Comparison of the DRASTIC + L and modified VABHAT models in vulnerability assessment of Karaj aquifer, central Iran, using MCDM, SWARA, and BWM methods

Abstract

One of the most important and perilous groundwater contaminants is nitrate. The study area is the unconfined (free) aquifer of Karaj, located in central Iran, which is subject to quantity and quality hazards due to unbalanced urban, industrial, and agricultural developments. Evaluation of the vulnerability condition of this aquifer against nitrate as the contamination index is essential since the most consumed water in the area is provided by groundwater. This paper describes a new model that integrates vulnerability of aquifer obtained by DRASTIC + L model (V), extraction rate (E), head changes (H), aquifer media (A), and transmissivity (T), i.e., Modified VEBHAT model. The study aims to detect vulnerable zones of the unconfined aquifer of Karaj using DRASTIC + L and Modified VEBHAT vulnerability models. The weighting of the parameters has been performed employing the recent Multiple-Criteria Decision-Making (MCDM) methods, including Stepwise Weight Assessment Ratio Analysis (SWARA) and Best Worst Method (BWM). The results indicated that the highest levels of vulnerability occurred from the east to the south of the aquifer (high to super-critical), including urban and residential areas, regarding both of the vulnerability models’ plots. The plots of the two methods were similar and did not exhibit significant differences. In addition, the Modified VEBHAT had more certainty than the DRASTIC + L and has optimized and improved the DRASTIC + L model because the most vulnerable zone in the output plots of the Modified VEBHAT model was in the east of the aquifer, which had good agreement with the nitrate contaminant mass with the highest concentration.