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Home My WebLink AboutGeoTech Report for BLD2002-01164 - BLD Engineering / Geo-tech Reports - 10/15/2002 r ' MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton,Wwhington99594 DATE: Oct. 15 02 INTER-DEPARTMENTAL COMMUNICATIONS FILE � TO: Rick Mraz, DCD - Planner P r. En COPY /W- Co. H d FROM: Alan A. Tahja, y gr. WO#PLG-02 SUBJ: Geo-Tech Report Review NAME: Berthiaume (& Bear Crk Dewatto Rd BLD2002-01164 Rick, The geotechnical report prepared for the proposed Jason Berthiaume Single Family Residence (SFR)to be constructed on Mason County Tax Parcel No. 123093190074,has been received and reviewed by Public Works. The report conforms to accepted standards of engineering/geotechnical principles and practices and appears in compliance with requirements of DCD for geotechnical reporting. The report indicates that no setback is required,but the site plan indicates a house location approximately 15' downslope from a low rock wall, and approximately 20' upslope from a gently increasing downslope on the southeast quadrant of the homesite. So long as the residence is sited in this general area,no concerns arise. The report also includes a roof runoff infiltration trench design which should be included in the site's development. The applicant and their contractor should be aware of their responsibility to protect neighboring properties and State waters from construction silt and stormwater runoff impacts. Delivery of silty water to neighboring properties would be a violation of the County's Stormwater Management Ordinance, and a violation of State Water Quality regulations. Please feel free to contact me at County extension 461 if you have anyquestions regarding these comments, or if you feel any features need further discussion or attention. Si cerely, Alan A. Tahj�a File: H:\WP\GEO\REVIEWS\Berthiaume.doc fl'd QL S � 1 AA a (� a-I u' 77 A .. �'► D1i+iM _1Y a /� I N D ITI N =l N 9i lot /ru.a�� vim, �� C, lP,/5 rC �43 M r SITE f LA N —LLis2t.'-`2 7-Y rj%gv r r I-C ROCK wA,L --- w - O Anc,a 6�o S,T��w�da y3 / o 6 1 6a Go gp a 7s' l� � d -4- � n� Geotechnical Report For Construction Parcel #1230931900 Rear Creek Dewatto Road Mason County, Washington Prepared For: Jason Berthiaume By: Geotechnical Testing Lab Olympia, WA October 8, 2002 GEOTECHNICAL TESTING LABORATORY JASON BERTHIAUME 3160 MILE HILL ROAD PORT ORCHARD, WA 98336 Re: Geotechnical Report Parcel#123093190074 Mason County, WA INTRODUCTION This report summarizes the results of our geotechnical engineering services for the proposed home to be located on off the Bear Creek Dewatto Road in Mason County, WA. The location of the site is shown relative to the surrounding area on the Vicinity Map, Figure 1. Our understanding of the project is based on our discussions with you and our explorations and review of the site. We understand that the triangular shaped site is to be developed as a residential home site with associated outbuildings, pavement areas and utilities. The site will be accessed by easement from the Bear Creek Dewatto Road. Stormwater runoff from the site, roof and hard surfaces, will be collected and directed to on-site retention facilities. The general layout of the site is shown on the Site Map, Figure 2. We further understand that very little grading is required at the site to reach design grade. In general, grading will consist of the excavation of the foundation; no structural fill is anticipated. We understand that the site will be served by local utility companies. The site is level, sloping up to the northwest and the down to the southeast,with the septic to be installed on the downslope side. A rock wall has been placed at the toe of the upper slope. The steepest slope measured on site was 41%. Therefore, Mason County requires that a geotechnical report be prepared in accordance with the Critical Areas Ordinance. The purpose of our services is to evaluate the surface and subsurface conditions at the site as a basis for providing geotechnical recommendations and design criteria for the project and to satisfy the requirements of the Mason County Critical Areas Ordinance. Geotechnical Testing Lab is therefore providing geologic and hydrogeologic services for the project. Specifically, our scope of services for this project will include the following: l. Review the available geologic, hydrogeologic and geotechnical data for the site area. 2. Conduct a geologic reconnaissance of the site area. 3. Explore the shallow subsurface conditions at the site by monitoring the excavation of boring test pits. 4. Evaluate the landslide and