GEOCHEMICAL EVIDENCE AND PHYSICAL FLOW CHARACTERIZATION OF SALTWATER INTRUSION: WORMSLOE STATE HISTORIC SITE, CHATHAM COUNTY, GEORGIA

The Wormsloe State Historic Site lies in the southeastern portion of Chatham County, Georgia. The study site is situated on the Isle of Hope, a marsh island that exists between Skidaway Island and mainland GA. Elevations for this area are approximately 16 ft. above mean sea level (MSL). The purpose of this research is to determine the baseline conditions of the aquifer system so future changes in the amount of saltwater intrusion can be evaluated. The Wormsloe Historic site has been occupied continuously since 1733, and is an important relic of the initial colonization of Georgia. Ecological conservation efforts on the site, including the introduction of Long leaf pine habitat and the reintroduction of gopher tortoises, will benefit from hydrological data and evidence of sea level rise. Four monitoring wells, constructed from 1 in. diameter PVC pipe and extending approximately 18 ft. below land surface (BLS) have been installed. The screened intervals are at 8 to 18 ft. BLS. Installation techniques include direct push technology. Lithological cores were collected using a macrosampling device. Groundwater samples were collected using a low-flow methods in accordance with USEPA Region IV Science and Ecosystem Support Division Standard Operating Procedures. Grab and discrete samples were collected at depth and conductivity readings were converted to salinity (conductivity to salinity conversion based on 1983 technical paper from UNESCO, “Algorithms for computation of fundamental properties of seawater”) to explore mixing zones. Water level data has been collected using level loggers and geochemical samples were collected from the wells and the tidal marsh, and data has been organized in Piper diagrams to determine the groundwater facies. The results to date indicate that saltwater intrusion is primarily being driven by diurnal tidal pumping, with lateral intrusion greater on the eastern edge of the Isle of Hope. An end-member mixing analysis has been performed to determine the relative contributions of seawater and freshwater at each well. Of particular note, saltwater intrusion appears to coincide with fractures that are suspected to connect the surficial aquifer and the underlying carbonate aquifer system that provides potable water to the region.