U.S. Department of the Interior

U.S. Geological Survey

HISTORICAL GROUND-WATER-FLOW PATTERNS

AND TRENDS IN IRON CONCENTRATIONS IN THE

POTOMAC-RARITAN-MAGOTHY AQUIFER SYSTEM

IN PARTS OF PHILADELPHIA, PENNSYLVANIA,

AND CAMDEN AND GLOUCESTER COUNTIES,

NEW JERSEY

by Ronald A. Sloto

Water-Resources Investigations Report 03-4255

In cooperation with the

U.S. ENVIRONMENTAL PROTECTION AGENCY

New Cumberland, Pennsylvania

2003
ii

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does not

constitute endorsement by the U.S. Geological Survey.

For additional information Copies of this report may be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

215 Limekiln Road Box 25286

New Cumberland, Pennsylvania 17070 Denver, Colorado 80225-0286

Email: dc_pa@usgs.gov Telephone: 1-888-ASK-USGS

Internet Address: http://pa.water.usgs.gov
iii

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

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

Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Previous investigations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Ground-water-flow patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Regional hydrogeologic framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Hydraulic connection between aquifers and the Delaware River . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Pre-development flow system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Development of ground-water supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Post-development flow system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Iron, manganese, and sulfate concentrations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Changes in iron, manganese, and sulfate concentrations with time . . . . . . . . . . . . . . . . . . . . . . . 21

Role of bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Suggestions for further study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

References cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

CONTENTS

Page
iv

Figure 1. Map showing location of the study area and hydrogeologic sections A-A′and B-B′ . . . . . . 3

2. Generalized hydrogeologic section of the Potomac-Raritan-Magothy aquifer system

in Pennsylvania and New Jersey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3. Hydrogeologic cross section through the Potomac-Raritan-Magothy aquifer system,

Philadelphia, Pa., and Gloucester County, N.J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4. Hydrogeologic cross section through the Potomac-Raritan-Magothy aquifer system,

Philadelphia, Pa., and Camden County, N.J. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5. Maps showing simulated flow between the Delaware River and the lower aquifer of

the Potomac-Raritan-Magothy aquifer system and simulated river-influenced

zones, 1983-88. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

6. Graph showing estimated water withdrawal from the lower sand unit and lower aquifer

of the Potomac-Raritan-Magothy aquifer system in Philadelphia and adjacent

parts of New Jersey, 1904-95. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

7-8. Maps showing potentiometric surface of the lower sand unit of the Potomac-RaritanMagothy aquifer system in south Philadelphia:

7. 1940 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8. March 24, 1954 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

9. Map showing regional potentiometric surface of the lower aquifer of the PotomacRaritan-Magothy aquifer system, 1978. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

10. Graph showing estimated water withdrawals from the Potomac-Raritan-Magothy

aquifer system, southern New Jersey counties, 1978-97. . . . . . . . . . . . . . . . . . . . . . 15

11-13. Maps showing the regional potentiometric surface of the lower aquifer of the

Potomac-Raritan-Magothy aquifer system:

11. 1988 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

12. 1996 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

13. 1998 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

14. Conceptual section illustrating geochemical regimes in the aquifer affected by

lowering and recovery of water levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

15. Map showing locations of wells screened in the lower aquifer of the PotomacRaritan-Magothy aquifer system with historical dissolved iron concentrations. . . . . . 22

16-19. Graphs showing concentrations of dissolved iron in water from:

16. Wells screened in the lower sand unit of the Potomac-Raritan-Magothy

aquifer system at the former Philadelphia Naval Ship Yard, 1943-85. . . . . 23

17. Industrial supply wells screened in the lower sand unit of the

Potomac-Raritan-Magothy aquifer system in Philadelphia, 1947-79 . . . . . 24

18. Wells screened in the lower aquifer of the Potomac-Raritan-Magothy

aquifer system at the Eagle Point Refinery, Gloucester County, N.J.,

1950-85 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

19. Wells screened in the lower aquifer of the Potomac-Raritan-Magothy

aquifer system in Gloucester County, N.J., 1951-66 . . . . . . . . . . . . . . . . . 26

ILLUSTRATIONS

Page
v

Figure 20. Map showing concentrations of dissolved iron in water from the lower aquifer of the

Potomac-Raritan-Magothy aquifer system, Philadelphia, Pa., and

Camden and Gloucester Counties, N.J., 1980-86. . . . . . . . . . . . . . . . . . . . . . . . . . 27

21-22. Graphs showing:

21. Concentrations of dissolved manganese in water from wells screened

in the lower sand unit of the Potomac-Raritan-Magothy aquifer system

at the former Philadelphia Naval Ship Yard, 1945-82. . . . . . . . . . . . . . . . . 28

22. Concentrations of dissolved sulfate in water from wells screened in the

lower sand unit of the Potomac-Raritan-Magothy aquifer system at the

former Philadelphia Naval Ship Yard, 1942-82. . . . . . . . . . . . . . . . . . . . . . 29

23-24. Maps showing:

23. Concentrations of dissolved manganese in water from the lower aquifer

of the Potomac-Raritan-Magothy aquifer system, Philadelphia,

Pa., and Camden and Gloucester Counties, N.J., 1980-86 . . . . . . . . . . . . 30

24. Concentrations of dissolved sulfate in water from the lower aquifer of the

Potomac-Raritan-Magothy aquifer system, Philadelphia, Pa.,

and Camden and Gloucester Counties, N.J., 1980-86. . . . . . . . . . . . . . . . 31

ILLUSTRATIONS—Continued

Page
vi

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29)

and the North American Vertical Datum of 1988 (NAVD 88).

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

North American Datum of 1983 (NAD 83).

Abbreviated water-quality units used in report:

mg/L, milligrams per liter

Length

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Volume

gallon (gal) 3.785 liter

million gallons (Mgal) 3,785 cubic meter

billion gallons (Bgal) 3,785,000 cubic meter

Flow rate

million gallons per day (Mgal/d) 3,785 cubic meter per day

billion gallons per year (Bgal/yr) 3,785,000 cubic meter per year

Gradient

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

CONVERSION FACTORS AND ABBREVIATIONS

Multiply By To obtain
1

by Ronald A. Sloto

ABSTRACT

The Potomac-Raritan-Magothy (PRM) aquifer

system is an important sole-source ground-water

supply in Camden and Gloucester Counties, N.J.

Elevated iron concentrations are a persistent

water-quality problem associated with ground

water from the PRM. In Philadelphia, the PRM no

longer is usable as a water supply because of

highly elevated concentrations of iron (as high as

429 mg/L [milligrams per liter]), manganese (as

high as 4 mg/L), and sulfate (as high as

1,720 mg/L). A strongly reducing environment in

the PRM in south Philadelphia causes these constituents to be remobilized by reductive dissolution

of the aquifer matrix.

By the 1920s, ground-water pumping changed

the natural ground-water-flow patterns, and ground

water flowed toward pumping centers in Philadelphia. By 1940, recharge areas changed from the

topographically high areas east of Trenton, N.J., to

the outcrop area of the PRM in Philadelphia, and

the Delaware River became a source of recharge

instead of a point of ground-water discharge. By

1954, the cone of depression caused by pumping

at the former Philadelphia Naval Ship Yard (PNSY)

exceeded 50 feet below NGVD 29, and the direction of ground-water flow was from New Jersey

toward Philadelphia. Because of highly elevated

concentrations of iron and manganese, pumping at

the former PNSY ceased in the mid-1960s. Beginning about 1951, increased ground-water withdrawals from the PRM in New Jersey reversed the

hydraulic gradient so that ground-water flow was

from Philadelphia toward New Jersey under the

Delaware River, making Philadelphia a recharge

area for the PRM aquifer system in parts of Camden and Gloucester Counties. By 1988, water levels in the lower aquifer of the PRM in New Jersey

had declined to 103 feet below NAVD 88.

In 1943, dissolved iron concentrations ranged

from 0.07 to 0.6 mg/L at the former PNSY. By 1967

when the wells at the PNSY were abandoned, dissolved iron concentrations had reached 46 mg/L.

Dissolved iron concentrations in water from industrial wells in Philadelphia increased from 0.17 mg/L

in 1949 to 19 mg/L in 1979. The concentration of

dissolved iron in water from wells screened in the

lower aquifer in New Jersey also increased with

time. By 1985, dissolved iron concentrations were

as high as 16 mg/L for Eagle Point refinery wells.

INTRODUCTION

The Potomac-Raritan-Magothy (PRM) aquifer

system has been designated a sole-source aquifer

by the U.S. Environmental Protection Agency

(USEPA). A sole-source aquifer designation is

intended to protect ground-water supplies in areas

with few or no alternative drinking-water sources,

and where, if contamination occurred, using an

alternative source would be extremely expensive.

This unconsolidated aquifer system is an important

water-supply source in New Jersey. In 1998, about

167 Mgal/d were withdrawn from the PRM aquifer

system in New Jersey for a variety of uses including public supply (Lacombe and Rosman, 2001).

Most withdrawals from the lower aquifer of the

PRM are in Camden and Gloucester Counties, N.J.

