EPA/600/R-10/126 

September 2010

FIELD STUDY ON ENVIRONMENTAL DREDGING 

RESIDUALS: ASHTABULA RIVER

VOLUME I. FINAL REPORT

by

Battelle 

Columbus, Ohio 43201 

and

Sea Engineering, Inc.

Santa Cruz, CA 95060 

Contract No. EP-C-05-057 

Task Order 50

Co-Principal Investigators

Marc A. Mills and Richard C. Brenner

Land Remediation and Pollution Control Division

National Risk Management Research Laboratory

Cincinnati, OH 45268

National Risk Management Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Cincinnati, OH 45268
iii

NOTICE

The U.S. Environmental Protection Agency (U.S. EPA), through its Office of Research and Development 

(ORD), funded and managed the research described herein under Contract No. EP-C-05-057. This report 

has been subjected to the Agency’s peer and administrative review and has been approved for publication 

as a U.S. EPA document.
iv

FOREWORD

The U.S. Environmental Protection Agency (U.S. EPA) is charged by Congress with protecting the 

Nation’s land, air, and water resources. Under a mandate of national environmental laws, the Agency 

strives to formulate and implement actions leading to a compatible balance between human activities and 

the ability of natural systems to support and nurture life. To meet this mandate, U.S. EPA’s research 

program is providing data and technical support for solving environmental problems today and building a 

science knowledge base necessary to manage our ecological resources wisely, understand how pollutants 

affect our health, and prevent or reduce environmental risks in the future.

The National Risk Management Research Laboratory (NRMRL) is the Agency’s center for investigation 

of technological and management approaches for preventing and reducing risks from pollution that 

threaten human health and the environment. The focus of the Laboratory’s research program is on 

methods and their cost-effectiveness for prevention and control of pollution to air, land, water, and 

subsurface resources; protection of water quality in public water systems; remediation of contaminated 

sites, sediments, and ground water; prevention and control of indoor air pollution; and restoration of 

ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies that 

reduce the cost of compliance and to anticipate emerging problems. NRMRL’s research provides 

solutions to environmental problems by: developing and promoting technologies that protect and improve 

the environment; advancing scientific and engineering information to support regulatory and policy 

decisions; and providing the technical support and information transfer to ensure implementation of 

environmental regulations and strategies at the national, state, and community levels.

This publication has been produced as part of the Laboratory’s strategic long-term research plan. It is 

published and made available by U.S. EPA’s Office of Research and Development to assist the user 

community and to link researchers with their clients.

Sally C. Gutierrez, Director

 National Risk Management Research Laboratory
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vi

CONTENTS 

NOTICE.......................................................................................................................................................iii

FOREWORD............................................................................................................................................... iv

FIGURES.................................................................................................................................................... vii

TABLES .................................................................................................................................................... viii

ACRONYMS AND ABBREVIATIONS .................................................................................................... ix

ACKNOWLEDGEMENTS......................................................................................................................... xi

EXECUTIVE SUMMARY ........................................................................................................................ xii

1.0 PROJECT DESCRIPTION AND OBJECTIVES.................................................................................. 1

1.1 Purpose ...................................................................................................................................... 1

1.2 Dredge Residuals....................................................................................................................... 2

1.3 Site Description ......................................................................................................................... 3

1.4 Dredge Operations..................................................................................................................... 5

1.5 Research Goals and Objectives................................................................................................. 7

2.0 EXPERIMENTAL APPROACH......................................................................................................... 10

2.1 General Approach.................................................................................................................... 10

2.2 Study Design ........................................................................................................................... 10

2.3 Data Collection Strategy ......................................................................................................... 12

2.3.1 Sediment Core Collection ............................................................................................ 12

2.3.2 Sonar Monitoring......................................................................................................... 13

3.0 CONTAMINATED SEDIMENT CHARACTERIZATION AND DREDGE RESIDUALS 

ASSESSMENT USING A WEIGHT OF EVIDENCE APPROACH................................................ 16

3.1 Vertical Alignment and Physical Examination of the Pre- and Post-Dredge Sediment 

Cores ........................................................................................................................................ 16

3.1.1 Vertical Alignment of the Pre- and Post Dredge Sediment Cores............................... 16

3.1.2 Physical Examination of the Pre- and Post-Dredge Sediment Cores........................... 17

3.2 Physical Parameter Analysis of Sediment Core Segments...................................................... 18

3.3 Sediment PCB Chemistry and Data Analysis of Core Segments............................................ 22

3.3.1 Characterization of the Pre-Dredge Sediment PCB Inventory..................................... 22

3.3.2 Characterization of the Post-Dredge Sediment PCB Inventory................................... 29

3.3.3 Post-Dredge PCB Characteristics and Implications for Dredged Residuals................ 43

3.4 Two (2)- and Three (3)-Dimensional PCB Modeling of Pre- and Post Dredge Areas............ 43

3.5 Bathymetric Surveys Prior to, During, and Following Dredging............................................ 48

3.6 Survey and Dredge Position Data to Calculate Residuals....................................................... 50

3.6.1 Determination of the Maximum Dredge Cut Depth .................................................... 55

3.6.2 Determination of the Post-Dredge Sediment Surface .................................................. 58

3.6.3 Estimation of the Post-Dredge Residuals ..................................................................... 58

4.0 DISCUSSION AND CONCLUSIONS ............................................................................................... 66

5.0 REFERENCES .................................................................................................................................... 69
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FIGURES

Figure 1-1. Conceptual Model of Sediment Residuals During a Typical Dredging Operation................ 2

Figure 1-2. Overview Map of the Ashtabula River and Project Study Site.............................................. 4

Figure 1-3. Ashtabula River Dredging Site and ORD Study Area ........................................................... 4

Figure 1-4. Michael B. Dredge at Ashtabula River .................................................................................. 5

Figure 1-5. Cutter-Head on the Michael B. Dredge at Ashtabula River................................................... 6

Figure 1-6. HDPE Sediment Slurry Conveyance Piping .......................................................................... 6

Figure 1-7. Fields Brook Corridor............................................................................................................ 7

Figure 1-8. Ashtabula River Dredge Site Dredge Management Unit (DMU) Locations ......................... 8

Figure 2-1. Transect Locations in the Ashtabula River .......................................................................... 11

Figure 2-2. Sediment Core Sample Locations in the Ashtabula River Study Area for Phase 1 

and 3 (Pre- and Post-Dredging, respectively) ...................................................................... 12

Figure 2-3. Multi-Beam Sonar System Setup for the Ashtabula River Study ........................................ 14

Figure 2-4. Side Scan Sonar System Setup for the Ashtabula River Study............................................ 14

Figure 3-1. Typical Pre-Dredge Sediment Core ..................................................................................... 17

Figure 3-2. Comparison of Pre- and Post-Dredge Particle Size Distributions in Sediment at 

T172 ..................................................................................................................................... 19

Figure 3-3. Comparison of Pre- and Post-Dredge TOC Concentrations in Sediment at T172............... 20

Figure 3-4. Comparison of Pre- and Post-Dredge Dry Bulk Densities in Sediment at T172 ................. 21

Figure 3-5. Pre-Dredge Sediment t-PCB Concentration Profiles in the Study Area (> 0 ppb) .............. 24

Figure 3-6. Pre-Dredge Sediment t-PCB Concentration Profiles in the Study Area (> 100 ppb) .......... 25

Figure 3-7. Pre-Dredge Sediment t-PCB Concentration Profiles in the Study Area(> 1,000 ppb) ........ 26

Figure 3-8. Pre-Dredge Sediment Concentration Profiles in the Study Area (> 10,000 ppb) ................ 27

Figure 3-9. Pre-Dredge Sediment t-PCB Concentration Profiles in the Study Area 

(> 100,000 ppb).................................................................................................................... 28

Figure 3-10. Composition Analysis Showing the Similarity in the PCB Composition of Surface 

Sediment Sample T174A (A) and a 3:1 Mixture of Aroclor 1248:1260 (B) ....................... 30

Figure 3-11. Composition Analysis Showing the Similarity in the PCB Composition of 

Sediment Sample T174A from a Depth of 6.4–7.4 ft (A) and Aroclor 1248 (B) ................ 31

Figure 3-12. Composition Analysis Showing the PCB Composition of Sediment Sample T174A 

from a Depth of 11.4–12.4 ft (A; Homolog Composition) and T178C from a Depth 

of 16-16.5 ft (B; Congener Composition)............................................................................ 32

Figure 3-13. Average t-PCB Concentrations in Pre-Dredge Surface, High-Level, and Lower 

Sediments and Post-Dredge Surface Sediments................................................................... 33

Figure 3-14. The Total PCB Concentration in Pre-Dredge Lower Sediments and Post-Dredge 

Surface Sediments at the Sediment Coring Locations Presented in Table 3-2 .................... 33

Figure 3-15. The Total PCB Concentration in Pre-Dredge Lower Sediments and Post-Dredge 

Surface Sediments at the Sediment Coring Locations Presented in Table 3-2 .................... 34

Figure 3-16. Total PCB Concentrations in Pre- and Post-Dredge Core Samples from Locations 

T170B and T172B................................................................................................................ 35

Figure 3-17. Pre-Dredge and Post-Dredge Comparison of PCB Homolog Composition in 

Sediment Within the Study Area (T181 through T170)....................................................... 37

Figure 3-18. PCB Congener Composition in a Representative Mid-Depth Sample (A) and in a 

Pre-Dredge Lower Depth Sample (B).................................................................................. 38

Figure 3-19. Principal Component Analysis (PCA) Using PCB Homolog Data for Pre- and PostDredge Sediments in the Study Area; Full View (upper) and Zoomed View (lower)........ 41

Figure 3-20. Principal Component Analysis (PCA) Using PCB Congener Data for Pre- and PostDredge Sediments in the Study Area; Full View (upper) and Zoomed View (lower)........ 42

Figure 3-21. Comparison of Pre- and Post-Dredge Cross-Section t-PCBs in Sediment at T175 ............. 44

Figure 3-22. Comparison of Pre- and Post-Dredge Cross-Section t-PCBs in Sediment at T174 ............. 45
viii

Figure 3-23. Comparison of Pre- and Post-Dredge Cross-Section t-PCBs in Sediment at T173 ............. 46

Figure 3-24. Comparison of Pre- and Post-Dredge Cross-Section t-PCBs in Sediment at T172 ............. 47

Figure 3-25. Pre-Dredge Bathymetric Survey Results for the Study Area ............................................... 48

Figure 3-26. Post-Dredge Bathymetric Survey Results of the Study Area............................................... 49

Figure 3-27. Cross-Section View at T175 Showing the Change in Bathymetry During Dredging.......... 51

Figure 3-28. Cross-Section View at T174 Showing the Change in Bathymetry During Dredging.......... 52

Figure 3-29. Cross-Section View at T173 Showing the Change in Bathymetry During Dredging.......... 53

Figure 3-30. Cross-Section View at T172 Showing the Change in Bathymetry During Dredging.......... 54

Figure 3-31. Conceptual Model River Cross-Section Showing the XYZ Dredge Cutter-Head 

Position and Approximated Cut Line................................................................................... 56

Figure 3-32. Plan View of Dredge Activity in the Study Area................................................................. 57

Figure 3-33. Estimated Dredge Cut Line in Between T176 and 172 in the Study Area........................... 59

Figure 3-34. Cross-Section of T175 Showing Estimated Dredge Cut Line vs. Post-Dredge 

Bathymetry........................................................................................................................... 62

Figure 3-35. Cross-Section of T174 Showing Estimated Dredge Cut Line vs. Post-Dredge 

Bathymetry........................................................................................................................... 63

Figure 3-36. Cross-Section of T173 Showing Estimated Dredge Cut Line vs. Post-Dredge 

Bathymetry........................................................................................................................... 64

Figure 3-37. Cross-Section of T172 Showing Estimated Dredge Cut Line vs. Post-Dredge 

Bathymetry........................................................................................................................... 65

TABLES 

Table 3-1. Vertical Disagreement of Specific Pre-Dredge Cores............................................................. 16

Table 3-2. Total PCB Concentration (ppb) of Pre-Dredge Surface Sediment, Typical Pre-Dredge 

High-Level Sediment, Pre-Dredge Sediment at Post-Dredge Surface Sediment Depth, 

and Post-Dredge Surface Sediment......................................................................................... 23

Table 3-3. Estimates of Sediment and t-PCB Removals and Residuals................................................... 60
ix

ACRONYMS AND ABBREVIATIONS

2-D 2-Dimensional (view)

3-D 3-Dimensional (view)

AOC Area of Concern

AOCs Areas of Concern

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

COC chemical of concern

DMS dynamic motion sensor

DMU dredge management unit

GcGPS Satellite Subscription Globally-Corrected GPS 

GLLA Great Lakes Legacy Act

GLNPO Great Lakes National Program Office

GPS global positioning system

HDPE high density polypropylene

IGLD International Great Lakes Datum, 1985

JFB J.F. Brennan Company, Inc.

LOE line of evidence

LOEs lines of evidence

MBS multi-beam sonar

MRU motion reference unit

NA not applicable

NERL National Exposure Research Laboratory

NPDES National Pollutant Discharge Elimination System

NRMRL National Risk Management Research Laboratory

ORD Office of Research and Development

PAH polycyclic aromatic hydrocarbon

PAHs polycyclic aromatic hydrocarbons

PCA Principal Component Analysis

PCB polychlorinated biphenyl

PCBs polychlorinated biphenyls

PE polypropylene

QA quality assurance

QAPP quality assurance project plan

QC quality control

RSD relative standard deviation
x 

RTK-GPS Real-Time Kinematic Global Positioning System

SDR Standard Dimension Ratio

SPMDs Semipermeable Membrane Devices

SPME Solid Phase Micro-Extraction

SSS side scan sonar

TOC total organic carbon

t-PCBs total polychlorinated biphenyls

TSS total suspended solids

UCF Upland Containment Facility

USACE U.S. Army Corp of Engineers

U.S. EPA U.S. Environmental Protection Agency

VOCs volatile organic compounds

WOE weight of evidence

XYZ horizontal and vertical position data
xi

ACKNOWLEDGEMENTS 

The support and participation of many researchers, administrators, and support staff were necessary to 

carry out a multi-year project of this scope and magnitude. Funding provided by the National Risk 

Management Research Laboratory (NRMRL) of the U.S. Environmental Protection Agency (U.S. EPA) 

and the U.S. EPA Great Lakes National Program Office (GLNPO) to enable this project to be conducted 

is gratefully acknowledged. Collaborative efforts and mutual support between NRMRL, GLNPO, and 

U.S. EPA’s National Exposure Research Laboratory (NERL) provided a forum for exchanging ideas and 

concepts and were vital to the success of this project. The partnership and cooperation engendered on this 

study has already begun to pay dividends on other projects. The excellent service and attention to detail 

of the project’s contractor, Battelle, simplified and optimized the implementation of complex sampling 

and analytical programs that generated the project’s large and comprehensive dataset. The cooperation of 

the project’s dredging contractor, J.F. Brennan, in providing dredge data and welcome advice was 

essential in relating research field measurements to sediment inventories and dredging operations. 

