Chapter 11 HTML2

Table of Contents

 

11.1     Introduction. 1

11.1.1       Main Themes. 2

11.1.2       Scope of the Chapter 3

11.1.3       Content of Chapter 4

11.2     Planning For Closure. 5

11.2.1       Early and Continuous Planning for Closure. 6

11.2.1.1    Design for Closure. 6

11.2.1.2    Ongoing Closure Planning. 9

11.2.1.3    Comprehensive Closure Planning. 10

11.2.2       Closure Vision, Principles and Objectives. 12

11.2.3       Stakeholder Engagement 13

11.2.4       Scope of Closure Plans. 14

11.2.5       Closure Permitting. 17

11.2.6       Closure Knowledge Base. 18

11.2.7       Closure Planning Tools. 18

11.2.7.1    Multiple Accounts Analysis. 19

11.2.7.2    Failure Modes and Effects Analysis. 19

11.2.7.3    Human Health and Ecological Risk Assessment (HHERA) 21

11.2.8       Integration of Technical Disciplines. 22

11.2.9       Drainage Treatment 24

11.2.10     Adapting to Climate Change. 25

11.2.11     Closure of Legacy Sites. 27

11.3     Implementing Closure. 29

11.3.1       ARD Management through Progressive Closure Works. 29

11.3.2       End of Mine Life. 30

11.3.2.1    Closure Readiness. 31

11.3.2.2    Sequencing of Closure Works. 31

11.3.2.3    Construction Records and Quality Control/Quality Assurance. 32

11.3.2.4    Construction Issues. 32

11.3.3       ARD Issues in Temporary and Sudden Closure. 33

11.3.3.1    Temporary Closure. 33

11.3.3.2    Permanent Sudden Closure. 34

11.4     Durability through the Post-Closure Period. 36

11.4.1       Monitoring and Maintenance. 36

11.4.1.1    Monitoring. 36

11.4.1.2    Maintenance. 39

11.4.2       Managing Residual Risks. 39

11.4.3       Pathways to Relinquishment 40

11.5     Mine Closure Planning for Sustainable Outcomes. 42

11.5.1       Post-Closure Sustainable Land Use. 42

11.5.2       Social License and Social Transition for ARD Impacted Mines. 43

11.5.3       Biodiversity. 44

11.5.4       Resources for Planning Sustainable Mine Closure. 45

11.6     References. 47

 

TABLES

Table 11-1: Potential Climate Change Impacts on Closure Activities. 25

Table 11-2: List of documents on sustainable development with application to ARD management 45

 

FIGURES

Figure 11-1: The Hierarchy of Closure Needs (APEC 2018) 1

Figure 11-2: The Mine Closure Framework (ICMM 2019a) 2

Figure 11-3: Role of Activities Related to ARD Management in Each Stage of Closure Planning. 7

Figure 11-4: FMEAs at Different Stages of Closure Planning. 20

Figure 11-5: Integration of Technical Disciplines over Time. 24

Figure 11-6: Post-closure water quality trajectory (adapted from Grant 2006) 38

 

APPENDICES

Appendix 11A

Mine Closure Planning Tools

 

11.1  Introduction

The GARD Guide provides extensive information on addressing ARD and sustainability issues throughout the mining life cycle. Viewed through the lens of ARD, mine closure is just one more of the phases of mine life, as illustrated in Figure 3-3 (Chapter 3). As described in Chapter 1 of the Guide, considerations for ARD evolve from exploration through to post-closure.

However, when ARD is looked at through the lens of sustainable mine closure, ARD is a key issue that must be addressed in early stages of project design, operations and closure planning. Other key issues include physical stability, reclamation to sustain a beneficial post-closure land use, and managing the social transition to a post-mining economy. Although ARD management is one issue among many, experience has shown it to be one of the most important, in terms of cost, risk, residual liability, and long-term management implications. As such, the prediction, prevention, and management of ARD, which is the core subject matter of the Guide, is a critical component of operations and closure planning for any mine where there is a potential for the generation of ARD.

Incorporating ARD management in closure planning requires looking at the larger picture, and balancing ARD considerations with other considerations. Figure 11-1 illustrates the “hierarchy of closure needs”.  ARD management is critically important as part of addressing chemical stability, and this importance is underpinned by the necessity to provide physically stable landforms. 

 

Figure 11-1: The Hierarchy of Closure Needs (APEC 2018)

Many of the best practices in mine closure parallel the best practices for ARD management outlined in the GARD Guide. Closure issues – including ARD – should be addressed from the earliest stages of exploration and planning. Like the iterative processes outlined in Chapter 9 (Figure 9-7) for the implementation of ARD management plans, Closure Plans, sometimes also referred to as Closure and Reclamation Plans, are also developed iteratively, with increasing levels of detail and problem understanding over the life of the mine. Indeed, ARD management plans should be prepared and implemented with consideration for eventual mine closure.

11.1.1         Main Themes

A successful mining operation is one that provides long-lived benefits that outweigh the costs of the operation in financial, social and environmental terms. Achieving this requires planning, both in terms of planning for sustainable development through the life of mine, and for effective closure at the end of asset life. Achieving a net positive outcome can be challenging when ARD issues persist after the productive mine life, with ongoing environmental, social and economic costs.

As illustrated in Figure 11-2, mine planning and design, ARD characterization and closure must be continually advanced beyond exploration, throughout mine development and operation, to ensure effective mine closure. For a successful end to the mine life, effectively addressing ARD can be the most critical issue. If ARD is not addressed effectively throughout the life of mine, including closure, the pathway to a fully closed site is unclear, and it is highly unlikely that it will be possible to relinquish the site to the next land user, or fully transition to a different type of land use post-closure. Further, ongoing needs for water treatment or active control of water discharges can represent an ongoing or perpetual cost, risk, and potentially permanent environmental and social liability.

Figure 11-2: The Mine Closure Framework (ICMM 2019a)

Mining activities that involve the excavation and/or processing of rock containing sulphide minerals accelerate the oxidation process, as sulphides are exposed to air and water within built structures such as open pits, mine rock piles, underground mine voids and tailings storage facilities. Addressing the long-term fate of these facilities is a cornerstone of closure planning. Where there is a potential for ARD generation, chemical stability requires returning sulphide-bearing minerals to a condition of effective long-term isolation as much as possible by reducing oxygen ingress and the flow of water that can act as a transport medium for oxidation products. Failing the achievement of sufficient isolation, long-term collection and treatment of impacted water may be required. In either case, oxidation and chemical impact potential tend to persist over time, while isolation measures may degrade. This may make some degree of ongoing intervention necessary. It should be noted that water management may also be required in the absence of ARD as neutral or alkaline mine waters can also have deleterious effects on human health and the environment (see Chapter 2 for more detail).

The flow of water at both the surface (hydrology) and subsurface as groundwater (hydrogeology) is the primary mechanism for release of ARD into the environment. Water management requires particular attention in closure planning. Given the long timeframe over which the closure design must function, a good understanding of the hydrology and hydrogeology is essential in defining the pathways and receiving environments, noting a limited ability to predict the impacts of a changing climate on the water cycle.

There are a variety of approaches, methodologies, and alternatives for ARD control in the post-closure landscape. Costs, social impacts, and residual risk can be large and can vary widely between closure concepts. The choice between alternative closure concepts requires careful and robust risk assessment, together with transparency and stakeholder inclusion, to ensure that the selected closure concept(s) will address community and regulatory expectations and sustainability requirements over the long term. The long-term physical and chemical stability of the rehabilitated landforms is critical to meeting the closure objectives and the sustainable development goals of the mine, and thus achieving successful mine closure.

This chapter discusses ARD from the perspective of mine closure. However, the issue of ARD is not strictly the domain or responsibility of mine closure practitioners, as discussed in Section 9.2.3. This is to emphasize that ARD management requires an interdisciplinary approach across operational functions within the mine organization to best address the problem in a manner that leads to sustainable closure practices.

11.1.2         Scope of the Chapter

This chapter addresses the implications of ARD for achieving effective mine closure and for achieving sustainable mine closure.

To put these ARD-specific considerations into context, broader issues of sustainable mine closure are also discussed. However, this chapter is not intended to address all aspects of sustainable mine closure. References to key industry guidance are provided for readers who wish to explore these areas in more detail.

For the scope of this chapter, “mine closure” is considered in its broadest sense, applying to the phases of mine life and activities conducted after productive mining has ceased, as well as partial or progressive closure activities that may occur during operations, including some activities that may be conducted under an ARD management plan (e.g., encapsulation). The concept of mine closure includes planning for the eventual closure of the site, and the implementation of these works either in accordance with the plans, or to address unexpected closures or abandoned sites.  It also includes the long-term monitoring, maintenance, and management of the site post-closure. The term “mine closure” is taken to include reclamation/rehabilitation, remediation, and decommissioning activities, as well as any treatment, maintenance, or monitoring needed after the completion of the mine’s productive life. It may also be applied to all associated remote facilities that are not classified as ‘mines’, such as processing or concentrating facilities that produce waste or tailings. Active closure is the phase of mine life where ore is no longer being produced but there is still the presence of personnel (owner or contractor) on site, executing activities to remediate, reclaim and close the site. Post-closure is the phase following active closure where all major activities have been executed and monitoring is now being undertaken to assess the performance of these measures. The site may or may not have permanent personnel in place depending on the requirements associated with post-closure activities.

In the context of this document, ‘sustainability’ is taken as sustainable development[1], addressing the overall contributions to the post-closure development goals of the area in which the mine is located. This also provides consistency with the concepts in Chapters 1, 3 and 10 of the GARD Guide that address the importance of life-cycle thinking in making these contributions.

Some mine closure documents also use ‘sustainability’ to refer to the durability, longevity or resilience of the closure measures implemented – i.e., the long-term effectiveness of the measures in relation to maintaining physical and chemical stability. This chapter will use the term ‘durability’ for this concept to avoid confusion.

11.1.3         Content of Chapter

This chapter is organized in five sections.

§   Section 11.2 describes the specifics of planning for closure, including progressive closure works and closure works implemented at the end of mine life. This section also addresses ARD management in the context of tools and technologies that may be used in mine closure planning, connecting previous chapters of the GARD Guide with the specific challenges associated with the last – and likely longest – stage of the mining cycle.  

§   Section 11.3 addresses the challenges of implementing closure works at mines with potential ARD, either as part of progressive closure or at the end of mine life, and dealing with ARD issues in a temporary or sudden closure.

§   Section 11.4 looks at the post-closure period, considered through the lens of the sustainability of ARD management solutions.

§   Section 11.5 provides an overview of the importance of sustainable mine closure in the context of ARD management.

 

 

11.2  Planning For Closure

This section describes an approach to establishing effective and cost-efficient Closure Plans and designs, highlighting the unique aspects of closing facilities with ARD present or ARD potential. The objective is to emphasize and expand on those closure issues that are related to closing mines at which ARD is occurring or has the potential to occur, and to supplement what is contained in these other references.

Key considerations for closure include the following (ICMM 2019a):

§   Conduct early and continuous planning to achieve cost-effective closure and a smooth transition from the operational to the post-closure phases (Section 11.2.1).

§   Establish a clear closure vision, principles and objectives that consider the needs and concerns of stakeholders to establish closure outcomes that will endure with time (Section 11.2.2).

§   Provide for effective engagement with stakeholders, including communities of interest, throughout the planning process so their concerns and issues are addressed thus minimizing the risks of future issues with stakeholders (Section 11.2.3).

§   Prepare robust and resilient Closure Plans and designs to reduce the long-term post-closure risks and care and maintenance requirements (Section 11.2.4).

§   Establish permits that provide for sufficient flexibility to accommodate changes and refinements to the Closure Plan and designs during the operational phase (Section 11.2.5).

§   Establish a comprehensive and accessible knowledge base that provides a solid basis for closure planning and a record for posterity and future generations during the post-closure phase (Section 11.2.6).

§   Conduct comprehensive closure planning by carefully selecting closure activities from a range of feasible alternatives to increase the effectiveness of Closure Plans, and to maximize opportunities and minimize risks associated with closure (Section 11.2.7).

§   Integrate knowledge across a range of technical disciplines to effectively control and manage ARD in closure (Section 11.2.8).

§   In the instance source control is not fully achievable, understand the implications of long-term water treatment in the context of sustainable mine closure (Section 11.2.9).

§   Create resilient closure solutions for mines potentially impacted by ARD in the face of climate change (Section 11.2.10).

§   Consideration of planning for legacy sites (Section 11.2.11).

Closure Plans are required both for final closure on completion of mining as well as for temporarily halting of operations (care and maintenance). Also considered is the potential for early final closure in the event the mine is permanently closed due to poor market, financial, or social conditions, or other reasons. The scope of these Closure Plans is dependent on regulatory environment and/or company standards; however, accepted international best practice for Closure Plan content is ICMM (2019a).

For operating mines without up-to-date Closure Plans, mine closure planning should be addressed immediately, in order to minimize the number of lost opportunities for ARD control, regardless and independent of jurisdictional requirements. 

11.2.1         Early and Continuous Planning for Closure

11.2.1.1  Design for Closure

Early planning for closure, including establishing likely or potential post-closure land-use, commences with the initial mine development planning, which is captured by the “Design for Closure” concept introduced in Section 9.2.5. It is particularly important at mines with ARD issues since these can represent significant closure challenges that in some cases are best mitigated by changes to the mine plan and the designs of the waste storage facilities. This planning is included in the environmental and socio-economic assessment and permitting of the mining project, which is then reviewed on an ongoing basis and periodically refined and updated thereafter as necessary to reflect changes in mine plans, stakeholder expectations, the regulatory landscape, and developments in the practice of science and engineering.

Key approaches when implementing the “Design for Closure” concept include:

§  Adapt the design of the mine’s components, to the extent practical, to accommodate easier and more cost-effective and robust mine closure measures.

§  Avoid mine designs that result in unacceptable future land uses and/or impractical or costly mine closure implementation and/or require extensive post-closure care.

§  Avoid mine designs that unnecessarily increase the liability associated with the closed mine during the post-closure period.

§  Maximize the potential for progressive mine closure and reclamation during operations as this both reduces the cost of final closure and also allows the performance of closure measures to be assessed and improved as necessary. This also has the benefit of reducing closure liability.

Implementing the “Design for Closure” approach is achieved by integrating closure planning with Life-of-Mine (LoM) asset planning.

Figure 11-3 illustrates the role of activities related to ARD management (referenced in earlier chapters of this Guide) in each phase of closure planning, from the earliest stages of planning (ideally conducted as part of initial mine planning at the exploration stage), through to the preparation of detailed plans for the execution of closure works throughout the entire lifecycle and to be completed at the end of mine life, and post-closure maintenance and monitoring.

Figure 11-3: Role of Activities Related to ARD Management in Each Stage of Closure Planning

The early phase planning is critically important. While the scoping and conceptual designs are necessarily limited in detail, they must feed into the overall mine plan, and the evaluation of the overall economic and social viability of the mine. While the characterization and predictions for ARD will be refined over the life of the mine, there is an imperative for the earliest work to identify the nature and extent of any ARD issues. Ideally, it should be known at the earliest stages of mine planning if there will be need for significant mitigation works, or ongoing treatment.

As shown in Figure 11-3, early closure planning initially considers a range of feasible mine and closure alternatives, which are progressively eliminated until final options are selected that, on balance, achieve most of the closure objectives (Section 11.2.2) and requirements. Where there is a potential for ARD, a key element in closure planning is to incorporate measures to prevent that potential from being realized or mitigate environmental impacts. This is the subject of Chapter 6 and is a core focus of closure design. Avoidance of particularly reactive rock types, special handling methods and other best practices discussed in Section 6.6 may be implemented during this stage to reduce the risk of ARD.

Note that even at early stages, it will be necessary to identify an option that will be used as the basis for planning and cost estimations. This is typically the option that, on the basis of available information, best balances cost considerations with confidence that the approach will meet regulatory requirements, design goals and long-term closure objectives.

Closure designs should be established at a conceptual level in parallel with the design of the mine, processing, and waste storage facilities and should influence these designs. It can be a regulatory requirement to complete the closure designs to a higher level prior to the start of mining and processing, to provide a higher level of assurance closure planning can proceed, and that the estimated closure costs are realistic since these may be used for establishing financial assurances. However, the reality is that these plans often change during the mine life.

The following are examples of waste management concepts and designs that can be considered during early mine planning to reduce closure liabilities and costs:

§  Optimizing mine planning through incorporation of potentially acid generating (PAG) material into ore block models to allow for avoidance or effective management of PAG material to minimize the potential for ARD occurrence.

§  Minimizing PAG material disturbance and handling by placement of PAG material directly into a closure configuration and minimization of ARD generation through progressive reclamation.

§  Constructing landforms during operations to enable rehabilitation designs that are appropriate for the material types. Locating tailings storage facilities (TSFs) and waste rock dumps to minimize surface runoff collection and the need for large surface water diversions.

§  Utilizing thickened tailings to increase their density and/or strategic tailings deposition to make cover design and construction easier and less costly.

§  Designing waste and tailings facilities that do not rely on long-term water treatment to meet water quality objectives, e.g., consider a design that permanently encapsulates PAG material.

§  Progressive backfilling of pit voids with waste rock, particularly with PAG materials, to minimize oxygen ingress compared with surface dumps.

§  Segregating non-acid forming waste rock and topsoil for temporary storage before being utilized in the final closure of ARD generating landforms.

§  Minimizing the number of catchments/watersheds disturbed with waste rock dumps/tailings storage facilities

§  Providing for effective clean water management, such as surface water diversions, that will endure during the post-closure phase. This will minimize contact water volumes that may require special handling.

§  Avoiding or engineering for foundation conditions that may otherwise become unstable in the long term, such as thawing permafrost or liquefiable soils under seismic loading.

