Location

Annacis Island, British Columbia

Client

Metro Vancouver

Delivery

2019 2023

Contract type

Lump sum, in partnership

Project

As part of a major upgrade of the wastewater treatment facility, build a new outfall system to meet the needs of a growing population for the next century, and safely release treated wastewater into the Fraser River. The plant treats 175 billion litres of wastewater every year.

Challenges

Technically complex project: Construct two concrete tunnels spanning 820 metres, with two 40-metre deep on-land shafts and a marine diffuser in the Fraser River.

Ensure seismic resilience and continuous, reliable and safe management of liquid waste.

Solutions

Use a tunnel-boring machine to excavate underground and bring soil back to the surface by hydraulic means.

Bury the outfall pipe by tunnelling at a depth of 30 metres; and in addition to precast curved concrete seg- ments lining the tunnels, use steel lining at each end of the tunnels to withstand seismic activity.

Milestone

Completed the excavation of the first tunnel. Achieved the first underwater concrete pouring using a watertight pipe over a 26-hour non-stop work period and requiring 130 deliveries by trucks transported on barges to the cofferdam.

Underwater work to expand a wastewater treatment plant

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