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Nabarlek Pit decommissioning migration of sulphate, nitrate and radium ions in groundwater - preliminary modelling



Nabarlek Pit decommissioning migration of sulphate, nitrate and radium ions in groundwater - preliminary modelling


Appleyard, S.


E-Publications; E-Books; PublicationNT; Report ; 41/1984




Made available via the Publications (Legal Deposit) Act 2004 (NT).





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Dept. of Transport and Works

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Report ; 41/1984

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Technical Report WRD84041 Viewed at 14:07:09 on 29/07/2010 Page 8 of 34. I I I I I I I I I I I I I I I I I I I I AGC (1984) estimated that groundwater velocities out of the pit are likely to be in the range 0.02 to 0.6 m/day. Assuming a discharge volume of 35m3 /day, gives values of ranging from 60m 2 to 2000m 2 for the tube in the model. The constant which is subject to the greatest uncertainty is the combined rate constant, k. This was determined by fitting a curve to the observed distribution of radium concentrations in groundwater near the pit. The Nabar1ek orebody acted as a source of radionuclides for millions of years prior to mining, and so the distribution of radium in groundvlater near the pit should have attained a state of equilibrium with aquifer host rocKs. This equilibrium state should still exist in groundwater here despite the fact that the orebody has been removed, because of the slow nature of groundwater-rock interactions. Values of C/Co for several bores as a function of distance from the pit are plotted in Fig 3.1, where: where C - long term a"'irerage radium concentration in the bore Co - concentration of radium in the original orebody, or about 1 to 2 Bq/L (see AGC, 1984) The curve of best fit has a value for the combined constant (incorporates k, A and G) of 3 x 10-2 . Assuming values for A and G derived above gives values for k in the range 50 to 2000 Bq day/mO. 3.2 Sensitivity Analysis Since equation (8) contains three constant terms which are not accurately known, it is necessary to carry out a sensitivity analysis to test the effect of varying one SA2 / 11: TJ

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