The URL can be used to link to this page

Home My WebLink AboutGEO2012-00014 for BLD2012-00150 - GEO General - 10/1/2009 ` MAR-29-2012 20:24 FROM:EARTH SOLUTIONS NW,L 4254494711 T0:13604277798 P.2/3 Mason County Department of Community Development Submittal Checklist Far a Geotochnicat Rapgrt Instructions: This checklist must be submitted with a Geotechnlcal Report and completed,signed,and stamped by the licensed professional(s)who prepared the Geatechnical Reportfor review by Mason County pursuant to the Mason County Resource Ordinance. If an item found to be not applicable,the report should explain the basis for the conclusion. Applicant/Owner `Y or. _J o h n l atkir,s Parcei v aa6 26- ID-4bb85 Site Address 55o i�F aSt N r Go f t lane, I�cc v5�}-C rt l51 G►�r-t.,l�✓ 1 (1) (a)A discussion of general geologic conditions In the vicinity of the proposed development, Located on page(s) ,3- (b) A discussion of specific soil types Located on page(s) a,-A nag r'tIx (a.Bnr,nc) I"L,0-*1d 3 (c) A discussion of ground water conditions Located on page(s) 3 (d) A discussion of the upslop geomorphology Located on page(s) `! ,5 (e) A discussion of the location f upland wate and wetlands Located on page(s) N R-� = rat (f) A discussion of history of landslide activity in the activity in the vicinity,as available in the referenced maps and recgrds Located on page(s) (2) A site plan which identifies the important deye(opmen'and geologic features. Located on Map(s) P1p �a (,c 11�.s4� t • (3) Locations and logs of exploratory holes or probes, Z d nd 3 Locatedon Maps) Plat, j,9ga2A� iy &ring �r i (4) The area of the proposed development,the boundaries of the hazard,and associated buffers and setbacks shall be delineated (too..both sides, arid foe) a geologic map of the site. Located on Map(s) +4Z. =�r�oW �,N — 2 i I(�s-kt4es,5e" �e�1t✓ (5) A minimum of one cross section at a scale which adequately depicts the subsurface profile, and which incorporates the details of proposed orade rhannwa Located on Map(s) (6) A description and results of slope stability analyses performed for both static and seismic loading conditions.Analysis should examine worst case failures,The analysis should Include the Simplified Bishop's Method of Circles. The minimum static safety factor is 1.5,the minimum seismic safety factor is .1. apd the,„,-Laf—ic analysis coeffie s should be a value of 0.15. Located on pages) Rs,�-)Mrf— rt --- • q (7) (a)Appropriate restrictions on place of dral age f tures Located on pages) �� (b) Appropriate restrictions ort place t et I s nhelrl5Located on page(s) � (c) Appropriate restrictions on place e t of comps ed fi lr and footings Located on pages) TI Page I of 2 Farm Effective June 2008 Disclaimer. Mason County does not certify the quality of the work done in this Geotechnical Report. ` MAR-29-2012 20:24 FROM:EARTH SOLUTIONS NW,L 4254494711 TO:13604277798 P.3/3 (d) Recommended buffers from the landslide hazard areas shoreline bluffs and the tops of other slopes on the property. Located on page(s) i3 (a) Recommended setbacks from the landslide hazard areas shoreline bluffs and the tops of other slopes on the property. Located on page(s) (8) Recommendations for the preparation of a detailed clearing and grading plan which specifically identifies vegetation to be removed,a schedule for vegetation removal and replanting,a d the method of vegetation removal. (( { Located on page(s) 6 _� c., (tP�Q�Ytk'c1d�. `CtCt,� LJ�K' i G'�•�� 1 (9) Recommendations for the preparation of a detailed temporary erosion control plan which identifies the specific mitigating measures to be implemented during construction to protect the slope from erosion,landslides and Pa f4lconstruction methods Located on page(s) ." e _ -�,QA- Cam- -101 (10) An analysis of both on-site and off-&to impacts of the proposed development_ Located on page(s) 1 (11) Specifications of final development conditions such as,vegetative management,drainage, erosion control,and buffer widths. Located on page(s) (12) Recommendations for the preparation of structural mitigation or details of other proposed mitigation_ S � .� r ` � Located An page 17 s) T.� a'�a t'i;- (13) 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. Located on Maps) _Pints�- ,.. I, 1 hereby certify under penalty of perjury thdWAa civil engineer licen the State of Washington with Specialized knowledge of geotechnieaVgeological engineering or a geologist or engineering geologist licensed in the State of Washington with spacial knowledge of the local conditions. I also certify that the Geotechnical Report,dated and entitledti meet all a requlrements of the Mason County Resource ordinance �andsi a Hazard Section is complete and true that the assessment , pl , demonstrates conclusively that.the risks posed by the landslide hazard can be mitigated through the i eluded otechnical design recommendations and that all hazards are mitigated in such a marine to prevent harm to property and public health and safe y, Signature and Stamp u7(3�joe /12- j aJ l e a Ca if ga(ts �s' a� �. �: � .as�c..ai km�c' Fx tie: •« Page 2 of 2 Form Effe rve June Zpa Mason Countj does not certify the jualiity of the worts donne in this Geotechnical Report. E02oalw004 PLANNING PREPARED FOR MR. JOHN WATKINS fr October 1, 2009 �s o g . enior Projec eologist Y / �?, . { its Raymond A. Coglas, P.E. Principal M 2 2012 GEOTECHNICAL ENGINEERING STUDY MASON. (DOUN) PROPOSED SINGLE-FAMILY RESIDENCE 550 EAST NICOLE LANE HARTSTENE ISLAND, WASHINGTON ES-1570 Earth Solutions NW, LLC 1805 - 136th Place Northeast, Bellevue, Washington 98005 Ph: 425-284-3300 Fax: 425-449-4711 Toll Free: 866-336-8710 t IMPOP1801 tion About YOUP Coolechni.ce! Eflulfleepolmno ■ ! ■ Subsurfaceproblems are principal • of constructiondelays, 1 overruns, • • I disputes. ' following information is provided I help you manage Geotechnical Services Are Performed for • elevation,configuration,location,orientation,or weight of the Specific Purposes, Persons, and Projects proposed structure, Geotechnical engineers structure their services to meet the specific needs of • composition of the design team,or their clients.A geotechnical engineering study conducted for a civil engi- • project ownership. neer may not fulfill the needs of a construction contractor or even another civil engineer.Because each geotechnical engineering study is unique,each As a general rule,always inform your geotechnical engineer of project geotechnical engineering report is unique,prepared solelyfor the client.No changes—even