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Home My WebLink AboutFPA2007-00003 Geologic Assesment, Review - GEO Geological Review - 6/21/2007 ALKAI CONSULTANTS, LLC . Environmental Engineering • Geotechnical Engineering • Wetland Consulting June 18, 2007 ACL07-06-G179.001 : _. IVED Mason County Department of Community Development J U N 2 12007 P.O.Box 2 .,ASON W.E �, Mn. Shelton, WAA 98584 Attn: Mr. Michael Mac Sems Geologic Assessment Review r',-)ozJ 4- O 1 - O Z04- Permit#FPA 2007-00003 Applicant: GDG Construction Dear Mr. Mac Sems, At your request, we have reviewed a Geologic Assessment for the above referenced permit. The assessment was prepared by Geotechnical Testing Laboratory(GTL)dated April 23,2007. In our opinion, the geologic assessment was prepared in general accordance with the Mason County Resource Ordinance —Geologically Hazardous Areas with one exception. On page 5 of the assessment, GTL states "The proposed building locations will be over 200 feet from any slope over 40 percent. Hence,Mason County requires a geologic assessment. 17.01.100 Landslide Hazard Areas, E Special Reports, 1. Applicability, Category a states that development within 300 feet of any slope over 40 percent will require a Geotechnical Report. Therefore,we recommend that GTL provide confirmation that development will be more than 300 feet from any slope over 40 percent. Should you have any questions or concerns, or if we may be of additional assistance, please call our office at (360)613-2407 or contact us by e-mail at Todd@alkai.net. Sincerely, —4 04 o � a Todd S.Parkington,P.E. Senior Geotechnical Engineer ��Qq�EO SIDNAL Attachments: Geo Tech Work Order Geologic Assessment by Geotechnical Testing Laboratory EXPIRES 5/01/�9 9465 Provost Road NW, Suite 202 • Silverdale. Washington 98383 • (360) 613-2407 • Fax: (360) 613-2408 G EOT'ECHNICAL TESTING LABORATORY MICHAEL MACSEMS MASON COUNTY BUILDING DEPARTMENT P.O. Box 331 BELFACR, WASHINGTON 98528-0331 RE: GEOLOGICAL ASSESSMENT GDG CONSTRUCTION, LLC SITE INFORMATION: OFF KATC>HM.A,C LANE OFF LOG XARD RD. WEST OF SR-3 BELFAI ', WASHINGTON 98528 GPS LOCATION: N470 28.502' W122° 48.749' PARCEL NUMBER: 1232121 00000 Mr. MacSems: As per your request, we have reviewed our report GDG Construction Geological Assessment(GTL Project# 07- 0204) regarding the distance to slopes from potential building locations at this proposed development. We have reviewed topographic naps of the area, reviewed field notes, reviewed topographic information from the Mason County website, and reviewed photos from our reconnaissance. Base upon our review, the proposed building locations will be more than 300 feet from any slope over 40 percent. Please call with any questions regarding this submittal. Respectfully Submitted, GEOTECHNICA,L TESTING LABORATORY ,Blaise Jelinek, EIT Hydrogeological Engineer 10011 Blomberg Street SW,Olympia, WA 98512 i Phone#. (360) 754-4612 Fax #: (360) 754-4848 Ed WdOZ:TT ZOOE 9E 'unf 8b817bSZ092 : 'ON BNOHd 90-l1S3iO30 WONA GEOLOGICAL ASSESSMENT 40 ACRES OFF LOG YARD ROAD BELFAIR, WASHINGTON PREPARED FOR GDG CONSTRUCTION, LLC. BY GEOTEC14NICAL TESTING LABORATORY OLYMPIA, WASHINGTON APRIL 23, 2007 RECEDE APR 3 0 2007 GEOTECHNICAL TESTING LABORATORY CONTACT INFORMATION PREPARER INFORMATION GTL PROJECT NUMBER: 07-0204 CONTACT: BLAISE JELINEK ADDRESS: 10011 BLOMBERG STREET SOUTHWEST OLYMPIA,WASHINGTON 98512 TELEPHONE: (360)754-4612 FACSIMILE: (360)754-4848 EMAIL ADDRESS: GEOTESTLAB@COMCAST.NET CLIENT INFORMATION CLIENT: GDG CONSTRUCTION,LLC. CONTACT: DAVIN MILLER OFFICE TELEPHONE: (360)275-6878 CELLULAR TELEPHONE: (360)271-2304 MAILING ADDRESS: P.O.Box 331 BELFAIR,WASHINGTON 98528 SITE ADDRESS: OFF KATCHMAC LANE OFF LOG YARD ROAD WEST OF SR-3 BELFAIR,WASHINGTON 98528 PARCEL NUMBER: 1232121 00000 GPS LOCATION: N47°28.502' W122°48.749' 10011 Blomberg Street SW, Olympia, WA 98512 2 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY SCOPE OF UNDERSTANDING DAVIN MILLER GDG CONSTRUCTION,LLC. P.O.Box 331 BELFAIR,WASHINGTON 98528-0331 RE: GEOLOGICAL ASSESSMENT SITE INFORMATION: OFF KATCHMAC LANE OFF LOG YARD RD.WEST OF SR-3 BELFAIR,WASHINGTON 98528 GPS LOCATION: N47o 28.5021 W122o 48.7491 PARCEL NUMBER: 123212100000 Mr.Miller: As per your request, we have conducted a geological assessment and analysis for the above-mentioned parcel. A site reconnaissance was performed on April 17, 2007. The results of this investigation are to be found in the following assessment. We have provided three copies for your review and distribution. We are also a full service laboratory that