Assessment of saltwater migration through the Upper Floridan confining unit in the Savannah Harbor area

Abstract

Pumping in the Savannah vicinity has decreased the potentiometric surface of the Upper Floridan aquifer and induced a cone of depression, and saltwater is assumed to leak downward through the confining layer toward the aquifer. Marine seismic subbottom profiling, core drilling, and porewater geochemistry data collected as part of the ongoing Supplemental Studies to Determine Ground-water Impacts to the Upper Floridan Aquifer were used to better define the stratigraphy and hydraulic characteristics of the confining layer. The current study focuses primarily on the “area of concern” from Field’s Cut to approximately two miles offshore of Tybee Island, where the confining layer naturally thins and several deep buried paleochannels have cut further down into the confining layer. The results of the porewater data derived from this work are believed to demonstrate the depth to which seawater has penetrated downward through the confining layer and indicate that chloride breakthrough has occurred in some locations along the Savannah River channel.