Saltwater contamination along the northern part of Hilton Head Island probably is a result of lateral encroachment of seawater, combined with some downward vertical leakage of seawater where the Upper Floridan aquifer is exposed or nearly exposed. In the vicinity of Port Royal Sound, and possibly other estuaries, downcutting by ancient river systems during periods of lower ocean levels that existed during the most recent ice age exposed rocks that form the Upper Floridan aquifer, causing direct connection between seawater and fresh ground water.

Regional ground-water pumping, but most importantly, pumping on the island, has locally lowered the pressure in the Upper Floridan aquifer and reversed the natural hydraulic gradient, causing the lateral encroachment of saltwater. Features that formerly were submarine springs prior to development, now are conduits for the encroachment of saltwater from the ocean, sounds, and estuaries.

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