Amendment 09_Debris Survey Technical Memo_PPI 197.pdf

Technical Memorandum

Date Issued: 3/03/2023 Page 1 of 35 Gravity Marine, LLC.

Overview

Gravity Marine, LLC was contracted by AECOM to perform a debris survey at Slip 36, the USCG base in Seattle, Washington. These surveys included: a multibeam echosounder (MBES) survey, a side scan sonar (SSS) survey, a magnetometer survey and a sub-bottom profile survey (SBP).

The primary objectives of this study were to update the existing bathymetry data at the site and to identify debris on or below the seabed that may require removal prior to commencing dredging operations. The surveys were performed on January 17th and 18th, 2023. To map seabed debris in high-resolution, a multibeam-echosounder (MBES) with side scan sonar capabilities was used in parallel with an inertial navigation system (INS) to collect swath bathymetry of the seafloor. A magnetometer was used paired with a GNSS navigation system to search for any ferrous objects on the seabed in the project site. Additionally, a sub-bottom sonar was used to search for any other debris not detected by the magnetometer, multibeam and side scan surveys.

The following memo summarizes the survey methodology, data QA/QC, processing methods and results from this study.

To:

AECOM

From:

Gravity Marine LLC

Date:

March 3rd, 2023

Subject:

Seabed Debris Survey Data Summary

Project: Debris Survey at USCG Base Seattle

AECOM – USCG Seattle

Debris Survey 2023

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Multibeam Bathymetric and Side Scan Survey

Survey Coverage

The survey was conducted at slip 36 at the USCG base in Seattle, Washington. The extent of the survey was focused the full width of slip 36 and out past 100 feet into the Duwamish East

Waterway Channel.

Survey Vessel Platform

The MBES survey was conducted on R/V Spieden, a 26-ft aluminum survey vessel owned and operated by Gravity Marine, LLC. It is powered with twin Yamaha 150hp outboard motors. The vessel is outfitted with a custom-built survey pole which holds the multibeam sonar. The survey pole is retractable and is deployed using a stern mounted davit arm with a winch.

Survey Equipment

The following survey equipment was used to conduct the MBES survey.

Table 1. MBES Survey Equipment

Sensor Category Manufacturer/Model

Multibeam Echosounder (MBES) & Side

Scan Sonar NORBIT WBMS

Inertial Navigation System (INS) Applanix POS MV

Position/Heading Applanix POS MV

Sound Velocity Profiler YSI CastAway CTD

MBES Integrated Sound Velocity AML Micro X SV

Acquisition/Processing Software Hypack Hysweep 2022

DATA ACQUISTION

MBES data was acquired through the survey and navigation software package HYPACK 2022, using the SURVEY and HYSWEEP modules to facilitate the MBES sonar data acquisition. This acquisition software also collects all INS, GNSS, and sound velocity data. The MBES sonar system collected swath bathymetry at varying angles and distances based upon survey depth.

Vessel offsets were derived individually for the MBES system, INS, and GNSS systems so the acquisition software could accurately derive real-earth bathymetric soundings from the merged acoustic and GNSS data. Per the manufacturer recommendations, hardware offsets were derived separately for the INS and MBES relative to the centre of motion of the vessel. Lever arms for the

GNSS antennas relative to the attitude sensor were configured directly in PosView, where final

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position data from the INS was corrected to the vessel reference center. Sonar offsets from the reference center to the acoustic phase centers were measured and input in HYPACK/HYSWEEP.

Geodetic Settings

Geodetic settings were configured in HYPACK/HYSWEEP prior to data acquisition. Geodetic settings are summarized in Table 2. Survey Geodetic Parameters.

Table 2. Survey Geodetic Parameters

Parameter Setting

Grids NAD 83/2011

Zone WA State Plane North FIPS 4601

Horizontal Unit U.S. Survey Feet

Vertical Unit U.S. Survey Feet

Geoid CONUS 12B

Vertical Datum NAVD88

MBES QA/QC

Patch Test

Once all equipment was properly installed and configured on the survey vessel, a patch test was conducted to measure angular misalignment between the GNSS, INS, and sonar systems.

