4328 HOYT AVE Geotech Report 2022-10-25

Geotechnical Engineering Evaluation—REVISED NGA File No.1148519 Staniford Residence Remodel June 23,2020 Everett,Washington Page 5 Erosion Hazard The criteria used for determination of the erosion hazard for affected areas include soil type, slope gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil types, which are related to the underlying geologic soil units. We reviewed data from the Soil Survey of the Snohomish County Area, Washington, by the Natural Resources Conservation Service (NRCS). The soils on the site are listed as Alderwood-Urban land complex, 2 to 8 percent slopes and the erosion hazard is listed as slight. Based on our experience in the area and our observations in the field, it is our opinion that the soils encountered around the residence would have a low erosion hazard for areas where the native soils aren't exposed. CONCLUSIONS AND RECOMMENDATIONS General During our visit, we observed the exposed existing residence foundation on the western side of the structure. The residence appeared to be partially supported on approximately 12- to 18-inch concrete sonotube type piers as observed in the southwest corner of the building. We also observed cracking within the foundation on the western side of the residence. During our explorations near the residence, we found up to 11 feet of undocumented fill material in a loose to medium dense condition as measured from approximately bottom of existing structure foundations. Based on these explorations and our observations, it is our opinion that the western and likely portions of the central and eastern portions of the existing residence are supported on some degree of undocumented fill soils. In this case, only supporting the proposed additions on deep foundation systems could lead to differential structure settlement. We therefore recommend that the existing residence be at least partially supported on pin piles. Based on conversations with the homeowner, significant drainage improvements and interior foundation work has been previously performed on the existing residence structure. We were informed the structural improvements consisted of releveling the house, adding east-west trending grade beam foundations as well as adding approximately 2-foot by 2-foot footing pads throughout the crawl space area. We were also informed stormwater that previously discharged directly from the downspouts was directed away from the residence and foundations. We recommend that a structural engineer determine the actual extent of areas that should be underpinned, but at a minimum, we recommend the western portion of the existing residence be supported on deep foundation systems, along with the new addition foundations. NELSON GEOTECHNICAL ASSOCIATES,INC.