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APPROVED STM RESUB1 BLD2021-0742+Storm_Drainage_Report+2.4.2022_10.26.21_AM+2661917LITCHFIELD ENGINEERING Civil Engineering & Development Services RES U B BLD2021-0742 Feb 04 2022 DEVITYOEDSEDSCESECHNICAL INFORMATION REPORT DEPARTMENT forth e Ramella-Pezza Residence Prepared for: Massimo Ramella-Pezza 702 Cedar St Edmonds, WA 98020 Prepared By: Keith A. Litchfield, P.E. Date Issued: May 17, 2021 I COMPLIES WITH APPLICABLE CITY STO/RMWATER CODE 03/22/2022 12840 81ST AVENUE NE ♦ KIRKLAND, WA 98034 PH 425-821-5038 FAX 425-821-5739 TABLE OF CONTENTS A. Project Overview....................................................................................................1 B. Minimum Requirements.........................................................................................4 FIGURES Figure 1: Vicinity Map Figure 2: Soils Map Figure 3: Flow Chart for Determining Requirements for New Development APPENDICES Appendix A: Geotechnical Investigation A. Project Overview Existing Conditions The site is located at 702 Cedar St in Edmonds, WA, Tax Parcel No. 004484500300100. The property is 6,582 SF (approximately 0.15 AC) and bordered to the north, south, east, and west by single-family residences. The project site slopes from southeast to the north at an average grade of approximately 11%, ranging from flat to 20%. The site is currently developed with a single- family residence, carport and shed and is vegetated with lawn areas, shrubs, and few trees. The site is accessed from an existing driveway from 7t" Avenue South. The site soils are mapped as Alderwood-Urban land complex, 8 to 15 percent slopes. Runoff from the site sheet flows to the north into the public drainage system located within Cedar Street. Proposed Conditions The project incorporates the construction of on and off -site infrastructure to support the construction of a new single-family residence. The new residence will access in the existing driveway location on 7t" Avenue South via a new 32.5' wide pervious concrete driveway. The site impervious area as a result of the new home construction is provided below. Summary of Proposed Site Improvements: Surface Type Area (SF) Onsite Roof 2,717 Total Impervious: 2,717 Pervious Driveway 932 Pervious Walkways 260 Total Area: 6,582 1 Site Maps Figure 1: Vcinity Map w Ur _ -TF---TTIFWTI-- Walnut yi EEM= TI= Cedar Spruce St 0 Hemlock St e S Figure 2: Soils Map B. Minimum Requirements The existing impervious surface coverage is less than 35%, therefore the project is classified as new development. The Department of Ecology's Figure 1-2.4.1: Flow Chart for Determining Requirements for New Development (Figure 3, page 7) was utilized to determine the project requirements relative to stormwater management. The project adds less than 5,000 sq. ft. of new impervious surface but more than 2,000 sq. ft. of new plus replaced impervious surface, therefore minimum requirements 1 through 5 apply to the project. Implementing Minimum Requirements #1 - #5 Minimum Requirement No. 1— Preparation of Stormwater Site Plan A stormwater site plan is included in the permit submittal. Minimum Requirement No. 2 — Construction Stormwater Pollution Prevention Plan All new development and redevelopment projects in which new, replaced, or new plus replaced impervious surfaces total 2,000 square feet or more, shall comply with Construction SWPPP Elements #1 through #13. A CSWPPP has been incorporated into the Stormwater Site Plans. Element 1— Mark Clearing Limits — Clearing limits at the property lines will be delineated with silt fence and orange construction fencing (if necessary). Element 2 — Establish Construction Access — The existing driveway will provide adequate access during construction, however a quarry spall construction entrance will be provided, if necessary. Element 3 — Control Flow Rates — Given the existing topography and small scope of work, a silt fence will be adequate to control the minimal flows generated during construction. Element 4— Install Sediment Controls — Silt fencing will be constructed and is expected to provide construction stormwater sediment control during construction. Element 5 — Stabilize Soils — Stockpiled or unworked soils will be protected during construction by covering with plastic or temporary or permanent seeding. All exposed soils will be landscaped or seeded at the conclusion of the project. Element 6 — Protect Slopes — Cut/fill slopes are not anticipated but if necessary will be protected as required. Element 7 — Protect Drain Inlets — The existing and newly constructed conveyance system inlets will be protected during construction if warranted. Element 8 — Stabilize Channels and Outlets — There are no existing or proposed surface channels or outfalls. 