12815 19TH AVE SE 2018-01-02 MF Import

Silver Lake Elementary Additions Schematic Design Narrative Water Sewer & Drainage October 19, 2006 The proposed approach for site sewer assumes the existing sewer main is adequate and will not need to be replaced. The proposed approach also assumes a connection to the existing sewer can occur within 50 feet of the building. Encroachment of new sewer improvements into the south parking lot is not anticipated. As a result of annexation, any proposed sewer services will be permitted through the City of Everett. See Schematic Water & Sewer Plan for more information. DRAINAGE Existing stormwater conditions on the elementary school site in the vicinity of the project is described as Ulows: Two thirds or mere of the elementary school site generally drains northeasterly into an existing biofiltration Swale located at the northeast corner of the site. This system is routed offsite through an existing subdivision detention pond. A smaller portion of the site -including the westerly bus loading area and school entry and the northwest parking lot- discharge into a stormwater detention and water quality treatment system located within the northwest parking lot. This system discharges northwesterly into SR-527 and into the Trout Pond. All drainage from the site eventually flows to Silver Lake Creek. The location of existing roof drain collector systems and point of discharge for these systems is generally not available or known from ground surface observation or topography. One existing catch basin is located on the north side of building A. It has no apparent outlet pipe. Proposed stormwater conditions on the elementary school site in the vicinity of the project is described as follows: The proposed north building including new gymnasium and administration additions, referred to as Building A, will have new roof structure and associated new downspout systems. New tightline drainage systems for collection of roof drainage on all four sides of this building are assumed to be needed. Trench pavement restoration will be required. Drainage improvements are assumed to not be required for the west and south buildings. The east and north sides and possibly the south side of Building A may require some adjustment of pavement grades in order to achieve surface drainage away from all existing buildings and into the existing or proposed collections systems. This may require new catch basins and/or new paving. Kirkland 011ice 750 Sir10 Slreel Soulk I Midland. WA 98033 p 425.827.2014 1 [425.027.5043 paceengrs.eom