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REVIEWED RESUB1 BLD2023-1499+Geo_Letter+2.16.2024_3.50.31_PM+4066104RESUB Feb 20 2024 CITY OF EDMONDS DEVELOPMENT SERVICES DEPARTMENT COBALT GE0SCIENCES January 8, 2024 Skyler Owen Skyler.owenPpcfgroup.com BLD2023-1499 RE: Geotechnical/Geologic Evaluation Proposed Deck 215 loth Place North Edmonds, Washington Cobalt Geosciences, LLC P.O. Box 1792 North Bend, WA 98045 REVIEWED BY CITY OF EDMONDS In accordance with your authorization, Cobalt Geosciences, LLC has prepared this letter to discuss the results of our geotechnical evaluation at the referenced site. The purpose of our evaluation was to provide recommendations for foundation design, grading, and earthwork. Site & Project Description The site is located at 215 loth Place North in Edmonds, Washington. The site consists of one rectangular shaped parcel (No. 004342o6602100) with a total area of about o.18 acres. The central portion of the site is developed with a single-family residence with daylight basement areas, driveway, and attached deck. The site is vegetated with local grasses, understory, and variable diameter trees. Overall, the site slopes downward from east to west and southwest at magnitudes of about 10 to 6o percent and relief of about 40 feet. There are walkways and variable height modular block and timber walls in yard areas near the residence and backyard areas. The walls are generally 3 to 4 feet tall and terraced with 3 to 4 foot benches between walls. The lowest wall is a timber structure. The site is bordered to the east and west by residential properties, to the north by an access road, and to the south by undeveloped right of way. The proposed development includes a replacement deck along the south side of the residence. The deck system will have stairs and will likely be supported on isolated foundation elements. Site grading may include cuts and fills of 3 feet or less and foundation loads are expected to be light. Area Geology The Geologic Maw of the Edmonds East Quadrangle indicates that the site is underlain by Vashon Advance Outwash. Vashon Advance Outwash includes fine to medium grained sands that become relatively dense below a weathered zone. These deposits are typically overlain by the glacial till. www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page 2 of 11 Geotechnical Evaluation Soil & Groundwater Conditions As part of our evaluation, we excavated a hand boring within the property areas, where accessible. The exploration encountered approximately 6 inches of vegetation and topsoil underlain by approximately 3.5 feet of loose to medium dense, silty -fine to medium grained sand with gravel (Fill and Weathered Advance Outwash). These materials were underlain by medium dense, fine to medium grained sand trace gravel (Vashon Advance Outwash), which continued to the termination depths of the explorations. Groundwater was not encountered during the exploration work. There is a slight chance that light volumes of groundwater may develop on the denser glacial till at variable depths below the site. Groundwater would most likely be present during the wet season. Water table elevations often fluctuate over time. The groundwater level will depend on a variety of factors that may include seasonal precipitation, irrigation, land use, climatic conditions and soil permeability. Water levels at the time of the field investigation may be different from those encountered during the construction phase of the project. Steep Slope/Landslide Hazards Overall, the site slopes downward from east to west and southwest at magnitudes of about 10 to 6o percent and relief of about 40 feet. There are walkways and variable height modular block and timber walls in yard areas near the residence and backyard areas. The walls are generally 3 to 4 feet tall and terraced with 3 to 4 foot benches between walls. The lowest wall is a timber structure. Overall, the steep slope and other nearby slopes appear stable at this time with no evidence of instability or erosion. While these areas consist of steep slope hazards, they do not exhibit evidence or characteristics of landslide hazard areas. We provide additional discussion of hazard areas in the subsequent sections. Erosion Hazard The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that the property is underlain by Alderwood Everett gravelly sandy loams (25 to 70 percent slopes). These soils can have moderate to very erosion potential when exposed on slope magnitudes greater than about 15 percent. It is our opinion that soil erosion potential at this project site can be reduced through landscaping and surface water runoff control. Typically, erosion of exposed soils will be most noticeable during periods of rainfall and may be controlled by the use of normal temporary erosion control measures, such as silt fences, hay bales, mulching, control ditches and diversion trenches. The typical wet weather season, with regard to site grading, is from October 31st to April ist. Erosion control measures should be in place before the onset of wet weather. Code Information 23.80.o6o Development standards — General requirements. A. Alterations of geologically hazardous areas or associated buffers may only occur for activities that: www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page 3 of ii Geotechnical Evaluation 1. Will not increase the threat of the geological hazard to adjacent properties beyond predevelopment conditions; 2. Will not adversely impact other critical areas; 3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less than predevelopment conditions; and 4. Are certified as safe as designed and under anticipated conditions by a qualified engineer or geologist, licensed in the state of Washington. The currently proposed project includes relatively small excavations to prepare isolated foundation elements south of the residence in areas that are already graded and developed. Excavations may vary from 2 to 4 feet in depth depending on the soil conditions and planned elevations. This report provides recommendations to facilitate safe construction, including temporary excavation recommendations, fill compaction and placement, drainage and foundation design. It is our opinion that this work will not affect global or local stability_ provided work is monitored by the geotechnical engineer and erosion control measures are in place during construction. The proposed construction will not increase the threat of geologic hazards on adjacent properties, will not impact other critical areas, and are safe as designed under anticipated conditions. 23.80.07o Development standards — Specific hazards. A. Erosion and Landslide Hazard Areas. Activities on sites containing erosion or landslide hazards shall meet the requirements of ECDC 23.80.o6o, Development standards — General requirements, and the specific following requirements: 1. Minimum Building Setback. The minimum setback shall be the distance required to ensure the proposed structure will not be at risk from landslides for the life of the structure, considered to be 120 years, and will not cause an increased risk of landslides taking place on or off the site. A setback shall be established from all edges of landslide hazard areas. The size of the setback shall be determined by the director consistent with recommendations provided in the geotechnical report to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by the development, based upon review of and concurrence with a critical areas report prepared by a qualified professional; The area of the new decks slopes downward at variable magnitudes. We recommend a minimum effective setback of 5 feet for new deck footings from any slopes with magnitudes of 35 percent or more (including terraced walls). The effective setback is the horizontal distance measured from the base of the foundation closest to the slope to the face of the adjacent slope. By deepening footings, an effective setback can be increased. Pin piles could also be utilized to create the effective setback. Pin piles can also be used to ensure footings do not surcharge existing walls (depends on final planned locations of footings). 2. Buffer Requirements. A buffer may be established with specific requirements and limitations, including but not limited to, drainage, grading, irrigation, and vegetation. Buffer requirements shall be determined by the director consistent with recommendations provided in the geotechnical report to eliminate or minimize the risk of property damage, death, or injury resulting from landslides caused in whole or part by activities within the buffer area, based upon review of and concurrence with a critical areas report prepared by a qualified professional; No specific buffer is required based on the pre-existing graded condition of the site. www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page 4 of ii Geotechnical Evaluation 3. Alterations. Alterations of an erosion or landslide hazard area, minimum building setback and/or buffer may only occur for activities for which a hazards analysis is submitted and certifies that: a. The alteration will not increase surface water discharge or sedimentation to adjacent properties beyond predevelopment conditions; b. The alteration will not decrease slope stability on adjacent properties; and c. Such alterations will not adversely impact other critical areas; Provided earthwork activities are performed in accordance with the approved plans, all runoff is fully controlled, and periodic geotechnical oversight is performed, the development will not decrease slope stability on adjacent properties, will not increase surface water discharge or sedimentation beyond current levels, and will not impact other critical areas. Temporary and permanent erosion and sediment control devices should be in at all times during construction. 