Question 1 of 6: Risk Assessment and Management Principles

Question 1: Risk Assessment and Management Principles (20 marks, MANDATORY)

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.

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

Foundation or internal slope instability, frequently culminating in static liquefaction of loosely placed, saturated tailings. Independent published failure reviews (e.g. Bowker & Chambers) repeatedly identify inadequate foundation characterization and a subsequent loss of shear strength in an upstream-raised or otherwise hydraulically-placed tailings mass as the single most common root cause behind the worst modern failures. Mount Polley (British Columbia, 2014) failed when an undetected weak glaciolacustrine clay layer beneath the perimeter embankment's foundation was progressively overloaded as the dam was raised, while Fundão/Samarco (Brazil, 2015) and Brumadinho (Brazil, 2019) both involved static liquefaction of upstream-raised tailings once rising pore pressure collapsed the material's undrained shear strength – in all three, the trigger was a geotechnical strength problem, not a flood.

Overtopping from inadequate water management. Insufficient freeboard, an undersized or blocked spillway/decant system, or a design flood that underestimated actual site hydrology remains one of the most frequently cited failure triggers worldwide, because it needs no rare geotechnical defect – simply more water reporting to the pond than the structure and its outlet works were sized to pass safely. Both causes share the same management lesson developed in Question 1.2: routine surveillance exists specifically to catch a rising phreatic surface, a shrinking freeboard margin, or an unexpected deformation trend long before it develops into an uncontrolled breach.

2. Industry best practice for tailings dam safety inspections and reporting

Modern best practice is built around a documented management system led by a named, accountable Engineer of Record (EoR) and formalized in an Operation, Maintenance and Surveillance (OMS) manual that every operating tailings facility maintains. Surveillance runs at several nested frequencies: site personnel perform daily-to-weekly visual walk-around inspections looking for new seepage, cracking, settlement or erosion; instrumented monitoring – piezometers for pore pressure and phreatic surface position, inclinometers for internal deformation, and survey monuments or InSAR for crest movement – is read on a schedule tied to the dam's consequence classification, with predefined trigger and action levels that automatically escalate to the EoR 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 trend data. For a High, Very High or Extreme consequence-classified dam (the CDA's own classification, which covers essentially every tailings dam of meaningful size), an Independent Tailings Review Board (ITRB) of external experts reviews design, construction and performance on an ongoing basis, and a full independent Dam Safety Review (DSR) – performed by a qualified professional not otherwise involved in day-to-day engineering of the facility – is conducted on a fixed interval, typically every three to seven years depending on classification, to assess the dam against current guidelines and flag any needed remediation.

Reporting runs on two tracks. Internally, inspection findings, instrumentation trends and any trigger-level exceedance are logged and escalated through the chain of responsibility defined in the OMS manual, up to the accountable executive. Externally, an Annual Dam Safety Inspection report is filed with the applicable provincial or territorial regulator – in British Columbia, with the Chief Inspector of Mines under the Mines Act and Part 10 of the Health, Safety and Reclamation Code, strengthened after Mount Polley by the 2016/2017 independent expert panel reforms that now require a registered Qualified Person's sign-off – and a documented, periodically-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 requires an equivalent internal governance structure (accountable executive, OMS manual, independent third-party verification every three years), and the Global Industry Standard on Tailings Management layers a public-disclosure obligation on top for high-consequence facilities – both now function as a de facto minimum industry expectation regardless of what a given province's own regulations strictly require.