Rupture of Thompson's tailing dams could kill nearly 100 people, Vale reveals

A mining giant reeling from a deadly dam collapse in Brazil says it is investigating one of its dams in Thompson, Man., over fears a rupture could kill as many as 100 people.

Active mine dam in Thompson, Man., records a 'very high' hazard rating

Vale says 'known zones in the dam foundation' are being analyzed after it was noted that the company's dams in Thompson, Man., are a 'very high' hazard, as determined by the Canadian Dam Association. (CBC)

A mining giant reeling from a deadly dam collapse in Brazil says it is investigating one of its dams in Thompson, Man., over fears a rupture could kill as many as 100 people.

Vale revealed one of the six active mine dams in the northern Manitoba city recorded a "very high" hazard rating, as determined by the Canadian Dam Association, which means a collapse could result in up to 100 deaths, significant loss of environmental and cultural values and "very high economic losses" affecting important infrastructure. 

The mining company disclosed the safety of its dam operations worldwide, after facing pressure from the Church of England Pensions Board and a group of Swedish investors in the wake of a January dam failure at Brumadinho, Brazil, that killed 270 people.

Vale employees and contract safety inspectors knew of dangerous conditions at the Brazilian dam for months, the Wall Street Journal has reported.

'People on the ground' ignored: MP

"Based on internal and external investigations, known zones in the dam foundation are under further analysis and we are undertaking additional assessment and precautions while the investigation is ongoing with the oversight of the TRB [Tailings Review Board]," Vale said in its report.

The company's records state the Thompson tailing dams have, at some point, failed to be confirmed as stable, or experienced notable stability concerns, as cited by an independent engineer. 

Tailing dams are physical structures that store the remnants of mining operations. 

The company's disclosure first came to the attention of local MP Niki Ashton when it was reported by the Wall Street Journal.

Vale stands as Thompson's largest employer with about 850 employees.

"Vale told its shareholders of this, but not people on the ground," she told the House of Commons on Monday, after writing to federal Environment Minister Catherine McKenna and Natural Resources Minister Amarjeet Sohi to ask the Liberal government to intervene against a company she alleges is disregarding safety. 

Sohi said he would follow up with the area MP. 

Vale said it publicly disclosed its findings on its website a few days ago.

The company said a review in the last few weeks found one containment dam did not meet the standard of the Canadian Dams Association, but Vale is reviewing the analysis by an independent engineering consultant since the finding does not correspond with the dam's actual performance.

"In reality, all phreatic surfaces — those below the water table — are reporting normally. There are no increases in pore pressure, no displacements or movement in the dam whatsoever," Vale spokesperson Angie Robson said in a statement.

She said the dam is continuing to perform well. 

"There is no imminent threat of dam failure. This is an issue that was surfaced through effective monitoring and inspection and is being addressed responsibly and appropriately. In other words, the system is working," she continued.

Safety our highest priority: Vale

"The integrity of tailings facilities across the entire mining industry is under greater scrutiny than ever. Ensuring the safe operation and maintenance of our facilities, including in Thompson, is our highest priority."

It added that a discussion on tailings management comes up when Vale's community liaison committee in Thompson meets.

The Thompson tailings dam has been in operation since 1971 and was last evaluated by an independent expert in Sept. 2018, Vale said. The company said it last conducted an analysis in 2017 of the downstream impact on communities, ecosystems and critical infrastructure in the event of a catastrophic failure. 

Vale has been trimming its operations in Thompson after it closed a nickel mine in 2017 and shuttered its smelting and refining facilities a year later. 

The mining company employed about 1,450 full-time employees in early 2017, but the total has since dropped to about 850. 

About the Author

Ian Froese


Ian Froese is a reporter with CBC Manitoba. He has previously worked for newspapers in Brandon and Steinbach. Story idea? Email:


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