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
61 experience at Ranger over the past number of years. We have taken the approach of adopting a conservative value for the concentration of uranium (which is applied to the risk assessment for both radiation exposure of members of the public and for ecosystems) and then being as realistic as possible in assessing the probable effects on people and aquatic animals. Thus, both safe and effects concentrations are considered in the assessment. Sulphate is a common anion of natural surface waters and is not regarded as a toxic compound. To increase the concentration of sulphate it is necessary to increase the concentration of some cation and it is the toxicity of the cation that needs to be assessed rather than that of sulphate. For these reasons, the Supervising Scientist recommended to the Northern Territory that the receiving water standard for sulphate be set on human health grounds; 200 mg/L was the recommended limit. This is considered to be the safe concentration. No effects concentration has been considered for sulphate since uranium is the dominant toxicant. Magnesium is not normally considered to be a toxic substance and few studies of its toxicity have been carried out. No recommendation was given for a water quality guideline in the Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC 1992). In his recommendations to the Northern Territory, the Supervising Scientist noted the limited data on the toxicity of magnesium and recommended a limit of 20 mg/L, a figure that was more than 100 times lower than the reported LC50 value for Daphnia hyalina (Baudouin & Scoppa 1974). Of more significance to aquatic animals would be a change in the ratio of magnesium to calcium in the water but this would only be of relevance if the change were prolonged rather than the transient scenario being considered here. The safe concentration is taken as 20 mg/L and, as for sulphate, no effects concentration is considered. Table 5.3.2 Estimates of concentrations of U, Mg and SO4 in runoff from the ore stockpile at Jabiluka and the resulting concentrations in Swift Creek under normal and extreme dilution conditions. Also given for comparison are the safe and effects concentrations. Stockpile Runoff mg/L Swift Creek (Normal) mg/L Swift Creek (Extreme) mg/L Safe Concentration mg/L Effects Concentration mg/L Uranium 80 0.012 0.11 .018 0.19 Magnesium 500 0.08 0.70 20 na1 Sulphate 2,000 0.30 2.8 200 na1 1 Not applicable A summary of the above data is presented in table 5.3.2 where the estimated concentrations of uranium, magnesium and sulphate in Swift Creek resulting from discharge of excess water from the ore stockpile are compared to the concentration limits at which it is estimated adverse effects will be observed. It can be seen that, under the dilution scenario envisaged (Swift Creek Normal in the table), no effect on the aquatic animals living in Swift Creek would be expected to occur even when the volume of excess water discharged is that with an exceedence probability of 1 in 50,000 over the life of the mine. The above dilution scenario would not apply if the rainfall event is very intense and of short duration. In these circumstances, because of the finite size of the catchment there will be a delay between the rainfall event over the whole catchment and the peak of the stream hydrograph at the catchment outlet point. This implies that the full dilution expected under normal circumstances would not be available because the water from the mine site, which is relatively close to the creek, would not be delayed significantly.
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