Decades of gold mining spewed out enough toxic tailings at the Giant Mine site in Yellowknife, N.W.T., to last for millenniums.
Now, the federal government’s challenge is to keep the thousands of tonnes of arsenic trioxide dust frozen in the ground forever.
Environmental and engineering experts wrapped up their week-long talks about cleaning up the site on Friday.
Some groups are worried about maintaining the site, especially as climate change brings uncertainty in the centuries ahead.
The government is freezing the 237,000 tonnes of toxic dust underground by pumping coolant deep into the mine – similar to how an ice rink is kept frozen. Officials say they've planned for the risks that could happen in a 100-year period.
"This is the solution. There is no other solution right now," said Adrian Paradis from the Department of Aboriginal Affairs and Northern Development.
The Giant Mine cleanup team admits planning for the future won’t be easy because the site will require constant maintenance. Even after the dust is frozen, Paradis says about eight people are needed to monitor the arsenic and treat the water year-round, forever.
In a worst-case scenario, if no one maintains the site, it would take 20 years for the arsenic to thaw.
It’s up to future governments to consider new technology and cope with climate change.
"We no longer get the hard frosts we get in October; we get the rain like you see today in mid-late October. And it is a dynamic system," said Paradis.
Kevin O’Reilly from Alternatives North said planning for forever means coming up with worst-case scenarios and ways to deal with them.
This includes everything from earthquakes, to flooding, to melting permafrost.
"Is the precipitation going to change? The timing of it? The duration?" O'Reilly asked. "It’s really difficult for us to peer into the future, but we should be designing things with whatever understanding we have now."
O'Reilly said another challenge to the long-term management is ensuring future generations understand the risks the mine site poses.
"Information management – how do we preserve and protect the documents about what's happened at the site over the years, while it was an active mine, when it was being remediated," said O'Reilly.
"How do we have access to those documents, not only now, but forever? Paper degrades, it disappears. You put something on CDs, the assumption is you have computers, electricity."
The same department which is in charge of the cleanup, Aboriginal Affairs and Northern Development, is also in charge of monitoring the project.
O’Reilly, as well as the Yellowknives Dene, wants more independent oversight.
Todd Slack, the Yellowknives Dene First Nation’s director of lands and environment, said if something goes wrong there is potential for damage throughout the Mackenzie Valley.
"I doubt anyone in Yellowknife wants people in Ottawa to be making decisions about our health or environment," said Slack. "I think that type of oversight has to be maintained here in the territory."
There will be more public hearings this winter and all parties hope people living in Yellowknife can contribute ideas for how to guard for the future – long after these buildings, and the government running the project, are gone.