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SOUNDVIEW TECHNOLOGY CENTER EVERETT, WA <br /> • Full Dispersion: Determined infeasible due to the vegetated flowpath setbacks from the <br /> proposed walls and property line, which leaves an insufficient on-site area to provide the <br /> required vegetated pervious area. <br /> • Bioretention: Determined infeasible due to insufficient on-site area to provide the <br /> required bioretention area to treat the full roof area. Additionally, bioretention would <br /> allow a significant amount of runoff to infiltrate behind the 10'-20'on-site walls, which is <br /> not an acceptable design. <br /> • Downspout Dispersion Systems: Determined infeasible, as there is insufficient area to <br /> provide the required vegetated flowpath on-site with the required vegetated flowpath <br /> setbacks from the proposed walls, steep slopes, and property line. <br /> • Perforated Stub-out Connections: Infiltration on this site is not recommended due to <br /> reasonable concerns regarding erosion and down gradient flooding. <br /> Other Hard Surfaces: <br /> • Full Dispersion: Determined infeasible, as there is insufficient area to provide the <br /> required vegetated flowpath on-site with the required vegetated flowpath setbacks from <br /> the proposed walls and property line. <br /> • Permeable pavement: Infiltration on this site is not recommended due to reasonable <br /> concerns regarding erosion and down gradient flooding. <br /> • Bioretention BMPs: Infiltration on this site is not recommended due to reasonable concerns <br /> regarding erosion and down gradient flooding. <br /> • Sheet Flow Dispersion: Determined infeasible, as there is insufficient area to provide the <br /> required vegetated flowpath on-site with the required vegetated flowpath setbacks from <br /> the proposed walls and property line. <br /> All finished landscape areas on-site will contain compost amended soils. Refer to Earth Solutions <br /> NW Infiltration and Low Impact Development Evaluation in Appendix C for further analysis on the <br /> storm water design. <br /> Minimum Requirement#6: Runoff Treatment <br /> Thresholds <br /> The following require construction of stormwater treatment facilities (see Table 2.1): <br /> • Projects in which the total of effective, pollution-generating impervious surface (PGIS) is 5,000 square <br /> feet or more in a threshold discharge area of the project, or <br /> • Projects in which the total of pollution-generating pervious surfaces (PGPS) is three-quarters (3/4) of <br /> an acre or more in a threshold discharge area, and from which there is a surface discharge in a natural <br /> or man-made conveyance system from the site. <br /> Response: Stormwater from detention systems 1, 2, and 5 only collect roof runoff and do not require <br /> treatment. Two Oldscastle BioPod water quality treatment systems will be located downstream of vaults #3 <br /> &4. Each BioPod will be sized for the full two year release rate. <br /> Minimum Requirement#7: Flow Control <br /> Projects must provide flow control to reduce the impacts of stormwater runoff from impervious surfaces <br /> and land cover conversions. The requirement below applies to projects that discharge stormwater directly, <br /> or indirectly through a conveyance system, into a fresh water. <br /> SEPTEMBER 23, 2022 STORMWATER DRAINAGE REPORT PAGE 6 <br />