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HomeMy WebLinkAboutGEO2023-00091 BLD2023-01406 Hazard Area Report - BLD Engineering / Geo-tech Reports - 10/29/2022 (JEO Z62.,3 -� Mud Bay Geotechnical Services, LLC 1001 Cooper Pt Rd SW,Suite 140,PMB##108 1 Olympia,WA 98502 1360.481.9784 1 CHeathman@MudBayGeotech.com October 29, 2022 1947-MAS Page 1 Subject: Geologically Hazardous Area—Geotechnical Report 121 N Lakefront Loop, Hoodsport, WA 98548 Parcel #42332-50-00011 Dear Tom Martineau, Per your request, Mud Bay Geotechnical Services, LLC is providing a slope and soil assessment to meet the permit requirements for the development of a new detached garage structure at Parcel #42332-50-00011 located in Hoodsport, Washington. This report specifically addresses Mason County code section 8.52.140, which pertains to the requirements for land development on or near steep slopes and or landslide hazards. Geologically hazardous areas are defined as any area with a slope of 15 percent or greater as well as any area with a slope of 40 percent or steeper and with a vertical relief of ten or more feet except areas composed of consolidated rock. The purpose of this assessment is to assist you in meeting the minimum requirements of the Mason County ordinance for permitting,and to provide geotechnical recommendations to facilitate the design and construction of a new detached garage structure. The proposed locations of development fall within 300 feet of slopes greater than 40 percent. As such, the site fits the classification of a Category A. Geologically Hazardous Area per MCC section 8.52.140(5) and requires a geotechnical report. Mason County provides a checklist for geotechnical reports to be completed, signed, sealed, and dated by a qualified professional. We will provide a completed copy of the checklist form separate from this report.The recommendations contained in this report are based on available informational resources including published online geologic information, a geologic hazard assessment performed, two (2)shallow-hand augured borings performed for the subject project on May 13, 2022, and our experience with similar geologic conditions. Should on- site conditions vary from those described in this report, we should be notified immediately for further investigation. IQ47 - kIAf; 1 ? 1 N Lakef —qt Loop , Hoodsport , WA 98548 Page 12 LOCATION AND PROJECT DESCRIPTION Parcel #42332-50-0001 consists of approximately 0.45 acres in Hoodsport, Washington. The property is bounded by N Marine View Drive, along the eastern parcel boundary and the shoreline of Lake Cushman to the west. Neighboring residential properties border the site location to the north and south. The approximate site location and parcel boundaries are identified on the attached Figure 1, Site Map. The parcel is bisected by N Lakefront Loop (an easement roadway) extending southward from N Marine View Drive. This shared easement provides access to the existing single-family residence just west of the roadway. Continuing west, the topography slopes at a roughly 2H:1 V gradient down to the shoreline of Lake Cushman, approximately 40 feet below. To the east of the aforementioned N Lakefront Loop easement, the parcel is undeveloped, featuring gently to moderately sloping topography leading upslope to N Marine View Drive. Based on conversations with the client, it is our understanding that the proposed developments on-site include the construction of a new, detached garage structure to supplement the existing single-family residence. The undeveloped portion east of the easement is the proposed location for the new detached garage structure measuring approximately 26' x 30'. We anticipate that the structure will be supported by shallow strip footings. SITE GEOLOGY AND SOILS As part of this project, a review of the available geologic data mapped at a 1:24,000 scale, was performed and a site-specific geologic map was prepared. The project vicinity geologic map available from the Washington State Department of Natural Resources is attached to this report as Figure 2, WA DNR Geologic Map. Figure 2 indicates that the regional geology consists of Tertiary volcanic rocks. Mapped directly on-site