Geotechnical Data Report_IliuliukBay.pdf

FINAL SUBMITTAL

REVISION 0

OFFSHORE GEOTECHNICAL INVESTIGATION

GEOTECHNICAL DATA REPORT

ILIULIUK BAY CHANNEL NAVIGATION IMPROVEMENTS

UNALASKA (DUTCH HARBOR), ALASKA

CONTRACT NO. W911KB-22-D-0002

DELIVERY ORDER NO. W911KB-22-F-0057

PREPARED BY:

R&M CONSULTANTS, INC.

9101 VANGUARD DRIVE

ANCHORAGE, AK 99507

PREPARED FOR:

U.S. ARMY ENGINEER

DISTRICT, ALASKA

CEPOA-EC-G-GM, COLEMAN CHALUP

2204 TALLEY AVE

JBER, AK 99506

15 NOVEMBER 2022

15 November 2022 R&M No. 2930.03

Mr. Coleman Chalup Contracting Officers Representative U.S. Army Corps of Engineers, Alaska District JBER, Alaska 99506

RE: Final Geotechnical Data Report Iliuliuk Bay Channel Navigation Improvements

Unalaska (Dutch Harbor), Alaska IDIQ Contract for Geotechnical Design and Related Services

Contract No. W911KB-21-D-0002, Delivery Order No. W911KB-22-F-0057

Dear Mr. Chalup:

Enclosed, please find our final geotechnical data report prepared for the above referenced project. This work has been completed in accordance with Contract No.

W911KB-21-D-0002, Delivery Order No. W911KB-22-F-0057.

We trust that this report is found to be responsive to your requirements and addresses the submitted review comments. Should you have any questions or desire for additional information, please do not hesitate to call. It has been a pleasure to be of service to the USACE Alaska District on this effort.

Sincerely, R&M CONSULTANTS, INC.

Robert M Pintner, P.E.

Group Manager: Geotechnical Engineering and Geology

GEOTECHNICAL DATA REPORT – FINAL USACE

ILIULIUK BAY CHANNEL NAVIGATION IMPROVEMENTS UNALASKA (DUTCH HARBOR), ALASKA

November 2022 Page i R&M No. 2930.03

GEOTECHNICAL DATA REPORT

ILIULIUK BAY CHANNEL NAVIGATION IMPROVEMENTS

UNALASKA (DUTCH HARBOR), ALASKA

The following report presents the results of R&Ms geotechnical investigation completed to support design and construction of the programed Iliuliuk Bay Channel Navigation Improvements project at Unalaska (Dutch Harbor), Alaska. The report includes discussion and results associated with R&Ms geotechnical subsurface exploration, and laboratory testing. The geotechnical engineering services performed by R&M Consultants, Inc. were authorized by the USACE under Contract No. W911KB-21- D-0002, Delivery Order No. W911KB-22-F-0057.

This report includes both factual and interpretative information and is intended to provide the project designers, construction inspectors, and construction contractors with a summary of the geotechnical conditions expected at the site, and to qualify a baseline for assessing changes in geotechnical conditions if or when they are suspected during construction. This report is intended solely for use by USACE and its contractors directly involved with the Channel Navigation Improvements project design and construction; contingent upon the reader possessing basic understanding of geotechnical terminology and principles, as well as the referenced documents.

R&M Consultants, Inc. has performed this work in a manner consistent with the level of skill ordinarily exercised by members of the profession currently practicing under similar conditions. No warranty, express or implied, beyond exercise of reasonable care and professional diligence, is made. R&Ms services for the project were performed by, or under the responsible charge of the individuals listed below.

Alan L. Pasikowski Staff Engineer

Aaron T. Banks, C.P.G Senior Geologist

REVIEWED BY:

Robert M. Pintner, P.E.

Group Manager: Geotechnical Engineering and Geology

11/15/2022

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TABLE OF CONTENTS

Page Preface and Signatures ............................................................................................................................ i Table of Contents ..................................................................................................................................... ii List of Tables ............................................................................................................................................. iv List of Figures ........................................................................................................................................... iv List of Appendices ................................................................................................................................... iv Acronyms and Abbreviations ................................................................................................................ v Executive Summary ................................................................................................................................ vi

Introduction

1.1 Background

1.2 Contract Authorization

1.3 Concept Plan

1.4 Investigation Objectives

1.5 Purpose and Scope-of-Work

1.6 Previous Investigations

1.7 Geotechnical Work Plan Deviations

1.7.1 Modification 1: Test Hole Positioning and Locating

1.7.2 Modification 2: Early Termination of AP-025

1.7.3 Modification 3: Location Shift of AP-031

1.7.4 Modification 4: LPT Sample Interval Adjustment

Regional Setting and General Site Conditions

2.1 Regional Setting

2.1.1 Location

2.1.2 General Geology

2.1.3 General Seismicity

2.1.4 Climate

2.2 General Site Conditions

2.2.1 Topography & Drainage

2.2.2 Seafloor Topography

2.2.3 Tides and Currents

2.2.4 Vegetative Cover

2.2.5 Soils

2.2.6 Bedrock

2.2.7 Groundwater

2.2.8 Thermal Conditions

2.2.9 Geologic Hazards

Geotechnical Investigation Methods

3.1 Drilling Platform

3.2 Test Boring Positioning

3.3 Test Borings

3.4 Environmental Sampling

3.5 Backfilling

3.6 MEC Avoidance Program

3.7 Marine Mammal Observation

Geotechnical Laboratory Testing Program

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4.1 Index Tests and Soil Classification

