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18-102604Geotechnical Engineering Services Report Federal Way Free -Standing Emergency Center Federal Way, Washington for PhiloWilke Partnership September 29, 2017 GMENGINEERS.�57 1101 South Fawcett Avenue, Suite 200 Tacoma, Washington 98402 253.383.4940 Geotechnical Engineering Services Report Federal Way Free -Standing Emergency Center Federal Way, Washington File No. 2868-017-00 September 29, 2017 Prepared for: PhiloWilke Partnership 11275 Sam Houston Parkway West, Suite 200 Houston, Texas 77031 Attention: Greg Johnson, AIA, LEED AP Prepared by: GeoEngineers, Inc. 1101 South Fawcett Avenue, Suite 200 Tacoma, Washington 98402 253.383.4940 Brett E. Larabee, PE Geotechnical Engineer BEL:MM:DJT:tt :J Disclaimer. Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document The original document is stored by Geobigneers, Inc. and will serve as the official document of record. GMENGINEER� Table of Contents INTRODUCTION AND PROJECT UNDERSTANDING.................................................................................................1 SCOPEOF SERVICES.......................................................................................................................I.......................1 SITECONDITIONS.....................................................................................................................................................2 SurfaceConditions...............................................................................................................................................2 LiteratureReview.................................................................................................................................................2 SubsurfaceConditions........................................................................................................................................2 Subsurface Exploration and Laboratory Testing.........................................................................................2 Soiland Groundwater Conditions................................................................................................................3 CONCLUSIONSAND RECOMMENDATIONS............................................................................................................3 Primary Geotechnical Considerations................................................................................................................3 SeismicDesign Considerations...........................................................................................................................4 LiquefactionAnalysis....................................................................................................................................4 LateralSpreading Potential..........................................................................................................................4 SurfaceRupture Potential............................................................................................................................4 SiteDevelopment and Earthwork.......................................................................................................................5 General..........................................................................................................................................................5 Clearingand Stripping..................................................................................................................................5 Erosionand Sedimentation Control.............................................................................................................5 TemporaryExcavations.................................................................................................................................6 ExistingPermanent Slopes...........................................................................................................................6 Groundwater Handling Considerations........................................................................................................7 SurfaceDrainage..........................................................................................................................................7 SubgradePreparation...................................................................................................................................7 Subgrade Protection and Wet Weather Considerations.............................................................................7 FillMaterials.........................................................................................................................................................8 StructuralFill.................................................................................................................................................8 SelectGranular Fill........................................................................................................................................8 PipeBedding.................................................................................................................................................8 TrenchBackfill...............................................................................................................................................9 On -Site Soil....................................................................................................................................................9 FillPlacement and Compaction...................................................................................................................9 FoundationSupport .......................................................................................................................................... 10 General.......................................................................................................................................................10 Foundation Bearing Surface Preparation................................................................................................. 10 Allowable Soil Bearing Pressure................................................................................................................ 11 FoundationSettlement.............................................................................................................................. 11 LateralResistance..................................................................................................................................... 11 PerimeterFooting Drains........................................................................................................................... 12 Slab -on -Grade Floors...-. .................... _ ...... ..................................................................................................... 12 Retaining Walls and Below -Grade Structures................................................................................................. 13 DesignParameters.................................................................................................................................... 13 Drainage..................................................................................................................................................... 13 GEOENGINEERSr September29, 20171 Page i File No- 2868-017-00 StormwaterInfiltration...................................................................................................................................... 14 General.......................................................................................................................................................14 InfiltrationSuitability.................................................................................................................................. 14 Design Infiltration Rate Estimate.............................................................................................................. 14 PavementRecommendations.......................................................................................................................... 15 Conventional Asphalt Concrete Pavements............................................................................................. 15 PerviousPavement.................................................................................................................................... 16 Pavement.................................................................................................................................................... 16 PermeableBallast...................................................................................................................................... 17 TreatmentLayer......................................................................................................................................... 17 SubgradePreparation................................................................................................................................ 17 Protection, Maintenance and Icing........................................................................................................... 18 LIMITATIONS.................................................. 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I............................. 18 LIST OF FIGURES Figure 1. Vicinity Map Figure 2. Site Plan APPENDICES Appendix A. Subsurface Explorations and Laboratory Testing Figure A-1 - Key to Exploration Logs Figure A-2 through A-7 - Logs of Borings Figures A-8 and A-9 - Sieve Analysis Results Appendix B. Report Limitations and Guidelines for Use GEOENGINEER5 September29, 2017 Page ii .15 File No 2668-017-00 INTRODUCTION AND PROJECT UNDERSTANDING This report presents the results of our geotechnical engineering services for the proposed Free -Standing Emergency Center in Federal Way, Washington. The project site is located at 29805 Pacific Highway South as shown on the Vicinity Map, Figure 1. Our understanding of the project is based on our discussions with PhiloWilke, information provided including a preliminary Site Plan dated August 16, 2017, and our experience working on the Free -Standing Emergency Center Projects. We understand that this site is under evaluation for constructing a single -story emergency center. The conceptual Site Plan shows that the proposed building would be located near the center of the site with parking, access roads, and landscaping located around the building. We understand that the proposed building would be about 9,600 square feet and will be steel -framed with an exterior clad in masonry, metal panels and glazing. Parking areas at the site would be paved to accommodate patient parking with an ambulance bay abutting the building. The preferred foundation system for the structure is conventional spread and continuous footings. We understand that stormwater infiltration facilities such as permeable pavements may be considered as part of the development. We understand that stormwater facilities will be designed in accordance with the 2016 King County Surface Water Design Manual (SWDM), which has been adopted by the City of Federal Way. SCOPE OF SERVICES The purpose of our services is to explore subsurface conditions to form a basis for providing geotechnical design and construction recommendations for the proposed site improvements. Our services have been completed in general accordance with our signed agreement dated June 21, 2017. Our specific scope of services included the following tasks. 