RIO DE JANEIRO—Brazilian police said a catastrophic dam failure last year was the result of mining company Samarco Mineração SA’s attempts to expand the structure too quickly without proper monitoring.
Police in Minas Gerais state on Tuesday said that they will seek charges of “qualified homicide” for the deaths of 19 people following the disaster, and are requesting arrest warrants for six Samarco officials and one engineer at consultancy Vogbr Recursos Hídricos & Geotecnica Ltda. Among those accused was former Samarco Chief Executive Ricardo Vescovi, who stepped down in January to prepare his defense after federal police named him in a probe into environmental crimes.
The accusations leveled Tuesday have no exact equivalent in the U.S. legal system and fall a step short of formal charges, which in Brazil can be filed only by prosecutors. Qualified homicide is more serious than the Brazilian version of manslaughter and carries sentences of 12 to 30 years, the maximum amount of time that Brazilian law allows prisoners to be detained.
Samarco said in an email it considers the accusations and the arrest request for its officials mistaken, adding it will await a judge’s decision for its next actions. Vogbr didn’t respond to a request to comment.
Considered Brazil’s worst-ever environmental calamity, the collapse of Samarco’s so-called Fundão tailings dam on Nov. 5, 2015, released a tsunami of mine waste that flowed hundreds of miles from the hills of Minas Gerais to the Atlantic Ocean, destroying everything in its path. Neither Samarco nor its parent companies—global mining giants BHP Billiton Ltd. of Australia and Vale SA of Brazil—have said what caused the accident.
But following a 15-week investigation begun the day after the dam burst and involving some 100 witness testimonies, police investigators said Tuesday that they identified the cause.
The Fundão dam consisted mostly of sandy mine detritus, called tailings, that were plowed into successive embankments until it stood more than 100 meters tall and held back some 55 million cubic meters of waste. It was built according to the “upstream” design, whereby dam embankments are placed directly on top of dried tailings. The method is cheaper and less robust than other designs, but some experts say it is unsafe for large dams.
Police say Samarco raised the height of Fundão at an average rate of around 20 meters a year. They cited technical literature that recommends a maximum rate of rise of 10 meters a year.
Raising the dam quickly would have increased its waste-storage capacity, allowing Samarco to operate its mines at a brisker pace. But if the tailings beneath the dam embankments were still wet or hadn’t completely settled, the dam could become unstable, some engineers say.
Police said the rupture occurred through liquefaction, a geophysical phenomenon whereby soil loses its solid structure after becoming saturated with water.
Samarco’s monitoring system, police say, failed to detect a high level of water saturation within the sandy walls of the dam before it burst. Police also said Samarco didn’t have enough monitoring instruments installed in the dam and that several of the instruments that were in place were defective.
The dam also had drainage problems that allowed water to accumulate, police added.
Samarco said it would “carefully analyze the conclusions presented by the police,” and that it will continue working with authorities in response to the disaster. The company added that it, along with Vale and BHP Billiton, has hired geologists, engineers, seismologist and an international company to carry out an independent investigation into the causes of the dam break.
“The accident with the Fundão dam was an episode that caused extreme consternation at Samarco,” the company said. “We can’t undo the damage caused, but we remain committed to the job of reconstruction and recovery.”