11 Element 9 — Control Pollutants — The small size of this project will limit the opportunity for discharge of pollutants. Waste/demolition debris will not be stockpiled, fueling will be done off - site and concrete trucks will be washed out off -site. Element 10— Control De -watering— De -watering is not anticipated, as construction will take place during the dry season. Element 11 — Maintain BMPs — BMPs will be maintained as necessary to assure continued functioning. Element 12 — Manage the Project — An inspector (sites less than 1 acre) will be present or on call to ensure BMPs are maintained and assess effectiveness of ESC measures. Rainy season requirements will be implemented if necessary. Element 13 — Protect Low Impact Development BMPs —The locations of the proposed infiltration trench and permeable pavement shall be protected from compaction to the maximum extent feasible during construction. Orange construction fencing shall be provided around the location for the proposed infiltration trench. Minimum Requirement No. 3 — Source Control of Pollution Permanent source control BMPs are not proposed. Construction source control BMPs are shown on the CSWPPP. Minimum Requirement No. 4— Preservation of Natural Drainage Systems and Outfalls The natural drainage pattern for the site will be maintained. The surface runoff from the proposed impervious surfaces will be collected and routed to an onsite infiltration trench with an overflow outlet to the existing conveyance system within Cedar Street. Minimum Requirement No. 5 — On -Site Stormwater Management The project triggers Minimum Requirements #1-5 therefore, On -Site Stormwater Management BMPs from List #1 will be implemented to the maximum extent feasible. Please see below for the feasibility evaluation of the BMPs from List #1 by surface type. Lawn and Landscaped Areas: 1. Post Construction Soil Quality and Depth — This BMP is feasible and will be implemented per City of Edmonds Standard Detail SD-642 for all disturbed and converted vegetated areas. Roofs: 1. Full Dispersion and Downspout Full Infiltration Systems — Infiltration is feasible and will be implemented for the proposed roof area per City of Edmonds Standard Detail SD-636 and Department of Ecology BMP T5.10A. 2. Raingarden or Bioretention — N/A, roof area will be mitigated with and infiltration trench. 5 3. Downspout Dispersion Systems— N/A, roof area will be mitigated with and infiltration trench. 4. Perforated Stub -out Connection — N/A, roof area will be mitigated with and infiltration trench. Other Hard Surfaces: 1. Full Dispersion — Infeasible. The minimum flow path length of 100 LF cannot be met. 2. Permeable Pavement, Rain Garden, or Bioretention —Permeable pavement is feasible and will be implemented for the proposed walkway and driveway. 3. Sheet Flow Dispersion — N/A, hard surfaces will be mitigated with permeable pavement. Summary — Post construction soil quality and depth will be implemented for all proposed pervious areas. Downspout full infiltration will be implemented for the proposed roof area and permeable pavement will be used for the proposed walkway and driveway. Infiltration Trench Sizing: A review of the site soil conditions was conducted by Cobalt Geosciences. Per the geotechnical investigation, the soils on the site are conducive to infiltration and characterized as outwash sands and gravel. Therefore, an infiltration trench is proposed and will be located along the western edge of the project site. Refer to Appendix A for the Geotechnical Investigation prepared by Cobalt Geosciences, dated December 2, 2020. Per Volume III, Section 3.1.1 — Downspout Full Infiltration Systems (BMP T5.10A) of the DOE Manual, for sites with outwash sand and gravel, 30 LF of 2' wide x 1.5' deep infiltration trench is required per 1,000 SF of roof area (60 SF of trench per 1,000 SF of roof). The proposed roof area is 2,717 square feet, which results in 82 LF of 2' wide x 1.5' deep infiltration trench. This proposal will provide an equivalent trench of infiltration by providing an infiltration trench that is 33' long and 5' wide. Therefore; Roof Area = 2,717 SF Required Infiltration Trench = 2'WIDE X 30 LF x (2,570 SF / 1,000 SF) = 164 SF Proposed