Integrated hydrogeological, hydrochemical and environmental isotope investigation of the area around the Kusile Power Station, Mpumalanga, South Africa

Abstract

This integrated hydrogeological, hydrochemical and environmental isotopes (δ2H, δ18O, 3H) study has been undertaken to investigate the hydrogeological conditions around the Kusile coal-fired power station located in Mpumalanga province of South Africa. The study area is characterized by mainly weathered and fractured and fractured secondary aquifer systems. Boreholes drilled in both aquifer systems have yields ranging from 0.1 to 2 L/s. The regional groundwater flow directions follow the topographic gradient. Hydrochemical analysis of water samples from 25 boreholes, 6 springs, and 19 surface water points show electrical conductivity (EC) values less than 700 μS/cm, pH values range from 5.2 to 9.6. The hydrochemical data shows six hydro-chemical facies with Mg–HCO3 as the most dominant facies indicating a shallow circulating less evolved recharge area groundwater. The results of the statistical multivariate factor analysis of hydrochemical data indicates three factors that explain the main ions’ contribution to water salinity (EC), some reducing conditions and carbonate buffering on the pH of the system, respectively. Environmental isotope data indicates that groundwater is recharged from local rainfall and the residence time of groundwater in the aquifer system is relatively short, ranging from 7 to 36 years. Similarity in isotopic signature between surface water and groundwater samples indicate groundwater - surface water interactions. The results of high sulphate concentration in some groundwater and surface water samples indicates that the coal mining activities taking place within the catchment and the coal-fired Power plant operations have impacted the water resources. However, due to natural carbonate buffering reactions, the pH of the high sulphate groundwater and surface water is neutral to alkaline and the EC is moderately low.