is Pleistocene continental glacial drift. These sediments are described by the DNR as mostly loose, moderately to well-stratified deposits of gravel, sand, and silt. The mapped geology is generally consistent with the subsurface conditions observed on-site. Along with the site geology, soil data was also reviewed and is represented in attached Figure 3, USDA Soil Map. The soil in this area was mapped by the United States Department of Agriculture, (USDA) as Unit Rc— Rough mountainous land, Hoodsport soil material. This unit is described as a mixture of 50 percent Rough mountainous land and 40 percent Hoodsport soil. The Rough mountainous land soil series is described by the USDA as an excessively drained, stratified extremely gravelly sandy loam. The Hoodsport soils are classified as a moderately well drained, 1947 - MAS 121 N Lakefront Loop , Hoodsport , WA 98548 Page 13 gravelly sandy loam sourced from basal glacial till. The mapped soil deposits are generally consistent with the soil types observed on-site. SUBSURFACE EXPLORATION As part of the geotechnical investigation, a site reconnaissance and subsurface investigation was performed on May 13, 2022. A total of two (2) hand auger borings, designated BH-1-22 & BH-2- 22 were performed to collect subsurface across the project area and within the footprint of the proposed garage. BH-1-22 was performed along the eastern margin of the proposed structure footprint; BH-2-22 was completed 3 feet below the elevation of BH-1-22, near the access easement. The approximate locations of the borings are shown on Figure 4, Site Exploration Map. Each boring was completed using a Humboldt Manufacturing model H-4414QC hand auger with a 4-inch diameter bucket tube sampler. In situ testing was performed at selected depths using a Humboldt Manufacturing model H-4202A dynamic cone penetrometer to estimate the density of the soil. The dynamic cone penetrometer uses a 15-lb steel mass falling a height of 20-inches onto an anvil to penetrate a 1.5-inch diameter 45-degree cone tip seated into the bottom of the hole. The penetrometer is driven 1-inch through the upper slough within the boring and the number of blows is recorded, after which the number of blows required to achieve a total of 3/4 inches of penetration into the undisturbed soil is recorded. The number of blows required for each of the three intervals of 3/4 inches are averaged and recorded as the field N-value. This recorded blow count is correlated to the Standard Penetration Test (SPT) field N-value blow count determined in accordance with ASTM D1586, which is the standard in situ test method for determining relative density of cohesionless soils and the consistency of cohesive soils. Hand auger samples were removed from the bottom of the hole after the dynamic cone penetration testing was performed to observe the soil material at the approximate depth the test was performed. The soil samples were classified visually in the field in general accordance with ASTM D2488, the Standard Practice for Description and Identification of Soils (Visual-Manual Procedure) and placed in sealed plastic bags. Upon completion, the holes were backfilled to the original ground surface using excavated material from the spoil pile. Once transported back to the office, the samples were re-examined, and the field classifications were modified accordingly. Summary logs of the borings are included in Appendix A. Note the soil descriptions and interfaces shown on the logs are interpretive, and actual changes may be gradual. 1947 - MAS 121 N Lakefront Loop , Hoodsport , WA 98548 Page 14 SUBSURFACE CONDITIONS BH-1-22 was performed to a final depth of 36 inches below existing grade. BH-1-22 consisted of: Dark brown to black, moist, gravelly silt with sand (ML) from ground surface to 20 inches; and Loose, gray-brown, moist, well-graded gravel with silt and sand (GW-GM) from 20 inches to the base of the boring. BH-2-22 was completed to a final depth of 32 inches, near the elevation of N Lakefront Loop (the easement road). BH-2-22 consisted of: Dark brown to black, moist, gravelly silt with sand (ML) from 0 to 20 inches; and Loose, gray-brown, moist, well-graded gravel with silt and sand (GW- GM) from 20 inches to 32 inches. Groundwater was not observed within either boring performed nor were any indications of groundwater movement observed during our site exploration on May 13, 2022. No upland waterbodies or wetlands were observed on-site nor during our review of available online resources. To supplement our subsurface explorations,we performed a review of regional well log data made available by the Washington State Department of Ecology. Based on our review of this data, it is our interpretation that the depth to groundwater within the region varies from 40 to 80 feet below ground surface. In each well log, groundwater was encountered within fractured bedrock. Bedrock was found at depths greater than 6 feet throughout the region. GEOLOGIC HAZARD ASSESSMENT Liquefaction Hazard As part of the geotechnical assessment, we reviewed the liquefaction hazard map available from the Washington Department of Natural Resources. This data is displayed in the attached Figure 5, Liquefaction Hazard Map. Liquefaction is a phenomenon whereby saturated soil deposits temporarily lose strength and behave as a viscous fluid in response to cyclic loading. These behaviors are most common in saturated, loose, sandy soils with lesser impacts occurring in silty soils. Figure 5 indicates that the western half of the parcel is mapped as Bedrock and is considered not to be susceptible to liquefaction behavior. The eastern half of the parcel, within the proposed work area, is mapped with a Very Low risk of soil liquefaction. Based on our observations of the site and our subsurface explorations, we agree that the unsaturated silty and very gravelly soils on-site are of Very Low liquefaction susceptibility. 1 Q47 - MAS 121 N Lakefront Loop , Hoodsport , WA 98548 Page 15 Landslide Hazard As part of the investigation of the site, we reviewed the landslide hazard mapping available from the Washington Department of Natural Resources. The current landslide hazard mapping inventory available from the Washington State Department of Natural Resources (DNR) shows that the site is positioned along the eastern shoreline of Lake Cushman. The topography within the area surrounding the parcel is moderately to steeply sloping and with established stream corridors incising into the topography. The nearest landslide deposits are positioned approximately 0.5 miles away from the project location. Our observations on-site support that no deep-seated landslide activity has occurred within the bounds of the subject parcel nor within the surrounding vicinity. The mapped landslides in the region appear to be positioned along over steepened slopes near stream corridors. The landslide map of discussion is included with this report as Figure 6, WA DNR Landslide Map. We also reviewed available LiDAR data from the Washington Department of Natural Resources. The geomorphology (shape of the land) was analyzed during the site evaluation and compared to the Light Detection and Ranging images (LiDAR). LiDAR is a remote sensing method where light is pulsed down to the surface of the Earth and back to a sensor. This methodology enables bare earth images of the surface to be analyzed for the presence of geologic landforms. The most recent available LiDAR data from the region was collected in 2019 and is shown in the attached Figure 7, WA DNR LiDAR Map (2019). The data in Figure 7 reveals that the subject parcel is positioned within an area of moderately sloping and gently undulating topography resulting from previous glacial erosion and depositional processes. Further east of the project area the topography becomes significantly steeper, where the region is composed of basalt bedrock outcrops. The bare earth imagery lacks geomorphic landforms such as arcuate head scarps, mid- slope benches, and hummocky landslide debris at the toe of slopes, suggesting previous mass- wasting in the project vicinity. Overall, it is our interpretation that no past or present landslide activity has occurred on-site nor within 300 feet of the site. The UDAR imagery was processed through Quantum Geographic Information Systems software (QGIS) to superimpose two-foot and ten-foot contour lines and slope percentages onto