2018: Clare (Queensland) – E.coli
Clare WTP – E.Coli Detection (23/4/2018)
After routine mains flushing on 19/4/2018 elevated turbidity levels were detected in the reticulation network. An E.Coli sample was taken at the three regular sample points to assess the risk of contamination and this returned positive. This was accompanied with no detections of HPC, and with adequate free chlorine and pH levels. Supplementary samples were taken and these all returned no further detections of E.Coli.
“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
2015 – Clare (Queensland) – Chlorine
2 – The sample taken from Clare WTP on 10/7/2015 does reflect the hand written operator logs and are therefore believed to be an accurate recording of the sample taken, however the sample location is prior to the clear water storage and does not represent the final treated water. The sample taken on the same day on the outlet of the clear water storage shows a total chlorine of 3.52 mg/L and the next day 11/7/2015 shows 2.24 mg/L at the tank outlet. This data indicates that no water exceeding 5 mg/L of total chlorine was released by the WTP.
3 & 4 – The samples taken from Clare WTP on 3/9/2015 show 5.9 mg/L of total chlorine at the outlet of the clear water storage, and 5.3 mg/L of total chlorine at the town pool reservoir sample point. These recordings reflect the operator hand-written logs and are therefore believed to be an accurate recording of the sample taken. The logs state that on 3/9/2015 the operators identified an air lock in the chlorine dosing pump which had been preventing chlorine dosing. In order to ensure all water leaving the plant was disinfected sodium hypochlorite was added directly to the clear water storage tank. It is believed that this has resulted in the high total chlorine readings.
The two sample points above, while treated water, do not represent the final water provided to customers “at the tap”. The SunWater office, and school sample points are at customer tap locations and these two sample points showed 3.37 mg/L and 3.10 mg/L of total chlorine respectively on 3/9/2015, and 0.61 mg/L and 0.64 mg/L the following day on 4/9/2015.
At no time in any of the above instances were any customer complaints received by SunWater, and there have been no reports (suspected or confirmed) of any illnesses.
Sunwater Annual Drinking Water Quality Plan 2015/16
GENERAL DESCRIPTION
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
2014/18 – Clare (Queensland) – Turbidity
2014/15 – Clare (Queensland) – Turbidity 37.87NTU (max), 1.31NTU (av)
2017/18 – Clare (Queensland) – Turbidity > 5 NTU (23/10/2017). Due to a failure in the coagulant dosing pump during the night the WTP operated for a period without adequate flocculation of sediment in the clarifier which resulted in levels of elevated turbidity.
In March 2018, due to extreme rainfall and releases from the Burdekin falls dam causing major localised flooding there was a significant deterioration in raw water quality at the Clare WTP (up to 600 NTU).
When it became apparent that the WTP was not capable of treating the raw water while maintaining the treated water quality requirements supply was ceased on 14/3/2018 to prevent delivery of out of spec water to the community. This resulted in an unplanned interruption to supply. The community was notified and free bottled water was supplied from the SunWater office. A tanker of potable water was used to supplement the network supply on 15/3/2018.
Preventive actions undertaken
SunWater has reviewed the circumstances leading to the event. The turbidity increase was more severe and more prolonged than expected. This has been noted and in future events a decision to provide an alternate supply of water will be made earlier to ensure that supply is not restricted to the township.
Sun Water Water Quality Management Plan 2017/18
Chlorine-resistant pathogen reduction: Where filtration alone is used as the water treatment
process to address identified risks from Cryptosporidium and Giardia, it is essential
that filtration is optimised and consequently the target for the turbidity of water leaving
individual filters should be less than 0.2 NTU, and should not exceed 0.5 NTU at any time
Disinfection: A turbidity of less than 1 NTU is desirable at the time of disinfection with
chlorine unless a higher value can be validated in a specific context.
Aesthetic: Based on aesthetic considerations, the turbidity should not exceed 5 NTU at the
consumer’s tap
Clare (Queensland) – pH (alkaline)
2014/15: Clare (Queensland) pH 8.6739 (av)
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.