2017/18 – Greenvale Reservoir (Queensland) – Cadmium
Cadmium detection – Greenvale Reservoir 07/06/17: Routine testing detected an elevated level of Cadmium in the reservoir water (0.0039ppm), DEWS were immediately advised – Incident No. DWI-7-479-00018. After discussion with DEWS and Department of Health that no action was required until further testing confirmed the presence of Cadmium. Subsequent testing showed no detectable traces of Cadmium.
29/1/18 Greenvale Reservoir (Queensland). Cadmium detection
Routine testing detected an elevated level of Cadmium in the reservoir sample (0.0042mg/L), DNRME was immediately notified – Incident No. DWI-7-479-00027. A ‘Boil Water’ alert was already in place due to high turbidity. There were no other detections of metals that supports leeching of the pipe-line or reservoir. A follow up sample was conducted on 5/2/2018 with a Cadmium result of <0.0001mg/L
ADWG Cadmium Guideline. 0.002mg/L
The primary route of exposure of cadmium is via contaminated water or food. Fertiliser can be a source of excessive cadmium as can rainwater tanks. It has been linked to cancer, lung disorders, kidney disease and autoimmune disease.
Greenvale Reservoir (Queensland) – Chlorine
2017/18: Greenvale Reservoir (Qld) Chlorine 5.63mg/L (max), 2.71mg/L (av.)
High Chlorine level – Greenvale Reservoir 18/10/16: A short term high chlorine level was detected at the Greenvale reservoir, this was immediately reported to DEWS – Incident No. DWI-7-479-00013. Test results taken at the same time from the reticulation showed values below 3ppm. Subsequent testing (internal & external) showed the level had returned to below 5ppm
Charters Towers Annual Drinking Water Quality Management Plan 2016/17
Free chlorine levels exceeding the health guideline value of 5.0 mg/L were measured on 8 December 2014 from the chlorine sampling point for the Athelstane Range Reservoir B. In situ free chlorine levels within the reservoir were measured at 5.4 and 8.8 mg/L. The short-lived spikes in free chlorine residual recorded during the event were caused by a power outage as a result of a recent thunderstorm and lightning strike which led to dosing occurring due to a faulty inlet flow meter.
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
2015/18: Greenvale Reservoir (Queensland) – Turbidity
2015/16: Greenvale Reservoir (Queensland) – Turbidity 11.20 NTU (max), av. 3.09NTU
High Turbidity event – Greenvale Reservoir 17/1/17: Due to a high rainfall event the turbidity in the Greenvale reservoir rose to 21.8NTU, DEWS were immediately notified – Incident No. DWI-7-479-00016. Whilst chlorine levels were fine and there was no indication of biological activity the Queensland Health Department recommended a boiled water alert be activated given the treatment process was incapable of addressing the turbidity. The boiled water alert was finally removed 28/4/17 once the turbidity dropped below 1NTU.
High Turbidity event – Greenvale Reservoir 22/5/17: Due to a high rainfall event the turbidity in the Greenvale reservoir rose to 8.4NTU, DEWS were immediately notified – Incident No. DWI-7-479-00017. Whilst chlorine levels were fine and there was no indication of biological activity the Queensland Health Department recommended a boiled water alert be activated given the treatment process was incapable of addressing the turbidity. The boiled water alert was finally removed 8/6/17 once the turbidity dropped below 1NTU.
Charters Towers Annual Drinking Water Quality Management Plan 2016/17
High turbidity event – Greenvale Reservoir 11/8/2017: Repairs were carried out on bore pumps at Greenvale on 9/8/17. The pumps were cleaned and flushed prior to starting however upon starting, there was a turbidity spike at the inlet to the reservoir, of 33NTU. DNRME was immediately notified – Incident No. DWI-7-479-00021. The residual chlorine remained above 2.4ppm. Queensland Health recommended a ‘Boil Water’ alert. Verification testing on 14/8/17 indicated the reservoir turbidity of 0.8NTU and the ‘Boil Water’ alert was lifted on 25/8/2018.
High Turbidity event – Greenvale Reservoir 8/1/2018: Due to a rainfall event the turbidity in the Greenvale reservoir rose to 40 NTU. DNRmE were immediately notified – Incident No. DWI-7-479-00025. The residual chlorine was above 2.0ppm. Queensland Health recommended a ‘Boil Water’ alert. The raw water supply in Greenvale is influenced by surface water at the source and turbidity is highly variable, rainfall events consistently contributed to elevated turbidity. Greenvale remained on a ‘Boil Water’ alert until 12/8/2018.
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.