Risk Intensity Mapping of Complex Aquifer Systems Using the Phosphate-Drastic Model: Insights From the Penjween Basin, NE, Iraq

Groundwater contamination from human activities is a significant concern for sustainable water resource management, particularly in Mediterranean climates such as the Penjween Basin (PB). Effective management requires comprehensive risk assessments, including hazard and vulnerability mapping. This study presents a novel approach by using phosphate (PO4⁻3) concentrations rather than nitrate (NO3-) to validate groundwater vulnerability assessments, providing a new perspective for contamination risk studies. Adhering to the European COST Action 620 guidelines, the methodology integrates hazard and vulnerability mapping with the PO4-3-DRASTIC model. Both standard and pesticide DRASTIC indices were employed to analyze vulnerability and determine the more reliable method for constructing a risk intensity map tailored to the region’s complex aquifer system. The standard DRASTIC index categorized groundwater pollution vulnerability into four classes: Very low (23.2%), Low (47.7%), Moderate, and High. The pesticide DRASTIC index (88 - 207) identified five classes: Very low, Low, Moderate (39.9%), High (33.9%), and very high. Validation with phosphate concentrations from 40 groundwater sources (ranging from 0.01 to 4.86 mg/l, with 70% exceeding the Iraqi guideline of 0.4 mg/l) indicated that the pesticide DRASTIC model provided a more accurate representation of groundwater vulnerability in this region. The highest-risk areas, located in the southwestern region (Braim Awa Plain, Penjween Town) and along stream banks, are characterized by intergranular aquifers, intensive agricultural practices, and urban development. This study's novelty lies in the use of PO4³⁻ as a validation parameter and the comparative analysis of standard and pesticide DRASTIC models to address complex hydrogeological conditions. The findings emphasize the importance of targeted management strategies, including restrictions on agrochemical use in high-vulnerability zones. Future research should focus on dynamic evaluation methods, improved monitoring systems, and sustainable agrochemical management to ensure long-term groundwater protection in regions with similar aquifer systems.