minor ones—and request an assessment of their impact. one except you should rely on your geotechnical engineering report without Geotechnical engineers cannot accept responsibility or liability for problems first conferring with the geotechnical engineer who prepared it.And no one that occur because their reports do not consider developments of which —not even you—should apply the report for any purpose or project they were not informed. except the one originally contemplated. Subsurface Conditions Can Change Read the Full Report A geotechnical engineering report is based on conditions that existed at Serious problems have occurred because those relying on a geotechnical the time the study was performed. Do not rely on a geotechnical engineer- engineering report did not read it all.Do not rely on an executive summary. ing report whose adequacy may have been affected by:the passage of Do not read selected elements only. time;by man-made events,such as construction on or adjacent to the site; or by natural events,such as floods,earthquakes,or groundwater fluctua- A Geotechnical Engineering Report Is Based on tions.Always contact the geotechnical engineer before applying the report A Unique Set of Project-Specific Factors to determine if it is still reliable.A minor amount of additional testing or Geotechnical engineers consider a number of unique, project-specific fac- analysis could prevent major problems. tors when establishing the scope of a study.Typical factors include:the client's goals,objectives,and risk management preferences;the general Most Geotechnical Findings Are Professional nature of the structure involved,its size,and configuration;the location of Opinions the structure on the site;and other planned or existing site improvements, Site exploration identifies subsurface conditions only at those points where such as access roads,parking lots,and underground utilities.Unless the subsurface tests are conducted or samples are taken.Geotechnical engi- geotechnical engineer who conducted the study specifically indicates oth- neers review field and laboratory data and then apply their professional erwise,do not rely on a geotechnical engineering report that was: judgment to render an opinion about subsurface conditions throughout the • not prepared for you, site.Actual subsurface conditions may differ—sometimes significantly— • not prepared for your project, from those indicated in your report.Retaining the geotechnical engineer • not prepared for the specific site explored, or who developed your report to provide construction observation is the • completed before important project changes were made. most effective method of managing the risks associated with unanticipated conditions. Typical changes that can erode the reliability of an existing geotechnical engineering report include those that affect: A Report's Recommendations Are Not Final • the function of the proposed structure,as when it's changed from a Do not overrely on the construction recommendations included in your parking garage to an office building,or from a light industrial plant report. Those recommendations are not final,because geotechnical engi- to a refrigerated warehouse, neers develop them principally from judgment and opinion.Geotechnical engineers can finalize their recommendations only by observing actual ( ' I Y October 1, 2009 Earth Solutions NVV I_LC ES-1570 'Crntru:_lilu �.1•inli .,, Mr. John Watkins 21232 - 1"Avenue South Des Moines, Washington 98198 Dear Mr. Watkins: Earth Solutions NW, LLC (ESNW) is pleased to present this report titled "Geotechnical Engineering Study, Proposed Single-Family Residence, 550 East Nicole Lane, Hartstene Island, Washington". Based on the results of our fieldwork, the site is underlain primarily by native soils consisting of medium dense to very dense glacially consolidated deposits. Groundwater seepage was not observed in the test sites explored at the time of our fieldwork (September 2009). Based on our review and results of the subsurface exploration, the planned development and currently proposed building footprint area are feasible from a geotechnical standpoint. In our opinion, new foundations for the proposed single-family residence can be supported on competent or recompacted native soils or structural fill used to modify existing site grades. We anticipate competent native soil capable of providing adequate foundation support will be encountered at depths of about two to four feet below existing grades. If loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with structural fill, may be necessary. The opportunity to be of service to you is appreciated. If you have questions regarding the content of this geotechnical engineering study, please call. Sincerely, ,EARTH SOLUTIONS NW, LLB," 1 J Ka mond A. Coglas, P.E. Principal TABLE OF CONTENTS ES-1570 PAGE INTRODUCTION ........................................................................ 1 General ......................................................................."" 1 Proiect Description ........................................................... 2 Surface............ ................................................................ 2 Subsurface....................................................................... 3 Geologic Setting...................................................... 3 Groundwater..................................................................... 3 CRITICAL AREAS REVIEW.......................................................... 4 Landslide Hazard Area Assessment ................................... 4 Seismic Hazard Area Assessment.............................................. 4 Erosion Hazard Area Assessment....................................... 5 DISCUSSION AND RECOMMENDATIONS..................................... 5 General........................................................................... 5 Site Preparation and Earthwork.......................................... 6 Erosion Control.................................................................. 6 In-situ Soils............................................................ 6 Structural Fill Placement.......................................... 6 Slope Fill Placement................................................ 7 Excavations and Slopes........................................... 7 Rockeries and Modular Block Walls........................... 7 Utility Support and Trench Backfill............................ 8 Foundations .................................................................... 