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|Perforated pipe||North york, ON<ref name=SWAMP/>||Silty sand||89 %
|Perforated pipe||North york, ON<ref name=SWAMP/>||Silty sand||89 %
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Runoff reduction estimate = 85 % on HSG A and B soils.<br>
Runoff reduction estimate = 45 % on HSG C and D soils.
===Pollutant removal capacity===
Performance results from a limited number of field studies indicate that subsurface stormwater infiltration practices are effective BMPs for pollutant removal <ref>Toronto and Region Conservation (TRCA). 2009. Review of the Science and Practice of Stormwater Infiltration in Cold Climates. Prepared under the Sustainable Technologies Evaluation Program (STEP). Toronto, Ontario.</ref>. These types of practices provide effective removal for many pollutants as a result of sedimentation, filtering, and soil adsorption. It is also important to note that there is a relationship between the water balance and water quality functions. If an infiltration practice infiltrates and evaporates 100% of the runoff from a site, then there is essentially no pollution leaving the site in surface runoff. Furthermore, treatment of infiltrated runoff continues to occur as it leaves the facility and moves through the native soil. The performance of perforated pipe systems would be expected to reduce pollutants in runoff in a manner similar to infiltration trenches.
Several studies of exfiltration systems in Ontario have examined their water quality benefits. Seasonal contaminant load reductions in the order of 80% were observed for most constituents, with the exception of chloride, in the study of the system installed in a low density residential neighbourhood in Etobicoke <ref>Stormwater Assessment Monitoring and Performance (SWAMP) Program. 2002. Performance Assessment of a Swale/Perforated Pipe Stormwater Infiltration System – Toronto, Ontario. Toronto and Region Conservation Authority, Toronto, Ontario.</ref><ref>Stormwater Assessment Monitoring and Performance (SWAMP) Program. 2005.
Synthesis of Monitoring Studies Conducted Under the Stormwater Assessment
Monitoring and Performance Program.. Toronto and Region Conservation Authority,
Toronto, Ontario.</ref>. Perforated pipe systems that incorporate grassed [[swales]] as [[pretreatment]] have been observed to reduce loads of suspended sediment, [[phosphorus]], [[nitrogen]], copper, lead and zinc in runoff flowing from the system between 75 to 90% in comparison to a similar catchment with conventional catchbasins and storm sewers (J.F. Sabourin and Associates, 1999; and 2008a). The Nepean systems were shown to release significantly less pollutants than the conventional sewer system, even after 20 years of operation (J.F. Sabourin and Associates, 2008a).
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