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HomeMy WebLinkAbout901135002 Geotech Assessment (2007)STRATUM GROUP ]451 Grant Street, Bellingham, WA 98225 Phone (360)714-9409 _. March 30, 2007 Kevin Hansen P.O. Box 327 Chimacum, WA 98325 Re: Foundation Bearing and Storm Water Plans 692 Sugar Hill Road Chimacum, Washington Dear Mr, Hansen: I have reviewed the site plan and layout including the storm water drainage for the proposed residence at building 692 Sugar Hill Road. All shallow footings supported on properly prepared subgrade may be proportioned using a net allowable bearing pressure of 2,000 psf. The term net allowable bearing pressure refers to the pressure which can be imposed on the soil at foundation level due to the total of all dead plus live loads exclusive of the weight of the footing or any backfill placed above the footing. These values may be increased by one-third for transient wind or seismic loads. The location of storm water dispersion trench is consistent with my recommendations for development of this site near a potentially hazardous slope. Dispersion of storm water as indicated on the site plan will not pose a risk to the slopes on or off the subject property. Stratum Group appreciates the opportunity to be of service to you. Should you have any questions regarding our assessment please contact our office at (360) 714-9409. Sincerely yours, Stratum Group ~' n McShane, L.E.G., M.Sc. Licensed Engineering Geologist ~~ 1(~lE~;~~'~I~11) 3?~' , . ~. ~.,~ ., ~r~ ^ ~,~ ~, _ ._ ' ~ -- ~„ { w Y1 FJ z 4` g `~ o i~ I p ti ! o ~~ ~ ~ ,~ .. I ~ gg~~ J a U~ ~ O ~~ s~ o ,- .. g ~~ ~ ~ d ' i i 0 n ~ ~$ a <; ~~ ~~ ~~ O ~~ ~ ~` ~ ~ n ~ ~ Z( u o "~ ~ ~' 8 ~ ~ ~ a l~ ~ s ~ V z O ~, { ~' ~'' tl }~ ! t ~~ a'1,,,. ; ~ ~ l B "11 ~ 3 m ~ , ~' j ~ ~~ ~ ~-' ~~ ®- ~ ~ ~ i ~ g~ ,~( O JYFI R ~ ; ~ ~ o ' Zp Z~ F~ ~X K _ f ii. { ~•r~, F ~ ~ 8 8 ~ 4~ ~ ~' ~ ~- ~n t ~ ~ ~ ~ a } ~ ~ ~~ = zo ~ .. ~ t (~ . ~ ~ Q ~ i A ~ ~ O ~ ` '~ ~~ a 3 N ~~r ~1 ~"~_ y < O 12!19/2003 14:18 3603794451 JEFF CO DCD PAGE 02 Terry McHugh ,fin ~...Mt' REAL E$YATE TAIL J~WnELYTbw~lldul Oflfm 7~ Novenober 7, 2003 Al Scalf Jefferson Cavpnty DCD, Directox 621 Sheridan Street Port Towlr~sei}d, WA. 9836$ IZE: Geology R.evloauatio>a Lots 1-4 Sugar Hill Estates Dear t~l, NQV 14 ~3 ~~~RSON COUNI'1(DCD As you ca>x see I'm still B to get carne relief fmm the uimecessary set-backs up ax Sugar Bill. Before Jerry Smith retired lxe was workaxxg an this case anal giving z>Iae feedback fro~oa yau. He me>ationed to me that you were not inclined to accept the Stxatrn~a Group's GeaTech report dated November 8, 2002 because you did not believe it to be as thorough as the Shaxraon /Wilson report that was recaxded with the plat. Due to that comment I asked Dan McShane of the Stmturn Crroup to review the 58~W report more thoroughly and comment on it as it relates to the actual site conditions. As you can- see by his enclosed letter he feels strongly that S&'VV report does not accurately describe the conditions and the slope location itself I realize that the UDC states a minimum of l5' as a set back and the Stratum Group recommends a 10' set-back. Harry Properties lnc.(the current owner) would be satis~xed with the TJDC l S' set- back and feels that is necessary fox the end user to be able to use that additaaz~al 15' to ensure a more build able and enjoyable parcel. Thank you fvr taking the time to review this nr7e~~w information. -~t ~ We took forward to your prompt response. Imo- V~v~ ~~~v~ _ UfJG Sincerely, ~ ~G ~• ~ • ~ • b • ~ M'w Terry McHugh 5 t~~.-+- T~~. {3 ~ ~- '~i1 E 0 ~ ~ B~ 1~.~~ ~o ~ S3 ~ ~~ Cjs) ~.~ ~r r..C: Harry PropertYes ~~ r i~ v~~ ~M ~p ~~~ Encl. ~,i~:~& '~,~ ~~ ~. :.. .. ._. 