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Home My WebLink About921094025 Geotech Assessmenti M ~ ~ ~ ~`~ 4 GEOTECHNICAL REPORT Prepared For Mary Baffaro Se tember 7, 2006 p For the Property Described as ~~~ ax # 921094025 Lip Lip Lane, Marrowstone Island Section 9, Town 'hip 29 North, Range 1 East, W.I~. Jefferson County, Washington Prepared by NTI Engineering and Surveying 717 S. Peabody Street Port Angeles, Washington 98362 Phone 360-4'~2-8491 Fax 360-452-8498 We~ Site www.nti4u.com E-mail info@nti4u.com ~,~~~~~~1Rc~~E~va~- . ,.', } NT/ JLS GROUP, INC. NORTHWESTERN TI A JLS GROUP 717 SOUTH PEABODY STREET, Engineers Land Sun Construction Inspection (360) 452-8491 FAX 452-8498 www.r (TORIES, INC. MPANY DRT ANGELES, WA 98382 yors Geologists Materials Testing tu.com E-Mail: info~nti4u.com ~otechnical Report -ax # 921094025 \~ ~~ ~p~11$~ ~~~~V ~~~ ,S~~t~~~~~~ 1 September 7, 2006 Mary Baffaro 6528 148th Place SW Edmonds, WA 98026 Subject Geotechnical Report fr Tax # 921094025 located in Section 9, Township 29 North, Range 1 Ea t, W.M., Jefferson County, WA Dear Mrs. Baffaro: Background At your request, NTI Engineering ar inspection at the above referenced I inspection was to examine the marii to provide an opinion regarding the recommendations in regards to the residence. It is our understanding th the location of an existing chicken c~ from the edge of the bluff. Site Description d Surveying (NTI) conducted a bluff stability ocation on August 10,2006. The purpose of this ie bluff at the subject site by visual means in order ~elative stability of the bluff and make proposed future construction of a single family at you plan to construct a home on the property in pop (Photo 1), which is approximately 100' back The subject waterfront property is lo' ated just south of 121 Lip Lip Lane off of Moen Road on Marrowstone Island (Figur s 1, 2, & 3). The property overlooks Puget Sound to the east and is bounded on then rth and south by residential property. The upland portion of the property i~' roughly flat and slopes gradually to the east towards the top of the bluff. There is a slight depression northwest of the chicken coop that had greener grass and horsetail, ferns growing in it which suggests that runoff collects here. The property is partiall', cleared, and vegetation consists of young to 1 i~ iT2!F~°~~~t~~F2D JAN 18 2007 mature native trees and shrubs in t e wooded areas with grass in the I +~' ~ i is a thick hedge of salal along the t p of the bluff. There is a rough be~ ~ ~~~ the south side of the property. The bluff at the property is approxi ' ately 70 feet high (Photo 2). The upper 1/3 of the bluff has a slope angle of approxim' tely 60° to 70°, the mid bluff slopes at about 40°, and the lower 1/3 of the bluff varieslin slope from about 40° to near vertical (Photo 3). There have been recent slides on t ' e bluff. The bluff is predominantly devoid of vegetation except for patches of gr ~'ss and a few small trees. There were occasional small seeps on the bluff face: Ther 'are outcrops of seaweed covered sandstone bedrock on the beach (Photo 4). Site Geology The Washington State Department and upper bluff soils as Vashon lod outwash (Qva) (Figure 4). North of 1 and mudstone (Tg). The till is descr boulder to sand size particles with s excellent for foundation stability, go~ steep natural and/or cut slopes for I of well sorted, well stratified sandy ~ predominates, which is the case at '~ mudstone is described as interbedd stability of the upland as Stable and ~f Ecology's Coastal Zone Atlas maps the upland ment till (Qvt1), the lower bluff as Vashon advance ~e property, the beach is mapped as Tertiary shale red as consisting mostly of a compact mixture of •me silt and clay. The Atlas lists this soil as d for seismic stability, and. says that that it stands in ng periods. The advance outwash typically consists ~bble to cobble size gravel. In some places, sand ~e subject property. The Tertiary shale and ~d siltstone and sandstone. The Atlas maps the e bluff as Unstable -recent slide. The Department of Ecology's "Geol gy and Ground-Water Resources of Eastern Jefferson County, Washington" map'. the soils in the area of the subject property essentially the same as the. Coastal', one Atlas. According to the Soil Survey of Jeff 'rson County Area, Washington (United States Department of Agriculture, 1975), the property is in an area mapped as Indianola and Cassolary soils derived from glacial ' nd marine sediments. These soils are predominantly composed of silty sa 'd, with a thin clay layer about 2' below the surface in the Cassolary soil. The Soil Surve descriptions pertain to the upper 5' of soil only. Visual observations of the soil the above descriptions. Mechanics of Bluff Recession There are many forms of bluff reees: Washington. Two. common processE action, and the sloughing of upper bl season. Both of these processes seE on the bluff face are generally consistent with >n that occur in the coastal regions of northwest are the erosion of the toe of the bluff by wave f soils due to saturation of the soil during the rainy ~ to be occurring at the subject property. 