1304 80TH ST SW EVERETT SCHOOL DISTRICT 2018-01-02 MF Import

Everett School District— Bus Facility March 24, 2006— Storm Drainage Report Page 3 A small amount of offsite area drains onto the project site. This area is located just off the west property line and is comprised of a 10 foot wide landscaped slope for the entire distance of the west property line (please see Proposed Areas Figure in Appendix A). Above and west of th. landscaped slope is asphalt pavement for parking for the neighboring property. Stormwater from this asphalt area is contained Ln the neighboring property and conveyed away from the subject project site. Snohomish County Soil Survey mapping for the area Indicates that soils onsite consist of "Alderwood Urban Land Complex"soils (2-8% slopes). Alderwood Gravelly Sandy loams are a Hydrologic Soil Group Type 'C' soil. The geotechnical engineering report (see Section VII) confirms that soils onsite generally consist of fill that is overlying glacially consolidated "till" soils. A small portion of the northeast site, near the existing wetland, contain thin layer of peat and lacustrine sand below the fill. Existing conditions used for calculations were assumed to be prior to site development in 1980 to closer mimic existing runoff rates from the project site (further described in Section V. under Runoff Control Analysis). See Appendix A for Existing Site Coverage areas map. The existing condition areas were compiled from the original storm drainage reports by Kegel & Associates, Inc. and Lovell-Sauerland & Associates, Inc. See Appendices D & E for Storm Reports. The project area analyzed for flow control Includes approximately 7 acres. The following table gives the existing condition land use covers and respective Curve Numbers for the existing drainage area for Type'C'soils. Table 1. Existing Area S readsheet Pre-1980 Total Existing On Site Off Site Drainage Area Tvpe Area Acres Area Acres Acres Pervious -Gravel CN = 89 1.31 0.89 2.20 Pervious -Pasture CN = 85 1.31 0.89 2.20 Pervious -Second Growth CN = 81 2.63 1 0 2.63 Sub-Total Draina a Area 5.25 1.78_ _. 7.03 Proposed Conditions The proposed bus facility for the Everett School District will develop approximately 5.2 acres of the proposed project site. The existing metal fabrication building located near the northwest corner of the property will be renovated to accommodate school bus drivers. All other existing structures on-site are planned to be demolished.