Hydrogeochemistry and quality assessment of surface and sub-surface water resources in Raniganj coalfield area, Damodar Valley, India

Mining and associated activities are largely accountable for contamination of water resources and creating the problem of safe water availability to a larger population residing in mining areas. Forty-nine water samples from the surface and sub-surface water resources were collected from the Raniganj coalfield area and analysed for water quality parameters using standard analytical methods. The analysis data were used to assess major ion chemistry, hydrogeochemical processes controlling water chemistry and water quality status for different uses. Results display that both groundwater and surface water of the area was alkaline in nature. HCO₃⁻>Cl⁻>SO₄^2->NO₃⁻>F⁻ abundance order was observed for anions in both groundwater and surface water resources. While for cations, Ca²⁺>Mg²⁺>Na⁺>K⁺ abundance order was noticed in groundwater and Ca²⁺>Na⁺>Mg²⁺>K⁺ in surface water sources. Ca-Mg-HCO₃ and Ca-Mg-Cl were the dominant water types in the groundwater and Ca-Mg-HCO₃, Ca-Mg-Cl and Na-HCO₃-Cl in surface water resources. Gibbs, scatter plots and ionic ratios show that the chemical composition of the water resources in Raniganj coal mining region was mainly controlled by weathering of rock-forming minerals, sulphide oxidation and ion exchange processes. Concentration of F⁻, Ca²⁺, Mg²⁺, SO₄^2- and TH exceeded the drinking water acceptable limits established by the Bureau of Indian Standards. Computed water quality index (WQI) values suggest that 36% groundwater and 21% surface water samples were of poor water quality and requires appropriate treatment prior to utilisation. Furthermore, high values of salinity, residual sodium carbonate (RSC), Kelley index (KI), per cent sodium (%Na) and magnesium hazard (MH) at some sites limit the applicability of water for irrigation uses and demands appropriate water management strategy for the area.