25B5002 - Appendix G- Site Characterization Report - AOC Part 1.pdf

FUGRO ATLANTIC

DRAFT SITE CHARACTERIZATION REPORT

ATLANTIC OCEAN CHANNEL

OFFSHORE SOUTHEASTERN VIRGINIA

Prepared for:

Craney Island Design Partners, LLC

November 2009 Fugro Job No. 3582.006 Task 23

November 9, 2009 Project No. 3582.006, Task 24

Craney Island Design Partners, LLC 800 World Trade Center Norfolk, Virginia 23510

Attention: Mike Crist, Vice President

Subject: Draft Site Characterization Report, Atlantic Ocean Channel, Offshore Southeastern Virginia

Dear Mr. Crist:

Fugro Atlantic is pleased to submit this draft report describing the site and subsurface conditions in the potential Atlantic Ocean Channel borrow area. This report has been prepared by Fugro Atlantic to assess and map sand resources within the Atlantic Ocean Channel for use in the planned Craney Island Eastward Expansion.

Fugro has conducted this assignment under contract to the Craney Island Design Partners, LLC, who are under contract to the Virginia Port Authority. The data integration, mapping, and assessments provided herein utilize various geophysical survey and subsurface data collected by others under contract to the U.S. Army Corps of Engineers. The evaluation reported herein has used and integrated both historical and recent data to provide a holistic assessment of the subsurface conditions and materials that is more comprehensive that can be developed when the different data are used independently.

We look forward to continuing our association with and service to the Craney Island Design Partners and Virginia Port Authority on the development of the Craney Island Eastward Expansion and subsequent Craney Island Marine Terminal development.

Sincerely, FUGRO ATLANTIC

Kevin R. Smith, PG Senior Engineering Geologist

Thomas W. McNeilan, PE Vice President

Copies Submitted: (#) Recipient, Company

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FUGRO ATLANTIC

350 World Trade Center Norfolk, Virginia 23510

Tel: (757) 625-3350

A member of the Fugro group of companies with offices throughout the world.

Craney Island Design Partners, LLC November 9, 2009 (Project No. 3582.006)

CONTENTS

Page

1.0 INTRODUCTION

1.1 PROJECT OVERVIEW

2.0 OVERVIEW OF WORK PERFORMED

3.0 DATABASE AND DATA ANALYSIS AND MAPPING METHODS

3.1 Geotechnical and Geophysical Database

3.1.1 Bathymetric Data and Map Datums

3.1.2 2008 Vibracore Explorations

3.1.3 2008 Mini-Cone Penetrometer Tests

3.1.4 2007 Vibracore Explorations

3.1.5 2007 Mini-Cone Penetrometer Tests

3.1.6 Historical Geotechnical Data Review

3.1.7 Geophysical Data (2007 Survey)

3.2 Data Analysis and Mapping Methods

3.2.1 Sediment Classification From CPT and Vibracore Data

3.2.2 Integration of Geotechnical and Geophysical Data

3.2.3 Mapping Overburden and Sand Horizons

3.2.4 Cross Sections

4.0 ATLANTIC OCEAN CHANNEL SITE CONDITIONS

4.1 Description of Site

4.1.1 Bathymetry

4.2 Geology and Shallow Sediment Stratigraphy

4.2.1 Geologic Setting

4.2.2 Shallow Sediment Stratigraphy

4.3 Isopach (Thickness) Contour Maps

4.4 Cross Sections

5.0 SOIL ENGINEERING PROPERTIES

5.1 Grain Size Characteristics

5.1.1 Grain Size Envelopes

5.1.2 Grain Size Profiles

5.1.3 Fines Content Profiles

5.1.4 Estimate of Fines Content From Mini-Cone Penetration Test Data .. 20

5.1.5 Spatial Distribution of Fines Content within PBU (Above El. -63 feet)20

5.1.6 Median Grain Size Profiles

5.1.7 Median Grain Size (d50) and Fines Content Comparison

5.2 Water Content

5.3 Cone Tip Resistance

5.4 Plasticity

6.0 VOLUME ESTIMATES AND COMMENTARY

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6.1 Volume Calculations

6.1.1 Methodology

6.1.2 Estimated Available Borrow Volumes

6.2 Relative Desirability of Different Units

7.0 REFERENCES

TABLES

Page

2-1 Summary of Exploration Data 2-2 Summary of Laboratory Test Data 4-1 Summary of Potential Borrow Unit Thickness 5-1 PBU Subarea Grain Size Characteristics (+/- Std. Deviation) 6-1 Summary of Potential Borrow Unit Volume Calculations 6-2 PBU Subarea Grain Size Characteristics and Desirability

