7500 HARDESON RD 2021-06-09 - Laserfiche WebLink

4.2 Topography and Drainage The existing site is at a higher grade than the adjacent roadways.The existing pile of fill in the central and northern portions of the site is approximately 20 feet higher than the grade of ' Hardeson Road. The existing fill slope along the northeastern edge of the property is relatively steep, with slopes ranging from 25 to 65 percent. The majority of stormwater runoff flows south and enters the existing detention and water quality pond. Runoff from the north portion of the site flows north onto 75th Street SW. Runoff from the northeast slopes flows toward Hardeson Road. Runoff from the western edge of the site flows toward a low point near the west property line. Onsite elevations range from 485 at the northeast corner of the site to 504 at the top of the fill pile. The elevation at the proposed connection to Hardeson Road is 487, and the elevation at the proposed connection to 76th_Street SW is 489. Onsite slopes generally range from 2 to 10 percent,with the exception of the northeastern slopes and the slopes along the sides of the existing gravel access road. 4.3 100-Year Flood Analysis The site is not mapped as a floodplain per the FEMA National Flood Hazard Layer FlRMette, effective September 16, 2005. Refer to Appendix A-6 for the FEMA Flood Map. 4.4 Adjacent Areas The site is bounded by 75th Street SW to the north, Hardeson Road to the east, an existing wetland to the southeast, the recently constructed Mtorres warehouse development to the south, an office building to the southwest, and a wetland directly to the west. 5.0 Critical Areas Several wetlands are located near the site. The wetland to the southeast was partially mitigated as part of the Mtorres development to the south, and it is separated from our site with a recently constructed grass-lined channel. There is another wetland located offsite to the west, and another wetland located to the northeast across Hardeson Road. There are no landslide or erosion hazard areas located onsite. ' The site is mapped outside of the area of potential seismic hazard. The liquefaction susceptibility of the site is mapped very low to low. There are no fish and wildlife habitat conservation areas within the site or immediately adjacent. Refer to Appendix A-5 for the Critical Areas Maps. 6.0 Soils South Sound Geotechnical Consulting prepared a geotechnical report for the site dated September 18, 2018. Five test pits were completed for the site ranging from 12 to 21 feet below the existing grade.A layer of fill was found in all of the test pits, which varies in depth across the site. The deepest layer of fill was on the eastern edge of the site, where the fill extended to a depth of 20.5 feet below existing grade. The north/central portion of the site had between 11 to 15 feet of fill, and the southwest portion of the site had between 1 to 3 feet of fill. A 1-foot layer of topsoil was found in the test pit near the south property line. The native soil found in all test pits consisted of silty sand with gravel and variable cobbles and clay. Most of the native soils were medium dense to dense and were interpreted as glacial till Groundwater was only found in the test pit near the south central portion of the site at a depth of 17.5 feet below existing grade (elevation 483.5). Refer to Appendix E for the full Geotechnical Report. Construction Stormwater Pollution Prevention Plan Everett 7-Eleven 3 OCIOIll 2180309.10