7016 EVERGREEN WAY 2016-01-01 MF Import

� Sunrise Services-Urninage Study 6. WATER QUALITY S/ZING � Developed \Vater Quality was to be addresscd as a dead storagc/setUing tank locmed upstrcam of the detcntion tank cyual to Aie volumc of ihc developed 6-month water quality stoim. All stormwater tlows from the paved surCaces wcre to be collected and conveyed through the upstream end of thc water quality tank. The City of �verett staff has indicated that because the project is commercial, the open pond requirements apply �- even thoueh the new paved area is less than 10,000 SF. Since the site arezi available is very limited, a water quality pond is not suitable for die location. VVATER QUALITY DESIGN CRITCRIA For a commercial with less than 10,000 sf of proposed pnvement, the water quality BMP � must be addressed as a combination open/closed system. 7'his statement assumes [hnt it is not practical for reasons of topogrnphy, soil conditions, etc. to dispose of the design volwne of nmoff by infiltration. For the instant project, wnditions are as follows: ( a. The total volume must equal the 6 mo.-24 hour developed stonn; I'or the Sunrise Services proposal, the required volumc is G25 CF. b. The Snn�a Barbnra calculation method is acceptable; � a The "pe�mnnent" pool starage volume shall bc equal to the volume of nmo(f in the G-month �'�'Q storm. ]n the instant casc, the volume equals 332 cf for the 6- month storm runoCf from the asphalt surfaces. Pervious areas wilf not be directed to the storm drains. i. The maximum volume of the open water cell is SSO7a of the peimanent L pool volume. Max. Volumc = 0.85 * G25.0 cf = 531 cf. ii. The minimum of the shallow treatment cell is 15% of die permanent pool volume. Min. Volume = 0.15 * 625 cf = 93.75 cf. The i reatment cell must be 94 cf or greater with a minimum depth of LS feet. � d. The wet pond water quality volume is divided bctween an "open watcr" cell and a wetland treatmen[ celL Thc miniminn depth in the opcn water cell shall be 3 fee[ deep. In the instant case, with less than 10,000 sf of paved surface areci tributary to detention, we have selected a 3.S diameter stora;c cell anchored with two 54" manholes. [ I wesr�a� 3