EarthEarth SolutionsSolutions NW LLC

Geotechnical Engineering Construction Observation/Testing Environmental Services

UPDATED GEOTECHNICAL ENGINEERING STUDY PROPOSED TOGETHER CENTER MIXED-USE DEVELOPMENT 16225 NORTHEAST 87TH STREET REDMOND, WASHINGTON

ES-6857

15365 N.E. 90th Street, Suite 100 Redmond, WA 98052 (425) 449-4704 Fax (425) 449-4711 www.earthsolutionsnw.com PREPARED FOR

INLAND WASHINGTON, LLC

September 13, 2019 Updated September 3, 2020

______Scott S. Riegel, L.G., L.E.G. Senior Project Manager

09/03/2020 ______Raymond A. Coglas, P.E. Principal Engineer

UPDATED GEOTECHNICAL ENGINEERING STUDY PROPOSED TOGETHER CENTER MIXED-USE DEVELOPMENT 16225 NORTHEAST 87TH STREET REDMOND, WASHINGTON

ES-6857

Earth Solutions NW, LLC 15365 Northeast 90th Street, Suite 100 Redmond, Washington 98052 Phone: 425-449-4704 | Fax: 425-449-4711 www.earthsolutionsnw.com Important Information about This Geotechnical-Engineering Report

Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.

While you cannot eliminate all such risks, you can manage them. The following information is provided to help.

The Geoprofessional Business Association (GBA) will not likely meet the needs of a civil-works constructor or even a has prepared this advisory to help you – assumedly different civil engineer. Because each geotechnical-engineering study a client representative – interpret and apply this is unique, each geotechnical-engineering report is unique, prepared geotechnical-engineering report as effectively as solely for the client. possible. In that way, you can benefit from a lowered Likewise, geotechnical-engineering services are performed for a specific exposure to problems associated with subsurface project and purpose. For example, it is unlikely that a geotechnical- conditions at project sites and development of engineering study for a refrigerated warehouse will be the same as them that, for decades, have been a principal cause one prepared for a parking garage; and a few borings drilled during of construction delays, cost overruns, claims, a preliminary study to evaluate site feasibility will not be adequate to and disputes. If you have questions or want more develop geotechnical design recommendations for the project. information about any of the issues discussed herein, contact your GBA-member geotechnical engineer. Do not rely on this report if your geotechnical engineer prepared it: Active engagement in GBA exposes geotechnical • for a different client; engineers to a wide array of risk-confrontation • for a different project or purpose; techniques that can be of genuine benefit for • for a different site (that may or may not include all or a portion of the original site); or everyone involved with a construction project. • before important events occurred at the site or adjacent to it; e.g., man-made events like construction or environmental Understand the Geotechnical-Engineering Services remediation, or natural events like floods, droughts, earthquakes, Provided for this Report or groundwater fluctuations. Geotechnical-engineering services typically include the planning, collection, interpretation, and analysis of exploratory data from Note, too, the reliability of a geotechnical-engineering report can widely spaced borings and/or test pits. Field data are combined be affected by the passage of time, because of factors like changed with results from laboratory tests of soil and rock samples obtained subsurface conditions; new or modified codes, standards, or from field exploration (if applicable), observations made during site regulations; or new techniques or tools. If you are the least bit uncertain reconnaissance, and historical information to form one or more models about the continued reliability of this report, contact your geotechnical of the expected subsurface conditions beneath the site. Local geology engineer before applying the recommendations in it. A minor amount and alterations of the site surface and subsurface by previous and of additional testing or analysis after the passage of time – if any is proposed construction are also important considerations. Geotechnical required at all – could prevent major problems. engineers apply their engineering training, experience, and judgment to adapt the requirements of the prospective project to the subsurface Read this Report in Full model(s). Estimates are made of the subsurface conditions that Costly problems have occurred because those relying on a geotechnical- will likely be exposed during construction as well as the expected engineering report did not read the report in its entirety. Do not rely on performance of foundations and other structures being planned and/or an executive summary. Do not read selective elements only. Read and affected by construction activities. refer to the report in full.

The culmination of these geotechnical-engineering services is typically a You Need to Inform Your Geotechnical Engineer geotechnical-engineering report providing the data obtained, a discussion About Change of the subsurface model(s), the engineering and geologic engineering Your geotechnical engineer considered unique, project-specific factors assessments and analyses made, and the recommendations developed when developing the scope of study behind this report and developing to satisfy the given requirements of the project. These reports may be the confirmation-dependent recommendations the report conveys. titled investigations, explorations, studies, assessments, or evaluations. Typical changes that could erode the reliability of this report include Regardless of the title used, the geotechnical-engineering report is an those that affect: engineering interpretation of the subsurface conditions within the context • the site’s size or shape; of the project and does not represent a close examination, systematic • the elevation, configuration, location, orientation, inquiry, or thorough investigation of all site and subsurface conditions. function or weight of the proposed structure and the desired performance criteria; Geotechnical-Engineering Services are Performed • the composition of the design team; or for Specific Purposes, Persons, and Projects, • project ownership. and At Specific Times Geotechnical engineers structure their services to meet the specific As a general rule, always inform your geotechnical engineer of project needs, goals, and risk management preferences of their clients. A or site changes – even minor ones – and request an assessment of their geotechnical-engineering study conducted for a given civil engineer impact. The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical conspicuously that you’ve included the material for information purposes engineer was not informed about developments the engineer otherwise only. To avoid misunderstanding, you may also want to note that would have considered. “informational purposes” means constructors have no right to rely on the interpretations, opinions, conclusions, or recommendations in the Most of the “Findings” Related in This Report report. Be certain that constructors know they may learn about specific Are Professional Opinions project requirements, including options selected from the report, only Before construction begins, geotechnical engineers explore a site’s from the design drawings and specifications. Remind constructors subsurface using various sampling and testing procedures. Geotechnical that they may perform their own studies if they want to, and be sure to engineers can observe actual subsurface conditions only at those specific allow enough time to permit them to do so. Only then might you be in locations where sampling and testing is performed. The data derived from a position to give constructors the information available to you, while that sampling and testing were reviewed by your geotechnical engineer, requiring them to at least share some of the financial responsibilities who then applied professional judgement to form opinions about stemming from unanticipated conditions. Conducting prebid and subsurface conditions throughout the site. Actual sitewide-subsurface preconstruction conferences can also be valuable in this respect. conditions may differ – maybe significantly – from those indicated in this report. Confront that risk by retaining your geotechnical engineer Read Responsibility Provisions Closely to serve on the design team through project completion to obtain Some client representatives, design professionals, and constructors do informed guidance quickly, whenever needed. not realize that geotechnical engineering is far less exact than other engineering disciplines. This happens in part because soil and rock on This Report’s Recommendations Are project sites are typically heterogeneous and not manufactured materials Confirmation-Dependent with well-defined engineering properties like steel and concrete. That The recommendations included in this report – including any options or lack of understanding has nurtured unrealistic expectations that have alternatives – are confirmation-dependent. In other words, they arenot resulted in disappointments, delays, cost overruns, claims, and disputes. final, because the geotechnical engineer who developed them relied heavily To confront that risk, geotechnical engineers commonly include on judgement and opinion to do so. Your geotechnical engineer can finalize explanatory provisions in their reports. Sometimes labeled “limitations,” the recommendations only after observing actual subsurface conditions many of these provisions indicate where geotechnical engineers’ exposed during construction. If through observation your geotechnical responsibilities begin and end, to help others recognize their own engineer confirms that the conditions assumed to exist actually do exist, responsibilities and risks. Read these provisions closely. Ask questions. the recommendations can be relied upon, assuming no other changes have Your geotechnical engineer should respond fully and frankly. occurred. The geotechnical engineer who prepared this report cannot assume responsibility or liability for confirmation-dependent recommendations if you Geoenvironmental Concerns Are Not Covered fail to retain that engineer to perform construction observation. The personnel, equipment, and techniques used to perform an environmental study – e.g., a “phase-one” or “phase-two” environmental This Report Could Be Misinterpreted site assessment – differ significantly from those used to perform a Other design professionals’ misinterpretation of geotechnical- geotechnical-engineering study. For that reason, a geotechnical-engineering engineering reports has resulted in costly problems. Confront that risk report does not usually provide environmental findings, conclusions, or by having your geotechnical engineer serve as a continuing member of recommendations; e.g., about the likelihood of encountering underground the design team, to: storage tanks or regulated contaminants. Unanticipated subsurface • confer with other design-team members; environmental problems have led to project failures. If you have not • help develop specifications; obtained your own environmental information about the project site, • review pertinent elements of other design professionals’ plans and ask your geotechnical consultant for a recommendation on how to find specifications; and environmental risk-management guidance. • be available whenever geotechnical-engineering guidance is needed. Obtain Professional Assistance to Deal with You should also confront the risk of constructors misinterpreting this Moisture Infiltration and Mold report. Do so by retaining your geotechnical engineer to participate in While your geotechnical engineer may have addressed groundwater, prebid and preconstruction conferences and to perform construction- water infiltration, or similar issues in this report, the engineer’s phase observations. services were not designed, conducted, or intended to prevent migration of moisture – including water vapor – from the soil Give Constructors a Complete Report and Guidance through building slabs and walls and into the building interior, where Some owners and design professionals mistakenly believe they can shift it can cause mold growth and material-performance deficiencies. unanticipated-subsurface-conditions liability to constructors by limiting Accordingly, proper implementation of the geotechnical engineer’s the information they provide for bid preparation. To help prevent recommendations will not of itself be sufficient to prevent the costly, contentious problems this practice has caused, include the moisture infiltration. Confront the risk of moisture infiltration by complete geotechnical-engineering report, along with any attachments including building-envelope or mold specialists on the design team. or appendices, with your contract documents, but be certain to note Geotechnical engineers are not building-envelope or mold specialists.

