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associated earth sciences incorporated Associated Earth Sciences, Inc. 911 5th Avenue Kirkland, WA 98033 P (425) 827 7701 Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report SE 172ND ST. AND 125TH AVE. SE GSI Prepared For: OSBORN CONSULTING, INC. Project No. 20190100H001 March 23, 2020 RECEIVED Clark Close 02/05/2024 PLANNING DIVISION DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Kirkland | Tacoma | Mount Vernon 425-827-7701 | www.aesgeo.com March 23, 2020 Project No. 20190100H001 Osborn Consulting, Inc. 1800 112th Avenue NE, Suite 220-E Bellevue, Washington 98004 Attention: Mr. Cheyenne Covington, P.E. Subject: Subsurface Exploration, Geologic Hazard, and Geotechnical Engineering Report SE 172nd St. and 125th Ave. SE GSI Renton, Washington Dear Mr. Covington: We are pleased to present the enclosed copies of the above-referenced report. This report summarizes the results of our subsurface exploration, geologic hazard, and geotechnical engineering studies and offers recommendations for the design and development of the proposed project, as currently envisioned. Our recommendations are preliminary in that construction details have not been finalized at the time this report was prepared. We have enjoyed working with you on this study and are confident that the recommendations presented in this report will aid in the successful completion of your project. If you should have any questions, or if we can be of additional help to you, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington ______________________________ Jennifer H. Saltonstall, L.G., L.Hg. Principal Geologist/Hydrogeologist JHS/ld - 20190100H001-2 DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 SUBSURFACE EXPLORATION, GEOLOGIC HAZARD, AND GEOTECHNICAL ENGINEERING REPORT SE 172ND ST. AND 125TH AVE. SE GSI Renton, Washington Prepared for: Osborn Consulting, Inc. 1800 112th Avenue NE, Suite 220-E Bellevue, Washington 98004 Prepared by: Associated Earth Sciences, Inc. 911 5th Avenue Kirkland, Washington 98033 425-827-7701 March 23, 2020 Project No. 20190100H001 DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 1 I. PROJECT AND SITE CONDITIONS 1.0 INTRODUCTION This report presents the results of Associated Earth Sciences, Inc.’s (AESI’s) subsurface exploration, geologic hazard, and geotechnical engineering study for the proposed SE 172nd Street and 125th Avenue SE Green Stormwater Infrastructure (GSI) project located in Renton, Washington. (See the “Vicinity Map,” Figure 1.) The approximate locations of the explorations accomplished for this study are presented on Figure 2. An aerial image and LIDAR-based topography for the near-project area are presented on Figure 3. In the event that any changes in the nature, design, or location of the stormwater improvements are planned, the conclusions and recommendations contained in this report should be reviewed and modified, or verified, as necessary. 1.1 Purpose and Scope The purpose of this study was to provide subsurface data to be utilized in the design and construction of the above-referenced project. Our study included reviewing available geologic literature, drilling five exploration borings, and performing geologic studies to assess the type, thickness, distribution, and physical properties of the subsurface sediments and groundwater conditions. Geologic hazard evaluations and geotechnical engineering studies were also conducted to determine suitable geologic hazard mitigation techniques, temporary shoring/excavation, backfill recommendations, dewatering recommendations, and infiltration feasibility recommendations. This report summarizes our current geotechnical fieldwork and offers geotechnical hazard mitigation and development recommendations based on our present understanding of the project. 1.2 Authorization Written authorization to proceed with this study was granted by Osborn Consulting, Inc. by means of our signed “Agreement for Professional Services - Subconsultant,” dated April 24, 2019. This report has been prepared for the exclusive use of Osborn Consulting, Inc., the City of Renton, and their agents, for specific application to this project. Within the limitations of scope, schedule, and budget, our services have been performed in accordance with generally accepted geotechnical engineering and engineering geology practices in effect in this area at the time our report was prepared. No other warranty, express or implied, is made. DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 2 2.0 PROJECT AND SITE DESCRIPTION The City of Renton SE 172nd St. and 125th Ave. SE GSI project area consists of approximately 4,500 lineal feet of full street right-of-way within the City of Renton extending approximately half a block north of SE 172nd Street along 122nd Avenue SE, 123rd Avenue SE, 124th Avenue SE, 125th Avenue SE, and approximately two blocks along SE 172nd Street. Stormwater runoff from these streets is currently collected and conveyed east through private parcels and south within a street right-of-way into a storm system on SE 172nd Street where it discharges into a wetland located approximately 150 feet south of the intersection of SE 172nd Street and 127th Avenue SE. This runoff eventually flows into Big Soos Creek. The topography in the site area is generally flat lying to gently sloping, with asphalt-surfaced roadways and gravel or grass-covered shoulders. The existing paved surfaces include patching related to the installation of a waterline. Based on our review of project plans provided by Osborn Consulting, Inc., we understand that the current water system is a replacement of an abandoned water system which included lines under the eastern shoulders of 122nd through 125th Avenues. The proposed improvements include a new stormwater conveyance system, with 12- and 18-inch-diameter stormlines, and various green infrastructure improvements, such as bioretention facilities and pervious concrete sidewalks supplemented with General Use Level Designation (GULD) facilities to collect and treat stormwater runoff from approximately 2 acres of impervious surfaces. Based on our review of “60% submittal” plan set by Osborn Consulting, Inc., dated September 27, 2019, we anticipate site grading to include limited cuts and fills, and stormline installation to include trench depths ranging from approximately 3 to 10 feet. Much of the alignment of the proposed sidewalks will be at or near to the alignment of the above-mentioned abandoned water system. 