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3. OFFSITE ANALYSIS AND MITIGATION <br /> This site proposes to construct approximately 2,498 sf of new/replaced impervious <br /> surfaces The following table summarizes the new PGIS and NPGIS proposed both on <br /> and off-site forthis project. <br /> PGIS NPGIS Total � <br /> � -- �� -�SfZ--7 <br /> _ _ - - 0 <br /> Existing _ 0 ____ � __—_� <br /> Pro�osed __ 569 1 ,929 2A98 <br /> _ Replaced 0 __� � <br /> — New 569__,_. 1,929 2,498 <br /> The new impervious surtaces will be mitigated using on-site st�rmwater management <br /> BMPs including splash biocks spread over amended soils 8 soil management <br /> A. UPSTREAM ANALYSIS <br /> During the site visit it was observed that the only runoH entenng ihis site is trom the east is <br /> from the neighboring landscaping. As a result none of these offsite flows will be affected <br /> by the proposed improvements on this site. <br /> B. DOWNSTREAM ANALYSIS <br /> RunoN irom the proposed disturbance area of the existing site sheet flows over the <br /> southern property line. The runoff is collected in the existing stream channel to the south <br /> which drains to the wesi. The channel appears to enter a piped conveyance system <br /> approximately 175-teet west ot the site, however the pipe inlet was not located. The <br /> conveyance system appears to travel to the soutliwest lhrough private property and the <br /> Dakota Way R.O,W. <br /> Based on the fact that the new NPGIS runoff will be dispersed with splash blocks and lhe <br /> PGIS will be dispersed using a transition zone to sheet flow any runoff over the future <br /> amended soils and landscaping before the runoH leaves the site the developed flows will <br /> be equal to slighliy more than the existing conditions for this project and the offsite <br /> drainage systems in the downstream path fcr this site are large enough and accommodate <br /> such a large existing basin, any minor change in the fluw rate from this project will not <br /> have an affect on the natural drainage system. During the site visit and review of the <br /> downstream system visited, no portion of the system appeared to be inadequate and there <br /> were no signs o( erosion on-site or in ar�y oi the downsiream areas visited <br /> nd:w tUl�" I ut tp Sfit 12-1205-10 . � , ' <br /> I .: �O1� Page5 <br />