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• <br /> IN <br /> engineering p c <br /> HORIZON ELEMENTARY SCHOOL <br /> CLASSROOM PORTABLE INSTALLATIONS <br /> STORM DRAINAGE REPORT <br /> JUNE 5,20 19 <br /> PROJECT OVERVIEW <br /> This Storm Drainage Report is for the installation of a double classroom portable structure at <br /> Horizon Elementary School. The site is located at 222 W Casino Road in Everett, Washington <br /> (parcel#28041300102100). Refer to Figure 1—Vicinity Map for the site location. The project has <br /> been designed in accordance with Chapter 14.28—Surface and Storm Drainage of the current <br /> Everett Municipal Code (last updated through Ordinance 3673-19 that passed on April 24, 2019), <br /> and the 2014 Department of Ecology (DOE) Stormwater Management Manual for Western <br /> Washington(SWMMWW) as adopted by the City of Everett. Refer to the minimum requirements <br /> section of this report for the project classification and the minimum requirements that are <br /> applicable to the project area. <br /> The project will include the installation of a double classroom portable structure southeast of the <br /> existing school building in an area currently developed as a sand playfield. The new portable <br /> structure will be located adjacent to 5 existing portable classrooms. In addition,perforated metal <br /> decks,ramps and stairs and new asphalt pathways approaching the portables will be included to <br /> accommodate pedestrian access. <br /> Existing Conditions <br /> Horizon Elementary School resides on an approximately 18.99-acre parcel. The parcel consists of <br /> elementary school buildings, parking lots, portables, playfield, and a wetland area. It is bounded by <br /> W Casino Road to the north,multifamily residential properties to the east and west, and both a <br /> single-family residence and corporate/manufacturing property to the south. The proposed <br /> installation area is within the southeast portion of the school property. The total project disturbance <br /> area is approximately 14,250 square feet(0.097 acres). <br /> The project area currently consists of the sand playfield with an adjacent concrete gutter, asphalt <br /> path and lawn area. Refer to Figure 3—Existing Impervious Coverage, which outlines the <br /> existing impervious area within the project disturbance limits. <br /> Topographically,the overall school site generally slopes from the northeast to the southeast from a <br /> high elevation point of approximately 586-feet. More specifically,the area of the proposed <br /> classroom portable building installation is relatively flat and level with the lawn area sloping gently <br /> to the east. To the east of the proposed project area,the grade slopes more steeply towards the east <br /> with an existing rockery at the base of the slope located on the multifamily residential development <br /> adjacent to the east. The overall change in elevation east of the project area,including the slope and <br /> rockery, is approximately 8-feet. <br /> Runoff from the project area that does not infiltrate through the sand surface is collected in the <br /> adjacent concrete gutter or the existing type 1 catch basin located just to the east of the concrete <br /> gutter. There is an inlet associated with the concrete gutter just north of the project area; however, <br /> at the time of our site visit this inlet appeared to be clogged with dirt and debris.Runoff from the <br />