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20250430_PWD3985_Geotech Report
Geotechnical Engineering Report Harmony at Arlington 7417 204th Street Northeast Arlington, Washington Prepared for: Harmony at Arlington, LLC 2033 E Lake Sammamish Place SE Sammamish, Washington 98075 May 21, 2024 PBS Project 73672.000 i,Nwhmw P B S BAN APEX COMPANY 4412 S CORBETT AVENUE PORTLAND, OR 97239 503.248.1939 MAIN 866.727.0140 FAX PBSUSA.COM PBS Geotechnical Engineering Report Harmony at Arlington 7417 204th Street Northeast Arlington, Washington Prepared for: Harmony at Arlington, LLC 2033 E Lake Sammamish Place SE Sammamish, Washington 98075 May 21, 2024 PBS Project 73672.000 Prepared by: Reviewed by: Cc�R J.AA1 ti F wAsk/���'� 57583 � w4 O SS10NAL Spencer Ambauen, PE Ry n White, PE, GE (OR) Senior Geotechnical Engineer Principal Geotechnical Engineer ©2024 PBS Engineering and Environmental LLC 4412 S CORBETT AVENUE, PORTLAND, OR 97239 503.248.1939 MAIN • 866.727.0140 FAX PBSUSA.COM Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Table of Contents ExecutiveSummary..............................................................................................................................................iv 1 INTRODUCTION..............................................................................................................................................1 1.1 General...........................................................................................................................................................................................1 1.2 Purpose and Scope................................................................................................................................................................... 1 1.2.1 Literature and Records Review................................................................................................................................1 1.2.2 Subsurface Explorations.............................................................................................................................................1 1.2.3 Field Infiltration Testing..............................................................................................................................................1 1.2.4 Soils Testing.................................................................................................................................................................... 1 1.2.5 Geotechnical Engineering Analysis........................................................................................................................2 1.2.6 Report Preparation.......................................................................................................................................................2 1.3 Project Understanding.............................................................................................................................................................2 2 SITE CONDITIONS...........................................................................................................................................3 2.1 Surface Description...................................................................................................................................................................3 2.2 Regional Geologic Setting.....................................................................................................................................................3 2.3 Local Geology..............................................................................................................................................................................3 2.4 Subsurface Conditions.............................................................................................................................................................3 2.5 Groundwater................................................................................................................................................................................4 2.6 Infiltration Testing.....................................................................................................................................................................5 3 SEISMIC HAZARD...........................................................................................................................................5 3.1 Liquefaction Potential..............................................................................................................................................................5 3.2 Seismicity and Faulting............................................................................................................................................................6 3.2.1 Seismic Sources..............................................................................................................................................................6 3.2.2 Crustal Earthquakes and Faults................................................................................................................................6 3.2.3 Cascadia Subduction Zone (CSZ) — Interface Earthquakes...........................................................................6 3.2.4 Intraslab Earthquakes..................................................................................................................................................6 4 CONCLUSIONS AND RECOMMENDATIONS................................................................................................7 4.1 Geotechnical Design Considerations.................................................................................................................................7 4.2 Seismic Design Considerations............................................................................................................................................7 4.2.1 Code-Based Seismic Design Parameters.............................................................................................................7 4.2.2 Liquefaction Evaluation...............................................................................................................................................8 4.3 Foundation Alternatives..........................................................................................................................................................8 4.3.1 Shallow Foundations over Ground Improvement............................................................................................8 4.3.1.1 Stone Columns..............................................................................................................................................8 4.3.2 Mat Foundations on Non-Liquefiable Crust.......................................................................................................9 4.3.2.1 Design Bearing Pressure............................................................................................................................9 4.3.2.2 Foundation Embedment Depth..............................................................................................................9 4.3.2.3 Subgrade Preparation.................................................................................................................................9 4.3.2.4 Modulus of Subgrade Reaction............................................................................................................10 4.3.2.5 Lateral Resistance.......................................................................................................................................10 4.3.3 Stiffened Conventional Foundations over Reinforced Fill...........................................................................10 4.3.3.1 Reinforced Fill..............................................................................................................................................11 4.3.3.2 Minimum Footing Widths and Design Bearing Pressure...........................................................12 May 21,2024 PBSC H An Apex Company i PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 4.3.3.3 Footing Embedment Depths..................................................................................................................12 4.3.3.4 Footing Preparation...................................................................................................................................12 4.3.3.5 Lateral Resistance.......................................................................................................................................12 4.3.3.6 Floor Slabs.....................................................................................................................................................13 4.4 Retaining Walls.........................................................................................................................................................................13 4.4.1 Wall Drainage...............................................................................................................................................................13 4.5 Temporary and Permanent Slopes...................................................................................................................................13 4.6 Ground Moisture......................................................................................................................................................................14 4.6.1 General............................................................................................................................................................................14 4.6.2 Perimeter Footing Drains.........................................................................................................................................14 4.6.3 Vapor Flow Retarder..................................................................................................................................................14 4.7 Pavement Design.....................................................................................................................................................................15 5 CONSTRUCTION RECOMMENDATIONS....................................................................................................15 5.1 Site Preparation........................................................................................................................................................................15 5.1.1 Proof rol ling/Su bgrade Verification......................................................................................................................15 5.1.2 Wet/Freezing Weather and Wet Soil Conditions...........................................................................................16 5.1.3 Compacting Test Pit Locations..............................................................................................................................16 5.2 Excavation...................................................................................................................................................................................16 5.3 Structural Fill..............................................................................................................................................................................17 5.3.1 On-Site Soil....................................................................................................................................................................17 5.3.2 Imported Granular Materials..................................................................................................................................17 5.3.3 Base Aggregate............................................................................................................................................................17 5.3.4 Foundation Base Aggregate...................................................................................................................................17 5.3.5 Trench Backfill...............................................................................................................................................................18 5.3.6 Retaining Wall Backfill...............................................................................................................................................18 5.3.7 Stabilization Material.................................................................................................................................................18 6 ADDITIONAL SERVICES AND CONSTRUCTION OBSERVATIONS............................................................19 7 LIMITATIONS................................................................................................................................................19 8 REFERENCES..................................................................................................................................................20 May 21,2024 PBSC H An Apex Company ii PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Supporting Data TABLES Table 1. Measured Groundwater Depths Table 2. Infiltration Test Results Table 3. Faults Within the Site Vicinity Table 4. 