Groundwater flow and transport of metals under deposits of mine tailings: A case study in Brumadinho, Minas Gerais, Brazil

The deposits of mine tailings can be a source of groundwater contamination by metals. In this study, we simulated the concentrations of iron, manganese and aluminum in groundwater potentially affected by drainage from tailings deposits located in Brumadinho (Brazil). The aim was to verify whether the concentrations observed in the region can be attributed to these drainages. The simulation used the FREEWAT graphical interface, which incorporates the MODFLOW model, the hydraulic properties of existing unconfined and confined aquifers, the spatial distribution of the tailings' deposits, and the dissolved iron concentrations measured in drilled wells. The simulation period was 20 years, starting in 2019 after the collapse of B1 tailings dam of Córrego do Feijão mine of Vale, S.A. The modeling results revealed plumes of metal contamination progressively less dispersed over time, in the unconfined aquifer, and increased metal concentrations in the confined aquifer. The simulated concentrations in both aquifers were generally lower than the legal limits imposed for human consumption, although some areas in the vicinity of the deposits had iron and manganese concentrations higher than those limits, especially in the unconfined aquifer, and these areas widened over time. The most relevant result was the revelation that the contribution of tailings drainage to the iron concentrations observed in the drilled wells might have not exceeded 1%. This is important from a management standpoint, because monitoring of anthropogenic groundwater contamination in these cases (where rock weathering dominates groundwater chemistry) becomes more challenging.