Section 00 90 01_Para 3.4_Att A_Mapping of protective plates AD EXAMPLE.pdf

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Maint Dredging Port Jersey Channel, NYNJ, Port Jersey Channel, Bayonne, NJ

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ENG FORM 4025-R, JUL 2015 REPLACES EDITION OF MAR 2012, WHICH IS OBSOLETEPage 1 of 1

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Contract #W912DS-20-C-0018, GLDD #015896 Mapping of the protective plates after dredging in

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All interpretations are opinions based on inferences from seismic or other measurements. We cannot, and do not, guarantee the accuracy or correctness of any interpretation. We shall not, except in the case of gross or willful negligence on our part, be liable or responsible for any loss, costs, damages or expenses incurred or sustained by anyone resulting from any interpretations made by any of our officers, agents or employees.

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Executive Summary

From November 2011 to August 2012, 430 steel plates were placed above the Passaic Valley Sewerage Commission (PVSC) Tunnel in order to protect this valuable infrastructure from harbor deepening and deep-draft navigation projects. In 2020, as part of Maintenance Dredging of New York and New Jersey Harbor, Port Jersey channel, Federal Navigation Project, the United States Army Corps of Engineers, New York District (USACE-NAN), contracted Great Lakes Dredge & Dock (GLDD) to maintenance dredge the sediments that accumulated above an elevation of -50ft mean lower low water (MLLW) in Port Jersey. This includes dredging the sediment above and around Plates 303 to 430 to an elevation of -50ft MLLW.

For the 2020 round of maintenance dredging over the PVSC Tunnel’s protective plates, GLDD assigned e4sciences (e4) to measure and map the position of the protective plates within and adjacent to the Port Jersey Federal Navigation Channel both before dredging (BD) and after dredging (AD). e4 submitted the BD report in August 2020. This report presents the result and analysis of AD geophysical measurements made directly above and adjacent to the protective plates.

GLDD performed dredging operations between August 21 and September 4, 2020. The USACE approved the area to grade on September 8, 2020 based on an AD bathymetric survey. e4 performed reflection seismology surveys on September 10 and side-scan sonar surveys on September 11, 2020.

The sea state during the seismic data collection was calm, well suited for the surveys.

The BD survey showed that Plates 226 to 288 were free of sediments or partially covered with thin sediments, and Plates 289 to 430 were covered. Plates 320 through 430 had sediments above -50ft MLLW. The purpose of the maintenance dredging was to remove the sediment above -50ft MLLW.

After maintenance dredging, the AD bathymetric survey showed that none of the dredging depth over the steel plates exceeded 50.5 feet MLLW, and Plates 315 to 430 have approximately 1ft to 2.6ft of sediment over the plates. Comparison of the BD and AD geophysical surveys has determined that there is no evidence that the position of the plates changed during dredging or that any plates are above -52.6ft MLLW (National Tidal Datum Epoch of 1981-2001).

Overall, the locations and elevations of the plates are consistent between the BD and AD surveys.

However, there are three discrete locations where there exist higher degrees of uncertainty in the AD seismic interpretation of the location and elevation of the plates. One hypothesis for the localized increases in uncertainty is the geometry of sediments scarred by the dredge bucket. The uneven distribution of sediment over the plates creates seismic artifacts that mask the signal reflecting off the top of the plates; the reflection from the plates is obscured by the signal from the sediments above. In the areas of Plates 341-345, Plates 354-358, and Plates 386-400 dredge scars have steep angles and vertical relief that varies on the order of 0.7ft to 2.0ft. In these areas dredge scars are unevenly distributed and unevenly oriented.

To test the hypothesis, e4 modeled the effect of the uneven distribution of sediments on seismic response of the protective plates. Modeling results indicate that rough geometry of sediments above the plates generates strong seismic diffractions that are masking the response from the top of the steel plates. After integrating the modeling analysis of the AD seismic data and comparing the result to the 2020 July BD seismic data, the 2016 September AD surveys, and the survey after the plates were installed in 2012, we have determined that there is no evidence that the location and elevation of the plates have changed as a result of the 2020 maintenance dredging operations. This conclusion is further supported with discussions of the dredging operations with GLDD.

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Table of contents Executive Summary ........................................................................................................................ iii Table of contents .............................................................................................................................. iv List of figures ................................................................................................................................... iv List of tables ..................................................................................................................................... v List of plates ..................................................................................................................................... v

