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Home My WebLink About22-102032-UP ILH AESI Geotech Report 2021.09.03b-5-4-22a s s e a r t h i n c o c i a t e d s c i e n c e s r p o r a t e d Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, and Preliminary Geotechnical Engineering Report ILLAHEE MIDDLE SCHOOL Federal Way, Washington Prepared For: FEDERAL WAY SCHOOL DISTRICT NO. 210 Project No. 20180138E002 September 3, 2021 a s s o c i a t e d earth sciences i n c o r p o r a t e d September 3, 2021 Project No. 20180138EO02 Federal Way School District No. 210 1211 South 332"d Street Federal Way, Washington 98003 Attention: Mr. Mike Kwaske Subject: Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, and Preliminary Geotechnical Engineering Report Illahee Middle School 36001 111 Avenue South Federal Way, Washington Dear Mr. Kwaske: We are pleased to present the enclosed copy of the referenced report. This report summarizes the results of tasks including subsurface exploration, geologic hazard analysis, infiltration feasibility assessment, and preliminary geotechnical engineering, and offers preliminary recommendations for design of the project. We have enjoyed working with you on this study and are confident that the preliminary recommendations presented in this report will aid in the successful completion of your project. Please contact me if you have any questions or if we can be of additional help to you. Sincerely, ASSOCIATED EARTH SCIENCES, INC. Kirkland, Washington 4JL�'�� Kurt D. Merriman, P.E. Senior Principal Engineer KDM/ld - 2018013SE002-002 Kirkland I Tacoma I Mount Vernon 425-827-7701 1 www.aesgeo.com SUBSURFACE EXPLORATION, GEOLOGIC HAZARD, INFILTRATION FEASIBILITY, AND PRELIMINARY GEOTECHNICAL ENGINEERING REPORT ILLAHEE MIDDLE SCHOOL Federal Way, Washington Prepared for: Federal Way School District No. 210 1211 South 332,d Street Federal Way, Washington 98003 Prepared by: Associated Earth Sciences, Inc. 911 5th Avenue Kirkland, Washington 98033 425-827-7701 September 3, 2021 Project No. 20180138EO02 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions 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 analysis, preliminary geotechnical engineering, and stormwater infiltration feasibility study for the proposed demolition and replacement of the existing Illahee Middle School in Federal Way, Washington. Our recommendations are preliminary in that the project is in the early design phase. The site location is shown on the "Vicinity Map," Figure 1. The approximate locations of explorations completed for this study are shown on the "Site and Exploration Plan," Figure 2. A Light Detection and Ranging (LIDAR)-based site and exploration map is included as "LIDAR Based Topography," Figure 3. Cross -sections representing interpreted subsurface conditions are represented on Figures 4 and 5. Interpretive exploration logs of subsurface explorations completed for this study are included in Appendix A. 1.1 Purpose and Scope The purpose of this study is to provide subsurface soil and groundwater data to be utilized in the preliminary design of the Illahee Middle School replacement project. Our study included reviewing selected available geologic literature, advancing eight exploration borings (EB-1 through EB-8), completing two subsurface geologic cross -sections, and performing a geologic study of subsurface sediment and groundwater conditions. Geotechnical engineering studies were completed to determine the type of suitable foundations, allowable foundation soil bearing pressures, anticipated foundation settlements, erosion considerations, drainage considerations, and to provide infiltration feasibility recommendations. This report summarizes our current fieldwork and offers preliminary design recommendations based on our present understanding of the project. 1.2 Authorization Authorization to proceed with this study was given to AESI by means of District Purchase Order 21001929 dated July 9, 2021. Our study was accomplished in general accordance with our proposal dated June 28, 2021. This report has been prepared for the exclusive use of Federal Way School District and its 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. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id - 20180138EO02-002 Page 1 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions 2.0 PROJECT AND SITE DESCRIPTION The project site is that of the existing Illahee Middle School. The existing building is a single -story structure of approximately 109,000 square feet constructed in 1970. The site is irregularly shaped in plan view and includes a total of 28.9 acres. Topography includes a relatively flat area on the east part of the site where the existing building and athletic fields were constructed, and a hilly undeveloped area on the west part of the site with vertical relief across the site on the order of approximately 60 feet. The east portion of the site is fully developed and landscaped, and the west portion is wooded. We understand that the project will include demolition of the existing school and construction of a new school. No site development plan has been created at the time this report was written. We anticipate that the new school will be built on the flatter portion of the site close to existing grades without deep excavations, substantial earthwork fills, or tall retaining walls. 3.0 SITE EXPLORATION Our field investigation for the current study was conducted in July 2021 and included advancing eight exploration borings. The existing site conditions, and the approximate locations of subsurface explorations referenced in this study, are presented on the "Site and Exploration Plan" (Figure 2). The various types of sediments, as well as the depths where the characteristics of the sediments 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 sediment types. If changes occurred between sample intervals in our exploration borings, they were interpreted. Our explorations were approximately located in the field by measuring from known site features depicted on the aerial photograph used as a basis for Figure 2. The conclusions and recommendations presented in this report are based, in part, on the explorations completed for this study. The number, locations, and depths of the explorations were completed within site and budgetary constraints. Because of the nature of exploratory work below ground, extrapolation 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 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. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 2 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions 3.1 Exploration Borings For this study, the eight exploration borings were completed by advancing a 3.25-inch, inside -diameter hollow -stem auger using a track -mounted drill. During the drilling process, samples were generally obtained at 2%- to 5-foot-depth intervals. The 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 visual observation of the samples collected. 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 is recorded within 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 exploration 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. 4.0 SUBSURFACE CONDITIONS 4.1 Regional Geology and Soils Mapping Published geologic mapping for the site and immediate vicinity were reviewed on the United States Geological Survey (USGS) National Geologic Map Database', and on the Washington State Department of Natural Resources (DNR) Geologic Information Porta12. These published regional geologic maps indicate that the site is underlain at shallow depths by Vashon ice -contact sediments. Ice -contact sediments are usually deposited on or within a glacial ice mass and were redeposited when the ice melted. Ice -contact sediments are suitable for support of lightly to moderately loaded structures with normal preparation and are usually not suitable for use as receptors for collected stormwater. The stratigraphic framework of the project area suggests that the ice -contact sediments are likely underlain at some depth by Vashon lodgement till sediments, which is consistent with our subsurface observations and interpretations discussed later in this ' https://ngmdb.usgs.gov/ngmdb/ngmdb home.html 2 https://www.dnr.wa.gov/geologyportal September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 3 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions report. Subsurface conditions observed in explorations for this study were generally consistent with the referenced published geologic mapping. Review of the Natural Resources Conservation Service (NRCS) Web Soils Survey shows that the site has multiple mapped surface soil types, Everett-Alderwood gravelly sandy loam (EwC), Everett very gravelly sandy loam (EvB), and Alderwood gravelly sandy loam (AgD), with EwC as the unit mapped most extensively onsite. 4.2 Site Stratigraphy Subsurface conditions at the project site were inferred from the field explorations accomplished for this study, visual reconnaissance of the site, and review of selected applicable geologic literature. As shown on the exploration logs, soils encountered at the site consisted of topsoil, fill of variable thickness overlying native sediments interpreted as Vashon-age recessional outwash, ice -contact sediments, and lodgement till. The following section presents more detailed subsurface information on the sediment types encountered at the site. Topsoil Grass and organic -rich brown topsoil and grass were observed at the ground surface in borings EB-2, EB-3, EB-5, EB-6, and EB-7. The observed thicknesses of topsoil ranged between 4 and 6 inches at the boring locations and are shown on the exploration logs. Existing topsoil should be stripped from structural areas and exported or reused in landscape applications if specifically permitted by project specifications. Fill Fill soils (those not naturally placed), were observed in all borings except EB-4. The observed fill depths ranged between 1.5 feet (EB-6) and 11.5 feet (EB-8). Figures 2 and 3 include the observed fill depths at each of the exploration locations. The fill generally consisted of loose to medium dense, moist, light brown to brown, fine to medium sand with variable silt content and variable gravel content. Organics (wood pieces) and faint organic odors were observed in the fill at the locations of EB-1, EB-2, EB-5, EB-7, and EB-8. Existing fill is not recommended for foundation support and may require remedial preparation below new paving. Excavated existing fill material is suitable for reuse in structural fill applications if such reuse is specifically allowed by project plans and specifications, if excessively organic and any other deleterious materials are removed, and if moisture content is adjusted to allow compaction to the specified level and to a firm and unyielding condition. Existing fill is not suitable for infiltration of stormwater. