Hydrogeochemical evaluation and groundwater quality assessment for drinking and irrigation purposes in Bushbuckridge, South Africa.

Abstract

This study was conducted in Bushbuckridge, situated within the Sand River Catchment (SRC), Mpumalanga Province, South Africa, with the aim of evaluating the hydrochemistry and assessing the quality of groundwater for drinking and irrigation purposes. Groundwater samples (n= 40) were collected from different boreholes in different locations around the study area. Groundwater hydrochemical parameters including pH, total dissolved solids (TDS), electrical conductivity (EC), total hardness, major cations (Ca2+, Na+, K+ and Mg2+) and major anions (F-, Cl-, NO3- HCO3-and SO42) concentrations were assessed for the study area. Suitability for drinking was assessed based on comparison with selected standards and guidelines, such as the South African National Standard (SANS), Department of Water and Sanitation (DWS), World Health Organization (WHO) and by computation of Water Quality Index (WQI). Groundwater suitability for irrigation was assessed using eight irrigation indices: TDS, EC, Sodium Adsorption Rate (SAR), Sodium Percent (%Na), Kelly's Index (KI), Residual Sodium Carbonate (RSC), Permeability Index (PI) and Magnesium Hazard (MH). Groundwater type and facies characteristics was determined with the Piper diagram while geochemical controls were ascertained using Gibbs diagram. The results indicate cation and anion concentrations in the order; Na+ > Ca2+> Mg2+ > K+, and HCO3- > Cl- > SO42- > F- > NO3- respectively, while EC (14 – 551mS/m), TDS (99 – 4411 mg/l), Cl (1.1 – 1290.6 mg/l), Na (16 – 758 mg/l), Mg (0.54 – 181 mg/l) and TH (15 – 1085) were variables with upper ranges significantly above SANS and WHO guidelines. According to the DWS guidelines the suitability of groundwater for drinking was classified as class – 0 (ideal; 10%), class – 1 (good; 24%), class – 2 (marginal; 40%), class – 3 (poor; 20%) and class – 4 (unsuitable; slightly over 7%). The WQI indicated that 40% of the analysed groundwater samples were of excellent quality, 56% good and 4% were found to be poor to unsuitable for drinking. Results for groundwater irrigation suitability potential for the analysed samples (n=40) revealed four clusters; (a) most or all the samples are suitable based on TDS (65%), EC (75%) and SAR (100%), (b) just over half are suitable based on PI (59%) and %Na (55% permissible), (c) most of the samples are unsuitable based on RSC (77%), and (d) equal distribution between suitable and unsuitable based on MH and KI (50%). According to the dominant cations and anions, the main water types were Na-HCO3, Ca-HCO3 and Mg-Ca-HCO3 mixed type. Rock weathering was the dominant geochemical process, associated with evaporation. Water-rock interactions through silicate weathering and ion exchange reactions between Ca2+, Mg2+ and Na+ were determining factors influencing the hydrochemical evolution of groundwater in the study area. The findings of the study suggest that the groundwater quality in the Bushbuckridge area is under threat. There is need for prompt mitigation actions that seek to intensify water quality monitoring, more in-depth studies to characterize the source and fate of potential pollutants in the area.