Aquatic habitat remediation following a mine tailings storage facility embankment breach

Authors: Wernick, BG; Nikl, LH; Stevens, CE Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2215_67

Cite As:
Wernick, BG, Nikl, LH & Stevens, CE 2022, 'Aquatic habitat remediation following a mine tailings storage facility embankment breach', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 927-940, https://doi.org/10.36487/ACG_repo/2215_67



Abstract:
The Mount Polley Mine in British Columbia, Canada, is an open pit and underground copper and gold mine. In August 2014, the failure of a glacial lacustrine layer beneath the perimeter embankment of the tailings storage facility (TSF) resulted in the release of a slurry of water, tailings, and dam construction material. The material released from the breach and the resulting debris flow resulted in physical impacts to adjacent creek and lake environments. Following the TSF breach, an adaptive remediation framework was developed to guide and communicate the process of investigation, pollution abatement measures, and remediation of areas affected by the breach. Following the initial response that was focused on the immediate need of establishing safe work conditions and controlling further release from the TSF, a tabular format remediation plan was used to communicate short-term actions, such as re-establishing an erosion-resisting creek channel, presumed longer-term actions based on information yet to come in, and steps being taken to address those information gaps to the public, government and Indigenous groups on whose traditional territory the mine is located. A conceptual, and then final, remediation plan was developed while remedial actions based on decisions already being made were implemented. Remedial construction in the creek habitats concluded in the fall of 2021, in time for a run of sockeye salmon to spawn in the newly constructed channel. The preliminary assessment of effects on aquatic and terrestrial resources found that copper, the contaminant of primary concern associated with the tailings, had low bioavailability. This was a key finding that helped focus remediation efforts on impacts associated with physical scouring of natural sediments, soils and vegetation, and deposit of tailings in riparian areas and water bodies. In creek habitats, the overall remediation objective was to restore the life history functions of fish by first constructing an erosion-resistant, field-engineered stream base in the otherwise erodible glacial lacustrine native soils underlying the area, onto which habitat features (cover, riffle-to-pool ratios, substrate, etc.) were added to enhance aquatic ecosystem functions for spawning and rearing fish. Adjacent riparian areas were stabilised through contouring and planting a mix of local species to establish a successional vegetation community. Evaluation of post-construction habitat suggests that remediation will restore the productive capacity of the aquatic ecosystem for salmonids, and that recovery will be relatively quick, with projected population sizes stabilising above historical levels within 20 years of the TSF breach event. In the lake habitats, monitored natural recovery was recommended based on a net environmental benefit assessment that found that physical removal of deposited tailings would be detrimental to natural recovery already taking place.

Keywords: habitat reconstruction, remediation framework

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