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Home My WebLink About502112020 Geotech Assessment~t_pb~ - O6 i ~ !o STRATUM GROUP 1451 Grant Street, Bellingham, WA 98225 Phone (360) 714-9409 January 20, 2006 Cecile Culp 906 178` Ave NE Bellevue, WA 98008 Re: Geology Hazard Assessment Report Tax Parce1502112020, Eagle View Brinnon, Washington Dear Ms Culp: SY'y~ f ! `! r t...~ IE .~ ~~ + ~l 4 ~ ~~ if ? d,. ~t ~ • ~ _ ~l .l ~ I ~ I Sai`1 g ~„. ,t ~~ .... Stratum Group is pleased to present the results of our geology evaluation of Tax Parcel 502112020 within the Eagle View subdivision south of Brinnon, Washington. The purpose of this geology evaluation was to qualitatively evaluate the risk of slope failures impacting proposed development on the property 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. 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 1. The property is located in the northwest quarter of Section 11, Township 25N, Range 2 West W.M. 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 abovethe 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. 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 ~~ January 20, 2006 Tax Parcel 502112020, Brinon, WA Geology Hazard Ass~scment 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 Sur6cial Depa-sits in the Seattle 30' by 60' Quadrangle Washington (Yount, Menard and Dembroi~, 1993) indicates that the subject property and vicm><ty is underlain by glacial till and bedrock. Observations on the subject property are consistent with this mapping. The property is underlain by a veneer of glacial till and very compact ice-contact deposits over bedrock that consists of basalt. The Bedrock Geolosic Ma~of the Seattle 30' by 60' Quadrangle, WashingLton (Yount and Gower,1991) indicates that mapped bedrock in the vicinity is basalt of the lower Eocene Crescent Formation. The ridge along the western side of 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. This formed from lava flows within seawater. Glacial striations are also readily observed on the exposed bedrock surfaces at several locations. The striations are oriented approximately north-south indicating the last ice movement over the area was part of the Puget lobe. 'fhe till and ice contact deposits underlie the lower eastern portion of the property. The till and ice-contact deposits generally are poorly sorted coarse-grained material with ample cobbles and boulders. The till deposits consist of cobbles and boulders within a matrix of sand silt and clay. SPECIFIC SITE OBSERVATIONS The subject property is located on a slope above Hood Canal and U.S. Highway 101 on the west side of Hood Canal within the Eagle View subdivision. The property is located at the end of Talons Roost Road on the upper, westernmost portion of the subdivision. I inspected the slope conditions throughout the property. Generally the slopes on the site and in the vicinity are fairly gentle. Due to the glacial erosion of the bedrock there are steep slopes on the site and vicinity that are on the order of 30 degrees. These steep slopes are underlain by bedrock and are very stable. Slopes appear to be stable throughout the site. The property is tree and brush covered with a few areas of smooth bedrock or moss covered bedrock on the top of the ridgeline on the western portion of the property. No springs or seeps were observed anywhere on the site at the time of my site visit in January 2006. ~ y . t ~, ~';c~'%C~1I~ ~~,~~ll Stratwn Group Fill: 12.20.05 ~,....: 2 January 20, 2006 Tax Parcel 502 1 1 2020, Brinon, WA Geology Hazard Assessm~t CONCLUSIONS AND RECOMMENDATIONS It is my opinion that slopes throughout the site are stable and building can take place anywhere on the site from a geologic perspective. Development on the site will not be at risk.from landslides or other slope stability problems nor will the proposed development cause any instability off the property. If building is to take place on the uppermost portion of the property on the bedrock ridge an access road will be required. This should be readily achievable by angling a road up the slope. A road angled up this slope may require minor cutting into the bedrock slope. The bedrock is very hard and competent and will likely require blasting as the bedrock is very hard and does not have any developed fracture zones. Blasting of the bedrock will not cause any problems with future stability of the slope unless the blasting is extremely excessive. Storm water run off from the roof gutters and road access should be routed in such a manner as to avoid excessive concentration of water at a single point. As the site is underlain by bedrock or very compact glacial deposits over bedrock building, the impact of structures on storm water will be minimal. Because the depth to bedrock is relatively shallow or at the surface, I suggest that the buildings be founded on bedrock if feasible. However, on the sites where bedrock is not very near the surface founding on the glacial till or recessional deposits will be acceptable. The slopes to the east of the building sites should be maintained in natural vegetation. Topping and limbing of trees for view purposes will not cause any slope problems. Stratum Group appreciates the opportunity to be of service to you. Should you have any questions regarding please contact our office at (360) 714-9409. Sincerely yours, Strsttum Group '~-~ Dan McShane, L.E.G., M.Sc. Licensed Engineering Geologist Stratum Group 1.~. J e ~ .,c ._. ~ .._,.1 F; Fik: 1220.05 3 Figure 1. Sit Vtdrpty Map 122°56.000' W 122°55.000' W 1ZZ°54.000' W WGSl34 122°53.000' W r- r~ ~.. •'`' ~ r r u ~'~`~'EL. `~ f .r •, ~ ~ y •,,: ti .~ .5 ~r ~ `\ '~ ti r ..i~`-- Ft%o '`.~``ti ~J B l'f !! 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