2008/18 – Cressy (Victoria) – E.coli, pH, Chlorine

Cressy (Victoria) – E.coli
10/3/2010 (1 MPN/100mL and 4 MPN/100mL) – On 10th March 2010, routine sampling of the Cressy water quality sampling locality (1 MPN/100ml) and Cressy tank (4 MPN/100ml) detected the presence of E. coli. The Cressy tank floats on the system. Upon notification of the detection, the tank was isolated and disinfected. In addition, the reticulation system was flushed and disinfected using a mobile disinfection unit. Follow up sampling and analysis did not detect any further E. coli. Inspection of the tank failed to identify any signs of potential contamination. There were no faults or failures with the operation of the Colac Water Treatment Plant prior to or after the incident. While the source of the E. coli could not be determined, prior to the detection there was a major burst of the supply main into the Cressy Township. The burst caused significant increases of flows from the Cressy tank.

1/10/14 Detection of Escherichia coli in drinking water (24 MPN/100ml). System operators inspected the tank at Cressy for any sign of failure or contamination including tank damage or animal ingress. None was found. The laboratory was engaged to conduct follow up samples. No

E. Coli or Coliforms were detected in the follow up sample taken on October 2. Mobile Disinfection Unit had already been deployed to disinfect the Cressy water quality locality – which includes the affected area – as part of the routine weekly mobile disinfection program. Repair of a burst water main the day prior to the sample being taken is identified as the most likely cause of the detection.

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

Cressy (Victoria) – pH (alkaline)

Average pH: 2008 July-2009 June: 8.58 pH units

Average pH: 2009 July-2010 June: 8.72 pH units

Average pH: 2010 July-2011 June: 8.94 pH units

Average pH: 2011 July-2012 June: 8.78 pH units

Average pH: 2013 July-2014 June: 8.7 pH units

Based on the need to reduce corrosion and encrustation in pipes and fittings, the pH of
drinking water should be between 6.5 and 8.5.

New concrete tanks and cement-mortar lined pipes can significantly increase pH and
a value up to 9.2 may be tolerated, provided monitoring indicates no deterioration in
microbiological quality.

pH is a measure of the hydrogen ion concentration of water. It is measured on a logarithmic scale from 0 to 14. A pH of 7 is neutral, greater than 7 is alkaline, and less than 7 is acidic.

One of the major objectives in controlling pH is to minimise corrosion and encrustation in pipes and fittings. Corrosion can be reduced by the formation of a protective layer of calcium carbonate on the inside of the pipe or fitting, and the formation of this layer is affected by pH, temperature, the availability of calcium (hardness) and carbon dioxide. If the water is too alkaline (above pH 8.5), the rapid deposition and build-up of calcium carbonate that can result may eventually block the pipe.

2017/18 – Cressy (Victoria) – Chlorine

2017/18: Cressy (Victoria). Chlorine 6.1mg/L (max) 0.68mg/L (av)

Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion. Chlorine and hypochlorites are toxic to microorganisms and are used extensively as disinfectants for drinking water supplies. Chlorine is also used to disinfect sewage and wastewater, swimming pool water, in-plant supplies, and industrial cooling water.

Chlorine has an odour threshold in drinking water of about 0.6 mg/L, but some people are particularly sensitive and can detect amounts as low as 0.2 mg/L. Water authorities may need to exceed the odour threshold value of 0.6 mg/L in order to maintain an effective disinfectant residual.

In the food industry, chlorine and hypochlorites are used for general sanitation and for odour control. Large amounts of chlorine are used in the production of industrial and domestic disinfectants and bleaches, and it is used in the synthesis of a large range of chemical compounds.

Free chlorine reacts with ammonia and certain nitrogen compounds to form combined chlorine. With ammonia, chlorine forms chloramines (monochloramine, dichloramine and nitrogen trichloride or trichloramine) (APHA 2012). Chloramines are used for disinfection but are weaker oxidising agents than free chlorine.

Free chlorine and combined chlorine may be present simultaneously (APHA 2012). The term totalchlorine refers to the sum of free chlorine and combined chlorine present in a sample.

Chlorine (Free) ADWG Guideline: 5mg/L (Chlorine in chloraminated supplies 4.1mg/L). Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion.

Chlorine (Total) ADWG Guideline 5mg/L (chloraminated supplies 4.1mg/L): The term total chlorine refers to the sum of free chlorine and combined chlorine present in a sample