Groundwater vulnerability assessment using a GIS-based modified DRASTIC model: the case of the Borkena Subbasin, Awash River, Ethiopia

A crucial initial phase toward ensuring the sustainability of groundwater resources is the assessment of groundwater vulnerability. Therefore, this study aims to evaluate groundwater vulnerability through generic and modified DRAS-TIC approaches using the Geographic Information System (GIS) in the Borkena sub-basin, Awash River, Ethiopia. In this study, the standard DRASTIC model was improved through rating and weight modifications of the parameters and application of additional parameters, land use/land cover (LULC), and geological lineament density. The nitrate concentration was used in this study to validate the models’ accuracy. The correlation analysis between the nitrate concentration and the standard/modified DRASTIC models revealed that the most promising result (R² = 0.76) was obtained when weight and rate modification were combined. According to the weight and rate-based modified DRASTIC Index, the study area was separated into very high, high, moderate, low, and very low susceptibility zones for groundwater pollution, with corresponding area coverage of 10.1% (165.8 km²), 22.6% (370 km²), 40% (654.7 km²), 22.9% (375.4 km²), and 5% (82.3 km²), respectively. The single-parameter sensitivity analysis indicated that the following DRASTC parameters, in order of significance, influence groundwater vulnerability in the Borkena subbasin: aquifer media, depth to the groundwater table, and net recharge, whereas hydraulic conductivity was least influential. These findings empower stakeholders to implement appropriate management practices for the protection of vital water resources and for policymakers to apprise sustainable and sound policies.