Shallow Hazards Survey Former Gas Light Company MGP ...gloucestermgpsite.com/wp-content/uploads/2013/12/Appendix-L-2013... · Former Gas Light Company MGP Project Area . Gloucester

Shallow Hazards Survey Former Gas Light Company MGP Project Area

Gloucester Harbor, Gloucester, Massachusetts

Magnetic Contour Map Gloucester, Massachusetts

Prepared for:

ANCHOR QEA

26300 La Alameda, Suite 240 Mission Viejo, California 92691

Prepared by:

CR Environmental, Inc. 639 Boxberry Hill Road

East Falmouth, MA 02536

December 2013

2013 Shallow Hazards Survey December 2013 Gloucester Harbor MGP Project Area

639 Boxberry Hill Road, East Falmouth, MA 02536 Phone/Fax 508 563-7970 www.crenvironmental.com

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TABLE OF CONTENTS

Page Number 1.0 INTRODUCTION…………………………………………………………………… 1 2.0 VESSEL & NAVIGATION ………………………................................................ 1 3.0 ACQUISITION AND DATA PROCESSING METHODS………………………. 2

3.1 Side Scan Sonar Acquisition ………………………………………………. 2 3.2 Side Scan Sonar Processing …….…………………………………............. 2

3.3 Sub-Bottom Profiling Acquisition ............................................................... 2 3.4 Sub-bottom Processing ……………………………………………………… 2

3.5 Magnetic Data Acquisition ………………………………………………….. 3

3.6 Magnetic Data Processing ...………………………………………………… 3

4.0 GIS PROCESSING AND DATA VISUALIZATION …………………………….. 3 5.0 SURVEY RESULTS ………………………………………….................................. 4 5.1 Side Scan Sonar Results …………………………………………………… 4

5.2 Sub-bottom Results ………………………………. ……………………….. 5

5.3 Magnetic Results …………………………………………………………… 6 6.0 CONCLUSIONS AND RECOMMENDATIONS ………………………………… 6 REFERENCES

http://www.crenvironmental.com/



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TABLE 1 Magnetic Anomalies Gloucester, MA FIGURES Figure 1 Survey Locus

Gloucester Inner Harbor, MA Figures 2 Side Scan Sonar Mosaic and Contacts Proposed Project Area,

Gloucester MGP Remediation Figure 3 Side Scan Sonar Mosaic and Contacts Remediation Support Area,

Gloucester MGP Remediation Figure 4 Depth to First Acoustic Reflector Overlaying Bathymetric Relief

Gloucester MGP Remediation

Figure 5 Total Field Magnetism Overlaying Bathymetric Relief Gloucester MGP Remediation APPENDIX A Side Scan Sonar Contact Report Gloucester, MA APPENDIX B Geophysical Survey Limitations




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1.0 INTRODUCTION

Gophysical surveys of Gloucester Inner Harbor were conducted by CR Environmental, Inc. of East Falmouth, MA to support Massachusetts Contingency Plan Remediation for the former Gloucester Gas Light Company Manufactured Gas Plant. The geophysical investigations were conducted within the former Gloucester MGP Remediation Proposed Project Area Limit of Work and property to the north proposed for use as a Remediation Support Area on October 8 and 9, 2013 (Figure 1). Additional focused investigations of a charted wreck and two historic marine railways (one abandoned and one active) were conducted on October 10 and 11, 2013 (Figure 1).

Remote sensing technologies included: side scan sonar, sub-bottom profiling and magnetometry. Only side scan sonar was conducted at the proposed Remediation Support Area. CR also provided support for archaeological diver inspections and a sediment probing effort by DSRA in the vicinity of the marine railways.

The following Sections detail remote sensing data acquisition and processing methods and provide a summary of the survey results. All data have been delivered digitally in GIS compatible formats (where applicable) and have been projected to Massachusetts State Plane, NAD83, US Foot.

2.0 VESSEL AND NAVIGATION

Survey operations and diving support were performed from the 26-foot aluminum survey boat, RV Lophius equipped with a bow-mounted hydraulic A-frame, stern pilothouse, over-the-side transducer mount, and 12 volt power supplies.

Navigation for the surveys was accomplished using a Hemisphere VS-110 12-channel Differential Global Positioning System (DGPS) and Digital Compass system capable of receiving satellite-based differential corrections (SBAS) and U.S. Coast Guard (USCG) Beacon corrections. Trimble DGPS systems were available as necessary as backups. Both systems are capable of sub-meter horizontal position accuracy. The DGPS system was interfaced to a laptop computer running HYPACK MAX® hydrographic survey software. HYPACK MAX® continually recorded vessel position and DGPS satellite quality and provided a steering display for the vessel captain to accurately maintain the position of the vessel along pre-established survey transects and targets.




