The dam, belonging to the Vale company, collapsed in the Brumadinho municipality on January 25, triggering heavy mud floods that caused multiple fatalities and injuries.
The deadly disaster occurred January 25 at an iron-ore mine owned by Vale, a Brazilian mining company.
"An internal study showed the miner knew as recently as a year ago that some of the areas hit were at risk if its tailings dam burst, according to a report by Folha de S.Paulo newspaper", Reuters reported.
The danger is widespread - a 2017 report from the National Water Agency classified more than 700 dams nationwide as a high risk of collapse and with high potential for causing damage.
At least 60 people have been confirmed dead and an estimated 292 remained missing at Vale SA after a dam storing mine waste at the Corrego de Feijao mine in Brumadinho on Friday. Vale described the document as a routine disaster preparation plan required by regulators.
Authorities and environmental organisations have begun testing water quality around the mining complex, while state and federal authorities have told residents to refrain from using water directly from the Paraopeba or 109 yards around it.
The death toll from the tailings dam collapse in the Brazilian town of Brumadinho reached 115 with another 248 were still unaccounted for, according to the state civil defense department on Friday.
The study envisaged that sirens would alert workers if the dam burst.
"This tragedy will be remembered not just here but all over Brazil", said 23-year-old Jonatan Silva Santos, who lost friends that worked at Vale.
Vale Chief Executive Fabio Schvartsman has said the miner built its facilities to comply with regulations and that equipment had shown the dam was stable.
Vale is linked to another dam disaster in the same region in 2015.