Patch tests determine the misalignment relative to the motion sensor and gyro, as well as the time-offset to the GPS system. All patch test data was post-processed using software to calculate offset errors.

MBES Bar Check

A bar check was conducted by placing a static object below the transducer at a specified depth and recording the sonar’s measurement of the object’s depth. This is done by placing a flat plate or solid lead weight below the transducer. Both the depth of the object and the sonar draft should be confirmed during the bar check.

Sound Velocity Profiles

Sound velocity profiles (SVP) were collected using the YSI Cast Away, a conductivity-temperature-depth sensor, which was lowered through the water column along deeper sections of the river. Using these parameters, the sensor creates a sound velocity profile as a function of depth for the water column. SVP is vital to MBES data collection and dictates the

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proper time series of acoustic beam transmission and return. SVP data is used in final processing to calculate accurate depth measurements from the sonar.

Position Accuracy Verification

Real-Time Kinematic (RTK) formatted corrections were received from Trimble RTX, a satellite-based correction service. These corrections were received by the survey vessel through a dedicated auxiliary GNSS antenna (Trimble R10), and the real-time corrections were sent directly to the Applanix POS MV.

As a quality control check for the RTK corrections, a GNSS rover was used to occupy an existing

WSDOT monument on land and compared to published coordinates. Horizontal and vertical comparisons showed an agreement within 0.037 feet and 0.035 feet respectively, at the monument.

Published Position GNSS Recorded Position Separation (ft)

Check Point

Northing Easting Elevation

(ft) Northing Easting Elevation (ft) dH dV

WSDOT 6242 220964.604 1256980.623 17.195 220964.635 1256980.643 17.230 0.037 0.035

MBES Data Processing

The multibeam data was processed using Hypack 2022 HYSWEEPs MBMAX64 data processing module. The bathymetric data processing approach was conducted using the following steps:

1. Review and editing of position, tide, sound velocity, heading, roll, pitch, and heave data.

2. Review of swath data from each discrete survey data file.

3. Perform area-based editing of all data, comparison of overlapping lines, and removal of spurious/erroneous data points.

4. Export final edited data and create a gridded surface file.

The horizontal and vertical position data for the survey was post-processed with Applanix

Position and Orientation System Post-Processing Package (POSPac). This complete post-processing solution for recorded real-time data allows the user to construct a network of base stations and apply the corrections to the real-time position data collected during the survey.

This process identifies and removes erroneous position data, improves heading, improves motion angles, and dramatically increases vessel heave accuracies. A post-processed position file from POSPAC was input into MBMAX64 to provide further position corrections and to calculate more accurate soundings.

Final concatenated XYZ files were used to create triangular irregular networks (TIN) of the survey data. These networks were converted to gridded matrices and were used to display

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survey area, bathymetric contours and relief. Drawings were created using ESRI ArcMap 10.8

GIS platform.

The final data was transformed to represent bathymetric elevations in MLLW for Bremerton, WA. Since the survey data was acquired in the vertical datum NAVD88, the vertical data was adjusted to the MLLW datum. The value of +2.34 (ft) was used to adjust the data from NAVD88 to MLLW. The conversion value used is based on the data from NOAA’s tide station in Seattle

(ID: 9447130).

Side Scan Imagery Processing

The side scan imagery collected during the survey is first processed to smooth out vessel heading for each transect track. This help to identify bottom and range of each scan which is used in processing the nadir gap inherent in each image.

Data is then processed to review each scan in a “waterfall” configuration, which stack individual scans to get a complete picture of each scan. In this stage edits are made to the gain settings for each file as well as the colorization options.

Finally, a single mosaic of all side scan files to create a single image of all the side scan data. The individual files are stitched together and filtered to create a complete picture of the survey area. This product is used for overlaying on final drawings and help with orientation of identified targets.

Multibeam and Side Scan Results

Throughout the data processing procedures, targets were identified with the multibeam data and some were verified with the side scan imagery. The multibeam data was initially processed with high resolution to allow for seabed target identification. The side scan imagery was then used to confirm targets seen in the bathymetry data. Each identified target was then reviewed in the raw 3D point-cloud data. Appendix A summarizes each target and shows a 3D point-cloud image.

