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Home My WebLink About976500009 Geotech AssessmentGEOTECHNICAL REPORT Prepared For SeaHome Services, Inc. LOG ~T~~ December 14, 2005 ~~ ~. For the Property Described as :~~~g- Of.~--- 7701 Oak Bay Road Tax # 976500009 Section 4, Township 28 North, Range 1 East, W.M. Jefferson County, Washington Prepared by NTI Engineering and Surveying 717 S. Peabody Street Q Port Angeles,. Washington 98362 Phone 360-452-8491 Fax 360-452-849 ; ~ p E~ 2 2 2005 Web Site www.nti4u.com ; '~ E-mail info@nti4u.com ~ -- ------- '~ -~~ NORTHWESTERN TERRITORIES,. INC. ~~ A JLS GROUP COMPANY i~ ~~~ ~ 717 SOUTH PE,ABODY STREET, PORT ANGELES, WA 98362 Engineers Land Surveyors Geologists Construction Inspection Materials Testing ~~~ (360) 452-8491 FAX 452-8498 www nti4u.com E-Mail: info@nti4u.com ' :JLS. GROUP, FNC. , l~,.o Geotechnical Report } 3 ; , ! ; ~ Tax # 976500009 f I ` ~ ! !: DEC 2 2 2005 '~' ~` December 14, 2005 ~._. __ __ ~ _~_. SeaHome Services, Inc. ! Attn: Greg Barron 7425 Thorndyk~e Rd. ~~ ~ Quilcene., WA98376 Subject: Geotechriical Report for Tax # 976500009 located in Section 4, Township 28 North, Range 1 East, W.M., Jefferson County, WA Qear Mr. Barron: Back round g At your request, Bill Payton, Engineering Geologist with NTI Engineering and Surveying (NTI) conducted a bluffstability inspection at the above referenced location on November 15, 2005. The purpose of this inspection was to examine the marine bluff at the subject site by visual means and provide an opinion regarding the relative impact that a proposed beach access stairway would have on the stability of the bluff. Concurrent with this inspection is an engineered drainage, sediment and erosion control plan that is being performed by David Hanna, P.E., also of'NTI. It is our understanding that you desire to construct a stair tower behind the ordinary high water mark with abridge leading from the top of the bluff to the tower as shown in Figure 1. We further i '_ understand Ghat the stair system will be founded on piers and thaf the toe of the bluff will not be excavated.out in order to construct the stairs. And further, that bluff disturbance will be limited to the immediate vicinity of the stair location and will not encroach onto adjacent properties, and that disturbed. areas bn'fhe bluff will be restored upon completion of the stairs. Site Description. ' The sub~eGt waterfront propert is located at 7701 Oak Bay Road, north of Port Ludlow. The Y property overlooks-Puget Sound to the east and is bounded on the north by a gully and on the ' south by residential property (Figures 2, 3 and 4). .Existing developments to the property include a gravel driveway, cabin (Photo 1), drainage features, and a septic system. Currently the septic drainfield is located near the top of the bluff ' but we understand that the drainfield will be moved to the west side of the cabin, away from the bluff. We also understand that the area along the top of the bluff will be revegetated with natural vegetated as opposed to the existing lawn grass. 1 i ' The upland portion of,the property is predominantly open and vegetated with grass, with some frees and shrubs: Some of the upland trees have curved trunks, and what appeared to be thin separations in the grass between the cabin and bluff were noticed. The property, especially ' along the south side was wet. The topography of the upland slopes northeast and east toward the bluff. t appears that the property between the cabin and bluff has been cut on the south side and filled; on the north side to create a more level yard. ~~ ~ _ The blufi~~at the property