United States
Environmental Protection
Agency
Great Lakes
National Program Office
77 West Jackson Boulevard
Chicago, Illinois 60604
EPA 905-R94-003
October 1994
EPA Assessment and
Remediation
Of Contaminated Sediments
(ARCS) Program
REMEDIATION GUIDANCE DOCUMENT
United States Areas of Concern
ARCS Priority Areas of Concern
printed on recycled paper
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ASSESSMENT AND REMEDIATION OF CONTAMINATED SEDIMENTS
(ARCS) PROGRAM
REMEDIATION GUIDANCE DOCUMENT
AWBERC LIBRARY
U.S. EPA
25 W. MARTIN HITHER KING DR.
CINCINNATI, OHIO 45268
00
Great Lakes National Program Office
U.S. Environmental Protection Agency
77 West Jackson Boulevard
Chicago, Illinois 60604-3590
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DISCLAIMER
This document has been subject to the U.S. Environmental
Protection Agency's (USEPA) peer and administrative
review, and it has been approved for publication as a
USEPA document. Mention of trade names or commercial
products does not constitute endorsement or recommenda-
tion for use by USEPA or any of the contributing authors.
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ACKNO WLEDGMENTS
This report was prepared by the Engineering/Technology Work Group (ETWG) as part
of the Assessment and Remediation of Contaminated Sediments (ARCS) Program. Dr.
Stephen Yaksich, U.S. Army Corps of Engineers (Corps) Buffalo District, was chairman
of the ETWG. Mr. Jan Miller of the Corps North Central Division coordinated the
preparation of this report and was the technical editor. Mr. Ojas Patel, of the Corps North
Central Division, contributed editing and technical support throughout the production of
the document.
The ARCS Program was managed by the U.S. Environmental Protection Agency
(USEPA), Great Lakes National Program Office (GLNPO). Mr. David Cowgill and Dr.
Marc Tuchman of GLNPO were the ARCS Program managers. Mr. Stephen Garbaciak
of GLNPO was the technical project manager and project officer for this project.
This report was drafted through the Corps support to the ARCS Program provided under
interagency agreements DW96947581-0, DW96947595-0, and DW96947629-0.
Principal authors of chapters of this document were:
Chapter 1 Jan Miller, Corps North Central Division
Chapter 2 Jan Miller
Chapter 3 Michael Palermo, Corps Waterways Experiment Station
Chapter 4 Donald Hughes, Hughes Consulting Services/Great Lakes United
Chapter 5 Paul Zappi, Corps Waterways Experiment Station
Chapter 6 Donald Hughes and James Allen, Bureau of Mines Salt Lake City
Research Center
Chapter 7 Daniel Averett, Corps Waterways Experiment Station
Chapter 8 Jan Miller
Chapter 9 Donald Hughes and Trudy Olin, Corps Waterways Experiment Station
Chapter 10 M, Pamela Hoemer, Corps Detroit District
Chapter 11 Jan Miller and Stephen Garbaciak, GLNPO
Contributors to this document included:
Ron Church, Bureau of Mines Tuscaloosa Research Center, Chapter 9
Carla Fisher, Corps Detroit District, Chapter 10
Stephen Garbaciak, Chapter 7
Tommy Myers, Corps Waterways Experiment Station, Chapters 2-9
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John Rogers, USEPA Environmental Research Laboratory-Athens, Chapters 3 and 7
H.T. (Dave) Wong, Corps Detroit District, Chapters 2-9
In addition to those provided by the principal and contributing authors, comments from
the following reviewers aided greatly in the completion of this document:
Jack Adams, Bureau of Mines Salt Lake City Research Center
Jim Brannon, Corps Waterways Experiment Station
David Conboy, Corps Buffalo District
John Cullinane, Corps Waterways Experiment Station
Linda Diez, Corps Chicago District
Bonnie Eleder, USEPA Region 5
William Fitzpatrick, Wisconsin Department of Natural Resources
Norman Francinques, Corps Waterways Experiment Station
James Galloway, Corps Detroit District
Edward Hanlon, USEPA Region 5
Phil Keillor, Wisconsin Sea Grant Institute
Thomas Kenna, Corps Buffalo District
Charles Lee, Corps Waterways Experiment Station
Thomas Murphy, National Water Research Institute, Canada
Danny Reible, Louisiana State University
Roger Santiago, Environment Canada
Paul Schroeder, Corps Waterways Experiment Station
Jay Semmler, Corps Chicago District
Frank Snitz, Corps Detroit District
Dennis Timberlake, USEPA Risk Reduction Engineering Laboratory
Mark Zappi, Corps Waterways Experiment Station
Alex Zeman, National Water Research Institute, Canada
This report was edited and produced by PTI Environmental Services for Battelle Ocean
Sciences under USEPA Contract No. 68-C2-0134.
.V
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ABSTRACT
Contaminated sediments are present in many of the waterways in the Great Lakes basin
and contribute to the impairment of the beneficial uses of these waterways and the lakes.
This document presents guidance on the planning, design, and implementation of actions
to remediate contaminated bottom sediments, and is intended to be used in conjunction
with other technical reports prepared by the ARCS Program. This guidance was
developed for application in Remedial Action Plans (RAPs) at Great Lakes Areas of
Concern (AOCs), but is generally applicable to contaminated sediments in other areas as
well.
Sediment remediation may involve one or more component technologies. In situ remedial
alternatives are somewhat limited, and generally involve a single technology such as
capping. Ex situ remedial alternatives typically require a number of component
technologies to remove, transport, pretreat, treat, and/or dispose sediments and treatment
residues. Some technologies, such as dredging and confined disposal, have been widely
used with sediments. Most pretreatment and treatment technologies were developed for
use with other media (i.e., sludges, soils, etc.) and have only been demonstrated with
contaminated sediments at bench- or pilot-scale applications.
The feasibility of applying treatment technologies to contaminated sediments is influenced
by the chemical and physical properties of the material. Bottom sediments commonly
contain a variety of contaminants at concentrations far below those at which treatment
technologies are most efficient. The physical properties of contaminated sediments, in
particular their particle size and solids/water composition, may necessitate the application
of one or more pretreatment technologies prior to the processing of the sediment through
a treatment unit.
The evaluation of sediment remedial alternatives should consider their technical
feasibility, contaminant losses and overall environmental impacts, and total project costs.
This document provides brief descriptions of available technologies, examines factors for
selecting technologies, discusses available methods to estimate contaminant losses during
remediation, and provides information about project costs. The level of detail in the
guidance provided here reflects the state of development and use of the various
technologies.
This report should be cited as follows:
U.S. Environmental Protection Agency. 1994. "ARCS Remediation Guidance Docu-
ment." EPA 905-B94-003. Great Lakes National Program Office, Chicago, IL.
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CONTENTS
Page
DISCLAIMER ii
ACKNOWLEDGMENTS iii
ABSTRACT v
LIST OF FIGURES xv
LIST OF TABLES xvii
ACRONYMS AND ABBREVIATIONS xx
GLOSSARY xxii
1. INTRODUCTION 1
APPLICABILITY OF GUIDANCE 2
2. REMEDIAL PLANNING AND DESIGN 4
DECISION-MAKING STRATEGIES 4
Corps/USEPA Sediment Management Framework 4
Superfund RI/FS Framework 6
Comparison of Strategies 7
Recommended Strategy for Sediment Remediation 7
Project Objectives 10
Project Scope 11
Screening of Technologies 12
Preliminary Design 14
Implementation 19
ESTIMATING PROJECT COSTS 22
Purpose of Cost Estimates 22
Elements of a Cost Estimate 23
Development of Cost Estimates 26
Technology Screening 26
Preliminary Design 26
Implementation 27
Sources of Information 27
VI
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ESTIMATING CONTAMINANT LOSSES 28
Contaminant Loss Pathways 29
Estimating Techniques 31
Losses During Dredging 31
Losses During Transportation 32
Losses During Treatment 32
Losses During Disposal 33
Preparing Loss Estimates 33
Level of Effort Required 33
Type of Data Required 34
REGULATORY AND LEGAL CONSIDERATIONS 34
Construction in Waterways 36
Discharge of Dredged or Fill Materials 36
Discharges of Water 37
Solid Waste Disposal 38
Hazardous and Toxic Waste Disposal 39
Atmospheric Discharges 40
Health and Safety 41
Environmental Assessments/Impact Statements 41
Other Regulations 42
3. NONREMOVAL TECHNOLOGIES 43
DESCRIPTIONS OF TECHNOLOGIES 43
In situ Capping 43
In situ Containment 44
In situ Treatment 46
In situ Chemical Treatment 48
In situ Biological Treatment 49
In situ Immobilization 49
SELECTION FACTORS 50
In situ Capping 50
Design Process for In situ Capping 52
In situ Containment 55
In situ Treatment 55
ESTIMATING COSTS 56
In situ Capping 56
In situ Containment 56
In situ Treatment 56
ESTIMATING CONTAMINANT LOSSES 56
4. REMOVAL TECHNOLOGIES 61
DESCRIPTIONS OF TECHNOLOGIES 62
Mechanical Dredges 62
Clamshell Bucket Dredges 63
Backhoes 64
VII
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Page
Hydraulic Dredges 65
Dredgeheads 66
Dredgehead Support 68
Hydraulic Pumps 68
Pipelines 71
Portable Hydraulic Dredges 71
Self-Propelled Hopper Dredges 71
Vessel or Dredgehead Positioning Systems 71
Containment Barriers 76
Monitoring 77
SELECTION FACTORS 79
Dredge Selection 79
Solids Concentration 81
Production Rate 81
Dredging Accuracy 81
Dredging Depth 82
Ability to Handle Debris 82
Other Factors 82
Containment Barriers 83
Monitoring 85
ESTIMATING COSTS 85
Mobilization/Demobilization 87
Dredge Operation 88
Containment Barriers 89
Monitoring 90
Health and Safety 90
Equipment Decontamination 90
ESTIMATING CONTAMINANT LOSSES 90
Particulate Contaminant Releases 91
Dissolved Contaminant Releases 92
Volatile Contaminant Releases 92
5. TRANSPORT TECHNOLOGIES 95
DESCRIPTIONS OF TECHNOLOGIES 96
Pipeline Transport 96
Discharge Pipeline 96
Booster Pump 98
Barge Transport 98
Barge Types 99
Tow Operations 99
Loading/Unloading Operations 101
Railcar Transport 102
Tank Railcars 102
Hopper Railcars 102
Truck Trailer Transport 104
Conveyor Transport 104
viii
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SELECTION FACTORS 107
Compatibility with Other Remedial Components 107
Equipment and Route Availability 109
Equipment Availability 109
Route Availability 110
Compatibility with Environmental Objectives 111
ESTIMATING COSTS 112
Pipeline Transport 115
Barge Transport 116
Railcar Transport 117
Truck Trailer Transport 119
Conveyor Transport 120
ESTIMATING CONTAMINANT LOSSES 121
6. PRETREATMENT TECHNOLOGIES 122
DESCRIPTIONS OF TECHNOLOGIES 123
Dewatering Technologies 123
Passive Dewatering Technologies 124
Mechanical Dewatering Technologies 125
Active Evaporative Technologies 130
Physical Separation Technologies 131
Debris Removal Technologies 131
Screens and Classifiers 135
Hydrocyclones 136
Gravity Separation 136
Froth Flotation 137
Magnetic Separation 137
SELECTION FACTORS 138
Dewatering Technologies 138
Physical Separation Technologies 141
Debris Removal Technologies 144
Screens and Classifiers 146
Hydrocyclones 146
Gravity Separation 147
Froth Flotation 148
Magnetic Separation 149
ESTIMATING COSTS 149
Dewatering Technologies 149
Passive Dewatering Technologies 149
Mechanical Dewatering Technologies 150
Evaporative Technologies 154
Physical Separation Technologies 154
Debris Removal Technologies 155
Screens and Classifiers 155
Hydrocyclones 155
Gravity Separation 156
Froth Flotation 156
Magnetic Separation 157
IX
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ESTIMATING CONTAMINANT LOSSES 157
Dewatering Technologies 157
Passive Dewatering Technologies 157
Mechanical Dewatering Technologies 157
Active Evaporative Technologies 157
Physical Separation Technologies 158
Debris Removal Technologies 158
Screens and Classifiers 158
Hydrocyclones 158
Gravity Separation 158
Froth Flotation 159
Magnetic Separation 159
7. TREATMENT TECHNOLOGIES 160
DESCRIPTIONS OF TECHNOLOGIES 161
Thermal Destruction Technologies 161
Incineration 162
Pyrolysis 163
High-Pressure Oxidation 167
Vitrification 168
Summary of Thermal Destruction Technologies 168
Thermal Desorption Technologies 168
High-Temperature Thermal Processor 170
Low-Temperature Thermal Treatment System 170
X*TRAX System 171
Desorption and Vaporization Extraction System 171
Low-Temperature Thermal Aeration System 172
Anaerobic Thermal Processor Systems 172
Summary of Thermal Desorption Technologies 172
Immobilization Technologies 172
Extraction Technologies 178
Basic Extractive Sludge Treatment Process 180
CF Systems Solvent Extraction 181
Carver-Greenfield Process 181
Soil-Washing 181
Other Extraction Processes 182
Factors Affecting Solvent Extraction Processes 182
Chemical Treatment Technologies 182
Chelation Processes 186
Dechlorination Processes 186
Oxidation Processes 187
Other Chemical Treatment Processes 188
Summary of Chemical Treatment Technologies 189
Bioremediation Technologies 189
Bioslurry Processes 196
Contained Land Treatment Systems 196
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age
Composting 198
Contained Treatment Facility 198
Summary of Bioremediation Technologies 200
SELECTION FACTORS 200
Target Contaminants 200
Sediment Characteristics 204
Implementation Factors 204
FEASIBILITY EVALUATIONS 207
Identifying Testing Needs 207
Purpose and Design of Bench-Scale Tests 208
Purpose and Design of Pilot-Scale Tests 209
Data Collection and Interpretation from Treatability Tests 211
ESTIMATING COSTS 211
Treatment Cost Components 212
Cost Elements 212
Real Estate and Contingencies 213
Factors Affecting Treatment Costs 213
Representative Treatment Costs 215
ESTIMATING CONTAMINANT LOSSES 215
Techniques for Estimating Contaminant Losses 215
Collection of Contaminant Loss Data 219
8. DISPOSAL TECHNOLOGIES 221
DESCRIPTIONS OF TECHNOLOGIES 221
Open-Water Disposal 221
Unrestricted 221
Level-Bottom Capping 223
Contained Aquatic Disposal 223
Beneficial Uses 223
Beach Nourishment 226
Land Application 226
General Construction Fill 226
Solid Waste Management 226
Confined Disposal 227
Commercial Landfills 227
Confined Disposal Facilities 228
Temporary Storage Facilities 230
SELECTION FACTORS 230
Open-Water Disposal 232
Unrestricted 232
Level-Bottom Capping 234
Contained Aquatic Disposal 235
Beneficial Uses 235
Beach Nourishment 236
Land Application 236
XI
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Page
General Construction Fill 236
Solid Waste Management 237
Confined Disposal 237
Commercial Landfills 237
Confined Disposal Facilities 238
Temporary Storage Facilities 245
ESTIMATING COSTS 245
Open-Water Disposal 245
Unrestricted 245
Level-Bottom Capping 247
Contained Aquatic Disposal 247
Beneficial Uses 248
Beach Nourishment 248
Land Application 248
General Construction Fill 248
Solid Waste Management 248
Confined Disposal 249
Commercial Landfills 249
Confined Disposal Facilities 250
Temporary Storage Facilities 253
ESTIMATING CONTAMINANT LOSSES 253
Open-Water Disposal 253
Beneficial Use 254
Confined Disposal 254
9. RESIDUE MANAGEMENT 257
WATER RESIDUES 257
SOLID RESIDUES 258
ORGANIC LIQUID AND OIL RESIDUES 258
AIR AND GASEOUS RESIDUES 258
DESCRIPTIONS OF TECHNOLOGIES 259
Water Residue Treatment 259
Suspended Solids Removal Technologies 259
Metals Removal Technologies 263
Organic Contaminant Removal Technologies 263
Solid Residues Management 265
Organic Residue Treatment 266
Air and Gaseous Residues 266
SELECTION FACTORS 267
Water Residues 267
Suspended Solids Removal 268
Metal and Organic Contaminant Removal 270
Solid Residues 272
Organic Liquid and Oil Residues 276
Air and Gaseous Residues 276
xii
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Page
COST ESTIMATING 277
Water Residues 279
Solid Residues 282
Organic Residues 282
Air and Gaseous Residues 282
CONTAMINANT LOSSES 283
Water Residues 283
Solid Residues 283
Organic Residues 283
Air and Gaseous Residues 283
10. OPERATIONAL CONSIDERATIONS 284
CONTRACTING 284
Contract Administration 284
Contract Requirements and Clauses 285
Dredging 285
General Clauses 286
WATER-BASED ACTIVITIES 287
Equipment/Limitations 287
Access 288
Authorized Crossings 288
LAND-BASED ACTIVITIES 289
Water Management 291
Management of Plants and Animals 292
Management of Plants 292
Management of Animals 292
Botulism Prevention 293
Health and Safety Requirements 294
Equipment Decontamination 294
Site Maintenance and Security 294
Site Monitoring 295
Materials Handling 295
Storage of Chemicals, Reagents, and Treatment Residues 296
Dust Management 296
Energy/Power Generation and Distribution 296
Site Closure and Post-Closure Maintenance 297
11. SUMMARY AND CONCLUSIONS 298
SUMMARY 298
Sediment Remediation Technologies 298
Nonremoval Technologies 299
Removal Technologies 299
Transport Technologies 301
XIII
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Pretreatment Technologies 301
Treatment Technologies 301
Disposal Technologies 302
Residue Management Technologies 302
Decision-Making Process 302
CONCLUSIONS 303
12. REFERENCES 307
XIV
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LIST OF FIGURES
Page
Figure 2-1. Corps/USEPA framework for evaluating dredged material
disposal alternatives. 5
Figure 2-2. Superfund framework for evaluating contaminated
sediments. 6
Figure 2-3. Approaches for evaluating potential remedial alternatives. 8
Figure 2-4. Decision-making framework for evaluating remedial
alternatives. 9
Figure 2-5. Example of a complex sediment remedial alternative. 10
Figure 2-6. Potential contaminant loss pathways from a confined
disposal facility. 30
Figure 3-1. Cross section of in situ cap used in Sheboygan River. 46
Figure 3-2. System for injecting chemicals into sediments. 48
Figure 3-3. In situ treatment application using a sheetpile caisson. 48
Figure 4-1. General types of commonly used dredges. 63
Figure 4-2. Specialized mechanical dredge buckets. 65
Figure 4-3. Typical design of a center-tension silt curtain section. 78
Figure 4-4. Typical configuration of silt curtains and screens. 86
Figure 5-1. Examples of chutes used for transporting dredged material. 108
Figure 5-2. Example sediment remedial alternative using various
transport technologies. 113
Figure 5-3. Unit costs for pipeline transport of selected dredged
material volumes. 116
Figure 5-4. Unit costs for tank barge transport of selected dredged
material volumes. 117
Figure 5-5. Unit costs for rehandling and hopper railcar transport of
selected dredged material volumes. 118
Figure 5-6. Unit costs for rehandling and truck trailer transport of
selected dredged material volumes. 119
Figure 5-7. Unit costs for rehandling and belt conveyor transport of
selected dredged material volumes. 120
Figure 6-1. Example multiunit pretreatment system. 139
Figure 6-2. Distribution of selected contaminants in Saginaw River
sediments. 145
Figure 7-1. Diagram of an incineration process. 162
Figure 7-2. Diagram of a thermal desorption process. 170
xv
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Figure 7-3. Diagram of an immobilization process. 178
Figure 7-4. Diagram of an extraction process. 179
Figure 7-5. Biodegradation potential for classes of organic compounds. 193
Figure 7-6. Diagram of an aerobic bioslurry process. 197
Figure 7-7. Diagram of a contained land treatment system. 199
Figure 8-1. Placement methods for unrestricted, open-water disposal. 224
Figure 8-2. Examples of level-bottom capping and contained aquatic
disposal. 225
Figure 8-3. Control systems for selected landfills. 229
Figure 8-4. Framework for testing and evaluation for open-water
disposal. 233
Figure 8-5. Framework for testing and evaluation for confined
disposal. 240
Figure 8-6. Surface area and dike height required for hypothetical
100,000 yd3 (76,000 m3)-capacity confined disposal
facility for mechanically dredged sediments. 242
Figure 8-7. Surface area and dike height required for hypothetical
100,000 yd3 (76,000 m3)-capacity confined disposal
facility for hydraulically dredged sediments. 244
Figure 8-8. Capital costs for a hypothetical confined disposal facility
assuming hydraulic dredging and disposal. 251
Figure 8-9. Construction contract costs (January 1993) for Great Lakes
confined disposal facilities. 252
Figure 9-1. Confined disposal facility with cross dike. 260
Figure 9-2. Cross section of a confined disposal facility dike with a
filter layer. 262
Figure 9-3. Cross section of an in-dike filter cell. 262
Figure 10-1. Hypothetical sediment remediation facility. 290
xvi
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LIST OF TABLES
Table 2-1. Technology types for sediment remediation
Table 2-2. Recommended analytical methods for measuring physical and
engineering properties of sediments
Table 2-3. General information requirements and sources for evaluation
of sediment remedial alternatives
Table 2-4. Contingency rates for cost estimates
Table 2-5. Sources of information for cost data
Table 2-6. Potentially applicable Federal environmental laws and
regulations
Table 3-1. Specialized equipment for in situ capping
Table 3-2. Selection factors for nonremoval technologies
Table 3-3. Design considerations for in situ capping
Table 3-4. Costs for in situ technologies
Table 3-5. Mechanisms of contaminant loss for nonremoval technologies
Table 4-1. Cutterhead dredges
Table 4-2. Suction dredges
Table 4-3. Hybrid dredges
Table 4-4. Pump characteristics
Table 4-5. Portable hydraulic dredges
Table 4-6. Operational characteristics of various dredges
Table 4-7. Inventory of dredging equipment stationed in the Great Lakes
Table 4-8. Availability of dredges for sediment remediation
Table 4-9. Typical unit costs for maintenance dredging
Table 4-10. Typical unit costs for containment barriers
Table 4-11. Factors that affect contaminant losses
Table 4-12. Suspended solids concentrations produced by various dredges
Table 5-1. Barge types
Table 5-2. Railcar types
Table 5-3. Truck trailer types
Table 5-4. Conveyor types
Table 5-5. Comparative analysis of transport modes
Table 6-1. Example feed material
Table 6-2. Mechanical dewatering technologies
Table 6-3. Physical separation technologies
12
16
20
25
28
35
45
51
52
57
59
67
69
70
72
75
80
83
84
89
89
91
93
100
103
105
106
114
122
127
132
xvii
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Page
Table 6-4. Advantages and disadvantages of passive and mechanical
dewatering 140
Table 6-5. Selection factors for mechanical dewatering technologies 142
Table 6-6. Operation and performance specifications for selected
physical separation technologies 143
Table 6-7. Sediment characterization for pretreatment evaluation 143
Table 6-8. Concentration criteria for gravity separation 148
Table 6-9. Unit costs for belt filter press dewatering 150
Table 6-10. Capital costs for mechanical dewatering 151
Table 6-11. Example operation and maintenance costs from municipal
wastewater treatment plants for the solid bowl centrifuge 153
Table 6-12. Example calculated cost estimates for dewatering dredged
material with a solid bowl centrifuge 153
Table 6-13. Requirements for filter presses 154
Table 6-14. Example cost estimates for separation of particle sizes for
dredged material 156
Table 7-1. Summary of conventional incineration technologies 164
Table 7-2. Summary of innovative incineration technologies 165
Table 7-3. Summary of proprietary pyrolysis technologies 166
Table 7-4. Operating conditions for high-pressure oxidation processes 167
Table 7-5. Summary of thermal destruction technologies 169
Table 7-6. Summary of thermal desorption technologies 173
Table 7-7. Factors affecting thermal desorption processes 176
Table 7-8. Factors affecting immobilization processes 177
Table 7-9. Results of bench- and pilot-scale tests of the B.E.S.T.®
process 180
Table 7-10. Summary of extraction technologies 183
Table 7-11. Factors affecting solvent extraction processes 185
Table 7-12. Suitability of organic compounds for oxidation 188
Table 7-13. Summary of chemical treatment technologies 190
Table 7-14. Characteristics that limit biodegradation processes 195
Table 7-15. Summary of bioremediation technologies 201
Table 7-16. Selection of treatment technologies based on target
contaminants 203
Table 7-17. Effects of selected sediment characteristics on the
performance of treatment technologies 205
Table 7-18. Critical factors that affect treatment process selection 206
Table 7-19. Analytical parameters for bench-scale testing performed
during the ARCS Program 210
Table 7-20. Review of significant cost factors for selected treatment
technologies 214
Table 7-21. Cost ranges and major factors affecting costs for selected
treatment technologies 216
Table 7-22. Treatment technology costs based on field demonstrations 218
XVIII
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Table 7-23. Important contaminant loss components for treatment
technologies
Table 8-1. Features of disposal technologies
Table 8-2. Requirements of disposal technologies
Table 8-3. Laboratory tests for evaluating confined disposal
Table 8-4. Unit costs for disposal technologies
Table 8-5. Unit costs for commercial landfill disposal
Table 9-1. Examples of pretreatment standards
Table 9-2. Selection factors for suspended solids removal processes
Table 9-3. Selection factors for metals removal processes
Table 9-4. Selection factors for organic contaminant removal processes
Table 9-5. Selection factors for control of air emissions during sediment
remediation
Table 9-6. Sample costs for effluent/leachate treatment systems
Table 11-1. Ranking of remediation components
Pat
220
222
231
241
246
249
269
271
273
274
278
280
300
XIX
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ACRONYMS AND ABBREVIATIONS
ADDAMS
AOC
APEG
ARCS
ATP®
BCI
B.E.S.T.®
BOD
CCI
CDF
CERCLA
CFR
COD
Corps
COSTTEP
CSRP
CTF
CZM
DAVES®
DMSO
EA
EDTA
EIS
ENR
ETWG
FAR
GLNPO
HOPE
HELP
KOH
KPEG
LaMP
MCACES
NAAQS
NEPA
NESHAPS
Automated Dredging and Disposal Alternatives Management
System
Area of Concern
alkaline metal hydroxide/polyethylene glycol
Assessment and Remediation of Contaminated Sediments
Anaerobic Thermal Processor®
Building Cost Index
Basic Extractive Sludge Treatment®
biological oxygen demand
Construction Cost Index
confined disposal facility
Comprehensive Environmental Response, Compensation and
Liability Act (Superfund)
Code of Federal Regulations
chemical oxygen demand
U.S. Army Corps of Engineers
Contaminated Sediment Treatment Technology Program
(Canada)
Contaminated Sediment Removal Program
confined treatment facility
Coastal Zone Management
Desorption and Vaporization Extraction System®
dimethyl sulfoxide
environmental assessment
ethylenediaminetetraacetic acid
environmental impact statement
Engineering News Record
Engineering/Technology Work Group
Federal Acquisition Regulation
Great Lakes National Program Office
high-density polyethylene
Hydrologic Evaluation of Landfill Performance
potassium hydroxide
potassium polyethyleneglycol
Lakewide Management Plan
Micro-Computer Aided Cost Engineering System
National Ambient Air Quality Standards
National Environmental Policy Act
National Emission Standards for Hazardous Pollutants
xx
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NOAA
NPDES
NPL
OSHA
PAH
PCB
PCDDF
PEG
PPE
QAPjP
QAMP
RAM
RAP
RCRA
ReTec
RI/FS
RREL
SARA
SEDTEC
SITE
TCLP
TEA
TSCA
U.S.C.
USAGE
USEPA
UV
VE
VISITT
Weston
WHIMS
National Oceanic and Atmospheric Administration
National Pollutant Discharge Elimination System
National Priorities List
Occupational Safety and Health Administration
polynuclear aromatic hydrocarbon
polychlorinated biphenyl
Primary Consolidation and Desiccation of Dredged Fill
polyethylene glycol
personal protective equipment
quality assurance project plan
quality assurance management plan
Risk Assessment/Modeling Work Group
Remedial Action Plan
Resource Conservation and Recovery Act
Remediation Technologies, Inc.
remedial investigation/feasibility study
Risk Reduction Engineering Laboratory
Superfund Amendments and Reauthorization Act
Sediment Treatment Technologies Database
Superfund Innovative Technology Evaluation
toxicity characteristic leaching procedure
triethylamine
Toxic Substances Control Act
United States Code
U.S. Army Corps of Engineers
U.S. Environmental Protection Agency
ultraviolet
value engineering
Vendor Information System for Innovative Treatment Tech-
nologies
Roy F. Weston, Inc.
wet, high-intensity magnetic separation
XXI
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GLOSSARY
a priori - a predictive technique for estimating losses that is also suitable for planning-
level assessments.
alternative - a combination of technologies used in series or parallel to alter the sediment
or sediment contaminants to achieve specific project objectives.
bench-scale - testing and evaluation of a treatment technology on small quantities of
sediment (several kilograms) using laboratory-based equipment not directly similar to the
full-sized processor.
capping - a disposal technology where the principle is to place contaminated sediments
on the bottom of a waterway and cover with clean sediments or fill.
component - a phase of a remedial alternative.
contaminant loss - the movement or release of a contaminant from a remediation
component into an uncontrolled environment.
demobilization - the process of removing construction equipment from a work site.
desiccation limit - a stage of drying where evaporation of any additional water from the
dredged material will effectively cease.
effluent - dilute wastewaters resulting from sediment treatment and handling; this
includes discharges, surface runoff, wastewater, etc. from a Confined disposal facility or
landfill.
feasibility study - a study that includes evaluation of all reasonable remedial alternatives,
including treatment and nontreatment options.
in situ - in its original place.
leachate - includes waters that specifically flowed through the sediment, or precipitation
that has infiltrated sediments in a confined disposal facility or landfill.
mobilization - the process of bringing construction equipment to the work site.
XXII
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moisture content - a measurement of the amount of moisture in a soil sample commonly
used in engineering and geological applications, calculated (as a percentage) as follows:
wet weight - dry weight v 1 m
dry weight
Note: Moisture content is not the complement of solids content.
passive dewatering - dewatering techniques that rely on natural evaporation and drainage
to remove moisture.
pilot-scale - when referring to the testing or demonstration of a sediment treatment
technology, the use of scaled-down but essentially similar processors and support
equipment as used in full-sized operation to treat up to several hundred cubic meters of
sediment.
pontoon - a buoyant collar used to support a pipe section.
pretreatment - a component of remediation in which sediments are modified prior to
treatment or disposal.
process option - a specific equipment item, process, or operation.
remedial investigation - the determination of the character of sediments and the extent
of contamination for a Superfund site.
solids content - a measure of the mass of dry solids/mass of whole sediment or slurry
in percent form.
vadose - the zone of soil above the groundwater level.
value engineering (VE) - a process where cost estimates are used to compare technically
equivalent features during detailed design.
water content - also called moisture content, an engineering term which is determined
as the mass of water in a sample divided by the mass of dry solids, expressed as a
percentage.
windrow - a long row of material that has been left to dewater and air dry.
xxiii
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1. INTRODUCTION
Although toxic discharges into the Great Lakes and elsewhere have been reduced in the
last 20 years, persistent contaminants in sediments continue to pose a potential risk to
human health and the environment. High concentrations of contaminants in bottom
sediments and associated adverse effects have been well documented throughout the Great
Lakes and associated connecting channels. The extent of sediment contamination and its
associated adverse effects have been the subject of considerable concern and study in the
Great Lakes community and elsewhere. For example, contaminated sediments can have
direct toxic effects on aquatic life, such as the development of cancerous tumors in
bottom-feeding fish exposed to polynuclear aromatic hydrocarbons (PAHs) in sediments.
In addition, the bioaccumulation of toxic contaminants in the food chain can also pose a
risk to humans, wildlife, and aquatic organisms. As a result, advisories against consump-
tion of fish are in place in many areas of the Great Lakes. These advisories have had a
negative economic impact on the affected areas.
To address concerns about the adverse effects of contaminated sediments in the Great
Lakes, Annex 14 of the Great Lakes Water Quality Agreement (1978) between the United
States and Canada (as amended by the 1987 Protocol) stipulates that the cooperating
parties will identify the nature and extent of sediment contamination in the Great Lakes,
develop methods to assess impacts, and evaluate the technological capability of programs
to remedy such contamination. The 1987 amendments to the Clear Water Act, in
§118(c)(3), authorized the Great Lakes National Program Office (GLNPO) to coordinate
and conduct a 5-year study and demonstration projects relating to the appropriate
treatment of toxic contaminants in bottom sediments. Five areas were specified in the Act
as requiring priority consideration in conducting demonstration projects: Saginaw Bay,
Michigan; Sheboygan Harbor, Wisconsin; Grand Calumet River, Indiana; Ashtabula River,
Ohio; and Buffalo River, New York. To fulfill the requirements of the Act, GLNPO
initiated the Assessment and Remediation of Contaminated Sediments (ARCS) Program.
In addition, the Great Lakes Critical Programs Act of 1990 amended the section, now
§118(c)(7), by extending the program by one year and specifying completion dates for
certain interim activities. ARCS is an integrated program for the development and testing
of assessment techniques and remedial action alternatives for contaminated sediments.
Information from ARCS Program activities will help address contaminated sediment
concerns in the development of Remedial Action Plans (RAPs) for all 43 Great Lakes
Areas of Concern (AOCs, as identified by the United States and Canadian governments),
as well as similar concerns in the development of Lakewide Management Plans (LaMPs).
To accomplish the ARCS Program objectives, the following work groups were estab-
lished:
• The Toxicity/Chemistry Work Group was responsible for assessing the
current nature and extent of contaminated sediments in three of the five
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Chapter 1. Introduction
priority AOCs (i.e., Buffalo River, Indiana Harbor Canal, and Saginaw
Bay) by studying the chemical, physical, and biological characteristics of
contaminated sediments, and for demonstrating cost-effective assessment
techniques that can be used at other Great Lakes AOCs and elsewhere.
Superfund activities have provided good characterizations of Ashtabula
River and Sheboygan Harbor, so the ARCS Program focused the assess-
ment activities on the other three priority AOCs.
The Risk Assessment/Modeling (RAM) Work Group was responsible for
assessing the current and future risks presented by contaminated sediments
to human and ecological receptors under various remedial alternatives
(including the no-action alternative).
The Engineering/Technology Work Group (ETWG) was responsible for
evaluating and testing available removal and remediation technologies for
contaminated sediments, for selecting promising technologies for further
testing, and for performing field demonstrations at each of the five priority
AOCs.
The Communication/Liaison Work Group was responsible for facilitating
the flow of information from the technical work groups and the overall
ARCS Program to the interested public and for providing feedback from
the public to the ARCS Program on needs, expectations, and perceived
problems.
APPLICABILITY OF GUIDANCE
This document is focused on the remediation of contaminated sediments in the Great
Lakes, and will provide guidance on the selection, design, and implementation of
sediment remediation technologies. This document has been written for use by profes-
sionals involved in the development or implementation of RAPs for Great Lakes AOCs.
This report will describe the procedures for evaluating the feasibility of remediation
technologies, testing technologies on a bench- and pilot-scale, identifying the components
of a remedial design, estimating contaminant losses, and developing cost estimates for
full-scale applications.
It is recommended that this document be used in conjunction with other reports prepared
under the ARCS Program which provide detailed information on specific technologies
(Averett et al., in prep.), contaminant loss estimation procedures (Myers et al., in prep.),
and examples of full-scale remediation plans (USEPA, in prep.b). Also, the U.S. Environ-
mental Protection Agency (USEPA) report Selecting Remediation Techniques for
Contaminated Sediment (USEPA 1993d) is recommended as a reference, particularly for
those sites involving the Superfund program.
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Chapter 1. Introduction
The decision to remediate contaminated sediments in a waterway and the selection of the
appropriate remediation technology(s) are part of a step-wise process using the guidance
developed by the three ARCS technical work groups. The ARCS Assessment Guidance
Document (USEPA 1994a) is used to characterize the chemical and toxicological
properties of bottom sediments. The guidance herein provides tools for evaluating the
feasibility of remediation technologies and estimating their costs and contaminant losses.
The ARCS Risk Assessment and Modeling Overview Document (USEPA 1993a) provides
a framework for integrating the information developed in the other two steps and
evaluating the ecological and human health risks and benefits of remedial alternatives,
including no action.
The procedures described herein can be used iteratively within a modeling and risk
assessment framework to evaluate a series of remedial alternatives (which may consist of
multiple remediation technologies) of varying costs and benefits. These procedures may
also be used to determine the most economical option for cases where the scope and
objectives for sediment remediation are already fully defined.
While the ARCS Program was specifically designed for the Great Lakes AOCs, most of
the guidance provided herein is applicable to contaminated sediments in other waterways.
However, marine and estuarine sediments may have some physicochemical differences
from freshwater sediments that may affect the applicability of some remediation
technologies. In addition, many of the technologies evaluated by the ETWG were
originally developed for media other than bottom sediments, such as soils, sludges, water,
mineral ores, and industrial waste streams. As a result, the guidance presented herein has
some applicability to the remediation of other media, although the applicability to
contaminated soils is the most direct.
-------
2. REMEDIAL PLANNING AND DESIGN
This chapter presents general procedures for developing sediment remedial alternatives,
evaluating their feasibility, estimating project costs, and estimating contaminant losses that
may occur as a result of remediation activities. Before discussing these procedures, the
decision-making strategies that may be applied to sediment remediation are examined.
The chapter also summaries the various Federal laws and regulations that may be
applicable to sediment remediation activities.
DECISION-MAKING STRATEGIES
Decision-making strategies are pathways for approaching a complex issue or problem in
a logical order or sequence. A strategy can be represented as a flow chart or framework
of activities and decisions to be made. Decision-making strategies are usually developed
for very specific applications. The management of contaminated sediments occurs for a
variety of purposes other than environmental remediation and restoration. Other purposes
include the construction and maintenance of navigation channels, the clearing of sediment
deposits from water supply intakes, construction within waterways, and the operation and
maintenance of reservoirs and impoundments for flood control, water supply, recreation,
or other purposes. There is no single decision-making strategy for the management of
contaminated sediments that suits all purposes. Two established strategies that have been
applied to the management of contaminated sediments are 1) a technical management
framework developed jointly by the U.S. Army Corps of Engineers (Corps) and USEPA
and 2) the decision framework established for Superfund projects. These two strategies
are discussed below.
Corps/USEPA Sediment Management Framework
The Corps and USEPA have developed a management framework for determining the
environmental acceptability of dredged material disposal alternatives (USACE/USEPA
1992). This framework, shown in Figure 2-1, is structured to meet the regulatory
requirements of the Clean Water Act; Marine Protection, Research and Sanctuaries Act;
and the National Environmental Policy Act (NEPA). This framework was developed for
the management of clean as well as contaminated dredged material and has evolved from
earlier decision-making strategies (Francinques et al. 1985; Lee et al. 1991).
The Corps/USEPA management framework is a tiered decision-making process. Informa-
tion about the sediments to be dredged is evaluated to determine the suitability of disposal
alternatives in order of increasing complexity. Sediments that are determined to be
4
-------
°i§
c 8 §
.20- E
| g>£
If!
•Z 5!
*|
0) <
2-5
Evaluate dredging and disposal needs |
Yes
NEPA/CWA/MPRSA
alternatives analysis adequate
C Reared }*—No
Coordinate with agencies and/or
affected public
Identify all potential
alternatives and no action
I Perform Initial screening of all potential disposal alternatives using available Information |
Alternatives
Reasonable
Yes
•C
Eliminate unreasonable
alternatives
I Retain reasonable alternatives
Existing data
adequate and timely
No ->\ Conduct Initial evaluation of sediments to be dredged |
I *
| Perform appropriate assessments for reasonable altematlve(s) |
Assess open-water
disposal alternatives
and/or
Assess confined
disposal alternatives
and/or
Assess beneficial
uses alternatives
Yes
1
^acceptable alternatives^/
| Evaluate socioeconomic, technical, management, and other environmental considerations
+
Public notice of
EA/Draft FONSI and/or
103/404 coordination
•" EA 1 Select preferred alternative | EIS ••
Notice of availability
of draft EIS/SEIS and
103/404 coordination
_L
Initiate 401 Water
Quality Certification
Select recommended
alternative
Coordinate
45 days
Initiate 401 water
quality certification
Final EIS/SEIS and 103/404 evaluation
and 401 certification and other
Coordinate
30-90 days
Signed FONSI or SOF
Project compliance with NEPAand all applicable
environmental laws and regulations
ROD
and public notice
Legend: • if at any time in the EA process, the
Federal action Is reassessed as being
significant, EIS scoping Is initiated.
Source: USACE/USEPA(1692)
CWA = Clean Water Act
EA = Environmental Assessment
EIS/SEIS » Environmental Impact Statement/
Supplement EIS
FONSI - Finding of no significant Impact
MPRSA = Marine Protection, Research and
Sanctuaries Act
NEPA = National Environmental Policy Act
ROD - Record of Decision
SOF - Statement of findings
Figure 2-1. Cprps/USEPA framework for evaluating dredged material
disposal alternatives.
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Chapter 2. Remedial Planning and Design
uncontaminated are suitable for a wider variety of disposal options, and decisions can be
made early in the evaluation process. Sediments that are contaminated require a more
extensive evaluation within the decision-making framework, have additional testing
requirements, and usually have fewer disposal options.
Corps regulations (33 CFR 230-250) require that this framework be used in the manage-
ment of dredged material from navigation projects and in the administration of the permit
program for dredged material disposal under §404 of the Clean Water Act. The Corps/
USEPA framework may be applicable to many sediment remediation projects; however,
the process does not fully address sediment treatment technologies.
Superfund RI/FS Framework
The Comprehensive Environmental Response, Compensation, and Liability Act of 1980
(CERCLA) and Superfund Amendments and Reauthorization Act of 1986 (SARA) estab-
lished and reauthorized the Superfund Program. The decision-making framework for
Superfund projects is shown in Figure 2-2 and is described in detail in USEPA (1988a).
Development
of work plan
Site
characterization
Treatability
investigations
Alternative development
and screening
Detailed analysis
of alternatives
/ Selection of \
\ alternative /
Record of
Decision
Remedial
design
Remedial
action
Source: USEPA (1988a)
Figure 2-2. Superfund framework for evaluating contaminated sediments.
The Superfund decision-making framework has two major components: the remedial
investigation and the feasibility study (RI/FS). For a Superfund site with contaminated
sediments, the remedial investigation would identify the character of the sediments and
the extent of contamination, among other information. The feasibility study would
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Chapter 2. Remedial Planning and Design
include an evaluation of all reasonable remedial alternatives, including treatment and
nontreatment options.
Comparison of Strategies
Either of the decision-making strategies discussed above might be applied to a sediment
remediation project with equal success. These strategies represent two different
approaches to the evaluation and selection of remedial alternatives. In the Superfund
strategy, remedial alternatives are evaluated in a parallel fashion (Figure 2-3) (i.e., a wide
range of possible alternatives are evaluated simultaneously, and then a selection is made
among the leading candidates). Another possible strategy is a linear or sequential
approach to evaluating disposal alternatives (Figure 2-3). Portions of the Corps/USEPA
management framework use this approach, in which, for example, disposal options are
examined in order of increasing complexity until a suitable alternative is found.
Each of these approaches has advantages and disadvantages. The advantages of the
parallel approach over the sequential approach can be summarized as follows:
• The approach has been widely used for RI/FS efforts at Superfund sites
contained in the National Priorities List (NPL) and at other non-Superfund
sites
• Most environmental consultants and regulatory agencies are more familiar
with this approach
• The approach is consistent with the requirements of NEPA
• The approach generally provides decision-makers with more than one
option for consideration.
The primary disadvantage of the parallel approach is that the evaluation of numerous
alternatives may require significant resources and time.
Projects that are on the NPL are required to follow Superfund RI/FS procedures (the
parallel approach). However, many (if not most) contaminated sediment sites, including
the majority of AOCs in the Great Lakes, are not NPL sites. For projects where
resources, funding, or time may not allow a detailed evaluation of numerous alternatives,
a hybrid approach may be considered that incorporates elements of both the parallel and
sequential approaches.
Recommended Strategy for Sediment Remediation
A simple decision-making framework for evaluating sediment remedial alternatives is
shown in Figure 2-4, and contains elements of both of the decision-making strategies
discussed above. This framework contains four major activities (boxes) and one decision
point (diamond). The first activity is to define the objectives and scope of the project.
-------
Parallel Approach
Define
objectives
and scope
1
' 1
Evaluate
Alternative
A
i
Evaluate
Alternative
B
' i
Evaluate
Alternative
C
i
* i
Evaluate
Alternative
D
p i
Evaluate
Alternative
E
r
Evaluate
Alternative
F
r
Select
alternative
Implement
selected
alternative
Sequential Approach
Evaluate
Alternative
A
Feasible >-Wo
Evaluate
Alternative
B
Yes
Evaluate
Alternative
C
-Wo-*-
Yes
Implement
selected alternative
Figure 2-3. Approaches for evaluating potential remedial alternatives.
8
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Chapter 2. Remedial Planning and Design
The next two activities involve the screening and preliminary design of remedial alter-
natives. The products of these activities are preliminary designs, cost estimates, and
estimates of contaminant loss, which are used to determine if there is a feasible alterna-
tive that meets the project objectives. If there is more than one alternative that meets
these objectives, the preferred alternative is selected. If there are no feasible alternatives
that meet the project objectives, the evaluator must return to the first activity to reevaluate
the project objectives and/or scope. The final major activity, once a preferred alternative
has been selected, is implementation. The elements of this decision-making framework
are described in the following sections, preceded by a brief definition of several relevant
terms used throughout this guidance document.
Define project
objectives and scope
Technology
screening
Preliminary
design
No
Yes
Select and implement
preferred alternative
Figure 2-4. Decision-making framework for evaluating remedial alternatives.
A sediment remedial alternative is a combination of technologies that is used in series
and/or in parallel to alter the sediments or concentrations of sediment contaminants in
order to achieve specific project objectives (discussed below). The simplest alternative
would employ a single technology, such as in situ capping. However, a more complex
alternative, as shown in Figure 2-5, may involve several different technologies and, in the
process, generate a number of separate residues or waste streams.
A component is a phase of a remedial alternative, such as removal, transport, pretreat-
ment, treatment, disposal, or residue management. Chapters 4-10 of this report discuss
the available technologies for each of these components. Nonremoval technologies (e.g.,
in situ containment), which could be considered components or complete remedial alterna-
tives, are discussed in Chapter 3.
9
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Chapter 2. Remedial Planning and Design
Removal
Transport
Air/gas residue
treatment
Contaminated
solids
Treatment
Disposal
Figure 2-5. Example of a complex sediment remedial alternative.
For each component, several technology types may be considered. For example, the
removal component could involve the use of hydraulic or mechanical dredges. A subcate-
gory of a technology type, referred to as a process option, is a specific equipment item,
process, or operation. For example, a horizontal auger dredge is a process option under
the hydraulic dredge technology type of the removal component.
Project Objectives
To simplify the use of this document, a key assumption is made that a decision to
remediate contaminated sediments in some portion(s) of a river, channel, harbor, or lake
has already been made. The reasons for that decision, although critical to the successful
remediation of the impacted area, are not essential to the use of this guidance; however,
the objectives of the remediation project will need to be established to guide the
evaluation of remedial alternatives. In addition, the scope of the remediation effort will
also have to be defined as clearly as possible.
The objectives of a sediment remediation project are usually designed to correct
site-specific environmental problems. In some cases, the objective is in the form of a
statement of the desired results to be achieved by remediation. In other cases, the
objective may be defined in the authority under which the project is initiated. For
example, the objective of the remedial action plans for the Great Lakes AOCs, as defined
in the Great Lakes Water Quality Agreement, is to restore the beneficial uses of each
area.
The objectives of a sediment remediation project can be quantitative, qualitative, or a
combination of both. In some cases, the objectives are fully quantified, such as in the
10
-------
Chapter 2. Remedial Planning and Design
case of an enforcement action where the contaminated material is localized and its source
is known (e.g., an illegal fill or spill). In such cases, the objective might be defined in
quantitative terms, such as to remove sediments exceeding a specified level of contamina-
tion, or to remove a specific quantity of sediment. In this case, the objectives and scope
of the project are virtually the same.
In many cases, however, sediment contamination is widely dispersed and the objectives
of the remediation project are more qualitative. For example, an objective might be to
reduce the human health risk caused by the consumption of fish contaminated by the
sediments, or to enhance the diversity of aquatic life that is depressed by sediment
contamination. Such objectives may become quantified by setting specific targets for
remediation (e.g., fish tissue contaminant concentration).
The objectives of a sediment remediation project may be defined through risk analysis
and modeling methods, as outlined in the ARCS Risk Assessment and Modeling Overview
Document (USEPA 1993a). These methods can be used to determine the environmental
impacts of the no action alternative as well as various remedial alternatives. When the
objectives are established by risk assessment and modeling, the ability of remedial
alternatives to meet these objectives can generally be determined using the same
procedures.
Defining the objectives of a sediment remediation project is often a very complicated
process, requiring coordination at many levels. It is not always possible to define
specific, quantifiable objectives and proceed directly to the project design and construction
stage. If there is more than one proponent for a remediation project, there may be
different objectives, not all of which may be compatible or feasible. In this case, project
objectives and scopes may need to be formulated in an iterative fashion, as shown in
Figure 2-4. This approach is especially useful when the objectives are less certain or
poorly quantified.
Project Scope
The scope of a sediment remediation project defines the extent of the remediation in
terms of both space and time. The scope is generally an extension of the project
objectives. The scope may be defined through detailed analysis, including risk assessment
and modeling. It may be defined by statute or through a negotiated or adjudicated
settlement. The scope may also be scaled to fit funding or other constraints through an
iterative process, as shown in Figure 2-4.
The spatial scope of a sediment remediation project is typically defined as an area or
reach of a river, channel, harbor, or lake. The scope may be defined in terms of sediment
depth or thickness. For example, the project objective may be to decrease the level of
contamination in fish to some threshold by reducing the exposure to sediment contami-
nants. The scope might then be defined as the creation, in a specific reach of river, of
a new sediment surface with an acceptable level of contamination. This new sediment
11
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Chapter 2. Remedial Planning and Design
surface might be created by removing existing sediments, covering them, or treating them
in place.
The objectives of a project may require that the scope include (or exclude) specific
technologies. For example, project objectives may require the removal of contaminated
sediments or the destruction of a particular contaminant. These restrictions may be
mandated by authorizing legislation or applicable regulations.
The time element of a sediment remediation project may be fixed or open ended. Restric-
tions on the time to complete a remediation project can have significant effects on its
feasibility and cost of implementation.
Screening of Technologies
Once the project objectives and scope have been defined, the next step in the decision-
making framework (Figure 2-4) is the screening of technologies. The purpose of this step
is to eliminate from further consideration technologies that are not feasible or practicable,
using available information. This is best done by first attempting to eliminate broad
categories of options and then focusing on technology types. In the simplest context,
there are two forms of remediation (containment and treatment) that can be performed on
contaminated sediments under two possible conditions (in place or excavated). These
options create the following four modes of sediment remediation:
• Containment in place
• Treatment in place
• Excavation and containment
• Excavation and treatment.
A summary of the containment and treatment technology types for these four modes of
remediation is shown in Table 2-1.
TABLE 2-1. TECHNOLOGY TYPES FOR SEDIMENT REMEDIATION
In Place Excavated
Containment Capping Beneficial use
Capping/confined aquatic disposal
Commercial landfills
Confined disposal facility
Treatment Bioremediation Chemical
Chemical Biological
Immobilization Extraction
Immobilization
Physical separation
Thermal
12
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Chapter 2. Remedial Planning and Design
The state of development and experience with these modes of remediation are quite
varied. The containment of contaminated sediments in place has been applied on a full
or demonstration scale at a few locations, including the Sheboygan River and Waukegan
Harbor Superfund sites on the Great Lakes. To date, the treatment of sediments in place
has been demonstrated in the Great Lakes on a limited scale with a few technologies, but
the results of these demonstrations are not yet available.
The containment of contaminated sediments dredged from navigation projects has been
practiced for many years, and a significant amount of engineering and design information
and guidance is available on this mode (Saucier et al. 1978; USACE 1980c, 1987b). The
treatment of excavated sediments has been demonstrated on a pilot scale at a number of
locations (including several ARCS AOCs) and implemented on a full scale at only one
site on the Great Lakes. Much of the engineering and design information about treatment
technologies for contaminated sediments has come from applications with materials other
than sediments (e.g., soils, sludges).
The evaluator should begin the screening process by considering the four modes of
sediment remediation listed in Table 2-1 in light of the objectives and scope of the
project. It is possible that one or more of these modes might be eliminated categorically
by the project objectives or scope. For example, if the project area is a navigation
channel, and must be maintained at some depth for recreational or commercial navigation,
in-place (nonremoval) options might be eliminated from further consideration. In some
cases, the project objectives may require treatment of a specific contaminant. This would
eliminate containment options (alone) from further consideration.
For the remaining modes of sediment remediation, the evaluator should next consider the
technology types available for the critical components. In-place remediation is considered
a single-component alternative. It is expected that the critical component of a remedial
alternative involving sediment removal will either be the treatment or disposal component.
In most remediation projects involving dredging, one or both of these components will
largely determine if the alternative is ultimately feasible.
The evaluator should screen technology types for the critical components based on criteria
developed by or with the project proponent. The criteria for screening remedial
alternatives under Superfund are defined (USEPA 1988a) as:
• Overall protection of human health and the environment
• Compliance with applicable and relevant regulations
• Long-term effectiveness and permanence
• Short-term effectiveness
• Reductions in toxicity, mobility, and/or volume of contaminants
• Implementability
13
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Chapter 2. Remedial Planning and Design
• Cost
• State and community acceptance.
These criteria are appropriate for an RI/FS investigation, but require more detailed
information than necessary for the screening level in the sediment remediation framework
described herein. A shortened list of screening criteria for this framework might include:
• State of development and availability
• Compatibility with sediments and contaminants
• Effectiveness
• Implementability
• Cost.
The initial screening of remediation technologies is conducted using readily available
information on technologies and project-specific information on sediment conditions. No
new data are collected. It is generally not necessary to identify specific process options
at this point. If more than one remediation technology provides the same results, it may
be possible to eliminate those technologies whose costs are greater by an order of
magnitude (Cullinane et al. 1986a). After potential technology types for critical
components have been evaluated based on the project-specific criteria, other components
needed for each complete remedial alternative need only be identified to the extent
necessary to determine the overall implementability and cost. Because of the importance
of this initial screening step, and because the level of information on technologies varies
greatly, screening should be conducted by persons experienced in such evaluations. This
guidance document and the literature review of removal, containment, and treatment
technologies prepared for the ARCS Program (Averett et al. 1990 and in prep.) may be
used as primary sources for this effort.
At the conclusion of the screening step, the evaluator should have identified a limited
number of technology types for the critical components of each remedial alternative.
With the wide diversity of sediment remediation approaches available, it is recommended
that at least one alternative be considered in the next step (preliminary design) for each
of the remediation modes determined to be consistent with the project objectives and
scope. For a majority of cases, at least one nonremoval technology, one confined disposal
option, and one or more treatment technologies should be considered.
Preliminary Design
The next step in the decision-making framework (Figure 2-4) is the development of
preliminary designs for those technologies that have passed the screening-level evaluation.
This step involves the design of a limited number of remedial alternatives in sufficient
14
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Chapter 2. Remedial Planning and Design
detail to make a selection for implementation. Some additional data on the sediments,
technologies, and locations for implementation may be collected during this step.
The preliminary design is a complex process that involves many separate decisions. A
remedial alternative may include a number of components, and the preliminary design
process must ensure that the process option selected for each component is technically
feasible, compatible with other components, and capable of meeting applicable environ-
mental regulations and project-specific constraints.
The following aspects of a sediment remedial alternative and the preliminary design
analysis are discussed briefly below:
• Material characteristics
• Materials handling
• Compatibility of components/technologies
• How to begin the design phase
• Information requirements.
Material Characteristics—Sediments are soil and water mixtures transported by
and deposited in aquatic environments. In most cases, the relative amounts of gravel,
sand, silt, clay, and organic matter in a sediment reflect the particle size characteristics
of the soil in the watershed and the sorting that occurred during transport. In a limited
number of waterways, sediment physical characteristics are more influenced by the nature
of the anthropogenic discharges to the system. Chemical contaminants in the sediments
represent only a small portion of its mass and do not, with few exceptions, significantly
alter the grain size distribution. Sediment contaminants tend to be associated more with
silt and clay fractions and less with sand and gravel fractions, because fine-grained
sediments, particularly those with significant organic carbon content, have a higher
affinity for some contaminants. In addition, sand and gravel deposits are usually present
in areas of high energy (i.e., erosion and scouring) where fine-grained sediments and
contaminants have been "washed away."
The physical and chemical characteristics of the sediments in a waterway are site specific
and may vary both laterally and vertically. Some sediment deposits have layers with
distinct physical and chemical properties. In other areas, the sediment properties may be
relatively homogeneous. The distribution of contaminants in a sediment deposit may
reflect activities over many years or decades. Evaluators should not expect to be able to
develop contaminant distribution profiles in sediments with as high a level of resolution
as for other environmental media.
Most fine-grained, contaminated sediments have been deposited in recent (geologic) time
and are not well consolidated, particularly in navigation channels that have been dredged
in the past. Sediments may have significant amounts of oversized materials and debris.
15
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Chapter 2. Remedial Planning and Design
Cobbles, gravel, coal, and other bulk commodities may have been spilled from adjacent
docks or passing ships. Bottles, cans, tires, bicycles, shopping carts, and entire car bodies
have been recovered in dredging operations.
The amount of water in sediments is one of its most important physical properties, but
there is considerable confusion about the terminology for this property (see Glossary for
definitions). This manual will refer to the solids content of a sediment and avoid using
the terms moisture or water content, which have a layman definition at odds with their
engineering definition.
Site-specific analysis of the physical and engineering properties of sediments should
always be obtained before even the most preliminary design is begun. Recommended
physical and engineering properties for analysis are shown in Table 2-2 (detailed
analytical procedures are available in USAGE 1970). Also shown are typical values for
contaminated sediments in Great Lakes tributaries.
TABLE 2-2. RECOMMENDED ANALYTICAL METHODS FOR MEASURING
PHYSICAL AND ENGINEERING PROPERTIES OF SEDIMENTS
Property Method Typical Values
Particle size distribution Sieve analysis Variable
Hydrometer analysis
Organic content Total volatile solids 5-25%
Solids content Gravimetric 40-70%
Atterburg limits Liquid limit test 20-210% moisture
Plastic limit test 10-160% moisture
Void ratio Gravimetric 0.25-0.60
Specific gravity (density) Pycnometer 2.5-2.7 g/cm3
A general rule-of-thumb is that in-place, predominantly fine-grained, contaminated
sediments have a solids content of approximately 50 percent, and that dry sediment solids
generally have a density between 2.5 and 2.7 g/cm3. Using these values, a unit of
sediment (in place) is roughly one-third solids by volume. With this solids content,
sediments are only slightly fluid, and would not readily flow. The physical properties of
a sediment can be altered by components of a remedial alternative. In some cases, this
is done intentionally to facilitate handling or treatment. In other cases, changes to
sediment physical properties by a component may increase material quantities and greatly
affect costs.
Materials Handling—Each component of a sediment remedial alternative (except
nonremoval) involves a significant amount of materials handling. The removal compo-
nent involves the excavation of the sediment from the bottom of the waterway. The
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Chapter 2. Remedial Planning and Design
transportation component involves moving excavated sediment to a location where the
material may be placed into a holding area, moved into pretreatment units, and then
carried into treatment units. In addition to the solids, there are other materials that must
be handled. For example, the residual water from dewatering, effluent, and leachate
systems must be collected and routed. In addition, some treatment technologies create
residues other than solids and water that must be handled.
One of the most important factors that affects materials handling is how the sediments are
removed. Sediments that are dredged mechanically are generally removed at or near their
in situ solids content. In contrast, hydraulic dredging entrains additional water with the
sediments and produces a slurry that may have a solids content ranging from 10-20
percent. In creating this slurry, the total material volume increases 3-6 times. This
increase in volume affects all subsequent components of the remedial alternative. For
example, the use of hydraulic dredging may eliminate certain transportation options,
increase the size requirements of a disposal area, and necessitate larger and more
sophisticated effluent treatment systems.
A common goal of most sediment remedial alternatives is to separate the solids from the
water fraction of the sediment (i.e., dewater) to the maximum extent possible. This is
done to minimize disposal costs for the solids and is a requirement of some treatment
technologies. Sediments may be dewatered through a variety of processes to a solids
content greater than 50 percent. Depending on the process used, there may be little or
no volume reduction, because water is replaced by air in the voids between the sediment
solids.
Contaminated sediments may be handled and rehandled a number of times during the
implementation of a remedial alternative. The costs and contaminant losses of each of
these handling operations may be significant.
Compatibility—The need for and compatibility of components and technologies is
determined by a number of factors, including physical requirements, material characteris-
tics, rate of processes, and logistical considerations.
The consideration of these factors is best illustrated by example. Assume that the critical
component is treatment, and the technology type being considered is solvent extraction.
Most process options of this technology have similar requirements on the feed material.
Process options could be constructed that are capable of treating 100-500 tonnes per day,
generating three residues: solids, water, and extracted organic compounds. These process
requirements will have the following effects on other components:
• The process, even with multiple units, cannot keep pace with dredging. An
area for temporary storage of sediments is necessary.
• The feed material must have a high solids content. This can be accom-
plished by restricting dredging to mechanical methods or using hydraulic
dredging followed by one or more dewatering steps.
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Chapter 2. Remedial Planning and Design
• The feed material must have oversized material (i.e., larger than 5 mm)
removed. A pretreatment component, involving screening or other
technologies, must be applied.
• The water from the treatment process and the water from sediment
dewatering must be treated and discharged. Different water treatment tech-
nologies may be needed for these residues, depending on the nature and
concentrations of contaminants present.
• Disposal methods must be identified for the solid and organic residues.
Additional treatment may be required for one or both of these residues
prior to disposal.
As illustrated above, the development of a sediment remedial alternative begins by
describing a single component and identifying its requirements and limitations. The other
components can then be identified and technology types can be considered and evaluated
for compatibility. There is no particular sequence for evaluating components. In most
cases, they must be considered concurrently.
How to Begin the Design Phase—Although subsequent chapters in this
document discuss remediation components in a logical process sequence (i.e., removal is
followed by transport, which is followed by pretreatment, etc.), the formulation of an
overall remedial alternative is not as simple as following this linear sequence to select the
optimal technology for individual components. The preliminary design phase usually
begins with the disposal component because it represents the terminal point of two
components (removal and transport) and the disposal facility location may be used to
implement other components (pretreatment, treatment, and residue treatment). Most
treatment technologies will require a disposal facility and some form of pretreatment to
support the treatment process. The disposal facility (or a secure land area) is needed for
storing, pretreatment, and handling of dredged sediments; as a base for treatment
operations; and possibly for long-term disposal of residues. While it is possible to
perform these functions at different sites, there would be increased difficulties associated
with obtaining lands for managing contaminated materials.
The availability and location of lands for handling or disposing of sediments can often
influence the selection of remediation technologies. For example, if the only available
lands for a disposal site are several kilometers from the removal site, hydraulic dredging
and pipeline transport technologies may not be feasible. Some technologies, such as
confined disposal, gravity dewatering, and land application of sediments, require a great
deal of land. In contrast, most technologies that rely on process equipment (e.g., mechan-
ical dewatering, solvent extraction, thermal treatment) are relatively compact and have
smaller land requirements.
Selection of disposal and/or treatment sites for contaminated sediments may be the most
controversial and time-consuming decision of the entire project. In fact, the public and
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Chapter 2. Remedial Planning and Design
agency acceptability of a project may be determined largely by this decision. In areas
adjacent to urban waterways, land is a limited resource. It is therefore recommended that
preliminary design begin with the identification of suitable lands. A technically feasible
alternative without a site for implementation is of limited value.
Information Requirements—Specific types of information are required to prepare
a preliminary design, evaluate its feasibility, and develop estimates of project costs and
contaminant losses. A list of the most basic information required to initiate an evaluation
of sediment remedial alternatives is provided in Table 2-3. Potential sources of historical
information are also provided.
Additional information needed to evaluate the feasibility of specific technologies and
estimate their costs and contaminant losses is discussed in subsequent chapters on each
technology type. To obtain this information may require analysis of the physical and
engineering properties of sediments, bench- or pilot-scale evaluations of treatment and/or
pretreatment technologies, laboratory tests to determine contaminant losses, laboratory
tests that simulate dewatering and residue treatment, and surveys and geotechnical
explorations of lands to be used. Some of these data collection activities may be
postponed until the detailed design phase of the project. Best professional judgment must
be exercised in making this decision.
Implementation
Ideally, more than one remedial alternative will be identified that is feasible and meets
the project objectives. In this case, the project proponent must decide which alternative
to recommend and support. The implementation of the selected remedial alternative may
involve a number of activities, including:
• Securing funding
• Development of detailed design, plans, and specifications
• Acquiring real estate and rights-of-way
• Obtaining appropriate permits
• Contract advertisement, negotiation, and award
• Construction, operation, and maintenance.
These activities are discussed briefly below.
Funding—While discussion of the sources and methods for securing funding for
implementation is beyond the scope of this guidance document, a few consequences of
the timing of funding are worth mentioning. For large remediation projects, funding may
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TABLE 2-3. GENERAL INFORMATION REQUIREMENTS AND SOURCES FOR
EVALUATION OF SEDIMENT REMEDIAL ALTERNATIVES
Information Requirement
Potential Sources
Volume and distribution of contaminated
sediments
Remedial Action Plans
USEPA or Corps district offices
State resource agencies
Sediment chemical and physical characteris-
tics
Remedial Action Plans
USEPA, Corps, or other Federal agencies
State resource agencies
Waterway bathymetry and hydraulic charac-
teristics
Navigation charts from the National Oceanic and
Atmospheric Administration, the U.S. Coast
Guard, or the Corps
Flood control/insurance studies by the Federal
Emergency Management Agency or the Corps
State resource agencies
Local harbor/port authorities
Waterway navigation use
Waterborne Commerce of the United States
(USACE 1989)
U.S. Coast Guard offices
State transportation and resource agencies
Local harbor/port authorities
Availability of local lands for use
State transportation and resource agencies
Local agencies (departments of planning, zoning,
or economic development)
Significant environmental resources to be
protected
State resource agencies
U.S. Fish and Wildlife Service
State and local environmental regulations
State resource agencies
County departments of health
Local agencies (departments of zoning, transpor-
tation, or environment)
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Chapter 2. Remedial Planning and Design
not be available all at one time but in increments, perhaps coinciding with budgetary
cycles. It may therefore be appropriate to plan the implementation of remediation in
increments. The challenge is to divide the project into increments that can "stand alone"
from environmental and engineering feasibility perspectives should the next funding
increment be delayed or unavailable. For additional information on funding opportunities
for RAP activities, the reader is referred to the series of Apogee Research, Inc. reports
on this subject (Apogee Research, Inc. 1992a,b, 1993a,b).
Detailed Des/flf/J—This step of implementation involves the detailed design of the
remedial alternative and preparation of plans and specifications for construction. During
this step, extensive data collection may be conducted, including pilot- or full-scale testing
of process equipment, detailed surveys, and geotechnical explorations of lands to be
acquired. It is not uncommon for significant changes in the project design to occur at this
stage as a result of the new data collected and the application of more sophisticated
design analytical methods. It is quite possible that the alternative recommended by the
preliminary design/feasibility study is determined to be infeasible. By the completion of
this step, virtually every aspect of the construction and operation of the remedial
alternative should be designed and thoroughly reviewed to ensure the technical accuracy
and engineering feasibility of the alternative.
Real Estate—The acquisition of real estate, easements, and rights-of-way for
project construction and operation need to be completed before a construction contract is
advertised. These acquisitions may include land for pretreatment, treatment, and disposal
operations; easements for an area to mobilize dredging equipment; or a right-of-way for
construction equipment and sediment transportation. Easements or rights-of-way may also
have to be obtained from riparian property owners along the waterway.
Permits—Applicable permits and certifications for project construction and opera-
tion should be obtained before a construction contract is advertised. A detailed discussion
of the legal and regulatory requirements for sediment remediation is provided later in this
chapter.
Confraef/n<7—Contracting mechanisms and regulations are organization-specific and
are beyond the scope of this guidance document. Parts of the remediation project, or the
entire effort, may be contracted. Superfund remedial planning and design are often
contracted separately from the remediation construction. The most common contracting
approach for remediation construction is to advertise the entire remediation project as a
single contract for a "turn-key" operation. In this case, a prime contractor would be
responsible for obtaining the necessary subcontractors with the specialized equipment or
experience required. An alternative approach is for the project proponent to purchase
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Chapter 2. Remedial Planning and Design
some of the equipment and contract for its operation. This approach may be advanta-
geous if the project is large and must be conducted in a number of operational cycles, or
if there are several project areas that can be remediated using the same equipment.
Modifications are often required in the design and operation of a project after construction
has been initiated because of changes in site conditions, changes in materials, or the
failure of a component to operate as expected. These design and operational modifica-
tions should always be coordinated with the designers and with regulatory agencies.
Construction, Operation, and Maintenance—These activities are discussed in
detail in Chapter 10.
ESTIMATING PROJECT COSTS
This section discusses the development of cost estimates for sediment remedial alterna-
tives to support the decision-making and implementation processes. There is no existing
guidance on estimating costs specifically for sediment remediation projects; however,
there is considerable guidance on estimating costs for general construction and some
guidance for hazardous waste remediation projects. This discussion presents the cost
estimating procedures used by the Corps for civil works projects and those used by the
US EPA for Superfund projects. The appropriate guidance for most sediment remediation
projects would include a combination of these approaches. Additional guidance for
estimating the costs of specific components of sediment remedial alternatives is provided
in subsequent chapters of this document.
Purpose of Cost Estimates
Project cost estimates are required during all phases of a sediment remediation project,
from initial planning, through detailed design, and during construction and operation. The
purpose of the cost estimates will change as the project progresses. During the planning
stages, cost estimates are used as a criterion for screening technologies and selecting the
preferred alternative. At the detailed design stage, cost estimates are often used to
compare technically equivalent features and identify those that may be suitable for value
engineering (VE) studies. Following detailed design and preparation of plans and
specifications, cost estimates are used to evaluate bids on project construction and
operation. During construction, cost estimates are used for scheduling payments, contract
negotiation, and dispute resolution.
The reliability of a cost estimate depends largely on the level of detail available at the
time it is prepared. It also depends on the predictability of variables and factors used to
develop the cost estimate. A thorough knowledge and understanding of the scope of work
and all components associated with site remediation is necessary for the development of
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Chapter 2. Remedial Planning and Design
a reliable cost estimate, including a clear understanding of the construction operations and
techniques that would be used.
Cost estimates should complement the decision path. For civil works projects, such as
maintenance dredging, there are two types of cost estimates in the decision-making
process: the current working estimate and the government estimate. The current working
estimate is an estimate that is prepared and updated periodically during the planning and
design of a project. The level of detail and reliability of this estimate reflect the current
state of project evaluation and design (USAGE 1980c). The current working estimate is
a total project cost estimate, which includes all reasonable costs that will be required
during project implementation (i.e., the estimated costs of construction and operation
contracts, engineering and design efforts, construction management and real estate ease-
ments, and land acquisition). The current working estimate is used as a tool to support
the decision-making process and control costs, and should be prepared with as much
accuracy as possible, so that the total project cost estimate for site remediation can be
relied upon at the earliest possible stage in the decision-making process.
For virtually all projects that are funded by the Federal government, and for most projects
funded by other governmental agencies, a government estimate or equivalent is developed
at the end of detailed design and immediately prior to the advertisement of the contract(s)
for construction and operation (USACE 1982). The government estimate is used to
evaluate construction contract bids, control negotiations, establish a pricing objective for
procurement and contracting purposes, and serve as a guide in developing progress
payment schedules. It is a detailed construction cost estimate and does not include the
other noncontract items of the current working estimate. The development of a govern-
ment estimate for a Federal project must follow the procedures and guidelines of the
Federal Acquisition Regulation (FAR) (48 CFR Chapters 1-99).
Elements of a Cost Estimate
A sediment remediation project has capital, operation, and maintenance costs. Capital
costs include expenditures that are initially incurred to develop and implement a remedial
action (e.g., dredging and transportation, construction and operation of a treatment system,
construction of a disposal facility) and major capital expenditures anticipated in future
years (e.g., capping a confined disposal facility [CDF] or decontamination of treatment
equipment) (Burgher et al. 1987). The following elements should be considered in
developing estimates of capital costs (Cullinane et al. 1986a; Burgher et al. 1987):
• Relocation costs
• Costs of lands, easements, and rights-of-way
• Land and site development costs
• Costs for buildings and services
• Equipment costs
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Chapter 2. Remedial Planning and Design
• Replacement costs
• Disposal costs
• Engineering expenses
• Construction expenses
• Legal fees, licenses, and permits
• Contingency allowances
• Startup and shakedown costs
• Costs of health and safety requirements during construction.
Operation and maintenance are post-construction activities needed to ensure the effective-
ness of a remedial action (Burgher et al. 1987). These activities might include treatment
plant operations, surface water and leachate management at a disposal facility, and
monitoring and routine maintenance at disposal sites. The following elements should be
considered in developing estimates of operation and maintenance costs (Cullinane et al.
1986a; Burgher et al. 1987):
• Operating labor costs
• Maintenance materials and labor costs
• Costs of auxiliary materials and energy
• Purchased service costs
• Administrative costs
• Insurance, taxes, and licensing costs
• Maintenance reserve and contingency fund.
The capital, operation, and maintenance cost data needed for preparing estimates are
divided into two categories, direct costs and indirect costs. The direct costs are those that
are directly attributable to a unit of work. They are generally referred to as labor,
equipment, and material/supply costs. The labor rate, equipment rate, and material/supply
quotes are readily available from many sources, some of which are discussed in later
chapters. However, production rates, hours of work, size of crew, selection of equipment
and treatment plants, and schedules are estimated largely from site-specific data.
There are some differences between the civil works and Superfund guidance for
estimating indirect costs. The Corps approach considers indirect costs, sometimes referred
to as distributed costs, to include all costs that are not directly attributable to a unit of
work, but are required for the project. These costs might include field office and home
office operations, permits, and insurance. The USEPA guidance for hazardous waste
remediation (Burgher et al. 1987) includes these costs, plus engineering expenses, startup/
shakedown costs, and contingency allowances, as indirect costs. Indirect costs are
typically estimated as a fixed percentage of the total direct costs.
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Chapter 2. Remedial Planning and Design
For preliminary cost estimates, indirect costs (as defined by the Corps) may be estimated
as 10-15 percent of direct costs. The USEPA guidance (Burgher et al. 1987) offers the
following numbers for estimating specific indirect costs:
• Engineering expenses (7-15 percent of direct capital costs)
• Legal fees, licenses, and permits (1-5 percent of total project costs)
• Startup and shakedown costs (5-20 percent of capital costs)
• Contingency allowances (15-25 percent of total capital costs).
When screening-level construction cost estimates are prepared, there are generally few
details available that would warrant a detailed analysis of direct and indirect costs; total
unit price data are often used instead. However, when a detailed construction cost
estimate is required in the later stages of design and implementation, direct and indirect
cost data are estimated separately.
