Investigation of factors influencing groundwater quality in a typical Karoo aquifer in Beaufort West town of South Africa

The study investigates factors that influence the evolution of groundwater chemistry and groundwater quality in a typical Karoo aquifer in South Africa. Groundwater samples were collected from production and monitoring boreholes during spring, summer and autumn seasons. The samples were analysed for inorganic chemistry species. Bivariate plots, stoichiometric analysis and principal component analysis were used as complimentary tools to identify and describe main factors that control the evolution of groundwater chemistry and quality. Groundwater quality was assessed to determine its suitability for domestic and irrigation uses. Three main hydrochemical facies were identified in all seasons; Ca-HCO3, Na-SO4 and mixed water types. The Ca-HCO3 facie evolves from the hydrogeochemical process of calcite dissolution by weak rain carbonic acid and is associated with recently recharged groundwater at higher elevations. The Na in the Na-SO4 facie evolves through cation exchange between calcium and sodium while gypsum dissolution accounts for SO4. Principal component analysis suggests that there is an influence of anthropogenic activities mineralising the groundwater resulting in saline water at lower elevation which negatively affects the groundwater quality. The Ca-HCO3 facie that dominated groundwater at higher elevation is fresher and therefore suitable for both irrigation and domestic uses. The study highlighted the value of using hydrochemical facies, bivariate correlation plots and principal component analysis as complimentary tools to understand hydrogeochemical processes and their influence on groundwater quality.