2631 WALNUT ST JACKSONS 2025-07-28

Stormwater Pollution Prevention Plan 2.0 Site Description 1 2.1 Existing Conditions The total site area is approximately 0.64 acres±with an existing fuel service canopy, underground fuel storage tanks, convenience store building, carwash, paved parking, and drive ' aisles. The site generally slopes from west to east and north to south. There are existing catch basins located along the east boundary that collects the surface runoff and discharge to the combined sanitary sewer system located in the Alley to the north. The on-site soils are not ' conducive to infiltration due to the significant silt content and dense nature of the native soils. The test pits conducted for the site encountered loose fill that extends to depths of up to about 5 feet in the area of the proposed convenience store building and native medium-dense soils at shallow depths in the area of the proposed canopy. The existing site consists of approximately 86 percent impervious surfaces. f2,2 Proposed Construction Activities The proposed development is located within a portion of the northeast quarter of the southeast quarter of Section 20, Township 29 North, Range 5 East, Willamette Meridian, Snohomish ' County, Washington. More particularly, the site lies on the northeast corner of the intersection of Walnut Street and Everett Avenue. The overall site comprises approximately 0.64 acres that is currently developed as a gas station, convenience store, and carwash. The proposed project is to demolish the existing fueling canopy, 1,065-square-foot convenience store and 882- square-foot carwash to construct a new 2,996 square-foot convenience store and in northeast corner of the site and a new 4,800-square-foot canopy in the west portion of the site. Site redevelopment will include new underground storage tanks, reconstruction of the trash enclosure, installation of perimeter and parking lot landscaping and irrigation, installation of stormwater biofilter cells, and reconnection of utilities to the new store location. Construction ' activities will include site preparation, TESC installation, building construction, stormwater, and utility appurtenance installation, and asphalt paving. The schedule and phasing of BMPs during construction is provided in Section 4.0. Stormwater runoff rates and volumes were calculated using the WWHM hydrology model and the detention vaults were sized by matching durations from 1/2 the 2-year pre to the 2-year design up to the 50-year for the entire range of historic storm events. The following summarizes details regarding site areas: • Total site area: 0,64 acre • Percent impervious area before construction: 86.0% ■ Percent impervious area after construction: 82.8% ® Disturbed area during construction: 0.64 acre ' ■ Disturbed area that is characterized as impervious (i.e., access roads, staging, parking): 0.55 acre All stormwater flow calculations are provided in Appendix F. ' 3 16580.006.doc