Cyclic Evaluation of Plans at Various Stages of a Mine's Life

Each development, operating and closure plan comprises a design with drawings; specifications that define what will be constructed, and an operating plan which describes how the constructed facilities or machines will be operated. The design is completed to satisfy a number of design criteria and the operating plan specifies a number of operating constraints. Sometimes the permit conditions specified by the regulatory authorities include certain design criteria and operating constraints.

During the development of the design, the design engineer is continually doing informal risk assessments (or failure mode and effects analyses - FMEAs) to check that his/her design will meet operating requirements. If the current design has unacceptable risks of not meeting the design objectives, either the design or the operating procedures are modified until adequate performance characteristics are achieved (this evaluation process is represented by the upper half of the top circle on Figure 2). It is becoming more common for large mine developments to appoint Boards of Review to provide an independent check (audit or review) of the designs and operating manuals to ensure the appropriate 'International" standards of safety and environmental impact (risk or liability) are achieved. In effect these Boards perform FMEA's within the scope of their audits or review.

The FMEA primarily addresses the risk of designs and operating procedures not achieving the design intent. There are a number of other assessments that are important in deciding if a particular mine development or closure option is appropriate and represents a reasonably optimized plan. These assessments include impacts on the environment, the local and distant communities, costs etc (represented by the bottom half of the top circle on Figure 2). All significant stakeholders may need to participate in all or part of these evaluations and accounts must be taken of their values and concerns. A methodology, termed the multiple accounts analysis (MAA) has been developed as one of the tools (together with EA's, EIS's or ERA's) to perform such assessments (see Robertson and Shaw, 1998; Robertson and Shaw, 1999; and Shaw et al., 2001 for more details). The end result is the selection of a preferred Closure Plan.

Closure plans should be re-evaluated as the mine site development progresses since the initial plans are based on projected conditions which are expected to change in response to additional ore discoveries, changing conditions of product and mining economics, advances in technology and new regulatory requirements. Once the initial plan has been developed and is accepted, periodic, iterative re-assessments and revisions should be completed to ensure that the plan remains current, relevant and optimized. This results in a cyclical development of the plan and mine design over various stages of a mine's life as illustrated in Figure 2.

Figure 2. Cyclic Development of Plans and Designs at Various Stages of a Mine's Life.

Figure 2 provides an illustration of the successive activities at various stages of a mine project's life. The mining process, and the mine closure planning process, involve stages that evolve from conceptual to feasibility to permitting to operating to closure and finally to a post closure stage. These stages are shown on the figure down the left hand side. The circle at the top of the figure illustrates the decision-making activities as discussed above that are typically involved at each stage.

During the period of design, operating plan development and FMEA and MAA evaluations of a Closure Plan, there will be iterative modifications to the designs and operating procedures until a revised plan is agreed. The entire process is typically repeated periocidally at intervals of about 5 years to ensure that the plans always remain relevant and current.

The FMEA is intended to minimize risk (financial as well as environmental) associated with complex, long duration engineered systems as represented by the closure measures. The MAA provides a basis for the evaluation of impacts and tradeoffs where large, high economic value projects also have high, and potentially long term, social and environmental impacts. The MAA provides the mechanism for communication of stakeholder values, as well as the accounting system by which they can be taken into consideration in the development of control and closure plans that addres concerns from all stakeholders.

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