P-2002 Manchester Tank Farm Improvements Final GeoTech Report Rev1.pdf

Geotechnical Engineering Report Phase 2 Manchester Tank Farm Improvements (P-2002)

Fleet Logistics Center Puget Sound Manchester, Washington N44255-18-D-2000 for The United States Navy and Burns & McDonnell Engineering Company, Inc.

September 29, 2022

Improvements (P-2002)

Fleet Logistics Center Puget Sound Manchester, Washington N44255-18-D-2000 for The United States Navy and Burns & McDonnell Engineering Company, Inc.

September 29, 2022

17425 NE Union Hill Road, Suite 250 Redmond, Washington 98052 425.861.6000

Improvements (P-2002)

Fleet Logistics Center Puget Sound Manchester, Washington

N44255-18-D-2000 File No. 0144-418-05

September 29, 2022

Prepared for:

The United States Navy c/o Burns & McDonnell Engineering Company, Inc.

9400 Ward Parkway Kansas City, Missouri 64114

Attention: Robert S. Kulash, PE

Prepared by:

GeoEngineers, Inc.

17425 NE Union Hill Road, Suite 250 Redmond, Washington 98052 425.861.6000

Hamilton Puangnak, PE Aaron J. Hartvigsen, PE Geotechnical Engineer Senior Geotechnical Engineer

King H. Chin, PE Matthew W. Smith, PE Principal Senior Principal

HP:JSO:AJH:KHC:MWS:leh

Disclaimer: Any electronic form, facsimile or hard copy of the original document (email, text, table, and/or figure), if provided, and any attachments are only a copy of the original document. The original document is stored by GeoEngineers, Inc. and will serve as the official document of record.

September 29, 2022 | Page i File No. 0144-418-05

Table of Contents

1.0 INTRODUCTION

2.0 PROJECT DESCRIPTION

3.0 PREVIOUS STUDIES

4.0 SITE CONDITIONS

4.1. Geologic Setting

5.0 SEISMICITY

5.1. Cascadia Subduction Zone

5.1.1. Interface Earthquakes

5.1.2. Intraslab Earthquakes

5.2. Shallow Crustal Seismicity

5.3. Manchester Fuel Depot Fault Evaluation

6.0 SURFACE CONDITIONS

6.1. Subsurface Conditions

6.1.1. Soil

6.1.2. Groundwater

7.0 CONCLUSIONS AND RECOMMENDATIONS

7.1. Earthquake Engineering

7.1.1. Surface Fault Rupture

7.1.2. Liquefaction Potential

7.1.3. Lateral Spreading

7.1.4. Site-Specific MCER and DE Response Spectra

7.1.5. ASCE 7-16 Seismic Design Parameters

7.2. Temporary Dewatering

7.3. Decommissioning of Existing Underground Storage Tanks

7.4. Environmental Field Screening and Chemical Analytical Testing

7.5. Aboveground Storage Tanks Foundation Support

7.5.1. Allowable Bearing Pressure

7.5.2. Tank Settlement

7.5.3. Lateral Resistance

7.5.4. Construction Considerations

7.5.5. Aboveground Storage Tank Hydrotesting

7.6. Shallow Foundations – Non-Tank Structures

7.6.1. Lateral Resistance

7.6.2. Construction Considerations

7.7. Mass Grading

7.8. Earthwork

7.8.1. General

7.8.2. Clearing and Site Preparation

7.8.3. Subgrade Preparation

7.8.4. Fill Materials

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7.8.5. Reuse of On-site Soil as Fill

7.8.6. Fill Placement and Compaction

7.8.7. Weather Considerations

7.8.8. Temporary Cut Slopes

7.8.9. Permanent Cut and Fill Slopes

7.8.10. Utility Trenches

7.9. Cast-in-Place Concrete Walls

7.9.1. Drainage

7.10. Global Stability Analyses

7.10.1. Critical Slopes/Site Specific Seismic Response Spectrum Loading

7.11. Reinforced Soil Slopes

7.12. Structural Earth Walls

7.12.1. Soil Properties

7.12.2. SEW Global Stability

7.12.3. Groundwater

7.12.4. Surcharge Loading

7.12.5. Earthquake Loads

7.13. Pavement Recommendations

7.13.1. Subgrade Preparation

7.13.2. New Hot Mix Asphalt Pavement

7.13.3. Asphalt-treated Base

7.14. Erosion Control

8.0 LIMITATIONS

9.0 REFERENCES

LIST OF FIGURES

Figure 1. Vicinity Map Figure 2A. Site Plan – Existing Conditions Figure 2B. Site Plan – Proposed Conditions Figure 2C. Site Plan – Relationship Between Planned and Existing Tanks Figure 2D – Bearing Contour Map Figure 3A. Cross Section A-A’ Figure 3B. Cross Section B-B’ Figure 3C. Cross Section C-C’ Figure 3D. Cross Section D-D’ Figure 4. Regional Geology

APPENDICES

Appendix A. Field Explorations Figure A-1. Key to Exploration Logs Figures A-2 through A-5. Log of Borings Figures A-6 through A-11. Log of Test Pits

Appendix B. Laboratory Testing Figure B-1. Atterberg Limits Test Results

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Figures B-2 through B-4 Sieve Analysis Results Figure B-5 through B-10. Compaction Report Figures

Appendix C. Subsurface Information from Previous Studies Appendix D. Geophysical Testing Appendix E. Historical Photographs Appendix F. Site-Specific Response Spectra