erosion hazards at the site per the Mason County Critical Areas Ordinance regulations 5. Provide geotechnical recommendations for site grading including site preparation, subgrade preparation, fill placement criteria (including hillside grading), suitability of on-site soils for use as structural fill, temporary and permanent cut and fill slopes, drainage and erosion control measures 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206) 754-4848 GEOTECHNICAL TESTING LABORATORY 6. Provide recommendations and design criteria for the structural foundation and floor slab support, including allowable bearing capacity, subgrade modulus, lateral resistance values and estimates of settlement 7. Provide our opinion regarding the feasibility of the location/construction of the stormwater outfall SITE CONDITIONS SURFACE CONDITIONS The proposed building site is located in an area of limited development in the lower portion of the Kitsap Peninsula at the end of the Hood Canal glacial upland area. The proposed layout of the site is shown on the Site Plan, Figure 2. We conducted a reconnaissance of the site area and monitored the soil test pits at the site. Elevations in the building area are level. The lot slopes to the south from the Bear Creek Dewatto Road. We observed no evidence of erosion. Surficial sloughing and soil movement was not observed on the site and adjacent areas. No evidence of deep-seated slope instability was observed on the site slope or areas adjacent to this site at the time of our investigation. The building area of the site has very little vegetation with the upland area covered with trees and understory native to the northwest. No evidence of surface water flow was observed in the site area at the time of our reconnaissance. The general topography of the site area indicates that the site drains towards the south. SITE GEOLOGY The site is generally situated within the Puget Sound glacial upland. The existing topography, as well as the surficial and shallow subsurface soils in the area, are the result of the most recent Vashon stade of the Fraser glaciation that occurred between about 12,000 and 15,000 years ago, and weathering and erosion that has occurred since. A description of the surficial soils is included in the"Site Soils"section of this report. In general, Vashon glacial till underlay the soils of the site. SITE SOILS The Mason County Soil Conservation Survey (1960) has mapped the site soils as an Everett gravelly sandy loam (Ek) in the building area of the site. The Everett soils typically form in sandy glacial till areas and are described as having a high permeability and a low erosion hazard. These soils are typically classified as a"Group C" relative to surficial runoff. We observed no active erosion or slope disturbance in the site area during our reconnaissance. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206) 754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY SUBSURFACE EXPLORATIONS Subsurface conditions at the sites were evaluated by observing soil log test pits previously dug on the site. The test pits extended to a depth of four feet below the existing ground surface. The approximate locations of the test pits are indicated on the attached Site Plan, Figure 2. SUBSURFACE CONDITIONS In general, undisturbed dense till was encountered in the test pits and cut slopes located in the building portion of the site. The undisturbed till was encountered at depths of four feet below the existing ground surface. No groundwater seepage was observed in the test pit excavation at the site. Based on the nature of the near surface soil(intermittent outwash and weathered sands and gravel over undisturbed sand and gravel in the building area), seasonally perched groundwater conditions should not be expected even during periods of extended wet weather. SLOPE STABILITY Slopes as steep as 41% were observed on the site. Since slopes of 40% or greater with 10 feet or more of vertical relief occur on portions of the site, Mason County requires that a geologic hazards report be completed per the Critical Areas Ordinance. Slopes of 0 to 5 %found within the building area are identified on Figure 2. In general, the undisturbed native soils in level portions of the site consist of a mixture of sands with variable amounts of gravel. These soil materials are in a dense to very dense condition except where they have been disturbed by weathering activity. The near-surface recessional, weathered advance outwash soils are in a medium dense to dense condition except at the ground surface. The surficial soils are generally in a loose to medium dense condition. These soils are generally stable relative to deep-seated failure. No evidence of deep-seated landslide activity or significant erosion was observed at the site at the time of our investigation. Weathering, erosion, and the resulting sloughing and shallow landsliding are natural processes that can affect steep slope areas. Instability of this nature is typically confined to the upper weathered or disturbed zone, which has been disturbed and has a lower strength. No evidence of local surficial erosion, raveling and sloughing was observed in the site area at the time of our investigative visits. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles, and freeze/thaw cycles. Erosion in steep slope areas such as this can be reduced through proper design and construction of the storm water systems. Erosion control recommendations for the sloping areas are provided in the "Building Setback"and "Erosion Control"sections of this report. 1001 1 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY CONCLUSIONS AND RECOMMENDATIONS GENERAL Based on the results of our site reconnaissance and subsurface exploration program, and our experience in the area, it is our opinion that the site is suitable for the proposed home. The slopes located in or near the building portion of the site area and the adjacent property are stable relative to deep- seated instability and will not be affected by the proposed home. Proper drainage control measures will reduce or eliminate the potential for erosion in this area, and improve slope stability. In general,the sand and gravel soils observed at the site are suitable for use as structural fill material. Material with less than 10%fines should be considered equivalent to gravel base material. The soils that occur on the site are moisture-sensitive and susceptible to disturbance when wet. Saturated soil conditions may be associated with these soils during or following extended periods of rainfall. To reduce grading time and construction costs, we recommend that earthwork be undertaken during favorable weather conditions. Conventional construction equipment may be utilized for work at the site. Conventional spread footings may be utilized at the site for support of the structure. We do recommend that roof drains be used for mobile homes and roof and footing drains be installed for homes with normal spread footings. A vapor barrier is recommended for all slab- on-grades. Infiltration of the stormwater is possible at the site. Pertinent conclusions and geotechnical recommendations regarding the design and construction of the proposed development are presented below. LANDSLIDE—EROSION HAZARD AREAS Classification The Mason County Critical Areas Ordinance defines a landslide hazard area as 1)one containing slopes equal to or greater than 40%with more than a I0-foot vertical relief, and 2)one containing soils described by the Soil Conservation Service(SCS) Soil Survey as having a"severe"limitation for building site development due to erosion. The slopes located in the area north of the site are in excess of 40%and the vertical relief is in excess of 10 feet. Based on this, this site does meet the technical criteria of a landslide hazard. The soils at the site are mapped as Everett gravelly sand (Ek) in the building portions of the site. The Everett soils are described as having a low erosion hazard, based on the present slope inclination. These soils do not meet the technical criteria of an erosion hazard. Slope Stability Based on our field observations, explorations and our experience with the soil types encountered on the property, we conclude that although portions of the slopes on the lot exceed 40%, they are generally stable relative to deep-seated failure in their present configuration. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206) 754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY No changes in slope stability are expected as a result of the proposed development of the site. Development will occur in the level portions of the site based on appropriate engineering and building setback recommendations. Grading in the building portion of the site should be conducted in accordance with geotechnical recommendations provided herein. Site drainage will be collected and directed to the site's stormwater system. As previously discussed, weathering, erosion, and the resulting surficial sloughing and landsliding are natural processes that affect slope areas. Significant weathering typically occurs in the upper 2 to 3 feet and is the result of oxidation, root penetration, wet/dry cycles and