Cancer risk sees ozone water treatment plan abandoned

Monday, 2 July 2018

Ozone has been ruled out as an alternative to chlorine for treating Christchurch's vulnerable drinking water supply over fears it could lead to cancer.

City council officials examined whether the gas could be used alongside ultraviolet light treatment following a public backlash to the chlorination programme.

But analysis of the city's groundwater found the concentration of bromide, a chemical compound, was too high for ozone to be used safely.

Ozone reacts with bromide to create bromate, which can potentially cause cancer, leaving officials no choice but to reject it as an option.

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Helen Beaumont, who is heading up the council's water supply improvement programme, says UV is the only treatment alternative to chlorine after ozone was found to be unsafe.

* Christchurch City Council launches external review to uncover events leading to water chlorination

* Christchurch drinking water to be chlorinated for a year as councillors approve plan to keep it safe**

The discovery means that UV is now the only treatment alternative to chlorination – an option that comes with a hefty price tag of between $21.6 million and $86.4m.

Helen Beaumont, head of the council's water supply improvement programme, said bromide could be removed from the groundwater but the cost would be prohibitive.

The council is now pinning its hopes on UV treatment so chlorine can be removed within the planned 12-month timeframe – but it could still be a year before such treated water comes out of taps.

Beaumont said: 'We are looking at a concept plan for ultraviolet disinfection at the main pump site down in Beckenham.

Christchurch City Council hopes it can make improvements at some pump stations so chlorinated wells can be turned off in favour of others that have not been treated.

'We're pretty sure UV will work down there, so it's just putting a concept plan together and getting it costed.

'We are going to do a concept design, and we have scoped out that we've got space at the main pumps facility to install the gear.

'If we put it in place it would be nine to 12 months to from design to a detailed design, tender and installation before turning it on.'

While UV is being investigated the council is trying to reduce the number of pumping stations that need chlorine, and chlorinated below-ground wells could be switched off once repairs to untreated above-ground well heads are completed.

Eight pump stations are being looked at as potential sites to switch off chlorination.

Christchurch Mayor Lianne Dalziel hopes a forthcoming review will shed light on exactly what led to the city losing its treasured secure status for its drinking water.

Meanwhile, a review launched six months ago examining the events that led to Christchurch's water supply chlorination is expected to be signed off within the next few weeks.

Mayor Lianne Dalziel hoped the report would reveal exactly why the city's drinking water supply lost its secure status – and suggested it could potentially pave the way for chlorine removal earlier than 12 months.

The mayor, who has not yet seen the report, told Stuff: 'If we don't understand what happened, we're not necessarily going to be in a position to understand what we need to do.

'It may well be that we don't need to chlorinate our water in order to deliver the standard which, quoting the Minister of Health, is 'demonstrably safe'.

She said she believed the report would help clarify the difference between water supply problems in Christchurch and Havelock North, where contamination contributed to deaths, and what level of risk was faced.

'We need to understand what's happened, and that will help us understand what our next steps will be – we may take the chlorine out earlier.

'I don't want to absolutely commit to a date until I've had a time to read the report and absorb it.'