2015/16: Townsville Reticulation – Chlorate 0.995mg/L (highest level) 0.565mg/L (av)

2017/18: January – March 2018 DWI-7-506-00054. Townsville Drinking Water Scheme. Chlorates >700 μg/L (Townsville Water’s self-imposed limit). Townsville has ongoing issues with chlorates in hot weather; compounded for the past few years by higher chlorine set points due to water restrictions. All mitigation measures available have been put in place. Old stock replaced with new stock, reducing the size of storage tanks, stock emptied before refilling, keeping chlorine residuals as low as possible, lowering of reservoir levels to turn over reservoirs. Chlorates reduced as the temperatures cooled. Investigations are underway to convert Douglas WTP to chlorine gas to reduce chlorate formation. (Chlorate levels 1057mg/L (max) in transmission reservoirs (752mg/L av.)). (Chlorate levels 869mg/L (max) in reticulation (701.5mg/L av.)).

Chlorite: ADWG Health 0.3mg/L.

Chlorite and chlorate are disinfection by-products of chlorine dioxide disinfection process.

“… industry are having serious problems meeting chlorite/chlorate limits that were proposed in the new Australian Drinking Water Guidelines, especially for disinfection in long distance pipelines that are dosed with sodium hyptochlorite” pers comm 18/5/11.

“Chlorite occurs in drinking water when chlorine dioxide is used for purification purposes. The
International Agency for Research on Cancer (IARC) has concluded that chlorite is not classifiable as carcinogenic to humans and is listed in the Group 3 category. Changes in red blood vessels due to oxidative stress are a major concern with excessive levels of Chlorite in drinking water. According to the US EPA, potential health problems for people drinking Chorite above safe drinking water guideline include: Anemia in infants and young children and nervous system effects.” https://water.epa.gov/drink/contaminants/index.cfm

“Chlorine dioxide (chlorite) is rarely used as a disinfectant in Australian reticulated supplies.
When used, the chlorite residual is generally maintained between 0.2mg/L and 0.4mg/L. It is
particularly effective inthe control of manganese-reducing bacteria. Few data are available on
chlorate levels in Australian water supplies….Chlorine dioxide, chlorite, and chlorate are all
absorbed rapidly by the gastrointestinal tract into blood plasma and distributed to the major
organs. All compounds appear to be rapidly metabolised. Chlorine dioxide has been shown to
impair neurobehavioural and neurological development in rats exposed before birth. Experimental studies with rats and monkeys exposed to chlorine dioxide in drinking water have shown some evidence of thyroid toxicity; however, because of the studies’ limitations, it is difficult to draw firm conclusions (WHO 2005) The primary concern with chlorite and chlorate is oxidative stress resulting in changes in red blood cells. This end point is seen in laboratory animals and, by analogy with chlorate, in humans exposed to high doses in poisoning incidents (WHO 2005).” Australian Drinking Water Guidelines – National Health and Medical Research Centre

“…Subchronic studies in animals (cats, mice, rats and monkeys) indicate that chlorite and chlorate cause haematological changes (osmotic fragility, oxidative stress, increase in mean corpuscular volume), stomach lesions and increased spleen and adrenal weights… Neurobehavioural effects (lowered auditory startle amplitude, decreased brain weight and decreased exploratory activity) are the most sensitive endpoints following oral exposure to chlorite…” https://www.hc-sc.gc.ca/ewh-semt/pubs/water-eau/chlorite-chlorate/indexeng.
php#sec10_1Guidelines for Canadian Drinking Water Quality.

Townsville (Queensland) – Turbidity

2014/15: Townsville (Queensland) – Turbidity 13.8 NTU (Maximum detection during year)

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

24/8/20 – Dahl Reservoir Townsville (Queensland) – Chlorine

On 24 August 2020 Operator daily checks detected a high chlorine residual of 7.3mg/L in Dahl Reservoir and 6.75 mg/L in reticulation supplied by Dahl Reservoir. The dosing pumps were disabled, and the affected area was extensively flushed. The reservoir was refilled with
minimally chlorinated water to dilute the water that was in the reservoir. Investigation confirmed that the pump had been manually left on 100%, after bleeding to remove an air bubble, over the weekend in error. The site is not attended at weekends.
A Grundfos DDA pump will be installed December 2021. This type of pump has a button which is depressed when bleeding/priming pumps, and once finger is removed it returns to normal pump configuration so removing the “human error” factor. This will mitigate against the pump being set to 100%.

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.

2020/21: Townsville (Queensland) Manganese

Due to the discolouration event (DWI-506-21-08862) an increase of manganese monitoring was occurring across the network. These samples detected manganese above ADWG limits. As per event DWI-506-21-08862 description. These results were from dead ends of the network with possible inadequate flushing before sampling. All resamples detected manganese (whilst
above aesthetic limits) back within health guideline limits. Once pre-chlorination was established the filter media coating removed the soluble manganese.
Pre-chlorination has been set up across all modules (Mod 1-4). DO analysers have been installed at DWTP as prewarning that raw water quality has reduced. Aeration has been installed in RRD and operated to improve DO in bottom layers and throughout the profile.

Manganese: ADWG Guidelines 0.5mg/L. ADWG Aesthetic Guideline 0.1mg/L
Manganese is found in the natural environment. Manganese in drinking water above 0.1mg/L can give water an unpleasant taste and stain plumbing fixtures and laundry.