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3. OFFSITE ANALYSISMITIGATION <br /> This development is expected to add approximately 391 sf of new roof hard surfaces <br /> on-site. Because this project is proposing more than 200 sf and less than 5,000 sf of <br /> impervious surfaces and is in the combined sewer area of the city, minimum <br /> requirements 1-5 and 7 are triggered for this project. The following table summarizes <br /> the new PG1S and NPGIS proposed for the entire project. <br /> PGIS s NPGIS s Total s <br /> Existing (To Be Removed) 0 0 0 <br /> Existing (To be Replaced) 0 0 0 <br /> Existing (To Remain) 0 1,964 1,964 <br /> New + Replaced 0 391 391 <br /> Total Site Impervious 0 2,355 2,355 <br /> Net New 0 391 391 <br /> The new impervious surfaces will be mitigated using on-site stormwater management <br /> BMPs (see Sections 7 and 8 for details). <br /> B. UPSTREAM ANALYSIS <br /> During the site visit it was observed that there was little significant off-site area that <br /> drained toward the proposed project area. It was clear that all off-site flows will pass <br /> through or around this site and remain that way during construction. Based on the <br /> location of the proposed improvements the existing runoff from the upstream area will <br /> continue to flow unaffected around this site after the project has been constructed. <br /> C. DOWNSTREAM ANALYSIS <br /> Runoff from the proposed disturbance area of the existing site sheet flows west from the <br /> project parcel until it reaches the western property line. From here runoff flows south <br /> approximately 170 feet until it reaches a drainage catch basin located near the <br /> intersection of Grand Ave and 23rd St. From there the runoff reaches the combined storm <br /> sewer system through a 6-inch diameter concrete pipe. The downstream analysis was <br /> concluded here. <br /> Based on the fact that the new impervious surfaces will be dispersed on-site and that <br /> this has shown to meet the flow control performance standards, the developed flows are <br /> expected to be less than in the existing conditions. During the site visit and review of <br /> the downstream system, no portion of the system appeared to be inadequate. <br /> City of Everett <br /> EVERETT Reviewed for Permit 11/18/2021 <br /> Bedle Garage 21-0421 <br /> November 2021 Page 6 <br />