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3. OFFSITE ANALYSIS AND MITIGATION <br />This site proposes to construct approximately 4,998 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 To Be Removed <br />0 <br />0 <br />0 <br />Existing To Be Replaced) <br />0 <br />0 <br />0 <br />Existing To remain <br />2 141 <br />0 <br />2 141 <br />New + Replaced <br />1,571 <br />3 427 <br />4,998 <br />Total Site Improvements <br />3,712 <br />3 427 <br />7 139 <br />Net New <br />1, 571 <br />3,427 <br />4,998 <br />The new impervious surfaces will be mitigated using on -site stormwater management <br />BMPs (see Sections 7 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 />Runoff from the proposed disturbance area of the existing site, sheet flows northwest <br />until it reaches the western property line. From there, the runoff flows into a catch basin <br />on the side of Ocean Ave. From there, it is directed north into the storm drainage system <br />via a 12" diameter PE pipe. 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 />Ocean Ave SFR 21-0634 <br />February 2022 Page 5 <br />