Telephone: 301/565-2733 e-mail: [email protected] www.geoprofessional.org

Copyright 2019 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any kind. Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent or intentional (fraudulent) misrepresentation. September 13, 2019 Earth Solutions NW LLC Updated September 3, 2020 Geotechnical Engineering, Construction ES-6857 Observation/Testing and Environmental Services

Inland Washington, LLC 120 West Cataldo Avenue, Suite 100 Spokane, Washington 99201

Attention: Mr. John Fisher

Dear Mr. Fisher:

Earth Solutions NW, LLC (ESNW) is pleased to present this updated geotechnical engineering study for the proposed mixed-use project to be constructed in Redmond, Washington”. This updated report provides additional information requested in Round 3 of the Redmond PREP review matrix Natural Resources section. Specifically, preliminary values provided in the temporary dewatering calculations have been coordinated with the values stated in this updated report. Based on the results of the geotechnical investigation, the proposed residential development is feasible from a geotechnical standpoint.

Soils are comprised largely of sand and gravel alluvial deposits with variable in situ strength conditions. At the time of our August 2019 exploration, the groundwater table was at a depth of about 13.5 feet below existing grades and based on results of our groundwater monitoring program, the seasonal high groundwater is about 7 feet below existing grade. The proposed structure will include one level of below-grade parking that will require excavations of roughly 10 to 12 feet, with deeper isolated excavations required for the elevator pit and brace frame elements. Given the variable nature of the alluvial soil conditions anticipated to be exposed at the foundation subgrade, we recommend a structural mat slab foundation system be used for this project. To support below-grade parking level excavations, temporary shoring utilizing cantilever and single tieback soldier pile walls should be anticipated. Based on the planned excavation depths, temporary dewatering of the subject site will likely be necessary during construction. Because dewatering can vary greatly depending on planned excavations and time of year excavation occurs, we recommend a targeted dewatering plan be prepared by a hydrogeologist as project plans develop. Permanent protection of the completed structure from groundwater intrusion will require installation of an impermeable membrane below the structure.

15365 N.E. 90th Street, Suite 100 • Redmond, WA 98052 • (425) 449-4704 • FAX (425) 449-4711 Inland Washington, LLC ES-6857 September 13, 2019 Executive Summary –Page 2 Updated September 3, 2020

Recommendations for foundation design, excavation support, earthwork, and other pertinent geotechnical recommendations are provided in this report. If you have any questions regarding the content of this geotechnical engineering study, please contact us.

Sincerely,

EARTH SOLUTIONS NW, LLC

Scott S. Riegel, L.G., L.E.G. Senior Project Manager

Earth Solutions NW, LLC

Table of Contents

ES-6857

PAGE

INTRODUCTION …………………………………………………………… 1 General ………………………………………………………….. …. 1 Project Description .……………………………………………….. 2 Surface………... …………………………………………………….. 2 Subsurface…….…………………………………………………….. 3 Fill……………………………………………………………... 3 Native Soil and Geologic Setting………………………… 3 Groundwater...……………………………………………………….. 4 Critical Areas………………………………………………………… 4 Seismic Hazard Evaluation……………………………….. 4 Wellhead Protection Zones………………………………. 5 Hydrogeologic Assessment………………………………. 5

DISCUSSION AND RECOMMENDATIONS…...……………………….... 9 General…..…………………………………………………………… 9 Site Preparation and Earthwork………..………………………... 10 Temporary Erosion Control………………………………. 10 In-situ and Imported Soils……………………………..….. 10 Temporary Excavations and Slopes……………………. 11 Structural Fill ……………………………………………….. 11 Shoring Recommendations.…..………………………….…….... 12 Cantilever and Single Tieback Soldier Piles…………... 12 Soldier Piles………..………………………………………... 13 Timber Lagging….………………………………………….. 13 Tieback Anchors……………………………………………. 13 Shoring Wall Drainage…………………………………….. 14 Shoring Monitoring ……………….……………………….. 14 Preliminary Construction Dewatering Recommendations…. 14 Existing Conveyance System……………………………. 15 Typical Dewatering System………………………………. 16 Dewatering Monitoring……………………………………. 16 Structural Mat Foundations………………………………………. 16 Slab-on-Grade Floors...……………………………………………. 17 Seismic Design…………...... ……………………….. 17 Retaining Walls (Independent of Foundation Walls).………... 17 Drainage……………………….…………………………………..… 18 Infiltration Feasibility……………………………………… 19 Utility Support and Trench Backfill………..……………………. 19 Preliminary Pavement Sections…………...……………………. 19

Earth Solutions NW, LLC

Table of Contents

Cont’d

ES-6857

PAGE

LIMITATIONS…………………………………...…………………………… 20 Additional Services………………………………………………… 20

GRAPHICS

Plate 1 Vicinity Map

Plate 2 Boring Location Plan

Plate 3 Cantilever & Single Tieback Wall

Plate 4 Retaining Wall Drainage Detail

Plate 5 Footing Drain Detail

APPENDICES

Appendix A Subsurface Exploration Boring Logs

Appendix B Laboratory Test Results

Appendix C LiquefyPro Output

Earth Solutions NW, LLC

UPDATED GEOTECHNICAL ENGINEERING STUDY PROPOSED TOGETHER CENTER MIXED-USE DEVELOPMENT 16225 NORTHEAST 87TH STREET REDMOND, WASHINGTON

ES-6857

INTRODUCTION

General

This updated geotechnical engineering study was prepared for the proposed mixed-use development to be constructed southwest of the intersection between Northeast 87th Street and 164th Avenue Northeast in Redmond, Washington. This updated report reflects the current project scope that has been further refined since the initial version of this report was prepared and addresses Round 2 of the City of Redmond PREP Natural Resources review matrix items. Specifically, preliminary values provided in the temporary dewatering calculations have been coordinated with the values stated in this updated report. The approximate location of the subject property is illustrated on the Vicinity Map (Plate 1). The purpose of this study was to develop geotechnical recommendations for the proposed project. The scope of services for completing this geotechnical engineering study included the following:

 Completing borings and installing groundwater monitoring wells to characterize soil and groundwater conditions;

 Laboratory testing of soil samples collected at the boring locations;

 Conducting engineering analyses, and;

 Preparing this report.

The following documents were reviewed as part of preparing this geotechnical engineering study:

 Architectural Plans, prepared by Olson Projects, dated September 24, 2019;  Preliminary Temporary Construction Dewatering Feasibility Study – Conveyance Analysis, Prepared by KPFF, dated August 28, 2020;

 Appendix 1 – Critical Areas Reporting Requirements of the Redmond Zoning Code (RZC);

 Groundwater Sampling Summary, prepared by the City of Redmond, dated Winter 2019;

 Critical Area’s Maps, prepared by the City of Redmond, dated April 16, 2011;

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 2 Updated September 3, 2020

 City of Redmond Water Table Map, endorsed by the King County Groundwater Protection Program, dated October 2005;

 Online Web Soil Survey (WSS) resource, maintained by the Natural Resources Conservation Service under the United States Department of Agriculture;

 King County Liquefaction Susceptibility Map, endorsed by the King County Flood Control District, May 2010, and;

 Geologic Map of the Redmond Quadrangle, Washington, by James P. Minard and Derek B. Booth, 1988.

Project Description

Development plans will include construction of a mixed-use apartment building and associated infrastructure improvements. The building may include four to five residential stories above a podium and at-grade commercial space. Cuts up to about 10 to 12 feet below the existing ground surface (bgs) will be required to achieve subgrade elevations for a below-grade parking level with possible deeper isolated cuts for the elevator pit(s) and brace frame elements. Shoring will be required to support the temporary excavation for the below-grade level. Recommendations for shoring systems are provided in the Shoring Recommendations section of this report. Dewatering will be required to lower the local groundwater table prior to excavation and will need to continue during below-grade construction activities. The subject site is underlain by a regional critical aquifer recharge area (CARA) which provides drinking water for the City of Redmond (City). As such, a hydrogeological assessment has been included in this report based on conditions encountered during our fieldwork and our understanding of the proposed project.

We anticipate post-tensioned slab construction will be used for the street grade, podium, and underground garage level with conventional wood or steel stud framing above. Based on our experience with similar projects, we estimate wall loads to be on the order of 5 to 7 kips per lineal foot, column loads in the range of 300 to 600 kips, and slab-on-grade loading of 150 pounds per square foot (psf).

If the above design assumptions are incorrect or change, ESNW should be contacted to review the recommendations in this report, and provide supplement recommendations.

Surface

The subject property is located southwest of the intersection between Northeast 87th Street and 164th Avenue Northeast in Redmond, Washington. The approximate location of the site is illustrated on the Vicinity Map (Plate 1). The property is rectangular in shape with an overall area of approximately 2.47 acres. The site is bordered to the north by Northeast 87th Street, to the south by existing mixed-use developments, to the west by a retail business, and to the east by 164th Avenue Northeast. The approximate limits of the property are illustrated on the Boring Location Plan (Plate 2). The property is currently occupied by three, one-story commercial structures with asphalt paved parking areas, and associated improvements. Topography is relatively level across the site with an average elevation of about 40 feet.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 3 Updated September 3, 2020

Subsurface

A representative of ESNW observed logged and sampled four borings at the site on August 13, 2019 for purposes of assessing soil and groundwater conditions. The approximate locations of the borings are illustrated on the Boring Location Plan (Plate 2). Please refer to the boring logs provided in Appendix A for a more detailed description of the subsurface conditions. Representative soil samples collected at the boring locations were analyzed in general accordance with Unified Soil Classification System (USCS) and United States Department of Agriculture (USDA) methods and procedures.

Fill

The boring locations were surfaced with about one to two inches of existing asphalt paving. Underlying the asphalt, fill was encountered at the boring locations to limited depths of about six inches bgs. The fill was classified in the field as crushed rock, typical of base coarse material underlying asphalt and pavement areas.

Native Soil and Geologic Setting

Underlying fills, native soils were encountered consisting primarily of loose to dense sands and gravels with variable silt content (USCS: SM, SP, SP-SM, GP, GW, and GW-GM) extending to the maximum exploration depth of 41.5 feet bgs. An isolated layer of silt (USCS: ML) was encountered at boring location B-2 at about 30.5 feet bgs. Standard penetration test (SPT) blow counts indicate variable in situ relative density of native soils and include some loose layers within the soil profile. The soils encountered at the boring locations are typical of the Redmond valley area, consisting primarily of alluvial sands and gravels.

