The collapse of a Brazilian dam controlled by miner Vale a week ago likely happened because parts of the sand and dried-mud structure dissolved into liquid, a state regulator said in an interview, similar to the cause of another deadly mining disaster less than four years ago.
With 110 people confirmed dead and another 238 missing, according to a firefighters’ count on Thursday evening, the tailings dam collapse in the town of Brumadinho could be Brazil’s deadliest mine disaster.
The burst tailings dam at the Corrego do Feijao mine last Friday has ignited intense public anger against Vale, which was co-owner of Samarco, the previous dam that collapsed.
An internal study showed the miner knew as recently as last year that some of the areas hit were at risk if its tailings dam burst, according to a report by Folha de S.Paulo newspaper. Vale described the study as a routine disaster preparation plan required by regulators.
The disaster poses a headache for the new government of far-right President Jair Bolsonaro, whose new business-friendly administration must juggle public anger over the tragedy and its own desire to ease mining and environmental regulations to kick-start growth.
Hildebrando Neto, deputy minister for environmental regulations in the state of Minas Gerais where the collapsed dam is based, told Reuters late on Thursday that all evidence suggests that the burst was caused by liquefaction, a process whereby a solid material such as sand loses strength and stiffness and behaves more like a liquid.
Dams holding mining waste, known as tailings, sometimes collapse for this reason.
Neto said liquefaction caused the 2015 collapse of the Samarco dam, which is co-owned by Vale and led to the deaths of 19 people.
The internal study reported by the Folha newspaper was dated April 18, 2018, and outlined the likely impact of a collapse at the dam. It found that the mine restaurant, where many Vale workers were likely to have died, would be hit by toxic mud.
The study envisaged that sirens would alert workers if the dam burst. The company has said the mud flow destroyed the sirens before they could sound the alarm.
Vale said in a statement that the plan was “built on the basis of technical studies of hypothetical scenarios in the event of a breach” although it did not directly reference Folha’s story.
Officials with the Mines and Energy Ministry and the National Mining Agency (ANM) told reporters on Friday that the cause of the rupture was still unclear and that all documentation regularly submitted by Vale had indicated that the dam was stable.
“If we had known (what the problem was), maybe this tragedy would have never happened,” The ministry’s mining secretary Alexandre Vidigal said. “We are in the investigation phase and we cannot say whether the (inspection) model was adequate or not.”
Vale Chief Executive Fabio Schvartsman has said the miner built its facilities to comply with regulations and that equipment had shown the dam was stable.
In the wake of the disaster, Vale has said it will take up to 10 percent of its production offline and spend 5 billion reais ($1.36 billion) to decommission 10 dams.