Mine Tailings Storage: Safety Is No Accident
Case study: Stava, Italy, 1985
In July 1985, the tailings dam of the Prestavel fluorite mine in northern Italy collapsed, causing the deaths of 268 people. Since the end of World War II the mine had a number of owners, but from 1980 to the time of the dam collapse, it was managed by Prealpi Mineraria. The mine tailings had been stored in two upstream cascading dams, built on a small tributary of the Stava Creek. Around lunch time on a summer’s day, the upper dam collapsed without warning onto the lower dam, which subsequently also collapsed. Approximately 180 000 cubic metres of semi-fluid tailings were released, burying the downstream villages of Stava and Tesero (Figure 12). The tailings dams had been constructed on a steep mountain slope with poor foundations and inadequate drainage systems (Sammarco 2004). The lower dam was built in 1961 and the upper dam in 1969. The method of construction for the upper dam, which involved part of the base of the dam resting on the weakly consolidated lower dam tailings, has been identified as one of the principle causes of the failure (Campanella et al. 1989). The mine operators assumed that the tailings in both dams would consolidate soon after deposition and that the tailings stored in the lower dam could support the load of the upper dam. However, due to poor management, this assumption was never verified and the construction and expansion of the tailings basins occurred in the absence of any monitoring or geotechnical testing. Essentially, the dams were an accident waiting to happen. The exact nature of the failure sequence has never been established, but the heavy rainfall that occurred in the two days prior to the disaster has been considered as a contributing factor (Takahashi 2007). This was compounded by the fact that in the month before the disaster, widespread land clearing had been carried out on the slope directly above the upper dam. There were no water diversion structures upstream of the dams and drainage pipes below the dams were not functioning
effectively – evidence suggests they failed at least twice in 1985 (Luino and de Graff 2012). Combined, these factors lead to increased water seepage and retention in the dams. At the criminal trial which followed the disaster, 10 people were convicted of multiple manslaughter offences. Among those convicted were the mine managers, employees of companies contracted by the mine and the local government officials who failed to competently monitor the dams. Compensation was paid by companies who had contributed to the construction and management of the upper dam and by the local government. The mining company, Prealpi Mineraria, was declared bankrupt and paid no compensation (Stava 1985 Foundation).
Made with FlippingBook Online newsletter