From my limited understanding of the Mount Polley mine it was certified in 1992 under the old Mine Development Assessment Act. That Act changed in 2002 to the current one which has been updated through the years.

They had a tailings pond held back by an earth dam. The tailings had a ph of 8.5 and are not considered acid-generating. This is close enough to SC it will be interesting to see if there is damage and how much.

They were raising the walls of the dam over time, as they mined and needed it and somehow it failed.

In my opinion, this might indicate a review is needed of older mines that have environmental certificates from the previous Act to ensure they comply with current standards.