was controlled chiefly by 

adjustments to leakage through the confining layer. 

Storage Coefficient 

The storage coefficient in the outcrop area is assumed to be 

8 x 10- 3 • This is an approximation to allow for the prevalence of 

interlayered sand and clay beds within the outcrop, thus causing 

both water-table and confined conditions. For the clearly 

confined portions of the aquifer system, the storage coefficient 

is probably within the range of 2 to 6 x 10- 4

• It could reach a 

minimum of 8 x 10- 5 in the southwest end of the model in the area 

roughly enclosed by the 10,000 ft 2 /day transmissivity line that 

passes near wells 1 and 13 (fig. 7).. These values approximately 

agree with those reported by Barksdale and others (1958, p. 97) 

and Rush (1968, p. 33). The model was found to be relatively 

insensitive to storage coefficient, particularly in the outcrop 

area. Constant-head nodes, such as those used to simulate the 

23 
EXPLANATION 

---- 15,000~ 

Line of equ1111 transmissivity ( t t 11 d) 

Contour interval 5,000 f t2 1 d, ' 

®6 

Location and number of observation 

well referred to in text. 

---........ r-- _, ' 

\ 

GLOUCESTER 

c::,~ COUNTY 

""" ·""~ 

\ 

\ 

\ 

\ 

\ ATLANTIC COUNTY 

.,....-...._ \ CAPE MAY /;tv 

1/ ~~ 

I >v"?-

IQ«; 

DELAWARE MEMORIAL 1 BRIDGE 

0 8 Mlltl:S ,__~~~_...; 

12 KILOMETERS 

---

CUMBERLAND COUNTY 

\ COUNTY 

\ 

'I 

I 

\..., 

--- - ----- ..l2EJ.e.'ftAor: ...., -I!AY ~­ --

Figure 7 .--Distribution of transmissivity used in the model for the PotmaacRaritan-Magothy aquifer system. 

24 

---

I 
Delaware River, tended to mask out such influence 

nodes of the narrow outcrop strip. 

ad ace 

The storage coefficient used in the confin portions of 

aqui r system is allowed to convert to the same order of 

magnitude used in the outcrop area if the ad falls below the 

of the aqui r system. This is an approximation; actually th 

conversion is probably more complicated and slower. the end f 

1973, heads had dropped below the bottom of the overlying 

confining layer in a relatively small area near the outcrop in 

Camden County. 

As indicated previously, the fine-grained beds become more 

prominent in the aquifer system downdip from the outcrop. The 

great thickness of silt and clay m~y have higher storage 

coefficient than the aquifer material. The aquifer storage 

coefficient, therefore, includes the combined storage properties 

of the aquifer material and the fine-grained material. This is an 

approximation that is valid when the fine-grained beds are 

relatively thin and well distributed throughout the aqui r 

(Jacob, p. 577). 

Confining Layer 

The Merchantville Formation and Woodbury Clay together 

constitute one of the most widespread confining layers in the 

Coastal Plain of New Jersey (fig. 8). The combined thickness 

increases downdip to more than 300 ft along the coast and to more 

than 500 ft offshore. The stratigraphy of the two units is 

discussed in detail by Perry and others (1975), Owens and others 

(1970), Petters (1976), and in lesser detail by workers cited 

earlier. The two units are considered to be of Late Cretaceous 

age and consist of dark-grey, micaceous silty-clay, or clayey sil 

containing marine fossils. According to Petters (1976, p. 87), 

the Merchantville Formation was deposited as the offshore facies 

of the Magothy Formation during a marine transgression, followed 

by the Woodbury Clay as the shoal facies. Furthermore, according 

to Petters (1976, p. 102), the Woodbury Clay may interfinger with 

the overlying Englishtown Formation in some downdip regions. 

In the model, transient leakage from the confining layer is 

ignored. The possibility for significant leakage does exist, 

especially downdip where the confining unit thickens. While e 

model was successfully calibrated without including transient 

leakage, users should be aware that other stress conditions might 

cause erroneous results because of this assumption. Downdip 

development of the aquifer system would be the most likely stress 

to cause such problems. 

boratory determined vertical hydraulic conductivities of 

cores from wells at Lakewood, N.J., and at Fort Dix are included 

in table 3. The vertical hydraulic conductivities were measur 

in the laboratory through a range of simulated overburden 

pressures or effective stresses existing in the coastal plain. As 

25 
PENNSYLVANIA 

_ ... ...._ 

/-<(;-«., 

~~ 

( -y"?- 1 <;)«; 

DELAWARE MEMORIAL 1 BRIDGE 

I 

I 

,x 

8 MILES ~---~~~__, 

12 KILOMETERS 

EXPLANATION 

Line of equal thickness of the Merchantville 

Formation -Woodbury Clay confining layer. 

Contour interval is 50 feet. 

@6 

Location and number of observation 

well referred to in text. 

0 

I() 

C"' I" 

/ 

/"'"" 

-" 

\ CAPE MAY 

\ COUNTY \. 

) 

I 

....... 

X 

/ 

Figure B.--Thickness of the Merchantville Formation-Woodbury Clay ~onfining 

layer (modified from H. E. Gill, personal communication, 1974). 

26 
Table 3 

Well No and Coring Simulated effective earth 

location depth stress in pound-force per 

(see . 6) (ft) square inch (psi), and 

equivalent depths of burial 

(psi) (ft) 

Lakewood Water 795 100 (130) 4.93 X 1 0 

Co. Well 10 610 (800) 4. 18 X 1 1 

(Well 12) 1' 150 (1,500) 1. 67 X 1 1 

(on fig. 6) 

845 115 ( 150) 1 f-.4. v V._) .n, 1 645 (850) 5. 32 X 

1' 190 (1,550) 8. 35 X 

2 

896 145 (200) 4.94 X 1 

690 (900) 5.69 X 1 

1' 225 (1,600) 1. 44 X 1 

928 180 (250) 5 .. 69 X 

0 

0 715 (900) 1.63 X 0 1' 245 (1,600) 1. 18 X 

U.S. Army Ft. 523 111 (150) 1.44 X 

0 

1 Dix Well 6 222 (300) 8.83 X 0 (Well 11) 403 (500) 1. 39 X 

(on fig. 6) 

546 111 ( 150) 7.62 X 

222 (300) 6.07 X 

444 (600) 4.25 X 

889 ( 1' 150) 3.20 X 

569 111 (150) 2.70 X 1 

222 (300) 1.42 X 1 

444 (600) 9. 33 X 1 

889 (1,150) 8.67 X 1 

625 111 ( 150) 1..22 X 1 0 222 (300) 6 .. 39 X 1 

444 (600) 3. 46 X 1 0 

889 ( 1' 150) 1.92 X 1 0 

27 
with most coring operations, the selection of coring intervals i 

somewhat biased by ease in core recovery towards the finer-grained 

nd therefore, tighter horizons in the formation. Most of the 

m nitudes of vertical hydraulic conductivities used in the final 

el (fig. 9) ll within the range of values shown in table 3. 

In addition, most cores show decreasing hydraulic conductivities 

s d s of burial increase. This decreasing trend is also 

ly apparent from figure 9 which shows a downdip decrease in 

ical h raulic conductivity of the confining layer. Beyond 

1 x 10 10 ft/s contour line, all values fall within the range 

to 8 x 10- 11 ft/s, with the minimum value farthest downdip. 

An extension in the model of the Merchantville-Woodbury 

nfining la r was made in the Philadelphia area and near the 

laware Memorial Bridge (see fig. 9) in order to better 

roximate field conditions. The thickn~ss of the confining 

r modeled for the Philadelphia area ranged approximately from 

to 90 ft as based on the thickness of a confining layer mapped 

by Greenman and others ( 1961, . 18). For the area near the 

laware Memorial Bridge, an arbitrary thickness of 100ft was 

ass ned. 

Rechar ifers and Preci itation 

Recharge to the confined portion of the aquifer system is 

modeled primarily as steady leakage passing through the 

Merchantville Formation-Woodbury Clay confining layer from the 

erlying Englishtown and the Wenonah-Mount Laurel aquifers. 

ese two aquifers seem to function together as a hydrologic 

ystem in areas of Ocean and Monmouth Counties where detailed 

t ies have been made ( Nemickas, 1976 and Nichols, 1977). In 

add tion, throughout most of the coastal plain the head 

di tribution of each aqui r is similar. In much of southern New 

Jersey, the Englishtown Formation is a confining unit (Nemickas, 

976, p .. 21). 

Tne overlying head distribution used in the model as the 

d ving force for steady leakage is chiefly that of the 

Wenonah-Mount Laurel aquifer in southern New Jersey (fig. 10), and 

s a composite head with that of the Englishtown aquifer in the 

eastern and northeastern parts of the coastal plain. Where the 

confining layer is exposed at land surface, the modeled overlying 

e is set equal to shallow water levels and streams. For those 

ou crop areas in which an extension of the confining layer (fig. 

