SOLUTE-TRANSPORT MODELING IN SUPPORT OF MANAGEMENT OF SALTWATER INTRUSION IN THE SAVANNAH, GEORGIA—HILTON HEAD ISLAND, SOUTH CAROLINA, AREA

Pumping from the Upper Floridan aquifer, the principal source of water in the coastal Georgia (Ga.) and adjacent South Carolina (S.C.) area, has resulted in substantial water-level decline near Savannah, Ga., and contributed to saltwater intrusion in the Hilton Head Island, S.C., area. Saltwater contamination of supply wells at Hilton Head Island has constrained further development of the Upper Floridan aquifer in this area. As part of the Georgia Environmental Protection Division's (GaEPD) Coastal Sound Science Initiative, the U.S. Geological Survey developed a solute-transport model to evaluate ground-water flow, and the occurrence and remediation of saltwater contamination in the study area. The GaEPD and other stakeholders are using the results of simulations to develop a management strategy for area ground-water resources.

Initially, the model was used to examine how variations in the conceptual model and different initial conditions affect current and future extent of saltwater migration. Numerical simulations were then used to test the effects of variable pumpage reductions in the Savannah and Hilton Head Island areas on the movement of saltwater migration and distribution in the Upper Floridan aquifer at and near Hilton Head Island. Simulation results indicate that (1) pumping in both the Savannah and Hilton Head Island area contributes to saltwater intrusion; (2) substantial reductions may be required to stop all plume expansion and salinity increase; (3) even if all pumping in the area is eliminated, the existing saltwater may persist for the foreseeable future.

Simulation results must be interpreted in light of uncertainties and approximations inherent in the formulation of the model. These limitations, however, do not invalidate the model results or interpretation thereof. This type of model is a valuable tool for adaptive management strategies.