The authors of this report, Eric Foote, Greg Durell, Shane Williams, and John Hardin from Battelle; Marc 

Mills and Richard Brenner from U.S. EPA/NRMRL; and Craig Jones and Jason Magalen from Sea 

Engineering, Inc. (a subcontractor to Battelle) wish to express their appreciation to the following 

individuals for their substantial and valuable contributions to this research undertaking:

Battelle U.S. EPA/NRMRL

Greg Headington

U.S. EPA/GLNPO

Pat Clark Scott Cieniawski

Jim Hicks Terry Lyons Marc Tuchman

Bob Mandeville Paul McCauley

Shane Walton Joe Schubauer-Berigan

Dennis Timberlake

U.S. EPA/NERL J.F. Brennan

Ken Fritz

The McConnell Group

Mark Binsfeld Brandon Armstrong

Brent Johnson Paul Olander Jason Berninger

Jim Lazorchak Mark Berninger

John Meier Herman Haring

Paul Wernsing Paul Weaver

U.S. Geological Survey

Paul Baumann (retired)
xii

EXECUTIVE SUMMARY

An interdisciplinary and collaborative research project to develop evaluation tools and methods for 

environmental dredging was initiated in 2006 between the National Risk Management Research 

Laboratory (NRMRL) and the National Exposure Research Laboratory (NERL) of the U.S Environmental 

Protection Agency’s (U.S. EPA’s) Office of Research and Development (ORD), hereafter collectively 

referred to as ORD, and U.S. EPA’s Great Lakes National Program Office (GLNPO). GLNPO, through 

the Great Lakes Legacy Act (GLLA), is charged with undertaking and overseeing the remediation of 

contaminated sediments in the Great Lakes Areas of Concern (AOCs). ORD, through its research 

mission is directed to evaluate the application and efficacy of contaminated sediment remediation 

technologies, such as environmental dredging. Based on these mutual interests, the two U.S. EPA 

organizations formed a partnership to comprehensively monitor and assess progress on the Ashtabula 

River Environmental Dredging Project in Ashtabula, OH. Dredging was selected by GLNPO as the 

remedy of choice for the Ashtabula River to remove sediment contaminated with polychlorinated 

biphenyls (PCBs), the chemical of concern (COC) for this site.

Under this partnership, a series of environmental measurements were conducted on the Ashtabula River 

beginning in the fall of 2006 to support the development of measures of remedy effectiveness. These 

measurements were made to evaluate the efficacy of environmental dredging in removing a large quantity 

of sediment contaminated with PCBs. Samples of sediment and overlying water were collected and 

analyzed before, during, and after dredging. In addition, measurements were made to characterize the 

river’s ecosystem also before, during, and after dredging to determine the impact that dredging had on the 

ecosystem. Bathymetry measurements before and after dredging using multi-beam and side-scan sonar 

were also carried out. 

Environmental dredging activities were performed on a 1.2-mile long reach of the Ashtabula River from 

River Station 194-00 to River Station 139-00 near its confluence with Lake Erie beginning in the fall of 

2006 and ending in the fall of 2007. Extensive pre-dredging characterization efforts were undertaken in 

the summer of 2006. Numerous sediment resuspension, sediment mapping (bathymetry), and ecological 

measurements were made during the dredging process in 2007. Immediate post-dredging characterization 

of sediment residuals was conducted in the fall and early winter of 2007. Additional long-term 

monitoring studies were implemented from 2008 to 2010. These studies evaluated remediation response 

within indigenous food web species and measures to determine the effect of sediment depositional 

processes on the original residual sediment layer. Long-term monitoring is needed to understand the rate 

and extent to which ongoing natural processes impact surface sediment and whether newly deposited 

sediment is intermixing with the original residual sediment layer. Another ORD evaluation is being 

planned for 2011 to continue the long-term investigation of sediment deposition following dredging and 

the documentation of post-dredging ecosystem recovery. This investigation will be coordinated with 

GLNPO as it plans a final post-dredging characterization of surface sediment in 2011 to measure remedy 

effectiveness. 

This report evaluates and summarizes dredge residuals and dredge removal efficiency in support of 

GLNPO’s objectives for this joint project. This evaluation is restricted to pre-dredging characterization 

studies conducted in 2006 and post-dredging residuals information generated after completion of dredging 

operations in 2007. Long-term residuals data produced from follow-on post-dredging field studies in 

2009 are still being analyzed and are not included in this report. Investigative results of immediate and 

long-term effects of dredging operations on ecosystem health and restoration using biological indicator, 

food web, and surrogate sample data will be presented in a subsequent report.
xiii

The primary goals of this phase of the project were to develop: 1) an understanding of sediment residual 

formation during dredging operations on the Ashtabula River, and 2) methods to assist in generating more 

realistic predictions of post-dredging residual mass/volume and contaminant concentrations. To achieve 

these goals, extensive monitoring studies and physical and chemical measurements were carried out prior 

to, during, and after dredging. Field efforts focused on: 

1) estimating the volume and concentration of contaminated sediment residuals remaining after 

completion of dredging in a selected study area within the dredge zone, and 

2) comparing pre- and post-dredging sediment mass and concentration characterization data to 

assess the PCB concentration relationship of the residual sediment to the contaminated 

material removed. 

A weight of evidence (WOE) approach was developed by ORD to characterize dredging residuals. The 

WOE approach relied on multiple lines of evidence (LOEs) to measure residuals generated during 

dredging. Six LOEs consisting of chemical and physical measures were used to evaluate dredge residuals 

in an attempt to address study objectives. These LOEs included: 

1) vertical alignment and physical examination of pre- and post-dredge sediment cores, 

2) physical parameter analysis of the sediment, 

3) sediment PCB chemistry and data analysis of core segments, 

4) two- and three-dimensional PCB modeling of pre- and post-dredge areas, 

5) bathymetric surveys prior to, during, and following dredging , and 

6) dredge cutter head horizontal and vertical positioning. 

The above tools, methods, and interpretations drawn were not applied on a site-wide basis, but rather to 

ORD’s selected study area of a 1,100-ft long stretch of the river from River Station 181-00 to River 

Station 170-00. These approaches are being evaluated on spatial and temporal scales as necessary for 

their development, and, therefore, cannot be used to evaluate the success of dredging for the entire site. 

The residuals data produced in the project study area indicated consistent sediment and PCB mass 

removals equal to or in excess of 95%. The data also revealed that the sediment residuals layer was 

composed of more highly contaminated sediments originating from higher elevations in the vertical 

sediment profile, rather than the lower-concentrated sediments removed from immediately above the final 

post-dredge sediment surface.

This final report is presented as Volume I of the Ashtabula River dredge residuals project. Due to the 

large amount of data generated on this project, an additional data report (Volume II) will be issued by

ORD as an extended set of Appendices with additional data tables and figures. A subset of these data is 

included in this report to illustrate the approaches, methods, and interpretations applied on this project.
1 

1.0 PROJECT DESCRIPTION AND OBJECTIVES

1.1 Purpose

A joint dredging evaluation project was initiated in 2006 between the National Risk Management 

Research Laboratory (NRMRL) and the National Exposure Research Laboratory (NERL) of the U.S 

Environmental Protection Agency’s (U.S. EPA’s) Office of Research and Development (ORD), hereafter 

collectively referred to as ORD, and U.S. EPA’s Great Lakes National Program Office (GLNPO). 

GLNPO via its Great Lakes Legacy Act (GLLA) mandate is charged with undertaking and overseeing the 

cleanup/remediation of contaminated sediments in the Great Lakes Areas of Concern (AOCs). ORD, 

through its research mission, is directed to evaluate the application and efficacy of environmental 

dredging. Based on these mutual interests, the two U.S. EPA organizations entered into an agreement to 

form a partnership to carry out a comprehensive effort to monitor progress on the Ashtabula River 

Environmental Dredging Project in Ashtabula, OH. Dredging was selected by GLNPO as the remedy of

choice for the Ashtabula River to remove sediments contaminated with polychlorinated biphenyls (PCBs) 

and other chemicals. PCBs constitute the chemicals of concern (COCs) for this project.

Environmental dredging activities were carried out on a 1-mile long reach of the Ashtabula River 

beginning in the fall of 2006 and ending in the fall of 2007. Dredging was not performed during the 

2006/2007 winter. Extensive pre-dredging characterization efforts were undertaken in the summer of 

2006 (Phase 1). Numerous sediment resuspension, sediment mapping (bathymetry), and ecological 

measurements were made during the dredging process in 2007 (Phase 2). Post-dredging characterization 

of sediment residuals was conducted in the fall and early winter of 2007 (Phase 3). Particular emphasis 

was given in Phase 3 to measuring the quantity and composition of sediment residuals and the fraction of 

contaminated sediment removed by the dredging operation, i.e., estimating dredge removal efficiency. 

Follow-up out-year studies were implemented in 2008 and 2010 to evaluate the degree of recovery 

achieved in indigenous food web species 1 year and 3 years, respectively, after dredging and in 2009 to 

determine the rate and extent that new clean sediment was being deposited on top of the original residual 

sediment layer 2 years after dredging and whether that newly deposited sediment was intermixing with 

the original residual sediment layer. To assist in defining river bottom (i.e., sediment surface) topography 

before and after dredging, multi-beam and side-scan bathymetry measurements were also conducted. 

Additional out-year evaluations are being planned. GLNPO will implement a final post-dredging

characterization of sediment residuals at an unspecified future date to determine whether the site can be 

closed in compliance with GLLA regulations. 

In addition to the extensive physical and chemical characterization of sediment and water column quality 

performed throughout the project, a comprehensive suite of companion biological studies was also carried 

out. These studies were conducted for the purpose of evaluating ecosystem recovery brought about by the 

removal of contaminated sediments in the affected portion of the Ashtabula River over the course of the 

dredging operation and for an extended period following removal. Chemical and toxicity measurements 

were made on tissue of indigenous fish, clams, worms, and macrobenthos organisms. Measurements of 

PCB uptake by surrogate samplers known as semipermeable membrane devices (SPMDs) and solid phase 

micro-extraction (SPME) systems in contact with surface sediment and the water column were also 

performed. 

This report constitutes a summary of the results on sediment removal efficiency and the quantity and 

composition of the dredge residuals. Results of the biological (i.e., ecological restoration) segment of this 

evaluation and the follow-on sediment residuals studies will be addressed in a subsequent report. 
2 

1.2 Dredge Residuals

The remediation of contaminated sediments often involves the dredging of bed-sediment. Dredging, 

whether used alone or in conjunction with other remediation technologies such as in-situ capping or 

natural recovery, can result in the generation and release of COCs in the form of aqueous or particleassociated contamination. The release of contaminants in particle-bound form is one of the possible 

mechanisms for recontamination or deposition following dredge removal actions. These residual 

sediments (hereafter referred to as ‘residuals’) can spread from both within dredged areas (near field) and 

downstream or off site (far field). A number of factors and suspected mechanisms can influence residual 

levels including: dredging equipment; operator technique; debris; dredging to bedrock; over-dredging; 

cut lines, slopes, and depths; sediment characteristics; contaminant characteristics and distribution; and 

the accuracy and resolution of contaminant characterization (USACE, 2008a). Figure 1-1 is a conceptual 

model illustrating mechanisms by which residuals can occur at a dredge site.

Figure 1-1. Conceptual Model of Sediment Residuals During a Typical Dredging Operation

Residuals can be categorized as either undredged or dredge generated. Undredged residuals are the result 

of missed areas and incomplete characterization. Dredge-generated residuals are released via 

resuspension, transport, and downstream deposition; dredge mixing and immediate deposition; and 

sloughing or slumping (USACE, 2008b). 

The primary generated residual release sources applicable to all dredging operations are resuspension and 

dispersion of bedded sediment particles and pore water by dredging operations, including dredge heads, 

boat props, and anchors. Additionally, residuals are generated by erosion and resuspension of sediments 

and other high solids concentration layers on the bed surface, including fluff layers and fluid mud.
3 

1.3 Site Description

The Ashtabula River lies in extreme northeast Ohio, flowing into Lake Erie’s central basin at the City of 

Ashtabula (Figure 1-2). Its drainage basin covers an area of 137 sq mi, with 8.9 sq mi in western 

Pennsylvania. Major tributaries include Fields Brook, Hubbard Run, and Ashtabula Creek. The City of 

Ashtabula, with an estimated population of approximately 21,000 (Year 2000 census), is the only 

significant urban center in the watershed, with the rest of the drainage basin being predominantly rural 

and agricultural. Concentrated industrial development exists around Fields Brook (east of the Ashtabula 

River) and east of the Ashtabula River mouth. Sediments in portions of the Ashtabula River are 

contaminated with a variety of chemicals, including PCBs.

The PCBs were thought to have originated primarily from Fields Brook, a stream that drains into the 

Ashtabula River in the area of the upper Turning Basin. Fields Brook and its five tributary streams that 

drain the 5.6-sq mi watershed have been identified as the primary source of contamination to the 

Ashtabula River. The eastern portion of the watershed drains Ashtabula Township, and the western 

portion drains the eastern section of the City of Ashtabula. The 3.5-mile main channel of Fields Brook 

begins south of U.S. Highway 20, about 1 mile east of State Highway 11. From this point, the stream 

flows northwesterly, just under U.S. Highway 20 and Cook Road, to the north of Middle Road. The 

stream then flows westerly to its confluence with the Ashtabula River near the Railroad Bridge and 

Turning Basin. The industrial zone of Ashtabula is concentrated around the upstream reach of Fields 

Brook from Cook Road downstream to State Highway 11.

Up to 20 separate industrial manufacturing activities, ranging from metal fabrication to chemical 

production, have occurred in the area since the early 1940s. The decades of manufacturing activity and

waste management practices at industrial facilities resulted in the discharge or release of a variety of 

hazardous substances to Fields Brook and its watershed, including the floodplain and wetlands area. 

Sediments at the Fields Brook site were contaminated with PCBs, volatile organic compounds (VOCs), 

polycyclic aromatic hydrocarbons (PAHs), heavy metals, phthalates, and low level radionuclides. VOCs 

and heavy metals including mercury, lead, zinc, and cadmium have been detected in surface water from 

Fields Brook and the Detrex tributary. Contaminants detected in fish include VOCs and PCBs. The site 

posed a potential health risk to individuals who ingested or came into direct contact with contaminated 

water from Fields Brook and with contaminated fish or sediments. 

Fields Brook has been eliminated as a source of contamination (or recontamination) of the Ashtabula 

River. A Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) cleanup 

of Fields Brook was completed in 2003. Subsequently, a post-cleanup monitoring program was put in 

place to protect against recontamination of Fields Brook as well as the Ashtabula River.