9) has been used, the overlying head is the water table as defined 

by wells, streams, an~ swamps. 

Figure 11 shows a perspec ve view of the overlying head 

tribution. The depression below sea lev , on the right 

side of figure 11, is caused by pumping in both the Englishtown 

and Wenona unt Laurel aqui rs along coastal Ocean and Monmouth 

Counties. Heads observed in that a~ea were approximately 20 to 80 

below mean sea level in 1959 ( Nemickas, 1976, p. 16, and 

Nic ls, 1977, p. 29). By fall of 1973, the heads dropped to 

28 
OCEAN COUNTY 

----

08 

BURLINGTON couNT'< 

,.---1-1 

I 

I 

I 

I 

010 I 

...._ 

' ' ' ' ' 

EXPLANATION 

Merchantville Fm. 

and Woodbury Clay 

Potomac Group and 

Raritan and Magothy 

Formations 

Line of equal hydraulic conductivity 

(It/sec). Contour interval variable. 

®6 Location and number of ohc:~~:~.- ...... : __ 

well referred to in text. -~"'"QliVII 

Shaded areas show approximate extension 

of confining layer used to approximate 

of confinement within outcrop of system. 

' ' \ 

i 

_.r 

z 

;;5 

v 

0 

I'.-~,..._ I r- -1 v 

;::: 

z GLOUCESTER I "' ~ couNT'< I ;J-"" .cf I .~ r-

__ , __ J..----1~...._\ ,.""/,. 

,...--- " " / '\ \ .... 

' \ 

_ ... ' > \ \. CAPE MAY 

COUNTY 

( 

,_---

1 

I 

I 

) 

\ 

l 

r 

'" .... 

MILES 

KILOMETERS 

CUMBERLAND COUNTY 

) 

{ 

'-

- - - - ----- ..QE~ ~~ BAy 

----

Figure 9.--Distribution of vertical hydraulic conductivity of the 

Merchantville Formation-Woodbury Clay confining layer 

used in the mode 1. 29 

................ 

~ <( 

--....... 

I 
NEW JERSEY 

\ 

l 

EXPLANATION 

Potentiometric Contour shows altitude of 

the potentiometric surface in feet. Contour 

Interval 20 feet. Datum is NGVD of 1929. 

PENNSYLVANIA 

8 MILES '---, ___,, 8 12 KILOMETERS 

./ 

'- ,I \-' 

{""' 

/ .... /·' 

\ CAPEMAY 

\ COUNTY 

\. 

) 

I 

'"' 

Figure 10.--Composite potentiometric surface of the Englishtown and 

Wenonah-M.ount Laurel aquifers, 1959 (modified from Nemickas, 

1976, figure 8 and Nichols, 1977, figure 15). 

30 

/ 
.--Perspective view of the composite potentiometric surface 

(1959) over the confining and the computed s 

state (1900±) potentiometric surface of the PotomacRaritan-Magothy aquifer system. 

31 
imately 140 to 200 NGVD of 1929. An average head r 

node in the depression for the period of 1959-73 was us for 

ations. Thus, with the exception of the averaging 

preach us in a few nodes that span the small depression, the 

sur ce as shown in figure 10 was used throughout the 

ation period. 

Recharge om precipitation in the outcrop area estimated by 

dale and others (1958, p. 102) was approximately 1.0 f yr 

Mgal/d), assuming that water falling on clay members would 

off and be absorbed by more permeable aqui rs. During model 

ation recharge to the outcrop, 0.1 to 1.0 ft/yr, was used 

est runs, and it was und that the recharge rate was not 

tive to model results, probably because of the proximity of 

stant heads along the Delaware River and the outcrop area. The 

values used for recharge in the model were 0.35 f yr in the 

area southwest of Camden and 0.90 ft/yr northeast of 

Areas where the confining layer has been extended (fig. 

re modeled without recharge from precipitation. 

Annual ground-water extractions for the 18-year period 

56 3) were collected r the entire aquifer system within the 

al Plain of New rsey. Most of the extraction data were 

ined as metered monthly totals from files maintained by the 

e sey artment of Environmental Protection (NJDEP). In 

instances where breakdowns by well or aquifer were not 

lable estimates were made on the bases of interviews with 

Extraction data in the adjacent areas outside of New 

( Ph i ad e l i a , P a . a n d N e w C a s t l e Co u n t y , Del $ ) we r e 

ined om Greenman and others (1961, p. 84-92), Sundstrom and 

ett 1971 p. 56 and 73), and from estimates made on the basis 

terviews with users In New Jersey, about 90 percent of the 

t on wells are metered and reported to NJDEP quarterly. 

erly installed and maintained flowmeters may have an accuracy 

n ±2 percent. However, because of wear, most meters may 

reg ster somewhat. Thus, the reported extractions from old 

alla ions may be lower than actual. Other ctors affecting 

ab 1 ty of extractions may include misreporting, estimation 

s by users and the author, particularly for the earlier years 

e simulation period, and errors occurring during at least 

ata transfer steps from the meter reading to computer 

e by the U.S. Geological Survey. Because of these potential 

rs, a eat deal of care was exercised in the collection and 

lation of pumping data. Cross-checks, examination for 

sistencies retr cing numerous well-numbering changes, 

ating "grandfather" wells and diversion records were all 

ed out or resolved on a well-by-well, user-by-user basis in 

to minimize errors. The accuracy of nearly all well 

ions was field checked. 

Ground-water extraction data were manually processed and all 

m pu ations, such as conversion of monthly totals to annual 

32 
averages and the locating of all pumping wells in the proper 

elements of the model for the correct year, were done by a 

separate computer program and stored on disk for direct acces by 

the model. To demonstrate how extractions were assigned on a 

nodal basis, a model element row 33, column 60 (33,60) is used as 

an example (fig. 6). Utilizing the dimen ons of the model grid 

the angle of rotation of the grid counterclockwise 38 degrees from 

east-west and converted and rotated x, y coordinates derived from 

latitude-longitude of well locations, the program determin tha 

five pumping wells were located within that particular elemen in 

1968. The sum of the pumping rates (5.2 ft 3 /s) was comput in 

1968 for that node. The procedure was repeated for all-wells an 

nodes for each of the 18 years until a complete master file was 

created for direct input to the model. Using this procedure a 

potential error of determining rates and locating pumping node 

can be eliminated. Estimated overall accuracy of pumping rates 

used in the model within New Jersey would be approximately 80 t 

90 percent. 

Extraction rates from the Potomac-Raritan-Magothy aquifer 

system have risen almost continuously during the period 1956-7 

(table 4). For the entire Coastal Plain of New Jersey, extrac n 

rates increased from about 182 ft 3 /s in 1956 to about 336 ft 3 s in 

1973. Rates during the same period in the fine-grid area cover ng 

parts of Burlington, Camden, Gloucester, and Salem Counties 

increased from about 117 ft 3 /s to about 224 ft 3 /s. 

Figure 12 shows, in perspective, the distribution of 

extractions for the years 1956, 1965, and 1973. The two most 

prominent peaks are pumping centers in Camden City (opposite 

Philadelphia) and near Raritan Bay in Middlesex County3 For 

scale, the spike-like peak near Philadelphia represents a pump n 

rate of about 25 ft 2 /s in 1973; rates of less than 1 ft 2 /s are 

generally not visible. During the 18-year period, there had been 

a noticeable addition of pumping centers in the downdip direction 

towards the salty ground water. Three small pumping centers lined 

up in a north-trending row in the transition zone, south of Camden 

City, are located at Clayton, Glassboro, and Pitman (fig 2). 

PARAMETER ADJUSTMENT AND ACCEPTANCE OF THE MODEL 

Historical responses of the aquifer system to past stresses 

must be reasonably reproduced by the simulations in order to 

produce an acceptable model. Simulations were started in 1956 

because drilling activity was sharply increased in the mid-1950's 

More data points would be available over a relatively short pe od 

from which a starting head distribution could be constructed ( ig 

13). Also, pumping records prior to 1956 were difficult or 

impossible to obtain. During a 6-week period in November-December 

in 1973, heads were measured at available wells after a period o 

shutdown. The resulting potentiometric surface observed in 197 

is shown in figure 14. Perspective potentiometric surfaces are 

shown in figure 15. The potentiometric surfaces were constructed 

on the basis of head measurements from wells that are screened at 

33 
Table JL --Annual extraction rates, 1956-73* 

Entire model area area Total nunber 

of nodes with 

(ft 3 /s) (ft 3 /s) pumping well 

0 116.8 

200.3 128. 1 

7 123.3 

.4 131.2 

21 6 .6 

1. <I .0 

5 156. 1 

5 167.0 

1.9 176.3 

277.8 183.8 

6 188.2 

. 9 186 6 

8 201.0 

313.7 201.4 

330.8 214.2 

1.9 216.9 

326.9 215.3 

336.3 223e5 

Includes 8 to 14 ft 3 /s in Philadelphia area, and about 17 ft 3 /s 

in New Castle County, Delaware. 

act well count is not available but is estimated to range from 

more than 400 wells in 1956, to more than 600 wells in 1973. 

