Tailings facilities can fail in many ways and with varying degrees of severity. A tailings failure is an unintended or uncontrolled release of materials, including tailings, water or dust, from a tailings disposal facility. A Safety First document, written by Earthworks, outlines guidelines aimed at preventing catastrophic failures, defined as failures that constitute a rapid shock, and that happen without warning. Here are its top 10 guidelines for responsible tailings management.
10: Ensure independence of reviews to ensure safety
There must be an independent evaluation of all aspects of the design, construction, operation, and maintenance - including during closure and rehabilitation - of tailings and other mine waste facilities, regardless of the projected consequences of failure of the mine waste facility, by a group of competent, objective, third-party reviewers.
09: Appropriate monitoring systems must identify and mitigate risk
Tailings facilities must have appropriate monitoring systems in place to identify and mitigate risk, and have a clearly defined Adaptive Management Plan (AMP) linked to tailings monitoring results that encompasses a complete set of predictions and pre-planned actions.
08: Ensure detailed evaluation of dam foundations and tailings' properties
Prior to permitting approval, operating companies must provide relevant regulatory agencies a detailed engineering evaluation of the dam foundation, and a physical and chemical characterization of the tailings, with special attention to tailings clay content, brittleness and susceptibility to liquefaction.
The characterisation of the underlying geology must be conducted before the dam and the impoundment are constructed. The failure of the Mount Polley dam was related in part to the presence of an unstable glaciolacustrine layer underlying the dam.
07: Implement rigorous controls for safety
The design, construction, operation, and closure of any tailings facility must be subject to best available technologies and practices. An annual report must verify that dam operations and construction adhere to the approved final dam design.
If a feature of the design was approved by a regulatory agency, all requested changes to that design must be submitted to the same regulatory agency for approval. Any deviation from the original design must be justified, documented, and evaluated by an Independent Tailings Review Board (ITRB).
06: Mandate the use of Best Available Technology for tailings, in particular filtered tailings
All new mines that create tailings must begin with an analysis of the best available technology (BAT) for tailings disposal. BAT has three components that derive from first principles of soil mechanics:
1. Eliminate surface water from the impoundment
2. Promote unsaturated conditions in the tailings with drainage provisions
3. Achieve dilatant conditions throughout the tailings deposit by compaction
05: Any potential loss of life is an extreme event and design must respond accordingly
If an operating company, regulatory agency, or independent third-party identifies any potential loss of life as a result of a tailings dam failure, the dam must be designed to withstand the Probable Maximum Flood (PMF), the largest flood that is theoretically possible at a given location, and the Maximum Credible Earthquake (MCE), which is the largest earthquake that is theoretically possible at a given location.
Where the failure of a tailings dam would have no potential for the loss of human life, the facility must be designed to withstand a 10,000-year flood and a 10,000-year earthquake.
04: Ban upstream dams at new mines and close existing upstream facilities
Because of the demonstrated risk associated with upstream dam construction, upstream dams must not be built at any new facilities. Upstream construction is especially problematic in areas with moderate or high seismic risk, or in wet climate areas with net precipitation (more precipitation than evaporation), especially as weather events become increasingly severe with climate change.
The structural zone of a filtered tailings stack must not be constructed on top of uncompacted or lightly-compacted filtered tailings. If it is, it would be an upstream dam and must be prohibited.
03: Ban new tailings facilities where inhabited areas are in the path of a tailings dam failure
The most effective way to minimize risk to people is to prevent the construction of new tailings facilities where there is a population living or working in close proximity, downstream, or down gradient from the facility. Operating companies must not build infrastructure in which workers are likely to be present - offices, cafeterias, warehouses - in the zone of influence.
The zone of influence is the “area that would be significantly affected in case of a [tailings facility] failure and should be categorized as a risk zone.” New tailings facilities must not be constructed if the operating company cannot ensure the safe and timely assisted evacuation of any population that lives in the zone of influence.
02: Consent of affected communities
Consent must be achieved through an ongoing dialogue over the life of the mine for both proposed and existing facilities. The First Nations Mining and Energy Council states that, “consent is simple - it is the right to say yes, the right to say no, or the right to say yes with conditions.”
Consent can be given or withheld at distinct stages of a project, including exploration. Operating companies must ensure the meaningful engagement, participation, and consent of all affected communities for any tailings facility.
01: Make safety the guiding principle in design, construction, operation and closure
Given the hazardous nature of mine tailings, the fundamental goal of tailings management must be to “ensure that public safety, environmental safety, and economic safety are the determinative factors in governing what tailings disposal system will be implemented.”
Specifically, tailings management must ensure zero harm to people and zero tolerance for human fatalities. It is important to recognize that mining is a fundamentally destructive industry, meaning that a goal of zero harm to the environment is impossible to achieve.
Nevertheless, operating companies must do all that they can to minimize environmental harm everywhere. In particular, they must limit any environmental harm that inevitably occurs to within the mine site.
Safety must be evaluated by independent third-parties, such as an Independent Tailings Review Board, to ensure that cost reduction is not prioritized at the expense of people and the environment. Operating companies must document that, at all points of design, operation, closure, and post-closure of tailings facilities, protecting human and environmental health and safety is the primary concern.
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