1108 CHESTNUT CT 2017-06-09 - Laserfiche WebLink

C 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) and driveway proposed on the lot. The site is located at 182X Chestnut Street, Everett, WA 98203; refer to Figure 1 for a vicinity map. The parcel area is approximately 0.14 acres. A building permit application has already been submitted to the City of Everett and approved for a proposed SFR located on the adjacent parcel to the south. Prior to the submittal for the building permit application, the existing site consisted of landscaping, an existing SFR, carport, concrete patio and walkway. These have all been removed under the current building application. The slope of the site is flat to moderate with a slope to the north/northeast, approximately 6 percent. The proposed SFR will be located approximately 5 feet from the southern property line. The new driveway will take access from the existing paved alleyway to the west. This project proposes to construct less than 5,000 sf of new impervious surfaces on the parcel. Since the 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, developed. Therefore, minimum requirements 1-5 apply to all of the new 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 the site. The runoff in the existing conditions will spread over the pervious, moderately sloped landscaped surfaces to the north/northeast and drain toward the northern property line. In the developed conditions all of the runoff from the new roofs will be dispersed via splash blocks and leave the project parcel as sheet flow or naturally infiltrate on-site via shallow swales. Any overflows will be collected via a catch basin at the northeast corner of the site and tightlined to a bubble-up catch basin in Chestnut Street, which have been permitted under the current building permit application for the south lot. The general soil conditions for the property as mapped by the USDA Web-Soil 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 laid out per the COE 2010 Stormwater Management Manual. The downstream system for this project is comprised of underground pipes and catch basins. 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. Chestnut North Lot 16-0213 February 2016 Page 3