1023 100TH ST SW 2022-05-12 - Laserfiche WebLink

• 1. PROJECT OVERVIEW This document is intended to provide engineering information necessary to support the preliminary plat application to the City of Everett for the proposed 5-lot plat on this parcel. The site is located at 1023 100th St SW, Everett, WA 98204; refer to Figure 1 for a vicinity map. The gross site area is approximately 0.58 acres. The existing site is developed and contains an existing house, .a couple-sheds and driveway, all to be removed or replaced for this project. The slope of the site is flat and averages approximately 5 percent down to the east. The project site will take access from 100th St SW. All the lots will take access via a shared private road. Work within the right-of-way of 100th. St SW for utilities will be required. Frontage improvements are existing and consist of curb and sidewalk. No additional frontage improvements are proposed at this time. This project proposes to create five new lots and a shared private road. For this permit the proposed improvements will require the construction of a private road, stormwater facilities and other utilities. Figures 2 & 3 are provided to show the existing and developed basins and runoff conditions for the short plat. The runoff in the existing conditions spreads over the pervious surfaces on-site and sheet flows to the southeast. Runoff is then collected within the 100th St SW right-of-way. The downstream system for this project is comprised of catch basins and underground pipes. The drainage design has been laid out per the DOE 2019 Stormwater Management Manual for Western Washington (SWMMWW), as well as Chapter 4 of the City of Everett's current Design and Construction Standards and.Specifications .for Development manual. Due to the size of this project Minimum requirements 1-9 apply to all of the new plus replaced impervious surfaces, .as well as any converted..pervious,surfaces. Stormwater management will be met using a combination of stormwater BMPs such as rain gardens and permeable pavement. Since all pollution generating hard surfaces will be constructed of permeable pavement, water quality treatments are not required. The project proposes 13,540 sf of hard surfaces, however as mentioned above all PGIS will be permeable and roof runoff from two of the houses will be directed to rain gardens. Therefore, the only impermeable surfaces proposed will be the roof areas on lots 3-5, which total 4,222 sf. A geotechnical investigation was performed on this site by Cobalt Geosciences. The general soil conditions for the site were found to be loose to medium dense, silty-fine to medium grained sand with gravel underlain by dense to very dense silty-fine to medium grained sand with gravel. Explorations were done to a depth of 8 feet with no groundwater encountered, however winter high groundwater elevation is anticipated to be 5 feet below ground surface, per Cobalt Geosciences. See Appendix B for geotechnical evaluation. 3