FIGURES

Figure

Project Location Map .......................................................................................................... 1-1 2007/2008 Exploration Location Map ................................................................................. 2-1 Bathymetry.......................................................................................................................... 2-2a-2-2c Bathymetry (3D Rendering) ................................................................................................ 2-2d Historical Exploration Location Map.................................................................................... 2-3a-2-3b Comparison of Fines Content From Laboratory Test and CPT Sounding Data.................. 3-1 Line 11, Chirp Seismic Data Example ................................................................................ 3-2 Line 10NW, Boomer Seismic Data Example ...................................................................... 3-3a Line 28, Boomer Seismic Data Example ............................................................................ 3-3b Key to Subsurface Cross Sections ..................................................................................... 3-4 Annotated Chirp Record, Line 11........................................................................................ 3-5 Annotated Boomer Record, Line 10NW.............................................................................. 3-6a Annotated Boomer Record, Line 28.................................................................................... 3-6b Geologic Setting.................................................................................................................. 4-1 Three Major Quaternary Paleochannel Systems of the Susquehanna River...................... 4-2 Site Features....................................................................................................................... 4-3 Isopach (Thickness) of Potential Borrow Unit ..................................................................... 4-4a-4-4c Cross Section Location Map ............................................................................................... 4-5 Subsurface Cross Section 21-21’ ....................................................................................... 4-6 Subsurface Cross Section 22-22’ ....................................................................................... 4-7 Subsurface Cross Section 23-23’ ....................................................................................... 4-8 Subsurface Cross Section 24-24’ ....................................................................................... 4-9 Subsurface Cross Section 25-25’ ....................................................................................... 4-10 Subsurface Cross Section 26-26’ ....................................................................................... 4-11

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Subsurface Cross Section 27-27’ ....................................................................................... 4-12 Subsurface Cross Section 28-28’ ....................................................................................... 4-13 Subsurface Cross Section 29-29’ ....................................................................................... 4-14 Subsurface Cross Section 30-30’ ....................................................................................... 4-15 Subsurface Cross Section 31-31’ ....................................................................................... 4-16 Subsurface Cross Section 32-32’ ....................................................................................... 4-17 Subsurface Cross Section 33-33’ ....................................................................................... 4-18 Subsurface Cross Section 34-34’ ....................................................................................... 4-19 Subsurface Cross Section 35-35’ ....................................................................................... 4-20 Subsurface Cross Section 36-36’ ....................................................................................... 4-21 Subsurface Cross Section 37-37’ ....................................................................................... 4-22 Subsurface Cross Section 38-38’ ....................................................................................... 4-23 Grain Size Distribution Curves............................................................................................ 5-1a- 5-1g Grain Size Distribution Profiles ........................................................................................... 5-2a- 5-2g Fines Content Profile From Laboratory Test Data .............................................................. 5-3a- 5-3g Fines Content Profile From mCPT and Laboratory Data .................................................... 5-4a- 5-4g Median Grain Size (D50) Profile ......................................................................................... 5-5a- 5-5g Fines Content and Median Grain Size (D50) Comparison Plot .......................................... 5-6a- 5-6g Water Content Profile.......................................................................................................... 5-7a- 5-7g mCPT Measured Tip Resistance (qc) ................................................................................. 5-8a-5-8g Plasticity Chart .................................................................................................................... 5-9

CHARTS

Chart

Exploration Locations Bathymetry (2007 OSI Single-beam Survey)...................................................................... 2a Bathymetry (2007 USACE Multibeam Survey) ................................................................... 2b Isopach (Thickness) of Potential Borrow Unit Subsurface Cross Sections 9NW-9NW’, 10NW-10NW’, and 11NW-11NW’ Subsurface Cross Sections 9SE-9SE’, 10SE-10SE’, and 11SE-11SE’ Fines Content (%) of Sand Layers in Potential Borrow Material

APPENDICES

APPENDIX A 2008 EXPLORATIONS

APPENDIX B 2007 EXPLORATIONS

APPENDIX C 1995 VIBRACORES

APPENDIX D 1990 VIBRACORES

APPENDIX E 1983-1985 VIBRACORES

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1.0 INTRODUCTION

1.1 PROJECT OVERVIEW

The development of the Craney Island Eastward Expansion (CIEE) project is a joint local-federal project being pursued by the Virginia Port Authority (VPA) and the Norfolk District of the U.S. Army Corps of Engineers (USACE). The construction of the CIEE will both: 1) extend the life of the USACE’s existing Craney Island Dredged Material Management Area (CIDMMA) and 2) provide new land for the future development (by the VPA) of the Craney Island Marine terminal (CIMT).

The development of the CIEE is anticipated to require mining of sands for placement into the CIEE: 1) behind the eastern perimeter rock dike, 2) to construct the east-west cross dikes, and 3) possibly at other locations within the CIEE land reclamation. As part of the USACE funded FY07 investigations for the CIEE, investigations for the potential of obtaining desirable sands (by S&ME and subcontractors, under contract to the USACE) from the 1) Atlantic Ocean Channel, 2) Thimble Shoal Channel, and 3) Newport News Channel were conducted during the fall of 2007. Subsequent to those USACE FY07 studies, supplemental explorations funded by the USACE were conducted in the Atlantic Ocean Channel in conjunction with an integrated geotechnical and geophysical site investigation of the Cape Henry Navigation Channel (CHC) In the fall of 2008. The project area is shown on Figure 1-1.

This report presents the current data collected within the Atlantic Ocean Channel area along with the available historical data used to define subsurface sediment conditions, provides graphics depicting those conditions, and presents a preliminary evaluation of suitable material available within the Atlantic Ocean Channel for use in the CIEE land reclamation. The Atlantic Ocean Channel has been subdivided into seven areas based on available material type and desirability of material for construction use in the CIEE project.

2.0 OVERVIEW OF WORK PERFORMED

This site characterization report presents a summary of site conditions and potential sand resources in the Atlantic Ocean Navigation Channel and vicinity. This summary is based on an evaluation of data from an integrated geotechnical and geophysical site investigation conducted in the last quarter of 2007, supplemental geotechnical explorations conducted in the last quarter of 2008, and historical explorations.

