Hydrochemistry and Environmental Isotopes to Identify the Origin of Barapukuria Coal Mine Inflow Water, Northwestern Bangladesh

Groundwater, coal mine inflow water, and river water samples were collected during November and December 2006 from the Barapukuria coal mine area in Dinajpur District, northwest Bangladesh. Groundwater samples were collected from existing shallow wells. All water samples were analysed for major ions, stable oxygen and hydrogen isotopes, and for tritium. High Electrical Conductance (EC) values, alkaline pH, and high temperature of collected coal mine inflow water signify a good hydraulic connectivity between the most fractured coal seam bearing Gondwana aquifers and the overlying Dupi Tila aquifers. Both groundwater and coal mine inflow water were dominantly of Na–Ca–HCO3 and Ca–Na–HCO3 type. The clustering of groundwater and coal mine inflow water samples along the Local Meteoric Water Line (LMWL) within narrow range indicates a common origin for the collected water samples, and thus indicates that the groundwater and coal mine inflow water originate from local rainfalls. The similarity between the average δ18O composition of groundwater and coal mine inflow water indicates that the groundwater percolates into the coal seam bearing Gondwana aquifers without changing recharging groundwater δ18O compositions. Both the groundwater and mine water tritium values were <1.0 TU, which could be considered as old water recharged prior to 1952. Finally, it can be concluded that the Barapukuria coal mine inflow water is of meteoric origin, which have been recharged within the aquifers prior to 1952 and there is connectivity between the shallow Dupi Tila aquifer and the coal seam bearing Gondwana aquifer.