1. Introduction

2. Scope of work

3. Methodology

3.1 Task 1: Bathymetry

3.2 Task 2: Side-scan sonography

3.2.1 Side-scan processing

3.3 Task 3: Sub-bottom reflection seismology

3.3.1 Sub-bottom seismic processing

3.3.2 Seismic modeling

3.4 Task 4: Integration

3.4.1 Uncertainty

4. Results

4.1 Evaluation of USACE multibeam bathymetry

4.2 After dredge survey results

4.2.1 Seismic data interpretation and modeling

4.3 Plates 226 to 350

4.4 Plates 351 to 430

5. Conclusions Appendix I A-1 Plates 101 to 225 Appendix II

List of figures Figure 1. Location map Figure 2. Sub-bottom tracklines Figure 3. USACE AD multibeam bathymetry (#4990) Figure 4. USACE BD multibeam bathymetry (#4966) Figure 5. Bathymetry difference map between USACE AD (#4990) and BD (#4966) Figure 6. AD Side-scan orthosonograph insonified from the northeast Figure 7. AD Side-scan orthosonograph insonified from the southwest Figure 8. Synthetic model and results for Plates 391 to 400 Figure 9. Synthetic model and results for Plates 356 Figure 10. Synthetic model and results for Plates 394 Figure 11. Close-up of AD side-scan orthosonograph for Plates 341-345 Figure 12. Close-up of AD side-scan orthosonograph for Plates 354-358 Figure 13. Close-up of AD side-scan orthosonograph for Plates 386-400 Figure 14. Seismic interpretation results plotted on top of the AD side-scan orthosonograph Figure 15. Plates 226 – 350: USACE BD and AD bathymetry comparison Figure 16. Plates 226 – 350: USACE bathymetry difference map Figure 17. Plates 226 – 350: comparison of BD versus AD side-scan orthosonograph Figure 18. Plates 226 – 350: comparison of BD versus AD side-scan orthosonograph Figure 19. Plates 251 – 260: sub-bottom comparison AD (above) versus BD (below) Figure 20. Plates 261 – 270: sub-bottom comparison AD (above) versus BD (below) v

Figure 21. Plates 271 – 280: sub-bottom comparison AD (above) versus BD (below) Figure 22. Plates 281 – 290: sub-bottom comparison AD (above) versus BD (below) Figure 23. Plates 291 – 300: sub-bottom comparison AD (above) versus BD (below) Figure 24. Plates 301 – 310: sub-bottom comparison AD (above) versus BD (below) Figure 25. Plates 311 – 320: sub-bottom comparison AD (above) versus BD (below) Figure 26. Plates 321 – 330: sub-bottom comparison AD (above) versus BD (below) Figure 27. Plates 331 – 340: sub-bottom comparison AD (above) versus BD (below) Figure 28. Plates 341 – 350: sub-bottom comparison AD (above) versus BD (below) Figure 29. Plate 304: sub-bottom cross section comparison AD (above) versus BD (below) Figure 30. Plate 307: sub-bottom cross section comparison AD (above) versus BD (below) Figure 31. September 2020 AD sub-bottom cross section at plate 318 Figure 32. Plates 351 – 430: USACE BD and AD bathymetry comparison Figure 33. Plates 351 – 430: USACE bathymetry difference map Figure 34. Plates 351 – 430: comparison of BD versus AD side-scan orthosonograph Figure 35. Plates 351 – 430: comparison of BD versus AD side-scan orthosonograph Figure 36. Plates 351 – 360: sub-bottom comparison AD (above) versus BD (below) Figure 37. Plates 361 – 370: sub-bottom comparison AD (above) versus BD (below) Figure 38. Plates 371 – 380: sub-bottom comparison AD (above) versus BD (below) Figure 39. Plates 381 – 390: sub-bottom comparison AD (above) versus BD (below) Figure 40. Plates 391 – 400: sub-bottom comparison AD (above) versus BD (below) Figure 41. Plates 401 – 410: sub-bottom comparison AD (above) versus BD (below) Figure 42. Plates 411 – 420: sub-bottom comparison AD (above) versus BD (below) Figure 43. Plates 421 – 430: sub-bottom comparison AD (above) versus BD (below) Figure 44. September 2020 AD sub-bottom cross section at plate 356 Figure 45. September 2020 AD sub-bottom cross section at plate 389 Figure 46. September 2020 AD sub-bottom cross section at plate 394 Figure A-1. Plates 101 – 225: comparison of BD versus AD side-scan orthosonograph Figure A-2. Plates 101 – 225: comparison of BD versus AD side-scan orthosonograph

List of tables Table 1. Project chronology

List of plates Plate 01. Location map Plate 02. USACE Bathymetries AD and BD 2020 Plate 03. USACE difference maps Plate 04. Side-scan orthosonograph 2020 from northeast Plate 05. Side-scan orthosonograph 2020 from southwest Plate 06. Seismic cross sections Plate 07. Seismic cross sections

1. Introduction

From November 2011 to August 2012, 430 steel plates were placed above the Passaic Valley Sewerage Commission (PVSC) Tunnel in order to protect this valuable infrastructure from harbor deepening and deep-draft navigation projects. In 2020, as part of Maintenance Dredging of New York and New Jersey Harbor, Port Jersey channel, Federal Navigation Project, the United States Army Corps of Engineers, New York District (USACE-NAN), contracted Great Lakes Dredge & Dock (GLDD) to maintenance dredge the sediments that accumulated above an elevation of -50ft mean lower low water (MLLW) in Port Jersey. This includes dredging the sediment above and around Plates 303 to 430 to an elevation of -50ft MLLW.

For the 2020 round of maintenance dredging over the PVSC Tunnel’s protective plates, GLDD assigned e4sciences (e4) to measure and map the position of the protective plates within and adjacent to the Port Jersey Federal Navigation Channel both before dredging (BD) and after dredging (AD). e4 submitted the BD report in August 2020. This report presents the result and analysis of AD geophysical measurements made directly above and adjacent to the protective plates.

