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Home My WebLink AboutEx_09_Geotech_Report Geotechnical Engineering Report Walker’s Renton Subaru 519 SW 12th Street Renton, WA 980057 P/N. 3340404265, 3340404148 December 11, 2024 prepared for: HHJ Construction Attention: John Manuel 601 St Helens Avenue Tacoma, WA 98402 prepared by: Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 (253) 537-9400 MGI Project Z0816 Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 i TABLE OF CONTENTS Page No. 1.0 SITE AND PROJECT DESCRIPTION .............................................................................................. 1 2.0 EXPLORATORY METHODS ............................................................................................................ 2 2.1 Auger Boring Procedures...................................................................................................... 3 3.0 SITE CONDITIONS ............................................................................................................................ 3 3.1 Surface Conditions ................................................................................................................. 3 3.2 Soil Conditions ....................................................................................................................... 4 3.3 Groundwater Conditions ...................................................................................................... 6 3.4 Infiltration Conditions ........................................................................................................... 6 3.5 Seismic Conditions ................................................................................................................. 6 3.6 Liquefaction Potential ........................................................................................................... 7 4.0 CONCLUSIONS AND RECOMMENDATIONS............................................................................ 8 4.1 Site Preparation ...................................................................................................................... 9 4.2 Spread Footings and Bearing Pads .................................................................................... 12 4.3 Slab-On-Grade-Floors .......................................................................................................... 13 4.4 Drainage Systems ................................................................................................................. 14 4.5 Asphalt Pavement ................................................................................................................. 14 4.6 Structural Fill ........................................................................................................................ 16 5.0 RECOMMENDED ADDITIONAL SERVICES ............................................................................. 17 6.0 CLOSURE ........................................................................................................................................... 18 List of Tables Table 1. Approximate Locations and Depths of Explorations ............................................................................. 2 Table 2. Seismic Design Parameters ........................................................................................................................ 7 List of Figures Figure 1. Topographic and Location Map Figure 2. Site and Exploration Plan Figure 3. Geologic Map of Immediate Project Area Figure 2. Regional Liquefaction Susceptibility Map APPENDIX A Soil Classification Chart and Key to Test Data .................................................................................................. A-1 Logs of Auger Borings B-1 through B-5 .................................................................................................... A-2…A-6 Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 Page 1 of 16 MIGIZI GROUP, INC. PO Box 44840 PHONE (253) 537-9400 Tacoma, Washington 98448 FAX (253) 537-9401 December 11, 2024 HHJ Construction 601 St Helens Ave Tacoma, WA 98402 Attention: John Manuel Subject: Geotechnical Engineering Report Walker’s Renton Subaru 519 SW 12th Street Renton, WA 98057 Parcel Nos. 3340404265, -4148 MGI Project Z0816 Dear Mr. Manuel: Migizi Group, Inc. (MGI) is pleased to submit this report describing the results of our geotechnical engineering evaluation of the improvements proposed for the existing Walker’s Renton Subaru facility located in Renton, Washington. This report has been prepared for the exclusive use of HHJ Construction and their consultants for specific application to this project, in accordance with generally accepted geotechnical engineering practices. 1.0 SITE AND PROJECT DESCRIPTION The project site consists of two contiguous tax parcels along the south side of SW 12th Street, between Seneca Ave SW and Lind Ave SW, towards the western city limits of Renton, Washington, as shown on the enclosed Topographic and Location Map (Figure 1). The larger parcel incorporate the existing Subaru parts, service, and repair facility, while the smaller parcel contains an outbuilding for additional parts and vehicle storage. The existing Subaru facility consists of a 19,292-sf building, with a customer waiting area, parts and services department and offices, and a large repair facility with multiple vehicle lifts for servicing. The work area is irregularly shaped, encompassing a total area of approximately 2.30 acres. Asphalt pavement surrounds the primary building for vehicle storage and drive lanes, with only asphalt parking in front of the ancillary parts building. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 2 of 18 Improvement plans involve the partial demolition of the existing Subaru facility, and expansion of the existing service shop to provide additional vehicle bays. The western end of the building addition will be a 2,380-sf, two story facility, constructed to expand the parts department. The building will be a pre-engineering, metal-frame structure, with slab-on-grade at the existing elevation of the current facility. Plans also call for onsite stormwater to be retained and treated onsite in a new precast concrete vault at the southeast corner of the parcel. This stormwater facility will be buried, with asphalt pavement over top for additional vehicle parking. 2.0 EXPLORATORY METHODS We explored surface and subsurface conditions at the project site on November 4-5, 2024. Our exploration and evaluation program comprised the following elements: • Surface reconnaissance of the site, • Five auger boring explorations (designated B-1 through B-5), advanced on November 4-5, 2024, and • A review of published geologic and seismologic maps and literature. Table 1 summarizes the approximate functional locations and termination depths of our subsurface explorations, and Figure 2 depicts their approximate relative locations. The following sections describe the procedures used for excavation of borings. TABLE 1 APPROXIMATE LOCATIONS AND DEPTHS OF EXPLORATIONS Exploration Functional Location Termination Depth (feet) B-1 B-2 B-3 B-4 B-5 Parking Lot, Outbuilding; 47.468761, -122.224168 SE Property corner; 47.467968, -122.223976 SW Building corner; 47.468043, -122.225023 Southern parking lot; 47.468083, -122.224413 NW customer parking; 47.468596, -122.225141 21.5 31.5 31.5 31.5 31.5 The specific number and locations of our explorations were selected by your office, in relation to the existing site features and underground utility conflicts. It should be realized that the explorations performed and utilized for this evaluation reveal subsurface conditions only at discrete locations across the project site and that actual conditions in other areas could vary. Furthermore, the nature and extent of any such variations would not become evident until additional explorations are performed or until construction activities have begun. If significant variations are observed at that time, we may need to modify our conclusions and recommendations contained in this report to reflect the actual site conditions. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 3 of 18 2.1 Auger Boring Procedures Our exploratory borings were advanced through the soil with a hollow stem auger, using a track- mounted drill rig operated by an independent drilling firm working under subcontract to MGI. An engineering geologist from our firm continuously observed the borings, logged the subsurface conditions, and collected representative soil samples. All samples were stored in watertight containers and later transported to a laboratory for further visual examination. After the borings were completed, they were backfilled with bentonite chips and topped with mixed concrete and black dye to better match existing asphalt. Throughout the drilling operation, soil samples were obtained at 2½ or 5-foot depth intervals by means of the Standard Penetration Test (SPT) per ASTM:D-1586. This testing and sampling procedure consists of driving a standard 2-inch-diameter steel split-spoon sampler 18 inches into the soil with a 140-pound hammer free-falling 30 inches. The number of blows required to drive the sampler through each 6-inch interval is counted, and the total number of blows struck during the final 12 inches is recorded as the Standard Penetration Resistance, or "SPT blow count." If a total of 50 blows are struck within any 6-inch interval, the driving is stopped, and the blow count is recorded as 50 blows for the actual penetration distance. The resulting Standard Penetration Resistance values indicate the relative density of granular soils and the relative consistency of cohesive soils. The enclosed boring logs (Appendix A) describe the vertical sequence of soils and materials encountered in the borings, based primarily on our field classifications and supported by our subsequent laboratory examination and testing. Where soil contact was observed to be gradational, our logs indicate the average contact depth. Where a soil type changed between sample intervals, we inferred the contact depth. Our logs also graphically indicate the blow count, sample type, sample number, and approximate depth of each soil sample obtained from the boring, as well as any laboratory tests performed on these soil samples. If any groundwater was encountered in the borehole, the approximate groundwater depth is depicted on the boring log. Groundwater depth estimates are typically based on the moisture content of soil samples, the wet height on the drilling rods, and the water level measured in the borehole after the auger has been extracted. The soils were classified visually in general accordance with the system described in Figure A-1, which includes a key to the exploration logs. Summary logs of our explorations are included as Figures A-2 through A-6. 3.0 SITE CONDITIONS The following sections present our observations, measurements, findings, and interpretations regarding surface, soil, groundwater, infiltration and seismic conditions, and liquefaction potential. 3.1 Surface Conditions As noted above, the project site consists of two contiguous tax parcels along the south side of SW 12th Street, between Seneca Ave SW and Lind Ave SW, towards the western city limits of Renton, Washington. The larger parcel incorporates the existing Walker’s Renton Subaru facility, a 19,292- sf building used for vehicle servicing, office space, and a customer waiting area. The smaller Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 4 of 18 outbuilding is used for additional parts storage. The two parcels total 2.30 acres in size and create an irregular-shaped project area. The service building is surrounded by asphalt pavement used for customer parking, vehicle storage, and drive lanes, while the outbuilding has asphalt pavement along the north side of the structure. The site is situated south of the Bryn Mawr - Skyway highlands, in the valley between the Black River 2,000 feet to the west and the Cedar River 1.4 miles to the east. Topographically, the project area is flat, with minimal grade changes being observed across the paved areas. The topographic low point of the site, sitting roughly 5 to 8 feet below adjacent asphalt, occurs at the southeast corner of the property. Site vegetation is limited to immature deciduous trees and some small flower planting areas around the existing building and in small landscaping planters across the parking areas. In addition, the open stormwater facility is moderately overgrown with thick grass, blackberries, and small deciduous trees. No natural hydrologic features were observed on site, such as seeps, springs, ponds, and streams, nor were there indications of surface hydrology, such ripple marks or scouring present. The property’s existing open stormwater retention facility is located at the southeast corner. 3.2 Soil Conditions Subsurface conditions were observed through the advancement of five auger boring explorations, with three located adjacent to the existing facility, and two located towards the perimeter of the property. All five explorations revealed relatively consistent subgrade conditions, consisting of a typical asphalt section, with loose to medium dense non-native asphalt subbase. The underlying native soil consists of very soft silts and sands, grading to coarser, medium dense sands and gravels at approximately 23 feet. The alluvial deposits encountered onsite are generally associated with flood plain deposits and the historic Black River channel, which drained Lake Washington until 1916, when the opening of the Lake Washington Ship Canal lowered the lake level, causing this portion of the Black River to dry up. All explorations encountered loose to medium dense imported gravely sand between 2 to 4 thick beneath the asphalt base course. This layer of structural fill was observed to be somewhat thicker in B-4, where the exploration was drilled adjacent to a located trench line, with the bottom of the non-native soil being deeper than the surrounding gravel borrow section. Native soils that underlie the project area consist of thick beds of silt and fine to medium sand in varying amounts. This very soft and loose soil was relatively consistent across the project area and were generally found to be on the order of 5 to 11 feet thick. Some organic content (i.e. vegetation roots, small-diameter woody fibers) was also observed within thicker zones of silt-rich soil. Soils were generally observed to increase in density with both depth and increased grain size. Beginning approximately 20 feet below surrounding grade in all four of the deeper explorations (B-2 through B-5), soils graded to more dense and coarse-grained sands with varying amounts of Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 5 of 18 gravel. These soils were observed throughout the termination of the four noted auger bore holes down to a maximum depth of 31.5 feet below grade. In the Geologic Map of the Tacoma 1:100,000-scale Quadrangle, Washington, as prepared by the Washington State Department of Natural Resources Division of Geology and Earth Resources (WSDNR) (2015), the entire project area is mapped as containing Qa, or Holocene alluvium, which is described as loose, stratified to massively bedded fluvial silt, sand, and gravel; typically, well rounded and moderately to well sorted; locally includes sandy to silty estuarine deposits. An excerpt of this map is shown below as Figure 3. Fig. 3: Excerpt from the Geologic Map of the Tacoma 1:100,000-scale Quadrangle, Washington (WSDNR) (2015) The National Resources Conservation Services (NRCS) for King County classifies soils onsite as Ur - Urban Land, indicating that the project site and surrounding areas have been significantly modified through manmade activities. Our field observations generally correspond with the site classifications performed by both the WSDNR and the NRCS. The enclosed exploration logs (Appendix A) provide a detailed description of the soil strata encountered in our subsurface explorations. Project Site Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 6 of 18 3.3 Groundwater Conditions We encountered groundwater in four of the five subsurface explorations at a depth of approximately 8 to 14 feet below existing grade. Given the fact that our explorations were conducted within what is generally considered the rainy season in Western Washington (November 1 to March 31), we anticipate that groundwater levels will rise somewhat higher than that which we observed. Seasonally perched groundwater should be anticipated atop fine- grained soil lenses in close proximity to existing grade. Groundwater levels will fluctuate with localized geology and levels of precipitation. 