4. Design Standards within Erosion and Landslide Hazard Areas. Development within an erosion or landslide hazard area and/or buffer shall be designed to meet the following basic requirements unless it can be demonstrated that an alternative design that deviates from one or more of these standards provides greater long-term slope stability while meeting all other provisions of this title. The requirement for long-term slope stability shall exclude designs that require regular and periodic maintenance to maintain their level of function. The basic development design standards are: a. The proposed development shall not decrease the factor of safety for landslide occurrences below the limits of 1.5 for static conditions and 1.2 for dynamic conditions. If stability at the proposed development site is below these limits, the proposed development shall provide practicable approaches to reduce risk to human safety and improve the factor of safety for landsliding. In no case shall the existing factor of safety be reduced for the subject property or adjacent properties; b. Structures and improvements shall be clustered to avoid geologically hazardous areas and other critical areas; c. Structures and improvements shall minimize alterations to the natural contour of the slope, and foundations shall be tiered where possible to conform to existing topography; d. Structures and improvements shall be located to preserve the most critical portion of the site and its natural landforms and vegetation; e. The proposed development shall not result in greater risk or a need for increased buffers on neighboring properties; f. The use of retaining walls that allow the maintenance of existing natural slope area is preferred over graded artificial slopes; and g. Development shall be designed to minimize impervious lot coverage; The project scope does not pose a risk to critical areas or the need to increase buffers on adjacent properties. The site plan shows the location of the new features, generally to fit existing topography. Factors of safety against landslide movements are well above minimum values based on the soil tykes, topography, and locations of the development. These will not be increased or decreased following construction. www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page 5 of ii Geotechnical Evaluation 5. Vegetation Retention. Unless otherwise provided or as part of an approved alteration, removal of vegetation from an erosion or landslide hazard area or related buffer shall be prohibited; 6. Seasonal Restriction. Clearing shall be allowed only from May ist to October ist of each year; provided, that the director may extend or shorten the dry season on a case -by -case basis depending on actual weather conditions, except that timber harvest, not including brush clearing or stump removal, may be allowed pursuant to an approved forest practice permit issued by the city of Edmonds or the Washington State Department of Natural Resources; 7. Point Discharges. Point discharges from surface water facilities and roof drains onto or upstream from an erosion or landslide hazard area shall be prohibited except as follows: a. Conveyed via continuous storm pipe downslope to a point where there are no erosion hazard areas downstream from the discharge; b. Discharged at flow durations matching predeveloped conditions, with adequate energy dissipation, into existing channels that previously conveyed storm water runoff in the predeveloped state; or c. Dispersed discharge upslope of the steep slope onto a low -gradient, undisturbed buffer demonstrated to be adequate to infiltrate all surface and storm water runoff, and where it can be demonstrated that such discharge will not increase the saturation of the slope; and We concur with the above code items and have no additional comments at this time. Seismic Hazard The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the International Building Code (IBC). A Site Class D applies to an overall profile consisting of medium dense to very dense soils within the upper ioo feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for Ss, Sl, Fa, and F,,. The USGS website includes the most updated published data on seismic conditions. The following tables provide seismic parameters from the USGS web site with referenced parameters from ASCE 7-16. Seismic Design Parameters (ASCE 7-16) Site Spectral Spectral Site Design Spectral Design Class Acceleration Acceleration Coefficients Response Parameters PGA at 0.2 sec. (g) at l.o sec. (g) Fa Fv SDs •SD1 D 1.287 0.453 1.0 Null o.858 Null 0.548 Additional seismic considerations include liquefaction potential and amplification of ground motions by soft/loose soil deposits. The liquefaction potential is highest for loose sand with a high groundwater table. The site has a low likelihood of liquefaction. For items listed as "Null' see Section 11.4.8 of the ASCE. www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page 6 of ii Geotechnical Evaluation Conclusions and Recommendations General The site is underlain by local areas of fill and at depth by outwash deposits which becomes denser with depth. The proposed deck structure may be supported on a shallow foundation system bearing on medium dense or firmer native soils or on structural fill placed on the native soils. Local overexcavation or recompaction of fill and loose weathered native soils will likely be necessary based on our site observations. This could require excavations of up to 3 feet below grade. Alternatively, and