Ottawa has now completed all six kilometres of tunneling for its Combined Sewage Storage Tunnel project, which aims to significantly reduce overflows when wastewater combines with surface water and debris washes off the streets.
The two tunnels are designed to hold up to 43 million litres of surface runoff and wastewater and prevent it from entering the Ottawa River, according to City of Ottawa documents about the project. The City says the $232.3-million project will virtually eliminate combined sewage overflow during a typical year.
The tunnels are 4.4 km and 1.6 km long, respectively, and 3 m each in diameter, adding 43,600 cubic metres of storage. The tunnels range from 20 m to 35 m deep with six major drop shafts 2 m to 3 m in diameter.
“With a capacity of approximately 18 Olympic-sized swimming pools, the Combined Sewage Storage Tunnel will help protect the Ottawa River for the future,” City officials said in an announcement about the completion of the tunneling. “The project will also reduce the risk of basement flooding in some low-lying areas in the city’s core and help future-proof our existing downtown sewer infrastructure by adding capacity and redundancy,” the officials added.
Ottawa used a special tunnel boring machine for the project specifically designed to cut through solid rock at a pace of roughly 20 to 25 metres per day. (Watch a video of the recent tunneling breakthrough here). More than 113,000 cubic metres of rock was removed from deep below the city during tunneling – enough to fill every lock in the Rideau Canal waterway between the Ottawa River and Lake Ontario in Kingston – twice.
Construction on the project began in 2016, and city officials say they hope to have the project operational in 2020. In the coming months, work will continue at surface locations in New Edinburgh, LeBreton Flats, Sandy Hill, New Edinburgh, Centretown and the northernmost tip of the Glebe to complete underground chambers and odour control facilities.
Wastewater Plant Upgrades
Also in Ottawa news this week is the announcement of $57.2 million in upgrades to the cogeneration system at the City’s Robert O. Pickard Environmental Centre. The cogeneration system converts methane from the wastewater treatment process into electricity and heat for the plant. The methane can also be used as gas for the plant’s boilers, reducing how much natural gas the City needs to purchase.
Since the system came online in 1997, it has saved the City between $1 million and $1.4 million in utility costs per year. The City could save an additional $80 million in utility costs over 25 years with the new upgrades.
The project is expected to reduce the plant’s greenhouse gas emissions by up to an additional 1,565 tonnes per year over the current system, which is at the end of its service life. They upgrades would also allow the plant to operate during a sustained power outage, keeping the Ottawa River safe from untreated wastewater discharge.
The City’s wastewater is collected through a system comprised of 2,853 km of sanitary sewers and 102 km of combined sewers. The upgrades are expected to be completed by the end of 2024.