The 2007 integrated site investigation program performed by S&ME and subcontractors, under contract to the USACE was comprised of 53 mini-cone penetration test (mCPT) soundings, 28 vibracores, single-beam bathymetric survey, and 210 nautical miles of high-resolution, 2-dimensional seismic reflection survey. Laboratory testing of the vibracore samples was completed by S&ME. Figure 2-1 shows the locations of the 2007 explorations and seismic tracklines. Bathymetric contours from the single-beam survey are shown on Figure 2-2.

During October and November of 2008, S&ME and subcontractors, under contract to the USACE performed 22 mCPT soundings and 5 vibracore explorations to supplement the program performed in 2007. Those explorations are shown on Figure 2-1.

Logs and geotechnical data from 125 vibracores conducted during the 1980s and 1990s were identified and incorporated into this study. Figure 2-3 shows the locations of the historical vibracore explorations.

The geotechnical and geophysical data were compiled by Fugro into a database that was used to:

Interpret subsurface conditions, Map shallow stratigraphy, sand bodies, and overburden, Evaluate the engineering properties of shallow sediments, and

Estimate the quantity of accessible sand resources.

Tables 2-1 and 2-2 provide a summary of the data compiled and used for this study.

Table 2-1. Summary of Exploration Data

Exploration Type Year Performed Quantity Company

Vibracore 2008 5 Alpine/S&ME mCPT 2008 22 ConeTec/S&ME

Vibracore 2007 28 AquaSurvey/S&ME mCPT 2007 53 ConeTec/S&ME

Seismic Reflection 2007 210 NM OSI

Vibracore 1995 6 USACE

Vibracore 1989 - 1990 74 USACE

Vibracore 1985 24 USACE

Vibracore 1983 21 USACE

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The following table summarizes the laboratory test data entered by Fugro into the GIS geotechnical database for our evaluation.

Table 2-2. Summary of Laboratory Testing Data

Year Performed Grain Size (Sieve)

Fines Content (No. 200) Water Content Specific Gravity Atterberg Limit

2008 10 0 10 0 1

2007 68 0 67 0 8

1995 0 0 0 0 0

1990 212 0 0 0 0

1985 49 47 49 20 8

1983 63 65 65 4 14

Work flow was generally comprised of the following sequence and steps. Each step is preceded by a letter which indicates the responsible party. The company codes are: (Al) Alpine Seismic Survey, (Aq) Aqua Survey, (O) Ocean Surveys, Inc. (OSI), (C) ConeTec, (F) Fugro, (S) S&ME, and (U) USACE.

1. (U) 125 historical vibracores and laboratory testing performed by USACE subcontractors during the 1970s and 1980s.

2. (F) Review of historical data in Atlantic Ocean Channel. Historical geotechnical data populated into GIS database.

3. (O) 210 nautical miles of high-resolution seismic reflection survey completed in November 2007.

4. Processing of seismic data initiated by (O) in 2007 and completed by (F) during October-December of 2008.

5. 28 vibracore explorations completed by (Aq) and logged by (S) in November 2007.

6. (S) Laboratory testing of vibracore samples in November 2007.

7. (C) 53 mCPT soundings advanced November-December 2007.

8. Preliminary geophysical and geotechnical data evaluation (A) and (O) December 2007-January 2008.

9. (F) Planning of supplemental geotechnical explorations.

10. 5 vibracore explorations completed by (Al) and logged by (S) in October 2008.

11. (S) Laboratory testing of vibracore samples in October 2008.

12. (C) 22 mCPT soundings advanced October-November 2008.

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13. (F) Corrected MLLW water depths based on bathymetric survey for 2007 seismic and 2008 vibracore exploration data.

14. (F) Integrated geophysical and geotechnical data and completed seismic data interpretation.

15. (F) Incorporated geotechnical data and mapped horizons into GIS database for further evaluation.

16. (F) Generate cross sections, structural and isopach maps.

17. (F) Geotechnical property evaluation of sand bodies within delineated subareas.

18. (F) Volumetric estimates of sand bodies.

The following section provides a description of data reviewed and used during this site characterization study.

3.0 DATABASE AND DATA ANALYSIS AND MAPPING METHODS

3.1 GEOTECHNICAL AND GEOPHYSICAL DATABASE

This study incorporates data from separate investigations collected by multiple contractors over several decades. Prior to performing our mapping and site characterization, we reviewed the data for consistency between soil classification schemes, coordinate systems and datums, quality, integrity, and relevance. When we identified data that was spurious and we could not reconcile problems, we omitted from them our evaluation and data presentations herein. Common issues that we reconciled where reliable and pertinent information was available included:

Logs were preliminary field logs that did not incorporate laboratory test results. For example, the field log may have classified the entire 18-feet of recovered soil as “Mud” or “Sand.” If laboratory tests data were available we classified the soils based on the test data.

Soil classifications used on logs were inconsistent with the Unified Soil Classification System (USCS). If test data were available, we classified the soils according to USCS and noted on the logs provided in the Appendices.

Where adequate, reliable data were available, Fugro reclassified soils in general accordance with ASTM 2487.

Measured water depths at 2008 vibracore exploration locations differed from single-beam surveyed water depths by 4 to 6 feet in some cases. Water depths derived from the single-beam surveys were adopted.

We put all geotechnical data into the same horizontal coordinate system. The project used the Virginia State Plane, South Zone, NAD 83 coordinate system with map units of feet.

