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Program to Maintain and Update Groundwater Models

Groundwater flow in the New Jersey Coastal Plain

By Mary Martin

Map of the model's study area

STATUS: Superseded by RASA-98

MODEL VERSION/TYPE: MODFLOW-96, steady state and transient

AREA STUDIED: New Jersey Coastal Plain

AQUIFERS SIMULATED: 10 regional New Jersey Coastal Plain aquifers


MODEL SIZE: 10 layers, 29 rows, 51 columns

MINIMUM GRID SPACING:2.5 miles x 2.5 miles

REPORT SERIES AND NUMBER: USGS Professional Paper 1404-H

REPORT URL: USGS Proffessional Paper 1404-H


Download this set of model files Original RASA model not available. See RASA-98.

Report Abstract

Groundwater flow was simulated in 10 aquifers and 9 intervening confining units of the New Jersey Coastal Plain, which consists of unconsolidated gravel, sand, silt, and clay of early Cretaceous to Holocene age. A multilayer finite-difference model was used to simulate both prepumping steady-state conditions and transient conditions from 1896 through 1980. Model calibration indicates that the highest transmissivity, greater than 10,000 feet squared per day, is in Camden and Gloucester Counties in the three Potomac-Raritan-Magothy aquifers; in Monmouth and Ocean Counties in the middle Potomac-Raritan-Magothy aquifer; in Atlantic and Cape May Counties in the confined Kirkwood aquifer; and in Ocean, Burlington, Atlantic, and Cape May Counties in the lower and upper Kirkwood-Cohansey aquifers. Confining-unit vertical leakance is highest, greater than 1x103 feet per day per foot, in updip areas and lowest, less than 1x105 feet per day per foot, in downdip areas.

Sensitivity analyses show that the model was useful in refining initial estimates of transmissivity and confining unit vertical leakance near the major cones of depression, and that the assumptions associated with the lateral and downdip boundary conditions do not seriously limit the usefulness of the model results. However, simulated water levels near the major cones of depression, in several aquifers, are fairly sensitive to parts of the model framework, including confining-unit characteristics along the outcrop of the Potomac-Raritan-Magothy aquifers, the updip limit of the confined Kirkwood aquifer, and the downdip limit of the upper and lower sand units of the Englishtown aquifer system.

Calibration and sensitivity analysis also show that aquifer storage coefficients are about 1x104, except in downdip areas of the Potomac-Raritan-Magothy aquifers, where they may be as much as eight times higher. Confining-unit specific storage is about 6x106 per foot. Areas near the center of the major cones of depression in the Potomac-Raritan-Magothy, Englishtown, Wenonah-Mount Laurel, and Kirkwood-Cohansey aquifers approximate steady-state conditions in 1981. However, downdip and offshore areas are under transient-flow conditions. Simulated changes in water levels along the saltwater- freshwater interface boundary (the occurrence of groundwater with greater than 10,000 milligrams per liter chloride concentrations) indicate that the lower Potomac-Raritan-Magothy aquifer and the confined Kirkwood aquifer have the greatest potential for movement of the interface. However, simulated hydraulic gradients within the aquifers near the interface boundary cannot be used to quantify movement of the interface. The simulated sources of water to wells in 1978 include 3 percent from aquifer storage, 3 percent from boundary flows, 4 percent from the ocean and bays, and 90 percent from decreased discharge to or increased recharge from streams--that is, a reduction in streamflow.

The prepumping regional flow system recharged in upland areas in Mercer, Middlesex, and western Monmouth Counties; in western Ocean and central Burlington Counties; and in central Gloucester and Camden Counties and discharged to the Atlantic Ocean, Delaware River, Delaware Bay, Raritan Bay, and large rivers in the Coastal Plain. Under pumping conditions, regional cones of depression formed in the three Potomac-Raritan-Magothy aquifers, Englishtown aquifer, Wenonah-Mount Laurel aquifer, and the confined Kirkwood aquifer.

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