Construction commenced in 2016 to build two interconnected tunnels, totalling 6.2 km, to intercept surface runoff and wastewater (“combined sewage”) from the most significant overflow locations and store it until it may be treated at the Robert O. Pickard Environmental Centre and returned safely to the Ottawa River. In addition to the tunnels, construction included 15 major access shafts and four odour control facilities housing a host of instrumentation.
CSST Project Facts
The CSST project was a $232.3 million investment funded by the Government of Canada and the Government of Ontario ($62.09 million each) and the City of Ottawa ($108 million).
A tunnel boring machine (TBM) was used to construct the tunnels. The face of a TBM has a rotating cutter wheel that chips away the rock in various sizes ranging from tiny gravel to fist size pieces as the machine moves forward. This material is then transferred from the tunnel by conveyors back to the shaft entrance to be taken away. As the machine mines the tunnel, precast concrete liners are placed in segments behind the machine and grout is added to permanently seal the tunnel.
Stantec Consulting Ltd. and Jacobs Engineering Group (formerly CH2M Hill) completed the detailed design, contract administration and construction support services for the project, with geotechnical support from Golder Associates Ltd. Construction was led by Dragados Tomlinson Joint Venture.
Site map: Tunnels and associated sites
The east-west tunnel (EWT) runs through the downtown core from LeBreton Flats to New Edinburgh Park, generally below Cumberland Street and Slater Street, and the north-south tunnel (NST) runs below Kent Street from Chamberlain Avenue to the Ottawa River, just behind the Supreme Court. The tunnels are approximately three metres in diameter and between 10 and 31 metres below ground level.
Site 1: West End Shaft – LeBreton Flats
Site 1 is the western end of the East-West Tunnel (EWT) and houses a flow diversion chamber, an access point for operations staff and large equipment, and an odour control facility. The flow diversion chamber structure diverts potential overflows from the Booth Street Sewer and Cave Creek Collector toward the EWT.
Site 2: East-West Tunnel/North-South Tunnel Intersection – Kent and Slater Streets
Site 2 is the intersection of the two tunnels deep below Kent and Slater Streets. This location houses an underground access shaft for inspection of both tunnels via a maintenance hole.
Site 3a: Rideau Canal Interceptor Diversion/Drop – Confederation Park
Site 3a includes an odour control facility and an underground diversion chamber and drop structure below Confederation Park, which is accessed by maintenance staff via a maintenance hole. Excess flows from the existing Rideau Canal Interceptor can be diverted to the EWT at this location.
Site 3b: Rideau Canal Regulator - Rideau Canal
Site 3b is where the pre-existing Rideau Canal Regulator is located. This ensures operational efficiency of the CSST and prevent flooding as a result of elevated flow levels.
Site 3cR: Wilbrod Shaft – Cumberland Street at Wilbrod Street
Site 3cR houses an underground access shaft for inspection of the EWT via a maintenance hole.
Site 5 - EWT Outlet / Rideau River Collector RC Diversion – New Edinburgh
Site 5 is the downstream end of the EWT and the connection point to other sewer infrastructure – including the sewer that carries flow to the treatment facility. Here, there are access points for operations staff and large equipment, and an odour control facility.
Site 6: North South Tunnel Overflow/Kent Street Outfall - Ottawa River Pathway
Site 6 is the northern end of the North-South Tunnel (NST) and includes a necessary sewer outfall. Here, potential overflows from the Kent Street Sewer are diverted to the NST and monitored.
Site 8: McLeod Street Drop – McLeod Street and Kent Street
Site 8 is where flows from the McLeod Relief Sewer are directed to the NST via an underground connection that may be accessed via a maintenance hole.
Site 9: Catherine Street Drop – Catherine Street at Kent Street
Site 9 includes an odour control facility and an underground diversion chamber and drop structure, which is accessed by maintenance staff via a maintenance hole. Excess flows from the Catherine Street sewer are diverted to the NST at this location.
Site 10: Chamberlain Shaft – Chamberlain Avenue at Kent Street
Site 10 is the upstream end and southern extremity of the NST. Here, an underground chamber serves as a means to flush the NST and allows operations staff and equipment to access the tunnel.