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id - 20180138EO02-002 Page 4 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions Vashon Recessional Outwash In exploration borings EB-1 and EB-6 we observed thin layers of loose to medium dense fine sands with trace silt and trace medium sands, ranging to fine sandy silt in EB-1, interpreted to represent recessional outwash. Recessional outwash is suitable for support of lightly to moderately loaded structures with proper preparation. Recessional outwash can sometimes be suitable for use as a stormwater infiltration receptor, but based on existing subsurface data the recessional outwash at the site does not occur over a large enough area to serve as an infiltration receptor. Excavated recessional outwash sediments are suitable for reuse in structural fill applications if allowed by project specifications and if the moisture content is adjusted to allow compaction to a firm and unyielding condition at the specified level. Vashon Ice -Contact Sediments Exploration borings EB-1, EB-2, and EB-5 through EB-7 encountered typically dense to very dense silty sand with varying content of medium to coarse sand and gravel. This material was differentiated from the recessional outwash observed in EB-1 and EB-6 based on fines content (siltier) and density (more dense). The ice -contact sediments ranged from till -like to stratified. This material is suitable for structural support with proper preparation, and is not recommended for use as an infiltration receptor due to its high density and generally high silt content. Vashon ice -contact sediments are suitable for reuse in structural fill applications if allowed by project specifications and if the moisture content is adjusted to allow compaction to a firm and unyielding condition at the specified level. Vashon Lodgement Till In exploration borings EB-2, EB-3, EB-4, EB-6, and EB-8, we observed dense to very dense, unsorted, silty fine sand with varying amounts of gravels interpreted to represent lodgement till sediments. The observed depth to the top of lodgement till sediments in borings where they were observed ranged between the existing ground surface (EB-4) and 22.5 feet (EB-6). In each boring that lodgement till was observed it extended beyond the depths of the explorations, with the deepest observations at 30 feet (EB-2 and EB-6). The upper 5 feet of the lodgement till in EB-4 was generally weathered and less dense, oxidized, and siltier than the lower, unweathered portions of the unit seen in other explorations. The 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. Consequently, these materials are dense to very dense, possess high -strength and low -compressibility characteristics, and are relatively impermeable. The lodgement till is suitable for foundation support with proper preparation and excavated lodgement till is suitable for use in structural fill applications if allowed by project specifications and provided that the moisture content is adjusted to allow September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 5 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Project and Site Conditions compaction to a firm and unyielding condition at the specified level. The lodgement till has a large proportion of fine-grained material making it susceptible to disturbance when wet. Lodgement till is not a suitable infiltration receptor. 4.3 Hydrology Groundwater was observed in exploration borings EB-1 and EB-5 at the time of drilling (July 2021). The groundwater in EB-1 was observed in the recessional outwash at a depth of approximately 10 feet below ground surface, perched above the siltier ice -contact sediments. Perched water occurs when surface water infiltrates down through relatively permeable soils, such as existing fill or coarser -grained recessional outwash strata, and becomes trapped or "perched" atop a comparatively low -permeability barrier, such as the underlying silty ice -contact sediments. When water becomes perched, it may travel laterally and may follow flow paths related to permeable zones that may not correspond to ground surface topography. The groundwater observed in EB-5 started at a cleaner, sandy layer (25 feet below ground surface) in the ice -contact unit and continued down to the bottom of the exploration at 35 feet. The groundwater in EB-5 is interpreted to represent an isolated groundwater occurrence occurring in more -permeable strata of the ice -contact sediments. The presence and quantity of groundwater will largely depend on the soil grain -size distribution, topography, seasonal precipitation, site use, on- and off -site land usage, and other factors. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id - 20180138EO02-002 Page 6 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Geologic Hazards and Mitigations II. GEOLOGIC HAZARDS AND MITIGATIONS We reviewed mapped geologic hazards on the City of Federal Way Critical Areas Map' and King County iMap2, and the previously referenced DNR map. The reviewed maps do not indicate the presence of regulated critical slopes or liquefaction areas. The DNR map shows an inferred tectonic fault trace mapped approximately 2.5 miles northeast of the site which is discussed in further detail below. The City of Federal Way Critical Areas Map shows that a small section on the western boundary of the parcel is mapped as an erosion hazard which is also discussed in further detail below. 5.0 LANDSLIDE HAZARDS AND MITIGATIONS The topography of the developed portion of the site is relatively flat to gently sloping. We reviewed topographic contours presented on Figures 2 and 3 created from LIDAR data. Topography includes a relatively flat area on the east part of the site where the existing building and athletic fields were constructed, and a hilly undeveloped area on the west part with slope inclinations ranging between 8 and 10 percent. Based on visual reconnaissance of the site, the existing slopes to the west appear to have performed well, with no visual indication of unusual erosion or slope instability. No emergent seepage was observed on the slopes during our site visit. Given the subsurface conditions on the site and the inclination and height of the slopes, it is our opinion that the risk of damage to the proposed improvements by landslide activity on these slopes as they currently exist under both static and seismic conditions is low. No detailed quantitative assessment of slope stability was completed as part of this study, and none is warranted to support the project as currently proposed, in our opinion. If the west slopes will be modified as part of the project a quantitative assessment of slope stability may be warranted. 6.0 SEISMIC HAZARDS AND MITIGATIONS The site does not include areas designated as Seismic Hazard Areas on the previously -referenced City of Federal Way Critical Areas Map. The following discussion is a more general assessment of seismic hazards that is intended to be useful to the project design team in terms of understanding seismic issues, and to the structural engineer for preliminary structural design. ' https://www.citvoffederalway.com/sites/default/files/maps/sensitive 2016.0 2 https://gismaps.kingcounty.gov/iMap/ September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id - 20180138EO02-002 Page 7 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Geologic Hazards and Mitigations All of Western Washington is at risk of strong seismic events resulting from movement of the tectonic plates associated with the Cascadia Subduction Zone (CSZ), where the offshore Juan de Fuca plate subducts beneath the continental North American plate. The site lies within a zone of strong potential shaking from subduction zone earthquakes associated with the CSZ. The CSZ can produce earthquakes up to magnitude 9.0, and the recurrence interval is estimated to be on the order of 500 years. Geologists infer the most recent subduction zone earthquake occurred in 1700 (Goldfinger et al., 20123). Three main types of earthquakes are typically associated with subduction zone environments: crustal, intraplate, and interplate earthquakes. Seismic records in the Puget Sound region document a distinct zone of shallow crustal seismicity (e.g., the Seattle Fault Zone). These shallow fault zones may include surficial expressions of previous seismic events, such as fault scarps, displaced shorelines, and shallow bedrock exposures. The shallow fault zones typically extend from the surface to depths ranging from 16 to 19 miles. A deeper zone of seismicity is associated with the subducting Juan de Fuca plate. Subduction zone seismic events produce intraplate earthquakes at depths ranging from 25 to 45 miles beneath the Puget Lowland including the 1949, 7.2-magnitude event; the 1965, 6.5-magnitude event; and the 2001, 6.8-magnitude event) and interplate earthquakes at shallow depths near the Washington coast including the 1700 earthquake, which had a magnitude of approximately 9.0. The 1949 earthquake appears to have been the largest in this region during recorded history and was centered in the Olympia area. Evaluation of earthquake return rates indicates that an earthquake of the magnitude between 5.5 and 6.0 is likely within a given 20-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides or lateral spreading, 3) liquefaction, 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 subject property is a possible southern branch of the Tacoma Fault, referred to as Lineament "C' (Sherrod et al., 20034) approximately 2.5 miles northwest of the site. Lineament "C" is defined by aeromagnetic data and a tomography velocity model. The geophysical datasets indicate that the vertical displacement of this fault increases to the west. Evidence of uplift or subsidence is recorded in marshes along inlets of southern Puget Sound near Lynch Cove, Burley, North Bay, and Wollochet Bay. This movement suggests a seismic event associated with the Tacoma Fault approximately 1,100 years ago, with up to 3 meters of 3 Goldfinger, C., Nelson, C.H., Morey, A.E., Johnson, J.E., Patton, J.R., Karabanov, E., Gutierrez -Pastor, J., Eriksson, A.T., Gracia, E., Dunhill, G., Enkin, R.J, Dallimore, A., and Vallier, T., 2012, Turbidite Event History —Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone: U.S. Geological Survey Professional Paper 1661—F, 170 . 