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Home My WebLink About990600152 Geotech Assessment ~j NT' NTI ENGINEERING & SURVEYING 717 SOUTH PEABODY STREET, PORT ANGELES, WA 98362 Engineers. Land Surveyors. Geologists Construction Inspection. Materials Testing (360) 452-8491 1-800-654-5545 FAX 452-8498 E-Mail: infci@nti4u.com www.nti4u.com Mr. Jim Cannon 641 Highland Drive Pt. Ludlow, WA. 98365 July 12, 2007 Subject: Lot54 Port Ludlow Division # 2 --- Tax Parcel 990600152 Clarification of Setback Recommendation FAX URGENTLY 360 4372244 Mail Original Dear Mr. Cannon, NT! Engineering and the undersignedge()technica1 engineer completed asetback and bluff stability analysis on the subj ect parcel in June of 2007. In the report, we recommended a setback of40 feet west from the south-easterly survey monUment on the southerly property line. That monument was set byNTI Engineering in June of2007 and it is marked "Roorda 36825." The monument is actually a point online rather than a "property comer", the inaccurate description used in the original report. The recommended foundation setback line isthat line lying 40 feet west of the monument that is also approximately parallel to the lie of the bluff. .The average lie of the bluff is approximately parallel to the westJine ofthe lot whose endpoints were marked in the field by NT!'. This setback is approximately the same as observed by the adjoining' houses on the north and south. I hope this letter clarifies the recommended setback. Sincerely yours, S~5" ~i ~ \ ','-'i. Steve S. Luxton MSc. PE Professional Engineer [j~9: 3l!3Iqg .J . Geotechnical Review of Lot 54, Port Ludlow #2 Marine Bluff Setback Analysis In June of2007, Steve S. Luxton PE, a geotechnical engineer, studied the site conditions at the following parcel ofland in Jefferson County: Parcel Tax Number 990600152 Port Ludlow Division Number 2 Lot 54 on Montgomery Lane at Port Ludlow in Section 9 of Township 28 North, Range 1 East, WWM At the time of the investigation in June of 2007, the single family residential lot was pending purchase by Jim Cannon who plans to build a house there. The parcel lies at the top of an approximately 60-foot high marine bluff offering views to the east across Port Ludlow Bay and Hood Canal. This report provides insight into the stability of the bluff, a recommended setback and recommendations for an undisturbed natural vegetation buffer. 1.0 Geologic and Structural Setting The Port Ludlow area has been the site of several glacial advances and recessions during the past 25,000 years. The region is underlain by impervious marine siltstone and sandstones that are of Eocene age. These materials were observed in outcrops along the beach below the subject parcel at low tide. During the most recent glacial epoch, advancing glacial ice left deposits of consolidated till over the underlying siltstone. The till is a moderately cemented mixture of rock, sand and silt that has been over-ridden by glacial ice and hence, consolidated. The thickness of the consolidated till member is variable along the bluff in the vicinity of Port Ludlow. At Lot 54 the till extends to about 40 feet above sea level with the uppermost 20 or so feet being a mixture of till and glacially consolidated gravelly sand outwash. 