By using the multibeam sonar with its built-in side scan imagery capabilities, a list of 34 targets on the seabed around the project site were identified. Many of these targets appear to be logs or broken pilings on the seabed. 9 targets along the Southern pier wall (T02-T10) appear to be 3 cylindrical shapes in line with each other. Outside port facilities to the Southern shallower area, T32 is a target that looks like a large debris pile or possible concrete. T31 possibly shows what appears to be a small vessel (approximately 9ft x 4ft). Many other targets are small and appear to be random debris, these include: T13, T17-T22 and T24-T26.

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Table 3: Target Location and Description

Name X Y WGS84 Lat WGS84 Lon Depth Size Notes t-01 1267911.93 218878.89 47.59002996 N 122.34299522 W -42 10 ft log t-02 1267930.10 218848.72 47.58994824 N 122.3429192 W -39 10x8 ft 3 cylindrical shapes t-03 1267963.23 218846.35 47.58994353 N 122.34278478 W -40 10x8 ft 3 cylindrical shapes t-04 1268008.97 218851.87 47.58996111 N 122.3425999 W -41 10x8 ft 3 cylindrical shapes t-05 1268111.88 218849.51 47.58996017 N 122.34218275 W -41 10x8 ft 3 cylindrical shapes t-06 1268161.96 218849.90 47.58996394 N 122.34197987 W -40 10x8 ft 3 cylindrical shapes t-07 1268217.16 218847.14 47.58995933 N 122.341756 W -40 10x8 ft 3 cylindrical shapes t-08 1268292.48 218844.78 47.58995692 N 122.34145064 W -40 10x8 ft 3 cylindrical shapes t-09 1268312.02 218842.90 47.58995282 N 122.34137132 W -39 10x8 ft 3 cylindrical shapes t-10 1268337.94 218841.57 47.58995056 N 122.34126619 W -39 10x8 ft 3 cylindrical shapes t-11 1268318.61 218879.47 47.59005341 N 122.34134752 W -40 10ft possible log t-12 1268419.78 218921.08 47.59017289 N 122.34094092 W -39 16ft long log or group of small debris t-13 1268962.79 218965.75 47.59032447 N 122.33874434 W -34 4ft diameter round object t-14 1268977.10 218957.85 47.59030358 N 122.33868573 W -34 11ft long possible log t-15 1268913.28 219039.73 47.59052458 N 122.3389508 W -32 11ft possible piling t-16 1268834.48 219039.25 47.59051906 N 122.33927004 W -40 14ft possible log t-17 1268388.84 218998.50 47.59038344 N 122.34107242 W -41 5ft x 4ft unknown t-18 1268302.31 219052.54 47.59052692 N 122.34142731 W -41 3ft diameter unknown t-19 1268398.80 219019.63 47.59044189 N 122.34103374 W -41 3ft diameter Unknown t-20 1268194.40 219047.86 47.59050828 N 122.34186416 W -41 2ft diameter small unknown debris t-21 1268117.45 219059.45 47.59053592 N 122.34217686 W -41 2ft diameter small unknown debris t-22 1268094.46 219054.89 47.59052219 N 122.34226965 W -42 1.5ft diameter small unknown debris t-23 1267547.47 219515.68 47.59175578 N 122.34452257 W -56 18ft long possible log t-24 1267467.63 219392.22 47.59141308 N 122.34483624 W -60 6ft diameter round unknown object t-25 1267436.10 219151.04 47.59075031 N 122.3449448 W -58 2ft x 1ft small unknown object t-26 1267453.06 219086.29 47.59057375 N 122.34487093 W -58 2ft x 1ft small unknown object t-27 1267721.04 218456.76 47.58886265 N 122.34373507 W -52 24ft x 3ft possible log t-28 1267718.96 218503.84 47.58899158 N 122.34374725 W -52 20ft long possible log t-29 1267713.18 218557.05 47.58913711 N 122.3437749 W -52 18ft long possible log t-30 1267735.30 218671.57 47.5894522 N 122.34369438 W -52 27ft possible log t-31 1267938.90 218690.94 47.58951625 N 122.34287101 W -12 9ft x 4ft possible small boat t-32 1267912.97 218689.54 47.58951101 N 122.34297595 W -13 17ft x 9ft grouping of large debris t-33 1267935.36 218718.52 47.58959164 N 122.34288754 W -14 20ft long possible log t-34 1267857.48 218744.14 47.58965769 N 122.34320512 W -35 30ft long possible log

