Sydney Sewer Maintenance

The Northern Suburbs Ocean Outfall Sewer (NSOOS) is the third major sewerage system in Sydney, supporting the city’s wastewater needs. As part of the Sydney Water Corporations Network and Facilities Renewal Program, over 28kms of the NSOOS network is being rehabilitated to support the growing wastewater demands of Sydney.

Our client Monadelphous is commissioned by Sydney Water for an ongoing project for desilting, internal rehabilitation, additional flow management plans and systems and site restoration.

Specialised fabrication of an amphibious vehicle

Silt tends to build in localised spots in the tunnel known as ‘silt banks’ much like dunes on the beach.

This requires a fully customised amphibious Dumper to drive into the silt banks and lift debris into a capture basket lined with a bulk-a-bag for transportation and disposal.

Silver Raven was briefed on fabrication for the third and latest Dumper which included:

  • Building the new hydraulic power pack out of the original diesel motor. The power pack is mounted high up on the frame to stay out of the water.
  • Installing new hydraulic lines and fittings about the dumper from the pump.
  • Installing a new bucket to suit the profile of the tunnel floor.
  • New engine electricals, dashboard, ignition pack and power harness.
  • New Polycarbonate Windshield. Foam-filled tyres.
  • New R.O.P.S. (rollover protection system), fabricated and welded.

Silver Raven has completed all the modifications except the communications, gas monitoring and video camera systems.

Some interesting info:

  • The Dumper seats 2 operators, runs on diesel and includes a hydraulic power pack.
  • The dumper cannot stay in the tunnel overnight or outside work hours and so is lifted in and out of the tunnel daily.
  • The tunnel is always live; even with certain controls in place to divert water and reduce the flow height; the water can be up to 1.2m deep.
  • The dumper is able to function in the water semi-submerged but requires regular checks and maintenance
  • Video Cameras view multiple angles on the front, back and within the cabin to monitor the operators – video is linked to a live feed in office.
  • Gas monitors measure levels of oxygen, hydrogen sulfide, carbon monoxide and flammables such as methane. An Alarm is tripped if the levels become hazardous. If the gas levels reach dangerous levels – the operators have access to Breathing Apparatuses with full face masks mounted in the cabin of the dumper with bottled air.
  • Dumper also contains a radio communication booster – the operators carry a portable radio on their harness which is boosted by the dumper to reach the office and confined space watch.
  • The tunnel is ventilated during the work to dilute and extract exhaust fumes and toxic sewer gases. 3-Phase barrel fans, ducting, OCUs (odour control units), compressed air venturis and manhole fans are set up in a long system along the sewer tunnel to achieve this.

The original crew building the tunnel. Picture: Sydney Water/WaterNSW Historical Research Archive