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The total price tag was estimated at under $25 million when the federal government agreed to pay for half the cleanup of a radioactive Cold-War-era uranium mine in northern Saskatchewan.

But a decade later, the expected cost for remediation of the remote Gunnar mine has swelled to about 10 times that and Ottawa isn't offering any more money, even as the province starts this summer to remediate millions of tonnes of tailings and waste rock left when the mine closed in 1964.

"With Gunnar, just the size of the waste-rock piles and the tailings area alone, it's fairly unavoidable that costs were significantly more," said Cory Hughes, executive director of mineral policy at the Saskatchewan Ministry of the Economy.

"You really have to be there to appreciate the size of the project."

The Gunnar mine near Uranium City opened in 1955. The federal, Crown-operated Eldorado Mining and Refining Corp. supplied refined uranium yellowcake that was an essential ingredient for U.S. atomic weapons.

Over the course of its operation, the mine produced 4.4 million tonnes of tailings and 2.2 million tonnes of waste rock. It also left behind an open pit more than 100 metres deep.

Canada officially stopped exporting uranium for weapons production in 1965.

The Gunnar pit was flooded with water from Lake Athabasca when the mine closed and the tailings and waste rock were left to the elements. Dust blew in the wind and rain and runoff drained over the tailings and into the lake.

The Crown's mining and surface rights lapsed in 1990 and the property reverted to the Saskatchewan government. In 2006, Saskatchewan and Natural Resources Canada agreed to share the remediation costs, although the province would be responsible for building demolition.

The estimated cost was $24.6 million over 17 years.

"Really, the original estimate is a starting point to get the ball rolling," explained Ian Wilson with the Saskatchewan Research Council, which has been contracted to do the cleanup.

Over the last decade, detailed environmental impact studies have been completed, public consultations have been held and regulatory hurdles of the Canadian Nuclear Safety Council have been cleared.

Wilson said preliminary work to build roads for crews has already started and workers are to begin using waste rock to cover the tailings this summer.

The work so far hasn't been cheap. A Natural Resources Canada report from 2012 said the buildings, some of which contained asbestos, cost $20 million to tear down. Heavy equipment has to travel to the site in winter on an ice road.

The job is expected to take three to four years.

In 2014, the province set up a liability for the remaining work, then expected to be $208.5 million, Hughes said.

The province will spend just under $25 million for the work that's being done this year, he said. The province is hoping Ottawa will kick in to cover more of the cleanup's cost, but the response so far hasn't been promising.

Natural Resources Canada says Saskatchewan owns the site and is responsible for funding the project.

"The liability for the Gunnar site is held by Saskatchewan," the department said in an emailed statement. "There are no plans to provide additional federal funds to Saskatchewan for the remediation beyond the $12.3 million federal commitment in the agreement."

Ugo Lapointe, of the advocacy group Mining Watch Canada, said initial cleanup estimates frequently fall far short of true costs. He noted that expected costs for remediating the Giant gold mine in Yellowknife have also skyrocketed.

Lapointe said initial cleanup assessments are often completed by few staff with only limited information.

It's when field work begins that costs start to grow, he said.

"It's a trend that's not unique."

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