Groundwater vulnerability assessment using the GALDIT model and the improved DRASTIC model: a case in Weibei Plain,...

This study employed a modified DRASTIC model (AHP-DRASTIC model) and GALDIT model to evaluate the inherent vulnerability of shallow groundwater in Weibei Plain in Shandong Province of China and its vulnerability to seawater intrusion. The AHP-DRASTIC model uses the analytic hierarchy process (AHP) to determine the weight of each parameter and reduces the subjectivity of evaluation. The vulnerability map generated by the AHP-DRASTIC model shows four types of vulnerability: high (25.0%), higher (28.0%), moderate (29.7%), and low (17.3%), and the high-vulnerability areas are mainly distributed in the area north of Qingxiang Town and south of Changyi County. The distribution of high-vulnerability areas mainly related to the depth of groundwater table is 4-8 m, and the recharge of rainfall is 100-175 mm/year. The vulnerability map generated by the GALDIT model shows four types of vulnerability: high (33.5%), higher (23.4%), moderate (22.1%), and low (21.0%), and the high-vulnerability areas are mainly distributed in the coastal areas of Hanting District-Zhuli Town, the areas north of Linqu County, and the areas south of Shouguang County. The distribution of high-vulnerability areas mainly related to the distance between these areas and the coast is < 2.5 km, with aquifer thickness > 15 m. Total dissolved solid, NO₃^-, Cl^-, and SO₄^2- are used to verify the accuracy of the DRASTIC model, the AHP-DRASTIC model, and the GALDIT model. The results show that the AHP-DRASTIC model is more suitable for the assessment of inherent vulnerability of shallow groundwater in the study area than the DRASTIC model, and human activities have a major impact on the verification of vulnerability and should be considered when conducting groundwater vulnerability verification. The results of this study can provide grounds for groundwater management and protection and land use planning in the study area and provide new ideas for groundwater vulnerability assessment in coastal areas.