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1 <br /> I <br /> � 1 Section One <br /> A requircment of the Final Environmental Impact Statement for <br /> I Seaway Center Industrial Park states that storm�tiater runoff needs <br /> to be provided to the native growth protection area. Prior to <br /> ' development stormwater was dischazged in natural swales and <br /> convc}•ed to Powder Mill Gulch. The do�mstrcam analysis showed <br /> no obvious signs of ovcrland flow. Therefore, post�evelopment <br /> Ipoint discharge or concentration of flo�vs needs to be very limited. <br /> The design limits the volume of stormwater runoff and detains the <br /> � pcak flows of the postdeveloped 100 year, 24 hour stortn, to 1/2 <br /> the pre-developed 2 yea�flows. This results in a peak flow rate of <br /> 0.02 CFS. With this very low flow rate for the 100-year stocm, <br /> I minunal impacu to downstream areas are anticipated. The <br /> discharge point was further mitigated by installing a 15-foot <br /> perforated pipe that was used to disperse the flow. <br /> � <br /> Analysis and Design of Zhe major earthwork for the site w�s undertaken during the drier, <br /> � Required Erosion and summer months and complcted by the end of August 1997. The <br /> Sedlment Control erosion and sediment control BMPs that �vcre installeci during the <br /> BMPs preliminary grading consisted uf silt fences and interceptor swales. <br /> � The final stortnwater watcr quality ponds are also used for siltatlon <br /> ponds. The stormwater �vater quality ponds µ�ere initially sized <br /> using pre��ous City of Everett design standards and are larger than <br /> ' is required for sediment control. See Appendix B for siltation pond <br /> sizing calculations. These siltation ponds will be converted to <br /> storm«�atcr water qualiry ponds by cicaning out the sediment at the <br /> � end of constcuction and planting with vegetation. This convcrsion <br /> from siltation ponds to stormwater quality ponds will occur afier the <br /> wtial phase has bcen fully developed or fully stabiliud. <br /> � <br /> i Analysfs and Design of Thc developed site will have two discharge locations. One will <br /> � Requfred Runoff disr,harge into the regional detcntion pond and the other will <br /> Control BMPs d�scharge into the native growth protection area. <br /> ( The majority of the post-developed stormwater runoff will be <br /> directed into the regional stortnwater detention pond. There are two <br /> I t}pes of areas that will discharge dircctly into the regiional <br /> � stormwater detention basin. 'llie parking and landscape areac and <br /> the building rooftop arcas. <br /> Stormwater flow from the parking and landscape are:u dces not <br /> Solec(ron Corporation Lot 1FojSeawovCenter i:IProjectll934010/IwordlSLR2FDRN.doc <br /> IV&NPacific November7, /997/Poge1 <br />