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Home My WebLink AboutGeoTech Report and Addendum for BLD2006-00031 - BLD Engineering / Geo-tech Reports - 3/1/2006 a ALKAI CONSULTANTS LLC . Y Environmental Engineering • Geotechnical Engineering • Wetland Consulting March 1, 2006 C ASE gLp 200b"w031�e�►ntProject No. ACL06-01-G005 er MaYet� Mr. Dale Oien N4n . CAI kC k MC Coy P-0, Box P4 seamK, \N A (T83? Subject: Geotechnical Report Addendum Letter 242 NE Riverside Place Belfair, Washington Mr. Oien, The following is an Addendum Letter for our original Geotechnical Report dated February 10, 2006 and follows comments by Mason County regarding addressing the 10 requirements for a Geotechnical Report as follows. (1) A discussion of general geologic conditions, specific soil types, groundwater conditions, and history of landslide activity. See Site Surface and Subsurface Conditions on pages 2 and 3. (2) A site plan which identifies important development and geologic features. See amended site plan following this letter. (3) Locations and logs of exploratory holes or probes. See amended site plan and typical log following this letter. (4) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and which incorporates the details of the proposed grade changes. See amended cross section following this letter. (5) A description and results of slope stability analysis performed for both seismic and static loading conditions. See Conclusions on page 4. (6) Appropriate restrictions on placement of drainage features, septic drain fields, and compacted fills and footings, including recommended setbacks from setbacks from shoreline bluffs and the tops of other slopes on the property. No restrictions on drainage features. No restrictions for septic drain fields beyond the septic design. No structural fill is anticipated,but should be 95 percent by ASTM D1557. No footing restrictions or modifications, but footings should bear on dense native soil. No top or toe of slope setback with the proposed daylight basement. The lower slope is stable and less than 40 percent grade. The upper slope will be graded to a stable configuration,but will need to be vegetated. (7) A detailed clearing and grading plan which specifically identifies vegetation to be removed, a schedule for vegetation removal and replanting, and the method for vegetation removal. Grading will be minimal and will mostly be for the house foundation (see cross section). The slope behind the house will be graded to a 2 Horizontal to 1 Vertical slope. Small trees,blackberries,Scotch broom,and other brush will be removed in the house footprint and slope behind the house.The areas disturbed by vegetation removal should be revegetated by a minimum of a grass lawn immediately following completion of construction activities that impact disturbed areas or cause disturbance. Vegetation may be removed with excavation equipment such as back-hoe,track-hoe,or dozer. (8) A detailed temporary erosion control plan which identifies the specific mitigation measures to be implemented during construction to protect the slope from erosion, landslides, and harmful construction methods. A silt fence should be installed on the slope in the area below the proposed house and disturbed areas protected with straw. GEOLOGIC AND GEOTECHNICAL CONSULTING • J Project No.ACL06-01-G005 Addendum Letter 242 NE Riverside Place,Belfair,WA March 1,2006 Page No.2 (9) An analysis of both on-site and off-site impacts of the proposed development. Off-site impacts will be minimal. On-site impacts will be temporary(disturbance during the construction process)and will be mitigated by the erosion control measures. (10) Specifications of final development conditions such as vegetative management, drainage, erosion control, and buffer widths. Vegetation should be maintained and monitored during wet weather until it becomes established. The drainage properties of the on-site soils should allow for sufficient infiltration of surface water on the property. Erosion control will be managed by maintaining vegetation. No buffer widths are recommended. Should you have any questions or concerns,which have not been addressed,or if we may be of additional assistance, please call our office at(360)613-2407. Sincerely, 01 le David Hurum,L.G. Shawn E. Williams L.E.G.,R.E.A. Senior Licensed Geologist Senior Licensed Engineering Geologist Attachments: Revised Site Plan Typical Soil Log Revised Cross Section s:\alkai shared files\projects\geotechnical\06 projects\06-01-g005 riverside place\riverside place addendum letter ac106-01-g005.doc ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 • Silverdale,Washington 98383 • Ph.: (360) 613-2407 • Fax: (360) 613-2408 t m w G7`-Pat m the . • 3 � r= j f, i � 1 adstirg I / � - w l -�4 oJy m 13 / 4 — Note: Figure adapted from septic plan generated by B.J. Septic - FIGURE 2 Site Plan OFA LK A I CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair,Washington Environmental Engineering•Geotechnical Engineering•Wetland Consulting Project No.: ACL06-01-G005 Client: Mr. Dale Oien Looking North Scale: 1 inch = 20 feet Proposed Graded Slope 0' 5- 10' 1, 21) ....... Approximate Location of ................ Proposed Residence ..................................... ...................... Al—� Foundation ..... Road .......Road......... .............................. See Soil Log .......................Road .............................. for Description . .............. ---------------- --------- ---------------------------------------------------------------------- ----- Figure generated from field measurements by ALKAI using fiberglass tape and Brunton Pocket Transit FIGURE 3 SLOPE PROFILE ALKAI CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair, Washington Environmental Engineering- Geotechnical Engineering- Wetland Consulting Project: ACL06-01-GOOS Client: Mr. Dale Oien RESULTS TYPICAL SOIL LOG FOR H a LABORATORY w w ANALYSES F U W W zVISUAL PHYSICAL DESCRIPTION a Q Q UU 0 (TOPSOIL) 0.5 POORLY GRADED SAND WITH GRAVEL(SP-SM), POORLY GRADED GRAVEL WITH SILT AND SAND(GP-GM) Loose to medium dense,fine to medium grained sand,brown,moist. Becomes dense at approximately 3 feet. 5 Bottom of excavation at 5 feet. 10 Typical soil log of existing excavations performed February 2, 2006 ALKAI CONSULTANTS, LLC . Environmental Engineering • Geotechnical Engineering • Wetland Consulting February 10,2006 Project No. ACL06-01-G005 Mr.Dale Oien P. 0. Sax a4q ,SeAl2bex k, w P% 9 93 6c) Subject: Geotechnical Report 242 NE Riverside Place Belfair, Washington Mr. Oien, Presented herein is ALKAI Consultants,LLC's(ALKAI)geotechnical report for the subject parcel. This investigation was conducted in accordance with our contract agreement dated February 1,2006. The Mason County Resource Ordinance 17.01.100 for Landslide Hazard Areas and a septic design were reviewed in preparation of this report. This Geotechnical Report has been performed in general compliance with Mason County Resource Ordinance 17.01.100. This geotechnical report is based on observed conditions during ALKAI's site reconnaissance of the parcel on February 1,2006 and February 2,2006,and a review of readily available reference resources. The readily available resources listed below were reviewed. • "Soil Survey of Mason County Washington",United States Department of Agriculture, 1960. • The Washington Division of Geology and Earth Resource(WDGER),Geologic Map of Washington- Northwest Quadrant. • The Washington Division of Natural Resources,Division of Ecology and Earth Resources,Folio of the Southern Hood Canal Area, Washington dated 1977. Soil and slope conditions of the subject property were visually examined and evaluated by observing existing test pit excavations on the property and performing a slope reconnaissance. This evaluation combined with available reference material on the site provided a basis for a general understanding of the surface and subsurface conditions as discussed below. R�EC.E �D FEB 1 5 2006 MASON COUNTY-2c- - P 2001 GEOLOGIC AD GEOTECHNICAL CONSULTING Project No.ACL06-01-Go05 242 NE Riverside Place,Belfair,WA February 10,2006 Page No.2 I. SITE CHARACTERISTICS The subject parcel is 0.89 acres located in Mason County near Belfair in Section 20, Township 23 North,Range 1 West,as shown on Figure 1,"Vicinity Map". The subject parcel is currently partially cleared and graded with primitive roads. Access to the parcel is provided by Riverside Place. The proposed development is illustrated on Figure 2,"Site Plan"and shows the locations of a single family residence with a daylight basement and associated onsite septic system. The current and proposed slope configurations are illustrated on Figure 3,"Slope Profile". The parcel is bound to the north, south,and east by single family residences and greenbelt. Vegetation on the slope consists of young Madrona,Maple,Alder,Cedar and Douglas fir. Understory vegetation consists of scotchbroom, Organ grape,and blackberries. Based on these site characteristics,the hill slope is considered a"Landslide Hazard Area"because it meets the following criteria: • Slopes greater than 40 percent with a vertical relief of greater than 10 feet. • Areas with artificial cuts(i.e.road cuts). H. SITE SURFACE AND SUBSURFACE CONDITIONS The Washington Division of Geology and Earth Resource(WDGER),Geologic Map of Washington-Northwest Quadrant, dated 2002, indicates that the site lies on glacial till. In general, glacial till consists of an unsorted, unstratified,highly compacted mixture of clay, silt, sand,gravel, cobbles,and boulders deposited by glacial ice and may contain interbedded stratified sand, silt,and gravel. Materials below the glacial till layer are generally identified as advance outwash or other pre-glacial deposits,consisting of zones of dense to very dense, somewhat cleaner materials, showing some degree of sorting or bedding,or materials of a mixed or indefinite origin incorporated into the till unit. The United States Department of Agriculture (USDA) Soil Survey of Kitsap County Area, Washington, infonnation indicates the following soil type exists on the project site: • Everett gravelly loamy sand with 15 to 30 percent slopes(Ef)over the majority of the site and 5 to 15 percent slopes(Ee)along the northern edge. • Mukilteo peat with 0 to 2 percent slopes(Mg)along the eastern edge of the site. The soil survey description of this soil type is summarized in the following table. USDA Soil Everett gravelly loamy sand Mukilteo peat Survey Name USCS Soil 0-7 inches,gravelly loamy sand,GP-GM, 0-12 inches,peat,PT. Type SW-SM. 12-60 inches,peat,PT. 7-21 inches,very gravelly loamy sand, very gravelly sandy loam,extremely gravelly sand,GP-GM. 21-60 inches,very gravelly coarse sand, very gravelly sand,extremely gravelly coarse sand,GP. Origination Outwash channels Decomposed organic material. ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 • Silverdale, Washington 98383 • Ph.: (360) 613-2407 9 Fax: (360) 613-2408 Project No.ACL06-01-GO05 242 NE Riverside Place,Belfair,WA February 10,2006 Page No.3 USDA Soil Everett gravelly loamy sand Mukilteo peat Survey Name Typical Profile The surface soil is loose, single-grained, The surface layer consists of leaves, twigs, pale-brown, gravelly sandy loam 6 to 8 and small roots 1 to 2 inches thick. The upper inches thick. The upper 2 or 3 inches 10 to 12 inches of peat is a granular, fibrous normally contains aggregates that are dark brown mixture of partly decomposed slightly hard and redder than the others in roots, twigs, and fibrous sedges. This is the layer. To depth ranging from 18 to 24 underlain by more fibrous, less decomposed, inches, the subsoil is loose, single- brown peat. This grades through fibrous grained, light yellowish-brown gravelly sedge peat, sedimentary peat, or mucky sandy loam or gravelly loamy sand. The mineral soil to