Groundwater as an alternative source to irregular surface water in the O'Kiep area, Namaqualand, South Africa

Abstract

Water insecurity is a growing concern globally and the role of groundwater and aquifers in buffering the effects of climate variability and change is increasingly acknowledged due to extended periods of drought in arid regions. Water security can only be fully realised with a more robust understanding of groundwater as a water resource, especially in the O'Kiep area which is in Namaqualand, South Africa. Results of analyses of groundwater samples (n = 8) indicated that pH values met acceptable standards for drinking, while the total dissolved solids (TDS) and electrical conductivity (EC) were however not within the recommended limits. The chemical composition of the groundwater indicated Eh values −34.1 to −87.2 mV, indicative of reducing geochemical conditions with the most abundant ions being Cl-, SO42-, NO3-, F-, Na+, Ca2+, Mg2+ and K+. Furthermore, some of the ions were not within the guidelines, i.e. Cl−, SO42+, Na+, Ca2+ and Mg2+, but all the potential toxic elements, namely: Al, S, As, Cd, Cr, Co, Cu, Fe, Mn, Hg, Ni, Se, V, Zn and CN, were within acceptable values for drinking groundwater as recommended by the SANS241-1 (2015) and WHO (2011). Hydrogeochemical characteristics of the water indicated that the continuous consumption of the groundwater without pretreatment might result in possible human health risk as the Groundwater Quality Index (GWQI) confirmed that the groundwater quality could be classified as being of moderate concern. Furthermore, the hydrogeochemical indices (CaCO3/Cl and Mg/Ca) and cationic exchange values indicated that the aquifer is of inland origin while the piper trilinear diagram revealed that the groundwater type in the area is categorised as sodium – potassium – chloride – sulphate- (Na–K–Cl–SO4), carbonate – chloride – sulphate- (CaCO3–Cl–SO4) and sodium – chloride (Na–Cl) type water. Additionally, the Sodium Adsorption Ratio (SAR) values up to 11.7 indicated that the groundwater is brackish and its excessive usage may have undesirable effect on plant growth. Therefore, this study recommends the consideration of suitable measures to improve the GWQI for the benefit of the community which have access to limited water resources.