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3.0 ACQUISITION AND PROCESSING METHODS

3.1 Side Scan Sonar Acquisition

Side scan sonar data were acquired using an Edgetech, Inc., Model 4125 400/900-kHz system. Sonar controls and digital recording were conducted using Edgetech Discover software. Side scan data were recorded in both Edgetech .JSF and standard .XTF formats.

The majority of sonar data were collected using an 82 foot (25 meter) range scale. Survey transects spacing was set to 50 feet, resulting in a coverage of more than 200-percent (i.e., all portions of the seafloor imaged at least two times). Narrower swath settings were utilized for inspections of the reported wreck and marine railways. Swath width in the northern dredge area was set to 164 feet (50 meters) to allow imaging of portions of the area too shallow for safe navigation. Layback position offsets were recorded to the nearest foot and applied to data during post-processing. A draft sonar mosaic was produced in near real-time during the survey to ensure adequate survey coverage and to allow identification of noteworthy features.

3.2 Side Scan Sonar Processing

JSF side scan data were imported to Chesapeake Technology’s SonarWizMAP-Pro software. Bottom tracking was confirmed and moderate Time Varied Gain (TVG) adjustments were made to sonar data. Mosaics of side scan data were created and exported in georeferenced TIF format using a resolution of 0.2 feet per pixel. Individual GEOTIF files were generated for each file to facilitate construction of area-specific mosaics.

3.3 Sub-Bottom Profiling Acquisition

Sub-bottom sonar data were acquired along transects spaced 25 feet apart using an Edgetech 3200-XS (FSSB) profiling system interfaced to an SB-216S towfish. The transmit signal was a frequency modulated Chirp swept from 2 to 12 kHz using a 20 millisecond pulse. The offset between the towfish and the DGPS antenna was recorded to aid position correction during post-processing.

3.4 Sub-Bottom Profiling Processing

Sub-bottom data were processed using Chesapeake Technology’s SonarWizMAP-Pro software. Appropriate adjustments to TVG were made during processing. Sub-bottom profiles were exported in JPG format with accompanying GIS shapefiles (polylines) of transect navigation data.




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In order to characterize variations in surficial sediment thickness, the distance between the sediment surface and the first strong subsurface reflector was digitized, extracted in ASCII format and used to create georeferenced maps. The data from this effort has been delivered in grid and TIF formats.

3.5 Magnetic Data Acquisition

Magnetic data were collected simultaneously with the side scan and sub-bottom sonar data along the same survey transects. Magnetic data were acquired using a Marine Magnetics, Inc. Explorer high resolution marine magnetometer system. The magnetic data acquisition system consisted of a towfish-mounted Overhauser magnetic sensor and pressure/depth sensor, an onboard power supply and serial interface, and a data acquisition computer. The 1 Hz data stream from the magnetic sensor was routed to the HYPACK navigation computer via a serial port, and HYPACK recorded magnetic readings in nanoTeslas (1.0 gamma = 1 nanoTesla) as a separate field within the same raw data files containing navigation data. The position of the magnetometer towfish was calculated in real-time using a HYPACK mobile device driver which considered “cable out” relative to the DGPS antenna, the cable catenary curve, and the effects of vessel course corrections.

3.6 Magnetic Data Processing

Magnetometer data were processed using HYPACK’s Single-Beam Processor Module. Each magnetic survey transect was first inspected in profile format for characteristic signals which indicate the presence of ferrous anomalies (objects). Observed or suspected magnetic anomalies were digitized and used to create a GIS database which included the approximate anomaly location, amplitude and duration. After inspecting each data file, magnetic measurements were merged into a single ASCII comma-delimited database containing all total field (TF) magnetic intensity measurements. The database contained fields for Northing, Easting, and magnitude. This combined data set was imported to Golden Software, Inc. Surfer V.11 Surface Modeling Software. Grids of magnetic intensity were created using interpolation methods constrained by a search radius of 75 feet (>3 survey transects) and a 5 foot node interval. Contour maps were created from these grids depicting TF magnetism using a 2.0 nT contour interval and the maps were exported in SHP, TIF and ESRI FLT Raster formats.

4.0 GIS PROCESSING AND DATA VISUALIZATION

Processed data from each of the three sensors were imported to ESRI ArcGIS projects created for each sensor type. Relationships between digitized Contacts (side scan and sub-bottom), magnetic anomalies and textural variations suggested by side scan sonar were qualitatively assessed by




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redundantly adjusting each layer’s transparency or display order. The extensive overlap between side scan sonar data files allowed iterative data review at the approximate locations of digitized sonar Contacts and magnetic anomalies. This review was conducted through fine-scale (e.g., <1:200) review of individual georeferenced side scan sonar swaths in conjunction with contoured magnetic data.

