Federal Authority Advice Record - Natural Resources Canada

Hi again,

Just wanted to add some info, which might be useful for later discussions, regarding Selenium. I believe in our last meeting IAAC wanted to check regarding selenium impacts, open pit mining vs underground mining. Please see the below response:

“ Regarding the statement that underground mining has lower impacts associated with selenium exposures than open pit mining. NRCan acknowledges that open pit mining produces higher volume of waste rock than underground mining and hence, the potential sources of selenium from waste rock piles could be lower for underground mining compared to open pit mining. However, this statement is too broad of a generalisation. Selenium impacts to the aquatic environment depends on the following reasons:

1. Size/volume/dimensions of waste rock storage areas
2. Grain size of rock which depends on the lithology of the mined area
3. Relative distribution of selenium containing minerals which can be site specific
4. Reactivity of rock surface areas to generate selenium containing leachate, which can also be site specific
5. Water availability at the site and associated dilution potential in mine site water quality
6. Presence of sulfate in mining effluent that reduce selenium bioaccumulation in the receiving environment
7. Assimilative capacity of the receiving environment, which differs from one mining site to the other. Indeed, some mining operations may discharge in large rivers, small creek or lakes, discharge in similar water bodies than other operations (i.e. cumulative effects)”

Happy to discuss more during our 2PM meeting today.