3.0 SUBSURFACE EXPLORATION AESI completed a subsurface exploration program consisting of five exploration borings on February 4, 2020, to gain subsurface information about the site. The various types of soils, as well as the depths where characteristics of the soils changed, are indicated on the exploration logs presented in Appendix A. The depths indicated on the logs where conditions changed may represent gradational variations between soil types. Our explorations were approximately located in the field by measuring from known site features and are shown on Figure 2 and Figure 3. The conclusions and recommendations presented in this report are based, in part, on the exploration borings completed for this study. The number, locations, and depths of the explorations were completed within site/access constraints including those posed by existing DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 3 buried utilities, overhead lines, and driveways. The boring locations were selected to provide both general site information and area-specific information based on the proposed site layout. Changes to the site layout may require the completion of additional subsurface explorations. Because of the nature of exploratory work below ground, interpolation of subsurface conditions between field explorations is necessary. It should be noted that differing subsurface conditions may be present due to the random nature of deposition and the alteration of topography by past grading and/or filling. The nature and extent of any variations between the field explorations may not become fully evident until construction. If variations are observed at that time, it may be necessary to re-evaluate specific recommendations in this report and make appropriate changes. 3.1 Exploration Borings To avoid damaging existing utilities, a vacuum truck was used to remove the uppermost 4 feet of soil from each boring. The exploration borings were then completed by a track-mounted drill rig advancing a hollow-stem auger. During the drilling process, samples were obtained at generally 2.5- or 5-foot-depth intervals. The exploration borings were continuously observed and logged by a geologist from our firm. The exploration logs presented in Appendix A are based on the field logs, drilling action, and inspection of the samples secured. Disturbed but representative samples were obtained by using the Standard Penetration Test (SPT) procedure in accordance with ASTM International (ASTM) D-1586. This test and sampling method consists of driving a standard 2-inch, outside-diameter, split-barrel sampler a distance of 18 inches into the soil with a 140-pound hammer free-falling a distance of 30 inches. The number of blows for each 6-inch interval is recorded, and the number of blows required to drive the sampler the final 12 inches is known as the Standard Penetration Resistance (“N”) or blow count. If a total of 50 blows are recorded at or before the end of one 6-inch interval, the blow count is recorded as the number of blows for the corresponding number of inches of penetration. The resistance, or N-value, provides a measure of the relative density of granular soils or the relative consistency of cohesive soils. These values are plotted on the attached boring logs. The samples obtained from the split-barrel sampler were classified in the field, and representative portions placed in watertight containers. The samples were then transported to our laboratory for further visual classification and geotechnical laboratory testing, as necessary. The various types of soil and groundwater elevations, as well as the depths where soil and groundwater characteristics changed, are indicated on the exploration boring logs presented in Appendix A of this report. DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 4 4.0 SUBSURFACE CONDITIONS Subsurface conditions at the project site were inferred from the field explorations completed for this study, visual reconnaissance of the site, and review of applicable geologic literature. As shown on the boring logs, the exploration borings generally encountered a variable thickness of fill over glacial sediments. The following section presents more detailed subsurface information organized from the youngest (shallowest) to the oldest (deepest) soil types. 4.1 Stratigraphy Asphalt/Crushed Rock A surficial layer of asphalt pavement underlain by crushed rock road base was encountered at all exploration locations. Asphalt pavement thickness was generally 4 to 6 inches thick, with approximately 4 inches of crushed rock road base underneath. Fill Fill soils (soils not naturally placed) were encountered at the locations of exploration borings EB-2 through EB-4 to approximate depths of 3 feet to 5 feet below the ground surface. This fill generally consisted of medium dense, dark brown, sandy gravel with some silt. We interpret the encountered fill as likely resulting from past grading activities associated with roadway and/or plat construction. Fill thicknesses can vary over short distances and may be deeper than observed in our explorations. We are not aware of available documentation for placement of the existing fill or trench backfill. As our explorations were located to avoid existing buried utilities, we did not encounter trench backfill. From the plans provided by Osborn Consulting, it is likely that the proposed improvements will encounter existing fill and trench backfill associated with the existing buried utilities. Although our explorations did not encounter large debris, cobbles, or boulders within the fill, these materials may be present at random locations and depths. Due to their variable density and content, the existing fill soils are not suitable for direct support of grade-sensitive pipelines. Depending on site conditions at the time of construction, remediation of the fill may be feasible with recompaction or removal and replacement with structural fill. Vashon Ice Contact Deposits At exploration boring EB-2, beneath the fill, our exploration encountered medium dense, silty, fine sand ranging to stiff, sandy silt with trace coarse sand dropstones, interpreted as ice contact deposits. Ice contact deposits can consist of a wide variety of sediment types initially deposited above, adjacent to, or within a glacial ice mass and later re-deposited when the ice melts. Ice contact sediments can be normally consolidated or glacially overridden. Ice contact deposits at this site primarily consist of fine sand and silt and are considered moisture sensitive. At the Can we still infiltrate into fill? DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 5 location of EB-2, the ice contact sediments extended below the maximum depth explored of 11.5 feet below the ground surface. Vashon Lodgement Till Sediments encountered below the fill at exploration borings EB-1, EB-3, EB-4, and EB-5 generally consisted of dense to very dense, silty sand with some gravel. We interpret these sediments to be representative of Vashon lodgement till. The Vashon lodgement till was deposited directly from basal, debris-laden glacial ice during the Vashon Stade of the Fraser Glaciation approximately 12,500 to 15,000 years ago. The high relative density of the unweathered till is due to its consolidation by the massive weight of the glacial ice from which it was deposited. This unit is generally suitable for support of pipelines. All sediments of glacial origin may contain large cobbles or boulders at random locations. At the locations of EB-1, EB-3, EB-4, and EB-5, the lodgement till extended below the maximum depths explored of 10.3 feet below the ground surface. 