Approximately 600,000 cu yd of contaminated sediments were initially targeted for removal between the 

Upper Turning Basin at the mouth of Fields Brook and the 5th Street Bridge (Figure 1-3). The COCs in 

this stretch of the river included PCBs; PAHs; hexachlorobenzene; hexachlorobutadiene; metals; and the 

radionuclides uranium, radium, and thorium. The radionuclides were above background levels but below 

regulatory criteria. In Phase 1 of this dredge residuals research project, GLNPO, under its GLLA 

mandate, conducted a baseline characterization of the river that included all of these COCs, while ORD 

focused only on the PCBs in selected areas of the river (as indicated by the yellow shading in Figure 1-3). 

In Phases 2 and 3, ORD continued to focus on only the PCB inventory in the study area and selected areas 

of the river where biological collections and surrogate deployments were made.
4 

Figure 1-2. Overview Map of the Ashtabula River and Project Study Site 

Figure 1-3. Ashtabula River Dredging Site and ORD Study Area
5 

1.4 Dredge Operations

Dredging in the Ashtabula River was performed by J.F. Brennan Company, Inc. (JFB), a private marine 

contractor headquartered in La Crosse, WI. Dredging operations were conducted in two stages. Stage I 

included hydraulic removal of sediment from the upper portion of the GLLA project area down to an area 

just above the Ashtabula Harbor (River Station 194-00 to 139-00), with U.S. EPA-GLNPO operating as 

the lead agency. Stage II included environmental and maintenance dredging, hydraulic removal of 

sediment from just south of the 5th Street Bridge and extended northward into the inner harbor (River 

Station 139-00 to 120-00), with the U.S. Army Corp of Engineers (USACE) operating as the lead agency.

This report is focused on research carried out in conjunction with the GLLA dredging conducted during 

Stage I, which began September 9, 2006 and was completed October 14, 2007. Stage I dredging 

operations resulted in the removal, transport, and dewatering of approximately 491,711 cu yd of 

contaminated sediment. Of particular interest are the dredging operations that were conducted between 

River Station 181-00 to 170-00, hereafter referred to as the project study area, where the target dredge cut 

line elevation was established to achieve a final water column of 20 ft. Based on the low water datum for 

International Great Lakes Datum (IGLD) 1985, Lake Erie IGLD85 of 569.2 ft, the final cut line target 

elevation was set at 549.2 ft.

Sediment removal was achieved within the project study area by using a 12-in. hydraulic swinging-ladder 

cutter-head dredge shown in Figures 1-4 and 1-5. The dredge was outfitted with a real-time kinematic 

global positioning system (RTK-GPS). The RTK-GPS signals were combined with various sensors 

onboard the dredge including sensors measuring rotation, ladder inclination, and pitch and roll.

Figure 1-4. Michael B. Dredge at Ashtabula River

The GPS system and associated sensors were processed in real time and combined through Hypack, Inc. 

Dredgepack® software to allow for dredge operator guidance to achieve maximum dredge accuracies.
Figure 1-5. Cutter-Head on the Michael B. Dredge at Ashtabula River

6 

The complete dredging system consisted of a hydraulic dredge with associated equipment, a bargemounted slurry booster pump, and interconnecting piping for transferring the dredged sediment to the 

land-based transport pipeline system. The barge-mounted slurry booster pump, with a 750-hp capacity, 

was placed between the dredge and the land-based transport system. The dredge discharge and booster 

pump interconnecting pipe was standard dimension ratio (SDR) 17 high density polypropylene (HDPE) 

with PE3408 resin, shown in Figure 1-6. 

Figure 1-6. HDPE Sediment Slurry Conveyance Piping

The land-based transport system was comprised of three in-line booster pumps and 12-in. double-walled 

slurry transport pipe extending over 2.5 miles along the Fields Brook Corridor (Figure 1-7) from its 

mouth to the Upland Containment Facility (UCF). A slurry of water and sediment, consisting of 8 to 15% 

solids, was treated at a rate of 5,000 gpm at the UCF. The UCF consisted of chemical conditioning of the 

dredge sediment slurry, geotextile containment, and weep water collection/treatment. Following weep 

water treatment to remove fine suspended solids and associated organic contaminants, water was returned 

to the river under the conditions of the National Pollutant Discharge Elimination System (NPDES) permit 

issued by Ohio EPA.
Figure 1-7. Fields Brook Corridor

7 

The Ashtabula River dredge site was organized into 27 discrete areas called dredge management units 

(DMUs). The DMU layout is shown in Figure 1-8 and was organized as follows:

The “Upper Turning Basin” – The Upper Turning Basin defined the upstream boundary of the dredge site 

and is where Fields Brook converges with the Ashtabula River. DMUs 1 through 14 comprised the 

dredge management plan in the Upper Turning Basin.

The “River Run” – The River Run made up an approximate 1,300ft stretch of the Ashtabula River and 

comprises parts of DMUs 13 and 14 at its southern boundary and continues northward encompassing 

DMUs 15 through 24, and parts of DMUs 25 and 26. The ORD residuals research study occurred in 

portions of DMUs 15 through 22.

The “River Bend” – The River Bend was defined by the area just south of the 5th Street Bridge where the 

Ashtabula River ‘bends’ to the east. Parts of DMUs 25 and 26 and all of DMUs 27 and 28 were within 

this area of the river.

1.5 Research Goals and Objectives

This research project was designed to provide an understanding of sediment residual formation during 

dredging operations at the Ashtabula River and to develop methods to obtain more realistic 

estimates/projections of post-dredging residuals mass/volume and contaminant concentrations based on 

pre-, during- and post-dredging information and data. More specifically, the research goals were as 

follows: 

1) Develop baseline chemical and biological data prior to dredging to provide a basis of 

comparison with post-dredging residuals data for determining contaminated sediment 

removal efficiency.
Figure 1-8. Ashtabula River Dredge Site Dredge Management Unit (DMU) Locations 

8
9 

2) Measure both pre- and post-dredging sediment topography and chemical concentrations (as a 

function of sediment depth) to determine whether a relationship exists between pre-dredging 

concentration profiles and dredge-generated residuals concentrations.

3) If a pre-dredging/post-dredging relationship exists, determine whether it can be used to 

predict residuals formation at other sites.

4) Determine whether generated residuals created by near-bed mixing and slumping can be 

differentiated from residuals created by sediment resuspension and deposition.

5) Perform biological studies to evaluate the immediate impacts of contaminant removal on 

ecosystem measures of health and analyze long-term ecosystem changes in response to 

dredging.

The research objectives that were developed to accomplish these goals were as follows: 

1) Generate physical, chemical, and biological data, as needed, on the contaminated sediments 

and surrounding ecosystem and water column of the Ashtabula River to evaluate and model 

resuspension of solids and release of PCBs during dredging operations in the designated 

study area. 

2) Estimate the volume and concentration of contaminated sediment residuals remaining in the 

study area of the Ashtabula River following dredging. Characterize the solids and determine 

PCB concentrations in the sediment residual inventory.

3) Compare pre- and post-dredging sediment mass (determined from depth, moisture content, 

and bulk density measurements) and concentration characterization data (both solids and PCB 

concentrations) to assess: a) dredging removal efficiency (both solids and PCBs) in the 

residuals study area, and b) the PCB concentration relationship of the residual sediment to the 

contaminated material removed.

4) Generate reliable biological data on the Ashtabula River ecosystem following dredging.

5) Compare pre-, during-, and post-dredging biological data to define, if possible, ecosystem 

response to the impacts of environmental dredging on the Ashtabula River.

The project was implemented in three discrete phases of work, hereafter referred to as Phase 1, Phase 2 

and Phase 3, and defined as follows:

• Phase 1 – Measurements conducted prior to dredging

• Phase 2 – Measurements conducted during dredging

• Phase 3 – Measurements conducted post-dredging.

This report evaluates and summarizes dredge residuals and dredge removal efficiency as specified in 

Goals 1 through 4 and Objectives 2 and 3. This evaluation is restricted to pre-dredging characterization 

studies conducted in 2006 (Phase 1) and post-dredging residuals information generated after completion 

of dredging operations in 2007 (Phase 3). Long-term monitoring data on the behavior and fate of dredge 

residuals from post-dredging field studies conducted in 2009 are still being analyzed and are not included 

in this report. Also, data specific to sediment resuspension and soluble releases during dredging (Phase 2) 

as described in Objective 1 are not covered in this report. Investigative results of immediate and longterm effects of dredging operations on ecosystem health and restoration using food web and surrogate 

sample data (Goal 5 and Objectives 4 and 5) will be presented in a subsequent report.
10

2.0 EXPERIMENTAL APPROACH

2.1 General Approach

Field sampling activities carried out before, during, and after dredging consisted of a multi-faceted

approach to physical, chemical and biological characterization of the sediment inventory. During 

dredging, sediment resupsension, sediment mapping, and contaminant release were measured using a 

number of in-situ and ex-situ analyses. After dredging was completed, physical, chemical and biological 

characterization of the sediment residuals was implemented using similar techniques with an emphasis on 

measuring the quantity of sediment residuals and the fraction removed by the dredging operation. The 

following sections of this report focus on the physical and chemical measures of the sediment residuals 

portion of the investigation.

2.2 Study Design

The primary sediment investigation occurred in the “River Run” and specifically within the area bounded 

by transects (T) 181 and 170 (Figure 2-1). This study area was chosen as a location of specific interest 

for the following reasons:

• River hydrodynamics were anticipated to be easier to characterize compared to the ‘Upper 

Turning Basin’ (located approximately between T186 and T192) and the ‘River Bend’ 

sections of the river (the remaining two dredge areas selected for the Ashtabula River). 

• A preliminary assessment of the historic data indicated that the ‘River Run’ had among the 

highest concentrations of total PCBs (t-PCBs) in the river due to its proximity to the historical 

Fields Brook source located at the beginning of the ‘River Run’ around T186. These elevated 

contaminant levels were anticipated to be an asset in characterizing pre- and post-dredging 

PCBs. 

• The ‘River Run’ appeared to exhibit a t-PCB concentration gradient with the highest 

concentrations upstream near Fields Brook and the lowest concentrations downstream near 

the ‘River Bend’ area. This gradient was in turn thought to be useful when assessing postdredge residuals in Phase 3.

• A section of the ‘River Run’ was designed to be dredged to bedrock below the sediment layer

(upstream of T178), while lower-numbered transects with similar t-PCB concentrations were

not planned to be dredged completely to bedrock, thus allowing the evaluation of dredging

performance and residuals in areas of “soft sediment” vs. areas dredged to bedrock.

The sampling grid was constructed using 50- × 100-ft spacing. A semi-variogram analysis was conducted 

to determine the requisite grid size using existing data acquired by the USACE in 1990 and 1995. The 

variogram analysis provided a quantitative descriptive statistic that could be used graphically to 

characterize the spatial continuity of the dataset. Using this approach, it was determined that samples 

collected at a grid spacing of less than 50 ×100 ft would result in redundant observations and samples 

collected on a grid spacing larger than 50 × 100 ft would be spatially independent, which could lead to 

excessive smoothing or loss of information at some point. 

As shown in Figure 2-2, the sample design resulted in a combination of two to four sampling locations 

per transect depending on the width of the river (blue squares). The sampling grid was designed to take 

into account sediment sloughing that might occur on the perimeter of the dredge area, and, therefore, all 

sediment cores were restricted to a 50-ft distance from the river bank (or bulkhead that occurs along some 

eastern lengths of the study area).
Figure 2-1. Transect Locations in the Ashtabula River 

11
12

Figure 2-2. Sediment Core Sample Locations in the Ashtabula River Study Area for Phase 1 and 3 

(Pre- and Post-Dredging, respectively) 

2.3 Data Collection Strategy

The following sections describe the collection of data to support the evaluation of sediment residuals. 

Additional details for this sampling strategy can also be found in the EPA-approved Quality Assurance 

Project Plans (QAPPs) for Phase 1 and Phases 2 and 3 (Battelle, 2006; 2007).

2.3.1 Sediment Core Collection. 

A total of 30 sediment cores were collected from the study area prior to and following dredging activities. 

Sediment cores collected prior to dredging, where sediment thickness was at its maximum extent, were 

collected using a vibracoring method. All pre-dredge sediment cores were sampled until encountering

refusal. Consistent with the original plan, it was presumed that T181 to T177 would be dredged to a 

depth confined by the bedrock layer, while dredging would continue only to 20 ft below the IGLD85 at

T177 to T170, leaving a layer of soft sediment above bedrock. As such, collection of sediment cores to 

refusal ensured that the pre-dredge sediment cores would be as deep as or deeper than the target cut line. 

In this way, a total of 16 sediment cores were collected in the area that was planned for dredging to 

bedrock and 14 sediment cores were collected in the soft sediment area. When coupled with chemical 

analysis, this allowed for a full PCB vertical profile of the sediment above and below the target cut line. 

Each sediment core was sectioned into intervals of 1 ft or less and submitted to the laboratory for 

processing and analysis. Sediment cores lengths were “reconstructed” on the laboratory bench top and 

photographs of each core were taken and recorded. The length of each sediment segment was determined 

upon physical observation of the core with greater delineation focused in the range of the target cut line. 

Each core segment was processed further by mixing in a laboratory blender for approximately 5 minutes 
13

before analysis. Core segments were analyzed for 117 PCB congeners, total organic carbon, particle size 

distribution, and bulk density.

Since post-dredge sediments were substantially reduced in thickness, cores were collected using a 

hydraulically-driven piston core device. Samples were collected to a maximum depth of approximately 5 

ft in some areas, with the intention to capture the post-dredge surface sediment and native (un-dredged) 

sediment below. Post-dredge sediment cores were processed in the same manner previously described. 

The sediment segment thickness decreased in the range of the target cut line and the frequency of 

segments in this range increased. The post-dredge bathymetric survey (described below), as well as 

visual observations of note and consideration of the target cut line elevation, played a major role in the 

decision process as to where the post-dredge sediment cores would be sectioned. Post-dredge core 

sections were processed and analyzed for the same parameters as the pre-dredge core sections.

2.3.2 Sonar Monitoring. 

Multi-beam sonar/side scan sonar (MBS/SSS) was deployed by boat to survey the sediment surface of the 

river prior to and following dredging operations. To the extent possible, the receding sediment surface 

was mapped while dredging was being conducted. 

The surveying equipment was mounted on a 7.3-m pontoon vessel. A wooden beam manufactured from 

three 5 cm × 30 cm boards was laid (port to starboard) across the deck of the vessel and cantilevered over 

each side. Construction straps were extended under the pontoons and around the ends of the beam, 

fastening the beam securely to the deck. The MBS was mounted off the vessel port side through a pole 

mount affixed to the cantilevered end of the beam. Guyed wires were attached near the bow and stern of 

the vessel and to the MBS head. The SSS was mounted similarly off the vessel starboard side. Figures 2-

3 and 2-4, respectively, show the MBS and SSS mounted on the vessel as deployed for use on these 

surveys.