GLDD performed dredging operations between August 21 and September 4, 2020. The USACE approved the area to grade on September 8, 2020 based on an AD bathymetric survey. e4 performed reflection seismology surveys on September 10 and side-scan sonar surveys on September 11, 2020.

The sea state during the seismic data collection was calm, well suited for the surveys.

Figure 1 is a location map. This map includes (a) the as-built template (measured by Weeks Marine Inc. – Construction, contractor for the placement of the plates) and envelope for the plates, (b) the outline of the no-spud zone around the plates, (c) the -50ft MLLW contour from the September 2020 USACE-NAN survey branch multibeam bathymetry (#4990), and (d) the location of the New York Bay shaft.

Table 1 lists the chronology of the project through the before and after dredging mapping.

Table 1. Project chronology.

Task Start Complete yyyy.mm.dd yyyy.mm.dd

1 Notice to proceed 2020.07.07 2 Side-scan acquisition before dredging 2020.07.08 2020.07.08 3 Sub-bottom reflection acquisition before dredging 2020.07.09 2020.07.09 4 Side-scan processing before dredging 2020.07.09 2020.07.10 5 Sub-bottom reflection processing before dredging 2020.07.10 2020.07.24 6 Report for before dredging survey 2020.07.21 2020.08.17 7 Sub-bottom reflection acquisition after dredging 2020.09.10 2020.09.10 8 Side-scan acquisition after dredging 2020.09.11 2020.09.11 9 Sub-bottom reflection processing after dredging 2020.09.14 2020.10.01

10 Side-scan processing after dredging 2020.09.14 2020.09.16 11 Report for after dredging survey 2020.09.28 2020.10.14

Figure 1. Location map including the (a) as-built template and envelope for steel plates in white, (b) no-spud zone around the plates in red, (c) -50ft and -51ft MLLW (NTDE 1981-2001) contours from the September 2020 USACE-NAN multibeam bathymetry (#4990) in gray, and (d) the New York Bay shaft location in red.

2. Scope of work

GLDD assigned e4ciences to perform geophysical surveys before and after dredging in Port Jersey as part of the maintenance dredging contract with the USACE-NAN. e4sciences was the third-party surveyor responsible for quality assurance for the USACE-NAN during the original contract with Weeks Marine Inc. to place the steel plates from 2011 to 2012. e4sciences also performed the geophysical surveys before and after dredging during the 2016 maintenance dredging operations.

e4sciences was contracted to acquire sub-bottom reflection seismology and side-scan sonar measurements and to process and interpret the field data to map the plates exposed in the water column and those hidden beneath the sediments. Sub-bottom seismology was selected because seismic signals penetrate the sediment and reflect off the top of the plates to locate their position in xyz. Successive profiles of each plate determined their relative and absolute locations.

The agreed upon method of quantifying error in the locations of the plates was to compare the orthosonographs and multibeam bathymetry in the areas where the plates were exposed after construction in 2012 and after 2016 maintenance dredging with those acquired before dredging operations in 2020. e4sciences expected the horizontal error to be influenced by the error of the RTK positioning elements and geometric spreading in the measurements.

e4sciences’ before dredging (BD) survey results were delivered to GLDD on August 17, 2020.

e4sciences performed sub-bottom reflection seismology and side-scan sonography to map the plates exposed in the water column and those hidden beneath the sediments for the after dredging (AD) survey. e4sciences used the same equipment and methods in the AD survey as the BD survey.

e4 compared the 2020 AD surveys to (1) the 2020 BD surveys, (2) the 2016 September AD surveys, and (3) the 2012 post-plate-placement survey to determine if GLDD disturbed any plates in the course of the dredging process.

3. Methodology

The horizontal reference frame is New Jersey State Plane, NAD83 (U.S. Survey Feet). The vertical datum is the tidal datum of mean lower low water (MLLW) as defined by the National Tidal Datum Epoch (NTDE) 1983 to 2001, referred through this report as MLLW (NTDE 1983-2001). All elevations show the negative sign where elevations are referenced to MLLW (NTDE 1983-2001).

Measurements are made in feet and tenths of feet. Note that vertical datum has changed from past surveys. The 2012 and 2016 surveys and reports reference elevations relative to the USACE MLW, which is 0.6ft lower than MLLW (NTDE 1983-2001).

e4sciences employed its geophysical research vessel Time and Tide for all marine surveys. The Time and Tide is 55ft in length and fully equipped for geophysical exploration in shallow waters.

3.1 Task 1: Bathymetry

e4sciences analyzed and compared the USACE multibeam bathymetry surveys from before and after dredging operations, that is July (#4966) and September (#4990) 2020.

e4sciences acquired multibeam bathymetry and side-scan sonar on September 11, 2020. The multibeam bathymetry was not part of the scope of work. e4 used the bathymetry as an additional measurement to constrain horizontal and vertical uncertainty of the investigation.

3.2 Task 2: Side-scan sonography

e4 used an Edgetech 6205 at 550kHz to acquire side-scan data and produce the orthosonographs on September 11, 2020 along the channel trajectory. The side-scan sonar transmits ultrasonic waves obliquely into the water and measures the amplitude of the backscatter from the bottom as a function of range. The reflectivity is a function of the bottom roughness, angle of incidence, and sediment acoustic properties. e4’s proprietary processing produces two independent orthosonographs insonified from opposite directions. e4’s reflectivity maps display seamless high-definition images of the structures, sediment, and debris on the channel floor.