4.2 Regional Mapping Geologic Mapping Review of the regional geologic map titled Geologic Map of the Renton Quadrangle, King County, Washington, U.S. Geological Survey (USGS) Publication GQ-405, by D.R. Mullineaux (1965) indicates that the site is underlain by Vashon lodgement till (Qvt). Our interpretation of the sediments encountered at the subject site is in general agreement with the regional geology map. Soil Mapping Review of the US Department of Agriculture Natural Resources Conservation Service (NRCS) Web Soil Survey indicates that the soil in the vicinity of the site consists of Arents-Alderwood and Alderwood soils series. Arents-Alderwood soils are Alderwoods soils that have been disturbed by urbanization. Alderwood soils generally form from the weathering of glacial till. An area of as Seattle muck (Sk) soils is present in a low area extending south from 127th Avenue. Seattle muck soils are generally associated with wetland areas. Our interpretation of the sediments encountered at the subject site is in general agreement with the regional soils map. 4.3 Hydrology At the time of our explorations, we encountered groundwater seepage in exploration borings EB-1, EB-3, EB-4, and EB-5 at depths of approximately 4 feet to 6 feet. These depths generally corresponded with the slightly oxidized, moist soils that were observed within the upper portion of the Vashon lodgement till sediments indicating that perched groundwater likely occurs Groundwater at 4' -6' DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Project and Site Conditions March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 6 seasonally. Perched groundwater, also known as “interflow,” occurs when vertical infiltration is impeded by less-permeable soils and horizontal migration occurs. It should be noted that groundwater levels below the site fluctuate in response to such factors as changes in season, precipitation, and on- and off-site land use. Our field explorations were conducted in early February when groundwater levels are typically elevated. 4.4 Laboratory Testing We completed laboratory testing of selected soil samples collected from our exploratory borings. A total of four grain-size analyses were performed. Copies of the laboratory test results are included in Appendix B. DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 7 II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic conditions as observed and discussed herein. 5.0 LANDSLIDE HAZARDS AND MITIGATION Due to the relatively flat site topography and distance to significant slopes, it is our opinion that the risk of damage to the proposed project by landsliding is low. Provided that the recommendations presented in this report are properly followed, no additional landslide hazard mitigation is recommended for this project. 6.0 SEISMIC HAZARDS AND MITIGATION Earthquakes occur in the Puget Lowland with great regularity. The vast majority of these events are small and are usually not felt by people. However, large earthquakes do occur, as evidenced by the 1949, 7.2-magnitude event; the 1965, 6.5-magnitude event; and the 2001, 6.8-magnitude event. The 1949 earthquake appears to have been the largest in this area during recorded history. Evaluation of return rates indicates that an earthquake of a magnitude between 6.0 and 7.0 is likely within a given 25- to 40-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides, 3) liquefaction, and 4) ground motion. The potential for each of these hazards to adversely impact the proposed project is discussed below. 6.1 Surficial Ground Rupture The nearest known fault trace to the project site is the Seattle Fault Zone, which lies approximately 4 miles to the northeast. Recent studies by the USGS (e.g., Johnson et al., 1994, Origin and Evolution of the Seattle Fault and Seattle Basin, Washington, Geology, v. 22, p.71-74; and Johnson et al., 1999, Active Tectonics of the Seattle Fault and Central Puget Sound Washington - Implications for Earthquake Hazard, geological Society of America Bulletin, July 1999, v. 111, n. 7, p. 1042-1053) have provided evidence of surficial ground rupture along a northern splay of the Seattle Fault. The recognition of this fault is relatively new, and data pertaining to it are limited, with the studies still ongoing. According to the USGS studies, the latest movement of this fault was about 1,100 years ago when about 20 feet of surficial displacement took place. This displacement can presently be seen in the form of raised, wave-cut beach DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 8 terraces along Alki Point in West Seattle and Restoration Point at the south end of Bainbridge Island. The recurrence interval of movement along this fault system is still unknown, although it is hypothesized to be in excess of several thousand years. Due to the suspected long recurrence interval, the potential for surficial ground rupture is considered to be low during the expected life of the project, and no mitigation efforts beyond complying with the current 2015 International Building Code (IBC) are recommended. 6.2 Seismically Induced Landslides Due to the relatively flat site topography and distance to significant slopes, it is our opinion that the risk of damage to the proposed project by seismically induced landsliding is low. Provided that the recommendations presented in this report are properly followed, no additional landslide hazard mitigation is recommended for this project. 