2018 IBC Seismic Design Parameters Table 5. Geogrid Reinforcement Requirements Table 6. Minimum AC Pavement Sections FIGURES Figure 1.Vicinity Map Figure 2. Site Plan Figure 3. Schematic of Reinforced Fill Zone Figure 4. Retaining Wall Earth Pressure Diagram Figure 5. Lateral Surcharge Detail APPENDICES Appendix A: Field Explorations Table A-1. Terminology Used to Describe Soil Table A-2. Key to Test Pit and Boring Log Symbols Figures Al—A4. Logs for Borings B-1 through B-4 Figure A5. Logs for Test Pits TP-1 and TP-2 Appendix B: Laboratory Testing Figure B1. Summary of Laboratory Data May 21,2024 PBSC H An Apex Company iii PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Executive Summary PBS Engineering and Environmental LLC (PBS) has prepared a Geotechnical Engineering Report (GER) for the proposed Harmony at Arlington project located at 7417 204th Street Northeast in Arlington,Washington. This Executive Summary is provided for convenience only and should only be used in conjunction with the full GER (text and attachments) for the project in design. PBS is not responsible for utilization of less than the complete report. Topic Summary Statement ReportSection The two parcels will be developed with approximately 60 three-story, three- to four-bedroom, wood-frame townhomes placed on fill a few feet above existing grades. Project 1.3 Understanding The following loads were provided by the structural engineer: • Max wall loads 2 to 4 kips per linear foot • Max slab loads 250 psf Soil profile includes: • Existing gravel fill to depths of 0.5 to 5 feet bgs • Medium dense to dense sand with silt and cobbles and silty gravel to Subsurface depths of 7.5 to 25 feet bgs 2.4 Conditions 0 Dense, well-graded sand with silt/cobbles to depths of 25 feet bgs • Liquefiable, medium dense, poorly graded sand with silt below 25 feet bgs and extending to the depths explored (31.5 to 71.5 feet bgs) Groundwater is present at depths of 9 to 17 feet bgs. Spread footing foundations over ground improvement: • Ground improvement (such as stone columns) is required • Could be designed for an allowable bearing pressure of about 3,000 psf Mat slab foundations on non-liquefiable crust: • Average allowable bearing pressure 1,000 psf • Modulus of subgrade reaction (k) 100 pounds per cubic inch (pci) Foundation 0 1.5-foot-thick crush rock pads are required 4.3 Alternatives Stiffened conventional foundations over reinforced fill: • Min 2.5-foot-thick reinforced structural fill section with geogrid • Grade beams or additional reinforcement to stiffen the footings/slabs • Allowable bearing pressure 2,000 psf • Modulus of subgrade reaction (k) 150 pounds per cubic inch (pci) Perimeter foundation drains are recommended. Soil Due to the potential for liquefaction at the site, soil improvement is 4.3.1 Improvement recommended as one alternative for the project. May 21,2024 PBS C H An Apex Company iv PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Topic Summary Statement Report Section • On-site soils are generally suitable for placement as structural fill. Site Preparation 5.1 • Existing fill may be reused if it meets the requirements for structural fill. This section contains important information about the limitations of this Limitations 7 geotechnical engineering report. May 21,2024 PBSC H An Apex Company v PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 1 INTRODUCTION 1.1 General This report presents results of PBS Engineering and Environmental LLC (PBS) geotechnical engineering services for the proposed development located at 7417 204th Street Northeast in Arlington, Washington (site). The general site location is shown on the Vicinity Map, Figure 1.The locations of PBS' explorations in relation to existing site features are shown on the Site Plan, Figure 2. PBS previously completed geotechnical engineering services for a different project (Reserve at Arlington) at the project site for Reserve at Arlington Partners LLLP, owned by AVS Community Development, LLC (AVS), and presented the results in a geotechnical engineering report (GER) dated July 8, 2019 (PBS, 2019). 1.2 Purpose and Scope The purpose of PBS' services for the Harmony at Arlington project was to develop geotechnical design and construction recommendations in support of the planned new development.This was accomplished by performing the following scope of services. 1.2.1 Literature and Records Review PBS reviewed geologic and hazard mapping of the site area and previous nearby explorations for information regarding geologic conditions and hazards at or near the site. PBS also reviewed previously completed reports for the project site and vicinity. 1.2.2 Subsurface Explorations For the previous Reserve at Arlington project, subsurface conditions were explored by completing four borings and two test pits with pilot infiltration testing. The borings were advanced to depths of 31.5 to 71.5 feet below the existing ground surface (bgs) within the development footprint.The borings were logged and representative soil samples collected by a member of the PBS geotechnical engineering staff. The approximate boring locations are shown on the Site Plan, Figure 2. The interpreted boring logs are presented as Figures Al through A4 in Appendix A, Field Explorations. The two test pits were excavated within the proposed development footprint to depths of 10 feet bgs.The test pits were logged and representative soil samples collected by a member of the PBS geotechnical engineering staff. Interpreted test pit logs are included as Figure AS in Appendix A, Field Explorations. Two piezometers were constructed within borings B-2 and B-4 to monitor the depth of groundwater and seasonal fluctuations; however, only B-4 appears to still exist on the site. No additional subsurface explorations were completed specifically for the Harmony at Arlington project. 1.2.3 Field Infiltration Testing Two small-scale pilot infiltration tests (PIT) were completed in test pits TP-1 and TP-2 within the property development at a depth of 5 feet bgs. Infiltration testing was monitored by PBS geotechnical engineering staff. 1.2.4 Soils Testing Soil samples were returned to our laboratory and classified in general accordance with the Unified Soil Classification System (ASTM D2487) and/or the Visual-Manual Procedure (ASTM D2488). Laboratory tests included natural moisture contents and grain-size analyses. Laboratory test results are included in the exploration logs in Appendix A, Field Explorations; and in Appendix B, Laboratory Testing. May 21,2024 MINE� PBS H An Apex Company 1 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 1.2.5 Geotechnical Engineering Analysis Data collected during the subsurface exploration, literature research, and testing were used to develop site- specific geotechnical design parameters and construction recommendations. 1.2.6 Report Preparation This Geotechnical Engineering Report summarizes the results of our explorations,testing, and analyses, including information relating to the following: • Field exploration logs and site plan showing approximate exploration locations • Laboratory test results • Infiltration test results • Groundwater levels and considerations • Liquefaction potential • Shallow foundation (conventional and mat slabs) recommendations: o Ground improvement o Minimum embedment o Allowable bearing pressure o Estimated settlement o Sliding coefficient • Lateral earth pressures for retaining wall design including: o Active, passive, and at-rest earth pressures o Seismic lateral force o Allowable bearing pressure o Sliding coefficient o Groundwater and drainage considerations • Earthwork and grading, cut, and fill recommendations: o Structural fill materials and preparation o Utility trench excavation and backfill requirements o Slab and pavement subgrade preparation o Wet weather considerations o Temporary and permanent slope inclinations • Seismic design criteria in accordance with the 2018 International Building Code (IBC) with state of Washington amendments • Slab-on-grade design recommendations • Asphalt concrete (AC) pavement section recommendations 1.3 Project Understanding PBS understands the client intends to develop two parcels (31051100304000 and 31051100400700) on the northwest corner of Highway 9 and 204th Street NE. Development plans are currently in the conceptual stages; however, the proposed development will include approximately 60 three-story, three-to four-bedroom, wood- frame townhomes with paved parking and drive lanes, utilities, and stormwater facilities. Based on conversations with the structural engineer, we understand loads for the three-story buildings will be about 2 to 4 kips per linear foot for walls and less than 250 pounds per square foot (psf) for floors.The extent May 21,2024 MINE� PBS H An Apex Company 2 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington of site grading is currently unknown; however, based on preliminary conversations, fills on the order of 5 feet may be required. 2 SITE CONDITIONS 2.1 Surface Description The site is currently an undeveloped rectangular parcel of land bordered to the east by Washington Highway 9, to the south by a commercial structure and paved parking area, to the west by open parcels with several outbuilding structures or sheds, and to the north by a commercial property and Portage Creek. Based on available topographic data, the site is generally flat, with the majority of ground surface elevations ranging between 120 to 122 feet above mean sea level (amsl) (NAVD88;WADNR, 2019a).The eastern portion of the property gently rises to 124 feet amsl as the site slopes to meet Highway 9. Outside of the site, the ground surface is relatively flat in all directions except for the shallow drainage of Portage Creek immediately north of the site. 2.2 Regional Geologic Setting The site is located within the northern portion of the Puget Lowland, a tectonic depression within the physiographic province that separates the Cascade Range from the Olympic Peninsula, and extends from the Puget Sound to Eugene, Oregon (Yeats et al., 1996). The Puget Lowland is situated along the Cascadia Subduction Zone (CSZ) where oceanic rocks of the Juan de Fuca Plate are subducting beneath the North American Plate, resulting in deformation and uplift of the Olympic Mountains and volcanism in the Cascade Range. Numerous faults are located throughout the Puget Lowland, including prominent east- and west- northwest-trending faults of the Darrington-Devils Mountain fault zone approximately 17 km north of the site (USGS fault no. 574) and the Utsalady Point Island fault zone approximately 24 km to the northwest of the site (USGS fault no. 573; USGS, 2019). The Arlington and greater Seattle area has been repeatedly glaciated over the last 2 million years during the systematic advance and retreat of continental ice sheets moving southward from British Columbia (Booth et al., 2009). The modern topography reflects these cyclic modes of glacial scouring during advancement of the Puget Ice Lobe, with compacted glacial till forming undulating hills (drumlins) elongated in the direction of ice flow. 2.3 Local Geology Pleistocene glacial scouring, deposition, and fluvial reworking of material dominate the topography around the site. Review of lidar topographic data indicate the hills east and west of the site have expansive northwest- trending drumlin complexes parallel to Pleistocene glacial advancement (WADNR, 2019a). North of the site, numerous river terraces, meander belts, and oxbows can be identified as the modern-day Stillaguamish River incises into and reworks glacial outwash sediments. Review of published geologic mapping of the Arlington West 7.5-minute quadrangle indicates the site is mapped within Quaternary glacial outwash of the Vashon Drift Marysville Sand Member (Minard, 1985). This unconsolidated, stratified, massive outwash sand was deposited during the early Quaternary by meltwaters flowing southward from the retreat of the Vashon Glacier near the end of the Frasier Glaciation. Thicknesses of this unit are believed to be between 60 to 120 feet within the mapped area. 2.4 Subsurface Conditions The site was previously explored by drilling four borings, designated B-1 through B-4, to depths of 31.5 to 71.5 feet bgs.The drilling was performed by Holt Services, Inc., of Seattle, Washington, using a truck-mounted CME- 85 drill rig and mud rotary drilling techniques.Two test pits, designated TP-1 and TP-2,were also excavated to May 21,2024 MINE� PBS H An Apex Company 3 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington a depth of 10 feet bgs for the purpose of infiltration testing. Test pit excavation was performed by Taylor's Excavations, Inc., of Seattle, Washington, using a track-mounted Komatsu 170LC excavator and a 36-inch toothed bucket. PBS has summarized the subsurface units as follows: GRAVEL FILL TO Variable fill consisting of well-graded gravel fill to clayey sand with gravel was CLAYEY SAND encountered at the ground surface to 5 feet bgs in boring B-2 and to 6 inches bgs in FILL (GW FILL/SC boring B-3. The material in B-2 was dense, gray to brown, moist, fine- to coarse-grained FILL): sand,with medium plasticity fines and subrounded gravels. SAND WITH SILT Sand with silt and cobbles to silty gravel was encountered in all borings and test pits: TO SILTY GRAVEL from the surface to 7.5 feet bgs in boring B-1, from 5 to 15 feet bgs in boring B-2, (SP-SM/GM ): between the surface and 25 feet bgs in boring B-3, from the surface to 10 feet bgs in boring B-4, and from the surface to approximately 4 feet bgs in test pits TP-1 and TP-2. The material was medium dense to dense, brown to gray, moist to wet, contained fine- to medium-grained sand, and non-plastic fines. WELL-GRADED Well-graded sand with cobbles was encountered in TP-1 and TP-2 from approximately 4 SAND WITH SILT feet bgs to a termination depth of 10 feet bgs and well-graded sand with silt was AND COBBLES encountered in boring B-1 from 15 to 25 feet bgs.The material was dense, light brown (SW): to brown, moist, with fine- to coarse-grained sand, rounded cobbles, and non-plastic fines. Percent passing the No. 200 sieve for samples taken at 5 feet bgs in TP-1 and TP-2 were 1%fines. POORLY Poorly graded sand with silt was encountered in all borings: below 25 feet bgs in GRADED SAND borings B-1 and B-3, below 15 feet bgs in boring B-2, and below 10 feet bgs in boring WITH SILT (SP— B-3, to termination depths of 31.5 feet bgs in borings B-1, B-2, and B-4, and to 71.5 feet SM): bgs in boring B-3.The material was medium dense, light to dark brown with areas of olive brown, moist to wet,with fine-to medium-grained sand and non-plastic fines. Percent fines passing the No. 200 sieve for this unit were between 7 to 11%. 2.5 Groundwater The depth of groundwater was not directly measured during our explorations. Piezometers were installed in borings B-2 and B-4 to obtain depths to groundwater during different times of the year. Measured groundwater depths are included in Table 1. The piezometer installed in B-2 was not accessible or did not exist during the second round of measurements, completed in 2024. Table 1. Measured Groundwater Depths Depth to Groundwater (ft bgs) Date B-2 B-4 March 1, 2019 16.9 17.2 March 26, 2024 N/A 9.0 May 21,2024 PBS H An Apex Company 4 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Please note that groundwater levels can fluctuate during the year depending on climate, irrigation season, extended periods of precipitation, drought, and other factors. 2.6 Infiltration Testing PBS previously completed two infiltration tests in test pits TP-1 and TP-2 at a depth of approximately 5 feet bgs using the small pilot infiltration test (PIT) method procedures of the 2019 Stormwater Management Manual for Western Washington (SWMMWW). Following the saturation period, water was added to the excavation to achieve a head (water height) of 1 foot.The flow rate was adjusted to maintain a relatively constant head in the test pit (static head). The flow rate and volume of water used were recorded;the water was then turned off and allowed to drain while the water level was recorded at regular time intervals. Results of our field infiltration testing are presented in Table 2. Table 2. Infiltration Test Results Depth of Steady State Falling Head Recommended Test Infiltration Infiltration Rate Infiltration Rate Infiltration Rate' Soil Classification Location Test (ft b s) (in/hr) (in/hr) (in/hr) TP-1 5 81 39 12 Well-graded SAND (SW) with cobbles TP-2 5 52 34 10.5 Well-graded SAND (SW)with cobbles Based on a total correction factor CFT=0.315;CF=0.7;CFt=0.5;CFm=0.9 The infiltration rates listed in Table 2 are not permeabilities/hydraulic conductivities, but field-measured rates. The recommended rates include correction factors related to long-term infiltration rates. In accordance with the SWMMWW, the infiltration rate obtained in the field must be reduced using correction factors that are appropriate for the design situation and the appropriate correction factors should account for the planned level of pre-treatment, maintenance, vegetation, siltation, etc. These factors account for site variability, number of tests conducted, uncertainty of the test method, and the potential for long-term clogging. Soil types can vary significantly over relatively short distances. The infiltration rates noted above are representative of discrete locations and depths. Installation of infiltration systems within the layer the field rate was measured is considered critical to proper performance of the systems. 