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Figure 1. MBES Bathymetric Overview DEM

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Figure 2 Side Scan Imagery

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Figure 3. MBES seabed debris targets identified

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Figure 4 MBES seabed debris targets identified

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Magnetometer Geophysical Survey

A Marine Magnetics Explorer was used to collect total magnetic field data within the project area which was located at slip 36 at the USCG base in Seattle, Washington. The extent of the survey was focused the full width of slip 36 and out past 100 feet into the Duwamish East

Waterway Channel. The magnetometer was towed behind the survey vessel along transects spaced approximately every 25’ within the survey area.

The following survey equipment was used to conduct the magnetometer survey:

Magnetometer Marine Magnetics Explorer

Position/Heading Applanix POS MV

Navigation Software Hypack Survey 2022

Acquisition/Processing Software BOB Software – Marine Magnetics

Data Acquisition

Data acquisition for the magnetometer survey was done through BOB – a software platform built by the magnetometer manufacturer, Marine Magnetics. The software interfaces directly with the magnetometer and collects total magnetic field data along with all positioning information. The software allows for real-time assessment of data and sensor diagnostics as well as calculates magnetometer layback in real-time.

Magnetometer QA/QC

System Assessment

The magnetometer is a sensitive instrument, and many factors influence the quality of the data collected. The magnetometer is a passive instrument that records the total strength of the earth’s magnetic field in nano-Teslas (nT). The earth’s magnetic field vectors change based on the given latitude of the survey area.

Prior to commencing the magnetometer survey, a full system assessment was conducted to ensure all proper checks and procedures were in place to execute a successful SBP survey. This includes assessment of the following items:

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• Confirm magnetometer system is powered and transmitting/receiving data

• Confirm GPS system is powered and transmitting/receiving position data, and position data seems reasonable given the geographic location

• Check survey acquisition software is running properly, and all sensors are communicating properly with the software

• Check survey computer that it has sufficient hard drive space and memory to conduct survey and run current version of acquisition software.

• Review raw total field data values to ensure instrument is recording reasonable data for the given geographic location.

Magnetometer Processing

Magnetometer data was processed in several steps using a combination of the BOB and GIS software. The BOB software allows for removal of any data that contains errors from a weak signal, poor reading, mistuning of the instrument or a gradient condition in the data. GIS software was then used to analyze the data geographically. This allowed for further assessment of signal strength and erroneous spikes not supported by the surrounding data.

The processed data was used to define a total magnetic field with track lines and surface grids.

These maps were compared with the identified targets from the multibeam survey.

Magnetometer Results

Given the geographic latitude of the project site, the total estimated background magnetic field values in the vicinity of the project site are approximately 52,000 Nano Teslas. After processing the magnetometer data and looking at the total magnetic field recorded by the magnetometer, it is clear that the data is heavily influenced by the close proximity of the port facility and large ships at dock. Large ferrous objects such as vessels, steel pilings, and materials used to build docks and piers can bias the magnetometer data. Electrical infrastructure, which is found on vessels and around port facilities, can also manipulate magnetometer fields. Interference from the port on the total magnetic field was apparent in the data. No significant magnetic anomaly targets were found with the magnetometer. The effects of the port’s infrastructure on the magnetometer may have impacted the survey’s ability to detect smaller magnetic disturbances near the seabed. In addition, there were no magnetometer anomalies that correlated with targets identified from the multibeam survey.

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Figure 5. Magnetometer survey track lines

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Figure 6 Magnetic Field

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SBP Geophysical Survey

SURVEY METHODOLOGY

An Edgetech 3100 SB-216S was used to collect sub bottom profile data within the project area which was located at slip 36 at the USCG base in Seattle, Washington. The extent of the survey s focused on the full width of slip 36 and out past 100 feet into the Duwamish East Waterway

Channel. The SBP was towed behind the survey vessel along transects spaced approximately every 25’ within the survey area.

