General ORE2 tailings workflow

General ORE2 tailings workflow

Sep 1st, 2021

ORE2_Tailings™ is a quantitative risk assessment platform. Riskope designed it specifically for tailings systems (active and inactive). When we deploy ORE2_Tailings™ to a portfolio of dams, possibly over multiple properties, it allows for tactical and strategic planning. Our practice has shown that ORE2_Tailings™ and the general ORE2 tailings workflow, delivers results similar to those of common practice quantitative approaches (Event trees, Failure trees, Bowties). Furthermore ORE2_Tailings™  enables answering specific questions linked to the causality of potential failures, optimization of cost vs. mitigations and many more.

General ORE2 tailings workflow

ORE2_Tailings™ is compliant with ISO 31000 and supports ICMM GISTM (Global Industry Standard on Tailings Management) conformance protocols as we showed in detail in a recent Riskope’s communication. Indeed, dam portfolio ORE2_Tailings™ support for ICMM standard on tailings management (GISTM) is multifaceted.

A typical ORE2_Tailings™ report supports Risk-Informed Decision-Making (RIDM). The development is compatible with ISO 31000 and uses a clearly defined glossary. The study is based on archival documents the client delivers for each Tailings Storage Facility (TSF) and related dams as well as written Q/A. The archival documents may include bow-ties and FMEAs which we review and update using a variety of approaches. We compare existing assessments to ORE2_Tailings™ results.

Below we summarize the general structure of Riskope’s tailings system quantitative risk assessment reports. They are organized around Chapters 2 to 10, and closed in Chapter 11. Nine takeaways are formulated.

Chapter 2 summarily describes how Oboni Riskope Associates Inc. (Riskope) uses the semi-automated ORE2_Tailings™ (©Riskope, 2014-*) discovery platform. This helps building the knowledge base relative to the considered portfolio using received documents. The chapter closes with an archival gap analysis (Take away #1). The rest of the chapters refer to the received information.

Chapter 3 describes the sites, their TSFs and each one of their dams from a physical point of view.

Chapter 4 delivers the summary of the knowledge base evaluation. It attributes a general quality note to the knowledge base using the ORE2_Tailings™ KRI  for each TSF and each one of their dams’ system. The chapter closes with a final look on archival deficiencies (Take away #2). The raw data we extract from the archival documents will be delivered in an appendix, together with a review of public space observation imagery using various sensors.

Together, the first part of the report constitutes the context of the study in compliance with ISO 31000.

Chapter 5 explains the steps necessary for the ORE2_Tailings™ deployment, i.e. defining the:

  • success/failure criteria leading to the definition of what constitutes a failure. 
  • discusses failure causality (Take away #3) and probabilities of failure evaluation. This bears on probabilities of occurrence of the selected failure under various conditions as applicable. For instance: ESA, USA, Pseudostatic, residual strength, liquefaction (earthquake or storm, man-induced) as the available data allow. A comparison with the failure modes the client adopted for prior risk assessments is possible.

Chapter 6 uses all the information delivered in the prior chapters to deliver for each dam in each TSF the evaluation of:

  • probability of failure pf under various conditions and events using ORE2_Tailings™ proprietary algorithms. A general explanation is present  in our book Tailings Management for the Twenty-First Century  as well in numerous publications.  We compare these probabilities with those in prior risk assessments. If the client has a pre-existing specific format for risk assessment, we will evaluate the results in that manner as well.
  • consequences C. We provide consequences estimations details if the client did not provide their evaluations. In that case we activate a specific function of ORE2_Tailings™ . This chapter also benchmarks the hazard (probability of failure) of each dam with respect to the world-wide portfolio. This is based in the record of hundred years of failures established in 2013 by Oboni & Oboni and theoretically confirmed by a UBC thesis (Taguchi, 2014) (Take away #4). Chapter 6 then concludes with a rating based on decreasing pf*C risk (Take away #5) which are shown to be generally too fuzzy for risk-informed decision making.

Risk tolerance

Chapter 7 delves into defining the risk tolerance thresholds from a societal and corporate perspective. In general at the first deployment the corporate tolerance is an EXAMPLE drawn from prior major mining companies’ studies. Thus it DOES NOT represent yet the client own corporate tolerance.

Chapter 8 shows the evaluation of risks based on pf and C developed earlier in context with the risk tolerance thresholds.  Thus it is possible to rank risks in terms of intolerable part (Take away #6), prioritize TSFs and dams among themselves (Take away #7).

Chapter 9 discusses which risks are tolerable, intolerable but manageable, hence tactical, and finally intolerable and unmanageable, thus strategic (Take away #8).

Chapter 10 describes recommendations intended to raise the level of knowledge on the slopes/dams in the portfolio. The goal is to reach better risk estimates and constitutes Take away #9. It will use an example where we “narrate” the deployment of ORE2_Tailings™ from its inception. The chapter aims at showing how the methodology would support owner/EoR decision-making throughout a mitigation project. The starting point will be an a priori evaluation based on extant archival information. The end point being the selected sustainable and defensible mitigated level.

Finally

ORE2_Tailings™ can indeed be deployed during the mitigation design process in order to support decision-making. The process allows to transparently and rationally discuss what constitute an attainable and sustainable level of mitigation. That is possible even for:

  • slopes/dams that are above the societal acceptability criteria and
  • will remain above corporate tolerance despite rational, sustainable and well-balanced decisions related to risk mitigation.

The illustration below shows an example of quantitative mitigation cost vs. risk abatement. It defines the ALARP point discussed in the GISTM conformance protocols. In a coming post we will explain why the crossing is perhaps a simplistic way to define the optimum mitigation level. Thus we will propose to go a couple steps beyond this to account for public opinion and enhance decisions defensibility.

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Category: Consequences, Optimum Risk Estimates, ORE2_Tailings, Probabilities, Risk analysis, Risk management, Uncategorized

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