1. Reviewing readily available published geologic data and our relevant in-house files for existing information on subsurface conditions in the project vicinity. 2. Visiting the project site to mark the exploration locations and contacting the "One -Call" Utility Notification Center, as required by Washington State law. We also subcontracted a private utility locator. 3. Exploring subsurface conditions by advancing six soil borings to depths between about 10.75 and 21.5 feet below ground surface (bgs). 4. Conducting geotechnical laboratory testing on selected soil samples. 5. Providing geotechnical seismic design information in accordance with 2015 International Building Code (IBC) criteria and evaluating the potential for surface rupture, liquefaction and lateral spreading at the site. 6. Providing recommendations for site preparation and earthwork. 7. Providing recommendations for shallow spread footing design. 8. Providing recommended active, passive and at -rest lateral earth pressures for retaining walls. GEOENGINEERSSeptember29, 2017 1 Pagel File No 2868-017-00 9. Providing a discussion of suitability of site soils for stormwater infiltration, including preliminary estimates of long-term design infiltration rates based on laboratory sieve analysis results. 10. Providing layer thickness recommendations for asphalt concrete pavement (ACP) design sections, including subgrade preparation. 11. Providing layer thickness recommendations for pervious cement concrete pavement. SITE CONDITIONS Surface Conditions The site is generally rectangular and is bounded by South Dash Point Road to the north, Pacific Highway South to the east, a Motel property to the south and 161h Avenue South to the west. The site is currently occupied by a used car dealership. Single -story office and garage structures are located along the south boundary of the site. The remainder of the site is paved with asphalt concrete and is used as the car dealership lot. The parking lot is surrounded by a chain link fence, which generally delineates the property boundary. Outside of the fence to the north and east of the site are concrete sidewalks and landscaped boulevards. The project site is relatively flat. The property is built into a slope on the west site boundary. The slope grades downward from 16th Avenue South to the site. The slope height is around 30 feet tall at the south end of the site and grades to about 5 feet tall at the north end of the site. The grade of the slope appears to be at 1H to 1V (Horizontal to Vertical) or steeper. The slope is overgrown with vegetation and trees. Access to the slope is restricted by a fence at both the toe and crest of the slope. In our opinion, the slope appears to be a natural slope that was cut to a relatively uniform grade. We did not observe any obvious signs of instability or water seepage on the face of the slope; however, a majority of the slope face was covered with dense vegetation. Literature Review We reviewed the United State Geological Survey (USGS) "Geologic Map of the Poverty Bay 7.5-minute Quadrangle" (Booth and Others 2004). Accordingto the map the primarygeologic units in the project vicinity are advance glacial outwash (Qa) and glacial till (Qvt). Both of these geologic units are considered glacially consolidated soils, meaning they were compressed by a weight of the glacier either during or after deposition. Advance outwash in the area generally consists well sorted sand and gravel with a relatively low percentage of fines (silt and clay -sized soil particles smaller than the U.S. No. 200 sieve). Glacial till is general comprised of an unsorted mixture of sand and gravel in a silt matrix. Cobbles and boulders can also be found within glacial till deposits. Both of these deposits are typically medium dense to very dense. Subsurface Conditions Subsurface Exploration and Laboratory Testing We explored subsurface conditions atthe site by advancing six borings (B-1 through B-6) to nominal depths between 10.75 and 21.5 feet bgs at the approximate locations shown on the attached Site Plan, Figure 2. A representative from our firm continually monitored the explorations and collected soil samples. A more detailed description of our exploration program and the summary exploration logs are provided in Appendix A. GEoENGINEERS September 29, 20171 Page 2 File No. 2868-017-00 Selected samples collected from our borings were tested in our laboratory to confirm field classifications and to evaluate pertinent engineering properties. Our laboratory testing program included grain -size analyses and percent finer than the U.S. No. 200 sieve determinations. A summary of our laboratory testing program and the test results are provided in Appendix A. Soil and Groundwater Conditions Our explorations were advanced in areas paved with asphalt concrete. Pavement thickness was observed to be between 3 and 4 inches. Below the pavement in B-1 through B-5, we observed what we interpret to be fill material. Fill generally consisted of very loose to dense silty sand with variable gravel content. We observed debris (brick, asphalt) and organic matter within the fill in some locations. Explorations B-2 and B-5 were terminated within the fill material around 11.5 feet bgs. In borings B-1, B-3 and B-4, fill material extended to between 7.5 and 8.5 feet bgs and was underlain by what we interpret to be glacial till. Observed glacial till consisted of medium dense to very dense silty sand with gravel. B-1 was terminated within glacial till around 11.5 bgs. Glacial till extended to around 18 feet bgs in B-3 and around 13.5 feet bgs in B-4 and was underlain by what we interpret to be advance outwash. Observed advance outwash consisted of very dense sand with silt and gravel. B-3 and B-4 were terminated within advance outwash at 21.5 feet bgs. We did not observe fill in B-6. Starting below the pavement in B-6, we observed what we interpret to be recessional outwash comprised of very dense sand with silt and gravel. The recessional outwash deposit extended to around 8.5 feet bgs and was underlain by what we interpret to be glacial till. Observed glacial till in B-6 consisted of very dense silty sand with gravel. B-6 was terminated within glacial till around 10.75 feet bgs. We did not encounter what we interpret to be the regional groundwater table in our explorations. We encountered what we interpret to be perched groundwater within the fill around 2.5 feet bgs in B-3 and around 10 feet bgs in B-5. We anticipate that perched groundwater could also be present in other areas at the site depending on soil conditions, rainfall amounts, irrigation activities and other factors. We anticipate that perched groundwater levels will generally be highest during the wet season, typically October through May. We interpret the regional groundwater table to be below the depths of our explorations. CONCLUSIONS AND RECOMMENDATIONS Primary Geotechnical Considerations Based on our understanding of the project, the explorations performed for this study and our experience, it is our opinion that the proposed improvements can be designed and constructed generally as envisioned with regard to geotechnical considerations. A summary of the primary geotechnical considerations for the project is provided below and is followed by our detailed recommendations. E We observed fill starting below pavements across the majority of the site. The fill thickness in some areas of the site exceeded 10 feet and in most areas was greater than 7.5 feet thick. Observed fill material was loose to very loose in some areas. c Proposed structures at the site can be supported using shallow foundations provided that the foundation bearing surfaces are prepared as recommended. Loose fill soils may not be suitable for foundation support. Overexcavation of the fill could be required during foundation bearing surface preparation, or a reduced allowable bearing capacity must be used for foundation design. GEoENGINEERS September 29, 2017 1 Page 3 File No. 2868-017-00 ri We did not identify potentially liquefiable soils in our explorations and in our opinion the risk of liquefaction occurring at this site is low. * Near -surface soils observed at the site contain a significant amount of fines (silt and clay -sized soil particles smaller than the U.S. No. 200 sieve). These materials are highly moisture sensitive and will likely be very difficult or impossible to work with when wet. Infiltration capacity of the site soils could be limited by the underlying glacial till. If infiltration facilities are included in design, additional field testing will be required to determine the design soil infiltration rate as required by the SWDM. Seismic Design Considerations We used map -based methods to develop seismic design parameters, in general accordance with the 2015 IBC. The recommended seismic design parameters are shown in Table 1. TABLE 1: SEISMIC DESIGN CRITERIA 2015 IBC Seismic Design Parameters Site Class D Spectral Response Acceleration at Short Periods (Ss) 1.307g Spectral Response Acceleration at 1-Second Periods (Si) 0.500g Design Peak Ground Acceleration (PGAm) 0.53g Design Spectral Response Acceleration at Short Periods (SDS) 0.871g Design Spectral Response Acceleration at 1-Second Periods (SDI) 0.500g Liquefaction Analysis We did not observe the groundwater table in our explorations and the native soils at the site were generally medium dense to very dense and are glacially consolidated. In our opinion, the soils observed in our explorations are not susceptible to liquefaction. Lateral Spreading Potential Lateral spreading related to seismic activity typically involves lateral displacement of large, surficial blocks of non -liquefied soil when a layer of underlying soil loses strength during seismic shaking. Lateral spreading usually develops in areas where sloping ground or large grade changes (including retaining walls) are present. Based