It’s a week and a half after the massive tailings spill at Imperial Metals’ Mount Polley copper–gold mine in B.C.’s Cariboo region, and many unclear aspects of the disaster are coming into better focus.
Of immediate concern, the tailings have continued to flow in an uncontrolled manner out of the tailings lagoon all this time, but on Aug. 12, the B.C. government said that the flow had "decreased dramatically," and that Imperial had begun building a temporary dike to stop the flow. Lake and river water tests outside the contaminant plume show that this water is within safe drinking water guidelines, and so most water-drinking and fishing bans in the region have been lifted, except in the immediate area of the spill.
Engineering firms are usually pretty low-key when it comes to commenting on their clients’ projects, but the extraordinary scale of the Mount Polley breach has prompted both Knight Piésold and AMEC to go public and describe their roles in designing the tailings dam and its later expansions.
Knight Piésold describes itself as the "former engineer of record of the tailings storage facility at Mount Polley," and said that it informed Imperial that it would no longer continue in that role as of February 2011. Knight Piésold commented that during the time it acted as engineer of record, the tailings storage facility at Mount Polley "operated safely and as it was designed," and was subjected to multiple third-party reviews.
The firm said that since Feb. 10, 2011, it "has not had any responsibility or knowledge of any aspects of the design, modifications or performance monitoring of the tailings storage facility at Mount Polley. The original engineering done by Knight Piésold Ltd. accommodated a significantly lower water volume than the tailings storage facility reportedly held at the time of the breach. Significant engineering and design changes were made subsequent to our involvement, such that the tailings storage facility can no longer be considered a Knight Piésold Ltd. design."
And then the killer lines: "Upon completing all assignments as the engineer of record in 2010, Knight Piésold wrote to Mount Polley Mining Corp. and to the Government of British Columbia’s Chief Inspector of Mines and stated that ‘the embankments and the overall tailings impoundment are getting large and it is extremely important that they be monitored, constructed and operated properly to prevent problems in the future.’ A formal handover of design, construction and monitoring responsibilities was conducted on March 8, 2011, when AMEC Earth and Environmental was acknowledged as the new engineer of record for all future work at the Mount Polley tailings storage facility."
And the final washing of the hands: "Knight Piésold Ltd. is not familiar with, and therefore cannot comment on, the details of the incident, or on the design, construction, operations, water-management practices or any other aspects of the Mount Polley tailings storage facility."
While AMEC did not put out a press release on Mount Polley, it has been in touch with media outlets individually and emailed The Northern Miner to distance itself as much as it could from the failure, emphasizing that "while AMEC serves as the engineer of record on the most recent raising of the dam, implementation of the AMEC design has not been completed and some construction activity was still taking place to complete our design. Investigations at or near the breach are currently prohibited due to safety concerns and we are awaiting the results of field surveys by Imperial Metals to determine the status of dam construction at the time of the breach."
And of course, from the get-go, Imperial Metals has described the tailings dam as "an independently engineered structure that operated within design limits and specifications," and Imperial president Brian Kynoch has insisted his company followed the advice of its engineers.
To rework John F. Kennedy’s dictum: A working tailings dam has a thousand fathers, but a failed one is an orphan!
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