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Home My WebLink AboutGEO-Tech Review BLD2005-01058 - BLD Engineering / Geo-tech Reports - 7/29/2005 STA7- MASON COUNTY P o S°U = PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER y O N Shelton,Washington 99584 ~� N Y Y �0 lssa �c DATE: July 29` , 2005 INTER-DEPARTMENTAL COMMUNICATIONS TO: Tammi Clark, DCD -Planner FROM: Alan A. Tahja, P/W- Co. Hydr. Engr. WO#PLG-05 SUBJ: Geo-Tech Assessment Review NAME: Iverson SFR A 280 E Spruce St BLD2005-01058 The geotechnical assessment prepared for the proposed Don Iverson Single Family Residences (SFR)to be constructed at 280 East Spruce Street, Union,has been received and reviewed by Public Works. A search of the County's permit tracking program found no evidence that an access permit has been applied for or issued for this location. Kelle Medcalf at County extension 450 should be contacted by the applicant to receive information regarding applying for a County Road Department Access Permit. (Spruce Place listed as Co. Rd.No. 5137) The geotechnical assessment appears to satisfactorily fulfill County requirements for geotechnical assessment reporting. 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 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 prepared for the proposed Single Family Residence appears acceptable, and stability issues may be considered to have been adequately investigated and addressed, but the applicant should be directed to acquire an access permit before any land disturbing activities are permitted on the property. 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. Sin erely, • [ � an A.7d Tahj File: H: \WP\GEO\Assessments\lverson.doc WORK ORDER -PUBLIC WORKS DgkC. E I VI W. Otte: _ .,..�....,,.,.. PERMIT#1: U _' . Iq Work order Numaen I r415 - Requested br. . /CP } a MASON COUNTY r- S Authorized : "T "" Date. Type of Woft CHARGE TO: NAME rwid AGENCY/COMPANY BILLING ADDRESS PHONE - Pub. orke T . . in e: !QI e: m-to # Pr"ewt er114 as ' Edmd d>ta,Dds:. EiTNAATED TOTAL n., oosTNBTEAIITe IW 20Elmalo�wl fy ( TOTAL S os zz . 3 F zz EQwuncr usm 9 !�!Q gam. IWALft f FI A t d Cost 3 SARE: PRa,I/h DATE EQ Nam �� Ilovrs ( 'FdnW,S TOTAL$ EQUIPMENT USED: gal OTe43� MATERIAL.USED: TOTAL ALL 3) 81llED DATE PAID DATE REQJ F7V I`yes �� z vo5 TO SE KEFT IN THE PARCEL FILE ,-3 A A 35r Geotechnical Assessment 280 E. Spruce Street Union, WA Prepared for: Don Iverson by Geotechnical Testing Laboratory Olympia, Washington July 19, 2005 TO BE KEF 1" IN THE PARCEL FILE GEOTECHNICAL TESTING LABORATORY DON AND DONNA IVERSON P.O. BOX 521 UNION,WA 98592 RE: GEOLOGICAL ASSESSMENT 280 EAST SPRUCE STREET UNION,WA 98592 PARCEL 322325220017 N47020.995' W 123°05.802' 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 residence. Currently, an onsite septic system is undergoing approval. The site is serviced by community water. SITE CONDITIONS The subject site is approximately 0.3-acres located - 0.5 miles south of Union, Washington. The site is `-w.•• accessed from Spruce Street. The subject site is located in an area of moderate residential ' development. Some of the surrounding parcels are ; residentially developed. Currently the site is vacant and vegetated. The steepest portion of the site has slopes approaching 24 percent along the southern property line. The slopes are well 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)754-4612 Fax#: (360) 7544848 GEOTECHNICAL TESTING LABORATORY GEOLOGIC CONDITIONS The Soil Survey of Mason County, USDA Soil Conservation Service (1960) has mapped the site soils as an Alderwood gravelly sandy loam, 15 to 30 percent slopes (Ac). The Alderwood soil typically formed from glacial advance outwash. The soil is 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. r _ w 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. +�- 