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This site proposes to construct approximately 3,267 sf of new plus replaced impervious <br />surfaces. The following table summarizes the new PGIS and NPGIS proposed. <br />PGIS <br />s <br />NPGIS <br />s <br />Total <br />s <br />Existing <br />1,540 <br />0 <br />1,540 <br />Removed <br />1,378 <br />0 <br />1,378 <br />Replaced <br />163 <br />0 <br />163 <br />New <br />1,090 <br />2,014 <br />3,104 <br />New + Replaced <br />1,253 <br />2,014 <br />3,267 <br />Total Hard Surfaces <br />1,415 <br />2,014 <br />3,429 <br />The new impervious surfaces will be mitigated using on -site stormwater management <br />BMPs including splash block and amended soils meeting BMP T5.13 (see Sections 7 <br />and 8 for details). <br />A. 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 />B. DOWNSTREAM ANALYSIS <br />The runoff in the existing conditions sheet flows over vegetated and asphalt surfaces <br />northeast, following the topography, towards the northern and eastern property line. <br />From there it collects into a low spot on the neighboring property where it eventually <br />infiltrates into the ground. The downstream analysis was concluded here. <br />Based on the fact that this project proposes to construct less than 5,000 sf of effective <br />impervious surfaces, developed flows are expected to be slightly greater than in the <br />existing conditions. See Figure 5 for a depiction of the project basin and downstream <br />path. <br />Haack — 74th 22-0807 <br />September 2022 Page 5 <br />