3 SEISMIC HAZARD Seismic hazards are geologic hazards resulting from seismicity (earthquakes). Earthquakes produce shaking and ground motions that can result in damage and destruction of buildings and infrastructure, fault rupture of the ground surface, liquefaction, lateral spreading, tsunamis, earthquake-induced landslides, and seiches. Due to the location of the site away from slopes and water bodies, tsunamis, earthquake-induced landslides, seiches, and lateral spreading are not considered hazards for the site. 3.1 Liquefaction Potential Liquefaction is defined as a decrease in the shear resistance of loose, saturated, cohesionless soil (e.g., sand) or low plasticity silt soils, due to the buildup of excess pore pressures generated during an earthquake. This results in a temporary transformation of the soil deposit into a viscous fluid. Liquefaction can result in ground settlement, foundation bearing capacity failure, and lateral spreading of ground. May 21,2024 MINE� PBS H An Apex Company 5 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Based on a review of the Washington Division of Geology and Earth Resources and the Snohomish County Liquefaction Susceptibility Map (Palmer et al., 2004), the site is shown as mapped in a zone of low to moderate liquefaction hazard. Estimates of liquefaction settlement that could occur at the site as the result of a code- based earthquake are presented in section 4.2.2. 3.2 Seismicity and Faulting 3.2.1 Seismic Sources Several types of seismic sources exist in the Pacific Northwest, which are outlined below.Volcanic sources beneath the Cascade Range are not considered further in this study, as they rarely exceed about M=5.0 in size and are not considered to pose a significant ground-shaking hazard to the project site due to the distance to the Cascades. 3.2.2 Crustal Earthquakes and Faults Review of the US Geological Survey Quaternary Fault and Fold Database and WADNR Geologic hazards portal indicates the site is within close proximity(less than 25 km or 15.5 miles) to numerous faults. Due to their proximity, the crustal faults are considered potentially significant seismic sources for severe ground motion in Snohomish County. Table 3. Faults Within the Site Vicinity Fault Zone Name Fault ID Approximate Distance to Site (Surface Projection in km) Mount Washington fault zone 35 12 Devils Mountain fault 26 17 Utsalady Point fault 2120 24 Southern Whidbey Island fault zone 2210 25 3.2.3 Cascadia Subduction Zone (CSZ) — Interface Earthquakes The CSZ represents the boundary between the subducting Juan de Fuca tectonic plate and the overriding North American tectonic plate. Recurrence intervals for subduction zone earthquakes are based on studies of the geologic record, with studies estimating a recurrence interval between 500 to 530 years. Geologic evidence and written records from Japan suggest the most recent earthquake occurred in January 1700.The 1700 earthquake probably ruptured much of the approximate 620-mile (1,000 km) length of the CSZ and was estimated at moment magnitudes of Mw 9.0.The horizontal distance from the edge of the CSZ megathrust is located approximately 321 km (200 miles) west of Arlington, Washington, with an estimated depth to slab of approximately 50 km.The current US Geological Survey risk-based maximum credible earthquake for CSZ megathrust is Mw 9.0±0.2. 3.2.4 Intraslab Earthquakes Intraslab earthquakes occur within the subducting slab. They are problematic in the sense that they do not have a surface expression or rupture the ground surface, and their seismicity generates deformation along many faults within the slab. The CSZ has generated significant intraslab destructive earthquakes including the 2001 Mw 6.8 Nisqually earthquake in the Puget lowland. May 21,2024 PBS H An Apex Company 6 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 4 CONCLUSIONS AND RECOMMENDATIONS 4.1 Geotechnical Design Considerations The project site is underlain by zones of medium dense, saturated, potentially liquefiable sand containing variable amounts of silt. Due to the potential for liquefaction to occur at the site as a result of a code-based earthquake, and based on our observations and analyses, foundation support on shallow foundations is not feasible without some consideration of earthquake risk or mitigation. For our evaluation,we have considered three options for foundation support—each having different levels of risk associated with damage during an earthquake: • Conventional spread footings over ground improvement • Mat slab foundations on non-liquefiable crust • Stiffened conventional foundations over reinforced fill on non-liquefiable crust. The following sections provide a more detailed discussion of our analysis and recommendations. 4.2 Seismic Design Considerations 4.2.1 Code-Based Seismic Design Parameters The current seismic design criteria for this project are based on the 2018 International Building Code (IBC) with State of Washington amendments. According to the Site Class Map of Snohomish County, Washington (Palmer, 2004), the site is located within an area classified as Site Class D, characterizing the profile as stiff soil. Due to the potential for liquefaction of site soils, the site should be considered Site Class F. However, in accordance with ASCE 7-16, for structures having a fundamental period of less than 0.5 second, a site-response analysis is not required to determine the spectral accelerations of liquefied soils and seismic design parameters can be determined using the pre-liquefaction site class. Based on subsurface conditions encountered in our explorations combined with SPT blow counts, Site Class D is appropriate for use in design.The seismic design criteria, in accordance with the 2018 IBC, are summarized in Table 4. Table 4. 2018 IBC Seismic Design Parameters Parameter Short Period 1 Second Maximum Credible Earthquake Spectral Acceleration SS = 1.039 g S1 = 0.371 g Site Class D1 Site Coefficient Fa = 1.084 Fv = 1.9292,3 Adjusted Spectral Acceleration SMS = 1.127 g SMi = 0.716 g4 Design Spectral Response Acceleration Parameters SDs = 0.751 g SD1 = 0.477 g Adjusted Peak Ground Acceleration PGAM = 0.511 g g=Acceleration due to gravity Site Class D can be used if the fundamental period of the new structure is less than 0.5 second. If fundamental period is larger than 0.5 second,site shall be classified as Site Class F and site-specific ground motion hazard analysis will be provided in an addendum to this report. ZA ground motion hazard analysis shall be performed in accordance with the American Society of Civil Engineers'Minimum Design Loads and Associated Criteria for Buildings and Other Structures(ASCE/SEI 7-16)Section 21.2,unless exempted in accordance with Exception 2 or 3 of Section 11.4.8. s Use of site coefficient Fv= 1.929 requires adherence to Exception 2 criteria in Section 11.4.8 of ASCE 7-16. 4 Site-specific site response analysis is not required for structures on Site Class D sites with S, greater than or equal to 0.2,provided the value of the seismic response coefficient Cs is determined by Eq.(12.8-2)for values of T <_ 1.5T,and taken as equal to 1.5 times the value computed in accordance with either Eq.(12.8-3)for TL_>T> 1.5T,or Eq.(12.8-4)for T>TL. May 21,2024 PBS//An Apex Company 7 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 4.2.2 Liquefaction Evaluation The susceptibility of site soils to liquefaction (i.e., sand-like or clay-like behavior) was evaluated using criteria established by Boulanger and Idriss (2005) and Bray and Sancio (2006). The results of our analyses indicate liquefaction will likely occur in layers below depths of 25 to 35 feet bgs at the site during a code-based earthquake and probably result in 2 to 7 inches of total liquefaction-induced settlement, with less than 1 inch of differential liquefaction settlement over 30 feet. The risk of surface manifestation of liquefaction is reduced at the site by the presence of the existing non- liquefiable layer at the surface (i.e., "crust").This crust is approximately 20 to 40 feet thick (represented by the unsaturated and non-liquefiable soil). Using the estimated ground surface acceleration associated with a code- based earthquake, methods developed by Ishihara (1985), and the liquefiable layer thickness at the site, the crust would need to be on the order of 30 feet thick. Due to the relatively flat site topography, distance from the nearest free face (e.g., river or slough bank), and relative discontinuity of liquefiable layers at the site, our current opinion is that the risk of structurally damaging lateral spreading associated with liquefaction is low. 4.3 Foundation Alternatives Potential seismically induced settlement would affect the proposed building foundations; however, the presence of the existing, non-liquefiable crust would likely mask these effects. The magnitude of liquefaction- induced settlement could be reduced and/or mitigated with ground improvement, mat slab foundations, or by placing stiffened/structurally enhanced foundations over reinforced fill. A more detailed discussion of these alternatives is included in the paragraphs that follow. 4.3.1 Shallow Foundations over Ground Improvement Shallow spread footings bearing on site soils treated with ground improvement could potentially be used to support loads associated with the proposed development. Ground improvement techniques such as stone columns could be implemented to address the liquefaction hazards that are present at the site. However, due to the required depth of treatment and anticipated expense, PBS assumes ground improvement will not be economically feasible for this project. If requested, PBS can provide additional detailed ground improvement recommendations under a separate scope of services. The detailed design for ground improvement is typically completed by a design-build contractor. Depending on the settlement limitations of the new structures, improving all the potentially liquefiable soils at the site may not be necessary. 4.3.1.1 Stone Columns Stone columns could be designed to provide suitable static support for building foundations and possibly reduce the risk of liquefaction, but may not be as effective where sands contain large amounts of fine-grained silt or in predominantly silt soils. Installation of stone columns is a common method to mitigate liquefaction. Stone columns incorporate a vibratory probe that is advanced to the target depth, with the void created filled with compacted crushed rock as the probe is extracted, creating a series of stone columns.Advancing the probe as it vibrates can densify loose cohesionless sand, while the replacement with crushed rock acts to improve soft, fine-grained soils that cannot be densified due to their fine-grained nature by reinforcing them with better materials. Stone columns also provide a path for faster dissipation of excess pore water pressures during earthquake events, further reducing liquefaction potential. May 21,2024 MINE� PBS H An Apex Company 8 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Depending on the application, stone columns can be 2 to 3 feet in diameter and installed in a grid at about 6 to 10 feet on-center. The actual diameter and spacing is typically determined by a specialty subcontractor,with the design reviewed by the geotechnical engineer of record.The extent beyond the intended area of improvement is typically one-third the depth of improvement. Stone columns can be used in conjunction with appropriately designed building foundation systems, including spread footings or mats. 4.3.2 Mat Foundations on Non-Liquefiable Crust Use of mat foundations for the proposed structures would help reduce the impacts of possible differential settlement. The presence of the non-liquefiable crust does not reduce the risk of liquefaction in the deeper soils; however, our opinion is that settlement at the ground surface would be within tolerable limits for lightly loaded wood-frame structures. Mat foundations should be designed to span a distance of at least 10 feet in the case of surface manifestation of liquefaction and localized loss of ground support. Specific recommendations for design and construction are included in the following sections. This alternative requires an acceptance of risk by the owner that some settlement is likely to occur during a code-based seismic event and is representative of design and construction practices in the area. If the owner is unwilling to accept the risks of post-liquefaction settlement, ground improvement or a deep foundation system should be considered. 4.3.2.1 Design Bearing Pressure We recommend that the mat foundations be designed for an average allowable bearing pressure of 1,000 psf for combined dead plus long-term live loads, with a maximum localized bearing pressure of 1,500 psf. These pressures could be increased by up to one-third for seismic and wind loads. Subgrades should be compacted to a dense and unyielding condition prior to placement of at least 18 inches of compacted structural fill below the mat foundations. Foundations will settle in response to column and wall loads. Based on our evaluation of the subsurface conditions and our analysis, mat foundations designed and constructed as recommended in this report are estimated to undergo total post-construction settlement on the order of 1 inch under static loading conditions. Differential settlement will be on the order of one-half of the total settlement. 4.3.2.2 Foundation Embedment Depth PBS recommends that the perimeter of mat foundations be founded a minimum of 18 inches below the lowest adjacent grade.This can be accomplished with a thickened edge if the mat thickness is less than 18 inches. The foundations should be founded below an imaginary line projecting upward at a 1 H:1V(horizontal to vertical) slope from the base of any adjacent, parallel utility trenches or deeper excavations. 4.3.2.3 Subgrade Preparation Excavations for foundations should be carefully prepared to a neat and undisturbed state.A representative from PBS should confirm suitable bearing conditions and evaluate all exposed foundation subgrades. Observations should also confirm that loose or soft materials have been removed from new foundation excavation areas. Localized deepening of the excavations may be required to penetrate loose, wet, or deleterious materials. Any overexcavation should be backfilled with granular structural fill, such as clean crushed rock.The overexcavation width should extend at least one-half the overexcavation depth beyond the edges of the foundations.We suggest recompacting the exposed native subgrade prior to placing structural fill. May 21,2024 PBS H An Apex Company 9 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Satisfactory subgrade support for building mat foundations can be obtained from the on-site soil subgrade prepared in accordance with our recommendations presented in the Site Preparation, Wet/Freezing Weather and Wet Soil Conditions, and Imported Granular Materials sections of this report. A minimum 18-inch-thick layer of imported granular material should be placed and compacted over the prepared subgrade. Thicker aggregate sections may be necessary where undocumented fill is present, loose soils are present at subgrade elevation, and/or during wet conditions. Imported granular material should be composed of crushed rock or crushed gravel that is relatively well graded between coarse and fine, contains no deleterious materials, has a maximum particle size of 11/2 inch, and has less than 5% by dry weight passing the US Standard No. 200 Sieve. 