Abstract
Historically, tailings facilities have been designed primarily with consideration of the mine’s active life. This is problematic, as the lifespan of a tailings dam may far exceed the life of the mine. Over time, it is expected that these structures will transform into a mine waste structure and then eventually a landform. In Alberta, Canada, dam owners can submit a decommissioning, closure, and abandonment (DCA) plan and completion reports to apply for the facility to be de-registered as a dam. If successful, the structure would be considered a solid waste structure and may be reclassified and regulated as a mine waste dump. The Alberta Energy Regulator expects DCAs to be accompanied and supported by risk assessments that consider long-term physical failure modes, including failure modes that may not be applicable during operations, in accordance with Manual 019. To help support the process of de-registering a tailings dam, a risk management tool, referred to as a Generalized Failure Modes Effects (G-FMEA) framework, was developed and presented in the Journal of Minerals in the Special Issue Tailings Dams: Design, Characterization, Monitoring, and Risk Assessment. The G-FMEA was designed to be used for assessing risks of an external tailings facility in closure, with the goal of assessing the long-term risk of geotechnical failure to support the process of de-registration. In Alberta, a number of tailings dams are undergoing closure and reclamation activities. This paper applies the developed G-FMEA framework to an oil sands tailings dam in Alberta to demonstrate the application of the framework. The paper assesses two specific failure modes of two different elements, including clogging of the drains and surface erosion of the berm. The failure modes are assessed over different timescales to demonstrate how the consequence, likelihood, and risk rating may change over time. The results of this process are discussed in the context of the potential for the facility to be de-registered as a dam.
Highlights
Many tailings storage facilities (TSFs) in Alberta are in the process of being reclaimed and closed
The G-FMEA serves as a screening tool for the closure phase of an external tailings facility (ETF), where hazards that are assessed as acceptable will not require additional analyses, but hazards that are assessed to have a higher risk rating could require more detailed and/or quantitative risk assessments
The objective of the G-FMEA is: “How should geotechnical risks associated with an external tailings facility in Alberta be managed in the long-term to achieve an acceptable closure plan, such that the facility is able to be de-registered as a dam?” [2]
Summary
Many tailings storage facilities (TSFs) in Alberta are in the process of being reclaimed and closed. The goal following closure is for the dam owner to submit a decommissioning, closure, and abandonment (DCA) plan and completion reports to apply for the facility to undergo de-registration as a dam [1] Following this process, the structure would be reclassified and regulated as a mine waste dump under the Oil Sands Conservation Act or the Coal Conservation Act [1]. The goal of the G-FMEA is to assess the long-term geotechnical risks of an external tailings facility (ETF) during the closure phase to support the process of de-registration [2]. The G-FMEA charts from Schafer et al [2] are used to evaluate the potential failure modes of an oil sands ETF closure plan using an element approach This process demonstrates how the framework can be used to go from a generalized list of failure modes and applied directly to a case study. This supports long-term closure goals with a risk management focus
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