Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Evolution of groundwater chemistry in the Bukov Underground Research Facility and the Rožná uranium mine


Jaroslav Řihošek, Lenka Rukavičková, Jan Holeček, Oldřich Myška, Daniel Holéczy, Marek Vencl, Lukáš Vondrovic

Geoscience Research Reports 51, 2018, pages 69–74

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Published online: June 20, 2018

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Between the years 2013 and 2017, the Bukov Underground Research Facility (Bukov URF) was under construction on the 12th floor of the Rožná uranium mine (at a depth of approx. 520 m). This high-quality laboratory funded by the Czech Radioactive Waste Repository Authority (CRWRA) was established to assess the behavior of rock environment in the neighborhood of a potential deep-seated radioactive waste repository in process of the preparatory stage of its construction. A parallel hydrogeological research was focused on the flow regime and the chemistry of both shallow and deep groundwater. Rukavičková et al. (2016) earlier reported results of the first stage of hydrogeological investigation carried out at this site.
The aim of the current study was to evaluate the chemistry of groundwater and its temporal and spatial development in the recently built URF Bukov, and for comparison also in other parts of the Rožná mine. The groundwater of Ca-HCO3 type usually occurs at depths of up to 520 m (the 12th floor of the mine, the site of URF Bukov) below surface. The content of Na+ was found to be rising with increasing depth, and the groundwater of Na-HCO3 type is typical of deep parts of the Rožná mine. A stagnant water of Na-Cl type was identified in the deepest parts of the Rožná mine (the 24th floor, approx. 1150 m below surface).
Natural vertical hydrochemical zonation of groundwater is affected by anthropogenic intervention of underground mine ventilation system. The change of the redox potential in the environment of crystalline rocks containing sulfides resulted in the change of Na-HCO3 and Ca-HCO3 groundwater types towards Na-SO4 and Ca-SO4 types. As a result of this process, the groundwater of Ca-HCO3 type is completely absent in the long opened drifts of the Rožná mine, while the anthropogenic Ca-SO4 type of higher mineralization is widespread from the 3rd down to the 12th floor of the mine. The groundwater of Na-SO4 type (a result of sulfides oxidation due to ventilation of mine drifts) occurs in deeper parts of the mine along with Na-HCO3 and Na-Cl types.
Gradual increase of total dissolved solids (TDS) and change of ion content (decrease of HCO3?, increase of SO42?, Cl? and cations) have been observed in groundwater of inflows into URF Bukov since January 2014. It can be assumed that the groundwater of URF Bukov, which was primarily of the Ca-HCO3 type, will eventually attain the same chemistry as groundwater in the Rožná mine.


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