The URL can be used to link to this page

Home My WebLink About821151005 Geotech AssessmentJLS GROUP~ INC. NTI JLS GROUP INC PAGE 02 NORTHWESTERN TERRITORIES, INC, A JLS GROUP COMPANY 717 ~OUTH PEA~3OI3Y ~TREET, PORT ANCI=LES, WA ell352 D Construo~ion Inspe~tion ~ Matedal~ Testing (3~0) 452.~491 FAX 4S2-~8 w~.~.n[i4U.~m E-Mall: In[o~nlf4u,com JEFFERSON COUNTY DEPT, 01: COMMUNITY DEVELOPMENT C, EO'I'ECHNICAL REPORT For Tax P~r~l #'$ B211~,IUU~. & $211§1006 Located in Section 15, Town~hip 28 North, Range 1 East, ~N M Jefferson County, Washington Prepared for GARY and BETTY GREENE Prepared by NORTHWESTERN TERRITORIES, INC.. 717 S. Peabody Street Port Angeles, Washington 983~2 Phone 360-452-8491 Fax 360-452-8498 E-mail info@nti4u.com November 18, 2002 GEOTECHNICAL REPORT For Tax Parcel #'s 821151005 & 821151006 November 18, 2002 Gary and Betty Greene 7962 Grand Ave. Bainbridge Isiand, WA 98110 Subject: Geotechnical report for .Tax Parcel #'s 821151005 & 821181006, located in Section 15, Township 28 North, Range 1 East, W,M., Jefferson County, WA Dear Mr. and Mrs. Greene: Introduction. At your request, Bill Payton, geologist with Northwootorn Torritorioc, inc. (NTI) conducted a geotechnical inspection of the above referenced property on October 11; 2002, it is understood that the property is being considered for uu~ul~u~ u~,d tl,u~ Lf~ ~p~L wil! b~ used LO satisfy tl~,~ I"equil'en~e.n~ ~ ~h~ ~efferson County Unified Development Code for G~,nfc, nhnin~l RP, pnrt,s ,shr~l lid the property be purchased. I( ic our undorctanding that development plan~ for the property include the construction of a 2,400 square foot house about 50 feet back from the edge of the bluff (not including decks.or patios) and a garage with upstairs office/gym to be located about 35 feet west of the house. Site Description The subject property is located on Tala Shore Drive south of Port Ludlow. The property is bounded on the north and south by developed residential proper~y, on the west by Tala Shore Drive and on the east by a marine bluff and Hood Canal. The property iS heavily wooded with young to mature trees and dense u'nderbrush. There are small hills, gullies and depressions on the property with a stream channel running southward across the east portion of the lot. The stream channel was dry at the time of the site visit. The property generally slopes gently towards the east and south. The bluff at the property is also heavily vegetated with trees and brush, and no bare areas were visible, Some of the trees on the bluff face had curved trunks, wl',i¢l', ~d¢~test~ tl',al ,',G~o,' ~loc'e ,;,'eec, of the sud'ace so;Is ;~ 666Ui'1';i',¢d, Tl~e height of the bluff was measured to be about 60 feet high with an average slope of 47 de~rees from horizontal. At the time of the site visit, it appeared that recent high tidoo woro not roaching tho too of tho bluff. Nowovor, wintor high tidoo ond storm tides probably do reach the toe of the bluff. No evidence of seeps or springs were noticed on the bluff face. 2 A 12 inch culvert passes beneath Tala Shore Drive and discharges onto the property, This discharge occurs in an area designated for septic disposal and . should be redirected along Tala Shore Dr. southerly to an existing drainage easement that leads to the shore. Removal of this water from the site will not only aid the septic system but Will also reduce the amount of water reaching the cross.proper~y stream bed or the bluff face, Site Geology The USDA Soil Survey of Jefferson County maps the soil at the property as the Cassolary-Kitsap Complex (CkD). This soil is described as having formed in' reworked glacial, lacustrine or marine sediments. Further descriptions classify this soil as predominantly a silty sand with some gravel with a clay seam. from about 23" to 38". The Coastal Zone Atlas of Washington describes the soil at the subject property as the Vashon lodgement tilt (Qvtl), a compact mixture of boulders, cobbles, pebbles, sand, silt and clay, generally nve, rlain hy 1-fi fe, e,t nf ablat, ir~n till, The, Atlas also describes this soil as being excellent for foundation stability and good for seismic stability. The Atlas maps the slope stability of the property as Stable (S) and as Unstable (U). Visual observations made in one of the septic test pits revealed deposits of silty sand with gravel down to about four feet, C,r~ncl[~sions and R~.commendations The bluff at the subject