2410 WALNUT ST 2018-01-02 MF Import

1. PROJECT OVERVIEW This document is intended to provide engineering information necessary to support the SFR building permit application to the City of Everett for the proposed Single Family Residence (SFR), garage, sidewalk, and driveway proposed on this lot The site is located at 2410 Walnut Street, Everett, WA 98201, refer to Figure 1 for a vicinity map The parcel area is approximately 0.18 acres The existing site consists of landscaping with a few bushes/shrubs along the eastern and southern property lines and a previously removed SFR The slope of the site is flat with a slight slope to the east that averages approximately 5 percent The proposed SFR w,ll be located approximately 32 `eet from the eastern, property line and the proposed detached garage will be located approximately 10 feet from the western property line The new driveway will take access from the existing alley to the west and the new sidewalk will take access from the existing road to the east (Walnut St) This project proposes to construct less than 4,000 sf of new impervious surfaces Since this parcel is less than 1 acre in size per the COE 2010 stormwater manual the existing conditions will be modeled as they were pre 1997, which was the same as they are today, developed. Therefore, minimum requirements 1-5 apply to all of the new impervious surfaces for this project along w,th 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 this site. The runoff in the existing conditions will spread over the pervious, flat landscaped surfaces to the east and drain towards : ie eastern property line of the parcel In the developed conditions all of the runoff from the new roofs will be dispersed via splash blocks and either leave the parcel as sheet flow or be directed to one of two on - site swales The general soil conditions for this property as mapped by the USDA Web-Sc Survey were found to be Alderwood-urban land complex type soils. The water table depth ranges between 18 and 36 inches below grade. Therefore, dispersion will be used for the NPGIS on this project. The drainage design has been Ilid out per the COE 2010 Storr»water Management Manual The downstream system for this project is comprised of catch basins and pipe• -:ulverts. During the site visit there were no signs of flooding or capacity issues within the observed downstream systems Due to the size of this project only Minimum requirements 1-5 apply to the proposed -+rainage 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. Walnut SFR 14-0420 Vay 2014 Page 3