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
8 If a properly engineered spillway were installed in the wall of the retention pond, the dam would be protected from destruction under overtopping. This would result in the loss of much lower volumes of water over a longer period and would fully protect both Swift Creek and the Magela floodplain under the conditions considered here. It is recommended that such a spill-way be incorporated in the design of the retention pond. Risks associated with slope failure of the embankment of the water storage pond The probability of slope failure is estimated to be less than the probability of overtopping which was estimated above to be about 5 in 10,000. Since slope failure would only arise under circumstances similar to those considered for overtopping, the estimates of environmental impact derived above for overtopping would also apply to slope failure. Risks associated with a severe earthquake Over the period of the mine life, the probability of structural failure of the water retention pond arising from a severe earthquake has been estimated to be approximately 5 in 10,000. In deriving this estimate, only local and regional earthquakes were considered. The frequent but distant large earthquakes in the Banda Sea, Indonesia, should be considered in the design of a water retention pond since they give rise to many cycles of ground motion. It is recommended that ERA commissions such a study at the detailed design stage of the Jabiluka project. The risk of radiation exposure of members of the public resulting from such an earthquake would be extremely low. At the 1 in 10,000 level of probability, the estimated radiation exposure is about 30 Sv. The highest calculated exposure, which is less than one tenth of the internationally accepted limit, has an extremely small exceedence probability. For an earthquake that occurs in the Wet season, the maximum area of the Magela floodplain in which adverse effects on some aquatic invertebrates might be expected is about 1.5 km2 but the probability of this occurring is extremely small. The area affected at the 1 in 10,000 level of probability is less than 0.5 km2 which is less than 0.3% of the floodplain area. At the same level of probability, residual effects may occur for some species of invertebrates out to an area of about 5 km2. Even within these areas, the impact would be small (for example, fish should not be affected) and the system would fully recover following flushing by the natural waters of the Magela system. If an earthquake occurs in the Dry season, the area of impact would be greater. Nevertheless, the probability of such effects occurring remains very low and the system would recover during the following Wet season. Contingency measures It is recommended that runoff from the ore stockpile should be isolated from runoff from the remainder of the Total Containment Zone so that it is always directed to the water retention pond while, under extreme conditions, runoff from the rest of the TCZ is diverted away from the storage pond. This measure would reduce still further the risk associated with exceeding the capacity of the storage pond. It is recommended that the water retention pond be constructed with a properly engineered spillway to ensure that, even if diversion contingency measures fail, the pond structure would not fail when the overtopping height is reached. This would reduce substantially the impact arising in the event of overtopping because only a small volume of water would be released to the environment rather than the full volume of the pond.