15 FERN RD 2017-10-30 - Laserfiche WebLink

1. PROJECT OVERVIEW This document is intended to provide engineering information necessary to support the building permit application to the City of Everett for the new duplex and driveways proposed on this lot. The site is located at 15 W Fern Rd, Everett, WA 98203 at the end of the dead-end street; refer to Figure 1 for a vicinity map. The parcel area is approximately 0.20 acres. The existing site contains an SFR, shop, paved driveway, and lawn; all to be removed or replaced. The slope of the site is flat averages less than 5 percent down to the east. The proposed duplex will be located approximately 20 feet north from the southern property line. Each unit is proposed to have its own driveway. The driveways will take access from the existing roadway to the south (Fern Rd). This project proposes to construct less than 2,000 sf of new impervious surfaces with the net increase in impervious surfaces only totaling 782 sf. However, this project proposes to construct approximately 4,195 sf of new plus replaced impervious surfaces. Therefore, minimum requirements 1-5 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 this site. The runoff in the existing conditions appears to spread over the pervious surfaces to the east and drain towards the eastern property line of the parcel. In the developed conditions all of the runoff from the new roofs will either be dispersed via splash blocks with the minimum required flow path over vegetated surfaces or tightlined to a perforated stub-out connection and connected to the existing stormwater system within the right-of-way. See Section 7 of this report for more details. The downstream system for this project is comprised of catch basins and pipes/culverts. 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 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. 15 Fern Rd Duplex 16-0302 REVISED: June 2016 Page 3