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REVIEWED BLD2024-0266+(locked) Geotechnical_Report+2.28.2024_12.31.16_PM+4089076COBALT G E 0 S C I E N C E S Geotechnical Investigation Proposed Residential Development 648 Walnut Street Edmonds, Washington August 2, 2020 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON Table of Contents 1.o INTRODUCTION............................................................................................................. 1 2.0 PROJECT DESCRIPTION.............................................................................................. 1 3.0 SITE DESCRIPTION....................................................................................................... 1 4.o FIELD INVESTIGATION............................................................................................... 2 4.1.1 Site Investigation Program................................................................................... 2 5.0 SOIL AND GROUNDWATER CONDITIONS.............................................................. 2 5.1.1 Area Geology........................................................................................................ 2 5.1.2 Groundwater........................................................................................................ 3 6.o GEOLOGIC HAZARDS................................................................................................... 3 6.1 Erosion Hazard.................................................................................................... 3 6.2 Seismic Hazard.................................................................................................... 3 7.o DISCUSSION................................................................................................................... 4 7.1.1 General.................................................................................................................4 8.o RECOMMENDATIONS.................................................................................................. 4 8.1.1 Site Preparation................................................................................................... 4 8.1.2 Temporary Excavations........................................................................................ 4 8.1.3 Erosion and Sediment Control.............................................................................. 5 8.1.4 Foundation Design............................................................................................... 6 8.1.5 Stormwater Management..................................................................................... 7 8.1.6 Slab-on-Grade...................................................................................................... 7 8.1.E Groundwater Influence on Construction.............................................................. 8 8.1.8 Utilities................................................................................................................ 8 9.o CONSTRUCTION FIELD REVIEWS............................................................................ 8 io.o CLOSURE.................................................................................................................... 9 LIST OF APPENDICES Appendix A — Statement of General Conditions Appendix B — Figures Appendix C — Exploration Logs GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 1.o Introduction COBALT GEOSCIENCES In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical investigation for the proposed residential development located at 648 Walnut Street in Edmonds, Washington (Figure 1). The purpose of the geotechnical investigation was to identify subsurface conditions and to provide geotechnical recommendations for foundation design, stormwater management, earthwork, soil compaction, and suitability of the on -site soils for use as fill. The scope of work for the geotechnical evaluation consisted of a site investigation followed by engineering analyses to prepare this report. Recommendations presented herein pertain to various geotechnical aspects of the proposed development, including foundation support of the new building and stormwater management. 2.0 Project Description The project includes construction of a new single-family residence in the north -central portion of the property. Anticipated building loads are expected to be light to moderate and site grading will include cuts and fills on the order of 4 feet or less. Stormwater management will include infiltration devices, if feasible. We should be provided with the final plans when they become available. 3.0 Site Description The site is located at 648 Walnut Street in Edmonds, Washington (Figure 1). The property consists of two adjoining parcels (No.'s 00434209301500 & 27032500202600) with a total area of about 0.25 acres. The north -central portion of the property is developed with a residence. There is a joint -use driveway near the east property line on an adjacent property. The remainder of the property is undeveloped and vegetated with grasses, bushes, blackberry vines, ferns, ivy, and sparse trees. The site slopes gently downward from southeast to northwest at magnitudes of less than io percent and relief of about 15 feet. There is a short steep slope area on properties south of the subject property. These slope areas are well vegetated and locally developed with walls/structures. The slope area has magnitudes Of 50 to 8o percent and relief of about 20 feet. The toe of this slope is located at least 