Investigation of the groundwater hydrogeochemistry chracteristics in Beaufort West, South Africa
English: 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.
Afrikaans: Hierdie studie is uitgevoer om die hidrochemiese prosesse te ondersoek wat die evolusie van chemiese prosesse in grondwater beheer, en om die invloed daarvan op die kwaliteit van water in Beaufort-Wes te ondersoek. Beaufort-Wes is geleë in 'n dor en droë deel van Suid-Afrika en dus is grondwater 'n belangrike bron van water vir die dorp. Die studie is gedoen om die kwaliteit van die grondwater te evalueer om die geskiktheid van die grondwater vir huishoudelike en landbougebruike te bepaal. 'n Grondwatersteekproefneming is oor drie seisoene (lente, somer en herfs) gedoen. Twintig monsters is ingesamel vir beide die lente- en somerseisoene, terwyl twaalf monsters vir die herfsseisoen ingesamel is. Identifisering van die hidrochemiese prosesse wat die evolusie van die gehalte van grondwater en chemie beheer, is gedoen met behulp van verskeie aanvullende instrumente, naamlik klassifikasie van die belangrikste watertipes, evaluering van water:rots-interaksie deur middel van stoïgiometrie-ontleding en tweeveranderlike korrelasie ‘plots’, omgekeerde geochemiese modellering en statistiese ontleding (hiërargiese ‘cluster’-analise en hoofkomponent-analise). Die hooftipes water wat in die gebied gevind is, is kalsiumbikarbonaat, natriumchloried en gemengde water. Soortgelyke hidrochemiese prosesse is vir die verskillende seisoene in die grondwaterstelsel gevind. Sekere prosesse oorheers spesifieke gebiede, terwyl ander lukraak op verskillende gebiede gebeur. Die belangrikste hidrochemiese prosesse wat uit die grondwaterchemie en gehalte afgelei kon word, is ioonuitruiling, omgekeerde ioonuitruiling, silikaatverwering, karbonaatontbinding, gipsontbinding, en tot 'n mate verdamping. Ander prosesse wat plaasgevind het, al was dit nie dominant nie, is ontbinding van haliet en silvite. Antropogeniese bronne wat nitraat en ammoniak in die grondwater vrystel, is geïdentifiseer as bydraende faktore wat 'n negatiewe impak op die gehalte van grondwater het. Assessering van die grondwatergehalte het getoon dat die water geskik is vir besproeiingsdoeleindes, hoewel sommige van die watermonsters slegs gebruik behoort te word op gewasse wat minder sensitief is vir soutladings. Nie al die monsters is aanbeveel vir drinkwater nie. Slegs watermonsters wat hidrochemiese eienskappe van onlangse herlaaide water getoon het, is as geskik beskou vir drinkwater. Aan die ander kant, al die monsters was geskik vir gebruik deur vee. Die berekende totale hardheid het getoon dat die water in hierdie gebied hard tot baie hard was. Die bevindinge van hierdie studie het aangedui hoe belangrik hidrochemiese prosesse in die verandering van die waterchemie en gehalte van goed na swak langs die vloeipaaie is. Die studie het ook die waarde van die gebruik van verskillende assesseringsinstrumente beklemtoon wat gebruik kan word as aanvullende tegnieke om die begrip van hidrochemiese prosesse te verbeter, en die invloed daarvan op die evolusie van grondwaterchemie en kwaliteit.