2514 RAINIER AVE 2020-04-02 - Laserfiche WebLink

r NORTH MIDDLE SCHOOL 5 On-Site Stormwater Management Yes See below 6 Runoff Treatment N/A See VII Permanent Stormwater Control Plan 7 Flow Control Yes See VII Permanent Stormwater Control Plan 8 Wetlands Protection No See below 9 Operations and Maintenance Yes See VII Permanent Stormwater Control Plan MINIMUM REQUIREMENT #1: STORMWATER SITE PLAN PREPARATION This report has been prepared using the guidelines of the COESWMM. A Civil Site Plan has been prepared showing the extents of the stormwater system design. Drawings that provide additional information regarding the Permanent Stormwater Control Plan are located in a previous drainage report issued for permit for the main school project,dated October 20,2017. MINIMUM REQUIREMENT #4: NATURAL DRAINAGE SYSTEMS AND OUTFALLS PRESERVATION The routing of stormwater conveyance on the site will stay within the same basin and will outfall to the same public combined sewer main as the existing discharge. By maintaining the same discharge point,this requirement is met with no action required. MINIMUM REQUIREMENT #5: ON-SITE STORMWATER MANAGEMENT Minimum Requirement#5 states that on-site stormwater management best management practices(BMPs)should be implemented to infiltrate, retain,and disperse stormwater on-site,with the goal of reducing the hydrologic disruption of developed sites. In addition to the specific BMPs considered below,the project aims to retain existing site features that provide natural stormwater management and maintain the existing soil and vegetation to the extent feasible. Proposed site grading was designed to follow existing topography as close as possible in order to minimize earthwork impacts and disturbance footprint. • BMP 12.30—On-site Infiltration Areas. The landscape design proposes amended soils in disturbed area of the North Middle School site. For areas where full replanting is required, "Option 3—Import Topsoil Meeting Organic Matter Content Standards"will apply as described in Volume III, Chapter 12,of the COESWMM. Even lightly disturbed areas requiring minor regrading will also likely follow Option 3 standards. • BMP 12.50—Downspout Dispersion. This BMP will be implemented for the portable site. Runoff from downspouts from the ten portables on-site will be conveyed to splash blocks and then a vegetated flowpath of at least 25 ft. in length.These measures can be seen further in Figure 4:Downspout Dispersion System and on the Civil Site Plan included in Appendix B. MINIMUM REQUIREMENT #8: WETLANDS PROTECTION The project's stormwater will not discharge directly or indirectly to a wetland, so this requirement is met with no action required. COUGHLINPORTERLUNDEEN 3