Infiltration Trench = 33' Long x 5' Wide x 1.5' DeeD = 165 SF 0 Figure 3 — New Development Flow Chart Start Here Does the site have 35% or more of existing impervious coverage? Does the project result in 5.000 square feet. or greater, of new plus replaced hard surface area? Yes All Minimum Requirements apply to the new and replaced hard surfaces and converted vegetation areas. Yes See Redevelopment Minimum Requirements and Flow Chart (Figure 1-2.42)_ Yes Does the protect convert a acres or more of vegetation to lawn or landscaped areas, or convert 2.5 acres or more of native vegetation to pasture? Minimum Requirements #1 through #5 apply to the new and replaced hard surfaces and the land disturbed. in Does the project result in 2,000 square feet, or greater, of new plus replaced hard surface area? M Does the protect have land disturbing activibes of 7.000 Yes square feet or greater? No Minimum Requirement #2 applies. Figure 1-2.4.1 i6i Flow Chart for Determining Requirements for New Development D E 4 R T l,I E r. - F Revised June 2015 ECOLOGYPlease see httpJAvvw ecy.wa.govrcopynght.htmf for copyright notice including permissions State of Washington limitabon of liability. and disclaimer. 7 APPENDIX A GEOTECHNICAL INVESTIGATION COBALT G E 0 S C I E N C E S Geotechnical Investigation Proposed Residence 702 Cedar Street Edmonds, Washington December 2, 2020 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON Table of Contents i.o INTRODUCTION............................................................................................................. 1 2.o PROJECT DESCRIPTION.............................................................................................. 1 3.0 SITE DESCRIPTION....................................................................................................... 1 4.o FIELD INVESTIGATION............................................................................................... 2 4.1.1 Site Investigation Program................................................................................... 2 5.o 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.................................................................................................... 6 7.o DISCUSSION................................................................................................................... 6 7.1.1 General.................................................................................................................6 8.o RECOMMENDATIONS.................................................................................................. 7 8.1.1 Site Preparation................................................................................................... 7 8.1.2 Temporary Excavations........................................................................................ 7 8.1.3 Erosion and Sediment Control.............................................................................. 8 8.1.4 Foundation Design............................................................................................... 9 8.1.5 Reinforced Concrete Retaining Walls..................................................................10 8.1.6 Stormwater Management....................................................................................11 8.1.7 Slab-on-Grade.....................................................................................................11 8.1.8 Utilities...............................................................................................................12 8.1.9 Groundwater Influence on Construction.............................................................12 9.o CONSTRUCTION FIELD REVIEWS...........................................................................12 io.o CLOSURE...................................................................................................................13 LIST OF APPENDICES Appendix A — Statement of General Conditions Appendix B — Figures Appendix C — Exploration Logs GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 1.o Introduction COBALT GEOSCIENCES In accordance with your authorization, Cobalt Geosciences, LLC (Cobalt) has completed a geotechnical investigation for the proposed residence located at 702 Cedar Street in Edmonds, Washington (Figure 1). The purpose of the geotechnical investigation was to identify subsurface conditions and to provide preliminary geotechnical recommendations for foundation design, retaining walls, earthwork, soil compaction, and suitability of the on -site soils for use as fill. The scope of work for the geotechnical investigation 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 design, retaining walls, drainage, and earthwork. 