Figure F-1. Cascadia Subduction Zone Intraslab Basin Amplification Factors Figure F-2. Cascadia Subduction Zone Interface Basin Amplification Factors Figure F-3. Source-Specific Basin Amplification Factors Figure F-4. Probabilistic Rock Outcrop MCE UHS (Basin-adjusted) Figure F-5. As-recorded Response Spectra Figure F-6. Spectrally Matched and Filtered Response Spectra Figure F-7. 1989 Mw 6.9 – Loma-Prieta─Gilroy Array #3 – Fault Normal Figure F-8. 1994 Mw 6.7 – Northridge-01─Newhall Fire Station – Fault Normal Figure F-9. 2007 Mw 6.8 – Chuetsu-oki─Joetsu Kakizakiku Kakizki – Fault Normal Figure F-10. 2011 Mw 9.0 – Tohoku Ujiie─TCGH12 - EW Figure F-11. 2010 Mw 8.8 – Maule─Concepcion San Pedro - NS Figure F-12. 2011 Mw 9.0 – Tohoku─Onoda MYGH05 – EW Figure F-13. 2010 Mw 8.8 – Maule─Cerro Santa Lucia-NS Figure F-14. Shear Wave Velocity Profile Figure F-15. MCE Soil Amplification Factors Figure F-16. Seattle Fault Deterministic Response Spectrum (Mw7.2, Rrup=0.8 km) Figure F-17. CSZ Intraslab Deterministic Response Spectrum (Mw7.5, Rhyp=53 km) Figure F-18. CSZ Interface Deterministic Response Spectrum (Mw9.0, Rrup = 74 km) Figure F-19. Recommended Deterministic (MCER) Response Spectrum Figure F-20. Recommended Site-Specific MCER Response Spectrum

Appendix G. FLAC 2D Results Figure G-1. FLAC 2D Model Geometry, Section C-C’ Figure G-2. FLAC 2D Model Geometry, Section D-D’ Figure G-3. Shear Wave Velocity Profile Figure G-4. FLAC 2D Surface Response Spectra, Section C-C’ Figure G-5. FLAC 2D Surface Response Spectra, Section D-D’ Figure G-6. Section C-C’, Horizontal Displacement Contour, Chuetsu-oki Earthquake Figure G-7. Section C-C’, Vertical Settlement Contour, Chuetsu-oki Earthquake Figure G-8. Section C-C’, Horizontal Displacement Contour, Loma Prieta Earthquake Figure G-9. Section C-C’, Vertical Settlement Contour, Loma Prieta Earthquake Figure G-10. Section C-C’, Horizontal Displacement Contour, Northridge Earthquake Figure G-11. Section C-C’, Vertical Settlement Contour, Northridge Earthquake Figure G-12. Section D-D’, Horizontal Displacement Contour, Chuetsu-oki Earthquake Figure G-13. Section D-D’, Vertical Settlement Contour, Chuetsu-oki Earthquake Figure G-14. Section D-D’, Horizontal Displacement Contour, Loma Prieta Earthquake Figure G-15. Section D-D’, Vertical Settlement Contour, Loma Prieta Earthquake Figure G-16. Section D-D’, Horizontal Displacement Contour, Northridge Earthquake Figure G-17. Section D-D’, Vertical Settlement Contour, Northridge Earthquake

Appendix H. Report Limitations and Guidelines for Use

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1.0 INTRODUCTION

This report presents the results of GeoEngineers Inc.’s (GeoEngineers’) geotechnical site investigation for the Phase 2 Manchester Tank Farm Improvements (P-2002) project at Fleet Logistics Center Puget Sound (FLCPS), in Manchester, Washington. The project site is shown relative to surrounding physical features on the Vicinity Map (Figure 1) and the Site Plan (Figure 2A).

GeoEngineers’ services were completed in general accordance with the professional services agreement, between Burns & McDonnell Engineering Company, Inc. (Burns & McDonnell) and GeoEngineers for contract N44255-18-D-2000, Task Order N4425518F4257, dated December 3, 2021. GeoEngineers’ specific scope of services included:

■ Reviewing available geologic/geotechnical data in the project vicinity including previous reports and the TR-NAVFAC-EXWC-CIOFP-1305 report;

■ Completing additional subsurface investigation, including four borings and six test pits (Appendix A);

■ Completing laboratory testing on soil samples obtained from explorations (Appendix B);

■ Providing code updates to previously completed site-specific seismic hazard analysis;

■ Developing earthwork recommendations for the project;

■ Evaluating slope stability for temporary and permanent slopes;

■ Developing recommendations regarding groundwater;

■ Providing foundation recommendations for new structures including above ground fuel storage tanks, reinforced slopes, and retaining walls;

■ Providing recommendations for new pavements; and

■ Preparing this report.

2.0 PROJECT DESCRIPTION

GeoEngineers’ understanding of the project is based on information provided by the United States Navy (Navy) and Burns & McDonnell through telephone conversations, meetings, and email transmittals. The purpose of this study is to evaluate the subsurface conditions for Phase 2 of the proposed MILCON program.

The present-day FLCPS facility operations include fuel storage, receipt, and issue capability for F-76 Diesel, JP-8 Jet Fuel, JP-5 Jet Fuel, and FOR (Fuel Oil Recycled). The tank farm is comprised of 34 underground storage tanks (USTs) built in the 1940s and 1950s and five aboveground storage tanks (ASTs) constructed in 1955. The existing USTs are single-wall concrete tanks.

The proposed MILCON program will consist of three MILCON projects and will provide six 125,000-barrel ASTs with secondary containment. Phases 2 of 3 consists of constructing two of the six ASTs. Phase 1 is currently under construction. The overall MILCON program will replace the capacity currently in the 34 concrete USTs. Phase 2 will also involve the closure of five existing USTs including demolition to support earthwork and final grading for construction of the two new Phase 2 ASTs.

