6101 23RD DR W NORPRO Geotech Report 2025-07-29

II June 3, 2011 Project No.T-6578 4.1 Erosion Hazard Area Per Section 37.080(3)(a)of the EMC, Erosion Hazard areas are"areas that have a high to very high or severe risk I of erosion". Based on Section 3.3.2 of the referenced Dames and Moore publication, the "levels of erosion hazard generally exist under anyone of the following condition or combination thereof: a. All exposed slopes greater than 25 percent. b. All drainage features which receive storm water discharge." I The City of Everett Erosion Hazard Critical Areas Map 3 indicates that the site is located in an area designated as having a low erosion hazard. Site slops are inclined at less than 25 percent. A drainage feature, Narbeck Creek borders the site to the east, however stormwater from north and south adjacent developments is collected and routed for discharge under controlled storm sewer and detention pond features. We observed no indication of past or ongoing erosion on or adjacent the site. It is our opinion that based on the existing slope inclinations that the site does not meet the EMC definition of an erosion hazard area. Site soils will have a potential for erosion, when exposed however. hi our opinion, the potential for erosion at the site will be adequately mitigated with proper implementation and maintenance of Best Management Practices (BMPs) for erosion and sedimentation control. Application of BMPs should conform to City of Everett standards and should be in place prior to, during, and immediately following clearing and grading activities at the site. The erosion potential of the site soils and the effort required to control erosion during construction can be reduced substantially by excavating and grading during the drier summer months. Other management practices that should be applied to reduce the potential for erosion include covering exposed soils with straw mulch or plastic sheeting and controlling surface water runoff as required during grading. To contain sediment transport and prevent impacts to adjacent properties, construction stormwater should be routed through collection swales to temporary sedimentation ponds. Silt fencing should be installed at the site perimeter at the clearing limits. 4.2 Landslide Hazard Area I Per Section 37.080(1)(a) of the EMC, Landslide hazard areas are "areas that have a high to very high or severe risk of landslide hazard". Based on Section 3.3.1 of the referenced Dames and Moore publication, landslide hazard areas include but are not limited to the following: a. "All areas potentially underlain by Quaternary Vashon advanced outwash sands (Qva), Quaternary I Vashon till soils (Qvt), Quaternary old and young alluvium (Qoal and Qyal) as mapped by USGS (Menard)or representative soils,exposed on slopes greater than 25 percent." The City of Everett Landslide Hazard Critical Areas Map 2 indicates the site is located in an area designated as having a low landslide hazard. We did not observe indications of instability, emergent groundwater seepage, I significant erosion, or historical movement on or adjacent the site. The site is underlain by till and advanced outwash deposits, however were found in a medium dense to very dense, overridden condition. In addition, as previously mentioned site slopes are inclined at less than 25 percent. In light of this, and our review of critical areas maps, it is our opinion that the site conditions would not classify as a landslide hazard area as defined by the EMC. Page No.4 I