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11. Upstream Tributary Area <br />No storm drainage flows onto the site from areas upstream. The storm drainage that <br />develops upstream is collected in curb -side catch basins and conveyed through 12" <br />concrete pipe along the east and south side of Rucker Avenue and 41st Street, <br />respectively. <br />III. Downstream Analysis <br />It appears that all drainage that develops on the site sheet flows in a northeasterly <br />direction towards 41 st Street and is collected in catchbasins that are either connected <br />to either a storm drainage or a combined storm/sewer system. Based on <br />conversations with the City of Everett Public Works Department (PWD), the storm <br />drainage system located along 41 st Street discharges to the river. <br />IV. Hydrology <br />A. Existing Site Hydrology <br />The existing site is commercial property which is covered with asphalt and <br />gravel. The slope of the site is generally from the southwest to the northeast <br />at an average slope of 2.5%. The storm runoff dud develops on the site <br />generally sheet flows in a northeasterly direction towards the northeast <br />property comer where it flows out onto the alleyway and/or 41 st Street then <br />down the concrete gutter to the east. <br />R. Developed Site Hydrology <br />The proposed grade of the developed site will be consistent with the existing <br />grade. All runoff will be collected in catchbasins located in paved areas and <br />conveyed through A" PVC to a common location near the northeast property <br />corner. As approved by the Everett PWD, the storm drainage will then be <br />routed to the combined storm/sewer system via a conneroon that will be made <br />to the main line located in the alley. A new storm drainage system will also <br />be constructed in the alley that will be routed to the common collection point. <br />Prior to final discharge to the combined system, the drainage will be routed <br />through a flostables material separator and gas trap. <br />The canopy slab drainage will he conveyed through an oil/water separator <br />which will also provide 100 gallons of storage in the event of an accidents] <br />fuel spill. 71►c oil/water separator will then discharge to the combined sewer <br />system. 'rho canopy and convenience store roof drains will be routed to <br />catchbasins located in the paved areas. <br />3 <br />