In 1992, ground-water withdrawals from the unconfined and confined aquifers in the New Jersey Coastal Plain totaled about 300 million gallons per day, and about 70 percent (200 million galllons per day) of this water was pumped from confined aquifers. The withdrawals have created large cones of depression in several Coastal Plain aquifers near populated areas, particularly in Camden and Ocean Counties. The continued decline of water levels in confined aquifers could cause saltwater intrusion, reduction of stream discharge near the outcrop areas of these aquifers, and depletion of the ground-water supply. Because of this, withdrawals from wells located within these critical areas have been reduced in the Potomac-Raritan-Magothy aquifer system, the Englishtown aquifer system, and the Wenonah-Mount Laurel aquifer.
A computer-based model that simulates freshwater and saltwater flow was used to simulate transient ground-water flow conditions and the location of the freshwater-saltwater interface during 1989-92 in the New Jersey Coastal Plain. This simulation was used as the baseline for comparison of water levels and flow budgets. Four hypothetical withdrawal scenarios were simulated in which ground-water withdrawals were either increased or decreased. In scenario 1, withdrawals from wells located within critical area 2 in the Potomac-Raritan-Magothy aquifer system were reduced by amounts ranging from 0 to 35 percent of withdrawals prior to 1992. Critical area 2 is mainly located in Camden County, and most of Burlington and Gloucester Counties. With the reductions, water levels recovered about 30 feet in the regional cone of depression centered in Camden County in the Upper Potomac-Raritan-Magothy aquifer and by 20 ft in the Lower and Middle Potomac-Raritan-Magothy aquifers.
In scenarios 2 to 4, withdrawals projected for 2020 were input to the model. In scenario 2, withdrawal restrictions within the critical areas were imposed in the Potomac-Raritan-Magothy aquifer system, the Englishtown aquifer system, and the Wenonah-Mount Laurel aquifer, but withdrawals were increased outside the critical areas to the projected 2020 demand. With withdrawals restrictions in critical areas, water levels recovered about 20 feet at the center of the regional cone of depression in the Upper Potomac-Raritan Magothy aquifer. Water levels recovered by about 20 feet at the center of a regional cone of depression in the Englishtown aquifer system in Ocean County, and by about 20 feet in the Wenonah-Mount Laurel aquifer in the same area. In scenario 3, withdrawals were increased to the projected 2020 demand inside and outside the critical areas. As a result, water levels declined as much as 20 feet at the center of a regional cone of depression in the Englishtown aquifer system in Ocean County, and as much as 10 feet in the Wenonah-Mounty Laurel aquifer near this area. The Englishtown aquifer system and the Wenonah-Mount Laurel aquifer are particularly sensitive to increases and decreases in withdrawals because in certain areas the transmissivities of these aquifers are lower than the transmissivities of other confined aquifers of the New Jersey Coastal Plain, and because these aquifers are hydraulically connected. Simulated water levels declined by as much as 10 ft at the center of the regional cone of depression in Atlantic County. In scenario 4, withdrawal amounts were equal to that in scenario 2, except an additional 13.2 million gallons per day was withdrawn from hypothetical wells located outside the critical areas in the Upper Potomac-Raritan-Magothy aquifer, Englishtown aquifer system, and the Wenonah-Mount Laurel aquifer. The additional withdrawals resulted in increased leakage from overlying aquifers to the Wenonah-Mount Laurel aquifer and subsequently to the Englishtown aquifer system.