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3. OFF-SITE ANALYSIS AND MITIGATION <br /> This site proposes to construct approximately 3,917 sf of new plus replaced impervious <br /> surfaces. The following table summarizes the new PGIS and NPGIS proposed. <br /> PGIS (s� NPGIS (sfl Total (sfl <br /> Existin TBR 790 1,294 2,084 <br /> New + Re laced 905 3,012 3,917 <br /> Total Site Im ervious 905 3,012 3,917 <br /> Net New 115 1,718 1,833 <br /> The new impervious surfaces will be mitigated using on-site stormwater management <br /> BMPs including downspout splash blocks, driveway transition zone and soil management. <br /> A. UPSTREAM ANALYSIS <br /> During the site visit it was observed that there was no area which potentially contributes <br /> runoff to this site. It was clear that all off-site flows will pass through or around this site <br /> and will remain that way after construction. Based on the location of the proposed <br /> improvements the existing runoff from the upstream area will continue to flow unaffected <br /> around this site after the project has been constructed. <br /> B. DOWNSTREAM ANALYSIS <br /> Existinq Conditions <br /> During the site visit it was observed that runoff from the proposed disturbance area of the <br /> existing site sheet flows to the east over pervious surfaces toward the eastern property <br /> line. Runoff leaves the site over the eastern property line and drains to the vegetated <br /> right-of-way of Oakes Ave. Runoff is then collected by a catch basin found on the western <br /> side of the roadway. This catch basin appears to be connected to an existing stormwater <br /> system. The catch basin appears to direct runoff east, passing beneath Oakes Ave and <br /> connecting to another catch basin found on the east side of the roadway. The remainder <br /> of the downstream appears to consist of underground pipes and catch basins. <br /> Based on the fact that the net new impervious surfaces totals less than 2,000 sf the <br /> developed flows are expected to be slightly more than the existing conditions. During the <br /> site visit and review of the downstream system no portion of the system appeared to be <br /> inadequate. <br /> Haack—Lexington Duplex 16-1112 <br /> January 2017 Page 5 <br />