property appears grossiy stable at present. The. building setback from the bluff to the house should be at least 5d feet in order to provide an adequate setback for the propo.sed home for at least the economic life of the structure. Marine erosion is a' fact of life along most of the Puget Sound shoreline. Periodic shallow slides and occasional downed trees on the bluff should be expected in the future even though the bluff is currently stable. Tho following rocommondations should bo considered with regards to development of the subject property in order to reduce negative impact to.the bluff: Bare soils are subject to erosion, thus ground cover should be encouraged and maintained. Native vegetation that requires little or no irrigation would be most beneficial. Also, the existing established trees and brush on the bluff provide stabilization to the bluff and should be left in a relatively natural state. Selective thinning and pruning can be utilized to improve the view, 2. If beach acce,~8 8tail'S i~1'~3 desired, riley cuuld prub~bly bu designed arm 3 Based constructed in order to minimize negative impact,to'the bluff, rhisturbed areas would need to be revegetated after construction and erosion from runoff would' have to be controlled. An engineer with experience in this type of construction ~hould be consulted. Heavy irrigation or other activities that would contribute large quantities of water to the soil should be avoided. One cause of'landslides is the presence of excessive groundwater in the soil near the bluff, Runoff from roofs and other hard surfaces such as driveways and patios should be controlled and routed to the beach via tightline or into the stream through a time release system. These options are preferred rather than infiltration, which may cause destabitization of the bluff. Surface water discharge or sedimentation to adjacent properties should not be significantly higher than Pre-development conditions; bluff. Ail drainage, r;.,ontrol de~ioes should be maintained in good working order and inspected at least once a year. Silt fences or other sediment control devices may need to be utilized in nrde, r tn pre~ent sedimentation to adjacent properties during construction. A~I ur~gir~eer'ed drainage control plan should be developed for this property to address items 4, 6 and 7. Relocate off site drainage to allow septic system development. on the findings, recommendations and limitations of this report: There has probably been landslide activity on the bluff face in the past, However, no evidence of recent landslide activity was noticed. The recommended setback distance should provide for minimal landslide hazard to the proposed home. An .analysis of slope stability indicates that the proposed home would not be subject to risk of landslide under normal conditions. The proposal would not increase surface water discharge or sedimentation to adjacent properties, The proposal would not decrease slope stability on adjacent properties, The proposed homesite would be stable under normal geologic conditions. 4 11/1~, zH~lz 18: 3584528498 NTI JLS GROUP lNG PAGE 86 with tl~e. original of this roped, published by the Washington State Department of ' Ecology entitled: "Slope Stabilization and Erosion Control Using Vegetation", "Surface Water and Groundwater on Coastal Bluffs" and "Ve§etafion Management: A Guide for Puget SOund Bluff Property Owners", ' Limitations This report is based on a visual inspection of the existing site conditions. No scientific measurements, tests or calculations were performed. The findings and report are limited to the normal standard of care of the industry for an inve, stioatinn withnl ~t h~,ne, fif nf ,~nientifin data and naln~ dafinns The sole objective of thi.s investigation has' been to diagnose the geotechnical conditions at the site. The report has been prepared for the exclusive use of our client in conjunction with the above mentioned project, It may be used by other's only with expressed written permission of the Engineer. The observations, professional engineering and geologic principles and practice. This warranty is in lieu of all others, either expressed or implied. Sincerely, NORTHWESTERN TERRITORIES, IN(;, ' ,Robert A. Leach, P.E., MBA Principal Design Engineer EXPIRES 12f30/2002 ] Bill Payton, L,E.G. Engineering Geologist G:\Ge n\@ill~Reports\GREG0202,bLuff stability2.15(28-1E).Tala Shore Expires 11-06-03 5