2011 October – Portsea – Macgregor Avenue (Victoria) – E.coli

Portsea – Macgregor Av – Victoria – E.coli
The first event was due to failure of a backflow device at a property in Macgregor Avenue, Portsea, which was detected by South East Water’s plumbing group on 1 October 2011. The property in question was connected to a pumped bore that was cross-connected into the
potable water system. The backflow device on the meter had failed, causing the meter to go backwards. The bore was disconnected immediately. Field testing and hydraulic investigation confirmed the possible contamination would be restricted to the street. Pipes in the street were flushed and samples were then taken from nearby routine sample taps, from garden taps at the start of the street and from a hydrant at the end of the street near the property in question. A positive detection for E. coli and coliforms was returned from the sample at the end of the street, while all others were free of E. coli and coliforms. It is believed the positive detection may have been due to sampling from a hydrant, which is not standard sampling practice. Irrespective of this, pipes in the street were flushed again and resampled. All resamples were free of E. coli and coliforms.

Escherichia coli should not be detected in any 100 mL sample of drinking water. If detected
in drinking water, immediate action should be taken including investigation of potential
sources of faecal contamination.

“Coliforms are Gram-negative, non-spore-forming, rod-shaped bacteria that are capable of aerobic and facultative anaerobic growth in the presence of bile salts or other surface active agents with similar growth-inhibiting properties. They are found in large numbers in the faeces of humans and other warm-blooded animals, but many species also occur in the environment.

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 2011