The level of confidence of a cost estimate depends on the level of detail available at the
time it is prepared. One method to improve the confidence in the cost estimate is to
assess and include appropriate contingencies in the estimate. A contingency is a form of
allowance to cover unknowns, uncertainties, and/or unanticipated conditions that are not
possible to adequately evaluate from the available data. Computer software, such as
HAZRISK (Diekmann 1993) and REP/PC (Decision Sciences Corp. 1992), is available
to perform a more formal assessment and assign contingencies. If these programs are not
available, the contingency rates shown in Table 2-4 may be used instead. These rates are
empirical and are only a guide. USEPA contingency allowances for feasibility studies
(between 15 and 25 percent of capital costs) are in general agreement with the numbers
shown in Table 2-4.
TABLE 2-4 CONTINGENCY RATES FOR COST ESTIMATES
Construction Cost Range
Project Stage <$500K $500K-$1M $1M-$5M >$5M
Feasibility
Screening level 30% 25% 25% 25%
Preliminary design 25% 20% 20% 20%
Implementation
Detailed design 20% 15% 15% 15%
Plans and specifications 15% 10% 10% 10%
Contract award 5% 5% 5% 5%
Source: Adapted from USAGE (1992a).
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Chapter 2. Remedial Planning and Design
Development of Cost Estimates
Technology Screening
Cost estimates are one of the criteria used to screen remediation technologies for further
consideration. The screening cost analysis for an Rl/FS investigation involves order-of-
magnitude costs to eliminate alternatives with costs that are 10 times or higher than costs
for other alternatives (Burgher et al. 1987). The accuracy of costs at the screening level
for RI/FS investigations should be between +100 and -50 percent (Burgher et al. 1987).
At the screening level, the project cost analysis is very crude and limited to available
information on the sediments, site conditions, and technologies being considered. Because
the level of detail is minimal at this phase, historical data and parameters of similar past
projects are recommended for the development of the cost estimate. Substantial amounts
of historical cost data for some components of sediment remediation (i.e., removal,
transport, disposal, and residue management) are available and are summarized in later
chapters of this document. The USEPA has developed a Remedial Action Cost Compen-
dium (Yang et al. 1987) that shows the range of actual costs at Superfund projects.
Historical cost data on the pretreatment and treatment components are very limited, and
in some cases the only data available are projections made by technology vendors based
on bench- or pilot-scale applications. Cost projections for technologies that do not
already have full-scale equipment with some operating history should be approached with
a certain amount of skepticism. One of the major factors in the cost of many innovative
treatment technologies is the investment required for the development, scaleup,
construction, and testing of full-scale equipment. The amortization of these development
costs greatly affects their unit costs and the degree of uncertainty associated with those
costs. Very few remediation projects are able to bear these development costs alone, and
few companies are willing to make this investment unless there is a clear indication that
there will be a dependable market for the technology at several remediation sites. One
potential solution to this handicap is for interests from several AOCs having similar
sediment contamination problems to join forces in financing the development or
acquisition of a remediation technology.
Preliminary Design
During the preliminary design phase, a limited number of remedial alternatives are
evaluated in sufficient detail to make a selection for implementation. This phase is
comparable to the feasibility study for Superfund projects. The preliminary design should
contain sufficient engineering and design information that could readily lead into the next
phase (the detailed design). The cost estimate should be prepared based on the latest
information available and should include all reasonable costs required in the imple-
mentation phase. The estimate should incorporate costs for additional engineering and
design, real estate easements and land acquisition, and construction costs. This cost
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Chapter 2. Remedial Planning and Design
estimate will serve as a baseline current working estimate for project management through
the implementation phase.
The process for evaluating costs during a Superfund feasibility study includes the
following steps (Burgher et al. 1987):
• Estimation of costs
• Present worth analysis
• Sensitivity analysis
• Input to alternatives analysis.
The accuracy of cost estimates for feasibility studies for Superfund projects should be
within the range of +50 to -30 percent (Burgher et al. 1987).
Implementation
This phase should include preparation of a detailed design and the plans and specifica-
tions for contracting the construction and operation of the remedial alternative. During
the detailed design, cost estimates can be used to compare technically equivalent features
in a process known as VE. VE is directed at analyzing the function of construction,
equipment, and supplies for the purpose of achieving these functions at reduced life-cycle
cost without sacrificing quality, aesthetics, or operations and maintenance capability
(USAGE 1987f).
During the development of plans and specifications, a detailed government estimate is
prepared. This government estimate is used to evaluate bids on project construction and
operation contracts. Bids are evaluated for balance as well as dollar amount. Corps
regulations for civil works projects will not allow a contract award if the low bid exceeds
the government estimate by more than 25 percent. During construction, cost estimates
are used for scheduling payments, contract negotiations, and dispute resolution.
Sources of Information
The accuracy of a cost estimate depends on the reliability of the information used in its
development. For some of the components of a sediment remedial alternative there are
a large number of sources of cost data available. A list of a few sources that could be
consulted for cost estimates is shown in Table 2-5.
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Chapter 2. Remedial Planning and Design
TABLE 2-5. SOURCES OF INFORMATION FOR COST DATA
Source Type of Information
R.S. Means Cost Data Unit costs for various construction activities
Dodge Guide Unit costs for various construction activities
Corps Unit Price Books Unit costs for various construction activities
Marshall Stevens Index Treatment plant and equipment costs and cost index
Chemical Engineering Treatment plant and equipment costs
Engineering News Record Construction cost index for updating construction
capital costs
Civil Works Construction Cost Index System Regional adjustment factors for construction costs
U.S. Department of Energy Energy costs, including regional differences
U.S. Department of Labor Labor costs, including regional differences
Federal Emergency Management Admin- Relocation costs
istration
Construction costs may vary significantly from one region of the country to another. To
convert approximate costs, area adjustment factors may be applied. Some Federal
agencies, such as the U.S. Departments of Labor and Energy, maintain regional cost
information. The Corps maintains a Civil Works Construction Cost Index System
(CWCCIS), which may be used as a guide for regional construction cost adjustments.
Several computer software programs have been developed for cost estimating and are in
general use. The Corps has developed a Micro-Computer Aided Cost Engineering System
(MCACES) that is being used worldwide for construction cost engineering. This software
is available commercially from Building Systems Design (1992). The U.S. Department
of Energy has developed a summary of available cost estimating software applicable to
environmental remediation projects (Youngblood and Booth 1992), and the reader is
referred to this document for more information on how to obtain these software packages.
Software has been developed by or for the USEPA (CORA and RACES), the U.S. Air
Force (ENVEST and RACER), and the U.S. Department of Energy (FAST, MEPAS, and
RAAS). If computer software is not available, manual estimating techniques are readily
available (USAGE 1980c, 1982).
Cost information provided on sediment remediation technologies in this document has
been adjusted to January 1993 price levels using the indices in the Engineering News
Record (ENR).
ESTIMATING CONTAMINANT LOSSES
No remedial alternative for contaminated sediments is without some environmental
consequence. The balancing of environmental benefit vs. cost is a critical part of the
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Chapter 2. Remedial Planning and Design
evaluation of sediment remedial alternatives. Ideally, the alternative that maximizes this
benefit:cost relationship would be selected. However, the costs, as well as social, legal,
and political considerations, all have important roles in the final decision.
Environmental damages and benefits are not easy to quantify in measures that are readily
comparable. Risk assessment is one of the methods to quantify the environmental effects
of a project or condition. Risk assessment procedures determine the potential harm
caused by exposing humans or other organisms to contaminants. Contaminant exposures
may be measured directly or predicted using mathematical models, and may occur through
various media (e.g., air, water, solids, biota) and exposure routes (e.g., inhalation,
ingestion, dermal contact). A detailed discussion of risk assessment and modeling in
relation to contaminated sediment remediation is provided in the ARCS Risk Assessment
and Modeling Overview Document (USEPA 1993a).
To evaluate risks to human health or the environment, the exposure conditions must be
fully characterized. To use mathematical models to predict the exposure conditions, the
loadings of contaminants must be estimated and used as input to the model(s). The losses
of contaminants from sediment remedial alternatives may be estimated through a number
of techniques that were evaluated by the ARCS Program.
Contaminant Loss Pathways
Contaminant loss is the movement or release of a contaminant from a remediation compo-
nent into an uncontrolled environment. Examples of loss include spillage or leakage
during dredging and transport, seepage from a capped in situ site or from a CDF, and
residual contamination in the treated discharges from a disposal facility or sediment
treatment unit. Contaminants that remain within a controlled area or process stream, or
are modified or destroyed by a process, are not considered losses. The term "loss" is
reserved for the uncontrollable or unintentional discharge of contaminants.
Contaminant loss can occur during each component of a sediment remedial alternative
through one or more pathways. For example, the potential pathways for contaminant loss
from a CDF include surface runoff, effluent, seepage, leachate, volatilization, dust, and
uptake by plants and animals (Figure 2-6). The contaminant loss from a component is
the sum of the individual losses through the various pathways, and the contaminant loss
from a remedial alternative is the sum of the losses from each component.
The magnitude of contaminant loss may vary greatly between remedial components and
pathways and is influenced by the type of contaminant being considered. The losses
through one pathway may be thousands or hundreds of thousands of times greater than
the losses through other pathways in the same component. The losses through some path-
ways or from some components may be considered insignificant for specific evaluations.
As a result, it is worthwhile to assess the relative importance of different pathways of
contaminant loss before proceeding with detailed estimates. The contaminant losses
discussed in this document are not meant to be the final determinant in the complete
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Plant uptake
Volatilization
Precipitation
Surface
Runoff
Infiltration
Leachate
Figure 2-6. Potential contaminant loss pathways from a confined disposal facility.
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Chapter 2. Remedial Planning and Design
environmental efficacy of a particular sediment remedial alternative, however. The losses
are intended to be used as loadings in the implementation of a contaminant fate model
as described in the ARCS Risk Assessment and Modeling Overview Document (USEPA
1993a).
Estimating Techniques
A detailed investigation of contaminant losses from sediment remediation components was
conducted for the ARCS Program (Myers et al., in prep.). This study identified
contaminant migration pathways, examined existing predictive techniques for estimating
contaminant losses, and evaluated their applicability and reliability. This study (Myers
et al., in prep.) should be used as the primary reference for developing contaminant
loss estimates for sediment remedial alternatives. Key points from this study are
summarized below.
Predictive techniques for estimating contaminant losses generally fall into one of two
categories: a priori techniques and techniques based on pathway-specific laboratory test-
ing. A priori techniques are suitable for planning-level assessments. Techniques that use
pathway-specific test data provide state-of-the-art loss estimates.
The state of development of predictive techniques for estimating contaminant losses from
remediation components varies with the component and the loss pathways. For some
remediation components there are no pathway-specific tests available. In these cases, a
priori techniques may be the only techniques available; however, a priori techniques are
not always available for all pathways of all components.
The confidence and accuracy of the contaminant loss estimates depend on the state of
development and the amount of field verification data available. In some cases, there
may be a substantial amount of field data available, but predictive techniques are not
designed to produce data that are directly comparable to field data. In this case,
confidence is low and accuracy is unknown. For the prediction of contaminant losses
during dredging, field data on turbidity and suspended solids downstream of dredging
operations may be available; however, predictive techniques are used to estimate
contaminant flux in the water column at the point of dredging. In some cases, predictive
techniques (e.g., prediction of leachate losses) have a sound theoretical basis, but few
field verification data exist. In this case, confidence is high and accuracy is unknown.
Losses During Dredging
Predictive techniques for sediment losses during hydraulic and mechanical dredging are
available for conventional dredging equipment. Predictive techniques are not available
for innovative dredging equipment options. The available predictive techniques provide
estimates of sediment losses in terms of mass loss per time at the point of dredging.
Exposure concentrations are not estimated. To estimate exposure concentrations, the
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Chapter 2. Remedial Planning and Design
predicted fluxes of sediments and the associated chemical contaminants must be
incorporated into water quality or exposure assessment models.
Techniques for estimating contaminant losses during dredging are still in the early
development stage. Techniques have been proposed, but field validation data are scarce.
The available techniques are inherently a priori, although laboratory tests have been
considered. Efforts are ongoing in the Great Lakes to develop predictive techniques for
estimating contaminant losses during dredging, at the point of dredging. As previously
discussed, confidence is low for the prediction of losses during dredging, and accuracy
is unknown.
Losses During Transportation
Techniques for estimating losses of sediments and the associated chemical contaminants
during the transportation of dredged material are not available for most transportation
modes. Pipeline breaks, scow spillage, and truck accidents can be expected to occur, but
the frequency of such occurrences associated with dredged material transportation has not
been documented, and there has been little effort to quantify the associated losses.
Predictive techniques for losses from scows due to volatilization of contaminants are
available, but have not been field verified.
Losses During Treatment
The limited database for treatment of contaminated sediments and the strong influence of
sediment characteristics on treatability preclude the use of a priori loss estimates for most
treatment technologies. Laboratory techniques are available for estimating losses for most
treatment technologies. Most treatment technologies will generate waste streams that,
unless decontaminated, constitute a loss pathway. Even destruction technologies will have
some estimable loss because no treatment process is perfect. Treatment process losses
can be in the form of contaminated solid residuals requiring disposal (with attendant
losses) or in the form of contaminated fluids. Fluid losses include gaseous emissions,
discharged process wastewater, and other liquid releases.
Predictive techniques for contaminant losses during treatment are based on a materials
balance of the process treatment train. A process flow chart should identify waste streams
through which contaminants can escape treatment or control. However, detailed
information is not usually available until after treatability studies have been completed.
The technical basis for using data from treatability studies to estimate contaminant losses
is well developed, but there are few verification data for full-scale dredged material
treatment processes.
Loss estimates based on treatability studies are anticipated to be reliable and accurate.
A high degree of confidence is expected for those treatability studies with good materials
balance. If the materials balance is poor, then confidence will be low.
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Chapter 2. Remedial Planning and Design
Losses During Disposal
Predictive techniques are available for most of the key pathways by which contaminants
are lost from CDFs and confined aquatic disposal sites. Predictive techniques vary in
their stage of development, depending on the disposal alternative and pathway. A priori
techniques are available for estimating losses from confined aquatic disposal sites;
however, there are few field verification data for these techniques. A priori and
test-based techniques for estimating effluent losses during hydraulic filling of confined
disposal sites are well developed, but techniques for estimating losses during mechanical
disposal at in-water and nearshore CDFs are more crude and have only been conducted
at a few sites (USAGE Chicago District 1986).
Scientifically sound a priori and test-based techniques are available for estimating losses
from CDFs by leaching. Predictive techniques for leachate loss have not been field
verified. Well-developed, test-based techniques are available for estimating runoff losses
at CDFs, but there are no a priori predictive techniques available for runoff. The only
predictive techniques available for estimating volatile losses from CDFs are a priori
techniques. Estimation techniques for volatile losses from dredged material are available,
but have not been field verified.
Confidence and accuracy for a priori loss estimates from CDFs and confined aquatic
disposal sites are low. Confidence and accuracy for test-based loss estimates vary with
the stage of development of the test and interpretation procedures. Confidence and
accuracy are high for estimating effluent loss during hydraulic filling of CDFs.
Confidence is high for test-based estimates of leachate losses, but accuracy is unknown.
Confidence and accuracy are high for estimation of test-based runoff loss.
Preparing Loss Estimates
Level of Effort Required
A priori techniques require less effort than the test-based techniques for estimating
contaminant losses. The computational frameworks for both types of techniques are
similar so that computations performed using a priori techniques usually do not have to
be reconstructed for the test-based techniques. The major difference in effort is the time
and money required for test-based loss estimates. A priori loss estimates can be used to
guide resource allocation for pathway- and remediation component-specific testing.
Most a priori techniques can be implemented using spreadsheet software for desktop
computers. Some aspects of leachate loss estimation require running the Hydrologic
Evaluation of Landfill Performance (HELP) computer model (Schiroeder et al. 1984).
This model runs on desktop computers and is required for both a priori and test-based
estimates of leachate losses. Obtaining appropriate coefficients for the a priori equations
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Chapter 2. Remedial Planning and Design
can be a significant effort. A standardized default database for model coefficients is not
currently available.
Test-based predictive techniques require substantial time and money if a full suite of tests
are conducted. Resource requirements are relatively small for some key pathways such
as effluent losses. Other pathways, such as runoff losses, currently require a large volume
of sediments and the tests take several months to complete.
Type of Data Required
The minimum data required for most a priori techniques are bulk sediment chemistry and
project-specific design information. The project-specific design information needs are
numerous, but this information is usually available at the preliminary design phase. For
CDFs, for example, a dredging schedule, dredge production rates, site geometry,
foundation conditions, dike design, disposal mode (hydraulic or mechanical), and other
similar types of information are needed.
For remedial alternatives involving treatment, data from bench- or pilot-scale treatability
studies are needed. If sediment-specific treatability data are not available, the data for a
similar sediment and treatment process can be used. Pilot-scale data should be
considered, if available. Information on anticipated processing rates and pretreatment
and/or storage facility designs will also be needed.
Protocols for pathway-specific tests identify data requirements. A complete program for
estimating contaminant losses for an array of alternatives and components should be
carefully planned and coordinated to reduce replication of effort and ensure comparability
among the various pathways evaluated.
REGULATORY AND LEGAL CONSIDERATIONS
When conducting a sediment remediation project, it may be necessary to obtain various
permits or certifications as required by existing environmental laws and regulations, from
appropriate Federal, State, or local agencies. For example, permits may be required for
specific remedial activities or for discharges that may result from these activities. A
summary of activities and discharges that may require a permit or other form of
authorization under Federal law are listed in Table 2-6.
The discussion that follpws focuses on Federal environmental regulations. For some of
these regulations, the permitting and enforcement authority has been transferred or
delegated to the State. In addition, many states have other laws and regulations that may
be applicable to one or more sediment remediation activities. The regulations discussed
herein and listed in Table 2-6 are not all inclusive, and the proponent of a sediment
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TABLE 2-6. POTENTIALLY APPLICABLE FEDERAL ENVIRONMENTAL LAWS
AND REGULATIONS
Statute
Federal
Regulation
Lead Agency
Potentially Applicable Activities
Clean Air Act (44 U.S.C. §7401
et. seq.)
40 CFR 52-61
USEPA3
Emissions from pretreatment and
treatment processes
Clean Water Act (33 U.S.C.
§1251 et. seq.)
Section 307
Section 401
Section 402
40 CFR 403
40 CFR 121
40 CFR 122
USEPA3
State
USEPA3
Discharges to municipal sewer
Dredged and fill discharges
Discharges from pretreatment and
treatment processes; storm water dis-
charges from construction
Section 404
33 CFR 320-330
Corps3
Dredged and fill discharges to waters
of the United States.
Coastal Zone Management Act
(16 U.S.C. §1455bet. seq.)
15 CFR 923
State
Dredging, in situ capping, and any
construction in the coastal zone
40 CFR 300-373
USEPA
Comprehensive Environmental
Response, Compensation and
Liability Act, and Superfund Am-
endments and Reauthorization
Act (42 U.S.C. §9601 et. seq.)
National Environmental Policy Act 40 CFR 1 500-1 508 USEPAb
(42 U.S.C. §4321 et. seq.)
Any construction in or near a
Superfund site
Any Federal action significantly
affecting the human environment, in-
cluding Federally funded remediation
and actions requiring a Federal permit
Occupational Safety and Health
Act
29 CFR 1910
U.S. Department
of Labor
Any remedial construction activities
Resource Conservation and Re-
covery Act (42 U.S.C. §6901 et.
seq.)
40 CFR 257-258, USEPA3
260-268
Storage, treatment, and disposal of
any hazardous materials
Rivers and Harbors Act of 1899
Section 10(33 U.S.C. §401 et.
seq.)
33 CFR 403
Corps
Construction or obstruction in a navi-
gable waterway of the United States
Toxic Substances Control Act
(15 U.S.C. §2601 et. seq.)
40 CFR 761
USEPA
Transport, handling, and disposal of
polychlorinated biphenyl-contamina-
ted sediments or residues
'Program responsibility may be delegated to the State.
b Document preparation is the responsibility of the proponent(s) or permitting agency.
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Chapter 2. Remedial Planning and Design
remediation project should ensure that the requirements of all applicable Federal, State,
and local laws and regulations are addressed.
Construction in Waterways
Any structure or work that affects the course, capacity, or condition of a navigable water
of the United States must be permitted under §10 of the Rivers and Harbors Act of 1899
(33 U.S.C. 403). This permit program is managed by the Corps, and the regulations
addressing this program are contained in 33 CFR Parts 320-330 (Regulatory Programs of
the Corps of Engineers). Activities associated with a particular sediment remedial
alternative that would likely require a §10 permit include the placement of an in situ cap
on contaminated sediments in a waterway, dredging activities, the mooring of vessels, and
the construction of any structure in the waterway. Permits issued under the authority of
§10 of the Rivers and Harbors Act of 1899 and §404 of the Clean Water Act (see below)
are typically handled concurrently by Corps district offices. The Corps coordinates §10
permits with the U.S. Coast Guard, which issues a notice to navigation of when and
where the construction activities will take place.
Any development activities in an approved State coastal zone must be consistent to the
maximum extent practicable with the State plan developed under the Coastal Zone
Management Act of 1972 (16 U.S.C. §1455b et. seq.). Federal funds for Coastal Zone
Management (CZM) plan development are administered by the National Oceanic and
Atmospheric Administration (NOAA). Activities associated with a sediment remediation
project likely to require a CZM consistency determination by the State include dredging,
in situ capping, and construction and operation in the coastal zone of facilities for
sediment rehandling, treatment, and disposal. Four Great Lakes states (Michigan, New
York, Pennsylvania, and Wisconsin) have approved CZM plans.
Discharge of Dredged or Fill Materials
The disposal of dredged or fill materials to waters of the United States is regulated under
the Clean Water Act (33 U.S.C. §1251 et. seq.). Clean Water Act §404 in particular
designates the Corps as the lead Federal agency in the regulation of dredged and fill
discharges, using guidelines developed by the USEPA in conjunction with the Corps.
Regulations addressing this permit program are again contained in 33 CFR Parts 320-330
(Regulatory Programs of the Corps of Engineers). Activities associated with a particular
sediment remedial alternative that would likely require a permit under Clean Water Act
§404 authority include the placement of an in situ cap on contaminated sediments in a
waterway or wetland, the discharge of any dredged sediments or treatment residues into
a waterway or wetland, and the discharge of effluent, runoff, or leachate from a disposal
facility for sediments.
As noted above, Clean Water Act §404 permits for the disposal of dredged or fill
materials into waters of the United States are issued through Corps district offices. Some
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Chapter 2. Remedial Planning and Design
nationwide and regional permits have been issued to cover specific types of discharges.
Only one state (Michigan) has been delegated Clean Water Act §404 permitting
responsibilities as provided under Clean Water Act §404(g). Permit applicants must
provide sufficient information for the permitting office to complete an evaluation of the
discharge under the authority of §404(b)(l) of the Clean Water Act. The Clean Water
Act §404(b)(l) evaluation considers the overall impacts of the proposed discharge,
including ecological, social, and economic effects.
Finally, Clean Water Act §401 authorizes states to issue a "water-quality certification"
for proposed dredged and fill disposal activities. Issuance of this certification indicates
that the proposed dredged or fill disposal will not violate State water quality standards,
after allowance for dilution and dispersion of contaminants. A dredged or fill discharge
§404 permit may not be processed without a Clean Water Act §401 certification or
waiver.
Discharges of Water
Water discharges resulting from a sediment remedial alternative may be regulated under
various sections of the Clean Water Act. The administration of regulations developed
pursuant to the Clean Water Act is the responsibility of the USEPA, the Corps, or the
State, depending on the applicable section of the act.
Clean Water Act §307 directed the USEPA to develop pretreatment standards for
industries. The National Pretreatment Program was subsequently established to ensure
that major industrial and commercial users of municipal sewer systems pretreat their
discharges so that the discharges from publicly owned treatment works remain in
compliance with their discharge permits. Technology-based standards were developed by
the USEPA (40 CFR 403) to be implemented at municipal publicly owned treatment
works.
The responsibility for the administration of the pretreatment program has been delegated
by the USEPA to four of the Great Lakes states (Michigan, Minnesota, Ohio, and
Wisconsin). Local municipalities and sanitary districts are responsible for the manage-
ment of pretreatment programs for their wastewater systems and must issue pretreatment
permits to significant users. One activity associated with a sediment remedial alternative
that could require a pretreatment permit would be a discharge of water from a sediment
disposal facility or treatment system into a municipal wastewater treatment facility
through a sanitary sewer.
Clean Water Act §§404 and 401 apply to the discharge of effluent,-runoff, or leachate
from a disposal facility for sediments. These regulations were discussed above.
Clean Water Act §402 is the National Pollutant Discharge Elimination System (NPDES).
This is the principal program for the regulation of point-source discharges of pollutants
and is managed by the USEPA. The responsibility for NPDES permitting has been
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Chapter 2. Remedial Planning and Design
delegated by the USEPA to all of the Great Lakes states (Illinois, Indiana, Michigan,
Minnesota, New York, Ohio, Pennsylvania, and Wisconsin). Activities associated with
a sediment remedial alternative that would likely require an NPDES permit include a con-
tinuous point-source discharge of water from a sediment treatment system and the storm
water discharge from a sediment disposal or treatment site. As discussed above, the
discharge of water from a dredged material disposal facility is regulated under Clean
Water Act §§404 and 401. The USEPA Region 5 has stated that a point-source discharge
of leachate from a CDF should be regulated under the NPDES program.
Storm water discharges from disposal and treatment sites during initial construction would
also be regulated under the NPDES program. Most states have general permits that may
cover these construction activities. The storm water runoff inside an operating CDF or
treatment site would most likely have to be captured, routed, and treated before discharge.
This runoff might be combined with other water discharges from pretreatment and
treatment processes or effluent or leachate collection. In this case, the storm water
discharge would be regulated as part of these other discharges under the NPDES program
or §§404 or 401 of the Clean Water Act.
Solid Waste Disposal
The Resource Conservation and Recovery Act (RCRA; 42 U.S.C. §6901 et. seq.) broadly
defines solid waste as:
.. . any garbage, refuse, sludge from a waste treatment plant, water supply plant
or air pollution control facility and other discarded material, including solid,
liquid, semisolid, or contained gaseous material resulting from industrial,
commercial, mining, and agricultural operations, and from community activities,
but does not include solid or dissolved material in domestic sewage, or solid or
dissolved materials in irrigation return flows or industrial discharges which are
point sources subject to permits under §402 of the Federal Water Pollution
Control Act, or source, special nuclear, or byproduct material as defined by the
Atomic Energy Act of 1954, as amended.
Subtitle D of RCRA authorizes states to issue solid waste disposal permits. As illustrated
above, the RCRA definition of solid waste is very general, and few states have regulations
that specifically identify sediments or dredged material as a category or class of solid
waste. The Corps has a policy that dredged material is not a solid waste and is not
subject to solid waste regulations. However, some Federal and State agencies do not
concur with this policy. As a result, the application of solid waste regulations to
contaminated sediments is still open to question.
A technical framework for designing disposal facilities for dredged material has been
developed jointly by the Corps and USEPA and is discussed in Chapter 8 (USAGE/
USEPA 1992). This framework identifies potential pathways for contaminant loss and
migration and uses testing procedures developed specifically for sediments to evaluate the
contaminant losses or impacts through these pathways. Environmental controls, such as
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Chapter 2. Remedial Planning and Design
barriers, caps/covers, and leachate collection systems are used only when sediment-
specific testing and site-specific evaluation demonstrate a need. This strategy is quite
different from the minimum technology approach that is used under RCRA and most
State solid waste regulations. The minimum facility requirements for solid waste disposal
identified in RCRA (40 CFR 257-258) were structured for municipal solid waste. These
requirements include a minimum design for liners, caps, and leachate collection. They
also include restrictions on disposal of liquids in landfills that may be difficult to apply
directly to dredged sediments containing substantial amounts of water.
Because of the uncertainty about the applicability of State solid waste regulations to
contaminated sediments, most disposal site designs will reflect a compromise between a
sediment-specific design and the design dictated by a State's municipal solid waste
requirements.
Hazardous and Toxic Waste Disposal
RCRA and the Toxic Substances Control Act (TSCA; 15 U.S.C §2601 et. seq.) provide
for the regulation of materials that are classified as hazardous and toxic, respectively.
Regulations developed pursuant to RCRA address the storage, treatment, and disposal of
hazardous wastes (40 CFR 260-270). The USEPA is responsible for the administration
of RCRA and has established three lists of hazardous wastes under Subtitle C. If a waste
is not listed as hazardous, it may still be covered by RCRA if it exhibits one of four
hazardous waste characteristics: ignitability, corrosivity, reactivity, or toxicity.
A low percentage of contaminated sediments will meet the regulatory definitions of
hazardous or toxic materials. In some remediation projects, isolated areas or "hot spots"
of sediments containing TSCA- or RCRA-regulated materials may be located and require
different handling than the remainder of the less-contaminated sediments. Contaminated
sediments, except for sediments and sludges from specific industrial processes, are not
listed as hazardous wastes under RCRA. The USEPA policy is that sediments containing
one or more listed hazardous wastes require handling as a hazardous waste. The Corps
policy is that dredged material is not a solid waste and is not subject to RCRA regulat-
ions. As a result of this policy disagreement, there is some confusion about the
application of RCRA regulations to contaminated sediments. The USEPA Region 5 and
the Corps are currently preparing guidance for the construction of disposal facilities for
contaminated sediments that will address the regulatory intent of RCRA and TSCA.
Sediment remedial activities that might require a RCRA permit include the storage,
treatment, and disposal of contaminated sediments (or the residue from a pretreatment or
treatment process) that are defined or characterized as hazardous under RCRA. The
owner/operator of a facility that generates RCRA-hazardous materials must obtain a
permit. States are delegated RCRA permitting authority by the USEPA in a piecemeal
fashion as the State regulations are adopted. Some Great Lakes states do not have the
authority to issue RCRA corrective actions.
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Chapter 2. Remedial Planning and Design
RCRA and its amendments include a ban on the land disposal of specific wastes
(including dioxin), requiring adequate treatment prior to land disposal. The design and
operating requirements for a RCRA-hazardous landfill are defined in 40 CFR 264,
Subpart N and in USEPA (1989d).
TSCA regulates the manufacture, use, distribution, handling, and disposal of a very
limited number of materials defined as toxic substances. In effect, this Act regulates the
disposal of only two substances, asbestos and polychlorinated biphenyls (PCBs). The
latter of these is generally more relevant to contaminated sediment remediation. TSCA
is applicable to any material, specifically including dredged material, that contains 50 ppm
or greater PCBs. Sediment remedial activities that are regulated under TSCA include the
handling, transport, treatment, and disposal of a sediment or treatment residue that
contains 50 ppm or greater PCBs.
TSCA is managed by the USEPA, and this authority cannot be delegated. TSCA
regulations (40 CFR 761.60) specifically identify three disposal alternatives for PCB-
contaminated sediments and municipal sewage sludges: incineration, disposal in a
licensed chemical waste landfill (40 CFR 761.75), or other alternatives accepted by the
USEPA Regional Administrator. Some states have additional regulations addressing PCB-
contaminated materials independent of TSCA.
The permitting requirements of TSCA vary with the remediation technology to be applied.
Some technologies have been preapproved for treatment of PCBs, and no additional
permitting may be necessary. The remediation target for treatment technologies under
TSCA is to reduce the levels of PCB contamination to less than 2 ppm.
Atmospheric Discharges
The 1970 amendments to the Clean Air Act (44 U.S.C. §7401 et. seq.) directed the
USEPA to establish National Ambient Air Quality Standards (NAAQS) that would
provide safe concentrations of specific pollutants. NAAQS have been established for six
pollutants: sulfur dioxide, particulate matter, ozone, carbon monoxide, nitrogen dioxide,
and lead. In addition, National Emission Standards for Hazardous Pollutants (NESHAPS)
have been established for seven pollutants: beryllium, mercury, vinyl chloride, asbestos,
benzene, radionuclides, and arsenic. The USEPA regulations for the air program are
codified in 40 CFR 52-61.
Under the 1990 amendments to the Clean Air Act, 189 hazardous air pollutants are to be
regulated. Sources of these pollutants will be identified and regulations developed
according to source categories. These sources will be required to use the maximum
achievable control technology. Maximum achievable control technology standards for air
emissions from solid waste storage and disposal facilities are to be developed in 1994.
The development of discharge regulations and permitting of point-source emissions are
the states' responsibilities. States are required to develop State implementation plans,
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Chapter 2. Remedial Planning and Design
which assess the extent of air quality degradation and include plans for meeting the
NAAQS in nonattainment areas (areas that are not in compliance with the standards) and
for maintaining the NAAQS is areas that are in compliance. Regional plans for
improving air quality in nonattainment areas are typically developed and managed by
county or municipal governments, in cooperation with State regulatory agencies.
However, the USEPA can enforce an approved State implementation plan. Sediment
remedial activities likely to be subject to these regulations would be the point-source
emissions from a pretreatment or treatment process to the atmosphere. Area emissions
from disposal facilities may become regulated in the near future.
Health and Safety
The Occupational Safety and Health Act (OSHA; 29 U.S.C. §651 et. seq.) authorized the
Secretary of Labor to set mandatory occupational safety and health standards. The
secretary directed OSHA to develop these standards and administer their compliance.
OSHA has established minimum safety and health requirements for general construction
(29 CFR 1926). The Corps has developed a Safety and Health Requirements Manual
(USAGE 1987e), which is used to assure that Corps personnel and contractors maintain
compliance with OSHA regulations. These include requirements for personnel training,
medical surveillance, allowable exposure limits, and personal protective equipment (PPE).
Section 126 of SARA directed that standards be developed to protect the health and safety
of workers engaged in Superfund remediation activities. OSHA standards for hazard
communication, set forth in 29 CFR 1910.1200, require employers to provide information
to workers exposed to hazardous chemicals. This information consists of lists of all
hazardous chemicals at the site (workplace) and material safety data sheets. Workers at
sites with hazardous wastes are also required to be trained to recognize the health effects,
proper handling, spill control, PPE, and emergency procedures.
Environmental Assessments/Impact Statements
Section 309 of the 1970 amendments to the Clean Air Act and the NEPA of 1970 (42
U.S.C. §4321 et. seq.) require preparation of a detailed statement when a Federal action
may significantly impact the quality of the human environment. One of two types of
NEPA documents must be prepared for any major Federal action: an environmental
assessment (EA) or an environmental impact statement (EIS). The more detailed EIS is
required when significant impacts to an important resource are anticipated.
The USEPA administers the NEPA program, but the agency that has the lead in the
Federal action is responsible for preparing and coordinating the NEPA document. The
NEPA document is filed with the USEPA, which publishes a notice of availability in the
Federal Register.
A sediment remediation project conducted by a Federal agency or with Federal funds
would require NEPA compliance. In addition, the issuance of a permit under a Federal
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Chapter 2. Remedial Planning and Design
regulatory program requires NEPA compliance. The permittee is required to provide the
information and data required for a NEPA document to the permitting agency, which then
prepares the EA or EIS.
Other Regulations
There are many State and local regulations that may have to be addressed as part of a
sediment remediation project. These regulations include, but are not limited to:
• Zoning ordinances
• Transportation restrictions
• Riparian authorities
• Right-of-way restrictions
• Utility easements
• Water withdrawal regulations
• Floodplain/floodway construction restrictions.
The applicability of these and other State and local regulations would need to be
addressed on a site-specific basis.
For example, the owners of properties adjacent to a waterway may have certain riparian
rights, which can impact sediment remediation activities. These may include the rights
to any lands or fill constructed in the waterway, the rights to water withdrawal, and the
"ownership" of any materials below the ordinary high water mark. The riparian doctrine,
a development of English common law, is followed in most Great Lakes states. The
permission of all riparian owners would be required for virtually any sediment remedial
alternative.
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3. NONREMOVAL TECHNOLOGIES
Nonremoval technologies are those that involve the remediation of contaminated
sediments in situ (i.e., in place). Nonremoval technologies for contaminated sediments
include in situ capping, in situ containment, and in situ treatment.
Nonremoval technologies are single-component remedial alternatives. They do not require
sediment removal, transport, or pretreatment. As a result, nonremoval technologies are
often less complex and have lower costs than multicomponent alternatives (e.g.,
combinations of removal, transport, treatment, and disposal). In some cases (e.g., in situ
treatment), nonremoval technologies may be similar to the treatment and disposal
technologies used with dredged sediments.
This chapter provides descriptions of sediment remediation technologies that have been
demonstrated, designed, or considered for application in situ. Discussions of the factors
used to select from the available technology types and techniques for estimating costs and
contaminant losses are also provided.
DESCRIPTIONS OF TECHNOLOGIES
In situ Capping
In situ capping is the placement of a covering or cap over an in situ deposit of con-
taminated sediment. The cap may be constructed of clean sediments, sand, or gravel, or
may involve a more complex design using geotextiles, liners, and multiple layers. An
annotated bibliography prepared for the Canadian Cleanup Fund (Zeman et al. 1992)
summarizes most of the capping projects and studies that have been completed to date.
Capping is also a viable alternative for disposal of contaminated sediments that have been
dredged and placed in another aquatic location (this type of capping is discussed in
Chapter 8). Much of the technical information and guidance provided herein has been
adapted from that developed for dredged material capping in ocean waters. The guidance
provided in this section focuses on in situ capping of contaminated sediments in riverine
and sheltered harbor environments such as those commonly found in the Great Lakes
region.
A limited number of in situ capping operations have been accomplished in recent years
under varying site conditions. In situ capping has been applied in riverine, nearshore, and
estuarine settings. Conventional dredging and construction equipment and techniques can
be used for in situ capping projects, but these practices must be precisely controlled. The
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Chapter 3. Nonremoval Technologies
success of projects to date and available monitoring data at several sites indicate that in
situ capping may be an effective technique for long-term containment of contaminants.
In situ capping of contaminated sediments with sand has been demonstrated at a number
of sites in Japan (Zeman et al. 1992). Demonstration projects conducted at Hiroshima
Bay evaluated various types of placement equipment. More recent studies have examined
the efficiency of sand caps in reducing the diffusion of nutrients.
At the Denny Way project in Puget Sound, a layer of sandy sediment was spread over a
contaminated nearshore area, with water depths of 6-18 m, using bottom-dump barges
with provisions for controlled opening and movement of the barges (Sumeri 1989). This
was accomplished by slowly opening the conventional split-hull barge over a time frame
of 30-60 minutes, allowing the gradual release of the material in a sprinkling manner.
A tug was used to slowly move the barge laterally during the release, and the material
was spread in a thin layer over the desired area.
At the Simpson-Tacoma Kraft mill project in Puget Sound, an in situ capping project
involved spreading hydraulically dredged sediment with surface discharge through a
spreading device (Sumeri 1989). Hydraulic placement is well-suited to placement of thin
layers over large surface areas. Specialized equipment and placement techniques
developed for dredged material capping and in situ capping are shown in Table 3-1
(Palermo 199 Ib).
In situ capping using an armoring layer has also been demonstrated at a Superfund site
in Sheboygan Falls, Wisconsin. This project involved placement of a composite cap, with
layers of gravel and geotextile, to cover PCB-contaminated sediments in the shallow water
(<1.5 m) and floodway of the Sheboygan River. The cap was placed using land-based
construction equipment and manual labor. A typical cross section of the in situ cap for
this project is shown in Figure 3-1.
A variation of in situ capping would involve the removal of contaminated sediments to
some depth, followed by capping the remaining sediments in place. This method is
suitable when capping alone is not feasible because of hydraulic or navigation restrictions
on the waterway depth. It may also be used where it is desirable to leave the deeper,
more contaminated sediments capped in place (vertical stratification of sediment
contaminants is common in many Great Lakes tributaries).
In situ Containment
While in situ capping isolates the contaminated sediments from the water column
immediately above the sediments, in situ containment involves the complete isolation of
a portion of the waterway. Physical barriers used to isolate a portion of a waterway
include sheetpile, cofferdams, and stone or earthen dikes. The isolated area can be used
for the disposal of other contaminated sediments, treatment residues, or other fill material.
The area may have to be modified to prevent contaminant migration (e.g., slurry walls,
cap and cover).
44
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TABLE 3-1. SPECIALIZED EQUIPMENT FOR IN SITU CAPPING
xrtmcx
**rcfl SURFKE
D/SCHARGC UHE-
v ,. r-HWCH
^ =3 mtpzjib
OREOSED UfTEHI,
FLUID UUO UOUNO
iMCHOH
Submerged Diffuser
Source: Palermo <1991 b)
Specially designed flange, placed at the
end of a hydraulic discharge pipeline to
reduce exit velocities (Neal et al. 1978)
Developed by the Corps and demonstrated
at Calumet Harbor, Illinois (Hayes et al.
1988)
BAfiCE UNLOAOER WO SAHD SPREAGER
• Spreader pipe that hydraulically discharges
sand through a perforated head
• Specialized equipment for spreading sand
cap used in Japan (Kikegawa 1983; Sand-
erson and McKnight 1986)
Sand Spreader
Source: Kikegawa (1983)
• Gravity-fed downpipe for placement of
capping material
• Exit velocities may disturb sediments
• Used in Japan with conveyor unloading
barge (Togashi 1983; Sanderson and
McKnight 1986)
Trem/e Tube
Source: Togashi (1 983)
45
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Chapter 3. Nonremoval Technologies
Geotextile -
n
o a <=> a » £0 a <=> a a a
/-> _ —i
Gravel
a ao y
o -» o » o
Ri o» <£
38-"CG •?
Source: Blasland and Bouck Engineers (1990)
Figure 3-1. Cross section of r/i siVw cap used at Sheboygan River.
Perhaps the largest sediment remediation project undertaken to date has been at Minamata
Bay, Japan, where 58 hectares of the bay with the highest levels of mercury-contaminated
sediments was isolated using cofferdams, and 1.5 million m3 of contaminated sediments
from other areas of the bay were hydraulically dredged and placed into the enclosed area
(Hosokawa 1993). The contaminated sediments were capped with volcanic ash, sand, and
geotextile, and the area has been filled to grade.
On a far smaller scale, remediation at the Waukegan Harbor Superfund site included the
isolation of a boat slip containing the highest levels of PCB -contaminated sediments. The
slip was isolated using a double bentonite-filled sheetpile cutoff wall across the open end
and a bentonite slurry wall around the landward perimeter. About 15,000 m3 of contami-
nated sediment was hydraulically dredged from other areas of the harbor, placed into the
isolated slip, and capped with clay and topsoil. A series of drawdown wells were
installed around the perimeter of the isolated slip, and will be operated indefinitely to
maintain an inward hydraulic gradient.
In situ Treatment
Some treatment technologies have been developed specifically for in situ application,
while others have been adapted from ex situ treatment applications, including some of the
technologies discussed in Chapter 7, Treatment Technologies. Most in situ treatment
46
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Chapter 3. Nonremoval Technologies
technologies could also be applied to sediments that have been dredged and placed in a
disposal area.
In situ treatment has several limitations. One such limitation is the lack of process
control. Process control is contingent upon effectively monitoring conditions at the site,
typically by performing sampling and analysis at appropriate frequencies, before and after
treatment. The efficacy of I'M situ treatment of sediments is difficult to determine because
of the nonhomogeneous distribution of contaminants, sediment physical properties, and
treatment chemicals. One of the limitations of in situ treatment is the difficulty in
ensuring uniform dosages of chemical reagents or additives throughout the sediments to
be treated. Areas of sediment within the site may receive varying levels of treatment,
with some areas of sediment being untreated while others are overtreated relative to the
intended treatment goal. In situ treatment may be less cost effective than ex situ
treatment when these factors are considered.
Among the most significant limitations to I'M situ treatment is the impact of the process
on the water column. Processes that would release contaminants, reagents, or heat, or
produce other negative impacts on the overlying water column, are not likely to be
acceptable for I'M situ sediment remediation. A suitable in situ treatment technology is,
in most cases, one that can be applied with minimal disturbance of the sediment-water
interface or one in which the process is physically isolated from the water column. There
are two general methods of applying I'M situ treatment that address this limitation: surface
application and isolation of the sediments prior to treatment. Several types of treatment
processes might be used within these applications.
Surface application is the introduction of one or more materials (e.g., reagents, additives,
nutrients) onto the sediments by spreading and settling, or injecting them into the
sediments through tubes, pipes, or other devices. Researchers at the Canadian National
Water Research Institute have developed and demonstrated equipment that is capable of
injecting solutions of oxidizing chemicals into uncompacted sediments at a controlled rate
(Murphy et al. 1993). A schematic of this apparatus is shown in Figure 3-2.
The second method for applying sediment treatment in place is by isolating the sediment
from the surrounding environment. This method allows the use of reagents or process
conditions that might otherwise cause deleterious effects to the waterway. Various types
of equipment might be used for isolating the sediments, including a caisson, sheetpile cell,
tube, or box. A hypothetical application using a sheetpile caisson is shown in Figure 3-3.
Within the enclosing caisson, the water may be removed or left behind (if needed to
support the process). One proprietary system (MecTool, Millgard Environmental Corp.)
uses a bladder to isolate the sediments (and the treatment process) from the overlying
water. Within the enclosed caisson, sediments can be mixed and treatment reagents can
be added. After the treatment is completed, the caisson can be removed and reset at an
adjacent area.
Three types of sediment treatment technologies that have been demonstrated or at least
considered for I'M situ application will be discussed below: chemical, biological, and
immobilization.
47
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Chapter 3. Nonremoval Technologies
Direction of travel
Injector
system
River current
\\\\\
\ Sediments
\y///\
TJJ
Front view of injector
' filrto u
Side view of Injector
Reprint by permluion ol T. Murphy, NWRI, Burlington
Figure 3-2. System for injecting chemicals into sediments.
Caisson
Reprint by permission of T. Murphy. NWRI, Burlington
Figure 3-3. In situ treatment application using a sheetpile caisson.
In situ Chemical Treatment
Sediments in lakes and reservoirs have been treated in situ to control eutrophication or
other conditions (USEPA 1990i). Aluminum sulfate (alum) has been used to control the
release of phosphorus from bottom sediments and thereby limit algal growth (Kennedy
and Cooke 1982). The alum is typically spread over a large area of the lake, and allowed
to settle through the water column and deposit on the sediment surface. Alum treatment
is recommended for lake restoration in well-buffered, hard-water lakes (USEPA 1990i).
48
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Chapter 3. Nonremoval Technologies
The injection of calcium nitrate into sediments to promote the oxidation of organic matter
has been demonstrated in conjunction with lime and ferric chloride additions to promote
denitrification and phosphorus precipitation (USEPA 1990i). Calcium nitrate injection is
discussed below as part of a bioremediation application.
A detailed discussion of treatment technologies for toxic contaminants is provided in
Chapter 7. Perhaps because of the limitations associated with in situ treatment, develop-
ment in this area of treatment has been limited.
In situ Biological Treatment
Effective in situ bioremediation of fine-grained, saturated soils and sediments (as opposed
to more porous groundwater aquifers or soils within the vadose zone) poses a major
challenge. While delivery and transport of nutrient and electron acceptor amendments to
and through groundwater aquifers is a demonstrated technology, movement of these
materials through fine-grained sediments is difficult.
Contaminated sediments removed from the Sheboygan River Superfund site have been
evaluated for biodegradation of PCBs in a confined treatment facility (CTF). These
experiments as well as efforts to measure PCB dechlorination in sediments capped in situ
in the Sheboygan River have been inconclusive as of early 1994.
A form of bioremediation has been demonstrated on PAH-contaminated sediments in
Hamilton Harbor, Ontario (Murphy et al. 1993). Dissolved calcium nitrate was injected
into sediments over 1.4 hectares using the system shown in Figure 3-2. The chemical
injection oxidized about 80 percent of the hydrogen sulfide and stimulated the subsequent
biodegradation of low molecular weight organic compounds (79-percent reduction). More
moderate reductions in PAHs (25 percent) were shown.
In situ Immobilization
Immobilization alters the sediment's physical and/or chemical characteristics to reduce the
potential for contaminants to be released from the sediment to the surrounding environ-
ment (Myers and Zappi 1989). The principal environmental pathway affected by in situ
immobilization for sediments is leaching of contaminants from the treated sediment to
groundwater and/or surface water. Solidification/stabilization is a commonly used term
that covers the immobilization technologies discussed herein.
Binders used to immobilize contaminants in sediment or soils include cements, pozzolans,
and thermoplastics (Cullinane et al. 1986b). Many commercially available processes add
proprietary reagents to the basic solidification process to improve effectiveness of the
overall process or to target specific contaminants. The effectiveness of an immobilization
process for a particular sediment is difficult to predict and can only be evaluated by
laboratory tests conducted with that sediment.
49
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Chapter 3. Nonremoval Technologies
Ex situ solidification/stabilization processes are readily implemented using conventional
mixing equipment. However, injection of a reagent to achieve a complete and uniform
mix with in situ sediments is considerably more difficult and has not been demonstrated
on a large scale. Reagents for the solidification process can be injected into the sediment
in a liquid or slurry form. Porous tubes are sometimes used to distribute the reagents to
the required depth. Available commercial equipment includes a hollow drill with an
injection point at the bottom of the shaft. The drill is advanced into the sediment to the
desired depth. The chemical additive is then injected at low pressure to prevent excessive
spreading and is blended with the sediment as the drill rotates. The treated sediment
forms a solid vertical column. These solidified columns are overlapped by subsequent
borings to ensure sufficient coverage of the area (USEPA 1990e).
In situ solidification/stabilization has been demonstrated in sediments at Manitowoc
Harbor in Wisconsin, where a cement/fly ash slurry was injected through a hollow-stem
kelly bar using a proprietary mixing tool (MecTool) and slurry injector. This process
formed treated vertical columns 6 ft (1.8 m) in diameter to a depth of 6 m below the river
bed, using a 6x25-ft (1.8x7.6-m) steel cylinder placed 1.5 m into the sediments in 6 m
of water (similar to the setup shown in Figure 3-3). This demonstration experienced
difficulties in solidification of some sediments and management of liberated pore water
(Fitzpatrick 1994).
SELECTION FACTORS
The nonremoval technologies discussed in this section represent single-component
remedial alternatives, and are not as comparable as different technology types or process
options of a multicomponent alternative (e.g., different types of dredges). Most
nonremoval technologies are in the development stage and have only been applied at a
small scale at a limited number of sites. As a result, guidance on their feasibility, design,
and implementation is very limited. Factors for selecting nonremoval technologies, shown
in Table 3-2, are not intended for comparison purposes, but to screen these technologies
for overall feasibility at a particular project site.
In situ Capping
The primary technical considerations that affect the feasibility of in situ capping are the
physical and hydraulic characteristics and the existing and future uses of the waterway.
The suitability of in situ capping to a contaminated sediment site is less affected by the
type or level of contaminants present, because it physically isolates the sediments and
their associated contaminants.
50
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Chapter 3. Nonremoval Technologies
TABLE 3-2. SELECTION FACTORS FOR NONREMOVAL TECHNOLOGIES
Technology
Applications
Limitations
In situ Capping
In situ Containment
In situ Treatment
Most favorable conditions are in areas with
low currents and no navigation traffic; cap
may have to be armored to prevent erosion
Cap design must provide contaminant
isolation and address bioturbation (Palermo
and Reible, in prep.)
Special equipment for cap placement has
been developed (Palermo 1991b)
Abandoned slips and turning basins are
Well suited
Enclosed area can be used for disposal of
contaminated sediments from other areas
of the waterway
Oxidation and enhanced biodegradation of
low molecular weight organic compounds
appears promising. Other treatment tech-
nologies need substantial development
both in process and application tools
Cap will decrease water depth and po-
tentially limit future uses of the waterway
Potential impacts on flooding, stream-
bank erosion, navigation, and recreation
Portion of waterway to be filled must be
expendable
Potential impacts on flooding, stream-
bank erosion, and navigation
Potential impacts of process, reagents/
amendments, and sediment disturbance
on water column and aquatic environ-
ment
Ability to control process in situ and
effect a uniform level of treatment
Effectiveness of process under satu-
rated, anaerobic conditions at ambient
temperatures
Ability to treat deeper sediment deposits
The ideal area for in situ capping would be sheltered and not exposed to high erosive
forces, such as currents, waves, or navigation propeller wash, or to upwelling from
groundwater. Depending on the erosive forces present at a site, an in situ cap may have
to be armored with stone or other material to keep the cap intact. Areas on five tributaries
of the Great Lakes were examined under the ARCS Program in developing guidance on
the hydraulic design of in situ caps (Maynord and Oswalt 1993). River currents were the
dominant erosive force in only one of five areas. The scour caused by navigation
(recreational as well as commercial) was the dominant force in the other areas studied.
The potential scour caused by large commercial vessels would necessitate very large
armor stone, making in situ capping difficult in or near most active navigation channels
(Environmental Laboratory 1987; Maynord and Oswalt 1993).
For some waterways, in situ capping may not be consistent with local or regional plans
for waterway use. For example, if a reach of a river with contaminated sediment deposits
is already shallow, an in situ cap may further reduce water depths to levels that are not
safe for existing and planned recreational boating. Removal of some contaminated
sediments and in situ capping for the remaining portion may be an option in this case.
In all cases, the construction of an in situ cap represents a deliberate modification to the
51
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Chapter 3. Nonremoval Technologies
morphology of the bottom of a waterway. Future uses of the waterway may be limited
by this modification.
Design Process for In situ Capping
Capping is a dredged material disposal technology that has been used by the Corps for
over 10 years (discussed in detail in Chapter 8). Although there are many differences
between in situ capping and dredged material capping, some of the design guidance for
this disposal technology (Palermo et al., in prep.) is appropriate to in situ capping and is
presented herein.
An in situ capping operation should be treated as an engineering project with carefully
considered design, construction, and monitoring to ensure that the design is adequate.
The basic criterion for a successful in situ capping operation is simply that the cap
required to isolate the contaminated material from the environment be successfully placed
and maintained. The elements of in situ capping design are listed in Table 3-3. The
design considerations for in situ capping include selection and evaluation of capping
materials, cap thickness, equipment and placement techniques for the cap, cap stability,
and monitoring.
TABLE 3-3. DESIGN CONSIDERATIONS FOR IN SITU CAPPING
Design Element Design Considerations
Characterization of contaminated Level of contamination, grain size distribution, shear strength, resistance to
material in situ erosion, consolidation, plasticity, and density
Site characteristics Location and area to be capped, constraints on access, water depths, cur-
rents, wave climate, navigation traffic, flood flows, aquatic resources, ground-
water flow patterns
Capping material Dredged sediment from navigation projects, sediments from adjacent areas,
geotextiles, sand/stone/gravel, grout mattresses
Cap thickness Thickness components must account for chemical isolation, bioturbation,
erosion, gas formation, and consolidation
Equipment and placement tech- Placement by barge, pipeline, diffusers, spreaders, clamshell, or land-based
niques equipment
Monitoring Monitoring plans should be designed to ensure cap is placed as intended
and is effective in the long-term
Data Collection—A variety of information about the project site and sediments is
needed to prepare an in situ capping design. The areal extent and thickness of the
contaminated sediment deposit should be defined by surveys of the area. The site
conditions should also be defined to include bathymetry, currents, water depths, bottom
sediment characteristics, type and draft of adjacent navigation, and flood flow. The
52
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Chapter 3. Nonremoval Technologies
contaminated sediment deposit to be capped must be characterized for both physical and
chemical parameters.
Physical characteristics are important in determining the suitability of placement of
various capping materials. In situ density (or solids content), plasticity, shear strength,
consolidation, and grain size distribution are needed for evaluations of resistance to
displacement.
Capping Material—Various types of capping material may be used for in situ
capping. If available, dredged sediment from navigation projects can be used. This
option could be considered a beneficial use of material that might otherwise require
disposal elsewhere. In other cases, removal of bottom sediments from areas adjacent to
the capping site may be considered. Material other than sediments is also an option for
the cap, such as clean fill from offsite sources, geotextiles, stone/gravel, and grout
mattresses. In general, sandy sediments are suitable for use as a cap at sites with
relatively low erosive energy, while armoring materials may be required at sites with high
erosive energy.
Cap Thickness—-The cap must be designed to chemically and biologically isolate
the contaminated material from the aquatic environment. For sediment caps, the determi-
nation of the minimum required cap thickness is dependent on the physical and chemical
properties of the contaminated and capping sediments, the potential for bioturbation of
the cap by aquatic organisms, the potential for consolidation and erosion of the cap
material, and the type(s) of cap materials used. Laboratory tests have been developed to
determine the thickness of a capping sediment required to chemically isolate a contami-
nated sediment from the overlying water column (Sturgis and Gunnison 1988). The
minimum required cap thickness for chemical isolation is on the order of 30 cm for most
sediments tested to date. Bioturbation depths are highly variable; however, in Great
Lakes sediments they are typically on the order of 10 cm. The minimum thickness of
capping sediment for most projects will therefore be determined by constructability
constraints. Conventional equipment and placement accuracies will dictate minimum cap
thicknesses of 50-60 cm.
Geotextiles may be incorporated into in situ caps for a number of purposes, including:
stabilizing the cap, promoting uniform consolidation, and reducing erosion of the granular
capping materials.
Geotextiles and synthetic liners might also be incorporated into the cap design to limit
bioturbation and provide contaminant isolation (Palermo and Reible, hi prep.). A
geotextile was incorporated into.the cap used at the Sheboygan River (Figure 3-1), and
a geotextile has been used as part of a contaminated sediment cap in Sorfjord, Norway
(Zeman 1993).
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Chapter 3. Nonremoval Technologies
An armoring layer for resistance to erosion can also be considered in the cap design
(Environmental Laboratory 1987; Maynord and Oswalt 1993). For caps composed of
armoring layers, the chemical isolation would be dependent on a filter, while the armor
layer would normally prevent any disturbance of the cap by bioturbation and would be
designed to resist erosion. Consideration must be given, however, of the potential
attraction to benthic species of the new surface provided by the armoring layer.
Equipment and Placement Techniques—For sediment caps, the major con-
sideration in the selection of equipment and placement of the cap is the need for
controlled, accurate placement of the capping material (and the associated density and rate
of application of the capping material). In general, the capping material should be placed
so that it accumulates in a layer covering the contaminated material. The use of
equipment or placement rates that would result in the capping material displacing or
mixing with the contaminated material must be avoided.
Pipeline and barge placement of dredged material for in situ capping projects is ap-
propriate in more open areas such as harbors or wide rivers. Specialized equipment and
placement techniques developed for dredged material capping that might be considered
for in situ capping are shown in Table 3-1 (Palermo 1991b). In constricted areas, narrow
channels, or shallow nearshore areas, conventional land-based construction equipment may
be considered.
Once the equipment and placement techniques for the cap are selected, the need for land-
based surveys or navigation and positioning equipment and controls can be addressed.
The survey or navigation controls must be adequate to ensure that the cap can be placed
(whether by land-based equipment, bargeload, hopperload, or pipeline) at the desired
location in a consistently accurate manner.
Monitoring—A monitoring program should be considered as a part of any capping
project design (Palermo et al. 1992). The main objectives of monitoring for in situ
capping would normally be to ensure that the cap is placed as intended and the required
capping thickness is maintained, and that the cap is effective in isolating the contaminated
material from the environment.
Intensive monitoring is necessary at capping sites during and immediately after con-
struction, followed by long-term monitoring at less frequent intervals. Based on Corps
experience at dredged material capping sites in New England, long-term monitoring
should include bathymetric surveys, camera profiles, and occasional core samples
(Fredette 1993). In addition to physical and chemical monitoring, biological monitoring
may be conducted to track recolonization of benthos and evaluate contaminant migration.
In all cases, the objectives of the monitoring effort and any remedial actions to be
considered as a result of the monitoring should be clearly defined as a part of the overall
project design.
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Chapter 3. Nonremoval Technologies
In situ Containment
The technical feasibility of using in situ containment is determined primarily by the
physical conditions of the site. Areas that may be suitable for in situ containment include
backwater areas, slips, turning basins, and some wide areas of rivers. Areas within active
navigation channels are generally not suitable.
The primary factors limiting the feasibility of in situ containment are the potential impacts
of the new fill on flow patterns, flooding, navigation, and habitat. Slips and turning
basins are especially well suited, because they only need to be isolated at one end and can
generally be filled without reducing the hydraulic capacity of the adjacent river channel.
In situ containment will require structural measures and environmental controls to isolate
the containment area from the adjacent waterway and prevent unacceptable contaminant
migration. Testing and evaluation to determine the appropriate controls is discussed in
Chapter 8, Disposal Technologies.
It may also be possible to completely reroute waterways with contaminated sediments.
The waterway can then be dewatered, and the sediments removed, treated in place, or
confined in place. This is an extreme measure and is only likely to be feasible for small
waterways with limited flows.
In situ Treatment
There are three primary considerations in evaluating the suitability of in situ treatment.
The first consideration is whether the treatment process can work effectively under the
physical conditions of in situ sediments (i.e., saturated, anaerobic, and ambient tempera-
tures). Treatment technologies that require greatly different conditions are less likely to
be feasible for in situ application. Bench-scale testing of proposed treatment technologies
should be performed to determine if the process can operate effectively under in situ
conditions. Treatment technology testing is discussed further in Chapter 7.
The second consideration is the level of control needed to apply the treatment technology.
Some technologies require well-mixed systems in order for reagents and sediment
contaminants to react effectively. Specialized equipment may be needed to introduce
reagents and manipulate the sediments. The development of such equipment may require
pilot- or full-scale testing. Technologies that require greater levels of sediment manipula-
tion are less likely to be feasible for in situ applications.
The third consideration is the environmental impact on the water column and aquatic
environment. Suitable treatment technologies must be able to operate without dispersing
the sediments, releasing toxic reagents or contaminants, or creating conditions more
harmful to aquatic life than already exist. Examples of specialized equipment to isolate
the treatment process from the water column are shown in Figures 3-2 and 3-3.
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Chapter 3. Nonremoval Technologies
ESTIMATING COSTS
There is little detailed cost information in the literature about in situ remediation
technologies, even for those that have been implemented. Available information about
applications that have been implemented or proposed is summarized in Table 3-4.
In situ Capping
Capital costs for in situ capping include costs of capping materials, construction
equipment, and labor. These costs will be influenced by the complexity of the cap
design, accessibility of the capping site, water depth, and other factors. If clean dredged
material (e.g., from a navigation project) can be used in a capping application, capital
costs could be greatly reduced.
Operation and maintenance costs include monitoring and periodic cap replenishment.
Based on the experience of the Corps' New England Division with dredged material
capping, the costs for a routine long-term monitoring cycle (bathymetric surveys and
camera profile) are about $30,000 (Fredette 1993). This basic physical monitoring cycle
is conducted every 2-3 years. More extensive monitoring (including sediment cores and
biological monitoring) is conducted on a less frequent cycle.
In situ Containment
Capital costs for in situ containment include the materials, equipment, and labor needed
to construct the caisson, bulkhead, dike, or revetment, which isolates a portion of the
waterway. Typical costs for marine sheetpile construction in the Great Lakes are
$12-17/ft2 ($130-180/m2) (Wong 1994). Additional capital costs may be related to the
filling of the enclosed area with contaminated sediments (or other materials) and the
environmental controls necessary for the enclosed site. These dredging and confined
disposal costs are discussed in Chapter 4 (Removal Technologies) and Chapter 8 (Disposal
Technologies). Operation and maintenance costs for in situ containment include
monitoring and routine maintenance of the structure.
In situ Treatment
Capital costs for in situ treatment include the costs of equipment, materials, reagents, and
labor necessary to treat the sediments. The development and fabrication costs for the
application equipment may be significant. A substantial amount of development cost may
also be required for the treatment process itself, if it has not been applied in situ.
ESTIMATING CONTAMINANT LOSSES
The loss of contaminants from sediments in situ is a primary rationale for remediation.
The amounts of sediment contaminants lost during and after remediation need to be
56
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TABLE 3-4. COSTS FOR IN SITU TECHNOLOGIES
Application
Description
Cost3
In situ capping at Sheboygan
River, Wisconsin (Eleder
1993)
Cap design as shown in Figure 3-1
Capped surface area of 2,000 m2
Cap installed using land-based equipment
NA
In situ capping at Denny
Way, Seattle, Washington
(Sumeri 1989)
Dredged material removed and transported
from navigation project for use as cap at
no cost
Cap applied by slow release from split-hull
barge
Capping expenses related to precise posi-
tioning required
$4/m3 of capping
material (costs of dredg-
ing and transporting
capping material not
included)
In situ capping demonstra-
tion at Hamilton Harbour,
Ontario (Zeman 1993)
Demonstration proposed
Cap design is 0.5 m sand
Capped surface area is 10,000 m2
Cap placed using tremie tube
$648,000 demonstration
costs'1
In situ containment at Mina-
mata Bay, Japan (Hosokawa
1993)
Project enclosed 582,000 m2 of bay with
watertight revetment
Dredged 1,500,000 m3 of sediments from
other areas of the bay and disposed
them to the enclosed area
$388 million total project
costs0
In situ containment at Wau-
kegan Harbor, Illinois
{Albreck 1994)
Boat slip cutoff with double sheet pile wall,
filled with bentonite
22,000 m3 sediments placed in slip
New slip constructed for displaced users
$360,000 for slurry wall
$2,000,000 for new slip
In situ chemical treatment
with alum (USEPA 1990i)
Treatment effective for 6 years
Cost estimated for 40-hectare area of lake
$86/hectare (materials
only)
In situ bioremediation with
calcium nitrate (Murphy et
al. 1993)
Calcium nitrate injected using system
shown in Figure 3-2
Costs based on demonstration in Hamilton
Harbour (Murphy et al. 1993)
Equipment development costs not included
$7,800/hectareb
In situ solidification (Chapp
1993)
Solidification performed using system $20-45/m3
shown in Figure 3-3
(continued)
57
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TABLE 3-4. COSTS FOR IN SITU TECHNOLOGIES (continued)
Application
Description
Cost"
In situ capping at Little Lake
Butte des Morts, Wisconsin
(Fitzpatrick 1994)
Proposed capping of deposit "A," having
area of 1 7 hectares
Cap has two 30-cm layers of fill and cob-
bles and two geotextile layers
Temporary diversion of river during con-
struction
Silt curtains around site during construction
$7,738,500 estimated
project cost or approxi-
mately $445,000/hectare
In situ capping at New Bed-
ford Harbor, Massachusetts
(USEPA 19901)
Proposed capping of approximately
76 hectares of estuary
Cap has a 1 -m layer of sand on top of a
geotextile
A temporary hydraulic structure would be
built to maintain adequate depths in the
estuary during construction
$32,70,000 estimated
project cost or approxi-
mately $432,000/hectare
In situ solidification at Little
Lake Butte des Morts, Wis-
consin (Fitzpatrick 1994)
Proposed solidification of deposit "A,"
having 48,000 m3 sediments using
shallow soil mixing technology
Temporary diversion of river during con-
struction
Silt curtains around site during construction
$10,133,300 estimated
project cost or approxi-
mately $210/m3
Note: NA - not available
a Costs adjusted to January 1993 prices using ENR's Construction Cost Index, except where noted.
b Costs converted to U.S. dollars using exchange rates as of January 1993, and adjusted to January 1993
prices using ENR's Construction Cost Index.
0 Costs converted to U.S. dollars using exchange rates as of January 1993.
58
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Chapter 3. Nonremoval Technologies
estimated to determine the benefits of remediation and to evaluate the impacts of remedial
alternatives. The mechanisms for contaminant losses associated with nonremoval
technologies are summarized in Table 3-5.
TABLE 3-5. MECHANISMS OF CONTAMINANT LOSS
FOR NONREMOVAL TECHNOLOGIES
Technology Contaminant Loss Mechanisms
In situ Capping Resuspension/advection during
placement of cap
Long-term diffusion/advection
Long-term bioturbation
Long-term erosion
In situ Containment Resuspension during construction
Loss during dewatering/filling
Long-term seepage/leaching
In situ Treatment Resuspension during treatment
Long-term diffusion
Long-term bioturbation
Long-term erosion
Estimating contaminant losses for nonremoval technologies is difficult because of the lack
of field monitoring data and standard procedures for assessing nonremoval technologies.
Predictive models based on diffusion are conceptually applicable to most nonremoval
technologies. The seepage/leaching losses from an enclosed area constructed for in situ
containment can be estimated using the predictive models developed for CDFs (see
Chapter 8, Disposal Technologies). However, predictive techniques are not available that
account for any of the other mechanisms of contaminant loss associated with nonremoval
technologies.
Contaminant losses during placement of a cap, construction of an isolation wall, or the
injection of reagents or additives for chemical treatment or immobilization can result in
highly localized, but transient disturbances of contaminated sediment. For example,
during in situ immobilization, contaminant losses occur at the point of additive injection,
and injection-related losses last only as long as additives are being injected. These highly
localized and transient disturbances can be as important as long-term diffusion losses.
At present, highly localized, transient contaminant losses associated with the implementa-
tion of nonremoval technologies cannot be predicted. In addition, nonremoval technolo-
gies involving several processing steps, especially those involving mixing of the
contaminated sediments, will have more contaminant loss mechanisms to consider than
simpler nonremoval technologies, such as in situ capping.
Once the implementation phase of a nonremoval technology is completed, diffusion is the
major contaminant loss pathway. Advection, bioturbation, and biodegradation can also
be important in some cases, but can be avoided by careful planning, design, preproject
59:'~~
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Chapter 3. Nonremoval Technologies
testing, and monitoring. For example, sites with significant groundwater movement
through the sediment (and associated significant contaminant losses) are not good
candidates for nonremoval technologies. Controls for bioturbation should be part of
engineering design, and the potential for biodegradation of solidified matrices following
immobilization processing should be evaluated in a laboratory testing phase.
The application of diffusion models to certain nonremoval technologies, such as in situ
capping and in situ immobilization, is better established than the application of these
models to other nonremoval technologies, such as in situ chemical treatment. The
diffusion models are described in detail in Myers et al. (in prep.). Cap thickness, sorption
properties of the cap, contaminant chemical/physical property data, and sediment
chemical/physical property data are variables needed to evaluate in situ capping
effectiveness. For in situ immobilization, process-specific physical and chemical data are
needed, including bulk density, contaminant concentration after processing, effective
diffusion coefficients, and durability data. For other nonremoval technologies, there may
be additional information needs.
60
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4. REMOVAL TECHNOLOGIES
The removal or excavation of sediments from a water body, commonly known as
dredging, is a process that is carried out routinely around the world. The term "environ-
mental dredging" has evolved in recent years to distinguish dredging operations for the
primary purpose of environmental restoration from those operations for the purpose of
simply removing sediments. The most common purpose of dredging is to construct or
maintain channels for navigation or flood control (Hayes 1992). Environmental dredging
operations usually involve relatively small volumes of sediment, with the objective of
effectively removing contaminated material in a manner that minimizes the release of
sediments and contaminants to the aquatic environment. Other objectives may be
established for specific projects.
As noted by Hayes (1992):
The primary purpose of routine dredging operations is usually to remove large
volumes of subaqueous sediments as efficiently as possible within specified
operational and environmental restrictions. Environmental dredging operations,
on the other hand, would attempt to remove sediments with some known contam-
ination as effectively as possible. An effective method would include complete
removal of the desired sediment with as little environmental risk and consequence
as possible. The important distinction is that economics play a secondary role to
environmental protection in environmental dredging operations.
The loss of contaminants to the surrounding waters, or into the atmosphere, is of
particular concern when dredging contaminated sediments. Because contaminants are
generally bound to the fine particles, which are most easily resuspended, most efforts are
focused on minimizing the amount of resuspension through innovative equipment design
and operational controls. Further reductions in the transport of contaminants can be
accomplished with barriers such as silt curtains, silt screens, and oil booms.
The various types of mechanical and hydraulic dredges, as well as barriers, are described
in this chapter. Discussions of the factors used to select dredging equipment and
techniques for estimating costs and contaminant losses (e.g., via resuspension) are also
provided.
Different types of dredges were reviewed in the literature review prepared for the ARCS
Program (Averett et al., in prep.). Other general references on the subject of dredging
include the Handbook of Dredging Engineering (Herbich 1992), Fundamentals of
Hydraulic Dredging (Turner 1984), and Dredging and Dredged Material Disposal
(USAGE 1983).
61
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Chapter 4. Removal Technologies
DESCRIPTIONS OF TECHNOLOGIES
Dredging involves mechanically penetrating, grabbing, raking, cutting, or hydraulically
scouring the bottom of the waterway to dislodge the sediment. Once dislodged, the
sediment is lifted out of the waterway either mechanically, as with buckets, or hydrauli-
cally, through a pipe. Thus, dredges can be categorized as either mechanical or hydraulic
depending on the basic means of moving the dredged material. A subset of the hydraulic
dredges employs pneumatic systems to pump the sediments out of the waterway. These
are termed pneumatic dredges.
The most fundamental difference between mechanical and hydraulic dredging equipment
is the form in which the sediments are removed. Mechanical dredges offer the advantage
of removing the sediments at nearly the same solids content as the in situ material. That
is, little additional water is entrained with the sediments as they are removed, meaning
that the volume of the sediments is essentially the same before and after dredging. In
contrast, hydraulic dredges remove and transport sediment in slurry form. The total
volume of material is greatly increased, because the solids content of the slurry is
considerably less than that of the in situ sediments. (The relationship between the volume
of in situ sediment with various slurries is discussed in Chapter 6 in the Dewatering
Technologies section.)
The two general types of dredges most commonly used to perform navigation mainte-
nance and construction-related dredging, mechanical and hydraulic, are shown in
Figure 4-1. Both dredges are available in a wide variety of sizes, including small,
portable hydraulic dredges. The various types of dredges and dredging equipment, vessel
positioning systems, contaminant barriers, and monitoring requirements applicable to
sediment removal technologies are discussed below.
Mechanical Dredges
Mechanical dredges remove bottom sediment through the direct application of mechanical
force to dislodge and excavate the material. The dredged material is then lifted
mechanically to the surface at near-m situ densities (Averett et al., in prep.). As noted
above, this feature is significant because it minimizes the amount of contaminated
material to be handled. Mechanical dredges can be particularly effective for those
locations where dredged sediment must be transported by a barge to a disposal or
treatment facility (Zappi and Hayes 1991).
Production rates for mechanical dredges are typically lower than those for comparably
sized hydraulic dredges. However, high productivity is typically not the main priority for
environmental dredging projects. Mechanical dredges can operate in constricted areas and
do not interfere with shipping to the same extent as hydraulic dredges (Zappi and Hayes
1991). Mechanical dredges are often selected for small dredging projects in confined
areas such as docks and piers. They provide one of the few effective methods for
removing large debris (Averett et al., in prep.) and are adaptable to land-based operations.
62
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Chapter 4. Removal Technologies
Mechanical dredge
Hydraulic dredge
Source: USACE/USEPA(1992)
Figure 4-1. General types of commonly used dredges.
Major types of mechanical dredges include the following:
• Clamshell bucket
• Backhoe
• Bucket ladder
• Dipper
• Dragline.
Although it has not been proven by field or laboratory measurements, it is commonly
thought that the bucket ladder, dipper, and dragline dredges operate in a manner that
would lead to high sediment resuspension rates, making them unsuitable for dredging
contaminated material (Zappi and Hayes 1991). The clamshell bucket and backhoe
dredges are described below.
Clamshell Bucket Dredges
The clamshell bucket dredge, also known as the grab dredge, is the most commonly used
mechanical dredge in the United States, if not the world (Zappi and Hayes 1991). This
dredge may consist simply of a crane mounted on a spud barge, although most bucket
dredges have a crane/barge system specifically designed and constructed for dredging
63
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Chapter 4. Removal Technologies
(Figure 4-1) (Zappi and Hayes 1991). Buckets are classified by their capacities, which
range from <1 to 50 yd3 (<0.8 to 40 m3), with 2-10 yd3 (1.5-7.5 m3) being typical.
Bucket dredges are available from a wide variety of sources throughout North America.
