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BLD2021-0020+Geotechnical_Report+1.6.2021_12.38.26_PM+1976787GEOTECHNICAL ENGINEERING REPORT 76T" AVENUE WEST TOWNHOMES 7528 215TH STREET SW EDMONDS, WASHINGTON Project No. 1817.01 May 26, 2017 Prepared for: Northlake Capital & Development Prepared by: ZipperGeo Geoprofessional Consultants 19023 36t" Ave West, Suite D I Lynnwood, WA 98036 1 Phone: 425.582.9928 1 zippergeo.com Zipp Geo Geoprofessional Consultants Project No. 1817.01 May 26, 2017 Northlake Capital & Development c/o CDA + Pirscher Architects 23114 100 Avenue West Edmonds, Washington 98020 Attention: Mr. Jim Thorpe Subject: Geotechnical Engineering Report 76th Avenue West Townhomes 7528 215th Street SW Edmonds, Washington 98026 Dear Mr. Thorpe, In accordance with your request and written authorization, Zipper Geo Associates, LLC (ZGA) has completed the subsurface evaluation and geotechnical engineering report for the above -referenced project. This report presents the findings of the subsurface evaluation and geotechnical recommendations for the project. Our work was completed in general accordance with our Proposal for Geotechnical Engineering Services (Proposal No. P17160) dated April 12, 2017. Written authorization to proceed was provided by Northlake Capital & Development on April 29, 2017. We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we may be of further service, please contact us. Sincerely, Zipper Geo Associates, LLC o1 W a a y5126117 ` . ��+ 1783 �• ed G$0 4AMEs P. GEORGIS James P. Georgis, LG, LEG Principal Copies: Addressee (1) Thomas A. Jones, PE Managing Principal 19023 36th Ave West, Suite D I Lynnwood, WA 98036 1 Phone: 425.582.9928 I zippergeo.com TABLE OF CONTENTS Page INTRODUCTION...........................................................................................................................................1 SITEDESCRIPTION.....................................................................................................................................1 PROJECT UNDERSTANDING.....................................................................................................................2 SUBSURFACECONDITIONS......................................................................................................................2 RegionalGeology.............................................................................................................................................2 SoilConditions.................................................................................................................................................2 GroundwaterConditions.................................................................................................................................3 Summary of Laboratory Testing......................................................................................................................4 CONCLUSIONS AND RECOMMENDATIONS............................................................................................4 General..........................................................................................................................................................4 SitePreparation...............................................................................................................................................4 Structural Fill Materials and Preparation........................................................................................................7 Temporary and Permanent Slopes..................................................................................................................9 Seismic Design Considerations......................................................................................................................10 ShallowFoundations.....................................................................................................................................11 On -Grade Concrete Slabs..............................................................................................................................12 BackfilledRetaining Walls.............................................................................................................................13 DrainageConsiderations...............................................................................................................................14 Infiltration Considerations.............................................................................................................................14 Pavements.....................................................................................................................................................15 Existing Retaining Wall Considerations.........................................................................................................16 CLOSURE................................................................................................................................................... 17 FIGURES Figure 1— Site and Exploration Plan APPENDICES Appendix A —Subsurface Exploration Procedures and Logs Appendix B — Laboratory Testing Procedures and Results Cover Photo Credit: Google Earth 2017 GEOTECHNICAL ENGINEERING REPORT 76T" AVENUE WEST TOWNHOMES 7528 215T" STREET SW EDMONDS, WASHINGTON Project No. 1817.01 MAY 26, 2017 INTRODUCTION This report documents the surface and subsurface conditions encountered at the site and our geotechnical engineering recommendations for the proposed 76th Avenue West Townhomes project. The project description, site conditions, and our geotechnical conclusions and design recommendations are presented in the text of this report. Supporting data including detailed exploration logs and field exploration procedures, results of laboratory testing, and other supporting information are presented as appendices. Our geotechnical engineering scope of services for the project included a literature review, site reconnaissance, subsurface exploration, laboratory testing, geotechnical engineering analysis, and preparation of this report. The subsurface evaluation consisted of completing two exploratory borings (13- 1 and B-2) across the site. The borings extended to a depth of approximately 21% feet below the ground surface. SITE DESCRIPTION The site is located at 7528 2151h Street Southwest in Edmonds, Washington. The rectangular parcel is bordered by 215th Street Southwest to the north, 76th Avenue West to the west, a single-family residential parcel to the east, and an access drive and parking lot for Swedish Hospital to the south. The site includes a single -story, single-family residence with a daylight basement located in the north central portion of the site. It appears that the basement level is limited to the eastern half of the residence. In general, the site slopes gently down from west to east with about 3 feet of relief across the site. The single-family parcel to the east is lower than the subject property and a concrete masonry unit (CMU) block wall is located near the common property line. The northern half of the wall is about 4 feet tall. The southern half of the wall consists of two tiers with a combined height of about 9 to 10 feet. The horizontal distance from the face of the upper wall to the face of the lower wall is about 2% feet. Site vegetation includes ornamental shrubs such as rhododendron, arborvitae, and laurel with the majority of the yard north, west, and south of the existing residence covered with lawn. The property includes several moderately large trees including three conifers up to about 2 feet in diameter north of the house, two to three conifers up to about 1 foot in diameter west of the house, and about 7 to 9 conifers up to about 2% feet in diameter in the southwest corner of the site. Page 1 Zi pperGeo Geoprofessional Consultants PROJECT UNDERSTANDING 76T" Avenue West Townhomes Project No. 1817.01 May 26, 2017 We understand that the proposed project includes razing the existing residence and associated structures and construction of a three-story, four -unit townhome building located slightly west of the center of the lot. We understand that the bottom level will consist of daylight basement garages open to vehicle access from a driveway located along the east side of the site. A grading plan was not available at the time this report was prepared. However, we anticipate that excavations for foundation construction would likely extend about one to two feet below the basement level of the existing residence at elevation 405 feet. Existing site features and a preliminary development