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Home My WebLink About901172001 Geotech AssessmentSTRATUM GROUP 1451 Grant Street, Bellingham, WA 98225 Phone (360) 714-9409 November 25, 2003 Terry McHugh John L. Scott Real Estate 2219 West Simms Way Port Townsend, WA 98368 Re: Geology Evaluation, Shoreline Bluff Tax Parce1901172001, Section 17, Township 29 N, Range 1 W Jefferson County, Washington Dear Mr. McHugh: We are pleased to present the results of our geology evaluation of the above referenced property on a shoreline bluff. The purpose of this geology evaluation was to 1) determine the suitability of the property for the siting of a residence, 2) qualitatively evaluate the risk of slope failures, and 3) provide general site development and maintenance recommendations for development of the property adjacent to a potentially unstable bluff. This evaluation was limited to a visual inspection of the property and vicinity, a visual inspection of the bluff face, review of available geologic mapping in the area, and inspection of the shoreline at the base of the bluff. SCOPE OF SERVICES The scope of our services included the following: 1) Conducted a site visit to visually inspect the subject property including the bluff face slope conditions, shoreline conditions, and relevant conditions in the vicinity of the property. 2) Observed surface soil conditions on the bluff face and on the uplands above the bluff by excavating shallow hand dug test pits. 3) Prepared this report summarizing our findings, including an evaluation of the feasibility of building a residence on the subject property, a qualitative evaluation of the shoreline bluff stability, recommendations for site development, and recommendations for further investigation, if necessary. ~~ ~~~~~ ~~ j ~~ November 27, 2003 Tax Parcel 90 1 1 7200 1, Jefferson County, WA Geology Evaluation, Shoreline Bluff GENERAL GEOLOGY Northwestern Washington has been occupied by continental glaciers at least four times during the Pleistocene Epoch (l .6 million to 10,000 years ago). During these glacial and accompanying interglacial periods, the underlying bedrock was eroded and glacial related and interglacial fluvial sediments were deposited over the underlying bedrock in the vicinity of the subject property. The Surficial Geologic Ma~of the Port Townsend 30 by 60 Quadrangle PuPet Sound Re;;ion, Washington (Pessl, Dethier, Booth and Minard, 1989) indicate the steep shoreline bluff exposed on the subject property is underlain bedrock. The Bedrock Geologic Map of the Port Townsend 30 by 60 Quadrangle Puget Sound Region, Washington (Whetten, Carroll, Gower, and Brown, 1988) indicate the bedrock underlying the site and vicinity consists of Crescent Formation conglomerate. While bedrock consisting of Crescent Formation conglomerate and Crescent Formation basalt is present in the vicinity of the property, the property is underlain by glacial till and ice-contact deposits. These glacial related deposits are compact. SPECIFIC SITE OBSERVATIONS The site location map is provided on Figure 1 and a general site plan sketch is provided on Figure 2. The property is accessed via a gravel road off of Highway 20. The property slopes down to Port Discovery from Highway 20 and is approximately 6 acres in size. The upper, east end of the property adjacent to Highway 20 is at elevation of approximately 200 feet and the west end of the property is at the shoreline of Port Discovery. The overall slope of the property is approximately 13 degrees based on the topographic map. However, the slope on the property varies from gentle slopes to as steep as 35 degrees. The west end of the property at the shoreline consists of a former railroad grade that followed the shoreline along Port Discovery. The level railroad grade is approximately 8 feet above the high tide line. Most of the railroad grade along the property has been armored with rock and concrete debris. The beach consists of boulders and cobbles. Some minor erosion has taken place in areas not armored with rock and concrete debris. No unstable slopes were observed on the property except for minor soil creep on slopes greater than 30 degrees. The slope immediately above the railroad grade consists of a cut slope that was likely excavated at the time the railroad was constructed. The maximum height of the cut slope on the property is 20 feet. Soils on this cut slope consist of compact glacial deposits. Except for minor raveling and shallow sloughing, the cut slope is stable. Another small cut slope is present along an old road cut down to the railroad grade through the compact glacial soil. File: 11.8.03 Stratum Group .~ k ~~ November 27, 2003 Tax Parcel 901 172001, Jefferson County, WA Geology Evaluation, Shoreline Bluff The access road switchbacks down the slope past several very gentle slopes and nearly level areas. Most of the subject property is tree-covered with Douglas fir, western red cedar, big leaf maple and red alder with an understory of brush. A few cleared areas along the road are brush and grass covered. CONCLUSIONS AND RECOMMENDATIONS Based on my visual inspection of the subject property and vicinity, I conclude that a residence can be located on the property such that bluff erosion or landsliding will not threaten the structure within the expected life of the structure (75 years) as long as our recommendations are followed. Numerous building sites on level areas or areas with slopes less than 20 degrees are present on the subject property. Building in any such area will not require further review. The lower level area above the railroad grade cut slope is a suitable building site. If a home is constructed at this building site, it should be set back at least 15 feet from the top of the cut slope. If the house is to be set closer than 15 feet from the cut slope, I recommend that an engineer designed retaining wall or fill be used to support the cut slope. If the home site is located on slopes greater than 20 degrees, additional site specific evaluation on cut and fill slopes should be conducted and may require engineer design retaining and/or fill. We do not anticipate that the development of the subject property will cause any negative impacts on the stability of the slopes or the shoreline bluff as long as our recommendations are followed. We recommend that roof drains and any other drainage be discharged to a location that will not pose a risk of surface flow over the railroad cut slope. If the home is built above the cut slope, the storm water should be conveyed via tight line to an infiltration area on the level area of the former railroad grade. The septic drain field should not cause problems for slope stability and may be located within 50 feet of the top of the railroad cut slope. Stratum Group Fite: 11.8.03 November 27, 2003 Tax Parcel 901 172001, Jefferson County, WA Geology Evaluation, Shoreline Bluff Stratum Group appreciates the opportunity to be of service to you. 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. Should you have any questions regarding our reconnaissance please contact our office at (360) 714-9409. Sincerely yours, Stratum Group ~`-- -~ Dan McShane, M.Sc., L.E.G. Licensed Engineering Geologist e~ 376 ~ar+ie9 ~~~~~e Stratum Group Pilc_ 11.8.03 F4gme 1. V~cinityMap 122°51'52" W NAD27 122`4R'24" V/ • ~ E. o~,~l - " ~ ~ tom- ~i -~ ~ o ~ t~ ' {, Y ~ ~ i ~ f ~ (i~ ~..._~ __.. ~~{g~~yy ~ ~ I 5 _ tEk ~a 4 ~ _ ' t 1 f ]7]7//// p ~T ~ F J ~ `~ ~ ( r ;, ~" a ~ ! 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