is about 35 to 40 feet high with an average slope angle of about 38 to 40 degrees with some short steeper sections. There is a rough path leading down the bluff to the. beach. The bluff is mostly vegetated with young alders and brush. Some of the trees on the bluff have curved trunks, indicating that shallow down slope creep of the surface soils is occurring, and there was a tree fallen down on the beach. The steeper sections of the bluff are ' void of vegetation. The toe of the bluff is being undercut from wave action at high tides and during 5torrns. There is the remnant of a stairway on the bluff and there is an old concrete Iarlding with wooden piers/pilings at the base of the bluff. There is also a cut in the upper bluff fifiat maybe associated with the old stairway. Groundwater seeps were noticed on the bluff face about 12' down from the top. Site Geology ~~ Tha Washin ~ ton State De artment of Ecolo 's Coastal Zone Atlas ma s the soils on the east 9 p 9Y P Side of the property as Vashon lodgment till (Qvt1), and the soils on the west side of the ' property as Undifferentiated stratified sediments older than Vashon lodgement till (Qpf). The till soil is described as consisting mostly a compact mixture of boulder to sand size particles with some silf and clay. The Atlas lists this soil as excellent for foundation stability, good for seismic Y' stability,"-and says that that it stands in steep natural and/or cut slopes for long periods. The undifferentiated soil is described<as consisting mainly of sand and gravel, but in some areas contains silt, clay, peat, and possibly till. Environments of deposition of this unit include glacial ' outwash, glacial lake deposits, and interglacial alluvium and lake deposits. The Atlas maps the stability of the bluff in the vicinity of the property as Unstable recent slide and as Stable. The upland is mapped predominantly as Intermediate (See Appendix). ' The Department of Ecology's "Geology and Ground-Water Resources of Eastern Jefferson - Cbunty,Wash~'trigtan" maps the soils in the area of the subject property essentially the same as the Coastal Zone Atlas. ' Accordin to the Soil Surve of Jefferson Count Area Washin ton United States De artment g Y Y 9 ( P of Agriculture, 1975), the subject property is in an area mapped as the Swantown gravelly loam ' (SuB),and the Cassolary sahdy-loam (CfD) (See Appendix). The Swantown soil formed in :glacial till and is composed of silty sand or silty gravel. There is a very slowly permeable cemented layer at a depth of '16 to 20 inches. The Cassolary soil formed in reworked glacial and ~~~ ~ ~ marine sediments and is composed of stratified silty sand with a layer of clay. -Visual observations made in drain field test pits at the site (Photo 2), and from surface soils on ' the bluff face revealed gravelly sand deposits. Conclusions and Recommendations ~~ Based upon`,our understanding of the project and our site investigation, w ~_,.u beach access stairs will have minimal impact on the stability of the bluff. °N~1~~ processes of bluff retreat are occurring at the subject property and periodic" sla4 ,~ - '' ,; 2 tt~r~,tt~ral~," ~`~~ ~ ~~ ~r5g"ofi~ e u I ~ , , ~. DFC 2 2 2DQ5 ~`~:~ ~~ ." should be expected to continue which may necessitate future maintenance/repair of the stair system. As mentioned earlier, drainage is an issue at the property and is probably contributing to the bluff retreat process. Thus, anything that can be done to reduce the amount of water reaching the bluff should be beneficial to bluff stability. Controlling surface water and directing it away from the bluff as well as curtain drains