Quantifying rock stockpile infiltration for effective cover design: novel approaches to water management at the former Pitch uranium mine

Authors: Hay, M; Zhan, G; Wykoff, D; Lundvall, E; Silverman, D; Jackson, T; Osores, O; Brown, A Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_59

Cite As:
Hay, M, Zhan, G, Wykoff, D, Lundvall, E, Silverman, D, Jackson, T, Osores, O & Brown, A 2026, 'Quantifying rock stockpile infiltration for effective cover design: novel approaches to water management at the former Pitch uranium mine', in AB Fourie, G Boggs, J Heyes & M Tibbett (eds), Mine Closure 2026: Proceedings of the 19th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-14, https://doi.org/10.36487/ACG_repo/2615_59



Abstract:
Designing effective water management strategies for mine reclamation is critical to meeting long-term closure objectives associated with geotechnical stability, surface reclamation and water quality. The infiltration rate into mine facility surfaces (waste rock stockpiles, heap leach pads, tailing impoundments) is a key parameter influencing the long-term water balance, which in turn influences constituent release and water quality. Mine facility infiltration is complicated by many factors such as particle size, material placement methods, and temporal factors such as long-term compaction. Having a detailed understanding of infiltration rates and how they vary across different portions of each mine facility can result in substantial optimisation of cap/cover approaches. This study will describe an optimised cover evaluation approach currently underway at the former Pitch uranium mine. Waste rock stockpile seepage from infiltrating meteoric water is primarily associated with melting of snow that drifts by wind and accumulates on flat benches and within stormwater ditches rather than steep slopes. Data collection at the site has included a combination of lidar snow/bare-ground surveys, standard single-ring infiltrometers, in situ moisture sensors, and larger-scale ditch infiltration tests involving water addition and downstream flow measurement. Ditch flow infiltration test data have been evaluated using simple gain/loss water balance approaches, as well as a novel application of the Philip and Green-Ampt infiltration models. Spatial variability in surface hydraulic conductivity is quantified by running single-ring tests at different locations/slope angles and ditch tests of varying lengths; these results demonstrate lower permeability in ponding areas due to silt accumulation. This detailed analysis will be used in future evaluations of alternative cover options to limit infiltration for seepage reduction and to assess whether selective lining (bench/ditch impermeable lining with slope revegetation/reforestation) could be a more environmentally sustainable and cost-effective means of reducing infiltration.

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