3321 52ND PL SW 2016-01-01 MF Import

r. ' . Geotechnical Engineering Investigation Schwab Residence ]uly 13, 2001 NGA File No. 329401 Page 5 � the UBC description for Soil Profile Type S�. This corresponds to an effective peak horizontal ground acceleration of 033g. Ha7ards associated with seismic sctivity include liquefaction potential, slope instability, and amplification of ground motion due to soft soil. The medium dense to very dense glacial till and ouhvash sand interpreted to underlie this site does not have a significant potential for liquefaction, slope instability, or amplification of ground motion. Erosion Hazard The criteria used for evaluation of erosion hazards include soil type, slope gradient, vegetation cover and groundwater conditions. The surface soil types (group classification) are related to the underlying geologic soil units. The Soil Survey of Snohemish County Area, Washington, by the Soil Conservation Service (SCS), was reviewed to evaluate the erosion hazard of the on-site soils. The surface soils at the site were mapped by the SCS and classified as Alderwood-Everett gravelly sandy loamy (25 to 70 percent slopes). These soils are consistent with the glacial till and advance ouhvash deposits found within the site. The erosion ha7ard for this material is listed as moderate to high. Erosion ha�ard on the steep slope should be low if the vegetation cover is not disturbed. Landslide HazardlSlope Stability The steep portion of the site slope has an average inclination of between 57 and 70 percent and a ma�cimum relief of about 40 feet. The native soils that are inferred to fortn the core of the slope consist of dense glacial till and ourivash. We did not observe indications of past or current movemznt of the slope at the time of our visit, or any surficial or subsurface water seepage. Also, the slope is covered with several mature straight fir trees, and hvo old growth stumps. Based on the competent soils that are believed to be from the core of the slope, the absence of indications of past or curtent slope movement, the absence of water seepage on the slope, and the mature trees and old growth stumps on the slope, we consider the slope to be stable with respect to deep- seated movements. There is, huwever, potential for shallow sloughing events to occur within the steeper portions of NELSON GEOTECHN/CAL ASSOC/ATES, /NC. �f