Assessing groundwater vulnerability in the intermountain plains of Metro Hilir watershed Malang

Groundwater vulnerability assessment is crucial, particularly in developing regions. The Metro Hilir Watershed is located in an intermountain plain area dominated by rural agricultural land. The purpose of this study is to identify, map, and analyze the vulnerability of groundwater to pollution through the DRASTIC Landuse Model in the Metro Hilir watershed. The DRASTIC Landuse model was employed, a highly suitable approach for groundwater vulnerability assessment. Surveys on shallow dug wells were conducted to obtain depth to water table information, and well water samples were collected to determine Nitrate levels. Geoelectric tests were also used to gather aquifer information and hydraulic conductivity. Secondary data was utilized to acquire rainfall, soil media, and topography information. Google Earth Engine analysis was employed to obtain 2024 Landuse data. The DRASTIC Landuse analysis was classified to determine groundwater vulnerability classes for the aquifer. Results indicate that 91.63% of the study area falls within the moderate to high vulnerability class. Moderate vulnerability classes are distributed in the eastern and southwestern parts, while high classes are located from the northwest extending to the southern area of the study region. Model validation was conducted using water quality parameters, specifically Nitrate, and the model was deemed valid. Sensitivity analysis revealed that the Hydraulic Conductivity and Impact on the Vadose Zone parameters show sensitivity to input changes and have a substantial impact on vulnerability. The findings of this research can inform decision-making processes for groundwater quality management in the Metro Hilir Watershed.