The SBP is a single beam echosounder which operates at a frequency range of 2-16 kHz. This allows the acoustic beam to penetrate deep into the sediment for observing and measuring different layers of the subsurface. As a result, more lines were run for SBP compared to MBES to increase overlap for comparison and estimating the accuracy during data processing.

The following survey equipment was used to conduct the SBP survey:

Sub Bottom Sonar Edgetech 3100 SB-216s

Position/Heading Applanix POS MV

Sound Velocity Profiler YSI CastAway CTD

Navigation Software Hypack Survey 2022

Acquisition/Processing Software Discover Sub Bottom / Hypack 2022

Data Acquisition

Data acquisition for the SBP survey was collected using Edgetech’s Discover Sub bottom.

Edgetech’s proprietary software was utilized to control the settings for the sensor, and saves raw acoustic data in the native file format (*.jsf files) as well as industry standard *.segy files.

This software also receives GPS position data to georeference all acoustic data.

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SBP QA/QC

System Assessment

Prior to commencing SBP survey activities, a full system assessment was conducted to ensure all proper checks and procedures were in place to execute a successful SBP survey. This includes assessment of the following items:

• Confirm SBP system is powered and transmitting/receiving data

• Confirm GPS system is powered and transmitting/receiving position data, and position data seems reasonable given the geographic location

• Check survey acquisition software is running properly, and all sensors are communicating properly with software

• Check survey computer that it has sufficient hard drive space and memory to conduct survey and run current version of acquisition software.

• Review raw acoustic time series to ensure suitable depths and features are observed in the acoustic data, and acoustic imagery is void of excessive “noise”.

Sound Velocity Profiles

Sound velocity profiles were conducted at the beginning and end of the SBP survey. These were conducted using the YSI Cast Away, a conductivity-temperature-depth sensor lowered through the entire water column. This sensor uses these data to create a sound velocity profile as a function of depth for the entire water column. These data are used in final SBP processing to calculate accurate SBP data.

SBP PROCESSING

Processing of SBP data followed a two-stage approach. Raw data was initially converted from the native file format to a SEG-Y file (an industry standard seismic data file format). These processed data files were then used for further processing and interpretation. The sub-bottom processing tool in HYPACK 2022 was used to further process SBP data and interpret cross sections. The SBP processing method is summarize below:

1. Convert all files to SEG-Y.

2. Enter all files into the HYPACK 2022 project file.

3. Scale all data horizontally and vertically to best present the raw data for processing and interpretation.

4. Apply signal processing utilities, specifically frequency filters and gain controls, to best highlight the subsurface stratigraphy.

5. Conduct manual interpretation of the sub-bottom profiler sections and/or identify debris at or near seabed surface and create targets.

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SBP RESULTS

The purpose for this study was mainly to identify debris near the seabed at the project site. The sub bottom sonar analysis focused primarily near the surface of the seabed. The Sub bottom data reveals not only many layers deep below the seabed, but also diverse layering of surface and near surface sediments on the seabed. The data shows a wide range of density and acoustically reflective sediments. Because of the varied density near the bottom, it is difficult to distinguish between targets and dense sediments at or near the surface of the seabed.

This site posed a few challenges for the sub bottom sonar. The sub bottom data shows acoustic distortions and reflections near the large ships at dock and pier structures. The narrow east-west path between the large ships on the north and south piers, limited the vessel’s ability to approach from different angles with the towed sub bottom sonar. It also appears there may have been other sonars operating at the same time from vessels at dock that contributed to the complex returns from the sub bottom sonar.

In total, the Sub bottom sonar analysis identified 13 potential debris targets. All of the targets were at or near the surface of the seabed. Most all these targets are within a reasonable distance from the targets identified by the MBES & Side scan analysis. Only 3 of the 13 sub bottom sonar targets identified were not near MBES & side scan targets. These targets are SB-

6, SB-7 and SB-13. All 3 of them are outside the berthing area of the port facility. SB-6 is near the outside end of the southern piers. SB-7 and SB-13 are about 130 ft east of the port entrance in the main Duwamish East Waterway Channel.