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The proposed ASTs will be constructed in the following phases:

■ Phase 1 – Tanks 801 and 802

■ Phase 2 – Tanks 803 and 804

■ Phase 3 – Tanks 805 and 806

3.0 PREVIOUS STUDIES

The available database of existing geotechnical information and data for the FLCPS includes over 100 unique historical explorations dating back to the 1950s. These explorations include both on-shore and near-shore explorations. Of these historic explorations, only six are located in the vicinity of the planned MILCON program footprint and were completed in 2012 by NAVFAC. Additionally, GeoEngineers completed several borings for Phase 1 of the Manchester Tank Farm project. The approximate locations of these previous explorations are presented in Figures 2A through 2C, and the logs of the explorations are presented in Appendix C, Previous Explorations.

4.0 SITE CONDITIONS

The FLCPS site, located about 1 mile north of Manchester and about 5 miles northeast of Port Orchard, Washington, encompasses the Manchester Peninsula, a small, fist-shaped protuberance on the east side of the Kitsap Peninsula just south of Bainbridge Island, as shown on Figure 1.

4.1. Geologic Setting

The project area is located within the central portion of the Puget Lowland Physiographic Province. The Puget Lowland Physiographic Province consists of a broad, low-lying region of subdued topography situated between the Cascade Range to the east and the Olympic Mountains and Willapa Hills to the west.

The site is located within an uplifted area near the southern upthrusted margin, or hanging wall, of the Seattle fault zone. The Seattle fault zone is the seismically active zone between the Seattle Basin to the north and the Seattle Uplift to the south. South of this zone, bedrock is present at the ground surface and at relatively shallow depths and, to the north, the bedrock basement is several thousand feet below the surface and is overlain by both glacial and non-glacial deposits.

The surficial geologic units mapped across the site consist primarily of exposed Blakely Formation bedrock or relatively thin sequence of glacial deposits over the underlying bedrock. Published geologic information for the project vicinity includes Yount et al. (1993), Washington Division of Geology and Earth Resources (2003), Booth and Troost (2005) and Haugerud (Kilpatrick and Schneider 2013). The geology of the site and surrounding area is shown on the geologic map presented in Figure 4, Regional Geology. Descriptions of the surficial geologic units mapped across the site are as follows (listed youngest to oldest):

■ The area where the proposed MILCON program footprint is proposed to be located is primarily mapped as glacial till (Qvt). Glacial till consists of dense to very dense, non-sorted mixtures of clay, silt, sand, gravel, cobbles, and boulders deposited and consolidated by several thousand feet of glacial ice. The upper 2 to 5 feet of the glacial till is often weathered, and the consistency can range from medium dense to dense within the weathered zone.

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■ Esperance Sand Member of Vashon Drift (Qve) is mapped at the southern edge of the site and generally consists of dense to very dense, stratified, clean to silty sand with variable quantities of gravel and occasional layers or lenses of clay and silt. The sand was deposited by meltwater streams flowing from the advancing Vashon lobe of the Fraser glaciation. The Esperance sand subsequently was overridden and consolidated by several thousand feet of glacial ice.

■ Blakeley Formation (Tbt, Tb, Tbh) sandstone (bedrock) underlies much of the site east of Little Clam Bay and to a lesser degree, along the northern shoreline of the site west of Little Clam Bay. The sedimentary Blakeley Formation bedrock is late and middle Eocene in age and includes fine- to coarse-grained feldspathic to lithofeldspathic subquartzose sandstone with interbedded siltstone, claystone, and coal; derived from fluvial to near-shore marine rocks.

5.0 SEISMICITY

In the Puget Sound region, there are two major source-types that contribute to the seismic hazard: the Cascadia Subduction Zone (CSZ) (which can produce large magnitude subduction-interface earthquakes, and deep subduction-intraslab earthquakes), and the shallow crustal faults. The following sections present brief descriptions of each of the source-types.

5.1. Cascadia Subduction Zone

The Puget Sound region is located near the convergent continental boundary known as the CSZ. The CSZ is formed by the subduction of the oceanic Juan de Fuca and Gorda plates beneath the North American plate, and extends from Vancouver Island, Canada to the Mendocino Escarpment off northern California, United States (Goldfinger et al. 2012). Convergence rates along the plate boundary vary from 30 millimeters per year (mm/y) at the southern end to 45 mm/y at the northern end (McCrory et al. 2012).

The interaction between these converging plates results in two potential earthquake mechanisms:

(1) interface thrust earthquakes, and (2) intraslab earthquakes associated with the Wadati-Benioff zone.

5.1.1. Interface Earthquakes

CSZ interface earthquakes, also referred to as megathrust earthquakes, result from partial or full rupture of the convergent boundary between the subducting oceanic Juan de Fuca and Gorda plates and the overriding continental North American plate. The CSZ is considered to be capable of generating earthquakes up to about moment magnitude (Mw) 9.0 to 9.2. No large earthquakes on the CSZ have been instrumentally recorded; however, paleoseismic evidence from the Washington coast and historical records of an orphan-tsunami in Japan suggest the most recent CSZ event occurred in January 1700 (Atwater 2005; Satake et al. 1996). Recurrence intervals for CSZ interface earthquakes are thought to be on the order of approximately 434 years for Mw 8+ events along the Washington Coast based on offshore turbidite sediment sequences that are interpreted to correlate with Mw 8+ CSZ earthquakes (Goldfinger et

al. 2012, 2013, 2017) and 500 to 600 years for Mw 9 events based on onshore paleoseismic studies in coastal areas of Washington and on Vancouver Island, British Columbia (Atwater and Hemphill-Haley 1997;

Atwater et al. 1995; Blais-Stevens et al. 2011). The combined evidence suggests that up to 23 Mw 8+ earthquakes have occurred on the CSZ along the Washington margin over the past 10,000 years (Goldfinger et al. 2012, 2017). However, Atwater and Griggs (2012) and Atwater et al. (2014) question the synthesis of the Goldfinger et al. turbidite stratigraphy correlations to CSZ great earthquakes that, in Atwater et al.’s opinion, discount variability in turbidite facies.

