Conceptual models of stressor pathways for the operational phase of Ranger Uranium Mine
Internal Report 612
Supervising Scientist Division
Bartolo R, Parker S, van Dam R, Bollhöfer A, Kai-Nielsen K, Erskine W, Humphrey C & Jones
Department of Sustainability, Environment, Water, Population and Communities
- Conceptual models of stressor pathways for the operational phase of Ranger Uranium Mine (PDF - 6.95 MB)
- Sections 1-3: Conceptual models of stressor pathways for the operational phase of Ranger Uranium Mine (DOCX - 23.75 MB)
- Sections 4.1-4.5: Conceptual models of stressor pathways for the operational phase of Ranger Uranium Mine (DOCX - 47.42 MB)
- Sections 4.6-4.9: Conceptual models of stressor pathways for the operational phase of Ranger Uranium Mine (DOCX - 29.88 MB)
- Sections 5-6: Conceptual models of stressor pathways for the operational phase of Ranger Uranium Mine (DOCX - 65.59 KB)
Conceptual models of potential stressor pathways associated with uranium mining in the Alligator Rivers Region (ARR) have been developed as part of the evolving ecological risk assessment framework that was started by the Supervising Scientist in the early 1980s. In response to recommendations by the World Heritage Commission Independent Scientific Panel and the Alligator River Region Technical Committee (ARRTC), a specific project was initiated to produce a comprehensive conceptual model of stressor pathways associated with the operational phase of the Ranger Uranium Mine (RUM).
Development of a new conceptual model of stressor pathways associated with the operational mining phase was commenced in 2004. The primary purpose of the conceptual model was to place off-site environmental impact issues associated with the operational phase of mining at RUM into a risk management context. Sub-models for the multiple stressor pathways identified in the conceptual model were not finalised at that time. This project presents sub-models and supporting narratives for each of the stressor pathways identified in the conceptual model of stressor pathways for the operational mining phase. An assessment of the relative importance of each pathway in terms of its potential to cause adverse ecological effects to the off-site environment of the ARR was conducted using an expert panel approach.
A standard 3 x3 scoring matrix was developed with the magnitude of the assigned score being based on (a) the size/potential maximum generating capacity of the relevant stressor source (high, medium, or low); and (b) the potential maximum capacity (load and rate) of the relevant pathway to transport stressors from the mine site to the surrounding environment (high, medium, or low). The current level of scientific certainty based on existing research and monitoring information (high, medium, or low) and the current level of adverse ecological impact on receptors based on results from monitoring (yes, no or unknown) associated with each stressor pathway was also determined and is reported here. This report has been compiled so that the reader may select a single stressor/pathway of interest from the document and it will be able to be read as a stand-alone narrative. Therefore, if reading the report in sequence from start to finish, there will appear to be repetitive text between stressors/pathway narratives.
Five stressor pathways were assessed as being of high importance: i) inorganic toxicants via the surface water to surface water pathway; ii) inorganic toxicants via the airborne emissions pathway; iii) radionuclides via the surface water to surface water pathway; iv) radon-222 and radon decay products pathway; and v) transported sediments via the surface water to surface water pathway. For four of these five pathways the available comprehensive monitoring data indicates no detectable adverse ecological impact on the environment outside of the mining lease. For the case of the remaining pathway (inorganic toxicants via the airborne emissions pathway and impact on biota from the radon-222 and radon decay products pathway) it was judged that there was insufficient evidence to say that there was no measurable environment impact.
Three of the five pathways assessed as being of high importance relate to the transport of stressors via the surface water to surface water pathway. This is not unexpected given that the surrounding surface water systems are the primary potential receptors of stressors released in runoff from the mine site.
The relative importance of each pathway was assigned based on the unmitigated potential of the pathway to transport stressors from the mine site into the surrounding environment. However, this does not mean that high importance pathways are resulting in, or are likely to result in, impact on receptors within the ARR environment. The actual volume (load) of stressors transported by these pathways at any time (and therefore the level of potential risk to receptors) depends on a range of chemical, biological, physical, and radiological factors and the effectiveness of existing management controls. These latter control measures are designed to reduce risks to the environment to acceptable levels either by containing stressors on the mine site or minimising the volume and availability of stressors that may be transported via the various pathways. Given the importance of these controls, details about the risk mitigation measures applicable for each contaminant pathway have been included in the model narratives produced for each of these pathways.
The assessment identified some knowledge gaps which may be fed into the ARRTC Key Knowledge Needs (KKN) framework following further consideration. Key amongst these was a lack of knowledge about the fate of organic toxicants, for example, hydrocarbons and pesticides used on site; and inorganic toxicants from the mine site stacks, storage tanks and pipes. The specific issue for the organics is that these species have not been analysed, even at a screening level, in the water that exits at the site. Hence no specific assessment can be made about potential for impact, despite this likely being a no or low impact issue. In the case of the inorganic toxicants, emissions from the stacks are monitored by ERA Ltd. One additional factor that could also warrant closer attention is the potential for transport of weeds off site, despite the existence of an active weed identification and control program.
While knowledge gaps exist for some pathways and stressors, there is no evidence to suggest that any of these pathways are currently resulting in adverse ecological impacts on the environment within the ARR. Results of ongoing chemical, radiological and biological monitoring undertaken by the Supervising Scientist continues to show that the environment of the ARR remains protected from uranium mining related impacts via the aquatic pathway (the dominant potential vector) and from airborne radionuclides in the case of human health protection. This work will also inform the future development of conceptual models of stressor pathways associated with the mine closure and rehabilitation phases of mine life. The closure pathways conceptual model will inform and assist the development of closure criteria and the specifying of the monitoring framework needed to address them.