4 Sherrod, B.L. Nelson, A.R., Kelsey, H.M., Bracher, T.M., Blakely, R.J., Weaver, C.S., Rountree, N.K., Rhea, S.B., and Jackson, B.S., 2003, The Catfish Lake Scarp, Allyn, Washington: Preliminary Field Data and Implications for Earthquake Hazards Posed by the Tacoma Fault, U.S. Geological Survey (USGS) Open File Report 03-0455. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id - 20180138EO02-002 Page 8 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Geologic Hazards and Mitigations displacement. Data pertaining to the Tacoma Fault is limited, with studies still ongoing. The recurrence interval of movement along this fault system is still unknown, although it is hypothesized to be in excess of 1,000 years. Due to the suspected long recurrence interval, and the distance from mapped fault traces, the potential risk to the project from surficial ground rupture is considered to be low during the expected life of the proposed structures. We are available to discuss mapped faulting further on request. 6.2 Seismically Induced Landslides As stated above, given the subsurface conditions on the site and the inclination and height of the slopes, it is our opinion that the risk of damage to the proposed improvements by seismically induced landslides is low, in our opinion. No detailed quantitative assessment of slope stability was completed as part of this study. If redevelopment of the site will include modification of existing slopes on the west part of the site an assessment of the potential for seismically induced landslides may be warranted. 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 very soft to stiff, non -cohesive silt and very loose to medium dense, non -silty to silty sands with low relative densities, accompanied by a shallow water table. The project is not expected to have substantial risk of damage due to liquefaction because substantial deposits of loose saturated granular sediments were not observed. A detailed liquefaction hazard analysis was not performed as part of this study, and none is warranted based on existing subsurface data, in our opinion. 6.4 Ground Motion/Seismic Site Class (2018 International Building Code) Structural design of the new building should follow 2018 International Building Code (IBC) standards. We recommend that the project be designed in accordance with Site Class "D" in accordance with the 2018 IBC, and the publication American Society of Civil Engineers (ASCE) 7 referenced therein, the most recent version of which is ASCE 7-16. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id - 20180138EO02-002 Page 9 Illahee Middle School Federal Way, Washington Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, and Preliminary Geotechnical Engineering Report Geologic Hazards and Mitigations As stated above, the City of Federal Way Critical Areas Map shows that a small section on the western boundary of the parcel is mapped as an erosion hazard critical area. Due to the slope inclinations and vegetation, project plans should include implementation of temporary erosion controls in accordance with local standards of practice. In our opinion, implementation of the following recommendations should be adequate to address the Washington State Department of Ecology (Ecology) and City of Federal Way requirements for management of erosion hazards. The Ecology Construction Storm Water General Permit requires weekly Temporary Erosion and Sedimentation Control (TESC) inspections, turbidity monitoring and pH monitoring for all sites 1 or more acres in size that discharge stormwater to surface waters of the state. Because we anticipate that the proposed project will require disturbance of more than 1 acre, we anticipate that these inspection and reporting requirements will be triggered. The following recommendations are related to general erosion potential and mitigation. Best management practices (BMPs) should include but not be limited to: 1. Construction activity should be scheduled or phased as much as possible to reduce the amount of earthwork activity that is performed during the winter months. 2. The winter performance of a site is dependent on a well -conceived plan for control of site erosion and stormwater runoff. The site plan should include ground -cover measures, access roads, and staging areas. The contractor should be prepared to implement and maintain the required measures to reduce the amount of exposed ground. 3. TESC measures for a given area to be graded or otherwise worked should be installed soon after ground clearing. The recommended sequence of construction within a given area after clearing would be to install TESC elements and perimeter flow control prior to starting grading. 4. During the wetter months of the year, or when large storm events are predicted during the summer months, each work area should be stabilized so that if showers occur, the work area can receive the rainfall without excessive erosion or sediment transport. The required measures for an area to be "buttoned -up" will depend on the time of year and the duration the area will be left unworked. During the winter months, areas that are to be left unworked for more than 2 days should be mulched or covered with plastic. During the summer months, stabilization will usually consist of seal -rolling the subgrade. Such measures will aid in the contractor's ability to get back into a work area after a storm event. The stabilization process also includes establishing temporary stormwater September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 10 Illahee Middle School Federal Way, Washington Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, and Preliminary Geotechnical Engineering Report Geologic Hazards and Mitigations conveyance channels through work areas to route runoff to the approved treatment/discharge facilities. 5. All disturbed areas should be revegetated as soon as possible. If it is outside of the growing season, the disturbed areas should be covered with mulch, as recommended in the erosion control plan. Straw mulch provides a cost-effective cover measure and can be made wind -resistant with the application of a tackifier after it is placed. 6. Surface runoff and discharge should be controlled during and following development. Uncontrolled discharge may promote erosion and sediment transport. Under no circumstances should concentrated discharges be allowed to flow over the top of steep slopes. 7. Soils that are to be reused around the site should be stored in such a manner as to reduce erosion from the stockpile. Protective measures may include, but are not limited to, covering with plastic sheeting, the use of low stockpiles in flat areas, or the use of silt fences around pile perimeters. It is our opinion that with the proper implementation of the TESC plans and by field -adjusting appropriate mitigation elements (BMPs) during construction, the potential adverse impacts from erosion hazards on the project may be mitigated. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138E002-002 Page 11 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations III. PRELIMINARY DESIGN RECOMMENDATIONS 8.0 INTRODUCTION Our explorations indicates that, from a geotechnical engineering standpoint, the property is suitable for the proposed improvements provided the recommendations contained herein are properly followed. The subject site is underlain in places by a layer of existing fill that is variable in thickness and density. Existing fill or loose soils are not suitable for support of new foundations, and warrant remedial preparation where occurring below paving. Fill soils should be removed from below foundation areas and replaced with structural fill. Medium dense to very dense native deposits or structural fill placed over medium dense to very dense native deposits are suitable for support of shallow foundations with proper preparation. Since a project concept has not yet been selected at the time this report is written this report is preliminary. AESI should be allowed to review the final project plans once they have been developed to update our recommendations, as necessary. 