1 • ` ^ham• rD - a S 4 10011 Blomberg Street SW, Olympia,WA 98512 2 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY The Geologic Map of the Shelton 1:100,000 Quadrangle, Washington, by Logan(2003)describes the site as late Wisconsinan(Pleistocene). The glacial till (Qgt)is described as: Unsorted unstratified, highly compacted mixture of clay, silt, sand gravel, and boulders deposited by glacial ice of the Puget lobe; gray; may contain interbedded stratified sand, silt, and gravel, sand-size fraction is very angular and contains abundant polycrystalline quartz, which distinguishes this unit from alpine till; cobbles and boulders are commonly striated and(or)faceted, although unweathered almost everywhere, may contain cobbles or small boulders of deeply weathered granitic rock 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 presumed , " deep and beyond the scope of this report. Ponding was observed in a low point along Spruce Street. DEPTH TO COMPETENT SOIL Typically, dense gravelly sandy loam is found throughout the site. Competent soil can be expected approximately 8 to 12 inches below the ground surface. .-wt.. - 10011 Blomberg Street SW, Olympia,WA 98512 3 Phone#: (360)754-4612 Fax#: (360)7544848 GEOTECHNICAL TESTING LABORATORY 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. The Relative Slope Stability of the Southern Hood Canal Area, Washington, (1977) describes the site area as Class 2. Class 2 is described as: Areas believed to be stable under normal conditions, but may become unstable if disturbed by man's activities, if slope is oversteepened by erosion, or if subjected to strong seismic shaking. Slopes generally steeper than 15 percent, but may be less in some areas of weak geologic materials. Includes areas underlain by: well-drained sand and gravel, mostly on valley sides that lack known slope failures; glacial till with steep slopes; and bedrock. . +i .N .ab s .' Proposed Building Location ik F 1 View Looking Southeast ,.tar. 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. , ._ View Looking Northwest Proposed Building Location n ��r 10011 Blomberg Street SW, Olympia,WA 98512 4 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY r Septic Lomfim IN View L.00kingNalhwed POTENTIAL FOR LANDSLIDE ACTIVITY This site has no indication or record of old or recent landslide activity. Even though slopes approach 24 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 or soft rock. The Coastal Zone Atlas, Volume 9, Mason County (MA-7) maps the site as Vashon glacial till (Q„,) throughout the site. �41 Ayfe Foundation stability is described as "excellent." Seismic 4p' g stability is described as "good." The slope stability is described G 41 as"unstable." �1:24.000 E N D Yilo C- S Stable (S) Stable slopes generally rise less than " ""- 15 percent in grade, except in local areas of low groundwater concentration or competent — bedrock. Stable slopes include rolling uplands and lowlands HUD rtlli underlain by stable material such as unweathered till and/or peat deposits which, although inherently weak, have no significant slope. S 10011 Blomberg Street SW, Olympia,WA 98512 5 Phone#: (360)754-4612 Fax#: (360) 754-4848 f GEOTECHNICAL TEST ING LABORATORY nj �Tl t >. Septic Location ' r a Proposed Building Locatinl Ar: r ?2. View Looking NoRh � r RECOMAMNDATIONS , There is no evidence of soil erosion or deposition onsite to �� d�► 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. ♦0 0� Wash/. r0 Respectfully, GEOTECHNICAL TESTING LABORATORY �r leiMI�o Harold Parks, L.G., L.E.G. L. Senior Engineering Geologist NAROLD PARKS E,kp 7—3/—O k 10011 Blomberg Street SW, Olympia,WA 98512 6 Phone#: (360)754-4612 Fax#: (360)754-4848 • Sr�� uJrirr;r� �,■i1�ty��N��i�,�-Il�ii►lid,.�►��11`i1ut��/r�11;t�1��1r_•r:11`f%%JIF - /� rr l 1"W"Irdi ,