Data Processing and Interpretation

5.1 Test Boring Logs

5.2 Determination of Groundwater

5.3 Determination of the Thermal State of Soils

Conditions

6.1 Surface

6.2 Soil Conditions

6.2.1 Unit I – Cobble and Boulder Armor Layer

6.2.2 Unit II – Glacial Till

6.3 Bedrock Conditions

6.4 Groundwater

6.5 Thermal Conditions

6.6 Geologic and Seismic Hazards

Conclusions References

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LIST OF TABLES

Table 2-1: Dutch Harbor Climatological Data Table 3-1: Summary of R&M Test Borings, Iliuliuk Bay Channel Navigation Improvements Table 5-1: Laboratory Analysis Methods Table 6-1: Extents of Subsurface Units, Iliuliuk Bay Table 6-2: Unit I – Marine Sands Soil Properties Table 6-3: Unit II – Glacial Till Properties

LIST OF FIGURES

Figure 2-1: Unalaska Island Regional Geologic Map Figure 6-1 Marine Shoal Corrected Blow Count Densities

LIST OF APPENDICES

Appendix A – Site Maps and Geotechnical Cross Sections Location and Vicinity Map ....................................................................................................................... A-01 Investigation Location Map.................................................................................................................... A-02

Appendix B – Test Boring Logs General Notes .............................................................................................................................................. B-01 Explanation of Selected Symbols ......................................................................................................... B-02 Test Boring Logs AP-025 thru AP-031 ................................................................................ B-03 thru B-12

Appendix C – Laboratory Testing Results Classification of Soils for Engineering Purposes ASTM D 2487 ................................................... C-01 Summary of Laboratory Soils Data .................................................................................. C-02 thru C-08 Gradation Curves ............................................................................................................... ….C-09 thru C-20

Appendix D – Photograph Log Photograph Log ...................................................................................................................... D-01 thru D-04

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ACRONYMS AND ABBREVIATIONS

AP auger point ASCE American Society of Civil Engineers ASTM ASTM International bgs below ground surface DWG drawing eTrac eTrac, Inc.

GDR geotechnical data report GPS Global Positioning System I.D. inside diameter

in. inches LPT large penetration test MLLW mean lower low water MMO marine mammal observation N, n, No. number NAD83 North American Datum of 1983 NOAA National Oceanic and Atmospheric Administration O.D. outside diameter R&M R&M Consultants, Inc.

SOW statement of Work SPT standard penetration test TH test hole USACE-AD United States Army Corp of Engineers – Alaska District USCS Unified Soil Classification System WRCC Western Region Climate Center

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EXECUTIVE SUMMARY

The U.S. Army Corps of Engineers, Alaska District (USACE-AD) is conducting an offshore geotechnical investigation to provide design information for constructing the Iliuliuk Bay Channel Navigation Improvements project, located in Unalaska (Dutch Harbor), Alaska. R&M Consultants, Inc. (R&M), under contract with the USACE, performed a geotechnical field investigation at the site during the period of 10 September through 17 September 2022. The geotechnical investigation included drilling test borings, sampling, and laboratory testing. Especially significant was determination of the characteristics and index properties of the site soils. This report presents a summary of results from R&Ms field subsurface exploration program and our interpretation of geotechnical site conditions including geologic and seismic hazards.

The project area is located at the entrance to Dutch Harbor located between Amaknak Island and Unalaska Island, Alaska. Seafloor topography at the site is dominated by an underwater shoal trending northwest to southeast. It is understood that development at the project site will include excavation of a dredge prism to about -60 feet to allow for increased harbor operation efficiency at Dutch Harbor for deep draft ships and to provide a port of refuge for vessels requiring emergency anchorage while en route to the Arctic Ocean, Asia, and Europe via the Northern Sea Route. Other than the proposed footprint of the dredge prism; no other design information was provided.

A total of seven test borings were drilled and sampled by R&M, ranging in depth from 18.8 to 82.0 feet. The total footage drilled during this investigation was about 245 feet. Laboratory testing of soil samples obtained during the field program was also undertaken for the purposes of material classification and obtaining various index properties of the materials encountered.

Subsurface soils are interpreted to consist of two primary units; a cobble and boulder armor layer (Unit I), over glacial till (Unit II).

The northwestern portion of the shoal is interpreted to be armored with a layer of subrounded to subangular cobbles and boulders of varying thickness. This armor layer was most likely formed from the erosion of fines (sands and silts) due to wave action transporting the fines off the shoal, into deeper surrounding waters, and leaving the cobbles and boulders remaining on the shoal. Evidence of these cobbles and boulders was observed during sediment sampling operations both in recovered samples and in limited underwater video collected along the shoal (R&M, 2017).

The matrix of this armor layer unit generally consists of poorly graded gravel with sand to well graded sand with gravel. Due to the ability of the drilling system to potentially bypass surface cobbles and boulders, and the limited areal coverage of the project with drill tooling, this armor layer may be far more widespread than indicated by this geotechnical investigation.

A heterogenous deposit of glacial till consisting of highly varied soil units composed predominantly of coarse-grained, gravelly soils with varying amounts of sand and fines containing cobbles and boulders was interpreted to extend from mudline to 82.0 feet bgs in test borings drilled at the project site. This unit contained predominantly coarse grained, gravelly soils containing cobbles and boulders and varying amounts of sand and generally non-plastic silt.

The project area is predominately located offshore within Iliuliuk Bay. One test boring, drilled on the terrestrial marine spit, encountered groundwater at about 5 feet bgs. Offshore test borings were in water varying from 45.2 feet MLLW to 54.7 feet MLLW.

