Predicting long-term contamination potential of perched groundwater in a mine-waste heap using a random-walk method

Mine-waste heaps are potential long-term sources of contamination for surface-water courses and groundwater systems. Application of a novel physically based particle-tracking model to a mine-waste heap in northern England, UK, has enabled predictions to be made of the lifetime of contaminants leaching, revealing a pattern of source-mineral depletion. A mine-waste heap is conceptualised by a series of one-dimensional unsaturated “columns” in which active weathering of source minerals takes place. These columns drain into a saturated zone, through which the contaminants are transported to the heap discharge. Solute transport is simulated within the model by the random-walk method while reaction kinetics are incorporated to account for the timescales of source mineral depletion. Results reveal that the mine-waste heap is likely to remain polluting for several centuries, with the governing factor in the magnitude of pollution being the transport of the reactant, oxygen, to the source-mineral surfaces.