plan are shown on the enclosed Site and Exploration Plan, Figure 1. We understand that infiltration of roof and surface water runoff is currently under consideration. We anticipate that the design of infiltration systems will be completed in accordance with the City of Edmonds Bulletin # E72B and Appendix C of the City of Edmonds Stormwater Supplement. We anticipate that infiltration systems could include permeable pavement, rain gardens, drywells, infiltration trenches, and subsurface infiltration galleries such as StormTech systems. SUBSURFACE CONDITIONS Regional Geology We assessed the geologic setting of the site and surrounding vicinity by reviewing the Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangle, Washington, U.S. Geological Survey, Map MF-1541, by J.P. Minard 1983. The geologic map locates the site near the contact between Vashon glacial till (Qvt) and Vashon advance outwash (Qva) deposits. The Vashon till is described as a compact, poorly sorted mixture of clay, sand, pebbles, cobbles, and boulders. Vashon till is often referred to as "hardpan" in its unweathered state due to its very dense nature caused by compaction resulting from the weight of an overriding glacial mass thousands of years ago, which was hundreds of meters thick in some areas. The Vashon advance outwash deposit is described as typically consisting of a thick section of mostly clean, gray, pebbly sand with increasing amounts of gravel higher up in the deposit. The advance outwash was deposited by meltwater flowing from the advancing front of the glacier and was compacted by the overriding glacial mass. The Vashon advance outwash is younger than the Vashon glacial till and is often encountered stratigraphically below the glacial till deposits. The soil conditions encountered in the boring were generally consistent with the Vashon glacial till unit. Soil Conditions The subsurface evaluation for this project included two borings (B-1 and B-2) completed on the north and south sides of the existing residence. The borings extended to a depth of about 21% feet below the ground surface. The approximate exploration locations are shown on the enclosed Site and Exploration Plan, Figure 1. Page 2 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 Soils observed in the borings were visually classified in general accordance with the Unified Soil Classification System. Descriptive logs of the subsurface explorations and the procedures utilized in the subsurface exploration program are presented in Appendix A. A generalized description of soil conditions encountered in the borings is presented below. Please refer to the boring logs in Appendix for a more detailed description of the conditions encountered at the exploration locations. The subsurface conditions encountered in the explorations were relatively consistent with respect to soil type and relative density. In general, the explorations encountered about 2 to 3 inches of grass sod over fill soils over glacial till deposits. Description of the existing fill soils and underlying glacial till deposits are presented below. Existing Fill Soils: Soils interpreted as fill were encountered in borings B-1 and B-2 to depths of about 3% and 2 feet below existing grade, respectively. In general, the fill consisted of loose to medium dense, silty sand with organics and roots. Glacial Till Deposits: Glacial till deposits were encountered below the surficial fill in both explorations. The glacial till consisted of dense to very dense, silty sand with gravel to sand with silt and gravel. The glacial till deposits extended to the total depth explored of about 21% feet below existing grade. Soil types and conditions can vary between explorations. The nature and extent of variations between the explorations may not become evident until construction. Stratification boundaries on the boring logs represent the approximate depth of changes in soil types, although the transition between materials may have been gradual. If variations become apparent during construction, it may be necessary to reevaluate the recommendations of this report Groundwater Conditions Groundwater in the form of seepage at the exploration locations was not observed at the time of drilling. However, given the dense to very dense nature and low permeability of the glacial till soils encountered below the existing surficial fill, near surface perched groundwater conditions are expected to develop due to variations in the amount of precipitation, runoff, and other factors not evident at the time the exploration was performed. The periodic development of near -surface perched groundwater conditions is supported by iron oxide staining and soil mottling observed in in the upper portion of the glacial till deposits. Groundwater conditions should be expected to fluctuate due to variations in the amount of rainfall, runoff, and other factors not evident at the time the exploration was performed. Therefore, groundwater levels during construction or at other times in the life of the structure may vary from those indicated on the logs. Page 3 Zi pperGeo Geoprofessional Consultants 76TH Avenue West Townhomes Project No. 1817.01 May 26, 2017 Summary of Laboratory Testing Laboratory testing was completed on selected samples obtained from our explorations. Testing included moisture content and grain size analyses. The results of moisture content testing are presented on the boring logs. The results of the grain size analyses are presented in Appendix B. Moisture Content: Moisture content tests completed on glacial till samples indicate in -situ moisture contents ranging from about 9 to 11 percent within the upper 10 feet of existing site grade. Grain Size Analyses: Grain size analysis tests completed on samples of glacial till collected at depths of about 5 and 10 feet below grade indicate fines contents (silt and clay size particles passing a US No. 200 sieve) of about 28 and 35 percent, respectively. CONCLUSIONS AND RECOMMENDATIONS General Based on our subsurface exploration program and analysis, we conclude that the proposed development is feasible from a geotechnical standpoint, contingent on proper design and construction practices. Based on our analyses, conventional spread footings and slab -on -grade concrete floors can be used for the new development. The site borings completed in currently landscaped portions of the site encountered about 2 to 3% feet of organic rich undocumented fill. We do not recommend supporting new foundations on existing undocumented fill soils. Undocumented fill soils encountered within the proposed building area should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction. Geotechnical engineering recommendations for foundation systems and other earthwork related phases of the project are outlined below. The recommendations contained in this report are based upon the results of field and laboratory testing (which are presented in Appendices A and B), engineering analyses, and our current understanding of the proposed project. ASTM and Washington State Department of Transportation (WSDOT) specification codes cited herein respectively refer to the current manual published by the American Society for Testing & Materials and the current edition of the Standard Specifications for Road, Bridge, and Municipal Construction, (M41-10). Site Preparation Existing Structure Removal: The site is currently developed with a single-family residence, a concrete driveway, and concrete walkways. We recommend that any existing foundation elements or other below grade structures be completely demolished and removed from the proposed building footprint. Existing Utility Removal: We recommend that abandoned underground utilities within the proposed building envelope be completely removed. Utility pipes outside the building envelope could be abandoned in place, provided they are fully grouted with controlled density fill (CDF) and the trench Page 4 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 backfill is density tested to verify that it meets the compaction levels presented in the project specifications. Localized excavations made for removal of utilities or existing unsuitable trench backfill should be backfilled with structural fill as outlined in the following section of this report. Erosion Control Measures: Stripped surfaces and soil stockpiles are typically a source of runoff sediments. We recommend that silt fences, berms, and/or swales be installed around the downslope side of stripped areas and stockpiles in order to capture runoff water and sediment. If earthwork occurs during wet weather, we recommend that