Canada – The engineering firm that designed the Mount Polley tailings pond containment system that collapsed on August 4, also designed a tailings dam that failed catastrophically in South America on Aug. 19, 1995.
Knight Pisold designed the tailings containment facility for the Canadian-owned Omai gold mine in Guyana. Before the accident, it had handed off operational responsibility to the mining company, which then hired another engineering consultant, the Canadian firm Golder Associates.
The Omai tailings dam collapse spilled an estimated 2.9 million cubic metres of toxic waste into the Essequibo River, the country’s biggest and most important watershed. (Some estimates run higher.)
Guyana’s President Cheddi Jagan, whose government held a five per cent share of the mining venture — it was the poor country’s largest private sector employer — and had been championing its economic benefits, called it “the country’s worst environmental disaster.”
A subsequent inquiry found no criminal liability and a civil class action suit was later dismissed.
It’s worth noting, perhaps, that by comparison the Mount Polley tailings dam failure, which B.C.’s Mines Minister Bill Bennett has equated with a simple natural landslide, spilled 14.5 million cubic metres — about five times as much contaminated waste as at Omai — into the Fraser River system, B.C’s biggest and most economically important watershed.
The most hazardous component in the Guyana accident was cyanide. The accident at Mount Polley released sediments contaminated mostly with arsenic and heavy metals.
Environment Canada lists on-site tailings disposal totals for the Mount Polley mine as including 969,993 kilograms of arsenic, 625,322 kilograms of lead, 19,940 kilograms of cadmium and 5,197 kilograms of mercury.
Environment Canada says of these listed compounds:
“Arsenic has been consistently demonstrated in numerous studies to cause cancer in humans” and “there is believed to be some chance of adverse health effects at any level of exposure.”
“Cadmium compounds have been classified as ‘probably carcinogenic to humans’ … there is believed to be some chance of adverse health effects at any level of exposure.”
“Lead is a highly toxic metallic element…even small amounts of lead can be hazardous to human health.
“Mercury is toxic and has the ability to pass the blood-brain barrier and affect the central nervous system.” The most common form of mercury uptake is eating contaminated fish. It’s of particular concern for pregnant and lactating women and small children whose developing nervous systems are vulnerable.
So, however one might choose to characterize the Mount Polley spill — and even if water quality levels are safe for now with river levels at summer lows — seeking to quell public concern with a simplistic comparison to a landslide seems curiously insensitive.
In one eerie foreshadowing of the current situation near Quesnel Lake, Knight Pisold warned the mine operator in Guyana when it handed off responsibility that modifying the tailings containment structure to increase volume might exceed its designed capacity and safety margins.
The Guyanese newspaper Stabroek News reported from the inquiry into the Omai tailings dam collapse that “Knight Pisold has told foreign media that the dam failed at a height at which they were no longer responsible, having been replaced at the end of 1992 by Omai’s current dam consultants, Golder Associates.” After Knight Pisold had ended its relationship with the Omai mine, the dam was raised significantly, and subsequently failed.
At the Mount Polley mine, Knight Pisold says that in 2011 it warned both the B.C. mine’s owners, Imperial Metals, and the provincial government that its original engineering was designed to accommodate a significantly lower water volume than was reportedly present when the dam breached.
“Knight Pisold informed Imperial Metals that we would not continue as the engineer of record for the Mount Polley Mine on Feb. 10, 2011, and subsequently ceased to perform that role,” the company said in a statement posted to its website last week.
“During the time we acted as engineer of record, the tailings storage facility at Mount Polley operated safely and as it was designed.”
The engineering firm says the facility was subjected to an independent third party assessment in 2006 and was found safe and structurally sound.
However, the company says, the tailings containment was designed to accommodate “a significantly lower water volume than the tailings storage facility reportedly held at the time of the breach.”
“Significant engineering and design changes were made subsequent to our involvement.”
Knight Pisold says that it wrote the B.C. government in 2010, just before leaving the operation, to warn that “the embankments and the overall tailings impoundment are getting large and it is extremely important that they be monitored, constructed and operate properly to prevent problems in the future.”
The B.C. government says it inspected the dam 33 times after Knight Pisold raised its concerns, including a geotechnical survey in 2013 and eight inspections in 2014.
This would mean that any modifications to structure, volume or operation in the three years before the dam’s collapse occurred under the regulatory oversight of the provincial Mines Ministry.
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