70 feet from the area of the proposed residence (closest point). The site is bordered to the east, west, and south by residential developments and to the north by Walnut Street. PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 4.o Field Investigation 4.1.1 Site Investigation Program COBALT GEOSCIENCES The geotechnical field investigation program was completed on July 16, 202o and included excavating and sampling two test pits within the property for subsurface analysis. The soils encountered were logged in the field and are described in accordance with the Unified Soil Classification System (USCS). A Cobalt Geosciences field representative conducted the explorations, collected disturbed soil samples, classified the encountered soils, kept a detailed log of the explorations, and observed and recorded pertinent site features. The results of the sampling are presented on the exploration logs enclosed in Appendix C. 5.0 Soil and Groundwater Conditions 5.1.1 Area Geology The site lies within the Puget Lowland. The lowland is part of a regional north -south trending trough that extends from southwestern British Columbia to near Eugene, Oregon. North of Olympia, Washington, this lowland is glacially carved, with a depositional and erosional history including at least four separate glacial advances/retreats. The Puget Lowland is bounded to the west by the Olympic Mountains and to the east by the Cascade Range. The lowland is filled with glacial and non -glacial sediments consisting of interbedded gravel, sand, silt, till, and peat lenses. The Geologic Map of Washington — Northwest Quadrant, indicates that the site is underlain by Vashon Advance Outwash. Vashon Advance Outwash consists of poorly graded sand and are typically permeable. These soils are typically medium dense to very dense and are often underlain by silt and clay of either Pre -Fraser Deposits, Pre -Olympia Deposits, or Transitional Beds. In this area, Transitional Beds underlie the outwash. Groundwater is common at or near this contact. Explorations The test pits encountered about 6 inches of grass and topsoil underlain by approximately 3 to 4 feet of loose to medium dense, silty -fine to medium grained sand with organics and gravel (Fill and Weathered Outwash). These materials were underlain by medium dense to very dense, fine to medium grained sand with gravel and silt (Advance Outwash), which continued to the termination depths of the test pits. 2 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 5.1.2 Groundwater COBALT GEOSCIENCES Groundwater was encountered approximately 3.5 to 4 feet below grade in the test pits. We anticipate that the seasonal high groundwater table may be within 3 feet of the ground surface during the wet season. Groundwater appears to be perched on the underlying Transitional Beds or a silt/clay interbed at the base of the outwash. 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. 6.o Geologic Hazards 6.1 Erosion Hazard The Natural Resources Conservation Services (NRCS) maps for Snohomish County indicate that the site is underlain by Alderwood-Urban land complex (8 to 15 percent slopes). These soils would have a slight to moderate erosion potential in a disturbed state, depending on the slope magnitude. 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 1st. Erosion control measures should be in place before the onset of wet weather. 6.2 Seismic Hazard The overall subsurface profile corresponds to a Site Class D as defined by Table 1613.5.2 of the 2015 International Building Code (2015 IBC). A Site Class D applies to an overall profile consisting of dense to very dense soils within the upper too feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for Ss, S,, F,,. The USGS website includes the most updated published data on seismic conditions. The site specific seismic design parameters and adjusted maximum spectral response acceleration parameters are as follows: PGA (Peak Ground Acceleration, in percent of g) Ss 128.40% of g S, 45.20% of g FA 1.2 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 relatively dense soil deposits that underlie the site have a low liquefaction potential. 3 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 7.o DISCUSSION 7-1.1 General COBALT GEOSCIENCES The site is underlain by areas of fill and at depth by weathered and unweathered advance outwash. The proposed residential structure may be supported on a shallow foundation system bearing on medium dense or firmer native soils and/or structural fill placed on suitable native soils. Local overexcavation of fill and/or loose soils may be necessary below proposed foundation elements. Infiltration of stormwater runoff is not feasible due to a shallow groundwater table. Rain gardens or permeable pavements could be considered, if necessary. We recommend direction connection to City infrastructure for a majority of the collected runoff. While there is a localized steep slope extending downward toward the south property line, the proposed structure will be setback at least 70 feet from the toe of this slope. Landslide run out, if sloughing were to occur in this area, would not affect the proposed building. 8.o Recommendations 8.1.1 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 12 inches. Deeper excavations will be necessary below large trees and in any areas underlain by undocumented fill materials. The native soils consist of silty -sand with gravel and poorly graded sand with gravel. These 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. 