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Geotechnical Engineering Study.pdf1 Earth Solutions NW L�c Geotechnical Engineering Gcoiogy Environmental Scientists Construction Monitoring RECEIVE - fl."AICLOPMENT SERI,'rCE� CO U.ITER PROPOSED SINGLE-FAMILY RESIDENCES 9215 BOWDOIN WAY EDMONDS, WASHINGTON ES-5605 1805 l: - %QfQ 1 ~r-ti7utt PREPARED FOR SELECT HOMES, INC. October 31, 2017 Adam Z. Shier, G.I.T. Staff Geologist %`'►? v`r JAA b131 hi t; Henry T. Wright, P.E. Senior Project Engineer GEOTECHNICAL ENGINEERING STUDY PROPOSED SINGLE-FAMILY RESIDENCES 9216 BOWDOIN WAY EDMONDS, WASHINGTON ES-5605 Earth Solutions NW, LLC 1805 —136th Place Northeast, Suite 201 Bellevue, Washington 98005 Phone: 425-449-47041 Fax: 425-449-4711 www.earthsolutionsnw.com � - Geotechnical Engineering Report � Geotechnical Services Are Performed for Specific Purposes, Persons, and Projects Geotechnical engineers structure their services to meet the specific needs of their clients. A geotechnical engineering study conducted for a civil engi- neer may not fulfill the needs of a construction contractor or even another civil engineer. Because each geotechnical engineering study is unique, each geotechnical engineering report is -unique, prepared solelyfor the client. No one except you should rely on your geotechnical engineering report without first conferring with the geotechnical engineer who prepared it. And no one — not even you —should apply the report for any purpose or project except the one originally contemplated. Read the Full Report Serious problems have occurred because those relying on a geotechnical engineering report did not read it all. Do not rely on an executive summary. Do not read selected elements only. A Geotechnical Engineelring Report Is Based on A Unique Set of Plroject-Specific Factors Geotechnical engineers consider a number of unique, project -specific fac- tors when establishing the scope of a study. Typical factors include: the client's goals, objectives, and risk management preferences; the general nature of the structure involved, its size, and configuration; the location of the structure on the site; and other planned or existing site improvements, such as access roads, parking lots, and underground utilities. Unless the geotechnical engineer who conducted the study specifically indicates oth- erwise, do not rely on a geotechnical engineering report that was: • not prepared for you, • not prepared for your project, not prepared for the specific site explored, or completed before important project changes were made. Typical changes that can erode the reliability of an existing geotechnical engineering report include those that affect: the function of the proposed structure, as when it's changed from a parking garage to an office building, or from a light industrial plant to a refrigerated warehouse, • elevation, configuration, location, orientation, or weight of the proposed structure, composition of the design team, or + project ownership. As a general rule, always inform your geotechnical engineer of project changes —even minor ones —and request an assessment of their impact. Geotechnical engineers cannot accept responsibility or liability for problems that occur because their reports do not consider developments of which they were not informed. Subsurface Conditions Can Change A geotechnical engineering report is based on conditions that existed at the time the study was performed. Do not rely on a geotechnical engine» r- ing report whose adequacy may have been affected by: the passage of time; by man-made events, such as construction on or adjacent to the site; or by natural events, such as floods, earthquakes, or groundwater fluctua- tions. Always contact the geotechnical engineer before applying the report to determine if it is still reliable. A minor amount of additional testing or analysis could prevent major problems. Most Geotechnical Findings Are Professional Opinions Site exploration identifies subsurface conditions only at those points where subsurface tests are conducted or samples are taken. Geotechnical engi- neers review field and laboratory data and then apply their professional judgment to render an opinion about subsurface conditions throughout the site. Actual subsurface conditions may differ —sometimes significantly — from those indicated in your report. Retaining the geotechnical engineer who developed your report to provide construction observation is the most effective method of managing the risks associated with unanticipated conditions. A Report's Recommendations Are Not Final Do not overrely on the construction recommendations included in your report. Those recommendations are not final, because geotechnical engi- neers develop them principally from judgment and opinion. Geotechnical engineers can finalize their recommendations only by observing actual subsurface conditions revealed during construction. The geotechnical engineer who developed your report cannot assume responsibility or liability for the report's recommendations if that engineer does not perform construction observation, A Geotechnical Engineering Report Is Subject to Misinterpretation Other design team members' misinterpretation of geotechnical engineering reports has resulted in costly problems. Lower that risk by having your geo- technical engineer confer with appropriate members of the design team after submitting the report. Also retain your geotechnical engineer to review perti- nent elements of the design team's plans and specifications. Contractors can also misinterpret a geotechnical engineering report. Reduce that risk by having your geotechnical engineer participate in prebid and preconstruction conferences, and by providing construction observation. Do Not Redraw the Engineer's Logs Geotechnical engineers prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. To prevent errors or omissions, the logs included in a geotechnical engineering report should never be redrawn for inclusion in architectural or other design drawings. Only photographic or electronic reproduction is acceptable, but recognize that separating logs from the report can elevate risk. Give Contractors a Complete Report and Guidance Some owners and design professionals mistakenly believe they can make contractors liable for unanticipated subsurface conditions by limiting what they provide for bid preparation. To help prevent costly problems, give con- tractors the complete geotechnical engineering report, but preface it with a clearly written letter of transmittal. In that letter, advise