If anyone is curious, here is what the levels of selenium are from the Teck mines in BC. They had a lot of issues prior to 2014 and have spent an extensive amount of money on treatment facilities to try to get to the limits imposed on them.
https://elkvalleywaterquality.gov.bc...march-2024-q1/
More info:
https://elkvalleywaterquality.gov.bc...-and-timeline/
I suspect that if Alberta were to impose the same limits, they may find the treatment expenses to outweigh the benefit for a new mine. Teck was able to spend that as the mines were already quite established and large.