Assessment of the Jabiluka Project : report of the Supervising Scientist to the World Heritage Committee
Johnston, A.; Prendergast, J. B.; Bridgewater, Peter
E-Publications; E-Books; PublicationNT; Supervising Scientist Report; 138
Alligator Rivers Region
Main report--Appendix 2 of the Main Report. Submission to the Mission of the World Heritage Committee by some Australian Scientists ... --Attachment A. Johnston A. and Needham S. 1999. Protection of the environment near the Ranger uranium mine--Attachment B. Bureau of Meteorology 1999. Hydrometeorological analysis relevant to Jabiluka--Attachment C. Jones, R.N., Hennessy, K.J. and Abbs, D.J. 1999. Climate change analysis relevant to Jabiluka--Attachment D. Chiew, F and Wang, Q.J. 1999. Hydrological anaysis relevant to surface water storage at Jabiluka--Attachment E. Kalf, F. and Dudgeon, C. 1999. Analysis of long term groundwater dispersal of contaminants from proposed Jabiluka mine tailings repositories--Appendix 2 of Attachment E. Simulation of leaching on non-reactive and radionuclide contaminants from proposed Jabiluka silo banks.
Uranium mill tailings - Environmental aspects - Northern Territory - Alligator Rivers Region; Environmental impact analysis - Northern Territory - Jabiluka; Uranium mines and mining - Environmental aspects - Northern Territory - Jabiluka; Jabiluka - Environmental aspects
Supervising Scientist Report; 138
1 volume (various pagings) : illustrations, maps
https://hdl.handle.net/10070/462403; https://hdl.handle.net/10070/462400; https://hdl.handle.net/10070/462405; https://hdl.handle.net/10070/462406; https://hdl.handle.net/10070/462408; https://hdl.handle.net/10070/462409; https://hdl.handle.net/10070/462411
88 Predicted concentrations of solutes in the environment Modelling of the concentrations of solutes in the deep aquifer east of the tailings repositories in the direction of Swift Creek predicts that, after 200 years, sulphate concentrations should not exceed 20 mg/L even at distances as short as 100 m from the repositories. Uranium is not expected to move more than 50 m in 1000 years and for radium this distance is 15 m. The maximum distance moved by uranium under the most extreme (and very low probability) scenario considered in the Monte Carlo analysis is 300 m. Concentrations of uranium and radium at these distances will be negligible compared to naturally occurring concentrations. The transport of solutes to the west of the repositories is expected to be more rapid because of the higher permeability of the schists compared to that of the sandstone. Monte Carlo calculations indicate a probable migration distance of 500 m after 200 years for non-reactive solutes including sulphate, although greater distances are possible. The tailings derived solutes would be entering an area of already very poor quality water where natural sulphate concentrations are in the range 15007000 mg/L so that the impact of the migration of water from the tailings repository would be negligible. In addition, the floodplain is underlain by low permeability clays which act to limit any potential upflow of the groundwater into surface waters. The Monte Carlo calculations indicate that uranium is likely to travel up to 200 m in a westerly direction in about 1000 years at which point the concentration would be reduced to less than 1 mBq/L, a concentration that is significantly less than natural concentrations in the region. The calculations show that migration of uranium by up to 1200 m is possible but with a very low probability. It is concluded that radium and uranium will remain at background levels in the Magela floodplain. The groundwater modelling indicates that the upward component of groundwater flow is weak in both the groundwater movement to the east towards Swift Creek and to the west towards the Magela floodplain. The flow was found to be predominantly horizontal, implying that most of the solutes from the tailings repository will remain in the deep aquifer and move under the floodplain towards the sea. Only a small fraction of the groundwater in the deeper aquifer would be accessible to surface waters. All of the calculated groundwater concentrations discussed above refer to concentrations in the deep aquifer. Surface aquifer concentrations arising from the tailings repositories will be negligible. Any contaminants reaching the surface aquifer will be diluted and flushed away during the annual Wet seasons. The overall conclusion is that the wetlands of Kakadu will not be harmed as a result of the dispersal of tailings constituents in groundwater. Risk assessment on the long-term storage of tailings A risk assessment of the probable impact on people and the wetlands of Kakadu National Park arising from the long-term storage of tailings in the mine void and the silos has not been carried out to the extent conducted for storage of uranium on the surface. To carry out such an assessment would require the extension of the analysis of groundwater dispersion to the quantitative prediction, using Monte Carlo analysis methods, of the concentrations of solutes in the waters of the Magela floodplain and the probability with which these concentrations will occur. The range and quality of existing hydrogeological data do not enable such a detailed analysis to be carried out.