Corrected seismic data to reference MLLW.

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Once the (1) geotechnical data had been filtered for reliable and quality data, (2) exploration water depths corrected, (3) seismic data corrected to the project datum (MLLW), and (4) data put into the same coordinate system, the geotechnical and geophysical data correlated fairly well. After those steps were completed, the data interpretation and evaluation was performed.

3.1.1 Bathymetric Data and Map Datums

Two bathymetric data sets were utilized during this project. A single-beam survey was conducted simultaneously during the geophysical survey. The single-beam survey was conducted along the seismic reflection tracklines (Figure 2-1 and Chart 1). Although the tracklines were widely spaced, they provide data coverage across the survey area and are useful in identifying seafloor topography and geomorphology. The USACE conducted as multibeam survey as part of the maintenance program for the navigation channel around the same time that the geophysical survey was conducted. The multibeam survey was limited to the navigation channel but provide better resolution data of the seafloor in the navigation channel than the single-beam survey data. The USACE survey data were used to compute the PBU volume and is depicted as the seafloor on the cross sections in this report.

3.1.1.1 Single-beam Survey (2007)

A bathymetry survey was conducted by Ocean Surveys, Inc. (OSI) under contract to S&ME simultaneous with the seismic reflection survey of October 30 through November 20, 2007. Figure 2-2a and Figure 2.2b shows the bathymetric contours provided by OSI.

Water depths were measured along the boat paths of the seismic reflection survey with an Odom HydroTrac Digital single beam depth sounder. The single beam transducer was rigidly mounted on the starboard side of the vessel. Data was stored in HYPACK navigation files. Heave, pitch, and roll information was measured by a TSS DMS-05 Motion Sensor and saved in HYPACK navigation files. During data processing with HYPACK software, this information was used to correct the sub-bottom data for artifacts during acquisition. Tide corrections were performed using the NOAA tide gauge station 8638863 located at the Chesapeake Bay Bridge Tunnel. Water level data were downloaded from the NOAA website for the days encompassing the survey and applied to the sounding data.

3.1.1.2 Multibeam Survey (2007)

The USACE conducted a multibeam survey using a Reson 8101 system during September and October of 2007. The survey was limited to the navigation channel. The data were provided at a data point spacing of 1.5 to 5-foot spacing along a line perpendicular to the channel centerline at a line spacing of 100 feet. The data provide higher detailed water depth information than the wider spaced single beam survey. Therefore the multibeam data are using for volumetric computations and is used to depict the seafloor on cross sections in this report.

The bathymetric contours from the 2007 USACE survey are shown on Figures 2-2b and 2-2c and Chart 2b.

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3.1.1.3 Datums

Vertical measurements used in this report reference mean lower low water (MLLW) 1983-2001 epoch. The horizontal coordinate system used is Virginia State Plane, South Zone, NAD 83, and units of measurement are in feet.

3.1.2 2008 Vibracore Explorations

Five vibracores were advanced to depths ranging from 15.6 to 20 feet below the sea floor during October 6 and 9, 2008. The work was performed by Alpine under contract to S&ME. A self contained model 271 B Alpine Pneumatic Vibracore unit was used to collect the soil cores. Final vibracore logs were provided by S&ME and are included in Appendix A.

We note that the reported water depths at the time of the explorations are 5 to 14 feet shallower than the 2007 surveyed water depths. We do not have a plausible explanation for an infill of 5 to 14 feet of material between the 2007 and 2008 investigations. However, when the water depths from the 2007 survey are applied to the vibracore explorations, the lithologic transitions in the 2008 vibracores correlate well with adjacent explorations by others and seismic data. Therefore, our preferred water depth measurements for the 2008 vibracores are from the 2007 survey. We note that seafloor elevation may have changed between the 2007 survey and 2008 vibracores which would introduce error in the interpreted lithologic elevations, but feel these are likely minor relative to the reported seafloor elevations. Table A-1 in Appendix A summarizes the mudline elevations and magnitude of difference between the two sources.

3.1.2.1 Laboratory Test Data

Laboratory testing was performed by S&ME on the disturbed vibracore samples. The laboratory testing program was comprised of moisture contents and grain size analyses.

Appendix A presents a test result summary table and grain size curves which summarize the testing program.

3.1.3 2008 Mini-Cone Penetrometer Tests

Mini-cone penetration testing (mCPT) was performed during October 31, 2008 and November 10, 2008. Under contract to S&ME, ConeTech, Inc. of Charles City, Virginia performed 22 soundings using a 2 cm2 area mCPT. The mCPT soundings recorded depth, tip resistance, sleeve resistance, and friction ratio, however the system does not record pore pressure data. The soundings were advanced to a maximum depth of 32 feet below the seafloor. Seven mCPTs penetrated at least 30 feet, 13 penetrated between 10 and 20 feet, and 2 penetrated between 4 and 10 feet below the mudline. The mCPT logs are provided in Appendix A.

3.1.3.1 Fines Content Calculations

The processed mCPT data were provided to Fugro. The mCPT data was incorporated in the seismic data interpretation and used to estimate engineering properties of the soils. We

N:\MANAGEMENT\3582_CRANEYISLAND\LIBRARY\FA_DELIVERABLES\2009_AOC_SCR_DRAFT\REVISEDDRAFT_AOC_SITECHAR_110909.DOC 6 used the data to estimate fines content by two procedures (Robertson and Wride, 1988 and Baez et al., 2000). Figure 3-1 compares the fines content profile estimated from mCPT data and fines contents measured in grain size analysis of samples collected in a nearby vibracore.