in order to eliminate the need for variable -depth overexcavations to achieve suitable bearing soils, isolated footings could bear on small diameter pipe piles driven to refusal. Pin piles would likely penetrate 10 to 20 feet below grade. Note that pin piles should also be used if new foundation elements will surcharge existing wall structures. To avoid surcharging walls with shallow footings not supported on piles, a 1H:1V envelope must be maintained from the outside base of the new footing downward to the back base of any adjacent wall. We can provide additional input once a detailed plan is prepared showing walls and deck footings with elevations. Footings must be embedded in order to create a minimum 5 foot effective setback from the adjacent slope face. This will require deeper footings than may be originally proposed. Pin piles could be used to limit foundation excavation depths, also creating a greater setback through their embedment. Site Preparation Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich soil and fill. Based on observations from the site investigation program, it is anticipated that the stripping depth will be 6 to 18 inches. Deeper excavations will be necessary below large trees and in any areas underlain by undocumented fill. The native soils consist of silty -sand with gravel grading toward poorly graded sand trace silt and gravel. Most of the native soils may be used as structural fill provided they achieve compaction requirements and are within 3 percent of the optimum moisture. Some of these soils may only be suitable for use as fill during the summer months, as they will be above the optimum moisture levels in their current state. These soils are variably moisture sensitive and may degrade during periods of wet weather and under equipment traffic. Imported structural fill should consist of a sand and gravel mixture with a maximum grain size of 3 inches and less than 5 percent fines (material passing the U.S. Standard No. 200 Sieve). Structural fill should be placed in maximum lift thicknesses of 12 inches and should be compacted to a minimum of 95 percent of the modified proctor maximum dry density, as determined by the ASTM D 1557 test method. Temporary Excavations Based on our understanding of the project, we anticipate that the grading could include local cuts on the order of approximately 3 feet or less for foundation placement. Any deeper temporary excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose native soils and fill, 1H:1V in medium dense native soils and 3/4H:1V in dense to very dense native soils. www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page 7 of ii Geotechnical Evaluation If an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than 2H:1V, where room permits. Temporary cuts should be in accordance with the Washington Administrative Code (WAC) Part N, Excavation, Trenching, and Shoring. Temporary slopes should be visually inspected daily by a qualified person during construction activities and the inspections should be documented in daily reports. The contractor is responsible for maintaining the stability of the temporary cut slopes and reducing slope erosion during construction. Temporary cut slopes should be covered with visqueen to help reduce erosion during wet weather, and the slopes should be closely monitored until the permanent retaining systems or slope configurations are complete. Materials should not be stored or equipment operated within 10 feet of the top of any temporary cut slope. Soil conditions may not be completely known from the geotechnical investigation. In the case of temporary cuts, the existing soil conditions may not be completely revealed until the excavation work exposes the soil. Typically, as excavation work progresses the maximum inclination of temporary slopes will need to be re-evaluated by the geotechnical engineer so that supplemental recommendations can be made. Soil and groundwater conditions can be highly variable. Scheduling for soil work will need to be adjustable, to deal with unanticipated conditions, so that the project can proceed and required deadlines can be met. If any variations or undesirable conditions are encountered during construction, we should be notified so that supplemental recommendations can be made. If room constraints or groundwater conditions do not permit temporary slopes to be cut to the maximum angles allowed by the WAC, temporary shoring systems may be required. The contractor should be responsible for developing temporary shoring systems, if needed. We recommend that Cobalt Geosciences and the project structural engineer review temporary shoring designs prior to installation, to verify the suitability of the proposed systems. Foundation Design General The type of foundation (shallow isolated vs. pin pile supported isolated) will depend on the planned footing locations and elevations. Pin piles may be reuqired to avoid surcharging existing walls and/or to increase the effective setback of new footings to achieve the 5 foot minimum. Shallow Footings The proposed deck may be supported on isolated footings bearing