2015 March – Gloucester (New South Wales) – Chlorine

2015 March: Gloucester (New South Wales) – Chlorine

“Finally, sampling of the water quality was limited to a portable chlorine test kit, with a
limit of 8.8mg/L. Whilst this was an indicator of high chlorine and a further need to
flush, no formal testing was done and analysed; thus the true levels in the reticulation
were not actually quantified. It was not until a sample was provided by a customer taken
on Tuesday night, and submitted to the MCW laboratory several days later that an
understanding of the quantity of chlorine dosed in the system could be established.
Whilst the sample was not formal, it could not be ignored; the sample had a total and free
chlorine reading of 140mg/L. Formal sampling would have also allowed a more detailed
assessment of other analyte’s. It must also be noted that a number of customers in
Gloucester receive water directly off the rising main to the reservoirs, thus they would
have received a highly concentrated slug of chlorine straight from the plant.”



2pm update 26 March

Chlorine levels in Gloucester have now returned to normal.

Extensive testing has been undertaken over the last two days at a large number of locations across the township, along with flushing to remove the higher chlorinated water from the town water supply.

Customers in the Cemetery Road area may still experience some isolated chlorine taste and odour issues.

We do not believe that at any stage chlorine levels posed a risk to health. The warning to not drink the water was issued as a precautionary measure while we gathered further information on the situation. Chlorine limits set by the National Health and Medical Research Council are an aesthetic level and much higher levels have previously been experienced without any adverse health impacts.

However we do acknowledge the smell and taste of the water was not acceptable to our customers.

Representatives from MidCoast Water – including the chair, deputy chair and executive staff –  will be available in Gloucester tomorrow morning at the Meeting Place in Denison Street between 9am and noon.

MidCoast Water has engaged independent external consultants to undertake a full investigation into the incident.

Any members of the public interested in contributing to the independent investigation into the incident can email their concerns to investigations@midcoastwater.com.au

This will cease our regular updates on this issue, however will continue to issue advice if anything change

11.30am update:

MidCoast Water representatives will be at the Meeting Place, Denison Street from 9am-12 tomorrow, Friday March 27 to talk to residents.

Present will be the chair, Cr Tony Summers, deputy chair, Cr Aled Hoggett and executive staff.

10am update:

Water main flushing started at 6.30am in parts of Gloucester as chlorine levels continue to stabilise across the town.

Testing this morning has indicated chlorine has returned to normal levels in the hospital area and western side of town.

Problems may still be experienced in the northern and eastern parts of town, in the  Ravenshaw and Tyrell street areas.

Customers are once again reminded the water is safe for use. However anyone who feels they have health concerns is urged to seek medical advice.

Meanwhile we are continuing an internal investigation on the cause of the chlorine dosing pump failure.

We have launched an independent investigation into the incident. This investigation, to be undertaken by Hunter H2O, will look at the cause of the incident, the organisation’s response and any improvements that are required.

Hunter H20 is a consultancy with extensive water treatment and operational experience.

Copies of the draft independent report will be provided to all regulators for their comments and the report will then be released publicly.

No other water supplies have been affected by the issues in Gloucester.

We have been in contact with NSW Health, NSW Office of Water and the Environmental Protection Authority (EPA) throughout the incident.

We will be providing a $50 rebate on the next water account to every customer supplied by the Gloucester water supply scheme for the inconvenience caused by the outage and to offset water charges due to internal flushing…

A further update will be provided at 2.30pm

Wednesday March 25

6pm update:

Water main flushing is continuing in parts of Gloucester and MidCoast Water crews will continue to flush until sunset in the eastern part of town to reduce the chlorine levels in the water supply.

Flushing will then resume in the morning. If customers are still experiencing a chlorine taste and smell in their water they are assured that the water is safe to use and will continue to improve over the coming hours.

MidCoast Water has been in contact with NSW Health, NSW Office of Water and the Environmental Protection Authority (EPA) throughout the incident.

MidCoast Water is undertaking an in-depth internal investigation into the causes of the incident and the response.

MidCoast Water will be providing a $50 rebate on the next water account to every customer supplied by the Gloucester water supply scheme for the inconvenience caused by the outage and to offset water charges due to internal flushing.

Any commercial customers who feel they experienced significant financial loss as a direct result of the outage are asked to contact our customer service centre on 1300 133 455.

Representatives from MidCoast Water will be available in Gloucester on Friday morning to discuss any issues. Times and venues will be available on our website.

An update will be provided at 9.30am Thursday March 26

4pm update:

Gloucester residents are advised the town water supply is now safe to drink with current chlorine levels posing taste and odour issues only.

Chlorine readings in all three Gloucester reservoirs have returned to normal levels, however chlorine readings do remain high in the network in the Tyrell Street area.

MidCoast Water operators are continuing to flush this part of the network and chlorine levels are reducing. Flushing will continue until normal test readings are found in all parts of the network.

Gloucester residents are requested to flush their house pipes for at least 10 minutes before using water this evening. This will assist MidCoast Water in purging pockets of the network and ensure the water is sourced from the mains and not internal pipes.

2pm update:

Higher than normal chlorine levels are being experienced in the Gloucester water supply.

This appears to be due to an equipment failure.

Staff have currently flushed one third of the water supply network and are expected to flush the remaining parts of the system over the next two to three hours.

While it is not expected that high chlorine levels would have any adverse effects,  our precautionary advice continues to be not to drink the water until notified otherwise.


Gloucester residents are advised an overdose of chlorine has occurred and as a precautionary measure the water should not be consumed until further notice.

Caution is recommended for anyone with skin sensitivities.
This advice will be updated at 2pm today.

Additional information:

  • Higher than usual chlorine levels were detected in Gloucester during Tuesday March 24– and customers would have noticed increased chlorine smell and taste, however levels were well within guidelines.
  • We monitored and tested over the following 24 hours and testing mid-morning Wednesday March 25 that level rose to the point we issued a precautionary advice not to drink the water.
  • It should be noted this only affected the Gloucester water supply – nowhere else.
  • The Australian Drinking Water Guidelines indicate there are very few toxic effects associated with drinking water with high chlorine concentrations. In one report people drank water with substantially higher chlorine levels without adverse effects. However if anyone is concerned they should seek medical advice. The Australian Drinking Water Guidelines can be found here part V of the guidelines contain fact sheets for values of drinking water – pages 13-47 and 13-48 contain the advice of the National Health and Medical Research Council on chlorine.
  • Water mains were flushed across Gloucester and the water was onto grassed areas,roads and down drains after the completion of a risk assessment. Water was not directly released to the river and MidCoast Water is confident it has not presented a problem to local waterways.
  • Samples were taken from the Gloucester River and all results will be provided to the EPA.
  • It should be noted chlorine is removed from the water by aeration and exposure to sunlight as it is purged from the network.
  • Where possible flushing undertaken close to the river was directed to MidCoast Water’s sewer system.
  • We were in contact with the Environmental Protection Authority (EPA), NSW Office of Water and NSW Health throughout the incident.
  • We worked with local schools, preschools, the hospital and nursing home and are in regular contact with them. Provision for bottled water was made.

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