What is the Combined Sewage Storage Tunnel (CSST)? Why is this project necessary?
The CSST is a Term of Council Strategic Initiative and one of the most important projects of the Ottawa River Action Plan (ORAP), which is the City of Ottawa’s long-term strategy to improve stormwater management and to enhance and protect the health of the Ottawa River.
The CSST project includes the construction of two tunnels, an east-west tunnel (EWT) through the downtown core from LeBreton Flats to New Edinburgh Park, and a north-south tunnel (NST) along Kent Street from Chamberlain Avenue to the existing storm sewer outfall at the Ottawa River north of Wellington Street.
The CSST will greatly reduce the frequency of overflows from entering the Ottawa River; it will hold up to 43,000m3 of sewer overflow during major rainfalls, which can then be treated and returned safely to the Ottawa River. In addition to reducing overflows from entering the Ottawa River, benefits of the CSST project include reducing the risk of basement flooding for several low-lying lands in the Glebe/O’Connor area, and increasing operational flexibility and redundancy to major collector sewers in the downtown area.
Is this a new technology to deal with Combined Sewer Overflows (CSOs)?
The storage tunnel for Combined Sewer Overflows (CSOs) is not a new concept, and is in use in several other major cities in North America. Similar tunnel facilities have been constructed and are in use in Portland, OR, Boston, MA, Milwaukee, WI, Rochester, NY, Providence, RI, Washington, DC and Cleveland, OH, among others. A number of Canadian municipalities also have tank-style storage facilities for CSO control.
How big is the tunnel? Will there be construction on the street?
The inside diameter of the finished tunnel is three metres. The tunnel boring machine will be roughly four metres in diameter.
The tunnel will be 10 to 31 metres below surface level.
A boring technique will be used to excavate the tunnel. Construction at ground level will be limited to specific locations along each tunnel alignment where shafts or access points will be constructed. These are located on publicly owned land.
How will the tunnel be constructed?
A Tunnel Boring Machine (TBM) will be used to construct the tunnel. The face of the machine has a rotating cutter wheel that chips away the rock in various sizes ranging from tiny gravel to fist size pieces as the machine moves forward. This material is then transferred from the tunnel by conveyors back to the shaft entrance to be taken away. As the machine mines the tunnel, precast concrete liners are placed in segments behind the machine and grout is added to permanently seal the tunnel.
This is a commonly used technique in tunneling projects. A similar technique was used in Portland, OR during the construction of their CSO storage tunnel. A video on the project that provides more information on this technique can be found on the City of Portland Website.
Who will be doing the work?
The CSST is a City of Ottawa project, with construction led by Dragados Tomlinson Joint Venture (the contractor).
Has the contractor conducted this type of project before?
As part of the procurement process, the successful proponent was required to provide many examples of their experience and expertise in delivering similar types of projects and managing projects of a similar scope and budget. The City’s procurement standards require all contractors to demonstrate their experience and provide references.
Will access be required to homes or basements?
No access to homes will be required for the construction. The tunneling work will take place well below the depth of houses or other surface level structures.
Because of the tunneling technique, the only surface level construction for the tunnel will be located at access shafts created at key locations on publicly owned land along the two tunnels.
Depending on the proximity of the home to the construction area, the contractor may contact property owners before the start of construction to conduct a pre-construction survey. This will require access to their property to record the current condition. This is standard practice for any civil/excavation work.
Will we feel vibrations, and for how long?
Perception of how strong vibrations are can depend on a number of variables and individual sensitivity. Due to the bedrock in the area and the depth of the tunneling, it is not anticipated that residents will feel very strong vibrations.
In general, residents may feel some vibrations due to construction activities in the area located adjacent to the tunnel boring machine. As the machine will be moving slowly forward, the localized vibrations will pass by. It is anticipated that the speed of the tunnel boring machine will mean that any vibrations would only persist for a short number of days.
Will the contractor work outside of regular business hours?
To minimize the construction impacts and to move the project along, the contractor is likely to accelerate the tunnel boring work outside of regular construction hours. It is anticipated that the tunnel operation will continue 24 hours a day, in accordance with any issued Noise By-law Exemption. Most surface activities will occur during regular business hours in the daytime.
Where does construction begin for the CSST?
Construction for the CSST project began in the summer of 2016 at the intersection of Kent Street and Chamberlain Avenue, and the CSST will be in operation in 2020.
How will residents be kept informed about the construction?