compact glacial till that is a amount of shot decreases with depth; In varying depths below 3 feet. the lower part only a few shot occur. The subsoil grades to a substratum of poorly assorted predominantly yellowish-brown sand, gravel, and cobbly material that is extremely loose and porous. However, in places, this material will stand in banks. The color of this material is largely determined by the gravel, coarse sand, and cobbles, which are olive gray, pale olive, yellowish brown, light brownish gray, gray and dark gray. Many of the cobbles,as well as much of the gravel,are faintly to moderately stained by iron. Drainage Well. Poorly. Permeability Rapid. Slow. Surface Runoff Slight. Ponded. Erosion Hazard Slight. Slight. Development Everett soils are in capability subclass Mukilteo peat is in capability subclass IIIw. Considerations VIs. Site soils appear to be generally consistent with the mapped soils. The surficial soils appear consistent with sandy outwash. Soils were observed in existing excavations to depths of approximately 5 feet. The soils were consistently sandy soils with low silt content and significant gravel content. The soils were dense at approximately 3 feet below existing grade. Neither surface nor groundwater seepage was observed on the subject site. Ponded water was observed on the adjacent property to the east. Variations in groundwater can fluctuate with temperature and precipitation. These observations were made at a time when recent heavy rains had caused saturated soil conditions in much of the Puget Sound region. The area is mapped by the Folio of the Southern Hood Canal Area map as Class 1 and Class 2 slopes. Class 1 slopes are generally less than 15 percent,but may be steeper in localized areas and are believed to be stable. Class 2 slopes are generally steeper than 15 percent and are believed to be stable under normal conditions,but may become unstable when disturbed by man's activities. We believe that the slopes will be stable with the recommendations provided in this report. ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 • Silverdale, Washington 98383 • Ph.: (360) 613-2407 • Fax: (360) 613-2408 Project No.ACL06-01-GO05 242 NE Riverside Place,Belfair,WA February 10,2006 Page No.4 M.CONCLUSIONS Based on ALKAI's site observations, available topographic data,and review of pertinent materials,the subject property appears to meet the requirements of the Mason County Resource Ordinance as a Landside Hazard Area due to the presence of slopes slightly steeper than 40 percent and greater than 10 vertical feet. A qualitative slope stability analysis was performed for the slopes above and below the proposed structure. The slope below the proposed structure is less than 40 percent and is stable at its current grade. The slope above the proposed structure will be graded to a 2 Horizontal to 1 Vertical(2H:1V)excavation. This configuration will be stable for both static and seismic conditions, but there could be short term raveling of the surface sand and gravel. Landscaping walls may be constructed at a later time. The liquefaction potential appears low due to the drainage properties of the site soils which were observed at a time when many soils in the region were saturated. The placement of the residence on a daylight basement provides additional support for the structure and limits the potential for slope movement on the lower slope. IV.RECOMMENDATIONS A. Erosion Control and Slope Stability ALKAI recommends that vegetation may be removed as needed during construction,but disturbed areas in the construction area should be vegetated with a minimum of a grass lawn as soon as possible once construction activities are complete. The soils may be erodible in the disturbed state or under conditions of channelized water flow. Typical erosion control methods such as silt fences,diversion trenching,and placement of straw on bare areas should be utilized. Storm water runoff should be controlled and not directed to or allowed to free-flow toward,across or over the slope area. As noted above,deep slope failures appear unlikely. B. Seismic Concerns Based on ALKAI's observations,the overall slope currently appears to be stable(see our paragraph under conclusions). No geomorphic evidence of past slope instability were observed. In the event of an earthquake of adequate magnitude and/or duration some soil movement on the steeper slopes is possible if other conditions are right. The potential for soil movement on this property is no greater than that for properties elsewhere with similar slope and soil conditions. Based on observed subsurface conditions,the potential for liquefaction, soil settlement,and/or unstable slopes during a seismic event appears to be relatively low. Although poorly graded sand was observed on the slope area(a soil type that may be susceptible to liquefaction), it appeared to be dense and well drained and had a high gravel content. The liquefaction potential could increase briefly during periods of heavy rainfall if saturated soil conditions develop. ALKAI has reviewed the 2003 International Building Code(IBC)for seismic design criteria for the proposed construction. The IBC seismic design parameters for this site include a seismic zone soil profile type of (D), in accordance with Table 1615.1.1 Site Class Definitions from the above referenced standard. C. Further Investigation Based on our understanding of site conditions and the intended use of the property,ALKAI does not recommend that a more detailed investigation be prepared to further evaluate site conditions. V. REPORT LEWrATIONS ALKAI's geotechnical report has been prepared for the exclusive use of Mr.Dale Oien and his agents for use in obtaining a building permit for the subject parcel. The conclusions and recommendations in this report are based on our interpretation of site conditions,as they presently exist,anticipated future construction activities, and the ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 •Silverdale,Washington 98383 • Ph.: (360)613-2407 9 Fax: (360) 613-2408 Project No.ACL06-01-G005 242 NE Riverside Place,Belfair,WA February 10,2006 Page No.5 expectation that the evaluation adequately defines the subsurface conditions across the site. The soil conditions described in this report and the conclusions and recommendations contained in this report are provided for this specific site only and should not be expanded for use on adjacent properties without additional exploration and review of those sites by ALKAI. The report should be provided to prospective contractors for their bidding or estimating purposes,but the report conclusions and interpretations should not be construed as a warranty of the subsurface conditions. There are possible variations in subsurface conditions. In the event that the subsurface conditions different from those encountered during this study be observed or suspected,ALKAI should be advised. At that time a review of the changed conditions will be made,and alternative or remedial recommendations given as required. ALKAI has examined subsurface conditions to a limited extent as part of this study, but we have not evaluated the site for the potential presence of contaminated soil,nor have we evaluated or addressed groundwater conditions or concerns except as noted in this report. The evaluation of possible environmental or geo-environmental considerations is beyond the scope of this report. The owner and any contractor should make themselves aware of and become familiar with applicable local, state,and federal safety regulations, including current OSHA/WISHA excavation and trench safety standards. Construction site safety generally is the sole responsibility of the contractor. The contractor shall also be solely responsible for the means,method,techniques, sequences,and operations of construction operations. ALKAI is providing the preceding information and recommendations solely as a service to Mr.Dale Oien. Under no circumstances should the provision of this information or recommendations be construed to mean that ALKAI(or subcontractors)are assuming responsibility for construction site safety or the contractor's activities; such responsibility is not implied and should not be inferred. Within the limitations of scope, schedule, and budget for this work,ALKAI's work has been done in accordance with generally accepted practices followed in this area at the time this report was generated. No other warranty,expressed or implied is made. Should you have any questions or concerns,which have not been addressed, or if we may be of additional assistance, please call our office at(360)613-2407. Sincerely, o� Was/7i r no; ng Geoiog:st 2208 David Hurum,L.G. sed G eo Shawn E. Williams L.E.G.,R.E.A. Senior Licensed Geologist Shawn E. Williams Senior Licensed Engineering Geologist -- fo Attachments. Z �G Figure 1 - Site Vicinity Map Figure 3 -Slope Cross Section Figure 2- Site Plan See text on page 3 for subsurface soil observations s:\alkai shared files\projects\geotechnical\06 projects\06-01-g005 riverside place\riverside place ACL06-01-g005.doc ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 • Silverdale, Washington 98383 • Ph.: (360) 613-2407 9 Fax: (360) 613-2408 or I �' •� - � �- APPROXIMATE — — —.- SITE LOCATION % NE OLD BELFAIR HIGHWAY p a r G!ivel • ' �,� '• 1 :1t 1 a N Figure adapted from Topozone.com FIGURE 1 VICINITY MAP ALKA1 CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair,Washington Environmental Engineering• Geotechnical Engineering•Wetland Consulting Project No.: ACL06-01-GO05 Client: Mr. Dale Oien - 1 N III I / 7 11S the 3 f InEw a� ! I ,1 c. UJ c1 fan ait I �jc t-%c -Ui Q / ` o / -74 Note: Figure adapted from septic plan generated by B.J. Septic s �- FIGURE 2 Site Plan A LK A I CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair,Washington Environmental Engineering•Geotechnical Engineering•Wetland Consulting Project No.: ACL06-01-G005 Client: Team 4 Engineering Looking1 Scale: I inch = 1 feet 0' 5" 10' IS' 20' Approximate Location of Proposed Residence Road Road Figure generated from field measurements by ALKAI using fiberglass tape and Brunton Pocket Transit FIGURE 3 SLOPE PROFILE ALKAI CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair, Washington OFF vironmental Engineering • Geotechnical Engineering • Wetland Consulting Project: ACL06-01-GO05 Client: Mr. Dale Oien STprFp� MASON COUNTY �P C £"" PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER � �; A O o T s'z Shelton, Washington 98584 r� N V 1864 DATE: February 27, 2006 INTER-DEPARTMENTAL COMMUNICATIONS TO: Chuck McCoy PARCEL # FROM: Alan Berbisco, Project Engineer-PW BUILDING PERMIT NUMBER: Bld2006-00031 SUBJECT: Geotechnical Report NAME: Jennifer Mayer Chuck, The Geotechnical Report prepared for the proposed residential development located at 242 NE Riverside Place Belfair, has been received and reviewed by Public Works. There are several requirements for the preparation of Geotechnical Report that have not been discussed in the submitted report. The ten requirements for Geotechnical Report must be clearly discussed. The result of slope analysis with factor of safety both static and seismic must be incorporated with conclusion or recommendations. This report does not satisfactorily meet the ten county's requirement(s) for stability investigation and geotechnical reporting. Please feel free to contact me at 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, Ala B rbisco Project Engineer r WORK ORDER •PUBLIC WORKS DEPT, woft 000 PERMC, � lNom OH �r I�e�ue�ted IT G14o AdioftW bp Gale; Type of wok, CNMRo8 Tot NAM@ r Ff z A AGANCY10OMPANY ' BIUJNo ADDRfse PHONE fm Pmjod 11me e1 m A ee ' TO hoi* EtTiWUlT�O rOTN.lit (M Ao. �amft— "._.� IkbuM Oost eAs MooNN4 _ � � �npioyw qnw '• ' 1 Hours #A TOTAL i RQUIPMENT USM4. QAii ltnll rQTU 11 MAT(QRIA!