The Mt Polley mine disaster

At two am on the morning of 4 August, 2014, a tailings pond at Imperial Metals’ Mount Polley gold and copper mine broke through an earthen dam, sending 10 million cubic metres of tailings water and 4.5 cubic meters of tailings sediment pouring into Polley Lake and from there through Hazeltine Creek into Quesnel Lake. A complete water ban has been issued for the area, with no water use of any kind permitted.
This type of disaster is new to British Columbians, and no one really knows exactly what the impacts may be, though they seem to be downplayed by both the mining company and the BC Minister of Mines. The president of Imperial Metals has stated publicly that the tailings pond water was not contaminated and that he ‘would drink it.’ This seems to be at odds with 2013 data from Environment Canada that the tailings pond contained arsenic, mercury, and other heavy metals. Minister of Mines Bill Bennett released a statement suggesting only sand and water was released from the pond, but failing to mention contaminants.
This post avoids some of the trickier questions around politics to focus on three main areas of concern: water, sediments, and ecological impacts.
Water
The big question is whether or not there were contaminants in solution in the tailings pond water. One source notes that, according to Imperial Metals, the pond was alkaline (pH 8.5) rather than acidic, but Imperial should ultimately know the exact composition of their wastewater. If it does contain dissolved contaminants, these could spread not only through the surface water system but into the groundwater as well, where it becomes much more difficult to monitor and remediate. The other issue with a deep lake system like Quesnel Lake is that it likely doesn’t see a lot of water turnover, thus any contaminated water inputs would be diluted only by the volume of surface water that overturns in the lake.
Sediments
This is a huge one – and not only from the tailings themselves but from the debris scoured away in the path of the flood. The flood remodeled the formerly narrow Hazeltine Creek into a 150 ft wide spillway, flushing everything from fine sediments to boulders and trees ahead of it. While the coarse sediments would have been deposited soon after reaching the still waters of Quesnel Lake, the fine sediments can travel much farther in suspension. This has implications for salmon spawning in any tributaries from the lake, as these fine materials can potentially silt up spawning beds.
The other issue with sediment is that contaminants adsorb to sediment surfaces, so anywhere the sediment goes, the contaminants come along for the ride. The contaminants can even be released from stored sediment that’s disturbed at a later date.
Ecology
This is one of the more difficult aspect of the spill to examine. There are the direct effect of contaminants on both aquatic organisms such as the returning salmon (which DFO predicted would peak on 11 August at 4.1 million fish in the Chilko and Quesnel sockeye runs), and on terrestrial organisms that come in contact with the water. There is high concern that toxins will move through the food web via bioaccumulation and biomagnification, with implications for First Nations wild food and medicine sources.
What might be the process moving forward?
In the short term: fieldwork to test water quality in both surface and groundwater, sample in situ sediments to determine contaminant levels, and survey stream systems to determine changes in stream morphology and potential implications for aquatic organisms. Numerical modelling to simulate the event and determine the extent of the sediment plume and potential sediment deposition areas. Ecological surveys of the salmon run to assess returns, mortality rates, and spawning success. Ideas on other ways we can get a better picture of the effects of the spill are welcomed in the comments.
In the longer term: Sampling of aquatic and terrestrial organisms to quantify bioaccumulation and/or biomagnifications of contaminants. Continued water sampling and sediment sampling to determine whether the contaminants are changing over time in both concentration and mobility.
Researchers from the University of Northern British Columbia have already begun taking samples to study this event, and I look forward to hearing a lot more about their work. I hope Imperial Metals can afford the cleanup, estimated at $200 million or more. Especially given that their stock lost 40% of its value on the news of the tailings pond breach…

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