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D. STORMWATER FLOW CONTROL <br /> The proposal is to construct a three-story residential building with an underground <br /> parking garage. The total proposed impervious surfaces will be 9,875 SF. The access to the <br /> parking garage will be from the alley in between Rockefeller Ave and Oakes Ave. <br /> The project site is legally served by a combined storm and sanitary sewer system, in <br /> which case the stormwater standards shall be as determined by Public Works Department <br /> policy. The existing basin was modeled as existing conditions per section 6-10 of the City <br /> Design and Construction Standards and Specifications. Flow control requirements will be <br /> met by a 19LF 4-foot diameter detention pipe on the south side of the building. <br /> DETENTION ANALYSIS <br /> Total Site Area = 0.30 Acres <br /> From the NRCS of Snohomish County, the site contains Alderwood Soils that has a <br /> hydrologic classification of"C". <br /> Existing Conditions: <br /> Existing Basin Area = 0.30 Acres <br /> Impervious area: <br /> Existing Roof = 0.07 Acres (3,038 SF) <br /> Existing sidewalk = 0.04 Acres (1,750 SF) <br /> Total Impervious = 0.11 Acres (4,788 SF) <br /> Pervious area= 0.30 Acres - 0.11 Acres= 0.19 Acres <br /> The pervious area was modeled as existing condition (Lawn). <br /> Refer to the Existing Basin Map &WWHM Report attached later in this section for <br /> more details. <br /> Insight Engineering Co. - Stormwater Site Plan 12/30/20 <br /> -27 - <br />