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Based on the results of this geotechnical investigation, the potential geologic hazard considered most likely to affect long term performance of the Iliuliuk Bay Channel Navigation Improvements project are earthquakes (strong ground shaking) and liquefaction.

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INTRODUCTION

The U.S. Army Corps of Engineers, Alaska District (USACE-AD) retained R&M Consultants, Inc. (R&M) under Contract Number W911KB-21-D-0002, Delivery Order Number W911KB-22-F-0057 to manage and conduct an offshore geotechnical investigation for the Dutch Harbor Channel Navigation Improvements Study in Unalaska, Alaska. R&M subcontracted Discovery Drilling, Inc. to provide offshore geotechnical drilling services. A floating platform (RMG 300), provided by Resolve Marine Services, was utilized as the platform to perform the geotechnical investigation activities. R&M field geologists and engineers were on-site throughout the duration of the project to provide geotechnical sampling and logging services and to maintain daily logs of investigation activities.

Additionally, USACE-AD representatives were on-site throughout applicable portions of the project to provide project management and marine mammal observation services.

1.1 BACKGROUND

The USACE-AD has been conducting a channel navigation improvements feasibility study at the entrance to Iliuliuk Bay, between Amaknak Island and Unalaska Island. A shoal which crosses the channel limits access to Dutch Harbor by deep draft vessels. The Government’s feasibility study evaluates the benefits of channel dredging, to an elevation of about -60 feet, to alleviate the harbor access limitations.

In 2017, the USACE-AD contracted R&M, in association with eTrac, Inc. (eTrac), to provide marine geophysical survey and bathymetric survey services (R&M, 2017). Results from this marine geophysical survey indicated that the shoal structure was most likely glacial in origin and had experienced some post depositional consolidation resulting in a dense structure with dredging characteristics similar to some weaker rocks. Materials within the shoal were expected to consist of a consolidated, unsorted and unstratified heterogeneous mixture of clay, silt, sand, gravel and cobbles and boulders ranging widely in size and shape.

This report presents the results of the subsurface geotechnical investigation, and our interpretation of site conditions.

Site descriptions and subsurface conditions presented herein are based on our current understanding of the project and location as outlined within and illustrated on the drawings included in the appendices to this report. Any deviation from the proposed location would necessitate further evaluation of subsurface conditions.

1.2 CONTRACT AUTHORIZATION

This study has been conducted under the terms of Contract No. W911KB-21-D-0002 between the USACE-AD and R&M. This report is in specific fulfillment of Delivery Order No. W911KB-22-F-0057 of the contract. Measurements and weights presented in this report are generally shown as U.S.

Customary Units.

1.3 CONCEPT PLAN

The Iliuliuk Bay Channel Navigation Improvements project is planned to provide a dredge channel at the entrance to Iliuliuk Bay. This channel is intended to increase harbor operation efficiency at Dutch Harbor for deep draft ships and to provide a port of refuge for vessels requiring emergency

November 2022 Page 2 R&M No. 2930.03 anchorage while en route to the Arctic Ocean, Asia, and Europe via the Northern Sea Route. Water depths in this area have been surveyed at depths as shallow as -42 feet. It is understood that in order to assure safe passage for deep draft vessels making routine or emergency stops in Dutch Harbor, the USACE wishes to establish a dredged channel to about -60 feet in elevation.

Drawings A-01 through A-02 of Appendix A provide location and vicinity, and test boring location maps.

1.4 INVESTIGATION OBJECTIVES

The Alaska District-Corps of Engineers is conducting a Dutch Harbor Navigation Improvements feasibility study to support proposed dredging operations of a shallow bar structure (e.g., shoal) at the entrance to Dutch Harbor. This offshore geotechnical investigation is intended to provide sub bottom stratigraphy information.

The geotechnical investigation specifically focused on the following provisions:

• Characterization of the stratigraphic and geologic characterization of sediment, soil, and/or bedrock underlying the defined geophysical survey area.

• Description of the nature of the shallow bar structure.

• Definition of the relevant engineering properties of sea floor material expected within and adjacent to the planned dredge limits.

Drawings A-01, and A-02 of Appendix A provide a location, vicinity map and a project layout map of the project area.

1.5 PURPOSE AND SCOPE-OF-WORK

The purpose of this geotechnical investigation was to gather data on geologic and geotechnical conditions that could affect site planning, design, and construction of the proposed Channel Navigation Improvements project. The investigation provides specific geotechnical design information for earthwork, and construction at the proposed site. Geotechnical investigation consisted of drilling, sampling, and laboratory testing.

Geotechnical investigation services consisted of office research, geotechnical drilling, sampling, and laboratory testing. Of special significance was the determination of the classification of the index properties of the site soils.

A Statement of Work prepared by USACE, dated 22 April 2022, summarizes the Scope-of-Work for this project as follows:

• Provide management, subcontracted labor, materials, tools, equipment, and transportation necessary to perform the field work.

• Provide coordination of scheduling with USACE and Dutch Harbor personnel.

• Collection of daily logs of all operations, observations, and measurements.

• Provide a subcontract drilling contractor.

• Provide management of drilling, soil sampling, backfilling, and plugging of borings, moving between borings, and cleaning the work areas.

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• Provide all supervision, labor, materials, tools, and equipment necessary to perform laboratory testing of soils.

• Prepare draft and final soil laboratory test reports presenting the results of laboratory testing.

Test boring depths and locations were specified by the USACE-AD in the SOW.