The MBS system utilized was an Odom Echoscan II, a 90o, 3o-beam system. As such, it was equipped 

with 30 transducers at 3o spacing so that the furthest beam away from vertical transmits was at a 45o angle 

when the instrument was level in the water. A 90o swath was covered between the furthest port and 

starboard beams. The MBS head also contained a single beam transducer, which allowed for additional 

depth quality assurance (QA) and quality control (QC), and it contained a motion reference unit (MRU). 

The MRU was a total suspended solids (TSS) dynamic motion sensor (DMS-25) that measured pitch, roll, 

and heave.

The SSS was a dual frequency C-MAX CM2 sonar, operating at 325 khz or 780 khz. The user selected 

the desired horizontal imaging range from 12.5 m and 25.0 m at 780 khz, or 25.0 m, 50.0 m, 100.0 m and 

150.0 m at 325 khz. 

For both systems, a C-NAV satellite subscription globally-corrected global positioning system (GPS) 

(GcGPS) was used for accurate horizontal positioning. The antenna was fastened securely on the MBS 

pole mount (blue antenna in Figure 2-3). A CSI Wireless Vector sensor was used to record vessel 

heading, an integral component for both MBS and SSS surveying. Two CSI wireless GPS antennas were 

mounted on top of the wooden console. The remaining topside survey equipment was mounted at the 

base of the wooden console that was the data acquisition hub for the electronic equipment. Two laptop 

computers were used to individually control and acquire data from the MBS and SSS. 

A Global Water WL16U data logger measured water level fluctuations during the bathymetric surveys to 

establish highly accurate (1 cm resolution) vertical survey control. The water level logger was installed 

inside a 3.0 m length of polyvinyl chloride (PVC) pipe and affixed securely to a stationary georeference 
Figure 2-3. Multi-Beam Sonar System Setup for the Ashtabula River Study

Multi-Beam Sonar Head

Cantilevered Beam and Pole Mount

Globally-Corrected 

(satellite subscription) 

GPS (GcGPS)

14

Figure 2-4. Side Scan Sonar System Setup for the Ashtabula River Study

Submerged Side-Scan 

Sonar and Mount

Data Acquisition 

Console

CSI Vector Heading 

Sensors

(under blue cover) 
15

position (a bulkhead along one side of the river). The elevation of the logger sensor was determined from 

a proximate USACE #611 located within the Ashtabula Yacht Club property. Water level elevation data 

were referenced to the IGLD85. Daily water level records were downloaded during the project.

A Digibar sound velocity profiler provided a relatively quick method for verifying the MBS soundings 

and for calibrating the MBS daily. The sound velocity profile was most important in regions prone to 

density variations in the water column (typically a result of changes in salinity and/or temperature). 

Significant variations in the sound velocity were not observed in the Ashtabula River. To double check 

the accuracy of the MBS soundings, a daily bar check verified that proper depths were being recorded. 

The bar check is a simple method of holding a flat object at several predetermined distances beneath the 

MBS transducers and comparing the observed depth to the actual depth. 

Hypack/Hysweep data acquisition software was used to collect and synchronize MBS measurements, SSS 

measurements, GPS positioning, and GPS vessel heading measurements. Water level fluctuation and 

sound velocity measurements were included with the data during post-processing to correct raw 

soundings.

Survey QC was assured with daily verification of proper system operation. Daily QC included 

verification of accurate (satellite corrected) GPS position and heading data. QC of the MBS system was 

verified with sound velocity casts in the water column and bar checks for the sonar depth offsets. The 

vertical survey control was verified by comparing the water level logger real-time output with manual 

elevation measurements at the location of the logger.

MBS and SSS surveys were conducted on a daily basis to measure the bathymetric variability and dredge 

cut slump progression and to create the imagery of the modified riverbed. Surveys typically consisted of 

a collection of individual data files corresponding to individual surveyed lines.
16

3.0 CONTAMINATED SEDIMENT CHARACTERIZATION AND DREDGE RESIDUALS

ASSESSMENT USING A WEIGHT OF EVIDENCE APPROACH 

A weight of evidence (WOE) approach employing multiple lines of evidence (LOEs) was used to 

characterize dredge residuals. These included: (1) vertical alignment and physical examination of the preand post-dredge sediment cores; (2) physical parameter analysis of the sediment, including total organic 

carbon (TOC), bulk density, and particle size distribution; (3) sediment PCB chemistry and data analysis 

of core segments (congener and homolog) including Principal Component Analysis (PCA) of the PCB in 

the sediment; (4) two (2)- and three (3)-dimensional PCB modeling of pre- and post-dredge areas; (5) 

bathymetric and sonar surveys prior to, during, and following dredging; and (6) survey and dredge 

position data to calculate residuals. These LOEs were used independently and collectively to characterize 

the quantity and composition (chemical and physical) of the dredge residuals.

3.1 Vertical Alignment and Physical Examination of the Pre- and 

Post-Dredge Sediment Cores

3.1.1 Vertical Alignment of the Pre- and Post-Dredge Sediment Cores. 

Sediment cores collected during the pre- and post-dredge sampling events from each sampling station 

were aligned vertically in virtual space using elevation data in an effort to pair pre- and post-core 

segments and determine their commonality to the dredge cut line. Several parameters were used 

independently and in combination to verify alignment for pre- and post-dredge core comparisons. These 

included water depth information, core lengths, refusal depth, and pre- and post-dredge bathymetric 

survey data. 

Of the 30 sample locations, pre- and post-dredge cores from seven specific locations were difficult to pair. 

Of these seven stations shown in Table 3-1, the pre-dredge core surface elevations as determined by water 

depth and refusal were in disagreement with the sediment surface elevation determined by pre-dredge 

bathymetry. These cores resulted in offsets of greater than 1 ft and as much as 5 ft in one case (T179B).

Table 3-1. Vertical Disagreement of Specific Pre-Dredge Cores 

Core Location Discrepancy (ft)

T171A 1.2

T172A 1.0

T176B 3.6

T177B 3.1

T179B 5.0

T180A 1.2

T180B 1.1

As such, several additional parameters were taken into consideration to determine the variability in core 

pairing, including the core position in the study area and the accuracy of the bathymetric data in that 

region of the study footprint. In the end, the sediment surface elevation data from the in-field water 

column and core length records were used to place the top of the core positions for these pre-dredge cores 

and to pair them vertically with the post-dredge cores. The pre-dredge bathymetric data were used to 

determine the pre-dredge core surface for the remaining 23 locations. The following factors contributed

to this decision:
17

1) These specific pre-dredge locations were observed to be in shallow water, less than 3 ft

(T171A, T172A, T176B, and T177B) or near a significant slope at the river channel edge

(T179B, T180A, and T180B). 

2) The performance of the MBS at shallow depths was less accurate because the swath width 

became limited in shallower waters, resulting in less bottom coverage and the need for greater 

data interpolation across data gaps in these areas.

3) The stacked variability in the horizontal positioning was determined to be approximately ± 3 

ft at each sample station when considering a combination of the instrument accuracy and any 

variance associated with actual sampling. This resulted in a vertical variability in the 

sediment surface of 0.6 ft to 2.9 ft based on pre-dredge bathymetry and depending on 

location.

3.1.2 Physical Examination of the Pre- and Post-Dredge Sediment Cores

Sediment cores collected during the pre- and post-dredge sampling events were segmented and processed 

for chemical and physical analysis. Each core was carefully logged and photographed. Subsequent 

comparison of physical sediment characteristics was completed on pre-dredge and post-dredge cores. 

Figure 3-1 shows a section of a pre-dredge core collected at T181. Often the pre-dredge cores exhibited 

distinct sediment depositional features such as multiple thin layers of varying sediment color (Figure 3-1). 

These features indicate frequent, episodic events of particle suspension and sedimentation, resulting in 

highly stratified cores.

Figure 3-1. Typical Pre-Dredge Sediment Core 

This stratification generally occurred above the dredge target cut line and did not occur in deeper 

sediments. Therefore, post-dredge sediment cores did not exhibit this stratification, and this feature could 

not be used to pair the pre- and post-dredge cores in vertical space. Cores collected from the post-dredge 

event appeared more homogenous and consisted of fine clays mixed with sand with very little observable 

color patterns in the vertical profile. The coloration of post-dredge cores was very similar to pre-dredge 

core pairs at similar elevations.
18

While color and stratification could not be used to identify dredge residual layers, two primary 

observations were made of post-dredge cores that aided in their vertical positioning relative to pre-dredge 

core segments. First, post-dredge cores appeared to be less consolidated; secondly, organic particles and 

debris such as wood was observed in the estimated target cut zone, lending evidence to mixing due to 

dredge activity.

The core segmenting plan was based on a combination of variables that included visual observations, 

physical characteristics, the target dredge cut line and project budget. Both pre- and post-dredge cores 

were intentionally segmented at smaller intervals around the target cut line. The top (surface) of the postdredge core was also segmented into smaller intervals, to better detect differences due to residuals. Each 

segment was analyzed for PCB congeners as previously discussed and the chemistry of the pre- and postdredge core segments was compared. Elevation measurements collected during coring and surveying 

activities were used to vertically align the pre- and post-dredge core segments.

3.2 Physical Parameter Analysis of Sediment Core Segments

In addition to sediment chemistry, physical parameter data were collected on each pre- and post-dredge 

core segment (as sediment volume allowed). These parameters included dry and wet bulk density, TOC, 

moisture content, and particle size (fractions – gravel, coarse sand, medium sand, fine sand, silt, and 

clay). 

Two approaches were implemented to compare the pre- and post-dredge datasets. To conduct 

comparisons between pre- and post-dredge cores collected from the same location and at the same depth, 

pre- and post-dredge core segments were lined up in vertical space such that they corresponded in 

elevation. This resulted in comparisons made for 14 sampling stations where core segments aligned well 

vertically. For comparison purposes, this analysis focused on a 6-in. vertical horizon from an elevation of 

548 ft to an elevation of 547.5 ft. The 14 sampling stations were: T170A, T170B, T171A, T171B, 

T172A, T172B, T173A, T173B, T174A, T174B, T176A, T178B, T179A, and T181D. Simple summary 

statistics were developed (min, max, mean and standard deviation) for each of the 10 parameters 

measured (pre- and post-dredge), and scatter diagrams were developed plotting the post-dredging sample 

value against the corresponding pre-dredging sample values for the same sampling station. These data 

comparisons produced the following observations:

• The average dry bulk density was approximately 20% lower for post-dredge sediment 

segments

• The gravel, coarse sand and medium sand contents of the samples were generally lower after 

dredging than before – on average about 25%, 75%, and 40% lower, respectively. 

• The fine sand and clay contents of the sediment segment samples were approximately 50% 

and 7% higher, respectively, for post-dredge sediment samples.

A second approach was employed to analyze and compare the physical consistency of the pre- and postdredge sediments using 3-D block diagram visuals (Earth Vision, Dynamic Graphics, Inc., USA). These 

comparisons are shown as cross-section views for T172 in Figures 3-2 through 3-4. 

As shown in Figure 3-2, a consistent and dominant band of sands was evident in the dredge cut line at this 

transect with an overlying predominant layer of silt in the pre-dredge sediment. Post-dredge data 

indicated the sediments were composed primarily of silt at the cut line, presumably from mixing and 

settling of the overlying sediments. This pattern was substantiated by the shift in TOC from the 

overlying zone of the pre-dredge to the post-dredge sediment surface as shown in Figure 3-3. Higher 

levels of TOC are typically more characteristic of silt and clay sediments than of sand. Lastly, Figure 3-4 
19

Figure 3-2. Comparison of Pre- and Post-Dredge Particle Size Distributions in Sediment at T172 
20

Figure 3-3. Comparison of Pre- and Post-Dredge TOC Concentrations in Sediment at T172 
21

Figure 3-4. Comparison of Pre- and Post-Dredge Dry Bulk Densities in Sediment at T172
22

shows a decrease of dry bulk density in the post-dredge sediment surface as compared to the pre-dredge 

sediments at the dredge cut line. This indicated mixing at and below the estimated dredge cut line, further 

supporting the maximum dredge cut elevations discussed in subsequent sections.

3.3 Sediment PCB Chemistry and Data Analysis of Core Segments 

PCB chemistry analysis was conducted using samples collected prior to and following dredging in the 

study area. PCB concentration and composition analyses were conducted on both pre- and post-dredge 

sediment cores using congener and homolog data and PCA.

3.3.1 Characterization of the Pre-Dredge Sediment PCB Inventory. 

Table 3-2 presents representative total PCB data for the surface, high-level (high concentration section), 

and lower sections of the pre-dredge sediment cores, and also for the surface of the post-dredge sediment. 

The pre-dredge surface sediment data are based on the single surface segment, which was the top 1-ft 

section of the core for most of the samples (the top 0.4 to 0.75 ft was used for a few of the cores). The 

pre-dredge high-level sediment data are based on a single representative sample from the most 

contaminated section of the core; it is the segment of the core that had the highest PCB concentration. 

Most of these pre-dredge high-level samples were observed for a sediment depth of 5 to 8 ft, but they 

covered a depth range of just less than 2 ft (T180A) to just over 10 ft (T181D). The pre-dredge lower 

sediment in Table 3-2 was a single sample from the depth (elevation) closest to that of the post-dredge 

surface sediment.

Figures 3-5 through 3-9 illustrate a 3-D model of the pre-dredge PCB concentration sediment profile in 

the study area. Each figure shows a distinct isoconcentration profile (shell) that varies both horizontally 

and vertically. The lower isoconcentration shells are removed consecutively in each succeeding figure. 