all stripped surfaces be covered with straw to reduce runoff erosion, whereas soil stockpiles should be protected with anchored plastic sheeting. Temporary Drainage: Stripping, excavation, grading, and subgrade preparation should be performed in a manner and sequence that will provide drainage at all times and provide proper control of erosion. The site should be graded to prevent water from ponding in construction areas and/or flowing into and/or over excavations. Exposed grades should be crowned, sloped, and smooth -drum rolled at the end of each day to facilitate drainage if inclement weather is forecasted. Accumulated water must be removed from subgrades and work areas immediately and prior to performing further work in the area. Equipment access may be limited and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely manner. Clearing and Stripping: The site is surfaced with a concrete driveway and walkways. As such, extensive clearing, grubbing, and topsoil stripping activities in paved areas are not anticipated. Our explorations were completed in landscaped portions of the site and encountered about 2 to 3% feet of organic rich fill. In our opinion, these organic rich fill soils are not suitable for use as structural fill. As such, clearing, grubbing, and topsoil stripping activities in landscaped portion of the site are anticipated to range from about 2 to 4 feet. The site currently supports a number of relatively large conifer trees and it appears that the site may have supported more trees prior to development. Thicker deposits of organic rich soil and tree root systems may be encountered were trees were previously removed or currently exist. Topsoil or other organic rich soils should be removed and utilized for non-structural landscape fill or be disposed of at a suitable off -site location. Any excavations that extend below finish grades should be backfilled with structural fill as outlined in the Structural Fill section in this report. Subgrade Preparation: Existing organic -rich fill soils were encountered in the site explorations to depths ranging from 2 to 3% feet below existing grade. We do not recommend the construction of building foundations, interior floor slabs, or pavements over undocumented fill soils. Based on the proposed daylight basement configuration of the building, it appears that most of the fill soils will be removed from the building envelope as part of the planned excavation. We recommend that existing fill soils be removed from below foundation and floor slab areas and replaced with structural fill as outlined in the Structural Fill section of this report. Existing fill soils encountered in pavement areas should be evaluated by ZGA at the time of construction relative to pavement support. Page 5 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 Once site preparation is complete, all areas that are at design subgrade elevation or areas that will receive new structural fill should be compacted to a firm and non -yielding condition and to a compaction level of at least 95 percent of the maximum laboratory density (per ASTM D 1557) within the upper 12 inches. Some moisture conditioning of site soils may be required to achieve an appropriate moisture content for compaction within ±2 percent of the soils laboratory optimum moisture content. Our laboratory testing indicates that, at the time our explorations were completed, in -situ moisture contents of the glacial till soils ranging from 9 to 11 percent with within the upper 10 feet of existing site grades. These moisture contents are near to slightly above the estimated optimum moisture content of the site soils. Asa result, we expect that moisture conditioning of site soils during construction may be required to achieve suitable moisture contents (plus or minus two percent of optimum) for compaction in areas. Earthwork should be completed during drier periods of the year when soil moisture content can be controlled by aeration and drying if possible. If earthwork or construction activities take place during extended periods of wet weather, if will be difficult to achieve a firm, non -yielding surface and recommended compaction levels. In the event the exposed subgrade becomes unstable, yielding, or unable to be compacted due to high moisture conditions, we recommend that the materials be removed to a sufficient depth in order to develop stable subgrade soils that can be compacted to the minimum recommended levels. The severity of construction problems will be dependent, in part, on the precautions that are taken by the contractor to protect the subgrade soils. Once compacted, subgrades should be evaluated through density testing and, if possible, proof rolling with a loaded dump truck or heavy rubber -tired construction equipment weighing at least 20 tons to assess the subgrade adequacy and to detect soft and/or yielding soils. In the event that soft or yielding areas are detected during proof rolling, the upper 12 inches of subgrade should be scarified, moisture conditioned and re -compacted as necessary to obtain at least 95 percent of the maximum laboratory density (per ASTM D 557) and a firm, non -yielding condition. Those soils which are soft, yielding, or unable to be compacted to the specified criteria should be over -excavated and replaced with suitable on -site or imported material as recommended in the Structural Fill section of this report. Once subgrades are compacted, depending on the time of year, it may be desirable to protect prepared foundation and floor slab subgrades from wet weather. To protect stable subgrades, we recommend using crushed rock or crushed recycled concrete. The thickness of the protective layer should be determined at the time of construction and be based on the moisture condition of the soil and the amount of anticipated traffic. Freezing Conditions: If earthwork takes place during freezing conditions, all exposed subgrades should be allowed to thaw and then be compacted prior to placing subsequent lifts of structural fill. Alternatively, the frozen material could be stripped from the subgrade to expose unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. Page 6 Zi pperGeo Geoprofessional Consultants 76TH Avenue West Townhomes Project No. 1817.01 May 26, 2017 Structural Fill Materials and Preparation Structural fill includes any material placed below foundations and pavement sections, within utility trenches, and behind retaining walls. Prior to the placement of structural fill, all surfaces to receive fill should be prepared as previously recommended in the Site Preparation section of this report. Laboratory Testing: Representative samples of on -site and imported soils to be used as structural fill should be submitted for laboratory testing at least 4 days in advance of its intended use in order to complete appropriate laboratory testing. Re -Use of Site Soils as Structural Fill: The existing fill soils encountered in our explorations generally consisted of silty sand with organics and roots and are not suitable for reuse as structural fill. Field and laboratory test data indicates that the native glacial till soils encountered below the existing fill are generally suitable for reuse as structural fill from a compositional standpoint provided the soil is placed and compacted in accordance with the compaction recommendations presented in this report. However, based on drilling action and depositional environment, some oversized material may be encountered in the glacial till soils. Material greater than 3-inches in diameter should be removed from soils to be reused as structural fill. Site glacial till soils at the time of our evaluation appeared to be near to slightly wet of their estimated optimum moisture content. Excavations completed during extended wet periods may encounter perched groundwater and as a result, drying of wet, over -optimum soils may be required for re -use of site soils as structural fill. Drying of over -optimum moisture soils may be achieved by scarifying or windrowing surficial materials during extended periods of dry weather. If encountered, soils which are dry of optimum may be moistened through the application of water and thorough blending to facilitate a uniform moisture distribution in the soil prior to compaction. We recommend that site soils used as structural fill have less than 4 percent organics by weight and have no woody debris greater than % inch in diameter. We recommend that all pieces of organic material greater than % inch in diameter be picked out of the fill before it is compacted. Any organic -rich soil derived from earthwork activities should