5830 EVERGREEN WAY 2016-01-01 MF Import

i Housing Hope Short Plat I Drainage Analysis Page 3 • n i maintaining fiows at or below pie-developed rates, and should not have an impact on the downsveam area. Soils and Cround Water Condiliuns I _ 'The soils on the site are classified by the Soil Conservation Service as an Aldtrwood soil which is characterized as moderately well drained,soil underlain by glaciel till at 2 to 4 feet of depth. The Hydrologic Soil Group Classificatiorr for this unit is "C" according to the Washington State Department of Ecology's Stonnwater Manageirn:nt Manual for the Puget Sound Basin (DOE � Manual). IProposed grading for the site would involve excavation for building foundations and cut and fill ' for road, parking lots,and drainage and detention facilides. Deeper excavations for building I foundations are likely to experience some seepage from "perched" ground water above the till layer. This seepage is expected to be nunimal and should not affect construction. The installation � of footing drains around the buildings is recommended to prevent water from accumulating in cr�wl space areas and basements. ( Pruposed Development � The proposed shoiY plat involves the design of two detention systems for drainage from Basin A and B, respeciively (see Figure C). � Lots I to 3, located in Basin A, would include consvuction of tl�ree duplexes with paved access � road and d�iveway for the residential units. Tlie footing drains and roof downspouts will be directed to tlie stortn cL-ainage system. Otlier tlows originating on site will drain to Ihe access road as sheet (lows znd then travel along the side of the road ro catch basins. Runoff collected from the Croad and parking areas will be directed to a catch basin for grit remova�. Drainage from the basins will d�en be directed to an underground detention pipe below the access road. The,pipe will be 6 Ifeet in dia�neter a�id 70 feet long. The pipe will be placed at zero percent slope. Three feet of dead storagc will be available in the pipe to allow for sediment removal,aee�vif-se}�e�en. I I