10 Apr 2018

Investigations are under way into whether it is better to convert some below ground well heads to above ground, boosting the likelihood of the city’s water returning to its unchlorinated state in the long term.

In December, the Drinking Water Assessor advised the Council it no longer considered the city’s groundwater supply provisionally secure because some of the below ground well heads needed to be upgraded.

On January 25, the Council decided to temporarily treat the supply with chlorine while well head improvement work was completed.

Now staff have prepared a report to the Infrastructure, Transport and Environment Committee(external link) outlining a variety of options along with their pros and cons.  The final approach will probably contain a mix of options. 

“Our preferred approach seeks to return to a non-chlorinated water supply as soon as we can and staff are well aware of Councils resolution that permits chlorination for a period of up to one year.” says City Services General Manager David Adamson.

“Converting most of the below ground wells to above ground and integrating some UV treatment into the water scheme gives us the best chance of returning to an unchlorinated water supply in the long term. Above ground well heads offer a better safeguard against possible contamination, are easier to access for maintenance and converting them gives us a better chance of gaining an exemption should the government make treatment mandatory.”

The preferred option could also include installing UV treatment for a number of pump stations where the Council may not be able to get secure status, or as a medium term option while new wells are drilled or upgrades done.

“The advantage of UV treatment is it doesn’t affect the taste or smell of water —most bottled water is treated this way. It can be more expensive to implement UV treatment, and unlike chlorine, it doesn’t provide protection beyond the site where treatment occurs. However where the installation of UV treatment replaces the need to upgrade a number of well heads it can be an economical solution.

“We’re hoping to reduce the amount of time we need to chlorinate. With careful management of the various pump stations as well as limiting demand where we can, we may be able to provide enough unchlorinated water for the city. It is intended to turn off the chlorine at individual pump stations as soon as they regain their secure status.

“One of the challenges is that our network is made up of parts that were built at different times — one of our well heads dates back to 1927 — and to different design specifications. This means a one-size-fits-all approach simply will not work. There are elements at each site that are unique and this makes it hard to cost it with accuracy until we have detailed solutions for each site.”

Mr Adamson said once the Council had indicated their preferred option to staff, they would finalise the programme of work, including timing and cost taking into account the issues at well, pump station zone and network level.