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REVIEWED BLD2023-1060+Geotechnical_Report+8.30.2023_6.48.50_AM+3754635................................................ RECEIVED BY CITY OF EDMONDS Sep 15 2023 EDMONDS BUILDING DEPARTMENTS DEVELo MFENTSERVICES DEPARTMENT BLD2023-1060 GEOTECHNICAL REPORT Niesel Residence 18500 Olympic View Drive Edmonds, Washington Prepared for: Sean Niesel Project No. 220625 • August 28, 2023 FINAL %10 s pect /CONSULTING %AsN ect ICOLTING GEOTECHNICAL REPORT Niesel Residence 18500 Olympic View Drive Edmonds, Washington Prepared for: Sean Niesel Project No. 220625 • August 28, 2023 FINAL Aspect Consulting, LLC w a sh e ?;-�Z� F/Ar/' �-' � Engineering Geologist 'v 2931 8/28/2023 wed Geo�o I Matthew A. von der Ahe I Matthew von der Ahe, LEG Project Geologist mvonderahe@aspectconsulting.com !8/2023 Erik O. Andersen, PE Principal Geotechnical Engineer eandersen@aspectconsulting.com V:\220625 Niesel Property\Deliverables\Final Geotech Report\Niesel geotech repo rt_Final_08282023.docx ASPECT CONSULTING Contents ExecutiveSummary...................................................................................... ES-1 1 Introduction.................................................................................................1 1.1 Project Description.......................................................................................1 1.2 Scope of Work..............................................................................................1 2 Surface Conditions.....................................................................................2 2.1 Site Description............................................................................................2 2.2 Site Vegetation.............................................................................................3 2.3 Site Topography...........................................................................................3 2.4 Evidence of Recent Landslide Activity.........................................................3 2.5 Site Drainage...............................................................................................4 3 Subsurface Conditions............................................................................... 5 3.1 Geologic Setting...........................................................................................5 3.2 Subsurface Investigation..............................................................................5 3.3 Stratigraphy..................................................................................................6 3.3.1 Fill 6 3.3.2 Transitional Beds (Disturbed)................................................................6 3.3.3 Olympia Gravel (Disturbed)...................................................................6 3.4 Groundwater................................................................................................7 4 Geologic Hazards........................................................................................ 8 4.1 Seismic Hazards..........................................................................................8 4.2 Surficial Ground Rupture..............................................................................8 4.3 Liquefaction..................................................................................................9 4.4 Erosion Hazard............................................................................................9 4.5 Landslide Hazards.......................................................................................9 4.5.1 Deep -Seated Rotational Landslides.......................................................9 4.5.2 Translational Slides..............................................................................10 4.5.3 Toppling Failures.................................................................................10 4.5.4 Shallow Flow Landslides...................................................................... 10 4.6 Slope Stability Analysis..............................................................................11 5 Conclusions and Recommendations......................................................12 5.1 Slope Stabilization Options........................................................................12 5.1.1 Anchored Mesh with Slope Regrading ................................................. 12 5.1.2 Soldier Pile Wall at Top of the Slope .................................................... 12 5.2 Drainage Considerations............................................................................13 PROJECT NO. 220625 • AUGUST 28, 2023 FINAL i ASPECT CONSULTING 6 Additional Services...................................................................................14 7 References.................................................................................................15 8 Limitations..................................................................................................16 List of Figures 1 Site Location Map 2 Site Exploration Plan List of Appendices A Boring Logs B Report Limitations and Guidelines for Use ii FINAL PROJECT NO. 220625 • AUGUST 28, 2023 ASPECT CONSULTING Executive Summary The property at 18500 Olympic View Drive in Edmonds, Washington (Site) lies at the top of steep, northwest -facing slope above Puget Sound. Site improvements include a single-family residence with an attached deck and associated infrastructure. On December 27, 2022, a landslide occurred on the west side of the Site along the steep slope. As a result of the slide, tension cracks formed in a narrow gravel pathway that traverses the top of the bluff and the surface of the path dropped up to several inches in some locations. The tension cracks are immediately adjacent to the edge of the deck attached to the house. The slope failure has compromised one of the deck's support posts. Unless the slope failure is mitigated, future failures will result in loss of support for other parts of the deck, and eventually other improvements on the Site. Aspect Consulting, LLC (Aspect) conducted a geotechnical investigation and preliminary geotechnical analysis to develop conceptual stabilization alternatives that will reduce the risk for future landslide damage (Project). To evaluate the feasibility of this Project, we performed a data review, geologic reconnaissance, subsurface exploration, and conceptual stabilization design. Based on our observations and analysis, we recommend that a soldier pile wall be constructed across the top of the steep slope at the Site. A soldier pile wall would stabilize the steep slope and retain the backyard more effectively than the other stabilization methods we evaluated. The cost of construction of a soldier pile wall would be roughly $250,000. PROJECT NO. 220625 • AUGUST 28, 2023 FINAL ES-1 ASPECT CONSULTING 1 Introduction This report presents the results of a geotechnical engineering investigation and analysis performed by Aspect Consulting, LLC (Aspect) regarding the slope stabilization (Project) at 18500 Olympic View Way in Edmonds, Washington (Site; Figure 1), also known as Snohomish County (County) parcel number 00565600200202. We performed a data review, slope reconnaissance, subsurface exploration, and conceptual wall design in accordance with the scope of work detailed in our proposal dated December 29, 2022, and contract change dated January 10, 2023. 1.1 Project Description The Site consists of a single-family residence, attached deck, and other associated infrastructure sitting at the top of a steep, northwest -facing slope above Puget Sound. The steep slope is approximately 70 feet tall. At the base of the slope, the BNSF railroad runs parallel to the Puget Sound shoreline. On December 27, 2022, during a period of heavy precipitation, a landslide occurred downslope of the residence, between the residence and the Puget Sound shoreline. On December 29, 2022, we performed a Site reconnaissance where we observed landslide debris including soil, mud, vegetation, pipe segments, and concrete blocks from the Site deposited along the slope. On the top of the slope, we observed bare soil, tension cracks, and scarps (vertical offsets). We observed damage to a chain -link fence and concrete block retaining wall along the gravel path at the Site, and minor damage to the deck attached to the house. We did not observe any structural damage to the house. 