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Geotechnical Engineering Evaluation NGA File No.1033518 Larsen Property Garage May 8,2018 Everett,Washington Page 8 This site is underlain by moisture-sensitive soils. Due to theseconditions, special site stripping and grading techniques might be necessary, especially if grading is attempted in wet weather. These could include using large excavators equipped with wide tracks and a smooth bucket to complete site grading and promptly covering exposed subgrades with a layer of crushed rock for protection. If wet conditions are encountered or construction is attempted in wet weather,the subgrade should not be compacted as this could cause further subgrade disturbance. In wet conditions it.may be necessary to cover the exposed subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from disturbance by machine or foot.traffic during construction. The prepared subgrade should beprotected from construction traffic and surface water should be diverted around prepared subgrade. Shallow groundwater, if encountered, should be intercepted with cut-off drains and routed around the planned grading area, or the groundwater should be controlled with sump-pumps or dewatering systems. Failure to follow these recommendations could cause erosion and failures on the slopes, as well as result in inadequate subgrades. Structure Setbacks Uncertainties related to building along steep slopes are typically addressed by the use of building setbacks. The purpose of the setback is to establish a"buffer zone"between a structure and the top of a slope so that ample room is allowed for normal slope recession during a reasonable life span of a structure. In a general sense, the greater the setback distance, the lower the risk of slope failures impacting the structure. From a geological standpoint, the setback dimension is based on the slope's physical characteristics, such as slope height, surface angle,material composition, and hydrology. `Other factors such as historical slope activity, rate of regression, and the type and desired life span of the development are important considerations as well. To minimize any potential impacts associated with the proposed garage construction on the sloping areas and neighboring concrete rubble retaining wall above and to the east of the proposed garage, we recommend that the proposed garage and temporary excavation associated with the proposed garage be located to maintain a minimum 2 Horizontal to 1 Vertical (2H:1V) gradient between the toe of the temporary excavation and the base of the concrete rubble retaining wall above. In addition to the proposed setback, we recommend that the entire eastern garage wall be designed as a concrete retaining wall and extend the full height of the garage on the eastern side to act a debris catchment wall. This is intended to provide a catchment measure should any sloughing debris travel towards the proposed garage from the sloping area or the existing concrete rubble wall above. We should be retained to evaluate the garage foundation setback distances and subgrade soil prior to placing foundation forms. Any proposed development within the setback area should be the subject of a specific geotechnical evaluation. Under no circumstances should water be allowed to concentrate on the slopes,during or after construction. NELSON GEOTECHNICAL ASSOCIATES,INC.