Anchor QEA provided CR with a database of bathymetric sounding data which included coverage for the survey area. CR used these data to create a bathymetric surface suitable for analysis and visualization using GIS and IVS3D Fledermaus software. This bathymetric surface was used as a base layer upon which georeferenced side scan sonar and magnetic imagery were draped, and facilitated the characterization of textural and magnetic anomalies.

5.0 SURVEY RESULTS

The Sections below summarize remote sensing data results. Ground truth data such as, core sample characterizations, were not provided to aid the analysis of seabed conditions.

5.1 Side Scan Sonar Results

Side scan sonar data is invaluable for identification of objects which pose a hazard to remediation efforts or safe navigation. Side scan sonar data may also be used for semi-quantitative mapping of substrate characteristics when coupled with adequate ground truth data.

Sonar Interpretation Guide

Side scan sonar results are presented as mosaics of gray shaded imagery. The shade of gray corresponds to the strength of the returning signal and is used to infer bottom type (sediment texture) and to identify underwater structures or debris. A key to sonar shading is provided below.

Key to Side-scan Sonar Image Shading

Sonar shadow------------ Weak Signal Return-------------------------Strong Signal Return




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In general, weak signal returns correspond to smooth substrates (e.g., fine sediments with little microtopography), soft materials that absorb the signal, or topography that slopes away from the signal source (towfish). These features appear lighter gray in sonar imagery. Strong signal returns correspond to rough substrates (e.g., gravel, cobble), highly reflective materials, or to a topography that slopes towards the signal source. These features appear as dark gray to black in the sonar imagery.

Features that rise above the bed (e.g., boulders) reflect more of the sonar energy than the surrounding substrate resulting in strong signal returns due to the decreased angle of incidence. These features often prevent insonification of the area opposite the signal source, resulting in a sonar “shadow” (white imagery). The length of these shadows can be used to calculate the approximate height of the feature above the bed.

Mosaics of the 900 kHz side scan sonar data are shown on Figures 2 and 3 for the Proposed Remediation Project Area Limit of Work and the Remediation Support Area to the north, respectively. Digitized sonar Contacts and fish/lobster traps are identified on these Figures. High resolution imagery and mensuration for each Contact is provided in Appendix A. Debris, traps and tires were widespread throughout the survey areas. Debris density appeared highest in the nearshore northwestern portion of the Remediation Project Area Limit of Work. Anchor and chain scours are clearly visible in the anchorage area at the northeastern edge of the proposed project area limit of work.

Sonar data indicated that the charted wreck adjacent to the USCG Station was a large rock or area of ledge (Figure 2, and Contacts 12 and 23 in Appendix A). Subsequent observations made by a DSRA diver confirmed this characterization.

Side scan records also allowed mapping of those portions of the abandoned and active marine railways present above the mudline (Figure 2, and Contacts 26, 28, 30, 31 and 32 in Appendix A). These data were used to guide DSRA’s archaeological dive inspection of the railways. Data were also used to guide a probing effort focused on detection of buried portions of the railways.

5.2 Sub-Bottom Sonar Results

Sub-bottom sonar penetration depth below the seafloor to the first strong reflector ranged from approximately 0.5 feet to 16 feet (Figure 4). Intermittent deeper reflectors with characteristics consistent with bedrock or lodgment till were infrequently observed at depths greater than 20 feet beneath the harbor bottom. Data suggest the presence of entrained natural gases (byproducts of microbial activity) throughout the majority of the survey area. Exceptions include the areas




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adjacent to the USCG Docks and the marine railways where frequent prop turbulence and hull contact have likely minimized gas entrainment.

5.3 Magnetic Results

Total field (TF) magnetism and digitized anomalies are shown on Figure 5. Many anomalies were approximately co-located with debris or fishing gear (lobster traps) observed in side scan data (Table 1). Data did not indicate the presence of utilities or wreckage.

Magnetic data quality appeared to be influenced by several parameters outside of the control of the survey team. First and foremost, strong magnetic field interferences were associated with shoreline structures (e.g., cranes, sheet piles) and may have obscured some features of potential interest. It is also important to note that temporal (e.g., diurnal) fluctuations in the Earth's magnetic field associated with a coronal mass ejection occurred during the survey.

Lastly, the Gloucester / Cape Ann region has been charted as an area with anomalously high magnetic intensities of concern for navigators (see NOAA Chart 13274_5 Local Magnetic Disturbance Note). These properties are thought to be associated with the Nahant Gabbro formation which is projected to lie beneath the surficial Cape Ann Granite (e.g., Brady and Cheney, 2004). Both formations are iron rich with varying and potentially significant concentrations of magnetite.

