1921 W MUKILTEO BLVD 2018-01-02 MF Import

Preliminary Geotechnical Engineering Evaluation 1919 Mukilteo Boulevard October 20, 2005 NGA File No. 718805 Page 5 the specific surface soil types, which are related to the underlying geologic soil units. The Soil Survey of Snohomish County Area. Washington, by the Soil Conservation Service (SCS) was reviewed to determine the erosion hazard of the on -site soils. The site surface soils were classified using the SCS classification system as Alderwood-Everett gravelly sandy loam, 25 to 70 percent slopes. This unit is listed as having a high erosion hazard for areas where the soils are exposed. It is our opinion that the erosion hazard for site soils should be low to moderate in areas where vegetation is not disturbed. Landslide Hazard/Slope Stability The criteria used for evaluation of landslide hazards include soil type, slope gradient, and groundwater conditions. A steep north -facing slope with a gradient of up to approximately 40 degrees (84 percent) with a height of approximately 100 feet is located below the planned building area. We observed evidence of significant sloughing along the eastern portion of the top of the slope. Sloughing soil was noted from a near vertical portion of the top of the slope near the east property line. The area of sloughed soil was about 10 feet wide and exposed silty sand material. We did not observe any other scarps on the slope during our site visits. We did not observe seepage or other areas of erosion on the slopes. Our explorations indicate that the core of the steep slope consists primarily of medium dense to very dense sand. Inclinations of up to 40 degrees on the slope indicate high strength and internal friction angle within the underlying soils. Relatively shallow failures as well as surficial erosion are natural processes and should be expected on these slopes. It is our opinion that while there is potential for erosion, soil creep, and shallow failures within the loose surficial soils on the steep slope; there is not a significant potential for deep-seated slope failure under current site conditions. Proper site grading and drainage as recommended in this report should help maintain current stability conditions. LABORATORY ANALYSIS We performed three grain -size analyses on selected soil samples obtained from the explorations for soil classification. Samples were taken from Boring I at 10.0 and 41.5 feet, and from Boring 2 at 12.5 feet. The results of the sieve analyses are presented as Figures 10 through 12. CONCLUSIONS AND RECOMMENDATIONS General It is our opinion that the planned development is feasible from a geotechnical standpoint, provided that NELSON GEOTECHNICAL ASSOCIATES, INC.