The City of Toronto is building a massive tunnel underneath part of its downtown – one that has nothing to do with any transit projects.

On May 8, the city celebrated the launch of a tunnel boring machine that will operate at a depth of 40 metres and drive the construction of a three-kilometre long, 4.5-diametre storm sewer.

The exercise is part of the $380-million Fairbank Silverthorn Storm Trunk Sewer System project – the largest flood-prevention project in Toronto’s history. Once complete, the new tunnel will collect, store and move stormwater from the Fairbank-Silverthorn area to Black Creek to help reduce the risk of basement flooding.

The machine was deployed at a shaft inside Fairbank Memorial Park, located on Dufferin Street south of Eglinton Avenue West. Its route will see it dig underneath four city wards: Toronto-St. Paul’s, Eglinton-Lawrence, Davenport and York South-Weston.

Once complete, the tunnel project will help mitigate basement flooding and sewer backups for more than 12,500 people living in 4,645 homes and reduce 40 million litres of annual combined sewer overflows into Black Creek and other local waterways.

“I am pleased to mark this important milestone in the Fairbank Silverthorn Storm Trunk Sewer System project that will help protect thousands of basements from flooding,” said Deputy Mayor Jennifer McKelvie. “This is particularly important as we see the increased frequency of impactful storms that can damage people’s homes and cherished belongings. This project will also help reduce combined sewer overflows from being released into local waterways.”

The project consists of a three-kilometre storm sewer from Fairbank Memorial Park in the east to Black Creek in the west. Once complete, the new sewer will hold and store stormwater and release it gradually into Black Creek at a controlled rate. A series of smaller storm sewers, totalling 17 kilometres in length, will also be constructed and connected to local catch basins to carry rainwater to this large new storm sewer. The project also includes installing more than 320 devices to control rainwater flow in catch basins to reduce the risk of basement flooding and combined sewer overflows.

The project started in 2021 and will be completed in 2026. The total project cost is approximately $380 million. The federal government has agreed to contribute $73.2 million in funding under its Disaster Mitigation and Adaption Fund. The remainder of the project cost is funded by Toronto’s Basement Flooding Protection Program.