Hydrogeological Evaluation of Groundwater Vulnerability Assessment Using the DRASTIC and Pesticide DRASTIC Model: A Case Study from the Qushtapa and Shamamik Area, within Erbil Basin, Kurdistan Region, Iraq

Groundwater is a vital freshwater resource. Evaluating its vulnerability to contamination has emerged as a powerful tool for preventing and managing groundwater pollution. This study applied GIS-based standard DRASTIC and Pesticide DRASTIC models to the Qushtapa and Shamamik area to evaluate and delineate groundwater sensitivity zones. The DRASTIC index ranges from 74 to 130, while the Pesticide DRASTIC index ranges from 96 to 168. According to both methods, the examined area is classified into four classes: very low, low, moderate, and high vulnerability zones. The results show that the low vulnerability class for both models occupy the largest area, which is approximately 45.92% and 53.47% of the total area. Additionally, sensitivity analysis for a single parameter has shown that for DRASTIC, the vadose zone is the most effective impact parameter of the vulnerability index, while for Pesticide, the DRASTIC soil media parameter has the most impact on the vulnerability index. The models are validated with NO₃ concentration that ranges between 12-43 mg/l in Qushtapa area and 18-44 mg/l in Shamamik area. The findings show that Pesticide DRASTIC has a higher coefficient of determination R² of about 0.62 than DRASTIC, which is about 0.58, indicating that Pesticide DRASTIC is a more precise model for evaluating aquifer vulnerability in the study area.