Largest wastewater outfall in Canada being built in Toronto

Hatch Mott MacDonald has been selected by the City of Toronto to provide detailed design and construction administration services for a new tunnelled outfall that will convey treated effluent from its Ashbridges Bay Treatment Plant into Lake Ontario.

The new outfall will be built to replace an older outfall and will be the largest wastewater outfall in Canada, conveying up to 3,920 million litres per day. The project will require the mining of a tunnel 3,500 metres long and 7 metres in internal diameter through rock beneath the lakebed. The project also includes a drop shaft, a connection to lakebed risers constructed by barge from the lake above, and land-based plant connections.

“The Ashbridges outfall project will draw on HMM’s strengths in tunnelling and in wastewater treatment,” said Michael Schatz, HMM’s Managing Director for Canada. “We are proud to have won several awards for our work on the Keswick Effluent Outfall in Lake Simcoe and we will bring the same care and expertise to this new challenge.”

The design and investigations phase of the project work is planned through the end of 2017, with construction starting in the first quarter of 2018 and likely extending to the end of 2022.