SAO PAULO – Brazilian miner Vale's tailings dam in the town of Barao de Cocais in Minas Gerais has up to a 15% chance of breaking, the state's environment secretary said on Monday.
The dam at Vale's Gongo Soco mine is about 64 km from Brumadinho, where a tailings dam collapse unleashed a torrent of toxic mud in late January, killing more than 240 people.
Environment Secretary Germano Vieira disclosed the estimate after discussing the matter with prosecutors and the company itself.
Vale said last week that the dam was at risk of rupturing.
The warnings about another possible dam collapse have underlined concern about the stability of Vale's tailings dams in general after the world's largest iron ore miner suffered two deadly accidents in a little over three years.
A dam burst could be triggered by slippage in the embankment at the Gongo Soco mine, Vieira said.
"The breach of the embankment is going to happen," he told reporters. "What we don't know is whether that breach will affect the dam."
He then cited an estimate from an independent auditing firm that the chance of a dam burst was "one in ten, or one in eight, leading to a 10% to 15% probability" of collapse.
Although Vale has previously said it remains unclear whether an embankment slippage could trigger a collapse, it announced on Saturday that it had begun building a concrete structure 6 km downstream of the dam that could contain a large portion of the tailings.
"The goal is to reduce potential impacts on people and the environment in the extreme case of a breach," Vale said.