Major aquifers in New Jersey

Principal Aquifers

The principal aquifers of New Jersey are classified into two groups-Coastal Plain aquifers south of the Fall Line and non-Coastal Plain aquifers north of the Fall Line. The aquifers are described below and in Water Supply Paper 2275, pages 309-317, from youngest to oldest; their areal distribution is shown in figure 1.

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Coastal Plain Aquifers

The principal Coastal Plain aquifers are the Kirkwood-Cohansey aquifer system, the Atlantic City 800-foot sand, the Wenonah-Mount Laurel aquifer, the Englishtown aquifer system, and the upper, middle, and lower aquifers of the Potomac-Raritan-Magothy aquifer system. Other aquifers include the Rio Grande water-bearing zone, the Piney Point aquifer, and the Vincentown aquifer. All but the Kirkwood-Cohansey are confined except where they crop out or are overlain by permeable surficial deposits. The aquifers are recharged directly by precipitation in outcrop areas, by vertical leakage through confining beds, and by seepage from surface-water bodies.

More than 75 percent of the freshwater supply in the New Jersey Coastal Plain is from groundwater, although a shift to surface water resources have occurred in recent decades to prevent depletion of groundwater levels in the aquifers. In the Coastal Plain, high-capacity production wells used for public supply commonly yield 500 to 1,000 gallons per minute (gal/min), and many exceed 1,000 gal/min. Water quality is satisfactory except for local excessive iron concentrations [as much as 460 milligrams per liter (mg/L)] in several aquifers, including the Potomac-Raritan-Magothy, and for local contamination from saltwater intrusion and waste disposal. In the unconfined Kirkwood-Cohansey aquifer system water is brackish or salty in some coastal areas. In confined aquifers, salinity generally increases with depth in the southern and southeastern parts of the Coastal Plain.

Non-Coastal Plain Aquifers

North of the Fall Line, the principal aquifers consist of glacial valley-fill deposits; fractured shales, mudstones, limestones, sandstones, conglomerate, and crystalline rocks. These aquifers include the glacial valley-fill aquifers, the Newark Group aquifers, the carbonate aquifers within the Valley and Ridge sedimentary units, and the igneous and metamorphic crystalline rocks of the Highlands.

Stratified drift and till underlie valleys north of the Wisconsin terminal moraine (fig. 1). The stratified drift, poorly sorted sand and gravel with interbedded silt, silty sand, and clay, forms the glacial valley-fill aquifers. The aquifers generally are not more than 30 to 40 ft. thick. However, the aquifers may comprise channels up to 300 ft thick in pre-Pleistocene stream valleys. These glacial valley-fill aquifers are narrow beltlike deposits that are too small in areal extent to be shown in figure 1. The stratified drift can yield water to wells and can retain substantial amounts of water from precipitation, which increases yields in the underlying bedrock aquifers. In some areas, till, which consists of a veneer of unsorted clay, silt, sand, and gravel 10 to 30 ft thick, acts as a confining unit (Barksdale and others, 1943).

Glacial valley-fill aquifers are the most productive source of groundwater in some northeastern counties in New Jersey (Vecchioli and Miller, 1973). These aquifers may yield as much as 2,000 gal/min to public supply and industrial wells. 

Aquifers in the Newark Group, present in the Piedmont physiographic province (fig. 1), consist of shale and sandstone. Water generally is present in weathered joint and fracture systems in the upper 200 or 300 ft (Barksdale and others, 1958). Below a depth of 500 ft, fractures are fewer and smaller, and water availability is reduced, depending on rock type. In coarse-grained sandstones, groundwater also is present in intergranular pore spaces. In several counties, the shale and sandstone of the Newark Group are the most productive aquifers and yield as much as 1,500 gal/min (Carswell and Rooney, 1976; Nemickas, 1976).

In the Valley and Ridge sedimentary units, the most productive aquifers are carbonate rocks that commonly yield large supplies of water, especially where overlain by stratified glacial deposits. Cavities and solution channels in the rock provide storage and avenues for water movement. In the crystalline Highlands, water is available in weathered and fractured zones, usually within 300 ft of the land surface. With the exception of carbonates, yields from other consolidated sedimentary rocks (poorly fractured sandstones and shales) and from crystalline rocks are limited by the degree of weathering and fracturing and do not exceed more than a few hundred gallons per minute.

Non-Coastal Plain aquifers generally yield water of satisfactory quality but are susceptible to local contamination because of their proximity to the land surface. The water in valley and ridge sedimentary units and in aquifers of the Newark Group generally is hard (concentrations exceeding 120 mg/L hardness as calcium carbonate) and may have locally excessive concentrations of iron (11 mg/L) and sulfate (1,800 mg/L) (Nemickas, 1967). Near tidal areas, pumping has caused saltwater intrusion in some aquifers.