on our understanding of the proposed improvements and current site topography, it is our opinion that the risk of lateral spreading is low. Surface Rupture Potential According to the Washington State Department of Natural Resources (DNR) Interactive Natural Hazards Map (accessed September 21, 2017), traces of the Tacoma Fault cross through the project site. Due to the proximity of the mapped fault to the proposed improvements, it is our opinion that there is a risk for surface rupture if an earthquake occurs along the Tacoma Fault. Determining the magnitude of surface rupture is made difficult by the thickness of glacial deposits that cover bedrock in the area and is beyond the scope of this study. GEOENGINEERSSeptember 29, 2017 Page 4 File No. 2868-017-00 Site Development and Earthwork General We anticipate that site development and earthwork will include demolition of existing improvements including hardscaping, pavements and the existing structures, excavating for shallow foundations, utilities and other improvements, establishing subgrades for foundations and roadways and placing and compacting fill and backfill materials. We expect that site grading and earthwork can be accomplished with conventional earthmoving equipment. The following sections provide specific recommendations for site development and earthwork. Clearing and Stripping We anticipate that clearing and stripping depths in undeveloped areas of the site will likely be on the order of 1 inch. However, greater stripping depths could be required within structural areas or areas of unsuitable soils, if present. During demolition of structures and existing pavements or hardscaping excessive disturbance of surFicial soils may occur, especially if left exposed to wet conditions. Disturbed soils may require additional remediation during construction and grading. The foundation system of the existing buildings should be completely removed from within the structural areas of the proposed improvements. While not observed in our explorations, cobbles and boulders can be present in glacial till deposits in the area. Accordingly, the contractor should be prepared to remove boulders and cobbles, if encountered during grading or excavation. Boulders may be removed from the site or used in landscape areas. Voids caused by boulder removal should be backfilled with structural fill. Erosion and Sedimentation Control Erosion and sedimentation rates and quantities can be influenced by construction methods, slope length and gradient, amount of soil exposed and/or disturbed, soil type, construction sequencing and weather. Implementing an erosion and sedimentation control plan will reduce the project impact on erosion -prone areas. The plan should be designed in accordance with applicable city, county and/or state standards. The plan should incorporate basic planning principles, including: Scheduling grading and construction to reduce soil exposure; o Re -vegetating or mulching denuded areas; ri Directing runoff away from exposed soils; Reducing the length and steepness of slopes with exposed soils; L Decreasing runoff velocities; ii Preparing drainage ways and outlets to handle concentrated or increased runoff; ri Confining sediment to the project site; Inspecting and maintaining control measures frequently. Some sloughing and raveling of exposed or disturbed soil on slopes should be expected. We recommend that disturbed soil be restored promptly so that surface runoff does not become channeled. GEoENGINEERSSeptember 29, 20171 Page 5 File Na 2868-017-00 Temporary erosion protection should be used and maintained in areas with exposed or disturbed soils to help reduce erosion and reduce transport of sediment to adjacent areas and receiving waters. Permanent erosion protection should be provided by paving, structure construction or landscape planting. Until the permanent erosion protection is established and the site is stabilized, site monitoring may be required by qualified personnel to evaluate the effectiveness of the erosion control measures and to repair and/or modify them as appropriate. Provisions for modifications to the erosion control system based on monitoring observations should be included in the erosion and sedimentation control plan. Temporary Excavations Excavations deeper than 4 feet must be shored or laid back at a stable slope if workers are required to enter. Shoring and temporary slope inclinations must conform to the provisions of Title 296 Washington Administrative Code (WAC), Part N, "Excavation, Trenching and Shoring." Regardless of the soil type encountered in the excavation, shoring, trench boxes or sloped sidewalls will be required under Washington Industrial Safety and Health Act (WISHA). The contract documents should specify that the contractor is responsible for selecting excavation and dewatering methods, monitoring the excavations for safety and providing shoring, as required, to protect personnel and structures. In general, temporary cut slopes at this site should be inclined no steeper than about 11/2H to 1V. This guideline assumes that all surface loads are kept at a minimum distance of at least one-half the depth of the cut away from the top of the slope and that seepage is not present on the slope face. Flatter cut slopes will be necessary where seepage occurs or if surcharge loads are anticipated. Temporary covering with heavy plastic sheeting should be used to protect slopes during periods of wet weather. Existing Permanent Slopes Based on our understanding of the proposed improvements and proposed site layout, modifications to the existing slope on the west site boundary are not planned. The existing slope grade is steeper then what is typically recommended for permanent slopes (2H to 1V). Based on the observed condition of the slope and our understanding of the geology in the area, we anticipate that the slope is cut into dense to very dense glacially consolidated soils. Relatively steeper permanent slopes are typically acceptable in glacially consolidated soils. Based on geology review and observations, it is our opinion that the risk of a larger global failure of the slope under static conditions is relatively low. Although not observed during our site visits, shallow surficial sloughing could occur on the slope face at any time of the year. The conceptual site plan shows that the building will be set back about 40 to 50 feet away from the toe of the slope. In our opinion the risk of shallow surficial sloughing impacting the building area at this distance is low. If the building location is changed, we should be notified to reevaluate potential impacts of slope failures on the building. Provided the proposed improvements do not require modifying the existing slope, it is our opinion the slope can be left in its current configuration; however, run -out from shallow surficial sloughing could impact the parking area proposed near the toe of the slope. We did not conduct an evaluation of this slope under seismic conditions. Evaluating seismic slope stability is beyond the scope of this project. To complete a seismic evaluation of the slope, additional subsurface explorations should be completed in the area and a limit equilibrium slope stability analysis should be performed. GEoENGINEERSSeptember29, 20171 Page 6 File No. 2868-017-00 Groundwater Handling Considerations Based on our understanding of the proposed site improvements we do not anticipate that the regional groundwater table will be encountered during excavations at the site. We encountered what we interpret to be perched groundwater around 2.5 feet bgs in B-3 and around 10 feet bgs in B-5. The interface between the fill material and native soils and contacts between relatively more permeable and relatively less permeable materials are likely locations for accumulation of perched groundwater. Groundwater handling needs will typically be lower during the late summer and early fall months. We anticipate that shallow perched groundwater can be handled adequately with sumps, pumps, and/or diversion ditches, as necessary. Ultimately, we recommend thatthe contractor performing the work be made responsible for controlling and collecting groundwater encountered. Surface Drainage Surface water from roofs, driveways and landscape areas should be collected and controlled. Curbs or other appropriate measures such as sloping pavements, sidewalks and landscape areas should be used to direct surface flow away from buildings, erosion sensitive areas and from behind retaining structures. Roof and catchment drains should not be connected to wall or foundation drains. Subgrade Preparation Subgrades that will support structures and roadways should be thoroughly compacted to a uniformly firm and unyielding condition on completion of stripping and before placing structural fill. We recommend that subgrades for structures and roadways be evaluated, as appropriate, to identify areas of yielding or soft soil. Probing with a steel probe rod or proof -rolling with a heavy piece of wheeled construction equipment are appropriate methods of evaluation. If soft or otherwise unsuitable subgrade areas are revealed during evaluation that cannot be compacted to a stable and uniformly firm condition, we recommend that: (1) the unsuitable soils be scarified (e.g., with a ripper or farmer's disc), aerated and recompacted, if practical; or (2) the unsuitable soils be removed and replaced with compacted structural fill, as needed. Subgrade Protection and Wet Weather Considerations Most of the near -surface soils encountered in our explorations contain a significant amount of fines and will be susceptible to disturbance during periods of wet weather. The wet weather season generally begins in October and continues through May in western Washington; however, periods of wet weather can occur during any month of the year. In our opinion, earthwork at the site can be considered during wet weather months provided appropriate measures are implemented to protect exposed soil. If earthwork is scheduled during the wet weather months we offer the following recommendations: u Measures should be implemented to remove or eliminate the accumulation of surface water from work areas. The ground surface in and around the work area should be sloped so that surface water is directed away and graded so that areas of ponded water do not develop. Measures should be taken by the contractor to prevent surface water from collecting in excavations and trenches. .