Effect of mining on geochemistry of groundwater in Permo-carboniferous Gondwana coalfields: Raniganj Basin, India

Lack of proper reclamation strategy and indiscriminate mining of various economic resources, particularly coal from Permo-carboniferous Gondwana coalfields affects the groundwater quality of the concerned regions. Leaching from mine-tailings along with seasonal fluctuation of water table caused a significant change in groundwater geochemistry of Raniganj coalfield area. Gondwana sequences, developed in intracratonic rift basin, are characterized by numerous longitudinal and cross faults. This results in the formation of many small aquifer systems which may be interconnected laterally as well as vertically providing the conduit for homogenization of aquifers. Although the predominance of major cations (Ca>Na>Mg>K) and anions (HCO₃>Cl>SO₄>NO₃) remain same irrespective of season, the dominance of Na and SO₄ have significantly increased in post-monsoon season. The types of groundwater in pre-monsoon and postmonsoon seasons are CaMgCl and CaHCO₃ respectively. Leaching of SO₄ from surface sources (mine tailings) has increased TDS in post-monsoon. Base exchange (direct and reverse) reactions have taken place between aquifer materials and groundwater.