University of British Columbia mining engineers have launched a plugging project to stop the toxic run-off from one of North America’s most polluted mines that could revolutionise mine reclamation and closure techniques worldwide.
The Millennium Plug project involves the construction of two plugs in a tunnel of the old Britannia copper mine near Squamish. Over 9000 tonnes of copper, zinc and sulphuric acid have been seeping from the site since it closed more than 25 years ago, running into a creek that empties into Howe Sound.
The acid rock drainage contamination has created a two-kilometre marine dead zone that has been classified as Canada’s worst mining pollution problem.
One of the plugs being constructed is a 25-metre-long earth dam made of layers of soil, sand, and clay.
Dubbed the Millennium Plug because its creator, UBC PhD candidate Brennan Lang, expects it to function for 1,000 years, the barrier is designed to withstand high pressures and seismic activity.
Unlike the conventional concrete plugs usually used in mine closure, the Millennium Plug won’t corrode in the mine tunnel’s acidic environment and is also less costly to build than concrete.
While compacted earth barriers have been studied extensively for use in underground nuclear waste disposal, UBC is said to be leading the way in studying their effectiveness in mine reclamation.
Once installed, the Millennium Plug, and a second concrete plug being built in the same tunnel, will become an on-site research station for UBC faculty and students to test different mine closure methods that can be incorporated in plans for operational mines. The goal is to develop ‘walk-away’ solutions for mine reclamation that can be marketed globally.
‘Virtually every hard rock mine and coal mine in the world suffers from acid rock drainage problems to some degree,’ said Professor John Meech, of UBC’s Centre for Environmental Research in Minerals, Metals and Materials (CERM3). ‘By next year, we will know how to design these plugs for virtually any place in the world.’
Once in place, the plug is expected to cut off 45 per cent of the copper pollution currently flowing from the mine. The BC government has plans to build a treatment plant on site, which engineers expect will reduce the pollution by an additional 45 per cent.