be utilized in landscape areas or wasted from the site. Imported Structural Fill: Imported structural fill may be required for raising site grades or as replacement fill for unsuitable site soils. The appropriate type of imported structural fill will depend on the prevailing weather conditions. During extended periods of dry weather, we recommend imported fill, at a minimum, meet the requirements of Common Borrow as specified in Section 9-03.14(3) of the 2016 Washington State Department of Transportation, Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT Standard Specifications). During wet weather, higher -quality structural fill might be required, as Common Borrow may contain sufficient fines to be moisture sensitive. During wet weather we recommend that imported structural fill meet the requirements of Gravel Borrow as specified in Section 9-03.14(1) of the WSDOT Standard Specifications. Page 7 Zi pperGeo 76T" Avenue West Townhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 Pavement Subgrades: Any structural fill used within the upper one foot below pavement sections should have a minimum California Bearing Ratio (CBR) of 15 when compacted to a minimum of 95 percent of the modified Proctor maximum dry density. A CBR value of 15 is representative of the on -site soils and Common Borrow import fill, and has been used to develop our pavement section recommendations. Samples of proposed imported fill should be submitted for laboratory testing and approval prior to use. Moisture Content: The suitability of soil for use as structural fill will depend on the time of year, the moisture content of the soil, and the fines content (that portion passing the U.S. No. 200 sieve) of the soil. As the amount of fines increases, the soil becomes increasingly sensitive to small changes in moisture content. Soils containing more than about 5 percent fines cannot be consistently compacted to the appropriate levels when the moisture content is more than approximately 2 percent above or below the optimum moisture content (per ASTM D 1557). Optimum moisture content is that moisture content which results in the greatest compacted dry density with a specified compactive effort. Moisture content of fill at the time of placement should be within plus or minus 2 percent of optimum moisture content for compaction as determined by the ASTM D 1557 test method. Fill Placement: Structural fill should be placed in horizontal lifts not exceeding 10 inches in loose thickness. Each lift of fill should be compacted using compaction equipment suitable for the soil type and lift thickness. Compaction Criteria: Each lift of fill should be compacted to the minimum levels recommended in the table below based on the maximum laboratory dry density as determined by the ASTM D 1557 Modified Proctor Compaction Test. Structural fill placed in municipal rights -of -way should be placed and compacted in accordance with the jurisdiction codes and standards. We recommend that a geotechnical engineer be present during grading so that an adequate number of density tests may be conducted as structural fill placement occurs. In this way, the adequacy of the earthwork may be evaluated as it proceeds. RECOMMENDED SOIL COMPACTION LEVELS Location Minimum Percent Compaction* Stripped native subgrade soils, prior to fill placement (upper 12 inches) 95 All fill below building floor slabs and foundations 95 Upper 2 feet of fill below pavements 95 Pavement fill below two feet 92 Upper two feet of utility trench backfill 95 Utility trenches below two feet 92 Landscape Areas 90 * ASTM D 1557 Modified Proctor Maximum Dry Density Page 8 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 Placing Fill on Slopes: Permanent fill placed on slopes steeper than 5H:1V (Horizontal:Vertical) should be keyed and benched into natural soils of the underlying slope. We recommend that the base downslope key be cut into undisturbed native soil. The key slot should be at least 8 feet wide and 3 feet deep. The hillside benches cut into the native soil should be at least 4 feet in width. The face of the embankment should be compacted to the same relative compaction as the body of the fill. This may be accomplished by over -building the embankment and cutting back to the compacted core. Alternatively, the surface of the slope may be compacted as it is built, or upon completion of the embankment fill placement. Temporary and Permanent Slopes Temporary excavation slope stability is a function of many factors, including: • The presence and abundance of groundwater; • The type and density of the various soil strata; • The depth of cut; • Surcharge loadings adjacent to the excavation; and • The length of time the excavation remains open. As the cut is deepened, or as the length of time an excavation is open, the likelihood of bank failure increases; therefore, maintenance of safe slopes and worker safety should remain the responsibility of the contractor, who is present at the site, able to observe changes in the soil conditions, and monitor the performance of the excavation. It is exceedingly difficult under the variable circumstances to pre -establish a safe and "maintenance -free" temporary cut slope angle. Therefore, it should be the responsibility of the contractor to maintain safe temporary slope configurations since the contractor is continuously at the job site, able to observe the nature and condition of the cut slopes, and able to monitor the subsurface materials and groundwater conditions encountered. Unsupported vertical slopes or cuts deeper than 4 feet are not recommended if worker access is necessary. The cuts should be adequately sloped, shored, or supported to prevent injury to personnel from local sloughing and spalling. The excavation should conform to applicable Federal, State, and Local regulations. According to Chapter 296-155 of the Washington Administrative Code (WAC), the contractor should make a determination of excavation side slopes based on classification of soils encountered at the time of excavation. Temporary cuts may need to be constructed at flatter angles based upon changes in soil moisture and groundwater conditions during construction. Adjustments to the slope angles should be determined by the contractor at that time. We recommend that all permanent cut or fill slopes constructed in native soils or with imported structural fill be designed at a 2H: 1V (Horizontal: Vertical) inclination or flatter. All permanent cut and fill slopes should be adequately protected from erosion both temporarily and permanently. If the slopes are exposed to prolonged rainfall before vegetation becomes established, the surficial soils will be prone to erosion and possible shallow sloughing. We recommend covering permanent slopes with a rolled erosion Page 9 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 protection material, such as Jute matting or Curlex II, if vegetation has not been established by the regional wet season (typically November through May). Seismic Design Considerations The seismic performance of the development was evaluated relative to seismic hazards resulting from ground shaking associated with the Maximum Considered Earthquake Geometric Mean (MCEG) Peak Ground Acceleration and the Risk -Targeted Maximum Considered Earthquake (MCER) Ground Motion Response Acceleration in accordance with the 2012/2015 International Building Code (IBC). Conformance to the above criteria for seismic excitation does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a maximum considered earthquake occurs. The primary goal of the IBC seismic design procedure is to protect life and not to avoid all damage, since such design may be economically prohibitive. Following a major earthquake, a building may be damaged beyond repair, yet not collapse. Ground Surface Rupture: We evaluated the potential for seismic ground surface rupture at the site by reviewing the USGS Quaternary Fault Web Mapping Application. The mapping application indicates that there are no mapped Quaternary faults within 5 miles of the site. It is our opinion that the risk of ground surface rupture at the site is low. Landsliding: Based on the topography of the site and surrounding vicinity and the density of the site glacial till soils, the risk of earthquake -induced landsliding is low. Soil Liquefaction & Lateral Spread: Liquefaction is a phenomenon wherein saturated cohesionless soils build up excess pore water pressures during earthquake loading. Liquefaction typically occurs in loose soils, but may occur in denser soils if the ground shaking is sufficiently strong. The explorations primarily