contractors that the report was not prepared for purposes of bid development and that the report's accuracy is limited; encourage them to confer with the geotechnical engineer who prepared the report (a modest fee may be required) and/or to conduct additional study to obtain the specific types of information they need or prefer. A prebid conference can also be valuable. Be sure contrac- tors have sufficient time to perform additional study. Only then might you be in a position to give contractors the best information available to you, while requiring them to at least share some of the financial responsibilities stemming from unanticipated conditions. Read Responsibility Provisions Closely Some clients, design professionals, and contractors do not recognize that geotechnical engineering is far less exact than other engineering disci- plines. This lack of understanding has created unrealistic expectations that have led to disappointments, claims, and disputes. To help reduce the risk of such outcomes, geotechnical engineers commonly include a variety of explanatory provisions in their reports. Sometimes labeled "limitations" many of these provisions indicate where geotechnical engineers' responsi- bilities begin and end, to help others recognize their own responsibilities and risks. Read these provisions closely. Ask questions. Your geotechnical engineer should respond fully and frankly. Geoenvironmental Concerns Are Not Covered The equipment, techniques, and personnel used to perform a geoenviron- mental study differ significantly from those used to perform a geotechnical study. For that reason, a geotechnical engineering report does not usually relate any geoenvironmental findings, conclusions, or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Unanticipated environmental problems have led to numerous project failures. If you have not yet obtained your own geoen- vironmental information, ask your geotechnical consultant for risk man- agement guidance. Do not rely on an environmental report prepared for someone else. Obtain Professional Assistance To Deal with Mold Diverse strategies can be applied during building design, construction, operation, and maintenance to prevent significant amounts of mold from growing on indoor surfaces. To be effective, all such strategies should be devised for the express purpose of mold prevention, integrated into a com- prehensive plan, and executed with diligent oversight by a professional mold prevention consultant. Because just a small amount of water or moisture can lead to the development of severe mold infestations, a num- ber of mold prevention strategies focus on keeping building surfaces dry. While groundwater, water infiltration, and similar issues may have been addressed as part of the geotechnical engineering study whose findings are conveyed in -this report, the geotechnical engineer in charge of this project is not a mold prevention consultant; none of the services per- formed in connection with the geotechnical engineer's study were designed or conducted for the purpose of mold preven- tion. Proper implementation of the recommendations conveyed in this report will not of itself he sufficient to prevent mold from growing in or on the structure involved. Rely, on Your ASFE-Member Geotechncial Engineer lop Additional Assistance Membership in ASFE/The Best People on Earth exposes geotechnical engineers to a wide array of risk management techniques that can be of genuine benefit for everyone involved with a construction project. Confer with you ASFE-member geotechnical engineer for more information. ASFE 8811 Colesville Road/Suite G106, Silver Spring, MD 20910 Telephone:301/565-2733 Facsimile:301/589-2017 e-mail: info@asfe,org www.asfe.org Copyright 2004 by ASFE, fac. Duplication, reproduction, or copying of this document, in whale or fn part by any means whatsoever, is strictly prohibited, except with ASFE's specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of ASFE, and only for purposes of scholarly research or book review. Only members of ASFF may use this document as a complement to or as an element of a geotechnical engineering report. Any other firm, individual, or other entity that so uses this document without being an ASFF member could be committing negligent or intentional (fraudulent) misrepresentation. IIGER06045 OM October 31, 2017 ES-5605 Select Homes, Inc. 16531 —13th Avenue West, A107 Lynnwood, Washington 98037. Attention: Ms. Kayla Clark Dear Ms. Clark: Earth Solutions NWLLC Earth Solutions NW LLC • Geotechnical Engineering • Construction Monitoring • Environmental Sciences Earth Solutions NW, LLC (ESNW) is pleased to present this report titled "Geotechnical Engineering Study, Proposed Single -Family Residences, 9215 Bowdoin Way, Edmonds, Washington". Based on the results of our investigation, the proposed project is feasible from a geotechnical standpoint. The proposed residential structures can be constructed on conventional continuous and spread footing foundations bearing on competent native soil, recompacted native soil, or new structural fill. In general, competent native soil suitable for support of foundations will likely be encountered beginning at depths of one to two feet below existing grades. Where loose or unsuitable soil conditions are exposed at foundation subgrade elevations, compaction of soils to the specifications of structural fill, or overexcavation and replacement with suitable structural fill, will be necessary. Pertinent geotechnical recommendations are provided in this study. We appreciate the opportunity to be of service to you on this project. If you have questions regarding the content of this geotechnical engineering study, please call. Sincerely, EARTH SOLUTIONS NW, LLC Adam Z. Shier, G.I.T. Staff Geologist 1805 - 136th Place N.E., Suite 201 1 Bellevue, WA 98005 0 (425) 449-4704 1 FAX (425) 449-4711 Table of Contents ES-5606 PAGE INTRODUCTION................................................................................ General..................................................................................... 1 Proiect Description................................................................ 1 SITECONDITIONS............................................................ I ......... I ... 1— 2 Surface..................................................................................... 2 Subsurface............................................................................... 2 Topsoiland Fill............................................................. 2 NativeSoil..................................................................... 