The case in the High Court in London against mining company BHP, on behalf of 620,000 people affected by the collapse of the Fundão tailings dam in Brazil in 2015, is reaching its conclusion. The final speeches by lawyers for the company and for those affected by the collapse of the tailings dam will be heard over seven working days, starting on 5th March 2025.
The collapse of the tailings dam, in the Mariana District of Minas Gerais state on 5th November 2015, released 45 million cubic metres of mining waste into the Rio Doce river system reaching the Atlantic Ocean more than 600 kms away. This affected water supply, farming and fishing along the length of the river and its long-term effects are still being investigated.
The iron ore mine and its tailings dam were owned by SAMARCO, owned 50:50 by the Brazilian company Vale and the Australian company BHP. In 2018 the law firm Pogust Goodhead launched a group lawsuit in England against the owners of the mine and the tailings dam. The case was then in and out of court with arguments over jurisdiction, as the mining companies argued against it being heard in an English court. In 2020, the High Court ruled in favour of BHP and struck out the group action, but the Court of Appeal overturned this ruling in 2022. BHP then applied to the Supreme Court for permission to appeal the Court of Appeal’s decision but this was denied.
The substantive case began in October 2024 and initially focused on questions of liability and environmental law. How the tailings dam collapsed became the focus of the hearings in January 2025 and concluded at the end of the month. There is now a pause in proceedings to allow both parties to prepare their final presentations in early March.
The sequence of events that led up to the collapse of the Fundão tailings dam was established by the Fundão Tailings Dam Review Panel, chaired by Norbert R. Morgenstern, which reported in August 2016. Tailings are a slurry of fine particles of waste material that result from mining operations. Iron ore contains only about 30% metal and this is separated from the rest of the ore by grinding and flotation at the mine site. The waste material is a mixture of water, silt and sand and this is deposited behind an earth embankment near the mine site.
Tailings dams are potentially unstable and require careful design, implementation and monitoring. The Morgenstern Report found that the dam collapsed due to liquefaction, a process in which a solid material loses nearly all of its strength and begins to flow like a fluid. The trigger for this may have been a series of small earthquakes on 5th November 2015, but the tailings dam was already in a critical state and collapse would probably have occurred anyhow at some time. A series of incidents, beginning in 2009 in the initial stages of dam construction, led to fundamental changes in the design concept which increased the saturation of the waste material and introduced the potential for sand liquefaction. The contention of the lawyers for the claimants is that the engineers of the mining companies failed to recognise signs that the tailings dam was in a critical state and failed to take appropriate action. It is claimed that data available to engineers was not acted on, and a supposedly temporary measure of adjusting the alignment of the tailings dam remained in place for three years, which compromised the dam’s stability. It is also claimed that a proper design and stability assessment for this temporary measure was not carried out, and requests by a tailings review board for documents about the temporary re-alignment went unanswered. A serious cracking incident 15 months before the collapse of the tailings dam led to emergency reinforcement of the dam but this did not give the factor of safety recommended by the original designer of the dam.