2.0 Project Description The project includes construction of a new residence within the property. Based on topography, a daylight basement may be incorporated into the design. We anticipate that structural loads will generally be light and site grading will include cuts and fills on the order of 10 feet or less for daylight basement construction. We should be provided with the plans once they become available so that we may update our recommendations, if necessary. Stormwater runoff will be infiltrated, if determined to be feasible. 3.0 Site Description The site is located at 702 Cedar Street in Edmonds, Washington (Figure 1). The property consists of one rectangular shaped parcel (No. 00484500300100) with a total area of 0.15 acres. The north -central portion of the site is developed with a single-family residence. There is a driveway and carport near the southern margin. There are local concrete retaining walls along the southeast and south portions of the property. These walls are 3 to 7 feet tall and face into the site. The site slopes downward from south to north at magnitudes of 5 to 30 percent and relief of about 15 feet. The steeper slopes are along the north property line and are about 7 feet tall at 50 to 8o percent magnitude. The site is vegetated with grasses, sparse trees, bushes, shrubs, and other low-lying vegetation. The site is bordered to the east by a residence, to the south by an alley/driveway, to the west by 7th Avenue South, and to the north by Cedar Street. PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 4.o Field Investigation COBALT GEOSCIENCES 4.1.1 Site Investigation Program The geotechnical field investigation program was completed on December 1, 202o and included excavating one test pit and one hand boring within the property for subsurface analysis. There was very limited space to excavate additional test pits. 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 test pit and auger boring 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 Composite Geologic Map of the Edmonds East and West Quadrangle, indicates that the site is underlain by Vashon Advance Outwash and/or Esperance Sand. Esperance Sand generally correlates to Vashon Advance Outwash. These materials consist of sand with variable amounts of gravel which are generally dense to very dense and relatively permeable. Esperance Sand often contains more gravel than typical advance outwash. Explorations The test pit encountered approximately 6 inches of topsoil and grass underlain by approximately 3.5 feet of loose to medium dense, silty -fine to medium grained sand trace gravel (Weathered Advance Outwash). This layer was underlain by medium dense, fine to medium grained sand with gravel trace to some silt (Esperance Sand or Vashon Advance Outwash), which continued to the termination depth of the test pit. The hand boring encountered about 6 inches of topsoil and grass underlain by 3 feet of loose, silty -fine to medium grained sand trace gravel (Weathered Outwash). These deposits were underlain by medium dense to dense, fine to medium grained sand trace to with gravel (Advance Outwash), which continued to the termination depth of the hand borings. 2 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 5.1.2 Groundwater COBALT GEOSCIENCES Groundwater was not encountered during our investigation. Based on our observations and review of nearby explorations, groundwater is likely more than 20 feet below site elevations. Light amounts of perched groundwater could be encountered on fine grained interbeds within the outwash at multiple depths below the site. 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 property is underlain by Alderwood-Urban Land Complex (8 to 15 percent slopes). In general, these soils have a low to moderate erosion potential in a disturbed state. This site is more accurately underlain by outwash-like soils which have a severe erosion potential when exposed on slope magnitudes greater than about 15 percent. These soils are included in the Edmonds Municipal Code section 23.80.020 under Al. It is our opinion that typical erosion control measures will be suitable to limit/reduce erosion potential during construction. 