8.1 Site Preparation Erosion and surface water control should be established around the perimeter of the excavation to satisfy City of Federal Way requirements. Building Pad Areas Site preparation should include removal of all existing pavement, structures, buried utilities, and any other deleterious material from below the new building. Existing fill should be removed to expose suitable native materials suitable for structural support. Structural Fill may then be placed as needed to reach building pad grade. At the time this report is written a site development plan has not been selected. Depending on the location selected for new school building(s), other support alternatives may be feasible that would not require the removal of all existing fill. Aggregate piers may be appropriate depending on how laterally and vertically extensive existing fill is beneath the building pad. We should be allowed to review the site development plan when one is selected and discuss possible site preparation and structural support plans that are appropriate to the project plan. Paving Areas Areas of planned paving should be prepared by stripping existing vegetation and topsoil, removing structures and utilities to be demolished, and excavating to planned paving subgrade elevation. The resulting subgrade should then be evaluated visually, compacted, and September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 12 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations proof -rolled. Exposed soils are expected to consist of existing fill, recessional outwash, ice -contact sediments, or lodgement till depending on the location and finished subgrade elevation. Areas with organic or deleterious material, or areas that yield during proof -rolling should receive additional preparation tailored to proof -rolling results and field conditions at the time of construction. 8.2 Site Drainage and Surface Water Control The site should be graded to prevent water from ponding in construction areas and/or flowing into excavations. Exposed grades should be crowned, sloped, and smooth drum -rolled at the end of each day to facilitate drainage. Accumulated water must be removed from subgrades and work areas immediately prior to performing further work in the area. Equipment access may be limited, and the amount of soil rendered unfit for use as structural fill may be greatly increased if drainage efforts are not accomplished in a timely sequence. If an effective drainage system is not utilized, project delays and increased costs could be incurred due to the greater quantities of wet and unsuitable fill, or poor access and unstable conditions. We do not anticipate the need for extensive dewatering in advance of excavations. However, the contractor should be prepared to intercept any groundwater seepage entering the excavations and route it to a suitable discharge location. The depth to groundwater in EB-1 was observed to be at 10 feet below ground surface at the time of drilling in July 2021. The rest of the groundwater observations were 25 feet below ground surface elevation (EB-5). Explorations were completed during seasonal dry weather and wetter conditions may be present at the time of construction. Final exterior grades should promote free and positive drainage away from buildings at all times. Water must not be allowed to pond or to collect adjacent to foundations or within immediate building areas. We recommend that a gradient of at least 3 percent for a minimum distance of 10 feet from the building perimeters be provided, except in paved locations. In paved locations, a minimum gradient of 1 percent should be provided, unless provisions are included for collection and disposal of surface water adjacent to the structure. 8.3 Subgrade Protection If building construction will proceed during the winter, we recommend the use of a working surface of sand and gravel, crushed rock, or quarry spalls to protect exposed soils, particularly in areas supporting concentrated equipment traffic. In winter construction staging areas and areas that will be subjected to repeated heavy loads, such as those that occur during construction of masonry walls, a minimum thickness of 12 inches of quarry spalls or 18 inches of pit run sand and gravel is recommended. If subgrade conditions are soft and silty, a geotextile separation fabric, such as Mirafi 50OX or approved equivalent, should be used between the subgrade and the new fill. For building pads where floor slabs and foundation construction will be completed in the September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 13 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations winter, a similar working surface should be used, composed of at least 6 inches of pit run sand and gravel or crushed rock. Construction of working surfaces from advancing fill pads could be used to avoid directly exposing the subgrade soils to vehicular traffic. Foundation subgrades may require protection from foot and equipment traffic and ponding of runoff during wet weather conditions. Typically, compacted crushed rock or a lean -mix concrete mat placed over a properly prepared subgrade provides adequate subgrade protection. Foundation concrete should be placed and excavations backfilled as soon as possible to protect the bearing surface. 8.4 Proof -Rolling and Subgrade Compaction Following the recommended clearing, site stripping, planned excavation, and any overexcavation required to remove existing fill, the stripped subgrade within the building areas should be proof -rolled with heavy, rubber -tired construction equipment, such as a fully -loaded tandem - axle dump truck. Proof -rolling should be performed prior to structural fill placement or foundation excavation. The proof -roll should be monitored by the geotechnical engineer so that any soft or yielding subgrade soils can be identified. Any soft/loose, yielding soils should be removed to a stable subgrade. The subgrade should then be scarified, adjusted in moisture content, and recompacted to the required density. Proof -rolling should only be attempted if soil moisture contents are at or near optimum moisture content. Proof -rolling of wet subgrades could result in further degradation. Low areas and excavations may then be raised to the planned finished grade with compacted structural fill. Subgrade preparation and selection, placement, and compaction of structural fill should be performed under engineering -controlled conditions in accordance with the project specifications. 8.5 Overexcavation/Stabilization Construction during extended wet weather periods could create the need to overexcavate exposed soils if they become disturbed and cannot be recompacted due to elevated moisture content and/or weather conditions. Even during dry weather periods, soft/wet soils, which may need to be overexcavated, may be encountered in some portions of the site. If overexcavation is necessary, it should be confirmed through continuous observation and testing by AESI. Soils that have become unstable may require remedial measures in the form of one or more of the following: 1. Drying and recompaction. Selective drying may be accomplished by scarifying or windrowing surficial material during extended periods of dry and warm weather. 2. Removal of affected soils to expose a suitable bearing subgrade and replacement with compacted structural fill. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 14 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations 3. Mechanical stabilization with a coarse crushed aggregate compacted into the subgrade, possibly in conjunction with a geotextile. 4. Soil/cement admixture stabilization. 8.6 Wet Weather Conditions If construction proceeds during an extended wet weather construction period and the moisture -sensitive site soils become wet, they will become unstable. Therefore, the bids for site grading operations should be based upon the time of year that construction will proceed. It is expected that in wet conditions additional soils may need to be removed and/or other stabilization methods used, such as a coarse crushed rock working mat to develop a stable condition if silty subgrade soils are disturbed in the presence of excess moisture. The severity of construction disturbance will be dependent, in part, on the precautions that are taken by the contractor to protect the moisture- and disturbance -sensitive site soils. If overexcavation is necessary, it should be confirmed through continuous observation and testing by a representative of our firm. 8.7 Temporary and Permanent Cut Slopes In our opinion, stable construction slopes should be the responsibility of the contractor and should be determined during construction. For estimating purposes, however, we anticipate that temporary, unsupported cut slopes in the existing fill or loose to medium dense native deposits can be made at a maximum slope of 1.5H:1V (Horizontal:Vertical) or flatter. Temporary slopes in dense to very dense till sediments may be planned at 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. Permanent cut and structural fill slopes that are not intended to be exposed to surface water should be designed at inclinations of 2H:1V or flatter. All permanent cut or fill slopes should be compacted to at least 95 percent of the modified Proctor maximum dry density, as determined by ASTM D-1557, and the slopes should be protected from erosion by sheet plastic until vegetation cover can be established during favorable weather. 8.8 Frozen Subgrades If earthwork takes place during freezing conditions, all exposed subgrades should be allowed to thaw and then be recompacted prior to placing subsequent lifts of structural fill or foundation components. Alternatively, the frozen material could be stripped from the subgrade to reveal unfrozen soil prior to placing subsequent lifts of fill or foundation components. The frozen soil September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 15 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations should not be reused as structural fill until allowed to thaw and adjusted to the proper moisture content, which may not be possible during winter months. 