Hydrogeochemical evolution of multilayer aquifers in a massive coalfield

Abstract

Groundwater is an important drinking water resource worldwide. However, mining could influence the natural groundwater geochemistry, reducing the correct discrimination of inrush sources and affecting mine safety. To accurately identify potential inrush sources in the future, hydrogeochemical processes and their evolution should be investigated using multiple analytical methods. In the study, based on hydrochemical analysis and multivariate statistical methods, the major ion chemistry of groundwater in multi-aquifer groundwater systems was analyzed in the Huainan coalfield (Anhui Province, China). The results showed that the hydrogeochemical processes in this area consisted of the three subprocesses: dissolution, desulfidation, and cation exchange. For the Cenozoic bottom aquifer and the Ordovician aquifer, the major hydrogeochemical processes are the dissolution of salt rock, silicate, carbonate, and sulfate, followed by cation exchange; for the Permian and Carboniferous aquifers, the main hydrogeochemical processes are desulfidation and cation exchange, followed by dissolution. From the Permian aquifer to the Carboniferous aquifer and then to the Ordovician aquifer, the concentration of SO42− increased, while the concentration of HCO3− decreased due to enhanced sulfate dissolution and weakened desulfurization. However, long-term mining activities changed the groundwater seepage field and the hydrogeochemical field, causing hydrogeochemical evolutionary processes with obvious zoning. The eastern discharge zone showed the strongest dissolution and the weakest desulfidation and cation exchange; from the eastern discharge zone to the central runoff zone, dissolution weakened, while desulfidation and cation exchange were enhanced; and in the western recharge zone, desulfidation and cation exchange were the strongest, while dissolution was the weakest.