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4 <br /> Octobcr I I,2011 <br /> Mr.IItu��ey�JuUic <br /> [,cYcA Jub Nu. 11-064 <br /> Pagc 3 <br /> Geulogic Setting and Soil CuvJitiuus <br /> l'he Geoloeic nlap of the F�erett 7 � Minute Uuadr:uiele Snohomish Counn�, Weshineton. mid <br /> the Gooloeic bian of thc �fan�sville Ou�dr�u�alc Snohomish Countv. Washineton. both by James <br /> P. �4iu:vd, publishcd by U. S. Geological Sun�ey in 1985, «'ere referenced lor the geologic and <br /> soil cunditi�ins at the subject residence sitc. According to tlus publication, the surlicial soil units <br /> at and in thc vicinih' of Uoth the subject site mid the Refercnce Sitc are mappeJ as Vashon Till <br /> (Q�t)w�derllin by Advunce Out��•ash (Q�u)• <br /> 'lhe gcology of the Pugct Sowid Lo�vluid ha�s Ueen modificd by thc advwice a�id retreat oC <br /> sc��cr�l gluciers in thc past a�id subsequent depusits and crosion. Tlm latest glucier advat�ced to <br /> the Yuget Sound i.o��'land is rcferred to us the Vashun Stadc of tlic Pmscr Gluciation. which lias <br /> occuiTed dwing thc later stages of the Plcistocene Gpocli and reveated from du region some <br /> 14,500 years a�u. <br /> 'fhc Vashon till soil unit is plowcd undcr glacial ice Juring the most rcecnt glacial period us it <br /> ad�•�uiced over an eroded, irregular surface of older I'urn�utions and sediments. It is ti ven� dense <br /> mixturc of imsorted clay, silt. sand. gravcl, and scattered cobbles und bouldcrs, oftcn refeaed tu <br /> as "hard pa�i'. 'Chc Vnshon till suil o��er the top t��u to U�rcc fcct is nonnally ��'euthered to a <br /> medium-dense state, and is moderately penueable and compressible. "1'hc underlying fresh till <br /> soil is ��ery densc a��d pnctically impervious to stunn�cater infiltration. Tlie fresh till hw the <br /> compressive strengtli comp�u'able to tha� of lo���-gradc concrcte and cun stand in steep nawral or <br /> cut slopes for u lung period. lf rcmains imdisturbed az�d ti�ell-druined, the fresli till soil can <br /> provide csccilent foundation suPport �+ith li[Uc sctticmcnt cxpected. <br /> LlU & A�SOCIATES, INC. <br />