Significantly less tailings were released than originally estimated following the fatal dam breach at Samarco Mineração iron ore operation in Minas Gerais, Brazil in November 2015, BHP Billiton has announced.

In a statement on its website, the firm – which owns a 50 per cent interest in Samarco – said that satellite assessments showed the volume of tailings material released during the dam breach was approximately 32Mm3, much less than the 50Mm3+ originally estimated. Approximately 85 per cent of the released tailings were retained within 85km of the Fundão dam, it said.

Samarco has undertaken several activities to stabilise the released tailings and prevent more material from entering the Rio Doce system. These include the construction of dikes to contain tailings and revegetation along the Gualaxo and Doce rivers. The native revegetation is intended to reduce the risk of erosion in heavy rainfall.

Dredging of the Candonga hydroelectric dam is planned which will also improve water quality.

Samarco also recently reported that work to repair and reinforce the Selinha dike above the Fundão dam in the Germano complex is complete. The company is continuing to reinforce the Santarém water dam which overflowed, but which retained some of the tailings from Fundão.

Reports issued by the companies responsible for water supply in the affected municipalities along Rio Doce confirm the water treatment facilities along the Rio Doce are operational and capable of treating water for human consumption and industrial and agricultural use. Work is also being performed by a number of organisations, including Samarco, SAAE, Copasa, water supply companies and local councils to control any ongoing impacts to hydroelectric power plants from turbidity and sediment accumulation.

Samarco also reported findings from ongoing mapping of the Rio Doce river, with a study carried out in early December by ACQUA Consultoria finding fish -individuals and shoals – living in the river.