A bucket dredge is operated similarly to a land-based crane and bucket. The crane
operator drops the bucket through the water column, allowing it to sink into the sediment
on contact. The loaded bucket is then lifted, causing the jaws to close, and raised through
the water column. Once above the water surface, the operator swings the bucket over the
receiving container (usually a barge) and lowers the bucket to release its load (Zappi and
Hayes 1991). The bucket dredge usually leaves an irregular, cratered sediment surface
(Herbich and Brahme 1991). The bucket has been used at numerous sites throughout the
Great Lakes for removing both contaminated and clean sediments. It is estimated that 77
bucket dredges are stationed in Great Lakes ports.
A variation of the conventional dredge bucket, the enclosed dredge bucket, has been
developed to limit spillage and leakage from the bucket. Although originally designed
by the Japanese Port and Harbor Institute and produced in Japan by Mitsubishi Seiko Co.,
Ltd., variations of this design have been produced by several U.S. manufacturers (Zappi
and Hayes 1991). The operation and deployment of the enclosed dredge bucket is
identical to that of the conventional clamshell bucket discussed above.
The original enclosed dredge bucket (Figure 4-2) features covers designed to prevent
material from spilling out of the bucket while it is raised through the water column. The
design also employs rubber gaskets or tongue-in-groove joints that reduce leakage through
the bottom of the closed bucket. An alternative design, developed by Cable Arm, Inc.
(Figure 4-2), offers several advantages over the standard clamshell design, including the
ability to remove sediment in layers, leaving a flat sediment surface.
Enclosed bucket dredges have been used routinely in various Great Lakes ports for the
maintenance of navigation channels. They have also been used in sediment remediation
projects in the Black River near Lorain, Ohio, in 1990, and in the Sheboygan River,
Wisconsin, in 1990 and 1991. The Cable Arm bucket was demonstrated by the Contami-
nated Sediment Removal Program (CSRP) on contaminated sediments in the Toronto and
Hamilton Harbors in Canada in 1992 (Environment Canada 1993) and has been used for
navigation maintenance dredging in the Cuyahoga and Fox Rivers.
Backhoes
Backhoes, although normally thought of as excavating rather than dredging equipment,
can be used for removing contaminated sediments under certain circumstances. Backhoes
are normally land based, but may be operated from a barge, and have been used
infrequently for navigation dredging in deep-draft (20-ft [6-m]) channels. Backhoes have
received limited use for removing PCB-contaminated sediments from the Sheboygan
River. A backhoe was recently used to remove 13,000 m3 of contaminated sediments
from Starkweather Creek in Madison, Wisconsin. Sediment resuspension from the
dredging was monitored and found to be no greater than that expected with other types
of dredging equipment (Fitzpatrick 1994).
64
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Chapter 4. Removal Technologies
Enclosed Bucket
Cable Arm Bucket
Source: Herbich and Brahme (1991).
Source: Cable Arm, Inc.
Figure 4-2. Specialized mechanical dredge buckets.
Specialized backhoes include closed-bucket versions and a pontoon-mounted model
especially adapted to dredging applications (see "WaterMaster" described in St. Lawrence
Centre 1993). The latter may be equipped with a suction pump as well.
Hydraulic Dredges
Hydraulic dredges remove and transport sediments in the form of a slurry. They are
routinely used throughout the United States to move millions of cubic meters of sediment
each year (Zappi and Hayes 1991). The hydraulic dredges used most commonly in the
United States include the conventional cutterhead, dustpan, and bucket-wheel. Certain
hydraulic dredges, such as the modified dustpan, clean-up, and matchbox dredges, have
been specifically developed to reduce resuspension at the point of dredging.
Hydraulic dredges provide an economical means of removing large quantities of
contaminated sediments. The capacity of the dredge is generally defined by the diameter
of the dredge pump discharge. Size classifications are: small (4-14 in., 10-36 cm),
medium (16-22 in., 41-56 cm), and large (24-36 in., 61-91 cm) (Averett et ah, in prep.).
The dredged material is usually pumped to a storage or disposal area through a pipeline,
with a solids content of typically 10-20 percent by weight (Herbich and Brahme 1991).
Souder et al. (1978) indicated that slurry concentrations are a function of the suction
pipeline inlet velocity, the physical characteristics of the in situ sediment, and effective
operational controls. The slurry uniformity is controlled by the cutterhead (if one is
65
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Chapter 4. Removal Technologies
employed) and suction intake design and operation. The cutterhead (both conventional
and innovative) should be designed to grind and direct the sediment to the suction intake
with minimal hydraulic losses. Water jets can also be used to loosen the in situ material
and provide a uniform slurry concentration. The dredgehead and intake suction pipeline
should be designed to maintain velocities that are capable of breaking the in situ sediment
into pieces that the pump can handle while minimizing entrance and friction losses.
The dredge pump and dredgehead (e.g., cutterhead) should work in tandem so that the
entire volume of contaminated sediment comes into the system, while maintaining a slurry
concentration that the dredge pump is capable of handling. The pump must impart
enough energy to the slurry so that the velocities in the pipeline prevent the solids from
settling out in the line prior to reaching the next transport mode or remediation process.
A properly designed and operated dredgehead, suction intake and pipe, pump, and
discharge pipeline system can minimize sediment resuspension while significantly
reducing system maintenance and the likelihood of pump failure.
Fundamentally, there are four key components of a hydraulic dredge:
• The dredgehead is the part of the dredge that is actually submerged into
the sediment
• The dredgehead support is usually a "ladder" as shown in Figure 4-1, but
may instead be a simple cable or a sophisticated hydraulic arm
• The hydraulic pump provides suction at the dredgehead and propels the
sediment slurry through a pipeline (It may be submerged or deck-mounted.)
• The pipeline carries the sediment slurry away from the dredgehead to the
receiving area (e.g., CDF, lagoon).
Dredgeheads
Various types of dredgehead configurations are used to facilitate the initial loosening and
gathering of bottom sediment. Most hydraulic dredges are usually identified 'by the type
of dredgehead (e.g., bucket wheel dredge). Various types of dredgeheads are discussed
below.
Cutterhead Dredges—Conventional cutterhead dredges are the most common
hydraulic dredges in the United States. According to Averett et al. (in prep.), there are
300 such dredges operating in the United States today. A conventional "open basket"
cutterhead is shown in Table 4-1.
Cutterhead dredges are usually operated by swinging the dredgehead in a zig-zag pattern
of arcs across the bottom, which tends to leave windrows of material on the bottom
(Herbich and Brahme 1991). Innovative operating techniques, including overlapping
dredge or step cuts, can reduce or eliminate windrows. Cutterhead dredges can be
66
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TABLE 4-1. CUTTERHEAD DREDGES
CHAHNfL tOTTOH
Conventional (Open Basket)
Dredgehead Source: Zappi and Hayes (1 991!
• One of the most versatile and efficient
dredging systems (Zappi and Hayes 1991)
• Capable of dredging nearly all types of
material, including clay, silt, sand, hard-
pan, gravel, and rock
• Widely available; commonly used for main-
tenance dredging
Developed by TOA Harbor Works (Japan)
Six dredges in operation in Japan (as of
1991)
Features: Auger cutter (to provide a slurry
of uniform density to the pump); cover
with moveable shutters (to prevent the
escape of resuspended sediments and
minimize inflow of excess water); sonar
and TV camera (to monitor elevation and
turbidity around the dredge, respectively);
grates (to keep large debris from clogging
the dredgehead)
Clean-up Dredgehead
Source: Zappi and Hayes (1991)
UNDSRWATtR TV CAMERA
UONITOH PLATE
OATHERHEAO
• ' SHUTTER •—".
• Developed by Penta Ocean Construction
Company, Ltd. (Japan)
• Three such dredges operate in Japan (two
medium to large and one small scale—for
narrow areas)
• Features: Helical auger (to cut and guide
material into suction pipe); cover and
shutter (to prevent sediment resuspen-
sion); positioning equipment (to maintain
the cutterhead parallel to bottom); check
valves (to prevent backflow of sediment
slurry during emergency shutdown of
pump)
Refresher Dredgehead
Source: Zappi and Hayes (1991)
67
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Chapter 4. Removal Technologies
operated to reduce resuspension or losses of volatile contaminants using additional
equipment such as sediment shields, gas collection systems, underwater cameras, and
bottom sensors.
Innovative dredgehead designs have been developed specifically for removing con-
taminated materials. Such dredgeheads put a premium on minimizing sediment resuspen-
sion and on accurate control of the depth of sediments removed. Two such dredgeheads,
the Clean-up and the Refresher, are shown in Table 4-1.
Suction Dredges—This category includes those hydraulic dredges that do not
employ a cutterhead. Such dredges may use water jets to help loosen sediments.
Examples of three dredgehead designs used for such dredges are provided in Table 4-2.
Hybrid Dredges—These dredges use a combination of mechanical action and
hydraulic pumping, but would not be considered cutterhead dredges. Examples of
dredgehead designs used by hybrid dredges are shown in Table 4-3, and include the
bucket wheel, screw impeller, and disc-bottom dredgeheads.
Dredgehead Support
The physical support for the dredgehead, or ladder, is largely interchangeable among the
various dredges and will not be discussed further in this document.
Hydraulic Pumps
The three main applications of hydraulic pumps in the dredging process are:
• Dredge plant pumps—used to remove in situ sediments
• Booster pumps—used to maintain slurry velocities
• Pumpout stations—used to rehandle sediment from hoppers, barges, and
railcars.
Dredge plant pumps are discussed in this section. The other two types of pump
applications are discussed in Chapter 5, Transport Technologies.
Fundamentally, pumps are used to convert mechanical or pumping energy into slurry
energy. Usually they are driven by electric or diesel motors, although air-driven (pneu-
matic) pumps have also become popular. Energy put into a slurry by a pump is used to
maintain pipeline velocities while overcoming elevation heads and friction and entrance
losses.
68
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TABLE 4-2. SUCTION DREDGES
Plain Suction Dredgehead
• Simply a pipeline hydraulic dredge without
a cutterhead
• Generates low levels of turbidity
• Limited to dredging soft, free-flowing
granular material such as sand (Averett et
al., in prep.; Herbich and Brahme 1991)
• May be supplemented by water jets at
suction point mouth, but may then gene-
rate significant turbidity at the bottom
ROLLOVER
PLATE
WINS
PLATE
WING
PLATE
• Developed by the Corps specifically for
dredging free-flowing granular material
• Used almost exclusively in the United
States, especially for removing large sand
deposits in the Mississippi River (Zappi and
Hayes 1991; Herbich and Brahme 1991)
• The dredgehead, resembling a vacuum
cleaner or dustpan, is nearly as wide as
the hull of the dredge
• Equipped with high-pressure water jets for
agitating the material (Herbich and Brahme
1991)
Modified Dustpan Dredgehead Source: Zappi and Hayes <1991]
ATE
Matchbox Dredgehead
• Developed by Volker Stevin Dredging
Company (Netherlands)
• Used to remove highly contaminated sedi-
ment from First Petroleum Harbor
• Features: Triangular cover (to prevent
dispersion of sediments and inflow of
excess water, and to contain released
gases); funnel intake (to guide sediment
toward the suction intake); hydraulic pis-
tons (to maintain the dredgehead parallel
to sediment bottom regardless of depth);
grates (to prevent large debris from clog-
ging the intake)
Source: Zappi and Hayes (19911
69
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TABLE 4-3. HYBRID DREDGES
Bucket Wheel Dredgehead Source: Palermo and Pankow (1988)
Designed by Dutch and American engi-
neers combining the positive aspects of
the conventional cutterhead and bucket-
line dredges
Consists of numerous overlapping bottom-
less buckets that excavate the sediment
and immediately guide it into the suction
intake (Zappi and Hayes 1991; Herbich
and Brahme 1991)
The Japanese have developed an
tight" bucket wheel dredge
air-
• Dredged sediments are conveyed to the
surface via a combination of a feed screw
and pneumatic pump
6
_L
1 Agitator
2 Screw
3 Pressurizing device
4 Compressed air
5 Compressed air nozzle
6 Plug flow
7 Delivery line
• Designed by the Japanese, this technology
was recently demonstrated at the Shin-
Moji Port in Japan
• Description: The dredgehead is forced
below the surface of the sediment where
an agitator (located at the bottom of the
vertical screw) loosens the sediment and
conveys it upward to a centrifugal pump;
the pressurized sediment slurry is deliv-
ered, via pipeline, with the aid of com-
pressed air
Screw Impeller Dredgehead
Source: Randall (1992)
• Designed at Delft University in the Nether-
lands in the 1970s; a field test of a "modi-
fied" disc-bottom cutter was conducted
near Rotterdam
• Consists of a flat-bottom plate and top
ring with vertically oriented cutting blades;
the suction mouth is located inside the
cutter
Disc-Bottom Dredgehead
70
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Chapter 4. Removal Technologies
The two general classes of dredge plant pumps are kinetic and positive displacement
(Lindeburg 1992). A summary of the characteristics of selected examples of these pump
types is provided in Table 4-4.
Pipelines
Details on slurry pipelines are provided in Chapter 5, Transport Technologies.
Portable Hydraulic Dredges
Portable hydraulic dredges are relatively small machines that can be transported over land.
They are convenient for isolated, hard-to-reach areas and are economical for small jobs.
These dredges are also capable of operating in very shallow water (approximately 0.5 m).
Two such dredges are the horizontal auger dredge and the Delta dredge (Delta Dredge and
Pump Corp.). These two dredges are shown in Table 4-5. Two examples of horizontal
auger dredges are the Mudcat, manufactured by Ellicott Machine Co. and the Little
Monster, manufactured by the H & H Pump and Dredge Co. A Mudcat dredge with
several equipment modifications was demonstrated by the CSRP in November 1991 at the
Welland River, Ontario (Acres International Ltd. 1993).
A third type of portable dredge is the hand-held hydraulic dredge. This dredge can be
as simple as a hose connected to a vacuum truck, such as the one used to remove PCB-
contaminated sediments from the Shiawasee River in Michigan (USEPA 1985b). In
another example, diaphragm sludge pumps were used by the USEPA's Inland Response
Team to remove PCB-contaminated sediments from the Duwamish River Waterway in
Seattle, Washington (Averett et al., in prep.). The primary application of such dredges
is the removal of small volumes of contaminated materials that can be easily accessed
from the surface or by divers.
Sell-Propelled Hopper Dredges
A self-propelled hopper dredge operates hydraulically, but it is often described as a
separate type of dredge because the dredged material is retained onboard rather than being
discharged through a pipeline (Figure 4-1). Self-propelled hopper dredges are well suited
for dredging large quantities of sediments in open areas. They are not well suited for
small dredging projects, especially in close quarters. For these reasons, they are not likely
to be used for sediment remediation projects around the Great Lakes and will not be
discussed in further detail in this document.
Vessel or Dredgehead Positioning Systems
A critical element of sediment remediation is the precision of the dredge cut, both
horizontally and vertically. Technological developments in surveying and positioning
instruments have improved both aspects of dredging.
71
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TABLE 4-4. PUMP CHARACTERISTICS
Air Lift Pump
• Operates by the release of compressed air into a riser pipe with open top and bot-
tom; the slurry is then dragged through the riser pipe and separated from the dif-
fused air with special discharge equipment
• Has no moving parts
• Can be fabricated relatively easily
• Sensitive to suction and discharge head variations in addition to depth of buoyant
gas release
• Slurries of 25-percent solids (average) achieved using this pump (d'Angremond et al.
1978)
• Cannot operate economically in water depths of less than 7 m (Hand et al. 1978);
not suitable for moving dredged sediments long distances in pipelines (Averett et al.,
in prep.)
Water Eductor Pump
• Uses a suction force (vacuum) by passing high-pressure water through a streamlined
confining or venturi tube
• Has no moving parts
• Convenient for solids that must be slurried
• Cannot pump slurries with a particle size greater than 5 cm
Radial-Flow Pump
• Most common type of dredge and booster pump
• Impeller vanes capture the influent slurry and throw it to the outside of the pump
casing where the velocity imparted by the vanes is converted to pressure energy
• Has a screened suction intake
• Capable of passing large solids without clogging yet small enough to prevent over-
dilution with transport water (Lindeberg 1992)
• Operates well only if pumping head is within a relatively narrow range (USEPA 1979)
Axial-Flow Pump
• Uses rotating impellers to impart a spiralling motion to the fluid entering the pump
• More reliable and lasts longer
• Relatively inefficient compared to radial flow centrifugal pumps
• Size of particles is limited by the diameter of the suction or discharge openings and
by the spiral lift provided by the impeller (USEPA 1979)
(continued)
72
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TABLE 4-4. PUMP CHARACTERISTICS (continued)
Diaphragm Pump (Generic)
• Reciprocating diaphragm pumps use a flexible membrane that is operated on a two-
stroke cycle that pushes and pulls the membrane to contract or enlarge an enclosed
cavity or pump chamber
• Can be mechanically (push rod or spring) or hydraulically (air or water) operated
• Has few moving parts, thus minimizing operator attention and maintenance require-
ments and simplifying equipment operation
• Power required to drive a hydraulic driven diaphragm pump is typically double that
required to operate a mechanically driven pump of similar capacity; however, hydrau-
lically driven pumps generally last longer than mechanical pumps
• Two or more pump stations operated in sequence can increase system capacity and
smooth out flow (USEPA 1979)
PNEUMA® Pump
• Developed in Italy, the PNEUMA® pump uses compressed air to convey sediments
through a pipeline; may be suspended from a crane or barge, or mounted on a
ladder, which operates like a cutterhead dredge
• Used extensively in Europe and Japan (Averett et al., in prep.), on a limited basis in
the United States, and demonstrated by the CSRP in 1992 at Collingwood, Ontario
• Features: Three submerged pressure vessels (to collect sediment in cyclical fashion);
air compressor(s) and compressed air distributors; vacuum system (to aid dredging in
shallow water); dredging attachments (to penetrate and collect sediments)
• Normally suspended from a crane and pulled into sediments with second cable
Oozer Pump
• Japanese version of the PNEUMA® pump (but has two pressure vessels rather than
three)
• Used throughout Japan
• Mounted on a ladder and operated like a conventional cutterhead; the Japanese
dredge, Taian Maru, obtained a maximum production rate of 350 m3/hour dredging
nearly 1.4 million m3 of contaminated sediment between 1974 and 1980
• Low-power efficiency compared to conventional centrifugal pump (applies to the
PNEUMA® pump as well)
(continued)
73
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TABLE 4-4. PUMP CHARACTERISTICS (continued)
Plunger Pump
• Consists of pistons driven by an exposed drive crank
• Eccentricity of the drive crank is adjustable, offering a variable stroke length and
hence a variable positive displacement pumping action
• Plunger pumps require daily routine servicing by the operator, but overhaul mainte-
nance effort and costs are low (USEPA 1979)
Piston Pump
• Similar to the plunger pump in its action, but consists of a cable guide and a fluid
powered piston
• Capable of generating high pressures at low flows
• More expensive than other positive displacement pumps, and as a result used only
for special applications (USEPA 1979)
Progressive Cavity Pump
• Consists of a single-threaded rotor that spins inside a double-threaded helix rubber
stator
• Total head produced by the pump is divided equally between the number of cavities
created when the threaded rotor and helix stator come into contact
• Because the wear on the rotors is high, the maintenance cost for this type of pump
is the highest of any slurry pump
• Although expensive to maintain, flow rates are easily controlled, pulsation is minimal,
and operation is clean {USEPA 1979)
Lobe Pump
• Uses two rotating synchronous lobes to essentially push the slurry through the
pump; the lobe configuration can be designed to fit the type of slurry being pumped
• Rotational speed and shearing stresses are low
• Lobe clearances are set by the manufacturers according to the slurry solids to ensure
the pump lobes do not contact each other and to minimize abrasive wear (USEPA
1979).
74
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TABLE 4-5. PORTABLE HYDRAULIC DREDGES
Horizontal Auger Dredge
Source: Ellicott Machine Co.
• A small, portable unit rated between 40
and 90 m3/hour (50 and 120 yd3/hour)
(Herbich and Brahme 1991)
• Solids concentration ranges from 10 to 30
percent (Herbich and Brahme 1991)
• Features: Horizontal cutterhead/auger
(cuts and removes sediment laterally
toward a suction pipe in the center of the
cutter); retractable mud shield (reduces
turbidity but may cause clogging)
• Can remove a layer of material 0.5 m thick
and 2.5 m wide, leaving the dredged
bottom flat
• Used to maintain industrial lagoons and
small waterways
Features: Two counter-rotating, low-
speed, reversible cutters and 30-cm
diameter pump
Capable of making a relatively shallow
2.3-m wide cut
Delta Dredge
Source: Barnard (1 978)
75
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Chapter 4. Removal Technologies
Vertical control is particularly important where contamination occurs as a relatively thin
or uneven layer. Video cameras can be used to continuously monitor dredging operations.
The depth of the dredgehead can be measured using acoustic instrumentation and by
monitoring dredged slurry densities. In addition, surveying software packages can be
used to generate pre- and post-dredging bathymetric (water depth) charts, determine the
volume dredged, locate obstacles, and calculate surface areas (St. Lawrence Centre 1993).
A digital dredging method, which enables dredge operators to follow a complex sediment
contour, has been developed in the Netherlands (van Oostrum 1992).
The horizontal position of the dredge may be continuously monitored during dredging.
Satellite- or transmitter-based positioning systems (e.g., global positioning system,
SATNAV, LORAN C) may be used to define the dredge position. In some cases,
however, the accuracy of these systems is inadequate for precise dredging control. Very
accurate control is possible through the use of optical (laser) surveying instruments set
up at one or more locations onshore. These techniques, in conjunction with on-vessel
instruments and control of spud placement, can enable the dredge operator to target
specific sediment deposits.
The positioning technology described above may enhance the accuracy of dredging in
some circumstances. However, planners and designers should not develop unrealistic
expectations of dredging accuracy. Contaminated sediments cannot be removed with
"surgical" accuracy even with the most sophisticated equipment. Equipment is not the
only factor affecting the accuracy of a dredge. Site conditions (e.g., weather, currents),
sediment conditions (e.g., bathymetry, physical character), and the skill of the dredge
operator are all important factors. In addition, the distribution of sediment contaminants
can, in many cases, only be resolved at a crude level and with a substantial margin for
error. The level of accuracy required for environmental dredging should reflect the
accuracy at which the sediment contamination distribution is resolved.
Containment Barriers
When dredging contaminated sediments, it may be advisable to limit the spread of
contaminants by using physical barriers around the dredging operation. Such barriers may
be appropriate when contaminant concentrations are high or site conditions dictate the
need for minimal adverse impacts. A number of physical barriers commonly used in the
construction industry may be adapted to this purpose. Structural barriers, such as
cofferdams, are not generally applicable as temporary barriers, but are options for in situ
containment (see Chapter 3, Nonremoval Technologies). The determination of whether
these types of barriers are necessary, aside from regulatory requirements, should be made
based on a thorough evaluation of the relative risks posed by the anticipated release of
contaminants from the dredging operation, the predicted extent and duration of such
releases, and the long-term benefits gained by the overall remediation project. The ARCS
Risk Assessment and Modeling Overview Document (USEPA 1993 a) and the Estimating
Contaminant Losses from Components of Remediation Alternatives for Contaminated
Sediment (Myers et al., in prep.) should be used to make this determination.
76
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Chapter 4, Removal Technologies
More commonly, nonstructural barriers, such as oil booms, silt curtains, and silt screens,
have been used to reduce the spread of contaminants during dredging. Oil booms are
appropriate for sediments that are likely to release oils when disturbed. Such booms
typically consist of a series of synthetic foam floats encased in fabric and connected with
a cable or chains. Oil booms may be supplemented with oil absorbent materials (e.g.,
polypropylene mats).
Silt curtains and silt screens are flexible barriers that hang down from the water surface.
Figure 4-3 shows a typical design of a silt curtain. Both systems use a series of floats
on the surface, and a ballast chain or anchors along the bottom. Although the terms silt
curtain and silt screen are frequently used interchangeably, there are fundamental
differences. Silt curtains are made from impervious material such as coated nylon and
primarily redirect flow around the dredging area rather than blocking the entire water
column. In contrast, silt screens are made from synthetic geotextile fabrics, which allow
water to flow through but retain a fraction of the suspended solids (Averett et al., in
prep.).
Silt curtains have been used at many locations with varying degrees of success. For
example, silt curtains were found to be ineffective during a demonstration in New
Bedford Harbor, primarily as a result of tidal fluctuation and wind (Averett et al., in
prep.). Similar problems were experienced when Dokai Bay (Japan) was dredged in 1972
(Kido et al. 1992). Barriers consisting of a silt curtain/silt screen combination were
effectively applied during dredging of the Sheboygan River in 1990 and 1991. Water
depths were generally 2 m or less. A silt curtain was found to reduce suspended solids
from approximately 400 mg/L (inside) to 5 mg/L (outside) during rock fill and dredging
activities in Halifax Harbor, Canada (MacKnight 1992). A silt curtain was employed
during a dredging demonstration at Welland, Ontario (Acres International Ltd. 1993). The
curtain minimized flow through the dredging area, although there were problems in the
installation and removal.
Monitoring
Monitoring may be conducted during environmental dredging for a number of purposes,
including:
• Measure contaminated sediment removal efficiency
• Determine dredged volumes
• Measure sediment resuspension at dredge
• Track contaminant transport
• Check performance of barriers and other controls.
During maintenance dredging, monitoring is generally focused on the quantity of material
dredged because the contractor is paid according to this quantity. The quantity of dredged
77
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BUOYANCY
FLOAT
SKIRT
BALLAST
CHAIN —.
XTRA FLOTATION TO
OMPENSATE FOR WEIGHT A_
IF END CONNECTOR-.
, Ao
^-TENSION
CABLE
>)
o
o
o
o
s
-—
—
EN
ID CONNECTOR
O
1
i
I
0
^-HANDHOLD
1
n
DESIGN
WATERLINE
FLOTATION /
SEGMENT '
SKIRT
0
\
n
> —
_
GROMMET^
0 6
O
O
0
0
FREEBOARD
I
0.
UJ
0
1-
a
*
VIEW A-A
• BALLAST CHAIN
t
Source: Barnard (1978)
Figure 4-3. Typical design of a center-tension silt curtain section.
-------
Chapter 4. Removal Technologies
material may be estimated from bathymetric surveys conducted before and after the
dredging, or from other measurements, such as barge counts or pumping rates and
duration.
Measurements of turbidity or suspended solids are made during sediment remediation and
during some maintenance dredging operations to monitor the level of sediment resuspen-
sion caused by the dredge. Water samples are typically collected at one location upstream
and several locations downstream from the dredging site. Additional water quality
monitoring around the dredging site may be required by the State or other regulatory
agencies. Monitoring programs for tracking contaminant transport and checking the
efficiency of barriers and other controls are site-specific. During remedial dredging
projects, sediment samples may be collected and analyzed after dredging to monitor the
removal efficiency and to determine if additional passes by the dredge are needed.
SELECTION FACTORS
A number of publications on the selection of dredges for environmental applications have
been published, including the Guide to Selecting a Dredge for Minimizing Resuspension
of Sediment (Hayes 1986) and Selecting and Operating Dredging Equipment: A Guide
to Sound Environmental Practices (St. Lawrence Centre 1993). Generally one of the key
considerations in any dredging project involving contaminated sediments is the
minimization of sediment resuspension. While this subsection focuses on the selection
of dredging equipment, it should .be noted that the operation of the dredge also has a
profound effect on the rate of sediment resuspension (Hayes 1986). Selection of specialty
dredges designed for minimal sediment resuspension does not guarantee superior results.
The keys to an effective and environmentally safe dredging operation are:
• Selection of equipment compatible with the conditions at the site and the
constraints of the project
• Use of highly skilled dredge operators
• Close monitoring and management of the dredging operation.
Conventional dredging equipment, employed in a careful and efficient manner, can
achieve results comparable to specialty dredging equipment.
Dredge Selection
The operational characteristics of selected dredges are summarized in Table 4-6. These
characteristics may be used to help narrow the range of dredges potentially suited to a
given remediation project. Other factors that can be used to guide the selection of an
appropriate dredge for a site are discussed below.
79
-------
TABLE 4-6. OPERATIONAL CHARACTERISTICS OF VARIOUS DREDGES
do
O
Dredge Type
Clamshell
Suction
Dustpan
Cutterhead
6-8 in. (15-20 cm)
10- 12 in. (25-30 cm)
14-16 in. (36-41 cm)
20-24 in. (51-61 cm)
30 in. (76 cm)
Hopper
Horizontal auger
PNEUMA®
Oozer
Clean-up
Refresher
Backhoe
Matchbox
Airlift
Percent
Solids by
Weight3
near in situ
10-15
10-20
10-20
10-20
10-20
10-20
10-20
10-20
10-30
25-40
25-40
30-40
30-40
near in situ
5-15
25-40
Range of
Production -
Rates
(m3/hr)
23-460
19-3,800
19-3,800
25-105
60-540
1 60-875
310-1,615
575-2,500
380-1,500
46-120
46-300
340-500
380-1,500
1 50-990
20-150
18-60
NA
Dredging Accuracy
Vertical
(cm)
60
30
15
30
30
30
30
30
60
15
30
30
30
30
30
30
30
Horizontal
(m)
0.3
~1
~1
~1
~1
~1
~1
~1
~3
0.15
0.3
~1
-1
-1
~1
~1
0.3
Operational Dredging Depth
Minimum
(m)
Oc
2
2-5
1.2
1.4
1.5
1.6
1.7
3-9
0.5
Oc
Oc
1-5
1-5
Oc
1-5
6
Maximum
(m)
48d
16-196
16-196
46
8e
12e
15e
15e
21e
5
48d
48d
4-21
4-21
7-15
4-21
Vf
Debris
Removal
+
-
-
—
—
—
-
-
—
-
-
—
-
-
-
+
—
-
Note: NA - not available
Source: Adapted from Hand et al. (1978) and Philips and Malek (1984), as cited in Palermo and Pankow (1988). Additional data from
Averett et al. (in prep.) and USEPA (1985b).
a Typical solids concentration under optimal conditions. Percent solids may be lower if operational difficulties (e.g., excess debris) are
encountered.
b Ratings for debris removal: ( + ) can remove debris; (-) debris removal is limited.
c Zero if used alongside of waterway; otherwise, draft of vessel will determine the operational depth.
d Demonstrated operational depth; theoretically could be used much deeper.
e With submerged dredge pumps, operational dredging depths have been increased to 30 m or more.
f V - theoretically unlimited.
-------
Chapter 4. Removal Technologies
Solids Concentration
There are two major factors that affect the desired solids concentration:
• Compatibility with Other Components—In most cases, it is preferable
to use a dredging system that is capable of delivering material at high
solids concentrations. This tends to minimize the costs of handling,
treating, and disposing of sediments. Mechanically dredged sediments do
not require intensive dewatering, which is an expensive pretreatment
process (see Chapter 6). Mechanical dredging keeps the volume of
dredged material to a minimum and greatly reduces the costs of water
treatment (see Chapter 9).
• Distance to Treatment/Disposal Site—The feasibility of pipeline transport
to the treatment/disposal site is discussed in Chapter 5, Transport Tech-
nologies. The ability to deploy pipelines, even temporarily, in highly
urbanized areas can be limited. If access is unlimited, slurried sediments
can be transported by pipeline several kilometers with the use of booster
pumps. If pipeline transport is not feasible, sediments can be transported
at high solids concentrations (e.g., as produced with mechanical or pneu-
matic dredges) by scows or barges.
Production Rate
For navigation dredging, the size of the dredge (and number of dredges) is largely
dictated by the volume of sediments to be removed and the time allowed. The quantities
of sediments dredged at remediation projects are small in comparison to navigation dredg-
ing, and factors other than sediment volume may influence the dredge size and production
rates. Production rates may be deliberately reduced to minimize sediment resuspension
or because of constraints caused by sediment transport, pretreatment, treatment, or
disposal components.
Dredging Accuracy
Precise control of operational dredging depth is particularly important when dredged
sediments are to be handled in expensive treatment and disposal facilities (Averett et al.,
in prep.). The vertical and lateral accuracy of the dredge is important to ensure that
contaminated sediments are removed, while minimizing the amount of clean sediments
removed. The accuracy of a dredging operation is only partially influenced by the type
of dredge selected. Conditions of the site and sediments, the proficiency of the operator,
and the rate of production all influence the accuracy of the dredge cut.
81
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Chapter 4. Removal Technologies
Dredging Depth
Dredges are limited to dredging areas with an adequate depth of water to accommodate
the draft of the dredging vessel. This factor becomes important when contaminated
sediments are located outside of navigable waterways. Some dredging equipment can be
operated from land to access sediments in shallow waterways. The maximum depth to
which dredges can reach is also limited. Some dredges are limited by the length of the
dredging arm or ladder. Hydraulic dredging in very deep water (>20 m) may require
submerged pumps or remotely operated dredges.
Ability to Handle Debris
Sediment, especially in urban areas, often contains large rocks, concrete, timber, tires,
and other discarded materials. In cargo loading/unloading areas, pockets of coal, iron ore
pellets, or other bulk materials may occur from spillage. Very large debris (e.g., greater
than 0.5 m in any dimension) can only be removed mechanically (further discussion of
specialized debris removal equipment is provided in Chapter 6). Mechanical dredges will
generally remove large debris with the sediments, but are likely to produce greater
turbidity in the process. Dredgeheads equipped with cutters are able to reduce the size
of some debris such as wood. Although debris that is larger than the diameter of the
suction pipe and not cut by the cutter simply cannot be removed by hydraulic dredges,
smaller debris can also clog hydraulic pipelines and damage pumps.
Other Factors
In addition to the selection factors shown in Table 4-6, there are a number of other factors
that may be significant in the selection of a dredge for a remediation project, including
sediment resuspension, dredge availability, and site restrictions. These factors are
discussed below.
Sediment Resuspension—In areas where sediments have high contaminant con-
centrations, toxicity, mobility, or a combination thereof, extraordinary care and expense
may be required to minimize sediment resuspension or spillage. In such cases, releases
of contaminants to the water are a primary concern, and may override other factors in
selecting a dredge. As noted above, the degree of resuspension is influenced by both the
type of dredge and its operation. Resuspension characteristics of dredges are discussed
later in this chapter in regard to estimating contaminant losses.
Dredge Availability—A wide variety of dredging equipment is available through-
out North America and in the Great Lakes region. A summary of dredges stationed in
the Great Lakes is shown in Table 4-7. A summary of the availability of specialty
82
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Chapter 4. Removal Technologies
dredges is provided in Table 4-8. As shown, many of the specialty dredges developed
in Japan and Europe are not readily obtainable in the United States. The International
Dredging Review publishes an annual directory of dredge owners and operators, which
should be consulted for an up-to-date listing of dredging contractors and available
equipment.
TABLE 4-7. INVENTORY OF DREDGING EQUIPMENT
STATIONED IN THE GREAT LAKES
Dredge Type
Clamshell
Hydraulic (pipeline)
Hopper
Size Class
<5 yd3 (4 m3)
5-1 Oyd3 (4-7.5 m3)
>10 yd3 (7.5 m3)
8-12 in. (20-30 cm)
14-1 8 in. (36-46 cm)
20 in. (51 cm) and greater
3,600 yd3 (2,700 m3)
16,000 yd3 (12,000m3)
Number on
Great Lakes
44
18
15
11
11
11
1
5
Source: Averett et al. (in prep.).
Site Restrictions—Channel widths, surface and submerged obstructions, overhead
restrictions such as bridges, and other site access restrictions may also limit the type and
size of equipment that can be used. For example, hopper dredges are ships that require
navigable depths, cutterhead dredges require anchoring cables for operation, while bucket
dredges can operate in confined areas. In some cases, it may be more appropriate to
remove material from shore, as was done with contaminated sediments from Starkweather
Creek in Madison, Wisconsin (Fitzpatrick 1994).
Containment Barriers
The effectiveness of nonstructural containment barriers at a sediment remediation site is
primarily determined by the hydrodynamic conditions at the site. Conditions that will
reduce the effectiveness of barriers include:
• Strong currents
• High winds
• Changing water levels
• Excessive wave height (including ship wakes)
• Drifting ice and debris.
83
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TABLE 4-8. AVAILABILITY OF DREDGES FOR SEDIMENT REMEDIATION
Dredge Type
Enclosed clamshell
Backhoe
Cutterhead
Clean-up
Matchbox
Refresher
Plain suction
Dustpan
Hopper dredges
Horizontal auger
Delta
PNEUMA®
Oozer
Airlift
Bucket wheel
Screw-impeller
Disc-bottom
Note: M
H
H(M) -
H(P) -
Availability
Worldwide
Worldwide
Worldwide
Japan
Netherlands
Japan
Worldwide
United States
Worldwide
Worldwide
United States
Worldwide
Japan
Worldwide
Worldwide
Japan
Netherlands
mechanical
Manufacturer(s)
Numerous
Numerous
Numerous
TOA Harbor Works
Volker Stevin Dredging Co.
Penta Ocean Construction Co.
Numerous
Numerous
Numerous
Numerous
Delta Dredge & Pump
PNEUMA S.R.L. (Italy)
Toyo Construction Co.
Numerous
Numerous
Ube Industries, Ltd.
Unknown
Classification
M
M
H(M)
H(M)
H
H(M)
H
H
H
H(M)
H(M)
H(P)
HIP)
HIP)
H(M)
HIM)
H(M)
hydraulic
hydraulic with mechanical cutter
hydraulic with pneumatic pump
84
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Chapter 4. Removal Technologies
As a generalization, silt curtains and screens are most effective in relatively shallow,
quiescent water. As water depth increases, and turbulence caused by currents and waves
increases, it becomes increasingly difficult to effectively isolate the dredging operation
from the ambient water. The St. Lawrence Centre (1993) advises against the use of silt
curtains in water deeper than 6.5 m or in currents greater than 50 cm/sec.
The effectiveness of containment barriers is also influenced by the quantity and type of
suspended solids, the mooring method, and the characteristics of the barrier (JBF Scien-
tific Corp. 1978). Typical configurations for silt curtains and screens are shown in
Figure 4-4. To be effective, barriers are deployed around the dredging operation and
must remain in place until the operation is completed at that site. For large projects, it
may be necessary to relocate the barriers as the dredge moves to new areas. Care must
be taken that the barriers do not impede navigation traffic. Containment barriers may also
be used to protect specific areas (e.g., valuable habitat, water intakes, or recreational
areas) from suspended sediment contamination.
Monitoring
A monitoring program for environmental dredging should be designed to meet project-
specific objectives. Monitoring can be used to evaluate the performance of the dredging
contractor, equipment, and the barriers and environmental controls in use. Monitoring
may also be integrated into the health and safety plan for the dredging operation to ensure
that exposure threshold levels are not exceeded.
The monitoring program must be designed to provide information quickly so that
appropriate changes to dredging operations or equipment can be made to correct any
problems. Simple, direct, and preferably instantaneous measurements are most useful.
Measurements of turbidity, conductivity, and dissolved oxygen can be used as real-time
indicators of excessive sediment resuspension. Project-specific guidelines for interpreting
monitoring results should be developed in advance, as well as potential operational or
equipment modifications.
ESTIMATING COSTS
The basic principles of cost estimating, and the use of cost estimates to support the
decision-making process are discussed in Chapter 2. More detailed guidance specific to
estimating the costs of dredging operations is provided in this section. This guidance is
applicable to feasibility studies, but is not adequate for preparing a detailed dredging cost
estimate.
This document discusses the removal (Chapter 4) and transport (Chapter 5) components
of a sediment remedial alternative separately. However, these components are likely to
be part of a single contract, and their costs would, in most cases, be estimated together.
Virtually all costs associated with the removal component of a sediment remediation
85
-------
Maze
Legend
D Mooring buoy
X Anchor
.£, Single anchor or piling
U-shaped, instream
Movement due to
reversing currents
U-shaped, anchored onshore
ESTUARY
\
Circular or elliptical
Source: Barnard (1978)
Figure 4-4. Typical configuration of silt curtains and screens.
86
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Chapter 4. Removal Technologies
project are capital costs (direct and indirect). The elements of environmental dredging
costs include:
• Mobilization/demobilization
• Dredge operation
• Contaminant barriers
• Monitoring
• Health and safety
• Equipment decontamination.
Each of these elements is discussed below, and available unit prices are presented.
Although many of these unit prices are obtained from navigation dredging experience,
only the operational costs are likely to be increased significantly during sediment
remediation dredging as a result of the more slowed operation and decreased production.
Cost information is available from some historical sediment remediation projects. A total
of 13,000 m3 of sediments was excavated from Starkweather Creek in Wisconsin by
backhoe at a cost of approximately $10.00/m3 (Fitzpatrick 1994). The Waukegan Harbor
Superfund project in Illinois removed 23,000 m3 by dredging at a cost of $1.1 million
(Albreck 1994). However, these and other unit dredging costs from historical remediation
projects should only be used when all cost items are known.
Mobilization/Demobilization
The first cost incurred in any dredging project is that of bringing the dredging equipment
to the dredging site and preparing it for operation. This process is referred to as mobili-
zation. Demobilization occurs at the end of the project operation and typically costs one-
half the mobilization expense. Typical mobilization/demobilization costs for the Great
Lakes region (provided by USAGE Detroit District) are as follows:
Cost
(per 100 km)*
Mechanical dredge (clamshell) $37,500
Hopper dredge (<4,000 m3) $75,000
Hydraulic (pipeline) dredge $18,750
* Distance the dredge must be transported to the
project site.
87
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Chapter 4. Removal Technologies
Mobilization costs for backhoes (without the requirement for a floating platform) are
typically less than $400 (USEPA 1985a). Portable dredges are often leased or purchased
outright.
Mobilization/demobilization may represent the largest single cost element in the dredging
project, especially for projects with small dredging quantities. Additional costs will be
incurred if specialized pumps or unconventional dredgeheads are employed. Generally,
specialty dredging equipment may be transported separately to the site and used with the
conventional dredging equipment. The costs for specialty dredging equipment must be
developed on a site-specific basis.
Dredge Operation
The costs of a dredging operation depend on the size of the dredge employed and the
amount of time that the equipment is onsite (i.e., the cost of dredging is largely a function
of the production rate). In conventional dredging, the rate of production is fairly
predictable, based on the consistency of the sediments and the size of the dredge
employed. Algorithms for predicting the production rates of different dredge types are
provided in Church (1981).
During environmental dredging, additional time must be allowed for other factors, such
as:
• Greater precision of cut
• Slower production rates to minimize resuspension
• Multiple passes needed to achieve cleanup goals
• Use of contaminant barriers
• Restrictions posed by other remedial components.
In most cases, additional costs will be incurred as the production rates are lowered.
One of the goals of environmental dredging is to remove only those sediments that are
contaminated. Because of the costliness of treating or disposing of contaminated sedi-
ments, the quantity of clean sediments removed must be minimized. The production rate
of the dredge may be deliberately slowed so that downstream components such as sedi-
ment handling and transport, pretreatment, treatment, disposal, and/or effluent treatment
are not overwhelmed. This is particularly true for hydraulic (pipeline) dredging, in which
adequate time must be allowed for sediments to settle out in the receiving basin (see
Chapter 8). In fact, it may be more cost effective, in such instances, to select a smaller
dredge that can be operated at a constant rate close to its capacity, rather than a large
dredge with an operating schedule that is frequently interrupted.
Typical unit costs for various types of maintenance dredges are provided in Table 4-9.
They reflect the costs of dredge operation for rates of production typical of maintenance
88
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Chapter 4. Removal Technologies
dredging in the Great Lakes. These costs should be adjusted to account for the lower
production rates anticipated with environmental dredging. The adjustment for environ-
mental dredging production rates may be as much as 2-3 fold (or more) for specific
applications. For example, the hydraulic dredging of 23,000 m3 of sediments during the
Waukegan Harbor Superfund cleanup cost $1.1 million, or roughly $48/m3 (Albreck
1994). This cost included the deployment of a contaminant barrier (silt curtain).
TABLE 4-9. TYPICAL UNIT COSTS FOR MAINTENANCE DREDGING
Dredge Type
Hydraulic (pipeline)
Clamshell
Backhoe
Size Class
Under 10 in. (25cm)
10-1 4 in. (25-36 cm)
Over 14 in. (36 cm)
Under 2 yd3 (1.5m3)
2-5 yd3 (1. 5-4 m3)
Over 5 yd3 (4 m3)
0.5-1 yd3 (0.4-0.8 m3)
1-3.5 yd3 (0.8-2.7 m3)
Soft
Sediments8
$2.40/yd3
$2.50/yd3
$2.60/yd3
$6.00/yd3
SS-OO/yd3
S^OO/yd3
SS-OO/yd3
$2.50/yd3
Medium
Sediments'1
$4.00/yd3
$4.50/yd3
$5.00/yd3
$7.00/yd3
$5.00/yd3
$4.00/yd3
$7.00/yd3
$4.00/yd3
Note: This table represents average unit costs derived from harbor maintenance dredging.
Additional costs are discussed in the text.
Hydraulic dredge costs do not include booster pumps, which are required for long-
distance pumping (see Chapter 5).
Mechanical dredging costs do not include off-loading facility construction or costs for
barge transport (see Chapter 5).
Multiply costs by 1.32 for $/m3.
a Density of 1,000-1,500 g/L.
" Density of 1,500-2,000 g/L.
Containment Barriers
Several types of containment barriers are available to contain contaminants released
during dredging. Current unit costs for oil booms and silt curtains and screens are
summarized in Table 4-10,
TABLE 4-10. TYPICAL UNIT COSTS FOR CONTAINMENT BARRIERS
Barrier Unit Costs
Oil booms8 $7-€6/ft ($23-r216/m)
Silt curtains"
Geotextile (silt screen) SS/ft2 ($32/m2)
Vinyl-coated $28^ ($300/m2)
Polyurethane-coated SSS/ft2 ($375/m2)
9 Source: Averett et al. (in prep.).
"Source: USEPA (1985a).
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Chapter 4. Removal Technologies
Monitoring
The costs of a monitoring program for an environmental dredging operation may be
significant. However, these costs are project specific, and few generalizations can be
made. Among the potentially more costly items of a monitoring program are detailed
bathymetric surveys (before and after dredging), post-dredging sediment contaminant
analysis, and sediment resuspension monitoring. The cost of sediment analysis will
depend on the contaminants analyzed and the turnaround time requested of the laboratory.
The primary costs for resuspension monitoring are for field sampling, as turbidity and
suspended solids analyses are relatively inexpensive.
Health and Safety
The removal of contaminated materials from a waterway can be a hazardous activity,
especially if contaminant concentrations are high. Depending on the types of con-
taminants present, the concentrations expected, and the degree of contact workers may
have with the sediment, it may be necessary to provide workers with special PPE, such
as respirators and Tyvek® coveralls. Such gear can decrease the productivity of workers
and thereby greatly increase operating costs. This is particularly true if workers are
required to wear respirators or use supplied air. However, in most cases sediment
contaminants are not volatile, and therefore respiratory protection is rarely needed.
Another health and safety consideration is the training of site workers. Workers at all
Federal Superfund sites, as well as other hazardous waste sites, are required to undergo
40 hours of health and safety training (29 CFR 1910.120). This requirement may
represent an additional expense not anticipated by the dredging contractor.
Equipment Decontamination
Reusable equipment that comes into contact with contaminated materials may have to be
decontaminated prior to leaving the site. This is an expense not normally included with
demobilization costs. The level of decontamination required will depend on the nature
of the sediment contaminants and the laws and regulations governing the remediation.
Large equipment such as dredges may have to be steam-cleaned or washed with
detergents, unless it can be shown that contamination can be effectively removed using
less intensive methods. It may be possible to clean pumps and pipelines by pumping
clean water or clean sediment through them. All wash water from these operations would
have to be captured and probably treated before being released.
ESTIMATING CONTAMINANT LOSSES
The loss of contaminants during dredging may need to be estimated for a number of
reasons, including:
• Comparison and selection of dredging equipment
• Evaluation of the overall losses from remedial alternatives
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• Determination of compliance with water quality requirements
• Determination of short-term impacts on sensitive resources.
Factors that potentially affect contaminant losses from dredging are listed in Table 4-11.
TABLE 4-11. FACTORS THAT AFFECT CONTAMINANT LOSSES
Sediment Type and
Quality
Dredging Equipment and
Methods
Grain size
Sediment density
Sediment cohesion
Organic matter concentration
Volatile substance concentration
Type of dredge
Dredge capacity or production rate
Condition of equipment
Equipment modifications
Equipment reliability under varied conditions
Operating precision of equipment
Sediment loss during operations
Training and skill of operators
Hydro-dynamic Conditions Water depth
Morphology of shoreline and configuration of existing structures
Flows and suspended solids concentrations
Waves, tides, currents
Wind speed and direction
Hydrological phenomena caused by dredging operations
Water Quality
Temperature
Salinity
Density
Source: St. Lawrence Center (1993).
A study conducted under the ARCS Program examined the available predictive tools for
estimating contaminant losses from dredging (Myers et al., in prep.). The three mecha-
nisms of contaminant loss from dredging are:
• Particulate contaminant releases
• Dissolved contaminant releases
• Volatile contaminant releases.
Particulate Contaminant Releases
Methods for predicting sediment resuspension have been developed for cutterhead and
mechanical (bucket) dredges. These methods predict the resuspension of particulates as
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Chapter 4. Removal Technologies
a function of dredging equipment, operation, and sediment properties. These techniques
have not been field verified, and are therefore not fully developed (Myers et al., in prep.).
Limited field studies have indicated that the type of dredging equipment used may have
less effect on sediment resuspension than how it is used. The care with which a dredge
operator excavates material has a significant effect on sediment resuspension (Hayes
1992). For example, variables such as cutter speed, swing speed, and degree of burial
(bank factor) have been incorporated into models for cutterhead dredges (Myers et al., in
prep.). Decreasing each of these parameters can reduce the resuspension caused by
hydraulic dredging. Similarly, smooth and controlled hoisting can limit resuspension
during clamshell dredging (McClellan et al. 1989).
Sediment properties are site-specific variables that cannot be controlled. In general, fine-
grained, less-cohesive sediments have the greatest potential for resuspension and will
travel further before resettling to the bottom.
The resuspension characteristics of numerous dredge types have been measured at various
locations. A summary of resuspension tests is provided in Table 4-12, as compiled by
Herbich and Brahme (1991), Zappi and Hayes (1991), and others. The comparability of
sediment resuspension results from different sites is highly limited due to differences in
the monitoring programs, sediment types, site conditions, and other factors. As indicated
above, the type of dredge used is not always the most significant factor affecting sediment
resuspension.
Dissolved Contaminant Releases
Resuspension of sediment solids during dredging can impact water quality through the
release of contaminants in dissolved form. Dredging exposes sediments to major shifts
in liquid/solids ratio and reduction/oxidation potential (redox). Initially upon
resuspension, the bulk of the contaminants are sorbed to paniculate matter. As the
resuspended particles are diluted by the surrounding waters, sorbed contaminants may be
released, increasing the fraction of dissolved contaminants in the water. Changes in redox
potential (i.e., from an anaerobic to an aerobic environment) can affect metal speciation.
This may increase the solubility of metals (e.g., oxidation of mercury sulfides) or decrease
metal concentrations (e.g., metal scavenging by oxidized iron floes) (Myers et al., in
prep.). Organic contaminants are largely unaffected by redox shifts.
Methods for predicting the release of dissolved contaminants during dredging are less
developed than those for sediment resuspension. A method using equilibrium partitioning
concepts has been proposed for estimating the concentrations of dissolved organic
contaminants, and a laboratory elutriate-type test has also been evaluated (Myers et al.,
in prep.).
Volatile Contaminant Releases
Dissolved organic chemicals are available at the air-water interface where volatilization
can occur. Although the dissolved phase concentrations and therefore the evaporative flux
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TABLE 4-12. SUSPENDED SOLIDS CONCENTRATIONS PRODUCED BY VARIOUS DREDGES
Dredge Type
Suspended Solids Concentration
Remarks
Cutterhead
10 rpm
20 rpm
30 rpm
18 rpm
18 rpm
161 mg/L (sandy clay), 52 mg/L (medium clay)
187 mg/L (sandy clay), 177 mg/L (medium clay)
580 mg/L, 266 mg/L
1 -4 g/L within 3 m of cutter
2-31 g/L within 1 m of cutter
Observations in the Corpus Christi
Channel (Huston and Huston 1976)
Soft mud at Yokkaichi Harbor,
Japan (Yagi et al. 1975)
Trailing suction
(hopper dredge)
Several hundred milligrams per liter at overflow
2 g/L at overflow
200 mg/L at 200 m behind pump
San Francisco Bay (Barnard 1978)
Chesapeake Bay (Barnard 1978)
Mudcat
1.5 m from auger, 1 g/L near bottom (background
level 500 mg/L)
1.5-3.5 m in front of auger, 200 mg/L surface and
mid-depth (background level 40 to 65 mg/L)
PNEUMA* pump
48 mg/L at 1 m above bottom
4 mg/L at 7 m above bottom (5 m in front of pump)
13 mg/L at 1 m above bottom
Port of Chofu, Japan
Kitakyushu City, Japan
Clean-up
1.1-7.0 mg/L at 3 m above suction
1.7-3.5 mg/L at surface
Toa Harbor, Japan
Grab/bucket/clamshell
Less than 200 mg/L and average 30-90 mg/L at
50 m downstream (background level 40 mg/L)
168 mg/L near bottom
68 mg/L at surface
150-300 mg/L at 3.5-m depth
San Francisco Bay (Barnard 1978)
100 m downstream at lower
Thames River, Connecticut (Bohlen
and Tramontaro 1977)
Japanese observations (Yagi et al.
1975)
Enclosed buckets 30-70 percent less turbidity than typical buckets
500 mg/L at 10 m downstream from a 4 m3 water
tight bucket
Based on comparison of 1-m3 buck-
et (Barnard 1978)
Source: Herbich and Brahme (1991) except where noted
Note:
nature of sediment resuspension rates
This table serves as a summary of many different studies on the resuspension characteristics of multiple dredge
types. The reader should use caution in the use of values presented in this table due to the extremely site-specific
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are highest near the dredge, the mass release rate (flux times area) may be dominated by
the lower concentration region away from the dredge.
Methods for predicting the rate of volatilization across the sediment-water interface are
fairly well developed. To apply these methods at a dredging site requires the application
of a mixing model to define both the area of the contaminant plume and the average
dissolved-phase contaminant concentrations within that plume (Myers et al., in prep.).
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5. TRANSPORT TECHNOLOGIES
Transport technologies are used to move sediments and treatment residues between
components of a remedial alternative. In most cases, the first element of the transport
component is to convey sediments dredged during the removal process to the disposal or
rehandling site. Sediments may then be transported for pretreatment and then treatment,
and treated residues may be transported to a disposal site. Transport is the component
that links the other components of a remedial alternative, and may involve several
different technologies or modes of transport.
Transport modes can include waterborne, overland, or a combination of these tech-
nologies. Waterborne transport modes include pipeline transport, hopper dredges, and
barge systems. Overland transport modes include pipeline, railcar, truck trailer, and
conveyor systems. In most cases, contaminated sediments are initially moved using a
waterborne transport mode (pipeline or barge) during the removal process (one exception
is when land-based dredging is used). Hydraulic removal technologies produce contami-
nated, dredged material slurries that are typically hauled by pipeline transport to either
a disposal or rehandling site. Mechanical removal technologies typically produce dense,
contaminated dredged material or excavated basin material for rehandling, which is hauled
by barge, railcar, truck trailer, or conveyor systems.
Averett et al. (in prep.) provide a literature review of dredged material transport tech-
nologies. Other key resources for information on transport technologies include Church-
ward et al. (1981), Souder et al. (1978), Turner (1984), and USEPA (1979). Much of the
information on transport technologies in the literature cited herein was developed for
application to municipal sewage sludge, dredged material, and mining materials. The
intended applications were generally scaled for very large quantities of materials. In
many instances, these materials were transported over long distances, using permanently
installed systems as part of long-term operations. In contrast, sediment remediation
projects will typically move relatively small quantities of material over short distances and
are often short-term operations. The feasibility and costs of transportation modes will be
influenced by the scale of the remediation project.
This chapter provides a brief description of the pipeline, barge, railcar, truck trailer, and
conveyor transport technologies. Discussions of the factors for selecting the appropriate
transport technology and techniques for estimating costs and contaminant losses during
transport are also provided. When transport modes are compared and contrasted with
each other, the volumes of material being discussed are in-place cubic yards or cubic
meters of sediment.
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Chapter 5. Transport Technologies
DESCRIPTIONS OF TECHNOLOGIES
Pipeline Transport
Temporary dredge pipelines are the most economically feasible mode for hauling
contaminated dredged material slurries and water. For a sediment remedial alternative,
pipelines may be used for the discharge from a hydraulic dredge; with the hydraulic
pumpout from a tank barge, railcar, or truck trailer; and in routing process water, effluent,
or leachate to treatment systems.
The amount of dredged material slurry generated during sediment removal is greatly
affected by the contaminated sediment characteristics, removal equipment design, and
removal equipment operation. Pipeline transport systems should be hydraulically designed
and operated to minimize downtime while effectively moving this slurry. Equipment
durability and pipeline routing greatly affect system downtime. Effective slurry transport
consists of moving the slurry with minimal particle sedimentation in the line and with
good line connections and minimal line wear and corrosion. Other factors being equal,
fine-grained dredged material can be less costly to move (i.e., require less energy) than
coarse-grained material (Denning 1980; Souder et al. 1978; USEPA 1979).
It is periodically necessary to halt dredging operations to add or remove sections of the
pipeline to permit vessel passage or dredge advance, repair leaks, or reroute the line.
Therefore, pipeline sections should be quick and easy to assemble, maintain, and
dismantle. Although leaks can be welded, extra pipe sections should be readily available
onsite to replace both land- and water-based pipeline sections that are clogged or leaking.
Frequent monitoring helps to prevent excess leakage (Cullinane et al. 1986a).
Discharge Pipeline
Hydraulic dredge discharge pipelines can be identified by their properties (i.e., construc-
tion material, internal diameter, relative strength or schedule number, length, wall
thickness, or pressure rating) or method of deployment (i.e., floating, submerged, or
overland). Discharge pipelines typically range in length from <3 to >15 km (with
boosters) (Cullinane et al. 1986a; Souder et al. 1978; Turner 1984). Souder et al. (1978)
indicate that during commercial land reclamation projects slurries have been moved
through pipelines of up to 24 km in length, and that a well-designed hydraulic dredge
system can theoretically move some slurries >200 km using multiple booster pumps.
Discharge pipe sections are available in a variety of wall thicknesses and standard section
lengths. The internal diameter, which is slightly larger than the diameter of the dredge
suction line, ranges from 6 to 42 in. (15 to 105 cm; Turner 1984). Internal pipe section
linings of cement, plastic, or glass can reduce the abrasion caused by slurry-entrained
gravel, sand, and site debris; metal corrosion caused by sediment-bound contaminants and
saline transport water; and the internal pipe roughness. In addition, internal abrasion and
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corrosion can be evenly distributed by periodically rotating each pipe section. External
metal pipe corrosion can be controlled with coatings and/or cathodic protection.
Several types of discharge pipelines available for use are discussed below.
Rigid Pipeline—Rigid pipe sections can be constructed of steel, cast and ductile
iron, thermoplastic, and fiberglass-reinforced plastic; the steel and iron sections are most
commonly used. These sections can be joined by ball, sleeve, or flange joints to form
discharge lines of varying lengths. The rigid nature of these sections permits longer,
unsupported line spans and reduces the potential for damage while handling. Standard
steel and iron pipe section lengths are 20, 30, and 40 ft (6.1, 9.1, and 12.1 m).
Flexible Pipeline—Flexible discharge pipe sections are constructed of either high-
density polyethylene (HDPE) or rubber. The flexibility of the materials allows these
sections to naturally adjust to wave action and shore contours. Therefore, these pipelines
are easier to route than rigid pipelines. In addition, the flexible nature of these pipelines
allows long-sweeping and more hydraulically efficient routing. However, flexible
pipelines are far less commonly used than rigid pipelines.
Floating Pipeline—Discharge pipelines typically include a floating pipeline
connected to the dredge pump(s) at the stern of the dredge hull. The floating pipeline can
subsequently be run to a shore-based pipeline routed to the disposal or rehandling site.
Because of concerns about obstructions in these pipelines and their overall stability, their
use is typically limited to sections that connect the dredge pump to the land-based line.
These sections provide for easy dredge movement (i.e., swing and advance). The dredge
pump is connected to a floating rigid pipeline by either a rubber hose, swivel elbow, or
ball joint(s). These lines are typically anchored at various locations.
Pipeline flotation is accomplished using pontoons or buoyant collars. Pontoons are
typically constructed of metal cylinders with tapered ends, mounted to each end of a pipe
section. The pontoons are joined together by rigid, wooden or steel beams. The rigid
pipe section is attached to wooden pontoon saddles. Tender boats are used to move
floating pipeline sections.
Obstruction of the waterway can be minimized by routing the pipeline to and along the
shoreline. However, these pipelines should be placed in waters of adequate depth and
distance from the shoreline to prevent the lines from dragging on the bottom and/or
ramming the shoreline. When obstruction of the waterway is of little concern, the
pipeline should be floated in a wide arc so that the dredge can advance without frequent
stops to add additional pipe sections (Huston 1970).
Submerged Pipeline—Submerged pipelines can be used in place of floating
pipelines in waterways where vessel traffic would require frequent dredge downtime to
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Chapter 5. Transport Technologies
disconnect the line and permit passage. Submerged pipelines require two stationary points
where the ends of the line can be fixed as they rise out of the water. For temporary lines,
these points are typically well-moored barges (Huston 1970). Although less susceptible
to damaging wave action, submerged pipelines should be used conservatively because
inspection for plugs and leakage is difficult.
Shore Pipeline—Relative to floating and submerged pipelines, shore pipelines are
made up of shorter (10-15 ft [3-5 m]) and generally lighter pipe sections. Pipe sections
are joined and placed aboveground or on a cribbing. These lines should only be covered
to protect the line from damage (i.e., traffic crossings, freezing/thaw conditions) because
detection of leakage is difficult. Shore pipelines generally flow into a disposal or
rehandling site.
Booster Pump
Booster pumps (kinetic or positive displacement) supplement the dredge pump(s) by
increasing the distance a slurry can be pumped without particle sedimentation. Booster
pumps are used when the output of the dredge pump(s) is so reduced by line routing that
the cost of a booster pump is justified by the increased productivity it achieves. Although
easier to design, booster pumps do not have to be identical to the dredge pump(s). For
dredges that operate with long discharge lines and require booster pumps, Turner (1984)
indicated that installing a booster pump on the dredge hull would reduce labor and
maintenance costs. This layout would lower the labor costs typical of line booster pumps
but would increase material costs for pipelines necessary to withstand increased pressures.
Booster pumps are installed to form a series of identical pumping stations (barge- or land-
based) generally spaced uniformly from the dredge to the disposal or rehandling site. At
each pumping station, two essentially similar pumps are arranged in series. However, if
deemed necessary to optimize the reliability of the operation, an auxiliary spare pump and
motor with all pertinent piping, valves, and connections can be provided for emergency
use in the event of a major breakdown in the primary equipment. Positive displacement
booster pumps used in combination with a centrifugal dredge pump would require a
booster pump holding facility because it is practically impossible to match positive
displacement pumping rates to centrifugal pumping rates (USEPA 1979).
Barge Transport
Transport barges or scows can be defined as cargo-carrying craft that are towed or pushed
by a powered vessel on both inland and ocean waters (McGraw-Hill 1984). Barge
transport is the most common means of transport for mechanically dredged material.
Features of barge transport that are discussed in this section are barge types, tow
operations, and loading/unloading operations.
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Barge Types
Three types of barges that are applicable to sediment remediation projects are the tank,
hopper, and deck barges. The features of these barges are provided in Table 5-1. Tank
barges are most frequently used to haul coal, petroleum and petroleum products,
agricultural products, iron, steel, and chemicals. Sectionalized compartments provide
structural stability to the barge hull, distribute cargo loads more evenly, help prevent
cargo from shifting while in tow, and allow each section to carry different types of cargo.
Hopper barges are designed specifically to deliver bulk material to open-water disposal
sites, and are the most commonly used barges for transporting dredged material. Early
hopper barge designs used mechanically driven chain, cable, sheave, and releases to open
the cargo compartment door(s). Recent designs use high-pressure hydraulic systems.
Split-hull and continuous compartment bottom and side-dump hopper barges are simul-
taneously dumped, whereas bottom and side-dump hopper barge sections can be dumped
individually.
The Buffalo District studied the leakage from hopper barges and concluded that all hopper
barges leak to some degree. They concluded that all hull seams should be carefully shut
and stabilized with sandbags, hay bales, and/or plastic liners to help minimize hull
leakage.
Deck barges are simply a flat work surface and may be used as a work barge (i.e., anchor,
derrick, jack-up, mooring, office, pontoon, quarterboat, service, shop, store, or survey
barges) or the platform for the dredge. During a sediment remediation project on the
Black River in Lorain, Ohio, a single deck barge was used as the platform for a bucket
dredge and several dumpsters that were used to contain the dredged sediments. After the
dumpsters were filled, the barge was brought to the shore, where the dumpsters were
offloaded to flatbed trucks and hauled to a nearby disposal site.
Barge hulls can be of either single- or double-walled construction. The bow and/or stern
of a barge hull is either vertical (box-shaped) or raked (angled). Raked hulls provide less
tow resistance, thereby resulting in fuel savings, while box-shaped hulls are typically
limited to barges on the interior of an integrated tow of multiple barges. Barges operated
in moderately high wave areas can be constructed with a notched stem in which the
towboat bow fits. This connection provides greater resistance to longitudinal movement
along the vessel interface and enhances control under adverse conditions (Churchward et
al. 1981).
Tow Operations
In the absence of significant wave action, the best position for a towboat is at the barge
stern (Churchward et al. 1981). While the main factor in selecting a towboat is its ability
to maneuver and push or tow the barges, the towboat's draft is also an important factor.
The towboat draft should be consistent with site and transport route water depths to
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TABLE 5-1. BARGE TYPES
Contaminated dredged material
Tank Barge
• Cargo compartments are one continuous
section or divided into several sections
• Hydraulically or mechanically loaded and
unloaded from the top
• Inland and nearshore bulk material tank
barge capacities typically range from 100
to 6,000 yd3 (75 to 4,600 m3; Souder et
al. 1978; Watanabe 1970)
Contaminated dredged material
Hopper Barge
• Barges have funnel-shaped hull interiors
that are either longitudinally split or con-
structed with side- or bottom-mounted
discharge door(s)
• Mechanically loaded from the top;
unloaded hydraulically or mechanically
from the top or dumped through side or
bottom doors
• Inland and nearshore bulk material tank
barge capacities typically range from 100
to 6,000 yd3 (75 to 4,600 m3)
Contaminated dredged material
in storage bins
• Barge with open deck, providing little
cargo containment
• Suitable as work barge and for hauling
dredging debris
• Suitable for hauling sediments in bins or
dumpsters (as shown)
Deck Barge
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prevent sediment resuspension from propwash and hull dragging. Towboats are also used
to move the dredge floating plant (when not self-propelled).
Although grain- or coal-filled barges are typically moved in large, integrated tows (up to
40 barges), dredged material-filled barges are generally hauled individually. A typical
maintenance dredging operation might use two barges (one is filled by the dredge while
the other is being transported to or from the disposal or rehandling site). If the distance
between the dredging and disposal or rehandling site is long, additional barges and
towboats may be used. The objective is to have sufficient barges and towboats available
to keep the dredge operating continuously.
Spillage during transport can result from overfilling the barge or from a leaky hull. Risks
of spillage are especially great when moving through rough waters. Overfilling can be
prevented by filling the barge only to the bottom of the barge coaming. Spillage while
in tow can be prevented by placing removable covers over the barge coaming. Barge
hulls should be inspected regularly to ensure that they are completely sealed.
Loading/Unloading Operations
Tank and hopper barges are typically loaded by first pulling the barge adjacent to the
dredge floating plant. Dredged sediment is frequently splashed or dropped onto the deck
of a barge during loading operations. Spillage can be reduced by minimizing the height
from which the bucket releases its load. Dredge operators should place the bucket into
the cargo compartment before releasing the load and not drop it with any freefall. In
addition, tank barges should be loaded uniformly to prevent excessive tilting or overturn-
ing.
During maintenance dredging of uncontaminated sediments, supernatant is allowed to
overflow during filling to increase the barge's payload (i.e., reduce the amount of water
hauled). Because of the potential for contaminant release and the inefficiency of barge
overflow for fine-grained sediment, supernatant overflow should not be permitted on
contaminated sediment dredging projects. Methods to remove free-standing water from
barges, including the use of polymer flocculants, have been investigated by some Corps
districts to produce more economical loads with contaminated dredged material (Palermo
and Randall 1990).
Most barges can be unloaded using a variety of mechanical equipment, including cable,
hydraulic, or electrohydraulic rehandling buckets (Hawco 1993). Backhoes and belt
conveyors or bucket line dredges can also be used to unload barges. All unloading
facilities should be equipped with drip pans or aprons to collect material spilled while
unloading the barge and loading the material onto a railcar, truck trailer, or conveyor or
directly into a disposal or rehandling facility.
Mechanically dredged sediments have been unloaded from barges to CDFs using a
modified hydraulic dredge or submerged dredge pump. Water from the rehandling site
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Chapter 5. Transport Technologies
or disposal facility (where available) is added to the barge and mixed in with the sediment
to provide a uniform slurry for the rehandling dredge pump.
Railcar Transport
Railcar transport is widely used in the transport of sewage sludge, but has not been used
for the transport of dredged material (according to available literature). However, railcar
transport of contaminated sediments may be feasible when travel distances are especially
long (i.e., >160 km).
Railcar designs can include tank, hopper, deck, and box cars (Churchward et al. 1981).
Mechanically filled tank and hopper railcars are most likely the only economical means
of hauling contaminated dredged material. The features of tank and hopper railcars are
summarized in Table 5-2. Tank cars might also be used to haul liquid treatment residues.
Souder et al. (1978) indicate that railcars of the 70- to 100-net ton class are preferable for
hauling bulk materials such as dredged sediment. Tank and hopper railcars can be
constructed with permanent or hatched covers to prevent weather effects and spilling or
leaking of material or water from the car. Like barges, railcars should be uniformly
loaded.
Railcars are pulled by either diesel- or electric-powered locomotives. However, with the
exception of switching facilities, railcars must be hauled by a railroad company locomo-
tive, requiring a contract that can take several months to obtain (USEPA 1979). Larger
trains (railcar capacity and number of cars) are limited by track system designs and
crossing times.
Tank Railcars
Rectangular tank railcars are typically used to haul dense materials. They are unloaded
by moving them off the mainline track to an elevated loop track, disassembling the train,
and dumping each car using rotary car unloading equipment. The rotary car technique
turns the railcar upside down to allow gravity drainage. Swivel tank car connections can
be used to avoid disassembling the train during rotary dumping. Rotary dumping
equipment is very expensive and generally works best for non-cohesive materials (Souder
et al. 1978). Shaker units can be used to help unload the typically cohesive contaminated
dredged material.
Cylindrical railcars are typically used for hauling liquid cargo and could be used for
hauling dredged material slurries. These cars are hydraulically filled and are unloaded
by moving them to an elevated track to allow gravity drainage through a hatch or valve
opening(s) on the car body. Tank cars can also be pumped out.
Hopper Railcars
Similar to tank railcars, hopper railcars are typically unloaded by moving them to an
elevated loop track. Hopper railcars are unloaded by opening the bottom-mounted hopper
102
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TABLE 5-2. RAILCAR TYPES
XXX
XXX
XXX
Tank Railcar
• Constructed with either rectangular or
cylinder-shaped cargo compartments
• Capacities typically range from 10,000
20,000 gal (38,000 to 76,000 L)
• Rectangular tank cars are mechanically
loaded from the top and rotary dumped
• Cylindrical railcars are hydraulically filled
and unloaded by gravity drainage or pump-
out
I
\ A A
\ / \ i \
W W A
' I
Av1
i \ i
xxx:
XXX
XXX XXX
Hopper Railcar
• Has funnel-shaped cargo compartments)
that slope to one or more mechanical or
hydraulic doors
• Capacities range from 10,000 to 20,000
gal (38,000 to 76,000 L)
• Mechanically loaded from top
• Unloaded by opening the bottom-mounted
hopper door(s) or hatch(es) to allow gra-
vity drainage
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Chapter 5. Transport Technologies
door(s) or hatch(es) to allow gravity drainage (Souder et al. 1978). Unlike rotary
unloading, bottom dumping of hopper railcars does not require disassembly from the train
prior to unloading and, depending on the material cohesion, the train may not even have
to come to a complete stop.
Truck Trailer Transport
Truck trailer transport is the most common mode of transportation for hauling mechani-
cally dredged material to upland disposal sites. Truck cargo compartments can include
van (open and closed tops), flat, tank (liquid or pneumatic cargo), dump, depression deck,
rack, or refrigerated (van or tank) types (Churchward et al. 1981). However, only tank
and dump compartments are suitable for hauling dredged material and liquid treatment
residues. The features of these types of trailers are summarized in Table 5-3.
Tank and dump compartments can be mounted on a single diesel- or gas-powered tractor
chassis or mounted on a trailer chassis and towed by a tractor over both paved and
unpaved roads. To minimize the number of drivers required and to allow loading to
continue while other trucks are en route, it is desirable to use excess trailers. As with
barge and railcar transport, mechanically filled trailers are the only economical means of
hauling contaminated dredged material by truck. Liquid treatment residues (e.g., con-
taminated oil residue from solvent or thermal extraction processes) can be hauled in
cylindrical tank trailers.
Trailer gates and hatches can be sealed with rubber gaskets, straw, or other materials to
prevent leakage or spillage. During a dredging operation at Michigan City, Indiana, the
bottom of dump truck flap gates were lined with sand, and a street sweeper was used to
clean any drippage on public roads. Dump truck gates fitted with neoprene seals and
double redundant locking latch mechanisms were used to haul dredged material during
the Starkweather Creek cleanup in 1992 (Fitzpatrick 1993). Like barges and railcars,
trailer covers can be installed to minimize odor releases during transport, to prevent
spillage from sudden stops or accidents, and to prevent weather damage. Trailers should
also be uniformly loaded;
Conveyor Transport
Conveyor systems have been widely used for the transport of sewage sludge and for
material transport in mining and mineral processing (USEPA 1979). Within a sediment
remedial alternative, conveyors might be used to transport mechanically dredged sedi-
ments from barges to disposal or rehandling sites, from rehandling sites to pretreatment
and/or treatment systems, between process units of a pretreatment/treatment system, and,
for solid residues, from treatment systems to disposal sites or to other transport modes.
Conveyor transport systems include belt, screw, tabular, and chute systems. The features
of the belt and screw conveyor systems are summarized in Table 5-4. These conveyor
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TABLE 5-3. TRUCK TRAILER TYPES
Tank Trailer
• Trailers constructed with rectangular or
cylinder-shaped cargo compartments
• Rectangular tank trailers top loaded and
either mechanically or hydraulically
unloaded
• Cylindrical-shaped trailers limited to haul-
ing treated liquids
• Available in sizes ranging from 500 to
6,000 gal (2,000 to 23,000 L; Metcalf &
Eddy, Inc. 1991)
• Trailer loaded from the top
• Can be constructed with watertight (not
welded) tailgate-dump or bottom-dump
doors or hatches
• Catch basins have been welded onto the
exterior of tailgates to catch leaks
• Tailgate-dump trailers used for hauling
sewage sludge range in size from 8 to
30 yd3 (6 to 23 m3; Metcalf & Eddy, Inc.
