Two months after a deadly dam collapse in Brazil, mining company Vale says that another one of its upstream tailing dams is on the verge of falling apart, and that the area surrounding it has been evacuated.
On January 25, a tailing dam at Vale’s Córrego do Feijão mine burst, letting loose a torrent of toxic mud filled with discarded mine tailings. The flood killed at least 206 people, making it Brazil’s largest environmental disaster. Now, the government has ordered the city of Barao de Cocais evacuated after a risk evaluation from an independent auditor put one of the company’s dams there at the highest possible level of collapse risk.
The evacuation is another blow to the embattled upstream tailing dam, a common mining structure that has been under public scrutiny since the Brumadinho collapse. Tailing ponds are “lakes” of mud, water and ground-up mining waste that allow miners to separate out the water from the solid waste. They are contained by tailing dams that are built higher as the “water” level in the lake rises, typically made from compacted dirt. “Upstream” tailing dams are built by piling more earth on top of the mud that has dried at the edge of the dam, building an uphill slope. Their shape makes them easy and inexpensive to build, but also gives them a fatal weakness: they’re vulnerable to liquefaction, where waterlogged soil behaves like a liquid under pressure or disruption.
After the Brumadinho collapse, Brazil’s Agência Nacional de Mineração (ANM) banned the construction of any new upstream tailing dams. The agency also asked the companies that own the country’s 88 existing upstream dams to come up with a plan to decommission them by August 2021. "The industry doesn't know how to react. It will be difficult for some companies to carry on, and they may have to stop operations due to the time it will take to get new licenses," Frank Baker, operations manager at Amarillo Gold in Brazil, told Mining Magazine.
Anxiety about the safety of upstream dams has spread outside of Brazil. In February, the International Council on Mining and Metals (ICMM) began developing a global standard for tailing ponds. Currently, there is no international standard for the systems, but the ICMM plans to develop its own by the end of the year.
For longtime industry insiders, like mining engineer Chandra Durve, the conversation about upstream tailing dams can't come soon enough. Over 30 years ago, Durve wrote a paper on their vulnerabilities. "These dams have been failing for many years," he told Geographical. “There isn’t a lack of knowledge, though unfortunately there aren’t too many experts around in this field and people who profess to be experts unfortunately may not have a full understanding of the intricacies of tailings.”