4.3.2.4 Modulus of Subgrade Reaction We recommend designing the mat foundations using a preliminary modulus of vertical subgrade reaction of 100 pounds per cubic inch (pci). This value was calculated based on the allowable bearing pressure and estimated static settlement. The dimensions of the loaded area and load concentrations across the mat should be considered in evaluating the modulus of subgrade reaction.The structural engineer should consult with PBS to refine the subgrade modulus values once the structural design is finalized. 4.3.2.5 Lateral Resistance Lateral loads can be resisted by passive earth pressure on the sides of the mat and by friction on the base of the mat.A passive earth pressure calculated using an equivalent fluid weight (EFW) of 300 pounds per cubic foot (pcf) may be used for foundations confined by native soils and new structural fills.The allowable passive pressure has been reduced by a factor of two to account for the large amount of deformation required to mobilize full passive resistance.Adjacent floor slabs, pavements, or the upper 12-inch depth of adjacent unpaved areas should not be considered when calculating passive resistance. For foundations supported on new structural fills, use a coefficient of friction equal to 0.35 when calculating resistance to sliding.This value includes a factor of safety(FS) of 1.5. 4.3.3 Stiffened Conventional Foundations over Reinforced Fill As an alternative to mat foundations,the proposed lightly loaded wood-frame structures may be supported on conventional foundations bearing on the reinforced structural fill, provided the structures can be designed to accommodate anticipated static and seismic settlements. PBS recommends that the structural engineer incorporate an interconnected, grade-beam-supported floor system or include additional reinforcing steel to "stiffen" the conventional foundations (footings and slabs) so that if settlement occurs,the foundation can settle as a unit and reduce the amount of differential settlement that can occur under seismic conditions. The inclusion of an interconnected, grade-beam-supported floor system or the addition of structural steel will not address the liquefaction potential that underlies the site but it will help to reduce the damage to floor slabs and foundations that can occur during a seismic event. Considering the presence and contribution of the reinforced fill section, the stiffened footings and slabs should be designed to span a distance of at least 4 feet to accommodate potential localized loss of ground support. This alternative requires an acceptance of risk by the owner that some settlement is likely to occur during a code-based seismic event and is representative of design and construction practices in the area. If the owner is unwilling to accept the risks of post-liquefaction settlement, ground improvement or a deep foundation system should be considered. May 21,2024 PBS H An Apex Company 10 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 4.3.3.1 Reinforced Fill Due to the potential for surface manifestations of liquefaction (sand boils) at the site, PBS recommends including layers of geosynthetic reinforcement (geogrid) within the proposed structural fill if conventional (non-mat) foundations are used to support the proposed structures without ground improvement.The reinforcement should be placed in the lower portion of the fill to avoid conflict with utilities below the structures. The geosynthetic reinforcement will provide an economical settlement mitigation solution that creates a composite reinforced zone (reinforced soil mass) to resist liquefaction surface manifestations and provide more uniform bearing pressure to the building foundations. The reinforced zone should be at least 2.5 feet thick and extend at least 3 feet beyond the edges of structure foundations.The reinforced zone should be fully encapsulated in nonwoven separation geotextile per the Washington Department of Transportation Standard Specification (WSDOT SS) 9-33.2(1), Table 3.The separation geotextile shall be placed with a 3-foot minimum overlap at the edges between adjacent sheets. The interior of the reinforced fill zone should consist of alternating layers of compacted backfill and four equally spaced layers of geogrid reinforcement. Backfill within the reinforced zone shall consist of crushed surfacing base course (CSBC) per WSDOT SS 9-03.9(3). The CSBC should be compacted to a minimum of 95% of the maximum dry density (MDD) as determined by test method ASTM D1557 (modified proctor). The function of the geogrid reinforcement within the reinforced zone is to provide lateral confinement of the aggregate and to enhance soil arching.The tensile load in the reinforcement is estimated based on tension membrane theory and is a function of the amount of strain in the reinforcement. The initial strain of the reinforcement was limited to 2% in design.A minimum of four layers of Tensar Biaxial Geogrid BX-1100 geosynthetic reinforcement (or equivalent) should be installed with a vertical spacing of 6 inches. Figure 3 below shows the conceptual layout of separation geotextile and geogrid reinforcement in the lower portion of reinforced fill zone. Table 5 below provides additional geogrid reinforcement requirements. Gravel backfill compacted to 95% MDD ° Fopndations./ St;uctural Fill a. f _ 0.5' v_ 0.5' 2.5' 1f 0.5' l------- ------------ -- ) Separation Geotextile Geogrid Reinforcement Figure 3. Schematic of Reinforced Fill Zone The end result would be a "stiff" reinforced section of structural fill that could better tolerate total settlement and would limit differential settlements across the structural fill section. May 21,2024 PBS H An Apex Company 11 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Table S. Geogrid Reinforcement Requirements Property Value Test Method Ultimate tensile strength (both directions) 850 Ib/ft ASTM D6637-10 A Tensile strength at 5% 580 Win ASTM D6637-10 A Mass/unit area Min. 8 oz/sq.yd ASTM D5261 Aperture size 1.0 inch ASTM D4759-02 Resistance to long-term and UV degradation 100% EPA 9090 and ASTM D4355-05 Notes:Ib/ft—pounds per foot,lb/in—pounds per inch,oz/sq.yd—ounces per square yard 4.3.3.2 Minimum Footing Widths and Design Bearing Pressure Continuous wall and isolated spread footings should be at least 18 and 24 inches wide, respectively. Footings should be sized using a maximum allowable bearing pressure of 2,000 pounds per square foot (psf). This is a net bearing pressure and the weight of the footing and overlying backfill can be disregarded in calculating footing sizes. The recommended allowable bearing pressure applies to the total of dead plus long-term live loads. Allowable bearing pressures may be increased by one-third for seismic and wind loads. Footings founded on the proposed reinforced fill section will still experience static settlement in response to column and wall loads. Based on our evaluation of the subsurface conditions and our analysis, we estimate post-construction static settlement under the allowable bearing pressure will be less than 1 inch for foundation loads. Differential settlement will be on the order of one-half of the total settlement. 4.3.3.3 Footing Embedment Depths PBS recommends that all footings be founded a minimum of 18 inches below the lowest, adjacent grade. The footings should be founded below an imaginary line projecting upward at a 1 HIV slope from the base of any adjacent, parallel utility trenches or deeper excavations. 4.3.3.4 Footing Preparation A representative from PBS should confirm suitable bearing conditions and evaluate the reinforced fill and footing subgrades. Observations should also confirm that loose or soft materials have been removed from excavations and concrete slab-on-grade areas. Localized deepening of footing excavations may be required to penetrate loose, wet, or deleterious materials.Any overexcavation should be backfilled with granular structural fill, such as clean crushed rock.The overexcavation width should extend at least one-half the overexcavation depth beyond the edges of the foundations. We suggest recompacting the exposed native subgrade prior to placing structural fill. PBS recommends a minimum 4-inch-thick-layer of compacted, crushed rock be placed over the footing subgrades to help protect them from disturbance due to foot traffic and the elements.The footing subgrade (reinforced fill section) should be in a dense and undisturbed condition prior to pouring concrete. 4.3.3.5 Lateral Resistance Lateral loads can be resisted by passive earth pressure on the sides of footings and grade beams, and by friction at the base of the footings. A passive earth pressure calculated using an EFW of 300 pcf may be used for footings confined by the new structural fill.The allowable passive pressure has been reduced by a factor of two to account for the large amount of deformation required to mobilize full passive resistance. Adjacent floor slabs, pavements, or the upper 12-inch depth of adjacent unpaved areas should not be considered when May 21,2024 PBS//An Apex Company 12 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington calculating passive resistance. For footings supported on structural fills, use a coefficient of friction equal to 0.35 when calculating resistance to sliding. This value includes an FS of 1.5. 4.3.3.6 Floor Slabs PBS recommends the inclusion of structural elements and/or reinforcement to add an element of rigidity to the foundations and concrete slabs of the structures. The structural engineer should incorporate additional reinforcing steel to connect the footings to the slabs so that the structure can settle as a unit.The additional structural steel will help to reduce the amount of damage to concrete slabs. Floor slabs supported on the reinforced fill section prepared in accordance with the preceding recommendations may be designed using a modulus of subgrade reaction (k) of 150 pci. 4.4 Retaining Walls The following recommendations are based on the assumption of flat conditions in front of and behind the wall and fully drained backfill. For unrestrained walls allowed to rotate at least 0.005H about the base, where H is the height of the wall, we recommend using an active earth pressure calculated using an EFW of 35 pcf.Where walls are constrained against rotation, we recommend using an at-rest earth pressure calculated using an EFW of 55 pcf.We recommend any retaining walls founded on native soil or compacted structural fill be provided with adequate drainage and backfilled with clean, angular, crushed rock fill, in accordance with the recommendations provided in section 5.3. For seismic loading on retaining walls over 6 feet in exposed (retained) height, we recommend using a triangular distribution (seismic surcharge) equivalent using an EFW of 11 pcf.Walls should be designed by applying the active earth pressure plus the seismic loading, or applying at-rest earth pressures, whichever is greater. If vertical surcharge loads, q, are present within 0.5H of the wall, a lateral surcharge of 0.3q (for walls allowed to rotate) and 0.5q (for restrained walls) should be applied as a uniform horizontal surcharge active over the full height of the wall. These values assume that the wall is vertical and the backfill behind the wall is horizontal. Seismic lateral earth pressures were computed using the Mononobe-Okabe equation. Recommended lateral earth pressure distributions are shown on Figure 4, Retaining Wall Earth Pressure Diagram. Additional lateral pressures due to surcharge loads can be estimated using the guidelines shown on Figure 5, Lateral Surcharge Detail. Lateral loads can also be resisted by a passive resistance calculated using an EFW of 300 pcf acting against retaining walls and foundations, and by friction acting on the base of spread footings or mats using a friction coefficient of 0.35. 4.4.1 Wall Drainage Recommended lateral earth pressures assume that walls are fully drained and no hydrostatic pressures develop. For cantilevered concrete walls, a minimum 2-foot-wide zone of free-draining material should be installed immediately behind the wall. A 4-inch diameter perforated drainpipe should be installed at the base of the drain rock and routed to a suitable discharge point approved by the civil engineer. 4.5 Temporary and Permanent Slopes Temporary excavation and slopes should not exceed the limits specified by local, state, and federal regulations. The stability of temporary excavations and slopes shall be the responsibility of the contractor. We recommend that temporary slopes of up to 10 feet tall, made in fill or thicknesses of disturbed native soils, not be steeper than 1.5H:1V, and temporary slopes made in undisturbed native and glacially consolidated soils not be steeper May 21,2024 PBS H An Apex Company 13 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington than 1 HIV.The presence of seepage or groundwater may require that slopes be flattened further to remain stable. We also make the following recommendations: • Temporary cut slopes should be excavated with a smooth-bucket excavator, with the slope surface repaired if disturbed. • Upslope surface runoff should be rerouted to not run down the face of the slopes. • Slopes should be protected using plastic sheeting, flash coating, or tarps, as necessary, to reduce erosion. • The duration that excavations or slopes are open should be limited to the shortest time possible (3 months or less). • Equipment should not be allowed to induce vibration or infiltrate water above the slopes, and no surcharges are allowed within 10 feet of the slope crest. • The conditions of the excavations and slopes should be periodically observed by the geotechnical engineer. PBS understands no permanent cut or fill slopes are anticipated for the project. 4.6 Ground Moisture 4.6.1 General The perimeter ground surface and hard-scape should be sloped to drain away from all structures and away from adjacent slopes. Gutters should be tight-lined to a suitable discharge and maintained as free-flowing.All crawl spaces should be adequately ventilated and sloped to drain to a suitable, exterior discharge. 4.6.2 Perimeter Footing Drains Due to the relatively low permeability of site soils and the potential for perched groundwater at the site, we recommend perimeter foundation drains be installed around all proposed structures. The foundation subdrainage system should include a minimum 4-inch diameter perforated pipe in a drain rock envelope.A non-woven geotextile filter fabric, such as Mirafi 140N or equivalent, should be used to completely wrap the drain rock envelope, separating it from the native soil and footing backfill materials.The invert of the perimeter drain lines should be placed approximately at the bottom of footing elevation.Also,the subdrainage system should be sealed at the ground surface.The perforated subdrainage pipe should be laid to drain by gravity into a non-perforated solid pipe and finally connected to the site drainage stem at a suitable location. Water from downspouts and surface water should be independently collected and routed to a storm sewer or other positive outlet.This water must not be allowed to enter the bearing soils. 