City of Ottawa

Project Update - Combined Sewage Storage Tunnel (CSST) - January 2019

Picture of the Ottawa River, showing Parliament in the background

Building a healthy and resilient future for the Ottawa River

This $232.3 million construction project is a key part of the Ottawa River Action Plan (ORAP), which is aimed at enhancing the health of the Ottawa River and protecting our water environment for future generations. A healthy water environment provides safe, abundant drinking water; supports agriculture, recreation and tourism; lessens the impact of flood events; and helps sustain fish and wildlife.

Construction Site Map

The map below identifies construction sites for the CSST project within the City of Ottawa, which are described in more detail here.
Map of the CSST alignment and sites. The East-West tunnel runs through the downtown core from LeBreton Flats to New Edinburgh, and the North-South tunnel runs from Chamberlain Avenue to behind the Supreme Court of Canada. Description of sites, indicated by orange dots, are as follows: Site 1: West End Shaft - LeBreton Flats
Site 2: East West Tunnel/North South Tunnel Intersection - Kent and Slater Streets Site 3a: Rideau Canal Interceptor Diversion Chamber - Confederation Park Site 3b: Rideau Canal Regulator – Rideau Canal Site 3cR: Wilbrod and Cumberland Streets Site 4: St. Patrick Shaft - York and Cumberland Streets Site 5: East West Tunnel Outlet and Rideau River Collector Diversion - New Edinburgh Park Site 6: NST Overflow/Kent Street Outfall - Ottawa River Pathway Site 7: Identified with a grey dot, as this site was eliminated during the design phase of the project Site 8: McLeod Street Drop - Kent and McLeod Streets Site 9: Catherine Street Drop - Kent and Catherine Streets Site 10: Chamberlain Shaft - Kent and Chamberlain Streets
The CSST will consist of two inter-connected tunnels over six kilometres in total length, three metres in diameter, located 10 to 31 metres below surface level. The North-South Tunnel (NST) will run below Kent Street, from Chamberlain Avenue to just behind the Supreme Court of Canada, and the East-West Tunnel (EWT) will run through the downtown core, from Stanley Park to LeBreton Flats, generally under Cumberland and Slater Streets.

Construction is underway at several sites.


Construction Activity Progress


East-West Tunnel (EWT)

Tunneling of the East-West tunnel from Stanley Park to LeBreton Flats (Site 5 to Site 1) is underway, and progressing under Cumberland Street through the Lowertown and Sandy Hill areas.
A picture of a tunnel showing rail tracks on the ground.
Assembly of the tunnel boring machine (TBM) at the bottom of the 5a shaft.

Site 1: West End Shaft – LeBreton Flats

Site 1 is the western end of the East-West Tunnel (EWT) and the tunnel boring machine’s final exit point. Ultimately, Site 1 will house a flow diversion chamber, an access point for operations staff and large equipment, and an odour control facility (OCF).

Site 1 construction activities of interest:
  • Continued formwork for the OCF walls.
  • Backfilling at the TBM exit shaft location.
A picture containing construction of walls on a building
Construction of the OCF walls.

Site 2: East-West Tunnel/North-South Tunnel Intersection – Kent and Slater Streets

Site 2 is where the two tunnels intersect. Preparations for construction of an underground access chamber at this location have begun.

Site 2 construction activities of interest:
  • Signage installation and set-up of traffic control measures.
  • Utility location works in preparation for relocations (gas, water, lighting, etc.).
  • Continuing underground chamber construction preparations within the North-South Tunnel.

A picture of a street with orange and black cones and a piece of construction equipment
Utility location works in advance of construction mobilization, on Slater at Kent.

Site 3A: Rideau Canal Interceptor Diversion/Drop – Confederation Park

Construction of a new underground diversion chamber drop structure and odour control facility is underway at Site 3A. Excess flows from the existing Rideau Canal Interceptor will be diverted to the EWT at this location.