1991)
Dump Trailer
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TABLE 5-4. CONVEYOR TYPES
Contaminated dredged material
I feed bin
u
O O O O D O O O O
Feedout bin
Belt Conveyor
• Motor-driven pulley and belt system sup-
ported by trough-shaped or flat idlers
• Shape of the belt, system inclination, and
speed of movement are dependent on the
solids content and consistency o1 the
material; typical conveyor speed is 11-16
km/hour
• Conveyor belts range in size from 30- to
72-in. (76- to 182-cm) wide with trough
angles of 20° to 30°
• Conveyor flight lengths are available in
lengths of 900 to 26,400 ft (275 to
8,000 m)
Contaminated dredged material
, feed bin
\
AAAAAAAA _T\ _f\ A
\/
\/
Feedout bin
Screw Conveyor
• Motor-driven screw or auger
• Screw conveyor flights limited to 20 ft
(6 m) to prevent material accumulation
around the internal bearing system
• Conveyors are constructed with reversible
motors and several gate-controlled, bot-
tom-dump discharge points to provide
flexibility
• Objects such as rags and sticks should be
screened out of the dredged material to
prevent jamming of the conveyor (USEPA
1979)
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Chapter 5. Transport Technologies
systems typically require a loading or feeder bin from which the material is placed on the
conveyor. An unloading or feedout bin may also be required, depending on whether the
material is going to a disposal/rehandling site, a pretreatment or treatment unit, or another
mode of transport.
Commercially available conveyor systems can be permanently installed or portable.
Portable conveyors provide system flexibility and allow material to be placed over a
wider area. These systems are most practical for handling small volumes of mechanically
dredged material (USEPA 1979; Souder et al. 1978). For example, a small conveyor
system was used to transport materials in the pilot-scale demonstration of sediment
washing technologies conducted for the ARCS Program at Saginaw Bay, Michigan
(USAGE Detroit District,'in prep.).
Conveyors have low operating costs and move high volumes with minimal noise and air
pollution. However, they can be expensive to purchase and very labor intensive and, like
pipelines, may require right-of-way permission. Chute systems that lead from one flight
to another can become clogged by oversized pieces. Like pumps and pipelines, conveyors
are a continuous system; therefore, if one segment fails the whole system fails (Souder
et al. 1978).
Chute or inclined plane conveyors or slides have no mechanical parts. Chutes have been
used to move mechanically dredged sediments from barges into CDFs adjacent to
navigable waterways. Examples of chutes used at the Chicago Area CDF are shown in
Figure 5-1. Sediments were unloaded from the barges using a crane and small bucket and
placed onto the chute, which carried the sediments into the CDF. In some cases, water
was sprayed onto the chute to help move the material. Based on the use of chutes for
sewage sludge, it is recommended that the incline be greater than 60° for dewatered
material and greater than the material's natural angle of repose for dried material. These
systems can be open or covered to prevent spillage (USEPA 1979). Relatively shallow
slopes (30° and less) have been used with slides transporting wet dredged material.
SELECTION FACTORS
The limitations of each transport technology should be considered prior to selecting the
contaminated sediment transport mode(s). These limitations might include legal, political,
sociological, environmental, physical, technical, and economic practicality. Souder et al.
(1978) developed a generalized sequence for selecting alternatives for inland transport of
clean dredged material. The selection factors for contaminated sediment transport adapted
from Souder et al. (1978) include: compatibility with other remedial components,
equipment and route availability, compatibility with environmental objectives, and costs.
Compatibility with Other Remedial Components
The selection of transport modes should be among the last decisions in the planning of
a sediment remedial alternative. In many cases, the selection of other remedial compo-
nents will eliminate all but one or two transport modes for consideration. For example,
707
-------
Harbor
Floating plant
(stationary)
Slide formed of 2 railroad
tank cars cut in half
Hopper
Harbor
Figure 5-1. Examples of chutes used for transporting dredged material.
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Chapter 5. Transport Technologies
a remedial alternative involving hydraulic dredging will, with few exceptions, necessitate
pipeline transport. Mechanically dredged sediments, on the other hand, can be transported
using any of the modes discussed, including pipeline transport (although sediments will
have to be slurried).
Some disposal/rehandling facilities can accommodate both hydraulically or mechanically
transported sediments. Others, because of limited size or design features, cannot
accommodate loadings by hydraulic slurry. Many treatment and pretreatment technologies
have rigid restrictions on both the character and rate of feed material delivery. Residues
from pretreatment or treatment systems may require continuous handling to subsequent
components, or may be stockpiled for bulk handling. Transport modes must therefore be
compatible with all components of a remedial alternative.
Equipment and Route Availability
Equipment A vailability
Availability is rarely a limiting factor in the selection of transportation equipment. Most
contaminated sediment sites are in urban areas, with transportation equipment available
from several sources. At worst, equipment will have to be brought in from a greater
distance, increasing the mobilization and demobilization costs.
Pipeline and Barge Transport—Equipment for waterborne transport is readily
available for leasing from dredging and marine construction contractors. The availability
of specific equipment, including pipelines and barges, will reflect regional markets for
their use and the dimensional restrictions (e.g., vertical clearance, width, draft) of regional
waterways. Dredging/marine construction trade journals, such as International Dredging
Review, Terra et Aqua, World Dredging, Mining and Construction, and The Waterways
Journal, contain the names of contractors and advertisements for equipment lease or
purchase.
Railcar Transport—Railcars filled with sediments or treatment residues may be
added to an existing train route or transported as an entire trainload of railcars or "unit
train." Single-car transport can require that a railcar be switched from train to train
several times, resulting in increased costs. A unit train operation, commonly applied to
hauling coal, is negotiated with a railroad company and is dedicated to carrying only one
commodity from one point to another on a tightly regulated and continuing schedule.
A unit train operation could haul from 70 to 140, 100-ton (91 tonne) railcars (approxi-
mately 10,000 tonnes of contaminated dredged material) over distances of 80-2,400 km.
Souder et al. (1978) recommended haul volumes of greater than 380,000 m3 and haul
distances greater than 80 km to support a unit train operation. A shorter haul distance
increases the cost significance of loading and unloading.
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Chapter 5. Transport Technologies
Trailer Transport—A variety of truck trailer rigs may be leased or contracted
through most large construction companies. There are numerous State and Federal
restrictions on the size (vehicle width, height, and length) and weight of truck trailer rigs.
Some regulations limit the number of trailers in tow by a tractor. Some weight regula-
tions provide for the maximum weight that can be carried on single and multiple tandem
(two grouped) axle groupings. However, most weight restrictions relate the overall or
gross weight to the vehicle's wheel base. Most State regulations limit truck trailer loads
to about 25 tons (23 tonnes). Other regulations include speed limits; requirements for
safety features such as speedometers, brakes, horns, lights, windshield wipers, mirrors,
and bumpers; and requirements for liability insurance. Some local ordinances even
restrict truck operations to certain hours of the day and to certain routes (Souder et al.
1978).
Conveyor Transport—Conveyor systems are widely used in wastewater treatment
and mining applications. Conveyor equipment may be purchased from suppliers to these
industries identified in trade journals, including Water and Waste Digest and Waterworld
Review. Some types of conveyor equipment may also be available for lease from the
manufacturers or from dredging and construction contractors. Chutes and slides are
typically fabricated by the dredging/transport contractor from purchased or available
material. One dredging contractor split two abandoned railroad tank cars in half
lengthwise and welded them into an open slide for transporting dredged material into the
Chicago Area CDF (Figure 5-1).
Route Availability
Factors associated with transport routing include route constraints and scheduling. Route
constraints include the availability of existing routes, rights-of-way for access, size and
weight limits, and site obstructions. Transportation routes should run through areas that
would be the least sensitive to accidental releases, where possible. The entire route
should be easily accessible for maintenance, monitoring, and spill response. Site
obstructions can affect the transport modes, or the transport modes can block traffic flow
on existing routes. Scheduling difficulties may result from traffic interruption, overloads,
and shutdowns due to harsh weather conditions (Souder et al. 1978). Routing difficulties
can result in lengthy transport times, decreased efficiency, and increased costs.
Pipeline Transport—To deploy pipelines for a sediment remediation project,
easements and rights-of-way must be obtained .for the entire route. The ability to obtain
even temporary easements for pipelines will be complicated because of the contaminated
nature of the sediments. Pipeline crossings at roads and railroads may require special
construction or excavation. Because sediment remediation projects are most likely in
highly urbanized/industrialized areas, routing may be a major limitation in the use of
pipelines.
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Chapter 5. Transport Technologies
Barge Transport—Barge selection, routing, and transit time are greatly affected
by channel dimensions, site obstructions, other channel and seasonal conditions, speed
limits and other restrictions, traffic congestion, and user fees. In addition to the length,
width, and depth of a channel, other factors affecting barge access include lock sizes,
bend radii, and structures (e.g., piers, jetties). Barge and tow boat drafts (loaded) should
be less than the shallowest channel depth in the dredging area and on the tow route. Site
obstructions can include height limitations caused by bridges or power lines and
submerged objects such as cables, pipelines, piles, and rock. Transient or seasonal
conditions that can affect barge access include water depths, currents, tidal influence,
wave action, and icing. The number of barges required for a project will depend on the
dredge production rate, haul volume, and travel time (distance, routing, unloading).
The majority of barge traffic in the Great Lakes area is limited to relatively short hauls
that run close to lake shorelines. However, barge dimensions allowed in the Great Lakes
area are typically larger than those of other inland barges because of larger lock
dimensions (Churchward et al. 1981). The potential for substantial wave action generally
demands that ocean-going barges (self-propelled or towed) or ships traverse the Great
Lakes.
The U.S. Coast Pilot (a National Ocean Service annual report) contains detailed
information about navigation regulations and channel restrictions for the Great Lakes and
connecting channels. Navigation charts are available from NOAA. Additional informa-
tion about channel restrictions, traffic, and user fees can be obtained from local harbor
authorities, the Corps, or the U.S. Coast Guard.
Railcar Transport—With the exception of short spurs constructed to provide access
to a disposal site, economic railcar transport typically demands the use of existing railroad
track lines. These track lines are readily available in most industrialized areas. Mainline
spur construction, if permitted, would be too expensive for low-volume dredged material
transport. In addition, efficient railcar loading and unloading (bottom or rotary dump)
facilities are required to make the unit train concept work and to realize the benefits
derived from reduced rates on a large haul.
Truck Trailer Transport—There are about 5.6 million km of paved roads in the
United States, of which about 912,000 km (25,600 km of interstate) can be considered for
a transport system route (Souder et al. 1978). However, unpaved roads can be con-
structed relatively quickly at nearly any project site. Therefore, truck routes are more
flexible and faster to construct than either waterway or railroad track routes. Because
terminal points and routes can be changed readily at little cost, truck trailer transport
provides a flexibility not found with other modes of transportation.
Compatibility with Environmental Objectives
Transport technologies are inherently designed to contain their cargo during transport.
With the exception of volatilization, contaminant losses (e.g., leakage during transport or
. _ —_ _
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Chapter 5. Transport Technologies
spillage during loading or unloading) are generally the result of poorly maintained or
operated equipment. Most transport modes have one or more controls that can be applied
to limit leakage occurring as a result of transport and spills during loading and unloading
(e.g., covers, gate seals, splash aprons); however, these controls are only a few of the
necessary steps to minimize contaminant losses. Transport equipment should be tested
for leaks prior to hauling contaminated material and should be carefully monitored during
operation. As with dredging operations, the amount of spillage during rehandling is
greatly affected by the time and care taken by equipment operators.
The exteriors of barges, railcars, and truck trailers should be cleaned prior to leaving the
loading or unloading facilities. These loading/unloading areas should be designed so that
cleaning and runoff water can be collected at a central location and treated as necessary.
After final use, barge, railcar, truck trailer, and conveyor interiors can be decontaminated
using high-pressure water sprays. Pump/pipeline systems can be decontaminated by
pumping several pipeline volumes of clean water through the system.
The applicability of Federal, State, and local environmental laws and regulations on the
transport of contaminated sediments and treatment residues should be investigated on a
case-specific basis. Federal regulations on the transport of hazardous and toxic materials
include the Hazardous Materials Transportation Uniform Safety Act, RCRA, and TSCA.
Specific requirements exist for transport, including registration, labeling, packaging,
placarding, and material handling (UAB 1993).
Waterborne transport of contaminated materials may also be regulated by the International
Maritime Dangerous Goods Code, which identifies some materials as "marine pollutants"
with specific stowing requirements (Currie 1991). Federal regulations generally address
interstate transport, and State and local regulations covering intrastate transport may differ
from the Federal regulations (UAB 1993).
Virtually all transport modes have environmental effects unrelated to their cargo.
Towboats, trucks, trains, and conveyors all have exhaust from their diesel- or gas-powered
engines or generators. Towboats used to transport barges may cause sediment
resuspension along the route, especially at locations where the barge accelerates,
decelerates, or changes directions. A number of studies have been conducted to evaluate
the physical, biological, and chemical effects of commercial navigation traffic in large
waterways (Miller et al. 1987, 1990; Way et al. 1990; Miller and Payne 1992, 1993a,b).
ESTIMATING COSTS
The transport component of a sediment remedial alternative may incorporate several
modes of transport to connect different components. For example, the remedial alter-
native shown schematically in Figure 5-2 uses pipeline transport between the hydraulic
dredge and the rehandling facility. Dewatered sediments are removed from the rehandling
facility using a front-end loader and placed onto a conveyor for transport to a pretreat-
ment unit (rotary trommel screen). The primary residue of the pretreatment unit is
transported to the thermal desorption treatment unit by another conveyor. The oversized
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Chapter 5. Transport Technologies
Pipeline transport
from hydraulic dredge
All water to wastewater
treatment plant
Rehandling
facility
Dewatered
sediments
J
Water pipeline
Oil residual
Pretreatment
unit
Oversized
residues
Conveyor
Treatment
unit
Solid
residues
Conveyor
Tank truck
P
Transport to
Incinerator
Confined
disposal
facility
Figure 5-2. Example sediment remedial alternative using various transport
technologies.
residues of the pretreatment unit and the solids residues of the treatment unit are
transported to the disposal facility by conveyor. The liquid (organic) residue of the
treatment process is placed into a tank trailer for transport to a commercial incinerator.
Water from the rehandling, pretreatment, treatment, and disposal units is routed to a
wastewater treatment system through pipelines.
For a remedial alternative such as the one shown in Figure 5-2, it is likely that some
modes of transport would be subcontracted as parts of other components (e.g., the pipeline
would be supplied by the hydraulic dredging contractor), while others (e.g., conveyors)
might be subcontracted separately. For most sediment remediation projects, all transport
equipment would be leased or contracted. The transport costs would therefore be entirely
capital costs, with no operation and maintenance costs.
Churchward et al. (1981) indicate that the main considerations for selection of the
transport modes include cost, flexibility, capacity, and speed. A comparative analysis of
these characteristics for pump, barge, railcar, and truck trailer transport, as developed by
Churchward et al. (1981), is shown in Table 5-5.
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Chapter 5. Transport Technologies
TABLE 5-5. COMPARATIVE ANALYSIS OF TRANSPORT MODES
Transport
Mode
Pipeline
Barge
Railcar
Truck Trailer
Cost3
(cents/tonne-km)
0.39 to 1.30
0.39 to 3.90
1.30 to 10.32
5.16 to 19.34
Service Flexibility
Must be hydraulically linked
Must be adjacent to waterway
Most inland ports
Almost all inland points
Unit Capacity
(tonnes)
27,000-2,300,000
910-55,000
45-11,000
9-23
Linehaul
Speed
(km/hour)
5-10
5-16
32-72
16-96
Source: Churchward et al. (1981).
a Adjusted from 1977 prices to January 1993 prices using ENR's Business Cost Index (BCI) of 1.87.
In comparison with the other components, especially treatment, transport unit costs are
relatively low. Therefore, the transport process should be scheduled for continuous
operation to ensure that the other, more expensive processes can operate without
interruption.
Souder et al. (1978) indicate that cost estimates should be regarded as generalized
evaluations of the related costs of selected transportation modes under representative
operating conditions. When specific applications are considered, the unique aspects of
each application (e.g., terrain, weather conditions, labor rates) should be evaluated
individually and more precise costs related to each specific application should be derived.
The Corps' Construction Equipment Ownership and Operating Expense Schedule
(USAGE 1988) contains a method for computing dredging plant operating rates, which
includes methods for estimating pipeline and barge transport costs.
Dredged material transport involves three major operations: loading, transport, and
unloading. The loading and unloading activities are situation-dependent and are the major
cost items for short-distance transport.
Souder et al. (1978) evaluated the costs of transporting large volumes (300,000 to
>2.3 million m3) of clean dredged material over long distances (up to 500 km) as part of
a study conducted by the Dredged Material Research Program. They indicate that,
irrespective of the volume of material to be transported, the truck trailer and conveyor
transport modes were considerably more expensive than the pipeline, barge, or railcar
transport modes. They further concluded that truck trailer transport is labor- and fuel-
intensive in comparison to other transport systems. Conveyors have a high investment
cost but can move material efficiently. At lower volumes, conveyor costs are much
higher than for other systems. However, at high volumes and shorter haul distances
(<30 km) conveyor costs are competitive with all other transport modes except the
pipeline system (not including conveyor chute systems for unloading facilities).
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Chapter 5. Transport Technologies
Based on technical considerations and cost derivation assumptions, Souder et al. (1978)
concluded that pipeline transport is the most economical choice in most instances for
transport volumes up to 760,000 m3 and distances up to 160 km. Depending on the
transport volume, barge or railcar transport will be the most economical systems for long-
distance hauls. Railcar transport becomes more economical at higher volumes. Because
of routing limitations, not all haul distances will be the same for each transport system.
Souder et al. (1978) indicated that for haul volumes <380,000 m3 it is very difficult to
realize the economies of scale required to achieve the relatively low transport rates
derived in their analysis. If the transport costs developed by Souder et al. (1978) were
modified for application to sediment remediation projects, it is likely that the loading/
unloading costs for barge, truck trailer, and rail transport would increase because of the
controls required to limit spills, and the relative costs of conveyors might be more
favorable for the short hauling distances, such as those between remediation components
(i.e., <1.5 km).
Pipeline Transport
For projects involving hydraulic dredging and pipeline transport over short distances
(<3 km), the costs for pipeline equipment, mobilization, and labor are included in the
dredging costs, as described in Chapter 4. Separate transport costs should be developed
for pipeline transport over longer distances, or for pipeline transport of sediment or
residues independent of the dredging contract.
Souder et al. (1978) developed unit cost information for pipeline transport of various
dredged material haul volumes from a rehandling basin to a disposal site at various haul
distances. This hypothetical operation involved using a portable dredge to remove the
dredged material from the rehandling basin and transporting the material by a permanently
installed pipeline, operated by a contractor. However, the unit cost information provided
here was adjusted to include only the discharge pipeline, centrifugal booster pump, and
related labor costs. No real estate or right-of-way costs were considered.
Unit cost estimates for this hypothetical operation are shown in Figure 5-3. These unit
costs include the discharge pipeline and booster pump costs, including installation,
maintenance and repair, lay-up time, insurance, and miscellaneous costs. Discharge
pipeline costs include annual costs for the purchase of the pipeline. Centrifugal booster
pump costs include annual costs for the pump and motor, reduction gears, controls,
foundation, and housing, and costs for power and a sealing water supply (Souder et al.
1978).
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Chapter 5. Transport Technologies
-•- 1,000,000yd3
-O- 3,000,000 yd3
-f- 5,000,000 yd3
30 40 50
HAUL DISTANCE (miles)
a Slurry density of 1,300 g/L assumed. Unit cost adjusted from
1976 prices to January 1993 prices using ENR's BCI of 2.03.
Source:
Souderetal. (1978).
Note: 1 yd3 = 0.76 m3 and 1 mile = 1.6 km
Figure 5-3. Unit costs for pipeline transport of selected dredged material volumes.
Barge Transport
Barge carriers include major-line, branch-line, and local operations. Barge transport on
the Great Lakes is provided under contract rates or long-term charters, with 26 percent
of services provided by independent carriers (Churchward et al. 1981). Many dredging
firms own barges and will subcontract additional barges as needed for a large job. For
a project involving mechanical dredging and barge transport over short distances (i.e.,
<5 km), the costs for. barge transport are included in the dredging costs presented in
Chapter 4. If longer haul distances are required, or for barge transport of sediments or
residues independent of the dredging contract, additional transport costs need to be
estimated.
Souder et al. (1978) developed unit cost information for contracted tank barge transport
of various dredged material haul volumes from a rehandling basin to a disposal site at
various haul distances. This hypothetical operation involved using a bulldozer and
backhoe to excavate the rehandling basin material, placing the material in a dump truck,
moving the material from the truck into the tank barge, towing the barge to the disposal
site, removing the material from the barge using a rehandling bucket, placing the material
into a dump truck, and dumping the material into the disposal site.
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Chapter 5. Transport Technologies
Unit cost estimates for this hypothetical operation are shown in Figure 5-4. The cost
information assumes that the rehandling basin and disposal site are both 2.4 km, by way
of an existing road, from an existing barge mooring dock. As with the pipeline transport
operation, this operation assumes that dredged material is transported under ideal
conditions. Project-specific conditions may greatly affect these costs. The operation costs
include annual costs for barge loading and unloading and the towboat and barge. Loading
costs include backhoe, bulldozer, dump truck, and road maintenance costs. Unloading
costs include crane and dump truck costs. Transport costs include towboat and barge
costs, crew quarters and subsistence pay, and miscellaneous costs.
25 T
500,000 yd3
5,000,000 yd3
100
150 200 250 300 350
HAUL DISTANCE (miles)
400
450
500
a Material density of 1,600 g/L assumed. Unit cost adjusted from
1976 prices to January 1993 prices using ENR's BCI of 2.03.
Note: 1 yd3 = 0.76 m3 and 1 mile = 1.6 km
Source:
Souderetal. (1978).
Figure 5-4. Unit costs for tank barge transport of selected dredged material
volumes.
The cost engineering office of the Detroit District typically uses unit costs in the range
of $0.70 to $1.50/yd3-mile ($0.57 to $1.23/m3-km) for preliminary estimates of barge
transport of dredged material in the Great Lakes (Wong 1993).
Railcar Transport
Railcar rates are quoted by either a class rate or commodity rate. Class rates generally
apply to small-volume shipments like single-car transport and occur on an irregular basis.
These rates are influenced by route terrain and distance, the number of railcar switches
required, and the haul volume. Class rates are readily obtained, but are usually prohibi-
tively expensive for hauling dredged material. Commodity rates generally apply to
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Chapter 5. Transport Technologies
regularly scheduled shipments of large volumes, like unit train transport, and are obtained
from local rail carriers on a case-by-case basis. Commodity rates are lower than class
rates (USEPA 1979; Souder et al. 1978).
Souder et al. (1978) developed unit cost information for contracted hopper railcar
transport of various dredged material haul volumes from a rehandling basin to a disposal
site at various haul distances. This hypothetical operation involved excavating the
rehandling basin material using a backhoe and placing it on a conveyor system that
emptied into a hopper railcar. The railcars were towed by a locomotive to the elevated
loop track at the disposal site where the material was emptied.
Unit cost estimates for this hypothetical operation are shown in Figure 5-5. The operation
costs include annual costs for hopper railcar loading and unloading and the locomotive
and railcars. Loading costs include a backhoe, portable and fixed conveyor systems
(including feed and feedout bins), and elevated loop track construction costs. Unloading
costs include elevated loop track construction costs. Transport costs include locomotive
and railcar carrier costs.
25 -r
-»- 500,000 yd3
-0-1,000.000 yd3
3,000,000 yd3
5,000.000 yd3
50 100 150 200 250 300 350 400 450 500 550
HAUL DISTANCE (miles)
a Material density of 1,600 g/L assumed. Unit cost adjusted from
1976 prices to January 1993 prices using ENR's BCI of 2.03.
Note: 1 yd3 = 0.76 m3 and 1 mile = 1.6 km
Source:
Souder eta). (1978).
Figure 5-5. Unit costs for rehandling and hopper railcar transport of selected
dredged material volumes.
Tank railcars are usually leased by the month from a private tank car rental company,
with a 5-year minimum lease. In 1978, a large tank car rented for $450/month (USEPA
1979). Hopper railcars are usually leased from the carrier.
778
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Chapter 5. Transport Technologies
Truck Trailer Transport
Souder et al. (1978) developed unit cost information for contracted dump trailer transport
of various dredged material haul volumes from a rehandling basin to a disposal site at
various haul distances. This hypothetical operation involved using a backhoe to excavate
the rehandling basin material and placing the material on a conveyor system that emptied
into the dump trailer. The filled trailer was towed on an existing roadway to a newly
constructed road leading into the disposal site and emptied.
Unit cost estimates for this hypothetical operation are provided in Figure 5-6. The
operation costs include annual costs for loading the dump trailer and transporting it to the
disposal site. Similar to railcar loading, trailer loading costs include backhoe and portable
and fixed conveyor system (including feed and feedout bin) costs. Transport costs include
truck trailer, driver, and fuel costs/ Unloading costs are limited to the cost of constructing
a temporary road into the disposal site.
35 -T
30-
^, 25-
fc
8
20-
15-
10
500,000 yd3
1,000,000yd3
3,000,000 yd3
5,000,000 yd3
60 90 120
HAUL DISTANCE (miles)
a Material density of 1,600 g/L assumed. Unit cost adjusted from
1976 prices to January 1993 prices using ENR's BCI of 2.03.
Note: 1 yd3 = 0.76 m3 and 1 mile = 1.6 km
150
180
Source:
Souder etal. (1978).
Figure 5-6. Unit costs for rehandling and truck trailer transport of selected
dredged material volumes.
The Detroit District uses unit costs between $1.30 and $2.50/yd3-mile ($1.07 to $2.057
m3-km) for preliminary estimates of truck trailer transport of dredged material (Wong
1994). The Chicago District estimated dump truck trailer unit costs (including truck
trailer rental and labor) for 1-, 19-, and 32-mile (1.6-,. 30-, and 51-km) haul distances to
119
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Chapter 5. Transport Technologies
be $2.21/yd3 ($2.91/m3), $11.25/yd3 ($14.80/m3), and $17.80/yd3 ($23.42/m3), respec-
tively. They also estimated a unit cost of $2.72/yd3 ($3.58/m3) to remove dredged
material from a barge and place it into a truck trailer (Engel 1994).
Conveyor Transport
Souder et al. (1978) developed unit cost information for contracted belt conveyor transport
of various dredged material haul volumes from a rehandling basin to a disposal site at
various haul distances. This hypothetical operation involved using a bulldozer and
backhoe to excavate the rehandling basin material and placing the material on a conveyor
system that moved the material to the disposal site where it was dumped. The operation
assumed that the conveyor was routed over flat terrain and that there were no costs
associated with obtaining right-of-ways and other real estate.
Unit cost estimates for this hypothetical operation are provided in Figure 5-7. The
operation costs include annual costs for loading and operating (energy and labor costs)
a portable and fixed conveyor system. Conveyor loading costs include backhoe and
bulldozer costs. Conveyors do not require additional equipment for unloading.
1,000,000yd3
3,000,000 yd3
5,000,000 yd3
20 30 40 50
HAUL DISTANCE (miles)
a Material density of 1,600 g/L assumed. Unit cost adjusted from
1976 prices to January 1993 prices using ENR's BCI of 2.03.
Note: 1 yd3 = 0.76 m3 and 1 mile = 1.6 km
Source:
Souder etal. (1978).
Figure 5-7. Unit costs for rehandling and belt conveyor transport of selected
dredged material volumes.
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Chapter 5. Transport Technologies
ESTIMATING CONTAMINANT LOSSES
There are a limited number of mechanisms for contaminant loss during the transport of
contaminated sediments, and only one mechanism of contaminant loss can be predicted
using a priori techniques (Myers et al., in prep.). Contaminant losses during loading and
unloading operations are primarily the result of spills and volatilization. The amount of
spillage during loading and unloading reflects the level of care taken by the operators and
the efficiencies of any controls (e.g., drip aprons). Loading and unloading areas should
be designed with systems to collect spillage and water used to wash transport vessels.
This water should be routed to wastewater treatment systems. Contaminant losses from
such treatment systems are discussed in Chapter 9, Residue Management.
Losses during transport are the result of leaks, volatilization, and accidental spills. The
amount of leakage during transport reflects the containment efficiencies of the carrier
vehicles. Accidental spills may occur as a result of equipment failure, operator error, or
external influences (e.g., meteorological conditions). Although it is not feasible to
entirely eliminate spills and leakage from transport systems for contaminated sediments,
it is easier to design controls for these mechanisms of contaminant loss than to quantify
them.
There is no a priori method for predicting the amounts of contaminants lost by spillage,
leaks, and accidents from a transport mode. The only mechanism of contaminant loss that
can be predicted is volatilization from transport systems without covers (i.e., barges,
trains, trucks, and conveyors). Methods for predicting the loss of volatile and semivolatile
organic contaminants from exposed sediments and ponded water have been developed,
and are summarized in Myers et al. (in prep.). These predictive methods are almost
entirely theoretical and have not yet been field verified.
121
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6. PRETREATMENT TECHNOLOGIES
Pretreatment is a component of a remedial alternative in which sediments are modified
or conditioned prior to final treatment or disposal. This definition is somewhat artificial,
because some of the pretreatment technologies do "treat" the sediments, and if conducted
alone, could logically be called a treatment component.
There are two primary reasons for pretreating contaminated sediments. The first reason
is to condition the material such that it meets the requirements of the treatment and/or
disposal components of the remedial alternative. Most treatment technologies require that
the feed material (e.g., sediment) be relatively homogeneous and that its physical
characteristics (e.g., solids content, particle size) be within a narrow range for efficient
processing. Pretreatment technologies may be employed to modify the physical characte-
ristics of the feed material to meet subsequent processing needs. Examples of the feed
requirements for selected treatment technologies are shown in Table 6-1. Sediment
treatment technologies that use a continuous feed system generally have more stringent
requirements for pretreatment than those using a batch feed system. For example,
oversized material can cause blockage or ruptures in conveyance systems. In addition,
excessive fluctuations in the solids content can alter the process conditions, thereby
reducing treatment efficiencies. Pretreatment requirements for sediment disposal are
generally less stringent than those for treatment.
TABLE 6-1. EXAMPLE FEED MATERIAL
Maximum Particle Size Optimal Solids Content
Technology (cm) (%)
Chemical extraction8
Thermal desorption
Incineration
Chemical treatment (K-Peg)b
Immobilization
Hydrocyclone
0.6
0.6
15
2.5
15
__c
>20
50-100
95-100
>80
>60
5-25
a Based on Basic Extractive Sludge Treatment (B.E.S.T.®) process (USACE Chicago
District 1994; Diez 1994).
b Based on alkaline metal hydroxide/polyethylene glycol (APEG) process (USEPA1991 f).
c Not more than one-quarter the diameter of the hydrocyclone apex (discharge) opening,
or smaller if required for protection of the pump.
The second reason for pretreating contaminated sediments is to reduce the volume and/or
weight of sediments that require transport, treatment, or restricted disposal. Some
122
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Chapter 6. Pretreatment Technologies
physical separation technologies can separate fractions of sediments that may be suitable
for unrestricted disposal or beneficial use, and concentrate the contaminants in a smaller
fraction of the sediments.
Most of the design and operating experience with the pretreatment technologies discussed
in this chapter was developed from applications involving municipal and industrial
sludges and mining and mineral processing. These applications are generally of a larger
scale than that expected for most sediment remediation projects and are usually part of
a permanent process operation, whereas most sediment remediation projects will be of
shorter duration. These differences should be considered when applying guidance
developed for processing municipal and industrial sludges and mining materials to
contaminated sediment sites.
The applicability of pretreatment technologies to dredged material was examined by the
Corps as part of a pilot program to investigate alternative disposal methods for dredged
material from the Great Lakes (USAGE Buffalo District 1969) and as part of the Dredged
Material Research Program (Mallory and Nawrocki 1974). A detailed literature review
of pretreatment technologies is provided by Averett et al. (in prep.).
This chapter provides descriptions of two types of pretreatment technologies—dewatering
and physical separation. Discussions of the factors for selecting the appropriate
technology and techniques for estimating costs and contaminant losses are also provided.
DESCRIPTIONS OF TECHNOLOGIES
Dewatering Technologies
Dewatering technologies are used in sediment remedial alternatives to reduce the amount
of water in sediments or residues and to prepare the sediments for further treatment or
disposal. The need for dewatering is determined by the water requirements or limitations
of the treatment or disposal technologies and the solids content of the sediments following
removal and transport.
Mechanically dredged sediments typically have a solids content comparable to that of in
situ sediments (about 50 percent by weight for most fine-grained sediments). Hydrauli-
cally dredged sediments are in a slurry with a solids content typically in the range of
10-20 percent. Some hydraulic dredge pumps are able to move slurries with higher solids
content, but the average solids content in an extended dredging operation is rarely greater
than 20 percent. To prepare dredged sediments for most treatment or disposal technolo-
gies, water must be removed and/or the solids content of the sediments must be made
more uniform. Dewatering will be required for most sediment remedial alternatives that
involve hydraulic dredging or transport. If the sediments are mechanically dredged and
transported, the dewatering requirements may be greatly reduced or eliminated.
123
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Chapter 6. Pretreatment Technologies
Another function performed by dewatering is the reduction of the volume and weight of
the sediments, which decreases the subsequent costs of handling, transport, and treatment
and/or disposal of the solids. Dewatering will reduce the weight of a sediment load, but
the effects of dewatering on the volume of a sediment load are more complex. When a
sediment slurry is dewatered, the removal of free water will directly reduce the volume
of material remaining in a nearly one-to-one relationship. Sediments that have been
partially dewatered or mechanically dredged will lose additional water, but the volume
will not always be reduced because the water driven from the voids between sediment
particles is replaced by air. Some dewatering processes may even increase the volume
of the sediments. The water removed during dewatering may be contaminated and require
further treatment, as discussed in Chapter 9, Residue Management.
Three general types of dewatering technologies are discussed below:
• Passive dewatering technologies
• Mechanical dewatering technologies
• Active evaporative technologies.
Passive Dewatering Technologies
In this document, the term "passive dewatering" refers to those dewatering techniques that
rely on natural evaporation and drainage to remove moisture. Drainage may occur by
gravity or may be assisted (e.g., using vacuum pumps). Some mechanical movement of
the sediments, such as the construction of trenches, may also take place.
Dewatering of dredged material has traditionally been accomplished in CDFs, which rely
on primary settling, surface drainage, consolidation, and evaporation. Subsurface drainage
and wick (vertical strip) drains have also been demonstrated or used at CDFs to promote
dewatering and consolidation. These technologies require significant amounts of land and
are most effective if the sediments can be spread out in thin layers or "lifts."
Sediments can also be dewatered in temporary holding/rehandling facilities, tanks, and
lagoons using the same design principles developed for CDFs. CDFs are discussed in
more detail in Chapter 8, Disposal Technologies. Specific aspects of dewatering within
a CDF or CDF-like structure are described below.
Surface Drainage—Drainage of surface water can be accomplished through a
number of mechanisms. Most existing in-water CDFs on the Great Lakes have dikes
constructed of stone and granular material that remain permeable as they become filled.
Water drains through the permeable sections, and suspended sediments become entrapped
by the dike material (Miller 1990). At upland facilities, and at in-water CDFs that have
filled above the water table, surface water is drained to the discharge point(s), which may
include overflow weirs, filter cells, or pump control structures. Drainage water from a
CDF includes both the water in the sediment slurry and rainfall runoff. Progressive
124
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Chapter 6. Pretreatment Technologies
trenching is a method employed to aid the drainage of water in CDFs and hasten
evaporative drying.
Evaporative Drying—The desiccation of dredged material by evaporative drying
results in the formation of a crust at the sediment surface. This method of drying is a
two-stage process. The first stage of drying occurs until all free-standing water has been
decanted from the dredged material surface. The corresponding void ratio at this point
is termed the initial void ratio (e00) and has been determined to occur at a water content
of approximately 2.5 times the Atterberg liquid limit of the material. The second stage
of drying occurs until the material reaches a void ratio called the desiccation limit (edl).
At this point, evaporation of any additional water from the dredged material will
effectively cease. The edl corresponds to a water content of 1.2 times the Atterberg
plastic limit (USAGE 1987b). The thickness of the crust and rate of evaporative drying
and consolidation are dependent on local conditions and sediment properties, and can be
estimated using the Primary Consolidation and Desiccation of Dredged Fill (PCDDF)
module of the Automated Dredging and Disposal Alternatives Management System
(ADDAMS) model (Schroeder and Palermo 1990).
Subsurface Drainage—A subsurface drainage system can be used at a CDF for
dewatering of dredged material and/or leachate collection. One approach is the placement
of perforated pipes under or around the perimeter of a CDF that drain into a series of
sumps from which water is withdrawn. The pipes can be placed in a thin layer or
trenches of drainage material, typically sand or gravel. The feasibility of subsurface
drainage as a sediment dewatering technology may be limited where several layers of
fine-grained sediments are to be disposed because they may clog the drainage materials.
Several variations of subsurface drainage systems can be used, including the gravity
underdrain, vacuum-assisted underdrain, vacuum-assisted drying beds, and electro-
osmosis. The gravity underdrain system provides free drainage at the base of the dredged
material by the gravity-induced downward flow of water. The vacuum-assisted under-
drain is the same as the gravity-fed system, but uses an induced partial vacuum in the
underdrainage layer. The latter system improves dewatering by 50 percent (Haliburton
1978), but requires considerable maintenance and supervision.
Wick Drains—Wick drains or "wicks" are polymeric vertical strips that provide a
conduit for upward transport of pore water, which is under pressure from the overlying
weight of the material. By placing the vertical strips on 5-ft (1.5-m) centers to depths of
40 ft (12 m), both radial and vertical drainage are promoted. Wick drains can reduce
consolidation time by a factor of 10 compared to natural consolidation (Koerner et al.
1986).
Mechanical Dewatering Technologies
Mechanical dewatering systems have been extensively used for conditioning municipal
and industrial sludges and slurries, as well as mineral processing applications. These
125
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Chapter 6. Pretreatment Technologies
systems require the input of energy to squeeze, press, or draw water from the feed
material. Generally, mechanical dewatering technologies can increase the solids content
up to 70 percent by weight. The features and requirements of six mechanical dewatering
processes are summarized in Table 6-2.
The performance of a mechanical dewatering system is measured by a number of
parameters, including:
• Chemical conditioning dosage, measured as the mass of conditioner per
mass of dry solids
• Solids capture, defined as the dry mass of dewatered solids per dry mass
of solids fed into the process
• Solids content of the dewatered material.
With sewage sludges, the dosage of organic (polymer) conditioners in mechanical
dewatering systems is generally <0.1 percent by weight, while the dosage of inorganic
conditioners is substantially higher. For example, lime and ferric chloride may be used
in dosages as high as 20 percent (Dick 1972).
A high solids capture is desirable, because solids lost from the process (i.e., in the filtrate
or centrate) represent a route for contaminant loss. Some paniculate loss during
mechanical dewatering is inevitable; therefore, the effluent stream must be treated using
treatment technologies described in Chapter 9.
Most mechanical dewatering processes increase the solids content of the feed material to
a level comparable to that of the in situ sediment deposits (about 50-percent solids).
These dewatering processes work best with homogeneous waste streams at a constant flow
rate. Because hydraulic dredging produces highly variable flow rates and solids
concentrations, direct dewatering of hydraulically dredged slurries would be inappropriate.
Temporary storage in a tank, lagoon, or CDF would be necessary to equalize flows and
concentrations prior to further dewatering by one of the mechanical processes.
Mechanical dewatering has been tested with dredged sediments on a limited scale (Averett
et al,, in prep.). A vacuum filtration unit was tested on sediments from Toledo Harbor,
Ohio (Long and Grana 1978). The solids content prior to conditioning with lime ranged
from 15 to 23 percent. The post-treatment solids content was consistently above 43
percent. An 2.5-m belt filter press was demonstrated on sediment from the Ashtabula
River in Ohio at a rate of 23 tonnes/hour. Solids were increased to 50-60 percent by
weight, with solids losses of 2-5 percent (Rexnord, Inc. 1986).
A substantial amount of design and operating guidance on mechanical dewatering systems
has been developed for municipal and industrial wastewater applications (USEPA 1987b)
and mineral processing applications (Weiss 1986). There are some fundamental
differences between sediments and sludges that need to be considered when using this
guidance, including:
• Sediments are usually less compressible, less gelatinous, and lower in
organic content than wastewater sludges, and thus are generally easier to
dewater
126
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TABLE 6-2. MECHANICAL DEWATERING TECHNOLOGIES
Independent High
Pressure Secnon
Free Drainage
Zone
Belt Filter Press
• Uses single- or double-moving belts to
dewater sludges. With double-moving
belt, upper belt operates as the press belt
and lower belt operates as the filter bel?
• A flocculant is injected to condition th(
solids in a mix tank positioned in front c
the belt filter
• Dewatering occurs in three stages: 1) gra-
vity drainage of free water, 2) low-pres-
sure compression, and 3) high-pressure
compression and shear; the dewatered
solids are discharged from the high-pres-
sure zone
• Important operational variables include:
belt speed, feed concentration, polymer
conditioner type and dosage, belt charac-
teristics (type, tension), and washwater
flow
Caka Forms in
This Volume Fiher Cloth
Sludge Feed
Filler Plata Assembly
Holds Filter Cloth
Filtrate
Recessed Plate Filter
Uses rigid individual filtration chambers
operated in parallel under high pressure
Consists of parallel vertical plates placed
in series and covered on both sides with
replaceable fabric filters; slurry is pumped
under pressure into the press and passes
through feed pores in trays that lie along
the length; water flows through the filter
media while solids form a cake on the
filter's surface; when dewatering ceases,
the filter press is opened and individual
vertical plates are moved sequentially over
a gap allowing the caked solids to fall off;
after the cake is removed, the plates are
pushed back into place and the press is
closed for the next dewatering cycle
Important operational variables include:
feed pressure, filtration time, conditioner
type and dosage, use of precoat, and type
of filter cloth
(continued)
727
-------
TABLE 6-2. MECHANICAL DEWATERING TECHNOLOGIES (continued)
Membrane Squeeza
Air Inlet Ports
Filter Cake Complete
Filter Cake
- Filtrate Outlet
Diaphragm Plate Filter
• Commercialized in the United States in the
1980s
• Similar to the recessed plate filter, except
that an inflatable diaphragm is incor-
porated into the design; at the end of the
pumping cycle, pressures up to
14-17 atmospheres (1.4-1.7 MPa) are
applied to the diaphragm for additional
dewatering
• Percent solids usually 5-8 percent higher
compared to conventional filter press;
also, organic polymers, rather than ferric
salts and lime, may be used as condi-
tioners
• Important operational variables include:
diaphragm and feed sludge pressures,
conditioner type and dosage, filtration and
diaphragm squeezing times, and type of
filter cloth
CLOTH CAULKING
STRIPS-
AUTOMATIC VALVE
DRUM
FILTRATE PIPING
CAKE SCRAPER
SLURRY AGITATOR
VAT
AIR BLOW-BACK LINE SLURRY FEED
• Continuous process with self-cleaning
filter media consists of a rotating cylindri-
cal drum mounted horizontally and par-
tially submerged in a trough containing a
slurry; the drum, covered by fabric or wire
mesh, allows moist solids to adhere via
negative pressure from a vacuum supply;
water flows through the filter into the
center of the drum and exits the unit for
further treatment or disposal; solids are
scraped off the drum as it rotates
• Usually requires ferric salt and/or lime
conditioner
• Important operational parameters include:
drum submergence, drum speed/cycle
time, solids content in feed, washwater
quantity, conditioning chemicals, and filter
media used
Vacuum Filter
(continued)
725
-------
TABLE 6-2. MECHANICAL DEWATERING TECHNOLOGIES (continued)
Cover
Differential speed
gear box
Main drive
sheave
Connate
discharge
port
(adjustable)
Bearing
Feed pipes
(sludge and
conditioning chemicals)
Base not shown
Centrifugation
Uses rapid rotation of a fluid mixture
inside a rigid vessel to separate the com-
ponents based on their mass
Centrifuges are generally used in conjunc-
tion with flocculants and can be used to
dewater or concentrate soils and sedi-
ments ranging in decreasing size from fine
gravel to silt; incorporation of a paper
cloth filter in the centrifuge or the injection
of flocculants improves the recovery and
removal efficiencies
The solid bowl centrifuge is most com-
monly used for dewatering, although other
designs (basket and disc) are available
Important operational variables for solid
bowl centrifuges are: bowl/scroll differen-
tial speed, pool depth, polymer dosage,
and point of addition
SCRAPER BLADES
UNDERFLOW
ELEVATION
Gravity Thickening
• Operates on differences in specific gravity
between solids and water to accomplish
separation; an effluent with a reduced
concentration of suspended solids is pro-
duced and removed while a thickened
mass of solids remains in a smaller slurry
volume
• Gravity thickening usually occurs in a
circular vessel constructed of concrete or
steel designed similarly to a conventional
clarifier; slurry is pumped into a feed well
and allowed to thicken via gravity settling;
clarified liquid overflows an effluent weir
and leaves through an effluent pipe, while
the concentrated sludge is raked to the
center of the vessel and discharged by
gravity or pumping
• Important operational parameters include:
polymer dosage and overflow rate
729
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Chapter 6. Pretreatment Technologies
• The solids content of feed material, typically 3-6 percent in a wastewater
treatment plant, will be considerably higher for sediments (15-25 percent)
• Sediments can contain rocks and large particles that can interfere with or
damage dewatering equipment, necessitating pretreatment by screening
• Municipal sludges are generated on a continuous basis, whereas dredging
produces sediments over a relatively short time scale
• The disposal of wastewater and filtrate is a relatively minor concern for
municipal sludges because this water can be easily returned to the treatment
process; however, wastewater from the dewatering of contaminated
sediments is a significant concern, and separate treatment for this water
may need to be employed.
There are numerous manufacturers of mechanical dewatering equipment. Vendor contacts
are listed in USEPA (1987b) and may be obtained through wastewater treatment and
mining/mineral processing trade journals.
Active Evaporative Technologies
Active evaporative technologies are different from the evaporative drying techniques used
at CDFs in that artificial energy sources are used to heat the sediments, as opposed to
solar radiation. Evaporation is the most expensive dewatering technology, but has been
effectively used to prepare municipal sludges for incineration or for sale as fertilizer (Dick
1972). Nearly all of the water is removed, resulting in a solids content of about 90
percent. Technologies applied to sludges that may be applicable to fine-grained sediments
include:
• Flash dryers
• Rotary dryers
• Modified multiple hearth furnaces
• Heated auger dryers.
The most common conventional evaporation process used for waste recycling is agitated
thin-film evaporation (Averett et al., in prep.). This process is capable of handling high-
solids content slurries and viscous liquids. It may also be possible to use conventional
evaporation equipment commonly found in the chemical- and food-processing industries.
These technologies remove water in the form of steam and may also remove volatile
contaminants.
Evaporative dewatering technologies have not been demonstrated with sediments on any
scale. Most of the design and operating experience and guidance on these technologies
are from municipal and industrial wastewater applications (USEPA 1987b).
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Chapter 6. Pretreatment Technologies
Physical Separation Technologies
Physical separation technologies are used in sediment remedial alternatives to remove
oversized material and debris in order to produce an acceptable feed material for
subsequent handling and treatment. These technologies are also used to separate the
sediments into two or more fractions based on physical properties or characteristics to
reduce the quantity of material requiring treatment or confined disposal.
The following types of physical separation technologies may be applicable to contami-
nated sediments:
• Debris removal
• Screens and classifiers
• Hydrocyclones
• Gravity separation
• Froth flotation
• Magnetic separation.
The general features of these technology types are summarized in Table 6-3 and discussed
in the following paragraphs. Many of the physical separation technologies discussed
below are mineral processing technologies, which have been widely used in the mining
industry to recover valuable minerals or metals from ores. Methods such as size
classification, magnetic separation, gravity separation, or froth flotation, collectively
known as mineral processing, can be applied in some cases to separate contaminated
sediment fractions from the bulk sediments.
Debris Removal Technologies
Dredged material often has significant quantities of debris and oversized materials.
Examples of debris commonly encountered during dredging include: cobbles, bricks,
large rocks, tires, cables, bicycles, shopping carts, steel drums, timbers, pilings, and
automobiles.
Pockets of bulk materials, such as coal or gravel, may be encountered near docks and
loading areas. The amount of debris is generally greatest in sediments along riverbanks
and at bridge crossings, especially where there is unrestricted public access to the
waterway.
Debris can be a significant problem for a dredging operation because it can clog hydraulic
cutterheads and cause bucket dredges to be raised without full closure, resulting in
increased sediment resuspension. Debris can also complicate the transport of dredged
sediments, possibly requiring separate handling. Large debris must be separated and
131
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TABLE 6-3. PHYSICAL SEPARATION TECHNOLOGIES
Grizzly
• Grizzlies are composed of parallel iron or
steel bars, usually inclined, of 2- to 30-cm
spacing
• Used for very coarse separations
• The most common application in mineral
processing is to "scalp" the feed to a
primary crusher, which prevents clogging
and improves capacity by removing feed
material smaller than the crusher's product
size
• Can be used to screen cobbles, rock, and
debris from sediments
• Rotating, slightly inclined cylinder of
sturdy wire mesh, with openings from 6 to
55 mm across
• Trommels have poor capacities, because
only part of the screen surface is used at
any one time
• Rugged, inexpensive, and relatively free of
maintenance
Trommel
• Overflow (fines)
Feed chamber
Vortex finder
Cone section
Underflow
(coarse material)
Hydroc yclone
• High-throughput, continuously operating
size classification device that uses centri-
fugal force to accelerate the settling rate
of particles
• Widely used in the mineral processing
industry
• Most common applications make separa-
tions from 40-400 ^m in particle diam-
eter, although separations as fine as 5 fjm,
or as coarse as 1,000//m, are well known
• Capacity (200-13,500 L/min) is depen-
dent on diameter
• There are more than 50 hydrocyclone
manufacturers worldwide (Edmiston 1 983)
732
(continued)
-------
TABLE 6-3. PHYSICAL SEPARATION TECHNOLOGIES (continued)
Feed slurry [ ^>
Gravity Separator
• Separates particles based on density dif-
ferences
• Works best on particles larger than 75 fjm,
but separations among particles as small
as 10 //m can be achieved at low capacity
with certain equipment
• Equipment commonly used includes dense
medium separators (as shown), jigs,
shaking tables, flowing film concentrators,
centrifugal separators, and elutriators
Air
£^>#;
0 ° 00
° 00
Vjr-
feJ^fcaS
0
0 0
o a
°a Air bub
ISz i
Contaminant-bearing froth
Contaminant particle
°o Air bubbles attaches to air bubbles
Used to process millions of tonnes of ore
daily
Flotation successfully applied to particles
as small as 10 fjm
Almost all flotation is conducted in stirred,
aerated tanks of up to 56 m3 (2,000 ft3),
although vertical columns and air-sparged
hydrocyclones are used occasionally
Agitator
Froth Flotation
Expendable outer covers on drum shell Totally enclosed geared motor unit and chain drive
Drum rotation /
» , Surge overflow with
-a i»-y [ pipe outlet flange
Overflow weir
Stainless steel
removable tanK
Calibrated orifice plates
in tailings outlet
11 Tailing
Overflow discharge t » Tailings discharge
• Low-intensity separators (as shown)
employ permanent magnets, and are most
often used for material coarser than about
75 /jm of high magnetic susceptibility,
such as iron ore
• Rotating drum separators (as shown)
commonly used for wet applications
• High-intensity separations employ electro-
magnets and are much more versatile and
capable of recovering iron-stained or
rusted silicate minerals from other purer,
nonmagnetic phases
Drum-type Magnetic Separator
133
(continued)
-------
TABLE 6-3. PHYSICAL SEPARATION TECHNOLOGIES (continued)
Vibrating Screen
• Reciprocating, gyrating, and vibrating
screens are used to make wet or dry sepa-
rations from 25 cm down to 40 fjm
• Can be stacked to produce multiple sized
products
• May have very limited throughput, particu-
larly when there is a large amount of
material near the size of the mesh opening
• Blinding of screens is a frequent problem,
and is controlled in some applications with
a "ball tray" (a tray of hard rubber balls
that continually bounce against the under-
side of the screen fabric to dislodge stuck
particles)
• Screen cloth is subject to extreme wear
and requires frequent replacement (Wills
1988)
• Mechanical classifiers are based on the
differing terminal settling velocities of
dissimilar particles in a fluid, usually water
• A rake or screw (as shown) is used to
drag the fastest settling (and therefore
largest) particles up an incline against the
fluid flow; slower-settling (and therefore
smaller) particles travel with the fluid flow
out of the device through an overflow weir
• Operate at less than 50-percent solids by
weight (careful control of slurry density is
of the utmost importance, especially in
making very fine separations)
• Effective particle size range is approxi-
mately 50-1,500/;m
Spiral Classifier
134
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Chapter 6. Pretreatment Technologies
removed prior to any other pretreatment or treatment process. The size requirements of
feed materials for various treatment technologies are shown in Table 6-1.
Debris may be separated during removal (dredging) or as part of material handling
activities in between other components. For example, debris might be separated while
sediments are being removed from a barge and transferred into truck trailers for transport,
or while sediments are being removed from a disposal/storage area and fed into a pretreat-
ment process. The technologies available for debris removal are relatively simple, such
as a drag-line, grapple bucket, mechanical removal, and screens (discussed in later
sections of this chapter).
A drag-line is a grappling hook or rake that is dragged along the river bottom with a steel
cable from a boat or from a land-based winch. A grapple bucket is a specialized crane-
operated bucket, commonly used for placement of large stones, that can be used to
remove debris from a waterway. Large debris can be cleared from the sediments prior
to dredging. This method may also be used to clear debris from a CDF prior to
excavating sediments for treatment.
Mechanical removal is the separation of large debris using mechanical dredging or
construction equipment. During a dredging operation employing a clamshell dredge or
backhoe, large debris can be separated from the bulk of the dredged material. This
requires a skilled operator and a place to store the debris. For a land-based operation, the
debris might be separated and placed in a bin or dumpster for storage and transport.
During marine operations, a clamshell dredge is often placed on a large floating platform,
which may provide sufficient space for storing debris. Conventional earthmoving
equipment that may be used for handling and rehandling of sediments between other
components could also be used for separating large debris. Large plants may require
grinding to ease rehandling and disposal.
Debris that has been separated is generally covered with contaminated sediments and may
need to be decontaminated. Possible reasons for decontaminating debris include:
• The cost of disposal of the decontaminated debris is lower than the cost of
disposal along with contaminated sediments
• The disposal facility for sediments will not accept the contaminated debris
• Transport of the contaminated debris is not allowable
• The decontaminated debris has a salvage value.
Contaminated debris should be stored in a secure place or container until disposed or
decontaminated. Decontamination may involve washing with water or steam. Wash
water must be collected and treated as necessary.
Screens and Classifiers
While hydrocyclones are the most popular separation devices, grizzlies, trommels,
vibrating screens, and mechanical classifiers are all widely used in mineral processing
135
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Chapter 6. Pretreatment Technologies
applications. Screens and classifiers may be the first units in a complex separation
process or the only units in a simple process. A trommel and vibrating screen were used
in the ARCS Program demonstration at Saginaw, Michigan (USAGE Detroit District
1994). A grizzly, vibrating screen, and screw classifier were used at a sediment
remediation demonstration conducted at Welland, Ontario (Acres International Ltd. 1993).
Hydrocyclones
A hydrocyclone is a high-throughput, particle-size classifier that can accurately separate
sediments into coarse- and fine-grained portions. The typical hydrocyclone (Wills 1988)
is a cone-shaped vessel with a cylindrical section containing a tangential feed entry port
and axial overflow port on top and an open apex at the bottom (the underflow). A slurry
of the particles to be separated enters at high velocity and pressure through the feed port
and swirls downward toward the apex. Near the apex the flow reverses into an upward
direction and leaves the hydrocyclone through the overflow. Coarse particles settle
rapidly toward the walls and exit at the apex through a nozzle. Fine particles are carried
with the fluid flow to the axial overflow port.
The particle size at which separation occurs is primarily determined by the diameter of
the hydrocyclone. Hydrocyclones from 0.4-50 in. (0-125 cm) in diameter make
separations from 1 to 500 um. The common practice is to employ several identical
cyclones from a central manifold to achieve the desired capacity. Most manufacturers
provide detailed manuals for selecting and sizing hydrocyclones (Arterburn 1976; Mular
and lull 1980).
The feasibility of using hydrocyclones for processing dredged material was investigated
by the USAGE Buffalo District (1969) and Mallory and Nawrocki (1974). A 12-in.
(30-cm) hydrocyclone was tested using sediments from the Rouge River in Michigan.
The physical separation was considered good, but the coarse fraction contained a large
amount of volatile solids, determined to be detritus and light organic matter (USAGE
Buffalo District 1969).
Hydrocyclones were the major process unit used in a pilot-scale demonstration of particle
size separation technologies conducted at Saginaw, Michigan, by the ARCS Program
(USAGE Detroit District 1994) and at a similar demonstration in Toronto, Ontario
(Toronto Harbour Commission 1993). At the Saginaw demonstration about 75 percent
of the sediments were successfully separated into a sand fraction, reducing the concentra-
tions of PCBs from 1.2 ppm in the feed material to 0.2 ppm in the sand fraction.
Gravity Separation
Gravity separators separate particles based on differences in their density. Organic
contamination in sediments is often associated with solid organic material or detritus,
which have much lower densities than the natural mineral particles of the sediment.
736
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Chapter 6. Pretreatment Technologies
Particles with high concentrations of heavy metals would be significantly more dense than
the natural mineral particles. A dense media separator was used at the ARCS Program
demonstration at Saginaw, Michigan (USAGE Detroit District 1994), and at the demon-
stration conducted in Toronto, Ontario (Toronto Harbour Commission 1993).
Froth Flotation
Froth flotation is used in the mining industry to process millions of tonnes of ore per day.
Copper, iron, phosphates, coal, and potash are a few of the materials that can be
economically concentrated using this process. The process is based on manipulating the
surface properties of minerals with reagents so that the mineral of interest has a
hydrophobic surface (i.e., lacks affinity for water) such as wax. The minerals to be
rejected have, or are made to have, a hydrophilic surface (i.e., a strong affinity for water).
When air bubbles are introduced, the hydrophobic minerals attach themselves to the
bubbles and are carried to the surface and skimmed away.
When using flotation to remove oily contaminants from sediments, a surfactant is used
in a manner that resembles a detergent. Most organic contaminants are naturally
hydrophobic, and the objective in using a surfactant is to reduce the hydrophobicity of the
oil phase to the point where it will be wetted by the water phase and detach itself from
solid surfaces. Surfactants are able to accomplish this because such molecules have a
lipophilic (fat-soluble) head, which is absorbed into the oil phase, and a hydrophilic tail,
which extends into the water phase. The result of this is that the overall hydrophobicity
of the oil phase is decreased. The strength of a surfactant's attachment to an oil phase
is approximated by the hydrophile-lipophile balance of the surfactant. Once freed of the
solid surface, an oil droplet is assisted to the surface by air bubbles and skimmed away.
Magnetic Separation
Magnetic separations are classified as two types depending on the intensity of the
magnetic field employed (or the magnetic susceptibility of the minerals to be separated).
Low-intensity separations usually employ permanent magnets, and are most often used
for material coarser than about 75 urn with high magnetic susceptibility, such as iron ore.
High-intensity separations that employ electromagnets are much more versatile and
capable of recovering iron-stained or rusted silicate minerals from other purer, nonmag-
netic phases.
Wet, high-intensity magnetic separation (WHIMS) appears to be most applicable to
sediment remediation, with separations possible down to 5 um, although at very low
capacity. The WHIMS unit is essentially a large solenoid. Magnetic material is trapped
on magnetized media in the chamber of the device, then flushed free in a rinse cycle
when the feeding of sediment and magnetic current are stopped. Thus, the WHIMS is
not technically a continuous throughput device, but operates in separate loading and
rinsing cycles (Bronkala 1980).
737
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Chapter 6. Pretreatment Technologies
Magnetic separation was used during part of the dredging and treatment demonstration
conducted with sediments from the Welland River, Ontario (Acres International Ltd.
1993).
SELECTION FACTORS
Not all remedial alternatives will require a pretreatment component, while others may
require several process options for pretreatment. The need for pretreatment is generally
driven by the treatment and/or disposal components selected for a remedial alternative and
the physical characteristics of the sediments. A treatment technology with restrictive feed
requirements may necessitate a multiunit pretreatment system, as illustrated in Figure 6-1.
The design of a pretreatment system must be compatible with other remedial components.
Sufficient lands must be available at the treatment or disposal sites to operate pretreatment
units and accommodate residues. Water extracted from dewatering technologies and
process water from separation technologies may require a separate treatment system from
that used for disposal site effluent or leachate. Some of the pretreatment water may be
reusable within the process system.
Dewatering Technologies
The selection of a dewatering technology usually involves choosing between a passive and
a mechanical approach. Active evaporative technologies would only be employed where
subsequent processes (e.g., thermal desorption or incineration) require extremely dry
materials. The advantages and disadvantages of passive and mechanical dewatering are
listed in Table 6-4.
If a permanent or temporary confined (diked) facility is a part of the remedial alternative,
passive dewatering can be conducted within this facility. Facility design might accom-
modate a number of functions, including settling, dewatering, storage, rehandling, and
disposal. Other pretreatment and treatment equipment might be stationed within or
adjacent to the facility to minimize transport distances. Separate cells might be con-
structed in the facility to accommodate different functions. The design of CDFs is
discussed in Chapter 8, Disposal Technologies.
Haliburton (1978) and the Corps' engineering and design manual, Confined Disposal of
Dredged Material (USAGE 1987b), provide detailed guidance on the use of CDFs for
dewatering and consolidating sediments. The Corps developed computer software for
evaluating the primary consolidation and desiccation of dredged material as part of
ADDAMS (Stark 1991).
Mechanical dewatering is most suitable where land is not available for a temporary or
permanent diked facility. Selection of a specific type of mechanical dewatering
equipment depends on the requirements of the treatment or disposal components to
138
-------
Feed
Water
Attrition
scrubber
Clarifier
Oversized material (>6 mm)
Recycle water
Fines to confined
disposal facility
Particulate organic
compounds
Sand
Figure 6-1. Example multiunit pretreatment system.
-------
TABLE 6-4. ADVANTAGES AND DISADVANTAGES OF PASSIVE
AND MECHANICAL DEWATERING
Advantages
Disadvantages
Passive Dewatering
Able to dewater large quantities of sediments
concurrently
Very low operating costs
Can accommodate high flow rates and rapidly
varying flows and solids concentrations, such
as those produced from a hydraulic dredge
The site used for passive dewatering can pro-
vide intermediate storage and, in the case of
confined disposal facilities, a final disposal site
for dredged material
Land/area requirements are large
Dewatering times range from months to years
Material must be excavated if subsequent
treatment and/or disposal is to take place
Contaminant loss by volatilization is not easily
controlled
Provides a method of increasing sediment
solids content quickly and efficiently
Requires small space
Mechanical Dewatering
Fine-grained sediments may blind or clog filters
Equipment is usually housed in a building
Operator attention is required
Contaminant losses, including volatile losses,
can be controlled
Requires conditioning chemicals that may
increase the weight of dry solids
Dewatered solids must be removed on a con-
tinuous or semicontinuous basis
140
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Chapter 6. Pretreatment Technologies
follow. Maximum solids content is generally achieved using a recessed plate or
diaphragm plate filter. However, if lower solids content is acceptable (e.g., for transport
to a landfill), less costly processes such as centrifugation or belt filter presses may be
more appropriate. A summary of selection factors is provided in Table 6-5.
Laboratory methods are available for predicting the performance of some mechanical
dewatering systems. Prediction of vacuum and pressure filtration performance and
capacity can be done with a filter-leaf test, which involves filtration on a filter medium
disc of known area (Dahlstrom and Silverblatt 1980). Laboratory methods are also
available to predict the performance of gravity thickening. The method of Coe and
Clevenger (1916) is standard for simple gravity thickening, while the method of Kynch
(1952) is more useful for coagulated or flocculated solids. For some mechanical
dewatering systems, bench-scale or pilot-scale applications may be needed to fully assess
equipment performance and operating conditions, and to select conditioning agents.
Evaporative (drying) technologies, which are by far the most expensive form of dewater-
ing, would usually not be employed for sediments. In certain cases, such as when sedi-
ments are to be processed in a thermal treatment system, the removal of water is a
primary consideration in reducing the cost of treatment. In these cases, thermal treatment
systems may provide a source of waste heat that could be used for evaporation. The
primary concern regarding use of this technology is volatile emissions. Because
sediments are heated, volatile and semivolatile contaminants are released. Contaminants
of concern for this process include low molecular weight PAHs, PCBs, and mercury.
Subsequent treatment of off-gases would probably be required and could add significant
costs to the process.
Physical Separation Technologies
The factors for selecting a physical separation technology will depend on the objective
of pretreatment. If the objective is to remove materials from the sediments that may
interfere with subsequent handling, treatment, or disposal, selection factors would be
related to the feed requirements of these subsequent components and the physical
character of the sediments delivered by front-end components. If the objective is to
separate the sediments into two or more fractions with differing treatment and disposal
requirements, the selection factors would be related to the distribution of contaminants
within the sediment matrix and their separability based on physical characteristics.
The selection of equipment for removing oversized material from a process stream is
fairly straightforward. Each process unit will have a maximum feed size (above which
the unit might be damaged) and a target particle size separation, as summarized in
Table 6-6. Most of the equipment is available in different screen sizes or diameters to
accommodate a range of particle size separations. Equipment selection must consider the
characteristics of the incoming sediments and the feed requirements of subsequent
components with the operation and performance specifications of the pretreatment unit.
141
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TABLE 6-5. SELECTION FACTORS FOR MECHANICAL DEWATERING TECHNOLOGIES
Technology
Cake Solids Solids Recovery
Advantages/Disadvantages
Belt Filter Press
31-383
30-90b
90-953 Generally best suited for mobile treatment systems
Performance is sensitive to feed characteristics
and chemical conditions
Belts can deteriorate quickly in presence of
abrasive material
Clogging with fines or oily materials can occur
Generates a substantial amount of wash water
that must be treated
Filter Press
Recessed plate
Diaphragm
Batch plate and
frame filter
40-463
up to 90b
45-503
up to 90b
up to 90b
98+E
98+J
NA
Available in portable units
Costly and energy intensive
Replacement of filter media is time consuming
Clogging with fines or oily materials can occur
Gtnerates wash water that must be treated
Vacuum Filtration
25-33a
up to 70b
85-90" Vacuum disc and drum filters account for about
90 percent of mineral processing filtration units
Filter media blinding can be eliminated by use of
continuous drum filter
Vacuum filtration less effective than other
dewatering technologies with sewage sludge
Solid Bowl Centrifuge
29-36"
90-953 Adaptable to either thickening or dewatering
slurries
Suitable tor areas with space limitations
Most compatible with oily solids
Process may result in a buildup of fines in effluent
from centrifuge
Scroll is subject to abrasion
Gravity Thickening
10-183
15-50b
NA Effective method for thickening sediment slurries
Traditional thickeners require much space, but high
rate and lamella thickeners occupy much less
space
Potential for localized odor and air pollution
problems
Note: NA - not available or applicable
8 Percent solids and solids recovery values for raw primary sludge (USEPA 1987b). Dredged sediments are expected to
yield a somewhat higher percentage of cake solids, although fine-grained sediments may cause operational problems with
some equipment.
b Percent solids values representative of mineral processing applications (Dahlstrom and Fitch 1986).
742
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Chapter 6. Pretreatment Technologies
TABLE 6-6. OPERATION AND PERFORMANCE SPECIFICATIONS
FOR SELECTED PHYSICAL SEPARATION TECHNOLOGIES
Technology
Drag-line
Mechanical removal
Grizzly
Trommel
Vibrating screen
Hydrocyclone
Maximum Feed Size
(cm)
Unlimited
Unlimited
Unlimited
4
1
0.25a
Target Separation Range
(cm)
>30
>60
2-30
0.006-0.055
0.001-2.5
5x10'6-1x10~3
a Not more than one-quarter the diameter of the hydrocyclone apex (discharge) opening, or
smaller if required for protection of the pump.
Aside from removing oversized materials that might disrupt subsequent pretreatment or
treatment processes, physical separation processes may reduce the quantity of materials
requiring expensive treatment or disposal. Virtually any sediment can be separated into
two or more fractions based on one or more physical properties (i.e., particle size,
mineralogy, density, magnetic, and particle surface properties). With some sediments,
contaminants can be separated into specific fractions by mineral processing technologies
that use these same physical properties.
Best results will be obtained wTien the pretreatment system is chosen based on a detailed
knowledge of the physical and chemical characteristics of the sediment. Mineral
processing unit operations appropriate to the physical characteristics of the sediment can
then be arranged into an integrated system. Detailed characterization of the physical
properties of the sediment, including the analyses shown in Table 6-7, and chemical
analysis of separable fractions are needed to determine the selection of a mineral
processing method or methods.
TABLE 6-7. SEDIMENT CHARACTERIZATION FOR PRETREATMENT EVALUATION
Technology
Characterization
Reference
Hydrocyclones, screens,
and classifiers
Density separation
Flotation
Magnetic separation
Particle size analysis using sieves,
hydrocyclones, and settling
Density measurements using the helium
pycnometer and sink-float separations in
dense media
Evaluation of surface properties appli-
cable to froth flotation using zeta poten-
tial measurements and microflotation
tests
Magnetic separability, using high-
intensity wet and dry separators
Herbst and Sepulvada 1986
ASTM Method E-276
Mills 1986
Somasundran and Anantha-
padmanabhan 1986
MacDonald et al. 1986
Hopstock 1986
143
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Chapter 6. Pretreatment Technologies
Other testing that is helpful is sediment mineralogy, or identification of chemical phases,
using scanning electron microscopy with energy-dispersive techniques and possibly x-ray
diffraction. Equally important is knowledge of the history of the contaminated site, which
could provide information about the nature of the contaminant-bearing phases.
If discrete sediment phases containing contamination have been identified, then an
appropriate mineral processing method can be selected. Mineral processing methods are
selected to separate sediments based on the known physical properties of the phases found
to be present. For example, if most of the contamination is found to be associated with
fine silt or clay particles, size classification techniques may be appropriate. The
distribution of PCBs in relation to particle size in sediments from the Saginaw River is
shown in Figure 6-2. As illustrated, most of the PCBs were associated with a relatively
small particle size fraction of the sediments. Particle size separation of the Saginaw River
sediments during a pilot-scale demonstration yielded a small fraction (20 percent of
original material) of silt and clay containing most of the PCBs, and a large fraction
(80 percent of original material) of sand with reduced concentrations of PCBs (USAGE
Detroit District 1994). Toxicity testing of the sand fraction showed a slight decrease in
comparison to the untreated sediments, indicating that these materials may be suitable for
unrestricted disposal, pending further analyses.
A few important points about mineral processing technologies should be noted. Mineral
processing makes particle-particle separations. No chemical bonds are broken, and no
contaminants are destroyed. This is in contrast to many other remediation technologies,
where a process such as incineration actually destroys the contaminants. In addition,
mineral processing separations are based on differences in the physical properties of
particles, so that no separation can be achieved if all particles are physically similar.
Finally, the capacity and efficiency of most mineral processing operations decreases with
particle size. Each individual mineral processing operation has a range of particle sizes
for which the technology is effective. Further information on mineral processing methods
is available from several sources, including Collins and Read (1979) and Somasundran
(1979).
Selection and feasibility testing of mineral processing methods are described in an
extensive handbook published by the Society of Mining Engineers (Weiss 1986). Bench-
scale testing to verify mineral processing performance is inexpensive, and scale-up
reliability is well documented. Most plants with capacities up to 2,700 tonnes/day are
designed from laboratory studies without pilot-scale plant testing.
Debris Removal Technologies
Large debris is most likely encountered during mechanical dredging, especially in urban
areas with unrestricted public access to the waterfront. Debris may be separated by the
dredge operator as it is removed and placed into a barge, or it may be separated at the
first transfer point where the sediments are placed into a disposal facility or loaded for
transport. The advantages of removing debris at the first transfer point include: 1)
144
-------
100
S 80
u
<5
a
OQ
E
«
Q
I-
O
U
60 -\
40
20 -
0
40 60
MASS DISTRIBUTION (percent)
80
100
Source: Allen (in prep.)
Figure 6-2. Distribution of selected contaminants in Saginaw River sediments.
-------
Chapter 6. Pretreatment Technologies
mechanical equipment (i.e., cranes and backhoes) used for rehandling are typically smaller
than the dredge, 2) more space is available to store debris, 3) it is easier to contain
drippage, and 4) a properly designed site can also be used for decontamination.
Screens and Classifiers
Grizzlies and trommels are frequently used to remove small debris and are useful in
sediment processing to capture driftwood, junk, or large rocks that would foul or damage
other processing equipment. Vibrating or other moving screens are often chosen for
separations of particles larger than about 100 um in diameter (Colman 1980; Reithmann
and Burnell 1980).
Grizzlies are the simplest and coarsest devices for removing small debris. Their most
likely application in sediment remediation would be to remove rocks and debris 5 cm or
larger in diameter to prevent damage to subsequent equipment. A grizzly should always
be used if there is a possibility of equipment damage from large rocks or foreign objects.
Trommels are used to remove gravel, rocks, or trash 1-10 cm in diameter from sediment
prior to further processing. Difficulty has been reported with the formation of clay balls
on trommel screens, effectively trapping fine particles that should pass through the device.
If a significant clay fraction is present in the sediment, a water spray may be helpful to
prevent the formation of clay balls. A log washer or similar disaggregating device might
be used in conjunction with a trommel.
Vibrating screens are used to make particle size separations in sediments with particle
diameters from 4,000 to 100 um. Hydrocyclones could also be used for separations in
this range, usually with a lower unit cost. Selection of a vibrating screen over a
hydrocyclone might be justified if variations in feed rate are anticipated, lower volumetric
capacity is required, there is a wide variation in particle densities, or the feed solids
content exceeds 25-30 percent.
Mechanical classifiers such as spiral or rake classifiers can also be used for separations
in the same size range as hydrocyclones. A spiral or rake classifier might be selected for
a sand-silt separation when a high solids content is required in the sand product (e.g.,
when sand is to be transported by belt conveyor). Mechanical classifiers are very
sensitive to variations in the solids content of the feed material, and require a constant
volumetric feed rate for reliable performance.
Hydrocyclones
The selection of hydrocycloning pretreatment to reduce the volume of contaminated
material to be treated is dependent on three factors. First, the contamination must be
strongly distributed toward either the coarse- or fine-grained particles (usually the fines),
so that the remaining fraction of the sediment is clean enough to be suitable for disposal
146
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Chapter 6. Pretreatment Technologies
without treatment or for unrestricted disposal (van Veen and Annokkee 1991). Second,
the mass of the sediment must be sufficiently distributed toward the cleaner fraction so
that an appreciable amount of clean material is recovered. As a general guideline, this
would require that the contaminated material make up no more than about 40 percent of
the total sediment weight. Third, the subsequent treatment to be used on the contami-
nated material must be as efficient and economical with a smaller volume of more heavily
contaminated material as it would with the unseparated bulk sediment.
In the usual hydrocyclone application, it is the fine particles that carry the most con-
tamination. Therefore, it is important in making a separation that the coarse product or
underflow be as free of misplaced fine particles as possible. Some fine particles are
always carried along with the water that exits the cyclone with the underflow, so the
amount of this water should be kept to a minimum. Proper selection of the size and
design of the apex nozzle will accomplish this. Another way of ensuring a clean
underflow product is double-desliming, where the underflow product is subjected to a
second hydrocyclone treatment, resulting in fewer misplaced fine particles. A final option
recommended by at least one hydrocyclone manufacturer is to add clear water to the
hydrocyclone just above the apex nozzle. The additional water forces some of the water
containing misplaced fine particles back to the overflow, resulting in a cleaner underflow
product.
