Groundwater Hydrogeochemical Processes and the Connectivity of Multilayer Aquifers in a Coal Mine with Karst Collapse Columns

Abstract

Understanding groundwater hydrogeochemical processes and the connectivity of multilayer aquifers in a coal mine with karst collapse columns (KCCs) is very important for mine safety and groundwater resource management. In this study, 52 groundwater samples from the main aquifers in the Xieqiao coal mine (Anhui Province, China) were analyzed using hydrochemical, multivariate statistical methods, and stable isotope analyses. In the Permian aquifer, the main hydrogeochemical processes are halite and silicate dissolution and sulfate reduction, followed by cation exchange, while in the Carboniferous and Ordovician aquifers, the main hydrogeochemical processes are carbonate, gypsum, and halite dissolution, followed by cation exchange. This causes the hydrochemical characteristics of these two aquifers to be similar. The Permian aquifer contains less SO42−, more HCO3− concentration, and a concentration ratio of SO42− to HCO3− less than 0.25 due to sulfate reduction, which allows the Permian aquifer to be distinguished easily from the other two. Both hierarchical cluster and stable isotope analysis show that water samples from both aquifers appear to have been mixed via the KCCs, which may serve as a potential channel for groundwater inrush into the coal mine. These results may assist in accurately predicting potential water inrush sources in this coal mine as well as in other mines.