3 GeologicSetting........................................................... 3 Groundwater................................................................. 3 GEOLOGICALLY HAZARDOUS AREAS ASSESSMENT ............... 3 DISCUSSION AND RECOMMENDATIONS ........................................ 3 General..................................................................................... 3 Site Preparation and Earthwork ............................................. 4 Temporary Erosion Control ......................................... 4 In -situ and Imported Soils ............................................ 4 Subgrade Preparation .................................................. 5 StructuralFill................................................................ 5 Excavations and Slopes ............................................... 6 Foundations............................................................................. 6 Seismic Desiqn Considerations ............................................. 7 Slab -on -Grade Floors.............................................................. 7 RetainingWalls....................................................................... 7 Drainage................................................................................... 8 On -site Stormwater Management .......................................... 8 Utility Support and Trench Backfill....................................... 10 PavementSections................................................................. 10 LIMITATIONS.............. .................. ....... ................ ..... ........... ............... 10 Additional Services................................................................. 10 Earth Solutions NW, LLC Table of Contents Cont'd ES-5605 GRAPHIGS Plate 1 Vicinity Map Plate 2 Test Pit Location Plan Plate 3 Retaining Wall Drainage Detail Plate 4 Footing Drain Detail APPENDICES Appendix A Subsurface Exploration Test Pit Logs Appendix B Laboratory Test Results Grain Size Distribution Earth Solutions NW, LLC GEOTECHNICAL ENGINEERING STUDY PROPOSED SINGLE-FAMILY RESIDENCES 9215 BOWDOIN WAY EDMONDS, WASHINGTON ES-6605 INTRODUCTION General This geotechnical engineering study was prepared for the proposed single-family residential structures to be constructed at 9215 Bowdin Way in Edmonds, Washington. To complete the scope of services detailed in our proposal PES-5605 dated September 21, 2017, we performed the following: • Completing test pits for purposes of characterizing site soil conditions; • Completing laboratory testing of soil samples collected at the test pit locations; • Conducting engineering analyses, and; • Preparation of this report. The following documents and resources were reviewed as part of our report preparation; • Preliminary Site Plan, provided by Select Homes, Inc.; • Geologic Map of the Edmonds East and Part of the Edmonds West Quadrangle, Washington, prepared by James P. Minard, dated 1983; • Stormwater Management Manual for Western Washington, prepared by Department of Ecology, as amended December 2014; • Edmonds City Code, Chapter 23.80 (Geologically Hazardous Areas), and; • Online Web Soil Survey (WSS) resource, provided by United States Department of Agriculture (USDA), Natural Resources Conservation Services. Proiect Description We understand the existing single-family residential structure will be demolished and three new single-family residential structures will be constructed. We anticipate grading activities will include cuts and fills to establish the planned building alignments. Based on the existing grades, we estimate cuts to establish building pad and foundation subgrade elevations will be up to five to seven feet. However, grading plans were not available at the time this report was prepared. Site improvements will also include underground utility installations. Earth Solutions NW, LLC Select Homes, Inc. ES-5605 October 31, 2017 Page 2 Based on our previous experience with similar projects, the proposed residential structures will likely be two to three stories in height and constructed utilizing relatively lightly -loaded wood framing supported on conventional foundations. Perimeter footing loads of about one to two kips per lineal foot are expected. Slab -on -grade loading is anticipated to be approximately 150 pounds per square foot (psf). If the above design assumptions are incorrect or change, ESNW should be contacted to review the recommendations in this report. ESNW should review the final design to verify the geotechnical recommendations provided in this report have been incorporated into the plans. SITE CONDITIONS Surface The subject site located at 9215 Bowdoin Way in Edmonds, Washington, as illustrated on the Vicinity Map (Plate 1). The site consists of two. residential tax parcels (Snohomish County parcel numbers 00836400000100 and -0200) totaling approximately 0.57 acres of land area. The property is currently developed with a single-family residence and associated improvements. The site is bordered to the north by a single-family residence, to the east by Park Road, to the south by Bowdoin Way, and to the west by 92nd Place West. Site topography is relatively level, with total elevation change of approximately five feet across the site. A rockery along the southern property boundary supports the transition between the subject site and Bowdoin Way. The maximum total height of this rockery is on the order of eight feet (or less). Vegetation consists primarily of field grass throughout the property. Subsurface An ESNW representative observed, logged, and sampled five test pits, excavated at accessible locations within the proposed development area, on September 28, 2017, using a mini-trackhoe and operator provided by the client. The test pits were completed for purposes of assessing soil conditions, classifying site soils, and characterizing groundwater conditions within the proposed development area. The approximate locations of the test pits are depicted on Plate 2 (Test Pit Location Plan). Please refer to the test pit logs provided in Appendix A for a more detailed description of subsurface conditions. Representative soil samples collected at the test pit locations were analyzed in general accordance with the Unified Soil Classification System (USCS) and United States Department of Agriculture (USDA) methods and procedures. Topsoil and Fill Topsoil was generally encountered within the upper two to nine inches of existing grades at the test pit locations. The