encountered glacially consolidated glacial till deposits. Based on the dense to very dense nature of these soils, it is our opinion that the potential for liquefaction at the site is low. Lateral spreading is a phenomenon in which soil deposits which underlie a site can experience significant lateral displacements associated with the reduction in soil strength caused by soil liquefaction. This phenomenon tends to occur most commonly at sites where the soil deposits can flow toward a "free - face", such as a water body. Due to the lack of liquefiable soils at the site and the lack of a nearby "free - face" condition, it is our opinion that the risk of lateral spreading at the site is low. IBC Seismic Design Parameters: 2012/2015 IBC Seismic Design parameters are summarized on the table below. Page 10 Zi pperGeo Geoprofessional Consultants 76TH Avenue West Townhomes Project No. 1817.01 May 26, 2017 Code Used Site Classification 2012/2015 International Building Code (IBC) 1 C 2 Ss Spectral Acceleration for a Short Period 1.271g (Site Class B) S1Spectral Acceleration for a 1-Second Period 0.496g (site Class B) Fa Site Coefficient for a Short Period 1.000 (Site Class C) F Site Coefficient for a 1-Second Period 1.304 (Site Class C) SMs Maximum considered spectral response acceleration 1.271g (Site Class C) for a Short Period SMi Maximum considered spectral response acceleration 0.647g (Site Class C) for a 1-Second Period Sos Five -percent damped design spectral response 0.847g (Site Class C) acceleration for a Short Period Sol Five -percent damped design spectral response 0.431g (Site Class C) acceleration for a 1-Second Period 1. In general accordance with the 201212015 International Building Code, Section 1613.3.2 and ASCE 7-10, Chapter 20. IBC Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile. 2. The borings completed for this study extended to a maximum depth of 21% feet below grade. ZGA therefore determined the Site Class assuming that dense to very dense glacially consolidated soils extend to 100 feet as suggested by published geologic maps for the project area. Shallow Foundations Based on our analyses, conventional spread footings will provide adequate support for the proposed building and retaining walls provided that the foundation subgrades are properly prepared. We anticipate that foundation subgrade soils will generally consist of medium dense to very dense silty sand with gravel to sand with silt and gravel. Borings completed in landscaped portions of the site encountered about 2 to 3% feet of organic -rich fill and the proposed townhome building encompasses about half of the existing building footprint and extends north and south into currently landscaped areas. We do not recommend supporting new foundations on existing undocumented fill soils. If fills are encountered within the proposed building area, such fills should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction. We recommend that any over -excavation of unsuitable fill soils extend outside the limits of the footings a distance equal to the depth of over -excavation. Design recommendations for foundations and related structural elements are presented in the following sections. Allowable Bearing Pressure: Continuous and isolated column footings bearing on medium dense to very dense glacial till soils or structural fill placed and compacted in accordance with this report may be designed for a maximum allowable, net, bearing capacity of 3,000 psf. A one-third increase of the bearing Page 11 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 pressure may be used for short-term transient loads such as wind and seismic forces. The above - recommended allowable bearing pressure includes a 3.0 factor of safety. Shallow Foundation Depth and Width: For frost protection, the bottom of all exterior footings should bear at least 18 inches below the lowest adjacent outside grade, whereas the bottoms of interior footings should bear at least 12 inches below the surrounding slab surface level. We recommend that all continuous wall and isolated column footings be at least 12 and 24 inches wide, respectively. Lateral Resistance: Resistance to lateral loads can be calculated assuming an ultimate passive resistance of 450 pcf equivalent fluid pressure (triangular distribution) and an ultimate base friction coefficient of 0.60. An appropriate safety factor (or load/resistance factors) should be included for calculating resistance to lateral loads. For allowable stress design, we recommend a minimum 1.5 safety factor. We recommend that passive resistance be neglected in the upper 18 inches of embedment. Estimated Static Settlement: Assuming the foundation subgrade soils are prepared in accordance with recommendations presented herein, we estimate that total and differential settlements will be less than 1 inch and % inch over a distance of about 50 feet, respectively. On -Grade Concrete Slabs Floor slabs for the proposed building may be supported on the medium dense to very dense glacial till deposits or new structural fill placed in accordance with the recommendations provided in this report. Floor slabs should not be supported on existing fill soils. If unsatisfactory fills are encountered within the slab area, such fills should be removed and the excavation thoroughly cleaned prior to backfill placement and/or construction The following sections provide recommendations for on -grade floor slabs. Subgrade Preparation: Subgrades for on -grade slabs should be prepared in accordance with the Site Preparation and Structural Fill sections of this report. Capillary Break: To provide a capillary break, uniform slab bearing surface, and a minimum subgrade modulus of 150 pci, we recommend the on -grade slabs be underlain by a 5-inch thick layer of compacted, crushed rock meeting the requirements of WSDOT Standard Specification Section 9-03.9(3), Crushed Surfacing Top Course, with the modification of a maximum of 7 percent passing the U.S. No. 200 sieve. Alternatively, a clean angular gravel such as No. 7 aggregate per WSDOT: 9-03.1(4)C could be used for this purpose. Alternative capillary break materials should be submitted to the geotechnical engineer for review and approval before use. Vapor Retarder: From a geotechnical standpoint, a vapor barrier is not considered to be necessary for the proposed building. Where potential slab moisture is a concern or where moisture sensitive floor coverings are planned, we recommend using a puncture -resistant 10- to 15-mil thick product such as Stego Wrap, or an approved equivalent, that is classified as a Class A vapor retarder in accordance with ASTM E 1745. Page 12 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 To avoid puncturing of the vapor barrier, construction equipment should not be allowed to drive over any vapor retarder material. Where pipes and other objects penetrate the barrier, we recommend taping these per the manufacturer's recommendations. We recommend the slab designer and slab contractor refer to ACI 302 and ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder/barrier. Backfilled Retaining Walls We expect the project to include backfilled, cast -in -place (c.i.p.) concrete retaining walls for the proposed daylight basement level of the building, and possibly other minor site walls. For recommended bearing capacities and lateral resistance parameters, refer to the Shallow Foundations section of this report. Retaining walls must be founded on suitable native soils or compacted structural fill placed above suitable native soils. If fills are encountered, we recommend that the fill be removed and replaced with structural fill. Additional recommendations for retaining walls are provided below. Lateral Earth Pressures: The lateral soil pressures acting on backfilled retaining walls will depend on the nature and density of the soil behind the wall, and the ability of the wall to yield in response to the earth loads. Yielding walls (i.e. walls that are free to translate or rotate) that are able to displace laterally at least 0.001H, where H is the height of the wall, may be designed for active earth pressures. Non -yielding walls (i.e. walls that are not free to translate or rotate) should be designed for at -rest earth pressures. Non -yielding walls include walls that are braced to another wall or structure, and wall corners. If walls are backfilled and drained as described in the following paragraphs, we recommend that yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 35 pcf (active earth pressure). Non -yielding walls should be designed using an equivalent fluid density of 55 pcf (at -rest