1.6 PREVIOUS INVESTIGATIONS

In August 2015, a Geotechnical Feasibility Report was published in support of the Dutch Harbor Navigation Improvements by the USACE. It details several previous investigations within the Dutch Harbor area, however; the previous investigations revealed mostly historical, environmental, and economical documentation with very little geologic or geotechnical data relevant to the geophysical survey area (USACE, 2015).

In April 2017, a Geophysical Survey Report was published in support of the Dutch Harbor Navigation Improvements by R&M for the USACE. It details the finding of a geophysical survey performed at the project site. Results from this investigation indicate that the general sub bottom profile revealed by the geophysical survey consisted of dense glacial till (or possibly bedrock) overlain by granular sediments, up to 100 feet thick. The overlying unconsolidated materials are interpreted to consist primarily of sand and gravel, with some silt (R&M, 2017)

Several other previous investigations including Preliminary Assessments (NAVFAC, 2013), Site Inspections (NAVFAC, 2016), Reconnaissance Studies (Tryck Nyman Hayes, 1995) and Underwater Surveys (Jacobs, 1999) have been performed within the Dutch Harbor and Unalaska Island area.

Results from these studies document that the U.S. Navy established a significant presence in the Unalaska-Dutch Harbor area during the World War II era, from approximately 1940 through 1944.

Dutch Harbor is currently the operations center for commercial fishing in the Bering Sea, servicing both the large domestic fleet and foreign vessels fishing for ground-fish and crab.

1.7 GEOTECHNICAL WORK PLAN DEVIATIONS

Four modifications of the approved work plan (R&M, 2022) geotechnical scope occurred during completion of the investigation and were as follows:

1.7.1 MODIFICATION 1: TEST HOLE POSITIONING AND LOCATING

Offshore test boring locations were established utilizing recreational grade GPS techniques. The drilling platform would be maneuvered into position using the Makushin Bay and sometimes a secondary tug. A combination of spuds and anchors would then be utilized to secure the drilling platform at the location of the proposed test borings. The final locations of the test borings were then established utilizing survey grade GPS techniques. Due to the complexity of maneuvering to and securing the drilling platform over proposed locations, the actual location versus the proposed location sometimes differed by as much as 100 feet. This was discussed with the on-site COR (Justin Miller) and it was determined that this variance was acceptable and still allowed the project team to meet project objectives.

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1.7.2 MODIFICATION 2: EARLY TERMINATION OF AP-025

While drilling AP-025, the project team became aware of the approach of Former Typhoon Merbok which threatened to severely impact our ability to conduct offshore drilling operations. Aaron Banks discussed this development with the on-site COR and made the decision to terminate AP-025 at 18.8 feet and move over to AP-029 and AP-030. The reasoning behind this decision was to increase our areal understanding of site conditions prior to experiencing any potential serious impacts from the Merbok storm system. This decision was reviewed by the project COR (Coleman Chalup) and a variance was granted to terminate AP-025 at 18.8 feet. This variance was granted in part due to AP- 025 terminating at -73.5 feet in elevation or about 13.5 feet below any planned dredging depths.

1.7.3 MODIFICATION 3: LOCATION SHIFT OF AP-031

Upon arrival on-site, the R&M surveyor located the proposed position of the onshore test boring, AP-031. Aaron Banks then reviewed the proposed location and began coordinating with the landowner (Ounalashka Corporation) for access approval. Conditions at the proposed site precluded access by the project drill rig and Ounalashka Corporation had some concerns about potential archeological impacts. R&M then proposed that the borehole be moved about 85 feet to the north-northeast to a developed portion of the marine spit. Access approval was then granted by Ounalashka Corporation and the new test boring location was resurveyed. This variance was detailed in daily reports and the variance was approved by the project COR.

1.7.4 MODIFICATION 4: LPT SAMPLE INTERVAL ADJUSTMENT

Due to variable swell amplitude and limited drilling stroke, LPT samples were collected as close to planned intervals as conditions allowed and under approval of the COR.

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REGIONAL SETTING AND GENERAL SITE CONDITIONS

2.1 REGIONAL SETTING

2.1.1 LOCATION

The geotechnical investigation area is located at the entrance to Dutch Harbor located between Amaknak Island and Unalaska Island, Alaska. The area is bounded on the northwest by an exposed marine spit that extends into the harbor approximately 6,500 feet and is bounded on the southeast by steep bedrock walls rising from the ocean surface. To the northeast lies the expansive Bering Sea, while to the southwest, lies Dutch Harbor proper and the City of Unalaska.

2.1.2 GENERAL GEOLOGY

The project area lies in the Aleutian Islands physiographic province. These islands are a chain of islands surmounting the crest of a submarine ridge 1,400 miles long, 20 to 60 miles wide, and 12,000 feet high above the sea floor on either side. The linear chain of volcanos on the north side of the islands is of constructional origin and late Cenozoic age and includes many calderas. The remaining islands appear to be emerged parts of tilted fault blocks consisting chiefly of faulted and folded Cenozoic volcanic rocks, locally mildly metamorphosed; granitic intrusions of Cenozoic age are present on Unalaska, Sedenka, Ilak and other islands (Wahrhaftig, 1965).

During the late Pleistocene, glaciers covered much of Unalaska Island, excluding the Makushin Volcano cone. The entirety of Dutch Harbor proper is inferred to have been glaciated up to 13 miles offshore based on submarine topography (Coulter, 1965). Submarine moraines have been mapped north of Unalaska Bay and are interpreted to form the Chelan Bank as shown on Figure 2-1. The upland areas at the project area are considered to generally be free of permafrost (Ferrians, 1965).

Much of the island is discontinuously veneered by a thin mantle of till, volcanic ash, humus and soil.

