6200 12TH DR SE 2020-10-22 - Laserfiche WebLink

Stormwater Site Plan January 9,2018 Catholic Housing Services—Everett Safe Streets Supportive Housing I. Project Description The site for the future Catholic Housing Services' (CHS)Everett Safe Streets Supportive Housing(ESSSH) is located at 6200 12th Drive, Everett,Washington 98203,Township 28 N, and Range 5 E,at approximately 47.9415 degrees North latitude,and 122.2165 degrees West longitude. Multi-family housing is proposed in addition to parking,site and utility improvements within 1.18 acres of disturbance,with an additional 0.47 acres of native vegetation restoration. In addition to the site improvements,off-site right-of-way(ROW) improvements will include new curb,gutter,sidewalk,a small rockery and associated drainage improvements for Berkshire Drive along the project frontage. The property size is 53,575 sf,of which the proposed four(4)story, multi-family residential,70-unit building will occupy an approximately 11,000 sf footprint. Proposed Parking for 21 vehicles will replace approximately 6,100 sf of existing pavement. An additional 18,000 sf of other impervious areas will be constructed as parking and sidewalks. The project follows the requirements set forth by the State of Washington Department of Ecology(DOE) in the Storm water Management Manual for Western Washington of 2014 and the City of Everett(COE) Design and Construction Standards and Specifications for Development(DCSS,June 2017). II. Site Assessment The ESSSH project site is currently partially occupied by an existing fire training facility that is situated in the middle of a large tarmac. A gravel lined area also resides adjacent to and west of the tarmac. Topographic relief,one(1)-ft contours,and other data was obtained through a land survey performed by Alpha Subdivision Pro's Inc. Land Surveying and Planning in October 2016(Appendix B). Two(2)-ft contours for offsite areas surrounding the site, along with utility and building locations were obtained from the COE geographical information systems (GIS)department October 27,2016. A geotechnical investigation was performed on November 1, 2016 by Geotech Consultants, Inc for the project site(Appendix C). Multiple borings and test pits were dug with samples tested. The report showed that the site soils are loose to medium-dense un-engineered fill soil generally comprised of gravelly silty-sand,presumably from the excavation of the nearby reservoir site. These findings confirm the United States Geological Survey's (USGS)Soil Survey Geographical Database(SSURGO)that classifies the soil as having moderately low runoff potential when thoroughly wet,with unimpeded water transmission. Stormwater runoff west of the tarmac sheet flows to the west and down the steep slope where it is collected by a series of catch basins at the toe of slope. Runoff from the existing tarmac,drains to one of two clusters-of-three catch basins located on the west and south edges of said pavement. This runoff is conveyed to the storm mains along Berkshire Dr.and Evergreen Way. These storm mains both empty to Pigeon Creek Number 1,and ultimately to Possession Sound. The Site is located adjacent to a steep slope that is classified as a Landslide Hazard Area (COE,Critical Area)with"medium"slopes of 25%to 40% (COE,Class 2)on geologic unit Qg1t,Younger Glacial Drift, Pleistocene. The soil type for the entire project site and property is Alderwood-Urban Land Complex, hydrologic soil group(HSG) B, per the Natural Resources Conservation Service(NRCS). Pigeon Creek Number 1 runs to the north along the toe of this slope in an underground pipe and is classified as an 11Page