earth pressure). Design of permanent retaining walls should consider additional earth pressure resulting from the design seismic event. For the seismic case, walls should be designed for an additional uniform, total seismic earth pressure distribution of 11H. The above -recommended lateral earth pressures do not include the effects of sloping backfill surfaces, surcharges such as traffic loads, other surface loading, or hydrostatic pressures. If such conditions exist, we should be consulted to provide revised earth pressure recommendations. Drainage: Adequate drainage measures must be installed to collect and direct subsurface water away from subgrade walls. All backfilled walls should include a drainage aggregate zone extending two feet from the back of wall for the full height of the wall. The drainage aggregate should consist of material meeting the requirements of WSDOT 9-03.12(2) Gravel Backfill for Walls. A minimum 4-inch diameter, perforated PVC drain pipe should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate discharge point. We recommend placing a non -woven geotextile, such as Mirafi 140N, or equivalent, around the free draining backfill material. Wall drainage systems should be independent of other drainage systems such as roof drains. Page 13 Zi pperGeo Geoprofessional Consultants Drainage Considerations 76T" Avenue West Townhomes Project No. 1817.01 May 26, 2017 Surface Drainage: Final site grades should be sloped to carry surface water away from the building and other drainage -sensitive areas. Additionally, site grades should be designed such that concentrated runoff on softscape surfaces is avoided. Any surface runoff directed towards softscaped slopes should be collected at the top of the slope and routed to the bottom of the slope and discharged in a manner that prevents erosion. Building Perimeter Footing Drains and Retaining Wall Drains: We recommend that the new building and retaining walls be provided with a footing drain system to reduce the risk of future moisture problems and the buildup of hydrostatic pressures. The footing drains should consist of a minimum 4-inch diameter, Schedule 40, rigid, perforated PVC pipe placed at the base of the heel of the footing with the perforations facing down. The pipe should be surrounded by a minimum of 6 inches of clean free -draining granular material conforming to WSDOT Standard Specification 9-03.12(4), Gravel Backfill for Drains. A non -woven filter fabric such as Mirafi 140N, or equivalent, should envelope the free -draining granular material. At appropriate intervals such that water backup does not occur, the drainpipe should be connected to a tightline system leading to a suitable discharge. Cleanouts should be provided for future maintenance. The tightline system must be separate from the roof drain system. Roof drains should be connected to a separate solid wall PVC tightline system and routed to a suitable discharge location. Infiltration Considerations We understand that infiltration of roof and surface water runoff is currently under consideration. We anticipate that the design of infiltration systems will be completed in accordance with the City of Edmonds Bulletin # E72B and Appendix C of the City of Edmonds Stormwater Supplement. We anticipate that infiltration systems could include permeable pavement, rain gardens, drywells, infiltration trenches, and subsurface infiltration galleries such as StormTech systems. In general, the site is mantled by about 2 to 3% feet of fill over dense to very dense glacial till deposits. The upper portion of the glacial till exhibits mottling and iron oxide staining indicative of near -surface perched groundwater conditions. Given the very low permeability of the dense to very dense glacial till deposits and indications of shallow perched groundwater, it is our opinion that the feasibility for shallow infiltration systems such as rain gardens, permeable pavement, and surface dispersion appears low and we anticipate that the use of these systems could result in wet or soggy ground surface conditions during the wet season. In addition, infiltrated water would tend to migrate along the top of the low permeability, dense to very dense glacial till soils to the basement walls, thereby contributing the water in the wall and footing drain systems and an increased potential for groundwater intrusion into the building. Deeper infiltration systems such as conventional infiltration trenches, gravelless chambers, and drywells would be socketed into impermeable glacial till deposits and are not considered feasible. We therefore recommend that surface water and groundwater collected by the wall/footing drain system be tightlined to a City stormwater or combined storm/sewer system, if feasible. Page 14 Zi pperGeo Geoprofessional Consultants Pavements 76T" Avenue West Townhomes Project No. 1817.01 May 26, 2017 We anticipate that the access driveway for the four townhome units will consist of flexible asphalt pavement or rigid concrete pavement. The following sections provide pavement recommendations for the development. Asphalt Pavement Pavement Life and Maintenance: It should be realized that asphaltic pavements are not maintenance - free. The following pavement sections represent our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. A 20-year pavement life typically assumes that an overlay will be placed after about 12 years. Thicker asphalt, base, and subbase courses would offer better long-term performance, but would cost more initially. Conversely, thinner courses would be more susceptible to "alligator" cracking and other failure modes. As such, pavement design can be considered a compromise between a high initial cost and low maintenance costs versus a low initial cost and higher maintenance costs. The recommendations presented below are based on AASHTO Low -Volume Road Design methodologies as presented in the 1993 AASHTO Guide for Design of Pavement Structures. Traffic Design Values: No traffic loading was provided for this project. We have assumed relatively low traffic volumes. Soil Design Values: Pavement subgrade soils are anticipated to consist of on -site soils or, at a minimum, imported structural fill meeting the requirements of Common Borrow. Our analysis assumes the imported fill will have a minimum California Bearing Ration (CBR) value of 15. Recommended Pavement Sections: For light -duty pavements, we recommend 2 inches of asphalt concrete over 4 inches of crushed rock base course. For heavy-duty pavements, we recommend 3 inches of asphalt concrete over 6 inches of crushed rock base course. Materials and Construction: We recommend the following regarding asphalt pavement materials and pavement construction. • Subgrade Preparation and Compaction: Upper 12 inches of native stripped subgrade should be prepared in accordance with the recommendations presented in the Subgrade Preparation section of this report, and all fill should be compacted in accordance with the recommendations presented in the Structural Fill section of this report. • Asphalt Concrete: We recommend that the asphalt concrete conform to Section 9-02.1(4) for PG 58-22 or PG 64-22 Performance Graded Asphalt Binder as presented in the 2016 WSDOT Standard Specifications. We also recommend that the gradation of the asphalt aggregate conform to the Page 15 Zi pperGeo Geoprofessional Consultants 76TH Avenue West Townhomes Project No. 1817.01 May 26, 2017 aggregate gradation control points for %-inch mixes as presented in Section 9-03.8(6), HMA Proportions of Materials. • Base Course: We recommend that the crushed aggregate base course conform to Section 9- 03.9(3) of the WSDOT Standard Specifications. • Compaction and Paving: All base material should be compacted to at least 95 percent of the maximum dry density determined in accordance with ASTM D 1557. We recommend that asphalt be compacted to a minimum of 92 percent of the Rice (theoretical maximum) density or 96 percent of Marshall (Maximum laboratory) density. Placement and compaction of asphalt should conform to requirements of Section 5-04 of the 2016 WSDOT Standard Specifications Concrete Pavement Concrete Properties and Thickness: Concrete pavement design recommendations are based on an assumed modulus of rupture of 600 psi and a minimum compressive strength of4,000 psi forthe concrete. For light duty pavements, we recommend 5 inches of concrete over 3 inches of crushed aggregate base. For heavy duty pavements, we recommend 6 inches of concrete over 3 inches of crushed aggregate base. Concrete Pavement Joints and Reinforcing: Based on the soils encountered, we recommend