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11111 <br /> engineering p c <br /> type 1 catch basin is conveyed in an underground pipe to the northeast, and eventually discharges <br /> to an existing stormwater swale. Discharge from the stormwater swale combines with flows from <br /> Merrill and Ring Creek and is conveyed north through the school property eventually outfalling to <br /> Merrill and Ring Creek on the north side of W Casino Road. Refer to the Offsite Analysis section <br /> of this report for more information on the downstream drainage course.The site is located in the <br /> Merrill and Ring Creek drainage basin, which ultimately discharges into Port Gardner Bay in the <br /> Puget Sound. <br /> Based on City of Everett critical areas mapping,there is an expansive delineated wetland area <br /> occupying the entire southwest portion of the school property, located west of the portable <br /> installation area. Additionally,the previously mentioned Merrill and Ring Creek, classified as a <br /> "type NS"or non-fish bearing creek, flows northerly through the northwest portion of the parcel <br /> from its origination point within this designated on-site wetland area. <br /> According to USDA Natural Resources Conservation Service Web Soil Survey,the site consists of <br /> Alderwood-Urban land complex, 2 to 8 percent slopes. Additionally, a Geotechnical Report was <br /> prepared by GeoTest Services,Inc. dated May 3,2019. Based on the geotechnical report,the field <br /> investigation included four test pits to explore soil and groundwater underlying the proposed <br /> portable location. The explorations typically encountered Pleistocene aged glacial till(Vashon Till) <br /> deposits from the Vashon Stade of the Fraser Glaciation.The test pits were advanced to depths of <br /> between 8.5 and 9.0 feet and consisted of playfield surfacing comprised of loose to medium dense <br /> silty sand at the top,followed by previously placed fill consisting of dense, gravelly, silty sand, and <br /> then native glacial till at 8.5 feet below the ground surface. During the subsurface investigation, <br /> groundwater was not encountered. As concluded by the geotechnical engineer, infiltration is not <br /> suitable due to the presence of unstable fill soils and very dense, low permeable native soil. Refer <br /> to Figure 2—Soils Map. <br /> MINIMUM REQUIREMENTS <br /> According to the 2014 SWMMWW, a"redevelopment" is defined as a project site that has 35%or <br /> more of existing hard surface. The existing hard surface for the project area was delineated within <br /> AutoCAD using an aerial image for the property. Hard surfaces included existing school building <br /> roof areas,portables,paved parking lots and surrounding walkways. Refer to Figure 3—Existing <br /> Impervious Coverage. The existing hard surface for the total site was determined to be <br /> approximately 28.7%. Therefore,the project is not a redevelopment,and thus, considered to be a <br /> new development. Figure 1-2.4.1 of the 2014 SWMMWW was used to determine the minimum <br /> requirements applicable to the proposed project. <br /> LPD Engineering, PLLC Page 2 Horizon Elementary School — Classroom Portable Installation <br /> Storm Drainage Report,June 5, 2019 <br />