Integrated variable weight model and improved DRASTIC model for groundwater vulnerability assessment in a shallow porous aquifer

Abstract

Accurate and effective assessment of groundwater vulnerability is very important for ensuring a healthy groundwater ecosystem. We evaluate the vulnerability of shallow porous aquifers by modifying the DRASTIC model and verify the effectiveness of the variable weight model (VWM). Firstly, topography, aquifer media, and the impact of the vadose zone are replaced by land-use type, aquifer thickness, and the hydraulic resistance of the vadose zone. Second, the weighting is optimized using the analytical hierarchy process (AHP) and variable weight theory (VWT). Thirdly, the original and the improved DRASTIC methods were used to evaluate groundwater vulnerability. Finally, three sets of samples hydrochemical parameters (NO3-, Mg2+,COD) were used to verify the improved frameworks using the Receiver Operating Curve (ROC) method. The improved model increases the dispersion degree of groundwater vulnerability. Compared with the original DRASTIC method, the correlation of the VWM is significantly improved in terms of the area under curve (AUC) for NO3- (0.786), COD (0.753), and Mg2+ (0.831). In short, it is necessary to optimize the parameters and weights of the model in order to realize reliable estimations of groundwater vulnerability. In particular, the use of VWM brings the results in line with the actual situation by changing the weights.