Reciprocal analysis of groundwater potentiality and vulnerability modeling in the Bahabad Plain, Iran

Heuristic and statistical groundwater quality assessment models are efficient tools in the zoning of groundwater vulnerability to contamination. An important reciprocal methodology, yet neglected in Iran, was conducted to assess the performance of three groundwater vulnerability models, namely GODS, SI, and DRASTIC, and a data mining model for groundwater potential, maximum entropy (MaxEnt). For both the training and validation stages for the MaxEnt model, the Mahalanobis distance technique was adopted. The vulnerability rates obtained from the DRASTIC model with a coefficient of determination (R-2) value of 0.76 had a statistically significant correlation with nitrate concentrations in the 21 wells, compared to SI and GODS. The DRASTIC model can better reflect the vulnerability of groundwater resources to contamination. The impact of the vadose zone with an average effective weight of 33 is more important than other parameters, followed by depth than groundwater (D) (32.01), net recharge (R) (28.95), and the aquifer media (A) (18.1). These weights may not be changed. MaxEnt showed significant performance in both the training and validation stages with the respective area under the receiver operating characteristic curve (AUROC) values of 0.907 and 0.901. A reciprocal analysis between the vulnerability map in the superior model and the groundwater potential map derived from MaxEnt revealed that areas with high groundwater potential are still in safe state but require more attention as the top priority for amendment practices. In addition, approximately 8.7% of the entire study area has a high vulnerability to contamination, which requires immediate pragmatic actions.