to intercept shallow groundwater are possibly two ways to achieve this .goal. A more involved approach that could deal with deeper groundwater would be, o install ~ series of wells across the yard at some distance back from the edge of the bluff at a depth hat would intercept groundwater and to continuously pump the water out. Specific ' drainage recommendations will be in the drainage, sediment and erosion control plan being completed for this property, also by NTI. ' The following recommendations should also be considered with regards to the proposal: 1. ' -1t will be necessary to maintain ground cover in order to reduce erosion from surface ' runoff.. Any bare areas that develop, on the- bluff or on the upland, should be revegetated. Native deep-rooted vegetation that requires little or no irrigation would be the most beneficial. Please consult the enclosed publications for further information. :' 2. Vegetation on the bluff face provides stabilization to the bluff face soils and helps ;remove water from the soi-. Existing established vegetation should be left in as natural 'state as possible. Once construction of the stair system is completed, any areas that were disturbed should be revegetated as needed. As far as pruning for a better view, minor thinning and pruning should be done in such a way that minimizes disturbance `to the soil and root zone and that insures the continued health of the vegetation.. 3. Tree limbs, lawn clippings, etc. should not be thrown over the bluff because these piles --have a tendency to damage/kill the underlying vegetation which in turn increases the erosion potential of the bluff soils. ~~.~ ~. Heavy irrigation or other activities that would contribute large quantities of water to the ' soil should be avoided. 5: Surface runoff from hard surfaces such as roofs, driveways, walkways and patios should be controlled and routed to a drainage control device such that surface water < .:discharge to,adjacent properties does not significantly exceed predevelopment condtions.,We recommend that on site infiltration of this water not be considered for this site, This issue, as well as on site surface and groundwater derived from off site ' sources.(i.e: not from roof's, etc.) will be addressed in the above mentioned drainage, sediment and erosion control plan being completed for this property. ' ;: 6. Silt fences or other sediment control devices may be needed during construction such 'that sedimentation to adjacent properties does not significantly exceed predevelopment conditions. ' 7. :Drainage control devices should be maintained in good working order and inspected at `least once a year. ~. ~-- ' Fot' further information please review the three publications (included .itv~~~ .ei,on~rn ~l of~~h~ ~~ ~'~ >, report) published by the Washington State Department of Ecology (DOE9_e; .t+~leew `s~bfre-~-~~- St~bilization an~i_ Erosion Control Using Vegetation", "Vegetation Management: A Guide for ~ , ! ~' ~~ ~ ~ ~~~ ~ 2 z~~o5 ~ ~;~ 3 ___ Puget Sound Bluff Property-Owners" and "Surface Water and Groundwater on Coastal Bluffs". These publications can also `be viewed on the DOE website at: httpalwww.ecYwa.govlbibiiolseahtml under the 1993 and 1994 year heading. The DOE website also contains additional useful information regarding slope stability and site development; this ' - reference is highly recommended. Limitatrons This re ort has,~been re ared for our exclusive use in con'unction with the above referenced p P p Y J project. The report has not been prepared for use by others or for other locations. It may be used forother purposes only with the expressed