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Home My WebLink About977700053 Geotech AssessmentJames B. Scott, P.E. GEOTECHNICAL CONSULTANT 360-293-6044 FAX 3b0-293-6044 Email ~eoscott26(~comcast.net J. B. SCOTT & AS SOCI An Engineering Corporation 3601 West 5th Street Anacortes, WA 98221 May 27, 2004 Mr. Richard Roth c/o Waves Waterfront Properties, Inc. P. O. Box 1668 Port Townsend, WA 98368 ~ , ~ 1 ~ ~' y ,~ ~ ~ ~; 1 ~... UEfi7 0(y(;t~}~F4~y,Ut~t3~ DEI'EI.OF~~~f`i~'3' Project File 04-1134A RE: Geotechnical inspection of Parcel #921094014 which i5 located in Sec. 9, T. 29 N., R. 1 E.W.M., Jefferson County, WA Dear Mr. Roth: At the request of Ms. Barbara Blowers of Waves Waterfront. Properties and with your authorization, a geotechnical evaluation was made of the subject parcel. Since conditions exist that are classed as critical, as defined in the Jefferson County Critical Areas Ordinance, a Geological Hazardous Area Site Assessment will be required by the county before permits can be issued for building purposes. This report should satisfy that requirement. The field reconnaissance phase of the evaluation, in the presence of Ms. Blowers, was made on May 19, 2004. Photographs were #aken to document field conditions. ~.o ~.~9-a. ~- _- ,~ j' - ROAD _ ~. -- s~,cl~ot4 TAX t 6 ~~ ~ _- 4.87 0. ~1,. {.. .1094017 ~21~9401~ `~ ~ a4 `~ `~~ ~. TA V 7v ~, FIGURE 1 -PLOT MAP OF PARCEL The subject evaluation consisted of the review of (1) Coastal Zone Atlas of Washington, volume 11, Jefferson County, Washington Department of Ecology, 1978; (2) Soil Survey of Jefferson County, Washington, USDA Soil Conservation Service, 1975; and (3) the field reconnaissance that consisted of walking over the proposed building site area to observe surface conditions, a drainfeld test hole, IyJlr. Richard Roth May 27, 2004 slope stability, attitude of conifer trees, bluff slope conditions, and surface drainage. SUMMARY ~ RECOMMENDATIONS -Based on the Coastal Zone Atlas the entire bluff slope zone in the general LipLip Point area, is classed as being a Unstable Recent Landslide area. I question that classification since it implies a "landslide" condition. Based on my evalua#ion, while the bluff slope is unstable becomes of a near vertical slope, I would class the bluff as undergoing excessive erosion by the action of both wind and water as shown in Photo 2. , ~= ' j ' 4 z ~: .~ } .; ~r.3 i , ~ , ;k ~'~ ~ ~~~ Ii~' ;' ' ;'~,, ~ s ~ 2004 ~, 1~ 1 PHOTO 1 -VIEW OF BLUFF SLOPE LOOKING NORTH FROM SUBJECT PARCEL The face of the bluff slope is sand as shown in Photo 1. At the base of this slope, in the low tide zone, outcrops of what appears to be Vashon till is present. ~' ~~ ; ,. `.: ~ ~f. ` ~ ~ f _ ~ ~ .~ ,~ ~~ f ;,~ ~,,~ ~~ ~~ , ~~ ; ; . _ ,k - #- ~ti ~ - e t _ i". ,. _ ti - 4 ~_ ' «- .kT PHOTO 2 -VIEW OF SEPTIC DRAINFIELD TEST HOLE 2 Mr. Richard Roth May 27, 20Q4 Then back from the bluff slope near the proposed building site, a drainfield test hole encounter till {see red arrow) material at a shallow depth, as shown in Photo2. A rather thin topsoil zone of sand lies above the till. Subject parcel PHOTO 3 -COASTAL ZONE ATLAS MAP OF PROJECT AREA This "till" like material was confirmed in the Coastal Zone Atlas, as shown in Photo 3, which indicates the present of Qvt (till). The presence of till both at the low tide zone and then back about 60 feet from the top of the bluff, does bring up the question, "How did that sand get deposited to the depth as exposed along the bluff'. I suspect that the near level bench or shelf is an old terrace. During that period the sea level was at least 60 feet higher than at the present time. Then, as the sea level dropped, beach sand was also deposited on the slope. Also any loose sand, as the level dropped, was being blown by southeast winds up and over the bluff. If this is true, since the proposed building site is underlain by till at a rather shallow depth, foundation conditions wilt be excellent. Also, as more of the till is exposed in the bluff slope, starting at sea level, that should slow down the landward migration of the bluff slope. Therefore, this would allow for a setback of 60 feet for any proposed structure since the rate of landward migration will become very slow after more of the till is exposed. A proposed life of well over 100 years would then seem to be reasonable. To prove this hypotheses, it will be necessary to place several backhoe trenches out toward the bluff from the proposed location of the structure. The sand topsoil zone has a very high infiltration rate, therefore natural surface drainage should not be problem. However, concentrated flows toward the bluff will result in excessive erosion as already noted at various points along the bluff on properties to the north. Any such flows should be collected and placed into a tightline for disposal down the bluff slope. Mr. Richard Roth I~ay 27, 2004 Vile appreciate this opportunity to be of service to you. If you have any questions regarding this report, please contact the undersigned. Sincerely, James S. Scott, P.E. ~ '~~ ~ ~~ ~ ~. .~ ~ .~ ~ ,~ ii~29 ~} ~,. ~0~ .u, 4 LOHSE May 27, 2004 As discussed in the Job 04-1134A report, it appears that the sand was deposited during a period of a higher sea level condition and #hen as the sea level dropped, beach sand was deposited on the Vashon till slope. This means that foundation conditions will be excellent for any structure located as least 60 feet back from the existing bluff slope. ~' S.....a..._..~1 The sand topsoil zone has a very high infiltration rate, so natural surface flow drainage should not be a problem. However, concentrated flows toward the bluff will result in excessive erosion as was noted at various locations along the bluff slope toward the north. One example can been seen in Photo 1, where erosion has occurred in the bluff slope, as shown by red arrow. Anyway, concentrated flows toward the bluff should be collected and placed into a tightline for disposal down at the base of the bluff slope. Therefore, allowing for a minimum setback of 60 feet for any proposed structure since the rate of bluff slope landward migration should become slower as more of the ti11 is exposed in the bluff, a projec# life of 100 years is considered as being reasonable. However, I would recommend that a setback more on the order of 80 feet would provide a project life well exceeding 100 years. We appreciate this opportunity to be of service to you. If you have any questions regarding this report, please contact the undersigned. Sincerely, James B. Scott, P.E. ~- o $ s~ ~ O ~ :, ,., ~~ ~. ,, ;. e. ~_. ~- •e ~ ~,: ~ ~r~~ ~y. V `6 ~ ~ ~ ~~~ I.~ ~u ~ ~~~ it '~ ~'' , L' J FEr,~'J} CUJ~~ I"Y . , r.~ r~/~f~ ~( ~ ~~%~ C ~ ~~ C~