Simulation of Abnormal Evolution and Source Identification of Groundwater Chemistry in Coal-Bearing Aquifers at Gaohe Coal Mine, China

Abstract

Numerous scholars worldwide have conducted extensive research on the identification of water sources for mine water inflows, among which the utilization of groundwater’s chemical properties for water source discrimination is characterized by its rapidity, effectiveness, and economy. In the Gaohe Coal Mine of Shanxi Province, anomalous water discharge has been observed from boreholes in some coal-bearing aquifers. The water quality differs from both coal-bearing aquifer water and Ordovician limestone aquifer water. Analysis of K+, Na+, and SO42- suggests that the water does not belong to coal-bearing aquifer water, while the analysis of Ca2+ indicates it is not Ordovician limestone aquifer water. Particularly, in the 8# Coal-Bearing Aquifer Observation Borehole, the concentration of Ca2+ is extremely low, consistent with coal-bearing aquifer water, yet the concentration of SO42- is extremely high, resembling Ordovician limestone water. This is speculated to be due to Ordovician limestone water replenishing the aquifer where the observation borehole is located, triggering a series of chemical reactions. Using the PHREEQC (Version 2) hydrochemical simulation software, hydrochemical simulation experiments were conducted to model the process of different proportions of Ordovician limestone water entering the coal-bearing aquifer. This study explored the reaction mechanisms between Ordovician limestone water, coal-bearing aquifer water, and coal measure aquifer rock samples, validated the hydrochemical and water–rock interactions occurring during this process, and estimated the proportion of water sources in the anomalous borehole water discharge based on the ion concentration profiles of the simulated mixed water. These findings can be applied to the prevention and control of Ordovician limestone water hazards, especially those caused by water-conducting pathways.