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
9 Long-term storage of tailings Erosion of tailings in the long-term Once the Jabiluka mine is backfilled and sealed following completion of mining, the only mechanism for physical dispersal of the tailings solids will be erosion of the overlying bedrock. Since the mine void and the tailings silos will be about 100 m below the surface and the upper surface of these storage facilities will be below sea level, the whole land mass would need to be eroded away and by that time the wetlands of Kakadu would no longer exist. Thus, physical dispersal of the tailings does not pose a threat to the wetlands of Kakadu. The time required to erode the bedrock overlying the tailings in the mine void and the silos would be about 2 million years. Hence, the excess concentrations of all the radioactive progeny will have decayed away by the time the tailings are exposed and they will be in equilibrium with the residual uranium. Dispersal of tailings in the very long term will not constitute a hazard for future generations. Hydrogeological features of the area The permeability of the Cahill Formation schists west of the orebody is significantly greater than that of the Kombolgie sandstone to the east. For this reason, it is recommended that the additional tailings silos should be excavated in the Kombolgie sandstone east of the orebody, as is currently planned by ERA. This choice of location will minimise potential environmental impacts. The excavation of the silos will result in additional material being placed on the surface. The location of the silos in the sandstone rather than in the schists to the west is also preferable from the perspective of minimising environmental hazards on the surface because the sandstone is relatively low in the concentrations of hazardous chemicals. This material will require additional attention during the rehabilitation phase, but control of potential impacts on surface waters will be straightforward. The quality of groundwaters in the vicinity of the Jabiluka orebody, both to the west in Mine Valley and to the east towards Swift Creek, is high. Soluble salt concentrations are relatively low and radionuclide concentrations are very low. It is concluded that there is very little movement of radionuclides into the groundwater aquifer from the orebody. In contrast, the groundwater underlying the acid sulphate soils of the Magela floodplain is of high salinity, is acidic, and has high sulphate concentrations. The observed natural sulphate concentrations are up to one third of the concentration of sulphate expected in the Jabiluka tailings. Modelling of the dispersion of solutes in groundwater A two dimensional finite element model was used to determine flow directions, head distributions and the range of velocities. A three dimensional numerical solute transport model was applied to determine the concentrations of solutes leached from the tailings paste material for use as the source concentrations in an analytical model. An analytical contaminant transport model was used to determine concentrations due to advection, dispersion in three co-ordinate directions and retardation. This model used as input the range of velocities and source concentrations determined from the first two models. This model was combined with Monte Carlo calculations to determine
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