An increasing trend of shallow ground-water withdrawal over the first part of this century on the Cape May Peninsula of New Jersey has resulted in the intrusion of saltwater into the aquifers that comprise the shallow ground-water system. The U.S. Geological Survey has developed a mathematical model of the flow system that simulates the flow regime at the freshwater-saltwater interface in the aquifers. The steady-state hydraulic-head distribution and interface position simulated by the model are in good agreement with those observed.