New Jersey Water Science Center

Hydrogeologic Framework of the Shallow Ground-Water System in the Cox Hall Creek Basin, Cape May County, New Jersey

In Cooperation with the Cape May County Board of Chosen Freeholders and the New Jersey Department of Environmental Protection

By Pierre J. Lacombe and Otto S. Zapecza

Open-File Report 2006-1044

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Cape May County is investigating the feasibility of restoring the lowermost reach of Cox Hall Creek to its former state as a tidal saltwater wetland; however, the potential for contamination of the shallow ground-water system, which provides water to hundreds of nearby privately owned domestic wells, with saltwater from the restored wetland is of particular concern. To evaluate the potential effectiveness and risks of restoring the saltwater wetlands, the County needs information about the hydrogeologic framework in the area, and about the potential vulnerability of the domestic wells to contamination.

The shallow ground-water system in the Cox Hall Creek area consists of unconsolidated Holocene and Pleistocene deposits. The Holly Beach water-bearing zone, the unconfined (water-table) aquifer, is about 35 feet thick and contains a 2- to 4-foot-thick clay lens about 10 feet below land surface; a lower, more discontinuous clay lens about 30 to 35 feet below land surface ranges up to 5 feet in thickness. A 75-foot-thick confining unit separates the Holly Beach water-bearing zone from the underlying estuarine sand aquifer. The clay lenses in the Holly Beach water-bearing zone likely retard the movement of contaminants from septic tanks, lawns, and other surficial sources, protecting wells that tap the lower, sandy part of the aquifer.

The clay lenses also may protect these wells from salty surface water if withdrawals from the Holly Beach water-bearing zone are not increased substantially. Deeper wells that tap the estuarine sand aquifer are more effectively protected from saltwater from surface sources because of the presence of the overlying confining unit.




Purpose and Scope

Previous Investigations

Methods of Investigation

Ground-Penetrating-Radar Surveys

Interpretation of Natural Gamma-Ray Geophysical Well Log

Review of Well Drillers’ Logs

Hydrogeologic Framework

Holly Beach Water-Bearing Zone

Confining Unit Overlying the Estuarine Sand Aquifer

Estuarine Sand Aquifer

Effect of Clay Lenses and the Confining Layer on Potential Vulnerability of Wells to Contamination



References Cited

Download: PDF of OFR2006-1044 (1.4Mb).

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