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Home My WebLink About964501501 Geotech Assessment~ p L~~ vu?~ Z~ ~I ~~~ ~t b~-i ~o I ~ STRATUM GROUP 1451 Grant Street, Bellingham, WA 98225 Phone (360) 714-9409 November 18, 2004 Dick Broders 4503 Old Gardner Road Port Townsend, WA 98368 Re: Geology Evaluation ~ Tax Parce1964501501 Jefferson County, Washington Dear Mr. Broder: f~~ ~~VJN'CRl ~:~ We herein present the results of our geology evaluation of the above referenced property on a shoreline bluff. The purpose of this geology evaluation was to determine the suitability of the property for the siting of a residence and qualitatively evaluate the risk of slope failures. This evaluation was limited to a visual inspection of the property and vicinity, a visual inspection of the steep slopes on the property and vicinity, review of available geologic mapping in the area, and inspection of the other slopes in the area. 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 eroded and glacial related and interglacial fluvial sediments were deposited over the underlying bedrock in the vicinity of the subject property. The Surficial Geologic MaP of the Port Townsend 30 by 60 Quadrangle, Puget Sound Region, Washington (Pessl, Dethier, Booth and Minard, 1989) and Geo1o ig c Map of Northwestern Jefferson County (Gayer 1976) indicate recessional outwash deposits underlie the area where the subject property is located. Site observations are consistent with the mapping. The subject property is underlain by sandy gravel and cobbles consistent with the interpretation of recessional outwash deposits. The recessional outwash deposits were deposited by melt water rivers and streams from the retreating glacial ice at the end of the last glacial period approximately 12,000 years ago. SPECIFIC SITE OBSERVATIONS A site location map is provided on Figure 1 and a general site plan sketch is provided on Figure 2. The property located west of U.S. Highway 101 on the west side of D~~SCO,very Bay in Jefferson County. The property is located at an elevation of approximately 130 feet ors the east-facing slope above Discovery Bay. The site is accessed via a gravel road that loops around' the building site. ~~: ~` `~` DEC 3 0 2004 November 18, 2004 Tax Parcel 964501501 Geology Evaluation, Jefferson County, WA The overall slope of the area is less than 15 degrees. The proposed building site has been created by cutting into the slope and by some minor filling down the slope. The cut slope above the building site slopes up at an angle of approximately 40 degrees and a total height of approximately 16 feet. The slope above the cut slope is less than 10 degrees for at least 150 feet. The slope below the level building area slopes downward at an angle of approximately 40 degrees and has a total height of approximately 15 feet. The slope below this slope is very gentle and slopes at an angle of less than 10 degrees. Both slopes appear stable with the exception of minor gravel ravelling on the bare ground of the cute slope above the building area. The level building=area is 75 feet wide and extends from the base of the cut slope to the top of the steep slope below the building area. The length of the building area is 125 feet. 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 erosion or landsliding will not threaten the structure. Any structure should be set back from the base of the cut slope on the northwest side of the building area property at least 5 feet and the structure should be setback from the top of the slope on the southeast side of the level area 5 feet. I do not anticipate that the development of the subject property will cause any negative impacts on the stability of the slopes as long as our recommendations are followed. Roof drains and any other drainage should be discharged to a location that will not pose a risk of surface flow on the steep slope below the building area. I recommend that drainage should be directed via tightline(s) to the ground at the base of the slope. The gravelly soil should be very well drained and will readily infiltrate water run off. 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 asrequired. Should you have any questions regarding our reconnaissance please contact our office at (360) 714-9409. Sincerely yours, Stratum Group an McShane, M.Sc., L.E.G. Licensed Engineering Geologist Stratum Group 122°53'42' Vl z' 0 ,122°53'42' W TN'~ /MN 19° Figuee 1. 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