Transformation of groundwater hydrodynamic and hydrogeochemical regimes under the influence of long-term coal mine operation in the Western Donbas

The article presents the results of a comprehensive study of the transformation of the hydrodynamic and hydrogeochemical regimes of groundwater within the zone of influence of coal mining enterprises in the Western Donbas. The research is based on long-term monitoring of groundwater levels in different aquifers during 2010–2025, together with data on mine water mineralization and groundwater inflow rates. Spatial-statistical, cartographic, trend, and correlation analyses integrated with GIS technologies were applied to assess the long-term evolution of the groundwater system. The study identified the principal patterns of spatio-temporal transformation of the hydrodynamic regime caused by prolonged mine dewatering. Localized cones of depression were found to develop within the Paleogene aquifers, where groundwater levels declined by up to 8 m, while the Quaternary aquifer experienced a regional groundwater-level decrease of up to 2.5 m. A mechanism explaining the inversion of piezometric level changes in the Buchak and Obukhiv formation aquifers is proposed and substantiated. This inversion is associated with the transformation of the natural groundwater recharge and drainage system under the influence of continuous mine drainage. Analysis of long-term monitoring data demonstrated that groundwater inflow to the Dniprovska Mine increased more than tenfold, whereas the average mineralization of mine water increased almost fourfold. Third-order polynomial trend models (R2 = 0.6855 and R2 = 0.7375) reveal the staged transformation of the hydrodynamic and hydrogeochemical regimes during prolonged coal mining. The scientific novelty of the study lies in identifying the regularities of the spatio-temporal transformation of groundwater within different aquifers of the WD based on a fifteen-year monitoring dataset and in substantiating the mechanism responsible for the inversion of piezometric levels induced by long-term mine drainage. The practical significance of the research consists in the applicability of the obtained results for predicting the development of groundwater depression cones, assessing environmental risks, improving groundwater monitoring systems, and supporting sustainable groundwater resource management in mining regions.