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Table 4 SBP Targets

Name X Y WGS84 Lat WGS84 Lon Time Date

SB-1 1268033.38 219072.32 47.59056667 N 122.34251852 W 20:25:49 1/17/2023

SB-2 1268318.72 219070.37 47.59057667 N 122.34136222 W 20:24:26 1/17/2023

SB-3 1268075.92 218855.01 47.58997333 N 122.34232889 W 21:37:20 1/17/2023

SB-4 1267979.57 218860.55 47.58998333 N 122.34271972 W 21:37:48 1/17/2023

SB-5 1267902.79 219144.2 47.59075667 N 122.34305333 W 21:45:48 1/17/2023

SB-6 1267896.01 218798.65 47.58980917 N 122.34305333 W 21:44:24 1/17/2023

SB-7 1267769.9 218912.09 47.59011333 N 122.34357333 W 22:23:19 1/17/2023

SB-8 1267742.6 218694.95 47.58951667 N 122.34366667 W 22:22:30 1/17/2023

SB-9 1268350.83 219001.64 47.59039 N 122.34122667 W 23:43:56 1/17/2023

SB-10 1268179.32 219080.4 47.59059667 N 122.34192783 W 23:50:10 1/17/2023

SB-11 1267989.35 218883.47 47.59004667 N 122.3426819 W 21:23:38 1/17/2023

SB-12 1268858.6 219032.94 47.59050306 N 122.33917182 W 21:30:16 1/17/2023

SB-13 1267744.79 218806.78 47.58982333 N 122.34366667 W 22:33:10 1/17/2023

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Figure 7 SBP Tracklines

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Figure 8 SBP Targets

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Figure 9 SBP Target SB-1 & SB-2

Figure 10 SBP Target SB-3 & SB-4

Figure 11 SBP Target SB-5 & SB-6

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Figure 12 SBP Target SB-7 & SB-8

Figure 13 SBP Target SB-9

Figure 14 SBP Target SB-10

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Figure 15 SB-11

Figure 16 SB-12

Figure 17 SB-13

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APPENDIX A – Multibeam Point-cloud Target Log