the imagery to assist in visualizing the topography of the project vicinity. This imagery shows that the subject parcel spans an elevation difference of approximately 76 feet as measured east to west across the site. The slopes west of the existing single-family residence average 40 to 60 percent, comprising a total elevation difference of approximately 40 feet. The eastern half of the parcel contains slopes of 15 to 30 percent with a maximum elevation difference of roughly 26 feet 1 947 - MAS 1 21 N [ akefront Loop , Hoodsport . WA 98548 Page 16 between N Lakefront Loop (the easement road) and N Marine View Drive above. It is our interpretation that the slopes between N Lakefront Loop (the easement road) and the existing residence as well as the slopes just west of N Marine View Drive have been artificially steepened through previous grading and development activities. The slope map is included as Figure 8, QGIS Slope & Contour Map. Using QGIS software, a single slope transect was drawn roughly west to east across the site and through the proposed building area. This transect was designated Line A-A' and is shown in the attached Figure 9, Slope Transect & Profile. Figure 9 shows the locations the existing residence, easement road, the proposed development area. The steep slopes surrounding the project vicinity were explored and investigated during on-site reconnaissance. The slope face was noted to be densely vegetated with native Pacific Northwest vegetation and groundcover. Trees growing from the slope face were noted as straight trunked and lacked the bent, pistol-butt, geometry exhibited in trees experiencing downslope creep over their lifespan. Surface soils throughout the slope face were noted to be competent underfoot and the use of a Humboldt Manufacturing model H-4188 soil probe found the conditions underlying shallow forest duff topsoil to be unyielding. No signs of groundwater seepage or springing was noted during on-site investigation. Mud Bay Geotechnical Services is of the opinion that the steep slope hazard on site is very low to low. GEOTECHNICAL RECOMMENDATIONS Critical Area Geologic Setbacks Based on field observations, available online resources, and LiDAR images, we conclude this parcel shows no indications of past or present deep-seated mass-wasting. Our observations suggest that the critical slopes near the project location are stable in their present morphology. It is our opinion that the dominant geologic hazard is surface erosion of thin horizons of loose soil where it's exposed on steep topography. As such, the proposed development activities should not serve to increase the risk of geologic hazards on-site nor in the surrounding vicinity given the geotechnical recommendations made in this report are implemented. We recommend a 25-foot setback from the top and toe of all natural steep slopes, as shown on Figure 10. The currently proposed design consists of constructing the garage structure within the flatter portion of the artificially steep cut slope that projects up to N Marine View Drive from the flat development pad. The back of the garage will be positioned at the transition where the slope steepens to greater than 40 percent, as shown on Figure 11. We recommend a minimum embedment of 2 feet below the existing ground at the structure foundation locations. In addition, 1947 - MAS 121 N Lakefront Loon . Hoodsport . WA 98548 Page 17 the wedge in between the back footing and the slope will be backfilled. This will serve to increase slope stability by adding additional toe resistance. The material used as fill within this area should consist of Gravel Backfill for Walls meeting the criteria in the WSDOT Standard Specifications. Foundation Support Shallow strip footings and shallow pier pads can be used to support the new detached garage structure. Based on the observed soil conditions, we recommend locating the bottom of the new footings on the native soil deposits at a minimum depth of approximately 2 feet below the existing ground surface. Footings can be stepped into the existing topography to achieve the minimum embedment criteria. However, the footings should be stepped at a maximum equivalent slope angle of 10 percent