3.4 Infiltration Conditions As indicated in the Soil Conditions section of the report, the site is underlain by alluvial soils, which can be readily subdivided into three soil horizons: upper fine-grained, intermediate fine- grained sands, and deeper coarse sands and gravels. Given the fact that groundwater levels were observed at between 8 to 14 feet below surrounding grades, the upper soil horizon is the only horizon which could potentially support infiltration. However, these soils range in composition from silty fine sand to silt, the latter of which should be considered relatively impermeable. Given the hydrogeologic setting of the project area, we do not interpret infiltration as being feasible for this project, and site produced stormwater should be managed through detention, and/or diverted to an appropriate discharge location along SW 12th St. 3.5 Seismic Conditions The site is in the Puget Sound basin which has experienced several earthquakes. A detailed description of the regional seismicity is beyond the scope of this report; however, previous regional earthquakes can be split into two general categories: 1.) large earthquakes with a moment magnitude greater than 8.0 (MW > 8.0), and 2.) modest size earthquakes with a moment magnitude generally less than 7.25 (MW < 7.25). In all cases, the thickness of the soil between the bedrock and the ground surface can change (usually amplify) the seismically induced ground motions and therefore the inertial loads acting on surface structures. “Site Class” is a classification system used by the IBC and ASCE 7 to provide some insight to the potential for ground motion amplification. The site class is based on the properties of the upper 100 feet of the soil and rock materials at the site. MGI used a combination of onsite explorations, and our review of the geologic mapping of the site to derive a site class for the site. Based on evaluation and the definitions of Site Class as provided in Table 20.3-1 of ASCE 7-16 (as required by the 2018 International Building Code), the soil conditions on this site satisfy the definition of Site Class D - Default. Our evaluation assumes the soil conditions encountered in the bottom of our explorations, and those from nearby properties, is similar to or increasing in density/consistency down to 100 feet below ground surface. The 2018 IBC considers earthquake shaking to have a 2 percent probability of exceedance in 50 years (i.e. a 2475-year return period), as the code-based design requirement. Using the third- party graphical user interface tools made available by the USGS at https://seismicmaps.org, MGI derived the design ground motions to be used for design of the structures. Our evaluation used Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 7 of 18 IBC 2018 as the code reference, Risk Category I/II/III, and Site Class D - Default. The results of our evaluation are provided in Table 2 (below). TABLE 2 SEISMIC DESIGN PARAMETERS Parameter Value Basis Site Class D - Default Table 20.3-1 of ASCE 7-16 SS 1.444 seismicmaps.org Fa 1.2A seismicmaps.org SMS 1.733 = Fa · SS, 2018 IBC Eqn. 16-36 SDS 1.155 = 2/3 SMS, 2018 IBC Eqn. 16-38 S1 0.492 seismicmaps.org FV 1.808B, C 2018 IBC SM1 0.889B, C = FV · S1, 2018 IBC Eqn. 16-37 SD1 0.593B, C = 2/3 SM1, 2018 IBC Eqn. 16-39 PGA 0.615g seismicmaps.org PGAM 0.737g seismicmaps.org T0 -- C Not applicable TS -- C Not applicable TL 6 sec. seismicmaps.org Notes: A. Use the value provided unless the simplified design procedure of ASCE 7 Section 12.14 is used. If this occurs, please contact our office for more information. B. Based on Table 1613.2.3(2) of the 2018 IBC – An ASCE 7-16 Chapter 21 analysis has not been performed. C. More detailed seismic design criteria are available upon request. Please contact MGI’s office for more information. 3.6 Liquefaction Potential Liquefaction is a sudden increase in pore water pressure and a sudden loss of soil shear strength caused by shear strains, as could result from an earthquake. Research has shown that saturated, loose, fine to medium sands with a fine (silt and clay) content of less than about 20 percent are most susceptible to liquefaction. Subsurface explorations performed within the confines of the project area revealed that native soils are comprised of soft silts and fine sands between 4 to 20 feet beneath the project area. Based on observed groundwater at 8 to 14 feet, these native soils will generally stay in a saturated condition. Given the geologic/hydrogeologic conditions of the project area, we interpret this site as having a moderate to high susceptibility to liquefaction. This interpretation corresponds to the findings by the King County Flood Control map of Liquefaction Susceptibility. The liquefaction susceptibility map of the immediate project area is shown in Figure 4. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 8 of 18 Figure 4: Excerpt of the Liquefaction Susceptibility map of King Co. (2010). During large-scale seismic events, some degree of liquefaction and related post-construction settlement should be anticipated. To potentially mitigate these risks, we recommend constructing engineered structural fill bearing pads beneath the foundation elements, as discussed in Section 4.2 of this report. Section 4.2 provides detailed recommendations on the design and implementation of these bearing pads, including material specifications, compaction requirements, and thickness to improve load distribution and reduce settlement potential. The use of structural fill bearing pads could help improve the performance of the foundations in these challenging soil conditions, particularly regarding liquefaction-related risks. These measures may provide a practical approach to mitigating the identified challenges, depending on the specific site conditions and design requirements. 4.0 CONCLUSIONS AND RECOMMENDATIONS Improvement plans involve the partial demolition of the existing Walker’s Renton Subaru facility, expansion of the existing vehicle service area, and construction of a new 2-story addition on the Project Site Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 9 of 18 western end of the building. The building addition plans to be metal-framed, with a slab-on- grade at existing elevation. This addition will serve as a customer waiting area and include office space for employees. Construction plans also call for the existing asphalt around the building to be removed and replaced with a new asphalt surface. Plans call for stripping and grading the existing stormwater facility, and installation of a new concrete, pre-cast stormwater vault in the southeast corner of the property. After installation of the new facility, the vault will be filled around and over, with new asphalt pavement placed over top for expanded parking. We offer these recommendations: • Feasibility: Based on our field explorations, research and analyses, the proposed structures and pavements appear feasible from a geotechnical standpoint. • Foundation Options: Over-excavation of spread footing subgrades, to a depth of 3 to 5 feet, and the construction of structural fill bearing pads will be necessary for foundation support of the new structure. If foundation construction occurs during wet conditions, it is likely that a geotextile fabric, placed between bearing pads and native soils, will also be necessary. Recommendations for spread footings are provided in Section 4.2. • Floor Options: We recommend over-excavation of slab-on-grade floor subgrades to a minimum depth of 2 feet, then placement of properly compacted structural fill as a floor subbase. If floor construction occurs during wet conditions, it is likely that a geotextile fabric, placed between the structural fill floor subbase and native soils, will be necessary. Recommendations for slab-on-grade floors are included in Section 4.3. Fill underlying floor slabs should be compacted to 95 percent (ASTM:D-1557). • Pavement Sections: We recommend over-excavation of pavement subgrades to a minimum depth of 12 inches, then placement of properly compacted structural fill as pavement subbase. We recommend a conventional pavement section comprised of an asphalt concrete pavement over a crushed rock base course over a properly prepared (compacted) subgrade or a granular subbase, depending on subgrade conditions during pavement subgrade preparation. All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling operation should be over-excavated to a depth of 2 feet and replaced with a suitable structural fill material. • Infiltration Conditions: As indicated in the Soil Conditions section of the report, the site is underlain by shallow, fine-grained alluvial soils. Given the fact that groundwater levels are likely to rise higher than 8 feet below existing grade, which was the shallowest groundwater encountered during explorations, the upper fine-grained soil horizon would be the only horizon which could potentially support infiltration. However, this material ranges in compositions from silty fine sand to silt, the latter of which should be considered relatively impermeable. Given the hydrogeologic setting of the project area, we do not interpret infiltration as being feasible for this project, and site produced stormwater should be managed onsite through detention, or diverted to a suitable discharge location along SW 12th St. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 10 of 18 The following sections of this report present our specific geotechnical conclusions and recommendations concerning site preparation, spread footings, slab-on-grade floors, subgrade and retaining walls, asphalt pavement, and structural fill. The Washington State Department of Transportation (WSDOT) Standard Specifications and Standard Plans cited herein refer to WSDOT publications M41-10, Standard Specifications for Road, Bridge, and Municipal Construction, and M21-01, Standard Plans for Road, Bridge, and Municipal Construction, respectively. 