6.3 Liquefaction Liquefaction is a process through which unconsolidated soil loses strength as a result of vibrations, such as those which occur during a seismic event. During normal conditions, the weight of the soil is supported by both grain-to-grain contacts and by the fluid pressure within the pore spaces of the soil below the water table. Extreme vibratory shaking can disrupt the grain-to-grain contact, increase the pore pressure, and result in a temporary decrease in soil shear strength. The soil is said to be liquefied when nearly all of the weight of the soil is supported by pore pressure alone. Liquefaction can result in deformation of the sediment and settlement of overlying structures. Areas most susceptible to liquefaction include those areas underlain by non-cohesive silt and sand with low relative densities, accompanied by a shallow water table. The subsurface conditions encountered at the site pose a low risk of liquefaction due to their relatively high density from glacial consolidation. No detailed liquefaction analysis was completed as part of this study, and none is warranted, in our opinion. 6.4 Ground Motion Design of structural elements should follow 2015 IBC standards using Site Class “D” as defined in Table 20.3-1 of American Society of Civil Engineers (ASCE) 7 – Minimum Design Loads for Buildings and Other Structures. DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 9 7.0 EROSION HAZARDS AND MITIGATION The Renton Municipal Code defines Low Erosion Hazard Areas as soils characterized by the Natural Resource Conservation Service (NRCS) as having slight or moderate erosion potential, and a slope less than fifteen percent (15%). The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Web Soil Survey maps the soil in the vicinity of the site as Arents-Alderwood materials, 6 to 15 percent slopes (AmC), and Alderwood gravelly sandy loam, 0 to 15 percent slopes (AgB, AgC). These soils have a slight erosion potential and are situated on slopes ranging from 0 to 15 percent. Therefore, the project site is classified as a Low Erosion Hazard Area under the Renton Municipal Code. Based on the relatively flat site topography and presence of fine-grained soils, the erosion hazard at the site is considered low to moderate, and a properly developed, constructed, and maintained erosion control plan consistent with local standards and best management practices is recommended for this project. Maintaining cover measures atop disturbed ground provides significant reduction to the potential generation of turbid runoff and sediment transport. During the local wet season (October 1st through March 31st), exposed soil should not remain uncovered for more than 2 days, unless it is actively being worked. Ground-cover measures can include erosion control matting, plastic sheeting, straw mulch, crushed rock, recycled concrete, or mature hydroseed. To reduce the potential for off-site sediment transport during construction, we recommend the following: 1. If possible, construction should proceed during the drier periods of the year, and disturbed areas should be revegetated, paved, or otherwise protected as soon as possible. 2. All stormwater from impermeable surfaces should be directed to a stormwater drainage system or temporary storage facilities and kept away from the proposed work areas. 3. Ground disturbance beyond the project alignment should be kept to a minimum. 4. Temporary sediment catchment facilities adjacent to the proposed stormwater alignment should be cleaned out and maintained periodically, as necessary, to maintain their capacity and function. Provide and maintain inlet protection of catch basins and drain systems that receive runoff from planned work areas. DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Geologic Hazards and Mitigations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 10 5. Soils that will be stockpiled at the site should be stored in such a manner as to reduce erosion. Protective measures may include, but are not necessarily limited to, covering with plastic sheeting or the use of straw bales/silt fences. 6. Where needed, construction access should be constructed with quarry spall surfacing or equivalent according to City of Renton regulations. Maintain existing paved surfaces, where practical, and sweep as needed. It is our opinion that with the proper implementation of the Temporary Erosion and Sedimentation Control (TESC) plans and by field-adjusting appropriate erosion mitigation (BMPs) throughout construction, the potential adverse impacts from erosion hazards on the project may be mitigated. 8.0 COAL MINE HAZARDS AND MITIGATION According to the City of Renton GIS Services COR Maps, the nearest mapped coal mine hazard lies approximately 0.25 miles to the west. No coal mine hazard analysis was completed for this study, and none is warranted in our opinion. DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Design Recommendations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 11 III. DESIGN RECOMMENDATIONS 9.0 INTRODUCTION Our explorations indicate that, from a geotechnical standpoint, the planned stormwater improvements are feasible provided that the recommendations in this report are followed. The sediment types excavated during trenching will likely be Vashon lodgement till, Vashon ice contact deposits, or previously placed fill. These materials will largely consist of sand with variable but significant quantities of gravel and silt, and possibly random cobbles and/or boulders. As stated above, we encountered groundwater seepage in exploration borings EB 1, EB-3, EB-4, and EB-5 at depths of approximately 4 feet to 6 feet below the ground surface, and interpreted that seepage as perched groundwater, also known as “interflow,” that likely occurs seasonally. For portions of the planned stormwater alignment extending below the interflow zone, suitable temporary shoring and trench sidewall slopes will be required to mitigate seepage and potential caving conditions. For these reasons, we recommend that construction occur during the dry season, typically between June and September, and that the contractor be prepared for saturated soils that are prone to caving and groundwater flow along the pipe alignment. New infrastructure for the project includes excavations for the drainage facilities and associated underdrains, and other piping along with street restoration. The following recommendations pertain to the site and infrastructure improvements for work occurring within the City’s public right-of-way. In general, all work shall be done in accordance with current City of Renton specifications. Based on our subsurface exploration, the material exposed at the base of the stormwater trenches is anticipated to consist of native glacial till in most areas. Ice-contact deposits (silt) were encountered in exploration boring EB-2 and may be exposed at the base of trench excavation in this area. Existing fill was encountered in most of the explorations, ranging in thickness from 3 to 5 feet. Both the glacial till and ice-contact deposits contain a significant amount of fine-grained sediments and are, therefore, not considered suitable receptor sediments for infiltrating large volumes of stormwater. 