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21-102066-UP-Geotech Report-2021-05-26-V1    GEOTECHNICAL REPORT 9th Avenue South Industrial 34520 – 9th Avenue South Federal Way, Washington Project No. T-8425 Prepared for: Smith Brothers Farms c/o KG Investments Bellevue, Washington May 25, 2021     May 25, 2021 Project No. T-8425 Mr. Dustin Highland Smith Brothers Farms c/o KG Investments 11225 – SE 6th Street, Suite 215 Bellevue, Washington 98004 Subject: Geotechnical Report 9th Avenue South Industrial 34520 – 9th Avenue South Federal Way, Washington Dear Mr. Highland: As requested, we have conducted a geotechnical engineering study for the subject project. The attached report presents our findings and recommendations for the geotechnical aspects of project design and construction. Soil conditions at the site generally consisted of approximately five- to- eight inches of sod overlying approximately one to five feet of medium-dense, inorganic, fill material over medium dense to very dense sand with varying amounts of silt and gravel to the termination of the test pits. The fill material generally consisted of silty sand with gravel and sand with silt and gravel. There were 3 exceptions to this general condition. In Test Pits TP-1 and TP-6, we observed an approximately five-foot layer of silt between 3 and 5 feet below current site grades. In Test Pits TP-1 and TP-2, we did not observe any fill material overlying the native soils. Test Pit TP-7 was excavated in the stockpile in the approximate center of the site. This test pit noted medium dense, inorganic fill material to the termination of the test pit. No groundwater seepage was observed during our explorations. In our opinion, the soil conditions we observed at the site will be suitable for support of the proposed development, provided the recommendations presented in this report are incorporated into project design and construction. 12220 113th Avenue NE, Ste. 130, Kirkland, Washington 98034  Phone (425) 821‐7777 • Fax (425) 821‐4334  5-25-2021     TABLE OF CONTENTS Page No. 1.0 Project Description ........................................................................................................... 1 2.0 Scope of Work ................................................................................................................. 1 3.0 Site Conditions ................................................................................................................. 2 3.1 Surface ................................................................................................................ 2 3.2 Subsurface ........................................................................................................... 2 3.3 Groundwater ....................................................................................................... 3 3.4 Geologic Hazards ................................................................................................ 3 3.4.1 Landslide Hazard Areas ............................................................................. 4 3.4.2 Erosion Hazard Areas ................................................................................ 4 3.4.3 Seismic Hazard Areas ................................................................................ 5 3.5 Seismic Design Parameters ................................................................................. 5 4.0 Discussion and Recommendations ................................................................................... 5 4.1 General ................................................................................................................ 5 4.2 Site Preparation and Grading .............................................................................. 6 4.3 Excavation ........................................................................................................... 7 4.4 Foundation Support ............................................................................................. 7 4.5 Floor Slab-on-Grade ........................................................................................... 8 4.6 Lateral Earth Pressures on Lower-Level Walls .................................................. 8 4.7 Infiltration Feasibility ......................................................................................... 9 4.8 Drainage ............................................................................................................ 10 4.9 Utilities .............................................................................................................. 10 4.10 Pavement ........................................................................................................... 10 5.0 Additional Services ........................................................................................................ 11 6.0 Limitations ..................................................................................................................... 12 Figures Vicinity Map ......................................................................................................................... Figure 1 Exploration Location Plan..................................................................................................... Figure 2 Typical Wall Drainage Detail ............................................................................................... Figure 3 Appendix Field Exploration and Laboratory Testing ....................................................................... Appendix A Geotechnical Report 9th Avenue South Industrial 34520 – 9th Avenue South Federal Way, Washington 1.0 PROJECT DESCRIPTION The project consists of developing the site with an approximately 45,000 square foot industrial building, a stormwater infiltration gallery, and associated access and utilities. Based on the preliminary grading and drainage plan prepared by Barghausen Consulting Engineers dated May 19, 2021, the building will be located in the approximate center of the site with