Hydrogeochemical impacts of coal mining on multi-aquifer systems: A case study in the Linhuan Mining District, China

Coal mining activities present significant threats to groundwater quality in multi-aquifer systems. This study examines the hydrogeochemical processes and evolutionary pathways induced by mining operations in the Linhuan mining district, located in the Huaibei coalfield, China. Through a combination of mineralogical analysis, hydrogeochemical data, and inverse geochemical modelling, carbonate minerals, gypsum, and clay minerals were identified as the primary reactants, with dissolution/precipitation of minerals, sulfate reduction, and cation exchange as the predominant processes. The modelling results revealed three distinct runoff patterns: (1) fault-controlled recharge from shallow-to-intermediate aquifers to mine water, (2) anticline-guided recharge from shallow-to-deep aquifers to limestone water, and (3) mining-induced recharge to shallow unconsolidated aquifers. These processes facilitate interactions between loose pore water, coal-bearing sandstone water, and limestone water. Therefore, rising water levels in abandoned mines could exacerbate flooding risks and foster cross-aquifer contamination, thereby posing a significant threat to the pristine Carboniferous limestone aquifer. This study provides invaluable insights for predicting the evolution of water quality and for informing water resource management in this and other mining regions characterised by complex hydrogeological conditions.