10.0 SITE PREPARATION Site preparation should include removal of all trees, brush, debris, and any other deleterious material within the proposed work area. Additionally, organic soil, if encountered, should be segregated from mineral soils in the trench excavation. Since the density and composition of the soil can vary in existing utility trenches, random soft/organic pockets may exist, and the depth DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Design Recommendations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 12 and extent of organics/stripping depths can best be determined in the field by the geotechnical engineer or engineering geologist. 10.1 Temporary Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction based on the local soil and groundwater conditions encountered at the particular location at that time. We anticipate that trenched excavations for the planned stormwater improvements will likely be vertical, with trench boxes used where warranted, as described in the “Trenching Considerations” section of this report. For estimating purposes, however, we anticipate that temporary, unsupported cut slopes in fill soils or in Vashon ice contact sediments can be planned at a maximum slope of 1.5H:1V (Horizontal:Vertical), and that cut slopes in dense to very dense Vashon lodgement till sediments can be made at a maximum slope of about 1H:1V. As is typical with earthwork operations, some sloughing and raveling may occur, and cut slopes may have to be adjusted in the field. If groundwater seepage is encountered in cut slopes, or if surface water is not routed away from temporary cut slope faces, flatter slopes will be required. In addition, WISHA/OSHA regulations should be followed at all times. 10.2 Site Disturbance The contractor must use care during site preparation and excavation operations so that the underlying soils are not softened, particularly during wet weather conditions. If disturbance occurs, the softened soils should be removed and the area brought to grade with structural fill. Softened soils are defined as any soil not in a firm and unyielding condition. We anticipate that wet weather construction would increase the earthwork costs over dry weather construction. 11.0 TRENCHING CONSIDERATIONS 11.1 Excavation Much of the planned stormwater improvements will likely run below paved areas. Therefore, it will be necessary to sawcut the existing pavement prior to trenching operations. There will also likely be existing buried utilities that will complicate the excavation process. Overhead power lines are not expected to interfere with the planned construction, but nearby tree limbs may limit the pick-and-swing radius of the trenching equipment. We anticipate that the installation of new stormwater conveyance system, where needed, will require vertically sided trench excavations. For trenches less than 4 feet in depth, where caving DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Design Recommendations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 13 or groundwater seepage is not encountered, the trenches may be open-cut for access. For trenches 4 feet or deeper, or where caving, sloughing, or groundwater seepage is encountered, we recommend the use of suitable trench boxes or the temporary cut slopes described above. We anticipate that soils to be encountered during the excavation process will provide moderate resistance to digging. Cobbles and boulders should be expected during excavation. Groundwater seepage into the trench, if present, can cause some caving/sloughing to occur. The contractor should be experienced with excavating in moist to wet subgrade conditions. 11.2 Pipe Subgrade The undisturbed native soils are suitable for support of the pipe. In the event that soft, organic, or disturbed soils are encountered at the bottom of the trench, these soils should be overexcavated, up to 1 foot where needed, and replaced with structural backfill where it is encountered. An AESI representative should be onsite to observe subgrade conditions and document backfill operations. 11.3 Pipe Bedding Pipe zone bedding material should be specified by the civil engineer following the pipe manufacturer’s requirements. We recommend that pipe bedding placement should conform to Washington State Department of Transportation (WSDOT) Standard Specification 7-08.3(1)C. 11.4 Backfill The majority of the near-surface soils excavated for the proposed improvements will likely be moist, silty, fine to medium sand with gravel. These soils are suitable for use as backfill material provided they are placed at or near (within 2 percent) optimum moisture contents. The backfill soils should be substantially free of organic materials and rocks larger than about 6 inches in nominal dimension. We anticipate that during the wet season the on-site soils will not likely be suitable for backfill due to moisture contents being elevated above optimum moisture for the soil to achieve suitable compaction. Above the pipe zone bedding material, on-site sediments may be used for backfill provided that they can be compacted to at least 95 percent of the modified Proctor maximum dry density, as defined by ASTM D-1557. If the material excavated from the trench is not suitable for backfill due to high moisture or a high degree of deleterious material, then imported backfill soil consisting of material conforming to WSDOT Standard Specification 9-03.10 “Bank Run Gravel for Trench Backfill” may be used and compacted to the required density. If select import material is not available, or if there is a need for a higher strength material or in areas congested by other utilities making compaction difficult, a controlled density fill (CDF) may be used. We recommend the use DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Design Recommendations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 14 of 50 to 100 pounds per square inch (psi) compressive strength CDF mix to facilitate future excavation and provide performance equivalent to well compacted soil backfill. Trench backfill should be placed in uniform, horizontal lifts and compacted to the above standard. Thickness of structural backfill layers before compaction should not exceed 1.5 feet for a large, excavator-mounted, vibratory plate-type compactor. Smaller compaction equipment will require use of thinner lifts; hand-operated mechanical compactors should be used to compact lifts no thicker than 6 inches. Final lift thickness should be based on field performance testing using actual materials under field conditions and uniform compactive effort. In some cases, additional pipe zone bedding material above the pipe