Assessment of Groundwater Vulnerability in Dili City, Timor-Leste Using an Improved DRASTIC and Analytic Hierarchy Process (AHP) Method: Implications for Wastewater Management

Groundwater resources are critical in sustaining rapidly growing coastal urban regions like Dili City, Timor-Leste, where aquifers are prone to contamination. To inform groundwater pollution prevention and control in the Quaternary intergranular aquifer, a GIS-based groundwater vulnerability assessment was carried out using DRASTIC, modified DRASTIC, and modified DRASTIC–AHP methodologies. It confirmed that the central to northern urban area was the most vulnerable, while the southern part was the least vulnerable to contamination. Model performance was validated by correlating vulnerability indices with measured groundwater quality parameters, showing that the modified DRASTIC–AHP was the most accurate. The areas classified as having very low, low, moderate, high and very high vulnerability were 23.1%, 23.1%, 20.6%, 12.8%, and 19.2%, respectively, with high vulnerability along the northern coastline and Comoro River alluvial channel. Sensitivity analysis supports model robustness and identifies recharge, aquifer media, and hydraulic conductivity as the dominant controlling factors. The integrated modeling and sensitivity framework provides an efficient basis for prioritizing protection measures and infrastructure upgrades (e.g., sewerage) to reduce contamination risks. A key management implication is that centralized wastewater management is preferable to current practices for mitigating ongoing groundwater degradation.