34 

181 

186 

191 

228 

238 

258 

262 

279 

273 

276 

273 

270 
Figure 12.--Perspective view of the distribution of ground-water 

extractions from the Potomac-Raritan-Magothy 

system in 1956, 1965, and 1973. 

35 
0 8 MILES 

12 KrtOMETERS 

BURLINGTON COUNTY 

--.................. , __ .., ,..... \ 

;/ \ 

I I 

\ 

EXPLANATION 

------10~ 

c altitude of Potentiometric t ~c ntour surface shows In feet. Contour 

h potentlome r I NGVD of 1929. interval t e 1 0 feet. Datum s 

d number 06 o f observation location an to In text. well referred 

>< 

I 

\ ATLANTIC COUNTY• 

CUMBERLAND COUNTY 

I 

........ 

CAPE MAY 

COUNTY 

- - - - - - - .l>E.Lf. \tA~ -fl~ 

-- -----............ 

I 

13 tric surface of the .--Potentiome 1956. Figure aquifer system, 36 Potomac-Rar~ 'tan-Magothy 
-50 FEET NGVD 

EXPLANATION 

Potentiometric Contour shows altitude 

of the potentiometric surface in feet. 

Contour Inter v a r v a r i a b 1 e. Datum is 

NGVDol 1929 

®6 Location and number of observation 

wall referred to in text. 

( 

X 

BURliNGTON COUNTY\ -/ ~ 

\ .r--- __ .., ---..-.... ' .> --~ 0 

I .._.,. c-4 

I . 

~I ., 

\ 

I 

_\ 

ATLANTIC C 

I 

I 

I 

\ 

.1----f3i' 

Figure 14,--Potentiometric surface of the Potomac-RaritanMagothy aquifer system, November-December, 1973. 

37 

........ __ 

/ 
Raritan Bay 

Figure 15.--Perspective view of the potentiometric surfaces of the PotomacRaritan-Magothy aquifer system observed in 1956 and 1973, 

respectively. 

38 
various depths. At locations where head dif rences with d h 

existed (usually less than 10ft), the head of lowest altitude was 

used for control. 

If the parameters and boundary conditions used in the model 

are able to approximat y simulate the aquif~r system, then by 

using the 1956 potentiometric surface as the initial starting 

heads, it should be possible to reproduce the 1973 observed 

potentiometric surface, in addition to well hydrographs observed 

during the period of 1956 through 1973. However, h h degrees of 

uncertainty usually involve parameter and boundary determinations; 

therefore, it is necessary to run test simulations for adjusting 

parameters and boundaries of the model in an effort to reproduce 

hydrograph trends and the observed 1973 potentiometric surface. 

During the test simulation, some parameters were fixed, such as 

grid size and physical hydrologic boundaries, pumping rates, and 

starting heads. Others were adjusted, such as transmissivity, 

vertical hydraulic conductivity of the confining layer, storage 

coefficient, and recharge in the outcrop area. 

M tric Surface 

Parameters were adjusted during test simulations by 

comparison of the model results with the observed 1973 

potentiometric surface (figs. 14 and 16) and 10 hydrographs (figs. 

17, 18, and 19). 

The observed hydrographs were constructed on the basis of the 

maximum recovery during each spring. Nearly all the observation 

wells are far enough away from pumping wells that continuous 

recorders show only gentle, somewhat sinosoidal fluctuations 

caused by increased pumping during the summer, with amplitudes 

ranging from about 2 to 8 ft. It should be noted that wells 6, 9, 

and 10 are each within a cluster of other observation wells 

drilled at the same location, but are screened at different depths 

in the aquifer system. At each site, the trends measured at 

different depths are essentially identical, although the head 

altitude may be slightly different. 

The results of modifying any parameter in the model were 

quickly noticeable in the computed trends. The hydrographs 

represent wells widely distributed in the study area and were used 

in conjunction with matching of the 1973 potentiometric surface 

produced at the end of each run. The criteria used in trying to 

achieve a best fit was that the difference between the computed 

and observed potentiometric surfaces and well hydrographs should 

be within ±8 ft. All adjustable parameters were kept within the 

range that is considered reasonable and are shown below. 

39 
/-:J? - //~~ 

I v"'~­ !0«; 

DELAWARE MEM 1 BRIDGE 

0 8 MILES 

EXP.LANATION 

0 

Potentiometric Contour shows altitude of 

the potenliometric surface in feet. Contour 

interval 1 o feet. Datum is NGVD o 1 1 9 2 9. 

@6 

Location and number of observation 

well referred to In text. 

X 

I"' 

/ 

\ ., .. /"' 

..... , ,I ... 

\ CAPE MAY 

\ COUNTY \. 

CUMBERlAND COUNTY 

-...... 

-...... _ 

1----,-~~--j 

12 KILOM~ERS 

Figure 16.--Potentiometric surface of the Potomac-RaritanMagothy aguifer system, December 1973, computed 

by model. 

40 
1-

w 

w 

u. 

z 

c 

> 

-HI 

-22 

-34 

-10 

~ -22 

z 

s: 

0 ii -34 

Ill 

a: 

0 

w 

> 0 

Ill 

<( 

l WEll NO.3 

DEPTH 266 FEET ,.,.... - - - ,_... -'- ....-

---

ii -58~----~----~-----L-----J------L-----~-----L----~----~~----~----~----~ 

~ 0 ...J 

a: 

w 

~ s: 

u.. 

0 

w 

c 

::> 

1-

i= 

WELLI\!0.4 

DEPTH 116 FEET 

...J -36L-----~-----L----~----~L_ ____ L_ ____ J_ ____ _L ____ ~ ______ L_ ____ L_ ____ J_ ____ ~ 

<( 

-------...... 

---- COMPUTED 

----- MEASURED 

WEll NO.5 

441 FEET 

......... ___ ....... 

' 

-36L---__ J_ ____ _L ____ ~----~------L-----J---~-L----~----~~----L-----~--~~ 

1954 1956 1958 1960 1962 1964 1966 1968 1970 1912 1974 1976 

YEAR 

Figure 17.--0bserved and computed hydrographs of wells lel 

to or located wifhin the outcrop area along the 

northwestern side of the cone of depressione 

41 

1978 
1-

w 

w -2l IJ..,, 

z 

-36 

c 

> 

(;, -48 z 

s: 24 

0 

..J 

w 

m 12 0::: 

0 

w 

> 0 0 m 

<1: 

..J 

w 

> -12 w 

..J 

0::: 

w 

1- -24 <1: 

s: 24 1.1.. 

0 

w 

0 

::> 12 1-

~ ..J 

<1: 

0 

-12 

-24 

-36 

1954 

COMPUTED 

WEll N0.6 

DEPTH= 410 FEET 

WEll NO.7 

DEPTH= 650 FEET 

WEll NO.8 

DEPTH= 2111 FEET 

-----MEASURED 

1956 1958 1960 1962 1966 

YEAR 

1968 1970 1972 1974 1976 

18.--0bserved and computed hydrographs of wells located 

in the northwestern part of the cone of depression. 

42 

1978 
---- COMPUTED 

----- MEASURED 

WEll NO.9 

DEPTH= 717 fEET 

WEll N0.10 

DEPTH= 848 FEET 

Figure 19.--0bserved and computed hydrographs of wells located 

in the southern part of the cone of depression. 

43 

j 

I 
rameter 

e coefficient 

ensionless) 

r ical raulic 

nductivity of the 

confini layer 

s) 

R harge due to 

precipitation in 

utcrop ( /yr) 

Assumed limits 

5,000 to 40,000 

1 x 10- 5 to 0.20 

0. 1 to 1 7 

Range used in 

model 

6,000 to 

35,000 

8 x 1 0- 5 to 

8 X 10- 3 

1 x 10- 11 to 

2 X 1 0 8 

0.35 to 0.90 

It is also reasonable to assume that parameters probably vary 

aqui r geometry. r example, near the outcrop area the 

rage coefficient for the aquifer system and vertical 

nductivity of the confining layer probably would be h her. 

charge also probably increases with elevation. Flat swampy 

eas near sea level, where the aquifer system is fully saturated, 

probably would not accept much recharge. 

e observed 1973 potentiometric surface was matched 

asonably well by the model generated surface as shown in figures 

4 and 16. The greatest discrepancies between the computed and 

observed 1973 potentiometric heads in and near the ne-grid 

a occurr in areas near Mount Holly (northeast of well 6), and 

ar the Delaware Memorial Bridge (west of well 1). A better fit 

uld not be obtained in the Mount Holly area without forcing some 

he parameters out of the reasonable range. Computer 

lations also failed to accurately duplicate a small cone of 

ession near the Delaware Memorial Bridge; however, this may be 

e to r data definition including water levels and pumping 

Delaware. 

