Investigating the possibility of targeting major dolerite intrusives to supplement municipal water supply in Bloemfontein: a geophysical approach

Abstract

The city of Bloemfontein is currently relying on surface water sources for its potable water supply. However, Bloemfontein is located in a semi-arid area, which means that the surface water resources are unreliable and susceptible to droughts. In addition, the water demand in the city has increased significantly during recent years due to population increases, agricultural growth and industrial development. It is expected that the surface water resources will soon not be adequate to meet the increasing water demand. This study investigated the possibility of using groundwater resources associated with a major dolerite intrusive to supplement the water supply to the Mangaung Metropolitan Municipality in which the city of Bloemfontein is located. As part of the investigations, geophysical surveys were conducted to detect and delineate a prominent dolerite structure in an area south of the Bloemfontein CBD. The results of the geophysical investigations were used to determine the geometry of the structure and to suggest positions for the installation of boreholes. Due to funding problems, no boreholes could be drilled as part of the current investigations. The groundwater quality and aquifer parameters could therefore not be investigated directly. A limited hydrocensus was therefore conducted to investigate the geohydrological conditions in the vicinity of another prominent dolerite intrusion known to occur with the city limits. The groundwater conditions at boreholes occurring near this intrusion were investigated and considered to be representative of the conditions at the dolerite structure targeted during the current investigations. Although no final conclusions can at present be drawn on the possibility of using the groundwater associated with the dolerite structure to augment the municipal water supply, indications are that the aquifer system is high-yielding and the groundwater is expected to be of a good quality. Since the current investigation was severely limited due to the fact that no boreholes could be drilled on the targeted structure, recommendations for future actions were made. These recommendations include a) the installation of boreholes at the positions suggested by the results of the geophysical survey, b) groundwater sampling and chemical analyses to determine the groundwater quality, c) hydraulic testing of the aquifer system to determine a sustainable yield, and d) the development of a monitoring programme to detect changes in the groundwater conditions that may indicate either over-exploitation or contaminant impacts.