Gravity Separation
The traditional methods for evaluating the feasibility of gravity separation in the
laboratory are "sink-float" tests using a variety of dense liquids, such as bromochloro-
methane and tetrabromoethane (Mills 1985). A sediment sample can be separated into
fractions of differing specific gravity using these liquids and specially constructed
separatory funnels. These heavy liquids are suitable for density separations of sediment
for metal contaminants. Density separations of organic contaminants can be predicted
using water elutriation, in which closely sized material is allowed to settle against a rising
current of water.
A density-based separation may be successful if contamination is found to reside
disproportionately in a phase of different specific gravity than the bulk of the sediment
matrix. For example, organic contaminants are frequently found attached to detrital
material such as wood and leaf fragments. This material is much less dense than mineral
matter and can be easily separated in a gravity separator. Most metallic phases are
considerably denser than most sediment matrices, and can also be recovered. A specific
gravity difference (between the phases to be separated) of about 0.4 is usually enough to
effect a separation with most equipment.
The applicability of gravity separation to a contaminated sediment is dependent on the
size of the sediment, sediment density, and the concentration criterion (C), defined as:
147
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Chapter 6. Pretreatment Technologies
PL-P'
where:
pH = the density of the heavy material
pL = the density of the light material
p' = the density of the liquid (separation) media.
The feasibility of gravity separation for sediments of varying particle sizes is related to
the concentration criteria in Table 6-8 (from Apian 1980).
TABLE 6-8. CONCENTRATION CRITERIA FOR GRAVITY SEPARATION
Concentration Criterion
>2.50
2.50->1.75
1.75->1.50
1.50->1.25
<1.25
Gravity Separation Feasibility
Effective down to 74 jim
Effective to 150 \un
Possible to 1.68 mm, although difficult
Possible to 6.35 mm, although difficult
Not applicable except for dense media
separations
Source: Apian (1980).
Froth Flotation
The use of froth flotation is warranted when most of the contamination is found in a
phase (or phases) distinct from the bulk of the sediments. The most promising application
would be with sediments containing an oily phase, where surfactants could be used to aid
in detaching the organic-phase contaminants from sediment particles, followed by
collection of the contaminants in an organic-laden froth. Another possible application
might be in connection with a minerals industry-related site, where metal contamination
is associated with a specific mineral phase. In this case, a flotation system could be
designed to recover that phase.
Determining the feasibility of froth flotation for a given assemblage of particles involves
two components. First, the phases present must be identified. In minerals processing,
phases are usually identified using a combination of microscopic analysis and x-ray
diffraction. Infrared spectroscopy might be used to identify principal organic phases.
Second, bench-scale testing is used to identify surfactants and operating conditions for an
effective separation. This is an expensive and time-consuming process relative to the
characterization required for a particle size separation, for example. Accurate and
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Chapter 6. Pretreatment Technologies
complete knowledge of the identity of phases in the system will hasten and economize
this process.
Magnetic Separation
Only the low-intensity, rotating, drum-type separators and the WHIMS system appear to
have significant applicability to sediment remediation, because they operate on wet
material. The choice between these two devices is based on the particle size and mag-
netic susceptibility of the phase(s) to be recovered. Fine or paramagnetic material
requires the WHIMS system. The low-intensity systems are generally applicable only
when the material to be recovered is ferromagnetic.
The most practical method of evaluating the feasibility of magnetic separation is to
conduct separability tests using laboratory-scale equipment.
ESTIMATING COSTS
There is considerable cost estimating guidance available on applications of mechanical
and evaporative dewatering technologies to municipal and industrial sludges, and con-
siderable cost data exist on applications of physical separation technologies in the mining
and mineral processing industries. Most of these applications involve permanent
installations that process large quantities of materials at controlled rates under near-ideal
conditions. Sediment remediation will typically have none of these features. Cost
information from wastewater and mineral processing operations will be provided in this
document because it is the best or only information available, but applications to sediment
remediation should be expected to be significantly more expensive.
Dewatering Technologies
Passive Dewatering Technologies
The capital costs for construction of CDFs are discussed in Chapter 8, Disposal
Technologies. Capital costs for temporary diked facilities for dewatering can be estimated
in a manner similar to that for CDFs. Although the design, requirements may be less
stringent for temporary facilities, one additional cost that would be incurred after the
remediation is completed is the removal of the facility and decontamination of the site.
Costs for sand drying beds may be adapted from guidance published for municipal sludge
(USEPA 1985a). No cost data are available on the installation of wick drains at CDFs.
Activities associated with operating a CDF for dewatering may include water-level
management, operation and maintenance of pumps and overflow weirs, and progressive
trenching. At Corps CDFs around the Great Lakes, water level management is typically
conducted by the dredging contractor (or subcontractor) and represents a relatively small
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Chapter 6. Pretreatment Technologies
effort. The cost of progressive trenching is highly site-specific. Haliburton (1978)
estimates that the cost of implementing three trenching cycles over 2 years at a 100-acre
(41-hectare) CDF would be approximately $128,000 (updated to January 1993 dollars).
This cost assumes 70-percent operational efficiency, with administrative costs assumed
to be 20 percent.
Mechanical Dewatering Technologies
Mechanical dewatering equipment may be purchased outright or leased. In addition,
dewatering services are available on a contractual basis. If sediment dewatering is to be
performed intermittently, or just once, contracted services may prove to be more cost
effective. Contractors generally offer belt filter presses and recessed plate filters, although
centrifuges are also sometimes available. Several vendors contacted during preparation
of this document indicated "typical" pricing in the range of $3-$ 10 per hundred gallons
($0.79-$2.64 per hundred liters) of feed material. This can be expressed on a dry-ton
basis if the feed solids concentration is known, as shown in Table 6-9:
TABLE 6-9. UNIT COSTS FOR BELT FILTER PRESS DEWATERING
Feed
(percent solids) $/tona Dry Solids $/yd3 b
10 136-452 83-275
20 63-211 38-129
30 39-131 24-80
40 27-91 16-55
a English tons are used here; multiply by 1.1 for cost per dry tonne.
b Unit cost per cubic yard of sediment (in place) assumes sediments are
50 percent solids and have a dry density of 2.6-2.7 g/cm3 (i.e., 1 yd3
contains approximately 1,200 Ibs of dry solids); multiply by 1.32 for cost
per cubic meter.
Contractual costs are controlled by the quantity of the material to be processed, the
dewaterability of the material, and the required cake solids concentration. The volume
of slurry generated during a sediment remediation project might be considered moderately
"large" when considering mobile dewatering. For example, 10,000 yd3 (7,600 m3) of
in situ sediments in a 10-percent slurry would result in a total volume of approximately
10 million gal (38 million L). Contaminant concentrations may influence cost as well.
Capital costs for construction of mechanical dewatering systems, based on municipal
wastewater applications, are presented in Table 6-10. These costs include equipment
purchase, installation, and housing costs. All equipment (except gravity thickener) is
assumed to be housed in a building.
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TABLE 6-10. CAPITAL COSTS FOR MECHANICAL DEWATERING
Technology
Size/Capacity
Capital Costa
Solid Bowl Centrifuge
(4 Ib polymer/ton; 1.65 kg/tonne)
20 gpm (76 L/min) $ 276,000
100 gpm (380 L/min) 550,000
500 gpm (1,900 L/min) 1,377,000
(8 Ib polymer/ton; 3.3 kg/tonne) 217,000
20 gpm (76 L/min) 435,000
100 gpm (380 L/min) 943,000
500 gpm (1,900 L/min)
Belt Filter Press
Belt Widthb
1 m
2m
$ 318,000
435,000
Gravity Thickener
Surface area
300 ft2 (28 m2)
3,000 ft2 (280 m2)
$ 166,000
394,000
Diaphragm Filter Press
1,200 gpm (4,500 L/min) $ 1,305,000
6,000 gpm (23,000 L/min) 5,798,000
a Capital costs from USEPA (1985a) updated to January 1993 dollars using ENR's
Construction Cost Index of 1.22.
b Capacity is measured by the width of the press; hydraulic loading is typically 40
to 50 gpm/m (150 to 190 L/min/m; USEPA 1987b).
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Chapter 6. Pretreatment Technologies
Operation and maintenance costs for mechanical dewatering include the following
components:
• Maintenance of equipment and facilities
• Power requirements
• Chemical costs
• Labor.
The operating costs for specific mechanical dewatering systems are discussed in the
following paragraphs. The costs of treating and disposing of wastewater streams resulting
from dewatering are discussed in Chapter 9, Residue Management.
Belt Filter Press—Belt filter presses are probably the most energy conservative
and, therefore, the most economical mechanical dewatering units to operate. The average
power requirements range from 0.8 kW (1 hp) to 5.7 kW (8 hp) per meter of belt width.
Replacement of the filter belts is one of the most common maintenance items. The main
reasons for failure of the belts are tearing at the clipper seam, inferior quality belt
material, ineffective tracking systems, and poor operation and maintenance. Average belt
life is about 2,700 running hours with a range of 400-12,000 running hours (USEPA
1987b).
Process control is extremely important to ensure optimum performance of the dewatering
system. By keeping accurate records (i.e., a log) the operator can determine how well the
press is performing. In addition, preventive maintenance and waste minimization can be
integrated to deter unnecessary shutdown and reduce chemical costs, respectively (USEPA
1987b).
Solid Bowl Centrifuge—Operating costs for centrifuge technologies depend on the
solids capacity of the centrifuge and polymer dosage. Additional factors such as bowl
speed and temperature can affect the final sludge cake. Particular attention should be
focused on polymer dosage. Continual laboratory testing will minimize polymer dosage
and maximize the dryness of the cake solids, thus minimizing costs (USEPA 1987b). In
addition, replacement costs for centrifuge scrolls and bearings can be significant.
Examples of operation and maintenance costs for centrifuges from two wastewater
treatment works operated by the Metropolitan Water Reclamation District of Greater
Chicago are shown in Table 6-11.
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Chapter 6. Pretreatment Technologies
TABLE 6-11. EXAMPLE OPERATION AND MAINTENANCE COSTS
FROM MUNICIPAL WASTEWATER TREATMENT PLANTS
FOR THE SOLID BOWL CENTRIFUGE
Cost Element
Calumet Works3
($/ton dry solids)
West Southwest Works3
($/ton dry solids)
Polymer
Power
Maintenance
Labor
TOTAL
TOTAL ($/yd3)b
19.16
42.30
(included with power)
26.60
88.06
' 52.80
14.68
4.86
7.59
2.47
29.60
17.80
Source: USEPA (1987b).
a Costs adjusted to January 1993 prices using ENR's Construction Cost Index
(CCI), of 1.22. English tons are used here; multiply by 1.1 for cost per dry tonne.
b Unit cost per cubic yard of sediment (in place) assumes sediments are 50 per-
cent solids and have a dry density of 2.6-2.7 g/cm3 (i.e., 1 yd3 contains approxi-
mately 1,200 Ibs of dry solids); multiply by 1.32 for cost per cubic meter.
An evaluation of the costs of dewatering dredged material using mechanical dewatering
methods was conducted by the USAGE Buffalo District (1969) for various dredging
volumes. The system consisted of slurried dredged material fed into solid bowl centri-
fuges by pipeline. The centrifuges were sized at 12,500 pounds (27,500 kg) per unit per
hour, producing a cake of approximately 50-percent solids. A summary of the system
costs is provided in Table 6-12. Total costs are based on a term of 10 years with a 4.625
percent annual interest rate. Operating costs are based on labor, utility, and maintenance.
TABLE 6-12. EXAMPLE CALCULATED COST ESTIMATES FOR DEWATERING
DREDGED MATERIAL WITH A SOLID BOWL CENTRIFUGE8
Annual Volume of
Dredged Material
(yd3)"
1,500,000
1,000,000
500,000
100,000
Capital
Cost
($)
17,794,000
12,804,000
6,884,000
1,860,000
Financing
Cost
($)
2,280,000
1,628,000
876,000
236,000
Labor
Cost
($)
568,000
568,000
436,000
436,000
Utility
Cost
($)
1,456,000
1,128,000
688,000
192,000
Maintenance
Cost
($)
2,692,000
1,920,000
1,032,000
280,000
Total Annual
Cost
($)
6,966,000
5,244,000
3,032,000
1,144,000
Unit Cost
($/yd3)b
4.67
5.24
6.06
11.44
Source: USAGE Buffalo District (1969).
a Costs adjusted to January 1993 prices using ENR's CCI.
b 1 yd3 = 0.76 m3; multiply by 1.32 for cost per cubic meter.
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Chapter 6. Pretreatment Technologies
Filter Press—Proper sludge conditioning is a key component of an efficient and
effective filter press operation. Routine evaluations and recordkeeping are recommended,
because operating conditions may vary, leading to conditioner changes (USEPA 1987b).
Operation and maintenance costs include the labor needed to operate the press, power to
pressurize the feed material, and maintenance of the equipment. Most of the maintenance
costs are for replacement of the filter cloths (USEPA 1985a). Requirements for power
and materials costs, based on municipal waste water experience, are shown in Table 6-13.
Manpower and polymer requirements are a function of processing rate and dewatering
characteristics, respectively.
TABLE 6-13. REQUIREMENTS FOR FILTER PRESSES
Cost Element 3 Million Gal 30 Million Gal
(11.4 million LJ/Year3 (114 million LJ/Year3
Power, kW hours
Materials
70,000
$4,500b
270,000
$16,700b
Source: USEPA (1985a).
a Based on 6-percent solids in feed materials.
b Costs adjusted to January 1993 prices using ENR's CCI.
Evaporative Technologies
No cost data are available on evaporation of sediments. In general, there is very limited
information on evaporation of waste solids. Probably the best indication of evaporative
costs are those for the Carver-Greenfield process "discussed in Chapter 7, Treatment
Technologies. Based on a hypothetical site with 21,000 tonnes of drilling mud wastes,
with a solids content of 52 percent and an oil and grease content of 7-17 percent,
processing costs have been estimated to range from $180-$200 per tonne of feed material
(Schindler 1992).
Physical Separation Technologies
Because physical separation technologies are economically applied on a large scale to ores
of low value-to-mass ratio, they are among the least expensive processes in modern
industry. For example, in processing copper, five or six separate mineral processing
operations are performed, plus smelting and refining, at a rate of more than 91,000
tonnes/day, all on an ore that contains less that $10 worth of copper per tonne. It is
important to note that large economies of scale are seen in mineral processing operating
costs. The cost of treating a tonne of ore in a small operation may be 2-3 times the cost
of treating the same amount in one of the larger facilities.
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Chapter 6. Pretreatment Technologies
Mining industry costs for all major mineral-processing unit operations are well docu-
mented; however, considerable difficulty is encountered in applying these costs to an
environmental remediation project. The U.S. Bureau of Mines has published and uses a
cost estimating system to calculate capital and operating costs based on plant throughput
by summing incremental costs of the unit operations and other contributions to cost. In
sediment remediation, this system would appear to be most useful for larger projects, in
excess of about 500 tonnes/day of sediment (U.S. Bureau of Mines 1987).
Debris Removal Technologies
Debris removal is an anticipated inconvenience during most maintenance dredging
projects at Great Lakes harbors. Contractors are typically advised in dredging contracts
to expect some debris and be prepared to remove it. Removal generally requires
additional time by dredge operators to handle large debris and causes decreased produc-
tion. The costs of debris removal are generally factored into the dredging cost estimates.
During sediment remediation, additional provisions may be necessary because of the
highly contaminated nature of the sediments. Most of these costs can also be factored
into the costs of other components. If the debris is removed by the dredge operator or
during mechanical rehandling or transport, the costs will be reflected as decreased
productivity. The costs of additional equipment and labor needed to store the debris and
costs for decontamination are project specific.
Screens and Classifiers
Few data are available in the mining industry for these (coarse) size separations. Their
cost is typically calculated as part of a larger grinding or mineral processing system. As
an example, the operating cost for a washing and screening circuit consisting of a
trommel, log washer, and vibrating screens, with ancillary equipment, is estimated to be
$8.25/tonne. Such a circuit might be encountered in the gravel or crushed stone
industries. With screens and classifiers, equipment costs are generally incidental to the
costs of moving material to and through the system.
Hydrocyclones
A typical hydrocyclone designed for soil or sediment remediation, which makes a
separation at 75-150 urn with a throughput of 18-55 dry tonnes per hour, would cost
from $3,750-7,500 (1993 dollars), depending on the exact size and configuration (costs
are adjusted from 1990 prices using ENR's CCI factor of 1.07). Because capacity is
determined by hydrocyclone size, the cost increment for higher throughput would be
linear (i.e., capacity would be increased by increasing the number of hydrocyclones).
Pumping and support equipment must also be provided.
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Chapter 6. Pretreatment Technologies
Operating costs for hydrocyclones are essentially the cost of pumping the slurry through
the unit and costs for occasional replacement of the hydrocyclone liners. These costs are
estimated at about $0.12-0.35 per dry tonne (1993 dollars; costs are adjusted from 1990
prices using ENR's CCI factor of 1.07). The highest costs associated with hydrocyclone
applications are the manpower costs associated with operating the plant.
An evaluation of the costs of particle size separation of dredged material was conducted
by the USAGE Buffalo District (1969) for various dredging volumes. The system
consisted of a dredged material slurry pumped from a wet well (equalization basin) into
hydrocyclones. The underflow (fine fraction) was discharged to a CDF and the overflow
(coarse fraction) passed through a spiral classifier before being disposed. A summary of
the system costs is shown in Table 6-14. Total costs are based on a term of 10 years
with a 4.625 percent annual interest rate. Operating costs are based on labor, utility, and
maintenance.
TABLE 6-14. EXAMPLE COST ESTIMATES FOR SEPARATION OF PARTICLE SIZES FOR
DREDGED MATERIAL8
Annual Volume of
Dredged Material
(yd3)b
3,000,000
1,000,000
500,000
Capital
Cost
($)
2,156,000
1,140,000
1,240,000
Financing
Cost
($)
276,000
144,000
156,000
Labor
Cost
($)
612,000
436,000
436,000
Utility
Cost
($)
10.000
4,000
1.200
Maintenance
Cost
($)
216,000
1 16,000
142,000
Total Annual
Cost
($)
1,114,000
700,000
702,800
Unit Cost
<$/yd3)b
0.37
0.70
1.41
Source: USACE Buffalo District (1969).
a Costs adjusted to January 1993 prices using ENR's CCI.
b 1 yd3 = 0.76 m3; multiply by 1.32 for cost per cubic meter.
Gravity Separation
A typical gravity separation circuit, employing Humphreys spirals, in a mineral processing
plant is estimated to have an operating cost of $6.05/tonne. The capital cost for a
91-tonne/day Humphreys spiral circuit is estimated to be $270,000.
Froth Flotation
Based on mineral processing industry experience, the capital cost of a froth flotation plant
designed to process 91 tonnes/day is estimated to be $750,000 (Allen, in prep.).
Operating costs for froth flotation are about twice those for gravity separation, because
of the cost of reagents. Many of the surfactants proposed for sediment treatment are
rather expensive and would drive the operating costs even higher.
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Chapter 6. Pretreatment Technologies
Magnetic Separation
Magnetic separation plants are used in the iron-ore industry and are quite large. No data
are available for magnetic separation plants that operate at capacities lower than about
1,900 tonnes/day. Generally, magnetic separation plants will be more costly to build than
gravity separation facilities, but will be about equal in cost to operate.
ESTIMATING CONTAMINANT LOSSES
While methods for predicting contaminant losses from passive dewatering technologies
(primarily CDFs) are fairly well developed, a priori methods for predicting contaminant
losses from mechanical dewatering and physical separation technologies do not exist. For
these technologies, mechanisms for contaminant loss can be identified, and controls can
be installed to minimize loss.
Dewatering Technologies
Passive Dewatering Technologies
Contaminant losses from passive dewatering systems are expected to be comparable to
those experienced at CDFs. Chapter 8, Disposal Technologies, and Myers et al. (in prep.)
provide further discussion of these losses.
Mechanical Dewatering Technologies
The mechanisms for contaminant loss from mechanical dewatering systems will include
volatilization and leakage/spillage of solids or water. Systems that are housed can be
equipped with controls to collect and route all leakage/spillage for treatment as necessary.
Leakage/spillage would most likely be washed into a wet well and pumped to the water
residue treatment system.
If the sediments have significant concentrations of volatile or semivolatile contaminants,
controls can be implemented to capture and treat any contaminant losses. Contaminant
losses will ultimately be limited to the quantity of emission permitted by the regulatory
agencies and the residuals generated during the treatment of the off-gas (e.g., spent
carbon). Volatilization losses from systems that cannot be housed (i.e., gravity thicken-
ers) may be estimated using the same methods used for CDFs (Chapter 8, Disposal
Technologies).
Active Evaporative Technologies
Contaminant loss mechanisms for active evaporative technologies would be similar to
those for mechanical dewatering technologies. Because the sediments are heated,
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Chapter 6. Pretreatment Technologies
volatilization is more likely to be significant, and more elaborate controls would be
required.
Physical Separation Technologies
Debris Removal Technologies
The mechanisms for contaminant loss during debris removal include sediment drippage
during handling, volatilization, and wash water. If debris is separated during dredging,
there are few controls that can be implemented other than having an adequate storage
container for debris. If debris is separated during rehandling (between components),
drippage can be controlled using drip aprons or by constructing a low-permeability,
drained rehandling area. Drippage from a rehandling area and wash water from debris
decontamination should be collected and routed for treatment.
Screens and Classifiers
Contaminant losses from screens and classifiers are the result of volatilization, splashing,
or spillage. Mechanical classifiers can readily be fitted with covers to recover volatile
contaminants; because these devices require a quiescent flow regime, it is not expected
that volatile losses would be much greater than those from sediment in place. Significant
losses are not expected from grizzlies. The mixing in trommels and the high-frequency
vibration of some moving screens may impart sufficient energy to effect contaminant
volatilization; however, substitution of reciprocating or gyratory screens would reduce this
possibility.
Hydrocyclones
Contaminant losses from hydrocyclone treatment are expected to be minimal, because the
hydrocyclone is an enclosed unit, and material is transferred to and from the hydrocyclone
by pumping through rigid pipes. It is possible that some contaminants could be
volatilized in the turbulence of the hydrocyclone, but provisions can be made for capture
of the escaping gases.
Gravity Separation
Contaminant losses from gravity separation devices are expected to be relatively low. An
exception to this may be volatile losses from shaking tables or other flowing-film
concentrators. These losses could be controlled if the equipment was enclosed or housed
in a building with air capture and treatment capability.
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Chapter 6. Pretreatment Technologies
Froth Flotation
The most likely loss pathway for froth flotation is volatilization of organic contaminants,
which results from forcing quantities of air through the sediment pulp. Ventilation hoods
can be fitted on flotation cells to capture volatile emissions.
Magnetic Separation
Contaminant losses from magnetic separations will be no greater than from any other
simple materials-handling operation, because no heating or significant increase in air-
slurry interface is involved.
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7. TREATMENT TECHNOLOGIES
There are numerous treatment technologies for sediments contaminated with hazardous
substances. Many of these technologies have been developed for treating contaminated
soils at hazardous waste sites, especially those designated under the Superfund Program.
This chapter provides an introduction to some of the better-established technologies,
particularly those that have been demonstrated on contaminated sediments. However,
other sources of information should be consulted for more up-to-date and detailed infor-
mation on specific applications.
The list of potential remediation technologies is continually changing as new technologies
are developed and become available, and other technologies are withdrawn from use. The
need for an up-to-date database of treatment technologies has been recognized by
governmental agencies in both the United States and Canada. Three of the more useful
databases developed to date are described below:
Sediment Treatment Technologies Database (SEDTEC)
Available from: Wastewater Technology Centre
867 Lakeshore Road
Burlington, Ontario L7R 4L7
Sponsored by: Environment Canada
Great Lakes Cleanup Fund
Description: Currently in its second edition, SEDTEC provides fact sheets
on 168 different technologies submitted to the Wastewater
Technology Centre from vendors and technology developers
around the world.
Vendor Information System for Innovative Treatment Technologies (VISITT)
Available from: PRC Environmental Management, Inc.
1505 PRC Drive
McLean, Virginia 22102
Sponsored by: U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
Technology Innovation Office
Washington, DC 20460
Description: Similar to SEDTEC, except that only innovative technologies
are included, and technologies are not specific to sediments.
The current Version 1.0 contains 94 technologies for treating
sediments. Specific performance data may be included.
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Chapter 7, Treatment Technologies
Risk Reduction Engineering Laboratory (RREL) Treatability Database
Available from: U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
Description: Provides results of published treatability studies that have
passed the USEPA's quality assurance review. Although the
most current data are for wastewater treatment, recently avail-
able treatment data for soils and sediments will likely be
added in future updates.
New technologies must be subjected to a lengthy process of testing and evaluation before
they can be applied in a full-scale remediation project. Many innovative technologies
have only been demonstrated in bench-scale (i.e., laboratory) tests, while others have
undergone pilot-scale testing. In general, both bench- and pilot-scale testing of any
treatment technology must be conducted prior to the application of that technology for
full-scale remediation.
Sediment that is contaminated to the extent that it requires decontamination or detoxifica-
tion in order to meet environmental cleanup goals may be treated by using one or more
of a number of physical, chemical, or biological treatment technologies. Treatment tech-
nologies reduce contaminant concentrations, contaminant mobility, and/or toxicity of the
sediments by one or more of four means:
• Destroying the contaminants or converting the contaminants to less toxic
forms
• Separating or extracting the contaminants from the sediment solids
• Reducing the volume of contaminated material by separation of cleaner
sediment particles from particles with greater affinity for the contaminants
• Physically and/or chemically stabilizing the contaminants in the dredged
material so that the contaminants are fixed to the solids and are resistant
to losses by leaching, erosion, volatilization, or other environmental
pathways.
Destruction technologies described in this chapter include thermal destruction, chemical
treatment, and bioremediation; separation technologies include extraction and thermal
desorption. Volume reduction using particle separation techniques was discussed in
Chapter 6, Pretreatment Technologies. Immobilization or stabilization techniques are also
described in this chapter. Discussions of the factors for selecting from the available
technology types, methods for evaluating their feasibility, and techniques for estimating
costs and contaminant losses are also provided.
DESCRIPTIONS OF TECHNOLOGIES
Thermal Destruction Technologies
The processes considered in this section are those that heat the sediment several hundreds
or thousands of degrees above ambient temperature. These processes are generally the
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Chapter 7. Treatment Technologies
most effective options for destroying organic contaminants, but are also the most
expensive. Included in this category are:
• Incineration
• Pyrolysis
• High-pressure oxidation
• Vitrification.
Most of the thermal technologies are highly effective in destroying a wide variety of
organic compounds, including PCBs, PAHs, chlorinated dioxins and furans, petroleum
hydrocarbons, and pesticides. They do not destroy metals, although some technologies
(e.g., vitrification) immobilize metals in a glassy matrix. Volatile metals, particularly
mercury, will tend to be released into the flue gas. Additional equipment for emission
control may be needed to remove these contaminants.
These technologies will be briefly summarized here; for a more complete discussion see
Averett et al. (in prep.) and USEPA (1985b, 1991e, 1992g).
Incineration
Incineration is by far the most commonly used process for destroying organic compounds
in industrial wastes. Incineration basically involves heating the sediments in the presence
of oxygen to burn or oxidize organic materials, including organic compounds. A critical
component of the overall treatment process is the emission control system for the gases
produced by the process. A diagram of an incineration process is shown in Figure 7-1.
Stack
emissions
Sediment
preparation
Sediment
feed
Incinerator
Flue
gases
Air pollution
control
Ash
Residue
handling
Residue
handling
Treated solids
Solids Water
Figure 7-1. Diagram of an incineration process.
Source: USEPA (1990f)
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Chapter 7. Treatment Technologies
Application of incineration to wet solids such as sediments is relatively uncommon; all
traces of moisture must be driven off before the solids will burn. This requires the
expenditure of large quantities of energy, which makes the process very expensive.
Moreover, incineration tends to be a very controversial issue for communities where such
facilities are to be sited.
As with most processes that destroy organic compounds, incineration does not remove
heavy metal contamination. Most incineration processes increase the leachability of
metals through the process of oxidation (exceptions include the slagging or vitrifying
technologies, which produce a nonleachable, basalt-like residue). This increased leach-
ability of metals would be advantageous only if the resulting ash were to be treated using
a metals extraction process; otherwise, it is a distinct disadvantage. The leachability of
metals is generally measured using the toxicity characteristic leaching procedure (TCLP)
test. Incinerator ash that "fails" this test must be disposed of as a hazardous waste in
accordance with RCRA.
Incineration technologies can be subdivided into two categories: conventional and
innovative. Because gaseous emissions from incinerators present a potentially large
contaminant loss pathway, the emission control system is a critical component for both
categories. Conventional technologies include rotary kiln, fluidized bed, multiple hearth,
and infrared incineration. These technologies, summarized in Table 7-1, typically heat
the feed materials to between 650 and 980°C. An afterburner, or secondary combustion
chamber, is generally required to achieve complete destruction of the volatilized organic
compounds. All of these processes produce a dry ash residue.
In contrast, there are a number of innovative processes that are designed specifically for
hazardous and toxic wastes. These proprietary technologies, listed in Table 7-2, operate
at higher temperatures and generally achieve greater destruction and removal efficiencies
compared with conventional incineration. Most of these technologies produce a dense
slag or vitrified (glass-like) solid instead of a free-flowing ash. These technologies tend
to be very expensive, but offer the advantage of producing a nonleachable end product.
Pyrolysis
In contrast to incineration, pyrolysis involves the heating of solids in the absence of
oxygen. A pyrolysis system consists of a primary combustion chamber, a secondary
combustion chamber, and pollution control devices. High temperatures, ranging from 540
to 760°C, cause large, complex molecules to decompose into simpler ones. The resulting
gaseous products can then be collected (e.g., on a carbon bed) or destroyed in an after-
burner at 1,200°C. A summary of proprietary technologies is provided in Table 7-3.
The Thermal Gas Phase Reduction Process is a specialized process in which a reducing
agent (hydrogen gas) is introduced to remove chlorine atoms from PCBs or dioxins. In
Hamilton, Ontario, a pilot-scale reactor was used to process PAH- and PCB-contaminated
harbor sediments in July 1991. This process produced high destruction efficiencies for
PAHs.(99.92-99.99999 percent) and PCBs (99.999-99^99999 percent) in dilute sediment
slurries (5-10 percent solids) (ELI Eco Logic International 1992). In late 1992, this
163
-------
TABLE 7-1. SUMMARY OF CONVENTIONAL INCINERATION TECHNOLOGIES
Technology
Description
System Name/Vendor
Rotary Kiln
Incineration
Consists of a solid feed material system; a primary
combustion chamber; an inclined, rotating refracto-
ry-lined cylinder; an afterburner; an air pollution
control unit; and a process stack. Temperatures
range from 650 to 980°C with a retention time of
1 5 minutes up to several hours. The secondary
chamber reaches a temperature of 1,300°C with a
retention time of 2 seconds.
Aqua-Guard Thermal Oxidation
- Aqua-Guard Technologies, Inc.
(Vancouver, B.C.)
B.A. Brown Thermal Oxidation
- Bruce Brown Associates Ltd.
(Toronto, Ontario)
Vesta 100 Incinerator
- Vesta Technology Ltd.
(Ft. Lauderdale, Florida)
PYROX Transportable Thermal Destruction
System
- Chemical Waste Management, Inc.
(Oak Brook, Illinois)
BOVAR Environmental Services
(Calgary, Alberta)
Modular Waste Processor
- ENSCO (Williamsville, New York)
Fluidized Bed
Incineration
Consists of a cylindrical, vertical, refractory-lined
vessel containing inert granular material (sand) on a
perforated metal plate. Combustion air is intro-
duced at the bottom of the incinerator causing
bedding material to become fluidized. Tempera-
tures range from 760 to 870°C. Exhaust gases
and volatile compounds pass into a secondary com-
bustion chamber where they are combusted for a
retention time of 2 seconds.
DJN Zerofuel Fluid Bed Sludge Incineration
- Jan De Nul N.V.
(Aalst, Belgium)
MK Thermal Treatment Units
- Morrison Knudsen Corp.
(Boise, Idaho)
OES Circulating Bed Combustor Incinerator
- Ogden Environmental Services
(San Diego, California)
Multiple Hearth
Incineration
Consists of a refractory, steel-lined shell; a rotating
central shaft; a series of solid flat hearths; a series
of rabble arms with teeth for each hearth; an air
blower; waste feeding and ash removal systems;
and fuel burners mounted on the walls. Tempera-
tures range from 760 to 980 °C.
NA
Infrared
(SHIRCO)
Incineration
Consists of a waste preparation system and weigh
hopper, an infrared primary combustion chamber, a
propane-fired afterburner, emission control sys-
tems, and a process management and monitoring
control center. Temperatures reach up to 1,010°C
with retention times of 10-180 minutes in the pri-
mary combustion chamber. Afterburner tempera-
tures range from 1,200 to 1,300°C.
OHM Mobile Infrared Incineration Systems
- OH Materials Corp.
(Findlay, Ohio, and Oakville, Ontario)
- Ecova Corp.
(Redmond, Washington)
- Westinghouse Haztech, Inc.
(Atlanta, Georgia)
Note: NA - information not available.
164
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TABLE 7-2. SUMMARY OF INNOVATIVE INCINERATION TECHNOLOGIES
System Name/Vendor
Cyclone Furnace
- Babcock & Wilcox
(Alliance, Ohio)
EER Spouted Bed ("Hybrid
Fluidized Bed")
- Energy and Environmental Re-
search Corp.
(Irvine, California)
Two-stage Incineration
- Institute of Gas Technology
(Chicago, Illinois)
Plasmawaste/Plasmadestruct8
- Enviro-Tech B.G.F.
(Montreal, Quebec)
Pyretron Oxygen Burner
- American Combustion, Inc.
(Norcross, Georgia)
Plasma Centrifugal Furnace
(Plasma Arc Vitrification)
- Retech, Inc.
(Ukiah, California)
Pyrokiln Thermal Encapsulation
- Allis Mineral Systems, Inc.
(Milwaukee, Wisconsin)
Oxidation and Vitrification Pro-
cess
- VORTEC Corp.
(Collegeville, Pennsylvania)
Status of
Development
Pilot scale
{0.1 tonne/hr)
Pilot scale
(1 tonne/hr)
Pilot scale
(5.5 tonne/hr)
Pilot scale
(used in
Sweden)
Pilot scale
Full scale
(up to 1.1
tonne/hr)
Pilot scale
Pilot scale
(1 tonne/hr)
Application
All organic com-
pounds; feed
material must be
screened and dry
All organic com-
pounds, suitable for
40-50 percent mois-
ture content
All organic com-
pounds; feed
material must be
screened
All organic
compounds
Secondary burner for
any incinerator;
treats off-gas only
All organic com-
pounds; feed
material must be
screened
All organic com-
pounds and metals
All organic com-
pounds and metals
End Product
Vitrified slag
Ash
Vitrified
pellets
Slag
Ash
Vitrified slag
Slag
Vitrified Slag
Source
1
1, 2
1
2
1
1,2
1
1
a This process may be either oxidizing or reducing.
Source:
1 - SITE Program (USEPA 1991e, 1992g).
2 - SEDTEC {Wastewater Technology Centre 1993).
165
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TABLE 7-3. SUMMARY OF PROPRIETARY PYROLYSIS TECHNOLOGIES
System Name/Vendor
Advanced Electric Reactor
- J.M. Huber Corp.
(Borger, Texas)
Flame Reactor Process
- Horsehead Resource Develop-
ment Comp.
(Monaca, Pennsylvania)
Thermal Gas Phase Reduction
Process
- ELI Eco Logic International,
Inc.
(Rockwood, Ontario)
Pyroplasma Pyrolysis Process
- Vendor unknown
Status of
Development
,_a
Pilot scale
(1.4-2.7
tonne/hr)
Pilot scale
Pilot scale
(1 tonne/hr)
Application
Screened solids (<35
mesh); all organic
compounds
Metal-contaminated
solids; low moisture,
finely screened
All organic compounds
All organic compounds
End Product
Ash, carbon
Vitrified slag
Grit and slag
Carbon
particulates
and slag
Source
2
1
1
2
a Not commercially available at this time.
Source:
1 - SITE Program (USEPA 1991e, 1992g).
2 - Averett et al. (in prep.).
166
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Chapter 7. Treatment Technologies
technology was tested under the Superfund Innovative Technology Evaluation (SITE)
Program with PCB-contaminated soil from a landfill in Bay City, Michigan (USEPA
1994b).
Pyrometallurgy, or smelting/calcination, is a nonproprietary form of pyrolysis. This
commercial technology is commonly used to treat metal-bearing ores. High levels of
metals or metal oxides can be recovered from waste materials of similar metal content
because the effectiveness of recovery is directly proportional to the metal content of the
waste. However, this process has the potential for forming toxic sludges and has high
process costs (Averett et al., in prep.).
High-Pressure Oxidation
This category includes two related technologies: wet air oxidation and supercritical water
oxidation. Both processes use the combination of high temperature and pressure to break
down organic compounds. Typical operating conditions for both processes are shown in
Table 7-4. As indicated in the table, wet air oxidation can operate at pressures of one-
tenth those used during supercritical water oxidation.
TABLE 7-4. OPERATING CONDITIONS FOR HIGH-PRESSURE OXIDATION PROCESSES
Process
Wet air oxidation
Supercritical water oxidation
Operating
Temperature
(°C)
150-300
400-600
Operating
Pressure
(MPa)
2,000-20,000
22,300
Source: USEPA (1991 b); Kiang and Metry (1982).
Wet air oxidation is a commercially proven technology, although its use has generally
been limited to conditioning of municipal wastewater sludges. This technology can
degrade hydrocarbons (including PAHs), some pesticides, phenolic compounds, cyanides,
and other organic compounds (USEPA 1987a). A bench-scale test using sediments from
Indiana Harbor showed greater than 99 percent destruction of PAHs (USEPA, in prep.a).
However, destruction of halogenated organic compounds (e.g., PCBs) with this process
is poor. In bench-scale testing of the process conducted under the ARCS Program, using
sediments from Indiana Harbor, it was found that only 35 percent of influent PCBs were
destroyed (USEPA, in prep.a). It may be possible to improve oxidation through the use
of catalysts (Averett et al., in prep.). One vendor of this technology is Zimpro Passavant
(Rothschild, Wisconsin).
The supercritical water oxidation process is a relatively new technology that has received
limited bench- and pilot-scale testing. Available data have shown essentially complete
destruction of PCBs and other stable compounds. Vendors of this process include Modar,
167
-------
Chapter 7. Treatment Technologies
Inc. (Natick, Massachusetts) and VerTech Treatment Systems (Air Products and Chem-
icals, Allentown, Pennsylvania). Modar uses high-pressure pumps and an above-ground
reactor. In contrast, VerTech uses a well between 2,500 and 3,000 m deep to achieve the
necessary pressures.
Vitrification
Vitrification is an emerging technology that uses electricity to heat and destroy organic
compounds and immobilize inert contaminants. A typical unit consists of a reaction
chamber divided into two sections: the upper section introduces the feed material
containing gases and pyrolysis products, while the lower section contains a two-layer
molten zone for the metal and siliceous components of the waste. Wastes are vitrified
by passing high electrical currents through the material. Electrodes are inserted into the
waste solids, and graphite is applied to the surface to enhance its electrical conductivity.
A large current is applied, resulting in rapid heating of the solids and causing the siliceous
components of the material to melt. The end product is a solid, glass-like material that
is very resistant to leaching. Temperatures of about 1,600°C are typically achieved.
Vitrification units demonstrated in pilot- scale and full-scale tests have solidified 300,000
kg/melt. Vitrifix N.A. (Alexandria, Virginia) is developing a full-scale unit for asbestos
waste. Geotech Development Corp. and Penberthy Electromelt also offer vitrification
systems.
In situ vitrification is a patented thermal destruction technology developed by the Battelle
Memorial Institute's Pacific Northwest Laboratory. Although it was designed to treat
contaminated soils in place, it could presumably be adapted to treat dredged sediments.
This technology is available commercially from Geosafe Corp., (Kirkland, Washington).
Summary of Thermal Destruction Technologies
The advantages and disadvantages of the five thermal destruction processes reviewed in
this section are summarized in Table 7-5 for comparative purposes.
Thermal Desorption Technologies
Thermal desorption physically separates volatile and semivolatile compounds from
sediments by heating the sediment to temperatures ranging from 90 to 540°C. Water,
organic compounds, and some volatile metals are vaporized by the heating process and
are subsequently condensed and collected as liquid, captured on activated carbon, and/or
destroyed in an afterburner. An inert atmosphere is usually maintained in the heating step
to minimize oxidation of organic compounds and to avoid the formation of compounds
such as dioxins and furans. Figure 7-2 shows a typical process for thermal desorption.
The temperature of the soil in the desorption unit and retention time are the primary
variables affecting performance of the process. Heating may be accomplished by
indirectly fired rotary kilns* heated screw conveyors, a series of externally heated
distillation chambers, or fluidized beds (USEPA 1991c).
168
-------
TABLE 7-5. SUMMARY OF THERMAL
DESTRUCTION TECHNOLOGIES
Technology
Advantages
Disadvantages
Conventional
Incineration
Innovative Incineration
Can process large waste volumes
Proven commercially at full-scale portable
equipment
Widely available
Can achieve >99.99 percent destruction
of organic compounds
Applicable to a wide variety of compounds
Recognized as a destructive process under
RCRA and TSCA
Can achieve greater destruction and
removal efficiencies than conventional
incineration
Most processes produce an inert slag,
which is resistant to leaching
Generates large volumes of exhaust
gas that must be treated
Can volatilize heavy metals,
especially mercury
Increases teachability of metals in
treated solids
Public opposition is usually very
high
Can produce chlorinated dioxins and
furans
Extensive pretreatment (drying and
screening) may be required
Most technologies still in develop-
ment stage; permitting may be
difficult; technical problems may
remain
Extensive pretreatment (drying and
screening) may be required
More expensive than conventional
incineration
Public opposition is likely
Can produce chlorinated dioxins and
furans
Pyrolysis
Can achieve greater destruction and
removal efficiencies than conventional
incineration
Can produce inert slag
Most technologies still in devel-
opment stage; permitting may be
difficult; technical problems may
remain
Extensive pretreatment (drying and
screening) may be required
More expensive than conventional
incineration
High-Pressure
Oxidation
Does not require dewatering and drying of Wet air oxidation not effective for
Vitrification
sediments
Costs less than incineration
Supercritical water oxidation effective for
many types of organic compounds, in-
cluding polychlorinated biphenyls
Produces an inert glass/slag that is
resistant to leaching
polychlorinated biphenyls and
other chlorinated organic
compounds
Supercritical water oxidation is still
in the development stage
Most technologies still in the de-
velopment stage; permitting may
be difficult; technical problems
may remain
More expensive than conventional
incineration
Not feasible for sediments contain-
ing high levels of electrically
conducting metals
Molten product may take months to
years to cool
169
-------
Chapter 7. Treatment Technologies
Dredged
sediment
Sediment
screening
Thermal
desorption
-»• Clean off-gas
Gas treatment
system
• Spent carbon
-*• Concentrated contaminants
Water
for dust
control
-••Water to disposal
Oversized
material
Treated
solids
Source: USEPA(1991c)
Figure 7-2. Diagram of a thermal desorption process.
High-Temperature Thermal Processor
The high-temperature thermal processor (Remediation Technologies, Inc. [ReTec]) uses
a Holoflite™ dryer, which is a heated screw conveyor, to heat the sediment and drive off
water vapors, organic compounds, and other volatile compounds. The screws for the
dryer are heated by a hot molten salt that circulates through the stems and blades of the
augers, as well as through the trough that houses the augers. The molten salt is a mixture
of salts, primarily potassium nitrate. Maximum soil temperatures of 450°C are attainable
(USEPA 1992g). The motion of the screws mixes the sediment to improve heat transfer
and conveys the sediment through the dryer. Off-gases are controlled by cyclones,
condensers, and activated carbon. This technology was evaluated in ARCS Program
bench- and pilot-scale demonstrations. Removal efficiencies from 42 to 96 percent were
achieved for PAHs in Buffalo River sediments (USAGE Buffalo District 1993). Greater
than 89 percent of the PCBs in Ashtabula River sediments were removed by the ReTec
pilot unit (USACE Buffalo District, in prep.).
Low-Temperature Thermal Treatment System
The low-temperature thermal treatment system (Roy F. Weston, Inc. [Weston]) also uses
a Holoflite™ dryer, similar to the ReTec process. However, Weston's heating fluid is a
thermal oil heated by a separate, gas-fired unit. Maximum temperature for the heating
fluid is a limiting factor for this process. The typical oil medium has a maximum
operating temperature of 350°C, which allows soils to be heated to approximately 290°C
(Parker and Sisk 1991); however, higher temperatures would likely be required to
770
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Chapter 7. Treatment Technologies
effectively remove PCBs from sediments. Vapors from the contaminated material are
passed through a particulate filter, scrubbers or condensers, and carbon adsorption
columns, and may require additional post-treatment. In past demonstrations, Weston has
attached an afterburner to the gas stream at temperatures as high as 1,200°C to destroy
the organic compounds. Removal efficiencies >99 percent have been reported for volatile
organic compounds; removal efficiencies of about 90 percent have been reported for
PAHs (USEPA 1991c). Bench-, pilot-, and full-scale units are available. The capacity
of the full-scale system is 6.8 tonnes/hour (Parker and Sisk 1991).
X*TRAX System
The X*TRAX thermal desorption system (Chemical Waste Management) uses an
externally fired rotary kiln to heat soil to temperatures ranging from 90 to 480°C. Water
and organic compounds volatilized by the process are transported by a nitrogen carrier
gas to the gas treatment system. First, a high-energy scrubber removes dust particles and
10-30 percent of the organic compounds. The gases are then cooled to condense most
of the remaining vapors. About 90-95 percent of the cleaned gas is reheated and recycled
to the kiln. The remaining 5-10 percent is passed through a particulate filter and
activated carbon and is then released to the atmosphere (USEPA 1992g). Pretreatment
requirements include screening or grinding to reduce the particle size to less than 5 cm.
Post-treatment includes treatment or disposal of the condensates and spent carbon.
Removal efficiencies greater than 99 percent have been demonstrated for volatile organic
compounds, pesticides, and PCBs. USEPA (1992g) reported that mercury, one of the
more volatile metals, had been reduced from a soil concentration of 5,100 ppm to 1.3
ppm using this process. The X*TRAX system is available in bench-, pilot-, and full-scale
units, although this particular thermal desorption process has not been demonstrated with
contaminated sediments.
Desorption and Vaporization Extraction System
The Desorption and Vaporization Extraction System (DAVES®) process (Recycling
Sciences International, Inc.) uses a fluidized bed maintained at a temperature of about
160°C and a concurrent flow of 540-760°C air from a gas-fired heater. As the contami-
nated material is fed to the dryer, water and contaminants are removed from the solids
by contact with the hot air. Gases from the dryer are treated using cyclone separators and
bag houses for removal of particulates and using a venturi scrubber, counter-current
washer, and carbon adsorption system for removal of water and organic compounds.
Onsite treatment of liquid residues is available as a part of the process. The mobile
DAVES® unit has a capacity of 10-66 tonnes/hour. It is applicable to most volatile and
semivolatile organic compounds and PCBs (USEPA 1992g). The process was tested
with sediments from Waukegan Harbor, Illinois, with reported reductions in PCB
concentrations from 250 ppm to <2 ppm (USEPA 199 Ic).
777
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Chapter 7. Treatment Technologies
Low-Temperature Thermal Aeration System
The low-temperature thermal aeration system (Canonic Environmental Services Corp.)
uses a direct-fired rotary dryer that can heat soil to temperatures of 430°C. The gas
stream from the dryer is treated for particulate removal in cyclones and/or baghouses.
Organic compounds may be destroyed in an afterburner or scrubbed and adsorbed onto
activated carbon. The full-scale unit can process 11-15 nrVhour. Effective separation
of volatile organic compounds and PAHs from contaminated soils has been demonstrated
(USEPA 1992g).
Anaerobic Thermal Processor Systems
The Anaerobic Thermal Processor® (ATP®) system (SoilTech ATP Systems, Inc.) also
known as the AOSTRA-Taciuk process, consists of four processing zones. Contaminated
material is fed into a preheat zone maintained at temperatures of 200-340°C where steam
and light organic compounds are separated from the solids. The solids then move into
a 480-620°C retort zone, which vaporizes the heavier organic compounds and thermally
cracks hydrocarbons, forming coke and low molecular weight gases. Coked solids pass
to a combustion zone (650-790°C) where they are combusted. The final zone is a
cooling zone for the flue gases. The organic vapors are collected for particulate removal
and for recovery or adsorption on activated carbon (USEPA 1992g). This system was
used for the cleanup of PCB-contaminated sediments and soil from the Outboard Marine
Corp. Superfund site in Waukegan Harbor, Illinois. A full-scale unit, rated at 23 tonnes/
hour was used and produced PCB removals of 99.98 percent (Hutton and Shanks 1992).
Pretreatment is necessary to reduce the feed materials to less than 5 cm. in diameter.
Summary of Thermal Desorption Technologies
Thermal desorption processes offer several advantages over thermal destructive processes,
including reduced energy requirements, less potential for formation of toxic emissions,
and smaller volumes of-gaseous emissions. Disadvantages include the need for a follow-
on destruction process for the volatilized organic compounds and reduced effectiveness
for less volatile organic compounds. Table 7-6 provides a summary of various thermal
desorption technologies, and Table 7-7 identifies factors that affect the efficiency of the
thermal desorption process.
Immobilization Technologies
Immobilization alters the physical and/or chemical characteristics of the sediment to
reduce the potential for contaminants to be released from the sediment when placed in a
disposal site. The principal contaminant loss pathway reduced by immobilization is con-
taminant leaching from the disposal site to groundwater and/or surface water; however,
contaminant losses at the sediment surface may also be reduced by immobilization
772
-------
TABLE 7-6. SUMMARY OF THERMAL DESORPTION TECHNOLOGIES
System Name Vendor
Fuel Conversion System
Rust Remedial Services, Inc.
Oak Brook, IL
Mobile Solid Waste Desorption
Texarome, Inc., Leakey, TX
Recycle Oil Pyrolysis and Ex-
traction (ROPE*)
Western Research Institute
Laramie, WY
Westinghouse Infrared Thermal
Desorption Unit
Westinghouse Remediation
Services, Inc.
Ariel SST Low Temperature
Thermal Desorber
Ariel Industries, Inc.
Chattanooga, TN
Carson Environmental
Los Angeles, CA
Thermal Desorber*
Cleansoils, Inc.
New Brighton, MN
Conteck Environmental Ser-
vices, Inc., Elk River, MN
Thermal Desorber®
CSE, Inc., Roseville, MN
DBA, Inc, Livermore, CA
The KLEAN MACHINE
Enviro-Klean Soils, Inc.
Snoqualmie, WA
Hazen Research, Inc. and The
Chlorine Institute
Golden, CO
HRUBOUT*
Hrubetz Environmental Services,
Inc., Dallas, TX
IT Corporation
Knoxville, TN
Heating Equipment
Steam or hot oil heated
thermal screw
Superheated steam
(Direct)
Heated thermal screw
Infrared heating rods on'
a steel belt conveyor
Rotary drum dryer
Heated paddle augers
with UV light and with
ozone and hydrogen
peroxide circulated
above the soil
nrb
Rotary drum dryer
nr"
Rotary kiln
Direct
Stationary hearth or
rotary furnace
(for mercury removal)
Hot air injection and re-
covery (possible CDF
application)
Indirectly heated rotary
drum
' Status
(Scale)
Full
Pilot
Pilot
Full
Full
Pilot
Full
Full
Full
Full
nrb
Pilot
Full
Pilot
Maximum Solids
Temperature
Achieved (°C)
1 80 (steam)
260 (hot oil)
480
480
760
480
230
400
540
400
230
nrb
nr"
430
nrb
Off-gas Control
Condensers, activated
carbon
Particulate filters,
condensers, activated
carbon
Activated carbon
Condensers
Cyclones, scrubber,
afterburner, baghouse,
wet scrubber
Condensers, activated
carbon
Baghouse, high tem-
perature thermal oxi-
dizer, wet scrubbers
Cyclones, baghouse,
afterburner
Baghouse, high tem-
perature thermal oxi-
dizer, wet scrubbers
Cyclone, baghouse,
thermal oxidizer
Thermal oxidizer
Condensers, scrub-
bers, afterburner
Afterburner
Secondary combustor,
or condensers and
paniculate removal
Reference8
1
1,3
1
1
1
1
1
1
1
1
1
1
1,2,3
1, 2
(continued)
773
-------
TABLE 7-6. SUMMARY OF THERMAL DESORPTION TECHNOLOGIES (continued)
System Name Vendor
Kalkaska Construction Service,
Inc., Kalkaska, Ml
Astec Thermal Desorption Unit
Mittlehauser Corp.
Naperville, IL
Low Temperature Thermal
Desorption (LTTD)
OBQ Technical Services, Inc.
Thermatek
Remediation Technologies
(RETEC), Inc., Concord, MA
Low Temperature Thermal
Treatment (LT3*)
Roy F. Weston, Inc.
Westchester, PA
X*TRAX®
Chemical Waste Management,
Geneva, IL &
Rust Remedial Services, Inc.
Anderson, SC
HT-V Thermal Distillation
Seaview Thermal Systems
Blue Bell, PA
SAREX MX- 1500/2000/2500
Separation and Recovery Sys-
tems, Inc., Irvine, CA
Astec Soil Purification LTTD
Soil Purification, Inc.
Chattanooga, TN
SoilTech ATP® System
SoilTech ATP® Systems, Inc.
Englewood, CO
Low Temperature Thermal
Desorption
Southwest Soil Remediation,
Inc., Tucson, AZ
Tandem SRU
Thermotech Systems Corp.
Orlando, FL
Desorption and Recovery Unit
(DRU), Golden, CO
Desorption and Vaporization
Extraction System (DAVES®)
Recycling Sciences Interna-
tional, Inc., Chicago, IL
Heating Equipment
Rotary drum dryer
Rotary drum dryer
Rotary drum dryer
Molten salt heated
screws (augers)
Hot oil heated screws
(augers)
Indirectly heated rotary
dryer
nrb
Indirect
Rotary drum dryer
Indirectly fired rotary
kiln
Rotary dryer
nrb
nrb
Fluidized bed
Status
(Scale)
Full
Full
Full
Full
Full
Full
Full
Full
Full
Full
Full
Full
Full
Full
Maximum Solids
Temperature
Achieved (°C)
480
480
430
480
290
480
1,200
320
480
650
480
760
510
760
Off-gas Control
Baghouse, thermal
oxidizer
Cyclones, afterburner
nrb
Cyclones, condensers,
activated carbon
Baghouse, condensers,
activated carbon
Scrubber, condensers,
filters, activated
carbon
Scrubbers, cooling,
liquid separation, com-
pression
Particulate removal,
condensers
Cyclones, afterburner,
baghouse
Cyclones, condensers,
scrubbers, activated
carbon
Thermal or catalytic
oxidizer, baghouse,
scrubber
Afterburner, cyclone,
quench system
Condensation, water
treatment
Cyclones, bag filter,
scrubber, activated
carbon
Reference3
1
1, 2
1
1, 2, 3
1, 2, 3
1,2,3
1
1, 2,3
1,2
1,2, 3
1
1
1
1, 3
(continued)
174
-------
TABLE 7-6. SUMMARY OF THERMAL DESORPTION TECHNOLOGIES (continued)
System Name Vendor
Low Temperature Thermal
Aeration (LTTA)
Canonie Environmental Services,
Inc., Porter, IN
Agglo Activated Thermo-
Chemical Process
Agglo Recovery, Inc.
Rexdale, Ontario
Indirectly-Heated Thermal
Desorption
NBM Bodemsanering B.V.
The Netherlands
OHM Mobile Thermal Volatil-
ization System (MTVS)
OHM Materials, Findlay, OH
The Soil Recycler
Laidlaw Waste Systems, Ltd.
Burlington, Ontario
Thermal Soil Treatment Process
Remco Environmental Service,
Ltd., Surrey, British Columbia
VESTA Thermal Desorption
Vesta Technology, Ltd.
Ft. Lauderdale, FL
Heating Equipment
Rotary dryer, direct fire
Fluidized bed and
vacuum distillation
Indirectly heated rotary
dryer
nrb
nrb
Indirect heat and steam
Rotary kiln
Status
(Scale)
Full
Pilot
Full
Full
Full
Full
Full
Maximum Solids
Temperature
Achieved (°C)
470
1,150
650
430
290
300
nrb
Off-gas Control
Cyclones, bag filter,
scrubber, activated
carbon
Condensers,
desublimation
exchanger (metal
immobilization)
Ceramic filters, con-
densers, after-burner
Scrubbers, after-burner
Cyclones, thermal oxi-
dation
Condensers, oil-water
separators
Baghouse
Reference3
1, 3
2
2
2
2
2
2
• References: 1. USEPA 1993b (VISITT)
2. Wastewater Technology Centre 1993 (SEDTEC)
3. USEPA 1992g (SITE Program)
b "nr" indicates that this information was not reported in the three references cited.
775
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TABLE 7-7. FACTORS AFFECTING THERMAL DESORPTION PROCESSES
Factor
Effect
Sediment type
Solids content
Presence of volatile metals
pH<5, >11
Operating temperature
Particle size
Contaminant flammability
High concentrations of clay or silt increase fugitive dust emis-
sions after processing. Cohesive clays may clump into aggre-
gates that reduce contaminant desorption effectiveness and
result in caking, which may interfere with the operation of
process equipment.
Low solids content increases the energy required to heat the
sediment to desorption temperatures. Solids content should
generally be greater than 40 percent.
Volatile metals (such as mercury) will volatilize during thermal
desorption processing and must be captured by an emission
control system.
Corrosive effects on process equipment.
Contaminants with higher boiling points require processes
capable of achieving higher temperatures.
Oversized particles must be screened out or reduced in size
prior to processing. Maximum size is generally 5 cm.
An oxygen deficient atmosphere should be maintained during
processing because of the potential for ignition of volatile com-
pounds by the heating operation.
Source: USEPA (1988b, 1991c).
776
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Chapter 7. Treatment Technologies
processes. Solidification/stabilization is a commonly used term that covers the immo-
bilization technologies discussed in this chapter. Table 7-8 lists some of the sediment
characteristics that can affect the immobilization process.
TABLE 7-8. FACTORS AFFECTING IMMOBILIZATION PROCESSES
Factor __ Effect
Organic compounds Interfere with bonding of waste materials
Oil and grease Interfere with the hydration of cement, reduce product
strength, and weaken bonds between waste particles
Cyanides Affect bonding of contaminants
Inorganic salts (e.g., nitrates, Reduce product strength and affect curing rates
sulfates, chlorides)
Halides (e.g., chlorides) Retard setting and leach easily
Particle size Small particles can coat larger particles and weaken bonds
Volatile organic compounds May produce air emissions due to heat generation of the
reaction
Solids content Low solids content requires large amounts of reagent
Source: USEPA (1988b).
Physical stabilization processes improve the engineering properties of the sediments, such
as compressive strength, bearing capacity, resistance to wear and erosion, and permea-
bility. Alteration of the physical character of the sediments to form a solid material (e.g.,
a cement matrix) reduces the accessibility of the contaminants to water and entraps or
microencapsulates the contaminated solids within a stable matrix. Because most of the
contaminants in dredged material are tightly bound to the particulate fraction, physical
stabilization is an important immobilization mechanism (Myers and Zappi 1989).
Solidification processes may also reduce contaminant losses by binding the free water in
dredged material (a large contributor to the initial leachate volume from dredged material
in a disposal site) into a hydrated solid.
Chemical stabilization is the alteration of the chemical form of the contaminants to make
them resistant to aqueous leaching. Solidification/stabilization processes are formulated
to minimize the solubility of metals by controlling pH and alkalinity. Anions, which are
more difficult to bind in insoluble compounds, may be immobilized by entrapment or
microencapsulation. Chemical stabilization of organic compounds may be possible, but
the mechanisms involved are not well understood (Myers and Zappi 1989).
Binders used to immobilize contaminants in sediment or soils include cements, pozzolans,
and thermoplastics (Cullinane et al; 1986b; Portland Cement Association 1991). In many
commercially available processes, proprietary reagents are added during the basic
solidification process to improve the effectiveness of the overall process or to target
specific contaminants. The effectiveness of an immobilization process for a particular
sediment is difficult to predict, and can only be evaluated using laboratory leaching tests.
A diagram of an immobilization process is shown in Figure 7-3.
_
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Chapter 7. Treatment Technologies
Binder
Dredged sediment -
Chemical reagent
Water
Mixer
Foam and
cure
Disposal
site
Disposal
site
Figure 7-3. Diagram of an immobilization process.
Immobilization technologies have been evaluated for treatment of contaminated sediments
from both freshwater and saltwater environments. These investigations have shown that
physical stabilization of sediments is easily achieved using a variety of binders, including
proprietary processes. Results of leaching tests on the solidified products have been
mixed; the mobility of some contaminants has been reduced while the mobility of other
contaminants has been increased (Myers and Zappi 1992). The ARCS Program evaluated
solidification/stabilization of Buffalo River sediments using three generic binders:
Portland cement, lime-fly ash, and kiln dust. Leaching of lead, nickel, and zinc was
reduced by the cement process, but leachate concentrations of copper were significantly
higher for the solidified sediments compared to leachates from the untreated sediments
(Fleming et al. 1991). Immobilization of organic compounds in sediments is generally
thought to be less effective than for heavy metals; however, Myers and Zappi (1989)
demonstrated reductions in PCB teachability in New Bedford Harbor sediments using a
solidification process. The results of these studies demonstrate the importance of
laboratory evaluations of appropriate protocols for specific sediments, binders, and
contaminants prior to selecting an immobilization process for remediation.
Extraction Technologies
Solvent extraction processes are used to separate contaminated sediments into three
fractions: particulate solids, water, and concentrated organic compounds. Contaminants
are dissolved or physically separated from the particulate solids using a solvent that is
mixed thoroughly with the contaminated sediment. Most extraction processes do not
destroy or detoxify contaminants, but they reduce the volume of contaminated material
that must be subsequently treated or disposed. Volume reductions of 20-fold or more are
possible, depending on the initial concentration of extractable contaminants in the feed
material and the efficiency of separation of the concentrated organic (oil) stream and the
178
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Chapter 7. Treatment Technologies
water evaporated by the process. Another advantage of the volume reduction is that most
of the contaminants are transferred from the solid phase to a liquid phase, which is more
easily managed in subsequent treatment or disposal processes. The primary application
of solvent extraction is to remove organic contaminants such as PCBs, volatile organic
compounds, halogenated solvents, and petroleum hydrocarbons. Extraction processes may
also be used to extract metals and inorganic compounds, but these applications, which
usually involve acid extraction, are potentially more costly than those used for removing
organic contaminants. Solvents used for extraction processes can represent a significant
cost; therefore, a key component of an extraction process is to separate the solvents from
the organic compounds and reuse them in subsequent extraction steps. Usually several
extraction cycles are required to reduce contaminant concentrations in the sediments to
target levels.
The principal pretreatment operation required for solvent extraction is screening or
particle-size reduction to remove or reduce oversized debris (see Chapter 6). The
maximum particle size depends on the scale and configuration of the extraction process,
but the recommended maximum size is 0.5 cm (USEPA 1988b). A wide range of solids
contents are acceptable for sediment treated by extraction processes. Some processes
require that the feed material be pumped, which would require that water be added to the
sediment to decrease the solids content.
Extraction processes can operate in a batch mode or continuous mode. Sediments and
solvents are mixed together in. an extractor (Figure 7-4). Extracted organic compounds
are removed from the extractor using the solvent and are transferred to a separator where
the solvent and organic compounds are separated from the water and the contaminants are
separated from the solvent by changes in temperature or pressure, or differences in
density. Concentrated organic contaminants are usually associated with an oil phase,
which is removed from the separator for post-treatment. The solvent is recycled to the
extractor to remove additional contaminants. This cycle is repeated several times before
the treated solids are finally removed from the extractor.
Dredged sediment
Sediment
preparation
Extractor
Recycled solvent
Solvent with
- organic -
contaminants
, Air/gas
Solids
Separator
Oversized material
Water
Concentrated contaminants
Source: USEPA (19900
Figure 7-4. Diagram of an extraction process.
179
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Chapter 7. Treatment Technologies
When treated solids are removed from the extractor, traces of solvent will be present.
The solvents selected for these processes generally vaporize or are biodegradable. Some
processes include an additional separation step designed to further remove, by distillation
or other means, most of the solvent from the product solids.
A number of process options for extraction are commercially available; however, most
of them are proprietary. Most of the processes discussed in this chapter have been used
in the USEPA SITE Program, and two of them have been demonstrated with contami-
nated sediments.
Basic Extractive Sludge Treatment Process
The B.E.S.T.® process (Resources Conservation Co.) uses a combination of tertiary
amines, usually triethylamine (TEA), as the solvent. The first extraction is conducted at
temperatures below 4°C where TEA is soluble with water and at a pH greater than 10.
Hydrocarbons and water in the sediment simultaneously solubilize with the TEA, creating
a homogenous mixture (USEPA 1992g). In the next step of the process, solids are
separated from the liquid mixture by settling. The remaining solvent is removed from the
solids fraction by indirect steam heating. Water is separated from the water-organic
compound-TEA mixture by heating the solution to temperatures above the miscibility
point (about 54°C). Organic compounds and TEA are separated by distillation, and the
TEA is recycled to the extraction step. This process was demonstrated at the Grand
Calumet River as a combination ARCS and SITE program demonstration in 1992
(USAGE Chicago District 1994), and bench-scale tests were performed for Buffalo River,
Saginaw River, and Grand Calumet River sediments (USEPA, in prep.a). A summary of
the bench- and pilot-scale results for PCBs and PAHs is provided in Table 7-9.
TABLE 7-9. RESULTS OF BENCH- AND PILOT-SCALE TESTS OF THE B.E.S.T.® PROCESS
Bench-Scale Test
Contaminant
Parameter
Grand
Buffalo Saginaw Calumet
Pilot-Scale Test
at Grand Calumet River
Sediment Sediment
A B
PCBs
PAHs
Feed material
(mg/kg)
Treated solids
(mg/kg)
Removal efficiency
(percent)
Feed material
(mg/kg)
Treated solids
(mg/kg)
Removal efficiency
(percent)
0.32
<0.3
>6
9.9
0.37
96
21.9
0.24
99
27
0.95
65
15.0
0.44
97
230
37.1
84
12.1
0.04
99.7
548
22
96.0
425
1.8
99.6
70.920
510
99.3
Source: USEPA (In prep.a); USAGE Chicago District (1994).
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Chapter 7. Treatment Technologies
CF Systems Solvent Extraction
The solvent extraction process offered by CF Systems uses compressed propane at
supercritical conditions as the solvent. Sediment is screened to remove oversized material
and debris and can then be pumped through the system as a slurry in a continuous mode.
The solvent is mixed with the sediment under normal temperatures and high pressures.
Organic compounds are extracted from the sediment and water into the solvent. The
solvent-organic compound stream is removed from the extractor, and the propane is
separated from the organic compounds by reducing the pressure and allowing the propane
gas to vaporize. After recompression, the gas is recycled to the extraction step. Three
or more extraction stages are usually required to achieve contaminant removal efficiencies
of 90-98 percent (USEPA 1992g). This process was demonstrated using contaminated
sediments from the New Bedford Harbor Superfund site during a SITE Program demon-
stration (USEPA 1990c,h).
Carver-Greenfield Process
The Carver-Greenfield process (Dehydro-Tech Corp.) is a physical process that can be
used to separate oil-soluble organic compounds from contaminated sediments by
dissolving the contaminants in a food-grade oil with a boiling point of approximately
204°C. Five to ten kilograms of carrier oil per kilogram of solids is combined in a
mixing tank where the extraction takes place. Three or more extraction stages may be
necessary. From the mixing tanks, the slurry is transferred to a high-efficiency evaporator
where the water is removed. The oil is separated from the dewatered solids initially by
centrifugation and then by a hydroextraction process that uses hot nitrogen gas to strip
the remaining oil from the solids. After separating the contaminants from the oil by
distillation, the oil is recycled to the extraction step and the concentrated contaminants
are further treated or disposed. Low solids content is not a problem for this process, but
particle size must be reduced to less than 0.5 cm in diameter. Demonstration projects
have been conducted on drilling mud wastes, a relatively fine-grain material. The
requirements of this process for fine particle sizes and wet feed material favor applica-
tions to contaminated sediments.
So/7 Washing
The term soil washing is generally used to describe extraction processes that use a water-
based fluid as the solvent (USEPA 1990b). Many soil washing processes rely on particle-
size separation to reduce the volume of contaminated material. These processes were
discussed in Chapter 6, Pretreatment Technologies, and will not be addressed in this
section. Other water-based techniques involve dissolving or suspending the contaminants
in the water-based fluid. Because most sediment contaminants are tightly bound to
paniculate matter, water alone is not a suitable extraction fluid. Surfactants, acids, or
chelating agents may be used with water to effect separation of some contaminants. The
particle size and type of contaminant are important factors in the effectiveness of soil
181
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Chapter 7. Treatment Technologies
washing as an extraction process. Soil washing for clays and silts is only marginally
applicable. The U.S. Bureau of Mines evaluated acid extraction for heavy metals in Great
Lakes sediments from three AOCs under the ARCS Program and found minor reductions
in sediment metal concentrations (Allen, in prep.). The use of surfactants may be
successful for removing organic compounds from sandy sediments.
Other Extraction Processes
Other extraction processes are emerging that have the potential for removing organic, and
perhaps inorganic, compounds from contaminated sediments. Table 7-10 lists a number
of extraction processes that are commercially available and are advertised as being
applicable to contaminated sediments. This list was developed from those technologies
in the SEDTEC database (Wastewater Technology Centre 1993). The table lists the name
of the process, the classes of contaminants affected, and the extraction fluid or other
medium used to separate the contaminants. Most of the vendors of these technologies do
not specify a particular solvent, stating that it depends on the contaminant and material
characteristics.
Factors Affecting Solvent Extraction Processes
Sediment characteristics and their effect on performance of extraction processes are shown
in Table 7-11.
Chemical Treatment Technologies
For the purposes of this document, the definition of chemical treatment is restricted to
processes in which chemical reagents are added to a sediment matrix for the purpose of
contaminant destruction. Certain immobilization, extraction, and thermal procedures also
involve chemical inputs, but they are typically added to alter the phase of the con-
taminant, thus facilitating removal or binding the contaminant in the sediment. A clear
distinction between categories cannot always be made, and some overlap may occur
between this and other chapters of this document.
Chemical treatment technologies used during the removal component involve mixing
chemical additives with sediments or with a sediment slurry. This mixing is typically
done in batch operations in some type of process vessel. Chemical treatments may
destroy contaminants completely, may alter the form of the contaminants so that they are
amenable to other treatments, or may be used to optimize process conditions for other
treatment processes. Treated sediments may then be permanently disposed of or put to
some beneficial use, depending on the nature and extent of residuals, including reagents
and contaminants.
For the ARCS Program, Averett et al. (1990 and in prep.) reviewed eight general
categories of chemical treatment for suitability to dredged material. Chelation, dechlori-
nation, and oxidation of organic compounds were considered most promising. The
182
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TABLE 7-10. SUMMARY OF EXTRACTION TECHNOLOGIES
Technology
Contaminants Extracted
Extraction Medium
Acid Extraction Treatment Sys-
tem
ALTECH Mobile Soil Washer
ARC/EPRI Clean Soil Process
Basic Extractive Sludge Tech-
nology® (B.E.S.T.®)
Beak Extraction with Methanol
BioGenesis Soil Washing Pro-
cess
Biogenie Physico-Chemical
Extraction
Carver-Greenfield
CF Systems Solvent Extraction
COGNIS Coupled Metal Extrac-
tion
Desorption & Vapor Extraction
System
Dravo Rotocel
Ecotechniek Extraction
Electrokinetic Soil Processing
Extraksol
Ghea Extraction
Heavy Metal Extraction Process
IGT Extraction
IHC Metal Extraction
In-Pulp Extraction Process
Metals
All organic compounds, all inor-
ganic compounds
Hydrocarbons
Specified organic compounds
Specified organic compounds
Hydrocarbons
All inorganic compounds
Specified organic compounds
All organic compounds
All metals
Hydrocarbons, volatile organic
compounds
Hydrocarbons
Hydrocarbons
Specified organic compounds,
specified inorganic compounds,
metals
Hydrocarbons
All organic compounds, metals
Metals
Specified organic compounds
Metals
All organic compounds, metals
Low Energy Extraction Process All organic compounds
Mackie Vat Leaching Jig
Metals
Unspecified acid
Unspecified
Fine coal particles
Triethylamine
Methanol
Unspecified
Unspecified
Food-grade oil
Propane
Unspecified
Thermal
Unspecified
Unspecified
Electro-osmosis
Organic solvent
Surfactants
Acid and ion exchange
resin
Supercritical gas
Acid or complexing
agents
Carbon-in-pulp, resin-in-
pulp resins
Hydrophilic leaching sol-
vent, hydrophobia strip-
ping solvent
Unspecified
(continued)
183
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TABLE 7-10. SUMMARY OF EXTRACTION TECHNOLOGIES (continued)
Technology
Contaminants Extracted
Extraction Medium
MBI Metal Extraction
METALEX
Metanetix Technology
Metals
Metals
Metals
Modular Vapor Extraction Sys- Volatile organic compounds
tem
NRCC Adsorption Approach
Oleophilic Sieve
Sequential Metal Leaching Sys-
tem
Solvent Extraction Sand
Agglomeration
SILT Extraction
Soil Restoration Unit
All organic compounds
Hydrocarbons, metals
Metals
Hydrocarbons
Unspecified
All organic compounds
Solvent Extraction for Dredged Specified organic compounds
Soils
Texarome Process
Volatile organic compounds
Thorne Vapour Extraction Sys- Volatile organic compounds
tem
University of Wisconsin
Extraction
All organic compounds
VITROKELE Soil Remediation All inorganic compounds, speci-
Technology fied organic compounds
Source: Wastewater Technology Centre (1993).
Unspecified acid
Unspecified
Unspecified solvent and
chelating agent
Air, vacuum
Coal, shredded rubber, or
other adsorbents
Oleophilic surfaces
Hydrochloric acid, chel-
ating agent
Oil displacement mecha-
nism
Unspecified
Various unspecified sol-
vents
Polar/nonpolar mixture
Superheated steam
Vacuum extraction
Surfactants/solvents
Various unspecified leach-
ing agents
184
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TABLE 7-11. FACTORS AFFECTING SOLVENT EXTRACTION PROCESSES
Factor
Effect
Particle size
Solids content
Solvent characteristics
pH
Presence of detergents and/or
emulsifiers
Metals
Types of organic compounds
Reactivity
Fine-grain materials are more difficult to extract. Larger par-
ticles may not pass through close clearances in process
equipment and may interfere with the pumping of sediment
slurry (where required). Particle size depends on the process
selected and scale of processing equipment. Ranges of
0.5-2.5 cm have been reported as maximum values.
Depends on the process selected. Most require slurries of
20-60 percent solids. Some batch processes may require
minimal water, depending on the solvent used.
Most organic solvents are relatively volatile, requiring control
of emissions. Some solvents may be toxic to some
organisms, requiring very efficient separation of the solvent
from the solids prior to disposal.
Depends on the process selected. For example, pH ad-
justment to greater than 10 is required for triethylamine ex-
traction.
Adversely impacts oil/water separation. Retains contaminants
in competition with solvents. Foaming hinders separation and
settling.
Metals in fine-grain sediment are not easily removed by sol-
vent extraction processes. Organically bound metals may be
extracted and become a component of an organic waste
stream, creating additional-restrictions on disposal.
Solvent extraction is less effective for high molecular weight
organic compounds and very hydrophobic substances because
of a strong affinity for fine-grained particles.
