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

80 17 and 350 S/cm (ERAES 1998). This range of values is supported by other measurements (as listed in ERAES 1998). The groundwaters in the vicinity of the orebody, both to the west in Mine Valley and to the east towards Swift Creek, are in stark contrast to the groundwater underlying the Magela floodplain, which is of high salinity, is acidic, and has high sulphate concentrations. Pyritic layers in the estuarine sediments underlying the plain are extensively oxidised to form acid sulphate soils (East et al 1992) as a result of seasonal wetting and drying cycles. The soils on the floodplain are dominated by grey clays (East et al 1992). The chemistry of the groundwaters is consistent with these conditions. Deutscher et al (1980) reported sulphate concentrations of between 1500 and 6854 mg/L, accompanied by low pH (3 to 4) and high concentrations of Fe2+ (200700 mg/L) where sulphate concentrations were high. The location of tested bores is given in figure 6.3.2. An interesting feature of the groundwater underlying the Magela floodplain is the low concentrations of radionuclides present with uranium exceeding 1 g/L (125 mBq/L) in only two of forty seven samples collected by Deutscher et al (1980). 6.3.2 Description of the solute transport modelling A hybrid modelling approach has been used in this review (Kalf & Dudgeon 1999) to model the fractured rock aquifer in the project area. The modelling incorporated the three main processes that control the movement of solutes in groundwater, viz advection, dispersion and retardation. Retardation is the term given to describe the collective processes of adsorption, precipitation/dissolution and other complex ion exchange reactions. A full description of the modelling and a list of the assumptions used in the approach are given by Kalf and Dudgeon (1999). The models used were: A two dimensional section finite element model (SEEP/W) of section A-B-C (see fig 6.3.1) to determine flow directions, head distributions and the range of Darcy velocities along the section. A three dimensional numerical solute transport model (MODFLOW-SURFACT) applied to determine the concentrations of solutes leached from the tailings paste material for use as the source concentrations in the analytical model. An analytical contaminant transport model to determine concentrations due to advection, dispersion in three co-ordinate directions and retardation. This model used as input the range of velocities and source concentrations determined from the first two models. This model was combined with Monte Carlo calculations to determine concentration profiles for a large number of different parameter values within selected ranges. The three models above were used to predict downstream effects of the solutes stored in the Jabiluka tailings as follows. Firstly, the assumed steady state water heads were computed by the finite element model SEEP. The water surface from the model was fitted to approximate the measured water surface at Jabiluka. These heads were used to drive the contaminant transport through the three dimensional model MODFLOW-SURFACT to produce the source groundwater solute concentrations at a nominal 2 m downstream from the silos. The three dimensional model is necessary because of the complexity of the tailings storage geometry. These source concentrations, along with groundwater velocities from SEEP, were then used as input to the analytical model to compute solute concentrations further downstream. Use of the analytical model enables a large range of solutions to be derived for different model parameters, and in this way the sensitivity of the model predictions to a range of inputs can be assessed through Monte Carlo simulations. The hybrid model was run for the


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