2.0 Unstable Slides Areas Are Present in the Region But Do Not Affect the Parcel About 600 feet south of the site and at another site on the north the till is absent. Ground water that cannot percolate through the underlying siltstone, flows in a near-horizontal direction to a series of springs along the beach in those areas. Above these spring zones the slopes are unstable and the toe ofthe marine bluff has been revetted locally with large basalt boulders. A shallow quick-sand occurs in some areas where the ground water rises through beach sands as it flows across the underlying siltstone. These unstable areas may have been mapped as landslide hazard areas. I \ ( ~ ( \ ( \ ( I l I [ I ( I ( I ( ( I [ I ( I [ I ( I [ I 3.0 Erosion Mechanisms and Geotechnical Indicators In general, the till forming the lower portion of the bluff at the Cannon Prospect is unlikely to form rotation slides due to its high internal shear strength. Instead the material erodes by thin slab failures with limited volume of debris. A recent slide of that type was noted on the parcel that adjoins the subject parcel on the south. Evidence from a nearby portion of the bluff and the composition of the upper soils suggests that glacial drift forming the top 20 feet of the bluff will fail in sudden slides that will normally not exceed 15 to 20 feet in width. Because the general rate of shoreline erosion at this site is slow to moderate, such slides may occur infrequently on the order of once every 50 years or so. Once a slide occurs, it is quite improbable for another slide to occur at the same point until the erosion of the lateral area progresses for a long period. The underlying till unit is quite resistant to shoreline marine erosion and it controls the general rate of recession which is limited to a few inches in a decade. These observations suggest that the "maximum probable slide" condition on Lot 54 will be limited to about 20 feet during the economic life of the proposed residence at the parcel. ~ additional setback of35 feet from the line of that slide cusp increases the desirable setback to ~5 feet from the rim of the bluff as shown in Figure 1. 4.0 Conclusions and Recommendations . Setback The recommended setback line is 40 feet west of the east property line that is approximately parallel to the line of the bluff. This setback allows a reasonable factor of safety for slides given the erosional mechanisms operating on the bluff below. The setback geometry provides about 55 feet oftotal setback to the foundation exterior line of the residence foundation. Please see Figure 1. . Undisturbed Buffer Red Alder trees and brush that clad the bluff should remain undisturbed so as to reduce the rate of erosion. If trees must be removed from the view space, top them rather than cutting them down at the base. The undisturbed buffer should include at least 20 feet of the 40 foot setback from the line passing through the property comer described above. -That line will result in an undisturbed buffer whose total width is about 35 feet from the rim of the buff as it was observed in June of 2007. 2 Due to the observation that the formerly mapped slide area does not extend into this property, no other slide zone buffer is required here. . Decks and Deck Footings Decks that extend from the permanent residence toward the bluff should not be built into the buffer. As discussed at the site, the ideal deck footings will extend down into augered holes that are 4 feet in depth. I a-inch diameter concrete piers that are cast in place in boreholes of that depth will readily support deck loads of 2000 pounds per pier. Bored piers tend to remain in place and resist soil creep. 