Groundwater is the most precious and irreplaceable natural resource, and understanding ground water quality is of paramount importance for effective groundwater management. Change in the groundwater chemistry due to mining, anthropogenic sources and farming may change the quality and suitability of groundwater
The study area is located in the Northern Cape Province, South Africa, and is underlain by Proterozoic rocks of the Namaqua-Natal Metamorphic Province, also referred to as the Namaqua Sector. The rocks in the Namaqua Province comprise a variety of metamorphic rocks, and different types of schists as well as Cenozoic sediments. The area is a typical semi-arid area with mountainous areas receiving higher rainfall than the arid lowland due to orographic effects. Some granitic rocks as well as surficial sediments in the Namaqualand contain high uranium values.
Exploration of surficial uranium deposits in the Namaqualand region began in the early 1970s, and then in the mid-1970s there was a discovery of surficial and granitic uranium occurrences which resulted in major exploration. Many studies in the area have been conducted on the quality of groundwater and its impact on human health but there are no studies related to the high uranium values in the groundwater of Namaqualand.
This study aims to evaluate the water quality in Namaqualand region and, subsequently, use the groundwater chemistry to delineated potential areas for surficial uranium deposits. Fieldwork was done in July 2017 and a total of 85 water samples were collected from existing boreholes in six different catchments. Physicochemical properties (TDS, EC, pH, DO, Eh, and salinity) were measured on site and samples were taken to the laboratory and analysed for major ions and trace elements. . Speciation diagrams were plotted using the Eh-pH data to understand the dominant uranium species in the water samples.
Groundwater of the area is alkaline, with high elevated concentrations of EC and TDS. The predominant water types are found to be Na-Cl, Na-HCO3 and Mg-HCO3 followed by water types Na-SO4 and Ca-HCO3. The results indicate a large number of groundwater samples with high uranium values above the South African water quality guidelines of 1.5 µg/L. This poses health risk such as cancer or radiological related diseases to communities living in, and around the study area. Data analysis shows that in the presence of carbonates, uranium mostly occurs in solution as UO2(CO3)22- field with few samples also plotted as UO2(CO3)34-. More sampling of groundwater is recommended to conduct a study on medical geology and passive treatment of uranium in the area.