The stark choices presented in a technical analysis of the four short-listed options at a workshop yesterday were summed up by Queenstown Lakes District Mayor John Glover as a case of choosing the "least worst" option.
The Environment Court has given the council until the end of 2030 to deliver a new disposal system to replace the treatment plant’s failed disposal field on the Shotover delta.
It was taken offline when council management invoked emergency powers to begin discharging directly into the Shotover River on March 31.
Senior project manager Andrew Hill told councillors one option had emerged from the analysis as the most cost-effective — direct discharge into the Kawarau River via a rock-lined channel.
At an estimated cost of up to $44m, it would be the cheapest to build and operate, could deal with projected future volumes of wastewater with certainty, and was expected to be consistent with new national wastewater standards.
All councils were now required to choose the most cost-effective option when making decisions on wastewater infrastructure, Mr Hill said.
Option B was a "sub-surface" wetland on the Shotover delta through which the treated wastewater would flow before entering a surface channel or pipe that would convey it to the Kawarau River.
It would have a gravel base with planting on top, and be designed to avoid ponding.
Council operations and maintenance manager Simon Mason said it would give a "perception" of ground disposal, but from a technical standpoint was the same as option A.
The final two options involve discharging treated wastewater into holes drilled in council-owned land on the Frankton Flats, including sports fields and road corridors: option C involves 10 deep bores of about 100m in depth, spaced between 100m and 200m apart; while option D has 50 "soak holes" of about 20m in depth and spaced about 10m apart.
Mr Hill said they were "hybrid" options that would operate in combination with the wetland because the analysis had indicated neither would have the capacity to dispose of all the plant’s output.
He emphasised all the options would have "approximately" the same impact on the Kawarau River, with the impact on water quality expected to be "less than minor" once dilution had occurred.
However, their estimated impact on rates and development contributions in Queenstown would differ greatly, with option A adding a maximum of $98 per property to rates by 2031, while option D would add up to $400 per property by 2037.
The options had been discussed with iwi representatives, who had made it "very clear" that all four involved some discharge to water, and were therefore "unacceptable from the perspective of cultural values", he said.
Iwi wanted a "more holistic" investigation of alternatives for managing Queenstown’s wastewater that did not rely on treatment at the Shotover site.
When Cr Samuel Belk suggested the presentation was effectively "selling" one option, Mr Hill said option A was "not a recommendation, but just the conclusion of the analysis".
The preferred option would be presented to councillors in February.