The referenced geologic map resource identifies younger alluvium (Qyal) across the site and immediate areas. According to the geologic map resource, younger alluvium deposits accumulate in the low energy parts of the stream valleys. Site specific alluvial soils consist largely of finer-grained sand overlying coarser-grained channel sediments such as gravels and coarse sand.

The referenced WSS resource identifies Everett very gravelly sandy loam (Map Unit Symbol: EvB) across the site and surrounding areas. The Everett series was formed in sandy glacial outwash deposits and are primarily found in esker and terrace landforms. Based on our field observations, native soils likely to be exposed during grading activities will be consistent with the geologic setting of younger alluvium as outlined in this section.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 4 Updated September 3, 2020

Groundwater

Piezometers were installed at two boring locations (B-1 and B-4) to allow for groundwater level monitoring. Upon equilibration, the groundwater level was measured on August 22, 2019 at a depth of roughly 13.5 feet bgs. Groundwater levels recently measured following a period of heavy precipitation (February 2020), indicated levels at approximately seven feet bgs which represents the seasonal high level for this site during the 2019/2020 monitoring period. As of April 7, 2020, groundwater levels have receded to about 10 feet bgs. Data provided by the City of Redmond (COR) indicate seasonal high and low groundwater levels near this site seasonally range from depths of about 4.6 to 20.8 feet bgs. This information is based on monitoring well data records maintained by the City staff. Using the closest monitoring well data provided by the COR indicates historical groundwater levels are about 10 feet below existing grade. Therefore, we used the data collected at the monitoring wells installed on the site, which yielded a seasonal high groundwater level of seven feet below existing grade.

Groundwater seepage rates and elevations fluctuate depending on many factors, including precipitation duration and intensity, the time of year, and soil conditions. Based on the geographic setting and our experience with similar projects in this area, the hydraulic conductivity and associated flow volumes within the groundwater zone can be characterized as high. This condition must be addressed during the site designs to accommodate temporary dewatering where excavations will be advanced below the groundwater table.

Critical Areas

The site is not located within wetland, stream, fish, wildlife habitat or frequently flooded hazard areas. The site does contain conditions which meet the code definition for seismic hazard and is located within a critical aquifer recharge overlay, both of which are addressed below.

Seismic Hazard Evaluation

We evaluated the potential seismic hazard for this site in general accordance with RZC Appendix I. Our evaluation was based on existing development conditions and models the native soil conditions. We completed four borings on this site that extended to a maximum depth of 41.5 feet below existing grade as part of our geotechnical engineering study. The site is underlain primarily by medium dense to dense alluvial sand and gravel deposits. There were isolated layers of loose soil at depth and groundwater levels range from about 13 feet (seasonal low) to 7 feet (seasonal high) below existing grade. We used the LiquefyPro (V5) software program to assess the liquefaction potential resulting from a maximum credible earthquake event. This design event consisted of a moment magnitude 7.0 earthquake that generates a peak horizontal acceleration of 0.48g based on USGS seismic mapping resources. We used the subsurface information in borings B-2 and B-3 for our analysis and used the seasonal high groundwater condition, all of which, represent highest sensitivity conditions. Based on this analysis, maximum predicted post- liquefaction settlement at these modeled locations was less than 2 inches. Output is provided in Appendix C. The soil conditions at the other boring locations were less susceptible to liquefaction, i.e. more fines contents and higher raw blow counts. Therefore, our analysis represents a worst-case scenario.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 5 Updated September 3, 2020

In our opinion, site susceptibility to liquefaction is properly classified as low to moderate. The building will be supported on a structural mat foundation which will help mitigate the effects of potential liquefaction induced settlements. On this basis, no further mitigation is required to meet current minimum design standards for liquefaction hazards. Additional discussion is provided in the Seismic Design section of this report.

Wellhead Protection Zones

The site has been designated within a Level One CARA by the City of Redmond. Given a defined radial distance from a municipal supply well, site associated groundwater within the level one CARA radial distance will have a travel time of five years or less to reach the municipal supply well. These CARA’s are the most vulnerable to contamination from pollutants. Where feasible, recharge through infiltration is encouraged within these overlays to maintain groundwater quality and quantity conditions. On this basis, we have prepared a hydrogeologic assessment in accordance with Appendix 1 of the referenced RZC. The minimum required report elements and/or information are listed in italics, followed by our responses based on available information.

Hydrogeologic Assessment a. Available information regarding geologic and hydrogeologic characteristics of the site, including the surface location of all critical aquifer recharge areas located on site or immediately adjacent to the site, and permeability of the unsaturated zone.

The regional unconfined aquifer lies directly below the subject site and transitions to an upland area toward the east. The aquifer is presumed to be primarily recharged by direct infiltration of precipitation and groundwater flow.

The alluvial aquifer is unconfined and native soils primarily consist of sand and gravel deposits. The depth to the groundwater table during our August 2019 site investigation was on the order of 13.5 feet bgs. The upper unsaturated soils include a fines content of about 10 percent, or less, and presents a high infiltration capacity. In this respect, the permeability of the unsaturated zone at the subject site is high. b. Groundwater depth, flow direction, and gradient based on available information.

The local groundwater table was encountered at a depth of roughly 13.5 feet during our August 2019 fieldwork. On February 11, 2020, following a period of heavy precipitation, groundwater levels were measured about 7 feet below the existing ground surface at the boring locations.

The referenced water table map indicates that the flow direction of the aquifer underlying the subject site is generally toward the southwest, and based on review of existing well information, the hydraulic gradient of the aquifer in the immediate vicinity is approximately 0.001 feet per feet.

Currently available data on wells and springs within 1,300 feet of the project area.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 6 Updated September 3, 2020

As part of this study, public records on wells within approximately 1,300 feet of the project were requested. The following monitoring wells (MW) are located in proximity to the site:

MW Location Yearly High Yearly Low (feet bgs) (feet bgs) MW-003 Approximately 500 feet west 9.8 (2/1/2011) 20.0 (6/6/2018)

MW-004 Approximately 500 feet southwest 8.9 (12/21/2015) 18.7 (9/12/2018)

MW-005 Approximately 700 feet southwest 10.1 (12/6/2009) 19.0 (8/6/2009)

MW-006 Approximately 200 feet south 10.2 (2/1/2011) 19.6 (7/31/2019)

MW-007 Approximately 200 feet south 10.0 (2/1/2011) 19.5 (7/31/2018)

MW-031 Approximately 1,300 feet northwest 4.6 (12/11/015) 12.8 (10/2/2017)

MW-032 Approximately 1,300 feet northwest 6.9 (12/15/2010) 16.9 (6/12/2018)

MW-033 Approximately 1,000 feet northwest 9.9 (12/12/2015) 20.0 (6/7/2018)

MW-036 Approximately 800 feet northwest 10.3 (1/23/2013) 18.5 (8/12/2015)

MW-331 Approximately 800 feet south 5.9 (2/2/2012) 20.8 (8/21/2018)

MW-391 Approximately 1,000 feet southwest 7.2 (12/1/2016) 14.1 (7/31/2018)

Based on review of the collected well data, seasonal groundwater table fluctuations between 4.6 feet bgs (seasonal high) and 20.8 feet bgs (seasonal low) are possible throughout areas surrounding the site; however, the data from the closest monitoring well indicates a historical high groundwater level of about 10 feet below existing ground surface. c. Location of other critical areas, including surface waters, within 1,300 feet of the project site.

To the best of our knowledge, there are no other critical areas or surface waters within 1,300 feet of the site. d. Available historic water quality data for the area to be affected by the proposed activity.

The subject site is located nearest to Supply Well 4, which is located approximately 1,500 feet northwest of the subject site. While aquifer gradients drain away from the well, it should be noted that the supply well has detected concentrations above maximum contaminant levels (MCLs) for iron and manganese. While the supply well has exceeded MCL for the two contaminants, the recorded levels have been relatively stable. Concentrations of PCE, PFOS, and PFOA have been encountered within the proximity of supply well 4, but are below MCLs.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 7 Updated September 3, 2020

e. Best management practices proposed to be utilized.

With respect to grading/construction activities, existing asphalt on the surface or exposed during grading shall not be used as fill or utility trench backfill. Fill either generated from site excavations or imported for placement must comply with RZC 15.24.080 and .095. Section 15.24.095-2 provides minimum criteria for evaluating suitability of new fill placed on sites. These criteria can effectively be evaluated during construction using field site and/or source screening techniques.

Best management practices (BMPs) for this project will be determined during the ongoing project design phase and submitted to the City for review and approval. At a minimum, site BMPs shall comply with current RZC requirements. BMPs are typically specified by the project civil engineer and indicated on the plans. f. Historic water quality and elevation data for the area to be affected by the proposed activity compiled for at least the previous five-year period.

As stated above, the depth of the groundwater table in the site area ranges from approximately 4.6 to 20.8 feet bgs. Water quality in the area includes iron and manganese above MCL, with minor concentrations of PCE, PFOS, and PFOA. g. Groundwater monitoring plan provisions.

The owner or representatives will perform groundwater monitoring of nearby monitoring wells over the course of the project. We will work with the City during the design phase to determine an appropriate monitoring program. Baseline measurements will be recorded prior to dewatering and will conclude upon project completion. h. Discussion of the effects of the proposed project on the groundwater quality and quantity, including: Predictive evaluation of groundwater withdrawal effects on nearby wells and surface water features, predictive evaluation of contaminant transport based on potential releases to groundwater, and predictive evaluation of groundwater (recharge, elevation, dewatering feasibility, constructability, discharge permitting, etc.) on the proposed project.

