6200 12TH DR SE 2020-10-22 - Laserfiche WebLink

Stormwater Site Plan January 9,2018 Catholic Housing Services—Everett Safe Streets Supportive Housing beehive grated drains to be detained in the tanks. The bioretention cell shall adhere to the standards and guidelines from DOE BMPT7.30. By collecting the runoff from the roof and parking lot,the site will follow the DOE Stormwater Management Manual for post development release rates and treatment. Moreover,the post development runoff from half of the 2-yr through the 50-yr storm events will be less than pre-development runoff rates(DOE,Vol I,Sec 2.5.7)for the Till, Forest land use condition. The detention tank shall be constructed of precast vault sections with internal restrictors for the effluent (COE standard detail 415). The designed structure will house the total volume required to properly mitigate flows. The detention system shall drain via controlled release to the existing 12-inch storm drain running along the north side of Berkshire Dr. Additionally,6 inches of dead storage shall be provided for sediment removal thus placing the vault invert and lowest outlet invert at elevations 410 and 410.50, respectively. Right of Way Development The Right of Way(ROW)along Berkshire Dr on the southern property line is to be improved with a sidewalk curb and gutter. Improvements are shown in the Right of Way Improvement Plan in Appendix A. This area, measuring approximately 3,500 sf, is considered a separate threshold area for the purposes of water quality and flow control by the DOE (App E). A standard (COE Detail 312)4-in thick concrete sidewalk with standard(COE Detail 307)Type A-1 curb and gutter shall be placed with the back of sidewalk parallel to the southern property line and offset 1.5 ft. An approximately 2 to 3Lft tall rockery(COE Standard Detail 324)shall be placed from approximate Station 13+09 to 13+68 to stabilize the cut slope necessary to place the proposed sidewalk.A three- tiered rockery of 3 rockeries with a maximum height of 3 ft each,shall be placed from station 13+68 to 13+89 to stabilize slopes behind the site water service vaults. Runoff shall continue to flow along its historic flow path to the west along the north side of Berkshire Dr. Runoff shall be collected by a concrete inlet at the west end of proposed ROW improvements. Collected runoff shall be conveyed to the existing storm drain vault nearby. COE GIS shows a cast in place vault, partially comprised of timber. Extreme care shall be taken in modifying the structure.The contractor shall coordinate with Brian Doolan ((425) 257-8828, bdoolan@everettwa.gov)on the appropriate method of modification. IV. Construction Stormwater Pollution Prevention Plan All construction shall be performed under the site Construction Stormwater Pollution Prevention Plan (CSWPPP) (Temporary Erosion and Sediment Control Plan,TESC,Appendix A). The SWPPP was prepared under Volume II of the DOE's Stormwater Management Manual. Perimeter control for the Site shall be a high visibility silt fence as noted on the TESC(Appendix A). The chosen perimeter control measure shall surround the site along the entire limits of disturbance shown on the TESC. Since the existing fence at the top of slope is to remain,the fence shall be placed inside of the existing fence. A stabilized construction entrance shall be constructed as per COE standard drawing 201. This measure is to help prevent tracking of soil and sediment off site. A sediment trap shall be constructed at the top of the existing slope on the western edge of the construction site.The sediment trap shall be constructed per WSDOT Std Plan 1-80.10-01.The outlet Wage