Modification of DRASTIC Model to Assess Groundwater Vulnerability by Applying two Approaches: Single Parameter Sensitivity Analysis (SPSA) and Analytical Hierarchy Process (AHP)

Groundwater vulnerability assessment plays a key role in the conservation and proper usage of these strategic resources. Various methods have been proposed to assess the vulnerability and the most common is the DRASTIC model. The DRASTIC model consists of seven hydrogeologic factors to compute for the vulnerability index. The main problem with this method is fixed rates and weights related to each parameters in this model. So the main purpose of this research is to modify primary DRASTIC model by Single Parameter Sensitivity Analysis (SPSA) and Analytical Hierarchy Process (AHP) and finally to produce vulnerability map in GIS environmental software. Yasuj plain located in southwest of Iran is chosen as a study area. Nitrate concentration related to 24 wells are used to compare which method make better prediction based on real pollution in study area. Finally SPSA method has shown the best correlation with sample Nitrate, by specifying more suitable weight for DRASTIC parameters in each polygon. Also AHP method has assigned new weights to each parameters based on the importance and better result was achieved compare with basic DRASTIC. These results can be used to map groundwater susceptibility to pollution.