The project is expected to incorporate one level of below grade construction. In this respect, the basement level portions of the building structure will penetrate the underlying aquifer during the wetter winter and spring seasons, and temporary dewatering to locally lower the groundwater table around the site perimeter during construction will be required. Based on preliminary evaluation and review of existing well locations, we anticipate the temporary dewatering activities would not adversely impact water quality or the performance of City well installations. With respect to contaminant release during construction, effective measures will need to be in place during (and after) construction to mitigate potential contaminant release. In any case, the portion of the basement structure penetrating the aquifer will be required to be waterproofed and watertight upon completion. On this basis, and assuming a final “watertight” condition, no adverse impacts to public production wells or monitoring wells are anticipated as a result of the proposed project.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 8 Updated September 3, 2020

With respect to dewatering volumes, a formal dewatering plan and analysis prepared by a hydrogeologist will be necessary during final design. Aquifer characteristics combined with anticipated depth of dewatering will be necessary input parameters for estimating the discharge volumes. The estimated radius of influence (cone of depression) resulting from the steady state temporary dewatering condition will also need to be evaluated. During the dewatering process, periodic monitoring of water quality will be required to ensure discharge is within allowable limits for suspended solids. If infiltration will be utilized (not currently proposed), the facilities will need to comply with current applicable stormwater code provisions for water quality. Additionally, consistent with code requirements, where subsurface drains are utilized, the drains will need to be tightlined to an approved discharge point. In any case, permanent subsurface (perforated) drains must not extend below the seasonal high groundwater table. i. Identification of the type and quantities of any deleterious substances or hazardous materials that will be stored, handled, treated, used, produced, recycled, or disposed of on the site, including but not limited to materials, such as elevator lift/hydraulic fluid, hazardous materials used during construction, materials used by the building occupants, proposed storage and manufacturing uses, etc.

Shoring will be required for the below-grade excavations. As such, inert/non-toxic fluids should be used for installing the drilled shafts. Construction entrance and truck wash, including a spill prevention kit and wash area plan will be in place prior to proceeding with construction. The type and quantity of deleterious materials and substances should be defined during the design phase of construction, and a safe means for storing the materials should be determined with approval from the City. j. Proposed methods of storing any of the above substances, including containment methods to be used during construction and/or use of the proposed facility.

The type and quantity of deleterious materials and substances should be defined during the design phase of construction, and a safe means for storing the materials should be determined with approval from the City. In general, dedicated storage areas should be utilized for contaminants during and post construction. A spill prevention plan should be prepared as part of site design. A surface water pollution prevention plan (SWPPP) will be prepared and approved prior to grading. k. Proposed plan for implementing RZC 21.64.050.D.3.f, Protection Standards During Construction.

The proposal will follow CARA performance standards as outlined in RZC 21.64.050. Fill material will comply with the standards outlined in RMC 15.24.095 and analytical results of proposed fills will be provided to ensure that fill materials are in compliance with the Model Toxics Control Act, and do not exceed cleanup standards.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 9 Updated September 3, 2020

l. A spill plan that identifies equipment and/or structures that could fail, resulting in an impact. Spill plans shall include provisions for regular inspection, repair, and replacement of structures and equipment that could fail.

Plans to provide mitigation on-site and not affect off-site areas during construction will be addressed by implementing an approved spill prevention plan. Dedicated storage areas and handling protocols for potentially hazardous materials and establishing dedicated fueling/maintenance areas on-site will be covered within the spill prevention plan. m. A complete discussion of past environmental investigations, sampling, spills, or incidents that may have resulted in or contributed to contaminated soil or groundwater at the site.

ESNW has prepared a Phase 1 environmental report for this site. Please see the transmitted Phase 1 environmental report for further discussion on site environmental history. In summary, no recognized environmental conditions were identified at the subject site.

DISCUSSION AND RECOMMENDATIONS

General

Based on the results of our study, construction of a mixed-use development is feasible from a geotechnical standpoint. Current plans include one level of below-grade parking which would intercept the static groundwater table during the wetter winter and spring seasons. This condition must be addressed and mitigated during design for both construction and permanent configurations. The groundwater condition will affect shoring, drainage and foundation support designs. As such, and due to the variable in-situ strength conditions at the anticipated subgrade level on this site (alluvial sands and gravels), we recommend the proposed structure be supported on a structural mat slab foundation.

Native soils are comprised largely of sand and gravel alluvial deposits with variable in situ strength conditions. At the time of our August 2019 exploration, the local groundwater table was observed at a depth of about 13.5 feet bgs. Based on review of City groundwater records, the seasonal high and low groundwater for this general area (within one mile) ranges from depths of about 4.6 to 20.8 feet below grades. Recent monitoring of groundwater levels indicates groundwater at roughly seven feet bgs (February 2020). The proposed structure will include one level of below-grade parking that would require excavations on the order 10 to 12 feet below existing grades. Elevator pit(s) and brace frame elements will require deeper cuts in isolated areas. To support cuts required to construct the below-grade parking levels, temporary shoring utilizing cantilever and single tieback soldier pile walls is recommended. Based on the depth to groundwater, temporary dewatering of the subject site will be necessary to accommodate the below grade construction activities. ESNW can provide further information regarding dewatering as project plans and preparation of a formal dewatering plan develop.

This study has been prepared for the exclusive use of Inland Washington, LLC and their representatives. No warranty, expressed or implied, is made. This study has been prepared in a manner consistent with the level of care and skill ordinarily exercised by other members of the profession currently practicing under similar conditions in this area. Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 10 Updated September 3, 2020

Site Preparation and Earthwork

Site preparation activities will likely include removing the existing buildings, asphalt and associated improvements from the development envelope, establishing clearing limits and installing temporary erosion control measures.

The primary geotechnical considerations during the proposed site preparation and earthwork activities will involve completing shoring to achieve subgrade elevation for the below-grade parking garage, temporary dewatering of the excavation, preparation of the mat foundation subgrade, underground utility installations, installation of the permanent waterproofing membrane, and final building and pavement area subgrade preparation.

Temporary Erosion Control

The following temporary erosion control measures should be considered:

 Temporary construction entrances and drive lanes, consisting of at least six inches of quarry spalls, should be considered to both minimize off-site soil tracking and provide a stable access entrance surface. Placing a woven geotextile fabric underneath the quarry spalls will provide greater stability, if needed.

 Silt fencing should be placed around the working perimeter.

 When not in use, soil stockpiles should be covered or otherwise protected to reduce the potential for soil erosion, especially during periods of wet weather.

 Temporary measures for controlling surface water runoff such as interceptor trenches, sumps, or swales, should be installed prior to beginning earthwork activities.

 Dry soils disturbed during construction should be wetted to minimize dust and airborne soil transport.

Additional BMPs, as specified by the project civil engineer and as indicated on the plans, should be incorporated into construction activities. Temporary erosion control measures may be modified during construction as site conditions require, as approved by the site erosion control lead.

In-situ and Imported Soils

Successful use of native soils as structural fill will largely be dictated by the moisture content at the time of placement and compaction. Remedial measures, such as soil aeration, may be necessary as part of site grading and earthwork activities. Stockpiled soils intended for use as structural fill should be covered or otherwise protected from excessive rainfall. Any fill placed under building footings should consist of clean crushed rock.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 11 Updated September 3, 2020

Imported soil intended for use as structural fill should consist of a well-graded, granular soil with a moisture content that is at, or slightly above, the optimum level. During wet weather conditions, imported soil intended for use as structural fill should consist of a well-graded, granular soil with a fines content of 5 percent or less (where the fines content is defined as the percent passing the Number 200 sieve, based on the minus three-quarter-inch fraction). If grading takes place during the winter, spring, or early summer months, a contingency in the project budget should be included to allow for either treatment of the on-site soils or export of on-site soils and subsequent import of structural fill, as described below.

Temporary Excavations and Slopes

Temporary excavation activities are likely to expose alluvial soils including variable in-situ strength conditions. Based on the soil conditions observed at the exploration locations, the following allowable temporary slope inclinations, as a function of horizontal to vertical (H:V) inclination, may be used. The applicable Federal Occupation Safety and Health Administration and Washington Industrial Safety and Health Act soil classifications are also provided:

 Areas exposing groundwater seepage 1.5H:1V (Type C)

 Fill soil 1.5H:1V (Type C)

 Alluvium soil 1.5H:1V (Type C)

Permanent slopes should be planted with vegetation to enhance stability and to minimize erosion, and should maintain a gradient of 2H:1V or flatter. The presence of perched groundwater may cause localized sloughing of temporary slopes due to excess seepage forces. An ESNW representative should observe temporary and permanent slopes to confirm the slope inclinations are suitable for the exposed soil conditions and to provide additional excavation and slope recommendations, as necessary.

Structural Fill

Structural fill placed and compacted during site grading activities should meet the following specifications and guidelines:

 Structural fill material Suitable granular material

 Moisture content At or slightly above optimum

 Relative compaction (minimum) 95 percent (Modified Proctor)

 Loose lift thickness (maximum) 12 inches

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 12 Updated September 3, 2020

With respect to underground utility installations and backfill, local jurisdictions may dictate soil type and compaction requirements. Areas of unsuitable material and debris should be removed from structural areas and replaced with structural fill. Topsoil and organic-rich soil is neither suitable for foundation support nor for use as structural fill, but may be used in non-structural areas, if desired.

Shoring Recommendations

We anticipate cuts up to about 10 to 12 feet below existing grades will be required to achieve subgrade for one level of underground parking. Temporary shoring will be necessary where the building will be sited in close proximity to the property limits. The static groundwater table was measured on February 11, 2020 at a depth of about seven feet bgs at the piezometer locations. Historical data provided by the City staff for nearby monitoring well locations indicate the seasonal groundwater levels in the area have a high of about 4.6 feet and a low of about 20.8 feet bgs.

In our opinion, where shoring is required, the use of a conventional cantilever or single tieback shoring system is feasible for temporary support of excavations. We have provided preliminary recommendations for cantilever and tieback shoring. It is important to note that if tiebacks are utilized, appropriate easements will be required from adjacent property owners to accommodate the tendons.

