3505 UPLAND AVE 2020-09-08 - Laserfiche WebLink

1. PROJECT OVERVIEW • This document is intended to provide engineering information necessary to support the permit application to the City of Everett for the three new SFRs and three driveways, and ROW improvements proposed for this short plat. The site is located at 3505 Upland Ave, Everett, WA 98203, refer to Figure 1 for a vicinity map. The gross short plat area is approximately 0.62 acres. The existing site contains 1 lot consisting of a SFR, gravel driveway and landscaping with a few mature evergreen trees. The slope of the site varies between flat and steep, and averages approximately 5 percent down to the west. Steep slopes are present along the northern property line. The toe of said slope is located approximately 10 feet south of the northern property line and the rise in elevation is approximately 9 feet up to the north. It is proposed that the existing site will be short platted into 3 lots of approximately equal size. The proposed new lot lines will run roughly north-south, and the new SFRs will be centrally located within each lot. The proposed new driveways will take access from the existing roadway(Upland Avenue) to the south. Each lot of this short plat proposes to construct less than 5,000 sf of new impervious surfaces with lot 2 already containing an existing SFR permitted under a recent building permit application. However, since the impervious surfaces on Lot 2 are recent they will be considered new and part of the drainage improvements for this project. The combined impervious surfaces between lots 1, 2 and 3 are over 10,000 sf. Therefore, minimum requirements 1-9 apply to all of the new and replaced impervious surfaces for this project along with all the disturbed pervious surfaces. This proposal does not meet any of the land-use criteria that require specific source control for the final use and a SWPPP has been prepared to address the runoff from the site during construction. Refer to Sections 4 and 5 for a detailed discussion. Figures 2 &3 are provided to show the existing and developed basins and runoff conditions for the three lots. The runoff from the three lots in the existing condition will spread over the pervious moderately sloped landscaping as sheet flow, to the western property line. In the developed conditions runoff generated by the proposed NPGIS will be collected and conveyed to a detention system along with the proposed PGIS and some of the landscaping along the south side of the future SFRs. The proposed detention system will discharge to an existing piped conveyance system located in the southwest corner of the site. The overall general slope of the site will not change, however, on-site grading will be required for the proposed structures. The general soil conditions for this property as mapped by the USDA Web-Soil Survey was found to be Alderwood Gravelly Sandy Loam. The hard pan for the Alderwood soil ranges between 20 and 40 inches below grade. Therefore, infiltration is not feasible for this project and other forms of flow control will be used. The drainage design has been laid out per the COE 2010 Stormwater Management Manual. Due to the size of this project Minimum requirements 1-9 apply to the proposed drainage design as noted above. Included on the following page is a copy of the MR flow chart out of the COE Drainage Manual showing how the applicable minimum requirements were determined. Uplands Short Plat 14-0108 June,2016 Page 3