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.

• Ottawa's next big dig set to start on $230M sewage tunnels
• Ottawa River full of untreated sewage during May flooding

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 startdigging, the city said Tuesday.

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

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 Slaterstreets.

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

During major rainfallsthe 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 willbe treated before being returned to the river.

The tunnel is also being built to aid the city's drainage system, and the city saidit's expected toreduce the risk of basement floodingin the downtown core.

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 than430-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.