Tragedy in Minas Gerais: Samarco's Dam Had More Mud Than Disclosed by the Company

01/22/2016 - 10h44

The amount of mud deposited by Samarco in the Fundão dam, which collapsed in November in Mariana, State of Minas Gerais, was greater than informed by the company.

The information is in the testimony given by Joaquim Pimenta de Ávila - the engineer who designed Fundão - to the Federal Police in December.

A greater amount of mud, if not planned, could compromise the stability of the dam, according to the engineer's testimony.

"Samarco reported that the proportion of mud to sandy tailings was 30% - 70%, but in practice, it was always 40% - 60%", says an excerpt from the document obtained by this newspaper.

Tailing is the residue originated from the processing of the ore. It is stored in dams or piles, in the form of sand or mud.

A research made by this newspaper on Samarco's sustainability annual reports shows that from 2009 to 2013 the mining company has produced, on average, 15.8 million tonnes of tailings per year in Mariana. Of this total, 26% were mud and 74% were sandy tailings, on average.

Dams like the one that burst, built with tailings material, need to have their water level controlled permanently, "otherwise hazard situations may arise," said Ávila to the police.

In some places, water can infiltrate the containment wall, leaving it so wet that it may suffer liquefaction (go from solid to liquid), losing resistance and falling apart.

Therefore, the company installed piezometers, which measure the pressure of the water in the soil. In alarming moments, the structure was reinforced.

Translated by JULIANA CALDERARI