The Frankton Flats and the Shotover Delta are the best locations for the disposal of Queenstown’s treated wastewater, a council analysis has found.
Queenstown Lakes district councillors were yesterday presented with a shortlist of five options for disposing of treated effluent from the Shotover wastewater treatment plant to land.
Until the chosen option is operational in 2030, it will continue to be directly discharged into the Shotover River.
A presentation by senior project manager Andrew Hill said the most expensive option, at from $120 million to $200 million, was "moderate-rate" disposal into a network of trenches on 90ha of land "in and around" Queenstown Airport.
The cheapest option was a "land-flow path" along one or two channels from the plant to the Kawarau River.
That option, estimated to cost $20m, was described by infrastructure operations manager Simon Mason as the "closest to a do-nothing minimum option", and not supported by iwi.
The other three short-listed options were estimated to cost from $40m to $75m, the report said.
One was injecting wastewater into deep bores on the Frankton Flats, each of up to four bores drilled to a depth of 70m-80m.
Another was the construction of a "sub-surface wetland" on the delta, in which wastewater would flow along a 1km channel, planted with wetland-type vegetation, to the Kawarau River.
The final option was the injection of wastewater into shallower bores or "soak holes" on Frankton Flats, Mr Hill said.
Whichever option the council chooses, it will be its second attempt.
The existing disposal field on the delta, commissioned in 2019, began failing the following year.
That prompted the Otago Regional Council to issue the council with a series of abatement and infringement notices for breaching its resource consent, and finally to apply for an enforcement order in the Environment Court in January.
In a controversial move, the council invoked emergency powers to begin direct discharge into the Shotover River on March 31, citing the concerns of its airport company over the heightened risk of bird strike from ponding on the disposal field.
It is expected to lodge a retrospective consent application with the ORC for the direct discharge tomorrow.
Mr Hill said the preferred option would be presented to the council for approval in September.
Cr Lyal Cocks said if a more expensive option was chosen because iwi did not like the "cultural impacts" of cheaper ones, councillors would have to explain that to the community.
Mr Mason said iwi representatives had been "realistic" in their discussions with the project team in November, and understood there were limited options available.