a finish floor elevation of 273.00 feet. Dock high loading in shown on the east side of the building with access and parking on the south, north, and west sides. Grading to achieve building lot and roadway elevations will consist of cuts and fills from 1 to 25 feet. Grade transitions will be supported with slopes and retaining walls. Site stormwater will be collected and directed to a stormwater infiltration gallery in the southern portion of the site. The gallery is approximately 250 feet by 70 feet with a bottom elevation of 253.00 feet. We expect the structure will be constructed using precast concrete tilt-up wall panels with interior isolated columns supporting the roof framing. The floor slab is anticipated to be constructed at grade with dock-high loading. Structural loading is expected to be relatively light, with isolated building columns carrying 100 to 150 kips and continuous bearing walls carrying 4 to 6 kips per foot. Product loading on the floor slab is not expected to exceed 350 pounds per square foot. The recommendations in the following sections of this report are based on the design discussed above. If actual features vary or changes are made, we should review the plans in order to modify our recommendations. We should review final design drawings and specifications to verify our recommendations have been properly interpreted and incorporated into the project design. 2.0 SCOPE OF WORK Our work was completed in accordance with our authorized proposal, dated October 19, 2020. Accordingly, on November 5, 2020, we observed soil and groundwater conditions by excavating 7 test pits to depths of approximately 7 to 16 feet below existing site grades using a track-mounted excavator. Using this data, along with laboratory testing, we performed analyses to develop geotechnical recommendations for project design and construction. Specifically, this report addresses the following:  Soil and groundwater conditions.  Geologic Hazards per the City of Federal Way Municipal Code.  Seismic.  Site preparation and grading.  Excavation. May 25, 2021 Project No. T-8425 Page No. 2    Foundations.  Floor slabs.  Lateral earth pressures for wall design.  Infiltration feasibility.  Subsurface drainage.  Utilities.  Pavements. It should be noted, recommendations outlined in this report regarding drainage are associated with soil strength, design earth pressures, erosion, and stability. Design and performance issues with respect to moisture as it relates to the structure environment are beyond Terra Associates, Inc.’s purview. A building envelope specialist or contractor should be consulted to address these issues, as needed. 3.0 SITE CONDITIONS 3.1 Surface The project site consists of 2 tax parcels totaling approximately 4.5 acres located at 34520 – 9th Avenue South in Federal Way, Washington. The approximate site location is shown on Figure 1. The site is currently undeveloped, with partially graded slopes and a large stockpile in the approximate center of the properties. The site is covered with light to moderate vegetation, scattered trees, and brush. General topography at the site slopes downward from the north-northeast to the south-southwest, with an overall relief of about 30 feet. The site is bordered by industrial buildings to the east and south, 344th Street to the north, and 9th Avenue South to the west. 3.2 Subsurface In general, the soil conditions at the site consisted of approximately five to eight inches of sod overlying approximately one to five feet of medium-dense, inorganic, fill material over medium-dense to very-dense sand with varying amounts of silt and gravel to the termination of the test pits. The fill material generally consisted of silty sand with gravel and sand with silt and gravel. There were three exceptions to this general condition; at Test Pits TP-1 and TP-6, we observed an approximately five-foot layer of silt between three and five feet below current site grades. At Test Pits TP-1 and TP-2, we did not observe any fill material overlying the native soils. Test Pit TP-7 was excavated in the stockpile in the approximate center of the site. This test pit noted medium-dense, inorganic fill material to the termination of the test pit. The Geologic Map of the Poverty Bay 7.5' Quadrangle, King and Pierce Counties, Washington, by D.B. Booth, H.H. Waldron, and K.G. Troost (2004) shows the site soils are mapped as Recessional Outwash (Qvr). The site soils appear to be more consistent with a transition between recessional outwash and glacial till. Glacial till is mapped approximately 1,200 feet east of the project site. May 25, 2021 Project No. T-8425 Page No. 3   The preceding discussion is intended to be a general review of the soil conditions encountered. For more detailed descriptions, please refer to the Test Pit Logs in Appendix A. The approximate locations of the test pits are shown on Figure 2. 3.3 Groundwater No groundwater seepage was observed during our explorations; however, faint mottling was observed within the sandy silt layers (TP-1 and TP-6). Mottling indicates a shallow groundwater table may develop at the site within the sandy silt soils during the wet winter months. Based on our experience, we would expect the volume to be minor. PVC piezometers were installed in three test pits to allow for groundwater monitoring. The following table shows the data and groundwater levels noted during our site visits. Date Test Pit 1 Test Pit 5 Test Pit 6 12/11/2020 N/A N/A N/A 12/28/2020 N/A N/A N/A 1/15/2021 N/A 8.5 feet N/A 1/29/2021 N/A N/A N/A 2/12/2021 N/A 9 feet N/A 2/26/2021 N/A N/A N/A 3/12/2021 N/A N/A N/A 3/26/2021 N/A N/A N/A Based on this analysis and our experience in the area, we concluded that the water onsite drains through the sands and gravels relatively quickly; water was only noted after heavy rainstorms. Accordingly, the seasonal high groundwater of 8.5 feet below current grade would be representative of the average conditions and should be used in design. 