Hydrochemical assessment of groundwater quality and its suitability for irrigation and domestic purposes in Breede water management area, Western Cape

Abstract

Groundwater is an essential part of food and water security. This critical resource must be managed appropriately and used sustainably. The study was conducted in the Breede Water Management Area in the Western Cape province in South Africa. The aim was to assess the status of groundwater quality, the suitability of the water for domestic and irrigation purposes and factors contributing to the groundwater chemistry. Twelve (12) monitoring boreholes were selected for sample collection. The samples were analysed for major ions such as potassium (K+), magnesium (Mg2+), sodium (Na+), calcium (Ca2+), chloride (Cl-), sulfate (SO42-), bicarbonate (HCO3-), nitrate (NO3-), fluoride (F-) and physical variables like pH, electrical conductivity (EC), total dissolved solids (TDS) and temperature. The suitability of groundwater for domestic use was assessed using the Water Quality Index (WQI) and Total Hardness (TH) in combination with the comparison of the major ion data with the South African Water Quality Guidelines (SAWQG) and the World Health Organisation (WHO) drinking water quality guidelines. The suitability of groundwater for irrigation was assessed using irrigation indices such as Permeability Index (PI), Magnesium Hazard (MH), Sodium Adsorption Ratio (SAR), Sodium Percentage (Na%) and graphical representation methods such as Wilcox Diagram and United States Salinity Laboratory (USSL) diagram. Multivariate statistical analysis and Piper diagrams were used to determine the geochemical processes influencing the groundwater quality in the Breede area. The total hardness results showed that water from most boreholes is soft, with few boreholes with moderately hard and hard water. The WQI revealed that the overall groundwater in Breede is suitable for drinking. Most of the irrigation suitability indices showed that groundwater is suitable for irrigation, with a few sites that are doubtful for irrigation. The dominating water type in the area is Na-Cl, followed by mixed Ca-Mg-Cl, according to the Piper diagram. Multivariate statistical methods revealed that the groundwater in the study area is affected by the dissolution of rock salts, calcite dissolution, cation exchange and agricultural activities.