4 is ~ l! f ~ n/d3 Offloe: (3~) 379-$570 Toll 96 E-~it: fitcll~olypen.com Address: Port7owneend ~ gnd, WA 88388 ~Ohn STRATUM GROUP i45i Grant Street, Bellingham, WA 98225 ificane {3bU} 7I4-9409 November 8, 2002 Ron Simpson Covenarn Mortgage Corporation 9725 SE 36~ Suite 304 Mercer Island, WA 98040-3840 Re: Geology Evaluation Lot 2, Sugar Bill Estates Section 13, Township 29 N, Range 1 W Jefferson County, Washington Dear Mr. Simpson: We are pleased to present the results of our geology evaluation of the above referenced property. _ The western portion of the lot consists of a steep potentially unstable slope. The purpose of this geology evaluation was to 1}determine the suitability o~the property for the siting of a residence, 2j qualitatively evahiate the risk of slope faihues, and`3) provide general site developmern and maintenance recommendations for development of the property adjacent to a potentially unstable slope. This evaluation was limited to a visual inspection of the property and vicinity, a visual inspection of the steep slopes on the property and in the vicinity of the property, and review of available geologic mapping in the area. SCOPE OF SERVICES The scope of our services included the following: 1) Conducted a site visit to visually inspect the subject property including the steep slope conditions and relevarrt conditions in the vicinity of the property. Z) Observed surface soil conditions on the steep slope and on the uplands above the slope by excavating shallow hand dug test pits. 3) Prepared this report summarizsng our findings, including an evaluation of the feastb~iiy of building a residence on the subject property, a slualitative evaluation of the slope stability, recommendationsfcr site development, and recommendations for fittther investigation, if necessary. November 8, 2002 Lot 2, Sugar' Dill Estates Geology Hazard Evalastion GENERAL GEOLOGY Northwestern Washington has been occupied by continental glaciers at least four times during the Pleistocene Epoch (1.b million to 10,0()0 years ago). During these glacial and accompanying interglacial periods, the underlying bedrock was eroded and a relatively thick layer of glacial related and interglacial fluvial sediments were deposited over the underlying bedrock in the vicinity of the subject property. The Surficial Geolo~c Map of the Port Townsend 30- by 60-Minute Ouadrang~ Puget Sound Reg,~on. Washington (Pessl, Deither, Booth and Mlnard, 1989) indicates the subject property is underlain. by two units: i j Glacial and nonglacial sedimentary deposits of Pre-Fraser Glaciation age and 2} glacial till. The Geologies Ma~Surficial Deposits in the Seattle 30' x b6' Ouadran~;le. Washin tg_on (Yount, lVlinard, and Dembro~ 1993) indicates the subj~t property is underlain by glacial till and the Pre Fraser Glaciation sediments consist of undiffererldated Pleistocene deposits and Possession Till. The pre-Fraser glaciation deposits are described as consisting of ilrterbedded oxidized brown, red- brown, and gray gravel, sand, silt, and clay. The layers are moderately to well bedded and the unit contains minor amoulrts of ice-colrtact deposits and outwash gravel and sand. Generally the unit is nonglacial and has abundant peat and woody debris. The two glacial tills consist of a poorly sorted mixture of rock fragmerts ranguag in size from clay, silt, sand and gravel and cobbles deposited directly by glacial ice. Observations on the steep slope and upland area of the subject property are consistent with the mapping described above except that a relatively thin deposit of loose glacial recession sand and gravel is present on the uppermost slopes and upland area of the subject property. The steep slope is for the most part underlain by very compact sih (Fre-Fraser deposits} and glacial till. Glacial till was observed near the top of the slope and near the base of the slope. The till near the base of the slope is likely the Possession Till. The property is located on the east side of Chinnacum Valley. The valley is a glacial valley created during the last ice age_ The valley was formed by the erosion ofpre-Fraser depots by the Vashon ice sheet andCor water flowing underneath the glacier. SPECITIC SITE OBSERVATIONS The site location map is provided on Figure 1 and a general site plan sketch is provided on Figure 2. The subject property consists of an upland area bounded on the west by the steep slope of Chimacum Valley. The elevation of the upland is approximately 3 80 feet _and the. base of the steep datum ~ Fik:10.6.OZn3 