5105 CHINOOK DR 2016-01-01 MF Import

5. SOURCECONTROL This project proposes to construct a new SFR on this parcel with a driveway. Per Volume 1 of the City of Everett 2010 Stormwater Management Manual residential development does not require source control. � 6. PRESERVATION OF NATURAL DRAINAGE SYSTEM The runoff from the site improvements will be dispersed over amended or native soils on- site and flow in the north and easl naturat downstream direction. However by not grading or compacting the soils in the northern and eastern portions of ihe site a maximum amount of site runoff from the developed project will be absorbed and infiltrated into the existing on-site soils. This will mimic the existing conditions by maintaining the existing direction and condition of(low (rom this site. 7. ON-SITE STORMWATER MANAGEMENT The soils for this projecl were found to be loamy sand with a maximum waler table/hard pan layer at over 6' below existing grade in areas ori the site by Jamie Batterman, refer to soil information in Appendix A. Since on-site infiltration was not found to be viable for this project then dispersion of the NPGIS and PGIS runoff is required when possib�e and for this project this will be done using level spreaders and transition zones. The roof runoH will be directed to one of two level spreaders, with a minimum tlow path of 25-feet before ' leaving the site. The proposed roof area is 2,719 which requires (BMP 12 50 Downspout Dispersion Systems) approximately 40LF of level spreader to provide 10-feet of spreader for each 700sf of rooi. This will be broken inlo two locations each receiving hal( of the roof area. However, a note has been added to the plan to direct the contractor to modify the length of lhe trenches if conditions warrant during construction to ensure the proper length spreader is provided for the aclual tributary roof area. For the approximately new PGIS, transition zones have been designed to collect and disperse the flows along the northwest and northeast side of the new driveway area. 7he dispersed flows from the transition zone will pass over a minimum of 10-feet of landscaping with amended soils prior to leaving the site. This project does not propose to conslruct more than 5,000 sf of PGIS so it is exempt from any water quality trealment systems per Minimum Requirement 6. Finally, any area of the site not proposed to be covered with impervious surfaces but graded or compacled will be lreated to meet the critena for BMP T.5.13. Please refer to the engineering plans for the locations o( the soil amendments and additional details Chinook SFR 12-��3 feb. 2012 Page 70. �3�9�� _ . �-