The Wall Street Journal obtained a copy of a report that was completed in September that raised concerns about the tailing dam at Vale’s Corrego do Feijao Mine that failed on Jan. 25, killing at least 150 people with nearly 200 more missing and feared dead.
German consultant and inspections company Tuev Sued completed the report that identified problems with the drainage infrastructure in the dam and faulty monitoring systems.
The dam collapse at Vale's Corrego do Feijao mine let loose a torrent of sludge that devastated the surrounding area near the city of Brumadinho.
The amount of water in a tailings pond is a significant concern, independent inspectors told the Journal. Too much water creates an issue called "liquefaction" that can contribute to a dam collapse, they said.
In the September report, Tuev Sued told Vale some of the systems used to monitor water levels in the tailings pond were faulty. The report also found that parts of the drainage system were clogged with vegetation or damaged due to trampling by large animals like cows.
The inspectors also said they could find little information about the 43-year-old dam, including its foundation, prior to Vale's 2001 purchase of the structure.
Despite those issues Tuev Sued ultimately concluded the dam was stable.
Vale told the Journal it followed up on Tuev Sued's recommendations after its September inspections. It added that 130 devices were monitoring the dam and there are no records of increases in water in the dam.
Separately, the German firm said in a statement that it had hired two external law firms to conduct an independent probe into its role in the dam collapse. Two of its employees were arrested following the accident but were released.
The Brazilian state of Minas Gerais canceled Vale SA’s license to operate a dam at one of its largest mines, the company said on Feb. 7.
The state canceled Vale’s license for Laranjeiras dam. It had been used in the operation of the Brucutu Mine, which had already been suspended by a court order, freezing nearly 9 percent of the company’s output.
Vale, which was already trying to appeal the court order, said it would also appeal the license cancellation.
Minas Gerais also canceled Vale’s license to operate its Jangada Mine, which has been paralyzed since the dam close to the Córrego do Feijão Mine burst in the state.
The cut in output from Brucutu forced Vale to declare force majeure in iron ore and pellets contracts.
Vale, which co-owned another dam whose 2015 collapse killed 19 people and polluted a major river, said on Tuesday it would invest some 1.5 billion reais ($400 million) starting in 2020 to reduce its reliance on giant dams to store the muddy detritus from mining, known as tailings.
It aims to boost the portion of the waste material that is dried rather than stored wet to 70 percent by 2023.
The company also said it would spend about $70 million on safety and maintenance at existing tailings dams in 2019, representing a 180-percent jump from 2015.