2 r ~~~~ ~~ ~~ ~~ Icy ~, JAN ~. 8 2007 When waves attack the toe of an ui away. Eventually, this erosion will c longer support itself at such a steeK material at the toe of the bluff. This of the bluff to a more stable angle, ~ttttfiJUN~UUNfYDCD protected bluff, the lower bluff soils are eroded versteepen the bluff to a point where the soil can no angle. Then the bluff soils will slough off, depositing will have the effect of temporarily reducing the angle ind then the whole process will start over again. Many of the landslides that occur in' our region happen in the winter or spring when the ground is saturated with water, and especially after heavy rainfall events. When the soil becomes saturated, there is a decr Vase in the cohesion between the soil grains and an increase in the pore-water pressure This condition can trigger landslides and debris flows on slopes. Often, there will bel an impermeable soil layer part way down the bluff, which prevents the downward migr 'tion of groundwater and causes the water to migrate laterally, exiting the bluff ab' ve the impermeable layer. Surface runoff flowing down the face of the bluff can also 'ause erosion and damage vegetation on the bluff. For this reason, it is important to co trol on-site drainage andrunoff in order to minimize negative impacts to the bluff. It is al o important to maintain vegetation on the bluff face, where possible, in order to reduce erosion of the bluff soils. Conclusions and Recommendatidns The bluff at the subject property is ajctively being eroded as evidenced by the recent sliding on the bluff face, and future tiding should be expected. Typically, bluff erosion and sliding are more common in the' winter and spring due to increased rainfall, higher tides and winter storms. It is imposs ble to predict when a slide will occur or how much the bluff will recede. Average rates f bluff recession for this area have been suggested to be on the order of 6" to 8" per yeah. However, several feet of bluff could be lost during one event. Based upon our investigation, and tl approximately 8" per year, we recon bluff be at least the 1:1 setback spec Management Master Program, whic is accurate (and it may not be), then bluff might recede 40', and be within accurately predict- the bluff erosion r for long term asset planning. The following recommendations s It will be necessary to mai surface runoff. Any bare a should be revegetated if p that requires little or no irri the enclosed publications that vegetation establishm possible. e possible average rate of recession of mend. that the building setback from the top of the ified in the. Jefferson County Shoreline ~ in this case is 70'. Assuming that the 8"/year rate in a typical 60 year economic life of a home, the 30' of the home. Since there is no way to ite, an increased setback may be more beneficial Id be considered with regards to the proposal: yin ground cover in order to reduce erosion from as that develop, on the bluff or on the upland, sible. Native deep-rooted low growing vegetation tion would be the most beneficial. Please consult further information. It should be noted however ~t on the steep eroding bluff soils may not be 3 ~~~ 1~~~ uau ~,r i~ 1L Y J ~~ 1 ~ 2~~7 ~~f~k~~l~~~~UUNjYUCD 2. Vegetation on the bluff face helps remove water from tl in as natural state as possi thinning and pruning shoul~ to the soil and root zone ar vegetation. Trees on the bl falling over should be eval~ does fall over, the wrenchir the bluff and adjacent vegE in place so that the root m~ tree expert could provide v. arise. provides stabilization to the bluff face soils and soil. Existing established vegetation should be left ale. As far as pruning for a better view, minor be done in such a way that minimizes disturbance 1 that insures the continued health of the iff or along the top of the bluff that are in danger of ~ted for possible removal. Because if a large tree ~ out of the large root mass can cause damage to ation. if trees are removed, the trunks should be left ~s can continue to provide stabilization to the soil. A luable consultation in this matter should the need 3. Maintenance/repairs to the' each access. path would probably not significantly increase bluff stability as to, g as they were performed to the normal standards of care associated with thislenvironment. 