By Samantha Pearson and Luciana Magalhaes 

SÃO PAULO -- Vale SA said experts hired by the miner have concluded that drainage problems were largely to blame for the collapse of its dam in January that killed 270 people in Brazil.

Experts said the original design of the dam prevented correct drainage at its base, allowing water to build up over time, according to their report released by Vale on Thursday. The dam was built in the 1970s by another Brazilian company, Ferteco Mineração, which Vale acquired in 2001. There were no significant attempts to introduce other internal-drainage mechanisms in the dam as it was gradually built up, experts said. Its stiff and brittle contents, which contained a particularly high level of iron, also helped destabilize the dam, they concluded.

While Vale stopped dumping mine waste in the dam in 2016, monitoring equipment at the structure showed the water level didn't decrease significantly, the experts said.

Unusually heavy rainfall during Brazil's wet season that came around the time of the collapse also prompted the structure to lose strength, the experts hired by Vale said.

Write to Samantha Pearson at samantha.pearson@wsj.com and Luciana Magalhaes at Luciana.Magalhaes@wsj.com

 

(END) Dow Jones Newswires

December 12, 2019 09:04 ET (14:04 GMT)

Copyright (c) 2019 Dow Jones & Company, Inc.
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