1.2 Scope of Work Our scope of services included a Site reconnaissance, subsurface explorations (drilled borings), completion of qualitative geotechnical engineering and slope stability evaluations, evaluation of conceptual slope stability measures, and completion of a geotechnical engineering report. This report includes: • Site and Project description • Distribution and characteristics of subsurface soils and groundwater conditions • Slope stabilization design recommendations PROJECT NO. 220625 • AUGUST 28, 2023 FINAL ASPECT CONSULTING 2 Surface Conditions Aspect assessed the surface conditions of the Site through a literature review and by field observations. We conducted visits to the Site and surrounding area on December 29, 2022, January 23, 2023, and February 9, 2023. To supplement our field observations, we performed a desktop review of County parcel maps, geologic maps and reports, geomorphic maps, light detection and ranging (LiDAR) studies and images, current and historical aerial photographs and topographic maps, nearby subsurface investigations, and nearby well logs. The following sections discuss the results of our assessment. 2.1 Site Description The Site is a 0.39-acre residential parcel located along the east side of Puget Sound in Edmonds, Washington, (Figure 1). It is bounded by the BNSF railroad to the northwest and single-family residences to the north, east, and west (Figure 2). Access to the Site is via paved driveway from Olympic View Drive. The BNSF railroad main line runs along the shoreline at the bottom of the slope. On the seaward side of the railroad embankment, a rock bulkhead protects the embankment from wave erosion. The residence is a two-story, 4,977 square foot home with an attached garage and deck that sits on the western side of the Site at the top of the bluff. The landslide occurred along the tall, steep, northwest -facing waterfront slope and damaged the fence, gravel path, and retaining wall at the Site (Photograph 1). Photograph 1. Site on December 29, 2022, looking south. Note bare soil and sagging ivy- covered chain -link fence below wooden curb FINAL PROJECT NO. 220625 • AUGUST 28, 2023 ASPECT CONSULTING 2.2 Site Vegetation The landslide area from the bluff top down to the shoreline is vegetated mostly with laurel, English ivy, blackberries, ferns, deciduous trees, and herbaceous ground cover. A few immature red alder trees grow at the bottom of the slope and a few mature conifers stand on the slope near the south edges of the Site. No mature conifers stand on the slope below the deck or house. 2.3 Site Topography The house, landscaping, parking areas, attached garage, and deck are located on a bench that slopes down gently to the northwest from approximately Elevation 115 feet near the driveway to Elevation 95' feet along the bluff edge. At the northwestern edge of the Site, where the landslide occurred, the bluff face below the bench is very steep and near vertical in some locations. From our review of LiDAR data (DNR, 2018), we estimated that this slope had an average inclination of approximately 45 degrees (100% slope), with locally oversteepened areas near vertical. At the southern edge of the Site, the ivy- and blackberry -covered ground surface slopes to the northwest at approximately 22 degrees for 25 feet from the gravel path, then steeply down to the shoreline. The total height of the slope is approximately 70 feet. 2.4 Evidence of Recent Landslide Activity The recent landslide activity occurred on December 27, 2022, after an extended period of high -intensity precipitation following a snow event. Surficial landslide movement resulted in offset cracking, bare soil, tension cracks, and scarps along and near the steep slope at the Site. The main headscarp at the Site is approximately 40 feet long and 8 to 15 feet high. The tension cracks on the top of the bluff have up to 1 foot of vertical offset and up to 1.5 feet of aperture. The headscarp is located approximately 30 feet from the residence and 4.5 feet from the westernmost edge of the deck. During the landslide, a concrete block wall and stormwater drainage system under the gravel path were damaged. The slide removed the soil that supported several posts for the ivy-covered chain -link fence that ran along the top of the bluff, and part of the fence fell down the slope. Soil supporting the structural post at the point of the deck closest to the headscarp settled fractionally. The recent landslide is shown in Photographs 2 and 3 below. 1 Elevations in feet referenced to the North American Vertical Datum of 1988 (NAVD88). PROJECT NO. 220625 • AUGUST 28, 2023 FINAL ASPECT CONSULTING Photograph 2. Tension cracks from the recent landslide along the gravel pathway. The corner of the deck is visible on the left. Photo viewing south-southwest. 2.5 Site Drainage Photograph 3. Headscarp of the recent landslide. Ivy-covered chain -link fence visible sagging on the slope. Photo viewing south-southwest. During our Site visit on December 29, 2022, we observed evidence that a significant flow of stormwater had occurred near the footprint of the December landslide on the north side of the Site and on the northern and eastern adjacent properties (18418 and 18430 Olympic View Drive). This flow had stopped as of our visit, and no flow was observed on follow-up visits. We did not observe standing water or flowing water on the remainder of the Site during any of our site visits. At least one drainage pipe near the headscarp was damaged by landslide activity. It is our understanding that this pipe has been repaired as of February 9, 2023. FINAL PROJECT NO. 220625 • AUGUST 28, 2023 ASPECT CONSULTING 3 Subsurface Conditions Subsurface conditions at the Site were inferred from our subsurface explorations advanced at the Site on February 9, 2023, review of applicable geologic literature, our experience with the local geology, and nearby well logs. The following sections discuss the results of our assessment. 3.1 Geologic Setting The Site is located within the Puget Lowland, a broad area of tectonic subsidence flanked by two mountain ranges: the Cascades to the east and the Olympics to the west. The sediments within the Puget Lowland are the result of repeated cycles of glacial and nonglacial deposition and erosion. The most recent cycle, the Vashon Stade of the Fraser Glaciation (about 13,000 to 16,000 years ago), is responsible for most of the present day geologic and topographic conditions. During the Vashon Stade, the 3,000-foot-thick Cordilleran Glacier advanced into the Puget Lowland. As the Cordilleran Glacier advanced southward, lacustrine and fluvial sediments were deposited in front of the glacier. Preglacial and proglacial sediments were overridden and consolidated by the advancing glacier, creating dense and hard soil deposits. At the interface between the advanced soils and the glacial ice, the Cordilleran Glacier sculpted and smoothed the surface, and then deposited a consolidated basal till. As the glacier retreated northward from the Puget Lowland to British Columbia, it left an unconsolidated sediment veneer over glacially consolidated deposits. The geologic map (Minard, 1983) indicates that the Site is underlain by Transitional Beds (Fraser Glaciation to Pre -Fraser Glaciation; map symbol Qtb) and Olympic Gravel (Pre - Fraser Glaciation; map symbol Qog). The Olympia Gravel unit was deposited in streams and rivers prior to the advance of the most recent (Fraser) glaciation. The Transitional Bed deposits overlie the Olympia Gravel at the Site and were deposited in lakes and streams prior to and during the advance of the Fraser glaciers. Both the units were overridden and consolidated by the weight of the 3,000-foot-thick Fraser ice sheet; therefore, the material is generally hard, dense, and strong. The Olympia Gravel unit consists of stratified sand and gravel. Weak cementation of the gravel can result in vertical exposures of this unit. The Transitional Bed deposits consist of gray clay, silt and fine sand with some layers of gravel and peaty sand. Jointing and high water content can lead to slope instability in this unit (Minard, 1983). At the Site, both the Olympic Gravel and Transitional Bed deposits appeared to have been disturbed after they were consolidated by the overriding ice sheet. Based on the proximity of active strands of the Southern Whidbey Island Fault (SWIF), we infer that the disturbance was caused by movement on the nearby fault. 