Physical and numerical modelling of a dual-porosity fractured rock surrounding an in-pit uranium tailings management facility

Abstract

In-pit tailings management facilities (TMFs) have been used to dispose of uranium mine tailings in northern Saskatchewan. The pervious surround method can be employed to reduce groundwater flow through the tailings, and thereby moderate the rate of flux of radioactive and metal contamination that could enter the local groundwater via advection. A laboratory-scale analogue of an in-pit TMF was constructed to evaluate the impacts of a dual-porosity representation of the host rock on the effectiveness of the pervious surround concept in reducing peak concentrations and mass flux at a downgradient receptor. This work complemented the work of West et al. (2003) in which similar laboratory-scale experiments were conducted, simulating the host rock using the equivalent porous media and discrete fracture approaches. The experiments were adequately simulated using SWIFT II, a dual-porosity flow and transport model. Finally, to illustrate the impact of a dual-porosity representation of a fractured host rock on a contaminant plume from a TMF in the field, a field-scale scenario was modelled. The simulations illustrate the impact of diffusion into the host rock matrix on the simulated peak concentrations and the time for the peak concentrations to reach a downgradient receptor.