8.9 Paving Areas Areas of planned paving should be prepared by stripping existing vegetation and topsoil, removing structures and utilities to be demolished, and excavating to planned paving subgrade elevation. The resulting subgrade should then be evaluated visually, compacted, and proof -rolled. Exposed soils are expected to consist of existing fill, recessional outwash, ice -contact sediments, or lodgement till depending on the location. Areas with organic or deleterious material, or areas that yield during proof -rolling should receive additional preparation. 9.0 STRUCTURAL FILL All references to structural fill in this report refer to subgrade preparation, fill type and placement, and compaction of materials, as discussed in this section. If a percentage of compaction is specified under another section of this report, the value given in that section should be used. After stripping, planned excavation, and any required overexcavation have been performed to the satisfaction of the geotechnical engineer, the upper 12 inches of exposed ground in areas to receive fill should be recompacted to a firm and unyielding condition as determined by the geotechnical engineer. If the subgrade contains silty soils and too much moisture, adequate recompaction may be difficult or impossible to obtain and should probably not be attempted. In lieu of recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. Where the exposed ground remains soft and further overexcavation is impractical, placement of an engineering stabilization fabric may be necessary to prevent contamination of the free -draining layer by silt migration from below. After recompaction of the exposed ground is tested and approved, or a free -draining rock course is laid, structural fill may be placed to attain desired grades. Structural fill is defined as non -organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift being compacted to 95 percent of the modified Proctor maximum density using ASTM D-1557 as the standard. For on -site utility trench backfill, including the backfill resulting from the removal of existing utility lines below the planned new school, we recommend the structural fill standard described above. In the case of roadway and utility trench filling within City rights -of -way, the backfill should be placed and compacted in accordance with current City of Federal Way codes and standards. The top of the compacted fill should extend horizontally September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 16 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations outward a minimum distance of 3 feet beyond the locations of the roadway edges before sloping down at an angle of 2H:1V. The contractor should note that any proposed fill soils must be evaluated by AESI prior to their use in fills. This would require that we have a sample of the material 72 hours in advance to perform a Proctor test and determine its field compaction standard. Soils in which the amount of fine-grained material (smaller than the No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture -sensitive. Use of moisture -sensitive soil in structural fills should be limited to favorable dry weather conditions. The native and existing fill soils present onsite contained variably high amounts of silt and are considered moisture -sensitive. Therefore, we anticipate that the use of on -site soils as structural fill may require moisture -conditioning to achieve proper compaction. For non-structural applications, the on -site material is generally considered suitable, as long as it is free of vegetation, topsoil, and any other deleterious materials. In addition, construction equipment traversing the site when the soils are wet can cause considerable disturbance. If fill is placed during wet weather or if proper compaction cannot be obtained, a select import material consisting of a clean, free -draining gravel and/or sand should be used. Free -draining fill consists of non -organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction with at least 25 percent retained on the No. 4 sieve. A representative from our firm should inspect the stripped subgrade and be present during placement of structural fill to observe the work and perform a representative number of in -place density tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses, and any problem areas may be corrected at that time. It is important to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid in developing a suitable monitoring and testing program. 10.0 FOUNDATIONS We expect the depth to bearing soil to vary across the building footprint relative to the foundation subgrade elevation of the planned building. The existing on -site fill was thickest (about 11.5 feet in depth) in the southeastern portion of the site, in the vicinity of EB-8. Where present, existing fill should be removed below the building pad, exposing medium dense to very dense native sediments. Spread footings may be used for building support when founded directly on undisturbed native sediments, on structural fill placed over suitable native sediments. If foundations will be supported by a combination of very dense native sediments and new structural fill, we recommend that an allowable bearing pressure of 3,500 pounds per square foot (psf) be used for September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 17 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations design purposes, including both dead and live loads. Higher foundation soil bearing pressures may be suitable if new footings will be supported entirely on dense to very dense native soils. We should be allowed to offer situation -specific recommendations if higher foundation soil -bearing pressures are needed. An increase of one-third may be used for short-term wind or seismic loading. Perimeter footings should be buried at least 18 inches into the surrounding soil for frost protection. However, all footings must penetrate to the prescribed bearing stratum, and no footing should be founded in or above organic or loose soils. It should be noted that the area bound by lines extending downward at 1H:1V from any footing must not intersect another footing or intersect a filled area that has not been compacted to at least 95 percent of ASTM D-1557. In addition, a 1.5H:1V line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. Anticipated settlement of footings founded as described above should be on the order of % inch or less. However, disturbed soil not removed from footing excavations prior to footing placement and footings placed above loose soils could result in increased settlements. All footing areas should be inspected by AESI prior to placing concrete to verify that the design bearing capacity of the soils has been attained and that construction conforms to the recommendations contained in this report. Such inspections may be required by the governing municipality. Perimeter footing drains should be provided, as discussed under the "Drainage Considerations" Section 13.0 of this report. 11.0 FLOOR SUPPORT If crawl -space floors are used, an impervious moisture barrier should be provided above the soil surface within the crawl space. Slab -on -grade floors may be used over medium dense to very dense native soils, or over structural fill placed as recommended in the "Site Preparation" and "Structural Fill" sections of this report. Slab -on -grade floors should be cast atop a minimum of 4 inches of washed pea gravel or washed crushed "chip" rock with less than 3 percent passing the U.S. No. 200 sieve to act as a capillary break. The floors should also be protected from dampness by covering the capillary break layer with an impervious moisture barrier at least 10 mils in thickness. September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 18 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations 12.0 FOUNDATION WALLS All backfill behind foundation walls or around foundation units should be placed as per our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls, which are free to yield laterally at least 0.1 percent of their height, may be designed to resist active earth pressure represented by an equivalent fluid equal to 35 pounds per cubic foot (pcf). Fully restrained, horizontally backfilled, rigid walls that cannot yield should be designed for an at -rest earth pressure represented by an equivalent fluid of 50 pcf. Walls with sloping backfill up to a maximum gradient of 2H:1V should be designed using an equivalent fluid of 55 pcf for yielding conditions or 75 pcf for fully restrained conditions. If parking areas are adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in determining lateral design forces. As required by the 2018 IBC, retaining wall design should include a seismic surcharge pressure in addition to the equivalent fluid pressures presented above. Considering the site soils and the recommended wall backfill materials, we recommend a seismic surcharge pressure of 5H and 10H psf, where H is the wall height in feet for the "active" and "at -rest" loading conditions, respectively. The seismic surcharge should be modeled as a rectangular distribution with the resultant applied at the midpoint of the walls. The lateral pressures presented above are based on the conditions of a uniform backfill consisting of excavated on -site soils, or imported structural fill compacted to 90 percent of ASTM D-1557. A higher degree of compaction is not recommended, as this will increase the pressure acting on the walls. A lower compaction may result in settlement of the slab -on -grade or other structures supported above the walls. Thus, the compaction level is critical and must be tested by our firm during placement. Surcharges from adjacent footings or heavy construction equipment must be added to the above values. Perimeter footing drains should be provided for all retaining walls, as discussed under the "Drainage Considerations" section of this report. It is imperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum, 1-foot-wide blanket drain to within 1 foot of finish grade for the full wall height using imported, washed gravel against the walls. A prefabricated drainage mat is not a suitable substitute for the gravel blanket drain unless all backfill against the wall is free -draining. 