Brazilian iron ore miner Samarco Mineração SA received serious danger warnings from ground sensors in 2014 and 2015, months before a deadly and environmentally destructive burst of a tailings dam, Globo TV's Fantastico newsmagazine said on Sunday.
The alerts, from probes driven deep into the dam's structure to detect ground moisture and stability, reached as high as "emergency" levels, Fantastico said, citing Samarco-commissioned engineering studies provided to prosecutors investigating the case.
Fishermen bury fish washed up in mining mudflow
Local fishermen are contracted by Brazilian miner Samarco to bury dead fish along the coastline after two burst dams triggered a mud flow that surged out to sea.
Samarco, a 50-50 joint venture between Brazil's Vale SA and Australia's BHP Billiton Ltd, is in talks with Brazilian federal and state prosecutors and environmental agencies to settle a 20 billion real ($5 billion) public lawsuit.
Fantastico said the studies did not include sensor data from areas critical to the integrity of recent enlargements to the dam, in a sign of scant regard for the sensor data, according to a prosecutor interviewed by the television program.
"It is an extremely grave omission that compromised the operational security of the dam," Carlos Eduardo Ferreira Pinto said about the sensor data. He is investigating the accident for Brazil's Minas Gerais state.
The dam's enlargement, he added, "compromised it in a way that was decisive to its rupture."
The November accident sent a tsunami of mud through hundreds of kilometres of valleys and rivers, killing 17 people, wiping out small towns, polluting drinking water for tens of thousands and destroying wildlife from Brazil's Minas Gerais highlands to the Atlantic Ocean.
A Samarco lawyer told Fantastico the company followed all dam safety and environmental laws in effect and that the area of the dam where sensor data was missing was the most secure part of the structure.
In response to Fantastico's reporting on the missing data, the company that provided the sensor data to Samarco said it was not required to supply data to the government that was within normal parameters.
Vale, Samarco and BHP did not immediately respond to requests for comment from Reuters.
BHP has previously said they will release the findings of an external investigation into the dam burst by New York-based law firm Cleary Gottlieb Steen & Hamilton when it is completed.