But councillors Rob Vinsen and Charlie Anderson said this week that, back in October, council agreed to seek an independent answer to the question of whether the $39 million Cardno-designed plant was the best process for Whanganui considering both environmental and cost issues.
Mr Vinsen said senior managers had decided to put the question in two stages, firstly asking consulting engineers CH2BECA whether there was a high likelihood that the council could obtain a new resource consent from Horizons Regional Council which would allow waste to be dumped in the sea at higher levels than the current consent allows.
"Unsurprisingly, the answer came back that a relaxed consent is unlikely," Mr Anderson said.
"But it's the assumptions that follow from that conclusion that are really concerning. It demonstrates that council senior management want nothing else considered.
"While relaxed limits would open up more options and far less costly options, it begs the question: Is the Cardno plant the best within the limits of the current resource consent?"
He said this critical question had not been asked.
"Not asking that question, and ignoring the council resolution, lets the public down and leaves doubt in the community."
Mr Vinsen said he was appalled that three months had been wasted on a simple question - "the answer to which was obvious".
"CH2BECA could have proceeded with the real question to remove any doubt that this $39 million plant is not the optimum plant for Whanganui as some experts allege."
He said it was a "hugely important" decision council was about to make because it would shackle the community to a rate increase of about 13 per cent over the next three years.
"We can't afford to get this one wrong again."
Mr Vinsen said there had been a concern among management that CH2BECA would propose something new, meaning more delays before construction started, and which would also get council offside with Horizons and local iwi.
Mr Vinsen said the CH2BECA report was hardly a "ringing endorsement". "They said while the Cardno concept represents an overall improvement from the current discharge, there are probably other treatment processes that would also meet these water quality targets after reasonable mixing.
"It's my view that senior management are sidelining the council resolution that sought an independent engineering opinion.
"Unfortunately, I think the majority of councillors will go along with it in the interest of expediency."
Councillor Philippa Baker-Hogan, who will be absent from tomorrow's meeting, is also frustrated with council resolutions not being followed through.
"This treatment plant has doubled in capital cost since its approval in 2014, and the delays have been necessary to investigate ways to reduce capital and operational cost."
She said, if councillors did not get answers to their original resolution before approving the Cardno design "they are failing this community on the most significant decision they will ever make".
The plant has been shut down since the summer of 2012-13 when malfunctions created sickening odours across the city. Since then, partially treated waste has been redirected through the marine outfall more than a kilometre off South Beach.
