Northern Suburbs Ocean Outfall Sewer (NSOOS)

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Construction of the NSOOS in the late 1920s

Courtesy: Sydney Water / Water NSW Historical Research Archive – 30.5.29-3


We own and operate 26,169 kilometres of wastewater pipes across a network that services over 5 million customers across Sydney, the Illawarra and the Blue Mountains.

The Northern Suburbs Ocean Outfall Sewer, commonly known as the NSOOS, is an important part of our wastewater network. This vital piece of infrastructure runs along the north side of the Parramatta River, extending as far west as Blacktown and transporting wastewater all the way to the North Head Water Resource Recovery Facility in Manly.

The NSOOS was built progressively between 1916 and 1933 and was mostly tunnelled through rock, deep underground. It was the third major wastewater system built to service a rapidly growing Sydney and was significant in the development of the north shore, inner and north western suburbs of Sydney.

Thanks to its impressive scale – around 3.5 metres high by 2.6 metres wide – the NSOOS delivers wastewater services to 1.7 million people across Sydney’s Western and Northern suburbs. In fact, the 28km-long NSOOS collects around 25% of Sydney’s total sewage each day.


We're making our wastewater network more reliable

When it was built, concrete was used to line the NSOOS and protect the rock from corrosion caused by wastewater. Over time, this concrete has deteriorated, resulting in large pieces falling from the roof of the sewer tunnel. These concrete pieces are now sitting on the tunnel floor, collecting further silt and debris from the hundreds of thousands of litres of wastewater that passes through it each day.

Work is happening inside the sewer to restore it to its optimum condition. We have developed custom made machines that can be driven through the wastewater tunnel by our specialist workers to remove the debris. The walls and roof are gaining new life through the application of spray-on abrasion-resistant concrete.

The once-in-a-generation restoration works taking place inside the NSOOS are crucial for protecting Sydney Harbour and other waterways from sewage overflows and will extend the life of the structure by at least 50 years.


Repairs, Lane Cove to Northwood

The 2.5 kilometre section of NSOOS between Lane Cove River and Woodford Bay Reserve, Northwood was repaired and rehabilitated between 2017 and late 2021.

The work required access into the tunnel at the following locations:

  • Burns Bay Road, Lane Cove
  • Burns Bay Reserve, Riverview
  • St Ignatius College, Riverview
  • Tambourine Bay Road, Riverview
  • Warraroon Reserve, Longueville
  • Woodford Bay Reserve, Longueville / Northwood

All sites have been restored in consultation and agreement with Lane Cove Council.


Silt and debris removal, Northwood to Crows Nest (West Street)

The 3.1 kilometre section of NSOOS between Woodford Bay Reserve, Northwood and West Street, Crows Nest had silt and debris removed from inside the tunnel between 2021 and 2022.

The work involved access into the tunnel at the following locations:

  • Gore Creek Reserve (Bob Campbell Oval), Greenwich
  • Carlotta Street, Greenwich
  • Russell Street, Wollstonecraft
  • Carlyle Street, Wollstonecraft
  • West Street, Crows Nest


Silt and debris removal and repairs, Cremorne (Park Avenue) to Crows Nest (West Street)

The 1 kilometre section of NSOOS tunnel between Park Avenue, Cremorne and West Street, Crows Nest has been repaired and rehabilitated, with work completed in August 2023.

This work required access into the sewer tunnel at the following locations.

  • Park Avenue, Cremorne
  • Cammeray Golf Course
  • ANZAC Park, Cammeray

All sites have been restored in consultation and agreement with North Sydney Council.


Repairs, Cremorne (Brightmore Reserve) to Mosman (Spit)

The 2.7 kilometre section of NSOOS tunnel between Brightmore Reserve, Cremorne and The Spit, Mosman is currently being desilted, repaired and rehabilitated. The work requires access into the tunnel at the following locations:

  • Brightmore Reserve, Cremorne
  • Brothers Memorial Park, Cremorne
  • Quakers Hat Bay, Bay Street, Mosman
  • Upper Spit Road, Mosman
  • The Spit Syphon, off Parriwi Road, Mosman

All sites will be restored in consultation and agreement with North Sydney Council and Mosman Council. We expect this work to be completed by late 2024, weather and tunnel conditions permitting.


