Combined Sewage Storage Tunnel

The Combined Sewage Storage Tunnel is a key component of the Ottawa River Action Plan, designed to reduce combined sewage overflows and improve wastewater management. The 6.2-kilometer system includes two interconnected tunnels that store excess surface runoff and wastewater during heavy rainfall, minimizing untreated sewage from entering the Ottawa River.

The tunnel system significantly reduces the frequency and volume of overflows, preventing up to 43,000 cubic meters of wastewater per event from reaching the river. The system also lowers the risk of basement flooding for about 7,000 homes in the region.

FlatironDragados, as the lead partner in a joint venture with Tomlinson, used a tunnel boring machine to excavate the route while placing precast concrete liners for structural support. The project also included 15 access shafts, four odor-control facilities and critical upgrades to Ottawa's aging sewer system.

The project, funded by the Governments of Canada, Ontario and the City of Ottawa, ensures the city meets provincial water quality targets while protecting public health and the environment.