A Habitat Reclaimed
On a remote corner of Vancouver Island, an open pit copper mine abandoned in 1967 became the source of contamination for a historically rich aquatic habitat, the Tsolum River. A number of remediation efforts were attempted over the years, but high copper concentrations continued to affect the watershed, worsening with rainfall and seasonal melt.
Ultimately, the mine’s toxic, copper-bearing run off decimated entire fish populations, including Pacific pink salmon stocks, worth millions to the area. The Tsolum River Partnership was formed and in 2006, QM became part of a 10-year, multi-phased, multi-partnered solution to reverse the environmental damage.
Tonnes of pyrite-bearing waste rock left behind at the abandoned mine were the source of serious acid rock drainage and subsequent copper leaching into the watershed. To reclaim this five hectare site, where decades of remediation efforts had previously been unsuccessful, QM faced a complex challenge.
The project plan called for the reconfiguration of the natural drainage patterns of the site, located on the side of a mountain, and sealing off the open-pit to reduce the interaction between surface water flows and the copper bearing rock. Steep, poorly maintained roads required upgrading before work could begin, a crucial first step, since the lack of till cover in the area meant it would need to be imported from other sites further down the mountain. Severe weather conditions made the construction season short and difficult.
An Integrated Approach
QM implemented a series of remediation efforts in three phases to isolate the subsurface, divert any runoff, and reduce the interaction between moisture and the waste rock, thereby stopping toxic copper from leaching into the river.
- Construction of a surface water drainage channel to divert drainage away from the site
- Installation of underdrains
- Placement of till buttresses against the high pit walls
- Installation of a till cushion atop the exposed open pit floor and waste rock
- Installation of a bituminous geomembrane over the till cushion, to seal in the entire five hectare pit
- Placement of a till cover over the geomembrane
- Construction of surface drainage channels in the till cover
- Placement of topsoil and woody debris over the till cover for growing medium
- Revegitation of the site with native plants to reclaim and stabilize the slope
- Revegetation and reclamation of the off site borrow areas
- Instrumentation installation
- Design and construction of a drainage system and settling pond for future implementation of a lime addition water treatment system if required
- The water quality in the Tsolum River improved significantly in 2009 at the completion of Phase 1
- Water quality goals set for the river were met for the first time in 2010 and continue to improve
- 77% decrease in copper contamination from the mine site
- All concentrations measured since the cover was completed have met the outcome target of under 11 parts per billion
- 40,000 pink salmon returned to the Tsolum River in 2009
- An estimated 1,000 coho also returned there to spawn in 2010, more than have been seen in a decade