Ashbridges Bay Treatment Plant Outfall

OWNER: City of Toronto

ENGINEER: Hatch Mott MacDonald

SOUTHLAND HOLDINGS TEAM:  Southland  Mole of Canada


The ABTP is the largest of four wastewater treatment plants in Toronto and treats wastewater from a combined sewer system. This $300 million project will replace the current outfall tunnel, which is at the end of its service life. Currently, the outfall can handle peak flows of 3,200 megaliters per day. Once complete, the improved outfall will be able to handle up to 3,923 megaliters per day. The project will consist of a seven-meter diameter outfall tunneled 3,5000 meters through the rock beneath Lake Ontario’s lakebed. Using a Tunnel Boring Machine, the outfall will be excavated to a 16-meter diameter outfall shaft that is 85 meters deep. There will be about 50 risers constructed in line with the tunnel along the diffuser that runs about 1,000 meters and extends from the top of the tunnel to the lakebed. The project is slated for completion in 2023