Reticulation system, 28 August 2014 (Romsey)
Issue – Routine sampling at the tank resulted in detection of 4org/100mL of E.coli in the presence of good chlorine residuals throughout the reticulation system.
Actions – There were no issues observed on SCADA for the treatment plant during this incident. Flushing of the main at the affected sentinel sampling site was performed, and resampling was conducted for three consecutive days with all results clear of E.coli. A root cause was not able to be established.
Romsey Tank A, 26 October 2014 (Romsey)
Issue – Routine sampling at the tank resulted in detection of 9org/100mL of E.coli in the presence of 0.65mg/L monochloramine and 0.88mg/L total chlorine. Actions – The tank was isolated from supply and resampled on three consecutive days to confirm clean samples prior
to return to supply. The chloramination contact time was examined and found to be adequate for disinfection purposes. The tank integrity was assessed and some ingress was detected after a recent wet weather event.
The root cause was suspected to be either an issue with the integrity of the sample collected (false-positive) or minor ingress of rainwater through the roof. Works to improve tank roof integrity – following the trial of new technology discussed earlier – is planned to commence across tanks in 2015/16.
E.coli detection at Romsey Water Filtration Plant Tank B, 10 April 2017 (Romsey)
Issue – During storm activity on 8 April 2017, Tank B at the Romsey Water Filtration Plant (picture below) experienced a small volume of rainwater intrusion. This resulted in a low-level E.coli detection (1 org/100ml), in the routine sample taken on 10 April 2017. There were no E.coli detections in the downstream network on the day of reporting, indicating the chloramine residual was efficiently protecting the network and the contamination was isolated to the tank.
Resampling was undertaken on the day of detection to verify the result and there was no E.coli detected in the tank or the downstream network. DHHS was notified on the day of the detection in accordance with the requirements of Section 18.
Actions – After resampling on the day of detection, some minor repairs were made to the tank roof and hatch as a result of storm damage and where rain water intrusion had occurred.
Outcome – The tank was reviewed as part of the Drinking Water Tank Integrity Program with appropriate work scheduled for 2017/18 based on priority. 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