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HomeMy WebLinkAbout964502305 Geotech Assessment- , ALKA-1 CQNSULTANT S, LLC. Environmental Engineering ~ Geotechnital Engineering • We#lattd Conswlting 3une 16,2005 ACL-OS-06-GO50 Page No. 1 Ms. Dianne Duncan 12196 NE Klabo Road Kingston, Washington 98346 { t t•~ JUN 2 Q 20u~ '~ GEOLOGIC ASSESSMENT REPORT i ,. PROPOSED SINGLE-FAMILY RESIDENCE JEFFERSON COUNTY PARCEL # 964-502-305,11 F[1LTON WAY- •` ` ` "~'' ~ ' ~ ' .TEFFERSON COUNTY, WASHINGTON This geological report presents the results of a soil and slope assessment directed at evaluating suitability for proposed development at the above referenced site. The scope of this study was developed during our initial site visit on June 6, 2005 and outlined in our proposal to you dated June 13, 2005. The services performed. under this authorization were in general compliance with the criteria for Geologicaily Hazardous Areas and geotechncal report requirements outlined in the Jefferson County Unified Development Code (UDC), sections 3.6.7 and 3.6.1 Og. Field work for this study was undertaken on June 11, 2005. Site Description The subject parcel is located to the west of State Highway 101 in Section 13 Township 29N Range 2W as shown on the Vicinity Map portion of Figure 1 of this report. Fulton Way provides access for the subject lot, which at the time of this report, was a primitive gravel road. The site consists of a level fill pad with relatively steep slopes to the south, east, and west. The slope to the south has a rockery at the toe of slope approximately 4 feet in height or less. The site is bound to the north by Fulton Way with a road cut and ascending wooded slope beyond, to the east by asingle-family residence, to the south by Manzanita Road, and to the west by a vacant lot. Figure 2, Site Plan and Figure 3, Slope Profiles illustrate site and slope features. Proposed Development Based on our discussions, we understand that the proposed development is to consist of the construction of a 1'/~ wood frame residential structure with a full daylight basement and attached garage. The general location for the proposed building was observed at the time of our site visits. Methodolo~v The subject property soil and slope conditions were visually examined and evaluated using available slope exposures in the site vicinity and the site slope itself. This information provided a basis for a general 9465 Provost Road NW, Suite 2046 • Silverdale, Washington 98383 • {360) 613-2407 • Fax: (360) 613-2408 o~~~~ ' - LVdi L V LVVV ~. ~ „______~ ACLOS-06-GO50 Page No. 2 ~' June 16 2005 understanding of the local soil and geologic conditions as discussed below. In addition to the observation of .,., ~.wd available soil exposures and reconnaissance of the nre~ theollowing readily` available resources were reviewed. Resources used: • "Soil Survey of Jefferson. County Washington", United States Department of Agriculture, 1975. • "Geologic Map of Washington -Northwest Quadrant", Washington State Department of Natural Resources, Division of Geology and Earth Resources, GM - 50, 2002. • "Geologic Map of Northeastern Jefferson County, Washington", Martin J. Gayer, 1976. • U.S.G.S. 7:5 minute series topographic map "Port Townsend South", "IJncas", "Center", and "Gardiner", Washington Quadrangle". • "Coastal Zone Atlas of Washington", Volume 11, Jefferson County, Washington Department of Ecology, 1979. • The "Jefferson County Washington Resource Inventory Area 17 Generalized Su~cial Geology and Relative Hydraulic Continuity Potential" map. • "Preliminary Investigation of Building Site Setback for Lot 3, Nelson Short Plat", Northwestern Territories, Inc., February, 1992. Geologic