4.0 Limitations of This Study and Report The recommendations and conclusions of this report apply only to the subject property and were prepared for Mr. Jim Cannon. As such they may not be used by others without his express permISSIOn. This report and the observations herein are based upon observation of the exposed features of the investigated site. The assessment did not include borings, test pits, or detailed measurements over time. Unknown and unexpected conditions might occur in the subsurface and they could affect the conclusions and recommendations made herein. This document and the work done to support it was completed in a diligent manner consistent with the practice of professional engineering and the principles of geologic science. No other warranty, neither expressed nor implied, is provided herewith. Sincerely, 'I . 5G..v-.. 5. G:\Gen\Steve L\Jim Cannon.doc 3 I [ ~ \ \ \ l \ r r GEOTECHNICAL REVIEW OF LOT 54, PORT LUDLOW #2 MARINE BLUFF SETBACKANALYSIS Prepared For Mr. Jim Cannon ! I \ t. t ( ( \ l 1 I I 1 Prepared by NTI Engineering and Land Surveying 717 Peabody Street Port Angeles, Washington 98362 (360) 452 8491 June 2007 4 ( \ ~ \ ( ( \ ! I l I I I l {u I I ( I l { I ( \ '" '" ~ w I z :J w f- W -' a. I ::a 0 u w I J: f- I r / 15 '"""14 UNP/fJ""IJK8t!!-t) '()ff~K '::i1i.l 7QrN- ~r,sJACk .fkoP~R'l'Y LINe #0' co/ll601-1 Pj471!.1> ,A;w~ Ii LJ... ------ -- -- ~ ~ .. ' . . . Z .. ;;e. CCIU;~~Il:>;+"'e'/) .. ~ .. GlACIAl- n~l ..... t::Asr b .' .. .' ': '1- .. -~, _... ~~.,.",'- .', ._~ ,- '"-,-'---":"-':. .,.- ---- '( .. .' ~ ... 1 ~.., _?~ .. Eac.E'..ve: 5/L.7STcJl/.e &SeA LEVEL. (? H/t;II riPE MARINE BLUFf" GeOLOGIC '5EC7iON S <7 T 2t!/IJ R Ie. DATE: 7- 0"$ -(;;'7 DESIGNED BY: 57.EvE ?, J..ux-rOA/ Fe PROJECT: t..or 50/ ?r /"UPMAJ #:z. FOR: ~,::::rlM C,AN'N"N SHT: I OF J ~ NT' NORTHWESTERN TERRITORIES, INC. Engineers. Land Surveyors. Planners Construction Coordination. Materials Testing 717 SOUTH PEABODY. PORT ANGELES, WASHINGTON 98362 · (360) 452-8491 FIGuRe 2007 Cannon Topographic Survey of Lot 54, Area 1, PortLudlowNo; 2 as recordedin Volume 5 of Plats, Pages 41-48, located in Section 9, Township 28 North, Range 1 ~ast,WM., Jefferson County, Washington 93.6 IT YELLOW SURVEY CAP STAMPED CARMAN 41.47 "'4 ~ 0\ "'4 I \ \ I \ I r>1\ gl ~ 01- -"1 tn\ \JI ~I ~I I \ I J I \ I i \: ., \.:, TOP OF BLUFF I I '''"''- MAPPED JUNE I 22, 2007 I I I I I I , l~\ II I' I I, II II 1\ , , _c .. . \J 0,- ? ,:,.- ,'0', .~ ~.I .;.;: .. ... ,...c :),..~, ..........tr...... ?'..,~ ." 40.0 FT ~RED SURVEY STAMPED NT/-ROORDA "'~ 0 ~ i z ; :t - :;; ., - ~ ~ C/) 'i '" .!!! ':: ClC J!.r ~ o i,i s .... ~.- :z - :.!! e ~ ~"i i w ~ i ; .- l1.. .. :z:1 ~ i ffil l ~ ~ ...,.s 0 U> ~~ ~ ~ ..~ !l! ~ i l! ~ :c ... ~ ~ t: lil o i; :z: ~ ii c: ~ ~ g ~ Q) ~ c: U) 0 Q) E :t::: E t:: :3 '_ 5 iii ""';) .~ .c t: Q:.~ -2 ::x: ,.: '" % o U .:; ... ~I~ l! t!1 ... _ - ,., '" . _:c: ~ ~ ~>- w .1.. : Iii Q - IaI w". ~~~i'i~t:; -ccn-cw>w UWD:::l:W.X Oli1DQOQ:Cf') . ' 1H€ B4SIS OF SEARING I'OR THIS SURVC'f IS NORTH 881$'SJ- WEST ALONG me NORTH UN[ OF rHC NORTHWEST QUARTER Of SCCT10N 16 AS SHOWN HEREON. AU. DISTANCES HAIIC BEEN REOUCfO BY A FACTOR OF a. ?1. TO OBTAIN GROUND DlSTANCCS, MULTIPLY DISTANCES SHOWN HEREON BY ,. n. THIS $l.