1910 W MUKILTEO BLVD Geotech Report 2022-10-25

Geotechnical Engineering Evaken 4110 NGA File No. 1238723. Spencer Garage Addition February 11,2021 Everett,Washington Page 5 within the site during our investigation, such as deep-seated. Iandsliding. We also did not observe any evidence of recent sloughing events on the site slopes during our site visit. The steep"sllopes`were generally vegetated. We did not observe groundwater seepage emitting from the steep slopes within` the site. The core of the slope is inferred to consist of competent deposits. Inclinations of up to 30 degrees on the site slopes indicate high internal strength within the native glacial soils. Relatively shallow sloughing failures as well as surficial erosion are natural processes and should be expected within the loose surficial soils on the slope during extreme weather conditions or as a result of seismic activity. It is our opinion that there is potential for erosion, soil creep, and shallow failures within the loose surficial soils on the steeper site slopes. However, we do not anticipate large-scale,' deep-seated rotational slides to develop on this site. Proper site grading, drainage, and foundation placement as recommended in this report should help reduce the impact of such events on the planned improvements. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the planned site development is feasible from a geotechnical standpoint. Our explorations indicated that the site was generally underlain by competent native glacial bearing soils at relatively shallow depths.The native glacial soils encountered at depth should provide adequate support for foundation, slab, and pavement loads. We recommend'that the planned structures be designed utilizing shallow foundations. Footings should extend through any loose soil or undocumented fill soils and be founded on the underlying medium dense or better native glacial bearing soils, or structural fill extending to these soils. The medium dense or better native glacial bearing soils should typically be encountered approximately 2.0 to 4.0 feet below the existing ground surface, based on our explorations. We should note that localized areas of deeper unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require additional excavations in foundation, slab, and pavement areas to remove the unsuitable soils. Based on the results of our infiltration testing and the presence of granular native soils at depth throughout the site, it is our opinion that`-the onsite native soils are not suitable for stormwater infiltration.This is further discussed in the Site Drainage section of this report. NELSON GEOTECHNICAL ASSOCIATES, INC.