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
46 probability over the life of the mine was not quantified but it would be expected to be less than 0.3% and probably about 0.1%. In both the Supplement to the EIS and the PER, ERA used Monte Carlo calculations to simulate 10,000 years of rainfall and then chose specific extreme sequences of wet years to determine the maximum storage required. The probability of the occurrence of the particular sequences used was not quantified but would be expected to be considerably less than 0.1% over the life of the mine and may have been expected to approach 0.01%. The approach that has been adopted in this review has been to determine the storage volume required to achieve a range of exceedence probabilities and then to perform a risk assessment for the protection of people and downstream ecosystems. The range of exceedence probabilities calculated is from about 10% to 0.002% over the life of the mine. The lowest value was chosen to ensure adequate precision for the storage volume required to achieve an exceedence probability of 0.01%. This procedure is one that not only enables the adoption of a risk assessment approach but it also enables a quantitative comparison with the outcomes of the results obtained by ERA. 5.2.2 Water balance modelling Water balance modelling has been carried out by the University of Melbourne (Chiew & Wang 1999, Attachment D) to assess the Jabiluka Mill AlternativeOriginal Concept as described in the PER but with the exclusion of the tailings ponds in that proposal. The reason for this choice is, as stated above, that the modified Original Concept is likely to be very similar to the amended proposal from ERA and because the results of modelling in this review can be compared quantitatively with the results obtained by ERA in the PER. The catchment areas within the Total Containment Zone, including the pond area of 9 ha, water input from mine dewatering and the water losses through mill consumption, ore and plant washdown, evaporation in the mine ventilation system and dust suppression were assumed to be those estimated by ERA in Appendix B1 of the PER. Ventilation system evaporative losses The feasibility of achieving the predicted losses by evaporation in the mine ventilation system has been assessed in section 3.4 where it was concluded that, unless a very expensive humidifier system is installed, the actual losses will be less than assumed by ERA. Nevertheless, ERAs estimates have been used in the modelling, partly because the modelling was being carried out simultaneously with the assessment of mine ventilation losses, but also because it was considered important to use ERAs assumptions so that a meaningful comparison with ERAs conclusions could be achieved. In the ERA water balance simulations, a constant ventilation loss was assumed throughout the year. However, the evaporation potential through the ventilation system is greater in the Dry season than in the Wet season because of the greater moisture deficit in the Dry season. This was taken into account by attributing 16% of the total water disposal from the ventilation system to the four wettest months (December to March) and the remaining 84% to the other months, as suggested in the Jabiluka PER Appendices (page B19). Runoff The runoff calculations used by ERA in its hydrological modelling were assessed by Chiew and Wang (1999) and it was concluded that they were very conservative. The same runoff coefficients were, therefore, used in the current review. However, Chiew and Wang (1999) used a water balance model to simulate the rainfall-runoff process in which the soil water storage capacity is the only parameter, and this parameter is optimised such that the total
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