across the profile of the structure in the downslope direction. Prior to placement of concrete, the footing subgrade should be cleared and grubbed, and the exposed native subgrade soils should be compacted in place. The subgrade should be inspected for any pockets of loose material. Loose material should be compacted in place to a firm and unyielding condition or removed and replaced with a minimum of 6-inches of CSBC. The CSBC should be placed in layers no greater than 6-inches and compacted to at least 95 percent of the maximum dry density. Footings bearing on a subgrade prepared as described above can be designed using a maximum allowable bearing pressure of 2,000 psf. We recommend a minimum footing width of 18 inches be used in the design. The maximum allowable bearing pressure may be increased by up to one- third for short-term transient loading conditions such as wind and seismic loading. We anticipate that total settlement will not exceed one inch, and differential settlement along an equivalent 50- foot length of footing will not exceed half of the total settlement. The settlement is expected to be elastic and will occur as the footings are loaded. We recommend footing subgrade preparation be evaluated by Mud Bay Geotechnical Services, LLC prior to placement of concrete. Foundation subgrade preparation should not be performed during periods of wet weather. We recommend staging the foundation subgrade excavation, compaction of native subgrade soils, and placement of CSBC to limit the time the foundation subgrade is exposed to weather. Material Backfill We recommend all material used as backfill for footings and stem walls be placed in horizontal layers no more than 6 inches thick with each layer compacted to 95 percent of the maximum ' 947 - MAS 121 N Lakefront Loop , Hoodsport , WA 98548 Page 18 density. The backfill material should be comprised of Gravel Backfill for Walls material meeting the requirements of Section 9-03.12(2) of the WSDOT Standard Specifications, or an equivalent free-draining material. Prior to backfilling, a perimeter footing drain system, consisting of a 4-inch diameter, perforated, or slotted, rigid plastic pipe placed at the base of the structure excavations wherever existing footings are exposed as part of the work. The drain should be embedded in a clean, free-draining sand and gravel meeting the requirements of Section 9-03.12(4) of the WSDOT Standard Specifications for Gravel Backfill for Drains. The drains should be sloped slightly to drain to an appropriate discharge area. Drainage Considerations Any groundwater seepage exposed during construction of the structure should be removed from the excavation area and/or directed away from the top of the steep slopes to an area where it can be discharged and stored until it fully infiltrates into the ground. The site should include a proper drainage design to control and properly discharge surface water. The surface of the developed portion of the parcel should be graded to allow water to flow and collect in a manner that does not increase the surface erosion. Stormwater should not be allowed to flow as surface water toward the top of steep slopes due to the severe erosion hazard at the site. Stormwater drainage falling directly onto impervious surfaces should be collected directly in catch basins, rain drains, and downspouts and directed via drain lines to an appropriate discharge area with slopes less than 15 percent. All drain lines discharging above the ground surface should terminate in a T-shaped elbow underlain by a quarry spall apron with a minimum width of 2 feet and a minimum length of 4 feet in order to dissipate the energy of the flowing water. The quarry spalls should be underlain by a geotextile meeting the requirements of a Construction Geosynthetic for Underground Drainage in Section 9-33 of the WSDOT Standard Specifications. Erosion Control Onsite materials are erodible when exposed on steep slope areas. No excavated material should be placed on the steep slopes. Soil stockpiles and exposed slope areas should be covered during heavy rainfall and siltation fences or other detention devices should be provided as required to control the transport of