can meet all your building, testing(soils compaction, asphalt, concrete) and other special inspection needs as well as erosion control and water quality testing. We appreciate this opportunity to be of service to you and we look forward to working with you in the future. If you have any questions concerning the above items,the procedures used, or if we can be of any further assistance please call us at the phone number listed below. Respectfully Submitted, GEOTECHNICAL TESTING LABORATORY Harold Parks, L.G., L.E.G. Senior Engineering Geologist e 0{ Washz Engineering doolagist 827 °�y Sed Ge HAROLD PARKS Fxpin.cs -57 o 10011 Blomberg Street SW, Olympia, WA 98512 3 Phone#: (360) 754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY TABLE OF CONTENTS CONTACTINFORMATION.......................................................................................................................................................2 SCOPEOF UNDERSTANDING.................................................................................................................................................3 TABLEOF CONTENTS..............................................................................................................................................................4 PURPOSE........................................................................................................................................................................................5 SITECONDITIONS...........................................................................................................................................................................6 GEOLOGICCONDITIONS.................................................................................................................................................................6 GROUNDWATERCONDITIONS.........................................................................................................................................................7 DEPTHTO COMPETENT SOIL..........................................................................................................................................................7 PASTSLOPE INSTABILITY...............................................................................................................................................................8 HISTORY OF LANDSLIDE ACTIVITY 9 ................................................................................................................................................ POTENTIALFOR LANDSLIDE ACTIVITY...........................................................................................................................................9 RECOMMENDATIONS....................................................................................................................................................................10 VICINITYMAP..............................................................................................................................................................................I I SITEPLAN.................................................................................................................................................................................... 12 �1• l Ye 1 .'. .i ♦ 1 Yi Ra 4 I v �' 1 � � l-Kt , � �•� �'' � ice,* ti r 't J 1a,yLE'rDR : •, w ' 10011 Blomberg Street SW,Olympia, WA 98512 4 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY PURPOSE The objective of the geological assessment is to assess the surface and subsurface conditions prevalent at the subject site according to Mason County Critical Areas Ordinance 17.01.100.E4. We understand the parcel will be developed by constructing six single-family residences. At the proposed building locations,the slopes range from 15 to 26 percent. The steepest slope measured onsite is approximately 30 percent in the western portion of the site. The Mason County Resource Ordinance Geologically Hazardous Areas(12-27-2006)contains the following: 17.01.100 Landslide Hazard Areas E. Special Reports 1. Applicability Category c. Development proposed within 100 feet of areas of oversteepened or otherwise potentially unstable slopes as a result of stream incision, stream bank erosion, and undercutting by wave action will require a Geotechnical Report. If the proposed development is 100 feet or more from these areas, but not more than 300 feet from them, then a Geological Assessment is required and a Geotechnical Report may be required based on findings of the assessment. The proposed