Brosnahan Reservoir, Belivah, Logan East (Qld) – E.coli

4/4/17: Brosnahan Reservoir, Belivah (Queensland)  1 MPN/100mL

Incident Description
As part of Council’s routine verification monitoring program, E. coli was detected in a sample
collected on the 4th April 2017 from Brosnahan reservoir. The E. coli result was 1 MPN/100mL
with a total chlorine residual of 0.07mg/L. Investigations found that the most likely cause of the
E. coli was a result of contaminated flood water entering broken mains that fed this reservoir,
during the flooding caused from ex-Tropical Cyclone Debbie.

Corrective and Preventative Actions
Brosnahan Reservoir supplying the area was isolated and manually dosed with liquid sodium
hypochlorite with surrounding areas flushed. Additional sampling found no detection of E. coli in the other Logan East WQZ sampling sites.
In consultation with Metro South Public Health Unit and DEWS, a precautionary boil water
notice was issued and then lifted with the reservoir put back online, once consecutive sample
results indicated no E. coli present.
Preventative actions included maintaining chlorine residual in the reservoir until it is replaced
with supply pumps during 2017-18 FY CAPEX program. Improved prompt reporting of health
breaches and events that could cause public health concerns, such as submerged mains in
contaminated flood water, has also been implemented.

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