Authors: Richardson, DL; Bourke, G; Rissik, D; Fisk, GW; Iles, M

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Richardson, DL, Bourke, G, Rissik, D, Fisk, GW & Iles, M 2019, 'Development of a vulnerability assessment framework to evaluate potential effects of mine water discharges from Ranger Uranium Mine, Northern Territory', in AB Fourie & M Tibbett (eds), Mine Closure 2019: Proceedings of the 13th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1519-1532,

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Energy Resources of Australia Ltd (ERA) is planning the closure of its Ranger Uranium Mine (RUM), with decommissioning planned to conclude in 2026. One challenge for closure is understanding the potential impacts of solutes, such as magnesium, that will continue to discharge from the site via groundwater and surface water. ERA has commissioned a water quality modelling study to predict solute concentrations in the receiving environments post-closure. The authors developed a vulnerability assessment framework (VAF) to aid the interpretation of modelling results, with an initial focus on the potential effects of magnesium on environmental and cultural values (ECVs) of the mine area. This paper describes the approach used to develop the VAF and the preliminary findings of the assessment. The VAF involved the following steps: (i) identification of ECVs, including ‘key species’ that are important from biodiversity and cultural perspectives, as well as important habitats and other groups; (ii) development of conceptual models of key processes and linkages with ECVs; (iii) assessment of the direct (i.e. toxicity) and indirect (i.e. food resources and habitats) sensitivity of ECVs to magnesium; (iv) assessment of the adaptive capacity of ECVs. The VAF was based on multiple information sources including ecotoxicology assessments and field studies. A multi-disciplinary scientific advisory committee provided expert guidance and input into the vulnerability assessments. The preliminary results of this assessment indicated that all of the key species are largely insensitive to elevated magnesium concentrations (>10 mg/L). There are several functional groups that contain species that are sensitive to magnesium (<3 mg/L), especially algae and invertebrates. The resilience of these groups is a key focus of the vulnerability assessment noting many of the species have high adaptive capacity. Key knowledge gaps were identified, and work is planned for 2020-2021 to address these gaps and refine the VAF.

Keywords: magnesium, Kakadu, biodiversity, aquatic ecosystems

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