The document is a bathymetric survey report of the Gowanus Canal in Brooklyn, New York. It was conducted in January 2010 by CR Environmental, Inc. for HDR Architecture and Engineering. The survey mapped seabed elevations using sonar equipment on boats. Elevations in the Canal ranged from -0.13 to -38 feet NAVD88. Access to some areas was limited by ice. The quality of the bathymetric data met US Army Corps of Engineers and International Hydrographic Organization guidelines for accuracy. Further surveys were recommended to map areas with limited access and locate debris.

1. AppendixB
Bathymetry
Contents
Bathymetric Survey Report
Bathymetric Survey Report, Addendum 1, Comparison of Gowanus Canal BottomElevations,
June 2003 versus January 2010

2. BATHYMETRIC SURVEY REPORT
GOWANUS CANAL
BROOKLYN, NEW YORK
3-D Visualization of a Portion of the Gowanus Canal Survey Area
Prepared for:
Henningson, Durham and Richardson Architecture and Engineering,P.C.
One Blue Hill Plaza, P.O. Box 1509
Pearl River, New York 10965
Prepared by:
CR Environmental, Inc.
639 Boxberry Hill Road
East Falmouth, MA 02536
April 2010

3. Bathymetric Survey Report
Gowanus Canal
Brooklyn, New York
CR Environmental, Inc.
April 2010
TABLE OF CONTENTS
Page
1.0 INTRODUCTION………………………………………………………………… 1
2.0 METHODS………………………………………………………………………… 1
2.1 Survey Vessel 1
2.2 Bathymetric Data Acquisition 2
2.3 Vertical Control 2
2.4 Bathymetric Data Processing 3
3.0 BATHYMETRIC RESULTS AND DELIVERABLES …………..…...………...… 4
4.0 CONCLUSIONS AND RECOMMENDATIONS ………………..…...…………… 5
FIGURES
Figure 1A Gowanus Canal Site Trackline Map (Southern Section)
Figure 1B Gowanus Canal Site Trackline Map (Northern Section)
Figure 2A Gowanus Canal Site Bathymetric Contour Map (Southern Section)
Figure 2B Gowanus Canal Site Bathymetric Contour Map (Northern Section)
LIMITATIONS
ATTACHMENT 1 GEOD Corporation Survey Information for the BM-1 Control
Point on the Carroll Street Bridge
PROJECT DATA CD
i

4. Bathymetric Survey Report
Gowanus Canal
Brooklyn, New York
CR Environmental, Inc.
April 2010
1.0 INTRODUCTION
CR Environmental, Inc. (CR) performed a bathymetric survey of part of Gowanus Bay
and all navigable portions of the Gowanus Canal, located in Brooklyn, NY, on January 5,
2010 for Henningson, Durham and Richardson Architecture and Engineering, P.C.
(HDR). The objective of the survey was to map seabed elevations within the Gowanus
Canal Study Area in support of the ongoing Remedial Investigation/Feasibility Study
(RI/FS). These data can be used to support volume calculations, estimates of changes in
depth over time, and to assist in planning sediment sampling investigations.
This draft report summarizes the methods used for bathymetric data acquisition and the
results obtained. Digital data products were transmitted electronically to HDR and CH2M
Hill, Inc. on January 25, 2010 and also on a CD with the draft report submitted February
2010. Data are projected to New York State Plane (Long Island), NAD-83, U. S. Survey
Feet. Seabed elevations are reported in U.S. Survey Feet relative to NAVD88 (estimated).
2.0 METHODS
The bathymetric survey was designed to meet or exceed the survey requirements
specified by HDR in an August 2009 Request for Proposal. The executed survey
methodology was in compliance with hydrographic survey standards promulgated by the
U.S. Army Corps of Engineers (USACE, EM-1110-2-1003).
Shore-parallel survey transects were spaced approximately 10 to 50 feet apart. Channel
cross-sections were spaced 100 feet apart. Navigation for the survey was accomplished
using Trimble AgGPS 132 and Trimble ProXRS 12-channel Differential Global
Positioning Systems (DGPS) capable of receiving U.S. Coast Guard (USCG) Beacon
corrections, and OmniStar subscription-based satellite differential corrections. Both
systems provided real time digital positions accurate to less than 1 meter horizontally.
2.1 Survey Vessel
Two vessels were utilized for the survey. The primary survey vessel was the M/V Donna
Miller, chartered from Miller’s Launch in Staten Island, NY. This 25-ft aluminum work
boat was used to conduct the survey in Gowanus Bay, and a portion of the work in the
lower Gowanus Canal. The 12-ft survey skiff was utilized in the shallower portions of the
Canal, and to conduct the survey work above the Carroll Street Bridge. Both vessels were
outfitted with over-the-side transducer mounts, DGPS antenna brackets, and data
acquisition computers. Neither vessel was equipped with ice breaking equipment, and
because of this, the surveys were limited by the extent of any ice encountered in the
Canal and turning basins.
1

