1415 BROADWAY CM HEATING 2023-09-25

C. DEVELOPED HYDROLOGY The proposed project CM Heating is located at 1415, 1411, and 1407 Broadway, Everett, WA 98201. More generally, the site is in Section 17, Township 29 North, and Range 5 East of the Willamette Meridian in the City of Everett, Washington. The site is currently developed with a home, a commercial building, and parking lot. The site contains one drainage basin that slopes to the slightly to the west. There are no critical areas located within the site. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have a hydrologic classification of Type "C". Please refer to the soils map and descriptions attached later in this report for more details. The proposal is to construct a new commercial building and parking lot which is proposed to be replaced. 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. The project is exempt from water quality as the project discharges to the combined sewer system. A floatable materials separator and gas trap are proposed for the project. Per Vol I figure 2.4.2 of the SWMMWW, Minimum requirements #1 through #9 shall apply for this project. Refer to section 1.2 for Minimum Requirements Summary. For onsite stormwater management (MR#5) list # 2 was used per Vol 1 section 2.5.5 of the SWIvIMWW. Full dispersion was considered first however it was deemed infeasible due to the lack of native vegetation. Downspout full infiltration was deemed infeasible due to the presence of iron oxide deposits at shallow depths, indicating poor infiltrating soils and a shallow low permeable layer. Please refer to the Geotechnical Report for more details. Bioretention was deemed infeasible as the site lacks the necessary area to accommodate Insight Engineering Co. -Stormwater Site Plan 3/25/2021 -27-