freeze/thaw cycles. These processes can be managed and the risk reduced through proper construction of the residence, including the stormwater system. Erosion control recommendations in the slope and buffer areas are provided in the"Building Setback"and"Erosion Control sections of this report. Building Setback A building setback area from landslide hazard areas is required unless evaluated and reduced by an engineering geologist or a licensed professional engineer. Grading and filling within the setback area may not be allowed because slope stability or the erosion hazard will be adversely impacted. Based on our geotechnical evaluation of the site and our experience in the area, no building setback will be needed for this lot. As previously discussed, weathering, erosion and the resulting surficial sloughing and shallow landsliding are natural processes that affect slope areas. As noted, no evidence of surficial raveling or sloughing was observed in the sloping portions of the site. To manage and reduce the potential for these natural processes, we recommend that drainage from the roof area be collected and tightlined to a disposal area at the level of and east of the drainfield and that the seepage rate be controlled to a slow seep(similar to a septic system)or seepage pit. SEISMIC—LIQUEFACTION HAZARD According to the Seismic Zone Map of the United States contained in Figure 16-2 of the 1997 UBC (Uniform Building Code), the project site is located within Seismic Risk Zone 3. Based on the subsurface conditions observed at the site, we interpret the site conditions to correspond to a seismic Soil Profile Type Sc, for Very Dense Soil, as defined by Table 16-J (UBC). This is based on the range of SPT (Standard Penetration Test)blow counts and/or probing with a ''/z-inch diameter steel probe rod. The shallow soil conditions were assumed to be representative for the site conditions beyond the depths explored. Based on our review of the subsurface conditions, we conclude that the site soils are not susceptible to liquefaction. The near-surface soils are generally in a dense condition and the static water table is located below the surface. Shaking of the already stiff/dense soil is not apt to produce a denser configuration and subsequently excess pore water pressures are not likely to be produced. 1001 1 Blomberg Street SW, Olympia, WA 98512 Phone#: (206) 754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY EROSION CONTROL It is our opinion that the potential erosion hazard of the site is not a limiting factor for the proposed development. Removal of natural vegetation should be minimized and limited to the active construction areas. Temporary and permanent erosion control measures should be installed and maintained during construction or as soon as practical thereafter to limit the additional influx of water to exposed areas and protect potential receiving waters. Erosion control measures should include, but not be limited to, berms and swales with ground cover/protection in exposed areas. No earth work is anticipated that would impact the sloping areas of the site. EARTHWORK Site Preparation All site work to be excavated has already been cleared of deleterious matter including any existing structures, debris and vegetation. Based on our explorations, we estimate that no stripping will be necessary because the root zone and surficial soils containing organics have already been removed. Where placement of fill material is required, the exposed subgrade areas should be proof-rolled-to a firm and unyielding surface prior to placement of any fill. We recommend that trees be removed in such a manner so that a majority of the roots are removed unless located on a slope. Excavations for tree stump removal in any building area should be backfilled with structural fill compacted to the density requirements described in the"Structural Fill' section of this report. We recommend that a member of our staff evaluate the exposed subgrade conditions after removal of vegetation and topsoil stripping is completed and prior to placement of structural fill(if needed). Any soft, loose or otherwise unsuitable areas delineated during proof-rolling or probing should be re-compacted, if practical, or over-excavated and replaced with structural fill, based on the recommendations of our site representative. Structural Fill All fill material should be placed as structural fill. The structural fill should be placed in horizontal lifts of appropriate thickness to allow adequate and uniform compaction of each lift. Fill should be compacted to at least 90%of MDD(maximum dry density as determined in accordance with ASTM D-1557/698)to within 2 feet of 0 subgrade and 95/o MDD in the upper 2 feet. The appropriate lift thickness will depend on the fill characteristics and compaction equipment used. We recommend that the appropriate lift thickness be evaluated by our field representative during construction. We recommend that our representative be present during site grading activities to observe the work and perform field density tests. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206) 754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY The suitability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines(material passing No. 200 sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and adequate compaction becomes more difficult to achieve. During wet weather, we recommend use of well-graded sand and gravel with less than 5 percent(by weight)passing the No. 200 sieve based on that fraction passing the%-inch sieve. If prolonged dry weather prevails during the earthwork and foundation installation phase of construction, a somewhat higher(up to 12 percent)fines content will be acceptable. Material placed for structural fill should be free of debris, organic matter, trash and cobbles greater than 6 inches in diameter. The moisture content of the fill material should be adjusted as necessary for proper compaction. Suitability of On-Site Soils as Fill During dry weather construction, any non-organic on-site soil may be considered for use as structural fill, provided it meets the criteria described above in the structural fill section and can be compacted as recommended. If the material has over-optimum moisture content when excavated, it will be necessary to aerate or dry the soil prior to placement as structural fill. The workability of a material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines increases, soil becomes more sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. In general,the native soils(sand and gravel)encountered in the test pit explorations at the site with less than 10% fines(material passing the US No. 200 Sieve)are suitable for use as structural fill. This material is comparable to WSDOT"gravel base". Material with less than 5% fines will be suitable as structural fill during wet weather conditions. If fill material is imported to the site for wet weather construction, we recommend that it be a sand and gravel mixture such as high quality pit run with less than 5%fines. CUT AND FILL SLOPES All job site safety issues and precautions are the responsibility of the contractor providing services and/or work. The following cut/fill slope guidelines are provided for planning purposes. Temporary cut slopes will likely be necessary during grading operations. As a general guide,temporary slopes of 1.5 to 1 (horizontal to vertical)or flatter may be used for temporary cuts in the upper 3 to 4 feet of the glacially consolidated soils that are weathered to a looselmedium dense condition. Temporary slopes of 1 to 1 or flatter may be used in the unweathered dense to very dense sands and gravels or till. These guidelines assume that all surface loads are kept at a minimum distance of at least one half the depth of the cut away from the top of the slope and that significant seepage is not present on the slope face. Flatter cut slopes will be necessary where significant raveling or seepage occurs. We recommend a maximum slope of 2 to 1 for permanent cut and fill slopes. Where 2 to 1 slopes are not feasible, shoring of the slopes should be considered. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#:(206)754-4612 Fax#:(206) 754-4848 GEOTECHNICAL TESTING LABORATORY Fill placed on slopes that are steeper than 4 to 1 should be"keyed" into the undisturbed native soils by cutting a series of horizontal benches. The benches should be 1'/z times the width of equipment used for grading and a maximum of 3 feet in height. Subsurface drainage may be required in seepage areas. Surface drainage should be directed away from all slope faces. Some minor raveling may occur with time. All slopes should be seeded as soon as practical to facilitate the development of a protective vegetative cover or otherwise protected. FOUNDATION SUPPORT All exterior footing elements for spread footings should be embedded as least 18 inches below grade for frost protection. ((CC We recommend a minimum width of feet for isolated footings nd at st 16 inches for continuous wall footin s� ootings founded as described above can be designed using an owable So�apacity of 2000 psf(pounds per square foot) for combined dead and long-term live