BHP Billiton expects to complete work by year-end to contain the remaining waste that spewed from the Samarco iron ore project after a dam collapsed last November in Brazil’s worst environmental disaster on record.

When the Fundao dam burst at the mine, owned 50-50 by BHP bhplf and Vale SA vale , enough mud to fill 12,000 Olympic swimming pools flattened an entire village, killed 19 people and left hundreds homeless.

“Works are underway by Samarco on the dam structures to contain the remaining tailings materials and to treat sediment,” BHP said in a statement on Friday, adding that work would be completed by Dec. 31.

Containing the waste involves keeping it in a single area, ready for cleanup.

It is still not known exactly why Fundao failed, but experts have suggested it was probably the result of a loss of stability in the tailings foundation, a process known as liquefaction.

A report commissioned by BHP and Vale in August concluded the collapse was caused by drainage and design flaws.

The report attributed the disaster to a chain of events dating back to 2009, but did not assign blame or highlight specific errors in corporate or regulatory practice.

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A BHP spokesman said no timeframe had been set for a restart of the operation, but added that it would not come in 2016.

Samarco is BHP’s only asset in Brazil, a country from which it has been gradually retreating over the years.

Vale, on the other hand, has a number of iron ore mines close to Samarco’s deposit, making it a valuable asset that could be used in the company’s wider mining system.