Northern Suburbs Ocean Outfall Sewer (NSOOS)

In late March 2025, we will commence work removing silt and debris from the NSOOS tunnel at Darley Road and Bluefish Drive, North Head (see map above).

Parking in the immediate surrounds of the work areas may be limited. Traffic and pedestrian management will be in place to safely escort motorists and pedestrians around the work areas.

At the Bluefish Drive work area, we will be clearing vegetation around the NSOOS access point. This is identified in the pink outlined area on the map above, and we have consulted with National Parks and Wildlife about the work. At the completion of work the area will be revegetated and returned to its original condition.

If you have any specific questions or feedback about the vegetation clearing, please contact us though the NSOOS rehabilitation contact details, by close of business Friday 28 March 2025.

We're continuing to refine our plans to desilt the next section of the NSOOS from Clontarf to North Head (Section 1).

You may recall from our last newsletter, as part of our preparation, we’re building an underground access cavern at the North Head facility. This involves excavating sandstone rock about 60 metres underground. The cavern will serve as a new NSOOS access point for our specialist desilting equipment and crews.

While the NSOOS rehabilitation is underway, we’ll temporarily redirect wastewater to the Northside Storage Tunnel (NST). To support this, we’re continuing with our planning to clean out silt from parts of the NST underground at our North Head facility so it can continue operating as a diversion to the NSOOS.

This important work will help to pave the way for future sections of the NSOOS to be rehabilitated and once completed, will increase capacity, assist in preventing overflows, and extend its lifespan.

Our 2024 Christmas holiday shutdown will start from close of business on Friday 20 December 2024.

We will return to work on Monday 13 January 2025.

Sites will be locked, security cameras will remain operational and random inspections will be carried out over the holiday period.

Over the past three months Sydney Water has been engaging with local precinct groups and North Sydney Council on improving the visual amenity of our work site at Brightmore Reserve, Cremorne. The image below depicts what the site will look like once the improvements are completed across June and July 2024.

An artists impression of what the site will look like after July 2024

Thanks for your patience and understanding while we complete this important work. We also aim to be good neighbours and appreciate community feedback.

We previously advised that we will complete our work at these locations in late 2024.

At the time we advised this estimated completion, we had insufficient information on other Sydney Water work that requires the ongoing access of the NSOOS tunnel using these sites. In addition, we used an arbitrary duration to forecast delays due to wet weather and other system events.

We have since identified additional Sydney Water work from 2023 and early 2024 in the Cremorne, Mosman, and North Head Water Resource Recovery Facility (WRRF) areas that require continued access to the NSOOS tunnel at these sites, including:

• A project to remove silt from the Northside Storage Tunnel (NST) access decline and wet well areas at North Head WRRF is expected to commence in mid-2024. This will require removing the NSOOS flow diversion into the NST. It is estimated that the current NSOOS works in Cremorne and Mosman will be delayed by three to four months in early 2025 while the work occurs in the NST wet well area at the North Head plant.
• More detailed repair work has been identified in the NSOOS tunnel between Quakers Hat Bay and the Spit Syphon at Mosman. We encountered some unforeseen tunnel conditions in this section of the NSOOS that slowed down our work. We also need to change our construction method to ensure the ongoing safety of our work crews inside the tunnel.
• We experienced greater impacts from wet weather and tunnel system conditions than we originally anticipated.

• Additional work has been identified to rehabilitate three large submains that flow into the NSOOS tunnel between Quakers Hat Bay and the Spit Syphon at Mosman. Planning the work on the Balmoral Slopes, Pearl Bay, and Spit Road submains has commenced and is in the early concept design phase. Our technical teams have yet to determine access requirements into the NSOOS tunnel this work will have.

In light of this, Sydney Water has revised its expected completion timing at these sites to be early 2027.

The early 2027 timing includes contingency for us not being able to access the NSOOS tunnel with wet weather and other network conditions.

It also allows for full demobilisation and restoration of the sites at

• Brightmore Reserve, Cremorne
• Brothers Memorial Park – Fifth Avenue, Cremorne
• Quakers Hat Bay – Bay Street, Mosman
• Upper Spit Road, Mosman

The Spit Syphon site will be demobilised with equipment and left secured for ongoing operational use by Sydney Water.

Please note our Christmas shutdown will start from close of business on Thursday 21 December 2023.

We will return to work on Monday 8 January 2024.

Sites will be locked, security cameras will remain operational and random inspections will be carried out over the holiday period.

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.

The Spit Syphon site was made ready in December 2022 for work to start completing rehabilitation of the 1.3km section of tunnel between Quakers Hat Bay and The Spit.

Crews are using custom made machinery to remove silt and other debris from inside the tunnel. After dewatering at the Quakers Hat Bay site, this material is transported daily in covered skips to a licensed waste facility.

Limited tunnel repairs (pinning of concrete) commenced inside this section of the NSOOS in the second quarter of 2023

A new cover was installed behind the Spit Syphon in late February. The temporary structure stops odours from escaping when tunnel lids in the Syphon are opened

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.

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.