Hydrogeochemical characteristics and evaluation of groundwater quality for domestic and irrigation purposes: a case study of the Heuningnes Catchment, Western Cape Province, South Africa

Knowing the quality of water is imperative if the water is meant for drinking or agricultural purposes. The spatial and temporal groundwater quality in the Heuningnes Catchment was investigated, and its appropriateness for irrigation and drinking purposes was considered. Thirty-one samples were collected and analysed for physical (pH, EC, TDS) and chemical (Na+, K+, Ca2+, Mg2+, HCO3-, Cl-, SO42-) parameters. Maps demonstrating the spatial and temporal distribution of groundwater quality were constructed using Geographical Information System software. These maps indicate variations in the concentration of various water quality parameters in the region. Groundwater in the region is mostly alkaline and is categorised as either fresh, brackish or saline based on TDS classification. Using Piper diagrams, it is shown that Na+-Cl- water type is the main water type in the area. The quality is mostly influenced by chemical weathering of rock-forming minerals. Over 50% of groundwater in the region is not fit for drinking purposes as established from WHO (2011) and SANS241 criteria. Following SAR criteria, looking at Na%, PI, MH, KR and salinity hazard for irrigation assessment, it was discovered that shallow groundwater in the region was not fit for irrigation purposes. However, groundwater from deeper boreholes proved otherwise. The study has shown that not all-available groundwater is suitable for either drinking or irrigation. Therefore, it recommends to plant crop varieties that are highly salinity tolerant, as treating the water prior to irrigation would not be economically viable, and it also recommends further exploration to make the available 50% of groundwater drinkable and to make the shallow groundwater fit for irrigation.