17 Aug 2018

A $2 million investment in ultra-violet (UV) light disinfection could bring an end to chlorination at Christchurch’s largest water supply pump station.

Next Thursday Christchurch City Council will consider a report that recommends installing UV light disinfection at the water supply pump station at the south end of Colombo Street.

Read the report.(external link)

Pipes at a pump station.

The Main Pumps water supply pump station supplies water to about 185,000 people.

The station - known as Main Pumps - takes water from six wells and feeds about 11 per cent of the central zone.

The central zone provides water to about 185,000 people – just over half the city’s population.

The six wells at Main Pumps are not considered secure under the Drinking Water Standards of New Zealand because they have below ground well heads. The six wells also draw water from a shallow aquifer and further modelling work needs to be done to demonstrate that the source water is secure.

Council staff have been investigating options for improving the security of the wells but drilling deeper wells at the site is not an option as a volcanic shelf extending out from the Port Hills means there is no deeper aquifer to tap in to.

Improving the security of the well heads by raising them above ground and overdrilling them to create a seal around the well casing is possible, but it would cost about $1.8 million.

The problem is that even once the well head work is complete, the wells may still not be considered secure because of the shallow depth of the aquifer feeding them.

Council staff have concluded the best option is to install UV light disinfection at Mains Pump to treat the water from all six wells.

UV improves the safety of the water without impacting on the taste and can be installed for about $2.3 million, although there will be ongoing maintenance costs of about $75,000 a year.

“The advantages of UV treatment is there are no taste and odour effects and it can be implemented in a relatively short period of time – we think we could have it installed at Main Pumps within 10 to 12 months,’’ says the Council’s Water Supply Programme Manager Helen Beaumont.

“It is well proven technology and once the UV system is installed and commissioned, we will be able to stop temporary chlorination at the city’s largest pump station. This is option we will be recommending to the Council,’’ Ms Beaumont says.