The project includes 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 Catherine Street to existing infrastructure, just behind the Supreme Court of Canada.

The tunnels will reduce the frequency of sewage overflows into the Ottawa River during storms, reduce the risk of basement flooding and increase operational flexibility and redundancy to major collector sewers. Once rainfall has subsided, water will be treated and returned safely to the Ottawa River.

"The Combined Sewage Storage Tunnel is one of the most important projects of the Ottawa River Action Plan, which is the City of Ottawa's roadmap for protecting the health and vitality of the Ottawa River for present and future generations,” said Ottawa’s mayor, Jim Watson.

The governments of Canada and Ontario are each providing CAD 62.09M (USD 47M). In addition, the City of Ottawa has committed CAD 107M (USD 81M). Construction has already begun on the CSST, with Dragados Tomlinson selected to build the project. Completion is anticipated in late 2019 with the intent of having the CSST in full operation by mid-2020.