topsoil was characterized by brown color, the presence of fine organic material, and small root intrusions. Fill deposits were not encountered at the test pit locations during our fieldwork. Fill may be present, however, within proximity to existing structural improvements. Where fill is encountered during construction, ESNW should be consulted to evaluate the suitability for support of the proposed structures and/or reuse as structural fill. Earth Solutions Nw, LLC Select Homes, Inc. October 31, 2017 Native Soil ES-5605 Page 3 Underlying topsoil, native soils were characterized primarily as silty sand (Unified Soil Classification System: SM), consistent with the typical makeup of Vashon till. The upper one - and -one-half to four feet of the Vashon till was characterized as "weathered". Unweathered, dense Vashon till was encountered at -depth, extending to the maximum exploration depth of about seven feet below the existing ground surface (bgs). Geologic Setting The referenced geologic map resource *identifies Vashon till (Qvt) across the site and surrounding areas. The referenced WSS resource identifies Alderwood-Urban land complex (Map Unit Symbol: 5 and 6) across the site and surrounding areas. The Alderwood series was formed in glacial till plains. Based on our field observations, native soils on site are generally consistent with the geologic setting outlined in this section. Groundwater Groundwater seepage was not observed during our fieldwork on September 28, 2017. Groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. In general, groundwater elevations and flow rates are higher during the winter, spring and early summer months. In this respect, we anticipate groundwater seepage to be encountered in a perched condition at the contact between the upper weathered and underlying Llweathered glacial till soil during the wet season. GEOLOGICALLY HAZARDOUS AREAS ASSESSMENT As part of this geotechnical engineering study, the referenced chapter of the Edmonds City Code was reviewed. Based on our investigation and review, there are no geologically hazardous areas present on or adjacent to the site. DISCUSSION AND RECOMMENDATIONS General Based on the results of our study, construction of the proposed residential structures at the subject site is feasible from a geotechnical standpoint. The primary geotechnical considerations associated with the proposed development include foundation support, temporary excavations, low impact development feasibility, and the suitability of the on -site soils for use as structural fill. Earth Solutions NW, LLC Select Homes, Inc. ES-5605 October 31, 2017 Page 4 The proposed structures can be supported on conventional spread and continuous foundations bearing on undisturbed competent native soil, recompacted native soil, or structural fill. Competent soils suitable for support of foundations should be encountered beginning at depths of roughly one to two feet bgs across the majority of the site. Slab -on -grade floors should be supported on dense native soil, re -compacted native soil, or structural fill. Organic material exposed at subgrade elevations must be removed below design elevation and grades restored with structural fill. Where loose, organic or other unsuitable materials are encountered at or below the footing subgrade elevation, the material should be removed and replaced with structural fill, as necessary. This study has been prepared for the exclusive use of Select Homes, Inc. and their representatives. No warranty, expressed or implied, is made. This study has been prepared in a manner consistent with the level of care and skill ordinarily exercised by other members of the profession currently practicing under similar conditions in this area. Site Preparation and Earthwork Based on the existing topography, we anticipate grading for the project will involve cuts of five to seven feet to establish building pad and foundation subgrade alignments. Silt fencing and temporary erosion control measures should be placed along the perimeter of the site prior to beginning grading activities. Temporary Erosion Control Temporary construction entrances, consisting of at least six inches of quarry spalls, can be considered in order to minimize off -site soil tracking and to provide a temporary road surface. Silt fences should be placed along the margins of the property. Interceptor swales and a temporary sediment pond may be necessary for control of surface water during construction. Erosion control measures should conform to the Washington State Department of Ecology (DOE) and City of Edmonds standards. In -situ and Imported Soils From a geotechnical standpoint, native soils may not be suitable for use as structural fill unless the soils are near the optimum moisture content at the time of placement and compaction. Based on relatively appreciable fines contents, native soils should be considered moisture sensitive. Successful use of native soils as structural fill will largely be dictated by the moisture content at the time of placement and compaction. In general, on -site soils that are at (or slightly above) the optimum moisture content at the time of placement and compaction may be used as structural fill. If the on -site soils cannot be successfully compacted, the use of an imported soil may be necessary. In our opinion, if grading activities take place during months of heavy rainfall activity, a contingency should be provided in the project budget for export of soil that cannot be successfully compacted as structural fill and subsequent import of granular structural fill. Soils with fines contents greater than 5 percent typically degrade rapidly when exposed to periods of rainfall. Earth Solutions NW, LLC Select Homes, Inc. ES-5605 October 31, 2017 Page 5 Imported soil intended for use as structural fill should consist of a well -graded, granular soil with a moisture content that is at (or slightly above) the optimum level. During wet weather conditions, imported soil intended for use as structural fill should consist of a well -graded, granular soil with a fines content of 5 percent or less (where the fines content is defined as the percent passing the Number 200 sieve, based on the minus three -quarter -inch fraction). Subgrade Preparation Following site stripping and removal of the existing structure, cuts and fills will be completed to establish proposed subgrade elevations across the site. ESNW should observe the subgrade(s) during initial site preparation activities to confirm soil conditions are as anticipated and to