4. Tree limbs, lawn clippings, these piles have a tendenc turn increases the erosion unnecessary weight to the 5. Heavy irrigation or other a to the soil should be avoid tc. should not be thrown over the bluff because to damage/kill the underlying vegetation which in rtential of the bluff soils. These piles also add uff soils, especially when saturated with water. ities that would contribute large quantities of water 6. Surface water should not b ' allowed to flow over the face of the bluff as an uncontrolled or concentrate', flow and cause erosion of the bluff face. This can be controlled with vegetatio and using berms or swales to direct runoff to a drainage system. Please se the attached DOE publications for more information on this subject. 7. Surface runoff from hard su aces such as roofs, driveways, walkways and patios should be controlled ' nd routed to a drainage control system such that surface water discharge to djacent properties does not exceed predevelopment conditions.'i 8. Silt fences or other sediment control devices may be needed during construction such that sedi entation to adjacent properties does not significantly exceed predev ' lopment conditions. 9. Drainage control devices sh~uld be maintained in good working order and inspected at least once a year. 10. NTI can develop an engin this project if desired. drainage, sediment and erosion control plan for 4 ~~ ~~~~~~ JAN 1 ~ 2QD7 11. The septic drainfield shout recommended building set For further information please revie~ this report) published by the Washir "Slope Stabilization and Erosion Co Guide for Puget Sound Bluff Proper Coastal Bluffs". These. publications http://www.ecy.wa.govlbiblio/sea. htr website also contains additional usE development; this reference is high) EXPIRES 12/3072006 Limitations also be located away from the bluff~~~~tb~tl~~~~t.Fl~+~~~ Eck line. the three publications (included with the original of lton State Department of Ecology (DOE) entitled: trot Using Vegetation", "Vegetation Management: A Owners" and "Surface Water and Groundwater on ~n also be viewed on the DOE website at: I under the 1993 and 1994 year heading. The DOE ul information regarding slope stability and site recommended. This report has been prepared. for y ur exclusive use in conjunction with the above referenced project. The report has riot been prepared for use by others or for other locations. It may be used for other p~,urposes only with the expressed written permission of the Engineer. Within the limits of scope, schedule nd budget, this report was prepared in general accordance with accepted professio al engineering and geological principles and practices in this or similar localities '.t the time the report was prepared. No other warranty, expressed or implied, is m de as to the conclusions and professional advice included in this report. The observations, conclusions and i based on our visual observations of laboratory tests were performed. So between test holes and/or surface o conditions at the site have changed report, we should be contacted and make modifications to our report if n Sincerely, NTI Engineering and .Surveying, li ~` ~~ Robert A. Leach, P.E., MBA Principal Engineer ~~ ~~ ~~- Bill Payton, L.E.G. Engineering Geologist G: \Ge n\Bil I\Reports\BAFM0601: doc 'commendations presented in this report were he subject property at the time of our site visit; no and geologic conditions can vary significantly tcrops. If there is a substantial lapse of time, Ir appear different than those described in this stained to evaluate the changed conditions and ary 5 ~O ~ pE uwSy~ ~y ~Qg °~ ~ ycr h ' °y i " , ,... ; "O ~PF 13772 RO ~ ~ /~ ~~.cFS~S TER G\a~~c. q j~l / 1.. S~OAIAL EN / / ` ~'~~ fa ~~ ~~ ~. ~,,~ ~i ~~~~~engruN+t+q,~ ~ ~~ ~) 11~~~~.. William C. Payton Jr. l~~F~~"~dYl~~ JAN 18 ~0~ JEFFEBSUN~UUN~VOC~ Appendix ~~ ~aNla2~~. .~EFfE~~oN~~uN~VOGD ~~~1~~~yliell V 'JAN 182007 JEfftHJUNCUUNIYUCII JAN 18 2U~7 ~ ~FFFHSI-~ ~:IIIINIY 0 CD i ~ .~ ~~,,~~~~a~~~1~1I- ~~~~S~z JEtttNJUN~UUN(YOCD L I • . 1 1~~4 ~~lCAa~9~ Ii Y 1 ~aN i a ~uut JEftEHSUN~;1111N~OCD o i o ~~ i~~Fn~~~~~p~~ JAN 18 ~0~ ttFtH~UN~;~UN1V~ICD ~,, r ~ ~ ~ ~ ,, ..,,,: ~ ~... .i ~e ~; ~ ~ ~~a ~ arc' ~ "?~ r ,, ,~"~s ~, }N F s `' ~p 4 Yya ~~ ~ ~,.,~€ ~~ ~,' 32 S t~S P~ S.'ra a, l,` ). ~ ~ .....~ .7C"~ x~c, . i~~~~'~~~`1~1~ JAN 18 2UU7 ~lttttli~UN~UUNI~ UCD .. r " 1 • ~~~, ~^ ~ ~p~ 1 y~V~~`1~~0