Regulation of the Distribution of Anthropogenic Contaminants by Physical Limnological Processes in a Relatively Pristine Watershed: the Breach of the Mount Polley Mine Tailings Impoundment, British Columbia, Canada

English Abstract:

On 4^th August 2014, the tailings impoundment of the Mount Polley copper and gold mine in British Columbia failed. Material from the impoundment (surface area = 2.7 km²) flowed into nearby Polley Lake and Hazeltine Creek, before discharging into Quesnel Lake, a large (ca. 100 km long, >500 m deep), relatively pristine lake. Estimates suggest that approximately 25 Mm³ of tailings (water and solids) and eroded soils and surficial materials from Hazeltine Creek were delivered to Quesnel Lake, raising the lake by 7.7 cm. Much of this material was deposited at the bottom of Quesnel Lake but a plume of fine-grained sediment (D₅₀ of ca. 1 µm) remained suspended in the water column. The distribution of this sediment was monitored over several months using water column profiling for temperature, conductivity, fluorescence, turbidity and oxygen with depth. The plume movement was regulated by natural processes associated with the physical limnology of this large fjord lake, specifically, seiche events which transferred suspended particles both up-lake, against the flow regime and down-lake into the Fraser River. Documentation of the distribution of the plume in the first few months following the spill is presented and indicates the value of background knowledge of natural systems in the vicinity of mining operations and other facilities where significant inputs of contaminants could occur.