3.4 Geologic Hazards Section 19.145.220 of the City of Federal Way Municipal Code (FWMC) defines geologically hazardous areas to include “areas susceptible to erosion, land sliding, seismic, or other geological events. Areas susceptible to one or more of the following types of hazards shall be designated as geologically hazardous areas: (a) Landslide hazard; (b) Erosion hazard; and (c) Seismic hazard.” Based on this, we evaluated current site conditions for the presence of geologic hazards, including: landslide hazard areas, erosion hazard areas, and seismic hazard areas. May 25, 2021 Project No. T-8425 Page No. 4   3.4.1 Landslide Hazard Areas Section 19.05.070 G of the FWMC defines a Landslide Hazard Area as “those areas potentially subject to episodic downslope movement of a mass of soil or rock including, but not limited to, the following areas: (a) Any area with a combination of: (i) Slopes greater than 15 percent; (ii) Permeable sediment, predominately sand and gravel, overlying relatively impermeable sediment or bedrock, typically silt and clay; and (iii) Springs or groundwater seepage. (b) Any area that has shown movement during the Holocene epoch, from 10,000 years ago to the present, or that is underlain by mass wastage debris of that epoch. (c) Any area potentially unstable as a result of rapid stream incision, stream bank erosion or undercutting by wave action. (d) Any area located in a ravine or on an active alluvial fan, presently or potentially subject to inundation by debris flows or flooding. (e) Those areas mapped as Class U (unstable), UOS (unstable old slides), and URS (unstable recent slides) by the Department of Ecology’s Coastal Zone Atlas. (f) Areas designated as quaternary slumps, earthflows, mudflows, lahars, or landslides on maps published by the U.S. Geological Survey or Washington State Department of Natural Resources. (g) Slopes having gradients greater than 80 percent subject to rockfall during seismic shaking. (h) Any area with a slope of 40 percent or steeper and with a vertical relief of 10 or more feet except areas composed of consolidated rock. A slope is delineated by establishing its toe and top and is measured by averaging the inclination over at least 10 feet of vertical relief.” None of the above conditions are present at the site; therefore, the site does not contain a landslide hazard as defined by the FWMC. 3.4.2 Erosion Hazard Areas Section 19.05.070 G of the FWMC defines an Erosion Hazard Area as “those areas identified by the U.S. Department of Agriculture’s Natural Resource Conservation Service as having a moderate to severe, or severe to very severe, rill and inter-rill erosion hazard due to natural agents such as wind, rain, splash, frost action, or stream flow; those areas containing the following group of soils when they occur on slopes of 15 percent or greater: Alderwood-Kitsap (“AkF”), Alderwood gravelly sandy loam (“AgD”), Kitsap silt loam (“KpD”), Everett (“EvD”), and Indianola (“InD”); and those areas impacted by shore land and/or stream bank erosion.” May 25, 2021 Project No. T-8425 Page No. 5   The United States Department of Agriculture Natural Resources Conservation Service (NRCS) maps the northern site soils as Indianola loamy sand, 5 to 15 percent slopes (InC), and the southern side soils as Everett-Alderwood gravelly sandy loams, 6 to 15 percent slopes (EwC). These soils will have a slight to moderate potential for erosion when disturbed; therefore, the site does not meet the definition for an erosion hazard area as defined by the FWMC. Regardless, erosion protection measures as required by the City of Federal Way will need to be in place prior to initiating grading activities onsite. This would include perimeter silt fencing to contain erosion on- site and cover measures to prevent or reduce soil erosion during and following construction. 3.4.3 Seismic Hazard Areas Section 19.05.070 G of the FWMC defines a Seismic Hazard Area as “those areas subject to severe risk of earthquake damage as a result of seismically induced ground shaking, slope failure, settlement or soil liquefaction, or surface faulting. These conditions occur in areas underlain by cohesionless soils of low density, usually in association with a shallow groundwater table.” Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibration. Liquefaction mainly affects geologically recent deposits of fine-grained sand below the groundwater table. Soils of this nature derive their strength from intergranular friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction, thus, eliminating the soil’s strength. The majority of the site is underlain by glacially consolidated and overridden sediments and no groundwater was observed. It is our opinion that the potential for earthquake damage at the site resulting from seismically induced differential settlement and ground shaking is negligible. Therefore, the site is not considered a seismic hazard area. 3.5 Seismic Design Parameters Based on soil conditions observed in the test pits and our knowledge of the area geology, the current International Building Code (IBC) site class “C” should be used in structural design. 4.0 DISCUSSION AND RECOMMENDATIONS 4.1 General Based on our study, there are no geotechnical considerations that would preclude development of the site as currently planned. The building can be supported on conventional spread footings bearing on competent existing fill soils, or competent native soils below the organic surficial soils, or on structural fill placed and compacted above the competent soils. Floor slabs and pavements can be similarly supported. The sand and gravel soils observed throughout the site would be suitable for use as structural fill during most weather conditions. However, the amount of silt throughout the site varied in percentage and depth. The silty sand and sandy silt soils contain a sufficient amount of fines such that they will be difficult to compact as structural fill when too wet. Accordingly, the ability to use the soils from site excavations as structural fill will depend on their moisture content and the prevailing weather conditions at the time of construction. Depending on the excavation depth and volume of clean sand soils available, the owner should be prepared to import free-draining granular material for use as structural fill and backfill if grading activities will take place during the winter season. May 25, 2021 Project No. T-8425 Page No. 6   The following sections provide detailed recommendations regarding the preceding issues and other geotechnical design and construction considerations. These recommendations should be incorporated into the final design drawings and construction specifications. 