that concrete pavements should be lightly reinforced to control cracking and have relatively closely spaced control joints on the order of 10 to 12 feet. We recommend that minimum reinforcement consist of 6x6-W2.OxW2.0 welded wire fabric or equivalent. Existing Retaining Wall Considerations The single-family parcel to the east is lower than the subject property and a concrete masonry unit (CMU) block wall is located near the common property line. The northern half of the wall is about 4 feet tall. The southern half of the wall consists of two tiers with a combined height of about 9 to 10 feet. The horizontal distance from the face of the upper wall to the face of the lower wall is about 2% feet. The CMU wall appears to include grout between horizontal layers of block, but does not include grout between vertical block joints (presumably to provide drainage through the wall face). It is not currently known if the CMU units are filled with concrete or include steel reinforcement. The foundation system for the walls is also unknown at this time. An invasive investigation of the walls and wall foundations was not completed by ZGA as the walls appear to be located off the subject property and the owner of the property to the east was not at home during our site visits (the home appears to be under renovation). At the time of our evaluation the existing walls appeared to be in serviceable condition with no obvious indications of distress or damage. The preliminary plan shows a private driveway for the 4 townhome units located within a few feet of the existing off -site retaining walls. Surcharge loads from construction equipment and post construction vehicle traffic including passenger vehicle and moving trucks could impart a significant load on the existing walls. The magnitude and effect of the surcharge load will depend greatly on the elevation of the driveway, which is currently unknown, relative to the bottom of wall elevation. Page 16 Zi pperGeo 76T" Avenue WestTownhomes Project No. 1817.01 Geoprofessional Consultants May 26, 2017 A conservative approach would be to replace the existing retaining walls with new walls designed for anticipated loading conditions. Alternatively, it appears feasible from a geotechnical perspective to proceed with the planned construction leaving the existing off -site walls as -is provided that the east edge of the new driveway is beyond a 1H:1V plane extending up and to the west from the front toe of the existing wall face. ZGA is available to further evaluate the existing off -site walls from a geotechnical perspective once final site grades have been established and access to the wall has been arranged with the adjacent property owner. A structural evaluation of the walls would likely require a structural engineer. CLOSURE The analysis and recommendations presented in this report are based, in part, on the explorations completed for this study. The number, location, and depth of the explorations were completed within the constraints of budget and site access so as to yield the information to formulate our recommendations. Project plans were in the preliminary stage at the time this report was prepared. We therefore recommend Zipper Geo Associates, LLC be provided an opportunity to review the final plans and specifications when they become available in order to assess that the recommendations and design considerations presented in this report have been properly interpreted and implemented into the project design. The performance of earthwork, structural fill, foundations, floor slabs, and pavements depend greatly on proper site preparation and construction procedures. We recommend that Zipper Geo Associates, LLC be retained to provide geotechnical engineering services during the foundation construction phases of the project. If variations in subsurface conditions are observed at that time, a qualified geotechnical engineer could provide additional geotechnical recommendations to the contractor and design team in a timely manner as the project construction progresses. This report has been prepared for the exclusive use of Northlake Capital and Development, and its agents, for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Zipper Geo Associates, LLC reviews the changes and either verifies or modifies the conclusions of this report in writing. Page 17 ANGLE N i i° 1 5 7 T I o f o2 14 2 1I ��ti D�411.9 6�/.p / / i � h T 412.22 \ �I D�� i' // O�1' �O 1N ii cgco 412.30 _ \\ I I `o(0 405.36 • �O 80.00' Q v-2 I� I —-----�---- ----� \IIIII II o,\a ��---�_ i TI—r------ --'-- Oj -;IIII I I m I Q 00Ln Cn / • i m. — IuII I� LLJ js- i 3 01 \ > 3—STORY TOWNHOME W/ 15,_m„ 2 CAR GARAGE, 3 oIp fRMT sEMACK TYP 4•j� + II ol° r I ° L SIDE j\-1 — — SEA o i ii 00 SF —I J / PER bLR, TYP ��°" / N I • d O / �ao7 1 N `— N I Co I 410. 4 }� .. O/ / I Y I \\� O I II L-FO Oo'� \—-------7------------- -----+—' --•---- T - 30.01';' 12" CED�R N88'02'01"W/ 80.00' a� / �� o 00 !; Cb, REFERENCE: SITE PLAN PREPARED BY CDA + PIRSCHER ARCHITECTS, DATED FEBRUARY 24, 2017. LEGEND 76th AVENUE WEST TOWNHOMES 7528 215th Street SW B_ BORING NUMBER AND Edmonds, WA APPROXIMATE LOCATION SITE AND EXPLORATION PLAN 20 0 10 20 DATE: MAY 2017 Job No. 1817.01 Zipper Geo Associates, LLC FIGURE SCALE IN FEET 19023 36th Ave. W.,Suite D Lynnwood, WA SHT. 1 of 1 APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS APPENDIX A SUBSURFACE EXPLORATION PROCEDURES AND LOGS Field Exploration Description Our field exploration for this project included two borings completed in May 2017. The approximate exploration locations are shown on the enclosed Site and Exploration Plan, Figure 1. The exploration locations were determined by measuring distances from existing site features with a fiberglass tape relative to Site Plan prepared by CDA+ Pirscher Architects dated February 24, 2017. As such, the exploration locations should be considered accurate only to the degree implied by the means and methods used to define them. Soil Borings The borings were advanced using a limited- access, track -mounted drill rig operated by an independent drilling company (Geologic Drilling, Inc.) working under subcontract to ZGA. The borings were advanced using hollow stem auger drilling methods. A geologist from our firm continuously observed the borings, logged the subsurface conditions encountered, and obtained representative soil samples. All samples were stored in moisture -tight containers and transported to our laboratory for further evaluation and testing. Samples were obtained by means of the Standard Penetration Test at 2.5- to 5-foot intervals throughout the drilling operation. The Standard Penetration Test (ASTM D 1586) procedure consists of driving a standard 2-inch outside diameter steel split spoon sampler 18 inches into the soil with a 140-pound hammer free falling 30 inches. The number of blows required to drive the sampler through each 6-inch interval is recorded, and the total number of blows struck during the final 12 inches is recorded as the Standard Penetration Resistance, or "blow count" (N value). If a total of 50 blows are struck within any 6- inch interval, the driving is stopped and the blow count is recorded as 50 blows for the actual penetration distance. The resulting Standard Penetration Resistance values indicate the relative density of granular soils and the relative consistency of cohesive soils. The enclosed boring logs describes the vertical sequence of soils and materials encountered in the borings, based primarily upon our field classifications. Where a soil contact was observed to be gradational, our logs indicate the average contact depth. Where a soil type changed between sample intervals, we inferred the contact depth. Our logs also graphically indicates the blow count, sample type, sample number, and approximate depth of each soil sample obtained from the borings. Groundwater monitoring wells were installed in all three borings completed for this project to monitor fluctuations in groundwater levels over time. Boring Location: See Figure 1, Site and Exploration Plan Drilling Company: Geologic Drill Bore Hole Dia.: 4.5 Inches Top Elevation: 410.5 Feet Drilling Method: HSA Hammer Type: Cathead 6-1 Date Drilled: 5/9/2017 Drill Rig: Mini -track Logged by_: JST v E m SOIL DESCRIPTION �� E J n U) � m a ° (D PENETRATION RESISTANCE (blows/foot) co o U m 0) ~ The stratification lines represent the approximate boundaries between soil types. The transition may be gradual. Refer to report text and appendices for additional information. Standard Penetration Test Q Hammer Weight and Drop: 0 20 40 60 2 inches grass sod. -----------------------------------------'� IIII ',II IIIIIIIII IIII -IIIIIIII IIIIIIIII Illlii Medium dense, moist, brown, silt SAND, with organics. Fill Y g (Fill) T S-1 6" IIII II 13 -f-ITT_717-f711 IIIII I -fTTTTTTTT IIIIIIIII TTTTTTT _ IIIIIII. ------------------------------------------- Dense, moist, gray SAND, with silt and gravel. (Glacial Till) 111 S-2 12,E �JJJJJJJ IIIIIIIII -IIIIIIII 11.11111.11 IIIIIIIII IIIIIIIII 1LLLLLL'_ IIIIIIII IIIIIIII 49 IIIIIIII IIIIIIIII IIII IIIIIIIII IIIIIIIII IIIIIIIII IIIIIIIII IIII . IIIIIIII Medium dense to dense, moist, gray SAND with silt and gravel. (Glacial Till) Dense, moist, gray, silty SAND with gravel, slight iron oxide staining. (Glacial Till) S-3 18" s-a I 1a 1 -I-IT T-f7 IIIIIIIII IIIIIIIII I I I I I I I I I 7TTT TTTT I�I II,IIIII,II IIIIIIIII I I I I I I I I I TTTTTTT -.. IIIIILL -v.. IIIIIII'. I I I I I I I I 30 as +.