Each figure, therefore, depicts the next highest isoconcentration shell until only the highest shell 

representing a concentration of greater than 100,000 ppb remains in Figure 3-9. The pre-dredge surface 

sediment t-PCB concentrations ranged from 152 ppb (T175B) to 8,610 ppb (T176B); the average surface 

sediment t-PCB concentration was approximately 1,000 ppb (Table 3-2). The pre-dredge subsurface 

sediment t-PCB concentrations were highly variable, ranging from less than 100 ppb to almost 200,000 

ppb. The average t-PCB concentration in the most contaminated zone was approximately 100,000 ppb 

(Table 3-2), while the sediments at greater depth had highly variable PCB concentrations that were more 

comparable to the surface sediment PCB concentrations. The most contaminated sediments were 

generally noted at 5 to 10 ft depth, but highly contaminated sediments were found at less depth at some 

locations. The t-PCB concentration at the most contaminated depth was generally between 50,000 ppb 

and 150,000 ppb, but was less than this at some locations (T178A, T179A, T180A, T181A, and T180B) 

and more at some locations (T173A, 177B, and T178C). The surface and subsurface PCB concentrations 

were variable within the study area, but no obvious pattern of increasing or decreasing concentrations 

geographically was evident. The largest volume of highly-PCB-contaminated sediment (i.e., the greatest 

depth of the highly contaminated zone) was in the eastern side of the river between transects T176 and 

T181.
23

Table 3-2. Total PCB Concentration (ppb) of Pre-Dredge Surface Sediment, Typical Pre-Dredge 

High-Level Sediment, Pre-Dredge Sediment at Post-Dredge Surface Sediment Depth, and PostDredge Surface Sediment

Sediment Core

Pre-Dredge

Sediment Post-Dredge Sediment

Surface(a) High-Level(b)

Lower(c)

(at post-dredge

surface depth)

Surface(d)

T170A 581 101,000 319 6,960

T170B 733 141,000 1,020 7,150

T171A 641 63,900 133 12,900

T171B 223 55,700 1,120 46,200

T172A 651 85,700 96.1 50,500

T172B 208 120,000 454 4,460

T173A 848 197,000 226 27,000

T173B 367 115,000 370 4,300

T174A 1,140 103,000 317 10,200

T174B 234 92,100 902 11,600 (0.92’)

T175A 174 84,300 52.7 9,250

T175B 152 100,000 22,700 6,960 (0.85’)

T176A 494 77,200 5,760 5,830

T176B 8,610 147,000 20,400 19,700

T177A 430 70,200 677 4,820

T177B 740 117,000 1,970 4,550

T178A 3,320 2,760 7.6 3,580

T178B 425 129,000 6,700 7,460

T178C 889 191,000 1,400 6,740

T179A 201 19.3 8.0 3,940

T179B 1,820 107,000 300 11,700 (0.6’)

T179C 1,250 127,000 1,010 8,260 (0.95’)

T180A 160 228 16.5 825

T180B 284 7,090 59.7 11,700

T180C 539 87,000 1,470 12,500

T180D 3,120 118,000 50.8 7,280

T181A 585 159 159 539

T181B 3,130 65,300 107 1,050 (0.8’)

T181C 820 144,000 3,660 6,320 (0.85’)

T181D 743 126,000 3,340 5,970 (0.9’)

Average 1,120 92,500 2,490 10,700

Std. Dev. 1,660 52,500 5,440 11,600

RSD (%) 149 57 218 108

(a) The pre-dredge surface sediment is the single sample representing the top 1 ft of the sediment core.

(b) The pre-dredge high-level sediment is the single sub-surface sediment sample with the highest PCB 

concentration representing the most contaminated sediment depth. 

(c) The pre-dredge lower sediment is a single sample from the approximate depth equivalent to the post-dredge 

surface sediment. 

(d) The post-dredge surface sediment data are a sample (core segment length)-weighted average concentration of 

the samples that represent the top 1 ft of the sediment core. Between two and seven segments were used, 

depending on the core. If the post-dredge core was less than 1 ft in length, the data represent a weighted 

average of all samples in the core, and the core length is indicated in parenthesis.
24

Figure 3-5. Pre-Dredge Sediment t-PCB Concentration Profiles in the Study Area (> 0 ppb) 
25

Figure 3-6. Pre-Dredge Sediment t-PCB Concentration Profiles in the Study Area (> 100 ppb)
26

Figure 3-7. Pre-Dredge Sediment t-PCB Concentration Profiles in the Study Area (> 1,000 ppb)
27

Figure 3-8. Pre-Dredge Sediment Concentration Profiles in the Study Area (> 10,000 ppb)
28

Figure 3-9. Pre-Dredge Sediment t-PCB Concentration Profiles in the Study Area (> 100,000 ppb)
29

The sediment PCB composition was evaluated using both homolog and congener-specific data. The 

analysis indicated that the PCB composition in the surface sediment was dominated by PCB Aroclor 

1248-type contamination, with some influence from PCB Aroclor 1260. An approximate 3:1 composition 

of Aroclor 1248:1260-type contamination was evident in most of the surface sediments as illustrated in 

Figure 3-10 with a pre-dredge surface sample from core T174A. The Aroclor 1248 predominance was 

strongest near Fields Brook, even in the surface sediments. Other investigations have noted historic 

sources of Aroclor 1260-type contamination from Strong Brook across the Upper Turning Basin from 

Fields Brook. The Aroclor 1260 contribution from this source was evident in most of the surface 

sediments; however, it was not observed at depth. This observation would suggest that the Strong Brook 

source of Aroclor 1260 may have been active only recently.

The most contaminated subsurface sediments had a PCB composition that closely resembled Aroclor 

1248 (as demonstrated for a mid-depth core segment in Figure 3-11). This close match with Aroclor 1248 

was observed throughout the study area in most sediment below 1 ft in depth and in all of the most 

contaminated sediment. Sediment samples with a total PCB concentration above 10,000 ppb all showed a 

very close compositional match with Aroclor 1248. The sediments collected from the greatest sediment 

depth (the lowest elevation) that were below the most contaminated zone exhibited a PCB composition 

that also was dominated by an Aroclor 1248 signature. However, these samples also had a noticeable 

contribution of highly-chlorinated PCB congeners (e.g., chlorination levels of 8, 9, and 10) that do not 

have a clear relationship to any particular Aroclor formulation as demonstrated in Figure 3-12. The high 

relative amounts of PCB209 (decachlorobiphenyl) compared to the octa- and nonachlorobiphenyls, for 

instance, were greater than in the more commonly-used highly-chlorinated Aroclor formulations (e.g., 

Aroclor 1268) and other commonly-used PCB formulations. The distribution may also not be explained 

by environmental alteration processes. Little information is available on the rarely-used Aroclors 1269, 

1270 and 1271, but it has been described that they contain high proportions of decachlorobiphenyl, so 

some contribution from one of those Aroclors possibly together with Aroclor 1268 might be a possibility 

in these deeper sediment. The sediments with this unique composition generally had low t-PCB 

concentrations ranging from less than 1,000 to approximately 3,000 ppb.

3.3.2 Characterization of the Post-Dredge Sediment PCB Inventory. 

An important objective of the study was to characterize the chemical and physical composition of the 

post-dredge sediment and evaluate whether these sediments were dredge-generated residuals. Table 3-2 

summarizes t-PCB data for the post-dredge surface sediments, along with representative pre-dredge 

sediment data. The post-dredge surface sediment data presented in Table 3-2 are the core segment-length 

weighted average concentration of the samples closest to the top (surface) of the post-dredge sediment 

cores, representing the top 1 ft. Between two and seven samples were used to determine the average 1-ft 

post-dredge surface sediment concentrations in Table 3-2; the number of samples depended on how the 

cores were segmented. A few post-dredge cores were collected to a depth of less than 1 ft (Table 3-2), 

and the concentration of the deepest segment was then assumed to be representative of the concentration 

to a depth of 1 ft. 

The post-dredge subsurface sediment t-PCB concentrations represented in Table 3-2 ranged from 539 to 

50,500 ppb, and averaged 10,700 ppb. The average t-PCB concentration was significantly higher in the 

post-dredge surface sediments than in both the pre-dredge surface sediment (1,120 ppb) and the predredge sediments at the post-dredge surface sediment elevation (2,490 ppb; Figure 3-13). In fact, the 

post-dredged surface sediment PCB concentrations were higher than the pre-dredge concentrations for 

similar elevations at 28 of the 30 locations (Figure 3-14). The two post-dredge locations with comparable 

or slightly lower PCB concentrations were from the same general area (T175B and T176B), suggesting 
A) Pre-Dredge Core Sample T174A (surface sediment)

B) PCB Aroclor 1248:1260 (3:1)

Figure 3-10. Composition Analysis Showing the Similarity in the PCB Composition of Surface 

Sediment Sample T174A (A) and a 3:1 Mixture of Aroclor 1248:1260 (B) 

0

10

20

30

40

50

1 2 3 4 5 6 7 8 9 10

Homolog as % of Total PCB

Level of Chlorination

PCB Homolog Composition - 174A Surface

0

10

20

30

40

50

1 2 3 4 5 6 7 8 9 10

Homolog as % of Total PCB

Level of Chlorination

PCB Homolog Composition (Aroclor)

Aroclor 1248/1260 (3:1)

30
A) Pre-Dredge Core Sample T174A (from 6.4–7.4 ft sediment depth)

B) PCB Aroclor 1248

Figure 3-11. Composition Analysis Showing the Similarity in the PCB Composition of Sediment 

Sample T174A from a Depth of 6.4–7.4 ft (A) and Aroclor 1248 (B)

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10

Homolog as % of Total PCB

Level of Chlorination

PCB Homolog Composition - T174A Center Depth (6.4 - 7.4 ft)

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10

Homolog as % of Total PCB

Level of Chlorination

PCB Homolog Composition (Aroclor)

Aroclor 1248

31
A) Pre-Dredge Core Sample T174A (from 11.4–12.4 ft sediment depth)

B) Pre-Dredge Core Sample T178C (from 16-16.5 ft sediment depth)

Figure 3-12. Composition Analysis Showing the PCB Composition of Sediment Sample T174A 

from a Depth of 11.4–12.4 ft (A; Homolog Composition) and T178C from a Depth of 16-16.5 ft 

(B; Congener Composition) 

0

10

20

30

40

50

1 2 3 4 5 6 7 8 9 10

Homolog as % of Total PCB

Level of Chlorination

PCB Homolog Composition - T174A Lower Depth (11-12 ft)

0

1

2

3

4

5

6

Cl2(4)/(10)

Cl2(13)Cl3(17)

Cl3(20)/(33)

Cl3(26)Cl3(31)Cl4(40)Cl4(43)Cl4(46)Cl4(49)Cl4(53)Cl4(64)Cl4(74)

Cl5(83)/(119)

Cl5(87)Cl5(92)Cl5(99)

Cl5(107)/(123)/( ...

Cl5(118)Cl6(130)Cl6(135)

Cl6(138)/(163)

Cl6(146)Cl6(156)Cl7(170)Cl7(174)Cl7(178)Cl7(183)Cl8(194)Cl8(199)Cl9(206)

Cl10(209)

Congener % of Total PCB

PCB Congener

PCB Congener Composition: T178C Lower Depth (16-16.5 ft)

32
Figure 3-13. Average t-PCB Concentrations in Pre-Dredge Surface, High-Level, and Lower 

Sediments and Post-Dredge Surface Sediments. Pre-Dredge Lower Sediments are from the Same 

Elevations as Post-Dredge Surface Sediments. Based on Data in Table 3-2. 

1,120

92,500

2,490

10,700

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

Pre-Dredge Surface Pre-Dredge HighLevelPre-Dredge Lower 

(at post-dredge 

surface depth)

Post-Dredge 

Surface

Average Sediment Total PCB Concentration (ppb)

33

Figure 3-14. The Total PCB Concentration in Pre-Dredge Lower Sediments and Post-Dredge 

Surface Sediments at the Sediment Coring Locations Presented in Table 3-2. Pre-Dredge Lower 

Sediment Samples are from the Same Elevation as Post-Dredge Surface Sediment. 

0

10,000

20,000

30,000

40,000

50,000

60,000

T170A

T170B

T171A

T171B

T172A

T172B

T173A

T173B

T174A

T174B

T175A

T175B

T176A

T176B

T177A

T177B

T178A

T178B

T178C

T179A

T179B

T179C

T180A

T180B

T180C

T180D

T181A

T181B

T181C

T181D

Sediment Total PCB Concentration (ppb)

Pre-Dredge Lower (at postdredge surface depth)

Post-Dredge Surface
Figure 3-15. The Total PCB Concentration in the Post-Dredge Surface Sediments at the Sediment 

Coring Locations Presented in Table 3-2. The Mean Concentration is Also Presented along with 

the Mean Pre-Dredge Concentration from the Same Elevation. 

0

10,000

20,000

30,000

40,000

50,000

T170A

T170B

T171A

T171B

T172A

T172B

T173A

T173B

T174A

T174B

T175A

T175B

T176A

T176B

T177A

T177B

T178A

T178B

T178C

T179A

T179B

T179C

T180A

T180B

T180C

T180D

T181A

T181B

T181C

T181D

Sediment Total PCB Concentration (ppb)

Post-Dredge Surface

Mean Pre-Dredge 

Concentration at PostDredge Surface Elevation

Mean Post-Dredge 

Surface Concentration

34

that this observation was likely due to some localized phenomenon. The average t-PCB concentration in 

the post-dredge surface sediments was approximately four times higher than in the pre-dredge sediments 

from the same elevation (i.e., from the depth equivalent to the post-dredge surface sediments; 

Figures 3-13 and 3-15). Figure 3-16 also illustrates the differences in the PCB concentrations in the preand post-dredge cores at different sediment depths. The post-dredge surface sediment PCB 

concentrations were generally higher than one would have expected based on the pre-dredge data from 

the same elevations. If the dredged sediments were removed with complete effectiveness, and no 

additional residuals were created during the dredging operation, one would expect the post-dredging 

surface sediment concentrations to be equivalent to those of the pre-dredged sediments at the same depth, 

not four times higher as was observed in this study.

The post-dredge surface sediment PCB concentrations were also more uniform than the pre-dredge 

surface sediment PCB concentrations and the pre-dredge PCB concentrations at the depth equivalent to 

the post-dredge surface (Table 3-2). This increase in surface sediment concentration uniformity suggests 

that sediment resuspension, mixing, and transport may have been occurring during the dredging 

operations, and that the sediments then settled over a larger area than from which they originated.

