South East Collector Sewer Project

The Southeast Collector (SEC) Main Sewage Project is a 15 km long tunnel that carries wastewater from the York region to a treatment plant in the Durham region. In addition, two deep shafts and a 6.3 km long tunnel drilled into rock were constructed in the Mid-Halton Outfall Tunnel. This tunnel was designed to transport treated wastewater from the Oakville water treatment plant to Lake Ontario.
 
The Southeast Collector (SEC) Trunk Sewer is a 15 km (49,200 ft) sewer that transports untreated sewage from York Region to a treatment plant in Durham Region, while also serving as a backup to the existing system.
The tunnel was excavated using four Earth Pressure Balance (EPB) TBMs with precast concrete segment lining, ranging 5 to 50 m below ground, and featured 16 shafts built using secant pile walls, ground freezing, slurry walls, and shotcrete, with a finished cast-in-place concrete lining.

The project included key supporting facilities, such as corrosion and odour control, flow diversion and metering, maintenance chambers, and interconnection chambers linking the new and existing sewers.

Additional works included 15 construction compounds, road widening, and traffic staging at select intersections. The SEC Trunk Sewer enhanced regional wastewater reliability, environmental protection, and operational flexibility for York and Durham Regions.