Impacts of Nickel Mine Tailings Storage Facility on Surface and Groundwater Quality at Onverwacht Farm, Mpumalanga Province, South Africa

An unlined oxidised sulphide nickel mining tailings storage facility (TSF) at Onverwacht farm, Mpumalanga province, South Africa was constructed within an area underlain by fractured dolerite dykes aquifer. This is known to provide a preferential flow path for migration of toxic pollutants to deeper horizons and the surrounding environment. Subsequently, the possible deterioration of surface and groundwater quality was investigated. From May 2016 until January 2018, 168 water samples collected from supernatant water, boreholes and downstream surface water were analysed for ions and metals of potential concern using ICP-MS, which were then used to determine the impact of the TSF on water quality. Findings from the study indicated that the TSF was a source of pollution, which caused significant deterioration in the quality of groundwater and downstream surface water in the study area. The results revealed concentrations of SO4, Cl, Ca, Mg, Na, CaCO3 and EC in groundwater and downstream surface water exceeded acceptable numerical limits for drinking water in the Water Use Licence, South African National Standards, World Health Organization guidelines for drinking water quality and the background water quality data. Unlike other sulphide TSFs, the Onverwacht facility contained high concentrations of CaCO3 (maximum of 231 mg/L), which was the main distinction between the reduction and neutralisation of heavy metal concentrations, and the absence of acid mine drainage in the area. This study has shown that the geology of an area is a major consideration before siting a mining tailings storage facility in order to reduce possible environmental damages to the surrounding environment.