The City of London, Ontario, is nearing completion of its $18-million Downtown Sewer Capacity Expansion Project, a major infrastructure initiative that will replace a nearly century-old sanitary sewer siphon beneath the Thames River and significantly increase wastewater capacity for future growth.
Construction began in 2025 and is expected to wrap up in the coming weeks. The project involves the installation of two new sewer tunnels beneath the Forks of the Thames, replacing a sanitary siphon originally constructed in 1934 that had reached the end of its service life.
The new infrastructure includes sewer pipes larger than the diameter of a passenger vehicle and extends to a maximum depth of approximately 14 metres below ground. Excavated using a specialized tunnel boring machine, the tunnels will carry sanitary sewage flows from downtown London and surrounding areas, providing additional system capacity while improving long-term reliability.
The project was undertaken alongside major upgrades at the Greenway wastewater treatment plant, forming part of a broader strategy to modernize London’s wastewater network and accommodate projected population growth.
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City officials estimate London’s population could reach 750,000 residents by 2050, increasing the need for expanded water and wastewater infrastructure.
The aging sewer crossing had become a significant constraint on development in the downtown core, where higher-density residential projects have been limited by infrastructure capacity. By replacing the aging siphon with a new parallel system and connecting it to upstream and downstream sanitary sewers, the city expects to unlock new development opportunities while reducing the environmental risks associated with aging wastewater infrastructure.
“I’m excited to share that the project just hit a breakthrough last week, and when it’s completed in the coming weeks, the expansion will play an important role in the Downtown Plan and the overall revitalization of our downtown core,” said David Ferreira, Ward 13 councillor, in a statement.
Ferreira said the additional sewer capacity will help enable significant downtown development projects, supporting population growth while strengthening the city’s urban core.
Once operational, the expanded system is expected to improve wastewater conveyance capacity, support future residential intensification, and provide a more resilient sewer connection beneath the Thames River for decades to come.