5. Bathymetric Survey Report
Gowanus Canal
Brooklyn, New York
CR Environmental, Inc.
April 2010
2.2 Bathymetric Data Acquisition
The echo sounders and DGPS were interfaced to the survey computers via RS-232 serial
and Ethernet ports. Most depth measurements on the Donna Miller were acquired by
simultaneous deployment of two survey-grade echo sounders in order to increase data
density, productivity, and usability. The two echo sounders on the Donna Miller were an
ODOM CV-100 precision echo sounder equipped with an 8-degree 200- kHz transducer,
and a SyQwest Bathy500 precision echo sounder equipped with a 3- degree 200-kHz
transducer. Depth measurements on the skiff were collected using a SyQwest HydroBox
precision echo sounder equipped with an 8-degree 200-kHz transducer.
The echo sounder transducers were mounted to the rails of the survey vessels
amidships using high-strength adjustable booms. The DGPS antenna on the skiff was
mounted directly over the transducer, eliminating the need to account for horizontal
offsets. The depth of each transducer below the water surface was measured both at the
start and end of the survey.
The accuracy of the CV-100, HydroBox, and Bathy500 was approximately 0.1% of the
water depth with a resolution of 0.1 foot. System accuracy was checked at the start and
end of the survey day by comparing each echo sounder’s water depth measurements to
known water depths obtained using the bar check method, in which a metal plate is
lowered beneath the echo sounder’s transducer to several known distances (e.g., 5, 10, 15
and 20 ft below the water surface). Based on these comparisons, the systems were
calibrated for shallow water conditions. Bar check calibrations for all three systems were
consistently accurate to within 0.1 foot throughout the survey.
Additional calibrations were conducted in-situ by collecting water column profiles of
sound velocity. Sound velocity in water can be determined based on measurements of
temperature and conductivity. Measurements of water column temperature and
conductivity were performed using a YSI, Inc. Model 6600 EDS-V2 water quality sonde,
and a YSI, Inc. Model 85 Handheld Water Quality Meter.
2.3 Vertical Control
Vertical control for this survey was accomplished by using a cost-effective combination
of techniques. GEOD Corporation, a NY Licensed Land Surveying firm, had established
three vertical control points in support of CR’s 2003 bathymetric surveying effort of the
Canal (see Attachment 1). One benchmark was located in outer Gowanus Bay at the
Columbia Street pier, one was located in the central reach of the Gowanus Canal at
Bayside Fuel Corporation (537 Smith Street), and one was near the head of the Canal at
the Carroll Street Bridge. GEOD was contacted and they conducted a site reconnaissance
2

