Wild weather dumped up to 100mm from storm cells over Braidwood on Thursday before Christmas causing flash flooding in Wallace Street and electrical blackouts, and also affected Council’s attempts to rectify the contamination of town drinking water at the busiest tourist time of year. Palerang Council Director of Works, Gordon Cunningham explains what happened.
“On the 22nd December 2011, Council was advised of a failure in a routine bacteriological sample taken from the Braidwood water supply network. These samples, taken on a weekly basis, are funded and tested by the NSW Department of Health at their laboratories in Sydney. Similar arrangements are also in place in Council’s other water supplies at Bungendore and Captains Flat.
The failure of 22nd December was in relation to the detection of Escherichia coli (E.coli), a specific type of indicator bacteria which is used to detect the presence of faecal contamination.
Most surface water supplies (like Braidwood) face a risk of such contamination particularly given the environmental conditions around their sources. Any warm blooded animal, for instance, can be a source of E.coli contamination for a surface water supply system.
Council routinely conducts full chemical and bacteriological sampling of its water supplies on a quarterly basis by way of supplementing those arrangements currently provided by the Health Department.
The most recent two tests under this regime have detected E.coli readings of 34 and 44 units at the Shoalhaven River intake; almost certainly the source of the problems associated with the events of 22 December.
Little has changed in the process of the Braidwood water supply since it was first commissioned in the mid 1950’s. Essentially a raw water supply, the quality of the water in the Shoalhaven largely reflects that ultimately supplied to the consumer. The only level of treatment employed is the dosing of chlorine for the purposes of disinfection.
Despite its effectiveness as a disinfectant, chlorine does have its limitations. Raw water, such as that supplied in the Braidwood scheme, also contains many organic and inorganic compounds that otherwise react with it and thereby reduce its ability to work. This, together with the changeable nature of the Shoalhaven supply, makes it very difficult to settle on and maintain a reliably safe target of residual chlorine throughout the network.
Standard Health Department protocol provides that a ‘Boil Water Alert’ is to be issued where a water utility has such a bacteriological failure and is not able to provide evidence of adequate disinfection within a reasonable period of time. The direction to issue the notice for Braidwood was made on 23 December despite Council’s attempts to boost chlorine residuals – a situation substantially hampered by electricity supply interruptions associated with thunderstorms around this same period.
Notices of the alert were issued by Council staff by hand on the same day and again on 24 December with additional assistance being kindly provided by the local community radio. Council staff continued to work on the chlorine system over the ensuing Christmas / New Year break with follow-up bacteriological samples being taken and tested at the first opportunity following Christmas. These tests confirmed the absence of both E.coli and coliforms generally as well as satisfactory levels of free chlorine. The Department of Health subsequently confirmed the lifting of the alert on 29 December. Notices to this effect were issued by hand and on the community radio on the following day.
Council staff continue to closely monitor the chlorination system with the aim of securing a more reliable chlorine residual. The task continues to be difficult given the characteristics of the system described above.
The planned water treatment plant (currently under construction) will provide the best long term means of addressing these problems.
The plant is due for completion in August this year.”
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