4.2 Site Preparation and Grading To prepare the site for construction, all vegetation and organic surface soils should be stripped and removed from below the building lots and roadway areas. Surface stripping depths of approximately five to eight inches should be expected to remove the organic surficial soils. Soil containing organic material will not be suitable for use as structural fill, but may be used for limited depths in nonstructural areas. Once stripping operations are complete, cut and fill operations can be initiated to establish desired grades. Prior to placing fill, all exposed bearing surfaces should be observed by a representative of Terra Associates, Inc. to verify soil conditions are as expected and suitable for support of building foundations and pavement elements, or placement of structural fill. Our representative may request proofrolling the exposed surface with a heavy rubber-tired vehicle to determine if any isolated soft and yielding areas are present. If unsuitable yielding areas are observed, they should be cut to firm bearing soil and filled to grade with structural fill. If depth of excavation to remove unstable soils is excessive, use of geotextile fabric such as Mirafi 500X or equivalent in conjunction with structural fill can be considered in order to limit the depth of removal. Our experience has shown, in general, a minimum of 18 inches of a clean, granular structural fill placed and compacted over the geotextile fabric should establish a stable bearing surface. Our study indicates portions of the existing fill material and silty sand, sandy silt native soils contain a sufficient percentage of fines (silt and clay size particles) that will make them difficult to compact as structural fill if they are too wet or too dry. Accordingly, the ability to use the existing fill and silty sand soils as structural fill will depend on their moisture content and the prevailing weather conditions when site grading activities take place. If wet soils are encountered, the contractor will need to dry the soils by aeration during dry weather conditions. Alternatively, the use of an additive such as Portland cement or lime to stabilize the soil moisture can be considered. If the soil is amended, additional Best Management Practices (BMPs) addressing the potential for elevated pH levels will need to be included in the Storm Water Pollution Prevention Program (SWPPP) prepared with the Temporary Erosion and Sedimentation Control (TESC) plan. The cleaner sand and gravel should be suitable for use as structural fill year-round. If grading activities are planned during the wet winter months, or if they are initiated during the summer and extend into fall and winter, the owner should be prepared to import wet-weather structural fill. For this purpose, we recommend importing a granular soil that meets the following grading requirements: U.S. Sieve Size Percent Passing 6 inches 100 No. 4 75 maximum No. 200 5 maximum* * Based on the ¾-inch fraction. Prior to use, Terra Associates, Inc. should examine and test all materials imported to the site for use as structural fill. May 25, 2021 Project No. T-8425 Page No. 7   Structural fill should be placed in uniform loose layers not exceeding 12 inches, and compacted to a minimum of 95 percent of the soil’s maximum dry density, as determined by American Society for Testing and Materials (ASTM) Test Designation D-1557 (Modified Proctor). The moisture content of the soil at the time of compaction should be within two percent of its optimum, as determined by this ASTM standard. In nonstructural areas, the degree of compaction can be reduced to 90 percent. 4.3 Excavation All excavations at the site associated with confined spaces, such as utility trenches, must be completed in accordance with local, state, and federal requirements. Based on regulations outlined in the Washington Industrial Safety and Health Act (WISHA), the upper medium-dense soils would be classified as Type C soil. The dense native soils would be classified as Type B soil. Accordingly, temporary excavations in Type C soils should have their slopes laid back at an inclination of 1.5:1 (Horizontal: Vertical) or flatter, from the toe to the crest of the slope. Side slopes in Type A soils can be laid back at a slope inclination of 1:1 or flatter. All exposed temporary slope faces that will remain open for an extended period of time should be covered with a durable reinforced plastic membrane during construction to prevent slope raveling and rutting during periods of precipitation. The above information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. It is understood that job site safety is the sole responsibility of the project general contractor. 