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1. PROJECT OVERVIEW <br />This document is intended to provide engineering information necessary to support the <br />preliminary plat application to the City of Everett for the proposed 6-lot plat on this <br />parcel. The site is located at 9530 Holly Drive, Everett, WA 98204; refer to Figure 1 for <br />a vicinity map. The gross site area is approximately 1.06 acres. The existing site is <br />developed and contains an existing run-down house, and gravel driveway, all to be <br />removed or replaced for this project. The slope of the site is mild and averages <br />approximately 3 percent. The project site will take access from Holly Drive. All the lots <br />will take access via a shared private road. Some work within the right-of-way of Holly <br />Drive for utilities and access will be required. Frontage improvements already exist <br />along the short, 70-foot stretch of property frontage and are not required except for the <br />new "driveway cut" for access. Sewer and Water main extensions are also proposed <br />for this project, and will be permitted through Mukilteo VWVD. No additional frontage <br />improvements are proposed at this time. <br />This project proposes to create six new lots and a shared private road. For this permit <br />the proposed improvements will require the construction of a private road, stormwater <br />facilities and other utilities. Approximately 25,000 sf of land conversion is anticipated <br />from native/unmaintained to lawn/landscaped areas. Figures 2 & 3 are provided to <br />show the existing and developed basins and runoff conditions for the short plat. The <br />runoff in the existing conditions spreads over the pervious surfaces on -site and sheet <br />flows in a generally southern direction. Runoff is then collected within the Holly Drive <br />right-of-way. The downstream system for this project is comprised of catch basins and <br />underground pipes. <br />The drainage design has been laid out per the DOE 2019 Stormwater Management <br />Manual for Western Washington (SWMMVVWj, as well as Chapter 4 of the City of <br />Everett's current Design and Construction Standards and Specifications for <br />Development manual. Due to the size of this project Minimum requirements 1-9 apply <br />to all of the new plus replaced impervious surfaces, as well as any converted pervious <br />surfaces. Stormwater management will be met using a combination of stormwater <br />BMPs such as bioretention cells and permeable pavement. Since more than 5,000 sf <br />of pollution generating hard surfaces (11,130 so will be constructed for this project, <br />water quality treatments are required. A small amount of asphalt (420 so at the <br />entrance of the new private road will not be collected and treated, which is less than <br />0.01 acres and the City accepts this as de minimis. <br />The project proposes approximately 29,679 sf of hard surfaces. However, a large <br />portion of the impervious surfaces will be infiltrated via permeable pavement and <br />bioretention. Therefore, the total "effective" impervious surfaces proposed will be less <br />than 10,000 square feet. A geotechnical investigation was performed on this site by <br />Cobalt Geosciences. The general soil conditions for the site were found to be loose to <br />medium dense, silty -fine to fine grained sand with gravel (Vashon Glacial Till) <br />extending to the termination depths of the explorations. Groundwater was not <br />encountered in any of the explorations; however, some mottling was present between <br />about 3 and 5 feet below grade. <br />Perez SP <br />March 2022 <br />Revised: June/August 2022 Page 3 <br />