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1 <br />Gustafson Residence Retaining Wall <br />1215 Madrona Avenue <br />Everett, Washington <br />NGA File No 924115 <br />June 12, 2015 <br />Page 2 <br />, We have previously provided recommendations for landslide stabilization measures that occurred on <br />this property and the neighboring property to the east in November 2012 in a letter titled "Landslide <br />' Evaluation Letter — Gustafson Property — 1215 Madrona Avenue, Everett, Washington," April 12, <br />2013. Since then we have also observed erosion control installation, drainage improvements, and <br />1 <br />1 <br />, <br />' <br />' <br />' <br />' <br />' <br />' <br />' <br />' <br />1 <br />' <br />' <br />' <br />revegetation of the steep slope area below the subject concrete rubble walls. <br />SCOPE <br />The purpose of this study is to explore and characterize the site subsurface conditions, and provide our <br />opinions and recommendations regarding the existing slope stability and proposed retaining wall. <br />Specifically, our scope of services includes the following: <br />1 <br />2 <br />Review available soil and geologic maps of the area along with previous reports perforined <br />within the vicinity of the site. <br />Explore the subsurface soil and groundwater conditions within the site and in the vicinity of <br />the existing retaining walls with a limited-access drill rig. Drill rig was subcontracied by <br />NGA. <br />3. Map the conditions on the slope below the proposed wall, perform hand-tool excavations as <br />needed, and evaluate current slope stability conditions. <br />4. Provide recoininendations for earthwork. <br />5. Provide recommendations for temporary and pennanent slopes. <br />6. Provide recommendations for retaining wall design and construction. <br />7. Provide recommendations for slope stabilization measures, as needed. <br />8. Provide recommendations for drainage improvements. <br />9. Document the results of our findings, conclusions, and recommendations in a written <br />geotechnical letter. <br />SITE CONDITIONS <br />Surface Conditions <br />The property is an irregular-shaped parcel covering approximately 0.31 acres. The property generally <br />slopes down to the north to a steep north and northeast-facing slope. The site is occupied by a single- <br />family residence with daylight basement within the southern portion of the property along Madrona <br />Avenue. A yard area and the tiered concrete rubble walls separate the residence from the steep slopes. <br />The observed that the concrete rubble walls were approximately four feet tall and in serious disrepair. <br />The lower concrete rubble wall appeared to be supported on a concrete slab that in turn was supported on <br />approximately 1-inch diameter steel pipes. An approximate 6-inch void space was observed below the <br />NELSON GEOTECHNICAL ASSOCIATES, INC. <br />