Mapping the threat of seawater intrusion in a regional coastal aquifer-aquitard system in the southeastern United States

The Upper Floridan aquifer (UFA) beneath the southeastern US Atlantic Coastal Plain and inner continental shelf is a major source of groundwater for coastal Georgia (GA) and South Carolina (SC), where it supplies over 50% of water requirements. Since pumping from the UFA first began at Savannah, GA in the late 1800s, a large (similar to50 km radius) cone of depression has developed on the aquifer's potentiometric surface. Where a regional Miocene-age aquitard overlying the UFA is thin or absent within this cone, the opportunity exists for seawater to leak downward through the seabed and into the aquifer. Recently completed marine reflection seismic surveys on the Georgia-South Carolina coast identified 11 areas of concern (AOCs) where the UFA is susceptible to seawater intrusion. Results from this project, and from an AOC test-drilling program recently completed, are contributing to a large database of information and models being developed for the UFA by several agencies and academic institutions. The results will provide input necessary for managing groundwater resources and mitigating potential seawater intrusion on the Georgia-South Carolina coast.