4600 BAKER DR Geotech Report 2025-03-03

January 12,2021 Page 2 of 7 Limited Geologic Evaluation Area Geology The Geologic Map of the Mukilteo Quadrangle,indicates that the site is near the contacts between Transitional Beds and Whidbey Formation. Transitional Beds include massive silts with areas and interbeds of clay and silty-sand. These materials are typically stiff to hard below a weathered zone. Whidbey Formation consists of dense/stiff layers of silty-sand, sandy silt, and drift-like materials. These deposits outcrop near the base of Puget Sound area bluffs. Geologic Hazards Most critical area ordinances designate slopes with magnitudes greater than about 4o percent and vertical relief of at least ro feet as potentially geologically hazardous (steep slope/landslide hazards). Erosion hazards are typically present in areas with slope magnitudes of 15 percent or more,depending on their composition. From the area of the residence and yard areas, the site slopes steep downward in multiple directions. The northern portion slopes downward to the north at magnitudes of 7o to 15o percent and relief of about 150 feet. The average gradient is about 90 percent. The western portion slopes downward to the west at magnitudes of 5o to 14o percent and relief of about 14o feet. The average gradient is about 7o percent. There are similar slopes extending downward to the southwest near the south property line. These slopes have lower magnitudes and vertical relief. All of the slope areas are well vegetated; however, the north facing slopes are predominately covered with low-lying deciduous vegetation (blackberry vines, ivy, ferns, grasses, small trees) with less large diameter evergreen trees. There is local evidence of historic landslide activity along portion of the north-facing slope(shallow sloughs). There is a stream near the west property line at the toe of the west-facing slope. This slope is well vegetated with trees and understory. Some of these trees are locally leaning and have curved trunks. The level of soil creep is moderate and we did not observe significant erosion or instability due to stream incision. The stream is likely incising; however,the rate appears typical and not resulting in significant side slope erosion at this time. The Coastal Zone Atlas indicates that the site slopes are Unstable. There is an area noted as Unstable Old Slide at least roo feet east of the site on north-facing slopes. We observed the current site conditions and visually assessed adjacent steep slope areas during our site visit on January 6, 2021. We did not observe exposed soils as a result of any recent or historic landslide activity. Nor did we observe spring activity of other indicators of ongoing landslide activity. All areas were fully vegetated and consistent with steep slope and bluff areas created over time through long term erosion,mass wasting,and bluff retreat. We observed evidence of soil creep which is typical on slopes with magnitudes greater than about 5o percent. We also note features consistent with shallow sloughs on the north slopes. These areas appear historic as they are currently heavily vegetated(not recent sloughs). We understand that there are erosion and steep slope/landslide hazard areas within the property and on adjacent properties. The following are code items with our comments underlined after the relevant sections. www.cobaltgeo.com ^ (206)331-1097