4.1 Site Preparation Preparation of the project site should involve erosion control, temporary drainage, clearing, stripping, excavations, cutting, subgrade compaction, and filling. Erosion Control: Before new construction begins, an appropriate erosion control system should be installed. This system should collect and filter all surface water runoff through silt fencing. We anticipate a system of berms and drainage ditches around construction areas will provide an adequate collection system. Silt fencing fabric should meet the requirements of WSDOT Standard Specification 9-33.2 Table 6. In addition, silt fencing should embed a minimum of 6 inches below existing grade. An erosion control system requires occasional observation and maintenance. Specifically, holes in the filter and areas where the filter has shifted above ground surface should be replaced or repaired as soon as they are identified. Temporary Drainage: We recommend intercepting and diverting any potential sources of surface or near-surface water within the construction zones before stripping begins. Because the selection of an appropriate drainage system will depend on the water quantity, season, weather conditions, construction sequence, and contractor's methods, final decisions regarding drainage systems are best made in the field at the time of construction. Based on our current understanding of the construction plans, surface, and subsurface conditions, we anticipate that curbs, berms, or ditches placed around the work areas will adequately intercept surface water runoff. As the existing site is covered by non-permeable asphalt, sediment-laden stormwater will quickly flow into the existing stormwater system; preventing stormwater from leaving the project area should be done well ahead of any forecasted heavy precipitation events. Clearing and Stripping: After surface and near-surface water sources have been controlled, sod, topsoil, and root-rich soil should be stripped from the site. Our subsurface explorations indicate that there are no organic-rich soils onsite below the existing asphalt pavement in the vicinity of the proposed site development. Stripping is best performed during a period of dry weather. Site Excavations: Based on our explorations, we expect that the vast majority of project excavations will encounter a layer of non-native structural fill under the existing structure and asphalt pavements, underlain by soft, poorly consolidated fine-grained alluvial soils. Both soil types can be readily excavated utilizing standard excavation equipment. Dewatering: Our explorations encountered groundwater in four of five subsurface boring, with the shallowest groundwater being encountered approximately 8 feet below surrounding grades. We anticipate that an internal system of ditches, sump holes, and pumps will be adequate to Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 11 of 18 temporarily dewater shallow excavations. In order to dewater deeper explorations below the regional water table, expensive dewatering equipment, such as well points will need to be utilized. Temporary Cut Slopes: At this time, final designs and construction sequencing have not been completed. To facilitate project planning we provide the following general comments regarding temporary slopes: • All temporary soil slopes associated with site cutting or excavations should be adequately inclined to prevent sloughing and collapse, • Temporary cut slopes in site soils should be no steeper than 1½H:1V, and • Temporary slopes should conform to Washington Industrial Safety and Health Act (WISHA) regulations. These general guidelines are necessarily somewhat conservative (steeper temporary slopes may be possible). As the project progresses, temporary grading plans are developed, final site features are better defined, and a contractor is engaged, MGI may modify these general guidelines to allow steeper slopes. Subgrade Compaction: Exposed subgrades for the foundation of the proposed structure should be compacted to a firm, unyielding state before new concrete or fill soils are placed. Any localized zones of loose granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding soils. In contrast, any organic, soft, or pumping soils observed within a subgrade should be overexcavated and replaced with suitable structural fill material. Site Filling: Our conclusions regarding the reuse of onsite soil and our comments regarding wet- weather filling are presented subsequently. Regardless of soil type, all fill should be placed and compacted according to our recommendations presented in the Structural Fill section of this report. Specifically, building pad fill soil should be compacted to a uniform density of at least 95 percent (based on ASTM:D-1557). Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as structural fill: • Non-native Gravelly Sand: Non-native gravelly sand structural fill underlies existing pavement, and most likely the existing Subaru building. This soil may be reused for structural fill, but a geotechnical engineer should first observe the soil prior to reuse. This soil may become difficult to reuse if placed in an over-optimum moisture condition and should be protected with plastic sheeting during forecasted wet weather. • Alluvial Silt and Silty Fine Sand: The alluvial silt and silty sand that underlies the site is highly moisture sensitive and will likely become impossible to reuse during most weather conditions. As observed, soils are currently above optimum moisture content and will not compact adequately unless aerated or cement treated. Reuse is not recommended, and Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 12 of 18 this material should only be used for non-structural purposes, such as in landscaping areas. • Coarse-Grained Alluvial Sands and Gravels: Native coarse-grained sands and sands with gravel were encountered at significant depths (greater than 20 feet) below ground surface in most explorations. Coarse-grained soils which underlie the site are relatively impervious to moisture content variations and can be reused as structural fill under most weather conditions. Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to reduce long-term raveling, sloughing, and erosion. We generally recommend that no permanent slopes be steeper than 2H:1V. For all soil types, the use of flatter slopes (such as 2½H:1V) would further reduce long-term erosion and facilitate revegetation. Slope Protection: We recommend that a permanent berm, swale, or curb be constructed along the top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover should be established as soon as feasible, to further protect the slopes from runoff water erosion. Alternatively, permanent slopes could be armored with quarry spalls or a geosynthetic erosion mat. 4.2 Spread Footings and Bearing Pads In our opinion, conventional spread footings built atop structural fill bearing pads will provide adequate support for the proposed structures if the subgrade is properly prepared. We offer the following comments and recommendations for spread footing design. Footing Depths and Widths: For frost and erosion protection, the bases of all exterior footings should bear at least 18 inches below adjacent outside grades, whereas the bases of interior footings need bear only 12 inches below the surrounding slab surface level. To reduce post-construction settlements, continuous (wall) and isolated (column) footings should be at least 18 and 24 inches wide, respectively. Bearing Subgrades: Given the poor consolidation of near surface soils in the immediate vicinity of the project area, structural fill bearing pads 3 to 5 feet thick and compacted to a density of at least 95 percent (based on ASTM:D-1557), should underlie all foundation elements on this site. If foundation construction occurs during wet conditions, a geotextile fabric may be necessary between the bearing pad and native soils. We should be consulted if any new foundations are to be placed adjacent to existing foundations. Refer to the Structural Fill section of this report for more detail. In general, before footing concrete is placed, any localized zones of loose soils exposed across the footing subgrades should be compacted to a firm, unyielding condition, and any localized zones of soft, organic, or debris-laden soils should be over-excavated and replaced with suitable structural fill. Lateral Over excavations: Because foundation stresses are transferred outward as well as downward into the bearing soils, all structural fill placed under footings, should extend Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 13 of 18 horizontally outward from the edge of each footing. This horizontal distance should be equal to the