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5.1.2. Intraslab Earthquakes

Earthquakes associated with the Wadati-Benioff zone are referred to as intraslab, intraplate, or deep-focus earthquakes. The release of geo-fluids during metamorphism can promote earthquake occurrence by enabling stick-slip frictional sliding, due to an increase in pore pressure that yields a decrease in effective normal stress, in material that would otherwise flow in a stable manner (McCrory et al. 2012).

Wadati-Benioff zone earthquakes primarily occur within three geographic areas: at shallow depths beneath western Vancouver Island and beneath northwestern California, and at intermediate depths beneath Strait of Georgia-Puget Sound (McCrory et al. 2012). In western Washington, intraslab earthquakes are concentrated between depths of 30 to 60 kilometers (km).

The 1949 Mw 6.8 Olympia, 1965 Mw 6.6 Seattle-Tacoma, and 2001 Mw 6.8 Nisqually earthquakes (Ichinose et al. 2004; Ichinose et al. 2006) originated on the Wadati-Benioff zone (Wong 2005). The Wadati-Benioff zone is considered to be capable of generating earthquakes up to Mw 8.0 in the 2014 update of the United States National Seismic Hazard Maps (Petersen et al. 2014). Damaging intraplate earthquakes in Western Washington have occurred with an average recurrence of 26 years since 1949.

The mean annual rate for Mw 7.2 to Mw 8.0 intraslab earthquakes occurring in western Washington is estimated to be about 1,000 to 1,600 years (Petersen et al. 2014).

5.2. Shallow Crustal Seismicity

Oblique subduction of the Juan de Fuca plate results in northeast migration of coastal regions of Washington State. This northeast motion is resisted by older, more stable, continental rocks, thereby resulting in compression of the Puget Lowland region of about 4 mm/y. There have been no historical Mw 6.0 or greater shallow crustal fault earthquakes in western Washington. However, post-glacial compression of the Puget Lowland has generated a series of active faults within the lowland, most notably the Seattle fault zone. In addition to the Seattle fault, shallow crustal faults with known or suspected Quaternary displacements within the project area include the Saddle Mountain fault and the Tacoma fault.

The site is located within the southern portion of the Seattle fault zone near its southern boundary, 13 miles northeast of the Tacoma fault zone, and 30 miles east of the Saddle Mountain fault zone.

The Seattle fault zone extends approximately 44 miles (70 km) in the east-west direction across the Puget Lowland from near Hood Canal to the foothills of the Cascade Mountains (Johnson et al. 1999; Liberty and Pratt 2008). This fault zone is comprised of south-dipping thrust faults and north-dipping back thrusts. In the site region, the Seattle fault zone consists of several surface faults and a broad area of uplift on southern Bainbridge Island and the Kitsap Peninsula to the south on the upper plate of the south-dipping, main trace of the Seattle fault. Two fault traces, the Point Glover and Waterman Point faults, are located about 1.8 to 3.4 miles to the north of the site and a Quaternary fault is mapped crossing the Manchester facility (Haugerud 2009; Sherrod et al. 2013). Paleoseismic evidence indicates a magnitude Mw 7.0 to 7.2 earthquake occurred on the Seattle fault between 900 to 930 A.D. that caused broad uplift south of the fault and there have been several additional large earthquakes on the fault in the mid-to-late Holocene (Bucknam et al. 1992; Kelsey et al. 2008; Nelson et al. 2003a, 2003b, 2014; Sherrod et al. 2000; Ten Brink et al. 2006). Per the 2014 United States National Seismic Hazard Map, the estimated recurrence times for large earthquakes of Mw 6.5 to 7.5 on the Seattle fault range from 1,000 to 5,000 years (Petersen et al. 2014).

The Tacoma fault zone is a northwest-southeast trending fault zone ranging up to about 10 miles wide. The Tacoma fault zone consists of a series of faults and folds with a north-dipping reverse fault on its western

September 29, 2022 | Page 5 end. There is a fold above a deeper fault beneath Case Inlet and a fault on its eastern end that exhibit post-glacial deformation (Brocher et al. 2001, 2004; Clement et al. 2010; Johnson et al. 2004; Pratt et al.

1997). Stratigraphic and fault trenching investigations have identified 12 locations of Holocene uplift or subsidence, typically of 1 meter or greater, and post-glacial surface fault scarps up to 6 meters high within the Tacoma fault zone (Sherrod et al. 2004a, 2004b; Nelson et al. 2008, 2014).

Recent evidence suggests the western end of the Seattle fault zone is kinematically linked to active faults that border the Olympic Mountains Massif including the Saddle Mountain fault zone (Barnett et al. 2015;

Lamb et al. 2012). The Saddle Mountain fault zone most recently ruptured the ground about 1,000 years ago, similar to the age of the most recent Seattle fault earthquake. There is also paleoseismic evidence for two earlier Holocene earthquakes, which collectively generated three prominent subparallel fault scarps can be traced for 10 miles (Barnett et al. 2015).

5.3. Manchester Fuel Depot Fault Evaluation

GeoEngineers completed a geologic investigation, which is presented in a separate report, as part of the preliminary site investigation for the Manchester Tank Farm Improvement MILCON program. The following paragraphs summarize the findings of the geologic study.

GeoEngineers reviewed the information presented in the July 2013 seismic study by Kilpatrick and Schneider, with a focus on the study completed by the United States Geological Survey (USGS) (Sherrod et

al. 2013). Sherrod et al. concluded there is an active fault within the project vicinity. Based on GeoEngineers’ review of the Sherrod et al. (2013) report, review of light detection and ranging (LiDAR) data of the area, and surface reconnaissance at FLCPS, we conclude that a fault is present, and the fault is geologically active (i.e., active within the last 10,000 years).