4.4 Foundation Support The building may be supported on conventional isolated or continuous footing foundations bearing on competent existing fill soils, competent native soils, or new structural fills placed above competent soils. Foundation subgrades should be prepared as recommended in Section 4.2 of this report. Perimeter foundations exposed to the weather should be at a minimum depth of 18 inches below final exterior grades for frost protection. Interior foundations can be constructed at any convenient depth below the floor slab. We recommend designing foundations supported on competent soils for a net allowable bearing capacity of 2,500 pounds per square foot (psf). For short-term loads, such as wind and seismic, a one-third increase in this allowable capacity can be used. With the anticipated building loads and this bearing stress applied to the soil, we estimate total foundation settlement would not exceed one inch. For designing foundations to resist lateral loads, a base friction coefficient of 0.35 can be used. Passive earth pressures acting on the side of the footing and buried portion of the foundation stem wall can also be considered. We recommend calculating this lateral resistance using an equivalent fluid weight of 350 pcf. We recommend not including the upper 12 inches of soil in this computation because they can be affected by weather or disturbed by future grading activity. This value assumes the foundation will be constructed neat against competent native soil or backfilled with structural fill as described in Section 4.2 of this report. The values recommended include a safety factor of 1.5. May 25, 2021 Project No. T-8425 Page No. 8   4.5 Floor Slab-on-Grade Slab-on-grade floors may be supported on a subgrade as recommended in Section 4.2. Immediately below the floor slab, we recommend placing a four-inch thick capillary break layer composed of clean, coarse sand, or fine gravel that has less than five percent passing the No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. The capillary break layer will not prevent moisture intrusion by water vapor transmission through the slab caused by water vapor transmission. Where moisture by vapor transmission is undesirable, such as covered floor areas, a common practice is to place a durable plastic membrane on the capillary break layer and then cover the membrane with a layer of clean sand or fine gravel to protect it from damage during construction, and to aid in uniform curing of the concrete slab. It should be noted, if the sand or gravel layer overlying the membrane is saturated prior to pouring the slab, it will not be effective in assisting uniform curing of the slab and can actually serve as a water supply for moisture bleeding through the slab, potentially affecting floor coverings. Therefore, in our opinion, covering the membrane with a layer of sand or gravel should be avoided if floor slab construction occurs during the wet winter months and the layer cannot be effectively drained. We recommend floor designers and contractors refer to the current American Concrete Institute (ACI) Manual of Concrete Practice for further information regarding vapor barrier installation below slab-on-grade floors. 4.6 Lateral Earth Pressures on Lower-Level Walls The magnitude of earth pressure development on retaining walls will partly depend on the quality of the wall backfill. We recommend placing and compacting wall backfill as structural fill as described in Section 4.2 of this report. To guard against hydrostatic pressure development, drainage must be installed behind the wall. A typical wall drainage detail is shown on Figure 3. With wall backfill placed and compacted as recommended and drainage properly installed, we recommend designing unrestrained walls for an active earth pressure equivalent to a fluid weighing 35 pounds per cubic foot (pcf). For restrained walls, an additional uniform load of 100 psf should be added to the 35 pcf. To account for typical traffic surcharge loading, the walls can be designed for an additional imaginary height of two feet (two-foot soil surcharge). For evaluation of wall performance under seismic loading, a uniform pressure equivalent to 8H psf (where H is the height of the below-grade portion of the wall) should be applied in addition to the static lateral earth pressure. These values assume a horizontal backfill condition and that no other surcharge loading, sloping embankments, or adjacent buildings will act on the wall. If such conditions exist, then the imposed loading must be included in the wall design. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. Values for these parameters are provided in Section 4.4 of this report. May 25, 2021 Project No. T-8425 Page No. 9   4.7 Infiltration Feasibility Our evaluation of feasibility for site infiltration as a means for site stormwater disposal was based on review of the Test Pit Logs and laboratory grain size distribution testing. Based on our evaluation of soil conditions, discharge of development stormwater by use of infiltration may be feasible for facilities that are founded in the sand and gravel formation typically observed about two to eight feet below current site grades. The ability to utilize infiltration should be based on the proposed location of the facilities, with additional analysis undertaken to determine the depth of the infiltratable soils. We used the Soil Grain Size Analysis Method as outlined in Volume III, Section 3.3.6 of the 2014 Washington State Department of Ecology Stormwater Management Manual for Western Washington, to determine a preliminary long-term design infiltration rate. This method correlates the saturated hydraulic conductivity with the D10, D60, and D90 particle sizes determined from gradation testing of the soils in accordance with ASTM Test Designation D-422. The D10 particle size represents the grain size below which ten percent of the soil is smaller in size. The D60 particle size represents the grain size below which 60 percent of the soil is smaller in size. The D90 particle size represents the grain size below which 90 percent of the soil is smaller in size. The particle sizes are put in the Massman formula to determine the saturated hydraulic conductivity. Gradation curves from laboratory testing on the soils are attached in Appendix A. Based on the results of the testing, a long-term design infiltration rate of one inch per hour can be used. In the absence of a groundwater mounding analysis, the 2016 King County Surface Water Design Manual (KCSWDM) requires a minimum five-foot separation between the bottom of the infiltration facility and the seasonal-high