Site 3A construction activities of interest:
  • Continued construction of the underground chamber, including installation of rebar and concrete.
  • Continued exterior roofing and interior electrical, mechanical, and plumbing works at the OCF.

A picture showing a large piece of construction equipment on a snow covered ground
View of chamber construction activity from the surface.
A picture of a brown and white building, with City hall in the background
Exterior cladding on the OCF.

Site 3CR: Wilbrod Shaft – Cumberland Street at Wilbrod Street

Preparation for construction of an underground access chamber has begun at this location.

Site 3CR construction activities of interest:

  • Site signage installation and set-up of traffic control measures.
  • Utility relocations underway.
A picture showing construction machinery digging into the middle of a concrete cylinder, underground.
Utility relocation works on Cumberland Street.

Site 5: East-West Tunnel Outlet and Rideau River Collector Diversion (New Edinburgh)

Construction continues in New Edinburgh's Stanley Park, where the tunnel boring machine has started its east-west journey, and at the intersection of Queen Victoria Street and River Lane (to connect to existing overflow sewer infrastructure).

Site 5 construction activities of interest:
  • Tunneling support operations on the surface, at 5A (the main site).
  • Completed excavation for the connection to the existing Interceptor Outfall Sewer – an existing pipe to which the CSST will outlet.
  • Preparation for concrete work within the IOS shaft.
  • At 5B, preparation for installation of concrete pipe within diversion sewer between shafts.
  • At 5C (the intersection of Queen Victoria and River Lane), tunneling for installation of a diversion sewer was completed.
A picture of a pipe, at the bottom of a large cylindrical shaft.
View inside the Interceptor Outfall Sewer shaft.

Site 6: North-South Tunnel Overflow/Kent Street Outfall - Ottawa River Pathway

Site 6 was the exit point for the tunnel boring machine and the northern end of the North-South Tunnel. Potential overflows from the Kent Street Sewer will be diverted to the NST and monitored here. An underground connection and an improved sewer outfall will also be constructed at this location.

Site 6 construction activities of interest:
  • Continued installation of rebar and concrete for the NST overflow chamber.
A picture of a rock cliff, showing a piece of green construction machinery working on a wood structure, on a snow covered ground
Construction of the NST overflow chamber. 

Site 8: McLeod Street Drop – McLeod Street and Kent Street

Work on McLeod Street, near Kent Street, is underway to complete the McLeod relief sewer, and construct underground chambers to convey flows to the NST.

Site 8 construction activities of interest:
  • Excavation of a shaft, using large drill with auger attachment.

A picture of a large machine and drill in the ground, sitting on dirt
Excavation of the shaft, using a large drill with auger attachment.

Site 9: Catherine Street Drop – Catherine Street at Kent Street

Work at the corner of Catherine and Kent Street, will include construction of two underground chambers to convey flows from the existing sewer on Catherine Street to the new CSST. An odour control facility will also be constructed at this location.

Site 9 construction activities of interest:
  • Continuing underground chamber construction preparations.
  • Preparation for excavation of a second shaft.
A picture of a circular hole at the top of a large cylindrical tunnel
View of site 9 shaft connection from within the north-south tunnel.

Site 10: Chamberlain Shaft (Kent/Chamberlain Streets)

Site 10 was the launch shaft for the north-south tunneling operation and, ultimately this shaft will house a chamber which will allow operations staff and equipment to access the tunnel.

Site 10 construction activities of interest:
  • Demobilization and clean-up of site 10B (Chamberlain at Bronson).
  • Preparatory works in advance of chamber construction at site10A.

Mobility & You

Stay informed about capital infrastructure projects. Check out the City’s interactive traffic map and traffic report or call 3-1-1 for updates about when and where construction is happening.

Contact Us

The CSST Project Team is committed to sharing information that may help affected residents and businesses plan around construction in their neighbourhoods.

For more information:
The CSST dedicated phone number is 613-580-2424 ext 2CSST (22778).
(This does not replace 3-1-1).

Visit us on the web at or email the project team at

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