Modelling the closure-related geochemical evolution of groundwater at a former uranium mine

A newly developed reactive transport model was used to evaluate the potenti al effects of mine closure on the geochemical evolution in the aquifer down gradient from a mine site. The simulations were conducted for the Konigstei n uranium mine located in Saxony, Germany. During decades of operation, ura nium at the former mine site had been extracted by in situ acid leaching of the ore underground, while the mine was maintained in a dewatered conditio n. One option for decommissioning is to allow the groundwater level to rise to its natural level, flooding the mine workings. As a result, pore water containing high concentrations of dissolved metals, radionuclides, and sulf ate may be released. Additional contamination may arise due to the dissolut ion of minerals contained in the aquifer downgradient of the mine. On the o ther hand, dissolved metals may be attenuated by reactions within the aquif er. The geochemical processes and interactions involved are highly non-line ar and their impact on the quality of the groundwater and surface water dow nstream of the mine is not always intuitive. The multicomponent reactive tr ansport model MIN3P, which can describe mineral dissolution-precipitation r eactions, aqueous complexation, and oxidation-reduction reactions, is shown to be a powerful tool for investigating these processes. The predictive ca pabilities of the model are, however, limited by the availability of key Ge ochemical parameters such as the presence and quantities of primary and sec ondary mineral phases. Under these conditions, the model can provide valuab le insight by means of sensitivity analyses. (C) 2001 Elsevier Science B.V. All rights reserved.