8 Foundation Setbacks............................................... 8 Seismic Considerations......................... ............................... 9 Slab-on-Grade Floors......................................................... 9 Retaining Walls................................................................. 9 Drainage........................................................................... 10 Pavement Section Recommendations........................................ 10 LIMITATIONS.............................................................................. 11 Additional Services............................................................ 11 Earth Solutions NW,LLC TABLE OF CONTENTS Cont'd ES-1570 GRAPHICS PLATE 1 VICINITY MAP PLATE 2 BORING LOCATION PLAN PLATE 3 SLOPE FILL DETAIL PLATE 4 RETAINING WALL DRAINAGE DETAIL PLATE 5 FOOTING DRAIN DETAIL APPENDICES Appendix A Subsurface Exploration Boring Logs Earth Solutions NW, LLC GEOTECHNICAL ENGINEERING STUDY PROPOSED SINGLE-FAMILY RESIDENCE 550 EAST NICOLE LANE HARTSTENE ISLAND, WASHINGTON ES-1570 INTRODUCTION General This geotechnical engineering study was prepared for the proposed single-family residence to be constructed at 550 East Nicole Lane, located on the west side of Hartstene Island, Washington. The purpose of this study was to conduct subsurface explorations, perform selective geotechnical analyses and develop geotechnical recommendations for the proposed development. Our scope of services for completing this geotechnical engineering study included the following: • Observing, logging and sampling three borings for purposes of characterizing the soil and groundwater conditions; • Identifying and characterizing critical area hazards as defined by the Mason County Code and recommendations for mitigation; • Providing an evaluation of the proposed steep slope buffer and recommendations for grading activities within steep slope areas, as necessary, for the new single-family residence and associated improvements; • Providing geotechnical recommendations for earthwork, structural fill requirements and drainage considerations; • Assessing the suitability of site soils for use as structural fill; • Providing recommendations for soil bearing capacity, subgrade preparation, and recommendations for foundation support, and; • Providing additional geotechnical recommendations, as appropriate. Earth Solutions NW,LLC , 1 Mr. John Watkins ES-1570 October 1, 2009 Page 2 The following resources were reviewed as part of preparing this Geotechnical Engineering Study: • Geotechnical Evaluation Report prepared by Insight Geologic, Inc., File Number 447- 001-0, dated April 15, 2009; • Partial Site Plan provided by Rick Anderson Architect, undated; • Mason County Resource Ordinance, Chapter 17.01.100, 102 and 104; • State of Washington Department of Ecology Coastal Zone Atlas Map; • Geologic Map of Washington State, Southwest Quarter, and; • Mason County USDA Soil Conservation Survey (SCS). Proiect Description We understand the subject site will be developed with a single-family residence and associated improvements consistent with surrounding rural residential properties in this area. The proposed building site is located in the western part of the property and will partially span a natural shallow ravine feature, effectively reducing the amount of grading required to construct the building. The site will be accessed off East Nicole Lane and will utilize an asphalt paved driveway which will require cuts of up to about ten feet to accommodate the grade change to achieve a finish floor elevation of about 50 feet for the garage. The driveway cuts may utilize rockeries or retaining walls. We anticipate grading for the building site will generally require cuts and fills of about eight feet or less to achieve design subgrade elevations for portions of the residential foundation. Portions of the new residence spanning the shallow ravine will be supported on columns to accommodate the elevated portion of the structure. The proposed residential structure will largely consist of relatively lightly loaded wood framing. Based on our experience with similar developments, we anticipate wall loads on the order of 1 to 3 kips per lineal foot and slab-on-grade loading of about 150 pounds per square foot (psf). If the above design assumptions are incorrect or change, ESNW should be contacted to review the recommendations in this report. ESNW should review the final design to verify that our geotechnical recommendations have been incorporated into the plans. Surface The site is located off the west side of East Nicole Lane along the west side of Hartstene Island in unincorporated Mason County, Washington. The approximate location of the subject property is illustrated on the Vicinity Map (Plate 1). The property consists of a single, irregular- shaped tax parcel approximately 1.0 acre in size. The site is bordered to the north and south by residential properties, to the east by East Nicole Lane and to the west by the Peale Passage area of Puget Sound. The approximate limits of the property are illustrated on the Boring Location Plan (Plate 2). Earth Solutions NW,LLC Mr. John Watkins ES-1570 October 1, 2009 Page 3 The site is currently occupied with a camper trailer and wood deck located in the northeastern corner. A gravel pathway meanders through the property to provide egress to the beach area. An on-site septic system is located in the mid-section of the property. Vegetation throughout the site consists primarily of forested areas including mature evergreen and deciduous trees with a dense understory. Topography consists of a west-facing slope descending from East Nicole Lane to the beach area. A relatively shallow ravine area within the west facing slope roughly bisects the site. Grades range from a high along East Nicole Lane of about 78 feet to the beach elevation. Subsurface A representative of ESNW observed, logged and sampled three borings advanced across the development envelope of the site for purposes of assessing soil and groundwater conditions, and for characterizing and classifying the site soils. The borings were advanced using a limited-access drill rig and operator contracted by ESNW. Please refer to the boring logs provided in Appendix A for a more detailed description of the subsurface conditions. Topsoil was encountered at all of the test sites and was on the order of four to six inches thick. Indications of extensive areas of fill were not observed during our