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PG IS ; <br />s <br />NPGIS <br />s <br />Total <br />s <br />Existing To Be Removed <br />3,0041 <br />155 <br />3,159 <br />Existing To Be Replaced) <br />0 <br />382 <br />.382 <br />New +' Replaced `' <br />1,577 <br />6,031 <br />7,608 <br />Total Site Improvements <br />1,577 <br />6.031 <br />7,608 <br />Net New <br />1,577 <br />5,649 "" <br />7; 226 <br />The new - impervious surfaces will be mitigated using stormwater management BMPs <br />including an infiltration trench, perforated stub out connection, sheet flow dispersion and soil <br />management. <br />A. UPSTREAM ANALYSIS <br />.During the site visit it was observed that there was no significant off -site area that appears <br />to drain`toward the proposed'project area.* It was clear that all off -site flows will pass through <br />or around this site and remain that. way after construction. <br />B. DOWNSTREAM ANALYSIS. <br />Runoff' from the area of disturbance in- the existing, conditions sheet flows in a '. <br />northern/western direction and into a catch basin located just west of the property, between <br />Baker Dr and the property line. Out of this catch basin, runoff flows southwest across Baker <br />Drive and through.a series..of ::catch ,basins rand..1.2" storm...m irns.:approximately 450 fe..et <br />northwest where a 12" plastic pipe on the .surface .can be seen conveying runoff down the <br />steep ravine . slopes. At this, point, the on -site downstream analysis was concluded. <br />However, topographic contours on the City of Everett website indicate. that runoff flows <br />approximately 300 feet in this pipe and is discharged at the bottom of the slope in Powder <br />Mill Gulch. Powder Mill Gulch flows approximately 600 feet northwest/north and into the <br />Sound. <br />Site runoff will continue to follow this downstream path during and after construction. The <br />bioretention overflow will-connect,to.,the:.CB,.just,as-the,.existing-iâ–ºafiltrationtrench does. <br />Based on the fact that this project proposes to construct less than 5,000 sf of effective <br />impervious surfaces and that the new roof surfaces will be infiltrated, developed flows are. <br />expected to be approximately the same as in the existing conditions. See Figure for a. <br />depiction of the project basin and downstream path. <br />Dhaliwal SFR 19-1208 <br />December 2020. <br />ReUr' O. Ja»uar}>7021 Page 5 <br />