The match between computed and observed well hydrographs is 

shown in figures 17, 18, and 19. The large head recovery at the 

U S. Navy base well (well 3) was caused by shutdown of nearly all 

ls at the Navy base in March 1966. A long history of 

increasi ly contaminated ground water on the Philadelphia side of 

he Delaware River contributed to this shutdown. The Navy base 

ad previously accounted for most of the extractions in the 

Ph adel ia area. 

44 
The model was run without pumping wells and allowed to reach 

equilibrium or steady state after obtaining aq acceptable match o 

the observed 1973 potentiometric surface and ~he hydrograph 

trends. The steady-state head solution (fig. 20 and fig 11, lower 

view) was controlled by constant head elevations of recharge and 

discharge areas, transmissivity, the amount of recharge specified 

in the outcrop, the head over the confining layer (fig. 11, middle 

view), and the vertical hydraulic conductivity of the confining 

layer. If the model was a perfect mimic of the physical aquifer 

system, the steady-state head distribution would precisely 

reproduce the prepumping head distribution. The year of 1900 was 

considered to represent the predevelopment conditions, but few 

wells would have been available for head measurement at that time 

Barksdale and others (1958, p. 112-113) prepared a map showing the 

general head distribution (also included on fig. 20) based upon 

the earliest known well measurements, some spanning a period of 

about 50 years. 

The comparison between the model produced steady-state 

potentiometric surface (1900±) and the observed potentiometric 

surface indicates a good agreement between the two surfaces (fig. 

20). A theoretical flow pattern for nonpumping conditions was 

also prepared by Barksdale and others ( 1958, p. 109-111) and is 

reproduced here (fig. 21) for comparison with the contoured 

perspective view of the model generated steady-state solution 

(fig. 11). 

Sensitivit of Parameter nt 

Sensitivity tests have been made by modifying modelwide, one 

parameter at a time and observing the effects. Figure 22 

illustrates the effect of parameter changes on water-level trends 

at a deep observation well near the center of the fine-grid area. 

Increase or decrease of transmissivity by 20 percent has about 

doubled the effect on drawdown (after 18 years) that an equivalent 

change in confining layer vertical hydraulic conductivity causes. 

Departures from the observed trend caused by changing the two 

parameters gradually increase with time; however, the change was 

almost negligible during the first 6 years. 

Figure 22 also shows the effect of reducing total steady 

leakage through the confining layer from 69 ft 3 /s to 0.2 ft 3 /s by 

setting the vertical hydraulic conductivity everywhere to the 

smallest value, 1 x 10- 11 ft/s. This change had a major effect on 

heads. Because the amount of leakage was virtually eliminated as 

a source of recharge, only precipitation on the outcrop and 

constant heads along the Delaware River remained as major sources 

of recharge. Thus, induced flow from the river increased from 95 

to 162 ft 3 /s because of the loss in head and the increase in 

hydraulic gradient in the aquifer system. 

45 
NE'&. JERSEY - -..._ ..... --so...., 

PENNSYLVANIA 

SALEM COUNTY 

DELAWARE MEMORIAL 1 BRIDGE 

I 

0 

N 

' - ...... l 

I 

I 

... ... / 

OCEAN 

08 ....... 

' ' ' ' ' ' '\ 

_ _,. 

ATLANTIC COUNTY 

CUMBERLAND COUNTY 

--- --

EXPLANATION 

-----10---

Computed 

10.---- Potentiometric Contour ahowll altitude of 

potentiometric eurface In feet. Contour 

Interval variable. Datum Ia NOVO of 

1 9 2 9. 

@6 

location and nu111ber of observation 

'IIHIII referred to in text. 

CAPE MAY 

COUNTY 

----..£>f.L.6.\:'(A I!.I~"iX .... 

0 MILES 

12 KILOMETERS 

Figure 20.--Comparison of model produced steady-state (1900±) 

potentiometric surface of the Potomac-RaritanMagothy aquifer system and that of Barksdale and 

others (1958, figure 19), 

46 

-----

/ 
EXPLANATION 

Aquifer system outcrop 

Potentiometric contours (theoretical) 

Flow lines 

High-level Intake area 

Interface between freshwater and salty water 

P E N N S Y L 

N 

1 

I 

0 10 20 30 40 

h .....1._,.,___,,,..,__.,..., i I I I ___,.,____,,r-d 

0 20 40 60 

... 

"'-Boundary of area shown 

in perspective views. 

MILES 

KILOMETERS 

Figure 21.--Theoretical flow pattern and location of the interface 

between freshwater and salty water in the PotomacRaritan-Magothy aquifer system before any pumptng of 

ground water (after Barksdale and others, 1958, figure 18). 

47 
1-

w 

w 

IJ.. 

z 

-4'i> 

c 

> 

CJ 

z 

s: 

0 

...J 

w 

ro 

...J 

w 

> 

w 

..,J 

a: 

w 

1-

<( 

s: 

u.. 

0 

Or---------~---------~--------~--------~-------·--~--------~--· 

-18 

-36 

-54 

-72 

/OBSERVED TREND 

/ r CALCULATED MATCH 

TRANSMISSIVITY RAISED 200/o 

TRANSMISSIVITY LOWERED 20% '-r 

·VERTICAl HYDRAULIC CONDUCTIVITY 

RAISED 20% 

VERTICAL HYDRAULIC CONDUCTIVITY LOWERED 20%___/ ~ 

VERTICAL HYDRAULIC CONDUCTIVITY OF CONFINING LAYER LOWERED TO txto-11_/ ~ 

-90 ---~----------~- 1956 1958 1960 1962 19641 1966 1968 uno 1972 

YEAR 

Figure 22.--Effect of model-wide changes in parameters at observation well 9. 

1974 

CD
ee ther sens vi y te ts we e made which esul 

head changes of ess than 1 ft at the end o the 18-year p i 

The 1956 starting head distribution in the aq ifer system was 

raised 20 percent, the seaward no- ow boundary of the model was 

changed to a constant head boundary; and the s ward no-flow 

boundary was moved 76 mi closer to the New Jer"sey coastline, 

thereby placing the boundary about 30 mi of shore The ef ct o 

raising the starting heads quickly dissipated (within 2 years 

probably because the aqui r system is so close to stead state a 

the end of each pumping period This test demonstrated that th 

model is relatively insensitive to errors in the initial head 

distribution. In addition, the failure of the boundary tests t 

af ct head distribution suggests that errors in defining the 

seaward boundary more accurately are not significant. 

MODEL APPLICATION IN ER MANAGE~1ENT 

Pro 

The model has been used to simulate water level response t 

the year 2000 under several sets of scheduled pumping rates The 

projections described below were made on the assumption that 

location of pumping sites will remain the same as those observe 

in 1973. Any additional demands for ground water would be met b 

increasing pumping rates of wells which were pumping in 1973 and 

by adding new wells in the same model elements that had purnpi 

wells in 1973. The first projection assumes that ground-water 

extractions are he constant at the 1973 level (zero growth); th 

second projection assumes compounded annual growth in extractio 

rates of 1 7 percent and 3.0 percent; and a third projection 

assumes a 3.0 percent annual growth rate, but with a freshwater 

head barrier activat and superposed on the pumping stress 

starting in 1984. The head barrier was placed along the u ip 

edge of the salty water body. 

On the basis of population projections (1980 to 2020) in 

eight coastal-plain counties by the State of New Jersey, 

Department of Labor and Industry (1975, p. 4 and 6), two pumping 

growth rates of 107 and 3.0 percent were selected to represent th 

most 1 ly growth rate to be expected (fig. 23). 

Other assumptions involved in the following projections are 

those inherent in the construction of' the simulation model. Thes 

include the assumption that the head over the confining layer and 

recharge in the outcrop area do not change with time. However, i 

certain areas, some reduction in head over the confining layer 

will likely take place, thus reducing the driving force for stead 

leakage. Conversely, some increase in recharge rates in the 

outcrop area could be expected as more space is made available in 

the aquifer system by head reduction. The actual impact of thes 

two assumptions in any projection is probably not great, however 

because most large changes in head over the confining layer are 

likely to occur in coastal areas remote om the fine-grid area as 

49 
V1 

0 

SIMU PROJECTIONS 

Figure 23.--Actual and projected ground-water extractions from 

the Petomac-br:f.tan-Masotb.y a~uifer system, 1956-2000 •. 