NSOOS News -15 October 2022 - Red carpet rolled out for community at Quakers Hat Bay, Mosman

Critical Sewer Solutions, a joint venture of Metrocorp Technologies and Interflow in partnership with @Sydney Water, rolled out the red carpet at their Quakers Hat Bay NSOOS rehabilitation worksite on Saturday 15 October. It was a great day where we shared with residents our project’s scope of work, what a typical day is like for crews, and our challenges.

Repairs to the NSOOS started between Brightmore Reserve, Cremorne, and Quakers Hat Bay, Mosman, in mid-2021.

Staff and community chatting at Saturday's Open Day

NSOOS News -11 October 2022 - Rehabilitation contractor helps repair ANZAC Park Memorial Community Garden, Cammeray

Our work on the NSOOS at Anzac Park, Cammeray, involves close cooperation with the ANZAC Park Memorial Community Garden. After heavy rains between March and June, Metrocorp Technologies offered to supply and spread coarse gravel inside the garden to improve access. The recycled gravel used on Tuesday 11 October was chosen after consultation with North Sydney Council. Vehicle mats helped protect the park surface.

Work went smoothly despite more wet weather, and the pathway is now in much better shape. Garden volunteer coordinator and local resident Sue Wright greatly appreciated the effort.

Work crew and Ms Wright repairing the flood damage

NSOOS News - 12 May 2023 - Tunnel rehabilitation between Cremorne and Wollstonecraft to be completed this month

Sydney Water awarded packages of work to Metrocorp Technologies in 2017 and 2019 to desilt and rehabilitate the Northern Suburbs Ocean Outfall Sewer (NSOSS) between Cammeray Golf Course, Cremorne, and Russell Street, Wollstonecraft, a total of 2.2kms. Around 200,000 man hours later, all repairs to the near century old sewer are set to be completed this month.

Staff faced 61m and 63m descents at the golf course and ANZAC Park sites respectively, so access was challenging and safety paramount. This was a project of big numbers. Around 800 tonnes of sand and other debris was removed, 1300 tonnes of shotcrete sprayed, and 500 tonnes of calcium aluminate cement applied as the strong acid-resistant top layer.

Critical Sewer Solutions in partnership with @Sydney Water continues to rehabilitate the NSOOS between Brightmore Reserve, Cremorne, and The Spit, Mosman.



Construction of the NSOOS in the late 1920s

Courtesy: Sydney Water / Water NSW Historical Research Archive – 30.5.29-3


We own and operate 26,169 kilometres of wastewater pipes across a network that services over 5 million customers across Sydney, the Illawarra and the Blue Mountains.

The Northern Suburbs Ocean Outfall Sewer, commonly known as the NSOOS, is an important part of our wastewater network. This vital piece of infrastructure runs along the north side of the Parramatta River, extending as far west as Blacktown and transporting wastewater all the way to the North Head Water Resource Recovery Facility in Manly.

The NSOOS was built progressively between 1916 and 1933 and was mostly tunnelled through rock, deep underground. It was the third major wastewater system built to service a rapidly growing Sydney and was significant in the development of the north shore, inner and north western suburbs of Sydney.

Thanks to its impressive scale – around 3.5 metres high by 2.6 metres wide – the NSOOS delivers wastewater services to 1.7 million people across Sydney’s Western and Northern suburbs. In fact, the 28km-long NSOOS collects around 25% of Sydney’s total sewage each day.


We're making our wastewater network more reliable

When it was built, concrete was used to line the NSOOS and protect the rock from corrosion caused by wastewater. Over time, this concrete has deteriorated, resulting in large pieces falling from the roof of the sewer tunnel. These concrete pieces are now sitting on the tunnel floor, collecting further silt and debris from the hundreds of thousands of litres of wastewater that passes through it each day.

Work is happening inside the sewer to restore it to its optimum condition. We have developed custom made machines that can be driven through the wastewater tunnel by our specialist workers to remove the debris. The walls and roof are gaining new life through the application of spray-on abrasion-resistant concrete.

The once-in-a-generation restoration works taking place inside the NSOOS are crucial for protecting Sydney Harbour and other waterways from sewage overflows and will extend the life of the structure by at least 50 years.


Repairs, Lane Cove to Northwood

The 2.5 kilometre section of NSOOS between Lane Cove River and Woodford Bay Reserve, Northwood was repaired and rehabilitated between 2017 and late 2021.

