The Vale dam collapse which occurred last week likely occurred due to portions of the sand and dried-mud structure dissolving into a liquid, according to a state regulator on Friday.
There are at least 110 people confirmed dead while more than 230 people are still missing, according to a firefighters' count on Thursday night, which would make it the deadliest mine disaster in Brazil.
The burst tailings dam at the Corrego de Feijao mine collapsed directly over the town of Brumadinho and has ignited public anger against the mining company Vale, who was also co-owner of the Smarco mine which collapsed in 2015.
An internal study revealed the mining company knew as recently as last year some areas hit were at risk if the tailing dam burst, according to the Folha de S.Paulo newspaper, though Vale said the study was only a routine disaster preparation plan as required by Brazilian regulators.
The disaster is one of the first major challenges facing far-right President Jair Bolsonaro, who only took office a few weeks ago, but has been promising to curb regulations for industry and agribusiness.
Hildebrando Neto, deputy minister for environmental regulations in the state of Minas Gerais where the collapsed dam is based, told Reuters the current evidence suggests the dam burst was caused by liquefaction.
Liquefaction is a process where solid material, such as sand, loses strength and stiffness over time and starts to behave more like a liquid.
Neto said that was the cause of the 2015 collapse of the Smarco dam, which killed 19 people.
The internal study published by the Folha newspaper was from April 2018 and detailed the likely impact if the dam were to collapse.
The study said sirens would alert workers if the dam burst, but the company admitted last week the mudflow destroyed the sirens before they could warn the employees and locals in the nearby town.
Vale released a statement which said the plan was “built on the basis of technical studies of hypothetical scenarios in the event of a breach.”
Officials with the Mines and Energy Ministry and the National Mining Agency (ANM) said the cause of the current collapse was still unclear and that Vale submitted documentation that indicated it was still 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 also announced the plans for dealing with the massive amount of debris unleashed into the area after the collapse.
They would build barriers to contain the mud in the area around the dam collapse, dredge a section of the nearby river, and construct barriers to sift out any fine residue.
"It isn't just mud there, it's people's families. Everything will depend on how rescue efforts go. And it will take a long time," said Anderson Amparo, from Brazil's Environmental Protection Agency (Ibama).
Amparo also said even if authorities were confident there were no more bodies buried in the mud, it would not need to be cleared entirely.
"In some areas it is best to plant over the land to restore it to its original use, whether it be agriculture or forest," Amparo said.
But Miguel Felippe, a professor of geoscience at the Federal University of Juiz de Fora, said it's unclear if the mud itself is toxic, but there is some environmental damage that will come from the disaster.
"This debris is very likely to contain harmful chemical substances," he said. "Even if there are no traces of heavy metals, which are the most worrisome, like arsenic, there are others which are sure to be there and will float downstream, as the mud has already reached a river, so, environmentally speaking, it would be best to remove the material."
The tailings of the mine could contain traces of nickel, magnesium, cadmium, iron oxide, ammonia, silica, silt, clay, mercury and arsenic, explainedBráulio Magalhães Fonseca, a geologist at the Federal University of Minas Gerais.
But the level of toxicity depends on the concentration of those substances.
-WN.com, Maureen Foody
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