Because of their cost, importance, and ongoing technological development, the selection of prevention and mitigation technologies requires rigorous evaluation of alternatives. As discussed in more detail in Section 11.2.7, formal decision-making processes are often applied to help ensure that a full range of potentially viable alternatives is considered, and the process and inputs used to select the preferred option(s) are fully documented.

In this process, the assessment should take into consideration the potentially distorting effect of net present value (NPV) analyses, which lower the profile of future costs such as those associated with closure and long-term water treatment, as discussed in Section 11.2.9. Measures for the prevention and mitigation of ARD can be one of the largest costs associated with implementing Closure Plans. It is important that short-term financial or operational priorities should not prevail over designs and operational practices that would have higher long-term success in mitigating ARD impacts, closure complexities and/or other post-closure risks. They can also be a critical source of long-term cost savings where they can help eliminate or reduce the need for long-term treatment. Cash flow costs in the closure and post-closure phases are, therefore, an important consideration in closure planning.

Regulators and other stakeholders generally expect to know prior to approving a new mine if there will be requirements for permanent environmental controls post-closure. These inputs are also important for developing the mine plan. Key decisions, such as which deposits to develop, the sequence of mining, the waste rock types and their locations in the deposit, should all be made with due consideration of the implications for closure, and the associated long-term liability.

There is considerable tension between this desire for clarity early in the mine design and the natural progression of Closure Plans and the collection of materials characterization data, environmental baseline data and prediction information. Characterization and prediction of ARD (the subjects of Chapter 4 and 5, respectively), are key to responsible mine and closure planning and should be addressed from the earliest stage of mine planning. Both mine design and materials characterization are iterative processes, with refinement expected and required over the life of mine as information is collected.

It is not uncommon to make important determinations on closure technologies during the operation of the mine (such as: Is treatment needed? Which constituents need to be removed by treatment? How long will treatment be needed? Is active or passive treatment required?). Similarly, adaptive management is frequently employed during mine operation to adjust practices related to ARD management. It is, however, desirable and in the interest of both the mine operator and other stakeholders to make such decisions with a clear understanding of their long-term implications. This implies expending additional resources early in the mine life to collect materials characterization and baseline data, and model ARD issues to support credible projections of long-term closure implications. This allows the development of an optimized mine design, ideally with a focus on ARD avoidance rather than relying on mitigation or treatment at closure.

11.2.1.2  Ongoing Closure Planning

During operations, the Closure Plan should be revisited periodically and adapted as the mine plan changes and knowledge is gained from ongoing environmental monitoring. Many jurisdictions and corporate standards stipulate the frequency at which this update is required to take place, typically every few years.  Refining the Closure Plan on an ongoing basis provides for, among other aspects:

 

§  Opportunity to update the Closure Plan to account for mining and processing changes that are made during the operational phase of the mine as well as the availability of additional geochemical information and monitoring data as mining is advanced and environmental monitoring continues.

§  Adjustments and improvements to be made to the post-closure land uses based on the knowledge gained during operations and input from ongoing stakeholder engagement. This is particularly relevant where the stakeholders change and/or stakeholder expectations evolve over the life of mine.

§  Adapting operating procedures that make implementation of closure more effective and efficient.

As discussed in Section 9.2.2, updating the Closure Plan is particularly important for mines with ARD issues since a significant amount of information on the ARD sources, characterization (maturity) and prediction of future ARD generation is obtained during operations.

As closure planning progresses during operations, alternative closure measures are typically identified, field trials implemented and designs refined. This process, along with additional geochemical testing, provides direct feedback to the ARD characterization and prediction programs, identifying knowledge gaps that may need to be addressed through those programs before design choices can be finalized. When developing a characterization and prediction program for operations, it should always be expected that it will be refined based on the evolving needs of the mine and Closure Plans.

Examples of evolving mine closure and reclamation planning include:

§  Adapting the sizes and locations of mine waste storage facilities to changes in the mine production plans.

§  Altering or refining how the mine waste is being managed and placed in the storage facilities in line with best practice mine waste storage construction principles (INAP 2020) based on geochemical characterization and prediction information obtained during operations, which can differ from the characteristics and design parameters used for the initial design and operating plans.

§  Optimising water use during operations to reduce impacts to water quality and quantity which may need to be addressed at closure.

§  Implementing strategic tailings deposition in the later years of mining to support the proposed closure strategy for the facility.

§  Considering desulphurization of tailings, to limit ARD generation.

§  Reshaping rock piles to final slopes during construction to minimize rehandling during the mine closure phase.

§  Managing waste to minimize ARD potential by encapsulating the reactive waste with low-permeability, non-reactive materials, or by adding neutralizing agents to the waste as it is placed (INAP 2020).

§  Performing “pilot scale” testing of waste cover construction to optimize the closure design.

It is common (and generally considered good practice) to implement progressive closure where practical. Progressive closure is the implementation of closure works during the operations phase. For example, select waste rock facilities may be closed and fully reclaimed with covers placed while other facilities are still in operation. As needed, and on an incremental basis, detailed (construction) level designs are developed during operations for any progressive closure activities. In addition to reducing the overall closure liability for the site, progressive closures provide a practical way to evaluate performance and refine the technologies that will be applied in the final closure. This cycle is illustrated schematically in Figure 11-2.

The ideal of periodic review and update of Closure Plans is not always realized, and closure planning sometimes needs to address ARD issues that were not suitably identified or realized until late into operations.  Similarly, sometimes it is necessary to identify and implement proper closure measures for legacy or abandoned sites that have not undergone sufficient study and characterization. In these cases, the same stages of closure planning typically apply in some form (such as conceptual designs before detailed designs), but the iterative process of design refinement over years or decades typical of systematic closure planning needs to be collapsed to a much shorter time frame, often with increased costs and greatly limited options.

An essential component of closure planning is the ARD management plan, which is discussed in Sections 9.2 through 9.4. As with the Design for Closure concept, it is important these plans are developed with closure in mind and are updated as necessary during the operational phase of the mine. As discussed in Section 9.2.4, the onset of ARD may occur during the life of the mine but may also occur many years into post-closure. Predictions and management of future ARD are, therefore, an essential and integral part of mine and closure planning. These predictions become more reliable and robust as materials characterization and environmental data are collected during the operational phase of the mine.

11.2.1.3  Comprehensive Closure Planning

Closure planning is a complex and essential process. Comprehensive closure planning can be expected to achieve the integration of all aspects that influence and ultimately determine the scope of the Closure Plan and the associated design bases and criteria:

§  Accommodate current and future mining plans with the flexibility to adapt to unexpected changes in these plans.

§  Meet the technical requirements that provide for long-term physical and chemical stability of mine waste facilities.

§  Establish the necessary post-closure monitoring and maintenance, such as surface and groundwater monitoring, cover inspections and repairs.

§  Meet the closure vision and objectives.

§  Comply with established closure principles and regulatory requirements.

§  Maximize post-closure land use opportunities and minimize long-term post-closure risks.

§  Provide planning for the transition of local communities and the local socio-economic framework from operations through closure to the post-closure period.

§  Provide planning for the transition of the mine staff.

To achieve this, the development of an effective Closure Plan requires an integrated, multi-disciplinary team and a structured planning process to make sure all the relevant aspects are considered.

Closure Plans for sites nearing the end of LoM include feasibility level closure designs, which are then further developed to detailed designs. This usually occurs several years before closure of the mine or earlier as required by regulation.

Section 9.4.1 of this Guide mentions that some designs and cost estimates are conducted for a time horizon of 100 years. For cost estimates using NPV considerations, 100 years is likely sufficient, and does not result in meaningful differences with an evaluation extended out into perpetuity at most discount rates. For closure engineering design considerations, particularly where ARD materials are concerned, it may be appropriate to consider a longer, e.g., 200-year, period and include the provision that there be no plausible catastrophic failures modes that could occur in the long term after this period. The evaluation of long-term catastrophic failure modes reduces the likelihood of any failure over the much longer post-closure period and also recognizes that there may not be a presence on site to respond to any failures. This is in line with references (e.g., APEC 2018) that suggest a design life of 200 years be used for closure design as it represents the limits of typical engineering practice but that given the near-permanent nature of closed mining facilities, longer periods should be considered in at least a qualitative assessment (see for example APEC 2018, Logsdon 2013).

Global Tailings Review 2020, ICOLD Bulletin 153, the Canadian Dam Association (CDA 2014) and others provide design criteria for closure, such as design storms and earthquakes, and standards, such as the required embankment or fill slope factors of safety for the operational and post-closure periods. The CDA also considers criteria and standards for “active care” closure and more stringent criteria for “passive care” closure. The criteria for "passive” closure also exceed those required for the operational period. To the extent it is practical, for a “passive care” closure, the design criteria for “passive care” should be used for the initial closure designs. If this is not considered practical, the closure designs should include provision for upgrading the closure facilities at closure to meet the "passive care” criteria to make sure these are feasible and are accounted for in evaluating the economics of the mining operation.

In addition to documenting the “what” is to be done in the Closure Plan, it is generally advisable to prepare a separate Closure Execution Plan (ICMM 2019a). Such a plan describes how the engineering designs would be finalized, how the closure facilities would be constructed, what the expectations are related to stakeholder involvement, how the socio-economic transitioning would be undertaken, and how, and by whom, the post-closure monitoring and maintenance would be conducted, amongst other execution-related aspects. The Closure Execution Plan typically would also include clear identification of responsibilities for advancing and/or implementing closure works.

11.2.2         Closure Vision, Principles and Objectives

A clear closure vision and defined closure principles and objectives are necessary to plan for and achieve effective closure. These are also necessary to ensure members of the mining company, investors, regulatory agencies, and other stakeholders are informed and aligned on what is to be achieved by closure. As discussed in Section 11.2.7 the closure principles and objectives guide the comparison of alternative closure strategies, shaping the final Closure Plan.

The terminology used here (vision, principles, and objectives) is aligned with that used by ICMM (2019a). Companies and various regulatory agencies may prefer their own, different terminology. In either case, it is important that these guidelines are set with increasing levels of detail, moving from general guidance to specifics that are sufficiently detailed to be used in the alternative selection process discussed in Section 11.2.7.

A shared, site-specific vision should be established that articulates what a company wants to achieve post-closure and the legacy it plans to leave behind, how the other stakeholders will benefit from the post-closure land use created, and how the Closure Plan aligns with regulatory requirements. For example, a closure vision for a mine impacted by ARD may include the preservation of Indigenous Rights in relation to the land. This vision embodies the undertaking of activities traditionally carried out on the land, such as drinking the water, hunting wildlife and gathering plants for food and medicinal purposes.

Closure principles are general in nature, typically applicable to a wide range of sites, and provide a generally acceptable framework for the closure vision. They must be site-specific, concrete/tangible and measurable. Examples of such principles relating to ARD are:

§  Meet legal and regulatory requirements.

§  Provide long-term chemical stability.

§  Provide long-term geotechnical stability (where this may be impacted by ARD formation).

§  Minimize environmental impacts.

§  Meet agreed-to sustainable development goals.

§  Minimize long-term risks.

§  Minimize need for long-term care and maintenance.

§  Provide for cost-effective closure and post-closure.

Based on these principles, closure objectives are defined that provide the details and design criteria necessary for meeting the closure visions and principles. Closure objectives are site-specific, are generally determined to establish an effective and durable engineered closure, and are shaped by the geochemical/geotechnical characteristics of the waste material (particularly its ARD potential), and post-closure land use considerations. Establishment of these objectives also includes consideration of the mining company’s policies and guidelines, potential socio-economic impacts and risks, and local regulatory and international guidelines and requirements. It is important that the objectives do not simply repeat the principles.

Some typical examples of closure objectives relevant to operations with ARD issues include the following:

§  Water quality goals to be achieved in groundwater and surface water at the site.

§  Description of the type of ecosystem to be established, including the types of fauna and flora.

§  Waste management and/or treatment requirements to meet a specific level of chemical and physical stability. Objectives related to chemical stability (often expressed as water quality) are extremely important for wastes with ARD potential.

§  Engineering design bases.

§  Description of the types of landforms remaining post-closure.

Success criteria are defined as a means of determining the achievement of closure criteria. Success criteria should be measurable. In many cases, success can be measured through binary statements. For example, surface water quality achieves specific guidance concentrations, or a pit lake remains stratified, thereby isolating poor quality water below a chemocline.

11.2.3         Stakeholder Engagement

Developing sustainable Closure Plans requires engagement of relevant stakeholders. Stakeholder engagement should be undertaken in parallel with closure planning to share knowledge, collaborate, and reach agreement on mine closure and reclamation objectives, post-closure land use, sustainable development, and the timing of the closure works, amongst other aspects.

Early and ongoing engagement is important for all aspects of sustainable mine closure planning but is particularly relevant where there is the potential for ongoing issues, such as ARD, that may extend into the post-closure period. Buy-in on key aspects of the Closure Plan such as post-mining land use, reclamation objectives and key closure activities will allow a smoother and more sustainable transition through closure to a post-closure state. Transparency is important so that stakeholders can see how their issues and concerns have been addressed.

Key best practices for engagement of communities and Indigenous groups are:

§  Understand corporate stakeholder engagement objective (i.e., inform, consult, involve, collaborate, or empower [IAP2 International 2018]).

§  Engagement of stakeholders and Indigenous communities occurs throughout the mine life cycle.

§  Effective and ongoing tracking of commitments to communities.

§  Communicate project impacts to communities with transparency.

§  Participatory monitoring.

§  Collaboration with Indigenous communities.

§  Traditional knowledge integration.

§  Indigenous cross-cultural understanding.

§  Inclusion of Human Rights.

Engagement should incorporate discussion of specific topics relevant to ARD, such as:

§  Preferred closure design – what technologies are applicable to manage PAG material and/or ARD in the specific context of the site in question, and what are the pros and cons of each option (e.g., active vs passive water treatment; wet vs dry tailings covers, encapsulation of tailings, etc.).

§  Timeframe for ARD management and/or treatment – In many instances, managing ARD can be a multigenerational undertaking with action required over the long term or even in perpetuity.

§  Monitoring and water quality triggers for action – Are the right indicators being monitored? Will monitoring be at locations and frequencies that are sufficient and appropriate for catching problems early on and allow mitigation?

§  Adaptive management – what will trigger further monitoring or action on site?

§  Contingency plan – What is the plan if the preferred closure methodology to mitigate ARD does not work?

§  Funding – Who will pay for long-term monitoring, maintenance and treatment (if required)? Local communities and government agencies may be concerned that they will be left with impacts that must be cleaned up at their expense. In some instances, a trust fund or government bond may be the mechanism to fund ongoing ARD monitoring and/or management.

§  Employment opportunities – If ongoing work is required for ARD monitoring and/or management, can this provide the local community with an economic benefit that may help to reduce any socio-economic impacts of the mine closure?

§  Watershed management – the impact of ARD on the downstream watershed may be of concern. How do mitigation measures minimise or prevent downstream impacts? (see Section 11.5.5 for further discussion of watershed management and stewardship).

§  Residual impacts – despite best efforts, it is possible there will there be some residual impacts on the post-closure landholder, the environment and other stakeholders. Stakeholders may be particularly interested or concerned if these impacts occur to valued environmental components and heritage sites. Are stakeholders willing to accept these impacts? Can anything be done to address these impacts (e.g., controls to keep wildlife away from acidic water)?

In many jurisdictions, the process to obtain regulatory permits required for mine closure will be smoother and less prone to delay if stakeholders have been actively engaged early on in the closure planning process, and engagement has been consistent and transparent throughout the mining life cycle. Even when there is not a regulatory impetus, this engagement will be needed for social licence purposes (see Section 11.5.2). This type of engagement may also facilitate eventual site relinquishment, by developing a consensus on the pathway to relinquishment (see Section 11.4.3).

Engagement in the context of ARD is discussed in greater detail in Chapter 10.

11.2.4         Scope of Closure Plans

As discussed in Section 9.2.5, Closure Plans are required both for final closure on completion of mining as well as for temporarily halting of operations. Also considered in closure planning is the potential for early final closure.

For sites with ARD potential, Closure Plans will be a tool to document and communicate the degree of knowledge and understanding of the principal ARD drivers (i.e., the problem or risk) and also the means by which ARD will be addressed (i.e., the mitigations). This may be drawn in part from ARD management plans used during operation, however, the key differentiating factors are that the Closure Plans provide a wholistic view of the mine closure and present measures to address and monitor the closure mine in the long term, whereas ARD management plans are typically focussed on shorter-term, operational monitoring and management. Closure Plans should be clear and concise, drawing on relevant information, where needed, and including more detail in appendices, where necessary. Typically, a Closure Plan would address the following topics:

§  The mine history through closure.

§  Site conditions, including geology, soils, geochemistry, hydrogeology, climate, hydrology, fauna and flora, socioeconomic and cultural conditions, traditional knowledge, and the relevant stakeholders.

§  Closure vision, principles and objectives, post-closure land-use, and success criteria.

§  The organization of the closure team and associated responsibilities.

§  Identification and evaluation of closure alternatives, and selection of preferred alternatives.

§  Closure activities, construction, operation, and social transition, including the timing of these activities.

§  Closure opportunities, risks, and risk management.

§  Progressive, capital and long-term care and maintenance costs related to closure.

§  Closure requirements in the case of temporary halting of operations.

§  References to the contents and evolution of earlier Closure Plans.

For sites with an ARD potential, each aspect of the Closure Plan will be expected to address the relevant items related to ARD prevention, minimisation and/or mitigation.

Closure Plans frequently include a progressive closure component (i.e., closure occurring during operation) and describe those closure activities that are planned to be implemented during operations.  These typically include encapsulating wastes in low permeability cells, grading, covers and re-vegetation of completed portions of tailings or waste piles, chemical treatment and physical stabilization of wastes, among others.

