Authors: Richardson, DL; Heeley, B; Rissik, D; Iles, M

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Richardson, DL, Heeley, B, Rissik, D & Iles, M 2022, 'Application of a vulnerability assessment framework to assess environmental risks of solutes at Ranger Mine, Northern Territory, Australia', 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. 613-622,

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Energy Resources of Australia Ltd (ERA) is planning the closure of Ranger Mine. An ecological vulnerability assessment framework (VAF) was applied to water quality modelling results to understand the potential effects of magnesium (Mg) in mine affected waters on aquatic ecosystem values within the mine site. The VAF assessed three elements: (i) understanding contaminant exposure, which was based on water modelling and species/community (ecological component) distributions; (ii) sensitivity of the ecological component to the contaminant, as determined from laboratory ecotoxicity experiments and field-based studies (monitoring, mesocosm experiments), and (iii) the recovery capacity of the ecological component, based on a review of the traits of ecological components. The VAF was applied to four waterbodies – two billabongs and two seasonal creek sites. The VAF identified that at three of the waterbodies, only the most sensitive algae and invertebrates were predicted to be intermittently affected by Mg, but would recover during periods of low Mg. All other ecological components (including other invertebrates, plants, fish and other vertebrates) at these three waterbodies had low vulnerability. Results for the fourth water body indicated that most ecological components were potentially vulnerable to predicted Mg concentrations. The assessment findings for the fourth water body had low confidence due to knowledge gaps regarding the sensitivity of some ecological components, especially aquatic plants on which most species depend. The VAF findings were applied in conjunction with an environmental risk assessment to identify where closure strategies for contaminant management needed review and inform decisions on whether impacts from those strategies would be as low as reasonably achievable (ALARA).

Keywords: aquatic ecosystems, water quality, risk

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