Risk management | j
The tailings dams that failed at Mount Polley in Canada, plus Samarco and Corrego de Feijao mines in Brazil were all upstream dams. The Mount Polley dam was converted into an upstream dam in violation of permits. Upstream dams are now prohibited in Brazil, Chile, Ecuador and Peru. Emerman went on to explain why a closed status of a tailings facility can also be a driver of risk. Such a facility is only safely closed when deposition of tailings has ceased, and all closure activities have been completed so the facility requires only routine monitoring, inspection and maintenance in perpetuity, or until there are no credible failure modes. However, for closure, system failure is considered to be “basically inevitable”. Over time there are simply too many things that could go wrong. Just recently a closed tailings dam collapsed in Jagersfontein in South Africa on 11 September 2022. It is reported that three people were killed, 40 injured, homes were swept away and at least 20 were damaged. The mine was closed more than ten years ago. “Tragedies like these show how communities bear the brunt of irresponsible mine waste management. South Africa has the largest number of upstream tailings dams worldwide, a construction method that is considered unsafe and has actually been banned in some countries. Mining companies must not be allowed to simply walk away from unstable tailings dams,” Hassen Lorgat said. “This means that governments must ensure the laws and practices of corporations change to protect communities and ecosystems.”
Emerman goes on to say that the key questions to ask about closed tailings facilities include: ● Is there a realistic plan to monitor, inspect and maintain the tailings storage facility in perpetuity? ● Does the facility still have credible failure modes?
British Columbia Back in British Columbia pressure is growing to
address the risks posed by tailings dams across the province. The waste created by an accelerating mining boom is not only seen as a threat to communities and watersheds in the region, but the increase in extreme weather events brought on by climate change has intensified this threat. Severe flooding is one of the main causes of tailings dam failure at mine sites around the world. According to MiningWatch Canada, British Columbians find themselves on the front lines of climate change, facing more extreme weather. In 2021, the province experienced ‘atmospheric rivers’ that caused severe flooding, loss of homes and infrastructure, and billions of dollars of damage. “Extreme rainfall driven by climate change adds
stress to the structures holding mine tailings. Even tailings facilities designed for today’s most extreme weather events may not be able to withstand future extremes under the influence of climate change, or multiple events such as heat domes, atmospheric rivers, and recurring flooding,” the organisation stated. Following the Mount Polley tailings disaster in BC during 2014, the Mount Polley Independent Expert Engineering Investigation and Review Panel found that to get on a path to zero failures, the province needed to reduce its tailings facility inventory by half and use best available technology for the remaining facilities. However, as the years rolled by, there was concern that the province had not yet produced a clear strategy to reduce active tailings dams to prevent further disaster. This led the BC Mining Law Reform Network and SkeenaWild Conservation Trust to create a database of mines with tailings storage facilities (TSF) across the province.
Tailings facility disclosures reveal risks
In a paper published in Scientific Reports in 2021, Franks et al conducted a survey and compiled a database with information on tailings facilities disclosed by extractive companies at the request of institutional investors. Despite limitations in the data, the authors say this request represents the most comprehensive survey of tailings facilities ever undertaken. The compiled dataset includes 1743 tailings facilities and
provides insights into a range of topics including construction method, stability, consequence of failure, stored volume, and the rate of uptake of alternative technologies to dewater tailings and reduce geotechnical risk. The analysis reveals that 10 per cent of tailings facilities reported notable stability concerns, or failure to be confirmed or certified as stable at some point in their history, with distinct trends according to construction method, governance, age, height, volume and seismic hazard. Although a solid step in the right direction, the authors said there is still plenty to improve in the way in which mining companies disclose information about their tailings facilities. This current database accounts, on average, for 30% of different types of commodity production. Investors are continuing to engage with non-responsive companies but their focus is on publicly-listed companies. Engagement with privately-owned and state-owned companies is also necessary to improve coverage.
Record keeping also appears to be a significant issue, with companies unable to report complete engineering records for 257 of the 1743 facilities (15%), the majority of which are facilities that are no longer active (76%). The sheer scale of global tailings production and the high impact of tailings facility failures highlights the need to improve all aspects of tailings disposal and management. Furthermore, the data highlight the need to continue developing management options and technologies to both minimise tailings production and to repurpose tailings to reduce storage requirements and their associated risks. In the short term, the authors say that ever larger tailings storage facilities will continue to be built in locations with ever higher consequences of failure. Greater transparency brought about by these and future disclosures could play an important role in the reduction, and ideally elimination, of catastrophic tailings facility failures.
REFERENCE: Tailings facility disclosures reveal stability risks by Daniel M. Franks, Martin Stringer,
LuisA.Torres Cruz, Elaine Baker, RickValenta , KristinaThygesen , Adam Matthews , John Howchin & Stephen Barrie. Scientific Reports (2021) 11:5353.
https://doi.org/10.1038/s41598-021-84897-
36 | November 2022 |
www.waterpowermagazine.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53
