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hengeo9.12.04.pdfASSOCIATES 4862746 P.01 LZU & ASSOCIATES, INC. STREET FILE --- Gootechnica l Engmeenng ---- — Engineering Geology S.aflh Science September 12, 2004 Mr. Jim Henricks c/o 13DZ Developers, Inc. 3207 Pacific Avenue Everett, WA 98201 Dear Mr. Henricks: RESUB SEP 12 2005 BUILDING DEPARTMENT CITY OF EDMONDS Subject: Site Stability and Setback Evaluation Renovation of Single -Family Residence 8711 Talbot Road Edmonds, Washington 1:,&A Job No. SA l IS - X43-11OWIT-CO7►1 At your request, we have completed an evaluation: of site stability and building setback from critical areas for the subject residence which is to be renovated. This evaluation is based on a review of the geologic and soil conditions of the site based on a published geologic map and the site conditions observed during our site visit. Presented in this letter are our findings, conclusions and recommendations. SITE CONDITJONS The subject site is a medium -high -bluffs property overlooking Puget Sound in I dmonds• Washington. The site is mostly gently sloped down westward to the crest of a very-sicep mediurn-high bluff bordering the west side of the site. The gently sloped portion of the site is estimated at about 10 to IS percent grade, and the steep bluff bordering the west side of the site is close to 100 percent grade. The steep bluff is considered to be in critical areas. An cxisting single-family residcnce, with a clay -tiled open patio abutting its west sick, is sited over the gently sloped portion of the site. The setbacks ofthe existing house and its patio from the crest of the 19213 Kenlake Place NE Kenmore, WA 98028 Phone (425) 483-9134 Fax (425) 486-2746 h_IU & ASSOCIATES Scptember 12, 2005 Mr. Jiro Merricks L&A Job No. 5AI 1$ Page 2 4862746 P-02 steep bluff were measured to be IKO feet and 79.0 feet, respectively, during our site visit oil September 9, 2005. The unpaved area over the gently sloped portion of the site is mostly covered with lawn grass with occasional tall evergreen trees dotting its fringes, and the sicep bluff is mostly covered with dense shrubs and brush. GEOLOGIC SETTING AND SOIL CONDITIONS The Geologic Ma of the East Edmonds and fart of the West l dtt>"onc�s__Quadranik- Washin�_ gLarr, by James P. Minard, published by U. S. Geological Survey in 1983. was referenced for the geologic and soil conditions at the site. according to this publication. the surficial soil unit at and in the vicinity of the residence site is snapped as Vashon Till (Qvt). The geology of the Puget Lowland hw been modified by the advance and retreat of several glaciers in the past and the subsequent deposits and erosions. The most recent one was the Vashon glacier that retreated from the Puget Lowland about 14,500 years ago. The Vashon till soil unit was deposited directly by glacial ice during the most recent glacial period a,: it advanced over an eroded, irregular surface of older formations and sediments. it is a very dense mixture of unsorted clay, silt, sand, gravel, and scattered cobbles and boulders, often referred to as "hard part". The Vashon till over the top two to three feet is weathered to a medium dense state. and is moderately permeable and compressible. The underlying fresh till is very dense and is practically impervious to stonnwater infiltration. The fresh: till has the strength ()f low-grade concrete and can stand in a steep natural or cut slope for a long period. 11` remains undisturbed and weU-drained.. the fresh till can provide excellent foundation support with littlr settlement expected_ LIU & ASSOCIATES, INC. LIC) & ASSOCIATES 4$62746 P_0:5 r - . September 12, 2005 Mr_ Jim Ilcnricks L&A .lob No. 5A118 Page 3 SITE STABILITY The subject site is most likely underlain by very -dense, fresh till soils of high shear strength at shallow depth. The fresh: till soils have very high resistance against slope failures. It is our opinion that the risk for deep-seated landslides to occur on the site should be. minimal. 'I'lic potential for landslides can be further reduced by: 1) not allowing concentrated storiuwtatcr to be dischrtrged onto the ground within the site or onto the steep bluff bordering. the Nvest side of the site. 2) maintaining a well-established vegetation cover over areas not paved and over the steep bluff'. 3) capturing sto�rmwater runoff over impervious sutfaees, such gas roofs and p:avod driveways with underground roof drain systems and catch basins in the driveways and discharging water into a storrrE sewer or a suitable stortnwate'r disposal facility. BUILDING SETBACK We understand that a new elevatcd wood deck is to be constructed off the west side: of the Irc��.ise. and that the outer foundation supports of the deck will be extended about 14 feet beyond the: we=st side of the house, or about 90 feet froth the crest of the steep bluff. The purpose of building setb=ack from the top or toe or an overly steep portion of a slope is to establish a safe buffo such that if a Slope failure should occur the stability of the structure can be maintained and elttmages to the structure minimized. fused on the geologic and soil conditions of the site as indicated on the above -referenced geologic ii -Lap, it is our opinion that the setback of the deck at 90 tCLI from the crest of the steep bluff will be more than adequate, and that the construction est the deck will not be in critical areas or have any significant impact on the n=earby critical aroas. CONCLUSIONS It is our conclusion that the site would remain stable for the proposed renovation of the Subject residence. It is also our conclusion that the proposed wood deck is sct back sufficiently from tlic MU & ASSOCIATES, INC. LIU & ASSOCIATES 4862746 P.04 September 12, 2005 Mr. J1111 l;-lenricks L&A :fob No. SAI IS Pap ze 4 crest ['the steep bluff and that the construction; of the deck will have little or no impact on twtrhy critical areas. LIMITATIONS This report is prepared for the specific application to the subject residence site and the exclusiVC use by Jim f fenricks, and his associates, consultants and contractors. Our findings. conclusion and recommendations etre preliminary iii nature and are based on the conditions of the site we observcd and the geologic and soil condition indicated on the above -referenced geologic snap. No subsurface exploration was done on the site. CLOSURE We arc pleased to be of service to you. Please call if you have any questions regarding this report or need further consultation. 501yr-J a j 8. J. S. (Julian) Liu, Ph.D., P.1:.. Consulting Geotechnical Enbincer Yours very truly, LI:U & ASSOCIATES. INC. 2 NOV � p 11;A} LI U & ASSOCIATES., INC.