building locations will be over 200 feet from any slope over 40 percent. Hence, Mason County requires a geological assessment. � 1 . r .'r -v 10011 Blomberg Street SW,Olympia, WA 98512 5 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY SITE CONDITIONS The subject site is located approximately 2 miles north of the center of Belfair, Washington. The parcel is located in an area of sparse residential development; see the Vicinity Map (Figure 1)following this report. The site is currently bounded by residential parcels to the west and east sides. Forested parcels are to the north and south. Access will occur from a proposed easement from the western portion of the site. Slope angles on this site range from 15 to 26 percent at the proposed building locations. The lot is mostly vegetated with holly, sword ferns, bracken - ferns, blackberry, rhododendron, huckleberry, Oregon grape, ivy as well as hemlock, maple, alder, and fir trees. Surface water was not observed onsite. No slope instability was observed at or around the proposed building locations. Onsite and surrounding trees are straight and vertical. GEOLOGIC CONDITIONS The Soil Survey of Mason County, USDA Soil Conservation Service(1960)has mapped the site soils as Indianola loamy sand, 5 to 15 percent slopes(Ib). The report reads: This is the dominant soil of the Indianola series. It is associated with other Indianola soils and the Everett and Alderwood soils. Forested areas have a 1- to 2-inch surface layer of organic litter consisting of partly decomposed needles, leaves, twigs, roots, and moss. The surface soil, to a depth of 5 inches, is brown, very friable, single-grain loamy sand that contains a few rounded shot and many roots. The upper 2 or 3 inches of surface soil contains intermittent,firm or slightly hard, irregular aggregates stained with iron. The surface soil is dark brown when moist. The next 10 inches of soil, a transitional layer, is slightly lighter in color than the surface layer and contains fewer shot. The subsoil, a pale-brown loamy sand, begins at 15 inches and continues to depths of 26 to 30 inches. It is dark yellowish brown when moist. This loamy sand is massive but readily crushes to loose, single grains. Yellow and olive colored sands are common. The subsoil gradually changes to the substratum, which is gray and dark-gray sand. The substratum is massive but crumbles readily to single grains when removed. It contains some light-gray,yellow, and yellowish-brown sand. A few pebbles are scattered throughout the profile where this soil merges with the Everett or Alderwood soils. The reaction is medium to strongly acid and is less acid with depth. 10011 Blomberg Street SW,Olympia, WA 98512 6 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 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. a- w .�..� GROUNDWATER CONDITIONS Groundwater seepage was not observed at the proposed building locations or throughout the site. Wetland vegetation was not observed at the proposed building locations or throughout the site. Searches of the local wells from the records available from the Washington State Department of Ecology indicate that depth to static groundwater ranges from 19 to 98 feet. DEPTH TO COMPETENT SOIL The building location is underlain by Vashon glacial till material. Competent material (sand and gravel) was observed at approximately 10 inches below the existing ground surface. 4 s� - � r r y 10011 Blomberg Street SW, Olympia, WA 98512 7 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY -as 4a `N PAST SLOPE INSTABILITY Surrounding the subject site, trees were observed to be straight and vertical. No indication of past instability was discerned at the proposed building locations. No slumping and sliding was observed onsite. At the building location,the slope is between 15 and 26 percent;no signs of instability were observed. 1 i A < r } ,� r.'" _ 10011 Blomberg Street SW,Olympia, WA 98512 8 Phone#:(360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY HISTORY OF LANDSLIDE ACTIVITY Slumping and sliding was not observed at the site. At the proposed building locations, the slopes are well vegetated with no indication of previous landsliding. The onsite trees are straight and vertical. 6 POTENTIAL FOR LANDSLIDE ACTIVITY Even though slopes approach 28 percent at the proposed building location, the potential for landslide activity is very slight. The onsite and offsite slopes are not a concern for potential landslide activity. The surrounding area includes moderate slopes that are well vegetated. 