Setting The subject site lies within the Puget Lowland. The lowland is part of a regional north-south trending trough that extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington, this lowland is glacially carved with a depositional and erosional history including at least four separate glacial advance/retreats. The Puget Lowland is bounded on the west by the Olympic Mountains and on the east by the Cascade Range. The lowland is filled with glacial and nonglacial sediments consisting of interbedded gravel, sand, silt, till, and peat lenses. The Washington Division of Geology and Earth Resource (WDGER), Geologic Map of Washington - Northwest Quadrant, dated 2002, indicates that the site is mapped as glacial till (Qgt). Glacial till .consists of an unsorted, unstratified, highly compacted mixtwe of clay, silt, sand, gravel and boulders deposited by glacial ice. It also may contain interbedded stratified sand, silt, and gravel. Concealed faults are mapped approximately 1 mile east and west and 3.5 miles to the north. The "Jefferson County Washington Resource Inventory Area 17 Generalized Su~cial Geology and Relative Hydraulic Continuity Potential" map indicates the site is near the contact of basil till and coarser unconsolidated sediments (e.g. outwash, alluvium) to the south. The Geologic Map of Northeastern Jefferson County, Washington indicated that the site is mapped as Vashon lodgement till. A1kai Consultants ACLOS-06-G050 1 ~ Page No. 3 111nP. l Fi 7Of1S The USDA Soil Conservation Service Soil Survey of Jefferson. County Area, Washington,- 1.975, indicates the surface soils in the northern area of the site of thesite°are mapped as Clailatn gr~'vell~r~saih~d'y loam with 15 to 30 percent slopes (CmD) and the soils in the southern area of the site are mapped as Hoypus gravelly loamy sand with 15 to 30 percent slopes (HuD). The Clallam soil formed in glacial till under a forest of mixed coniferous and deciduous trees. There is a very slowly permeable cemented layer at a depth of 20 to 40 inches. Runoff is medium and water erosion hazard is moderate for this soil. The Hoypus soil formed in glacial outwash. Runoff is .medium and the erosion hazard is moderate. The "Coastal Zone Atlas of Washington", Volume 11, Jefferson County, Washington Department of Ecology, 1479 identifies slope stability in the site vicinity as Intermediate (I) near a contact of Unstable (iJ) fo the -south. Intermediate slopes are described as generally steeper than 15 percent slopes, but can include areas of more gentle slopes .where weak material. or groundwater conditions reduce stability. Unstable slopes are considered unstable due to erosional, stratigraphic, slope gradient, or groundwater conditions. They may show indications of past or present movement. It should be noted that the mapping was performed in the late 1970's and does not reflect more recent. activity. Surface .and Subsurface Conditions The site consists of a level fill pad terminated by steep downward slopes to the south, east, and west. It is our understanding that the fill was placed in the early 1980's. The slopes range from 30 to 34 degrees and have a vertical height of up to 35 feet. It is our understanding that n existing septic. tank and drainfield is located to the northwest of the main building site. The access for the tank was located at the time of our field work. Testpits were excavated using a Kobelko mini-trackhoe capable of depths up to approximately 9 feet and in the south central portion of the site (apparent deepest portion of the fill) revealed dense fill to a depth of approximately 5 to 6 feet underlain by loose to medium dense filUoriginal native (with roots at 7 feet) to