View of the Ottawa River from Ontario, looking over the Portage Bridge.

Project Update

Combined Sewage Storage Tunnel (CSST)

Building a healthy and resilient future for the Ottawa River

Ottawa River
Ottawa River

What's it all about?

Canadian Environment Week 2017 was celebrated earlier this month.  What a great time to take a look at one of the City’s biggest projects with important environmental benefits – the Combined Sewage Storage Tunnel (CSST).

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.

Did you know?

The CSST will consist of two massive inter-connected underground tunnels over six kilometres in total length and approximately three metres in diameter, located 10 to 31 metres below ground level.

The east-west tunnel will run through the downtown core from LeBreton Flats to New Edinburgh Park, and the north-south tunnel will run below Kent Street from Chamberlain Avenue to just behind the Supreme Court.
The Tunnel Boring Machine (TBM)
The Tunnel Boring Machine (TBM)
The TBM has been specifically designed to cut through solid rock at a pace of roughly 20 to 25 metres per day and it’s going to start tunneling for the CSST this summer!  Work will continue to late summer 2019, and the CSST will be in operation in 2020.

Why?  Protecting our waterways

The CSST will greatly reduce the frequency of sewage overflows during storms from entering the Ottawa River. During major rainfalls, such as the storms we experienced during the flooding in May, the tunnels will hold up to 43,000m3 of sewer overflow – that’s as much as approximately 18 Olympic-sized pools!

Once the rainfall subsides, the water held in the tunnel will be thoroughly treated at the Robert O. Pickard Environmental Centre to ensure it is safe for the public’s health and the environment before being returned to the river.
Kent Street storm sewer outfall
Kent Street storm sewer outfall
By keeping sewage overflow from entering the Ottawa River, the CSST will protect the health of our aquatic ecosystem, lower the amount of contaminants released to the river, and improve the water quality.

The CSST is also good for our drainage system. It will reduce the risk of basement flooding in the city’s core, and support our major sewer collectors by giving them a reliable backup, additional conveyance capacity, and the flexibility that comes with all that extra storage space.

What's happening in your neighbourhood?

Read on to find out how construction is progressing and what is planned in your neighbourhood.
The map below identifies construction sites for the CSST project within the City of Ottawa.  Construction has either started or activities are imminent, at the sites indicated in green. The red dots indicate future or inactive construction sites. Site 7, identified with the grey dot, was eliminated during the design phase of the project.
Map of the CSST sites numbers 1 to 10. Sites 5, 6 and 10 are green, site 7 is grey and all other sites are red
Please continue to visit for updated information and construction site activity.

North South Tunnel (Kent and Chamberlain Streets to the Ottawa River

  •   Tunneling to begin this summer

Site 5: East West Tunnel Outlet/Rideau River Collector Diversion – Stanley Park/New Edinburgh Park

Construction activity continues in New Edinburgh, in Stanley Park and at River Lane/Queen Victoria.

Ongoing construction activities at this site: 
  • Construction of the shoring system for the TBM access shaft; this includes drilling of secant piles.
  • Excavation for the new odour control facility foundations.
  • Continuation with the relocation of the existing water main and other utilities

As the construction site in the park develops, the contractor continues to use the requisite interim truck route in and out of the park, wherever possible. Trucks may also need to travel within New Edinburgh between Stanley Park and River Lane/Queen Victoria. 
Formwork for secant shoring system
Formwork for secant shoring system
Drill rig for construction for shaft 5A secant wall
Drill rig for construction for shaft 5A secant wall
Construction of the new Odour Control Facility in Stanley Park
Construction of the new Odour Control Facility in Stanley Park
Arrival of equipment in Stanley Park
Arrival of equipment in Stanley Park

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

Construction activity will begin this summer. This site will be the exit point for the TBM after it completes the tunneling of the North-South Tunnel. It will also be a permanent access point to the CSST once complete.  Fencing around the site will be installed in late June/early July.

Site 8: McLeod Street Drop - Kent and McLeod Streets

A Community Information Session took place on May 24th at McNabb Community Centre. At this session, residents had the opportunity to:
  • Review background information on the CSST Project
  • Review construction activities and impacts in the neighbourhood
  • Provide feedback on the project and aspects for consideration

Construction activity at this site is anticipated to begin in early 2018.

Site 10: Chamberlain Shaft – Kent and Chamberlain Street

This site will be the access point for the TBM; a shaft is being constructed to launch the tunnelling operation for the North-South Tunnel to the Ottawa River.

Construction activities continue:
  • Installation of temporary water service into the access shaft to support the TBM during tunneling
  • The TBM components have arrived and are being stored
Tunneling of the North-South Tunnel is anticipated to launch from site 10 this summer.

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 now has a dedicated phone line to field questions and comments from community members and  stakeholders. During regular business hours, the CSST phone line will be monitored by the CSST field ambassadors and project team members.
The phone number is 613-580-2424 ext 2CSST (22778) and does not replace 3-1-1.
If your matter requires urgent attention, please report your concern by calling 3-1-1. Voice messages will be returned the next business day.
Visit us on the web at or email the project team at Note that the website is continuously updated with information on Open Houses, Public Information Sessions, and materials distributed at these events. Please continue to visit for updated information.

Tell your friends and neighbours to sign up to this newsletter at
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