Cantilever and Single Tieback Soldier Piles

Temporary cantilever and single tieback shoring should be designed to resist lateral soil pressure based on an active earth pressure condition. Surcharge loading from adjacent roadways, buildings, and temporary slopes should be included in the shoring design, as necessary. For design, assuming excavation dewatering, the following earth pressure and surcharge values should be used:

 Active earth pressure (level backfill) 35 pcf (equivalent fluid)

 Active earth pressure (sloped backfill, 1.5H:1V max) 52 pcf *

 At-rest earth pressure (restrained) 55 pcf (no slope surcharge)

 Traffic surcharge (where appropriate) 70 psf (rectangular distribution)

 Construction staging surcharge 150 psf (rectangular distribution)

 Preliminary building surcharge (where applicable) 150 psf (rectangular distribution)**

 Passive earth pressure (Apply over 2 pile diameters) 150 pcf (water bearing)

* Preliminary values, based on ten-foot-high broken slope above shoring. Values should be reevaluated based on final slope geometry. ** Building surcharge values should be reevaluated based on further assessment of adjacent building foundation levels, proximity, and loading. Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 13 Updated September 3, 2020

A typical earth pressure distribution for cantilever and single tieback shoring is provided on Plate 3 of this study. Allowable soldier pile deflections for walls subjected to active (or at-rest) earth pressures should be limited to one inch.

Soldier Piles

Soldier pile installation should be observed by ESNW to confirm pile depths and soil conditions. Sloughing of soldier pile excavations should be expected, particularly where groundwater seepage is encountered in excavations. The contractor should be prepared to case soldier pile excavations.

We have had recent success driving large I-beams in conditions such as those present on the subject site. This method does produce high speed vibration; however, it does not require drilling and casing of the holes or grout/concrete filling. If this method will be pursued, ESNW can provide a more detailed description and recommendations upon further evaluation of feasibility.

Timber Lagging

Due to the cohesionless nature of the sand and gravels, lagging should be installed in maximum two to three-foot lifts as the excavation is advanced. ESNW representatives should observe the shoring excavation to assess the stability of the cut. The lagging should be backfilled as the excavation is advanced to minimize voids between the lagging and cut face, and to reduce the potential for ground subsidence behind the shoring wall. Where sloughing of the excavation results in the development of a large void the void must be filled and restored daily with lean mix. Excavations should be supported by either lagging or soil berm (extending at least one foot above the cut) at the end of any work day. Due to the potential for excavation sloughing during lagging operations, a contingency in the budget for greater than typical lean mix volumes should be included.

Due to anticipated soil arching between soldier piles, the timber lagging for temporary walls can be designed with a reduced pressure equal to 50 percent of the design lateral earth pressure.

Lagging shall not consist of pressure treated timbers.

Tieback Anchors

Tiebacks should be located as high on the wall as possible and should be designed based on the following parameters:

 Allowable Anchor Pullout 1.75 kips/ft*

 Declination Angle 15 to 20 degrees (from horizontal)

 Anchor No-Load Zone H/4 then 60 degrees

 Soldier Pile End Bearing 8,000 psf

* Assumes application of secondary grouting as needed to achieve pullout capacity.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 14 Updated September 3, 2020

Tieback anchors should be verification tested and proof tested in general accordance with Section 8.3 of the Recommendations for Prestressed Rock and Soil Anchors (Post-Tensioning Institute, 1996). A minimum of two verification tests (200 percent design load) should be performed. Verification test anchors can be used as production anchors, provided the anchor is successfully tested and is acceptable. The production anchors should be proof tested to 130 percent of the design load. ESNW should observe the anchor testing and provide documentation of the test results. Tieback anchors should be locked-off at 90 percent to 100 percent of the design load.

Shoring Wall Drainage

Temporary shoring walls should be provided with adequate drainage to reduce the potential for excess hydrostatic pressure build-up. During construction, drainage occurring between the timber lagging is usually sufficient to prevent the development of excessive hydrostatic pressures. With respect to permanent drainage, it is expected that the building structure will be fully waterproofed below the water table per City of Redmond requirements.

Shoring Monitoring

Due to the close proximity of public rights-of-way and adjacent private properties, an optical monitoring program should be implemented as part of the temporary shoring design. The monitoring program should consist of a photo survey prior to beginning the building excavations to document the current conditions of the surrounding features. Initial survey points should be placed at strategic locations along adjacent foundations and right-of-way alignments that will allow for periodic measurement during and after the shoring installation. This will allow for efficient monitoring of the site to identify and remediate excessive deflections or excavation related movements, if they occur. Prior to the start of construction, the geotechnical engineer, owner, and contractor should review the project and develop a monitoring program for the site.

Following installation of the soldier piles, monitoring points should be established on the top of every other pile and an initial baseline reading should be acquired prior to proceeding with the excavation. Readings should be acquired twice weekly during the excavation phase of the construction. ESNW should be provided the data for review as it becomes available during the course of construction (within 24 hours of acquisition). The monitoring program will be supplemented with periodic observations by ESNW during the excavation phase of construction.

Preliminary Construction Dewatering Recommendations

Excavations will extend below the static groundwater elevation, particularly during the wetter winter and spring months; therefore, temporary construction dewatering will be required. Our preliminary construction dewatering estimates are based on maximum excavations of 15 feet below existing grade that would provide about two feet of separation between the lowermost excavation and dewatered level (in most cases). It should be noted that a hydrogeologist specializing in construction dewatering has now been engaged and has recently prepared preliminary dewatering volumes.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 15 Updated September 3, 2020

In any case, an estimate of the dewatering rate was prepared by ESNW using equation 14-5 from Foundation Analysis and Design, Bowles, 4th ed. For simplicity, we assumed a single, equivalent well diameter based on the physical dimensions of the proposed project, although multiple well points will be used to dewater the project area. The following parameters were used to estimate the construction dewatering volumes:

 Effective radius of dewatering 160 feet

 Static high groundwater level* 7 feet bgs

 Bottom of dewatering 15 feet bgs

 Hydraulic conductivity 0.1 – 0.3 ft/min

 Specific yield 0.15 (unitless)

 Radius of influence 600 feet

 Aquifer thickness 30 feet

* The seasonal high groundwater level was recorded in February 2020 at about 7 feet below existing grade. This level reflects an unusually high amount of recent prolonged rainfall. However, it is possible that this level (or higher) may occur during the construction phase and is accounted for in our estimate.

Based on the above, initial dewatering volumes may range between 1,500 to 3,000 gallons per minute (gpm) during the seasonal high groundwater conditions and between about 200 to 500 gpm during the seasonal low conditions. It should be noted that the project hydrogeologist recently estimated 2,000 gpm for the steady state seasonal high condition, which is in fairly good agreement with our estimates. These flows would attenuate after the dewatering is initiated and tend to equilibrate. However, the actual flows will depend greatly on the depth of excavation and actual groundwater levels at the time of construction. The project hydrogeologist, however, will ultimately prepare a final dewatering design with better defined estimates based on final plans.

Existing Conveyance System

Based on information provided by City staff, the current stormwater conveyance system is located along Northeast 87th Street and consists of two 8-inch diameter pipes that cross Northeast 87th Street and tie into an 18-inch diameter pipe that transitions to a 24-inch pipe and ultimately ties into the Northeast 85th Street system that consists of a 42-inch diameter pipe that discharges directly to the Sammamish River. The referenced Conveyance Analysis has been submitted by KPFF to the COR for review and was based largely on input provided the COR staff. The referenced Conveyance Analysis concludes that the proposed routing has sufficient capacity and will comply with local applicable temporary dewatering requirements.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 16 Updated September 3, 2020

Typical Dewatering System

Based on our experience with similar projects in this area, we anticipate the dewatering system will consist of perimeter, small-diameter well points that are installed around the project perimeter. Monitoring wells will typically be installed to monitor the local water levels and allow for adjustment of the system to ensure minimum dewatering levels are achieved and maintained.

Dewatering Monitoring

During dewatering, established City monitoring wells will also need to be periodically measured to determine effects of dewatering on the water table in the site vicinity. The City prohibits permanent dewatering for new development. Therefore, the below-grade elements must be designed for permanent waterproofed conditions. This solution will also require the below-grade portion of the building to resist hydrostatic uplift.

We recommend installing surveyed monitoring points along durable, hard surfaces surrounding the project perimeter to detect settlement that may be induced by the temporary dewatering activities. The monitoring points should be optically surveyed on a weekly basis and data distributed to the project team within 24 hours of acquisition. If settlement is detected, all work related to the dewatering system should be immediately suspended until a thorough evaluation has been completed and remedial measures determined, if necessary.

Structural Mat Foundations

Alluvial sand and gravel deposits of varying relative densities are expected to be exposed throughout the foundation subgrade areas of the building excavation. The building foundations and lower portions of the underground garage structure are also expected to permanently reside below the seasonal high groundwater table. Given the variability of the alluvial deposits and expectation that a portion of the garage-level foundation will penetrate below the seasonal high groundwater level, building support derived on a structural mat foundation with an underlying waterproofing membrane is recommended for project planning purposes. The following soil parameters should be used for mat foundation design:

 Subgrade Preparation 1-foot (min.) “clean” crushed rock*

 Woven geotextile Mirafi 600x (or equivalent)

 Allowable soil bearing capacity 3,000 psf

 Modulus of subgrade reaction 175 pci

 Passive earth pressure 150 pcf (Equivalent Fluid)**

 Coefficient of friction 0.30

* Crushed rock to be underlain by a woven geotextile. ** Assumes buoyant conditions around the base of foundation.

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 17 Updated September 3, 2020

The specified modulus of subgrade reaction is intended as a design value, i.e., scale effects and subgrade improvements have been accounted for. Elastic settlement of the soil-supported mat slab foundation is expected to be relatively small, on the order of one-half inch or less. Due to the effective “unloading” of the building site by virtue of the planned garage-level excavation, there will be a partially compensating condition with respect to the new building loads. In this respect, settlements associated with the new building loads will be sufficiently mitigated. We expect total and differential settlements on the order of one-inch and one-half inch, respectively, across the width of the mat foundation.

Slab-on-Grade Floors

With respect to the basement level slab, the structural mat is expected to function as the floor slab. In terms of areas independent of the basement, the slab-on-grade floors should be supported on well-compacted, firm and unyielding subgrade. Unstable or yielding areas of the subgrade should be recompacted, or overexcavated and replaced with suitable structural fill, prior to slab construction.