It is our opinion that the fault traces are likely located farther to the north of the trench locations presented in a separate report. Based on the geologic study and fault trenching, there is, in our opinion, a low potential for surface fault rupture within the MILCON program footprint.

6.0 SURFACE CONDITIONS

The site is bordered on the north by Clam Bay, on the east by Puget Sound, and Bainbridge Island across Rich Passage to the northeast. The non-shoreline northern, western, and southern perimeters of the site are bordered by access roads which separate the installation from the surrounding, non-government, property. Several water bodies are present within the site; most notably Little Clam Bay which separates the eastern and western sides of the FLCPS facility.

The topography of the FLCPS facility rises from the surrounding shorelines of Clam Bay/Puget Sound and Little Clam Bay to a maximum elevation relief of about 200 to 240 feet. Generally, the topographic rise and fall across the site is gradual; however, locally steeper areas with percent slope greater than 40 percent are along the shoreline, knolls, and constructed slopes.

Extensive grading has been completed at the FLCPS site as part of construction of the existing tank farm.

Selected historic photographs from the original tank farm construction are included in Appendix E for reference and illustrate some of the historic grading activities.

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In the immediate vicinity of the planned MILCON program (presented on Figure 2B), slopes are generally less than 20 percent; however, locally steeper slopes are present where cut and or fill slopes have been constructed in the immediate vicinity of existing USTs.

6.1. Subsurface Conditions

6.1.1. Soil

The subsurface conditions at the site were further evaluated by completing four borings and six test pits between January 24 and January 27, 2022. The test pit and geotechnical soil boring locations were surveyed by AHBL, Inc. The locations of the test pits and geotechnical soil borings are shown in Figures 2A through 2C.

The borings and test pits were completed in areas of the site with vegetation at the ground surface. The explorations typically encountered fill below the surficial vegetation. The fill encountered in the explorations consists of loose/soft to medium dense/medium stiff sands and silts with variable gravel content. The thickness of the fill deposits encountered in the explorations extended up to 17 feet below existing site grades (besg). Based on review of drawings, photographs, and construction techniques consistent with the period during which the existing USTs were constructed, the fill soils that surround the existing USTs is interpreted to consist of the following:

■ The UST backfill zone is estimated to consist of a zone with a steep cutslope (on the order of 1H:1V [horizontal to vertical]) in the native soils with a 5-foot offset at the base of the cutslope and the perimeter of the existing USTs.

■ Fill material used to backfill the existing USTs consists of on-site soil borrow generated during excavation of the existing USTs or site grading.

■ The backfill surrounding the existing USTs is generally loose to medium dense and was not placed as structural fill.

Glacially consolidated soils were typically encountered underlying the fill and generally consisted of silt with variable sand and gravel content as well as sand with variable silt and gravel content. The glacially consolidated soils extended to the depth explored in each of the borings completed for this study.

Interpreted soil conditions are presented in Cross Sections A-A’ through D-D’, Figures 3A through 3D.

Occasional cobbles and boulders are frequently encountered in glacially consolidated soils and should be expected at the site. Review of the historic photos from the construction of the existing USTs indicates that occasional boulders are present at the site.

6.1.2. Groundwater

Groundwater was encountered at 25½ feet besg in B-21 completed as part of this study. Slow perched groundwater seepage was observed at 4½ feet besg in TP-11.

Perched groundwater should be anticipated locally within cleaner sand layers located above lower permeability soils. Groundwater conditions should be expected to fluctuate as a function of season, precipitation, and other factors.

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7.0 CONCLUSIONS AND RECOMMENDATIONS

A summary of the geotechnical considerations is provided below. The summary is presented for introductory purposes and should be used in conjunction with the complete recommendations presented in this report.

While some of the subsurface information and figures presented or referenced for the report encompassed the footprint of all three phases of the proposed improvements, the design recommendations presented herein are for Phase 2 which encompasses Tank 803 and Tank 804.

■ The site is located within the Seattle fault zone. Research completed by the USGS indicates the presence of a potential earthquake fault(s) at the FLCPS site. GeoEngineers completed a geologic study that included supplemental geophysical testing and fault trenching. The geophysical testing identified an anomaly consistent with a potential fault located near the fault mapped by the USGS. No indication of fault offset, or deformation was observed at the two fault trench locations. Based on GeoEngineers’ review of the USGS research, surface reconnaissance at FLCPS, supplemental geophysical testing and fault trenching, we conclude that an active fault is present at FLCPS and that the fault is most likely located to the north of the area where the trenches were completed. The results of GeoEngineers’ geologic study are presented in a separate report.

■ The planned ASTs for the MILCON program will be located more than 190 feet south of the mapped fault location. The setback between the planned ASTs and the fault is considered acceptable, even with the uncertainty in the fault location. The risk of fault rupture within the footprint of the planned ASTs is considered to be low.

■ Based on site specific shear wave velocity testing, the best-estimate time-averaged shear wave velocity of the upper 30 meters (100 feet) of soil (Vs30) for the site was computed as about 1,470 feet per second (ft/sec). Accordingly, the site is classified as Site Class C per API 650 and ASCE 7-16.

■ Given the site’s location relative to the Seattle fault zone, a site-specific seismic evaluation was completed and is presented in Appendix F. A site-specific risk-targeted maximum-considered earthquake (MCER) response spectrum was developed per ASCE 7-16 Chapter 21. The site-specific response spectrum is to be used only for the design of tanks and tank foundations per Design Clarification DC-024A. Design of other supporting systems and structures should be completed using ASCE 7-16 seismic parameters.

