Sydney Water, Metrocorp Technologies, SASTTI and Interflow have received the New South Wales Excellence in Concrete Award, 2021, from the Concrete Institute of Australia. 

Interflow’s General Manager NSW & ACT, Paul Everett, said, “Along with Sydney Water and the SASTTI joint venture, we have come first in the NSW ‘Repair, Restoration and Retrofit’ category for our outstanding work improving the almost century-old Northern Suburbs Ocean Outfall Sewer (NSOOS).

“Side by side with Metrocorp since June 2017, we enter Sydney’s second largest sewer each weekday, using modern equipment and work methods to ensure high productivity and a safe work environment for our crews. We are making the tunnel free-flowing and much more durable.”

The NSOOS delivers wastewater services to 1.7 million people across Sydney’s Western and Northern suburbs, servicing 416km² and collecting 310ML daily, or 25 per cent of total sewage across the Sydney Basin. 

In late 2016, Sydney Water engaged delivery partners, SASTTI JV, Interflow and Metrocorp, to desilt and rehabilitate the degrading 90-year-old tunnel. The goal was to return the NSOOS to its full operational capacity and extend asset life by 50 more years. 

The multi-stage NSOOS project will:

  • Remove debris, to restore hydraulic capacity
  • Use mesh and dry shotcrete to repair the NSOOS structural arch
  • Apply a Calcium Aluminate Cement (CAC) coating for corrosion protection

All works in the NSOOS occur in a live sewer with continuous flows between 800 to 1300mm deep without impacting services. The project exemplifies excellence in concrete by combining product and construction innovation with rigorous safety practices to deliver a quality product.

Innovations include:

  • Using a rock wheel (originally developed in mining) for acid affected concrete removal
  • Deploying unmanned automated desilting and shotcrete machines
  • Using dry shotcrete and CAC, allowing products to be mixed underground; increasing the distance that material can be delivered (improving product quality) and reducing community impact
  • Managing dust generation with complex ventilation systems
  • Managing odour emissions from the tunnel

Metrocorp’s Managing Director, Paul Smith, added, “Our crews are deep underground on the Lower North Shore in a workplace that is completely alien to most people, and consistently do an outstanding job working in an extremely high-risk environment. They extract silt and debris from the tunnel, remove the deteriorated concrete surface, then reinstate the structure by installing mesh and shotcrete, and then apply a protective layer to  the roof and walls to resist future acid attack.

“This industry excellence award would not have been possible but for the sustained efforts, exceptional hard work and dedication of sewer crews, the above ground delivery team, and management. The next phase of this work is being performed by Critical Sewer Solutions. The newly formed Interflow/Metrocorp Joint Venture will continue to innovate to deliver the highest levels of safety and quality.”

Sydney Water’s Senior Project Manager, Paul Denyer, said, “It is such an achievement for the partnership to be recognised with this award.

“There is real innovation in successfully being able to do this work in an extremely challenging ‘live flows’, which delivers great outcomes for our Northern Sydney customers and our iconic harbour.

“This work is made possible because of great collaboration between Sydney Water and our partners Interflow, Metrocorp and SASTTI. We’re delighted that our efforts are recognised in delivering innovative solutions alongside ensuring rigorous safety practices to achieve quality results in a highly constrained live wastewater environment.”

This sponsored editorial was brought to you by Interflow. For more information, please visit

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