Groundwater flow and solute transport in a laboratory-scale analogue of a decommissioned in-pit tailings management facility

Abstract

A laboratory-scale analogue of an in-pit tailings management facility (TMF) was constructed using mortar sand, fluorescent-dye-containing ground silica, and filter gravel to represent fractured host rock, tailings, and a pervious surround, respectively. In a series of experiments, the performance of the analogue was observed through collection of hydraulic head, groundwater discharge, and solute concentration data. These data were found to be sufficient to validate numerical simulations of the experiments carried out using FRAC3DVS. The validation exercise indicated that adequate discretization of the tailings' periphery was critical to accurate simulation of early time solute release from the ground silica, while accurate simulation of groundwater flow and hydrodynamic dispersion adjacent to the ground silica was critical to accurate simulation of the down-gradient solute plumes. The validated model was used to predict how the analogue would have performed over its entire "contaminating lifespan." The results of the experiments and subsequent numerical modelling were used to support the argument that, assuming no dissolution of tailings solids, solute mass flux out of a decommissioned in-pit TMF would decrease asymptotically with time from a rate controlled by diffusion at the tailings' periphery towards a steady rate controlled by advection through their core.Key words: tailings, groundwater contamination, in-pit disposal, physical model, numerical model, advection-dispersion.