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4• <br /> A 2707 Wetmore Avenue <br /> eOMEGA Everett, WA 98201 <br /> ENGINEERING, INC. t 425.387:3820 <br /> f 425.259,1958 <br /> July 9th, 2018 CITY OF EVERETT <br /> Chris Thompson REVIEWED FOR PERMIT <br /> 1805 -006 - /s <br /> Infiltration Trench Sizing for Thompson SP <br /> This letter is intended to address infiltration trench sizing for roof area on Lot 1 over the allotted amount <br /> described in the drainage report prepared by Omega Engineering May 2011 for the short plat located at. <br /> 4618 Seahurst Ave, Everett,WA 98201. <br /> Stormwater mitigation for Lots 1 and 2 of the Thompson Short Plat utilizes infiltration. Per the drainage <br /> report prepared by Omega Engineering in May 2011, the infiltration trench was sized to serve roof areas <br /> on Lots 1 and 2 up to a total of 4,240 sf. The infiltration trench was designed to be 5.5 feet wide, 60 feet <br /> long and 4 feet deep. It is our understanding the roof area for Lot 1 will be constructed over the allotted <br /> amount. Therefore, it has been determined that any roof area over the allowed 4,240 sf shall be directed <br /> to a separate infiltration trench. <br /> The contractor shall install 7.5 linear feet of trench per 500 sf of additional roof area for a 5.5 foot wide <br /> infiltration trench. The minimum depth of infiltration trench shall be 4 feet, however per the geotechnical <br /> recommendations for this project, the bottom of the trench shall extend a minimum of 1 foot into the <br /> gravelly sand layer. Additional trench depth may be necessary based on the soil conditions in the <br /> location of the new trench. The new trench shall be located on the southeast side of Lot 1, near TP-8, as <br /> shown on Plate 2 of the geotechnical report prepared by Liu &Associates, Inc. <br /> The contractor/builder shallfollow all recommendations described in the Geotech report prepared by Liu <br /> &Associates, Inc. in July 2011, as well as recommendations described in the Drainage report prepared <br /> by Omega Engineering, approved by the City of Everett. <br /> Sincerely, fi @Qt <br /> CLI7R ID) <br /> AUGOg2p18 <br /> Joseph Smeby, P.E. +CITY <br /> Permit servicesTT <br /> .cmz Permit#: PW1805-006 <br /> ' Site Address: 4620 SEAHURST AVE <br /> '°'a �" 'te <br /> * t Owner: THOMPSON PAULA&H JOAN <br /> . *- '14!----. Tenant: [TenNamel <br /> :aas4` App.Date: 5/2/2018 <br /> %/77 <br /> ' ? ¢' Proposed Use: NEW SFR DETACHED <br /> mss*a�` <br /> ,: .F. Description: CONNECT TO EXTG SEWER AND WATER <br /> -*at 1 , i , <br /> Reviewed By:, -A' Date m,y 5 ye. <br /> le Office Set Job Site Set Fire/Planning Set <br />