Presentation Title:
Field Performance of Final Covers for High Elevation Mine Waste Containment / Performance sur le terrain de couvertures finales pour des sites d'entreposage de résidus miniers en haute élévation

Resume/ Abstract:

Hydrology of four North American final covers used for mine wate containment has been monitored for a decade: a water balance cover with a capillary break, a conventional earthen cover with a compacted fine-textured soil hydraulic barrier, a conventional earthen cover with a compacted soil-bentonite hydraulic barrier overlain by a gravel drainage layer, and a geosynthetic cover with a geosynthetic clay liner laminated with a geomembrane overlain by a geocomposite drain. All have a 0.9-m vegetated surface layer of fine-textured soil. The hydrology is dominated by spring snowmelt during a 2-4-week period in March-April each year. Snowmelt induces substantial infiltration and soil water storage, lateral flow within the cover, and percolation from the base of the cover. Percolation normally commences in mid-April, reaches a peak in late April or May, tails in June, and ceases in early fall. During the remainder of the year, the hydrology is dominated by processes close to the surface, with storage as snowpack or soil water rapidly transmitted to the atmosphere via evapotranspiration. Percolation rates on the order of 115-225 mm/y can be expected for water balance covers. Conventional earthen covers with a shallow hydraulic barrier layer and no lateral drainage have percolation rates on the order of 230 mm/y. With a deep hydraulic barrier and a drainage layer, percolation rates are on the order of 75 mm/y or lower. Percolation rates for geosynthetic covers with a composite barrier overlain by a geosynthetic drainage layer are on the order of 2 mm/y.

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Prof. Craig Benson

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