written permission of the Engineer. Within the limits of scope, schedule and budget, this report was prepared in general accordance with accepted professional engineering and geological principles and practices in this or similar localities'at the time the report was prepared. No other warranty, expressed or implied, is made as to the conclusions and professional advice included in this report. The observations, conclusions and recommendations presented in this report were based on ' our visuaF 6bservations of the subject property at the time of our site visit; no laboratory tests were performed. Soil and geologic conditions can vary significantly between test holes and/or surface putcrops. If there is a substantial lapse of time, conditions at the site have changed or ' appear different than, those described in this report, we should be contacted and retained to evaluate 'the changed:°conditions and make modifications to our report if necessary. ~~ Sir7cerely, ~ . R~ A ~ NORTHWESTERN TERRITORIES, INC. ~~~~~~ H~ti ~ti ~~ ~ ~ ~ ~~ ~ ~ ~ ~ ~ ~~ ~~ ~~ ~~~ Robert A. Leach, P.E., MBA ~o,~ ~FCis~ER`~°- ~~``~ !Z- l3 -OS Principal Engineer FSS~ONAL ENG\ ' - EXPIRES 12/30/2006 Bill Payton,~~.E.G. Engineering Geologist ~~~ ~~ ~~ _ G:\Gen\Bill\Reports\SEAH0501.b1uff stabitity.4(28-1 E).Port Ludlow.doc ~~ , ~", ~+gh,G ~ ~ a-13-o5 "~-~, 191 ~~ ~~ ~ _ _. .. ~-~- ~~8~,. ~ao~ i ~ E~- ~`~ r_ ~! ~ ' ~' William G. Payton ,,ir. '_ I, ' '~ '~ ~, ~, r~ ~~ Expires 11/06/06 .~ ', - ~ .< 4 Appendix t,- ;~ { of +~~`~! DEC 2 2 2005 ~E~F, i ~o ~i o ~~'+r- z _.=: ~~ ,~ ~ ~ ~z :~_ lr ~L r~ u~ ~ ° ~r ~ -~ ~ y 3 Cb z -zj [ ~ ~`i-y M o z ~~~ ~ ~ rn j(~ D~C7 -i ~ ~ Tl ~ 3 + f N A o ~ N -~ ~ -b1 f r= ~ ~ D ~ rr~ ~o ~~ rn 7U _ vx ~ fir rn~ ~ N j :~ !~ !~ tl (~ ~~ z~ ~~ o r -~ ~ p ~ ~..~ ~~ ~ ~~~~p~ ~ ~F DEC 2 2 2005 ..~ r -- Figure 1 Provided by SeaHome Services 1 ~ Q P ~ ~~~ DEC 2 2 2005 ~ ~`~. E r ~.. ~~ ii ~~~ i~ u u ,~~t~ ~I~~'~ ~~. ~~ DEC 2 2 2005 ~ .,~ .: ~~ ~~ ~fs~C~9d~ ~I~DEC 22 2005 ~"', ~_~ _I i `" ~ ~ ..~ ' ~~~ DEC 2 2 2005 ~, ~~ k ...- ~- i y. Geology ~~ , ~5:,~; ,~ -~:- T '~K+' Y, ~ ~ s - 4~_. }~ ~~ Q~3 ' , 4` C3;Qie Point 4 ~,. .` ' g' ._ ~ l~ ~ CV ~i / `~. f liE ~ ~ - ~ r1 ~~ f\ f ~r ~},I ~r r,: - . ~ .i'4`~ i - _._ _ } 1.-. - ~~ ^~ ., r t Qai ~ 7fi~ l ~ f+ - Tc~ r .. of ,r af-~ ~~ ~~r. l.~ 4~Fi; t ~4 ({ 13 cr ~ = _ ,x~ ~ ~ !~ !! k C // (. 4 1~ ~ S }j e >, DEC 2 ~ 2005 ~ Qvr2 ,F ~~.. i Approximate fP.~rc i location Of subject --*-- property. JQpd Coastal Zone Atlas Geologic Map ,F Slope Stability ,~~_ ~r#`E ~~ '1~ '.. ,~w' ~S.y41 ~~~~ h ~6 `. S- ~ '" h 4 , ~, b ~ ty'ky,Li l L { i'+ ~~~y R4 ~~ ';-` y~~ ~ ~ _ _IF -.~ ~' ~/ r'.'~- 3 A++'Y 1 '4 111' 'b ~~ ~ b dr.«.."'~Y-r ~ s i ti _ ~y /~~d ~ ~- Y : T~f~S~ A Z y }' - ` r / a~ - ~, r r. ~ ~ : ~ ~ t? } }! L ..-r„~.., ~ ~ ~ ~~, -~.~~~' F,~~~(~. ~_f ~ ~.,: M 4' t 1 ~~ `~t~~s ~~~~~~~t~ ~ ~ ti b ~ `\' ~ s ~ ~ '+ '''tt ~i ~' ~ `'xe, ~V~.: ~# -at n . ~~ ,, w -. , ~, ~` , ~~~ ~'~ ~' t y ~' .,~ ~~ '~ \ '~ ~ _5 t~'~ ;~~"ir,'i ~". ,~ ~~ { ~ ~ ~`T ~ (~'at~i I ~ ~~' ~ ~'ti "~ t ~ ' ~ ~~~; ~~ •r° ~'' ~~~ 1 ~' Coastal Zone Atlas Slope Stability Map ~ ~ ~ ~ - f ~.' ~: ~~~- s!, :~, 7 ,~8ie Point ~y~, -, ~ f f~ ~~ ~f~ - ^-xs t ,~ r~ s y~ ~ Y ~` ~. r~ I t~.~ (~~,..h F. ~ ~ 3 t } ~ .~ I s ~`~~~., a ~,~ -7 ~~ r . -~ ~,-. ti' }~ w ;~.~ i 'rM~a ,,. ~: ~~ t, L~~f -U rs Approximate location of subject ~~ U rs ~ ~ ~ ~ ~ V m,- ,i 4 ~~ Urs ~~~~~ ~~ ~} DEC.. 2 2 2005 ~ _~ ~~ I ~ ~k z ,... ii i~ ii i~ i~ -- ~ ~~ ~I ~~ ~ t _~ c~ w j,. ~` ,.~ ~ ~ r~ } ~ ~ ' ~ ~ . r ,sic P .~ ?~ ;, ~ ~ , sus - -x ~ ~ ~ ~ ~ ~~ ~~ ~ ~ ~ ~ ~ ~ ~ . - ~~ - ~la,~~"oinY USDA Soii Survey Map ~ ~ ,~- ., ~ _ ,.. f. ii