The PRM aquifer system no longer is used as

a source of water supply in Philadelphia because

of highly elevated concentrations of iron (as high

as 429 mg/L), manganese (as high as 4 mg/L), and

sulfate (as high as 1,720 mg/L) that have contaminated the aquifer in south Philadelphia and have

made the ground water unusable for most purposes (Paulachok, 1991). A strongly reducing environment in the PRM in south Philadelphia causes

these constituents to be remobilized by reductive

dissolution of the aquifer matrix. The reducing environment results from oxygen depletion by organic

wastes, such as sewage, leachate from landfills,

dumped or spilled hydrocarbons, and other chemiHISTORICAL GROUND-WATER-FLOW PATTERNS

AND TRENDS IN IRON CONCENTRATIONS IN THE

POTOMAC-RARITAN-MAGOTHY AQUIFER SYSTEM

IN PARTS OF PHILADELPHIA, PENNSYLVANIA,

AND CAMDEN AND GLOUCESTER COUNTIES, NEW JERSEY
2

cals decomposed within the aquifer (Langmuir,

1969, p. 21). The microbiological decomposition of

organic substances in ground water consumes

oxygen. In low dissolved oxygen waters, naturally

occurring iron, manganese, and sulfate leach from

the aquifer matrix. Subsequently, when ground

water containing these reduced constituents is

exposed to oxygen, the metals reoxidize and

hydroxides precipitate from the water. The precipitates can clog well screens, accumulate in treatment and distribution systems, stain fixtures, and

impart an objectionable taste and color to the

water. Many wells in Philadelphia, including those

at the former Philadelphia Naval Ship Yard (PNSY),

were abandoned primarily because of problems

associated with the precipitation of iron hydroxides.

Organic compounds from industrial waste

sources in south Philadelphia have the potential to

effect the quality of ground water withdrawn from

the lower aquifer of the PRM in adjacent areas of

New Jersey where the lower aquifer is not in direct

hydraulic connection with the Delaware River. During most of the 1940s and 1950s, ground water

flowed under the Delaware River from New Jersey

to Pennsylvania in response to heavy pumping in

Philadelphia. However, with the cessation of

ground-water pumping in Philadelphia in the mid1960s and in response to heavy pumping in Camden and Gloucester Counties, hydraulic gradients

reversed, and ground water began to flow beneath

the Delaware River from Pennsylvania toward New

Jersey (Navoy and Carleton, 1995, p. 33). The outcrop area of the PRM in Philadelphia became a

recharge area for the lower aquifer of the PRM in

parts of New Jersey.

Although ground-water withdrawals in New

Jersey have declined since the 1980s, ground

water of poor quality may still be flowing under the

Delaware River from Pennsylvania toward pumping

centers in parts of New Jersey. Potentiometric-surface maps show that the cones of depression

caused by pumping of wells in the lower aquifer of

the PRM in New Jersey extend under the Delaware

River into Pennsylvania. Under the present pumping conditions, the quality of water in the PRM

aquifer system in New Jersey is likely to degrade

with time. Although direct withdrawal of the organic

contaminants themselves is always a concern, the

primary threat to supply wells is elevated concentrations of iron and manganese remobilized by

degradation of organic contaminants.

Purpose and Scope

This report, which was prepared in cooperation with the USEPA, documents ground-water-flow

patterns and water-quality trends in the lower aquifer of the PRM aquifer system. This report provides

an overview of the geology of the PRM underlying

south Philadelphia and adjacent parts of Camden

and Gloucester Counties, N.J. (fig. 1). It presents a

summary of historical and current ground-water

withdrawals and flow in the lower aquifer of the

PRM and a summary of historical iron concentration data, which shows a substantial increase with

time. The report presents suggestions for further

study of the effects of ground-water withdrawals on

iron concentrations in the PRM aquifer system in

south Philadelphia and adjacent areas in New Jersey.

Previous Investigations

The hydrogeology of Philadelphia County was

described by Greenman and others (1961) and

Paulachok (1991). Data for wells in Philadelphia

County are given by Paulachok and others (1984).

The hydrology of Camden County was described

by Farlekas and others (1976). The hydrology of

Gloucester County was described by Hardt and

Hilton (1969). The hydrogeology of Gloucester and

Salem Counties was described by Cauller and others (1999). Zapecza (1989) provided maps of

structure contours and thickness for the principal

aquifers and confining units of the New Jersey

Coastal Plain.

Potentiometric-surface maps of the PRM aquifer system in Philadelphia in the 1920s, 1945, and

1954 were presented in Greenman and others

(1961). Generalized potentiometric-surface maps

of the PRM aquifer system in New Jersey were

presented by Gill and Farlekas (1976) for 1956 and

1968, and by Luzier (1980) for 1973. Detailed

potentiometric-surface maps of the PRM aquifer

system in New Jersey were constructed for 1978

by Walker (1983), for 1983 by Eckel and Walker

(1986), for 1988 by Rosman and others (1995), for

1993 by Lacombe and Rosman (1997), and for

1998 by Lacombe and Rosman (2001). Potentiometric-surface maps for the PRM near National

Park, N.J., for 1996 were presented by Rosman

(1997).

Ground-water-flow models were constructed

by Sloto (1988) for the lower sand unit of the PRM

aquifer system in Philadelphia and adjacent New

Jersey and by Schreffler (2001) for the PRM aqui-
3

fer system in Philadelphia and adjacent New Jersey. Luzier (1980) used a single-layer model of the

New Jersey Coastal Plain to determine groundwater-flow paths. Martin (1998) developed an

11-layer model of the New Jersey Coastal Plain.

Navoy and Carleton (1995) used a flow model to

evaluate induced flow from the Delaware River into

the PRM in the Camden area.

Water-quality data for wells in Philadelphia

County are given by Paulachok and others (1984).

Studies of ground-water quality in the Camden

area were conducted by Rush (1962), Donsky

(1963), Langmuir (1969), Fusillo and Voronin

(1981), and Fusillo and others (1984). Water-quality data for wells in the PRM aquifer system in

Camden County are given by Fusillo and others

(1984).

Figure 1. Location of the study area and hydrogeologic sections A-A′ (shown in fig. 3) and B-B′

(shown in fig. 4).

39°45′

40°00′

75°15′ 75°00′
4

Acknowledgments

A technical advisory committee was formed to

discuss issues related to ground-water contamination and to guide development of the Suggestions

for Further Study section in this report. The members of the committee were Hon Lee and Dale

Long, USEPA, Region III; Ruth Izraeli, USEPA,

Region II; Patrick Anderson, David Burke, and

Michelle Geissler, Pennsylvania Department of

Environmental Protection; Karl Muessig, New Jersey Geological Survey; Greg Cavallo, Delaware

River Basin Commission; and Daryll Pope, USGS.

The assistance of water purveyors in providing data and discussing ground-water issues is

greatly appreciated, especially Mark Huff, Bellmawr Water Department; Donna Demico,

Brooklawn and Westville Borough Water Departments; John Meier, Collingswood Borough Water

Department; Ed Deak, Deptford Township Municipal Authority; Tom Souch, National Park Borough

Water Department; Ken Christy and Kevin Dixon,

New Jersey American Water Company; Michael

Stevens, U.S. Water, Camden Water Division; Ed

Phelps, West Deptford Township Water Department; and Richard Midland and Richard Leidy,

Woodbury City Water Department.

The author thanks Charles A. Cravotta, III of

the USGS Pennsylvania District for his critical

review of the report and his assistance with the

geochemistry. Daryll Pope of the USGS New Jersey District also provided a critical review of this

report.

GROUND-WATER-FLOW PATTERNS

The PRM aquifer system is the largest and

most productive of the Coastal Plain aquifers in

New Jersey. The aquifers of the PRM generally are

confined; however, they can be unconfined at their

outcrop areas. Development of the Coastal Plain

aquifers for water supply has greatly altered the

natural ground-water-flow system. The high rate of

water withdrawal has created large, regional cones

of depression in the potentiometric surface of all

three PRM aquifers in New Jersey. The cones of

depression extend to more than 80 ft below

NAVD 88. Large withdrawals of ground water have

caused hydraulic gradients and ground-water-flow

directions to reverse.

Regional Hydrogeologic Framework

The Cretaceous-age PRM aquifer system

underlies the southeastern part of Philadelphia and

southern New Jersey. These sediments unconformably overlie pre-Cretaceous basement crystalline rocks southeast of the Fall Line, which is the

demarcation between consolidated rocks and

unconsolidated sediments. Beginning at the Fall

Line, the sediments of the PRM form an eastwardthickening wedge that dips gently to the southeast

from 40 to 60 ft/mi (Zapecza, 1989, p. 5). The sediments were deposited in a complex fluvial-deltaic

environment (Owens and others, 1968) and are

considered to be nonmarine in the Delaware Valley.

Regionally, the PRM is divided into three aquifers and two confining units in Pennsylvania and

New Jersey (fig. 2). Beneath and near the Delaware River, however, differentiation of the units of

the PRM is particularly difficult. In this area, the

units commonly do not seem to fit the “layer-cake”

model of the coastal plain (figs. 3 and 4). The following description of the PRM was compiled from

Greenman and others (1961) and Zapecza (1989).

