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Home My WebLink About502294010 Geotech Assessmentc .. g - , s .. ~1 STRATUM GROUP -__.. , ,. 1451 Grant Street, Bellingham, WA 98225 F E B 2 ~ Z~(~$ ' ~' Phone (360) 714-9409 _..._.__ January 8, 2008 ~ : `'" ~.~Fj,Fra~ Dan Carlson .2019 NE 179th Street Apartment 2113 Ridgefield, WA 98642 Re: Geology Hazard Assessment 120 Rocky Point Road Tax Parcel 502294010 Brinnon, Washington Dear Mr. Carlson: Stratum Group is pleased to present the results of our geology evaluation of Tax Parcel 502294010 at 120 Rocky Pont Road south of Brinnon, Washington. The purpose of this geology evaluation was to evaluate the. risk of slope failures impacting proposed :development on the properly and to provide general site maintenance recommendations for the property. This. evaluation included a visual inspection of the property and vicinity and review of available geologic mapping in the area. A home is already located on the property. A garage is proposed to be constructed on the property upslope from the home on an existing level area. The property is located on the east side of the Olympic Peninsula on a slope above Hood Canal. The location of the property is indicated on Figure L 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 the proposed garage and residence on the property, recommendations for site development, and recommendations for further investigation, if necessary. { /~ t ~ ._.... ~~~ L O LOOv ~ 1 j January 8, 2008 _ .:J s+ Tax Parce1502294010, Brinon, WA . Geology Assessment - ..i~~ ,;;ENT GENERAL GEOLOGY Northwestern 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 properly. The Geologic Man of Surficial Deposits in the Seattle 30'_ by 60' Quadrangle, Washington (Yount, Menard and Dembroff, 1993) indicates that the subject properly and vicinity is underlain by bedrock. Observations on the subject property. are consistent with this mapping. The Bedrock Geolo ig c 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 property is underlain by massive reddish brown to black basalt that has been very slightly metamorphosed. Pillow structures are apparent within the basalt exposed on the property. SPECIFIC SITE-OBSERVATIONS The subject property is located on a slope above Hood Canal between U.S. Highway 141 and the water on the west side of Hood Canal. The property is access via a gravel road that is part of the access to several other properties west. of the subject property. A home. is already present on the property. A garage had been formerly ocated on the level area at the end of the road. The proposed garage foot print has been shifted from the original garage site. The level area for the proposed garage is bounded on the. south by a reinforced concrete retaining wall downslope of the proposed garage location to support the level area and maintain the septic tank location below. A cut slope is located on the northwest side of the level building area. The slope above the level garage area slopes up towards Highway 101 at an angle of 30 degrees and is approximately 20 feet high. the tap of the slope is:Highway 101 itself The slope is tree- covered with straight Douglas fir trees, a few madrone trees and a thick understory of salal and evergreen huckleberry. The lower part of the slope. has been cut with the cut slope approximately 5 to 8 feet high. The cut slope is cut into bedrock with the exception of the uppermost topsoil layerthat is approximately 2 feet thick. The bedrock is hard and competent with the exception of minor fracturing on the upper part of the exposed bedrock. Stratum Group File: 12.20.07 2 ~- January 8, 2008 Tax Parcel 502294010, Brinon, WA Geology Assessment CONCLUSIONS AND RECOMMENDATIONS It is my opinion that proposed garage building site is not located within a landslide hazard area. The slope above the level building area is stable and the cut into bedrock at the base of the slope will not cause any slope stability problems. Beyond minor raveling of occasional loose material on the cut slope, the slope and the cut slope are stable. Based on my assessment of the geology conditions on the slope, the proposed