approximately 8.5 feet. It appeared that dense glacial till was encountered at approximately 8.5 feet. Vegetation on the fill pad consisted of grass and Scotch broom. Vegetation on the slopes consisted of immature Cedar, Douglas fir, and Alder with an understory of brush such as salal and sword fern. No evidence of surficial or deep-seated or rotational landsliding was observed on the property. Based on the soils exposed on and around the property it is our opinion that the site soil conditions are generally consistent with those shown on the geologic and SCS maps of the area. Generally differences between the geologic and soil maps and observed soil conditions occur as a result of mapping scale, availability of exposures, and intended map usage. These differences are generally minor and not unexpected. There was no visible evidence of ground water, springs or seeps observed on the slope face or within 1000 feet of the subject site at the time of the site visit. Our reconnaissance off the subject site was limited by private property access. Water seepage could occur during periods of heavy rainfall. Alkai Consultants I t JUN 2 U 2005 } ~,. ~~ ACL05-o5-G050 ~.'.~ ~..:~_ Page No. 4 R,na t ~ ~nnc Conclusions and Recommendations The subject site appears to be feasible for development of a residential structure as long as the footings bear on firm native soil and the appropriate setback from the iop of the. fill slope'is'achieved:Although it appears from our test pits that firm native soil will be encountered at a depth of 9 feet below existing grade, there may be areas where deeper excavation is .required. A previous preliminary investigation by Northwestern Territories, Inc. dated February, 1992 recommended a 15 foot setback based on their field observations and requirements of the Uniform Building Code and allows for a reduction of the setback ~if the footings are deeper. The current Jefferson :County Unified Development Code (which we believe. supersedes the UBC and current IBC for .setback requirements) specifies a 30 foot setback from landslide hazard areas, but will allow a reduction of the buffer to no less than 15 feet provided the 30 foot- buffer can not be achieved and reducing the buffer will still allow for the protection of the landslide hazard area and proposed development. At the time of this report, basic house plans were available, but the exact location of the footprint was still preliminary. For design/layout considerations, Figure 3, Slope Profiles, illustrates that a 15 foot setback from the top of slope at current grade would be approximately 30 feet from the slope face at a depth of 9 feet below current grade.. We believe the hazard would be minimal if the structure bears on the firm native soil, so we believe the setback may be reduced to 15 feet at this depth, especially if a daylight basement is utilized so that a large portion of the existing fill is removed from the building area, which is our understanding at this time. More specific recommendations may be provided as the plans are fmalized and the project progresses. It is recommended that a representative of ALKAI monitor the excavation activities as needed, especially if conditions are encountered that require deeper excavation. than planned for the proposed development to address areas of deeper fill. It is also recommended that ALKAI view the footing subgrade to verify that the building is bearing on fum native soil and to verify the appropriate setback from the top of the 5ll slope. We recommend that roof and parking drainage be directed to an existing ditch that runs along Fulton Way. This may involve obtaining permission from the property owner to the east if it