In Pennsylvania, the upper sand unit unconformably overlies the middle clay unit and consists

mainly of fairly well-sorted medium to coarse sand

that contains minor amounts of fine to very fine

sand. Gravel beds are common, especially at the

base. The upper sand unit occupies erosional

depressions or scour channels in the underlying

middle clay unit. The upper sand unit apparently

was deposited by the same streams that scoured

channels in the middle clay unit. Therefore, it is

assumed that erosion of the middle clay unit took

place contemporaneously with deposition of the

upper sand unit. In a few places, the middle clay

unit was completely removed, and the upper sand

was deposited directly on the middle sand unit. In

south Philadelphia, the upper sand unit is about 35

to 50 ft thick. Throughout most of its area of occurrence, the upper sand unit forms a hydraulically

continuous unit with overlying deposits of Pleistocene sand and gravel. In New Jersey, the upper

aquifer is the least extensive unit of the PRM. It is

composed predominantly of quartzose sand and

silt with clayey layers and lenses. The upper aquifer is as much as 100 ft thick.

In Pennsylvania, the middle clay unit consists

of a tough, red and white clay, which is uniformly

massive. It commonly contains relatively little

sandy material. The surface of the clay is characterized by several elongated depressions caused
5

by erosion, which are oriented parallel to the trend

of the underlying bedrock channels. The base of

the middle clay unit is marked by a conspicuous

bed of lignite. However, where the middle clay unit

lies directly on the lower clay unit, as it does in

much of Philadelphia, it is difficult to differentiate

the two units. In New Jersey, the confining unit

between the middle and upper aquifers consists of

discontinuous, alternating layers and lenses of clay,

silt, and sand. It is about 50-150 ft thick but locally

may be less than 20 ft thick, and in some places, it

may be absent.

In Pennsylvania, the middle sand unit fills

shallow channels in the lower clay unit but is not

areally extensive in south Philadelphia. The middle

sand unit consists of a sequence of light colored,

very fine to coarse sand beds and a few beds of

light gray clay. The sediments are fairly well sorted,

and grain size decreases away from the heads of

the depositional channels. The middle sand unit is

as much as 25 ft thick in Philadelphia, and it commonly is less than 20 ft thick. In New Jersey, the

middle aquifer primarily consists of medium to

coarse quartzose sand and gravel with a few interbedded layers and lenses of silty clay. It is as much

as 150 ft thick. In and near the outcrop area near

the Delaware River, sand makes up 60 to 100 percent of the middle aquifer.

In Pennsylvania, the lower clay unit consists of

a tough clay containing beds of softer, well-stratified clay and thin lenses of fine sand. It unconformably overlies either the lower sand unit or the

residual clay of the underlying crystalline bedrock.

The lower clay unit occurs in the same bedrock

channels as the lower sand unit but its distribution

differs. Along the margins of the troughs, the lower

clay unit overlies the lower sand unit, but it is

absent at the heads of the troughs where it was

removed by stream erosion. The lower clay unit is

up to 61 ft thick but generally is about 20 to 40 ft

thick. In New Jersey, the confining unit between the

lower and middle aquifers consists primarily of red,

white, and gray silty clay with some interbedded

clayey silt and sand. It is less than 50 ft thick over

half of its mappable area but can exceed 100 ft in

thickness.

1 From Paulachok (1991, p. 13).

2 From Zapecza (1989, p. 4).

SYSTEM SERIES

HYDROGEOLOGIC UNIT

PENNSYLVANIA1 NEW JERSEY2

Cretaceous

Upper

Cretaceous

Potomac-Raritan-Magothy aquifer system

Upper clay unit Confining unit

Upper sand unit

Potomac-Raritan-Magothy aquifer system

Upper aquifer

Middle clay unit Confining unit

Middle sand unit Middle aquifer

Lower clay unit Confining unit

Lower sand unit

Lower

Cretaceous Lower aquifer

Figure 2. Generalized hydrogeologic section of the Potomac-Raritan-Magothy aquifer system in

Pennsylvania and New Jersey.
6

Figure 3. Hydrogeologic cross section through the Potomac-Raritan-Magothy aquifer system, Philadelphia, Pa., and Gloucester Co

from Navoy and Carleton,1995, pl. 1). Location of section shown on figure 1.

100

0

-100

-200

-300

-400

PENNSYLVANIA NEW JERSEY

LOWERSAND UNITOUTCROP

UPPER AQUIFER OUTCROP

DelawareRiver

0 10,000 20,000 30,000

FEET

ALTITUDE, IN FEET ABOVE NAVD 88

LAND 

BEDROCK

LOWER AQUIFER

MIDDLE 

UPPER AQUIFER

MIDDLE SAND

A 

LOWER SAND UNIT

UNIT OUTCROP

MIDDLE SAND UNIT

CONFINING UNIT CONFINING UNIT C

(Northwest) 
7

Figure 4. Hydrogeologic cross section through the Potomac-Raritan-Magothy aquifer system, Philadelphia, Pa., and GCounty, N.J. (modified from Navoy and Carleton,1995, pl. 1). Location of section shown on figure 1.

100

0

-100

-200

-300

-400

PENNSYLVANIA NEW JERSEY UPPER AQUIFER

DelawareRiver

0 10,000 20,000 30,000

FEET

LAND SUR

BEDROCK

LOWER AQUIFER MIDDLE AQUIFE

UPPER AQUIFER

B 

-500

OUTCROP

MIDDLE SAND UNIT

ALTITUDE, IN FEET ABOVE NAVD 88

MIDDLE SANDUNIT OUTCROP

CONFINING UNIT

CONFINING U

(Northwest) (So

CONFINING U
8

In Pennsylvania, the lower sand unit is the

basal member of the PRM. It occupies channels

carved into the underlying crystalline bedrock by a

pre-Cretaceous drainage system; five troughs were

mapped by Greenman and others (1961) in Philadelphia. The lower sand unit consists predominantly of fairly well-sorted coarse sand and fine

gravel that grades upward into medium to fine sand

containing a few beds of white clay. It is thickest in

the axial parts of the troughs and thins rapidly

toward the margins. The lower sand unit is as

much as 90 ft thick, but rarely attains a thickness

greater than 60 ft. In New Jersey, the lower aquifer

primarily consists of medium to coarse quartzose

sand and gravel with a few interbedded layers and

lenses of silty clay. Because of the fluvial depositional environment, considerable amounts of silt

and clay are interbedded locally with sand and

gravel. Sand makes up more than 70 percent of the

lower aquifer. It is greater than 250 ft thick in some

places.

Hydraulic Connection Between Aquifers and

the Delaware River

The interaction between the Delaware River

and the aquifer system probably is the most important factor influencing movement of contaminated

ground water from Pennsylvania to New Jersey.

This interaction depends on the physical characteristics and orientation of the geologic material

beneath the river and the hydraulic conditions controlling flow. The aquifer system and related confining units are laterally extensive and lie under or are

adjacent to the river. The riverbed material, which

is superimposed over these regional units, is composed of river deposits or reworked material, all

modified by dredging operations. The riverbed

material does not have a hydraulically significant

contact with laterally adjacent regional geologic

units, but it does have a significant vertical connection to the river. Given the aquifer system’s physical

contact with the river, the rate and magnitude of

flow are controlled by the relative hydraulic potential across the connection and by the hydraulic conductivities of the aquifer system and riverbed

(Navoy and Carleton, 1995, p. 35).

Where the course of the Delaware River

crosses troughs in the bedrock surface, a significant thickness of the PRM aquifer system and

hydraulically associated Cenozoic deposits fills the

troughs and allows exchange of water with the river

and flow under the river. Where bedrock highs exist

under the riverbed, flow under the river is impeded,

and interactions between the river and the aquifer

are limited to lateral infiltration along the banks.

Therefore, the hydrogeologic framework of the

deposits within these troughs controls the interaction between the river and aquifer system and flow

under the river (Navoy and Carleton, 1995, p. 35).

The Delaware River in the downstream area is

in contact with the middle aquifer (fig. 4). The Delaware River in the upstream area is in contact with

the middle and lower aquifers (fig. 3). Where a confining unit is present above the lower aquifer

(fig. 3), ground water flows from Philadelphia

beneath the Delaware River to New Jersey; this is

the case in the area around the former PNSY. However, in areas northeast of the former PNSY along

the Delaware River, the confining unit may be thin

or absent, and the Delaware River may be in direct

hydraulic contact with the lower aquifer (fig. 4). In

these places, little or no ground water may flow

from Pennsylvania to New Jersey.

Navoy and Carleton (1995) used a groundwater-flow model to determine areas of induced

recharge from the Delaware River in the vicinity of

Camden, N.J. Navoy and Carleton (1995, p. 104)

determined that recharge induced from the Delaware River by pumping was a local process with

recharge directed primarily toward wells or well

fields proximal to the river rather than being distributed along the length of the river as a broad-scale

process. Wells in cones of depression in regional

potentiometric surfaces, caused by ground-water

withdrawals far from the river, draw flow primarily

from the aquifer’s outcrop area on land, from intervening and overlying confining units, and from

other parts of the aquifer system, but not from the

river. The rate and magnitude of flow from the river

to the aquifer system are controlled by the relative

head difference across the aquifer-river interface

and by the riverbed and aquifer-system hydraulic

conductivities. Model simulations showed that the

lower aquifer in New Jersey across the Delaware

River from the former PNSY and the areas to the

east and west of the former PNSY receive little

recharge from the river (fig. 5).
9

Figure 5. Simulated (A) flow between the Delaware River and the lower aquifer of the Potomac-Raritan-Magothy

aquifer system and (B) simulated river-influenced zones, 1983-88 (from Navoy and Carleton, 1995, p. 79 and 81).