provide supplementary recommendations for subgrade preparation, as necessary. The process of removing existing structures may produce voids where old foundations and/or crawl space areas may have been present. Complete restoration of voids resulting from demolition activities must be executed as part of overall subgrade and building pad preparation activities. The following guidelines for preparing building subgrade areas should be incorporated into the final design: • Where voids and related demolition disturbances extend below planned subgrade elevations, restoration of these areas should be completed. Structural fill should be used to restore voids or unstable areas resulting from the removal of existing structural elements. ® Recompact, or overexcavate and replace, areas of existing fill, if present, exposed at building subgrade elevations. Overexcavations should extend into competent native soils and structural fill should be utilized to restore subgrade elevations as necessary. • ESNW should confirm subgrade conditions, as well as the required level of recompaction and/or overexcavation and replacement, during site preparation activities. ESNW should also evaluate the overall suitability of prepared subgrade areas following site preparation activities. Structural Fill Structural fill is defined as compacted soil placed in foundation, slab -on -grade, and roadway areas. Fills placed to construct permanent slopes and throughout retaining wall and utility trench backfill areas are also considered structural fill. Soils placed in structural areas should be placed in loose lifts of 12 inches or less and compacted to a relative compaction of 95 percent, based on the laboratory maximum dry density as determined by the Modified Proctor Method (ASTM D-1557 Earth Solutions NW, LLC Select Homes, Inc. October 31, 2017 Excavations and Slopes ES-5605 Page 6 The Federal Occupation Safety and Health Administration (OSHA) and the Washington Industrial Safety and Health Act (WISHA) provide soil classification in terms of temporary slope inclinations. Loose native soil, existing fill, and soil where groundwater seepage is encountered are classified as Type C soils by OSHA/WISHA. Temporary slopes over four feet in height in Type C soils must be sloped no steeper than 1.5H:1V (Horizontai:Verticai). Dense to very dense glacial till soils are classified as Type A soils by OSHA/WISHA. Temporary slopes over four feet in height in Type A soils must be sloped no steeper than 0.75H:1V. The presence of perched groundwater may cause caving of the temporary slopes due to seepage forces. ESNW should observe site excavations to confirm the soil type and allowable slope inclination are appropriate for the soil exposed by the excavation. If the recommended temporary slope inclination cannot be achieved, temporary shoring may be necessary to support excavations. Permanent slopes should maintain a gradient of 2H:1V, or flatter, and should be planted with vegetation to enhance stability and to minimize erosion. A representative of ESNW should observe temporary and permanent slopes to confirm the slope inclinations are suitable for the exposed soil conditions, and to provide additional excavation and slope recommendations, as necessary. Foundations The proposed residential structures can be supported on conventional spread and continuous footings bearing on competent native soil, recompacted native soil, or structural fill. Based on the soil conditions encountered at the test pit locations, competent native soils suitable for Support of foundations should be encountered beginning at depths of roughly one to two feet below existing grades. Where loose or unsuitable soil conditions are observed at foundation subgrade elevations, compaction of the soils to the specifications of structural fill, or overexcavation and replacement with granular structural fill will be necessary. Organic material exposed at foundation subgrade elevations must be removed and grades restored with structural fill. Provided the structures will be supported as described above, the following parameters can be used for design of the new foundations: • Allowable soil bearing capacity 2,500 psf • Passive earth pressure 300 pcf (equivalent fluid) • Coefficient of friction 0.40 A one-third increase in the allowable soil bearing capacity can be assumed for short-term wind and seismic loading conditions. With structural loading as expected, total settlement in the range of one inch is anticipated, with differential settlement of about one-half inch. The majority of the settlements should occur during construction, as dead loads are applied. Earth Solutions NW, LLC Select Homes, Inc. October 31, 2017 Seismic Design Considerations ES-5605 Page 7 The 2015 IBC recognizes ASCE for seismic site class definitions. If the project will be permitted under the 2015 IBC, in accordance with Table 20.3-1 of ASCE, Minimum Design Loads for Buildings and Other Structures, Site Class D, should be used for design. In our opinion, the site is not susceptible to liquefaction. The soil relative density and the absence of an established, shallow groundwater table are the primary bases for this opinion. Slab -On -Grade Floors Slab -on -grade floors should be supported on a firm and unyielding subgrade consisting of competent native soil or at least 12 inches of structural fill. Unstable or yielding areas of the subgrade should be recompacted or overexcavated and replaced with suitable structural fill prior to construction of the slab. A capillary break consisting of a minimum of four inches of free -draining crushed rock or gravel should be placed below the slab. The free -draining material should have a fines content of 5 percent or less defined as the percent passing the Number 200 sieve, based on the minus three-quarters inch fraction. In areas where slab moisture is undesirable, installation of a vapor barrier below the slab should be considered. If used, the vapor barrier should consist of a material specifically designed to function as a vapor barrier and should be installed in accordance with the manufacturer's specifications. Retaining Walls If retaining walls will be utilized, they should be designed to resist earth pressures and applicable surcharge loads. The following parameters can be used for retaining wall design: • Active earth pressure (yielding condition) O At -rest earth pressure (restrained condition) O Traffic surcharge (passenger vehicles) O Passive earth pressure O Coefficient of friction 0 Seismic surcharge *Where H equals retained