Laserfiche WebLink
Broadway Everett Expansion Storm Drainage Report <br /> November 16, 2022 <br /> 7.0 — CONSTRUCTION STORMWATER POLLUTION PREVENTION (MR-2) <br /> The CSWPPP was developed per the requirements in Volume II of the 2019 Stormwater Management <br /> Manual for Western Washington. <br /> 13 Elements: <br /> 1. Preserve Vegetation/Mark Clearing Limits <br /> Construction Limits will be marked by chain link fencing and/or high visibility fence where <br /> necessary(BMP C103), which will be moved as necessary for construction phasing of the various <br /> project elements. <br /> 2. Establish Construction Access <br /> Entrance to the site will be off the existing private driveway as shown in the TESC plan. Trucks will <br /> be positioned to avoid exposed soil and excavation equipment will be washed on-site prior to <br /> transfer off-site, per BMP C106. <br /> 3. Control Flow Rates <br /> Exposed soils are mostly limited to the area within the new foundation, which will contain sediment <br /> and runoff. <br /> A sediment trap will be used as necessary to contain runoff from the construction area. The <br /> sediment trap was sized using the provided formula in the SWMMWW from BMP C240: Sediment <br /> Trap. The 2-year flow(Q2)was determined using the Rational Method. The surface type is <br /> assumed to be pavement and roof, with C = 0.90. The area A= 0.577 ac. The intensity i was <br /> determined to be 0.065 in/hr per the DCSS. <br /> i = m/TCn <br /> Tc=L/60V <br /> V=k(SO)1/2 <br /> where: <br /> m,n = dimensionless coefficients (see Table 4-3.1(1)-1) (m=3.69; n=0.556) <br /> V = velocity (ft/s) <br /> K = time of concentration velocity factor(ft/s) (27) <br /> So = slope of flow path (ft/ft) (0.036) <br /> L=flow length (ft) (333 ft) <br /> Page 9 <br />