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1. PROJECT OVERVIEW <br /> This document is intended to provide engineering information necessary to support the <br /> grading and site improvements engineering permit application to the City of Everett for the <br /> proposed townhomes to be built on this site. The site is located at 10604 16th Ave. SE, <br /> Everett, WA, refer to Figure 1 for a vicinity map. The gross site area is approximately 5.14 <br /> acres. However, the west side of the site is encumbered by wetlands and the total area to <br /> be developed/disturbed will be 3.11 acres. The existing site is currently forested and <br /> fronts the 16th Ave SE R.O.W. to the east. <br /> This project will eventually construct 56 townhome units on this site along with access <br /> roads, and utilities to serve each unit. The effective impervious surfaces for this project <br /> exceeds 10,000 sf. Therefore, minimum requirements 1-9 apply to all of the new <br /> impervious surfaces for this project along with all the disturbed pervious surfaces. A <br /> SWPPP has been prepared to address the runoff from the site during construction and <br /> prior to final stabilization. Refer to Sections 4 and 5 for a detailed discussion. <br /> Figures 2 &3 are provided to show the existing and developed basins and runoff <br /> conditions for the proposed project. There is a high point on the site that causes <br /> approximately 1.20 acres of the area to be disturbed for this project to drain west and 1.91 <br /> acres drains east. The runoff to the west is collected in one of two on-site wetlands. The <br /> southern wetland drains south and the northern wetland drains north. They are divided by <br /> an old road fill. The eastern basin is collected by the conveyance system within the 16th <br /> Ave SE R.O.W. However, all the basins combine within the 16th Ave SE R.O.W. near the <br /> southeast corner of the site. In order to maintain the hydrology to the existing wetlands <br /> this project will be analyzed as three independent basins. However, in the developed <br /> conditions the eastern basin is slightly larger then in the existing condition due to the final <br /> grades, but the existing wetlands will receive ample surface flows from the associated <br /> basins, this will be discussed later in this report. <br /> In the developed conditions runoff generated by the proposed impervious surfaces will be <br /> collected by roof downspout conveyance system, yard drains and catch basins. The site <br /> has been broken into three basins, NW, SW and East. All of the site runoff from the NW <br /> basin will be directed to one of three level spreaders designed to discharge the runoff from <br /> the roof and pavement areas along with some of the landscaping as sheet flow along the <br /> east edge of the wetland tract/buffer. Some of the landscaping will be allowed to sheet <br /> flow west without being collected. In addition, the footing drains for the three buildings <br /> fronting the wetland buffer will also discharge to the west. The same is true for the SW <br /> basin using two level spreaders. For the east basin the developed basin area will be 2.11 <br /> acres with approximately 0.17 acres of bypass including portions of the entrance and fire <br /> lane that are too low to be collected and conveyed to the detention vault along with some <br /> landscaping. However, approximately 0.18 acres of off-site landscaping is directed toward <br /> this project and this area will be collected and detained to provide an offset or equivalent <br /> area to account for the bypass. <br /> Runoff from the new road surfaces will be treated by Perk Filter catch basin filters prior to <br /> release to the detention vault. The vault outfall is in the southeast corner of the vault and <br /> connects to an existing CB along the west side of 16th Ave SE located near the SE corner <br /> of this project. <br /> Northlake Court Townhomes 13-0609 <br /> May,2014 Page 3 <br />