Sewer separation project to clean up St Marys Bay

Planning and design is underway on a project to separate the wastewater and stormwater networks in St Marys Bay to improve water quality in the area.
The project, which is part of a joint Watercare and Auckland Council initiative, involves the construction of a new public wastewater network, and extensions to the existing network so it can be used for stormwater. Individual private property networks will also be separated. 
Watercare improvement programme manager Anin Nama says the $33.4 million project will prevent wet-weather overflows into the Waitematā Harbour.
“In older parts of Auckland, one network was built to handle both wastewater and stormwater flows. In dry periods, the wastewater flows end up at the Māngere Wastewater Treatment Plant, but when it rains, the pipes are inundated and diluted wastewater and stormwater enters the waterways,” Nama says.
“The pipes we are separating were built in the early 1900s. St Marys Bay is a problem area for water quality – it receives wet-weather overflows about 100 times a year – every time it rains. The work we are doing will reduce overflows to between two and six times a year. It’s about fixing a legacy issue and cleaning up an area that is a popular spot for recreation.”
The project in St Marys Bay is part of the wider Western Isthmus Programme – a 10-year programme of works to improve the water quality in urban streams, and ultimately our harbours. It is jointly funded by Watercare and Auckland Council’s Water Quality Targeted Rate.
More than 450 St Marys Bay properties will have their private stormwater and wastewater pipes separated. Watercare will be in touch with property owners over the next few months to confirm existing drainage locations and assess the best options for separation.
Construction is expected to begin mid-2021 and will be delivered by Watercare’s design and construction partners GHD and Fletcher Construction.
The separation programme is aligned with Auckland Council’s Healthy Waters stormwater tunnel currently under construction. The new pipeline will collect and screen stormwater, and discharge it at a new marine outfall location, reducing wet weather overflows and significantly improving water quality.
Healthy Waters general manager Craig McIlroy says: “The St Marys Bay Area Water Quality Improvement Project will restore St Marys Bay and Masefield Beach to being thriving, lively places where people come together to enjoy themselves.”