The two results compare moderately to fairly well. Fines contents are presented on cross sections and data plots in subsequent sections.

Caution should be exercised when using mCPT data to estimate various engineering properties based on procedures empirically derived from full-size cones. The empirically derived procedures are typically based on cones with larger tip areas (e.g. 15 cm2). Care should be exercised when applying empirical relationships to the small cones and erred toward conservationism.

3.1.4 2007 Vibracore Explorations

Twenty-eight vibracores were advanced to depths ranging from 4.5 to 20.4 feet below the sea floor from November 1 through 18, 2007. The work was performed by AquaSurvey under contract to S&ME using a Rossfelder VT-6 Vibracore unit with 20-foot-long core barrels.

Final vibracore logs were provided by S&ME and are included in Appendix B.

3.1.4.1 Laboratory Test Data

Laboratory testing was performed by S&ME on the disturbed vibracore samples. The laboratory testing program was comprised of moisture content, Atterberg limits, and grain size analyses. Appendix B presents a test result summary table, grain size curves, and plasticity chart which summarize the testing program.

3.1.5 2007 Mini-Cone Penetrometer Tests

Mini-cone penetration testing (mCPT) was performed from November 12, 2007 through December 7, 2007. Under contract to S&ME, ConeTech, Inc. of Charles City, Virginia performed 53 soundings using a 2 cm2 area mCPT. The mCPT soundings recorded depth, tip resistance, sleeve resistance, and friction ratio, however the system does not record pore pressure data. The soundings were advanced to a maximum depth of 32.7 feet below the seafloor. Eight mCPTs penetrated at least 30 feet, 14 penetrated between 20 and 30 feet, 30 penetrated between 10 and 20 feet, and 1 penetrated between 9 and 10 feet. The mCPT logs are provided in Appendix B.

3.1.5.1 Fines Content Calculations

The processed mCPT data were provided to Fugro. The mCPT data was incorporated in the seismic data interpretation and used to estimate engineering properties of the soils. We used the data to estimate fines content by the two procedures described in Section 3.1.3.

3.1.6 Historical Geotechnical Data Review

Readily available historical data and reports were identified, obtained and reviewed to better understand the subsurface stratigraphy before and after previous dredging events within

N:\MANAGEMENT\3582_CRANEYISLAND\LIBRARY\FA_DELIVERABLES\2009_AOC_SCR_DRAFT\REVISEDDRAFT_AOC_SITECHAR_110909.DOC 7 the channel. Bathymetry data surveyed by the U.S. Army Corps of Engineers in 2005 along with three previous reports that present results of vibracore sampling in Atlantic Ocean Channel were obtained and integrated into Fugro’s GIS database. The reports include:

United States Army Corps of Engineers Baltimore District (1995), “Subsurface Investigation by Vibracoring for Sandbridge Beach and Virginia Beach Erosion Control and Hurricane Protection Project,” dated October 1995.

United States Army Corps of Engineers Norfolk District (1990), “Subsurface Investigation by Vibracoring, Atlantic Ocean Channel, Thimble Shoal Channel, and Off Sandbridge,” performed by Exmar, September and October of 1989, and June and July of 1990

United States Army Corps of Engineers Baltimore District (1986), “Geology and Soils, Subsurface Investigation, Atlantic Ocean Channel, Norfolk Harbor and Channels, Virginia,” Appendix C, Vol. 4, dated June 1986.

A total of 125 historical vibracores were available. Those 125 historical vibracore explorations are located throughout the full length of the Atlantic Ocean Channel area with the majority located in the southeastern portion. Of the 125 explorations, 105 are located within the existing Navigation Channel. The exploration locations are shown in Figure 2-3 and Chart 1 and listed in summary tables in Appendices C, D, and E. The exploration summary tables also list the mudline elevation reported at the time of the vibracore exploration and mudline elevation from the 2007 bathymetric survey.

3.1.6.1 USACE 1995 Vibracores

In 1987, 6 vibracore explorations were completed to depths of 9.2 to 20 feet below mudline. The logs are provided in Appendix C. The logs contain the original vibracore identification number and the number (lower right corner of logs) used on the charts and cross sections in this report.

Laboratory Test Data. No laboratory data are available.

3.1.6.2 USACE 1990 Vibracores

Seventy-four vibracore explorations were available in the USACE 1990 report. Forty-seven vibracores were conduced in 1989 penetrated between 12 and 20 feet below the mudline. Twenty-five vibracore explorations were conducted in 1990 and penetrated between 12 and 20 feet below the mudline. The logs are provided in Appendix D.

Laboratory Test Data. Available laboratory test data include grain size curves (see Table 2-2). The test results are provided in Appendix D.

3.1.6.3 USACE 1985 and 1983 Vibracores

The available historical geotechnical data from the USACE (1986) issued report includes 24 vibracore explorations from 1985 that were completed to depths of 17 to 20 feet below the

N:\MANAGEMENT\3582_CRANEYISLAND\LIBRARY\FA_DELIVERABLES\2009_AOC_SCR_DRAFT\REVISEDDRAFT_AOC_SITECHAR_110909.DOC 8 mudline and 21 vibracores ranging from 15.2 to 20 feet below the mudline. Appendix E provides original logs from the 1985 and 1983 geotechnical investigations and include the original vibracore identification number and the number (lower right corner of logs) used on the charts and cross sections in this report.

