2611 ROCKEFELLER AVE ROCKEFELLER SQUARE 2 2024-08-12

I I SECTION VIII: PERMANENT STORMWATER CONTROL PLAN I A. OFF-SITE ANALYSIS IA site reconnaissance was performed by Brian Kalab of Insight engineering on December Pt, 2019 to verify the downstream flow paths and observe any drainage Iproblems downstream of the site. The sky was partly cloudy and overcast with a temperature of 45 degrees. IThe site is currently developed with four residential homes. The site contains one drainage that slopes to the slightly to the east. There are no critical areas located within the Isite. Per NRCS survey of Snohomish County, the project site contains Alderwood soils that have a hydrologic classification of Type "C". No visible on-site drainage problems were Iobserved at the time of field investigations. Upstream Analysis IBased on the site reconnaissance and the topographic survey of the site, the off-site area entering the site is very minimal. Refer to the Downstream Analysis Map attached in Ithe next page for more details. Downstream Analysis 1 The site contains one drainage basins that slopes slightly to west. The runoff from the site flows to the west and enters the existing combined storm and sanitary sewer system Ialong alley in between Rockefeller Ave and Oakes Ave. The flow travels east beneath Everett Ave for approximately 685 feet through 10, 15, and 18-inch pipes. The flows Icontinue east to cross Broadway and enter a 36 inch brick system. This is where the drainage analysis was completed. There did not appear to be any Irestrictions or erosion problems within 1 mile of the site. In the mitigated state the runoff from the site will be connected to the existing storm Iand sanitary sewer system on the eastern portion of the property. The flow is minimal and therefore the downstream channel should not experience any problems in the future. I I I Insight Engineering Co. -Stormwater Site Plan 12/30/20 -