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
85 The Monte Carlo simulations conducted for uranium using a paste permeability of 10-9 m/s indicated a contaminant front would move 50m downstream to the east after 1000 yrs. The maximum computed distance (which the Monte Carlo simulations indicated was of very low probability) was 300 m. For this paste permeability, which is at the upper end of range considered in the risk assessment process, the uranium concentration just outside the silos is predicted to be about 2.7 Bq/L and at 45 m from the silos it is predicted to fall to less than 1 mBq/L. The latter value is much less than naturally occurring concentrations in groundwater in the region which are about 30 mBq/L. For the median result, the distance for radium transport to the east was less than 15 m at which point the concentration would be less than 1 mBq/L, again much less than naturally occurring concentrations. The transport of solutes to the west is calculated to be somewhat more rapid because of the greater permeability of the aquifer there. The velocities east of the divide in the sandstone are between 5x10-5 and 5x10-6 m/day, whilst in schists to the the west the range is 5x10-4 to 5x10-5 m/day. The results obtained for the migration of sulphate, uranium and radium to the west are shown in figure 6.3.6. These data indicate a probable migration distance of 500 m after 200 years for sulphate, although greater distances are possible (Kalf & Dudgeon 1999). Again, the three dimensional solute transport model shows that for a tailings permeability of 10-9 m/s, the sulphate source concentration immediately downstream from the mine void tailings would be about 2000 mg/L. The data in figure 6.3.6 show that the median concentration of sulphate would drop to less than 20 mg/L about 500 m downstream. This water would be entering an area of already very poor quality water (see section 6.3.1) where natural sulphate concentrations are in the range 15007000 mg/L so that the impact of the migration of water from the tailings repository would be negligible. In addition, the floodplain is underlain by low permeability clays (East et al 1992) which act to limit any potential upflow of the groundwater into surface waters. Figure 6.3.6 Variation of the median concentrations of SO4, U and Ra with distance west of the tailings in the mine void at Jabiluka. Concentrations are expressed as ratios to the source concentration immediately downstream of the void. The SO4 concentrations were calculated 200 years after placement. The U and Ra concentrations were calculated 1000 years after placement. The data in figure 6.3.6 indicate that uranium is likely to travel up to 200 m in a westerly direction at which point the concentration would be reduced to less than 1 mBq/L, a concentration that is significantly less than natural concentrations in the region. The Monte Distance from Tailings Repository (m) 0 200 400 600 800 C on ce nt ra tio n R el at iv e to S ou rc e 0.0 0.2 0.4 0.6 0.8 1.0 SO4 200 years U 1000 years Ra 1000 years
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