Application of a modified DRASTIC method to create a temporal Aquifer Recharge Potential Map for Alabama

The DRASTIC method was developed by the USEPA in 1985 to model the groundwater contamination potential of hydrogeological regions. The method references seven factors: Depth to water table, Recharge (net), Aquifer media, Soil media, Topography, Impact of vadose zone, and Conductivity (hydraulic). Each factor is rated. Rated factors are weighted and combined to produce a numerical value, the DRASTIC Index, which provides a relative assessment of an area's contamination potential. An evaluation of the DRASTIC conceptual model reveals an intrinsic component comprising relatively invariable factors (aquifer media, soil media, topography, and aquifer conductivity) and an acquired component comprising variable factors (net recharge and vadose zone impact). Land use/land cover was not included in the original DRASTIC method. A modified DRASTIC method has been used to produce an Aquifer Recharge Potential map for Alabama using the intrinsic/acquired factor model. The intent of the map is to show the potential of an area for groundwater recharge given a set of acquired conditions. The map uses a combination of intrinsic factors (soils, topography, and aquifer hydraulic conductivity), which are used to create an intrinsic properties base map, and variable factors (net recharge, depth to water table, and land use) to create the final Recharge Potential Index (RPI) map. Variable factors can be changed to address specific temporal questions, such as "What is the potential for recharge in an area given a set of land use and climatic conditions?" Two weighting techniques: an analytic hierarchy process and a single parameter sensitivity analysis are used to modify the weighting system and a Wilcoxon rank sum nonparametric statistical test is used to modify the rating to create a more accurate RPI. The RPI is found by multiplying the modified ratings by the modified weights for each factor and then summing the products within a GIS platform to create a final map product. The map is intended to provide stakeholders a tool for evaluating the potential effects of land use changes, drought, and flooding for groundwater availability in Alabama.