The slab-on-grade areas should be provided with a minimum four-inch capillary break. Capillary break soils should consist of a granular, free-draining material that contains less than 5 percent fines (percent passing the Number 200 sieve, based on the minus three-quarter-inch fraction). In areas where slab moisture is undesirable, installation of a vapor barrier placed below the slab should be considered. If a vapor barrier will be utilized, it should consist of a material specifically designed for that use and should be installed in accordance with the specifications of the manufacturer.

Seismic Design

The 2015 International Building Code recognizes the American Society of Civil Engineers (ASCE) for seismic site class definitions. In accordance with Table 20.3-1 of the ASCE Minimum Design Loads for Buildings and Other Structures manual, Site Class D should be used for design.

The referenced liquefaction susceptibility mapping indicates the subject site lies within a low to moderate liquefaction hazard area. Liquefaction is a phenomenon where saturated, loose, and sandy soils suddenly lose internal strength and behave as a fluid. This behavior is in response to increased pore water pressures resulting from an earthquake or other intense ground shaking. In our opinion, site susceptibility to liquefaction is properly classified as low to moderate. The building will be supported on a structural mat foundation which will help mitigate the effects of potential liquefaction induced settlements. On this basis, no further mitigation is required to meet current minimum design standards for liquefaction hazards.

Retaining Walls (Independent of Foundation Walls)

Site retaining walls independent of the building walls should be designed to resist earth pressures and any applicable surcharge loads. With respect to the building foundation walls, the relevant earth pressure values provided in the Shoring Recommendations section of this report should be considered. Hydrostatic pressures for the permanent building wall condition will also need to be considered, as applicable. Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 18 Updated September 3, 2020

The following parameters can be used for retaining walls independent of the building foundation walls:

 Active earth pressure (yielding condition) 35 pcf (equivalent fluid)

 At-rest earth pressure (restrained condition) 50 pcf

 Traffic surcharge (passenger vehicles) 70 psf (rectangular distribution)

 Passive earth pressure 275 pcf*

 Coefficient of friction 0.40

 Lateral seismic surcharge 6H yielding condition** 14H restrained condition

* ESNW should review retaining wall designs to confirm passive earth pressures. ** May also be applied for permanent building wall design.

Additional surcharge loading from foundations, sloped backfill, or other loading should be included in the retaining wall design. Drainage should be provided behind retaining walls and above the seasonal high groundwater level such that hydrostatic pressures do not develop. If drainage is not provided, hydrostatic pressures should be included in the wall design. ESNW should review retaining wall designs to confirm that appropriate earth pressure values have been incorporated into the design, and to provide additional recommendations.

Retaining walls should be backfilled with free draining material that extends along the height of the wall, and a distance of at least 18 inches behind the wall. The upper one foot of the wall backfill can consist of a less permeable soil, if desired. A rigid, perforated drain pipe should be placed along the base of the wall, and connected to an approved discharge location. A retaining wall drainage detail is provided on Plate 4. Where desired, the use of a sheet drain in lieu of free draining backfill can be considered. However, ESNW should review the proposed use of sheet drain and provide supplemental drainage recommendations.

Drainage

Where zones of groundwater seepage are encountered, temporary measures to control groundwater seepage may be needed. Temporary measures to control groundwater seepage and surface water runoff during construction will likely involve passive elements, such as interceptor trenches and sumps, as necessary.

Surface grades must be designed to direct water away from the building. The grade adjacent to the building should be sloped away at a gradient of at least 2 percent for a horizontal distance of at least 10 feet, or as setbacks allow. In our opinion, perimeter footing drains should be installed at or below the invert of the proposed building footings located above the water table where waterproofing will not be necessary. A typical footing drain detail is provided on Plate 5 of this report. Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 19 Updated September 3, 2020

Infiltration Feasibility

The native soil encountered at the boring locations consisted primarily of about four to seven feet of silty sand before transitioning to relatively free draining sand and gravel alluvial deposits. In our opinion, infiltration is not feasible on this site due to shallow seasonal high groundwater conditions that would not allow for adequate separation and low permeable soils within the upper approximately four to seven feet of the soil profile.

Utility Support and Trench Backfill

Utility trench excavations advanced below the groundwater table will require dewatering prior to utility installations. Native (dewatered) soils encountered at the boring locations will generally be suitable for support of utilities. Organic-rich soil is not considered suitable for direct support of utilities and will likely require remedial action, such as removal and replacement with structural fill, where encountered at utility subgrades.

Native soils encountered at the boring locations will not be suitable for use as structural backfill in the utility trench excavations unless the soil is at, or slightly above, the optimum moisture content at the time of placement and compaction. Moisture conditioning may be necessary at some locations prior to use as structural fill. Each section of utility lines must be adequately supported in the bedding material. Utility trench backfill should be placed and compacted to the specifications of structural fill as previously detailed in this report, or to the applicable specifications of the City or another responsible jurisdiction or agency.

Preliminary Pavement Sections

Pavement performance is largely related to the condition of the underlying subgrade. To ensure adequate pavement performance, the subgrade should be in a firm and unyielding condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement areas should be compacted to the specifications previously detailed in this report. Soft, wet, or otherwise unsuitable subgrade areas may still exist after base grading activities. Areas containing unsuitable or yielding subgrade conditions will require remedial measures, such as overexcavation and/or placement of thicker crushed rock or structural fill sections, prior to pavement.

We anticipate new pavement sections will be subjected primarily to passenger vehicle traffic. For lightly loaded pavement areas subjected primarily to passenger vehicles, the following preliminary pavement sections may be considered:

 A minimum of two inches of hot-mix asphalt (HMA) placed over four inches of crushed rock base (CRB), or;

 A minimum of two inches of HMA placed over three inches of asphalt-treated base (ATB).

Earth Solutions NW, LLC Inland Washington, LLC ES-6857 September 13, 2019 Page 20 Updated September 3, 2020

For relatively high volume, heavily loaded pavements areas subjected to occasional truck traffic, the following preliminary pavement sections may be considered:

 A minimum of three inches of HMA placed over six inches of CRB, or;

 A minimum of three inches of HMA placed over four inches of ATB.

The HMA, ATB, and CRB materials should conform to WSDOT and/or City specifications. All soil base material should be compacted to at least 95 percent of the maximum dry density. Final pavement design recommendations can be provided once final traffic loading has been determined. City road standards may supersede the recommendations provided in this report.

An ESNW representative should be requested to observe the subgrade conditions prior to placement of crushed rock or ATB. Supplemental recommendations for achieving subgrade stability and drainage can be provided, as necessary.

LIMITATIONS

The recommendations and conclusions provided in this geotechnical engineering study are professional opinions consistent with the level of care and skill that is typical of other members in the profession currently practicing under similar conditions in this area. A warranty is not expressed or implied. Variations in the soil and groundwater conditions observed at the test sites may exist, and may not become evident until construction. ESNW should reevaluate the conclusions in this geotechnical engineering study if variations are encountered.

Additional Services

ESNW should have an opportunity to review the final design with respect to the geotechnical recommendations provided in this report. ESNW should also be retained to provide testing and consultation services during construction.

Earth Solutions NW, LLC SITE

Reference: NORTH EarthEarth Earth Solutions NWLLC King County, Washington SolutionsSolutions NW LLC Geotechnical Engineering, Construction Map 537 Observation/Testing and Environmental Services By The Thomas Guide Rand McNally 32nd Edition Vicinity Map Together Center Redmond, Washington

NOTE: This plate may contain areas of color. ESNW cannot be responsible for any subsequent misinterpretation of the information Drwn. MRS Date 08/20/2019 Proj. No. 6857 resulting from black & white reproductions of this plate. CheckedBST Date Aug. 2019 Plate 1 LEGEND

Approximate Location of Together Center B-1 Boring Location Plan N ESNW Boring, Proj. No. Redmond, Washington .E. 87TH STREET ES-6857, Aug. 2019

Subject Site

B-1 . B-3 .E Proposed Building

N

Building A

y

r Building B t

E

n

E

U

e

N

g

a

E r Plaza a Plaza Play V G Plaza NORTH

A

Area

B-2

H

T

B-4 4

6

1

Pedestrian Path Geotechnical Engineering, Construction Observation/Testing and Environmental Services

NOT - TO - SCALE Earth Solutions NW LLC LLC LLC Earth NW NW NOTE: The graphics shown on this plate are not intended for design Earth Solutions purposes or precise scale measurements, but only to illustrate the Solutions approximate test locations relative to the approximate locations of existing and / or proposed site features. The information illustrated is largely based on data provided by the client at the time of our study. ESNW cannot be responsible for subsequent design changes Drwn. By or interpretation of the data by others. MRS Checked By BST NOTE: This plate may contain areas of color. ESNW cannot be responsible for any subsequent misinterpretation of the information Date resulting from black & white reproductions of this plate. 08/19/2019 Proj. No. 6857 Plate 2 Traffic Surcharge or Building Surcharge (Where Applicable)

Active Earth Pressure

H *NOTE: (Wall Height) See text for recommended allowable tieback anchor loads. Active Earth Pressure assumes Excavation will be Dewatered Neglect Upper 2 feet during Construction. of Passive Pressure

EFP=35pcf*

Excavation Level 2' Passive Surcharge Earth (Where Applicable) Pressure

D = Pile Embedment (per Structural Eng.)

EFP=150pcf SCHEMATIC ONLY - NOT TO SCALE NOT A CONSTRUCTION DRAWING

NOTES: EarthEarth LLC SolutionsSolutions Earth Solutions NW Diagram for pressure distribution illustration NW LLC Geotechnical Engineering, Construction only, not a design drawing. Observation/Testing and Environmental Services

Passive Pressure includes a factor of Cantilever & Single Tieback Wall safety of 1.5. Together Center For adjacent building or traffic surcharge Redmond, Washington see text. Drwn. CAM Date 02/17/2020 Proj. No. 6857

Checked RAC Date Feb. 2020 Plate 3 18" Min.

