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Geotechnical Engineering Evaluation NGA File No. 1333322 <br />Miller Property Slope Stabilization July 1, 2022 <br />Everett, Washington Summary - Page 2 <br />The soil explorations revealed a relatively thick section of saturated undocumented fill soils mantling the <br />top of slope has likely contributed to the recent slope failure. We anticipate stormwater runoff and <br />exceptional atmospheric conditions are also key driving factors that decreased slope stability along the <br />top of slope. Additionally, based on aerial image review it appears the top of slope has been <br />modified/landscaped over the years; particularly between the years 2018 and 2020 we noted the <br />introduction of a playset area, landscape block wall, and what appeared to be tree removal or tree fall <br />along the southern portion of the property and top of slope area. Stability conditions prior to failure are <br />unclear, but were likely marginal, evidenced by landslide -derived topography and historically documented <br />events in the nearby vicinity. We have concluded that the recent landslide has likely been triggered by <br />the heavy rain experienced during the 2021-2022 winter months, along with the presence of weaker <br />undocumented fill soils mantling the upper portion of the slope. Under current configuration, the affected <br />area is considered hazardous and subsequent movement will likely continue to occur. <br />Permanent stabilization of the slope, and protection of the residence will require a subsurface pile wall, <br />as well as implementing drainage improvements. The attached report presents our stability analysis and <br />the recommended stabilization methods. <br />Further monitoring of the slope instrumentation and surface morphology will be necessary to evaluate <br />effectiveness of any repair measures. We anticipate being involved during development of stabilization <br />plans, as well as installation of repairs, to provide feedback and alternative recommendations should <br />some aspects exposed during installation differ from assumptions made, and to develop initial <br />recommendations as presented hereon. <br />It has been a pleasure to provide service to you on this project. Please contact us if you have any questions <br />regarding this report. <br />Sincerely, <br />NELSON GEOTECHNICAL ASSOCIATES, INC. <br />Khaled M. Shawish, PE <br />Principal <br />NELSON GEOTECHNICAL ASSOCIATES, INC. <br />