Laboratory Test Data. Available laboratory test data include grain size curves, fines content from No. 200 wash sieves, Atterberg limits, and specific gravity (see Table 2-2). The test results are provided in Appendix E.

3.1.7 Geophysical Data (2007 Survey)

Seismic reflection records are produced when an acoustic energy source generates a pulse of sound that travels through the water column and penetrates into the seabed. The media (water, sediment, rock) through which the sound passes affects the acoustic signal in various ways. The more dense a medium, the faster is the speed of sound, and thus as the wave front passes through materials with different densities, its rate of progress varies. At the interface between layers of different velocities (velocity contrasts or reflectors), some of the energy is reflected. These reflections are detected by the hydrophone array.

The seismic reflection survey for the Atlantic Ocean Channel was conducted between October 30th and December 5, 2007 by Alpine Ocean Seismic Survey, Inc. (Alpine) under contract to S&ME. During that period, when weather permitted, surveying was performed at the Atlantic Ocean Channel. When sea state conditions were unfavorable for surveying, operations were performed at one of the other more protected potential borrow sites. The survey utilized two seismic reflection systems simultaneously: 1) an EdgeTech XStar Full Spectrum “Chirp” Subbottom Profiler system operating with frequencies of 2-16 kHz, and 2) a 300-joule “Boomer” source (0.5-8 kHz) with a single-channel hydrophone array.

The survey was conducted along a predefined grid of tracklines that totaled about 209 nautical miles. The survey grid consisted of 19 primary lines (Lines 1 to 19) oriented parallel to the navigation channel spaced 550-feet apart and 20 tie lines (Lines 20 to 39) oriented perpendicular to the channel spaced 3,000-feet apart. Vessel trackline locations are shown on Figure 2-1 and Chart 1.

Vessel navigation and positioning used a Trimble 4000 differential global positioning system interfacing with a Trimble ProBeacan Coast Guard beacon receiver. The Coast Guard beacon used during the survey was located at Driver, Virginia (frequency of 289 kHz at 100 bps). The positioning accuracy of the vessel’s GPS antenna with this configuration is considered to be within 3 feet (sub-meter). Hypack navigation software was used to collect the positioning information. Hypack software was also used to process postioning data, make adjustments for equipment layback and offset, and provide the positioning information for the Chirp system and mid-point between the boomer source and receiver.

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3.1.7.1 Chirp Sub-bottom Profiler (2-16 kHz)

The EdgeTech 3200 XS “Chirp” sub-bottom profiler was used to image the upper 30 feet of sediments. The system transmits and receives an FM pulse signal linearly swept over a full spectrum range of 2-16 kHz for a period of approximately 20 milliseconds.

Following the data acquisition, OSI performed data processing using the Discover software (S&ME, 2009). The initially recorded in proprietary JSF file format were converted to SEG-Y file format. OSI provided the SEG-Y data to Fugro. Fugro converted the navigation into the project coordinate system and adjusted the data to MLLW for integration with the geotechnical data. The SEG-Y data were then loaded into Seismic MicroTechnology’s Kingdom Suite Software for interpretation.

Figure 3-2 shows an example of the Chirp data. The Chirp data penetrated up to 50 feet below the seafloor in the large paleochannel area. Several smaller, shallow paleochannels were also identified with the Chirp data.

3.1.7.2 Single-channel Hydrophone Array, Boomer System

An OSI 300J “Boomer” system consisting of an AA200 boomer plate and catamaran, OSI 300-joule power supply, and single-channel hydrophone array was used to image the upper 100-feet of sediments. The source energy had a general frequency distribution of 500-8,000 Hz. Coda’s Octopus 760 acquisition system was used to digitally record the data.

Following the data acquisition, OSI performed seismic data processing using the REFLEXW (Sendmeier Software Version 2.5) software package. Data processing generally consisted of the following steps (OSI, 2008):

File conversions, navigation and geometry checks

Band Pass Filtering: A 1-D bandpass filter (~1,000-4,000 Hz) used to increase signal-to-noise ratio and minimize interference from the second seismic acquisition system.

Deconvolution: Spiking-deconvolution using the recursion-algorithm of Levinson (Wiener-Filter method) to smooth and improve the wavelet shape.

Envelope Calculation: Trace analysis was performed using the Hilbert- Transformation to calculate the envelope or instantaneous amplitude. The instantaneious attribute gave an overview of the energy distribution of the traces and facilitated the determination of signal arrivals.

Swell Filtering: A lowpass filter in the distance dimension was applied to eliminate fluctuations in the x-direction smaller than a choosen wavelength. This was used for smoothening data to remove the effect of sea conditions.

Static Corrections: A muting curve was used to set water column amplitudes to zero. A time cut was performed to trim the record length to 60 milliseconds.

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Gain Adjustment: Automatic gain control (AGC) or manual gain adjustments along with a time variable gain (TVG) may have been applied to adjust gain settings. It is unclear whether this performed or the data are true amplitude.

Trace editing: It is unclear whether trace editing was performed or not. This is commonly performed to remove a “bad” or noisy trace resulting from vessel noise, or rough sea state among other things.

Following the processing steps above, the seismic data were converted to SEG-Y files and transmitted to Fugro. Fugro converted the seismic data navigation into the project coordinate system and adjusted to MLLW for integration with the geotechnical data. The SEG- Y data were then loaded into Seismic MicroTechncology’s Kingdom Suite Software for interpretation.

