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5. SOURCE CONTROL <br /> This project proposes to construct 3 new SFRs on this short plat with 3 new driveways. <br /> Per Volume 1 of the City of Everett 2010 Stormwater Management Manual residential <br /> development does not require source control. <br /> 6. PRESERVATION OF NATURAL DRAINAGE SYSTEM <br /> The runoff from the NPGIS improvements will be collected and tight lined directly to a <br /> detention facility that drains to the existing piped conveyance system on this site. In <br /> addition, by not grading or compacting the majority of the pervious surfaces to remain after <br /> construction in the area of disturbance a maximum amount of site runoff from the <br /> developed project will be absorbed and naturally infiltrated into the existing on-site soils. <br /> This will mimic the existing conditions by maintaining the existing direction and condition of <br /> flow from this site. <br /> 7. ON-SITE STORMWATER MANAGEMENT <br /> The soils for this project were found to be Alderwood Gravelly Sandy Loam. The.hard pan <br /> for the Alderwood soil ranges between 20 and 40 inches below grade and the water table <br /> varies between 18-36 inches below grade. Since the use of infiltration is not feasible a <br /> detention system has been designed for this project. <br /> Since the total parcel area is less than 1 acre the modified detention requirements are <br /> allowed for this project. This allows the site be modeled with software using the SBUH <br /> method and the current conditions on the site are used as the existing land cover in the <br /> model. For this project StormShed 2g was used for the modeling software. <br /> The inputs to StormShed are as follows. <br /> PreDeveloped: <br /> Lawn/Landscaping: 0.52 acres, Cn 86 <br /> Roof& D/W: 0.10 acres, Cn 98 <br /> ROW Pervious: 0.08 acres, Cn 86 <br /> Developed conditions: <br /> Lawn/Landscaping: 0.33 acres, Cn 86 <br /> Roof& D/W: 0.29 acres, Cn 98 <br /> ROW Impervious: 0.08 acres, Cn 98 <br /> Using the software it was calculated that a 55' long 4' diameter detention pipe could be <br /> used to meet the flow control requirement. However a FOS of 1.3 must be added to the <br /> system so the final design includes a 72' long 4' diameter pipe. Refer to Appendix A for <br /> the software printout. <br /> Uplands Short Plat 14-0108 <br /> June,2016 Page 10 <br />