6.0 CONCLUSIONS AND RECOMMENDATIONS

Remote sensing data (side scan sonar, sub-bottom profiling, and magnetometry) were acquired to support remediation and archaeological investigations. Acquisition and processing methods conformed to Performance Standards published by the US Army Corps of Engineers, NOAA and the International Hydrographic Organization. Geophysical survey limitations are provided in Appendix B.

Remote sensing data did not suggest the presence of buried utilities. Side scan sonar data allowed characterization of man-made objects within the project area, including active and abandoned marine railways and debris of potential interest to dredging contractors. Importantly, side scan data indicated that a NOAA charted wreck was actually a large rock (area of ledge or boulder). This was subsequently corroborated by a diver’s visual inspection.

Sub-bottom sonar penetration was generally limited by the assumed presence of a sub-surface layer of entrained gases. CR strongly suggests that profile data be quantitatively compared to available geotechnical and laboratory analytical data from cores and borings to:




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(1) Corroborate the presence of the entrained gas layer;

(2) Investigate potential correlations between sonar intensity (backscatter) and sediment texture; and

(3) Identify potential correlations between sonar data and separate phase contaminants which may be present in sub-surface strata.

Magnetic data were shown to be of sufficient sensitivity to detect low-magnitude anomalies such as lobster traps. Linear anomalies indicative of utilities were not observed in magnetic data. As previously noted, magnetic data quality and sensitivity was at times adversely affected by large ferrous shoreline structures or a magnetic storm. Nonetheless, these interferences are not judged to have impacted the sensor’s ability to detect buried pipelines or cables. Magnetic data appear to indicate fine-scale variations in either sediment composition or depth to bedrock. CR suggests that the magnetic surface layer delivered digitally could be used to investigate potential correlations with geotechnical parameters (e.g., depth to bedrock), and transformed to allow mapping of correlated strata of interest

The re-processed raw multibeam bathymetric and backscatter data collected by others was used to investigate correlations between CR’s remote sensing data and seabed morphology. Future bathymetric mapping needs should be discussed as the current bathymetric data were found to be non-compliant with the least stringent Performance Standards and, therefore, would not be suitable for remedial dredging operations or dredge volume estimates.

REFERENCES

Brady, J.B., and Cheney, J.T. (2004). The Cape Ann Plutonic Suite: A field trip for petrology classes. In Hanson, L.S., ed., Guidebook, 96th Annual Meeting of the New England Intercollegiate Geological Conference, Salem, Massachusetts, B1-B25


TABLES

ID X Y File Minimum Maximum Range Signature Duration (ft) SSS Contact

M-1 882994.6 3048058 061_1111 52560.45 52633.56 73.11 DP 22 No SSS Contact at surfaceM-2 882665.4 3048442 041_1448 52579.93 52612.68 32.75 DP 23 Near trap-like objectsM-3 882800.5 3048557 041_1448 52641.47 52663.07 21.6 DP- 12 Near trap-like objects and debris clusterM-4 882885 3048620 041_1448 52589.39 52649.77 60.38 MP- 18 No SSS Contact at surfaceM-5 882824 3048607 041_1512 52650.61 52687.3 36.69 MP- 17 No SSS Contact at surfaceM-6 883255.6 3048355 058_1055 52625.25 52670.67 45.42 DP 38 Fine debrisM-7 883147.6 3048151 062_1121 52575.64 52599.82 24.18 MP- Complex 45 Near trap-like objectsM-8 883102 3048114 062_1121 52593.3 52630.45 37.15 MP+ Complex 34 No SSS Contact at surfaceM-9 883183.8 3048507 052_1216 52655.79 52705.62 49.83 DP Complex 55 Fine debrisM-10 882960.2 3048546 045_1424 52655.05 52672.79 17.74 MP+ 20 Fine debrisM-11 882833.1 3048461 045_1424 52655.97 52677.53 21.56 MP+ 20 Near trap-like objects and debris M-12 883082.7 3048531 049_1428 52659.67 52695.1 35.43 DP 29 No SSS Contact but surrounded by debris and trapsM-13 883033.2 3048633 044_1432 52603.51 52654.31 50.8 DP 30 Fine debrisM-14 882706.2 3048453 042_1439 52603.68 52669.21 65.53 DP 28 Near trap-like objectsM-15 882836.5 3048621 040_1446 52625.03 52646.22 21.19 MP- 15 Co-Located with Probe P-16

Notes:

1. Magnetic values reported as nanoTeslas (nT).2. Grid: Massachusetts State Plane, NAD83, US Foot.

TABLE 1

Magnetic Anomalies Digitized from Raw ProfilesGloucester Inner Harbor Gloucester, Massachusetts

FIGURES

Survey LocusGloucester Inner Harbor, Massachusetts

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Figure 10 200 400

FeetNOTES:

1) Surveys conducted October 2013.2) Grid MA State Plane, NAD 83, US Foot.