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. Relevant code sections with our comments/discussion are as follows: 23.80.o6o Development standards — General requirements. A. Alterations of geologically hazardous areas or associated buffers may only occur for activities that: 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. 3 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 COBALT GEOSCIENCES The site is situated on a low -magnitude slope that extends downward to the north. The slope was created over a long period of time through natural erosion along with grading associated with roadwUs and adjacent properties. The site does not contain steep slope or landslide hazards. We understand that the shallow soils may have significant erosion potential and constitute an erosion hazard area. The proposed residence 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. This assume construction activities will be performed with typical engineering standards, permit requirements and with proper temporary excavations and erosion control measures. The level of risk due to the proposed development will be the same or lower than what is currently_ present provided temporary and permanent runoff is fully controlled. 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; No specific setback is required for erosion hazards provided all permanent graded or created slopes have magnitudes of 2H:1V or flatter and are fully landscaped following construction. 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; The site currently fully developed. No specific buffer is required from a geotechnical standpoint. We recommend that all site soils be vegetated or protected from erosion through placement of surface landscaping materials/hardscapes. 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; PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 COBALT GEOSCIENCES Provided earthwork activities are performed in accordance with the approved plans, all runoff is fu11X control, and periodic geotechnical oversight is performed, the development will not decrease slope stabili , on adjacent properties, will not increase surface water discharge or sedimentation bg and 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; Based on site topography, underling soil conditions, and our experience with similar projects, the estimated static and seismic factors of safety are well above minimum requirements. The factor of safety for landslide activity will not be affected by the proposed development. The building loads and where they will be located will not affect global stability. The site is not within a landslide or steep slope hazard area. The development does not pose a risk to critical areas or the need to increase buffers on adjacent properties. 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 5 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 COBALT GEOSCIENCES 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. 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 medium dense or stiff soils within the upper too feet. We referenced the U.S. Geological Survey (USGS) Earthquake Hazards Program Website to obtain values for Ss, S,, FQ, and 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 126.8o% of g S, 49.70% of g FA 1.00 Fv 1.503 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 glacially consolidated materials that underlie the site have a low potential for liquefaction. 7.o DISCUSSION 7.m General It is our opinion that the proposed residence may be supported on a shallow foundation system bearing on medium dense or firmer native soils. These soils will likely be encountered 3 to 4 feet below existing site elevations. 6 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 COBALT GEOSCIENCES This report was prepared prior to receipt of a final site plan with building elevations. If a basement is proposed, temporary shoring could be required along some portions of the property lines depending on the location and elevation of the new building. We should be provided with the final plans to verify that our recommendations remain valid or if they need to be updated. It is our opinion that the proposed development will not increase the potential for soil movement or erosion at the property, and the risk of damage to the proposed development and adjacent properties will be minimal, provided the work is performed in accordance with approved plans and our recommendations and is monitored by the geotechnical engineer. 