Performance Assessment of the Eastern Beaches Detention Tank – Toronto, Ontario


iIn 1994, the City of Toronto constructed a 8000 cubic metre underground tank to address beach closure and waterfront pollution issues associated with combined (sanitary and storm) sewer overflows (CSOs) and untreated stormwater runoff. The tank consists of two compartments, one for stormwater runoff, the other for CSOs.  The CSOs are temporarily stored in the tank before being pumped to a lakefront interceptor and then to the sewage treatment plant once capacity is available.  Runoff in the stormwater compartment is detained for an 8 hour sedimentation period before it is pumped 400 m offshore.  The sludge (or subnatant) in the bottom of the tank is drained into the CSO compartment after each event where it is eventually conveyed to the treatment plant.  In the future, construction of a relief sewer nearby will provide in-line storage for the CSOs such that the Eastern Beaches tank will only receive stormwater runoff.

Monitoring of this facility for water quality and quantity was undertaken by the City of Toronto and SWAMP program staff in 1995 and 1996.  Final analysis of data, probabilistic modeling and report editing/writing were completed by Lijing Xu and Barry Adams from the University of Toronto.