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Marine Railways

Designated Survey Area

Charlotte

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Proposed Remediation Support Area

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Figure 20 50 100FeetNOTES:

1) Survey conducted October 2013.2) Grid MA State Plane, NAD 83, US Foot.

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#0 Sonar Contacts") Lobster Traps

Survey Area

900-kHz Side Scan Sonar Mosaic and ContactsProposed Project Area


Charlotte

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Charted "wreck"

Charlotte

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Anchor & chain scour

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US Coast Guard

900-kHz Side Scan Sonar Mosaic and ContactsRemediation Support Area


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Figure 30 50Feet

NOTES:

1) Survey conducted October 2013.2) Grid MA State Plane, NAD 83, US Foot.

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#0 Sonar ContactsSurvey Area

Depth Below Sediment Surface to First Acoustic Reflector(1.0 foot contour interval)

Overlaying Bathymetric Relief Gloucester MGP Remediation

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Figure 40 50 100Feet

NOTES:

1) Survey conducted October 8, 2013.2) Grid MA State Plane, NAD 83, US Foot.

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Figure 50 50 100Feet

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1) Survey conducted October 8, 2013.2) Grid MA State Plane, NAD 83, US Foot.3) Magnetic survey tracklines spaced 25 feet apart.

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Survey Area#0 Magnetic Anomalies

2.0 nT Contours

APPENDIX A

Side Scan Sonar Contacts Gloucester MGP Remediation Study Area

Gloucester Side Scan Sonar

Contact Report

(Projection: MA83F)

Contacts in this report:

Contact 1 10/08/2013 12:14:32 42.6090783876 Lat -70.6567124906 Lon

Contact 2 10/08/2013 12:14:59 42.6094686342 Lat -70.6567861934 Lon

Contact 3 10/08/2013 12:15:44 42.6097150368 Lat -70.6562179306 Lon

Contact 4 10/08/2013 12:25:09 42.6101799827 Lat -70.6562705919 Lon

Contact 5 10/08/2013 12:31:02 42.6095821769 Lat -70.6575500587 Lon

Contact 6 10/08/2013 12:35:45 42.6095682576 Lat -70.6575648049 Lon

Contact 7 10/08/2013 12:39:26 42.6097102397 Lat -70.6574682647 Lon

Contact 8 10/08/2013 12:42:21 42.6103127550 Lat -70.6571518778 Lon

Contact 9 10/08/2013 12:43:07 42.6099807719 Lat -70.6579344366 Lon

Contact 10 10/08/2013 12:48:15 42.6104895342 Lat -70.6571474383 Lon

Contact 12 10/08/2013 12:53:56 42.6102069939 Lat -70.6583726962 Lon

Contact 13 10/08/2013 12:54:36 42.6103988542 Lat -70.6577724755 Lon

Contact 14 10/08/2013 12:58:40 42.6107324493 Lat -70.6579023564 Lon

Contact 15 10/08/2013 12:59:22 42.6104426578 Lat -70.6582505902 Lon

Contact 16 10/08/2013 12:59:38 42.6103867813 Lat -70.6584362977 Lon

Contact 17 10/08/2013 13:03:53 42.6103697391 Lat -70.6586366294 Lon

Contact 18 10/08/2013 13:03:40 42.6103043180 Lat -70.6588264600 Lon

Contact 19 10/08/2013 17:29:41 42.6132457134 Lat -70.6571890855 Lon

Contact 20 10/08/2013 17:29:57 42.6132394228 Lat -70.6569048357 Lon

Contact 21 10/08/2013 17:29:24 42.6131130315 Lat -70.6568737124 Lon

Contact 22 10/08/2013 17:30:31 42.6131443404 Lat -70.6564930513 Lon

Contact 23 10/08/2013 17:42:45 42.6101832887 Lat -70.6584108604 Lon

Contact 24 10/09/2013 18:34:58 42.6103807806 Lat -70.6588421968 Lon

Contact 26 10/09/2013 18:42:52 42.6108757436 Lat -70.6583848942 Lon

Contact 28 10/09/2013 18:46:05 42.6110215843 Lat -70.6583802266 Lon

Contact 30 10/09/2013 18:50:28 42.6109124159 Lat -70.6584144987 Lon

Contact 31 10/09/2013 18:52:46 42.6109072474 Lat -70.6582443358 Lon

Contact 32 10/09/2013 19:19:14 42.6109850097 Lat -70.6584065452 Lon

Contact 1

Contact Info: Contact 1 User Entered Info

• Sonar Time at Target: 10/08/2013 12:14:32

• Click Position (Lat/Lon Coordinates)

