Integrated Hydrogeological, Hydrochemical And Environmental Isotope Investigation Of The Area Around The Kusile Power Station, Mpumalanga, South Africa

Industrial areas are major sources of surface and groundwater pollution. As a result, constant monitoring of water quality is of vital importance to detect pollution incidences in time and to take corrective actions. This integrated hydrogeological, hydrochemical and environmental isotopes (?2H, ?18O, 3H) study has been undertaken to investigate the hydrogeological conditions around the Kusile coal-fired power station located in the quaternary catchment B20F. The study area is characterized by mainly weathered and fractured and fractured aquifer systems. The weathered and fractured aquifers are made up of the Ecca Group shale lithologies, with weathering depths ranging between 5 and 12 m below ground surface (b.g.l.), while the fractured aquifer system is made up of the Pretoria Group quartzites, chert and shale units. Both aquifer systems have borehole yields ranging from 0.1 to 2 L/s. The depth to groundwater ranges from few cms to 22.7 m, with an average depth of 7.6 m b.g.l. Regional groundwater flow direction is from south-east to north-west, following the topographic gradient. The hydrochemical analysis from 25 boreholes, 6 springs, and 19 surface water points show electrical conductivity (EC) values less than 70 mS/m, pH values in the range from 5.2 to 9.6. High concentrations of Fe, Mn and Zn were measured in some samples that have high turbidity (> 5 NTU). The hydrochemical data shows six hydro-chemical facies with Mg-HCO3 as the most dominant indicating a shallow circulating less evolved recharge area groundwater. Multivariate statistical methods in the form of factor and cluster analyses were applied in the analyses of the hydrochemical data collected. The results of Factor analysis indicated three factors which explained 81.5% of the total variance in the hydrochemical data. The first factor is characterised by strong loadings of EC, Mg, SO42-, Ca, and Cl which could explain the contribution of the major ions to the salinity. The second factor has high positive loadings of Fe, turbidity, and a strong negative loading of dissolved oxygen indicating reducing conditions. Factor three shows high positive loadings of HCO3-, pH and Na, where the positive correlation of HCO3- and pH shows carbonate buffering on the pH of the system. The Hierarchial Cluster Analysis subdivided the samples into two clusters and two sub-clusters. Cluster 1 is dominated by surface water samples which are characterised by elevated concentration of HCO3-, turbidity, and SO42-. The second cluster has two sub-clusters. Cluster C-2-1 is characterised by lower Cl and K concentrations while cluster C-2-2 contains boreholes which are dominated by Mg-HCO3 water type. Environmental isotope data indicates that groundwater recharge is from a mixture between sub-modern and recent precipitation. Four surface water samples along a stream line show a similar isotopic signature as the groundwater samples indicative of an interaction between the groundwater and surface water. The preliminary results of the inorganic hydrochemical data doesn't indicate pollution from the Kusile coal-fired Power Station.