This is what remediation at Giant Mine looks like. It's going to cost more than expected

A massive undertaking to remediate Giant Mine in Yellowknife is going to cost significantly more than expected. 

The project's budget was pegged at nearly a billion dollars back in 2014, but on Wednesday, during the first media tour since remediation at the site began, officials said the figure had grown.

They wouldn't say by how much, however. Natalie Plato, the deputy director of the Giant Mine Remediation Project, said they'd unveil the new figure once it was approved by Canada's Treasury Board — something she expects to happen on Oct. 27. 

The scope of the work has changed over the past eight years, explained Plato. The timeline to get it all done was also extended from 2031 to 2038. 

Plato said some of the big changes since the last cost estimate have been forming the Giant Mine Oversight Board, launching a project to monitor health effects of arsenic exposure, and a decision to fill eight open pits with waste rock that were previously going to be left open. 

When probed by a reporter that the new budget must be significantly higher, Plato responded: "you're on the right track." 

Project officials want to extend the timeline, in part, to avoid any aggressive peaks in labour demand — and provide more opportunities for northern and Indigenous businesses. Since the federal government took over the site in 2005, $648 million have been spent on contractors — $313 million of which have gone to Indigenous contractors. 

The remediation project's labour demand is expected to peak in 2031, with 260 full time jobs. 

Remediation officially began at Giant Mine in 2021.

The project team said it's continuing to stabilize extensive underground spaces by filling them with a mixture of tailings, cement and chemical additives. Plato said the paste is made on site and pumped underground through drill holes. 

Brad Thompson, the regional project advisor for Public Service and Procurement Canada, said 40,000 cubic metres of material has been poured this year — and there's 400,000 cubic metres of empty space that needs to be filled, in all. 

This work is of particular importance around the site's arsenic chambers — where 237,000 tonnes of highly toxic arsenic trioxide dust is being stored. The dangerous material will eventually be locked underground forever by "freezing" the rock around it with thermosiphons.

There are four spots where rows of thermosiphons will be installed. Plato said work has been done to prepare the first spot, dubbed Area 1, by blasting and levelling it. The space needs to be flat, she said, so that rigs can come in and drill holes for the technology.

Technically, rock can't be frozen — but the thermosiphons will cool it to -5 C. That way, if water ever gets close to the arsenic chambers, it will freeze, preventing the water from reaching the arsenic trioxide or carrying it anywhere.