PNSY

PNSY

PNSY Former Philadelphia Naval Ship Yard

PNSY Former Philadelphia Naval Ship Yard

A. SIMULATED FLOW BETWEEN THE DELAWARE RIVER AND THE LOWER AQUIFER OF THE

 POTOMAC-RARITAN-MAGOTHY AQUIFER SYSTEM

B. SIMULATED RIVER-INFLUENCED ZONES

39°45′

39°45′

75°15′

75°

40°

40°

75°

75°15′

75

40

°

°

75°15′

39°45′

75°15′

39°45′

75°

40°
10

Pre-Development Flow System

Before development of the Coastal Plain aquifers for water supply, water flowed in response to

natural hydraulic gradients. Barksdale and others

(1958, p. 108-111) theorized that before groundwater withdrawals began, regional ground-water

flow in New Jersey was from topographically high

outcrop areas east of Trenton, N.J., towards the

Delaware River, the regional point of discharge.

Ground-water flow in Pennsylvania was to the Delaware River. Most water that entered the aquifer

discharged to local streams, but some water percolated downward through confining beds and moved

to more distant points of discharge. Vertical

hydraulic gradients were upward in the discharge

area.

Development of Ground-Water Supplies

Development of the Coastal Plain aquifers as

a source of water supply began before 1900.

Bascom (1904) lists many wells tapping the unconsolidated deposits in Pennsylvania and New Jersey. A number of industrial wells are listed for

Philadelphia. Schreffler (2001, p. 15) estimated

and compiled pumpage from the PRM for 1904-95

for his modeled area in Philadelphia and adjacent

parts of New Jersey (fig. 6). In Pennsylvania,

ground-water withdrawals rose steadily from about

1900 until the peak of 7.4 Bgal/yr in 1949. By 1982,

pumping from the PRM in Pennsylvania was negligible.

Prior to 1941, the former PNSY obtained its

entire water supply from the city of Philadelphia.

After the start of World War II, the demand of the

PNSY exceeded the capabilities of the city pumping and distribution system. To meet increased

demands, the PNSY drilled wells and began using

ground water. Ground-water withdrawals from the

PRM in Philadelphia, mainly from industrial wells,

was 3.9 Bgal/yr in 1940. In 1943, the year of peak

pumping at the PNSY, ground-water withdrawals

rose to 6.6 Bgal/yr (fig. 6).

Figure 6. Estimated water withdrawal from the lower sand unit and lower aquifer of the Potomac-Raritan-Magothy

aquifer system in Philadelphia and adjacent parts of New Jersey, 1904-95 (from Schreffler, 2001, p. 15).

1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995

0

18

2

4

6

8

10

12

14

16

WITHDRAWALS, IN BILLION GALLONS PER YEAR

ANNUAL WITHDRAWALS FROM WELLS IN PENNSYLVANIA

ANNUAL WITHDRAWALS FROM WELLS IN NEW JERSEY
11

Post-Development Flow System

By the 1920s, pumping in Philadelphia had

changed the natural ground-water-flow patterns in

the PRM aquifer system. The principal change in

the direction of ground-water flow from pre-development to the 1920s was in the area near the Walt

Whitman Bridge where the greatest withdrawals

from the lower sand unit were made (Paulachok,

1991, p. 40). Withdrawals created cones of depression in this area, and ground water flowed toward

the pumping centers. By 1940, continued and

increased pumping from the lower sand unit near

the Walt Whitman Bridge caused greater waterlevel declines in the lower sand unit with an even

steeper hydraulic gradient towards the pumping

centers (fig. 7). Lower heads in the lower sand unit

relative to the heads in the alluvial and upper and

middle sand units developed, which created a

downward vertical ground-water-flow component.

Recharge areas changed from the topographically

high areas east of Trenton, N.J., to the outcrop

area. The Delaware River was no longer a point of

ground-water discharge. Because of increasing

withdrawals from the unconfined alluvium and the

confined PRM units, hydraulic heads were lowered

below the levels of the Delaware and Schuylkill

Rivers. Barksdale and others (1958) and Greenman and others (1961) documented induced

recharge from these rivers.

Ground-water development for supply at the

former PNSY started in 1940, and large withdrawals at the facility continued until the mid-1960s.

Pumping at the PNSY created a large cone of

depression in the lower sand unit that was documented by Greenman and others (1961). Potentiometric-surface maps presented by Greenman and

others (1961), however, do not appear to have

taken water levels in New Jersey into account. By

1954, the cone of depression at the PNSY

exceeded 50 ft below NGVD 29 (fig. 8). Between

1943 and 1960, vertical leakage was the most

important source of recharge to the lower sand unit

in the vicinity of the PNSY (Paulachok, 1991).

Because of poor water quality, mainly highly

elevated concentrations of iron (as high as

166 mg/L) and manganese (as high as 3.2 mg/L)

(Paulachok and others, 1984), ground-water withdrawals at the PNSY were discontinued in the mid1960s. The decrease in pumping allowed water

levels to recover in Pennsylvania. This facilitated

the flow of ground water from Philadelphia to New

Jersey under the Delaware River, making Philadelphia a recharge area for the PRM aquifer system in

parts of Camden and Gloucester Counties where

the lower aquifer is not in direct hydraulic connection with the Delaware River.

Ground-water withdrawals from the PRM on

the New Jersey side of the Delaware River began

to increase sharply beginning about 1951.

Although pumping stopped at the PNSY and water

levels in the lower sand unit recovered, the

increased pumping in New Jersey maintained

downward vertical gradients. Total annual pumpage from the PRM in New Jersey in 1956 was

120 Mgal/d and increased to 195 Mgal/d by 1966

(Vowinkel, 1984). A generalized regional potentiometric-surface map for the PRM aquifer system for

1968 was presented by Gill and Farlekas (1976).

The map shows six cones of depression in the

PRM in New Jersey with water levels as deep as

70 ft below NGVD 29. The direction of groundwater flow was from Philadelphia to New Jersey.

Regional potentiometric-surface maps for the

lower and upper aquifers of the PRM for 1978 were

presented by Walker (1983). The map for the lower

aquifer shows a large cone of depression with

water levels as deep as 80 ft below NGVD 29 and

a smaller cone of depression with water levels as

deep as 60 ft below NGVD 29 (fig. 9). The map for

the upper aquifer shows one large cone of depression with water levels as deep as 80 ft below

NGVD 29 containing smaller cones of depression

with water levels as deep as 70 ft below NGVD 29.
12

39 52 39 55 '30" ‘

75 15 ‘75 07 '30"

Figure 7. Potentiometric surface of the lower sand unit of the Potomac-Raritan-Magothy aquifer system in south

Philadelphia, 1940 (modified from Greenman and others, 1961, figure 15).

LIMIT OF LOWER SAND UNIT (from

Greenman and others, 1961)

FALL LINE

POTENTIOMETRIC CONTOUR - Shows altitude of

EXPLANATION

0 0.5 1

0 0.5 1

MILE

KILOMETER potentiometric surface. Contour interval 10 feet.

Datum is sea level.

-10

10

0

0

0

0

0

-10

-10

-10

-10

-20

-20

-30

-30

-40

-50

-50

-60

-40

PHILADELPHIA

CAMDEN COUNTY

GLOUCESTER COUNTY

DELAWARE RIVER

PHILADELPHIA

NAVAL SHIP YARD

WALT WHITMAN

BRIDGE

SCHUYLKILL RIVER

PENNSYLVANIA

NEW JERSEY

39°52′30′′

39°55′

75°15′ 75°07′30′′
13

Figure 8. Potentiometric surface of the lower sand unit of the Potomac-Raritan-Magothy aquifer system in south

Philadelphia, March 24, 1954 (modified from Greenman and others, 1961, figure 17 by Schreffler, 2001, p. 20).

LIMIT OF LOWER SAND UNIT (from

Greenman and others, 1961).

FALL LINE

POTENTIOMETRIC CONTOUR - Shows altitude of

EXPLANATION

-30 0 0.5 1

0 0.5 1

MILE

KILOMETER

39°52′30′′

39°55′

75°12′30′′ 75°40′ 75°07′30′′ 0

-10

-40

-40

-40

-50

-70

-60

-30

-10

-20

-30

-40

-50

-20

-10

potentiometric surface. Contour interval 10 feet.

Datum is sea level.

PHILADELPHIA

DELAWARE RIVER

PHILADELPHIA

NAVAL SHIP YARD

SCHUYLKILL RIVER

WALT WHITMAN

BRIDGE
14

Figure 9. Regional potentiometric surface of the lower aquifer of the Potomac-Raritan-Magothy aquifer

system, 1978 (from Walker, 1983, pl. 1).

39°45′

75°10′ 75°00′

OUTCROP AREA OF THE LOWER AQUIFER

POTENTIOMETRIC CONTOUR - Shows altitude of the potentiometric

EXPLANATION

surface. Contour interval is 10 feet. Datum is NGVD 29.