42.6090783876 -70.6567124906 (WGS84)

• Click Position (Projected Coordinates)

(X) 883183.82 (Y) 3048108.43

• Map Proj: MA83F

• Acoustic Source File: E:\Projects\DR-Gloucester\Glo-

SSS\All_Lophius_JSF\20131008121414.jsf

• Ping Number: 4544

• Range to Target: 12.88 US Feet

• Fish Height: 4.02 US Feet

• Heading: 52.290 degrees

• Event Number: 0

• Water Depth: 2.99

• Line Name: 20131008121414

Target Height: = 0.6 US Feet

Target Length: 2.4 US Feet

Target Shadow: 1.9 US Feet

Target Width: 1.9 US Feet

Classification 1: trap

Classification 2:

Area:

Description: Typical lobster trap

Contact 2




42.6094686342 -70.6567861934 (WGS84)


(X) 883162.57 (Y) 3048250.45

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008121414





Classification 1: debris

Classification 2:

Area:

Description:

Contact 3




42.6097150368 -70.6562179306 (WGS84)


(X) 883314.66 (Y) 3048341.76

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008121414





Classification 1: trap

Classification 2:

Area:

Description: Typical lobster trap

Contact 4




42.6101799827 -70.6562705919 (WGS84)


(X) 883298.81 (Y) 3048511.06

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008122457






Classification 2:

Area:

Description:

Contact 5




42.6095821769 -70.6575500587 (WGS84)


(X) 882956.54 (Y) 3048289.80

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008122958





Classification 1: buoy

Classification 2:

Area:

Description: Bouy mooring with chain and surface line

Contact 6




42.6095682576 -70.6575648049 (WGS84)


(X) 882952.62 (Y) 3048284.69

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008123340





Classification 1: buoy

Classification 2:

Area:

Description: Mooring and chain

Contact 7




42.6097102397 -70.6574682647 (WGS84)


(X) 882978.09 (Y) 3048336.69

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008123800






Classification 2:

Area:

Description: Debris cluster. Likey tires and traps

Contact 8




42.6103127550 -70.6571518778 (WGS84)


(X) 883061.09 (Y) 3048557.10

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008124142





Classification 1: Mooring

Classification 2:

Area:

Description: Debris or mooring

Contact 9




42.6099807719 -70.6579344366 (WGS84)


(X) 882851.63 (Y) 3048434.04

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008124142






Classification 2:

Area:

Description: Likely metallic debris

Contact 10




42.6104895342 -70.6571474383 (WGS84)


(X) 883061.65 (Y) 3048621.54

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008124607






Classification 2:

Area:

Description:

Contact 12




42.6102069939 -70.6583726962 (WGS84)


(X) 882732.84 (Y) 3048515.32

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008125308





Classification 1: rock

Classification 2:

Area:

Description:

Contact 13




42.6103988542 -70.6577724755 (WGS84)


(X) 882893.73 (Y) 3048586.83

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008125308





Classification 1: tires

Classification 2:

Area:

Description: Typical tire

Contact 14




42.6107324493 -70.6579023564 (WGS84)


(X) 882857.56 (Y) 3048708.06

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008125805

Target Height: >= 0.7 US Feet





Classification 2:

Area:

Description:

Contact 15




42.6104426578 -70.6582505902 (WGS84)


(X) 882764.86 (Y) 3048601.52

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008125805






Classification 2:

Area:

Description: Debris cluster at end of pier

Contact 16




42.6103867813 -70.6584362977 (WGS84)


(X) 882715.07 (Y) 3048580.67

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008125805





Classification 1: debris or rock

Classification 2:

Area:

Description:

Contact 17




42.6103697391 -70.6586366294 (WGS84)


(X) 882661.21 (Y) 3048573.93

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008130233





Classification 1: rock and debris

Classification 2:

Area:

Description:

Contact 18




42.6103043180 -70.6588264600 (WGS84)


(X) 882610.34 (Y) 3048549.58

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008130233






Classification 2:

Area:

Description: debris cluster and derelict pilings

Contact 19




42.6132457134 -70.6571890855 (WGS84)


(X) 883040.52 (Y) 3049625.87

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008172836






Classification 2:

Area:

Description:

Contact 20




42.6132394228 -70.6569048357 (WGS84)


(X) 883117.05 (Y) 3049624.33

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008172836






Classification 2:

Area:

Description: likely fallen pilings

Contact 21




42.6131130315 -70.6568737124 (WGS84)


(X) 883125.89 (Y) 3049578.35

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008172836





Classification 1: debris or rock

Classification 2:

Area:

Description:

Contact 22




42.6131443404 -70.6564930513 (WGS84)


(X) 883228.24 (Y) 3049590.77

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008172836






Classification 2:

