Hydrological response of a multi-aquifer groundwater system to long-term clustered mine drainage

Long-term mine drainage represents one of the most intensive anthropogenic stresses imposed on groundwater systems, yet its system-scale hydrological impacts in multi-aquifer settings remain insufficiently understood. In this study, we investigate the response of a regional, vertically layered groundwater system to approximately 50 years of sustained mine drainage, with particular emphasis on the contrasting effects of single-well and group-well pumping. A physically based transient groundwater flow model was developed for a coal-bearing sedimentary basin and applied to simulate baseline conditions, staged single-mine drainage, and multi-mine group drainage scenarios. The results show that prolonged drainage induces a systematic reorganization of groundwater flow fields that extends well beyond localized drawdown around mining panels. Groundwater system behavior exhibits a clear transition from an initial storage-dominated response toward a boundary-controlled and vertically integrated flow regime, driven by enhanced lateral recharge and inter-aquifer leakage under sustained pumping. Importantly, groundwater responses under group-well pumping are inherently non-linear and cannot be approximated as a linear superposition of single-well effects. Interaction and overlap of capture zones among multiple drainage centers redistribute hydraulic gradients and produce pronounced spatial heterogeneity in groundwater-level responses. Aquifer stratification and vertical connectivity are shown to play a critical role in controlling the magnitude, spatial extent, and persistence of drainage-induced impacts. Although derived from a mining context, the identified hydrological mechanisms are applicable to other groundwater systems subjected to sustained, spatially clustered extraction. The findings highlight the need to treat long-term, clustered pumping as a system-scale hydraulic forcing in groundwater impact assessment and management.