-70

0

0 1 2 3 KILOMETERS

1 2 3 MILES

39°55′

75°50′

7-315

WATER-LEVEL MEASUREMENT SITE AND IDENTIFICATION NUMBER

PHILADELPHIA

CAMDEN

COUNTY

GLOUCESTER

 COUNTY

BURLINGTON

COUNTY
15

Ground-water pumpage data for 1978-97 presented by Lacombe and Rosman (2001) for southern New Jersey counties indicate that withdrawals

peaked and then began to decline in 1981 in the

middle aquifer, in 1983 in the lower aquifer, and in

1989 in the upper aquifer (fig. 10). Regional potentiometric-surface maps for the PRM aquifer system

for 1988 were presented by Rosman and others

(1995). The map for the lower aquifer (Rosman and

others, 1995, pl. 8) shows that water levels were as

deep as 103 ft below NAVD 88 in New Jersey and

8 ft below NAVD 88 in Philadelphia (fig. 11). The

map for the middle and undifferentiated aquifer

shows a large cone of depression with water levels

as deep as 107 ft below NAVD 88 in New Jersey

and 6 ft below NAVD 88 in Philadelphia (Rosman

and others, 1995, pl. 7). The map for the upper

aquifer shows a large cone of depression with

water levels as deep as 88 ft below NAVD 88 in

New Jersey and 7 ft below NAVD 88 in Philadelphia (Rosman and others, 1995, pl. 6).

In 1994, the New Jersey Department of Environmental Protection designated Water Supply

Critical Area Number 2, which identified the PRM

aquifer system in parts of Camden and Gloucester

Counties as depleted and reduced water-supply

allocations by an average of 22 percent in that area

(New Jersey Department of Environmental Protection, 2002). In response, surface-water supplies

are being developed and brought into the area.

More detailed potentiometric-surface maps for

the PRM aquifer system for 1996 in the vicinity of

the PNSY were presented by Rosman (1997). The

map for the lower aquifer (Rosman, 1997, sheet 4)

shows water levels in Philadelphia as deep as 13 ft

below NAVD 88 and cones of depression directly

south of the PNSY in New Jersey with water levels

as deep as 57 ft below NAVD 88 (fig. 12).

Regional potentiometric-surface maps for the

PRM aquifer system for 1998 were presented by

Lacombe and Rosman (2001). The map for the

lower aquifer (Lacombe and Rosman, 2001, sheet

10) shows a large cone of depression with water

levels recovering to 62 ft below NAVD 88 in New

Jersey but declining to 16 ft below NAVD 88 in Philadelphia (fig. 13). This reflects a rise in water level

of 41 ft at the center of the cone of depression in

New Jersey. The map for the middle and undifferentiated aquifer (Lacombe and Rosman, 2001,

sheet 9) shows a large cone of depression with

water levels recovering to 66 ft below NAVD 88 and

a smaller cone of depression with water levels

recovering to 61 ft below NAVD 88; water levels in

Philadelphia are as deep as 4 ft below NAVD 88.

The map for the upper aquifer (Lacombe and Rosman, 2001, sheet 8) shows a large cone of depression containing two smaller cones of depression

with water levels as deep as 102 ft below NAVD 88

in New Jersey and 6 ft below NAVD 88 in Philadelphia.

Figure 10. Estimated water withdrawals from the Potomac-Raritan-Magothy aquifer system, southern

New Jersey counties, 1978-97 (modified from Lacombe and Rosman, 2001).

UPPER AQUIFER

LOWER AQUIFER

MIDDLE AQUIFER
16

Figure 11. Regional potentiometric surface of the lower aquifer of the Potomac-Raritan-Magothy aquifer system,

1988 (from Rosman and others, 1995, pl. 8).

39°45′

75°07′30′′ 75°00′

0

0 2 4

2 4 6 MILES

40°00′

74°52′30′′

39°52′30′′

75°15′

OUTCROP AREA OF THE LOWER AQUIFER

POTENTIOMETRIC CONTOUR - Shows altitude of the potentiometric

EXPLANATION

surface. Contour interval is 20 feet. Datum is NGVD 29

-80

7-315

WATER-LEVEL MEASUREMENT SITE (PRODUCTION WELL) - Upper -77

number is site identification number. Lower number is water-level altitude

APPROXIMATE NORTHERN LIMIT OF THE UPPER AQUIFER

7-185 WATER-LEVEL MEASUREMENT SITE (OBSERVATION WELL) - Upper

-86 number is site identification number. Lower number is water-level

in feet above NGVD 29

altitude in feet above NGVD 29

6 KILOMETERS

PHILADELPHIA

CAMDEN

COUNTY

GLOUCESTER

COUNTY

BURLINGTON

COUNTY
17

CAMDENCOUNTY

GLOUCESTER

COUNTY

0

0 0.5

0.5 1 MILE

1 KILOMETE

Figure 12. Regional potentiometric surface of the lower aquifer of the Potomac-Raritan-Magothy aquifer system, 1996 (moRosman, 1997, sheet 4).

39°50′

75°15′ 75°07′30′′

39°55′

PNSY

PNSY FORMER

 PHILADELPHIA

, in feet above NAVD 88

above NAVD 88

above NAVD 88

NAVAL SHIPYARD
18

Figure 13. Regional potentiometric surface of the lower aquifer of the Potomac-Raritan-Magothy aquifer

system, 1998 (modified from Rosman, 1997, sheet 10).
19

IRON, MANGANESE, AND SULFATE

CONCENTRATIONS

The outcrop area of the PRM aquifer system

is densely populated and intensely developed.

Thus, the area is highly susceptible to contamination from human point and nonpoint sources. The

spread of contamination in the subsurface has

been exacerbated by changes in the ground-waterflow system as a result of the withdrawal of large

quantities of ground water.

Barksdale and others (1958, p. 121) noted in

the late 1950s that “the heaviest pumping and lowest water levels or artesian pressures are on the

Pennsylvania side of the river, and water of good

quality is being drawn across the river from the

New Jersey side, beneath the aquiclude. Thus, in

effect, the heavy pumping at the Naval Base has

shielded the wells on the New Jersey side of the

river from the mineralized water. If the pumping at

the Naval Base should be greatly curtailed, the

highly mineralized waters would tend to move past

the wells there and beneath the river to the wells in

New Jersey, creating a situation similar to that now

existing in southern Camden.”

Barksdale and others (1958, p. 118) also

noted that “The mineral content of the water from

some wells in southern Camden is now also higher

than that of the river waters or of any surrounding

ground water except that in southern Philadelphia.

These data seem to indicate that the highly mineralized water originating in southeastern Philadelphia may have spread to the area of heavy

pumping in southern Camden. They are, however,

inadequate for a positive conclusion, and the question should receive further study. They do serve to

emphasize the fact that it is possible to draw water

under the river from one side to the other, depending upon the gradients created by the pumping.”

Elevated iron concentrations are responsible

for the most persistent water-quality problems

associated with ground water from the PRM aquifer

system (Ervin and others, 1994, p. 59). Iron concentrations in ground water can be increased

directly by contamination or indirectly by processes

that cause dissolution of iron minerals. Microbial

decomposition of organic wastes from sources

such as leaky sewers, septic systems, landfills, and

municipal and industrial wastewater disposal consumes oxygen and leads to reducing conditions in

ground water; under these conditions, dissolved

iron concentrations can be as high as 1,000 mg/L

(Langmuir, 1969, p. 21). The decomposition process also can release protons (H+) into the groundwater system, lowering the pH and thereby promoting leaching of iron from iron-bearing minerals in

the aquifer matrix.

The subsurface environment in the vicinity of

large water-supply wells can vary from aerobic

(oxidizing) to anaerobic (reducing) with resultant

variations in mineral stability and dissolved constituent concentrations (fig. 14). Aerobic conditions

may be facilitated by pumping or other stresses

that remove water from the aquifer or draw shallow

oxygenated water to deeper zones. Reducing or

anaerobic conditions can develop because of sustained organic loading associated with municipal

waste, leaking sewer pipes, and industrial or chemical discharges that deplete oxygen.

Elevated concentrations of sulfate generally

are a consequence of oxidation processes,

whereas elevated concentrations of dissolved iron

and manganese can be a consequence of oxidation and (or) reduction processes. The oxidation

processes typically are acid-forming reactions that

can consume bicarbonate and cause pH to

decrease. For example, the introduction of oxygenated water or air into shallow zones (aerobic zone

in figure 14) can facilitate the oxidation of organic

compounds (eqn. 1) and inorganic compounds

such as pyrite (eqn. 2), producing sulfate (SO4

2-),

iron (Fe2+), protons (H+), and carbon dioxide

(CO2).

CH2O + O2 → CO2 + H2O (1)

FeS2 + 3.5 O2 + H2O → Fe2+ + 2 SO4

2- + 2 H+ (2)

Fe2+ + 0.25 O2 + 2.5 H2O → Fe(OH)3 (s) + 2 H+ (3)

In equation 1, “CH2O” is a simplified representation of organic compounds; the accumulation of

CO2 would tend to lower the pH of the system. In

equation 2, only pyritic sulfur is oxidized; dissolved

ferrous iron (Fe2+) is a product. At near-neutral pH,

the solubility of Fe2+ is many orders of magnitude

greater than that of oxidized, ferric iron (Fe3+). The

oxidation of Fe2+ to Fe3+ can be catalyzed by ironoxidizing bacteria that are native or introduced to

the subsurface environment (Ehrlich, 1990). In

equation 3, the Fe2+ ions oxidize and hydrolyze

forming solid Fe(III) oxyhydroxide. The Fe(III) compounds accumulate, forming encrustations on well

screens where O2 and Fe2+ are locally available.
20

Under anoxic conditions (anaerobic zone in

figure 14), facultative bacteria may use other terminal electron acceptors (ions or compounds containing oxygen molecules) such as NO3

-

, NO2

-

,

SO4

2-, Mn(IV), or Fe(III) oxides to oxidize organic

compounds. For example, the reduction of previously oxidized iron compounds such as ferrihydrite

(eqn. 4) or goethite (eqn. 5) can produce elevated

concentrations of dissolved iron.