■ Perched groundwater should be anticipated to be encountered within the planned MILCON program footprint. Active dewatering is not anticipated to be required to construct the planned tank farm improvements. Where perched groundwater is encountered, dewatering is anticipated to be completed using casual dewatering by means of sumps and pumps. It is likely to encounter perched groundwater seepage during demolition of the existing USTs and the contractor should be prepared to remove perched groundwater seepage along with precipitation and surface water that flows into the excavations completed to demolish existing USTs.

■ The planned ASTs should bear on structural fill consisting of imported gravel borrow extending down to competent glacially consolidated soils, or on glacially consolidated soils where present at the AST foundation elevation. Existing fill soils should be completely removed down to native glacially consolidated soils prior to placement of imported gravel borrow.

■ The existing fill soils present in the planned MILCON program footprint are not suitable to support settlement sensitive improvements such as cast-in-place retaining walls. Where existing fill is present below planned structures, the fill should be removed and replaced with structural fill.

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■ For small non-tank structures and pipe supports, foundations may bear on competent glacially consolidated soils or on a minimum 2-foot thickness of compacted structural fill overlying existing fill.

■ The soils present within the MILCON program footprint that will be excavated as part of the planned grading are highly moisture sensitive. The following options are available for placement of structural fill for the planned MILCON program:

During extended periods of dry weather (typically June through September), on-site soils are anticipated to be suitable for use as structural fill; however, moisture conditioning should be anticipated to be required to achieve the required compaction criteria (drying of wet soils or wetting of dry soils).

Use imported gravel borrow during periods of wet weather. Imported gravel borrow is anticipated to reliably achieve the required compaction criteria for structural fill during both wet and dry weather conditions and is planned where structural fill is required below Tanks 803 and 804.

■ New cut/fill slopes should be designed at 2H:1V or flatter. Slopes located in areas where existing fill soils are present are more prone to instability, depending on slope inclination. Slopes inclined at up to 1.5H:1V may be used if slopes are reinforced with geosynthetics.

■ Retaining walls can consist of either conventional cast-in-place concrete walls, soldier pile walls or structural earth walls (SEW).

GeoEngineers’ specific geotechnical recommendations are presented in the following sections of this report.

7.1. Earthquake Engineering

7.1.1. Surface Fault Rupture

As discussed in the seismicity section, the potential for surface fault rupture within the tank footprints is considered to be low. Please refer to the separate geologic report for additional detail regarding evaluation of seismic fault(s) at the FLCPS facility.

7.1.2. Liquefaction Potential

Liquefaction refers to a condition in which vibration or shaking of the ground, usually from earthquake forces, results in development of high excess pore water pressures in saturated soils and subsequent loss of stiffness and/or strength in the deposit of soil so affected. In general, soils that are susceptible to liquefaction include very loose to medium dense, clean to silty sands that are below the water table. Based on the unsaturated fill and glacially consolidated soils encountered in our explorations, there is a low potential for liquefaction and liquefaction-induced displacements within the planned MILCON program footprint.

7.1.3. Lateral Spreading

Lateral spreading involves lateral displacement of large, surficial blocks of soils as the underlying soil layer liquefies. Because the potential for liquefaction is low within the planned MILCON program footprint, the potential for lateral spreading is also considered to be low.

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7.1.4. Site-Specific MCER and DE Response Spectra

The results of the geophysical testing completed during the Phase 1 evaluation were used to determine the Site Class. The best-estimate time-averaged shear wave velocity of the upper 30 meters (100 feet) of soil (Vs30) for the site is approximately 1,470 ft/sec. Accordingly the site is classified as Site Class C per

API 650.

The site is located within 10 km of a known active fault. Therefore, per API 650 Section E.4.2, site-specific ground motions following ASCE 7 are required for seismic design of the project. A nonlinear site-specific response analysis was completed to develop the site-specific MCER response spectrum per ASCE 7-16 Chapter 21. The design earthquake (DE) response spectrum is taken as 2/3 of the site-specific MCER response spectrum. Table 1 and Figure F-20 present the recommended site-specific MCER and DE response spectra. Refer to Appendix F for details of the site-specific response analysis. The site-specific response spectrum is to be used only for the design of tanks and tank foundations per Design Clarification DC-024A.

TABLE 1. RECOMMENDED SITE-SPECIFIC MCER AND DE RESPONSE SPECTRA

Period (sec)

5% Damped MCER Spectral Response Acceleration, SaM (g)

5% Damped DE Spectral Response Acceleration, Sa (g)

0.01 1.35 0.90

0.05 1.67 1.11

0.075 2.27 1.51

0.1 2.76 1.84

0.2 3.90 2.60

0.3 3.41 2.27

0.4 2.82 1.88

0.5 2.24 1.49

0.75 1.41 0.94

1 0.90 0.60

2 0.37 0.25

3 0.21 0.14

4 0.16 0.11

5 0.13 0.09

6 0.11 0.07

7.5 0.07 0.05

10 0.04 0.03

7.1.5. ASCE 7-16 Seismic Design Parameters

The ASCE 7-16 seismic design parameters for Site Class, short period spectral response acceleration (SS), 1-second period spectral response acceleration (S1), and seismic coefficients FA and FV are presented in the Table 2. Note that the SS and S1 values in Table 2 are for Site Class B/C boundary conditions. The FA and FV values modify the parameters to the recommended Site Class C. Per Design Clarification DC-024A, September 29, 2022 | Page 10 design of tank farm improvements other than tanks or tank foundations should be completed using ASCE 7-16 seismic parameters.