Certain contaminants are incompatible with some solvents
and may react adversely. Requires careful selection of con-
taminants and laboratory testing.
Source: USEPA (1988b, 1990k).
185
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Chapter 7. Treatment Technologies
specific processes under these three categories that have been demonstrated to be useful
or that are sufficiently developed for consideration are further described in this section.
Other promising, emerging technologies are also discussed.
Chelation Processes
Chelation is the process of stable complex formation (a chelate) between a metal cation
and a ligand (chelating agent). This process could also be considered an immobilization
process, and some extraction processes also use chelating agents. Binding of the metal
cation in a stable complex renders it unavailable for further reaction with other reagents
in chemical or biological systems. The stability of a complex generally increases as the
number of bonds increases between the ligand and the metal cation (Snoeyink and Jenkins
1980). A ligand forming a single bond is known as monodentate, a ligand forming two
bonds is known as bidentate, while a ligand forming more than two bonds is known as
polydentate. Ethylenediaminetetraacetic acid (EDTA) is a well-known example of a
polydentate ligand (Brady and Humiston 1986). pH is one of the most important
parameters that affects the treatment process. Efficiency varies with the chelating agent
and dosage used (Averett et al., in prep.).
The ENSOL and LANDTREAT process uses a polysilicate as an adsorptive agent
(LANDTREAT) to solidify metal hydroxide silicate complexes produced by the ENSOL,
which contains sodium silicate and a proprietary chelating agent. The process is carried
out in an enclosed, continuous-reaction chamber (Wastewater Technology Centre 1993).
The process is available at the full-scale commercial level.
Dechlorination Processes
Dechlorination processes remove chlorine molecules from contaminants such as PCBs,
dioxins, and pentachlorophenol through the addition of a chemical reagent under alkaline
conditions at increased temperatures (USEPA 1990aj). The resulting products are much
less toxic than the original contaminants. Typically, chemical reagents are mixed with
the contaminated sediments and heated to temperatures of 110-340°C for several hours,
producing the chemical reaction and releasing steam and volatile organic vapors. The
vapors are removed from the processor, condensed, and further treated using activated
carbon. The treated residue is rinsed to remove reactor by-products and reagent and is
then dewatered prior to disposal. Adjustment of the pH of the residue may also be
required. The wastewater produced may require further treatment. Processing feed
streams with lower solids contents, such as sediments, require greater amounts of reagent,
increase energy requirements, and produce larger volumes of wastewater for disposal, all
distinct disadvantages of this process for contaminated sediments. Four representative
dechlorination processes are discussed in the following paragraphs, other vendors may
offer similar processes.
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Chapter 7. Treatment Technologies
APEG Chemical Dehalogenation Treatment—This process typically uses an
APEG to treat aromatic halogenated compounds (USEPA 1990J). Potassium hydroxide
(KOH) is most commonly used with polyethylene glycol (PEG), to form the polymeric
alkoxide (potassium polyethyleneglycol [KPEG]), although sodium hydroxide is less
expensive and has been used for this purpose. Another reagent is KOH or sodium
hydroxide/tetraethylene glycol, which is more effective on halogenated aliphatic com-
pounds. Dimethyl sulfoxide (DMSO) may be added to "enhance reaction rate kinetics"
(USEPA 1990J). Products of the reaction are a glycol ether and/or a hydroxylated
compound and an alkali metal salt - water-soluble by-products.
DeChlor/KGME Process—KGME is a proprietary reagent of Chemical Waste
Management, Inc., and is the active species in a nucleophilic substitution (dechlorination)
reaction. Principally used for liquid-phase halogenated compounds (particularly PCBs),
KGME has been successfully used to treat contaminated soils in the laboratory. PCBs
have been treated in both liquid and solid matrices (USEPA 1992g).
Base-Catalyzed Dechlorination Process—The base-catalyzed dechlorination
process combines chemical addition with thermal inputs to dechlorinate organic com-
pounds without the use of PEG (USEPA 1992g). The mechanism appears to be a
hydrogenation reaction (Rogers 1993). The hydrogen source is a high-boiling-point oil
plus a catalyst. The process has been used for both liquids and solids in in situ and ex
situ applications. The SITE program demonstrated the process at a North Carolina site
in 1993, and the Navy with support from the SITE program is also evaluating the process
for PCB-contaminated soil.
Ultrasonically Assisted Detoxification of Hazardous Materials—This
process affects the chemical destruction of PCBs in soil using an aprotic solvent, other
reagents, and ultrasonic irradiation (USEPA 1992g). The dechlorination of PCBs in the
process is believed to result from a nucleophilic substitution reaction, although this is
presently unverified. The purpose of the ultrasonic irradiation is to add heat to the
reaction. The technology is currently being tested using a moderate-temperature, heated
reactor and reflux column (Kaszalka 1993). The process is suitable for ex situ application
only; to be economically feasible the reagents must be recovered. This technology
currently exists at the pilot-scale development level.
Oxidation Processes
Chemical oxidation involves the use of chemical additives to transform, degrade, or
immobilize organic wastes. Oxidizing agents most commonly used (singly or in combina-
tion with ultraviolet [UV] light) are ozone, hydrogen peroxide, peroxone (combination of
ozone and hydrogen peroxide), potassium permanganate, calcium nitrate, and oxygen.
The use of ozone, peroxide, and peroxone has come to be known as.advanced oxidation
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Chapter 7. Treatment Technologies
processes. Strictly defined, oxidation is the addition of oxygen to a compound (creation
of carbon to oxygen bonds) or the loss of electrons from a compound (increase in the
positive valence). Oxidation is used to transform or break down compounds into less
toxic, mobile, or biologically available forms. Theoretically, compounds can be
decomposed completely to carbon dioxide and water. Adequate process control of pH,
temperature, and contact time is important to prevent the formation of hazardous
intermediate compounds, such as trihalomethanes, epoxides, and nitrosamines, from
incomplete oxidation.
Oxidation is commonly used to treat amines, phenols, chlorophenols, cyanides, haloge-
nated aliphatic compounds, mercaptans, and certain pesticides in liquid waste streams
(USEPA 199Ib). It can also be used on soil slurries and sludge. The effectiveness of
oxidation depends on the organic compound as shown in Table 7-12.
TABLE 7-12. SUITABILITY OF ORGANIC COMPOUNDS FOR OXIDATION
Oxidation Suitability Compound
High Phenols, aldehydes, amines, some sulfur compounds
Medium Alcohols, ketones, organic acids, esters, alkyl-substituted aro-
matics, nitro-substituted aromatic compounds, carbohydrates
Low Halogenated hydrocarbons, saturated aliphatic compounds,
benzene
Source: USEPA (1991 b).
Oxidation is nonselective, and all chemically oxidizable material (including detritus and
other naturally occurring organic material) will compete for the oxidizing agent. It is not
applicable to highly halogenated organic compounds (Averett et aL,. in prep.). Certain
contaminants, such as PCBs and dioxins, that will not react with ozone alone require the
use of UV light with the oxidizing agent. This limits the effectiveness of the process with
slurries because the UV light cannot penetrate the mixture.
The LANDTREAT and PETROXY process uses a synthetic polysilicate (LANDTREAT)
for adsorption of organic compounds to facilitate the oxidation by the PETROXY reagent,
which includes a combination of hydrogen peroxide and other additives. A secondary
reaction is the conversion of heavy metal cations to metal silicates on active sites of the
LANDTREAT (Wastewater Technology Centre 1993).
Other Chemical Treatment Processes
Chemical and Biological Treatment Process—This process combines chemical
oxidation and biological treatment for the purpose of enhancing biodegradation processes
(USEPA 1992g). The mechanism provides oxygen for biological use, oxidation of
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Chapter 7. Treatment Technologies
organopollutants, and alteration of the soil matrix. The process produces chemical
intermediates that are both more biodegradable and, due to the apparent alteration of the
soil matrix, more bioavailable. This can be beneficial with high waste concentrations that
would typically be toxic to microorganisms.
D-Plus (Sinre/DRATJ—This process (Wastewater Technology Centre 1993)
involves the use of chemical inputs to stimulate enzymes and to provide a favorable
chemical environment (alkaline, reducing, anaerobic) for hydrogenation, dehalogenation,
and hydrolysis chemical reactions. A biochemical process, the technology uses heat to
break carbon-halogen bonds and to volatilize light organic compounds. Although not yet
available on a commercial scale, it may be feasible at the current stage of development
to treat up to 900 tonnes of contaminated sediments. There is potential for future
development of in situ application as well.
Summary of Chemical Treatment Technologies
Table 7-13 lists the processes discussed above and presents specific applications,
limitations, specifications, and efficiencies of these processes.
Bloremediation Technologies
Bioremediation, sometimes called biorestoration, is a managed or spontaneous process in
which microbiological processes are used to degrade or transform contaminants to less
toxic or nontoxic forms, thereby remedying or eliminating environmental contamination.
Microorganisms depend on nutrients and carbon to provide the energy needed for their
growth and survival. Degradation of natural substances in soils and sediments provides
the necessary food for the development of microbial populations in these media.
Bioremediation technologies harness these natural processes by promoting the enzymatic
production and microbial growth necessary to convert the target contaminants to nontoxic
end products.
Biological treatment has been used for decades to treat domestic and industrial
wastewaters, and in recent years has been demonstrated as a technology for destroying
some organic compounds in soils, sediment, and sludges. Bench-scale testing of
bioremediation was conducted for the ARCS Program with sediments from Great Lakes
sites (Jones et al., in prep.a). The chemical and physical structure of organic compounds
affects the ability of microorganisms to use them as a food source. The degradation
potential for different classes of organic compounds is illustrated in Figure 7-5.
Bioremediation of organic compounds in sediment is a complex process, and its
application to specific compounds is based on an understanding of the microbiology,
biochemistry, genetics, metabolic processes, structure, and function of natural microbial
communities. Microbiology must be combined with engineering to develop effective
bioremediation processes. The ARCS Program conducted a workshop on bioremediation
189
-------
TABLE 7-13. SUMMARY OF CHEMICAL TREATMENT TECHNOLOGIES
Treatment Technology
Application
Process Limitations and Specifications
Efficiency
dictation Processes
ENSOL and LANDTREAT
(Wastewater Technology
Centre 1993)
Dechlorination Processes
APEG Chemical Dehalogen-
ation(USEPA1990j)
CO
KPEG Process (Averett et
al., in prep.)
Ex situ treatment of metals in soils and dewatered sediments
Ex situ soils, sludges, sediments, and oils containing:
PCBs
Dioxins
Furans
Some halogenated pesticides
May not be suitable if contaminants other than halogenated
compounds are present (USEPA 1990j)
Demonstrated effectiveness at some scale for PCBs;
dioxins/furans in sediments, oils, soil, and sludges; and halo-
genated pesticides in oils and soil
Potential effectiveness for halogenated volatile organic com-
pounds and halogenated semivolatile organic compounds in
sediments, oils, soil, and sludge, and halogenated pesticides
in sediments and sludge (USEPA 1990a)
Waste oils containing dioxins
Diesel fuel containing PCBs, dioxins, and chlorobenzenes
(Averett et al., in prep.)
Soil containing PCBs
Full-scale commercial, portable
Feed rate range: 90 m3/8 hrs/METS machine
Chemically inert, multibound metal silicate
complex formed
Requires dewatering of sediments to no less
than 93% solids (USEPA 1987a); requires
nitrogen atmosphere; reactions to occur at
120-180°C unless less than 93% solids
By-products include:
Chloride salts
Polymers
Heavy metals (COM 1986)
Post-treatment soil washing may be required
to remove residual reagent and by-products
Same as APEG
>99% reduction in
metals solubility
PCB concentrations
up to 45,000 ppm
have been reduced
to <2 ppm per con-
gener
Dioxins and furans to
nondetectable levels
at ppt sensitivity
99.999% reduction
of PCBs in field
study (Chan et al.
1989, as cited by
Averett et al., in
prep.)
(continued)
-------
TABLE 7-13. SUMMARY OF CHEMICAL TREATMENT TECHNOLOGIES (continued)
Treatment Technology
Application
Process Limitations and Specifications
Efficiency
DeChlor/KGME (USEPA
1992g)
Base-Catalyzed Dechlori-
nation (USEPA 1992g)
Ultrasonically Assisted
Detoxification (dehalogena-
tion) (USEPA 1992g)
D-PLUS (Sinre/DRAT)
(Wastewater Technology
Centre 1993)
Liquid-phase halogenated compounds, particularly PCBs
Dechlorination of liquid and solid wastes to allow for proper
disposal (dioxins) (Palmer 1993)
DeChlor most effective on highly chlorinated PCBs (Palmer
1993)
Numerous bench-scale demonstrations on PCBs, dioxins, and
furans
In situ or ex situ treatment of solid or liquid waste streams
contaminated with:
Halogenated volatile organic compounds
Halogenated semivolatile organic compounds
PCBs
PCP
Halogenated herbicides
Halogenated pesticides
Dioxins/furans
Ex situ treatment of soil contaminated with PCS Aroclors®
and congeners
Potentially applicable to soils contaminated with chlorinated
hydrocarbons including:
Pesticides
Herbicides
PCP
Dioxins
Furans
Currently at pilot-scale development level
Contaminated sediments containing:
Volatile organic compounds
Semivolatile organic compounds
Chlorinated organic compounds
PCBs treated in both liquid and solid matrices
May require post-treatment such as incinera-
tion or other approved disposal of residuals;
residuals volume may exceed that of contami-
nants before treatment (see process descrip-
tion)
Reaction time is 3-6 hours at 100°C;
nitrogen atmosphere required in reactor
headspace (Wastewater Technology Centre
1993)
High clay and low solids content may increase
treatment cost slightly
Ex situ feed material rate: approximately
1 tonne soil/hour batch
Residuals: clean solids, clean solids within oil,
clean gas/vapors, treated water {Wastewater
Technology Center 1993)
Solvent recovery is key to lowering costs
Pilot-scale development stage; could feasibly
treat up to 900 tonnes with present
equipment, but may not be economic without
further scaleup
Up to 99.99%
removal of PCBs in
liquid and solid
matrices
>99.99% reduction
of PCBs
Treatment to
<10ppbPCP
(Rogers 1993)
>99% destruction
of PCBs at
25-1,700 ppm
90-99% reduction of
PCBs at pilot scale
from initial maximum
concentrations of
3,000 ppm
(continued)
-------
TABLE 7-13. SUMMARY OF CHEMICAL TREATMENT TECHNOLOGIES (continued)
Treatment Technology
Application
Process Limitations and Specifications
Efficiency
Oxidation Processes
LANDTREAT and PET-
ROXY (Wastewater Tech-
nology Centre 1993}
Ex situ treatment of halogenated organic compounds,
hydrocarbons, and volatile organic compounds in soils and
dewatered sediments
Full-scale commercial
Feed rate range: 90 m /8 hr/METS machine
Emissions: CO2, H2O, basic calcium carbon-
ate/bicarbonate, carbon filtered air < 10 ppm
volatile organic compounds
Not given
CO
-------
Compound class
Straight-chain
hydrocarbon
compounds
Aromatic
compounds
Chlorinated
straight-chain
compounds
Chlorinated
aromatic
compounds
Example
HHHHHHHH
H-C-C-C-C-C-C-C-C-H
i i i i i i i i
HHHHHHHH
Octane
CH^ "^CH
II 1
CH CH
Benzene
>=< ;
cr ^ci
Trichloroethylene (TCE) \
X X X X ;
\ / \ /
/ \ / \ u
X X X X
X = H or Cl !:
Polychlorinated biphenyl (PCB) ,!
High potential
Source: USEPA(1991d)
Figure 7-5. Biodegradation potential for classes of organic compounds.
193
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Chapter 7. Treatment Technologies
of contaminated sediments to document laboratory research and field applications of this
technology. The proceedings of this workshop (Jafvert and Rogers 1991) provide an
excellent discussion of the state of the art with an emphasis on the microbial and
chemical processes involved.
Many of the more persistent contaminants in the environment, such as PCBs and PAHs,
are resistant to microbial degradation because of 1) the compound's toxicity to the
organisms, 2) preferential feeding of microorganisms on other substrates, 3) the micro-
organism's lack of genetic capability to use the compound as a source of carbon and
energy, or 4) unfavorable environmental conditions in the sediment for propagating the
appropriate strain of microorganisms. Alteration of the environmental conditions can
often stimulate development of appropriate microbial populations that can degrade the
organic compounds. Such changes may include adjusting the concentration of the
compound, pH, oxygen concentration, or temperature, or adding nutrients or microbes that
have been acclimated to the compound. A summary of sediment characteristics and
environmental conditions that limit bioremediation processes, and actions to minimize the
effects of these limitations, is presented in Table 7-14.
Biodegradation of refractory organic compounds is not uncommon in nature, but can take
many years. The key to improving the usefulness of bioremediation for cleaning up
contaminated sediment sites is to determine how to accelerate the rate of biodegradation
to detoxify the target compounds in a finite time period (i.e., weeks or months rather than
years).
Ideally, biodegradation of organic compounds in sediments would be accelerated in situ.
However, because of the complexity of the sediment-water ecosystem; the difficulties in
controlling physical and chemical, as well as biological, processes in the sediment, and
the need to adjust environmental conditions for various stages of the biodegradation
process; limited effectiveness has been demonstrated for in situ bioremediation. Much
research is underway in the area of in situ treatment, and future efforts will likely
overcome some of these difficulties for certain sites and specific contaminants. However,
the best current prospects for successful bioremediation of xenobiotic compounds are
engineered treatment systems in which environmental conditions can be carefully
controlled and adjusted as the biotransformation processes progress with time.
Biodegradation is accomplished either aerobically or anaerobically. Aerobic respiration
is energy-yielding microbial metabolism in which the terminal electron acceptor for
substrate oxidation is molecular oxygen, and carbon dioxide and water are the end
products. Free oxygen must be present for aerobic reactions to occur. Anaerobic
respiration is energy-yielding metabolism in which the terminal electron acceptor is a
compound other than molecular oxygen, such as sulfate, nitrate, or carbon dioxide, and
methane, sulfides, and organic acids are the typical end products. Aerobic processes
generally proceed more quickly and provide a more complete degradation of the organic
compounds than anaerobic processes. However, some compounds can only be changed
by anaerobic organisms. For example, dechlorination of the more highly chlorinated
PCBs by anaerobic processes has been demonstrated in laboratory and field studies. On
194
-------
TABLE 7-14. CHARACTERISTICS THAT LIMIT BIODEGRADATION PROCESSES
Limiting Characteristic
Reason for Potential Effects
Action to Minimize Effects
CO
01
Variable sediment composition
Nonuniform particle size
Water solubility
Biodegradability
Temperature outside 15-35°C
range
Nutrient deficiency
Oxygen deficiency
Insufficient mixing
pH outside 4.5-8.8 range
Microbial population
Water and air emissions dis-
charges
Inconsistent biodegradation caused by variation in
biological activity
Minimizes the contact with microorganisms
Contaminants with low solubility are harder to bio-
degrade
Low rate of destruction inhibits the process
Less microbial activity outside this range
Lack of adequate nutrients for biological activity
Lack of oxygen is rate limiting
Inadequate microbe/solids/organic compound
contact
Inhibition of biological activity
Insufficient population results in low biodegrada-
tion rates
Potential environmental and/or health effects
Presence of elevated, dissolved Can be highly toxic to microorganisms
concentrations of:
Heavy metals
Highly chlorinated organic
compounds
Some pesticides and herbicides
Inorganic salts
Dilution of contaminated sediment; increased mixing or
blending of sediment
Physical separation to remove coarse-grained material prior
to bioremediation, particularly for bioslurry
Addition of surfactants or other emulsifiers
Addition of microbial culture capable of degrading par-
ticularly difficult compounds or longer residence time
Temperature monitoring and adjustments
Adjustment of the carbon/nitrogen/phosphorus ratio
Oxygen monitoring and adjustments
Optimization of mixing characteristics; increasing per-
meability
Sediment pH monitoring; addition of acidic or alkaline com-
pounds
Addition of culture strains
Post-treatment emission collection and treatment processes
(e.g., air scrubbing, carbon filtration)
Pretreatment processes or dilution with amendments to
reduce the concentration of toxic compounds in the con-
stituents in the sediment to the nontoxic range
Source: USEPA (1988b, 1990d).
-------
Chapter 7. Treatment Technologies
the other hand, the less chlorinated PCBs are susceptible to degradation by aerobic
organisms. Sequential anaerobic treatment followed by aerobic processes appears to offer
an effective destruction technology for PCBs (Quensen et al. 1991).
This section addresses surface bioremediation techniques in which sediments are removed
from the waterway and treated in bioslurry reactors, contained land treatment systems,
compost piles, or CTFs. Pretreatment requirements for these processes include removal
of oversized particles for bioslurry reactors and possible adjustment of solids content for
all of the processes. One of the advantages of bioremediation technologies is that the
physical and basic chemical characteristics of the treated sediments are very similar to the
feed material, allowing a wide range of choices for beneficial use of the treated sediment.
Bioslurry Processes
Bioslurry reactors are a relatively new technology that has been applied to contaminated
solids mostly in the last 5-10 years. There have been a number of pilot-scale applica-
tions, but few full-scale installations. Bioslurry reactors are best suited to treating fine-
grained materials that are easily maintained in suspension. In a bioslurry system, a
sediment-water slurry is continuously mixed with appropriate nutrients under controlled
conditions in an open or closed impoundment or tank. Aerobic treatment, which involves
adding air or another oxygen source, is the most common mode of operation. However,
conditions suitable for anaerobic microorganisms can also be maintained in the reactor
where this oxic state is an essential step in the biodegradation process. Sequential
anaerobic/aerobic treatments are also possible in these systems. Contaminants with
potential for volatilization during the mixing and/or aeration process can be controlled
using emission control equipment. A schematic diagram of an aerobic bioslurry process
is shown in Figure 7-6. . Systems for treating soils or sediments are often operated in
batch mode, because typical retention times are on the order of 2-12 weeks. Once the
treatment period is completed, the solids may be separated from the water and disposed
of separately. The slurry solids concentrations range from 15-40 percent; therefore,
adjustments in solids contents for slurry treatment of sediments may be minor.
The degradation of PCBs using the bioslurry reactor technology was investigated by
General Electric Co. (Abramowicz et al. 1992). Researchers concluded that between 35
and 55 percent of the initial PCBs were degraded over a 10-week test period in reactors
amended with biphenyl. Remediation of contaminated sediments from Toronto Harbor,
Ontario, was tested in pilot-scale reactors in 1992 (Toronto Harbour Commission 1993).
Although complicated by analytical interferences, the results showed that oil and grease
was completely degraded in several week's time, with a partial degradation of PAHs.
Contained Land Treatment Systems
Contained land treatment systems, which have been demonstrated in Europe, require
mixing of appropriate amendments with the sediments, followed by placement of the
196
-------
Dredged sediment
to
NJ
Sediment
pretreatment
Water
Oxygen
Nutrients
Oversized material
Bioreactor
Emissions
control
Dewatering
-*• Gases
-*• Water
-*• Solids
Figure 7-6. Diagram of an aerobic bioslurry process.
-------
Chapter 7. Treatment Technologies
material in an enclosure such as a building or tank and on a pad or prepared surface
(USEPA 199Id). The enclosure protects the material from precipitation, moderates
temperature changes, allows moisture control, and provides the capability to control
volatile organic compound emissions. A schematic diagram of a contained land treatment
system is shown in Figure 7-7.
Leachate from the sediment is collected by underdrains for further treatment as necessary.
The layer of sediment treated for each lift is generally no deeper than 6-8 in. (15-20 cm).
Regular cultivation of the sediments and the addition of nutrients, and in some cases
bacterial inocula, are typically required to optimize environmental conditions for rapid
bioremediation. The excess water associated with the sediment as it is placed in the
treatment bed may create operational problems for startup and will likely require that the
system be designed for lateral confinement of the material.
Composting
Composting is a biological treatment process used primarily for contaminated solid
materials. Bulking agents (e.g., wood chips, bark, sawdust, straw) are added to the solid
material to absorb moisture, increase porosity, and provide a source of degradable carbon.
Water, oxygen, and nutrients are needed to facilitate bacterial growth. Sediment solids
contents will likely be sufficient for composting operations, and in some cases dewatering
of the sediment may be necessary as a pretreatment step. Available composting
techniques include aerated static pile, windrowing, and closed reactor designs (USEPA
199Id). Volatilization of contaminants may be a concern during composting and may
require controls such as enclosures or pulling air through the compost pile rather than
pushing air into and out of the pile. Use of composting to treat sediments should increase
permeability of the sediment, allowing for more effective transfer of oxygen or nutrients
to the microorganisms. A pilot-scale demonstration of composting is being conducted for
Environment Canada's Cleanup Fund at a site in Burlington, Ontario. Approximately
150 tonnes of PAH-contaminated sediments from Hamilton Harbor were placed in a
temporary shelter and tilled periodically with additions of a proprietary organic amend-
ment (Seech et al. 1993). The treatment was executed over an 11-month period.
Sediments that were tilled with the amendment showed reductions of PAHs of over 90
percent, while controls with tillage and no amendment showed reductions of 51 percent.
Controls with no tillage or amendment showed reductions of 73 percent (Grace Dearborn
Inc., in prep.).
Contained Treatment Facility
CDFs routinely used for dredged material may be used as contained treatment facilities
for bioremediation of sediments. These facilities often provide long-term to permanent
storage. The size of the CDF and the depth (1.5-5 m) of sediments may limit the
capability to control conditions compared to other bioremediation systems. These limita-
tions are similar to those for in situ bioremediation processes for contaminated soil sites,
198
-------
Overhead
distribution
system
Microorganisms
Nutrients
Aeration
Cover
/T\ /T\ /T\ /T\ /T\ /T\
Air
management
system
Leachate collection system
Figure 7-7. Diagram of a contained land treatment system.
199
-------
Chapter 7. Treatment Technologies
except that engineering the biotreatment system for upland CDFs is not as difficult
compared to in situ systems. A pilot evaluation of a contained treatment facility for PCB-
contaminated sediments is underway at the Sheboygan River AOC. Rather than a diked
disposal facility, the contained treatment facility is constructed with sheet pile walls and
includes an underdrain system that could be used for leachate control and to add nutrients,
oxygen, and other additives. The ARCS Program has contributed to the scientific
assessment of the operation; a report documenting these investigations will be published
at a later date; however, these experiments were inconclusive as of early 1994.
Bioremediation in a CDF would offer an economical process for reducing sediment
organic contamination, but more research is needed to develop techniques for implemen-
tation.
Summary of Bioremediation Technologies
The advantages and disadvantages of the bioremediation technologies reviewed in this
section are summarized in Table 7-15.
SELECTION FACTORS
Selection factors for treatment technologies will be discussed in terms of three general
categories: target contaminants, sediment characteristics, and implementation factors.
The discussion is based on selection of a type of technology (e.g., thermal destruction,
extraction, immobilization) for a particular project. Selection of a process option within
a technology type will require further evaluation using treatability studies and con-
sideration of the factors affecting the technologies discussed earlier in this chapter. In
addition, the evaluation of the overall remedial alternative must consider the effects of
each step of the process on preceding and succeeding steps.
Target Contaminants
Selection of a treatment technology for a particular contaminated sediment site should
first consider the contaminants of concern and the effectiveness of each technology in
destroying, removing, or immobilizing those contaminants. Table 7-16 rates the
effectiveness of each of the major technology types on organic and inorganic compounds
typically found in contaminated sediments. For many contaminant/technology com-
binations, effectiveness of removal or destruction has been demonstrated; however, as the
table notes, in some cases the effects are not known or the process is only partially
effective in treating the contaminant. A note is also made where a technology may
increase contaminant loss for a nontarget contaminant present in the sediment. When
both organic and inorganic contaminants are targeted, more than one technology may be
required to accomplish project objectives.
200
-------
TABLE 7-15. SUMMARY OF BIOREMEDIATION TECHNOLOGIES
Treatment Technology
Advantages
Disadvantages
Bioslurry Treatment
Contained Land Treatment
NJ
Composting
Offers most control of the physical/chemical environment
Easy to monitor in terms of effectiveness
Enclosed reactors can capture fugitive volatile emissions
Provides highest biological reaction rates
Offers capability to treat the broadest range of organic com-
pounds and sediment types
Treatability testing and engineering scaleup is relatively
simple
Reduced operation and maintenance required compared to
bioslurry systems
Leachate collection system minimizes groundwater impacts
Treatment in an enclosure allows more environmental control
and opportunity to collect and treat volatile contaminants
Less energy intensive than slurry systems
Reduced operation and maintenance compared to bioslurry
systems
Added bulky organic materials enhance biotransformation
and improve permeability of sediment, which provides for
improved control of environmental conditions in the compost
pile
Static piles can be several feet thick requiring less land area
compared to contained land treatment
Produces material suitable for a wide array of beneficial uses
Considerable energy may be required to keep solids in suspension (thereby
adding to cost)
Potential materials handling problems may require significant pretreatment
Equipment intensive compared to other bioremediation options—operation
and maintenance of system is a critical component
Sampling and analysis to verify treatment effectiveness more difficult
compared to bioslurry systems
Leachate collection and treatment for sediments will complicate system
operations and add to the costs
Operational control to optimize biotransformation somewhat difficult to
maintain
Large surface areas required for thin lifts of sediment
Sediment moisture adequate initially, but irrigation may be required as
evaporation and drainage progress
Control of volatile emissions requires enclosure or innovative aeration
techniques
Source of bulking agent required
Materials handling problems may develop in mixing and placing wet sedi-
ment in compost piles
(continued)
-------
TABLE 7-15. SUMMARY OF BIOREMEDIATION TECHNOLOGIES (continued)
o
KJ
Treatment Technology
Advantages
Disadvantages
Contained Treatment
Facility
Under favorable conditions, offers the lowest cost
Although the reaction rate is lowest, a large volume of sedi-
ment may be treated at once
Favors anaerobic processes, which show promising results
for reductive dechlorination
Materials handling of sediment and rehandling of treated
material is relatively easy
Applications limited to favorable sediment characteristics, such as coarser
materials with high permeability
Extensive treatability studies, sediment characterization, and site infor-
mation required
Leachate controls may be necessary
Difficult to monitor cleanup efficiency
Difficult to transport oxygen, nutrients, or other amendments through fine-
grained sediment with low permeability; significant pumping and drainage
system may be necessary
Source: USEPA (1991 d; 1989a,c).
-------
TABLE 7-16. SELECTION OF TREATMENT TECHNOLOGIES BASED ON TARGET CONTAMINANTS
o
Co
Organic Contaminants
Treatment Technology
Conventional Incineration
Innovative Incineration3
Pyrolysis3
Vitrification3
Supercritical Water Oxidation
Wet Air Oxidation
Thermal Desorption
Immobilization
Solvent Extraction
Soil Washing5
Dechlorination
Oxidation0
Bioremediationd
PCBs
D
D
D
D
D
PD
R
Pi
R
pR
D
N/D
N/pD
PAHs
D
D
D
D
D
D
R
Pi
R
pR
N
N/D
N/D
Pesticides
D
D
D
D
D
U
R
Pi
R
pR
PD
N/D
N/D
Petroleum
Hydrocarbons
D
D
D
D
D
D
R
pl
R
pR
N
N/D
D
Phenolic
Compounds
D
D
D
D
D
D
U
P«
R
pR
N
N/D
D
Inorganic Contaminants
Cyanide
D
D
D
D
D
D
U
Pl
pR
pR
N
N/D
N/D
Mercury
xR
xR
xR
xR
U
U
xR
U
N
pR
N
U
N
Other
Heavy Metals
pR
I
I
I
U
U
N
I
N
pR
N
xN
N
Note: PCBs - polychlorinated biphenyls
PAHs - polynuclear aromatic hydrocarbons
Prefixes
p = partial
x = may cause release of nontarget contaminant
Primary designation
D = effectively destroys contaminant
R = effectively removes contaminant
I = effectively immobilizes contaminant
N = no significant effect
N/D = effectiveness varies from no effect to highly efficient depending on the type of contaminant within each class
U = effect not known
3 This process is assumed to produce a vitrified slag.
b The effectiveness of soil washing is highly dependent on the particle size of the sediment matrix, contaminant characteristics, and the
type of extractive agents used.
c The effectiveness of oxidation depends strongly on the types of oxidant(s) involved and the target contaminants.
d The effectiveness of bioremediation is controlled by a large number of variables as discussed in the text.
-------
Chapter 7. Treatment Technologies
Sediment Characteristics
Table 7-17 shows how three major sediment characteristics can affect the performance
of various treatment technologies. These characteristics are predominant particle size,
solids content, and high contaminant concentration. Particle size may be the most
important limiting characteristic for application of treatment technologies to sediments.
Most treatment technologies are very effective on sandy soils and sediments. The
presence of fine-grained material adversely affects treatment system emission controls
because it increases particulate generation during thermal drying, it is more difficult to
dewater, and it has greater attraction to the contaminants (particularly clays). Clayey
sediments that are cohesive also present materials handling problems in most processing
systems.
Another sediment characteristic that affects process performance is solids content. Two
classes of solids contents are shown in Table 7-17: high, representing material at near
the in situ solids content (30-60 percent solids by weight); and low, representing a
hydraulically dredged sediment (10-30 percent solids by weight). Technologies that
require the sediments to be in a slurry for treatment are favored for the lower solids
contents; however, high solids contents are easily changed to lower solids contents by
water addition at the time of processing. Changing from a lower to a higher solids
content requires more processing. Thermal processes are adversely affected by lower
solids contents primarily because of increased energy consumption. Dechlorination
processes are adversely affected because of increased chemical costs and increased
wastewater treatment requirements.
The last set of characteristics shown in Table 7-17 is the presence of organic compounds
or heavy metals in high concentrations. Incineration and oxidation processes are generally
favored for higher organic carbon concentrations (not necessarily the target contaminant).
Higher metal concentrations may make a technology less favorable because of the
increased mobility of certain metal species following application of the technology.
Implementation Factors
A number of other factors may affect selection of a treatment technology other than its
effectiveness for treatment. Seven of these factors are listed in Table 7-18. Each of these
factors must be weighed for each technology. The table indicates with a check mark the
technology-factor combination for which the factor may be critical to evaluation of the
technology. For example, vitrification and supercritical water oxidation have only been
used for relatively small projects and would be very difficult to implement for full-scale
sediment projects. Regulatory compliance and community acceptance become prominent
issues for any type of incineration system. Land requirements are more of a concern for
solidification and solid-phase bioremediation projects. Residuals disposal must be
addressed for those processes (i.e., thermal desorption, extraction, soil washing) that
204
-------
TABLE 7-17. EFFECTS OF SELECTED SEDIMENT CHARACTERISTICS ON
THE PERFORMANCE OF TREATMENT TECHNOLOGIES
Predominant Particle
Treatment Technology
Conventional Incineration
Innovative Incineration
Pyrolysis
Vitrification
Supercritical Water Oxidation
Wet Air Oxidation
Thermal Desorption
Immobilization
Solvent Extraction
Soil Washing
Dechlorination
Oxidation
Bioslurry Process
Composting
Contained Treatment Facility
Sand
N
N
N
F
X
X
F
F
F
F
U
F
N
F
F
Silt
X
X
N
X
F
F
X
X
F
F
U
X
F
N
N
Size
Clay
X
X
N
X
F
F
X
X
X
X
U
X
N
X
X
Solids
High
(slurry)
F
F
F
F
X
X
F
F
F
N
F
N
N
F
F
Content
Low
(in situ)
X
X
X
X
F
F
X
X
X
F
X
F
F
X
X
High Contaminant
Concentration
Organic
Compounds
F
F
F
F
F
F
F
X
X
N
X
X
X
F
X
Metals
X
F
F
F
X
X
N
N
N
N
N
X
X
X
X
Note: F - sediment characteristic favorable to the effectiveness of the process
N - sediment characteristic has no significant effect on process performance
U - effect of sediment characteristic on process is unknown
X - sediment characteristic may impede process performance or increase cost
-------
TABLE 7-18. CRITICAL FACTORS THAT AFFECT TREATMENT PROCESS SELECTION
Treatment Technology
Implementability
at Full Scale
Regulatory Community Land Residuals
Compliance Acceptance Requirements Disposal
Wastewater Air Emissions
Treatment Control
Conventional Incineration
Innovative Incineration
Pyrolysis
Vitrification
Supercritical Water Oxidation
Wet Air Oxidation
Thermal Desorption
Immobilization
Solvent Extraction
Soil Washing
Dechlorination
Oxidation
Bioslurry Process
Composting
Contained Treatment Facility
S
S
Note: / - the factor is critical in the evaluation of the technology
-------
Chapter 7. Treatment Technologies
generate a contaminated, potentially hazardous, waste stream. Wastewater treatment and
air emission control are more of a concern when the technology generates these releases.
FEASIBILITY EVALUATIONS
It is evident from the previous discussion that there may be several different types of
technologies that have potential for successfully remediating a specific contaminated
sediment site. A screening process, considering such factors as contaminant type and
sediment physical characteristics, will typically narrow the range of applicable technology
candidates, but will not reduce them to a single process option.
To proceed from a site screening analysis or remedial investigation to the selection of an
optimum technology for full-scale application in the remediation of a contaminated
sediment site, there are several types of tests that can be used to further reduce the range
of options. The following sections discuss the various testing options, the implications
surrounding them, and some general cost ranges for such tests.
Identifying Testing Needs
The need for technology testing, either in the laboratory (bench-scale) or on a larger scale
in a field setting (pilot- or full-scale), is a function of both the particular sediment
contamination problem and the state of development of the technology. As Averett et al.
(in prep.) have noted, the application of hazardous waste or mineral processing tech-
nologies to full-scale sediment remediation projects is in its infancy at this time. The
recent completion of the cleanup of the Outboard Marine Corp./Waukegan Harbor Super-
fund site, which employed a thermal desorption unit to treat more than 11,000 tonnes of
contaminated sediments, is the only full-scale, sediment treatment project completed in
North America to date.
Until the implementation of the ARCS Program in the United States and the Contami-
nated Sediment Treatment Technology Program (COSTTEP) in Canada, very few
treatment technologies had been evaluated for contaminated sediments in the laboratory
or in the field. Through these programs, however, as of summer 1993, about 30
technologies have been tested on sediments in the laboratory. Pilot-scale demonstrations
in the field have now been conducted with 12 processes. The experience gained through
these programs, in addition to other studies conducted by the Corps and through the SITE
Program, has helped advance the state of knowledge on the general effectiveness of
treatment technologies for contaminated sediments and will serve as a useful guide for
others attempting to select a technology for their site.
Because of the unique characteristics of each contaminated sediment site, some amount
of laboratory testing will be necessary to determine if the technology being considered
is capable of obtaining the desired treatment efficiencies. Spatial variabilities within a
207
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Chapter 7. Treatment Technologies
given site may require testing of several sediment samples with different physical and/or
chemical characteristics. Only in very rare cases will there be no testing required prior
to full-scale remediation efforts. At a minimum, the technology vendor will need to set
operating parameters for its full-size treatment unit, requiring at least the performance of
glassware simulations of the main components of the treatment technology using samples
representative of the specific sediments to be remediated.
The need for pilot-scale tests, using process equipment that closely mimics the unit
operations of a full-scale technology, will have to be determined on a case-by-case basis.
The decision to conduct pilot-scale tests is a joint one between the parties responsible for
the cleanup, the Federal and State agencies regulating the cleanup, and the technology
vendor. It is sometimes beneficial, for contracting purposes, to allow the technology
vendor flexibility in reaching established treatment goals, as opposed to conducting
extensive testing prior to the full-scale operations. Minor changes in field operations can
adversely affect processes for which very narrow operating parameters were specified.
Purpose and Design of Bench-Scale Tests
The purpose of conducting bench-scale, or laboratory, tests on small quantities of
sediments (typically less than 1 kg) can range from simply determining gross process
efficiencies to setting specific operating parameters for a full-scale technology application.
Each sediment sample is unique, combining different contaminant types and concentra-
tions with certain physical characteristics, and all of these variables can affect the ability
of a technology to "treat" the sediments.
In an ideal situation, specific cleanup goals will have been set for a site, either expressed
as a maximum residual concentration of a specific contaminant (e.g., 2 mg/kg PCBs) or
as a minimum percent of the contaminant that must be removed from the raw material.
In addition, the contaminant concentrations that are expected in the final, treated products
would ideally be measurable using current analytical techniques. By working with the
technology vendor, an experimental design can be established to determine the optimum
configuration of a process (e.g., operating temperature, residence time, extraction cycles)
to meet the cleanup goals. A factorial design, varying two or more parameters in a
systematic pattern, is useful to examine the sensitivity of a process when treating the
sediment of concern. The USEPA document, Guide for Conducting Treatability Studies
Under CERCLA (USEPA 1989b), is an excellent reference on this subject.
Under the ARCS Program, bench-scale tests were conducted with no specific treatability
goals established. Instead, vendors were directed to optimize the application of their
process to one or more sediment samples, keeping in mind that economics would be a
prime consideration in the full-scale application of the technology by the users of the
information generated by the ARCS Program. A two-phased approach was used. During
Phase I, the vendors were allowed to adjust operating parameters to determine optimum
conditions. During Phase II, the process was run under these optimum conditions, with
extensive analyses conducted on all the feed and residual materials produced by the
208
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Chapter 7. Treatment Technologies
technology to determine process efficiency. A matrix of the parameters analyzed in these
tests is provided in Table 7-19.
The selection criteria listed in Table 7-16 should serve as a starting point for other
technology evaluations. Contaminants should be added or deleted from the list as
appropriate for the specific sediment sample and technology being evaluated. Chemicals
used in the process that may be problematic if encountered in treatment residuals should
also be monitored. In addition, if concerns exist over the status of the untreated
sediments being regulated as a hazardous waste (e.g., the sediments fail the TCLP test for
one or more parameters), or if the technology may alter the sediments such that the solid
residue produced by the process may fail the TCLP, then appropriate analyses of the raw
and treated materials should be conducted.
Quality assurance and quality control issues should receive utmost priority in conducting
any evaluation of treatment technologies. Quality assurance project plans (QAPjP) were
prepared and followed for all of the bench-scale tests performed under the ARCS
Program, in accordance with the Quality Assurance Management Plan (QAMP) for the
overall ARCS Program (USEPA 1992c). The ARCS QAMP serves as a useful guide for
conducting sediment sampling and analysis activities, and is recommended for further
information on this subject.
In addition to analyzing for contaminant concentrations in raw and treated materials, an
attempt should be made to perform a mass balance analysis for each bench-scale test.
However, the degree of certainty that can be obtained with a mass balance analysis is
highly dependent on the representativeness of that sample for the sediments as a whole.
Any error in this analysis is magnified when the total mass of the contaminant is
calculated by multiplying the contaminant concentration by the total weight of the sample.
Weights for all materials entering or exiting a process should be accurately and precisely
determined. The masses measured directly for materials such as solids, water, and oil
may produce more reliable mass balance results.
Purpose and Design of Pilot-Scale Tests
The need for pilot-scale demonstrations and testing of a technology will be influenced by
the state of development of the technology (whether pilot- or full-scale treatment units
exist), the success of previous testing on similar sediment types, and the vendor's
confidence in scaling up from bench-scale test results. An additional factor may be the
need to demonstrate to the local community that a technology is safe, effective, and
aesthetically acceptable. This can be best accomplished through an onsite, pilot-scale
demonstration.
Certain critical elements of a sediment remediation process can also be analyzed more
realistically during a pilot-scale demonstration than in a bench-scale test. Because a pilot-
scale unit uses pieces of equipment and process flow patterns that more closely simulate
the full-scale technology, the ability for the unit to deal with the physical characteristics
209
-------
TABLE 7-19. ANALYTICAL PARAMETERS FOR BENCH-SCALE TESTING
PERFORMED DURING THE ARCS PROGRAM
Parameter
Total solids
Volatile solids
Oil and grease
Metals3
Polychlorinated
Untreated
Sediments
X
X
X
X
X
Treated
Solids
X
X
X
X
X
Water
Residual
X
xb
xb
Oil
Residual
X
X
X
c
biphenyls
Polynuclear aromatic X X Xb X
hydrocarbons'1
Total organic carbon
Total cyanide
Total phosphorus
pH
Biochemical oxygen
demand
Total suspended solids
Conductivity
Toxicity characteristic
leaching procedure
X
X
X
X
X
X
X
X
X
X
xb
X
X
X
X
X
X
X
X
X
X
X
X
X
a Metals analyzed were arsenic, barium, cadmium, chromium, copper, iron, lead, manga-
nese, mercury, nickel, and selenium.
b Both particle-bound and dissolved components should be analyzed (for assessments of
subsequent treatment).
c Total polychlorinated biphenyls, measured as Aroclors®. Congener-specific analyses are
more appropriate if treatment goals are established for individual or homologs of conge-
ners, or where the treatment process significantly alters Aroclor® patterns (e.g.,
bioremediation).
d Individual and total of 16 Priority Pollutant List polynuclear aromatic hydrocarbons.
210
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Chapter 7. Treatment Technologies
of the contaminated sediments is better evaluated. In addition, the effects of particle size,
solids content, and high contaminant concentrations can be evaluated more easily than in
the laboratory. The pilot-scale demonstrations conducted under the ARCS Program were
most successful in expanding the body of knowledge for engineering issues concerning
the application of treatment technologies to contaminated sediments.
The experimental design for a pilot-scale testing program should follow the same logic
as that described for the bench-scale test. If bench-scale tests precede the pilot-scale test,
the optimum settings for the operating parameters should already be established. The
pilot-scale test can then be used to evaluate the effects of other variables (e.g., solids
content in the feed material, processor throughput rates, operating temperatures) on the
effectiveness of the process.
The larger-scale, high-volume processes in the pilot-scale demonstration may require the
sampling and analysis of additional process streams including: air emissions (including
carbon canisters used as emission control devices), wastewater discharges, chemical
reagent or solvent stocks, and multiple solid product streams (e.g., cyclone residuals).
Monitoring of some of these process streams may be necessary to ensure compliance with
permits obtained for the demonstration.
Data Collection and Interpretation from Treatability Tests
The success of a treatability test is usually judged by comparing the concentrations of the
contaminants of concern in the untreated sediments with those in the treated solids
produced by the process. The evaluation can be made as to whether the residual contami-
nant concentrations are below the established cleanup goals or the percentage removal
from the untreated sediments meets or exceeds an established guideline. These cleanup
goals or removal guidelines may be established by regulation or on a project-specific
basis.
Consideration must also be given to the potential transformation and fate of contaminants.
This is a concern with any process that uses heat to treat chlorinated hydrocarbons,
particularly PCBs, because dioxins and furans can be formed at temperatures less than
those required for complete destruction by incineration. Any process that causes a
chemical transformation to occur should also be evaluated to determine the possibility of
the formation of intermediary products that may be of concern. If any such products are
expected, they should also be analyzed for in the appropriate process stream. In addition,
those technologies that extract or separate contaminants from the sediment matrix require
that all residuals be analyzed for the extracted contaminants, to ensure that unexpected
and uncontrolled losses are not occurring. It may be necessary to develop specialized
analytical protocols for unusual matrices (e.g., activated carbon or condensed oils).
ESTIMATING COSTS
General cost estimating guidance was provided in Chapter 2. This section provides
guidance for estimating the costs associated with the treatment step of the overall
211
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Chapter 7. Treatment Technologies
remedial action process. Treatment costs will in most cases be the step requiring the
largest expenditure of funds. Unfortunately, costs for the treatment step are the most
difficult to estimate accurately. Treatment technologies have not been widely applied to
full-scale remediation projects for soils or sediments. Historical project construction data
and data for relatively standard construction practices are available for other components,
such as removal and disposal, but such data are not available for treatment technologies.
Most treatment cost estimates are based on information provided by the vendor. Though
vendors may act in good faith in providing cost information, comparability of the data
from various vendors is often poor because of variability in the items included in the
estimates, the effects of variable sediment characteristics on process operations, and other
uncertainties in the process.
Treatment Cost Components
Cost Elements
The costs directly attributable to the treatment component are discussed below in terms
of the cost elements generally used by the SITE Program for evaluating treatment costs
based on field (usually pilot-scale) tests for the treatment technologies. The relative
importance of each element in selecting various treatment technologies depends on the
unit operations involved in the process, the importance of chemical additives for the
process, the energy requirements and costs, and project-specific factors.
Site Preparation Costs—These costs are for the site used to construct and operate
the treatment facility. This element includes site design and layout, surveys and site
logistics, legal searches, access rights and roads, preparation of support facilities,
decontamination facilities, utility connections, and auxiliary buildings. Where the site is
used for more than just the treatment technology (e.g., pretreatment or disposal of
residues), site preparation costs may be partially included in the costs for other compo-
nents.
Permitting and Regulatory Requirements—This element includes permits,
system monitoring requirements, and development of monitoring and analytical protocols
and procedures.
Capital Equipment—Major equipment items, process equipment, and residual
materials handling equipment are included in this element. The annualized equipment
cost is based on the life of the equipment, the salvage value, and.the annual interest rate.
Startup and Fixed Costs—This element includes mobilization, shakedown,
testing, insurance, taxes, and initiation of environmental monitoring programs. Mobiliza-
tion costs represent a larger share of the total treatment costs for smaller-scale projects.
212
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Chapter 7. Treatment Technologies
Labor Costs—Labor charges for operational, supervisory, administrative, profes-
sional, technical, maintenance, and clerical personnel supporting the treatment processes
must be estimated for this element.
Supplies, Consumables, and Utilities Costs—Fuel, electricity, raw materials,
and supplies required to process the material are included in this element.
Residue Treatment and Disposal Costs—Treatment systems may generate one
or more residues (e.g., water, oil, solids, sludges, air/gas) that require further treatment
before discharge or disposal. Technologies for treatment and disposal of these residues
are discussed in Chapter 9.
Monitoring and Analytical Costs—Field and laboratory costs for monitoring the
conditions of the treatment process and the quality of residues are included in this
element.
Facility Modification, Repair, and Replacement Costs—This element includes
design adjustments, facility modifications, scheduled maintenance, and equipment
replacement.
Demobilization—Once the sediment cleanup project is completed, all equipment
will have to be dismantled and removed from the treatment site and the land will likely
have to be restored to its original condition.
Real Estate and Contingencies
Other major cost items that should be included in the overall estimate are land purchase
or lease and overall contingency costs.
Factors Affecting Treatment Costs
Table 7-20 lists a number of factors that affect the cost of treatment technologies included
in the VISITT database (USEPA 1993b). In USEPA's query of vendors for the database,
the vendor was asked to identify the factors that most affected the cost of each process.
The top three factors listed in Table 7-20 were the cost factors identified most frequently
by the vendors. These factors are waste quantity, initial contaminant concentration, and
target contaminant concentration. A wide range of sediment remediation technologies
may be available for a. given project, and the costs will vary depending on the volume of
213
-------
TABLE 7-20. REVIEW OF SIGNIFICANT COST FACTORS FOR
SELECTED TREATMENT TECHNOLOGIES
No. of Occurrences
Factor
Waste Quantity
Initial Contaminant Concentration
Target Contaminant Concentration
Labor Rates
Moisture Content
Utility/Fuel Rates
Sediment Physical/Chemical Char-
acteristics
Waste Handling/Preprocessing
Site Preparation
Residual Waste Characteristics
Amount of Debris
Analytical Cost
Depth of Contamination
Depth to Groundwater
Code
(WQ)
(ICC)
(TCC)
(LR)
(MC)
(UFR)
(SPCC)
(WHP)
(SP)
(RWC)
(AOD)
(ANAL)
(DOC)
(DTGW)
First Second
14 4
7 10
6 11
3 3
5 2
3
2 2
2
1
1
1
Third
7
7
6
1
3
1
3
4
3
1
Total
Top 3
25
24
23
7
7
6
5
5
4
3
1
1
1
1
Source: USEPA Vendor Information System for Innovative Treatment Technologies (VISITT) database
(USEPA 1993b).
214
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Chapter 7. Treatment Technologies
sediment to be treated and the contaminant concentrations in the feed and treated material.
Table 7-21 lists selected vendors from the VISITT database, the cost range reported by
each vendor for a technology type, and the three major cost factors affecting that vendor's
costs. Although this table shows cost information for individual process options
(vendors), the comparability of these costs (within a given technology type) is limited.
In other words, a vendor should not be selected based on the costs shown here. This
table should only be used to compare the range of costs and cost factors for the various
technology types.
Representative Treatment Costs
Few remediation projects, including those at Superfund sites, have employed the treatment
technologies discussed in this section. However, through demonstrations conducted by
the SITE Program, the ARCS Program, the Canadian Cleanup Fund, and others, example
costs for a number of technologies applied to specific sites have been documented.
Information selected from published SITE and ARCS Program reports is presented in
Table 7-22. These data were generated based on operational data from field demonstra-
tions of a few cubic meters. The field data were extrapolated to projects of a specific size
based on the particular site. For the four ARCS Program demonstration projects, a range
of project sizes and associated costs was reported.
Estimating costs for treatment technologies requires defining the project requirements,
acquiring treatability data for the sediments, determining cleanup levels, reviewing
available cost reports for treatment technologies, and communicating with vendors of the
technologies. A consistent set of rules, site conditions, sediment characteristics, target
cleanup levels, and cost elements should be provided to each vendor to obtain information
for a comparative analysis of treatment costs.
ESTIMA TING CONTAMINANT LOSSES
Techniques for Estimating Contaminant Losses
Methods for estimating or modeling contaminant losses from various combinations of
treatment technologies are complicated by the wide range of chemical and physical
characteristics of contaminated sediments, the strong affinity of most contaminants for
fine-grained sediment particles, and the limited application of treatment technologies to
contaminated sediments. Basic mathematical models may be available for simple process
operations, such as extraction or thermal vaporization applied to single contaminants in
relatively pure systems. However, such models have not been validated for the sediment
treatment technologies discussed in this chapter because of the limited database on
treatment technologies for contaminated sediments or soils.
Standard engineering practice for evaluating the effectiveness of treatment technologies
for any type of contaminated media (solids, liquids, or gases) is to perform a treatability
275
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TABLE 7-21. COST RANGES AND MAJOR FACTORS AFFECTING COSTS FOR
SELECTED TREATMENT TECHNOLOGIES
NO
Estimated Cost Range
(in dollars)3
Major Cost Factors
Vendor Name
Chester Environmental
Eimco Process Equipment Co.
OHM Corp.
Remediation Technologies, Inc.
SBP Technologies, Inc.
IT Corp.
ABB Environmental Services, Inc.
Chester Environmental
Roy F. Weston, Inc.
Remediation Technologies, Inc.
IT Corp.
Cognis, Inc.
ABB Environmental Services, Inc.
SDTX Technologies, Inc.
A. L. Sandpiper Corp.
ELI Eco Logic International, Inc.
Scientific Ecology Group, Inc.
Westinghouse Remediation Services, Inc.
OHM Corp.
Canonie Environmental Services Corp.
Terra-Kleen Corp.
Dehydro-Tech Corp. (Carver-Greenfield)
Resources Conservation Co. (B.E.S.T.®)
Technology Type
Bioremediation-//? situ soil
Bioremediation-slurry phase
Bioremediation-slurry phase
Bioremediation-slurry phase
Bioremediation-slurry phase
Bioremediation-slurry phase
Bioremediation-solid phase
Bioremediation-solid phase
Bioremediation-solid phase
Bioremediation-solid phase
Bioremediation-solid phase
Bioremediation-solid phase
Bioremediation-solid phase
Chemical-dechlorination
Chemical-dechlorination
Chemical treatment-other
Soil washing
Sojl washing
Soil washing
Soil washing
Solvent extraction
Solvent extraction
Solvent extraction
Lower
20
100
75
30
100
150
25
40
100
20
35
50
25
100
100
400
100
150
50
50
130
50
100
Upper
60
180
250
600
150
270
75
200
200
125
75
100
100
300
175
500
300
250
125
100
900
100
400
Unit"
Yd3
yd3
ton
ton
m3
yd3
yd2
yd3
ton
yd3
ton
yd3
yd3
ton
ton
tonne
ton
ton
ton
ton
ton
ton
ton
First
TCC
WQ
ICC
ICC
LR
TCC
ICC
TCC
WQ
SPCC
WQ
WQ
ICC
WQ
MC
ICC
SPCC
SPCC
WQ
TCC
ICC
WQ
WQ
Second
ICC
ICC
TCC
TCC
ICC
ICC
TCC
WQ
TCC
TCC
WHP
DOC
TCC
SPCC
LR
LR
WQ
WQ
TCC
SPCC
TCC
ICC
ICC
Third
ANAL
TCC
WQ
SPCC
TCC
WQ
SP
WHP
ICC
ICC
SP
SP
SP
UFR
UFR
UFR
RWC
ICC
ICC
WQ
WQ
TCC
TCC
(continued)
-------
TABLE 7-21. COST RANGES AND MAJOR FACTORS AFFECTING COSTS FOR
SELECTED TREATMENT TECHNOLOGIES (continued)
K)
-*
vj
Estimated Cost Range
(in dollars)9
Vendor Name
Technology Type
Lower
Upper
Unitb
Major Cost Factors
First Second Third
Art International, lnc.(LEEP)(SM)
CF Systems Corp.
Soil Purification, Inc./ASTEC
Rust Remedial Services, Inc.
OBG Technical Services, Inc.
Ariel Industries, Inc.
Remediation Technologies, Inc.
Roy F. Weston, Inc.
Texarome, Inc.
Westinghouse Remediation Services, Inc.
SoilTech ATP® Systems, Inc.
Southwest Soil Remediation, Inc.
ReTec, Inc.
Solvent extraction
Solvent extraction
Thermal desorption
Thermal desorption
Thermal desorption
Thermal desorption
Thermal desorption
Thermal desorption
Thermal desorption
Thermal desorption
Thermal desorption
Thermal desorption
Vitrification
100
75
25
125
50
65
100
100
200
150
120
45
600
150
400
75
225
100
200
600
150
1,000
300
400
250
1,000
ton
ton
ton
ton
ton
ton
ton
ton
ton
ton
ton
ton
ton
LR
WQ
WQ
WQ
WQ
MC
WQ
MC
AOD
MC
WQ
TCC
MC
UFR
TCC
WHP
ICC
UFR
WQ
TCC
LR
UFR
ICC
MC
ICC
SPCC
WQ
ICC
ICC
RWC
WHP
TCC
ICC
UFR
RWC
WQ
ICC
WQ
WHP
Source: USEPA
Note:
ANAL
AOD
DOC
ICC
LR
MC
RWC
SP
SPCC
TCC
UFR
WHP
WQ
Vendor Information System for Innovative Treatment Technologies (VISITT) database (USEPA 1993b).
analytical cost
amount of debris
depth of contamination
initial contaminant concentration
labor rates
moisture content
residual waste characteristics
site preparation
sediment physical/chemical characteristics
target contaminant concentration
utility/fuel rates
waste handling/preprocessing
waste quantity
a Costs are expressed in January 1993 dollars.
b 1 yd3 = 0.76 m3; 1 ton = 0.91 tonne.
-------
TABLE 7-22. TREATMENT TECHNOLOGY COSTS BASED ON FIELD DEMONSTRATIONS
Technology
Type
Thermal
Destruction
Thermal
Destruction
Thermal
Destruction
Thermal
Destruction
Thermal
Destruction
Thermal
Desorption
Thermal
Desorption
Immobilization
Immobilization
Extraction
Extraction
Extraction
Bioremediation
Soil Washing
Soil Washing
Process
Option
Retech Plasma
Centrifugal
HRD Flame
reactor
B&W Cyclone
Furnace
vitrification
system
Shirco Infrared
Incineration
EcoLogic
ReTec
SoilTech ATP®
Chemfix
International
Waste
Carver-
Greenfield
CF Systems
Resource Con-
servation Co.
(B.E.S.T®)
Composting-
Grace Dearborn
Bergmann
Acres
International
Media
Treated
Soil
Secondary lead
Synthetic soil
matrix
Waste sludge
Sediment
Sediment
Soil and Sedi-
ment
Soil
Soil
Drilling mud
Sediment
Sediment
Sediment
Sediment
Sediment
Site
Evaluated
Butte, Montana
Monaca,
Pennsylvania
Alliance, Ohio
Brandon, Florida
Rose Township,
Michigan
Burlington,
Ontario
(COSTTEP)
Ashtabula, Ohio
(ARCS)
Waukegan,
Illinois
4 sites
Hialeah, Florida
Abbeville,
Louisiana
New Bedford,
Massachusetts
(SITE)
Grand Calumet
River
(ARCS/SITE)
Burlington,
Ontario
(COSTTEP)
Saginaw River
(ARCS/SITE)
Welland, Ontario
Scale of
Evaluation8
1 ,440 Ibs
18 tons
3 tons
7,000 tons
3,967 Ibs
5 yd3
12yd3
10,000yd3
32
200
640 Ibs
0.7 yd3
1 yd3
150 tons
300 yd3
127m3
Total
Project
Volume3
2,000 tons
72 tons
20,000 tons
NR
25,550 tons
100,000yd3
10,000 yd3
30,000
30,000
23,000 tons
50,000 yd3
695,000 yd3
5,000 tons
25,000 tons
50,000 tons
1 00,000 tons
10,000 tons
50,000 tons
200,000 tons
1 6,000 tons
98,000 tons
245,000 tons
1,638,000 tons
30,000 m3
Process
Rate3
500 Ib/hr
6,700 tons/yr
1 70 Ibs/hr
100 tons/day
100 tons/day
1 50 yd3/day
NR
130
NR
1.4ton/hr
500 tons/day
500 tons/day
1 86 tons/day
186 tons/day
186 tons/day
186 tons/day
2 years
5 years
1 0 years
5 tons/hr
1 5 tons/hr
25 tons/hr
1 00 tons/hr
51 m3/hr
Treatment
Cost"
$720/yd3
$338/ton
$408/ton
$166/ton
$256/tonc
$211 /yd3
$150-250/ton
$90/yd3
NR
$221 /yd3
$251 /yd3
$71 /yd3
$357/ton
$180/ton
$149/ton
$138/ton
$86/tonc
$70/tonc
$62/tonc
$132/ton
$64/ton
$47/ton
$27/ton
$52-211 /ton0
Other
Cost"
$37/yd3
$594/ton
$83/ton
$33/ton
NR
$124/yd3
NR
NR
NR
$302/yd3
$196/yd3
$77/yd3
NR
NR
$19/ton
S17/ton
$16/ton
$15/ton
NR
Total
Cost"
$757/yd3
$932/ton
$429/ton
$200/ton
NR
$335/yd3
NR
NR
$112/yd3
$523/yd3
$447/yd3
$148/yd3
NR
NR
151 /ton
81 /ton
63/ton
42/ton
NR
Reference
USEPA (1992e)
USEPA (1992g)
USEPA (1992f)
USEPA (1989c)
ELI Eco Logic
International Inc.
(1992)
USAGE Buffalo
District (1993 and
in prep.)
Mutton and Shanks
(1992)
USEPA (1991e)
USEPA (1990i)
USEPA (1992b)
USEPA (1990b)
USAGE Chicago
District (1994)
Grace Dearborn
(in prep.)
USAGE Detroit
District (1994)
Acres International
(1993)
Note: NR - not reported
3 1 yd3 = 0.76 m3: 1 ton = 0.91 tonne; 1 Ib = 0.45 kg.
b Multiply S/yd3 costs by 1.32 for costs in $/m3; multiply $fton costs by 1.1 for costs in $ftonne.
c Costs converted tton\ Canadian to U.S. doUars us'mg exchanae rates as a\ January 1993.
-------
Chapter 7. Treatment Technologies
study for a sample that is representative of the contaminated material. In a management
review of the Superfund Program, USEPA (1989b) concluded that "To evaluate the
application of treatment technologies to particular sites, it is essential to conduct
laboratory or pilot-scale tests on actual wastes from the site, including, if needed and
feasible, tests of actual operating units prior to remedy selection." The performance data
generated by the treatability studies will usually provide a reliable estimate of the
contaminant concentrations for the residual sediment following treatment. Contaminant
concentrations and weights for waste streams generated by a technology can also be
determined from treatability studies, but the need for this information must be clearly
identified as one of the objectives of the treatability study so that appropriate data will
be collected. Treatability studies may be performed at the bench-scale and/or pilot-scale
level.
Collection of Contaminant Loss Data
Most treatment technologies include post-treatment or controls for waste streams produced
by the processing. The contaminant losses can be defined as the residual contaminant
concentrations in the liquid or gaseous streams released to the environment. For
technologies that extract or separate the contaminants from the bulk of the sediment, a
concentrated waste stream may be produced that requires treatment offsite at a hazardous
waste treatment facility, where permit requirements may require destruction and removal
efficiencies greater than 99.9999 percent. The other source of contaminant loss for
treatment technologies is the residual contamination in the sediment after treatment.
Wherever the treated material is disposed, it is subject to leaching, volatilization, and
losses by other pathways. The significance of these pathways depends on the type and
level of contamination that is not removed or treated by the treatment process. Various
waste streams for each type of technology that should be considered in treatability
evaluations are listed in Table 7-23.
219
-------
TABLE 7-23. IMPORTANT CONTAMINANT LOSS COMPONENTS FOR TREATMENT TECHNOLOGIES
CO
NJ
O
Contaminant Loss
Stream Biological
Residual solids X
Wastewater X
Oil/organic compounds
Leachate
Stack gas
Adsorption media
Scrubber water
Particulates
(filter/cyclone)
Treatment Technology
Type
Thermal Thermal
Chemical Extraction Desorption Destruction
XXX
XXX
X X
X
X X
X
X
X
X
X
Particle
Immobilization Separation
X X
X
X
Xa
a Long-term contaminant losses must be estimated using leaching tests and contaminant transport modeling similar to that used for sediment
placed in a confined disposal facility. Leaching could be important for residual solids for other processes as well.
-------
8. DISPOSAL TECHNOLOGIES
Disposal is the placement of material into a site, structure, or facility on a temporary or
permanent basis. The disposal component of a remedial alternative may include the
disposal of the dredged sediments or the disposal of residues from pretreatment and/or
treatment components. This chapter briefly discusses the temporary storage of sediments
and residues, but focuses primarily on permanent disposal.
Disposal is a major component of virtually any sediment remedial alternative, except for
nonremoval alternatives. The site or location used for disposal may also be used to
implement other components, including pretreatment, treatment, and residue management.
The identification of disposal sites is often the most controversial part of remedial
planning and design.
This chapter provides descriptions of technologies for the disposal of contaminated
sediments. Discussions of the factors for selecting from the available technology types
and techniques for estimating costs and contaminant losses are also provided.
DESCRIPTIONS OF TECHNOLOGIES
Technologies for the disposal of contaminated sediments and residues from pretreatment
or treatment components include open-water disposal, beneficial use, and confined (diked)
disposal.
A detailed literature review of the disposal technologies is provided in Averett et al. (in
prep.). The general features of these technologies are summarized in Table 8-1.
Open-Water Disposal
Dredged sediments and the residues from pretreatment or treatment technologies may be
suitable for the following types of open-water disposal: unrestricted, open-water disposal;
level-bottom capping; and contained aquatic disposal.
Unrestricted
Open-water disposal is the most common disposal technology used for uncontaminated
dredged material worldwide. Approximately 2.3 million m3 of sediments are dredged and
discharged into the Great Lakes annually (IJC 1982). Most of these materials are
221
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TABLE 8-1. FEATURES OF DISPOSAL TECHNOLOGIES
Technology
Description
Extent of Use
Ni
Open-Water Disposal
Unrestricted
Capping/contained
aquatic disposal
Beneficial Use
Beach nourishment
Land application
General construction fill
Habitat and recreation
Solid waste management
Confined Disposal
Commercial landfill
Confined disposal facility
Material disposed from the water surface that settles to the Most common disposal method for all dredged
bottom material
Material placed on a flat bottom or into a depression and cov- Routinely used for ocean disposal of contaminated
ered with a layer of clean sediment sediments in the Northeast
Material placed directly onto a beach or into shallow water to
reform eroded beach
Material placed directly onto a field; dikes sometimes used to
enhance settling
Dewatered sediments used as soil fill for construction
projects
Islands formed with material that provides habitat or shelter
in shoreline wetlands; confined disposal facilities used for rec-
reation or habitat development after filled
Sediments used as daily cover or in the construction of dikes
or caps
Routinely used for disposal along all coasts and
Great Lakes
Routine disposal of dredged material from naviga-
tion channels along inland waterways
Sediments occasionally reclaimed from disposal
sites for use
Applications are very site specific
Has been infrequently used in the Great Lakes
Dewatered materials disposed to a properly licensed landfill Commonly used for disposal of small quantities of
sediment from marine construction
Diked facility constructed for disposal of contaminated sedi- Used for disposal of one-half of the dredged
ments from one or more projects; design and controls are site terial from the Great Lakes
specific
ma-
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Chapter 8. Disposal Technologies
discharged into shallow waters (<18 m) within a few kilometers of the dredging location.
Some materials are discharged into nearshore waters to "feed" the littoral drift and
nourish eroded beaches. Materials are typically discharged from bottom-dump scows and
hoppers, or from dredge pipelines, as shown in Figure 8-1.
Level-Bottom Capping
Capping is a disposal technology that has been used for contaminated dredged material
in ocean and estuarine waters. Contaminated materials are placed on the bottom and then
covered with a cap of clean materials to isolate the contaminants both physically and
chemically (Palermo et al., in prep.). Level-bottom capping involves the placement of the
contaminated materials on a relatively flat surface, forming a mound, as shown in
Figure 8-2. The capping material is placed on top of the mound. The thickness and
material characteristics of the cap must be carefully designed to ensure that it isolates the
contaminants and can withstand the forces of scour and erosion within acceptable
maintenance (replenishment) requirements.
Contained Aquatic Disposal
Contained aquatic disposal is a type of capping in which the contaminated materials are
placed into a natural or excavated depression or trench, as shown in Figure 8-2. This
depression or trench provides lateral containment of the contaminated material. The
design and placement of the cap is essentially the same as for the level-bottom cap. One
advantage of contained aquatic disposal is mat without a mound the cap may be more
resistant to erosion and require less maintenance. The depression for contained aquatic
disposal can be excavated using conventional dredging equipment or natural depressions
or previously mined pits (sand mining from near7shore areas has occurred in the Great
Lakes). Uncontaminated material excavated from the depression can subsequently be
used for the cap. Palermo et al. (in prep.) provides detailed guidance on contained
aquatic disposal and cap planning and design.
Beneficial Uses
Dredged sediments and solid residues from pretreatment or treatment technologies may
be suitable for a variety of beneficial and productive uses, including beach nourishment,
land application, general construction fill, and solid waste management.
The feasibility of these disposal technologies depends on the physical properties of the
material, the type and level of contamination, and the local need for materials for these
or other beneficial uses. A general discussion of beneficial uses is provided in Averett
et al. (in prep.). The Corps' engineering and design manual, Beneficial Uses of Dredged
Material (USAGE 1987a), should be consulted for more detailed information.
223
-------
Pipeline placement Hopper placement Barge placement
No
Source: Palermo (1991 b)
Figure 8-1. Placement methods for unrestricted, open-water disposal.
-------
Level bottom capping
Contained aquatic disposal
Capping material
Contaminated material
Capping material
Lateral confinement
Capping material
Contaminated material
Source: Palermo (1991 b)
Figure 8-2. Examples of level-bottom capping and contained aquatic disposal.
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Chapter 8. Disposal Technologies
Beach Nourishment
Shoreline erosion is a chronic problem throughout the Great Lakes and is responsible for
damage to public and private properties and the destruction of valuable habitat (IJC 1993).
About 10-20 percent of the sediments dredged by the Corps from Great Lakes harbors
and tributaries are used to nourish existing beaches or are placed into shallow waters to
reform or renourish eroded beaches and shorelines. In most cases, beach nourishment is
accomplished using hydraulic (cutterhead) dredging with pipeline transport to a nearby
beach or shoreline. Sediments are mounded on the beach and the pipeline discharge is
moved periodically to distribute the sediments as desired. Residues of pretreatment or
treatment technologies found suitable for beach nourishment would have to be transported
from the pretreatment or treatment location, offloaded, and possibly redistributed using
earth-moving equipment.
Land Application
Sediments and residues from pretreatment or treatment technologies may be used to
replace eroded soils or amend marginal soils for agriculture, horticulture, and forestry.
Materials such as silt or sandy silt can be readily incorporated into existing silt and clay
soils, and may improve drainage and add nutrients (USAGE 1987a). Substantial
quantities of the sediments dredged from navigation channels on the Mississippi River,
Ohio River, and Illinois River are discharged directly onto adjacent fields and incorpo-
rated into existing agricultural soils (USAGE 1987a). In most cases, the sediments are
dredged hydraulically and transported to farm fields by pipeline. Sediments or residues
might also be reclaimed from a CDF or treatment operation and transported to the
application site.
General Construction Fill
Sediments and treatment residues may be used as a fill material for a variety of construc-
tion projects. Some dredged material has poor foundation qualities; thus its applicability
to a particular construction project would depend on the physical and engineering
properties of the material and the specific requirements of the project. Sandy sediments
were reclaimed from a CDF in Duluth, Minnesota, and used for road construction fill
(Bedore and Bowman 1990). Some sediments/residues may be suitable for use in the
production of concrete (see discussion of solidification in Chapter 6).
Solid Waste Management
Sediments and treatment residues may be used by municipal or commercial landfills for
dike and cap/cover construction and/or as daily cover. Most landfills will only accept
materials that have low organic content and are dewatered sufficiently to pass a paint
filter test (EPA Method 9095, SW-846; USEPA 1991h). Sediments reclaimed from a
226
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Chapter 8. Disposal Technologies
CDF and residues from treatment operations might be transported by truck to a nearby
landfill for use. At the landfill, the sediments/residues could be stockpiled for later use
and spread out using conventional earth-moving equipment. Some landfills will offer a
discounted rate for disposal of contaminated sediments if the sediments can be used for
daily cover.
Confined Disposal
Confined disposal is the placement of dredged material into a site or facility designed to
contain the material and control contaminant loss. The two types of confined disposal are
commercial landfills and CDFs.
Technically, the designs of these facilities may be quite similar. The primary difference
between them is the types of materials for which they are constructed. Commercial and
municipal landfills may be constructed to receive a variety of wastes, including municipal
and commercial refuse, sewage sludge, construction debris, industrial solid wastes,
contaminated soils, and other materials. In the Great Lakes, CDFs have been constructed
solely for the disposal of contaminated dredged material.
The difference in materials can have major effects on the operation of these facilities.
Most solid waste landfills are designed to accept a physically heterogeneous mixture of
materials that has very little water. A CDF is designed to receive a physically homoge-
neous material that may be 10- to 50-percent solids by weight.
A general discussion of confined disposal is provided in Averett et al. (1990 and in prep.).
The Corps' engineering and design manual, Confined Disposal of Dredged Material
(USAGE 1987b), should be consulted for more detailed information. In addition to the
above disposal technologies, temporary storage facilities for sediments awaiting treatment
or residues awaiting transport are discussed below.
Commercial Landfills
Landfills are operated by municipalities and commercial interests for the disposal of
various wastes. Landfills are categorized by the types of wastes they accept and the laws
regulating them. Some landfills are constructed for specific materials, such as municipal
sewage sludge and construction wastes. Most solid waste landfills will accept all types
of materials that are not regulated as RCRA-hazardous or TSCA-toxic materials. There
are a relatively limited number of landfills that are licensed to receive RCRA-hazardous
and TSCA-toxic materials. Only a few licensed chemical waste landfills in the country
can accept TSCA-regulated materials. There are 86 commercial RCRA-regulated land
disposal facilities in the United States.
A landfill is constructed in an existing or excavated depression or using earthen dikes.
The design of a landfill involves one or more of the following types of controls to reduce
227
-------
Chapter 8. Disposal Technologies
the loss of contaminants: barrier systems, caps/covers, drainage systems, and leachate
collection systems.