6. Bathymetric Survey Report
Gowanus Canal
Brooklyn, New York
CR Environmental, Inc.
April 2010
which concluded that only the benchmark in the Bay and the benchmark at Carroll Street
were still in existence and usable.
CR set two time-synchronized water level recorders, one near the upstream extent of the
survey area and one near the downstream extent of the survey area in order to evaluate
time and range offsets in water surface elevation during the survey. A new temporary
benchmark (TBM-1) was established near the downstream limit of the survey area,
adjacent to 629 Smith Street, and an In Situ, Inc. LevelTroll 500 water level recorder was
suspended beneath this benchmark. An In Situ, Inc. LevelTroll 100 water level recorder
was suspended beneath the upstream Carroll Street Bridge control point (BM-1). After
the survey was completed, data from the two synchronized tide recorders were compared.
CR determined that there was no quantifiable difference in tidal range or timing between
the two locations during the survey (both flood and ebb around high tide). Thus, for the
purposes of this survey, occupation of TBM-1 by a land survey firm was not required.
Note, however, that the tidal gradient in the Canal surrounding low tide or under different
wind conditions is unknown. The TBM-1 benchmark was clearly marked, and could be
surveyed at any time if needed.
Per the request of Project advisors from CH2M Hill, Inc., the elevations from the January
2010 survey have been reported as “estimated” NAVD88 elevations. The Carroll Street
benchmark elevation was reported by GEOD relative to NGVD29 (Attachment 1), and
three methods were used to convert the benchmark elevation to NAVD88. First, the U.S.
Army Corps of Engineers’ (ACOE) datum conversion routine, Corpscon, was run to
determine the offset between the two datums. Corpscon gave a result of -1.109 U.S.
Survey Feet between NGVD29 and NAVD88. CR then contacted GEOD Corporation,
and they confirmed that the separation between NGVD29 and NAVD88 was -1.11 feet.
This value has been used to convert the soundings to estimated NAVD88 seabed
elevations. The accuracy of the conversion was verified by comparing the NAVD88
adjusted tide data to NOAA’s Battery tide series (Station ID: 8518750), adjusted for
Gowanus Bay. This comparison suggested a -1.19 foot separation between datums.
2.4 Bathymetric Data Processing
Individual transect data were visually inspected in profile format, and components of
processing included:
 Removal of outlying soundings associated with water column interference (e.g.,
fish, vegetation, or mid-water column debris);
 Adjustments of soundings for variations in sound velocity;
 Filtering of DGPS position data; and
 Conversion of soundings to estimated NAVD88 elevations based on a benchmark
surveyed by GEOD Corporation in 2003, located near the Carroll Street Bridge.
See Section 2.3 for a discussion of the vertical control for this project.
3

7. Bathymetric Survey Report
Gowanus Canal
Brooklyn, New York
CR Environmental, Inc.
April 2010
Neither water column interference nor sound velocity gradients influenced data quality,
likely due to the cold dry weather which preceded the survey. However, DGPS position
uncertainty was substantially increased by overhead obstruction and signal multipath near
each of the bridge overpasses. Position data were filtered to retain only differentially
corrected fixes with low dilution of position values. The locations of soundings beneath
bridges were estimated based on interpolation between high-confidence DGPS fixes on
either side of each bridge.
After performing data adjustments, the processed bathymetric data were combined into
comma-delimited ASCII text files including fields for Northing, Easting, and Elevation.
The data were imported to Golden Software, Inc. Surfer V.9.3 Surface Modeling
Software and a digital elevation model (DEM) of seabed elevations was created using
triangulation interpolation methods. A contour map depicting bottom elevations using a
0.5-foot contour interval was created from the DEM and the map was exported in DXF
and SHP formats. A surface map of the bathymetric data was created using conventional
hydrographic shading, artificial illumination, and a 2x vertical exaggeration to better
illustrate bottom morphology. The surface map was exported as a georeferenced TIF
image file.
3.0 BATHYMETRIC RESULTS ANDDELIVERABLES
Processed bathymetric data, map layers, figures, and a copy of this report are attached on
the project CD. Occupied survey transects (i.e., sounding tracklines) are depicted on
Figures 1A and 1B. The increased data density afforded through simultaneous use of two
echo sounders is readily apparent. Access to inner portions of all four turning basins was
precluded by ice. DGPS signal quality was compromised near all bridges. This
degradation was most severe beneath the 9th
Street Bridge.
Elevations reported during the survey ranged from approximately -0.13 feet to -38 feet
NAVD88, as illustrated by the contour and DEM layers presented on Figures 2A and 2B.
Prop scours from tug boat operations are visible on the seabed near the downstream limit
of the survey area.
Although single-beam bathymetry is not considered an effective tool for identifying
underwater obstructions, wreckage is clearly visible in data collected from the turning
basin between 5th
Street and 6th
Street. This feature extends above the water surface at all
tides and is clearly visible from shore and in aerial photographs. Submerged wreckage or
large debris is also suggested near the mouth of the upstream turning basin. Data suggests
the widespread presence of other debris throughout the survey area. Mapping of these
features will require side scan or multibeam sonar surveys.
Bathymetric data quality was assessed by comparing approximately co-located
soundings along perpendicular transects. These “cross-tie” comparisons were conducted
on the final merged data set, and included points collected using all three sounding
systems on both vessels over a tidal range of 2.6 feet. Examination of 337 of these co-
located soundings revealed a negligible arithmetic mean difference (depth bias) of -0.025
4