„WOEM TOTAL ALL 3)' BILLED DATE�„„I►NI►�_ PAID-DATflr„____„_,.� a�al� a�►,�..�..�,.� . w r ' CD0A,STgr 0 MASON COUNTY > PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER h Shelton, Washington 98584 T r 2 Z 1 u � Y OJ �� 1864 DATE: March 17, 2006 INTER-DEPARTMENTAL COMMUNICATIONS TO: Chuck McCoy PARCEL # 12320-10-93343 FROM: Alan Berbisco, Project Engineer-PW BUILDING PERMIT NUMBER: BLD2006-00031 SUBJECT: Geotech. ReRort Review NAME: Jennifer Mayer Chuck, The Addendum of Geotechnical Report prepared for the proposed residence located at 242 NE Reverside Place Belfair,has been received and reviewed by Public Works. I appreciate that ALKAI Consultants,LLC sent an addendum letter to comply the County's requirements for Geotechnical Reporting. All ten requirements for Geotechnical Report were properly addressed. But there is no recommendation about the storm water coming from the slope at the back of the proposed residence, driveway,parking and roof.Furthermore,what are the author's recommendation on how or where to discharge the storm water?Directing storm water to the other properties may cause legal action from the neighbors. I'm also requesting the ALKAI Consultants, LLC to provide more information or discussion about the performed Slope Analysis,which indicate w at are a actor o safety of the slope in both Static and Seismic Please feel free to contact me at 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, Alan Berbisco Project Engineer 1 y t f I b: r S � 17 i TOPOGRAPHY PROF E: Direction: Scale: / Approval:for otfceuse Building Permit number: / '� Building: Owner/Applicant:Me, Date of Planning: Parcel Number: _ /�� d 1� � applica ion: Env. Health: 06_ 91-D2006-00031 CsennAer M0.yer� ALKAI CONSULTANTS , LLC . Environmental Engineering - Geotechnical Engineering - Wetland Consulting March 1, 2006 Project No. ACL06-01-G005 Mr. Dale Oien P.C. 60')� 2-4q Se IOCCK, w A C1163BO Subject: Geotechnical Report Addendum Letter 242 NE Riverside Place Belfair, Washington Mr. Oien, The following is an Addendum Letter for our original Geotechnical Report dated February 10, 2006 and follows comments by Mason County regarding addressing the 10 requirements for a Geotechnical Report as follows. (1) A discussion of general geologic conditions, specific soil types, groundwater conditions, and history of landslide activity. See Site Surface and Subsurface Conditions on pages 2 and 3. (2) A site plan which identifies important development and geologic features. See amended site plan following this letter. 3) Locations and logs of exploratory holes or probes. See amended site plan and typical log following this letter. (4) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and which ( incorporates the details of the proposed grade changes. See amended cross section following this letter. (5�) A description and results of slope stability analysis performed for both seismic and static loading conditions. See Conclusions on page 4. (6) Appropriate restrictions on placement of drainage features, septic drain fields, and compacted fills and footings, including recommended setbacks from setbacks from shoreline bluffs and the tops of other slopes on the property. No restrictions on drainage features. No restrictions for septic drain fields beyond the septic design. No structural fill is anticipated, but should be 95 percent by ASTM D1557. No footing restrictions or modifications, but footings should bear on dense native soil. No top or toe of slope setback with the proposed daylight basement. The lower slope is stable and less than 40 percent grade. The upper slope will be graded to a stable configuration, but will need to be vegetated. (7) A detailed clearing and grading plan which specifically identifies vegetation to be removed, a schedule for vegetation removal and replanting, and the method for vegetation removal. Grading will be minimal and will mostly be for the house foundation (see cross section). The slope behind the house will be graded to a 2 Horizontal to 1 Vertical slope. Small trees, blackberries, Scotch broom,and other brush will be removed in the house footprint and slope behind the house.The areas disturbed by vegetation removal should be revegetated by a minimum of a grass lawn immediately following completion of construction activities that impact disturbed areas or cause disturbance. Vegetation may be removed with excavation equipment such as back-hoe,track-hoe,or dozer. (8) A detailed temporary erosion control plan which identifies the specific mitigation measures to be implemented during construction to protect the slope from erosion, landslides, and harmful construction methods. A silt fence should be installed on the slope in the area below the proposed house and disturbed areas protected with straw. GEOLOGIC AND GEOTECHNICAL CONSULTING y Project No.ACL06-01-G005 ! ' Addendum Letter 242 NE Riverside Place,Belfair,WA ! March 1,2006 Page No.2 (9) An analysis of both on-site and off-site impacts of the proposed development. Off-site impacts will be minimal. On-site impacts will be temporary(disturbance during the construction process)and will be mitigated by the erosion control measures. (10) Specifications of final development conditions such as vegetative management, drainage, erosion control, and buffer widths. Vegetation should be maintained and monitored during wet weather until it becomes established. The drainage properties of the on-site soils should allow for sufficient infiltration of surface water on the property. Erosion control will be managed by maintaining vegetation. No buffer widths are recommended. Should you have any questions or concerns, which have not been addressed, or if we may be of additional assistance, please call our office at(360)613-2407. Sincerely, David Hurum, L.G. Shawn E. Williams L.E.G., R.E.A. Senior Licensed Geologist Senior Licensed Engineering Geologist ----achments: Revised Site Plan Typical Soil Log Revised Cross Section s:\alkai shared files\projects\geotechnical\06 projects\06-0 1-g005 riverside place\riverside place addendum letter ac106-01-g005.doc ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 • Silverdale,Washington 98383 • Ph.: (360) 613-2407 • Fax: (360) 613-2408 c IV N m � � w art t his _pxticn c f the — — — edstirx3 'w"B' ;Ih f AO V; clean a± septic U) / k Vl � .zi y Note: Figure adapted from septic plan generated by B.J. Septic — s �- ------- FIGURE 2 Site Plan IF A LK A I CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair, Washington Environmental Engineering •Geotechnical Engineering•Wetland Consulting Project No.: ACL06-01-GO05 Client: Mr. Dale Oien = L 4111,, Add ffi _ a lol .