12.1 Passive Resistance and Friction Factors Lateral loads can be resisted by friction between the foundation and the natural glacial soils or supporting structural fill soils, and by passive earth pressure acting on the buried portions of the foundations. The foundations must be backfilled with structural fill and compacted to at least September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 19 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations 95 percent of the maximum dry density to achieve the passive resistance provided below. We recommend the following allowable design parameters: • Passive equivalent fluid = 250 pcf • Coefficient of friction = 0.35 13.0 DRAINAGE CONSIDERATIONS All retaining and perimeter foundation walls should be provided with a drain at the base of the footing elevation. Drains should consist of rigid, perforated, PVC pipe surrounded by washed pea gravel. The level of the perforations in the pipe should be set at or slightly below the bottom of the footing grade beam, and the drains should be constructed with sufficient gradient to allow gravity discharge away from the building. In addition, all retaining walls should be lined with a minimum, 12-inch-thick, washed gravel blanket that extends to within 1 foot of the surface and is continuous with the foundation drain. Roof and surface runoff should not discharge into the foundation drain system, but should be handled by a separate, rigid, tightline drain. In planning, exterior grades adjacent to walls should be sloped downward away from the structure to achieve surface drainage. 14.0 PAVEMENT AND SIDEWALK RECOMMENDATIONS The pavement sections included in this report section are for driveway and parking areas onsite, and are not applicable to right-of-way improvements. At this time, we are not aware of any planned right-of-way improvements; however, if any new paving of public streets is required, we should be allowed to offer situation -specific recommendations. Pavement and sidewalk areas should be prepared in accordance with the "Site Preparation" section of this report. Soft or yielding areas should be overexcavated to provide a suitable subgrade and backfilled with structural fill. New paving may include areas subject only to light traffic loads from passenger vehicles driving and parking, and may also include areas subject to heavier loading from vehicles that may include buses, fire trucks, food service trucks, and garbage trucks. In light traffic areas, we recommend a pavement section consisting of 3 inches of hot -mix asphalt (HMA) underlain by 4 inches of crushed surfacing base course. In heavy traffic areas, we recommend a minimum pavement section consisting of 4 inches of HMA underlain by 2 inches of crushed surfacing top course and 4 inches of crushed surfacing base course. The crushed rock courses must be compacted to 95 percent of the maximum density, as determined by ASTM D-1557. All paving materials should September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 20 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations meet gradation criteria contained in the current Washington State Department of Transportation (WSDOT) Standard Specifications. Depending on construction staging and desired performance, the crushed base course material may be substituted with asphalt treated base (ATB) beneath the final asphalt surfacing, if desired. The substitution of ATB should be as follows: 4 inches of crushed rock can be substituted with 3 inches of ATB, and 6 inches of crushed rock may be substituted with 4 inches of ATB. ATB should be placed over a native or structural fill subgrade compacted to a minimum of 95 percent relative density, and a 1%- to 2-inch thickness of crushed rock to act as a working surface. If ATB is used for construction access and staging areas, some rutting and disturbance of the ATB surface should be expected to result from construction traffic. The general contractor should remove affected areas and replace them with properly compacted ATB prior to final surfacing. Infiltration of surface water is not recommended based on currently available data. The site is underlain by existing fill material that ranges in thickness from 0 to 11.5 feet below the existing ground surface. The existing fill is not suitable for use as an infiltration receptor. Existing fill was observed to be underlain by a thin section of recessional outwash in two borings (EB-1 and EB-6). Recessional outwash observed in subsurface explorations was not laterally or vertically extensive enough to serve as an infiltration receptor, in our opinion. Ice -contact and lodgement till sediments stratigraphically below the recessional outwash were typically dense to very dense and silty, and not suitable for use as an infiltration receptor. 15.1 Recommendations for Future Infiltration -Related Stud There may be some potential for limited infiltration of stormwater in the vicinity of borings EB-1 and EB-6 using strategies such as rain gardens with limited tributary areas. Large infiltration facilities with large tributary areas and higher flows are not feasible, and at best a small fraction of the overall stormwater generated onsite could be infiltrated. If limited infiltration is pursued, only the area around EB-1 and EB-6 should be considered, and additional explorations are recommended to determine if the recessional outwash is suitable to act as a limited stormwater receptor. 16.0 PROJECT DESIGN AND CONSTRUCTION MONITORING We recommend that AESI perform a geotechnical review of the plans prior to final design completion. In this way, we can confirm that our recommendations have been correctly September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 21 Subsurface Exploration, Geologic Hazard, Infiltration Feasibility, Illahee Middle School and Preliminary Geotechnical Engineering Report Federal Way, Washington Preliminary Design Recommendations interpreted and implemented in the design. The City of Federal Way may require a plan review by the geotechnical engineer as a condition of permitting. We recommend that AESI be retained to provide geotechnical special inspections during construction, and preparation of a final summary letter when construction is complete. The City of Federal Way may require such geotechnical special inspections. The integrity of the earthwork and foundations 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. We have enjoyed working with you on this study and are confident 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 L i Aaron `R. urnley, G.I.T. Senior Staff Geologist Am 6w;lz�sr Bruce W. Guerzler, L.E.G. Senior Associate Geologist Attachments: Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Appendix A. Digitally signed by Kurt D. Kurt D. Merriman, P.E. Merriman, P.E. Date: zazi.as-o7 34 -07'00 �. MR9! yrPc�o` ' A��ry�� c 23560 �GISTQ Z Kurt D. Merriman, P.E. Senior Principal Engineer Vicinity Map Site and Exploration Plan LIDAR Topography Map Cross -Section (N-S) Cross -Section (NW -SE) Exploration Logs September 3, 2021 ASSOCIATED EARTH SCIENCES, INC. ART/Id-20180138EO02-002 Page 22 y 11 �' �• r• . `� �� w F Fit I All 11114 1111C%Ull 0 MEMO elf ��► _ _\ ilk ;^� � , -. i�roll a s s.c a t eVICINITY . ■ .- DATA SOURCES I REFERENCES: NOTE -BLACK AND WHITE ILLAHEE MS IMPROVEMENTS USGS: 7.5' SERIES TOPOGRAPHIC MAPS, ESRIII-CUBEDINGS 2013 REPRODUCTION OF THIS COLOR FEDERAL WAY, WAS H l NGTO N KING CO: STREETS, CITY LIMITS, PARCELS, PARKS 3120 ORIGINAL MAY REDUCE ITS LCCATI0NSANDDISTANCESSHOWN ARE APPRONIMATE EFFECTIVENESSAND LEAD TO PROD NO. DATE:FIGURE: I N 0 ORRECT INTERPR ETATION 20180138E002 8/21 1 a N) k . \,� `� , __" I T •ma's � , EB1.; 4FT Il; 0EB-5, 6.5FT f.AW EB-2, 3FT DEB-6, 1_.5FT ► �' 1• S 361st PI , �L�E f ' L .P' •T � •e ,� .�I .5 363rd PI of �s HylehoS. 1�� R _ WetlandsJkl7l LEGEND 0 SITE 0 EXPLORATION BORING, DEPTH OF FILL PARK PARCEL CONTOUR 20 FT CONTOUR 5 FT DATA SOURCES I REFERENCES: PSLC: KING COUNTY 2016, GRID CELL SIZE IS 3'. DELIVERY 2 FLOWN 2125116 - 3Q6116 PIERCE COUNTY LIDAR: 201012011, GRID CELL SIZE IS 3'" CONTCURS FROM LIDAR KING CO: STREETS, PARCELS, 3120 AERIAL PICTOMETRY INT. 201S LOCATIONS AND DISTANCES SHOWN ARE APPROXIMATE is N 0 200 ierce Co FEET BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIV_NESSAND LEAD TO INCORRECT INTERPRETATION a s s o c i a t e d earth sciences i n c 0 r p❑ r a t e d EXISTING SITE AND EXPLORATION PLAN ILLAHEE MS IMPROVEMENTS FEDERAL WAY, WASHINGTON PROJ NO I DATE: FIGLiRE: 20180138EO02 8/21 2 7rw-.. EB-4.., 0FT EB-1 ; 4FT E „ '� !ate � `� � ■ 0EB-5, 6.5FT EB-6, 1.5FT 0 EB-3, .5F1.=1�,,� EB-2, 3F .00 F J EB-7, 6FT� r l m i S 361$t Pl 9za-J, '. -gon�L ' f S3rd PI r.ylehos 'Wetlands ! LEGEND SITE Q EXPLORATION BORING, DEPTH OF FILL CROSS-SECTION PARK PARCEL r\_1 CONTOUR 20 FT CONTOUR 5 FT DATA SOURCES I REFERENCES: PSLC: KING COUNTY 2016, GRID CELL SIZE IS T. DELIVERY 2 FLOWN 2125116 - 3f28116 PIERCE COUNTY LIDAR: 201012011, GRID CELL SIZE IS 3'. CONTCURS FROM LIDAR KING CO: STREETS, PARCELS, 3120 LOCATIONS AND DISTANCES SHOWN ARE APPROXIMATE L Pierce Co N A n 200 FEET BLACK AND WHITE REPRODUCTION OF THIS COLOR ORIGINAL MAY REDUCE ITS EFFECTIV_NESSAND LEAD TO INCORRECT INTERPRETATION a s s❑ c i a t e d )a,earth sciences i n c,) r p o r a t e d LIDAR BASED TOPOGRAPHY ILLAHEE MS IMPROVEMENTS FEDERAL WAY, WASHINGTON PROD NO. DATE FIGURE: 20180138EO02 8121 3 A SOUTH 310 300 290 280 270 260 250 240 H LU W LL z 230 O Q 220 UJI 210 200 190 180 170 160 150 0 0 0 0 0 0 0 N (D 00 O N 'T HORIZONTAL DISTANCE (FEET) A' NORTH 310 300 290 280 270 260 250 240 230 220 210 200 190 180 170 160 150 LEGEND: Fill FILL Qv0 VASHON RECESSIONAL OUTWASH Qvi VASHON ICE CONTACT Qvt VASHON LODGEMENT TILL 1 BORING T WATER LEVEL AT TIME OF DRILLING TD TOTAL DEPTH OF BORING 171 SPT N-VALUES 32 \ GEOLOGIC CONTACT VERTICAL EXAGGERATION = I OX NOTE: LOCATION AND DISTANCES SHOWN ARE APPROXIMATE NOTES: 1. THE SUBSURFACE CONDITIONS PRESENTED IN THIS GEOLOGIC CROSS-SECTION ARE BASED ON AN INTERPRETATION OF CONDITIONS ENCOUNTERED IN WIDELY SPACED EXPLORATIONS COMPLETED AT THE SUBJECT SITE AND RELEVANT SITE INFORMATION DEVELOPED AND PROVIDED BY OTHERS. THE SUBSURFACE INTERPRETATIONS PRESENTED IN THIS GEOLOGIC CROSS-SECTION SHOULD NOT BE CONSTRUED AS A WARRANTY OF ACTUAL SUBSURFACE CONDITIONS AT THE SITE. OUR EXPERIENCE HAS SHOWN THAT SOIL AND GROUNDWATER CONDITIONS CAN VARY SIGNIFICANTLY OVER SMALL DISTANCES. 