Two Hawke’s Bay wastewater plants to replace outfall pipes in $60m-plus projects

The Hastings wastewater treatment plant (left) and a boat working on the Awatoto outfall pipe in 2020. Photo / NZME composite

Hawke’s Bay’s two largest wastewater plants, which service Napier and Hastings, will begin replacement work on their leak-prone outfall pipes next year – at a combined cost of over $60 million.

Napier City Council’s wastewater treatment plant at Awatoto and Hastings District Council’s plant at nearby Clive both have ageing outfall pipes with failing sections.

Those pipes send treated wastewater out to sea in Hawke Bay.

The Napier outfall pipe is 1.6km long and the Hastings outfall pipe is 3.1km long.

Napier City Council is planning a full replacement of its outfall pipe with a budget of $30m-$45m, while Hastings District Council will replace the first 150 metres of its outfall pipe (and also replace its outfall pumps and add a new pump station) with a budget of $29m-$36m.

Construction is expected to begin in 2026 for both projects.

“Commissioned in 1973, the outfall pipe has required extensive repairs to leaks in 1984, 2012 and 2020, and damaged or blocked diffusers,” a project description for the Napier outfall project stated.

“Each repair is complex and expensive, as specialist teams from across council must work together to fix damage quickly while the treatment plant is shut down and the pipe out of action.

“The outfall pipe is reaching the end of its life.”

The new pipe will be built alongside the existing pipe and then hooked up to the Awatoto plant, and that project is expected to begin in late 2026 and be completed in 2028.

In terms of the $30m-$45m price tag, a council spokeswoman said that included “geotechnical investigations, consenting, design and construction of the pipe and diffuser section”.

A contractor has yet to be appointed for the project, which is in the procurement stage.

Meanwhile, Hastings District Council has plans to replace the first 150 metres of its outfall pipe at the East Clive Wastewater Treatment Plant due to corrosion.

The original pipe was installed in the late 1970s and early 1980s.

Tenders have been put out for that work, which includes replacement of the first 150m of outfall pipe with high-density polyethylene pipe, replacement of pumps in the existing outfall pump station, and an additional pump station that will enable temporary diversion during construction.

The earliest that work will begin is early 2026, and the project is expected to be completed by 2029.

“The East Clive Wastewater Treatment Plant [WWTP] outfall system is a critical piece of infrastructure that discharges treated wastewater offshore,” a Hastings District Council spokeswoman said.

“The first 150 metres of the land-based outfall pipe has been identified as beyond its design life and the steel manifold has had multiple failures over the past decade.

“This poses a significant risk to the future reliability of the WWTP operations if a serious structural failure were to occur.”

The remainder of that pipe out to sea “remains in good condition based on recent condition assessments”.