2010/16 – Newstead (Victoria) E.coli
2010/11 Newstead E.coli 1/100mL (98.1% samples no e.coli ) (1 positive)
22/2/12 Newstead E.coli 1/100mL
1/2/16 Newstead E.coli 1/100mL
12/6/18 Newstead: E. coli were detected (5 orgs/100mL) in a routine sample collected on 12 June 2018 at the outlet of the Newstead Treated Water Tank. Note that no E.coli or coliforms were detected in a routine sample collected in the Newstead water distribution network on the same day.
The Newstead tank and the distribution network receives treated water from the Castlemaine WTP. There have been difficulties in maintaining chlorine residual in the Newstead tank and the distribution network primarily due to nitrification. To improve chlorine residual, the tank has a program for manual dosing using chlorine tablets. The investigation on tablet dosing revealed that the last scheduled tablet dosing was missed. This would have contributed to the low chlorine residual recorded on the day the sample that had positive E.coli was collected.
A visual inspection of the tank identified that the roof of the Newstead tank was not draining effectively and that it was holding water. Additionally, there were rain events on the day respective sample was collected.
Therefore, the combination of low chlorine residual, rain events and issues with the tank roof likely led to the presence of E. coli in the tank and the sample could be considered as representative of the drinking water being supplied at the time of collection, which did
not meet the water quality standard for 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