More than 250 people were killed and several tons of toxic mining waste was spewed across the countryside in the mineral-rich state of Minas Gerais in January following the disaster.
A report released on Tuesday by the National Mining Agency (ANM) detailed several problems that it said Vale should have reported.
Internal Vale documents seen by ANM investigators show the mining company was aware of problems with a horizontal drainage system installed seven months before the dam collapsed on January 25. The system is designed to control the water level of the dam.
Installation of these pipes requires the injection of pressurised water into the structure, which can “destabilise” the mining waste, ANM said.
On January 10 – two weeks before the dam in Brumadinho ruptured – two devices measuring liquid pressure had reached emergency levels.
“The increase in pressure of the piezometers compromised the stability of the dam. ANM was not informed,” the government agency said.
A Vale report of a survey conducted three days before the breach, but only filed on February 15, showed “all the irregularities” of the dam.
“If ANM had been correctly informed, it could have taken precautionary measures and forced the company (Vale) to take emergency actions that could have avoided the disaster,” ANM said.
In a statement, the iron ore miner said it would not comment on the “technical decisions taken by its geotechnical team at the time”.
The company said it would wait for the “expert, technical and scientific conclusions on the cause of the dam rupture”.
ANM said it would forward its findings to the federal police and prosecutors.
The report comes amid growing pressure on the global mining giant.
Police said in September they have enough evidence to charge employees of Vale and its German auditor over false information used to certify the safety of the dam.
It is up to prosecutors to decide whether to charge seven Vale workers, none of whom are senior managers, and six employees of the auditor TUV SUD.
The TUV SUD employees include a German-based business development director, engineers and consultants who certified the dam’s stability in 2018.
That came after a judge ordered Vale to pay nearly $3m to the families of three victims of the tragedy.
A separate court ruling in July ordered Vale to pay for all the damage caused by the disaster, without quantifying the amount of money.
Brazil has since banned the construction of new upstream dams, which are cheaper but less stable than other types of tailings dams, and ordered the decommissioning of existing ones.
ANM’s damning accusations came on the fourth anniversary of the collapse of another tailings dam owned by a joint venture between Vale and the Anglo-Australian miner BHP.
The failure of the Fundao tailings dam unleashed a torrent of nearly 40 million cubic metres of highly toxic mine sludge over areas of the Mariana district, also in Minas Gerais. The mud killed 19 people and flooded 39 towns, marking Brazil’s worst environmental disaster.