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
65 that of the stockpile. This is considered conservative because it ignores the substantial input of relatively good quality water from the mine. The resulting estimates of the concentrations of the various constituents in the water retention pond are given in table 5.3.3. Overtopping of the pond The probability of the pond overtopping in the absence of contingency measures can be derived from figure 5.2.1 using a volume equal to the total volume of the pond including the freeboard volume. For a total depth of 9.5 m (PER p 452) the pond volume would be 855,000 m3. From figure 5.2.1, the exceedence probability for this volume over the life of the mine is about 0.0005 or 5 in 10,000. The radiological impact on people living downstream from the mine, and consuming traditional foods collected from downstream waterbodies, has been estimated following the procedures outlined in section 5.3.2. It was assumed that overtopping of the dam would, in the absence of an engineered spillway, lead to structural failure of the pond embankment and all of the water in the pond, 855,000 m3, would be discharged to Swift Creek. The concentrations of radionuclides given in table 5.3.3 were multiplied by this water volume to obtain the loads of each nuclide and the dose conversion factors for the Ranger radiological assessment model from Martin et al (1998) were used to estimate the radiation dose for each radionuclide. These doses were added to obtain the overall dose estimate of 150 Sv. Thus, even for this catastrophic event, the expected dose received by members of the public would not be greater than 15% of the annual limit recommended by the International Commission on Radiological Protection. The ecological impact in Swift Creek resulting from overtopping of the pond will depend considerably on the flow conditions in the creek at the time of dam failure and the time taken to drain the dam. Since such an event could only occur towards the end of a very exceptional Wet season, it would be expected that creek flow would be relatively high. However, assuming that the flow in the creek would be equal to the average Wet season flow (about 3.5 m3/s, and that the time taken to drain the dam is 12 hours, the total volume of creek water in which the dam water would be diluted would be about 150,000 m3 which is small compared to the volume of water in the pond. Hence, the concentrations of uranium, magnesium and sulphate in the creek during this time would be those given in table 5.3.3. Both the Mg and SO4 concentrations would, therefore, be lower than the concentration limits given in table 5.3.2 and, while greater than natural concentrations, would not be expected to cause significant impact on ecosystems. The uranium concentration in table 5.3.3 is higher than the Lowest Observed Effect Concentration for hydra viridissima given in table 5.3.2 and effects on some aquatic animals could, therefore be expected in Swift Creek. However, from the results of Bywater at al (1991) and Holdway (1992) effects on fish would not be expected. In terms of broader ecological impact on the wetlands of Kakadu National Park, the water from the pond would be diluted in floodplain waters until concentrations of uranium become lower than 190 g/L. During the Wet season, the depth of water on the floodplain is about 2 metres. Hence the maximum affected area of the floodplain for a discharge of 855,000 m3 would be 1.8 km2. Thus, in the case of overtopping the retention pond, there is a risk of about 5 in 10,000 that an area that is about 1% of the Magela floodplain would experience some adverse effects on aquatic animals. Fish and many other species would not be affected. Between about 2 km2 and 20 km2, adverse effects may persist but beyond 20 km2 no effects should be observed. In addition, any effects will be transitory and the system would fully recover following flushing by the natural waters of the Magela Creek.