Assessment of quaternary aquifer pollution sensitivity using modified DRASTIC models around stressed Canal in Eastern Nile delta, Egypt

Groundwater is generally less prone to contamination than surface water; however, pollutant infiltration can occur due to aquifer characteristics and anthropogenic land use (LU) changes. This study presents the first DRASTIC-based groundwater contamination risk (GwCR) framework for stressed aquifers around the Ismailia Canal, a newly developed artificial canal in Egypt. It evaluates the standard DRASTIC, Pesticide DRASTIC, DRASTIC-Lu, and Pesticide DRASTIC-Lu models, along with their modified versions, using Single Parameter Sensitivity Analysis (SPSA) and GIS techniques. SPSA identified the following parameter weights for the pesticide-specific DRASTIC model: D > S > T > A > I > C > R. One- Map Removal Sensitivity Analysis (MRSA) analysis showed the Pesticide DRASTIC model was most sensitive to net recharge (1.36%) and soil media (1.0%), with moderate sensitivity to the vadose zone (0.65%), topography (0.45%), and hydraulic conductivity (0.42%). Excluding key parameters, particularly D, A, and S, caused significant variability, impacting vulnerability assessments. The Pesticide DRASTIC_SPSA model outperformed others, with 82.6% of groundwater samples, along with relative frequency greater than 0.8 in moderate to very high vulnerability zones. The Pesticide DRASTIC_SPSA map indicated that 36.21 km², 6.26 km², 19.03 km², 31.0 km², and 13.09 km² of the study area were in very high, high, moderate, low, and very low susceptibility zones, respectively. The high and very high vulnerability zones were primarily located in the northern and southern regions of the Ismailia Canal, where the protective clay layer is absent and shallow groundwater and sandy vadose zones prevail. The very high vulnerability area increased from 27.3 km² in the original DRASTIC model to 30.52 km² under the Pesticide DRASTIC_SPSA model. These findings apply to other regions with similar hydrogeological and socio-economic conditions, offering insights for future freshwater canal system development in Egypt.