� IIIII111I + IIIIIIIII IIIIIIII IIIIIIII --I11_f++t- IIIIIIII IIIIIIIII ++t t t t.t.t t IIIIIIIII IIi1I1'... IIII Very dense, moist, gray, silty SAND with gravel. (Glacial Till) S-5 I 16 IIIIIIII I-I-�-�T-irt IIIIIIIII IIIIIII 5o,4" �� .'...IIIIIIII IIIIIII t t r-rT-r-rTT IIIIIIIII IIIIIIIII -r-r-rTTTr IIIIIIII IrIIIIIII IIIIIIII IIIIIIIII IIII IIIIIIIII +-1++++-4+ IIIIIIIII IIIIIIIII ++a-++++++ IIIIIIIII IIII +++a- - IIII -i��rtrtrtrtrt IIIIIIIII rtrtrtrtrtrt*rtt IIIIIIIII III trrrrr.. IIIIIIIII IIIIIIII IIIIIIIII IIIIIIIII T f7 '..�IIIIII TTTTTTTTT III�I111� TTTTTi-T '- IIIIIII Very dense, moist, gray, silty SAND, with gravel. (Glacial Till) s-s T 1z" 1 50/4" IIIIIIIII IIIIIIIII -+--4-i-4+ IIIIIIIII IIIIIIIII ++44+++++ IIII IIII +++44- 1-- -- Boring completed at about 21.5 feet. No groundwater observed at time of drilling. g. IIIIIIIII 11 f-t-r-t- IIIIIIIII IIIIIIIII fiat t t t.tt t IIIIIIIII IIII tt r - - , IIII�� IIIIIIIII IIIIIIIII IIIIIIII 7177-1777 77777TTTT TTTTTTT:- SAMPLE LEGEND GROUNDWATER LEGEND O % Fines (<0.075 mm) I2-inch O.D. split spoon sample Clean Sand 0 % Water (Moisture) Content 3-inch I.D. Shelby tube sample ® Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content ® Screened Casing 76th Ave. West Townhomes TESTING KEY n Blank Casing 7528 215th Street SW GSA = Grain Size Analysis V Groundwater level at Edmonds, WA time of drilling (ATD) or 200W = 200 Wash Analysis N on date of Date: May 2017 Project No.: 1817.01 Consol. = Consolidation Test N measurement. Zipper Geo Associates BORING Att. = Atterberq Limits B-1 19023 36th Ave. W, Suite D LOG; Lynnwood, WA Page 1 of 1 Boring Location: See Figure 1, Site and Exploration Plan Drilling Company: Geologic Drill Bore Hole Dia.: 4.5 Inches Top Elevation: 410.5 Feet Drilling Method: HAS Hammer Type: Cathead B-2 Date Drilled: 5/9/2017 Drill Rig: Mini -track Logged by_: JST SOIL DESCRIPTION PENETRATION RESISTANCE (blows/foot) v �� E m co o 0) Standard Penetration Test E The stratification lines represent the approximate boundaries J n a Q Hammer Weight and Drop: U m between soil types. The transition may be gradual. Refer to ~ report text and appendices for additional information. U) � ° m (D 0 20 40 60 3 inches grass sod. , -----------------------------------------'-�I Loose to medium dense, moist, brown, silty SAND, with III .II (IIIIIIII (III " organics and roots. (Fill) -------------------------------------------- �� rrt rrt -IIIIIIII rt T1 T TT IIIIIIIII Trrrrrrr _ Dense, moist, gray -brown SAND, with silt and gravel, Wthd Glacial Till moderate iron oxide staining. (Weathered ) s-1 18" IIIIIIII 42 ��T�� (III III 7T T T TTTTT IIIIIIIII �TTTTTT - IIIIII -------------------------------------------- Ve dense, moist, gray SAND, with silt and ravel. ry 9 Y g (Glacial Till) S-2 12' IIIIIIIII -IIIIIIII I I LLL IIIIIIIII IIIIIIIII L 1LILL L ! IIIIIIII IIIIIIII 51 GSA 1111 IIIIIIII (IIIIIIIII III IIIII IIIIIIIII Ili � - (III �.._I7yrtttrtrt '..IIIIIII IIIIIIIII rtt-t t t t..ttt IIIIIIIII (III t t...- t- r ` :... IIIIIIII Ve dense, moist, gray, silt SAND, with ravel, slight iron rY 9 Y Y 9 9 T S-3 I 1$" I 63 i I-IT�777 7777T TTTT TTT-TTI-T � oxide staining. (Glacial Till) Very dense, moist, gray, silty SAND, with gravel. (Glacial Till) 11 S-4 181, IIIIIIIII IIIIIIIII I I I I I I I I I 1 1 1 1 1 1 1 1 1 II,,,IIIII,II IIIIIIIII I I I I I I I I I 1 1 1 1 1 1 IIIIILL! IIIIIII'. I I I I I I I I 64 GSA + IIIIIIIII IIIIIIIII ��-f _f _f _f_+ 11111111 IIIIIIIII IIIIIIIII tttttt 111111111 (III (III '... ttt 1111 Very dense, moist, gray, silty SAND, with gravel. (Glacial Till) s-5 10.5° 1-I-17 111 11 r7- 11111 50i4.5° -�-�T-irt I� '11111111 t t r-rT-r-rTT 111111111 -r-r-rTTTT 1111111i 0 11 111111111 1111 ...11 ...11 I1111111 111111111 111111111 1111 1111 -I��rtrtrtrtrt 111111111 rttrtrtrtrt*rtt 111111111 r T_ trrrrr.. 11111111i 11111111 111111111 111111111 77-77-17 f7 -IIIIIIII 77777TTTT III�I111� TTTTTi-T '- 1111�111 Very dense, moist, gray, silty SAND, with gravel. (Glacial Till) S-6 I n° 50/5" 111111111 111111111 y - LL...a IIIIIIIII IIIIIIIII +++++++++ y (III (III ++++- Boring completed at about 21.5 feet. 1 No groundwater observed at time of drilling. g g IIIIIIIII -r11-f-t-t-t-t 111111111 IIIIIIIII fittttt.+tt 111111111 (III tt-rr�- 1111�� 111111111 111111111 11111111 T11T7T77 77777TTTT TTTTTTT:- SAMPLE LEGEND GROUNDWATER LEGEND O % Fines (<0.075 mm) I2-inch O.D. split spoon sample Clean Sand 0 % Water (Moisture) Content 3-inch I.D. Shelby tube sample ® Bentonite Plastic Limit Liquid Limit Grout/Concrete Natural Water Content ® Screened Casing 76th Ave. West Townhomes TESTING KEY n Blank Casing 7528 215th Street SW GSA = Grain Size Analysis V Groundwater level at Edmonds, WA time of drilling (ATD) or 200W = 200 Wash Analysis N on date of Date: May 2017 Project No.: 1817.01 Consol. = Consolidation Test N measurement. BORING Zipper Geo Associates Att. = Atterberq Limits B-2 19023 36th Ave. W, Suite D LOG; Lynnwood, WA Page 1 of 1 APPENDIX B LABORATORY TESTING PROCEDURES AND RESULTS APPENDIX B LABORATORY TESTING PROCEDURES AND RESULTS A series of laboratory tests were performed by ZGA during the course of this study to evaluate the index and geotechnical engineering properties of the subsurface soils. Descriptions of the types of tests performed are given below. Visual Classification Samples recovered from the exploration locations were visually classified in the field during the exploration program. Representative portions of the samples were carefully packaged in moisture tight containers and transported to our laboratory where the field classifications were verified or modified as required. Visual classification was generally done in accordance with ASTM D 2488. Visual soil classification includes evaluation of color, relative moisture content, soil type based upon grain size, and accessory soil types included in the sample. Soil classifications are presented on the exploration logs in Appendix A. Moisture Content Determinations Moisture content determinations were performed on representative samples obtained from the explorations in order to aid in identification and correlation of soil types. The determinations were made in general accordance with the test procedures described in ASTM D 2216. Moisture contents are presented on the exploration logs in Appendix A. Grain Size Analysis A grain size analysis indicates the range in diameter of soil particles included in a particular sample. Grain size analyses were performed on representative samples in general accordance with ASTM D 422. The results of the grain size determinations for the samples were used in classification of the soils, and are presented in this appendix. GRAIN SIZE ANALYSIS Test Results Summary ASTM D 422 100 90 = 80 W ?� 70 Im IW 60 W Z 50 Z W tU W 40 W a 30 20 10 0 1000.000 100.000 10.000 1.000 0.100 0.010 0.001 PARTICLE SIZE IN MILLIMETERS Coarse Fine Coarse Medium Fine Silt Clay BOULDERS COBBLES GRAVEL SAND FINE GRAINED Comments: Exploration Sample Depth (feet) Moisture (%) Fines (%) Description B-2 S-2 5.0 9.1 27.9 SAND with silt and gravel Project No.: 1817.01 PROJECT NAME: Zipper Geo Associates, LLC Geotechnical and Environmental Consultants DATE OF TESTING: 5/11/2017 76th Ave. W. Townhomes GRAIN SIZE ANALYSIS Test Results Summary ASTM D 422 100 90 = 80 W ?� 70 Im IW 60 W Z 50 Z W tU W 40 W a 30 20 10 0 1000.000 100.000 10.000 1.000 0.100 0.010 0.001 PARTICLE SIZE IN MILLIMETERS Coarse Fine Coarse Medium Fine Silt Clay BOULDERS COBBLES GRAVEL SAND FINE GRAINED Comments: Exploration Sample Depth (feet) Moisture (%) Fines (%) Description B-2 S-4 10.0 9.9 35.2 Silty SAND with gravel Project No.: 1817.01 PROJECT NAME: Zipper Geo Associates, LLC Geotechnical and Environmental Consultants DATE OF TESTING: 5/11/2017 76th Ave. W. Townhomes