City of Ottawa

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

Tunneling of the East-West tunnel from Stanley Park to LeBreton Flats (Site 5 to Site 1) is underway, and progressing through Sandy Hill. The tunnel boring machine (TBM) is several storeys below Laurier Avenue East in the vicinity of Waller Street.
Picture showing a map of Ottawa and an orange line from Stanley Park south to Rideau Street showing the east-west tunnel has been completed to that point and a green dotted line showing the entire alignment traveling south along Cumberland Street then heading West on Laurier and up to Slater Street and ending in LeBreton
Progress on the east-west tunnel (EWT).
A picture from inside a large cylindrical hole underground, looking up showing sky and construction machinery.
View from the bottom of the access shaft of the EWT, showing the yellow gantry crane at surface.

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:
  • Construction of the OCF walls are complete.
  • Commenced work on the roof slab, involving scaffolding and formwork.
  • Construction of the chamber base slab is underway in the shaft.
Picture of a large concrete building being constructed with a crane in the background.
Removal of wall formwork at the OCF, in preparation for roof construction.

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:
  • Utility relocations continue, with watermain works complete.
  • Chamber construction preparations continue underground, at the future intersection of the North-South Tunnel.

Picture of a large piece of construction equipment digging to remove earth.
Watermain works on Slater Street.

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.
  • OCF exterior works are complete, and interior electrical, mechanical, and plumbing works continue.

Picture looking into a large rectangular shaft below ground with a wooden structure being built along its interior.
View of chamber construction activity within the shaft.

Site 3B: Rideau Canal Regulator – Rideau Canal

Work has commenced on the existing Rideau Canal Regulator in order to ensure operational efficiency of the CSST.

Site 3B construction activities of interest:
  • Underground maintenance and modifications within the existing Rideau Canal Regulator are underway. The CSST contractor has demobilized, but is expected to return for a few days in April to complete work.
Picture showing large construction machinery under a bridge.
Concrete works in the existing Rideau Canal Regulator, below the Plaza Bridge.

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

Construction of an underground access chamber is underway at this location.

Site 3CR construction activities of interest:
  • Site signage and traffic control remain in place.
  • Excavation of the shaft using a large drill with an auger attachment is near completion.
  • Work to temporarily re-instate the roadway is expected in the coming weeks.
Picture showing a large drill in the ground, attached to a piece of large construction machinery.
Shaft excavation using large drill 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 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 continue on the surface, at 5A (the main site).
  • Construction of the concrete Interceptor Outfall Sewer chamber is underway.
  • Additional rock removal has been completed in preparation for the installation of a concrete pipe diversion sewer between the main shaft and shaft 5C (the intersection of Queen Victoria and River Lane).
  • Concrete and steel work has commenced in preparation for chamber construction within the shaft at 5C.
Picture showing a large concrete ring at the bottom of a large cylindrical shaft.
Installation of concrete pipe for the diversion sewer.

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:
  • Installation of rebar and concrete for the NST overflow chamber is complete.
  • Final works on the NST overflow chamber continue.
Picture showing construction equipment and concrete chamber beside a rock cliff.
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 the deepest shaft by drilled auger is complete.
  • Earth excavation at the second shaft is complete.
  • Rock breaking at the bottom of the 24-metre-deep shaft, to connect horizontally to the new tunnel below Kent Street is underway.

Picture from within a large rectangular shaft below ground, showing steel frames along its interior.
Installation of excavation shoring support system within the shaft.

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 preparation preparation (in the North-South Tunnel).
  • Earth excavation at the second shaft is underway.

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:
  • Work continues within the North-South Tunnel, with access through the main shaft at Site 10.
  • 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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