fieldwork. At the test sites, the topsoil was underlain by alternating layers of medium dense to very dense sand and gravel (SP, SP-SM and GP-GM) and silty sand with gravel (SM). A layer of very dense fine sandy silt (ML) was encountered near the termination depth in boring location B-2. Soil relative density generally increased with depth. Geologic Setting Our review of the referenced geologic map indicates the site is located near the transition zone between glacial till (Qvt) and Advance sand (Qva) deposits. The Mason County Soil Survey for the area identifies Harstine gravelly sandy loam (Hb) 15 to 30 percent slopes along the sloped areas of the site. The soil conditions encountered during our fieldwork generally correlate with the geologic and soil map designations. We interpret the native soils exposed at the test sites to represent the transition zone between Advance outwash sand and Transitional bed deposits. Groundwater Groundwater seepage was not observed at the test sites during our fieldwork (September 2009). However, groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. In general, groundwater flow rates are higher during the wetter, winter months. Perched groundwater seepage should be anticipated in deeper site excavations. Earth Solutions NW,LLC Mr. John Watkins ES-1570 October 1, 2009 Page 4 CRITICAL AREAS REVIEW As part of our report preparation, we reviewed the Mason County Resource Ordinance Chapter 17.01.100, 102 and 104 — Landslide, Seismic and Erosion Hazard Areas, respectively. Landslide Hazard Area Assessment As part of our report preparation, ESNW reviewed the Department of Ecology (DOE) online Coastal Zone Atlas GIS mapping resource. This resource has identified the upper slope area of the site as stable and the lower slope areas as intermediate to unstable. The overall topography across the site descends to the west with gradients generally 20 to 40 percent. No slippage planes or indications of past movement were observed at our test sites, or surrounding areas of steeper slopes. The soils observed at our test sites consisted primarily of undisturbed and firm glacial deposits. Signs of soil creep were observed at isolated locations during the fieldwork (September 2009) consisting of "gun-stock" tree trunks. Soil creep is a natural phenomenon where loose surficial soil becomes saturated and loses shear strength, resulting in slow migration downslope. Soil creep does not indicate deep-seated rotational failure or large- scale slope instability. Groundwater seepage was not observed at the test sites at the time of our fieldwork (September 2009). In our opinion, based on the conditions encountered during the fieldwork the site has a low susceptibility to landslide activity. Based on the conditions encountered at the boring locations and visual observations made during the fieldwork, in our opinion the site slopes are stable in the current configuration. Given the soil and groundwater conditions observed at the test sites, in our opinion the most likely mode of failure would be limited to shallow debris-flow or skin slide failures throughout the more steeply inclined portions of the site. In our opinion, the site soils are relatively resistant to deep- seated rotational failure. The currently proposed building setback from the steeply inclined west- facing slope is 35 feet. ESNW should review the final grading plans to confirm appropriate separation from steep slopes is incorporated into site designs and to provide supplemental recommendations, as appropriate. However, in our opinion the currently proposed 35 foot building setback is appropriate for this site. In our opinion the proposed lot layout and access improvements, as currently proposed will not increase the potential for slope instability on site or to surrounding properties, provided the recommendations detailed in this report, and Best Management Practices (BMPs) consistent with Mason County design standards are incorporated into final site designs. Seismic Hazard Area Assessment With respect to seismic hazards, in our opinion the most likely manifestation of seismic activity on the subject site would be debris-flow failure. We do not anticipate liquefaction-induced settlement to occur at this site given the dense granular nature of the soil deposits. Given the proposed building setback from the more steeply inclined west facing slope areas, seismically induced debris flow activity is not expected to adversely impact the proposed structure. Earth Solutions NW,LLC Mr. John Watkins ES-1570 October 1, 2009 Page 5 Erosion Hazard Area Assessment The subject site is located along a westerly-facing slope. The existing surface topography is largely the result of post-glacial erosion and stream incision from both perennial and seasonal fluvial flows. The soils anticipated to be exposed during grading activities should consist primarily of firm granular, glacially consolidated soils. The slope gradients in the proposed development envelope and along the access corridor are generally up to 40 percent. In our opinion, the erosion hazard throughout the proposed development area can be characterized as moderate. In our opinion, the proposed homesite represents a reasonable location with respect to minimizing disturbance and potential critical areas impacts. To help mitigate erosion hazards, Best Management Practices (BMPs) consistent with current Mason County Code standards should be incorporated into final site design. At a minimum, silt fencing should be placed along the entire down-slope development envelope. Construction entrances should be surfaced with quarry spalls to minimize off-site tracking of silt and soil generated during site construction. DISCUSSION AND RECOMMENDATIONS General Based on the results of our study, construction of the proposed single-family residence at the subject site is feasible from a geotechnical standpoint. The primary geotechnical considerations associated with the proposed development include site grading, foundation support, structural fill placements, and erosion control measures. Based on the results of our study, the proposed residential structure can be supported on conventional spread and continuous foundations bearing on competent or recompacted native soils, or structural fill, as necessary. We anticipate competent soil capable of providing adequate foundation support will be encountered at depths of between about two to four feet below existing grades. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with structural fill may be necessary. In our opinion, the soils generated from cuts throughout the site should generally be suitable for use as structural fill provided the soil moisture content is at or near the optimum level. The silty sand and sand soils encountered at the majority of the test sites will generally exhibit good soil strength when compacted to structural fill specifications. In our opinion, the use of rockeries or retaining wall systems to accommodate the driveway cuts is feasible for this project. The presence of perched groundwater seepage in site excavations should be anticipated, depending on depth and seasonal weather conditions. Based on the data obtained from the test sites, and our overall characterization of subsurface conditions, extensive site dewatering will likely not be necessary for the proposed site development. However, supplemental recommendations for controlling groundwater seepage should be provided by the geotechnical engineer during the grading activities, if necessary. Earth Solutions NW, LLC Mr. John Watkins ES-1570 October 1, 2009 Page 6 This study has been prepared for the exclusive use of Mr. John Watkins and his representatives. No warranty, expressed or implied, is made. This study has been prepared in a manner consistent with the level of care and skill ordinarily exercised by other members of the profession currently practicing under similar conditions in this area. Site Preparation and Earthwork The primary geotechnical considerations during the proposed site preparation and earthwork activities will involve site grading, fill placement, utility installations, and rockery or retaining wall construction. We anticipate site preparation will include clearing and grubbing within the development envelope, grading to establish the building pad area, and improvements along the driveway including widening, retaining wall construction, and installing utilities. Erosion Control Silt fencing should be placed around the development areas where earthwork is expected. Exposed earth surfaces should be protected as necessary to reduce sediment transport, and stormwater should be infiltrated onsite or directed to an appropriate temporary pond, as necessary. In-situ Soils From a geotechnical standpoint, the native soils encountered at our test sites are generally suitable for use as structural fill. The moisture sensitivity of the native soils anticipated to be exposed during site grading activities can be generally characterized as moderate. As such, successful use of the on-site soils will largely be dictated by the moisture content of the soils at the time of placement and compaction. Soils encountered during site excavations that are excessively over the optimum moisture content may require moisture conditioning prior to placement and compaction. Conversely, if the native soils are found to be dry at the time of placement, moisture conditioning through the application of water may be necessary prior to compacting the soil. If the site soils cannot be successfully compacted, the use of an imported soil may be necessary. Imported soil intended for use as structural fill should consist of a well graded granular soil with a maximum aggregate grain size of six inches, and a moisture content that is at or near the optimum level. During wet weather conditions, imported soil intended for use as structural fill should consist of a well graded granular soil with a fines content of five percent or less defined as the percent passing the #200 sieve, based on the minus three-quarter inch fraction. Structural Fill Placement In general, areas to receive structural fill should be sufficiently stripped of organic matter and other deleterious material. The geotechnical engineer should observe cleared and stripped areas of the site prior to structural fill placement. Earth Solutions NW,LLC Mr. John Watkins ES-1570 October 1, 2009 Page 7 Structural fill is defined as compacted soil placed in foundation, slab-on-grade, and roadway areas. Fills placed to construct permanent slopes and throughout retaining wall and utility trench backfill areas are also considered structural fill. Soils placed in structural areas should be placed in maximum 12-inch loose lifts and compacted to a relative compaction of 95 percent, in general accordance with the maximum dry density as determined by the Modified Proctor Method (ASTM D-1557). Slope Fill Placement In general, fill placement throughout the existing sloped areas of the site is feasible, provided appropriate measures to bench and key the fill into the existing slope surfaces are utilized. General guidelines for slope fill placement are provided on Plate 3 of this report. The project geotechnical engineer should be on-site during the fill placement to assess the slope fill construction, and to provide supplement recommendations for the fill placement, as necessary. During the construction of the slope fill, appropriate means of compacting the slope face should be utilized. Excavations and Slopes The Federal Occupation Safety and Health Administration (OSHA) and the Washington Industrial Safety and Health Act (WISHA) provide soil classification in terms of temporary slope inclinations. Based on the soil conditions encountered at the site, the native soils are classified as Type C by OSHA/WISHA. Temporary slopes over four feet in height in Type C soils must be sloped no steeper than 1.5H:1 V (Horizontal:Vertical). If the recommended temporary slope inclinations cannot be achieved, temporary shoring may be necessary to support excavations. Permanent slopes should maintain a gradient of 2H:1 V, or flatter, and should be planted with an appropriate species of vegetation to enhance stability and to minimize erosion. The project geotechnical engineer should observe temporary and permanent slopes to verify that the inclination is appropriate, and to provide additional grading recommendations, as necessary. Rockeries and Modular Block Walls In our opinion, the use of rockeries and/or modular block walls at this site is feasible from a geotechnical standpoint. Walls over four feet in height will require an engineered design. The geotechnical engineer should review the final wall alignments and wall heights with respect to the proposed site grading and provide engineering, as necessary. Earth Solutions NW, LLC Mr. John Watkins ES-1570 October 1, 2009 Page 8 Utility Support and Trench Backfill In our opinion, the soils observed at the test sites are generally suitable for support of