Saturated-unsaturated numerical modelling of a vertically heterogeneous monolayer cover with an elevated water table: the Manitou site case study

ABSTRACT: Acid mine drainage production by reactive mine tailings can be controlled by installing a monolayer cover with an elevated water table (MC+EWT). This reclamation technique was implemented at the abandoned Manitou tailings storage facility 2 (TSF 2) located in Abitibi, Québec. The MC made of non-acid generating fine-grained tailings was placed hydraulically at a pulp density of approximately 45-50%. This disposal method induced segregation of particles according to their grain size and created some vertical heterogeneities into the cover material. In this study, numerical modelling was used to quantify the impact of the vertical heterogeneity of particle size distribution on the hydrogeological behavior of the monolayer cover and its performance as an oxygen barrier. Modelling results from May to October 2016 are presented and discussed here. The results showed that particle size vertical heterogeneity can affect but to a limited extent volumetric water content dynamics (RMSE < 0.03 m3 m-3) and thereby the hydrogeological behavior of the MC+EWT.