This exfiltration system in Toronto (formerly Etobicoke) consists of an innovative underground piping concept designed to reduce stormwater volumes and pollutant loads that discharge to receiving waters by promoting infiltration of stormwater runoff.  In this system, stormwater passes through catchbasins into a conventional storm sewer until it reaches the next downstream manhole. The flow then drops into two perforated pipes which are installed below and parallel to the storm sewer. From the perforated pipe, the water exfiltrates into a gravel filled trench, and from there seeps into the surrounding native soil. When flow exceeds the exfiltration capacity of the system, the water surcharges and continues in the conventional storm sewer located above.

Monitoring for water quality and quantity was undertaken under the SWAMP Program for two years from 1996 to 1998.  Two other exfiltration and filtration systems nearby were also monitored, but the studies were terminated after a single runoff season because the systems were not considered to be representative of their respective design objectives.

For detailed monitoring results on this project, see the report entitled Performance Assessment of a Perforated Pipe Stormwater Exfiltration System – Toronto, Ontario