2013/16 – Gisborne Road Tank, Western Water (Victoria). Streptococci, E.coli

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Incidents reported under section 22 Safe Drinking Water Act 2003

Gisborne Road Tank, 2 Dec 2013 (Lerderderg locality)

Routine sampling at the tank resulted in detection of 1 org/100ml of faecal streptococci in the presence of 0.01mg/L free chlorine and 0.06mg/L of total chlorine.

Actions

The tank was isolated from supply and spot dosed. While the tank was isolated, freshly chlorinated water was pumped into the reticulation system via a local chlorine
booster station.

Flushing was also conducted at the extremities of the system in order to ensure increases in chlorine residuals were met.

Operational site visits to the tank were increased along with spot dosing and works to increase water turnover in the tank.

Resampling was conducted for three consecutive days with all results clear for the tank.

However, one reticulation site downstream of the tank returned positive results for faecal
streptoccoci despite increases in chlorine across the system.

The reticulation site in question was inspected. The sample tap was an old garden-style tap fitting which brought into question the integrity of the sample collected. A new clickin
fitting was installed and the reticulation site resampled for three further days with all results remaining clear.

E.coli detection in Gisborne Road Tank and network, 30 December 2016 (Bacchus Marsh)

Issue – During storm activity on 29 December 2016, the Gisborne Road Tank in Bacchus Marsh had a small volume of rainwater intrusion. This resulted in a low-level E.coli detection (1 org/100ml) in the routine sample taken on 30 December.

Resampling was undertaken that day to verify the result. While the tank reported no E.coli presence in this sample, testing confirmed the presence of low-level E.coli (1 org/100ml) in the downstream network.

The Gisborne Road Tank supplies to an isolated part of the network near Bacchus Marsh, 55 properties in total. DHHS was notified on the day of detection in accordance with the requirements of Section 18.

Actions – After resampling on the day of detection, the tank and network were spot dosed with chlorine to disinfect the water supply.

Sampling on the following three days confirmed that the tank and network had no contamination present and some minor repairs were made to the tank roof and hatch as a result of storm damage.

Outcome – The tank was reviewed as part of the Drinking Water Tank Integrity Program with appropriate work scheduled for 2017/18, based on priority. In early 2017, improvements to chlorine online monitoring were made at the tank to ensure adequate chlorine levels. The tank is audited yearly as part of the HACCP system.

“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