Mount Polley Mining Corporation

The Mount Polley tailings-storage-facility breach was not a mystery that can be reduced to one missed reading, one rainy season, or one regulator who failed to spot an obvious crack. The independent engineering panel traced the initiating failure to a weak glaciolacustrine foundation layer that had not been adequately characterized and to a design that did not account for how that layer would behave under the embankment. The Chief Inspector of Mines accepted a closely related physical sequence but examined a wider operating system: steepened geometry, an unfilled toe excavation, water and beach management, changing engineers of record, corporate oversight, and the regulator's reliance on professionals. The Auditor General of British Columbia asked a different question again—whether the province's compliance-and-enforcement system was designed and operated to protect the public from significant environmental risk. Those findings overlap, but they are not interchangeable. A causal engineering opinion is not a regulatory performance audit. A professional-discipline decision is not a criminal judgment. A permit to restart is not a declaration that remediation is complete. And a water sample that meets a guideline at one station and time cannot establish the absence of lasting effects across water, sediment, benthic communities, fish, groundwater, and altered habitat. The accountability lesson is therefore less convenient than a single culprit narrative: tailings safety depends on whether site knowledge, design assumptions, construction records, water controls, instruments, independent challenge, regulatory verification, and board-level decisions remain connected throughout a facility's life. That distinction matters now because federal Fisheries Act charges laid in December 2024 remain allegations in the public sources reviewed for this article. The engineering record can explain mechanisms and missed controls; it cannot determine the elements, defences, or outcome of a pending prosecution. Mount Polley is an accountability test precisely because the record must be read in layers—and because every layer has a boundary.