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 0 earth sciences incorporated GEOLOGIC CROSS-SECTION A - A' ILLAHEE MS IMPROVEMENTS FEDERAL WAY, WASHINGTON PROJ NO. DATE: FIGURE: 20180138EO02 8/21 4 B NORTHWEST 310 300 290 280 270 260 250 240 H LU LU LL_ z 230 O Q 220 UJI 210 200 190 180 170 160 150 B' SOUTHEAST 310 300 290 280 270 260 250 240 0 0 0 0 0 0 0 0 N (0 00 O N 'T CO HORIZONTAL DISTANCE (FEET) 230 220 210 200 190 180 170 160 150 LEGEND: Fill FILL Qv0 VASHON RECESSIONAL OUTWASH Qvi VASHON ICE CONTACT Qvt VASHON LODGEMENT TILL 1 BORING T WATER LEVEL AT TIME OF DRILLING TD TOTAL DEPTH OF BORING 171 SPT N-VALUES 32 \ GEOLOGIC CONTACT VERTICAL EXAGGERATION = I OX NOTE: LOCATION AND DISTANCES SHOWN ARE APPROXIMATE NOTES: 1. THE SUBSURFACE CONDITIONS PRESENTED IN THIS GEOLOGIC CROSS-SECTION ARE BASED ON AN INTERPRETATION OF CONDITIONS ENCOUNTERED IN WIDELY SPACED EXPLORATIONS COMPLETED AT THE SUBJECT SITE AND RELEVANT SITE INFORMATION DEVELOPED AND PROVIDED BY OTHERS. THE SUBSURFACE INTERPRETATIONS PRESENTED IN THIS GEOLOGIC CROSS-SECTION SHOULD NOT BE CONSTRUED AS A WARRANTY OF ACTUAL SUBSURFACE CONDITIONS AT THE SITE. OUR EXPERIENCE HAS SHOWN THAT SOIL AND GROUNDWATER CONDITIONS CAN VARY SIGNIFICANTLY OVER SMALL DISTANCES. 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 0 earth sciences incorporated GEOLOGIC CROSS-SECTION B - B' ILLAHEE MS IMPROVEMENTS FEDERAL WAY, WASHINGTON PROJ NO. DATE: FIGURE: 20180138EO02 8/21 5 APPENDIX A Exploration Logs °0 0 Well -graded gravel and Terms Describing Relative Density and Consistency �° �° 0 0 0 0 OW g ravel with sand, little to i2) Density SPT blows/foot CD 9 o q no fines Very Loose 0 to 4 Coarse- Loose 4 to 10 ° ° ° ° ° ° ° ° 0 0 GP Poorly -graded gravel o ' ; °' MI �l Grained Soils Medium Dense 10 to 30 Test Symbols co o v o 0 o and gravel with sand, Dense 30 to 50 CD 0 00000°° ° ° ° little to no fines Very Dense >50 G =Grain Size o z° ° o ° o ° M = Moisture Content ° 0 ° 0 Silty gravel and silty z 0 o Consistency SPTt2)blows/foot A = Atterberg Limits C: a GM gravel with sand Very Soft 0 to 2 C = Chemical Fine- _0Soft y `vim o ° 0 ° 0 2 to 4 DD = Dry Density Grained Soils 0 C Medium Stiff 4 to 8 K = Permeability ° � o Stiff 8 to 15 N Clayey gravel and Very Stiff 15 to 30 GC clayey gravel with sand Hard >30 L Component Definitions o Well sand and r Descriptive Term Size Range and Sieve Number m Syy sand with gravel, little Boulders Larger than 12" o CUCUD, e to no fines Cobbles 3" to 12" eeeeevoe ti o �, a� � _ Gravel 3" to No. 4 (4.75 mm) - - Poorly -graded sand 0 co 0 > c) °' `c vl SP and sand with gravel, Coarse Gravel 3" to 3/4" Fine Gravel 3/4to No. 4 4 75 mm " ( ) c cn o It m o little to no fines Sand No. 4 (4.75 mm) to No. 200 (0.075 mm) 0 z Coarse Sand No. 4 (4.75 mm) to No. 10 (2.00 mm) ti o a) SM Silty sand and Medium Sand No. 10 (2.00 mm) to No. 40 (0.425 mm) N -.: silty sand with Fine Sand No. 40 (0.425 mm) to No. 200 (0.075 mm) U 0 o a gravel Silt and Clay Smaller than No. 200 (0.075 mm) LO (3Estimated Percentage Moisture Content NI SC Clayey sand and clayey sand with gravel Component Percentage by Weight Dry - Absence of moisture, Trace <5 dusty, dry to the touch Slightly Moist - Perceptible Silt, sandy silt, gravelly silt, moisture (D o MIL silt with sand or gravel Some 5 to <12 - Damp but no visible in C:Moist W cc Modifier 12 to <30 water Clay of low to medium C) m w (silty, sandy, gravelly) Very Moist - Water visible but o Uo CL plasticity; silty, sandy, or not free draining z Co -= E gravelly clay, lean clay Very modifier 30 to <50 Wet -Visible free water, usual b (silty, sandy, gravelly) from below water table Organic clay or silt of low Symbols _— OL plasticity Blows/6" or 0 = Sampler portion of 6" Cement grout o Type / surface seal Elastic silt, clayey silt, silt 2.0" OD I Sampler Type o o �, MH with micaceous or s Description c•� Split - Spoon Bentonite seal LO 0 2 1 diatomaceous fine sand or Sampler 3.0" OD Split -Spoon Sam ler p -- Finer pack with o y m o silt (SPT) 3.25" OD Split -Spoon Ring Sampler t4> : :: blank casing Clay of high plasticity, o c � CH sandy or gravelly clay, fat Bulk sample 3.0" OD Thin Wall Tube Sampler Z section Screened casing m u E clay with sand or gravel (including Shelby tube) _ or Hydrotip =with finer pack — ' Grab Sample End cap i °' ii i Organic clay or silt of O Portion not recoveredLL J OH medium to high (1) �4) Percentage by dry weight Depth of ground water plasticity (2) (SPT) Standard Penetration Test (ASTM D-1586) Z ATD = At time of drilling (s) Q Static water level (date) In General Accordance with > •° c Peat, muck and other rn = rn PT highly organic soils Standard Practice for Description (5) Combined USCS symbols used for O and Identification of Soils (ASTM D-2488) fines between 5% and 12% Classifications of soils in this report are based on visual field and/or laboratory observations, which include density/consistency, moisture condition, grain size, and plasticity estimates and should not be construed to imply field or laboratory testing unless presented herein. Visual -manual and/or laboratory classification 3 methods of ASTM D-2487 and D-2488 were used as an identification guide for the Unified Soil Classification System. a s s o c i a t e d earth sciences i n c o r p o r a t e d EXPLORATION LOG KEY FIGURE Al egsnciatad Exploration Borin earth sciences Project Number Exploration Number Sheet IRCOrpO ra t ed 20180138EO02 EB-1 1of1 Project Name Illahee Middle School Ground Surface Elevation (ft) --245 Location Federal Way, WA Datum NA\/I) RR Driller/Equipment Advanced Drill Technologies / Track Mounted Drill Date Start/Finish 7/9R/21 7/96/21 Hammer Weight/Drop 140# / 30 Hole Diameter (in) '3 95 (n .2L U O c O — a) � N J N Blows/Foot Y N T (D rn m ca L o u) DESCRIPTION o Q 10 20 30 40 ° Asphalt - 2 inches 6 S-1 5 10 Fill Moist, light brown, silty, fine SAND, some gravel; occasional organics; 5 unsorted (SM). 5 Upper 6 inches: moist, brown, silty, fine SAND, some gravel; asphalt 4 S-2 bserved; unsorted (SM). 6 Al2 Vashon Recessional Outwash 6 Lower 12 inches: moist, brown, fine SAND, trace silt, trace medium sand; massive (SP). 10 t 4 Wet, light brown with faint iron oxide staining, fine sandy, SILT to silty, fine S-3 SAND, trace gravel; occasional stratification otherwise massive (ML-SM). 5 10 5 Vashon Ice contact Driller reports gravel. 15 S-4 Moist, brown, silty, fine SAND, some gravel; blowcounts overstated due to 45 " A L50/E" gravel; poor recovery (SM). 0/ Broken gravel at 16 feet. 20 Very moist, grayish brown, silty, fine SAND, some medium to coarse sand, 4 S-5 some gravel; unsorted (SM). 6 �1 10 25 Moist, grayish brown, silty, fine SAND, some medium to coarse sand, 10 S-6 some gravel; unsorted (SM). 12 A43 31 Bottom of exploration boring at 26.5 feet Groundwater encountered at 10 feet. 30 35 Sampler Type (ST): m 2" OD Split Spoon Sampler (SPT) ❑ No Recovery M - Moisture Logged by: AT m 3" OD Split Spoon Sampler (D & M) Ring Sample Q Water Level() Approved by: JHS ® Grab Sample 0 Shelby Tube Sample 1 Water Level at time of drilling (ATD) egsnciatad Exploration Borin earth sciences Project Number Exploration Number Sheet IRCOrpO ra t ed 20180138EO02 EB-2 1of1 Project Name Illahee Middle School Ground Surface Elevation (ft) --230 Location Federal Way, WA Datum NA\/I) RR Driller/Equipment Advanced Drill Technologies / Track Mounted Drill Date Start/Finish 7/9R/21 7/96/21 Hammer Weight/Drop 140# / 30 Hole Diameter (in) '3 95 (n °' U O L c O — a) � N J N Blows/Foot Y N T� (D rn m m L o DESCRIPTION o Q 10 20 30 40 ° Grass / Topsoil - 4 to 6 inches Fill Upper 6 inches: Moist, brownish gray, silty, fine SAND, some gravel, some 12 S-1 edium to coarse sand; occasional rootlets; unsorted (SM). 14 A28 Vashon Ice Contact 14 5 Lower 12 inches: Moist, grayish brown, fine sandy, SILT; slightly stratified otherwise massive (ML). 17 S-2 Moist, brownish gray, silty, fine SAND, some gravel, some medium to 21 A42 coarse sand, trace silt; contains broken gravels; slightly stratified otherwise 21 massive (SM). riller reports gravel. Vashon Lodgement Till 10 Moist, grayish brown, silty, fine SAND, some gravel, some medium to 17 S-3 coarse sand, some broken gravel; unsorted becoming more cohesive 23 AL59 (SM). 36 15 S-4 Moist, grayish brown, silty, fine SAND, some gravel, trace medium to 21 coarse sand; diamict (SM). 31 5W " 0/ " 20 As above. 38 S-5 38 75 37 25 As above; becomes cohesive. 22 S-6 - 21 49 28 30 S-7 As above. 47 0/ " 50/ " Bottom of exploration boring at 31 feet No groundwater encountered. 35 Sampler Type (ST): m 2" OD Split Spoon Sampler (SPT) ❑ No Recovery M - Moisture Logged by: AT m 3" OD Split Spoon Sampler (D & M) Ring Sample Q Water Level() Approved by: JHS ® Grab Sample 0 Shelby Tube Sample 1 Water Level at time of drilling (ATD) associated Exploration Borin earth sciences Project Number Exploration Number Sheet iaoorporaled 20180138EO02 EB-3 1Of1 Project Name Illahee Middle School Ground Surface Elevation (ft) --230 Location Federal Way, WA Datum NA\/I) RR Driller/Equipment Advanced Drill Technologies / Track Mounted Drill Date Start/Finish 7/9R/21 7/96/21 Hammer Weight/Drop 140# / 30 Hole Diameter (in) '3 95 N .2 3 O — a) m > J N Blows/Foot 12 U) S @ 3:E -? o p T� (0 u) DESCRIPTION o@ U 3: m ° 10 20 30 40 S-1 = = Topsoil - 3 inches 7 A Fill 19 39 Moist, light brown, fine SAND, some silt, some gravel, some medium to 20 coarse sand; unsorted (SP-SM). = - riller reports gravel. Vashon Lodgement Till 5 - Moist, grayish brown, silty, fine SAND, some gravel, some medium to 20 S-2 _ - coarse sand; diamict (SM). 