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Gcotcchnical L•nginecring Lcucr NGA 1'ilc No. R65712 <br />�7;Z Sound Acenuc Slope G��nluation Decembcr I9, 2012 <br />li��crcti, �Vashington Pagc 2 <br />nor�licnslcrn portion of Ihc silc. A small addition wns cons�nictcd along �hc castcm portion of thc garagc <br />thal extends over Ihc top of the slopc and is founded on picr blocks within Ihc steep slope area. Ne <br />undcrs�and ihat this nddilion will bc rcmoecd, ns it is located within an cnvironntcnlal scnsi�i��c an;a. \Vc <br />were inforn�ed that the garage foundation �aas cmbcddcd npproximatcly one to t�eo fcet below the <br />cxisling ground surf;ice. During our site visi�, �vc did not obscrvc any indications of setUement or <br />insiabilily such as significant cracking in the garage sl�b or founda�ion. }fowever, a�c did observc some <br />minor scttlemcnt of somc cmicrctc slabs and of thc addition foundations along �hc top of thc slopc. <br />The stcep cast-I'aciug slope below thc garagc descends from the garagc and backyard arca to a creck <br />bdow at an avengc inclination of approsimntcly 27 degrecs (51 percent). �Vc did obsen•c some minor <br />amounts of sloughing vid movcmcnt ���ithin somc undoci�mcntcd fill ncar thc top of thc slopc to thc soutl� <br />of the garagc. \Vc did not obscrvc groundwatcr scepage on ihe site slopc or indica�inns of rccent decp- <br />scntcd slopc stnbility issucs during our sitc visit on Dcccmbcr l d. "_'012. <br />Stornn��atcr runo(T Gom thc residcncc and garagc is dircctcd to pipcs that dcsccnd do«�n tl�c slopc �nd <br />daylight on ihe slope above the creck. The pipes consist of d-inch corrugatecl plastic. 1Ve ��•cre able to <br />obsen�c �hc outict of the garage dnins: howcver, �vc wero unable to ��erify �I�e rcsidence drains on Ihc <br />slopc. <br />Subsurfacc Conditions <br />'1'hc gcologic units for this arca are sl�own on thc 1'rcliminarv Gcolocic �lan of �hc \lukiltco and 1?vcrett <br />CJuadraneles. Snohotnish Counh�. Nashinelon, by �takcy Sntith (U.S.G.S., 197G). Thc sitc is mappcd as <br />Qvt (Vashon'I'ill). Thc Vashon'I'ill is dcscribcd as a misturc of clay, sil�, sand, pcbblcs, and cobblcs. <br />R'c anticipale that lhe site and core of Ihe s�eep slope are composed of compctent glxial till soils at <br />dcpth. Flo�rc��cr, �lic upper soils on tl�e slopc consisi o(' mainly a( loosc topsoil ancl wcathcrcd matcrial <br />that can bc susccp�iblc to sloughing and crosion. <br />Ilydrolotiic Cm�dilious <br />Ne did nol oUsenc �roundwatcr scepage on tl�c slope bclow thc residence and garage during our site <br />��isit. Ilowever, �ac anticipate thal perched �valer conditions may develop on �his site during extcndcd <br />periods of �vct ���ealher. Perched a�ater ocwrs when surface watcr infillratcs Ihrough Icss dense, more <br />pcnncablc soils, such as thc fill and topsoil, and accumulatcs on top of � rclativcly low pernicabilily <br />m;ucrial such as ihe underlying dcnse silty smid soil. Perched water does not represent a regional <br />� <br />NELSON GEOTECHNICAL ASSOC/ATES, INC. I, ' <br />, � i <br />J , <br />