groundwater elevation. A separation of three feet may be considered if a groundwater mounding analysis demonstrates the facility would function and not overflow. The bottom of the facility is at elevation 253.00 feet. Based on the seasonal-high groundwater study completed for the site, this is approximately five feet above the seasonal-high groundwater level. Therefore, a mounding analysis is not required for the site. We recommend a representative of Terra Associates, Inc. observe the subgrade of the infiltration facility during construction to ensure the soils exposed are as expected and suitable for infiltration of development stormwater. Our analysis included size factors that were assumed based on our experience. Once the facilities have been sized and located, we will need to perform onsite infiltration tests in accordance with the 2016 KCSWDM to confirm the design infiltration rates. The permeability of the native sand and gravel soils will be significantly impacted by the intrusion of soil fines (silt- and clay-sized particles). Even a relatively minor amount of soil fines can reduce the permeability of the formation by a factor of ten. The greatest exposure to soil fines contamination will occur during mass grading and construction. Therefore, we recommend that the Temporary Erosion and Sedimentation Control (TESC) plans route construction stormwater to a location other than the permanent infiltration trenches. May 25, 2021 Project No. T-8425 Page No. 10   4.8 Drainage Surface Final exterior grades should promote free and positive drainage away from the site at all times. Water must not be allowed to pond or collect adjacent to foundations or within the immediate building areas. We recommend providing a positive drainage gradient away from the building perimeters. If this gradient cannot be provided, surface water should be collected adjacent to the structures and disposed to appropriate storm facilities. Subsurface Installation of perimeter foundation drains will not be required where site pavements extend to the building perimeters and positive drainage away from the building is provided. Where landscaping is placed adjacent to the building, we recommend installing a continuous drain along the outside lower edge of the perimeter building foundation. The drains can be laid to grade at an invert elevation equivalent to the bottom of footing grade. The drains can consist of four-inch diameter perforated PVC pipe that is enveloped in washed pea gravel-sized drainage aggregate. The aggregate should extend six inches above and to the sides of the pipe. Roof and foundation drains should be tightlined separately to the storm drains. All drains should be provided with cleanouts at easily accessible locations. 4.9 Utilities Utility pipes should be bedded and backfilled in accordance with American Public Works Association (APWA) or the local jurisdiction’s specifications. At a minimum, trench backfill should be placed and compacted as structural fill as described in Section 4.2 of this report. As noted, depending on the soil moisture when excavated, most inorganic native soils on the site should be suitable for use as backfill material during dry weather conditions. However, if utility construction takes place during the wet winter months, it will likely be necessary to import suitable wet-weather fill for utility trench backfilling. The cleaner sands and gravels should be suitable to reuse as structural fill in most weather conditions. 4.10 Pavement Pavements should be constructed on subgrades prepared as recommended in Section 4.2 of this report. Regardless of the degree of relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. Proofrolling the subgrade with heavy construction equipment should be completed to verify this condition. The pavement design section is dependent upon the supporting capability of the subgrade soils and the traffic conditions to which it will be subjected. We expect traffic at the facility will consist of cars and light trucks, along with heavy traffic in the form of semi-trucks. For design considerations, we have assumed traffic in parking and in car/light truck access pavement areas can be represented by an 18-kip Equivalent Single Axle Loading (ESAL) of 50,000 over a 20-year design life. For heavy traffic pavement areas, we have assumed an ESAL of 300,000 would be representative of the expected loading. These ESALs represent loading approximately equivalent to 3 and 18, loaded (80,000 pound GVW) tractor-trailer rigs traversing the pavement daily in each area, respectively. May 25, 2021 Project No. T-8425 Page No. 11   With a stable subgrade prepared as recommended for the design ESAL values, we recommend the following pavement sections: Light Traffic/Car Access:  Two inches of hot mix asphalt (HMA) over four inches of crushed rock.  Full depth HMA – 3.5 inches. Heavy Traffic/Truck Access:  Three inches of HMA over six inches of crushed rock.  Full depth HMA – 5 inches. For exterior Portland cement concrete (PCC) pavement, we recommend the following:  Six inches of PCC over two inches of crushed surfacing top course. o 28-day compressive strength – 4,000 psi. o Control joints spaced at a maximum of 15 feet. The paving materials used should conform to the Washington State Department of Transportation (WSDOT) specifications for half-inch class HMA, PCC, and CRB. Long-term pavement performance will depend on surface drainage. A poorly-drained pavement section will be subject to premature failure resulting from surface water infiltrating the subgrade soils and reducing their supporting capability. For optimum performance, we recommend surface drainage gradients of at least two percent. Some degree of longitudinal and transverse cracking of the pavement surface should be expected over time. Regular maintenance should be planned to seal cracks as they occur. 