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Home My WebLink About502103021 Geotech Assessment September 24, 2008 STRATUM GROUP PO Box 2546, Bellingham, Washington 98227 Phone (360) 714-9409 )'~~\Ilff"~Yil'~~'t. ('~\1'" ....- -.Ii' Bill Buchholz 114 NE 64th Street Seattle, Washington 98115 itwN ]. 't: ~L"j !' .rf-a:Il~r~' COtJIttTfOI;I) Re: Geology Hazard Assessment 224 Lovers Lane Jefferson County Tax Parcel 502103021 Brinnon, Washington Dear Mr. Buchholz: Stratum Group is pleased to present the results of our geology hazard assessment of tax parcel 502103021, south of Brinnon, Washington. The purpose of this geology hazard assessment is to evaluate the risk of slope failures on the site due to proposed development or development in the vicinity. This evaluation included review of geologic mapping of the area, a visual inspection of the property and vicinity, and observations of shallow soil conditions. The property is located on the east side of the Olympic Peninsula on a slope above Highway 101 and Hood Canal. The location of the property is indicated on Figure 1. SCOPE OF SERVICES The scope of our services included the following: 1) Conducted a site visit to visually inspect the subject property including slope conditions and relevant conditions in the vicinity of the property. 2) Observed surface soil conditions on the slopes and on the uplands above the slopes. 3) Prepared this report summarizing our findings, including a qualitative evaluation of the stability in regards to proposed development on the property, recommendations for site development, and recommendations for further investigation, if necessary. /' September 24, 2008 224 Lovers Lane, Tax Parcel 502103021, Brinon, W A Geology Hazard Assessment GENERAL GEOLOGY N orthwestern Washington has been occupied by continental glaciers at least four times during the Pleistocene Epoch (1.6 million to 10,000 years ago). During these glacial and accompanying interglacial periods, the underlying bedrock was deeply eroded. Glacial related deposits were deposited over the bedrock in various places on and in the vicinity of the subject property. The Geologic Map of Surficial Deposits in the Seattle 30' by 60' Quadrangle. Washington (Yount, Menard and Dembroff, 1993) indicates that the subject property and vicinity is underlain by continental glacial till of the Fraser glaciation. Observations on the subject property are consistent with this mapping. The Bedrock Geologic Map of the Seattle 30' by 60' Quadrangle. Washington (Yount and Gower, 1991) indicates that mapped bedrock in the vicinity is basalt of the lower Eocene Crescent Formation. The glacial till mantles the basalt bedrock with numerous bedrock outcrops in the area. The proposed building site is underlain by compact, reddish-brown sand, gravel, and cobbles with some fines. Septic drain field test pits indicate exposed this material to a depth of at least six feet. Both rounded and very angular basalt gravel and cobbles were observed in the testpits. Very compact glacial till material is present along the east side of an access road that extends south through the central portion of the property and is present along road cuts in the vicinity of the site. No bedrock outcrops were observed on the subject parcel, but are present in the vicinity of the property. . SPECIFIC SITE OBSERV A TIONS The subject property is located on an east-southeast facing slope above U.S. Highway 101 and Hood Canal, on the west side of Hood Canal. The property is accessed via Lovers Lane from the north end of the property. A gravel driveway extends from the north end of the property to the proposed building area in the northwest portion of the site. A second driveway extends through the central portion of the property from Lovers Lane and provides access to an adjacent property. The proposed building area is located on fairly level to gently south sloping bench area that extends along the northwestern property boundary. The bench ranges from approximately 50 to 90 feet wide. The bench area has .been cleared of trees and is covered with grasses and thin soil over coarse glacial till materials. Numerous test pits have been excavated in the south end of the bench area and exposed the subsurface materials to a depth of six feet. The building area is bound to the west by a forest with 45% slopes to the southeast. The forested slopes to the west of the building area are on the adjacent