The project area lies within an area mapped as containing the oldest rocks on the island, the Unalaska formation. This formation consists of altered andesitic intrusive and extrusive rocks and sedimentary rocks derived from similar rocks. Conglomerates and coarse breccias are the dominant sedimentary rocks in the northern and eastern part of the island (Drewes et al., 1961).

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FIGURE 2-1: UNALASKA ISLAND REGIONAL GEOLOGIC MAP (Drewes et al., 1961)

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FIGURE 2-1: UNALASKA ISLAND REGIONAL GEOLOGIC MAP (CONTINUED)

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2.1.3 GENERAL SEISMICITY

Unalaska Island is located about midway along the Aleutian Arc, a 1,900-mile long arcuate chain of mountain ranges extending from the Russian Kamchatka Peninsula to Cook Inlet, Alaska. The Aleutian Arc forms the northern rim of the Pacific Ocean basin, where the Pacific and North American lithospheric plates are converging at an average rate of about 3.3 to 3.5 inches per year.

This on-going convergence results in southern Alaska and the Aleutian Arc being one of the most seismically active regions in the world. This region has experienced the largest magnitude earthquakes and largest measured co-seismic deformations recorded in North America.

2.1.4 CLIMATE

Unalaska and Dutch Harbor are subject to a Maritime climate regime, characterized by heavy precipitation, moderate winters, and cool summers. Storms are frequent and violent williwaws are experienced with southerly gales and winds from the southeast, southwest and northeast sometimes attaining hurricane velocity (Tryck Nyman Hayes, 1995).

The weather is usually characterized by wind, rain, fog, and overcast skies. Based on climate data recorded at the Dutch Harbor weather station from 1951 to 2006: the mean annual air temperature is approximately 40.9 °F, with mean monthly averages ranging between approximately 32.2 °F (February) and 53.5 °F (August); and the area received an average of about 62.7 inches of precipitation per year, with about 88.5 inches of snow (WRCC, 2022).

A summary of climatological data obtained from the Dutch Harbor recording station is presented in Table 2-1.

TABLE 2-1: DUTCH HARBOR CLIMATOLOGICAL DATA

Weather Station Parameter Dutch Harbor (Station No. 502587)

Period of Record 1951 to 2006 Mean Annual Temperature (°F) 40.9

Mean Max. Daily Temperature (°F) 46.0 Mean Min. Daily Temperature (°F) 35.8

Record High Temperature (°F) 79 (13 August 2001) Record Low Temperature (°F) -8 (22 January 1986)

Mean Annual Precipitation (in.) 62.71 Mean Maximum Monthly Precipitation (in.) 8.18 (December)

Maximum Daily Precipitation (in.) 4.8 (20 July 2003) Mean Annual Snowfall (in.) 88.5

Mean Maximum Monthly Snowfall (in.) 23.0 (January) Maximum Monthly Snowfall (in.) 93.0 (January 2000)

NOTES:

Western Regional Climate Center (www.wrcc.dri.edu)

2.2 GENERAL SITE CONDITIONS

2.2.1 TOPOGRAPHY & DRAINAGE

The area of investigation lies entirely within Norton Sound. No terrestrial topography exists to describe, and all precipitation falls directly into the sea. Mudline topography below seawater in this area is relatively complex and discussed further in Section 2.2.2.

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2.2.2 SEAFLOOR TOPOGRAPHY

Seafloor topography at the site is dominated by an underwater shoal trending northwest to southeast. Within the project area, the shoal rises to a maximum elevation of approximately -6.75 fathoms (-40 feet) within the center of the project area and -3.5 fathoms (-21 feet) near the marine spit adjacent to the northwestern extent of the project area. Maximum water depths within the survey area are approximately 17 fathoms (102 feet) on the harbor-side of the shoal within the west-central portion of the project area. Water depths on the exposed ocean-side of the survey area range from 8 fathoms (48 feet) in the southeast to 12 fathoms (72 feet) in the northeast (R&M, 2017).

2.2.3 TIDES AND CURRENTS

The published mean tide range at Dutch Harbor is about 3 feet and the maximum diurnal range is about 4.1 feet (NOAA, 2022). Tides are mixed semi-diurnal with two highs and lows generally occurring daily. Currents are estimated to generally be less than one knot.

2.2.4 VEGETATIVE COVER

Most of the project area is entirely offshore in Iliuliuk Bay with no vegetative cover. The nearby marine spit was observed to support grasses.

2.2.5 SOILS

The following paragraph presents general comments regarding area-wide soil types. Detailed discussion of subsurface soils encountered at the project site during R&M’s subsurface investigation is provided in Section 7.0.

Volcanic rocks dominate the lower Alaska Peninsula and the Aleutian Islands. Glacial deposits, including moraines and associated outwash materials, occupy the lowlands of the peninsula and Unimak Island. Volcanic deposits mantle most surfaces except for the steepest portions of mountains. The soils derived from the ash are cindery in areas close to volcanic cones but have sandy or silty textures on most lower slopes.

Well-drained cindery soils with little vegetation occur especially on slopes of active volcanos. Large areas of these soils extend to the coast in places, most notably in northern Unimak Island. Ash soils with loamy textures are found more extensively throughout the Aleutian Subregion, occupying most areas at low elevations. These soils are generally well drained and have high organic matter content. Depressions on coastal plains and some lower slopes are occupied by peat soils.

Erodibility of the soils is related to slope and texture. Cindery soils generally have low potential even on strong slopes. The erodibility of loamy soils is low on coastal plains but moderate to high on slopes. High winds, which occur throughout the year, cause erosional damage on exposed sites, especially disturbed coastal dunes (AEIDC, 1976).