may be advisable to minimize required compactive effort needed to achieve the specified density in this area. 12.0 PERVIOUS CONCRETE SIDEWALKS From “60% submittal” plans provided to AESI by Osborn Consulting, we understand that pervious concrete sidewalks are proposed along the east shoulders of 122nd Avenue SE, 123rd Avenue SE, 124th Avenue SE, 125th Avenue SE, and along the north shoulder of SE 172nd Street. The pervious concrete detail specifies 4 inches of pervious cement concrete placed over a minimum 6 inches of aggregate base surrounded by a geotextile fabric layer. An underdrain is not included. We anticipate that stormwater that passes through the pervious concrete sidewalk section will encounter existing fill, existing utility trench backfill, or the natural, glacially derived sediments. It is likely that this stormwater will enter the fill soils and migrate horizontally as vertical infiltration will be impeded by the underlying Vashon lodgement till and ice contact deposits, both of which contain large quantities of silt and fine sand. Horizontal migration of perched groundwater, known as “interflow”, occurs naturally within the subsurface, causing groundwater to infiltrate into and along the fill soils. If the current interflow within the existing fill and utility trench backfill has not caused adverse impacts to nearby utilities or roadways, it is our opinion that the relatively small amount of additional groundwater from the proposed pervious concrete sidewalks should not result in a significant increase in the risk of adverse impacts to nearby infrastructure, relative to the existing condition. The pervious sidewalk areas will generally mimic the interflow of the converted landscaped areas. 13.0 DRAINAGE AND DEWATERING CONSIDERATIONS Groundwater seepage was encountered in exploration borings EB-1, EB-3, EB-4, and EB-5 at the time of drilling, February 4, 2020. The depth of groundwater observed ranged from 4 feet to 6 feet and was interpreted as perched on the underlying Vashon lodgement till. It should be Horizontal interflow expected vs vertical infiltration No increased risk Previous concrete sidewalks DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd St. & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Design Recommendations March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/ld - 20190100H001-2 Page 15 noted that the depth or occurrence of groundwater seepage may vary in response to such factors as changes in season, precipitation, and site use. The quantity and duration of flow from an excavation that encounters groundwater depends on a number of factors including topography, size and depth of the excavation, proximity to surface water features, soil grain size, lateral extent of the water-bearing zone or aquifer, and season. We expect that the majority of groundwater seepage can be managed by the installation of temporary trench sump systems during trench excavation, and we recommend work proceed during the drier summer months. 14.0 INFILTRATION FEASIBILITY RECOMMENDATIONS The feasibility of stormwater infiltration depends upon the presence of a suitable receptor native soil of sufficient thickness, extent, permeability, and vertical separation from groundwater. Our explorations completed for this study encountered medium dense fill underlain by very dense, silty, Vashon lodgement till sediments or stiff Vashon ice contact deposits. Laboratory sieve analyses of samples of the Vashon lodgement till collected from borings EB-1, EB-3, EB-4, and EB-5 indicate that the lodgement till contains between 23.7 percent and 34.9 percent silt and clay-sized particles. A copy of the laboratory results is included in Appendix B. The existing fill is not a suitable infiltration receptor due to its variable texture, silt, and organic content. Because of their elevated silt content, the Vashon lodgement till and Vashon ice contact sediments underlying the site exhibit a low permeability and are not considered to be suitable receptor soils for stormwater infiltration. Therefore, infiltration is not recommended for concentrated flows; however, dispersed flow through pervious sidewalks should mimic that resulting from the to-be-converted pervious landscaped areas. 15.0 PROJECT DESIGN AND CONSTRUCTION MONITORING We are available to provide additional geotechnical consultation as the project design develops and possibly changes from that upon which this report is based. We recommend that AESI perform a geotechnical review of the plans prior to final design completion. In this way, our earthwork and foundation recommendations may be properly interpreted and implemented in the design. This review is not included in the current scope of work and budget. We are also available to provide geotechnical engineering and monitoring services during construction. The integrity of the new system depends on proper site preparation and construction procedures. In addition, engineering decisions may have to be made in the field in the event that variations in subsurface conditions become apparent. Construction monitoring Pervious sidewalks expected to mimic existing pervious landscaped areas. Infiltration not recommended for concentrated flows.Not suitable for infiltration DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Subsurface Exploration, Geologic Hazard, and SE 172nd 5• & 125th Ave. SE GSI Geotechnical Engineering Report Renton, Washington Design Recommendations services are not part of this current scope of work. If these services are desired, please let us know, and we will prepare a proposal. We have enjoyed working with you on this study and are confident that these recommendations will aid in the successful completion of your project. If you should have any questions, or require further assistance, please do not hesitate to call. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington Joshua S. P. Greer, G.I.T. Staff Geologist Jeffrey P. Laub, L.G., L.E.G. Bruce L. Blyton, P.E. Senior Engineering Geologist Senior Principal Engineer Attachments:Figure 1:Vicinity Map Figure 2:Site and Exploration Plan Figure 3:Site Aerial and Topography Appendix A: Exploration Logs Appendix B: Laboratory Testing Results March 23, 2020 ASSOCIATED EARTH SCIENCES, INC. JG/Id - 20190100H001-2 Page 16 Do we need infiltration rate? Cation Exchange Capacity? Organic Matter Content? DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 KING COUNTY KENT RENTON Copyright:© 2013 National Geographic Society, i-cubed King County 125th Ave SESE 168th St SE 172nd St121st Ave SESE170t h Pl122nd Ave SE124th Ave SE123rd Ave SE± NOTE: BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION VICINITY MAP PROJ NO. DATE: FIGURE:\\kirkfile2\GIS\GIS_Projects\aaY2019\VM\190100H001 F1 VM_SE172nd.aprx!