The spill, where water with red mud and bauxite residue overflowed the drainage channels around a deposit, occurred two years before Hydro acquired a majority stake in the world’s largest alumina refinery.

About 6000 lawsuits have been submitted before a small-claims court in Barcarena, in the state of Pará, but have still not been served to Alunorte, where Hydro increased its ownership interest from 34 to 91% in 2011.

"The court has informally notified us that due to the holiday season, it could still take several weeks before we are formally served with all the lawsuits," says executive vice president Johnny Undeli, head of Hydro's Bauxite and Alumina operations.

"We are taking the lawsuits seriously, however, we find it difficult to see how the plaintiffs can succeed with their claims if related to the 2009 incident," he added.

Unusually heavy rainfall

The red mud spill happened after heavy and long rainfall in April 2009. At its most intense, the region had 105mm of rain in 90 minutes. The extreme rain made water containing red mud from the deposit seep into the Murucupi river.

In 2010, Alunorte was fined nearly BRL20M after the spill, but has not accepted the fine.

Both Alunorte and independent authorities have made repeated tests of the water quality in the Murucupi river as well as in the much larger Pará river. The tests show that the spill has had no significant effects on the water or on life in and around the river.

15 court cases

A total of 15 individuals have previously disagreed with this conclusion and have brought an action against Alunorte, by claiming that fish had disappeared in the river or that crops had deteriorated after the spill. However, it has not been proven that the incident has caused such effects.

Alunorte lost the first two cases, but won the 13 next in the first court. All the 15 cases were appealed and are now being tried in the state capital Belém. A judgment has not yet been served, and it is not known when this will happen.