8. Bathymetric Survey Report
Gowanus Canal
Brooklyn, New York
CR Environmental, Inc.
April 2010
feet, and a standard deviation (SD) of the residuals of +0.30 feet. Considering cross-tie
comparisons across the full project depth range (38 feet), the root mean squared (RMS)
error was 0.62 feet at the 95% Confidence Interval (CI), less than the most stringent
Army Corps of Engineers (ACOE) requirement of 1.0 foot for navigation and dredging
projects in water depths of 15 to 40 feet. Data collected from the skiff in water depths less
than 15 feet had a RMS at the 95% CI of 0.27 feet, less than the 0.5-foot ACOE
specification for this water depth.
International Hydrographic Organization (IHO) Special Order specifications for a survey
in depths of 5 meters (16.4 feet) would call for a 95% CI of 0.8 feet (max SD =
0.42). IHO Special Order specifications for a survey in depths of 10 meters (32.8 feet)
calls for a 95% CI of 0.9 feet (max SD = 0.44).
We, therefore, conclude that the quality of data generated by this survey is compliant
with ACOE and IHO guidelines. Some of the variation in “cross-tie” comparisons is
associated with the steep slopes and engineered headwalls which dominate the Canal
margins. These slopes and headwalls cause vertical discontinuity between soundings run
in different directions. In addition, the slight variation between some soundings suggests
the presence of a surficial floc layer on the seabed which was intermittently penetrated by
the ODOM and SyQwest sounding systems.
4.1 CONCLUSIONS AND RECOMMENDATIONS
The January 2010 bathymetric survey of the Gowanus Canal generated an accurate
database and map of seabed elevations and morphometry. Ice prevented access to small
sections of the Canal’s turning basins, and active and derelict barges and other vessels
hindered navigation in some portions of the Canal’s main channel. Further bathymetric
survey work will be required to characterize these areas, and additional soundings should
be collected in the vicinity of the 9th
Street Bridge using a smaller vessel which does not
require Bridge openings for access. Finally, the use of side scan sonar to accurately locate
and characterize submerged debris which could pose a danger to sediment sampling or
potential future dredging efforts is recommended.
5

9. Bathymetric Survey Report
Gowanus Canal
Brooklyn, New York
CR Environmental, Inc.
April 2010
CR ENVIRONMENTAL, INC.
GEOPHYSICAL AND HYDROGRAPHIC SURVEY
UNCERTAINTIES AND LIMITATIONS
1. Acoustic methods of remote sensing in aquatic environments are influenced
by the chemical and physical characteristics of the waterbody and underlying
sediment. Water column characteristics which introduce uncertainty include:
biological interference (e.g. fish or debris in mid-water column);
conductivity/salinity and temperature as they affect sound velocity; and
weather and other surface conditions as they effect navigation. Sediment and
bottom characteristics which introduce uncertainty include supersaturated
flocculent sediments; sediments which contain entrained natural gases (e.g.,
sulfides, methane) which limit sonar penetration; steep slopes which may limit
sonar bottom penetration due to increased angle of incidence or scattering;
and rooted vegetation. CR Environmental, Inc. (CR) has made all technically
feasible attempts to minimize the above uncertainties as described in the
report.
2. The observations described in this report were made under the conditions
stated therein. The conclusions presented in the report were based solely upon
the services described therein, and not on scientific tasks or procedures
beyond the scope of services or the time and budgetary constraints imposed by
the Client.
3. The conclusions and recommendations contained in this report are based in
part upon the data obtained using acoustic remote sensing observations
obtained along survey transects spaced approximately 10 to 50 feet apart.
Information presented in this report between the survey transects (i.e., depth
contours) is based on mathematical interpolation, and thus may not be suitable
for navigation.
CR Environmental, Inc. respectfully reserves the right to amend this report should new
information become available.

