Territory Stories

Assessment of the Jabiluka Project : report of the Supervising Scientist to the World Heritage Committee

Details:

Title

Assessment of the Jabiluka Project : report of the Supervising Scientist to the World Heritage Committee

Creator

Johnston, A.; Prendergast, J. B.; Bridgewater, Peter

Collection

E-Publications; E-Books; PublicationNT; Supervising Scientist Report; 138

Date

1999

Location

Alligator Rivers Region

Table of contents

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.

Language

English

Subject

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

Publisher name

Environment Australia

Place of publication

Canberra (A.C.T.)

Series

Supervising Scientist Report; 138

Format

1 volume (various pagings) : illustrations, maps

File type

application/pdf

ISBN

642243417

Use

Copyright

Copyright owner

Environment Australia

License

https://www.legislation.gov.au/Details/C2019C00042

Parent handle

https://hdl.handle.net/10070/264982

Citation address

https://hdl.handle.net/10070/462402

Related items

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

Page content

75 below mean sea level and about 100 m below the land suface in Mine Valley. The highest point of the tailings silos (as currently planned by ERA) is about 40 m below sea level and about 110 m below the land surface of the crest between Mine Valley and the location of the mine portal and surface facilities at Jabiluka. Thus, once the mine is backfilled and sealed following completion of mining at Jabiluka, the only mechanism for physical dispersal of the tailings solids will be erosion of the overlying bedrock. Clearly, the whole land mass would need to be eroded away and by that time the wetlands of Kakadu would no longer exist. Physical dispersal of the tailings does not, therefore, pose a threat to the wetlands of Kakadu. Geologic denudation rates in the Alligator Rivers Region have been summarised by the Supervising Scientist (Cull et al 1992). The mean and standard deviation of 45 measurements were 0.040.03 mm per annum. These data included a number of measurements made in the vicinity of the Jabiluka No 1 orebody so that they are directly applicable to the current assessment. These data are consistent with other measurements in the region. For example, Williams (1973 and 1976) recorded denudation rates between 0.011 and 0.054 mm per annum. Following extraction of uranium in the mill, the tailings will contain uranium at concentrations about 5% of the original concentration in the ore, but all of the radioactive progeny will be present at approximately their original ore concentrations. Assuming that erosion rates will be similar in the future and using the mean denudation rate of 0.04 mm per annum, the time required to erode the bedrock overlying the tailings in the mine void and the silos would be about 2 million years. This time scale is about 25 times the radioactive halflife of 230Th, the longest lived radioactive product of uranium. Hence the excess concentrations of all the radioactive progeny will have decayed away by the time the tailings are exposed and they will be in equilibrium with the residual uranium. This residual uranium concentration is about 30 times greater than the average concentration of uranium in the rocks of the Alligator Rivers Region but clearly any tailings dispersed from the site in the very long term would be mixed with, and diluted by, very large quantities of inert material from the surrounding bedrock. Thus, dispersal of tailings in the very long term will not constitute a hazard for future generations. 6.3 Leaching of contaminants from tailings 6.3.1 Hydrogeological description of the area A detailed study of the hydrogeology of the Jabiluka area and modelling of groundwater contaminant dispersion has been carried out by Kalf and Dudgeon (1999) (Attachment E) as part of this review. Groundwater flow in the vicinity of the mine is topographically controlled. A relatively high mean annual rainfall of about 1500 mm, which occurs mainly in the annual Wet seasons, and relatively low permeability of the sandstone hills surrounding the mine site maintain high water table levels in the hills. Both surface water and groundwater drainage is from the hills towards the major valleys which run approximately east and west from the surface water divide which is located near the mine site. Groundwater flow in both of these directions eventually reaches the Magela floodplain in Kakadu National Park (see fig 6.3.1). The westward flow towards the floodplain follows the general line of Mine Valley. The eastward flow must turn north to follow the course of Swift Creek and flow further before it can reach the floodplain.


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