8/1/21 – Dereel (Victoria) – E.coli

8/1/21: Dereel (Vic) – E.coli.
8 January 2021. Dereel Tank (Ballarat system). E. coli – 1 MPN/100mL. 150 connections in the
distribution system downstream of the network treated water storage tank. Informed DH and initiated incident team response. Confirmed residual disinfection in the tank and upstream
and downstream system. Resampled tank. Conducted an external and internal inspection of tank integrity. A potential minor ingress point on the side of the hatch identified as the most likely source of contamination. Sealing repair conducted on hatch. Spot dosed the tank with disinfectant and verified adequate residual in tank and surrounding reticulation. Resamples post corrective actions clear of contamination. Reviewed Nitrification Action Plan trigger
levels. Reviewed suitability of hatch design and whether the same design was present on any other CHW storages. Connected upstream basin mixer to telemetry system with
fail alarm capability. Investigation report submitted to DH.

“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