Mine Tailings Storage: Safety Is No Accident
Case study: Samarco, Brazil, 2015
The mineral-rich area known as the Iron Quadrangle is located in Minas Gerais state in south-east Brazil. There are more than 300 mines in operation (including gold, topaz, niobium, manganese, diamond and other ores and gems), producing more than 17 per cent of the state’s revenue. Mining activity dates back to the eighteenth century and has shaped both the environment and urban development. Among these mines is the Germano mine, close to the city of Mariana, which is operated by Samarco – a joint venture between Vale SA and BHP Billiton, two of the largest mining companies in the world. It produced just over 23 million tonnes of iron ore pellets in 2014 and in the process, generated almost 20 million tonnes of tailings (Samarco 2015). On 5 November 2015, the mine’s Fundão dam breached, releasing an estimated 33 million cubic metres of mine waste (Samarco 2015a; Grupo da Força-Tarefa 2016). The tailings slurry flowed down the valley as a high-density mudflow and inundated parts of the village of Bento Rodrigues. Nineteen people were killed, including village residents and Samarco employees. The slurry reached the Doce River Valley, the fifth largest river basin in Brazil, and travelled for 650 kilometres until it reached the Atlantic coast 17 days later. The flow and its impacts are illustrated in Figure 4. The investigation to determine the cause of the dam failure identified a number of issues that cumulatively led to the failure. These included inappropriate dam construction procedures, improper maintenance of drainage structures and inadequate monitoring (Morgenstern et al. 2016). Prior to the collapse there had been several incidents that necessitated alterations to the original dam design. These changes established the conditions for failure by creating drainage problems that resulted in large volumes of saturated sand adjacent to the dam wall. Immediately prior to the collapse, three small earthquakes exacerbated the structural weakness of the sand, initiating the flow slide (Morgenstern et al. 2016). The final government report (GFT 2015) listed 36 factors that contributed to the dam failure and noted that the mining company did not have an emergency plan, or even warning lights and sirens that could be activated to alert employees or villages in the event of a disaster. Brazilian authorities charged 22 individuals over the incident, which killed 19 people (Wood 2017). The Brazilian government has suspended Samarco´s environmental and operation licences. A compensation agreement was reached in March 2016 between the relevant Brazilian authorities and the mining companies, however, Samarco is also facing a civil claim, which it expects to settle in 2017.
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