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Geotechnical Engineering E��aluatic�n <br />Packer Property <br />Retaining Walls and Steep Slope Evaluation <br />Everett, Vdashington <br />NGA File Iv�o. 870113 <br />March I 1, 2013 <br />Page 6 <br />is dependent upon the amount of rainfall. We would expect the amount of �roundwater to sli�htly <br />ciecrease during drier times of the year and increase during �retter periods. <br />SE?�SIT'Ii�E AREA EVAL�IATIQN <br />Seism�c F3azard <br />We T•eviewed the 20Q9 International Building Cc}de (IBC) for seismic site classification for this project. <br />Since medium denseistiff to dense/hard silty sand and silt sols u�ere encountered underlying the site, the <br />site contiitions best fit the iBC descrigtion for Site Class D. <br />�-�azards associated with seismic acti��ity inelude liquefaction potential and amplifcation of �n-aund <br />motion by soft de�osits. I.,iquefaction is caused by a rise in po�•e pressures in a loose, fine sand deposit <br />beneath the groundwater table. The dense/hard silty sand and silt soils interpreted to underlie the site <br />have a loul potential far liquefaction or amplification of ground motion. <br />The competent silty sand and silt sails iuterpreied to form the care of the site slope are cansidered stable <br />with respect to deep-seated slope failures. Hor�rever, the overiying loose surficial materials on the slopes <br />have the potential %r shallow slaughing failures during seismic events. Such eYrents should not affect the <br />proposed slape and wall configuration provided the recozzrmendations in this report are followed. <br />Erosion Hazard <br />The criteria used for determination af erosion hazard areas include soil type, slope gradient, vegetation <br />cover, and ground��ater conditions. The erosion sensitivity is related to vegetative cover and the specific <br />surface sail types, which are �-elated to the underlying gealogic soil units. The S�il Survev of Snohomish <br />Countv Area. 'VJashin�ton, by the Soil Conservation Senrice (SCS) tia�as reviewed to determine the erosian <br />hazard af the on-site soils. The site surface soiis were classified using the SCS classification system as <br />Alderwood-Everett gravelly sandy loams, 2� to 70 percent slapes. This unit is listed as having a <br />nlc�derate erosion hazard. Tlie on-site soils s�ould have a low hazard f'or erosian where the vegetation is <br />not disturbed. <br />�ELSOI� GEC?TEC�iA1JCAL ASSOCIATES, 1tUC. <br />