eroded material. Silt fences should be used as an erosion control measure and to separate the critical area boundary from the work area where disturbance is allowed. This is particularly important regarding the steep slopes west of the parcel which are a severe erosion 1947 - MAS 1 21 N Lakefront Loop , Hoodsport , WA 98548 Page 19 risk, as described previously. Stormwater should not be allowed to flow toward the steep slopes, both during the construction as well as under the final stormwater configuration. Jute, coir, or turf reinforcement mat should be placed on the surface of all exposed ground surfaces and spoil piles that are not intended for reuse during and following construction, pinned using 9-inch landscaping staples at a 16-inch spacing. The erosion condition adjacent to the structures should be monitored periodically for any signs of surface erosion, degradation, and shallow failures. If significant erosion or failures are observed, then those should be mitigated as soon as possible. Vegetation should be maintained where disturbance is not necessary as part of construction. Existing bare and disturbed soil areas should be planted immediately with grass and deep-rooted plants and native conifers to help reduce erosion potential. Where felling of trees is necessary on the existing slopes, stumps should be left intact. All graded slopes and exposed areas should be hydroseeded as soon as possible after grading is complete. If the construction is not completed until the later part of the summer or fall and winter months, then the slopes should be left covered until the springtime growing season. Excavations Temporary cuts will be stable at a vertical angle up to 4 feet in height and may be used in the design where temporary excavations less than or equal to 4 feet will be necessary to construct the project. We anticipate that temporary excavation cuts greater than 4 feet in height will be stable at a maximum slope angle of 1 H:1 V. The ground surface at the top of the temporary cuts should be periodically monitored for vertical movement, cracks, and other signs of instability. If signs of instability are observed, we should be contacted immediately so that we can assist and provide additional geotechnical recommendations. Site Gradinq Permanent cuts should be stable at a slope angle of less than 26 degrees (2H:1 V). Permanent fills constructed of WSDOT Standard Specifications Select Borrow or Common Borrow should be stable at a maximum slope of less than or equal to 26 degrees (2H:1 V). Select Borrow should be used within the footprint of structures. We recommend limiting any new permanent fills to a height of five feet and limited to the approved development area outside of the minimum 25-foot setback buffer from natural steep slopes. 1947 - MAS 121 N Lakefront Loop , Hoodsport , WA 98548 Page 110 RECOMMENDED ADDITIONAL SERVICES Mud Bay Geotechnical Services, LLC is available to provide geotechnical engineering and construction monitoring services throughout the remainder of the design and construction process. The integrity of the geotechnical elements of a project depends on proper site preparation and construction procedures. In addition, engineering decisions may need to be made in the field if conditions encountered differ from those described in this report. During the construction phase of the project, we recommend that Mud Bay Geotechnical Services, LLC be retained to review construction submittals, evaluate subgrade for footings, monitor excavation and slope stability, backfill placement and compaction, drainage installation, and provide recommendations for any other geotechnical considerations that may arise during construction. INTENDED USE AND LIMITATIONS This report was prepared based on observations of the surface and subsurface conditions at the site, review of geology and other information available for the site, and conversations with the property owner about the soil and surface water conditions on the property and the nature of the proposed development. The geotechnical recommendations in this report are based on the current site conditions and understanding of the proposed development as described previously. Any modification