G 
they have in the past. Also, most of the outcrop area of the 

aquifer system near the fine grid contains major rivers that are 

treated as constant heads, which tend to outweigh any changes in 

recharge from precipitation. Additionally, the assumption was made 

that there is no transient leakage from the Merchantville-Woodbur 

confining layer. This assumption becomes l€ss valid as the cone 

of depression expands downdip. 

Extractions Held at Zero Growth Rate 

The first projected potentiometric head distribution the 

year 2000 was simulated without increase in pumping rates after 

1973. The predicted hydrograph trends (figs. 24, 25, and 26) show 

that head reduction in the aquifer system would cease within 

2 years over a large portion of the study area. The predicted 

potentiometric surface for the year 2000 is nearly the same as the 

1973 computed surface (fig. 16), except that the main cone of 

depression for the year 2000 is slightly shallower by several feet 

and slightly expanded. This projection suggests that a general 

reduction in extraction rates would reduce head loss which would 

in turn decrease recharge from constant head sources due to lower 

hydraulic gradients along the outcrop. Likewise, hydraulic 

gradients would flatten somewhat along the southeastern margin of 

the fine grid resulting in slightly less lateral inflow from that 

direction. 

Extractions Increasing at 1.7 Percent Per Year 

The second projected potentiometric head distribution for the 

year 2000 was made by allowing the 1973 pumping rates to increase 

at 1.7 percent per year. Most of the projected hydrograph trends 

(figs. 24, 25, and 26) show a reduced rate of head reduction after 

1973. This simulation result indicates that the historical 

pumping growth rates probably were greater than 1.7 percent per 

year. The simulated potentiometric surface for the year 2000 

(fig. 27) shows a well developed cone of depression with nearly 

the same shape as that computed for the year 1973 (fig. 16), but 

with heads in the confined portions of the aquifer system ranging 

from about 20 to 30 ft lower than the heads in 1973. Hydraulic 

gradients within and perpendicular to boundaries of the transition 

zone north of Clayton (fig. 27) would increase to about 4 ft/mi 

relative to that of 1973 and give ground-water velocities of about 

55ft/yr. Hydraulic gradients beneath the Delaware River estuary, 

adjacent but parallel to the transition zone near well 2, would 

reach 7 ft/mi and give ground-water velocities of about 420 f yr 

A perspective view of the year 2000 potentiometric surface is 

included in figure 28. This view shows a large, well developed 

cone of depression with its steeper side roughly parallel to tne 

Delaware River. Compared to the 1973 surface, hydraulic gradients 

for the year 2000 beneath the Delaware would be increased 

considerably. Induced recharge, as calculated by the model, from 

the Delaware River for the year 2000 would more than double in the 

fine-grid area. Steady leakage would account for about 27 percent 

51 
0 

> 

(!) 

z 

~ 0 

....! 

U.J 

IX) 

a: 

0 

U.J 

> 

0 

IXl 

<( 

1-

U.J 

u..t 

u.. 

z 

....~· u..t 

> 

u..t 

....! 

a: 

u..t 

1-

<( 

3: 

u.. 

0 

U.J 

0 

::::> 

1-

1-

....! 

< 

-13 /wi"ihh"e;;-- (3.0%) I barrier--~ 

0% 

-31 

49 Pt. Airy Obs. Well, node 23,85 

3% 

0 

-1 B 0% ~ 

'lt:' ··.)0 

-54 Shell Obs. Well node 

ft. 

31' 73 ~% 

3% 

-18 

0% 

36 

-54 

-10 

-28 0% 

-46 

WELL 4 

64 Amon Hgts. Obs. Well 2) node 36,49 

Top of screen- 88 ft. 

0 

-18 0% 

-3 6 

WELL 5 

-54 Willingboro Obs. Well 2, node 29,29 

Top of screen- 391 ft. 

1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 

24.--0bserved and projected hydrograph trends of wells 1, 

2, 3, 4r and 5 (percentage indicates extraction growth 

rates). 

52 
-11 

-29 

-47 

. 6 5 

-83 

-10 

-28 

--I 

~ -46 u.J 

--I 

1.1.. 

0 

4 

-14 

-32 

-50 

-68 

I OBSERVED 

Well 

COMPUTED 

I 

, node 18,33 

ft. 

Helis Obs. Well, node 19,13 

Top of screen- 661 ft. 

Butler Place Obs. Well 1, node 8,15 

Top of screen- 1986 ft. 

0% 

0% 

3% 

3% 

1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 

Figure 25.--0bserved and projected hydrograph trends of wells 6, 

7, and 8 (percentage indicates extraction growth rates). 

53 
3: 

0 

....1 

-17 

-35 

-531 

-71 I 

-89 

~ -107 

u..l -125 > 

0 

lXI 

< 

....1 

u..l 

> 

u..l 

....1 

1.1-

0 

-143 

0 

-18 

54 

-72 

-90 

-108 New Brooklyn Obs. Well 2, node 10,59 

Top of screen- 727 ft. 

,.. ___ _ I With headb.i7"r;;;: 

I 

I 

3% 

(3.0%) 

0% 

3% 

1954 1958 1962 1966 1970 1974 1978 1982 1986 1990 1994 1998 2002 

26.--0bserved and projected hydrograph trends of wells 9 

and 10 (percentage indicates extraction growth rates). 

54 
...-........_...._, 

PENNSYLVANIA 

----

O 4 8 MILES 

~2 KILOMETERS 

oCEAN 

I 

!_ 

II!XI"LANATION 

:COnfTnlnq Ti)<ir-oufclel>" Merchantville Fm. 

----------------------.-.:..: and Woodbury Clay 

; •• :. Aq'ul;e;·~yate'm'·:; • Potomac Group and 

• • • • '- • outcrof> • • • •• • Raritan and Magothy 

.:::·.·.··:.·.·.·.· .. ::.· .. ·.·:Formations 

i I iii litft,:Pii 11 1 IIIII 

Bedrock 

Potentle1111etrh: Ce~tte11r 'eltewlll altitude ef 

JPote~ttle-.tr141 81ilrface Ita feet . CNttew 

Interval 20 feet Dat11111 Ia N«<IYD of 11tlll. 

<t• Location and number of observation 

wall referred to In text. 

- ~ - - - -2 50 m g 1 L- -

Chloride concentration near bottom 

of aquifer system In llllllllsramll 

per liter. 

TRANSITION ZONE 

--2150 mg/L-- -----

Chioride concentration near top of 

aquifer ayatelll In llllilllgrams per liter. 

' ,1 \ .... 

,,. 

./""' 

\ CAPE MAY 

\ COUNTY 

' 

u 

;:: 

z 

~ 

< 

CUMBERLAND COUNTY 

- - - - ----- ..QE~ ~RE BAy 

----........ --...... 

I 

Figure 27. --Potentiometric surface of the Poj:omac-Rari tan-Mage thy 

aquifer syste!ll at year 2000 computed ll>y model with 

annual extractien growth rate of 1. 7 percent, 

55 
2000(1.7%) 

80 

level 

2000(3.0%) 

28e--Perspective potentiometric surfaces of the PotomacRaritan-Magothy system observed in 1973, and 

projected to year 2000 using annual extraction growth 

rates of 1.7 and 3.0 

56 

80 

Sea level 

-80 

-160 
(93 ft 3 /s) of the total extracted. 

Extractions Increasing at 3.0 Percent Per Year 

A third projected potentiometric head distribution for 

year 2000 was made by allowing the 1973 pump~ng rates to incr a 

at 3.0 percent per year. Hydrograph trends after 1973 (f s 24 

25, and 26) continue to follow those established during the 

simulation period. The year 2000 potentiometric surface (fig 29) 

shows an extremely large cone of depression with heads in confi 

parts of the aquifer system ranging from about 40 to 80 ft lower 

than the heads in 1973. Hydraulic gradients perpendicular to the 

boundary of the transition zone near Clayton would increase the 

year 2000 to about 7ft/mi. Hydraulic gradients beneath the 

Delaware River toward well 2 would increase to about 11 ft/mi. 

A perspective view of the year 2000 potentiometric sur ce is 

included on figure 28 for comparison with that computed for the 

year 1973. Steepened gradients along the Delaware River would 

greatly increase the amount of induced recharge reaching wells in 

the fine-grid area to about 62 percent or 300 ft 3 /s of the total 

extractions in the year 2000. Steady leakage through the 

confining layer would account for about 24 percent (116 ft 3 /s). 

A model run was made to explore the effects of an injected 

freshwater head barrier placed near the updip edge of the 

freshwater-saltwater transition zone. Imposition of such a head 

barrier would prevent migration of salty ground water into the 

large cone of depression (fig. 30). The model run was made by 

supposition on a 3 percent pumping growth rate in 1984, with 19 

constant heads nodes, with head elevations maintained at 10ft 

above mean sea level along the updip edge of the fresh-saltwater 

transition zone. These 19 nodes extended 35 mi across Gloucester, 

Camden, and Burlington Counties. Recharge rates average initially 

about 3 ft 3 /s and increase to an average of about 5 ft 3 /s for each 

node by the year 2000 and are summarized below. 

