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Home My WebLink AboutGeoTech Assessment - BLD Engineering / Geo-tech Reports - 5/9/2005 TO BE KEPT 1N 7 PARCEL H� FILE Geotechnical Assessment 181 & 191 Jolly Roger Lane Belfair, WA Prepared for Gary Gordon Olympia, WA by Geotechnical Testing Laboratory Olympia, Washington May 9, 2005 GEOTECHNICAL TESTING LABORATORY GARY GORDON P.O. Box 3282 BELFAIR,WA 98528-3282 RE: GEOLOGICAL ASSESSMENT 181 & 191 JOLLY ROGER LANE BELFAIR,WA 98548 PARCEL 12330-54-00019 & 12331-51-00066 N47026.848' W 122°51.354' PURPOSE The objective of the geological assessment is to assess the surface and subsurface conditions prevalent at the subject site according to Mason County Ordinance 17.01.100.E4. The parcel is to be developed with a single-family modular residence. Currently, an approved septic system has been constructed on site. f y, +r SITE CONDITIONS The subject site is approximately 0.46-acre parcel located north of Lynch Cove on the Hood Canal. The site is accessed from NE Larson Lake Road. The subject site is located in an area of moderate residential development. Two mobile homes are on the site. The mobile homes are placed on fill material that is assumed to be native material, which was graded to a level surface prior to the placing of the mobile homes. The steepest portion of the site, with slopes approaching 25 percent, is situated downhill and to the east of the mobile home pads. The slopes are vegetated with native plant species. Rapid stream incision was not identified at the site. Slope instability was not discerned onsite or on adjoining parcels. 10011 Blomberg Street SW, Olympia,WA 98512 1 Phone#: (360) 7544612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY • } t o A �c s P 1 J Y_ 31 !PAIR � ATE P GEOLOGIC CONDITIONS The Geologic Map of Washington—Northwest Quadrant(2002)has mapped the site geology as glacial till deposits (Qgt)of continental glacial origin. The report reads: Till— Unsorted, unstratified, highly compacted mixture of clay, silt, sand, gravel, and boulders deposited by glacial ice; may contain interbedded stratified sand, silt, and gravel. Includes part of the Vashon Drift undivided. The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as Everett gravelly loamy sand, 15 to 30 percent slopes (Ef). The survey describes the soil as follows: The Everett series consists of somewhat excessively drained, pale- P. . brown gravelly soils. They occur as inextensive gravel ridges on the glacial moraines, or, more commonly, as continuous outwash channels between ridges of Alderwood soils. They have developed .. upon assorted glacial till and outwash material. The rainfall is 45 to 60 inches a year. The vegetation is mainly drought-resistant madrone, manzanita, and kinnikinnick. Everett soils are droughty because the loose gravel and sand subsoil and substratum offer little resistance to downward movement of water. The capacity of the surface soil to hold available moisture is low. Everett soils are in the eastern half of the country, in association with Alderwood soils. They also occur in intricate patterns with the Kitsap and Indianola soils. Compared to the Grove soils, the Everett soils have a paler surface soil and subsoil and, in development, were dominated more by acid igneous parent rock. 10011 Blomberg Street SW, Olympia,WA 98512 2 Phone#: (360) 7544612 Fax#: (360) 7544848 I 1 GEOTECHNICAL TESTING LABORATORY Everett gravelly loamy sand, 15 to 30 percent slopes (Ef). Except for slopes, this soil is similar to Everett gravelly loamy sand, S to 15 percent slopes. Profile characteristics vary greatly from place to place, especially on the steeper slopes. GROUNDWATER CONDITIONS Groundwater seepage was not observed at the building location or near the pads of the trailers. No wetland vegetation was observed at or near the proposed building location. Depth to static groundwater is unknown, but neighboring wells list the depth to static groundwater at 29 feet below ground surface. DEPTH TO COMPETENT SOIL Typically, dense gravelly loamy sand is found throughout the site. Competent soil can be expected approximately 12 inches below the ground surface. PAST SLOPE INSTABILITY Near the proposed building location, trees were found straight and vertical. No indication of past instability was discerned at the proposed building location or throughout the site. Adjoining parcels display similar signs of stability as the subject site. HISTORY OF LANDSLIDE ACTIVITY No historical landsliding was observed during our site investigation onsite or near the subject parcel. At the proposed building location,the low angle slope is compact and dense. Onsite trees are straight and vertical. The Relative Slope Stability of the Southern Hood Canal Area, Washington, (1977)describes the site area as Class 1. Class 1 is expressed as: Areas believed to be stable. Slopes generally less than 15 percent, but may be greater locally in areas too small to be shown at the map scale. - Largely comprises rolling uplands underlain by 5; very stable material such as young glacial till, mantled in places by a thin layer of sandy gravel 1 or other permeable material; also includes flood plains, deltas, alluvial fans, and some beach deposits. Class I areas immediately adjacent to steep slopes of class 3 areas may be threatened by potential landsliding. Normal, proper engineering practices generally are adequate to insure stability y i in these areas. 4' 10011 Blomberg Street SW, Olympia,WA 98512 3 Phone#: (360)7544612 Fax#: (360) 7544848 J G EOTECHNICAL TESTING LABORATORY POTENTIAL FOR LANDSLIDE ACTIVITY This site has very little potential for landslide activity. The pads the trailers are placed upon are relatively flat. To the east of the trailers is a retaining wall constructed of logs. This j retaining wall is not vertical and does not appear to have a drain in the wall to relieve water pressure. To the east of the trailer pads, the slope approaches 25 percent. The steeper slopes are highly vegetated. The Liquefaction Susceptibility Map of Mason County, Washington by Palmer, Magsino, Poelstra, Bilderback, Folger, and Niggema.nn (September 2004) maps the site area as having a very low to low liquefaction potential. . The Site Class Map of Mason County, Washington by Pahner, Magsino, Bilderback, Poelstra, Folger, and Niggemann (September 2004) maps the site area as site class C to D. Site class C is a very stiff soil or soft rock and site class D is a stiff soil. r � f WIN RECOMMENDATIONS _ There is no evidence of soil erosion or deposition onsite to suggest that the site should be included in the Erosion Hazard Area designation. Site conditions for the proposed development do not warrant a more comprehensive Geotechnical Report. We recommend no further action is needed unless areas of concern are unearthed during construction or damage ensues from vegetation clearing. To minimize erosion and sedimentation, we recommend that underbrush remain for areas outside the building location. 10011 Blomberg Street SW, Olympia,WA 98512 4 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY If there are any changes in the loads, grades, locations, configurations or types of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. Respectfully, GEOTECHNICAL TESTING LABORATORY Wash�n r Harold Parks, L.G., L.E.G. Senior Engineering Geologist 827 0 9 HAROLD PARKS �.X�•-7-3 j-�S`s 10011 Blomberg Street SW, Olympia,WA 98512 5 Phone#: (360)754-4612 Fax#: (360)754-4848 I .V .. lor MAJ IBM- r�� )� � � �J_.' �s.r.F�.s..ya t` ir• '�,t yxul ,� k� 3� � K+''i:._ , �'`_� /r ��....\�.`\/ /� I}F i l� 577._.. 77 c Oft. LF E COPY CHANGES SUBMIT CHANGES FOR APPROVAD PRIOR TO PERFORMING WORTS 1 -- ti C � c f G � a L