The plants were commissioned in 2012 for $6.4m to meet increasing river water quality conditions. At the time, Hawke's Bay regional council proposed a scheme whereby treated sewage would be discharged over land it had bought for a forestry enterprise. But the CHB council of the day said the estimated cost of more than $8.5 million was "too expensive" for ratepayers.
Since the upgrade, council has had to spend another $2.6m at the Waipukurau plant, building an additional pond to cater for stormwater infiltration and an anaerobic pond which, after a few months of operation, was closed because it was contributing to strong odour from the plant.
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 in the past five years.
The 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 and work with the regional council, central government and the wider community.
Regional council chief executive James Palmer agreed, saying the forestry 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 a long-term solution to be found.
"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, including central government, would be crucial in finding the funds needed.
"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 for 2018-2028 but that plan would include an allocation of funding to investigate the options, she said.
Former CHB mayor Peter Butler, who headed the council when the floating wetland 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."
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".