The horizontal accuracy in the side-scan orthosonographs is ±2ft. The orthosonograph resolution is ~0.3ft.

3.2.1 Side-scan processing

e4 processed all of the side-scan data with a 0.3ft resolution – that is an order of resolution better than achieved by standard processing. e4 produced georeferenced images illuminated from a single direction that can be imported into any geospatial interpretation software, such as ArcGIS or AutoCAD.

e4’s proprietary method for creating side-scan orthosonographs produces images that present high acoustic reflectivity as bright (white) and low reflectivity areas as dark (dark brown). This differs from the common use of side-scan images in strip charts, which often invert the colors. e4’s method produces images that can be interpreted more intuitively. Acoustic shadows (areas of no reflection) are also easier to detect visually in e4’s orthosonograph images because they are plotted as black pixels.

The processing applies a time varying gain (TVG) for relative amplitude balancing based on the location of the project and the project objectives. All GeoTIFF files are created with the same TVG values throughout the project to allow for direct comparison of data acquired at different times.

Orthosonographs are made as 8-bit images. e4 applies a standard sepia color scale to the mosaic images to create the GeoTIFF. The values of the TVG for the mosaic are specific for the Port Jersey contract area. e4 applied the same processing scheme and values as in the data acquired in 2012, 2016 and 2020 BD survey, allowing for one to one comparison of all datasets.

3.3 Task 3: Sub-bottom reflection seismology

e4 used an Edgetech 512i sub-bottom profiler to acquire the seismic data with a 1-10kHz frequency chirp. Sub-bottom profiling works similarly to single-beam bathymetry. The 1-10kHz chirp successfully penetrated through recently deposited sediments that have accumulated on top of the plates. The sub-bottom data showed strong reflections from the plates in the areas where sediment covered the plates.

Figure 2 plots the sub-bottom tracklines.

The horizontal accuracy in the reflection seismology is ±1.5ft. The vertical accuracy is ±1ft for every 10ft of penetration below the channel floor.

e4 acquired a total of 151 seismic lines; 14 of the lines are along the trajectory of the tunnel, 68 of the lines are perpendicular to the tunnel trajectory, and 69 of the lines are turn lines. e4 focused the perpendicular lines in the area of Plates 310 to 430. This area is the one with the largest amount of sediment cover within the area to be dredged. The combination of the data acquired in two perpendicular directions allows us to reduce the uncertainty by correlating multiple arrivals to image the plates below the sediment layer.

3.3.1 Sub-bottom seismic processing

e4 has developed a proprietary set of protocols for processing high-frequency, shallow water, reflection seismic data for determination of sediments and rock in harbors.1 e4 filters every line.

The processing generates six different images for every line. The six images facilitate interpretation of the data.

The standard format of representing sub-bottom seismic data is the raw format, that is, the envelope of the chirp signal. The chirp signal has a time-varying frequency. e4’s proprietary processing allows the generation of the real and imaginary components of the time-varying frequency signal.

The real analytical component of the chirp data allows processing of the images using wave-equation techniques. The data is migrated to depth with an initial constant velocity model derived from field water velocity measurements. The depth migration depends on the data frequency content.

1 William Murphy III, W. Bruce Ward, Beckett Boyd, Gary Fleming, William Murphy IV, Richard Nolen-Hoeksema, Matthew Art, and Daniel A. Rosales, High-resolution shallow geophysics and geology in the Hudson-Raritan Estuary Ecosystem Restoration, New Jersey, The Leading Edge, February 2011, Vol. 30, No. 2: pp. 182-190.

The navigation of the seismic data is processed using Kalman filters. The dGPS position is 1Hz frequency. The data has a 0.25Hz repetition rate. The Kalman filter interpolates the spatial location data using the sensor positioning, the speed of the boat, and the heading. The average trace spacing for the seismic lines is 0.33ft.

e4 measured the speed of sound in the water column. The water-velocity measurement from field operations is 4,992ft/sec.

Using the sub-bottom seismic data independently, e4 interprets each of the seismic lines. The interpretation process produces maps of the first arrival and the geological surfaces identified as horizons of interest. e4 used the same data processing steps from the 2012, 2016, and 2020 BD surveys in order to make a time variant comparison of the plates.

3.3.2 Seismic modeling

e4 modeled the effect of the uneven distribution of sediments on seismic response of the protective plates. Modeling results indicate that rough geometry of sediment above the plates generates strong seismic diffractions that are masking the response from the top of the steel plates. This process allows for a visual que of the sub-bottom data to aid interpretation.

The seismic modeling results are presented in section 4.2.1.

3.4 Task 4: Integration

e4 uses redundant measurements to quantify all results. Each survey is calibrated in the local area with a proprietary test. All measurements are processed independently and integrated into a single georeferenced frame after processing. Redundant measurements (repeat lines or scans) quantify the precision and delineate uncertainty in the measurements. Repeat lines are not always delivered to the client but are available for review upon request. Orthosonographs provide contextual images beyond the geometry of the channel floor. e4 produced a series of geophysical cross sections from the sub-bottom reflection seismic data. e4 used the multibeam bathymetry collected out of scope to support the interpretation of the other measurements.

