Hydrogeochemical investigation and quality assessment of mine water resources in the Korba coalfield, India

Hydrogeochemical investigation of water discharged from the mines of Korba coalfield was carried out to assess mine water geochemistry, solute acquisition processes, and its suitability for domestic, irrigation, and industrial uses. A total of 44 mine water samples were collected from coal mines of Korba coalfield and analyzed for pH, electrical conductivity (EC), total dissolved solids (TDS), major cations (Ca2+, Mg2+, Na+, K+), major anions (HCO3-, Cl-, SO42-, NO3-), dissolved silica (H4SiO4), and trace metals. pH of the analyzed mine water samples varied from 6.7 to 8.5, indicating mildly acidic to alkaline nature of water. Concentration of total dissolved solids ranged from 97 to 785 mg L-1, and spatial differences in TDS values reflect variation in lithology, surface activities, and hydrological regime prevailing in the mining region. HCO3- and SO42- were the dominant anions in mine water of the area, while Ca2+ and Mg2+ dominated in cation chemistry. Higher contribution of SO42- to the total anions (TZ(-)) may be attributed to weathering of pyrites associated with the coal strata. High concentrations of Ca2+, Mg2+, HCO3-, and SO42- and the average HCO3-/(HCO3- + SO42-) ratio of 0.58 suggest coupled reactions involving both sulfuric acid- and carbonic acid- aided weathering which largely controls the solute acquisition processes. The factor and cluster analyses of hydrochemical data also suggest the reaction paths expected from solution interacting with carbonate and silicate rocks attacked by H2CO3 and/or H2SO4. Ca-Mg-SO4-Cl and Ca-Mg-HCO3 were the dominant water types in mine water of the Korba coalfield. The computed saturation indices demonstrate oversaturation condition with respect to calcite, dolomite, and aragonite and undersaturation with respect to gypsum, anhydrite, and halite. The quality assessment for drinking uses indicates that TDS, total hardness, and concentration of some trace metals (Fe, Mn, Ni, Al) exceeded the acceptable levels in a number of mine water samples and need treatment before its utilization. In general, the mine waters of the Korba coalfield are of good to permissible quality and can be used for livestock and irrigation in most cases. Higher salinity and magnesium hazard values at some sites limit its suitability for irrigation uses.