Saltwater intrusion into the Potomac-Raritan-Magothy aquifer in the central New Jersey Coastal Plain has contaminated the groundwater in the vicinity of Raritan Bay and resulted in the closing of wells that provide potable water to numerous towns in the region. An understanding of the geologic composition of this region, in particular the three-dimensional geometry, permeability, and physical relationships of adjacent lithologic units, can be obtained from geophysical and coring techniques and sequence stratigraphic data. A meandering Pleistocene channel filled with glacial outwash (sands and gravels) is delineated near the southern shoreline of Raritan Bay using high-resolution seismic data and VibracoresTM. The coarse-grained buried Pleistocene channel deposits and Holocene fine-grained estuarine muds beneath the bay are in contact with the Cretaceous Coastal Plain stratigraphy. Buried channel deposits have high permeability and are adjacent to the Cretaceous aquifer. Estuarine muds form an aquitard, preventing the intrusion of salt water into the aquifer. However, overpumping of Coastal Plain wells had resulted in excessive drawdown and intrusion of saline waters into the Cretaceous aquifer through buried channel deposits. This study has delineated the hydraulic conduit by which polluted estuarine water may be pumped into municipal water wells.

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