Area:

Description:

Contact 23




42.6101832887 -70.6584108604 (WGS84)


(X) 882722.65 (Y) 3048506.58

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131008174228





Classification 1: rock

Classification 2:

Area:

Description:

Contact 24




42.6103807806 -70.6588421968 (WGS84)


(X) 882605.83 (Y) 3048577.40

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131009183329





Classification 1: piling

Classification 2:

Area:

Description: series of pilings

Contact 26




42.6108757436 -70.6583848942 (WGS84)


(X) 882727.15 (Y) 3048759.00

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131009184203





Classification 1: railway

Classification 2:

Area:

Description: Southwestern marine railway remnants

Contact 28




42.6110215843 -70.6583802266 (WGS84)


(X) 882727.88 (Y) 3048812.16

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131009184503






Classification 2:

Area:

Description: Existing marine railway

Contact 30




42.6109124159 -70.6584144987 (WGS84)


(X) 882719.05 (Y) 3048772.28

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131009185009






Classification 2:

Area:

Description: Southwestern marine railway remnants

Contact 31




42.6109072474 -70.6582443358 (WGS84)


(X) 882764.88 (Y) 3048770.85

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131009185159






Classification 2:

Area:

Description: Existing marine railway

Contact 32




42.6109850097 -70.6584065452 (WGS84)


(X) 882720.93 (Y) 3048798.76

• Map Proj: MA83F







• Event Number: 0


• Line Name: 20131009191829





Classification 1: railways

Classification 2:

Area:

Description: Point between southwestern railway (left)

and existing railway (right). Upper portion of image is

southeast, bottom is shoreward. Width between rails is

approximately 10 ft.

APPENDIX B

Geophysical Survey Limitations

i

APPENDIX B

CR ENVIRONMENTAL, INC. LIMITATIONS FOR GEOPHYSICAL SURVEYS

The following general limitations apply to all geophysical surveys conducted by CR Environmental, Inc. or its subcontractors: Every attempt has been made to conduct this survey in such a fashion so as to maximize the quality of the data collected and the interpretations rendered. However, a geophysical investigation is an indirect method of exploration whereby subsurface characteristics are inferred or interpreted from measurements collected at the sediment surface. Many variables may affect these measurements. Due to the indirect, interpretive nature of geophysics, findings are generally considered precursory and subject to verification by more direct methods of investigation such as coring, test borings, drilling, etc. The following general limitations are considered when evaluating geophysical data. (1) Subsurface features can be interpreted from the appropriate geophysical methods only insofar as they produce a discernable geophysical signature. They must have adequate homogeneity, size, and appropriate physical or chemical properties sufficient to contrast with the surrounding medium and be within reasonable proximity to the sensors. Additionally, their signature must be distinguishable from and not masked by background noise or interference. (2) Lithologic data inferred on the basis of geophysical data may not be identical to geologic data. Some complex geological configurations may be impossible to resolve with surface geophysical methods. (3) CR cannot be responsible for losses caused through any misrepresentation of the data presented or the interpretation rendered for this project. CR has provided the data and interpretations presented in the report in good faith. CR is not responsible for any misuse of the data by the Client, its affiliates and/ or subcontractors. Use and Limitations of Survey Technologies Each of the three remote sensing technologies (i.e. , side-scan sonar, sub-bottom sonar, and magnetometer) has detection capabilities and limitations. Understanding these systems’ capabilities and limitations is essential to understanding how they affect data interpretation, and conclusions that may be drawn from the data. Co-located evidence of bottom features or anomalies using different technologies provides added detail and certainty. Generally surficial debris < 1 ft in any dimension is difficult to distinguish. In addition, small buried ferrous objects between magnetometer survey transect lines, and buried non-ferrous objects between sub-bottom survey lines cannot be detected.

