A three-step modification of the DRASTIC model using spatial multi criteria decision making methods to assess groundwater vulnerability

Abstract

Groundwater vulnerability assessment, as a key tool, is essential for assisting decision-makers and experts in identifying highly vulnerable areas and devising efficient pollution reduction strategies. The widely utilized DRASTIC model for assessing groundwater vulnerability incorporates seven key geological and hydrological parameters. To address the limitations of the DRASTIC model, this study proposes a novel three-step modification by introducing an extra parameter, adjusting default weights, and utilizing alternative aggregation methods. These modifications aim to capture the unique characteristics of a specific region more accurately. The first step involves incorporating the Land Use (LU) parameter as the eighth parameter in the DRASTIC model, resulting in an updated 8-parameter model. The second step involves integrating the Analytic Hierarchy Process (AHP) to adjust parameter weights based on input from local experts. Lastly, while the Weighted Linear Combination (WLC) technique has conventionally been used for aggregating layers in the GIS environment, this study suggests employing the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). Furthermore, to consider decision makers' risk attitudes, the Ordered Weighted Averaging (OWA) method is utilized.

To assess its effectiveness, the modified model was applied to Khoy County in Iran. Then, the results were compared to the DRASTIC model using correlation analysis based on nitrate concentrations. The results indicated a correlation coefficient of 0.67 for the modified model compared to 0.47 for the DRASTIC model. This suggests that the proposed modified model is an enhanced and highly effective approach for evaluating groundwater vulnerability.