4.6.3 Vapor Flow Retarder A continuous, impervious vapor flow retarder must be installed over the ground surface in the crawl space and under slabs of all structures.Vapor flow retarders are often required by flooring manufacturers to protect flooring and adhesives from moisture intrusion and mold. Many flooring manufacturers will warrant their product only if it is installed according to their recommendations.The PBS geotechnical team can provide additional information, as necessary, to assist with vapor flow retarder selection. May 21,2024 PBS H An Apex Company 14 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 4.7 Pavement Design The provided pavement recommendations were developed based on our experience with similar developments and references the associated Washington Department of Transportation (WSDOT) specifications for construction. The minimum recommended pavement section thicknesses are provided in Table 6. Depending on weather conditions at the time of construction, a thicker aggregate base course section could be required to support construction traffic during preparation and placement of the pavement section. Table 6. Minimum AC Pavement Sections Traffic Loading AC (inches) Base Course (inches) Subgrade Pull-in Car Parking Only 3 8 Firm subgrade as verified Drive Lanes and Access 4 8 by PBS personnel* Roads *Subgrade must pass proofroll The asphalt cement binder should be selected following WSDOT SS 9-02.1(4)— Performance Graded Asphalt Binder.The AC should consist of hot mix asphalt (HMA) with a maximum lift thickness of 3 inches.The AC should conform to WSDOT SS 5-04.3(7)A— Mix Design, WSDOT SS 9-03.8(2)— HMA Test Requirements, and WSDOT SS 9-03.8(6)— HMA Proportions of Materials. The AC should be compacted to 91% of the maximum theoretical density(Rice value) of the mix, as determined in accordance with ASTM D2041, following the guidelines set in WSDOT SS 5-04.3(10)—Compaction. Heavy construction traffic on new pavements or partial pavement sections (such as base course over the prepared subgrade) will likely exceed the design loads and could potentially damage or shorten the pavement life;therefore,we recommend construction traffic not be allowed on new pavements, or that the contractor take appropriate precautions to protect the subgrade and pavement during construction. If construction traffic is to be allowed on newly constructed road sections, an allowance for this additional traffic will need to be made in the design pavement section. 5 CONSTRUCTION RECOMMENDATIONS 5.1 Site Preparation Construction of the proposed structures will involve clearing and grubbing of the existing vegetation or demolition of possible existing structures. In vegetated areas, site stripping should include removing topsoil, roots, and other deleterious materials to a minimum depth of 6 inches bgs. Demolition should include removing existing pavement, utilities, etc., throughout the proposed new development. Underground utility lines or other abandoned structural elements should also be removed. The voids resulting from removal of foundations or loose soil in utility lines should be backfilled with compacted structural fill.The base of these excavations should be excavated to stiff native subgrade before filling, with sides sloped at a minimum of 1 H:1 V to allow for uniform compaction. Materials generated during demolition should be transported off site or stockpiled in areas designated by the owner's representative. 5.1.1 Proofrolling/Subgrade Verification Following site preparation and prior to placing aggregate base over shallow foundation, floor slab, and pavement subgrades, the exposed subgrade should be evaluated either by proofrolling or another method of May 21,2024 MINE� PBS H An Apex Company 15 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington subgrade verification.The subgrade should be proofrolled with a fully loaded dump truck or similar heavy, rubber-tire construction equipment to identify unsuitable areas. If evaluation of the subgrades occurs during wet conditions, or if proofrolling the subgrades will result in disturbance, they should be evaluated by PBS using a steel foundation probe.We recommend that PBS be retained to observe the proofrolling and perform the subgrade verifications. Unsuitable areas identified during the field evaluation should be compacted to a stiff condition or be excavated and replaced with structural fill. 5.1.2 Wet/Freezing Weather and Wet Soil Conditions Due to the presence of fine-grained silt and sands in the near-surface materials at the site, construction equipment may have difficulty operating on the near-surface soils when the moisture content of the surface soil is more than a few percentage points above the optimum moisture required for compaction. Soils disturbed during site preparation activities, or unsuitable areas identified during proofrolling or probing, should be removed and replaced with compacted structural fill. Site earthwork and subgrade preparation should not be completed during freezing conditions, except for mass excavation to the subgrade design elevations.We recommend the earthwork construction at the site be performed during the dry season. Protection of the subgrade is the responsibility of the contractor. Construction of granular haul roads to the project site entrance may help reduce further damage to the pavement and disturbance of site soils. The actual thickness of haul roads and staging areas should be based on the contractors' approach to site development, and the amount and type of construction traffic.The imported granular material should be placed in one lift over the prepared undisturbed subgrade and compacted using a smooth-drum, non-vibratory roller. A geotextile fabric should be used to separate the subgrade from the imported granular material in areas of repeated construction traffic. Depending on site conditions, the geotextile should meet Washington State Department of Transportation (WSDOT) SS 9-33.2—Geosynthetic Properties for soil separation or stabilization. The geotextile should be installed in conformance with WSDOT SS 2-12.3—Construction Geosynthetic (Construction Requirements) and, as applicable, WSDOT SS 2-12.3(2)—Separation or WSDOT SS 2-12.3(3)— Stabilization. 5.1.3 Compacting Test Pit Locations The test pit excavations were backfilled using the excavator bucket and relatively minimal compactive effort; therefore, soft spots can be expected at these locations.We recommend that the relatively uncompacted soil be removed from the test pits to a depth of at least 3 feet below finished subgrade elevation in pavement areas and to full depth in building areas.The resulting excavation should be backfilled with structural fill. 5.2 Excavation The near-surface soils at the site can be excavated with conventional earthwork equipment. Sloughing and caving should be anticipated. All excavations should be made in accordance with applicable Occupational Safety and Health Administration (OSHA) and state regulations.The contractor is solely responsible for adherence to the OSHA requirements. Trench cuts should stand relatively vertical to a depth of approximately 4 feet bgs, provided no groundwater seepage is present in the trench walls. Open excavation techniques may be used provided the excavation is configured in accordance with the OSHA requirements, groundwater seepage is not present, and with the understanding that some sloughing may occur. Trenches/excavations should be flattened if sloughing occurs or seepage is present. Use of a trench shield or other approved temporary shoring is recommended if vertical walls are desired for cuts deeper than 4 feet bgs. If dewatering is used, we recommend that the type and design of the dewatering system be the responsibility of the contractor, who is in the best position to choose systems that fit the overall plan of operation. May 21,2024 MINE� PBS H An Apex Company 16 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 5.3 Structural Fill The extent of site grading is currently unknown; however, PBS estimates that fills will be on the order of up to 5 feet to raise the grades within the proposed site. Structural fill should be placed over subgrade that has been prepared in conformance with the Site Preparation and Wet/Freezing Weather and Wet Soil Conditions sections of this report. Structural fill material should consist of relatively well-graded soil, or an approved rock product that is free of organic material and debris, and contains particles not greater than 4 inches nominal dimension. The suitability of soil for use as compacted structural fill will depend on the gradation and moisture content of the soil when it is placed.As the amount of fines (material finer than the US Standard No. 200 Sieve) increases, soil becomes increasingly sensitive to small changes in moisture content and compaction becomes more difficult to achieve. Soils containing more than about 5%fines cannot consistently be compacted to a dense, non-yielding condition when the water content is significantly greater(or significantly less) than optimum. If fill and excavated material will be placed on slopes steeper than 5H:1V,these must be keyed/benched into the existing slopes and installed in horizontal lifts. Vertical steps between benches should be approximately 2 feet. 5.3.1 On-Site Soil On-site soils encountered in our explorations are generally suitable for placement as structural fill during moderate, dry weather when moisture content can be maintained by air drying and/or addition of water.The fine-grained fraction of the site soils are moisture sensitive, and during wet weather, may become unworkable because of excess moisture content. In order to reduce moisture content, some aerating and drying of fine- grained soils may be required.The material should be placed in lifts with a maximum uncompacted thickness of approximately 8 inches and compacted to at least 92% of the maximum dry density, as determined by ASTM D1557 (modified proctor). 5.3.2 Imported Granular Materials Imported granular material used during periods of wet weather or for haul roads, building pad subgrades, staging areas, etc., should be pit or quarry run rock, crushed rock, or crushed gravel and sand, and should meet the specifications provided in WSDOT SS 9-03.14(2)—Select Borrow. In addition, the imported granular material should be fairly well graded between coarse and fine, and of the fraction passing the US Standard No. 4 Sieve, less than 5% by dry weight should pass the US Standard No. 200 Sieve. Imported granular material should be placed in lifts with a maximum uncompacted thickness of 9 inches and be compacted to not less than 95%of the maximum dry density, as determined by ASTM D1557. 5.3.3 Base Aggregate Base aggregate for floor slabs and beneath pavements should be clean crushed rock or crushed gravel. The base aggregate should contain no deleterious materials, meet specifications provided in WSDOT SS 9-03.9(3)— Crushed Surfacing Base Course, and have less than 5% (by dry weight) passing the US Standard No. 200 Sieve. The imported granular material should be placed in one lift and compacted to at least 95% of the maximum dry density, as determined by ASTM D1557. 5.3.4 Foundation Base Aggregate Imported granular material placed at the base of excavations for spread footings, slabs-on-grade, and other below-grade structures should be clean, crushed rock or crushed gravel and sand that is fairly well graded May 21,2024 MINE� PBS H An Apex Company 17 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington between coarse and fine. The granular materials should contain no deleterious materials, have a maximum particle size of 11/2 inch, and meet WSDOT SS 9-03.12(1)A—Gravel Backfill for Foundations (Class A).The imported granular material should be placed in one lift and compacted to not less than 95% of the maximum dry density, as determined by ASTM D1557. 5.3.5 Trench Backfill Trench backfill placed beneath, adjacent to, and for at least 2 feet above utility lines (i.e., the pipe zone) should consist of well-graded granular material with a maximum particle size of 1 inch and less than 10% by dry weight passing the US Standard No. 200 Sieve, and should meet the standards prescribed by WSDOT SS 9- 03.12(3)—Gravel Backfill for Pipe Zone Bedding. The pipe zone backfill should be compacted to at least 90% of the maximum dry density as determined by ASTM D1557, or as required by the pipe manufacturer or local building department. Within pavement areas or beneath building pads,the remainder of the trench backfill should consist of well- graded granular material with a maximum particle size of 11/2 inches, less than 10% by dry weight passing the US Standard No. 200 Sieve, and should meet standards prescribed by WSDOT SS 9-03.19— Bank Run Gravel for Trench Backfill.This material should be compacted to at least 92% of the maximum dry density, as determined by ASTM D1557, or as required by the pipe manufacturer or local building department.The upper 2 feet of the trench backfill should be compacted to at least 95% of the maximum dry density, as determined by ASTM D1557. Outside of structural improvement areas (e.g., roadway alignments or building pads), trench backfill placed above the pipe zone should consist of excavated material free of wood waste, debris, clods, or rocks greater than 6 inches in diameter and meet WSDOT SS 9-03.14— Borrow and WSDOT SS 9-03.15— Native Material for Trench Backfill. This general trench backfill should be compacted to at least 90% of the maximum dry density, as determined by ASTM D1557, or as required by the pipe manufacturer or local building department. 5.3.6 Retaining Wall Backfill Backfill material placed behind retaining walls and extending a horizontal distance of 0.5H, where H is the height of the retaining wall, should consist of granular material meeting WSDOT SS 9-03.12(2)—Gravel Backfill for Walls. We recommend the granular wall backfill be separated from general fill, native soil, and/or topsoil using a geotextile fabric that meets the requirements provided in WSDOT SS 9-33.2—Geosynthetic Properties, Table 3, for separation geotextile. The wall backfill should be compacted to a minimum of 92%of the maximum dry density, as determined by ASTM D1557. However, backfill located within a horizontal distance of 3 feet from the retaining walls should only be compacted to approximately 90% of the maximum dry density, as determined by ASTM D1557. Backfill placed within 3 feet of the wall should be compacted in lifts less than 6 inches thick using hand-operated tamping equipment (such as,jumping jack or vibratory plate compactor). 