TABLE 2. ASCE 7-16 SEISMIC DESIGN PARAMETERS

Parameters Recommended Value

Site Class C

Short Period Spectral Response Acceleration – Site Class B/C, SS (g) 1.612

1-Second Period Spectral Response Acceleration – Site Class B/C, S1 (g) 0.560

Seismic Coefficient, FA 1.20

Seismic Coefficient, FV 1.44

7.2. Temporary Dewatering

The regional groundwater table in the MILCON program vicinity is located more than 30 feet bgs and is not anticipated to be encountered during earthwork construction. Perched groundwater is expected to be present locally within the planned excavation depth. Active dewatering is not anticipated to be necessary to complete the planned excavations. Localized sumps and pumps should be anticipated for temporary dewatering associated with perched groundwater seepage and removal of surface water from precipitation.

Surface water flows should be diverted and dispersed in a manner that does not alter stability of existing or temporary slopes. It is likely to encounter perched groundwater seepage during demolition of the existing USTs and the contractor should be prepared to remove perched groundwater seepage along with precipitation and surface water that flows into the excavations completed to demolish existing USTs.

Groundwater flow rates of up to 10 gallons per minute can be assumed for the planned excavation. Surface water from rainfall will likely contribute significantly to the volume of water that needs to be removed from the excavation during construction and will vary as a function of season and precipitation.

7.3. Decommissioning of Existing Underground Storage Tanks

Existing USTs within the project area will be decommissioned as part of this project.

■ Existing UST lids are anticipated to be demolished.

■ Where new ASTs will be constructed above existing USTs, the existing UST walls should be removed where they are located within a 0.5H:1V projection from the new AST ringwall. This will provide uniform bearing for the new ASTs and will eliminate hard points that may result in differential settlement of the new ASTs.

■ Concrete from the demolition of the existing improvements should be disposed of per environmental recommendations.

7.4. Environmental Field Screening and Chemical Analytical Testing

As part of the Phase 1 geotechnical site investigation, field screening (sheen and headspace vapor testing) was completed on soil samples obtained from the explorations; no sheen or vapor concentration was observed. Additionally, chemical analytical testing (petroleum screen NWTPH-HCID and total lead) was completed on selected samples obtained from the explorations. The results of the chemical analytical testing are presented in the chemical analytical data report, under separate cover.

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7.5. Aboveground Storage Tanks Foundation Support

Based on the soil conditions encountered in the explorations completed for this study and the planned finish floor elevations of the MILCON program ASTs, existing fill or glacially consolidated soils are present at the planned AST foundation elevations for Tank 803 and Tank 804. The existing fill is not suitable for foundation support and will be removed and replaced with structural fill. The native glacially consolidated soils represent competent bearing for the planned ASTs.

The planned ASTs should bear on properly compacted structural fill extending down to glacially consolidated soils or on glacially consolidated soils where present at the foundation subgrade elevation.

Where structural fill is used below Tanks 803 and 804, the structural fill should be compacted to at least 95 percent of the maximum dry density (MDD) per ASTM International (ASTM) D1557 and should consist of imported gravel borrow.

For Tanks 803 and 804, excavation will be required to remove the existing fill (much of which is associated with the backfill for the existing UST’s 26 and 27 which will be demolished prior to construction of Tanks 803 and 804) down to the dense to very dense/hard glacially consolidated soils. The zone of imported gravel borrow that will replace the unsuitable existing fill materials for Tanks 803 and 804 should be located between the glacially consolidated soils and a 1H:1V projection from a 5-foot offset from the tank footprint (fill above a 1H:1V projection/outside the zone of influence of the AST may consist of common borrow).

7.5.1. Allowable Bearing Pressure

The planned ASTs can be supported at-grade on structural fill extending down to glacially consolidated soils (or glacially consolidated soils where present at the tank foundation elevation) with the tank shells supported on reinforced concrete ringwall foundations. We recommend using an allowable bearing pressure of 5 kips per square foot (ksf). The allowable soil bearing pressure applies to the total of dead and long-term live loads and may be increased by up to one-third for wind or seismic loads.

7.5.2. Tank Settlement

Settlement analyses for the proposed tank foundations were completed for Tanks 803 and 804 using the computer program Settle3D developed by RocScience, Inc. A tank diameter of 146 feet was used for the settlement analyses. The results of the analyses are summarized in Table 3 below.

The settlement analyses were completed for the condition where the existing fill was replaced with structural fill. The settlement values presented in Table 3 include the maximum estimated static settlement below the AST and the range in settlement at the AST ringwall. For the settlement values presented in Table 3, a uniform pressure of 4 ksf, representing the maximum dead plus long-term live loads, was modeled.

Tanks 803 and 804 have a mixed bearing profile with glacially consolidated soils near the foundation elevation on one side of the tank and a thicker profile of structural fill on the other side.

TABLE 3. ESTIMATED AST FOUNDATION SETTLEMENT

AST ID Bearing Profile Structural Fill/Improved Ground Thickness

Estimated Elastic Settlement (in)

Center Edge

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Tank

Mixed Glacial and Structural Fill 22 feet 1 to 1½ ¾ to 1

Tank

Mixed Glacial and Structural Fill 28 feet 1 to 1½ ¾ to 1

Settlement monitoring of the hydrotesting program is recommended to confirm that the settlement response of the foundation soils is consistent with estimated performance prior to making final piping connections and product filling.

Given the unsaturated granular soils and competent glacially consolidated soils at the site, settlement is anticipated to result from elastic response of the foundation soils to the applied AST loads. This settlement is anticipated to occur as the load is applied. No significant long-term (consolidation) settlement is anticipated because saturated cohesive soils are not present within the planned Tank 803 and Tank 804 footprints.

7.5.3. Lateral Resistance

Lateral foundation loads may be resisted by passive resistance on the sides of ringwall footing and by friction on the base of the ringwall foundation and AST. For ringwall foundations supported on structural fill/improved ground or glacially consolidated soils, the allowable frictional resistance may be computed using a coefficient of friction of 0.5 applied to vertical dead-load forces. The allowable frictional resistance for the AST is a function on the nature of the flexible membrane liner placed below the AST.

