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Thc upper Uvice fect of ex�;loration pit EP-2 consistcd of loosc,dry, broµn, silty sand with some <br /> E;ravcl, organic waste and consWction rubble. 'The fill soil cncountered in this exploration did <br /> not originatc fiom this property nor was it placcd swctwally. It was also visually apparcnt that <br /> [he east slope of E3roadway, adjacent to the west cnd of the property, was compriscd of fill soil. <br /> Prcsumably, sincc this soil is supporting a Ciry street,ihis fill slope should be structwal fill. <br /> lJndcrlying thc fill soil in EP-2 and undcr a thin layer of topsoil in EP-1 was a dcnsc sand unit. <br /> The subsurface conditions at deptli in both exploration pits consisted otdcnse,damp, light <br /> brown-gey, medium sand widi Uace gravcl. 'Ilic upper 2 to 3 fcet was wc:ithcred to a slightly <br /> Icss dense condition. "I'he sand extendcd bcyond the tertnination depths of the explorations at 15 <br /> to 16 fect bclow existing ground surface. This sand has becn interpreted to be Vashon advan�c <br /> outwash. "I'he Vashon adv:uice outwash was d��osited prior to the ndvance of the last glacial icc <br /> shcel in thc Puget Sound rcgion. The sand and gravcls wcre deposited by tluvial processes <br /> associatcd with runofT from thc icc s6cet. '17ie sand and gravcl dcposits wcre subsequcntly over- <br /> run by scvcral thousand fcct of glacial ice rcsulting in thcir dcnse condition. <br /> Thcn: was no ground waler encountered in the exploration pit completed for this study. '1'hc <br /> sand and gravcl scdiments have a good pemicabiliry and allow surfacc runoff to infiltritc <br /> vcrtically. 'I'he pertneablc sand and gravcl should allow thc infiltration of the majority of <br /> potential storm water during consUvction except from large storm events or storm cvcnts of long <br /> duration. Thc permcablc sand and �vel will tx:�blc to support infihration of�stomi watcr <br /> runolTfrom the plannecl impermcahlc surfaccs. <br /> Gcologic Hazards <br /> 'ITie following discussiun of potcntial gwlogic h�uanls is bascd on thc visual reconnaiss;uue of <br /> the site, thc subsurface cxploralions, :uid rr.vicws of acrial phutographs and regiomil lopogr.iphic <br /> maps of ihc arc:�. <br /> Stcen Slonc Ha7;vd <br /> 'llic property is considcmd to be a stcep slopc h:�ard arca duc to Uic inclination uf thc slopc. <br /> 'll�e slope was at inclinations of about 45 percent and wat about 40 fect high. 7�hc slope was <br /> undcrlain by dcnse, glacially consolidated, advaiuc outwash sand sulimcnts. '17�c slo� was wcll <br /> vegetaled with good gmund c;over. 'I�hem was no evidence ol'rccenl crosion or slope instability <br /> ohscrvcd on Uic slopc. <br /> T'he advmu:c: oulwash sand auid gtavcl sedinicnls encountered on the site are not prone to decp <br /> set�tcd, rotational f:iilures due to thcir h�gh intcmal strengtl� and good permcability. Tlrere werc <br /> no indications of past dcbris tlow ot rot�tional failurc occurrenccs on this or thc adjaccnt <br /> prope:rties. 'fhe plannc;d dcvclopment proposes to conswct a rctaining wall thal �vill bc <br /> embedded into the densc s:u�d soil ncar thc toe of lhe slope. A buttress oC gcogrid reinforce fill <br /> will bc notchcd into the slope to ctcnte stepped building pad for the house and garage aru2s. <br /> Provided that conswction of the rctaining wall and struciural fill are donc in accordance with the <br /> recommendations contained in this tcport, il is our professional opinion that the risk of a debris <br /> ilow or othcr mass wasting cvcnts occurring on this propeKy aficr conswction would bc low. <br /> BGC, pllc 14267 209'h Avenue NE, Woodinville, WA 9R077 (425) 273-5062 <br />