8.1.2 Temporary Excavations Based on our understanding of the project, we anticipate that the grading could include local cuts on the order of approximately 4 feet or less for foundation and utility placement. Any deeper excavations should be sloped no steeper than 1.5H:1V in loose soils, 1H:1V in medium dense native soils and 3/411:1V in dense to very dense native soils above the groundwater table. 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. 4 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 COBALT GEOSCIENCES 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 io 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. 8.1.3 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). 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. 5 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 8.1.4 Foundation Design COBALT GEOSCIENCES The proposed residential building may be supported on a shallow spread footing foundation system bearing on undisturbed medium dense or firmer native soils or on properly compacted structural fill placed on the suitable native soils. If structural fill is used to support foundations, then the zone of structural fill should extend beyond the faces of the footing a lateral distance at least equal to the thickness of the structural fill. 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 2,500 pounds per square foot (psf) may be used for design. 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 allowable friction factor and allowable equivalent fluid passive pressure values include a factor of safety of 1.5. 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. 6 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 8.1.5 Stormwater Management COBALT GEOSCIENCES The site is underlain by advance outwash. Groundwater was encountered in the test pits at shallow depths and there is inadequate clearance for infiltration systems above the groundwater table. It was not necessary to perform an infiltration test due to the lack of clearance above groundwater. Shallow systems such as rain gardens or permeable pavements could be considered, if necessary. Otherwise, we recommend direct connection of stormwater collection devices to be tightlined (via perforated connection) to City infrastructure in Walnut Street. We can provide additional recommendations once a civil plan has been prepared. We should be provided with final plans for review to determine if the intent of our recommendations has been incorporated or if additional modifications are needed. 8.1.6 Slab -on -Grade We recommend that the upper 18 inches of the existing fill and/or native soils within slab areas be re - compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). Often, a vapor barrier is considered below concrete slab areas. However, the usage of a vapor barrier could result in curling of the concrete slab at joints. Floor covers sensitive to moisture typically requires the usage of a vapor barrier. A materials or structural engineer should be consulted regarding the detailing of the vapor barrier below concrete slabs. Exterior slabs typically do not utilize vapor barriers. The American Concrete Institutes ACI 36olt-o6 Design of Slabs on Grade and ACI 302JR-04 Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. A minimum 4 inch thick capillary break should be placed over the prepared subgrade. This may consist of pea gravel or 5/8 inch clean angular rock. Slabs on grade may be designed using a coefficient of subgrade reaction of 18o pounds per cubic inch (pci) assuming the slab -on -grade base course is underlain by structural fill placed and compacted as outlined in Section 8.1. A 4 inch thick capillary break material should be placed over the prepared subgrade. This could include pea gravel or 5/8 inch clean angular rock. A perimeter drainage system is recommended unless interior slab areas are elevated a minimum of 12 inches above adjacent exterior grades. If installed, a perimeter drainage system should consist of a 4 inch diameter perforated drain pipe surrounded by a minimum 6 inches of drain rock wrapped in a non -woven geosynthetic filter fabric to reduce migration of soil particles into the drainage system. The perimeter drainage system should discharge by gravity flow to a suitable stormwater system. Exterior grades surrounding buildings should be sloped at a minimum of one percent to facilitate surface water flow away from the building and preferably with a relatively impermeable surface cover immediately adjacent to the building. 7 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 COBALT GEOTECHNICAL INVESTIGATION GEOSCIENCES EDMONDS, WASHINGTON August 2, 2020 8.1.7 Groundwater Influence on Construction Groundwater was encountered approximately 3.5 to 4 feet below grade in the test pits. We anticipate that the seasonal high groundwater table may be within 3 feet of the ground surface during the wet season. Groundwater appears to be perched on the underlying Transitional Beds or a silt/clay interbed at the base of the outwash. If groundwater is encountered, we anticipate that sump excavations and small diameter pumps systems will adequately de -water short-term excavations, if required. Any system should be designed by the contractor. We can provide additional recommendations upon request. 