10. ATTACHMENT 1
GEOD Corporation
Survey Information for the BM-1 Control Point
on the Carroll Street Bridge

11. 08/06/2003 11:36 973838643< GEOD CORP PA<:£ 132/03
GEOD COR?ORATION
PHOTOGRAMt.lETRIC SCIENCES·SURVEYTECHNOLOGIES
August 5,2003
Mr, Chri Wrillhl
CR EnvironmentalInc.
639 Boxberry HillRoad
t:astt-almoutn,MA•Jb:.!::ll$
RE: semNG ELEVATION REFERENCE MARKS ALONG THE GOWANUS CANAL
(GEOD PROJECT # 2089)
Dear Sir,
I
As requested, GEOD Corporation established 3 elevation reference marl<s (ench marks) for
the sub-surface survey to be pelforrnedalongthe Gowanus Canalby CR Envirnmental.
These elevation reference marks were established In the NationalGeodetic iertlcel Datum of
1929 (NGVD 1929) and MLW Mean Low Wat.er Datum uncler the dlect upervision of a
surveyorlicensed in the State of New Yori<. •
Nome:
Ii
i
l'le83e do IIOt Msitate!¢c.eo11tol11,., with your oomments or questions.
Very TrulyYours, IGEOD_CORPORATION
i
"--:. --"- - •D - -
Stanley 8. Palinski
VlcePresident
OORPORAT&Ol'FICE,
t&.24 Ka,,o.., Ad..,...wloundla,d. H.J.07435
(ffl) 69741:13 F"AX• (013)
OFFICES:
SBRRollrl SWOl,!!oslmMAQa!29
{ti1/J // t'A!Ul /J / fbo(..,14$4

12. I
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1t·24 K>Muse Road,Newl:i.NJ07435
(973)$912122 • l'ax:(973)83&-6433
E-Mail: ooCgeo<lc<>rp.com
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14. CR Environmental, Inc. April 2010
BATHYMETRIC SURVEY REPORT
GOWANUS CANAL
BROOKLYN, NEW YORK
ADDENDUM 1
Comparison of Gowanus Canal Bottom Elevations
June 2003 versus January 2010
CR Environmental, Inc. compared Gowanus Canal bottom elevations recorded during
bathymetric survey efforts conducted in 2003 and 2010 to estimate areas of sedimentation
and erosion within the canal. The sections that follow provide the methods used to
compare the elevation data, and briefly describe the results of the comparison.
Methods
Prior to conducting the elevation data comparison, the June 25, 2003 data were re-
processed to adjust soundings to estimated NAVD88 elevations using correction factors
detailed in Section 2.3 of the April 2010 Bathymetric Survey for Gowanus Canal,
Brooklyn, New York report. These data were acquired along cross-sections spaced 25 to
200 feet apart (see Figure A1). The root mean squared (RMS) error of the reprocessed
data was calculated as approximately 0.3 feet using Army Corps of Engineers (ACOE)
methods (see Section 3.0), similar to the error value calculated for data collected in 2010.
The reprocessed 2003 data were then gridded using a 20-foot node interval. The extent
of the grid (surface model) was limited to the boundary of the 2010 survey effort.
The approximate thalweg (deepest continuous line) of the Canal as interpreted from the
2010 data was digitized. Points from the 2003 and 2010 grids which intersected the
thalweg were extracted and exported in ASCII text format. These points were used to
generate comparative profiles of thalweg elevation differences between the two surveys.
The points have been delivered digitally in MS Excel tabular format.
The grids from each survey were next converted to an ASCII format suitable for analysis
using IVS3D Fledermaus software. This software was used to compare the two surface
models. The elevation values from 2003 were subtracted from co-located values on the
2010 surface model, resulting in a new surface for which positive values indicated
shallower 2010 depths (sedimentation) and negative values indicated portions of the
canal which were deeper in 2010 (erosion, scour, dredging or other anthropogenic
activities). This elevation comparison grid was used to generate a contour map of
elevation differences (Figure A2). The map was imported to GIS in DXF and TIF
formats for comparison with bathymetry. These layers have been delivered
electronically.
Results
The distribution of bathymetric data points for the two surveys are shown on Figure A1
Detailed maps of the 2010 data distribution have been provided on Figures 1A and 1B in
CR Environmental’s April 2010 Bathymetric Survey Report for the Gowanus Canal,
639 Boxberry Hill Road, East Falmouth, MA 02536 1
508 563-7970 phone/fax www.crenvironmental.com