� i e �,of A• SON_STA7- MASON COUNTY �P I NJ C - 7 PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER ` z Shelton,Washington 98584 T TO BE KEPT IN THE °J 1%4PARCEL FIDE DATE: April 18.2006 INTER-DEPARTMENTAL COMMUNICATIONS TO: Chuck MacCoy PARCEL# FROM: Alan Berbisco, Project Engineer-PW BUILDING PERMIT NUMBER: BLD2006-00031 SUBJECT: Geotechnical Report NAME: Jennifer Maw Chuck, The addendum e-mail letter and design calculation for infiltration trench prepared for the proposed single family residence located at 141 NE Captain James Ln. Tahuya, has been received and reviewed by Public Works. David Hurum of Alkai Consultants is planning to re-grade the slope at the back of the house of Jennifer Mayer to less than 40% slope. The author plan will relieve him from performing a Slope Stability Analysis. He should write an addendum letter specifying his proposed plan, and I have no objection to his proposal. Please feel free to contact me at 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. Sincerely, n er isco Pr 'ect Engineer Cfls� b:L 00031 ( 3enn'fer Mayer> ALKAI CONSULTANTS, LLC . Environmental Engineering • Geotechnical Engineering • Wetland Consulting February 10, 2006 Project No.ACL06-01-G005 Mr. Dale Oien P.a 60A 24q SMbeCl<- DN A 016W0 Subject: Geotechnical Report 242 NE Riverside Place Belfair, Washington Mr. Oien, Presented herein is ALKAI Consultants,LLC's(ALKAI)geotechnical report for the subject parcel. This investigation was conducted in accordance with our contract agreement dated February 1,2006. The Mason County Resource Ordinance 17.01.100 for Landslide Hazard Areas and a septic design were reviewed in preparation of this report. This Geotechnical Report has been performed in general compliance with Mason County Resource Ordinance 17.01.100. This geotechnical report is based on observed conditions during ALKAI's site reconnaissance of the parcel on February 1,2006 and February 2,2006,and a review of readily available reference resources. The readily available resources listed below were reviewed. • "Soil Survey of Mason County Washington",United States Department of Agriculture, 1960. • The Washington Division of Geology and Earth Resource(WDGER), Geologic Map of Washington- Northwest Quadrant. • The Washington Division of Natural Resources,Division of Ecology and Earth Resources,Folio of the Southern Hood Canal Area, Washington dated 1977. Soil and slope conditions of the subject property were visually examined and evaluated by observing existing test pit excavations on the property and performing a slope reconnaissance. This evaluation combined with available reference material on the site provided a basis for a general understanding of the surface and subsurface conditions as discussed below. GEOLOGIC AND GEOTECHNICAL CONSULTING Project No.ACL06-0I-G005 242 NE Riverside Place,Belfair,WA February 10,2006 Page No.2 I. SITE CHARACTERISTICS The subject parcel is 0.89 acres located in Mason County near Belfair in Section 20, Township 23 North,Range 1 West,as shown on Figure 1,"Vicinity Map". The subject parcel is currently partially cleared and graded with primitive roads. Access to the parcel is provided by Riverside Place. The proposed development is illustrated on Figure 2,"Site Plan"and shows the locations of a single family residence with a daylight basement and associated onsite septic system. The current and proposed slope configurations are illustrated on Figure 3,"Slope Profile". The parcel is bound to the north, south,and east by single family residences and greenbelt. Vegetation on the slope consists of young Madrona,Maple,Alder, Cedar and Douglas fir. Understory vegetation consists of scotchbroom, Organ grape,and blackberries. Based on these site characteristics,the hill slope is considered a"Landslide Hazard Area" because it meets the following criteria: • Slopes greater than 40 percent with a vertical relief of greater than 10 feet. • Areas with artificial cuts(i.e.road cuts). U. SITE SURFACE AND SUBSURFACE CONDITIONS The Washington Division of Geology and Earth Resource WDGER� gy ( ), Geologic Map of Washington-Northwest � Quadrant,dated 2002, indicates that the site lies on glacial till. In general,glacial till consists of an unsorted, unstratified, highly compacted mixture of clay, silt, sand,gravel,cobbles,and boulders deposited by glacial ice and may contain interbedded stratified sand, silt,and gravel. Materials below the glacial till layer are generally identified as advance outwash or other pre-glacial deposits, consisting of zones of dense to very dense, somewhat cleaner materials, showing some degree of sorting or bedding,or materials of a mixed or indefinite origin incorporated into the till unit. The United States Department of Agriculture (USDA) Soil Survey of Kitsap County Area, Washington, information indicates the following soil type exists on the project site: • Everett gravelly loamy sand with 15 to 30 percent slopes(Ef)over the majority of the site and 5 to 15 percent slopes(Ee)along the northern edge. • Mukilteo peat with 0 to 2 percent slopes(Mg)along the eastern edge of the site. The soil survey description of this soil type is summarized in the following table. USDA Soil Everett gravelly loamy sand Mukilteo peat Survey Name USCS Soil 0-7 inches, gravelly loamy sand,GP-GM, 0-12 inches,peat,PT. Type SW-SM. 12-60 inches,peat,PT. 7-21 inches,very gravelly loamy sand, very gravelly sandy loam, extremely gravelly sand,GP-GM. 21-60 inches,very gravelly coarse sand, very gravelly sand,extremely gravelly coarse sand,GP. Origination Outwash channels Decomposed organic material. ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 • Silverdale, Washington 98383 • Ph.: (360) 613-2407 • Fax: (360) 613-2408 Project No.ACL06-01-G005 242 NE Riverside Place,Belfair,WA February 10,2006 Page No.3 USDA Soil Everett gravelly loamy sand Mukilteo peat Survey Name Typical Profile The surface soil is loose, single-grained, The surface layer consists of leaves, twigs, pale-brown, gravelly sandy loam. 6 to 8 and small roots 1 to 2 inches thick. The upper inches thick. The upper 2 or 3 inches 10 to 12 inches of peat is a granular, fibrous normally contains aggregates that are dark brown mixture of partly decomposed slightly hard and redder than the others in roots, twigs, and fibrous sedges. This is the layer. To depth ranging from 18 to 24 underlain by more fibrous, less decomposed, inches, the subsoil is loose, single- brown peat. This grades through fibrous grained, light yellowish-brown gravelly sedge peat, sedimentary peat, or mucky sandy loam or gravelly loamy sand. The mineral soil to compact glacial till that is a amount of shot decreases with depth; In varying depths below 3 feet. the lower part only a few shot occur. The subsoil grades to a substratum of poorly assorted predominantly yellowish-brown sand, gravel, and cobbly material that is extremely loose and porous. However, in places, this material will stand in banks. The color of this material is largely determined by the gravel, coarse sand, and cobbles, which are olive gray, pale olive, yellowish brown, light brownish gray, gray and dark gray. Many of the cobbles,as well as much of the gravel are faintly to moderately stained by iron. Drainage Well. Poorly. Permeability Rapid. Slow. Surface Runoff Slight. Ponded. Erosion Hazard Slight. Slight. Development Everett soils are in capability subclass Mukilteo peat is in capability subclass IIIw. Considerations VIs. Site soils appear to be generally consistent with the mapped soils. The surficial soils appear consistent with sandy outwash. Soils were observed in existing excavations to depths of approximately 5 feet. The soils were consistently sandy soils with low silt content and significant gravel content. The soils were dense at approximately 3 feet below existing grade. Neither surface nor groundwater seepage was observed on the subject site. Ponded water was observed on the adjacent property to the east. Variations in groundwater can fluctuate with temperature and precipitation. These observations were made at a time when recent heavy rains had caused saturated soil conditions in much of the Puget Sound region. The area is mapped by the Folio of the Southern Hood Canal Area map as Class 1 and Class 2 slopes. Class I slopes are generally less than 15 percent,but may be steeper in localized areas and are believed to be stable. Class 2 slopes are generally steeper than 15 percent and are believed to be stable under normal conditions, but may become unstable when disturbed by man's activities. We believe that the slopes will be stable with the recommendations provided in this report. ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 • Silverdale, Washington 98383 • Ph.: (360) 613-2407 • Fax: (360) 613-2408 Project No.ACL06-01-G005 242 NE Riverside Place,Belfair,WA February 10,2006 Page No.4 III.CONCLUSIONS Based on ALKAI's site observations,available topographic data, and review of pertinent materials,the subject property appears to meet the requirements of the Mason County Resource Ordinance as a Landside Hazard Area due to the presence of slopes slightly steeper than 40 percent and greater than 10 vertical feet. A qualitative slope stability analysis was performed for the slopes above and below the proposed structure. The slope below the proposed structure is less than 40 percent and is stable at its current grade. The slope above the proposed structure will be graded to a 2 Horizontal to 1 Vertical(2H:IV)excavation. This configuration will be stable for both static and seismic conditions,but there could be short term raveling of the surface sand and gravel. Landscaping walls may be constructed at a later time. The liquefaction potential appears low due to the drainage properties of the site soils which were observed at a time when many soils in the region were saturated. The placement of the residence on a daylight basement provides additional support for the structure and limits the potential for slope movement on the lower slope. IV. RECOMMENDATIONS A. Erosion Control and Slope Stability ALKAI recommends that vegetation may be removed as needed during construction,but disturbed areas in the construction area should be vegetated with a minimum of a grass lawn as soon as possible once construction activities are complete. The soils may be erodible in the disturbed state or under conditions of channelized water flow. Typical erosion control methods such as silt fences,diversion trenching, and placement of straw on bare areas should be utilized. Storm water runoff should be controlled and not directed to or allowed to free-flow toward,across or over the slope area. As noted above, deep slope failures appear unlikely. B. Seismic Concerns Based on ALKAI's observations,the overall slope currently appears to be stable(see our paragraph under conclusions). No geomorphic evidence of past slope instability were observed. In the event of an earthquake of adequate magnitude and/or duration some soil movement on the steeper slopes is possible if other conditions are right. The potential for soil movement on this property is no greater than that for properties