Geospatial modelling of groundwater quality in semi‑arid environments of South Africa.

Abstract

Groundwater as a scarce freshwater resource requires extensive quality assessment, control and protection through innovative methods and efficient strategies in light of growing human population, pollution, and over–extraction. Groundwater is critical in arid and semi–arid regions of the world such as the Beaufort West area in the Karoo region of South Africa. Thus, this study investigated the key processes affecting groundwater quality using factor analysis and geospatial models to determine the spatial variability of groundwater quality. To achieve this objective, groundwater samples collected from 49 boreholes located in and around the town of Beaufort West and analysed for electrical conductivity (EC), pH, total dissolved solids (TDS), calcium ( Ca2+), magnesium ( Mg2+), sodium ( Na+), potassium ( K+), bicarbonates ( HCO3 –), chlorides ( Cl–), nitrates ( NO3 –) and sulphates ( SO4 2–) using recommended standard methods. Factor analysis produced three factors explaining 81.4% of groundwater quality variation. Factor 1 (hardness) was characterised by high concentrations of Cl–, SO4 2–, Ca2+, Mg2+ and Na+; factor 2 (alkalinity) with HCO3 – and K+, and factor 3 (anthropogenic) was characterised by high NO3 – concentrations. Derived groundwater quality thematic maps using selected hydrochemical variables and factor scores showed the delineation of areas with hardness, alkalinity and anthropogenic influence on groundwater quality. These findings underscore the relevance of factor analysis and geospatial models in assessing groundwater quality at a catchment scale.