3.4.1 Uncertainty

High-definition mapping determines the horizontal and vertical position of the plates relative to the locations in the as-built drawings. The challenge in mapping the configuration of the plates is to image the plates under a variable thickness of sediment. At three discrete locations e4’s ability to clearly interpret the seismic response to the plates is diminished. One hypothesis for the localized increases in uncertainty is the geometry of sediments above the plates scarred by the dredge bucket.

The uneven distribution of sediment cover creates seismic artifacts that mask the signal reflecting off the top of the plates; the reflection from the plates is obscured by the signal from the sediment above. The combination of side-scan orthosonographs, bathymetry, and sub-bottom seismic reflection cross sections provides repeatable accuracy of ±0.3ft vertically and ±0.3ft horizontally at best. Between Plates 341-345, Plates 354-358, and Plates 386-400 the interpretation uncertainty increases the uncertainty by an additional ±0.3ft. The seismic modeling supports this hypothesis.

We compare the AD survey with the (1) 2020 BD survey, (2) existing as-built drawings, (3) post-construction imaging, (4) the AD surveys from 2016 maintenance dredging.

Our strategy for this report is to compare the integrated AD analysis results with the BD survey report. Please note that 0.3ft horizontal and 0.3ft vertical measurement errors exist in both the AD and BD investigations.

It is crucial to determine if at any time (a) the elevation of the plates reaches above -50.0ft MLLW (NTDE 1981-2001) or (b) the plates have been horizontally displaced more than 1ft. The allowed displacement along the tunnel trajectory is limited to 4inches and the allowed displacement normal to the tunnel trajectory can be several feet. For the exposed plates, the horizontal displacement error is less that 1ft, therefore it is adequate to determine the horizontal displacement larger than 1ft for exposed plates. The vertical measurement of the top of buried plates is the difficult goal to achieve.

Method applied Sub-bottom reflection seismology (10kHz) Penetration ~10ft Horizontal accuracy ~ ±1.5ft with dGPS (3ft) Vertical accuracy ~ ±0.1 – 0.5ft (for sediment coverage up to 10ft).

Interpretation uncertainty ~+/ 0.3ft (for uneven sediment coverage 1-3ft) Vertical precision ~ ±0.2ft

Side-scan orthosonograph Penetration ~0.1ft Horizontal accuracy ~ ±0.3ft

Multibeam Bathymetry Penetration ~0.1ft Horizontal accuracy ~ ±0.3ft Vertical accuracy ~ ±0.2ft

By correlating the measurements, e4 estimates that:

Penetration ~10ft Horizontal accuracy ~ ±1.5ft (3ft) Vertical accuracy ~ ±0.3ft In areas of higher uncertainty, vertical accuracy ~ ±0.6ft; horizontal accuracy ±2.0ft Vertical precision ~ ±0.2ft

Figure 2. Sub-bottom tracklines. The lines perpendicular to the tunnel trajectory are concentrated between Plates 310 to 430. These lines produce coverage that allowed us to reduce the uncertainty in the elevations.

4. Results

All data presented in the report are located in the coordinate system of NAD83 New Jersey State Plane in U.S. Survey Feet and the vertical datum mean lower low water (MLLW) as defined by the National Tidal Datum Epoch (NTDE) from 1983 to 2001.

4.1 Evaluation of USACE multibeam bathymetry

e4sciences compared USACE AD bathymetry acquired on September 8, 2020 (#4990) minimum with the BD bathymetry acquired in July 2020 (#4966) minimum.

Figure 3 plots the USACE AD multibeam bathymetry. Figure 4 shows the USACE BD multibeam bathymetry. Both bathymetry maps are gridded with 1x1ft bins and plot minimum (highest elevation) selections for points within each 1x1ft bin. The color map plots elevations above -50.0ft MLLW as red pixels; elevations from -52ft MLLW to -50.0ft MLLW are displayed as orange to green pixels, and elevations deeper than -52.0ft MLLW are displayed as shades of blue.

Figure 5 shows the difference map between September 2020 and July 2020 USACE bathymetries at a 1x1ft grid.

AD bathymetric survey showed that none of the dredging depth over the steel plates exceeded 50.5 ft MLLW.

4.2 After dredge survey results

e4sciences measured the channel bottom reflectivity along tracklines following the centerline of the tunnel trajectory. Figure 6 shows the AD orthosonograph insonified from the northeast. Figure 7 shows the AD orthosonograph insonified from the southwest.

The dredging operations occurred from Plates 315 to 430. e4 AD survey results above Plates 226 to 350 are presented in section 4.3, and results above Plates 351 to 430 are presented in section 4.4.

4.2.1 Seismic data interpretation and modeling

The AD seismic survey was acquired during a calm sea state following the same method and protocols as the BD survey. However, at three discrete subsets of plates there exist higher degrees of uncertainty when interpreting the top of the plates buried below sediment. One hypothesis for the localized increases in uncertainty is the geometry of sediments above the plates scarred by the dredge bucket. The uneven distribution of sediment covering the plates creates seismic artifacts that mask the signal reflecting off the top of the plates; the reflection from the plates is obscured by the signal from the sediments above.

