City of Ottawa

Project Update - Combined Sewage Storage Tunnel (CSST) - October 2018

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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 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)

Assembly of the TBM underground is still progressing. To do so, the machine has been mining very slowly forward. In the coming weeks, the TBM will accelerate and tunneling will be underway. Stay tuned for progress updates.

A picture showing a large piece of machinery at the bottom of a cylindrical shaft
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 excavation of soil and rock in preparation for construction of the OCF foundation.
  • Completed pouring of a concrete slab in preparation for foundation.

A picture showing a large piece of equipment digging earth on a slope
Rock excavation in preparation for construction of the odour control facility (OCF).
A picture showing poured concrete for a building foundation
Pouring of a concerete slab in preparation for foundation installation.

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

Construction of a new underground diversion chamber drop structure and odoour 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:

  • Completed rock excavation, rock support and shotcrete application within the shaft at 3A.
  • Commenced construction of the chamber, within the shaft, including installation of concrete slab and formwork.
  • Continued exterior cladding and interior electrical, mechanical, and plumbing works at the odour control facility (OCF).
a picture showing a part of a concrete pipe
Installation of deaeration chamber, insulation, and other support materials.
a picture of a building with white and brown walls showing construction equipment around it
Exterior works on the odour control facility (OCF).

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

Construction continues in New Edinburgh's Stanley Park, where the TBM will start its east-west journey soon, and at the intersection of Queen Victoria Street and River Lane (to connect to existing overflow sewer infrastructure).

Site 5 construction activities of interest:

  • Continued installation and assembly of the (TBM) within the main shaft, in preparation for tunneling.
  • Ongoing excavation for the connection to the existing Interceptor Outfall Sewer – an existing pipe that directs flow.
  • At 5C (the intersection of Queen Victoria and River Lane), tunneling of a diversion sewer to direct flow to the new CSST continues.
A picture showing a large yellow crane with blue sky in background and construction equipment around
Installation of the gantry crane near the 5A shaft.
a concrete cylindrical shaft showing construction equipment at the bottom
Rock excavation within 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 TBM 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:

  • Geotechnical monitoring continues.
  • Installation of the headwall at the Ottawa River, using concrete blocks, is underway.
  • Backfilling around the headwall, at the Ottawa River continues.
  • Continued installation of and backfilling around overflow piping between the Kent St by-pass chamber and the CSST overflow chamber.
A picture showing a concrete wall at the Ottawa River
Installation of rock shoreline structure, to prevent erosion.
A picture showing a hole in earth for a pipe with a large piece of construction equipment
Excavation around the CSST 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:

  • Utility relocations are ongoing, including gas and temporary water servicing.
  • Installation of an excavation shoring support system will begin in the coming weeks.
A picture showing construction equipment digging in earth, below ground
Excavation in support of utility relocation along Kent Street at McLeod Street.

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:

  • Relocation of underground utility (gas) is complete.
  • Continued rock excavation using large drill with auger attachment.

A picture showing a large piece of construction equipment drilling into ground
Drilling the shaft at site 9, using a large drill and auger attachment.
A picture showing a large cylindrical shaft with a large steel drill in the middle
View inside the shaft at site 9.

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:

  • Tunnel support equipment disassembly and transportation to the EWT launch site is complete.
  • Preparatory works in advance of chamber construction have commenced.

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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