5.3.7 Stabilization Material Stabilization rock should consist of pit or quarry run rock that is well-graded, angular, crushed rock consisting of 4- or 6-inch-minus material with less than 5% passing the US Standard No.4 Sieve.The material should be free of organic matter and other deleterious material. WSDOT SS 9-13.1(5)—Quarry Spalls can be used as a general specification for this material with the stipulation of limiting the maximum size to 6 inches. May 21,2024 PBS H An Apex Company 18 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 6 ADDITIONAL SERVICES AND CONSTRUCTION OBSERVATIONS In most cases, other services beyond completion of a final geotechnical engineering report are necessary or desirable to complete the project. Occasionally, conditions or circumstances arise that require additional work that was not anticipated when the geotechnical report was written. PBS offers a range of environmental, geological, geotechnical, and construction services to suit the varying needs of our clients. PBS should be retained to review the plans and specifications for this project before they are finalized. Such a review allows us to verify that our recommendations and concerns have been adequately addressed in the design. Satisfactory earthwork performance depends on the quality of construction. Sufficient observation of the contractor's activities is a key part of determining that the work is completed in accordance with the construction drawings and specifications. We recommend that PBS be retained to observe general excavation, stripping, fill placement, footing subgrades, and/or pile installation. Subsurface conditions observed during construction should be compared with those encountered during the subsurface explorations. Recognition of changed conditions requires experience; therefore, qualified personnel should visit the site with sufficient frequency to detect whether subsurface conditions change significantly from those anticipated. 7 LIMITATIONS This report has been prepared for the exclusive use of the addressee, and their architects and engineers, for aiding in the design and construction of the proposed development and is not to be relied upon by other parties. It is not to be photographed, photocopied, or similarly reproduced, in total or in part, without express written consent of the client and PBS. It is the addressee's responsibility to provide this report to the appropriate design professionals, building officials, and contractors to ensure correct implementation of the recommendations. The opinions, comments, and conclusions presented in this report are based upon information derived from our literature review, field explorations, laboratory testing, and engineering analyses. It is possible that soil, rock, or groundwater conditions could vary between or beyond the points explored. If soil, rock, or groundwater conditions are encountered during construction that differ from those described herein, the client is responsible for ensuring that PBS is notified immediately so that we may reevaluate the recommendations of this report. Unanticipated fill, soil and rock conditions, and seasonal soil moisture and groundwater variations are commonly encountered and cannot be fully determined by merely taking soil samples or completing explorations such as soil borings or test pits. Such variations may result in changes to our recommendations and may require additional funds for expenses to attain a properly constructed project;therefore, we recommend a contingency fund to accommodate such potential extra costs. The scope of work for this subsurface exploration and geotechnical report did not include environmental assessments or evaluations regarding the presence or absence of wetlands or hazardous substances in the soil, surface water, or groundwater at this site. If there is a substantial lapse of time between the submission of this report and the start of work at the site, if conditions have changed due to natural causes or construction operations at or adjacent to the site, or if the basic project scheme is significantly modified from that assumed, this report should be reviewed to determine the applicability of the conclusions and recommendations presented herein. Land use, site conditions (both on and off site), or other factors may change over time and could materially affect our findings;therefore, this report should not be relied upon after three years from its issue, or in the event that the site conditions change. May 21,2024 MINE� PBS H An Apex Company 19 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington 8 REFERENCES ASCE. (2016). Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 7-16). American Society of Civil Engineers. Booth, D. B., Troost, K. G., and Schimel, S.A. (2009). Geologic map of Northern Seattle (Part of the Seattle North 7.5'x15' Quadrangle), King County,Washington. US Geological Survey, Scientific Investigations Map 3036. Boulanger, R.W., and Idriss, I. M. (2005). Evaluating the Potential for Liquefaction or Cyclic Failure of Silts and Clays. Report UCD/CGM-04/01, Center for Geotechnical Modeling, University of California, Davis, CA. Bray,J.D. and Sancio, R.B. (2006). Assessment of the Liquefaction Susceptibility of Fine-Grained Soils.Journal of Geotechnical and Geoenvironmental Engineering, Vol. 132, No.9, pp. 1165-1177. IBC. (2018). International Building Code. Country Club Hills, IL: International Code Council, Inc.Washington State Amendments to the International Building Code. Ishihara, K. (1985). Stability of Natural Deposits During Earthquakes. Proc., 11th International Conference on Soil Mechanics and Foundation Engineering, ASCE 121(4), pp. 316-329. Minard, J. P. (1985) Geologic map of the Arlington West 7.5-minute quadrangle, Snohomish County, Washington: US Geological Survey, Miscellaneous Field Studies Map MF-1740, scale 1:24,000. PBS Engineering and Environmental Inc. (July 8, 2019). Reserve at Arlington, 7423 204th Street NE,Arlington, Washington. Prepared for Reserve at Arlington Partners LLLP. PBS Project 41391.004. Palmer, S. P., Magsino, S. L., Bilderback, E. L., Poelstra,J. L., Folger, D. S., Niggeman, R. A. (2004). Liquefaction Map of Snohomish County, Washington.Washington State Department of Natural Resources. US Geological Survey (2019). Quaternary fault and fold database for the United States, accessed March 2019, from USGS web site: https://earthquake.usgs.gov/hazards/gfauIts/. Washington Department of Natural Resources (WADNR) Washington Lidar Portal [Interactive Map]. (2019a). Washington Department of Natural Resources.Accessed March 2019 from http://lidarportal.dnr.wa.gov/. Washington Department of Natural Resources (WADNR) Geologic Information Portal [Interactive Map]. (2019b).Washington Department of Natural Resources. Accessed March 2019 from https:Hgeologyportal.dnr.wa.gov/. Washington State Department of Ecology (2019). Stormwater Management Manual for Western Washington, publication number 14-10-055. Washington State Department of Transportation (WSDOT SS). (2023). Standard Specifications for Road, Bridge, and Municipal Construction, M 41-10, Olympia, Washington. Yeats, R. S., Graven, E. P., Werner, K. S., Goldfinger, Chris, and Popowski, T.A. (1996). Tectonics of the Willamette Valley, Oregon, in Rogers, A. M., Walsh, T.J., Kockelman, W.J., and Priest, G. R., eds., Assessing earthquake hazards and reducing risk in the Pacific Northwest: US Geological Survey Professional Paper 1650, v. 1, p. 183-222. May 21,2024 PBS H An Apex Company 20 PBS Project 73672.000 IMPOPIOnt InfOPM81100 Rhout GeolechnicalmEngineeping SubWhile . . . following . . . . . _ . .cost overruns, claims, and help. The Geoprofessional Business Association (GBA) will not likely meet the needs of a civil-works constructor or even a has prepared this advisory to help you—assumedly different civil engineer.Because each geotechnical-engineering study a client representative—interpret and apply this is unique,each geotechnical-engineering report is unique,prepared geotechnical-engineering report as effectively as solely for the client. possible. In that way, you can benefit from a lowered Likewise,geotechnical-engineering services are performed for a specific exposure to problems associated with subsurface project and purpose.For example,it is unlikely that a geotechnical- conditions at project sites and development of engineering study for a refrigerated warehouse will be the same as them that,for decades, have been a principal cause one prepared for a parking garage;and a few borings drilled during of construction delays, cost overruns, claims, a preliminary study to evaluate site feasibility will not be adequate to and disputes. If you have questions or want more develop geotechnical design recommendations for the project. information about any of the issues discussed herein, contact your GBA-member geotechnical engineer. Do not rely on this report if your geotechnical engineer prepared it: Active engagement in GBA exposes geotechnical • for a different client; engineers to a wide array of risk-confrontation • for a different project or purpose; techniques that can be of genuine benefit for • for a different site(that may or may not include all or a portion of everyone involved with a construction project. the original site);or before important events occurred at the site or adjacent to it; e.g.,man-made events like construction or environmental Understand the Geotechnical-Engineering Services remediation,or natural events like floods,droughts,earthquakes, Provided for this Report or groundwater fluctuations. Geotechnical-engineering services typically include the planning, collection,interpretation,and analysis of exploratory data from Note,too,the reliability of a geotechnical-engineering report can widely spaced borings and/or test pits.Field data are combined be affected by the passage of time,because of factors like changed with results from laboratory tests of soil and rock samples obtained subsurface conditions;new or modified codes,standards,or from field exploration(if applicable),observations made during site regulations;or new techniques or tools.If you are the least bit uncertain reconnaissance,and historical information to form one or more models about the continued reliability of this report,contact your geotechnical of the expected subsurface conditions beneath the site.Local geology engineer before applying the recommendations in it.A minor amount and alterations of the site surface and subsurface by previous and of additional testing or analysis after the passage of time-if any is proposed construction are also important considerations.Geotechnical required at all-could prevent major problems. engineers apply their engineering training,experience,and judgment to adapt the requirements of the prospective project to the subsurface Read this Report in Full model(s). Estimates are made of the subsurface conditions that Costly problems have occurred because those relying on a geotechnical- will likely be exposed during construction as well as the expected engineering report did not read the report in its entirety.Do not rely on performance of foundations and other structures being planned and/or an executive summary.Do not read selective elements only.Read and affected by construction activities. refer to the report in full. The culmination of these geotechnical-engineering services is typically a You Need to Inform Your Geotechnical Engineer geotechnical-engineering report providing the data obtained,a discussion About Change of the subsurface model(s),the engineering and geologic engineering Your geotechnical engineer considered unique,project-specific factors assessments and analyses made,and the recommendations developed when developing the scope of study behind this report and developing to satisfy the given requirements of the project.These reports may be the confirmation-dependent recommendations the report conveys. titled investigations,explorations,studies,assessments,or evaluations. Typical changes that could erode the reliability of this report include Regardless of the title used,the geotechnical-engineering report is an those that affect: engineering interpretation of the subsurface conditions within the context - the site's size or shape; of the project and does not represent a close examination,systematic inquiry,or thorough investigation of all site and subsurface conditions. the elevation,configuration,location,orientation, function or weight of the proposed structure and Geotechnical-Engineering Services are Performed the desired performance criteria; the composition of the design team;or for Specific Purposes, Persons, and Projects, . project ownership. and At Specific Times Geotechnical engineers structure their services to meet the specific As a general rule,always inform your geotechnical engineer of project needs,goals,and risk management preferences of their clients.A or site changes-even minor ones-and request an assessment of their geotechnical-engineering study conducted for a given civil engineer impact.The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical conspicuously that you've included the material for information purposes engineer was not informed about developments the engineer otherwise only.To avoid misunderstanding,you may also want to note that would have considered. "informational purposes"means constructors have no right to rely on the interpretations,opinions,conclusions,or recommendations in the Most of the "Findings" Related in This Report report.Be certain that constructors know they may learn about specific Are Professional Opinions project requirements,including options selected from the report,only Before construction begins,geotechnical engineers explore a site's from the design drawings and specifications.Remind constructors subsurface using various sampling and testing procedures.Geotechnical that they may perform their own studies if they want to,and be sure to engineers can observe actual subsurface conditions only at those specific allow enough time to permit them to do so.Only then might you be in locations where sampling and testing is performed.The data derived from a position to give constructors the information available to you,while that sampling and testing were reviewed by your geotechnical engineer, requiring them to at least share some of the financial responsibilities who then applied professional judgement to form opinions about stemming from unanticipated conditions.Conducting prebid and subsurface conditions throughout the site.Actual sitewide-subsurface preconstruction conferences can also be valuable in this respect. conditions may differ-maybe significantly-from those indicated in this report.Confront that risk by retaining your geotechnical engineer Read Responsibility Provisions Closely to serve on the design team through project completion to obtain Some client representatives,design professionals,and constructors do informed guidance quickly,whenever needed. not realize that geotechnical engineering is far less exact than other engineering disciplines.This happens in part because soil and rock on This Report's Recommendations Are project sites are typically heterogeneous and not manufactured materials Confirmation-Dependent with well-defined engineering properties like steel and concrete.That The recommendations included in this report-including any options or lack of understanding has nurtured unrealistic expectations