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Mikc Vancc � � <br /> April 9 2004 <br /> Pagc 3 <br /> percolating iNo Ihc wcaihcred lill �vill usually pond and mi6�ratc lalerally betwcen Ihc weathcred and <br /> unwcathercd laycrs. In its native undisWrbcd state, glacial till soils arc competem load-bearing soils. <br /> Undcrlying [he glacial till is adcancc ouhvash of thc Vashon Drift cansisting of mostly gray, <br /> well-stratificd sand with variablc amounts of silt, pebblcs, and cobblcs. The advance ouhvash sand is <br /> usually cxposcd whcrc the overlying glacial till cap has been croded away, typically in ravines and bluff <br /> margins. Advancc outwash sand is mapped west of ihe sitc where the till cap has been eroded. In the <br /> Everctt arca, thc thiclmess of the advance outwash sand is as much as 200 fect. <br /> SLOPE STAHILITY � � — ' � —' ` L\, <br /> 1_ S I <br /> Thc wcst-facing slopc on thc property is modcratcly stecp with indinations ranging from about <br /> 211:I V to SH:1 V, an� isolated areas approaching 1 H:1 V. Thc exposcd surficial soils on the terraccd arca <br /> consist of fill overlying glacial till. E3ascd on our discussions with you, wc understand that ihe terracing <br /> arca consists primarily of horizontal cuts inro thc densc nativc soils with a minor quantiry of backfill <br /> bchind thc uppermost blocks. 'Thc blocks werc obscrved to fit tight with no evidence of setqemcnt. A <br /> thickcr section of fill and �ecathered till was cncountcred near the rop of the slupe as summarizcd in thc <br /> following scction. <br /> As discusscd in the previous section, glacial till consists primarily uf densc ro very dense silty sand <br /> that has hccn glacially ovcrriddcn by ihousands of fecl af icc. Glacial till can bc s�ablc at almos[ vcrtical <br /> slopes for long periods of timc. <br /> �Ve did not obscrve evidencc of slopc instability at the site. We also obscrved that thc foundation far <br /> the existing swcturc did not appcar to ha��c any significant cracks or other cvidencc indicative of <br /> prcvious sctllcmcnt or slopc instabiliry. <br /> NEAR-SURFACE SOIL CONDITIONS <br /> Our inte�pretation ol' subsurfacc condiiions at thc sitc is based on the mappcd geology, our sitc <br /> rcconnaissancc, and soil conditions obscn�cd in shallow hand holcs excavatcd at thc proposcd <br /> improvemcnt localinns. �Ve advanccd h1�o hand holcs at thc site along the edge of thc Icvcl upland arca. <br /> "I'hc hand hules werc lac��ed within thc proposcd deck arca approzimately 10 fcet west of the cxis(ing <br /> slructurc. <br /> 13oth h:md holc cxcavations encountcrcd loosc to mcdium dcnsc sihy sand«ith occasional b�ravcl to a <br /> dcpth of al Icast 5 (cct bclow ground surfacc. 1Vc cncountcrcd a soti silt la��cr in onc of the hand holcs <br /> het�ccen a dcpth of aboW 3 to�l feet. Onc hanJ holc was tcrniinatcd at a depth of G C�:et mccting refusal in <br /> coarse gravcl. "fhc othcr hanJ hulc c�uo��mcrcd dcnse glacial lill at a depth of 5 feet. TL•c hand holes <br /> �vcrc nut Jrcp enougL• or opcn lung cnough fur ground waicr obscn�ations. Sccpagc was not obscrvcJ <br /> alon� Ihe slupe, though moist to �cet soil was observed Jirecdy abo��e the dense �ill layee As previoosly <br /> discusscd, shallo��� perchcd gramdwatcr is oftcn prescnt as �eatcr percola�cs through thc upper weathercd <br /> soils and moccs latrrally abuvc thc dcnsc,widisturbcJ soils. Ground watcr Ic�•cls will Iikcly iluctuate duc <br /> �u rcccnl prccipi�ation, scasunal variations,and othcr factors. <br /> ; <br /> G c o I! n g i n c c r s IIn7e-0nl-0U HfI� . <br /> � <br />