involves placing tightlines on their property in order to convey the water from the subject site to the nearest point of the existing ditch. An additional option for roof drains would be to tightline the roof drains to the toe of the fill slope, which is still on the subject site. >f tighdines are utilized, an energy dissipater feature such as quarry spalls should be utilized at the point of discharge to reduce erosion. All disturbed areas should be revegetated as soon as possible. REPORT LIlVIITATIONS This report has been prepared for the exclusive use of Mrs. Dianne Duncan and her agents for use in planning of the referenced development. The conclusions and recommendations in this report are based on our interpretation of site conditions, as they presently exist, anticipated future construction activities, and the expectation that the exploratory efforts adequately define the subsurface conditions across the site. The soil conditions described in this report and the conclusions and recommendations contained in this report .are Alkai Consultants . ACU35-Ub-GO50 Page No. 5 ' June 16 2005 provided for this specifc site only-and should not be expanded for use on adjacent properties without additional exploration and review of those .sites by our firm. The data and report should be provided to .prospective contractors for their bidding. or estimating purposes, but the report correlusions and. interpretations should.not be construed as a warranty of the subsurface conditions. There are possible variations in subsurface conditions~In the event that the scope or location of the project should change or subsurface conditions dii~erent from those encountered during this study be observed or suspected, we should be advised. At that time a review of the changed conditions will be made,. and alternative or remedial recommendations given as required. NOTE: We have not evaluated the site for the potential presence of contaminated soil, nor have we evaluated or addressed ground water conditions or concerns except as noted in this report. The evaluation of possible environmental or geo-environmental considerations is beyond the scope of this report. The owner and the contractor should make themselves aware of and become familiar with applicable local, state, and federal safety regulations, including current OSHA excavation and trench safety standards. Construction site safety .generally is the sole responsibility of the contractor. The contractor shall also be solely responsible for the means, method, techniques, sequences, and operations of construction operations. The firm, Alkai Consultants, LLC is providing the preceding information and recommendations solely as a service to Mrs. Dianne Duncan. Under no circumstances should the provision of this information. or recommendations be construed to mean that the firm Alkai Consultants, LLC (or subcontractors) are assuming responsibility for construction site safety or the contractor's activities; such responsibility is not..implied and should not be inferred. -Within the limitations of scope, schedule, and budget for this work, it is warranted that the work has been done in accordance with generally accepted practices followed in this area at the time this is report was made. No other warranty, expressed or implied is made. Should you have any questions or concerns, which have not been addressed, or if we may be of additional assistance, please call our office at (360) 613-2407. Sincerely, ~.. ~A . _._ _ David Hurum, L.G. Senior Staff Geologist ~` _.~._.~ . _ _ _ 1 ~. ~ ti 1~ i ~i J l iv ~ -'~ t,.;~ ,'EVE u,~r,~a ~ t.':' r -= ~ ~ ~ 1121 •~y used Geo~o DAVID C, HURUM ~~/a~.