Gold mining on the Witwatersrand started in the late nineteenth century as sporadic open-cast mining and ceased in the late twentieth century, leaving a complex network of haulage, tunnels and ultra-deep vertical shafts/sub-vertical shafts. At least three ore bodies (conglomeritic horizons) were mined down to a depth in excess of 3,000 m from the surface. Three large mining basins resulted from the mining methodology applied, namely the Western, Central and Eastern (Rand) Basins (van Wyk, 2013). This gold ore body was one of the largest in the world. The mines needed to be dewatered to safely mine and due to the geology of the area sinkholes formed, including the Wonderfonteinspruit stream.
In the 1960s, a pipeline was constructed to control the flow of the Wonderfonteinspruit stream across a dolomitic area in the West Wits mining region west of Johannesburg. The pipeline managed the water inundation and recharge into the underground mine workings, maintaining safe working conditions.
Recently, however, significant urbanization of the Upper Wonderfonteinspruit has increased the rate and volume of runoff into the stream, particularly during storms. These problems have been exacerbated by significant leaks from water systems, as well as the discharge of partially treated sewage from the Flip Human wastewater treatment plant, which previously transferred water into the Vaal River catchment but is no longer operational.
During the rainy seasons, flow into the pipeline has exceeded its capacity, and water overtops the attenuation dams. This not only expands the number and extent of sinkholes along the Wonderfonteinspruit watercourse, but also contributes to excessive ingress of water into the underlying mine workings, requiring expensive dewatering activities. Seepage from the attenuation dams poses further potential risks of sinkhole formation and system failure over time.
The Sibanye-Stillwater mine in the area has been actively investigating options to minimize the amount of discharge from the dams. Together with SRK, the mining company has conducted an option analysis of the ways to accommodate the additional flow so that it does not exceed the capacity of the attenuation dams.
SRK is undertaking a feasibility study to install a temporary pump station at the attenuation dams. This would increase the velocity of flow through the pipeline and control the water level accumulation in these dams during the rainy season.
Part of this study is the lining and engineering of the attenuation ponds to minimise discharge into the dolomitic areas.
