Mine closure plans (MCPs) detail the post mining land use (PMLU) of landforms constructed during mining that are left at closure and how they are intended to perform. Completion criteria are used to demonstrate, in an unequivocal manner, that closure landforms have achieved the objectives of the PMLU, and are likely to do so into the foreseeable future. Pit lakes are no different, although as a drastic change of the previous land use, defining their (re)purposing and suitable criteria to demonstrate these purposes are more challenging than for other legacy landforms. However, there are many factors and influence to consider when deciding what constitutes useful completion criteria for any mine closure landform.
Our work undertaken in review and revision of leading company closure plans consistently shows some key areas for improvement to meet both jurisdictional guidance and also international industry good practice.
Legislation
Most MCPs include relevant regulations for both mining and non-mining in their “Legislative Framework” section. However, this section is often little more than a review of what regulations might exist regarding the mine, with minimal discussion on how the resulting obligations and legal frameworks may influence closure processes and outcomes. The MCP should demonstrate that stakeholder requirements and commitments have not just been captured, but also fully understood and followed in closure planning, for example, in final landform design and in relation to any requirements for rehabilitation.
Planning should also aim to address not just current regulations, but also likely changes in regulation and community expectations. Recent inter-state and international changes often permeate across to other mining jurisdictions. In particular, the MCP should detail obligations with actionable plans on how to achieve the discharge of liability through criteria. The MCP should be updated to include details on how the MCP proposes to comply with these frameworks, an understanding on how the frameworks have evolved and are anticipated to evolve so that the MCP can consistently maintain compliance. This update should take the form of an obligations/commitments register that is routinely updated through the life-of-mine of the project.
Stakeholder engagement
Best practice for closure planning completion criteria is to include engagement of stakeholders that are relevant to the pit lake. Stakeholders will be both internal and external, from mine planning teams working at the site, to external community groups and regulators. Stakeholder engagement for developing and refining criteria can be organised via workshops throughout the development of the MCP to ensure appropriate scope, inclusion of sufficient data and review of MCP.
The MCP should always demonstrate that external stakeholders, including communities, regulators, landowners, and others, have been involved in the development of success criteria, and should show a documented agreement in place as to what the criteria are.
Siloing
The many subject matter experts (SMEs) involved in developing the documentation that contributes to pit lake closure planning in an MCP are often “siloed”, with little interaction between various technical disciplines. This can particularly be so when an MCP is written largely by a single individual (often a third-party consultant). It is important that, even with an MCP author of good technical breadth, that SMEs review and contribute to their relevant sections. Ideally, MCP chapters should be reviewed by all relevant SMEs to ensure that their technical discipline, and often even their own work, has been accurately synthesised. A multi-author MCP is a great MCP!
Achievability
It is important to ensure that criteria are achievable during the closure phase. However, if criteria are not achievable; then the MCP needs to:
- establish more practicable criteria as an alternative; or,
- undertake management action to ensure criteria are achieved.
Revisiting completion criteria when they have been found to be unachievable or otherwise unsuitable can seem to feel like the previous criteria failed. However, it is important to remember that closure guidelines recommend regular revision of criteria as required. Revising and otherwise updating completion criteria should be seen as a good thing, as it means that criteria meaningful to the success of closure are being critically evaluated; and that closure is not just being left to run its course with a belated assessment of whether objectives will be able to be achieved.
Regardless of whether criteria are maintained or revised, the MCP should always reference an up-to-date and appropriately detailed knowledge pool when updating criteria or suggesting required management.
Leading indicators
Although criteria are typically thought of as “lagging” indicators showing that closure objectives have been achieved, “Leading” indicators should be incorporated where available so that problems can be identified quickly and resolved before the turn into larger more costly and difficult issues. For instance, water level as a pit lake fills can be a leading indicator of long-term water quality. If monitored water level rise is accurately predicted by water level modelling, then there can be more confidence that the water balance modelling underpinning both is also likely to be reliable. Equally, erosion rates will predict later revegetation success on slopes, so loss of topsoil, gullying, etc. are all good leading indicators for revegetation success as well as lagging criteria in their own right.
Conclusions
Awareness of these key weaknesses in many current closure plans can provide for improvement opportunities. In particular, ensuring that an MCP is not an end goal in itself, but rather a means to the end. The end of mining, and the beginning of a new purpose for the project area and surrounds.