Authors: Welideniya, S; Tucker, N; Mesquita, A

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Welideniya, S, Tucker, N & Mesquita, A 2023, 'Open pits, underground mines and tailings storage facilities—geotechnical and legislative aspects at closure in Western Australia', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth,

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All mining proposals (MP) submitted with mine closure plans (MCP) to be accepted by the Department of Mines, Industry Regulation and Safety (DMIRS) in Western Australia (WA) must comply with strict engineering, environmental and legislative requirements, as overseen by the regulatory agency, WorkSafe Western Australia. To meet all legislative requirements, including engineering and environmental laws, mine closures must face and meet these challenges. The Work Health and Safety Act 2020 (WHS Act), the Work Health and Safety (Mines) Regulations 2022 (WHS Mines Regulations), the Mining Act 1978, the Mining Regulations 1981 and the Environmental Protection Act 1986 provide clear and consistent guidelines for exploration, design and construction, operation, and closure of mines across WA. The Mining Act 1978 requires mining activities to be rehabilitated and closed in a manner that leaves the land safe, stable and non-polluting without unacceptable liability to the state. A mine closure plan is required under the Mining Act 1978 and enforced via tenement conditions applicable to the mining lease. Traditional land owner’s involvement on the land used for mining applies from the beginning of the project during the exploration and mining phases and continues onto the closure considering post mining land use which may also include the land access for cultural and ceremonial use. The legislation regarding mining and environmental protection were also developed with the intention of minimising environmental damage, enforcing professional commitments on ore reserve exploitation and upholding traditional land owner’s interests to their lands. When planning the post mining closure of open pit mining operations many geotechnical engineering aspects related to perpetual pit slope stability, the stability of waste dumps, pit lakes and access controls using abandonment bunding for the safety of people as well as wildlife will need to be applied. Planning for the closure of underground mines, depending on the mining method, will need to address the elimination of any potential unplanned subsidence by well-proven geotechnical modelling. Other areas to address may be impacts on changes to the surface water flow and ground water table and inadvertent access to any mining areas through shafts or portals. Dealing with tailings facilities could be the most challenging aspect of a mine closure. The mine closure plan regarding tailings will need to address embankment stability, ground water contamination and liquefaction potentials, seepage and dust. The closure will be required to promote the regrowth of natural endemic plants that were impacted by the mining operation in order to bring the location back to the pre-mining natural environment as much as possible. Tailings could contain materials having the potential of acid mine drainage (AMD) which will need to be effectively managed to prevent any environmental impacts.

Keywords: geotechnical, underground, open pit, tailings, subsidence, mine closure, WHS, environmental, AMD, stability, liquefaction, tenements

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