Structural Fill

Perforated Rigid Drain Pipe NOTES: (Surround in Drain Rock)

Free-draining Backfill should consist of soil having less than 5 percent fines. Percent passing No. 4 sieve should be 25 to 75 percent. SCHEMATIC ONLY - NOT TO SCALE Sheet Drain may be feasible in lieu NOT A CONSTRUCTION DRAWING of Free-draining Backfill, per ESNW recommendations.

Drain Pipe should consist of perforated, rigid PVC Pipe surrounded with 1-inch Drain Rock.

LEGEND: EarthEarth SolutionsSolutions Earth Solutions NWLLC Free-draining Structural Backfill NW LLC Geotechnical Engineering,Construction Observation/Testing and Environmental Services

1-inch Drain Rock Retaining Wall Drainage Detail Together Center Redmond, Washington

Drwn. MRS Date 09/12/2019 Proj. No. 6857

CheckedBST Date Sept. 2019 Plate 4 Slope

18" Min.

Perforated Rigid Drain Pipe (Surround in Drain Rock)

NOTES:

Do NOT tie roof downspouts to Footing Drain. SCHEMATIC ONLY - NOT TO SCALE Surface Seal to consist of NOT A CONSTRUCTION DRAWING 12" of less permeable, suitable soil. Slope away from building.

LEGEND:

Surface Seal: native soil or other low-permeability material.

Earth LLC SolutionsSolutions Earth Solutions NW 1-inch Drain Rock Geotechnical Engineering, Construction NW LLC Observation/Testing and Environmental Services

Footing Drain Detail Together Center Redmond, Washington

Drwn. MRS Date 09/12/2019 Proj. No. 6857

CheckedBST Date Sept. 2019 Plate 5

Appendix A

Subsurface Exploration Boring Logs

ES-6857

The subsurface conditions at the site were explored by drilling four borings on August 13, 2019, advanced to a maximum depth of about 41.5 feet bgs, at the approximate locations illustrated on Plate 2 of this report. The boring logs are provided in this Appendix. The final logs represent the interpretations of the field logs and the results of laboratory analyses. The stratification lines on the logs represent the approximate boundaries between soil types. In actuality, the transitions may be more gradual.

Earth Solutions NW, LLC Earth Solutions NWLLC SOIL CLASSIFICATION CHART SYMBOLS TYPICAL MAJOR DIVISIONS GRAPH LETTER DESCRIPTIONS

CLEAN WELL-GRADED GRAVELS, GRAVEL - GW SAND MIXTURES, LITTLE OR NO GRAVEL GRAVELS FINES AND GRAVELLY SOILS POORLY-GRADED GRAVELS, (LITTLE OR NO FINES) GP GRAVEL - SAND MIXTURES, LITTLE OR NO FINES COARSE GRAINED GRAVELS WITH SILTY GRAVELS, GRAVEL - SAND - SOILS MORE THAN 50% FINES GM SILT MIXTURES OF COARSE FRACTION RETAINED ON NO. 4 SIEVE (APPRECIABLE CLAYEY GRAVELS, GRAVEL - SAND - AMOUNT OF FINES) GC CLAY MIXTURES

CLEAN SANDS SW WELL-GRADED SANDS, GRAVELLY MORE THAN 50% SAND SANDS, LITTLE OR NO FINES OF MATERIAL IS AND LARGER THAN SANDY NO. 200 SIEVE SOILS POORLY-GRADED SANDS, SIZE (LITTLE OR NO FINES) SP GRAVELLY SAND, LITTLE OR NO FINES

SANDS WITH SILTY SANDS, SAND - SILT MORE THAN 50% FINES SM MIXTURES OF COARSE FRACTION PASSING ON NO. 4 SIEVE (APPRECIABLE CLAYEY SANDS, SAND - CLAY AMOUNT OF FINES) SC MIXTURES

INORGANIC SILTS AND VERY FINE SANDS, ROCK FLOUR, SILTY OR ML CLAYEY FINE SANDS OR CLAYEY SILTS WITH SLIGHT PLASTICITY SILTS INORGANIC CLAYS OF LOW TO FINE LIQUID LIMIT MEDIUM PLASTICITY, GRAVELLY AND LESS THAN 50 CL CLAYS, SANDY CLAYS, SILTY CLAYS, GRAINED CLAYS LEAN CLAYS SOILS

ORGANIC SILTS AND ORGANIC OL SILTY CLAYS OF LOW PLASTICITY

MORE THAN 50% INORGANIC SILTS, MICACEOUS OR OF MATERIAL IS MH DIATOMACEOUS FINE SAND OR SMALLER THAN SILTY SOILS NO. 200 SIEVE SIZE SILTS LIQUID LIMIT INORGANIC CLAYS OF HIGH AND GREATER THAN 50 CH PLASTICITY CLAYS

ORGANIC CLAYS OF MEDIUM TO OH HIGH PLASTICITY, ORGANIC SILTS

PEAT, HUMUS, SWAMP SOILS WITH HIGHLY ORGANIC SOILS PT HIGH ORGANIC CONTENTS

DUAL SYMBOLS are used to indicate borderline soil classifications.

The discussion in the text of this report is necessary for a proper understanding of the nature of the material presented in the attached logs. Earth Solutions NW 15365 N.E. 90th Street, Suite 100 BORING NUMBER B-1 Redmond, Washington 98052 PAGE 1 OF 2 Telephone: 425-449-4704 Fax: 425-449-4711

PROJECT NUMBER ES-6857 PROJECT NAME Together Center DATE STARTED 8/13/19 COMPLETED 8/13/19 GROUND ELEVATION HOLE SIZE DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: DRILLING METHOD HSA AT TIME OF DRILLING 13.5 ft LOGGED BY BST CHECKED BY SSR AT END OF DRILLING --- NOTES Surface Conditions: 1"-2" of asphalt AFTER DRILLING ---

TESTS MATERIAL DESCRIPTION (ft) LOG BLOW DEPTH U.S.C.S. COUNTS NUMBER GRAPHIC (N VALUE) RECOVERY % SAMPLE TYPE 0 FILL 0.3 Crushed ROCK base coarse (Fill) Brown silty SAND, loose, moist -light iron oxide staining -scattered organics

SM

6-3-2 SS 56 MC = 11.60% (5)

4.5 5 Brown poorly graded SAND with gravel, medium dense, moist -scattered cobbles 7-10-13 SS 33 MC = 4.80% (23) SP

8.0 -increasing gravel content 16-19-18 SS 44 MC = 3.70% Gray poorly graded GRAVEL with sand, dense, moist (37) -becomes dense

10 -no recovery 21-24-21 SS 0 (45)

GP -groundwater table, becomes saturated

15

38-25-21 SS 33 MC = 6.10% (46)

-decreasing gravel content

18.5 Brown silty SAND, medium dense, saturated SM

GENERAL BH / TP / WELL 6857.GPJ GINT US.GDT 2/17/20 / TP WELL 6857.GPJ GINT US.GDT BH GENERAL 20 (Continued Next Page) Earth Solutions NW 15365 N.E. 90th Street, Suite 100 BORING NUMBER B-1 Redmond, Washington 98052 PAGE 2 OF 2 Telephone: 425-449-4704 Fax: 425-449-4711

PROJECT NUMBER ES-6857 PROJECT NAME Together Center

TESTS MATERIAL DESCRIPTION (ft) LOG BLOW DEPTH U.S.C.S. COUNTS NUMBER GRAPHIC (N VALUE) RECOVERY % SAMPLE TYPE 20 Brown silty SAND, medium dense, saturated (continued) 3-3-12 SS 78 MC = 28.10% (15) SM

23.0 Gray poorly graded SAND with gravel, loose to medium dense, saturated

25 [USDA Classification: very gravelly coarse SAND] 1-3-5 MC = 13.00% SS 44 (8) Fines = 1.40% -"6 of heave SP

30 30.5 3-5-10 SS 100 MC = 32.00% Gray silty SAND, medium dense, saturated (15) SM 31.5 Boring terminated at 31.5 feet below existing grade. Groundwater table encountered at 13.5 feet during drilling. 2" PVC standpipe installed to bottom of boring. Lower 10.0 feet slotted. Boring backfilled with sand and bentonite chips. Well ID: BLU043 Bottom of hole at 31.5 feet. GENERAL BH / TP / WELL 6857.GPJ GINT US.GDT 2/17/20 / TP WELL 6857.GPJ GINT US.GDT BH GENERAL Earth Solutions NW 15365 N.E. 90th Street, Suite 100 BORING NUMBER B-2 Redmond, Washington 98052 PAGE 1 OF 2 Telephone: 425-449-4704 Fax: 425-449-4711

PROJECT NUMBER ES-6857 PROJECT NAME Together Center DATE STARTED 8/13/19 COMPLETED 8/13/19 GROUND ELEVATION HOLE SIZE DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: DRILLING METHOD HSA AT TIME OF DRILLING 13.5 ft LOGGED BY BST CHECKED BY SSR AT END OF DRILLING --- NOTES Surface Conditions: 1"-2" of asphalt AFTER DRILLING ---

TESTS MATERIAL DESCRIPTION (ft) LOG BLOW DEPTH U.S.C.S. COUNTS NUMBER GRAPHIC (N VALUE) RECOVERY % SAMPLE TYPE 0 FILL 0.3 Crushed ROCK base coarse (Fill) Brown silty SAND, loose, moist -trace gravel to medium dense -scattered organics

6-15-22 SS 22 MC = 9.70% SM -high blow counts due to gravel obstruction (37)

5 -increasing gravel content

6-12-14 SS 33 MC = 2.90% (26) 6.0 Gray poorly graded SAND with gravel, medium dense, moist

10-9-10 SS 44 MC = 5.30% (19)

10 -increasing gravel content

11-12-11 SS 33 MC = 4.20% (23)

SP

-groundwater table, becomes saturated

15 -abundant pebbles 5-11-17 SS 56 MC = 12.60% (28)

GENERAL BH / TP / WELL 6857.GPJ GINT US.GDT 2/17/20 / TP WELL 6857.GPJ GINT US.GDT BH GENERAL 20 20.0 (Continued Next Page) Earth Solutions NW 15365 N.E. 90th Street, Suite 100 BORING NUMBER B-2 Redmond, Washington 98052 PAGE 2 OF 2 Telephone: 425-449-4704 Fax: 425-449-4711