Several resources are available to residents to obtain updates on construction activities, impacts and progress through the duration of the CSST construction, including:
- Regularly distributed e-newsletter with updates on construction activities, impacts, and progress. Sign up to receive updates automatically at Ottawa.ca/esubscriptions;
- Webpage (Ottawa.ca/CSST) with information on the overall project including updates;
- Email address (CSST@ottawa.ca) for inquiries; and
- Dedicated CSST phone line: 613-580-2424 ext. 2CSST (22778).
Protection of Heritage Structures
Does the City of Ottawa permit controlled blasting?
Rock excavation is completed on both City projects and private property via either mechanical excavation or controlled blasting.As dense rock is commonly found close to the surface in various geographical areas within the city, controlled blasting is an acceptable and common construction practice within the City of Ottawa. (Blasting may be required in a variety of construction projects, including the construction and/or installation of roads, sewers, water mains, utilities, foundations, tunnels, etc.)
Whether using mechanical excavation or controlled blasting, adjacent properties will be able to hear the noise produced and feel the vibrations transmitted by the work. In either case, there are standards and regulations that apply in order to reduce the noise/impact of the work and ensure the vibration levels are low enough not to cause damage to adjacent properties. These standards and regulations also cover topics such as: how the work will be conducted, information to be provided to adjacent properties in advance of the work, preparatory work that must be completed, and monitoring activities before, during, and after the work.
You can read more about blasting in the City of Ottawa, including applicable regulatory standards and specifications.
How does the contractor ensure that my property will not be damaged by the vibrations caused by the CSST Project?
Residents should be aware that they may feel vibrations from the construction activity, but these will be well below the levels that could cause damage. The contractor’s plans ensure that the specifications outlined in the City of Ottawa Special Provision F-1201 will be followed. These guidelines define the limits placed on vibration levels in order to protect nearby structures. Controlled blasting is designed to meet regulatory requirements, and every blast is carefully monitored by an independent engineering consultant to ensure compliance to these limits.
By regulation, the excavation contractor must reduce the size of the blast the closer it gets to existing structures. The smaller the blast, the lower the vibration – thus helping protect the integrity of adjacent structures. The CSST Project specifications implement further reductions to the limits placed on vibration levels by the City of Ottawa F-1201
My house is very old and has a rubble stone foundation wall. Will it fall down due to the vibrations?
Well-built rubble foundation walls are not inferior to cast concrete. Buildings with rubble foundations, as opposed to rigid cast concrete basement walls, tend to flex and absorb vibrations that might otherwise be transferred to the upper building structure.
Regardless of foundation type, the strict construction vibration limits set within CSST project specifications serve to reduce the possibility of damage to any existing buildings.
Why am I being asked to allow a survey of my home before the construction has started?
A pre-construction survey, to record pre-construction conditions, is required for comparison should a damage claim be entered. This is a measure taken to protect homeowners during certain construction projects. A pre-construction survey is required for all buildings, utilities, structures, water wells and facilities within 75 m of the location of a controlled blast. In additional to the pre-construction survey, the Contractor must carry liability insurance before any work may proceed.
I feel vibration. Does that mean that damage is being caused?
People (and animals) are very perceptive to a small amount of vibration. However, without scientific instruments (seismographs), people cannot accurately place a value on the amount of vibration generated. Human perception of vibration is around a peak particle velocity (PPV) of between 0.2 mm/s and 0.5mm/s. By comparison, the industry-accepted PPV for residential structures is 50mm/s. A door slamming, thunderstorm activity and wind all produce vibrations that we feel but discount since these are “everyday” events.
Why do some of the vibrations feel much stronger than others?
The position and orientation of the vibration source may cause the perception that one vibration is stronger than another. Your location - within a building or outdoors - will also change your perception of the vibrations. Seismographs are used to accurately measure vibrations.
Why are there cracks in my foundation or cracks in my drywall?
The average person is not aware of the stresses that a home in Canada must endure. The Building Code requires that homes be designed to be flexible to try and accommodate these stresses. There are many reasons for cracks; shortly after a new building is constructed, cracks may appear due to drying of construction materials, and in older buildings, cracks often occur as a result of extreme environmental conditions or simply aging materials.
What should residents do if they discover damage they believe is a result of the CSST project?
Residents should notify the CSST Project Team through the dedicated email address firstname.lastname@example.org to resolve the issue directly or for guidance on submitting a claim to the contractor.