depth of placed fill. Therefore, placed fill that extends 3 feet below the bottom elevation of the foundation should also extend 3 feet outward, in both directions, from the footing edges. Subgrade Observation: All footing subgrades should consist of firm, unyielding, native soils, or structural fill materials that have been compacted to a density of at least 95 percent (based on ASTM:D-1557). Footings should never be cast atop loose, soft, or frozen soil, slough, debris, existing uncontrolled fill, or surfaces covered by standing water. Bearing Pressures: For static loading purposes, footings that bear on dense, properly prepared structural fill bearing pads can be designed for maximum allowable soil bearing pressures listed in the table on the following page: Bearing Pad Thickness (feet) Allowable Bearing Pressure (psf) 3 1,500 4 2,000 5 2,500 A one-third increase in allowable soil bearing capacity may be used for short-term loads created by seismic or wind related activities. Footing Settlements: Assuming that structural fill soils are compacted to a medium dense or denser state, we estimate that total post-construction settlements of properly designed footings bearing on properly prepared subgrades will not exceed 1 inch under static conditions. Differential settlements for comparably loaded elements may approach one-half of the actual total settlement over horizontal distances of approximately 50 feet. Footing Backfill: We recommend all footing excavations be backfilled on both sides of the footings and stem walls after the concrete has been cured. This will provide erosion protection and lateral load resistance. Only imported structural fill should be used for this purpose, contingent on suitable moisture content at the time of placement. Onsite native fine-grained soils should not be used. Regardless of soil type, all footing backfill soil should be compacted to a density of at least 90 percent (based on ASTM:D-1557). 4.3 Slab-On-Grade Floors In our opinion, soil-supported slab-on-grade floors can be used for the planned structures if the subgrades are properly prepared. We offer the following comments and recommendations concerning slab-on-grade floors. Floor Subbase: Given the poor consolidation of near surface soil observed across the project area, we recommend over-excavation of slab-on-grade floor subgrades to a minimum depth of 2 feet, with placement and thorough compaction of structural fill as a floor subbase. If floor construction occurs during wet conditions, it is likely that a geotextile fabric, placed between the structural fill Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 14 of 18 floor subbase and native soils, will be necessary. All subbase fill should be compacted to a density of at least 95 percent (based on ASTM:D-1557). Capillary Break and Vapor Barrier: To retard the upward wicking of moisture beneath the floor slab, we recommend that a capillary break be placed over the floor subbase and beneath the slab vapor barrier. Ideally, this capillary break would consist of a 4-inch-thick layer of pea gravel or other clean, uniform, well-rounded gravel, such as “Gravel Backfill for Drains” per WSDOT Standard Specification 9-03.12(4), but clean angular gravel can be used if it adequately prevents capillary wicking. A manufactured product, such as 5/8 inch minus crushed rock, should not be used as cap break, as the “minus” component of the crushed rock facilitates moisture wicking beneath a poured slab. In addition, a layer of plastic sheeting (such as Crosstuff, Visqueen, or Moistop) should be placed over the capillary break to serve as a vapor barrier. During subsequent casting of the concrete slab, the contractor should exercise care to avoid puncturing this vapor barrier. 4.4 Drainage Systems In our opinion, the proposed structure should be provided with a permanent drainage system to reduce the risk of future moisture problems, given the low permeability nature of the shallow non- native soils which underlie the project area. We offer the following recommendations and comments for drainage design and construction purposes. Perimeter Drains: We recommend that the structure be encircled with a perimeter drain system to collect seepage water. This drain should consist of a 6-inch-diameter perforated pipe within an envelope of pea gravel or washed rock, extending at least 6 inches on all sides of the pipe, and the gravel envelope should be wrapped with filter fabric to reduce migration of fines from the surrounding soils. Ideally, the drain invert would be installed no more than 8 inches above the base of the perimeter footings. Discharge Considerations: If possible, all perimeter drains should discharge to a sewer system, the proposed stormwater facility, or other suitable location by gravity flow. Check valves should be installed along any drainpipes that discharge to a sewer system to prevent sewage backflow into the drain system. If gravity flow is not feasible, a pump system is recommended to discharge any water that enters the drainage system. Runoff Water: Roof- and surface-runoff water should not discharge into the perimeter drain system. Instead, these sources should discharge into separate tightline pipes and be routed away from the structure to a storm drain or other appropriate location. Grading and Capping: Final site grades should slope downward away from the structure so that runoff water will flow by gravity to suitable collection points, rather than ponding near the building. Ideally, the area surrounding the building will be capped with concrete, asphalt, or low- permeability (silty) soils to minimize or preclude surface-water infiltration. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 15 of 18 4.5 Asphalt Pavement Plans call for the eventual replacement of existing asphalt across the project area after major construction operations have been completed. We offer the following comments and recommendations for pavement design and construction. Subgrade Preparation: We recommend over-excavation of pavement subgrades to depths of 12 or 24 inches, based on geotechnical observation, then placement of properly compacted structural fill as pavement subbase. If construction occurs during wet conditions, it is likely that a geotextile fabric, placed between the structural fill pavement subbase and native soils, will be necessary. We recommend a conventional pavement section comprised of an asphalt concrete pavement over a crushed rock base course over a properly prepared (compacted) subgrade or a granular subbase, depending on subgrade conditions during pavement subgrade preparation. All soil subgrades should be thoroughly compacted, then proof-rolled with a loaded dump truck or heavy compactor. Any localized zones of yielding subgrade disclosed during this proof-rolling operation should be over-excavated to a depth of 2 feet and replaced with a suitable structural fill material. All structural fill should be compacted according to our recommendations given in the Structural Fill section. Specifically, the upper 2 feet of soils underlying pavement section should be compacted to at least 95 percent (based on ASTM D-1557), and all soils below 2 feet should be compacted to at least 90 percent. Pavement Materials: We recommend using imported washed crushed rock, such as "Crushed Surfacing Base Course” per WSDOT Standard Specification 9-03.9(3) but with a fines content of less than 5 percent passing the No. 200 Sieve for the asphalt sections base course. Observations made during explorations do not indicate a need for a pavement subbase. We recommend using imported, clean, well-graded sand and gravel such as “Ballast” or “Gravel Borrow” per WSDOT Standard Specifications 9-03.9(1) and 9-03.14, respectively, should a subbase course be needed based on geotechnical observations. Conventional Asphalt Sections: A conventional pavement section typically comprises an asphalt concrete pavement over a crushed rock base course. We recommend using the following conventional pavement sections: Minimum Thickness Pavement Course Parking Areas High Traffic Driveways Asphalt Concrete Pavement 3 inches 4 inches Crushed Rock Base 6 inches 8 inches Granular Fill Subbase (if needed) 12 inches 24 inches Compaction and Observation: All subbase and base course material should be compacted to at least 95 percent of the Modified Proctor maximum dry density (ASTM D-1557), and all asphalt concrete should be compacted to at least 92 percent of the Rice value (ASTM D-2041). We recommend that an MGI representative be retained to observe the compaction of each course before any overlying layer is placed. For the subbase and pavement course, compaction is best Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 16 of 18 observed by means of frequent density testing. For the base course, methodology observations and hand-probing are more appropriate than density testing. Pavement Life and Maintenance: No asphalt pavement is maintenance-free. The above-described pavement sections present our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. Furthermore, a 20-year pavement life typically assumes that an overlay will be placed after about 10 years. Thicker asphalt and/or thicker base and subbase courses would offer better long-term performance but would cost more initially; thinner courses would be more susceptible to “alligator” cracking and other failure modes. As such, pavement design can be considered a compromise between a high initial cost and low maintenance costs versus a low initial cost and higher maintenance costs. 