The types of controls at a landfill reflect the nature and level of contamination in the
materials approved for disposal and the regulatory requirements of the permitting
authority. Landfills for RCRA-hazardous and TSCA-toxic materials have more sophis-
ticated and redundant control systems. A comparison of the control systems of solid
waste (RCRA Subtitle D), hazardous waste (RCRA Subtitle C), and chemical waste
(TSCA) landfills is shown in Figure 8-3.
Contaminated sediments that have been dewatered and residues from pretreatment or
treatment technologies may be disposed in commercial or municipal landfills. The current
use of commercial landfills for disposal of contaminated sediments is generally limited
to small quantities of materials from marine construction projects (e.g., bridge rehabilita-
tion, pipeline and cable crossings). Some landfills have used sediments for daily cover
or for the construction of interior dikes and caps/covers.
Confined Disposal Facilities
For many years, dredged material from navigation projects in which open-water disposal
was impractical has been disposed in diked structures. The purpose of the diked
structures was to promote settling so that the sediments would not return to the waterway
and need to be dredged again. It was not until the 1960s that dredged material was
confined because of environmental concerns. In 1967, the Corps, in cooperation with the
Federal Water Pollution Control Administration (the predecessor of the USEPA), initiated
a 2-year pilot investigation of alternative methods for dredged material disposal in the
Great Lakes (USAGE Buffalo District 1969). The first CDFs on the Great Lakes were
constructed as part of this program.
CDFs are the most widely used disposal technology for contaminated sediments from both
navigation dredging and remediation projects. Since the 1960s, approximately 50 CDFs
have been constructed around the Great Lakes, in the United States and Canada, for
dredged material from navigation projects. About two-thirds of these facilities are
lakefills, constructed with stone dikes. The remainder are upland facilities, constructed
with earthen dikes or placed within existing or excavated depressions. CDFs around the
Great Lakes currently contain sediments dredged over periods of 10 or more years, have
capacities from less than 38,000 to more than 3 million m3, and have areas from a few
to several hundred hectares (Miller 1990).
The goal of confined disposal is to isolate and contain sediment contaminants. Because
of the nature of dredged material, a CDF must have features of both a wastewater
treatment facility and a solid waste landfill to effectively meet this goal. A CDF that
receives sediments that are hydraulically dredged or transported must provide for the
settling of the sediments and primary treatment of the effluent water (see Chapter 9).
Through effective solids retention, a CDF can retain most of the sediment contaminants
228
-------
Resource Conservation
and Recovery Act
(Subtitle D)
Soil
(6 in.)
Clay
(1-5 ft)
Waste
Leachate collection
Clay
(2ft)
Resource Conservation
and Recovery Act
(Subtitle C)
Soil
(site specific)
Drainage collection
(1 ft sand/gravel)
Plastic liner
(20 mil)
Clay
(3 ft compacted)
Waste
Leachate collection
(1 ft with drains)
Plastic liner
(30 mil)
Leachate collection
(1 ft with drains)
Plastic liner
(30 mil)
Clay
(3 ft compacted)
Toxic Substances
Control Act
Cap unspecified
Waste
Leachate collection
Clay
(3ft)
Note: 1ft=30.5 cm
Figure 8-3. Control systems for selected landfills.
-------
Chapter 8. Disposal Technologies
(Saucier et al. 1978). Most CDFs are capable of retaining more than 99.9 percent of
suspended solids discharged in hydraulic slurries.
A CDF must also provide for the dewatering of sediments to facilitate consolidation and
compaction and to maximize the usable space in the facility (as discussed in Chapter 6).
CDFs have been constructed with the same types of controls used in commercial landfills
to limit contaminant loss, although some of these controls may be less feasible at in-water
CDFs and the efficiency of others may be affected by fine-grained sediments within the
CDF.
Temporary Storage Facilities
Remedial alternatives that involve treating sediments and disposing of the residues at
locations remote from the treatment site will usually require a facility for the temporary
storage of sediments and/or residues. Temporary storage may be necessary for a number
of reasons and purposes, including:
• Treatment processes cannot keep pace with dredging operations
• It is more economical to store residues and transport them all at one time
• Residues must be separated for different disposal locations or by different
methods
• A secure land area is needed for or to support pretreatment or treatment
operations.
A temporary storage facility is usually part of the property where pretreatment or
treatment operations are conducted, and might be divided into two or more compartments
or cells to accommodate the different types of sediments and residues: The facility may
also be part of a CDF used for the permanent disposal of residues. Locations where
materials are transferred from one means of conveyance to another (e.g., a site where
sediments are removed from a barge and placed in truck trailers) are not included in this
category.
The types of environmental controls (i.e., barrier and leachate collection systems)
constructed at the temporary storage facility would depend on the physical properties and
contaminant concentrations in the sediments and/or residues to be stored.
SELECTION FACTORS
Within the evaluation and decision-making process discussed in Chapter 2, disposal
technologies must be screened for feasibility and compatibility with other components.
Factors that can be used to determine the suitability of a disposal technology for a
specific application are discussed in this section; these factors are summarized in
Table 8-2.
230
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Chapter 8. Disposal Technologies
TABLE 8-2. REQUIREMENTS OF DISPOSAL TECHNOLOGIES
Material Characteristics
Technology
Open-Water Disposal
Unrestricted
Capping/contained
Contamination
Uncontaminated
Contaminated
Physical
Site specific
Site specific
Land8
No
No
Other
Requirements
Clean capping material
aquatic disposal
Beneficial Use
Beach nourishment
Land application
General construction fill
Solid waste management
Confined Disposal
Commercial landfill
Confined disposal facility
needed
Uncontaminated
Uncontaminated,
contaminated13
Uncontaminated,
contaminated6
Uncontaminated,
contaminated15
Contaminated,
RCRA-hazardous,
TSCA-toxic
Contaminated,
RCRA-hazardous,
TSCA-toxic
Coarse grained Temp
Site specific Temp
Site specific
Site specific
None
None
Temp
Noc
No
Yes
Material must be
dewatered
Material must be
dewatered
are
a Yes = acquisition of land required. No = no lands are required. Temp = rights-of-way or easements
needed from landowners or project sponsors.
b Beneficial use with contaminated material may require some types of controls.
e Beneficial use at a landfill assumes the material is accepted at no cost.
The most critical factors in determining the feasibility of a disposal alternative are the
availability and location of a disposal site. These factors are common to all disposal
technologies (and are therefore not shown in Table 8-2). The location of a potential
disposal site, its distance from the dredging location, and its accessibility from existing
transportation routes are factors that may limit the choice of dredging and transportation
equipment and increase transportation costs (see Chapter 5, Transport Technologies).
The boundaries of the area for disposal site evaluation should be established with some
consideration of reasonable travel distances. In some cases, there may be reasons for
limiting the site consideration to certain political boundaries. For example, if the project
proponent is a city or county government, they may require that the disposal site be
within their jurisdiction. The availability of sites or facilities for the various disposal
technologies is highly site specific. The task of identifying potential sites is best
conducted with a team of representatives from local governmental and public organiza-
tions who are familiar with the region.
231
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Chapter 8. Disposal Technologies
Open-Water Disposal
Unrestricted
The discharge of dredged or fill materials into waters of the United States is regulated
under §404 of the Clean Water Act. The unrestricted discharge of contaminated dredged
material is prohibited; therefore, sediments that have been removed as part of a
remediation project are not likely to be suitable for unrestricted, open-water disposal.
However, the solid residues from sediment pretreatment or treatment processes (treated
sediments) may be suitable for such disposal.
The acceptability of this disposal technology can be determined through the application
of a technical framework developed by the USEPA and the Corps for evaluating the
environmental effects of dredged material management alternatives (USACE/USEPA
1992). This framework, introduced in Chapter 2 (Figure 2-1), was developed to address
the regulatory requirements under §404 of the Clean Water Act and NEPA.
The framework begins with an evaluation of the dredging and disposal needs. Disposal
alternatives are then identified and screened. The detailed assessment of open-water
disposal includes the testing of proposed dredged or fill materials to show that they are
not contaminated and are suitable for open-water disposal. The Corps/USEPA framework
for testing and evaluation for open-water disposal is shown in Figure 8-4. National
guidance (USEP A/US ACE 1994) and regional guidance specific to the Great Lakes
(USEPA/NCD 1994) are available on testing and evaluation procedures for making this
determination. The framework integrates physical, chemical, and biological effects tests
to make a decision.
Guidance on the designation of disposal sites in the ocean has been prepared by the
USEPA and the Corps (USACE/USEPA 1984; USEPA 1986a; Pequegnat et al. 1990).
No comparable guidance for the selection of disposal sites in inland waters has been
developed; however, the ocean disposal site designation guidance is generally applicable
with a few exceptions. Factors to consider in selecting a disposal site include, but are not
limited to:
• Currents and wave regime
• Water depth and bathymetry
• Potential changes in deposition or erosion patterns
• Chemical and biological characteristics of the site
• Other uses of the site that may conflict with disposal.
Most of the open-water disposal sites around the Great Lakes are dispersive, meaning that
materials discharged are rapidly dispersed and transported away from the disposal site.
232
-------
Determine characteristics of all potential sites
Evaluate direct physical impacts and site capacity |
Evaluate management options:
• Submerged discharge
• Operational modification
• Lateral containment
• Thin layer disposal
• Others
Eliminate
open-water
disposal
Yes
Evaluate contaminant pathways of concern
Apply 103/404 testing
and assessment
procedures
*-
Evaluate
benthic
impacts
and/or
Evaluate
water-column
impacts
Apply 103/404 testing
and assessment
procedures
I
Yes-
I Evaluate control measures for contaminant pathways of concern [
±
Water-column controls:
• Submerged discharge
• Operational modification
• Treatment
• Others
Benthic controls:
• Capping
• Contained aquatic disposal
•Others
Eliminate
open-water disposal
1
Retain environmentally
acceptable alternatives
}
Source: USACE/USEPA(1992)
Figure 8-4. Framework for testing and evaluation for open-water disposal.
233
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Chapter 8. Disposal Technologies
The most common concern with unrestricted, open-water disposal in the Great Lakes,
other than the contamination, is the potential impact on aquatic habitat and water supply
intakes.
Level-Bottom Capping
The placement of contaminated material into waters of the United States can be permitted
under §404 (40 CFR 230.60(d)) if "constraints are available to reduce contamination to
acceptable levels within the disposal site and to prevent contamination from being trans-
ported beyond the boundaries of the disposal site." The Corps/USEPA framework for
open-water disposal testing and evaluation (Figure 8-4) considers capping and other
benthic controls.
Capping may be suitable for sediments or residues with moderate levels of contamination.
Grossly contaminated materials are not likely to be suitable for capping. The determina-
tion of suitability requires the concurrence of the Corps and the USEPA on controls and
monitoring requirements.
The Corps has developed guidance on capping contaminated dredged material (Palermo
et al., in prep.), and additional guidance on in situ capping in the Great Lakes is being
developed under the ARCS Program (Palermo and Reible, in prep.). The major elements
in the planning and design of a capping disposal project are:
• Characterization of contaminated and capping sediments
• Selection of capping site
• Selection of placement equipment and techniques
• Determining cap thickness
• Determining maintenance and monitoring requirements.
Each of these elements is discussed below.
Characterization of Contaminated and Capping Sediments—Physical
properties of the contaminated sediments and potential capping materials that need to be
tested include visual classification, natural solids content, plasticity indices, organic
content, grain size distribution, specific gravity, and Unified Soil classification (Palermo
et al., in prep.). Standard methods for these tests are provided in the Corps' soils testing
manual (USAGE 1970).
Selection of Capping Site—Potential capping sites must be evaluated with con-
sideration of the same factors as for unrestricted, open-water disposal. In addition to
these considerations, the capping site should be in a relatively low-energy environment
234
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Chapter 8. Disposal Technologies
with little"potential for erosion of the cap (Palermo et al., in prep.). This may require that
sites be in deeper waters than are commonly used for most unrestricted disposal in the
Great Lakes.
Selection of Placement Equipment and Techniques—Conventional dredging
and transport equipment have been used for capping. The objective is to reduce water-
column dispersion and bottom spread to the greatest extent possible. Cap material must
be placed so that it does not displace or mix with the contaminated sediments. Special-
ized equipment has been developed and demonstrated for precise placement of con-
taminated materials on the bottom and the application of a cap (Palermo et al., in prep.).
Determining Cap Thickness—The cap must be designed to chemically and
biologically isolate the contaminated materials from the aquatic environment. Cap
thickness is determined by the physical and chemical properties of the contaminated
sediments and capping material, the potential bioturbation by aquatic organisms, and the
potential for consolidation and erosion of the cap material (Palermo et al., in prep.). A
capping effectiveness test has been developed to determine the thickness required for
chemical isolation (Sturgis and Gunnison 1988).
Determining Maintenance and Monitoring Requirements—A monitoring
program is needed to ensure that the contaminated material and cap are placed as intended
and that the cap is effectively isolating the contaminants (Palermo et al., in prep.).
Monitoring is also necessary to determine when additional capping material or other
maintenance is required.
Contained Aquatic Disposal
The major requirements and design elements for contained aquatic disposal are generally
the same as those discussed for level-bottom capping.
Beneficial Uses
The acceptability of sediments or treated sediments for beneficial use is addressed in the
Corps/USEPA technical framework introduced in Chapter 2 (USACE/USEPA 1992). In
most cases, the suitability of a sediment will depend on its physical properties as well as
its contaminant properties. A beneficial use typically requires specific physical properties
(i.e., coarse- or fine-grained, low or high organic content).
Most beneficial use technologies have some land requirements to be provided by the
project sponsor or proponent. Lands may be purchased for use, or a temporary easement
or right-of-way may be obtained from the existing landowners. In some cases, a fee or
235
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Chapter 8. Disposal Technologies
other consideration may be paid to the landowner. Beneficial use is most feasible where
the conditions of the site are improved and the landowner derives benefits from the
sediments.
Beach Nourishment
Disposal by beach nourishment is regulated under §404 of the Clean Water Act, and
contaminated sediments are not likely to be suitable for beach nourishment. However,
sediments that have been treated may be suitable for such disposal. The suitability of a
material for beach nourishment is generally determined by its physical properties,
particularly grain size distribution. Evaluation of the suitability of sediments for beach
nourishment is usually made by comparison with existing beach sand. The general rule
of thumb is that nourishment material should be as coarse, if not coarser, than native
beach material (Johnson 1994). Uncontaminated treatment residues that have a high
percentage of sand and gravel, such as those from physical separation technologies (see
Chapter 6), are most likely to be suited for this use.
Land Application
The application of sediments and treated sediments to upland sites may be suitable for
materials with moderate levels of contamination. This type of land application is
regulated by State or local statutes. Materials including any associated water discharges
that are returned to a stream, river, or lake would be regulated under §404 of the Clean
Water Act.
The suitability of a material for agricultural or other land applications is determined by
its physical and chemical characteristics. The physical requirements are often determined
by the needs of the existing soil to be amended. Sandy materials may be needed to
enhance drainage in clay soils while silty materials may be needed to supplement sandy
soils. Other suitability factors include the need for pH adjustment (with lime) and control
of weed infestation (USAGE 1987a).
Sediments and treated sediments with some types and concentrations of contaminants may
still be suitable for land application. The mobility or availability of contaminants through
appropriate pathways must be considered (USACE/USEPA 1992). Laboratory tests to
evaluate the potential for contaminant leaching (Myers and Brannon 1991) and
bioaccumulation in plants and animals (Folsom and Lee 1985; Simmers et al. 1986) have
been developed for dredged material. Materials with acceptable ranges of contaminant
mobility and bioavailability may be used for agricultural lands, nonconsumptive uses (i.e.,
horticulture and silvaculture), or landscaping.
General Construction Fill
The regulations, requirements, and suitability factors for use of sediments and treated
sediments as construction fill are generally the same as for land applications. Potential
236
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Chapter 8. Disposal Technologies
disposal sites may be identified through construction proponents (e.g., city, county, or
State departments of highways, or public works) or construction contractors. The physical
requirements for construction fill will depend on the application. Construction contractors
are likely to require that materials be suitably dewatered and free of debris, and that
regulatory agencies have preapproved the material for use. The laboratory tests for
measuring the leaching and bioaccumulation potential of contaminants (cited for land
application) may be appropriate, depending on the application.
Solid Waste Management
The use of sediments or treated sediments in landfill management is regulated by the
State and Federal statutes under which the landfill is permitted. Contaminated materials
are generally suitable for use as daily cover and for construction of internal dikes,
providing they meet certain physical requirements. For example, materials must be
sufficiently dewatered to pass the paint-filter test (EPA Method 9095, SW-846; USEPA
1991h) and free of debris. Contaminated materials may also be suitable for use as part
of the landfill cap or cover, provided they will not promote bioaccumulation in the
vegetation grown on it. However, some states may have restrictions on the use of
"waste" materials for landfill caps and covers.
Confined Disposal
Commercial Landfills
Municipal and commercial landfills are available that can accept most types of con-
taminated sediments and treatment residues. The suitability of a material for a landfill
is determined by the type and concentrations of contaminants and the regulatory
requirements (as addressed in Chapter 2). Most contaminated sediments and treatment
residues are not RCRA-hazardous or TSCA-toxic and are suitable for disposal in
municipal or commercial solid waste or sanitary landfills.
Location and cost are the primary factors in identifying potential landfills for disposal.
While there are numerous commercial solid waste and sanitary landfills, there are only
86 commercial RCRA landfills and 4 commercial TSCA landfills in the country
(Petrovski 1994). Another factor to be considered is the remaining capacity of the
landfill. A remediation project with a large volume of contaminated sediments to dispose
could overwhelm a single landfill, and the rapid loss of landfill Capacity might have
adverse impacts on regional waste management practices.
The only requirements for the material's physical characteristics for landfill disposal are
related to solids content. RCRA requires that all materials disposed to a solid waste or
RCRA-hazardous landfill pass the paint-filter test (EPA Method 9095, SW-846; USEPA
237
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Chapter 8. Disposal Technologies
1991h); however, there are no published data on the paint-filter test using dredged
sediments, and it is not known at what solids content sediments are likely to fail.
Confined Disposal Facilities
Most of the contaminated sediments dredged from navigation and remediation projects
are placed in CDFs. A CDF may be used solely for the disposal of contaminated
sediments, or it may also serve as the staging area where pretreatment, treatment, and
residue treatment/disposal are implemented. A CDF can therefore serve as the base upon
which preliminary designs for other remedial alternatives are developed, and as a baseline
for comparing the costs and impacts of alternatives.
Regulation—The construction and operation of a CDF may be regulated under a
number of environmental laws. The construction of CDFs in water or wetlands is
regulated under §404 of the Clean Water Act. The effluent from a CDF, if discharged
to waters of the United States, is also regulated under §404. If the materials to be
disposed (or handled) in the CDF are TSCA- or RCRA-regulated, the facility must be
permitted as appropriate. RCRA (40 CFR 268) requires the treatment of hazardous
wastes prior to land disposal. Other site-specific State and local statutes may also apply.
Currently, the Corps has no policy concerning the disposal of sediments or treatment
residues from remediation projects in existing CDFs. CDFs operated by the Corps were
constructed for specific navigation projects, and there is limited capacity in these
facilities. Materials dredged by industries, municipalities, or others from the slips and
docking areas adjacent to the navigation channel are routinely disposed in these existing
CDFs, at cost.
The suitability of materials for disposal in an existing CDF is determined by the level of
contamination. Materials with levels of contamination comparable to those of sediments
for which the facility was constructed are generally acceptable for disposal. The disposal
in a CDF of materials that are more ..highly contaminated may require that the §404
evaluation and §401 water quality certification for the facility be modified. In addition,
the EIS for the CDF may have to be revised if sediments other than those evaluated in
the original EIS are proposed for disposal.
Physical Properties—There are generally no limitations on the physical character-
istics of sediments and residues disposed in a CDF. Most facilities are designed to accept
materials that have been dredged hydraulically or mechanically and contain variable
amounts of oversized material and debris, with a few exceptions. For example, some
small CDFs and larger facilities that are nearly full do not have the capacity to handle
hydraulically dredged material because they cannot provide adequate settling times for
efficient solids retention. Mechanical dredging and transportation may be required if the
dredged material is to be disposed in such facilities.
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Chapter 8. Disposal Technologies
Contaminant Properties—The suitability of a material for disposal in a CDF and
the design of the facility are primarily determined by the nature of contamination in the
sediments and the potential for contaminant release. The Corps/USEPA technical
framework, discussed in Chapter 2, includes a framework for testing and evaluation for
confined disposal, as shown in Figure 8-5. This framework identifies the following
contaminant pathways of concern: effluent, surface runoff, groundwater leachate, and
plant and animal uptake.
The Corps/USEPA framework uses a series of laboratory tests to evaluate the potential
contaminant loss or migration from the sediment disposed in a CDF through these
pathways. Specific requirements for these tests, as well as approximate costs for analysis,
are summarized in Table 8-3.
The modified elutriate, surface runoff, and plant/animal uptake testing protocols are well
established and have been verified in the field. The leachate tests have been developed,
but no field confirmation has been conducted. A contaminant pathway (not shown in
Figure 8-5) that has only recently been considered for sediments is volatile loss to the
atmosphere. A test to evaluate volatilization losses from dredged sediments is still in
development (Semmler 1990). Sites where the testing and evaluation framework has been
fully applied include Puget Sound (Cullinane et al. 1986a), Indiana Harbor (USAGE
1987), the New Bedford Superfund site (Francinques and Averett 1988), and the Navy
Homeport at Everett, Washington (Palermo et-al. 1989).
Basic Design—Detailed guidance on CDF design and operation is provided in the
Corps' engineering and design manual (USAGE 1987c). The most fundamental features
of a CDF design are the surface area and dike height. The design of these features is
dependent on the following factors:
• Quantity of material to be disposed
• Dredging and transport methods
• Operating plan
• Material physical properties
• Target raw effluent quality.
The first two of these factors are self-explanatory. The operating plan is the way in
which the facility is filled (e.g., in a one-time operation or in two or more operations
separated by some period of time). The physical properties of the material relevant to the
basic design are settling and consolidation characteristics. Recommended laboratory
testing procedures for these properties are summarized in USAGE (1987c). The target
raw effluent quality is the maximum level of suspended solids in the primary (raw)
effluent from the CDF during disposal.
The ADDAMS model is a series of computer models developed by the Corps for
evaluating disposal alternatives and assisting in CDF design (Schroeder and Palermo
239
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1
Evaluate contaminant pathways of concern
J
Evaluate
effluent
quality
i
.
Evaluate
surface
runoff
Modified
elutriate
tesfing/bioassay
i
Evaluate
groundwater
leachate
,
Surface runoff
testing/
bioassay
Evaluate
plant
uptake
.
Leachate
testing
Evaluate
animal
uptake
Plant
bioassay
Animal
bioassay
1
Applicable
standards met
Yes
No
I
Evaluate control measures for contaminant pathways of concern
Effluent controls:
• Treatment
• Operational
modifications
• Others
Surface runoff controls:
• Ponding
• Treatment
• Others
Leachate controls:
• Covers
» Liners
• Treatment
• Others
Plant uptake controls:
• Covers
• Selective
vegetation
• Others
Animal uptake controls:
• Covers
• Others
c
Eliminate confined
disposal alternatives
J
Yes
C
Retain environmentally
acceptable alternatives
Source: USACE/USEPA(1992)
Figure 8-5. Framework for testing and evaluation for confined disposal.
24O
-------
TABLE 8-3. LABORATORY TESTS FOR EVALUATING CONFINED DISPOSAL
Test Requirements
Pathway
Effluent
Surface runoff
Grpundwater leachate
Plant and animal uptake
Test
Column settling test
Modified elutriate test
Rainfall runoff test
Batch and column leachate tests
Plant bioaccum ulation test
Earthworm bioaccum ulation test
Citation
USAGE 1987b; Palermo 1986
Palermo and Thaxton 1988
Lee and Skogerboe 1983
Myers and Brannon 1991
Folsom and Lee 1985
Simmers et al. 1986
Sample
Size'
(gai)
10
5
550
5
10
10
Test
Time6
(month)
1
2
6
4
4
4
Number of Test
Samples
NA*
6
15
35
16
12
Cost0
(I)
500.
1,000
30,000
60,000
25,000
20,000
Note: NA - not applicable
Source: Modified from Lee et al. (1991).
• Volume of sediment sample required. This volume is reduced if fewer replicates are analyzed. Elutriate also requires 5 gal of site water (1 gal = 3.8 L).
b Time required to execute the test, including chemical analysis.
c Estimated costs for a single sample with routine chemical analyses (metals, nutrients, polychlorinated biphenyls). Costs are greatly affected by quality assurance and quality
control requirements. Most of these tests are routinely performed in duplicate or triplicate; the costs are reduced if the number of replicates is reduced. No chemical analysis
is included for the column settling test. Costs are presented in January 1993 dollars.
" Column tests are not routinely required for freshwater sediments.
-------
Chapter 8. Disposal Technologies
1990). For purposes of illustration, a hypothetical CDF design was developed using the
ADDAMS model and the following assumptions:
• Design capacity: 100,000 yd3 (76,000 m3)
• CDF shape: rectangular
• Dike construction: earthen dikes
• Dike slope: 3 horizontal, 1 vertical
• Dike crest width: 10 ft (3 m).
If the materials disposed in this hypothetical CDF are mechanically dredged and
transported sediments, or residues that are of comparable solids content, the design of the
CDF surface area and dike height would be relatively simple. For this hypothetical CDF,
the relationship between surface area and dike height required for 100,000 yd3
(76,000 m3) of sediments (in place) is shown in Figure 8-6. In this case, the CDF design
is driven by the volume of sediments. No additional dike height is needed for ponding
or settling with mechanically dredged sediments. The facility could be designed to fit
within land or height restrictions, or optimized to cost. Sediment dewatering and
consolidation would provide additional capacity, which might be used for more sediments
or the placement of a cap/cover. The experience of the Buffalo and Detroit Districts has
shown dredged material consolidation in CDFs of about 20 percent.
26 -I
I
Q
UJ
£t
O
UJ
oc
I-
o
UJ
X
UJ
*
Q
24
22
20
18
16
14
12
10
8
6
4
2
0
\
8
12
16
20
24
28
Note:
Figure
SURFACE AREA (acres)
1 ft = 0.3 m and 1 acre = 0.4 hectares
8-6. Surface area and dike height required for hypothetical 100,000 yd3
(76,000 m3)-capacity confined disposal facility for mechanically
dredged sediments.
242
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Chapter 8. Disposal Technologies
If the materials disposed in the CDF are hydraulically dredged or transported, the design
must accommodate more variables. Because the material is contained in a slurry, the
CDF design must provide adequate conditions for settling to occur, not just bulk storage
capacity for the solids. The SETTLE model of ADDAMS can be used to determine the
basic design of a CDF needed to achieve the target raw effluent quality. For illustration,
the above hypothetical CDF was designed for hydraulic disposal using the following
additional assumptions:
• Average solids concentration: 740 g/L
• Minimum freeboard: 2 ft (0.6 m)
• Depth of withdrawal: 3 ft (0.9 m)
• Percent of area ponded at end of disposal: 80 percent
• Hydraulic efficiency: 60 percent
• Target raw effluent concentration after primary settling: 1,000 mg/L
suspended solids.
The physical, settling, and consolidation properties of the sediments were based on
laboratory tests with Indiana Harbor sediments (Environmental Laboratory 1987).
Comparable data should be obtained for a detailed CDF design. For preliminary designs,
Schaefer and Schroeder (1988) have compiled physical, settling, and consolidation data
from dredged material from numerous locations for application to ADDAMS.
The relationship between surface area and dike height for the hypothetical upland CDF
with production (dredging) rates of 1,000 and 5,000 yd3 (760 and 3,800 m3; in place) per
day is shown in Figure 8-7, By limiting the production of the dredge, the surface area
requirements of the CDF can be significantly reduced. In a CDF with a fixed surface
area and dike height (other factors being equal), greater production rates would result in
reduced solids retention and higher levels of suspended solids in the raw effluent. The
basic design of a CDF for hydraulically dredged sediments should achieve a balance
among the.key factors: dredge production, surface area, dike height, and raw effluent
quality. The design of a CDF must therefore be interactive with the design of the
dredging, transport, and residue management components of the remedial alternative.
Selection of Contaminant Controls—The types of controls selected for a CDF
are determined using the Cqrps/USEPA testing and evaluation framework (Figure 8-5).
The results from the laboratory testing described previously are used with information
about the disposal site and computer models to evaluate the potential for contaminant
migration and to determine the need for and efficiency of environmental controls
(Francinques et al. 1985).
Computer programs that have been used to evaluate CDF environmental controls include
the ADDAMS program for characterizing primary effluent quality (Schroeder and Palermo
1990) and the HELP model, developed to assist the design of landfill caps, liners, and
leachate collection systems (Schroeder et al. 1984). A modified version of HELP has
been developed specifically for CDFs.
243
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Chapter 8. Disposal Technologies
O
UJ
cc
i
DC
O
ED
I
20 -
18 -
16 -
14
12
10
8
6
4
2 -
1,000yd3/day
5,000 yd3/day
i
20
I
30
I
40
0 10
SURFACE AREA (acres)
Note: 1 ft = 0.3 m, 1 acre = 0.4 hectares, and 1 yd3 = 0.76 m3
Figure 8-7. Surface area and dike height required for hypothetical 100,000 yd3
(76,000 m3)-capacity confined disposal facility for hydraulically
dredged sediments.
The type and number of controls in a CDF design depend on the characteristics of the
sediments and the site. There is no generic or default design. " Available control
technologies, and their application at existing CDFs, are discussed in the ARCS Program
literature review (Averett et al., in prep.) and in the Corps' engineering and design manual
(USAGE 1987c). Designers are cautioned in applying controls commonly used at solid
and hazardous waste landfills without due consideration of the physical properties of
sediments and the quantities of water that may need to be drained, routed for collection,
and treated.
Fine-grained sediments, when properly consolidated, can have very low permeabilities.
Laboratory tests with Indiana Harbor sediments produced permeabilities on the order of
10~8 cm/sec (Environmental Laboratory 1987). Fine-grained sediments dredged as part
of sediment remediation or for other purposes might be an integral part of the con-
taminant controls for a CDF. For example, a CDF designed for contaminated and TSCA-
regulated sediments might place the contaminated sediments in a manner that creates an
additional barrier between the TSCA-regulated sediments and the outside of the CDF.
Operation and Maintenance—A detailed discussion of the construction,
operation, and maintenance of CDFs is provided in Chapter 10.
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Chapter 8. Disposal Technologies
Temporary Storage Facilities
The construction and operation of a temporary storage facility are regulated in the same
manner as CDFs. The fact that the structure is temporary will not affect the applicability
of Federal regulations such as the Clean Water Act. The requirements of State and local
regulations are site specific. Some environmental regulations have restrictions on the
temporary storage of materials. For example, RCRA-hazardous waste can be stored 90
days without a storage permit. Permits are issued under both RCRA and TSCA for the
temporary storage of regulated hazardous and toxic wastes for up to 1 year.
Temporary storage facilities are designed to accommodate the physical and chemical
characteristics of the project sediments and fulfill the needs of other components of the
remedial alternative. If sediments are to be processed using a treatment technology, a
facility may be needed to store the dredged sediments while awaiting pretreatment and
treatment. The temporary storage facility may be used to perform some types of
pretreatment, such as dewatering or physical separation. The size and capacity of the
facility may be determined by several factors:
• Quantity of materials to be dredged
• Production rate of the dredging
• Pretreatment requirements of the treatment technology
• Process rate of the treatment technology.
The design of a temporary storage facility is determined by the same factors that apply
to CDFs. Because the facility is not permanent and will be removed when the remedia-
tion is completed, controls for long-term contaminant migration may not be necessary.
However, temporary facilities should be designed with consideration of how the site will
be cleared and decontaminated when the remediation is completed.
ESTIMATING COSTS
For some of the disposal technologies described in this chapter, there is no disposal cost.
This means that the costs for dredging, transportation, or other components include any
equipment or labor costs associated with disposal. For other disposal technologies,
information is provided about disposal costs that are separate from other component costs.
In this section, the equipment and effort required for each disposal technology are
described, and unit costs from the literature or other project cost estimates are provided,
when available. The elements of the disposal technologies and available unit costs are
summarized in Table 8-4.
Open-Water Disposal
Unrestricted
Unrestricted, open-water disposal is generally the least costly disposal technology for
uncontaminated sediments and residues. The disposal process does not require any
245
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TABLE 8-4. UNIT COSTS FOR DISPOSAL TECHNOLOGIES
Technology
Unit Cost3
($/yd3)
Elements
Open-Water Disposal
Unrestricted 0
Capping/contained aquatic disposal 3-20
Beneficial Use
Beach nourishment 0
Land application 0-5
General construction fill 0-5
Solid waste management 0-5
Monitoring (if required)13
Cap material
Maintenance
Monitoring
Dewatering costs
Dewatering costs
Dewatering costs
Confined Disposal
Commercial landfill
Solid waste
RCRA-hazardous waste
TSCA-toxic waste
Confined disposal facility
Temporary storage facility
20-25
150-200
250
5-50
5-50
Dewatering costs'1
User fee and taxes
Lands and easements6
Dike construction
Contaminant controls
Operation and maintenance11
Lands and easements
Dike construction
Contaminant controls
Operation and maintenance
Demolition/decontamination
a These costs are for the disposal component only {i.e., they do not include dredging,
transportation, or other remedial component costs). A zero unit cost ($0) means that disposal
costs are included in other component costs. Multiply by 1.32 for cost per cubic meter.
b Unit costs shown are exclusive of the cost of this element.
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Chapter 8. Disposal Technologies
additional equipment, other than the equipment used for dredging and transportation, or
any additional effort on the part of the contractor, other than opening the barge doors or
positioning the pipeline discharge. Monitoring requirements for unrestricted, open-water
disposal are site specific, but are generally limited, if any. There are, therefore, no
separate costs for unrestricted, open-water disposal.
Level-Bottom Capping
Not all of the costs of capping are covered by the dredging and transportation compo-
nents. Specialized equipment, such as a submerged diffuser and sophisticated positioning
equipment, may be required. The contractor will need additional time to place the
material with greater levels of precision and control than necessary with unrestricted,
open-water disposal.
The material for the cap and its placement can be a major cost item. If the capping is
conducted in conjunction with the disposal of suitable uncontaminated sediments from
another project, there may be no additional cost for the cap. This presumes that the
capping material was planned to be dredged and disposed in the vicinity of the capping
site with or without the remediation project. If the cap material must be furnished solely
for the capping, the costs for dredging, transportation, and placement will be included in
the disposal costs.
Ideally, the cap is situated in a location that is depositional, where natural settling
paniculate matter will deposit on the cap and further isolate the contaminated sediments.
In other locations, the cap may have to be replenished periodically. The maintenance of
the cap should be included in the disposal costs, unless the maintenance material is
provided without cost from other dredging projects.
The monitoring requirements for capping may include periodic bathymetric surveys and
camera profiles. Less frequent monitoring might also include analysis of core sediment
samples and toxicity or bioaccumulation measurements (Fredette et al. 1990a,b). The type
and frequency of monitoring are site specific, but the costs of monitoring and cap
performance evaluation are part of the disposal costs. Experience with dredged material
capping in New England indicates that routine monitoring, consisting of a bathymetric
survey and a camera profile, is conducted every 2-3 years at a cost of about $30,000 per
cycle (Fredette 1993).
Contained Aquatic Disposal
The cost items for contained aquatic disposal are basically the same as those described
for level-bottom capping. The only additional disposal costs are related to the construc-
tion of the depression or trench for placement of contaminated material. If the contained
aquatic disposal site is in deep water, the selection of dredging equipment may be limited
to mechanical (bucket) dredges. If the material excavated to form the depression or
trench is suitable for the cap, the cost for cap material may be offset, although there may
247
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Chapter 8. Disposal Technologies
be additional costs associated with temporarily stockpiling and rehandling the excavated
material for later use as the cap material.
Beneficial Uses
Beach Nourishment
The placement of uncontaminated materials onto beaches will generally not require
additional equipment, effort, or costs beyond those included in the dredging and
transportation components. The only disposal cost would be for the earthmoving
equipment and effort needed to spread the material across the beach or to form dunes.
Land Application
The land application of sediments or treatment residues that have been mechanically
dredged or have been suitably dewatered will generally not require additional equipment,
effort, or costs beyond those included in the dredging and transportation components.
The only disposal cost would be for the equipment and effort needed to spread the
material, incorporate it into the existing soil, and properly grade the site. It is assumed
that the landowner or local government would be responsible for any seeding or planting.
If the sediments or residues to be applied on land are hydraulically dredged or
transported, additional effort and equipment will be needed to promote the retention of
solids. A diked area or CDF will have to be constructed onsite. The level of sophis-
tication for this structure would be very basic, and the only environmental controls would
be related to effluent quality. Costs for dike construction are discussed for CDFs below.
Costs for effluent treatment are discussed in Chapter 9.
General Construction Fill
The use of sediments or treatment residues as construction fill will generally not require
additional equipment, effort, or costs beyond those included in the other remediation
components. It is assumed that suitable sediments or residues would be appropriately
dewatered, and the materials would be either picked up by the construction contractor or
delivered to the construction site. If fill material is in demand, construction contractors
may be willing to pay for the excavation and transport of sediments from a CDF.
Solid Waste Management
The use of sediments or treatment residues as daily cover or for construction in municipal
or commercial landfills will generally not require additional equipment, effort, or costs
beyond those included in the other remediation components. It is assumed that suitable
sediments or residues would be appropriately dewatered, and the materials would be either
picked up by the landfill operator or delivered to the landfill.
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Chapter 8. Disposal Technologies
Confined Disposal
Commercial Landfills
Costs for the disposal of contaminated materials to municipal or commercial landfills are
determined by the market value of landfill space in a particular region. There are no
additional equipment or effort requirements beyond those included in other remediation
components. The transportation contractor will place the material as directed by the
landfill operator, who will be responsible for its spreading and compaction.
Representative costs of disposal to commercial landfills in the metropolitan areas of
Buffalo, Chicago, and Detroit were obtained through telephone interviews with landfill
owners/operators in April, 1993, and are summarized in Table 8-5. Unit costs are based
on weight ($/ton) or volume ($/yd3). Although a landfill operator is ultimately basing the
quoted price on how much capacity (volume) the disposed material will require, many
operators are now using weight-based payment because it can be measured more
accurately at delivery (Payne 1993).
TABLE 8-5. UNIT COSTS FOR COMMERCIAL LANDFILL DISPOSAL
Unit Cost
Landfill Type
Solid waste9
RCRA-hazardous
($/ton)
35-50
150-200
($/yd3)b
20-24
120
waste
Chemical Waste0 250
a Solid waste landfill; not for RCRA-hazardous or TSCA-toxic wastes.
b Costs per cubic yard of as-received material. Multiply by 1.32 for cost
per cubic meter.
c TSCA-licensed landfill.
d No cost available.
The landfill unit costs that are based on weight are consistently higher than unit costs
based on volume. This is because the majority of materials disposed in commercial
landfills have a density of less than 1 tonne/yd3. Residential and commercial solid wastes
(uncompacted) typically have densities less than 0.5 tonne/yd3 (Tchobanoglous et al.
1977).
The weight of a given volume of sediments or treatment residues will depend on its grain
size distribution, solids content, and amount of organic material. A typical saturated
sediment (50 percent solids) with about 70 percent silt and clay and 10 percent organic
material (volatile solids) would probably weigh about 2,400-2,700 lbs/yd3 (1,400-
1,600 kg/m3).
249
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Chapter 8. Disposal Technologies
Because the density of sediments and treatment residues is much higher than that of most
materials disposed in commercial landfills, the weight-based unit costs may not accurately
reflect market price. The volume-based unit costs are probably more representative.
Therefore, landfill owners/operators should be provided information about the density and
other physical properties of the sediments or residues in order to form a competitive unit
cost.
As discussed above, landfills may accept sediments for beneficial use as daily cover.
Depending on the local availability of cover material, the landfill may accept the material
at no cost or offer a price discount. The discount should be approximately equal to the
amount the landfill has to pay for daily cover from other sources. Most of the landfill
operators contacted indicated a willingness to offer a price discount. A discount of
$10/ton was offered by one operator. Some states or municipalities have restrictions on
the type of material used for daily cover at landfills.
Confined Disposal Facilities
The principal elements of the capital costs for a CDF include:
• Engineering and design costs
• Lands and easements
• Materials for dikes
• Materials for contaminant controls
• Construction equipment and labor costs.
Of these elements, the costs for lands and materials for dikes and contaminant controls
typically are the highest of the capital costs. As an illustration the capital costs of
hypothetical, upland CDFs with a design capacity of 100,000 yd3 (76,000 m3) were
estimated for two sizes and three contaminant control system designs. The CDFs had the
same basic design assumptions discussed earlier in this chapter, with the following unit
costs provided by Corps district personnel as being representative of the Great Lakes
region:
• Cost of land: $10,000/acre ($24,700/hectare)
• Cost of dike material (constructed): $3/yd3 ($4/m3)
• Cost of clay (compacted): $3/yd3 ($4/m3)
• Cost of plastic liner (70 mil): $1.5/ft2 ($16/m2)
• Cost of leachate collection system (4-in. [10-cm] polyvinyl chloride):
$5/linear ft ($16/linear m)
• Cost of sand/gravel: $12/yd3 ($16/m3)
The capital costs for these hypothetical, upland CDFs are shown in Figure 8-8. The two
sizes shown (10 and 30 acres; 4 and 12 hectares) reflect the areas needed to handle
hydraulic dredge production rates of 1,000 and 5,000 yd3/day (760 and 3,800 m3/day),
250
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Chapters. Disposal Technologies
8 3H
No control system
RCRA Subtitle D
control system
RCRA Subtitle C
control system
10 acres (4 hectares) 30 acres (12 hectares)
CONFINED DISPOSAL FACILITY AREA
Figure 8-8.
Capital costs for a hypothetical confined disposal facility assuming
hydraulic dredging and disposal.
respectively, and produce equal levels of suspended solids removal. As shown, the rate
of hydraulic dredging can significantly affect the surface area and cost of the CDF
required. Had the sediments been dredged mechanically, an even smaller area could be
used for the CDF.
Figure 8-8 also compares the capital costs for these CDFs with earthen dikes and no cap
or liner (no control system) to identical facilities with RCRA Subtitle C and RCRA
Subtitle D control systems (as depicted in Figure 8-3). The costs of these types of
controls increases with CDF surface area. The costs shown in Figure 8-8 do not include
the costs for engineering and design, construction oversight, permits, or systems for
treating effluent or leachate. The costs shown reflect facilities where dike and contami-
nant control materials had to be imported. Sites with native soils suitable for dike
construction would have lower costs. The availability of clay for contaminant barriers
(e.g., liners and caps) can also affect CDF costs.
The most complete actual costs for CDF construction are available for the facilities
constructed by the Corps around the Great Lakes under the authority of the Rivers and
Harbors Act of 1970 (PL 91-611), §123. These costs, shown in Figure 8-9, represent the
construction contract costs for facilities constructed between 1970 and 1988, adjusted to
January 1993 costs using ENR's CCI. Figure 8-9 shows unit costs ($/yd3) for CDFs vs.
total CDF capacity. CDFs are also indicated as being upland or in-water. These costs
do not include the costs for engineering and design, construction oversight, or permits,
but may include costs for effluent treatment systems (e.g., weirs and filter cells). The
CDF costs shown do not include any costs for land acquisition, which was a requirement
of local sponsors under this authority.
Although there is a general trend showing the economy of scale (lower unit costs for
larger CDFs), the variation attributable to site-specific conditions and designs (as indicated
by the amount of scatter) predominates.
251
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cT
13
$
b
0
o
H
Z
=>
30 -
28 -
26 -
24 -
22 -
20 -
18 -
16 -
14 -
12 -
10 -
8 -
6 -
4 —
2 -
0 -
10,
A
•
D
D
A ^ . m
A A A
• • ^
^
A
A
) 1 1)11)11 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 I I
)00 100,000 1,000,000 10,000,000 100,000,000
CONFINED DISPOSAL FACILITY CAPACITY (yd*)
(log 10 scale)
NOTE: i yd3 = 0.76 m3; In-lake: • 1 980 to present A 1 976 to 1 979 • 1 970 to 1 975
multiply by 1 .32 for r
cost per cubic meter. Upland: D 1 980 to present A 1 976 to 1 979 o 1 970 to 1 975
Figure 8-9. Construction contract costs (January 1993) for Great Lakes confined disposal facilities.
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Chapter 8. Disposal Technologies
Temporary Storage Facilities
The costs for a temporary storage or rehandling facility can be estimated using the capital
cost information for CDFs provided above. The types of contaminant controls in a
temporary facility may be less stringent than those designed for a permanent CDF. Land
costs may not be appropriate if a limited easement or right-of-way is obtained. Long-term
maintenance costs would also not be incurred.
An additional cost for temporary facilities would result from the demolition of the
structures and decontamination of the site. Materials that have contacted contaminated
sediments or residues may have to be treated or disposed in the same manner as the
sediments.
ESTIMATING CONTAMINANT LOSSES
Disposal technologies have more mechanisms for contaminant loss than most other
remediation components. Procedures to estimate contaminant losses from disposal
technologies are also more developed than for other components, primarily as a result of
research conducted by the Corps in relation to dredged material disposal and broad-based
research on landfills of all types. Myers et al.. (in prep.) provides a summary of predictive
tools for estimating contaminant losses from sediment disposal technologies.
Contaminant loss pathways of concern for open-water disposal technologies are different
from those for beneficial use and confined disposal. One of the primary differences is
the movement of dredged material through the water column and subsequent water
column impacts associated with open-water disposal. Beneficial use and confined
disposal technologies usually do not involve the type of direct water column impacts
associated with open-water disposal.
Contaminant migration pathways for beneficial uses and confined disposal alternatives are
similar because both types of disposal options involve some type of confinement in most
cases. There is always a potential for leachate and volatile loss pathways to be of
concern when considering beneficial use and confined disposal. In addition, hydraulic
placement will involve an effluent pathway for both beneficial use and confined disposal.
The relative significance of plant and animal uptake depends on the ultimate use and
engineering design of the disposal site.
Open-Water Disposal
Within a sediment remedial alternative, unrestricted, open-water disposal is feasible only
for sediments or residues that have been decontaminated. Regulatory testing procedures
to determine if dredged or fill materials are suitable for unrestricted, open-water disposal
are contained in USEPA/USACE (1990) for ocean disposal and in USEPA/USACE (1994)
for disposal to inland and near coastal waters.
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Chapter 8. Disposal Technologies
Capping and contained aquatic disposal may be viable disposal technologies for
contaminated sediments or residues from treatment technologies. Procedures for
evaluating the acceptability of capping and contained aquatic disposal technologies are
identified in USACE/USEPA (1992). The main objectives are to determine water column
impacts during dredged material placement and impacts on benthic organisms after
placement. The procedures for evaluating water column impacts can be adapted to
estimating contaminant losses. Equipment to reduce water column impacts (i.e., tremies
and submerged diffusers) is available. Controls on benthic impacts are generally the
primary concern in determining cap design.
In addition to water column and benthic impacts associated with capping and contained
aquatic disposal, there is a potential for contaminant loss associated with diffusion through
caps. Techniques for estimating diffusion losses are described in Myers et al. (in prep.).
The information needed for estimating diffusion losses is described in Chapter 3,
Nonremoval Technologies. Some type of mathematical tool (e.g., spreadsheets, numerical
models, commercially available software for performing mathematical calculations) is
needed to solve the model equations described in Myers et al. (in prep.).
Beneficial Use
For beneficial use technologies, the potential for plant and animal uptake of contaminants
can be a major concern. Some beneficial uses, such as construction fill, may eliminate
plant and animal uptake pathways through engineering design.
Solid waste management uses (daily sanitary landfill cover) also may not involve plant
and animal uptake pathways, unless the material is used as final cover. The contributions
of contaminated sediments or treatment residues to leachate generation can be a concern
for solid waste uses. Because sanitary landfills are now required to be lined, groundwater
impacts should be minimal if the landfill is properly designed and nstructed.
Volatile emissions will be a major factor for land application alternatives. In a land
application scenario, volatilization may potentially account for more loss than any other
mechanism, depending on the chemical properties and land application operations. For
this reason, worker health and safety, and air quality impacts are potential concerns for
land application of sediments or treatment residues containing certain organic chemicals.
Leachate and volatile loss pathways are potentially significant for most sediment remedial
alternatives, including those involving beneficial use. Construction fill and solid waste
management use alternatives are especially likely to require evaluation of these losses.
Because the basic mechanisms by which contaminants are lost along these pathways are
the same for beneficial uses and CDFs, the estimation techniques developed for CDFs
(Myers et al., in prep.) can be applied to beneficial uses. Modification of procedures and
interpretation may be appropriate, depending on project-specific conditions.
Confined Disposal
Contaminant migration pathways for an upland CDF are shown in Figure 2-6. Pathways
involving movement of large masses of water, such as CDF effluent during hydraulic
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Chapter 8. Disposal Technologies
filling, have the greatest potential for releasing significant quantities of contaminants from
CDFs. Pathways such as volatilization may also result in the release of organic chemicals
in highly contaminated dredged material at certain stages in the filling of a CDF.
Techniques for estimating effluent, leachate, and volatile losses are described in Myers
et al. (in prep.).
If dredged material is placed hydraulically, effluent will be a temporary, but major,
contaminant loss pathway. Effluent from a CDF is considered a dredged material
discharge under §404 of the Clean Water Act and is also subject to water quality
certification under §401. Losses along this pathway can be controlled by proper design
of the disposal site, management of disposal operations for minimizing losses, and
effluent treatment. Techniques for estimating effluent losses are described in Myers et
al. (in prep.). Modified elutriate and column settling tests (see Table 8-3) are required
for CDF design and effluent loss calculations.
Subsurface seepage from CDFs may reach adjacent aquifers or enter surface waters.
Fine-grained sediments tend to form their own disposal-area liner as they settle and
consolidate. Evaluation of leachate quality from a CDF must include a prediction of
which contaminants may leach and the mass release potential. Laboratory procedures are
available for prediction of leachate quality (Myers et al. 1992). These procedures are
based on theoretical analysis of laboratory batch and column leach data. Experimental
testing procedures only provide data on leachate quality. Estimates of leachate quantity
must be made by considering site-specific hydrology. Computerized procedures such as
the USEPA HELP model (Schroeder et al. 1984) can be used to estimate water balance
for CDFs (Myers et al., in prep.).
The potential for volatile emissions should be evaluated in cases where sediments contain
volatile or semivolatile organic compounds. Volatile emissions should be evaluated to
protect workers and others who could inhale contaminants released through this pathway.
Although no laboratory procedures for measuring volatilization from dredged sediments
have been developed, volatile flux equations based on chemical vapor equilibrium
concepts and transport phenomena fundamentals are available for estimating volatile
losses (Myers et al., in prep.). Volatile emission rates are primarily dependent on the
chemical concentration in the dredged material, the surface area through which emission
occurs, and climatic factors such as wind speed.
Some contaminants in exposed dredged material can bioaccumulate in plant and animal
tissue and become further available to the food web. Prediction of uptake is based on
plant or animal bioassays (Folsom and Lee 1985; Simmers et al. 1986). Contaminants
in plant or animal tissue are chemically analyzed, and the results are compared with
Federal criteria for food or forage. Management strategies can be formulated to minimize
plant and animal uptake by directing where to place dredged material (e.g., using cleaner
materials to cover more contaminated materials).
Immediately after dredged material placement (beneficial use or confined disposal) and
after ponding water is drawn down, rainfall may generate contaminated runoff from the
settled dredged material. Presently, there is no simplified procedure for predicting runoff
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Chapter 8. Disposal Technologies
quality. A soil lysimeter testing protocol (Lee and Skogerboe 1983) has been used to
predict surface runoff quality with good results. If runoff concentrations exceed
standards, appropriate controls may include placement of a cap, maintenance of ponded
water conditions (although this may conflict with other management goals), vegetation to
stabilize the surface, treatments such as liming to raise the pH, and treatment of the runoff
(as for effluent).
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9. RESIDUE MANAGEMENT
Residues are materials, products, or waste streams generated by components of a sediment
remedial alternative. Residues may be water, wastewater, solids, oil fractions, or air and
gas emissions. The management of these residues may involve treatment, containment,
or discharge to the environment.
The types of residues anticipated from most sediment remedial alternatives and manage-
ment options for them are provided below. Some sediment treatment technologies may
generate unique residues, requiring special management considerations. At a minimum,
the inert solid particles that were present in the original, untreated sediment, will still be
present following the application of any treatment technology.
WATER RESIDUES
Water is likely to be the most important residue for consideration at most sediment
remediation projects simply because of the volumes generated. The removal and transport
technologies selected will have a profound effect on how much water residue is generated
through the treatment process. For example, if the sediments are dredged hydraulically
and transported by pipeline, a large area will probably be needed for gravity settling. In
contrast, if the sediments were removed with a mechanical dredge and transported by
truck, there would be much less "free water" to handle.
Some pretreatment and treatment processes may require the addition of even more water.
For final disposal of sediments and solids residues, most of this water must be removed.
Depending on how the sediments are handled, treated, and disposed, the volume of water
that must ultimately be managed can be less than one-half of the volume of sediments (in
place) dredged, or greater than five times this volume.
Water residues from a sediment remedial alternative are commonly referred to as effluent
or leachate. The term "effluent" may be applied to a wide variety of water residues,
including:
• Discharges from an active CDF
• Surface runoff from a landfill or CDF
• Sidestreams from a dewatering process (e.g., filtrate from a filter press or
centrate from a centrifuge)
• Wastewater or condensate from a pretreatment or treatment process.
The term "leachate" refers specifically to water that has flowed through the sediment,
such as pore water, or precipitation that has infiltrated sediments in a CDF or landfill.
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Chapter 9. Residue Management
The volume of leachate is generally much smaller than that of effluent, but the concentra-
tion of dissolved contaminants is typically higher.
The flow rate of effluents and leachates is highly dependent on their source. The effluent
from a CDF during filling operations from a hydraulic dredge can be quite substantial—
hundreds or even thousands of liters per minute. The duration of such discharges,
however, is limited to the duration of dredging, which is typically on the order of weeks
or months. Sidestreams from pretreatment or treatment operations are technology-
dependent, but generally will produce smaller flows over a longer period of time (months
to years). Once the remediation project is completed, the need for effluent treatment is
limited to storm water (runoff), which could remain a long-term source if water comes
into contact with contaminated sediments.
Leachate is generated over very long time periods, and therefore a permanent leachate
collection and treatment system is a common requirement at municipal and industrial
landfills.
SOLID RESIDUES
Solid residues include the bulk of sediment solids following treatment as well as smaller
fractions of solids separated from the sediments or produced by the treatment processes.
For most remedial alternatives involving a properly designed and thorough treatment
system, the treated solids will not require additional treatment and can be disposed using
the technologies discussed in Chapter 8. Exceptions to this may include solid residues
with special physical properties or concentrations of contaminants requiring special
handling. Some treatment technologies produce small volumes of sludges. Other solid
residues include debris and oversized materials separated during dredging or pretreatment,
sludges from water or wastewater treatment systems, spent media from granular filters or
carbon adsorption systems, and particulates collected from air pollution control systems.
ORGANIC LIQUID AND OIL RESIDUES
Thermal desorption and solvent extraction technologies, as discussed in Chapter 7, can
produce fractions of concentrated organic liquids and oil materials. These residues are
generally small in volume but contain high concentrations of organic contaminants. An
organic liquid fraction extracted from sediments with relatively low levels of PCBs may
require treatment or disposal in accordance with TSCA requirements, because these
processes concentrate the majority of the PCBs in a volume of oil and other organic
liquids that is much smaller than the original sediment volume.
AIR AND GASEOUS RESIDUES
A number of treatment technologies produce emissions of air or gas that may require
treatment before discharge to the atmosphere. Thermal destruction and thermal desorption
treatment technologies commonly have substantial volumes of air and gas emissions,
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Chapter 9. Residue Management
while (solvent) extraction and chemical treatment technologies are typically in closed
reactors with incidental air venting:
"Active" biological treatment technologies, such as bioslurry processes, require an input
of oxygen and are likely to have larger quantities of air emissions than passive
bioremediation systems. Volatilization of organic contaminants may have to be controlled
in some pretreatment and disposal technologies, as well as in treatment technologies.
Processes that involve the agitation and mixing of sediments contaminated with volatile
and semivolatile compounds should be considered as possible sources of contaminant
emissions.
DESCRIPTIONS OF TECHNOLOGIES
Water Residue Treatment
Technologies for treating wastewater from municipal and industrial sources are well
established and well documented (Weber 1972; Metcalf & Eddy, Inc. 1979; Corbitt 1990).
Averett et al. (in prep.) evaluated the applicability of these technologies to effluent and
leachate from sediment remedial alternatives on the basis of cost, effectiveness,
implementability, and availability.
Effluent/leachate treatment technologies may be categorized according to the type(s) of
contaminants that are removed. This chapter discusses technologies that remove the
following contaminant categories:
• Suspended solids
• Metals
• Organic compounds.
While there is some degree of overlap between the processes, these categories reflect the
primary areas of treatment. There are a number of other contaminants that may also need
to be addressed during a sediment remediation project, including:
• Ammonia
• Sulfides (especially hydrogen sulfide)
• Oxygen demand (biological oxygen demand [BOD5]; chemical oxygen
demand [COD])
• Cyanide.
Suspended Solids Removal Technologies
The removal of suspended matter is generally the most important process in the treatment
of effluents and leachates from sediment remedial alternatives because most of the
contaminants in water residues are associated with the solid particles. An effective solids
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Chapter 9. Residue Management
removal system can significantly reduce contaminant concentrations, leaving behind only
those contaminants that are dissolved or associated with colloidal material. Solids
removal is a frequently required pretreatment for processes that remove dissolved
contaminants (e.g., ion exchange, carbon adsorption). The primary technology types for
suspended solids removal are sedimentation and filtration.
Sedimentation—Sedimentation is the basic form of primary treatment employed
at most municipal and industrial wastewater treatment facilities. There are a number of
process options available to enhance gravity settling of suspended particles, including
chemical flocculants, CDFs, sedimentation basins, and clarifiers (Averett et al., in prep.).
Of these, gravity settling in CDFs has been used most extensively with contaminated
sediments.
CDFs have long served the dual role of a settling basin and storage or disposal facility
for dredged sediments (see Chapter 8 for more information on CDFs). Gravity settling
in CDFs, with proper design and operation, can take a hydraulically dredged slurry
(typically having 10-15 percent solids by weight) and produce an effluent with 1-2 giL
suspended solids (USAGE 1987b). Many CDFs on the Great Lakes produce effluents
with suspended solids less than 1 g/L (e.g., 100 mg/L) by gravity settling alone.
At most CDFs, a hydraulically dredged slurry is discharged into the CDF at one end and
effluent is released over a fixed or adjustable overflow weir at the opposite end, as shown
in Figure 9-1. Settling times of several days are commonly achieved at larger CDFs.
Improved settling efficiencies can be achieved by dividing the CDF into two or more cells
or through operational controls to increase the detention time and prevent short-circuiting.
As the CDF becomes filled, and detention times shorten, dredging production rates may
have to be reduced or mechanical dredging used instead of hydraulic dredging to provide
From
dredge
Main dike
I
Discharge pipe
|— Outfall pipes
Overflow weir
• Cross dike
Figure 9-1. Confined disposal facility with cross dike.
Source: USAGE (1987U)
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Chapter 9. Residue Management
suitable settling efficiencies. Design guidance for sedimentation in CDFs is contained in
Confined Disposal of Dredged Material (USAGE 1987b).
Sedimentation basins or clarifiers are typically open, concrete or steel tanks with some
type of solids collection system that operates on the bottom. Inclined plates may be
incorporated into the tanks to improve solids capture for a given flow rate and reduce the
size of the clarifier. Rectangular and circular clarifiers are commonly used in municipal
and industrial wastewater treatment, but have only been used on a limited basis in
applications with contaminated sediments. A cross flow, inclined plate clarifier was used
at the ARCS Program's pilot-scale demonstration in Saginaw, Michigan (USAGE Detroit
District 1994).
Flocculating agents are routinely used in municipal and industrial wastewater treatment
in conjunction with clarifiers. There are many proprietary surfactant-type polymers
designed for this purpose, although inorganic chemicals such as ferric chloride may also
be used. Schroeder (1983) found that low-viscosity, highly cationic liquid polymers were
most effective for dredged material effluent treatment and required minimal equipment
to implement.
A liquid cationic polymer flocculant was injected into the hydraulic discharge line at
dosages of 10 ppm to enhance settling of sediments and fly ash dredged during construc-
tion of the Chicago Area CDF (USAGE Chicago District 1984). Flocculants were also
used during two demonstrations of soil washing technologies on the Great Lakes.
Nonionic and anionic polymers were used during the ARCS Program's pilot-scale
demonstration at Saginaw, Michigan (USAGE Detroit District 1994). A coagulant and
a polymer flocculant were used to promote the removal of silty-clay sediments during the
pilot-scale dredging and sediment washing demonstration at Welland, Ontario (Acres
International Ltd. 1993).
Filtration—Filtration is typically used as a polishing step for water that has been
pretreated by flocculation and sedimentation in municipal and industrial wastewater
applications. This technology is also widely used for treatment of drinking water.
Granular media filtration has been used to treat effluents at most in-water and some
upland CDFs in the Great Lakes using either filter dikes (Figure 9-2) or filter cells
(Figure 9-3). Permeable dikes provide gravity filtration through horizontal flow, and
are nonrenewable once clogged. Most in-water CDF dikes have a core of crushed stone.
Some have discrete lenses of sand for filtration, as shown in Figure 9-2. Filter cells and
sand-filled weirs are vertical-flow gravity filters that can be replaced or regenerated when
exhausted. Filter cells may be incorporated into the CDF dike, as shown in Figure 9-3,
or can be freestanding structures constructed of concrete, steel, or plastic.
Gravity and pressure filters can be obtained as "package" units, or constructed onsite for
larger applications. Package filtration units are available for purchase or lease. These
units are typically mounted on a flatbed trailer for transportation to the site. The flow and
filtration capacities of package units can often be designed to fit most small projects.
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Chapter 9. Residue Management
Disposal side
Lake side
Steel sheet piling
Note: 1 ft = 0.3 m
Source: Miller (1990)
Figure 9-2. Cross section of a confined disposal facility dike with a filter layer.
Lake side
CDF side
Top of
dredge fill
PSA 23 steel
pile with
asphalt
interlocks
Fine gravel
Filter
holes
Note: 1 in = 2.54 cm
Figure 9-3. Cross section of an in-dike filter cell.
Source: Miller (1990)
Prefabricated filtration units were used as part of sediment remediation projects in Lorain,
Ohio, and Waukegan, Illinois.
Gravity and pressure filters must be taken off line and backwashed periodically to remove
accumulated solids. Continuous backwashing systems, which clean a portion of the filter
at a time, are also available. The backwash water has high suspended solids content, and
must be returned to the sediment disposal/holding area or handled in a sludge treatment
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Chapter 9. Residue Management
system. The operation of one or more filters, including the backwash cycle, can be fully
automated.
Filtration media used in Great Lakes CDFs are typically sand and/or graded stone. The
filter cell at the Chicago Area CDF uses a combination of sand and anthracite. Alterna-
tive media can include limestone, crushed shells, activated carbon, or glauconitic green
sands (zeolites). Beds constructed with ion exchange resins may effect ion exchange or
precipitation reactions in addition to simple filtration (Averett et al. 1990 and in prep.).
Metals Removal Technologies
Metal contaminants are primarily associated with suspended particulates in most water
residues from sediment remedial alternatives. Suspended solids removal technologies
should therefore be sufficient to address metals removal needs for the majority of
applications. Removal of dissolved metals from water residues can be conducted using
ion exchange or precipitation. These technologies have been widely used for industrial
wastewater treatment, but have not been applied to water residues from sediment remedial
alternatives.
Ion Exchange—Ion exchange is a process in which ions held by electrostatic forces
of charged functional groups on the surface of a solid are exchanged for ions of similar
charge in a solution in which the solids are immersed (Weber 1972). The "solids" are
specific resins (usually in the form of beads) that have an affinity for metallic ions. The
most common configuration is the fixed bed system, in which the wastewater flows
through resin contained in a column (Cullinane et al. 1986a). Ion exchange resins are
either highly selective for specific metal contaminants or non-specific for a wide variety
of metals.
Precipitation—Precipitation is a chemical process in which soluble chemicals are
removed from solution by the addition of a reagent with which they react to form a
(solid) precipitate. This precipitate can then be removed by standard flocculation,
sedimentation, and/or filtration processes. Most heavy metals can be precipitated from
water as hydroxides with the addition of a caustic (e.g., sodium hydroxide or lime).
Alternatively, sodium sulfide or ferric sulfide may be added to precipitate metals as
sulfides. The sulfide process is effective for certain metals, such as mercury, which do
not precipitate as hydroxides. Precipitation processes produce a sludge that may have to
be managed as hazardous waste due to the presence of concentrated heavy metals.
Disposal costs for these sludges may therefore be significant.
Organic Contaminant Removal Technologies
Most organic contaminants, particularly the hydrophobia compounds, are strongly bound
to sediment particulates and will be captured through the suspended solids removal
technologies discussed above. Removal of dissolved organic contaminants may be
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Chapter 9, Residue Management
necessary where unacceptable concentrations are present in water residues following
sedimentation and/or filtration. Most of the organic contaminant removal technologies
discussed here require that suspended solids be removed first.
Carbon Adsorption—Carbon adsorption is a technology that has been used widely
in the drinking water treatment industry, and that is being used with increasing frequency
in the wastewater and hazardous waste industry (Corbitt 1990). The process takes
advantage of the highly adsorptive properties of specially prepared carbon known as
activated carbon. The porous structure of the carbon provides a large internal surface area
onto which organic molecules may become attached. Many organic substances, including
chlorinated solvents, PCBs, PAHs, pesticides, and others, may be removed from solution
using carbon adsorption.
Carbon adsorption is achieved by passing water residues through one or more columns
containing granular activated carbon operated in parallel or in series. Carbon columns
may be operated in either an upflow (expanded bed) or a downflow (fixed bed) mode.
In theory, spent carbon may be regenerated. In practice, however, spent carbon must
frequently be discarded, especially if high concentrations of PCBs are present.
Activated carbon was used to remove dissolved PCBs from the water drained from
sediment storage lagoons and process water from the thermal desorption process at the
Superfund remediation at Waukegan, Illinois (Sorensen 1994). Activated carbon was also
used to remove phenols from water drained from a CDF used for the disposal of
sediments dredged as part of a remediation project at Lorain, Ohio (Kovach 1994).
Oil Separation—Some sediments contain very high concentrations of oil and
grease. In most cases, the oil and grease will remain attached to the sediment particulates
and be captured by suspended solids removal technologies. In some cases, oil and grease
is released from sediment particles, forming a slick, a suspension of discrete particles, or
an emulsion in the water residue. In such cases, the oil and grease must be captured or
removed prior to treatment processes such as ion exchange, carbon adsorption, and
filtration, because oily compounds will foul the surfaces of exchange resins and filters.
Oil booms and skimmers are routinely used in CDFs to capture oil and floating debris.
Coalescing plate separators employ a medium that provides a surface for the aggregation
of small, emulsified oil droplets, which can then be removed by gravity separation.
Emulsified oils are much more difficult to separate from water. Chemical de-emulsifying
agents, heat, and/or acids are generally effective for breaking emulsions. Once the
emulsion is broken, the oil is amenable to the treatment processes described above.
Oxidation—Oxidation is used to partially or completely degrade organic com-
pounds. Complete oxidation of organic compounds can theoretically reduce complex
molecules to carbon dioxide and water. Halogenated organic compounds will produce
minor amounts of mineral acids (e.g., hydrochloric acid). However, oxidation is often not
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Chapter 9. Residue Management
complete, resulting in the formation of simpler "daughter" compounds that are usually
much less toxic or persistent than the original contaminants (Weber 1972).
Two forms of oxidation that might be applicable to water residues from sediment
remedial alternatives are chemical oxidation and UV-assisted oxidation. Chemical
oxidants suitable for treating wastewater include oxygen, ozone (O3), hydrogen peroxide
(H2O2), potassium permanganate, chlorine (or hypochlorites), and chlorine dioxide (Weber
1972). The oxidizing power of hydrogen peroxide and ozone can be significantly
enhanced through the use of UV light. This technology is effective for treating a wide
variety of organic compounds, including PCBs and PAHs.
Solid Residues Management
Most of the sediment solids generated by pretreatment or treatment technologies will be
disposed using the technologies discussed in Chapter 8. Treated solids may be suitable
for beneficial uses, while residues that are still contaminated will likely require confined
disposal or subsequent treatment. Sand reclaimed from a CDF in Duluth through a crude
soil washing process has been used for road construction fill (Bedore and Bowman 1990).
Sediments from Waukegan Harbor treated with a thermal desorption process were con-
fined onsite because of the residual concentrations of PCBs and heavy metal contami-
nants.
Many of the thermal treatment processes produce solid residues with very little moisture.
For example, the solid residues from the thermal desorption process demonstrated at
Buffalo, New York, were almost all greater than 99 percent solids by weight (USAGE
Buffalo District 1993). Fine-grained sediments that have been almost completely
dewatered may be difficult to handle and transport without substantial losses as wind-
blown dust. Water residues or excess process water may be used to wet the sediments
to a manageable consistency.
The easiest place to wet the treated solids is immediately as they exit the treatment
process, perhaps by applying a water spray to the residues on a belt or screw conveyer.
Other options are to mix the dry residues with wet sediments that are not to be treated
or to solidify the residues through the addition of cement, binding agents, and water.
These options would require a large mixing tank and agitator.
Other solid residues likely to require special handling include debris and oversized
materials removed during dredging or pretreatment, treatment process residues with
special properties, spent filter media or carbon from water treatment systems, and
particulates collected by air pollution control systems.
Large debris that might be separated during dredging or rehandling may be suitable for
salvage or scrap if the contaminated sediments can be washed off. If this is not practical,
it may still be necessary to cut or compact the debris into smaller pieces for transport to
a landfill. Smaller debris and oversized materials separated during pretreatment will
likely require confined disposal.
265
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Chapter 9. Residue Management
Filter media and carbon used to treat water residues and particulates collected from air
pollution control systems may contain high concentrations of contaminants. These
materials may be suitable for co-treatment or co-disposal with the sediments. Granular
filter media from the filter cells at the Chicago Area CDF have been routinely disposed
in the CDF.
Organic Residue Treatment
Fractions of concentrated organic materials from thermal desorption and solvent extraction
technologies are likely to be relatively small in volume, provided that the treatment
process made a good separation of organic and water fractions and there was a good
recovery of solvent (if used). For example, 15 kg of oil was collected from 415 kg of
sediment during the demonstration of a solvent extraction process at the Grand Calumet
River in Indiana (USAGE Chicago District 1994). In contrast, a poor separation of oil
and water fractions during the pilot demonstrations of a thermal desorption process at the
Buffalo and Ashtabula Rivers resulted in a mixed (oil-water) residue with a mass equal
to more than one-half that of the feed material (USAGE Buffalo District 1993; USAGE
Buffalo District, in prep.).
Because of their relatively small volume and high concentrations of contaminants (with
good separation), subsequent treatment of organic residues is quite feasible and, in many
cases, required by regulation. Thermal destructive, chemical treatment, and
bioremediation technologies discussed in Chapter 7 may be used to treat organic residues.
Some of these technologies were originally developed to treat oil/organic wastes and
therefore are more fully developed for organic residues than for sediments. These
technologies are also likely to be more efficient with the highly concentrated organic
residue than with the sediments.
Oil residues collected from the thermal desorption process used at the-Waukegan, Illinois,
Superfund cleanup and from the solvent extraction process demonstrated at the Grand
Calumet River, Indiana, were incinerated at a licensed TSCA facility. The oil residue
from the thermal desorption process demonstrated at Buffalo, New York, and Ashtabula,
Ohio, was sent to a commercial oil treatment facility.
Storage onsite, or at a licensed landfill, may be a short-term option for organic residues
if a treatment facility is not readily available. The applicability of confined disposal as
a permanent option for organic residues will depend largely on regulatory requirements.
Air and Gaseous Residues
The emission of contaminants to the air is a potential contaminant loss pathway for most
sediment remediation components. These air emissions may be a point source, such as
the stack or vent from unit operations for a treatment process, or a diffuse source, such
as volatilized organic compounds from the surface of a CDF. Although organic com-
pounds are usually the contaminants of concern, inorganic contaminants (heavy metals)
may be associated with dust generated by remediation processes that remove water from
266
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Chapter 9. Residue Management
the sediment. Thermal processes that separate volatile heavy metals such as mercury
from the sediment are also a potential source of air contamination.
Point sources are generally easier to control because they are already contained and can
be piped through an air pollution control system. Point vapor sources from sediment
treatment processes can be treated by adsorption (activated carbon or other media),
condensation, spray towers, scrubbers, packed columns, thermal oxidation systems, or
catalytic oxidation systems. Paniculate control may be accomplished by cyclones,
scrubbers, bag filters, and similar systems.
Fugitive emission controls for process equipment such as those used for pretreatment and
treatment technologies generally require enclosing the entire process in a structure, either
a building or an inflatable bubble. Gases vented from these systems would be pumped
through a treatment unit, probably activated carbon.
Volatile emissions from large surface areas, such as CDFs or storage tanks, are more
difficult to control. Volatilization from these sites may be reduced by limiting the contact
between the contaminated sediment or supernatant and air. Options for covering the CDF
include buildings or bubbles, floating covers, foams, and sorbent materials. Mixing and
splashing during filling from a pipeline can be reduced by submerging the discharge
below the surface. The rate of volatilization can also be reduced by shielding the wind
from the pond surface through the construction of fences around the perimeter of the
facility.
SELECTION FACTORS
Water Residues
The need for treatment of water residues from a sediment remedial alternative is con-
trolled primarily by the regulatory requirements on the discharge. Water residues may
be discharged directly into a waterway or into a municipal wastewater treatment plant.
The former is termed "direct discharge," while the latter is an "indirect discharge." Both
discharges are regulated under the Clean Water Act (PL-92-500), but the treatment
requirements may be quite different.
Water that is returned from any dredged material disposal operation back to a river, lake,
harbor, wetland, or other "waters of the United States" is considered "dredged material"
and regulated under §§404 and 401 of the Clean Water Act. This would include the
effluent from a CDF and water separated from dredged sediments during pretreatment.
Water from treatment processes and leachate from disposal facilities may be regulated
under §402 of the Clean Water Act (NPDES). Regardless of which of these permitting
authorities applies, the direct discharge must meet State water quality standards for the
receiving waterway. In some cases, NPDES effluent limitations are based on technology
standards (e.g., Best Available Technology).
267
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Chapter 9. Residue Management
For direct discharges, the flow rate will usually not be limited. Mixing zones may or may
not be allowed for the initial dilution and dispersion of the discharge. Discharge to a
small stream or lake with little dilution may not be feasible for some water residues.
Discharges to a wastewater treatment facility are permitted through the local sewer
authority or municipality. A "pretreatment" or "industrial discharger" permit must be
obtained in accordance with §307 of the Clean Water Act. Sewer use charges are likely
to be levied, although these are usually considerably less than the cost of building a
separate treatment system. Effluent limitations for conventional pollutants (e.g., BOD,
nitrogen, phosphorus) and heavy metals are generally less stringent than direct discharges,
because the water undergoes further treatment at the municipal wastewater treatment
plant. However, limitations for toxic organic compounds, such as PCBs, PAHs, and
phenolic compounds, may be nearly as strict as those for direct discharge. Representative
pretreatment standards for three municipalities are shown in Table 9-1.
Discharges to municipal wastewater treatment facilities are typically through existing
sewer systems. The rate of discharge may be limited by the capacity of the wastewater
treatment facility or the sewers. Small volumes of water residues can also be trucked
from unsewered areas to the wastewater treatment facility.
