The new tunnel will replace an older outfall used to convey treated effluent from the city’s Ashbridges Bay Treatment Plant into Lake Ontario.
It will be the largest wastewater outfall in Canada, conveying up to 1,040 million gallons per day (3,920 million litres per day). The project will require the mining of a tunnel 3.5km long and 7m in internal diameter through rock beneath the lake-bed. The project also includes a drop shaft, a connection to lake-bed risers constructed by barge from the lake above, and land-based plant connections.
The design and investigations phase of the project work is planned through to the end of 2017, with construction starting in the first quarter of 2018 and likely extending to the end of 2022.