Tailings Dams: Why They Fail and What Can Be Done

RICHARD P. STAHL, B.AP.SC., PH.D., M.SC. (SLOAN), P.ENG., CENG., FICE

Tailings dams remain complex structures to design, construct, operate and maintain within the ever-changing mining industry.

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Tailings dams hold the water and waste byproducts (i.e., tailings) that result from mineral and metal extraction during the mining process. Though no complete inventory exists, it is well established that there are over 12,000 tailings dams worldwide. Billions of cubic metres of mining tailings comprised of sand, silt, clay and in some cases hazardous chemicals are produced and processed annually and held by these dams.

In recent years, several high-profile tailings dam collapses have highlighted the urgent need to address the safety of these unique structures. The 2015 and 2019 Samarco and Brumadinho tailings dam failures in Brazil, for example, have been wake-up calls to the industry. These two disasters alone resulted in a combined release of about 45 million cubic metres of mining waste and 290 fatalities.

While tailings dams have evolved in recent years, they remain complex structures to design, construct, operate and maintain within an ever-changing mining environment. By understanding the inherent risks of tailings dams and identifying root causes of collapse, the mining industry can implement effective solutions to reduce the frequency of dam failures while also protecting surrounding communities and the environment.

Why are Tailings Dams so Challenging to Manage?

Estimates suggest that tailings dam failures over the last 60 years have resulted in the unexpected release of over 200 million cubic metres of waste from storage facilities and over 2,300 reported fatalities. Tailings dam breaches can lead to environmental contamination, socio-economic consequences in surrounding communities, business interruption, and stakeholder revenue and reputational losses. It becomes critical then to identify and understand the circumstances that lead these failures.

Unlike conventional water resource dams, which are typically built under one owner using a fixed design with one engineer and contractor, tailings dams may start their life as a starter dyke and evolve over time as mining operations expand. Often, this means a changing climate, environment, regulations and system needs, and in some cases ownership.

Their unique long-life development invites many opportunities for human errors or omissions that impact the site investigation, dam design and construction, ongoing operation, and ultimate closure. As stated in the 2015 “Report on Mount Polley Tailings Storage Facility Breach”, “[Tailings dams] are also unforgiving systems, in terms of the number of things that have to go right. Their reliability is contingent on consistently flawless execution” from concept to completion."

How is Industry Mitigating the Risk of Future Collapses?

The global mining community along with other stakeholders around the world are accelerating long overdue action in efforts to reduce, if not eliminate, these tailings dam failures. In addition to developing best available technologies (BATs) for physical and chemical stability, universities, governments, mining organizations, and learned societies are improving upon and enforcing standards to reduce the impact of human errors and omissions moving “towards zero failure.”

The underlying principle for future tailings management involves a performance-based, risk-informed safe construction, operation, and closure approach that is centered on accountability. The 2020 Global Industry Standard on Tailings Management (GISTM) presents the latest standard for consultants, designers, owners, operators, regulators, and investors in the strive towards “zero harm to people and the environment with zero tolerance for human fatality.”

It is essential that all stakeholders in the mining industry understand the potential mechanisms and root causes of tailings dam failures. Using this knowledge, redundancies and resiliencies can be built into tailings storage facilities ultimately reducing and eliminating catastrophic failures and subsequent harm.

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About the author

Richard Stahl
Dr. Richard Stahl has more than 30 years of international experience as a geotechnical engineer, forensic investigator and expert witness.

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