Process Description:
DRASTIC is a system developed jointly by the U.S. Environmental Protection Agency (USEPA) and the National Water Well Association (NWWA) to map potential aquifer vulnerability. The methodology utilizes existing hydrogeological information to produce color-coded maps which display areas that are more or less likely to be affected by pollution introduced on the ground's surface. These maps depict areas which are more or less sensitive to land use changes which may affect ground water quality. Drastic maps are composites made up of eight individually mapped hydrogeological parameters. Seven of these parameters (depth to water - Dw, net recharge - Nr, aquifer media - Am, soil media - Sm, topography - T, impact of the vadose zone - Iv and hydraulic conductivity - Hc) are used to derive the DRASTIC summary index score. The eighth, hydrogeologic setting, is useful for general map interpretation but, it is not included in the summary index. A separate polygon coverage was built for each parameter and then the eight coverages are composited into a single coverage with all information from the originals for the FASTCAD drawings. These drawings were then converted to ARC/INFO coverages which edited by county. The county coverages were then edgematched and mapjoined into a statewide coverage. The statewide coverages, for each aquifer, was then dissolved for the individual DRASTIC parameters for further error checking of the composite coverages. Once all errors were corrected, the composite attributes were recalculated for the final statewide DRASTIC coverages. The original county CAD DRASTIC drawings were converted to ARC/INFO files, built as point, line and polygon coverages and edited for digitizing errors. The Dbase files containing the attribute data were then joined to polygon attribute tables in ARC/INFO. County coverages were then edgematched and mapjoined to create a statewide coverage. The statewide coverage was then projected to Albers HPGN and dissolved on the individual DRASTIC parameters and edited for county boundary discrepancies. The dissolved layers were intersected back together, the weighted fields were calculated and summed to produce the final DRASTIC Index values which were then used to color, according to prescribed ranges, the final coverage. In November, 1999, the shapefile of this dataset was inserted into Spatial Database Engine (SDE 3.0.2).