utilities. Organic or highly compressible soils encountered in the trench excavations should not be used for supporting utilities. In general, the native soils anticipated to be exposed during grading should be suitable for use as structural backfill in the utility trench excavations, provided the soil is at or near the optimum moisture content at the time of placement and compaction and fines contents are within acceptable limits to maintain stability. Moisture conditioning of the soils may be necessary at some locations prior to use as structural fill. Utility trench backfill should be placed and compacted to the specifications of structural fill provided in this report, or to the applicable specifications of Mason County, as appropriate. Foundations In our opinion, the proposed building can be supported on conventional spread and continuous footings bearing on competent, undisturbed or recompacted, native soils or structural fill. Assuming the building will be supported as described above, the following parameters can be considered for design of the new foundations: ■ Allowable soil bearing capacity 2,500 psf ■ Passive resistance 350 pcf(equivalent fluid) ■ Coefficient of friction 0.40 ■ IBC site class Site Class C (Table 1613.5.2, 2006 IBC) ■ Liquefaction susceptibility Low A one-third increase in the allowable soil bearing capacity can be assumed for short-term wind and seismic loading conditions. A factor of safety of 1.5 has been applied to the passive earth pressure and friction values. Competent soils suitable for support of foundations are anticipated to be encountered at depths of approximately two to four feet below existing grades. Where loose or unsuitable soils are encountered at the foundation subgrade elevation, the soil should be recompacted or replaced with a suitable structural fill soil, as necessary. Foundation Setbacks The current site plan indicates a minimum approved setback of 35 feet from the top of the delineated steep slope/bluff area. Based on the results of our study, the proposed homesite is acceptable from a geotechnical standpoint and in our opinion will not increase the potential for slope instability or erosion. The competent soil conditions observed at our tests sites, and the observed stability of the slopes located at the site is the primary basis for our opinion. In our opinion, the proposed homesite location has been reasonably evaluated to minimize disturbance to critical areas present on the site. Earth Solutions NW,LLC Mr. John Watkins ES-1570 October 1, 2009 Page 9 Seismic Considerations The 2006 International Building Code specifies several soil profiles that are used as a basis for seismic design of structures. As previously mentioned, based on the soil conditions observed at the test sites, Site Class C, from table 1613.5.2, should be used for design. In our opinion, liquefaction susceptibility at this site is low. The relative density of the site soils and the absence of a relatively shallow groundwater table is the primary basis for this designation. Slab-On-Grade Floors Slab-on-grade floors should be supported on a firm and unyielding subgrade consisting of competent native soil or structural fill. Unstable or yielding areas of the subgrade should be recompacted or overexcavated and replaced with suitable structural fill prior to construction of the slab. A capillary break consisting of a minimum of four inches of free draining crushed rock or gravel should be placed below the slab. The free draining material should have a fines content of five percent or less (percent passing the #200 sieve, based on the minus three- quarter inch fraction). In areas where slab moisture is undesirable, installation of a vapor barrier below the slab should be considered. If a vapor barrier is utilized it should consist of a material specifically designed for that use and installed in accordance with the manufacturer's specifications. Retaining Walls Retaining walls should be designed to resist earth pressures and any applicable surcharge loads. For design, the following parameters can be assumed for retaining wall design: • Active earth pressure (yielding wall) 35 pcf (equivalent fluid) • At-rest earth pressure (restrained wall) 50 pcf • Traffic surcharge (passenger vehicles) 70 psf (rectangular distribution) • Passive resistance 350 pcf (equivalent fluid) • Coefficient of friction 0.40 Additional surcharge loading from foundations, sloped backfill, or other loading should be included in the retaining wall design, as appropriate. Drainage should be provided behind retaining walls such that hydrostatic pressures do not develop. If drainage is not provided, hydrostatic pressures should be included in the wall design, as appropriate. ESNW should review retaining wall designs to verify that appropriate earth pressure values and drainage have been incorporated into design, and to provide additional recommendations, as necessary. Earth Solutions NW,LLC Mr. John Watkins ES-1570 October 1, 2009 Page 10 Retaining walls should be backfilled with free draining material that extends along the height of the wall, and a distance of at least eighteen inches behind the wall. The upper one foot of the wall backfili can consist of a less permeable (surface seal) soil, if desired. A rigid, perforated drain pipe should be placed along the base of the wail, and connected to an appropriate discharge location. A typical retaining wall drainage detail is provided on Plate 4 of this report. Drainage Groundwater seepage was not observed at the time of our fieldwork (September 2009). However, groundwater seepage should be anticipated in general site excavations, particularly during the wetter winter months. Temporary measures to control groundwater seepage and surface water runoff during construction would likely involve interceptor trenches and sumps, as necessary. In our opinion, perimeter` drains should be installed at or below the invert of the building envelope footings. A typical footing drain detail is provided on Plate 5 of this report. Pavement Section Recommendations The performance of site pavements is largely related to the condition of the underlying subgrade. To ensure adequate pavement performance, the subgrade should be in a firm and unyielding condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement areas should be compacted to the specifications detailed in the Site Preparation and Earthwork section of this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may still exist after base grading