Our very own yellow La Machine?

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Site #10, located on Chamberlain Avenue, is the launch shaft for the north-south tunnelling operation. The Combined Sewage Storage Tunnel is expected to be completed by 2020. Photo: Matthew Horwood

by Matthew Horwood

The Combined Sewage Storage Tunnel (CSST), one leg of which will run from Chamberlain Avenue north along Kent Street, is on track to be completed by 2020.

The CSST project will include the construction of two tunnels: an east-west tunnel through the downtown core from LeBreton Flats to New Edinburgh Park, and a north-south tunnel along Kent Street from Chamberlain Avenue to just behind the Supreme Court.

The aim of the CSST project is to reduce the frequency of sewage overflows entering the Ottawa River during storms. It will also help reduce the chances of basement flooding in the core of the city.

When completed, the two inter-connected tunnels will be a total length of six kilometres, approximately three metres in diameter and 10–31 metres below ground level. The tunnels will be able to hold up to 43 million litres of surface runoff and wastewater, approximately equal to 18 Olympic-sized pools, to help mitigate sewage overflow during heavy rainfalls.

The $232.3 million construction project is a key part of the Ottawa River Action Plan (ORAP). The plan is aimed at “enhancing the health of the Ottawa River and protecting our water environment for future generations” according to the City of Ottawa’s website.

Funding for the project comes from the federal and provincial governments, each providing $62.09 million, and the city has committed $108 million. Storage tunnels for combined sewer overflows have been used in several other major cities in North America including Portland, Boston, Rochester and Washington, DC.

A tunnel-boring machine is being used to construct the tunnel. The face of the machine has a rotating cutter wheel that chips away at rock as the machine moves forward. This material is then transferred from the tunnel by conveyors back to the shaft entrance to be taken away.

Construction at ground level will be limited to specific locations along each tunnel where shafts or access points will be constructed. Access to homes has not been required for the construction, as the tunnelling work takes place well below the depth of houses or other surface-level structures.

Site #10, located on Chamberlain Avenue in the Glebe, is the launch shaft for the north-south tunnelling operation. Controlled blasting was completed inside the access shaft to facilitate rock excavation. Rock excavation activities and mining have not affected vehicle or pedestrian traffic, and notices were sent to nearby residents informing them of blasting and excavation activities.

While the CSST project team does not have information on the potential savings to individual property owners for flood damage, the infrastructure’s north-south tunnel could help reduce the risk of basement flooding for several low-lying lands in the city’s core and in the Glebe, according to Ziad Ghadban, manager at CSST. Ghadban stressed that the north-south tunnel is only one component of an overall flood control program for this area.

According to Ghadban, there have been a few complaints by nearby residents about noise and vibrations from the drilling as is expected with such a complex construction project. “The CSST project team has placed a significant focus on ensuring frequent and consistent communication with area councillors and adjacent residents and businesses, including via our field ambassador, our dedicated phone number and email, as well as to manage potential nuisances and maintain traffic flow throughout construction,” Ghadban said.

Construction on the tunnel began in the summer of 2016. While there have been some delays, the CSST remains on track for commissioning in 2020.

Matthew Horwood is originally from Belleville, Ontario, and moved to Ottawa in 2013. This year he will be completing his final year of journalism at Carleton University.

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