Toronto set to begin $3B bypass tunnel project to keep CSOs out of waterways


A tunnel boring machine (TBM) named Donnie is nearly ready to dig the City of Toronto’s new 10.5-kilometre long Coxwell Bypass Tunnel, in a effort to stop the flow of rain-driven sewage into Lake Ontario, officials have announced.

As the first phase of a five-phase $3-billion venture, the project marks the largest and most significant stormwater management program in the city’s history. The tunnel will capture, store and transport combined sewer overflows and a mix of rainwater and sewage for treatment at the city’s Ashbridges Bay Treatment Plant.

According to City of Toronto officials, this program “will greatly improve the water quality in the Lower Don River, Taylor-Massey Creek and along Toronto’s Inner Harbour, by keeping combined sewer overflow out of our waterways through the upgrading of technology and capacity to capture, transport and treat it.”

Toronto Mayor John Tory has stated that he will continue to urge the federal and provincial governments to chip in for the huge financial price tag of the project.


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“Once this work is complete, it will capture and store combined water-sewer outflows during significant rainfall,” Tory told reporters at the unveiling of the TBM.

Following testing early in the new year, the TBM will bore a tunnel approximately 6.3 metres wide and 50 metres deep, parallel to the Don River, at a cost of some $400 million. The machine is 115 metres in length and weighs nearly 1,000 tonnes. It can bore at least 20 metres of tunnel per day and is expected to have completed its duties some time in 2024.

“The grand scale of the tunnel boring machine makes you realize the incredible scope and complexity of this project,” announced Toronto Councillor Jennifer McKelvie, vice-chair of the Infrastructure and Environment Committee. “I’m delighted to be here today to mark this momentous next step in a project that will bring considerable benefits in cleaning up Toronto’s waterways and aquatic habitat and enhancing recreational opportunities for residents and visitors,” added McKelvie.

The Don River and Central Waterfront Tunnel System will consist of three integrated tunnels, 12 wet weather flow storage shafts along the tunnels, 12 connection points to the tunnels for stormwater and combined sewer overflows, seven offline storage tanks, and the technology necessary to regulate the flows inside the city’s sewer system. 

Five stages of the project:

  • Don River and Central Waterfront wet weather flow system
  • Ashbridges Bay landform project/site of future high-rate treatment facility
  • New integrated pumping system
  • New outfall
  • New UV disinfection wastewater treatment system

The video below explains further details of the project.


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