QLDC uses cheaper, less effective UV option in water quality 'quick fix'

by Kim Bowden - Nov 23, 2023

The Queenstown Lakes District Council is banking on bringing all non-compliant water supplies across the district up to standard for a little less than $11 million.

The end figure feels like a relative bargain considering Mayor Glyn Lewers told a media stand up during the first week of a boil water notice in response to a cryptosporidium outbreak that the bill for ramping up treatment of the problematic Two Mile supply alone could cost in the vicinity of $30 million.

Now, nine weeks later, the council is opting to put in UV treatment kit at the facility to protect against contamination by protozoa like cryptosporidium with a price tag of just $1.4 million.

It's a quick fix that, once installed, should make the facility compliant with national drinking water standards, meaning regulator Taumata Arowai can allow the water boil notice to be lifted.

The council doesn't plan to stop there.

For an estimated $9.4 million more, UV treatment systems will be installed at all currently non-compliant drinking water supplies across the district.

Included in the price, swapping out the first Two Mile UV treatment solution, which will be installed at the Western Wanaka treatment plant where it is needed, in favour of a gruntier piece of kit, hopefully by May next year.

"The permanent solution at Two Mile will include features that are not part of the temporary solution, including insulation and air conditioning for the plant room, as well as larger UV reactors. These aspects are not essential to meet compliance but are preferable for ongoing operations," a council spokesperson says.

For a cash-strapped council it almost sounds too good to be true.

The potential catch? The council is relying on UV disinfection systems rather than membrane filtration.

The spokesperson says, "This approach has been chosen because the equipment is more readily available from within New Zealand and is far more suitable for the rapid deployment needed in the context of the recent crypto outbreak".

They say the $30 million referenced by the mayor back in September was associated with the cost of constructing an entirely new membrane filtration treatment plant.

"This approach – whilst having performance, resilience and longevity benefits associated with the higher cost – is unsuitable for a rapid response situation due to equipment lead times, land requirements, (and) planning approvals.

"However, this option remains in our plans for the long-term. Our current investment in UV technology will result in a compliant water supply across the district in the quickest possible time."

So, what does Taumata Arowai make of this call?

Steve Taylor, the head of regulatory for Taumata Arowai, confirms while it has been working with the council on its plans for the Two Mile plant since issuing the compliance notice, district-wide solutions to meet drinking water safety standards have not been on the agenda.

He would not categorically say whether the council's UV disinfection approach was sufficiently robust.

There is no prescriptive instruction in the new national rules detailing exactly for what gear should be used to treat water to make it safe for drinking. 

"This allows a number of different kinds of protozoa treatment systems to be used, either alone or in combination, so long as a certain level of performance - known as ‘log credit’ - is achieved," Mr Taylor says in a written reply to questions from Crux.

At the risk of getting too techie on you, there's more:

"Each drinking water supply must have a protozoa barrier that provides treatment equal to or exceeding the log level requirement for its source water class. Protozoal treatment using UV can obtain up to 4-Log credit, depending on the system. In general terms, this provides an effective protozoa barrier for the highest risk class of source water (Class 3), which includes shallow bores and surface water sources like lakes.

"Whether the system installed by QLDC achieves a full 4-Log credit will depend on the detailed system design and performance parameters." 

He says there are limitations with UV disinfection, like any other technology.

"Adverse events such as rainfall and algal blooms can affect water treatment in any supply.   

"The Water Services Act 2021 requires drinking water suppliers to ensure their drinking water is safe, including a multi-barrier approach to managing risks. This recognises the risk that not all barriers may be effective all of the time, and requires suppliers to proactively plan to manage, control or eliminate the risk. 

"Issuing boil water notices in response to rainfall events is not an acceptable approach to demonstrating compliance with the Drinking Water Quality Assurance Rules."

Whatever happens, he says the council will need to demonstrate the protozoa barrier is in place and operating to comply with national rules.

"It is the drinking water supplier’s responsibility to plan for and implement the necessary infrastructure to comply with legislative requirements and we will keep engaging with QLDC to ensure it continues on the pathway towards compliance for all of its supplies."

For now, the QLDC and its contractors keep working on the task at hand - sorting the Two Mile plant to lift the boil water notice.

Yesterday they began flushing the network, in a bid to rid it of any hidden traces of cryptosporidium.

"Whilst this is a planned and controlled process, you may notice QLDC contractor Veolia teams out and about opening hydrants with water flowing into stormwater drains as a result," the council says in a Facebook post yesterday.

"We are working to minimise any disruption but there is a chance of temporary, brief water shutdowns to some properties over the next two weeks."

The council is reminding residents and visitors to keep boiling tap water in the following areas:

  • Queenstown town centre
  • Gorge Road out to and including Industrial Place
  • Fernhill
  • Sunshine Bay
  • Queenstown Hill above Frankton Road out to and including Goldridge Way and Goldrush Way

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