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University of the Free State (2017)

Investigation of the groundwater hydrogeochemistry chracteristics in Beaufort West, South Africa

Ligavha-Mbelengwa, Lufuno

Titre : Investigation of the groundwater hydrogeochemistry chracteristics in Beaufort West, South Africa

Auteur : Ligavha-Mbelengwa, Lufuno

Université de soutenance : University of the Free State

Grade : Master of Science (Geohydrology) 2017

Résumé
This study was conducted to investigate hydrogeochemical processes controlling the evolution of groundwater chemistry and their influence on water quality in the Beaufort West town. Beaufort West is located in a dry and arid part of South Africa and thus groundwater is an important source of water for the town. The study further assessed the quality of the groundwater to determine its suitability for domestic and agricultural uses. Groundwater sampling was done for three seasons (spring, summer and autumn). Twenty samples were collected for both spring and summer seasons, whereas twelve samples were collected for autumn. Identification of the hydrogeochemical processes controlling the evolution of the groundwater quality and chemistry was done using various complementary tools. These tools are : 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 principal component analysis). The main water types that were found at the area are calcium bicarbonate, sodium chloride and mixed water. Similar hydrogeochemical processes were found to be occurring in the groundwater system for different seasons. However, certain processes were dominating specific areas, whereas others were happening randomly at different areas. The main hydrogeochemical processes that were inferred to be influencing the groundwater chemistry and quality are ion exchange, reverse ion exchange, silicate weathering, carbonate dissolution, gypsum dissolution, and to some extent evaporation. Other processes that took place though were not dominant, are dissolution of halite and sylvite. Anthropogenic sources releasing nitrate and ammonia to the groundwater were also identified to play a role in negatively impacting the groundwater quality. Assessment of the groundwater quality showed that the water is suitable for irrigation purposes, although some of the water samples should be used only to crops less sensitive to salt load. Furthermore, not all the samples were recommended for drinking water. Only water samples that showed hydrogeochemical characteristics of recent recharge were suitable for drinking. Conversely, all the samples were suitable for use by livestock. The calculated total hardness showed that the water at this area was hard to very hard. The findings of this study indicated the importance of hydrogeochemical processes in changing the water chemistry and quality from good to poor along the flow paths. The study also demonstrated the value of utilising various assessment tools as complementary techniques to improve the understanding of hydrogeochemical processes, and its influence on evolution of groundwater chemistry and quality.

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