Temporary halting of operations typically requires that mining and processing equipment be shut down but maintained on standby, while other activities, such as site security and maintenance, water management, water treatment, etc., are continued.

Early final closure needs to be considered to provide for cost-effective closure in the event mining operations cease prematurely. For instance, leaving waste storage facilities partially completed may require waste relocation and/or extensive regrading, which is to be avoided due to the significant cost implications. In some instances, the consideration of early final closure may lead to the selection of different waste storage configurations during the initial mine planning and design phase.

Plans and reports that typically accompany a final Closure Plan include the following:

§  Background information, such as an Environmental Impact Assessment, baselines studies, and additional knowledge gained during operations. Of particular interest for sites with ARD potential will be surface and groundwater quality, water balance, geochemical monitoring and water quality predictions.

§  Relevant Closure Permits, such as those for wastewater discharge.

§  Design Basis Report, describing the bases and assumptions used for the designs and the applicable design criteria. The presentation of the design basis should include discussion of criteria specific to closure conditions as discussed in Section 11.2.2.

§  Design Report, describing the design and containing the construction design drawings and specifications. These will be required for all engineered components on site, such as waste rock dumps, tailings storage facilities, covers, water management structures and water treatment plants.

Robust Closure Plans and Designs

A robust closure design is essential since the post-closure period may extend to well over 100 years. The following components are important to achieving the required robustness:

§  Use of conservative design criteria and assumptions, including consideration of climate change.

§  Development of a comprehensive understanding of the potential sources for ARD and their geochemical (and geotechnical, as needed) characteristics, e.g., their reactivity, the ARD generation mechanism(s), the presence and implications of stored acidity, and the time period over which acidic conditions may occur, including the lag time to ARD generation.

§  Use of a Failure Modes and Effects Analysis (FMEA) to identify any residual unacceptable risks associated with a design or a constructed facility and to address these by design and/or construction modifications.

Examples of robust design approaches include use of more stringent design criteria for tailings facilities as recommended by the CDA (2014) and the GISTM (Global Tailings Review 2020) for the post-closure period versus the operational phase of a mine. A comprehensive understanding of the ARD characteristics of a waste allows for more appropriate and focused ARD controls to be implemented during operations and incorporated in the Closure Plan. Performing the FMEA allows identification of those design elements that are not robust so that the design can be improved to remove the associated vulnerabilities. This approach is discussed in more detail in Section 11.2.7.2. 

An FMEA conducted for closure design should look at performance over a longer period (e.g., 100 or 200 years) than is typical for an operational FMEA. This increases the likelihood that the FMEA will incorporate scenarios involving exposure of the facility to infrequent extreme events, such as floods or earthquakes, during the assessment period, focusing attention on the need to design for the resulting increased post-closure risks.

Examples of design elements that can be factored in to make closure designs more robust include:

§  use of durable materials for construction that are less prone to physical and chemical weathering over time.

§  over-design of key features, such as internal embankment drains needed to prevent the increase of phreatic pressures.

§  use of natural granular materials as filters under riprap installed in surface water diversion channels, rather than a geofabrics, when material availability permits.

Specific to ARD issues, robustness can be increased by designing for the worst-case long-term ARD projections, including containment systems and closure covers that limit the intrusion of water and air, submerging subsurface drainage systems to avoid air intrusion, and use of easily repairable drainage systems such as open channels if practical.

Resilient Closure Plans and Designs

Resilience, or the ability to “bounce back”, applies both to the closed mining facility as well as to the receiving environment that would potentially be affected by the failure of that facility. 

Increasing the resilience of the environment within which the closed facility is located can be achieved by selecting locations for mine infrastructure that are less prone to failure or where potential impacts of failure are minimized. This may include working with local government to prevent future downstream developments that would increase the likelihood and/or consequences should a closed facility fail.

During the closure planning process, the FMEA can be used to favour selection of closure alternatives that are less prone to any catastrophic failures. Examples of design choices that can improve resilience include:

§  Incorporation of geomorphic design principles, such that facilities preserve function even as they erode and evolve over time.

§  Design facilities that will still retain critical functions if damaged by earthquakes or floods (such as dams that would still provide retention after earthquake induced deformation, or ditches that still provide conveyance if overtopped).

§  Design low permeability structures (such as some types of covers) considering anticipated long-term geotechnical/geochemical characteristics of the cover materials rather than the characteristics immediately post-construction.

§  Design facilities and their individual components, such as covers or water management structures, in consideration of climate change projections for the site.

11.2.5         Closure Permitting

Permitting requirements for Closure Plans vary widely among mining jurisdictions. Where a formal environmental assessment procedure is in place for the licensing of new mines, it is typical to have some requirements for the mine plan to include closure measures, although the level of detail expected varies. In jurisdictions with more mine closure regulation, there may be a permitting phase required to obtain approval for specific closure designs prior to the start of mine construction. There also may also be requirements for regular updates of the Closure Plan over the LoM, with financial assurance mechanisms to demonstrate that adequate funding will be available to execute the required closure works. In the case an ARD potential has been identified, regulators will typically develop a direct focus on ARD-related issues, particularly when long-term water treatment may be needed.

The specific regulatory requirements related to closure planning are based on the requirements of the local jurisdictions. However, the following general considerations can be applied to a wide variety of assessment and permitting processes:

§  It is essential to permit Closure Plans that are both technically and financially feasible and include closure designs that are constructable. While in some regulatory jurisdictions it may be possible to permit general concepts and approaches that have not been considered in sufficient detail to confirm their feasibility or constructability, this should be avoided since it may lead to distrust amongst the regulatory agencies and other stakeholders over time when it is perceived that promises are not kept.

§  In applying for permits for closure, it may be advisable to obtain permits for a range of potential closure configurations to avoid re-permitting steps each time there is a change in site conditions or the mine plan that require changes to the Closure Plan. This approach is referred to as “envelope permitting”. Regulatory agencies are not always comfortable with using flexible permits, so it is important to discuss and reach agreement on their need and practicality. Part of that conversation should identify how this approach can reduce closure risk.

§  It is usually preferred to obtain approvals for performance-based specifications, rather than prescriptive definitions of what is to be done. For example, by defining the discharge water quality criteria (e.g., by adopting relevant guidelines or standards) rather than the type of water treatment, there is more flexibility to incorporate technological advances. Prescriptive specifications are easier to develop and audit, however, which means that the advantages of performance-bases specifications should be clearly identified.

§  Typically, both good science as well as the regulatory requirements for a specific closure feature should be assessed and the most appropriate science/regulation applied. If a situation develops where regulatory requirements are contrary to the current state of science (e.g., water quality criteria that are more stringent than baseline or background conditions), discussions with the regulator should be held at the needed level to adopt the best approach for all.

§  Permitting requirements should be mapped out from the earliest stages of closure planning. There are many cases where the implementation of closure works has been delayed because the appropriate permits/approvals were not in place. This can have consequences not only in terms of budget and schedule, but also on the environment, with (for example) materials exposed to oxidation for longer periods than necessary, resulting in ongoing generation of ARD. Careful mapping of permitting requirements can help to avoid delays. This mapping should also include tracking of changes, as environmental regulations often evolve over the course of mine life. It is important to maintain good relationships through frequent meetings and knowledge exchange with the regulatory agencies and other stakeholders involved in the permitting processes. Documentation should be maintained to develop a continuous and reliable record for what is typically a multi-year process.

Globally, permitting requirements and mine closure regulations are in a state of evolution. General consensus on good practice is increasing (see, for example, APEC 2018), but it will take additional time and effort for the various jurisdictions to come into alignment.

11.2.6         Closure Knowledge Base

The development and maintenance of an integrated knowledge base is essential to support effective closure planning, design, construction, post-closure monitoring and maintenance, and stakeholder engagement. It is particularly important for the post-closure phase since the staff responsible at that time may not be familiar with the earlier planning, design and construction decisions that were made because institutional knowledge frequently disappears with the departure of operational mine personnel. The GISTM (Global Tailings Review 2020) also stresses the need for such a knowledge base to support safe tailings management throughout the TSF lifecycle, including closure. Data related to ARD potential that should be retained are described in Section 9.4.3.

Based on the ICMM (2019a) guidance, a knowledge base, in the form of a virtual and/or physical repository, should include the relevant physical, environmental, social / socioeconomic and regulatory information. ICMM also recommends that a knowledge base gap analysis be undertaken at regular intervals throughout the mine life to identify further information, studies, research, or field trials that may be required. This process may be informed by periodic risk assessments. Development and maintenance of a reliable knowledge base is particularly important for sites with ARD potential, where the availability of continually updated information allows continuous improvement of the understanding of ARD generation as well as prevention/control/mitigation measures. Such information derives from the mining model, which should reflect the geochemical properties of the ore and waste rock, as well as from ongoing laboratory and field scale test work, site water quality monitoring, observational data, and refinements to the geo-environmental waste domains. This information is critical to updating Closure Plans during the operational phase and interpreting conditions observed during the post-closure phase. More details are provided in Section 9.2.8.

11.2.7         Closure Planning Tools

Section 6.7 of the GARD Guide discusses the selection and evaluation of alternatives for the prevention, control and mitigation of ARD. Details are provided on the various technical alternatives that can be considered and the need for an evaluation of cost is stressed. This section follows up with a methodology, referred to as Multiple Accounts Analysis (MAA; also known as a multi-criteria assessment) that can be used to perform comparative evaluations of a range of closure alternatives. It is important to note that there are considerations beyond cost that affect the selection of the most suitable closure alternatives, as discussed further in this section. 

Section 9.2.7 discusses the approach to risk assessment, management, and contingency plans. It identifies Failure Modes Effects Analysis (FMEA) as being best suited to engineering designs and the use of an Environmental Risk Assessment (ERA) to evaluate environmental effects more directly. The development of source-pathway-receptor conceptual models allow evaluation of potential ARD impacts under a range of scenarios. Social effects resulting from ARD and its management may be include in FMEAs/ERAs as well. These general concepts and approaches are further elaborated in this section, which describes procedures for conducting these assessments. An ERA is sometimes combined with a Human Health Risk Assessment (HHRA), used to support broader based closure planning. When combined, these two risk assessments are referred to as an HHERA.

This section discusses tools that are most commonly used in mine closure planning and design, and provides guidance on how to perform the evaluations described in Chapter 9. However, these are not the only tools used and others, such as general risk assessments and cost-benefit analyses, are also routinely applied during closure planning. Useful guidance is provided in ICMM’s Integrated Mine Closure: Good Practice Guide (ICMM 2019a). This key tool has seen development, review and acceptance by industry, academic, and other stakeholders.

11.2.7.1  Multiple Accounts Analysis

The identification and analysis of closure alternatives is fundamental to mine closure planning. A formal assessment process provides a basis for demonstrating that the most appropriate mine closure approaches have been selected, considering a range of factors that influence their selection. Furthermore, it can help remove inherent biases of the team undertaking the mine closure planning and design, support the engagement process, demonstrate to internal and external stakeholders that all alternatives have been considered, and provide the rationale for the preferred alternative. The methodology discussed in this Guide is referred to as the Multiple Accounts Analysis (MAA) process, which is widely used and accepted in current practice.

A formal alternatives analysis should be used to select the preferred alternative that, on balance, best meets the site conditions, the closure vision, and the objectives of the mine operator and the various other stakeholders involved. The formal identification and analysis of alternatives should be used to identify different approaches to closing each mining facility, such as TSF, open pits, underground mine voids, waste rock piles, and spent heap leach piles. In addition to evaluation of closure approaches for physical domains within the mine, MAAs may also be used to evaluate specific technical choices, such as between water treatment alternatives or cover designs. These analyses are typically conducted during the initial closure planning and also when significant changes to the Closure Plan are needed.

The MAA process is a tool to support decision-making, but it should not be interpreted as a tool that makes decisions. A clearly documented process of alternatives identification and analysis also facilitates opportunities for the participation of governments, communities, Indigenous Peoples and independent review boards in the alternatives evaluation and selection process.

The process does require numerical scoring and develops total scores for the various alternatives considered. While it does result in a ranking of the alternatives, this tool should not be the only factor in selecting a closure option. Other factors, for example, the company’s need to adopt a low risk profile in the future, relinquish the mine site to another entity after closure, adjust the closure activities to allow for longer-term phased implementation to match the company’s cash flow, or address urgent concerns by stakeholders, should also be considered. Such factors can also be included as accounts or sub-accounts in the scoring system.

Further detail on the MAA process is available in Appendix 11A.

11.2.7.2  Failure Modes and Effects Analysis

The role of risk assessment in establishing an ARD management plan is discussed in Section 9.2.7. The purpose of a risk assessment is to not only provide a logical and comprehensive basis for decision making, but also to provide transparency, inform decision makers, and develop input for priority setting. In the context of an FMEA, “risk” is defined as a function of the likelihood and consequence a failure occurring. FMEA may assist in determining what mitigation measures to incorporate in any Closure Plan or designs and also outlines a six-step risk management procedure for a mine site. These analyses are typically conducted during the closure planning and design preparations and also on a completed mine closure scenario.

This section provides guidance on performing a FMEA for mines with an ARD potential and incorporates approaches contained in the ICMM Integrated Mine Closure Good Practice Guide (2019a). Further information on FMEAs for closure is provided in Appendix 11A.

The FMEA typically focuses on potential structural and geochemical failures of mine facilities that result in significant and wide-ranging consequences in areas adjacent to the failed structure. For closure, it also deals with evaluating these structures over periods from decades to centuries. An FMEA generally considers a broad range of consequences including, for example, schedule, financial, safety, environmental, legal and regulatory, social/communities, and company reputation.

An FMEA is one of the key tools used in evaluating closure design alternatives, and in improving selected closure designs to increase their geotechnical and environmental robustness and resilience over the long term.

While risk assessments are also performed for the operational phases of mine facilities, additional analyses for the facilities in their closure configuration are generally performed in recognition of the different types of risks that could occur. Many of the differences are related to the fact that the post-closure period is typically much longer than the operational period, making long-term durability of a facility more critical, in particular when a long-term ARD potential has been identified. The longer period also increases the likelihood of occurrence of identified risks (for example, relatively speaking, a 1 in 200-year flood is unlikely to occur in a 10-year operational period, and very likely to occur in a 1,000-year period post-closure).

As shown in Figure 11-4, FMEAs can be used effectively not only in the initial planning stages of a closure project, but also in advancing designs, during implementation, and for the post-closure phase.

Figure 11-4: FMEAs at Different Stages of Closure Planning

Properly applied, an FMEA can provide information on the types and severity or failures that could occur during the post-closure period. Risks are typically categorized as either Low, Medium, Significant, or Extreme, with each category requiring a specific risk mitigation approach. Closure design robustness can be increased by taking a more conservative approach in interpreting the prescribed risk mitigation approaches. Examples for each of the risk categories are as follows:

§  Low risk category: While low risks generally do not require mitigation, consider mitigating those that might have significant consequences, particularly in the long term. Provide for ongoing monitoring of key parameters for a period of time that would inform whether the risk in this category is increasing over time and potentially require mitigation. In the case of ARD, key monitoring parameters typically include pH, conductivity, sulphate, and select trace metals.

§  Medium risk: While some risks can require monitoring to establish whether future mitigation may become necessary, consider mitigating medium risks prior to and/or during closure to minimize reliance on monitoring to trigger the potential need for mitigation measures.

§  Significant risk: Mitigation of these risks can include engineering measures installed prior to and during closure, contingency measures that can be installed at some time in the future should they become necessary, and actions required in the Emergency Response Plans (ERPs) to reduce the likelihood and consequences of potential failures. To demonstrate that the mining company has undertaken all reasonable measures to mitigate these risks, consider applying the As Low as Reasonably Achievable (ALARP) approach.  This approach provides for a balance between the scope of the mitigation measure and associated risk reduction and the effort required for its implementation while accounting for the added risks and social and environmental impacts incurred during closure and the post-closure period. The ALARP provides a scientific basis for establishing the appropriate amount of engineering resilience and redundancy that needs to be incorporated in the closure design. In the case of ARD, it needs to be understood that the greatest risks may not materialize until well into the post-closure period, requiring a solid scientific basis for the prediction of the onset of ARD generation.

§  Extreme risk: These are generally considered to be unacceptable and will require engineering measures or design changes to reduce likelihood and/or consequences. Controls on an extreme risk may require separate analysis, to determine their risk of failure, and confirmation that risk will be reduced to an acceptable level.

11.2.7.3  Human Health and Ecological Risk Assessment (HHERA)

A Human Health and Ecological Risk Assessment (HHERA) provides a scientifically defensible tool to establish whether a closed or legacy mine site can be safely used by the most sensitive human and ecological receptors likely to occupy it. An HHERA involves a staged, formal, and reproducible process that incorporates procedures accepted by the regulatory authorities in the jurisdiction within which the study is being undertaken. HHERAs can also be conducted during closure planning as necessary to confirm the proposed closure of the site will not pose unacceptable long-term health risks to the projected future human and biological receptors. In addition, the assessment can be performed on legacy sites to inform decision-making. The results of HHERAs are used to help assess the adequacy of a Closure Plan and, hence, what additional engineering or other measures may be required to reduce risks, including those related to ARD.

Procedures for assessing the HHERA are discussed in several references by Health Canada (2010a and 2010b), the CCME (1995, 1996) and the Federal Contaminated Sites Action Plan (Environment Canada 2012). The steps generally include the following:

§  Site Characterization: Describes the main features of the site and provides a summary of the most pertinent information from surveys of surface water and groundwater quality, sediment quality and soil. These data are used in the subsequent assessment. Similarly, concentration levels measured in fish, aquatic vegetation, and benthic invertebrates in the study area are summarized. These data are used as inputs to the HHERA. It is important to document any geological, mineralogical, or geochemical conditions that can result or have resulted in ARD being generated naturally as well as any incremental ARD impacts attributed to the mining, processing, and waste disposal activities.

