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Metro Vancouver’s Annacis Island Wastewater Treatment Plant (WWTP) located on Annacis Island, in Delta BC, is one of the region’s largest wastewater treatment facilities. The facility receives wastewater from 14 municipalities across the Lower Mainland which, once treated, is released into the Fraser River through an outfall pipe.

In order to increase the capacity of the current facility to meet the needs of the region’s growing population, a new outfall pipe was required. The installation of the new outfall  diffuser pipes was contracted to Ruskin Construction Ltd., who engaged Allnorth to provide the engineering required for the project.

The project involves lowering two diffuser pipes, weighing 500t each, are 130m long, and 2.5m in diameter, down into trenches at the bottom of the Fraser River, under 19m of water.

The large diffuser pipe and river depth presented some challenges which were effectively addressed by Allnorth’s engineering solution developed for this project. The solution involves a large overhead support structure to support the pipe, with eleven, 25-ton capacity winches used to lower the pipe into place. The support structure also includes systems to manipulate the pipe to adjust it vertically, longitudinally, laterally and along its axis, to allow it to be bolted to the outfall riser.

In addition, the loading scenarios created by the river velocities and tidal influences, were accommodated in Allnorth’s design. The installation procedure had to allow for precise installation while providing enough tolerance to allow for adjustments in the field.

The two diffuser pipes were successfully lowered into place in November 2022 and January 2023.


  • Structural engineering
  • Construction engineering


Vancouver, BC

Innovation  Magazine May – June 

Metro Vancouver’s Project Highlights

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