Die hidrologie van karstgebiede met spesiale verwysing na grondwaterbesoedeling suid van Pretoria

Abstract

Karst aquifers frequently consist of large interconnected solution cavities and fracture zones in the bedrock or as highly leached residual materials. The high recharge rate, permeability and storativity of these aquifers permit rapid penetration and spreading of pollutants. In South-Africa, a large portion of the highly populated Pretoria-Witwatersrand-Vereening area, as well as several other towns are located on these dolomite rocks and increasingly more people are depending on groundwater as the only or supplementary source of water. Recent studies have indicated that serious pollution of these waters has already taken place at various localities. The effect of overburden materials on the vulnerability of dolomite aquifers has not yet received much attention. This research project has thus been undertaken to accumulate not only general information concerning the hydrogeological properties of the karst aquifers, but also, to determine the influence of the geotechnical and geohydrological properties of the aquifer and the unsaturated zone in a specific dolomite area in the Transvaal. The chosen study areas are located south of Pretoria, between Olifantsfontein and Irene where the Kaalspruit is being influenced and polluted by surface run-off from an informal housing area, a sewerage treatment plant, a refuse dumping site and agricultural holdings. Overburden material in the study area comprises mainly of gravelly sand with small amounts of clay and is moderately to highly permeable. The dolomite itself is impermeable, but water can flow freely through open solution cavities. The general quality of the groundwater in the area is good, but adjacent to the pollution sources, within a radius of 30 metres, highly polluted water (bacteriological, nitrate, TDS) occur. It has been proven that karst aquifers are extremely sensitive to pollution. It is thus recommended that development in dolomite areas be strictly managed to ensure that no further deterioration of this important water source, takes place.