� Earthwork activities should not take place during periods of heavy precipitation. r Slopes with exposed soils should be covered with plastic sheeting. GEoENGINEERSSeptember29, 2017 Page 7 File No 2868-017-00 The contractor should take necessary measures to prevent on -site soils and other soils to be used as fill from becoming wet or unstable. These measures may include the use of plastic sheeting, sumps with pumps and grading. The site soils should not be left uncompacted and exposed to moisture. Sealing exposed soils by rolling with a smooth -drum roller prior to periods of precipitation will help reduce the extent to which these soils become wet or unstable. L Construction traffic should be restricted to specific areas of the site, preferably areas that are surfaced with working pad materials not susceptible to wet weather disturbance. Construction activities should be scheduled so that the length of time that soils are left exposed to moisture is reduced to the extent practical. L. Protective surfacing such as placing asphalt -treated base (ATB) or haul roads made of quarry spalls or a layer of free -draining material such as well -graded pit -run sand and gravel may be necessary to protect completed areas. Minimum quarry spall thicknesses should be on the order of 12 to 18 inches. Typically, minimum gravel thicknesses on the order of 24 inches are necessary to provide adequate subgrade protection. Fill Materials Structural Fill The workability of material for use as structural fill will depend on the gradation and moisture content of the soil. We recommend that washed crushed rock or select granular fill, as described below, be used for structural fill during the rainy season. If prolonged dry weather prevails during the earthwork phase of construction, materials with a somewhat higher fines content may be acceptable. Weather and site conditions should be considered when determining the type of import fill materials purchased and brought to the site for use as structural fill. Material used for structural fill should be free of debris, organic contaminants and rock fragments larger than 6 inches. For most applications, we recommend that structural fill material consist of material similar to "Select Borrow" or "Gravel Borrow" as described in Section 9-03.14 of the Washington State Department of Transportation (WSDOT) Standard Specifications. Select Granular Fill Select granular fill should consist of well -graded sand and gravel or crushed rock with a maximum particle size of 6 inches and less than 5 percentfines by weight based on the minus 3/4-inch fraction. Organic matter, debris or other deleterious material should not be present. In our opinion, material with gradation characteristics similar to WSDOT Specification 9-03.9 (Aggregates for Ballast and Crushed Surfacing), or 9-03.14 (Borrow) is suitable for use as select granular fill, provided that the fines content is less than 5 percent (based on the minus 3/4-inch fraction) and the maximum particle size is 6 inches. Pipe Bedding Trench backfill for the bedding and pipe zone should consist of well -graded granular material similar to "gravel backfill for pipe zone bedding" described in Section 9-03.12(3) of the WSDOT Standard Specifications. The material must be free of roots, debris, organic matter and other deleterious material. Other materials may be appropriate depending on manufacturer specifications and/or local jurisdiction requirements. GEoENGINEERS September 29, 20171 Page 8 File Nu. 2866-017-00 Trench Backfill Trench backfill must be free of debris, organic material and rock fragments larger than 6 inches. We recommend that trench backfill material consist of material similar to "Select Borrow" or "Gravel Borrow" as described in Section 9-03.14 of the WSDOT Standard Specifications. Where excavations occur in the wet, alternative materials such as select granular fill should be considered. On -Site Soil Based on our subsurface explorations and experience, it is our opinion that existing site soils including the existingfill may be considered for use as structural fill and trench backfill, provided that it can be adequately moisture conditioned, placed and compacted as recommended and does not contain organic or other deleterious material. Based on our experience, silty sand materials present at the site are extremely moisture sensitive and will be very difficult or impossible to properly compact when wet. In addition, it is possible that existing soils will be generated at moisture contents above optimum or within zones of seepage. Some segregation may also be required to remove organic and deleterious materials as observed in the explorations. If possible, on -site material should be reserved for use as fill in non-structural areas or as initial lifts in structural areas where thicker fills are proposed. If earthwork occurs during a typical wet season, or if the soils are persistently wet and cannot be dried back due to prevailing wet weather conditions, we recommend the use of imported structural fill or select granular fill, as described above. Fill Placement and Compaction General To obtain proper compaction, fill soil should be compacted near optimum moisture content and in uniform horizontal lifts. Lift thickness and compaction procedures will depend on the moisture content and gradation characteristics of the soil and the type of equipment used. The maximum allowable moisture content varies with the soil gradation and should be evaluated during construction. Generally, 12-inch loose lifts are appropriate for steel -drum vibratory roller compaction equipment. Compaction should be achieved by mechanical means. During fill and backfill placement, sufficient testing of in -place density should be conducted to check that adequate compaction is being achieved. Area Fills and Pavement Bases Fill placed to raise site grades and materials under pavements and structural areas should be placed on subgrades prepared as previously recommended. Fill material placed below structures and footings should be compacted to at least 95 percent of the theoretical maximum dry density (MDD) per ASTM International (ASTM) D 1557. Fill material placed shallower than 2 feet below pavement sections should be compacted to at least 95 percent of the MDD. Fill placed deeper than 2 feet below pavement sections should be compacted to at least 90 percent of the MDD. Fill material placed in landscaping areas should be compacted to a firm condition that will support construction equipment, as necessary, typically around 85 to 90 percent of the MDD. Backfill Behind Below -Grade Structures Backfill behind retaining walls or below -grade structures should be compacted to between 90 and 92 percent of the MDD. Overcompaction of fill placed directly behind below -grade structures should be avoided. We recommend use of hand -operated compaction equipment and maximum 6-inch loose lift thickness when compacting fill within about 5 feet behind below -grade structures. GEOENGINEERS� September 29, 2017 1 Page 9 File No- 2868-017-00 Tench Backfill For utility excavations, we recommend that the initial lift of fill over the pipe be thick enough to reduce the potential for damage during compaction, but generally should not be greater than about 18 inches above the pipe. In addition, rock fragments greater than about 1 inch in maximum dimension should be excluded from this lift. Trench backfill material placed below structures and footings should be compacted to at least 95 percent of the MDD. In paved areas, trench backfill should be uniformly compacted in horizontal lifts to at least 95 percent of the MDD in the upper 2 feet below subgrade. Fill placed below a depth of 2 feet from subgrade in paved areas must be compacted to at least 90 percent of the MDD. In non-structural areas, trench backfill should be compacted to a firm condition that will support construction equipment as necessary. Foundation Support General The proposed structure at the site can be satisfactorily supported on continuous wall and isolated column footings. Exterior footings should be established at least 18 inches below the lowest adjacent grade. Interior footings can be founded a minimum of 12 inches below the top of the floor slab. Isolated column and continuous wall footings should have minimum widths of 24 and 18 inches, respectively. Based on the groundwater conditions in our explorations and our understanding of the proposed footing elevations (bottom of footings established at or within a few feet of existing site grade) it is our opinion footing drains are not necessary to maintain overall bearing support. However, because of the potential for near -surface seepage during wetter times of the year, footing drains are recommended to maintain dryer conditions around the structure and for local areas that may collect more water than others. The sections below provide our recommendations for foundation bearing surface preparation, foundation design parameters and footing drains. Foundation Bearing Surface Preparation Soil within the upper approximately 8 feet of the ground surface across most of the project site was generally observed to consist of loose to medium dense fill with some organic material and debris. Because of this and to reduce the potential for foundation settlement, we recommend that (1) foundations bear on the existing soil that has been thoroughly compacted and designed with a reduced bearing capacity or (2) the loose soils be overexcavated 4 feet below the bottom of footing elevation, or until dense soils are encountered and replaced with structural fill following the recommendations in this report. For this condition, a nominal increase in bearing capacity is provided. Overexcavation limits should extend laterally beyond the foundation perimeter a distance equal to the depth of overexcavation (measured from the base of the footing where necessary), or 3 feet, whichever is less. It may be possible to re -use the excavated material as replacement backfill provided it meets the criteria for structural fill described above and can be compacted as recommended. We discuss the use of on -site material previously. If overexcavation and replacement of loose fill below footings is not completed, the bearing soils must be thoroughly compacted in place to a uniformly firm and unyielding condition and a lower bearing capacity must be used for design as described in the following section. GEoENGINEERS September29, 2017 1 Page 10 File No 2868-017-00 We recommend a member of our firm be on site during footing excavation activities to provide recommendations on limits for overexcavation and to observe foundation excavations before placement of reinforcing steel in order to confirm that bearing surfaces have been prepared in accordance with our recommendations, or to provide recommendations for compaction or removal of unsuitable soil. Foundation bearing surfaces should not be exposed to standing water. If water is present in the