| dc.description.abstract | This study was conducted to investigate hydrogeochemical processes controlling the evolution of groundwater chemistry and their influence on water quality in the Heuningnes Catchment. The role or influence of hydrogeochemical processes in groundwater quality in aquifer systems remains poorly understood. One of the ways of improving such understanding is to employ different techniques to explore key processes that govern groundwater quality in aquifer systems. Therefore, the present study investigated hydrogeochemical processes of groundwater resources and identified key processes that explained its quality from a spatiotemporal perspective. The quantitative approach that provides the ability to assess relationships between variables both spatially and temporally was applied. Groundwater sampling was done on four occasions during July 2017, October 2017, March 2018, and July 2018. Identification of hydrogeochemical processes controlling the evolution of groundwater chemistry and quality was done using various complementary tools. These tools included classification of the main water types, evaluation of water-rock interaction by means of stoichiometry analysis and bivariate correlation plots, inverse geochemical modelling, and statistical analysis (hierarchical cluster analysis and factor analysis). Physical parameters were measured in situ, while water samples were collected from boreholes, piezometers, springs, and artesian boreholes for laboratory analysis for major ions analysis. Descriptive and bivariate statistical methods were used to summarise and evaluate the strength of the relationship between variables, while multivariate statistical methods were applied to group similar samples based on their chemical compositions. Tri linear Piper diagrams were generated to characterize water type based on double normalizing the proportions of cations and anions, while correlation and stoichiometric analysis were applied to identify hydrogeochemical processes influencing groundwater chemistry. The results generated from the trilinear Piper diagrams confirmed the dominance of sodium and chloride ions in waters of the Heuningnes Catchment. Groundwater of a Na/Cl type is typical for a coastal aquifer characterised by saline, deep ancient groundwater. The lower parts of the Catchment were characterised by saline groundwater. The results indicated that shallow groundwater samples within the study area were more mineralised as compared to deep groundwater with EC values ranging between 20.8 and 2990 mS/m, with waters within the Table Mountain Group region (TMG), recording the lowest values. Deep groundwater for boreholes and artesian boreholes located upstream in the Catchment was fresh and yielded some of the lowest EC values recorded with an EC value below 50 mS/m. Generally, EC values increased from the upper TMG region of the Catchment towards the Bokkeveld shale region downstream and were highest during the dry season of 2018. The results indicated strong geological influences on water chemistry. Bivariate correlation and stoichiometric analysis identified cation exchange, adsorption, evaporation, weathering of carbonates, sulphates and silicate minerals as processes influencing the chemistry of groundwater in the Heuningnes Catchment. The Saturation Index (SI) results showed a change of calcite, dolomite, aragonite, gypsum, anhydrite, halite, melantinterite, siderite and sylvite from being undersaturated to oversaturated at some areas for the different seasons along the flow path. The mass-balance modelling results indicated that ion exchange and reverse ion exchange processes were more dominant at low elevations along the same flow path during the dry periods. However, at high elevations along the flow path, silicate weathering was the dominant process taking place. The findings of this study demonstrated the influence of hydrogeochemical processes in changing the water chemistry along the flow paths. In conclusion, the study showed the value of utilising various assessment tools as complementary techniques to improve the understanding about hydrogeochemical processes, and its influence on evolution of groundwater chemistry and quality. Based on the findings of the study the following recommendations were made for future studies; the sample points or sample boreholes in the study Catchment should be increased; and to have more sampling trips to enable better comparison between the possible processes | en_US |