loads in areas of medium dense to dense soils. The weight of the footing and any overlying backfill may be neglected. The allowable bearing value may be increased by one-third for transient loads such as those induced by seismic events or wind loads. Lateral loads may be resisted by friction on the base of footings and floor slabs and as passive pressure on the sides of footings. We recommend that an allowable coefficient of friction of 0.40 be used to calculate friction between the concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent fluid density of 275 pcf(pounds per cubic foot). Factors of safety have been applied to these values. We estimate that settlements of footings designed and constructed as recommended will be less than 1 inch, for the anticipated load conditions, with differential settlements between comparably loaded footings of%z inch or less. Most of the settlements should occur essentially as loads are being applied. However, disturbance of the foundation sub- grade during construction could result in larger settlements than predicted. FLOOR SLAB SUPPORT Slabs-on-grade should be supported on medium dense or dense native soils or on structural fill prepared as described in the"Structural Fill"section of this report. We recommend that floor slabs be directly underlain by a minimum 6- inch thickness of coarse sand and/or gravel containing less than 3 percent fines(by weight). The drainage material should be placed in one lift and compacted to an unyielding condition. A synthetic vapor barrier should be used for the control of moisture migration through the slab, particularly where adhesives are used to anchor carpet or tile to the slab. A thin layer of sand may be placed over the vapor barrier and immediate) below the slab to protect the liner during steel and/or concrete placement. The lack of a vapor barrier Y P g P P could result in wet spots on the slab, particularly in storage areas. A subgrade modulus of 400 kcf(kips per cubic foot)may be used for floor slab design. We estimate that settlement of the floor slabs designed and constructed as recommended, will be % inch or less over a span of 50 feet. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#:(206)754-4612 Fax#:(206)754-4848 GEOTECHNICAL TESTING LABORATORY Retaining Wall Retaining walls will likely be utilized in the development of the site to retain fill material, and a retaining wall has been installed at the toe of the upslope, north of the home site. The lateral pressures acting on the subgrade and retaining walls will depend upon the nature and density of the soil behind the wall. It is also dependent upon the presence or absence of hydrostatic pressure. The adjacent exterior wall space on the existing rock wall is backfilled with clean granular material. A drain pipe was placed at the bottom of the backfill. Retaining walls located on or near the toe of any slope that extends up behind the wall should be designed for a lateral pressure, which includes the surcharge effects of the steep slope in proximity to the wall. Although not expected at this site, the following data is provided for planning purposes. For an irregular or composite slope,the equivalent slope angle may be determined by extending a line upwards from the toe of the wall at an angle of 1 to 1 (Horizontal to Vertical)to a point where the line intersects the ground surface. The surcharge effects may be modeled by increasing the equivalent fluid pressure for flat ground by the percentage given in the following table: Slope Inclina tion: Equivalent Fluid Pressure Slope Angle Percent Increase Equivalent Fluid Pressure Horizontal 0% 35 pcf 3H:1 V 25% 44 pcf 2H:1 V 50% 53 pcf 1 HA V 75% 61 pcf If the walls are greater than 5 ft. in height, exclusive of the footing, additional design considerations should be applied. Positive drainage, which controls the development of hydrostatic pressure,can be accomplished by placing a zone of coarse sand and gravel behind the walls. The granular drainage material should contain less than 5% fines. The drainage zone should extend horizontally at least 18 inches from the back of the wall. The drainage zone should also extend from the base of the wall to within one ft. of the top of the wall. The drainage zone should be compacted to approximately 90%of the Maximum Dry Density. Over compaction should be avoided as this can lead to excessive lateral pressures. A perforated PVC pipe with a minimum diameter of four inches should be placed in the drainage zone along the base of the wall to direct accumulated water to an appropriate discharge location. We recommend