of the current property conditions or the nature of the proposed development beyond what is described in this report would render these geotechnical recommendations invalid. It should not be used, in part or in whole for other purposes without contacting Mud Bay Geotechnical Services, LLC for a review of the applicability of such reuse. We have enjoyed the opportunity to work with you and serve your geotechnical needs for this project. Please contact me at your earliest convenience if you have any questions or would like to discuss any of the content of this report. Sincerely, Ep dOHIyH s`�Q�o4w y�qs Digitally signed by o Chris Heathman, PE Chris Heathman. P.E. nssss � Date: 2022.10.29 Mud Bay Geotechnical Services, LLC , SS�UNAL�� 16:41 :44 -07 00 R � �, .(�.5,:rc,5 Legend s Site Location Approximate Parcel Boundary Mud Bay Geotechnical Services, LLC JOB #:1947-MAS I Date: June 2022 t' Figure 1: Site Map 121 N Lakefront Lp, Hoodsport, WA 98548 �� Critical Area Geotechnical Report Legend k1E3 J Site Location Geologic Units 24K Pleistocene continental glacial drift l Tertiary volcanic rocks e 6 Mud Bay Geotechnical Services, LLC ! , JOB #:1947-MAS Date: June 2022 1*16 Figure 2: WA DNR Geologic Map F6OO m121 N Lakefront Lp, N ft ' - Hoodsport, WA 98548 d - Critical Area Geotechnical Report Soil Map—Mason County.Washington ¢ USDx Natural Resources Conservation Service 4. Le end ' Approximate Parcel Boundary 'o• l �+ y- Map Unit Symbol Map Unit Name Rc Rough mountainous land, 10 { Hoodsport soil material .� "1 �.r► w Water t , s' " r S of fl t.,, n.s i 6i,•v,liol..I Lt ati�onl . Mud Bay Geotechnical Services, U.0 JOB #:1947-MAS I Date: June 2022 Figure 3: USDA Soil Map lisp Scale:1:2,=ipiiEsl onAlamnmpe(11'x8Y)sI 121 N Lakefront Lp, N o 3D 60 tm �O Hoodsport, WA 98548 Feet ° 10D 2° 4W °°° Critical Area Geotechnical Report IMDP�:Wpb Mata� eane<m�,a�:%xsea p ' r�t� � •ti+ � tom. ;� �•' lot44 ' .• w! • •' ,a. dw �• � �_ • 41 . --• M BGS k - •: •. Figure 4: Site Exploration Map +, 121 N Lakefront • N l ft ... .. •: . 200 .� Area Report �aahNp•p4 • • RESOURCES y�N ' DIVISION OF GEOLOGY AND EARTH RESOURCES V Legend $ Site Location o Liquefaction Susceptibility High Nloderate to high toderate • Low to moderate Low 4 Very low to low Very low B Bedrock �i Peat Mud Bay Geotechnical Services, LLC r © JOB #:1947-MAS I Date: June 2022 p Figure 5: Liquefaction Hazard Map 100 m O' 121 N Lakefront Lp, N 1200 ft Hoodsport, WA 98548 Critical Area Geotechnical Report —._—.. � �.— �' • aid • • � • • G. ,. �� - - ,:�"0ti Legend Of Aw \,t w .♦, f �:; Site Location •` fir; i- _! Landslide Compilation •24 0 1. 00-scale Landslides from Geologic Mapping �• * 1:24,000-scale and Watershed Analysis Study Extents )IF Mud Bay Geotechnical Services, LLC JOB #:1947-MAS I Date: June 2022 Figure 6: WA DNR Landslide Map 121 N Lakefront Lp, r Hoods port, WA 98548 - ' ,r r - - '� > r`' Critical Area Geotechnical Report WASHINGTON STATE DFPARtMENT Of ' ■ • • , � DIVISION OF GEOLOGY AND EART14 RESOURCES . Legend s, Approximate Parcel Boundary lie ew A, 0 250 500 ft Mud Bay Geotechnical Services, LLC JOB #:1947-MAS I Date: June 2022 Figure 7: WA DNR LiDAR Map (2019) 121 N Lakefront Lp, Hoodsport, WA 98548 ,r Critical Area Geotechnical Report f Legend fw Slope Percentage 0-5% O 5-15% I 1 a 15-20% Q 20-30% Q 30-40% I - - -40 50% 50 60% -60 70% = 70-80% Q 80-90% Q 90-100% i 0100-119%(45-50°) > 119%(50 ) Ili o 1 ratio 10 Contour Line 0 2' Contour Line t Approx. Parcel Location 0 50 100 ft r / Mud Bay Geotechnical Services, LLC JOB #:1947-MAS Date: June 2022 r' Figure 8: QGIS Slope & Contour Map 121 N Lakefront Lp, /J Hoodsport, WA 98548 k Critical Area Geotechnical Report i -- Legend o Slope Percentage 0-5% 0 5-15% 15-20/0 � = 20-30/o 30-40% 40-50% 50-60% 60-70% Q 70-80% Q 80-90% Q 90-100% 0 50 100 ft R } / 100-119% (45-50°) -> 119%(50°) I ne Existing SFR & Driveway 800 ----- / 10' Contour Line 2' Contour Line 780 Approx. Parcel Location 760 Easement Roadway 740720 Mud Bay Geotechnical Services, LLC JOB #:1947-MAS I Date: June 2022 Figure 9: Slope Transect & Profile 700 ___� 121 N Lakefront Lp,' Hoodsport, WA 98548 EK Elevation Profile (ft) 0 50 100 150 200 250 Critical Area Geotechnical Report Legend Slope Percentage 0-5% 5-15% 15-20/0° 20-30/o° 30-40% 0 Q J 0 40 50% 0 50-60% -60-70% In Approved Development Area Q 70-80% = 80-90% Q 90-100% r 100-119% (45-50°) > 119% (50°) i / 10' Contour Line I �r '.S� 2' Contour Line o G Approx. Parcel Location $ ¢i 1 ` Top/Toe of Slope _�� 1 1 I 25' Buffer (natural slopes) Mud Bay Geotechnical Services, LLC Artificially Steepened Slopes JOB #:1947-MAS Date: June 2022 Figure 10: Geologic Buffer Map 0 25 50 ft ! 