Hydrogeochemical implications of pumped hydropower storage in former open-pit lignite mines: conclusions of comprehensive modelling studies

Pumped Hydropower Storages (PHS) in former open-pit lignite mines offer significant potential for large-scale energy storage, supporting Europe’s energy transition. The reuse concept draws on proven, efficient technology that synergises economically with the subsequent use of former mines and transport infrastructure, local energy storage needs, and favourable ecological site conditions. While such projects must demonstrate economic and technical feasibility, their environmental compatibility is equally critical. This study presents conclusions of the first comprehensive modelling assessment of the hydrochemical implications associated with PHS operations in these settings. By combining a newly developed generic reaction path modelling framework with geochemical and hydrochemical data from two European lignite mines, we derive general insights into the evolution of pH, sulfate, and iron concentrations over a potential PHS operational period. Heterogeneities in internal mine dump sediments are analysed via reactive transport simulations since these emerge as important source for potential water contamination.

Results show that the direct hydrochemical impact of PHS operation is generally negligible compared to the influence of local geochemical and hydrological conditions. As in conventional mine flooding, the key drivers of hydrochemistry are the extent of pyrite oxidation in mine dump sediments and the availability of acid-neutralising minerals, such as calcite. The degree of acidification and sulfate release depends primarily on oxygen availability in the sediments and the amount of oxidised pyrite. The importance of site-specific analysis is underlined by field data since the water balance of surface run-off and groundwater dominated systems fundamentally differ, affecting the responsiveness of the hydrochemical system. If the flooded open-pit mine includes an internal mine dump, the dump’s internal structure is important for quantifying the timing and quantity of solute outflux as the sediments are the main source of pyrite oxidation products in the system.

In conclusion, a detailed, site-specific analysis of geochemical and hydrochemical conditions is essential for planning PHS projects in former open-pit lignite mines. While the PHS infrastructure itself is unlikely to substantially alter water chemistry in most scenarios, pre-existing site conditions may lead to environmental or economic challenges during operation.

Literature

Schnepper, T., Kühn, M. and Kempka, T. (2025a): Reaction Path Modeling of Water Pollution Implications of Pumped Hydropower Storage in Closed Open-pit Lignite Mines. Mine Water and the Environment, 44, 107-121. DOI: 10.1007/s10230-025-01039-y

Schnepper, T., Kapusta, K., Strugała-Wilczek, A., Roumpos, C., Louloudis, G., Mertiri, E., Pyrgaki, K., Darmosz, J., Orkisz, D., Najgebauer, D., Kowalczyk, D. and Kempka, T. (2025b): Potential hydrochemical impacts of pumped hydropower storage operation in two European coal regions in transition: the Szczerców-Bełchatów mining complex, Poland, and the Kardia Mine, Greece. Environmental Earth Sciences, 84, 9, 247. DOI: 10.1007/s12665-025-12198-0

Schnepper, T., Kühn, M. and Kempka, T. (2025c): Effects of Permeability and Pyrite Distribution Heterogeneity on Pyrite Oxidation in Flooded Lignite Mine Dumps. Water, 17, 21, 3157. DOI: 10.3390/w17213157