2012 March – Somers – Banksia Square (Victoria) – E.coli

Somers – Banksia Square – Victoria – E.coli
The fourth event was a detection of E. coli from a routine sample taken in Banksia Square in Somers on 26 March 2012. 3 organisms per 100mL were detected, and the free chlorine residual at the site of the detection was <0.01 mg/L. This sample tap falls within the Balnarring
locality and is supplied by the Somers tank, which provides backup supply to a small area. The area was chlorinated and flushed and all system checks were clear. The Somers tank was left offline as it was suspected that the tank was the cause of the detection due to the very low turnover in the tank. Resamples were taken the following day from the sample tap in question and two nearby sample taps and all were free of E. coli. The Somers tank was also sampled and it returned a positive detection, showing the contamination was from the tank. The tank was
subsequently drained, cleaned and chlorinated. The tank was left offline, although it continued to be sampled routinely to ensure its safe use in case of emergency.

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