The South African mining sector is a critical pillar and driver of the South African economy. However, mining activities are also associated with environmental contamination such as acid mine drainage.
View of the defunct West Wits opencast mine workings outside Krugersdorp showing erosion gullies
Acid mine drainage is highly acidic water, usually containing high concentrations of metals, sulphides and salts as a consequence of mining activity. Drainage from abandoned underground mine shafts into surface water systems (decant) may occur as the mine shafts fill with water. Although the chemistry of acid mine drainage generation is straightforward, the final product is a function of the geology of the mining region, presence of micro-organisms, temperature and also of the availability of water and oxygen. These factors are highly variable from one region to another, and, for this reason, the prediction, prevention, containment and treatment of acid mine drainage must be considered carefully and with great specificity.
In one project, CSIR geohydrologists are keeping a close eye on the impact of acid mine drainage on surface water and groundwater resources in the Cradle of Humankind World Heritage Site.
The Western Basin outside Krugersdorp started decanting in late January this year - partly-treated and raw mine water discharges into the Tweelopie Spruit, which then flows through the reserve and beyond, where it enters the dolomitic Zwartkrans Compartment and the southern portion of the Cradle of Humankind. Apart from mine water, the area is also impacted by municipal wastewater effluent.
Tasked by the Cradle's Management Authority, the CSIR leads a joint venture to establish a comprehensive surface and groundwater monitoring programme for the area. The study includes the development of a sound conceptual model of the groundwater regime in terms of flow directions, boundary conditions and water quality aspects based on historical information, long-term monitoring data and new data and information. It is also developing a better understanding of the close relationship and interaction between groundwater and surface waters in the largely dolomitic environment. This is crucial for the implementation of a relevant and effective water resource monitoring programme. The study is also assessing the risk posed to the numerous UNESCO-inscribed fossil sites, such as Sterkfontein and Zwartkrans, by changes in the quality of surface water and groundwater.
The Cradle of Humankind is one of seven World Heritage Sites in South Africa, and the only one in Gauteng.