To test this hypothesis, e4 modeled the effect of the uneven distribution of sediments on seismic response to the protective plates. Modeling results indicate that rough geometry of surface sediments does generate strong seismic diffractions that are masking the response from the top of the steel plates.

The schematic models of the subsurface include the actual seafloor bathymetry from the 2020 AD survey; the sediment distribution assumes homogeneous sediment layering on top of the plates, and the plates are located following the as-built locations. Sediment thickness varies from 1-3ft on top of the plates within a 5ft horizontal distance. e4 developed three modeling experiments: a) the first experiment goes along the trajectory of the tunnel between Plates 391-400; b) the second experiment goes perpendicular to the trajectory of the tunnel at Plate 356; and c) the third experiment also goes perpendicular to the trajectory of the tunnel at Plate 394.

Figures 8, 9, and 10 show the results of the three experiments respectively. The top figure shows the schematic model and the bottom shows the synthetic seismic results. The artifacts that mask and/or disturb the signal of the plates are produced by multiple diffractions (chevrons) that cross through the signal of the plates. The signals from the plates are themselves also diffractions and are fundamental to interpret the location of the plates.

There are seismic processing algorithms to suppress the diffractions caused by the uneven sediments; however, applying this process will also suppress the signals of the plates. The results of this experiment support the hypothesis that the roughness of the sediment surface may interfere with the signal of the plates.

We compared the modeling results with all the seismic data acquired before and after dredging, with the results from the 2016 dredging operations, and with the data from the 2012 placement of the plates. Figures 11, 12, and 13 show close-ups of the side-scan orthosonographs for the areas of Plates 341-345, 354-358, and 386-400. The side-scan orthosonographs show the uneven distribution of sediments on top of the plates.

We used the results from the modeling, the seismic data from multiple adjacent lines, and the data from past surveys to interpret the location of the plates in the areas of Plates 341-345, 354-358, and 386-400.

Figure 14 shows a summary of the interpretation results on a plate by plate basis. This interpretation is plotted on top of a side-scan orthosonograph. Examples of seismic cross sections over the plates in the dredge template are discussed in the following section.

Figure 3. USACE AD multibeam bathymetry September 8, 2020 (#4990) minimum, 1x1ft grid.

Figure 4. USACE BD multibeam bathymetry July 2020 (#4966) minimum, 1x1ft grid.

Figure 5. Bathymetry difference map between USACE September 2020, AD (#4990) and July 2020, BD (#4966).

Figure 6. AD Side-scan orthosonograph insonified from the northeast. Data acquired on September 11, 2020.

Figure 7. AD Side-scan orthosonograph insonified from the southwest. Data acquired September 11, 2020.

Figure 8. Synthetic model for Plates 391 to 400 parallel to tunnel trajectory (top) and modeled seismic response (bottom). The modeled response contains the effects of the uneven distribution of sediments overlying the plates. The top of the sediment is extracted from the AD bathymetry.

Figure 9. Synthetic model for Plate 356 perpendicular to tunnel trajectory (top) and modeled seismic

Figure 10. Synthetic model for Plate 394 perpendicular to tunnel trajectory (top) and modeled seismic

Figure 11. Close-ups of AD side-scan orthosonographs insonified from the northeast (left) and southwest (right) for Plates 341-345. The red circles highlight the areas with an uneven distribution of sediments.

Figure 12. Close-ups of AD side-scan orthosonographs insonified from the northeast (left) and southwest (right) for Plates 354-358. The red circles highlight the areas with an uneven distribution of sediments.

Figure 13. Close-ups of AD side-scan orthosonographs insonified from the northeast (left) and southwest (right) for Plates 386-400. The red circles highlight the areas with an uneven distribution of sediments.

Figure 14. Seismic interpretation results. The yellow dots correspond to interpreted observations for the location of the protective plates. The results are plotted on top of the AD side-scan orthosonograph insonified from the southwest. The gray contour corresponds to -50ft MLLW.

4.3 Plates 226 to 350

Plates 226 to 286 are exposed. A continuous sediment layer covering the plates starts at Plate 289.

The thickness of sediment covering the plates is variable. This sediment layer becomes shallower than -52ft MLLW from Plates 303 to 309, winnows over Plates 309 to 312, and thickens again to become shallower than -52ft starting at Plate 313. A 1-3ft sediment layer covers Plates 315-350.

USACE AD multibeam bathymetry reported no high spots shallower than -50.0ft. There is no clear evidence of plates exposed or disrupted between Plates 226 and 350.

Figure 15 is a close-up of the USACE AD and BD (2020) bathymetry data. Figure 16 is the close-up of the bathymetry difference map created by subtracting USACE BD data from AD data.

Figure 17 plots a comparison between the AD and BD side-scan orthosonographs. The side-scan orthosonographs from September and July are both insonified from the northeast.

Figure 18 plots another comparison between the AD and BD side-scan orthosonographs. The side-scan orthosonographs from September and July are both insonified from the southwest.

Figures 19 to 28 compare the sub-bottom seismic investigation from the before-dredge (BD) and after-dredge (AD) surveys. After sediment removal the signal from the plates is clearer and stronger.

