Dam fixes were months from completion
Mount Polley mine. (REUTERS)
Work that would’ve made the Mount Polley tailings dam both taller and thicker was ongoing at the time of the Aug. 4 breach and wouldn’t have been completed until October, according to Imperial Metals Ltd.
Steve Robertson, a vice-president with the company operating the mine, told 24 hours on Wednesday the company had been in the midst of adding another four metres to the height of the dam.
Work had begun in mid-May, he said, and was being performed uniformly around the large structure.
This would have occurred days before a government assessment that found tailings levels were too high in one area of the pond. The tailings level was promptly reduced by the end of the next month, according to government.
Robertson said when the breach occurred, the area of the dam that broke had “one of the highest core elevations on the structure” at the time.
“We had clearly, two-plus metres, over two metres of freeboard at the area where the breach occurred,” he said.
Robertson said height is added to the structure generally every one to two years to provide more storage for mine tailings.
“You can’t do a dam raise without the widening, you can assume if the dam was going up — it was going out,” he said.
“We were well within our permit requirements for freeboard ... there’s no requirement in the permit to do with the width, but the engineers know how high it has to be so they determine how wide it has to be.”
Robertson said the construction “could not have been a factor in this incident,” but added that a forensic investigation has not yet begun because of safety issues — though employees at the mine have now been interviewed.