excavation, it must be removed before placing formwork and reinforcing steel. Protection of exposed soil, such as placing a 6- to 12-inch-thick layer of crushed rock or quarry spalls, or a 2- to 4-inch layer of lean -mix concrete, may be needed to limit disturbance to bearing surfaces. Allowable Soil Bearing Pressure For foundations bearing on at least 4 feet of structural fill, or structural fill extending to native soil or on native soil, an allowable downward soil bearing pressure of 3,500 pounds per square foot (psf) may be used for design. If loose soils are not removed and replaced below footings, and the bearing soils are only compacted in place and prepared as recommended, an allowable downward soil bearing pressure of 2,000 psf may be used for design. These bearing pressures apply to the total of dead and long-term live loads and may be increased by one- third when considering total loads, including earthquake or wind loads. These are net bearing pressures. The weight of the footing and overlying backfill can be ignored in calculating footing sizes. Foundation Settlement Disturbed soil must be removed from the base of footing excavations and the bearing surface should be prepared as recommended. Provided these measures are taken, we estimate the total static settlement of shallow foundations will be on the order of 1/2 to 1 inch for the bearing pressures presented above. Differential settlements could be on the order of 1/4 to 1/2 inch between similarly loaded foundations or over a distance of 100 feet of continuous footings. The settlements should occur rapidly, essentially as loads are applied. Settlements could be greater than estimated if disturbed or saturated soil is present below footings. Lateral Resistance The ability of the soil to resist lateral loads is a function of the base friction, which develops on the base of footings and slabs, and the passive resistance, which develops on the face of below -grade elements of the structure as these elements move into the soil. For footings founded in accordance with the recommendations presented above, the allowable frictional resistance on the base of the footing may be computed using a coefficient of friction of 0.40 applied to the vertical dead -load forces. The allowable passive resistance on the face of the footing or other embedded foundation elements may be computed using an equivalent fluid density of 325 pounds per cubic foot (pcf). These values include a factor of safety of about 1.5. The passive earth pressure and friction components may be combined provided that the passive component does not exceed two-thirds of the total. The top foot of soil should be neglected when calculating passive lateral earth pressure unless the area adjacent to the foundation is covered with pavement or a slab -on -grade. GEOENGINEERS September 29, 2017 J Page11 File No- 2868-017-00 Perimeter Footing Drains To maintain dryer conditions around the structure and due to the potential for seepage, we recommend that footing drains be included around exterior footings. Footing drains should be installed at the base of exterior footings and include cleanouts. All drains at the site should have adequate slope (typically 1 percent or more) to allow positive drainage to appropriate discharge locations. Some variation of pipe location is acceptable to accommodate other utilities, foundation elements and other structural components. In addition, it is possible that some variations will be required in the field depending on conditions observed during construction. The drains should be installed within a 12-inch-deep trench and consist of at least 4-inch-diameter perforated pipe placed on an approximate 3- to 4-inch bed of, and surrounded by 5 to 6 inches of drainage material enclosed in a non -woven geotextile fabric to prevent fine soil from migrating into the drain material. The drainage material should consist of coarse sand and gravel containing less than 5 percent fines based on the fraction of material passing the 3/4-inch sieve. We recommend that the drainpipe consist of heavy -wall solid pipe (SDR-35 polyvinyl chloride [PVC], or equal). We do not recommend using flexible tubing. The drainage pipe should be either machine -slotted or perforated and extend over the lower 60-degree perimeter of the pipe. For slotted pipe, the slots should be a maximum of 1/8 inch wide with four slots per inch. Perforated pipe should have two rows of 1/2-inch holes spaced 120 degrees apart and at 4 inches on center. Roof downspout and retaining wall drain lines should not be routed to footing drain lines. Slab -on -Grade Floors Slab -on -grade floors should bear on proof compacted existing mineral fill or structural prepared as recommended in the "Subgrade Preparation" section of this report. We recommend the slab subgrades be observed by a member of our firm during construction. Disturbed areas should be compacted, if possible, or removed and replaced with compacted structural fill. In all cases, the exposed soil should be firm and unyielding. It may be appropriate to compact the exposed subgrade with a smooth -drum vibratory roller to a dense and unyielding condition. Ideally, the subgrade should be compacted to at least 95 percent of the MDD in accordance with ASTM D 1557, or as recommended by the geotechnical engineer. We recommend the slab -on -grade floors be underlain by a minimum 8-inch-thick capillary break layer consisting of clean sand and gravel or crushed rock. Overall, the capillary break material should contain less than 3 percent fine material based on the percent passing the 3/4-inch sieve size. Provided that loose soil is removed and the subgrade is prepared as recommended, we recommend slabs -on -grade be designed using a modulus of subgrade reaction of 200 pounds per cubic inch (pci). We estimate that settlement for slabs -on -grade constructed as recommended will be less than 3/4 inch for a floor load of up to 500 psf. Based on our understanding of subsurface conditions at the site it is our opinion that an underslab drain system is not necessary. If dry slabs are required (e.g., where adhesives are used to anchor carpet or tile to slab), a waterproof liner may be placed as a vapor barrier below the slab. GEoENGINEERS� September29, 2017 Page 12 File No. 2868-017-00 Retaining Walls and Below -Grade Structures Design Parameters We recommend the following lateral earth pressures be used for design of conventional retaining walls and below -grade structures. Our design pressures assume that the ground surface around the structures will be level or near level. If drained design parameters are used, drainage systems must be included in the design in accordance with the recommendations presented in the "Drainage" section below. e Active soil pressure may be estimated using an equivalent fluid density of 35 pcf for the drained condition. Active soil pressure may be estimated using an equivalent fluid density of 80 pcf for the undrained condition; this value includes hydrostatic pressures. e At -rest soil pressure may be estimated using an equivalent fluid density of 50 pcf for the drained condition. _ij At -rest soil pressure may be estimated using an equivalent fluid density of 90 pcf for the undrained condition; this value includes hydrostatic pressures. For seismic considerations, a uniform lateral pressure of 10H psf (where H is the height of the retaining structure or the depth of a structure below ground surface) should be added to the lateral earth pressure. a An additional 2 feet of fill representing a typical traffic surcharge of 250 psf should be included if vehicles are allowed to operate within 1/2 the height of the retaining walls. Other surcharge loads should be considered on a case by case basis. The active soil pressure condition assumes the wall is free to move laterally 0.001 H, where H is the wall height). The at -rest condition is applicable where walls are restrained from movement. The above recommended lateral soil pressures do not include other surcharge loads than described or the effects of sloping backfill surfaces. Overcompaction of fill placed directly behind retaining walls or below -grade structures must be avoided. We recommend use of hand -operated compaction equipment and maximum 6-inch loose lift thickness when compacting fill within about 5 feet behind retaining walls and below -grade structures. Retaining wall foundation bearing surfaces should be prepared following the "Foundation Bearing Surface Preparation" section of this report. Provided bearing surfaces are prepared as recommended, retaining wall foundations may be designed using the allowable soil bearing values and lateral resistance values presented above for building foundation design matching the design condition described. We estimate settlement of retaining structures will be similar to the values previously presented for building foundations. Drainage If retaining walls or below -grade structures are designed using drained parameters, a drainage system behind the structure must be constructed to collect water and prevent the buildup of hydrostatic pressure against the structure. We recommend the drainage system include a zone of free -draining backfill a minimum of 18 inches in width against the back of the wall. Free -draining backfill should conform to the WSDOT Standard Specification 9-03.12(2) "Gravel Backfill for Walls." GEoENGINEERSSeptember 29, 2017 Page13 File No 2868-017-00 A perforated, rigid, smooth -walled drain pipe with a minimum diameter of 4 inches should be placed along the base of the structure within the free -draining backfill and extend for the entire wall length. The drain pipe should be metal or rigid PVC pipe and be sloped to drain by gravity. Discharge should be routed properly to reduce erosion potential. Alternate drainage systems, such as drainage boards may also be appropriate for use with retaining and below -grade walls. Cleanouts should be provided to allow routine maintenance. We recommend roof downspouts or other types of drainage systems not be connected to retaining wall drain systems. Stormwater Infiltration General The site is underlain by glacial till that in our opinion has a low infiltration potential and could limit the effectiveness of large concentrated stormwater infiltration facilities (e.g., ponds or subsurface vaults). Large area infiltration facilities such as permeable pavements or small concentrated facilities such as bioswales may still be feasible for use. Infiltration facilities should be designed followingthe 2016 King County SWDM. Infiltration Suitability General In our opinion, the fill and recessional outwash soils observed at the site are suitable for infiltration. We do not recommend that the