height 35 pcf 55 pcf 70 psf (rectangular distribution) 300 pcf 0.40 6H* Where sloping or other surcharge conditions will be present, supplement recommendations and design earth pressure values should be provided by ESNW. Drainage should be provided behind retaining walls such that hydrostatic pressures do not develop. If drainage is not provided, hydrostatic pressures should be included in the wall design. Earth Solutions NW, LLC Select Homes, Inc. ES-5605 October 31, 2017 Page 8 Retaining walls should be backfilled with free -draining material that extends along the height of the wall, and a distance of at least 18 inches behind the wall. The upper one foot of the wall backfill can consist of a less permeable soil, if desired. A perforated drain pipe should be placed along the base of the wall, and should be connected to an approved discharge location. A typical retaining wall drainage detail is provided as Plate 3. Drainage Groundwater seepage was not observed during our fieldwork on September 21, 2017. Water seepage is possible in site excavations, particularly in the winter, spring and early summer months. Temporary measures to control groundwater seepage and surface water runoff during construction will likely involve passive elements such as interceptor trenches and sumps, as necessary. Surface water should not be allowed to runoff over sloped areas and should not be allowed to pond near the top of sloped areas or retaining structures. Surface grades must be designed to direct water away from buildings. The grade adjacent to buildings should be sloped away from the buildings at a gradient of at least 2 percent for a horizontal distance of ten feet. In our opinion, perimeter footing drains should be installed at or below the invert of the building footings. A typical footing drain detail is provided on Plate 4 of this report. On -site Stormwater Management Pursuant to City of Edmonds stormwater management requirements, implementation of on -site stormwater BMPs are required for proposed developments in accordance with specified thresholds, standards, and lists. The intent of BMP implementation is to infiltrate, disperse, and retain stormwater runoff on site to the extent feasible. The table below summarizes our evaluation of low impact development methods, as outlined in the referenced stormwater manual, from a geotechnical standpoint. It is instructed in the referenced stormwater manual that BMPs are to be considered in the order listed (from top to bottom) for each surface type, and the first BMP that is determined to be viable should be used. For completeness, however, we have evaluated each listed BMP for the proposed surface types. Earth Solutions NW, LLC Select Homes, Inc. October 31. 2017 ES-5605 Page 9 — -- ---- - -Viable? Limitations or BMR ! Infeasibility Criteria Lawns and Landscaped Areas T5,13: Post -construction soil quality and depth vow Considered infeasible on slopes of 33 (Volume V, Chapter 5) I ' "" I percent or greater. `Roofs T5.30: The proposed project will not T5,30: Full dispersion (Volume V, Chapter 5) No preserve at least 65 percent of the site. T5.10A: The unweathered glacial till T5.10A: Downspout full infiltration systems No soils observed at relatively shallow (Volume III, Chapter 3) depths generally exhibit very poor soil infiltration characteristics. The unweathered glacial till soils Bioretention (Volume V, Chapter 7) No observed at relatively shallow depths generally exhibit very poor soil infiltration characteristics. No flooding or erosion impacts are -- T5.10B: Downspout dispersion systems No anticipated. However, adequate (Volume III, Chapter 3) vegetative flow paths are likely not available. T5.10C: Perforated stub -out connections Perforated stub -out connections are considered feasible within the upper Yes (Volume III, Chapter 3) weathered native soils. Other Hard Surfaces T5.30: Full dispersion (Volume V, Chapter 5) No The proposed project will not preserve at least 65 percent of the site. The unweathered glacial till soils T5,15: Permeable pavement (Volume V, No observed at relatively shallow depths Chapter 5) generally exhibit very poor soil infiltration characteristics, The unweathered glacial fill soils Bioretention (Volume V, Chapter 7) No observed at relatively shallow depths generally exhibit very poor soil infiltration characteristics. Sheet flow dispersion and T5.12: Sheet flow dispersion concentrated flow dispersion are not T5.11: Concentrated flow dispersion (Volume No feasible due to insufficient setbacks V, Chapter 5) and vegetated flow paths. Earth Solutions NW, LLC Select Homes, Inc. October 31, 2017 Utility Trench Support and Backfill ES-5605 Page 10 In our opinion, the soils observed at the test pit locations are generally suitable for support of utilities. In general, the soils observed at the test pit locations should be suitable for use as structural Backfill in the utility trench excavations, provided the soil is at or near the optimum moisture content at the time of placement and compaction. Moisture conditioning of the soils may be necessary at some locations prior to use as structural fill. utility ireiiuh bdGkfili should be placed and compacted to the specifications of structural fill provided in this report, or to the applicable requirements of the City of Edmonds. Pavement Sections The performance of site pavements is largely related to the condition of the underlying subgrade. To ensure adequate pavement performance, the subgrade should be in a firm and unyielding condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement areas should be compacted to the specifications detailed in the Site Preparation and Earthwork section of this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may still exist after base grading activities. Areas of unsuitable or yielding subgrade conditions may require remedial measures such as overexcavation and replacement with structural fill or thicker crushed rock sections prior to pavement. For relatively lightly loaded pavements subjected to automobiles and occasional truck traffic, the following sections can be considered for preliminary design: • Two inches of hot mix asphalt (HMA) placed over four inches of crushed rock base (CRB), or; Y Two inches of HMA placed over three inches of asphalt treated base (ATB). The HMA, CRB and ATB materials should conform to WSDOT specifications. LIMITATIONS The recommendations and conclusions provided in this geotechnical engineering study are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in the soil and groundwater conditions observed at the test pit locations may exist, and may not become evident until construction. ESNW should reevaluate the conclusions in this geotechnical engineering study if variations are encountered. Additional Services ESNW should have an opportunity to review the final design with respect to the geotechnical recommendations provided in this report. ESNW should also be retained to provide testing and consultation services during construction. Earth Solutions NW, LLC llvrr WI teul M Vfua Ot #I" lki LAS Aw r- sum v t- Ft 4 x -4 U SW I E- r Fil IfP RKA, A to &AW" Il kalvis A on MAN 13 on z"C As rMh t MrrinlOO LVU Is CQ jW ILI is 'Ism vW tl 9n, I'M tfi pr ta+a lot Armw 1T?J A111- �rxvr-v IM11121 AY 21 -4111iff r PAM TEVALDLIM SI L .. 