2005-16: Darwin (Northern Territory) – N. fowleri, E.coli

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Darwin (Northern Territory) – N. fowleri

“… In Darwin, six per cent of samples from the routine monitoring for N. fowleri exceed the 2004 ADWG trigger value of two organisms per litre in the treated water system. Regular monitoring was undertaken in Darwin for the full 12 months of this reporting period after starting in July 2005.” “Power and Water Water Quality Report 2006 in Darwin, six per cent (14 samples) of routine monitoring samples for N. fowleri exceed the 2004 ADWG trigger value of
two organisms per litre in the treated water system.”

2010/11 Power and Water Coproration: Since the initial detection of N. fowleri in the Darwin distribution system in 2005, Power and Water have undertaken extensive monitoring of water supplies and implemented procedures to control this amoeba…N. fowleri was detected only in the Darwin distribution system. N. fowleri was detected on four occasions at the Manton Dam Park Tap sampling point. At the time the free chlorine residual was low. Remedial action included mains flushing and re-establishment of an effective free chlorine residual. Follow-up investigations did not fi nd N. fowleri present at that location…Special investigations during sediment removal from six tanks in the Darwin distribution system found N. fowleri present in the sediment of four tanks. These results are reported in table 4. In response the cleaning of tanks was completed, dosed to 1 mg/L free chlorine and held off-line until laboratory results confirmed them to be clear of N. fowleri. Long term strategies to control N. fowleri in tanks include an increase in the frequency of tank cleaning to minimise sediment accumulation. The Manton Dam Park Tap is the drinking water supply for visitors to Manton Dam. As this site is at the end of the distribution system and is used infrequently, the free chlorine residual is often inadequate. As a consequence there have been several detections of N. fowleri over the past few years. Power and Water has improved the free chlorine residual at this site by installing an automatic irrigation system which routinely draws water through the pipeline displacing chlorine depleted water.

2011/12:  N. fowleri was only detected in the Darwin distribution system and only during hydrant flushing to remove iron and manganese sediments. All other distribution systems and sources monitored during the 2010-11 period were free of N. fowleri.  N. fowleri is the amoeba of primary concern but the detection of any thermophilic amoeba is considered significant. The detection of  thermophilic amoeba indicates conditions in the water supply are conducive for the growth of N. fowleri and further investigation or remedial action maybe warranted. Naegleria spp. other than N. fowleri were detected in the Darwin, Gunn Point and Tennant Creek distribution systems and Darwin groundwater. Naegleria spp. were not detected in surface waters.

Investigations during sediment removal from Darwin distribution storage tanks through the period 2012-16 found N. fowleri present in the sediment of seven tanks. This finding supports the long term strategy to control N. fowleri growth in tanks by increasing the frequency of tank cleaning and minimising sediment accumulation. Power and Water Corporation Water Quality Report 2016
Darwin (Northern Territory) – E.coli

2007/08: Darwin E. coli 2 exceedances 99.5% compliance for year

2008/9: Darwin 1mpn/100mL 1 exceedance. 99.7% compliance for year.

2009/10: Darwin E. coli  1 exceedance during year. 99.7% compliance for year

“E.coli

Thermotolerant coliforms are a sub-group of coliforms that are able to grow at 44.5 ± 0.2°C. E. coli is the most common thermotolerant coliform present in faeces and is regarded as the most specific indicator of recent faecal contamination because generally it is not capable of growth in the environment. In contrast, some other thermotolerant coliforms (including strains of Klebsiella, Citrobacter and Enterobacter) are able to grow in the environment and their presence is not necessarily related to faecal contamination. While tests for thermotolerant coliforms can be simpler than for E. coli, E. coli is considered a superior indicator for detecting faecal contamination…” ADWG