4 Fe(OH)3 + CH2O + 7 H+ → 4 Fe2+ + HCO3

-

+ 10 H2O (4)

4 FeOOH + CH2O + 7 H+ → 4 Fe2+ + HCO3

-

+ 6 H2O (5)

The reductive dissolution of Fe(III) oxide, coupled

with the oxidation of organic matter, can increase

alkalinity and pH. Similar reactions can be written

for the reductive dissolution of Mn(III-IV)

oxyhydroxide compounds and the consequent

release of manganous ions (Mn2+).

The overall reactions given above will proceed

spontaneously, yielding energy for the organisms

involved. Generally, in addition to elevated concentrations of Fe2+ and Mn2+, environments favoring

reductive dissolution of Fe(III) and Mn(IV) compounds may have elevated concentrations of CO2

and other reduced species, such as ammonia

(NH4

+, NH3) and hydrogen sulfide (H2S, HS-

). Aeration of these solutions can promote the exsolution

of the dissolved gases and a consequent increase

in pH. For example, the exsolution of CO2 can

cause pH to increase in the vicinity of a pumped

well (eqn. 6).

HCO3

-

 → CO2 (g) + OH- (6)

Hence, aeration introduces O2 and can

increase pH, both of which favor the formation of

Fe(III) and Mn(IV) oxides. Sustained or pulsed

pumping can cause aeration in the vicinity of a well

and lead to localized well-screen encrustation

where Fe2+ and Mn2+ are abundant in the pumped

water and insoluble iron and manganese hydroxides are formed.

Figure 14. Conceptual section illustrating geochemical regimes in the aquifer affected by lowering and recovery of

water levels.

WASTE

PUMPED WELL

ZONE OF AEROBIC

OXIDATION PROCESSES

ZONE OF DISSOLUTION

ZONE OF ANAEROBIC

OXIDATION-REDUCTION PROCESSES

Reductive dissolution of previously

formed products and aquifer materials

PRE-1900 POTENTIOMETRIC SURFACE

1954 POTENTIOMETRIC SURFACE

2003 POTENTIOMETRIC SURFACE

OF OXIDATION PRODUCTS
21

Changes in Iron, Manganese, and Sulfate

Concentrations With Time

Historical ground-water-quality data for wells

screened in the lower aquifer of the PRM collected

by the USGS are available for south Philadelphia

beginning in 1943, for the adjacent part of Camden

County beginning in 1949, and for the adjacent

part of Gloucester County beginning in 1950

(fig. 15). Data presented in this section were

retrieved from the USGS National Water Information System (NWIS) database. However, the historical data are sparse and temporally and spatially

discontinuous and are not sufficient to permit a

complete picture of changes in iron, manganese,

and sulfate concentration.

Major ground-water withdrawals at the former

PNSY began in 1941. The USGS collected the first

samples for water-quality analysis in 1943, the

peak year for pumping. In 1943, dissolved iron concentrations ranged from 0.07 to 0.6 mg/L. By 1945,

dissolved iron concentrations exceeded 1 mg/L,

and by 1956, dissolved iron concentrations

exceeded 9 mg/L. In 1967, when the wells at the

PNSY were abandoned, dissolved iron concentrations had reached 46 mg/L (fig. 16).

Each of the wells at the PNSY (except for well

PH-5) produced water of acceptable quality for a

period of about 1 to 5 years. This time probably

represents the amount of time required by each

well to discharge the original water of good quality

in storage in the aquifer and to start yielding water

from surface recharge areas. Well PH-8, situated

the farthest downdip and partially shielded from the

surface recharge area by the other PNSY wells,

produced water of good quality from 1944 to 1950.

In July 1950, the mineral concentration in the water

from well PH-8 increased sharply. It is probable

that this rapid change was due in part to the shutdown of several wells to the north, thereby permitting more surface-recharge water with a higher

concentration of dissolved minerals to reach well

PH-8 by moving past the idle wells (Graham and

Kammerer, 1952, p. 69-70).

Data for dissolved iron concentrations for

water samples from industrial wells in Philadelphia

prior to 1946 are not available. Water samples collected by USGS in 1947 from two industrial wells

screened in the lower sand unit had a dissolved

iron concentration of 0.17 mg/L. By 1979, the dissolved iron concentration in water from well PH-83

was 19 mg/L (fig. 17).

Dissolved iron concentrations in water samples from wells screened in the lower aquifer in

New Jersey sampled by USGS in 1949-50 ranged

from 0.02 to 0.73 mg/L. Water samples collected

from four wells screened in the lower aquifer at the

Eagle Point Refinery, which is directly across the

Delaware River from the former PNSY, had dissolved iron concentrations ranging from 0.11 to

0.73 mg/L. Iron concentrations in water samples

from wells at the Eagle Point Refinery have

increased with time (fig. 18).

The concentration of dissolved iron in water

samples from other wells screened in the lower

aquifer in New Jersey also increased with time. By

1966-67, dissolved iron concentrations were as

high as 4.8 mg/L for Gloucester City wells (fig. 19),

and 1.4 mg/L for Eagle Point Refinery wells. By

1985, dissolved iron concentrations were as high

as 16 mg/L for Eagle Point Refinery wells. Current

(2002) iron concentrations reported by water purveyors in water from production wells in New Jersey commonly exceed 1 mg/L and are as high as

16 mg/L.

Ervin and others (1994, p. 74) presented a

map of dissolved iron concentrations in water from

the lower aquifer for 1980-86 (fig. 20). The map

shows dissolved iron concentrations greater than

25 mg/L in Philadelphia and greater than 10 mg/L

in New Jersey south of the former PNSY.
22

Figure 15. Location of wells screened in the lower aquifer of the Potomac-Raritan-Magothy aquifer system with

historical dissolved iron concentrations.

PH-8

PH-6

PH-5

PH-3

PH-83

PH-48

NP1

EP6

EP4

EP3

EP2

EP5

EP1

GC40

GC38

PHILADELPHIA

NATIONAL PARK

GLOUCESTER CITY

EAGLE POINT REFINERY

PHILADELPHIA

NAVAL SHIP YARD

EXPLANATION

LOCATION OF WELL - Number is well-identification number PH-5

GLOUCESTER CITY

39°57′30′′

39°55′

39°52′30′′

75°12′30′′ 75°10′ 75°07′30′′

Base from U.S. Geological Survey 1:24,000 Camden 1995, Philadelphia 1995,

Runnemede 1967, and Woodbury 1995

0 0.5 1

0 0.5 1

MILE

KILOMETER
23

Figure 16. Concentrations of dissolved iron in water from wells screened in the lower sand unit of the PotomacRaritan-Magothy aquifer system at the former Philadelphia Naval Ship Yard, 1943-85. Well locations are shown on

figure 15. (Data from U.S. Geological Survey National Water Information System.)

1940 1950 1960 1970 1980 1990

DISSOLVED IRON CONCENTRATION, IN MILLIGRAMS PER LITER

0

50

5

10

15

20

25

30

35

40

45

WELL PH-3

WELL PH-5

WELL PH-6

WELL PH-8
24

Figure 17. Concentrations of dissolved iron in water from industrial supply wells screened in the lower sand

unit of the Potomac-Raritan-Magothy aquifer system in Philadelphia, 1947-79. Well locations are shown on

figure 15. (Data from U.S. Geological Survey National Water Information System.)

1940 1950 1960 1970 1980

DISSOLVED IRON CONCENTRATION, IN MILLIGRAMS PER LITER

0

20

2

4

6

8

10

12

14

16

18

WELL PH-83

WELL PH-48
25

Figure 18. Concentrations of dissolved iron in water from wells screened in the lower aquifer of the Potomac-RaritanMagothy aquifer system at the Eagle Point Refinery, Gloucester County, N.J., 1950-85. Well locations are shown on

figure 15. (Data from U.S. Geological Survey National Water Information System.)

1940 1950 1960 1970 1980 1990

0

18

2

4

6

8

10

12

14

16

EAGLE POINT WELL EP1

EAGLE POINT WELL EP3

EAGLE POINT WELL EP4

EAGLE POINT WELL EP5

EAGLE POINT WELL EP6

DISSOLVED IRON CONCENTRATION, IN MILLIGRAMS PER LITER
26

Figure 19. Concentrations of dissolved iron in water from wells screened in the lower aquifer of the PotomacRaritan-Magothy aquifer system in Gloucester County, N.J., 1951-66. Well locations are shown on figure 15.

(Data from U.S. Geological Survey National Water Information System.)

1950 1955 1960 1965 1970

0

5.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

GLOUCESTER WATER DEPARTMENT WELL GC38

GLOUCESTER WATER DEPARTMENT WELL GC40

NATIONAL PARK WATER DEPARTMENT WELL NP1

DISSOLVED IRON CONCENTRATION, IN MILLIGRAMS PER LITER
27

Figure 20. Concentrations of dissolved iron in water from the lower aquifer of the Potomac-Raritan-Magothy aquifer

system, Philadelphia, Pa., and Camden and Gloucester Counties, N.J., 1980-86 (from Ervin and others, 1994,

p. 74).