57 
NEW 

eo OCEAN co(JNTY 

" ~ 

~ 

0 

"' ---- "' I 

-8 I 

@I 

EXPLANATION 

·~ ~ _; ;~~:~~:~~?.~:.:>-~·~_:; iliiiliililllllllllil 

Bedrock 

Potomac Group and 

Raritan and Magothy 

Formations 

Potentiometric Contour ahowa altltu«M of 

t~~otentlometrlc surface In feet. Cotttoesr 

lntervel 20 feet. Oetulll 111 NGVD of 1 fll2 9 

ee Lecatlon and number of observation 

well referred to in text. 

--- ---250mg/L---

Chlorlde concentration near bottom 

of aquifer ayatem In milligrams 

per liter. 

TRANSITION ZONE 

---- 250mg/L - --

Chloride concentration near top of 

in ~~tiiiigrama per liter. 

' ,I \"" 

,,.. .-""" 

\ CAPE MAY 

\ COUNTY \. 

z 

~ u 

0 

u 

;:: 

z 

~ <( 

--------.... ..QE~~RE BAY 

---

MILES 

KILOMETERS 

Figure 29. --Petentimnetric surface of the Potomac-Rari tan-Mllgethy 

a~uifer system cmuputed by IIK)del with annual extraction 

grewth rate of 3.0 percent, 

58 

-.... _ 

---

I 
0 • 4 8 MILES 1-----r--"-----r----l 

0 4 8 12 KILOMETERS 

............ ( 

-----~ 8 ( 

0) " 

s"C;; 

~ .... '<}\'-'<} 

\ 

\ 

i 

EXPLANATION 

Potentiometric Contour shows altitude of 

potentiometric 1urface In feet. Contour 

Interval variable. D11tum is NGVD of 1 9 2 9. 

0 

Approximate nodal location of element 

used for freshwater Injection. 

____ 250 mg/L chloride concentration near 

bottom of aquifer system in milligrams 

per liter. 

Transition Zone 

- 250 mg/L chloride concentration near 

top of aquifer system in milligrams 

per liter. 

Location and num.ber of observation 

well referred to in text. 

X 

-- 3'....... ,./'"' 

\ /"" 

'"_../ 

\ CAPE MAY 

\ COUNTY \ 

CUMBERLAND COUNTY 

- - - - - - - - - _Qf~ 'EtA 

8.f ~1'( ....... .._ ................ 

............ 

'> 

I 

Figure 30. --Potentiometric surface of the 

aquifer sys tern in the year 2000 computed by 

freshwater head barrier activated in 1984 and main tali ned 

at an altitude of 10 feet. (annual growth rate of 3.0 

percent) 59 
charge rates required 

r eshwater barrier to 

prevent saltwater m ration 

g node 

1-5 

2 

2 8 

3 

4 

5 

Total r 

19 nodes 

(ft 3 /s) 

56 

78 

95 

Percent of 

extractions 

in fine-grid 

area 

18 

20 

20 

e aver e rec ge ates are asible t retically thro h 

more wells per node, however, it may be difficult to 

e or to maintain such recharge rates. In addition, by 1992, 

es close to the center of the cone of d ession near 

n (fig. ) m ht re ire recharge rates as high as 7 ft 3 /s. 

e than one well would be requir in each of the 19 nodes to 

ntain a fre er barrier under the assumptions us a 

1 situation, many ba rier wells would be used in the area 

sented by one no Use of widely spaced wells would require 

heads in the wells be maintain greater than 10 ft in order 

ake the minimum head between wells 10ft. 

In order to maintain the head along the freshwater barrier at 

above of 1929, the projected 1984 potentiometric 

ce would have to be raised a minimum of about.25 ft near the 

end of the barrier and a maximum of about 90 ft near Pitman 

spective view of the sequential head buildup along the 

er is shown in gure 31 1.3 da , 13 days, and 16 years 

ar 2000) after freshwater i ection started. Exce for the 

sence of the barrier, potentiometric surface at the year 2000 

31) is similar to the one shown in the lower view off ure 

Figures 24, 25, 26, and 30 demonstrate the impact of the 

er on he s in the aquifer system. 

Figures 24, 25, and 26 show the head increases at great 

tances om the barrier (well 1, 9 mi from the barrier; well 6 

d well 5, 14 mi; and well 7, 23 mi). Well 4 shows the least 

increase (4 ft) because it is located only 1 mi from the 

laware River. Over large areas of the cone of depression north 

the barrier (figs. 28 and 30) water levels are raised about 30 

o 60 ft as a result of the barrier. The barrier prevents the 

pi stresses in the north from reaching the aquifer system to 

the south. There e, south of the barrier the aquifer system is 

s y recovering, mostly because of steady leakage accumulation 

and only in part because of recharge from the barrier. Some 

pumpi centers exist on the south side of the barrier (fig. 12), 

60 
80 

-80 

16 years(2000) 

80 

Sea 

-80 

Figure 31.--Perspective potentiometric surfaces of the PotomacRaritan-Magothy aquifer system computed by model at 

various time periods after activation of freshwater 

head barrier in 1984. 

61 
they are relatively small. In addition to preventing 

ation of the salty ground water, the freshwater head barrier 

as a significant source of recharge to the nearby pumping 

r Tertiary Cohansey Sand, a highly productive 

e ifer exposed throughout the Pine Barrens of the 

Coastal Plain of New Jersey (Barksdale and others, 1958, 

55), could probably supply all the water needed to maintain 

barrier. This can be achieved in part by gravity wells that 

lly screened and gravel packed throughout the Cohansey Sand 

and. the tomac-Raritan-Magothy aquifers. Feasibility study and 

nomic considerations associated with such a barrier would have 

o ex ored in a pilot operation. 

G NO-WATER VELOCITIES NEAR FRESH-SALTY WATER TRANSITION ZONE 

According to Lohman (1972, p. 10), the average ground-water 

locity may be computed by the following equation 

ere 

K dh/dl 

= v 8 

..... 

v = average velocity in ft/d 

K = h aulic conductivity in ft/d 

(transmissivity divided by aquifer thickness) 

d dl = hydraulic gradient in ft/ft and 

8 = porosity (dimensionless) 

(4) 

cause the water density varies within the fresh-salty water 

ansition zone, the rate of movement of the transition zone 

a not be calculated. However, the water density near the leading 

ge of the transition zone can be assumed to be close to the 

esh ground water, and the rate of movement of the leading edge 

bably can be approximated by the calculation obtained from 

quation (4). The results are summarized in table 5. 

MODEL-E IMATED GROUND-WATER BUDGETS 

A mass balance was computed by the model for each simulation 

der to check the numerical accuracy of the solutions. As 

f t computation, each individual net flux component is 

emiz and tabulated to form a ground-water budget for the 

e model and for the fine-grid area. Such a budget provides a 

m asure of the relative importance of each flux component in the 

all solution. Table 6 summarizes the groun ater budget 

within the fine-grid area computed by the model r the 

om 1900 to 2000. 

e computed ground-water budgets in the fine-grid area were 

tt and shown in figure 32. In the projection period only the 

62 
Q\ 

lN 

TBble 5.--Estimated average ground-water velocities near the leading edge 

of the transition zone 

Area north of Clayton ll Area between Delaware River 

and well 2 2/ 

Projected 

extraction Average 

growth Hydraulic ground-water 

rate gradient velocity 

(percent) Year (ft/mi) (ft/yr) 

1956 (meas.) 0.8 12 

1 3 (meas.) 1 . 4 20 

1973 (calc.) 2. 1 31 

1 . 7 2000 (calc.) 3.8 55 

3.0 2000 (calc.) 6.5 95 

1/ Velocities north of Clayton based on average sand thickness of 225 ft 

(25 percent aquifer thickness), porosity of 25 percent, transmissivity 

Hydraulic 

gradient 

( ft/m i) 

0.6 

4.5 

5.0 

7. 1 

10.5 

of 12,000 ft 2 /d and, gradients from contour maps presented in this report. 

2/ Velocities between Delaware River and well 2 based on average sand 

thickness of 117ft (50 percent of aquifer system thickness, porosity of 

25 percent, transmissivity of 25,000 ft 2 /d, and gradients from contour 

maps presented in this report. 

-

Average 

ground-water 

velocity 

(ft/yr) 

35 

268 

296 

422 

620 
G\ 

.j:::. 

Run 

No. 