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 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 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. r 1001 1 Blomberg Street SW,Olympia, WA 98512 9 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY i 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. Proposed activities and site conditions for the 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 removing vegetation. To minimize erosion and sedimentation,we recommend that vegetation remain or be cultivated in 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. Changes to the Mason County Code require our firm to revisit the subject site prior to development, if six months has elapsed,to ensure the conditions are in agreement with our original report. r 4 .2 ..r�. Y) A • 10011 Blomberg Street SW, Olympia, WA 98512 10 Phone#: (360)754-4612 Fax#: (360) 754-4848 INP, No Mill IVAD oA I 1/2 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE CORRUGATED TIGHTLINE 4 INCH /M/Hiiy� MINIMUM,6 INCH SUGGESTED M 10 .aF�;.4� ��.t.M?�•r4Y - ;iy ice` a •...i3.'^.��. -�••','~::7�ta iaw�M's y�..<�"r i�r:'lt:a r!.c., .:.?i'.._v�: .;�v. 45' 4.'i: mii_ w. ' .:)•�:'.r wig :)'-�t',e♦ r,i.Yy- _ -... TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. JLFURE END SECTIONQUARRYSPALL OR ENERGY " DISPERSION DEVICE GRASS-LINED SWALE SHOULD BE A MINIMUM ONE FOOT WIDE AT THE BOTTOM AND ONE FOOT DEEP WITH A MAXIMUM SLOPE OF 5 PERCENT. MINIMUM 4 FEET LEVEL SECTION GEOTEXTILE FABRIC Geotechnical Testing Laboratory Geotechnical Services 10011 ftrrh g St.SW FIGURE 3 QA/QC Services Ph m:(WA 98812 P-:(:0)754484872 DRAINAGE DETAILS Testing Services Fau:(380)754�848 Not to scale ere c tor E N G I N E E R I N G I N C 309 WASHINGTON STREET NE . OLYMPIA WA 98501 . TEL: 360 352-2477. FAX: 360 352-0179 www.vectorengineeringinc.com July 3,2007 RECEIVED Mr.Robert D.Fink,AICP J�� ! � ""fit "� Mason County—Department of Community Development Wen Mason County Bldg 1 P.O.Box 279 Shelton,WA 98584 Subject: Geological Assessment Review Permit#: MEP 2007-00048 Applicant: Levine/GDG Construction Planner: Michael MacSems VEI#: 7054-001 The geological assessment prepared by Geotechnical Testing Laboratory, 10011 Blomberg Street Southwest, Olympia, Washington 98512 for an access road easement at 512 NE Riverhill Drive,Belfair,Washington 98528 Parcel(12321204120)was received and reviewed by Vector Engineering, Inc. The Department of Community Development requested the review for the purpose assisting the Department in determining the amount of potential for landslide activity and the proposed development would not cause significant adverse impacts or there is adequate geological information available on the area to determine the impacts of the proposed development and appropriate mitigating measures. The Department of Community Development reviews all development applications to determine if they are likely to be in or near a landslide hazard area per Mason County Resource Ordinance, Geologically Hazardous Areas, Landslide Hazard Areas 17.01.100, Seismic Hazard Areas 17.01.102, and Erosion Hazard Areas 17.01.104 approved December 27,2006. The geological assessment states the access road will be 50' by 336' with slopes at that location ranging from 5 to 25 percent. The steepest slope is in the eastern portion of the site. Findings 1. Areas identified on the Mason County Soil Survey Map as having slopes greater than 15%is one guide used by the County to indicate areas that have a higher likelihood of meeting the classification criteria for landslide hazard areas. 2. The preparer of the geological assessment, Harold Parks, L.G., L.E.G., is a licensed geologist. 3. The assessment includes a discussion of geologic conditions in the general vicinity. 4. The assessment includes a discussion of the ground water conditions at the site. Page 1 of 3 X:\7000 Files\7054 Mason County Geotech Reviews\7054-001 Mason_Co(Levine_GDG)\Admin\Transmittal Letters\Geological Assessment MEP 2007 00048 Review.doc 5. The approximate depth to hard or dense soil was implied with the Section labeled, "DEPTH TO COMPETENT SOIL". 6. The assessment includes a discussion of the history of landslide activity at the site. 7. The assessment includes an opinion on the potential for landslide activity being low instead on whether the proposed development is within the landslide hazard area or its associated buffer or setback. 8. The assessment includes a determination that a geotechnical report is not warranted unless there are changes to the loads, grades, locations, configurations, or types of facilities to be constructed. 