Assessment of groundwater vulnerability using the DRASTIC model: A case study of Quaternary catchment A21C, Limpopo River Basin, South Africa

Groundwater is a vital resource for domestic, agricultural, industrial activities and ecosystem services. Despite its multiple purposes, the resource is under significant threat owing to increasing contamination from anthropogenic activities and climate change. Hence, in order to ensure the reliability and sustainable use of groundwater for the present and future generations, effective management of groundwater (quality and quantity) is highly important. This can be achieved by identifying areas more vulnerable to contamination and implementing protective measures. The present study aims at assessing the vulnerability of groundwater using GIS-based DRASTIC index in the Quaternary catchment (A21C) within Limpopo River Basin. The vulnerability index varied from 87 to 207. About 53.6% (408 km²) of the catchment area also exhibited high risk of groundwater contamination mostly in central, north-eastern and western part of the sub-catchment. The medium and low vulnerability classes cover only 18.1% (137.5 km²) and 21.7% (165.1 km²) of the study area, respectively. The shallow groundwater at the Doornfontein Campus belongs to very high vulnerability area. The sensitivity analysis indicates that depth to water level, recharge, aquifer media, soil and topography are the important contributors to vulnerability assessment. The correlation analysis performed to validate the final vulnerability map shows a moderate positive correlation, indicating the model’s applicability to the urbanised environment. The study indicates an area that is highly vulnerable to pollution, and hence protective measures are necessary for sustainable management of the groundwater resource in the study area. The result of this study can also be further improved and verified by using other vulnerability assessment models.