Ottawa

Sewage tunnel dig to begin later this fall under Kent Street

The City of Ottawa has reached an early milestone on its other major underground project — the sewage storage tunnels meant to keep sewage overflows from entering the Ottawa River.

$232M project scheduled to be complete by 2020

A component of the tunnel boring machine is lowered down an access shaft at Kent Street and Chamberlain Avenue. Work to dig the tunnel from Chamberlain north to the Ottawa River is expected to be completed in the spring of 2018. (Front Page Media Group)

The City of Ottawa has reached an early milestone on its other major underground project — the sewage storage tunnels meant to keep sewage overflows from entering the Ottawa River.

The Combined Sewage Storage Tunnel is a $232.3-million project funded by all three levels of government, but it's been overshadowed by work on the multi-billion-dollar light-rail transit system.

Work began in June 2016 on an access shaft to the site of the future sewage tunnel at the intersection of Kent Street and Chamberlain Avenue.

The 23-metre deep shaft is now complete, and a tunnel boring machine is being assembled underground to start digging, the city said Tuesday.

That machine will work its way under Kent Street starting later this fall and surface behind the Supreme Court of Canada in the spring of 2018.

The access shaft below Kent Street and Chamberlain Avenue is where the tunnel boring machine will begin its work. (City of Ottawa)

Tunnel to handle excess wastewater

A second, inter-connected east-west tunnel will run through the downtown core, from Stanley Park to LeBreton Flats, generally under Cumberland and Slater streets.

The tunnels will be three metres in diameter and located 10 to 31 metres below surface level.

During major rainfalls the tunnels will hold up to 43 million litres of surface runoff and wastewater — as much as approximately 18 Olympic-sized pools. Once the rainfall subsides, the water will be treated before being returned to the river.

The tunnel is also being built to aid the city's drainage system, and the city said it's expected to reduce the risk of basement flooding in the downtown core.

The 250-metre-long tunnel boring machine has a rotating cutter wheel that chips away rock in various sizes, ranging from tiny gravel to fist-sized pieces, as the machine moves forward. Conveyors then take the pieces back to the shaft entrance to be taken away. (City of Ottawa)

Sewage overflow has been a persistent problem for the Ottawa River for years, but it was particularly bad during this spring's record rainfall.

From May 5 to May 7, more than 430-million litres of sewage overflowed into the river, far more than the sewage tunnel could handle.

Work on building the sewage tunnel is scheduled to be complete in 2019, with the tunnel operational in 2020.

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