Multicomponent reactive transport modeling at the Ratones uranium mine, Cáceres (Spain)

Flooding of abandoned mines may have a major impact in groundwater quality. Predicting the long-term evolution of the water quality is, therefore, a relevant matter for environmental management. The Ratones uranium mine was abandoned and flooded in 1974. Due to its reducing underground environment uranium concentration is very low, although some points show high concentration in Fe and As. Within the works prior to a remediation strategy, reactive transport modelling were performed of the mine and surrounding groundwater system. The results of the calculations were compared with analyses of groundwater samples collected in selected points. Modelling based on water-rock reactions taking place only in the mine galleries indicates the rapid exhaustion of dissolved oxygen and predicts solute concentrations that are much lower than those measured in the boreholes. In contrast, modelling that includes weathering processes taking place in the unsaturated zone of the surrounding rock indicates high dissolution of minerals (even if present in small amounts) and concentrations of solutes and values of pH and redox potential that better match the measured values. Therefore, current models based only on water-rock reactions in the walls of the mine galleries may clearly underestimate the impact of mineralization in groundwater, and processes taking place in the shallow surrounding rock must also be considered.