that a non-woven geotextile filter fabric be placed between the drainage material and the remaining wall backfill on any additional walls to reduce the permeability of the granular material. The filter fabric should be placed such that it fully separates the drainage material and the backfill, and should be extended over the top of the drainage zone. I i 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206)754-4848 I I GEOTECHNICAL TESTING LABORATORY Lateral loads may be resisted by friction on the base of footings and as passive pressure on the sides of footings and the buried portion of the wall. We recommend that an allowable coefficient of friction of 0.35 be used to calculate friction between the concrete and the underlying soil. Passive pressure may be determined using an allowable equivalent fluid density of 300 pcf(pounds per cubic ft). Factors of safety have been applied to these values. Retaining Wall Alternatives Retaining walls will likely be utilized in developing the site. Options for retaining material other than conventional concrete retaining walls include reinforced earth systems such as small or large block walls, or rolled-faced walls. Typically,reinforced-earth block wall systems are more cost effective for long term walls than the other options. Specific design criteria for these options can be provided by the block manufacturers. PAVEMENT SUBGRADE We recommend that pavement subgrades be prepared in accordance with the previously described site preparation and structural fill recommendations. The upper 2 feet of roadway subgrade should have a density of at least 95%of the MDD(ASTM D-1577) SITE DRAINAGE All ground surfaces, pavements and sidewalks should be sloped away from the residences and associated structures. Surface water runoff should be controlled by a system of curbs, berms, drainage swales, and/or catch basins, and conveyed to the site's retention system. (see Figure 3) We recommend that conventional roof and footing drains be installed for the home or garage. A roof drain should not be connected to the footing drain. A footing drain will not be necessary for a mobile home. We recommend that the collected stormwater runoff at the site be directed to the site's stormwater system. Based on the soils encountered in the building portion of the site, it is our opinion that it is feasible to infiltrate a portion of the site's stormwater in properly designed and constructed facilities. Based on the results of our test pits in the building portion of the site, we recommend a design infiltration rate of 16 inches per hour. An appropriate factor of safety should be applied to this infiltration rate. We do not expect any adverse affects on the recharge condition of the groundwater system. The infiltration of a portion of the site's stormwater runoff will match the existing shallow groundwater recharge conditions. Because the recharge of the local shallow aquifer will not be significantly affected, the net impact to the regional aquifer will be insignificant. The recharge area for the regional aquifer essentially occurs over the entire Hood Canal area. 10011 Blomberg Street SW, Olympia, WA 98512 Phone#: (206)754-4612 Fax#: (206)754-4848 GEOTECHNICAL TESTING LABORATORY LIMITATIONS We have prepared this report for the use of Jason Berthiaume and members of his design team, to use in the design of a portion of this project. The data used in preparing this report, and this report, should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on data from others and our site reconnaissance, and should not be construed as a warranty of the subsurface conditions. Variations in subsurface conditions are possible between the explorations and may also occur with time. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient consultation with our firm during construction should continue,to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork and foundation installation activities comply with contract plans and specifications. - If our analysis and recommendations are followed, we do not anticipate any on site or off site impact from the construction. It is our conclusion that potential landslide hazards from the landslide area can be overcome so as not to cause harm to property, public health and safety, or the environment. The scope of our services does not include services related to environmental remediation and construction safety precautions. Our recommendations are not intended to direct the contractor's methods, techniques, sequences or procedures, except as specifically described in our report for consideration in design. If