-- Alkai Consultants g 2 0~,200~ ~,. ~r {~_: ~~, i ,ti ~ ~ A ~~. A ~~~~ ask =~ c"'1~ "-"''` ? ~ .~,~ ~ ~s~ ti~ - ti * ~ ~ '` ~ ~ ~ f' ~ t ,~~.s,~- ~ ~., `_ -~.~ ,~ ,~.: `' ~> • ~ y~ ~~:~ !l~1;1 `Po ink ~, ,. '~ ~+ ' . i~ , ~ ,a ._ ~ g ~~~, ,.,~~' fr fir' f r' '~ ~ ..;•- ~ -st~i~,;; %~ f r ~ SITE : r t ~ I ~ ~`~,: ~ dj1~t~ f~1 ` I • / ~' t~ ~~ ~' - W _-~'' ..~ ,ter ..~ ~'`~.,:' !:~ ~' ~` `~--1 _?rte...-r`_~,,p~~- ~~~,' ~.-~ ._. f - ~ Q ~• ~ y , ,~ ,^ ~, i~ , : '~, ~ f ~a " .~....~ :.~ ..--- ,: .- .. , . ~`fi / ~{ j_ '~~~~,_ .~~ • # a.. P' ~vl ~ 7 ice, ~~t{-•1f! '~f 1 t I ` ~~• ~.~ ~ •` ~ ~ _..:~-ms`s . . --d /~. ~ ~~f_~•%"~/ ,- Figure adapted from TopoZone.com FIGURE 1 VICINITY MAP Project Name: Duncan SFR N A~.K/~~ CONSULTANTS, LLC. Location: Jefferson Co., Washington Project No.: ACL 05-05-6050 Environmental Engineering • Geotechnical Engineering • Wetland Consulting Client: Mrs. Dianne Duncan Date: 6!13/05 ~ _ _; t~ ~~ r ~ ;~ h,;:~ ~ ~ ~. ~ f ,; ! ,t'" • N ~ r h 2' d.• 7 + . ~ ', t.,: r Y.._...«... .._. .. Iwl \ ~~'~~ 5 ~ ~ ~ Pq ` ~. ~' ~, ~ ~ ^ \ 1 \ ~ 1 ~' H N 1 ,~ ~ ~ ~ 3 ~ ~ .~ ~ ~ "" w f 1 H ~, ~ ..z ~~ ~~~ ~ i ~~ ~./ 1 ~ ~Zi•1~ ,, ~ ~ ~, - o. a ~ i ~ ~ ,/ s J ' / ~• ~ 0 ~ '~ U x e ~ . 1 v 8 .~ ~ ~ ~~ ~ ~ .~ Q .~ ~ ~ ; ;~ ~~ z . gg t~ :~ ~ g z 'd J d~ '~_` 4 ~ . ~ ± eg y `~' i ~R i Gam ~ .C F N ~"~ ~';ry Z y ~: ~ ~ ~ -~ I 3 i ~'' ~.r _..,..~ . _ ~~ !! U g t~ T~ ~~a ~~ ~~ N O II ~~ ~~ ~ z o .l~yyy! P~ a ~ 8 ~ ~ ~~~~ ~.~~~ . ~ o o .~ ~ ~: r ~ z '~ ~~ 0 ~ z ~ ~' h ~ O € u c~ p--I z J ~ '~ ALKA1 CONSULTANTS LLC. Environmental Engineering • Geotechnical Engineering • Wetland consulting ,, "r August 17, 2005 ACL-OS-06-GO50 Page No. 1 Ms. Dianne Duncan 12196 NE Klabo Road. Kingston, Washington 98346 ADDENDUM LETTER FOR GEOLOGIC ASSESSMENT REPORT DATED JUNE 16, 2005 PROPOSED SINGLE-FAMILY RESIDENCE JEFFERSON COUNTY PARCEL # 964-502-305,11 FULTON WAY % 'JEFFERSON COUNTY, WASHINGTON ~.-. s' Dear Mrs. Duncan: This letter addresses questions asked by Jefferson County and Terhune Custom Homes personnel and follows an e-mail correspondence from Jefferson County. Two of the main concerns regard stormwater manageirient and building setback.:`ALKAI proposed tightlining roof runoff to the toe of the slope to the south, past the septic ''`~ "drainfield, and to place the tightlines to discharge into an existing drainage ditch adjacent to the property along (/'`~ Manzinita Road. We recommend an energy dissipater of quarry spalls be placed at the point of discharge. If runoff from the parking lo# flown toward the garage, we recommend a small catch basin be installed at the low point of the driveway and also tightlined to Manzinita Road. Tightlines may be placed on the ground surface or buried as shallow as desired for aesthetic purposes. We recommend two 4-inch tightlines for the roof drains as illustrated on the site plan generated by Terhune Homes. `Regarding the setback, the attached figure (Figure 4) illustrates that a 9 foot cut from the top of slope will provide a 15 foot setback from the top of slope which should be sufficient as stated in sentence 7 of the Conclusions and Recommendations on page 4 of the original report. - We appreciate the opportunity to work with you on this project. If we can be of further assistance or if you have any questions regarding this project, please contact or office. ~~ Sincerely, ~~G~ David Hurum, L.G. Senior Staff Geologist ~~~rl~~ 9465 Provost Road NW, Suite 202 • Silverdale, Washington 98383 • (360) 613-2407 • Fax: (360) 613-2408 1+° t;` ~; i "..3+ t U ~` ' h 3 a .~ _ I~ M P~ VJ ~ ~ , i ~~ ji ~a yey~~ Qi ~ ~ W Or N p °' 3 ~~ a~ ~ ~ A~ q~ ~ f a H ~C c ~' ~ ~ i ! x a eQH ,~ '" ~ ~ ~ F .