1304 80TH ST SW EVERETT SCHOOL DISTRICT 2018-01-02 MF Import

Everett School District — Bus Facility March 24, 2006 — Storm Drainage Report Page 11 VI. ANALYSIS AND DESIGN OF SOURCE CONTROL BMP'S Stormwater treatment for the subject site is required since more than 5,000 square feet of impervious pollution generating area will be added under proposed conditions. Stormwater runoff for the site drainage basin will be treated using a wet volume method as part of the combined detention/wet vault. The water treatment volume is based on the developed condition 6-month, 24-hour storm runoff volume, resulting in a required volume for the subject site of 13,659-cubic feet. Water treatment will be provided for all site runoff since runoff from pollution and non-pollution generating areas is collected together upstream of the detention/wet vault facility. The total provided water treatment volume is approximately 14,571-cubic feet. To meet the City of Everett requirements for runoff treatment BMP, a media stormfilter will be located downstream of the 8 foot detention/wet tank. The stormfilter will be designed to treat the discharged stormwater from the primary orifice from the Flow control structure in the detention/wet vault. A high-Flow bypass will be p•ovided to bypass all Flows greater than the discharged stormwater from the primary orifice. The southern 3-acres of the project site will be used for school bus parking and is considered to be high-use by the City of Everett. Prior to entering the detention facility, the stormwater runoff from this"high-use"area will be sent through frop tee's located in ( the catch basins immediately upstream of detention. The frop tee's will act as spill control separators and intercept and contain any accidental spills from the parking lot.