there are any changes in the loads, grades, locations, configurations or type of facilities to be constructed, the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. Respectfully, o{ Wash . L/ /�� o' Harold Parks, Engineering Geologist Oleo CO g� �'aed Qeo�o NA W PARKS 10011 Blomberg Street SW, Olympia, WA 98512 Phone#:(206) 754-4612 Fax#: (206)754-4848 rive V-"—Y s �a 0 C O 4 i � •fit? j 9�J r } Jason Berthiaume Bear Creek Dewatto Rd . N-ason County, WA Parcel #123093190074 1,r = 20 ' Countour Intervals : 2 ' 2 � r ► g • 2 PROPERTY LINE 10' MIN. 10' MIN- 1 5, C�i�-I 5' MIN. CAP LEVEL SEpIME1�IT ST�ucTu�.E 10 MIN. 15 � 2' S' 1 4"-6" PERFORATED MIN_ RIDGED PIPE HOUSE r/ �-- DOWN SPOUT INFILTRATION TRENCH 4"-6" PIPE SLOPE 1% MIN. SEDIMENT CONTROL STRUCTURE OUSSAANDSC-MC �,Dp SOKYBACK RL - 4--6-PEMORA=P1PC i 6 to fEm7" N TRg4cF. Ln \, ,/z _ S- rVn%SHM water table Fi 3 9 _ r s GEOTECHNICAL TESTING LAB Date: Sept.,2002 File#: Boring Log#: 1 Client: Berthiaumc Boring Type: Bach Hoe Depth Drilled: 4 feet Depth Field Change Percent Minus (in) Description in Soils %M perc. Q„ Qr, V LL PI, PI 3/4" #4 #200 Comments 6 mixed soil tram dozing 12 black sandy sill root zone 18 min 24 brn.Sand&:gravel fine roots 30 36 brn.Sand K Gravel `!' 42 48 54 end borine 60 66 72 78 84 g 90 96 102 108 114 120 126 132 138 142 148 154 160 166 172 178 1 194 GEOTECHNICAL TESTING LAB Date: Sept.,2002 File#: Boring Log#: 2 Client: Berthiaume Boring Type: Back Hoe Depth Drilled: 4 feet Depth Field Change Percent Minus (in) Description in Soils %M perc. Q QP V LL PL PI 3/4" #4 4200 Comments 6 mixed soil from dozing 12 root zone 18 3min P 24 brn.Sand&gravel fine roots 30 36 brn.Sand&Gravel \T 42 48 54 end boring 60 iJ 66 N- 72 • 78 84 O 90 96 102 108 114 120 126 132 138 142 148 154 160 166 172 178 184 GEOTECHNICAL TESTING LAB Jason Berthiaume angle: 34.5' Unit Wei0t: 130.6. Critical Slope Angle.Saturated: 19.7' Horizontal Sectional Sectional Angie of Total Saturated Saturated Unnaturatec Unsaturated X 1' Z Elevation Distance % Slope Factor Two Total Total Total Internal Factor Section Total Section Total Sectional Grid Station Elevation Change From Last Slope Angle of Safety Horizontal Change Slolx Angie Friction of Safeh (i> (i> p> (1> Factor Line Point Feet Feet Sta.Pt.(ft) P F Feet Feet '% a +' F Critical Critical 4 ` of Safety From To 1 0 215.00 0.00 0.00 0 0.0 3 n/a 0 0 0 0.0' 17.25 a/a F Stu, Sin. 1 1 210.00 5.00 30.00 16.7% 9.3° 1.86 30.00 5 16.7% 9.5° 17.25 1.86 Safe Safe Safe Safe 1.86 0 1 1 2 205,00 5.00 25.00 20.0 ce 11.3' 1.55 55.00 10 18.2% 10.3° 17.25 1.71 Safe Safe Safe Safe 1.55 0 2 1 31 200.00 3.00 23.00 20.0% 11.3' 1.55 80.00 15 18.8% 10.6 c 17.23 1." Safe Safe Safe Safe 1.55 0 3 1 4 195.00 3.00 24.00 20.9% 11.8' 1.49 104.00 20 19 2% 10.9° 17.25 1.61 Safe Safe Safe Safe 1.49 0 4 1 5 190.00 5.00 20.00 25.0% 14.01 1.24 124.00 25 20.2% 11.4° 17.25 1.54 Safe Safe Safe Safe 1.24 0 5 1 6 185.00 5.00 13.00 33.3°,e I8A' 0.93 139.00 30 21.6% 12.2° 17.23 1.44 Safe Safe Safe Safe 0.93 0 6 1 7 190.00 5.00 12.00 41.7% 22.6° 0.75 151.00 35 23.2% 13.1' 17.25 1.34 Yea Safe Safe Safe 0.75 0 7 1 8 175.00 5.00 12.00 41.7% 22.6° 0.75 163.00 40 24.3% 13.8` 17.25 1.27 Yea Safe Safe Safe 0.75 0 8 1 9 170.00 3.00 12.00 41.7% 22.6' 0.75 175.00 45 25.7% 14.4° 17.25 1.21 Yea Safe Safe Safe 0.75 0 9 1 10 165.00 5.00 0.50 1000.0% 94.3' 0.03 175.50 50 28.5% 15.9' 17.23 1.09 Yea Safe Yes Safe 0.03 0 10 1 11 165A0 0.00 75.00 0.0% 0.01 n/a 250.50 50 20.0% 11.3' 17.25 1.% Safe Safe Safe Safe 1.61 4 11 1 12 160.00 5.00 20.00 25.0% 14.0' 1.24 270.50 55 20.3% 11.5° 17.25 1.53 Safe Safe Safe Safe 1.24 0 12 1 13 155.00 5.00 24.00 20.8% 11.8' 1.49 294.50 60 20.4% 11.5° 17.25 1.52 Safe Safe Safe Safe 1.37 12 13 1 14 150.00 5.00 24.00 20.8% 11.8° 1.49 319.50 65 20.4% 11.5' 17.25 1.52 Safe Safe Safe Safe 1.41 12 14 'TJ 1 I5 145.00 5.00 24.00 20.9% 11.81 1.49 342.50 70 20.4% 11.6' 17.23 1.52 Safe Safe Safe Safe 1.43 12 15 1 16 140.00 5.00 24.00 20.8% 11.8° 1.49 366.50 75 20.5% 11.6° 17.23 1.52 Safe Safe Safe Safe 1." 12 16 1 17 135.00 5.00 60.00 8.3% 4.8° 3.73 426.50 80 19.8% 10.61 17.23 1." Safe Safe Safe Safe 1.64 2 17 1 IS 130.00 5,00 24.00 20.8% 11.8° 1.49 450.50 85 18.9% 10.7' 17.23 1.65 Safe Safe Safe Safe 1.49 0 18 U1 1 19 125.00 3.00 30.00 16.7% 9.5° 1.86 490.30 90 18.7% 10.6° 17.23 1.66 Safe Safe Safe Safe 1.65 2 19 1 20 120.00 5.00 40.00 12.5% 7.1° 2.48 520.50 95 18.3% 10.3' 17.25 1.70 Safe Safe Safe Safe 1.69 2 20 Slope Proflle 240.00 220.00 rock ret ning wall 200.00 home site Elevation 180.00 (fed) 160.00 drain field 140.00 120.00 100.00 -� 0 100 200 300 400 500 600 Horizontal Distance(Feet(