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ROOF DOWNSPOUT BMPS <br />Roof downspout BMPs include infiltration trenches, dry wells, and partial dispersion systems <br />BMP T5.10A Roof Downspout Full Infiltration <br />Downspout full infiltration systems are trench or drywell designs intended for use in infiltrating runoff from <br />roof downspout drains. <br />InfllbaRon Trermh <br />The minimum trench length is based upon the soil type in the location of the infiltration trench. <br />The soils report will provide the USDA Soil Type. The table below provides the minimum trench <br />length per 1,000 ft' of contributing roof area. Roof downspout infiltration trenches shall be <br />designed in accordance with the SWMMWW. <br />• <br />"Coarse sand" <br />(more than 50%of sand fraction remains on k4 sieve) <br />20 <br />"Medium sand" (more than 50%of sand fraction remains on*40 sieve) <br />30 <br />Loamy sand <br />75 <br />Sandyloam <br />125 <br />Loam <br />190 <br />Silt loam <br />275 <br />Fill (only per SWMMWW requirements) <br />60 <br />Trench length required (ft) = Roof area (112) *((minimum trench length) (11)) <br />City of Everett Public Works <br />Small Pmjact Stormwater Site Plan Report nec 2019 <br />