3.2 Subsurface Investigation Aspect conducted a subsurface investigation consisting of three machine -drilled borings, AB-01 through AB-03, completed to depths of 19, 29, and 16.5 feet below ground surface (bgs), respectively. The borings were advanced in the gravel path along the edge of the bluff. Locations of the explorations are shown on Figure 2. PROJECT NO. 220625 • AUGUST 28, 2023 FINAL ASPECT CONSULTING A summary of our field explorations, including geologic soil units and groundwater observations, are presented in the following sections. Detailed descriptions of the subsurface conditions encountered in our explorations, as well as the depths where characteristics of the soils changed, are on the boring logs in Appendix A. 3.3 Stratigraphy The results of our subsurface investigation indicate that the Site is underlain by fill over Disturbed Transitional Bed deposits and Disturbed Olympia Gravel. These units are described in stratigraphic order from top to bottom below. 3.3.1 Fill Fill refers to human -placed material. Fill was encountered at the ground surface extending to between 5 and 6 feet bgs in borings AB-01 and AB-02 and 4.5 feet in AB- 03. The fill material consisted of very loose to medium dense, moist, brown, silty sand with angular gravel and fragments of organic materials. It is classified as a silty sand (SM) in the United Soil Classification System (USCS) (ASTM, 2018). 3.3.2 Transitional Beds (Disturbed) Transitional Bed deposits were encountered underlying the fill in AB-01, AB-02, and AB-03. Transitional Bed deposits were distinguished from the overlying unit based on color, density, consistency, and presence of organic matter. The deposits generally consisted of brown, silty sand with gravel to sand with silt and gravel, with trace organic fragments and peat. The Standard Penetration Test (SPT)2 blow counts (N-values) for the Pre -Fraser to Fraser Transitional Bed deposits ranged from 3 to 34 blows per foot (bpf), indicating that it is very loose to dense. The strength of the Transitional Beds encountered was less than would be expected if the material had not been disturbed after it was consolidated by the overriding ice sheet. We infer the disturbance was seismic, based on the proximity of the Site to an active strand of the SWIF. The Transitional Beds unit possesses low compressibility and moderately high strength characteristics. 3.3.3 Olympia Gravel (Disturbed) The Olympia Gravel unit was encountered underlying the Transitional Bed deposits in AB-01, AB-02, and AB-03. Compared to the overlying Transitional Beds, the Olympia Gravel deposits were generally more dense, sandier, and stratified or laminated. The N-values for the Olympia Gravel ranged from 13 to 43 bpf, which translates to medium dense to dense. These N-values were also less than would be expected with a glacially consolidated, sandy, gravelly geologic unit, implying the unit was disturbed after deposition and consolidation. 2 SPT blow count refers to standard penetration test (SPT) N-values, in accordance with ASTM D 15 86 (ASTM, 2018). FINAL PROJECT NO. 220625 • AUGUST 28, 2023 ASPECT CONSULTING 3.4 Groundwater Groundwater was not encountered in the explorations; however, we noted wet soils in the fill above the contact with the Transitional Beds in AB-01. We interpret the wet soil as evidence of leaks in the buried stormwater pipes that were damaged when the slide occurred in December. The groundwater levels and presence of shallow perched groundwater at the Site will fluctuate seasonally with precipitation as well as with changes in Site and near -Site drainage and usage (such as irrigation). Perched groundwater occurs when surface water percolates into the shallow subsurface and collects on the top of relatively impermeable underlying materials. At this Site, the topsoil and fill are considered permeable, while the Transitional Beds are less permeable; water may accumulate at the contact between them (about 5 to 6 feet below ground surface) following periods of prolonged wet weather. PROJECT NO. 220625 • AUGUST 28, 2023 FINAL ASPECT CONSULTING 4 Geologic Hazards The following sections describe the geologic hazards at and near the Site and associated Project design considerations for seismic design, erosion hazards, and slope stability. 4.1 Seismic Hazards The Site is located within the Puget Lowland physiographic province, an area of active seismicity that is subject to earthquakes on shallow crustal faults and deeper subduction zone earthquakes. The Site lies with a few hundred feet of a strand of the Southern Whidbey Island Fault (SWIF) Zone. The SWIF Zone consists of shallow folds and faults that are considered active (i.e., there is evidence for movement within the Holocene [most recent 15,000 years]) and is believed to be capable of producing earthquakes of magnitude 7.1. The recurrence interval of earthquakes on this fault zone is believed to be on the order of 3,000 years or more. The most recent large earthquake on the SWIF occurred about 3,200 to 2,800 years ago. There are also several other shallow crustal faults in the region capable of producing earthquakes and strong ground shaking (Sherrod et al, 2008). The Site lies about 16 miles north of the Seattle Fault Zone (SFZ), which consists of shallow crustal tectonic structures that are also considered active. SFZ faults are believed to be capable of producing earthquakes of magnitude 7.3 or greater. The recurrence interval of earthquakes on this fault zone is believed to be on the order of 1,000 years or more. The most recent large earthquake on the Seattle fault occurred about 1,100 years ago (Pratt et al., 2015). The Site area also lies within the zone of strong ground shaking from earthquakes associated with the Cascadia Subduction Zone (CSZ). The CSZ can produce earthquakes up to magnitude 9.3 and the recurrence interval is thought to be on the order of about 500 years. A recent study estimates the most recent subduction zone earthquake occurred around 1700 (Atwater et al., 2015). Deep intraslab earthquakes, which occur from tensional rupture of the sinking oceanic plate, are also associated with the CSZ. An example of this type of seismicity is the 2001 Nisqually earthquake. Deep intraslab earthquakes typically are magnitude 7.5 or less and occur approximately every 10 to 30 years. The Site's seismic hazards will be considered in the slope stability analysis for the Site. 4.2 Surficial Ground Rupture The strand of the SWIF mapped a few hundred feet south of the Site is capable of producing surficial ground ruptures (Sherrod et al., 2008). Aspect reviewed the latest publicly available LiDAR data for the Site and surrounding area (DNR, 2018) and confirmed the likely location of the fault strand. Due to the suspected long recurrence interval of earthquakes on the SWIF, the potential for surficial ground rupture at the Site is considered low during the expected life of the structure and does not need to be considered for design. 