activities. Areas of unsuitable or yielding subgrade will require remedial measures such as overexcavation and thicker crushed rock or structural fill sections prior to pavement. For relatively lightly loaded pavements subjected to automobiles and occasional truck traffic, the following pavement sections can be considered: • Two inches of asphalt concrete (AC) placed over four inches of crushed rock base (CRB), or; • Two inches of AC placed over three inches of asphalt treated base (ATB). The AC, ATB and CRIB materials should conform to WSDOT specifications. Heavier truck-traffic areas generally require thicker pavement sections depending on site usage, pavement life expectancy, and site traffic. The geotechnical engineer should provide appropriate pavement section design recommendations for truck traffic areas and right-of-way improvements, as necessary. Additionally, Mason County road standards may supersede the recommendations provided in this report. Earth Solutions NW, LLC Mr. John Watkins ES-1570 October 1, 2009 Page 11 LIMITATIONS The recommendations and conclusions provided in this geotechnical engineering study are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in the soil and groundwater conditions observed at the test sites may exist, and may not become evident until construction. ESNW should reevaluate the conclusions in this geotechnical engineering study if variations are encountered. Additional Services ESNW should have an opportunity to review the final design with respect to the geotechnical recommendations provided in this report. ESNW should also be retained to provide testing and consultation services during construction. Earth Solutions NW, LLC H-er--n Cove JC, �ndyhAc^� s'.ara v°U ^Q 0 E ed : J N _ c — Z . �� uC c G NORTH .. Y Reference: Mason County Map 40 By A Good Map Co., Inc. NIX Dated 2007 Vicinity Map Watkins Property Hartstene Island, Washington NOTE:This plate may contain areas of color.ESNW cannot be Drwn. GLS Date 09/28/2009 Proj. No. 1570 responsible for any subsequent misinterpretation of the information resulting from black&white reproductions of this plate. Checked SSR Date Sept. 2009 Plate 1 — — — — Property Line — — — Driveway -3 S �B-2 Proposed Single Story � Residence Bridging Ravine 0 B-1 NORTH r Prope Y LEGEND � - B-1-4—Approximate Location of 0 15 30 60 ESNW Boring, Proj. No. 1"=30' Sc ES-1570, Sept. 2009 _ ale in Feet Proposed Building �w NOTE:The graphics shown on this plate are not intended for design purposes or precise scale measurements,but only to illustrate the Boring Location Plan approximate test locations relative to the approximate locations of existing and/or proposed site features.The information illustrated Watkins Property is largely based on data provided by the client at the time of our Hartstene Island, Washington study.ESNW cannot be responsible for subsequent design changes or interpretation of the data by others. Drwn. GLS Date 09/28/2009 Proj. No. 1570 NOTE:This plate may contain areas of color. ESNW cannot be responsible for any subsequent misinterpretation of the information Checked SSR Date Sept. 2009 Plate 2 resulting from black&white reproductions of this plate. j SCHEMATIC ONLY - NOT TO SCALE NG T A CONSTRUCT ION DRAWING Final Slope Gradient Compacted Slope Face Bench and Keyway Fill to consist of suitable granular material approved by the 2 ---- Geotechncial Engineer i Existing Grade I i Typical"Bench" j i-———— Keyed into Existing Slope Face Geotechnical Engineer to Verify I "Key" (Minimum 2' Deep by 6'Wide) I NOTES: o Slope should be stripped of topsoil and o Structural fill should be placed in thin loose unsuitable materials prior to excavating lifts not exceeding 12 inches in thickness. Key Way or benches. Each lift should be compacted to no less than j the degree specified in the "Site Preparation o Benches will typically be equal to a dozer and Earth Work" section of this report. No blade width, approximately 8 feet, but a additional lift should be placed until compaction minimum of 4 feet. is achieved. o Final slope gradient should be 2 : 1 (horizontal : vertical). i o Final slope face should be densified by over-building with compacted fill and trimming back to shape or by compaction with dozer or roller. o Planting or hydroseeding slope face with s a rapid growth deep rooted vegetative mat SLOPE FILL DETAIL will reduce erosion potential of slope area. Watkins Property o Use of pegged in place jute matting or Hartstene Island, Washington geotechnical fabric will help maintain the seed and mulch in place until the root Drwn. GLS Date 09/29/2009 Proj. No. 1570 system has an opportunity to germinate. Checked SSR Date Sept. 2009 Plate 3 18" Min. 0 0 0 0 0 00 0 0 o 00 0 0 0b Oo� o O 000 oOo B 00 � o • o o ° o o 0 00 0 0 0o 0 0000 00 00 o0 o q p -o o,O o0 0 0 oo Vo 0 00 0 0 0 o O o 0 0 0 0 0 0 o 0 0 0 0 0 00 o -0 00 o 0 00 oC 0 0 o 0 0 0 0 0 00 00000 oa o0 000 o o0 0o o o 0 000 o o 0 o O o 0 o A o Structural �J Fill oa . C o0 0 0 a ;�, o 0 o Q o o O o 0 0 0 0 00 00 o 0 0 o0O o o 0 o o O o o 0 0 0o00 00 0 oo 00 0 00 0 00 00 0 00 0 0 0 0 0 0 oo 0 o 0 0o 0 o 0 8 11 = _ ° o o B � o0 0 00 0 0 0 0 0 r•r• o {. �•ti Perforated Drain Pipe NOTES: (Surround In Drain Rock) • Free Draining Backfill should consist of soil having less than 5 percent fines. Percent passing#4 should be 25 to 75 percent. • Sheet Drain may be feasible in lieu SCHEMATIC ONLY- NOT TO SCALE of Free Draining Backfill, per ESNW NOT A CONSTRUCTION DRAWING recommendations. • Drain Pipe should consist of perforated, rigid PVC Pipe surrounded with 1" Drain Rock. LEGEND: 0.0o O 1 1 ° 00 0 o 0 Free Draining Structural Backfill ,r •r•r•r•r• •..ti••..ti 1 inch Drain Rock RETAINING WALL DRAINAGE DETAIL •r•r•r•r• Watkins Property Hartstene Island, Washington Drwn. GLS Date 09/29/2009 Proj. No. 1570 Checked SSR Date Sept. 2009 Plate 4 'a3 Slope '" " � L•L•L•L•L•L•. ,r,f•r,r,r,r.r L•L•L L•L•L• •rL•.�L•L / 2" (Min.) Perforated Rigid Drain Pipe (Surround with 1" Rock) NOTES: • Do NOT tie roof downspouts to Footing Drain. SCHEMATIC ONLY- NOT OT SCALE • Surface Seal to consist of NOT CONSTRUCTION DRAWING 12" of less permeable, suitable soil. Slope away from building. LEGEND: Surface Seal; native soil or other low permeability material. 