As previously mentioned, the pre-dredge sediment inventory had a PCB composition that closely 

resembled Aroclor 1248. The surface sediments also exhibited some contributions of Aroclor 1260, and 

some of the deep sediments had some contributions from Aroclor 1268 or other highly-chlorinated PCB 

material, but all sediments were predominantly Aroclor 1248. Figure 3-17 shows the overall pre- and 

post-dredge PCB homolog composition of all analyzed sediment on a t-PCB mass basis; the composition 

closely resembled Aroclor 1248 both before and after dredging.
35

Figure 3-16. Total PCB Concentrations in Pre- and Post-Dredge Core 

Samples from Locations T170B and T172B

542

544

546

548

550

552

554

556

558

560

562

0 20,000 40,000 60,000 80,000 100,000 120,000 140,000 160,000

Elevation (ft)

Total PCB by SUM (ng/g)

Core: 170b

Pre-dredge

Post-dredge

544

546

548

550

552

554

556

558

560

562

0 20,000 40,000 60,000 80,000 100,000 120,000 140,000

Elevation (ft)

Total PCB by SUM (ng/g)

Core: 172b

Pre-dredge

Post-dredge
Figure 3-16. Total PCB Concentrations in Pre- and Post-Dredge Core Samples 

from Locations T173A and T175A (Continued)

542

544

546

548

550

552

554

556

558

560

562

564

0 50,000 100,000 150,000 200,000 250,000

Elevation (ft)

Total PCB by SUM (ng/g)

Core: 173a

Pre-dredge

Post-dredge

544

546

548

550

552

554

556

558

560

0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000

Elevation (ft)

Total PCB by SUM (ng/g)

CoreL: 175a

Pre-dredge

Post-dredge

36
Figure 3-17. Pre-Dredge and Post-Dredge Comparison of PCB Homolog 

Composition in Sediment Within the Study Area (T181 through T170)

0

10

20

30

40

50

60

1 2 3 4 5 6 7 8 9 10

Homolog as % of Total PCB

Level of Chlorination

PCB Homolog Composition 

(based on total PCB mass)

Pre-Dredge

Post-Dredge

37

The PCB composition of the pre-dredge sediments with the highest PCB concentrations closely 

resembled Aroclors 1248 (Figures 3-18A and D). The composition of the pre-dredge sediments at the 

elevations (sediment depths) of the actual post-dredge cut line had a PCB composition with a significant 

proportion of Aroclor 1248, but had a unique composition that also included notable amounts of highlychlorinated PCB congeners (Figure 3-18B), as can be seen in the right-hand corner of the congener 

distribution histogram from PCB170 to PCB209 (compare Figure 3-18B with Figure 3-18A). However, 

the post-dredge surface sediments had a PCB composition that closely resembled Aroclor 1248 without 

any notable contributions from most of the highly-chlorinated PCB congeners with the exception of some 

congener PCB209 (Figure 3-18C). The PCB composition of the post-dredge surface sediments did not 

resemble the composition of the sediments collected from the same pre-dredge elevation, but resembled 

the composition of the more contaminated sediments from a higher elevation. Again, if the dredged 

sediments were removed with complete effectiveness and no additional residuals were created during the 

dredging operation, one would expect the post-dredging surface sediment PCB composition to be 

equivalent to that of the pre-dredged sediments at the same depth, not to that of the highly contaminated 

sediments from a higher elevation as was observed in this study.

In addition to the PCB homolog and congener composition data review, similarities and dissimilarities in 

PCB composition were assessed using exploratory PCA techniques. PCA is an exploratory data analysis 

tool. Exploratory algorithms are designed to reduce large and complex datasets to a suite of best views. 

PCA is used as a means to explore the variability in the PCB composition of the samples. Specifically, 

one form of PCA output is 2- or 3-dimensional factor score plots in which the principal component scores 

for each sample are cross-plotted. If a significant portion of the variance in the dataset is accommodated 

in the first few principal components, then the Euclidean distances between sample points on such plots 

(e.g., PC1 v PC2 or PC2 v PC3) provide a measure of their chemical similarity. Samples that visually 

“cluster” are chemically similar and vice versa. 
A) Pre-Dredge Sample T181C (from the most contaminated depth)

B) Pre-Dredge Sample T178C (from a lower depth)

Figure 3-18. PCB Congener Compositions in a Representative Mid-Depth Sample (A) and in a PreDredge Lower Depth Sample (B). The Pre-Dredge Lower Sediment Sample (B) is from a 

Comparable Elevation as the Post-Dredge Surface Sediment Sample (C). 

0

2

4

6

8

Cl2(4)/(10)

Cl2(13)Cl3(17)

Cl3(20)/(33)

Cl3(26)Cl3(31)Cl4(40)Cl4(43)Cl4(46)Cl4(49)Cl4(53)Cl4(64)Cl4(74)

Cl5(83)/(119)

Cl5(87)Cl5(92)Cl5(99)

Cl5(107)/(123)/( ...

Cl5(118)Cl6(130)Cl6(135)

Cl6(138)/(163)

Cl6(146)Cl6(156)Cl7(170)Cl7(174)Cl7(178)Cl7(183)Cl8(194)Cl8(199)Cl9(206)

Cl10(209)

Congener % of Total PCB

PCB Congener

Percent Congener Composition: T181C Center Depth

0

1

2

3

4

5

6

Cl2(4)/(10)

Cl2(13)Cl3(17)

Cl3(20)/(33)

Cl3(26)Cl3(31)Cl4(40)Cl4(43)Cl4(46)Cl4(49)Cl4(53)Cl4(64)Cl4(74)

Cl5(83)/(119)

Cl5(87)Cl5(92)Cl5(99)

Cl5(107)/(123)/( ...

Cl5(118)Cl6(130)Cl6(135)

Cl6(138)/(163)

Cl6(146)Cl6(156)Cl7(170)Cl7(174)Cl7(178)Cl7(183)Cl8(194)Cl8(199)Cl9(206)

Cl10(209)

Congener % of Total PCB

PCB Congener

PCB Congener Composition: T178C Lower Depth

38
C) Post-Dredge Sample T175A (surface)

D) Aroclor 1248

Figure 3-18. PCB Congener Compositions in a Representative Post-Dredge Surface Sample (C)

and in Aroclor 1248 (D). The Pre-Dredge Lower Sediment Sample (B) is from a Comparable 

Elevation as the Post-Dredge Surface Sediment Sample (C). (Continued)

0

2

4

6

8

Cl2(4)/(10)

Cl2(13)Cl3(17)

Cl3(20)/(33)

Cl3(26)Cl3(31)Cl4(40)Cl4(43)Cl4(46)Cl4(49)Cl4(53)Cl4(64)Cl4(74)

Cl5(83)/(119)

Cl5(87)Cl5(92)Cl5(99)

Cl5(107)/(123)/(1 ...

Cl5(118)Cl6(130)Cl6(135)

Cl6(138)/(163)

Cl6(146)Cl6(156)Cl7(170)Cl7(174)Cl7(178)Cl7(183)Cl8(194)Cl8(199)Cl9(206)

Cl10(209)

Congener % of Total PCB

PCB Congener

Percent Congener Composition: T175A-SP Surface

0

2

4

6

8

10

Cl2(4)/(10)

Cl2(13)Cl3(17)

Cl3(20)/(33)

Cl3(26)Cl3(31)Cl4(40)Cl4(43)Cl4(46)Cl4(49)Cl4(53)Cl4(64)Cl4(74)

Cl5(83)/(119)

Cl5(87)Cl5(92)Cl5(99)

Cl5(107)/(123)/(124)

Cl5(118)Cl6(130)Cl6(135)

Cl6(138)/(163)

Cl6(146)Cl6(156)Cl7(170)Cl7(174)Cl7(178)Cl7(183)Cl8(194)Cl8(199)Cl9(206)

Cl10(209)

Congener % of Total PCB

PCB Congener

Percent Congener Composition: Aroclor 1248

39
40

Another form of PCA output, factor loading plots, is used to determine which individual variables (in our 

case PCB homologs and congeners) are responsible for any visual “clustering” observed. As such, PCA 

was a useful data analysis and exploration tool for this project dataset. 

This data visualization and exploration was performed using the software EinSight (v. 4.04) by 

InfoMetrix, Inc. (Woodinville, WA), which provides qualitative data exploration capabilities. The PCA 

exploratory technique was used to help recognize groups of samples that may have shared similar PCB 

composition (i.e., similar relative PCB homolog and congener concentrations) and those that have clearly 

different compositions. Prior to PCA analysis, the PCB congener data were normalized to the t-PCB 

concentration in each sample to eliminate influences caused by concentration alone. The goal of these 

analyses was to identify difference and similarities between samples based on PCB pattern recognition. 

Aroclor formulations were also included in the dataset for comparison purposes. 

The PCA analyses confirmed the observations made during the earlier described review of the PCB 

homolog and congener data and further documented the pre- and post-dredge sediment samples’ PCB 

compositional similarities and relationships. The PCA results were similar regardless of whether the 

analysis was conducted using homolog or individual congener data. The PCA results are shown in 

(Figures 3-19 and 3-20). The results clearly indicated that the majority of the pre-dredge subsurface 

samples from the depths with high PCB concentrations and the post-dredge surface samples had similar 

PCB compositions (likely from the same source of PCBs). These samples all appeared to be from the 

same Aroclor 1248 source, as these samples clustered closely with each other and at the Aroclor 1248 

reference composition. The pre-dredge surface sediments had a slightly different composition and were

drawn away from Aroclor 1248 towards Aroclor 1260 with many of the surface sediment samples 

clustering closely with a 3:1 mixture of Aroclor 1248:1260. These samples clearly had a significant 

contribution from the Aroclor 1248 source but also some contribution from a source of Aroclor 1260. 

The pre-dredge samples from below the most contaminated zone and at the elevation (sediment depth) 

equivalent to that of the post-dredge surface sediment were also drawn away from Aroclor 1248, but in a 

different direction. These pre-dredge samples from a greater depth were drawn towards Aroclor 1268, 

with a number of them clustering near a mixture of Aroclor 1248 and 1268, which indicated some 

contribution from a highly-chlorinated PCB source. 

The PCA results supported the earlier findings suggesting that the PCBs in the post-dredge surface 

sediments originated primarily from the most contaminated zone in the pre-dredge sediments. As before, 

if the dredged sediments were removed completely and no additional residuals were created during the 

dredging operation, one would expect the post-dredging surface sediment PCB compositions (and the 

PCA results) to be similar to those of the pre-dredged sediments from the equivalent sediment depths. 

Therefore, the post-dredge sediment samples would be expected to cluster towards the Aroclor 1248/1268 

material along with the pre-dredge deep sediment samples. Instead what was observed was that the postdredge surface sediments clustered with the pre-dredge samples from the highly contaminated zone 

typical of a higher elevation.
Figure 3-19. Principal Component Analysis (PCA) Using PCB Homolog Data for Pre- and PostDredge Sediments in the Study Area; Full View (upper) and Zoomed View (lower) 

Most pre-dredge sub-surface samples from the 

contaminated zone and post-dredge surface samples

Aroclor 1248/1260 (3:1)

Most pre-dredge surface samples

Most pre-dredge samples from the elevation 

(depth) equivalent to the post-dredge surface

Aroclor 1248/1268

Aroclor 1248

Aroclor 1248

Most pre-dredge sub-surface samples from the 

contaminated zone and post-dredge surface samples

41
Figure 3-20. Principal Component Analysis (PCA) Using PCB Congener Data for Pre- and PostDredge Sediments in the Study Area; Full View (upper) and Zoomed View (lower)

Aroclor 1248/1268

Aroclor 1248/1260 (3:1)

Aroclor 1248

Most pre-dredge samples from the elevation 

(depth) equivalent to the post-dredge surface

Most pre-dredge surface samples

Most pre-dredge sub-surface samples from the 

contaminated zone and post-dredge surface samples

Aroclor 1248

Most pre-dredge sub-surface samples from the 

contaminated zone and post-dredge surface samples

42
43

3.3.3 Post-Dredge PCB Characteristics and Implications for Dredged Residuals. 

The relatively uniform post-dredge surface sediment PCB concentrations and composition, compared to 

the pre-dredge samples, indicated that the post-dredge surface sediments generally did not originate from 

the less uniform pre-dredge sediments from the same location and elevation. In addition, the PCB 

concentrations and composition of the post-dredge surface were dissimilar from the pre-dredge sediments 

from the same elevation, indicating that they were not closely related. The significant increase in the 

PCB concentration of the post-dredge surface sediments, compared to the pre-dredge sediments from the 

same elevation, suggests that the post-dredge surface sediments originated from the more contaminated 

sediments. In addition, the PCB compositions of the post-dredge surface sediments were essentially 

identical to the PCB compositions of the highly contaminated pre-dredge sediments at higher elevations. 

Thus, the post-dredge surface sediments appeared to be dredge residuals originating from well-mixed predredge sediments from the most contaminated pre-dredge sediment depths. The most contaminated predredge sediments clearly had a significant influence on the concentration and composition of the postdredge surface sediments, even though those most contaminated pre-dredge sediments were generally 

found a few feet above the dredge cut line. 

3.4 Two (2)- and Three (3)-Dimensional PCB Modeling of Pre- and Post Dredge Areas

3-D block diagram visuals for t-PCBs in sediment before and after dredging were constructed using 

EarthVision modeling and visualization software. A total of 328 and 149 data points were used in the 

calculation of the t-PCB grid for the pre-dredge and post-dredge data, respectively. The 3-D minimum 

tension gridding algorithm calculated a smooth surface that closely fit the input data values using a 

bicubic spline technique. The t-PCB visuals shown in this report have a unit rectangular lattice or grid 

cell size of 20 ft in the X direction, 20 ft in the Y direction, and 1 ft in the Z (depth) direction. The grids 

were contoured using an irregular contour interval to best visualize the broad concentration data 

distribution for t-PCBs. 

Figures 3-21 through 3-24 provide cross section views of the pre- vs. post-dredge sediment t-PCB 

concentrations as a function of elevation for T175, T174, T173, and T172, respectively. In these figures, 

the post-dredge t-PCB concentration contour is shown at the top and the pre-dredge sediment t-PCB 

contour is shown at the lower portion of the figure. The elevation intervals and scale are consistent 

among figures, and the estimated dredge cut line and pre- and post-dredge bathymetry are consistent with 

the surfaces shown in subsequent figures (see Section 3.6 for methods used to determine the maximum 

dredge cut line). 

It is worth noting that in some cases post-dredge cores were not driven as deep as the pre-dredge cores in 

similar locations. As such, the post-dredge concentration contours represent greater interpolation from a 

general lack of local data in those cases. 

The post-dredge sediment surface at T174 increased an order of magnitude. This was also the case in 

Figures 3-22 and 3-23 where T173 and T172 are shown, respectively. Post-dredge sediment surface 

concentrations increased by 10 to 20 times, resulting in concentrations ranging from 2.7 to 4.6 ppm.
44

Figure 3-21. Comparison of Pre- and Post-Dredge Cross-Section t-PCBs in Sediment at T175
45

Figure 3-22. Comparison of Pre- and Post-Dredge Cross-Section t-PCBs in Sediment at T174
46

Figure 3-23. Comparison of Pre- and Post-Dredge Cross-Section t-PCBs in Sediment at T173
47

Figure 3-24. Comparison of Pre- and Post-Dredge Cross-Section t-PCBs in Sediment at T172
48

3.5 Bathymetric Surveys Prior to, During, and Following Dredging

Bathymetric surveys were conducted before and after dredging in 2007 and 2 years following the 

completion of dredging in 2009. The 2007 pre- and post-dredge bathymetry data are discussed herein, 

and the 2009 data will be presented in a subsequent report. Each bathymetric survey covered the entire 

extent of the GLLA dredge project area; however, only the bathymetric data specific to the ORD study 

area are discussed in this report. Additionally, the pre-dredge survey was implemented after dredging had 

already commenced in some areas including in the ‘Upper Turning Basin’. This specifically impacted the 

pre-dredge bathymetry in the study area in proximity to T181. Any interpretations related to pre-dredge 

surfaces in this area were conducted using pre-dredge bathymetric data supplied in-kind by J.F. Brennan 

or from other pre-dredge depth data recorded by the field team. Figures 3-25 and 3-26, respectively, 

depict the pre- and post dredge bathymetric survey results for the study area.

