1415 BROADWAY CM HEATING 2023-09-25

D. STORMWATER FLOW CONTROL The proposal is to construct a new commercial building and parking lot. The total proposed impervious surfaces will be 15,034 SF. The access to the site will be from the alley in between Broadway and McDougal Ave. The project site is legally served by a combined storm and sanitary sewer system, in which case the stormwater standards shall be as determined by Public Works Department policy. The existing basin was modeled as existing conditions per section 6-10 of the City Design and Construction Standards and Specifications. Flow control requirements will be met by a 15 LF 6-foot diameter detention pipe on the east side of the building. DETENTION ANALYSIS Site Area =0.38 Acres Frontage Area(+) =0.06 Acres Total Area Included in the Analysis =0.44 Acres From the NRC S of Snohomish County,the site contains Alderwood Soils that have a hydrologic classification of"C". Existing Conditions: Existing Basin Area = 0.38 Acres Impervious area: Existing Roof =0.11 Acres ( 4,652 SF) Existing Asphalt =0.15 Acres( 6,499 SF) Existing sidewalk =0.03 Acres( 1,442 SF) Total Impervious =0.29 Acres(12,593 SF) Pervious area =0.38 Acres-0.29 Acres =0.09 Acres The pervious area was modeled as existing condition(Lawn). Refer to the Existing Basin Map & WWHM Report attached later in this section for more details. Insight Engineering Co. -Stormwater Site Plan 3/25/2021 -29-