39°50′

75°10′ 75°05′

39°55′

75°15′

PHILADELPHIA

DELAWARE

CAMDEN

COUNTY

GLOUCESTER

COUNTY

 COUNTY
28

In addition to the increase in iron concentration with time, concentrations of manganese and

sulfate in ground water in the PRM aquifer system

also are increasing with time. Unfortunately, few

data are available for manganese and sulfate concentrations. Paulachok (1991, p. 59 and 62) presented graphs of manganese and sulfate

concentrations in water from wells screened in the

lower sand unit at the PNSY collected between

1945 and 1982 that showed concentrations

increasing with time (figs. 21 and 22). Ervin and

others (1994, p. 75) presented a map of dissolved

manganese concentrations in water from the lower

aquifer for 1980-86 (fig. 23). The map shows dissolved manganese concentrations greater than

5 mg/L in Philadelphia and greater than 0.25 mg/L

in New Jersey southeast of the former PNSY. Ervin

and others (1994, p. 77) also presented a map of

dissolved sulfate concentrations in water from the

lower aquifer for 1980-86 (fig. 24). The map shows

dissolved sulfate concentrations greater than

100 mg/L in Philadelphia and greater than 50 mg/L

in New Jersey south of the former PNSY.

Role of Bacteria

Iron-related well-screen incrustation, aquifer

biofouling, and subsequent loss in well yield are

costly problems that are a concern locally and

nationally. Iron-related yield declines are common

in wells screened in unconsolidated sediments,

such as those underlying the Pennsylvania-New

Jersey Coastal Plain. Iron-related well-screen

incrustation is an oxidation-reduction process that

involves the oxidation of ferrous iron to ferric iron

and its rapid precipitation as insoluble iron hydroxide. The rate of oxidation of ferrous iron in ground

water is strongly dependent on pH and dissolved

oxygen concentration. Iron-oxidizing bacteria can

catalyze the oxidation of ferrous iron, and biological

oxidation of ferrous iron can be substantial in lowpH waters. Well-screen incrustation and aquifer

Figure 21. Concentrations of dissolved manganese in water from wells screened in the lower sand unit of the

Potomac-Raritan-Magothy aquifer system at the former Philadelphia Naval Ship Yard, 1945-82 (from Paulachok,

1991, p. 59).1945

5,000

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

DISSOLVED MANGANESE CONCENTRATION,

1952

1953

1956

1957

1967

1971

1973

1979

1980

1982

IN MICROGRAMS PER LITER

0
29

Figure 22. Concentrations of dissolved sulfate in water from wells screened in the lower sand unit of the PotomacRaritan-Magothy aquifer system at the former Philadelphia Naval Ship Yard, 1942-82 (from Paulachok, 1991,

p. 62).

1945

DISSOLVED SULFATE CONCENTRATION,

1942

1952

1953

1956

1957

1967

1971

1973

1979

1980

1982

0

200

20

40

60

80

100

120

140

160

180

1943

1944

1946

1947

1948

1949

1950

1951

1954

IN MICROGRAMS PER LITER
30

Figure 23. Concentrations of dissolved manganese in water from the lower aquifer of the Potomac-RaritanMagothy aquifer system, Philadelphia, Pa., and Camden and Gloucester Counties, N.J., 1980-86 (from Ervin and

others, 1994, p. 75).

39°50′

75°10′ 75°05′

39°55′

75°15′

PHILADELPHIA

DELAWARE

GLOUCESTER

COUNTY

 COUNTY

CAMDEN

COUNTY
31

Figure 24. Concentrations of dissolved sulfate in water from the lower aquifer of the Potomac-Raritan-Magothy

aquifer system, Philadelphia, Pa., and Camden and Gloucester Counties, N.J., 1980-86 (from Ervin and others,

1994, p. 77).

39°50′

75°10′ 75°05′

39°55′

75°15′

PHILADELPHIA

DELAWARE

GLOUCESTER

COUNTY

 COUNTY

CAMDEN

COUNTY
32

biofouling occur when filamentous iron bacteria

produce large extracellular filaments that become

coated with iron oxyhydroxides. This combination

of ferric oxyhydroxides and extracellular material

can clog not only well screens but pore spaces in

the surrounding aquifer (Ghiorse, 1986). The

growth of iron-oxidizing bacteria on well screens

and in the surrounding aquifer begins when

nonfilamentous iron-related bacteria colonize the

surfaces of well screens and sediment grains. This

organic substrate allows filamentous iron bacteria

to form extensive biofilms. A typical biofilm consists

of a consortium of organisms that represent

several species of iron bacteria. Iron bacteria also

can catalyze the oxidation of manganese.

Manganese-related biofouling can occur in

environments with high pH and high manganese

concentrations.

The role of iron bacteria in well-screen incrustation, aquifer biofouling, and increasing iron concentration has not been investigated in the

Pennsylvania-New Jersey Coastal Plain. A study

by Walter (1997) in the Coastal Plain sediments of

the Magothy Formation on Long Island, N.Y., indicated that iron bacteria play an important role in

the incrustation and biofouling process and that

iron bacteria biofilms can alter ground-water chemistry by removing iron, manganese, and sulfate

from solution and increasing pH. Walter (1997)

found that the most common species of iron bacteria was Gallionella ferruginea, an effective biofouling agent that prefers water with low, but

detectable, dissolved oxygen concentrations and

high dissolved iron concentrations.

Walter (1997) found that lignite in aquifer

materials could act as a carbon source for heterotrophic iron bacteria, which could accelerate the

formation of iron-bacteria biofilms in wells

screened in some parts of the Magothy Formation.

The PRM aquifer system contains lignite (Bascom

and others, 1909, p. 9; Barksdale and others,

1958, p. 93). Lignin forms the base of microbial

food chains in ground-water systems. Walter

(1997) found that the presence of lignite near a well

screen can accelerate the formation of iron-bacteria biofilms. The growth of heterotrophic iron bacteria such as Pseudomonas forms the organic

substrate necessary for the growth of filamentous

bacteria such as Gallionella and allows the bacteria to colonize the surface of the well screen.

Sulfate-reducing bacteria and iron-sulfide mineral phases were observed by Walter (1997) in

some samples of incrusting material, indicating

that these bacteria could contribute to well-screen

incrustation in some geochemical environments.

Bacterially mediated reduction of sulfate to sulfide

and the precipitation of iron sulfide on well screens

could contribute to the incrustation process. Pyrite

in the PRM aquifer system (Barksdale and others,

1958, p. 93) may have formed where conditions

were sufficiently reducing.

SUGGESTIONS FOR FURTHER STUDY

Further study of the controls on ground-water

movement and aquifer geochemistry would help to

provide a better understanding of the potential

sources, extent, and spread of contaminated

ground water in the PRM aquifer system. The current knowledge of the geologic framework includes

the relation among the hydrogeologic units of the

Coastal Plain on a regional scale but lacks necessary local detail. More detailed knowledge of the

framework is needed in the area beneath and near

the Delaware River where the hydrogeologic units

may not fit the regional model of the Coastal Plain.

A more detailed geologic framework model could

be developed from available drilling, boring, and

geophysical logs and possibly additional drilling.

This would help to identify areas where the confining bed above the lower aquifer is present and

ground-water flow is occurring beneath the Delaware River. It also may identify areas where the

confining bed above the lower aquifer is missing

and ground-water flow beneath the Delaware River

is unlikely. It may help to identify areas in New Jersey where confining units are thin or absent and

where vertical pathways exist for water and contaminant movement.

A ground-water-flow model could be used with

forward and backward particle-tracking techniques

to determine the contributing area for supply wells

and time-of-travel of water and conservative solutes from source areas to wells. Particle tracking is

a process where hypothetical particles are simulated as if they are carried along with ground-water

flow. Particles are tracked through a flow field

explicitly by computing the directional components

of velocity at a particle’s current position and moving the particle to a new location that is determined

by multiplying those velocity components by a finite

time step to obtain the incremental changes in the

particle’s coordinates over that interval of time. As

this process is repeated, a series of coordinates
33

are produced that trace the path of a particle

through the flow field as a function of time (Pollock,

1988). Backward particle tracking introduces particles at a supply well and tracks them backward to

determine the source areas contributing water to

the well. Forward particle tracking introduces particles at the recharge area and tracks them along

ground-water-flow paths. Affected areas could be

identified, and travel-time contours could be generated.

Age dating of ground-water samples using tritium (3H) and tritium/helium-3 (3H/3He) methods

could be used to calibrate and (or) confirm simulated ground-water-flow model flow rates. 3H is the

radioactive isotope of hydrogen with a half-life of

12.43 years and is an excellent indicator of ground

water recharged since 1952. Production of 3H in

the atmosphere naturally occurs by cosmic-ray

spallation, but the principal source was the atmospheric testing of thermonuclear weapons that

began in 1953. The explosions of nuclear devices

produced peak 3H concentrations in precipitation

during 1963-64 and resulted in a large input of 3H

to the ground-water system. Atmospheric concentrations have declined gradually since 1964. Pumping at the former PNSY stopped in the mid-1960s,

and around that time the reversal of hydraulic gradients caused water to start moving from Philadelphia toward New Jersey. Because the reversal of

hydraulic gradients occurred around the mid1960s, the 3H/3He method is an excellent tool to

trace the movement of contaminated ground water

in the PRM aquifer system that originated as

recharge. 3H and 3He are virtually inert in ground

water, unaffected by other substances in water,

and unaffected by contamination from most anthropogenic sources. Apparent age estimates from the

3H/3He method can be extremely accurate (within

months) for confined ground water containing high

3H concentrations (waters recharged since 1963

that have not mixed with older water). Unlike other

dating methods, such as using chlorofluorocarbons, 3H/3He is a valid technique for areas contaminated with organic compounds.

