Mr Fell said it was vital that the investigator was someone completely independent of district council, Horizons Regional Council, their employees or any of the consultants previously engaged in the project.
The purpose of the inquiry is so council and community understand the circumstances and council processes which led to the failure of the old plant, from concept evaluation (2003) to the final failure (2012).
As well as reviewing the processes council followed from 2003 to 2012, it will also look at the management of the process, the reporting to council and the decisions council made at the time.
It would also try to establish what fault if any, was there in the council's input into the design parameters and its decision-making processes that led to accepting the design and build of the WWTP that was commissioned in 2007.
It would find out who was involved, and the decision-making process, starting from the initial design of the plant in 2003 to its opening four years later, and what fault if any, was in the council operation of the plant which would have led to its failure.
The investigation will also look for any evidence that wet industries underestimated their inputs during the design phase, or added non-consented, excessive or non-permitted inputs into the WWTP that contributed to its inability to function. And it will try to find out if there was any failure of timely reporting by plant staff to Horizons, council staff, the mayor or councillors of the failure of the plant.
There will be some limitations on what information can and cannot be used in the investigation. For example all evidence MWH presented in the court case remains confidential unless MWH agree to release that information. However, all the council evidence will be available.
Councillors agreed the community was anxious to get the issue thoroughly investigated.
Councillor Sue Westwood the workshop was not only to agree to an independent inquiry, it also meant establishing the processes to be followed "and make sure the questions being asked cover all the bases the council and this community expect".
"The inquiry is there so people of Whanganui understand what went wrong."
Mr Fell said a number of local names had been suggested to him to head the inquiry but he said it needed to be someone completely independent of the city and the issue.
Councillor Ray Stevens said he had no qualms about "naming names" because the process needed to be transparent but Mr Fell said doing that "leaves us open to a lot more than a $100,000 inquiry".
Councillor Rob Vinsen said there was some evidence there was political pressure put on council to reduce the costs of the plant and he expected the process around those decisions would also be covered.
Mayor Annette Main said the inquiry was about the processes that were followed rather than technical details of the old plant which have already been thoroughly investigated and made public. And it was not concerned with the decision to build the new plant.
The name of the independent investigator is expected to be released in the next few days.
