The future of the past: rational closure for legacy sites

Authors: Meikle, CD Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2515_07

Cite As:
Meikle, CD 2025, 'The future of the past: rational closure for legacy sites', in S Knutsson, AB Fourie & M Tibbett (eds), Mine Closure 2025: Proceedings of the 18th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-13, https://doi.org/10.36487/ACG_repo/2515_07



Abstract:
The application of contemporary closure performance standards to legacy mine landforms presents significant technical and regulatory challenges. Evolving stakeholder expectations regarding long-term geotechnical stability, environmental performance and post-mining land use frequently conflict with the physical constraints, data limitations and design uncertainties inherent to legacy sites. This paper presents selected case studies to illustrate closure decision-making in the context of such constraints and examines the role of risk-based frameworks in guiding proportionate closure responses. A key constraint is reconciling contemporary factors of safety with the limited geotechnical data typically available for historical landforms. Slopes historically regarded as stable often lack sufficient evidence to demonstrate ongoing performance against current standards, prompting costly investigations and, in some cases, complex or invasive remediation. Determining appropriate remedial actions is particularly nuanced where closure criteria are undefined, original designs are unavailable or future land uses remain uncertain. These uncertainties can result in interventions that generate additional disturbance or introduce new environmental risks, contrary to closure objectives. Uncertainty around post-mining land use(s) significantly complicates the definition of closure performance criteria. Many legacy landforms were constructed without an intended post-closure function and their potential repurposing, whether under a new tenure, a native ecosystem or industrial re-use, remains undefined. The concept of “designing for relinquishment” introduces further complexity by requiring clear performance thresholds for the transfer of liability, which may not be practically achievable under legacy conditions. In the context of mine waste landforms, the direct application of contemporary standards such as the Global Industry Standard on Tailings Management is often infeasible. The conservatism embedded within these frameworks, while appropriate for new facilities, may be disproportionate when applied retrospectively. This paper explores the growing use of pragmatic, risk-informed approaches such as ALARP (as low as reasonably practicable), which allow for performance-based assessments that maintain acceptable risk thresholds while acknowledging natural landform evolution and the diminishing hazard profile of aged structures. It is argued that regulatory frameworks must accommodate flexibility and proportionality in closure expectations. Imposing prescriptive standards without consideration of a legacy context may delay closure, increase long-term liability and divert resources from higher-risk or higher-value interventions. A tiered, riskbased regulatory model is proposed as a pathway to enable fit-for-purpose closure outcomes. This paper advocates for adaptive closure strategies that integrate geotechnical, environmental and land use considerations within a risk and performance-based design framework.

Keywords: legacy, stability, regulatory, ALARP, GISTM, mine waste, tailings

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