This allows for an identification of the top of the plates. In the AD survey, all the plates appear at the same elevation as in the BD survey. The solid cyan lines (AD bathymetry) and blue lines (BD bathymetry) plot the elevation of the channel floor on the seismic cross sections. The two solid red lines correspond to this project dredging depth (-50ft MLLW) and the plates’ as-built depth (-52.6ft

MLLW).

Figures 29 and 30 compare the sub-bottom seismic cross sections at Plate 304 and Plate 307 from the BD and AD surveys. Figure 31 shows AD sub-bottom cross sections at Plate 318.

Figure 15. Plates 226 – 350: USACE bathymetry comparison, (left) July 2020 bathymetry (#4966), BD; (right) September 2020 bathymetry (#4990), AD.

Figure 16. Plates 226 – 350: USACE bathymetry difference map between September 2020, AD (#4990) and July 2020, BD (#4966).

Figure 17. Plates 226 – 350: Comparison of BD (left) versus AD (right) side-scan orthosonograph insonified from the northeast.

Figure 18. Plates 226 – 350: Comparison of BD (left) versus AD (right) side-scan orthosonograph insonified from the southwest.

Figure 19. Plates 251 – 260: sub-bottom comparison of AD (above) versus BD (below).

Figure 20. Plates 261 – 270: sub-bottom comparison of AD (above) versus BD (below).

Figure 21. Plates 271 – 280: sub-bottom comparison of AD (above) versus BD (below).

Figure 22. Plates 281 – 290: sub-bottom comparison of AD (above) versus BD (below).

Figure 23. Plates 291 – 300: sub-bottom comparison of AD (above) versus BD (below).

Figure 24. Plates 301 – 310: sub-bottom comparison of AD (above) versus BD (below).

Figure 25. Plates 311 – 320: sub-bottom comparison of AD (above) versus BD (below).

Figure 26. Plates 321 – 330: sub-bottom comparison of AD (above) versus BD (below). More than two feet of sediment remains on top of the plates. In this area, one foot of sediments has been removed from the top of the plates.

Figure 27. Plates 331 – 340: sub-bottom comparison of AD (above) versus BD (below). One to three feet of sediment remains on top of the plates. More than one foot of sediment has been removed from the top of the plates.

Figure 28. Plates 341 – 350: sub-bottom comparison of AD (above) versus BD (below). One to three feet of sediment remains on top of the plates. More than two feet of sediment has been removed from the top of the

Figure 29. Plate 304: sub-bottom cross section comparison of AD (above) versus BD (below).

Figure 30. Plate 307: sub-bottom cross section comparison of AD (above) versus BD (below).

Figure 31. September 2020 AD sub-bottom cross section at Plate 318.

4.4 Plates 351 to 430

A thin sediment layer remains on top of Plates 351 to 430. The remaining sediment above the plates varies in thickness from 1 to 3ft. Side-scan orthosonographs show dredging marks throughout this area. The side-scan orthosonographs and the seismic images show an area of sandy sediments along Plates 367 to 370, as evidenced by less reflectivity from the side-scan and polarity reversal in the seismic image. There is no clear evidence of plates exposed or moved in this area.

Plate 430 is outside the channel on the slope.

Figure 32 is a close-up of the USACE bathymetries of September 8, 2020 (#4990) and July 2020 (#4966). Figure 33 is the close-up of the bathymetry difference map created by subtracting USACE BD data from AD data.

Figure 34 plots a comparison of the side-scan orthosonographs of September and July 2020. The side-scan orthosonographs from September and July are both insonified from the northeast.

Figure 35 plots another comparison of the side-scan orthosonographs of September and July 2020.

The side-scan orthosonographs from September and July are both insonified from the southwest.

Figures 36 to 43 compare the sub-bottom seismic investigation from the BD and AD surveys. After sediment removal the signal from the plates is clearer and stronger. This allows for an easier identification of the top of the plates. In the AD survey, Plates 351-430 appear at the same elevation as in the BD survey, within the margin of error from the seismic measurement. The solid cyan lines (AD bathymetry) and blue lines (BD bathymetry) plot the elevation of the channel floor on the seismic cross sections. The two solid red lines correspond to this project dredging depth (-50.0ft MLLW) and the plates’ as-built depth (-52.6ft MLLW).

Figures 44, 45, and 46 show AD sub-bottom cross sections at Plates 356, 389, and 394.

Figure 32. Plates 351 – 430: USACE bathymetry comparison, (left) July 2020, BD bathymetry (#4966); (right) September 2020, AD bathymetry (#4990).

Figure 33. Plates 351 – 430: USACE bathymetry difference map between September 2020, AD (#4990) and July 2020, BD (#4966).

Figure 34. Plates 351 – 430: Comparison of BD (left) versus AD (right) side-scan orthosonograph insonified from the northeast.

Figure 35. Plates 351 – 430: Comparison of BD (left) versus AD (right) side-scan orthosonograph insonified from the southwest.

Figure 36. Plates 351 – 360: sub-bottom comparison of AD (above) versus BD (below). More than two feet of sediments remains on top of the plates. More than two feet of sediment has been removed from the top of the plates.