elsewhere with similar slope and soil conditions. Based on observed subsurface conditions,the potential for liquefaction, soil settlement and/or P q , unstable slopes during a seismic event appears to be relatively low. Although poorly graded sand was observed on the slope area(a soil type that may be susceptible to liquefaction), it appeared to be dense and well drained and had a high gravel content. The liquefaction potential could increase briefly during periods of heavy rainfall if saturated soil conditions develop. ALKAI has reviewed the 2003 International Building Code(IBC)for seismic design criteria for the proposed construction. The IBC seismic design parameters for this site include a seismic zone soil profile type of (D), in accordance with Table 1615.1.1 Site Class Definitions from the above referenced standard. C. Further Investigation Based on our understanding of site conditions and the intended use of the property,ALKAI does not recommend that a more detailed investigation be prepared to further evaluate site conditions. V. REPORT LIMITATIONS ALKAI's geotechnical report has been prepared for the exclusive use of Mr. Dale Oien and his agents for use in obtaining a building permit for the subject parcel. The conclusions and recommendations in this report are based on our interpretation of site conditions,as they presently exist,anticipated future construction activities, and the ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 •Silverdale,Washington 98383 • Ph.: (360) 613-2407 9 Fax: (360) 613-2408 Project No.ACL06-01-G005 242 NE Riverside Place,Belfair,WA February 10,2006 Page No.5 expectation that the evaluation adequately defines the subsurface conditions across the site. The soil conditions described in this report and the conclusions and recommendations contained in this report are provided for this specific site only and should not be expanded for use on adjacent properties without additional exploration and review of those sites by ALKAI. The report should be provided to prospective contractors for their bidding or estimating purposes,but the report conclusions and interpretations should not be construed as a warranty of the subsurface conditions. There are possible variations in subsurface conditions.In the event that the subsurface conditions different from those encountered during this study be observed or suspected,ALKAI should be advised. At that time a review of the changed conditions will be made,and alternative or remedial recommendations given as required. ALKAI has examined subsurface conditions to a limited extent as part of this study,but we have not evaluated the site for the potential presence of contaminated soil,nor have we evaluated or addressed groundwater conditions or concerns except as noted in this report. The evaluation of possible environmental or geo-environmental considerations is beyond the scope of this report. The owner and any contractor should make themselves aware of and become familiar with applicable local,state,and federal safety regulations, including current OSHA/WISHA excavation and trench safety standards. Construction site safety generally is the sole responsibility of the contractor. The contractor shall also be solely responsible for the means, method,techniques, sequences,and operations of construction operations. ALKAI is providing the preceding information and recommendations solely as a service to Mr. Dale Oien. Under no circumstances should the provision of this information or recommendations be construed to mean that ALKAI(or subcontractors)are assuming responsibility for construction site safety or the contractor's activities; such responsibility is not implied and should not be inferred. Within the limitations of scope, schedule,and budget for this work,ALKAI's work has been done in accordance with generally accepted practices followed in this area at the time this report was generated. No other warranty, expressed or implied is made. Should you have any questions or concerns,which have not been addressed, or if we may be of additional assistance, please call our office at(360)613-2407. Sincerely, tis Of W` hi7 r— ngineering Geologist � 2208 d G e David Hurum,L.G. Shawn E. Wing E Williams L.E.G.,R.E.A. Senior Licensed Geologist . Senior icensed Engineering Geologist Attachments. Figure 1 -Site Vicinity Map Figure 3 - Slope Cross Section Figure 2 -Site Plan See text on page 3 for subsurface soil observations s:\alkai shared files\projects\geotechnical\06 projects\06-01-g005 riverside place\riverside place ACL06-01-g005.doc ALKAI Consultants, LLC 9465 • Provost Road NW, Suite 202 • Silverdale, Washington 98383 • Ph.: (360) 613-2407 • Fax: (360) 613-2408 o:f� •(� l fl� ��/,�� .�-'+ % r1 !v��l�I k •r'' 10 _ o t`f r APPROXIMATE -- SITE LOCATION NE OLD BELFAIR -, m 14TCT14WAY r .r •. . . S k :j Gr vet C 1 • t :/1 5�t J 7i . • , 1 Ct a 1 / / It �352x N Figure adapted from Topozone.com FIGURE 1 VICINITY MAP ALKAI CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair, Washington Environmental Engineering Geotechnical Engineering• Wetland Consulting Project No.: ACL06-01-GO05 Client: Mr. Dale Oien i a � 77--P=tjsm c fth-- . / dstx 3 r3 ay ko z, �f J u, *-Clem CL t � I .z 4 �a J IA , -74 Note: Figure adapted from septic plan generated by B.J. Septic s �- FIGURE 2 Site Plan A L K A i CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair,Washington Environmental Engineering-Geotechnical Engineering-Wetland Consulting Project No.: ACLO6-01-G005 Client: Team 4 Engineering Scale: I inch = I feet 0' 5" 10' 15' 20' Approximate Location of Proposed Residence 7ad Road Figure generated from field measurements by ALKAI using fiberglass tape and Brunton Pocket Transit FIGURE 3 SLOPE PROFILE ALKAI CONSULTANTS, LLC. Project Name: Riverside Place Location: Belfair, Washington Environmental Engineering • Geotechnical Engineering • Wetland Consulting Project: ACL06-01-GO05 Client: Mr. Dale Oien � J