8.1.8 Utilities Utility trenches should be excavated according to accepted engineering practices following OSHA (Occupational Safety and Health Administration) standards, by a contractor experienced in such work. The contractor is responsible for the safety of open trenches. Traffic and vibration adjacent to trench walls should be reduced; cyclic wetting and drying of excavation side slopes should be avoided. Depending upon the location and depth of some utility trenches, groundwater flow into open excavations could be experienced, especially during or shortly following periods of precipitation. In general, silty and sandy soils were encountered at shallow depths in the explorations at this site. These soils have low cohesion and density and will have a tendency to cave or slough in excavations. Shoring or sloping back trench sidewalls is required within these soils in excavations greater than 4 feet deep. All utility trench backfill should consist of imported structural fill or suitable on site soils. Utility trench backfill placed in or adjacent to buildings and exterior slabs should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. The upper 5 feet of utility trench backfill placed in pavement areas should be compacted to at least 95 percent of the maximum dry density based on ASTM Test Method D1557. Below 5 feet, utility trench backfill in pavement areas should be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. Pipe bedding should be in accordance with the pipe manufacturer's recommendations. The contractor is responsible for removing all water -sensitive soils from the trenches regardless of the backfill location and compaction requirements. Depending on the depth and location of the proposed utilities, we anticipate the need to re -compact existing fill soils below the utility structures and pipes. The contractor should use appropriate equipment and methods to avoid damage to the utilities and/or structures during fill placement and compaction procedures. 9.o 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: ■ Monitor and test structural fill placement and soil compaction ■ Observe bearing capacity at foundation locations ■ Observe slab -on -grade preparation 8 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON August 2, 2020 ■ Verify foundation drains ■ Observe excavation stability COBALT GEOSCIENCES 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. io.o Closure This report was prepared for the exclusive use of Rick Cuevas and his 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 Rick Cuevas 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. Respectfully submitted, Cobalt Geosciences, LLC Original signed by: HONry _WAsy��q��� a. 54896 Exp. 6/26/2020 Phil Haberman, PE, LG, LEG Principal PH/sc 9 PO Box 82243 Kenmore, WA 98028 cobaltgeoPgmail.com 2o6-331-1097 APPENDIX A Statement of General Conditions 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 party makes of this report is the responsibility of such third party. 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. 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'r i' 122'23.000' W 122122.000' W 122'21.000' W 122,20.000' W WG584 122119.000' W 0 5 I TN MN MS NATIONAL "`5w N 1000 0 1000 2000 30M 4000 16' GEOGRAPHIC 5 0 KILOMETERS "`t IA 1000 0 METERS 16W 11/26/14 Cobalt Geosciences, LLC P.O. Box 82243 t Kenmore, WA 98028 Proposed Residence P 648 Walnut Street VICINITY MAP _—` (2o6) 331-1097 _ www.cobaltgeo.com Edmonds, Washington FIGURE i cobaltgeo(&gmail.com i wt low l b40 b48 b3 4 SuMect b54 TP-i Approximate Test Pit N Location A Not to Scale Cobalt Geosciences, LLC Prop osed d Residence SITE PLAN P.O. Box 82243 p Kenmore, WA 98028 COBALT 648 Walnut Street (206) 331-1097 GEOSCIENCES Edmonds, Washington FIGURE 2 www.cobaltgeo.com cobaltgeopgmail.com APPENDIX C Exploration Logs 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 (206) 331-1097 _ www.cobaltgeo.com cobaltgeo(&gmail.com Test Pit TP-1 Date: July 16, 2020 Depth: 8' Groundwater: 4' Contractor: Jim Elevation: Logged By: PH Checked By: SC N U) o -0 6 Moisture Content ('.) Plastic I Liquid U N -6 Limit Limit N Material Description o c ? o DCP Equivalent N-Value O 0 10 20 30 40 50 ------ -- Topsoil/Grass -------------------------------- ---- 1 SM Loose to medium dense, silty -fine to medium grained sand with gravel dark yellowish brown, moist. 2 (Fill) ------ 3 ---- '.' -- SM --------------------------------------------- Loose to medium dense, silty -fine to medium grained sand with gravel SP reddish brown to yellowish brown, moist. 4 _ (Weathered Advance Outwash) _ ------ 5 ----" '+ -- SM --------------------------------------------- Dense to very dense, silty -fine to medium grained sand with gravel, SP grayish brown, moist. (Advance Outwash) 6 7 _ End of Test Pit 8' 9 10 Test Pit TP-2 Date: July 16, 2020 Depth: 6' Groundwater: 3.5' Contractor: Jim Elevation: Logged By: PH Checked By: SC N 0) J0-0 o Moisture Content (%) Plastic I Liquid U L T 3 Limit Limit � � N Material Description ? o DCP Equivalent N-Value o C 0 10 20 30 40 50 _______ 2 ____ _ __ SM TopsoilGrass Loose to medium dense, silty -fine to medium grained sand with gravel SJ��y�llt�with hrQyllfR�Cflvih hrQ�pLCL�EIi�---------- SP/ Loose to medium dense, silty -fine to medium grained sand with gravel �';; '4 SM grayish brown, moist to wet. (Weathered Advance Outwash) 3 4 SP Medium dense, fine to medium grained sand with gravel trace silt, +' grayish brown, moist to wet. (Advance Outwash) 5 :ti}"•. ` ' ` ` -Severe caving End of Test Pit 6' Refusal due to caving 7 8 9 10 Cobalt Geosciences, LLC COBALT • Proposed Residence 648 Walnut Street Edmonds, Washington Test Pit Logs P.O. Box 82243 Kenmore, WA 98028 (2o6) 331-109�7 www.cobaltgeo.com cobaltgeo(digmail.com