§  Identification of Constituents of Potential Concern (COPCs): These are those constituents whose concentrations exceed background or pre-mining baseline values and/or regulatory guidelines. In the case of ARD, these parameters typically include pH, sulphate, and trace metals/metalloids.

§  Problem Formulation and Receptor Characterization: Identifies the aquatic and terrestrial species selected for inclusion in the risk assessment as well as the human receptors who may spend time in the study area. Pathways to be considered are identified as well during this step.

§  Exposure Assessment: Provides the assumptions that have gone into the exposure assessment that was used to predict the fate of COPC in the environment, including their uptake by human and ecological receptors. It is important to separate exposures due to any naturally occurring ARD from those due to the mine operation.

§  Toxicity Assessment: Details the toxicity reference values used in the assessment to characterize the risks of potential effects from COPCs on the health of ecological species and humans.

§  Risk Characterization: Presents the results of the exposure assessment and the risk assessment for ecological species and humans. It is important to separately characterize risks associated with naturally occurring ARD from those caused by the mine operation, since the closure planning should focus on the incremental risks caused by mining. However, the extent to which a Closure Plan can be adjusted to also address some or all of the naturally occurring ARD, if practical, should also be considered, particularly if this maximizes achieving closure options that are more amenable to long-term sustainable development.

The results of the HHERA are used to characterize and identify specific human health and/or environmental risks that need to be addressed in the Closure Plan. HHERAs are particularly useful as a basis for the closure planning for legacy sites, as discussed in Section 11.2.11.

Formal documentation of the results of the HHERA is important, both to facilitate a third-party review and to support the closure planning process, including stakeholder engagement.

11.2.8         Integration of Technical Disciplines

As for all stages of project and operational design, planning for mine closure is inherently multidisciplinary. Similar to the development of an ARD management plan, discussed in Section 9.2.3, the integration of a number of technical disciplines will be required, such as those listed in Table 9-2. This includes disciplines related to real-time and short-term planning, mine geology, drilling and blasting, etc., that inform and execute mine development consistent with ARD management goals. For instance, how will benches and blast patterns be planned and executed to identify and help mitigate ARD risks? How will haul fleets be instructed on where to haul material and what is the reconciliation process to ensure proper delivery of waste rock? How will waste rock dump designs be modified based on the predicted and actual geochemical characteristics of the waste rock encountered during mining?

The integration of multidisciplinary teams can be thought of as having both a “vertical” and “horizontal” component when planning for closure. The “vertical” component is the integration at any one time of various teams of technical specialists working on the closure studies and designs. Concerted effort is required to ensure that specialists working on different aspects of closure, or addressing different physical domains of the site, are in communication and that disconnects do not develop between design components.

Some examples that illustrate the importance of vertical integration include:

§  The use of consistent assumptions for various aspects of the closure design (such as climate databases used for surface water designs, cover designs, pit lake water quality predictions and tailings facility spillways).

§  The use of connections (e.g., assumptions and data transfers) between models that are logically consistent where multiple models are used to support closure designs.

§  The use of data for water quality predictions that are consistent with the geochemical characterization works, site water balance and the surface water designs.

There are several design tools that can help bridge and unite the various disciplines working on the Closure Plans, including the development of an over-arching design basis memorandum (DBM), use of site-wide water balances and water quality models, and development of a site-wide material balance for all geotechnical materials to be used or generated in the course of closure works.

The “horizontal” component of Figure 11-5 refers to the integration of closure-related disciplines over the duration of closure planning. Unlike most engineering projects, the period from conceptual design to detailed design and implementation can stretch over many years or even decades. During this time, the type and timing of specialists involved in the closure design can be expected to evolve, with some specialists being involved almost continuously in updates to the Closure Plan over the mine life, with others becoming much more involved in the years immediately prior to implementation. In addition to the challenges of vertical integration, this horizontal integration requires robust information management, and the ability to leverage long-term institutional knowledge. As teams can be expected to evolve over time, it is important to identify and strengthen points of continuity. The DBM can be a useful tool to document assumptions, and clear documentation of decision-making processes such as MAAs will be necessary to minimize re-work.

Lastly, it is critical that, in addition to all technical disciplines, frequently represented by internal and external subject matter experts, all relevant functions at the mine operation are involved in closure planning and execution.  This includes, but is not limited to, staff responsible for geology, short-term planning, mining, processing, tailings management, waste rock management, water management, environmental compliance, social, legal, and financial activities. This is required to ensure the scope, development, and implementation of closure activities will meet the desired closure objectives and are consistent with the mine plan and corporate business plan. All closure planning should be conducted from a holistic perspective.

Figure 11-5: Integration of Technical Disciplines over Time

11.2.9         Drainage Treatment

Despite the best efforts to prevent ARD, some sites will require treatment of ARD. When this treatment is required for years or decades after the completion of other site closure works, it can be one of the most significant post-closure costs, resulting in a persistent liability for the mine owner. It is one of the most common technical issues that can impede or completely prevent full eventual relinquishment. Chapter 7 provides a detailed description of the available treatment approaches for ARD, highlighting active, passive, and in situ treatment technologies, with issues to be considered in the context of mine closure and post-closure highlighted in Section 7.8.  While the drivers for closure at each site will be different, expectations typically are to avoid treatment and the associated ongoing liabilities, if at all feasible. Where treatment cannot be avoided by implementation of source control or other measures, preference is usually given to reducing the volume of impacted water and passive or in situ treatment approaches, with a desire to minimize ongoing maintenance requirements.

Decision-making for water treatment in closure planning is often heavily influenced by the widespread use of cost discounting, and the evaluation of alternatives on an NPV basis (See ICMM (2019a) for a detailed discussion of NPV considerations in closure planning). In this approach, cost discounting is used to bring future costs to a present value, which can then be considered in options comparisons. While these types of calculations are valid and necessary for the assessment of engineering economics, they provide a framework in which future costs (such as for treatment over hundreds of years or even perpetuity) can appear trivial when compared to the present-day costs of prevention or mitigation measures. Net present value calculations can, therefore, affect closure planning decisions throughout the mine life, making it more challenging to justify current actions that will prevent future costs. One way to counterbalance the effects of NPV considerations on closure decisions is to also consider risk.

Due to the global history of environmental liabilities left behind with abandoned mine sites, regulators and the public have placed increased attention to mine closure issues in many jurisdictions and are increasingly involved in making or approving closure decisions. Given the history of mining company bankruptcies and abandoned sites, the public is less likely to be accepting of approaches to closure that hinge on the liquidity and presence of the mining company in the long term. Some of these concerns may be ameliorated through the use of separate sustaining funds or trusts for long-term maintenance needs.

11.2.10      Adapting to Climate Change

It is well-established that climate change considerations need to be factored into all aspects of mine planning, with particular importance in planning for closure (ICMM 2019b). Past practice in mine closure planning, including related to ARD management, assumed a stable climate. Practice has since evolved, and regulatory, stakeholder, corporate and financial interests in mine operations increasingly require that the risks associated with climate change are considered in closure planning. In addition, professional responsibility requirements (such as professional practice standards for engineers) make consideration of climate change necessary. 

Climate change will generally bring increases in the frequency and intensity of extreme events such as flooding, hurricanes, and droughts, as well as increases in average temperatures (IPCC 2021). This increased variability and alteration of both precipitation and temperature will have direct impacts on ARD generation and management, such as increased frequency of wetting and drying, increased reactivity, increased precipitation requiring management and extreme events such as droughts or floods. As a result, climate change may require modifications to the way ARD is managed in the long term. A good example of such effects is in Arctic regions, where freezing of reactive mine waste is used to prevent ARD generation and the transport of any reaction products.

Climate change is particularly relevant in the context of regional water resources, which may be vulnerable to the effects of ARD, with a sensitivity exacerbated by the effects of climate change. This puts pressure on governments, regulators and operators to ensure that the effects of climate change are properly incorporated into the design, operation and closure of mining projects that have a potential to generate ARD. Risks associated with climate change can be broadly categorized as two types, as summarized in Table 11-1. Each risk type requires identification and may require context-specific measures or mitigations to address when planning for closure of mines with ARD issues. Preparing to manage these risks provides the Closure Plan with climate resiliency.

 

Table 11-1: Potential Climate Change Impacts on Closure Activities

	Acute Risks	Chronic Risks
Definition	Sudden impacts to cost by extreme events	Change or loss of functionality of closure works due to conditions being different than design
Example Events	hurricanes, bushfires, floods (i.e., extreme precipitation), drought	- increase in average temperatures - shifting precipitation regimes,
Example Scenarios	- geotechnical failures of waste containment facilities (exposing and potentially transporting PAG wastes) - destruction of water management structures (with impacts such as loss of control of water flow or clean water separation), - disruption of supply chains needed to bring reagents or power to a water treatment facility - fire damage to treatment facilities or vegetated covers	- increase in geochemical reaction rates, increase in frequency and duration of wetting and drying of stored PAG material. - inability to maintain water balance for wet covers - increased erosion of soil covers - drying/cracking of soil covers - erosion of water management systems, - loss of vegetation needed to maintain the water balance on covers - disruption of frozen conditions used to isolate wastes in cold climates.

 

Understanding the implications of climate change on specific mine closure options requires at least a general understanding of the projected change in climate for the region of the mine location. This allows an understanding of post-closure risks and opportunities that may result from climate change. Closer to closure, site-specific predictions should be refined to allow incorporation of altered temperature and precipitation regimes into numerical models. Some jurisdictions are introducing standard methodology for deriving site-specific climate predictions. The Mining Association of Canada protocol introduced in March 2021 (MAC 2021) provides a practical guide for incorporating science-based projections of future climate into closure design.

Climate change projections do not provide certainty about future conditions. They do, however, represent a prudent, scientifically based methodology to identify probable and possible future climate scenarios, which can then be used as input into closure design. These inputs may either serve as a design basis (i.e., design for a probable projected future climate), or as an input to risk assessments (evaluate the potential effect on the design of various future climate scenarios).

A key shortcoming of climate change projections is the difficulty in making defensible projections beyond a timeline of approximately 100 years into the future. This limitation is relevant when considering the closure design of facilities that will need to perform adequately over a much longer time frame, such as when the ARD generating capacity of a waste deposit is projected to last for many hundreds of years into the future. Current practice is to evaluate climate change out to the furthest defensible scenario and assume that this scenario represents a future steady state, or that future conditions will continue to be predicted and risks/impacts re-assessed over the duration of the post-closure period.

Where long-term monitoring and/or treatment of ARD post-closure is required, periodic and systematic checking or re-assessment of the modelled climate predictions against the climate change trajectory can be implemented. This re-assessment can be used to confirm that the current ARD management strategy is sufficient or whether modifications are required. To support this approach, specific triggers or thresholds for further action can be developed by comparing monitoring data to predicted climate scenarios. For example, these triggers may be related to ongoing meteorological monitoring, thermal monitoring in waste facilities, runoff quantity monitoring, or pit lake water levels. This adaptive management approach, coupled with ongoing monitoring and re-assessment, will allow long-term flexibility to reduce risks posed by climate change to critical post-closure infrastructure or landforms.

While the greenhouse gas emissions associated with implementing mine closure can be demonstrated to be trivial compared to global emissions, mine operators can expect that they will experience regulatory and public expectations to consider carbon footprint in the selection of closure options, particularly when closure options require the operation of energy intensive infrastructure in the long term, such as a water treatment plant. It is relatively straightforward to project the energy needs for closure measures (including earthworks), and to use those projections to either compare options, or provide a comparison of the emissions of a closed/closing site to an operating mine. In undertaking this carbon accounting, there may also be the opportunity to account for carbon capture through direct uptake by mine wastes and/or revegetation. These projections can also be used to identify the scale of appropriate off-sets, if necessary.

11.2.11      Closure of Legacy Sites

While the ideal is to start planning for closure at the mine design stage, the reality is mining companies and governments need to address ARD issues at sites that have been abandoned or closed in a way that does not meet modern environmental and social standards. Thousands of abandoned and legacy mine sites exist around the world, and many of them have ARD issues.

While there are many similarities between addressing ARD issues at the closure of operating sites and legacy sites, there are two fundamental differences:

§  Less flexibility: Many ARD issues develop at the time of waste placement. At legacy sites, all waste management has been completed. All closure or remediation decisions must, therefore, be taken in the context of a site with fixed parameters in terms of the disposition of the mine waste.

§  Less information: Abandoned and legacy sites typically have less information available. There are often gaps in the knowledge of how the site was operated, locations where waste was deposited, and the design/construction details of waste management facilities (including dams), as well as deficiencies in the geochemical characterization of mine wastes and baseline environmental data.

While the approach to closure for legacy sites generally follows the path outlined in this chapter, the constraints and limitations will typically add steps to the process or change the importance of certain steps. The site evaluation often needs to extend beyond the actual site limits to include assessment of land use and the environment surrounding the mine site. The local context may have changed substantially since mining ceased and closure measures, if any, were implemented. The proximity of any human habitation and important infrastructure such as roads, railways and pipelines should be assessed since human development may have encroached on the mine site. With respect to ARD, geochemical characterization of the mine waste is usually needed to address knowledge gaps, assess risks, and determine the extent of any ARD issues or potential.

The general approach for evaluation of an abandoned or legacy site would typically include the following steps as necessary:

§  Assemble available site mining history and documentation, particularly the designs, as-built plans, Closure Plans and designs if any, and site climate, geologic, soils, geotechnical, hydrology and hydrogeologic data, results of any geochemical testing and any ground- and surface water monitoring data.

§  In the absence of sufficient site-specific information, assemble relevant regional and/or global information from analogue operating and/or closed sites.

§  Site inspections, including performing Dam Safety Reviews for any dams that are present.

§  Field data collection and laboratory testing as required to fill any data gaps identified and required for the steps below.

§  Conduct risk assessments using appropriate methodologies to assess risks to human health, the environment, and structural integrity of mine waste facilities (such as FMEAs and HHERAs).

§  Assess the hazard classification (as per GISTM, CDA, or the local jurisdiction) for any tailings embankment and water dams that may be present.

§  Consult with the regulators and any potentially impacted local stakeholders, including Indigenous communities, on their expectations, requirements, uses and concerns related to the legacy site.

§  Assess the adequacy of the current closure conditions, including the extent of any identified risks and compliance with current design standards.

§  As necessary, revise or establish a closure vision, principles, and objectives for the site.

§  As necessary, establish site remediation plans which address any unacceptable failure modes and unacceptable risks to human health and the environment.

It is also commonly necessary to assess the extent to which existing facilities meet regulatory and/or leading practice design criteria and standards for closure (ICOLD, GISTM, CDA, ANCOLD, etc.). While current design criteria and standards should be considered in developing the remediation plans and designs, it may not always be necessary or possible to implement remedial measures to achieve those criteria and standards.

The FMEA provides a useful tool to determine the extent of remediation required. The first step is to conduct sufficient data collection and/or field investigations to assess both the geotechnical (e.g., slope stability) and geochemical (extent of ARD and its migration potential) stability, and to determine the design criteria that the existing facilities actually meet. Those findings are then used to calculate the likelihood of failure when performing the FMEA.

The risks that are characterized using the above approach can then be compared to the risk profile of the facility had it been designed to current standards. This risk profile becomes the target standard which is used to guide the determination of the remedial measures needed. Implementation of remedial measures that result in a reduced, acceptable risk of failure may be feasible. The lower risk categorization for the remediated facility can be achieved either by retrofitting to the current day criterion, thus reducing the likelihood of failure, and/or reducing the consequence by, for example, relocating habitations from the surface of the waste storage facility and preventing future access.

Where it is impracticable to achieve the risk profile of a facility designed to current day standards, the ALARP approach can be used to establish measures that reduce risks to the extent practicable as illustrated in Section 11.2.7.2.

11.3  Implementing Closure

The timely implementation of closure activities is particularly important where these works will be carried out to control ARD. This section discusses the timing of this implementation and the benefits for ARD management. There are two periods when closure activities are undertaken to prepare the site for its post-closure land use:

§  During operations, usually defined as progressive (or concurrent) closure.

§  Immediately following the cessation of operations at the end of mine life.

The types of activities and the pros and cons for undertaking closure activities during each of these time frames are discussed in Sections 11.3.1 and 11.3.2, respectively. In both cases, it is assumed that mine closure is being conducted according to a planned schedule. However, in some circumstances, unexpected temporary (care and maintenance) or sudden closure is required, in which case there may not have been time to implement progressive closure activities. This specific situation is discussed in Section 11.3.3.

 

11.3.1         ARD Management through Progressive Closure Works

Many of the reasons presented in favour of undertaking progressive closure are even more pertinent when considering sites where the risk of ARD is present. These reasons are discussed in detail in the mine closure guidance listed in Section 11.5.6 and are summarised below.

When considering facilities with the potential to generate ARD, the objective of progressive closure is to carry out activities that prevent or minimize the geochemical reactions leading to ARD formation. Undertaking these activities during operations can have significant benefits in addressing ARD generation when compared to waiting until the site enters closure, particularly if the mine life is long.

Progressive closure works can:

§  Inhibit or prevent the geochemical processes that lead to ARD, thus resulting in long-term reduction of ARD generation, limiting post-closure impacts and long-term liabilities.

§  Be used to test the effectiveness of closure activities, in particular ARD management measures, validate modelling, and establish success criteria.

§  Be used to test the appropriateness of success criteria.

§  Build trust with stakeholders and regulators, particularly relating to their confidence in the mine operator’s ability to manage and mitigate potential ARD issues.

§  Provide lessons from early reclamation efforts, allowing incorporation into, and refinement of, plans for later progressive closure and final closure.

§  Allow for participation of local communities, for instance in the implementation of progressive closure measures (e.g., revegetation) and/or the monitoring of their effectiveness (e.g., biodiversity).

