REUTERS says it has seen an internal document that shows that Vale knew last year that its dam in Brazil was at risk of collapse. The dam collapsed on 25 January in Brumadinho, Minas Gerais, Brazil, and so far, 165 deaths have been confirmed whilst 155 remain missing.
The news agency said that the report’s existence raises questions as to why it seems Vale took no precautions before the collapse, and why an external audit conducted in September last year concluded that the dam was stable.
The report, dated 3 October 2018, states that the chance of collapse was 1 in 5,000, twice the tolerable “maximum level of risk”. According to Reuters, the report placed the dam within an “attention zone” with nine out of 57 other dams in Brazil which were also studied. The report said “all prevention and mitigation controls” should be applied, says Reuters.
According to Reuters, an e-mailed statement from Vale said: “There is no known report, audit or study with any mention of an imminent risk of collapse at Dam 1 in the Córrego do Feijão mine in Brumadinho.”
“To the contrary, the dam had all its certificates of safety and stability attested to by local and foreign specialists.”
Reportedly, a separate document, dated 15 November 2017, states that any structure with an annual chance of failure above 1 in 10,000 should be brought to the attention of the chief executive and the board. The creation of an alert system for top management was apparently studied, but Vale did not implement one.
Reuters reports it also saw the audit by international company TÜV SÜD, which specialises in geotechnics. The report apparently said that the dam adhered to the minimum legal requirements for stability, but the geotechnics specialist raised a number of concerns. In particular, dam drainage and monitoring systems were flagged.
TÜV SÜD reportedly made 17 recommendations to improve dam safety. Vale said these recommendations were routine and that it attended to all of them, reports Reuters.
The document from October reportedly identified static liquefaction and internal erosion as the most likely causes of a potential failure at the dam in Brumadinho. Liquefaction is a process by which materials such as sand lose their strength and stiffness and behave more like a liquid. This process led to the collapse of a Samarco tailings dam in 2015, which killed 19 people and caused Brazil’s worst-ever environmental disaster. Samarco is a joint venture between Vale and BHP Billiton. The tailings in the dam were already liquefying due to oversaturation, but the process was accelerated by small earthquakes which initiated a mudslide.
A recent statement by Vale claims that the water pressure in the dam which recently collapsed had been decreasing. This was stated in the TÜV SÜD report which therefore concluded that the dam was “stable with a safety factor above what's recommended by law,” said Executive Manager of Ferrous Metals and Coal Planning and Development, Lúcio Cavalli.
Following the recent dam collapse Vale CEO Fabio Schvartsman claimed that it came as a complete surprise for the company, and the company continues to insist that the dam was stable.
Vale says that the cause of the recent dam collapse is still under investigation. Reuters also says that Vale will invest some US$400m from 2020 to help reduce reliance on tailings dams.
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