8.o Recommendations 8.1.1 Site Preparation Trees, shrubs and other vegetation should be removed prior to stripping of surficial organic -rich soil. Based on observations from the site investigation program, it is anticipated that the stripping depth will range from 6 to 18 inches. Deeper excavations should be expected below larger vegetation and where undocumented fill is present. The near -surface soils consist of silty -sand with gravel and poorly graded sand with gravel and silt. These soils are suitable for use as structural fill if they are compacted when the moisture levels are within a few percent of optimum. This is typically only possible during mid -late summer and early fall when there are extended periods of warm, dry weather. All fill soils should be compacted when they are within 3 percent of the optimum moisture as determined by the ASTM D 1557 proctor analysis test. 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 10 feet or less for basement foundation placement, if proposed. These excavations should be sloped no steeper than 1.5H:1V (Horizontal:Vertical) in loose native soils (upper 2 to 5 feet) and 1H:1V in medium dense or firmer native soils. If an excavation is subject to heavy vibration or surcharge loads, we recommend that the excavations be sloped no steeper than 1.5H:1V, where room permits. The geotechnical engineer should be on site during excavation work to determine safe temporary slope angles. If the proposed residence will have a basement level and be located within about 10 feet of the south or east property lines, temporary shoring will likely be required. We can provide shoring recommendations upon request. 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 7 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 COBALT GEOSCIENCES 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. 8 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 8.1.4 Foundation Design COBALT GEOSCIENCES The proposed residence 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 structures. Provided that the footings are supported as recommended above, a net allowable bearing pressure of 2,000 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 250 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. A 1/3 increase in the above values may be used for short duration transient loads. 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. 9 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 8.1.5 Reinforced Concrete Retaining Walls COBALT GEOSCIENCES The following table, titled Wall Design Criteria, presents the recommended soil related design parameters for retaining walls with a level backslope. Contact Cobalt if an alternate retaining wall system is used. Wall Design Criteria "At -rest" Conditions (Lateral Earth Pressure — EFD+) 55 pcf (Equivalent Fluid Density) "Active" Conditions (Lateral Earth Pressure — EFD+) 35 pcf (Equivalent Fluid Density) Seismic Increase for "At -rest" Conditions (Lateral Earth Pressure) 21H* (Uniform Distribution)1 in 2,500 year event Seismic Increase for "At -rest" Conditions (Lateral Earth Pressure) 14H* (Uniform Distribution)1 in 500 year event Seismic Increase for "Active" Conditions (Lateral Earth Pressure) 7H* (Uniform Distribution) Passive Earth Pressure on Low Side of Wall (Allowable, includes F.S. = 1.5) Level Ground; Neglect upper 2 feet, then 250 pcf EFD+ Soil -Footing Coefficient of Sliding Friction (Allowable; includes F.S. = 1.5) 0.40 'H is the height of the wall; Increase based on one in 2,500 year seismic event (2 percent probability of being exceeded in 50 years), + EFD — Equivalent Fluid Density The stated lateral earth pressures do not include the effects of hydrostatic pressure generated by water accumulation behind the retaining walls. Uniform horizontal lateral active and at -rest pressures on the retaining walls from vertical surcharges behind the wall may be calculated using active and at -rest lateral earth pressure coefficients of 0.3 and 0.5, respectively. The soil unit weight of 125 pcf may be used to calculate vertical earth surcharges. To reduce the potential for the buildup of water pressure against the walls, continuous footing drains (with cleanouts) should be provided at the bases of the walls. The footing drains should consist of a minimum fl- inch diameter perforated pipe, sloped to drain, with perforations placed down and enveloped by a minimum 6 inches of pea gravel in all directions. The backfill adjacent to and extending a lateral distance behind the walls at least 2 feet should consist of free -draining granular material. All free draining backfill should contain less than 3 percent