2 

3 

4 

5 

6 

7 

8 

9 

* 

** 

*** 

b 6.--Comouted ground-wate budget ne ux ra s in cubic Del~ second wi thjL 

ea fo various uns of the model 

ea tnver 

extraction sources** Lateral :Lnflow( ) or Outflow(-) 

growth rate (constant Steady Precipitation 

(percent Year Extractions head) leakage on outcrop N E side SE side SW side 

per year) 

1900* 0.0 -69.5 14.7 38.6 1 3. 2 -0.4 2.8 

-- 1956 -116.8 19. 2 45.0 38.6 11.8 3. 3 -0. 1 

-- 1 1 -149.0 40.6 52.6 38.6 1 3. 0 5.2 -0.9 

-- 1967 -186.6 69.5 60.7 38.6 12. 4 5.9 -0.7 

-- 1 97 3 -223.5 9 5. 1 68.8 38.6 1 3. 4 7. 1 -0. 1 

0 2000* -223.5 96.5 69.0 38.6 1 3. 3 6.0 -0. 1 

1.7 2000 -346.4 192.4 9 3. 4 38.6 1 3. 3 1 0. 3 -1.7 

3.0 2000 -482.0 300.0 11 6. 2 38.6 1 3. 5 15. 9 -3.2 

3.0 2000*** -1}82.0 317.0 98.3 38.6 1 3. 1 21.1 -5.6 

Steady-state solutions. 

Negative rat indicates flow from the aquifer system to river; 

Positive r e indicates induced recharge from river (and minor outcrop reach near Philadelphia) 

to the aquifer system; for run no. 9 includes recharge from freshwater barrier injection nodes. 

Same as no. 8 but with freshwater barrier emplaced in 1984. 

NOTE: Percentages in second column indicate compound annual extraction growth rates 

for the period 1974-2000. 

Aquifer 

Storage 

0.0 

0. 16 

0.25 

0.03 

0.31 

0.002 

0.33 

1. 50 

0. 61 
:1 :1 

0 w 

a:: ... u.. fh 

> w 0 

<.? 

a:: a: 

< w 

J: u.. 

0 3 fit!~ C/) 0~ 

0 < = 

200 ~ 100~ 

PRECIPITATION ON OUTCROP 

0 

-100 

-200 

-300 

-400 SIMULATION PROJECTION 

PERIOD PERIOD 

-500 

HlOO 1910 1920 1930 1940 1950 1960 1970 1980 1990 

Figure 32.--Computed ground-water budget rates in the fine-grid area, 

1900± to the year 2000. (Budget rates after 1974 are 

plotted only for the 3.0 percent projection. Rates from 

s are too small to show.) 

65 

2000 
water budget related to the pumping growth rate of 3.0 percent per 

ar was plotted. The amount of departure of the curves above and' 

elow the zero line represents the net exchange between recharge 

and discharge. The steady-state analysis for the year 1900 

sts that nearly all the water recharged to the aquifer system 

was being discharged into the Delaware River. However, a small 

amount of outflow through the southeastern boundary of the fine 

d (table 6) was probably being discharged by upward leakage 

nto overlying aquif~rs. 

The computed budget suggests that under nonpumping conditions ~00) und-water discharge from the aquifer system to the 

laware River in the fine-gr region amounted to about 70 ft 3 /s. 

r the entire model, the computed discharge is 112 ft 3 /s. These 

gures are approximately close to an estimate of a total 

discharge from aquifers of 77 ft 3 /s made by Barksdale and others 

(1958, p. 129). Because the aquifer system was undeveloped and 

most of the outcrop was actually an area of discharge (figs. 11 

and 21), much of the precipitation (39 ft 3 /s) would be discharged 

into streams. In the fine-grid area, steady leakage was 15 ft 3 /s 

r 21 percent of the discharge to the Delaware River, while 

lateral inflow through boundaries was 16 ft 3 /s or about 23 percent 

of the total discharge to the river. At sometime between 1943 and 

1960 (fig. 32) net flow from the aquifer system to the river was 

adually reduced. Thereafter, the growth in extraction rates 

aus a rapid increase in induced recharge from the Delaware 

River. The model simulation which used a projected pumping growth 

ate of 3 percent per year, which is similar to that experienced 

uring the 18-year simulation period, suggests that by the year 

000 induced recharge from the Delaware River could account for 

approximately 62 percent of the total extractions; and the water 

om the steady leakage through the overlying aquifers accounts 

r 24 percent of extractions. These percentages compared with 

about 43 percent from induced recharge and about 31 percent from 

s eady leakage for 1973, and 16 and 39 percent, respectively, for 

956. se figures indicate that more and more water will be 

nduced from the Delaware River as extractions increase 

cordingly. 

SUGGESTIONS FOR FURTHER STUDY 

e presence of the large body of salty ground water in the 

aquifer system, in conjunction th the salty lower reaches of the 

Delaware River, represents the greatest threat to the 

ontamination of the aquifer system. Sources of industrial 

llution in the outcrop area are also potential threats for 

o tamination of ground water in local areas. Continuation of 

h decline due to pumping, however, does not appear to be 

ser ous unless compaction and land subsidence become evidenced. 

Since the Delaware River is an important source of induced 

echarge, the following suggestions are made: 

66 
1. The model could be used to help determine whether the 

conjunctive use of ground water and surface water could minimize 

or prevent contamination of wells by salty water in the Delaware 

River during extreme low-flow periods. For example, steep 

hydraulic gradients from the river to the aquifer sy~tem cause 

large amounts of induced recharge. The gradients could be 

reduced or possibly even reversed by (a) a combination of 

injecting river water into existing production wells, or using 

river water directly as a source during periods of excess esh 

flow (roughly December through May) and (b) by temporarily 

shutting down well fields close to the river during extreme low 

flow periods. This would shift pumping stress to wells further 

downdip. Conversely, during most years, optimal production of 

ground water from the aquifer system could be obtained by 

placing well fields as close as possible to freshwater reaches 

of the river. This would significantly lessen the impact of 

pumping stresses on the rest of the aquifer system and could 

reduce the rates of movement of salty ground water in the 

transition zone. The validity of using the model simulations 

for such water-management alternatives should be evaluated 

using monitoring data. 

2. One or a series of pilot injection wells should be 

constructed and put into operation for several years to determine 

the feasibility and costs of a freshwater-head barrier in the 

transition zone. 

3. Test drilling and water-quality sampling at different 

points in a vicinity of the transition zone near Clayton should be 

undertaken to determine the vertical and lateral variation in 

chloride concentration in an effort to assess needs and methods of 

monitoring the movement of the salty ground-water body. 

4. A comprehensive water-quality study should be undertaken 

within and near the transition zone and in the outcrop area from 

Mercer County to Salem County. This study should include sources 

of contamination, such as toxic waste disposal sites, and areas 

where poor quality river water has migrated into the aquifer 

system. 

5. The head distribution throughout the aquifer system and 

overlying aqui rs should be measured in March and April, about 

every 8 to 10 years, if rates of head decline continue at about 

1.5 to 2.5 ft/yr. 

6. The model should be updated with new extraction data and 

additional data on head distribution and well hydro aphs. 

1. The model could be improved so that less restrictive 

assum ions are made. Transient leakage could be added to the 

existing model, and a new multilayer model could be made. 

67 
SUMMARY AND CONCLUSIONS 

A two-d ensional finite difference model was used to 

response of the Potomac-Raritan-Magothy aqui r 

to pi stresses during the 18-year period, 1956 through 

Acceptance of the model as a means of projecting head 

ution in the aquifer system is based on a close correlation 

ween the tr s of observed and model computed water-level 

aphs r ten observation wells spaced throughout the area 

ucester, Camden, and Burlington Counties; close La~lon between observed and computed potentiometric surfaces 

e end of the simulation period (1973); goodness of fit 

ween the model-generated nonpumping steady-state potentiometric 

ce and the (1900±) sur ce determined by water-level 

ervations; and model-generated hydrolog~c budgets that appear 

a enable and supportable, both r the transient simulation and 

eady-state solution~ 

Since 1900 extractions have gradually increased, reaching 

t 80 ft 3 /s in 1956 to about 340 ft 3 /s in 1973. Continuous 

widespread reductions in head, averaging about 2 to 3 ft/yr, 

rmed broad cones of depression with elevations well below 

evel throughout most of the aquifer. 