9. No mention was found in the assessment of the presence of a hazard within 300 feet of the proposed development. If a hazard is determined to be within 300 feet of the proposed development, the boundaries of the hazard, and associated buffers and setbacks shall be delineated on a geologic/site map. 10. The assessment includes a site map drawn to scale showing the property boundaries, scale, north arrow, and the location and nature of existing and proposed development on the site. In the reviewer's opinion, provided the recommendations presented in this report are incorporated into the project design and construction, the proposed access road easement will not decrease slope stability at the site or on adjacent properties and the risk for such occurrence would be minimal. However future development in the area should require additional review. Cumulative impacts may have a landslide hazard potential. The geological assessment appears to satisfactorily address County requirements for Special Reports. Comments and recommendations contained in the report should be incorporated into the site development plans and made conditions for permit issuance. Adequate erosion and sediment 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. The conclusions presented in this report are based on Vector Engineering, Inc.' understanding of the project requirements.Vector Engineering,Inc.warrants that its services were performed with the level of care and skill ordinarily exercised by members of the same profession currently practicing in the same locality under similar conditions. No other warranty or representation,expressed or implied,is included or intended hereunder. Page 2 of 3 X:\7000 Files\7054 Mason County Geotech Reviews\7054-001 Mason_Co(Levine_GDG)\Admin\Transmittal Letters\Geological Assessment MEP 2007 00048 Review.doc We have enjoyed working with you on this geological assessement review to support the goals of the Department of Community Development of Mason County, Washington. We look forward to cooperating with you on any future project or review. The invoice,the geo tech work order,and the original geological assessment are enclosed. Please feel free to contact me if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, (Signature) Da Russell La Force, P.E. Design Engineer Vector Engineering, Inc. 309 Washington Street NE Olympia, WA 98501 (360) 352-2477 Seal: �1 Aa Y-%N� V,Asy190 ti 42651 01orr��s EXPIRES Os-25-oq Page 3 of 3 X:\7000 Files\7054 Mason County Geotech Reviews\7054-001 Mason_Co(Levine GDG)\Admin\Transmittal Letters\Geological Assessment MEP 2007 00048 Review.doc GEOLOGICAL ASSESSMENT ACCESS ROAD EASEMENT BELFAIR, WASHINGTON PREPARED FOR GDG CONSTRUCTION, LLC. BY GEOTECHNICAL TESTING LABORATORY OLYMPIA, WASHINGTON APRIL 23, 2007 APR 3 0.200 7 IASON CO. w a'twu GEOTECHNICAL TESTING LABORATORY CONTACT INFORMATION PREPARER INFORMATION GTL PROTECT NUMBER: 07-0214 CONTACT: LANCE LEVINE ADDRESS: 10011 BLOMBERG STREET SOUTHWEST OLYMPIA,WASHINGTON 98512 TELEPHONE: (360)754-4612 FACSIMILE: (360)754-4848 EMAIL ADDRESS: GEOTESTLAB@COMCAST.NET CLIENT INFORMATION CLIENT: GDG CONSTRUCTION,LLC. CONTACT: DAVIN MILLER OFFICE TELEPHONE: (360)275-6878 CELLULAR TELEPHONE: (360)271-2304 MAILING ADDRESS: P.O.Box 331 BELFAIR,WASHINGTON 98528 SITE ADDRESS: 512 NE RIVERHILL DRIVE BELFAIR,WASHINGTON 98528 PARCEL NUMBER: 123212094120 GPS LOCATION: N47°28.4531 W122o 49.0921 10011 Blomberg Street SW,Olympia, WA 98512 2 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY SCOPE OF UNDERSTANDING DAVIN MILLER GDG CONSTRUCTION,LLC. P.O.Box 331 BELFAIR,WASHINGTON 98528-0331 RE: ACCESS ROAD EASEMENT GEOLOGICAL ASSESSMENT SITE INFORMATION: 512 NE RIVERHILL DRIVE BELFAIR,WASHINGTON 98528 GPS LOCATION: N47o 28.4531 W122o 49.0921 PARCEL NUMBER: 123212094120 Mr. Miller: As per your request, we have conducted a geological assessment and analysis for the above-mentioned parcel. A site reconnaissance was performed on April 16, 2007. The results of this investigation are to be found in the following assessment. We have provided three copies for your review and distribution. We are also a full service laboratory that can meet all your building, testing (soils compaction, asphalt, concrete, resteel), and other inspection needs such as erosion control and water quality testing. We appreciate this opportunity to be of service to you and we look forward to working with you in the future. If you have any questions concerning the above items, the procedures used, or if we can be of any