On-Site Magazine

Boring starts on Toronto’s Coxwell Bypass Tunnel, first phase of $3B water infrastructure project

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December 16, 2019 by David Kennedy

Crews have excavated a shaft for the 10.6-kilometre Coxwell Bypass Tunnel at Toronto’s Ashbridges Bay Treatment Plant. PHOTO: City of Toronto

Components of a tunnel boring machine known as “Donnie” have been lowered and assembled at the bottom of a 50-metre shaft at a wastewater treatment plant on the east end of Toronto. The 1,000-tonne machine will begin moving material shortly for the 10.5-kilometre Coxwell Bypass Tunnel, a key component of the city’s long-term water infrastructure plan.

City officials, including Mayor John Tory, were at Ashbridges Bay Treatment Plant to mark the official start of tunnel construction Dec. 14.

“Through this tunnel we can capture and store rain and wastewater and transport it for treatment and disinfection so clean water is released into the lake,” Tory said in a release. “This project is of great importance to our city and the future of our waterways.”

Prep work for tunnel construction began last year, with crews carving out a 50-metre shaft with a diameter of about 20 metres to accomodate the boring machine. Once preliminary testing is complete and “Donnie” gets to work, the subsurface digger can bore through at least 20 metres of earth per day, leaving behind a 6.3-metre diameter tunnel.

“Years of planning, engineering and design will soon be realized as Donnie gets digging to create what will be a significant piece of infrastructure,” Coun. James Pasternak, said in a release.

The tunnel will run west from the Ashbridges Bay Treatment Plant below Lake Shore Boulevard East. Once it reaches the Don Valley, it will swing away from Lake Ontario, following the valley north and east until reaching Coxwell Ravine Park, where an exit shaft will be prepared. After it’s put in service, the tunnel will store and transport sewer overflows and stormwater to the east side wastewater plant for treatment, preventing this type of water from getting into the Don River, and ultimately, Lake Ontario.

The Coxwell tunnel project is phase one of the wider Don River and Central Waterfront Wet Weather Flow System that aims to improve water quality in the Lower Don River, Taylor-Massey Creek and along Toronto’s Inner Harbour. The five-stage project is expected to cost about $3 billion and will solve some of the problems caused by the city’s aging water infrastructure, which generally relies on combined sewers that can be overwhelmed during heavy rainfalls or intense snow melts.

Related: On-Site took a closer look at Toronto’s ambitious stormwater plans this fall

Several other components of the project include a new outfall at the Ashbridges Bay Treatment Plant, an integrated pumping station at the site and upgrades at the nearby Main Sewage Treatment Playground.

The new bypass tunnel is scheduled to be completed by 2024.