5.0 ADDITIONAL SERVICES Terra Associates, Inc. should review the final design drawings and specifications in order to verify earthwork and foundation recommendations have been properly interpreted and implemented in project design. We should also provide geotechnical service during construction to observe compliance with our design concepts, specifications, and recommendations. This will allow for design changes if subsurface conditions differ from those anticipated prior to the start of construction. May 25, 2021 Project No. T-8425 Page No. 12   6.0 LIMITATIONS We prepared this report in accordance with generally accepted geotechnical engineering practices. No other warranty, expressed or implied, is made. This report is the copyrighted property of Terra Associates, Inc. and is intended for specific application to the 9th Avenue South Industrial project in Federal Way, Washington. This report is for the exclusive use of KG Investments and their authorized representatives. The analyses and recommendations present in this report are based on data obtained from the subsurface explorations completed on-site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to reevaluate the recommendations in this report prior to proceeding with construction. © 2020 Microsoft Corporation © 2020 HERE SITE Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and Figure 1 VICINITY MAP 0 1000 2000 APPROXIMATE SCALE IN FEET REFERENCE: https://www.bing.com/maps ACCESSED 11/20/2020 Proj.No. T-8425 Date: MAY 2021 FEDERAL WAY, WASHINGTON 9th AVENUE SOUTH INDUSTRIAL TP-1 TP-2 TP-7 TP-6 TP-3 TP-5 TP-4 REFERENCE: REFERENCE ONLY AND SHOULD NOT BE USED FOR DESIGN OR CONSTRUCTION PURPOSES. DIMENSIONS ARE APPROXIMATE. IT IS INTENDED FOR THIS SITE PLAN IS SCHEMATIC. ALL LOCATIONS AND LEGEND: 0 100 200 APPROXIMATE SCALE IN FEETSITE PLAN PROVIDED BY BARGHAUSEN. APPROXIMATE TEST PIT LOCATION Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and EXPLORATION LOCATION PLAN Figure 2Proj.No. T-8425 Date: MAY 2021 FEDERAL WAY, WASHINGTON 9th AVENUE SOUTH INDUSTRIAL 12" COMPACTED STRUCTURAL FILL EXCAVATED SLOPE (SEE REPORT TEXT FOR APPROPRIATE INCLINATIONS) SLOPE TO DRAIN 12" MINIMUM 3/4" MINUS WASHED GRAVEL 3" BELOW PIPE 12" OVER PIPE 4" DIAMETER PERFORATED PVC PIPE SEE NOTE 6"(MIN.) NOT TO SCALE NOTE: MIRADRAIN G100N PREFABRICATED DRAINAGE PANELS OR SIMILAR PRODUCT CAN BE SUBSTITUTED FOR THE 12-INCH WIDE GRAVEL DRAIN BEHIND WALL. DRAINAGE PANELS SHOULD EXTEND A MINIMUM OF SIX INCHES INTO 12-INCH THICK DRAINAGE GRAVEL LAYER OVER PERFORATED DRAIN PIPE. Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and TYPICAL WALL DRAINAGE DETAIL Figure 3Proj.No. T-8425 Date: MAY 2021 FEDERAL WAY, WASHINGTON 9th AVENUE SOUTH INDUSTRIAL   Project No. T-8425 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING 9th Avenue South Industrial Federal Way, Washington On November 5, 2020, we explored subsurface conditions at the site by excavating 7 test pits to maximum depths of about 16 feet below existing surface grades using a track-mounted excavator. Three test pits along the western portion of the site (TP-1, TP-5, and TP-6) had two-inch diameter PVC pipes installed to an approximate maximum depth of nine feet upon completion of the test pit. The test pit locations were approximately determined in the field using GPS tracking from Google Earth™ and by pacing and sighting from existing site features. The approximate locations of the test pits are shown on the attached Exploration Location Plan, Figure 2. The Test Pit Logs are represented on Figures A-2 through A-8. A geotechnical engineer from our office conducted the field exploration. Our representative classified the soil conditions encountered, maintained a log of each test pit, obtained representative soil samples, and recorded water levels observed during subsurface exploration. All soil samples were visually classified in accordance with the Unified Soil Classification System (USCS) described on Figure A-1. Representative soil samples obtained from the test pits were placed in closed containers and taken to our laboratory for further examination and testing. The moisture content of each sample was measured and is reported on the individual Test Pit Logs. Grain size analysis was completed on select samples. Grain size analyses results are shown on Figures A-9 and A-10. Environmental Earth Sciences Terra Associates, Inc. Consultants in Geotechnical Engineering Geology and MAJOR DIVISIONS LETTER SYMBOL TYPICAL DESCRIPTION GRAVELS More than 50% of coarse fraction is larger than No. 4 sieve Clean Gravels (less than 5% fines) GW Well-graded gravels, gravel-sand mixtures, little or no fines. GP Poorly-graded gravels, gravel-sand mixtures, little or no fines. Gravels with fines GM Silty gravels, gravel-sand-silt mixtures, non-plastic fines. GC Clayey gravels, gravel-sand-clay mixtures, plastic fines. SANDS More than 50% of coarse fraction is smaller than No. 4 sieve Clean Sands (less than 5% fines) SW Well-graded sands, sands with gravel, little or no fines. SP Poorly-graded sands, sands with gravel, little or no fines. Sands with fines SM Silty sands, sand-silt mixtures, non-plastic fines. SC Clayey sands, sand-clay mixtures, plastic fines. SILTS AND CLAYS Liquid Limit is less than 50% ML Inorganic silts, rock flour, clayey silts with slight plasticity. CL Inorganic clays of low to medium plasticity. (Lean clay) OL Organic silts and organic clays of low plasticity. SILTS AND CLAYS Liquid Limit is greater than 50% MH Inorganic silts, elastic. CH Inorganic clays of high plasticity. (Fat clay) OH Organic clays of high plasticity. HIGHLY ORGANIC SOILS PT Peat.COARSE GRAINED SOILSMore than 50% material largerthan No. 200 sieve sizeFINE GRAINED SOILSMore than 50% material smallerthan No. 200 sieve sizeDEFINITION OF TERMS AND SYMBOLS COHESIONLESSCOHESIVE Standard Penetration Density Resistance in Blows/Foot Very Loose 0-4 Loose 4-10 Medium Dense 10-30 Dense 30-50 Very Dense >50 Standard Penetration Consistancy Resistance in Blows/Foot Very Soft 0-2 Soft 2-4 Medium Stiff 4-8 Stiff 8-16 Very Stiff 16-32 Hard >32 2" OUTSIDE DIAMETER SPILT SPOON SAMPLER 2.4" INSIDE DIAMETER RING SAMPLER OR SHELBY