The work required access into the tunnel at the following locations:

  • Burns Bay Road, Lane Cove
  • Burns Bay Reserve, Riverview
  • St Ignatius College, Riverview
  • Tambourine Bay Road, Riverview
  • Warraroon Reserve, Longueville
  • Woodford Bay Reserve, Longueville / Northwood

All sites have been restored in consultation and agreement with Lane Cove Council.


Silt and debris removal, Northwood to Crows Nest (West Street)

The 3.1 kilometre section of NSOOS between Woodford Bay Reserve, Northwood and West Street, Crows Nest had silt and debris removed from inside the tunnel between 2021 and 2022.

The work involved access into the tunnel at the following locations:

  • Gore Creek Reserve (Bob Campbell Oval), Greenwich
  • Carlotta Street, Greenwich
  • Russell Street, Wollstonecraft
  • Carlyle Street, Wollstonecraft
  • West Street, Crows Nest


Silt and debris removal and repairs, Cremorne (Park Avenue) to Crows Nest (West Street)

The 1 kilometre section of NSOOS tunnel between Park Avenue, Cremorne and West Street, Crows Nest has been repaired and rehabilitated, with work completed in August 2023.

This work required access into the sewer tunnel at the following locations.

  • Park Avenue, Cremorne
  • Cammeray Golf Course
  • ANZAC Park, Cammeray

All sites have been restored in consultation and agreement with North Sydney Council.


Repairs, Cremorne (Brightmore Reserve) to Mosman (Spit)

The 2.7 kilometre section of NSOOS tunnel between Brightmore Reserve, Cremorne and The Spit, Mosman is currently being desilted, repaired and rehabilitated. The work requires access into the tunnel at the following locations:

  • Brightmore Reserve, Cremorne
  • Brothers Memorial Park, Cremorne
  • Quakers Hat Bay, Bay Street, Mosman
  • Upper Spit Road, Mosman
  • The Spit Syphon, off Parriwi Road, Mosman

All sites will be restored in consultation and agreement with North Sydney Council and Mosman Council. We expect this work to be completed by late 2024, weather and tunnel conditions permitting.


NSOOS News -15 October 2022 - Red carpet rolled out for community at Quakers Hat Bay, Mosman

Critical Sewer Solutions, a joint venture of Metrocorp Technologies and Interflow in partnership with @Sydney Water, rolled out the red carpet at their Quakers Hat Bay NSOOS rehabilitation worksite on Saturday 15 October. It was a great day where we shared with residents our project’s scope of work, what a typical day is like for crews, and our challenges.

Repairs to the NSOOS started between Brightmore Reserve, Cremorne, and Quakers Hat Bay, Mosman, in mid-2021.

Staff and community chatting at Saturday's Open Day

NSOOS News -11 October 2022 - Rehabilitation contractor helps repair ANZAC Park Memorial Community Garden, Cammeray

Our work on the NSOOS at Anzac Park, Cammeray, involves close cooperation with the ANZAC Park Memorial Community Garden. After heavy rains between March and June, Metrocorp Technologies offered to supply and spread coarse gravel inside the garden to improve access. The recycled gravel used on Tuesday 11 October was chosen after consultation with North Sydney Council. Vehicle mats helped protect the park surface.

Work went smoothly despite more wet weather, and the pathway is now in much better shape. Garden volunteer coordinator and local resident Sue Wright greatly appreciated the effort.

Work crew and Ms Wright repairing the flood damage

NSOOS News - 12 May 2023 - Tunnel rehabilitation between Cremorne and Wollstonecraft to be completed this month

Sydney Water awarded packages of work to Metrocorp Technologies in 2017 and 2019 to desilt and rehabilitate the Northern Suburbs Ocean Outfall Sewer (NSOSS) between Cammeray Golf Course, Cremorne, and Russell Street, Wollstonecraft, a total of 2.2kms. Around 200,000 man hours later, all repairs to the near century old sewer are set to be completed this month.

Staff faced 61m and 63m descents at the golf course and ANZAC Park sites respectively, so access was challenging and safety paramount. This was a project of big numbers. Around 800 tonnes of sand and other debris was removed, 1300 tonnes of shotcrete sprayed, and 500 tonnes of calcium aluminate cement applied as the strong acid-resistant top layer.

Critical Sewer Solutions in partnership with @Sydney Water continues to rehabilitate the NSOOS between Brightmore Reserve, Cremorne, and The Spit, Mosman.


Page last updated: 20 Mar 2024, 09:19 AM