2.2.6 BEDROCK

Bedrock within the immediate Dutch Harbor area was observed to consist of altered andesite and basalt extrusive rocks, sills, and sedimentary rocks ranging in coarseness from argillite to conglomerate and consisting of the Unalaska Formation (Drewes et al., 1961). The overwhelming

November 2022 Page 10 R&M No. 2930.03 majority of bedrock exposures were observed to have been subjected to both regional and cataclastic metamorphism resulting in a tilted, fractured, and warped assemblage with little consistent regional structure (R&M, 2017).

Along the southeastern shore of Iliuliuk Bay, numerous exposed shelfs consisting of bedrock were observed within the intertidal zone. Immediately southeast of and in line with the longitudinal axis of the underwater shoal of interest, an exposed bedrock shelf was observed. This shelf was measured to be approximately 230 feet in width and extended about 150 feet into the bay. It was observed to consist of a gray, very hard, faintly to slightly weathered aphanitic andesite. This shelf exhibited consistent structure and its primary joint set was measured to strike in a northwest/southeast trend (≈160˚/340˚) and dip about 60˚ to 70˚ towards the northeast (R&M, 2017).

Much of the intertidal zone along the southeastern shore of Iliuliuk Bay was armored with a layer of rounded to subrounded cobbles and boulders generally consisting of gray to gray-green andesite and averaging about one to three feet in diameter (R&M, 2017).

Situated along the northwestern shore of Iliuliuk Bay is the Dutch Harbor marine spit. It is mapped as consisting of Quaternary alluvial beach deposits (Drewes et al., 1961). This spit was observed to be armored with a layer of gray, gray-green and brown mixture of andesitic and basaltic cobbles and boulders averaging about one to three feet in diameter. Average particle size of these cobbles and boulders was observed to decrease from the spit-toe, in the north, to the spit-head, in the south.

This particle size sorting may indicate that long-shore current deposition contributed to the formation and southward propagation of the marine spit (R&M, 2017).

Although no evidence of glacial drift, till or moraines were observed on land in the immediate vicinity of the project site, they are mapped in numerous terrestrial locations. Particularly in the vicinity of present glaciers and upon the flanks of Makushin Volcano. Even with the lack of terrestrial glacial deposits in the vicinity of the project site, the potential for submarine glacial drift, till, and moraine deposits should not be discounted as significant and widespread glaciation of Unalaska Island is well documented (R&M, 2017).

2.2.7 GROUNDWATER

Most of the project area lies entirely offshore in Iliuliuk Bay. One test boring (AP-031), drilled on the terrestrial marine spit, encountered groundwater at about 5 feet bgs.

2.2.8 THERMAL CONDITIONS

Perennially frozen soils are not anticipated to occur at the Iliuliuk Bay Channel Navigation Improvements project site because most site soils are completely submerged by sea water. Any project soils not submerged by sea water are mapped as being generally free of permafrost (Ferrians, 1965). Further discussion of site thermal conditions encountered is contained in Section 7.

2.2.9 GEOLOGIC HAZARDS

With the exception of earthquakes, there are no other known geologic hazards (e.g., avalanches, mass slope wasting, etc.).

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GEOTECHNICAL INVESTIGATION METHODS

Methods of investigation for the Iliuliuk Bay geotechnical field investigation are described in the following sections.

3.1 DRILLING PLATFORM

R&M in conjunction with Discovery Drilling contracted Resolve Marine, out of Dutch Harbor, to provide a drilling platform throughout the duration of our offshore geotechnical investigation. The drilling platform, named the RMG300, was a 142-foot steel deck-barge commercial work vessel.

Position over the work sites were maintained with a combination of a three-point anchoring system supplemented with two seventy-foot spuds.

The RMG300 was primarily powered and maneuvered by a 130-foot triple screw tow/supply vessel named the Makushin Bay. As the project progressed, a much smaller third party tug would be called to assist with moving between work sites.

Installation of the geotechnical drill rig, equipment, and tooling were accomplished at a permanent slip located at the Resolve Marine dock located within Dutch Harbor. Once the drill rig, equipment, and tooling, the drilling platform was towed to work site and generally remained moored on-site the entire time. One exception to this process was when the project team had to return to the dock on the evening of September 15th to allow storm Merbok to pass our location. A photograph of the drilling platform and support vessel is provided in Appendix D.

3.2 TEST BORING POSITIONING

Proposed test boring depths and locations for the project were specified by USACE in the SOW and plotted to proposed site maps by a R&M GIS specialist prior to field mobilization. A locate request was filed with 811 Alaska Digline and coordinated with the City of Unalaska prior to ground disturbance activities. No utility conflicts were identified through the 811 Alaska Digline process or through coordination with the City of Unalaska.

Offshore test boring locations were established using a non-survey grade global positioning system (GPS) device and operated by personnel trained on the equipment. USACE furnished initial test boring coordinates that were utilized to locate to proposed boring locations. Once the drilling platform was secured and stable, the final test boring locations were established by survey grade GPS techniques by an R&M surveyor.

The onshore test boring location was established via a survey grade GPS device by and R&M surveyor.

All borehole locations needed to be adjusted, with USACE approval, due to offshore drilling platform limitations and onshore conflicts as documented in Section 1.7.1. All final test boring coordinates presented in this report were established via a survey grade GPS device by and R&M surveyor.

