Analytical Approach to Estimate Salt Release from Tailings Sand Hummocks in Oil Sands Mine Closure

Integrated surface water and groundwater models are well suited for evaluating the long-term performance of oil sands mine closure landscapes to optimize reclamation designs that satisfy performance criteria. However, the scale of the problem makes it difficult to evaluate a large number of design alternatives using numerical models, while at the same time satisfying numerical criteria, such as the courant and peclet numbers. The problem becomes particularly challenging in the design of permeable sand tailings hummocks overlying relatively impermeable composite tailings, where vertical advective flushing of process-affected water through the tailings hummocks is coupled to lateral transport of diffusive release from the underlying composite tailings. We developed an analytical solution that rapidly estimates long-term mass loadings from the sand tailings without the challenges typically associated with numerical modelling. Advection and dispersion in the flushing zones, progressive diffusion into underlying low permeability layers, and purely diffusive release are all considered. A comparison of the analytical solutions to numerical simulations for a series of simple hypothetical cases demonstrated that the analytical solutions provide a reasonable simulation of the mass loadings from the reclaimed landscapes over the design life. Although the approach needs to be further verified and validated for more realistic complex mine reclamation conditions, the analytical framework provides a foundation for hydrologic analysis in mine reclamation and closure in the northern boreal environment.