Opposition is growing to a $44 million water quality improvement project that will see some diluted sewage discharged into the Waitematā Harbour near the Auckland Harbour Bridge.

Herne Bay and St Marys Bay residents are calling for the project - which aims to reduce local wastewater overflows by at least 90 per cent - to be put on hold until an independent review is carried out and alternative solutions have been fully considered.

Last year, Auckland Mayor Phil Goff said Auckland "shouldn't have wastewater overflows polluting our harbour" and pledged to clean up the city's beaches and waterways.

Goff has been reluctant to comment on the project. A spokesman said the mayor had been advised it will deliver considerable improvements in water quality, which is one of his top priorities.

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A better solution to the project, say locals, is to separate the 100-year-old combined stormwater/sewer pipes in the two inner-city harbourside suburbs.

The current plan by Auckland Council's Healthy Waters is to build a 1.8m diameter underground storage pipe from London St in St Marys Bay to Pt Erin where combined sewage and stormwater will be pumped to a larger main sewer system.

If the main pipe becomes full, a mix of mostly stormwater but some diluted sewage will be discharged into the harbour west of the Harbour Bridge in the main tidal channel, where the strong current will disperse it more efficiently.

The project is designed to quickly improve water quality after visible signs of pollution at Westhaven in 2015 were tracked to overflows from St Marys Bay.

The council is seeking resource consent to build the $44m project.

Phil Goff is reluctant to engage on the controversial St Marys Bay water improvement project.
Phil Goff is reluctant to engage on the controversial St Marys Bay water improvement project.

About 120 Herne Bay and St Marys Bay residents packed a public meeting two weeks ago where they unanimously called for the project to be put on hold until there was an independent peer review and a business case for separating the network was completed.

A letter was subsequently sent to Goff by the Herne Bay Residents Association and St Marys Bay Association, asking him to put the project on hold while the concerns of locals are addressed.

Healthy Waters general manager Craig McIlroy responded on Goff's behalf, saying the St Marys Bay project "is a transformational first step towards a cleaner Waitematā".

"We do not propose to put the project on hold and intend to proceed with the resource consent process as planned," McIlroy said.

He said the project will reduce the number of overflows from an average 200 a year to 20 in the medium term and lead to less wastewater discharged into the Waitematā Harbour.

The project is designed to integrate with and support any long-term solution that could be a combined network or separated networks, McIlroy said.

This approach does not wash with St Marys Bay Association chairman and former Associate High Court Judge David Abbott and Herne Bay Residents Association co-chair and retired merchant banker Dirk Hudig.

The two men are active in the Stop Auckland Sewage Overflows Coalition (SASOC), a coalition of community groups dedicated to improving the city's polluted stormwater overflows.

They support the underlying goal of the St Marys Bay project to improve water quality at local beaches and beyond, but are not convinced that discharging diluted sewage into a "strong recreational space" where people go fishing and sailing is the right solution.

These old combined pipes are not going to last for another 100 years

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They point to a council report from November last year saying separation of the old combined pipe into new separate pipes in St Marys Bay would cost $22m. No cost was given for separation in Herne Bay.

Separation will never be easier than now before intensification, said Hudig.

"These old combined pipes are not going to last for another 100 years," said Abbott, saying the council accepts that separation has to occur sometime in the future.

David Abbott, chairman of St.Marys Bay Association, and Dirk Hudig, co-chair of the Herne Bay Residents Association by Auckland Harbour Bridge. Photo / Doug Sherring
David Abbott, chairman of St.Marys Bay Association, and Dirk Hudig, co-chair of the Herne Bay Residents Association by Auckland Harbour Bridge. Photo / Doug Sherring

Abbott and Hudig are also not convinced the project dovetails with another water project to build a tunnel from Grey Lynn to Western Springs where a giant storage tunnel costing $1 billion, known as the central interceptor, will run to the Māngere wastewater treatment plant.

Network separation or the central interceptor extension could do away with the need for the St Marys Bay project, they say.

There are also concerns from St Mary's College and locals about planned 10m high ventilation pipes in St Mary Bay causing lingering odours, and ground effects from drilling the pipe under houses built on the cliff face at St Marys Bay.