~~ ~ ~< ~~ x ~ ~ ~ d~~ ~ ~ a ~~ J m H ~b ~ tq z ~i ~ ~ - ~ - Io ~ a ~ ~~ a ~ o -~ ~ ~ I ~ r a ~ z Q ~ AL~CA-1 CONSULTANTS, LLC. . Enviconmentai Engineering • Geotethnical Engineering • Wetland Gansutting September 8, 2~5 pCL=p~-p~_g Page No. 1 Ms. Dianne Duncan P.U. Box 1500 Port Townsend, Washington 98368 ADDENDUM LETTER # 2 FOR GEOLOGIC ASSESSaMENT REPORT DATED JUNE 16, 2005 PROPOSED Sn+tGLE-FAMILY RESIDENCE JEFFERSON COUNTY PARCEL # 964-502-305,11 FULTON WAY JEFFERSON COUNTY, WASHIIVGTON Dear Mrs. Duncan: This letter addresses the proposed infiltration dispersal trench for the above referenced property. A memo dated August 30, 2005 from Jefferson County Department of Community Development and plans from Terhune Custom Homes for the infiltration dispersal trench was reviewed prior to .the preparation of this letter. The property was also revisited by ALKAI on September '7, 2005. Based on a preliminary reconnaissance, it appears that the proposed infiltration dispersion trench. design. will be feasible in the area of the lot below the reserve drainfield as illustrated on Figure 5, Infiltration Dispersal Trench Location, and will have na significant impact on the slope. The trench or trenches will have to parallel slope contours and be installed in areas of slopes less than 20 percent grade. Trench plans provided by Terhune Custom Homes are included following Figure S. -We understand there will probably be 2 separate trenches (1 for each corner of the south side of the house). We appreciate the opportunity to work with you on this project. If we can be of further assistance or if you have any questions regarding this project, please contact or office. Sincerely, ///~~~ rye ~~ y t ~~' -_-.. .David Hurum, L.G. rc 112i Senior Staff Geologist e'sa~ a ~AV1D C. HURUM Attachments: Figure 1 ~ t,~ ~ -~ Infiltration Dispersal Trench Plan 9465 Provost Road 1VW, Suite 202 • Silverdale, Washington 98383 • (360) 613-2402 • Fax: (360) 613-2408 - - - ~ reams 2 :'_~- ~ ~ ~ `~ +l sea Ta•t4°E •R ~~ ao,~oa• ~ ~,.. swc~ ~ j f_ f ~-- ~ - r o ~ r t• _ r / NN #j O ~ jy 1 2 l }Pt `~ j- t ro. --« ~SI~ - tt 1 Q ~ -~ ~. l r t ~~ ~ ~ ~ ! qq .~ t Z O aS~' ~ ~ ~ $ 4 ~ ~ CC r } ~ ~ .a,_r 9J.tPE, O ` i 'w < o ( i ~ 1 JO z `~ ~ t ~ .- $ ~ ~ ~ ~ Gt ~ ~ ~ ~ ~ 1 i ( 4 l ~ ...t. J..._......... ;. , , (c' a x c .~ m c s a ~~„30 ~ v ~Q~~ Q O C p~,..i~ m~a~ -~ •• ~ 4 ~ O ... Z cZ'~~ .w . Q .a. O~ R m C Q ~ ~ ~ CL ..! d. V D ~~~ ~~~ ~ i ~ ~ ~ ~~~~ ~ ~ .2:s°a ~ E-~ a Q ~~ ~ i q A s '* ~~ ~ ~? li eo ~~, ,~'+~ tk' 4V ;~ eZ' J ~ Z ~i Q ~ p ~ m ~ S~ ~~`b ~ ~ ~ o ~ O W O ~ 'm gg .~ ~^~ ~ S~ dQ ~~ ~ V1 0 V C' ~ Q ~ !3' ~ C J ~ ~, Q iw z eG. 0. 1UU7 j:tlrw~ iernunP custom Homes 2" X 12" PRESSURE TREATED GRADE BOARD quo. 3Ub~ ~ . j °_. , ~ .} Min. Min. ~ . `---END .CAP OR PLUG CLEAN OUT WYE FROM PIPE 4" OR fi" PERF. PIPE LAID FLAT/BEVEL A iNFI~UENT PIPE (MAX ^ DESIGN FLOW=0,5 CFS PER TRENCH} TYPE 7 CATCH BASIN t+V% SOLD COVER (LOCKING} CLEAN OUT Vv'YE FROIv1 PIPE ~--- GRADE BOARD PLAN VIEW .- ,~ Min. Min. PIPE 20% ~ A~ O.D. ' 20~'"~~ C X o ~ E ~ GALVANl~ED r ~ BOLTS _~~~~ CLEAN (S 5% FINES} 3/4" -1 1/2" WASHED DRAIN RO 4" OR 6" PERF.. PVC PIPE LAID FLAT WITH HOLES UP 2" X 4" SUPPORT i l ~ POST ~'` FILTER FABRIC (2 SIDES AND (P T.) Section A-A (nfiltrc P. 5. IUQh ~:LlYM lerpune t,ustam games fYp. J+JQJ r. ~ u ~~ ,,; ~~ CB ..~ „ , SOLIQ COVER FLOW TO OTHER BRANCHING CB'S IF NECESSARY Notes: THIS .TRENCH SHALL BE CONSTRUCTED SO AS ~!~ ~~ PREVENT POINT DISCHARGE AND f OR ERC)SION,~ TRENCH AND GRADE BOAR[ MUST BE LEVEL, ALIGN TO FOLLOW CC3NTOURS OF SITE. GRADE BOARD SUPPORT . POST SPACING AS ,REQUIRED BY_ SOIL CONDITIONS. pISPERSAL TRENCH T0~ BE USED ONLY WHERE DOWNHILL AREA IS APPROPRIATE TO REC~~,VE FLOW rTn~) AS DETERMINED BY~ SOILS ENGINEER. :~or~ Dis ersal trench c-~,