( ¥ ¥ ¥ ¬«515 ¬« ¬« ¬« SITE 120190100H0012/20 0 20001000 FEET DATA SOURCES / REFERENCES: USGS: 7.5' SERIES TOPOGRAPHIC MAPS, ESRI/I-CUBED/NGS 2013 KING CO: STREETS, CITY LIMITS 1/19, PARCELS 4/19 LOCATIONS AND DISTANCES SHOWN ARE APPROXIMATE SE 172ND ST AND 125TH AVE SE GSI RENTON, WASHINGTON DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 NOTES: 1. BASE MAP REFERENCE: DUANE HARTMAN AND ASSOCIATES, INC., CITY OF RENTON - SE 172ND ST STORM WATER IMPROVEMENTS TOPOGRAPHIC SURVEY, DHA 19-2901, SURVEYED 6/19 190100 SE 172nd \ 20190100H001 F2 S-E.cdr SE 172ND ST AND 125TH AVE SE GSI RENTON, WASHINGTON SITE AND EXPLORATION PLAN PROJ NO.DATE:FIGURE: 20190100H001 2/20 2 BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION. a s s o c i a t e d e a r t h s c i e n c e s i n c o r p o r a t e d FEET 50 1000 N CONTOUR INTERVAL = 1’ LEGEND: EXPLORATION BORINGEB NOTE: LOCATION AND DISTANCES SHOWN ARE APPROXIMATE. EB-5 EB-3 EB-4 EB-2 EB-1 DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 King County ± BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIVENESS AND LEAD TO INCORRECT INTERPRETATION G:\GIS_Projects\aaY2019\190100 SE 172nd St\aprx_mxd\190100H001 F3_ES_172ndSt.aprxPROJ NO.DATE:FIGURE: 0 300 FEET DATA SOURCES / REFERENCES: PSLC: KING COUNTY 2016, GRID CELL SIZE IS 3'. DELIVERY 1 FLOWN 2/24/16 - 3/28/16 CONTOURS FROM LIDAR OSBORN CONSULTING, INC, PROJECT BOUNDARY, 172ND ST AND 125TH AVE GREEN STORMWATER INFRASTRUCTURE (GSI) PROJECT, 60% SUBMITTAL, 9/27/19 KING CO: STREETS, PARCELS 3/20 AERIAL PICTOMETRY INT. 2015 LOCATIONS AND DISTANCES SHOWN ARE APPROXIMATE 20190100H001 3/20 3 SITE AERIAL AND TOPOGRAPHY SE 172ND ST AND 125TH AVE SE GSI RENTON, WASHINGTON !( !( !( !( !( Kin g C o u n t y Ren t o nRenton424 4144264224344284204124164104044024324304144124044024284 2 4 420416438434436 422444442 440438388386418436408406400394392 3983963904324 2 6 418410 430408406400 398 440408 398 410 410SE 172nd Ln SE175thSt 128th Ave SESE 167th St 127th Ave SE121st Ave SESE174thLn119th Pl SE121stLnSE SE 168th St SE 170 th P l SE 170th St SE 172nd St SE Pet rovitsky Rd 1 1 9 th LnSESE170t h Pl 126th Pl SE126th Ave SESE 169 th P l SE167th Pl 120thAveSE120thLnSE119thAveSE 122ndLnSE120th Ter SESE 169th Pl SE 169th St 122nd Ave SE124th Ave SE123rd Ave SEEB-1 EB-2 EB-3 EB-4 EB-5 Pictometry International Corp. SITE !(EXPLORATION BORING PARCEL CONTOUR 10 FT CONTOUR 2 FT DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 APPENDIX A Exploration Logs DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 13 22 32 16 18 22 33 50/5" 50/5" 50/4" Bottom of exploration boring at 20.3 feet Perched groundwater encountered at ~6 feet. Asphalt - 6 inches Crushed Rock - 4 inches Vashon Lodgement Till Dense, moist, light brownish gray, silty, fine SAND, trace to some gravel, trace cobbles; unsorted; limited recovery due to APS (SP). Vacuum truck excavated 0 to 4 feet. Drilled 4 to 21.5 feet. Very moist, gray, silty, fine SAND, trace gravel; unsorted; poor recovery (SM). Driller notes rock in the way. Very moist to wet, gray, silty, fine SAND, some gravel; unsorted (SM). Driller notes difficult drilling 10 to 20 feet. S-1 S-2 S-3 S-4 S-5 S-6 1 of 1 NAVD 88 JG2" OD Split Spoon Sampler (SPT) 3" OD Split Spoon Sampler (D & M)Water LevelProject Name JHSWater Level ()Approved by: 30 Blows/Foot Samples Ground Surface Elevation (ft) Grab SampleSymbol 6.25 40 Datum Hammer Weight/Drop Sampler Type (ST): S T Project Number 20 Renton, WA Date Start/Finish CompletionLocation Sheet Depth (ft)Exploration Number 20190100H001 2/4/20,2/4/20 Logged by: Shelby Tube Sample 140# / 30 Boretec / Track Rig Well~387 5 10 15 20 EB-1 Ring Sample No RecoveryGraphic 10 Other TestsHole Diameter (in) DESCRIPTION Driller/Equipment Blows/6"Exploration Boring Water Level at time of drilling (ATD) SE 172nd St and 125th Ave SE GSI M - Moisture AESIBOR 20190100H001.GPJ February 25, 202054 4040 5050/5" 5050/5" 5050/4" DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 6 7 9 6 4 5 2 3 5 Bottom of exploration boring at 11.5 feet No groundwater encountered. Asphalt - 6 inches Crushed Rock - 4 inches Fill Medium dense, moist, dark brown, sandy, GRAVEL, some silt, trace organics; unsorted (GP-GM). Vacuum truck excavated 0 to 4 feet. Drilled 4 to 11.5 feet. Upper 4 inches: brown, fine to medium, SAND, some silt (SP-SM). Vashon Ice Contact Deposits Lower 8 inches: moist, gray with mottled orange oxidation, silty, fine SAND, trace gravel; massive (SM). Very moist, gray, fine sandy, SILT, trace gravel, trace coarse sand dropstones; massive (ML). S-1 S-2 S-3 S-4 1 of 1 NAVD 88 JG2" OD Split Spoon Sampler (SPT) 3" OD Split Spoon Sampler (D & M)Water LevelProject Name JHSWater Level ()Approved by: 30 Blows/Foot Samples Ground Surface Elevation (ft) Grab SampleSymbol 6.25 40 Datum Hammer Weight/Drop Sampler Type (ST): S T Project Number 20 Renton, WA Date Start/Finish CompletionLocation Sheet Depth (ft)Exploration Number 20190100H001 2/4/20,2/4/20 Logged by: Shelby Tube Sample 140# / 30 Boretec / Track Rig Well~389 5 10 15 20 EB-2 Ring Sample No RecoveryGraphic 10 Other TestsHole Diameter (in) DESCRIPTION Driller/Equipment Blows/6"Exploration Boring Water Level at time of drilling (ATD) SE 172nd St and 125th Ave SE GSI M - Moisture AESIBOR 20190100H001.GPJ February 25, 20201616 99 1818 DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 8 10 12 44 5/4" 50/5" Bottom of exploration boring at 10.4 feet Perched groundwater encountered at ~5 feet. Asphalt - 4 inches Crushed Rock - 4 inches Fill Medium dense, moist, dark brown, sandy, GRAVEL, some silt, trace fine organics; unsorted (GP-GM). Vashon Lodgement Till Vacuum truck excavated 0 to 4 feet. Drilled 4 to 10.4 feet. Very moist, light brownish gray, silty, fine SAND, trace gravel; unsorted (SM). S-1 S-2 S-3 S-4 1 of 1 NAVD 88 JG2" OD Split Spoon Sampler (SPT) 3" OD Split Spoon Sampler (D & M)Water LevelProject Name JHSWater Level ()Approved by: 30 Blows/Foot Samples Ground Surface Elevation (ft) Grab SampleSymbol 6.25 40 Datum Hammer Weight/Drop Sampler Type (ST): S T Project Number 20 Renton, WA Date Start/Finish CompletionLocation Sheet Depth (ft)Exploration Number 20190100H001 2/4/20,2/4/20 Logged by: Shelby Tube Sample 140# / 30 Boretec / Track Rig Well~395 5 10 15 20 EB-3 Ring Sample No RecoveryGraphic 10 Other TestsHole Diameter (in) DESCRIPTION Driller/Equipment Blows/6"Exploration Boring Water Level at time of drilling (ATD) SE 172nd St and 125th Ave SE GSI M - Moisture AESIBOR 20190100H001.GPJ February 25, 20202222 505/4" 5050/5" DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 13 19 18 9 17 20 14 21 33 Bottom of exploration boring at 11.5 feet Perched