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
35 Following completion of mining, all water in the water retention ponds will evaporate over a period of a few years. This will be possible because, on an annual average basis, true pond evaporation exceeds rainfall by about 500 mm per annum. Once the ponds have been evaporated to dryness, all contaminated sediment in the ponds will be collected and placed underground with the tailings. The pond structures will then be rehabilitated. There will be no water retention ponds following rehabilitation. For these reasons, the strongly worded criticism in Wasson et al (1998) that the proponent has assumed stationarity of climate over a period of 10,000 years is quite without foundation. 4.3 Probable maximum precipitation events The submission of Wasson et al (1998) notes that the criteria for design of bunds to prevent water from catchments adjacent to the TCZ entering the containment zone are conservative. These included the adoption of runoff coefficients of one and adoption of the 6-minute PMP as the design storm intensity. Similar positive comments were made about the design criteria to prevent water within the TCZ overtopping the containment bunds. They note, however, that PMPs over a 10,000 year period would probably be much greater. This issue has been addressed in the previous section where it was concluded that a 10,000 year period is not relevant to the design of surface structures. ERA gives a value for the 6-minute PMP in the Draft EIS but does not explain its origin. For this reason, the Supervising Scientist requested that a review of PMPs for the region be conducted by the Bureau of Meteorology. The results of this review are given in Bureau of Meteorology (1999). Point value PMPs for durations from 15 minutes (the minimum value normally calculated) to six hours were calculated for Jabiluka using the Generalised Short Duration Method (GSDM, Bureau of Meteorology 1994). Then, each PMP (depth in mm) was converted to intensity (mm/hr) and plotted against duration using linear scales. The best-fit to this intensity vs duration curve was a power law (R2 = 0.99). The curve was extrapolated back to obtain an estimate of the 6-minute intensity of 1380 mm/hr. A second approach adopted was based on the Intensity-Frequency-Duration (IFD) ratio. IFD information was produced for the nearest grid point to Jabiluka. For 100 year IFD, the ratio of the 6-minute to the 15-minute intensities was calculated. The 15-minute PMP intensity was then multiplied by this ratio to obtain an estimate of the 6-minute PMP of 1320 mm/hr. These two estimates of the 6-minute PMP differ by less than 4%, leading to some confidence in the estimate. In the interests of conservatism, the larger value of 1380 mm/hr is recommended. The 6-minute PMP intensity estimate adopted by ERA (Draft EIS, Appendix J, page J3) for the Jabiluka project is 1150 mm/hr, approximately 20% lower than the value recommended by the Bureau of Meteorology. It is recommended that the Bureau value be used in the detailed design of the Jabiluka project. A full set of PMP values appropriate for Jabiluka is provided by the Bureau of Meteorology (1999). The effect of climate change over the next 30 years is discussed in the next section. 4.4 Effect of climate change on hydrological modelling It was concluded in section 4.2 that the effects of climate change over the next 10,000 years need not be considered in the design of the surface water storage facilities at Jabiluka. However, what is required is that possible or likely variations in climate over the next 30 years are properly taken into account in the design of the water management system.