Distribution of chloride concentrations in the principal aquifers of the New Jersey coastal plain, 1977-81

The U.S. Geological Survey maintains a saltwater monitoring network in New Jersey to document and evaluate the movement of saline water into freshwater aquifers that serve as sources of water supply. Areas in the Coastal Plain with existing or potential saltwater intrusion are delineated. Data collected through 1981 indicate that freshwater aquifers in parts of seven Coastal-Plain counties are contaminated by saline water. Encroachment of saltwater into freshwater aquifers in the Sayreville area of Middlesex County and in the lower peninsula of Cape May County has been reported for about 40 years and is now more extensive. Several other areas are experiencing limited saltwater intrusion. These include the Keyport-Union Beach area in Monmouth County, areas along the Delaware estuary in Gloucester and Salem Counties, and at Point Pleasant Beach and Seaside Heights in Ocean County. The continuing updip movement of saline water in the Potomac-Raritan-Magothy aquifer system is also threatening existing freshwater supplies in the interior areas of Gloucester and Salem Counties. Saltwater intrusion has resulted from extensive ground-water withdrawals. The resultant freshwater head declines have caused reversals in the natural hydraulic gradients that permit inland movement of saline water from adjacent saltwater bodies. (USGS)