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Geochemical modelling of groundwater in the Namaqualand region, South Africa

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Namaqualand is one of the aridest areas in South Africa. In recent years, rapid development has created a higher demand for water which is increasingly fulfilled by groundwater abstraction. Comprehensive information of geochemical evolution of groundwater quality can improve the understanding of hydrochemical characteristics, and promote sustainable development and effective management of groundwater resources. The study aims were to use PHREEQC model to determine hydrogeochemical characteristics of groundwater, to determine how groundwater has deteriorated of time and to identify the major phases that control groundwater in such arid region. The model output showed phases that are governing the groundwater chemistry in this area. The geochemical reactions responsible for the evolution of groundwater chemistry along the flow path were the dissolution of the carbonate minerals such as aragonite, Ca3(PO4)2, calcite dolomite, ferrihydrite and vaterite keep gradually from undersaturation to supersaturating status and vice versa happed for Cd(CO3), Cr(OH)3. The precipitation of anapaite, chloroapatite, chromite, Cr2O3Fe5(OH)(PO4)3, ferryhydrite, goethite, hematite, hydroxyapatite, lepidocrocite, maghemite, magnetite. In contrast, magnesite changed from undersaturated to equilibrium phase. The SI of gypsum, siderite and halite remained undersaturated, indicating that these minerals may be subject to continuous dissolution. Groundwater hydrogeochemical evolution is mainly controlled by carbonate mineral dissolutions, cation exchange, precipitation and weathering.