PROJECT NUMBER ES-6857 PROJECT NAME Together Center

TESTS MATERIAL DESCRIPTION (ft) LOG BLOW DEPTH U.S.C.S. COUNTS NUMBER GRAPHIC (N VALUE) RECOVERY % SAMPLE TYPE 20 Gray poorly graded SAND with gravel, dense, saturated 4-10-25 SS 100 MC = 17.60% -abundant pebbles (35)

SP

24.5 25 Gray silty SAND, medium dense, saturated [USDA Classification: slightly gravelly fine sandy LOAM] 6-10-17 MC = 21.00% SS 100 (27) Fines = 32.50%

SM

30 30.5 3-5-3 SS 100 MC = 34.20% Gray SILT, medium stiff, saturated (8) ML 31.5 Boring terminated at 31.5 feet below existing grade. Groundwater table encountered at 13.5 feet during drilling. Boring backfilled with bentonite chips. Bottom of hole at 31.5 feet. GENERAL BH / TP / WELL 6857.GPJ GINT US.GDT 2/17/20 / TP WELL 6857.GPJ GINT US.GDT BH GENERAL Earth Solutions NW 15365 N.E. 90th Street, Suite 100 BORING NUMBER B-3 Redmond, Washington 98052 PAGE 1 OF 2 Telephone: 425-449-4704 Fax: 425-449-4711

PROJECT NUMBER ES-6857 PROJECT NAME Together Center DATE STARTED 8/13/19 COMPLETED 8/13/19 GROUND ELEVATION HOLE SIZE DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: DRILLING METHOD HSA AT TIME OF DRILLING 13.0 ft LOGGED BY BST CHECKED BY SSR AT END OF DRILLING --- NOTES Surface Conditions: 1"-2" of asphalt AFTER DRILLING ---

TESTS MATERIAL DESCRIPTION (ft) LOG BLOW DEPTH U.S.C.S. COUNTS NUMBER GRAPHIC (N VALUE) RECOVERY % SAMPLE TYPE 0 FILL 0.3 Crushed ROCK base coarse (Fill) Brown silty SAND, medium dense, moist

-scattered organcis

SM

5-10-13 SS 44 MC = 3.40% (23)

4.5 5 Gray poorly graded SAND, medium dense, moist -trace gravel 10-8-8 SS 33 MC = 3.30% (16)

SP

-increasing gravel content 5-8-9 SS 67 MC = 5.50% (17)

9.5 -decreasing gravel content 10 Gray poorly graded SAND with silt, medium dense, moist [USDA Classification: gravelly SAND] 4-4-5 MC = 6.10% SS 67 (9) Fines = 6.20%

-groundwater table, becomes saturated

-increasing gravel content, becomes dense SP- 15 SM -abundant pebbles 8-22-34 SS 44 MC = 8.60% (56)

GENERAL BH / TP / WELL 6857.GPJ GINT US.GDT 2/17/20 / TP WELL 6857.GPJ GINT US.GDT BH GENERAL 20 20.0 (Continued Next Page) Earth Solutions NW 15365 N.E. 90th Street, Suite 100 BORING NUMBER B-3 Redmond, Washington 98052 PAGE 2 OF 2 Telephone: 425-449-4704 Fax: 425-449-4711

PROJECT NUMBER ES-6857 PROJECT NAME Together Center

TESTS MATERIAL DESCRIPTION (ft) LOG BLOW DEPTH U.S.C.S. COUNTS NUMBER GRAPHIC (N VALUE) RECOVERY % SAMPLE TYPE 20 SP- Gray poorly graded SAND with silt, dense, saturated 7-10-30 SS 67 MC = 7.10% SM (40) 21.0 Gray poorly graded GRAVEL, dense, saturated -abundant pebbles

GP 25 MC = 6.10% [USDA Classification: extremely gravelly coarse SAND] SS 84 5-50/6" Fines = 0.30%

27.5 Gray poorly graded SAND, very dense, saturated

SP 30 SS 100 18-50/5" MC = 23.90%

31.5 Boring terminated at 31.5 feet below existing grade. Groundwater table encountered at 13.0 feet below existing drilling. Boring backfilled with bentonite chips. Bottom of hole at 31.5 feet. GENERAL BH / TP / WELL 6857.GPJ GINT US.GDT 2/17/20 / TP WELL 6857.GPJ GINT US.GDT BH GENERAL Earth Solutions NW 15365 N.E. 90th Street, Suite 100 BORING NUMBER B-4 Redmond, Washington 98052 PAGE 1 OF 2 Telephone: 425-449-4704 Fax: 425-449-4711

PROJECT NUMBER ES-6857 PROJECT NAME Together Center DATE STARTED 8/13/19 COMPLETED 8/13/19 GROUND ELEVATION HOLE SIZE DRILLING CONTRACTOR Holocene Drilling GROUND WATER LEVELS: DRILLING METHOD HSA AT TIME OF DRILLING 14.0 ft LOGGED BY BST CHECKED BY SSR AT END OF DRILLING --- NOTES Surface Conditions: 1"-2" of asphalt AFTER DRILLING ---

TESTS MATERIAL DESCRIPTION (ft) LOG BLOW DEPTH U.S.C.S. COUNTS NUMBER GRAPHIC (N VALUE) RECOVERY % SAMPLE TYPE 0 FILL 0.3 Crushed ROCK base coarse (Fill) Brown silty SAND, medium dense, moist -trace gravel

3-3-11 SS 22 MC = 7.60% (14)

5

18-20-19 SS 33 MC = 2.90% -increasing gravel content (39)

SM

8-23-26 SS 33 MC = 4.10% -high blow counts due to gravel obstruction (49)

10

18-21-19 SS 22 MC = 3.50% (40)

13.0 Gray poorly graded GRAVEL with sand, dense, wet

-groundwater table, becomes saturated 15 GP 15-17-19 SS 33 MC = 8.70% (36)

17.0 Gray poorly graded SAND with silt, medium dense, saturated -scattered pebbles SP- SM

GENERAL BH / TP / WELL 6857.GPJ GINT US.GDT 2/17/20 / TP WELL 6857.GPJ GINT US.GDT BH GENERAL 20 (Continued Next Page) Earth Solutions NW 15365 N.E. 90th Street, Suite 100 BORING NUMBER B-4 Redmond, Washington 98052 PAGE 2 OF 2 Telephone: 425-449-4704 Fax: 425-449-4711

PROJECT NUMBER ES-6857 PROJECT NAME Together Center

TESTS MATERIAL DESCRIPTION (ft) LOG BLOW DEPTH U.S.C.S. COUNTS NUMBER GRAPHIC (N VALUE) RECOVERY % SAMPLE TYPE 20 Gray poorly graded SAND with silt, medium dense, saturated (continued) 4-6-10 MC = 23.90% [USDA Classification: slightly gravelly coarse SAND] SS 100 (16) Fines = 7.90% -scattered pebbles

25 SP- -no recovery 2-3-8 SM SS 0 (11)

30 30.5 8-11-13 SS 78 MC = 26.80% Gray silty SAND, medium dense, saturated (24)

35 -becomes loose, decreasing silt content [USDA Classification: loamy SAND] 1-1-4 MC = 24.80% SS 89 (5) Fines = 15.60% SM

40

7-8-15 SS 89 MC = 26.60% (23) 41.5 Boring terminated at 41.5 feet below existing grade. Groundwater table encountered at 14.0 feet during drilling. 2" PVC standpipe installed to 30.0 feet. Lower 10.0 feet slotted. Boring backfilled with sand and bentonite chips. Well ID: BLU044 Bottom of hole at 41.5 feet. GENERAL BH / TP / WELL 6857.GPJ GINT US.GDT 2/17/20 / TP WELL 6857.GPJ GINT US.GDT BH GENERAL

Appendix B

Laboratory Test Results

ES-6857

Earth Solutions NW, LLC

Appendix C

LiquefyPro Output

ES-6857

Earth Solutions NW, LLC

LIQUEFACTION ANALYSIS Together Center

Hole No.=B-2 Water Depth=7 ft Magnitude=7 Acceleration=0.48g

Shear Stress Ratio Factor of Safety Settlement Raw Unit Fines Soil Description (ft) 0 1 0 1 5 0 (in.) 10 SPT Weight % 0 26 125 15 Silty sand w ith gravel

5 19 125 4 Poorly graded Sand

10

15 30 130 4

20

27 125 32 25 Silty Sand w ith gravel

30 8 125 55 fs1=1 S = 1.72 in. Sandy Silt CRR CSR fs1 Saturated Shaded Zone has Liquefaction Potential Unsaturat.

35 LiquefyPro CivilTech Software USA www.civiltech.com USA Software CivilTech LiquefyPro

CivilTech Corporation ES-6857 Plate A-1

LIQUEFACTION ANALYSIS Together Center

Hole No.=B-3 Water Depth=7 ft Magnitude=7 Acceleration=0.48g

Shear Stress Ratio Factor of Safety Settlement Raw Unit Fines Soil Description (ft) 0 1 0 1 5 0 (in.) 10 SPT Weight % 0 23 125 15 Silty sand w ith gravel

16 120 4 5 Poorly graded Sand

9 120 6 10 Sand w ith silt

15 56 125 6 Sand w ith silt

20 50 130 0.3 Poorly graded Gravel w ith sand

25

30

fs1=1 S = 1.39 in. 50 130 0.3 CRR CSR fs1 Saturated Poorly graded Sand Shaded Zone has Liquefaction Potential Unsaturat.

35 LiquefyPro CivilTech Software USA www.civiltech.com USA Software CivilTech LiquefyPro

CivilTech Corporation ES-6857 Plate A-1

Report Distribution

ES-6857

EMAIL ONLY Inland Washington, LLC 120 West Cataldo Avenue, Suite 100 Spokane, Washington 99201

Attention: Mr. John Fisher Mr. Reid Dickinson

Earth Solutions NW, LLC