10632 7TH AVE SE 2025-07-28 - Laserfiche WebLink

I Ithe driveways for unit's 2, 3, 4 & 5 and roof drainage from unit's 1, 2, 3, 4 & 5. Pervious areas (landscape and/or natural) complete the drainage for Basin 2A. 1 Basin 2B (South half)—This basin includes 0.48 acres of developed area which includes P I 0.24 acres of impervious and 0.24 acres of pervious area (landscaped and/or natural).) The basin has 4 rain gardens (flowing west) along the private road to collect drainage. The impervious area includes south half of the asphalt private roadway (12' including I curb), the driveways and roof drains for unit's 6, 7, 8 & 9. Pervious areas (landscape and/or natural) complete the drainage for Basin 2B. IDetention and water quality for Basin 2A and 2B will be accomplished through the rain gardens and at the bermed ponding area on the west end of the project. A large portion of the runoff will I infiltrate though the bottom of the rain gardens and into the native soils. The under drain perforated pipe and overflow risers running on both sides of the private roadway in the rain gardens will collect the remainder of the runoff located at the west end of the private road will I ultimately flow to a bermed infiltration area within the existing wetland buffer. All the storm water runoff for Basins 2A& 2B will infiltrate into the native foliage within the bermed wetland I buffer area at a long term infiltration rate of 1 inch/hour. The proposed driveways and sidewalks are to be constructed of pervious concrete over a crushed p p Y I washed rock base. These driveways will infiltrate to the natural ground through the washed rock sub base. I Runoff from Basin 2B back yards for the proposed units 6, 7, 8, 9, will flow to a trench system infiltrating and draining west to the bermed area at the west end of the project. I If the proposed rain gardens along the private road were removed from the site,the entire volume of runoff from a 100 year storm at developed conditions would still be contained within the western berm impermeable area that will be constructed near the edge of the wetland. Thus, the I berm will prevent storm water runoff from directly entering the wetland. Runoff will be contained behind the berm as it is dispersed through the existing native vegetation and infiltrated I through the native soil into the groundwater table. The bermed infiltration area has been sized to infiltrate the entire volume of water from a 100 year storm at an infiltration rate of 1 inch/hour using the Western Washington Hydrology Method required by the 2005 DOE manual. The I modeling software WWHM version 3 from Clear Creek Solutions was utilized to model the site and stormwater conditions. I I I 4 I