Spatial variability of flow in coarse, unsaturated mining material: Results from field-scale infiltration experiments

The spatial distribution of flow during unsaturated conditions within an active heap-leach facility was studied. Flow and percolate chemistry data was recorded from free-drainage lysimeters placed prior to construction of the final lift of the study facility. Highly variable flow was observed between lysimeters during steady-state conditions. In some areas of the heap, accelerated infiltration was observed. The cause of the variability was determined to be more the result of highly spatially variable hydraulic properties than the variable distribution of applied flux to the surface. Using stochastically distributed hydraulic conductivity scaling factors, the variability of flow was reasonably reproduced with Hydrus-2D. It was determined the majority of lysimeters were not collecting 100% of flow passing through their area. Simulations using Hydrus-2D determined the most likely cause of the lower collection efficiencies to be a combination of the material heterogeneity and a low saturated conductivity of the lysimeter fill material.