The fate of the lake after a dramatic mining disaster

On August 4, 2014, the Mount Polley mine in British Columbia, Canada, made international news when a dam burst, releasing millions of cubic meters of tailings—a hazardous mining byproduct—into the watershed. Much of this toxic sludge spilled into nearby Quesnel Lake, forming a layer of fine sediment up to 15 meters thick on some areas of the lake bed.

Although he did not claim anything human lives, the Polly Mountain disaster was the largest mine waste spill into a lake ever recorded. Since then, several studies have examined its impact on the surrounding watershed. Now Granger et al. to report a more in-depth analysis of the long-term fate of about 38,000 metric tons sediment which remained suspended in the westernmost of the two Quesnel Lake basins 1 month after the spill.

With a maximum depth of 512 meters, Quesnel Lake is the third deepest lake in North America. The researchers analyzed water quality data that was collected from various locations across the lake between August 2014 and 2020 by several stakeholders, including provincial and federal governments, mining industryand government research institutions.

Applying the concept of conservation of mass, the researchers found that the amount of suspended sediment in Quesnel Lake remained unusually high during the first three calendar seasons after the spill. During this time, some sediment left the western basin of the lake via the Quesnel River, but much of the sediment moved against the typical direction of water flow into the eastern basin. After June 2015, suspended sediment levels fluctuated according to the lake’s typical seasonal mixing schedule, reaching higher levels each fall and spring but declining steadily year after year.

The researchers then combined these findings with an analytical model of a simplified two-basin lake. Model simulations indicate that suspended sediment concentrations in the western basin will return to pre-spill levels by about 2024.

These findings deepen understanding of the consequences of the Mount Pauli accident and may inform further research into the long-term effects of environmental disasters.

The study was published in Water resources research.

Courtesy of Eos

This story is republished thanks to Eos, hosted by the American Geophysical Union. Read the original story here.