8 FINAL PROJECT NO. 220625 • AUGUST 28, 2023 ASPECT CONSULTING 4.3 Liquefaction Liquefaction occurs when loose, saturated, and relatively cohesionless soil deposits temporarily lose strength from seismic shaking. The primary factors controlling the onset of liquefaction include intensity and duration of strong ground motion, characteristics of subsurface soil, in situ stress conditions, and the depth to groundwater. The liquefaction susceptibility map indicates the Site has a very low susceptibility to liquefaction (Palmer et al., 2004). Due to the lack of a significant shallow groundwater table and grain size distribution of the soils underlying the Site, soil liquefaction is not a design consideration at this Site. 4.4 Erosion Hazard The City of Edmonds' (City) Critical Areas map shows the steep slope at the Site as having a severe erosion hazard (City, 2023). We concur with the City's assessment. Bare soils at the Site are at risk for erosion due to their fines content (i.e., silt and clay) and the steepness of the slope, whether the exposure of the soil is due to slope failure, such as exists at the Site due to the December 2022 landslide, or due to construction, or other causes. The erosion hazard at the Site can be reduced significantly by implementing slope stabilization measures. During construction, the erosion hazard should be addressed through standard temporary erosion and sedimentation controls (TESC) and best erosion management practices (BMPs). 4.5 Landslide Hazards The Washington State Department of Ecology (Ecology) classifies the steep slope at the Site as "Unstable" with regard to landslides due to the geology, groundwater, slope, or erosion factors (Ecology, 1979). A USGS landslide survey shows that the Site is located within a known unstable slope area (Baum et al., 2000). The City of Edmonds' Critical Areas map classifies the steep slope at the Site as having a high landslide hazard (City, 2023). After our assessment of the Site, we concur with the USGS, state, and City classifications. The Site, like similarly located sites around the Puget Sound, will continue to experience landslides. Construction of slope stability measures can substantially decrease the severity and frequency of landslides. Four types of landslides are possible on the Site and on similar sites and slopes along the shoreline in the Puget Sound area (Varnes, 1978): deep-seated rotational landslides, translational landslides, topples, and shallow flows (such as occurred in December 2022). 4.5.1 Deep -Seated Rotational Landslides Deep-seated rotational landslides consist of relatively deep (feet to tens of feet) failures that typically involve slipping along a curved shear plane. Rotational landslides may transport masses of semi -intact soil downslope, resulting in steep headscarps along the upper portion of the failure plane and level or back -rotated benches in the middle and bottom of the slope. PROJECT NO. 220625 • AUGUST 28, 2023 FINAL ASPECT CONSULTING At the Site, we did not observe any topographic evidence of recent or ancient rotational landslide activity, such as bowl -shaped topography or hummocky topography, and we consider it very unlikely such a slide will occur in the future. 4.5.2 Translational Slides Translational landslides consist of the landslide mass moving down the slope along a roughly planar surface with little rotation or backward tilting. Translational landslides can transport large, more -or -less intact masses of soil downslope, resulting in steep headscarps at the upper portion of the failure and flat "islands" or blocks of material deposited on the bottom of the failure, often with intact vegetation and upright trees. We did not observe evidence of recent or ancient translational slides at the Site and we consider it very unlikely such a slide will occur in the future. 4.5.3 Toppling Failures Toppling failures involve a mass of soil peeling off along tension cracks which form in soils at the crest of steep slopes and bluffs. These tension cracks may provide conduits for surface water migration and flow, and they can promote growth of tree roots that can extend many feet downward into the cracks. As the roots grow and the face of the slope progresses through freeze -thaw cycles, or when the toe of the layer becomes oversteepened and undermined by erosion, these cracks often become failure planes, and a slab of soil will spall or topple off the slope face. Failures of this kind are typically a few feet thick and occur only on very steep to near -vertical slope sections. The possibility of toppling failures will eventually exist along the near -vertical scarps at the Site if stabilization measures are not implemented. Topples pose a risk where erosion and past landslides have caused oversteepening of slopes, such as the downslope of the gravel pathway near the northwestern corner of the residence. We did not observe evidence of any recent or incipient topple failures at the Site. The tension cracks observed at the Site only extended through the thickness of the topsoil and fill on the path at the top of the bluff and did not penetrate deep into the native soil. The recommended slope stabilization, where implemented, will reduce the likelihood of toppling failures occurring at the Site. 4.5.4 Shallow Flow Landslides The landslide that occurred at the Site in December 2022 was an example of a shallow flow landslide. Shallow flow landslides consist of failures that involve sliding of loose fill, colluvium, and overlying vegetation that typically mantle steep slopes. Shallow flows are typically triggered by a significant increase in the moisture content within the upper few feet of soil on a slope and commonly result from periods of extended or heavy precipitation, groundwater seepage, or concentrated surface water discharge onto a slope. Such failures can be sudden; however, shallow flows can also occur slowly over time in a process called "creep." Surface creep is typically evidenced by "pistol -butt" curvatures in the lower trunks of trees on the slope. Shallow flows occur within the upper few feet of a slope and typically do not extensively affect the deep-seated or overall stability of a slope. 10 FINAL PROJECT NO. 220625 • AUGUST 28, 2023 ASPECT CONSULTING The Site and nearby areas contain steep slopes that have experienced shallow flows in the past and are susceptible to shallow flow failures in the future. The likelihood of future shallow flow landslide activity is dependent upon factors affecting shallow groundwater such as precipitation, drainage, upslope development, root reinforcement from vegetation on the slope, and seismic forces. The recommended slope stabilization will reduce the likelihood of shallow flow landslides occurring at the Site. 4.6 Slope Stability Analysis We performed numerical slope stability analyses for the Site using the Slide2 computer software program (Rocscience, 2022) to model the stability of the slope in its current condition, and after the installation of slope stabilization measures. We used soil unit engineering properties informed by our explorations and estimates of surcharge loading from the nearby deck and house to evaluate the slope under seismic and static conditions. The slope stability analysis shows that construction of stabilization measures at the top of the slope will increase the stability of the slope. The results of the stability analysis to support the design of the proposed stability measures will be reported in the Basis of Design report that accompanies that design. PROJECT NO. 220625 • AUGUST 28, 2023 FINAL 11 ASPECT CONSULTING 5 Conclusions and Recommendations This section presents our conclusions and recommendations for design and construction of the Project elements. These conclusions and recommendations are based on our observations of the Site, the subsurface conditions encountered, and the results of our preliminary geotechnical engineering analyses. 