§  Provide an understanding of costs for progressive closure, which can help in the refinement of closure cost estimation, thus reducing the associated uncertainty.

§  Provide an increased understanding of potential post-closure liabilities, including those associated with monitoring and maintenance.

In some jurisdictions, there may also be a reduction of the security or bond held by the regulator once progressive closure efforts have been undertaken and have been demonstrated to be successful.

Progressive closure is not always a priority during the operational stage of a mine. For instance, it may be perceived that there is a competition for limited financial and physical resources. The return on investment for progressive closure associated with ARD may not be quantifiable unless and until predictive modelling is sufficiently developed to clearly demonstrate the benefits of progressive closure action in mitigating a long-term ARD issue. However, it should be noted that economic return alone, particularly if NPV calculations are involved, does not represent a comprehensive business case and both the tangible and intangible benefits should also be considered, as well as risk reduction.

In addition to the requirement for operational resources, mine operations may be reluctant to undertake progressive closure due to uncertainty in the mine plan. A low-grade ore region, currently uneconomic to mine but that may be feasible in the future if ore prices increase, may be made significantly more expensive to access if progressive closure works have been undertaken, or may require undoing the closure works. For example, there could be a progressive closure benefit to early flooding of an open pit, but this could be at odds with the potential to develop an underground mine at the same pit in the future. These types of conflicts demonstrate the importance of incorporating closure planning into mine planning (and mine planning into closure planning). Where sterilization of resources is a concern, it may still be possible to look for an alternative or a temporary option that can assist in ARD mitigation, without creating costly barriers to possible future mining opportunities.  Deliberate mine planning and careful sequencing to enable progressive closure creates opportunities to manage ARD and mitigate the long-term risks.

The benefits of progressive closure are of particular relevance when associated with the management of ARD risks through source control. For example, by planning to:

§  Avoid reactive material where feasible and minimize exposure and handling of potentially reactive material.

§  Strategically place potentially reactive material to allow for easier isolation and avoidance of contact water.

§  Minimize duration of dewatering and accelerate flooding of open pits or underground mines so that exposed reactive material is resubmerged as soon as possible.

§  Prioritize in-pit dumping or backfill opportunities for reactive mine waste.

§  Actively manage surface water to minimize contact with reactive material.

§  Strategically mine reactive material taking into account seasonal considerations to minimize contact with precipitation.

§  Strategically stockpile material for cover construction or armouring.

Progressive closure requires a degree of certainty around closure actions to be undertaken for a particular mine landform or facility. Hence having a clear understanding of closure options, including source control, available to mitigate ARD early in the life of the mine and advancing the options selection process is essential to being able to successfully implement progressive closure activities. The ARD management plan plays an important role in this regard as the essence of this plan revolves around managing reactive rock for closure.

11.3.2         End of Mine Life

During active closure, the primary goal of most site owners is to rehabilitate the site to sustain an agreed beneficial post-closure land use as quickly as practical, thereby reducing their legal and economic liability for a minimum financial expenditure. Implementation of closure at the end of mine life will entail execution of planned closure activities not already undertaken as progressive closure and the enhancement or correction of any progressive closure works that have been deemed to not meet success criteria.

By the conclusion of mine life, closure actions should have been selected for each mine component, likely using some of the tools identified in Section 11.2.7. Ideally, there is also a clear understanding of the processes contributing to ARD generation and that understanding has contributed to the selection of closure activities for each component.

Common closure activities at the end of mine life include:

§  Flooding of open pits and underground workings (either actively or passively after the cessation of dewatering activities) so that exposed PAG material is resubmerged as soon as possible.

§  Resloping/reshaping or other stabilizing activities (e.g., armouring) to achieve long-term geotechnically stable configurations and/or facilitate cover placement, with the objective to minimize potential re-exposure of PAG material.

§  Cover placement over mine wastes to limit contact water and/or ingress of oxygen, or provide substrate to support revegetation.

§  Reconfiguration of surface water management infrastructure to direct non-contact water away from reactive material.

§  Construction or modification of water treatment facilities.

It is important to assess the effects on any of these activities on water quality. For instance, flooding of reactive material that has been exposed for decades may result in a slug of very poor quality water requiring special management.

11.3.2.1  Closure Readiness

The degree to which closure planning is completed prior to implementation of closure measures is termed “closure readiness”. This not only comprises the selection and detailed design of individual closure activities but also the scheduling of these activities to allow for complete and efficient mine closure and an accurate estimate of costs associated with their implementation. Corporate governance (Section 11.4.5) may dictate the degree of closure readiness required for operating sites based on their anticipated remaining mine life. However, even at companies with clearly stated closure readiness goals, not all sites may have attained the needed degree of readiness. A lack of readiness for closure can have considerable financial cost implications for mine owners, including those expenditures required for periods of “care and maintenance” while closure designs and permitting are completed. Annual care and maintenance costs are often significant, and commonly underestimated.

ICMM (2020) provides tools to assess a site’s closure readiness and guidance as to the degree of planning warranted at various LoM stages.

By the time a mine reaches its planned end of life, all aspects of closure planning outlined in Section 11.3.1 should be complete with a view to efficient implementation of closure activities, subsequent post-closure monitoring and maintenance, and eventual relinquishment where possible. This approach will minimise the unknowns associated with the transition to closure and associated risks. With respect to ARD management, this approach can serve to minimise potential environmental impacts, costs associated with their mitigation or management, and associated financial liability and reputational risk.

11.3.2.2  Sequencing of Closure Works

Not all mine components will be able to be closed at the same time, with some requiring more resources and/or a longer duration of construction activity to reach a stage where closure of the component is considered complete. For example, infrastructure demolition and the disposal of non-mining wastes may be undertaken over a fairly short duration, however the covering of a tailings facility may require more construction time due to the large areas and significant material quantities involved. Physical processes may also require time to conclude, independent of construction effort. A common example is the consolidation of tailings prior to implementation and finalization of the facility closure. Depending on the tailings characteristics, the draindown processes required for development of a workable surface can take years to complete.

As a result, the sequencing of closure activities during implementation is an important consideration, particularly in relation to any activities that relate to transitioning the ARD management from an operational to a closure condition. Sequencing should be determined prior to implementation of closure measures to avoid unnecessary expense and environmental impact due to the delays in the installation of infrastructure required to prevent, minimise, or mitigate ARD. Detailed sequencing of closure activities may be documented in a Closure Execution Plan.

An example is the timing for the removal of temporary ARD management measures. Removal of a temporary water cover on a tailings facility to allow placement of a permanent, engineered cover may expose reactive material to oxidizing conditions. Another example is the temporary placement of reactive rock on the surface prior to underground backfill or backfill in an open pit. Mitigation or management of such short-term conditions and related risks should be part of the closure planning process.  

11.3.2.3  Construction Records and Quality Control/Quality Assurance

Construction records are normally required by the owner and are often required by regulators to verify adherence to the Closure Plan and approved closure designs. It is imperative to document closure activities as implemented so that the designs and any deviations are recorded and available for future use if required. These records often go hand in hand with quality assurance and quality control efforts undertaken during construction activities. Once collected, these records should be managed as part of the closure knowledge base.

These documents should include surveys undertaken during and post-construction, results of monitoring or inspections undertaken during construction, rationale for any design deviations, and recommendations for any monitoring or inspections required in addition to those already proposed during closure planning. Mine owners may also require reconciliation of estimated closure costs with actual closure costs to inform future estimates.

Mines with an ARD potential typically require long-term monitoring and maintenance, and the challenges of maintaining institutional knowledge over the long term are well-known. Planning for ongoing knowledge base management is crucial. This knowledge base ideally includes not only accurate construction records but also monitoring data and updates/calibration/validation of numerical models that may have been developed for predicting and managing ARD. If ARD mitigation measures do not perform as predicted, this information will be of use in a root cause investigation, diagnosis, and adaptive management of the ARD-related issues. If mitigation measures do perform as predicted, this information will provide institutional (and, ideally, industry-wide) knowledge that can be used to replicate this success at other sites.

11.3.2.4  Construction Issues

There are several common issues that may impact mine closure activities, reducing their overall efficiency and increasing costs. These issues include:

§  Poor weather (drought, flood, snow, extreme temperatures) – while some extreme events are difficult to predict and plan for, general consideration should be given to the impacts of adverse weather on the scheduling of closure activities. Where possible, buffers should be built into the schedule for activities where weather may affect implementation of closure measures.

§  Supply chain and procurement delays – closure readiness includes the understanding of any resources or materials that require long lead times to procure. This understanding will be obtained through the detailed design process and these items should be flagged with the procurement team well in advance. For ARD, this may include components for water treatment plants, chemical reagents, borrow material, seed or seedlings, and geosynthetic liners.

§  Need for additional infrastructure – closure activities may require the construction of additional infrastructure, such as access roads, staging areas, and power supply. These activities should be built into the schedule so they do not delay closure.

§  Human resource shortages – for mines where the operator is undertaking the majority of closure activities, there may be an exodus of staff as the mine nears or enters closure, and difficulty in hiring replacements due to the relatively short duration of the work. This can be planned for in advance with well-developed exit strategies and assisting employees with job placement when their services are no longer required.

§  Regulatory delays – regulators that are not aware of the full scope of closure works or disagree with success criteria may delay the granting of necessary permits while they gain a greater understanding of the activities and their long-term implications. This is most easily dealt with in advance through active and ongoing engagement with regulatory authorities so there are no surprises when the time comes for formal assessment and approval of final Closure Plans. Nonetheless, in some jurisdictions, particularly where assessment timeframes are not mandated, the inclusion of additional time in the schedule to allow for regulatory delays may be prudent.

§  Stakeholder expectations – stakeholder expectations may change and affect closure construction activities. For example, local communities may require a different post-mining land use of a mine waste facility, necessitating different construction features to address access and safety. In the case of ARD, additional construction measures may need to be put in place that prevent disturbance of the reactive material. Similarly, communities may request post-mining use of certain mine buildings, affecting demolition and requiring that the buildings remain functional.

When the potential for construction issues is acknowledged in advance, mitigation strategies can be built into the overall closure planning approach to reduce the risk posed by each.

11.3.3         ARD Issues in Temporary and Sudden Closure

Closure does not always occur when planned. Temporary or sudden permanent closure both present unique challenges for ARD management, as discussed below.

11.3.3.1  Temporary Closure

In the instance of temporary closure, the mine will be placed in a state of care and maintenance with a view to resuming mining activity at some point in the future, be it months or years. Depending on when temporary closure occurs in the life of the mine, there may be limited opportunity to implement progressive closure. Hence, flexibility is an important consideration in ARD mitigation and management.

Mitigation activities that may provide more permanent ARD management, such as allowing open pits to flood or the installation of engineered covers over reactive waste, may not be possible during temporary closure due to the expense and time required to reverse such activities when the mine becomes operational again. However, there may be temporary measures that can be implemented to reduce ARD generation, such as revegetation with a cover species that is quick and easy to establish to promote evapotranspiration or control erosion, use of temporary flooding in select areas, or creation of low-permeability surfaces by compaction with heavy equipment. Selection of such measures will ideally require an understanding of the likely duration of temporary closure (e.g., months or years) and consideration of the mine plan when the mine does resume operations.

Management of water during temporary closure is of key importance for sites with ARD potential. It is likely that many aspects of operational water management may be required to continue under temporary closure, particularly those relating to diverting non-contact water away from reactive material stockpiled on the surface or present in a pit wall. There may also be an ongoing requirement for water treatment, although potentially at a reduced volume if operational contact water is not being generated. As a result, ongoing operation and maintenance of water treatment infrastructure may be required.

In most jurisdictions, there will be an ongoing requirement for environmental monitoring to a similar level as that undertaken during operations. As such, temporary closure may present an opportunity to gather additional data while the site is in a relatively static condition. This information may allow the validation of water balance and geochemical models for the site, which will be useful tools in later mine and closure planning. It also provides an opportunity to demonstrate to local communities that even when the site is not generating revenue, care is still taken to maintain it in such a state as to not cause environmental harm.

Temporary closure is typically focussed on maintaining the mine in a holding pattern while awaiting operations to recommence. Funding may be limited during this time due to the lack of revenue being generated by the mine. Therefore, although temporary closure may present an opportunity to undertake progressive closure activities, experience suggests that this is a rare occurrence. If implemented, concurrent reclamation activities focussed on ARD management should be of high priority due to the long-term advantages provided by early mitigation.

11.3.3.2  Permanent Sudden Closure

Sudden permanent closure may occur during the operational life of the mine, often when the mine is not in a state of closure readiness. In such an instance, the site configuration is unlikely to be that of the planned end of mine life. For instance, waste rock dumps may not be at full height or tailings facilities may not be at full capacity. Closure planning and implementation may be in different stages depending on the operation in question, ranging from planning that is in its infancy, when closure activities for some or all mine components have yet to be selected, to significant progressive closure. Sudden closure leads to the inevitable acceleration of the closure planning process. Until such a time as the final Closure Plan is ready to be implemented, the site will remain in a state of temporary closure with associated care and maintenance activities being undertaken.

This accelerated closure planning is typically undertaken by the company that owns the mine. In the case of a bankruptcy, planning will likely be a government-led process, with delays introduced by both the receivership process and bureaucratic considerations. Under any ownership scenario it is likely that funds will be limited for the planning and implementation of closure activities. As a consequence, it is possible that the site may well face issues similar to those of legacy sites (Section 11.2.11).

Accelerated closure planning should not mean that key aspects of good practice are ignored, such as community engagement processes. A sudden mine closure will impact the community in multiple ways and concern regarding ongoing, post-closure management of the site may be heightened, particularly where there is a risk of ARD. While stakeholder interaction may extend the duration of closure planning, community engagement is an important step for long-term acceptance and is often a regulatory requirement.

The limitation to the pace and effectiveness at which a Closure Plan can be developed and implemented for a mine experiencing sudden permanent closure may be the regulatory process and this should be taken into consideration when addressing permanent sudden closure. Regularly engaging with regulators and keeping them informed of mine Closure Plans, either formally or informally, can often smooth the path through the regulatory process and make sure there are no surprises on the journey to permitting mine closure activities during a sudden closure. This is particularly true when there is a risk of long-term environmental impacts related to ARD. Having a well-developed Closure Plan that accounts for sudden permanent mine closure and associated actions related to ARD mitigation is a significant asset in the case of such an event.

Some mines may require urgent closure works to be undertaken ahead of the closure planning process and permitting timeline. These works are usually identified and fast-tracked due to the need to prevent extreme environmental or safety impacts, such as the sudden and severe onset of ARD or ground instability. Urgent works are most often needed to mitigate sites where there has been a lack of understanding of the relevant geochemical/geotechnical characteristics of the mined materials, resulting in inadequate operational practices and/or designs for closure, leading to geochemical or geotechnical issues that require immediate attention.

 

 

11.4  Durability through the Post-Closure Period

The success of a mine closure is determined in the post-closure period, in the years to decades after completing the closure works. For mines with potential ARD issues, this is also the time frame over which these issues may become apparent.

In the planning process, goals for sustainable development will have been set. At the very highest level of durable mine closure planning, closure goals are set for the post-closure nature of the site, usually encompassing post-closure land use and socioeconomic and environmental targets for the site as applicable. As discussed in Section 11.2.2, the success of closure implementation needs to be understood in the context of the pre-defined closure objectives or success criteria.

In the case of ARD, where acid generation and its impacts may take years or decades to become evident, defining an appropriate temporal component of these success criteria is even more critical. Success criteria, particularly related to water quality, may be in place for decades and ongoing monitoring is likely to be required. In this situation, understanding whether the site is on a trajectory toward meeting the closure objectives is extremely valuable and allows for the adjustment of mitigation measures or monitoring as necessary. Doing so clears the path for future relinquishment by setting a clear vision of what environmental standard(s) and performance the site is expected to meet.

This section of the chapter addresses post-closure issues as they relate to durability of a mine closure, both in terms of carrying out the closure works in a way that will be long-lasting, and in terms of the agreed post-closure land use after the completion of closure works.

11.4.1         Monitoring and Maintenance

This section describes the general objectives of and approaches to post-closure monitoring and maintenance.

11.4.1.1  Monitoring

Post-closure monitoring aims to fulfill two main purposes:

1.     Determine if success criteria have been achieved and/or if the site is on a trajectory to achieve them.

2.     Identify the need for any maintenance or remedial activities.

Monitoring is usually tied to a wide range of physical, chemical, social, and environmental considerations. While the post-closure monitoring needs will always be site specific, typical requirements for post-closure monitoring include parameters related to physical stability, water quality, air quality, vegetation establishment (or re-establishment), biodiversity indices (depending on the post-closure land use and criteria), and a wide range of socio-economic indicators (depending on the proximity and influence of closure on local and regional communities). Some of these parameters may be monitored for a relatively short period of time, until it can be demonstrated that closure success criteria have been met and are durable, or that the parameters are on a trajectory towards meeting the success criteria. In other cases, longer-term monitoring may be required. This would be typical at a site where there is ongoing active treatment of water, where monitoring of influent, effluent, and receiving water quality (at a minimum) can be expected for at least as long as the treatment facility is operating. Longer-term monitoring is frequently associated with the presence of ARD-generating materials.  Water quality parameters diagnostic of ARD generation and typically included in such monitoring programs include pH, conductivity, sulphate, and trace metals/metalloids.  Some of these parameters (e.g., pH, conductivity) are amenable to automated monitoring.

Monitoring plans for sites with ARD potential should incorporate considerations discussed in Chapter 8. In the context of mine closure, thought should also be given to the following aspects during closure planning:

§  Will the presence of personnel on site be permanent or temporary?

§  If the presence of site personnel is temporary, how frequently will staff visit the site to conduct the various types of monitoring?

