Hydrogeochemical characterization and groundwater quality assessment in a coal mining area, India

The present study determines major and trace element chemistry of groundwater in the West Bokaro coalfield to assess the hydrogeochemical processes and groundwater quality for drinking and irrigation uses. For this purpose, 33 groundwater samples from different mining areas of the West Bokaro coalfield were collected and analysed for pH, electrical conductivity (EC), total dissolved solid (TDS), dissolved silica (SiO2), major cations (Ca2+, Mg2+, Na+, K+), anions (F-, Cl-, HCO3-, SO42- and NO3-) and trace metals (Mn, Cu, Pb, Zn, Ni, Co, As, Se, Al, Cd, Cr, Ba and Fe). The analytical results show the slightly acidic to alkaline nature of groundwater and dominance of HCO3- and SO42- in anionic and Ca2+ and Na+ in cationic abundance. High SO42- concentrations are attributed to the oxidative weathering of pyrite and gypsum dissolution. Supersaturation condition with respect to dolomite and calcite for most samples may result from the dissolution of gypsum after the water is saturated with respect to the carbonate minerals. The data plot on the Gibbs and Piper diagrams revealed that the groundwater chemistry is mainly controlled by rock weathering with secondary contribution from anthropogenic sources. In a majority of the groundwater samples, alkaline earth metals exceed alkalies and strong acids dominate over weak acid. Ca-Mg-HCO3, Ca-Mg-SO4-Cl and Ca-Mg-SO4 were the dominant hydrogeochemical facies. A comparison of groundwater quality parameters in relation to specified limits for drinking water shows that the concentrations of TDS, SO42-, NO3-, total hardness (TH), Fe and Ni are exceeding the desirable limits in many groundwater samples. Quality assessment for irrigation uses reveal that the groundwater is of good to suitable category. Higher salinity and magnesium hazard values at some sites restrict the suitability of groundwater for irrigation purposes.