Groundwater Modeling to Evaluate Interaquifer Leakage in the Floridan Aquifer System near Hunter Army Airfield and Fort Stewart, Georgia

Steady-state model simulations were conducted using a modified regional groundwater-flow model to determine the amount of leakage from the Upper Floridan aquifer. This leakage, through the confining unit into the Lower Floridan aquifer, results from pumping one million gallons per day of groundwater from newly constructed Lower Floridan aquifer production wells at Hunter Army Airfield and Fort Stewart. Existing model grid resolution and hydraulic properties were modified using data from new test wells constructed at each site. Results of model simulations indicate that interaquifer leakage accounted for 49 percent of the flow at Hunter Army Airfield, and 99 percent of the flow to the well at Fort Stewart. The Georgia Environmental Protection Division interim permit strategy for the Lower Floridan aquifer states that "the applicant must offset the impact of the Lower Floridan aquifer pumping by reducing nearby Upper Floridan aquifer permitted pumping in the same general area (within a 5-mile radius) by an amount equal to or greater than the determined Upper Floridan aquifer leakage." Model scenarios were developed at each of the two sites in accordance with Georgia Environmental Protection Division policy to assess the effect of these pumping reductions on groundwater flow in the coastal area.