Wells in Philadelphia were last sampled in

1985, and no water-quality data have been collected since then. A resampling of available wells in

Philadelphia could allow assessment of current

conditions in the PRM aquifer system, show how

the concentration of chemical constituents has

changed since the last sampling took place, and

help to estimate the mass of contaminants. Sampling recently drilled monitor wells in Philadelphia

could provide additional data points to supplement

historical data. In addition, active and unused supply wells and monitor wells in New Jersey in the

area south and southeast of the former PNSY

could be sampled to supplement data collected for

Philadelphia. Chemical constituents analyzed

could include 3H/3He for age determination; inorganic constituents including carbon, nitrogen, and

sulfur species; major cations; trace metals; organic

compounds, especially volatile organic compounds

(VOCs) and their degradation products; and radionuclides.

Geochemical-reaction modeling may help to

develop an understanding of the geochemical controls on the movement and precipitation of iron,

manganese, and sulfate in the PRM aquifer system. A reactive-transport model capable of simulating chemical reactions of contaminants in ground

water could be used to simulate aerobic and anaerobic degradation of organic chemicals and degradation pathways including reduction of Mn+4, Fe+3,

and SO4. Chemical-equilibria modeling may show

which mineral phases in ground water would be

thermodynamically favored to precipitate or dissolve.

To determine the types and sources of iron

and sulfur bacteria associated with aquifer biofouling and well-screen incrustation, core samples

from several locations within the PRM aquifer system could be tested. Analysis of cored aquifer sediments collected in the vicinity of public-supply

wells could provide data on types of bacteria, biofilms, and changes to aquifer mineralogy. Evaluation of Fe(III)-reducing and SO4-reducing activity of

sediment slurries may indicate the zones of greatest potential for such reactions. The analyses could

help define geochemical processes occurring in

the aquifer and in screen incrustations.
34

SUMMARY

This study, which was prepared in cooperation

with the U.S. Environmental Protection Agency,

documents ground-water-flow patterns and waterquality trends in the lower aquifer of the PotomacRaritan-Magothy (PRM) aquifer system. The solesource PRM aquifer system is the largest and most

productive of the Coastal Plain aquifers and is an

important water-supply source in New Jersey. Most

of the withdrawals from the lower aquifer of the

PRM are in Camden and Gloucester Counties, and

these supplies commonly contain elevated iron

concentrations. Elevated iron concentrations are

responsible for the most persistent and emerging

water-quality problems associated with the use of

ground water from the PRM aquifer system. Ironrelated well-screen incrustation, aquifer biofouling,

and well-yield loss are costly problems that are a

concern to public water suppliers and industrial

users. Much of the outcrop area of the PRM aquifer

system is densely populated and intensely developed and is highly susceptible to contamination

from point and nonpoint sources. The spread of

contamination in the subsurface has been exacerbated by changes in the ground-water-flow system

as a result of the withdrawal of large quantities of

ground water.

The PRM no longer is usable as a source of

water supply in Philadelphia because of highly elevated concentrations of iron, manganese, and sulfate. A strong reducing environment in the PRM in

south Philadelphia causes these constituents to be

remobilized by reductive dissolution of the aquifer

matrix. Elevated concentrations of sulfate generally

are a consequence of oxidation processes,

whereas elevated concentrations of dissolved iron

and manganese can be a consequence of oxidation and (or) reduction processes. The oxidation

processes typically are acid-forming reactions that

can consume bicarbonate and cause pH to

decrease. The oxidation of Fe2+ to Fe3+ can be catalyzed by iron-oxidizing bacteria that are native or

introduced to the subsurface environment. Fe2+

ions oxidize and hydrolyze forming solid Fe(III) oxyhydroxide. The Fe(III) compounds accumulate

forming encrustations on well screens where O2

and Fe2+ are locally available. Many wells in Philadelphia, including those at the former Philadelphia

Naval Ship Yard (PNSY), were abandoned primarily because of problems associated with the precipitation of Fe(III) oxyhydroxides.

Development of the Coastal Plain aquifers as

a source of water supply began before 1900. Prior

to development for water supply, the Delaware

River was the point of regional ground-water discharge from the PRM in Philadelphia and New Jersey. By the 1920s, pumping in Philadelphia

changed the natural ground-water-flow patterns.

Withdrawals in the area near the Walt Whitman

Bridge created cones of depression, and ground

water flowed toward these pumping centers.

By 1940, continued and increasing pumping from

the lower sand unit near the Walt Whitman Bridge

caused greater water-level declines in the lower

sand unit with an even steeper hydraulic gradient

towards the pumping centers. Lower heads in the

lower sand unit relative to the heads in the alluvial

and upper and middle sand units developed, which

created a downward ground-water-flow component. Recharge areas changed from the topographically high areas east of Trenton to the

outcrop area. The Delaware River was no longer

a point of ground-water discharge.

Ground-water development for supply at the

former PNSY started in 1940, and large withdrawals at the facility continued until the mid-1960s.

Pumping at the PNSY created a large cone of

depression in the lower sand unit. By 1954, the

cone of depression exceeded 50 ft below

NGVD 29. Between 1943 and 1960, vertical leakage was the most important source of recharge to

the lower sand unit in the vicinity of the PNSY. In

1943, dissolved iron concentrations in water samples from wells at the PNSY ranged from 0.07 to

0.6 mg/L. By 1945, dissolved iron concentrations

exceeded 1 mg/L, and by 1956, dissolved iron concentrations exceeded 9 mg/L. In 1967, when the

wells at the PNSY were abandoned, dissolved iron

concentrations had reached 46 mg/L. Other wells

in Philadelphia exhibited a similar pattern.

Ground-water withdrawals from the PRM in

New Jersey began to increase sharply beginning

about 1951, which caused the lateral head gradient

to reverse and facilitated the flow of ground water

from Philadelphia to New Jersey under the Delaware River. Although pumping stopped at the

PNSY and water levels in the lower sand unit in

Pennsylvania recovered, the increased pumping in

New Jersey maintained downward vertical gradients in Philadelphia and made the outcrop area of

the PRM in Philadelphia a recharge area for the

PRM aquifer system in parts of Camden and

Gloucester Counties. Where a confining unit is

present above the lower aquifer, ground water
35

flows from Philadelphia beneath the Delaware

River to New Jersey; this is the case in the area

around the former PNSY. However, in areas northeast of the former PNSY along the Delaware River,

the confining unit may be thin or absent, and the

Delaware River may be in direct hydraulic contact

with the lower aquifer. In these areas, little or no

ground water may flow from Pennsylvania to New

Jersey. Model simulations showed that the lower

aquifer in New Jersey across the Delaware River

from the former PNSY and the areas to the east

and west of the former PNSY received little

recharge from the river.

By 1968, cones of depression developed in

the PRM in New Jersey with water levels as deep

as 70 ft below NGVD 29. The direction of groundwater flow was from Philadelphia to New Jersey. By

1988, water levels in the lower aquifer were as

deep as 103 ft below NAVD 88 in New Jersey and

8 ft below NAVD 88 in Philadelphia. In 1994, the

New Jersey Department of Environmental Protection designated Water Supply Critical Area

Number 2, which identified the PRM aquifer system in parts of Camden and Gloucester Counties

as depleted and reduced water-supply allocations

by an average of 22 percent in that area. In

response to decreased pumping, water levels in

1998 in the lower aquifer recovered to 62 ft below

NAVD 88 in New Jersey but declined to 16 ft below

NAVD 88 in Philadelphia, reflecting a rise in water

level of 41 ft at the center of the cone of depression

in New Jersey.

Water samples collected in 1949-50 from

wells screened in the lower aquifer at the Eagle

Point Refinery, which is directly across the Delaware River from the former PNSY, had dissolved

iron concentrations ranging from 0.11 to 0.73 mg/L.

Iron concentrations in water samples from wells at

the Eagle Point Refinery have increased with time.

The concentration of dissolved iron in water samples from other wells screened in the lower aquifer

in New Jersey also increased with time. By 1966-

67, dissolved iron concentrations were as high as

4.8 mg/L for Gloucester City wells, and 1.4 mg/L

for Eagle Point Refinery wells. By 1985, dissolved

iron concentrations were as high as 16 mg/L for

Eagle Point Refinery wells. Current (2002) iron

concentrations reported by water purveyors in

water from production wells in New Jersey commonly exceeded 1 mg/L and were as high as

16 mg/L. In addition to the increase in iron concentration with time, concentrations of manganese and

sulfate in ground water in the PRM aquifer system

also are increasing with time.

Although ground-water withdrawals in New

Jersey have declined since the 1980s, water of

poor quality still may be moving under the Delaware River from Pennsylvania toward wells in New

Jersey in certain areas in response to pumping. In

addition, sources of contamination in New Jersey

also may be contributing to the elevated iron problem by vertical migration. Ground-water flow from

areas of contamination in south Philadelphia to

adjacent downgradient areas of New Jersey has

the potential to affect supply wells drawing water

from the lower aquifer of the PRM. Under present

pumping conditions, the quality of water in the

PRM aquifer system in New Jersey is likely to

degrade with time.

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