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Galiwinku Groundwater Resource and Evaluation DLH-492



Galiwinku Groundwater Resource and Evaluation DLH-492


Yin Foo, Des


E-Publications; E-Books; PublicationNT; Report ; 6/1984




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





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Dept. of Transport and Works

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Report ; 6/1984

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Technical Report WRD84006 Viewed at 14:07:13 on 29/07/2010 Page 33 of 60. 5. SUMMARY AND CONCLUSION the construction of two two 150 mm diameter bores The 1981 investigation resulted in 200 rom diameter production bores and to upgrade the community water investigation bores were also drilled. supply. Three other Information from these bores enabled two main rock units to be identified in the study area. An interbedded shale, siltstone, and fine glauconitic sandstone sequence overlying fine grained ferruginous sandstone which form the two lower members of the Elcho Island Formation. The formation in the vicinity of the community dips north west at approximately 1.5, striking at around 45 north. The aquifer was identified as existing in two situations. Where it is overlain by the impermeable shale, the aquifer is intersected below the interface with the basal sandstone. Its behavior is that of a confineS4 aquifer with a storage coefficient estimated to be 2 x 10 Bores drilled east of the contact behleen these units intersected the aquifer at the base of a weathered sandstone profile around 30 m. In this situation, the aquifer behaves in an unconfined manner with a specific yield of around 0.10. Test pumping results indicated a transmissivity of around 600 m'/day in most areas. A subsequent numerical model was developed using the above parameters. Simulation of the aquifer's performance under present and foreseeable extraction was undertaken. Results showed that salt water intrusion is not likely to occur. However, it should be critically examined if a proposed upgrading is to exceed that which has been recommended. The safe annual yield for the aquifer has been estimated in Appendix C to be in the order of 3000 ML. Projected water requirements to the year 1990 can be met by the recommended pumping configuration. At that stage, sufficient water level data should be available on Ivhich the model can be reappraised. A proposal for further extraction should then be made. The model highlighted that the north eastern segrr~nt of the aquifer is the most preferable area for further exploitation. Future borefield development should aim towards utilising the resources in this area. Bores constructed during the investigation have been recommended for rates up to 15 Lis. The water quality obtainable from bores is good in terms of its low T.D.S. However, it is of an acidic nature with a pH measured as low as 4.3 and has a high corrosion potential.

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