further assistance please call us at the phone number listed below. Respectfully Submitted, o{ Wash,� GEOTECHNICAL TESTING LABORATORY Harold Parks, L.G., L.E.G. Engineering Geobpiaf Senior Engineering Geologist �cN 827 �y ��Od GeO HAROLD PARKS �x7�ouetg 7'3(—OT 10011 Blomberg Street SW,Olympia, WA 98512 3 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY TABLE OF CONTENTS CONTACTINFORMATION.......................................................................................................................................................2 SCOPE OF UNDERSTANDING TABLEOF CONTENTS..............................................................................................................................................................4 PURPOSE........................................................................................................................................................................................5 SITECONDITIONS...........................................................................................................................................................................5 GEOLOGICCONDITIONS.................................................................................................................................................................6 GROUNDWATERCONDITIONS.........................................................................................................................................................7 DEPTHTO COMPETENT SOIL..........................................................................................................................................................7 PASTSLOPE INSTABILITY...............................................................................................................................................................8 HISTORYOF LANDSLIDE ACTIVITY................................................................................................................................................8 POTENTIALFOR LANDSLIDE ACTIVITY...........................................................................................................................................9 RECOMMENDATIONS....................................................................................................................................................................10 VICINITYMAP.............................................................................................................................................................................. I I SITEPLAN.................................................................................................................................................................................... 1 10011 Blomberg Street SW,Olympia, WA 98512 4 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY PURPOSE The objective of the geological assessment is to assess the surface and subsurface conditions prevalent at the subject site according to Mason County Critical Areas Ordinance 17.01.100.E4. We understand the parcel will be developed with an access road easement(50' by 336'). At the proposed road location, the slopes range from 5 to 25 percent. The steepest slope measured onsite is approximately 25 percent in the eastern portion of the site. '1 + t. SITE CONDITIONS The subject site is located approximately 2 miles northwest of the center of Belfair, Washington. The parcel is located in an area of moderate residential development; see the Vicinity Map (Figure 1) following this report. The site is currently bounded by residential parcels to the north and south sides. A forested parcel is to the east; Riverhill Drive is to the west. Access will occur from the west. Slope angles on this site range from 5 to 25 percent at the easement location. The lot is mostly vegetated with holly, sword ferns, bracken ferns, blackberry, huckleberry, Oregon grape, ivy as well as hemlock, maple, alder, and fir trees. Surface water was not observed onsite. No slope instability was observed at or around the proposed easement location. Onsite and surrounding trees are straight and vertical. 10011 Blomberg Street SW, Olympia, WA 98512 5 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY GEOLOGIC CONDITIONS The Soil Survey of Mason County, Washington, USDA Soil Conservation Service (1960) has mapped the site soils as an Indianola sandy loam, 5 to 15 percent slope(Ie)and is described ` as follows: In the Indianola series are excessively drained. } droughty, brown soils of the uplands. They have : developed on hummocky and rolling ridges from glacial i4 drift that consisted of loose, porous sand. The sand came mainly from acid igneous rocks. Stronger relief distinguishes this soil from Indianola sandy loam, 0 to 5 1 tr �•. percent slopes. The surface soil is very friable, weakly granular, brown sandy loam. The depth to sand is slightly greater than in Indianola loamy sand, 5 to 15 percent slopes, but the rest of the profile is similar. 