Horizontal coordinates are referenced to Alaska State Plan, Zone 10, NAD83, and are in U.S. Survey Feet. Mudline elevations at each test boring were determined, using the bathymetry survey performed by eTrac in 2017, to the closest 0.1-foot referenced to mean lower low water (MLLW).

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Locations of all test borings drilled during this investigation are presented in Appendix A on Drawing A-02. Coordinates and surface elevation information for the test borings completed during the investigation are also provided in tabular form on Table 3-1, below, and on the test boring logs in Appendix B.

3.3 TEST BORINGS

R&M completed a total of seven test borings, numbered AP-025 through AP-031 at the project site during the period of 10 September through 17 September 2022. The depth of the test borings ranged from 18.8 to 82.0 feet bgs. Total footage drilled was approximately 245 linear feet. The drilling program was conducted under the direct guidance of experienced R&M geologists who maintained detailed logs of the materials encountered and the samples collected. Each test boring was logged in accordance with standard engineering practices. Data obtained from the test borings were utilized for geologic interpretations. A key to the test boring log general notes, and an example of a typical log used are illustrated in Appendix B on Drawings B-01 and B-02, respectively. The test boring logs are illustrated on Drawings B-03 through B-12. Table 3-1 provides a summary of the R&M test borings performed for this project.

Drilling and sampling operations were performed by Discovery Drilling, Inc. under contract with R&M, utilizing a truck mounted CME75 drilling rig. All test borings were accomplished using a nominal 4-inch OD HWT casing advancement system. Drive samples were planned to be collected in all test borings at intervals of approximately 2.5 feet within the top 10 feet of the boreholes and at 5-foot intervals thereafter. Due to variable swell amplitude and limited drilling stroke, LPT samples were collected as close to planned intervals as conditions allowed and under approval of the COR.

TABLE 3-1: SUMMARY OF R&M TEST BORINGS, ILIULIUK BAY CHANNEL NAVIGATION IMPROVEMENTS

NOTES:

a Local horizontal system reported in Alaska State Plane Zone 10 NAD83 (1992), U.S. Survey Feet.

b Elevation data from the 2017 USACE contracted bathymetry survey, reported in feet below MLLW.

N.E. = Not Encountered

Soil samples were obtained using split-barrel sampling equipment in general accordance with ASTM D 1586, “Standard Penetration Test (SPT) and Split Barrel Sampling of Soils”. For this project, a Large Penetration Test (LPT) split-barrel sampling method was utilized for the purpose of collecting enough sample volume for coarse grained geotechnical samples. This sampling method is a modification of the SPT and was accomplished by driving a 2.5-inch I.D. by 3.0-inch O.D. heavy-wall split-barrel drive sampler by the impact of a 340-pound automatic hammer falling approximately 30 inches.

Test Boring

Number (Final)

Test Boring

Number (Field)

Coordinatesa Mudline

Elevationb Total Depth

(Feet)

Approximate Depth to

Groundwater (Feet)

Northing Easting

AP-025 TH-01 1195602.0594 5324371.8541 ‐54.73 18.8 N.E.

AP-026 TH-02 1195212.1224 5324423.4641 ‐51.11 29.6 N.E.

AP-027 TH-03 1194914.2406 5324145.6641 ‐49.90 27.3 N.E.

AP-028 TH-04 1194871.1712 5324239.1750 ‐45.19 35.8 N.E.

AP-029 TH-05 1194992.4867 5324577.8389 ‐53.10 25.3 N.E.

AP-030 TH-06 1194383.7161 5324400.0161 ‐47.14 25.9 N.E.

AP-031 TH-07 1195056.8060 5321080.8110 +11.81 82.0 5

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The penetration resistance, defined as the number of blows required to drive the sampler the last 12 inches of an 18-inch interval, gives an indication of the in-place relative density for unfrozen cohesionless soils. Blow counts reported per six-inch interval are shown on the boring logs in Appendix B. The SPT “N” value is the number of blows required to drive the 1.4-inch I.D. sampler, with a 140-pound hammer the last 12 inches of an 18-inch interval. Penetration resistance obtained with the 2.5-inch I.D. sampler can be factored to approximate the equivalent SPT “N” value by a hammer potential energy to sampler end-area ratio adjustment. Blow counts that appear on the log of test borings for the 2.5-inch I.D. samplers are actual values, not the converted SPT values.

Samplers may have been driven an additional six inches to provide additional sample material.

When this occurred a fourth blow count interval is reported on the test boring log.

After visual and tactile classification in the field, soil samples were returned to the R&Ms laboratory.

Representative samples were then selected for further examination and analysis.

3.4 ENVIRONMENTAL SAMPLING

For this project, the requirement to perform environmental screening and/or was removed from the scope of work due to the predominately undisturbed marine environment.

3.5 BACKFILLING

Upon completion of drilling test borings, the test borings were allowed to naturally collapse without backfilling of material from cuttings.

3.6 MEC AVOIDANCE PROGRAM

An MEC (munitions and Explosives of Concern) avoidance procedure was employed while drilling and geotechnical sampling activities are being performed. All personnel involved in the geotechnical investigation and drilling activities were trained in the 3Rs of Explosive Safety awareness training prior to drilling activities. This training was provided virtually by the USACE Baltimore District through the Alaska District prior to mobilization of equipment and personnel to Dutch Harbor.

Prior to contact with the seafloor with drill tooling, a submersible video camera with live feed, routed topside, was deployed to inspect the drill site for any signs of MECs. No potential MECs were observed from camera observations at any of the offshore drill sites.