5.1 Slope Stabilization Options Our preliminary observations and geotechnical analyses reviewed several stabilization alternatives to reduce the risk of future landslide movement. The two options that best fit the Site conditions and future use of the Site are: Installation of anchored mesh on the face of the steep slope at the location of the recent landslide. Construction of a soldier pile wall at the top of the slope, adjacent to the residence. The stabilization alternatives are described further in the following subsections. After discussions with the client and specialty contractors about stabilization effectiveness and estimated design and construction costs, we recommend installation of a soldier pile wall along the top of the slope at the site of the recent landslide. 5.1.1 Anchored Mesh with Slope Regrading In this method, soil nails (I-inch-diameteror larger threaded steel bar) are drilled or driven into the slope with a portable drilling wagon suspended over the face of the bluff. The exposed heads of the nails at the slope surface are anchored to the slope with a steel plate, and adjacent nails are interconnected by heavy-duty wire mesh. This option would stabilize the exposed headscarp and reduce erosion there. It would significantly slow recession of the headscarp toward the house. However, it would not effectively allow retention of soft and loose fill material on the top of the slope and would reduce the useable area to the west of the house and deck. Because the client has expressed interest in retaining as much of the backyard area as possible, this method is not recommended. 5.1.2 Soldier Pile Wall at Top of the Slope A soldier pile stabilization wall constructed at the top of the slope, between the residence and the edge of the slope along the gravel pathway, will help reduce the likelihood and severity of slope instability and therefore reduce risk to the house and deck. This type of wall can be installed and engineered to retain and increase the stability of the Site uplands (those areas east of the landslide headscarp) and to significantly slow future slope retreat and landward migration of the headscarp. Soldier pile walls typically consist of uniformly spaced drilled shafts with wide -flange steel beams inserted into each shaft. The annular space of each shaft is filled with concrete. Lagging is installed between each soldier pile beam to support the soil behind the wall. Soldier piles are typically installed with horizontal spacing of 6 to 8 feet. 12 FINAL PROJECT NO. 220625 • AUGUST 28, 2023 ASPECT CONSULTING Based on our experience with other, similar construction and on our conversation with an experienced contractor who had seen the Site, a very rough estimate of the cost for construction of this option (not including design and not including other preparatory and restoration Site earthwork and landscaping costs) is $250,000. Aspect has completed the engineering design for the wall and prepared the plan set. When construction is underway, Aspect can provide special inspections, including monitoring shaft drilling, pile installation, grouting of the shaft, and lagging installation. Verification and acceptance of the completed soldier pile wall would be the responsibility of Aspect. 5.2 Drainage Considerations The most likely impact from slope instability to the Site is shallow flow landslides triggered by saturation of the near -surface soils. Saturation can be caused by improperly managed storm and surface water runoff flowing near or over the top of the slope. Downspouts and roof drains should be connected to outfalls near the base of the slope. Drains should include cleanouts to allow for periodic maintenance and inspection. Uncontrolled runoff or surface water should never be allowed to flow across the Site slopes. We recommend maintaining dense vegetative groundcover or other permanent erosion control on the Site slope. If soils on or near the slope become exposed through erosion and/or shallow failures, we recommend immediately covering and aggressively revegetating the exposed area. This may require the placement of plastic sheeting replaced by a woven jute mat to provide temporary ground cover while vegetation takes root. For specific vegetation recommendations, Ecology has several good publications on the subject including: Vegetation Management: A Guide for Puget Sound Bluff Property Owners, Ecology Publication 93-31, at https:Happs.ecology.wa.gov/publications/documents/933 l .pdf • Slope Stabilization and Erosion Control Using Vegetation: A Manual of Practice for Coastal Property Owners, Ecology Publication 93-30, at https:Happs.ecology.wa.gov/publications/documents/9330.pdf. PROJECT NO. 220625 • AUGUST 28, 2023 FINAL 13 ASPECT CONSULTING 6 Additional Services Stabilization design and construction methods have been finalized. The numeric basis for the design for the recommended stabilization measures is presented in the Basis of Design report which accompanies this report. We are prepared to assist with permitting, selection of a construction contractor, and other services, as described in our proposal to the client dated March 22, 2023. Once construction starts, we will oversee the critical phases of construction, as specified in the plans and specifications and as required by City of Edmonds permit documents. 14 FINAL PROJECT NO. 220625 • AUGUST 28, 2023 ASPECT CONSULTING 7 References ASTM International (ASTM), 2018, Annual Book of ASTM Standards, West Conshohocken, Pennsylvania. Atwater, B.F., S. Musumi-Rokkaku, D. Satake, Y. Tsuji, K. Ueda, and D.K. Yamaguci (Atwater et al.), 2015, The orphan tsunami of 1700Japanese clues to a parent earthquake in North America, U.S. Geological Survey, Professional Paper 1707. Baum, R.L., Harp, E.L., and Hultman, W.A. (Baum et al.), 2000, Map showing recent and historic landslide activity on coastal bluffs of Puget Sound between Shilshole Bay and Everett, Washington, USGS, Miscellaneous Field Studies Map 2346. City of Edmonds GIS (City), 2023, https://maps.edmondswa.gov/, accessed March, 2023. Minard, J.P., 1983, Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangles, Washington, USGS, Miscellaneous Field Studies Map MF-1541. Palmer, S.P., Magsino, S.L., Bilderback, E.L., Poelstra, J.L., Folger, D.S., and Niggemann, R.A., 2004, Liquefaction Susceptibility and Site Class Maps of Washington State, By County, Washington Division of Geology and Earth Resources, Open File Report 2004-20. Pratt, T.L., K.G. Troost, J.K. Odum, and W.J. Stephenson (Pratt et al.), 2015, Kinematics of shallow backthrusts in the Seattle fault zone, Washington State, Geosphere, v. 11, no. 6, p. 1-27, doi:10.1130/GES01179.1. Rocscience, 2022, Slide 8.019 and 8.020 Analysis Program, accessed June 2023. Sherrod, Brian L.; Blakely, Richard J.; Weaver, Craig S.; Kelsey, Harvey M.; Barnett, Elizabeth; Liberty, Lee; Meagher, Karen L.; Pape, Kristin (Sherrod et al.), 2008, Finding concealed active faults --Extending the southern Whidbey Island fault across the Puget Lowland, Washington: Journal of Geophysical Research, v. 11. Varnes, D.J., 1978, Slope movement types and processes, in Schuster, R.L., and Krizek, R.J., eds., Landslides —Analysis and control: National Research Council, Washington, D.C., Transportation Research Board, Special Report 176, p. 11-33. Washington State Department of Ecology (Ecology), 1979, Coastal Zone Atlas of Washington, Shoreline and Coastal Zone Management Program, Volume 10, https:Hfortress.wa.gov/ecy/coastalatlas/tools/Map.aspx. Washington State Department of Natural Resources (DNR), 2018, Washington LiDAR Portal, Division of Geology and Earth Resources, https:Hlidarportal.dnr.wa.gov/, accessed March 2023. PROJECT NO. 220625 • AUGUST 28, 2023 FINAL 15 ASPECT CONSULTING 8 Limitations Work for this project was performed for Sean Niesel (Client), and this report was prepared consistent with recognized standards of professionals in the same locality and involving similar conditions, at the time the work was performed. No other warranty, expressed or implied, is made by Aspect Consulting, LLC (Aspect). Recommendations presented herein are based on our interpretation of site conditions, geotechnical engineering calculations, and judgment in accordance with our mutually agreed -upon scope of work. Our recommendations are unique and specific to the project, site, and Client. Application of this report for any purpose other than the project should be done only after consultation with Aspect. Variations may exist between the soil and groundwater conditions reported and those actually underlying the site. The nature and extent of such soil variations may change over time and may not be evident before construction begins. If any soil conditions are encountered at the site that are different from those described in this report, Aspect should be notified immediately to review the applicability of our recommendations. Risks are inherent with any site involving slopes and no recommendations, geologic analysis, or engineering design can assure slope stability. Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the Client. It is the Client's responsibility to see that all parties to this project, including the designer, contractor, subcontractors, and agents, are made aware of this report in its entirety. At the time of this report, design plans and construction methods have not been finalized, and the recommendations presented herein are based on preliminary project information. If project developments result in changes from the preliminary project information, Aspect should be contacted to determine if our recommendations contained in this report should be revised and/or expanded upon. The scope of work does not include services related to construction safety precautions. Site safety is typically the responsibility of the contractor, and our recommendations are not intended to direct the contractor's site safety methods, techniques, sequences, or procedures. The scope of our work also does not include the assessment of environmental characteristics, particularly those involving potentially hazardous substances in soil or groundwater. All reports prepared by Aspect for the Client apply only to the services described in the Agreement(s) with the Client. Any use or reuse by any party other than the Client is at the sole risk of that party, and without liability to Aspect. Aspect's original files/reports shall govern in the event of any dispute regarding the content of electronic documents furnished to others. Please refer to Appendix B titled "Report Limitations and Guidelines for Use" for additional information governing the use of this report. We appreciate the opportunity to perform these services. If you have any questions please call Matthew von der Ahe, project manager, at 206-838-6583. 16 FINAL PROJECT NO. 220625 • AUGUST 28, 2023 FIGURES SITE LOCATION is Hutl Pai. O, is v ice/ xNv Q J Blake PI C l it9N SI SW � 3 180th St Sw.A ` r Q a • wa Y A. 3 Linville = z C r o` r,• S a ID Cle rry St � 19 �� '�• > - tszna sl sw m sil o, 4 _ • r� I , a' 435s 1I er b - D,m I'I.IIn tiI SW 41 q DS q�I 1h'ay f ootl ,q; Auf 11•. cl� •=�G � _slR D _ tS _ � omm nrry - cony. Edmonds LLuli _ I -Bellingham -PortAngeles SITE t •- LOCATION 0 Seattle • Spokane -Wenatchee Olympia •Tacoma W A S H I P T O N •Yak a�. a �. 202 W St S v 202ntl PIINr'1M SI SW O1 203rd St S, ! 41h SI SIN d , DI a - - 0 2,000 `_ 4,000 SbM/O��Ck P:laln r.t _ - u.. Seattle Feet Heights Site Location Map Geotechnical Report Niesel Residence Edmonds, Washington %eY. FIGURE NO. Aspect AUG-2023 MH/SCC PROJECTNO. REVISED BY: CONSULTING 220625 MAV/SCC Basemap Layer Credits I I Esri, HERE, Garmin, (c) OpenStreetMap contributors, and the GIS user community Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), (c) OpenStreetMap contributors, and the GIS User Community 1 � � sr 4 Approximate Boring Location Site and Exploration Map Frl Subject Property Geotechnical Report King County Property Parcel Niesel Residence Edmonds, Washington 0 50 100 %As AUG eY. MH/SCC FIGURE NO. Feet (CONSULTING PROJECCTTNNO.pect O. 220625 REVISED BY: MAV/scc Basemap Layer Credits I I EagleView Technologies, Inc. APPENDIX A Exploration Logs ASPECT CONSULTING A. Subsurface Exploration Methodology On February 9, 2023, Aspect observed three machine -drilled borings, AB-01, AB-02, and AB-03, advanced using hollow -stem auger drilling techniques. The borings were advanced by CN Drilling, Inc., an experienced and licensed local driller, under subcontract to Aspect. Drilling was completed with a portable Acker Kodiak drill rig equipped with a rope and cathead safety hammer. The locations of explorations are shown on Figure 2 and were collocated in the field using a global positioning system (GPS) receiver. The hollow -stem auger method consisted of advancing a continuous string of 5-foot-long open -flight augers and a conical hollow -auger head with a 2.25-inch-inner-diameter and about a 6-inch outer diameter. The auger flight returns soil cuttings to the surface, leaving the hollow stem free from soil. Disturbed soil samples were obtained every 2.5 feet to 17.5 feet bgs in AB-01, to 15 feet bgs in AB-02, and to 10 feet bgs in AB-03, and then every 5 feet thereafter to the maximum depths explored. The disturbed soil samples were collected using the Standard Penetration Test (SPT) in general accordance with ASTM International (ASTM) Method D1586 (ASTM, 2018). The SPT method involves driving a 2-inch-outside-diameter split - barrel sampler with a 140-pound hammer free -falling a distance of 30 inches. The number of blows for each 6-inch interval is recorded, and the number of blows required to drive the sampler the final 12 inches is known as the Standard Penetration Resistance ("N") or blow count. The resistance, or N-value, provides a measure of the relative density of granular soils or the relative consistency of cohesive soils. If a total of 50 blows are recorded for a single 6-inch interval, the test is terminated, and the blow count is recorded as 50 blows for the total inches of penetration. An Aspect geologist was present throughout the field exploration program to observe the drilling procedure, assist in sampling, and to prepare descriptive logs of the exploration. Samples were placed in labeled plastic jars and taken to a laboratory for further classification. Soils were classified in general accordance with the ASTM D2488 (ASTM, 2018). Detailed descriptions of the subsurface conditions encountered in our explorations, as well as the depths where characteristics of the soils changed, are indicated on the logs presented in this appendix. The summary exploration log represents our interpretation of the contents of the field logs. The stratigraphic contacts shown on the individual summary logs represent the approximate boundaries between soil types; actual transitions may be more gradual. The subsurface conditions depicted are only for the specific date and locations reported, and therefore, are not necessarily representative of other locations and times. A key to the symbols and terms used on the logs is provided in the Exploration Log Key. Upon completion, borings AB-01 through AB-03 were sealed with bentonite chips to within approximately 4 feet of the ground surface and topped with native material to the ground surface elevation. Soil cuttings were spread along the vegetated portion of the undisturbed slope, away from the landscaping features. PROJECT NO. 220625 • AUGUST 28, 2023 FINAL A-1 00.0 o Well -graded GRAVEL ODOR GW Well -graded GRAVEL WITH SAND N J_ N N In > u- 0 O 00000 0 NI00000 Poorly -graded GRAVEL 0 0 00000 GP Poorly -graded GRAVEL WITH SAND 0 N 6 0 Z 00000 o0000 o Lo o 00,0 C M GM SILTY GRAVEL -oo W cc u o 0" 0 SILTY GRAVEL WITH SAND aD 'm o aNi NI CLAYEY GRAVEL o 2 GC CLAYEY GRAVEL WITH SAND o cs LID c m � o Well -graded SAND o SW Well -graded SAND WITH GRAVEL g U_ a _ o (D iZ . - U) wl -=. -- Poorly -graded SAND :_ SP Poorly -graded SAND WITH GRAVEL (D o - - m o Z N o (n SM SILTY SAND co 10 (a cna SILTY SAND WITH GRAVEL o c - SAND 0 LO �CLAYEY SC CLAYEY SAND WITH GRAVEL SILT ML SANDY or GRAVELLY SILT > Lo SILT WITH SAND m in c co SILT WITH GRAVEL o s 0 w LEAN CLAY o c Zn CL SANDY or GRAVELLY LEAN CLAY Z LEAN CLAY WITH SAND On LEAN CLAY WITH GRAVEL U) a — ORGANIC SILT m a — — IL SANDY or GRAVELLY ORGANIC SILT m o _ — — ORGANIC SILT WITH SAND 2 � ORGANIC SILT WITH GRAVEL O ELASTIC SILT o °' SANDY or GRAVELLY ELASTIC SILT Ln o MH ELASTIC SILT WITH SAND rn T ELASTIC SILT WITH GRAVEL cc 0 (� 5 ,� FAT CLAY c oLn CH SANDY or GRAVELLY FAT CLAY m = FAT CLAY WITH SAND E J FAT CLAY WITH GRAVEL CJ= 2 �i��i ORGANIC CLAY U- a i��ii OH SANDY or GRAVELLY ORGANIC CLAY ORGANIC CLAY WITH SAND ORGANIC CLAY WITH GRAVEL T PEAT and other oU) PT mostly organic soils "WITH SILT" or "WITH CLAY" means 5 to 15%silt and clay, denoted by a "" in the group name; e.g., SP-SM . "SILTY" or "CLAYEY" means >15%silt and clay. "WITH SAND" or "WITH GRAVEL" means 15 to 30%sand and gravel.. "SANDY" or "GRAVELLY" means >30%sand and gravel.. "Well -graded" means approximately equal amounts of fine to coarse grain sizes. "Poorly graded" means unequal amounts of grain sizes . Group names separated by "/" means soil contains layers of the two soil types; e.g., SM/ML. Soils were described and identified in the field in general accordance with the methods described in ASTM D2488. Where indicated in the log, soils were classified using ASTM D2487 or other laboratory tests as appropriate. Refer to the report accompanying these exploration logs for details. 