4.6 Structural Fill The term "structural fill" refers to any material placed under foundations, retaining walls, slab-on- grade floors, sidewalks, pavements, and other structures. Our comments, conclusions, and recommendations concerning structural fill are presented in the following paragraphs. Materials: Typical structural fill materials include clean sand, gravel, pea gravel, washed rock, crushed rock, well-graded mixtures of sand and gravel (commonly called "gravel borrow" or "pit- run"), and miscellaneous mixtures of silt, sand, and gravel. Import materials meeting WSDOT Standard Specification 9-03.14(1) gravel borrow will be satisfactory for use as structural fill during dry weather. Recycled asphalt, concrete, and glass, which are derived from pulverizing the parent materials, are also potentially useful as structural fill in certain applications. Soils used for structural fill should not contain any organic matter or debris, nor any individual particles greater than about 6 inches in diameter. Fill Placement: Clean sand, gravel, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a mechanical compactor. Compaction Criteria: Using the Modified Proctor test (ASTM:D-1557) as a standard, we recommend that structural fill used for various onsite applications be compacted to the following minimum densities: Fill Application Minimum Compaction Footing subgrade and bearing pad Foundation backfill Asphalt pavement base Asphalt pavement subgrade (upper 2 feet) Asphalt pavement subgrade (below 2 feet) 95 percent 90 percent 95 percent 95 percent 90 percent Subgrade Observation and Compaction Testing: Regardless of material or location, all structural fill should be placed over firm, unyielding subgrades prepared in accordance with the Site Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 17 of 18 Preparation section of this report. The condition of all subgrades should be observed by geotechnical personnel before filling or construction begins. Also, fill soil compaction should be verified by means of in-place density tests performed during fill placement so that adequacy of soil compaction efforts may be evaluated as earthwork progresses. Soil Moisture Considerations: The suitability of soils used for structural fill depends primarily on their grain-size distribution and moisture content when they are placed. As the "fines" content (that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot be consistently compacted to a firm, unyielding condition when the moisture content is more than 2 percentage points above or below optimum. For fill placement during wet-weather site work, we recommend using "clean" fill, which refers to soils that have a fines content of 5 percent or less (by weight) based on the soil fraction passing the U.S. No. 4 Sieve. 5.0 RECOMMENDED ADDITIONAL SERVICES Because the future performance and integrity of the structural elements will depend largely on proper site preparation, drainage, fill placement, and construction procedures, monitoring and testing by experienced geotechnical personnel should be considered an integral part of the construction process. Subsequently, we recommend that MGI be retained to provide the following post-report services: • Review all construction plans and specifications to verify that our design criteria presented in this report have been properly integrated into the design, • Prepare a letter summarizing all review comments (if required), • Check all completed subgrades for footings and slab-on-grade floors before concrete is poured, in order to verify their bearing capacity, and, • Prepare a post-construction letter summarizing all field observations, inspections, and test results (if required). Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 HHJ Const. – Walker’s Renton Subaru, 519 SW 12th Street, Renton, WA December 11, 2024 Geotechnical Engineering Report Z0816 Migizi Group, Inc. Page 18 of 18 6.0 CLOSURE The conclusions and recommendations presented in this report are based, in part, on the explorations that we observed for this study; therefore, if variations in the subgrade conditions are observed at a later time, we may need to modify this report to reflect those changes. Also, because the future performance and integrity of the project elements depend largely on proper initial site preparation, drainage, and construction procedures, monitoring and testing by experienced geotechnical personnel should be considered an integral part of the construction process. MGI is available to provide geotechnical monitoring of soils throughout construction. We appreciate the opportunity to be of service on this project. If you have any questions regarding this report or any aspects of the project, please feel free to contact our office. Respectfully submitted, MIGIZI GROUP, INC. Randall V. Conger-Best, L.G. James E. Brigham, P.E. Senior Staff Geologist Senior Principal Engineer Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 APPROXIMATE SITE LOCATION P.O. Box 44840 Tacoma, WA 98448 Location Job Number Figure DateTitle 519 SW 12th Street Renton, WA 98057 Topographic and Location Map 1 12/01/24 Z0816 Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 222000mmm 666000fffttt +– 47.46835 -122.22446 Degrees    JOB NO. PROJECT: SHEET TITLE: FILE: FIGURE: SCALE: DATE: CHECKED BY: DRAWN BY: DESIGNER: Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 253-537-9400 253-537-9401 fax www.migizigroup.com 519 SW 12th Street Renton, WA 98057 Site and Exploration Plan Nov. 08, 2024 JEB RVCB RVCB Z0816 NTS 2 Fig2.dwg Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 APPENDIX A SOIL CLASSIFICATION CHART AND KEY TO TEST DATA LOGS OF BORINGS Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 CLAYEY GRAVELS, POORLY GRADED GRAVEL-SAND-CLAY MIXTURES SILTS AND CLAYS CO A R S E G R A I N E D S O I L S Mo r e t h a n H a l f > # 2 0 0 s i e v e LIQUID LIMIT LESS THAN 50 LIQUID LIMIT GREATER THAN 50 CLEAN GRAVELS WITH LITTLE OR NO FINES GRAVELS WITH OVER 15% FINES CLEAN SANDS WITH LITTLE OR NO FINESMORE THAN HALF COARSE FRACTION IS SMALLER THAN NO. 4 SIEVE MORE THAN HALF COARSE FRACTION IS LARGER THAN NO. 4 SIEVE INORGANIC SILTS, MICACEOUS OR DIATOMACIOUS FINE SANDY OR SILTY SOILS, ELASTIC SILTS ORGANIC CLAYS AND ORGANIC SILTY CLAYS OF LOW PLASTICITY OH INORGANIC SILTS AND VERY FINE SANDS, ROCK FLOUR,SILTY OR CLAYEY FINE SANDS, OR CLAYEY SILTS WITH SLIGHT PLASTICITY CH SILTY GRAVELS, POORLY GRADED GRAVEL-SAND-SILT MIXTURES SANDS SILTS AND CLAYS Figure A-1 INORGANIC CLAYS OF LOW TO MEDIUM PLASTICITY, GRAVELLY CLAYS, SANDY CLAYS, SILTY CLAYS,LEAN CLAYS E3RA R-Value Sieve Analysis Swell Test Cyclic Triaxial Unconsolidated Undrained Triaxial Torvane Shear Unconfined Compression (Shear Strength, ksf) Wash Analysis (with % Passing No. 200 Sieve) Water Level at Time of Drilling Water Level after Drilling(with date measured) RV SA SW TC TX TV UC (1.2) WA (20) Modified California Split Spoon Pushed Shelby Tube Auger Cuttings Grab Sample Sample Attempt with No Recovery Chemical Analysis Consolidation Compaction Direct Shear Permeability Pocket Penetrometer CA CN CP DS PM PP PtHIGHLY ORGANIC SOILS TYPICAL NAMES GRAVELS ORGANIC CLAYS OF MEDIUM TO HIGH PLASTICITY, ORGANIC SILTS WELL GRADED GRAVELS, GRAVEL-SAND MIXTURES MAJOR DIVISIONS PEAT AND OTHER HIGHLY ORGANIC SOILS WELL GRADED SANDS, GRAVELLY SANDS POORLY GRADED SANDS, GRAVELLY SANDS SILTY SANDS, POOORLY GRADED SAND-SILT MIXTURES CLAYEY SANDS, POORLY GRADED SAND-CLAY MIXTURES POORLY GRADED GRAVELS, GRAVEL-SAND MIXTURES SOIL CLASSIFICATION CHART AND KEY TO TEST DATA GW GP GM GC SW SP SM SC ML FI N E G R A I N E D S O I L S Mo r e t h a n H a l f < # 2 0 0 s i e v e LG D A N N N N 0 2 G I N T U S L A B . G P J 1 1 / 4 / 0 5 INORGANIC CLAYS OF HIGH PLASTICITY, FAT CLAYS CL OL MH SANDS WITH OVER 15% FINES Migizi Group, Inc. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-1 SS S-2 SS S-3 SS S-4 20.8 20.3 16.8 14.0 12.0 11.5 5-3-2 (5) 1-2-8 (10) 5-7-9 (16) 3-3-5 (8) GP SP ML SP GP SP 0.3 0.7 4.3 7.0 9.0 9.5 Asphalt (GP) 5/8 inch minus crushed rock (Moist, Dense)Imported crushed surfacing base course (SP) Brown gravelly sand (Moist, Medium Dense)Imported asphalt section subbase (ML) Gray silt with gravel and sand (Moist, Very Soft) (SP) Brown gravelly sand (Moist, Medium Dense) (GP) Gray gravel with sand (Moist, Medium Dense) Coarse-grained lens (SP) Dark gray medium to coarse sand with fine gravel (Moist, Loose) NOTES LOGGED BY RVCB DRILLING METHOD Track Mounted Drill Rig DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 11/4/24 COMPLETED 11/4/24 AT TIME OF DRILLING 10.00 ft / Elev 11.00 ft AT END OF DRILLING --- AFTER DRILLING --- HOLE SIZE 4.25" HSAGROUND ELEVATION 21 ft SA M P L E T Y P E NU M B E R DE P T H (f t ) 0.0 2.5 5.0 7.5 10.0 (Continued Next Page) PAGE 1 OF 2 Figure A-2 BORING NUMBER B-1 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-5 SS S-6 5.0 3.0 -0.5 1-0-1 (1) 11-10-7 (17) SP ML SP 16.0 18.0 21.5 (SP) Dark gray medium to coarse sand with fine gravel (Moist, Loose) (continued) Grades to medium to coarse sand (ML) Gray fine sandy silt (Moist, Very Soft) (SP) Gray coarse sand with fine gravel (Moist, Medium Dense) Observed zone of heaving sands Bottom of borehole at 21.5 feet. SA M P L E T Y P E NU M B E R DE P T H (f t ) 12.5 15.0 17.5 20.0 PAGE 2 OF 2 Figure A-2 BORING NUMBER B-1 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-1 SS S-2 SS S-3 SS S-4 29.8 29.3 28.0 23.0 21.0 3-2-1 (3) 1-0-0 (0) 15-9-9 (18) 13-7-2 (9) GP SP ML SP SP 0.3 0.7 2.0 7.0 9.0 Asphalt (GP) 5/8 inch minus crushed rock (Moist, Dense)Imported crushed surfacing base course (SP) Brown gravelly sand (Moist, Medium Dense)Imported asphalt section subbase (ML) Mottled brown/gray silt with fine sand (Moist, Very Soft) (SP) Brown/gray sand with gravel (Moist, Loose) (SP) Gray fine to medium sand (Moist, Loose) NOTES LOGGED BY RVCB DRILLING METHOD Track Mounted Drill Rig DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 11/4/24 COMPLETED 11/4/24 AT TIME OF DRILLING 14.00 ft / Elev 16.00 ft AT END OF DRILLING --- AFTER DRILLING --- HOLE SIZE 4.25" HSAGROUND ELEVATION 30 ft SA M P L E T Y P E NU M B E R DE P T H (f t ) 0.0 2.5 5.0 7.5 10.0 (Continued Next Page) PAGE 1 OF 3 Figure A-3 BORING NUMBER B-2 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-5 SS S-6 15.0 6.0 1-0-1 (1) 2-1-2 (3) SP ML SP 15.0 24.0 (SP) Gray fine to medium sand (Moist, Loose) (continued) (ML) Gray organic-rich silt with fine sand (Moist, Very Soft) (SP) Gray fine to medium gravelly coarse sand (Moist, Medium Dense) SA M P L E T Y P E NU M B E R DE P T H (f t ) 12.5 15.0 17.5 20.0 22.5 25.0 (Continued Next Page) PAGE 2 OF 3 Figure A-3 BORING NUMBER B-2 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SSS-7 SS S-8 1.0 -1.0 -1.5 12-10-20(30) 16-21-21 (42) SP SP GP 29.0 31.0 31.5 (SP) Gray fine to medium gravelly coarse sand (Moist, Medium Dense) (continued) (SP) Gray medium to coarse sand (Moist, Dense) (GP) Gray medium gravel (Moist, Dense) Bottom of borehole at 31.5 feet. SA M P L E T Y P E NU M B E R DE P T H (f t ) 27.5 30.0 PAGE 3 OF 3 Figure A-3 BORING NUMBER B-2 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-1 SS S-2 SS S-3 SS S-4 29.8 29.3 28.0 19.0 4-2-2 (4) 2-2-1 (3) 1-0-0 (0) 0 GP SP ML SP 0.3 0.7 2.0 11.0 Asphalt (GP) 5/8 inch minus crushed rock (Moist, Dense)Imported crushed surfacing base course (SP) Brown gravelly sand (Moist, Medium Dense)Imported asphalt section subbase (ML) Gray silt with fine sand (Moist, Very Soft) (SP) Gray fine to medium sand (Moist, Loose) NOTES LOGGED BY RVCB DRILLING METHOD Track Mounted Drill Rig DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 11/4/24 COMPLETED 11/4/24 AT TIME OF DRILLING 10.00 ft / Elev 20.00 ft AT END OF DRILLING --- AFTER DRILLING --- HOLE SIZE 4.25" HSAGROUND ELEVATION 30 ft SA M P L E T Y P E NU M B E R DE P T H (f t ) 0.0 2.5 5.0 7.5 10.0 (Continued Next Page) PAGE 1 OF 3 Figure A-4 BORING NUMBER B-3 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-5 SS S-6 10.0 7.0 3-2-3 (5) 1-1-0 (1) SP ML SP 20.0 23.0 (SP) Gray fine to medium sand (Moist, Loose) (continued) (ML) Gray organic-rich silt (Moist, Very Soft) (SP) Gray fine to medium gravelly coarse sand (Moist, Loose) SA M P L E T Y P E NU M B E R DE P T H (f t ) 12.5 15.0 17.5 20.0 22.5 25.0 (Continued Next Page) PAGE 2 OF 3 Figure A-4 BORING NUMBER B-3 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SSS-7 SS S-8 3.0 -1.0 -1.5 7-2-7(9) 7-16-20 (36) SP SP SP 27.0 31.0 31.5 (SP) Gray fine to medium gravelly coarse sand (Moist, Loose) (continued) Soils grade to medium dense (SP) Gray medium to coarse sand (Moist, Dense) (SP) Brown coarse sandy fine to medium gravel (Moist, Dense) Bottom of borehole at 31.5 feet. SA M P L E T Y P E NU M B E R DE P T H (f t ) 27.5 30.0 PAGE 3 OF 3 Figure A-4 BORING NUMBER B-3 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-1 SS S-2 SS S-3 SS S-4 29.8 29.3 26.5 23.5 19-22-13 (35) 6-5-5 (10) 2-0-1 (1) 1-0-0 (0) GP SP SP ML 0.3 0.7 3.5 6.5 Asphalt (GP) 5/8 inch minus crushed rock (Moist, Dense)Imported crushed surfacing base course (SP) Brown gravelly sand (Moist, Medium Dense)Imported asphalt section subbase (SP) Brown gravelly sand (Moist, Loose) Imported trench backfill soils (ML) Gray silt with fine sand (Moist, Very Soft) Soils grade to fine sandy silt NOTES LOGGED BY RVCB DRILLING METHOD Track Mounted Drill Rig DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 11/5/24 COMPLETED 11/5/24 AT TIME OF DRILLING --- AT END OF DRILLING --- AFTER DRILLING --- HOLE SIZE 4.25" HSAGROUND ELEVATION 30 ft SA M P L E T Y P E NU M B E R DE P T H (f t ) 0.0 2.5 5.0 7.5 10.0 (Continued Next Page) PAGE 1 OF 3 Figure A-5 BORING NUMBER B-4 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-5 SS S-6 16.0 9.0 5.0 0 0-0-5 (5) ML ML SP-SM SP 14.0 21.0 25.0 (ML) Gray silt with fine sand (Moist, Very Soft) (continued) (ML) Gray organic-rich silt with fine sand (Moist, Very Soft) Soils grade to firm (SP-SM) Fine to coarse sand with silt (Moist, Medium Dense) (SP) Gray medium to coarse sand with fine gravel (Moist, Dense) SA M P L E T Y P E NU M B E R DE P T H (f t ) 12.5 15.0 17.5 20.0 22.5 25.0 (Continued Next Page) PAGE 2 OF 3 Figure A-5 BORING NUMBER B-4 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SSS-7 SS S-8 -1.0 -1.5 1-7-17(24) 10-21-30 (51) SP GP 31.0 31.5 (SP) Gray medium to coarse sand with fine gravel (Moist, Dense) (continued) Soils grade to medium to coarse gravel (GP) Gray/brown coarse sandy fine to coarse gravel (Moist, Dense) Bottom of borehole at 31.5 feet. SA M P L E T Y P E NU M B E R DE P T H (f t ) 27.5 30.0 PAGE 3 OF 3 Figure A-5 BORING NUMBER B-4 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-1 SS S-2 SS S-3 SS S-4 29.8 29.3 27.5 22.0 20.0 1-1-1 (2) 1-2-1 (3) 1-1-1 (2) 1-0-1 (1) GP SP ML ML SP-SM 0.3 0.7 2.5 8.0 10.0 Asphalt (GP) 5/8 inch minus crushed rock (Moist, Dense)Imported crushed surfacing base course (SP) Brown gravelly sand (Moist, Medium Dense)Imported asphalt section subbase (ML) Mottled brown/gray silt with fine sand (Moist, Very Soft) (ML) Mottled brown fine sandy silt (Moist, Very Soft) (SP-SM) Gray medium to coarse sand with silt (Moist, Loose) NOTES LOGGED BY RVCB DRILLING METHOD Track Mounted Drill Rig DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: CHECKED BY JEB DATE STARTED 11/5/24 COMPLETED 11/5/24 AT TIME OF DRILLING 8.00 ft / Elev 22.00 ft AT END OF DRILLING --- AFTER DRILLING --- HOLE SIZE 4.25" HSAGROUND ELEVATION 30 ft SA M P L E T Y P E NU M B E R DE P T H (f t ) 0.0 2.5 5.0 7.5 10.0 (Continued Next Page) PAGE 1 OF 3 Figure A-6 BORING NUMBER B-5 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SS S-5 SS S-6 17.0 9.0 0 2-8-16 (24) SP-SM ML SP 13.0 21.0 (SP-SM) Gray medium to coarse sand with silt (Moist, Loose) (continued) (ML) Gray/brown organic-rich silt with fine sand (Moist, Very Soft) (SP) Gray fine gravelly coarse sand (Moist, Medium Dense) SA M P L E T Y P E NU M B E R DE P T H (f t ) 12.5 15.0 17.5 20.0 22.5 25.0 (Continued Next Page) PAGE 2 OF 3 Figure A-6 BORING NUMBER B-5 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 SSS-7 SS S-8 4.0 3.0 0.0 -1.0 -1.5 7-5-13(18) 7-14-21 (35) SP SP SP SP GP 26.0 27.0 30.0 31.0 31.5 (SP) Gray fine gravelly coarse sand (Moist, Medium Dense) (continued) (SP) Gray medium to coarse sand (Moist, Medium Dense) (SP) Gray coarse sand with trace fine gravel (Moist, Dense) (SP) Gray medium to coarse sand (Moist, Dense) (GP) Gray coarse sandy fine gravel (Moist, Dense) Bottom of borehole at 31.5 feet. SA M P L E T Y P E NU M B E R DE P T H (f t ) 27.5 30.0 PAGE 3 OF 3 Figure A-6 BORING NUMBER B-5 CLIENT HHJ Construction PROJECT NUMBER Z0816 PROJECT NAME Walker's Renton Subaru PROJECT LOCATION 519 SW 12th Street, Renton WA CO P Y O F G E N E R A L B H / T P L O G S - F I G U R E . G D T - 1 1 / 2 6 / 2 4 1 2 : 4 0 - C : \ U S E R S \ J E S S I C A B I Z A K \ D E S K T O P \ T E S T P I T S A N D B O R I N G S - G I N T \ Z 0 8 1 6 \ Z 0 8 1 6 B O R I N G L O G . G P J Migizi Group, Inc. PO Box 44840 Tacoma, WA 98448 Telephone: 