Sewage storage plan costs increase

‘‘This project is important for the health of the harbour and the health of the people who live in the city.’’ Geoff Hayward Onepoto general ward councillor

A new sewage storage tank could cost Porirua ratepayers up to $15 million more than budgeted.

The tank would temporarily hold the equivalent of up to three Olympic-sized swimming pools of sewage during heavy rain before pumping it to the Porirua Wastewater Treatment Plant. The aim is to cut the amount of raw sewage overflowing into Porirua Stream and Te Awaruao-Porirua Harbour.

The Porirua City Council approved the project in February and $48m was budgeted for it in June.

A report updating councillors on the progress of the city’s development projects this week showed the wastewater tank’s cost could go to $63m. A final figure won’t be confirmed until a contract is awarded next month as part of the tender process.

The new storage tank will be located north of Porirua train station between State Highway 59 and the rail track.

The council’s deputy chief executive and infrastructure general manager, Andrew Dalziel, said the numbers were provided by Wellington Water and the initial figures were based on a concept design from early last year but further work on the design had changed the numbers.

‘‘The key contributing factor is inflation in the construction market, which has risen significantly since the first estimate was provided,’’ Dalziel said. ‘‘Another factor is the recently updated seismic standards from the Ministry of Business, Innovation and Employment, which we need to adhere to and these have been factored into the design. It is not uncommon for cost estimates to change as we work through the various stages of project design.’’

Other than finances, the update said the rest of the project was tracking to plan. A temporary access bridge crossing Kenepuru Stream for workers and equipment to get to the site has been completed and a peer review of the storage tank’s design is being finalised.

Dalziel told Te Puna Kōrero committee meeting yesterday that construction of the tank would begin next February and was expected to be completed by late 2024.

Onepoto general ward councillor Geoff Hayward said while no-one was fond of cost increases, it was important to have the wastewater tank because it was ‘‘vital’’ to improving water quality.

‘‘This project is important for the health of the harbour and the health of the people who live in the city,’’ he said.