Mine Water Rebound after The Closure of The Olkusz-Pomorzany Zn-Pb Ores Mine (Southern Poland) – Controlling Factors and Spatial Variability

The closure of the Olkusz-Pomorzany zinc and lead ore mine (southern Poland) and the cessation of mine dewatering in December 2021 initiated a groundwater rebound process. The rebound is taking place within the former cone of depression, which covered an area of more than 300 km². The objective of this study is to identify and assess the key factors controlling the rapid rate of groundwater table recovery and to explain both the spatial variability of the rebound and the underlying hydrogeological mechanisms driving this process. The study is based on hydrogeological monitoring data collected between 2022 and 2025 and on a detailed analysis of the geological and hydrogeological conditions of the Olkusz region. The study takes into account various types of hydraulic connections between aquifers, along with the presence of karst and abandoned underground mine workings. The results indicate that the rebound rate within Triassic carbonate formations is highly spatially variable and primarily influenced by three factors: (1) a large and poorly defined recharge area of the cone of depression; (2) recharge through erosional windows carved in the Upper Triassic (Keuper) clay formations, enabling hydraulic connection between Quaternary sands and underlying Triassic carbonates; and (3) karst conduit systems, additionally flushed of sediments during mine drainage. Furthermore, atmospheric precipitation infiltration and induced recharge from surface watercourses (particularly the Biała Przemsza River and its tributaries) play a significant role in accelerating groundwater rebound. The findings may serve as a reference for other mining regions with comparable hydrogeological conditions. The study also highlights the challenges in predicting the rate of groundwater rebound in areas with complex geological conditions, where insufficient data limits the development of reliable numerical models.