property. The lower 5 to 10 feet of the slope has some exposed soils and were likely disturbed when the subject property was logged or when the access to the bench area was created. The slope has been cut backto generally match Stratum .Group File: 8.12.08 September 24, 2008 224 Lovers Lane, Tax Parcel 50210302 I, Brinon, W A Geology Hazard Assessment the natural slope angle. A small drainage ditch has been excavated between the toe of the slope and the bench area. The slope is covered with numerous alder, fir, and cedar trees. An approximately 25 to 30% slope bounds the proposed building pad to the east. The slope has been cleared of trees and is thickly covered with Himalayan blackberries and scotch broom. The area cleared of trees extends across the second access road to the west. The remainder of the site is well forested with Douglas fir, madrona, maple, alder, and cedar trees and undergrowth of ocean spray, evergreen huckleberry, and ferns. No indications of springs or seeps and no indications of landslide movement were observed on the subject property. CONCLUSIONS AND RECOMMENDATIONS It is our opinion that no landslide hazards are present on the subject property. It is our opinion that proposed building area on the gentle sloping bench area located on the northwestern portion of the site will not be at risk from landslides or other slope stability problems nor will the proposed development cause any instability elsewhere on or off the property. The slope to the west of the building pad area is stable and is not subject to slope failures. No setbacks are required from this slope. Storm water run off from the roof gutters, foundation drains, and other impervious surfaces should be dispersed in such a manner as to avoid excessive concentration of water at a single point. The small drainage ditch should remain along the west side of the proposed development to drain any surface water to the south. The building foundation should be placed in undisturbed glacial till materials. We appreciate the opportunity to be of service to you. Should you have any questions regarding please contact our office at (360) 714-9409. 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. Stratum Group f4 MrUnJ-&r:J''tfl..;1L-- ii~'Ninnemann, B.S., L.G. I Licensed Geologist k:. GaO' (;.!.111 , - 2..f--# I ~~;~!ii~ File: 8.12.08 . .A If' ,~. Ct:'~~""i"'~J. ~.J* H?J.r h~ . .. --,."..-'~"'~""'-; 122056'00" W Figure 1, Site Vidnity Map 122055'00" W WGS84 122054'00" W z 1 \ ~~ W} 1\ ~ '\ I \. ~~ I .;.~~\ :~" ~'/~; ~~ z ~ ~\~I~_'- \' ~"-// ,.\' 0 ~'I ~'-T ' ~~) 'r'\" - 1 , / ~~/ 'L..";'f ~'----"'.A ~.oo~ /..::::t ~~l,,# ~ ~I/ f.." .: ~.JJJ ' fI ~ ;;-v//.. 'I:)..~ ~ / /f j ~~ .lc':~((~ .\../'////: ~ll ! <.,3/ '?'~ f',"f ~~1J/tf ~~~'/m' :;~~~i~'~'j~~, w TI~ ~~"" -r ~ ~~.t ~~~. 'i\":::H.i. r- "A V /1 t), ~' "'A ~ '/ ,," ."-N........,. V\ n"'- // ~ 0 +; U 'i, ""'" \ ~~ })(<' . ~ 4s ~~ ~ '/ ,.~!~ /' z \J ::::"'" .;..--...; ~ a SUBJECT PROPERTY~ {,' b 'I-,.~ ~ ~( ) I ) '/1/1/ /' *~ . ~ y:~~~ 'I, '-~ L;- ~./ /1~!c;<'(P< o ~ ~ .-..K.,..k:....~.,1 "'..., .~!! # / /'~ !;t ..,;, rr Bf- ---:::;r ",~'t~:.' ~~ M '/1 \..............--.. "~~.r . ~, ':. ~ ^ ~ - ~\,' "o..p~ " .~;;, ~ """l...- /.1 eJ "..:" } ~ 4$,r:::.~ ~ ,.""" Piles ,".' . '. ..." ':f; ~ ~ ~I:\~{! .. (f"'J(r ;Ii! ~/ .....,..,..... ',).'f" '/1 ;ffr~' lJO ~~ 1\\ " -~I · ')/ .' .", I Jf " ,:;0 ~. I ~r\,\1..----, · "{I I ~:;::;;-~ r-l ~I : ,it 'i -<R '"-"r ~ ~ ~ :of, ~~ . .~ @. ~n~,'~\J ~'~', 1+:\. ~. . ~ A ~ ~... ~"~ ~~ .~. .,,~, ~ ~'. :.'. ';.,., ~";L ',. ~ 1('( _\' ')3 .rfJ ;?~mO 0' ~~~~\ ~ z"" ~ ,..)fV~ ~,..ew~~1 ~ :7 Iii g } (.;..~ ' -- x" '" 14 M ,....... c. ~, J.! ~Ph~g~ ... ~~ .~~ : . . '" ~~~- _ ,J., . ....' Ouatsap ~ : '!3 ~ :"'- "..~ ,<:~:it:",".;;7"'P--"" Point ~ f~.\ ',=j J TNj !.MN V 180 122056'00" W 122055'00" W WGS84 122054'00" W o .5 I M11~ , L_ ~~9 ~ ~W~ Map Cleated with TOPOl@! @2003 National Geographic (www.namnalgeographic.comltopo) z b o .... .>t ,/ !;t , on z b o b v o ~ V z o o - (f\ (Y) o ~ V ~ ~ Foresteel Slopes (45%) ~ Ditch Approx. Bounelo.ry of Tree Cleo.reel "" Areo. "j ~ \ ) / ~ / ./"" - - - - For Site Sketch bo.sed off of Prelll'llno.ry Site Plo.n, To.x Po.rcel No. 502103021 t by Miles Y o.nlck o.nd COl'lpo.ny -I N STRATUM GROUP PO Box 2546 Bellingho.M, 'viA 98227 360-714-9409 $co.l... 1 Inch = -6lI Feet DeslgNd B)" KN Sept 2008 FIGURE 2. Site Sketch Jefferson County Po.rcel 502103021 224 Lovers Lo.ne) Brinnon) 'vi A