Figure 3-25. Pre-Dredge Bathymetric Survey Results for the Study Area

The pre-dredge bathymetric data illustrated in Figure 3-25 indicate shallow water and increased sediment 

thickness existed on the eastern bank of river between T181 and T176. This area corresponded with the 

highest pre-dredge PCB concentrations shown previously in Figure 3-9 and occurring approximately 9.5

ft below the pre-dredge sediment surface. The water column depth ranged from approximately 3 to 10 ft 

deep in the extended study area. A narrow channel was evident running from upstream at T181 to the 
49

downstream extent of the study area at T170. Figure 3-25 also shows the extent of dredging on the east 

bank just south of T181 that commenced prior to the first bathymetric recording. Sediment had been 

dredged to a depth of approximately 20 to 23 ft below the water surface (IGLD85).

The post-dredge bathymetric data generated after dredging are shown in Figure 3-26. Dredging in this 

area was completed on approximately June 18, 2007, with Stage I dredging of the river completed in late 

October 2007. The bathymetric survey shown here was completed on November 15, 2007. 

The post-dredge sediment surface was measured to be between 20 and 23 ft below the Lake Erie IGLD85 

in most locations. The target dredge depth was achieved within the ORD study area. It is understood

when interpreting these bathymetric data that the timing of such electronic surveys plays an important 

role in defining what is being measured. As the unconsolidated sediment is becoming more consolidated 

over time, it is expected that the sediment surface may change. Also, the unconsolidated sediment may be 

more susceptible to scour or erosional events. It is realized that additional research will be needed to 

identify optimal timing for collecting these data with specific consideration given to site-specific 

conditions. U.S. EPA will be conducting more bathymetric surveys over the next several years on the 

Ashtabula River to define the changes in the bathymetric profile over time. Coupled with sediment core 

sampling and analysis, the fate of contaminated sediment residuals will be monitored and reported along 

with other long-term parameters being measured in this investigation.

Figure 3-26. Post-Dredge Bathymetric Survey Results of the Study Area
50

To date, the following MBS have been conducted to support this research:

• Initial (pre-dredge) multi-beam bathymetric data were collected May 16-18, 2007.

• Daily multi-beam bathymetric surveys were conducted May 31 - June 10, 2007 (with the 

exception of June 4, 2007). 

• Final (post-dredge) multi-beam bathymetric data were collected November 13-15, 2007.

• An additional post-dredge multi-beam bathymetric survey was completed in November 2009 

and will be presented in a subsequent report.

In addition to the pre- and post-dredge bathymetric surveys, bathymetric surveys were also conducted on 

a daily basis during dredging operations to map the day-to-day morphology of the sediment bed. 

Figures 3-27 through 3-30 show a temporal view of the bathymetry contour compared to the estimated 

dredge cut lines for T175, T174, T173 and T172, respectively. These cross-sectional views capture the 

time period from initial dredging to near completion of dredging for T175 and T174; however, only a 

portion of dredging is captured at T173 and virtually no dredging was captured at T172. In most cases, 

the estimated dredge cut line appeared to be approximately 0.5 to 1.5 vertical ft below the post-dredge 

bathymetric elevations and in some cases near to or above the post-dredge bathymetry.

A more detailed review of the sediment bathymetry cross sections in Figure 3-27 suggests potential 

sloughing may have occurred along the western bank of the river at T175. The June 6 survey (blue line) 

indicates the bathymetric surface was lower in elevation than on the previous day (June 5). On June 6, 

the sediment thickness increased approximately 6 ft at a distance of approximately 10 to 20 ft from the 

western shoreline. This may have been due to sediment shifting as a result of slumping bank sediments or 

movement of sediment due to obstructions or debris encountered while dredging. Dredge reports for June 

6 do not indicate any specific problems noted in the vicinity of T175. The analysis was repeated on each 

cross section shown here.

3.6 Survey and Dredge Position Data to Calculate Residuals

One method of estimating dredge residuals evaluated in this study was the use of bathymetric surveys and 

dredge head position data to determine the inventory of sediment removed and the corresponding amount 

of dredge residuals remaining. Bathymetric surveys are routinely used in dredge operations to confirm 

the targeted dredge cut line has been attained. Typically, these surveys are completed with single-beam 

survey equipment; however, for the optimum development of this approach (and other project objectives) 

a high resolution multi-beam survey was performed as described below. Additionally, a dredge head 

positioning system was used in this project that provided real-time assessment and recording of the 

dredge head position (detailed below). Conceptually, dredge residuals thickness can be estimated by 

calculating the difference between the maximum depth (lowest elevation) attained by the dredge head in a 

specific location and the post-dredge sediment surface elevation measured bathymetrically at the same 

location. This approximation of dredge residuals thickness can be combined with pre- and post-dredge 

sediment physical and chemical characterization data to calculate estimates of the mass of sediment and 

contaminant residuals over the surveyed areas. 
Figure 3-27. Cross-Section View at T175 Showing the Change in Bathymetry During Dredging 

Potential sloughing 

of the river bank

51
52

Figure 3-28. Cross-Section View at T174 Showing the Change in Bathymetry During Dredging
53

Figure 3-29. Cross-Section View at T173 Showing the Change in Bathymetry During Dredging
54

Figure 3-30. Cross-Section View at T172 Showing the Change in Bathymetry During Dredging
55

Several steps were used for this approach. The maximum dredge cut depths were determined based on 

the recorded positions of the dredge head (shown as the dredge cut line in Figure 3-31). This information 

was used to develop a 3-D surface that represented the maximum extent (minimum elevation) of the 

dredging. A post-dredge bathymetric survey was conducted for the dredged area (also shown in 

Figure 3-31 as the post-dredge surface). Chemical and physical measurements were performed to 

adequately characterize pre- and post-dredge sediments. Once these steps were completed, the data were

processed using 3-D computer models to calculate post-dredge residuals volume and mass. The 

following sections (3.6.1 to 3.6.3) detail the processes used in this study to complete these steps. Selected 

examples on specific transects for which the complete datasets were available are used to demonstrate the 

approach. Additional data compilation and processing are ongoing to provide complete coverage of the 

entire research study area and will be discussed in subsequent reports. It should be noted that although 

the bathymetric survey data were designed to be used in this dredge residuals estimation process, the 

dredge head position data were being collected by the dredge contractor for operational purposes of 

indentifying targeted dredge areas and not necessarily with this specific analysis in mind. Therefore, 

additional data processing and QA/QC checks may be required before the data can be utilized as needed 

in this approach. The dredge contractor, J.F. Brennan, has cooperated fully and contributed greatly to this 

effect by providing data where available. On future projects, the researchers anticipate working more 

strategically with dredge contractors to collect and process this type of data to fulfill dredge operation 

needs, but also to allow for greater ease of use for this particular data application. 

3.6.1 Determination of the Maximum Dredge Cut Depth. 

In-field observations and dredge reports produced by the dredge contractor for operational purposes were 

gathered and reviewed to determine the date and time of actual dredging in the targeted study area. These 

records were used to identify and obtain dredge coordinate data, which were provided in-kind for this 

research by the dredging contractor, J.F. Brennan. These data were used to develop a 3-D surface of the 

maximum dredge cut depth. 

Horizontal and vertical position data (XYZ) for the dredge cutter head were supplied in various formats: 

raw Hypack© data, edited Hypack© data, and processed XYZ ASCII text files. XYZ data from the study 

area were extracted from all file formats, adjusted (to ensure that all data were in the same horizontal and 

vertical coordinate system), filtered, and then combined into one XYZ dataset. Figure 3-32 shows the 

2-D plan view (XY) of the XYZ data that were plotted.

The plotted data resulted in a “data cloud” representing approximately 1.5 million individual data points, 

identifying the dredge head position in space and varying in intervals between every 1 second and 30 

seconds of activity depending on the day of record. This information was used to approximate the 

maximum dredge depth, which was defined as the lowest elevation that the dredge cutter head reached 

during dredging operations in a specific XY space (described in more detail below).

For this analysis, the vertical position coordinate (elevation) extracted from the position data 

corresponded to the bottom of the cutter head at any given time. A surface grid was generated for the 

study area using the dredge position data. The area in which the surface grid was established for the 

calculations described in subsequent sections is shown in Figure 3-32 in red outline. Within each grid 

cell, the lowest elevation recorded was used as the maximum extent of the dredge cut for the entire grid 

cell. This surface grid was then used to generate a smoothed elevation surface. The conceptual model in 

Figure 3-31 shows a cross-section of the river study area with dredge cutter head XYZ position data and 

the calculated maximum dredge depth (cut line) generated from the elevation of the cutter head positions.
56

Figure 3-31. Conceptual Model River Cross-Section Showing the XYZ Dredge Cutter-Head 

Position and Approximated Cut Line
57

Figure 3-32. Plan View of Dredge Activity in the Study Area

More specifically the process to generate the maximum dredge cut depth surface is described below. The 

XYZ cutter head data were imported into ArcGIS and converted into a uniformly spaced raster surface. 

Several grid sizes (5 ft × 5 ft, 10 ft × 10 ft, 15 ft × 15 ft, 20 ft × 20 ft, and 25 ft × 25 ft) were tested. The 

lowest elevation within each grid cell was selected as the representative elevation of the cell, the end 

product being a uniformly spaced grid of the lowest dredged elevations in the study area. During the data 

filtering process, data were removed that represented the dredge-head position during time of “transiting” 

or when the dredge head was raised near or above the water surface. Elevations greater than 559.2 ft 

(IGLD85) were removed and decreased the total number of data points, making the dataset more 

manageable.

The selection of the grid cell dimensions was important. Smaller grid spacing allowed for a greater 

number of dredge head positions in a 2-D space; however, this spacing did not necessarily result in an 

interpretable dredge cut surface. Smaller grid cells resulted in many cells that did not contain dredge head 

position data at the lower surface elevations. As a result, the finer resolution grid surfaces contained 

artifically high dredge cut elevations (“spikes”) that do not accurately represent the maximum dredge cut 

surface. After careful review of a range of grid cell dimensions, it was determined that, for this site, cell 

dimensions and interpolated surface were optimal at a 15 ft × 15 ft grid size. This grid and surface were 

exported from ArcGIS and imported into Earth Vision software to create a 2-D dredge cut surface using 

minimum tension gridding. The maximum dredge cut depth is shown in Figure 3-33. 
58

Using the currently available data, the approach was demonstrated over a limited area of the study area. 

Transects 172-175 represent a series of transects with sufficient data coverage to utilize this approach. 

The researchers are continuing to process and evaluate data that may be used to extend the application of 

this approach over a broader area. This area included dredge activity in DMUs 19, 20, 21, and 22. The 

approximated dredge cut line in this part of the study area that was used for further processing to calculate 

residuals is shown in Figure 3-33. The red dashed line on this surface outlines the area in which dredge 

residual estimates were determined. These are described in Section 3.6.3.

3.6.2 Determination of the Post-Dredge Sediment Surface. 

The next step in this approach for estimating dredge residuals was to develop an elevation schematic for 

the post-dredge sediment surface. A post-dredge bathymetric survey was conducted between 

November 13 and November 24, 2007 following completion of Stage I dredging. This survey was 

completed using the instrumentation and procedures described in Section 2.3.2. It should be noted that 

further study is needed to determine the most appropriate timing and technical limitations for the multibeam survey approach used to characterize the post-dredge surface. Issues that need to be further 

considered include: the consolidation processes of the unconsolidated dredge residuals and how these 

impact the resolution of the bathymetric surface. The elapsed time after the completion of dredging 

before the post-dredge bathymetric survey is conducted could play an important role in defining the 

residuals. Dredge-generated residuals are generally composed of unconsolidated, recently-deposited 

sediment. Therefore, as natural sediment consolidation processes occur (such as dewatering, pore space 

reductions, particle re-arrangement, etc.), the measure of dredge residuals can change over time. A 

further complication is that the processes and extent/rates of those processes will be dependent on local 

site conditions such as the sediment’s geotechnical parameters (e.g., particle size), the site’s 

hydrodynamic conditions, and potentially the dredge technology used for the site. Significant research 

has been conducted on sediment consolidation processes under both natural and engineered conditions 

(e.g., sediment capping). This information combined with site-specific conditions should be considered 

in the development of full-scale implementation of this approach. Further study is warranted to identify 

the most appropriate timing for this type of measurement. Additionally, the selection of the appropriate 

bathymetric equipment should be considered in understanding how the density and characteristics of the 

residuals impact the bathymetric surface measured. The data developed in this study permit the 

demonstration of the approach with appropriate caveats and future improvements. 

3.6.3 Estimation of the Post-Dredge Residuals 

Estimation of the post-dredge residuals was completed for both total solids and t-PCBs. Sediment 

volumes were calculated for each of the 3-D isoconcentration shells generated from the PCB data 

interpolation described in Section 3.1.3 and shown in Figures 3-5 through 3-9. Each shell was bounded 

by 2-D planar bounding surfaces representing post-dredge bathymetry, maximum dredge cut depths, and 

core refusal surfaces. These 2-D surfaces were created using 2-D minimum tension gridding. Pre- and 

post-dredge sediment dry bulk density values were used to convert the sediment volume in these shells to 

a mass (dry kg). The mid-range concentration of each isoconcentration shell was multiplied by the 

sediment mass to estimate the mass of t-PCB in each shell range. 

To demonstrate this approach, the estimated volume and mass of sediment within a 5-ft band (Y) in the 

linear (river flow) direction and across the river (X) from bank to bank for each of T175, T174, T173, and 

T172 were determined and is shown in Table 3-3. In addition, Table 3-3 summarizes the estimated 

dredge residuals in this 5-ft band and dredge efficiencies in terms of volume and mass of sediment and 

mass of t-PCBs removed.
59

Figure 3-33. Estimated Dredge Cut Line in Between T176 and 172 in the Study Area

To convert sediment volumes to sediment mass, average dry bulk density values of 1.23 g/cm3 and 0.99 

g/cm3 were used for pre-dredge sediment and post-dredge sediment, respectively. These values were 

determined from sediment segment data comparisons made between pre- and post-dredge cores collected 

from the same location and at the same depth for 14 sampling stations where samples aligned well 

vertically. Averages were generated from these samples in the 548 ft to 547.5 ft elevation range.

In addition to determining sediment volume and residuals within a 5-ft river transect band, total bank-tobank sediment volume and residuals were estimated for an approximate 400-ft linear dimension of the 

river extending from T175 to T172. The area used to make this estimate is shown as the red polygon

(dashed-line) in Figure 3-33. The estimated volume of sediment between T175 and T172 was determined 

to be approximately 13,596 cu yd as calculated by the difference between the pre-dredge bathymetry and 

the estimated dredge cut depth surface. Applying an average dry bulk density of 1.23 g/cm3 resulted in an 

estimated pre-dredge sediment mass of 9,669,399 kg containing approximately 252 kg of t-PCBs. 

