Question 6 of 6: Risk Assessment and Management Principles

Question 6: Risk Assessment and Management Principles (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

a) Two leading causes of modern (post-2000) tailings dam failures

Slope/foundation instability, including static liquefaction of loose saturated tailings. Independent published failure reviews (e.g. Bowker & Chambers, and the post-incident investigations for individual dams) consistently identify inadequate site/foundation characterization and slope or foundation instability – frequently culminating in liquefaction of an upstream-raised or otherwise loosely-placed tailings mass – as the single most common root cause of the worst modern failures. Mount Polley (British Columbia, 2014) failed when an undetected weak glaciolacustrine clay layer beneath the perimeter embankment's foundation was overloaded as the dam was raised, and Brumadinho (Brazil, 2019) and Fundão/Samarco (Brazil, 2015) both involved static liquefaction of upstream-raised tailings once pore pressure rose enough to collapse the material's shear strength – in all three cases the mechanism was a foundation or internal-material strength problem rather than a hydrologic (flood) event.

Overtopping from inadequate water management. Insufficient freeboard, an undersized or blocked spillway/decant system, or a design inflow flood that underestimated actual site hydrology remains one of the most frequently cited failure triggers worldwide, since it does not require a rare geotechnical defect – simply accumulating more water in the pond than the structure and its spillway were sized to pass. Both causes point to the same underlying management lesson (Question 6b): routine surveillance (piezometers, visual inspection, water balance tracking) exists specifically to catch a rising phreatic surface or a shrinking freeboard margin long before either develops into a failure.

b) Industry best practice for tailings dam safety inspections and reporting

Modern best practice for tailings dam safety centres on a documented management system built around a named accountable Engineer of Record (EoR), formalized in an Operation, Maintenance and Surveillance (OMS) manual that every operating facility maintains. Routine surveillance operates at several nested frequencies: site personnel conduct daily-to-weekly visual walk-around inspections looking for seepage, cracking, settlement or erosion; instrumented monitoring (piezometers for pore pressure and phreatic surface position, inclinometers for internal deformation, and survey monuments/InSAR for crest movement) is read on a schedule set by the dam's consequence classification, with pre-defined trigger and action levels that escalate to the EoR automatically if exceeded; and the EoR (or a delegate) conducts a more thorough formal inspection at least annually, walking the full structure and reviewing the accumulated instrumentation trend data. For a Very High or Extreme consequence-classified dam (and for others where the regulator or corporate standard requires it) (the CDA's own classification system, applied to essentially every tailings dam of meaningful size), an Independent Tailings Review Board (ITRB) of external experts reviews the design, construction and performance on an ongoing basis, and a full independent Dam Safety Review (DSR) by a qualified professional not otherwise involved in the facility's day-to-day engineering is conducted on a fixed interval set by consequence classification (CDA guidance: typically every 5 years for Extreme/Very High, 7 for High and 10 for Significant consequence dams; BC's Code requires one at least every 5 years for a tailings storage facility) – assessing the dam against current guidelines and identifying any needed remediation. Reporting flows on two tracks: internally, inspection findings, instrumentation trends and any trigger-level exceedance are documented and escalated through the OMS manual's defined chain to the accountable executive; externally, an Annual Dam Safety Inspection report is filed with the applicable provincial/territorial regulator (in British Columbia, the Chief Inspector of Mines under the Mines Act and the Health, Safety and Reclamation Code, following the post-Mount Polley 2016/2017 independent expert panel reforms that strengthened HSRC Part 10 and require a registered Qualified Person's sign-off), and a documented, regularly-exercised Emergency Preparedness Plan (including downstream notification protocols for potentially affected communities and Indigenous nations) is maintained and tested. The Mining Association of Canada's Towards Sustainable Mining Tailings Management Protocol (Question 1e) requires an equivalent internal governance structure – an accountable executive, OMS manual, and independent third-party verification every three years – and the Global Industry Standard on Tailings Management adds a public-disclosure obligation for high-consequence facilities, both of which now function as the de facto minimum industry expectation layered on top of whatever a given province's regulations require.