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3. OFF-SITE ANALYSIS AND MITIGATION <br /> This development is expected to add approximately 388 sf of new roof hard surfaces on- <br /> site. Because this project is proposing more than 200 sf and less than 5,000 sf of <br /> impervious surfaces, and is in the combined sewer area of the city, minimum requirements <br /> 1-5 and 7 are triggered for this project. The following table summarizes the new PGIS and <br /> NPGIS proposed for the entire project. <br /> PGIS NPGIS Total <br /> (sf) (sf) (sf) <br /> Existing (To be removed) 0 0 0 <br /> Existing (To be replaced) 0 0 0 <br /> Existing (To remain) 1,458 1,972 3,430 <br /> New + Replaced 0 388 388 <br /> Total Site Impervious 1,458 2,360 3,818 <br /> Net New Impervious 0 388 388 <br /> The new impervious surfaces will be mitigated using on-site stormwater management <br /> BMPs including an infiltration/dispersion trench and soil management. <br /> B. UPSTREAM ANALYSIS <br /> During the site visit it was observed that no significant off-site area appears to drain <br /> towards the project area. It was clear that all off-site flows will pass through or around this <br /> site and remain that way during 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 /> C. .DOWNSTREAM,ANALYSIS <br /> Runoff from the proposed disturbance area of the existing site sheet flows southwest from <br /> the project parcel until it reaches the southern property line. From here runoff flow across <br /> the Legion Memorial Golf Course approximately 820 feet until it reaches a pond on the <br /> southern end of the gold course. From the pond a stormwater inlet allows runoff to enter <br /> the stormwater system through a 18 inch culvert. Runoff follows this initial culvert <br /> approximately 200 feet until it reaches the combined storm sewer system which flows <br /> southeast across the golf course. Flow continues through this system southeast another <br /> 700 feet, at which point the downstream analysis was concluded. <br /> Based of the fact that the new impervious surfaces will either be infiltrated or dispersed <br /> on-site and that this has shown to meet the flow control performance standards, the <br /> developed flows are expected to be less than in the existing conditions. During the site <br /> visit and review of the downstream system, no portion of the system appeared to be <br /> inadequate. <br /> Lalone Addition 20-0902 <br /> 'October2t720 Page 6 <br />