More than half a year on from yet another deadly tailings dam disaster in Brazil – at the Vale-operated Córrego do Feijão iron ore mine near the town of Brumadinho – there’s an air of self-reflection in the global mining industry.
The Brumadinho disaster, which claimed the lives of at least 248 people after a dam ruptured and released 12 million cubic metres of tailings through the mine’s administrative area and towards the Paraopeba River, is raising tough questions for Brazilian industry and regulators alike, especially as it came just three years after the similarly devastating Samarco disaster in the same state of Minas Gerais.
Reflecting on safety and mining waste
But lingering questions around the safety of tailings dams aren’t just being asked in Brazil. As the Mount Polley tailings pond breach in British Columbia, Canada proved in 2014, even the most regulated mining jurisdictions are prone to tailings dam incidents. And when the integrity of a mine’s tailings storage facility (TSF) fails, the consequences can be calamitous, both in loss of life and for the local environment, which can take decades to recover from the sudden release of contaminated water and slurry.
Australian miners are no exception to the industry’s navel-gazing over the storage of its waste. Although the country’s dry climate and topography presents lower risks for TSFs – as evidenced by a lower frequency and reduced severity of tailings dam incidents in recent decades when compared to other major mining nations.
Still, in the waste management game, complacency is a powerful enemy, as Minerals Council of Australia chief executive Tania Constable acknowledged during a June industry workshop on tailings facilities with representatives of around 45 Australian mining firms.
“We have no intention of being complacent in Australia,” Constable said, as reported by the Sydney Morning Herald. “And we need to make sure that we do get on the front foot and are managing and leading practices here in Australia and inputting at a global level…[tailings management] is an issue that is important for the whole industry, and we need to work together.”
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Brazil disasters prompt questions for Aussie miners
Of course, the questions for Australian miners aren’t just coming from within the industry – investors are increasingly scrutinising companies’ tailings management practices as part of their ethical investment commitments.
In April, led by the Church of England Pension Board and the Swedish Council on Ethics for the AP Public Pension Funds, 96 institutional investors in the mining industry issued a request for the sector to disclose the status of all TSFs and the risks they present. Among the 20 questions posed to companies in the letter were queries on closure and long-term monitoring plans, notable stability concerns and the extent of in-house oversight of facilities.
“The tragic loss of life from the Brumadinho and Samarco catastrophic tailings dam failures highlighted the devastating consequences when something goes wrong,” the investors’ letter noted. “As responsible investors, we are committed to working with the mining sector to ensure that verifiable best practice standards are developed, implemented and maintained.”
Member companies of the International Council on Mining and Metals (ICMM) recently responded to the request as part of a drive for greater transparency in the area of tailings management. ICMM’s members with Australian operations include BHP, Rio Tinto, Glencore and Perth-based BHP spinout South32.
Tailings management: Australian miners take stock
In the most notable responses to the investors’ request for the risk profiles of managed TSFs, three companies disclosed that they own tailings dams that are considered high or extreme-risk in the event of a catastrophic failure. High-risk indicates dams that would have an immediate impact upon failure, and could cause the deaths of at least 10 people, while extreme-risk dams could cause the deaths of 100 or more people if they fail.
The dams in question include four ‘extreme-risk’ tailings dams at BHP’s Olympic Dam mine, Mount Whaleback mine, Pilbara mine and Leinster mine. Two tailings dams at Rio Tinto’s Andoom and Torro mines in Queensland have been deemed ‘high-risk’, along with two dams at Glencore’s Mount Isa mining complex.
While these high-risk facilities made the headlines in Australian media, the risk assessment for these dams relates to the damage in case of failure, not the likelihood that they will fail. Indeed, in their responses, South32, Rio Tinto, BHP and Glencore were all confident about their tailings management processes, and detailed their routine maintenance practices as well as reviews that have been instigated since the Samarco disaster.
Glencore outlined its group-wide approach to evaluating hazards at TSFs, assessing dam integrity against more than 100 safety criteria, as compiled from standards bodies such as the Canadian Dam Association (CDA), the International Committee on Large Dams (ICOLD) and the Australian National Committee on Large Dams (ANCOLD). For external expertise and inspection, Glencore contracts geotechnical and engineering specialist Klohn Crippen Berger.
As well as providing an overview of its routine tailings management and risk assessment procedures, BHP’s tailings report detailed the company’s response to the collapse of the Fundão dam, which was owned by Samarco, a joint venture of BHP and Vale. In the aftermath of the disaster in 2015, BHP started a dam risk review for active and inactive TSFs across the business.
The review found no major issues with the stability of the company’s tailings dams, but assigned more than 400 actions to improve tailings management at the asset and group levels. In a February update, BHP noted that 93% of these actions have now been completed, with only low-priority items left on the list. The company has also established a ‘Tailings Taskforce’ to coordinate BHP’s efforts on tailings, develop new technologies and contribute to the establishment of new international tailings management standards.
“All significant tailings storage facilities have emergency response plans in place,” the company said in a February statement. “As part of our ongoing process of continuous improvement, external Dam Safety Inspections are conducted annually and risk-based Dam Safety Reviews every three to seven years, in line with CDA guidelines.”
Looking to the future
Despite the industry’s assurances, one doesn’t have to look far back to find a prominent example of a TSF failure in Australia. In March last year, a tailings dam was breached at gold producer Newcrest Mining’s Cadia mine in New South Wales. The breach was contained by a downstream dam and caused no injuries or environmental damage.
An independent review into the incident reported its findings in April, noting that excavation work at the base of the dam wall was a contributing factor in its failure, as it exposed a brittle and compressible section of earth at its foundation. Newcrest wants to reopen the dam, but will need to provide further assurances that there are no other structural weak points at the facility to achieve regulatory clearance.
The damage at the Cadia site may have been limited, but the incident serves as a reminder that potentially dangerous and environmentally devastating dam failures are an ever-present risk, even in a market as well-regulated as Australia. Safety systems can always be improved, and the industry is investing in R&D to do it.
The liquid content of tailings dams in many cases presents their biggest risk, as liquid waste can seep into and compromise a dam’s structure. Seemingly stable tailings can also undergo static liquefaction, causing sudden collapses that can be difficult to predict. Rio Tinto, Alcoa and BHP are working with the University of Western Australia to investigate the potential for full-scale deployment of dry stacking tailings at existing facilities, which would be inherently more stable. Rio Tinto has also mentioned another project with the same university to get a better understanding of how static liquefaction occurs and how it can best be prevented.
BHP, meanwhile, has been working for two years to apply the digital twinning concept to tailings dams, creating a digital twin of a dam to facilitate real-time and predictive monitoring of TSF stability.
Looking further ahead, the ICMM’s members have committed to creating an international standard for tailings management to improve the consistency and transparency of these efforts across the industry. With guidelines being followed from organisations such as the CDA, ICOLD and ANCOLD, as well as national regulations, a clear international standard – if it can achieve consensus around the industry – could provide much-needed clarity as miners continue to consider the diverse local conditions that influence the initial design and ongoing maintenance of upstream, downstream and centreline tailings dams. An independent multidisciplinary review to compile global best practices is expected to complete by the end of 2019, with the review informing the scope and details of the standard to come.
“The standard will be based on best practices to ensure that tailings facility risks are managed appropriately, consistently, and transparently,” said ICMM CEO Tom Butler. “While the standard would become a member commitment, ICMM will encourage others to join us in advocating for it to be adopted more broadly.”