A sediment remedial alternative may have water residues from several sources. Initially,
each water stream should be evaluated separately. Some water residues may be suitable
for combining for treatment, while others may have to be treated separately.
Once it has been determined that a water residue from a sediment remedial alternative
must be treated, the selection of treatment technologies is determined primarily by the
following factors:
• Characteristics of the water residue to be treated
• Required effluent quality
• Flow rate (both magnitude and variability).
The quantity and quality of a water residue reflect the characteristics of the sediments
being processed and the remediation component at which the residue is generated. The
rate of flow will depend on the processing rate of the component generating the water
residue and the water storage capacity available.
Other factors that may influence technology selection include:
• Land availability
• Power requirements
• Operator availability and experience.
Suspended Solids Removal
The treatment of water residues requires a-sequence of steps to achieve the desired
effluent quality. In most sediment remedial alternatives, the first and most important step
268
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TABLE 9-1. EXAMPLES OF PRETREATMENT STANDARDS
Pretreatment Standards
(mg/L)
Parameter
Inorganic Contaminants
Cadmium (total)
Chromium (total)
Copper (total)
Cyanide (total)
Iron (soluble)
Lead (total)
Mercury (total)
Nickel (total)
Silver (total)
Zinc (total)
Nutrients
Total phosphorus
Ammonia (as N)
Organic Contaminants
Fats, oil and grease
Phenolic compounds
Benzo-a-pyrene
Methylene chloride
Fluoranthene
Bis(2-ethylhexyl) phthalate
Milwaukee,
Wisconsin8
1.5
NS
6.0
5.0
NS
2.0
0.0026
4.0
5.8
8.0
NS
NS
300
NS
0.062
NS
NS
NS
Syracuse,
New York"
2.0
8.0
5.0
2.0
NS
1.0
0.02
5.0
1.0
5.0
NS
NS
100
4.5
NS
NS
NS
NS
E. Chicago,
Illinois0
0.140
0.282
0.170
0.407
2.40
0.224
0.003
0.390
0.05
5.5
5.5
77
50
14
NS
0.960
0.690
1.03
Note: NS - no standard
8 Milwaukee Metropolitan Sewerage District (1992).
b Onondaga County Department of Drainage and Sanitation (1983).
c City of East Chicago (1985).
269
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Chapter 9. Residue Management
will be the removal of suspended solids. Gravity settling is capable of removing between
90 and 99 percent of suspended solids. Selection factors for suspended solids removal
technologies are summarized in Table 9-2.
If the sediments are to be dredged or transported hydraulically, laboratory settling tests
should be conducted to predict settling properties and aid in the design of the settling/
containment area (USAGE 1987b). Additional information on these tests is provided in
Table 8-3. The USAGE manual Confined Disposal of Dredged Material (1987b)
provides guidance on the design and operation of CDFs for removal of suspended solids.
The SETTLE routine of the ADDAMS model (as discussed in Chapter 8) can be used to
predict gravity settling in a CDF (Schroeder and Palermo 1990).
Flocculants can be used to enhance suspended solids removal, but are generally only
recommended for application after primary settling. Schroeder (1983) discusses
approaches for applying flocculants to a CDF effluent and compares the effectiveness of
several flocculants. With secondary settling, removal efficiencies of 90 percent and
greater were readily achieved. Jar tests with a sediment slurry, after allowing for primary
settling, are a simple and inexpensive means for selecting flocculating agents and dosage
rates.
Filtration systems can provide suspended solids removal efficiencies of up to 90 percent
(one pass), but are generally only recommended for water residues with relatively low
suspended solids concentrations (less than 300 mg/L). Loadings with higher solids
concentrations will cause rapid filter clogging. Guidance on the design of filtration
systems for CDFs is provided in Krizek et al. (1976). Laboratory filtration tests are
generally not necessary to predict suspended solids removal efficiencies.
Filtration systems typically have a fixed design removal efficiency and flow rate, which
may be problematic if the influent water residue has highly variable flow rates or
suspended solids concentrations. Flocculant dosages can be adjusted to meet changing
flows and suspended solids concentrations, offering greater flexibility in operation.
"Package" filtration units can be leased for projects with limited flow rates, and require
little space. Filtration may be cost prohibitive for projects with large flow rates.
Flocculation and secondary settling can accommodate large flows, but require a secondary
settling tank or basin.
Metal and Organic Contaminant Removal
The need for water residue treatment beyond suspended solids removal is determined by
laboratory tests to predict the concentrations of dissolved contaminants. The modified
elutriate test was developed to predict the quality of an effluent from a CDF during
hydraulic dredging/discharge following primary settling (Palermo and Thaxton 1988).
The character of surface runoff and leachate from a CDF may be predicted using the
methods in Lee and Skogerboe (1983) and Myers and Brannon (1991), respectively.
Additional information on these tests is provided in Table 8-3.
270
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TABLE 9-2. SELECTION FACTORS FOR SUSPENDED SOLIDS REMOVAL PROCESSES
Treatment Technology
Applications
Process Limitations and Specifications
Efficiency/Reliability
Coagulation/Flocculation
Chemical Clarification
Suspended solids removal
Particutate-bound contaminants
(e.g., metals, PCBs, pesticides,
PAHs, etc.)
Synthetic flocculants (polymers) are more expensive
than inorganic compounds (lime, FeCI3), but require
much smaller doses, and therefore do not add to
sludge volume. More highly cationic and higher
molecular weight polymers most effective in bench-
scale testing (Schroeder 1983). Jar tests generally
required to select most suitable polymer for specific
waste water type.
Efficiency a function of mixing intensity and duration,
settling time, flocculant selected, feed concentration,
and dosage. Polymer dosage typically proportional to
turbidity treated and inversely proportional to amount
of mixing (Schroeder 1983).
Results may be somewhat variable
due to fluctuations in flow rates and
solids concentrations; effluent
concentrations of —50 mg/L
attainable (Schroeder 1983).
See Corbitt (1990) and Shuckrow et
al. (19811 for treatability studies and
removal efficiencies for certain
compounds.
NJ
vj
Permeable Treatment
Beds/Dikes
Granular Media Filtration
Membrane Microfiltration
Suspended solids removal
Particulate-bound contaminants
(e.g., metals, PCBs, pesticides,
PAHs, etc.)
Suspended solids
Particulate-bound contaminants
Suspended solids concentrations
10-300,000 ppm - particles down
to 0.1/mi in size
Paniculate-bound contaminants
Heavy metals precipitates
Permeable treatment beds and dikes can handle solids
concentrations up to 1 g/L for periods of approximately
1 year before clogging (Averett et al. in prep.).
Filter cells and sand-filled weirs can be regenerated.
Permeable dikes are nonrenewable once clogged.
Filter cells and sand-filled weirs can be regenerated.
Permeable dikes are nonrenewable once clogged.
Biological growth and oil and grease can plug filter.
Fitter unit recommended in Averett et al. (in prep.)
manufactured by E.I. Dupont De Nemours and Co.,
Oberlin Filter Co. operates at pressures up to 0.4 MPa
optimum solids concentrations < 5,000 ppm.
Solids and sediment-bound
contaminants removal of 60-98%
(Cullinane et al. 1986a).
Can generally reduce total
suspended solids by 50-90%
Metals - below detection in pilot
studies (USEPA 1989g).
-------
Chapter 9. Residue Management
Tests for predicting dissolved contaminant concentrations in water residues from treatment
technologies will have to be developed on a case-by-case basis. Water residues produced
in bench- or pilot-scale demonstrations can be evaluated, but may not adequately reflect
the water residues from a full-scale application because of differences in materials
handling equipment and the effects of smaller-scale operation.
If water residues require both organic compound and metal treatment technologies, site-
specific conditions will dictate which process is to come first. It may be preferable to
remove the organic compounds first, because they can interfere with metals removal
processes. This is particularly true when metals are chemically or physically bound to
organic compounds (e.g., methyl mercury, tetraethyl lead). Conversely, it may be
preferable to remove metals in conjunction with suspended solids removal. This would,
for example, produce a relatively clean waste stream to be polished with activated carbon.
Reported treatment efficiencies can be used as an initial screening tool in process option
selection. However, it is generally necessary to conduct treatability studies with the
actual water residue to determine the ultimate feasibility of a specific technology.
Treatability studies are particularly important for determining the feasibility of advanced
treatment methods (e.g., carbon adsorption, ion exchange) or technologies that are under
development (e.g., microfiltration). Selection factors for treatment technologies are
presented in Table 9-3 for metals removal and Table 9-4 for organic compound removal.
Solid Residues
The disposition of solid residues from a sediment remedial alternative will generally be
determined by the following factors:
" Material physical and chemical characteristics
• Volume of material
• Regulatory requirements.
Treated sediments that have little residual contamination may be suitable for the beneficial
use disposal technologies discussed in Chapter 8. Laboratory tests for predicting
contaminant mobility and impacts (see Table 8-3) can be used to screen these disposal
options. The selection factors for beneficial use discussed in Chapter 8 should apply to
solid residues as well as untreated dredged material.
Treated sediments and other solid residues with elevated levels of residual contamination
will require subsequent treatment or confined disposal in most cases. Although the
physical and chemical properties of treated solids may be quite different from those of
the untreated sediments, the selection factors for treatment technologies (Chapter 7) and
for confined disposal technologies (Chapter 8) should still apply.
Treated sediments, filter media, and carbon used to treat water residues and particulates
collected from air pollution control systems should be tested to determine if their disposal
is regulated by TSCA or RCRA.
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TABLE 9-3. SELECTION FACTORS FOR METALS REMOVAL PROCESSES
Treatment
Technology
Applications
Process Limitations and Specifications
Efficiency/Reliability
Ion Exchange
Precipitation
No
vj
Co
Dissolved heavy metals and other ions Organic compounds, oil and grease, and suspended
solids interfere/clog resin.
Cation resins:
High concentration of non-targeted ionic species
(Ca + + , Mg++, Na'1"1") can reduce resin capacity.
• Heavy metals (e.g. Fe+ +, Cu+
Ag++, Hg++l
• Ammonia
Anion resins:
• Cyanides
• Phenols
Dissolved metals
Strong acid resins effective for many heavy metals.
Algasorb process (USEPA 1992g) is particularly
applicable to mercury and uranium, and can tolerate
higher TDS.
Process is pH dependent.
Generally, sulfides tend to be less soluble and more
stable over broad pH range than hydroxides.
Widely varying flow rates and concentrations impede
process control.
Competing reactions can occur.
Reagent in excess of stoichiometric requirements
required due to common ton effect.
Produces sludge that may be regulated as hazardous
waste.
Well-documented, established industrial
process.
Soluble metals removal of >99% (Cullinane et
al. 1986a).
See Shuckrow et al. (1981) for treatability
studies for specific compounds using resin
adsorption.
Algasorb process (USEPA 1992g) at pilot-scale
level of development.
Varies - cannot attain removals below
minimum solubilities.
The presence of more than one metal species
may diminish removal efficiency.
Removal efficiencies for specific compounds
utilizing precipitation are found in Shuckrow et
al. (1981) and Cullinane et al. (1986a).
-------
TABLE 9-4. SELECTION FACTORS FOR ORGANIC CONTAMINANT REMOVAL PROCESSES
Treatment Technology
Applications
Process Limitations and Specifications
Efficiency/Reliability
Carbon Adsorption
Oil Separation
Dissolved organic compounds, some
particulate removal. Removes many
types of organic compounds
including:
• Aromatic solvents (benzene,
toluene, xylene)
• PAHs
• PCBs
• Chlorinated pesticides
• Phenolic compounds
• High molecular weight aliphatic
and aromatic amines
• Surfactants
• Soluble organic dyes
• Fuels (dissolved phase only)
• Chlorinated solvents
• Aliphatic and aromatic acids
• BOD, COD, and TOC
Generally not effective for highly
polar molecules (e.g., alcohols,
ketones).
Low solubility humic and fulvic acids
sorb most readily and may exhaust
carbon.
Some metals (e.g., Cr) have high
carbon affinity.
Gravity separation:
Free and dispersed oil removal
(droplets >2Q/jm) (Corbitt
1990)
Incidental suspended solids
Coalescing plate separators:
Fine oil droplets in mechanical
emulsions
Major concern is fouling of carbon columns with:
1) Oil and grease
• up to 10 mg/L allowable for standard operations
• up to 50 mg/L allowable if top layers of carbon
bed sacrificed
2) Suspended solids
• 65-70 mg/L allowable for downflow columns
• < 50 mg/L allowable solids concentrations for
upflow columns (Cullinane et al. 1986a)
3) Dissolved solids
• pH adjustment or scale inhibitor necessary if high
concentrations of calcium carbonate or calcium
sulfate present; dissolved iron (Fe"1"1") can be
problematic
4) Biological growth
• High organic carbon concentrations (TOC, DOC)
will promote bacterial growth on carbon;
pretreatment may be required.
Loading rate 2-10 gpm/ft2 (76-380 L/min-m2) for
pressure and gravity fed filter beds; bed depths
1.2-6.1 m (Cullinane et al 1986a).
Normal temperature variations do not substantially
affect adsorption.
Coalescing plate medium is matched to the type and
condition of oil being removed.
Optimum results obtained when targeting oil of only
one specific gravity.
Very fine oil droplets and chemical emulsions require
de-emulsifiers prior to oil separation.
Competitive adsorption can reduce
removal rates by 50-60% (Shuckrow
et al. 1981), and increase need for
carbon replacement.
Removal efficiencies vary according to
influent characteristics, competitive ad-
sorption, and process conditions.
Some reported removal efficiencies are
listed in Shuckrow et al. (1981),
O'Brien and Fisher (1983), Berger
(1987), and Averett et al. (in prep.).
Carbon adsorption capacities for
certain compounds and some
adsorption system parameters are
found in Berger (1987).
Dependent on influent concentrations
and size of oil particles. Effluents of
15 mg/L oil and grease are common.
(continued)
-------
TABLE 9-4. SELECTION FACTORS FOR ORGANIC CONTAMINANT REMOVAL PROCESSES {continued)
Treatment Technology
Applications
Process Limitations and Specifications
Efficiency/Reliability
Ozonation
Resin Adsorption
UV/Hydrogen Peroxide
UV/Ozonation
Many organic compounds, but not
effective for PCBs and other
resistant compounds.
Cyanides and sulfides.
Disinfection.
Pretreatment for biological
treatment; carbon adsorption.
Color, high concentrations of
dissolved organic compounds
(Cutlinane et al. 1986a).
Oxidation of (USEPA (1984a]) as
cited in Averett et al. [in prep.]):
Cyanides
Aldehydes
Dialdyl sulfides
Dithionate
Nitrogen compounds
Phenols
Dilute wastewaters containing
(Averett et al. [in prep.] citing
USEPA [1988cl):
Chlorinated solvents
Phenols
Pesticides
PCBs
Nonselective, oxidizes natural organic compounds and
some contaminants (Averett et al., in prep.I.
Ozone must be generated onsite. Emissions must be
treated to remove ozone.
Some process limitations as for activated carbon.
More expensive than activated carbon.
Ultraviolet light processes have limited effectiveness in
turbid or highly colored waters.
Ultraviolet tight processes limited in effectiveness in
highly colored or turbid waters.
Phenols at 380 ppb - 96.8% reduction
(Averett et al., in prep.).
Pathogens - 90-99% (Cullinane et al.
1986a).
Reported removal efficiencies range
from 23 to 100%.
Removal efficiencies for several
compounds are given in Shuckrow et
al. (1981).
Destruction of 91 -100% PCBs in
bench-scale testing (Averett et al. [in
prep.! citing Carpenter [1986]).
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Chapter 9. Residue Management
Organic Liquid and Oil Residues
The disposition of organic residues is most likely to be controlled by regulation. Thermal
desorption or solvent extraction of sediments containing relatively low concentrations
(1-5 ppm) of PCBs will probably produce an organic residue with concentrations over
50 ppm PCBs, which must be disposed in accordance with TSCA regulations. In most
cases, treatment at an existing, licensed facility will be more cost effective than setting
up a second treatment process onsite. As of June 1994, there are four commercial
incinerators in the United States licensed to treat TSCA-regulated materials. Other
treatment processes (i.e., dechlorination, oxidation, pyrolysis, bioremediation, etc.) may
be feasible if an operating, licensed facility is unavailable.
TSCA has specific requirements for the storage, labeling, and transport of PCBs. These,
or equally conservative, requirements are likely to be necessary for the storage and
handling of organic residues from a sediment remedial alternative. In addition to
contaminant control safeguards, the organic residue should also be evaluated for its
fire/explosion hazard potential.
Air and Gaseous Residues
Contaminant losses to the air during sediment handling, storage, or treatment are affected
by the following factors (USEPA 1992i):
• Contaminant Volatility—The tendency of a contaminant to volatilize from
sediments can generally be related to Henry's Constant, which is directly
proportional to vapor pressure and the molecular weight of the contaminant
and inversely proportional to the solubility of the contaminant in water.
Compounds such as PCBs having relatively low vapor pressures, but low
aqueous solubilities, may have high Henry's constants and be relatively
volatile—hence the need to evaluate potential losses to the atmosphere
during sediment remediation (see Myers et al. in prep).
• Residence Time—The longer the sediment or contaminated water is
exposed to the atmosphere, the larger the fraction of contaminant lost by
this pathway. Long storage periods should be avoided where air emissions
are an issue.
• Surface Area—Air emissions are generally directly proportional to surface
area. The exposed surface area should be minimized to reduce the mass
of contaminant volatilized.
• Turbulence—Agitation or aeration increases the contact time between the
contaminated liquid or slurry and increases volatilization.
• Wind Speed—Wind blowing across a CDF or pond or across exposed
sediment increases the rate of volatilization. Site location or fences to
divert the movement of air can reduce the effects of wind (Thibodeaux et
al. 1985).
276
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Chapter 9. Residue Management
• Temperature—Volatilization increases with increased temperatures.
Operations in cooler weather would reduce contaminant losses.
• Extent of Competing Mechanisms—Contaminant reduction by adsorption,
settling, biodegradation, or other treatment techniques could occur at a
faster rate than the processes necessary for volatilization, reducing the
concentration difference between water and air and consequently the
volatilization rate.
The selection of technologies for control of volatile emissions depends on the type of
source (point or diffuse), whether vapors or particulates are the concern, and the
practicality of capturing or controlling the emission. Selection factors for emission
controls for the various components and key technologies of sediment remediation are
provided in Table 9-5.
Most vendors of treatment technologies with point souces of air/gaseous emissions should
have some operating experience with one or more control systems. The compatability of
a specific process unit with a treatment technology will depend on the character and rate
of the emission. Control of diffuse emission sources requires changing one of the factors
discussed above to reduce the rate and/or mass of volatilization or paniculate loss, or
requires capturing the emission for treatment by one of the processes used for point
sources. The cost for construction and maintenance of structures to capture fugitive
emissions is one obvious disadvantage; another disadvantage is the additional health and
safety requirements for the personnel who have to operate the equipment and the
associated increase in cost and decrease in efficiency. Operation of these structures will
require a leak detection and repair program to maintain their effectiveness.
Volatile losses at facilities with large surface areas, such as CDFs, may not be practical
to contain and treat. Operational practices may be the only option for minimizing volatile
loss. Disposal sites for sediment have their highest emission rates when there is no free
water and the sediment is moist, and before a crust forms on the surface. Volatilization
losses may be reduced by maintaining ponded water over the sediments or by capping the
CDF surface with clean sediment prior to removing the free water.
COST ESTIMATING
Cost estimates provided by vendors of sediment treatment technologies do not typically
include the costs for managing all residues. When evaluating cost data, it is important
to identify residue management that is included and that which is not. Costs for the
storage, handling, and transportation of residues need to be estimated along with other
residue management costs.
The regulatory requirements for residue management may cause increased costs. If the
feed material is not RCRA- or TSCA-regulated, but one or more residues are regulated
by these statutes, the regulatory requirements can be relatively simple, provided the
residues are not stored or treated onsite. If a RCRA-regulated residue is produced, the
277
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TABLE 9-5. SELECTION FACTORS FOR CONTROL OF AIR EMISSIONS DURING SEDIMENT REMEDIATION
Remediation
Component
Technology
Type
Potential Air
Emission Source
Air Emission Control Measures
Disposal
CDF
fo
vj
00
Wastewater treatment
Any
Any
Any
Volatile organic
compounds from
CDF surface
Dust
Volatile organic
compounds
Volatile organic
compounds
Cover with building, air supported structure, or floating
membrane cover, capture and treat emissions
Install fences to reduce wind speed across surface
Prevent sediment solids from being exposed to air by maintaining
water cover or by capping with clean sediment
Minimize wetting and drying of exposed sediment solids
Prevent surface from drying out or cap with clean sediment or
other cover material
Avoid exposing large surface areas of highly contaminated liquids
Capture and treat emissions from process equipment, particularly
operations applying heat or mixing
Contain process in enclosure
Minimize surface area exposed
Minimize time of exposure for sediment to air
Locate facilities downwind of potential receptors
Operate during colder weather and calm winds
-------
Chapter 9, Residue Management
treatment process must be registered as a hazardous waste generator. If a RCRA- or
TSCA-regulated residue is stored or treated onsite, there are substantial cost increases
because of the regulatory requirements.
Water Residues
Considerable cost data are available on technologies to treat wastewater from municipal
and industrial applications. Relatively little cost data are available from applications with
contaminated sediments, except for CDFs (see Chapter 8). CDFs perform both effluent
treatment and disposal functions, and the costs of these are not readily separated.
Consequently, if a CDF or similar facility is used for sediment storage, dewatering,
rehandling, and/or disposal in a remedial alternative, the costs for effluent treatment
(gravity settling) are included in the facility costs.
Features of a CDF that are primarily for effluent treatment include cross dike(s) to
enhance settling or provide for secondary settling after flocculant addition, overflow
weir(s), oil booms, and special filter dikes. These features may not be included in the
basic CDF cost estimate, and should be added as water residue treatment cost items.
Water residue treatment costs are summarized in Table 9-6. The capital cost of water
pollution control structures and equipment is largely dependent on flow rate and contami-
nant loading. Table 9-6 illustrates example costs based primarily on flow capacities. For
metal and organic compound removal technologies, this provides a reasonable basis for
comparison. For suspended solids removal technologies, solids loadings are a more
critical factor for estimating costs.
Because of the importance of flow rates to the cost of water residue treatment, the ability
to store water and treat it over extended periods can be cost effective. This is particularly
relevant if hydraulic dredging or transport is used and large volumes of water residues are
created in a relatively short period of time. A comparison of the approximate volumes
of water residue produced from dredged sediments (volume of water per unit volume of
sediment) is as follows:
Hydraulic dredge, 10 percent slurry 1,200 gal/yd3 (6,000 L/m3)
Hydraulic dredge, 20 percent slurry 440 gal/yd3 (2,200 L/m3)
Mechanical dredge, 20 percent expansion 40 gal/yd3 (200 L/m3)
For the above example, it is assumed that the sediment has an in situ solids concentration
of SO percent, and that the final solids concentration after settling and consolidation is
also 50 percent.
If sufficient land is not available for gravity settling and for storing water for treatment,
mechanical dredging should be used to minimize the water residue produced. If the avail-
able land allows for water storage, hydraulic dredging may be feasible if the dredging rate
is compatible with the storage and treatment system.
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TABLE 9-6. SAMPLE COSTS FOR EFFLUENT/LEACHATE TREATMENT SYSTEMS
Flow Rate
Capital Cost3
Operation and
Maintenance Costb
(Annual)
Description
Source
Flocculation/Coagulation/Sedimentation (Chemical Clarification)
20 gpm
200 gpm
2,000 gpm
10 gpm
200 gpm
2,000 gpm
200 gpm
2,000 gpm
2,000 gpm
$40,000
$50,000
$200,000
$14,000
$51,600
$82,000
$16,000
$17,000
$866,000
Includes pH adjustment
and polymer addition, and
$3,700 inclined plate clarification
Not available Lamella clarifier
$2,500 Secondary sedimentation
basin (in confined disposal
facility) with polymer feed
system
$214,000b Multistage process
including rapid mixing,
flocculation with alum
and polymer, and sedi-
mentation
Vendor quote
Vendor quote
Corps estimate
USEPA (1985b)
Granular Media Filtration
15-30 gpm $2,400
125-250 gpm $10,000
1,200-2,300 gpm $82,000
2,250 gpm (each) $526,000°
Not available $630,000°
Dupont/Oberlin Microfiltration
1 gpm $54,000
1 5 gpm $257,000
Combination System (Precipitation/Filtration)
Not available
Not available
Not available
40 gpm
225 gpm
560 gpm
$156,000
$362,000
$765,000
Sulfide Precipitation (Sulfex* Process)
40 gpm $278,000
$181,000
$497,000
$32,000
$69,000
$110,000
Not available
High pressure sand filters
with automatic backwash
Two 34-ft-diameter cells
at Chicago Area CDF,
sand/carbon media,
85 percent TSS removal
Two 52-ft-diameter cells
at Monroe, Michigan,
CDF, sand media,
90 percent TSS removal
2.4-ft2 unit
36-ft2 unit
Includes chemical feed,
flocculation, filtration, and
pH adjustment
Includes clear well, chem-
ical feed systems, agita-
tors, pumps, pH controls,
and effluent filter
Vendor quote
Engel (1994)
Wong (1994)
USEPA (1991g)
SITE Program
USEPA (1985b)
USEPA (1985b)
(continued)
250
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TABLE 9-6. SAMPLE COSTS FOR EFFLUENT/LEACHATE TREATMENT SYSTEMS (continued)
Flow Rate
Ion Exchange
50 gpm
300 gpm
600 gpm
Capital Cost9
$104,000
$166,000
$222,000
Operation and
Maintenance Costb
(Annual)
$17,000b
$29,000b
$38,000b
Description
Fabricated steel contact
vessels with baked phe-
nolic linings, a resin depth
Source
USEPA <1985b)
20 gpm
200 gpm
2,000 gpm
Oil/Water Separation
20 gpm
200 gpm
2,000 gpm
Carbon Adsorption
10 gpm
20 gpm
10-20 gpm
200 gpm
2,000 gpm
17 gpm
175 gpm
350 gpm
$100,000
$235,000
$1,020,000
$18,000
$34,000
$230,000
$2,065d
$3,405d
$27,000
$120,300
$350,000
$29,000
$79,000
$116,000
Not available
Not available
Not available
of 6 ft, housing for the
columns, and all piping
and backwash facilities
Two cation columns; two
anion columns and batch
treatment (hydroxide pre-
cipitation) of waste pro-
duced by regenerating the
columns
7,100-gal unit
12,000-gal unit
4 x 35,000-gal unit
Carbon canisters (90 kg
each)
High-pressure carbon
adsorption; skid-mounted
system with piping
Pressurized activated car-
bon using two-vessel ad-
sorption
Vendor quote
Vendor quote
Vendor quote
Vendor quote
USEPA (198 5b)
UV/Oxidation
10 gpm
200 gpm
$180,000
$870,000
$1.80-$2.20/1,000
gal
Includes stainless-steel
treatment tank with UV
lamps, air ozone gen-
eration, and hydrogen
peroxide metering
Vendor quote
Note: TSS - total suspended solids
1 gal = 3.8 L, 1 ft = 0.3 m, and 1 ft2 = 0.1 m2
a Costs are for process equipment only and do not include site preparation, installation, or start-up. Costs from literature
sources updated to January 1993 using ENR's Construction Cost Index.
b Updated to January 1993 using ENR Averaged Specialized Labor and Materials Indices.
c Government estimates updated to January 1993 costs using ENR's Construction Cost Index.
d Assumes carbon replacement after 1.8 and 3.6 million gal, respectively.
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Chapter 9. Residue Management
For water residues with limited flow rates, leased treatment equipment or contracted
treatment services are likely to be most cost effective; however, some specialized
treatment equipment is only available for purchase. The second-hand market may also
offer opportunities for savings.
The operation and maintenance costs of water treatment systems are highly dependent on
flow rate. However, other variables, such as suspended solids loading, contaminant
concentrations, and water chemistry also have a significant impact on operating costs.
Some technologies require experienced operators. Water treatment systems can also
produce solid residues, such as spent filter media, activated carbon, and sludges, that
require disposal.
Solid Residues
Costs for the treatment or disposal of solid residues will generally be the same as those
discussed in Chapters 7 and 8. The physical and chemical properties of treated sediment
solids are likely to be more homogeneous than those of the untreated sediments.
Consequently, solid residues may require little or no pretreatment and may be treated
more efficiently and at lower unit costs.
Solid residues will require storage onsite until the material can be treated further, disposed
onsite, or transported for offsite treatment or disposal. Duplicate storage areas may be
necessary for storing one batch of residue while another is awaiting test results to show
that the materials were treated to acceptable levels for subsequent treatment or disposal.
Solid residues with high concentrations of contaminants (i.e., spent filter media and
carbon, treatment sludges, particulates from air pollution control systems) may require
special containers for storage, and may require disposal in RCRA- or TSCA-licensed
facilities.
Organic Residues
Incineration is likely to be the preferred treatment alternative for organic residues from
extraction processes. The unit cost for incineration at a TSCA-licensed facility is between
$0.55-$1.00/kg (Payne 1993). The availability and unit costs of other treatment processes
are difficult to predict because there are so few operating, licensed facilities.
Air and Gaseous Residues
Most vendors of thermal treatment processes do include the costs for air pollution control
equipment in their unit costs. Costs for controls of nonpoint emissions from other
treatment technologies and from pretreatment and disposal technologies must be estimated
separately. These costs may include shelters or bubbles to contain air emissions, air
treatment systems, and operational controls. Secondary costs include increased operating
costs and decreased production by treatment or pretreatment units that must operate inside
air containment structures.
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Chapter 9. Residue Management
CONTAMINANT LOSSES
Residuals are releases or discharges from a sediment remedial alternative to the environ-
ment that are managed or controlled. The contaminant concentrations in the residual and
the type and level of control exercised determine the contaminant loss.
Water Residues
Water residues must be treated to a level that meets regulatory requirements. The total
contaminant loss can be readily calculated from the estimated effluent contaminant con-
centration and the volume of water to be discharged. For a more conservative analysis,
the effluent contaminant concentration may be assumed to be equal to the discharge
standard. Methods for predicting effluent and leachate contaminant losses are discussed
in Myers et al. (in prep.). Additional losses can occur in the event of failure of the
treatment system, resulting in the discharge of untreated water. Such accidental losses
cannot be predicted, but should be preventable with suitable process control.
Another contaminant pathway from water residue treatment is volatile losses from the
surface of sedimentation basins or in the off-gasses from process equipment. Volatiliza-
tion from sedimentation basins can be estimated using the same procedures derived for
CDFs (Myers et al., in prep.). Air emissions from water treatment equipment are likely
to be minimal due to the relatively small surface areas and residence times involved.
Solid Residues
Contaminant losses from the treatment or disposal of solid residues can be estimated
using the procedures discussed in Chapters 7 and 8.
Organic Residues
Contaminant losses from the treatment of organic residues can be estimated using the
procedures discussed in Chapter 7.
Air and Gaseous Residues
Air and gaseous emissions from point sources, or fugitive sources that have been
contained, will be treated in pollution-control equipment to a level that meets regulatory
requirements. The total contaminant loss can be readily calculated from the estimated
emission contaminant concentration and the volume of air/gas to be discharged. For a
more conservative analysis, the emission contaminant concentration may be assumed to
be equal to the discharge standard.
Volatile losses from fugitive and nonpoint sources that cannot be contained may be
estimated using the methods discussed in Myers et al. (in prep.) for CDFs.
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10. OPERATIONAL CONSIDERATIONS
This chapter discusses operational considerations that are relevant to the remediation of
contaminated sediments. Topics discussed include contracts and contract administration,
water-based operations, and land-based operations.
Most of the experience in the management of contaminated sediments has been in the
maintenance dredging of navigation channels. The Corps has a limited fleet of dredges
nationwide, but most of the actual dredging is contracted to private dredging companies.
In addition, most dredged material transport and rehandling, and all construction of
disposal facilities for dredged material, are performed by contractors.
Guidance on contract administration for the design and implementation of Superfund
remedial actions is provided in USEPA (1986b). The Corps has developed several
pamphlets and manuals that provide guidance on contract administration and construction
oversight, including:
• Resident Engineer's Management Guide (USAGE 1973)
• Quality Assurance Representative's Guide (USAGE 1992b)
• Modifications and Claim Guide (USAGE 1987d)
• Safety and Health Requirements Manual (USAGE 1987e).
CONTRACTING
As discussed in Chapter 2, contract mechanisms and regulations for sediment remediation
projects are specific to the proponent and funding organizations. The number, type, and
scope of contracts for implementing a sediment remediation project will also be affected
by the complexity of the remedial alternative(s) selected for the site.
Contract Administration
Contract administration is a broad term that includes inspection and construction
management as well as general administrative activities. Inspection is necessary during
all phases of construction activities to ensure adherence to specified quantities and quality
standards. Construction management involves coordinating activities beyond the
contractor's scope or control, tracking progress, determining and making payments,
preparing and negotiating contract modifications, and project acceptance. Other contract
administration activities include preparing the project plans and specifications, soliciting
bids, and recordkeeping. Contract administration is an important step in the management
of a remediation project to control the costs of contractual equipment and labor. The
goals of contract administration are to ensure that the work is completed on time and that
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Chapter 10. Operational Considerations
the contractor receives proper compensation. Contract administration encompasses all
dealings with contractors from the time the contract is awarded until the work has been
completed and accepted, payment has been made, and disputes have been resolved.
Factors influencing the extent of contract administration activities include the nature of
the work, the type of contract, and the experience and attitudes of the personnel involved.
The Corps typically estimates the level of effort required for the administration of a
construction contract to be approximately 8 percent of the construction costs. Additional
funds may be required for administration of environmental remediation projects because
of the increase in regulation and safety requirements. Smaller projects (those with total
costs less than $500,000) require a higher percentage allowance for contract administra-
tion costs.
Contract Requirements and Clauses
Dredging
The following general requirements are included in Corps maintenance dredging contracts
and may be suitable for environmental remediation contracts:
Contractor Quality Control—The contractor is required to submit a Contractor
Quality Control Plan that identifies personnel, procedures, control, instruction, records,
and forms to be used for inspection of construction. Construction is allowed to proceed
after acceptance of this plan.
Quality assurance and quality control must be performed to ensure that the contractor
dredges to the appropriate depth and at the correct location specified in the contract. For
maintenance dredging, this is accomplished by conducting hydrographic surveys before
and after dredging. For sediment remediation projects, dredging contracts may be
structured around dredging areas, depths, and volumes, or by acceptable contaminant
concentrations to be left behind. At the Waukegan Harbor Superfund project, the consent
decree specified the elevations to which sediments were to be dredged. Completion of
the dredging was also contingent upon sampling and testing of the grain size of sediments
at the new surface (USEPA 1984b). Quality assurance also ensures that the dredged
material is placed at the location and in the manner specified in the contract.
Special Project Features—Special project features must be identified, such as
utility location plan, survey note format, Notice to Mariners, buoy relocation positions,
and survey information.
Real Estate—Real estate rights for the use of work and storage areas and access
to the disposal site must be obtained and provided in the contract. Any additional real
estate rights required by the contractor are obtained at the contractor's expense.
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Chapter JO. Operational Considerations
Payment—The Corps typically structures its dredging contracts for payment based
on lump sums for mobilization and demobilization and a unit price ($/yd3) for the
quantity of sediments dredged. An alternative method of payment is time-based, where
the dredge and operator are essentially "leased" for a period of time. These methods both
have their advantages and disadvantages.
A fixed or unit price contract is more readily used to obtain competitive bids for the
entire dredging project. This type of contract gives the contractor an incentive to finish
the job as rapidly as possible, which may be a problem if it is desired to slow the
dredging process to reduce resuspension or for other reasons. The contract specifications
must be tightly written to provide performance criteria for the dredging, penalties for not
meeting those criteria, and contingencies for most foreseeable events that could cause
delays. A poorly written contract and changes in site conditions are the primary reasons
for contract disputes and claims.
A time-based lease contract allows for greater control of the contractor's activities. This
type of contract may create a disincentive to the contractor to work quickly, and the total
dredging cost is not fixed up front. Specifications may not need to be as tight for a time-
based contract, although performance criteria and penalties still need to be defined.
Dredging contracts are typically structured with two unit prices. The first unit price
(dollars per time or volume) would apply for a base level of effort for which the
contractor is guaranteed payment. The second unit price would apply for additional time
or volume necessary beyond the base effort. This method of subdividing the unit price
item ensures the contractor a minimum level of effort on which to distribute indirect
costs, and typically provides the contracting agency with a reduced unit price for
additional effort if needed. Lump sum payments for mobilization and demobilization are
appropriate for either type of contract.
General Clauses
Construction contracts typically include several clauses to assist in contract administration,
including the following:
Liquidated Damages—Liquidated damage provisions establish a rate of as-
sessment that is representative of the harm expected to be suffered if a contractor fails to
perform on schedule. The contractor is required to pay a predetermined amount for
each day the project is completed late. This may be especially important in remediation
projects where highly contaminated materials are being handled, and poor performance,
accidents, and spills can create serious environmental problems. In addition, delays
caused by one contractor can have significant cost impacts on other contractors respon-
sible for follow-on processes.
Bonding Requirements—Bid guarantees, performance bonds, and payment bonds
are a form of security to ensure that the bidder will not withdraw a bid and will execute
a written contract and furnish required bonds.
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Chapter 10. Operational Considerations
WATER-BASED ACTIVITIES
Equipment/Limitations
The various types of dredging equipment are discussed in Chapter 4. Dredging contracts
can be advertised in several ways. The contract may specify the dredging equipment in
great detail or may offer a limited number of acceptable equipment types. Another
approach would be a contract in which all dredges meeting specific performance criteria
are considered. Performance criteria could include minimum production rate, average
solid content of dredged material, sediment resuspension characteristics, vertical and
lateral accuracy of cut, and others.
Qualification or performance-based contracts are more difficult to prepare and administer
than contracts for specified equipment. Contractors rarely have the type of quantitative
information on performance needed to compare with other equipment, making selection
more difficult. However, if performance criteria for the dredging operations are
developed, they provide an incentive for contractors to make innovative modifications to
their equipment and operations to meet the criteria, and develop the performance data
needed for qualification.
Contracts for Federal navigation dredging projects require removal of sediments down to
the project-specified depth and typically provide for payment of up to a 1-ft (0.3 m) over-
dredging to cover inaccuracies and variations in dredging methods. This serves as an
equitable means of payment for complete removal of the required sediments. Any
material in the allowable overdepth prism and allowable side slopes is not required to be
removed. Any dredging below the allowed 1 ft (0.3 m) is considered excessive, and
payment is not made for removal of the excess material.
In a sediment remediation project, consideration should be given to the effects of
sediments sliding or sloughing into the area dredged and the practicality of overdepth
dredging. As sediments are excavated, adjacent sediments will slide or slough into the
depression. The side slope of any excavation is determined by the physical properties of
the sediments and local hydraulic conditions. A side slope of 1:2 (verticalrhorizontal)
is commonly used by the USAGE Detroit District when estimating the quantity of
sediments to be dredged from Great Lakes navigation channels, although the natural angle
of repose may be much flatter (Wong 1994).
Extensive sampling and testing may be used to accurately delineate zones of sediment
contamination in three dimensions. When converting maps of sediment contamination
into dredging plans, however, it should be recognized that dredges are not capable of
removing sediments with precise accuracy, even with the most technologically sophis-
ticated equipment. Dredging specifications with complicated variations in depth and
width should be avoided. If a small hot spot is identified, it may not be practical for the
dredge to excavate the hot spot in isolation from the adjacent material. Under normal
operating conditions on Great Lakes tributaries, a vertical dredging accuracy of 0.5 ft
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Chapter JO. Operational Considerations
(15 cm) can be expected. To obtain a greater degree of accuracy, excavation would have
to be slowed significantly and limited to times when conditions (e.g., currents, waves,
wind) are ideal.
The scheduling of dredging and other water-based construction activities may be restricted
by a number of events, such as recreational boating traffic and the seasonal spawning of
migratory fish. On the Great Lakes, the maintenance dredging season generally coincides
with the opening (beginning of April) and closing (end of December) of the navigation
locks at Sault St. Marie, Michigan. Despite its logistical and operational problems, winter
dredging, as conducted at Waukegan Harbor, may be preferable to avoid the traffic and
other restrictions during the warmer seasons.
Access
Most Corps dredging projects are limited to existing navigation channels. Access,
therefore, is only limited by the existing shoal or deposit to be removed. For a
remediation project, accessibility to the project site may be a problem for the dredging
and transportation equipment. This is especially likely in areas outside of navigation
channels with naturally shallow depths. In some cases, channels can be dredged to the
remediation area to provide waterborne access.
Access and obstructions should be considered in the design phase. If the remediation area
is divided by bridges, pipelines, or other obstructions, dredging equipment may have to
be remobilized several times. Access points for mobilization should be identified in the
project plans, and easements or rights-of-way should be obtained prior to contract adver-
tisement. Another consideration for sediment remediation is the integrity of nearby
structures. If the contaminated sediment area is located adjacent to a bulkhead, pier,
bridge, or other structure, consideration should be given to the effect sediment removal
will have on the integrity of the structure. Dredging at the Superfund project in
Waukegan Harbor, Illinois, was prohibited within (6-9 m) because of this concern
(USEPA 1984b).
The above discussion applies to dredging and construction from marine plants, which may
not be practical for sediment remediation in small rivers and streams. Land-based
dredging and construction will require access to the entire length of the waterway to be
dredged. Easements and rights-of-way will have to be obtained from landowners, who
must be compensated for damages to their property and landscaping. Land-based
dredging will require construction equipment to operate in areas that are subject to
flooding. The accessibility of the waterway for land-based dredging may therefore vary
with the season.
Authorized Crossings
Authorized utility crossings exist in the bottom sediment of rivers and lakes. The type
of utilities with authorized crossings include natural gas pipelines, wellheads/water
intakes, electrical utilities, and telephone lines. If the dredge damages a utility, it could
result in personal injuries and extended environmental or economic damages to the
waterway or users of the utility.
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Chapter 10. Operational Considerations
When excavation is considered for a project, a determination of any potential authorized
utility crossings in the project area must be made. This can be done by contacting the
local utility companies in the area, the Corps district, and the U.S. Coast Guard.
LAND-BASED ACTIVITIES
The contracting options for land-based operations of a complex sediment remediation
alternative are similar to those discussed earlier for water-based (dredging and transport)
operations (also see discussion in Chapter 2). Contracts can be structured to a specific
technology type or process unit, or can be opened to all technologies that can meet
specified performance criteria. These performance criteria may include: minimum
destruction or removal efficiencies for target contaminants, physical and/or chemical
characteristics of solid residues, constraints on the quantity and quality of water or air
emissions, and maximum time to completion.
Because of the interdependence of transport, pretreatment, treatment, and residue
management components, the prime contractor should be responsible for providing all
equipment and technologies that deliver the material to and between pretreatment and
treatment units and manage all residues from them. The only land-based component that
might be divided into a separate contract is the initial construction of a CDF.
There is significant documentation on the construction, operation, and maintenance of
CDFs, including guidance provided by USAGE (1987b). The management of a CDF for
contaminated sediments should consider a number of issues, including:
• Water management
• Management of plants and animals
• Health and safety requirements
• Site maintenance and security
• Site monitoring.
For a complex sediment remedial alternative involving removal, it is likely that a facility,
similar to a CDF in many respects, would be used for the storage, handling, pretreatment,
and treatment of dredged sediments; treatment of water residues; and storage and possibly
disposal of solid residues. A hypothetical layout of such a remediation facility is shown
in Figure 10-1. At this facility, sediments are pumped into one of two settling basins.
After dewatering, the sediments are excavated from the settling basin and transferred to
an adjacent pretreatment system. Debris and coarse materials from the pretreatment
system are placed into one of three residue storage areas. The bulk of the sediments are
transferred to the treatment system. Solid residues from the treatment system are placed
in one of the residue storage areas. Two storage areas are needed because the residues
must be tested before they can be removed for final disposal offsite. The organic residue
is placed in a tank trailer for transport to an offsite incinerator. Water from the treatment
and pretreatment processes and the settling basins is routed to the water residue treatment
system. Some of the treated sediments are transported to a remote site for beneficial use
and others are disposed onsite.
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Dike
Treated
solid
residue
storage
Treated
solid
residue
storage
Debris
and
coarse
material
storage
Treatment
§
Administration
office and
laboratory
Pretreatment
Chemical
storage
Waste residue
treatment
Sediment settling basin
for dewatering/storage
Sediment settling basin
for dewatering/storage
Figure 10-1. Hypothetical sediment remediation facility.
-------
Chapter 10. Operational Considerations
Most of the operation and maintenance issues identified above for CDFs would apply to
this hypothetical facility. Some additional issues may have to be addressed including:
• Materials handling (e.g., supplies, waste streams)
• Storage of chemicals, reagents, and treatment residues
• Dust management
• Energy/power generation and distribution
• Onsite testing laboratory.
The management of a facility with several process technologies working concurrently
would require a significant level of effort.
All of the management issues listed in this section are discussed in the following
paragraphs. A discussion of site closure and post-closure maintenance is also provided.
Water Management
The volume of water to be managed will depend on how the sediments are dredged and
transported and on the process requirements of the pretreatment and treatment tech-
nologies. Hydraulic dredging will add a significantly greater amount of water to the
sediments than will mechanical dredging, which would require that the CDF provide the
ponding necessary for sedimentation and retention of suspended solids.
At most Great Lakes CDFs, the depth of the pond is typically maintained by placing
boards within the weir structure. Other types of water level control systems include filter
cells (passive control) and pumping (active control). Water level management will ensure
maximum possible efficiency of the containment area by increasing the retention time.
If inefficient settling is occurring in the basin, it may be necessary to operate the dredge
intermittently to allow for sufficient retention time and sedimentation, or to install more
extensive treatment systems for the CDF effluent. Effective management of the CDF
pond can therefore produce significant cost savings to the project.
After a hydraulic dredging operation is completed, the pond within an upland CDF can
be drawn down. The rate of drawdown can be slowed to allow settling to remove most
of the suspended sediments from the water column and to reduce the loading to effluent
treatment systems. Practices for dewatering dredged material are discussed in Chapter 6
and in detailed guidance provided by Haliburton (1978) and USAGE (1987b). To
facilitate dewatering, rainfall should be routed to one or more collection point(s) and
drained as quickly as possible. Trenching and other methods may be used to promote
drainage and desiccation.
There are a number of possible wastewater streams produced at a sediment remediation
site that will require collection and routing for treatment. Wastewater treatment systems
are discussed in Chapter 9. The raw effluent from a CDF during hydraulic dredging/
disposal represents the largest potential Water flow. Rainfall runoff, leachate, and process
water from pretreatment and treatment technologies will have varying flow rates and
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Chapter 10. Operational Considerations
durations. Depending on their quality and flow rate, some of these wastewater streams
may be routed together and mixed before treatment.
Management of Plants and Animals
Management of Plants
Contaminated sediments dredged from freshwater sites and placed in an upland area will
rapidly develop extensive vegetation without any inducement. In fact, fine-grained
sediments from the most contaminated sites seem to support the most extensive vegeta-
tion. From freshwater sites, only the most grossly contaminated sediments and sandy
sediments without nutrients have shown any limitations on vegetative growth. Sediments
deposited in upland areas on Great Lakes CDFs are typically covered with vegetation in
the first or second growing season.
Before a remediation project is initiated, the desirability of vegetation within the
containment area should be evaluated. Vegetation can be beneficial because it helps to
dewater dredged material, control dust, reduce volatilization losses, and improve effluent
quality by filtering. Dense vegetation, however, may severely reduce the available storage
capacity of the containment area, restrict the flow of dredged slurry within the area, and
have to be removed in order to construct a cap/cover. In addition, the management of
plant populations may be necessary to minimize uptake and environmental cycling of
sediment contaminants.
To assess the potential for contaminant uptake by plants, the laboratory procedure of
Folsom and Lee (1985) should be used. The Times Beach CDF in Buffalo, New York,
has been used for more than 10 years as a full-scale laboratory for evaluating plant and
animal uptake from contaminated sediments. A compilation of these studies was prepared
by Stafford et al. (1991). Subsequent studies have identified plant species that have lesser
uptake of certain contaminants (Simmers 1994) and may be suitable for some CDF
applications.
Options for managing vegetation include periodically cutting or burning the vegetation,
tilling, applying herbicides, planting acceptable species, and placing new sediments on top
of existing vegetation. Some of these control measures may cause significant contaminant
losses. The vegetation management plan for a disposal or holding site with contaminated
sediments must weigh the advantages and risks mentioned above.
Management of Animals
Various animals will use dredged material disposal and holding areas as a habitat, even
when facility management controls are in place. Most of the CDFs constructed within
the Great Lakes are inhabited by colonies of migratory birds. Vegetated areas are
inhabited by small mammals, and ponds (at in-lake CDFs) have limited fish populations.
Within highly urbanized areas, disposal facilities for contaminated sediments are some of
the most productive wildlife habitats in the area.
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Chapter 10. Operational Considerations
Unlike vegetation, animal populations provide no benefits to the operation of a disposal
or holding site for contaminated sediments. If migratory bird colonies are present and
establish nesting colonies on the facility, there may be conflicts in the scheduling of
operations in or around these nesting areas. Fish populations in ponded areas may
bioaccumulate contaminants to unacceptable levels and attract birds and humans. Birds
and small animals (e.g., rabbits, mice) can attract dogs, and the carrion can attract rats.
Controls that can be used to manage animal populations include the use of noisemakers,
predator images, and vegetation management (to discourage birds from using the site).
In addition, rotenone, shocking, and elimination of ponds may be used to remove fish
populations. Trapping and vegetation management may be used to control populations
of small mammals.
Botulism Prevention
Avian botulism has been recorded in naturally occurring wetlands in nearly all parts of
the world. It is due to ingestion of a toxin produced by the bacteria Clostridium
botulinum. Botulism becomes a concern at CDFs when dredged material forms shallow
ponds or is raised slightly above water. These shallow ponded areas provide an attractive
food source for waterfowl. When the conditions necessary for bacterial growth occur in
the CDFs, the potential for a botulism outbreak is established. Because botulism occurs
in mud flats and shallow ponded areas, a preventive strategy for botulism should be part
of the water management program. Proper placement of dredged material and drainage
of the CDF through an outlet structure will prevent development of extensive mud flats
and ponded areas.
A second approach for the prevention of botulism is to schedule the dredging/disposal
operations during the cooler seasons. If mud flats or ponded areas develop during these
cooler seasons, the potential for a botulism outbreak is minimized because of the
inhibition of toxin production by cooler temperatures.
If a botulism outbreak occurs, every possible effort must be made to control its spread.
Limitation of the spread of botulism can be implemented by attempting to eliminate the
toxin production and by making the site unattractive to waterfowl. This can be accom-
plished using short-term and long-term methods. Short-term methods include making the
site unattractive using noisemakers, power boats in the area, or imitation predators. The
removal of bird carcasses from the affected areas is also a necessary short-term action to
eliminate toxin production.
Long-term methods involve changing the environmental conditions to eliminate the toxin
production. Flooding the site with about 30 cm of water or draining the site to allow the
dredged material to dry would eliminate shallow ponded areas. Drainage of shallow pond
areas is an effective technique that can be accomplished by using pumps and/or construct-
ing trenches.
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Chapter 10. Operational Considerations
Health and Safety Requirements
The health and safety requirements for a CDF or a site where sediments are being
handled, pretreated, and treated may be determined by the project authority or by regula-
tions covering the materials being handled. The health and safety requirements for all
Corps activities and operations are provided in USAGE (1987e). A health and safety plan
should be developed for all sediment remediation projects, regardless of the funding
authority or applicable environmental regulations. Such plans are especially important
with treatment processes that use high temperatures, pressure, or reagents that are
hazardous, caustic, reactive, or combustible. Guidance on the development of health and
safety plans for Superfund remediation projects is provided by USEPA's Standard
Operating Safety Guides (USEPA 1992h) and Health and Safety Plan (HASP) (USEPA
1989f).
PPE, such as gloves, protective clothing, and respirators, is required by OSHA and
USEPA for all contractors working on Superfund sites. Some types of PPE are likely to
be necessary at sediment remediation sites as well. The purpose of PPE is to shield or
isolate individuals from the chemical, physical, and biological hazards that may be
encountered at a hazardous waste site when engineering and work practices are not
feasible to control exposures. Careful selection and use of adequate PPE should protect
the respiratory system, the skin, eyes, ears, face, hands, feet, and head.
The types of PPE that may be required will vary depending on the degree and type of
contamination of the material, as well as the methods to remove, transport, and dispose
of the material. PPE should be selected and used to meet the requirements of 29 CFR
Part 1910, Subpart I.
Safety or contingency plans should be developed to minimize the consequences of
accidents or natural disasters (USAGE 1987e).
Equipment Decontamination
Vehicles leaving the site may have to be decontaminated and safety checks provided to
ensure that materials are properly stored for transport, liners and cover tarpaulins are
secured, and manifests for materials are properly documented. Routine maintenance of
the site may also include periodic inspections and repairs to dikes, fence enclosures, and
other site features.
Site Maintenance and Security
The purpose of site maintenance is to prevent contamination of the workers, protect the
public from site hazards, and prevent vandalism. The degree of site controls necessary
depends on site characteristics, site size, and the surrounding community. A site control
plan should be developed, including a site map, site preparation, site work zones, site
security, and safe work practices.
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Chapter 10. Operational Considerations
Site security is necessary to prevent exposure of unauthorized, unprotected people to site
hazards; avoid vandalism; and prevent theft. To maintain site security, a physical barrier
can be erected around the site, signs can be posted, and access points can be limited. Site
security is a common problem at CDFs. Private citizens have vandalized or fished and
hunted inside the CDFs. Because of the nature of construction activities, personal injury
presents a liability concern at CDFs. Access should be limited during the filling stage
of a CDF. This can be accomplished by installing a fence and/or ppsting signs.
Vehicles leaving the site may have to be decontaminated and safety checks provided to
ensure that materials are properly stored for transport, liners and cover tarpaulins are
secured, and manifests for materials are properly documented. Routine maintenance of
the site may also include periodic inspections and repairs to dikes, fence enclosures, and
other site features.
Site Monitoring
The scope of a monitoring program for a sediment remediation project will be project-
and site-specific. For a complex remedial alternative conducted at an upland facility,
items that may be monitored include:
• Pond water levels
• Sediment delivery/flow rates
• Sediment inflow characteristics
• Pretreatment processes (internal and endpoints)
• Treatment processes (internal and endpoints)
• Raw effluent flow and quality
• Treated effluent/leachate flow and quality
• Ambient air quality
• Ambient surface and groundwater quality.
Certain analytical capabilities will be necessary onsite if a treatment technology is used.
An onsite laboratory is needed to rapidly measure chemical and physical parameters that
are indicators of the performance of the treatment process. These indicators may be
surrogates for the major contaminant'of concern that can be tested more rapidly and at
lower cost. The onsite laboratory may also be needed to support and maintain any
continuous or "real-time" monitoring equipment. Offsite laboratories can be used for
testing that is less time-critical to the operation of the remedial alternative.
Materials Handling
Within a typical CDF, contaminated dredged material is only handled once, during
placement. In contrast, facilities constructed for clean dredged material are often
constructed using the dredged material (i.e., the materials placed from one dredging
operation are excavated and used to build up the dikes for the next operation).
At a facility used for a complex sediment remedial alternative, various materials may be
handled on a continuing basis. Sediments can be dredged rapidly and placed into the
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Chapter 10. Operational Considerations
facility over a relatively short period (weeks to months). Pretreatment and treatment
equipment will require an extended period (months to years) to process the dredged
sediments. As the pretreatment and treatment units operate, residues are created that may
require immediate treatment, storage for later treatment, storage for transportation, or
disposal onsite (see Chapter 9). The logistics of materials handling and internal
transportation in such a facility may require detailed planning. Guidance on process plant
designs in textbooks on chemical engineering might be useful in developing materials
handling strategies.
Storage of Chemicals, Reagents, and Treatment Residues
A sediment remediation site, as illustrated in Figure 10-1, may require a number of
storage locations for the chemicals and reagents used in sediment and water treatment and
for residues of pretreatment and treatment technologies. Some of these materials may be
hazardous, toxic, reactive, or combustible and require special storage containers. The
number, size, location, and type of storage areas will be determined by the quantity and
character of chemicals and reagents used, or of residues produced, and how these
materials are to be rehandled, transported, or disposed.
Dust Management
Airborne contaminants can present a significant threat to worker health and safety,
especially when dewatered sediments are being excavated and rehandled. Air monitoring
may be required to determine if airborne contaminants are present and will aid in the
selection of PPE. Dust particles, aerosols, and gaseous by-products from all construction
activities, processing, and preparation of materials should be controlled at all times,
including weekends, holidays, and hours when work is not in progress.
Provisions should be included in contracts to ensure that the contractor maintains all
excavations, stockpiles, haul roads, permanent and temporary access roads, plant sites,
spoil areas, borrow areas, and all other work areas within or outside the project bound-
aries free from particulates that could cause the air pollution standards to be exceeded or
that could cause a hazard or a nuisance. Sprinkling systems, light bituminous treatment,
or other equipment can be used to control particulates in the work area. To be efficient,
sprinkling must be repeated at sufficient intervals to keep the disturbed area damp at all
times. Paniculate control should be performed as the work proceeds and whenever a
paniculate nuisance or hazard occurs.
Energy/Power Generation and Distribution
Some treatment technologies have significant energy requirements and may require special
utility connections. If the distance to existing utilities and cost for connection are
excessive, generators may be used to provide electrical power. Transportation and/or
storage of fuels should also be considered during the design of the project.
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Chapter 10. Operational Considerations
Site Closure and Post-Closure Maintenance
As part of site closure, much of the equipment used onsite may require decontamination.
Wash water from decontamination will have to be treated. Soil from the site that has
become contaminated by contact with the sediments or residues, and materials that cannot
be effectively decontaminated, such as plastic liners, may have to be disposed in a
licensed landfill or co-disposed with solid residues.
The placement of a cap and/or cover on dredged material in a CDF is not a simple
construction activity. Typically, the site has to be cleared of vegetation and large root
systems have to be unearthed. The site then has to be graded for positive drainage and
the sediments compacted before any cap/cover materials can be placed. Long-term
maintenance activities at a CDF would be essentially the same as those at a closed
landfill, including:
• Periodic inspections and repairs of dikes and controls (i.e., cap/cover)
• Operation of leachate collection systems
• Operation of leachate treatment systems
• Management of plants and animals
• Groundwater monitoring.
Plant species grown on a cap/cover are selected to provide erosion protection and should
be low maintenance and have shallow root systems. Site security may be required after
closure for areas where leachate collection/treatment systems are operated. Dredged
material in CDFs is not known to exhibit uneven settling and methane gas production,
which are common problems in sanitary landfills. Closed CDFs may be used for a
variety of productive purposes. CDFs around the Great Lakes have been used for harbor
and airport expansion, park and recreational areas, and wildlife habitat (Miller 1990).
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11. SUMMARY AND CONCLUSIONS
SUMMARY
Industrial and nonpoint pollution sources have historically contributed to diminished water
quality in the Great Lakes and other water bodies in the United States. Although most
point sources of pollution are now regulated and controlled, nonpoint sources, including
contaminated bottom sediments, have been identified as a contributing factor to continuing
water quality problems.
Areas of Concern (AOCs) with impaired beneficial uses in the Great Lakes waters have
been identified by the Great Lakes Water Quality Agreement between the United States
and Canada. Contaminated sediments are known to adversely impact water quality,
promote contamination of fish flesh, and cause contaminant uptake in other organisms,
including humans. Contamination in bottom sediments has also restricted the ability to
maintain navigation channels and marine structures. The remediation of contaminated
sediments is being considered in many of the Remedial Action Plans being prepared for
Great Lakes AOCs.
Under the auspices of the Water Quality Act of 1987, §118, paragraph (c)(3), the USEPA
was directed to "carry out a 5-year study and demonstration projects relating to the
control and removal of toxic pollutants in the Great Lakes, with emphasis on the removal
of toxic pollutants from bottom sediments." To fulfill the requirements of the Act, the
Great Lakes National Program Office initiated the Assessment and Remediation of Con-
taminated Sediments (ARCS) Program.
This document reflects the work effort of the ARCS EngineeringH'echnology Work
Group. The primary purpose of this document is to provide guidance on the evaluation,
selection, design, and implementation of technologies for sediment remediation. It is
intended to be used in conjunction with other documents developed under the ARCS
Program that address the chemistry and toxicity of contaminated sediments (the ARCS
Assessment Guidance Document [USEPA 1994aj), assessment and modeling of contami-
nated sediment impacts (the ARCS Risk Assessment and Modeling Overview Document
[USEPA 1993a]), a literature review of remediation technologies (Averett et al. 1990 and
in prep.), an evaluation of methods for predicting contaminant losses during sediment
remediation (Myers et al., in prep.), and others reporting on specific studies and
demonstrations.
Sediment Remediation Technologies
There are a number of technologies that may be used for the remediation of contaminated
sediments. Some technologies, such as dredging and confined disposal, have been widely
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Chapter 11. Summary
used for the removal and disposal of contaminated sediments from navigation projects.
Many of the treatment technologies have been applied to soils, sludges, or oils, but not
to sediments. Other technologies that might be used in sediment remediation are routinely
applied in the mining and mineral processing industry or at wastewater treatment
facilities.
A remedial alternative consists of a combination of technologies used in series or in
parallel to alter sediment or sediment contaminant characteristics and achieve the
remediation objectives. The technologies of a remedial alternative perform specific
functions. In this document, the technologies have been functionally grouped into the
following components:
• Nonremoval technologies
• Removal technologies
• Transport technologies
• Pretreatment technologies
• Treatment technologies
• Disposal technologies
• Residue management technologies.
A sediment remedial alternative may be as simple as a single component, as with in situ
capping, a nonremoval technology. An alternative may also have many components
interacting and supporting one another.
A matrix of the sediment remediation components that ranks their state of development,
relative potential for contaminant loss, and application costs is provided in Table 11-1.
As shown, some components are made up of well-developed, proven technologies, such
as removal, transport, and residue management. Other technologies are still in develop-
mental stages or have been implemented only at the bench- or pilot-scale level. Many
sediment treatment technologies, both in situ and ex situ, fall within the latter category.
Nonremoval Technologies
There are two general types of nonremoval technologies, those that isolate the sediments
from the surrounding aquatic environment and in situ (or in-place) treatment. In situ
capping and containment of contaminated sediments have been demonstrated at two
Superfund sites in the Great Lakes—the Sheboygan and Manistique Rivers. Bottom
sediments at a number of lakes and reservoirs have been treated to control the release of
nutrients and limit eutrophication. In situ treatment methods for toxic contaminants have
only been demonstrated on a limited scale, and the contaminant losses and operating costs
are largely unknown.
Removal Technologies
There has been more full-scale experience with removal (i.e., dredging) than with any
other remediation technology. For the two general types of dredges, mechanical and
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TABLE 11-1. RANKING OF REMEDIATION COMPONENTS
Component
Nonremoval
Removal
Transport
Pretreatment
Treatment
Disposal
Residue Management
State of
Development
L/M
H
H
M
L/M
H
H
Potential Contaminant
Loss
L
H
L
M
L/M
L/M
L
Cost
L/M
L
L
L/M
M/H
L/H
L/M
Note: H - high
L - low
M - medium
Ranking:
State of Development
High - technologies routinely used with contaminated sediments at full scale
Medium - technologies demonstrated with sediments at full or pilot scale and
with other media (soils/sludges) at full scale
Low - technologies demonstrated only at bench or pilot scale
Contaminant Loss
A relative scale of potential losses based on modeling/monitoring experience
developed through Great Lakes dredging operations and during the ARCS
Program.
Cost (estimate based on project size of 100,000 yd3 [76,000 m3])
High - >$50/yd3 (>$66/m3)
Medium - $10-50/yd3 ($13-66 m3)
Low - <$10/yd3«$13/m3)
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Chapter 11. Summary
hydraulic, there are numerous equipment variations, including a number of dredges
specifically developed to minimize the loss of contaminants, for which the removal
component is relatively high. Dredging is typically one of the least costly components
of a remedial alternative, and the dredging equipment can be selected to fit the require-
ments of other components.
Transport Technologies
Transportation modes, such as pipelines, railcars, trucks, and conveyors, are all well-
developed technologies, although not all have been widely applied to sediments. For a
simple remedial alternative, transportation may only involve the movement of sediments
from the dredging site to the disposal site. For more complex remedial alternatives,
sediments may be rehandled several times, and products (residues) of pretreatment and
treatment technologies may require handling and transportation as well. The handling
steps at each end of a transportation route are, in many cases, the most costly item of the
transport component, as well as the source of most contaminant losses during transport.
The costs and contaminant losses of the transport component are generally low in relation
to other remediation components.
Pretreatment Technologies
The physical properties of sediments, in particular the amount of water and the size of
sediment particles, represent one of the most challenging aspects of sediment remediation.
These properties must be modified, and in some cases, used to advantage by the
pretreatment technologies. Technologies commonly used in the mining and mineral
processing industry can be used to prepare sediments for subsequent treatment processes
and, in some cases, can separate sediments into specific fractions and thereby reduce the
quantity of material requiring treatment or confined disposal. Other pretreatment
technologies include passive dewatering methods used with dredged material from
navigation projects and mechanical dewatering equipment more commonly used in
wastewater treatment applications. The costs and contaminant losses from pretreatment
technologies are moderate in relation to other remediation components, although estimates
of these costs and losses from mining technologies are somewhat speculative.
Treatment Technologies
There are many technologies available for treating contaminated sediments. Treatment
is generally the most costly component of a remedial alternative, and the component with
the least amount of full-scale experience. Most of the treatment technologies that have
been proposed for contaminated sediments were initially developed for soils, sludges, or
other contaminated media. Many of the treatment technologies were developed for
cleaning up chemical spills or waste oils with extremely concentrated contaminants and
may be significantly less efficient with sediments having more dilute contaminant concen-
trations. Contaminant losses from most treatment technologies will be low in comparison
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Chapter 11. Summary
to those from other remediation components, although the type and performance of
controls associated with treatment technologies are quite varied.
Disposal Technologies
Technologies available for the disposal of sediments, treated sediments, and treatment
residues range from unrestricted, open-water disposal to RCRA-licensed hazardous waste
landfills. No single disposal method is appropriate for all materials, but confined disposal
is the most commonly used technology for the disposal of contaminated sediments
dredged for navigation or remediation. Remedial alternatives using almost any form of
treatment will need a site for the storage and rehandling of sediments, and possibly the
ultimate disposal of treatment residues. The availability and location of a suitable site for
these activities is likely to be the most crucial feature in a sediment remedial alternative.
Costs for disposal technologies are quite variable, although conventional confined disposal
costs are moderate to low in comparison to those for treatment technologies. Methods
for estimating contaminant losses from disposal technologies are well developed, although
losses are variable.
Residue Management Technologies
The last component of a sediment remedial alternative discussed in this document is the
management of water, solid, organic, and air residues generated by other components.
The character and quantity of these residues will depend on the component technologies
selected for the remedial alternative. Water is likely to be the most important residue to
manage because of its volume, although treatment technologies for wastewater are well
developed. Treatment and disposal technologies for residues will, in most cases, be
determined by regulatory considerations. Costs for residue management technologies may
be incorporated into other component costs. Contaminant loss rates are generally low in
comparison to those for other remediation components.
Decision-Making Process
The process of developing a remedial alternative involves a number of activities,
including:
• Determining a decision-making strategy
" Defining project objectives and scope
• Screening technologies
• Preliminary design
• Selection of preferred alternative
• Final design and implementation.
This process is discussed in more detail in Chapter 2.
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Chapter 11. Summary
Chapters 3 through 9 of this document are dedicated to the remedial components listed
above. For each component, available technology types and process options are briefly
described and information needed for the formulation of remedial alternatives and
selection of appropriate technologies is provided.
The first type of information needed to develop a remedial alternative is the technical
features and requirements of the specific technologies. Each component of a remedial
alternative must be evaluated to determine if it is compatible with the other components
being considered. Some components have restrictions on site conditions or the physical
properties of the materials they can accept. For example, most treatment technologies
have very strict requirements for acceptable feed materials. Other remediation compo-
nents (e.g., mechanical dredging) may have very few restrictions on the types of
sediments that can be handled. The selection of a technology for any component cannot
be made independently of those being considered for other components.
The second type of information is cost data. Cost estimates are used during all phases
of project planning, design, and implementation. Available cost data provided in this
document reflect January 1993 price levels. The accuracy of the available cost data
depends on the level of operating experience with particular technologies. In some cases,
the only available cost data are from applications of these technologies to media other
than sediments (e.g., sludges, mined materials). Cost data for the most expensive
technologies (e.g., treatment) are generally more speculative than for other technologies.
The third type of information is predictions of the amount of contaminant loss during
implementation of the remedial alternative. Contaminant losses will occur with all
components of a remedial alternative. Estimates of these losses are necessary to evaluate
the environmental impacts of remedial alternatives and to compare the benefits of
remediation vs. other options, including no action. These loss estimates may also be
needed to evaluate the ability of a remedial alternative to maintain compliance with
environmental laws and regulations. The tools for predicting contaminant losses from
remediation technologies are at varying states of development, but available information
suggests that losses occurring during the removal phase are greater than for other
remediation components. This is primarily because losses from other components are
more readily controlled.
CONCLUSIONS
The ARCS Program conducted a series of studies, investigations, and demonstrations
which examined the "state-of-the-art" for sediment remediation technologies. From the
information and experience gathered during this program, the following general conclu-
sions can be made:
• Feasible technologies for the remediation of contaminated sediments are
available, although most of the treatment processes will require additional
development for full-scale application.
- The level of development varies widely from technologies that
have been implemented on a full scale with sediments to those
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Chapter 11. Summary
that are merely a theoretical series of equations on a piece of
paper. Several technologies are developed to the point of having
operating pilot-scale units available and now await the capital
investment upon award of a remediation contract in order to
construct the first full-scale unit that can process contaminated
sediments. Other technologies that are well developed in other
related industries (e.g., mineral processing) may require very little
additional modification to be immediately applicable to treating
contaminated sediments.
Technologies for the removal, handling, transport, and disposal of contami-
nated sediments and residues are relatively well developed.
- As more contaminated sediments are being remediated, additional
modifications to these well-understood operations are anticipated;
however, none of these changes will be of the magnitude of
treatment technology development. Additional regulatory guid-
ance is being developed, particularly for the testing of dredged
material prior to disposal and for the design of confined disposal
facilities in the Great Lakes.
There is no panacea for sediment remediation. No single technology can
work in all applications or remediate all possible contaminants.
- Some technologies work on a broader range of contaminants than
other, more contaminant-specific processes. Sediment washing
and solidification may deal with a wider variety of both organic
and inorganic contaminants than a thermally based destruction or
extraction technique. Unfortunately, it is rare to find a contami-
nated sediment site in the Great Lakes where only one or two
contaminants pose the sole environmental threat.
The majority of contaminated sediments contain a diversity of pollutants
in concentrations below the optimal levels for most treatment technologies.
As a result, treatment technologies will operate with reduced removal or
destruction efficiencies and may produce residues with restricted disposal
options.
- The combination of this conclusion and the immediately pre-
ceding one poses one of the greatest dilemmas in the application
of treatment technologies to contaminated sediments. Applying
a process that somehow deals with the organic contaminants
present in a sediment may incur a substantial expense yet leave
a residue that is still contaminated with levels of inorganic
contaminants that do not allow any additional final disposal
options than were available with the original "raw" sediment.
The level of experience in sediment remediation, particularly with treatment
processes, is very limited, and there is a high degree of uncertainty with the
estimates of costs and contaminant losses for most of these technologies.
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Chapter II. Summary
- The ARCS Program has been able, along with the efforts of
similar Canadian and Dutch programs, to advance the knowledge
base of sediment treatment technologies. Reliable cost estimates
are only developed through the experience that comes from the
execution and observation of multiple full-scale remediation
projects. As has been evidenced in the hazardous waste treat-
ment field, costs for remediation take a long time to stabilize, if
they ever reach a completely predictable range.
Depending on one's point of view, the above conclusions may project a pessimistic
outlook on the implementability of most treatment technologies to contaminated
sediments. Only a limited number of contaminated sediment sites have been remediated
to date, and the technologies used for the majority of these sediments were containment
in place and confined disposal. Considering the entire volume of contaminated sediments
and the large number of individual sites in the Great Lakes, this pattern is not likely to
change on a wide scale in the near future for a number of reasons, not the least of which
is the high cost associated with most treatment technologies.
The feasibility of applying treatment technologies to contaminated sediments can be
greatly improved by reducing the volume of materials to be processed. For some cases,
this can be accomplished by selectively treating the sediments containing the highest
contaminant concentrations (i.e., "hot spots") or by using pretreatment technologies to
concentrate the contaminants into a small fraction of the original sediment volume.
The technical issues discussed in this document are only a part of what is limiting the
remediation of contaminated bottom sediments in the Great Lakes and other water bodies.
The broader limitations are the perception, both among the general public and government
managers, of sediment contamination problems and the priority these sites receive for
funding.
Contaminated sediments are an unseen problem, lying beneath rivers, harbors, and lakes
that rarely display the signs of their impacts in readily visualized ways. Sediment
contamination is a problem with boundaries that are not easily resolved, more often a
continuum than a discrete zone with clear limits. The immense volume of contaminated
sediments at some sites makes remediation seem impossible, and makes the remediation
of a small part of this mass seem insignificant. With these perceived limitations, the
presentation of the seriousness of sediment contamination problems and the solutions to
the remediation of contaminated sediments must be innovative.
In recent years, a number of initiatives have been taken by various levels of government
to overcome the above limitations. One of the most innovative efforts to remediate
contaminated sediments is being conducted on the Grand Calumet River in northwestern
Indiana. This effort has combined a series of enforcement actions by the USEPA
Region 5 and Indiana Department of Environmental Management with navigation mainte-
nance dredging by the Corps. Additional innovative approaches include the enforcement
initiative in southeastern Michigan and the cooperative approach being taken along the
Fox River in Wisconsin.
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Chapter 11. Summary
The philosophy that has arisen as a common thread among these initiatives, and which
may be applicable to other sites with sediment contamination, is to seek an integrated
solution composed of many individual pieces. Rather than looking for one authority or
responsible party to solve the problem at one time, the effort is diversified into seeking
out opportunities to implement sediment remediation in a systematic, piece-by-piece
fashion involving government, industry, and the public. Using such an approach, an
entire waterway can be remediated.
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12. REFERENCES
Abramowicz, D.A., M.R. Harkness, J.B. McDermott, and J.J. Salvo. 1992. 1991 In Situ
Hudson River research study: A field study on biodegradation of PCBs in Hudson River
sediments. Prepared by General Electric Corporate Research and Development,
Schenectady, NY.
Acres International Ltd. 1993. The Welland River dredging and treatment demonstration.
Prepared for Atlas Specialty Steels, Environment Canada, and Wastewater Technology
Centre, Niagara Falls, Ontario. Acres International Ltd.
Albreck, A. 1994. Personal communication. Clark Dietz, Inc., Champaign, IL.
Allen, J.P. (In prep). Mineral processing pre-treatment of contaminated sediment. U.S.
Department of Interior, Bureau of Mines, Salt Lake City Research Center, Salt Lake City,
UT.
Apian, F.F. 1980. Gravity concentration. Kirk-Othmer Encyclopedia of Chemical
Technology, Third Edition. Volume 12. M. Grayson (ed). John Wiley & Sons, New
York, NY.
Apogee Research, Inc. 1992a. Ohio guide to existing and potential financing sources for
RAPs implementation. Prepared for U.S. Environmental Protection Agency, Great Lakes
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