1. Estimated or measured percentage by dry weight 2. (SPT) Standard Penetration Test (ASTM D1586) 3. Determined by SPT, DCPT (ASTM STP399) or other field methods. See report text for details. MC = Natural Moisture Content GEOTECHNICAL LAB TESTS PS = Particle Size Distribution FC = Fines Content (% < 0.075 mm) GH = Hydrometer Test AL = Atterberg Limits C = Consolidation Test Str = Strength Test OC = Organic Content (% Loss by Ignition) Comp = Proctor Test K = Hydraulic Conductivity Test SG = Specific Gravity Test Organic Chemicals CHEMICAL LAB TESTS BTEX = Benzene, Toluene, Ethylbenzene, Xylenes TPH-Dx = Diesel and Oil -Range Petroleum Hydrocarbons TPH-G = Gasoline -Range Petroleum Hydrocarbons VOCs = Volatile Organic Compounds SVOCs = Semi -Volatile Organic Compounds PAHs = Polycyclic Aromatic Hydrocarbon Compounds PCBs = Polychlorinated Biphenyls Metals RCRA8 = As, Ba, Cd, Cr, Pb, Hg, Se, Ag, (d = dissolved, t = total) MTCA5 = As, Cd, Cr, Hg, Pb (d = dissolved, t = total) PP-13 = Ag, As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, TI, Zn (d=dissolved, t=total) PID = Photoionization Detector FIELD TESTS Sheen = Oil Sheen Test SPT2 = Standard Penetration Test NSPT = Non -Standard Penetration Test DCPT = Dynamic Cone Penetration Test Descriptive Term Size Range and Sieve Number COMPONENT Boulders = Larger than 12 inches DEFINITIONS Cobbles = 3 inches to 12 inches Coarse Gravel = 3 inches to 3/4 inches Fine Gravel = 3/4 inches to No. 4 (4.75 mm) Coarse Sand = No. 4 (4.75 mm) to No. 10 (2.00 mm) Medium Sand = No. 10 (2.00 mm) to No. 40 (0.425 mm) Fine Sand = No. 40 (0.425 mm) to No. 200 (0.075 mm) Silt and Clay = Smaller than No. 200 (0.075 mm) % by Weight Modifier % by Weight Modifier ESTIMATED' <1 = Subtrace 15 to 25 = Little PERCENTAGE 1 to <5 = Trace 30 to 45 = Some 5 to 10 = Few >50 = Mostly Dry = Absence of moisture, dusty, dry to the touch MOISTURE Slightly Moist = Perceptible moisture CONTENT Moist = Damp but no visible water Very Moist = Water visible but not free draining Wet = Visible free water, usually from below water table Non -Cohesive or Coarse -Grained Soils RELATIVE DENSITY Density3 SPT2 Blows/Foot Penetration with 1/2" Diameter Rod Very Loose = 0 to 4 >_ 2' Loose = 5 to 10 1' to 2' Medium Dense = 11 to 30 3" to 1' Dense = 31 to 50 1" to 3" Very Dense = > 50 < 1" Cohesive or Fine -Grained Soils CONSISTENCY Consistency3 SPT2 Blows/Foot Manual Test Very Soft = 0 to 1 Penetrated >1" easily by thumb. Extrudes between thumb & fingers. Soft = 2 to 4 Penetrated 1/4" to 1" easily by thumb. Easily molded. Medium Stiff = 5 to 8 Penetrated >1/4" with effort by thumb. Molded with strong pressure. Stiff = 9 to 15 Indented —1/4" with effort by thumb. Very Stiff = 16 to 30 Indented easily by thumbnail. Hard = > 30 Indented with difficulty by thumbnail. GEOLOGIC CONTACTS Observed and Distinct Observed and Gradual Inferred Aspect CONSULTING Exploration Log Key Niesel Residence - 220625 Geotechnical Ex loration Log %0��e�Ct Project Address & Site Specific Location Coordinates (Lat,Lon WGS84) Exploration Number I N G 18500 Olympic View Drive, Corner of hot tub 47.8315,-122.3619 (est) w B_0 1 Contractor Equipment Sampling Method Ground Surface Elev. /' 1 (NAVD88) CN Inc. Acker Drill Rig Rope & cathead; 140 lb hammer; 30" drop 94' (est) Operator Exploration Method(s) Work StarbCompletion Dates Top of Casing Elev. (NAVD88) Depth to Water (Below GS) 6" OD X 2.25" ID Hollow Mac Stem Auger 2/9/2023 NA No Water Encountered Depth (feet) Elev. (feet) Exploration Notes and Completion Details Sample Type/ID Blows/foot • water Content (%)* Blows/6 Tests Material Type Description Depth (ft) 0 10 20 4 2 GRAVEL (GP); gravel path, 4 inches. s 1 FILL 1 93 — — SILTY SAND WITH GRAVEL (SM); very loose, moist, 1 gray brown; fine to coarse sand; fine to coarse, 2 92 — — — subrounded to subangular gravel. 2 1 Becomes wet. 3 91 — — 0 3 O N 1 4 90 — — 4 5 89 1 5 6 88 Borehole backfilled 0 M — — 2 3 6 with bentonite chips — TRANSITIONAL BEDS 7 87 — — SILTY SAND WITH GRAVEL (SM); medium dense, 7 moist, light brown; fine to coarse sand; fine to coarse, 4 rounded to subangular gravel; trace dark organics; slight 8 86 — — — 9 oxidization. 8 • 7 9 85 — — 9 Becomes gray brown. 10 84 2 10 7 11 83 A — 7 11 12 82 — — — 12 6 13 81 — — 7 13 12 14 80 — — 14 OLYMPIA GRAVEL 15 79 11 - SAND WITH SILT AND GRAVEL (SP-SM); medium 15 12 _ _ dense, slightly moist, gray brown; fine to coarse sand; fine 16 78 — — 16 to coarse, rounded to subrounded gravel. 16 Drill chatter from 16 to 17 77 17 feet bgs 17 SAND WITH SILT (SP-SM); dense, slightly moist, gray 12 - brown; fine to coarse sand; trace fine to coarse 18 76 — — — 18 -_ subrounded to subangular gravel. 18 25 19 75 — — 19 Bottom of exploration at 19 ft. bgs. 20 74 20 21 73 — — 21 22 72 — — — 22 23 71 — — 23 24 70 24 Legend Plastic Limit Liquid Limit m E T 0No Soil Sample Recovery Split Barrel 2" X 1.375" (SPT) @ > No Water Encountered See Exploration Log Key for explanation of symbols Exploration Log Logged by: MRH ccc I— AB-01 Approved by: MvA Sheet 1 of 1 Niesel Residence - 220625 Geotechnical Ex loration Log %0��e�Ct Project Address & Site Specific Location Coordinates (Lat,Lon WGS84) Exploration Number I N G 18500 Olympic View Drive, South of hot tub 47.8314,-122.3620 (est) w B_02 Contractor Equipment Sampling Method Ground Surface Elev. /' 1 (NAVD88) CN Inc. Acker Drill Rig Rope & cathead; 140 lb hammer; 30" drop 95' (est) Operator Exploration Method(s) Work StarbCompletion Dates Top of Casing Elev. (NAVD88) Depth to Water (Below GS) 6" OD X 2.25" ID Hollow Mac Stem Auger 2/9/2023 NA No Water Encountered Depth (feet) Elev. (feet) Exploration Notes and Completion Details Sample Type/ID Blows/foot • water Content (%)* Blows/6 Tests Material Type Description Depth (ft) 0 10 20 4 2 ° o ° ° GRAVEL (GP); gravel path, 4 inches. FILL SILTY SAND WITH GRAVEL (SM); loose, moist, brown; � 2 3 1 fine to coarse sand; fine to coarse, rounded to subangular 2 93 — — — gravel; rootlets; dark organics. 2 1 3 92 — — 2 3 • 2 4 91 — — 4 5 90 2 TRANSITIONAL BEDS 5 M 2 - SAND WITH SILT AND GRAVEL (SP-SM); very loose, 6 89 Borehole backfilled — — 3 _ _ moist, gray brown; fine to coarse sand; fine to coarse, 6 with bentonite chips subrounded gravel; trace dark organics; disturbed fabric; trace oxidization. 7 88 — — 7 8 87 — — — 8 0 • 2 _ 9 10 85 _ -- 10 2 11 84 — — 2 - = 11 SILTY SAND WITH GRAVEL (SM); loose, moist, dark 12 83 — — — brown; fine to coarse sand; fine to coarse, rounded to 12 subrounded gravel; trace woody debris. 13 82 — — 2 13 0 3 14 81 — — SAND WITH SILT AND GRAVEL (SP-SM); loose, 14 - slightly moist, gray brown; fine to coarse sand; fine to 15 80 coarse, rounded to subrounded gravel; 0.5-inch-diameter 15 2 silt clasts; 0.25-inch-thick oxidized strata; trace roots and s twigs. 