on undisturbed medium dense or firmer native soils or on properly compacted structural fill placed on the suitable native soils. Any undocumented fill and/or loose native soils should be removed and replaced with structural fill below foundation elements. Structural fill below footings should consist of clean angular rock 5/8 to 4 inches in size. We should verify soil conditions during foundation excavation work. Local overexcavation may be required in areas where fill is present. Note that overexcavation will likely be necessary in some areas. For shallow foundation support, we recommend widths of at least 16 and 24 inches, respectively, for continuous wall and isolated column footings supporting the proposed structure. Provided that the footings are supported as recommended above, a net allowable bearing pressure of 1,500 pounds per square foot (psf) may be used for design. www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page 8 of ii Geotechnical Evaluation A 1/3 increase in the above value may be used for short duration loads, such as those imposed by wind and seismic events. Structural fill placed on bearing, native subgrade should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Footing excavations should be inspected to verify that the foundations will bear on suitable material. Exterior footings should have a minimum depth of 18 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. Interior footings should have a minimum depth of 12 inches below pad subgrade (soil grade) or adjacent exterior grade, whichever is lower. If constructed as recommended, the total foundation settlement is not expected to exceed 1 inch. Differential settlement, along a 25-foot exterior wall footing, or between adjoining column footings, should be less than 1/2 inch. This translates to an angular distortion of 0.002. Most settlement is expected to occur during construction, as the loads are applied. However, additional post -construction settlement may occur if the foundation soils are flooded or saturated. All footing excavations should be observed by a qualified geotechnical consultant. Resistance to lateral footing displacement can be determined using an allowable friction factor of 0.40 acting between the base of foundations and the supporting subgrades. Lateral resistance for footings can also be developed using an allowable equivalent fluid passive pressure of 225 pounds per cubic foot (pcf) acting against the appropriate vertical footing faces (neglect the upper 12 inches below grade in exterior areas). The frictional and passive resistance of the soil may be combined without reduction in determining the total lateral resistance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Any extremely wet or dry materials, or any loose or disturbed materials at the bottom of the footing excavations, should be removed prior to placing concrete. The potential for wetting or drying of the bearing materials can be reduced by pouring concrete as soon as possible after completing the footing excavation and evaluating the bearing surface by the geotechnical engineer or his representative. Pin Piles In order to eliminate the need for variable -depth overexcavations to achieve suitable bearing native soils as well as to avoid any potential surcharges from the new footings onto adjacent walls, small diameter pipe piles could be used to support isolated or strip footings. For 2 inch diameter, Schedule 8o galvanized pipe piles, an axial capacity of 3 tons each may be used for design. Battered piles could be used if required based on structural analysis. Pin piles should be driven with a 8o to 140 pound pneumatic hammer to refusal in dense native soils. Refusal criteria is 3 cycles of 6o inches per second of penetration. Pile depths will likely vary from 10 to 20 feet. The geotechnical engineer should be on site to verify refusal criteria and pile depths. Erosion and Sediment Control Erosion and sediment control (ESC) is used to reduce the transportation of eroded sediment to wetlands, streams, lakes, drainage systems, and adjacent properties. Erosion and sediment control measures should be implemented, and these measures should be in general accordance with local regulations. At a minimum, the following basic recommendations should be incorporated into the design of the erosion and sediment control features for the site: • Schedule the soil, foundation, utility, and other work requiring excavation or the disturbance of the site soils, to take place during the dry season (generally May through September). www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page 9 of ii Geotechnical Evaluation However, provided precautions are taken using Best Management Practices (BMP's), grading activities can be completed during the wet season (generally October through April). • All site work should be completed and stabilized as quickly as possible. Additional perimeter erosion and sediment control features may be required to reduce the possibility of sediment entering the surface water. This may include additional silt fences, silt fences with a higher Apparent Opening Size (AOS), construction of a berm, or other filtration systems. • Any runoff generated by dewatering discharge should be treated through construction of a sediment trap if there is sufficient space. If space is limited other filtration methods will need to be incorporated. CONSTRUCTION FIELD REVIEWS Cobalt Geosciences should be retained to provide part time field review during construction in order to verify that the soil conditions encountered are consistent with our design assumptions and that the intent of our recommendations is being met. This will require field and engineering review to: ■ Observe bearing capacity at foundation locations ■ Monitor pin pile embedments (if utilized) ■ Observe excavation stability Geotechnical design services should also be anticipated during the subsequent final design phase to support the structural design and address specific issues arising during this phase. Field and engineering review services will also be required during the construction phase in order to provide a Final Letter for the project. CLOSURE This report was prepared for the exclusive use of Skyler Owen and their appointed consultants. Any use of this report or the material contained herein by third parties, or for other than the intended purpose, should first be approved in writing by Cobalt Geosciences, LLC. The recommendations contained in this report are based on assumed continuity of soils with those of our test holes and assumed structural loads. Cobalt Geosciences should be provided with final architectural and civil drawings when they become available in order that we may review our design recommendations and advise of any revisions, if necessary. Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is the responsibility of Skyler Owen who is identified as "the Client" within the Statement of General Conditions, and its agents to review the conditions and to notify Cobalt Geosciences should any of these not be satisfied. www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page io of ii Geotechnical Evaluation Sincerely, Cobalt Geosciences, LLC �-c"ONry of W tic��� 54896 C1ST FSS�oN � �v 1/8/2o24 Phil Haberman, PE, LG, LEG Principal PHUJP HABES2W-N www.cobaltgeo.com (2o6) 331-1097 January 8, 2024 Page n of n Geotechnical Evaluation Statement of General Conditions USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its agent and may not be used by any third party without the express written consent of Cobalt Geosciences and the Client. Any use which a third parry makes of this report is the responsibility of such third parry. BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this report are in accordance with Cobalt Geosciences present understanding of the site specific project as described by the Client. The applicability of these is restricted to the site conditions encountered at the time of the investigation or study. If the proposed site specific project differs or is modified from what is described in this report or if the site conditions are altered, this report is no longer valid unless Cobalt Geosciences is requested by the Client to review and revise the report to reflect the differing or modified project specifics and/or the altered site conditions. STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in accordance with the normally accepted standard of care in the state of execution for the specific professional service provided to the Client. No other warranty is made. INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and statements regarding their condition, made in this report are based on site conditions encountered by Cobalt Geosciences at the time of the work and at the specific testing and/or sampling locations. Classifications and statements of condition have been made in accordance with normally accepted practices which are judgmental in nature; no specific description should be considered exact, but rather reflective of the anticipated material behavior. Extrapolation of in situ conditions can only be made to some limited extent beyond the sampling or test points. The extent depends on variability of the soil, rock and groundwater conditions as influenced by geological processes, construction activity, and site use. VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be encountered that are different from those described in this report or encountered at the test locations, Cobalt Geosciences must be notified immediately to assess if the varying or unexpected conditions are substantial and if reassessments of the report conclusions or recommendations are required. Cobalt Geosciences will not be responsible to any parry for damages incurred as a result of failing to notify Cobalt Geosciences that differing site or sub -surface conditions are present upon becoming aware of such conditions. PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and specifications should be reviewed by Cobalt Geosciences, sufficiently ahead of initiating the next project stage (property acquisition, tender, construction, etc), to confirm that this report completely addresses the elaborated project specifics and that the contents