2010 March/April – Hurstbridge (Victoria) – E.coli

Hurstbridge – (Victoria) – E.coli

On 9 March 2010, E. coli of 2 orgs/100mL was detected at the Nutfield Tank and also at a customer tap in Hurstbridge (Mernda/Hurstbridge sampling locality) caused by rainwater
seeping into the tank following a heavy rainfall event. The tank was inspected, using a new ‘floating camera’ technique (see explanation in Section 11.6 page 27), and necessary repair was conducted to prevent this event occurring in the future. The tank was also spot dosed
and chlorine levels checked. Block flushing of the mains in the area was also conducted until chlorine residuals reached acceptable levels. E. coli was not detected in the post samples
collected at the tank and customer sampling taps. Additional tank inspection and maintenance was initiated in response to the high rate of water quality events occurring with tanks and
reservoirs (see Section 11.5 on page 27). No subsequent action was required (Yarra Water Valley Drinking Water Quality Report 2009-10)
On 22 April 2010, E. coli of 1 org/100 mL was detected at the Nutfield Tank (Mernda/Hurstbridge sampling locality). As with the incident of 10 March, the event occurred after a high rainfall event. Following this incident, a simulation deluge was undertaken on the tank (see explanation on this simulation in Section 11.6 on page 27). This simulation found that water was backing up and causing water to seep into the tank during rainfall events, from spots that were not previously identified as they were harder to identify during dry times. These were subsequently repaired. The tank was spot dosed with chlorine. On 23 April, Hurstbridge Reservoir and a customer sampling tap in Hurstbridge sampling locality (both downstream of the Nutfield
Tank) returned E. coli detections, at 3 orgs/100 mL and 5 orgs/100 mL respectively. The tanks were spot dosed with chlorine and the mains in the area flushed. E. coli was not detected in the
post samples collected from both Nutfield and Hurstbridge tanks and customer sampling taps. No subsequent action was required. (Yarra Water Valley Drinking Water Quality Report 2009-10)

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