fines (passing the U.S. Standard No. 200 Sieve) based upon the fraction passing the U.S. Standard No. 4 Sieve with at least 30 percent of the material being retained on the U.S. Standard No. 4 Sieve. The primary purpose of the free -draining material is the reduction of hydrostatic pressure. Some potential for the moisture to 10 PO Box 82243 Kenmore, WA 98028 cobaltgeo(&gmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 COBALT GEOSCIENCES contact the back face of the wall may exist, even with treatment, which may require that more extensive waterproofing be specified for walls, which require interior moisture sensitive finishes. We recommend that the backfill be compacted to at least 90 percent of the maximum dry density based on ASTM Test Method D1557. In place density tests should be performed to verify adequate compaction. Soil compactors place transient surcharges on the backfill. Consequently, only light hand operated equipment is recommended within 3 feet of walls so that excessive stress is not imposed on the walls. 8.1.6 Stormwater Management The site is underlain by weathered and unweathered outwash sands and gravels. The outwash sands are suitable for infiltration of stormwater runoff; however, their use at this site is dependent on the location and elevation of the proposed residence. We must be provided with the final plans to confirm whether infiltration systems are feasible as well as the most suitable locations and elevations of any systems. We performed a small-scale pilot infiltration test (PIT) in TP-1 at a depth of 6 feet below grade. Following saturation, testing, and application of correction factors for site variability (0.7), influent control (o.9), and testing (0.5), the design infiltration rate was determined to be 2.3 inches per hour. Systems may be sized using this rate or Medium Sand criteria. In general, infiltration is feasible provided systems are adequately embedded so that stormwater does not migrate laterally onto adjacent properties. We should be provided with the final plans, including building locations and finish floor elevations, in order to determine if infiltration devices are suitable/feasible. 8.1.7 Slab -on -Grade We recommend that the upper 12 inches of the native soils within slab areas be re -compacted to at least 95 percent of the modified proctor (ASTM D1557 Test Method). If loose fill soils or deep topsoil/roots are encountered, they should be removed and replaced with structural fill. 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 36oR-o6 Design of Slabs on Grade and ACI 302.1R-04 Guide for Concrete Floor and Slab Construction are recommended references for vapor barrier selection and floor slab detailing. 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 minimum 4 inch thick capillary break is recommended over the prepared subgrade. This should consist of 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. 11 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 GEOTECHNICAL INVESTIGATION EDMONDS, WASHINGTON December 2, 2020 COBALT GEOSCIENCES 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. 8.1.8 Groundwater Influence on Construction Groundwater was not encountered in the test pit or hand boring. In general, we do not expect groundwater to be encountered in excavations at the site. There is a very slight chance that light volumes of perched groundwater could be encountered on any silty interbeds within the outwash deposits. If groundwater is encountered during construction, 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. 8.1.9 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, sandy soils were encountered at shallow depths in the explorations at this site. These soils have variable cohesion and density and may 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: 12 PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 COBALT GEOTECHNICAL INVESTIGATION G E O S C I E N C E S EDMONDS, WASHINGTON December 2, 2020 ■ Monitor and test structural fill placement and soil compaction ■ Verify soil conditions in infiltration systems, if utilized ■ Monitor temporary excavation stability ■ Verify footing drain installation ■ Observe bearing capacity at footing locations 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. lo.o Closure This report was prepared for the exclusive use of Massimo Ramella-Pezza 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 Massimo Ramella-Pezza 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: �"ONry WASti � 54896 �� Is FSS�ONAL 12/2/2020 Phil Haberman, PE, LG, LEG Principal PO Box 82243 Kenmore, WA 98028 cobaltgeoOgmail.com 2o6-331-1097 2513 d A. Haberman 13 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 party 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. APPENDIX B Figures: Vicinity Map, Site Plan 10.2 PO Box 82243 Kenmore, WA 98028 cobaltgeoogmail.com 2o6-331-1097 APPENDIX C Exploration Logs 1 122121.000' W 122`20.000' W WGS84 122c19.000' W WASHINGTON R r I; Irr 1 1 iQ fill id klan KirBag Project _ -, ' nec�;-.: = Y- d; . � , -:� J I I �� Location T�ybdcR \. 