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3. OFFSITE ANALYSIS AND MITIGATION <br /> This entire site proposes to construct approximately 3,876 sf of new and replaced <br /> impervious surfaces. The following table summarizes the new PGIS and NPGIS proposed <br /> for the entire project. <br /> PGIS (sf) NPGIS (sf) Total (sf) <br /> Existing 0 0 0 <br /> New+ Replaced 1,358 2,518 3,876 <br /> Total Site Impervious 1,358 2,518 3,876 <br /> Net New Impervious 1,358 2,518 3,876 <br /> The new impervious surfaces will be mitigated using on-site stormwater management <br /> BMPs including downspout dispersion, sheet flow dispersion and soil management. <br /> A. UPSTREAM ANALYSIS <br /> During the site visit it was observed that some off-site area from the parcel to the <br /> southeast could potentially drain toward the proposed project area due to the site grades, <br /> however no runoff was observed. It was clear that all off-site flows will pass through or <br /> around this site and remain that way during construction. Based on the location of the <br /> proposed improvements the existing runoff from the upstream area will continue to flow <br /> unaffected around this site after the project has been constructed. <br /> B. DOWNSTREAM ANALYSIS <br /> Runoff from the proposed disturbance area of the existing site sheet flows in the <br /> northeasterly/northerly direction over vegetated, grass surfaces toward the northern <br /> property line. Runoff appears to then flow in the northerly/northeasterly direction toward <br /> Narbeck Creek. Runoff is collected by Narbeck Creek approximately 250 feet from the <br /> project site. This creek flows in a northerly direction and enters Possession Sound. See <br /> Figure 4 for a depiction of the project basin and downstream path. <br /> Based on the fact that the new impervious surfaces will be dispersed on-site and that this <br /> project proposes to increase the total impervious surfaces on the site by less than 5,000 <br /> sf, the developed flows are expected to be slightly more than in the existing conditions. <br /> During the site visit and review of the downstream system, no portion of the system <br /> appeared to be inadequate. <br /> Bayview SFR 18-0806 <br /> August2018 Page 6 <br />