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Modifying the DRASTIC method to create an Aquifer Recharge Potential Map for Alabama
Proceedings of the 2020 Mississippi Water Resources Conference
Year: 2020 Authors: Guthrie G., Hastings Puckett M., Hastert G.
The DRASTIC method was developed by the USEPA in 1985 to model groundwater contamination potentials for diverse hydrogeological regions. The method combines seven factors: Depth to water table, Recharge (net), Aquifer media, Soil media, Topography, Impact of vadose zone, and Conductivity (hydraulic), which are rated and weighted to produce a numerical value, the DRASTIC Index, which provides a relative assessment of an area's contamination potential.
The DRASTIC conceptual model contains 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 modification to the DRASTIC methodology has been used to produce an Aquifer Recharge Potential map for Alabama using an 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 based on a Recharge Potential Index (RPI). The map combines intrinsic factors (soils, topography, and aquifer hydraulic conductivity) to create an intrinsic properties base map. Variable factors (net recharge, depth to water table, and land use) can then be added to create the potential recharge map. These factors to produce maps that reflect changing temporal conditions. The Analytic Hierarchy Process (AHP) is used to modify the weighting system to create a more accurate RPI. The AHP uses a pairwise comparison matrix to evaluate the relative importance of multiple criteria by generating a consistency index that measures the inconsistency of judgements used in the developmental model. 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.