garage site and the : slope above the garage site are not located in a geologic hazardous area. No set back is required from the base of the slope. However, since the base of the slope is a bedrock cut slope and .some fractures are present in the rock, the garage should be located 8 feet from the base of the cut slope unless a retaining structure is built on the slope or the wall of the garage is designed to support the weight of up to 4 feet of soil. Stratum Group appreciates the opportunity to be of service to you. Should you have any questions regarding please contact our office at (360) 71.4-9409. Sincerely yours, Strum Group t ~J .Dan McShane, L.E.G., M.Sc. Licensed Engineering Geologist ~ ~ ~` `1.~ _` `,~ FEB 2 0 2008 ,:~`~ stratum Group ~ File: t2~2. 0.07 ~ ~~~~ ~. 3 ~1'' _~ _ ~~~ ~r.Li~F'~„EiJT ~ Page.1 of 1 Cara Leckenby From: Dan McShane [mcshanedan@gmaiLcom] Sent: Friday, May 16, 2008 2:20 PM To: Cara Leckenby Subject: Fwd: Carlson Gargage ---------- Forwarded message ---------- From: Dan McShane. <mcshanedan(a~gmail.com> Date: May 16, 2008 1:26 PM Subject: Carlson Gargage To: cleckembvna,co.iefferson.wa.us Cara Question l: The proposed garage location was level at the time of my site visit and my evaluation of the proposed garage location was based on the conditions at the site at the time of my site visit. The site plan you sent me via email shows the proposed garage area as a hatched area behind (up slope of) a retaining wall. The proposed garage site hatch area crosses contour lines that presumably were present prior to the construction of the concrete retaining wall. Evaluating the structure of the concrete retaining wall is beyond the scope of what. I was evaluating. The slope upon which the retaining wall is located is a bedrock slope and that slope is stable. Question 2: At the time of my site visit, Mr. Carlson was unsure of the exact location of the garage related to the cut slope. The slope itself is stable by raveling of material should be expected. From a building design approach. either the wall should be able to support having a rock peal out of the. cut slope and hit the wall or it should be sef back to avoid the need to hold a rocks mass. The slope above the cut is stable and the cut slope itself is not a landslide hazard, but I felt the garage should be constructed or located in a manner that was appropriate for the potential a rock block could become dislodged from the cut slope. Hope this helps for your site visit. Dan McShane 5/19/2008 Sep 10 08 01:09p STR~lTU11+~ GRt}~." ~.0. ~c 2546„ Belt, ww 9227 r~ t~~~la-9a~ sips, 2uas ~ ca~lso~ 20141+iE 179x' Stra.~t Apart 2113 RidBeSeId, WA 9$G42 lie: Gars~e WaII 120 RncJcy Point Road Tax Pac~ce1542294414 $t»mQn, WasSingbaa Dear 11Qt: Csriscna: p.1 . ~~c~ -fig ~~~ It is mytmdeust~mdic~ #hat the garage to be coa~tvcted ou the slue will be laud 5 feet £eom t~1e base of the cut sivpc 1ac~ated on tln: northwest side of the level b tea. la my ga+dlo$y hs~rd assessment of tine sits dated Jarra~- 8, 2008 I concluded tiae proposed garage sires aad the slope abawe the garage site are tvtrt 1t~cated In a g~dogic ~ area. No set beds is Rquired fium the base of the slaps. Flovaevet'. I also t+ecom~adcd ~ aiElo6 the base of the slops is a bedrock cut slope aad sc~ fiat~res are p~seat in the rocdc, flit 8azage should be Wcated $ feet from tl~ base of the art unless a retaiaiug stitxxure is built oa the cut slope ar tihe wail of the garagc is designed to suptwct the weight ~f up to 4 ~ of roii.' Rased an the proposed lot~tion of the 8sra8e wan 5 faq: from the toe of the cut slope.l . . rccommaerd that eiti~s' a =staining stru~ct:u+t be built om the tart slope or due gst wall be deslgt!ted txf SappOt't tlta weight of 2 tlf soil a,~nst tl~e t-utssde wall. AlYeIY, ~ extenat' Wall may uaad t0 pe+arncant soil fr+oza. pilia$ ~ t the $ ~' Stratum Gaaup the oppoorh~astY to ba of service to yuu. Shouhi you nave any questi~s rrgarding please contact tiny td'fioe at (364) 714-94{f9: SiuceralY 3"e~ Saratnm Group ~~. L1an McSl~ne, E..E.G., M.Sc. Liaerrsed Trngituaeaing CTeolagiat ~..,.~ ~ ~~ ~ sa ~~ ra `~ ~~ ~~ SEP 102008. ~ E;OUyTY