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Gapuwiyak borefield, bore construction report. Dlh-500



Gapuwiyak borefield, bore construction report. Dlh-500


Prowse, G.


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Technical Report WRD83004 Viewed at 14:07:13 on 29/07/2010 Page 11 of 24. I I I I I I I I I I I I I I I I I I I I 6. WATER QUALITY Bacteriological and chemical analyses between 1970 and 1983 have been examined. The bacteriological count of the water extracted from the lake edge has varied considerably. Between 1970 and 1978, a deterioation in quality occurred each year from August to December, and the analyses showed unsatisfactory levels of bacteria being reached from 1976 to mid 1978. In mid 1978, the town water supply extraction point was changed from the edge to the centre of the lake. Since that date bacteriological levels have been satisfactory. From August 1978 until February 1983 only one set, out of thirteen sampling sets, resulted in counts above zero. While the above data indicates that water in the centre of the lake has satisfactory bacteriological levels, the potential exists for the pollution zone to expand to the lake centre. This is primarily due to the uncontrolled use of the lake waters by the community. The chemical analysis of water from the gave a total dissolved solids count (TDS) mg/L to 70 mg/L. lake edge intake ranging from 32 Following the reconstruction of the extraction point to the lake centre, a sample taken from the reticulation system on 16.8.78 was anlaysed to give a TDS of 74 mg/L. An analysis of the borefield groundwater gave a around 40 mg/L. The bores have been connected up combined system since 1977. TDS of to the Thus from a comparison of the TDS values, it appears that water from the lake has the higher TDS value. The pH of the water taken from the lake edge varied from 6.1 to 6.6. The pH of the water at the lake centre is not known. The pH of the groundwater from the borefie1d has varied from 5.5 to 6.5 for analyses from Bores RN 8899, 8900 and RN 21403. However these pH values are laboratory determinations. The pH of the groundwater water would be expected to be lower - possibly as low as 4. In summary, the potential for bacteriological contamination exists for a water supply obtained from the centre of the lake. The groundwater supply does not present this problem. Therefore a supply obtained solely from the borefield is the better option. The above pata indicates that the groundwater chemically is very corrosive. The lake water would also be corrosive but to a lesser degree. -8

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