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3. OFFSITE ANALYSIS AND MITIGATION <br /> This site proposes lo construct approximately 2.498 sf of naw/replaced impervious <br /> suriaces The following table summarizes the new PGIS and NPGIS proposed both on <br /> and oH-site for this pro�ect <br /> —_ _--_ __ _ _-- --- — - --- _— ---- - - <br /> ' PGIS NPGIS Total <br /> - - ---- -- _i __(� — --(st1--- - (�. _ <br /> __ Existing i _ 0 0 0 <br /> Proposed I 569 1 ,929 _ 2,498 <br /> - — — <br /> Re laced _; _ _0 0 0 <br /> P_ — --- - -- --- ---- - - <br /> New I 569 1.929 2.498 <br /> The new impervious surfaces will be mitigated using or.-site stormwater management <br /> BMPs includ�ng splash blocks spread over amended soils & soil management. <br /> A. UPSTREAM ANALYSIS <br /> Dunng the sde visit it was observed that the onty runoN entenng this site is (rom the east Is <br /> from the neighboring landscap�ng As a result none of ihese offsite Aows will be aNected <br /> by lhe proposed improvements on this site <br /> B. DOWNSTREAM ANALYSIS <br /> Runoff from the proposed disWrbance area of the existing site sheet flows over the <br /> southern property line. The runoH is collected in the existing stream channel to the south <br /> which drains to the west. The channel appears to enter a piped conveyance system <br /> approximately 400-feet west of the site, however the pipe inlet was not located The <br /> conveyance system appears to travel to Ihe southwest through private property and the <br /> Dakota Way R O W. <br /> Based on the (ad that the new NPGfS runofi will be dispersed with splash blocks and the <br /> PGIS will be dispersed usmg a iransdion zone to sheet flow any runoff over the (uture <br /> amended soils �nd landscaping before the runoff leaves tfie site the developed flows wiil <br /> be equal to slightly more Ihan the existing conditions for this pro�ect and the offsite <br /> dramage systems m ihe downstream path for this site are large enough and accommodate <br /> such a large existing basm, any minor change in the Oow rate from this project will nol <br /> have an afiect on the natural drainage system During the sde visd and review of;he <br /> downstream system wsited, no portion of the system appeared to be inadequate and ihere <br /> were no signs of erosion on sile or ir any of ihe downstream areas visited <br /> /� <br /> Adau 1001°Lot 7 SFR 12-7205 7 / I �t � <br /> Dec 2012 Page 5 �� � <br /> \ / <br /> \._/ <br />