Environmental Geochemistry and a Quality Assessment of Mine Water of the West Bokaro Coalfield, India

Mine water from the West Bokaro coalfield was qualitatively assessed with respect to domestic and irrigation criteria. Thirty water samples from different mines were collected and analyzed for pH, electrical conductivity, total dissolved solids (TDS), total hardness, major cations, anions, and dissolved silica. The pH of the samples ranged from 6.6 to 8.3 in the post-monsoon season and 6.7-8.4 in the pre-monsoon season, indicating its near-neutral to slightly alkaline nature. TDS ranged from 349 to 1029 mg L-1 in the post-monsoon season and 499-1458 mg L-1 in the pre-monsoon season. The spatial differences in TDS reflect the local lithology, surface activities, and hydrology. Ca-Mg-SO4 and Ca-Mg-HCO3 were the dominant hydrogeochemical facies; SO4 (2-) and HCO3 (-) were the dominant anions and Ca2+ and Mg2+ were the dominant cations during both seasons. High SO4 (2-) concentrations are attributed to oxidative weathering of pyrite and gypsum dissolution. Computed supersaturation 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. Despite moderate to high TDS, total hardness, and SO4 (2-) concentrations, most of the sampled mine water was of good to permissible quality for irrigation; however, locally higher salinity and Mg restrict its suitability for irrigation at some sites.