Ground-water resources of Monmouth County, New Jersey

Monmouth County includes an area of 538 square miles in east-central New Jersey. The climate is characterized by moderate temperature, moderate humidity, and moderate precipitation.

The exposed rocks in the area are chiefly sands and clays, which range in age from Late Cretaceous through Recent. The formations strike northeast-southwest and dip gently to the southeast. These rocks range in total thickness from about 500 to 1,200 feet or more and are underlain by basement rocks of late Precambrian (?) age.

The principal aquifers underlying Monmouth County occur in the Raritan and Magothy Formations, the Englishtown Formation, the Wenonah Formation and Mount Laurel Sand, the Vincentown Formation, and the Kirkwood Formation.

Ground water constituted about 50 percent of the total water use in 1958. The daily withdrawal of ground water was at an average rate of 21.6 mgd (million gallons per day) in 1958 and about 32 mgd in 1965 (N. J. Division of Water Policy and Supply). The water demand is expected to increase to about 133 mgd by the year 2000. An analysis of streamflow records for the period 1932 to 1950 suggests that, excluding the Raritan and Magothy Formations, the major aquifers that occur under water-table conditions in the county discharge an average of about 178 mgd to streams.

The aquifers in the Raritan and Magothy Formations contribute little or no water directly to streams in Monmouth County. These aquifers have been the most productive in the county. However, because salt water has been found in the lower parts of these formations in Ocean County, further development should proceed watchfully to assure that salt water does not threaten existing supplies.

Aquifers in the Raritan and Magothy Formations and the Englishtown Formation supplied 76 percent of the ground water used in 1958. These aquifers, in conjunction with the Wenonah Formation and Mount Laurel Sand of Late Cretaceous age, are capable of providing relatively large yields to wells. The average yield of 63 large-diameter wells tapping these aquifers is 580 gpm, at depths randing from 100 to 1,140 feet. In general, the concentrations of chemical constituents in water from the aquifers would not restrict the use of the water for most purposes. High concentrations of iron do occur and require treatment. The concentrations of dissolved solids in 39 to 41 samples were 160 ppm (parts per million) or less.