Geologic sensitivity and groundwater travel time map of the marine corps air station, Beaufort, South Carolina USA

Geographic information system (GIS) mapping of geologic sensitivity, defined in this study as the sensitivity of groundwater contamination based on geologic units, and modeling groundwater flow are important aids in establishing protocols for groundwater monitoring, determining guidelines for proper handling of hazardous substances, siting future facilities, emergency response, and designing remediation plans for the clean up of toxic spills. GIS technology is utilized to develop maps for the Marine Corps Air Station (MCAS) in Beaufort, South Carolina, USA of (1) the subsurface geology in three dimensions from land surface to the top of the Floridan aquifer, a regionally extensive and highly productive groundwater resource, (2) derivative geologic sensitivity/groundwater contamination potential, and (3) hydrogeology and groundwater flow. Soils data are also incorporated into the model to better understand how soil drainage enhances or inhibits recharge of groundwater and, together with organic matter affects the movement of contaminants through the soil column. A calibrated 3D groundwater flow model of MCAS-Beaufort and subsequent detailed flow path and travel time analyses are based on the 3D geologic characterization delineated on the geologic sensitivity map. The groundwater flow model can be displayed in two ways. One mode is as an ArcGIS project where groundwater pathlines with travel times of 5 to 500 years can be plotted from any 30 × 30 m cell within the boundaries of MCAS-Beaufort. Another mode is as a static map, which defines areas of the MCAS-Beaufort where groundwater travel time from the water table to the top of the Floridan aquifer is ≤ 10 years or ≤ 25 years. The 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. Methodologies developed for this study are applicable to other shallow aquifer settings.