0 a _- -- nwnNJ EPA ox SVI 9 till rN I aft, TAY Ul -9A 5 a IS C '61 4. ". t-1 rut oe Is [no's MAC - - 'd IX I A 459 :r- 11! iloTij S eo im! i I " -'s 7A A. 11144 - .. I r 1 .1 " It Mitt —31 1111111111111-M ",I Reference: NORTH Snohomish County, Washington Map 454 By The Thomas Guide Rand McNally Vicinity Map 32nd Edition 9215 Bowdoin Way Edmonds, Washington NOTE: This plate may contain areas of color. ESNW cannot be Drwn. MRS Date 10/24/2017 [Proj. No. 5605 responsible for any subsequent misinterpretation of the information Plate 1 resulting from black & white reproductions of this plate. Checked AZS Date Oct. 2017 I T - I� Tp_21 i I — ■TP-1 I 2 � I I I ( I I � I _ TP-4-I= I I I --------, 1 TP-3 Existing Lot 2 I I �✓ I ` — i Bowdoinwood I I TP-51 /30 �O/N LEGEND TP-1 Approximate Location of — ■ — ESNW Test Pit, Proj. No. ES-5605, Sept. 2017 Subject Site Proposed Lot Number NOTE: The graphics shown on this plate are not intended for design purposes or precise scale measurements, but only to illustrate the approximate test locations relative to the approximate locations of existing and / or proposed site features. The information illustrated is largely based on data provided by the client at the time of our study. ESNW cannot be responsible for subsequent design changes or interpretation of the data by others. NOTE: This plate may contain areas of color. ESNW cannot be responsible for any subsequent misinterpretation of the information resulting from black & white reproductions of this plate. NORTH 0 30 60 120 1 "=60'Scale in Feet Earth solutions NWuc Test Pit Location Plan 9215 Bowdoin Way Edmonds, Washington Drwn. MRS Date 10/24/2017 Proj. No. 5605 Checked AZS Date Oct. 2017 Plate 2 18" Min 0 o O o 0 0 0 00 0 0 O 0 00 0 00°OoOF 00 P. O00 00 0 0 0 0 0 0 0 0000 0 0 0 .0. 0 0 0 0 00 0 0 0 0 O 000� o00cO 80 00 0 ' o 0 0 0 0 0. 0 0 0 0 0 O o 00 0 0 Q 0Q 0 00 00 0 0 0 0 0 0 000 000 0 00000�� 0 000 00 0 O 0 0 0 co 0 0 0 0 O0 0 0 op o 0 0 0 `� 0 0 00op 0 C �o e og' 8 0 a 000"9 0 0 0 0 00 0..0 00 O 0 ° ' 00 00 0 ° 00000a �000 0, 0 a 0 0 0000 Oo 0 .0 0 0 NOTES: • Free -draining Backfill should consist of soil having less than 5 percent fines. Percent passing No. 4 sieve should be 25 to 75 percent. • Sheet Drain may be feasible in lieu of Free -draining Backfill, per ESNW recommendations. • Drain Pipe should consist of perforated, rigid PVC Pipe surrounded with 1-inch Drain Rock. LEGEND: 0 00o ° Free -draining Structural Backfill _„ o r• f 1-inch Drain Rock Structural Fill Perforated Rigid Drain Pipe (Surround in Drain Rock) SCHEMATIC ONLY - NOT TO SCALE NOT A CONSTRUCTION DRAWING Earth Solutions NW LLc RETAINING WALL DRAINAGE DETAIL 9215 Bowdoin Way Edmonds, Washington Drwn. MRS Date 10/24/2017 Proj. No. 5605 Checked AZS Date Oct. 2017 Plate 3 Perforated Rigid Drain Pipe (Surround in Drain Rock) NOTES: Do NOT tie roof downspouts to Footing Drain. • Surface Seal to consist of 12" of less permeable, suitable soil. Slope away from building. LEGEND: Surface Seal: native soil or other low -permeability material. R •r•r•r rrf1-inch Drain Rock ,,•, S SCHEMATIC ONLY - NOT TO SCALE NOT A CONSTRUCTION DRAWING Earth Solutions NW uc FOOTING DRAIN DETAIL 9215 Bowdoin Way Edmonds, Washington Drwn. MRS Date 10/24/2017 Proj. No. 5605 Checked AZS Date Oct. 2017 Plate 4 Appendix A Subsurface Exploration ES-5606 The subsurface conditions at the site were explored by excavating five test pits at the approximate locations illustrated on Plate 2 of this report. The test pit logs are provided in this Appendix. The subsurface exploration was completed on September 21, 2017. The test pits were excavated to a maximum depth of seven feet below existing grades. Logs of the test pits advanced by ESNW are presented in Appendix A. The final logs represent the interpretations of the field logs and the results of laboratory analyses. The stratification lines on the logs represent the approximate boundaries between soil types. In actuality, the transitions may be more gradual. Earth Solutions NW, LLC Earth Solutions NWLLC SOIL CLASSIFICATION CHART SYMBOLS TYPICAL MAJOR DIVISIONS GRAPH I LETTER DESCRIPTIONS CLEAN �� WELL -GRADED GRAVELS, GRAVEL GRAVEL GRAVELS • �'•Ah GW SAND MIXTURES, LITTLE OR NO °� FINES AND ° GRAVELLY SOILS FINES) 0 30 °3° GP POORLY -GRADED GRAVELS, GRAVEL- SAND MIXTURES, LITTLE (LITTLE OR NO o O�o 0 Q (3°Q OR NO FINES COARSE `° ° ° GRAINED GRAVELS WITH GM SILTY GRAVELS, GRAVEL -SAND - SOILS MORE THAN 50% FINES o D SILT MIXTURES OF COARSE +Q ° FRACTION RETAINED ON NO. 4 SIEVE (APPRECIABLE GC CLAYEY GRAVELS, GRAVEL- SAND - AMOUNT OF FINES) CLAY MIXTURES CLEAN SANDS SW WELL -GRADED SANDS, GRAVELLY MORE THAN 50% SAND SANDS, LITTLE OR NO FINES OF MATERIAL IS AND SP POORLY -GRADED SANDS, GRAVELLY SAND, LITTLE OR NO LARGER THAN NO. 200 SIEVE SANDY SOILS SIZE (LITTLE OR NO FINES) FINES SANDS WITH �Y� SM SILTY SANDS, SAND - SILT MORE THAN 50% FINES MIXTURES OF COARSE FRACTION PASSING ON NO. 4 SIEVE (APPRECIABLE Sc CLAYEY SANDS, SAND - CLAY AMOUNT OF FINES) MIXTURES INORGANIC SILTS AND VERY FINE ML SANDS, ROCK FLOUR, SILTY OR CLAYEY FINE SANDS OR CLAYEY SILTS WITH SLIGHT PLASTICITY SILTS INORGANIC CLAYS OF LOW TO FINE LIQUID LIMIT AND CL MEDIUM PLASTICITY, GRAVELLY GRAINED CLAYS LESS THAN 50 CLAYS, LEAN C AYCLAYS, SANDY CLAYS, SILTY SOILS OL ORGANIC SILTS AND ORGANIC — — — SILTY CLAYS OF LOW PLASTICITY MORE THAN 50% INORGANIC SILTS, MICACEOUS OR OF MATERIAL IS MH DIATOMACEOUS FINE SAND OR SMALLER THAN SILTY SOILS NO- 200 SIEVE SIZE SILTS LIQUID LIMIT CH INORGANIC CLAYS OF HIGH GREATER THAN 50 PLASTICITY CLAYSAND OH ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY, ORGANIC SILTS HIGHLY ORGANIC SOILS PT PEAT, HUMUS, SWAMP SOILS WITH HIGH ORGANIC CONTENTS DUAL SYMBOLS are used to indicate borderline soil classifications. The discussion in the text of this report