Figures 3-3a and 3-3b show examples of the boomer seismic data. In general the boomer seismic data provided fair to good quality data that were used as the primary source for mapping.

3.2 DATA ANALYSIS AND MAPPING METHODS

3.2.1 Sediment Classification From CPT and Vibracore Data

Empirical relationships have been developed to classify soils and evaluate material properties using data from full-size cones of CPT soundings. Figure 3-4 is an example of the of CPT sounding 08BC-49 as depicted on the cross sections. CPT soundings provide a near-continuous record (measurements are made at 5 millimeter [-mm] intervals assuming a constant 2-centimeter-per-second [-cm/sec] penetration rate) of sleeve friction, cone tip resistance, and friction ratio. The friction ratio, expressed as a percent, is computed by dividing the sleeve friction measurement taken at the depth of the center of the sleeve by the average of the tip resistance measured over the length of the sleeve. The mCPT did not collect pore pressure data.

Empirical relationships between full-size CPT measurements and soil classifications have been derived from thousands of measurements for all different classifications of soils. An example correlation chart (Robertson and Campanella, 1988) divides the graph of tip resistance

vs. friction ratio into 12 soil classification zones. This chart is shown in Figure 3-4. Each measurement can be identified with a specific soil classification zone. Those correlations were used to: 1) differentiate between primarily fine-grained and primarily coarse-grained soil layers, and 2) estimate the percentage of fine-grained materials within the primarily coarse-grained layers.

The soil classifications used herein for the mCPTs are based on the empirical classifications of Robertson and Campanella (1988) developed for full-size CPT data. We note that those classifications may err in their classification of transitional soils (such as silts) and in loose granular sediments near the seafloor.

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3.2.2 Integration of Geotechnical and Geophysical Data

Locating the geotechnical explorations conducted in 2008 along the geophysical survey lines facilitated the integration of the geophysical and geotechnical data. In fact, Figure 3-1 and Chart 1 show that the majority of the explorations were located at the intersections of geophysical survey lines. In general, many of the historical explorations were located within a few hundred feet of a survey line.

Geotechnical and geophysical data were loaded into Seismic MicroTechnology’s Kingdom Suite Version 8.3 software for correlation and interpretation. After correcting for elevation errors and adjusting the data to MLLW, the geotechnical and seismic data correlated fairly well.

Figures 3-5, 3-6a and 3-6b illustrate the process that was used to correlate the geotechnical explorations with the geophysical survey data. The vertical axis of the geophysical records represents two-way reflection time, which is the time for the sound energy to travel from the source to the reflector and back to the receiver at the water surface. This axis can be converted to an approximate depth scale using the velocity of sound in the water and the sediments. The approximate elevation scale shown on Figures 3-5, 3-6a and 3-6b is based on a constant velocity of sound in the water and sediment of 5,000 ft/sec.

To facilitate a direct comparison with the geophysical records, the depth scales on the geotechnical logs were converted to a reflection time scale using the same velocity. The logs were then overlaid on the geophysical records to identify the reflectors that correlated with lithologic transitions delineated with the geotechnical data. Once the reflectors were identified, they were traced throughout the mapping areas by loop tying, a process of insuring that the same reflectors are being mapped at the line intersections. If the mapped horizons were not identical at the intersections, the geophysical data were reviewed to determine if a reflector had pinched out or a "leg" (black-white-black) had been jumped. If that was not the case, the selection of unit boundaries on the appropriate geotechnical explorations was reviewed and adjusted as necessary.

The base of the Potential Borrow Unit (PBU) followed various reflectors but transitioned to another reflector when a reflector associated with the overlying sand layer either terminated due to pinch-out, facies change, or the fine-grained layers within the PBU comprised enough of a unit to make it an unviable sand resource.

3.2.3 Mapping Overburden and Sand Horizons

Isopach (thickness) maps of the Potential Borrow Unit (PBU) were constructed by integrating the geophysical and geotechnical data. Seismic reflections representing the base of the PBU were correlated with soil layers identified in the CPT soundings and vibracores. The geophysical data were then used to map the horizons in the areas between the geotechnical data points. The iterative process to accomplish the geotechnical-geophysical correlations is described above in Section 3.2.2.

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Reflection time differences between the seafloor reflection and the base of the PBU were measured on the seismic reflection records. Those reflection time differences were converted to thickness of the units using a value of 5,000 ft/sec for the velocity of sound. The thickness values were contoured to form the isopach maps of the units. The thickness values were subtracted from the seafloor elevation values from the single beam survey to produce elevation maps of the base of the PBU.

Data points from the geophysical records and geotechnical explorations were plotted and contoured using the ArcView GIS software package. Elevation maps of the base of units were then used to determine areas where material existed above El. -63 feet (MLLW), the authorized dredge limit based on NEPA documents.

3.2.4 Cross Sections

Cross sections were developed using proprietary software and Environmental Systems Research Institute’s (ESRI) ArcGIS program. ArcGIS is a software package used by Fugro for mapping spatial data. The cross sections depict a combination of geophysical and geotechnical data. Vibracore logs, and logs of CPT soundings are set to the same vertical scale and projected onto the line of cross section. Surfaces from the bathymetric maps and subsurface horizons mapped by the geophysical data also are projected onto the line of the section at the same vertical scale.

