Hydrogeochemical evaluation of groundwater quality in Dukwi wellfield in Botswana

Abstract

There has been a decline in groundwater quality in most wellfields in Botswana. This study evaluated the groundwater quality in Dukwi Wellfield for drinking and irrigation purposes and characterised the dominant hydrochemical processes in the wellfield area during winter and summer seasons. The parameters used to assess the water quality for irrigation purposes were percent sodium (%Na) and Sodium Adsorption Ratio (SAR), while for drinking purposes, Water Quality Index (WQI) was assessed. A piper plot was used for the geochemical characterisation of the groundwater while Gibbs plot was used to determine the dominant processes that govern groundwater chemistry. The results show that water from Borehole BH 2985 is excellent for drinking and irrigation as the average %Na, SAR and WQI values were 14.60%, 0.60 and less than 48.37 respectively. The water from Borehole BH 7521 is unsuitable for drinking and irrigation due to the high %Na values (> 90.47%). Also water from Borehole BH 4649 is of poor quality (WQI values > 162.15). The piper plots revealed that 70% of the samples of water in the area has sodium chloride while the Gibbs plots show that the groundwater is highly influenced by rock weathering and moderately by evaporation precipitation.