3.7 MARINE MAMMAL OBSERVATION

Marine mammal observation (MMO) activities were administered by multiple USACE observers in accordance with the approved marine mammal monitoring plan. It was understood that some marine mammals may be disturbed by certain marine geotechnical investigation activities including the LPT subsurface sampling system. When any marine mammals approached the drilling platform to within approved shutdown distances, the geotechnical investigation sampling activities were suspended. Geotechnical investigation then resumed after approval from the USACE observers that marine mammals have exited the established shutdown distances.

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GEOTECHNICAL LABORATORY TESTING PROGRAM

The laboratory testing program was developed to provide data on the important soil characteristics necessary for surface and subsurface characterization of the site. These tests verified and modified the field descriptions, improving the database for engineering application and geotechnical interpretation of site conditions. Laboratory testing was performed in accordance with the following ASTM procedures in Table 5-1 (ASTM, 2022).

TABLE 5-1: LABORATORY ANALYSIS METHODS

Test Procedure

ASTM

Designation

Classification of Soils for Engineering Purposes D 2487

Description and Identification of Soils (Visual-Manual Procedure) D 2488

Particle-Size Analysis of Soils (Standard sieve analysis which includes percent passing No. 200 sieve)

D 6913

Particle-Size Analysis of Soils (Sieve analysis and two-hour hydrometer for percent passing 0.02) D 7928

Liquid Limit, Plastic Limit, and Plasticity Index of Soils D 4318

4.1 INDEX TESTS AND SOIL CLASSIFICATION

Each soil sample was assigned a Unified Soil Classification System (USCS) classification. When the USCS classifications presented on the log of test boring and laboratory data summary was estimated, the estimated classification symbol is followed by an asterisk (*) on the log of test boring and is shown as estimated on the laboratory data summary.

For this project, the requirement to perform moisture content analysis was removed from the scope of work due to the predominately marine environment. Additionally, the requirement to assign a USACE Frost Design Soil Classification to laboratory tested samples was removed from the scope of work due to the predominately marine environment.

The Classification of Soils for Engineering Purposes ASTM D-2487 is presented in Appendix C on Drawings C-01. A summary of all surface and subsurface soil laboratory index test results (Soil Classification, Particle Size, Plasticity, and Specific Gravity) is provided on Drawings C-02 through C- 20.

It should be noted that the size of the gravel particles in the samples obtained with a 2.5-inch I.D.

spilt-spoon sampler is limited by the size of the opening of the sampler, therefore the sample is not necessarily representative of the coarse gravel fraction.

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DATA PROCESSING AND INTERPRETATION

Interpretation of geotechnical data included the integration of the field boring logs and laboratory test data. U.S. Geological Survey maps and reports in addition to on-site survey data were also helpful in interpreting site conditions.

5.1 TEST BORING LOGS

R&M engineers and geologists maintained field logs documenting the drilling method, progress, and samples attempted and recovered; a description of the recovered soil (following ASTM D 2488);

and our interpretation of the geotechnical conditions between the recovered samples. The formal logs provided in Appendix B include additional modifications based on further visual inspection of the recovered samples, and the results of the laboratory testing (Appendix C). It is imperative for users to recognize that the formal logs: (i) include factual data (e.g., SPT/LPT blow counts and laboratory test results) as well as interpretative information (e.g., conditions between sample depths, etc.); (ii) use soil group names assigned following the Unified Soil Classification System (USCS) per ASTM D 2487; and (iii) use USCS soil group names with an asterisk (e.g., SM*) where the grain-size distribution was measured but the plasticity was estimated using visual-manual procedures (ASTM D 2488). It is emphasized that because of the inclusion of laboratory data, our interpretations are based on the contents of the final logs and the information contained within, and not solely on the field logs.

The final logs included in Appendix B have a two-fold function: they present significant raw field and laboratory data gained and provide interpretation of data by delineating different soil strata encountered. In preparing the final logs, first field data was extracted and transferred from field logs. Second, interpretation requiring knowledge of soil mechanics, understanding of field soil sampling techniques, and geomorphic processes specific to northern environments were employed to define soil strata.

5.2 DETERMINATION OF GROUNDWATER

Groundwater determination was not performed at six of the seven boreholes completed during the investigation, as they were located entirely offshore and within Iliuliuk Bay. Groundwater at the onshore borehole, AP-031, was determined based on drilling and sampling observations by the R&M engineering geologist while drilling and on measurements collected from the HWT rotary wash assembly during drilling. No groundwater observation wells were installed for precise measurements or additional monitoring. Therefore, it is stressed that the groundwater information presented on the logs is approximate.

5.3 DETERMINATION OF THE THERMAL STATE OF SOILS

Determination of thermal state of site soils was based on drilling and sampling visual-manual observations by the R&M engineering geologists. No ground temperature monitoring equipment or casings were installed to enable precise measurement or additional monitoring.

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CONDITIONS

To facilitate a discussion of the soil, groundwater, thermal, and other site conditions, the following section has been set out to characterize each parameter on an individual basis. The reader is referred to the appendices of this report for graphic, tabular and photographic representations of the various conditions encountered.

6.1 SURFACE

The Iliuliuk Bay Channel Navigation Improvements project site is located predominately offshore. It is bounded on the west by an exposed marine spit that extends into the harbor approximately 6,500 feet and is bounded on the east by steep bedrock walls rising from the ocean surface. To the northeast lies the expansive Bering Sea, while to the southwest, lies Dutch Harbor proper and the City of Unalaska.

6.2 SOIL CONDITIONS

Subsurface soils at the Iliuliuk Bay Channel Navigation Improvements project site generally consisted of two distinct units; cobble and boulder armor layer (Unit I), over glacial till (Unit II).