Project Pure is the most expensive infrastructure project the district council has undertaken and the costs have continued to mount since a malfunction at the plant in January.
The council was working with Project Pure contractors United Group Ltd New Zealand to address concerns about the operational requirements of the plant, QLDC wastewater manager Martin O'Malley said.
The mounting cost to the council and ratepayers was a "conservative estimate" and mainly consisted of ongoing consultant and legal fees, he said.
There were five original areas of contention for the council about the plant's operational requirements, but United had since addressed concerns regarding noise at Project Pure.
An acoustic report had confirmed that noise levels at the plant were not exceeding district plan levels, he said.
Both parties wanted to resolve the remaining issues, which included operational reliability of the plant, odour, septic tank waste processing and staff work space, Mr O'Malley said.
During an Otago Daily Times tour of the sewage and wastewater plant, odour levels - when standing directly next to the main effluent containment areas - were almost non-existent.
• Project Pure: Wanaka
What: $21 million sewage and wastewater scheme.
Problem: Operational concerns since a plant malfunction in January have not been adequately addressed during a defect liability period, which lapsed on May 18.
