Hydrogeological study of the Glencoe Corobrik Factory Site, KwaZulu-Natal Province, South Africa

Abstract

Hydrogeological conditions at the Glencoe Corobrik Factory, KwaZulu-Natal, South Africa, are investigated in this study. The general geology of the area is made up of the Ecca Group metasedimentary sequence of the Karoo Supergroup. A hydrogeological conceptual site model is developed based on the data acquired during the study. The methods of data collection involved borehole drilling and logging, aquifer tests, water sampling and analyses. Aquifer tests were conducted using a slug test method on two newly drilled boreholes for this research. The calculated hydraulic conductivity and transmissivity values are 0.014 m/day and 0.033 m/day, 0.44 m2 /day and 1.19 m2 /day for BH01 and BH02, respectively. The underlying rocks are sandstones and siltstones of the Vryhied Formation that constitute the main lithology for the aquifer in the area. Dolerite dykes may be interfingered with the sandstones at depth, creating a flow barrier and conduit in some places. The weathered aquifer is made up of the upper sequence sandstones, while the dolerite emplacement presents a secondary fractured aquifer. Groundwater chemistry is dominated by two water types; Ca2+ - HCO3 - and Na+ - HCO3 - . The Durov diagram points to ion exchange processes where Ca2+ is exchanged for Na+ . The groundwater chemistry is influenced by weathering processes (silicates). The study revealed human activities have a low influence on the groundwater chemistry in the area. The Ca2+ and Mg2+ vs SO4 2- plots provided crucial evidence that the groundwater has not been influenced by acid mine drainage even though the area was previously dominated by coal mining activity. Surface water chemistry is represented by Ca2+ - HCO3 - water type with Mg2+ - SO4 2- and Na+ - HCO3 - also occurring as minor water types. Most samples are clustered towards the region of Mg2+ - SO4 2- , indicating a possible influence of sulphates that may be derived from the old mine dumps on the surface. Based on the current hydrochemical data, groundwater and surface water have distinct geochemical compositions, which implies that contaminants emanated from surface processes have less influence on the deep groundwater system. Results from the stable isotopes also support the hydrochemical results suggesting a very minimal link between the groundwater and surface water based on the current sampling. Groundwater samples were recharged directly from rainfall prior to evaporation, while surface water samples show an evaporation effect. Surface water samples showed an evaporation effect with an evaporation equation of δD = 4.31 δ18O+7‰ with a R 2 value of 0.98.