1" Drain Rock4 FOOTING DRAIN DETAIL Watkins Property Hartstene Island, Washington Drwn. GLS Date 09/29/2009 Proj. No. 1570 Checked SSR Date Sept. 2009 Plate 5 APPENDIX A SUBSURFACE EXPLORATION ES-1570 The subsurface conditions at the site were explored by drilling three borings at the approximate test site locations illustrated on Plate 2 of this report. The boring logs are provided in this Appendix. The subsurface exploration was completed in September 2009. Logs of the borings are presented in Appendix A. The stratification lines on the logs represent the approximate boundaries between soil types. In actuality, the transitions may be more gradual. Earth Solutions NW,LLC Earth Solutions NWLLC SOIL CLASSIFICATION CHART MAJOR DIVISIONS SYMBOLS TYPICAL GRAPH LETTER DESCRIPTIONS CLEAN ''° '� WELL-GRADED GRAVELS,GRAVEL- i 0•r _ GW SAND MIXTURES,LITTLE OR NO GRAVEL GRAVELS !I FINES AND GRAVELLY °Q° °Qo POORLY-GRADED GRAVELS, SOILS (LITTLE OR NO FINES) o DDo 0 GP GRAVEL-SAND MIXTURES,LITTLE Q Q°Q OR NO FINES COARSE ° GRAINED GRAVELS WITH SILTY GRAVELS,GRAVEL-SAND- SOILS MORE THAN 50% FINES Q ° GM SILT MIXTURES OF COARSE FRACTION RETAINED ON NO. 4 SIEVE (APPRECIABLE GC CLAYEY GRAVELS,GRAVEL•SAND- AMOUNT OF FINES) CLAY MIXTURES WELL-GSAND CLEAN SANDS SW SANDS,LITTLE OR NO F NREASVELLY DED SANDS, MORE THAN 50%OF MATERIAL IS AND LARGER THAN SANDY POORLY-GRADED SANDS, NO.200 SIEVE SOILS SIZE (LITTLE OR NO FINES) SP GRAVELLY SAND,LITTLE OR NO FINES MORE THAN 50% SANDS WITH SM SILTY SANDS,SAND-SILT OF COARSE FINES MIXTURES FRACTION PASSING ON NO. 4 SIEVE (APPRECIABLE SC CLAYEY SANDS,SAND-CLAY AMOUNT OF FINES) MIXTURES INORGANIC SILTS AND VERY FINE ML SANDS,ROCK FLOUR,SILTY OR CLAYEY FINE SANDS OR CLAYEY SILTS WITH SLIGHT PLASTICITY SILTS INORGANIC CLAYS OF LOW TO FINE LIQUID LIMIT MEDIUM PLASTICITY,GRAVELLY GRAINED AND LESS THAN 50 C�- CLAYS,SANDY CLAYS,SILTY CLAYS CLAYS,LEAN CLAYS SOILS — _ _ OL ORGANIC SILTS AND ORGANIC — — — SILTY CLAYS OF LOW PLASTICITY MORE THAN 50% INORGANIC SILTS,MICACEOUS OR OF MATERIAL IS MH DIATOMACEOUS FINE SAND OR SMALLER THAN SILTY SOILS NO.200 SIEVE slzE SILTS LIQUID LIMIT INORGANIC CLAYS OF HIGH AND CLAYS GREATER THAN 50 CH PLASTICITY OH ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY,ORGANIC SILTS �!• " PEAT,HUMUS,SWAMP SOILS WITH HIGHLY ORGANIC SOILS PT HIGH ORGANIC CONTENTS DUAL SYMBOLS are used to indicate borderline soil classifications. The discussion in the text of this report is necessary for a proper understanding of the nature of the material presented in the attached logs. Earth Solutions NW BORING NUMBER B-1 2881 152nd Avenue N.E. PAGE 1 OF 2 Redmond,Washington 98052 Telephone: 425-284-3300 Fax: 425-284-2855 CLIENT Watkins PROJECT NAME Watkins Property PROJECT NUMBER 1570 PROJECT LOCATION Hartstene Island Washington DATE STARTED 9/16/09 COMPLETED 9/16/09 GROUND ELEVATION 30 ft HOLE SIZE DRILLING CONTRACTOR Geologic Drill GROUND WATER LEVELS: DRILLING METHOD HSA AT TIME OF DRILLING -- LOGGED BY SSR CHECKED BY SSR AT END OF DRILLING --- NOTES Bare Surface AFTER DRILLING - wQ. o _ �w ►�� CO - ~" J CO > O Z¢ �? n-p MATERIAL DESCRIPTION J J ov QZ o 0000> 0 Tan poorly graded GRAVEL with silt and sand,loose,damp ° GP- o GM ° 2 0 -trace cobbles 28.0 Brown poorly graded SAND with silt and gravel,very dense,damp SS 100 43-50 5 SS 100 24-34-32 (66) SS 100 17-22-22 (44) 10 -increase silt content 17-18-17 -becomes moist SS 100 (35) SP- ::.:: '.: SM m 0 N m O 15 SS 100 50/5" z CL a 0 J WJ> a x m w � 20 20.0 1001 Earth Solutions NW BORING NUMBER B-1 2881 152nd Avenue N.E. PAGE 2 OF 2 Redmond,Washington 98052 Telephone: 425-284-3300 Fax: 425-284-2855 CLIENT Watkins PROJECT NAME Watkins Property PROJECT NUMBER 1570 PROJECT LOCATION Hartstene Island Washington LU }a:ul > W U a w s > O Z Q 0-0 MATERIAL DESCRIPTION ov �z a m0Z v � ¢ w 20 SS 100 31-50/4" SP- Brown poorly graded fine SAND with silt,very dense,moist SM :. 21.0 s.o Boring terminated at 21.0 feet below'existing grade. No groundwater encountered during drilling. Boring backfilled with bentonite. Bottom of hole at 21.0 feet. 0 o! m 0 c� Cn z c� a c� 0 h JW> x m J w z w 4 Earth Solutions NW BORING NUMBER B-2 2881 152nd Avenue N.E. PAGE 1 OF 2 Redmond,Washington 98052 Telephone: 425-284-3300 Fax: 425-284-2855 CLIENT Watkins PROJECT NAME Watkins Property PROJECT NUMBER 1570 PROJECT LOCATION Hartstene Island Washington DATE STARTED 9/16109 COMPLETED 9/16/09 GROUND ELEVATION 42 ft HOLE SIZE DRILLING CONTRACTOR Geologic Drill GROUND WATER LEVELS: DRILLING METHOD HSA AT TIME OF DRILLING LOGGED BY SSR CHECKED BY SSR AT END OF DRILLING --- NOTES Gravel Pathway AFTER DRILLING --- a = F}-W i- a uj CO uj p Z—' 0-0 MATERIAL DESCRIPTION Lu J� > _j uj Q� QZ g]�Z W Lu Brown poorly graded GRAVEL with silt and sand, loose,damp 0 0 a O GP- GM a O a O 5 s.o 37.0 Brown poorly graded SAND with gravel,medium dense,damp SS 100 7-8-13 (21) SP 10 -becomes moist 19-22-20 31.0 SS 100 (42) ».o Brown SILT with fine sand,dense, moist 0 m N r 0 15 -becomes very dense z SS 100 23-50 ML a d N_ J ti a m J W 2 2Q 20.0 22.0 M. Earth Solutions NW BORING NUMBER B-2 2881 152nd Avenue N.E. PAGE 2 OF 2 Redmond,Washington 98052 Telephone: 425-284-3300 Fax: 425-284-2855 CLIENT Watkins PROJECT NAME Watkins Property PROJECT NUMBER 1570 PROJECT LOCATION Hartstene Island Washington a ~a W Coo z Q �? a MATERIAL DESCRIPTION 0v 2Z O0 m0Z j �� W 20 Brown silty SAND with gravel,very dense,moist SS 100 33-50/5" SM 21.0 21.0 Boring terminated at 21.0 feet below existing grade. No groundwater encountered during drilling.Boring backfilled with bentonite. Bottom of hole at 21.0 feet. 0 N D Z O N_ W$J a r_ x m J Q Uj W Z W (7 Earth Solutions NW BORING NUMBER B-3 2881 152nd Avenue N.E. Redmond,Washington 98052 PAGE 1 OF 1 Wo Telephone: 425-284-3300 Fax: 425-284-2855 CLIENT Watkins PROJECT NAME Watkins Property PROJECT NUMBER 1570 PROJECT LOCATION Hartstene Island Washington DATE STARTED 9/16/09 COMPLETED 9/16/09 GROUND ELEVATION 50 ft HOLE SIZE DRILLING CONTRACTOR Geologic Drill GROUND WATER LEVELS: DRILLING METHOD HSA AT TIME OF DRILLING -- LOGGED BY SSR CHECKED BY SSR AT END OF DRILLING -- NOTES Gravel Pathway AFTER DRILLING -- a rW } tout U � 2 a j U a p MATERIAL DESCRIPTION O W v g-2 O m 0 '6 _, Q Z W L) 0 Brown poorly graded SAND with gravel,loose,damp SS 100 8-8-9 -becomes medium dense (17) 5 SS 100 9-11-8 SP (19) SS 100 9-11-18 (29) 10 SS 100 9-12-18 (30) 11.5 38.5 Boring terminated at 11.5 feet below existing grade.No groundwater encountered during drilling. Boring backfilled with bentonite. Bottom of hole at 11.5 feet. 0 m N 'm H O C7 Z_ a 0 w?J Q. H 2 0] W Z W REPORT DISTRIBUTION ES=15?0 1 COPY Mr. John Watkins 21232 - 15t Avenue South Des Moines, Washington 98198 4 COPIES Rick Anderson Architect AIA 935 Daley Street Edmonds, Washington 98020 Earth Solutions NW, LLC