The allowable passive resistance may be computed using an equivalent fluid density of 400 pounds per cubic foot (pcf) (triangular distribution). This allowable passive resistance value is appropriate for ringwall foundation elements that are backfilled with properly compacted structural fill.

The above coefficient of friction and passive equivalent fluid density values incorporate a factor of safety of about 1.5.

7.5.4. Construction Considerations

For Tanks 803 and 804, if ringwall construction occurs during wet weather conditions, it will be necessary to protect the ringwall subgrade from softening through the use of a 6-inch-thick layer of compacted crushed surfacing base course (CSBC) or a 4-inch-thick concrete rat slab.

We recommend that the preparation of the AST and ringwall foundations be observed by a licensed geotechnical engineer. This includes geotechnical special inspection during placement of structural fill, installation of ground improvement, and preparation/protection of the AST and ringwall subgrades.

7.5.5. Aboveground Storage Tank Hydrotesting

We recommend the controlled hydrotest be conducted according to API standards and guidelines including API 653. Before being placed into service, we recommend that the new ASTs be tested using a controlled and monitored, stage-loaded hydrotest. Hydrotesting generally consists of filling the AST with water after construction under controlled conditions to:

■ Check the competency of the welding, September 29, 2022 | Page 13

■ Verify the ability of the foundation materials to carry the loads imposed by the tank and its contents, and

■ Reduce the amount of settlement that the tank will experience after being placed in service.

7.5.5.1. Survey Control

We recommend that a series of reference points be established around the tank shells and that movements are monitored during hydrotesting. According to API specifications, the number of survey points should be equal to or greater than the tank diameter divided by 10 (and rounded up to the next whole number). The reference points should be equally spaced around the tank perimeter. The spacing between adjacent reference points should not exceed 30 feet. The elevations of the reference points should be measured prior to, during, and after hydrotesting to monitor tank movements. Elevation readings should be taken to the nearest 0.01 feet. Readings should be referenced to a benchmark located a sufficient distance from the tank being tested and surrounding tanks and structures (at least one tank diameter) such that the readings are not influenced by the movement of the tanks and other structures. In addition, a control should be established on the tank bottom to monitor movement before and after hydrotesting.

7.5.5.2. Tank Loading for Hydrotesting

We suggest that, initially, water for the hydrotest be added until reaching one-half (½) of the full tank height.

This water level should be maintained until settlement observations indicate no additional movement is occurring, the rate of settlement has decreased significantly according to predetermined criteria, or at least 1 week. Additional stage-loading increments should include three-quarters of the full tank height. After reaching a water level equal to about three-quarters of the full tank height, the full tank height should be applied. Each level should be maintained until settlement readings are smaller than a predetermined range as recommended by API or no greater than ⅛ inch over a 24-hour period. We recommend constructing any permanent piping connections to the tank only after hydrotesting has been completed.

7.5.5.3. Data Evaluation

Settlement observations should be reviewed as the hydrotesting proceeds to assess total settlement, differential settlement, local slope, tank tilt, and out-of-plane distortion. The structural engineer should establish criteria for acceptable settlement. If settlements begin to approach unacceptable limits, filling should be halted and not resumed until the situation is reviewed and evaluated by the structural engineer.

Settlement observations should be obtained frequently (preferably daily) to develop the data necessary to assess tank performance.

7.6. Shallow Foundations – Non-Tank Structures

Shallow foundations will be needed for non-tank structures including piping supports, small road bridges and dike retaining walls. The allowable bearing pressure for non-tank structures will depend on whether the foundations will bear on competent glacially consolidated soils or properly compacted structural fill extending down to glacially consolidated soils or if the foundations will be founded in areas where existing fill soils are present.

■ Foundations bearing in areas of the site where existing fill soils are present should bear on a minimum of 2-feet of compacted structural fill. For this condition, the foundations may be designed and proportioned using a maximum allowable soil bearing pressure of 2,500 pounds per square foot (psf) for dead plus live loads. If foundations are designed as a beam on an elastic foundation a subgrade modulus of 20 pound per cubic inch, (pci) may be used for design.

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■ Foundations bearing on competent glacially consolidated soils or properly compacted structural fill extending down to glacially consolidated soils may be designed and proportioned using a maximum allowable soil bearing pressure of 5,000 psf for dead plus live loads. If foundations are designed as a beam on an elastic foundation a subgrade modulus of 35 pci may be used for design.

■ The allowable soil bearing pressure may be increased by up to one-third for wind or seismic loads.

■ We recommend that individual column footings and continuous wall footings have minimum widths of 24 and 18 inches, respectively. The exterior footings should be founded a minimum of 18 inches below the lowest adjacent grade for frost protection.

7.6.1. Lateral Resistance

Lateral foundation loads may be resisted by passive resistance on the sides of foundations and by friction on the base of the foundation. For non-tank foundations supported as described above, the allowable frictional resistance may be computed using a coefficient of friction of 0.4 applied to vertical dead-load forces.

The allowable passive resistance may be computed using an equivalent fluid density of 400 pounds per cubic foot (pcf) (triangular distribution). This allowable passive resistance value is appropriate for foundation elements that are backfilled with properly compacted structural fill.

The above coefficient of friction and passive equivalent fluid density values incorporate a factor of safety of about 1.5.

7.6.2. Construction Considerations

The structural fill and glacially consolidated soils are susceptible to softening from water or construction traffic. If foundation construction occurs during wet weather conditions, it will be necessary to protect the subgrade from softening through the use of a 6-inch-thick layer of compacted CSBC or a 4-inch-thick concrete rat slab.

We recommend that the preparation/protection of the foundation subgrades be observed by a licensed geotechnical engineer. This includes geotechnical special inspection during placement of structural fill and preparation of the foundation subgrades.

7.7.