City of Ottawa

Project Update - Combined Sewage Storage Tunnel (CSST) - July 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


North-South Tunnel (NST)

Tunneling of the NST from Kent/Chamberlain Streets to the Ottawa River (Site 10 to Site 6) is complete!
Picture showing a map of Ottawa and an orange line from Kent and Chamberlain north along Kent Street to behind the Supreme Court of Canada showing that the north-south tunnel has been completed.
Progress on the north-south tunnel (NST).

East-West Tunnel (EWT)

July 20, 2019, marked another milestone as the tunnel boring machine (TBM) connected with the finished north-south tunnel, creating an underground intersection roughly eight storeys below Slater and Kent streets.

Check out this video of the TBM emerging from the rock!

Tunneling for the combined sewage storage tunnel (CSST) is now more than 85 per cent complete, and east-west tunneling is expected to be finished this fall.

Picture showing a map of Ottawa and an orange line from Stanley Park W to Cumberland, then south along Cumberland before turning west on Waller/ Laurier, going through Confederation Park then down Slater Street, stopping at Kent Street.
Progress on the east-west tunnel (EWT).
A picture of a large cylindrical machine with cutter wheels emerging from a rock face.
The tunnel boring machine breaking into the NST/EWT intersection.

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. This location includes 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:
  • Installation of masonry, insulation, and odour control equipment within the OCF.
  • Underground chamber formwork within the large shaft, including installation of roof slab.
A picture of a large cylindrical vessel being lifted and placed into a concrete building from the roof.
Installation of the odour control vessel within the odour control building, from an opening on the roof.

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

Site 2 is where the two tunnels intersect, and will include an underground access point.

Site 2 construction activities of interest:
  • Completed rock drilling and installation of supports within the excavation.
  • Preparation for the arrival of the tunnel boring machine within the cavern underground, at the future intersection of the tunnels.
  • Completed watermain reconnection on Slater Street.

A picture showing workers in a square large wooden chamber in between two cylindrical tunnels.
Preparation for tunnel boring machine arrival at the NST/EWT underground intersection.

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

Excess flows from the existing Rideau Canal Interceptor will be diverted to the EWT at this location, which requires construction of a new underground diversion chamber drop structure and odour control facility.

Site 3A construction activities of interest:
  • Continued construction of the underground chamber, at the bottom of the shaft.
  • Continued landscaping works around the OCF.

A photo taken above a building showing a grey roof and brown siding, with a light pole beside a sidewalk leading up to the building.
Landscaping works around the odour control facility, including installation of sidewalks and water fountain.
A photo looking down into a rectangular shaped concrete underground chamber, showing steel bars along the top edge and a steel ladder from the top of one corner to the bottom.
Chamber construction within the shaft at 3A.

Site 3B: Rideau Canal Regulator – Rideau Canal

Work is necessary on the existing Rideau Canal Regulator at this location in order to ensure operational efficiency of the CSST.

Site 3B construction activities of interest:
  • The CSST contractor has demobilized, but is expected to return for a few days later this fall to complete work.

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

This site requires construction of an underground access chamber.

Site 3CR construction activities of interest:
  • The CSST contractor has demobilized, but will return later in 2019.

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

Site 5 in New Edinburgh's Stanley Park is where the tunnel boring machine started its east-west journey, and work includes an underground connection to existing overflow sewer infrastructure at the intersection of Queen Victoria Street and River Lane.

Site 5 construction activities of interest:
  • Tunneling support operations continue on the surface, at 5A (the main site in Stanley Park).
  • Construction of the concrete Interceptor Outfall Sewer chamber is complete.
  • Installation of a concrete pipe diversion sewer between the main shaft and shaft 5C (the intersection of Queen Victoria Street and River Lane) is also complete.
  • Concrete and steel work underway for chamber construction within the shaft at 5C.
A photo looking into a concrete rectangular shaped concrete underground chamber showing wooden walls around a pipe.
Chamber construction at the bottom of the 5C shaft.

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

Site 6 was the first 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, requiring an underground connection and an improved sewer outfall.

Site 6 construction activities of interest:
  • Worker access to the NST through the portal at Site 6.
  • Backfilling around the site, in preparation for reinstatement.
A picture showing a dump truck dumping earth onto the ground with a large yellow machine adjacent to the pile and concrete structure in the background.
Grading and backfilling around the outfall chamber.

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

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

Site 8 construction activities of interest:
  • Continued rock breaking at the bottom of the 24-metre-deep shaft, to connect horizontally to the new tunnel below Kent Street.

A photo taken underground showing a large yellow machine with a bucket in front of a circular mark in a rock face.
Horizontal rock excavation at the bottom of the Site 8 shaft.

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

Work at the corner of Catherine and Kent Street includes construction of two underground chambers to convey flows from the existing sewer on Catherine Street to the new CSST, as well as an odour control facility.

Site 9 construction activities of interest:
  • Re-commenced excavation at the second chamber location.
  • Poured the OCF foundation.
A photo showing a rectangular wall structure made of wood, for a building foundation, above ground.
Construction of the odour control facility foundation walls.

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:
  • Filled the tail tunnel.
  • Commenced chamber construction works at the bottom of the shaft.
A photo showing a concrete wall within a large cylindrical concrete underground shaft, with steel bars on the floor.
Chamber construction preparations at the bottom of the shaft, showing filled tail tunnel.

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

Footer Banner. Supporting an environmentally sustainable Ottawa. The partnership of Ottawa River Action Plan and City of Ottawa.

This email was sent by the City of Ottawa to because you subscribed to Combined Sewage Storage Tunnel (CSST)

City of Ottawa, 110 Laurier Ave. W., Ottawa, Ontario K1P 1J1, Canada

© 2001-2020 City of Ottawa

Visit for a full list of newsletters | 3-1-1

TTY 613-580-2401


Visit the City's social media streams
City of Ottawa Twitter City of Ottawa Facebook City of Ottawa Youtube City of Ottawa Instagram City of Ottawa RSS


Email Marketing by ActiveCampaign