121 N Lakefront Lp, 1 Hoodsport, WA 98548 �. ? Critical Area Geotechnical Report @ 4! Flcpc HEADER WLL DETENIPke WALL W. 1f,w OA 09 „r,ns 'ys� Mud Bay Geotechnical Services, LLC JOB #:1947-MAS I Date: June 2022 Figure 11: Job Details Schematic x7 : t2 121 N Lakefront Lp, Hoodsport, WA 98548 w� . - Critical Area Geotechnical Report APPENDIX A - FINAL BORING LOGS Project: Client: Bore No. 1 of 2: Geotechnical Report Tom Martineau BH-1-22 • Project Number: Contractor: Equipment: Mud Bay Geotedvtical Services LLC 1947-MAS n/a Humboldt H-4414QC Au er Address: Started: Bit Type: Diameter: 121 N Lakefront Lp, 5/13/2022 Bucket Tube Auger 4 inches Hoodsport,WA 98548 2 Completed: Hammer Type: Fluid: 0 5/13/2022 Humboldt H-4202A n/a Logged By: Backfilled: Hammer Weight: Hammer Drop: Alex Yannello 5/13/2022 15 Ibs 20 inches Helper: Groundwater Depth: Elevation: Total Depth of Boring: Ian James Not Encountered I Existing Surface I 36 inches GPS Method: GPS Coordinates: GPS Elevation: n/a n/a n/a s rn ^ Lithology U w a E V 0 Soil Group Name:modifier,color,moisture density/consistency,grain size,other e Y O LZ O y v descriptors U) U o a m U ; s c `. O a a 3 o a d pM E m a Rock Description:modifier,color,hardness/degree of concentration,bedding and ioint vt characteristics.solutions,void conditions. N Q O Q Dark brown to black, moist,gravelly silt with sand (ML). 12 — Gravels angular to subrounded, up to 6"diameter. 24 _ Loose, gray-brown, moist,well-graded gravel with silt and sand ® S-1 6 36" S-2 10 (GW-GM). Gravel clasts faceted, up to 8"diameter. ® Obstruction at 36"-End of Boring Test Pit and Boring Log Symbols Soil Density Modifiers Standard Penetration Slit Spoon Sampler(SPT) Gravel, Sand, Non-Plastic Silt Elastic Silts and Clays 8 California Sampler Blows/3/4" Density Blows/3/4" Consistency ® Shelby Tube 0-4 Very Loose 0-1 Very Soft ® CPP Sampler 5-10 Loose 2-4 Soft 1 Stabllized Ground water 11-24 Medium Dense 5-8 Medium Stiff Groundwater At time of Drilling 25-50 Dense 9-15 Stiff ® Bulk/Bag Sample REF Very Dense 16-30 Very Stiff 31-60 Hard >60 Very Hard Project: Client: Bore No. 2 of 2: ® Geotechnical Report Tom Martineau BH-2-22 Project Number: Contractor: Equipment: Mud Bay Geotechnical Servlces,LLC 1947-MAS n/a Humboldt H-4414QC Auger Address: Started: Bit Type: Diameter: 121 N Lakefront Lp, 5/13/2022 Bucket Tube Auger 4 inches Hoodsport,WA 98548 @ Completed: Hammer Type: Fluid: ❑ 5/13/2022 Humboldt H-4202A n/a Logged By: Backfilled: Hammer Weight: Hammer Drop: Alex Yannello 5/13/2022 15 Ibs 20 inches Helper: Groundwater Depth: Elevation: Total Depth of Boring: Ian James Not Encountered Existing Surface 32 inches GPS Method: GPS Coordinates: GPS Elevation: n/a n/a n/a Lithology a) U CU Q ~ O C F— �� E v J Soil Group Name:modifier,color,moisture density/consistency,grain size other w O Z 0 y a descriptors U is c. d 3 s c ,"— c aai E o- CL p 0 0 p fn E m p I Rock Description:modifier,color,hardness/degree of concentration,bedding and joint y CO characteristics.solutions,void conditions. O Q Dark brown to black, moist, gravelly silt with sand (ML). 12 — Gravels angular to subrounded, up to 6"diameter. 24„ Loose,gray-brown, moist,well-graded gravel with silt and sand ® S-1 5 (GW-GM). 36" Gravel obstruction-End of Boring 32". Test Pit and Boring Log Symbols Soil Density Modifiers Standard Penetration Slit Spoon Sampler(SPT) Gravel, Sand, Non-Plastic Silt Elastic Silts and Clays 8 California Sampler Blows/3/4" Density Blows/3/4" Consistency ® Shelby Tube 0-4 Very Loose 0-1 Very Soft ® CPP Sampler 5-10 Loose 2-4 Soft 1 Stabllized Ground water 11-24 Medium Dense 5-8 Medium Stiff Groundwater At time of Drilling 25-50 Dense 9-15 Stiff ® Bulk/Bag Sample REF Very Dense 16-30 Very Stiff 31-60 Hard >60 Very Hard