A large y of salty ground water, with chloride 

entrations ranging from 250 to 27,000 mg/L, occupies the 

r system in the southern half of the coastal plain and 

ec s with the aquifer's fresher water across a broad diffusion 

of 6 to 12 mi in width. Head reductions caused by pumping 

been more than sufficient to cause slow m ration of the 

ground water towards pumping centers. The head reductions 

induce large volumes of freshwat~r and some salty water into 

aqui r s tern from the Delaware River estuary. 

general, the three stratigraphic units (Potomac Group, and 

Raritan and Magothy ations) that comprise the aquifer 

em ar to function together as a hydrologic system. 

g-term records at clustered observation wells, some of which 

quite remote from pumping centers, show rates of vertical head 

ne and su est that much of the aquifer system responds 

uni rmly to pumping stress. 

del results suggest that in 1900, the Delaware River 

uary, which was a major discharge area for the aquifer system 

ned about 70 ft 3 /s om the aquifer system in New Jersey 

ween en and the Delaware Memorial Bridge. Sometime in the 

od of 1943-60, due to increased ground-water extractions, 

un ater discharge into the Delaware River was gradually 

u ed ereafter, increased extractions through 1973 caused 

uced echarge om the Delaware River estuary to approach 95 

s, which is about 43 percent of the 224 ft 3 /s extracted in the 

ncipal interest area. Steady leakage from the overl ng 

rs accounted for 31 percent of extractions while other 

68 
sources account for 26 percent. 

Model projections to the year 2000, using the 1973 well 

distribution, suggest that if extractions were kept constant (zer 

growth), further head reduction in the aquifer system would cease 

within two years over large parts of the study area. If 

extractions grew at a compounded annual rate of three percent a 

cone of depression already encompassing most of the coastal ai 

would broaden and deepen with heads ranging om 60 to 160 f 

"below NGVD of 1929 by the year 2000. Steeper hydraulic gradients 

would increase the migration of salty ground water towards pumping 

centers. Induced recharge from the Delaware River estuary in the 

fine-grid area would increase to about 300 ft 3 /s or 62 percent o 

the extractions in this area. A line of injection wells could be 

established to maintain a freshwater head barrier in the 

transition zone to prevent further migration of salty ground wate 

across a 35-mi stretch in Gloucester, Camden, and Burlington 

Counties. Total rate of injection to the head barrier would rang 

from about 56 ft 3 /s in 1984 to about 95 ft 3 /s in 2000. rier 

recharge rates ~ould be equivalent to about 20 percent of the 

annual extractions in the fine-grid area for a pumping growth rate 

of 3 percent. 

The results of this study generally confirm the following 

conclusion made by Barksdale and others (1958, p. 126). 

"The great value of the ground-water 

supplies from the Raritan and Magothy 

formations justifies all reasonable measures 

to prevent or delay the serious and longlasting effects of saltwater encroachment. 

The maintenance of freshwater in the 

Delaware is probably the most important 

preventive measure that can be taken. Next 

in importance would be the careful and 

intelligent areal distribution of pumpage in 

such a way as to take maximum advantage of 

induced freshwater recharge and to avoid 

concentrated reductions of freshwater head 

near the margin of the saltwater in the 

aquifers." 

69 
REFERENCES 

derson, H. R., and Appel, C. A., 1969, Geology and ground-water 

esources of Ocean County, New Jersey: New Jersey Department 

of Conservation and Economic Development Special Report 29, 

93 p 

sdale, H. C., Greenman, D. W., Lang, S. M., Hilton, G. S., and 

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

region adjacent to the lower Delaware River: New Jersey 

Department of Conservation and Economic Development Special 

port 13, 190 p. 

k ale, 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 port 8, 154 p. 

own, 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. 

lekas, 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, 

14 6 p. 

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 

Invest ations Atlas HA-557. 

enman, D. W., Rima, D. R., Lockwood, W. N., and 

Meisler, Harold, 1961, Ground-water resources of the coastal 

plain area of southeastern Pennsylvania: Pennsylvania 

Geological Survey Bulletin, 4th ser., W13, 375 p. 

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

f Gloucester County, New Jersey: New Jersey Department of 

nservation and Economic Development Special Report 30, 

130 p. 

onski, L A , 1968, Ground-water resources of Monmouth County, 

w Jersey. New Jersey Department of Conservation and 

Economic Development Special Report 23, 117 p., 27 figs. 

C E., 1940, On the flow of water in an elastic artesian 

aquifer: American Geophysical Union Transactions, v. 21, p. 

574 86. 

70 
REFERENCES--Continued 

Lohman, S. W., 1972, Ground-water hydraulics: U,S 

Survey Professional Paper 708, 70 p. 

logical 

Luzier, J. E., and Burt, R. J., 1974, Hydrology of basalt aqui 

and depletion of ground water in east-central Washi ton 

Washington Department of Ecology Water-Supply Bullet n 33 

53 p. 

Luzier, J. E., and Skrivan, J. A., 1975, Digital-simulation and 

projection of water-level declines in basalt aquifers o t 

Odessa-Lind area, east central Washington: U.S. Geological 

Survey Water-Supply Paper 2036, 48 p. 

Matalas, Nicholas C., and Maddock III, Thomas, 1976, Hydrologic 

Semantics: Water Resources Research, v. 12, no. 1, p 12 

Nemickas, Bronius, 1976, Digital-simulation model of the WenonahMount Laurel aquifer in the coastal plain of New Jersey: 

U.S. Geological Survey Open-File Report 75-672, 42 p. 

New Jersey Department of Labor and Industry, 1975, New Jersey 

population projections 1980-2020: New Jersey Department o 

Labor and Industry, 6 p. 

Nichols, W. D., 1977, Digital computer simulation model of the 

Englishtown aq~ifer in the northern Coastal Plain of New 

Jersey: U.S. Geological Survey Open-File Report 77-73 

1 0 1 p • 

Owe n s , J . P . , M in a r d , J . P . , So h l , N .. F . , an d Me ll o , J . F . , 1 9 7 0 

Stratigraphy of the outcropping post-Magothy Upper Cretaceo 

formations in southern New Jersey and northern Delmarva 

Peninsula, Delaware and Maryland: U.S. Geological Survey 

Professional Paper 674, 60 p. 

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 Coasta 

Margin of United States north of Cape Hatteras-brief survey 

American Association of Petroleum Geologists Bullet , v. 59 

p. 1529-1548. 

Petters, S. W., 1976, Upper Cretaceous subsurface stratigraphy o 

Atlantic Coastal Plain of New Jersey: American Association 

of Petroleum Geologists Bulletin, v. 60, no. 1, p. 87-107. 

Pinder, G. F., 1970, An iterative digital model for aqui r 

evaluation: U.S. Geological Survey Open-File Report, 44 p 

71 
REFERENCES--Continued 

nder, G .. F .. , and Bredehoeft, J .. D .. , 1968, Application of d i tal 

computer r ifer evaluation: Water Resources Research, 

v. 4, no. 5, p .. 1069-1093. 

well, S. T .. , Consulting Engineers, Baltimore, Maryland, and 

Leggette and Brashears, Consulting Ground-Water Geologists, 

New k, 1954, Report on the effect of ship channel 

enlargement above Philadelphia: Report prepared for The 

Committee r udy of the Delaware River, Appendix A2-1. 

ice, W. G., Jr .. , 1976, PUR VUE: A program to plot perspective 

views of surfaces: Princeton University, Plasma Physics 

Laboratory report PPPL-1304, 14 p. 

ey, J. G., 1971, Ground-water resources Cumberland county, New 

Jersey: New Jersey Department of Environmental Protection 

Special Report 34, 65 p. 

senau, J. C., Lang, S. M., Hilton, G. S., and Rooney, J. G., 

1969, Geology and ground-water resources of Salem County, New 

Jersey: New Jersey Department of Conservation and Economic 

Development Special Report 33, 142 p. 

sh, F. E., 1968, Geology and ground-water resources of 

Burlington County, New Jersey: New Jersey Department of 

Conservation and Economic Development Special Report 26, 

65 p. 

Schlee, John, Behrendt, J. C., Grow, J. A., Robb, J. M., Mattick, 

R .. E., Taylor, P. T., and Lawson, B. J., 1976, Regional 

geologic framework of Northeastern United States: American 

sociation of troleum Geologists Bulletin, v. 60, no. 6, 

p. 926-951. 

Sheridan, R. E., and Knebel, H. J., 1976, Evidence of 

Post-Pleistocene faults on New Jersey Atlantic Outer 

Continental Shelf: American Association of Petroleum 

Geologists Bulletin, v. 60, no. 7, p. 1112-1117. 

ndstrom, R .. W., and Pickett, T. E., 1971, The availability of 

ground-water in New Castle County, Delaware: University of 

Delaware, Water Resources Center, 156 p. 

escott, P. C., Pinder, G .. F., and Larson, S. P .. , 1976, Finitedi renee model for aquifer simulation in two dimensions 

with results of numerical experiments: Techniques of 

W a ter-Re sour c e s In v est i g at ions , Book 7 , C h apt e r C 1 , 1 1 6 p . 

cchioli, John, and Palmer, N. N., 1962, Ground-water resources 

of Mercer County, New Jersey: New Jersey Department of 

Conservation and Economic Development Special Report 19, 

17 p. 

72