Impacts of Acid Mine Drainage on the Kromdraaispruit System

Abstract

The area of study, the Kromdraaispruit system, is located in the Mpumalanga Province of South Africa. The system consists of both a stream and a wetland, which are receiving environments of treated acid mine drainage emanating from the flooded underground coal workings. The mine management noted that, even after the water from the underground workings had passed through the liming plant, acidic seeps 200m downstream were polluting it. Sampling of the Kromdraaispruit system was done over a 12-month period. Different parameters including pH, EC, Total Dissolved Solids (TDS), Suspended Solids, Total Alkalinity (TAIK), Acidity, Chloride, Sulphate, Calcium, Magnesium, Sodium, Potassium, Iron, Manganese and Aluminium were analysed. The analysis revealed an acid mine drainage problem with maximum measured concentrations of >2000 mg/l S02, 15.84 mg/l Mn, 580.90 mg/l Ca, 49.14 mg/l Mg, 13.41 mg/l K and 98.25 mg/l Fe. The lowest pH in the region was pH 2.97 from the seeps around the liming plant area. Using different modelling packages like ILWIS and STASOFT, it was found that, compared to the acidic seep, the groundwater intercepting the stream at four points, one point along the liming plant stream and three in the wetland, did not have as big an impact on the concentration of some determinants like pH. In the Kromdraaispruit wetland, the wetland sediments act as a sink for contaminants, generally improving the quality of the water flowing through it. The concentration of some determinants passing through the wetland, such as SO, Mn, Ca, Mg, K and TDS, decreased. It was also noted that the efficiency of the wetland was greatly reduced by the high discharge of accumulated salts that simply flushed through it. In most cases, determinants like SO, Mn, AI, Ca, TDS, EC and pH decreased, but not to concentrations complying with the permissible levels stipulated by the Department of Water Affairs and Forestry. Due to the addition of lime downstream of the liming plant, a suspension of “yellow buoy” formed in the wetland. This decreased the potential of the wetland to reduce pollution. Soils were collected at different sites around the study area during the rainy and dry seasons. Laboratory analysis involved determination of total anions and cations, Sodium Adsorption Ratio (SAR), saturation, pH, electrical conductivity (EC) and the concentrations of Ca, Mg, K, Na, SO, F, CI, NO, NO and available PO. From the results obtained it was noted that the soils did not contribute to nor ameliorate acid mine drainage in the Kromdraaispruit system. This is because South Africa is an arid region and migration of ions in the soil to cause any significant impacts is slow. This study discusses the implications of these observations for the monitoring and management of the polluted system.