Hydrochemical Characteristics of Mine Water and Their Significance for the Site Selection of an Underground Reservoir in the Shendong Coal Mining Area

Underground reservoir technology can mitigate water shortage and pollution problems in water shortage coal mining areas and has a good application prospect. While still a new technology, the theory and method of underground reservoirs need to be improved. This research focused on the hydrochemical characteristics of mine water and their significance for the site selection of underground reservoirs. With the Shendong coal mining area as a case study, the hydrochemical major ions, toxicological indexes, and stable isotopes of hydrogen and oxygen were tested for the mine water samples, and the water quality was quantitatively evaluated and the origins of over-limit variables were investigated by hydrogeochemical numerical simulation and ionic ratio analysis. The influencing factors of water quality were analyzed and the significance of mine water quality for the site selection of underground reservoirs was discussed. The results show that the main over-standard variables are Na+, F-, SO42-, TDS, and sodium ion adsorption ratio (SAR), and a strong positive correlation exists between F- and SAR and a negative correlation exists between F- and Ca2+. Na+ in mine water originates from the dissolution of halite and silicate rocks, as well as reverse cation exchange. F- originates from reverse cation exchange and the displacement between OH- in alkaline water and F- adsorbed on the surface of minerals. On the whole, the mine water quality is better on the east than on the west of the WL River. The water-rock interactions in goaf increase the concentrations of F- and Ca2+ and SAR. The areas where the mine water samples have low concentrations of Na+, F-, and low SAR values, such as the shallow coal seams at the SGT, DLT, and WL mines, are favorable sites for the underground reservoir. The outcomes may benefit the reasonable site selection of underground reservoirs in similar coal mining areas with water shortage.