Road retrofit such as sewer replacement or road re-construction in existing urbanized area can provide a good opportunity to implement stormwater low impact development (LID) technologies. In Canada and northern USA, stormwater management should focus not only in summer and fall but also winter and spring. A stormwater exfiltration system was designed to manage stormwater over four seasons by retrofitting roads with two 200 mm (8 inches) perforated pipes with end capped below a storm sewer system. The design concept is to direct road runoff up to 13 mm of rainfall to these two perforated pipes with end capped and fill the void space of the sewer trench for exfiltration to the surround soil at all times (i.e. including snowmelt and winter rainfall). Two and a half kilometer of this exfiltration system was constructed in the City of Toronto and found (by monitoring) to be able to control rainfall up to 24 mm without overflowing to the storm sewer above. This paper presents the planning and design criteria, costs, construction and maintenance, and performance evaluation.
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