Relations of fresh and salty ground water along the southeastern U. S. Atlantic Coast

Abstract

Studies of the hydrogeologic environments and the dynamic and equilibrium relations of fresh and salt water in aquifers have been intensified at several places along the southeastern Atlantic Coast. Some salt-water problems involve the coastal water-table aquifer, and others involve parts of the artesian system. On the sandy coastal islands of North Carolina, freshwater lenses under water-table conditions float on salt water. Salt-water contamination may take place by (1) lateral encroachment from the ocean and bay; (2) vertical encroachment from below; (3) overland inundation by ocean water during storms; and (4) downward percolation of salt spray and salt-bearing precipitation. In the Savannah, Georgia, and South Carolina area, salt-water encroachment along two of five water-bearing zones in the principal artesian (limestone) aquifer has been caused by the decline of artesian pressure due to pumping. Some wells in the limestone at nearby Parris Island, South Carolina, yield salty water when overpumped. From Savannah southward at least to Fernandina, Florida, connate salty water occurs in the artesian aquifer below the fresh water. At Brunswick, Georgia, connate salty water is stratified between fresh-water bodies in the limestone aquifer above depths of 2,000 feet. Connate salty water has contaminated the aquifer between depths of 500 and 800 feet in a small area in the city. Along the southeast Florida coast drainage canals have been the primary cause of salt-water contamination of the highly permeable Biscayne aquifer. Criteria have been established for the operation of salinity-control dams to prevent encroachment. The salt-water front in the aquifer along the coast is dynamically stable under natural conditions.