Name t-01

X 1267911.93

Y 218878.89

WGS84 Lat 47.59002996 N

WGS84 Lon 122.34299522 W

Depth -42

Notes possible log

Size 10ft

Name t-02

X 1267930.1

Y 218848.72

WGS84 Lat 47.58994824 N

WGS84 Lon 122.3429192 W

Depth -39

Notes 3 cylindrical shapes

Size 10x8

Name t-03

X 1267963

Y 218846.4

WGS84 Lat 47.58994353 N

WGS84 Lon 122.34278478 W

Depth -40

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Name t-04

X 1268009

Y 218851.9

WGS84 Lat 47.58996111 N

WGS84 Lon 122.3425999 W

Depth -41

Name t-05

X 1268112

Y 218849.5

WGS84 Lat 47.58996017 N

WGS84 Lon 122.34218275 W

Depth -41

Name t-06

X 1268162

Y 218849.9

WGS84 Lat 47.58996394 N

WGS84 Lon 122.34197987 W

Depth -40

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Name t-07

X 1268217

Y 218847.1

WGS84 Lat 47.58995933 N

WGS84 Lon 122.341756 W

Depth -40

Name t-08

X 1268292

Y 218844.8

WGS84 Lat 47.58995692 N

WGS84 Lon 122.34145064 W

Depth -40

Name t-09

X 1268312

Y 218842.9

WGS84 Lat 47.58995282 N

WGS84 Lon 122.34137132 W

Depth -39

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Name t-10

X 1268338

Y 218841.6

WGS84 Lat 47.58995056 N

WGS84 Lon 122.34126619 W

Depth -39

Name t-11

X 1268319

Y 218879.5

WGS84 Lat 47.59005341 N

WGS84 Lon 122.34134752 W

Depth -40

Size 10ft

Name t-12

X 1268420

Y 218921.1

WGS84 Lat 47.59017289 N

WGS84 Lon 122.34094092 W

Depth -39

Notes log or group of small debris

Size 16ft long

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Name t-13

X 1268963

Y 218965.8

WGS84 Lat 47.59032447 N

WGS84 Lon 122.33874434 W

Depth -34

Notes round object

Size 4ft diameter

Name t-14

X 1268977

Y 218957.9

WGS84 Lat 47.59030358 N

WGS84 Lon 122.33868573 W

Depth -34

Size 11ft long

Name t-15

X 1268913

Y 219039.7

WGS84 Lat 47.59052458 N

WGS84 Lon 122.3389508 W

Depth -32

Notes Possible piling

Size 11ft

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Name t-16

X 1268834

Y 219039.3

WGS84 Lat 47.59051906 N

WGS84 Lon 122.33927004 W

Depth -40

Size 14ft

Name t-17

X 1268389

Y 218998.5

WGS84 Lat 47.59038344 N

WGS84 Lon 122.34107242 W

Depth -41

Notes unknown

Size 5ft x 4ft

Name t-18

X 1268302

Y 219052.5

WGS84 Lat 47.59052692 N

WGS84 Lon 122.34142731 W

Depth -41

Size 3ft diameter

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Name t-19

X 1268399

Y 219019.6

WGS84 Lat 47.59044189 N

WGS84 Lon 122.34103374 W

Depth -41

Size 3ft diameter

Name t-20

X 1268194

Y 219047.9

WGS84 Lat 47.59050828 N

WGS84 Lon 122.34186416 W

Depth -41

Notes small unknown debris

Size 2ft diameter

Name t-21

X 1268117

Y 219059.5

WGS84 Lat 47.59053592 N

WGS84 Lon 122.34217686 W

Depth -41

Size 2ft diameter

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Name t-22

X 1268094

Y 219054.9

WGS84 Lat 47.59052219 N

WGS84 Lon 122.34226965 W

Depth -42

Size 1.5ft diameter

Name t-23

X 1267547

Y 219515.7

WGS84 Lat 47.59175578 N

WGS84 Lon 122.34452257 W

Depth -56

Size 18ft long

Name t-24

X 1267468

Y 219392.2

WGS84 Lat 47.59141308 N

WGS84 Lon 122.34483624 W

Depth -60

Notes round unknown object

Size 6ft diameter

Date Issued: 03/3/2023 Page 32 of 35 Gravity Marine, LLC.

Name t-25

X 1267436

Y 219151

WGS84 Lat 47.59075031 N

WGS84 Lon 122.3449448 W

Depth -58

Notes small unknown object

Size 2ft x 1ft

Name t-26

X 1267453

Y 219086.3

WGS84 Lat 47.59057375 N

WGS84 Lon 122.34487093 W

Depth -58

Notes small unknown object

Size 2ft x 1ft

Name t-27

X 1267721

Y 218456.8

WGS84 Lat 47.58886265 N

WGS84 Lon 122.34373507 W

Depth -52

Size 24ft x 3ft

Date Issued: 03/3/2023 Page 33 of 35 Gravity Marine, LLC.

Name t-28

X 1267719

Y 218503.8

WGS84 Lat 47.58899158 N

WGS84 Lon 122.34374725 W

Depth -52

Size 20ft long

Name t-29

X 1267713

Y 218557.1

WGS84 Lat 47.58913711 N

WGS84 Lon 122.3437749 W

Depth -52

Size 18ft long

Name t-30

X 1267735

Y 218671.6

WGS84 Lat 47.5894522 N

WGS84 Lon 122.34369438 W

Depth -52

Size 27ft

Date Issued: 03/3/2023 Page 34 of 35 Gravity Marine, LLC.

Name t-31

X 1267939

Y 218690.9

WGS84 Lat 47.58951625 N

WGS84 Lon 122.34287101 W

Depth -12

Notes possible small boat

Size 9ft x 4ft

Name t-32

X 1267913

Y 218689.5

WGS84 Lat 47.58951101 N

WGS84 Lon 122.34297595 W

Depth -13

Notes grouping of large debris

Size 17ft x 9ft

Name t-33

X 1267935

Y 218718.5

WGS84 Lat 47.58959164 N

WGS84 Lon 122.34288754 W

Depth -14

Size 20ft long

Date Issued: 03/3/2023 Page 35 of 35 Gravity Marine, LLC.

Name t-34

X 1267857

Y 218744.1

WGS84 Lat 47.58965769 N

WGS84 Lon 122.34320512 W

Depth -35

Size 30ft long