4600 BAKER DR Geotech Report 2025-03-03

January 12,2021 Page 6 of 7 Limited Geologic Evaluation • All runoff is controlled on site during construction and is routed away from slope areas (permanent) Where applicable, all of the above-described criteria can be achieved or is present. The proposed project is relatively minor and localized. Conclusions & Recommendations It is our opinion that the site slopes are stable to locally unstable and/or marginally stable at this time. In general, the western and southwestern slopes are primarily stable with evidence of minor soil creep. The northern slope is generally marginally stable to locally unstable as evidenced by the predominance of small deciduous vegetation, very steep topography, and local shallow sloughs(historic and revegetated). The existing residence is situated at least 4o feet from the west slope area and about 5o feet from most of the north slope. The residence has a shallow basement, which does slightly increase the effective building setbacks. It is our opinion that the accessory deck may situated within these existing setbacks without affecting slope stability. The areas surrounding the residence consist of developed yard and patio areas and the addition of local isolated foundation elements will not increase instability of the adjacent slopes. The steep slope areas may experience landslide activity in the future due to a wide variety of factors. In general,the most likely slides would be surface sloughs of weathered soil deposits that overlie the dense native soils. Larger rotational slides could occur but have a lower likelihood due to the high density of the soils that are present within the slope system. Factors that affect slope stability in this area include surface water, spring activity (not observed), local stream incision, seismic activity,and decreases in vegetation coverage. The proposed construction should not adversely affect slope stability within the site and adjacent areas provided the work is performed in accordance with our recommendations, permit requirements, and adequate erosion control measures are put in place prior to construction. All temporary and permanent runoff must be controlled and directed away from the steep slope areas. Closure The information presented herein is based upon professional interpretation utilizing standard practices and a degree of conservatism deemed proper for this project. We emphasize that this report is valid for this project as outlined above and for the current site conditions and should not be used for any other site. www.cobaltgeo.com (206)331-1097