Figure 37. Plates 361 – 370: sub-bottom comparison of AD (above) versus BD (below). One to three feet of sediments remains on top of the plates. More than two feet of sediment has been removed from the top of the

Figure 38. Plates 371 – 380: sub-bottom comparison of AD (above) versus BD (below). More than two feet of sediments remains on top of the plates. More than two feet of sediment has been removed from the top of

Figure 39. Plates 381 – 390: sub-bottom comparison of AD (above) versus BD (below). One to three feet of sediments remains on top of the plates. More than two feet of sediment has been removed from the top of the

Figure 40. Plates 391 – 400: sub-bottom comparison of AD (above) versus BD (below). One to three feet of sediments remains on top of the plates. More than two feet of sediment has been removed from the top of the

Figure 41. Plates 401 – 410: sub-bottom comparison of AD (above) versus BD (below). More than two feet of sediments remains on top of the plates. More than two feet of sediment has been removed from the top of

Figure 42. Plates 411 – 420: sub-bottom comparison of AD (above) versus BD (below). One to three feet of sediments remains on top of the plates. More than two feet of sediment has been removed from the top of the

Figure 43. Plates 421 – 430: sub-bottom comparison of AD (above) versus BD (below). One to three feet of sediments remains on top of the plates. More than two feet of sediment has been removed from the top of the

Figure 44. September 2020 AD sub-bottom cross section at Plate 356.

Figure 45. September 2020 AD sub-bottom cross section at Plate 389.

Figure 46. September 2020 AD sub-bottom cross section at Plate 394.

5. Conclusions

From November 2011 to August 2012, 430 steel plates were placed above the Passaic Valley Sewerage Commission (PVSC) Tunnel in order to protect this valuable infrastructure from harbor deepening and deep-draft navigation projects. In 2020, as part of Maintenance Dredging of New York and New Jersey Harbor, Port Jersey channel, Federal Navigation Project, the United States Army Corps of Engineers, New York District (USACE-NAN), contracted Great Lakes Dredge & Dock (GLDD) to maintenance dredge the sediments that accumulated above an elevation of -50ft mean lower low water (MLLW) in Port Jersey. This includes dredging the sediment above and around Plates 303 to 430 to an elevation of -50ft MLLW.

For the 2020 round of maintenance dredging over the PVSC Tunnel’s protective plates, GLDD assigned e4sciences (e4) to measure and map the position of the protective plates within and adjacent to the Port Jersey Federal Navigation Channel both before dredging (BD) and after dredging (AD). e4 submitted the BD report in August 2020. This report presents the result and analysis of AD geophysical measurements made directly above and adjacent to the protective plates.

GLDD performed dredging operations between August 21 and September 4, 2020. The USACE approved the area to grade on September 8, 2020 based on an AD bathymetric survey. e4 performed reflection seismology surveys on September 10 and side-scan sonar surveys on September 11, 2020.

The sea state during the seismic data collection was calm, well suited for the surveys.

1. The AD bathymetric survey showed that none of the dredging depth over the steel plates exceeded 50.5 feet MLLW, and Plates 315 to 430 have approximately 1ft to 2.6ft of sediment over the plates. Comparison of the BD and AD geophysical surveys has determined that there is no evidence that the position of the plates changed during dredging or that any plates are above -52.6ft

MLLW (NTDE 1981-2001).

2. Overall, the locations and elevations of the plates are consistent between the BD and AD surveys.

However, there are three discrete locations where there exist higher degrees of uncertainty in the AD seismic interpretation of the location and elevation of the plates.

3. One hypothesis for the localized increases in uncertainty is the geometry of sediments scarred by the dredge bucket. The uneven distribution of sediment over the plates creates seismic artifacts that mask the signal reflecting off the top of the plates; the reflection from the plates is obscured by the signal from the sediments above.

4. In the areas of Plates 341-345, Plates 354-358, and Plates 386-400 dredge scars have steep angles and vertical relief that varies on the order of 0.7ft to 2.0ft. In these areas dredge scars are unevenly distributed and unevenly oriented.

5. e4’s modeling results indicate that rough geometry of sediments above the plates generates strong seismic diffractions that are masking the response from the top of the steel plates.

6. We have determined that there is no evidence that the location and elevation of the plates have changed as a result of the 2020 maintenance dredging operations. This conclusion is further supported with discussions of the dredging operations with GLDD.

Appendix I.

Plates 101 - 225

A-1 Plates 101 to 225

Plates 101 to 105 are all outside the channel in the northern section of the area of investigation toward the Global Marine Terminal berth. There are no changes in the plate locations with respect to the before dredge survey. The distribution of sediments covering the plates has changed. The amount of sediment covering the plates is less than 0.5ft thick.

Figure A-1 plots a comparison between the side-scan orthosonographs of September 2020 and July 2020. The side-scan orthosonographs from September and July are both insonified from the northeast.

Figure A-2 plots another comparison between the side-scan orthosonographs of September 2020 and July 2020. The side-scan orthosonographs from September and July are both insonified from the southwest.

Figure A-1. Plates 101 – 225: Comparison of BD (left) versus AD (right) side-scan orthosonograph insonified from the northeast.

Figure A-2. Plates 101 – 225: Comparison of BD (left) versus AD (right) side-scan orthosonograph insonified from the southwest.

Appendix II.

11x17 version of the plates