that have alternatives-are confirmation-dependent.In other words,they are not resulted in disappointments,delays,cost overruns,claims,and disputes. final,because the geotechnical engineer who developed them relied heavily To confront that risk,geotechnical engineers commonly include on judgement and opinion to do so.Your geotechnical engineer can finalize explanatory provisions in their reports.Sometimes labeled"limitations,' the recommendations only after observing actual subsurface conditions many of these provisions indicate where geotechnical engineers' exposed during construction.If through observation your geotechnical responsibilities begin and end,to help others recognize their own engineer confirms that the conditions assumed to exist actually do exist, responsibilities and risks.Read these provisions closely.Ask questions. the recommendations can be relied upon,assuming no other changes have Your geotechnical engineer should respond fully and frankly. occurred.The geotechnical engineer who prepared this report cannot assume responsibility or liabilityfor confirmation-dependent recommendations fyou Geoenvironmental Concerns Are Not Covered fail to retain that engineer to perform construction observation. The personnel,equipment,and techniques used to perform an environmental study-e.g.,a"phase-one"or"phase-two"environmental This Report Could Be Misinterpreted site assessment-differ significantly from those used to perform a Other design professionals'misinterpretation of geotechnical- geotechnical-engineering study.For that reason,a geotechnical-engineering engineering reports has resulted in costly problems.Confront that risk report does not usually provide environmental findings,conclusions,or by having your geotechnical engineer serve as a continuing member of recommendations;e.g.,about the likelihood of encountering underground the design team,to: storage tanks or regulated contaminants.Unanticipated subsurface • confer with other design-team members; environmental problems have led to project failures.If you have not • help develop specifications; obtained your own environmental information about the project site, review pertinent elements of other design professionals'plans and ask your geotechnical consultant for a recommendation on how to find specifications;and environmental risk-management guidance. • be available whenever geotechnical-engineering guidance is needed. Obtain Professional Assistance to Deal with You should also confront the risk of constructors misinterpreting this Moisture Infiltration and Mold report.Do so by retaining your geotechnical engineer to participate in While your geotechnical engineer may have addressed groundwater, prebid and preconstruction conferences and to perform construction- water infiltration,or similar issues in this report,the engineer's phase observations. services were not designed,conducted,or intended to prevent migration of moisture-including water vapor-from the soil Give Constructors a Complete Report and Guidance through building slabs and walls and into the building interior,where Some owners and design professionals mistakenly believe they can shift it can cause mold growth and material-performance deficiencies. unanticipated-subsurface-conditions liability to constructors by limiting Accordingly,proper implementation of the geotechnical engineer's the information they provide for bid preparation.To help prevent recommendations will not of itself be sufficient to prevent the costly,contentious problems this practice has caused,include the moisture infiltration.Confront the risk of moisture infiltration by complete geotechnical-engineering report,along with any attachments including building-envelope or mold specialists on the design team. or appendices,with your contract documents,but be certain to note Geotechnical engineers are not building-envelope or mold specialists. GEOPROFESSIONAL BUSINESS SEA ASSOCIATION Telephone:301/565-2733 e-mail:info@geoprofessional.org www.geoprofessional.org Copyright 2019 by Geoprofessional Business Association(GBA).Duplication,reproduction,or copying of this document,in whole or in part,by any means whatsoever,is strictly prohibited,except with GBAs specific written permission.Excerpting,quoting,or otherwise extracting wording from this document is permitted only with the express written permission of GBA,and only for purposes of scholarly research or book review.Only members of GBA may use this document or its wording as a complement to or as an element of a report of any kind. Any other firm,individual,or other entity that so uses this document without being a GBA member could be committing negligent or intentional(fraudulent)misrepresentation. Figures Hucxle 0pe < - N. j Arlington �r' P�.,lr ono Cree �rV�Ae Armstrong Ra Heights SYIYeguemieh � grriatbn - NCH ¢ .. 2381h St NE w5 stY �,r g I m�HeW 234ih St NE $ Q2 6 Country d/4rc tm ryryr / Nam2n Rd TwngR*n Chem,qrk� _ Z 228th St NE y OM T YW ft _ IYntl rk /,r. 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S:Lf fit` a i�• �• t � + + F �« a � v �Li�,�. r ti -� F�.C.�•#� h� .,� �1 s���', ,�✓.`,,�!� 5 r it �.. i �4� �.a��'Y4��,3�+ r j t c T• • Q� — ,�•�• ` 1 -,'^+ y4 ,�a4 :Lys�C'•�r , v fs i . iR.3,� 4"� SOURCES:Google Earth 2018 1 inch - 100 feet r 1 Feet 0 50 100 200 � S •;• �L 'tws" r SITE PLAN HARMONY AT ARLINGTON 44__ . - ARLINGTON, WASHINGTON o {�.- � 7"^ •_:;fir � t �. "' = _ - ti -, —•___`"- DATE:APR 2024 ' PROJECT: 73672.000 LU o PBS'204th FIGURE SY." SURCHARGE, q RETAINING PARAMETER VALUE Y WALL BACKFILL Ka 0.30 H ? Ko 0.50 Q 0 0 KAe 0.096 Y 115 pcf 4-INCH PERFORATED DRAIN PIPE WRAPPED IN I=111=1 I M I I: DRAIN ROCK AND GEOTEXTILE FILTER FABRIC ACTIVE SURCHARGE SEISMIC EARTH PRESSURE SURCHARGE PRESSURE (ACTIVE) PRESSURE 0 KfE �l PR PR PR %2 H 213 H %3 H KID'-I PR=Ka72 PR=Kaq H PR=OKaeY2z AT-REST EARTH SURCHARGE PRESSURE PRESSURE(AT-REST) PR PR %2 H TY3 H �E K,,yH Koq- 2 PR=Ko y 2 PR=Ko q H 09 RETAINING WALL EARTH PRESSURE DIAGRAM 736 2.000 HARMONY AT ARLINGTON FIGURE M ARLINGTON, WASHINGTON 4 X=mH ST RIP LOAD,q LINE LOAD,Qi a P/2 a Z=nH For m S 0.4: H ah= QL 0.2n 2 2 H H (0.16+n ) Form>0.4: 2 ah=n ((�-SING COS 2a) �h ah= QL 1.28m'n ah /r H (m'+n')' (P in radians) LINE LOAD PARALLEL TO WALL STRIP LOAD PARALLEL TO WALL X=mH POINT LOAD,Qp Z=nH For m S 0.4: A igir— ah� �A' _ Qv 0.28n2 H H' (0.16+n')3 Form>0.4: Q ah= Q 1.77m'n' jh H2 (m'+n2)3 Q'h=Qh COS'(1.10) NOTES: Qh 1. THESE GUIDELINES APPLY TO RIGID WALLS WITH POISSON'S O 0 A� RATIO ASSUMED TO BE 0.5 FOR BACKFILL MATERIALS. C—M 2. LATERAL PRESSURES FROM ANY COMBINATION OF ABOVE a'h LOADS MAY BE DETERMINED BY THE PRINCIPLE OF SUPERPOSITION. X=mH DISTRIBUTION OF HORIZONTAL PRESSURES VERTICAL POINT LOAD LATERAL SURCHARGE DETAIL 736 2000 P B S HARMONY AT ARLINGTON FIGURE ARLINGTON, WASHINGTON 5 Appendix A Field Explorations Table A-1 �. PBS Terminology Used to Describe Soil _ 1 of2 Soil Descriptions Soils exist in mixtures with varying proportions of components.The predominant soil, i.e.,greater than 50 percent based on total dry weight, is the primary soil type and is capitalized in our log descriptions (SAND,GRAVEL,SILT,or CLAY).Smaller percentages of other constituents in the soil mixture are indicated by use of modifier words in general accordance with the ASTM D2488-06 Visual-Manual Procedure."General Accordance" means that certain local and common descriptive practices may have been followed.In accordance with ASTM D2488-06, group symbols(such as GP or CH) are applied on the portion of soil passing the 3-inch (75mm)sieve based on visual examination.The following describes the use of soil names and modifying terms used to describe fine- and coarse-grained soils. Fine-Grained Soils(50%or greater fines passing 0.075 mm, No.200 sieve) The primary soil type, i.e., SILT or CLAY is designated through visual-manual procedures to evaluate soil toughness,dilatency, dry strength,and plasticity.The following outlines the terminology used to describe fine-grained soils, and varies from ASTM D2488 terminology in the use of some common terms. Primary soil NAME, Symbols, and Adjectives Plasticity Plasticity Description Index (PI) SILT(ML& MH) CLAY(CL&CH) ORGANIC SOIL (OL&OH) SILT Organic SILT Non-plastic 0-3 SILT Organic SILT Low plasticity 4—10 SILT/Elastic SILT Lean CLAY Organic SILT/Organic CLAY Medium Plasticity 10—20 Elastic SILT Lean/Fat CLAY Organic CLAY High Plasticity 20—40 Elastic SILT Fat CLAY Organic CLAY Very Plastic >40 Modifying terms describing secondary constituents,estimated to 5 percent increments,are applied as follows: Description %Composition With Sand %Sand >_ %Gravel With Gravel %Sand < %Gravel 15%to 25% plus No.200 Sandy %Sand >_ %Gravel <30%to 50% plus No.200 Gravelly %Sand < %Gravel Borderline Symbols, for example CH/MH, are used when soils are not distinctly in one category or when variable soil units contain more than one soil type. Dual Symbols, for example CL-ML, are used when two symbols are required in accordance with ASTM D2488. Soil Consistency terms are applied to fine-grained, plastic soils (i.e., PI > 7). Descriptive terms are based on direct measure or correlation to the Standard Penetration Test N-value as determined by ASTM D1586-84, as follows. SILT soils with low to non-plastic behavior (i.e., PI < 7) may be classified using relative density. Consistency SPT N-value Unconfined Compressive Strength Term tsf kPa Very soft Less than 2 Less than 0.25 Less than 24 Soft 2 -4 0.25 — 0.5 24—48 Medium stiff 5 -8 0.5 — 1.0 48—96 Stiff 9— 15 1.0 — 2.0 96— 192 Very stiff 16—30 2.0 — 4.0 192—383 Hard Over 30 Over 4.0 Over 383 Table A-1 A11111111111L PBSTerminology Used to Describe Soil 2of2 Soil Descriptions Coarse- Grained Soils (less than 50%fines) Coarse-grained soil descriptions, i.e., SAND or GRAVEL, are based on the portion of materials passing a 3-inch (75mm) sieve. Coarse-grained soil group symbols are applied in accordance with ASTM D2488-06 based on the degree of grading, or distribution of grain sizes of the soil. For example, well-graded sand containing a wide range of grain sizes is designated SW; poorly graded gravel, GP, contains high percentages of only certain grain sizes. Terms applied to grain sizes follow. Material NAME Particle Diameter Inches Millimeters SAND (SW or SP) 0.003—0.19 0.075—4.8 GRAVEL (GW or GP) 0.19—3 4.8—75 Additional Constituents: Cobble 3 — 12 75—300 Boulder 12— 120 300—3050 The primary soil type is capitalized, and the fines content in the soil are described as indicated by the following examples. Percentages are based on estimating amounts of fines, sand, and gravel to the nearest 5 percent. Other soil mixtures will have similar descriptive names. Example: Coarse-Grained Soil Descriptions with Fines >5%to < 15%fines (Dual Symbols) >_15%to < 50%fines Well graded GRAVEL with silt: GW-GM Silty GRAVEL: GM Poorly graded SAND with clay: SP-SC Silty SAND: SM Additional descriptive terminology applied to coarse-grained soils follow. Example: Coarse-Grained Soil Descriptions with Other Coarse-Grained Constituents Coarse-Grained Soil Containing Secondary Constituents With sand or with gravel >: 15% sand or gravel With cobbles;with boulders Any amount of cobbles or boulders. Cobble and boulder deposits may include a description of the matrix soils, as defined above. Relative Density terms are applied to granular, non-plastic soils based on direct measure or correlation to the Standard Penetration Test N-value as determined by ASTM D1586-84. Relative Density Term SPT N-value Very loose 0-4 Loose 5— 10 Medium dense 11—30 Dense 31— 50 Very dense > 50 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Appendix A: Field Explorations Al GENERAL PBS previously explored subsurface conditions at the project site by advancing four borings to depths of up to approximately 71.5 feet bgs on February 25 and 26, 2019. PBS also previously explored subsurface conditions at the project site by excavating two test pits to depths of up to 10 feet bgs on February 27, 2019, for the purpose of infiltration testing.The approximate locations of the explorations are shown on Figure 2, Site Plan. The procedures used to advance the borings and test pits, collect samples, and other field techniques are described in detail in the following paragraphs. Unless otherwise noted, all soil sampling and classification procedures followed engineering practices in general accordance with relevant ASTM procedures. "General accordance" means that certain local drilling/excavation and descriptive practices and methodologies have been followed. A2 BORINGS A2.1 Drilling Borings were advanced using a truck-mounted CME-85 drill rig provided and operated by Holt Services, Inc., of Seattle, Washington, using mud rotary drilling techniques.The borings were observed by a member of the PBS geotechnical staff, who maintained a detailed log of the subsurface conditions and materials encountered during the course of the work. A2.2 Sampling Disturbed soil samples were taken in the borings at selected depth intervals.The samples were obtained using a standard 2-inch outside diameter, split-spoon sampler following procedures prescribed for the standard penetration test (SPT). Using the SPT, the sampler is driven 18 inches into the soil using a 140-pound hammer dropped 30 inches.The number of blows required to drive the sampler the last 12 inches is defined as the standard penetration resistance (N-value).The N-value provides a measure of the relative density of granular soils such as sands and gravels, and the consistency of cohesive soils such as clays and plastic silts.The disturbed soil samples were examined by a member of the PBS geotechnical staff and then sealed in plastic bags for further examination and physical testing in our laboratory. A2.3 Boring Logs The boring logs show the various types of materials that were encountered in the borings and the depths where the materials and/or characteristics of these materials changed, although the changes may be gradual. Where material types and descriptions changed between samples,the contacts were interpreted. The types of samples taken during drilling, along with their sample identification number, are shown to the right of the classification of materials.The N-values and natural water (moisture) contents are shown farther to the right. A3 TEST PITS A3.1 Excavation Test pits were excavated using a using a track-mounted Komatsu 170LC excavator and a 36-inch bucket provided and operated by Taylor's Excavations, Inc., of Seattle, Washington.The test pits were observed by a member of the PBS geotechnical staff, who maintained a detailed log of the subsurface conditions and materials encountered during the course of the work. A3.2 Sampling Representative disturbed samples were taken at selected depths in the test pits.The disturbed soil samples were examined by a member of the PBS geotechnical staff and sealed in plastic bags for further examination. May 21,2024 PBS C H An Apex Company A-1 PBS Project 73672.000 Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington A3.3 Test Pit Logs The test pit logs show the various types of materials that were encountered in the excavations and the depths where the materials and/or characteristics of these materials changed, although the changes may be gradual. Where material types and descriptions changed