Brazil bans upstream dams

Article by Amanda Jasi

BRAZIL has decided to ban tailings dams built by the upstream method. The decision follows the fatal collapse of such a dam in Brumadinho, Minas Gerais, Brazil, on 25 January. So far 169 people have been reported dead and 141 people are missing.

Tailings are the waste product of ore processing, and they are typically stored as a slurry in tailings dams. Steven Edwards, Deputy Director of the University College London Hazards Centre, said “the upstream method is the worst… because of the potential likelihood of failure of that design”. Dams built by the centreline or downstream method are more resilient than upstream dams, but upstream dams are “basically quicker to build and cheaper.”

The decision to ban upstream dams was published as a resolution by Brazil’s National Mining Agency (ANM) in the official journal of the country’s federal government. Upstream dams in the country are to be decommissioned or removed by August 2021, reports Bloomberg. The report adds that by 15 August dam owners are to complete a technical plan, which should at a minimum include reinforcing existing structures or building new retention structures.

Brazil’s decision to ban upstream dams follows the collapse of Vale’s Dam 1 of the Córrego do Feijão mine located in Minas Gerais, Brazil. When the upstream dam failed it, released a torrent of muddy sludge which buried the surrounding area, affecting Vale employees, contractors, and members of a nearby community. 169 people have been reported dead, and 141 remain missing.

In 2015 another upstream dam collapsed in Brazil. The Fundão tailings dam was owned by Samarco, which is co-owned by Vale and BHP Billiton. When the dam collapsed, due to design flaws, it killed 19 people and contaminated several kilometres of a downstream river.

Recently, it was reported that Vale “knew” that Dam 1 was at risk of collapse, and that the company had placed the dam in an “attention zone”. Reportedly the dam was at twice the “maximum level of risk” tolerated by internal guidelines. Vale claims that it was unaware of any such risk.

Reuters reports that Vale is facing public pressure and criticism following the collapse. The arrests of several Vale employees in relation to the collapse have been reported.

According to Reuters, the ANM’s decision will impact about 50 dams alone in Minas Gerais, the “mining heartland”. It’s the “strongest governmental response yet to the disaster,” says Reuters. However, Bloomberg claims that this move is unlikely to affect global iron ore supplies significantly.

Vale decommissioning

Following the collapse of Dam 1 Vale decided to carry out an accelerated decommissioning project, in order to decommission its ten inactive upstream dams. In 2016, following the collapse of Fundão, Vale decided to decommission its 19 upstream dams. Since then only nine have been decommissioned. Vale expects that decommissioning the remaining dams will cost R$5bn (US$1.4bn).

Today, Vale announced the evacuation of residents in the Self-Saving Zones of five dams that are part of the accelerated decommissioning program. A Self-Saving Zone (ZAS) is a region of approximately 10 km that is downstream of the dam. In an emergency Vale is responsible for alerting the population in this region. In total about 125 residents were evacuated from the ZASs of relevant dams, as well as from areas that would be isolated.

On 16 February, Vale announced the evacuation of about 200 residents from the ZAS of the B3/B4 dam at the Mar Azul mine, in Nova Lima, Minas Gerais. This was amid “fears it was structurally weak and could collapse”, says Reuters. The decision was made after data from an analysis of the dam was reviewed.

Vale states that all the above evacuation are precautionary measures.

Article by Amanda Jasi

Staff reporter, The Chemical Engineer

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