TUBE SAMPLER WATER LEVEL (Date) Tr TORVANE READINGS, tsf Pp PENETROMETER READING, tsf DD DRY DENSITY, pounds per cubic foot LL LIQUID LIMIT, percent PI PLASTIC INDEX N STANDARD PENETRATION, blows per foot UNIFIED SOIL CLASSIFICATION SYSTEM Figure A-1Proj.No. T-8425 Date: MAY 2021 FEDERAL WAY, WASHINGTON 9th AVENUE SOUTH INDUSTRIAL Sample No.Depth (ft)PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W (%)interpreted as being indicative of other locations at the site.NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A-2 T-8425 SLK Federal Way, Washington Grass/Moss November 5, 2020 9th Avenue South Industrial LOG OF TEST PIT NO. TP-1 N/A N/A 3 to 8 ft 6.8 25.7 7.7 Medium Dense Medium Stiff to Medium Dense Medium Dense (5 inches SOD) Gray SAND with silt, fine to medium sand, moist, trace mottling, scattered gravel. (SP- SM) Gray sandy SILT, fine to medium sand, moist, some mottling. (ML) *Pocket of gray gravel with sand on northeast side of test pit from 3 to 6 feet. Gray SAND with silt and gravel, fine to medium sand, fine to coarse gravel, moist to wet. (SP-SM) Test pit terminated at approximately 15 feet. No groundwater observed. Moderate caving observed from 3 to 6 feet (northeast), slight caving 5 to 8 feet (southwest). 2-inch diameter piezometer set at 9 feet. Sample No.Depth (ft)PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W (%)interpreted as being indicative of other locations at the site.NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 A-3 T-8425 SLK Federal Way, Washington Grass November 5, 2020 9th Avenue South Industrial LOG OF TEST PIT NO. TP-2 N/A N/A N/A 8 6.1 Very Dense (7 inches SOD) Gray silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, scattered cobbles. (SM) Test pit terminated at approximately 7 feet due to practical rig refusal. No groundwater observed. No caving observed. Sample No.Depth (ft)PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W (%)interpreted as being indicative of other locations at the site.NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 A-4 T-8425 SLK Federal Way, Washington Grass November 5, 2020 9th Avenue South Industrial LOG OF TEST PIT NO. TP-3 N/A N/A N/A 8.5 14 5.6 4.8 6.8 Medium Dense Dense Very Dense (5 inches SOD) Fill(?): red/brown and gray silty GRAVEL with sand, fine to medium sand, fine to coarse gravel, moist. (GM) Fill (?): dark gray SILT with sand and gravel, fine to medium sand, fine gravel, moist. (ML) Red/brown silty SAND with gravel, fine to medium sand, fine gravel, moist, cobbles. (SM) Gray/brown SAND with silt and gravel, fine to medium sand, fine to coarse gravel, moist, cobbles. (SM) Test pit terminated at approximately 12 feet due to practical rig refusal. No groundwater observed. No caving observed. Sample No.Depth (ft)PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W (%)interpreted as being indicative of other locations at the site.NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 A-5 T-8425 SLK Federal Way, Washington Grass/Vegetation November 5, 2020 9th Avenue South Industrial LOG OF TEST PIT NO. TP-4 N/A N/A N/A 5 6.4 7.1 Medium Dense Dense Very Dense (5 inches SOD) Fill(?): red/brown and gray silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist. (GM) Gray GRAVEL with silt and sand, fine to coarse sand and gravel, moist, cobbles. (GP- GM) Test pit terminated at approximately 12 feet due to practical rig refusal. No groundwater observed. No caving observed. Sample No.Depth (ft)PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W (%)interpreted as being indicative of other locations at the site.NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 A-6 T-8425 SLK Federal Way, Washington Grass November 5, 2020 9th Avenue South Industrial LOG OF TEST PIT NO. TP-5 N/A N/A N/A 7.8 8.9 Medium Dense Dense Very Dense (5 inches SOD) Fill(?): red/brown silty SAND, fine to medium sand, moist, scattered roots. (SM) Gray silty SAND with gravel, fine to medium sand, fine gravel, moist, scattered cobbles. (SM) Gray SAND with silt and gravel, fine to medium sand, fine to coarse gravel, moist, cobbles. (SP-SM) Test pit terminated at approximately 10 feet due to practical rig refusal. No groundwater observed. No caving observed. 2-inch diameter piezometer set at 9 feet. Sample No.Depth (ft)PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W (%)interpreted as being indicative of other locations at the site.NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A-7 T-8425 SLK Federal Way, Washington Grass/Vegetation November 5, 2020 9th Avenue South Industrial LOG OF TEST PIT NO. TP-6 N/A N/A N/A 11.8 7.8 23.9 4.2 Medium Dense (8 inches SOD) FILL (?): Brown/red silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist. (SM) Gray/brown SAND with silt, fine to medium sand, moist. (SP-SM) Gray SILT with sand, fine sand, moist, trace mottling. (ML) Gray/brown SAND with gravel, fine to medium sand, fine gravel, moist, trace silt. (SP) Test pit terminated at approximately 15 feet. No groundwater observed. No caving observed. 2-inch diameter piezometer set at 8.5 feet. Sample No.Depth (ft)PROJECT NAME: PROJ. NO: LOGGED BY: LOCATION: DATE LOGGED: APPROX. ELEV: DEPTH TO CAVING: FIGURE DEPTH TO GROUNDWATER: SURFACE CONDITIONS: Description Consistency/ Relative Density W (%)interpreted as being indicative of other locations at the site.NOTE: This subsurface information pertains only to this test pit location and should not be 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A-8 T-8425 SLK Federal Way, Washington Grass/Moss November 5, 2020 9th Avenue South Industrial LOG OF TEST PIT NO. TP-7 N/A N/A N/A 6.4 5 8.5 Medium Dense Medium Dense to Dense (5 inches SOD) Fill: red/brown silty SAND with gravel, fine to medium sand, fine to coarse gravel, moist, scattered cobbles. (SM) Fill: gray/brown silty SAND with gravel to SAND with silt and gravel, fine to medium sand, fine to coarse gravel, moist, cobbles, scattered boulders. (SM/SP-SM) Test pit terminated at approximately 16 feet. No groundwater observed. No caving observed.