15. CR Environmental, Inc. April 2010
Brooklyn, New York). The substantially lower data density specified for the 2003 survey
effort is readily apparent, and is important to acknowledge during examination of the
surface model comparison results. The 2003 data density was highest upstream of the
Carroll Street Bridge where transect spacing was approximately 25 feet (Figure A1).
Figure A2 is a plan view comparison of the 2003 and 2010 surface models. Elevation
differences along the thalweg are depicted on Figures A3 and A4. The data comparisons
shown on Figures A2 and A4 highlight the area of highest uncertainty as +/- 0.6 feet, the
combined RMS error estimates for the two surveys. Despite efforts to minimize
modeling artifacts, the surface model comparison shown on Figure A2 shows regularly
spaced positive elevation difference “lobes” along each shoreline at intervals that mirror
the distance between the 2003 cross-sections. CR recommends that users of these data
simultaneously evaluate model data relative to sounding distribution in GIS to minimize
the likelihood of misinterpretation. Data comparisons along the thalweg are less subject
to grid interpolation errors.
Elevation differences appeared minor upstream of the floating boom adjacent to Sackett
Street (about 530 feet downstream of the head of the Canal). Some erosion was indicated
along the western shoreline (see Figure A2). Approximately 2 to 3 feet of sediment
accumulation was suggested between the boom and the Carroll Street Bridge (about
1,400 feet downstream of the head of the Canal). Data comparisons within this upper
portion of the Canal are considered robust from shore to shore due to the higher 2003
data density upstream of the Carroll Street Bridge.
Comparison of the two model surfaces along the thalweg suggests approximately 1 to 2
feet of sediment accumulation at the northern end of the Canal between Carroll Street and
3rd
Street (see Figures A3 and A4).
Elevation differences of approximately -1 to 1 foot dominated most of the reach between
3rd
Street and Interstate 278. Highest confidence is given to areas of elevation differences
greater than the summed RMS uncertainty of +0.6 feet (see Figure A4). Erosion in this
reach is suggested in an area subject to frequent tug and barge traffic adjacent to a gravel
shipping yard between 5th
Street and Huntington Street.
At the southern end of the Canal, the surface comparison suggests a wide (approximately
80,000 square foot) region of sediment accumulation along the thalweg adjacent to
Halleck Street (Figures A2 and A4). Also suggested in this southern reach were many
smaller areas of substantial elevation difference either erosional or depositional (Figure
A2).
Confidence for many of these areas decreases with increasing distance from the 2003
longitudinal centerline due to anomalies associated with interpolation between survey
transects spaced approximately 150 feet apart.
639 Boxberry Hill Road, East Falmouth, MA 02536
508 563-7970 phone/fax www.crenvironmental.com

16. 984000 985000 986000 987000 988000
Extracted Thalweg
Points (see Figures A3 andA4)
Union St.
Carroll St.
5th St.
3rd St.
Huntington St.
9th St.
I 278
Halleck St.
Feet
0 750 1,500
EROSION SEDIMENTATION
984000 985000 986000 987000 988000
Bathymetric Surface Model Comparison -
June 2003 and January 2010 Survey Data
Gowanus Canal Brooklyn, New York :NOTES:
1) Survey data collected by CR Environmental, Inc.
of East Falmouth, Massachusetts on June 25, 2003 and January 5, 2010.
2) Grid: NY State Plane (LI), NAD83, US Foot.
3) Elevation differences less than +/- 0.6 feet are transparent.
These values are within the combined RMS error range for the two surveys.
Figure A2
182000183000184000185000186000187000
182000183000184000185000186000187000