16 79 Drill chatter at 16 feet — — 6 16 PEAT (PT); medium dense, slightly moist, black; fine to bgs. coarse, angular sand; trace subangular gravel; trace 1-17 17 78 — — ibrous organics. OLYMPIA GRAVEL SILTY SAND WITH GRAVEL (SM); medium dense, 18 77 — — — slightly moist, brown; fine to coarse sand; fine to coarse, 18 subrounded to subangular gravel; oxidized strata; trace charcoal and fibrous organics. 19 76 — — 19 20 75 a 20 6 21 74 — 7 21 22 73 23 72 — — 23 SAND WITH SILT (SP-SM); dense, moist, gray brown; 24 71 — — — - fine to coarse sand; fine to coarse, subrounded to 24 _ subangular gravel; silt -fine sand laminations. Legend Plastic Limit Liquid Limit m E T ❑O No Soil Sample Recovery Split Barrel 2" X 1.375" (SPT) @ > No Water Encountered See Exploration Log Key for explanation of symbols Exploration Log Logged by: MRH ccc I— AB-02 Approved by: MvA Sheet 1 of 2 Niesel Residence - 220625 Geotechnical Ex loration Log %0��e�Ct Project Address & Site Specific Location Coordinates (Lat,Lon WGS84) Exploration Number I N G 18500 Olympic View Drive, South of hot tub 47.8314,-122.3620 (est) w B_02 Contractor Equipment Sampling Method Ground Surface Elev. /' 1 (NAVD88) CN Inc. Acker Drill Rig Rope & cathead; 140 lb hammer; 30" drop 95' (est) Operator Exploration Method(s) Work StarbCompletion Dates Top of Casing Elev. (NAVD88) Depth to Water (Below GS) 6" OD X 2.25" ID Hollow Mac Stem Auger 2/9/2023 NA No Water Encountered Depth Elev. Exploration Notes and Sample Blows/foot • water Content ( Blows/6 Tests Material Description Depth (feet) (feet) Completion Details Type/ID 4050 0 10 0 4 Type (ft) 6 _ SAND WITH SILT (SP-SM); dense, moist, gray brown; 01 15 fine to coarse sand; fine to coarse, subrounded to 26 69 — — 25 _ _ subangular gravel; silt -fine sand laminations. (continued) 26 Becomes slightly moist. 27 68 SAND (SP); medium dense, slightly moist, gray brown; 27 9 fine to coarse sand; fine, subrounded to subangular gravel. 28 67 0 — — 10 28 • 14 29 66 — — SILT (ML); light brown, very stiff, slightly moist; oxidized 29 laminations. 30 65 Bottom of exploration at 29 ft. bgs. 30 31 64 32 63 33 62 34 61 35 60 35 36 59 37 58 38 57 39 56 39 40 55 40 41 54 42 53 43 52 44 51 45 50 45 46 49 47 48 48 47 49 46 49 Legend Plastic Limit Liquid Limit m E T 0No Soil Sample Recovery Split Barrel 2" X 1.375" (SPT) @ > No Water Encountered See Exploration Log Key for explanation of symbols Exploration Log Logged by: MRH ccc I— AB-02 Approved by: MvA Sheet 2 of 2 Niesel Residence - 220625 Geotechnical Ex loration Log %0��e�Ct Project Address & Site Specific Locafion Coordinates (Lat,Lon WGS84) Exploration Number I N G 18500 Olympic View Drive, North of hot tub 47.8315,-122.3617 (est) w B_03 Contractor Equipment Sampling Method Ground Surface Elev. /' 1 (NAVD88) CN Inc. Acker Drill Rig Rope & cathead; 140 lb hammer; 30" drop 99' (est) Operator Exploration Method(s) Work StarbCompletion Dates Top of Casing Elev. (NAVD88) Depth to Water (Below GS) 6" OD X 2.25" ID Hollow Mac Stem Auger 2/9/2023 NA No Water Encountered Depth Elev. Exploration Notes and Sample Blows/foot • water Content (%)* Blows/6 Tests Material Description Depth (feet) (feet) Completion Details Type/ID 0 10 20 4 Type (ft) s GRAVEL (GP); gravel path, 2 inches. 1 98 D — — 7 4 1 FILL SILTY SAND WITH GRAVEL (SM); medium dense, moist, brown; fine to coarse sand; fine to coarse, 2 97 _ _ _ subrounded to angular gravel; organics.— — — — — — — 2 SILTY SAND (SM); loose, slightly moist, brown; fine to 6 coarse sand; fine, subrounded to subangular gravel. 3 96 N — — 6 3 4 4 95 — — — 4 TRANSITIONAL BEDS 5 94 16 SILTY SAND WITH GRAVEL (SM); dense, slightly moist, 5 M 15 gray brown; fine to coarse sand; fine to coarse, 6 93 Borehole backfilled — 19 subrounded to subangular gravel; diamict. 6 with bentonite chips 7 92 SILTY SAND (SM); medium dense, slightly moist, gray 7 9 brown; fine to coarse sand; fine, subrounded to subangular 8 91 Drill chatter at 8 feet — — — 10 gravel. 8 bgs. 9 9 90 — — 9 Becomes loose. 10 89 5 10 4 11 88 — — 6 11 12 87 — — — 12 13 86 — — 13 OLYMPIA GRAVEL 14 85 — — — SAND (SP); dense, slightly moist, gray brown; fine to 14 medium sand. 15 84 15 16 16 83 — 22 16 Bottom of exploration at 16.5 ft. bgs. 17 82 — — 17 18 81 — — — 18 19 80 — — 19 20 79 20 21 78 — — 21 22 77 — — — 22 23 76 — — 23 24 75 24 Legend Plastic Limit F Liquid Limit m E T ❑O No Soil Sample Recovery Split Barrel 2" X 1.375" (SPT) @ > No Water Encountered See Exploration Log Key for explanation of symbols Exploration Log Logged by: MRH ccc I— AB-03 Approved by: MvA Sheet 1 of 1 APPENDIX 6 Report Limitations and Guidelines for Use ASPECT CONSULTING REPORT LIMITATIONS AND GUIDELINES FOR USE Geoscience is Not Exact The geoscience practices (geotechnical engineering, geology, and environmental science) are far less exact than other engineering and natural science disciplines. It is important to recognize this limitation in evaluating the content of the report. If you are unclear how these "Report Limitations and Guidelines for Use" apply to your project or property, you should contact Aspect Consulting, LLC (Aspect). This Report and Project -Specific Factors Aspect's services are designed to meet the specific needs of our clients. Aspect has performed the services in general accordance with our agreement (the Agreement) with the Client (defined under the Limitations section of this project's work product). This report has been prepared for the exclusive use of the Client. This report should not be applied for any purpose or project except the purpose described in the Agreement. Aspect considered many unique, project -specific factors when establishing the Scope of Work for this project and report. You should not rely on this report if it was: • Not prepared for you; • Not prepared for the specific purpose identified in the Agreement; • Not prepared for the specific subject property assessed; or • Completed before important changes occurred concerning the subject property, project, or governmental regulatory actions. If changes are made to the project or subject property after the date of this report, Aspect should be retained to assess the impact of the changes with respect to the conclusions contained in the report. Reliance Conditions for Third Parties This report was prepared for the exclusive use of the Client. No other party may rely on the product of our services unless we agree in advance to such reliance in writing. This is to provide our firm with reasonable protection against liability claims by third parties with whom there would otherwise be no contractual limitations. Within the limitations of scope, schedule, and budget, our services have been executed in accordance with our Agreement with the Client and recognized geoscience practices in the same locality and involving similar conditions at the time this report was prepared. Property Conditions Change Over Time This report is based on conditions that existed at the time the study was performed. The findings and conclusions of this report may be affected by the passage of time, by events such as a change in property use or occupancy, or by natural events, such as floods, ASPECT CONSULTING earthquakes, slope instability, or groundwater fluctuations. If any of the described events may have occurred following the issuance of the report, you should contact Aspect so that we may evaluate whether changed conditions affect the continued reliability or applicability of our conclusions and recommendations. Geotechnical, Geologic, and Environmental Reports Are Not Interchangeable The equipment, techniques, and personnel used to perform a geotechnical or geologic study differ significantly from those used to perform an environmental study and vice versa. For that reason, a geotechnical engineering or geologic report does not usually address any environmental findings, conclusions, or recommendations (e.g., about the likelihood of encountering underground storage tanks or regulated contaminants). Similarly, environmental reports are not used to address geotechnical or geologic concerns regarding the subject property. We appreciate the opportunity to perform these services. If you have any questions, please contact the Aspect Project Manager for this project.