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Major aquifers in New Jersey
Moditied from: New Jersey Ground-Water Resources
The Coastal Plain is the largest physiographic province in New Jersey. It lies southeast of the Fall Line, where it intersects the Piedmont province in a series of falls along river courses. The geology of the Coastal Plain is characterized by unconsolidated sand, gravel, silt, and clay thickening seaward from a featheredge at the Fall Line to more than 6,500 feet (ft) thick in southern Cape May County (Gill and Farlekas, 1976). The highly permeable beds of coarse material form aquifers that differ in areal extent and thickness. Slightly permeable interbeds of silt and clay form confining beds, which restrict the vertical flow of water.
North of the Fall Line, areal boundaries of aquifers roughly correspond to the physiographic divisions of the State. Aquifers in the Newark Group underlie the Piedmont province, upland crystalline rocks underlie the Highlands province, and Paleozoic sedimentary rocks form the Valley and Ridge province (fig. 1).
New Jersey receives an average of 44 inches (in.) of precipitation annually, of which approximately 15 to 39 in. recharge the ground-water reservoir.
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 table 1 from youngest to oldest; their areal distribution is shown in figure 1.
Coastal Plain Aquifers
The five principal Coastal Plain aquifers are the Kirkwood-Cohansey aquifer system, the Atlantic City 800-foot sand, the Wenonah-Mount Laurel aquifer, the Englishtown aquifer, and the Potomac-Raritan-Magothy aquifer system. 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 ground water. 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, 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 crystalline units.
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 ground water 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. Their potential for supplying water has been largely overlooked in the north- western counties; however, the New Jersey Geological Survey and U.S. Geological Survey have begun programs to define this resource.
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, ground water 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.
Barksdale, H.C, Greenman, D.W., Lang, S.M., Hilton, G.S., and Outlaw, D.E., 1958, Ground-water resources in the tri-state region adjacent to the lower Delaware River: New Jersey Department of Conservation and Economic Development, Special Report 13, 190 p.