GIS MAPPING OF GEOLOGIC SENSITIVITY AND GROUNDWATER FLOW TO MODEL AQUIFER VULNERABILITY AT THE MARINE CORPS AIR STATION BEAUFORT, SC

Geographic Information System (GIS) technology is utilized to developed maps of the hydrogeology and groundwater flow in and around the Marine Corps Air Station (MCAS) in Beaufort, SC. These maps are used to model the contamination potential or aquifer sensitivity of the upper Floridan Aquifer, a regionally extensive and highly productive groundwater resource. The hydrogeology or geologic sensitivity map is based on mapping of the subsurface geology in three dimensions from land surface to the top of the Floridan Aquifer. Soils data, from U.S.D.A., are also incorporated into the model to better understand how soil drainage and organic matter might enhance or inhibit recharge of groundwater and affect the movement of potential contaminants. The geologic sensitivity map is especially effective in delineating land areas of MCAS, which are most/least sensitive to contaminants that are heavier than water and therefore, tend to move primarily in a downward direction under the influence of gravity.

A calibrated 3D groundwater flow model of MCAS and subsequent detailed flow path and travel time analyses are based on the 3D geologic characterization delineated in the geologic sensitivity map. The groundwater flow model can be displayed in two ways. One mode is as an ArcView or ArcGIS project where groundwater pathlines with travel times of 5 to 500 years can be plotted from any 30 X 30 m cell within the boundaries of MCAS Beaufort. Another mode is as a static map, which defines areas of the MCAS where groundwater travel time from the water table to the top of the Floridan Aquifer is < 10 years or < 25 years. This groundwater travel-time analysis can be used to evaluate the impact of particular land uses on the spread of contaminants introduced at the water table and transported to the upper Floridan Aquifer in the dissolved phase.

These map analyses are a critical aid in establishing protocols for groundwater monitoring, establishing protocols for handling of hazardous substances, siting of future facilities, emergency response, and designing remediation plans for cleaning-up spills.