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Home My WebLink AboutGeoTech Assessment Review for BLD2004-00726 - BLD Engineering / Geo-tech Reports - 10/29/2004 1 ST N,OATFo MASON COUNTY o AS t N_ PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER y ` Shelton,Washington 98584 °° 1864 \° DATE: October 29 h, 2004 INTER-DEPARTMENTAL COMMUNICATIONS TO: Rick Mraz, DCD -Planner FROM: Alan A. Tahja, P/W - Co. Hydr. Engr. WO#PLG-04 SUBJ: Geo-Tech Assessment Review NAME: Barber SFR @ Tahna River Road BLD2004-00726 Rick, The geotechnical assessment prepared for the proposed Larry Barber Single Family Residence (SFR)to be constructed at 811 NE Tahuya River Road, Tahuya,has been received and reviewed by Public Works. The report appears to satisfactorily fulfill County requirements for geotechnical assessment reporting. The assessment's author indicates that, in his opinion,the completed development of the property will not cause stability problems for either the subject property or neighboring properties, and that a more detailed investigation(report) is not warranted. From the contents of the assessment, I recommend accepting the report as satisfying the County's requirement(s) for stability investigation and geotechnical reporting. Recommendations contained in the assessment should be incorporated into the site's development and made conditions for permit issuance. Adequate Erosion and Sediment(E&S) control (Ecology Stormwater Best Management Practices(BMPs)) 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. In summary,the geotechnical assessment appears acceptable, and stability issues may be considered to have been adequately investigated and addressed. Please feel free to contact me at County extension 461 if you have any questions regarding these comments,or if you feel any features need further discussion or attention. S, cerely, Alan A. Tahja File: H: \WP\GEO\Assessments\Barber.doc WORK ORDER - PUBLIC WORKS DEPT. (A) Date: -� o (� Work Order PERMIT M a, 71� Number Requested by: I cr 4z Authorized by: Date: Type of Work: a ieL',� CHARGE TO: I MASON MUNTY PUaLI�; p NAME ��P � � L+�tR>( "-aut AGENCY/COMPANY BILLING ADDRESS , PHONE Y S 71 (B) Pub Works Person In Charge: n 7� ; (C) Project Time Line. (from to dates �joti TO Project Start date: Estkiw ed Fk*h Date: Appr°DkWe f10tirs: ESTIMATED TOTAL$IS: �j Z z COST ESTIMATE (D) P314 Employee 14 MQM SUM041 Frinae% TOTAL S 10 29 zz 3 z t3AIE EQUIPMENT USED: TOTAL$s MATERIAL USED: ,Y:::�::`<>- ;:,;�c:;:>;,»;»:-;;,:..;;,�«: - - - ,,.�:st�,x.?aL'.=�?:.,,-fit.+'b.4�`;�;• ...,"'!.;^.... .,t:c� .,K,.. ..,....,,,�-.,��,;,��<;�,;� '.;.::,,.. 13SE:O�.Y';:�:\.�.._ ..:4:, .. z.:.,...,v....?'-,„.�,rY•-Y^';cv, +uii;A:.:`..Zxac4:Sa..:c..n'ak-::'e'tkii9is�c7ot:iS'.Mia:u.a�:,r.:...w::...w...v:.v:aw.<cICYY:�`� ;o-'::.,::,.....::+ �,:t?._.�1•.w`i`�: %�r:"Gi:�._A.-:i:F.^.:::5. (F) Actual Cost s BARS: PROD P DATE EnploTee — -- Hours Frime% TOTAL$ EQUIPMENT USED: Date Vila Rate TOTAL SS MATERIAL USED: TOTAL ALL (G) BILLED DATE INV 0— PAID DATE REC.M Cat �v- 6ev RECEIVED OCT: 2 6 2004 426 W- CEDAR ST! Geotechnical Assessment 811 NE Tahuya River Road Tahuya, WA Parcel #322127500070 Prepared for Larry Barber Tahuya, WA bkA 200H CEO -7 Z CQ by Geotechnical Testing Laboratory Olympia, Washington Oct. 18, 2004 GEOTECHNICAL TESTING LABORATORY LARRY BARBER 811 NE TAHUYA RIvER ROAD TAHUYA,WA 98588 RE: GEOLOGICAL ASSESSMENT 811 NE TAHUYA RIVER ROAD TAHUYA, WASHINGTON PARCEL 322127500070 N47024.892' W 123°00.503' 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. A single-family residence with a daylight basement is proposed on the cleared parcel. The septic system and a groundwater well exists on the developed site. `Y i 1 « ' SITE CONDITIONS The subject site is a parcel located approximately 3.5 miles northeast of Tahuya, Washington. The lot is located east of Tahuya River Road, see attached vicinity map. The site is accessed from the Belfair Tahuya Road and then the Tahuya River Road. The subject site (5.15 acres) is located in an area of sparse residential development. The site slopes to the east from the proposed building location. The steepest portion of the site has a slope approaching 31 percent. Minimal grading is expected at the proposed building location except for the proposed daylight basement. The lot is vegetated with mixed vegetation but mostly grasses. 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)754-4612 Fax#: (360)754-4848 � .� a i• .,wrr,�� i��r+raRr:': ie'•ARM�,J jj �• a , WE% vim. lllio. �.� /,. � 1 :�1�► ,,�.!