between samples, the contacts were interpreted. The types of samples taken during excavation, along with their sample identification number, are shown to the right of the classification of materials.The natural water (moisture) contents are shown farther to the right. Measured seepage levels, if observed, are noted in the column to the right. A4 MATERIAL DESCRIPTION Initially, samples were classified visually in the field. Consistency, color, relative moisture, degree of plasticity, and other distinguishing characteristics of the soil samples were noted. Afterward, the samples were reexamined in the PBS laboratory,various standard classification tests were conducted, and the field classifications were modified where necessary.The terminology used in the soil classifications and other modifiers are defined in Table A-1, Terminology Used to Describe Soil. May 21,2024 PBSC H An Apex Company A-2 PBS Project 73672.000 Table A-2 iod—Ehl-ILIPBS Key To Test Pit and Boring Log Symbols SAMPLING DESCRIPTIONS �4? c °- o� zz ok 1 LOG GRAPHICS Soil and Rock Sampling Symbols Instrumentation Detail Lithology Boundary: -" - "'Ground Surface • : / separates distinct units (i.e., Fill,Alluvium, Sample Well CaD Bedrock)at Recovery Sample Well Seal approximate depths Interval Well PiDe o°c inciated Piezometer ° _ Soil-type or Material-type o _ Change Boundary: separates soil Well Screen v' -_= Sampler and material changes within the Type —Piezometer _-_-_ same lithographic unit at Ll approximate depth indicated Bottom of Hole Geotechnical Testing Acronym Explanations PP Pocket Penetrometer HYD Hydrometer Gradation TOR Torvane SIEV Sieve Gradation DCP Dynamic Cone Penetrometer DS Direct Shear ATT Atterberg Limits DD Dry Density PL Plasticity Limit CBR California Bearing Ratio LL Liquid Limit RES Resilient Modulus PI Plasticity Index VS Vane Shear P200 Percent Passing US Standard No. 200 Sieve bgs Below ground surface OC Organic Content MSL Mean Sea Level CON Consolidation HCL Hydrochloric Acid UC Unconfined Compressive Strength Details of soil and rock classification systems are available on request. Rev.oz/zoi7 HARMONY AT ARLINGTON BORING B-1 ARLINGTON,WASHINGTON PBS PBS PROJECT NUMBER: APPROX.BORING B-1 LOCATION: BAN APEX COMPANY 73672.000 (See Site Plan) Lat:--- Long:--- a p A UNCORRECTED N-VALUE v MATERIAL DESCRIPTION x z w O DYNAMIC CONE INSTALLATION AND DEPTH a c9 a- F w a PENETROMETER COMMENTS FEET NOTE: Lines representing the interface between soil/rock units of w w a 2 •MOISTURE CONTENT% 0 differing description are approximate only,inferred where p H ®RQD% ®CORE REC% Surface Conditions:Gravel between samples,and may indicate gradual transition. < 0 50 100 0.0 ;. Very dense, brown,silty GRAVEL(GM)with sand; low plasticity;fine to coarse sand;fine to coarse,subrounded gravel; moist 0 54 �U 5.0 N 50 rn Medium dense, brown,silty SAND(SM); ,.5 �M : non-plastic;fine to medium sand;trace,fine U) gravel; moist 10.0 29 U) 15.0 Dense, brown,well-graded SAND(SW-SM) 5.0 �L9 33: with silt; non-plastic;fine to coarse sand;trace, U) fine gravel; moist 20.0 becomes medium dense 18 25.0 Medium dense,dark brown, poorly graded 250 1s SAND (SIP-SM)with silt; non-plastic;fine sand; moist w 0 z a 30.0 becomes wet P200 17 P200=8% d 0 A 31.5 Final depth 31.5 feet bgs; boring backfilled with bentonite. Groundwater not measured at time of exploration due to mud rotary drilling. m a 35.0 4 m c5 2 40.0 cD 0 50 100 DRILLING METHOD:Mud Rotary-Tricone BIT DIAMETER:3 7/8 inches °m DRILLED BY:Holt Services,Inc. HAMMER EFFICIENCY PERCENT:90 FIGURE Al LOGGED BY:M.Bagley LOGGING COMPLETED:2/26/2019 Page 1 of 1 HARMONY AT ARLINGTON BORING B-2 ARLINGTON,WASHINGTON PBS PBS PROJECT NUMBER: APPROX.BORING B-2 LOCATION: BAN APEX COMPANY 73672.000 (See Site Plan) Lat:--- Long:--- a p A UNCORRECTED N-VALUE v MATERIAL DESCRIPTION x z w O DYNAMIC CONE DEPTH =c� I— w a- PENETROMETER INSTALLATION AND o_ o_ � �a FEET NOTE: Lines representing the interface between soil/rock units of Lu w a •MOISTURE CONTENT% COMMENTS V)0 differing description are approximate only,inferred where p H Q ®RQD% ®CORE REC% Surface Conditions:Gravel between samples,and may indicate gradual transition. 0 50 100 0.0 Dense, brown,clayey ; medium Y Y SAND(SC) Flush monument plasticity;fine to coarse sand; moist FILL 42 3.0 2-inch diameter Dense,gray-brown,well-graded SAND �U) PVC pipe (SW-SC)with clay and gravel; non-plastic;fine 5.0 to coarse sand;fine to coarse,subrounded 50 64 Bentonite gravel; moist �N Dense, brown with gray mottles,well-graded �' p�.. 9 Y 9 SAND(SW-SM)with silt and gravel; non-plastic;fine to coarse sand;fine to coarse, 36 a�. subrounded gravel; moist �C A: 10.0 becomes medium dense 23: U) '6Y Filter sand q .6y.. q 15.0 — ——— ———— -- -- 15.0 2-inch diameter Medium dense, light brown, poorly graded L9 slotted PVC screen SAND (SIP-SM)with silt; non-plastic;fine to medium sand;trace,fine gravel; moist 03/01/19 20.0 becomes dark brown;wet P200 15 P200=7% A Bentonite 25.0 d n 14 V) w F 0 z a 0 30.0 becomes olive-brown o? 23 v) 31.5 Final depth 31.5 feet bgs. Piezometer installed to 20 feet bgs; boring backfilled with bentonite from 20 to 31.5 feet bgs. Groundwater not measured at time of exploration due to mud rotary drilling. 35.0 4 m c5 0 40.0 cD 0 50 100 F DRILLING METHOD:Mud Rotary-Tricone BIT DIAMETER:3 7/8 inches °m DRILLED BY:Holt Services,Inc. HAMMER EFFICIENCY PERCENT:90 FIGURE A2 LOGGED BY:M.Bagley LOGGING COMPLETED:2/25/2019 Page 1 of 1 HARMONY AT ARLINGTON BORING B-3 ARLINGTON,WASHINGTON PBS PBS PROJECT NUMBER: APPROX.BORING B-3 LOCATION: BAN APEX COMPANY 73672.000 (See Site Plan) Lat:--- Long:--- a p A UNCORRECTED N-VALUE v MATERIAL DESCRIPTION x z w O DYNAMIC CONE INSTALLATION AND DEPTH a c9 a- F w a PENETROMETER COMMENTS FEET NOTE: Lines representing the interface between soil/rock units of w w a 2 •MOISTURE CONTENT% 0 differing description are approximate only,inferred where p H ®RQD% ®CORE REC% Surface Conditions:Gravel between samples,and may indicate gradual transition. < 0 50 100 0.0 GRAVEL FILL(-6 inches) 0:5 Dense, brown,silty SAND(SM); non-plastic; fine to medium sand; moist 38 A. 3.5 U) Dense,gray, poorly graded SAND (SIP-SM) d with silt and gravel; non-plastic;fine to coarse 5.0 sand;fine to coarse, rounded gravel; moist N 27 becomes medium dense, brown-gray;fine toA. o medium sand .v . �M 19 .. U) A ——— 9.5 10.o Very dense, brown poorly graded SAND (SP-SM) 55 with silt; non-plastic;fine to medium I 10.5 �� A: Isand_moist----------------� o Very dense, brown-gray, poorly graded GRAVEL(GP-GM)with silt and sand; non-plastic;fine to medium sand;fine to I 13.3 Ico_arse, rounded gravel; moist to wet__ 15.0 Medium dense, brown,well-graded_SAND P200 21 : P200=8% (SW-SM)with silt; non-plastic;fine to coarse �� A sand; moist 20.0 20.0 Medium dense, brown, poorly graded SAND b (SIP-SM)with silt and gravel;fine to medium ' sand;fine, rounded gravel; moist to wet .v . d 25.0 — —— ———— — — 25.0 P200 20 : P200=7% Medium dense, brown poorly graded SAND �n (SIP-SM)with silt; non-plastic;fine to medium A* sand;wet w 0 z a 30.0 24 d �U) 0 U) :A a a 0 m m a ? 35.0 P200 16 P200=8% �U) • 4 m 0 40.0 cD 0 50 100 DRILLING METHOD:Mud Rotary-Tricone BIT DIAMETER:3 7/8 inches °m DRILLED BY:Holt Services,Inc. HAMMER EFFICIENCY PERCENT:90 FIGURE A3 LOGGED BY:D.Eibert LOGGING COMPLETED:2/25/2019 Page 1 of 2 HARMONY AT ARLINGTON BORING B-3 ARLINGTON,WASHINGTON PBS (continued) PBS PROJECT NUMBER: APPROX.BORING B-3 LOCATION: BAN APEX COMPANYl111111111111IIIIIIIIIIIII 73672.000 (See Site Plan) Lat:--- Long:--- a p A UNCORRECTED N-VALUE v MATERIAL DESCRIPTION x z w O DYNAMIC CONE INSTALLATION AND DEPTH a c9 a- F w a PENETROMETER COMMENTS FEET NOTE: Lines representing the interface between soil/rock units of w w a 2 •MOISTURE CONTENT% 0 differing description are approximate only,inferred where p H ®RQD% ®CORE REC% Surface Conditions:Gravel between samples,and may indicate gradual transition. < 0 50 100 40.0 40.0 Medium dense, brown poorly graded SAND 0 16 (SP-SM)with silt; non-plastic;fine to medium v� sand;wet 45.0 P200 19 P200=11% �� • becomes gray 50.0 c� 18 �U 55.0 P200 h 21 : P200=9% [ AW � 60.0 26 : d 65.0 P200 22: P200=8% AP: w Rig chatter 0 z a 0 70.o becomes dense 32 w �U) v) 71.5 Final depth 71.5 feet bgs; boring backfilled with bentonite. Groundwater not measured at time of exploration due to mud rotary drilling. m a 75.0 4 m c� 0 80.0 (DI 0 50 100 DRILLING METHOD:Mud Rotary-Tricone BIT DIAMETER:3 7/8 inches °m DRILLED BY:Holt Services,Inc. HAMMER EFFICIENCY PERCENT:90 FIGURE A3 LOGGED BY:D.Eibert LOGGING COMPLETED:2/25/2019 Page of HARMONY AT ARLINGTON BORING B-4 ARLINGTON,WASHINGTON PBS PBS PROJECT NUMBER: APPROX.BORING B-4 LOCATION: BAN APEX COMPANY 73672.000 (See Site Plan) Lat:--- Long:--- a p A UNCORRECTED N-VALUE v MATERIAL DESCRIPTION x z w O DYNAMIC CONE DEPTH =c� I— w a- PENETROMETER INSTALLATION AND o_ o_ � �a FEET NOTE: Lines representing the interface between soil/rock units of Lu w a •MOISTURE CONTENT% COMMENTS 0 differing description are approximate only,inferred where p H Q ®RQD% ®CORE REC% Surface Conditions:Gravel between samples,and may indicate gradual transition. 0 50 100 0.0 ; Dense,dark brown,silty SAND(SM)with Flush monument gravel; low plasticity;fine to coarse sand;fine to coarse,subrounded gravel; moist 33 2-inch diameter �U) , ' PVC pipe Bentonite 5.0 Medium dense, brown,well-graded SAND 50 P2oo �N zo : P2oo=7°io (SW-SM)with silt and gravel; non-plastic to low U) *A plasticity;fine to coarse sand;fine,subrounded gravel; moist any. M zs o u) A. t 03/26/24 10.0 Medium dense, brown, poorly graded SAND 10.0 (SIP-SM)with silt; non-plastic;fine to medium sand; moist Filter sand 15.0 2-inch diameter becomes dark brown n 21 : slotted PVC screen v) A 1 03/01/19 20.0 1: Bentonite d 25.0 P200 18 P200=8% becomes moist to wet �n w 0 z a 30.0 24 d �U) � �: 31.5 Final depth 31.5 feet bgs; boring backfilled with bentonite. Piezometer installed to 20 feet bgs; boring backfilled with bentonite from 20 to 31.5 feet bgs. Groundwater not measured at time of exploration due to mud rotary drilling. 35.0 4 m c5 0 40.0 (DI 0 50 100 DRILLING METHOD:Mud Rotary-Tricone BIT DIAMETER:3 7/8 inches °m DRILLED BY:Holt Services,Inc. HAMMER EFFICIENCY PERCENT:90 FIGURE A4 LOGGED BY:M.Bagley LOGGING COMPLETED:2/26/2019 Page 1 of 1 HARMONY AT ARLINGTON ARLINGTON,WASHINGTON TEST PITS PBS _ PBS PROJECT NUMBER: TEST PIT LOCATION: BAN APEX COMPANY 73672.000 (See Site Plan) U w ❑ -0- DYNAMIC CONE PENETROMETER DEPT MATERIAL DESCRIPTION H a a ? a s m STATIC COMMENTS IN Q O NOTE: Lines representing the interface between soil/rock units of w U) Q g PENETROMETER FEET IY J differing description are approximate only,inferred where 0 H U) < 0 MOISTURE U' between samples,and may indicate gradual transition. CONTENT% TP.o 0 25 50 Brown,silty SAND(SM)with gravel and 0.0 cobbles; low plasticity; medium sand;coarse, subrounded gravel; moist 2.0 ---- -- — 2=0 o: .:. Light brown, poorly graded SAND (SIP)with 2.0 gravel and cobbles;fine to medium sand; coarse,subrounded gravel; moist Infiltration testing 4.0 ———— — — —— a_o completed at 5 feet Light brown,well-graded SAND(SW)with 4.0 bgs cobbles;fine to coarse sand; moist P200 ®� P200=1% W 6.0 8.0 10.0 10.0 Final depth 10.0 feet bgs;test pit backfilled with 10.0 excavated material to existing ground surface.Groundwater not encountered at time 12.0 of exploration. 14.0 Date Completed:2/27/2019 Elevation:--- Final Depth: 10 feet bgs Latitude:--- Longitude:--- TP.o 0 25 50 Brown,silty SAND(SM)with gravel,cobbles, o:o and roots; non-plastic;fine to medium sand; coarse,subrounded gravel; moist 2.0 o: .:. Light brown, poorly graded SAND (SIP)with 2.s Z gravel and cobbles;fine to medium sand; Infiltration testing 4.0 coarse,subrounded gravel; moist completed at 5 feet ____ ________________ 4_5 bgs Brown to light brown,well-graded SAND(SW) 4.5 P200 P200=1% o: with cobbles;fine to coarse sand; moist ®d) • 0 6.0 a 0 8.0 m a 10.0 10.0 Final depth 10.0 feet bgs;test pit backfilled with 10.0 excavated material to existing ground surface.Groundwater not encountered at time 12.0 of exploration. w d 14.0 w a °o Date Completed:2/27/2019 Elevation:--- Final Depth: 10 feet bgs Latitude:--- Longitude:--- EXCAVATION METHOD:Komatsu 170LC with 36"Bucket LOGGED BY:M. Bagley FIGURE A5 w EXCAVATED BY:Taylor's Excavators Inc. Page 1 of 9 Appendix 6 Laboratory Testing Geotechnical Engineering Report Harmony at Arlington Harmony at Arlington, LLC Arlington,Washington Appendix B: Laboratory Testing B1 GENERAL Samples obtained during the field explorations were examined in the PBS laboratory. The physical characteristics of the samples were noted and field classifications were modified where necessary. During the course of examination, representative samples were selected for further testing.The testing program for the soil samples included standard classification tests, which yield certain index properties of the soils important to an evaluation of soil behavior.The testing procedures are described in the following paragraphs. Unless noted otherwise, all test procedures are in general accordance with applicable ASTM standards. "General accordance" means that certain local and common descriptive practices and methodologies have been followed. B2 CLASSIFICATION TESTS B2.1 Visual Classification The soils were classified in accordance with the Unified Soil Classification System with certain other terminology, such as the relative density or consistency of the soil deposits, in general accordance with engineering practice. In determining the soil type (that is, gravel, sand, silt, or clay) the term that best described the major portion of the sample is used. Modifying terminology to further describe the samples is defined in Table A-1, Terminology Used to Describe Soil, in Appendix A. B2.2 Moisture (Water) Contents Natural moisture content determinations were made on samples of the fine-grained soils (that is, silts, clays, and silty sands).The natural moisture content is defined as the ratio of the weight of water to dry weight of soil, expressed as a percentage.The results of the moisture content determinations are presented on the exploration logs in Appendix A and on Figure B2, Summary of Laboratory Data, in Appendix B. B2.3 Grain-Size Analyses (P200 Wash) Washed sieve analyses (P200) were completed on samples to determine the portion of soil samples passing the No. 200 Sieve (i.e., silt and clay).The P200 test results are presented on the exploration logs in Appendix A and on Figure B2, Summary of Laboratory Data, in Appendix B. May 21,2024 PBSC H An Apex Company B-1 PBS Project 73672.000 SUMMARY OF LABORATORY DATA PBS HARMONY AT ARLINGTON PBS PROJECT NUMBER: BAN APEX COMPANY! ARLINGTON,WASHINGTON 73672.000 SAMPLE INFORMATION SIEVE ATTERBERG LIMITS MOISTURE DRY SAMPLE CONTENT DENSITY LIQUID PLASTIC PLASTICITY EXPLORATION SAMPLE DEPTH ELEVATION GRAVEL SAND P200 LIMIT LIMIT INDEX NUMBER NUMBER (FEET) (FEET) (PERCENT) (PCF) (PERCENT) (PERCENT) (PERCENT) (PERCENT) (PERCENT) (PERCENT) B-1 S-8 30 25.7 8 B-2 S-6 20 25.6 7 B-3 S-5 15 21.8 8 B-3 S-7 25 26.4 7 B-3 S-9 35 30.2 8 B-3 S-11 45 29.2 11 B-3 S-13 55 27.6 9 B-3 S-15 65 25.6 8 B-4 S-2 5 13.9 7 B-4 S-7 25 27.8 8 TP-1 S-1 5 5.0 4.1 1 TP-2 S-1 5 5.0 3.1 1 a m w F 0 z z a F 0 c� d w (7 a a a of m m a 'a (7 4 m r m FIGURE B1 ¢ Page 1 of 1