§  What will be the duration of the monitoring, and can the monitoring frequency be reduced at some point? Note, that this will vary by monitoring type.

§  How will the site and monitoring locations be accessed safely post-closure?

§  Will there be a requirement for specialised monitoring equipment?

§  Will this equipment be stored on site, or brought to site with personnel?

§  How will any samples be transported for analysis and to what laboratory (certain regulatory accreditations may be required while quality assurance/quality control may be an issue in certain regions)?

§  Is there any capacity for remote monitoring (e.g., drones, remote cameras, data loggers, satellite imagery)? This may reduce the frequency and related risks of in-person monitoring activities.

The answers to these questions may vary between mine components. It is worth viewing the various monitoring requirements within the overall monitoring program as a whole to understand if there are any synergies that can be obtained, such as minimising number of site visits by synchronising the timing of the various programs or training personal to fulfill multiple roles.

Post-closure monitoring may present an excellent opportunity to involve local communities through training them to undertake and/or manage certain aspects of the monitoring program. This allows local stakeholders an opportunity to feel greater responsibility and ownership of the closed site, rather than observing the site transition as an outsider.

Trajectory to Closure

For closed sites with ARD potential, it may take decades to consistently demonstrate closure criteria have been achieved and develop an understanding of the long-term trends that show the site is on a trajectory toward successful closure (or alternatively that further works may be required). Hence, post-closure monitoring data should not be viewed in isolation, but periodic review of all available information should be undertaken to allow for an assessment of trends that may not be obvious with datasets from a shorter timeframe.

Chapter 9 provides an overview of performance assessment, and particularly long-term considerations (Section 9.4). These long-term considerations are particularly relevant for providing answers to a typical closure planning question: how long do we need to monitor for? Being able to answer this question in a realistic manner is critical for estimating the duration of long-term site liability, and for providing adequate financial provisions for the long-term monitoring and maintenance, as required.

In addition to the considerations discussed in Chapter 9.4, closure planners also make use of the trajectory model.  Figure 11-6 (adapted from Grant 2006) illustrates the concept. This figure shows the progression of the concentrations of a water quality parameter over time.  In schematic form, the values leading up to closure represent the concentrations that have been measured during operations. The values shown in the dashed line after closure represent the projected trajectory leading to the eventual achievement of the closure objective, often an applicable water quality criterion, which may or may not be equivalent to background or baseline conditions.

 

Figure 11-6: Post-closure water quality trajectory (adapted from Grant 2006)

One approach to establishing this trajectory is to continue monitoring until it can be demonstrated that the threshold value has been achieved.  However, if the anticipated timeframe is extended (e.g., 100 years or more), an alternative approach may be to monitor for a sufficient period of time that the water quality models being used and their predictions are confirmed to be sufficiently accurate such that there is enough confidence in the remaining portion of the trajectory to terminate monitoring or reduce its frequency.

The suitability of a trajectory approach would need to be evaluated on a site-specific basis, taking into consideration the uncertainties in all inputs to the water quality projections.

Adaptive Management and Trigger Criteria

To maintain the site on a path to relinquishment, trigger criteria may be developed along with corresponding actions. Trigger criteria essentially serve as guard rails to the preferred trajectory, prompting action before significant impacts or risks develop and providing an opportunity for early mitigation or course correction. Actions related to ARD generation may include use of additional monitoring points, an increased frequency of monitoring or inclusion of additional water quality parameters, laboratory or field investigations, or modelling (geochemical, water balance, etc.) to gain a better understanding of the potential issue.

If an issue is identified, then appropriate remedial actions can be developed and implemented. This is often referred to as adaptive management and is suitable for implementation during closure. Adaptive management is an iterative process which allows for the evolution of management and monitoring as the site evolves during post-closure by establishing a feedback loop back to site management as additional site understanding is gained and hypotheses are tested. Adaptive management may be a particularly useful tool for addressing long-term processes such as ARD generation and climate change. In the case of climate change, where there may be a range of projected outcomes, adaptive management allows flexibility to amend monitoring protocols and implement those mitigative actions that will best address changes as they occur.

The list of contingency actions developed during closure planning, including defined trigger points for implementation, is typically referred to as a Trigger Action Response Plan (TARP). TARPs are commonly used in the mining industry. Development of a TARP allows for all interested parties to be familiar with, or engaged in, developing the actions that may be triggered. They can serve to increase the efficiency associated with implementation of responses or contingency actions, which may be particularly valuable where issues are time sensitive. The TARP may be prepared in support of an Adaptive Management Plan or may be prepared separately. TARPs need to be assessed and defined strategically as it is impractical to develop TARPs for every conceivable situation.

11.4.1.2  Maintenance

Post-closure monitoring may also be used to indicate the need for maintenance to be conducted on the site. For example, erosion of a cover with a geosynthetic liner may be observed during water quality monitoring and thus maintenance may be scheduled to repair the cover prior to exposure and subsequent degradation of the liner. Sites that are well maintained post-closure are typically able to withstand extreme events better than poorly maintained sites. All monitoring activities should be leveraged to identify maintenance needs.

The requirement of longer-term monitoring and maintenance of a site may necessitate the construction or refurbishment of facilities needed to facilitate post-closure maintenance and monitoring. Such facilities will reduce the requirement to transport resources to and from site for routine activities, which may be particularly beneficial for locations that are remote and/or difficult to access. Associated resources may include:

§  Construction equipment to facilitate routine maintenance of covers, berms or ditches.

§  Transportation, such as light vehicles, small boats, all-terrain vehicles or snowmobiles.

§  Power supply, such as generators, solar panels, wind turbines, or batteries.

§  Fuel storage to supply vehicles and generators.

§  Reagent storage and maintenance tools for water treatment plants.

§  Sampling equipment for routine sampling of surface water, groundwater, soil and sediment.

§  Temporary accommodation facilities.

§  Storage facilities to house resources when not in use.

As for monitoring, maintenance activities may be undertaken by local contractors, thus allowing full demobilisation of the owner from site. This may contribute to ongoing economic development of local communities and give them insight into the post-closure activities occurring on site.

The need to retain site access through a permanent road or air strip should be taken into consideration, as well as retaining some roads on site to enable easy access for monitoring and maintenance. For sites where permanent mine infrastructure is being retained, monitoring and maintenance facilities will need to be more permanent in nature than is the case when permanent infrastructure has been removed.

11.4.2         Managing Residual Risks

Effective mine closures will include identification of major risks and enaction of measures to control or eliminate those risks. For most closure measures, some degree of risk will remain after their application. These remaining, or “residual” risks should be clearly identified, and should represent a level of risk that is acceptable to the post-closure landholder. A quantitative risk assessment may be used to dimension residual risks. An acceptable level of residual risk is an outcome of good planning and proper closure execution.  

Characterization of residual risks should be done while planning for closure, and factor into the design of monitoring and maintenance plans. Residual risks should be documented along with the controls needed to address these risks. In some instances, this may be through ongoing monitoring, data evaluation, periodic modelling of the geochemical evolution of ARD, and water quality prediction to confirm alignment. It is also possible that some risks, even when closure measures reduce them to levels that are ALARP, will remain significant, and will require ongoing controls or contingency plans (i.e., management in the post-closure period). ARD is one of the principal potential residual risks.

Management of residual risks should tie into the post-closure monitoring plan. The nature of the risk will dictate both the appropriate monitoring and the reasonable contingency measures. In some cases, monitoring may allow identification of evolving conditions that change the risk profile, allowing corrective measures to be undertaken before unacceptable consequences occur. ARD generation and associated impacts on receiving water quality represent a common example of evolving conditions, with instances of ARD essentially “getting out of control” as well as diminishing over time, depending on the geochemical characteristics of the reactive material. In both cases, adaptive management is required and appropriate.

Residual risks may not only be environmental, but may also be societal, for instance, unauthorised site access for the purposes of re-mining, political instability preventing access for monitoring and maintenance activities, inadvertent site access leading to injury or fatality, or bankruptcy of the site owner.

Developing an adequate understanding of the residual risks and appropriate planning for these risks are key to long-term sustainable mine closure.

11.4.3         Pathways to Relinquishment

The ideal mining life cycle concludes with a successful closure and rehabilitation program, one that reduces risks associated with the site to levels that are comparable with those of the surrounding land (or the pre-mining conditions) and, in some cases, transitions the land to a new, beneficial post-closure land use. At some point on the pathway to this end state, transfer of ownership and responsibility for the land to the government, other stakeholders, or an independent third party may be an option. This transfer is called relinquishment and, while only infrequently obtained, is often regarded as the ultimate goal of closure works, and the culmination of mining as sustainable land use.

Even with responsible closure planning, relinquishment is typically difficult to obtain, particularly where there is a long-term risk of ARD generation. The legal framework that would support relinquishment is unclear, untested, or simply absent in many jurisdictions. Even in jurisdictions that do have some framework, there may be conflicting regulations.  “Polluter pays” or “joint and several liability” legislation exists in many jurisdictions, which can mean that even if a land title is transferred to a third party, environmental liability for mine wastes will remain with the original owner, i.e., the mining company.  This can create a roadblock to relinquishment, as the company could face a situation where it has no control over the site after transfer of title but retains full liability if anything should happen, for instance, damage to the integrity of the mine waste repositories containing material with ARD potential.

In the context of ARD management, this may, therefore, lead to plans for partial relinquishment, where the mine site is divided into physical domains, and some are relinquished while others, such as former TSFs or waste rock facilities, that remain under control of the mining company. In these cases, it may be useful to distinguish between “relinquishment”, where a third party takes over a site, and “relinquishable”, where the site remains under control of the mining company but is in a condition that, at least theoretically, allows it to be passed on a third party.

The theoretical pathway to relinquishment is relatively straightforward, and is laid out explicitly in the legislation of some jurisdictions:

§  Success criteria are defined during the closure planning stage and agreed upon with regulators and other stakeholders (Section 11.2.2).

§  A financial guarantee is put in place for the cost of closure.

§  Closure works are carried out progressively during operations and/or at the end of mine life.

§  Some or all the guarantee is returned to the owner for the completed closure works.

§  Post-closure monitoring takes place, with results compared to completion criteria.

§  As completion criteria are met, the remainder of the financial guarantee is returned to the mining company.

§  If a significant residual risk (e.g., potential ARD) remains for the site, then a “residual risk” payment can be paid to account for ongoing management costs over an agreed-upon duration.

§  Once all completion criteria have been met (or are on a trajectory to being met), the full guarantee is returned, and the former mine lands are returned to the governing body or transferred to a new landowner.

In practical applications, several complications emerge. ARD issues are one of the most common and difficult to deal with. If ongoing water treatment is needed, there are few mechanisms to transfer responsibility for that treatment to the government or another entity. In theory, there may be some possibility to transfer the land to a third party if there is a significantly attractive post-closure land use (for example, a site that generates surplus energy from a solar array may be an attractive investment for an energy company, even with the ongoing cost that water treatment would require). As the size and complexity of the residual risks increase, the number of potentially viable options for relinquishment tends to decrease.

The concept of a residual risk payment is a tool for moving sites towards relinquishment (Stevens 2023). This may consist of application of a trust fund concept for ongoing site monitoring and maintenance needs. In this approach, the future cost and NPV of ongoing maintenance are calculated, and this amount is used to establish a fund for these future works. Relinquishment then includes passing the trust fund and the responsibility for all future monitoring and maintenance of the site to the government (or potentially a third party). Such transitions raise a number of legal and liability issues that need to be addressed in a manner that is specific to the legal tools available in the jurisdiction.

In many jurisdictions around the world, mine sites do not have a clear pathway to relinquishment.  In these cases, it will be necessary to analyze on a site-specific basis what is the best target outcome for the mining company, government, and other stakeholders. When assessing possible outcomes, it may be useful to consider each physical domain of the site separately and evaluate if their pathways to relinquishment or near-relinquishment could be different.  It may also be beneficial to re-assess the pathway to relinquishment at multiple intervals over the life of the mine, as governing laws, operational practices, available technologies, and stakeholder priorities are continuing to evolve.

 

11.5  Mine Closure Planning for Sustainable Outcomes

Sustainable development has been shown throughout previous chapters of the GARD Guide to be a consistent theme in the permitting, operation, and closure of mine sites where ARD is a risk to be managed (Section 1.7, Chapter 1). Even though the economic gains from mining can be substantial at the local level, the potential environmental and social liabilities stemming from ARD can be detrimental to the overall benefits from mining, unless managed appropriately.

Current best practice dictates that decisions throughout the life cycle of the mine should consider environmental, social and governance (ESG) aspects (e.g., the Global Industry Standard on Tailings Management [GISTM; Global Tailings Review 2020, ICMM 2019a]). As such, in planning for the sustainable closure of a mine, ESG considerations must also be adequately considered in trade-off analyses. When mine planning is done properly and proactively, life cycle project decisions integrate ARD-related considerations in such trade-offs beyond just the economic costs and also consider an array of other potential risks and opportunities that may arise from ARD. Impacts resulting from ARD typically primarily pertain to water quality and its effects on fauna, flora, and ecosystem services[2] which, in turn, is directly linked to the wellbeing of communities.

In the context of ARD in mining, sustainable development is achieved by integrating closure planning throughout all phases of the project life cycle (from exploration through to post-closure) as practically as possible and to confirm that closure objectives are being met (ICMM 2019a). Improved mine planning may prevent ARD generation and avoid the requirement for water treatment, which may become a liability in the very long term. The importance of maximizing prevention controls through mine planning is emphasized throughout the GARD Guide and in several corporate guidance policies, and aligns with the principles of sustainable development.

Project financing by development banks such as the International Finance Corporation (IFC) may be easier to secure when operations demonstrate commitment to the ‘mitigation hierarchy’ for risks and impacts to the environment, workers, and affected communities (IFC 2012a). The mitigation hierarchy represents the sequence of actions relating to potential impacts and consist of avoidance, minimization, rehabilitation, and offsetting. This mitigation hierarchy should be applied to ARD considerations as well, with avoidance having a higher priority than the other steps in the mitigation hierarchy such as minimization, mitigation, and treatment. In the context of ARD, “avoidance” is typically understood to imply source control, although “true” avoidance of reactive materials may be achievable as well, for instance through appropriate mine sequencing.

11.5.1         Post-Closure Sustainable Land Use

Much has been written about potential future land use plans for mines. ISO 21795 (ISO 2021a, 2021b) and ICMM (2019a) refer to it in general, while documents from the Landform Design Institute (Landform Design Institute 2021) and others provide further details (e.g., McKenna and Van Zyl 2020). Proposals for post-closure land use are typically the responsibility of the mine owner, in consultation with all relevant external stakeholders, including regulators, local (Indigenous) communities and the post-closure landholders, and incorporated into closure planning. Closure Plans are refined throughout the mine life cycle and, in conjunction, land use decisions are also refined, ideally yet again with the input of all relevant stakeholders. The post-closure land use and details related to the implementation of corresponding closure activities must be fully defined at the time of final closure permitting.

When an ARD potential has been identified, post-closure land use plans may be constrained so as to avoid ARD generation or accommodate potential generation and management of ARD. For example, these constraints may include:

§  Long-term cover integrity for mine waste facilities. 

§  Ongoing maintenance of monitoring network for water quality sampling – surface water and groundwater. 

§  Long-term maintenance of water treatment infrastructure, including delivery of and storage for treatment chemicals, disposal of sludges and other wastes from the treatment processes, potential storage of contaminated water, etc. 

Where a water cover must be maintained to limit acid generation from tailings facilities, land use options are generally limited, albeit that certain specific alternatives may be available, for instance, the development of homes around the lake such as was done at Elliott Lake (Balasko et al. 2022). However, the presence of a water cover typically increases other risks, such as the integrity of containment and spillway facilities, maintenance of sufficient water cover, risks to biota and human health, and safety considerations related to unauthorized access.

In some instances, access to culturally protected areas (e.g., areas with archeological, religious, or symbolic significance) may also be required, especially in locations where Indigenous populations are present near the mine site. These areas should also, as much as is feasible, be protected from impacts resulting from the mining operation over the entire LoM. Mining operations may also include industrial heritage that is worth preserving. In some rare cases, ARD may itself be part of this heritage, which can pose a significant dilemma in terms of addressing the adverse impacts of ARD.

Ultimately, decisions related to post-closure land use are site-specific, must consider the input from all relevant stakeholders, and cannot be a unilateral effort by the mine owner. It should be noted that technical issues related to ARD can be complex and challenging to communicate to local stakeholders. Nevertheless, due to its high visibility (i.e., colored drainage), potential significant impacts on human health and the environment, and potential longevity, it is imperative that ARD and associated aspects be discussed, and in a manner understandable by all participants in the closure process. This may require the involvement of local resources (e.g., local consultants or community representatives) capable of translating the technical issues into language that is accessible to all.

11.5.2         Social License and Social Transition for ARD Impacted Mines

There is a growing need for socio-economic transition planning in relation to mine closure and oftentimes, a social license to mine depends on effective planning with communities for when the mining operation comes to a close.

Investments in social management of closure should result from a dialogue with local communities, Indigenous groups and other relevant stakeholders. Stakeholder engagement, discussed in Section 11.2.3, is the basis for building trust and gaining and sustaining the social license to operate, i.e., community acceptance towards a mining project or a specific activity associated with a mining project, such as mine closure.

Proactive, early, and ongoing stakeholder engagement that integrates the issues and perspectives of local and Indigenous communities and other stakeholders allows for a common and agreed upon understanding of the priority elements of a mining project’s social performance management system.

Social performance management criteria included in an alternatives selection process (e.g., MAA) need to address both perceived and actual risk, beyond mere permitting considerations. The involvement of affected communities in decision making is often a requirement by financiers and regulators, seen in the fourth iteration of the Equator Principle (EP4) and fully endorsed by this Guide.