�_ � ors... _ L� 1. -;� ��': ,»•� /�i , Won- gy GEOTECHNICAL TESTING LABORATORY GEOLOGIC CONDITIONS The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the western site soils as Alderwood gravelly sandy loam, 5-15 percent slopes (Ab). The report reads: The Alderwood soils typically formed from glacial advance outwash. They are described as having good natural drainage. Typically, there is no occurrence of a high water table. Internal drainage is described as medium. An erosion hazard may exist if the vegetation is removed, otherwise, the soil has a low erosion hazard in its present condition. Cementation is usually present. The soils are not considered hydric. The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the eastern site soils as an Everett very gravelly sandy loam, 15 to 30 percent slopes (Ek). The Everett soils are described as: Very deep, somewhat excessively drained soil on terraces and outwash plains formed in the glacial outwash stage of the most recent Fraser glaciation. Permeability is rapid(up to 20 inches per hour) with a high rate of water transmission. These soils are typically classified as a "Group A"relative to surficial runoff. The soils are further characterized as having medium runoff potential and moderate water erosion potential. Shrink-swell potential is described as low due to the low organic content. We observed no active erosion or slope disturbance in the site area during our reconnaissance. `i 10011 Blomberg Street SW, Olympia,WA 98512 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY The Geologic Map of Washington — Northwest Quadrant (2002) has mapped the site geology as advance outwash deposits (Qga) of continental glacial origin. The report reads: Advance outwash — Glaciofluvial sand and gravel and lacustrine clay, silt, and sand deposited during the advance of glaciers; sandy units commonly thick, well sorted, and fine grained, with interlayered coarser sand, gravel, and cobbles; locally contains nonglacial sediments and deposits mapped as transitional between glacial and nonglacial. Includes the Colvos and Esperance Sand Members of the Vashon Drift and part of the Vashon Drift undivided. The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan (2003) describes the western site as Advance outwash, late Wisconsinan (Pleistocene). The Advance outwash (Qga) is described as: Glaciof luvial sand and gravel and lacustrine clay, silt, and sand deposited during the advance of glaciers; sandy units commonly thick, well sorted, and fine grained with interlayered coarser sand, gravel, and cobbles and silt rip-up lag deposits at their base; may contain nonglacial sediments;generally overlain by till. GROUNDWATER CONDITIONS Groundwater seepage was not observed at or near the proposed building location. No wetland vegetation was observed at or near the proposed building location. Depth to static groundwater is unknown. 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. .y X 10011 Blomberg Street SW, Olympia,WA 98512 3 Phone#: (360)754-4612 Fax#: (360) 754-4848 IL GEOTECHNICAL TESTING LABORATORY DEPTH TO COMPETENT SOIL Typically, dense gravelly sandy loam is found throughout the site. Competent soil can be expected approximately zero to 20 inches below the ground surface. Glacial till is exposed at the proposed building location. 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 slopes are dense, compact, and moderate in slope angle. Onsite and neighboring 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 IS 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 areasAw 010 POTENTIAL FOR LANDSLIDE ACTIVITY This site has very little potential for landslide activity. Even though slopes approach 31 percent, the potential for landslide activity is not a concern. Surficial creep and sloughing at the proposed building location is not a concern. 10011 Blomberg Street SW,Olympia,WA 98512 4 Phone#: (360) 754-4612 Fax#: (360) 7544848 GEOTECHNICAL TESTING LABORATORY RECOM MNDATIONS 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. 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, of W$8h!' GEOTECHNICAL TESTING LABORATORY e G.. a Harold Parks, L.G., L.E.G. `g � Senior Engineering Geologist 827 0 eh8ed G9�� HAROLD PARKS 10011 Blomberg Street SW, Olympia,WA 98512 5 Phone#: (360) 754-4612 Fax#: (360)754-4848 CtL�:rli�i�3i .�:��::�Fi• MW� ,_�•- - .,,n�.�r .,1 �� . r' So C�VMS AO .VMA1, ..� NICE. , .- j I �- ._.r--,�r +' ��'��`-�.,.,r� Yam► r�1�► FA V3712�- m I 7f M, �.'-� ►,. _ ' ram;J��-"' �► I�Poll IKE ' J / � 0 o ICJ/