The cross sections present several key pieces of information including:

Soil type as logged and classified from vibracores, mCPT tip resistance, friction ratio, and soil behavior type, Fines content from laboratory tests with a red bar that represents the interval the sample was collected, Median grain size, Fine content estimated from mCPT data using two procedures (Baez et al., 2000 and Robertson and Wride, 1998), Seismic reflectors, Base of potential borrow unit, and

“Available” material for potential borrow unit. This is defined as material above El. - 63 ft and within the navigation channel.

Symbols used on the cross sections are shown on Figure 3-4.

The vertical scale for all cross sections in this report is the same, 1 inch = 10 feet. The horizontal scale was set at 1 inch = 200 feet on 11” x 17” cross sections and 1 inch = 600 feet on the Arch E size Charts 4 and 5.

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4.0 ATLANTIC OCEAN CHANNEL SITE CONDITIONS

4.1 DESCRIPTION OF SITE

The Atlantic Ocean Channel study area is located seaward of the mouth of the Chesapeake Bay and extends 8.7 nautical miles eastward from the three-nautical mile limit (Figure 2-1). The navigation channel is 1,300 feet wide and is maintained by the USACE.

4.1.1 Bathymetry

The bathymetry within the surveyed area is shaped by anthropogenic and natural processes (Figures 2-2a and 2-2b and Chart 2). Within the navigation channel, the USACE periodically authorizes dredging as part of the channel maintenance program. About 2,400 feet of the northwestern surveyed channel is lower than El. -63 feet (area shown in red on isopach maps). Much of the rest of the navigation channel is between El. -54 and -58 feet with the exception of the southeastern end of the channel where it drops below El. -60 feet.

Figure 2-2b presents a 3-dimensional rendering of the bathymetry. The northwestern 2/3 of the channel is flat due to dredging. However, the southeastern 1/3 is characterized by sand waves that are more prominent outside of the channel.

4.2 GEOLOGY AND SHALLOW SEDIMENT STRATIGRAPHY

4.2.1 Geologic Setting

The entrance to Chesapeake Bay and the adjacent offshore area lies within the submerged extension of the Coastal Plain Province. Shallow sediments include late Tertiary to modern, Holocene-age materials deposited during the various marine transgressions and regressions that occurred as sea level fluctuated between glacial and interglacial episodes.

The site is located within an area mapped as thin Holocene estuarine-marine deposits in channels (Figure 4-1) (Colman and Hobbs, 1987). In general, Holocene estuarine-marine deposits are considered to be transgressive and are comprised either of sand and clay infill of older incised channels or sands that blanket underlying older sediments and form various shoals.

Net transport of sediment is primarily westerly through modern tidal channels (e.g. Cape Henry Channel), up to tens of kilometers into the Bay (Colman et al., 1988; Newell et al., 2004).

The southeastern-third of the survey area is dominated by a sand wave field. These sand waves comprise most of the PBU in the Areas 5, 6, and 7 (Figure 2-2b). A smaller sand wave area exists southwest of the central portion of the navigation channel.

In general, Pleistocene sediments underlie the Holocene sediments and are separated by a major sea level lowstand unconformity. In turn, Pleistocene sediments are generally underlain by Tertiary (Chowan and/or Yorktown Formations) marine sediments.

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During sea level lowstand(s), Pleistocene and Tertiary sediments were incised and subsequently infilled as sea level rose. Figure 4-2 shows three generations of paleo- Susquehanna channels that were created during the three major glacial periods of the Pleistocene. The paleochannel systems form complex buried drainage networks that have been identified in the area by others and in this study (Figures 4-1 and 4-3). The paleochannels are inferred to be Pleistocene and Holocene in age. Both paleochannel systems influence the delineation of the PBU. In general, the larger Pleistocene paleochannels are infilled primarily with clayey materials and to a lesser extent interbedded or sandy materials. One sand body was identified extends above El. -63 feet (Area 2). The Holocene paleochannels are generally smaller (100s of feet wide), shallow (several to 10s of feet deep), and clay infilled. Historical vibracore 83V-109 penetrated one of those channels (see Figure 3-5).

4.2.2 Shallow Sediment Stratigraphy

The PBU is comprised mostly of Recent and Holocene age sediments and to a lesser extent of Pleistocene age sediments. Sediments within the PBU are in decreasing order of abundance, sand with silt, silty sand, and poorly graded sand. The sand fraction is mostly fine to medium sand. Gravel is present occasionally in the PBU and is noted on vibracore logs and cross sections where seismic reflectors were correlated to gravel layers Engineering properties of the PBU are described on subsequent sections.

The sediments underlying the PBU are fat clay, lean clay, or interbedded sand and fine-grained sediments. Geotechnical data can be used to characterize those materials to about 30 feet below the seafloor and seismic data can be used to extrapolate the characterization deeper. However, that is below the depth of the interest for this study.

4.2.2.1 Delineation of Potential Borrow Unit and Subareas

Delineating the PBU was performed using the following criteria.

Average fines content of less than 25%

Fine-grained overburden thickness did not exceed 2 feet

Fine-grained layers did not exceed 25% of the total vertical thickness

“Available” PBU material is further defined by:

Above El -63 feet

Within the navigation channel

The PBU within the navigation channel is divided into seven subareas as shown on Figure 4-3 and Charts 2 through 4. Subarea boundaries (reaches of the navigation channel) are defined by transitions of in the engineering and geologic character (fines content, median grain size (D50), presence of…