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Home My WebLink AboutGEO BLD2005-02021 - BLD Engineering / Geo-tech Reports - 9/2/2005 �oN sTArFo� MASON COUNTY �P A o PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER j s T z Shelton, Washington 98584 -� tZ \ y DATE: December 12, 2005 INTER-DEPARTMENTAL COMMUNICATIONS TO: Grace M. Planning PARCEL # 1221325300019 FROM: Patricia Carroll, PW BUILDING PERMIT NUMBER: BLD2005-02021 SUBJECT: Geo-Tech Assessment Review NAME: R&M Investors Hi Grace; The Geological assessment prepared for the proposed garage located at 273 East Spencer Glen Drive has been received and reviewed by Public Works. I concur that addition of the garage will not add any more need for further investigation. The evaluation raises no issues or concerns, and appears acceptable for the level of reporting required. From the contents of the report, I recommend accepting the report as satisfying the County's requirement(s) for stability investigation and Geotechnical reporting. Adequate Erosion and Sediment (E&S) control features need to be implemented during land disturbing activities to protect neighboring properties and State waters from adverse stormwater runoff impacts. The migration or release of silty water or mud from the applicant's property will be considered a violation of County and State water quality protection regulations. Please feel free to contact me at 461 or Bob Thuring ext. 452 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, z]-oc— Patricia Carroll Geological Assessment 273 East Spencer Glen Drive Shelton, WA Prepared for R & M Investors Shelton, WA by Geotechnical Testing Laboratory Olympia, Washington September 2, 2005 GEOTECHNICAL TESTING LABORATORY R & M INVESTORS 271 EAST SPENCER GLEN DRIVE SHELTON,WA 98584 RE: GEOLOGICAL ASSESSMENT 273 EAST SPENCER GLEN DRIVE SHELTON, WASHINGTON PARCEL 221325300019 N47016.315' W122057.643' 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 garage/shop. No septic system is proposed. The parcel is south and adjacent to the primary residence. SITE CONDITIONS The subject site is located 7.5 miles northeast of Shelton, Washington. The site is accessed from Spencer Glen Drive. The subject site is located in an area of heavy residential development. Most of the surrounding parcels are residentially developed. Currently the site is vacant and vegetated with grass. The steepest portion of the site has slopes approaching. 6 percent. Rapid stream incision was not identified at the site. Evidence of erosion was not observed. Slope instability was not discerned onsite or on adjoining parcels. 10011 Blomberg Street SW, Olympia, WA 98512 1 1 Phone#: (360) 754-4612 Fax#: (360) 754-4848 J GEOTECHNICAL TESTING LABORATORY GEOLOGIC CONDITIONS The Soil Survey of Mason County, USDA Soil Conservation Service(1960)has mapped the site soils as Alderwood gravelly sandy loam(Ab). The survey describes the site soil as follows: The Alderwood soils typically formed from mixed gravelly glacial till dominated by acid igneous rock. It occupies undulating to rolling moraines. In undisturbed areas a I-to 2-inch mat of very dark brown, acid organic matter is on the surface. This grades to a thin, dark grayish-brown, highly organic mineral soil. The surface soil consists of a friable, brown, medium acid gravelly sandy loam 8 to 13 inches deep. It has a weak granular structure and contains numerous rounded shot. Below the surface soil, to depths ranging from 18 to 24 inches, is a pale-brown gravelly sandy loam that is very friable, is single grained, and contains small to moderate amounts of shot. Between this layer and the cemented till is a 3- to 10-inch layer of very pale brown gravelly sandy loam. It contains no shot and is firmer but has the same texture as the layer above. However, it is faintly to distinctly spotted and horizontally streaked with brown and yellow. The cemented till consists of light-gray, gravelly sandy loam, and it normally occurs at depths ranging from 24 to 32 inches. It is impermeable to roots and very slowly permeable to water. The first few inches is usually laminated and streaked with reddish brown and yellow. Below this, to a depth of many feet, the till is uniformly cemented, fairly uniform light gray, and medium to strongly acid. A thin mat of roots often lies over the till. The cemented substratum tends to restrict the rapid J downward movement of moisture. The Geologic Map of Southeastern Mason County, Washington, USGS Water-Supply Bulletin 29 by Noble and Molenaar(1970)describes the site as till. The till(Qvt)is described as: Cobbles and coarse gravel in matrix of fine sand, silt, and clay. Generally a compact, unsorted mixture. Extensively underlies drift plains in thicknesses of a few feet to more than 50 feet. Poorly pervious, but has sand and gravel streaks that may yield small quantities of perched groundwater. Serves as confining aquiclude to artesian groundwater at some localities near sea level. lThe 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. lGROUNDWATER CONDITIONS Groundwater seepage was not observed at or near the proposed building location. Wetland vegetation was observed along Spencer Lake. Depth to static groun er is presumed shallow and approximately at the level of Spencer Lake '- 10011 Blomberg Street SW, Olympia, WA 98512 2 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECH NICAL TESTING LABORATORY DEPTH TO COMPETENT SOIL Typically, undisturbed gravelly sandy loam covers the site to a depth beyond the scope of this report. Competent soil can be expected approximately 6 to 12 inches below the ground surface. 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 very stable material such as young glacial till, mantled in places by a thin layer of sandy gravel or other permeable material; also includes flood plains, deltas, alluvial fans, and some beach deposits. Class 1 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 in these areas. R 4^^ 4 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. POTENTIAL FOR LANDSLIDE ACTIVITY This site has no indication or record of old or recent landslide activity. Even though slopes approach 16 percent, the potential for landslide activity is not a concern for the proposed development of this site. �— The Liquefaction Susceptibility Map of Mason County, Washington by Palmer, Magsino, Poelstra, Bilderback, Folger, and Niggemann(September 2004)maps the site area as having a very low liquefaction potential. The Site Class Map of Mason County, Washington by Palmer, Magsino, Bilderback, Poelstra, Folger, and Niggemann(September 2004)maps the site area as site class C. Site class C is a very stiff soil. 10011 Blomberg Street SW,Olympia, WA 98512 3 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATO RY ,a r t r 3Z r �L 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 or maintained landscaping remain or are added for areas outside the building location. 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 0{ Wash' �o (J Harold Parks, L.G., L.E.G. Senior Engineering Geologist HAROLD PARKS 10011 Blomberg Street SW, Olympia, WA 98512 4 Phone #: (360) 754-4612 Fax#: (360) 754-4848 r GEOTECHNICAL TESTING LABORATORY VICINITY MAP 54 t • ^�. ��:,. 'f -.yam ,:r„� + l 29 �f M,Aas-, VT f` f �`E `' � l� -��t�lf.� � � a✓r��';" .`�"i `'fr,� t+ter �,1 � �, '. 000 77 1/•'` :},i:. i �j`oar .�'"t' .,� s=.r � 1/��,� f��i r ,.'S u ,tip �w��_! �P 6 Ff- ( ti �:'Y r��.jr�� i. �✓��-�•, ,�' � f��i`;/.1 d�{�t/'''i`�,�� 10011 Blomberg Street SW,Olympia, WA 98512 Phone#:(360) 754-4612 Fax#: (360)754-4848