Since then another $1.6m had been spent at Waipukurau building an additional pond to cater for stormwater infiltration and an anaerobic pond, which after a few months of operating was closed down because it was adding to a strong odour emanating from the plant.
Over the last few years, breaches in the operating conditions had occurred, including exceeding E. coli limits, which resulted in the Hawke's Bay Regional Council prosecuting the CHB council earlier this year.
Mrs Davidson said the council acknowledged the outcome of the review was disappointing, although the quality of the water from the plants going into the river had improved markedly over the last five years.
The review's recommended solutions were either an activated sludge treatment, or discharge to land, which could be introduced for both sites either separately or jointly.
It put the cost of activated sludge treatment at between $11.9m and $20.2m, and estimated the effluent disposal to land option could cost $36m.
Mrs Davidson said the council would thoroughly investigate both options in partnership with the Hawke's Bay Regional Council, central government and the wider community.
She said it was too early to say whether the land purchased by the regional council, and previously offered to the CHB council for land discharge, at that time estimated to cost up to $11.2m, would be part of any future solution.
She reiterated the council was committed to work with the regional council on any solution, a sentiment that regional council chief executive James Palmer echoed, adding the land that had been bought had not been taken off the table as an option.
Mayor Alex Walker said the council was extremely disappointed by the review's final results but was confident the new information would enable long-term wastewater options to be explored.
"Affordability is a priority – we have to find a way to pay for it.
"While we have very high level estimates of potential capital costs, there's more investigations needed but I am confident in the clarity and quality of the information we have."
She said the role of other parties in how any new option would be funded, including potential central government involvement, would be crucial.
"From what I have seen with the priorities and behaviour of the new Government I am hopeful we could have some support."
It was unlikely a final solution and costs would be included in the draft long term plan 2018-2028, but that plan would include an allocation of funding to investigate the options.
Former CHB mayor Peter Butler, who headed the council when the floating wetland treatment system was adopted, said the situation was a real shame.
"What you have to remember though is that the councillors and mayor are lay people, who are professionals in their own jobs but rely on the best information that is given to them by the experts.
"I have always considered councillors and the mayor as trustees of other people's money and we have to pick the best solution that's the most cost-effective - and we did that."
He said that the current council would now have to put their trust in the next batch of experts.
Hawkes' Bay Regional Council chairman Rex Graham said he had "strong sympathy for the new mayor and chief executive who have to clean this mess up".
