Sediment-associated contaminant transport and storage dynamics in the Quesnel River from the Mount Polley Mine disaster

In August 2014, the tailings storage facility of the Mount Polley copper-gold mine was breached releasing ~25 million m3 of tailings water and solids into Polley Lake and Hazeltine Creek, which scoured local overburden (1.2 million m3), and deposited these materials in Quesnel Lake. This study examined temporal and spatial movements of sediment-associated elements in Quesnel River, downstream of the lake, between August 2014 and August 2015. Suspended river sediment was collected using active and passive samplers (a continuous-flow centrifuge and time-integrated samplers), while discrete bed sediment was collected using a re-suspension technique. Results indicated elevated trace element levels, especially copper, with significant differences between element concentrations at the upstream site, closer to the breach, compared to downstream sites. Contamination indices and comparison to sediment quality guidelines indicated contamination was present in the river and varied seasonally predominantly driven by Quesnel Lake’s autumnal cooling and overturns.