Iles, M & Rissik, D 2022, 'Risk-based contaminant management: Ranger Mine case study', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: 15th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 633-644, https://doi.org/10.36487/ACG_repo/2215_45
The Ranger Mine, operated by Energy Resources of Australia Ltd (ERA), is in a sensitive area in Australia’s Northern Territory. It is surrounded by (but separate from) Kakadu National Park (KNP) World Heritage Place and Ramsar wetland. Closure requirements include protecting the KNP values and health of the local people. Impacts from water and tailings contaminants must be as low as reasonably achievable and cause no detrimental impact to the biodiversity or ecological processes of the region. The Indigenous landowners, the Mirarr people, wish to resume cultural activities, including sourcing food, at the site after closure.
A source-pathway-receptors approach and a deep dive into environmental exposures and consequences were used to assess the risks from multiple contaminant sources and water pathways for up to 10,000 years after closure. The most hazardous contaminants were identified by comparing measured and modelled water and sediment concentrations against multiple guidelines for human health and ecosystem endpoints reflecting the regulatory environmental requirements for closure and the aspirations of ERA and its stakeholders.
Prioritised actions were identified to manage contaminant sources, including a review of key modelling assumptions influencing outcomes, targets for process water treatment and decommissioning plans for plumes and contaminated soils around the tailings storage facility.
The assessment used evidence from monitoring, ecological response studies and modelling. Risk descriptors were developed to match the evidence types and frequencies at which guideline values might be exceeded, giving a deep insight into impacts. This case study shows how to modify standard risk assessment tools to match different types of evidence, including probabilistic outcomes solute transport models. The water quality discussed in this report is not that expected after closure. The process discussed here has driven actions to improve water quality on, and downstream of, Ranger Mine after closure. The process can be applied iteratively to revise contaminant management plans thus improving water quality following closure.
Keywords: risk assessment, ecological vulnerability, as low as reasonably achievable (ALARA), closure criteria
ANZG 2018, Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Governments and Australian state and territory governments, www.waterquality.gov.au/anzguideline
Bartolo, R, Paulka, S, van Dam, R, Iles, S & Harford, A 2013, Rehabilitation and Closure Ecological Risk Assessment for Ranger Uranium Mine: Documentation of Initial Problem Formulation Activities, internal report 624, Supervising Scientist, Darwin.
Commonwealth of Australia 2000, s.41 Authority, Environmental Requirements of the Commonwealth of Australia for the Operation of Ranger Uranium Mine,
Dear, SE, Ahern, CR, O’Brien, LE, Dobos, SK, McElnea, AE, Moore, NG & Watling, KM 2014, Queensland Acid Sulfate Soil Technical Manual: Soil Management Guidelines, Queensland Government, Brisbane.
Doering, C, Carpenter, J, Orr, B & Urban, D 2019, ‘Whole organism concentration ratios in freshwater wildlife from an Australian tropical U mining environment and the derivation of a water radiological quality guideline value’, Journal of Environmental Radioactivity, vol. 198, pp. 27–35,
Energy Resources of Australia Ltd 2020, 2020 Ranger Mine Closure Plan, viewed 10 December 2020,
Kumar, D & Reid, S 2021, Ranger Project Area 2020/2021 Sediment Investigation Programme: Metals in Sediments Interpretive Report, report CDM.03–1114-NB-REP-00004, Energy Resources of Australia Ltd, Darwin.
Iles, M 2022, ‘Multiple frameworks informing closure criteria at Ranger Mine’, in M Tibbet, AB Fourie & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Mine Closure Conference, Australian Centre for Geomechanics, Perth,
Iles, M & Rissik, D 2021, Ranger Closure Aquatic Pathway Receptors Risk Assessment, Energy Resources of Australia Ltd and BMT report, CDM.03–1114-MR-RAS-00001, version 0.
INTERA 2021, Final Report: Groundwater Uncertainty Analysis for Ranger Mine Closure, report for Energy Resources of Australia Ltd.
Pollino, CA, Cuddy, SM & Gallant, S 2013, Ranger Rehabilitation and Closure Risk Assessment: Problem Formulation, CSIRO Water for a Healthy Country Flagship, Canberra.
Supervising Scientist 2021a, Uranium and Manganese in Surface Water — Rehabilitation Standard for the Ranger Uranium Mine (Version 2), Supervising Scientist Branch, Darwin, viewed 9 June 2021,
Supervising Scientist 2021b, Magnesium in Surface Water — Rehabilitation Standard for the Ranger Uranium Mine (Version 2), Supervising Scientist Branch, Darwin, viewed 9 June 2021,
Supervising Scientist 2021c, Ammonia in Surface Water — Rehabilitation Standard for the Ranger Uranium Mine (Version 1.1), Supervising Scientist Branch, Darwin, viewed 9 June 2021,
Supervising Scientist 2021d, Copper and zinc in surface water — Rehabilitation Standard for the Ranger Uranium Mine (Version 1), Supervising Scientist Branch, Darwin, viewed 9 June 2021,
Supervising Scientist 2021e, Sulfate in Surface Water — Rehabilitation Standard for the Ranger Uranium Mine (Version 1.1), Supervising Scientist Branch, Darwin, viewed 9 June 2021,
Supervising Scientist 2021f, Uranium in Sediments — Rehabilitation Standard for the Ranger Uranium Mine (Version 1), Supervising Scientist Branch, Darwin, viewed 9 June 2021,
Water Solutions 2021, ERA Ranger Mine Closure: Ranger Surface Water Model – Model Upgrade, Doc Number WS200149, Revision C, draft report to Energy Resources of Australia Ltd, Darwin.