Three more Brazil dams at critical alert

Article by Amanda Jasi

VALE has put three more of its Brazilian mine tailings dams on the highest level of alert – level 3 – bringing the total to four. Brazil’s Mining and Energy Secretary said that a level 3 alert means “a rupture is imminent or already happening,” reports The Guardian.

Earlier this year a Vale mine tailings dam collapsed in Brumadinho, Minas Gerais, Brazil. Dam 1 of the Córrego do Feijão mine collapsed on 25 January and as of 30 March 217 people are confirmed dead and 84 people are missing.

On 27 March, Vale raised the alert levels of the B3/B4 dam at the Mar Azul mine, in Nova Lima, Minas Gerais, and the Forquilha I and Forquilha III dams, at the Fábrica mine, in Ouro Preto, Minas Gerais. The dams are already part of an accelerated decommissioning project. This follows the decision on 22 March to raise the alert level of its Sul Superior Dam to level 3.

The areas surrounding B3/B4 and Forquilha I and III had been evacuated in February. About 250 people were removed in total. Nevertheless, as part of the protocol, sirens in the Self-Rescue Zone (ZAS) of the dams were triggered when the alert levels were raised. The ZAS is the area 10 km downstream of the dam, or “the equivalent to the arrival of the flood wave in 30 minutes”. Vale is responsible for alerting the population of the ZAS, in the event of an emergency.

The alerts were raised as a preventative measure because an independent safety auditor indicated that the structures would not receive stability condition declarations. This is because the safety factor of the dams is below the new limit established by Brazil’s National Mining Agency (ANM) on 18 February.

On 18 February a resolution by the ANM was published in an official journal of Brazil’s federal government. The resolution established regulatory measures aimed at ensuring the stability of mining dams. Measures included a ban on upstream tailings dams. Dam 1 was an upstream dam, as was a Samarco dam which collapsed in 2015, killing 19 people. Samarco is a joint-venture of BHP Billiton and Vale.

Vale says it will adopt measures, with the support of Minas Gerais’ Civil Defense and “other competent bodies”, to guide Secondary Self-Rescue Zone (ZSS) residents through training and evacuation drills in case of a dam breach. The ZSS is an area outside of the ZAS where flooding could occur in the event of a collapse.

Vale added that “it continues to adopt a series of preventive measures to increase the safety condition of its dams”.

Article by Amanda Jasi

Staff reporter, The Chemical Engineer

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