2 11V •Y11aVW O~ LVV~ Lot 2, Sugar ITill Estates Gcrology Hazard Evaluation slope is at an elevation of approximately 150 feet. A relatively level, sleazed building area is located an the upland portion of the property at the top of the steep slope. The steep slope slopes downwazd from the upland area at an angle of approximately 15 degrees for approximately 30 feet. The slope angle steepens to an average slope of approximately 35 degrees fiuther down the slope. The slope is well vegetated with a mix of trees and thick brush. Portions of the slope are steeper because a number of old logging skid roads have been cut into and switch back and forth up the slope. Except for Honor sloughing of cut slopes and topsoil creep, no evidence of slope failures was observed on the steep slope. The entire steep slope is underlain by very compact silt, sand, and gravel deposits and glacial till. Based on the age of the trees on the slope, we esf3mate that the slope was clear cut approximately 40 to 50 years ago. The upland area of the property consists of relatively gentle slopes. Except for the building azea just above the steep slope, the upland portion of the property slopes gernly to the east away from the steep slope. No water seeps were observed on the steep slope and no seasonal wet areas are presern. We did not observe any evidence (tension cracks or trees rotated inward away from the top of the bluff or indications of past uplift of the beach area) indicating an incipiern global-type or deep- seated failure on the subject property. CONCLUSIONS AND RECOMMENDATIONS Based an our visual inspection of the subject property, we conclude that the steep slope on the west side of the property is relatively stable and is only subject to minor topsoil and slope sloughing. A residence can be located on the relatively level upland portion of the property as long as it is located 10 feet back from the top of the steep slope. A residence can be built within the area indicated on the Figure Z Site Sketch Map. It is our opinion that a residence located within the area indicated on Figure 2 will be at minimal risk of being impacted by landslides. We da Hat anticipate that the development of the subject property will cause any negative impacts an the stability of the slope as long as our recommendations are followed. We recommend that any storm water generated be discharged to the east of the building away from the steep slope. ~ ~ ~~-~ '" S~ Cncx~ File:10.6.02$ 3~iovem~er 8, z~2 Lot z, s,~ ~u Geology >t slt Ev~luaiion Site grading soils or debris, landscape debris, or any other material should not be disposed of over the steep slope or placed at the top of steep slope. Trees on the steep slope may be limbed for view purposes, but no trees should be removed unless a thinning or harvest plan has been reviewed by a geologist familiar with slope stability and tree removal. Although the steep slope has previously been logged without causing obvious landsliding, the slope stability may respond differently to a second cut because of different forest cover. The proposed septic drain field is part of a community drain field to be used by several properties and is located 300 feet northeast of the proposed building area. The septic drain field should not cause problems for slope stability on the subject property or on any other properties as it is located such that it will not effect slope hydrology. Please note that there are inherent risks associated with building on lots near or adjacem to steep slopes. These are risks that the building owner should recognize and be urilling to accept. If conditions appear different than those described in this report, or other concerns arise, we request that we be notified so we can review those areas and modify our recommendations as required. We appreciate the opportunity to be of service to you. Should you have any questions regarding our reconnaissance please contact our office at (360} 714-9409. Sincerely yours, Stratum Grasp Dan McShane, M.S., P.E.G. Professional Engineering Geologist ~~ ,may. 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