A GIS-based DRASTIC approach to assessing aquifer vulnerability adapted for intrinsic risks posed by differing land uses (Rustenburg Municipality)

Abstract

Groundwater resources play a vital role in the sustainability of a vast majority of communities world-wide. Various anthropogenic activities (particularly related to agriculture, mining, and other diffuse and point sources of contamination), however, pose a significant threat to the quality of groundwater resources. Once contaminants reach the aquifer, the mitigation thereof becomes expensive and often not readily possible. A proactive approach to the assessment of aquifer vulnerability to contamination, rather than a reactive approach, is thus of utmost importance for the future sustainability of our groundwater resources. This dissertation deals with the assessment of aquifer vulnerability in the Rustenburg Municipality, South Africa. The assessment of aquifer vulnerability is conducted using a well-known vulnerability index called DRASTIC within a geographical information system (GIS) environment. DRASTIC is an acronym for a set of parameters that characterize the hydrogeological setting and combined evaluated aquifer vulnerability; viz.: Depth to water level, Nett Recharge, Aquifer media, Soil media, Topography, Impact of the vadose zone, and Hydraulic Conductivity. An additional objective is to adapt the current DRASTIC model to account for the potential influence of land surface uses on groundwater resources through the incorporation of land use as a vulnerability factor. The final vulnerability map shows that the highest vulnerability aquifer rating fell within the range of moderately high vulnerable (7-8) and the addition of the land use variable did not change the highest vulnerability rating. The spatial distribution of the moderately high vulnerable areas, however, was found to vary significantly with incorporation of the land use parameter. GIS proved great compatibility with an aquifer vulnerability model such as DRASTIC.