Smith, who’s standing in for Mayor Glyn Lewers while the latter’s overseas, says technical investigations now under way on the Shotover Delta and Frankton Flats could end up making councillors’ decision on the best option relatively clear-cut.
"It’s going to come down to which one is practical, feasible, and affordable."
Councillors were presented with a shortlist of five disposal options at a workshop on Tuesday.
Selected by a council project team following a desktop analysis, all five are confined to the delta or Frankton Flats, with only one directly discharging to the Kawarau River.
Site investigations will continue until July, with the preferred option to be presented to councillors for approval in September.
Until that option is up and running — the council’s given itself until late 2030 — treated effluent from the Shotover wastewater treatment plant will continue to directly discharge into the Shotover River.
Senior project manager Andrew Hill told councillors the five options ranged in estimated cost from $20 million to $200m.
The most expensive option, a network of trenches on 90 hectares of land "in and around" Queenstown Airport, was described by Cr Niki Gladding as "highly unfeasible" given its cost and land requirements.
The cheapest, in which wastewater would flow along one or two channels from the plant to the Kawarau, was likely to meet minimum national standards but would not be supported by iwi, Hill said.
The other three options are estimated to cost between $40m and $75m — within the $77.5m the council put aside in its long-term plan last year for developing a new disposal system.
Speaking at the workshop, Gladding asked why potential disposal sites outside the delta and Frankton Flats had not made the short list.
They included pasture land between the Kawarau River and the Park Ridge subdivision, river flats below Bridesdale Farm, and the southern slopes of Coronet Peak.
However, infrastructure operations manager Simon Mason said some areas, including the land south of the Kawarau, had been ruled out because technical studies carried out for different purposes had shown they were unsuitable.
Smith says his preferred solution of the five is injection of wastewater into deep bores on the Frankton Flats, but says it’s still early days.
"We’ve got to understand the capacity of that geology to cope, and the land issues with the airport."
It strikes him as a "middle-ground option" in terms of cost and complexity, which would address iwi and broader community concerns about discharging to the river.
Meanwhile, the council’s expected to lodge a retrospective consent application with the Otago Regional Council today for its direct discharge to the Shotover.
