New storage tank to improve environmental outcomes for Porirua

Construction is about to begin on a wastewater storage tank in Porirua which will reduce discharges to Te Awarua-o-Porirua Harbour.

The new storage tank will temporarily store wastewater and release it at levels that the wastewater treatment plant can manage when it rains. The Porirua Wastewater network is currently unable to cope with the large volume of water entering the network during heavy rainfall, which regularly results in partially treated or untreated wastewater overflows to the environment. Storing the wastewater to gradually release back into the network when there is capacity will reduce the frequency of these discharges and lessen impacts on the environment.

The tank will be located north of Porirua railway station, between SH59 and the railway line. It will hold up to seven million litres (about three Olympic-sized swimming pools) of wastewater when there is heavy rain.

The storage tank is part of a wider programme of improvements to the wastewater network that Wellington Water is carrying out on behalf of Porirua City Council.

The removal of wastewater from Te Awarua-o-Porirua is a high priority for the Porirua City Council and Ngāti Toa Rangatira and aligns with the principles of te Mana o te Wai which focuses on restoring and preserving the balance between water, the environment, and people, now and in the future. Once complete, the project will have immediate benefits to Te Awarua-o-Porirua. 

“We’re committed to improving the health of waterways across Wellington, and we’re particularly pleased that we can make a step towards improving the health of Te Awarua-o-Porirua.  It has been very gratifying to work with Porirua City Council to bring this important project to fruition,” said Tonia Haskell, acting Chief Executive Wellington Water.

In May, earthworks will start at the south side of the site, with construction of the tank itself beginning after winter. Extensive planting of kowhai/ngaio coastal forest, kahikatea/ marsh ribbonwood as swamp planting, and carex, tussock and rush on stream margins will screen the tank from view.

Porirua mayor Anita Baker is pleased construction of the storage tank will be underway shortly. “This is a hugely important piece of infrastructure and a major investment that will ultimately help protect Porirua’s harbour and build resilience in our city. I can’t wait to see it get started so we can get those benefits longer-term.”

The project includes the storage tank and associated pipework, a new pumping station, two weir structures, and a retaining wall. An access bridge has already been constructed. The project budget is $85m. It is expected to be completed in 2026.