Groundwater vulnerability assessment using modified DRASTIC method with integrated hydrological model

Since groundwater is a finite resource, assessing its vulnerability to pollution is crucial for sustainable management. Contamination poses a significant threat, potentially degrading both the quality and quantity of available groundwater. To enhance the efficiency of this vital tool in subsurface water management, this study aims to propose the approach integrating index-based vulnerability assessment (DRASTIC-L) with fully coupled surface water-groundwater model (SWAT-MODFLOW). Various thematic layers regarding hydrogeological characteristics and land use of the Yom and Nan River basins are analyzed and overlaid to calculate the weighted index as well as identify vulnerability classes. DRASTIC-L components (depth to water table, recharge, and hydraulic conductivity) are directly simulated by SWAT-MODFLOW, instead of using interpolated observation data. As a result, the high consistency between simulated river discharges and groundwater levels with observed data implies a high degree of accuracy in the vulnerability parameters obtained from the model. DRASTIC-L index ranges from 61 to 221, classifying the study area into four vulnerability categories: low (<100), moderate (100-140), high (140-200), and very high (>200). 15.8% of the watershed exhibits low susceptibility, while moderate susceptibility characterizes 36.9%. Notably, 42.4% of the area falls within the highly susceptible category, highlighting potential contamination risks. Very highly susceptible zones comprise a smaller portion (4.7%) of the watershed. Moreover, Nitrate concentration data shows spatial congruence with areas designated as highly vulnerable. By providing a more accurate characterization of aquifer vulnerability, this approach can inform decision-makers in developing targeted and efficient plans to protect both groundwater quantity and quality.