Building a strong relationship from the beginning of mining activities enables collaboration throughout the mine life cycle, which includes planning for a social transition. Social transition for mine closure acknowledges potential risks associated with local dependence on mining. Therefore, social transition aims to foster the development of post-closure options that both contribute to sustainable development and are long-lasting after the mine ceases operations. The development and implementation of mine Closure Plans involves shared decision-making with local communities, Indigenous groups, governments, and other affected and interested parties. In an ideal world, this ultimately facilitates government-led development and ownership by local communities and partners. Hence, the mining company should increase capacity of local communities, Indigenous communities and their governments so that they can meet their socio-economic needs without the mine’s involvement (ICMM 2019a).

There are four key areas for a successful social transition: multi-disciplinary stakeholder engagement, early planning and long-term vision, building local capacity and securing financial resources for social transition, which can be further explored in the ICMM Integrated Mine Closure Good Practice Guide (ICMM 2019a).

11.5.3         Biodiversity

The full impacts of ARD on biodiversity may take time to occur and can last for centuries. Therefore, it is crucial to understand the consequences of ARD early, so any decisions related to mine operation and closure consider the importance of the avoidance of ARD impact.

As part of mitigating ARD risks to biodiversity at closure, mine operators should consider how landforms that address ARD challenges might simultaneously support natural ecosystems and benefit biodiversity. Engineered designs for closure landscapes that are stable, address ARD issues, and benefit biodiversity can be challenging to develop. As such, the planning for such landscapes should start early in the mine life cycle. Robust reclamation and closure design can reduce offset obligations when working towards no net loss (NNL) or net positive impact (NPI) for biodiversity.

Anthropogenic activities, including infrastructure development, agriculture, and mining (along with other extractives), have caused rapid biodiversity loss (WWF 2018). Consequently, a mining operation that wishes to contribute to sustainable development must consider and mitigate biodiversity impacts. Not only is this required by most regulating bodies, but international financial pressures are also being applied to improve the performance of the mining industry in terms of its contribution to sustainable development with respect to biodiversity.

Best practice goes beyond simply minimizing impacts to biodiversity. Members of ICMM are expected to comply with Principle 7.2, which directs members to “assess and address risks and impacts to biodiversity and ecosystem services by implementing the mitigation hierarchy, with the ambition of achieving no-net-loss of biodiversity” (ICMM 2022). Restoration of biodiversity is, therefore, a critical component of closure planning and effective closure practices that integrate biodiversity considerations can be quite successful in supporting a neutral or positive outcome. However, good planning and rigorous implementation of the mitigation hierarchy is imperative throughout the mining lifecycle (as described in Chapter 6 of this Guide). This avoids and minimises impacts to biodiversity such that the obligations and costs related to biodiversity mitigation (including both rehabilitation and offsetting) are reduced when the mine closes.

 

 

 

 

 

11.5.4         Resources for Planning Sustainable Mine Closure

Resources on topics covered in this section can be explored in the documents listed in Table 11-2.

Table 11-2: List of documents on sustainable development with application to ARD management

Area	Document Name	Description of Resource	Link to Resource
Environmental and Social	IFC Guidance Note 1 Assessment and Management of Environmental and Social Risks and Impacts (updated in 2021)	Leading environmental and social practice – financiers’ requirements – International Finance Corporation (IFC)	https://www.ifc.org/wps/wcm/connect/6df1de8f-2a00-4d11-a07c-c09b038f947b/GN1_English_2012.pdf?MOD=AJPERES&CVID=mRQjKE9
Environmental and social performance to investees	Equator Principle 4 (EP4)	Equator Principles is a risk management framework adopted by financial institutions to identify, assess and manage the environmental and social risks in projects.	https://equator-principles.com/wp-content/uploads/2021/02/The-Equator-Principles-July-2020.pdf
Mining Specific: Environmental and Social	Environmental, Health and Safety Guidelines for Mining (2007)	Leading environmental and social practice for mining – financiers’ requirements	https://www.ifc.org/wps/wcm/connect/595149ed-8bef-4241-8d7c-50e91d8e459d/Final%2B-%2BMining.pdf?MOD=AJPERES&CVID=jqezAit&id=1323153264157
Water Stewardship	ICMM Water Stewardship Framework (WSF)	Standardized approach to water stewardship for the mining and metals industry – demonstrates how the operation is connected to other users in the watershed	https://www.icmm.com/en-gb/guidance/environmental-stewardship/2014/water-stewardship
Climate Change	Task Force and Climate Related Financial Disclosures	TCFD was created to promote consistent climate-related financial disclosures for companies.	https://assets.bbhub.io/company/sites/60/2020/10/FINAL-2017-TCFD-Report-11052018.pdf
Climate Change	Guide on Climate Change Adaptation for the Mining Sector	Practical guide by MAC applying climate change adaptation translated to the mining context, in alignment with TCFD recommendations.	https://mining.ca/wp-content/uploads/2021/05/MAC-Climate-Change-Guide-April-30.pdf
Stakeholder Engagement	IAP2 International. (2018). IAP2 Public Participation Spectrum. International Association for Public Participation.	Spectrum for companies to identify their intention of engagement	https://cdn.ymaws.com/www.iap2.org/resource/resmgr/foundations_course/IAP2_P2_Spectrum_FINAL.pdf
Mine Closure and Reclamation Planning	Integrated mine closure good practice guide	Comprehensive closure planning by ICMM	https://www.icmm.com/en-gb/guidance/environmental-stewardship/integrated-mine-closure-2019
Mine Closure and Reclamation Planning	International Organization for Standardization (ISO) ISO 21795 (2021) Mine Closure and Reclamation Planning	Part 1 – Requirements Part 2 – Guidance Explains mine closure and reclamation plan objectives and commitments.	ISO - ISO 21795-1:2021 - Mine closure and reclamation planning — Part 1: Requirements
Tailings Management	Global Industry Standard on Tailings Management	Global Standards on Tailings Management with important considerations for environmental and social management.	https://globaltailingsreview.org/
Tailings Management	Tailings Management Good Practice Guide	Guidance on tailings management by ICMM	https://www.icmm.com/en-gb/guidance/innovation/2021/tailings-management-good-practice
Landform design	Mining with the end in mind: Landform design for sustainable mining	Practical guidance on land reform.	https://www.landformdesign.com/position.html
Indigenous Knowledge	Indigenous Knowledge Under the Impact Assessment Act	Indigenous Knowledge under the Impact Assessment Act: Procedures for Working with Indigenous Communities	https://www.canada.ca/en/impact-assessment-agency/services/policy-guidance/practitioners-guide-impact-assessment-act/indigenous-knowledge-under-the-impact-assessment-act.html
Indigenous Communities	Good Practice Guide: Indigenous Peoples and Mining	ICMM Best Practice on Indigenous Communities	https://www.icmm.com/website/publications/pdfs/social-performance/2015/guidance_indigenous-peoples-mining.pdf
Indigenous Communities	Environmental and Social Performance Standards – Guidance Note for Performance Standard 7: Indigenous Peoples	IFC Performance Standards on Indigenous Peoples	https://www.ifc.org/wps/wcm/connect/9baef8f6-9bd9-4d95-a595 7373059081d4/GN7_English_2012.pdf?MOD=AJPERES&CVID=mRQk089

 

11.6  References

APEC (Asia-Pacific Economic Forum). 2018. Mine Closure Checklist for Governments. March 2018. https://www.apec.org/publications/2018/03/mine-closure---checklist-for-governments

Balasko, C., Willems, D., Gusikoski, A. and Watson, A. 2022. Water in Tailings: A Review of 20 Years of Post-Closure Performance. Proc. of Mine Water Solutions 2022 Conference, 63–72. https://www.mineconferences.com/files/ProceedingsofMineWaterSolutions2022.pdf

Brundtland, G. 1987. Our Common Future: World Commission on Environment and Development. In Report of the World Commission on Environment and Development: Our Common Future. United Nations General Assembly document A/42/427. https://doi.org/10.1016/0022-2364(91)90424-R

CCME (Canadian Council of Ministers of the Environment). 1995. Canadian Water Quality Guidelines. Prepared by the Task Force on Water Quality Guidelines of the Canadian Council of Ministers of the Environment. December.

CCME. 1996. A Protocol for the Derivation of Environmental and Human Health Soil Quality Guidelines. Report CCME EPC-101E, CCME. March.

CDA (Canadian Dam Association). 2014. Technical Bulletin: Application of Dam Safety Guidelines to Mining Dams.

Environment Canada. 2012. Federal Contaminated Sites Action Plan (FCSAP). Ecological risk assessment guidance. March.

Equator Principles. (2020). The Equator Principles (EP4). In The Equator Principles (Issue July). https://doi.org/10.4324/9781351278881-33 

Global Tailings Review. 2020. Global Industry Standard on Tailings Management. August 2020. https://globaltailingsreview.org/wp-content/uploads/2020/08/global-industry-standard-on-tailings-management.pdf

Grant, Carl D. 2006. ‘State-and-transition successional model for bauxite mining rehabilitation in the Jarrah forest of Western Australia’, Restoration Ecology 14: 28–37.

Health Canada. 2010a. Federal Contaminated Site Risk Assessment in Canada. Part I:Guidance on Human Health Preliminary Quantitative Risk Assessment (PQRA). September.

Health Canada. 2010b. Federal Contaminated Site Risk Assessment in Canada, Part V: Guidance on Human Health Detailed Quantitative Risk Assessment for Chemicals (DQRA Chem).

IAP2 International. 2018. IAP2 Public Participation Spectrum. International Association for Public Participation. https://cdn.ymaws.com/www.iap2.org/resource/resmgr/foundations_course/IAP2_P2_Spectrum_FINAL.pdf

ICMM (International Council on Mining and Metals). 2002. Mining Principles. https://www.icmm.com/website/publications/pdfs/mining-principles/mining-principles.pdf?cb=10319

ICMM. 2006. Good Practice Guidance for Mining and Biodiversity. https://www.icmm.com/website/publications/pdfs/environmental-stewardship/2006/guidance_mining-biodiversity.pdf

ICMM. 2014. Water Stewardship Framework. International Council on Mining and Metals, April 2014, 1–4. https://www.icmm.com/website/publications/pdfs/environmental-stewardship/2014/guidance_water-stewardship-framework.pdf

ICMM. 2015. Indigenous Peoples and Mining: Good Practice Guide. https://www.icmm.com/website/publications/pdfs/social-performance/2015/guidance_indigenous-peoples-mining.pdf

ICMM. 2019a. Integrated Mine Closure: Good Practice Guide, 2^nd edition.

 

ICMM. 2019b. Adapting to a Changing Climate, Building Resilience in the Mining and Metals Industry. https://www.icmm.com/website/publications/pdfs/environmental-stewardship/2019/guidance_changing-climate.pdf

ICMM. 2020. Closure Maturity Framework. Tool for Closure User Guide. https://www.icmm.com/en-gb/guidance/environmental-stewardship/2020/closure-maturity-framework

ICMM. 2022. ICMM Principle 7- Conservation of Biodiversity. ICMM. https://www.icmm.com/mining-principles/7

ICMM and IFC. 2021. Shared Water, Shared Reponsability Approach: Water in the Mining Sector. 44–45.

IFC (International Finance Corporation). (2007). Environmental, Health and Safety Guidelines for Mining. 92, 1–33.

IFC. (2012a). Guidance Note 1 Assessment and Management of Environmental and Social Risks and Impacts. 2012(i), 1–53.

IFC. (2012b). Guidance Note 7: Indigenous Peoples. https://www.ifc.org/wps/wcm/connect/9baef8f6-9bd9-4d95-a595-7373059081d4/GN7_English_2012.pdf?MOD=AJPERES&CVID=mRQk089

IFC. (2012c). IFC Performance Standards on Environmental and Social Sustainability - Effective January 1, 2012. International Finance Corporation (IFC) Website. http://www.ifc.org/wps/wcm/connect/topics_ext_content/ifc_external_corporate_site/ifc+sustainability/publications/publications_handbook_pps

INAP. 2020. Rock Placement Strategies to Enhance Operational and Closure Performance of Mine Rock Stockpiles. Available at: https://www.inap.com.au/wp-content/uploads/2020-Jan-INAP-Improving-Stockpile-Construction-Phase-1-Final-Report.pdf

IPCC (Intergovernmental Panel on Climate Change). 2021. Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press.

ISO. (2021a). Mine Closure and Reclamation Planning. Part 1 – Requirements. In ISO 21795-1:2021 Mine Closure and Reclamation Planning.

ISO. (2021b). Mine Closure and Reclamation Planning. Part 2 – Guidance. In ISO 21795-1:2021 Mine Closure and Reclamation Planning.

Landform Design Institute. 2021. Mining with the end in mind: Landform design for sustainable mining. Position Paper. March 2021. https://www.landformdesign.com/pdf/LDI-PositionPaper2021.pdf

Logsdon, M.J., 2013: What Does “Perpetual” Management and Treatment Mean? Toward a Framework for Determining an Appropriate Period-of-Performance for Management of Reactive, Sulfide-Bearing Mine Wastes. Proceedings of the 2013 Annual Conference of the International Mine Water Association, August 6-9, Golden, CO.

MAC (Mining Association of Canada). 2019. Developing an operation, maintenance and surveillance manual for the post-closure management of tailings facilities. In Second Edition. https://doi.org/10.36487/acg_rep/1152_90_crossley

MAC. 2021. Towards Sustainable Mining, Climate Change Protocol. March 2021.

McKenna, Gord; Van Zyl, D. 2020. Towards “ Zero Harm .” In Towards “ Zero Harm ”: A Compendium of Papers Prepared for the Global Tailings Review (Vol. 61, Issue October, pp. 1–26). Global Tailings Review. https://globaltailingsreview.org/.

MEND. (2012). Mend 1.61.5c Cold Regions Cover System Design Technical Guidance Document (Issue July).

Stevens, R., 2023: Relinquishment of Closed Mine Sites: Policy Steps for Governments. International Institute of Sustainable Development & Intergovernmental Forum on Mining, Minerals, Metals and Sustainable Development.

TCFD. 2017. Recommendations of the Task Force on Climate-related Financial Disclosures. Task Force on Climate-Related Fiancial Disclosures, June, 1–74. https://assets.bbhub.io/company/sites/60/2020/10/FINAL-TCFD-Annex-Amended-121517.pdf

TCFD. 2019. 2019 Status Report: Task Force on Climate-Related Financial Disclosures. June, 1–114. https://www.fsb-tcfd.org/wp-content/uploads/2019/06/2019-TCFD-Status-Report-FINAL-053119.pdf

United Nations. 2021. United Nations Climate Change. https://unfccc.int/event/cop-26

UN; WCMC. (n.d.). Biodiversity A-Z. https://www.biodiversitya-z.org/

WRI. 2012. The corporate ecosystem services review. Guidelines for Identifying Business Risks and Opportunities Arising from Ecosystem Change WRI WBCSD and Meridian Institute, 48. https://www.wri.org/research/corporate-ecosystem-ser

WWF (World Wildlife Fund). 2018. Living Planet Report. https://c402277.ssl.cf1.rackcdn.com/publications/1187/files/original/LPR2018_Full_Report_Spreads.pdf

 

 

 

 

Appendix 11A

Mine Closure Planning Tools

 

 

APP 11A 1         MULTIPLE ACCOUNTS ANALYSIS

APP 11A 1-1         Approach

A typical multiple accounts analysis (MAA) goes through the following overall process:

·       Identify a wide range of alternatives.

·       Screen out alternatives that not viable (“fatally flawed”).

·       Identify the decision parameters (or accounts) and sub-parameters (sub-accounts) that will be used to evaluate the remaining alternatives,

·       Apply weightings to each account/sub account.

·       Score the alternatives against each account/sub account.

·       Rank alternatives based on the scores, with highest scores indicating the potential preferred option.

The best practical timing to carry out the alternatives analysis is not always obvious. While it is ideal to identify and analyse alternatives during the initial development of the mine Closure Plan, there may not be sufficient design detail on options at this early stage to support the taking of final decisions. In this case, the MAA process may serve to highlight information gaps that should be addressed before final decisions are taken. 

The process requires input from appropriately qualified and experienced professionals. This is often done in a workshop format. When completed under the guidance of an experienced facilitator, this permits differing viewpoints and technical backgrounds to be incorporated when numerical scores are assigned to alternatives.

The MAA process is a tool to support decision-making, but it should not be interpreted as a tool that makes decisions. The major benefit of this methodology is its ability to consider sensitivity analyses that can be used to identify which accounts are the more important, how each alternative scores in each account and hence the reasons for the score and ranking of the alternatives. It allows the overall balance of how each alternative scores for the range of accounts being considered, to potentially avoid necessarily selecting those that might score highest in some accounts but lowest in others at the expense of those that more consistently score second or third for each account.

There is a limit to the number of such accounts that can be considered while maintaining a relatively straightforward and understandable process. While it is tempting to include every conceivable factor as an account or sub account, experience suggests that an MAA with too many accounts is both difficult to complete, and difficult to interpret. As the number of accounts increases, the value that can be assigned to any individual account decreases, to the point at which no single account has a meaningful impact on the decision taken.

The process does require numerical scoring and develops total scores for the various alternatives considered. While it does result in a ranking of the alternatives this tool should not be the only factor in selecting a Closure Plan. Other factors, for example, the company’s need to adopt a low risk profile in the future, relinquishing the mine site to another entity after closure, adjusting the closure activities to allow for longer term phased installation to match the company’s cash flow, or having to address urgent concerns by stakeholders should also be considered. These factors can also be including as accounts or sub-accounts in the scoring system

 

Once the overarching closure vision, principals and objectives have been identified as discussed in Section 11.4.1.2, the formal steps of the MAA process can be undertaken, as listed below and illustrated in Figure 1. 