ii

Side-scan sonar The towed side-scan sonar system provides complete coverage of the bottom in varying swath widths depending on the instrument’s frequency and water column characteristics. These swaths of data are pieced together to create mosaics providing a shaded image of the bottom based on the amplitude of the return signal and showing habitat features and substrate roughness and hardness. Side-scan sonar is an ideal instrument for identifying surficial obstructions and debris at the sediment surface. The forms and materials that make up obstructions and debris at the sediment mudline (the sediment-water interface) can be detected with side-scan sonar. Groundtruthing with grab sampling or video is important for substrate and image confirmation. The high frequency signal of the side-scan system does not substantially penetrate surficial sediments. Side-scan sonar data can be used to estimate the approximate dimensions of detected objects on the seabed, including object height above the mudline. These height measurements are made by measuring the length of sonar “shadows” behind objects, considering the height of the towfish and the corrected range to the object. The ability of the side-scan system to detect bottom features is related to several characteristics of the sonar system and the method of deployment. Integral system characteristics which influence image resolution include signal frequency, horizontal and vertical beam angles, signal (ping) duration, swath range selection, and operator adjustments of signal gain controls. The resolution and quality of sonar imagery is also influenced by towfish depth, vessel survey speed, the degree of overlap between survey transects, and water column characteristics. Based on the operations procedure detailed in this report, the approximate resolution of the side-scan sonar data collected for this project ranges from approximately 5 cm to 50 cm (about 2 to 20 inches), depending on the transect-specific settings. The positions reported for Contacts identified using side-scan sonar are subject to two uncertainties. The first uncertainty is associated with post-processing correction for the towfish layback (i.e., the distance between the DGPS antenna and the towfish). This correction has been applied to all data with demonstrable success. However, minor variations in vessel speed and towfish altitude can introduce some position uncertainty. The second Contact position uncertainty is integral to all side-scan sonar systems. The side-scan sonograph is a two-dimensional record of the strength of the return sonar signal. Raw sonar data is “slant-range” corrected by removing the water column portion of the sonograph. However, the two-dimensional nature of the data and the slant-range correction methods necessitate a geometric assumption of a flat seabed (horizontal bottom). For instance, consider a sonar transect which runs parallel to the shoreline near the toe of a substantially steep slope. Assume that the port channel is facing shoreward up the slope and that the sonar range is set to 82 feet. Because the sonar is recording the positions of bottom features using a range-calculation based on signal travel time, the reported “across-track” dimensions and position of a Contact observed mid-slope may be different than the actual position. Similarly, two objects at equal distance from the towfish (e.g., one object mid-slope at 50-foot range, another at the toe of the slope at 50-

iii

foot range) will overlap on the data record even though the true across-ground distance may be substantially different. This effect can introduce unwanted artifacts into the data. Sonar data acquired “up-slope” also results in decreased bottom grazing angles, shortening shadows associated with objects and skewing calculations of object height towards lower values. Additionally, more acoustic energy can be received on the up-slope channel, complicating classification of substrate reflectance relative to flat bottom areas The inverse of the uncertainties associated with the “flat-bottom” assumptions occurs with the down-slope oriented sonar channel. Sub-Bottom Sonar Sub-bottom sonar systems can be used to estimate the depth of various sediment strata or depth to bedrock, and can detect larger objects at or near the sediment surface. .The system used for this survey has been shown to penetrate and image up to 120 ft of sediment under ideal conditions. Sediment composition and geotechnical properties play a major role in determining sonar penetration. The acoustical impedance and sound absorption coefficient of sediments varies with grain size, pore space and several other characteristics, each of which influences penetration. Magnetometer A magnetometer was used to identify ferrous containing objects both above and below the sediment surface, and to determine if features identified by side-scan sonar (above the sediment surface) contained iron. The magnetometer employed for this survey allows discrimination of magnetic variations as low as 1 gamma. The magnitude of a magnetic anomaly detected depends on the ferrous mass of an object and its distance from the magnetometer. A list of common objects and the typical maximum magnetic anomaly that would be detected is provided below for reference: OBJECT NEAR DISTANCE FAR DISTANCE Ship (1000 tons) 300 to 700 gammas @100 ft 1 gamma @ 800 ft Automobile (1 ton) 40 gammas @ 30 ft 2 gammas @ 40 ft Pipeline (12 inch diameter) 50 to 200 gammas @ 25 ft 12 to 50 gammas @ 50 ft Fenceline 15 gammas @ 10 ft 1 to 2 gammas @ 25 ft File (10 inches long) 50 to 100 gammas @ 5 ft 5 to 10 gammas @ 10 ft (From G-881 Operating Manual 25831-OM, 2001) In addition to ferrous mass and distance, the orientation, composition and shape of a ferrous object influence the magnitude of the detected anomaly. For instance, a 12-inch pipeline will have a similar magnetic effect as 1 ton of iron at a range of about 50 ft. The position of the sensor relative to the object’s magnetic field and the orientation of the object on the seabed will influence the “shape” of the anomaly. For instance, consider an iron pipe lying flat on the seabed. If the magnetometer intersects only one lobe of the pipe’s magnetic field, the magnetic signature will likely be monopolar (i.e., in profile view, a positive or negative parabola), with the duration, response magnitude and tangent of the curve reflecting the size and proximity of the object. If the sensor intersects both

iv

lobes of the field, the response curve will appear dipolar (i.e., sinusoidal), with the actual position of the object corresponding to the midpoint between positive and negative responses. However, if the same pipe were embedded vertically in the sediment, even if the sensor is towed directly above the pipe, it is likely that the “shape” of the response in profile will be monopolar.

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