Likewise, the estimated volume of dredge-induced sediment residuals between T175 and T172 was 

approximately 625 cu yd as determined by the difference between the post-dredge bathymetry and the 

estimated maximum dredge cut depth. Applying an average dry bulk density of 0.99 g/cm3 yielded a total 

estimated dredge residuals mass of 361,668 kg. This sediment was estimated to contain approximately 

3.3 kg of t-PCBs. 
60

Therefore, dredging within the boundaries of T175 and T172 resulted in an approximate 96% removal of 

the sediment mass inventory, which in turn resulted in an approximate 99% removal of the t-PCB mass. 

Inversely, these removals correspond to approximately 4% residuals of the original sediment mass 

remaining that contains approximately 1% of the original PCB mass in this targeted dredge area. These 

dredge residuals are illustrated visually in Figures 3-33 to 3-36 that show each transect in 2-D 

representations for T175 to T172. 

In addition, 3-D block cross-section views of the river from T175 through T172 (Figures 3-34 through 

3-37) were created. These views show the estimated cut line surface compared to post-dredge and predredge bathymetry, refusal layer surface, and the location of each pre- and post-dredge sediment core 

with corresponding t-PCB concentration range data. As depicted in the conceptual drawing in Figure 

3-31, the pre- and post-dredge sediment cores are also shown in Figures 3-34 through 3-37 and are 

denoted with small squares for the pre-dredge sediment segments and larger squares for the post-dredge 

sediment segments. 

Table 3-3. Estimates of Sediment and t-PCB Removals and Residuals

Transect ID

Pre-Dredge Inventory Post-Dredge Inventory

Sediment t-PCBs Sediment t-PCBs

cu yd kg kg cu yd kg kg

T172(a) 229 163,071 4.16 17 9,811 0.1

T173(a) 263 185,315 6.12 14 8,167 0.1

T174(a) 96 69,350 1.37 1 530 0.0

T175(a) 197 141,193 4.59 8 4,533 0.0

T172 to T175(b) 13,596 9,669,399 251.66 625 361,668 3.3

Removal Residuals

Sediment t-PCBs Sediment t-PCBs

cu yd kg %vol %mass kg %mass %mass %mass

212 153,261 92.6 94.0 4.04 97.0 6.0 3.0

249 177,148 94.6 95.6 6.03 98.5 4.4 1.5

96 68,820 99.1 99.2 1.37 99.7 0.8 0.3

189 136,661 96.0 96.8 4.55 99.3 3.2 0.7

12,971 9,307,731 95.4 96.3 248.2 98.7 3.7 1.3

(a) Values calculated based on a band of sediment extending 5 ft in the linear (river flow) direction (2.5 ft on either 

side of the transect) and across the river from bank to bank.

(b) Values calculated based on a band of sediment extending 400 ft in the linear (river flow) direction from T175 to 

T172 and across the river from bank to bank.

Figure 3-34 presents the cross-section view for T175, where the post-dredge bathymetric line and the 

maximum dredge cut elevations are within 1.3 vertical ft distance between each other with some apparent 

overlap. The “dashed” line is used to show continuity of the post-dredge bathymetric line running from 

the east river bank to the west river bank (as it is partially hidden by the cut line). The dredge-induced 

residual sediment is shown in yellow and represents the sediment volume between the post-dredge 

bathymetric line and the estimated cut line. The tan or beige color represents the un-dredged sediment 

occurring between the dredge cut line and the refusal layer. The pink layer is the sediment that was 
61

dredged or removed and occurs between the pre-dredge sediment surface and the post-dredge sediment 

surface.

The cross-section view for T174 is shown in Figure 3-35. At T174, the dredge cut line and post-dredge 

bathymetry contour closely on the east side of the river. However, the cut line appears to trend upwards 

as it moves closer to the west bank. This is a data artifact that is due to the lack of dredge cutter head 

position data on the west side of the river (note the lack of grey squares in the figure left of the 

centerline). As a result, the Earth Vision software “forces” the estimated cut line to a false elevation 

approximately 4 vertical ft above the post-dredge bathymetry on the westernmost side of the river.

In Figure 3-36, a lack of deep dredge positioning immediately east of centerline results in a single point 

that causes an upward undulation of the dredge cut surface, creating an overlap of the cut line and postdredge bathymetry in the area of T173. Otherwise, the dredge cut line appears to be approximately 1.0 to 

1.6 vertical ft below the post-dredge bathymetric line.

For T172 (Figure 3-37), the cut line is consistently below the post-dredge bathymetric line in a range of 

approximately 0.75 to 1.6 vertical ft, resulting in a layer of dredge-induced residuals.
62 

Figure 3-34. Cross-Section of T175 Showing Estimated Dredge Cut Line vs. Post-Dredge 

Bathymetry
63

Figure 3-35. Cross-Section of T174 Showing Estimated Dredge Cut Line vs. Post-Dredge 

Bathymetry
64

Figure 3-36. Cross-Section of T173 Showing Estimated Dredge Cut Line vs. Post-Dredge 

Bathymetry
65

Figure 3-37. Cross-Section of T172 Showing Estimated Dredge Cut Line vs. Post-Dredge 

Bathymetry
66

4.0 DISCUSSION AND CONCLUSIONS

This research project was designed to provide an understanding of sediment residuals formation during 

environmental dredging. Selected tools and methods were developed and/or evaluated for their utility to 

characterize dredge residuals, and a portion of the Ashtabula River dredging project was used to test these 

approaches. Ultimately, the objective of the project was to obtain quantitative and qualitative 

estimates/projections of post-dredging residuals mass/volume and contaminant concentrations based on 

pre-, during- and post-dredging information and data. 

This document comprises an initial interpretative report for this research and uses a WOE approach 

employing multiple LOEs to evaluate the presence and extent of dredge-induced residuals in an effort to 

quantify residuals within the U.S. EPA-ORD study area at the GLLA Ashtabula River project. The work 

herein sought to accomplish the following two objectives:

1. Estimate the volume and concentration of contaminated sediment residuals remaining in the 

ORD study area of the Ashtabula River following dredging. Determine both solids and PCB 

concentrations in the sediment residual inventory.

2. Compare pre- and post-dredging sediment mass (determined from depth, moisture content, 

and bulk density measurements) and concentration characterization data (both solids and PCB 

concentrations) to assess the PCB concentration relationship of the residual sediment to the 

contaminated material removed.

Six primary LOEs were used to evaluate dredge residuals in an attempt to address the study objectives. 

The following is a brief discussion and summary of those findings:

Vertical Alignment and Physical Examination of the Pre- and Post-Dredge Sediment Cores. Individual 

pre- and post-dredge sediment cores were evaluated on a location basis to determine if significant 

differences existed in their physical composition. Cores were aligned in vertical space for specific 

comparability in the range of the target cut line (549.2 ft, GLSD85). Vertical alignment was determined 

using pre-and post-dredge MBS data with the exception of seven individual cores described in Table 3-1. 

These specific core surface elevations were determined based on field measurements of the water column 

depth, core length, and refusal records due to less reliable MBS data in these shallow core locations.

Further physical observations of the sediment cores revealed unstratified segments at elevations near the 

cut line that appeared to be of similar coloration to the post-dredge sediment cores in the same depth 

horizon. While color and geology did not appear to be definitive in identifying the dredge cut line and 

potential sediment residuals in the post-dredge cores, one could ascertain qualitatively the general vicinity 

of the cut line due to increased organic mixing and decreased bulk density associated with the regions of 

these cores.

Physical Parameter Analysis of the Sediment. 3-D block diagrams compared pre- and post-dredge crosssections (T172 as an example transect). The results indicated that TOC and silt horizons compared well, 

were within the same elevation, and appeared to have been deposited on the post-dredge sediments during 

dredging operations forming a horizon of TOC-enriched sediments at this elevation. Further, decreasing 

bulk density values observed near the estimated dredge cut line correlated well with the above TOC and 

silt horizons.

Sediment PCB Chemistry and Data Analysis of the Core Segments. Extensive PCB congener and 

homolog analysis of segmented sediment cores collected prior to and following dredging showed that the 

pre-dredge sediment inventory had a PCB composition closely resembling Aroclor 1248. The pre-dredge 
67

surface sediments also indicated some evidence of Aroclor 1260, and some of the deep sediments had 

minor contributions of Aroclor 1268 or other highly-chlorinated PCB material, but all sediments were 

predominantly contaminated with Aroclor 1248. Though not consistent throughout the sediment sampled 

at specific depths in the ORD study area, the higher-chlorinated PCBs in the deeper-sediments were used 

as an indicator of undredged residuals compared to dredge residuals. Generally, the surface sediments 

following dredging had congener and homolog profiles more similar to the dredged inventory of 

sediment. 

The relatively uniform post-dredge surface sediment t-PCB concentrations and composition, compared to 

the pre-dredge samples, indicated that the post-dredge surface sediments generally did not originate with 

the less uniform pre-dredge sediments from the same location and elevation. In addition, the t-PCB 

concentrations and composition of the post-dredge surface were dissimilar from the pre-dredge sediments 

from the same elevation, indicating that they were not closely related. The significant increase in the tPCB concentrations of the post-dredge surface sediments, compared to the pre-dredge sediments from the 

same elevation, suggest that the post-dredge surface sediments were substantially impacted by the 

overlying contaminated sediments.

In addition, the PCB composition of the post-dredge surface sediments was essentially identical to the 

PCB composition of highly-contaminated pre-dredge sediments at a higher elevation. The post-dredge 

surface sediments appeared to be well-mixed dredge residuals originating from the most contaminated 

zones of pre-dredge sediments. Thus, most contaminated pre-dredge sediments had a significant 

influence on the concentration and composition of the post-dredge surface sediments, indicating the 

presence of significant amounts of dredge-induced residuals.

2- and 3-D PCB Modeling of Pre- and Post Dredge Areas. 2- and 3-D models of the pre- and postdredging sediment t-PCB concentrations confirmed the concentration analysis performed independently, 

namely that increased post-dredge sediment surface t-PCB concentrations were noted at particular 

elevations compared to pre-dredge sediment.

Bathymetric Surveys Prior to, During, and Following Dredging. Bathymetric surveys were used to 

observe sediment surface change during dredging in the study area and to support the calculations used to 

determine sediment inventory and the dredge-induced residual layer. MBS proved to be a good tool for 

determining the elevation from which to vertically align pre- and post-dredge sediment cores. Using daily 

surveys, slope failures were evident during the dredge activities. This approach also helped to provide 

possible mechanisms to identify the origination of dredge residuals.

Daily multi-beam bathymetric surveys were conducted in locations that had been dredged on the previous 

day. Further efforts will focus on the timing of these surveys in relationship to site-specific conditions. 

Additional analyses will be conducted to determine if these surveys may be utilized to determine dredge 

residuals immediately following dredging operations in a specific location. These types of comparisons 

will be evaluated over relatively small areas (e.g., only where the dredging took place on a specific day).

It is realized that these interpretations are sensitive to temporal effects and site-specific conditions, and 

that the time that elapsed between the dredging and the post-dredge MBS may have allowed for change in 

the sediment surface, including impacts due to erosion, compaction, sedimentation, resuspension, and 

scouring. Additional analysis of during-dredge data and continued post-dredge surveys will be used to 

monitor the long-term fate of PCBs and dredge efficiency at this site. 

Dredge Cutter Head Horizontal and Vertical Positioning. The positioning of the dredge cutter head in the 

sediment profile was utilized as the primary method to quantify the extent of dredge-induced residuals 

and to achieving both Objectives 1 and 2. J.F. Brennan, the dredge contractor, conducted dredging 
68

operations in the Ashtabula River using RTK-GPS, electronic compasses, HPR compensators, electronic 

tide gauges, HypackTM software, and trained operators. As such, both horizontal and vertical accuracies 

are documented to be reliable within 3 in. (DeRugeris and Peňa, 2004). Personal communication with 

the dredge contractor indicated that vertical dimensions should be considered accurate within 6 in. These 

levels of accuracies coupled with the inherent inaccuracies of the MBS operation yielded a potential 

vertical error of approximately 9 to 12 in., resulting in a variability range that encroached upon the 

difference between the post-dredge bathymetric surface and estimated dredge cut line in this work (i.e., 

the calculated dredge cut line surface for some areas of specific transects fell within the margin of 

potential error). The situation was further complicated by the fact that the estimate could only be 

determined for an approximate 400-ft linear reach of the river. Within the limited study area, dredgeinduced residual inventory was estimated using these data and should be applied in conjunction with other 

LOEs in determining the presence of dredge residuals.

Estimates of sediment and t-PCB removals were made for four individual transects (T175 through T172) 

and for the entire bank-to-bank area bounded by the 400-ft long section between T175 and T172. The 

individual transect estimates were developed for 5-ft wide bands of sediment in the linear (river flow) 

direction (2.5 ft on either side of each transect) and across the river from bank to bank. Based on these 

estimates, sediment and mass t-PCB removals of approximately 96% and 99%, respectively, were 

calculated. 

Using the WOE approach, it was concluded that dredge-induced residuals were variable across the ORD 

study area. Though the LOEs were generally consistent with each other, they did provide different levels 

of quantitative and qualitative measures of residuals. Additional research is required to expand the area 

considered in this report and integrate the LOEs to develop a predictive approach or a single value of 

reported dredge residuals. Applying the LOEs to develop a single reportable value for the dredge 

residuals will provide a design end-point and a means of quantifying the removal efficiency of the dredge 

operations. ORD along with it partners at GLNPO and U.S. EPA’s Office of Solid Waste and Emergency 

Response (OSWER) will continue to process data collected on ongoing and future collaborative projects 

to refine the utility of the WOE approach in estimating residuals. 
69

5.0 REFERENCES

Battelle. 2007. Quality Assurance Project Plan. Joint U.S. EPA GLNPO/NRMRL/NERL Project for 

Evaluation of Environmental Dredging for Remediating Contaminated Sediment in the Ashtabula 

River: Phases 2 and 3. Prepared for U.S. EPA on Contract No. EP-C-05-057, May.

Battelle. 2006. Quality Assurance Project Plan. Joint U.S. EPA GLNPO/NRMRL/NERL Project for 

Evaluation of Environmental Dredging for Remediating Contaminated Sediment in the Ashtabula 

River. Prepared for U.S. EPA on Contract No. EP-W-04-021, July.

DeRugeris J.A. and C.G. Peňa. 2004. How Accurate is Accurate? The History, Present State, and Future 

of Dredging Accuracies and How it Relates to Dredging the Contaminated Environment. 

Proceedings, 36th Texas A&M Dredging Seminar, Orlando, FL. 

United States Army Corps of Engineers (USACE). 2008a. “The Four Rs of Environmental Dredging: 

Resuspension, Release, Residual, and Risk,” January.

United States Army Corps of Engineers (USACE). 2008b. “Technical Guidelines for Environmental 

Dredging of Contaminated Sediments,” September.