Authors: Sweeney, J; O'Farrell, C; Crosbie, J; Osgerby, B

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Sweeney, J, O'Farrell, C, Crosbie, J & Osgerby, B 2022, 'A risk-based framework for assessing non-metalliferous contamination prior to closure at MMG Rosebery Mine, Tasmania', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 281-294,

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Mining operations often have long and complex development histories, which results in equally complex site contamination risks when approaching closure. In many cases, the environmental monitoring conducted during operation only targets the contaminants of concern associated with mineral concentrates, processing reagents, and metalliferous drainage from mine waste. At closure, the focus of environmental assessment expands from preventing offsite impacts from mineral contaminants to assessing potential impacts from all activities and contaminants used during operations based on the site’s intended future use. Therefore, the greatest environmental data gaps at closure can often be due to contaminants perceived to be a lower risk, many of which are common across all mines and industrial facilities. A risk-based framework has been developed to assess the contamination not associated with mineralised waste or mineral concentrates at MMG’s Rosebery Mine in Tasmania. The site has been operating continuously for over 85 years and is currently scheduled to cease operations in under a decade if additional tailings storage capacity cannot be secured. The assessment framework adopts a phased, risk-based approach that employs a range of assessment techniques that can be implemented prior to closure in a staged and cost-effective process, which does not affect current operation, including: Comprehensive site history and source risk-ranking tool. Ground penetrating radar. Groundwater investigation as a tool to assess contamination migrating from suspected source areas inaccessible during operation. Targeted soil assessments. Passive soil vapour. Per- and poly-fluoroalkyl substances (PFAS) fingerprinting. The presentation will draw on examples from the contamination assessment for the Rosebery closure prefeasibility study where 76 features associated with mining infrastructure or operational practices have been identified with the potential to have resulted in soil, surface water, or groundwater contamination by nonmetalliferous contaminants. Of the 76 potential source areas, 64 were identified to have a moderate or higher risk to protected environmental values, and where further assessment and possibly remediation may be required to support relinquishment of the site. The risk-based approach identified a shortlist of priority features where a release of contamination may have occurred, and where early investigation and intervention was both feasible and beneficial due to an expanded range of remedial options. This presentation demonstrates the value of establishing a robust assessment framework early in a closure study so that a cost-effective, staged approach to contaminant assessment and remediation can be delivered to satisfy regulatory, internal and other stakeholder requirements. This proactive risk-based assessment approach provides opportunities to minimise future environmental impact, reduce total remediation costs, support stakeholder engagement and provide greater certainty for closure options, cost and schedule.

Keywords: contamination, pre-closure, remediation, risk assessment

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