Chapter 11 HTML

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.

11.1.1.1 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.

11.1.1.2 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.

11.1.2 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.

11.1.3 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.

11.1.4 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

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.

11.1.5 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.

11.1.6 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.

11.1.7 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.

11.1.7.1 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.

11.1.7.2 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.