253-537-9400 RE C O V E R Y ( i n ) (R Q D ) BL O W CO U N T S (N V A L U E ) U. S . C . S . GR A P H I C LO G MATERIAL DESCRIPTION Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 Preliminary Technical Information Report Walker Subaru Service Center 2240819.10 Appendix E Non-Structural BMPs A-1 .................... Required Best Management Practices (BMPs) for all Properties with Commercial Activities A-8 .................... Storage or Solid and Food Wastes (Including Cooking Grease) A-45 .................. Maintenance of Public and Private Utility Corridors and Facilities Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 Stormwater Pollution Prevention Manual • King County 27 A-1 Required Best Management Practices for all Properties with Commercial Activities The following Best Management Practices (BMPs) are required for all commercial, industrial, agricultural, public, or residential properties with commercial activities in unincorporated King County. Best Management Practices (BMPs) are required by King County Code 9.12. If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs: Clean and Maintain Storm Drainage System • Evaluate the condition of the catch basin by checking the amount of sediment in the bottom of the sump. Catch basins must be cleaned out when the solids, trash, and debris in the sump reaches one–half of the depth between the bottom of the sump and the bottom of the lowest inflow or outflow pipe connected to the catch basin or is at least 6 inches below this point. • Hire a professional drainage contractor to inspect and maintain your system or clean the system yourself. If there is sediment or other debris in the drainage pipes, then a professional contractor must be hired to flush or jet out the pipes. • Small amounts of floating oil can be soaked up with oil absorbent pads, bagged and disposed of as solid waste. • Up to one cubic yard of nonhazardous solid material may be disposed of as solid waste in your regular garbage. If you exceed this threshold hire a professional drainage contractor. All of the solids and stagnant water collected from catch basin sumps must be disposed of properly. None of the sump contents can be flushed into the catch basin outflow pipe. Depending on the nature of the pollutants in the sump, and the associated types of activities taking place on the site, the sump contents may need to be handled as contaminated waste. Contractors who perform catch basin clean–out services are required to follow appropriate disposal requirements. • Clean and maintain catch basins annually. Sites with activities generating a lot of sediments and other debris will have to inspect and clean out their catch basins more often. Frequent sweeping of paved parking and storage areas will save time and money in maintaining the drainage system. • Other components of drainage systems such as ponds, tanks, and bioswales must also be maintained. If this maintenance is beyond your ability, contractors are available to complete this work. Label All Storm Drain Inlets on Your Property • Stencil or apply storm drain markers adjacent to storm drains to help prevent the improper disposal of pollutants. If the storm drain grate is stamped with warnings against polluting, then additional marking may not be required if there is no evidence of pollutants being dumped or washed into the storm drain. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 Stormwater Pollution Prevention Manual • King County28 Eliminate Illicit Connections to the Storm Drainage System • Connections to the storm drainage system that convey substances other than stormwater are prohibited. Examples are connections from internal floor drains, HVAC systems, industrial processes, sinks, and toilets. • Illicit connections must be immediately removed, permanently plugged or re–plumbed. • The discharge must be re–plumbed so that it goes to the sanitary sewer, a septic system, an on–site treatment system, or a holding tank for off–site disposal. There are restrictions on what can be disposed of to the sanitary sewer and septic systems. You may be required to do additional investigation to determine where all stormwater and non–stormwater discharges go. This may include smoke, dye, and chemical testing or closed circuit television inspection. Additional Information: • Drainage System Maintenance Contractors Information Sheet • For stencils and instructions or to determine if you have an illicit connection, contact King County Stormwater Services at 206–477–4811 or kingcounty.gov/stormwater. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 Stormwater Pollution Prevention Manual • King County 35 A-8 Storage or Solid and Food Wastes (Including Cooking Grease) This refers to garbage dumpsters and outdoor waste containers such as cooking oil/grease receptacles. Best Management Practices (BMPs) are required by King County Code 9.12. If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs: • Store wastes in leak–proof containers with solid lids. • Keep dumpsters closed except when adding waste. • Used cooking oil/grease containers should be labeled with their contents. • Clean up any spills immediately using dry methods. Grease cannot be left on the ground. • Have spill cleanup materials nearby. • Use a lid or cover when transporting cooking oil/grease containers from kitchens to outside grease containers. • Ensure that drip pans or absorbent materials are used whenever grease containers are emptied by vacuum trucks or other means. • Dispose of collected cooking oil/grease as garbage if it is not being recycled. Do not dispose of fats, oils or grease (FOG) into the sanitary sewer or septic system. Required Routine Maintenance: • Keep the area around the grease container clean and free of debris. • Check storage containers frequently for leaks and to ensure that lids are on securely. • Replace leaking or damaged containers. Contact waste hauler for replacements. • Sweep and clean the storage area as needed if it is paved. Do not hose down waste storage areas. • When cleaning or rinsing waste containers, dispose of all wastewater into a sanitary sewer. If no sewer is available, store in a holding tank, dead end sump, or truck o site to an approved disposal location. Additional Information: • Disposal Information Sheet For more information or assistance contact the King County Stormwater Services at 206–477–4811 and visit kingcounty.gov/stormwater. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 Stormwater Pollution Prevention Manual • King County 77 A-45 Maintenance of Public and Private Utility Corridors and Facilities This covers maintenance activities associated with the transmission and distribution of public and private utilities such as petroleum products, natural gas, water, sewage, and electrical power. This includes the maintenance of underground utility vaults, pump stations, and similar facilities. Best Management Practices (BMPs) are required by King County Code 9.12. If the BMPs included here are not enough to prevent contamination of stormwater, you will be required to take additional measures. Required BMPs: • Minimize the amount of herbicides and other pesticides used to maintain access roads and facilities. • Stabilize access roads or areas of bare ground with gravel, crushed rock, or another method to prevent erosion. Use and manage vegetation to minimize bare ground/soils that may be susceptible to erosion. • Provide stormwater drainage for roads and maintenance areas. Grade roads with a crown or slope to minimize the potential for erosion from runo. Provide ditches, swales, and culverts to convey stormwater runo. • Keep ditches and culverts clear to reduce the possibility of the drainage becoming plugged or blocked, causing overows and erosion. • Check utility vaults or other underground structures for oil prior to pumping out any collected water. Contaminated water must be collected for proper disposal. Small amounts of oil may be captured with absorbent material. Never discharge contaminated water, including high or low pH, to storm drainage facilities or surface waters. • When removing water and/or sediment from electrical transformer vaults, determine from records or testing if the transformers contain PCBs. • Clean up any debris or spilled material immediately after completing maintenance and repair activities. Additional Information: • Landscaping Activities and Vegetation Management – Activity Sheet A-26 • Erosion and Sediment Control Standards – King County Surface Water Design Manual, Appendix D • Work in public road right of ways requires permission from King County Utility Inspection Program (206) 296–8122. Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697 Preliminary Technical Information Report Walker Subaru Service Center 2240819.10 Appendix F Not Used Docusign Envelope ID: A8A5BFC1-1B8B-45C4-AB62-B0960DC02697