5732 SOUND AVE 2016-01-01 MF Import

Gco�cchnicnl �nginccring Lcttcr NGA Pilc No. 865712 5732 Sound Avenuc Slopc I:ealuatiun DrcentUcr 19, 2012 I:ccrctt, \Vashington Pagc 3 groundwatcr "lablc" �vi�hin thc upper soil horizons. Pcrchcd wa�cr tends to vary spatially nnd is depcndent upon thc nmount of prccipitation. If perchecl watcr candi�ions cxis�, wc w�ald cxpcct ihc amount of perched wa�er to decrcase during dricr times of the ycar and incrensc during wctter periods. L:mdslidc Ilazard/Slopc Stability 'fhc critcria uscd for cvalualion of landslidc liarards includc soil t�Tc, slope gradicnt, and groundwa�cr conJitions. '1'hc si�c is situa�cd on a stccp norlh-facing slopc tvith indinations of approsimatcly U l0 40 degrees (31 �0 34 perccuQ. \Vc did not obsen�c any indications ol' rceent dcep-scatcd movemcnt of the slopc during our during our sitc visii; hu�acvcr, ��•c did obscn•c somc minor slou�_hing and slumping of �lic surficial fill and loosc surf'acc soils near thc tap of thc slopc. I3ascd on our obscrva�ions and thc mappcd gcology of thc arca, thc corc of �hc slopc is infcrccd to consist primarily of mcdium dcnsc or bcttcr nativc soil. Rclalivcly shallo�e sloughiug failures as �vell as surficial crosion are nntunl proccsses mid should be expectcd on thc slope. It is our opiniou that while there is potential for crosion, soil crccp, and sliallow failures ��•ithin thc loose surficial soils and undocumented fill on the slcep slope, there is not a signiticant potcntial for deep-scated slope f.�ilure under current si�e conditions. Proper sitc drainage and maintenance of Ihe slope, as �ecll as proper vegetation management on the slope, should hclp mainlain current s�ability conditions. 1Vc ha��e provided prelitninary rccomntendations for maintaining slopc s�ability in Ihc scction hclo�v. CONCLUSIONS AND RECODI�IENDATIONS It is our opinion �hal front a gwlechitical s�andpoint �hc sleep cast-f:uing slope bclow the residence and ,;arage is considcred stable o�ith respect �o decp-seated f.�ilures. It is also our opinion, based on our obscrvations and perfonnancc of thc esisting garagc founda�ion, that Q�c gangc sc�back front ihc stccp slapc is adcquate pro��ided �liat the more recent garage addition is removcd and viy espused soils after addition ,emoval are properly protected. R'c recommend that the garage addition be removed as plannccl and cxposed suils be covemcl �eith crosion control mattinS such as hcavy jute ne�ting and dcep-roo�ing vegctation be establisl�ed. "fhe stom� drain pipe associated �vitli �he gange should also bc extended down to thc toc of thc siccp slopc ncar thc crcck. A rock spall dissipatcr pad consisting oC 2- to 4-inch rock spalls should bc placed bclo�� the owlct of thc pipe to adequatcly dissipate the runoff from thc pipe. Ne �hould bc rctaincd to obscn-c tinal conditiuns and providc addilional rccommendations as ncedcd. NELSON GEOTECHNICAL ASSOC/ATES, /NC. ' :, �� \I ;