Surface impacts of gold mining activities on the Kromdraai/Koekemoerspruit : a situation analysis

Abstract

Six point sources of potential contamination from gold mine tailings were identified along the Kromdraai/Koekemoerspruit drainage basin. The degree of contamination of the tailings, soils, surface water, stream sediments and plants at each point source, as well as the individual contribution of these point sources to the contamination of downstream localities was determined by means of quantitative indices. These indices include availability percentage, threshold exceedance ratio, geoaccumulation index, bioaccumulation index and hyperaccumation threshold exceedance ratio. Both the total concentration pool as well as the available (soluble) fraction thereof were evaluated relative to pH and plant uptake, and as applicable to the sample type, by using the USEPA 3050b and DIN 19730 (NH4NO3) extraction methods, respectively. The results for the eight selected potentially toxic trace elements (Cr, Co, Ni, Cu, Pb, Zn, As and U) were further categorised under current and potential future contamination statuses and discussed according to a source-pathway-receptor model relative to individual localities. Composite sampling was employed to provide a representative average of each locality for an overall contamination profile of the study area. Plant species were classified according to accumulation degree and hyper-accumulation status in order to derive an indication of accumulation efficiency relative to the geochemical status of soils or tailings. A document was compiled in order to be used as a guideline for rehabilitation purposes specific to a geochemically-contaminated drainage system.