of this report have been properly interpreted. Specialty quality assurance services (field observations and testing) during construction are a necessary part of the evaluation of sub -subsurface conditions and site preparation works. Site work relating to the recommendations included in this report should only be carried out in the presence of a qualified geotechnical engineer; Cobalt Geosciences cannot be responsible for site work carried out without being present. www.cobaltgeo.com (2o6) 331-1097 Maximum 6' Tall Wall Max. 2H:1V Backslope 1.o Ft. Min. 2. o Ft. Max i Min. �o— 2 to 4 Inch Angular - Quarry Rock _ 6 Max. o��� �B DO o Medium Dense or Firmer nO� i Soils 5 Min. 1 Max. Dense to Very Dense Native Glacial Soils NOTES: 4" Perforated PVC Pipe Connected to Conveyance Not to Scale Cobalt to verify keyway, drainage, rock placement, and backslope. Proposed Residence 7397 Braemer Drive Edmonds, Washington ROCKERY DIAGRAM FIGURE 2 Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 (2o6) 331-1097 www.cobaltgeo.com cobaltgeopgmail.com Unified Soil Classification System (USCS) MAJOR DIVISIONS SYMBOL TYPICAL DESCRIPTION Clean Gravels Gw Well -graded gravels, gravels, gravel -sand mixtures, little or no fines Gravels (more than 50% (less than 5% fines) GP Poorly graded gravels, gravel -sand mixtures, little or no fines COARSE GRAINED SOILS of coarse fraction retained on No. 4 sieve) Gravels with Fines (more than 12% fines) GM Silty gravels, gravel -sand -silt mixtures GC Clayey gravels, gravel -sand -clay mixtures (more than 50% retained on Clean Sands :•: sw Well -graded sands, gravelly sands, little or no fines No. 200 sieve) Sands (50% or more of coarse fraction (less than 5% fines) sP Poorly graded sand, gravelly sands, little or no fines passes the No. 4 sieve) Sands with Fines sM Silty sands, sand -silt mixtures (more than 12% fines) sc Clayey sands, sand -clay mixtures ML Inorganic silts of low to medium plasticity, sandy silts, gravelly silts, FINE GRAINED (50% or more Silts and Clays (liquid limit less than 50) Inorganic cL or clayey silts with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays silty clays, lean clays Organic rganic oL Organic silts and organic silty clays of low plasticity passes the MH Inorganic silts, micaceous or diatomaceous fine sands or silty soils, No. 200 sieve) Silts and Clays (liquid limit 50 or more) Inorganic elastic silt CH Inorganic clays of medium to high plasticity, sandy fat clay, or gravelly fat clay Organic OHOrganic clays of medium to high plasticity, organic silts HIGHLY ORGANIC SOILS Primarily organic matter, dark in color, and organic odor PT Peat, humus, swamp soils with high organic content (ASTM D4427) Classification of Soil Constituents MAJOR constituents compose more than 50 percent, by weight, of the soil. Major constituents are capitalized (i.e., SAND). Minor constituents compose 12 to 50 percent of the soil and precede the major constituents (i.e., silty SAND). Minor constituents preceded by "slightly" compose 5 to 12 percent of the soil (i.e., slightly silty SAND). Trace constituents compose o to 5 percent of the soil (i.e., slightly silty SAND, trace gravel). Relative Density (Coarse Grained Soils) Consistency (Fine Grained Soils) N, SPT, Relative N, SPT, Relative Blows/FT Density Blows/FT Consistency 0-4 Very loose Under 2 Very soft 4 -10 Loose 2-4 Soft 10 - 30 Medium dense 4-8 Medium stiff 30 - 50 Dense 8 -15 Stiff Over 50 Very dense 15 - 30 Very stiff Over 3o Hard Grain Size Definitions Description Sieve Number and/or Size Fines <#200 (o.o8 mm) Sand -Fine #200 to #40 (o.o8 to 0.4 mm) -Medium #40 to #10 (0.4 to 2 mm) -Coarse #10 to #4 (2 to 5 mm) Gravel -Fine #4 to 3/4 inch (5 to 19 mm) -Coarse 3/4 to 3 inches (19 to 76 mm) Cobbles 3 to 12 inches (75 to 305 mm) Boulders >12 inches (305 mm) 1 Moisture Content Definitions 1 Dry Absence of moisture, dusty, dry to the touch Moist Damp but no visible water Wet Visible free water, from below water table Cobalt Geosciences, LLC P.O. Box 82243 Kenmore, WA 98028 Soil Classification Chart Figure Ci (2o6) 331-1097 _ www.cobaltgeo.com cobaltgeo(&gmail.com Log of Hand Boring HB-1 Date: January 2024 Depth: 6' Initial Groundwater: None Contractor: Elevation: N/A Sample Type: Grab Method: Hand Auger Logged By: PH Checked By: SC Final Groundwater: None o o Moisture Content (%) Plastic Liquid � t _ > O U - - o U t Q >_ L O Material Description Limit Limit DCP Equivalent N-Value o m "n o ? O 0 10 20 30 40 50 Vegetation/Topsoil --- ---- -- •ti. '`' --- SM/ --------------------------------------------- Loose to locally medium dense, silty -fine to medium grained sand — 1 SP trace to some gravel, yellowish brown to grayish brown, moist. (Fill over Weathered Outwash?) —2 — 3 ;. L: SM/ Medium dense, silty -fine to medium grained sand trace gravel, SP yellowish brown to grayish brown, moist. (Advance Outwash?) — 5 :may •L• End of Hand Boring 6' —7 —8 —9 — 10 Cobalt Geosciences, LLC _ Proposed Deck Hand P.O. Box 82243 COBALT 215 loth Place North Boring Kenmore, WA 98028 (2o6) 331-1097 • S C I E IN C E S Edmonds, Washington Log www.cobaltgeo.com cobaltgeopgmail.com