·       Identifying candidate closure alternatives.

·       Pre-screen candidate alternatives and select a short list for further, more detailed, evaluation.

·       Alternative characterization.

·       Multiple Accounts Ledger.

·       Alternatives analysis.

·       Sensitivity analyses.

·       Documentation.

In the sections below we provide brief discussions of the important aspects in each of the above steps.

 

APP 11A 1-2     Identifying Candidate Alternatives

These should include possible (reasonable, conceivable and realistic) candidate technologies and approaches to closure. At this stage it is useful to think broadly and consider the full range of approaches to closure that have been considered in the industry. Earlier chapters of the GARD Guide provide extensive guidance as to the range of technical options that are available for common needs such as the prevention of ARD generation through waste handling or cover design, or water treatment alternatives.

 

Figure 1: Flow Diagram of the Process of Assessing Alternatives for Mine Waste Disposal (Environment and Natural Resources Canada 2016)

 

APP 11A 1-3         Pre-screening of Candidate Alternatives

Pre-screening is typically performed using screening criteria that are used to eliminate those alternatives that do not meet a minimum threshold of the established goals and objectives or can be clearly stated not to meet minimum requirements for viability (“fatal flaws”). Pre-screening is a necessary step for the efficiency of the evaluation process, as it prevents wasting time on options that clearly will not be selected. At the same time, it provides an opportunity to demonstrate that a full range of options were considered before narrowing the list to those evaluated in the MAA.  

The reasons for screening out options should be clearly documented. Some common criteria for screening out options are as follows (US EPA 1988):

·       Effectiveness: Are not effective in achieving the goals and objectives.

·       Implementability: Are extremely challenging or impossible to implement (considering potential technical, environmental, regulatory, etc. issues)

·       Cost-effectiveness: Are not as cost-effective as another alternative which achieves the same objectives for a much lower cost.

Some companies may choose to include other criteria, such as avoiding unproven technologies.

 

APP 11A 1-4         Alternative Characterization

Alternatives that are carried into the MAA must be sufficiently defined to permit a meaningful comparison. It is of little value to evaluate, and then select, an alternative that during subsequent more detailed engineering studies is demonstrated to be infeasible either because of cost or technical aspects. It is particularly important to make sure the designs being evaluated are based on sufficient local and regional field data and design analyses to consider them to be feasible using reasonable engineering judgement to overcome any data gaps.

Typically, this means pre-feasibility level designs and at least order-of-magnitude cost estimates. While there are no hard and fast rules to determine if designs have been advanced to sufficient level, the following questions can be used to help evaluate if they are prepared to undergo an MAA:

·       Is the cost of each option understood to a level that permits them to be compared? (Including both capital and operating cost)

·       Does the level of design support comparison of technical/environmental performance of the options? (eg, difference in impacts on water quality, differences in total metal loading, differences in constructability)

·       Are the desires and preferences of the stakeholders understood sufficiently that stakeholder acceptance of the different options can be adequately judged? (Note that it is common for engineering teams to mis-judge stakeholder preferences.)

 

APP 11A 1-5         Multiple Accounts Ledger

This ledger is the heart of the alternatives evaluation process as it provides the basis for the ranking and numerical scoring of the alternatives. It typically includes the accounts, sub-accounts and indicator parameters. The accounts are generally established by the company, with input from stakeholders, for consideration at all sites. Sub-accounts are more reflective of the site-specific conditions and are modified/established for each specific mine site. The indicator parameters are important and determine how the sub-accounts are characterized and how the alternatives are therefore valued. An example from Environment and Natural Resources Canada (2016), which has been further adapted for this Guide is provided in Table 1.

This table is only an example and may be customized to fit the needs of any site. In developing a ledger, it is important to consider the following:

·       Accounts and sub-accounts should be independent. In the process of developing a new ledger, it is common to realize that the same aspect of a design may be counted twice. For instance, if “construction complexity” is a sub-account (as shown in the example), it should be clear in the definitions and evaluation that “complexity” is being evaluated for its own sake, and not as a proxy for capital cost, which has its own account. Buy having “construction complexity” as its own account, there is a value judgement implicit that this complexity will have an impact on the final decision, independent of the cost.

·       The number of accounts should be limited, with only the accounts that are truly important to decision-making included. The more accounts that are included, the more difficult it will be to trace what factors are most important decision making, and the less importance any individual account will have. This can be compensated to some degree by numerical weightings for accounts and sub accounts, but it is generally better to have fewer accounts as a starting point.

Numerical weightings are typically assigned to each account, and then further subdivided for each sub-account. Any weighting chosen implies a value judgement. For example, for the ledger shown in Table 1, weightings could be divided equally between each of the five accounts, resulting in an account weighting of 20% each. This gives each account (technical, environmental, cost, etc.) equal weight in the decision making. If this does not reflect their relative importance in the decision, weightings should be adjusted accordingly.

A similar process applies for the sub-accounts. The weight assigned to the parent account is distributed between the subaccounts, proportionally to their desired importance in the decision.

Table 1: Example of a Multiple Accounts Structure

Account	Sub-account	Indicator
Public and worker safety	Risk to the public	Risk profile based on dam breach and other analyses.
	Risk to workers	Worker risks based on occupational accident statistics during construction and long-term care functions.
Technical	Physical stability in the long-term	Static factors of safety, robustness of design in dealing with earthquake deformation, liquefaction, erosion, blockage for drainage systems in dams, etc.
	Chemical stability in the long-term	Potential for ARD or high salinity leachate generation and migration outside of the containment areas post-closure. Resilience of engineered facilities and elements to geochemical changes (e.g., clogging of drains).
	Closure construction complexity	Different levels of complexity.
	Post-closure care required	Levels of closure inspection, maintenance, operational requirements.
	Failure risks in the long-term	Results of a Failure Modes Effect Analysis (FMEA) type assessment – residual risks.
Costs	Capital Cost	Cost scale.
	Long-term costs	Cost scale.
Environmental	Aquatic life restored	Fish bearing water bodies restored.
	Terrestrial ecosystems restored	Area and type of ecosystems created.
Socio-economic	Local community benefits	Jobs created for closure and in the long-term.
	Post-closure land use / sustainable development achieved	Hierarchy of land use types and development.

 

APP 11A 1-6         Alternatives Analysis

This process entails ranking and scoring each of the alternatives against each sub-account using the indicator parameters. Each alternative is given a numerical score.

When setting the scoring approach:

·       A five point range is typically sufficient. Given that most scores assignments have an element of judgement, setting a broader range is more difficult to justify (e.g., on a 10-point scale, it may not be clear what makes the difference between and 7 or 8 point score in most accounts)

·       The first step in scoring is to rank the alternatives from best to worst for each of the sub-accounts. This is generally an easy step to undertake and provides a basis for then establishing the scores as described in the steps below.

·       Based on the above ranking assign specific scores to each alternative. Select the highest score for the highest ranked alternative and the lowest score for the lowest ranked. Scores for the other alternatives can then be based on the assessed differences in performance.

·       For each sub account, it may be useful to define clearly what constitutes an average, high, and low score in terms of performance.

Once the scores are assigned, it is straightforward math to calculate total scores for each of the alternatives, and the components of these scores for each account. This can be done in a spreadsheet, or with a commercially available dedicated software package.

Typically, alternatives with the highest total score are considered more favorably than the others. The selected alternative may be one of the highest scoring alternatives. However, when selecting the preferred alternatives, it is also important to consider which accounts or sub-accounts were responsible for the alternatives higher scores and whether the alternative scored high in most or all for the accounts rather than very high in some and very low in others (see the discussion of the sensitivity analysis below). This returns to the point that an MAA helps to inform and document a decision-making process, but does not make the decision.

 

APP 11A 1-7         Sensitivity Analyses

Sensitivity analyses should be done to determine how the scoring and ranking of the alternatives change with changes to the weights of the various accounts, and possibly also the sub-accounts. It is typical to perform an analysis where the cost account is removed, to see whether and how the scoring changes if costs are not considered. In addition, a benefit-cost analysis can be performed to determine which alternative/s provide the most value for the costs expended. This is typically done by plotting the cost against the total MAA scores calculated without the cost account. Where there is uncertainty in establishing suitable account weights, different weighting schemes can be used. Where there are valid differences in the specific scores assigned to certain sub-accounts the range of scores can be used to assess the effect on the overall ranking.

Where the sensitivity analyses yield significantly different alterative rankings, it generally means that further evaluations are needed for those weights or subaccounts responsible for the different ranking. This can mean additional engineering evaluations to resolve scoring difference and further evaluations of the reasons behind the differing assigned weights.

 

APP 11A 1-8         Documentation

The final step in the alternatives assessment process is thorough documentation of the results. This is best done through a comprehensive technical report, which systematically describes the outcome of each of the steps as recommended in these guidelines. The documentation should clearly explain the factors that resulted in preferred alternative being ranked most highly.

It is common to issue a preliminary alternatives analysis report which then provides a basis for engaging with stakeholders. After obtaining their input the analyses are then refined and the report is finalized.

 

APP 11A 2         FAILURE MODES AND EFFECTS ANALYSIS

APP 11A 2-1.      FMEA Templates

The following templates are required when performing a Failure Modes and Effects Analysis (FMEA):

·       A probability or likelihood rating scale used to categorize the likelihood of a specific failure mode of occurring.

·       A consequence rating scale is used to categorize the consequence of a specific failure mode being considered.

·       A risk-level matrix which determines the level for risk based on the likelihood and consequence of a specific failure mode.

·       A risk action table which describes the expected actions to be taken for the various risk levels determined for each failure mode.

Typical examples of these templates are provided below to illustrate what they should include and key aspects with each are discussed. It is recognized that many companies have their own system of templates, which can be followed provide they meet the general intent of the templates described below. 

A useful description of the likelihood scales is provided in Table 2. The categories are as for Table 9-3 in Chapter 9 with the addition of verbal descriptions and quantification of the likelihoods. Of importance is the use of both the verbal descriptions and quantified likelihoods since there may be differences in the interpretation of the verbal descriptions among the experts performing the FMEA. 

For convenience the annual likelihood levels have also been expressed as return period in years to allow for direct comparison with the design criteria for earthquakes and floods which are both expressed as return periods. It is also important to view the quantified likelihood for the period of mine closure being considered as this provides for a more realistic assessment. The table provides these for 100- and 200-year periods. However, using the annual probabilities the long-term period probabilities can be calculated using the following formula:

Return period, T_P years for an annual likelihood of P_A = 1/P_A years             Eqn. 1

Likelihood over T years, P_T = 1-(1-1/P_A)                                                     Eqn. 2

 

Table 2: Typical Likelihood Categories for use in Mine Closure FMEAs[3]

Likelihood Categories	Likelihood Descriptions[4] Apply to the Post-closure Time Period	Equivalent Return Period in Years	Annual Probability of the Failure Occurring	Probability During a 100-year Closure Period	Probability During a 200-year Closure Period
Not Likely	The physical conditions do not exist for the development of the FM	< 10,000 -year	< 0.01%	<1%	<2%
Low	The possibility of the FM cannot be ruled out	1,000 to 10,000-year	0.01% to 0.1%	1% to 10%	2% to 18%
Moderate	The FM is possible	1,000- to 100-year	0.1% to 1%	10% to 63%	18% to 87%
High	The Failure mode is considered likely, but is not certain	10- to 100-year	1% to 10%	63% to 100%	87% to 100%
Expected	The FM is expected to occur	10-year	> 10%	100%	100%

FM = Failure Mode

A typical consequence rating structure is provided in Table 3 (from ICMM 2019). The specific descriptions of the consequences need to be established considering the site conditions, including the social setting as well as the mining company’s risk management strategy.

Table 3: Typical Consequence Rating Table

 

Table 4 provides a typical risk-level matrix that defines the level of risk based on the likelihood and consequence of each identified failure mode. It is based on the risk-levels defined by ICMM (2019) and has been adjusted to fit with the likelihood and consequence scales discussed above.

Table 4: Typical Risk-level Matrix (based on ICMM 2019)

Likelihood	Consequence Scale
	Insignificant	Minor	Moderate	High	Major
Expected	Medium	Significant	Significant	High	High
High	Medium	Medium	Significant	High	High
Moderate	Low	Medium	Significant	Significant	High
Low	Low	Low	Medium	Significant	Significant
Not Likely	Low	Low	Medium	Medium	Significant

 

A typical risk actions table would prescribe actions that are required for each of the failure modes in the different risk-levels as defined by Table 4. Examples of such actions are provided in Table 5.

 

Table 5: Typical Risk Management Actions

Risk Level	Risk Management Actions
High	Risks in this category are not acceptable and require implementation of measures to reduce both the severity and the likelihood of the failure mode
Significant	Risks in this category are generally not acceptable unless a mining company can demonstrate all reasonable treatment measures have been implemented, there are suitable contingency plans that continue to minimize risks, and Emergency Preparedness and Response Plans to minimize the consequences should failure occur
Medium	Monitoring and reasonable risk mitigation measures or contingencies need to be considered and implemented as appropriate, to reduce these risks
Low	Generally acceptable risks

 

APP 11A 2-2.      Typical ARD Failure Modes and Mitigation Measures

Typical failure modes associated with closure include, amongst several others:

·       Planning/characterization failures:

o   Inadequate characterization of wastes, with ARD onset not developing until years after closure.

o   Lack of design to address specific sources (stockpiles not processed at end of mine life, exposed pit walls not identified as a source, borrow materials used for closure works construction as a source of ARD).

·       Source control failures:

o   Cover failures through effects such as erosion, freeze-thaw cycles, material degradation, geotechnical failures, inadequate construction.

o   Failures of water conveyance structures.

o   Inadequate sorting/segregation of potentially acid generating materials.

o   Failures of containment facilities, including catastrophic dam failures by various mechanisms (slope failure, piping, foundation failure) causing the outflow of liquid and solid mine waste.

o   Inadequate seepage control resulting in unacceptable impacts on groundwater or surface water.

·       Treatment system failures:

o   Passive treatment systems losing effectiveness over time due to lack of maintenance.

o   Mechanical failures at active systems.

o   Supply chain issues.

Specific failure modes attributed to ARD issues can include:

·       Blockages of gravel drains due to geochemical precipitates causing pressure buildup in embankments resulting in the failure and seepage of ARD resulting in groundwater quality impacts.

·       Upward wicking of ARD products through covers causing the destruction of vegetation on covers.

·       Damage to control systems caused by corrosive wastes.

Risk management approaches involve either preventative measures that reduce the likelihood of a specific failure mode or mitigation measures that reduce the consequences of the failure mode. Critical Controls (CCs) are used to identify when certain failures may develop and are used to identify the need for an action to prevent the failure mode from occurring. Contingency measures are actions that can be taken in the event CCs are exceeded or there are other indications that a specific failure mode may occur and result in an unacceptable risk.

Examples of Preventative Measures include, among others:

·       Relocation, redesign, or design changes of a proposed facility to avoid the identified risk.

·       Design changes for future stages of an existing facility to prevent the risk in the future.

·       Remedial engineering for existing facilities (e.g., buttress construction) to prevent embankment failures.

·       Alternative methods of either physically conditioning (treating) the waste before and during storages for new and subsequent stages of existing facilities to prevent environmental risks.

·       Operational changes to provide for safer operations.

Typical Mitigation Measures include, among others:

·       Emergency Preparedness and Response plans that mitigate the consequences of a failure by, for example, limiting human access to high-risk areas, providing for early warning of an impending failure, etc.

·       Design changes that reduce the consequences of a failure, such as, for example, placing a tailings pipeline inside a collection trench and basin system that can store tailings escaping due to pipeline leaks or breaks.

·       Providing for backup systems, for example electric generators that allow for continuation of key operations during a power failure.

Critical Controls can include:

·       A range of piezometric levels in a dam that represent increasing levels of a failure risk dam that are used to trigger response actions ranging from further evaluation and monitoring to the implementation of engineering measure to increase dam stability.

·       For ARD wastes CCs can include temperature, oxygen level, pH and conductivity measurements that are used to provide an indication of whether the ARD conditions are indicating faster rates than anticipated in the design and whether further remedial action would be necessary.

 

APP 11A 2-3.      As Low as Reasonably Practical (ALARP)

The “as low as reasonably practical” (ALARP) concept is important when considering the extent to which the medium risks, and possibly significant risks should be mitigated. The GISTM (Global Tailings Review 2020) defines “ALARP requires that all reasonable measures be taken with respect to ‘tolerable’ or acceptable risks to reduce them even further until the cost and other impacts of additional risk reduction are grossly disproportionate to the benefit.”

The ALARP approach involves identifying a range of additional incrementally increased mitigation measures that would achieve increased reductions in risk by either reducing the consequence, likelihood, or both. The reduction in risk attributable to each of these measures is then compared to the costs and other impacts of implementing the measure which typically includes, among other factors:

·       The increased financial cost.

·       The risks to worker safety during implementation of the measure.

·       The environmental impacts both during construction and in the long-term (such as additional land disturbance).

·       Social impacts both during construction and long-term (such a further limits to land use).

·       Reduce resilience or robustness of the Closure Plan.

A qualitative assessment is then made by sufficiently qualified and experienced team of the overall benefit of each of the proposed additional measures. This benefit includes the long-term reduction in risk achieved by the range of measures considered discounted by the short- and long-term costs and other impacts described above for each. The incremental mitigation measures are then considered reasonable if the long-term risk reduction is judged to significantly exceed the costs and other impacts until the incremental reduction in risk is considered grossly disproportionate the overall assessed benefit.

APP 11A 2-4.      Documenting Results of an FMEA

Formal documentation of the results is important both to facilitate a third-party review and well as to assess the need for and provide a starting point for future updates. Documentation of failure modes with risks that are not tolerable for closure provides a starting point for design refinement to reduce risks to an acceptable level or ALARP.