Salinization of soil over saline-sodic overburden from the oil sands in Alberta

Abstract

Saline-sodic mine overburden (also referred to as spoil) removed to access the oil sands in the Athabasca region of Alberta is used as backfill in open pits and is also placed in large upland structures. These deposits are reclaimed with a soil cover to support re-vegetation. The chemistry within reconstructed soil profiles over saline-sodic overburden was investigated to determine the nature and spatial distribution of salts in the soils. Four reclamation treatments were compared: three layered covers (35, 50 and 100 cm thick) and one non-layered cover (100 cm thick). Salts have accumulated in the cover soils 15 to 20 cm above the overburden, raising the electrical conductivity in the lower part of the soil to between 4.5 and 6.0 dS m-1, which is beyond the acceptable value for vegetation growth. Salt redistribution was not related to slope position and the pattern of salt ingress suggests that diffusion has been the main mechanism driving salt migration into the soils during the initial 4-yr period following placement. Cover thickness did not affect the extent of salt migration, but the overall quality of the thinner covers (35 and 50 cm) for vegetation growth was compromised by the increased salinity levels.

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