7030 LOWER RIDGE RD 2018-07-25 - Laserfiche WebLink

7 Introduction This report has been prepared at the request of Dynasty Homes in support of a single family residential home LDA and building permit for a site located on the west side of Lower Ridge Road in Everett, Washington in the NW'A of Section 12, Township 28 North,Range 09 East W.M. The site address is 7030 Lower Ridge Road, Everett WA. (Parcel #00392-000-036-030) (Refer to Site Location and Vicinity Map). This report addresses the drainage report contents and organization of MR 1 to MR 9 per DOE 2014 Stormwater Management Manual as adopted by the City of Everett. Specifically we have designed the drainage using the LID applications as outlined in Volume 1, Chapter 2, Table 2.5.1 of the DOE 2014 Stormwater Management Manual. Project Overview The project consists of construction of a duplex home on a 1.47 acre site. The existing lot contains an existing home and out-buildings(which will be removed) and an existing access driveway.The majority of the site has trees. To the west are slopes greater than 25-percent which are outside of any proposed development. Once developed,the site will add a new duplex and driveway with a total of 9,413 sf of new impervious area in the form of 3,570 sf for the building,walkway and patio.The parking and driveway will account for the remaining 4,812 sf. The area of disturbance is 19,300 sf. The site improvements are located into two separated sub-basins which DO NOT combine within 1/4 mile downstream: • East Sub-basin: In general contains the driveway at 4,812 sf and drains to Lower Ridge Road. • West Sub-basin: In general contains the house at 3,570 sf and drains to the wooded hillside. The City of Everett requires detention for all projects over 5,000sf of effective impervious surface.This threshold is applied at the TDA level. And,since the impervious area for each sub-basin/TDA is under 5,000 sf. Low Impact Development standards utilizing splash blocks along with 50-foot minimum flow paths through vegetation will be used to address roof drainage runoff along with driveway gravel dispersal trenches. Water quality:Since the PGHS area is under 5,000 sf water quality is not required for the Driveway. Addition on-site soils testing show the site soils to have evidence ofmottling at 18-inch and not suitable for infiltration.(see Soils Log Appendix A). Conditions of Approval Summary The City will issue the Conditions of approval once the project has been reviewed and approved. 7030 Lower Ridge RD Full Drainage Report Revised:November 3,2017 Page 2