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Western Beaches Tunnel Pumping System Improvements

Helping reduce combined sewer overflows into Lake Ontario

Toronto, Ontario

The Western Beaches Tunnel was constructed in 2000 to reduce the discharge of untreated storm water and combined sewer overflows (CSO) into Lake Ontario. It collects, stores, and treats CSOs from 10 sewer outlets before they reach the lake. The system consists of three large vertical shafts up to 60 m deep and multiple smaller drop shafts inter-connected by a 3.7 km long tunnel, providing a capacity of 85,000 m3.

Numerous problems plagued the pumping system due to the large range of operating conditions required by the existing configuration – it failed after the first storm event. City operations staff have experienced issues with system control, inability of the pumps to empty out stored CSO flows, removal and reinstallation of the pumps, inadequate sediment flushing and removal, flow surges causing damage to the structures, and flooding of surrounding areas. The UV disinfection system was also not in use.

Stantec helped the City simply the configuration to provide better functionality, control, and operation. This included installation of new shaft dewatering pumps with capacities up to 43 ML/d and addition of dedicated grit/debris pumps located at the bottom of the shaft. We also inspected and helped improve the three shafts and tunnel. A new sediment fluidization system was designed using Computational Fluid Dynamics modeling. Upgrades to other building systems support the system improvements.

Our services included preliminary design, detail design, contract administration, and inspection of the works.

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