groundwater encountered at ~5 to 6 feet. Asphalt - 4 inches Crushed Rock - 4 inches Fill Medium dense, moist dark brown, sandy, GRAVEL, some silt, trace fine organics; unsorted (GP-GM). Vashon Lodgement Till Vacuum truck excavated 0 to 4 feet. Drilled 4 to 11.5 feet. Poor recovery due to rock, interpreted as Lodgement Till due to blowcounts and consistent drill action with deeper samples. Moist to very moist, light brownish gray, silty, fine SAND, some gravel; unsorted (SM). S-1 S-2 S-3 S-4 1 of 1 NAVD 88 JG2" OD Split Spoon Sampler (SPT) 3" OD Split Spoon Sampler (D & M)Water LevelProject Name JHSWater Level ()Approved by: 30 Blows/Foot Samples Ground Surface Elevation (ft) Grab SampleSymbol 6.25 40 Datum Hammer Weight/Drop Sampler Type (ST): S T Project Number 20 Renton, WA Date Start/Finish CompletionLocation Sheet Depth (ft)Exploration Number 20190100H001 2/4/20,2/4/20 Logged by: Shelby Tube Sample 140# / 30 Boretec / Track Rig Well~402 5 10 15 20 EB-4 Ring Sample No RecoveryGraphic 10 Other TestsHole Diameter (in) DESCRIPTION Driller/Equipment Blows/6"Exploration Boring Water Level at time of drilling (ATD) SE 172nd St and 125th Ave SE GSI M - Moisture AESIBOR 20190100H001.GPJ February 25, 20203737 3737 54 DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 10 16 16 50/6" 50/4" Bottom of exploration boring at 10.3 feet Groundwater encountered at 4 feet. Asphalt - 4 inches Crushed Rock - 4 inches Vashon Lodgement Till Dense, moist, light brownish gray, silty, fine SAND, some gravel; unsorted (SM). Water present post Vacuum truck excavation at 4 feet. Vacuum truck excavated 0 to 4 feet. Drilled 4 to 10.3 feet. Moist to very moist, light brownish gray, silty, fine SAND, trace gravel; unsorted (SM). Poor recovery due to frequent gravel. S-1 S-2 S-3 S-4 1 of 1 NAVD 88 JG2" OD Split Spoon Sampler (SPT) 3" OD Split Spoon Sampler (D & M)Water LevelProject Name JHSWater Level ()Approved by: 30 Blows/Foot Samples Ground Surface Elevation (ft) Grab SampleSymbol 6.25 40 Datum Hammer Weight/Drop Sampler Type (ST): S T Project Number 20 Renton, WA Date Start/Finish CompletionLocation Sheet Depth (ft)Exploration Number 20190100H001 2/4/20,2/4/20 Logged by: Shelby Tube Sample 140# / 30 Boretec / Track Rig Well~403 5 10 15 20 EB-5 Ring Sample No RecoveryGraphic 10 Other TestsHole Diameter (in) DESCRIPTION Driller/Equipment Blows/6"Exploration Boring Water Level at time of drilling (ATD) SE 172nd St and 125th Ave SE GSI M - Moisture AESIBOR 20190100H001.GPJ February 25, 20203232 5050/6" 5050/4" DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 APPENDIX B Laboratory Testing Results DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Particle Size Distribution Report PERCENT FINER0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % +3"Coarse % Gravel Fine Coarse Medium % Sand Fine Silt % Fines Clay 0.0 0.0 6.3 3.8 14.2 40.8 34.96 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200TEST RESULTS Opening Percent Spec.*Pass? Size Finer (Percent)(X=Fail) Material Description Atterberg Limits (ASTM D 4318) Classification Coefficients Date Received:Date Tested: Tested By: Checked By: Title: Date Sampled:Location: Onsite Sample Number: EB-1 Depth: -7.5' Client: Project: Project No:Figure Very Silty SAND Some Gravel 3/4" 3/8" #4 #8 #10 #20 #40 #60 #100 #200 #270 100.0 97.3 93.7 90.6 89.9 86.0 75.7 55.7 44.7 34.9 32.0 np nv SM A-2-4(0) 2.0444 0.7312 0.2823 0.2016 2-14-20 2-14-20 MS JL 2-4-20 Osborn Consulting Inc 125Ave SE & 172nd St. Se. GSI 190100 H001 PL=LL=PI= USCS (D 2487)=AASHTO (M 145)= D90=D85=D60= D50=D30=D15= D10=Cu=Cc= Remarks *(no specification provided) DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Particle Size Distribution Report PERCENT FINER0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % +3"Coarse % Gravel Fine Coarse Medium % Sand Fine Silt % Fines Clay 0.0 0.0 7.5 4.8 16.7 47.3 23.76 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200TEST RESULTS Opening Percent Spec.*Pass? Size Finer (Percent)(X=Fail) Material Description Atterberg Limits (ASTM D 4318) Classification Coefficients Date Received:Date Tested: Tested By: Checked By: Title: Date Sampled:Location: Onsite Sample Number: EB-3 Depth: -5' Client: Project: Project No:Figure Silty SAND Some Gravel 3/4" 3/8" #4 #8 #10 #20 #40 #60 #100 #200 #270 100.0 95.9 92.5 88.8 87.7 81.1 71.0 52.4 37.8 23.7 20.1 np nv SM A-2-4(0) 2.9024 1.3856 0.3080 0.2330 0.1074 2-14-20 2-14-20 MS JL 2-4-20 Osborn Consulting Inc 125Ave SE & 172nd St. Se. GSI 190100 H001 PL=LL=PI= USCS (D 2487)=AASHTO (M 145)= D90=D85=D60= D50=D30=D15= D10=Cu=Cc= Remarks *(no specification provided) DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Particle Size Distribution Report PERCENT FINER0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % +3"Coarse % Gravel Fine Coarse Medium % Sand Fine Silt % Fines Clay 0.0 3.3 8.7 5.3 15.7 38.5 28.56 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200TEST RESULTS Opening Percent Spec.*Pass? Size Finer (Percent)(X=Fail) Material Description Atterberg Limits (ASTM D 4318) Classification Coefficients Date Received:Date Tested: Tested By: Checked By: Title: Date Sampled:Location: Onsite Sample Number: EB-4 Depth: -7.5' Client: Project: Project No:Figure Silty SAND Some Gravel 1" 3/4" 3/8" #4 #8 #10 #20 #40 #60 #100 #200 #270 100.0 96.7 94.4 88.0 83.7 82.7 77.4 67.0 48.7 38.0 28.5 25.6 np nv SM A-2-4(0) 5.8272 2.9680 0.3448 0.2609 0.0862 2-14-20 2-14-20 MS JL 2-4-20 Osborn Consulting Inc 125Ave SE & 172nd St. Se. GSI 190100 H001 PL=LL=PI= USCS (D 2487)=AASHTO (M 145)= D90=D85=D60= D50=D30=D15= D10=Cu=Cc= Remarks *(no specification provided) DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57 Particle Size Distribution Report PERCENT FINER0 10 20 30 40 50 60 70 80 90 100 GRAIN SIZE - mm. 0.0010.010.1110100 % +3"Coarse % Gravel Fine Coarse Medium % Sand Fine Silt % Fines Clay 0.0 4.2 13.9 8.0 14.6 28.0 31.36 in.3 in.2 in.1½ in.1 in.¾ in.½ in.3/8 in.#4#10#20#30#40#60#100#140#200TEST RESULTS Opening Percent Spec.*Pass? Size Finer (Percent)(X=Fail) Material Description Atterberg Limits (ASTM D 4318) Classification Coefficients Date Received:Date Tested: Tested By: Checked By: Title: Date Sampled:Location: Onsite Sample Number: EB-5 Depth: -2' Client: Project: Project No:Figure Very Silty Gravelly SAND 1" 3/4" 3/8" #4 #8 #10 #20 #40 #60 #100 #200 #270 100.0 95.8 89.9 81.9 75.2 73.9 68.2 59.3 48.5 39.0 31.3 29.7 np nv SM A-2-4(0) 9.5979 6.1422 0.4425 0.2680 0.0577 2-14-20 2-14-20 MS JL 2-4-20 Osborn Consulting Inc 125Ave SE & 172nd St. Se. GSI 190100 H001 PL=LL=PI= USCS (D 2487)=AASHTO (M 145)= D90=D85=D60= D50=D30=D15= D10=Cu=Cc= Remarks *(no specification provided) DocuSign Envelope ID: 01C814B1-0BBA-4C1D-A80D-C3E897DA2B57