881 OLYMPIC BLVD Geotech Report 2023-12-29

nuty24� en23 reacxore Liml[edCcolechnirvl8velnellon The Advance Dutwash includes loose to dense fine to medium grained sand. These deposits are typically susceptible in surface erosion. Transitional beds include silt and clay at the base of the outwasheands. These materials we typically stiff to hard below a weathered zone. Whidbey formation includes mixtures of sdty-sand, clayey soils, and other fine grained materials that often underlie Vashon era deposits near Puget Sound bluff. These materials are dense due to the Vashon glaciation which resulted in consolidation. The Department of Natural Resources (DNR) online database shows a landslide feature in the western portion of the property. This feature appears to include an upper scarp and lower deposition zone. The slide is noted as likely being a earth flow. We have included a light detection and ranging (LIDAR) image that shows the landslide feature along with the shallow nonref anturre and steeper ravine sliglnlynarth ofthe site. Geologic Hazards Most critical area ordinances desfgnateslopeswith magnitudes greater than about qo percent and vertical relief of at least to feet as potentially geologically hazardous (steep slope/landslide hazards). There is a shallow undulating ravine feature just west of the residence that was formerly overgrown with understory, invasive vegetation, and trees. The ravine has a northerly slope of 5 to 15 percent with 20 to So parent magnitude aide slopes extending downward to the east and west into the featme. The side slope relief is about 20 to 25 fact. This is the area where vegetation removal occurred. There are steep slopes located northwest of this feature that a#end downward to the northwest at magnitudes of about So to over can percent and relief of about 160 feet This slope is heavily vegetated with area and understery. No vegetation modification occurredin this arson. We observed the current site conditions and visually assessed adjacent steep slope areas during our site visit in June 2023. We did not observe evidence of severe erosion or instability in any of the areas where vegetation was removed. We note that the very steep slope areas west of the affected sure (the mapped landslide area) which may experience soil movements in the future. This likelihood has not been increased or decreased by the recent vegetation modifications to the east. All areas should remain fully vegetated. The following are code items with our comments underlined after the releventseotions. A. Designation. The following geologically hazardous areas shall not be altered except as Otherwise providedbythis chapter: r. landslide hazard areas: a. Those areas defined as high and very high/severe risk oflandslide hazard in the Dames and Moore Methodology for the inventory, Classification and Designation of Geologically Hazardous Areas, City of Everett, Washington: July 1, m91, or as revised through best available science: (1) Very bfgh/severe: slopes greater than fifteen percent in the Qtb, Qw, and Qls geologic units; and slopes greater than fifteen percent with uncontrolled fill. (2) High: slopes greater than forty percent in all other geologic unfts (not Qtb, Der, and Qls or uncontrolled fill). baltgeo cam (206) 331-1097