1:74th:stI�— L r}reede'_ R' r �F .� I `' err a' 476tfi St SW 78th>St<SW �--� j78D fS`W` 4� .° feo ,I:.. "•180 PISW o in �' �� 184th-Sr 1 � � x « 18tr6 Q• 186th S•51N•• s1'' c 1 asm_ t 1s8th st S ¢ �� �° �1.,� titer , � :I � � • rm ,� ; t 190th'9t SW �k I'I f= • e--{I Alky J ! SW f •• 1Qo ^ \.192nd PI SW - Palk ,_ i I �� !�'� ^ �0 I I' • ` a t A ,p FA ,ari Q l�c Q - I a.00 O > �� �• •y Viewlan• Wa 1 T • Ic • r a� g') i '.3 �(7\`I{, I\ �•1• I: .�v z_ - I 3, > ••IC 1 .1h o 2ootsLsWo W _ c I YY• 0 0z 202dd St -SW • Ir" t+'202od PI iW - .• 1 • " 02 n. f� V m a203rd St SW _• d n 204th'g svv (St" { =Spra u t' . a oeu� ..� 3 .f I I t • � Lc t � o �1 `4 0 3 I'1 - •P�' I /� r �' - _' r 1s I a a � •d 1206th StSW �' ..n,.d c r � _ .Sell StAlle v m' as > ' u I• 08t1iT9t SW o . Da Ion S' 't / Da, ton St'- T� M ec l�a•5 3 ^0[h >: _ to d Pr �r Spruce St - \\ 1 �.!�-.tic l as"tA77 '� -.�iQ N con / i--.tV _• _ II11IM °y '' nL. ' 215tt�� P Svr z 5 N�•. 1 ^ ��¢�.<'a'c `fpc ine..Si f < = r Pin St StS7216th•StSW Wt' 5��216tK.•`'� •�3�52 6th St JjM_ a n 7th St SW 21 z w se sw •1 ht S S D ' - ` 0. z o m > m'a I c` ��� a o 0 o a OD 4l n a 3 4 3 }s rr o •ni" t►3' 7 �.. _ ,co Q • ¢ • 222nd St -SW O 224 h S SW C Q �� " Z241h TSB W t i I I 224th SN7 Zi •� P,,66.. ,, a• 17" s °' y'21t5 h St W :a I• • SthS['SW r SW 22& > s S[,_ pIIda' l ♦ l77 Ql: �� - c.��l• cam...• •;�;In .230thStSW peel 4�' •_T ,�3�,,�� �, 1 ��+ 231 LI 2nd$ W t.�' A32nti St Sl'Y a l 12aP, ged[edi+aih 1 i (VaUonal'Geog h a©2D07 Tele AtlaS;.ReI!ti•/2007, I I •�• a t- 122'23.000' W 122-22.000' W 122" 21.000' W 122'20.000' W WGS84 122"19.000' W a s t 7N MN 1�T NATIONAL ^^ItEs l� IBM a ttao emu aaoo amo saoa 16° GEOGRAPHIC t 5 0 KILOMEFENS FEET I 1000 0 METM 10a0 11,26/14 Cobalt Geosciences, LLC Proposed Residence VICINITY P.O. Box 82243 Kenmore, WA 98028 COBALT 702 Cedar Street MAP (206) 331-1097 • S C I E N C E S Edmonds, Washington FIGURE i www.cobaltgeo.com cobaltgeo(&gmail.com 702 710 t i 1 _f TP-1 Approximate N HB-i Test Pit & Hand Boring Location Cobalt Geosciences, LLC Proposed Residence SITE P.O. Box 82243 Kenmore, WA 98028 COBALT 702 Cedar Street PLAN (206) 331-1097 GEOSCIENCES Edmonds, Washington FIGURE 2 www.cobaltgeo.com cobaltgeo(&gmail.com APPENDIX D Slope Stability Analyses 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 Test Pit TP-1 Date: December 1, 2020 Depth: 10' Groundwater: None Contractor: Jim Elevation: Logged By: PH Checked By: SC N 0) o Q Moisture Content (%) Plastic I Liquid U N Limit Limit N Material Description c ? o DCP Equivalent N-Value o O 0 10 20 30 40 50 Topsoil/Grass -------- 1 ------ — :• -- SM -------------------------------------------- Loose to medium dense, silty -fine to medium grained sand with .�; SP gravel, dark yellowish brown, moist. (Weathered Outwash) 2 3 rt:1. .4---- ----•i::-ci SP --------------------------------------------- Medium dense to dense,fine to medium grained sand with gravel, 5 s•, ' .ti yellowish brown to grayish brown, moist. (Advance Outwash) 6 ` -Local caving to 6 feet 6 7 8 .r 9 ti• End of Test Pit 10' Hand Boring HB-1 Date: December 1, 2020 Depth: 8' Groundwater: None Contractor: Cobalt Elevation: Logged By: PH Checked By: SC 0 J o Moisture Content (%) Plastic Liquid N15 U E 3 Limit Limit N Material Description c ? o DCP Equivalent N-Value o C 0 10 20 30 40 50 ----- 1 ---- --- SM/ -------------------------------------------- ' S P Loose to medium dense, silt flne to medium rained sand with y- g gravel, dark yellowish brown, moist. (Weathered Glacial Till) 2 3 ----- 4 ---- "- : -- SP --------------------------------------------- Medium dense to dense, fine to medium grained sand trace to with gravel, yellowish brown to grayish brown, moist. (Advance Outwash) 5 6 I• 7 End of Hand Boring 8' 9 10 Cobalt Geosciences, LLC Proposed Residence Test Pit & P.O. Box 82243 % 02 Cedar Street Hand Boring g Kenmore, 8 (206) 33i-1097o97 Edmonds, Washington Logs www.cobaltgeo.com cobaltgeo(digmail.com