base of infiltration facilities be located on top of or within 5 feet of the glacial till layer. The top of the glacial till layer was located around 7.5 to 8.5 feet bgs. The following sections address infiltration suitability criteria discussed in the SWDM. Groundwater Separation According to the SWDM a minimum separation of 1 to 5 feet between the bottom of infiltration facilities (separation distance depends on facility type) and the seasonal high groundwater level must be maintained. We anticipate that the seasonal high groundwater level at the site will remain below about 10 feet below existing grade. In our opinion, if the base of stormwater facilities are expected to be within 5 feet of the existing ground surface adequate separation from the groundwater level will be maintained. Design Infiltration Rate Estimate The SWDM requires that the long-term design infiltration rates be determined via a field infiltration test. We can assist in completing field testing if requested. To develop an estimate of the infiltration rates that might be feasible for design, we used the soil grain -size analysis method described in the 2014 Washington State Department of Ecology (Ecology) Stormwater Management Manual for Western Washington (SWMMWW) in conjunction with our laboratory test results. TABLE 2. SUMMARY OF CALCULATED LONG-TERM INFILTRATION RATES' Exploration Sample Depth Geologic Unit USCS Soil Percent (feet) Type Fines B-1 0.5 Fill SM 19 B-3 2.5 Fill GM 19 B-4 5 Fill SM 33 Estimated2 Kio.g-try„ (in/hr) 1.7 0.75 1.0 GEOENGINEERS September 29, 20171 Page 14 File Na 2868-017-00 Exploration Sample Depth (feet) B-5 5 B-6 0.5 Geologic Unit Fill Recessional Outwash USCS Soil Percent Fstimated2 Kiong-term Type Fines (in/hr) SM 23 1.5 SP-SM 7 4.75 Notes: 'Values presented in this table cannot be used for final design. The design infiltration rate for the site must be determined by afield infiltration test 2 Long-term infiltration rate range as determined by the grain -size analysis method including the reduction factors described in the SWMMWw The values presented above are for the samples obtained in a particular area at a particular depth and represent an estimate of soil infiltration rates as indicated by gradation characteristics. These values should not be used for final design of infiltration facilities. Pavement Recommendations Conventional Asphalt Concrete Pavements General Based on our experience, we provide recommended conventional ACP sections below. These pavement sections may not be adequate for heavy construction traffic loads such as those imposed by concrete transit mixers, dump trucks or cranes. Additional pavement thickness may be necessary to prevent pavement damage during construction. The recommended sections assume that final improvements surrounding the conventional ACP will be designed and constructed such that stormwater or excess irrigation water from landscape areas does not accumulate below the pavement section or pond on pavement surfaces. Pavement subgrade should be prepared, placed and observed as previously described. Crushed surfacing base course and subbase should be moisture conditioned to near optimum moisture content and compacted to at least 95 percent of MDD (ASTM D 1577). Crushed surfacing base course should conform to applicable sections of 4-04 and 9-03.9(3) of the WSDOT Standard Specifications. Hot mix asphalt should conform to applicable sections of 5-04, 9-02 and 9-03 of the WSDOT Standard Specifications. Standard -Duty ACP - Automobile Driveways and Parking Areas 2 inches of hot mix asphalt, class 1/2 inch, PG 58-22. 4 inches of crushed surfacing base course. n 6 inches of subbase consisting of select granular fill to provide uniform grading and pavement support, to maintain drainage, and to provide separation from subgrade soils. f_z Existing site soils or structural fill prepared in accordance with the "Subgrade Preparation" section. Heavy -Duty ACP - Areas Subject to Heavy Truck Traffic 3 inches of hot mix asphalt, class 1/2 inch, PG 58-22- r- 6 inches of crushed surfacing base course. GEOENGINEERs September29, 2017 Page 15 File No 2868-017-00 6 inches of subbase consisting of select granular fill to provide a uniform grading surface and pavement support, to maintain drainage, and to provide separation from subgrade soils. o Existing site soils or structural fill prepared accordance with the "Subgrade Preparation" section. Pervious Pavement General Our recommendations for pervious pavement design sections are based on information provided in the technical guidance manual for LID (Puget Sound LID manual), completed by the Puget Sound Partnership (December 2012) and our experience designing permeable pavements in the region. The pavement sections presented below are suitable for use in driveway and parking areas and may not be suitable for use on surface streets or in areas with heavy traffic loads such as the ambulance area or entrances to the site. The design of pervious pavements for stormwater management should consider storage capacity of the pervious pavement system and infiltration rate of the subgrade soils. Our general recommendations are provided in the following sections; however, we recommend that final pervious pavement design be completed in accordance with the complete recommendations provided in the Puget Sound LID manual. Sections for pervious cement concrete pavement and porous asphalt pavement are presented below followed by specific recommendations for each section. Pervious Cement Concrete Section ;,� 6 inches of pervious cement concrete. 6 inches (minimum) of permeable ballast, more permeable ballast may be required to provide adequate storage capacity for the section. L� Geotextile separation liner. Treatment layer (if necessary). r Subgrade prepared as recommended below. Porous Asphalt Concrete Section u 4 inches of porous hot mix asphalt concrete. r:j 6 inches (minimum) of permeable ballast, more permeable ballast may be required to provide adequate storage capacity for the section. Geotextile separation liner. Treatment layer (if necessary). Subgrade prepared as recommended below. Pavement Permeable pavements should be open graded and should have a minimum infiltration rate of at least 100 inches per hour when newly installed. Field infiltration tests should be considered on newly placed permeable pavements to verify the infiltration rate. GEoENGINEERs September29, 2017 Page 16 File Nu 2868-017-00 Permeable Ballast We recommend a minimum 6-inch thick permeable ballast layer that meets the specification for American Public Works Association (APWA) General Special Provision (GSP) 9-03.9(2) Option 1 (shown in Table 3 below). A thicker permeable ballast layer may be necessary to provide sufficient storage capacity for the design infiltration rate. In general, the permeable ballast can be considered to have a porosity of 30 percent. TABLE 3. GRADATION SPECIFICATION FOR PERMEABLE BALLAST Sieve Size Percent Passing 21/2 inch 99-100 2 inches 65-100 3/a inch 40-80 No. 4 0-5 No. 100 0-2 % Fracture 95 Permeable ballast layers between 6 and 12 inches thick should be placed as a single lift. The ballast should be lightly compacted to a firm unyielding condition. Overcompaction of the ballast can result in reduced permeability. The prepared ballast layer should be observed by the geotechnical engineer to ensure that the ballast has been adequately compacted prior to placement of the permeable pavement. If the permeable ballast layer is thicker than 12 inches, it should be placed and compacted in multiple lifts not exceeding 12 inches in thickness. Treatment Layer Stormwater must be treated prior to infiltration. Stormwater can be captured and pretreated prior to infiltration, treatment layers can be built into the infiltration systems, or the existing site must meet treatment criteria outlined in the SWDM. In order to be suitable for stormwater treatment existing site soils must have a cation exchange capacity (CEC) of 5 milliequivalents/100 grams and an organic content of at least 1 percent. Completing CEC and organic content tests on the site soils was beyond our scope. Site soils may require testing to determine if they are suitable for stormwater treatment. A geotextile separation fabric should be included between the bottom of the treatment layer and the prepared subgrade to prevent the treatment media from migrating into the subgrade soils. The separation geotextile should be non -woven and meet the requirement of WSDOT Standard Specification 9.33.1 for separation. Subgrade Preparation Subgrades below permeable pavement sections should be lightly compacted to a firm and unyielding condition before constructing the permeable pavement section; however, overcompaction of the subgrade should be avoided. Prepared subgrades should be protected from construction traffic, standing water or other disturbance. If portions of the subgrade become disturbed or are overcompacted, the subgrade should be scarified to a minimum depth of 8 inches and recompacted. The subgrade should be recompacted to between 90 and 92 percent of the MDD. GEOENGINEERS September29,2017; Page17 File Na 2868-017-00 Protection, Maintenance and Icing It is imperative that soils are not tracked onto pervious pavement surfaced areas during construction. Periodic visual inspections should be performed throughout the pavement life to determine if pervious pavement surfaces are clogged with fine soil or vegetation. Surfaces should be swept with a high -efficiency or vacuum sweeper regularly (typically at least two to four times per year) and washed with a high-pressure hose at least once per year. Because the relatively porous base and subbase layers allow some air movement below the pavement, pervious pavement surfaces may become icy more easily than conventional pavement surfaces. This problem is similar to differential icing of bridges and elevated road structures. Users should be made aware of the possibility of differential icing if pervious pavements are used. LIMITATIONS We have prepared this report for PhiloWilke Partnership, for the Federal Way Free -Standing Emergency Center in Federal Way, Washington. PhiloWilke Partnership may distribute copies of this report to owner's authorized agents and regulatory agencies as may be required for the Project. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices for geotechnical engineering services in this area at the time this report was prepared. The conclusions, recommendations, and opinions presented in this report are based on our professional knowledge, judgment and experience. No warranty, express or implied, applies to the services or this report. Please refer to Appendix B titled "Report Limitations and Guidelines for Use" for additional information pertaining to use of this report. GEoENGINEERS September29, 2017 Page 18 File No 2868-017-00 . N S 276th St - s S 277th P% N 0 St, Lake:... a N Q\ by ® W > S 279th St • .11e a h PI S 280th St a _ yl$M y y _ > > $ D �• S282nd St � S 282nd St- � N N „� tib • u oa ■ • a pro ■ t 5284th 5t N S 284th PI ... -. S Ot' m S S 285th St *yiS 'a� D r N X s 286tn St N < w ff� A N ur c 52881h St S 288th St r ^ 0 W NMi0dY6 aen.rury � � Q\'? .r. 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S[ 52°1■ SITE MARCHERI a PUGET SOUND s a a i ti S300thSt � 299m5t `' ^ HILLS �S m S N .2 53001 DaSt,Polnr� SY/ t < D D Wddwed tkm wy A a' S Dash Point Rd P; 5 3O2nd St H m N $ S 302nd S f,>� 5303rd S[ d N 5302nd Si • , SW 3O4th St t S 3O4[h St'- S 304th PI S 304th St rn S 304th St S 304th St 5 304th St SW 3051h Sty N S 305th St = 2 a a m w a Y H N N federal Way Wjft i e m S N 3 5[ S 308th St N S 308th St A LA. 6aere EkmeMar m t o m D a a 6 in 9S 310th S[ MIRROR LAKE N � i N a ' `n S 312th St S 312th St S 312th StRM �'■ Pak r S 312[h S[ � D , r 'fir • <' ^ 'o '^ Q � S 314th St S 314th S[ ireadr lake M Me -lake 1' S 315th S[ a n uCDi S a' n o 3,6['St N , St N roe Slade 63 / S&W S 316th PI ,� N S 316th St "' ® S 316th St y X S Trmm� IBQr S 316ttt }t ! Rea67-- 5317th P1 $317[hk s > L � < 5317[h S[ 5316th PI N W E f..I 2,000 0 2,000 Taco Feet Olympia Vicinity Map Notes: 1. The locations of all features shown are approximate. 2. This drawing is for information purposes. It is intended to assist in Federal Way Free Standing Emergency Center showingfeatures discussed in an attached document. GeoEngineers, Inc. Federal Way, Washington cannot guarantee the accuracy and content of electronic files. The master file is stared by GeoEngineers, Inc. and will serve as the official record of this communication. Data Source: Mapbox Open Street Map, 2015 G W E N G I N E E R S Figure 1 Projection: NAD 1983 StatePlane Washington North FIPS 4601 Feet — — �•a+zeea i F 16th Avenue South 77 r mii Hm�j�.•"�i . r� � vi A T I L' `D N z n o ZT Z d rn s = 'ICD R7 V13d a 73 CD 1Jf it m 3 m 3 c, -1. C - oil R p OR 3 N 7 p T A p - g,o C (7 c 3 (D N 7 N � APPENDIX A Subsurface Explorations and Laboratory Testing APPENDIX A SUBSURFACE EXPLORATIONS AND LABORATORY TESTING Subsurface Explorations Subsurface conditions were explored by advancing six hollow -stem auger borings on September 8, 2017. Subsurface exploratory services were provided by Holocene Drilling, Inc. under subcontract to GeoEngineers, Inc. The borings were advanced to between about 10.75 and 21.5 feet below surrounding site grade. The locations of the borings were determined by measuring from existing site features. The exploration locations and other site features are included on the Site Plan, Figure 2. The elevations on our explorations are computer generated based on the NAD83 Washington State Planes North Zone Projection. The locations and elevations of the explorations should be considered approximate. Our field representative collected samples, classified the soils, maintained a detailed log of the explorations and observed groundwater conditions. The samples were obtained with a standard split spoon sampler in general accordance with ASTM International (ASTM) D 1586. Field blow counts are presented on the log. The soils were classified visually in general accordance with the system described in Figure B-1, which includes a key to the exploration logs. Summary logs of the explorations are included as Figures B-2 through B-7. Laboratory Testing Soil samples obtained from the borings were transported to GeoEngineers laboratory. Representative soil samples were selected for laboratory tests to evaluate the pertinent geotechnical engineering characteristics of the site soils and to confirm our field classification. Our testing program consisted of the following: E.- Five - Grain -size distribution analyses (SA) u One - Percent passing U.S. No. 200 sieve (%F) Tests were performed in general accordance with test methods of ASTM or other applicable procedures. The following sections provide a general description of the tests performed. Grain -Size Grain -size analyses were performed on selected samples in general accordance with ASTM Test Method C 136. This test provides a quantitative determination of the distribution of particle sizes in soils. Grain -size analyses are used to classify soil and to aid in evaluating index properties. Figures A-8 and A-9 present the results of the grain -size analyses. GEoENGINEERSSeptember29,20171 PageA-1 File No- 2868-017-00 Percent Passing the U.S. No. 200 Sieve Selected samples were "washed" through the U.S. No. 200 sieve to estimate the relative percentages of coarse- and fine-grained particles in the soil. The percent passing value represents the percentage by weight of the sample finer than the U.S. No. 200 sieve (fines). The tests were conducted in general accordance with ASTM D 1140. The test results are presented on the exploration logs in Appendix A at the respective sample depths. GEOENGINEERS. September 29, 20171 Page A-2 File No.2868-017-00 SOIL CLASSIFICATION CHART ADDITIONAL MATERIAL SYMBOLS MAJOR DIVISIONS SYMBOLS TYPICAL GRAPH LETTER DESCRIPTIONS CLEAN GRAVELS o �o o Gw WELL -GRADED GRAVELS, GRAVEL SAND MIXTURES GRAVEL ) 0 0 0 0 0 o GP POORLY -GRADED GRAVELS, GRAVEL -SAND MIXTURES AND GRAVELLY SOILS (DTILE OR NO FINES) GRAVELS WITH FINES (APPRECIABLE AMOUNT OF FINES) N GM SILTY GRAVELS, GRAVEL -SAND - SILT MIXTURES COARSE GRAINED SOILS MORETHAN 50% OFCOARSE FRACTION RETAINE ON NO. 4 SIEVE . J 27` f % GC CLAYEY GRAVELS, GRAVEL -SAND - CLAY MIXTURES CLEAN SANDS sw WELL -GRADED SANDS, GRAVELLY SANDS MORE THAN 50% SAND SP POORLY -GRADED SANDS, GRAVELLY RETAINED RETAIN NOS EVAND SANDY IDTTLE OR NO FINEST SOILS SANDS WITH SM SILTY SANDS, SAND - SILT MIXTURES MORE THAN 50% OF COARSE FINES FRACTION PASSING ON NO. 4 SIEVE (APPRECIABLE AMOUNT OF FINEST _ /� SC CLAYEY SANDS, SAND - CLAY MIXTURES INORGANIC SILTS, ROCK FLOUR, ML CLAYEY SILTS WITH SLIGHT PLASTICITY INORGANIC CLAYS OF LOW TO FINE SILTS AND CLAYS LIQUID LIMIT LESS THAN 50 F CL MEDIUM PLASTICITY, GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS, LEAN CLAYS GRAINED SOILS ORGANIC SILTS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY MORE THAN 50% INORGANIC SILTS, MICACEOUS OR DIATOMACEOUS SILTY SOILS PASSING NO 200 SIEVE CCH INORGANIC CLAYS OF HIGH SILTS AND CLAYS LIQUID OMIT GREATER THANPLASTICITY ORGANIC CLAYS AND SILTS OF MEDIUM TO HIGH PLASTICITY HIGHLY ORGANIC SOILS PTI PEAT, HUMUS, SWAMP SOILS WITH HIGH ORGANIC CONTENTS NOTE: Multiple symbols are used to indicate borderline or dual soil classifications Sampler Symbol Descriptions ® 2.4-inch I.D. split barrel ® Standard Penetration Test (SPT) ■ Shelby tube ® Piston UDirect -Push m Bulk or grab ® Continuous Coring Blowcount is recorded for driven samplers as the number of blows required to advance sampler 12 inches (or distance noted). See exploration log for hammer weight and drop. "PIT indicates sampler pushed using the weight of the drill rig. "WOH" indicates sampler pushed using the weight of the hammer. sYMBOLs LETTER TYPICAL DESCRIPTIONS GRAPH AC Asphalt Concrete CC Cement Concrete CR Crushed Rock/ Quarry Spalls J 01 ),, SOD Sod/Forest Duff TS Topsoil Groundwater Contact _ Measured groundwater level in exploration, well, or piezometer W Measured free product in well or piezomete Graphic Log Contact Distinct contact between soil strata _ Approximate contact between soil strata Material Description Contact Contact between geologic units Contact between soil of the same geologic unit Laboratory / Field Tests %F Percent fines %G Percent gravel AL Atterberg limits CA Chemical analysis CP Laboratory compaction test CS Consolidation test DD Dry density DS Direct shear HA Hydrometer analysis MC Moisture content MD Moisture content and dry density Mohs Mohs hardness scale OC Organic content PM Permeability or hydraulic conductivity PI Plasticity index PP Pocket penetrometer SA Sieve analysis TX Triaxial compression UC Unconfined compression VS Vane shear Sheen Classification NS No Visible Sheen SS Slight Sheen MS Moderate Sheen HS Heavy Sheen NOTE: The reader must refer to the discussion in the report text and the logs of explorations for a proper understanding of subsurface conditions. Descriptions on the togs apply only at the specific exploration locations and at the time the explorations were made; they are not warranted to be representative of subsurface conditions at other locations or times. Key to Exploration Logs GMENGINEERS P FigureA-1 Total 11.5 Logged By CRG Driller Holocene Drilling, Inc. Method Hollo%,stem Auger Drilled 9/8/220017 9/8/2017 Depth (tt) Checked By BEL Surface Elevation (ft) 420 Hammer Auto Hammer Drilling D50 Track Rig Vertical Datum NAVD88 Data 140 (!bs) / 30 {in} Drop Equipment Easting o Q 1273546 System WA State Plane North DeAth to Water (ft1 Elevation (ftl Northing M 125925 Datum NAD83 {Feet] Notes: Log of Boring B-2 Project Federal Way Free -Standing Emergency Center GM E N G I N E E R5 Project Location: Federal Way, Washington .5 Project Number: 2868-017-00 Figure A-3 Sheet 1 of 1 Drilled 9/S/220017 9/8/2017 Depth (ft) 215 Surface Elevation (ft) 420 Vertical Datum NAVD88 125848 Notes: Logged By CRG Driller Holocene Drilling, Inc. Drilling Hollow -stem Auger Checked By BEL I Method Hammer Auto HamDrillingmer Equipment D50 Track Rig Data 140 } / 30 (in) Drop C?Lpt: ie System WA State Plane North „ Water (Hl Elevation (ft) Datum NAD83 (feet) 7 ' 2= End Total 21.5 Drilled 9/8/2017 9/8/2017 Depth (ft) Surface Elevation (ft) 420 Vertical Datum NAVD88 Easting (X) 1273588 Northing m 125780 Notes: Logged By CRG Driller Holocene Drilling, Inc. Checked W BEL Hammer Auto Hammer Drilling Data 140 (It] / 30 (in) Drop Equipment System WA State Plane North to Datum NAD83 (feet] Drilling Hollow -stem Auger Method D50 Track Rig �D--pn !o WC*2r _ttt Elevation (ft) Log of Boring B-4 Project: Federal Way Free -Standing Emergency Center G Fn F N c i N E E R 5 10/ Project Location: Federal Way, Washington Figure Pr5 Sheet 3 of 1 of —2dop" I Protect Number: 2868-017-00 %aft End Total 11.5 ' Drilled 9/8/2017 9/8/2017 Depth (ft) Surface Elevation (ft) 420 Vertical Datum NAVD88 Easting(X) 1273659 NolthingM 125768 Notes: Logged By CRG Driller Holocene Drilling, Inc. Checked By BEL Hammer Auto Hammer Drilling Data 140 (Ids) / 30 (in) Drop Equipment System WA State Plane North I�e� Datum NAD83 (feet) Drilling Hollow -stem Auger Method D50 Track Rig Mptn to 1'�ater i!ti Elevation fftl r Drilled 9/8/�2017 9/8/2017 Dew (ft) 10.75 Surface Bevation (ft) 420 Vertical Datum NAVD88 Easting (X) 1273515 Northing m 125731 Notes: Logged By CRG Driller Holocene Drilling, Inc. Checked By BEL _ Hammer Auto Hammer Drilling Data 140(Ibs)/30(in)Drop Equipment System WA State Plane North SDMIUMMO ep Datum NAD83 (feet) Drilling Hollow -stem Auger _a Log of Boring" Project: Federal Way Free -Standing Emergency Center G M E N G I N E E R5 Project Location: Federal Way, Washington Project Number: 2868-017-00 D50 Track Rig t} p:h to Figure A-7 Sheet 1 of 1 �U33NIDN 3 03E d u0j,�3@ USeM SeMje epa Je ueQ u@�b ew] 2@pues - a ] Aemie epa k msa ?j mSA mu¥ GAGIS PERCENT PASSING B WEIGHT FA o o § o o § § o § 0 0 z oCD » � x o on CD ■O¢A ]4 _ \ID CL n 1 o _ o § CD m z cn o - » ; \ = 9 9 t e c o CL 90 ]CD . CD E 0 / \{ 7 En — —i� - — Ln - - gCD . 