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Geotechnical Engineering Evaluation NGA File No.959616 Watson Residence Addition July 6,2016 Everett,Washington Page 9 undocumented fill soils and be embedded a minimum of one foot into the competent native soils at depth. We should be retained to evaluate the deck and addition footing subgrade soil and setback distances prior to placing the footings. Protection of the setback and steep slope areas should be performed as required by the City of Everett. Specifically, we recommend that the setback area and site slope not be disturbed or modified through placement of any fill or removal of the existing vegetation. No material of any kind should be placed within the setback area or be allowed to reach the slopes, such as excavation spoils, lawn clippings, debris, and soil stockpiles. Any sloping areas disturbed during construction should be planted as soon as practical to reduce the potential for erosion. The new vegetation should be maintained until it is established. Replacement of vegetation should be performed in accordance with the City of Everett code. Under no circumstances should water be allowed to concentrate on the slope. Foundations Deck Foundations: We recommend that the new deck be supported on 12-inch minimum diameter concrete piers (sonotubes) placed on undisturbed medium dense or better native soils. We also recommend that the concrete piers be embedded a minimum of one foot into the competent native soils. Based on our explorations, we would anticipate a minimum foundation depth of approximately two to three feet to achieve the recommended embedment depth. However, the depth to the competent native soils may be deeper in unexplored areas of the site. For deck foundations constructed as outlined above, we recommend an allowable design axial compression capacity of 1,000 pounds for each pier to be used for determining the number and spacing of the pier supports. We should be retained to review the final plans and evaluate the foundation subgrade soils and embedment depths prior to placing foundation forms. As an alternative to supporting the deck on individual deck supports, a concrete grade beam could also be constructed on top of the piers and be tied into the existing residence foundation. The concrete grade beam would support all of the deck posts. The grade beam should be sized for a soil bearing pressure of 2,000 pounds per square foot(psf). Addition Foundations: The proposed addition foundations should consist of conventional shallow spread foundations founded on medium dense or better native soils, or be supported on structural fill or rock spalls extending to those soils. We expect that competent soils will be found within the addition NELSON GEOTECHNICAL ASSOCIATES, INC,