is necessary for a proper understanding of the nature of the material presented in the attached logs. Earth Solutions NW 1805 - 136th Place N.E., Suite 201 Bellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425-449-4711 CLIENT Select Homes, Inc. PROJECT NUMBER ES-5605 DATE STARTED 9/28/17 COMPLETED 9/28/17 EXCAVATION CONTRACTOR Client Provided EXCAVATION METHOD LOGGED BY AZS CHECKED BY HTW NOTES Depth of Topsoil & Sod 9": grass w w vi g 0 � TESTS C6 Q O o_ Cr n TEST PIT NUMBER TP-1 PAGE 1 OF 1 PROJECT NAME. 9215 Bowdoin Way PROJECT LOCATION Edmonds, Washington GROUND ELEVATION TEST PIT SIZE GROUND WATER LEVELS: AT TIME OF EXCAVATION --- AT END OF EXCAVATION --- AFTER EXCAVATION -- MATERIAL DESCRIPTION Dark brown TOPSOIL _WS i Tan silty SAND with gravel, medium dense to dense, damp MC = 1.80% SM , I I -weakly cemented 3.0 MC = 1.50% 1 1111 Gray silty SAND, dense, damp (Unweathered Till) -weakly cemented -1 1 I SM -becomes very dense MC = 4.00% 7.0 [USDA Classification: gravelly loamy SAND] Fines = 21.00% Test pit terminated at 7.0 feet below existing grade. No groundwater encountered during excavation. No caving observed. Bottom of test pit at 7.0 feet. Earth Solutions NW TEST PIT NUMBER TP-2 1805 - 136th Place N.E., Suite 201 Bellevue, Washington 98005 PAGE 1 OF 1 Telephone: 425-449-4704 Fax: 425-449-4711 CLIENT Select Homes, Inc. PROJECT NAME _ 9215 Bowdoin Way PROJECT NUMBER ES-5605 PROJECT LOCATION Edmonds, Washington DATE STARTED 9128117 COMPLETED 9/28/17 GROUND ELEVATION TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION --- LOGGED BY AZS CHECKED BY HTW AT END OF EXCAVATION --- NOTES Depth of Topsoil & Sod 2": grass_ — AFTER EXCAVATION --- w w W TESTS 2 ¢ O MATERIAL DESCRIPTION Uj z Q C�7 w MC = 3.20% SM Tan silty SAND, medium dense, damp MC = 6.90% I —I I l4 c Gray silty SAND, dense, moist (Unweathered Till) SM -iron oxide staining, weakly cemented Test pit terminated at 7.0 feet below existing grade. No groundwater encountered during excavation. No caving observed. Bottom of test pit at 7.0 feet. Earth Solutions NW TEST PIT NUMBER TP-3 1805 - 136th Place N.E., Suite 201 PAGE 1 OF 1 Bellevue, Washington 98005 Telephone: 425-449-4704 1W& Fax: 425-449-4711 CLIENT Select Homes, Inc. PROJECT NAME 9215 Bowdoin Way PROJECT NUMBER ES-5605 PROJECT LOCATION Edmonds, Washington DATE STARTED 9/28/17 COMPLETED 9/28/17 GROUND ELEVATION TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION LOGGED BY AZS CHECKED BY HTW AT END OF EXCAVATION --- NOTES Depth of Topsoil & Sod 5':.grass AFTER EXCAVATION --- _ W 0 n_ w W wCo _j 2 0_ z co TESTS 06 :3 U O (� TPS MC = 4.30% Fines = 16.70% SM MC = 2.60% 5 SM MC = 3.70% MATERIAL DESCRIPTION Dark brown TOPSOIL Tan silty SAND, medium dense, moist -roots [USDA Classification: gravelly loamy SAND] Gray silty SAND, dense to very dense, damp (Unweathered Till) -strongly cemented, iron oxide staining Test pit terminated at 6.5 feet below existing grade due to refusal on very dense till. No groundwater encountered during excavation. No caving observed. Bottom of test pit at 6.5 feet. Earth Solutions NW TEST PIT NUMBER TP-4 1805 - 136th Place N.E., Suite 201 PAGE 1 OF 1 Bellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425-449-4711 CLIENT Select Homes, Inc. PROJECT NAME 9215 Bowdoin Way PROJECT NUMBER ES-5605 PROJECT LOCATION Edmonds, Washington DATE STARTED 9/28/17 COMPLETED 9/28/17 GROUND ELEVATION TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION — LOGGED BY AZS CHECKED BY HTW AT END OF EXCAVATION --- NOTES Depth of Topsoil & Sod 6"- 8": grass AFTER EXCAVATION --- w a v w g TESTS Q O MATERIAL DESCRIPTION M z 0 TPSL '=' " 0.5 Dark brown TOPSOIL Tan silty SAND, medium dense, damp -roots MC = 3.20% SM Fines = 18.10% [USDA Classification: very gravelly sandy LOAM] 3.5 Gray silty SAND, dense to very dense, damp (Unweathered " = MC 4.10% 5 SM -strongly cemented, iron oxide staining MC = 4.50% �—i-1 L�s o -69 Test pit terminated at 6.0 feet below existing grade aue to retusal on very groundwater encountered during excavation. No caving observed. Bottom of test pit at 6.0 feet. Solutions NW TEST PIT NUMBER TP-5 1805 - 136th Place N.E., Suite 201 - PAGE 1 OF 1 4mEarth Bellevue, Washington 98005 Telephone: 425-449-4704 Fax: 425-449-4711 CLIENT Select Homes, Inc. PROJECT NAME 9215 Bowdoin Way PROJECT NUMBER ES-5605 PROJECT LOCATION Edmonds, Washington DATE STARTED 9/28/17 _ COMPLETED 9/28/17 GROUND ELEVATION TEST PIT SIZE EXCAVATION CONTRACTOR Client Provided GROUND WATER LEVELS: EXCAVATION METHOD AT TIME OF EXCAVATION - LOGGED BY AZS CHECKED BY HTW AT END OF EXCAVATION --- NOTES Depth of Topsoil & Sod 6"_grass_ _ AFTER EXCAVATION --- w I I � U _ a W TESTS U a 0 MATERIAL DESCRIPTION ov o c6 a z c� 0 TPSL '=' 0,5 Dark brown TOPSOIL Tan silty SAND, medium dense, damp -roots MC = 4.50% SM 3.5 _ Gray silty SAND, dense, damp (Unweathered Till) MC = 3.80% 5 SM -strongly cemented MC = 4.20% _ _ 5.5 _ Test pit terminated at 6.5 feet below existing grade due to refusal on large rock. No groundwater encountered during excavation. No caving observed. Bottom of test pit at 6.5 feet. Appendix B Laboratory Test Results ES-5605 Earth Solutions NW, LLC Earth Solutions NW, LLC -- GRAIN SIZE DISTRIBUTION 1805 -136th PL N.E., Suite 201 Bellevue, WA 98005 NowTelephone: 425449-4704 Fax: 425-449-4711 CLIENT Select Homes, Inc. PROJECT NAME 9215 Bowdoin Wav PROJECT NUMBER ES-5605 PROJECT LOCATION Edmonds Washington U.S. SIEVE OPENING IN INCHES I U.S. SIEVE NUMBERS I HYDROMETER 6 4 3 2 1 5 1 1123/8 3 4 6 810 1416 20 30 40 50 60 100 140 200 100 j I I I I I I — - - 95 90 \ — — --- 85 - - 70- --- - - \ - — -- -- 65Zak h 2 — - -- — - � 60 - m '�- w 50 z - — - I- 45 z w 40 w -- -- - - ---- - -- - — - - — — - - - 35 - 30 - — - 25 - — - — - — -- — -- 20 — 15 100 10 1 01 0.01 0.001 GRAIN SIZE IN MILLIMETERS COBBLES GRAVEL SAND SILT OR CLAY coarse fine coarse I medium fine l I Specimen Identification Classification Cc Cu • TP-1 7.00ft. USDA: Gray Gravelly Loamy Sand. USCS: SM. M TP-3 1.00ft. USDA: Tan Gravelly Loamy Sand. USCS: SM with Gravel. A TP-4 2.00ft. USDA: Tan Very Gravelly Sandy Loam. USCS: SM with Gravel. Specimen Identification D100 D60 D30 0.136 D10 LL PL PI %Silt %Clay TP-1 7.0ft. 19 0.451 21.0 M TP-3 1.0ft. 19 0.847 0.207 16.7 A TP4 2.Oft. 37.5 2.267 0.195 18.1 Report Distribution ES-5605 EMAIL ONLY Select Homes, Inc. 16531 —13th Avenue West, A107 Lynnwood, Washington 98037 Attention: Ms. Kayla Clark EMAIL ONLY RAM Engineering, Inc. 16531 —13t" Avenue West, A108 Lynnwood, Washington 98037 Attention: Mr. Rob Long, P.E. Earth Solutions NW, LLC