The combined sewage storage tunnel will hold sewage and stormwater runoff -- which currently overflow into the Ottawa River, untreated -- during heavy rainfalls.

It's not as well-known as the tunnel for the O-Train's Confederation Line, but a second major tunnel through downtown Ottawa is now complete.

Excavation for the city's combined sewage storage tunnel was officially completed as the boring machine broke through the final few inches of dirt and rock, Monday.

Great news, the Combined Sewage Storage Tunnel project’s tunnel boring machine has completed its underground journey, marking a huge project milestone! Tunneling is now complete and work continues on this $232.3 M initiative to protect our Ottawa River: https://t.co/EOB3wPuWkV pic.twitter.com/rmdKAMtwbK — Jim Watson (@JimWatsonOttawa) September 23, 2019

The project consists of a north-south tunnel, under Kent Street, as well as an east-west tunnel between New Edinburgh and LeBreton Flats. The mayor posted a video of the tunnel-boring machine finishing its east-west journey, eating through the last bit of rock at LeBreton Flats.

The combined sewage storage tunnel will hold sewage and stormwater runoff -- which currently overflow into the Ottawa River, untreated -- during heavy rainfalls.

Construction will continue to finish underground chambers and odour control measures at surface locations in New Edinburgh, LeBreton Flats, Sandy Hill, New Edinburgh, Centretown and the northernmost tip of the Glebe.

The tunnel is expected to be operational next year.