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 1 undivided x t , 4 .15.. G 10011 Blomberg Street SW, Olympia, WA 98512 6 Phone#: (360)754-4612 Fax#: (360)754-4848 GEOTECHNICAL TESTING LABORATORY GROUNDWATER CONDITIONS Groundwater seepage was not observed throughout the site. Wetland vegetation was not observed throughout the site. Researches of the local wells from the records available from the Washington State Department of Ecology indicate that depth to static groundwater ranges from 33 to 98 feet. .: -', .r �.,,.o, -- .'Et`F•`. - 4 y~ui 4 i.► kaA- DEPTH TO COMPETENT SOIL The easement location is underlain by Vashon glacial till material. Competent material (sand and gravel) was observed at approximately 20 inches below the existing ground surface. T+.is � ..�i*�i'�(._ r':.►.}"• '., `a�1 -� tiYY J +^ t 10011 Blomberg Street SW,Olympia, WA 98512 7 Phone#: (360) 754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY WIN y a .. r t . t. 2 PAST SLOPE INSTABILITY Surrounding the subject site,trees were observed to be straight and vertical. No indication of past instability was discerned at the proposed easement location. No slumping and sliding was observed onsite. At the easement location,the slope is between 2 and 30 percent; no signs of instability were observed. VW ot(kX*' ULU HISTORY OF LANDSLIDE ACTIVITY Slumping and sliding was not observed at the site. At the proposed easement location, the slopes are well vegetated with no indication of previous landsliding. The onsite trees are straight and vertical. 10011 Blomberg Street SW,Olympia, WA 98512 8 Phone#: (360)754-4612 Fax#: (360) 754-4848 GEOTECHNICAL TESTING LABORATORY �111 Fit., � � i:, 'r• >_ �� '', " i T" eon, e �� r"`�;- �7�•�,�t ., � �� ' �it tit.�RAc',l`'. s• "'' �O',,,r.��.,�� . � . -i . s + �' POTENTIAL FOR LANDSLIDE ACTIVITY Even though slopes approach 30 percent at the proposed easement location, the potential for landslide activity is very slight. The onsite and offsite slopes are not a concern for potential landslide activity. The surrounding area includes moderate slopes that are well vegetated. 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 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 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. OF I� j•;�,�• = t'yY.11.1. ''. f l 1 \♦. .►Y. ` S'7 t J. 1 Y s i yet . Y ` i 10011 Blomberg Street SW,Olympia, WA 98512 q Phone#: (360)754-4612 Fax#: (360)754-4848 G EOTECHNICAL TESTING LABORATORY s jffp It VAC 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. Proposed activities and site conditions for the 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 removing vegetation. To minimize erosion and sedimentation,we recommend that vegetation remain or be cultivated in areas outside the easement 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. Changes to the Mason County Code require our firm to revisit the subject site prior to development, if six months has elapsed,to ensure the conditions are in agreement with our original report. 10011 Blomberg Street SW,Olympia, WA 98512 10 Phone#: (360) 754-4612 Fax#: (360) 754-4848 gioj,,2,Allb-11, t�ry 1/2 INCH MINIMUM DIAMETER STEEL ROD (STRAP)CLAMPED SECURELY TO PIPE CORRUGATED TIGHTLINE 4 INCH C N/ MINIMUM,6 INCH SUGGESTED �2.}ti :.t��1:..�•.: fit.i; :'ti"7"s 71.. .?.:�?s•i.:�.µ �>,...��•�.,!�-is,� 1 w• V.*Tr•.t�.�"i:� ,v.�l•.^L'':J�_i.•. ..F,i'�",SL_C.<..`tY :'r..�;':•:: ,.-.:,:-e',j \�-t.%�aa'1'�i�ii.�•,r',":. '�"� ��.•^•'T j;'oY'•�..� "`.y icy � rye. ..�•.. .:��:Y•-t.�'4r. •�y`.y� ::roc .}. . ;.`�' .,.�`i. •� `'IFS_:'.:;:' ';';',:�..��..`.•Yti •v'r+�'>:!\,•` j..�:.4.�� 'i .L:..L:<;:i`i:'��•��`z •^'1 �?�r'ti;>1.u�:••.�:� TIGHTLINE ANCHORED WITH TWO, 3 FOOT REBAR LENGTHS OR BOLTS. FLARE END SECTION QUARRY SPALL OR ENERGY DISPERSION DEVICE GRASS-LINED SWALE SHOULD BE A MINIMUM ONE FOOT WIDE AT THE BOTTOM AND ONE FOOT DEEP WITH A MAXIMUM SLOPE OF 5 PERCENT. MINIMUM 4 FEET LEVEL SECTION GEOTEXTILE FABRIC Geotechnical Testing Laboratory Geotechnical Services 10011 B10mbwg si sw FIGURE 3 P QA/QC Services hD-:(,WA 98512 Phone:380)754d812 Testing Services Fe (36o)754-4e48 Not to scale DRAINAGE DETAILS