31 63 32 Driller reports hard drilling. 10 S-3 -- - - As above. 30 0/ " 50/ " Driller reports hard drilling. 15 S-4 - =- = - - As above; poor recovery. 35 0/ " 50/ " - - Driller reports hard drilling. 20 S5 - s above; poor recovery. 0/„ 50/ " Bottom of exploration boring at 20.3 feet No groundwater encountered. 25 30 35 Sampler Type (ST): m 2" OD Split Spoon Sampler (SPT) ❑ No Recovery M - Moisture Logged by: AT m 3" OD Split Spoon Sampler (D & M) Ring Sample Q Water Level() Approved by: JHS ® Grab Sample 0 Shelby Tube Sample 1 Water Level at time of drilling (ATD) egsnciatad Exploration Borin earth sciences Project Number Exploration Number Sheet IRCOrpO ra t ed 20180138EO02 EB-4 1of1 Project Name Illahee Middle School Ground Surface Elevation (ft) --270 Location Federal Way, WA Datum NA\/I) RR Driller/Equipment Advanced Drill Technologies / Track Mounted Drill Date Start/Finish 7/9R/21 7/96/21 Hammer Weight/Drop 140# / 30 Hole Diameter (in) '3 95 (n °' U O L c O — a) � N J N Blows/Foot Y N T (D rn m ca L o C) DESCRIPTION o Q 10 20 30 40 ° Vashon Lodgement Till Moist, grayish brown to brownish gray, silty, fine SAND, some gravel, some 34 S 1 medium to coarse sand; occasional rootlets; contains broken gravel; 25 68 unsorted; blowcounts overstated (SM). 43 Driller reports hard drilling. 0/ „ 5 S 2 Moist, brownish gray, silty, fine SAND, some gravel, some medium to 50/ " coarse sand; contains broken gravel; unsorted; poor recovery; blowcounts overstated (SM). 10 S-3 Moist, grayish brown, silty, fine SAND, some gravel, some medium to 35 0/ 50/ " coarse sand; contains broken gravel; diamict; poor recovery; blowcounts overstated (SM). Driller reports hard drilling. 15 Moist, grayish brown, silty, fine SAND, some gravel, some medium sand, 19 S-4 trace coarse sand; contains broken gravel; becomes less cohesive; diamict 23 A17 (SM). 24 20 Moist, grayish brown, silty, fine SAND, some gravel, trace medium to S-5 coarse sand; diamict (SM). 26 A L88 45 43 Bottom of exploration boring at 21.5 feet No groundwater encountered. 25 30 35 Sampler Type (ST): m 2" OD Split Spoon Sampler (SPT) ❑ No Recovery M - Moisture Logged by: AT m 3" OD Split Spoon Sampler (D & M) Ring Sample Q Water Level() Approved by: JHS ® Grab Sample 0 Shelby Tube Sample 1 Water Level at time of drilling (ATD) egsnciatad Exploration Borin earth sciences Project Number Exploration Number Sheet IRCOrpO ra t ed 20180138EO02 EB-5 1of1 Project Name Illahee Middle School Ground Surface Elevation (ft) --230 Location Federal Way, WA Datum NA\/I) RR Driller/Equipment Advanced Drill Technologies / Track Mounted Drill Date Start/Finish 7/97/21 7/97/21 Hammer Weight/Drop 140# / 30 Hole Diameter (in) '3 95 (n °' U O L c O — a) � N J N Blows/Foot Y N T� (D rn m m L o DESCRIPTION o Q 10 20 30 40 ° Sod - 4 to 6 inches fE S-1 Fill Loose, moist, grayish brown, fine SAND, trace silt, massive; drainage sand (SP). Moist, dark brown, silty, fine SAND, some gravel, some medium to coarse 7 S-2 sand; contains broken gravel and wood pieces; unsorted; poor recovery 5 Akio (SM). 5 5 Moist, brownish gray, silty, fine SAND, some gravel, some medium to 3 S-3 coarse sand, trace wood pieces; poor recovery (SM). 7 A 29 .—Driller reports hard drilling. 22 Vashon Ice Contact 10 Moist, grayish brown, silty, fine SAND, some medium to coarse sand; 25 S-4 some broken gravel; unsorted; blowcounts overstated (SM). 46 91 45 15 Moist, grayish brown, silty, fine to medium SAND, some coarse sand, 25 S-5 some gravel, some broken gravel; unsorted (SM). 29 56 27 20 S-6 As above; poor recovery. 0/ 50/ " 25 Upper 12 inches: wet, grayish brown silty, fine SAND; massive (SM). t 11 S"� 1 Lower 6 inches: moist, grayish brown, fine sandy, SILT, some gravel, some 42 43 A 85 medium to coarse sand; unsorted (ML). 30 Wet, grayish brown, silty, fine SAND, some gravel, some medium to S 8 coarse sand; occasional lenses of fine sand; unsorted (SM). 14 20 4 26 35 S 9 As above; poor recovery; blowcounts overstated. 29 o/Ir A 50/ " Bottom of exploration boring at 36 feet Groundwater encountered 25-35 feet ATD. Sampler Type (ST): m 2" OD Split Spoon Sampler (SPT) ❑ No Recovery M - Moisture Logged by: AT m 3" OD Split Spoon Sampler (D & M) Ring Sample Q Water Level() Approved by: JHS ® Grab Sample 0 Shelby Tube Sample 1 Water Level at time of drilling (ATD) egsnciatad Exploration Borin earth sciences Project Number Exploration Number Sheet IRCOrpO ra t ed 20180138EO02 EB-6 1of1 Project Name Illahee Middle School Ground Surface Elevation (ft) --235 Location Federal Way, WA Datum NA\/I) RR Driller/Equipment Advanced Drill Technologies / Track Mounted Drill Date Start/Finish 7/97/21 7/97/21 Hammer Weight/Drop 140# / 30 Hole Diameter (in) '3 95 (n °' U O L c O — a) � N J N Blows/Foot Y N T (D un m ca L o u) DESCRIPTION o Q 10 20 30 40 ° Grass / Topsoil - 6 inches Fill I: I Loose, moist to dry, light brown, silty, fine SAND, some gravel, some Tedium to coarse sand, some cobbles; occasional rootlets (SM). Vashon Recessional Outwash S 1 g A33 —Moist, brownish gray, fine SAND, some gravel, trace silt; massive (SP). 15 18 Vashon Ice Contact 5 Moist, grayish brown with iron oxide staining, silty, fine SAND, some gravel, 12 S-2 some medium to coarse sand; diamict (SM). 32 65 33 Driller reports hard drilling. 10 Moist, grayish brown, silty, fine SAND, some gravel, some broken gravel, 18 S-3 some medium to coarse sand; unsorted (SM). 29 49 20 15 As above. 40 S-4 35 71 36 20 As above; poor recovery; broken gravel (SM). 49 S-5 34 66 32 Vashon Lodgement Till 25 Moist, grayish brown, silty, fine SAND, some gravel, trace medium to 22 S-6 coarse sand; contains broken gravel; unsorted (SM). 31 A L50/E" 0/ " 30 As above; poor recovery; driller reports sluff. 0/ S-7 50/ " Bottom of exploration boring at 30.5 feet No groundwater encountered. 35 Sampler Type (ST): m 2" OD Split Spoon Sampler (SPT) ❑ No Recovery M - Moisture Logged by: AT m 3" OD Split Spoon Sampler (D & M) Ring Sample Q Water Level() Approved by: JHS ® Grab Sample 0 Shelby Tube Sample 1 Water Level at time of drilling (ATD) egsnciatad Exploration Borin earth sciences Project Number Exploration Number Sheet IRCOrpO ra t ed 20180138EO02 EB-7 1of1 Project Name Illahee Middle School Ground Surface Elevation (ft) --230 Location Federal Way, WA Datum NA\/I) RR Driller/Equipment Advanced Drill Technologies / Track Mounted Drill Date Start/Finish 7/98/21 7/98/21 Hammer Weight/Drop 140# / 30 Hole Diameter (in) '3 95 (n .2L U O c O — a) � N J N Blows/Foot Y N T� (D rn m m L o DESCRIPTION o Q 10 20 30 40 ° Grass / Topsoil - 6 inches Fill No drainage sand. Moist, brownish gray, silty, fine SAND, some gravel, some medium to 6 S-1 coarse sand; darker organics observed; faint organic odor; unsorted (SM). 8 A14 6 5 Moist, light brown with slight iron oxide staining, fine sandy, SILT; S 2 occasional organics; unsorted to massive (ML). 3 4 5 9 Vashon Ice Contact Driller reports hard drilling. 10 Moist, grayish brown, silty, fine to medium SAND to medium SAND, some 11 S-3 silt, some gravel, trace medium to coarse sand; layer (12 inches thick) of 17 A44 cleaner sand; unsorted (SP-SM). 27 15 S-4 Moist, grayish brown, silty, fine SAND, some gravel, some medium to 12 0/ .. A L50/z" coarse sand; contains broken gravel; unsorted; blowcounts overstated; poor recovery (SM). 20 Upper 12 inches: Moist, grayish brown, fine SAND, trace silt; massive (SP). 13 S-5 21 4928 Lower 6 inches: Moist, grayish brown, silty, fine SAND, some gravel, trace medium to coarse sand; unsorted (SM). 25 S-6 No recovery with 2 inch sampler and Cal -Mod sampler. 0/ " 50/ " 30 Moist, grayish brown, fine SAND, some silt, some medium sand, some 35 S 7 gravel; contains broken gravel; unsorted (SP-SM). Switched to Cal -Mod 0/ 50/ " sampler to obtain sample after using 2-in sampler to record blowcounts w/ o recovery. 0 om of exploration During at 3 1 te-et No groundwater encountered. 35 Sampler Type (ST): m 2" OD Split Spoon Sampler (SPT) ❑ No Recovery M - Moisture Logged by: AT m 3" OD Split Spoon Sampler (D & M) Ring Sample Q Water Level() Approved by: JHS ® Grab Sample 0 Shelby Tube Sample 1 Water Level at time of drilling (ATD) egsnciatad Exploration Borin earth sciences Project Number Exploration Number Sheet IRCOrpO ra t ed 20180138EO02 EB-8 1of1 Project Name Illahee Middle School Ground Surface Elevation (ft) --220 Location Federal Way, WA Datum NA\/I) RR Driller/Equipment Advanced Drill Technologies / Track Mounted Drill Date Start/Finish 7/98/21 7/98/21 Hammer Weight/Drop 140# / 30 Hole Diameter (in) '3 95 (n °' U O L c O — a) � N J N Blows/Foot Y N T� (D rn m m L o DESCRIPTION o Q 10 20 30 40 ° S-1 Fill Moist, reddish brown, silty, fine SAND, some medium to coarse sand; 10 15 30 unsorted; poor recovery; track surfacing (SM). 15 Driller reports hard drilling. 5 Moist, grayish brown to brownish gray, silty, fine SAND, some gravel, trace 50 S-2 medium to coarse sand; contains broken gravel; unsorted; poor recovery 36 Ak68 (SM). 32 10 S3 Moist, dark brown, silty, fine SAND; some gravel, trace medium to coarse 0/„ A L50K" sand; contains broken gravel; occasional wood pieces (sluff); unsorted; —poor recovery (SM). Vashon Lodgement Till Driller reports hard drilling. 15 S-4 .: Moist, grayish brown, silty, fine SAND, some gravel, some medium to 44 014.. 50/ " coarse sand; contains broken gravel; diamict (SM). Driller reports hard drilling. 20 S 5 Moist, grayish brown, silty, fine SAND, some gravel, some medium to 0/ " " ,coarse sand; diamict (SM). 50/ Bottom of exploration boring at 20.3 feet No groundwater encountered. 25 30 35 Sampler Type (ST): m 2" OD Split Spoon Sampler (SPT) ❑ No Recovery M - Moisture Logged by: AT m 3" OD Split Spoon Sampler (D & M) Ring Sample Q Water Level() Approved by: JHS ® Grab Sample 0 Shelby Tube Sample 1 Water Level at time of drilling (ATD)