#MY cr.>>tPUCS Itf1J1 WAC. .D2-1JO-tOO AND WAS ACCOUPtJSHE1) BY FIE1.D ~~ METHODS USING A S-SCCONO 1HEODOUTC AND AS INFRARED DISTANCe MEASURING DEVICe WITH SOllIE DfSTANCE'S AiEASUREO tw1H A STEEL TAPE. Cannon Survey Survey and Topo of Lot 54 of Port Ludlow No.2, Area 1 located in Section 9, Township 28 North, Range 1 East, W.M.. Jefferson County, Washington THF: ~ PARCfl AMY Be SU8JCCT 1tl CASEMENtS OR OTHER t:NCW1JRANCC$ ETTHrR ReCORDED OR UNRECORDED NOT SHOWN HEReoN. 1H1S SURVEY H4S NOT OC1[RM!NEO mE: EXISTENCE OF' AU. SUCH CA$EIIOIT$ OR ENCUMBRANCCS OR THE1R CfFE'CT ON THE: S~ PARCfL EXCEPT AS $PCCIF1CN..LY SHOWN HEReON. THIS RECORD OF stM'Nf'Y AMY DCPICT EX1ST1NG FFNCC LINES AND OTHER OCCUPATIONAL 1NDICA7ORS IN ACCORfJANCC WITH W.A.C. CHAPTER .JJ2-13O. THESE OCCUA4T1ONAL INDICATORS oW4Y WDlCA1F A POTCNTW.. FOR Cl.AIIIS OF UNWRITTEN 71TLL LEGU. OWNtR$HIP SIlSB) UPON UNWRITTEN 11Tl.E CI.A/II$ fM\€ NOT BEeN R€SOLI/CO BY.. THIS SUR\ttY. _I, -- ~ ...... 0) -- .J:>.. :- I\) LeGENO ., SET 5/B-INCH ReBAR WITH PLASTIC CAP STAMPeD "ROOROA 36825" 8 FOUIIO 1/2-INCH ReBAR WITH YeLLOW PlASTIC CAP STAMPro 'CARMAN 20642" PeR VOLUMe B OF SURVf:YS, PAGe 70 . FOUNO t/2-INCH ReBAR WITH YeLLOW PlASTIC CAP STAMPeD "CARMAN 20642" PeR UIIReCORDro ReCORD OF SURVff exx XX-INCH OIAMfleR croAR TRee APPROXlUATE: TOP OF BLUFF IO'!! eLeCTRICAL SeRVICe BOX B COMMUNICATIONS BOX eOOe OF LAWN I><l WATE:R VALVE" AFN JUFUISON COUNTY AUDITOR'S ALe IIUM8f:R \ ~!'P-"~&1:f_~ \ (I \~ \ \ il~ 06/22/200" FOUND BOAT SPIKC l.l ..,tH PtJNa.tw.RK PER VOLUME S OF\"""PLA1S.PT<2 r - - - t- -- I \ \ \ \ \~ \ l\ \lilt \ \ ~~ \ ' \ \ ~I .., \ \ \ \ \ \ \ I II ~_ TOP OF FIRE HYDRANT". 3D JO \ ASSUMED fLEVA T10N - M8J \ i1>Il \ !alii 53 lil =l \ I r AFN 504854 \'00>< \ \ \ \ ~ I \ \--------,-,--- \ \ \ \ I \~ CAST COGC OF ~\ \I/" \ \ ~\t_ 52 \\ \ \ , \~ AFN 493248 \ \ 06j"J2/200" t".... BOAT J.- \ \ \ ..,TH PuNcHJiARK PER K:l.WC 57. OFLONGPLAiPACC42 ~""''':1~:fJ _ _ _ _ _ _ _ -.1_ _ 1- _ _ ---;0:00 \ \ 56 \ \ \ l~CK \ \ ~--\---1 \ \ \ \ \ \ BU\ I \ \ \ \ \ \ \ \ \ I AFN 424473 55 16 . 4 0. !ll c ~ lS .: ... '" !ll l:: ~ ~ NOTES I. FOR ADDITIONAL SeCTION SUBDMSION INFORl./ATfON, srr VOLUMe 5 OF LONG PLATS, PAGe 42. ReCORDS OF JeFFeRSON COUHTY. WASHINGTON. 2. FOR LeGAL DesCRIPTION. 5<e INSTRUUENTS ReCORDEO UllDER JeFFE:RSON COUIITY AUDrroR's ALe IIUMBeRS 200294 AHO 432474- 3 THe SURVf:YEO PARCa IS SUBJeCT TO INSTRUUeNTS RECORDro UNDER AFI/'S 200294 AND 200J94. 4. ALL UONUMeNTS ARe WITHIN 0.'0 of THFJR CALCULATE:O POSITIONS AIIO ACcePTeD, UllLeSS NOTE:O OTHF:RWlSe. 5. Aao WORK FOR THIS SURVff WAS PU/FORMro 011 JUNe 22, 2007. o 3D 60 l.r..."_ I I SCALe IN FeU SURVEYOR'S comF1CATE: THIS UAP CORReCTLY RePRt:SF:NTS A SURVF:Y UAD< BY Ue OR UIIOeR IIY DIReCTIOII III COIIFORMANCe WITH THe R<OUIRF:UENTS OF THe SURVE"Y ReCORDING ACT AT THe ReQUesT OF JIM CANNON IN JUNE. 2007. ;::r~~~"'~~(ItHJ) g NORTHrICSr'ERNTERR/TORIES200S SCI.IZ: ,- - JO' GATE: 0IJ/2'1. DRA," 8V= NLE PLAT omtlD ~ .............."'" SHEET 1 OF 1 THOl./AS O. ROOROA PLS 36825 AUDfTOR'S CERTIFICATE: ALec FOR ReCORD THIS _ OA Y OF 200s AT . M. IN BOOK _ OF SUR\f'l'S AT PAGe _ A T THe ReOUeST OF NORTHY€STE:RN TE:RRITORleS, INe. OATE: COUNTY AUDITOR ta NOR~=~~R:"'~~=IES. INC. ~ c-_ _Il0o._ r..... NT' 7T7 SOUTH PlA8OO'I. PORT IJIGElE$. WASItIIGTON t83e2. (38QJ 4I2--84tl ....nlUu.Cllnt Record of Survey Em 1(__1E) for: Jim Cannon