Memo to CIM Membership regarding Mount Polley Copper Mine Tailings Storage Facility Breach


Dear CIM Members,

The Independent Expert Engineering Investigation and Review Panel Report on the Mount Polley Tailings Storage Facility Breach at the Mount Polley copper/gold mine in British Columbia was released on Jan. 30, 2015. The full report of their investigation can be found at:

CIM extends its appreciation to the Independent Review Panel members for their efforts and the timely completion of the Report.

Some key findingsof the investigation are summarized below:


The dominant contribution to the failure resides in the design. The design did not take into account the complexity of the sub-glacial and pre-glacial geological environment associated with the Perimeter Embankment foundation. As a result, foundation investigations and associated site characterization failed to identify a continuous glacial lacustrine layer (“GLU”) in the vicinity of the breach and to recognize that it was susceptible to undrained failure when subject to the stresses associated with the embankment.

The specifics of the failure were triggered by the construction of the downstream rockfill zone at a steep slope of 1.3 horizontal to 1.0 vertical. Had the downstream slope in recent years been flattened to 2.0 horizontal to 1.0 vertical, as proposed in the original design, failure would have been avoided. The slope was on the way to being flattened to meet its ultimate design criteria at the time of the incident.


The Panel reviewed the roles and responsibilities of the British Columbia Ministry of Energy and Mines (the Regulator) and its interactions related to the Mt. Polley tailings storage facility. The Panel found that inspections of the tailings storage facility would not have prevented failure and that the regulatory staff are well qualified to perform their responsibilities. The Panel found that the performance of the Regulator was as expected.


The Panel has examined the historical risk profile of the current portfolio of tailings dams in British Columbia and concluded that the future requires not only an improved adoption of best applicable practices (BAP), but also a migration to best available technology (BAT). Examples of BAT are filtered, unsaturated, compacted tailings and reduction in the use of water covers in a closure setting. Examples of BAP bear on improvements in corporate design responsibilities, and adoption of Independent Tailings Review Boards.

CIM acknowledges that Canada is recognized internationally for its extremely high standards pertaining to dam design. Nevertheless, two dam breaches have occurred in the past two years – the perimeter tailings dam at Mount Polley in August 2014 and a water containment dam at the Obed Mountain mine in Alberta in 2013.

Members are also encouraged to consult the  press release prepared by the Mining Association of Canada (MAC) in which it commits “to review the information and recommendations with a view to enhancing tailings dam safety.” MAC’s Towards Sustainable Mining initiative was recognized in the panel’s report as “best available practice in corporate governance.” Mandatory for MAC members, TSM is designed to improve industry’s performance in key environmental and social areas, going beyond regulatory obligations.

Going forward, CIM will consult and coordinate with MAC and other relevant professional organizations and associations to champion the highest standards in Canadian dam design, operation and monitoring practices. Furthermore, CIM will facilitate ongoing discussion and continuing education through its conferences, seminars and technical publications. Of note, Best Practices in Tailings Management will be addressed during the technical program in the upcoming CIM Convention 2015 to be held in Montreal from May 10 to 13. Tailings management also figures prominently into CIM’s Symposium 2015 on Mines and the Environment to be held in Rouyn-Noranda from June 14 to 17 and will also be addressed in detail at the upcoming Tailings and Mine Waste 2015 Conference being organized by the Norman B. Keevil Institute of Mining Engineering at the University of British Columbia to be held in Vancouver from Oct. 25 to 28 (website coming soon).

Sean Waller

CIM President

Founded in 1898, the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) is the leading technical society of professionals in the minerals, metals, materials and energy industries with more than 14,000 members across Canada and globally. CIM is dedicated to the advancement of knowledge as well as the promotion of networking, innovation and sustainable practices for the mining industry.

[1] p. iv Independent Expert Engineering Investigation Review Panel, January 30, 2015