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CD CL $ \ m @ k CD z 7. o CD CD CD \} m k o , _ _ ID cn CD D § ) P }k § - (\ cb CD D o 0 0 e ƒ ❑+A 0 k _ = z 6 § § � �c \° k� �g �77g �f \ � \ � } 2 ( � / § o _ [ � / £ m \/� § � \\ \� APPENDIX B Report Limitations and Guidelines for Use I APPENDIX B REPORT LIMITATIONS AND GUIDELINES FOR USEi This appendix provides information to help you manage your risks with respect to the use of this report. Read These Provisions Closely It is important to recognize that the geoscience practices (geotechnical engineering, geology and environmental science) rely on professional judgment and opinion to a greater extent than other engineering and natural science disciplines, where more precise and/or readily observable data may exist. To help clients better understand how this difference pertains to our services, GeoEngineers includes the following explanatory "limitations" provisions in its reports. Please confer with GeoEngineers if you need to know more how these "Report Limitations and Guidelines for Use" apply to your project or site. Geotechnical Services are Performed for Specific Purposes, Persons and Projects This report has been prepared for PhiloWilke Partnership and for the Project(s) specifically identified in the report. The information contained herein is not applicable to other sites or projects. GeoEngineers structures its services to meet the specific needs of its clients. No party other than the party to whom this report is addressed may rely on the product of our services unless we agree to such reliance in advance and in writing. Within the limitations of the agreed scope of services for the Project, and its schedule and budget, our services have been executed in accordance with our Agreement with PhiloWilke Partnership dated August 30, 2017 and generally accepted geotechnical practices in this area at the time this report was prepared. We do not authorize, and will not be responsible for, the use of this report for any purposes or projects other than those identified in the report. A Geotechnical Engineering or Geologic Report is based on a Unique Set of Project -Specific Factors This report has been prepared for the Federal Way Free -Standing Emergency Center in Federal Way, Washington. GeoEngineers considered a number of unique, project -specific factors when establishing the scope of services for this project and report. Unless GeoEngineers specifically indicates otherwise, it is important not to rely on this report if it was: Ll not prepared for you, not prepared for your project, ai not prepared for the specific site explored, or a completed before important project changes were made. For example, changes that can affect the applicability of this report include those that affect: E the function of the proposed structure; elevation, configuration, location, orientation or weight of the proposed structure; 1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org. GEOENGINEERS� September 29, 2017 Page B-1 File No 2868-017-00 in u composition of the design team; or ri project ownership. If changes occur after the date of this report, GeoEngineers cannot be responsible for any consequences of such changes in relation to this report unless we have been given the opportunity to review our interpretations and recommendations. Based on that review, we can provide written modifications or confirmation, as appropriate. Environmental Concerns are Not Covered Unless environmental services were specifically included in our scope of services, this report does not provide any environmental findings, conclusions, or recommendations, including but not limited to, the likelihood of encountering underground storage tanks or regulated contaminants. Information Provided by Others GeoEngineers has relied upon certain data or information provided or compiled by others in the performance of our services. Although we use sources that we reasonably believe to be trustworthy, GeoEngineers cannot warrant or guarantee the accuracy or completeness of information provided or compiled by others. Subsurface Conditions Can Change This geotechnical or geologic report is based on conditions that existed atthe time the study was performed. The findings and conclusions of this report may be affected by the passage of time, by man-made events such as construction on or adjacent to the site, new information or technology that becomes available subsequent to the report date, or by natural events such as floods, earthquakes, slope instability or groundwater fluctuations. If more than a few months have passed since issuance of our report or work product, or if any of the described events may have occurred, please contact GeoEngineers before applying this report for its intended purpose so that we may evaluate whether changed conditions affect the continued reliability or applicability of our conclusions and recommendations. Information Provided by Others GeoEngineers has relied upon certain data or information provided or compiled by others in the performance of our services. Although we use sources that we reasonably believe to be trustworthy, GeoEngineers cannot warrant or guarantee the accuracy or completeness of information provided or compiled by others. Geotechnical and Geologic Findings are Professional Opinions Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies the specific subsurface conditions only atthose points where subsurface tests are conducted or samples are taken. GeoEngineers reviewed field and laboratory data and then applied its professional judgment to render an informed opinion about subsurface conditions at other locations. Actual subsurface conditions may differ, sometimes significantly, from the opinions presented in this report. Our report, conclusions and interpretations are not a warranty of the actual subsurface conditions. GEoENGINEERSSeptember29, 2017 Page B-2 File Na Geotechnical Engineering Report Recommendations are Not Final We have developed the following recommendations based on data gathered from subsurface investigation(s). These investigations sample just a small percentage of a site to create a snapshot of the subsurface conditions elsewhere on the site. Such sampling on its own cannot provide a complete and accurate view of subsurface conditions for the entire site. Therefore, the recommendations included in this report are preliminary and should not be considered final. GeoEngineers' recommendations can be finalized only by observing actual subsurface conditions revealed during construction. GeoEngineers cannot assume responsibility or liability for the recommendations in this report if we do not perform construction observation. We recommend that you allow sufficient monitoring, testing and consultation during construction by GeoEngineers to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes if the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork activities are completed in accordance with our recommendations. Retaining GeoEngineers for construction observation for this project is the most effective means of managing the risks associated with unanticipated conditions. If another party performs field observation and confirms our expectations, the other party must take full responsibility for both the observations and recommendations. Please note, however, that another party would lack our project - specific knowledge and resources. A Geotechnical Engineering or Geologic Report Could Be Subject to Misinterpretation Misinterpretation of this report by members of the design team or by contractors can result in costly problems. GeoEngineers can help reduce the risks of misinterpretation by conferring with appropriate members of the design team after submitting the report, reviewing pertinent elements of the design team's plans and specifications, participating in pre -bid and preconstruction conferences, and providing construction observation. Do Not Redraw the Exploration Logs Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. The logs included in a geotechnical engineering or geologic report should never be redrawn for inclusion in architectural or other design drawings. Photographic or electronic reproduction is acceptable, but separating logs from the report can create a risk of misinterpretation. Give Contractors a Complete Report and Guidance To help reduce the risk of problems associated with unanticipated subsurface conditions, GeoEngineers recommends giving contractors the complete geotechnical engineering or geologic report, including these "Report Limitations and Guidelines for Use." When providing the report, you should preface it with a clearly written letter of transmittal that: advises contractors that the report was not prepared for purposes of bid development and that its accuracy is limited; and encourages contractors to confer with GeoEngineers and/or to conduct additional study to obtain the specific types of information they need or prefer. GEOENGINEERS� September 29, 2017 1 Page B-3 File No. 2868-017-00 Contractors are Responsible for Site Safety on Their Own Construction Projects Our geotechnical recommendations are not intended to direct the contractor's procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on -site personnel and adjacent properties. Biological Pollutants GeoEngineers' Scope of Work specifically excludes the investigation, detection, prevention or assessment of the presence of Biological Pollutants. Accordingly, this report does not include any interpretations, recommendations, findings or conclusions regarding the detecting, assessing, preventing or abating of Biological Pollutants, and no conclusions or inferences should be drawn regarding Biological Pollutants as they may relate to this project. The term "Biological Pollutants" includes, but is not limited to, molds, fungi, spores, bacteria and viruses, and/or any of their byproducts. A Client that desires these specialized services is advised to obtain them from a consultant who offers services in this specialized field. GEOENGINEERSSeptember 29, 2017, PageB-4 File No. 2868-017.00