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• <br /> The general soil conditions for this property as mapped by the USDA Web-Soil Survey <br /> were found to be Alderwood — Urban Land Complex type soils. The hard pan for the <br /> Alderwood soil ranges between 20 and 40 inches below grade. Therefore, infiltration is not <br /> viable on this project. The drainage design has been laid out per the COE 2010 <br /> Stormwater Management Manual. <br /> The downstream system for this project is comprised of sheet flow collected in the existing <br /> wetlands to the west and the 16th Ave SE roadway to the east. There are two wetlands <br /> located west of the proposed development with the northern wetland draining north <br /> through the existing detention/water quality pond and then east through the 16th Ave SE <br /> cul-de-sac to a low area east of the R.O.W. that drains south and is eventually collected in <br /> an open detention/wet pond north of 107th PI. SE and east of this project. The southern <br /> wetland drains south and is collected by a conveyance system in the adjacent apartments. <br /> This system conveys the runoff through that project and discharges into the 16th Ave SE <br /> conveyance system south of this project. The flows in the R.O.W. drain north and into the <br /> same detention/wet pond as the northern wetland. Runoff from the east basin is collected <br /> in the 16th Ave SE roadway conveyance system and turns east in a CB located at the SE <br /> corner of this project. The pipe discharges into the same open detention/wet pond as the <br /> wetland basins. The pond outfall is to the south and into another pond system before <br /> being piped south and east and eventually discharging into Silver Lake. During the site <br /> visit there were no signs of flooding or capacity issues within the observed downstream <br /> systems. <br /> Due to the size of this project only Minimum requirements 1-9 apply to the proposed <br /> drainage design as noted above. Included on the following page is a copy of the MR flow <br /> chart out of the COE Drainage Manual showing how the applicable minimum requirements <br /> were determined. <br /> Northlake Court Townhomes 13-0609 <br /> May, 2014 Page 4 <br />